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[Shinsuke Ishihara](https://orcid.org/0000-0001-6854-6032), [Avijit Ghosh](https://orcid.org/0000-0001-9651-7474), Tatsuya Mori, Mandeep K. Chahal, [Daniel T. Payne](https://orcid.org/0000-0001-7707-8381), [Akinori Saeki](https://orcid.org/0000-0001-7429-2200), Tsuyoshi Hyakutake, [Takashi Nakanishi](https://orcid.org/0000-0002-8744-782X)

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[Luminescent core-isolated solvent-free liquids as a soft material platform for optical gas sensing](https://mdr.nims.go.jp/datasets/b641e455-5166-4e85-881e-4219c9550e6f)

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Luminescent core-isolated solvent-free liquids as a soft material platform for optical gas sensingChemicalScienceEDGE ARTICLELuminescent coraResearch Center for Materials NanoarchiMaterials Science (NIMS), 1-1 Namiki, TsuISHIHARA.Shinsuke@nims.go.jp; NAKANISHbSchool of Applied Science & TechnologTechnology, Maulana Abul Kalam Azad741249, West Bengal, IndiacSchool of Chemistry and Forensic Science, UUKdSchool of Life, Health & Chemical Sciences,6AA, UKeDepartment of Applied Chemistry, Graduate2-1 Yamadaoka, Suita, Osaka, 565-0871, JafInnovative Materials and Resources Researc1-6 Minamihara, Tsukuba, Ibaraki, 305-851† These authors contributed equally to th‡ Present address: Department of ChemIntegrated Research Consortium onUniversity, Furo, Chikusa, Nagoya, 464-86Cite this: Chem. Sci., 2026, 17, 5934All publication charges for this articlehave been paid for by the Royal Societyof ChemistryReceived 30th October 2025Accepted 21st January 2026DOI: 10.1039/d5sc08398brsc.li/chemical-science5934 | Chem. Sci., 2026, 17, 5934–5e-isolated solvent-free liquids asa soft material platform for optical gas sensingShinsuke Ishihara, †*a Avijit Ghosh, †ab Tatsuya Mori,‡a Mandeep K. Chahal,acDaniel T. Payne, ad Akinori Saeki, e Tsuyoshi Hyakutakefand Takashi Nakanishi *aSolvent-free functional molecular liquids have attracted great interest as a new class of stimuli-responsivesoft materials, yet their potential as optical gas sensors remains unexplored. Conventionally, luminescentorganic molecules are employed in combination with a solid support or matrix. However, theirperformance in chemical sensing and optoelectronic devices is often hindered by adverse phenomenasuch as aggregation, concentration quenching, and photodegradation. In this study, we employa strategy to isolate and wrap a phosphorescent Pt(II)-porphyrin core with bulky yet flexible branchedalkyl chains, resulting in a solvent-free liquid at room temperature that demonstrates excellent propertiesfor sensing oxygen (O2) gas. Compared to reference material composed of Pt(II)-tetraphenylporphyrinand a highly gas-permeable polymer matrix, our Pt(II)-porphyrin liquid shows comparable sensitivity (I0/I100 = 75 ∼ 90), better linearity, and greater photostability in its O2-responsive phosphorescence. This isattributed to the high homogeneity and gas solubility of the liquids, as well as to the shielding ofluminescent-core units by bulky alkyl chains. The liquid nature of the materials allows for ratiometricsensing, where the compatibility of a phosphorescent Pt(II)-porphyrin liquid (O2-sensitive) anda fluorescent alkyl-pyrene liquid (O2-insensitive) enables reproducible monitoring of O2 concentrationwithout specific calibration. Indeed, these results highlight the significant benefits of core-isolatedluminescent liquids in diverse sensing applications.IntroductionFunctional molecular liquids (FMLs) have recently becomea transformative category in so functional materials.1 Withinthis group, alkyl-p liquids—solvent-free systems with p-conju-gated molecular units isolated and wrapped by bulky yet exiblebranched alkyl chains—provide tunable optoelectronictectonics (MANA), National Institute forkuba, Ibaraki 305-0044, Japan. E-mail:I.Takashi@nims.go.jpy, Department of Forensic Science &University of Technology, Haringhataniversity of Kent, Canterbury, CT2 7NH,The Open University, Milton Keynes, MK7School of Engineering, Osaka University,panh Center, Public Works Research Institute,6, Japanis work.istry, Graduate School of Science andChemical Sciences (IRCCS), Nagoya02, Japan.943properties and liquid-phase behaviors that differ from tradi-tional solid-state frameworks.2–4 These alkyl-p liquids haveunique physical properties: molecular uniformity, uidity,deformability, miscibility, and guest solubility, etc. Owing totheir abundant designability for functional core units, varioustypes of FMLs have been developed to date (e.g., tunable lumi-nescence including phosphorescence,5–9 triplet-mediatedphotochemical functions,10,11 optoelectronic- and energy-related functions,12–14 permanent porosity and gas adsorp-tion,15,16 and guest- and mechano-responsiveness17–21). Amongthose intriguing FMLs, although alkyl-p liquids have beendeveloped as stimuli-responsive liquid materials, to the best ofour knowledge, no reports have demonstrated the utility of theirliquid properties for optical gas sensing. In related works, Isodaet al. reported alkylated N-heteroacene liquids that change theiruorescence color upon exposure to HCl vapor, where the vaporresponsiveness is accompanied by protonation-induced solidi-cation of the liquids.20,21 Unique aspects of alkyl-p liquidsinclude their ability to provide a distinct mode of operation asstable liquid media that retain responsiveness and miscibility.According to Henry's law, the dissolution of gas molecules intoliquids is proportional to their partial pressure.22 This moti-vated us to elucidate the potential of alkyl-p luminescentliquids as optical gas sensors and unveil any fundamental© 2026 The Author(s). Published by the Royal Society of Chemistryhttp://crossmark.crossref.org/dialog/?doi=10.1039/d5sc08398b&domain=pdf&date_stamp=2026-03-20http://orcid.org/0000-0001-6854-6032http://orcid.org/0000-0001-9651-7474http://orcid.org/0000-0001-7707-8381http://orcid.org/0000-0001-7429-2200http://orcid.org/0000-0002-8744-782XEdge Article Chemical Scienceaspects distinct from conventional solid support or matrixsystems.Luminescent organic molecules (LOMs) have been utilized foroptical sensing of physical, chemical, and biological events.23–26In particular, oxygen (O2) is a vital target analyte27–29 due to strongconnections with the atmospheric environment, energy, and life,as exemplied by the spatiotemporal visualization of aero-dynamics,30 fuel cell operation,31 and hypoxia in cancer cells.32,33Among the various optical detection modes (e.g., wavelength,intensity, ratiometric, frequency, upconversion, lifetime, etc.),monitoring of luminescence intensity is widely utilized in O2sensing due to the low cost and simplicity of the devices.24,29Triplet photo-excited states of LOMs can be effectively quenchedby O2, which makes their phosphorescence intensity sensitive toO2 levels. The interaction dynamics and correlation betweenluminescence intensity and a quencher's concentration aredescribed by the Stern–Volmer equation (eqn (1)).27I0/Ix − 1 = Ksv[Q] (1)where I0 and Ix are, respectively, the emission intensity in theabsence (0%) and the presence (x%) of a quencher (herein, O2),and KSV is the Stern–Volmer constant.Since the luminescence of LOMs is generally maximized intheir discrete (i.e., non-aggregated) states except for rare caseswhere molecular motion is restricted within the aggregate orconnement,34 optical sensing is oen performed in a solution(dissolved in water or organic solvent) or a composite with solidsupport or matrix (e.g., polymers,35–37 oxides,38,39 porousmaterials,40–42 and nanoparticles43–45). Consequently, the perfor-mance of optical O2 sensors is inuenced not only by LOMs butFig. 1 (a) Chemical structures of Pt(II) porphyrins; alkylated liquid (PtPLshowing solvent-free liquid appearance. (c) Phosphorescent property of PUV light with N2 flow (iii).© 2026 The Author(s). Published by the Royal Society of Chemistryalso by the compatibility and O2 permeability of the solid supportor matrix. Among various phosphorophores (e.g., polycyclicaromatic carbons, transition metal complexes, and fullerenes),Pt(II) and Pd(II)-porphyrins are extensively studied for optical O2sensing because of their intense phosphorescence at roomtemperature.27,46–48 For example, Amao et al. found that Pt(II)-octaethylporphyrin (PtOEP) embedded in a highly gas-permeablepoly(1-trimethylsilyl-1-propyne) (PTMSP)49 shows considerablesensitivity to O2 (I0/I100 = 225).50 In contrast, the same Pt(II)-porphyrin embedded in polystyrene or poly-(dimethylsiloxane)exhibits only moderate sensitivity (I0/I100 = ∼5).Here, we present the rst demonstration of an optical oxygen(O2) sensing based on a phosphorescent core-isolated solvent-free liquid, utilizing a Pt(II)-porphyrin core ([5,10,15,20-tetra-kis(3,5-bis((2-hexyldecyl)oxy)phenyl)porphyrinato]platinum(II)PtPL, Fig. 1). The liquid exhibits benchmark-level sensitivity (I0/I100 = 75 ∼ 90), superior linearity, and improved photostabilitycompared to conventional reference materials composed ofPt(II)-tetraphenylporphyrin (PtTPP)51 and PTMSP. Additionally,by mixing PtPL with a uorescent alkyl-pyrene liquid, wedevelop a robust ratiometric sensing that operates withoutspecic calibration. This work provides novel insights intooptical gas sensing, establishing luminescent solvent-freeliquids not only as responsive FMLs but also as active media,opening a versatile pathway toward a future so sensingplatform.Results and discussionTo obtain Pt(II)-porphyrin liquid PtPL, a free-base liquidporphyrin with 2-hexyldecyl branched alkyl chains13 was reacted) and solid PtTPP used in this study. (b) Photograph of PtPL at 20 °CtPL observed under daylight in air (i), under UV light in air (ii), and underChem. Sci., 2026, 17, 5934–5943 | 5935Chemical Science Edge Articlewith Pt(II)Cl2 in reuxing benzonitrile for 4–5 h under argon (Ar)(Fig. 1a).51 Aer purication and drying under vacuum, PtPLwas obtained as a viscous red-orange liquid (Fig. 1b). Disap-pearance of the inner pyrrolic protons in the 1H NMR spectrumof PtPL indicates the successful insertion of a Pt(II) ion into theporphyrin core, and the high-resolution mass spectrum of PtPLis in agreement with its chemical formula, [C172H285O8N4194Pt]+(Fig. S2–S5). Under ultraviolet (UV) irradiation, an intense redemission was observed from PtPL when under an N2 or Aratmosphere (Fig. 1c). The emission was largely quenched in airdue to energy transfer from photo-excited PtPL to O2. Thus,PtPL exhibits the expected phosphorescent properties fora long-lived triplet excited state. Even though branched alkylchains surround the Pt(II) porphyrin core, small gas moleculescan access the core through a mechanism akin to the facilita-tion of pyridine vapor into Zn(II) liquid porphyrin,13 which isstructurally similar to PtPL (see Fig. S6–9 and 21).It is revealed that PtPL is a stable liquid at room temperatureand shows optical properties in neat state almost identical toPtTPP in a diluted toluene solution (Fig. 2). A sample of PtPLsandwiched between glass plates is uidic, and its cross-polarized optical microscopy (POM) image shows no birefrin-gence, supporting the absence of long-range ordered domains(Fig. 2a). Differential scanning calorimetry (DSC) thermogramof PtPL shows only a reversible glass transition temperature (Tg)Fig. 2 (a) Optical microscopy images of PtPL sandwiched between glrepresent the identical positions within the samples. (b) DSC thermograa scan rate of 10 °C min−1. (c) Absorption spectra of PtPL in neat liquid sshown for comparison. (d) Emission spectra of PtPL in neat liquid state (letoluene (10−6 M) under Ar are shown for comparison. Note that these e5936 | Chem. Sci., 2026, 17, 5934–5943at around−40 °C; thus, PtPLmaintains a liquid state above thattemperature (Fig. 2b). Absorption and emission spectra of PtPLin neat liquid are similar to those of PtPL and PtTPP in toluenedue to the bulky alkyl chains isolating the Pt(II)-porphyrin corefrom the surrounding environment (Fig. 2c and d). Note that theluminescent lifetime and quantum yield of PtPL were slightlylonger and larger than those of PtTPP in toluene (Fig. S11 andTable S1).As shown in Fig. 3a–c, the emission from neat lm PtPL isquenched (signal intensity is reduced) as the concentration ofO2 in the atmosphere increases from 0% to 100%. There isa certain response to 0.03% O2, and the emission intensityhalved at an O2 concentration of 1% (Fig. 3a). The Stern–Volmerplot of neat lm PtPL shows linear correlations between O2concentration (x-axis) and I0/Ix − 1 (y-axis). The value of I0/I100 isoen used in the literature to represent O2 sensitivity, and I0/I100= ∼90 is much greater than most phosphorescent O2 sensingmaterials (I0/I100 = 5∼ 10).27,35,42 As described above, Amao et al.reported that PtOEP embedded in polystyrene or poly-(di-methylsiloxane) shows modest sensitivity (I0/I100 = ∼5).50Whereas, signicant sensitivity to O2 (I0/I100 = 225) was ob-tained when PtOEP was embedded in a highly gas-permeablePTMSP polymer. Thus, our solvent-free liquid PtPL is a suit-able medium for accommodating O2 molecules from the gasphase. The higher sensitivity of Amao's lm could be ascribed toass plates without (left) and with (right) cross polarizers. Asterisks (*)m in the 2nd heating and cooling trace of PtPL recorded under N2 attate. The absorption spectra of PtPL and PtTPP in toluene (10−6 M) arex= 410 nm) under argon (Ar). The emission spectra of PtPL and PtTPP inmissions were largely quenched under air (see Fig. S12–14).© 2026 The Author(s). Published by the Royal Society of ChemistryFig. 3 (a and b) Emission spectra of a neat film PtPL (lex = 412 nm) measured under various O2 concentrations (a; with higher emissionintensities, b; emission intensities lower than 30). See Fig. S10 for photographs illustrating the emission changes of neat PtPL films at different O2levels. (c) Plot of O2 concentration vs. emission intensity (lem = 657.5 nm) in a neat film PtPL. Inset shows intensities lower than 30. (d) Stern–Volmer plot of a neat film PtPL (lem = 657.5 nm) for O2 sensing. Inset shows the plot for lower O2 concentration than 1%. It is worth noting thatthe phosphorescence of PtPL shows little sensitivity to humidity, whereas it is sensitive to temperature and air pressure (see Fig. S15–17).Edge Article Chemical Sciencethe excellent gas permeability of PTMSP as well as minimumsubstituents around the Pt(II)-porphyrin unit, enabling efficientenergy transfer to proximal O2. However, it should be noted thatthe porphyrin concentration in the Amao's lm was very dilute(ca. 2.9 × 10−5 mol dm−3, estimated as ca. 0.003 wt% based onmolecular weight of the PtOEP (727.8 g mol−1) and density ofPTMSP (0.7 g cm−3)52), presumably for preventing undesirableaggregation of porphyrins in the polymer matrix. Therefore,compared to the neat liquid PtPL, the brightness of the PtOEP–PTMSP lm should be modest.To investigate the effect of the bulky alkyl side chainscompared to a porous polymer matrix, the O2 sensing perfor-mance of the neat liquid PtPL was compared with PtTPP–PTMSP and PtPL–PTMSP composites. A solution of PtTPP andPTMSP was spin-coated on a quartz substrate, and the opticalproperties of the thin lms were investigated (Fig. 4a).Absorption signals corresponding to the Soret-band (lmax = 401nm) of PtTPP linearly increased when the amount of PtTPP wasincreased from 0.2 to 20 wt% (Fig. 4b). However, the absorptionsignals did not grow beyond 20 wt%, suggesting aggregation orprecipitation of PtTPP either within or outside the polymermatrix. In contrast, absorption signals of PtPL blended intoPTMSP (lmax = 406 nm) did not saturate even at 80 wt% owingto the absence of aggregation of PtPL in the PtPL–PTMSPcomposite (Fig. 4c). Composite lms of PtTPP–PTMSP (1, 5, 20,and 50 wt%) exhibited slightly better sensitivity to O2 (I0/I100 =∼120) than a neat liquid lm of PtPL (I0/I100 = ∼90), which canbe attributed to the higher gas permeability of PTMSP© 2026 The Author(s). Published by the Royal Society of Chemistrycompared to PtPL (Fig. 4d). The linearity of each plot wasquantitatively assessed using the coefficient of determination(R2) obtained from linear tting, showing moderate linearity (R2= 0.84–0.97). In contrast, PtPL–PTMSP displays clearcomposition-dependent behavior (Fig. 4e). At low loadings (1, 5,and 20 wt%), a nonlinear response with high sensitivity isobserved. This high sensitivity can be attributed to the high gaspermeability of the PTMSP matrix as well as the increasednumber of O2 molecules available per PtPL molecule. Anotherpossible interpretation is that PtPL, bearing branched alkylchains reminiscent of those typically present in plasticizers,may slightly modify the local polymer environment, potentiallyfacilitating O2 diffusion. By contrast, at higher loadings (50 and100 wt%), the Stern–Volmer plots exhibit excellent linearity (R2> 0.99), while maintaining a sufficiently high level of sensitivitycompared with other materials, despite some reduction. Suchexcellent linearity is advantageous for the quantication ofa wide O2 range based on two-point calibration. Downward-curved Stern–Volmer plots are commonly observed in sensorlms and are oen attributed to the presence of multipleemissive states with different luminescence lifetimes and/orquenching efficiencies within heterogeneous matrices.27,53–56Thus, the improvement of linearity is likely due to the increasedhomogeneity of the sensing phase upon reducing the inuenceof the polymer matrix, which suppresses microenvironmentalheterogeneity. Although neat liquid PtPL shows the lowestsensitivity among the samples in Fig. 4e, this limitation isaddressed in the blended liquid system discussed in a laterChem. Sci., 2026, 17, 5934–5943 | 5937Fig. 4 (a) Preparation of polymer composite films. (b) Absorption spectra of PtTPP–PTMSP composite film with various amounts of PtTPP. (c)Absorption spectra of PtPL–PTMSP composite film with various amounts of PtPL. (d) Stern–Volmer plots of PtTPP–PTMSP composite films (1, 5,20, and 50 wt%). R2 denotes the coefficient of determination for the linear fit. (e) Stern–Volmer plots of neat liquid PtPL (100 wt%) and PtPL–PTMSP composite films (1, 5, 20, and 50 wt%). (f) Decay of emission intensity upon repeated exposure to excited beam irradiations under N2 and0.03% O2.Chemical Science Edge Articlesection, where both high sensitivity and good linearity aresimultaneously achieved.Notably, neat liquid PtPL shows better photostability thanPtTPP–PTMSP upon repeated measurements, which can beascribed to protecting the Pt(II)-porphyrin unit by the bulky alkylchains (Fig. 4f). Although uorinated porphyrins are known to5938 | Chem. Sci., 2026, 17, 5934–5943show improved photostability,57 uorinated organiccompounds potentially cause environmental concerns due topoor biodegradability. The core-shielding effect of phospho-rescent liquids (e.g., PtPL) by hydrocarbon alkyl chains isadvantageous in this regard. Toward practical implementation,photostability could be further improved by elongating or© 2026 The Author(s). Published by the Royal Society of ChemistryFig. 5 (a) Blending of phosphorescent liquid PtPL and fluorescent liquid PyL. (b) Absorption spectrum of the mixed liquid film of PtPL+PyL (1 : 2,by weight) measured in air. For comparison, the absorption spectra of the individual neat liquids (PtPL and PyL), measured separately, are alsoshown. (c) Emission spectra (lex = 360 nm) of the mixed liquid film of PtPL+PyL (1 : 2, by weight) under various O2 levels. The excitationwavelength was selected to simultaneously excite both PtPL and PyL while minimizing photobleaching caused by shorter-wavelength UVirradiation. Based on emission intensity, film A has approximately double the loading of liquids compared to film B. (d) Stern–Volmer plotsobtained from phosphorescence (lem= 656 nm) of films A and B. (e) Ratiometric plots obtained fromO2-insensitive fluorescence (lem= 428 nm)and O2-sensitive phosphorescence (lem = 656 nm) of films A and B.Edge Article Chemical Sciencedensifying the branched alkyl chains; however, this mayadversely affect O2 sensitivity because of reduced energy trans-fer efficiency. Therefore, photostability and sensitivity should© 2026 The Author(s). Published by the Royal Society of Chemistrybe balanced depending on the aim of the application. We notethat the present study focused on the equilibrium response toO2, and response time was not evaluated due to theChem. Sci., 2026, 17, 5934–5943 | 5939Chemical Science Edge Articleunavailability of appropriate equipment. Overall, these studieselucidated, for the rst time, that phosphorescent solvent-freeliquids can be a promising platform for creating advancedoptical gas sensors with high dye-loading amounts, excellentsensitivity, linearity, and photostability.Finally, ratiometric optical O2 sensing was performed simplyby blending PtPL with an alkylated pyrene uorescent (O2-insensitive) liquid PyL 58 (Fig. 5a and S18). The emissionintensity of dye-loaded polymeric lms can be inuenced byvarious factors such as beam intensity, lm thickness, andhomogeneity of LOMs in the polymer matrix, and the accuratedetermination of I0 (i.e., emission intensity in the absence of O2)is indispensable for reliable quantication of O2.24,27,59 To avoidfrequent calibrations, ratiometric O2 detection based on phos-phorescent (O2 sensitive) and uorescent (O2 insensitive) dyes isa promising approach.60–62 In the present study, ratiometric O2sensing was achieved simply by blending two types of liquids.Since both PtPL and PyL are hydrophobic and have similarliquid physical properties due to the same 2-hexyldecylbranched alkyl chains, the two liquids are miscible with eachother,63 and the blended liquid contains absorption prolesfrom both individual components (Fig. 5a and b). Two lms (Aand B) with different loadings were prepared from the blendedliquid of PtPL+PyL (1 : 2, by weight) and investigated for ratio-metric O2 sensing (Fig. 5c). Upon excitation at 360 nm, theuorescence (lem = 428 nm) from PyL is insensitive to O2, whilethe phosphorescence from PtPL (lem = 656 nm) is sensitive toO2. Stern–Volmer plots of the two lms are highly linear (R2 >0.999), and the value of I0/I100 in lm A reaches ∼120 (compa-rable to that of PtTPP–PTMSP in Fig. 4d). A increase in O2sensitivity in the liquid blend system (compared with a neatliquid lm of PtPL) may originate from enhanced O2 solubilityand/or diffusion in the liquid upon blending with the relativelysmaller-sized molecule PyL. Stern–Volmer plots of lms A and Bare slightly different, presumably due to differences in theloading amount of liquid or experimental errors. Nevertheless,when ratios of phosphorescence and uorescence are plottedagainst O2 levels, lms A and B demonstrate almost identicallinear lines despite nearly double the difference in their emis-sion intensity. Thus, the miscibility of liquids offers reliableratiometric O2 sensing without the need for elaborate synthesis,ne-tuning of lm loading, and frequent calibrations.To conrm the enhanced sensitivity in the blended system,the sensitivity (I0/I100) of six independently prepared PtPL andPtPL+PyL lms was statistically analyzed (Tables S2 and S3). Asa result, the average sensitivity of PtPL+PyL (I0/I100 = 113.2, s =3.3) was reproducibly higher than that of PtPL (I0/I100 = 75.3, s= 1.8). The sensitivity of PtPL in Fig. 3d (I0/I100 z 90) is slightlyhigher than that shown in Table S2 (I0/I100 = 75.3 on average).This moderate difference can be attributed to cumulative decayof the emission intensity upon repeated exposure to excitationlight (see Fig. 4f). The data in Fig. 3 were obtained at multiple O2levels, with 100% O2 measured at the nal stage of the experi-ment, which likely led to a reduction in the I100 value comparedto its actual value. In contrast, the data in Table S2 were ob-tained from only twomeasurements, namely under N2 for I0 and5940 | Chem. Sci., 2026, 17, 5934–5943under O2 for I100. Therefore, the values reported in Table S2 areconsidered to be more reliable.ConclusionsThis work reveals numerous benets of luminescent core-isolated solvent-free liquids for optical gas sensing applica-tions. Due to the liquid characteristics (e.g., homogeneity, gassolubility, diffusion, andmiscibility) and the shielding effects ofthe phosphorescent-core units by the bulky yet exible alkylchains, the Pt(II) porphyrin liquid demonstrates exceptionalsensitivity, linearity, photostability, and calibration-free ratio-metric operations in phosphorescent O2 sensing. The conceptpresented in this study is broadly applicable to other functionalp-chromophores and gaseous species, paving the way for a newplatform for optical sensing materials.MethodsSynthesis of PtPLA previously reported liquid free-base porphyrin13 was used toprepare a liquid Pt(II) porphyrin (PtPL). Typically, the alkylatedfree-base porphyrin (140 mg, 0.055 mmol) and Pt(II)Cl2 (147 mg,0.55mmol) were reuxed in dry benzonitrile (15ml) under an Aratmosphere,51 and the progress of metalation was monitored bythin-layer chromatography (TLC) and variation in the Q-bandsin the UV-vis spectrum. Aer the reaction (ca. 4–5 h) wascompleted, the solvent was removed under reduced pressure,and the crude product was puried by column chromatographyon silica gel (eluent: 10–20% CH2Cl2 in n-hexane). Aer dryingunder vacuum at 40 °C, a red-orange liquid (PtPL) was obtained(yield: 80%). 1H NMR (400 MHz, CDCl3) in ppm: 8.86 (s, 8H,pyrrole b-H), 7.29 (d, J = 2.4 Hz, 8H, Ar–H), 6.86 (t, J = 2.0 Hz,4H, Ar–H), 3.96 (d, J = 5.6 Hz, 16H, OCH2), 1.83 (m, 8H, CH),1.35–1.23 (m, 192H, CH2), 0.82 (m, 48H, CH3).13C NMR (100MHz, CDCl3) in ppm: 158.68, 143.04, 140.62, 130.64, 122.18,113.44, 101.21, 71.27, 38.10, 31.89, 31.86, 31.42, 30.03, 29.71,29.59, 29.33, 26.87, 22.66, 14.11. HR-ESI-MS (m/z): calculated for[C172H285O8N4194Pt]+ = 2729.1639 m/z, found 2729.1736 m/z.Preparation of liquid lmsLiquid lms for O2 sensing were obtained by spin-coatinga toluene solution of liquid materials onto a quartz substrate.Typically, it took 5 seconds to reach 3000 rpm, and the lm wasdried at 3000 rpm for 60 seconds. Thus, homogeneous liquidlms were obtained. The loading amount of the liquid lm wasadjusted by changing the concentration of the toluene solutionor repeating the spin-coating process. A blended liquid lm ofPtPL+PyL was prepared from a solution of PtPL and PyL intoluene (1 : 2, by weight). Liquid lms were dried in air for morethan 12 h before spectroscopic measurements. See Fig. S20 fora discussion of residual solvent in a liquid lm.Preparation of polymer lmsStock solutions of PtPL in dichloromethane (5.00 mg ml−1) andPTMSP 49,64 in toluene (10.0 mg ml−1) were mixed at various© 2026 The Author(s). Published by the Royal Society of ChemistryEdge Article Chemical Scienceratios. The mixed solutions were spin-coated on a quartzsubstrate, as described above. In the case of PtTPP, a morediluted stock solution (1.67 mg ml−1) in dichloromethane wasused due to limited solubility. See Fig. S19 for a discussion onthe homogeneity of PtPL in polymer lms.O2 sensingThe porphyrin lm containing quartz substrate was placed ina quartz cell (1 cm × 1 cm), as illustrated in Fig. S1. The quartzcell was capped with a rubber septum, and then dry N2 or Arcontaining various concentrations of O2 was owed through thecell using inlet and outlet needles to measure emission spectra(FP-8300 spectrophotometer, JASCO) under controlled O2 levels.The typical ow rate was 100 ml min−1, and 5 min ow wassufficient to replace the interior gases of the small cell (∼3 ml).The ow rate was adjusted andmonitored using a oat-ball-typeow meter (KOFLOCK) and a digital ow meter (7000 ow-meter, Ellutia). Dry N2 and O2 from laboratory lines were used as0% and 100% O2, respectively. Ambient air supplied bya battery-powered pump (GSP-400FT, GASTEC) was regarded as21% O2. For 0.1%, 1%, and 10% O2, standard gases suppliedfrom high-pressure gas cylinders were directly used. For 50%and 80% O2, dry N2 and O2 from laboratory lines were mixed atappropriate ow rates (monitored by digital ow meters).Similarly, 0.1% O2 with dry N2 dilution yielded 0.03% O2.Author contributionsA. G. and T. M. synthesized porphyrins. A. G., S. I., and T. M.performed sensing experiments. M. K. C. and D. T. P. conductedmaterial characterization. A. S. measured transient emissionproperties. T. H. provided PTMSP and discussed the results ofO2 sensing. S. I. wrote the manuscript with input from all otherauthors. All authors read and approved the nal version of themanuscript. S. I. and T. N. designed and directed the research.Conflicts of interestThe authors declare no conicts of interest.Note added after first publicationThis version replaces the manuscript published on 22ndJanuary 2026 which contained an error in the caption forFig. 4d. PtPL should have been PtTPP–PTMSP. The RSC apolo-gises for any confusion.Data availabilityThe data presented in this study are available upon reasonablerequest from the corresponding authors. Supplementary infor-mation (SI) is available for materials, methods, characteriza-tions, photophysical and statistical analyses, andmiscellaneousdata. 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