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[Minghan Tan](https://orcid.org/0000-0001-5426-6347), [Masayuki Takeuchi](https://orcid.org/0000-0002-0207-0665), [Atsuro Takai](https://orcid.org/0000-0003-3457-3352)

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[Spatiotemporal dynamics of supramolecular polymers by <i>in situ</i> quantitative catalyst-free hydroamination](https://mdr.nims.go.jp/datasets/69822432-2200-4d3d-a458-0f6b9f7046d8)

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Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationChemicalScienceEDGE ARTICLEOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal  | View IssueSpatiotemporal daMolecular Design and Function Group, N(NIMS), 1-2-1 Sengen, Tsukuba, IbarakiMasayuki@nims.go.jp; TAKAI.Atsuro@nimsbDepartment of Materials Science and EnSciences, University of Tsukuba, 1-1-1 Tenn† Electronic supplementary informa10.1039/d2sc00035kCite this: Chem. Sci., 2022, 13, 4413All publication charges for this articlehave been paid for by the Royal Societyof ChemistryReceived 4th January 2022Accepted 22nd March 2022DOI: 10.1039/d2sc00035krsc.li/chemical-science© 2022 The Author(s). Published byynamics of supramolecularpolymers by in situ quantitative catalyst-freehydroamination†Minghan Tan, ab Masayuki Takeuchi *ab and Atsuro Takai *aImplementing chemical reactivity into synthetic supramolecular polymers based on p-conjugatedmolecules has been of great interest to create functional materials with spatiotemporal dynamicproperties. However, the development of an in situ chemical reaction within supramolecular polymers isstill in its infancy, because one needs to design optimal p-conjugated monomers having excellentreactivity under mild conditions possibly without byproducts or a catalyst. Herein we report the synthesisof a supramolecular polymer based on ethynyl core-substituted naphthalenediimide (S-NDI2) moleculesthat react with various amines quantitatively in a nonpolar solvent, without a catalyst, at 298 K. Mostinterestingly, the in situ reaction of the S-NDI2 supramolecular polymer with a linear aliphatic diamineproceeded much faster than the homogeneous reaction of a monomeric naphthalenediimide with thesame diamine, affording diamine-linked S-NDI2 oligomers and polymers. The acceleration of in situhydroamination was presumably due to rapid intra-supramolecular cross-linking between ethynyl andamino groups fixed in close proximity within the supramolecular polymer. Such intra-supramolecularcross-linking did not occur efficiently with an incompatible diamine. The systematic kinetic studies of insitu catalyst-free hydroamination within supramolecular polymers provide us with a useful, facile andversatile tool kit for designing dynamic supramolecular polymeric materials based on electron-deficientp-conjugated monomers.IntroductionSupramolecular polymers composed of p-conjugated moleculeshave been attracting increasing attention as so materials thatcould play pivotal roles in organic electronics, energy conver-sion and life-like systems in a sustainable society.1–5 Towardthese goals, in addition to conventional static or thermody-namically controlled supramolecular polymers, the develop-ment of dynamic supramolecular materials that are responsiveto external stimuli such as chemical reactions has been exten-sively studied.6–18 To design supramolecular polymers based onp-conjugated monomers that can implement chemical reac-tivity, one needs to introduce a reaction site where the chemicalreaction proceeds under mild conditions without byproducts ora catalyst that could have unintended effects on the supramo-lecular polymers. These stringent requirements for the designof p-conjugated molecules hinder the further development ofational Institute for Materials Science305-0047, Japan. E-mail: TAKEUCHI..go.jpgineering, Faculty of Pure and Appliedodai, Tsukuba, Ibaraki 305-8577, Japantion (ESI) available. See DOI:the Royal Society of Chemistrydynamic supramolecular polymers, although elaboratedynamic supramolecular assemblies that incorporate efficientchemical reactions have been reported.9,19–38 Besides, there areonly a handful of in situ chemical reactions within the supra-molecular polymers, such as the topochemical photoreactionand redox reaction, that can lead to signicant changes in theoptical and electronic properties of the p-systems.33–38Meanwhile, we recently reported quantitative, catalyst-freereactions between an ethynyl group directly attached toelectron-accepting p-conjugated molecules and amines invarious media.39–41 An ethynyl core-substituted naph-thalenediimide (NDI) is a representative electron-accepting p-conjugated molecule that reacts with an amine rapidly undermild conditions without byproducts or a catalyst (Scheme 1).This atom-economical hydroamination of NDIs possessesunique characteristics that are distinctively different from otherexisting chemical reactions for p-systems: (1) various amines,many of which are commercially available, are applicable tofunctionalize the p-systems, and thus (2) the p-conjugatedstructure is changed by the reaction to exhibit remarkablechanges in the optical and electronic properties. In this context,considering that NDIs have been widely known as buildingblocks of supramolecular polymers,42–45 we conceived that ourcatalyst-free hydroamination of NDIs could be used as a newfamily of in situ reactions to trigger macroscopic changes ofChem. Sci., 2022, 13, 4413–4423 | 4413http://crossmark.crossref.org/dialog/?doi=10.1039/d2sc00035k&domain=pdf&date_stamp=2022-04-09http://orcid.org/0000-0001-5426-6347http://orcid.org/0000-0002-0207-0665http://orcid.org/0000-0003-3457-3352http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035khttps://pubs.rsc.org/en/journals/journal/SChttps://pubs.rsc.org/en/journals/journal/SC?issueid=SC013015Scheme 1 Quantitative catalyst-free hydroamination of an ethynylcore-substituted NDI without a catalyst.Chemical Science Edge ArticleOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinesupramolecular polymers based on NDI molecules usingvarious amines. The in situ reaction of p-conjugated moleculeswithin supramolecular polymers is also expected to exhibitcharacteristic reactivity different from that in homogeneousmonodisperse solutions, because the molecules are pre-organized and locally condensed. Such a proximity effect onchemical reactivity has been studied in intramolecular andenzymatic reactions,46–50 but little is known in supramolecularpolymers.We report herein the formation of a supramolecular polymerbased on ethynyl core-substituted NDI monomers in nonpolarsolvents, its unique reactivity with amines, and the spatiotem-poral dynamics through in situ catalyst-free hydroamination. Asshown in Fig. 1, we designed S-NDI2 having two ethynyl groupsat the NDI p-core as reaction sites. The imide side chains of S-NDI2 and a reference compound (ref-S-NDI) include the amideFig. 1 Structures of S-NDI2, ref-S-NDI and NDI2.4414 | Chem. Sci., 2022, 13, 4413–4423and trialkoxyphenyl groups, which reinforce the p-stacking ofthe NDIs to enhance the formation of supramolecular poly-mers.51–57 The butano –(CH2)4– spacer58 of the imide side chainwas introduced because it could facilitate supramolecularstructural changes upon external stimuli.53 The reactivity andthe reaction kinetics of the supramolecular polymers of S-NDI2with various monoamines and diamines were investigated byUV-vis absorption spectroscopy, mass spectrometry and chro-matography techniques. The morphological and structuralchanges of the supramolecular polymers of S-NDI2 during thecourse of hydroamination were studied by atomic forcemicroscopy (AFM), Fourier-transform infrared (FT-IR) spec-troscopy and the X-ray diffraction (XRD) method. Hydro-amination of a reference compound (NDI2) that does not formany supramolecular polymers was also studied for comparison.The present study shows for the rst time that in situ reactionswithin supramolecular polymers based on p-conjugatedmonomers gave completely different reaction kinetics andproducts from the homogeneous reactions in monodispersesolutions of p-conjugated molecules.Results and discussionSupramolecular polymerization of NDIsThe syntheses of S-NDI2 and ref-S-NDI and their full character-ization data are given in the ESI (S2. Synthesis and character-ization†). The synthesis of NDI2 was reported previously.39© 2022 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kFig. 2 (a) Temperature-dependent UV-vis absorption spectral changes of S-NDI2 (25 mM) in MCH/toluene (4 : 1 v/v) upon cooling from 363 K(red line) to 278 K (blue line) at a rate of 1 Kmin�1. (b) Plot of the degree of polymerization (aagg) calculated from the absorbance at 446 nm againsttemperature (blue circle). Blue solid line denotes a theoretical curve fitted by using a cooperative model with an R2 value of 0.996. (c) AFM imageof a spin-coated sample from the MCH/toluene (4 : 1 v/v) solution used for the UV-vis absorption measurement. Scale bar: 200 nm. (d) Theheight profile of the cross-section (cyan dashed line) in (c). (e) Optimized structure of S-NDI2 calculated at the B3LYP/6-31G* level. The alkoxygroups (–OC12H25) were substituted by methoxy groups for simplicity. Atom colour code: grey, C; red, O; blue, N; white, H.Edge Article Chemical ScienceOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineSupramolecular polymerization of S-NDI2 was examined inseveral solvents such as methylcyclohexane (MCH) and toluene.Among them, we chose a MCH/toluene (4 : 1 v/v) mixed solvent,owing to the optimal supramolecular polymerization behavior ofS-NDI2 and its stability; no precipitation was formed during theanalyses. When S-NDI2 (25 mM) in MCH/toluene (4 : 1 v/v) wascooled from 363 K to 278 K at a rate of 1 K min�1, the UV-visabsorption spectrum of S-NDI2 changed with a typical Davydovsplitting; a new red-shied absorption band at 446 nm anda blue-shied absorption band at 418 nm appeared, suggestingthe formation of supramolecular J-aggregates (Fig. 2a).59,60 Thedegree of polymerization (aagg) was calculated by using eqn (1);aagg z (A � AMonomer)/(APolymer � AMonomer) (1)where A is the absorbance at 446 nm, AMonomer is the absorbanceof the S-NDI2 monomer obtained from the absorbance at446 nm at 363 K (¼0.025) and APolymer is the absorbance of the S-NDI2 supramolecular polymer obtained from the absorbance at446 nm at 278 K (¼0.80). The plot of aagg versus temperatureexhibited an abrupt change at 332 K (Fig. 2b, blue circle). Theobserved non-sigmoidal curvature clearly indicates a coopera-tive polymerization process of S-NDI2.61 The elongation processof the S-NDI2 supramolecular polymer can be tted well byusing eqn (2);aagg ¼ aSAT[1 � exp(�DHe(T � Te)/RTe2)] (2)© 2022 The Author(s). Published by the Royal Society of Chemistrywhere DHe is an elongation enthalpy, R is the ideal gas constant,Te is the critical elongation temperature, T is the absolutetemperature and aSAT is the constant used to ensure that aagg/aSAT does not exceed unity. The curve tting yielded DHe(�66.8 kJ mol�1) and Te (332 K) at a total concentration (CT) of25 mM. The concentration dependence of S-NDI2 ranging 5 mMto 25 mM on the aggregation behavior showed the shi of the Tevalues to a lower temperature with a decrease in the concen-tration. The DHe value at CT of 25 mM was close to the standardenthalpy value calculated from a van't Hoff plot of supramo-lecular polymerization of S-NDI2 at different concentrations(�67.8 kJ mol�1; Fig. S1†). The S-NDI2 supramolecular polymerexisted in a stable manner in MCH/toluene (4 : 1 v/v) withoutthe formation of precipitate up to 2 hours.Similarly, when a MCH/toluene (4 : 1 v/v) solution of ref-S-NDI (25 mM) was cooled from 363 K to 298 K,62 the UV-visabsorption spectrum of ref-S-NDI changed with an abruptpoint at 323 K, indicating the cooperative formation ofa supramolecular assembly, as shown in Fig. S2.† Note that thedegree of polymerization of ref-S-NDI at 298 K (76%) wassmaller than that of S-NDI2 (96%). The DHe and the Te values ofref-S-NDI at CT of 25 mM are �47.3 kJ mol�1 and 323 K,respectively.AFM images for the spin-coated samples of the S-NDI2supramolecular assembly exhibited well-developed nanoberswith over micrometers in length (Fig. 2c). The average height ofChem. Sci., 2022, 13, 4413–4423 | 4415http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kTable 1 Second-order reaction rate constant (k) for hydroaminationof the S-NDI2 supramolecular polymer and NDI2 in MCH/toluene(4 : 1 v/v) at 298 KAmine NDI k (M�1 s�1)Diethylamine (DEA) S-NDI2 6.3(�0.3) � 10�2NDI2 2.9(�0.2) � 10�1Diisopropylamine S-NDI2 1.2(�0.06) � 10�4NDI2 3.1(�0.2) � 10�31,4-Diaminobutane S-NDI2 3.1(�0.2) � 10�1NDI2 6.5(�0.3) � 10�2cis-1,4-Cyclohexanediamine S-NDI2 8.7(�0.4) � 10�2NDI2 1.7(�0.09) � 10�2trans-1,4-Cyclohexanediamine S-NDI2 4.1(�0.2) � 10�2NDI2 2.8(�0.1) � 10�2Chemical Science Edge ArticleOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinethe nanobers (Fig. 2d) was comparable with the distancebetween the two ethynyl protons of S-NDI2 (1.2 nm) obtainedfrom the DFT calculations (Fig. 2e), indicating the formation ofnanobers with a unimolecular height. On the other hand, theAFM image of the ref-S-NDI supramolecular assemblies showedthe formation of nanoparticles (Fig. S2d†). NDI2 did not formany supramolecular assembly. These results indicate that theethynyl-extended p-core of S-NDI2 facilitates the formation ofthe supramolecular nanobers with the help of the imide sidechains.In situ hydroamination of the S-NDI2 supramolecular polymerwith monoaminesWe then decided to study the reactivity of the S-NDI2 supra-molecular polymer with an amine and its reaction kinetics. AsFig. 3 (a) UV-vis absorption spectral changes of the S-NDI2 supramolecMCH/toluene (4 : 1 v/v) at 298 K. (b) Time profiles of absorbance changefitted by pseudo-first-order kinetic curves with R2 values of 0.995. Theduring the reaction. The samples were prepared by spin-coating from t1200 min after the addition of DEA. Scale bar: 1 mm.4416 | Chem. Sci., 2022, 13, 4413–4423a rst step, we conrmed that hydroamination occurredbetween NDI2 and diethylamine (DEA), as a typical case, ina nonpolar solvent. Upon addition of DEA (1.24 mM) to a MCH/toluene (4 : 1 v/v) solution of NDI2 (25 mM) at 298 K, hydro-amination started to occur and the UV-vis absorption spectrumof NDI2 remarkably changed with isosbestic points (Fig. S3†).The appearance and saturation of a characteristic charge-transfer band at 607 nm indicates the quantitative formationof an amine monoadduct NDI2–DEA.39–41,63,64 The rate offormation of NDI2–DEA in the presence of excess DEA obeyedpseudo-rst order kinetics (eqn S1–S3†). The time prole of thechange in the absorbance at 607 nm was tted well by using eqnS3† with an R2 value of 0.999 to give a second-order rateconstant (k) as 2.9 � 10�1 M�1 s�1 (Fig. S3b† and Table 1).When DEA (1.24 mM) was added to a MCH/toluene (4 : 1 v/v)solution of S-NDI2 supramolecular polymers (CT ¼ 25 mM) at298 K, the UV-vis absorption spectrum was signicantlychanged as shown in Fig. 3a. The decrease in the absorptionband at 446 nm and the increase in the new absorption band at615 nm indicated that the reaction between the ethynyl group ofS-NDI2 and DEA proceeded. Judging from the UV-vis absorptionspectrum (see the latter discussion) and the MALDI TOF-MSchart (Fig. S4†) aer the reaction completed, the resultantproduct is a supramolecular assembly of the correspondingamine monoadduct (S-NDI2–DEA). The formation of an aminebisadduct, S-NDI2–(DEA)2 was much less than that of S-NDI2–DEA under the measurement conditions (Fig. S5†).65 It must benoted that, in the initial stage of the reaction, we observeddistinct peak shis of the charge-transfer band at 615 nm toa longer wavelength (ca. 645 nm) and that of thep–p* transitionular polymer (CT ¼ 25 mM) observed upon addition of DEA (1.24 mM) ins at 446 nm (black circle) and 615 nm (blue circle) during the reaction,inset shows the structure of S-NDI2–DEA. (c) AFM images observedhe MCH/toluene (4 : 1 v/v) solution at 13 min, 180 min, 414 min and© 2022 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kEdge Article Chemical ScienceOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineband at 446 nm toa shorter wavelength (ca. 440 nm) as shown inFig. 3a. This result strongly indicates the existence of an inter-mediate during the transition from the supramolecularassembly of S-NDI2 to that of S-NDI2–DEA. Despite the exis-tence of such an intermediate (Fig. 3b), the time proles of theabsorbance changes at 446 nm and 615 nm obeyed pseudo-rstorder kinetics with a high R2 value of 0.995, and the second-order rate constant (k) could be obtained as 6.3 � 10�2 M�1s�1. The rate constant for the S-NDI2 supramolecular polymerwas 4.7-fold smaller than that for NDI2 (Table 1), probablybecause the steric hindrance around the ethynyl groups withinthe S-NDI2 supramolecular polymer was larger than that in themonodisperse state. The slower reaction rate for the S-NDI2supramolecular polymer than that for NDI2 eliminates thepossibility that hydroamination took place at the terminal ofthe S-NDI2 supramolecular polymer or at the free S-NDI2monomer, considering that the S-NDI2 monomer has slightlyhigher reactivity than the NDI2monomer in pure toluene at 298K (see Fig. S6† for details). On the other hand, the reaction ofthe S-NDI2 supramolecular polymer with diisopropylamine was525-fold slower than the case of DEA (Fig. S7†), although thebasicity of diisopropylamine (pKa ¼ 11.05) and DEA (pKa ¼10.98) are almost the same.66 This result indicates that the sterichindrance of the nucleophile (amine) also critically affects thereaction rate.In conjunction with the UV-vis absorption spectral changes,the morphologies of the S-NDI2 supramolecular polymer werealso changed as shown in Fig. 3c. The pristine nanobersbecame gradually shorter until the unreacted S-NDI2 units wereconsumed. The short nanobers at 414 min when 89% of thereaction completed were then bundled to change into largerassemblies at 1200 min, although there was no signicant UV-vis absorption spectral change between 414 min andFig. 4 Schematic illustration of self-assembled behaviors of S-NDI2 andpolymer with DEA.© 2022 The Author(s). Published by the Royal Society of Chemistry1200 min. This result merely indicates that the number ofpolymerized monomers remains the same.27In order to clarify the reaction product and the kinetics of thein situ reaction of the S-NDI2 supramolecular polymer withDEA,we rst conrmed supramolecular polymerization behavior ofS-NDI2–DEA by means of UV-vis absorption spectroscopy andAFM (Fig. S8†). The amine monoadduct (S-NDI2–DEA) wasprepared by the reaction of S-NDI2 with DEA in CHCl3 at roomtemperature in 93% isolated yield (see the ESI† for details).When a MCH/toluene (4 : 1 v/v) solution of S-NDI2–DEA (25 mM)was cooled from 363 K to 298 K,67 the supramolecular polymerof S-NDI2–DEA was formed, showing a sigmoidal absorbancechange at its charge-transfer band. The plot of aagg versustemperature (Fig. S8b†) was tted by using an isodesmic modelexpressed in eqn S6,†61 giving an aggregation enthalpy (DH ¼�61.0 kJ mol�1) and a melting temperature (Tm ¼ 312 K) whereaagg is 0.5 at CT of 25 mM. The degree of polymerization of S-NDI2–DEA at 298 K was calculated to be 74%. A thin lm spin-coated from a MCH/toluene (4 : 1 v/v) solution aer cooling to298 K exhibited a morphology of short nanobers with anaverage height of 4 nm (Fig. S8e and f†). The height is compa-rable with twice the distance between the ethynyl proton andthe amine moiety of S-NDI2–DEA, which could be because S-NDI2–DEA tends to form a slipped-stack dimer to cancel out thelarge dipole moment in the p-plane (7.96 Debye; Fig. S8g†).68,69The UV-vis absorption spectrum and the morphology of thesupramolecular polymer of S-NDI2–DEA were fairly similar tothe one obtained from the in situ reaction between the S-NDI2supramolecular polymer and DEA (Fig. 3c). Based on theseresults, it is reasonable to conclude that the nal product of insitu hydroamination was the supramolecular assembly of S-NDI2–DEA.S-NDI2–DEA and in situ hydroamination of the S-NDI2 supramolecularChem. Sci., 2022, 13, 4413–4423 | 4417http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kChemical Science Edge ArticleOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineWe next conducted two control experiments: (i) mixing twodifferent supramolecular polymers of S-NDI2 and S-NDI2–DEAin a 1 : 1 ratio at 298 K and (ii) mixing two different monomersof S-NDI2 and S-NDI2–DEA in a 1 : 1 ratio at 363 K and coolingto 298 K. In both cases, the UV-vis absorption spectra wereconsistent with the sum of those of each supramolecularassembly (Fig. S9 and S10†), indicating the formation of self-sorted assemblies. This self-sorting behavior is reasonable,given that the elongation mechanisms of S-NDI2 and S-NDI2–DEA are different between cooperative and isodesmic, respec-tively. An AFM image of a spin-coated lm from the MCH/toluene (4 : 1 v/v) solution used for the UV-vis absorptionmeasurements also indicated the existence of two differentsupramolecular assemblies (Fig. S10c†). In contrast, the UV-visabsorption spectrum of the intermediate during in situ hydro-amination was different from that of the sum of the self-sortedsupramolecular assemblies as shown in Fig. S9.† The UV-visabsorption spectrum of the intermediate did not match withthat of the sum of monomeric S-NDI2 and S-NDI2–DEA, either.Thus, hydroamination should take place within the supramo-lecular polymer, not at the terminal of the S-NDI2 supramo-lecular polymer or the S-NDI2 monomer, and the intermediatesupramolecular assembly was only observed during in situhydroamination of the S-NDI2 supramolecular polymer, asshown in Fig. 4.70S-NDI2 followed a cooperative mechanism of self-assembly,whereas S-NDI2–DEA followed an isodesmic mechanism. Tounderstand this difference in the supramolecular polymeriza-tion processes, we measured the FT-IR spectra of the supra-molecular assemblies of S-NDI2, ref-S-NDI and S-NDI2–DEA andcompared the strength of the intermolecular hydrogen-bondingbetween the amide moieties. FT-IR samples were prepared bydrying MCH/toluene (4 : 1 v/v) solutions of S-NDI2, ref-S-NDIFig. 5 FT-IR spectra (ATRmode) of the supramolecular polymers of (a)S-NDI2, (b) ref-S-NDI and (c) S-NDI2–DEA. The peaks at 2100 cm�1and 3233 cm�1 of S-NDI2 and S-NDI2–DEA are assigned to thestretching vibrations of C^C and C–H of the terminal ethynyl group,respectively.39 The FT-IR spectrum of the S-NDI2–DEA supramolec-ular assembly in the range of 1500 cm�1 and 1750 cm�1 exhibitedmore peaks than the others owing to its asymmetric structure.4418 | Chem. Sci., 2022, 13, 4413–4423and S-NDI2–DEA that were cooled from 363 K to 298 K at a rateof 1 K min�1. We conrmed that the UV-vis absorption spec-trum of each sample was consistent with that in MCH/toluene(4 : 1 v/v) at 298 K, indicating that the dried sample retainedits supramolecular structure (Fig. S11†). As shown in Fig. 5, nopeaks at energies higher than 3400 cm�1 were observed, sug-gesting the absence of non-hydrogen-bonded amide moie-ties.53,54 The N–H stretching vibration of the supramolecularpolymer of S-NDI2 was found at 3210 cm�1, which wasa signicantly lower frequency compared to those of ref-S-NDIand S-NDI2–DEA. The peak shi of the N–H stretching vibrationto lower energy is indicative of stronger hydrogen-bondinginteractions among the amide moieties. Such a strong inter-molecular hydrogen-bonding interaction allows S-NDI2 to formits supramolecular polymers through a cooperative mechanism,unlike S-NDI2–DEA, which forms its supramolecular polymersthrough an isodesmic mechanism.XRD analyses also support the different packing structuresbetween the supramolecular polymers of S-NDI2 and S-NDI2–DEA. The XRD pattern of the S-NDI2 supramolecular polymerexhibited peaks attributed to the lamellar and p-stackingstructure of S-NDI2 molecules, whereas that of the S-NDI2–DEAsupramolecular polymer exhibited a peak matching with thelength of S-NDI2–DEA along the short axis (ca. 1.5 nm) anda broad peak attributed to the alkyl chain halo and p-stackingdistances, as shown in Fig. S12.†We infer that the difference inthe packing structures of the supramolecular polymers of S-NDI2 and S-NDI2–DEA may result from the steric effects of theDEAmoiety and the large dipole moment of S-NDI2–DEA in thep-plane (7.96 Debye), which diminishes long-range interactionsin the growth direction of the supramolecular polymer.39,71,72Indeed, the supramolecular assemblies of other amine adductssuch as S-NDI2–(DEA)2 showed different AFM morphologies(Fig. S5c†), suggesting different packing structures. Note thatthe inuence of excess DEA on the stability and the packingstructure of supramolecular assemblies during in situ hydro-amination was considered negligible; upon addition of DEA(1.24 mM) to a MCH/toluene (4 : 1 v/v) solution of the ref-S-NDIsupramolecular polymer (CT¼ 25 mM), there were no changes inboth the UV-vis absorption spectra and AFM images before andaer the addition of DEA (Fig. S13†).In situ hydroamination of the S-NDI2 supramolecular polymerwith diaminesThe S-NDI2 supramolecular nanobers also exhibited uniquereactivity toward a diamine for cross-linkage. When 1,4-dia-minobutane (0.62 mM)73 was added to the supramolecularnanobers of S-NDI2 (CT ¼ 25 mM) in MCH/toluene (4 : 1 v/v) at298 K, the UV-vis absorption spectrum was changed (Fig. 6a andb), as was observed for the reaction with DEA. The increase inthe new absorption band at around 615 nm indicated that thereaction of the ethynyl groups of S-NDI2 with an amino group in1,4-diaminobutane proceeded to show a charge-transfer band.The resulting charge-transfer band was broader than thatobserved in the reaction with DEA, reaching the near-IR (NIR)region above 1000 nm. From the time course of the absorbance© 2022 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kFig. 6 (a) UV-vis-NIR absorption spectral changes of the S-NDI2 supramolecular polymer (CT ¼ 25 mM) observed upon addition of 1,4-dia-minobutane (0.62 mM) in MCH/toluene (4 : 1 v/v) at 298 K. (b) Time profile of the absorbance change at 615 nm (blue circle) during the reaction,fitted by pseudo-first-order kinetic curves with an R2 value of 0.992. (c) MALDI TOF-MS (positive ion, linear mode) chart obtained 470 min afterthe reaction. Some oligomers' peaks were split into several peaks, which were assigned to the oligomers with different terminal groups, i.e.ethynyl and amino groups. (d) GPC charts obtained before (black line) and after (red line) the reaction of S-NDI2 (1.2 mM) with 1,4-diaminobutane(1.2 mM) in MCH/toluene (4 : 1 v/v) for 18.5 h at 298 K. The chromatograms were normalized to the highest peaks. (e) AFM images observedbefore and after the reaction of S-NDI2 (1.2 mM) with 1,4-diaminobutane (1.2 mM). The samples were prepared by spin-coating on silicon wafersfrom a MCH/toluene (4 : 1 v/v) solution. Scale bar: 2 mm.Edge Article Chemical ScienceOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineat 615 nm, the second-order rate constant was determined to be3.1 � 10�1 M�1 s�1.The MALDI TOF-MS chart aer the reaction showed theformation of oligomers and polymers up to 12-mer (Fig. 6c).This result strongly indicates that the cross-linking reactiontook place even in a diluted solution of S-NDI2 (CT ¼ 25 mM).The formation of the covalently linked oligomers and polymerswere also conrmed by gel permeation chromatography (GPC)aer the reaction of S-NDI2 (1.2 mM) with 1,4-diaminobutane(1.2 mM), as shown in Fig. 6d.74 There were two peaks withaverage molecular weights of 2.8 kDa and 8.1 kDa; the shorterone may be assigned to the S-NDI2 dimer linked by 1,4-dia-minobutane, while the longer one is assigned to the S-NDI2oligomers and polymers. The maximum molecular weightreached around 23 kDa, which corresponds to 12-mer.© 2022 The Author(s). Published by the Royal Society of ChemistryAFM studies before and aer the cross-linking reactionbetween S-NDI2 (1.2 mM) and 1,4-diaminobutane (1.2 mM)indicated that nano-brous structures of the S-NDI2 assemblieschanged two-dimensionally extended structures made up ofshort bers upon addition of 1,4-diaminobutane (Fig. 6e). Theinter-supramolecular cross-linking reaction should also occurat high concentrations as well as intra-supramolecular cross-linking. Such two-dimensionally extended morphologies werenot observed for the thin lms prepared from isolated S-NDI2oligomers and polymers (Fig. S14†), indicating that the net-likeassemblies are only formed through the in situ reaction betweenthe S-NDI2 supramolecular polymer and 1,4-diaminobutane.In contrast, the reaction of NDI2 (25 mM) with 1,4-dia-minobutane (0.62 mM) under the same experimental condi-tions mainly afforded its amine monoadduct as shown inChem. Sci., 2022, 13, 4413–4423 | 4419http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kFig. 7 Schematic illustration of the in situ cross-linking reaction of the S-NDI2 supramolecular assembly with diamines.Chemical Science Edge ArticleOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineFig. S15.† The UV-vis absorption spectrum aer the reactionshowed a charge-transfer band at 582 nm that was blue-shiedand much narrower than the case of the S-NDI2 supramolecularpolymer (Fig. 6a). MALDI TOF-MS and GPC results also indi-cated the formation of the corresponding amine monoadductas a main product and a trace amount of the NDI2 dimer. Theseresults indicated that the intermolecular cross-linking reactionscarcely occurred under the conditions where NDI2 was mon-odispersed in solution. In other words, it is indicated that thecross-linking reaction of the S-NDI2 supramolecular polymer atCT of 25 mM was mainly the intra-supramolecular reactionbetween the pre-organized NDI units and diamines.The second-order rate constants of the series of hydro-amination are summarized in Table 1. Interestingly, the second-order rate constant of the S-NDI2 supramolecular polymer with1,4-diaminobutane (3.1 � 10�1 M�1 s�1) was 4.8-fold largerthan the case of NDI2 (6.5 � 10�2 M�1 s�1). This tendency istotally opposite to the reaction with monoamines such as DEAand diisopropylamine. The acceleration of the reaction of the S-NDI2 supramolecular polymer with a diamine can be explainedby the proximity effect in a cross-linking reaction; once anamine moiety of 1,4-diaminobutane reacted with an ethynylgroup of S-NDI2, the other amine moiety simultaneously reac-ted with another ethynyl group of an adjacent S-NDI2 within thesupramolecular polymer, as shown in Fig. 7. Accordingly,despite the crowded circumstances of the ethynyl groups in thesupramolecular polymer, the in situ reaction of the S-NDI2supramolecular polymer with 1,4-diaminobutane was acceler-ated compared to the reaction of NDI2 with 1,4-diaminobutanein monodisperse solution.The reactivity of the S-NDI2 supramolecular polymer forcross-linking may depend on the shape of the diamines. Toverify this point, we compared the in situ reaction of the S-NDI24420 | Chem. Sci., 2022, 13, 4413–4423supramolecular polymer with different diamines; we chose cis-and trans-1,4-cyclohexanediamine. As in the case of 1,4-dia-minobutane, the reaction between the S-NDI2 supramolecularpolymer and cis-1,4-cyclohexanediamine afforded the corre-sponding oligomers and polymers through intra-supramolecular cross-linking (Fig. S16†). The reaction rateconstant for the S-NDI2 supramolecular polymer was 5.1-foldfaster than that for NDI2, as shown in Table 1 and Fig. S17.†In stark contrast, the reaction between the S-NDI2 supra-molecular polymer and trans-1,4-cyclohexanediamine onlyafforded an amine monoadduct and a dimer linked by thediamine (Fig. S18†). The reaction rate for the S-NDI2 supra-molecular polymer was comparable with that for NDI2, asshown in Table 1 and Fig. S19.† These results indicated that thereaction of the S-NDI2 supramolecular polymer with trans-1,4-cyclohexanediamine did not form cross-linked structures effi-ciently, but rather the reaction occurred similar to that ofa monodisperse solution. The reluctance of the cross-linkingreaction by trans-1,4-cyclohexanediamine was also supportedby the DFT optimized structure of the amine monoadductwhere the residual amine moiety faced away from the NDI units(Fig. S20†). On the basis of these results, the intra-supramolecular polymer cross-linking reaction of S-NDI2 pro-ceeded efficiently only when the orientation of the aminemoieties wasmatched with the conguration of the NDI units inthe supramolecular polymers (Fig. 7).ConclusionsIn summary, we have demonstrated dynamic structural changesof a supramolecular polymer based on ethynyl core-substitutednaphthalenediimide (S-NDI2) molecules by quantitativehydroamination at 298 K without a catalyst. The in situ reaction© 2022 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kEdge Article Chemical ScienceOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineof the S-NDI2 supramolecular polymer with a monoamineafforded another supramolecular assembly of the correspond-ing amine-adduct through transient intermediate supramolec-ular assemblies. The quantitative reaction of the S-NDI2supramolecular polymer with a remarkable change in its opticalproperties allowed us to determine the second-order reactionrate constant using UV-vis absorption spectroscopy. The rate ofthe reaction within the S-NDI2 supramolecular polymer wasslower than that in a monodisperse solution of a referencemonomer (NDI2), probably because of the large sterichindrance around the ethynyl groups within the supramolec-ular polymer. On the other hand, the reaction of the S-NDI2supramolecular polymer with a exible diamine such as 1,4-diaminobutane occurred faster than the homogeneous reactionof NDI2 in a monodisperse solution, affording unique diaminecross-linked oligomers and polymers of S-NDI2. The accelera-tion of this reaction should be due to intra-supramolecularcross-linking between preorganized S-NDI2 units and exiblediamines in close proximity. Intra-supramolecular cross-linkingdid not occur efficiently when an incompatible diamine wasused. The present study provides an excellent opportunity tosystematically compare the reaction kinetics of an in situ reac-tion within supramolecular polymers and a homogeneousreaction in monodisperse solutions. The molecular design thatcan implement chemical reactivity in supramolecular polymersand the proximity effect of in situ reactions shown here will beuseful for further development of supramolecular polymersbased on p-conjugated molecules with unique dynamic prop-erties and reactivity.Data availabilityThe datasets supporting this article have been uploaded as partof the ESI.†Author contributionsAtsuro Takai conceived and co-supervised the project. MinghanTan mainly performed the experiments, analyzed the data andco-wrote the original dra with Atsuro Takai. Masayuki Take-uchi co-supervised the project. All the authors reviewed andedited the manuscript.Conflicts of interestThere are no conicts to declare.AcknowledgementsWe acknowledge Ms Izumi Matsunaga, Ms Nozomi Kishida andDr Takanobu Hiroto (NIMS) for their help in the syntheses ofprecursor compounds, UV-vis absorption spectral measure-ments and XRD measurements, respectively. We are alsograteful to Ms Debbie Le and Dr Mark MacLachlan (TheUniversity of British Columbia) for their contribution in theearly stage of this work. This research was supported by a Grant-in-Aid for Scientic Research (C) from JSPS 19K05640 to A. T.,© 2022 The Author(s). Published by the Royal Society of Chemistrya Grant-in-Aid from the Murata Science Foundation to A. T.,a Grant-in-Aid for Transformative Research Areas (A)“Condensed Conjugation” fromMEXT (20H05868 to M. T.), anda MEXT “NIMS Molecule and Material Synthesis Platform”program and the Materials Analysis Station of NIMS. Thequantum chemical calculations in this study were partiallyperformed on the Numerical Materials Simulator at NIMS.References1 F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer andA. P. H. J. Schenning, Chem. Rev., 2005, 105, 1491.2 T. F. A. De Greef, M. M. J. Smulders, M. Wolffs,A. P. H. J. Schenning, R. P. Sijbesma and E. W. Meijer,Chem. Rev., 2009, 109, 5687.3 T. Aida, E. W. Meijer and S. I. 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In the presence of a large excess amount ofDEA (159 mM), we observed a two step reaction of the S-NDI2 supramolecular polymer, indicating the formation ofa supramolecular assembly based on S-NDI2–(DEA)2. Incontrast, in the presence of DEA (1.24 mM), theconcentration of S-NDI2–(DEA)2 is less than 3 mM even1200 min aer the start of the reaction. See Fig. S5† fordetails.66 H. K. Hall, J. Am. Chem. Soc., 1957, 79, 5441.67 It should be mentioned that the formation of precipitates ofS-NDI2–DEA aggregates was observed below 297 K.68 A. Arjona-Esteban, J. Krumrain, A. Liess, M. Stolte,L. Z. Huang, D. Schmidt, V. Stepanenko, M. Gsänger,D. Hertel, K. Meerholz and F. Würthner, J. Am. Chem. Soc.,2015, 137, 13524.69 F. Würthner, Acc. Chem. Res., 2016, 49, 868.70 Some reviewers pointed out the terminology of thesupramolecular assemblies observed in the middle of thereaction. We agree with the reviewers that these speciesare not the same as the transient assemblies of singlemonomers formed over time. On the other hand, we© 2022 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035kEdge Article Chemical ScienceOpen Access Article. Published on 23 March 2022. Downloaded on 8/22/2025 7:36:41 AM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineshould note that these species are also different from theconventional reaction intermediate that has a localpotential energy minimum.71 C. Kulkarni, S. Balasubramanian and S. J. George,ChemPhysChem, 2013, 14, 661.72 C. Kulkarni, K. K. Bejagam, S. P. Senanayak, K. S. Narayan,S. Balasubramanian and S. J. George, J. Am. Chem. Soc.,2015, 137, 3924.© 2022 The Author(s). Published by the Royal Society of Chemistry73 We unied the concentration of the amine to be 1.24 mM,which is the same as in the experiments using DEA.74 A. Ashcra, K. X. Liu, A. Mukhopadhyay, V. Paulino, C. Liu,B. Bernard, D. Husainy, T. Phan and J. H. Olivier, Angew.Chem., Int. Ed., 2020, 59, 7487.Chem. Sci., 2022, 13, 4413–4423 | 4423http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroaminationElectronic supplementary information (ESI) available. See DOI: 10.1039/d2sc00035k