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[Jiri Demuth](https://orcid.org/0000-0001-6847-768X), Stefan Bednarik, Radek Machan, Ivan Mocak, Tibor Malinsky, Mona Abo El Dahabova, Jakub Holcak, [Miroslav Miletin](https://orcid.org/0000-0001-6924-5960), [Jan Labuta](https://orcid.org/0000-0002-8329-0634), [Veronika Novakova](https://orcid.org/0000-0002-2183-1220), [Petr Zimcik](https://orcid.org/0000-0002-3533-3601)

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[J-dimers of phthalocyanine analogues: structural characterization and their use for determination of association constants between ligands and the central cation](https://mdr.nims.go.jp/datasets/ac6df95f-d72a-48b6-b845-227d01a0768b)

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J-dimers of phthalocyanine analogues: structural characterization and their use for determination of association constants between ligands and the central cationINORGANIC CHEMISTRYFRONTIERSRESEARCH ARTICLECite this: Inorg. Chem. Front., 2025,12, 1590Received 7th November 2024,Accepted 30th December 2024DOI: 10.1039/d4qi02834arsc.li/frontiers-inorganicJ-dimers of phthalocyanine analogues: structuralcharacterization and their use for determination ofassociation constants between ligands and thecentral cation†Jiri Demuth, a Stefan Bednarik,a Radek Machan,a Ivan Mocak,a Tibor Malinsky,aMona Abo El Dahabova,a Jakub Holcak,a Miroslav Miletin, a Jan Labuta, b,cVeronika Novakova a and Petr Zimcik *aThe characterization of the stability of self-assembled supramolecular systems is critical for numerousapplications that rely on non-covalent interactions between the components. However, in phthalocya-nines (Pcs), the coordination of ligands to the central metal is typically not accompanied by significantspectral changes, complicating the determination of association constants (K1). In this study, we devel-oped a reliable and widely applicable method based on fluorescence and absorption spectroscopy thatallows straightforward determination of K1 for a broad range of ligands, from heterocyclic to purely ali-phatic, with weak (K1 ∼ 102 M−1) to strong (K1 ∼ 107 M−1) binding affinities. The method benefits from thefull characterization of unique J-dimers of Pcs, which are formed via coordination between the peripheralsubstituent of one molecule and the central metal of another Pc in a series of metal octa(dialkylamino)azaphthalocyanines. These J-dimers exhibit significantly red-shifted absorption bands (up to ∼710 nm)and retain red fluorescence with significant Stokes shifts (∼35–40 nm), making them ideal for spectro-scopic analysis. The developed method allowed for the direct determination of dimerization constants(KD) by monitoring temperature-induced J-dimer disassembly. The determined KD values ranged from108 to 1015 M−1, with the bulkiness of the coordinating substituents being the primary factor affecting thedimerization strength. The insights gained could be instrumental in the rational design of self-coordinat-ing supramolecular systems that are important in, for example, energy and electron transfer processes.IntroductionPhthalocyanines (Pcs), with a history spanning nearly acentury, have been widely utilized in various applications,including pigments,1 nonlinear optics,2 dye-sensitized solarcells,3 and photodynamic therapy.4 In pursuit of expandingthe functional scope of Pcs, their aza analogues, azaphthalo-cyanines (AzaPcs), have been synthesized.5 Among AzaPcs, tet-rapyrazinoporphyrazines are the most extensively studied,finding use as sensors for metal cations6 or pH,7 photosensiti-zers,8 and quenchers of fluorescence in oligodeoxynucleotideprobes.9 It is well established that the unique photophysicalproperties of these dyes, critical for such applications, are pre-dominantly associated with their monomolecular form.However, the planar macrocyclic core of Pcs and AzaPcs exhi-bits a strong tendency to aggregate, leading to the formationof two distinct types of aggregates. The first and most com-monly observed type is the H-aggregate, where molecules alignin a parallel, sheet-like stacking arrangement. This type ofaggregation results in a hypsochromic shift of the Q-band inthe absorption spectrum, accompanied by a loss of fluo-rescence and other key photophysical properties (Fig. 1a). Incontrast, the J-aggregate involves a slipped arrangement ofmolecules, characterized by a bathochromic shift of theQ-band, with the retention of most photophysical properties(Fig. 1b). Despite being prevalent in other structural types ofdyes,10 the latter aggregates are exceedingly rare in Pcs wherehydrophobic and π–π interactions strongly favor H-aggregateformation. In Pcs and AzaPcs, the J-aggregates are formed bythe coordination of (non)peripheral substituents with the†Electronic supplementary information (ESI) available: NMR spectra, a bindingmodel, absorption and emission spectra, and a table with literature data forassociation constants. See DOI: https://doi.org/10.1039/d4qi02834aaDepartment of Pharmaceutical Chemistry and Pharmaceutical Analysis, Faculty ofPharmacy in Hradec Kralove, Charles University, Heyrovskeho 1203, Hradec Kralove,50005, Czech Republic. E-mail: zimcik@faf.cuni.czbInstitute of Organic Chemistry and Biochemistry (IOCB), Czech Academy of Sciences(CAS), Flemingovo nám. 2, 160 00 Prague, Czech RepubliccResearch Center for Materials Nanoarchitectonics (MANA), National Institute forMaterials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan1590 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal  | View Issuehttp://rsc.li/frontiers-inorganichttp://orcid.org/0000-0001-6847-768Xhttp://orcid.org/0000-0001-6924-5960http://orcid.org/0000-0002-8329-0634http://orcid.org/0000-0002-2183-1220http://orcid.org/0000-0002-3533-3601https://doi.org/10.1039/d4qi02834ahttps://doi.org/10.1039/d4qi02834ahttp://crossmark.crossref.org/dialog/?doi=10.1039/d4qi02834a&domain=pdf&date_stamp=2025-02-05http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834ahttps://pubs.rsc.org/en/journals/journal/QIhttps://pubs.rsc.org/en/journals/journal/QI?issueid=QI012004central cation of the neighboring molecule, thus enforcing theslipped formation. Despite the intriguing nature of theseassemblies, reports of J-aggregates in Pcs and AzaPcs areexceedingly scarce and often limited to basic observations orspecific applications,11–18 lacking comprehensive systemcharacterization and analysis of underlying relationships.The central metal, playing a crucial role in J-dimers, is alsowidely utilized in other supramolecular assemblies of Pcs.Complexes of metal Pcs with various ligands coordinated totheir central cations are well-documented in the literature.Pyridine is frequently employed as a coordinating ligand toreduce the formation of H-aggregates,13,19 while other nitrogen-donor ligands, such as imidazole, are utilized to modify com-pounds of interest, including fullerene,20 BODIPYs,21 and sub-phthalocyanines.22 These modifications, after coordination tothe central cation of Pcs, often lead to the formation of func-tional non-covalently bonded dyads. Understanding the associ-ation constants between these ligands and the central cation isessential for the characterization and design of such supramole-cular systems, which are applied in light harvesting,23,24 thedevelopment of organic solar cells,25 investigation of charge-transfer processes26,27 and other related fields. However, unlikein porphyrins, where ligand coordination induces significantspectral changes in the absorption spectra,28,29 the determi-nation of association constants in Pcs is more challenging. Thedifferences between the absorption spectra of free and ligand-coordinated Pcs are often minimal and, in some cases, nearlyundistinguishable (also see below).30–32 In such instances,association constants are typically derived from secondaryeffects following ligand binding, such as electron or energytransfer to or from the ligand-attached molecule. However,these methods impose significant limitations on the range ofstudied ligands, as they must be functionalized with appropriatephoton or electron donors/acceptors.In this study, we developed a straightforward UV/Vis andfluorescence-based method to determine the association con-stants between a wide range of ligands and the central cationin Pcs and AzaPcs, leveraging the dissociation of J-dimers ofthese self-assembled molecules. This was allowed by the prepa-ration of reliable mathematical models describing the assem-bly, followed by an in-depth investigation into the formation ofJ-aggregates in Pc analogues, focusing on their disassembly inrelation to the substituents involved in the coordination andelucidating fundamental structural relationships.Fig. 1 Basic differences between (a) H-aggregates and (b) J-aggregates in spatial arrangement, absorption, and emission spectra of Pcs andAzaPcs. Monomeric species are in red, and aggregated are in blue. Data adopted from ref. 17 (J-aggerates) and ref. 33 (H-aggregates).Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1591Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aResults and discussionDesign and synthesisIn this work, a series of zinc(II) AzaPcs of tetrapyrazinoporphyr-azine type was designed (Fig. 2) to explore the impact of peri-pheral substitution bulkiness and flexibility on J-aggregate for-mation. The series included both symmetrical (1Zn–7Zn) andunsymmetrical (8Zn–10Zn) derivatives. The nitrogen in N,N-dialkylamino substituents acted as an N-donor, coordinatingto the central zinc(II) of an adjacent molecule, thereby facilitat-ing J-aggregate formation in non-coordinating solvents. Theselection of AzaPc over Pc was primarily motivated by the syn-thetic availability of both the dicarbonitrile precursors and thefinal macrocycle, allowing the production of a wide range ofmolecules. In contrast, the synthesis of octa(dialkylamino)Pcsis typically very complex and yields are low,34 whereas the aza-analogues are readily available.17The synthesis of new compounds followed well-establishedprocedures. Most precursors (Scheme 1) were synthesizedfrom commercially available 5,6-dichloropyrazine-2,3-dicar-bonitrile through nucleophilic substitution with secondaryamines. This reaction was facilitated by strongly electron-deficient carbons at positions 5 and 6. The yields for theseprecursors were generally high, exceeding 70%, except com-pound 16, which had a lower yield of 48%. The reduced yieldwas likely due to its low solubility, leading to losses duringpurification. Of note, N,N,N′-trimethylethylenediamine wasused instead of a secondary amine during the synthesis ofcompound 17, resulting in the formation of a stable six-membered ring followed by dealkylation.35 Compound 19 wassynthesized by nucleophilic substitution of 5-chloropyrazine-2,3-dicarbonitrile (18), which was prepared according to apublished procedure,36 with dimethylamine in ethanolicsolution.The preparation of metal-free AzaPcs was carried out usingthe Linstead method, initiated by lithium butoxide. The purifi-cation of symmetric compounds 1H2–7H2 was straight-forward, with yields ranging from 11% to 58%. Lower yieldswere observed for 1H2, 6H2, and 7H2, primarily due to theirpoor solubility in most organic solvents. The isolation of low-symmetry compounds 8H2–10H2, produced by the statisticalcyclotetramerization of two different precursors, was morechallenging. It required the isolation of a single congener ofAAAB type from a mixture of six possible congeners, which wasFig. 2 Synthesized symmetrical (1–7) and unsymmetrical (8–10) AzaPcs.Scheme 1 Synthetic pathways: (i) dimethylamine (33% in EtOH), THF, r.t., 1 h; (ii) dipropylamine, THF, reflux, 2 h; (iii) dibutylamine, THF, reflux,2 h; (iv) piperidine, THF, r.t., 1 h; (v) morpholine, THF, r.t., 1 h; (vi) N,N,N’-trimethylethylenediamine, K2CO3, THF, reflux, 2.5 h; (vii) dimethylamine(33% in EtOH), THF, r.t., 1 h; (viii) Li, BuOH, reflux, 30 min; and (ix) Zn(OAc)2, pyridine, reflux, 3 h.Research Article Inorganic Chemistry Frontiers1592 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aachieved by column chromatography on silica, yielding 11% to22%. The final step in the synthesis of all cyclotetramersinvolved the incorporation of a zinc(II) cation into the center ofthe metal-free macrocycle. This was accomplished by reactingthe metal-free compounds with zinc(II) acetate in pyridine,yielding between 14% and 97%. Lower yields for 1Zn, 6Zn,and 7Zn were again attributed to their low solubility. Tofurther extend our study to other central metals, magnesium(II) complex 4Mg was prepared by cyclotetramerization of thecorresponding precursor using magnesium butoxide. All syn-thesized compounds were characterized by 1H and 13C NMRspectroscopy, and HRMS, with some exceptions due to the lowsolubility of some AzaPcs.Characterization of J-dimersThe formation of supramolecular interactions was initiallyconfirmed through NMR spectroscopy of the synthesizedAzaPcs in various solvents. The NMR spectra of 3H2 and 3Znare shown in Fig. 3 as representative examples. For the metal-free 3H2, 1H NMR spectra were recorded in both toluene-d8and pyridine-d5 (Fig. 3a). In both solvents, the spectra dis-played sharp and distinct triplets or quartets corresponding tothe propyl group, indicative of the monomeric form of 3H2.This form was expected, as the absence of a central cation pre-cludes any significant J-aggregation. Similar monomeric be-havior was observed for 3Zn in pyridine-d5, attributed to thecoordination of pyridine-d5 to the central zinc(II) ion (Fig. 3b).However, when 3Zn was analyzed in the non-coordinatingtoluene-d8, the 1H NMR spectrum became more complex,suggesting the formation of a supramolecular assembly (asschematically drawn in the inset to Fig. 3c). To further eluci-date the structure of this assembly, the HSQC NMR techniquewas employed (Fig. 3c), allowing for the assignment of specificsignals to their corresponding hydrogen atoms. The analysisrevealed two strongly shielded sets of –N(CH2)– signals at δ =3.04 and 2.89 ppm, which were attributed to the methylenesignals of those –N(CH2)– involved in the coordination to thezinc(II) ion and the neighboring vicinal –N(CH2)–. The ringcurrent effect of the macrocycle, which influenced the substi-tuents positioned above the core, was responsible for thisshielding. This effect was also evident for other hydrogens ofthe same substituent, even in the methyl groups observed at δ= 0.64 ppm. The ratio of the shielded –N(CH2)– signals (at δ =3.04 and 2.89 ppm) to the unaffected signals (δ = 3.8–4.3 ppm)is approximately 8 : 24 as determined from the integral ofHSQC spectra (see ESI, Fig. S1 and S2†). This ratio confirmedthat only one quarter of the macrocycle is involved in thecoordination, supporting the presence of the J-dimer structureconnected by two coordination bonds as drawn in Fig. 3c. Thedata ruled out potential supramolecular stair-like chain, whichwould have exhibited a 16 : 16 ratio. DOSY NMR experimentsfurther supported the presence of the supramolecular dimericstructure of 3Zn (Fig. S3a†), which can be disassembled uponthe addition of NMI (Fig. S3b†).The absorption and emission spectra provided further evi-dence for the formation of J-dimers of 3Zn. In pyridine, theFig. 3 NMR spectra of 3H2 (a) and 3Zn (b and c) in pyridine-d5 (black, upper spectra) and toluene-d8 (brown, lower spectra). Asterisks indicateresidual solvent signal and signal of the non-deuterated solvent. (a) 1H NMR of 3H2 in pyridine-d5 and toluene-d8 (monomeric form in both sol-vents). (b) 1H NMR spectra of 3Zn in pyridine-d5 (monomeric form) and in toluene-d8 (dimeric form). Color arrows indicate which signals belong towhich hydrogen. The resonance at 3.85 ppm in toluene-d8 is overlapped by a signal of water. (c) HSQC experiment of 3Zn in toluene-d8 and sche-matic illustration of the J-dimer formation. Green boxes (and green N,N-dipropylamino groups) indicate the hydrogens located above/below themacrocyclic core.Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1593Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aabsorption Q-band of 3Zn appeared as a single, sharp peak atλmax = 660 nm, characteristic of Pcs and their analogues in themonomeric state (Fig. 4b). This was accompanied by a corres-ponding mirrored emission peak at λem = 666 nm (Fig. 4c). Incontrast, when measured in toluene, the absorption spectrumof 3Zn broadened and exhibited a bathochromic shift to λmax =702 nm (Fig. 4b). The emission spectrum also showed a red-shifted peak at λem = 739 nm, with a significant Stokes shift ofΔλ = 37 nm (Fig. 4b) that can be explained by increased flexi-bility of the dimeric structure of the chromophore not con-nected by covalent but coordination bonds. The excitationspectra measured in toluene perfectly overlapped the corres-ponding absorption spectra (Fig. S4†) confirming the origin ofthe fluorescence signal. These spectral changes are consistentwith the formation of J-dimers in toluene, as supported by theNMR data. For comparison, the absorption spectra of metal-free 3H2 were consistent across both solvents (Fig. 4a), indicat-ing that 3H2 remained in the monomolecular form. Theobserved splitting of the Q-band is a typical feature of themetal-free Pcs and their analogues, resulting from the reducedD2h symmetry of the macrocycle.Photophysical propertiesFollowing the confirmation of J-dimer formation, we pro-ceeded with the photophysical characterization of all studiedderivatives in both monomeric and J-dimer forms. The spectralbehavior observed was consistent with that of 3Zn: the com-pounds exhibited monomeric characteristics in coordinatingsolvents, while in toluene, they formed J-dimers with nearlyidentical Q-band positions (Table 1). It is noteworthy that thepresence of eight dialkylamino substituents significantlyquenched the excited states through intramolecular chargetransfer (ICT). ICT, a predominant relaxation pathway for (di)alkylamino AzaPcs, is highly efficient (particularly in polar sol-vents) and surpasses other relaxation mechanisms such asintersystem crossing or fluorescence.37 To evaluate the impactof different solvents on the properties of AzaPcs, we employedthree solvents with distinct characteristics: DMF (a polarsolvent where AzaPcs remain monomeric), toluene (a nonpolarsolvent where AzaPcs form J-dimers), and toluene with 0.12 Mpyridine (nonpolar, but where AzaPcs are in the monomericform due to coordination to pyridine). Due to the low solubi-lity of compound 7Zn, accurate determination of all photo-physical parameters was not feasible.First, all photophysical parameters were measured in DMFto assess the properties of the derivatives in their monomericstate. In DMF, the spectra of all studied compounds were con-sistent with those observed in pyridine (Table 1). The quantumyields for these compounds were close to zero as a result ofhighly efficient ICT facilitated by the highly polar solvent. In anonpolar toluene/pyridine mixture, the ICT effect was dimin-ished, leading to a notable increase in quantum yields, thoughthey remained relatively low, with fluorescence quantum yieldsFig. 4 (a) Absorption spectra of 3H2 (5 μM) in toluene (blue) and pyri-dine (red). Absorption (b) and emission spectra (λex = 588 nm) (c) of 3Zn(5 μM) in toluene (blue) and in pyridine (red).Table 1 Photophysical parameters of the prepared AzaPcsDMF Toluene Toluene with 0.12 M pyridineλmax, nm λem, nm ΦΔ ΦF λmax, nm λem, nm ΦΔ ΦF λmax, nm λem, nm ΦΔ ΦF1Zn 654 675 0.0033 0.0005 630/702 752 0.063 0.0089a 655a 663a 0.034a 0.0002a2Zn 660 673 <0.005c <0.0001 c 635/699 738 0.28c 0.027c 659 664 0.056c 0.0004c3Zn 661 673 0.0049 0.000062 635/702 739 0.14 0.039 660 666 0.063 0.00564Zn 661 673 0.0073 <0.0001 635/708 756 0.26 0.029 660 675 0.081 0.00675Zn 660 673 <0.005 0.000048 640/706 752 0.10 0.0057 661 674 0.031 0.000926Zn 656 673 0.0041 0.000052 632/702 737 0.36 0.033c 657a 661a 0.044a 0.00177Zn 651 672 —b —b —b —b —b —b 651a 656a —b —b8Zn 660 673 0.0080 0.00007 634/707 744 0.28 0.019 659 669 0.037 0.00299Zn 665 673 0.0079 0.000050 636/722 766 0.35 0.022 665 674 0.061 0.002910Zn 660 673 0.0064 0.00001 637/706 749 0.22 0.010 659 668 0.032 0.0017a Concentration of pyridine was 0.62 M instead 0.12 M. b Cannot be determined due to insufficient solubility. c Taken from previouspublication.17Research Article Inorganic Chemistry Frontiers1594 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834a(ΦF) reaching up to 0.007 and singlet oxygen quantum yield(ΦΔ) ranging from 0.03–0.08. The formation of J-dimers inpure toluene further enhanced both quantum yields, with ΦFincreasing up to 0.04 and ΦΔ rising significantly to between0.06 and 0.36. This increase is likely due to the suppression ofICT within the supramolecular self-assembly of the J-dimersmost likely due to changed properties of the donor (AzaPc) ascoordination of one out of eight peripheral nitrogens cannotresult in such a change.Stability of J-dimers and their disassemblyThe stability of J-dimers is characterized using three constantsin an approach similar to that published by García-Iglesiaset al.12 The constant KL (Fig. 5a, eqn (1)) represents the apparentconstant for the dimer disassembly by the coordinating ligand(L). This apparent constant is a composite of two underlyingprocesses, which are the formation of the AzaPc J-dimer charac-terized by the dimerization constant (KD) (Fig. 5b, eqn (2)) andthe association between the monomeric AzaPc’s central cationand the coordinating ligand determined by the K1 constant(Fig. 5c, eqn (3)). Therefore, the apparent constant KL can beexpressed in terms of KD and K1 stepwise constants as KL = K12/KD. For details regarding the derivation of the binding model,please refer to the binding models section in the ESI.†To characterize the stability of the J-dimers in this series ofAzaPcs, the dimerization constant (KD) was determined foreach compound (Table 2). The concentration-dependentUV-Vis or fluorescence experiments (the dilution approach)could not be used due to the expected high dimerization con-stant KD where the monomeric and dimeric forms would notbe visible in reasonable concentration ranges. Instead, KD wasobtained by progressively disassembling the J-dimers throughincreasing temperature and monitoring the resulting changesin fluorescence spectra (Fig. 6b and Fig. S5, S6†), whichallowed direct KD determination as well as enthalpy andentropy of the dimerization process (Table 2). So far, the KDvalues for Pc J-dimers were reported only in two cases, more-over approximated indirectly from titration with the ligandand the known value of K1 for structurally similarcompounds.11,12 The details regarding our binding model anddetermination of KD at 23 °C are given in the Binding modelssection of the ESI.† The measurements were performed at aconcentration in a range of 0.05–5.0 μM, tailored to cover mostAzaPcs dimers’ stability range. Notably, the most stableJ-dimers, 1Zn and 6Zn, did not disassemble even at the lowestFig. 5 Schematics of the equilibrium processes and definition ofcorresponding equilibrium binding constants exemplified on 3Zn. (a)Dimer (AzaPc)2 disassembly by coordinating ligand L characterized bythe KL constant. (b) AzaPc J-dimerization process characterized by theKD constant. (c) Monomeric AzaPc association with coordinating ligandL characterized by the K1 constant.Table 2 List of calculated equilibrium binding constants (at 23 °C), enthalpies and entropies, which characterize J-dimer stability in toluene deter-mined by absorption (UV) or fluorescence (F) methodsKD [M−1] K1 (UV) [M−1] K1 (F) [M−1] KL (UV) [M−1] KL (F) [M−1] ΔH c [J mol−1] ΔS d [J mol−1 K−1]1Zn 1.24 × 1015 a n.d. n.d. 4.26 × 10−5 a 6.86 × 10−5 a n.d. n.d.2Zn 3.13 × 1011 1.54 × 105 3.17 × 105 7.61 × 10−2 3.22 × 10−1 −1.23 × 105 −1.97 × 1023Zn 5.32 × 109 2.90 × 105 2.62 × 105 1.58 × 101 1.29 × 101 −1.23 × 105 −2.30 × 1024Zn 1.51 × 108 b 4.24 × 105 4.58 × 105 1.19 × 103 1.40 × 103 −1.21 × 105 −2.53 × 1025Zn 1.71 × 109 b 2.67 × 105 2.45 × 105 4.14 × 101 3.51 × 101 −1.22 × 105 −2.35 × 1026Zn 3.73 × 1015 a n.d. n.d. 1.20 × 10−5 a 2.24 × 10−5 a n.d. n.d.7Zn n.d. n.d. n.d. n.d. n.d. n.d. n.d.8Zn 1.25 × 1011 1.60 × 105 1.62 × 105 2.05 × 10−1 2.10 × 10−1 −1.38 × 105 −2.54 × 1029Zn 3.09 × 1011 1.66 × 105 1.74 × 105 8.94 × 10−2 9.81 × 10−2 −1.49 × 105 −2.86 × 10210Zn 2.36 × 1012 2.63 × 105 4.05 × 105 2.94 × 10−2 6.95 × 10−2 −1.74 × 105 −3.55 × 102Ligand = pyridine. aDetermined from the titration of J-dimer by pyridine and average K1 = 2.46 ± 0.90 × 105 M−1 (UV) and K1 = 2.89 ± 1.03 × 105M−1 (F). n.d. = could not be determined. b Following KD values were obtained using absorption data: KD(4Zn) = 2.47 × 107 M−1, KD(5Zn) = 1.84 × 108M−1. c Experimental error is under 10% except for 10Zn (18%). d Experimental error is under 10% for 4Zn, 5Zn, 8Zn and 9Zn, under 20% for 2Znand 3Zn, and under 30% for 10Zn.Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1595Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834ameasurable concentration (0.05 μM), which was close to theinstrument’s detection limit. For these compounds, KD wasestimated using the later-determined K1 (see below) and valuesobtained from titration with a ligand and a combination ofeqn (1) and (2), i.e., KD = K12/KL. Due to 7Zn’s extremely lowsolubility, it was impossible to determine any constants forthis compound, and it was excluded from further experiments.Temperature-induced changes could also be tracked in absorp-tion spectra (Fig. 6a and Fig. S5†), however, due to the gener-ally lower sensitivity of UV-Vis spectrophotometry in compari-son to fluorescence methods, this was feasible only for 4Znand 5Zn where higher concentrations (10 μM) were employed.Fig. 6 Changes in the absorption (a) and emission (λex = 609 nm, isosbestic point) (b) spectra of 4Zn in toluene (c = 10 μM for UV/vis and 5 μM foremission) with increasing temperature. (c and d) Changes in the absorption (c) and emission (d, λex = 588 nm, isosbestic point) spectra of 4Zn (c =10 μM for UV/vis and 5 μM for emission) upon J-dimer disassembly by the addition of pyridine. (e) Dependence of KD values on the number of atomson nitrogen in the peripheral substituent (for 8Zn–10Zn, the number of atoms is considered four as it represents 34 of all substituents). (f )Disassembly of J-dimers of all AzaPcs (c = 10 μM) upon the addition of pyridine, monitored as absorbance at the monomer band maximum. In allfigures, dots represent experimental values, and lines represent the fit of the binding model.Research Article Inorganic Chemistry Frontiers1596 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aThe KD values obtained by both methods were consistent. Thevalues of KD are summarized in Table 2 and graphically rep-resented in Fig. 6e. From these results, it is evident that theprimary factor influencing J-dimer stability is the bulkiness ofthe substituents on the N-donor moiety. There was an almostlinear relationship between KD and the size of these substitu-ents (Fig. 6e, black points), especially when considering onlyhomologous series (1Zn–4Zn). Introducing an oxygen atom tothe alkyl chain (5Zn) slightly increases the dimerization. Tofurther explore the impact of bulky peripheral substituentsthat were not involved in coordination (such as dibutylaminogroups that make up three-quarters of the molecule), unsym-metrical compounds 8Zn–10Zn with one quarter featuringsmaller substituents were analyzed (due to steric reasons, it isexpected that the smaller moiety will be responsible for coordi-nation). Interestingly, their KD values (∼1011–1012 M−1) weresignificantly higher than that of the dibutyl-substituted 4Zn(KD = 1.51 × 108 M−1) but at the same time significantlysmaller than that of dimethyl-substituted 1Zn (KD = 1.22 × 1015M−1). This suggests that J-dimer stability was heavily driven bythe smaller (coordinating) quarter of the molecule, however, itstill had important contributions from the remaining substitu-ents. This can be utilized in the design of J-dimers with finelytuned dimerization. Overall, the KD values of all derivativesobserved were remarkably high, even for AzaPcs 4Zn and 5Znwith bulky substituents, aligning with the extreme stability ofthe few Pc J-dimers previously reported in the literature (KD ∼1011–1012 M−1).11,12 In contrast, H-dimers of Pcs and naphtha-locyanines which were stabilized by simple π–π stacking, typi-cally exhibit KD values in the range of 104–106 M−1 in varioussolvents.38,39To further investigate the stability of J-dimers in the pres-ence of competing ligands, toluene solutions of J-dimers (at aconcentration of 10 μM) were titrated with pyridine. Pyridinedisplaces the AzaPc N-donor from its coordination with thecentral zinc(II) ion, leading to the disassembly of the J-dimer.This process was tracked by observing changes in the absorp-tion and emission spectra (Fig. 6c, d and Fig. S7, S8†).Specifically, the characteristic J-dimer band at around 702 nm(with corresponding emission at 750 nm) decreased, while theQ-band of the monomer at around 660 nm (with emission at668 nm) increased, similarly to the temperature-induced disas-sembly described earlier. The spectra exhibited clear isosbesticpoints, indicating a direct transition between two states(monomer and dimer), which further confirmed the presenceof a simple dimeric structure rather than more complex multi-mers. The data were then plotted as AzaPc’s monomer absor-bance versus pyridine concentration (Fig. 6f), indicatingdifferent J-dimer stability. Using the previously determined KDvalues for 2Zn–5Zn and 8Zn–10Zn, the titration data werefitted using a binding model containing both dimerizationand association with ligand (see the Binding models section inthe ESI†), which allowed for determining KL and K1. The titra-tions were analyzed using both absorbance and fluorescencechanges, and the resulting KL values were in good agreement(Table 2). As expected, the order of KL values correlated closelywith the KD values, demonstrating consistency across theseries. Values of the determined K1 values (Table 2) werealmost the same, yielding the average value of K1 = (2.46 ±0.90) × 105 M−1 (from UV/vis) and K1 = (2.89 ± 1.03) × 105 M−1(from fluorescence). The similarity of the ligand bindingstrength in the whole series of AzaPcs is the expected resultsince the electronic effects in all studied AzaPcs are the sameand should not affect the strength of association between theligand and AzaPc’s central cation. The low variability of K1values across such an extensive series of compounds confirmsthe validity of the measurements and the overall methodology.The average K1 values and data from pyridine-induced disas-sembly were then used to calculate KD and KL for 1Zn and 6Zn,where the high stability of the J-dimer prevented direct deter-mination of KD through temperature changes. These experi-ments allowed for a comprehensive understanding of the stabi-lity and behavior of the J-dimers across the series, providingvaluable insights into the factors influencing their formationand stability.Determination of association constants with various ligandsAs briefly mentioned in the Introduction section, determiningK1 values for Pcs and their analogues is particularly challen-ging due to the limited spectral changes observed in bothabsorption and fluorescence spectra upon ligand binding.This difficulty can be demonstrated by the addition of severalligands to a toluene solution of zinc(II) octakis(tert-butylsulfa-nyl)AzaPc, which does not form J-dimers in toluene. In thiscase, almost no spectral changes were observed (refer to ESI,Fig. S15 and S16†). However, the situation is markedlydifferent when J-dimers are present, as shown in our dataabove.Given the robustness of the newly developed method fordetermining association constants K1, we extended its appli-cation to a variety of N-, O-, and S-ligands (Table 3). The spec-tral changes in both absorption and fluorescence of 2Zn uponthe addition of these ligands (Fig. S9–S11†) were similar tothose observed with pyridine, as exemplified by the additionof diethylamine (Fig. 7a and b). The data were analyzed withfixed KD(2Zn) = 3.13 × 1011 M−1, allowing for the calculation ofK1 for each ligand (Table 3). For ligands with lower affinity (i.e.,lower K1) that failed to disassemble the J-dimers of 2Zn (e.g.,THF, N,N-dimethylaniline, triethylamine Fig. 7c), J-dimerswith lower KD (3Zn and 5Zn, KD ∼ 109 M−1) were utilized. Asshown above, in the titration with pyridine, switching to AzaPcwith different KD values did not affect the determined K1value, which shows the expected consistency of our model(Table 3). This finding highlights the versatility of the method,enabling the determination of association constants forligands across a wide range of K1 values by simply adjustingthe strength of the J-dimer used in the experiments. The datarevealed that the most potent ligand binding was observedwith N-methylimidazole (NMI, K1(F) = 6.40 × 106 M−1), followedby other N-ligands. A comparison with the literature data avail-able for pyridine and NMI, actually the only two ligands avail-able in the literature to the best of our knowledge (seeInorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1597Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aTable S1†), shows slightly higher values than those determinedby other methods, however, they are still within a similarrange. From the other ligands, it is notable that piperidineexhibited one of the strongest binding affinities, nearly match-ing that of NMI with K1(F) = 3.01 × 106 M−1. This suggests thatpiperidine could be a valuable alternative strong ligand forTable 3 Comparison of K1 (M−1, 23 °C) for different coordinating ligands determined by absorption (UV) or fluorescence (F) methods for octakis(dialkylamino)AzaPcsLigand Zn(II) (UV) Zn(II) (F) Mg(II) (UV) Mg(II) (F)N-Methylimidazol 5.82 × 106 a 6.40 × 106 a 1.93 × 106 b 2.28 × 106 bPiperidine 3.00 × 106 a 3.01 × 106 a 2.04 × 105 b 2.03 × 105 b4,4′-Bipyridine 4.22 × 105 a 5.21 × 105 a 3.79 × 104 b 3.88 × 104 bPyridine 1.54 × 105 a 3.17 × 105 a 1.66 × 104 b 1.79 × 104 bDiethylamine 2.44 × 104 a 3.02 × 104 a 3.08 × 104 b 3.20 × 104 bPyrazine 8.26 × 103 a 1.04 × 104 a 2.36 × 103 b 3.39 × 103 bEthanol 2.92 × 103 a 1.06 × 104 a n.d. n.d.Triethylamine 4.11 × 103 c 4.03 × 103 c 7.82 × 104 b 7.08 × 104 bTetrahydrofuran 5.77 × 102 d 6.15 × 102 d 2.59 × 103 b 3.35 × 103 bN,N-Dimethylaniline 3.65 × 102 d 3.32 × 102 d n.d. n.d.Thiolan n.d. n.d. n.d. n.d.Butanthiol n.d. n.d. n.d. n.d.aDetermined using 2Zn. bDetermined using 4Mg. cDetermined using 3Zn. dDetermined using 5Zn.Fig. 7 Disassembly of the J-dimer of 2Zn in toluene (10 μM) by the addition of diethylamine monitored by UV-vis (a) and fluorescence (b) spectra at23 °C. (c) Disassembly of the J-dimer of 2Zn in toluene (10 μM) by the addition of various coordinating ligands monitored in UV-vis as maximumabsorbance of the monomeric form. In all figures, dots represent experimental values, and lines represent the fit of the binding model.Research Article Inorganic Chemistry Frontiers1598 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aconstructing non-covalently assembled supramolecularsystems—a potential that has been relatively underexploreduntil now. The rigidity introduced by the ring closure in piper-idine seems to play a crucial role, as a similar but more flexiblesecondary amine, diethylamine, showed a binding affinity twoorders of magnitude lower K1(F) = 3.02 × 104 M−1. In contrast,the O-ligands demonstrated significantly lower affinity for thecentral zinc(II), with K1 ∼ 102–104 M−1. Surprisingly, ethanol,with a K1(F) = 1.06 × 104 M−1 showed two orders of magnitudehigher binding ability than tetrahydrofuran (THF), which iscommonly used to reduce aggregation in Pcs and their ana-logues. Lastly, the selected S-ligands (thiolan, butan-1-thiol)were unable to disassemble the J-dimers, indicating very lowaffinity for the central zinc(II). These findings underscore theutility of this novel method in elucidating the bindingaffinities of various ligands expanding the range of ligandsthat can be effectively studied.To further validate the determination of the K1 value by analternative method, we explored changes in 1H NMR duringtitration with NMI (with the highest K1 among studiedligands), using AzaPc 3Zn in toluene-d8 (1 mM) as a represen-tative example (Fig. 8). During the titration, the methyl signalsof the J-dimer, initially observed at chemical shifts δ = 1.25,1.14 and 0.64 ppm gradually decreased in intensity as thecorresponding signal for the monomeric form started toappear at δ = 1.06 ppm. This behavior was consistent acrossother signals, clearly indicating that the disassembly of theJ-dimer as NMI was introduced. K1 was determined based onthe fitting of the binding model to the integrated intensity ofresonances at δ = 0.64 and 1.14 ppm, which are attributed tothe J-dimer methyl group, and with KD = 5.32 × 109 M−1. Thedetermined K1 = 9.04 × 106 M−1 corresponds well to K1 for NMIdetermined by spectroscopic methods (see also Table 3): K1(F)= 5.82 × 106 M−1 and K1(UV) = 6.40 × 106 M−1. This consistencybetween NMR and spectroscopic methods reinforces thereliability of our results and highlights the versatility of theapproaches used in characterizing the interaction between theligands and the central zinc(II) cation in these supramolecularsystems.However, the supramolecular systems are not always basedonly on zinc(II) Pcs. Other central metals can be utilized aswell. The same method was therefore subsequently applied tothe magnesium(II) complex of the AzaPc derivatives, specifi-cally to compound 4Mg, which was chosen as the representa-tive with potentially suitable KD value for determination of K1with a larger number of ligands. Compound 4Mg efficientlyformed J-dimers, similar to its zinc(II) counterpart (Fig. S12and S13†). Using the binding models and methods describedabove, the dimerization constant was determined to be KD(4Mg)= 9.88 × 1010 M−1. This value is significantly higher than thatobserved for the corresponding zinc(II) complex (KD(4Zn) = 1.51× 108 M−1), indicating a stronger dimerization tendency for themagnesium(II) complexes with smaller central cations.Following this, 4Mg was used in titrations with selectedN-ligands to determine K1, which are listed in Table 3. Whencomparing these values with those of the zinc(II) analogues(also shown in Table 3), it was observed that the associationconstants for the magnesium(II) complexes were consistentlylower. This trend suggests that while magnesium(II) complexeshave a stronger tendency to form J-dimers (as indicated byhigher KD values), their interaction with ligands, as measuredby K1, is weaker compared to their zinc(II) counterparts. Thisdifference might be attributed to the central metal ions’different electronic properties and coordination environments,affecting their ability to interact with external ligands.To further explore the effects of peripheral substituents onthe association constant K1 and further extend the variabilityin the used compounds, 20Zn (Fig. 9 and Fig. S14†) was syn-thesized from precursor 19 and 5,6-bis(pentan-3-ylsulfanyl)pyrazine-2,3-dicarbonitrile. The presence of one N,N-dimethyl-amino substituent in 20Zn induced J-dimer formation intoluene, consistent with the behavior observed for previousAzaPcs. The bulky pentan-3-yl substituents were responsiblefor good solubility in organic solvents and tuning the dimeri-zation constant as suggested above. The compound was alsodesigned so that the electronic effects of alkylsulfanyl substitu-ents differ significantly from those of dialkylamino groups, asindicated by Hammett substituent constants (data for theclosest available substituent are σp = 0.07 and σp = −0.93 for–SCH(CH3)2 and –N(C3H7)2, respectively).40 The presence ofjust one (instead of eight) N,N-dialkylamino fragment (donorfor ICT) also had a positive effect on the fluorescence intensitythat reached values of ΦF = 0.044 (J-dimer in toluene) and ΦF =0.23 (monomer in toluene with 0.12 M pyridine). By appli-cation of the above procedures, KD for 20Zn was determined tobe 1.65 × 1010 M−1, relatively closely correlating with the KD =3.09 × 1011 M−1 of compound 9Zn, which features the sameN,N-dimethylamino binding moiety but with different rest ofthe molecule containing six N,N-dibutylamino fragments. TheFig. 8 The course of titration of 3Zn in toluene-d8 (1 mM) by NMI at23 °C. Blue numbers and arrows belong to the dimeric form. Rednumbers and arrows belong to monomers. Inset: disassembly of theJ-dimer of 3Zn by NMI as monitored by integrated intensity of reso-nances due to the J-dimer at δ = 0.64 ppm (squares) and δ = 1.14 ppm(circles). Dots represent experimental values, and lines represent the fitof the binding model.Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1599Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aJ-dimer of 20Zn in toluene was then disassembled by pyridineand NMI (Fig. 9), allowing the determination of K1 values fromboth UV-vis and fluorescence data. The binding constantsobtained were K1(UV) = 6.05 × 104 M−1, K1(F) = 5.22 × 104 M−1and K1(UV) = 9.73 × 106 M−1, K1(F) = 8.13 × 106 M−1 for pyridineand NMI, respectively. When compared with K1 values for octa(dialkylamino)ZnAzaPcs in Table 3, there was only a slightdifference, despite significant variation in the electroniceffects of the substituents. This finding suggests that peri-pheral substituents have a rather small influence on theligand-binding strength of the central cation. Consequently,the K1 values obtained here can be considered broadly appli-cable, regardless of the specific peripheral substitution in thestudied Pc/AzaPc molecules. However, for precise determi-nation of K1 values for the target Pc/AzaPc molecules andligands of interest in the future, the Pcs/AzaPcs analogues thatform J-dimers should be designed structurally as close as poss-ible to the original target molecule. Then, the temperature-induced J-dimer disassembly (KD) and titration of J-dimer solu-tion with a ligand (KL) can be used as a proxy for the determi-nation of direct ligand binding strength (K1) using UV-Vis orfluorescence spectroscopy methods.ConclusionIn this study, we reported the formation of unique J-dimerswithin a series of alkylamino-substituted AzaPcs and quanti-fied their dimerization constants (KD). Our findings confirmedthat the spatial bulkiness of the AzaPc’s peripheral substituentcoordinating to the central cation plays a pivotal role in thestability of J-dimers, thereby influencing the corresponding KDvalues with further fine-tuning by the rest of the peripheralsubstituents. The J-dimers can be disassembled by variouscompeting ligands that bind to the central cation. The associ-ation constants (K1) of these ligands were independent of theJ-dimer stability, allowing the use of J-dimers as interchange-able probes for determining K1 values of ligands with varyingbinding strengths. Consequently, the disassembly of J-dimersoffers a straightforward method for determining K1 for a widerange of ligands, ranging from heterocyclic to purely aliphaticones, without the need for complex synthetic modifications,such as the addition of fluorophores or electron donors/accep-tors. Among the ligands investigated in this work, piperidineemerges as a particularly effective candidate, exhibitingbinding efficiency to zinc(II) AzaPc comparable to that of theFig. 9 (a and b) Disassembly of the J-dimer of 20Zn in toluene (10 μM) by pyridine monitored by UV-vis (a) and fluorescence (b) spectra at 23 °C. (c)Disassembly of the J-dimer of 20Zn in toluene (10 μM) by pyridine (green) and NMI (black) monitored by absorbance of its monomeric form.Research Article Inorganic Chemistry Frontiers1600 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834awidely used NMI. The significant spectral changes observedduring the formation and disassembly of J-dimers, coupledwith the consistently low variability in the K1 values deter-mined above across the entire series, underscore the reliabilityand robustness of the method. It opens its potential for thereliable determination of association constants between thecentral cation of Pcs (and their analogues) and the variousligands. Understanding these association constants couldfacilitate the rational design of self-coordinating supramolecu-lar systems currently employed in applications such as lightharvesting, solar cell development, and electron transferprocesses.Experimental sectionGeneralAll organic solvents were of analytical grade. Anhydrousbutanol used for the cyclotetramerization was freshly distilledfrom magnesium before use. All other chemicals for the synth-eses were purchased from certified suppliers (i.e., Sigma-Aldrich, TCI Europe, Acros, and Merck) and used as received.TLC was performed on Merck aluminum sheets coated withsilica gel 60 F254. Merck Kieselgel 60 (0.040–0.063 mm) wasused for column chromatography. The 1H and 13C NMRspectra were recorded on a Varian VNMR S500 (AgilentTechnologies, Santa Clara, USA) spectrometer or a JeolJNM-ECZ600R spectrometer (Jeol, Akishima, Japan). Thechemical shifts are reported as δ values in ppm and areindirectly referenced to Si(CH3)4 via the residual signal fromthe solvent. J values are given in Hz. IR spectra were measuredon Nicolet 6700 (Thermo Scientific, USA). The UV-Vis spectrawere recorded using a Shimadzu UV-2600 spectrophotometer(Shimadzu, Kyoto, Japan). Fluorescence spectra were recordedusing an FS5 or FLS-1000 spectrofluorometer (EdinburghInstruments, Edinburgh, UK). HRMS spectra were recorded onUHPLC system Acquity UPLC I-class (Waters, Milford, USA)coupled to the high-resolution mass spectrometer (HRMS)Synapt G2Si (Waters, Manchester, UK) based on Q-TOF.Chromatography involved an Acquity UPLC Protein BEH C4(2.1 × 50 mm, 1.7 μm, 300 Å) column using gradient elutionwith ACN and 0.1% formic acid at a flow-rate of 0.4 ml min−1.Electrospray ionization was operated in the positive ion mode.The ESI spectra were recorded in the range of 50–5000 m/zusing leucine-enkephalin as a lock mass reference and sodiumiodide for external calibration or in the range of 50–1200 m/zusing leucine-enkephalin as a lock mass reference and sodiumformate for external calibration. The following compoundswere prepared according to published procedures: AzaPcs2H2,41 2Zn,41 5H2,17 5Zn,17 5-chloropyrazine-2,3-dicarboni-trile,36 and 5,6-bis(pentan-3-ylthio)pyrazine-2,3-dicarbonitrile.42Synthesis5,6-Bis(dimethylamino)pyrazine-2,3-dicarbonitrile (12). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.00 g, 5.03 mmol) wasdissolved in THF (40 mL), and dimethylamine (33% solutionin EtOH, 5.38 mL, 30.13 mmol) was added. The reactionmixture was stirred for 1 hour at room temperature and moni-tored by TLC (hexane/ethyl acetate, 4 : 1, Rf = 0.61). After com-pletion, the reaction was filtered and evaporated underreduced pressure. The product was purified by recrystallizationfrom MeOH. Yield: 933 mg (86%), yellow crystals. 1H NMR(500 MHz, CDCl3) δ 3.02 (s, 12H). 13C NMR (126 MHz, CDCl3) δ147.64, 120.45, 114.87, 38.82. HRMS (ESI): m/z calculated forC10H13N6 [M + H]+: 217.1196; found: 217.1206. IR (ATR) ν 2970(CH), 2227 (CN), 1531, 1504, 1422, 1400, 1319, 1189,1141 cm−1.5,6-Bis(dipropylamino)pyrazine-2,3-dicarbonitrile (13). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.0 g, 5.03 mmol) was dis-solved in THF (100 mL), dipropylamine (4.13 mL, 30.15 mmol)was added dropwise and the reaction was heated to reflux. Thereaction mixture was refluxed for 2 hours and then evaporatedto dryness under reduced pressure. The crude residue was dis-solved in ethyl acetate (150 mL) and washed with water (3 ×75 mL). The organic layer was dried over anhydrous sodiumsulfate, filtered, and evaporated under reduced pressure. Thefinal product was recrystallized from hot methanol. Yield:1.23 g (74%), yellow crystals. 1H NMR (500 MHz, CDCl3) δ3.45–3.39 (m, 8H), 1.49 (h, J = 7.4 Hz, 8H), 0.81 (t, J = 7.4 Hz,12H). 13C NMR (126 MHz, CDCl3) δ 146.08, 120.01, 115.07,50.42, 20.82, 11.49. T. m.: 100.2–101.6 °C; HRMS (ESI): m/z cal-culated for C18H29N6 [M + H]+: 329.2448; found: 329.2463. IR(ATR) ν 2963 (CH), 2931 (CH), 2874 (CH), 2220 (CN),1524 cm−1.5,6-Bis(dibutylamino)pyrazine-2,3-dicarbonitrile (14). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.0 g, 5.03 mmol) was dis-solved in THF (40 mL), then, dibutylamine (5.04 mL,30.13 mmol) was added dropwise, and the reaction was heatedto reflux. The reaction mixture was refluxed for 2 h. The reac-tion was monitored by TLC (toluene, Rf = 0.56). The reactionmixture was cooled to room temperature, filtered, and evapor-ated under reduced pressure. The final product was purifiedby column chromatography on silica using toluene as themobile phase. Yield: 1.787 g (92%), yellow crystals. 1H NMR(500 MHz, CDCl3) δ 3.43 (t, J = 7.4 Hz, 8H), 1.48–1.37 (m, 8H),1.20 (h, J = 7.3 Hz, 8H), 0.88 (t, J = 7.5 Hz, 12H). 13C NMR(126 MHz, CDCl3) δ 146.10, 120.03, 115.10, 48.41, 29.68, 20.28,13.75. HRMS (ESI): m/z calculated for C22H37N6 [M + H]+:385.3074; found: 385.3086. IR (ATR) ν 2962 (CH), 2933 (CN),2219 (CN), 1521, 1500, 1442, 1373, 1338, 1087 cm−1.5,6-Di(piperidin-1-yl)pyrazine-2,3-dicarbonitrile (15). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.0 g, 5.03 mmol) was dis-solved in THF (100 mL), and piperidine (2.98 mL, 30.17 mmol)was added dropwise. The reaction mixture was stirred at roomtemperature for 1 hour and then evaporated to dryness underreduced pressure. The crude residue was dissolved in ethylacetate (150 mL) and washed by water (3 × 75 mL). The organiclayer was dried over anhydrous sodium sulfate, filtered, andevaporated under reduced pressure. The final product wasrecrystallized from hot methanol. Yield: 1.24 g (83%), yellowcrystals. 1H NMR (500 MHz, CDCl3) δ 3.49–3.44 (m, 8H),Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1601Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834a1.69–1.64 (m, 12H). 13C NMR (126 MHz, CDCl3) δ 146.79,120.46, 114.87, 47.23, 25.41, 24.24. HRMS (ESI): m/z calculatedfor C16H21N6 [M + H]+: 297.1822; found: 297.1835. IR (ATR) ν2944 (CH), 2857 (CH), 2227 (CN), 1516, 1460, 1273 cm−1.5,6-Dimorpholinopyrazine-2,3-dicarbonitrile (16). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.0 g, 5.03 mmol) was dis-solved in THF (70 mL), and morpholine (2.64 mL,30.16 mmol) was added dropwise. The reaction was stirred for1 hour at room temperature. The reaction mixture was filtered,and the filtrate was evaporated to dryness. The final productwas recrystallized from hot methanol. Yield: 720 mg (48%),white crystals. 1H NMR (500 MHz, CDCl3) δ 3.79 (t, J = 4.6 Hz,8H), 3.55 (t, J = 4.6 Hz, 8H). 13C NMR (126 MHz, CDCl3) δ146.63, 121.61, 114.21, 66.09, 46.83. HRMS (ESI): m/z calcu-lated for C14H17N6O2 [M + H]+: 301.1408; found: 301.1418. IR(ATR) ν 2994 (CH), 2978 (CH), 2891 (CH), 2851 (CH), 2234(CN), 1523, 1455, 1443, 1363, 1249, 1224, 1114, 1069, 1027,960, 882 cm−1.5,8-Dimethyl-5,6,7,8-tetrahydropyrazino[2,3-b]pyrazine-2,3-dicar-bonitrile (17). 5,6-Dichloropyrazine-2,3-dicarbonitrile (1.0 g,5.03 mmol) was dissolved in THF (70 mL), then potassium car-bonate (1.0 g, 7.53 mmol) and N,N,N′-trimethyl-ethylenediamine (789 μL, 6.03 mmol) were added, and thereaction was refluxed for 2.5 hours. The reaction mixture wascooled down, filtered, and evaporated. The final product wasrecrystallized from hot methanol. Yield: 757 mg (70%), yellow-brown crystals. 1H NMR (500 MHz, DMSO-d6) δ 3.63 (s, 4H),3.10 (s, 6H), 13C NMR (126 MHz, DMSO-d6) δ 143.9, 118.2,116.3, 45.7, 36.1. Tt = 239.5–242.0 °C. HRMS (ESI): m/z calcu-lated for C10H11N6 [M + H]+: 215.1040; found: 215.1043. IR(ATR) ν 2878 (CH), 2224 (CN), 2217 (CN), 1562, 1524, 1417,1361, 1302, 1123 cm−1.5-(Dimethylamino)pyrazine-2,3-dicarbonitrile (19). 5-Chloropyrazine-2,3-dicarbonitrile (2.0 g, 12.15 mmol) was dis-solved in THF (100 mL), and dimethylamine (33% solution ofin ethanol, 13 mL, 72.8 mmol) was added. The reactionmixture was stirred at room temperature for one hour, then fil-tered and evaporated under reduced pressure. The finalproduct was purified by column chromatography on silica withchloroform as a mobile phase. Yield: 1.68 g (80%), greenishcrystals. 1H NMR (600 MHz, CDCl3) δ 8.17 (s, 1H), 3.25 (s, 6H).13C NMR (150 MHz, CDCl3) δ 153.10, 133.26, 132.48, 118.44,114.75, 113.72, 38.09. HRMS (ESI): m/z calculated for C8H8N5[M + H]+: 174.0774; found: 174.0779. IR (ATR) ν 3076 (CH),2933 (CH), 2227 (CN), 1825, 1578, 1524, 1499, 1439, 1397,1296, 1251, 1230, 1184, 1109 cm−1.General procedure for synthesis of metal-free cyclotetramersFor symmetrical AzaPcs, the precursor (12–16, 1 equivalent)was dissolved in freshly distilled butanol (∼5 ml per 1 mmol ofprecursors), heated to reflux, and metal lithium (7 equivalents)was added to the boiling mixture. For unsymmetrical AzaPcs,precursor A (12, 17, 19, 1 equivalent) and compound 14(3 equivalents) were dissolved in freshly distilled butanol (∼5 mlper 1 mmol of all precursors), heated to reflux, and metallithium (28 equivalents) was added to the boiling mixture. Thereaction was refluxed for 30 minutes in both cases, and thenbutanol was evaporated under reduced pressure. The solidresidue was dissolved in a mixture of dichloromethane(∼50 mL per 1 mmol of precursor), water was added (∼25 mLper 1 mmol of precursor) and acidified with HCl (HCl wasadded in 1.2 equivalents per equivalent of lithium) beforebeing transferred to a separation funnel. The mixture wasextracted with dichloromethane (3 × 75 mL). The organiclayers were collected, dried over anhydrous sodium sulfate,and evaporated. Purification was performed by column chrom-atography on silica (the mobile phases for each compound arementioned below). Finally, the product was dissolved in aminimal amount of dichloromethane, added dropwise intomethanol (100 mL), and precipitated in a freezer for 24 hours.The solid was collected and dried under vacuum.2,3,9,10,16,17,23,24-Octakis(dimethylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (1H2). Compound 1H2 was pre-pared according to the general procedure above using com-pound 12 (870 mg, 4.02 mmol) and lithium (197 mg,28.19 mmol). Eluent: dichloromethane/methanol (25 : 1).Yield:140 mg (16%), a purple solid. 1H NMR (500 MHz, CDCl3/pyridine-d5 – 3 : 1) δ 3.40 (s, 48H), −1.46 (s, 2H). 13C NMR(126 MHz, CDCl3/pyridine-d5 – 3 : 1) δ 151.50, 39.51 (some aro-matic signals were not detected); HRMS (ESI): m/z calculatedfor C40H51N24 [M + H]+: 867.4723; found: 867.4711.2,3,9,10,16,17,23,24-Octakis(dipropylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (3H2). Compound 3H2 was pre-pared according to the general procedure above using com-pound 13 (400 mg, 1.22 mmol) and lithium (59 mg,8.52 mmol). Eluent: dichloromethane/acetone (30 : 1, Rf =0.67). Yield: 232 mg (58%), a purple solid. 1H NMR (500 MHz,CDCl3) δ 3.99 (t, J = 7.3 Hz, 32H), 1.79 (h, J = 7.3 Hz, 32H), 1.00(t, J = 7.3 Hz, 48H), −1.35 (s, 2H). 13C NMR (126 MHz, CDCl3) δ149.93, 147.17, 140.02, 50.70, 21.25, 11.90. HRMS (ESI): m/zcalculated for C72H115N24 [M + H]+: 1315.9731; found:1315.9723.2,3,9,10,16,17,23,24-Octakis(dibutylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (4H2). Compound 4H2 was pre-pared according to the general procedure above using com-pound 14 (1.73 g, 4.49 mmol) and lithium (220 mg,31.43 mmol). Eluent: dichloromethane/methanol (20 : 1).Yield: 736 mg (42%), a purple solid. 1H NMR (500 MHz, pyri-dine-d5) δ 4.10 (t, J = 7.4 Hz, 32H), 1.84 (p, J = 7.5 Hz, 32H),1.53 (h, J = 7.4 Hz, 32H), 1.02 (t, J = 7.4 Hz, 48H), −1.41 (s, 2H).13C NMR (126 MHz, pyridine-d5) δ 150.59, 141.02, 48.93, 30.46,21.04, 14.25 (one aromatic signal was not detected); HRMS(ESI): m/z calculated for C88H147N24 [M + H]+: 1540.2235;found: 1540.2224.2,3,9,10,16,17,23,24-Octa(piperidin-1-yl)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (6H2). Compound 6H2 was pre-pared according to the general procedure above using com-pound 15 (400 mg, 1.35 mmol) and lithium (66 mg,9.45 mmol). Eluent: dichloromethane/acetone (50 : 1, Rf =0.23). Yield: 131 mg (33%), a purple solid. 1H NMR (500 MHz,pyridine-d5) δ 4.11–3.54 (m, 32H), 1.89–1.69 (m, 32H),1.69–1.51 (m, 16H). Due to solubility reasons, the signals inResearch Article Inorganic Chemistry Frontiers1602 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834a13C NMR were not detected. HRMS could not be performeddue to solubility reasons.2,3,9,10,16,17,23,24-Octakis(morpholino)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (7H2). Compound 7H2 was pre-pared according to the general procedure above using com-pound 16 (677 mg. 2.25 mmol) and lithium (111 mg,15.78 mmol). Eluent: dichloromethane/methanol (20 : 1, Rf =0.41). Yield: 76 mg (11%), a green solid. 1H NMR (500 MHz,CDCl3/pyridine-d5 – 2 : 1) δ 4.57–3.06 (m, 64H), −1.49 (s, 2H).Due to solubility reasons, the signals in 13C NMR were notdetected. HRMS (ESI): m/z calculated for C56H67N24O8 [M +H]+: 1203.5568; found: 1203.5547.2,3,9,10,16,17-Hexakis(dibutylamino)-23,24-bis(dimethylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyane (8H2). Compound 8H2was prepared according to the general procedure above usingcompounds 12 (280 mg, 1.29 mmol), 14 (1494 mg,3.88 mmol), and lithium (226 mg, 36.25 mmol). Eluent: di-chloromethane/methanol (150 : 1). The second most lipophilicspot was isolated. Yield: 381 mg (22%), a purple solid. 1HNMR (500 MHz, pyridine-d5) δ 4.09 (q, J = 7.4 Hz, 16H), 3.97 (t,J = 7.4 Hz, 8H).3.28 (s, 12H), 1.88–1.79 (m, 16H), 1.78–1.68 (m,8H), 1.60–1.48 (m, 16H), 1.48–1.38 (m, 8H), 1.06–0.93 (m,36H), −1.40 (s, 2H). 13C NMR (126 MHz, pyridine-d5) δ 151.5,150.7, 150.6, 141.3, 141.2, 141.0, 49.0, 48.9, 48.7, 39.5, 30.5,30.3, 21.1, 21.1, 21.0, 14.3, 14.2 (some aromatic signals werenot detected). HRMS (ESI): m/z calculated for C76H123N24 [M +H]+: 1372.0357; found: 1372.0344.2,3,9,10,16,17-Hexakis(dibutylamino)-23-dimethylamino-1,4,8,11,15,18,22,25-octaazaphthalocyanine (9H2). Compound9H2 was prepared according to the general procedure aboveusing compounds 19 (259 mg, 1.50 mmol), 14 (1725 mg,4.49 mmol), and lithium (294 mg, 42.36 mmol). Eluent: di-chloromethane/methanol (100 : 1). Second most lipophilic spotwas isolated. Yield: 220 mg (11%), a purple solid. 1H NMR(600 MHz, pyridine-d5) δ 8.98 (s, 1H), 4.15–4.08 (m, 16H), 4.00(dt, J = 23.3, 7.4 Hz, 8H), 3.45 (s, 6H), 1.90–1.81 (m, 16H),1.77–1.69 (m, 8H), 1.59–1.50 (m, 16H), 1.47–1.37 (m, 8H), 1.04(q, J = 7.4 Hz, 24H), 0.96 (dt, J = 28.3, 7.4 Hz, 12H), −1.31 (s,2H). 13C NMR (150 MHz, pyridine-d5) δ 156.15, 150.93, 150.88,150.74, 142.88, 142.66, 139.53, 139.37, 138.98, 132.91, 48.86,48.77, 48.45, 38.05, 30.32, 30.24, 30.12, 20.91, 20.86, 20.76,14.10, 14.07, 13.99. HRMS (ESI): m/z calculated for C74H118N23[M + H]+: 1328.9935; found: 1328.9902.2,3,9,10,16,17-Hexakis(dibutylamino)-23,24-(2,5-diazahexane-2,5-diyl)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (10H2).Compound 10H2 was prepared according to the general pro-cedure above using compounds 17 (250 mg, 1.17 mmol), 14(1347 mg, 3.50 mmol), and lithium (228 mg, 32.76 mmol).Eluent: dichloromethane/methanol (150 : 1). Second most lipo-philic spot was isolated. Yield: 326 mg (20%), a purple solid.1H NMR (500 MHz, pyridine-d5) δ 4.09 (dt, J = 9.9, 7.3 Hz,16H), 3.95 (t, J = 7.4 Hz, 8H), 3.62 (s, 6H), 3.49 (s, 4H),1.89–1.78 (m, 16H), 1.74–1.65 (m, 8H), 1.58–1.47 (m, 16H),1.47–1.37 (m, 8H), 1.02 (q, J = 7.1 Hz, 24H), 0.96 (t, J = 7.3 Hz,12H), −1.44 (s, 2H). 13C NMR (126 MHz, pyridine-d5) δ 150.9,150.5, 150.3, 146.6, 142.7, 142.6, 139.3, 138.4, 49.0, 48.9, 48.4,46.7, 37.0, 30.5, 30.3, 21.1, 21.0, 14.3, 14.3, 14.2. HRMS (ESI):m/z calculated for C76H121N24 [M + H]+: 1370.0201; found:1370.0172.General procedure for the synthesis of a zinc(II) cyclotetramerMetal-free cyclotetramer (1 equivalent) was dissolved in pyri-dine (8 mL per 0.1 mmol of the metal-free compound), andzinc(II) acetate (10 equivalents) was added. The reactionmixture was refluxed for 3 hours, then pyridine was evaporatedunder reduced pressure. The crude residue was dissolved in di-chloromethane (50 mL) and washed with distilled water (3 ×50 mL). The organic phase was separated, dried over anhy-drous sodium sulfate, filtered, and evaporated under reducedpressure. Column chromatography on silica was performed topurify the products (mobile phases for each AzaPc are writtenin the following paragraphs). Finally, the product was dis-solved in a minimal amount of dichloromethane, added drop-wise into methanol (100 mL), and precipitated in a freezer for24 hours. The solid was collected and dried under vacuum.2,3,9,10,16,17,23,24-Octakis(dimethylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (1Zn). Compound 1Znwas prepared according to the general procedure above usingcompound 1H2 (100 mg, 0.12 mmol), and Zn(OAc)2 (127 mg,0.69 mmol). Eluent: dichloromethane/methanol (2500 : 1 →10 : 1). Yield: 28 mg (26%), a blue solid. 1H NMR (600 MHz,pyridine-d5) δ 3.21 (s, 48H). 13C NMR (150 MHz, pyridine-d5) δ165.43, 151.23, 150.92, 142.76, 134.10, 129.88, 39.31 (one aro-matic signal was not detected or overlapped with solventsignal). HRMS could not be performed due to solubilityreasons.2,3,9,10,16,17,23,24-Octakis(dipropylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (3Zn). Compound 3Zn wasprepared according to the general procedure above using com-pound 3H2 (232 mg, 0.18 mmol) and Zn(OAc)2 (324 mg,1.77 mmol). Eluent: dichloromethane/acetone (30 : 1). Yield:98 mg (42%), a blue solid. 1H NMR (600 MHz, pyridine-d5) δ3.89 (d, J = 7.8 Hz, 32H), 1.76–1.64 (m, 32H), 0.95 (t, J = 7.4 Hz,48H). 13C NMR (150 MHz, pyridine-d5) δ 151.13, 142.45, 50.86,21.30, 11.98 (one aromatic signal was not detected or over-lapped with solvent signal). HRMS (ESI): m/z calculated forC72H113N24Zn [M + H]+: 1377.8866; found: 1377.8844.2,3,9,10,16,17,23,24-Octakis(dibutylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (4Zn). Compound 4Zn wasprepared according to the general procedure above using com-pound 4H2 (558 mg, 0.36 mmol) and Zn(OAc)2 (399 mg,2.17 mmol). Eluent: dichloromethane/methanol (2500 : 1 →10 : 1). Yield: 566 mg (97%), a blue solid. 1H NMR (500 MHz,pyridine-d5) δ 4.07 (t, J = 7.5 Hz, 32H), 1.80 (q, J = 3.6 Hz, 32H),1.51 (h, J = 7.4 Hz, 32H), 0.99 (t, J = 7.4 Hz, 48H). 13C NMR(126 MHz, pyridine-d5) δ 151.04, 142.43, 48.77, 30.24, 20.85,14.05 (one aromatic signal was not detected or overlapped withsignal of solvent); HRMS (ESI): m/z calculated forC88H145N24Zn [M + H]+: 1602.1370; found: 1602.1343.2,3,9,10,16,17,23,24-Octa(piperidin-1-yl)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (6Zn). Compound 6Znwas prepared according to the general procedure above usingInorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1603Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834acompound 6H2 (131 mg, 0.11 mmol) and Zn(OAc)2 (203 mg,1.10 mmol). Eluent: dichloromethane/acetone (50 : 1). Yield:21 mg (14%), a dark green solid. NMR spectra and HRMScould not be performed for reasons of low solubility.2,3,9,10,16,17,23,24-Octakis(morpholino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (7Zn). Compound 7Znwas prepared according to the general procedure above usingcompound 7H2 (76 mg, 0.06 mmol) and Zn(OAc)2 (70 mg,0.38 mmol). Eluent: dichloromethane/pyridine (10 : 1). Yield:40 mg (50%), a dark blue solid. NMR spectra and HRMS couldnot be performed for reasons of low solubility.2,3,9,10,16,17-Hexakis(dibutylamino)-23,24-bis(dimethylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (8Zn).Compound 8Zn was prepared according to the general pro-cedure above using compound 8H2 (281 mg, 0.20 mmol) andZn(OAc)2 (225 mg, 1.23 mmol). Eluent: dichloromethane/methanol (150 : 1). Yield: 220 mg (74%), a dark blue solid. 1HNMR (500 MHz, pyridine-d5) δ 4.14–4.05 (m, 16H), 3.97 (t, J =7.4 Hz, 8H), 3.27 (s, 12H), 1.88–1.76 (m, 16H), 1.75–1.65 (m,8H), 1.58–1.48 (m, 16H), 1.48–1.39 (m, 8H), 1.05–0.94 (m,36H), 13C NMR (126 MHz, pyridine-d5) δ 151.2, 151.2, 151.1,150.9, 150.8, 142.6, 142.5, 142.5, 48.8, 48.8, 48.5, 39.2, 30.3,30.3, 30.1, 20.9, 20.8, 20.8, 14.1, 14.1, 14.0 (some aromaticsignals were not detected). HRMS (ESI): m/z calculated forC76H121N24Zn [M + H]+: 1433.9492; found: 1433.9454.2,3,9,10,16,17-Hexakis(dibutylamino)-23-dimethylamino-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II) (9Zn).Compound 9Zn was prepared according to the general pro-cedure above using compound 9H2 (200 mg, 0.15 mmol) andZn(OAc)2 (166 mg, 0.90 mmol). Eluent: dichloromethane/methanol (80 : 1). Yield: 95 mg (45%), a dark blue solid. 1HNMR (600 MHz, pyridine-d5) δ 8.97 (s, 1H), 4.13–4.07 (m, 16H),3.99 (dt, J = 20.8, 7.4 Hz, 8H), 3.43 (s, 6H), 1.87–1.80 (m, 16H),1.74–1.67 (m, 8H), 1.58–1.49 (m, 16H), 1.46–1.36 (m, 8H),1.04–0.98 (m, 24H), 0.96 (t, J = 7.4 Hz, 6H), 0.91 (t, J = 7.4 Hz,6H). 13C NMR (150 MHz, pyridine-d5) δ 155.9, 152.1, 151.5,150.8, 150.5, 142.7, 142.5, 142.4, 142.4, 139.5, 135.0, 132.7,48.9, 48.8, 48.4, 48.4, 38.0, 30.3, 30.2, 30.1, 20.9, 20.8, 14.1,14.0 (some aromatic signals were not detected). HRMS (ESI):m/z calculated for C74H116N23Zn [M + H]+: 1390.9070; found:1390.9034.2,3,9,10,16,17-Hexakis(dibutylamino)-23,24-(2,5-diazahexane-2,5-diyl)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II)(10Zn). 10Zn was prepared according to the general procedureabove using compound 10H2 (280 mg, 0.20 mmol) and Zn(OAc)2 (262 mg, 1.43 mmol). Eluent: dichloromethane/metha-nol (90 : 1). Yield: 280 mg (96%), a dark blue solid. 1H NMR(500 MHz, pyridine-d5) δ 4.09 (p, J = 6.5 Hz, 16H), 3.96 (t, J =7.4 Hz, 8H), 3.60 (s, 6H), 3.45 (s, 4H), 1.87–1.77 (m, 16H), 1.68(p, J = 6.6 Hz, 8H), 1.59–1.47 (m, 16H), 1.41 (h, J = 7.4 Hz, 8H),1.00 (q, J = 7.3 Hz, 24H), 0.94 (t, J = 7.4 Hz, 12H). 13C NMR(126 MHz, pyridine-d5) δ 152.3, 151.3, 150.9, 150.8, 149.7,145.8, 142.7, 142.6, 142.6, 141.2, 49.0, 49.0, 48.5, 46.9, 37.0,30.5, 30.2, 21.1, 21.1, 21.0, 20.5, 20.3, 20.1, 14.3, 14.2. HRMS(ESI): m/z calculated for C76H119N24Zn [M + H]+: 1431.9336;found: 1431.9302.2,3,9,10,16,17,23,24-Octakis(dibutylamino)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato magnesium(II) (4Mg). Magnesiumturnings (88 mg, 3.62 mmol) and a few iodine crystals wererefluxed in freshly distilled BuOH (10 mL) for 3 hours. Afterthat, compound 14 (200 mg, 0.52 mmol) was added, and thereaction mixture was refluxed overnight. Butanol was evaporatedunder reduced pressure. The crude residue was suspended in amixture of MeOH/water/acetic acid (ratio 1 : 1 : 1, 30 ml) andstirred for 30 min at r.t. Followed by extraction to dichloro-methane (3 × 30 ml). Organic phases were collected and washedwith 5% sodium bicarbonate solution (50 ml). The organicphase was collected and dried over anhydrous sodium sulfate,filtered, and evaporated. The final product was purified bycolumn chromatography on silica (eluent: dichloromethane/methanol (400 : 1)). Yield: 82 mg (40%), a dark blue solid. 1HNMR (600 MHz, pyridine-d5) δ 4.08 (t, J = 7.5 Hz, 32H), 1.81 (p, J= 7.4 Hz, 32H), 1.52 (h, J = 7.4 Hz, 32H), 1.00 (t, J = 7.4 Hz, 48H).13C NMR (151 MHz, pyridine-d5) δ 150.7, 142.8, 48.8, 30.3, 20.9,14.1 (one aromatic signal was not detected due to overlap withresidual solvent signal). HRMS (ESI): m/z calculated forC88H145MgN24 [M + H]+: 1562.1929; found: 1562.1902.2-Dimethylamino-9,10,16,17,23,24-hexakis(pentan-3-ylsulfanyl)-1,4,8,11,15,18,22,25-octaazaphthalocyanine (20H2). Magnesiumturnings (680 mg, 27.98 mmol) were covered by freshlydistilled butanol (28 mL), and a few iodine crystals were added.This reaction mixture was refluxed for 3 hours. Then, 5,6-bis(pentan-3-ylsulfanyl)pyrazine-2,3-dicarbonitrile (1.0 g,2.99 mmol) and compound 19 (174 mg, 1.0 mmol) were addedto the reaction, and heating was continued overnight. Rectionwas stopped, and butanol was evaporated under reducedpressure. The crude residue was dissolved in THF (30 mL), andp-toluenesulfonic acid monohydrate (7.98 g, 42.0 mmol) wasadded. The reaction was stirred at r.t. for 2 hours. Then, thesolvent was evaporated under reduced pressure. The cruderesidue was sonicated with chloroform (100 mL) for 10 minutesand transferred to a separation funnel. The organic phase waswashed with 5% sodium bicarbonate solution (100 mL) and col-lected, then the water phase was extracted two more times withchloroform (2 × 100 mL). The organic phase was collected anddried over anhydrous sodium sulfate, filtered, and evaporated.The metal-free congener was separated on silica (chloroform/THF – 50 : 1, Rf = 0.40). Finally, the product was scratched fromflask walls to methanol, filtered, dried and washed with hexaneon filter paper. Yield: 131 mg (11%), a dark green solid. 1HNMR (600 MHz, pyridine-d5) δ 8.94 (s, 1H), 5.07–4.97 (m, 4H),4.85–4.82 (m, 1H), 4.66 (p, J = 6.4 Hz, 1H), 3.42 (s, 6H),2.27–2.21 (m, 16H), 2.17–2.12 (m, 2H), 2.09–1.99 (m, 6H), 1.40(m, 24H), 1.32 (t, J = 7.4 Hz, 6H), 1.20 (t, J = 7.3 Hz, 6H), −1.70(s, 2H). 13C NMR (151 MHz, pyridine-d5) δ 159.78, 159.61,158.96, 158.82, 158.62, 158.52, 156.10, 145.28, 145.21, 144.73,144.52, 142.58, 142.52, 142.36, 50.18, 50.07, 49.91, 49.82, 49.70,37.97, 27.59, 27.54, 27.43, 27.32, 11.87, 11.75, 11.45. HRMS(ESI): m/z calculated for C56H76N17S6 [M + H]+: 1178.4788;found: 1178.4783.2-Dimethylamino-9,10,16,17,23,24-hexakis(pentan-3-ylsulfa-nyl)-1,4,8,11,15,18,22,25-octaazaphthalocyaninato zinc(II)Research Article Inorganic Chemistry Frontiers1604 | Inorg. Chem. Front., 2025, 12, 1590–1608 This journal is © the Partner Organisations 2025Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834a(20Zn). AzaPc 20H2 (50 mg, 0.04 mmol) was dissolved in pyri-dine (10 mL) and zinc(II) acetate (73 mg, 0.40 mmol) wasadded. The reaction mixture was refluxed for 30 minutes, andthen pyridine was evaporated under reduced pressure. Thecrude residue was dissolved in chloroform and then trans-ferred to the separation funnel. The organic phase was washedwith water (50 mL), collected, and then the water phase wasextracted two more times with chloroform (2 × 50 mL). Theorganic phase was collected and dried over anhydrous sodiumsulfate, filtered, and evaporated. The final compound was puri-fied on silica (toluene/pyridine – 10 : 1, Rf = 0.26). Finally, theproduct was scratched from flask walls to methanol, filtered,dried and washed with hexane on filter paper. Yield: 15 mg(28%), a dark green solid. 1H NMR (600 MHz, CDCl3/pyridine-d5 – 3 : 1) δ 9.00 (s, 1H), 5.08 (p, J = 6.5 Hz, 1H), 5.05–4.97 (m,4H), 4.89 (p, J = 6.3 Hz, 1H), 3.74 (s, 6H), 2.34–2.20 (m, 24H),1.51–1.48 (m, 6H), 1.48–1.43 (m, 24H), 1.41–1.38 (m, 6H). 13CNMR (151 MHz, CDCl3/pyridine-d5 – 3 : 1) δ 158.16, 157.98,157.83, 155.81, 153.09, 151.76, 150.97, 150.85, 150.52, 145.22,145.11, 144.90, 144.73, 132.61, 49.76, 49.35, 49.15, 38.30,27.16, 11.57, 11.28. HRMS (ESI): m/z calculated forC56H74N17S6Zn [M + H]+: 1240.3923; found: 1240.3903.Determination of the quantum yield of singlet oxygenQuantum yields of singlet oxygen production (ΦΔ) were deter-mined by the comparative method based on the decompositionof a chemical trap for singlet oxygen (1,3-diphenylisobenzofuran)and using unsubstituted zinc(II) phthalocyanine as a referencecompound (ΦΔ = 0.56 (DMF),43 0.58 (toluene)44). Details of themethod are described elsewhere.45 All the determinations wereperformed in triplicate, and the data represent the mean of themeasurements. The estimated experimental error was ±10%. Inthe case of the toluene/pyridine mixture, 1% (v/v) pyridine solu-tion in toluene was used, which corresponds to 0.12 M pyridinein toluene (unsubstituted zinc(II) phthalocyanine in toluene wasused as the reference), unless stated otherwise.Determination of the quantum yield of fluorescenceFluorescence quantum yields (ΦF) were determined on an FLS1000 spectrofluorometer (Edinburg Instruments) by the com-parative method46 using unsubstituted zinc(II) phthalocyanineas a reference compound (ΦF = 0.32 (THF) (ref. 47)). The deter-mination of ΦF values was performed in triplicate, and thedata represent the mean of these measurements. The esti-mated experimental error was ±10%. Absorption of thesamples at the excitation wavelength was kept below 0.05 andat a Q band maximum below 0.1 to avoid the inner filter effect.The results of ΦF were corrected for the refractive indices ofthe solvents. In the case of the toluene/pyridine mixture, 1%(v/v) pyridine solution in toluene was used, which correspondsto 0.12 M pyridine in toluene, unless stated otherwise.Determination of KD via temperatureAll synthesized compounds were subjected to a fluorescencetemperature dependency experiment in toluene to determineKD. The experiments were performed at different concen-trations (ranging between 5.0–0.05 μM) in dependence on thestability of the J-dimer. All experiments are presented inFig. S5 and S6.† The excitation wavelength was always chosenin an isosbestic point close to 600 nm. The temperature wasgradually changed from 10 °C to 100 °C in 5 °C steps with5 min intervals between each measurement to allow equili-bration. For compounds 4Zn and 5Zn, the spectral changeswere also monitored in absorption spectra at 10 μMconcertation.Determination of KL for pyridine in series with different peri-pheral substituentsStock solutions of AzaPcs were prepared in toluene (100 μM for2–5Zn, 8–10Zn, 4Mg, and 20Zn; 2 μM for 1Zn, and 25 μM for6Zn). The stock solution was added to the cuvette with tolueneto reach the desired concentration (see below), and then pyri-dine was added stepwise. During titration, changes in Q-bandabsorption (increasing band of the monomer) were observed,and titration was stopped when the plateau phase wasreached. Absorption and emission (excitation at isosbesticpoint close to 600 nm) spectra were measured after eachaddition of pyridine. Concentration in the cuvette was 15 μMfor 3Zn; 10 μM for AzaPcs 2Zn, 4Zn, 5Zn, 8–10Zn, 4Mg, and20Zn; 2 μM for 1Zn and 6Zn. Changes in the Q-band absorp-tion maxima of the monomer were used to determine KL. Inemission spectra, the decrease in dimer emission and increasein monomer emission were used to determine KL. All experi-ments were performed at 23 °C.Determination of KL for a series of different ligandsStock solutions of selected AzaPcs were prepared in toluene(100 μM). The stock solution was added to the cuvette withtoluene to reach a concentration of 10 μM, and then the ligandwas added stepwise. During titration, changes in Q-bandabsorption (increasing band of the monomer) were observed,and titration was stopped when the plateau phase wasreached. Absorption and emission (excitation at the isosbesticpoint close to 600 nm) spectra were measured after eachligand addition. Changes in the Q-band absorption maxima ofmonomer were used to determine KL. In emission spectra, thedecrease in dimer emission and increase in monomer emis-sion were used to determine KL. All experiments were per-formed at 23 °C.NMR titration of 3ZnA solution of 3Zn in toluene-d8 (1 mM, 600 μL) was taken inthe NMR cuvette, and 1H spectrum was measured. Then 3 μLof 40 mM solution N-methylimidazole (in toluene-d8) wasadded into the cuvette, gently mixed, and the 1H spectrum wasmeasured again. The previous step was repeated until nochanges in the 1H spectrum were observed. Finally, 3 μL of 1M N-methylimidazole was added to ensure that compound3Zn was in the monomeric form. KL was determined by fittingthe binding model to the integrated intensity of resonances atδ = 0.64 ppm and δ = 1.14 ppm, which belong to the J-dimer.The experiments were performed at 25 °C.Inorganic Chemistry Frontiers Research ArticleThis journal is © the Partner Organisations 2025 Inorg. Chem. Front., 2025, 12, 1590–1608 | 1605Open Access Article. Published on 31 December 2024. Downloaded on 2/12/2025 10:46:06 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4qi02834aAuthor contributionsJiri Demuth: investigation, data curation, formal analysis,writing – original draft, methodology, and supervision. StefanBednarik: investigation. Radek Machan: investigation. IvanMocak: investigation. Tibor Malinsky: investigation. Mona AboEl Dahabova: investigation. Jakub Holcak: investigation.Miroslav Miletin: supervision. Jan Labuta: methodology andformal analysis. Veronika Novakova: supervision, visualization,writing – review and editing, and funding acquisition. PetrZimcik: conceptualization, funding acquisition, methodology,project administration, and writing – review and editing,Data availabilityData for this article, including NMR data and absorption andfluorescence spectra are available at Zenodo at: https://doi.org/10.5281/zenodo.14047683.Conflicts of interestThere are no conflicts to declare.AcknowledgementsThe work was supported by the Czech Science Foundation (23-06177S) and the project New Technologies for TranslationalResearch in Pharmaceutical Sciences /NETPHARM, project IDCZ.02.01.01/00/22_008/0004607, co-funded by the EuropeanUnion. VN, MM and JD would also like to acknowledge finan-cial support from the Ministry of Education, Youth and Sports(ERC CZ programme, LL2318). This work was also supportedby the World Premier International Research Center Initiative(WPI Initiative), MEXT, Japan. Financial support from CharlesUniversity (SVV 260 666) is gratefully acknowledged as well.References1 R. Christie and A. 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