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[Ravindra Kumar Gupta](https://orcid.org/0000-0001-6859-6136), [Takashi Nakanishi](https://orcid.org/0000-0002-8744-782X), [Daniel T. Payne](https://orcid.org/0000-0003-3368-2485)

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[Alkyl‐π Liquids as Condensed‐State Singlet Oxygen Photosensitizers](https://mdr.nims.go.jp/datasets/434f0247-7e45-40c5-a74a-9cfcf604bfee)

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Alkyl‐π Liquids as Condensed‐State Singlet Oxygen PhotosensitizersChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739www.chemeurj.orgAlkyl-π LiquidsasCondensed-StateSingletOxygenPhotosensitizersRavindra Kumar Gupta,[a] Takashi Nakanishi,*[a] and Daniel T. Payne*[b, c]Functional materials capable of generating singlet oxygen (1O2),a highly reactive but short-lived species used to destroy organicmaterials, including chemical pollutants and biological entities,typically incorporate a chromophore that acts as a photosen-sitizer into a tertiary scaffold. Current functional materials thatproduce 1O2 include metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), polymeric nanoparticles, modifiedglasses, and supramolecular assemblies. Whilst multi-componentfunctional materials have been widely reported, producing func-tional materials using a single small molecule in a condensedstate has hardly been reported. Herein, we report the firstuse of functional molecular liquids (alkyl-π liquids), non-volatilesingle-component condensed-state fluidic materials, as photo-sensitizers for the generation of 1O2 at an alkyl-π liquid-waterinterface. We investigate the incorporation of various chro-mophores into alkyl-π liquids that are suitable for 1O2 productionand analyze the molecular structure required to produce effi-cient alkyl-π liquid photosensitizers. The alkyl-π liquids werestudied, impregnated into porous membranes, and as thin filmson quartz and Si wafers, the limitations of 1O2 production wereinvestigated. A system was successfully fabricated that can gen-erate 1O2 within an alkyl-π liquid impregnated membrane andmigrate across a membrane-water interface to destroy smallorganic molecules, demonstrating the potential of these systemsfor water decontamination.1. IntroductionSinglet oxygen (1O2) is a reactive oxygen species (ROS) formedby the excitation of diatomic oxygen from its triplet groundstate to an excited singlet state.[1] This is achieved using 1O2photosensitizers, which, when irradiated with light, are excitedinto a triplet state that can transfer energy to ground-statetriplet oxygen, causing excitation to the singlet state.[2] Sev-eral classes of chromophores can be used as 1O2 photosen-sitizers, including compounds containing extended π -systems(pyrenes, anthracenes, etc.), porphyrins and related compounds,fullerenes, Rose Bengal analogues, phenalenone (PN), andtris(2,2-bipyridine)ruthenium(II) salts.[3] 1O2 has several possibleapplications, including inorganic oxidative transformations,[4][a] Dr R. K. Gupta, Dr T. NakanishiResearch Center for Materials Nanoarchitectonics (MANA), National Institutefor Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, JapanE-mail: NAKANISHI.Takashi@nims.go.jp[b] Dr D. T. PayneInternational Center for Young Scientists (ICYS), National Institute forMaterials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, JapanE-mail: Daniel.Payne@open.ac.uk[c] Dr D. T. PayneSchool of Life, Health and Chemical Sciences, The Open University, WaltonHall, Milton Keynes MK7 6AA, UKSupporting information for this article is available on the WWW underhttps://doi.org/10.1002/chem.202500739© 2025 The Author(s). Chemistry – A European Journal published byWiley-VCH GmbH. This is an open access article under the terms of theCreative Commons Attribution License, which permits use, distribution andreproduction in any medium, provided the original work is properly cited.the destruction of environmental pollutants (especially forwater purification),[5] and most commonly in photodynamictherapy (PDT), including bacterial inactivation[6] and cancertreatments.[7] The effectiveness of 1O2 arises from its oxidativeproperties and high reactivity toward organic materials along-side its moderate lifetime (typically μs), which allows for thetargeted generation of the species in situ.[1,2]1O2 photosensitizers are typically organic or organometal-lic chromophores with peripheral water-solubilizing groups,as most 1O2 applications are carried out in an aqueousenvironment.[7d,8] However, extended π -systems, such as thosein photosensitizers, are prone to aggregation in aqueous media,leading to chro mophore deactivation for 1O2 generation.[9] Thishas led to the development of a variety of chromophore-containing functional materials that can be dispersed inwater for 1O2 production, including metal-organic frameworks(MOFs),[10] covalent-organic frameworks (COFs),[11] polymers,[12]modified glasses,[6a,13] and supramolecular assemblies.[14] Allexamples require a multi-component material architecture forsuitable chromophore spacing to inhibit chromophore deacti-vation, which can be time-consuming and tedious to produce.Recent studies into single-component functional materialshave had varied results; whilst nanomaterials can be producedreadily,[15] incorporating chromophores into single-componentmacroscale materials for 1O2 generation is more challenging.Perylene-based photosensitizers have been used to produce cm-scale materials capable of generating 1O2. Langmuir–Blodgettlifting of a perylene bisimide (PBI) gave an LS film but with poor1O2 generation once > 15 single-molecule layers are depositedonto the substrate,[16] and the drop-casting of PBI-dyads gavefilms capable of generating 1O2 but with no analysis of thethickness and how this affects efficiency.[17]Chem. Eur. J. 2025, 31, e202500739 (1 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbHwww.chemeurj.orghttps://orcid.org/0000-0001-6859-6136https://orcid.org/0000-0002-8744-782Xhttps://twitter.com/tnknshttps://orcid.org/0000-0003-3368-2485https://twitter.com/DTPayne_Chemmailto:NAKANISHI.Takashi@nims.go.jpmailto:Daniel.Payne@open.ac.ukhttps://doi.org/10.1002/chem.202500739http://creativecommons.org/licenses/by/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fchem.202500739&domain=pdf&date_stamp=2025-05-19Chemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Alkyl-π liquids are non-volatile single-componentcondensed-state fluidic materials.[18] The general moleculardesign of alkyl-π liquids features a core unit (typically a polyaro-matic conjugated π -system) with numerous bulky yet flexiblealkyl side chains, which contribute to the fluidic nature of thematerial at ambient temperature because of their relativelyhigh entropy.[19] These alkyl-π liquids are usually non-ionic andhydrophobic with very low glass transition temperatures (Tg),meaning they can flow freely at room temperature and can bedirectly placed on and filled into various shapes and geome-tries, which is desirable for flexible devices.[20] The π -core isresponsible for the functional nature of the liquid; for example,the inclusion of a chromophore imparts absorption-emissionproperties on the alkyl-π liquid, and chromophore modificationallows for tuneable optical properties.[21] The wrapping of the π -core with alkyl side chains isolates the π -core unit and providesadditional physical properties, including high photochemicaland thermal stability.[21d] In addition, the π -core isolation inhibitsintermolecular π–π interactions, which maintains the inherentsingle molecular optical properties in the condensed state.[21c,22]Alkyl-π liquids have been utilized in various research fields,including luminescent inks,[21d,23] liquid semiconductors,[24] MOFlike liquids with permanent porosity,[25] organic light emittingdiodes (OLEDs),[26] and liquid electrets.[20a,b,27]Whilst alkyl-π liquids have been used as functional organicsoft materials, including numerous optical applications, to date,they have not been used as 1O2-generating functional mate-rials, despite several examples having previously incorporated1O2 photosensitizers capable of accessing an excited tripletstate.[23c,28] Alkyl-π liquids have several beneficial propertiesfor this application, including high photochemical and thermalstability, tunable excitation parameters, and limited π–π inter-actions between chromophore units. This study investigates theability of alkyl-π liquids to be used as condensed-state func-tional materials containing 1O2 photosensitizers. Herein, a libraryof reported alkyl-π liquids has been studied that contains threeπ -core chromophores (anthracene, pyrene, and tetraphenylpor-phyrin) that have been modified with the same branched alkylside chains (2-hexyldecyl, C6C10) in varied substitution patterns,as this alkyl group has been shown to cause efficient π -core iso-lation when assembled in alkyl-π liquids (Figure 1).[21c,27a,29] Thisstudy aims to (i) determine if the general molecular design formodified alkyl-π liquids is capable of 1O2 generation, (ii) measurethe efficiency of 1O2 generation by alkyl-π liquids in a condensedstate, and (iii) investigate the migration of 1O2 at the alkyl-πliquid-water interface.2. Results and DiscussionThe chemical structures of the alkyl-π liquids and reference com-pounds used in this work are shown in Figure 2. A total offive previously reported alkyl-π liquids were used in this study:3,5-C6C10-DPA,[29] 3,5-C6C10-TPP,[27a] 2,5-C6C10-TPP,[27a] 3,5-C6C10-Pyr,[21c] and 2,5-C6C10-Pyr.[21c] Anthracene, tetraphenylporphyrin,and pyrene were used as chromophore cores as they have allFigure 1. Schematic of the overall concept of this work and arepresentative image of an alkyl π -liquid.been shown to generate 1O2 in organic solutions.[3b] In addi-tion, these chromophores are all common in alkyl-π liquids, andinformation regarding their additional photophysical properties,related to the generation of 1O2, may be of importance to inves-tigations into alternative applications. Porphyrin-related photo-sensitizers are of significant interest, as the majority of currentlyused 1O2 photosensitizers in clinical settings include a porphyrin-related chromophore.[30] Whilst anthracene and pyrene-basedphotosensitizers are less common due to their short wave-length absorption profiles (300–500 nm) and reported instabilitytowards 1O2 in the solution state. Phenyl groups were includedat the 9,10-positions of anthracene and the 1,3,6,8-positions ofpyrene to allow for the addition of multiple alkyl side chains.Phenyl ether modifications in either 2,5- or 3,5- substitution pat-terns on the peripheral phenyl groups of the chromophoresallowed for the installation of C6C10 alkyl chains, which inducedthe fluidic nature of the materials in the condensed state andfacilitated the chromophore separation.To give an indication of the quantum yields of 1O2 generation(��) for all compounds in solution, the electronic absorptionintensity of the photosensitizer of study must be normalized(ca. 0.1–0.3 a.u.) with that of a reference material, with a similarabsorption profile and a known ��, at an appropriately selectedexcitation wavelength in the same solvent.[31] A reliable valuefor �� was not available for anthracene in chloroform, andthe need for absorption spectrum overlap meant that PN wasrequired as an additional reference compound, which has a�� of 0.98 in chloroform.[3b] Anthracene and 3,5-C6C10-DPAwere normalized with PN to 0.27 a.u. at 380 nm (Figure 3a).Chem. Eur. J. 2025, 31, e202500739 (2 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Figure 2. Chemical structures of the compounds studied in this work. Abbreviations of the compounds are given for ease of reference in the text.3,5-C6C10-TPP and 2,5-C6C10-TPP were normalized with TPP to0.21 a.u. at 420 nm because TPP has a �� of 0.55 in chloroformwhen irradiating the Soret band (Figure 3b).[31] Both 3,5-C6C10-Pyr and 2,5-C6C10-Pyr were normalized with PN to 0.27 a.u. at384 nm (Figure 3c), whereas pyrene was normalized with PNto 0.17 a.u. at 341 nm due to its blue-shifted absorption profilecompared to the alkyl-π liquid derivatives (Figure S1).Relative phosphorescence intensity values were determined bymeasuring the intensity of 1O2 photoluminescence (ca. 1260–1270 nm) relative to that of a reference compound from thenormalized chloroform solutions of the compounds under irra-diation at the wavelength of normalization. All alkyl-π liquidsgenerated 1O2 in solution (Figure 3d–f), and the results are sum-marized in Table 1. Variations in relative phosphorescence intensitywere observed depending on molecular structure, where 3,5-C6C10-DPA had a lower relative phosphorescence intensity thananthracene (0.28 vs. 0.74), and both 3,5-C6C10-Pyr and 2,5-C6C10-Pyr had a lower relative phosphorescence intensity than pyrene(0.12 and 0.22 vs. 0.59). Whereas 3,5-C6C10-TPP and 2,5-C6C10-TPPboth had a considerably higher relative phosphorescence inten-sity compared to TPP (0.93 and 0.76 vs. 0.55), which is consistentwith �� trends reported for similar TPP derivatives.[31] While therelative phosphorescence intensities compared to known photo-sensitizers may give an indication of the approximate �� for thesolubilized alkyl-π liquids, the effect of the C6C10 alkyl chains on1O2 is not known and may affect the accuracy of these measure-ments. Stability in solution of the alkyl-π liquids compared tothe commonly used reference compounds was assessed by con-tinuous irradiation of normalized solutions of the compoundsat the absorption maxima whilst monitoring the 1O2 emissionsignal intensity at 1270 nm (Figure S2). Anthracene, pyrene, and3,5-C6C10-DPA showed some instability over 20 minutes of con-tinuous irradiation, most likely due to a reaction with 1O2 causingchromophore degradation and photodimerization in the caseof anthracene (diphenylanthracene derivatives are less proneto dimerization when irradiated).[32] 3,5-C6C10-TPP, 2,5-C6C10-TPP,Chem. Eur. J. 2025, 31, e202500739 (3 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Figure 3. Electronic absorption and photoluminescence spectra for alkyl-π liquids and reference compounds. a) UV-vis spectra of chloroform solutions ofanthracene, 3,5-C6C10-DPA, and a reference (PN) having approximately equivalent absorbances at the wavelength of irradiation (380 nm). b) UV-vis spectraof chloroform solutions of 3,5-C6C10-TPP, 2,5-C6C10-TPP, and a reference (TPP) having approximately equivalent absorbances at the wavelength of irradiation(420 nm). c) UV-vis spectra of chloroform solutions of 3,5-C6C10-Pyr, 2,5-C6C10-Pyr, and a reference (PN) having approximately equivalent absorbances at thewavelength of irradiation (384 nm). d) 1O2 photoluminescence spectra of the chloroform solutions of anthracene, 3,5-C6C10-DPA, and a reference (PN) underirradiation at 380 nm. e) 1O2 photoluminescence spectra of the chloroform solutions of 3,5-C6C10-TPP, 2,5-C6C10-TPP, and a reference (TPP) under irradiationat 420 nm. f ) 1O2 photoluminescence spectra of the chloroform solutions of 3,5-C6C10-Pyr, 2,5-C6C10-Pyr, and a reference (PN) under irradiation at 384 nm.Table 1. Summary of electronic absorption properties and 1O2 quantumyields for alkyl-π liquids and reference compounds in chloroform.CompoundUV-visλmax/nmReference[��ref] λex/nmRelativephosphores-cenceintensityAnthracene 378, 359, 342 PN (0.98) 380 0.743,5-C6C10-DPA 396, 377, 357 PN (0.98) 380 0.283,5-C6C10-TPP 423 TPP (0.55) 420 0.932,5-C6C10-TPP 422 TPP (0.55) 420 0.76Pyrene 338, 322 PN (0.98) 341 0.593,5-C6C10-Pyr 383 PN (0.98) 384 0.122,5-C6C10-Pyr 379 PN (0.98) 384 0.223,5-C6C10-Pyr, and 2,5-C6C10-Pyr all show good photostabilityin solution compared to PN and TPP, and the addition of theperipheral phenyl groups improved the stability of the pyrenealkyl-π liquids compared to pristine pyrene. An upward trend inphosphorescence intensity is observed over time for the threeporphyrin-based compounds, which was shown to be repeatableover two irradiation cycles (Figure S2b), which could be relatedto an increase in sample temperature during irradiation, as thiswas not controlled throughout the experiment.Whilst it was established that all alkyl-π liquids and refer-ence compounds could generate 1O2 in solution, to determineif they could generate 1O2 in a condensed state, thin filmswere prepared by spin coating alkyl-π liquid solutions in chloro-form at various concentrations onto quartz plates. The electronicabsorption spectra for all samples showed that with increasingcompound concentration in the spin coating solution, there wasan increasing amount of compound present per unit area onthe quartz plate based on the increasing absorbance intensity(Figure S3). Phosphorescence emission spectra for each thin filmwere recorded to determine if 1O2 was being generated uponirradiation (Figure 4a) and relative generation efficiencies can beinferred by comparison of absorbance values versus 1O2 emissionintensities, but �� cannot be calculated as there isn’t a referencecompound with a known quantum yield in a condensed-state.Reference compounds anthracene (Figure 4b), TPP (Figure 4d),and pyrene (Figure 4g) were unable to generate 1O2 in a con-densed state, likely due to the proximity of chromophorescausing deactivation. 3,5-C6C10-DPA also appeared to be unableto generate 1O2 when condensed into a thin film (Figure 4c);however, based on stability measurements (Figure S4), it appearsthat 1O2 was initially generated but quickly deactivated the filmwithin 10 seconds, most likely due to endoperoxide formation.[32]Both 3,5-C6C10-TPP (Figure 4e) and 2,5-C6C10-TPP (Figure 4f) gen-erate 1O2 and showed good stability for > 20 minutes undercontinuous irradiation. Both showed near linear relationshipsbetween the Soret band absorbance value and 1O2 phospho-rescence intensity, but 3,5-C6C10-TPP has a greater phosphores-cence intensity as an alkyl-π liquid thin film, compared to thinChem. Eur. J. 2025, 31, e202500739 (4 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Figure 4. Photoluminescence spectra for alkyl-π liquids and reference compounds as thin films on quartz. a) Schematic of the experimental setup. (b–i) 1O2photoluminescence spectra of thin films of anthracene b), 3,5-C6C10-DPA c), TPP d), 3,5-C6C10-TPP e), 2,5-C6C10-TPP f ), pyrene g), 3,5-C6C10-Pyr h), and2,5-C6C10-Pyr i) on quartz.films from 2,5-C6C10-TPP with similar absorbance values, whichmay indicate more 1O2 is being generated by 3,5-C6C10-TPP(Figure S5). Finally, 3,5-C6C10-Pyr (Figure 4h) and 2,5-C6C10-Pyr(Figure 4i) also generate 1O2 and showed good stability for > 20minutes under continuous irradiation. However, the intensity of1O2 phosphorescence does not correlate with the absorbanceintensity of the alkyl-pyrene liquid thin films (Figure S5).The absorbance values for thin films on quartz indicateincreasing film thickness as the concentration of the spin coat-ing solution is increased, but it cannot be used to determine theabsolute thickness value. Ellipsometry can be used to determinethe thickness of a thin film, but the substrate must be changedfrom quartz to a Si wafer, as an opaque reflective surface isrequired to carry out accurate ellipsometry measurements.[33] Arange of thin films of varying thickness were prepared on a Siwafer (Figure 5a) and analyzed by ellipsometry to give an aver-age thickness for the films (Table 2), which was determined bytaking the average of a series of measurements across the filmsTable 2. Summary of 3,5-C6C1o-TPP film thickness measured by ellipsom-etry and 1O2 phosphorescence signal intensities.Average thickness/nm Intensity @1265 nm/C.P.S.3,5-C6C1o-TPPmass in CHCl3 Sample 1 Sample 2 Sample 1 Sample 20 mg mL−1 1.67 ± 0.01 1.69 ± 0.01 193 1523 mg mL−1 17.23 ± 0.12 16.43 ± 0.72 2140 21116 mg mL−1 37.58 ± 0.21 37.77 ± 0.31 10,081 11,3809 mg mL−1 54.01 ± 7.77 65.3 ± 1.19 13,062 17,90012 mg mL−1 75.49 ± 3.73 81.95 ± 0.69 18,701 19,29915 mg mL−1 101.07 ± 2.65 103.53 ± 3.50 23,256 24,19518 mg mL−1 118.36 ± 1.86 118.73 ± 1.24 24,719 25,193(Table S1). A linear relationship is obtained between the con-centration of the spin coating solution and the film thicknessChem. Eur. J. 2025, 31, e202500739 (5 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Figure 5. Analysis of 3,5-C6C10-TPP films on Si wafer. (a) A series of samplesprepared by spin-coating with increasing concentration solution of3,5-C6C10-TPP in chloroform on Si wafer. (b) Schematic of the experimentalsetup for phosphorescence spectroscopy. (c) 1O2 photoluminescencespectra of thin films of 3,5-C6C10-TPP on Si wafer under irradiation at420 nm. (d) Correlation plot between film thickness and 1O2phosphorescence intensity with a linear fit line. (e) Photostability of a thinfilm (12 mg mL−1) of 3,5-C6C10-TPP by monitoring 1O2 photoluminescenceintensity at 1270 nm during continuous irradiation at 420 nm.(Figure S6) with average values ranging from approximately 16to 120 nm. Attempts were made to obtain quantitative absorp-tion spectra using an integrated sphere for the thin films onSi wafers (Figure S7), but the reflective nature of the substratehindered the measurements, and no clear correlation could befound between absorbance and film thickness. Phosphorescenceemission spectra for each thin film were recorded to deter-mine if 1O2 was being generated upon irradiation (Figure 5c),and an increase in phosphorescence intensity is observed asthe film thickness increases (Figure 5d and Table 2). A previousstudy using perylene-based photosensitisers had observed thatthe limiting factor in thin film 1O2 generation produced by theLangmuir–Schaefer technique was aggregation of chromophoresas film thickness was increased beyond 15 monomer layers.[16]However, using alkyl-π liquids appears to overcome this limi-tation, likely due to the alkyl side chains’ ability to effectivelyisolate chromophores, as the results in Figure 5d indicate thatthin film thickness trends linearly with the generation of 1O2.It appears that for alkyl-π liquids, the limiting factors are mostlikely the amount of light per unit area being delivered to thealkyl-π liquid surface, the adequate penetration depth of thelight through the alkyl-π liquid, and the diffusion of O2 throughthe alkyl-π liquid. Finally, the photostability of an alkyl-π liquidthin film was investigated by monitoring the 1O2 phosphores-cence intensity during continuous irradiation at 420 nm of asample produced through spin coating a 12 mg mL−1 solution of3,5-C6C10-TPP onto a Si wafer (Figure 5e) with an approximately38% signal decrease observed over 60 minutes.Most applications for 1O2 require an aqueous environment,but the alkyl-π liquids in this study require alkyl side chainsto induce fluidity, which renders the alkyl-π liquids hydropho-bic. While a water-alkyl-π liquid interface could be establishedby placing water droplets in contact with the alkyl-π liquidon a quartz plate, over time, the alkyl-π liquid migrates andspreads across the outer surface of the water droplet, which isnot ideal for the application of these materials. Previous studieshave utilized the mechanoelectrical properties of alkyl-π liquidsin wearable devices by permeating the alkyl-π liquid into a flex-ible polyurethane membrane.[27a] The same approach was usedfor 1O2 generating functional materials, and as the membrane ishydrophobic, the alkyl-π liquid impregnates the pores but is notexpelled when the membrane is placed in contact with water.The membrane was impregnated with alkyl-π liquid by past-ing it on the surface of the membrane, followed by standing at50°C for 2 hours. Alternatively, the alkyl-π liquid can be dissolvedin chloroform and the membrane submerged, followed by slowevaporation. The generation of 1O2 by alkyl-π liquid impreg-nated membranes was confirmed by 1O2 phosphorescence spec-troscopy in either a front-face or back-face excitation-emissionarrangement (Figure 6a), with both arrangements giving anobservable 1O2 phosphorescence signal (Figure 6b).Whilst 1O2 could be detected at the membrane-air interface,it is essential to ascertain whether this could be achieved at amembrane-water interface (Figure 6c). Due to the short lifetimeof 1O2, it is important to determine if it can be initially generatedby the hydrophobic alkyl-π liquids impregnated into the mem-brane and then diffuse into the water to carry out a function,Chem. Eur. J. 2025, 31, e202500739 (6 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739Figure 6. Analysis of 3,5-C6C10-TPP permeated into a membrane. (a) Schematic of 1O2 phosphorescence spectroscopy measurements in either a front-face(top) or back-face (bottom) excitation-emission arrangement. (b) 1O2 photoluminescence spectra of 3,5-C6C10-TPP in membranes under irradiation at420 nm. (c) Photos of a alkyl π -liquid impregnated membrane used for the detection of 1O2 at the membrane-water interface. (d) Schematic of theexperimental setup for 1O2 trapping studies using an anthracene probe. (e) Schematic of the experimental setup for 1O2 trapping studies using an amineprobe. (f ) UV-Vis 1O2 detection measurements using a basic solution of 3,3′-(anthracene-9,10-diyl)dipropionic acid on membranes in the presence (top) andabsence of 3,5-C6C10-TPP. (g) EPR 1O2 detection measurements using a solution of TEMPD (2,2,6,6-tetramethylpiperidone) on membranes in the presence(top) and absence of 3,5-C6C10-TPP.Chem. Eur. J. 2025, 31, e202500739 (7 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.202500739such as the destruction of organic materials dissolved in thewater. This analysis is not achievable using phosphorescencespectroscopy, as the spectrometer beam resolution would notbe able to selectively excite and differentiate between 1O2 gen-erated within the alkyl-π liquid-membrane at the membrane–airinterface or at the membrane–water interface. Therefore, 1O2trapping studies were carried out using either a water-solubleanthracene (Figure 6d) or amine (Figure 6e) 1O2 trap monitoredby either UV-vis or EPR spectroscopy, respectively.[15a,34] Thecycloaddition of 1O2 to 3,3′-(anthracene-9,10-diyl)dipropionic acidcan be observed through the reduction of the anthracene UV-visresponse at 350–400 nm, which occurs faster in the presence of3,5-C6C10-TPP (Figure 6f and Figure S8b,c), however, the irradi-ation source led to some background photodegradation of theanthracene-based probe due to photobleaching and possibledimerization. Therefore, the radical spin trap TEMPD (2,2,6,6-tetramethylpiperidone) was used as an alternative approach tomonitor the production of 1O2 through the formation of a stableradical. It can be monitored through the characteristic EPRresponse at 319–324 mT, which also occurs faster in the presenceof the 3,5-C6C10-TPP-impregnated membrane (Figure 6g andFigure S8d). Fluctuations in the background signal for TEMPD inFigure 6g are due to small changes in concentration during theremoval of the droplets from the membrane surface, as previousstudies have shown light irradiation to have no measurableeffect on TEMPD under continuous irradiation.[15a] Both of theseresults confirm that 1O2 can be generated by an alkyl-π liquidimpregnated into a porous membrane and transferred acrossan interface with water to perform a function, including thedestruction of organic materials, which could be beneficial forproducing functional materials for water decontamination.3. ConclusionIn conclusion, we have demonstrated that alkyl-π liquids canbe used as functional condensed-state materials to produce 1O2.A range of alkyl-π liquids with identical branched alkyl sidechains (2-hexyldecyl, C6C10) and varied chromophores known tobe 1O2 photosensitizers (pyrene, anthracene, and tetraphenyl-porphyrin) were studied for their ability to generate 1O2 inchloroform solutions, with all compounds generating reason-able amounts compared to reference compounds. Alkyl-π liquidscontaining porphyrin cores (3,5-C6C10-TPP and 2,5-C6C10-TPP) andpyrene cores (3,5-C6C10-Pyr and 2,5-C6C10-Pyr) were also able togenerate 1O2 as solvent-free thin films on quartz plates and Siwafers. Comparative analysis between the alkyl-π liquids showedthat 3,5-C6C10-TPP generated the most 1O2 and trended linearlywith film thickness. Whereas anthracene-based alkyl-π liquidswere not suitable for the generation of 1O2 in solvent-free thinfilms, likely due to the rapid formation of endoperoxides lead-ing to deactivation of the chromophore. Finally, alkyl-π liquidsimpregnated into porous membranes were fabricated with 3,5-C6C10-TPP for the generation of 1O2 in aqueous media, whichwas confirmed through both UV-vis analysis using an anthraceneprobe and EPR spectroscopy using an amine-based radical spintrap. The ability to fabricate systems, such as alkyl-π liquidimpregnated into porous membranes and alkyl-π liquid thinfilms, could be useful to produce systems for the decontam-ination of water, due to the ability of 1O2 to destroy organicpollutants and biological contaminants. The transfer of 1O2 acrossthe alkyl-π liquid-water and membrane-water interface demon-strated in our studies is of fundamental importance towardsthese future applications.4. ExperimentalReagents and dehydrated solvents (in septum-sealed bottles) usedfor syntheses and spectroscopic measurements were obtained fromTokyo Kasei Chemical Co., Wako Chemical Co., or Aldrich ChemicalCo. and were used without further purification. Optical absorptionspectra were measured using a JASCO V-570 UV/Vis/NIR spectropho-tometer. 1O2 photoluminescence spectra were measured using anInGaAs NIR photodetector (R5509-73, Hamamatsu Photonics, Japan)on a NanoLog Horiba Jovin Yvon spectrofluorometer with a 450-W xenon lamp as an excitation source at room temperature. Aright-angle detection method and quartz cuvettes with four opti-cal faces that were usable in the UV field were used for emissionmeasurements. ESR spectra were measured using a JEOL JES-FA200spectrometer with data recorded and processed using the A-Systemversion 1.6.5 PCI J/X-Band and FAManager version 1.2.9 V2 series. Filmthickness of Si wafers was measured using a high-speed spectro-scopic Ellipsometer (M-2000U; J. A. Woollam Co., Inc., Lincoln, NE). Allalkyl-π liquids used in this study have been previously reported: 3,5-C6C10-DPA,[29] 3,5-C6C10-TPP,[27a] 2,5-C6C10-TPP,[27a] 3,5-C6C10-Pyr,[21c]and 2,5-C6C10-Pyr.[21c] POREFLON PTFE membrane was used as aporous membrane for material fabrication.Film preparation: Quartz substrates (2 cm × 2 cm) were UV-ozone treated and rinsed with ethanol prior to use. Silicon wafersubstrates were cut into a size of 2 cm × 2 cm and thoroughly rinsedwith IPA prior to use. Samples were dissolved in chloroform at vari-ous concentrations (e.g., 3, 6, 9, 12, and 18 mg mL−1), and 50 μL wasspin-coated onto quartz plates and Si wafers at 2000 rpm for 60 s.Thickness measurements: The thickness of the spin-coated filmon a Si wafer was assessed using a high-speed spectroscopic Ellip-someter. Each sample was duplicated and measured at five differentpoints across the Si wafer, and an average of all measurementswas taken for the final thickness result. To ensure the measure-ment accuracy, a blank silicon substrate was also measured with athickness of ∼1.67 nm.1O2 relative phosphorescence intensity measurements: Emissionspectra and 1O2 photoluminescence spectra were measured usingan NIR photodetector (Hamamatsu Photonics, Japan) on a NanoLogHoriba Jovin Yvon spectrofluorometer with a 450 W xenon lamp asan excitation source at room temperature under ambient conditions(unless otherwise stated). To estimate 1O2 quantum yields, the solu-tions of compounds were absorbance normalized (ca. 0.10–0.30 a.u.)with a reference compound at the relevant excitation wavelength inchloroform. Relative phosphorescence intensity was determined bycomparison of the average 1O2 photoluminescence maxima valuesof the reference (Iref) and compound being studied (Isample) between1263 and 1267 nm:Relative phosphorescence intensity = IsampleIref× �ref�EPR 1O2 measurements: A 100 μL aliquot of the 2,2,6,6-tetramethylpiperidone (TEMPD, 0.26 M) solution in deionized waterwas placed on the membrane either with or without 3,5-C6C10-TPPand irradiated with blue LEDs (400–500 nm) for a period (0.0, 1.0,Chem. Eur. J. 2025, 31, e202500739 (8 of 10) © 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH 15213765, 2025, 33, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202500739 by Takashi Nakanishi - National Institute For , Wiley Online Library on [12/06/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseChemistry—A European JournalResearch Articledoi.org/10.1002/chem.2025007392.0, 3.0, 4.0, or 6.0 h). For irradiation times over 1 hour, 50 μL perhour of deionized water was added to the droplet to account forevaporation. After irradiation, the droplet was lifted from the mem-brane using a Hamilton 100 μL syringe, the volume of the dropletwas measured and diluted to a final volume of 100 μL, and an EPRspectrum at each time point was recorded in a Drummond 100 μLmicrocap capillary sealed at one end under ambient conditions.UV-Vis 1O2 measurements: Sodium hydroxide 1 M (20 μL,0.02 mmol, 3 equiv.) was added to a solution of 3,3′-(anthracene-9,10-diyl)dipropionic acid (DPA, 2.22 mg, 0.0068 mmol, 1 equiv.) indeionized water (2.2 mL). A 50 μL aliquot of the DPA solution wasplaced on the membrane either with or without 3,5-C6C10-TPP andirradiated with blue LEDs (400–500 nm) for a period (0.0, 1.0, 1.5, 2.5,3.0, or 3.5 h). For irradiation times over 1 hour, 50 μL per hour ofdeionized water was added to the droplet to account for evapo-ration. After irradiation, the droplet was lifted from the membraneusing a Hamilton 100 μL syringe, the volume of the droplet was mea-sured and diluted to a final volume of 0.5 mL, and an absorptionspectrum at each time point was recorded in a 1 mm path lengthquartz cell.Author ContributionsDaniel T. Payne and Takashi Nakanishi established the concept ofthe study. Ravindra Kumar Gupta performed alkyl-π liquid filmfabrication, electronic absorption spectroscopic measurements,and film thickness analysis. Daniel T. Payne performed phospho-rescence spectroscopic measurements, EPR experiments, spin-trap studies, and determined singlet oxygen quantum yieldsof the compounds. All authors contributed to the writing andediting of the manuscript.AcknowledgmentsThis research was partly supported by World Premier Interna-tional Research Center Initiative (WPI Initiative), MEXT, Japan,and by JSPS KAKENHI Grant Number JP24H01733 and JP25H01264in a Grant-in-Aid for Transformative Research Areas “Materi-als Science of Meso-Hierarchy” and “π -Molecular Complexity”,respectively. R.K.G. thanks the Japan Society for the Promotionof Science (JSPS) for a JSPS postdoctoral fellowship (P20041) andthe National Institute for Materials Science (NIMS) for a NIMSpostdoctoral fellowship. D.T.P is grateful to the National Institutefor Materials Science, International Center for Young Scientists,Japan (ICYS, NIMS) for an ICYS fellowship and research funds andto the Open University and the Open Societal challenges SPLICEnetwork for their continued support.Conflict of InterestsThe authors declare no conflict of interest.Data Availability StatementThe data that support the findings of this study are availablefrom the corresponding author upon reasonable request.Keywords: alkyl-π liquids • chromophores • functional materi-als • functional molecular liquids • singlet oxygen photosenstiz-ers[1] M. Bregnhøj, F. Thorning, P. R. Ogilby, Chem. Rev. 2024, 124, 9949.[2] M. C. DeRosa, R. J. Crutchley, Coord. Chem. Rev. 2002, 233, 351.[3] a) J. J. M. Lamberts, D. C. Neckers, Tetrahedron 1985, 41, 2183; b) F.Wilkinson, W. P. Helman, A. B. Ross, J. Phys. Chem. Ref. Data 1993, 22,113; c) R. W. Redmond, J. N. Gamlin, Photochem. Photobiol. 1999, 70,391.[4] a) W. Adam, H. G. Brunker, J. 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elax Alkyl- Liquids as Condensed-State Singlet Oxygen Photosensitizers 1. Introduction 2. Results and Discussion 3. Conclusion 4. Experimental Author Contributions Acknowledgments Conflict of Interests Data Availability Statement