Polymer matrix drives thermal stimulation-caused dynamic phosphorescence in dispersed chromophores

Domain: physics
Published: 2026-02-19
Editorial outcome: major_revision

Abstract
Polymer matrix has been extensively explored for decades to achieve efficient room-temperature phosphorescence from dispersed chromophores. However, the impact of the polymer matrix on the optical characteristics of chromophores remains elusive. Herein, we report that different asymmetric environments of polymer matrix delicately regulate the thermally stimulated phosphorescence property (estimated maximum total Φ : 92% at 298 K) of the molecularly dispersed chromophores. It essentially controls the degree of exo- and endothermic transition of excited states with the same and different multiplicity. The excited-state calculations demonstrate a significant influence of matrix environment on the dynamic phosphorescence property. Furthermore, we have investigated the impact of matrix-assisted conformers on dynamic phosphorescence for BANHPh and BANMePh in contrast to the completely locked geometry of BANH2. These matrix-induced, tunable phosphorescent emitters have been found to be highly competent in applications such as information encryption and afterglow display.

Introduction
Controlling the nature of dynamic phosphorescence demands precise dependent dynamic phosphorescence features resulting from the regulation of triplet excited state stability. The triplet-state involved strategic structural design of chromophores molecularly dispersed in a afterglow has been utilized for several advanced applications such as matrix environment. Despite having a rigid matrix environment, bioimaging, sensing, organic light-emitting diodes, lasers, and most emitters suffer from a reduced RTP quantum yield relative to anticounterfeiting. The organic room temperature phosphores- cryogenic conditions due to the thermal instability of long-lived triplet cence (RTP) emitter efficiency has been shown to improve by intro- excitons at room temperature. The best way to efficiently improve ducing sp2-boron localized (σ, Bp)→(π, Bp) transition, aromatic the RTP quantum yield is through the thermally stimulated delayed carbonyl group and halogen substitution, tailoring resonance phosphorescence (TSDP) mechanism. The radiative decay from a linkage, and through-space charge-transfer (TSCT) motif to facil- high-lying triplet state, populated by spin-allowed up-conversion (UC) itate the intersystem crossing (ISC) process from the lowest excited from an energetically close low-lying triplet state under thermal sti- singlet state (S1) to the triplet state (Tn; n≥1). On the other hand, mulation, results in the TSDP phenomenon. This process resembles encapsulation of ISC-efficient organic chromophores in rigid polymer thermal harvesting of excitons in classic thermally activated delayed matrices has garnered considerable research interest in an effort to fluorescence (TADF) emitters. Similarly, two closely lying triplet improve the stability of triplet excitons following the ISC process. excited states for the TSDP emitter establish a thermal equilibrium of Several reports on dopant-matrix systems demonstrated stimuli- population at room temperature through spin-allowed up-conversion (UC) and down-conversion (DC) processes. This non-adiabatic process recycles excitons for phosphorescence instead of non-radiative relaxation to the S0 state. The temperature-dependent relative population of two closely lying triplet excited states can exhibit an interesting phenomenon of tunable dynamic phosphorescence, distinct from other reported instances of dynamic phosphorescence. Yam and co-workers demonstrated the TSDP mechanism of the Au(III) complexes by varying the nature of the pincer and auxiliary ligands to create two close-lying triplet excited states. Wang et al. reported thermally stimulated dynamic phosphorescence in the crystalline state due to different molecular conformation in dimeric and trimeric states. Li et al. concluded that a thermal up-conversion caused dynamic phosphorescence of benzophenone-containing difluoroboron β-diketonate derivatives embedded in phenyl benzoate matrix due to anti-Kasha radiative decay of Tn (n≥2) states. However, the intriguing chemistry of dynamic phosphorescence, induced by a thermal stimulation effect, in a molecularly dispersed system within a matrix environment, has remained unexplored and unclear. Our group has been actively involved in developing organic RTP systems derived from the molecular dispersion of chromophores in Poly(methyl methacrylate) (PMMA) matrix. As part of the ongoing program, we set out to investigate the impact of the asymmetric environment created by the PMMA matrix on analyzing the credible origin of thermal stimulation-caused dynamic phosphorescence properties in purely organic and economically efficient molecularly dispersed systems.

In this work, we have selected metal-free borylaniline derivatives, comprising the amine donor and -BMes acceptor, as model compounds. Accordingly, BANH2 with efficient donor-acceptor property has been rationally designed with a locked geometry to suppress unwanted molecular motions. Moreover, BANHPh and BANMePh have also been analyzed to verify the influence of conformational change on the dynamic phosphorescence property. These chromophores are strategically allowed for conformational freedom only to the N-C(xylyl) group with locked geometry around the boron center (Fig. 1a). The temperature-dependent PL experiment indicates an excellent TSDP feature of PMMA matrix emitters due to the optimal energy gap of close-lying triplet states (ΔETT: 130 meV‒230 meV) of dispersed chromophores. The side-chain ester and α-methyl group-containing PMMA has been found to be a suitable matrix for the dispersed chromophores to efficiently utilize the up-converted excitons under thermal stimulation (Fig. 1a‒b). Further, control photophysical studies in poly(butyl methacrylate) (PBMA) matrix and polystyrene (PS) validate the matrix influence on thermally stimulated PL features. Thereafter, a theoretical investigation further reveals the importance of the matrix environment on the dynamic phosphorescence of the isolated chromophores, relative to calculations in the gaseous phase. In addition, we observe an intriguing finding where the matrix environment could lift the degeneracy of the conformers in the T1 state by providing an asymmetric environment, which is not likely to occur in the absence of matrix surroundings. These emitters are successfully explored for anticounterfeiting applications and promising afterglow materials.

Results
Moleculardesignandcharacterization
Thechromophoresweredesignedbymodifyingthesubstituentatthe nitrogen center of 4-(dimesitylboraneyl)−3,5-dimethylaniline (BANH2), while maintaining the core structure intact. A secondary aminederivative(BANHPh)wasdesignedtoenablethefeasibilityof non-degenerate conformers under external stimuli. The methylated derivative (BANMePh) was synthesized to investigate the photo- physicsofthesystemintheabsenceoftheH-bondingchannelpre- sentinthesecondaryaminederivative.Theunsubstitutedderivative (BANH2) was explored to examine the photophysical properties withouttheinterferenceofnon-degenerateconformationalisomers. Thepresenceofmesitylandxylylgroupscanprovidekineticprotec- tiontotheelectron-deficientboroncenter(Fig.1).Thecompound4- (dimesitylboraneyl)−3,5-dimethylanilinewassynthesizedfollowinga literature-reported procedure elsewhere. The detailed synthesis techniquesweredescribedinsupplementaryinformation.Thecom- poundswerecharacterizedby1H,13C,and11Bnuclearmagneticreso- nance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS) techniques. The purity of the compounds was confirmed by high-performance liquid chromato- graphy (HPLC) technique. The molecular structuresofthecompoundswerefurtherconfirmedbysinglecrystal X-ray diffraction (SC‒XRD) technique. Thepristinecompoundswerecharacterizedbypowder X-raydiffraction(PXRD)study,Thermogravimetricanalysis(TGA),and differentialscanningcalorimetry(DSC)study.

Single-crystalXRDanalysis
Theimpactoftemperatureonthemolecularstructurewasinvestigated throughSCXRDdatafrom100Kto300K. Themajorpackinginteractionsofthemolecularstructureswerefound tobestaticCH‒πorNH‒πinteractionsacrossalltemperatures,asdis- cussed in Supplementary Discussion 1. Molecules BANHPh and BAN- MePhshowedoneandtwoindependentmoleculesintheasymmetric unit,respectively.Thedihedralanglesbetweenthemeanplaneofthe xylyl carbon atoms and the mean plane of the phenyl carbon atoms remained constant with respect to temperature. In fact, the smalldifferenceofdihedralanglefrom100Kto300Kwereeitherin experimentalerrororduetodifferenceincrystalpackingenvironment.SimilarresultswerefoundforBANH2.Therefore,thetemperature-dependentvariationof thedihedralangleandpackinginteractionsofthemolecularstructures inthecrystallatticeappearstobeinsignificant.

OptoelectronicinvestigationinPMMAmatrix
ToanalyzetheinfluenceofthePMMAmatrixonmolecularproperties, photophysicswasinvestigatedforencapsulatedchromophoresinthe PMMAmatrix.Theabsorptionspectraofthecompoundswererecor- ded in a matrix environment at low weight concentrations under ambientconditionstoobtaintheground-statecharacteristicsofthe molecularly dispersed chromophores, without interference from intermolecular interactions. The higher energy absorption band (<350nm)ofchromophoresinPMMAmatrixoriginatedbecauseofπ‒ π*/n‒π* transitions and the low energy band (>350nm) presented aminetoborylintramolecularchargetransfer(ICT)transition.Thiswascorroboratedfromthesolvent dielectric dependent absorption study (compound conc. 10μM).
Thesteady-statephotoluminescence(PL)spectrumofthecom- pounds at 0.1wt.% concentration showed a structureless broad emission band in the range of 390nm to 550nm with associated transientlifetimeof5‒9ns.Thestrongsusceptibilityofthesteady-statePLbandtosolvent polarityexplainstheICTcharacteristicsoftheband. The PL study at 298K in a non-polar toluenesolutionshowedabroademissionbandat455nm. The time-gated measurements displayed the absence of delayed emissioninthesolutionstate,evenunderargon-purgedconditions. Thiscanbeduetothethermallyinducedvibrationalrelaxationofthe long-livedexcitedstateat298K.However,thePLmeasurementat77K showedavibrationallyresolvedred-shiftedphosphorescencebandat ~480nminfrozentoluenemedium.Thephosphorescentnatureofthe bands was validated by time-gated emission measurement (50 μs delay). In contrasttothesolutionstate,the rigidpolymer(PMMA)matrixeliminatesthepossibilityofvibrational- relaxation-causedquenchingoflong-livedexcitedstatesevenatroom temperatureunderdeaeratedconditions.Theemissioncharacteristics oftheemittersinthematrixwererecordedunderoxygen-freecon- ditionstoexplorethetripletexcited-statedynamicsinvolvedinthe emission bands. Time-gated PL measurement of 0.1wt.% BANHPh@PMMA (50μs delay) atroom temperature showed broad emissionbandat~442nmwithfeeblevibrationalfeatures.The delayedemissionband(λ=442nm)was~32meVlowerinenergythan thefluorescenceband(λ=437nm,steady-stateemissionbandinair).Suchsmallenergyshiftofdelayedemissioncould bepossibleforthermallyactivateddelayedfluorescence(TADF)phe- nomenon when nuclear configuration of short-lived (microsecond range)delayedcomponentofsingletexcitedstatecouldbeaffectedby tripletexcitedstateafterISCprocess.Incontrast,thelongerlifetime of the delayed emission band, on the millisecond timescale of the presentwork,rulesoutthepossibilityofsolelytheTADFphenomenon in the delayed emission. Furthermore, the intensity-dependent delayed emission study revealed a linear relationship between the delayed emission intensity and the excitation power source. This observation is not consistent with the possibility of triplet-fusion induceddelayedfluorescencecontributiontothedelayedemissionof the emitter. Notably, the steady-state emissionband(FWHM=60nm)undervacuumconditionswasfound tobemorebroadenedandslightlyred-shiftedcomparedtotheemis- sion band (FWHM=57nm) in the presence of oxygen.
Thisoxygen-sensitivespectralbehaviorofPLemissionbandinfers theassociationofthetripletexcitedstatecloselylyingtothesinglet excited state in the emission process. This is consistent with the excited-state absorption features in femtosecond and nanosecond transient absorption studies. Thetotalpho- toluminescence quantum yield (ΦPL) was found to be 81% under vacuum conditions (from 60 % fluorescence quantum yield in air). Moreover,thetime-resolveddecaykineticsexhibitedtri-exponential slowemissiondecay(λ445nm, 298K:τA1=7ms,τA2=35ms,τA3=136ms) for the delayed emission maxima. This indicates the existence of multiple emissive states for the emission processatroomtemperature.Furthertemperature-dependentemis- sionpropertieswererecordedtogaindeeperinsightsintothedelayed emissionband.
The temperature-dependent photophysical property investigation of 0.1wt.% BANHPh@PMMA revealed a bathochromic spectral shift(ΔE=230meV)ofdelayedemissionbandfrom442nmat298Kto 480nmat77K.Thesteady-stateemissionspectrumat77K alsoreflectedanadditionallowerenergybandwhichwasnotpromi- nentat298K.Thedelayedemissionbandat 77K of the emitter was found to exhibit long bi-exponential decay (λ480nm, 77K:τA1=630ms,τA2=1120ms). The prolongedlifetimeand43nmbathochromicshiftcomparedtofluor- escence emission peak maxima clearly infer the phosphorescence nature of the delayed emission band. Moreover, the phos- phorescencebandat77KinPMMAmatrixcloselyresembledthelow- lyingphosphorescencebandat77Kinfrozentoluenemedium.Thisindicatesthatthephosphorescence band observed at 77K originates due to isolated chromophores in dispersed state of PMMA matrix. A comparison of lower-energy phosphorescence (LEP) and higher-energy delayed emission(HEDE) spectrainfersthattheHEDEbandcomprisestheemissionfromboth higher-energyandlower-energyexcitedstates.However,thereisan insignificant contribution of the HEDE band (λ=445nm) in the LEP spectrumatlowtemperature(77K).TheHEDEbandaroseprogres- sivelyunderthermalstimulationaboveatemperatureregimewitha concomitant decrease in intensity of the LEP band. Additionally,theenergyshiftobservedinexcitationspectralbandpositions for 442nm and 480nm emission further corroborates the involve- mentofdifferentemissivestates. Time-resolved decay kinetics exhibited a gradual decrease in lifetimefortheemissionbandswithrisingtemperature.Thetailfittingofthephosphorescencelife- time decay profile (for both HEDE and LEP bands) revealed a temperature-dependentchangeinthecontributionofemissivestates. TheoriginoftheLEPbandcanbeattributed to the radiative decay of the lowest triplet excited state (T1). The complexbi-exponentialdecaykineticsforLEP(λmax)observedatlower temperature range might stem from the contribution of distinct emissivestate(s)(Tn),whichareactiveatlowertemperaturesinaddi- tion to the T1 state. However, the tri-exponential fitting and the observed relative variation of the three components in the higher temperatureregimesuggesttheinvolvementoftwodifferent,higher- energyemissivestates(otherthantheTnstate)inadditiontotheT1 state. SimilardecaykineticswerealsofoundfortheHEDE(λmax)ina highertemperatureregimewithalternativeamplitudepercentagesfor thethreecomponents.Specifically,thetri-exponentialdecaykinetics ofthedelayedemissionmaximashowedanincreaseinamplitudefor twocomponents,whiletheamplitudefortheslowestemissivecom- ponentdecreasedwiththeriseintemperature.Theslowest emissive component is due to the conventional phosphorescence processoriginatingfromtheT1state.Theothertwodelayedcompo- nents showed augmented contribution under thermal stimulation. Considering the spectral characteristics of the transient absorption studies and oxygen-sensitive steady-state emission nature (vide supra),itcanbeinferredthatthethermalstimulation-causedslower delayedcomponentstemsfromthehigh-lyingtripletstate(TH)and displayedphosphorescencethroughtheTSDPmechanism.Ontheotherhand,therelativelyfast decaycomponentcanbeattributedtoamodestcontributionofTADF by considering the overlap of fluorescence and delayed emission bands. Hence, the HEDE band originates from a higher energy phosphorescence(HEP)event,inadditiontoasmallcontributionfrom theTADFprocess.Therewasasmallchangeintherelativesteady-state PL integral with temperature, resulting in efficient PLQY at 298K (ΦPL 77K=91% and ΦPL 298K=81%). Furthermore, the excited state kinetics of HEDE band were analyzedbytime-resolveddelayedemissionspectra(TRDES)(50μs delay)at298K.Thegradualblue-shiftingof area-normalized TRDES exhibited evolution of high-lying emissive stateonamillisecondtimescale.
Toelucidatethegoverningparametersforthermalstimulation- derived shifting of delayed emission, photophysical studies were conductedforBANMePhandBANH2at0.1wt.%concentrationinthe PMMAmatrix.The presenceofahigher energytripletstatewassupportedbythetran- sient absorption studies, oxygen-sensitive steady-state spectra and intensity-dependent delayed emission experiments. Temperature-dependent steady-state and time-gated emission spectraoftheBANMePh and BANH2 emitters resembled the spectral behavior of the first emitter. The time-gated mea- surements of BANMePh showed a thermally promoted HEDE band intensity,accompaniedbya210meVshiftintheenergyofthedelayed emission band, when the temperature was changed from 77K (λ=485nm)to298K(λ=447nm).Thesimilarphotophysicalbehavior ofthemethylderivativecomparedtothesecondaryaminederivative suggeststhatnon-covalentinteractionsdonotplayadominantrolein the thermally stimulated delayed emission (TSDE) behavior of the secondary amine derivative. On the other hand, the absence of a nitrogen-coordinatedphenylgroupinBANH2resultedinarelatively smaller energetic transition (ΔE=130meV) of the delayed emission band,from470nm(at77K)to447nm(at298K),withathermalsti- mulationeffectontheHEDEband.TheLEPband,unliketheothertwo emitters,exhibitedasignificantemissioncontributionfromtheexci- statedesponsiblefortheHEDEbandevenatalowertemperature regime.Undervacuumconditions,BANMePhachievedanimpressive photoluminescencequantumyield(ΦPL)of92%,whileBANH2showed arobust77%at298K.Theunusual variation of steady-state PL integral (ΦPL 77K=82% and ΦPL 298K=92%forBANMePh;ΦPL 77K=76%andΦPL 298K=77%forBANH2) resulted in efficient PLQY at 298K, similar to the BANHPh emitter. Temperature-dependent lifetime measurements exhibited a com- parativelyshorterlifetimeoftheBANH2emitterthantheothertwo emitters with similardecaykinetics.TheTRDESstudyforBANMePhandBANH2(at298K) yieldsnearlyidenticalspectralbehaviortothatofBANHPh.

Inter-molecularinteractionseffectondynamic phosphorescence
The influence of intermolecular interactions on phosphorescence behaviorwasinvestigatedbyvaryingthechromophoreconcentration from 0.1wt.% to 10wt.% in the PMMA matrix. Upon increasing the chromophore concentration, a red shift was observed in both the steady-stateandtime-gatedemissionbands.However, red-shifted bands did not exhibit any vibrational pro- gression or new emission bands. The lifetime decay profile of the delayed emission maxima showed a gradual decrease of lifetime at higher wt.% concentration. Further, temperature-dependent studies for 10wt.% chromophore concentra- tionwascarriedouttoverifytheaggregationeffectonemissivestate.Time-gatedemissionmea- surementsofthechromophoresata10wt.%concentrationinthePMMA matrix exhibited a similar thermally stimulated HEDE band, with a comparativelynarrowerenergyshiftwithincreasingtemperature,rela- tivetothe0.1wt.%emitter.Thehighdis- persion concentration in the matrix resulted in a shorter lifetime for both LEP and HEDE bands, as well as diminished delayed emission quantumyield(ΦPL=68%;82%;77%).Thiscanbe (BANHPh;BANMePh;BANH2) attributed to the diffusion of excitons towards several non-radiative deactivation channels, which reduce the lifetime and quantum yield value. Although the growth in the intermolecular interactions of chromophoresmodulatestheelectronicenergylevelofthehigherwt.% emitter,ithasaninsignificantimpactofaggregation-originatedexcited stateemissiononthespectralbehaviorinresponsetothermalagitation. Thisstudyeliminatesthefeasibilityofmonomericandaggregatedstate emissionofchromophoresinthematrixforthetemperature-dependent dynamicsofphosphorescencebands.
The photophysical studies in the crystalline state were sub- stantiallydifferentfromthediscretemolecularpropertiesof0.1wt.% chromophore in the matrix. Crystalline solids of these compounds showedred-shiftedsteady-state(λPL:445–462nm)anddelayedemis- sionbands(λPH:500–525nm)withmuchshorterlifetimerelativeto their molecular properties in matrix environment. Time- gated emission spectra of crystals were a combination of delayed fluorescence(DF)and a lower energyphosphorescence (LEP) band, which showed a decrease in intensity with increasing temperature. Therewasnodetectablethermallystimulatedhigherenergydelayed emissionbandatelevatedtemperatures.ThereductioninrelativePLintegralathigher temperatureregimefurthersupportestheanticipation.Hence,thephoto-physicsof chromophores in a matrix environment and in the crystalline state clearly dictate the differential influence of the matrix environment relativetothestrongpackingeffectofthecrystalonthephosphor- escenceproperty.

Matriximpactondynamicphosphorescence
Further optical studies were carried out in both poly (butyl metha- crylate) (PBMA) and polystyrene (PS) matrices to investigate the matrix-dependentexcitedstatebehavioroftheseemitters.ThePBMA matrixpossessedasimilarelectronic naturetoPMMA,whileprovidingadistinctstericenvironmentforthe dispersedchromophore.Temperature-dependentsteady-statePLand phosphorescence behavior were found to be different inthe PBMA matrixenvironment.ThechromophoresinthePBMAmatrix exhibitednearlyidenticalenergyshiftsofthedelayedemissionbandas thePMMAmatrix,withvaryingtemperatures;however,theHEDEband showedareductioninintensityathighertemperatures.BANH2dis- playedbetterthermalstimulationeffectontheHEDEbandcompared to BANHPh and BANMePh. Thelifetimedecayprofileoftheemittersshoweda shorterlifetimeinthePBMAmatrixthaninthePMMAmatrix. Thenon-polarenvironmentofthePSmatrixresultedindifferent excited-statebehaviorofdispersedchromophoresunderthermalsti- mulation.Thedelayedemissionbandofthe chromo- phoresinthePSmatrixwasfoundtoshiftatahigherenergyregion comparedtothecorrespondingPMMAmatrixemitter.Thisresultedin a larger energy gap (ΔE=310meV, 300meV, and 220meV for BANHPh,BANMePh,andBANH2,respectively)betweentheLEPand HEDEbandsrelativetoothermatrices.However,PSmatrixemitters showed a moderate thermally stimulated effect on HEDE band and fasterdecaykineticsathighertemperatures,whencomparedwiththe PMMAmatrixemitters.Furthermore,therelativePLintegralobserved indifferentmatricesinthehighertemperatureregimeelucidatesthe differential impact of thermal stimulation on photoluminescence property. It wouldbeworthmen- tioningthatchromophoresdispersedinPMMAmatrixdisplayedthe mostconsistentthermalstabilityofhigherenergyemissivestatesin termsofPLintegralandlifetimeincomparisontoothermatrices.

Originofdynamicphosphorescence
We performedquantumchemicalcalculationstoelucidatetheelec- tronicoriginsofdynamicphosphorescenceandtestedtwohypotheses forthisphenomenon:(a)phosphorescencearisingfromlow-lyingtri- plet states (i.e., T2→S0, T1→S0) and (b) the role of possible room- temperature accessible conformers in the T1 state. Accordingly, we investigatedtheimpactofthePMMA,PBMA,andPSmatricesonthe electronicpropertiesofthesecompounds. For BANHPh@PMMA, we found the T1 state (2.98eV) lower in energy than the S1 state (3.28eV), while only the T2 state (3.39eV) wasrelativelycloselyingtotheS1 stateamonghigherenergy triplet excited states. We observed similartrendsforBANMePh@PMMAandBANH2@PMMA, wheretheT1 stateandT2 statewereenergeticallyclosetotheS1 state.However, BANH2@PMMA exhibited a relatively smaller T–T energy gap (0.30eV) than BANHPh@PMMA (0.41eV) and BANMePh@PMMA (0.44eV). Interestingly, BANH2@PMMA showed higher spin-orbit couplings(SOC)forS0–T2(0.75cm⁻¹)thanS0–T1(0.34cm⁻¹)unlike theothertwosystems[S0–T2(0.80cm⁻¹)andS0–T1(0.22cm⁻¹)for BANHPh@PMMA]. This observation suggests that the T2 state may playamoresignificantrolealongsidetheT1 stateinthephosphores- cenceprocessforBANH2@PMMAcomparedtotheothertwosystems. ForBANHPh,thesingletandtripletexcitedstatesexhibitedchanges inenergylevelsacrossdifferentmatrixenvironments. TheorbitalcontributionofS1 andclose-lyingtripletstateswas foundtobemodifiedbychangingthematrixenvironment. TheT–T energygapexhibitedaclearmatrix dependence,withthelargestgapobservedinPBMA,followedbyPS,and thesmallestinPMMA.Moreover,thespin-orbitcouplings(SOC)forS0–T1 (SOCPMMA=0.083cm−1, SOCPBMA=0.419cm−1, SOCPS=0.214cm−1) and S0–T2 (SOCPMMA=0.897cm−1, SOCPBMA=1.423cm−1, SOCPS=1.191cm−1) revealed an obvious variation in value with changing matrix. Similar observation was found for BANMePh and BANH2molecules. WefurthertestedtheexistenceofT1 conformersandtheirinflu- ence on phosphorescence behavior. Accordingly, we performed relaxedpotentialenergysurface(PES)calculations(usingGFN2-xTB) for both the S0 and T1 states, both in thegasphaseand within the polymermatrices,bychangingthedihedralanglebetweenthexylyl and phenyl group. For the T1 state of BANHPh and BANMePh, we identified five nearly isoenergeticconformers(all within 0–0.5kcal/ mol)inthegasphase,withthepotentialenergysurface(PES)minimum showingadihedralangleof155°and140°respectively.Inter- esting, upon embedding in the PMMA matrix, we found that the degeneracyoftheconformerswaslifted,withtheminimumstructure displaying a dihedralangle of320° and 325° for BANHPh and BAN- MePhrespectively.TheotherminimumfoundalongthePESwaswithin the thermally accessible energy range, and thesewereenergetically closeinproximitytotheT2 stateofthecorrespondingmolecules.We observed similar degeneracylifting inthe S0 state PES scanfor the PMMAmatrixcomparedtothegasphase.Thedegeneracyliftingrelativetothegasphasewasalsoobservedinthe caseoftherelaxedscansperformedinthePBMAandPSmatricesfor both BANHPh and BANMePh. However, PBMA and PS showed different cross-over energies for conformersandalternativedihedralanglesforPESminimumrelative to the PMMA matrix owing to different molecule-matrix interfaces. ThepossibilityofthermallyaccessibleconformersattheT1 stateand S0 statecaninfluenceexcitationenergiesandcontroltheISCofthe singlet and triplet states, governing the dynamic phosphorescence characteristics.
SincetheBANH2moleculepossessastructurallyrigidstructure withnophenylgroup,unliketheothertwomolecules,theroleoftheT1 conformersinthedynamicphosphorescenceinthecaseofBANH2can beruledout.Therefore,thepossibleinvolvementofbothT2 andT1 canbeattributedtothedynamicphosphorescenceevent. The PMMA matrix emitters displayed nearly identical delayed emissionintensityandsteady-statePLintensityat298Krelativeto77K. This suggests a negligible influence of non-radiative deactivation of excitons to the ground state through higher temperature-promoted vibronic coupling between the triplet excited states and the ground state.Therefore,thegradualdecreaseindelayedemissionlifetimewith increasingtemperaturecanbeinterpretedasafasterinterconversion ratebetweenthecloselylyingexcitedstates.Interestingly, BANH2exhibitedadistinctphoto-physicsthantheothertwochromo- phores.TheBANH2revealedarelativelyhigherknr/kr value(>1)com- pared to the other two chromophores, even in the PMMA matrix (despitethetemperature-dependentPLintegralsuggestingalesslikely non-radiative pathway). This signifies a higher degree of intersystem crossing(ISC)betweenthesingletexcitedstate(S1)andtripletexcited state(s)andthiscanenhancetheknr oftheS1 stateinthecaseofBANH2. ThevariationinISCforBANHPhandBANMePhrelativetoBANH2indi- catesthatBANHPhandBANMePhpossessdifferentcharactersforthe tripletexcitedstate(s)involvedintheISCprocess.TRDESdatadidnot revealsignificantdifferencesinexcitedstatekineticsforBANH2relative to the other two chromophores. Hence, the differential ISC of BANHPh and BANMePh relative to BANH2 can be reasonedasacombinedeffectofvariableorbitalcontributiontoexcited statesinvolvedintheISCprocessandprobablepresenceofdifferentor additionaltripletstate(s). According to the computational results, BANHPh and BANMePh may generate additional thermally accessible triplet states due to temperature-dependentconformationalchangesattheT1 state.How- ever,itisunlikelyinthecaseofstructurallyrigidBANH2.Thecalculation and transient absorption studies corroborate the above mechanistic interpretation.Furthermore,thevariationintheexcitedstatelifetimeof chromophoreswithinthePMMAmatrixprovidessignificantinsights intothetransitionrateofexcitedstates.TheBANH2emitterdisplayeda comparativelyshorterlifetimethanBANHPhandBANMePhemittersin thePMMAmatrix.Thiscanbeattributedtothecombinedeffectsofthe fasterinternalconversionratebetweentripletexcitedstatesandfaster reverseintersystemcrossingrateforBANH2(videsupra)relativetothe other two chromophores (since non-radiative decay to S0 is least probable).
Thetemperature-dependentlifetimevaluefortheslowestdelay component(ofLEPband)exhibiteddistinctbehavioracrossvarious matrices above a temperature regime. ThePMMAmatrixemittersexhibitedasluggishrateoflifetime variation for the delayed component with increasing temperature (relativetoothermatrices).Incontrast,thelifetimeofPBMAandPS matrixemittersshowedasuddendecreaseinlifetimesforthedelayed component in the temperature range, indicating that the corre- spondingemissivestate(s)wereinvolvedwithadditionalnon-radiative de-excitation channels in comparison to PMMA matrix emitters. Moreover,thedrasticreductioninsteady-statePLintensityandthe declineindelayedemissionbandintensityat298K(relativeto77K) are compatible with the mostprominent non-radiative deactivation channelsinthecaseofPBMAmatrixemitters.
Thehighnon-radiativerateconstant(knr=20×107s−1forBANHPh) comparedtotheradiativerateconstant(kr=0.9×107s−1forBANHPh)for thefluorescenceprocessofPBMAemittersalsocorroboratesthephe- nomenon.Ontheotherhand,PS matrixemittersexhibitedanincreaseinintensityforthesteady-statePL butadecreaseinintensityfortheHEDEbandat298K(relativeto 77K).ThiscanbereasonedasanalternativecontributionofTADFand TSDP to the HEDE band for PS matrix emitters compared to PMMA matrixemitters.Inaddition,thedifferenceinexcitedstatelifetimefor BANH2emitterrelativetoBANHPhandBANMePhemittersislesssig- nificantinthecaseofPBMAandPSmatrixemittersrelativetoPMMA matrixemitters.This discrepancycanbeattributedtothepresenceofadditionalnon-radiative deactivationchannelsanddifferencesinexcited-statecommunication (IC and ISC) for the chromophores dispersed in the PBMA and PS matrices. Hence, the distinct polymeric environments are found to influencethekineticsoftheexcited-statepopulation,whichcanregulate thelifetimeandquantumyield.

Methods
Measurements
1H,13C{1H},and11BNMRspectrawererecordedat25°ConaBruker Advance 400MHz NMR Spectrometer operating at a frequency of 400MHzfor1H,100MHzfor13C,and128MHzfor11Busingdeuterated solvent(CDCl3).1HNMRand13CNMRspectrawerereferencedtothe residualsolventsignal,and11BNMRspectrawere referencedtothe standard boron signal of BF3·Et2O. High-resolution mass spectra (HRMS)wererecordedonaMicromassQ-ToFHigh-ResolutionMass Spectrometer by the electrospray ionization (ESI) method. Powder X-raydiffraction patterns of the pristine compounds and thin films were collected from a XD-D1 Shimadzu X-ray diffractometer. Ther- mogravimetricanalysis(TGA)wasperformedusingaTAInstruments Q50TGAthermogravimetricanalyzerataheatingrateof10°C/min underanargonatmosphere.ThedecompositiontemperatureforTGA curves was determined at a threshold of 10% weight loss. DSC was performedusingMETTLER-TOLEDOandTAinstrumentsataheating andcoolingrateof10°C/minunderanargonatmosphere.
The absorption measurements were performed at room tem- peratureusingaSHIMADZUUV-2600spectrophotometer.Thepho- toluminescence properties were measured using an Edinburgh InstrumentFLS980spectrometerequippedwithaxenonarclamp,a microsecondflashlamp,andapicosecondLASERsourcewithatime- correlated single photon counting (TCSPC) setup. The steady-state andtime-gatedemissionspectrawererecordedusingthexenonarc lampandapulsedmicrosecondFlashLamp(μF1,pulsewidthof1.1μs) as excitation sources, respectively. Time-gated emission spectra measurements can be performed through a time-gated circuit syn- chronizedtothephotomultipliertube(PMT)detector.Temperature- dependent measurements were performed using an Oxford Instru- mentsOPTISTATDN2cryostat,controlledbyanOxfordInstruments Mercury iTC temperature controller, which was connected to the FLS980spectrometer.Sampleswereallowedtoreachauniformtem- perature distribution before any measurements were conducted. Photophysicalstudiesofthinfilmsandcrystallinesolidswererecorded under vacuum conditions unless otherwise mentioned. The fluores- cencequantumyieldsofthesolutionsandthinfilmsweremeasured underambientconditionsusingacalibratedintegratingspherefrom HoribacombinedwiththeHoribaJOBINYVONFluoromax-4spectro- meter. Transient absorption measurements were discussed in thesupplementaryinformation.

Preparationofthinfilms
The chromophores, poly(methyl methacrylate) (PMMA), poly(butyl methacrylate)(PBMA),andpolystyrene(PS)weredissolvedinHPLC dichloromethane solvent to prepare the stock solutions. The stock solutions were mixed in a particular proportion to obtain different weightconcentrationsofthecompoundinthepolymersolution.The wt.%indicatestheweightpercentageofthecompoundrelativetothe totalweightcontentofthepolymer.Eachfilmwaspreparedbyspin- coatingthecompound/PMMAsolutiononaquartzsubstrateat25°C. ThinfilmswerecharacterizedbyPXRDstudy.

Computationalmethodology
All matrix-chromophore systems were constructed using Chem3D 20.1.1software.ThesystemsizesforBANHPh,BANMePh,andBANH2 consistedof651,654,and641atoms,respectively.ThePMMA,PBMA, andPSmatricesweremodelledaslinearpolymericchainsthatfully encapsulate the compound. All compounds were first optimized withinthepolymermatricesintheirS0 andT1 statesusingtheGFN2- xTBapproach,whichresolvedanygeometricclasheswithinthesys- tem.RelaxedpotentialenergyscansforboththeS0 andT1 stateswere conductedusingGFN2-xTBbyvaryingthedihedralanglebetweenthe xylylandphenylgroups.Theconformationalsamplingforcompounds (along the T1 state) was computed using the CREST program. A CREST conformationalsearch (in the gasphase, for both T1 and S0 states) was conducted on all compounds, revealing that both BANHPh@PMMA and BANMePh@PMMA possessed multiple con- formers with flexible dihedral angles between the xylyl and phenyl groups.TheCRESTconformationalsearchinthecaseofBANH2along theT1 statesuggestsmainlytwodistinctstructures;however,theirenergygap(13.4kcalmol−1–0.6eV)wasfound to be quite higher compared to the experimental energy gap (0.11–0.22eV)forthephosphorescencebands.Thus,aPESscanwas notconductedfortheBANH2molecule.
Vertical excitation energies were calculated using the second- order Algebraic Diagrammatic Construction (ADC(2)) Method, combinedwith the def2-TZVP all-atom basis set,viatheTurbomole 7.5 suite. The matrix effect on the excited state calculations was incorporated using point charges (derived from the Merz-Kollman Restrained Electrostatic Potential), where the contributions of the charges were explicitly included in the one-electron matrices and nuclearrepulsionterms.
WenotethatthegeometriesobtainedviaGFN2-xTBwerehighly consistentwiththosefromfulloptimizationattheB3LYP/def2-TZVP leveloftheory,withanRMSDof0.0358Å.Forbenchmarking,wealso compared the ADC(2) excitation energies for BANHPh geometries optimized using both GFN2-xTB and B3LYP/def2-TZVP, and found similarexcitedstateenergetics,stateordering,andorbitalcontribu- tionsinthecanonicalbasis.Thespin-orbitcoupling(SOC)matrixelements werecalculated usingtime-dependentdensityfunctionaltheory(TDDFT)attheB3LYP/ def2-TZVPlevel,withTDDFTcomputationsperformedusingtheORCA 5.2program.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors designed and synthesized three borylaniline derivatives, which were found to show dual persistent emissions in PMMA matrix. After experimental and theoretical and experimental studies, the authors ascribed this to the existence of two conformers within T1 state (T1H and T1L) with the assistance of PMMA matrix. The luminescent phenomena reported in this work are interesting, but the internal mechanism should be further clarified before its publication.\n1. In this work, the persistent emission (@450 nm) at room temperature seems to be from TADF, science it is almost overlapped with the steady-state PL spectra. In previous literatures, such as Sci. China Chem. 2023, 66, 1120 and Chem. Mater. 2024, 36, 3000, the similar phenomena have been reported.\n2. Compounds BANHPh and BANMePh with asymmetrical structure could present conformational isomerism, which might show dual phosphorescence emissions from two different conformers. However, BANH2 with symmetrical structure also showed dual persistent emissions, as shown in Supplementary Fig. 25. The authors should clarify this point.\n3. As shown in Figure 6h, several stable conformers were presented in the relaxed potential energy scans of T1 state. Then, could the emission peaks be calculated for these T1 conformers to compare with those in experimental results? How about the potential energy scans of T1 state for compound BANH2?\n4. The phosphorescence property of organic luminogens was easily affected by the impurity, thus the HPLC should be carried out to certify the purity of these target compounds.\n5. The steady-state PL spectra were almost overlapped with the delayed ones. Then, how the RTP quantum yields were measured in this work? The authors should make a clear presentation.", "reviewer_2": "Comments\nIn the current report, Thilagar and Co-workers presented the dual phosphorescence behaviour of the borylaniline derivatives in the PMMA matrix. The presented organic chromophores show dual delayed emission behaviour under deaerated conditions, which is interesting in the field of triplet photophysics. However, authors have explained that the dual delayed emission phenomenon arises from the matrix-assisted, room-temperature accessible conformers within the T1 state via a thermally stimulated delayed phosphorescence mechanism, which may not be accurate. Thus, the current version of the manuscript requires proper justification of fundamental photophysical analysis and an explanation of the mechanism involved with proper experimental support, which is missing. Many experimental data, especially dual delayed emission behaviour, need reinvestigation with appropriate care. Hence, the present work requires major revisions for publication in a high-quality journal like Nature Communications. Moreover, the authors should address all the points raised below.\n1. Change in the dihedral angle at 100 K and 300 K is relatively low (negligible changes) in the single crystal data. However, the authors have concluded that dual emission arises from matrix-assisted, room-temperature accessible conformers within the T1 state. The authors should reinvestigate the mechanism using proper experimental data. What is the photophysics of the molecules in the crystalline state? The authors should do a detailed investigation.\n2. The asymmetric environment in the PMMA matrix could be due to the aggregation propensity of the chromophores, and 1 wt% chromophore doping may not prevent the aggregation. The authors should perform a wt% dependent study from 0.1% to 10 % and should take their delayed spectra and compare them. It might happen that authors are seeing phosphorescence from the monomeric and aggregated state of the chromophores. Please see one of the examples: https://doi.org/10.1002/anie.202101538\n3. Authors should experimentally find the original triplet state of the presented chromophores in a dilute solution state at cryogenic temperature.\n4. 'The rigid polymer (PMMA) matrix eliminates the possibility of vibrational relaxation-caused quenching of excited state species. Time-gated PL measurement of 1 wt.% BANHPh@PMMA (50 μs delay time) at room temperature showed a structureless broad emission band at 450 nm (Fig. 2a).' what about the role of oxygen? The authors presented all the observations in the PMMA matrix under oxygen-free conditions (according to Figure S21). The authors should mention it clearly. Harnessing triplet exciton under ambient conditions is always more important than oxygen-free conditions. The authors should clarify and present the observations, which should be very clear to the readers.\n5. 'The delayed emission band (λ = 450 nm) was slightly lower in energy than the prompt emission band (λ = 445 nm), as depicted in Fig. 2a and 2h.' The shift could be due to the change in the excited state geometry of the chromophores due their CT nature in the excited state. Please see also the other example: https://doi.org/10.1038/nphoton.2012.31.\n6. Page 5, lines 195-196: 'Moreover, the strong oxygen sensitivity and faster decay of delayed emission at elevated temperatures featured the possibility of RTP rather than TADF (Fig. 2d and Supplementary Fig. 24, 26).' In my opinion, this statement is incorrect without adequate experimental support.\n7. Suppose I claim that the high energy emission band is a delayed fluorescence band either by thermal activation derived or triplet fusion-induced delayed fluorescence emission; what extra experimental support author will present that my claim is wrong (or right)?\n8. In SI line 582, 'Fluorescence quantum yield was determined with an integrating sphere under ambient conditions. The total photoluminescence quantum yield and phosphorescence quantum yield were obtained by following the previous literatures.' According to the SI figure S21, the authors do not have a triplet contribution to the total emission under ambient conditions; how did the authors calculate the total QY under vacuum? Please show all quantum yield measurement spectra (snapshot) under air and vacuum and the phosphorescence quantum yield measurement. Also, show a snapshot, justify how authors measured the quantum yield at 77 K, and adequately write instruments and methods in the SI.\n9. Please explain and show detailed temperature dependence for two bands of all the chromophores for all the temperatures from 77 K to 298 K, not only from 225 K to 298 K) because the conclusion drawn from the temperature-dependent lifetime decay profile is unsatisfactory.\n10. Page 3, line 111 'We observe an extraordinary finding': Please refrain from an objective like this.\n11. Authors should check 'photo physics' throughout the manuscript appropriately.\n12. Authors should cite more appropriate literature where the organic chromophores show dual delayed emission (either dual phosphorescence or delayed fluorescence and phosphorescence).", "reviewer_3": "Subhajit Ghosh et al. analyzed the dual phosphorescence behavior of three chromophores molecularly dispersed (1 wt.% concentration) in the PMMA matrix. They employed second-order Algebraic Diagrammatic Construction (ADC2) excited state calculations to show that the dual phosphorescence observed in BANHPh and BANMePh does not stem from the T1 and T2 electronic states. Instead, this phenomenon arises from matrix-assisted, room-temperature accessible conformers within the T1 state (T1Hand T1L). The PMMA matrix creates an asymmetric environment around the chromophores, inducing structural and electronic modulations that result in spectral tuning of the singlet and triplet manifolds. In conclusion, conformation-dependent dual phosphorescence is unlikely to occur without the PMMA matrix. The present results can be utilized for temperature sensing from the ratiometric phosphorescence afterglow colour change-over in a short energy range. In this sense, I suggest that this work can be accepted after addressing the following concerns.\n1.What is the behaviour of phosphorescence when the mass concentration is between 1wt.% and 10wt.%?\n2.Is the dual phosphorescence behaviour similar in other polymer matrices besides PMMA and PBMA?\n3.Please note the uniform format of the paper, like “ADC(2)” and “ADC2”, and “T1/T2-S1 andT1/T2-S0” on page 9.\n4.Some typical recently literatures about long-lifetime RTP should be cited, such as 10.1038/s41467-024-47378-2; 10.1038/s41467-023-43133-1; 10.1021/jacs.2c02076； 10.1002/adma.202416397；10.1002/ange.202411323, et al.\n5.Please note the normality of the figures, like Fig. 1c."}, "author_response": "Reponses to Reviewer #1\nIn this manuscript, the authors designed and synthesized three borylaniline derivatives, which were found to show dual persistent emissions in PMMA matrix. After experimental and theoretical studies, the authors ascribed this to the existence of two conformers within T1 state (T1H and T1L) with the assistance of PMMA matrix. The luminescent phenomena reported in this work are interesting, but the internal mechanism should be further clarified before its publication.\nResponse: We thank the reviewer for the appreciating our effort on the work. We have re-investigated the photophysical behaviour of the chromophores at 0.1 wt.% concentration in three different matrices (PMMA, PBMA, and PS) with variable electronic and steric environment to understand the internal mechanism of the dynamic dual phosphorescence. Please see the text in page 14-16 of manuscript for detailed mechanistic insights.\nNB:\n• We have opted to change the phrase ‘dual phosphorescence’ to ‘dynamic phosphorescence’ by considering the presence of multiple triplet excited state for the temperature-dependent studies.\n• The thermally stimulated delayed emission phenomenon has also been highlighted in the manuscript since matrix plays an important role to control the thermal stimulation effect on delayed emission band. The title of the current work has been modified from “Polymer Matrix Drives Dual Phosphorescence in Dispersed Chromophores” to “Polymer Matrix Drives Thermal Stimulation-Caused Dynamic Phosphorescence in Dispersed Chromophores” to highlight the matrix-driven thermal stimulation effect on the dynamic delayed emission property.\nComment 1: In this work, the persistent emission (@450 nm) at room temperature seems to be from TADF, science it is almost overlapped with the steady-state PL spectra. In previous literatures, such as Sci. China Chem. 2023, 66, 1120 and Chem. Mater. 2024, 36, 3000, the similar phenomena have been reported.\nResponse: We thank the reviewer for the comment and sharing the related references. According to reviewer’s suggestion we have re-investigated the emission process.\n(a) The steady-state emission spectra and delayed emission spectra are almost overlapping. However, the distinct spectral nature of the prompt and delayed emission bands—specifically, the delayed emission's feeble vibrational feature (lower energy end) which is absent in the fluorescence band (recorded in presence of O2) infers different nature of the delayed emission band (Fig. 3b and Supplementary Figs. 23).\n(b) We have recorded the steady-state emission spectra under vacuum and in presence of O2 to distinguish the nature of the delayed emission (TADF or RTP), although it is difficult to realize the presence of triple excited state closely lying to S1 state. The steady-state emission band under vacuum condition is combination of fluorescence band and delayed emission band. On the other hand, delayed emission band is quenching in presence of oxygen and therefore, steady-state emission band exhibited an attenuated spectral area in presence of O2. Interestingly, normalization of spectra exhibited that there is a small blue-shift in spectral maxima for the steady-state emission band in presence of O2 with reduced fwhm value relative to spectrum under vacuum (Supplementary Figs. 45-47). This clearly indicates the presence of triplet excited state energetically close to singlet excited state and negates the possibility of solely TADF phenomenon for delayed emission band.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\n(c) We have also re-examined the tail-fitting of lifetime decay profile for the delayed emission maxima. The lifetime decay is found to exhibit a tri-exponential decay kinetics without compromising the shorter time range during fitting. For bi-exponential fitting, the shorter time range typically needs to be excluded (previous version of manuscript); however, this would not be suitable for this phenomenon. The O2-sensitive spectra behaviour and temperature dependent variation of amplitude percentage of three delayed component concludes that the delayed emission band at 298 K is a combination of higher energy phosphorescence (HEP) band, lower energy phosphorescence (LEP) band and a modest contribution of thermally activated delayed fluorescence (TADF) considering the spectral overlap of prompt and delayed emission band. Please see the text in page 5-7 of manuscript and Supplementary Tables 11-13, 15-17, 19-21 for detailed information.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\nAddition: We have included the normalized steady-state spectra of the emitters measured under vacuum condition and in presence of oxygen. The snapshots of the lifetime decay profile are provided showing tri-exponential, bi-exponential and mono-exponential fitting of decay (Supplementary Figs. 45-47).\nComment 2: Compounds BANHPh and BANMePh with asymmetrical structure could present conformational isomerism, which might show dual phosphorescence emissions from two different conformers. However, BANH2 with symmetrical structure also showed dual persistent emissions, as shown in Supplementary Fig. 25. The authors should clarify this point.\nResponse: We thank the reviewer for the comment. We have justified the dynamic dual phosphorescence for the emitters based on experimental support in addition to theoretical calculations as following.\nWe would also like to point out that our wavefunction-based ADC(2) calculations reveal a slightly higher T2–T1 gap in BANHPh@PMMA and BANMePh@PMMA compared to BANH2@PMMA, supporting the argument that the T2 state might be involved in the dual phosphorescence observed in BANH2 (see Fig. 4). Furthermore, unlike BANHPh and BANMePh, BANH2 exhibits a T2 state that lies below the S2 state and displays a significantly higher spin–orbit coupling (SOC) between T2–S2 than between T2–S2. These findings strongly suggest the involvement of the T2 state in the dual phosphorescence mechanism of BANH2.\n“BANH2 demonstrates relatively higher k nr / k r value (>1) compared to other two chromophores even in PMMA matrix (despite the temperature dependent PL integral suggesting a less likely non-radiative pathway). This signifies a higher degree of intersystem crossing (ISC) between singlet excited state (S1) and triplet excited states for BANH2. The variation of ISC for BANHPh and BANMePh relative to BANH2 indicated that BANHPh and BANMePh possessed different character for the triplet excited state(s) involved in ISC process to singlet excited state. Moreover, the temperature-dependent behaviour of the HEDE band in the delayed emission spectra of BANHPh and BANMePh in PBMA matrix differs significantly from that of BANH2, providing further support for the anticipation (Fig. 3c, supplementary Figs. 28b and 29b). This result is closely matching with the theoretical calculation. According to the computational result, dynamic dual phosphorescence of BANH2 emitter in PMMA matrix could be due to radiative emission from T2 (HEP) and T1 (LEP) state. In contrast, involvement of T1H and T1L originated due to temperature dependent conformational change at T1 state contributed to the origin of dual phosphorescence of BANHPh and BANMePh. Hence, the differential ISC of BANHPh and BANMePh relative to BANH2 could be reasoned as the presence of T1H state closely lying to singlet excited state in case of BANHPh and BANMePh as described in Fig. 3e and 3h. For BANHPh and BANMePh, intersystem crossing (ISC) to the T2 state is possible. However, significant vibrational overlap between the T2 and T1H states results in subsequent non-radiative transition to the T1H state.”\nPlease see the text in page 14-16 of manuscript for detailed information.\nAddition: We have included the plausible mechanism for BANH2 and BANHPh (/BANMePh) using stick diagram.\nComment 3: As shown in Figure 6h, several stable conformers were presented in the relaxed potential energy scans of T1 state. Then, could the emission peaks be calculated for these T1 conformers to compare with those in experimental results? How about the potential energy scans of T1 state for compound BANH2?\nResponse: Thank you for this insightful comment - it raises an important point. In the case of BANHPh@PMMA, the closest minima on the potential energy surface (PES) exhibit an energy difference of 5 kcal/mol (~0.22 eV), which aligns very well with the experimentally observed phosphorescence gap of 0.19 eV. Similarly, nearly degenerate conformational states were also identified for BANMePh, further supporting the claim that distinct T2 conformers contribute to the dual phosphorescence.\nFor BANH2, we performed extensive conformational sampling using the CREST algorithm, which did not reveal any relevant reaction coordinate (collective variable), in contrast to BANHPh and BANMePh where conformational flexibility arises due to the functional phenyl moiety. Consequently, no meaningful conformational scans could be carried out based on geometrical variables in the case of BANH2.\nComment 4: The phosphorescence property of organic luminogens was easily affected by the impurity, thus the HPLC should be carried out to certify the purity of these target compounds.\nResponse: We thank the reviewer for the comment. The purity of the compounds is confirmed by high-performance liquid chromatography (HPLC) technique (Supplementary Fig. 9).\nAddition: We have added the HPLC traces for the three compounds in Supplementary Fig. 9.\nComment 5: The steady-state PL spectra were almost overlapped with the delayed ones. Then, how the RTP quantum yields were measured in this work? The authors should make a clear presentation.\nResponse: We thank the reviewer for the comment. We have modified the text in quantum yield calculation section in supplementary information to make it more understandable to the reader. The total photoluminescence quantum yield (ΦPL) is indirectly calculated from the fluorescence quantum yield (ΦFL) by comparing the ratio of steady-state emission integral in absence of air and steady-state emission integral in presence of air by following the equation mentioned in supplementary information. Please see the text in page 39 of SI.\nIt has been analysed that the delayed emission band at 298 K has contribution from multiple emissive states (vide supra). At this moment, it is difficult to calculate the quantum yield contribution for a particular delayed component. Therefore, we have opted to refrain from the prediction of phosphorescence quantum yield by subtracting the fluorescence quantum yield (ΦFL) from total photoluminescence quantum yield (ΦPL). We have only highlighted the augmented quantum yield for ΦPL in absence of air relative to ΦFL in presence of air.\nAddition: The snapshot of quantum yield measurement (in presence of air) in addition with the calculation of total photoluminescence quantum yield (ΦPL) under vacuum condition has been reported in SI. (Supplementary Figs. 48-51)\nReponses to Reviewer #2\nIn the current report, Thilagar and Co-workers presented the dual phosphorescence behaviour of the borylaniline derivatives in the PMMA matrix. The presented organic chromophores show dual delayed emission behaviour under deaerated conditions, which is interesting in the field of triplet photophysics. However, authors have explained that the dual delayed emission phenomenon arises from the matrix-assisted, room-temperature accessible conformers within the T1 state via a thermally stimulated delayed phosphorescence mechanism, which may not be accurate. Thus, the current version of the manuscript requires proper justification of fundamental photophysical analysis and an explanation of the mechanism involved with proper experimental support, which is missing. Many experimental data, especially dual delayed emission behaviour, need reinvestigation with appropriate care. Hence, the present work requires major revisions for publication in a high quality journal like Nature Communications.\nResponse: We thank the reviewer for these comments. According to reviewer’s suggestion we have reinvestigated the experimental data including the nature of delayed emission behaviour. We have re-examined the photophysical behaviour of the chromophores at 0.1 wt.% concentration in three different matrices (PMMA, PBMA, and PS) with variable electronic and steric environment to understand the internal mechanism of the dynamic dual phosphorescence. Please see the text in page 14-16 of manuscript for detailed mechanistic insights. Additionally, each revised data has been discussed in a point-by-point manner.\nNB:\n• We have opted to change the phrase ‘dual phosphorescence’ to ‘dynamic phosphorescence’ by considering the presence of multiple triplet excited state for the temperature-dependent studies.\n• The thermally stimulated delayed emission phenomenon has also been highlighted in the manuscript since matrix plays an important role to control the thermal stimulation effect on delayed emission band. The title of the current work has been modified from “Polymer Matrix Drives Dual Phosphorescence in Dispersed Chromophores” to “Polymer Matrix Drives Thermal Stimulation-Caused Dynamic Phosphorescence in Dispersed Chromophores” to highlight the matrix-driven thermal stimulation effect on the dynamic delayed emission property.\nComment 1: Change in the dihedral angle at 100 K and 300 K is relatively low (negligible changes) in the single crystal data. However, the authors have concluded that dual emission arises from matrix assisted, room-temperature accessible conformers within the T1 state. The authors should reinvestigate the mechanism using proper experimental data. What is the photophysics of the molecules in the crystalline state? The authors should do a detailed investigation.\nResponse: We thank the reviewer for the comment. The photophysical properties in crystalline state are considerably different from the discrete molecular properties in matrix environment. The strong intermolecular interaction in crystalline state is found to change the relative energy level of the excited electronic states in addition to the consumption of the excited state energy for the emissive state resulting in the absence of thermal stimulation caused dynamic phosphorescence property. Moreover, the crystal packing environment would not allow for temperature-dependent conformational change in crystalline state for BANHPh and BANMePh (Please see the text in page 4 of manuscript). While 0.1 wt.% compound dispersed in polymer matrix eliminates the possibility of intermolecular interactions and it changes the electronic communication of excited states. At the same time, electronic and steric effect of matrix environment can regulate the temperature dependent conformation changes in case of BANHPh and BANMePh which is unlikely for crystalline state due to strong packing effect. That is why polymer matrix controls dynamic dual phosphorescence under thermal stimulation whereas, it is less probable in case of crystalline state. Please see the text in page 10 of the manuscript for detailed information.\nAddition: The photo-physics in crystalline state for three compounds are added in the manuscript and supplementary information according to reviewer’s suggestion (Fig: 2f-g and Supplementary Figs. 24d, 25d, 25d, 27, 28d, 29d, 30f, 31g, 32g, 34-35).\nComment 2: The asymmetric environment in the PMMA matrix could be due to the aggregation propensity of the chromophores, and 1 wt% chromophore doping may not prevent the aggregation. The authors should perform a wt% dependent study from 0.1% to 10 % and should take their delayed spectra and compare them. It might happen that authors are seeing phosphorescence from the monomeric and aggregated state of the chromophores. Please see one of the examples: https://doi.org/10.1002/anie.202101538\nResponse: We thank the reviewer for the comment and sharing the related reference. According to the reviewer, the dispersion of compounds at 1 wt.% concentration may originate the phosphorescence from the aggregated state. Following the reviewer’s suggestion we have examined the prompt and delayed emission property of compounds at different dispersion concentrations in PMMA matrix from 0.1 wt.% to 10 wt.% (0.1 wt.%, 0.5 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%). There is a red shifting of emission band for both prompt and delayed emission with increasing the compound concentration in matrix environment due to stabilization of excited states due to increase in intermolecular interactions. Notably, aggregation effect is more prominent above 1 wt.% dispersion concentration. Despite the aggregation effect, there was no such additional emission band for aggregation for both prompt and delayed emission spectra (following the concept of attached reference). Moreover, the temperature dependent study for 0.1 wt.% compound concentration in matrix showed the similar dynamic dual phosphorescence property as 1 wt.% emitters. This study further nullified the possibility of monomeric and aggregation state caused phosphorescence of the chromophores. Please see the text in page 8-10 of the manuscript for detailed information.\nAddition: The delayed emission spectra and corresponding lifetime decay profiles are recorded and compared for 0.1 wt.% to 10 wt.% chromophore @matrix according to reviewer’s suggestion (Supplementary Figs. 39-41).\nComment 3: Authors should experimentally find the original triplet state of the presented chromophores in a dilute solution state at cryogenic temperature.\nResponse: We thank the reviewer for the comment. We have recorded the steady-state and delayed emission spectra of chromophores in a dilute solution state of nonpolar toluene at 77 K to understand the energy level of low-lying triplet excited state. The phosphorescence spectra of all compounds in dilute solution state resembles the phosphorescence spectra of 0.1 wt.% compound in PMMA matrix with identical vibrational features (BANHPh: λ = 480 nm and λ = 480 nm; BANMePh: λ = 488 nm and λ = 485 nm; BANH2: λ = 465 nm and λ = 470 nm).\nAddition: The prompt and delayed emission spectra of the compounds in a dilute solution state (at 77 K and 298 K) are added in manuscript and supplementary information according to reviewer’s suggestion (Fig 2a, Supplementary Fig. 33).\nComment 4: 'The rigid polymer (PMMA) matrix eliminates the possibility of vibrational relaxation-caused quenching of excited state species. Time-gated PL measurement of 1 wt.% BANHPh@PMMA (50 μs delay time) at room temperature showed a structureless broad emission band at 450 nm (Fig. 2a).' what about the role of oxygen? The authors presented all the observations in the PMMA matrix under oxygen-free conditions (according to Figure S21). The authors should mention it clearly. Harnessing triplet exciton under ambient conditions is always more important than oxygen-free conditions. The authors should clarify and present the observations, which should be very clear to the readers.\nResponse: We thank the reviewer for the comment. The phosphorescence band of the emitters are sensitive to the oxygen. The behaviour of the steady-state and time-gated emission band in presence of oxygen and under vacuum condition have been demonstrated in the supplementary Fig. 45-47.\nThe photophysical observations has been conducted under oxygen free condition and it is mentioned in the measurement (method) section of the manuscript- “Photophysical studies of thin films were recorded under vacuum conditions unless otherwise mentioned”. Additionally, the emission property measurement conditions are highlighted in the optoelectronic investigation section of the manuscript.\nWe agree that photophysical behaviour of triplet excited state is important under ambient condition. We have conducted all the studies under oxygen free conditions to explore triplet excited state involved dynamics of emission bands without oxygen-caused quenching of triplet states. However, it is possible to achieve the same feature under ambient condition after using the oxygen barrier layer on the emitters. Please see the related references.\nhttps://doi.org/10.1002/anie.202215071 , https://doi.org/10.1126/sciadv.aau7310\nhttps://doi.org/10.1002/adma.202000880\nAddition: We have included the steady-state and time-gated emission spectra of the emitters measured under vacuum condition and in presence of oxygen (Supplementary Fig. 45-47).\nComment 5: 'The delayed emission band (λ = 450 nm) was slightly lower in energy than the prompt emission band (λ = 445 nm), as depicted in Fig. 2a and 2h.' The shift could be due to the change in the excited state geometry of the chromophores due their CT nature in the excited state. Please see also the other example: https://doi.org/10.1038/nphoton.2012.31.\nResponse: We thank the reviewer for the intriguing comment and sharing the related reference.\n• According to the reviewer, the shift delayed emission and prompt emission can be due to change in the excited state geometry of the chromophores while excited state possesses CT character.\n(a) We have investigated the emission property of chromophores in three different matrices (PMMA, PBMA, and PS) varying the electronic and steric environment and in dilute solution medium. Comparison of the phosphorescence band at 77 K in matrix environment and dilute solution state suggests a prominent locally excited (LE) character of the phosphorescence band. Therefore, low energy phosphorescence band is not expected to exhibit geometrical change in excited state. (Figs. 1a, 3b and Supplementary Figs. 23, 33).\n(b) The delayed emission band at 298 K shows shifting in the band position on changing the matrix environment. This indicates a certain degree of CT character of this band. However, the distinct spectral nature of the prompt and delayed emission bands—specifically, the delayed emission's feeble vibrational feature (lower energy end) which is absent in fluorescence band (recorded in presence of O2) infers different nature of the delayed emission band. In addition, the excited state geometrical change caused small energy shifting is unlikely in case of BANH2 since it does not have N-C(Phenyl) for conformational change relative to the other chromophores. Although BANH2 showed noticeable shift in the prompt and delayed emission band (more prominent shift in case of PBMA matrix). Hence, the excited state geometrical change cannot properly justify the shift in the delayed emission band compared to prompt emission band (Fig. 3b and Supplementary Fig. 23).\n• The reference shared by the reviewer highlights a noteworthy phenomenon. It describes the shift in prompt fluorescence and delayed fluorescence is caused by change in nuclear configuration of singlet excited state which is affected by triplet excited state after reverse intersystem crossing (RISC) process. However, it is feasible when delayed fluorescence is generated immediately after the RISC process (in shorter microsecond time scale). This kind of shifting is possible for the emitter reported in this shared reference (Nature Photonics) since the emitter shows very short lifetime in microsecond time scale. In contrast, the emitters in the present work demonstrated much longer lifetime in millisecond time scale. Therefore, the shifting of the delayed emission band cannot justify the triplet state influenced delayed fluorescence band in the present work.\nAddition: We have included the emission features of the chromophores in polystyrene matrix at 0.1 wt.% dispersion concentration to get further information about the emissive states (Fig. 3b and Supplementary Fig. 23).\nComment 6: Page 5, lines 195-196: 'Moreover, the strong oxygen sensitivity and faster decay of delayed emission at elevated temperatures featured the possibility of RTP rather than TADF (Fig. 2d and Supplementary Fig. 24, 26).' In my opinion, this statement is incorrect without adequate experimental support.\nResponse: We thank the reviewer for the comment. According to reviewer’s suggestion we have modified the sentence and re-investigated the emission process.\n(a) We have recorded the steady-state emission spectra under vacuum and in presence of O2 to distinguish the nature of the delayed emission (TADF or RTP), although it is difficult to realize the presence of triple excited state closely lying to S1 state. The steady-state emission band under vacuum condition is combination of fluorescence band and delayed emission band. On the other hand, delayed emission band is quenching in presence of oxygen and therefore, steady-state emission band exhibited an attenuated spectral area in presence of O2. Interestingly, normalization of spectra exhibited that there is a small blue-shift in spectral maxima for the steady-state emission band in present of O2 with reduced fwhm value relative to spectrum under vacuum (Supplementary Figs. 45-47). This clearly indicates the presence of triplet excited state energetically close to singlet excited state and negates the possibility of solely TADF phenomenon for delayed emission band.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\n(b) We have also re-examined the tail-fitting of lifetime decay profile for the delayed emission maxima. The lifetime decay is found to exhibit a tri-exponential decay kinetics without compromising the shorter time range during fitting. For bi-exponential fitting, the shorter time range typically needs to be excluded (previous version of manuscript); however, this would not be suitable for this phenomenon. The O2-sensitive spectra behaviour and temperature dependent variation of amplitude percentage of three delayed component concludes that the delayed emission band at 298 K is a combination of higher energy phosphorescence (HEP) band, lower energy phosphorescence (LEP) band and a modest contribution of thermally activated delayed fluorescence (TADF) considering the spectral overlap of prompt and delayed emission band. Please see the text in page 5-7 of manuscript and Supplementary Tables 11-13, 15-17, 19-21 for detailed information.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\nAddition: We have included the normalized steady-state spectra of the emitters measured under vacuum condition and in presence of oxygen. The snapshots of the lifetime decay profile are provided showing tri-exponential, bi-exponential and mono-exponential fitting of decay (Supplementary Figs. 45-47).\nComment 7: Suppose I claim that the high energy emission band is a delayed fluorescence band either by thermal activation derived or triplet fusion-induced delayed fluorescence emission; what extra experimental support author will present that my claim is wrong (or right)?\nResponse: We thank the reviewer for the comment. The delayed emission band exhibited a thermally stimulated intensity for the higher energy band with increasing temperature above 200 K. We have verified the underlying mechanism in the following manner for 0.1 wt.% compound in matrix environment.\n(a) We have recorded the steady-state emission spectra under vacuum and in presence of O2 to distinguish the nature of the delayed emission (TADF or RTP), although it is difficult to realize the presence of triple excited state closely lying to S1 state. The steady-state emission band under vacuum condition is combination of fluorescence band and delayed emission band. On the other hand, delayed emission band is quenching in presence of oxygen and therefore, steady-state emission band exhibited an attenuated spectral area in presence of O2. Interestingly, normalization of spectra exhibited that there is a small blue-shift in spectral maxima for the steady-state emission band in present of O2 with reduced fwhm value relative to spectrum under vacuum (Supplementary Figs. 45-47). This clearly indicates the presence of triplet excited state energetically close to singlet excited state and negates the possibility of solely TADF phenomenon for delayed emission band.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\n(b) We have also re-examined the tail-fitting of lifetime decay profile for the delayed emission maxima. The lifetime decay is found to exhibit a tri-exponential decay kinetics without compromising the shorter time range during fitting. For bi-exponential fitting, the shorter time range typically needs to be excluded (previous version of manuscript); however, this would not be suitable for this phenomenon. The O2-sensitive spectra behaviour and temperature dependent variation of amplitude percentage of three delayed component concludes that the delayed emission band at 298 K is a combination of higher energy phosphorescence (HEP) band, lower energy phosphorescence (LEP) band and a modest contribution of thermally activated delayed fluorescence (TADF) considering the spectral overlap of prompt and delayed emission band. Please see the text in page 5-7 of manuscript and Supplementary Tables 11-13, 15-17, 19-21 for detailed information.\nPlease see the related reference. https://doi.org/10.1021/jacs.4c02930\n(c) Temperature dependent photophysical properties are re-investigated in 0.1 wt.% dispersion concentration instead of 1 wt.% concentration. Similar thermal stimulation effect for the higher energy delayed emission band was observed for 0.1 wt.% emitters as 1 wt.% emitters. It is very unlikely to achieve triplet-fusion induced delayed emission for such a low weight (0.1 wt.%) concentration in matrix environment as it is bimolecular process. Hence, we can rule out the triplet-fusion caused delayed emission process in the present work.\nAddition: We have revised the photophysical experiments in 0.1 wt.% emitters. In addition, we have included the normalized steady-state spectra of the emitters measured under vacuum condition and in presence of oxygen. The snapshots of the lifetime decay profile are provided showing tri-exponential, bi-exponential and mono-exponential fitting of decay (Supplementary Figs. 45-47).\nComment 8: In SI line 582, 'Fluorescence quantum yield was determined with an integrating sphere under ambient conditions. The total photoluminescence quantum yield and phosphorescence quantum yield were obtained by following the previous literatures.' According to the SI figure S21, the authors do not have a triplet contribution to the total emission under ambient conditions; how did the authors calculate the total QY under vacuum? Please show all quantum yield measurement spectra (snapshot) under air and vacuum and the phosphorescence quantum yield measurement. Also, show a snapshot, justify how authors measured the quantum yield at 77 K, and adequately write instruments and methods in the SI.\nResponse: We thank the reviewer for the comment. We have modified the text in quantum yield calculation section in supplementary information to make it more understandable to the reader. The total photoluminescence quantum yield (ΦPL) is indirectly calculated from the fluorescence quantum yield (ΦFL) by comparing the ratio of steady-state emission integral in absence of air and steady-state emission integral in presence of air by following the equation mentioned in supplementary information. Please see the text in page 39 of SI.\nIt has been analysed that the delayed emission band at 298 K has contribution from multiple emissive states (vide supra). At this moment, it is difficult to calculate the quantum yield contribution for a particular delayed component. Therefore, we have opted to refrain from the prediction of phosphorescence quantum yield by subtracting the fluorescence quantum yield (ΦFL) from total photoluminescence quantum yield (ΦPL). We have only highlighted the augmented quantum yield for ΦPL in absence of air relative to ΦFL in presence of air.\nSimilarly, ΦPL at 77 K is calculated from the ΦPL at 298 K by comparing the ratio of steady-state emission integral at 77 K and steady-state emission integral at 298 K under vacuum condition. Please see the text in page 39 of SI.\nAddition: The snapshot of quantum yield measurement (in presence of air) in addition with the calculation of total photoluminescence quantum yield (ΦPL) under vacuum condition has been reported in SI (Supplementary Figs. 48-51).\nComment 9: Please explain and show detailed temperature dependence for two bands of all the chromophores for all the temperatures from 77 K to 298 K, not only from 225 K to 298 K) because the conclusion drawn from the temperature-dependent lifetime decay profile is unsatisfactory.\nResponse: We appreciate the reviewer’s comment as it has improved the quality of the work. We have revised the photophysical data for 0.1 wt.% chromophore concentration for three compounds (BANHPh, BANMePh, and BANH2) in three matrix environments (PMMA, PBMA and PS) at ten different temperatures (77K, 100K, 125K, 150K, 175K, 200K, 225K, 250K, 275K, and 298K). The observed data has been analysed with appropriate care and seriousness. The tail fitting of the lifetime decay profiles demonstrates an intriguing photo-physics which is quite different for 77 K to 200 K and 200 K and 298 K. At lower temperatures (below 200 K), the complex behaviour of amplitude percentage can be because of the contribution of higher energy locally excited triplet state (Tn). On the other hand, the emitters display the thermal stimulated delayed emission components with amplitude percentage appearing in more specific sequence above 200 K on the higher energy delayed emission band. The thermally stimulated delayed emission component could be due to higher energy phosphorescence band with a modest contribution of TADF phenomenon at elevated temperatures. Interestingly, the matrix environment plays a fascinating role in controlling the thermal stimulation effect of the chromophores, as a result, it modifies the nature of the dynamic dual phosphorescence. Please see the text in page 4-11 of the manuscript for detailed information. (Figs. 1c-d, 3c-d, Supplementary Figs. 24-32, Tables 11-13, 15-17, 19-21).\nAddition: The steady-state emission spectra, time-gated emission spectra (delay: 50 μs), excitation spectra, lifetime decay profiles for 0.1 wt.% emitters in different matrix at different temperatures and quantum yield measurements at ambient temperature are newly included in the manuscript and supplementary information (instead of 1 wt.% emitters in the previous version). Moreover, time-resolved delayed emission spectra (TRDES) at 298 K are incorporated in the SI for all emitters to get evidence about the close-lying excited states. The photophysical properties in polystyrene (PS) matrix for 0.1 wt.% emitters have been also added in the current version in addition to the PMMA and PBMA matrix for better understanding of the underpinning mechanism of the phenomenon (Figs. 1c-d, 3c-d, Supplementary Figs. 24-32, Tables 11-13, 15-17, 19-21).\nComment 10: Page 3, line 111 'We observe an extraordinary finding': Please refrain from an objective like this.\nResponse: We thank the reviewer for the comment. This work demonstrates an interesting phenomenon of thermal stimulation caused dynamic phosphorescence which is controlled by matrix environment. Although we have opted to modify the sentence following the reviewer’s suggestion. Now it reads as “We observe an intriguing finding where the PMMA matrix lifts the degeneracy of the conformers in the T1 state by providing an asymmetric environment”.\nComment 11: Authors should check 'photo physics' throughout the manuscript appropriately.\nResponse: We appreciate the reviewer’s comment as it has improved the quality of the work. We have revised the photophysical data for 0.1 wt.% chromophore concentration for three compounds (BANHPh, BANMePh, and BANH2) in three matrix environments (PMMA, PBMA and PS) at ten different temperatures (77K, 100K, 125K, 150K, 175K, 200K, 225K, 250K, 275K, and 298K). The observed data has been analysed with appropriate care and seriousness. The tail fitting of the lifetime decay profiles demonstrates an intriguing photo-physics which is quite different for 77 K to 200 K and 200 K and 298 K. At lower temperatures (below 200 K), the complex behaviour of amplitude percentage can be because of the contribution of higher energy triplet state (Tn). On the other hand, the emitters display the thermal stimulated delayed emission components with amplitude percentage appearing in more specific sequence above 200 K on the higher energy delayed emission band. The thermally stimulated delayed emission component could be due to higher energy phosphorescence band with a modest contribution of TADF phenomenon at elevated temperatures. Interestingly, the matrix environment plays a fascinating role in controlling the thermal stimulation effect of the chromophores, as a result, it modifies the nature of the dynamic dual phosphorescence. Please see the text in page 4-11 of the manuscript for detailed information. (Figs. 1c-d, 3c-d, Supplementary Figs. 24-32, Tables 11-13, 15-17, 19-21).\nComment 12: Authors should cite more appropriate literature where the organic chromophores show dual delayed emission (either dual phosphorescence or delayed fluorescence and phosphorescence).\nResponse: We thank the reviewer for the comment. We have cited appropriate literatures in the introduction section according to the current version of the manuscript.\nReponses to Reviewer #3\nSubhajit Ghosh et al. analyzed the dual phosphorescence behavior of three chromophores molecularly dispersed (1 wt.% concentration) in the PMMA matrix. They employed second-order Algebraic Diagrammatic Construction (ADC2) excited state calculations to show that the dual phosphorescence observed in BANHPh and BANMePh does not stem from the T1 and T2 electronic states. Instead, this phenomenon arises from matrix-assisted, room-temperature accessible conformers within the T1 state (T1Hand T1L). The PMMA matrix creates an asymmetric environment around the chromophores, inducing structural and electronic modulations that result in spectral tuning of the singlet and triplet manifolds. In conclusion, conformation-dependent dual phosphorescence is unlikely to occur without the PMMA matrix. The present results can be utilized for temperature sensing from the ratiometric phosphorescence afterglow colour change-over in a short energy range. In this sense, I suggest that this work can be accepted after addressing the following concerns.\nResponse: We thank the reviewer for the positive assessment of the work. The reviewer’s concerns have been addressed in a pointwise manner.\nNB:\n• We have opted to change the phrase ‘dual phosphorescence’ to ‘dynamic phosphorescence’ by considering the presence of multiple triplet excited state for the temperature-dependent studies.\n• The thermally stimulated delayed emission phenomenon has also been highlighted in the manuscript since matrix plays an important role to control the thermal stimulation effect on delayed emission band. The title of the current work has been modified from “Polymer Matrix Drives Dual Phosphorescence in Dispersed Chromophores” to “Polymer Matrix Drives Thermal Stimulation-Caused Dynamic Phosphorescence in Dispersed Chromophores” to highlight the matrix-driven thermal stimulation effect on the dynamic delayed emission property.\nComment 1: What is the behaviour of phosphorescence when the mass concentration is between 1wt.% and 10wt.%?\nResponse: We thank the reviewer for the comment. Following the reviewer’s suggestion we have examined the phosphorescence property of compounds at different dispersion concentrations in PMMA matrix from 0.1 wt.% to 10 wt.% (0.1 wt.%, 0.5 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%). There is a red shifting of phosphorescence band with increasing the compound concentration in matrix environment due to stabilization of excited states due to increase in intermolecular interactions. The lifetime decay profile of the emitters shows a gradual decrease in the lifetime with increasing the weight concentration (from 0.1 wt.% to 10 wt.%) in matrix. Comparison of phosphorescence property demonstrates the superior performance of 0.1 wt.% emitter relative to higher weight concentration emitters in terms of lifetime and quantum yield. Please see the page no 8-10 of the manuscript for detailed information (Supplementary Figs. 39-41).\nAddition: The phosphorescence spectra and corresponding lifetime decay profiles are added and compared for 0.1 wt.% to 10 wt.% chromophore @matrix according to reviewer’s suggestion (Supplementary Figs. 39-41).\nComment 2: Is the dual phosphorescence behaviour similar in other polymer matrices besides PMMA and PBMA?\nResponse: We appreciate the reviewer’s comment as it has improved the quality of the work. Following the reviewer’s comment, we have investigated the phosphorescence behaviour in nonpolar polystyrene (PS) matrix. The PS matrix-based emitters showed a distinct dynamic dual phosphorescence feature relative to PMMA and PBMA. The energy gap between lower energy phosphorescence band (LEP) and higher energy delayed emission band (HEDE) is found to be increased in case of polystyrene matrix (ΔE= 310 meV for BANHPh) compared two other two matrices (ΔE= 230 meV in both PMMA and PBMA for BANHPh). In addition, the time-resolved decay kinetics at different temperatures and thermal stimulation effect (above 200 K) on the HEDE band is quite different for PS matrix-based emitters. Please see the page no 11 of the manuscript for detailed information.\nAddition: The steady-state spectra, time-gated spectra and corresponding lifetime decay profiles are included for 0.1 wt.% chromophore @PS matrix (at different temperatures for three chromophores) in addition to the 0.1 wt.% emitters of PMMA and PBMA matrices (Fig. 3d, Supplementary Figs. 24c, 25c, 26c, 28c, 29c, 30d-e, 31e-f, 32e-f, 36-38 and Tables 10, 13, 14, 17, 18, 21).\nComment 3: Please note the uniform format of the paper, like “ADC(2)” and “ADC2”, and “T1/T2-S1 andT1/T2 S0” on page 9.\nResponse: We thank the reviewer for the comment. The format has been corrected in the manuscript following the reviewer’s suggestion.\nComment 4: Some typical recently literatures about long-lifetime RTP should be cited, such as 10.1038/s41467-024-47378-2; 10.1038/s41467-023-43133-1; 10.1021/jacs.2c02076； 10.1002/adma.202416397；10.1002/ange.202411323, et al.\nResponse: We thank the reviewer for the comment. The related references have been included in the introduction section of the manuscript following the reviewer’s suggestion.\nComment 5: Please note the normality of the figures, like Fig. 1c.\nResponse: We thank the reviewer for the comment. The temperature dependent delayed emission spectra of the emitters have been demonstrated as unnormalized spectra to understand the thermal stimulation effect under different matrix environments."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised version is suitable for publication.", "reviewer_2": "Comments:\nConsidering the interesting triplet photophysics presented in the current manuscript, I remain positive about the manuscript.\nHowever, the revised version is not entirely satisfactory. My opinion toward the author's hypothesis of the thermally stimulated delayed phosphorescence mechanism is that it needs adequate experimental support and evidence. Thus, without eliminating other possibilities of dual delayed luminescence behaviour, I cannot accept the manuscript in its current version. Below, I have mentioned my previous comments, the author's response, and the new suggestions to increase the manuscript's quality.\nPrevious Comment 1:\nChange in the dihedral angle at 100 K and 300 K is relatively low (negligible changes) in the single crystal data. However, the authors have concluded that dual emission arises from matrix-assisted, room-temperature accessible conformers within the T1 state. The authors should reinvestigate the mechanism using proper experimental data. What is the photophysics of the molecules in the crystalline state? The authors should do a detailed investigation.\nResponse and New Comment 1: The Authors performed the experiments; however, the explanations are not satisfactory.\nIn the current manuscript, authors mentioned that 'The strong intermolecular interaction in crystalline state is found to change the relative energy level of the excited electronic states in addition to the consumption of the excited state energy for the emissive state resulting in the absence of thermal stimulation caused dynamic phosphorescence property.'\nWhat is the band in the phosphorescence spectra (delay time of 50 microseconds) in the crystalline state from 400 to 475 nm in Figure 2f, S27, S28? Is it not similar to the band observed in the PMMA matrix? Authors should provide proper experimental analysis and justification.\nPrevious Comment 2:\nThe asymmetric environment in the PMMA matrix could be due to the aggregation propensity of the chromophores, and 1 wt% chromophore doping may not prevent the aggregation. The authors should perform a wt% dependent study from 0.1% to 10 % and should take their delayed spectra and compare them. It might happen that authors are seeing phosphorescence from the monomeric and aggregated state of the chromophores. Please see one of the examples: https://doi.org/10.1002/anie.202101538.", "reviewer_3": "The authors have revised the manuscript fully and it is suitable for publication as it is."}, "author_response": "Responses to reviewer #1\nThe revised version is suitable for publication.\nAuthor’s response: We are grateful to the reviewer for validating our work and accepting the manuscript for publication.\nResponses to reviewer #2\nConsidering the interesting triplet photophysics presented in the current manuscript, I remain positive about the manuscript. However, the revised version is not entirely satisfactory. My opinion toward the author's hypothesis of the thermally stimulated delayed phosphorescence mechanism is that it needs adequate experimental support and evidence. Thus, without eliminating other possibilities of dual delayed luminescence behaviour, I cannot accept the manuscript in its current version. Below, I have mentioned my previous comments, the author's response, and the new suggestions to increase the manuscript's quality.\nAuthor’s response: We thank Reviewer #2 for the continued positive assessment of the manuscript and for the detailed and constructive critique. We acknowledge the reviewer’s concern that the hypothesis of thermally stimulated delayed phosphorescence (TSDP) requires stronger experimental validation and clearer exclusion of alternative explanations for the observed dual delayed luminescence behavior. In response, we have substantially revised the manuscript to (i) provide additional experimental evidence supporting the proposed TSDP mechanism and (ii) explicitly discuss and evaluate other possible mechanisms, including thermally activated delayed fluorescence, triplet–triplet annihilation, and defect- or trap-assisted emission. These revisions aim to clarify the mechanistic interpretation and enhance the overall rigor of the work. All changes and new data are addressed point by point below.\nPrevious comment 1:\nChange in the dihedral angle at 100 K and 300 K is relatively low (negligible changes) in the single crystal data. However, the authors have concluded that dual emission arises from matrix-assisted, room-temperature accessible conformers within the T1 state. The authors should reinvestigate the mechanism using proper experimental data. What is the photophysics of the molecules in the crystalline state? The authors should do a detailed investigation.\nReviewer’s response to previous comment 1 and new comment 1:\nThe Authors performed the experiments; however, the explanations are not satisfactory. In the current manuscript, authors mentioned that 'The strong intermolecular interaction in crystalline state is found to change the relative energy level of the excited electronic states in addition to the consumption of the excited state energy for the emissive state resulting in the absence of thermal stimulation caused dynamic phosphorescence property.'\nWhat is the band in the phosphorescence spectra (delay time of 50 microseconds) in the crystalline state from 400 to 475 nm in Figure 2f, S27, S28? Is it not similar to the band observed in the PMMA matrix? Authors should provide proper experimental analysis and justification.\nAuthor’s response to previous comment 1 and new comment 1 (Photophysics in crystalline state):\nWe thank the reviewer for the careful reassessment and for highlighting the need to clearly distinguish the origin of delayed emission in the crystalline state from that observed for isolated chromophores in a PMMA matrix.\nThe delayed emission band observed between 400 and 475 nm at a delay time of 50 μs in the crystalline state (Figure 2f; Supplementary Figures S27 and S28) does not correspond to phosphorescence analogous to the low-energy or high-energy phosphorescence bands observed in PMMA. Instead, this band is assigned to delayed fluorescence, which coexists with a lower-energy phosphorescence band appearing at wavelengths above 500 nm.\nThis assignment is supported by several experimental observations. First, the higher-energy delayed band in the crystalline state spectrally overlaps with the prompt fluorescence, indicating a singlet origin. The peak maxima of this band lie in the range of 445–462 nm for all crystalline samples, whereas the phosphorescence band is consistently red-shifted (> 500 nm). As a result, emission in the 400–475 nm range cannot be attributed to phosphorescence in the crystalline phase.\nSecond, the phosphorescence observed in the crystalline state differs substantially from that of discrete chromophores in PMMA. The crystalline-state phosphorescence is red-shifted and exhibits shorter lifetimes than both the LEP and HEP bands in PMMA (Figure 2f; Supplementary Figures 34a–e). Moreover, the temperature dependence and temporal evolution of the delayed emission spectra differ qualitatively between the two environments, indicating distinct emissive mechanisms.\nStructural analysis further supports this distinction. Single-crystal data reveal a face-to-face antiparallel molecular arrangement; however, the centroid-to-centroid distances between xylyl rings (8.2 Å for BANHPh, 7.2 Å for BANMePh, and 5.9 Å for BANH2) are too large to support significant π–π stacking or H-aggregate formation in the ground state. In addition, the angles between the B–xylyl–N plane and the centroid-connecting axis (121.5°, 32.1°, and 91°, respectively) disfavour efficient orbital overlap.\nConsistent with this interpretation, excitation spectra of the crystalline samples exhibit a bathochromic shift relative to those of discrete chromophores in PMMA (Supplementary Figures 34f–h), indicating intermolecular stabilization of the excited states in the solid phase. We therefore attribute the red-shifted emission and altered decay dynamics in the crystalline state to intermolecularly modified excited-state energetics, rather than to the matrix-assisted triplet states' energetics responsible for dual phosphorescence in PMMA.\nThe manuscript and Supplementary Information have been revised accordingly (pages 8–9 of the main text; Supplementary Text 1, pages 10–11; Supplementary Text 2, pages 41–42). Supplementary Figure 11 has been updated to include additional intermolecular distance analyses, and Supplementary Figure 34 has been added to directly compare steady-state and time-gated emission in crystalline and dispersed states.\nIn addition, the supplementary figure 11 has been updated with additional figures demonstrating intermolecular distances in crystal packing. Supplementary Figure 34 is added to compare the steady-state and time-gated spectra of the crystalline state and dispersed state in the PMMA matrix.\nPrevious comment 2:\nThe asymmetric environment in the PMMA matrix could be due to the aggregation propensity of the chromophores, and 1 wt% chromophore doping may not prevent the aggregation. The authors should perform a wt% dependent study from 0.1% to 10 % and should take their delayed spectra and compare them. It might happen that authors are seeing phosphorescence from the monomeric and aggregated state of the chromophores. Please see one of the examples: https://doi.org/10.1002/anie.202101538.\nReviewer’s response to previous comment 2: The authors performed the experiments, and the explanations are satisfactory.\nAuthor’s Response to Previous Comment 2 (Aggregation in PMMA matrix):\nWe thank the reviewer for suggesting that we examine aggregation effects in the PMMA matrix through a systematic concentration-dependent study. As requested, we performed delayed emission measurements over a wide range of chromophore loadings (0.1–10 wt.%). The resulting spectra and decay characteristics did not show any evolution of a new band. These results rule out aggregation as the origin of the dual delayed emission observed at 0.1 wt.% and 1 wt.% loading, which are the concentrations discussed in the main manuscript. We therefore agree with the reviewer’s assessment that the explanation is satisfactory and have clarified this point in the revised text.\nPrevious comment 3:\nAuthors should experimentally find the original triplet state of the presented chromophores in a dilute solution state at cryogenic temperature\nReviewer’s response to previous comment 3: The Authors performed the experiments, and the explanations are satisfactory.\nAuthor’s response to previous comment 3 (Triplet state identification at cryogenic temperature):\nWe thank the reviewer for acknowledging that the cryogenic dilute-solution experiments satisfactorily identify the intrinsic triplet state of the chromophores. These measurements confirm the assignment of the lowest-energy triplet state (T1) and provide a reference for comparison with matrix-embedded and solid-state measurements. No further claims beyond this experimental scope are made in the revised manuscript.\nPrevious comment 4:\nThe rigid polymer (PMMA) matrix eliminates the possibility of vibrational relaxation-caused quenching of excited state species. Time-gated PL measurement of 1 wt.% BANHPh@PMMA (50 μs delay time) at room temperature showed a structureless broad emission band at 450 nm (Fig. 2a).' what about the role of oxygen? The authors presented all the observations in the PMMA matrix under oxygen-free conditions (according to Figure S21). The authors should mention it clearly. Harnessing triplet exciton under ambient conditions is always more important than oxygen-free conditions. The authors should clarify and present the observations, which should be very clear to the readers.\nReviewer’s response to previous comment 4 and new comment 2:\nThe authors' responses are not entirely satisfactory.\nExcept for Page 5, line 210, nowhere is it mentioned that all experiments are performed under deaerated conditions. I will request authors to mention this in the figure caption.\n\"However, it is possible to achieve the same feature under ambient condition after using the oxygen barrier layer on the emitters. Please see the related references https://doi.org/10.1002/anie.202215071, https://doi.org/10.1126/sciadv.aau7310, https://doi.org/10.1002/adma.202000880”\nThis reviewer is well aware of this literature, and the strategy of layering the oxygen barrier is one of the main novelties in the mentioned literature. Please see Response and New Comment 5.\nAuthor’s response to previous comment 4 and new comment 2 (Role of oxygen):\nWe appreciate the reviewer’s insistence on explicitly clarifying the role of oxygen. We fully agree that transparency regarding experimental conditions is essential, particularly when discussing triplet-mediated emission.\nAll measurements involving delayed emission in the PMMA matrix were performed under rigorously deaerated conditions. Following the reviewer’s request, this information has now been explicitly stated in the figure captions of Figures 2, 3, and 5, in addition to the description in the main text. We emphasize that the purpose of the present study is to elucidate the intrinsic photophysical mechanism under controlled conditions, rather than to demonstrate ambient-stable triplet harvesting. We acknowledge that oxygen-barrier strategies represent an important and distinct research direction, as demonstrated in the cited literature. However, implementing such encapsulation approaches constitutes a separate materials-design challenge and lies beyond the scope of the current mechanistic investigation. This distinction has been clarified to avoid any ambiguity regarding novelty or intent.\nPrevious comment 5:\n'The delayed emission band (λ = 450 nm) was slightly lower in energy than the prompt emission band (λ = 445 nm), as depicted in Fig. 2a and 2h.' The shift could be due to the change in the excited state geometry of the chromophores due their CT nature in the excited state. Please see also the other example: https://doi.org/10.1038/nphoton.2012.31.\nReviewer’s response to previous comment 5 and new comment 3:\nThe authors' responses are not satisfactory. Authors should perform excited-state dynamics to gain a detailed understanding of the involvement of another or multiple high-lying triplet states. The current experimental support is unable to justify one or multiple triplet states.\nAuthor’s response to previous comment 5 and new comment 3 (Excited-state dynamics and multiple triplet states):\nWe thank the reviewer for highlighting the need for direct experimental insight into excited-state dynamics and the possible involvement of multiple triplet states. In response, we have performed comprehensive femtosecond and nanosecond transient absorption (fs-TA and ns-TA) measurements in dilute toluene solution for all three compounds.\nThe fs-TA spectra reveal three principal features: (i) a narrow excited-state absorption band centered at ~430 nm (ESA1), (ii) a broad absorption band spanning 510–700 nm (ESA2), and (iii) a stimulated emission band centered at ~460 nm, consistent with steady-state fluorescence. Time-resolved spectral evolution and single-wavelength kinetics indicate that ESA1 is associated with triplet-state absorption, while ESA2 contains contributions from the singlet excited state and higher-lying triplet state(s). The appearance of multiple isosbestic points and subtle spectral shifts on the picosecond timescale supports the presence of state-to-state population transfer. Notably, BANHPh and BANMePh exhibit a time-dependent red shift of ESA1, suggesting the involvement of a barrier-mediated transition between triplet states, whereas such behavior is absent in BANH2. This distinction is consistent with differences observed in time-gated photophysics and theoretical calculations. The ns-TA measurements further confirm that the long-lived absorption in the 420–520 nm region corresponds to the T1 state, with microsecond lifetimes. The overlap between fs-TA and ns-TA triplet signatures provides consistency across time scales. Taken together, these results support the presence of at least one higher-lying triplet state in addition to T1. However, we deliberately refrain from assigning a specific number or ordering of triplet states beyond what is directly supported by the data. The revised manuscript explicitly frames these conclusions as experimentally supported indications rather than definitive state assignments.\nAddition: Figure 3 and the main text (page 12-14) have been updated accordingly, and additional transient absorption data and analysis are provided in Supplementary Figures 56–60 and Supplementary Text 5.\nPrevious comment 6:\nPage 5, lines 195-196: 'Moreover, the strong oxygen sensitivity and faster decay of delayed emission at elevated temperatures featured the possibility of RTP rather than TADF (Fig. 2d and Supplementary Fig. 24, 26).' In my opinion, this statement is incorrect without adequate experimental support.\nPrevious comment 7:\nSuppose I claim that the high energy emission band is a delayed fluorescence band either by thermal activation derived or triplet fusion-induced delayed fluorescence emission; what extra experimental support author will present that my claim is wrong (or right)?\nReviewer’s response to previous comment 6 & 7 and new comment 4:\nThe authors' responses are unsatisfactory for comments 6 and 7. Authors should perform a proper intensity-dependent study to rule out the possibility of triplet fusion-induced delayed fluorescence. Although a wt.%-dependent study can suggest that triplet fusion increases with increasing wt.% of the chromophores, it cannot rule out the possibility of triplet fusion-induced delayed fluorescence (which occurs due to Dexter transfer with less than 10 Å distance).\nResponse to previous comments 6 and 7 and new comment 4 (Delayed emission mechanism and exclusion of triplet–triplet annihilation):\nWe thank the reviewer for emphasizing the need for rigorous exclusion of alternative delayed emission pathways. To directly test the involvement of triplet–triplet annihilation-induced delayed fluorescence (TTA-DF), we performed excitation-intensity–dependent delayed emission measurements for all three compounds (0.1 wt.% in PMMA, PBMA, and PS matrices). As shown in Supplementary Figures 53–55, the integrated intensity of the higher-energy delayed emission (HEDE) band scales linearly with excitation power across the experimentally accessible range. No quadratic dependence, characteristic of TTA-DF, is observed. Within the sensitivity and power range of our measurements, this behavior is inconsistent with triplet fusion as the dominant contributor to the HEDE band. We therefore exclude TTA-DF as the primary delayed emission pathway under the conditions investigated. Accordingly, the manuscript text has been revised to avoid definitive mechanistic assignment and now states that the observed power dependence, together with oxygen sensitivity and temperature-dependent decay behavior, is compatible with a phosphorescence-based origin and not consistent with TTA-DF. We emphasize that this conclusion is limited to the experimental regime examined and does not exclude the possibility that other pathways may emerge under substantially different excitation or concentration conditions.\nPlease see the text of the main manuscript on pages 4-5 (Supplementary Figs 53-55).\nAddition: The supplementary figures 53-55 have been added.\nPrevious comment 8:\nIn SI line 582, 'Fluorescence quantum yield was determined with an integrating sphere under ambient conditions. The total photoluminescence quantum yield and phosphorescence quantum yield were obtained by following the previous literatures.' According to the SI figure S21, the authors do not have a triplet contribution to the total emission under ambient conditions; how did the authors calculate the total QY under vacuum? Please show all quantum yield measurement spectra (snapshot) under air and vacuum and the phosphorescence quantum yield measurement. Also, show a snapshot, justify how authors measured the quantum yield at 77 K, and adequately write instruments and methods in the SI.\nReviewer’s response to previous comment 8 and new comment 5:\nThanks to the authors for understanding the mistakes and correcting them in the current version.\nI want to refer \"However, it is possible to achieve the same feature under ambient condition after using the oxygen barrier layer on the emitters. Please see the related references https://doi.org/10.1002/anie.202215071, https://doi.org/10.1126/sciadv.aau7310, https://doi.org/10.1002/adma.202000880”\nThe authors may attempt to replicate the same feature under ambient conditions after using the oxygen barrier, making it easier to measure or predict QY under oxygen-free conditions. Although it may not be the same and easy, authors should try it.\nAuthor’s response to previous comment 8 and new comment 5 (Quantum yield determination and ambient-condition triplet emission) **:\nWe thank the reviewer for acknowledging the corrected quantum yield analysis. The fluorescence quantum yields were determined under ambient conditions using an integrating sphere, where triplet emission is fully quenched by molecular oxygen. The total photoluminescence quantum yields (both fluorescence and phosphorescence) were determined using an established protocol, as described in Supplementary Text 4. All relevant spectra, experimental snapshots, and methodological details are now explicitly documented in the revised Supplementary Information. We acknowledge the reviewer’s suggestion to stabilize triplet emission under ambient conditions using oxygen-barrier strategies. We attempted to suppress oxygen quenching by depositing a poly(vinyl alcohol) barrier layer on PMMA films; however, no steady-state phosphorescence was detected. This outcome likely reflects incomplete oxygen exclusion in the thin-film geometry rather than an intrinsic limitation of the emitters. We observed transient afterglow emission under ambient conditions following continuous UV irradiation, which we attribute to localized depletion of triplet oxygen. This effect is presented solely as qualitative evidence that triplet emission can be transiently accessed in air. Due to the non-steady-state nature of this condition and instrumental limitations, no quantitative photoluminescence quantum yields are reported, and no claims are made regarding ambient phosphorescence efficiency.\n**To the editor: To further reduce mechanistic overreach, we have implemented the following manuscript-wide revisions:\n1. All causal language (“demonstrates,” “confirms,” “proves”) has been replaced with constraint-based phrasing (“is consistent with,” “supports,” “is incompatible with”) for the explanation of photophysical properties.\n2. All mechanistic interpretations are explicitly tied to the specific experimental conditions under which they were observed.\n3. Claims regarding thermally stimulated delayed phosphorescence are limited to matrix-isolated chromophores under oxygen-free conditions.\nIn addition, We have added supplementary Figure 61 to demonstrate the captured phosphorescence image in air.\nPrevious comment 9:\nPlease explain and show detailed temperature dependence for two bands of all the chromophores for all the temperatures from 77 K to 298 K, not only from 225 K to 298 K) because the conclusion drawn from the temperature-dependent lifetime decay profile is unsatisfactory.\nReviewer’s response to previous comment 9 and new comment 6: Although authors have performed numerous experiments, detailed temperature dependence for the two bands of all chromophores across all temperatures from 77 K to 298 K is missing, which is surprising.\nAuthor’s response to previous comment 9 and new comment 6 (Complete temperature-dependent emission analysis, 77–298 K):\nWe thank the reviewer for reiterating the need for explicit and comprehensive temperature-dependent analysis across the full 77–298 K range. In response, we already performed systematic steady-state and time-gated emission measurements for all chromophores at ten discrete temperatures: 77 K, 100 K, 125 K, 150 K, 175 K, 200 K, 225 K, 250 K, 275 K, and 298 K. At each temperature, both the higher-energy delayed emission band and the lower-energy phosphorescence band were recorded under identical experimental conditions. The complete temperature-dependent datasets are explicitly presented and cross-referenced as follows: (i) temperature-resolved delayed emission spectra for all chromophores are shown in Figures 2c, and 3c–d of the main manuscript and Supplementary Figures S27-29; (ii) corresponding steady-state emission spectra are provided in Supplementary Figures S24–26; and (iii) Temperature-dependent decay profiles and integrated intensity trends for both bands are summarized in Figures 2d, 2g & 3f and Supplementary Figures S30–32 & S35–36. These figures collectively provide continuous spectral and temporal coverage from cryogenic to room temperature. We have revised the manuscript text to avoid describing any specific temperature as a “critical” or sharply defined transition point. Instead, the data are presented as showing gradual, band-specific evolution with temperature, including changes in relative intensity, spectral position, and decay behavior across the full range. No single temperature is assigned a privileged mechanistic role. Importantly, we no longer base interpretation solely on lifetime decay profiles over a limited temperature window. Rather, conclusions are constrained by the full temperature-dependent spectral dataset, which provides direct experimental observation of how both emission bands evolve continuously from 77 K to 298 K.\nPrevious Comment 11:\nAuthors should check 'photo physics' throughout the manuscript appropriately.\nReviewer’s response to previous comment 11 and new comment 7:\nThis comment was not only to address the unsatisfactory explanation of the manuscript, but also to verify proper scientific wording and correct minor mistakes. For example, caption Figure 2b 'Absorbance spectrum'. In the caption, Figure 2e is missing. Authors should carefully review the scientific wording and figure captions.\nAuthor’s response to Previous Comment 11 and New Comment 7 (Scientific wording, terminology, and figure captions):\nWe thank the reviewer for highlighting the need for careful review of scientific wording, terminology, and figure captions throughout the manuscript. In response, we have corrected the terminology in Figure 2b from “Absorbance spectrum” to “Absorption spectrum,” in accordance with standard photophysical nomenclature. We have also verified and clarified all figure captions to ensure completeness and internal consistency. In particular, the description corresponding to Figure 2e has been explicitly checked and is now clearly stated as “Temperature-dependent amplitude percentage of 0.1 wt.% BANHPh@PMMA at the 442 nm emission band in higher temperature regime.” Beyond these specific examples, we have conducted a comprehensive, line-by-line review of the entire manuscript and Supplementary Information to correct minor errors, improve scientific phrasing, and ensure consistent use of photophysical terminology (e.g., fluorescence, phosphorescence, steady-state emission, delayed emission, etc.). All figure labels, references, and captions have been cross-checked against the corresponding data.\nPrevious Comment 12: Authors should cite more appropriate literature where the organic chromophores show dual delayed emission (either dual phosphorescence or delayed fluorescence and phosphorescence).\nReviewer’s response to previous comment 12 and new comment 8: Authors should carefully review the citations. Few appropriate literature authors should cite which are listed below\nhttps://doi.org/10.3390/molecules24142552,\nhttps://doi.org/10.1002/adfm.201802407,\nhttps://pubs.acs.org/doi/10.1021/jacs.9b02765,\nhttps://doi.org/10.1002/adom.201900511,\nhttps://doi.org/10.1002/anie.201307601,\nhttps://doi.org/10.1039/D1SC04936D,\nhttps://doi.org/10.1002/adom.202300931,\nhttps://doi.org/10.1002/anie.201901672,\nhttps://pubs.acs.org/doi/10.1021/acs.jpclett.1c01552,\nhttps://doi.org/10.1038/s41467-020-15976-5.\nAuthor’s response to previous comment 12 and new comment 8 (Appropriate literature on dual delayed emission):\nWe thank the reviewer for identifying relevant and appropriate literature on organic chromophores exhibiting dual delayed emission, including dual phosphorescence and combined delayed fluorescence–phosphorescence behavior. Following the reviewer’s recommendations, we have carefully reviewed and incorporated the suggested references into the manuscript. These studies are now cited at appropriate points in the Introduction and Discussion sections, where they provide direct context for previously reported dual delayed emission phenomena and clearly position the present work within the existing literature. The added citations also help delineate similarities and distinctions between the reported systems and our findings.\nWe have additionally reviewed the reference list to ensure consistency, relevance, and balanced coverage of prior work in this area.\nReponses to reviewer #3\nThe authors have revised the manuscript fully, and it is suitable for publication as it is.\nAuthor’s response: We thank the Reviewer for the careful evaluation of the revised manuscript and for their positive assessment. We appreciate the reviewer’s support."}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have addressed the comments successfully, and the revised version of the manuscript is suitable for Publication."}, "author_response": "Responses to reviewer #2\nThe authors have addressed the comments successfully, and the revised version of the manuscript is suitable for Publication.\nAuthor’s response: We sincerely thank the reviewer for the careful evaluation of the revised manuscript and for recommending the manuscript for publication."}]

Decision letter