Charge transfer at the plasmon-molecule interfaces controls the collective chiroptical responses

Domain: physics
Published: 2025-11-28
Editorial outcome: major_revision

Abstract
Molecularexcitationsinteractingwithmetalplasmonshavefar-reachingimplicationsinnumerousfields.Electronicexcitationofchiralmoleculesorchiralsupramolecularassembliesattheplasmon-moleculeinterfacesisparticularlyofgreatinterest,butremainselusivesofar.Here,weconstructchemically-adsorbed,optically-resonantcomplexesofchiralmoleculesandplasmonicnanoparticlesfeaturingatomiccontrolovertheadsorptionofmoleculesonnanoparticlesurfaces.Interfacialchargetransferbetweenmoleculesandmetalsisrevealedtocausedelocalizedchiralmolecularexcitationsandintermolecularcouplings.Thedelocalizationofmolecularexcitonssignificantlyimpactedthechiropticalresponses,leadingtospectralshifting,broadening,andsignalintensityvariationsofcirculardichroism.Furthermore,thedominantinfluenceofinterfacialchargetransferisidentifiedcomparedtothenear-fieldelectromagneticcouplings.Thesefindingsprovidenewinsightsintotheopticalchiralityattheplasmon-moleculeinterfacesandinspireapproachesforthequantummanipulationofchiralmolecules,openingupavenuesforemergingapplications.

Introduction
Chiralinteractionsbetween(supra)molecularexcitationsandlocalizedsurfaceplasmonsinmetalnanostructuresgenerateaplethoraofemergingphotophysical/photochemicalphenomena.Forinstance,chiralmoleculescoulombicallyinducechiraldisplacementcurrentsonthesurfaceofmetalnanoparticles,resultinginchiralitytransferfrommoleculestonanoparticles1–3.Conversely,localizedchiralplasmonicfieldsaltertheelectromagneticfieldswithinachiralmolecules,leadingtoinductionofopticalchiralityinthemolecules4,5.Thesediscoverieshaveprofoundsignificanceforchiralnano/quantumphotonics6–8,asymmetricsynthesis9–11,biologicaldiagnostics12–15,etc16,17.Nevertheless,theexperimentalandtheoreticalstudiesinthepastprimarilyfocusedonthemechanismsofelectromagneticcouplingsbetweenmoleculesandmetals,whichmainlyinvolvelocalfieldenhancementand/orsuperchiralfield18. The potential effects of electronic excitationsandtransferattheplasmon-moleculeinterfacehaveoftenbeenignored.

When the separation between molecules and metal nanostructuresiswithinthesub-nanometerrangeorwhentheyaredirectlychemicallybonded,interfacialchargetransfer(CT)mayoccur.Thiscanbeattributedtotheoverlapandhybridizationofelectronicstatesbetweenmoleculesandmetals,and/orthegenerationandtransportofphoto-inducedhotcarriers19,20.Thisprocessiswidelydemonstratedtoaltertheopticalandoptoelectronicpropertiesofvariousresultingsystem21–23,forexample,generatingenhancedRamansignalsorrapidformationoftripletexcitedstatesofmolecules,andothers24–27. However, chiral molecule-metal complexes undergoinginterfacialCThasbeenrarelyexplored.Consequently,theimpactofpotentialmixingofelectronicstatesofchiralmoleculeswiththemetalsaswellasthecarriers’transportattheirinterfacesinthechiropticalresponsesisstillconfusing.Moreover,sincethenear-fieldelectromagneticcouplingcouldplayarole,methodstodistinguishtherespectiveinfluenceofthelocalfieldeffectandtheinterfacialCTprocessisdemanding,buthavenotbeenestablishedyet.

Therealready exist theoretical reports employing fullquantummodelsbasedonquantumelectrodynamics(QED)ortime-dependentdensityfunctionaltheory(TD-DFT)todescribetheelectrondensitydistributionandspectralbehaviorofmolecule-metalhybridcomplexes28,29.Thesestudieshavealsocomparedtheobtainedconclusionswithresultsbasedonclassicalelectromagnetictheory.Despite these advances, current full quantum approaches are stilllimitedtohybridstructuresclosethesizeofatomicclusters.Forlargerhybridsystems,itischallengingtoconsiderthemolecular-leveldetailssuchaselectronorbitalsandhybridizationsatthemolecule-metalinterface.Furthermore,intermolecularorbitalinteractionsaddanothercomplexityinthecollectively-coupledhybridsystems.Therefore,duetothelackofunifyingmultiscaleframeworkdescribingplasmons,CT,andmolecularexcitons,elucidatingtheCT-involvedcollectiveopticalresponsesofchiralmolecule-metalcomplexesisasignificanttheoreticalchallenge.Unfortunately,experimentalconstructionofrelevantmodelstructureshasbeenrareduetothestringentrequirementsinsystematicmoleculardesigns,suchastunablecontroloverthemolecule-surfacebindings,opticaltransitionenergy,andevenrotationalstrength.Thesechallengeshavegreatlyhamperedtoclarifytheentangledphysicalandchemicalmechanismsgoverningthechiralinteractionsattheinterfacebetweenmoleculesandmetals.

Inthisstudy,weatomicallytunethechemicaladsorptionofchiralmoleculesonthesurfaceofplasmonicmetalnanoparticles.Thesetwocomponentsaredesignedtobeopticallyresonantinthevisibleregion.InterfacialCTbetweenthemisunveiledthroughultrafasttransientabsorptionandRamanscatteringmeasurementcombinedwithquantumchemicalcalculations.Ground-stateelectronichybridizationbetweenmoleculesandmetalsaswellasphoto-inducedcarriers’transportarerevealed.TheinterfacialCTgreatlyimpactsthedelocalizedexcitationsofchiralmoleculesandhenceexcitoniccouplingsbetweenmolecules.Thisdelocalizationgeneratesdrasticallyalteredcirculardichroism(CD)responses,suchasstrongspectralshifting,broadening,andsignalintensityvariations.Furthermore,theCDsignalsassociatedwiththeintensityratiobetweenexcitationsatdifferentenergylevelsisseeminglydependentonthemetalnanoparticles’sizes,indicatingthecontributionoflocalelectromagneticfieldenhancementintheCDgeneration.However,theconsistentsignandbroadeningoftheCDspectra,irrespectiveofnanoparticlesizesandmolecularorientations,illustratetheleadingroleofinterfacialCTinalteringthechiropticalresponses.

Results
Opticalactivityofchiralcomplexesbeyondelectromagneticcoupling

Figure1aillustratestheformationofachiralmolecule-metalcomplex.Thechiralmolecule(SupplementaryFigs.1–11)isaderivativeofBINOL-BODIPYdye(BDP)30,denotedasBDP1,whichcontainsapyridinegroupcapableofchemicallybondingwiththesurfaceatomsofgoldnanoparticles(AuNPs)31,32.TheCDofBODIPYcoreoriginatesfromBINOL-to-BODIPYperturbationaccompaniedbyintramolecularCT33andoccursatapproximately504nm(inorganicsolvent),whichisproximaltothewavelengthoflocalizedsurfaceplasmonresonancesofAuNPs(520nm)(SupplementaryFigs.12–17).Therefore,BDP1andAuNPscanformanopticallyresonantchiralplasmoniccomplex(denotedasComplex1).ToexaminetheadsorptionofBDP1onthesurfacesofAuNPs,asurfaceligandexchangewasconductedonComplex1,andthealterationsinthesurface-enhancedRamanscattering(SERS)signalsweremonitored(Fig.1b).Complex1exhibitscharacteristicSERSsignalsintherangeof800~1620cm-1.Followingreplacementby4-mercaptobenzoicacid(4-MBA),thesignalsofComplex1disappeared,andthecharacteristicsignalsof4-MBAappearedat1074cm−1and1587cm−1,suggestingpyridine-mediatedchemisorptionofBDP1onthesurfacesofAuNPs.Thedispersionstabilityofchiralcomplexesinaqueoussolutionwasalsoinvestigated.Time-tracedmeasurementsofdynamiclightscattering(DLS)revealthat,undermoderateBDP1/AuNPmolarratios,thereisnonotableincreaseinthehydrodynamicdiameter,indicatingnegligibleaggregationofthecomplexes(Fig.1c,SupplementaryFigs.18–20).Thisdispersivestabilitycanbefurthercorroboratedbyverysmallorevenhardlyobservablepeakshiftintheabsorptionspectrum(SupplementaryFig.21).

TheCDspectrumofComplex1exhibitssignificantdifferencescomparedtoBDP1(Fig.1d).ThemainpeakpositionassociatedwiththeBODIPYcoreisred-shiftedfrom525nmto~550nmandisconsiderablybroadenedwithfullwidthathalfmaximum(FWHM)fromaround25nmto110nm.NewCDtransitionsappearinthelong-wavelengthregionbetween550and650nm.Besides,theintensitiesofmainCDpeaksaresubstantiallydecreasedcomparedtothepuremolecularCD(SupplementaryFig.12).Incontrast,thepurechiralmoleculesretainthesameCDlineshapeasinorganicsolvent,althoughthemoleculesarepronetoaggregationinaqueoussolution(SupplementaryFigs.12–16).TheseresultssuggesttheimportanceofthepresenceofAuNPsandthepossibleeffectofinterfacialCTbetweenBDP1andAuNPsunderstrongchemisorptionconditions34inmodifyingthemolecularCD.

TheAuNPs’sizeeffectwasstudiedinordertofurtheranalyzethemolecularCDalterations(Fig.1e–g,SupplementaryFig.22).WithincreasingBDP1concentration,theCDspectraexhibitedconsistentchangetrends.AtunsaturatedsurfaceconcentrationsofBDP1,allCDspectraexhibitsimilarred-shiftingandbroadening,regardlessofthechangeinAuNPs’sizes.TheseconsistentspectralchangesmaybeintrinsicallyrelatedtothesamechemicalbondinginteractionbetweenBDP1andAuNPsofdifferentsizes.Notably,asAuNPs’sizeincreased,theintensityoftheshort-wavelength(around525nm)CDisseeminglyincreasedcomparedtothatinthelong-wavelengthregion(around550–600nm).AsthesizeofAuNPsincreases,theintensityofthelocalelectromagneticfield(hotspot)becomesstronger35,36.Thisenhancednear-fieldelectromagneticcouplingbetweenmoleculesandmetalscouldcontributetotheslightenhancementofCDnearthesurfaceplasmonresonancewavelengths(around525nm).SimilarenhancementofopticalabsorptionofchiralmoleculesbymetalplasmonsandhencetheCDsignalshasbeenwellinterpretedtheoretically37,althoughpossibleinterfacialCTwasnottakenintoaccount.Besides,manystudiespointedoutthatduetonear-fieldelectromagneticcoupling(dipolarormultipolar)betweenchiralmoleculesandplasmonicnanoparticles,aninducedCDresponsecanbegeneratedatthesurfaceplasmonresonancewavelengths38.Thus,theinducedplasmonicCDcouldbeanotherfactorcontributingtotheweakenhancementofCDsignalsnear525nmforlarger-sizedcomplexes(SupplementaryFigs.23–24).

Furthermore,thechiralmolecularstructureswerefinelytailoredtomodulatethecouplinginteractionsbetweenmoleculesandmetals.Specifically,bychangingthepositionofpyridinegroupinthechiralmolecules,theiraverageadsorptionorientationonthesurfaceofAuNPswasadjusted(Fig.2a,b).Besides,thestrengthofmolecule-surfacebindingwasenhancedbyreplacingtheanchoringgroupfrompyridinetothiol(Fig.2c).ItshouldbementionedthatBDP1-3sharethesamechiralsourcegroup,i.e.,BINOL,thusexhibitingsimilarCDspectralshapesandsignalintensities.Crucially,theseadjustmentsinmolecularstructurewerefoundtostronglyinfluencethechiropticalresponsesofthemolecule-metalcomplexes,asdetailedbelow.

AscomparedtoComplex1,Complex2exhibitsstrongCDsignalsofunadsorbedmoleculesaswellasweaksignalsinthelong-wavelengthregion.ThismightbebecauseBDP2hashighsterichindrance,reducingitsadsorptionontheAuNPsurfaces(Fig.2d,e).Theorientationofchiralmoleculesrelativetothesurfaceofplasmonicnanoparticlesmaydeterminethesign(positiveornegative)ofemergentplasmonicCDinducedbythemolecules39.Forinstance,moleculesperpendicularorparalleltothenanoparticlesurfacecouldinducereverseplasmonicCDsignals38,40.Here,theBINOL-to-BODIPYdirectionofBDP2onAuNPs’surfacesisrotatedby90degreesascomparedtothatinBDP1becauseofthedifferentpyridinegrouppositions.However,theCDspectraofthetwocomplexesstillmaintainhighsimilarityintermsofthesignandbroadeningofCDsignalsatthelong-wavelengthregion,indicatingthatthemolecule-inducedplasmonicCDisweak,provideditexists.(Fig.2d,e,andSupplementaryFigs.23–26).ThisfindingisalsosubstantiatedbytheclosesimilarityoflargelybroadenedCDlineshapeatvariedAuNPs’sizes,albeitwithslightCDenhancementnearthesurfaceplasmonresonancewavelengthswithincreasingAuNP’ssizes(Fig.1e–g).Inbrief,theeffectsofmolecularorientationandnanoparticlesizetogetherillustratethattheinfluenceofnear-fieldelectromagneticcouplingbetweenmoleculesandmetalsislimitedinthissituation,whichisdistinctlydifferentfromthatofpotentialinterfacialCTbetweenthem.

TheeffectofinterfacialCTonchiralmolecularexcitationsandchiralinteractions

Complex1-2exhibitedbroadenedexciton-coupledCDathighmolecularconcentrations(Fig.2d,e),differentfromthoseinvarioussupramolecularassembliesduetoconventionaldipolarinteractions41(SupplementaryFig.15).ThisbroadeningmaybeascribedtodelocalizationofBDP1andBDP2excitationsarisingfromCTmixingeffects42,43(SupplementaryFigs.27–29).Incontrast,theCDlineofComplex3isonlyslightlybroadenednear500nmaccompaniedbysignalintensitydecreasecomparedtopuremolecules(SupplementaryFig.17).CDsignalswerehardlyobservedinthelong-wavelengthregion.TheseresultsillustratelessdelocalizationofBDP3excitationsandindicatewavelength-dependentinterfacialresponses(Fig.2f).OurpreviousstudiessuggestedthepresenceofCTstatebetweenclosely-spacedBDPderivatives39.GiventhedistancedependenceofintermolecularCT(3–4Å),evidentCTisexpectedatsufficientlyhighmolecularsurfacedensities.Weconductedinsitutime-dependentCDmeasurementsataverylowmolecularconcentration(BDP/AuNPmolarratioabout2)tosuppressthepossibleintermolecularCT(Fig.2g,h).Complex1showedprogressiveCDspectralbroadeningandsplittingwithin30minutes,confirmingstrongdelocalizednatureofBDP1excitationsandcouplings.Complex2displayedminimalexciton-coupledCDwithbroadening,potentiallyduetothesterichindranceofBDP2whichcausesalowerrateofadsorption.However,thepurechiralmolecules(BDP1-2)inaqueoussolutiondidnotdisplaysuchbroadeningoftheCDspectrumasobservedhere.Thus,itcanbededucedthatthestrongdelocalizationofBDP1-2excitationsprimarilyoriginatesfromtheinterfacialCTbetweenthemoleculesandthenanoparticles.Onthecontrary,Complex3consistentlyexhibitednarrowCDlineshape(Fig.2i),furtherdemonstratingmorelocalizednatureofBDP3excitations.Thisdifferenceemphasizesthecrucialroleoftheinterfacialchemicalbindingsbetweenthechiralmoleculesandmetalsurfaces.

ToexaminetheinterfacialCTwithinthechiralcomplexes,wemeasuredtheirfingerprintRamanscattering(Fig.2j–l).InterfacialCTbetweenmoleculesandmetals,thatisachemicalenhancementmechanism,canstronglymodifytheSERSspectralshapeassociatedwithvariedextentsofenhancementamongdifferentvibrationalmodesofmolecules26.AsexhibitedinSupplementaryFigs.30–32,theRamanspectralshapesofdriedsamples(Complex1-2)haveundergonegreatchangesatdifferentlaserexcitationwavelengths.Forexample,ascomparedto633nm,the532nmexcitationsignificantlyenhancesRamanscatteringfrompyridineorpyrroleringstretchinganddeformationinplane(1520cm−1),C-Csinglebondasymmetricstretching(1423cm−1),C-Hdeformationinplane(1167cm−1)andBODIPYcore(964cm−1)44,45.ThemonodispersedsolutionofComplex1-3wasalsomeasuredinordertoexcludethepotentialinfluenceoflocalelectricfieldenhancementindriednanoparticleaggregates.Thesmall-sized,isolatedAuNPs(3nm)supportconsiderablyweaklocalelectricfield,thuscontributingveryminorphysicalenhancementofRamanscattering.WefoundthattheRamansignalintensitiesofComplex1-3under532nmlaserconditionaresignificantlyincreased,while633nmirradiationgenerateshardlyobservablesignals(Fig.2j–l).TheseresultsindicatethecontributionofinterfacialCTtransitionsbetweenthechiralmoleculesandtheAuNPsunderexcitationat532nmwavelength.Notethat,resonantelectronictransitionsofmoleculescanoccurat532nmwavelength,althoughnocharacteristicsignalsweredetectedfrompuremolecules(BDP1-3).Thus,wecanspeculatethatinterfacialCTtransitionsaresynergisticallyoperatingwithresonantexcitationsofmoleculesintheSERSofthecomplexes46,47.

Ultrafasttransientabsorption(TA)spectroscopywasemployedtofurtherverifytheinterfacialCTinthechiralcomplexes.Figure3a,bandSupplementaryFigs.33–40showtheTAspectraofComplex1-3(bumpwavelength,504nm),whichallappearsimilartothatofAuNPs.TheTAspectrumexhibitstwopositivepeaksandonenegativepeakbetweenthem.Thenegativepeakismainlyattributedtothesurfaceplasmonresonances,48whilethetwopositivepeaksareassociatedwiththeintra/interbandtransitions.Uponphotoexcitation,hotcarriersaregeneratedduringtheplasmondecayprocess49,50,whicharesubsequentlyconsumedthroughelectron-electronscattering(e-e,~10to100fs),electron-phononscattering(e-ph,~1ps),andeventualthermalization51,52.Figure3cdepictsthecarrierdynamicscurvesprobedatawavelength(525nm)nearthesurfaceplasmonresonancewavelengths.ItwasfoundthatthecarrierrelaxationrateinComplex1-2isfasterthanthatofAuNPs.Thedynamicscurveswerefittedwithatwo-exponentialdecayaftertherisingedge,showingthatatimecomponentofcarriers(possiblyrelatedtoe-phscattering)isapproximately2.01psinAuNPsbutisreducedtoaround1.65psinthetwocomplexes.Thisfastercarrierrelaxationdenotesanadditionaldecaychannel,throughtransferringfromtheAuNPs to the chiral molecules53–55.

Moreover,weexaminedthecarriers’dynamicsprobedatalongwavelength(575nm)toavoidstrongbackgroundinterferenceofsurfaceplasmons(Fig.3d).ItisevidentthatComplex1-2exhibitprolongedcarriers’relaxationtimes(800fsand900fs,respectively)comparedtoAuNPs(500fs).AsdemonstratedinFig.3candFig.4,theinterfacialCTisbidirectional,exchangingbetweenthechiralmoleculesandtheAuNPs.Thus,theprolongedcarrier’slifetimesinComplex1-2observedat575nmsuggestslowerorlongerlastingcarrier’sexchangebetweenmoleculesandmetals.Thisresultisconsistentwiththeaboveconclusion,thatis,theinterfacialCTisprimarilyresponsibleforthedelocalizationofBDP1-2excitations.AscomparedtoComplex1-2,thecarrierrelaxationofComplex3probedat525nmisclosertothatofAuNPs.ThelackofevidentlifetimeshorteningindicatesthatinterfacialCTfromAuNPtoBDP3doesnotdominatethedynamics,thoughitmaystilloccur(Fig.2l).Also,thecarrierlifetimeofComplex3islittlechangedcomparedtothatofAuNPsat575nmprobingwavelengths(Fig.3e,f).TheminimalinterfacialCTinthelong-wavelengthregionmightbecorrelatedwiththelessdelocalizationofBDP3moleculesandhencenoapparentbroadeningofCDspectrainthisregion(Fig.2f,i).

Quantumchemistrycalculationonthechiralmolecularexcitations

Weperformeddensityfunctionaltheory(DFT)calculationsofthemolecularexcitationsatthemolecule-metalinterface.Asarepresentativeexample,thecalculationresultsofComplex1werepresented.TounderstandthecontributionoftransitionsbetweenmolecularorbitalstotheCDofComplex1,theelectronicCDspectrumoftheisolatedBDP1moleculewasfirstlycalculated.Althoughaslightblueshiftinpeakfrequencieswasobserved,thetheoreticallypredictedCDspectrumalignedwithexperimentalobservations.Thediscrepancyislikelyattributabletofactorssuchasmolecularconcentration,environment,andcomputationalmethodology.ThemostintensepeakintheCDspectrumofBDP1(SupplementaryFig.41)primarilyoriginatesfromtheHOMO-1→LUMOtransition.TheHOMO-LUMOtransitionexhibitsrelativelylowintensity,possiblyduetominimalspatialoverlapbetweentheseorbitals(SupplementaryFigs.42–44andTable1).WhenmodelingtheinteractionbetweentheBDP1moleculeandAuNPs,emphasiswasplacedontheadsorptionofthemolecule’sN-terminusatthetopsiteoftheAu(111)surface.TheAu-Nbondlengthwasdeterminedtobe2.19Å,withanadsorptionenergyof−0.99eV,indicatingtheformationofachemicalbondbetweentheBDP1moleculeandtheAu(111)surface.

ElectronicstructureanalysisdemonstratessignificantinteractionsbetweentheHOMO,LUMO,andthenearlydegenerateHOMO-3/HOMO-4orbitals(whichappearasonepeakinPDOSduetobroadening)ofBDP1andAu(Fig.4a–d,SupplementaryFigs.45–50).Incontrast,thenearlydegenerateHOMO-1/HOMO-2orbitalsshowminimaloverlapwithAustates.ElectronsonHOMOandHOMO-3/HOMO-4orbitalsofBDP1transfertoAu,whiletheinteractionbetweentheunoccupiedLUMO/LUMO+1/LUMO+2orbitalsandAuenhanceselectrondistributionontheN-containingsix-memberedring,indicativeofback-donationfromAutoBDP1.Notably,theadsorbedBDP1ontheAusurfaceinducesanorbitalexchangebetweenthemolecule’sLUMO+2andLUMO+3(SupplementaryFig.54),facilitatingtheback-donationprocess.ThedifferentialchargedensityindicatesthatelectrontransferbetweenBDP1andAuisbidirectional,involvingelectronexchange.Baderchargeanalysisrevealsanetelectrontransferof0.21efromBDP1toAu.SmallPDOSpeaksemergebetweentheHOMOandLUMO(SupplementaryFig.53),primarilylocalizedontheN-containingsix-memberedring,potentiallycontributingtolow-energyelectronictransitions.Moreover,stronghybridizationbetweenBDP1’sLUMO+1orbitalandAushiftstheLUMO+1orbitaltowardstheFermilevel(~0.58eV),bringingtheHOMO→LUMO+1electrontransitionintothelow-energyregion(1.72eV).TheenergygapoftheHOMO-1→LUMOelectrontransitionisalsodecreased(Fig.4e,f).Thesemechanismscouldbepartiallyresponsiblefortheobservedred-shiftofCDwavelengthsasaresultoftheinterfacialCTinteractions.

Further,theadsorptionofBDP1withdifferentsurfacecoverageswasinvestigated.Asthesurfacecoverageincreasedfrom7%to12%and30%,accompaniedbyenhancedintermolecularinteractions,theadsorptionenergyofBDP1ontheAusurfacewasobservedtostrengthen(from−0.99eVto−1.12eVand−1.34eV).ThiscomparisonsuggestspreferentialadsorptionofmoleculesontheAusurface,aligningwithexperimentalobservations.Furthermore,withincreasingsurfacecoverage,adecreaseintheenergygapbetweenHOMO-1andLUMOorbitalswasobserved(SupplementaryFig.57).Concurrently,localelectrondensityplotsrevealafurtherenhancementofelectronexchange(SupplementaryFigs.54–56).Atasurfacecoverageof7%ofindividualmolecules,thecaseoftwoBDP1adsorbingsimultaneously(denotedasBDP1-d)wasexamined.Inthisconfiguration,theshortestdistancebetweentwoBDP1moleculeswas3.50Å,andtheco-adsorptionenergywascalculatedtobe−2.27eV.Theresultsshowedthatthisconfigurationalsoexhibitedanincreaseofelectronexchangebetweenmolecularandmetalstates(Fig.4g,handSupplementaryFig.58).

Similarly,Complex2presentsstrongorbitalhybridizationsbetweenmoleculesandmetals,withnetelectrontransferof0.24efromBDP2toAu(SupplementaryFigs.41–50).Butthevaluewasreducedto0.15efromBDP3toAupossiblyduetostrongerbacktransferofelectronsasaresultofstableinterfacialchemicalbindings(Au-S).ThiscomparisonsuggeststhattheinterfacialCTvariationdeterminedbythedistinctmolecule-surfacebindingsispivotalfortheobservationoflocalized/delocalizedchiralmolecularexcitations.

Methods
SynthesisandcharacterizationofBDP1

ThesynthesisofBDP1isasfollows:Toasolutionof1,3,5,7-tetramethyl-8-(pyridin-4-yl)-F-BODIPY(0.18g,0.5536mmol)and(S)-1,1’-bi-2-naphthol((S)-BINOL)(0.7925g,2.768mmol)indryCH2Cl2(20mL)wasaddeddropwiseEt2AlCl(1.00M in Hexane, 1.1072mL, 1.1072mmol)undernitrogenatmosphereandthesolutionwasstirredinthedarkfor2h.Afterthesolventwasremoved,thecruderesiduepurifiedbysilica-gelcolumnchromatography(CH2Cl2/hexane,1/1to4/1,v/v)affordedBDP1(36.2mg,0.0634mmol)asredsolid;1HNMR(400MHz,Chloroform-d):δ8.84–8.78(m,2H),7.84(d,J=8.0Hz,2H),7.78(d,J=8.7Hz,2H),7.44–7.38(m,2H),7.32(ddd,J=8.0,6.6,1.2Hz,2H),7.25–7.11(m,6H),5.83(s,2H),1.66(s,6H),1.40(s,6H).13CNMR(101MHz,CDCl3):δ157.55,154.45,150.59,144.25,142.18,133.78,131.09,129.95,129.32,127.91,127.18,125.28,123.78,123.68,123.40,123.04,121.49,31.53,30.15,16.03,14.97.MS(ESI):calculated:571.4found:m/z572.4(M+H)+.

SynthesisandcharacterizationofBDP2

ThesynthesisofBDP2isasfollows:Toasolutionof1,3,5,7-tetramethyl-6-(pyridin-4-yl)-8-phenyl-F-BODIPY(0.3g,0.748mmol)and(S)-1,1’-bi-2-naphthol((S)-BINOL)(0.4718g,1.6456mmol)indryCH2Cl2(20mL)wasaddeddropwiseEt2AlCl(1.00M in Hexane, 1.5mL, 1.5mmol)undernitrogenatmosphereandthesolutionwasstirredinthedarkfor2h.Afterthesolventwasremoved,thecruderesiduepurifiedbysilica-gelcolumnchromatography(CH2Cl2/Hexane,1/1to4/1,v/v)affordedBDP2(51.4mg,0.0795mmol)asredsolid;1HNMR(400MHz,Chloroform-d)δ8.49(d,J=5.0Hz,2H),7.91–7.72(m,4H),7.60–7.27(m,8H),7.25–7.08(m,4H),6.87(d,J=5.0Hz,2H),5.85(s,1H),1.70(d,J=3.6Hz,6H),1.40(s,3H),1.31(s,3H).13CNMR(101MHz,CDCl3):δ157.75,153.36,153.21,151.79,148.47,143.23,141.59,141.01,137.22,134.46,132.76,132.72,132.18,130.53,129.73,128.97,128.82,128.30,128.23,128.18,128.15,128.05,127.21,127.17,126.87,126.78,126.13,126.06,124.30,124.26,124.17,122.67,122.59,122.40,122.30,120.62,120.20,52.39,30.55,30.40,29.16,28.67,21.62,15.01,13.79,13.57,13.10,11.84.MS(ESI):calculated:647.5found:m/z648.5(M+H)+.

SynthesisandcharacterizationofdimericBDP3

ThesynthesisofdimericBDP3isasfollows:Toasolutionof1,2-bis[4-(1,3,5,7-tetramethyl-F-BODIPY-8-yl)phenyl]disulfide(1.49g,2.097mmol)and(S)-1,1’-bi-2-naphthol((S)-BINOL)(3.6g,12.582mmol)indryCH2Cl2(30mL)wasaddeddropwiseEt2AlCl(1.00M in Hexane, 8.39mL, 8.39mmol)undernitrogenatmosphereandthesolutionwasstirredinthedarkfor2h.Afterthesolventwasremoved,thecruderesiduepurifiedbysilica-gelcolumnchromatography(EthylAcetate/Hexane,1/2,v/v)affordedBDP3(1.65g,1.37mmol)asredsolid;1HNMR(400MHz,Chloroform-d):δ7.83(d,J=6.8Hz,4H),7.77(d,J=8.7Hz,4H),7.66(d,J=8.2Hz,4H),7.38–7.28(m,8H),7.20(td,J=16.6,8.5Hz,12H),5.80(s,4H),1.64(s,12H),1.37(s,12H).13CNMR(101MHz,CDCl3):δ156.95,154.54,142.32,137.71,135.09,133.78,132.03,129.92,129.26,128.86,127.88,127.18,125.23,123.74,123.34,122.68,121.49,77.35,77.03,76.71,15.98,14.84.

Circulardichroismandabsorptionmeasurements

TheCDspectrawererecordedusingaChirascanV100CDspectrometer,scanningfrom300to700nmwitha2nmbandwidth,a1cmpathlength,andascanspeedof120nm·min⁻¹.Absorptionspectraweresimultaneouslyrecordedonthesameinstrument.BaselinecorrectionforCDandabsorptionspectrawasperformedusingbackgroundmeasurementsofdeionizedwater.

Ramanscatteringmeasurements

Raman scattering measurements were performed using a Renishaw inViaReflexRamanmicroscopeequippedwitha50×objectivelensanda532/633nm laser. Spectra were acquired in air using a 5s integrationtime.

Femtosecondandnanosecondtransientabsorptionspectroscopy

Atitaniumsapphirefemtosecondlaser(Astrella,CoherentInc.)wasemployedastheexcitationsource,generating100fspulsescenteredat800nmwitharepetitionrateof1kHz.The800nmoutputwassplitintotwobeamsusingabeamsplitter.Onebeamwasdirectedintoanopticalparametricamplifier(OPerASolo,CoherentInc.)togeneratepumplightatthedesiredwavelengthfortheexperiment.Theotherbeamwaspassedthroughadelaylineandfocusedontoanonlinearsapphirecrystalwithinatransientabsorptionspectrometer(Helios,UltrafastSystems)togenerateasupercontinuumprobebeamspanning450to750nm.Thisprobebeamwasthenfocusedontothesampleusinganoff-axisparabolicmirror.Thepumpbeamwasmodulatedto500Hzbyachopperandpolarizedto54.7°relativetotheprobebeamusingahalf-waveplatebeforebeingfocusedontothesample.Liquidsampleswereplacedina2mmquartzcuvette.AGlan-Taylorprism,positionedafterthesample,filteredoutscatteredpumplightduetotheperpendicularpolarizationofthepumpandprobebeams,enablingonlytheprobebeamtopassthrough.Theprobebeam,carryinginformationabouttheexcitedandgroundstatesofthesample,wasdetectedbyafiber-opticprobeafterpassingthroughthesample.Byadjustingthedelaybetweentheprobeandpumpbeamsusingadelayline,thespectralinformationofthesampleatdifferenttimedelaysafterexcitationcouldbeobtained.Theinstrumentalresponseofthesystemwasapproximately120fs.Thesamplesolutionswerepreparedindeionizedwaterwithasteady-stateabsorbanceofapproximately0.2–0.3ODattheexcitationwavelength(504nm)ina2mmquartzcuvette.

Densityfunctionaltheorycalculation

AllthecalculationswereperformedusingtheViennaAbinitioSimulationPackage(VASP)60,61.Theprojectedaugmentedwave62methodandthePerdew-Burke-Ernzerhof(PBE)functional63withinthegeneralizedgradientapproximation(GGA)wereemployedtodescribenuclei-electronandelectron-electroninteractions.WeakinteractionsweredescribedusingtheDFT-D3method64.Theplane-wavecutoffenergywassetas400eV.Convergencecriteriaforenergyandforceinself-consistentiterationsweresetto10−5eVand0.02eV/Å,respectively.

TheAunanoparticlewassimulatedasathree-layer(8×8)Au(111)surfacewithbottomtwolayersfixedattheirbulkpositionsandthedistancebetweenadsorbedBDP1moleculeswaslargerthan15Åwithsurfacecoverageofabout7%.Toavoidinterlayerinteractions,a30Åvacuumlayerwasimplementedinthez-direction.OnlythegammapointwasusedforthesamplingoftheBrillouinzoneforthelargesystem65.Toexaminethesurfacecoverageeffects,wereducedtheAu(111)unitcellto(6×6)and(3×5)surfacesusinga2×2×1and3×3×1k-pointmesh65,resultinginminimumdistancesbetweenBDP1moleculesof8.72Åand2.51Åwithmolecularsurfacecoverageof12%,and30%,respectively.

Theadsorptionenergy(Ea)wascalculatedusingthefollowingformula:

Ea=Esub−Eslab−Emole

whereEsubrepresentsthetotalenergyoftheadsorbedsystem,EslabdenotestheenergyoftheAu(111),andEmoleistheenergyoftheisolatedmolecules.

ThemolecularsurfacecoverageisthemaximumlengthofthemoleculemultipliedbythewidestpointdividedbythesurfaceareaoftheAu(111)surface.

MolecularorbitalanalysesandCDspectrumcalculationsforisolatedBDP1moleculeswereperformedusingtheGaussian09program66.AllcalculationswithinthisprogramutilizedtheB3LYPfunctional67,68.The6-311G**basisset69–72wasappliedtoallatoms(non-metallic)forstructureoptimizationandorbitalanalysis,followedbyCDspectrumcalculationsusingthe6-311++G**basisset73–75.TheCDspectrumwasanalyzedusingMultiwfn3.8software76.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The presented study provides an exploration of interfacial charge transfer and its influence on chiral optical properties at the plasmon-molecule interface. The manuscript suffers from poor articulation of the novelty and experimental design. In addition, the results and data are not convincing or need improvement in terms of the clarity. The detailed comments are proposed for the author to consider to further improve clarity and impact of the findings:\n1. In Figure 1, the authors present results for Complex1 and AuNP + BDP1, yet the distinction between AuNP+BDP1 and Complex1 is not clearly described in the text. By the preparation methos Complex1 is actually the AuNP+BDP1. The authors need to elaborate on the differences between these two samples.\n2. Figure 1C: The hydrodynamic size of small sized AuNPs should not be measured by DLS (Intensity) since the scattering is weak and it gives very large values. It’s unclear how the authors have measured the hydrodynamic size based on intensity? The authors need to clearly describe this aspect.\n3. BDP-based complexes have been shown to form aggregate (nanoparticles) indicating they are not soluble in water. It’s unclear how the surface modification of AuNPs with the BDP-complexes could lead to stable nanoparticles.\n4. Chemical modification of BDP molecules will lead to the formation of a different molecule. Although the orientations are different, the observed results cannot be solely attributed to different molecular orientations on surface. The authors should elaborate more in details about this observation.\n5. BDP molecules in water was used as a control, however, like metal-enhancement effects (e.g. metal-enhanced fluorescence), the authors should use silica nanoparticles with the same size as the control.\n6. While the authors examine size effects using AuNPs with diameters ranging from 3 nm to 16 nm, the observed alterations in plasmonic effects seem subtle. AuNP with 3 nm are technically nanoclusters. This means they have unique optical properties. I believe the size reported for AuNPs is not reliable in this work. Increasing the nanoparticle sizes to 25 or even 50 nm could provide a clearer observation of plasmonic field enhancements and Stark effect variations. The authors should consider investigating larger size of AuNPs for their plasmonic effect. In addition, to confirm the hypothesis, using silver nanoparticles with comparable sizes is suggested.\n7. Raman spectra have been obtained on quartz plate. Aggregation can lead to electromagnetic field enhancement and different aggregation degrees (due to uncontrolled conditions) could lead to different degrees of hotspot formation. The authors should perform the Raman measurement in liquid/solution phase to ensure the consistent and reproducible results.\n8. The authors should perform the wavelength-dependent Raman spectroscopy to prove and validate the charge-transfer experimentally.\n9. The authors have emphasized the interfacial charge-transfer as the dominant mechanism influencing chiral optical properties, with near-field electromagnetic coupling playing a secondary role. A control experiment isolating these mechanisms, such as comparative studies using systems lacking CT effects, could further bolster this claim.\n10. The increase in short-wavelength CD intensity with larger AuNPs was noted by authors. Could this be partially attributed to higher grafting capacity of larger particles, allowing more BDP1 molecules to bind, thus resulting in larger enhancement rather than electromagnetic field enhancement?\n11. The claim that the Stark effect is negligible is compelling but might benefit from additional validation. Variations in local electric field intensities due to larger nanoparticle sizes could still influence CD spectral features. Incorporating EM modelling for different sizes might strengthen this argument.\n12. Minor comment: the authors need to include the detailed synthesis method of AuNPs in the manuscript.", "reviewer_2": "The manuscript, titled \"Delocalized Chiral Molecular Excitations and Interactions Originating from Charge Transfer/Exchange at the Plasmon-Molecule Interface\", presents an intriguing study on chiral molecule-plasmon nanoparticle complexes with a focus on interfacial charge transfer (CT) effects. The experimental approach combining ultrafast spectroscopy, circular dichroism (CD), and Raman spectroscopy with quantum chemical calculations is thorough and well-executed. However, the manuscript requires substantial revisions to improve clarity, data presentation, and interpretation.\n1. The synthesis procedures for gold nanoparticles (AuNPs) of different sizes are not described adequately. The manuscript must specify the surfactants and exact conditions used during the synthesis.\n2. Include transmission electron microscopy (TEM) images of AuNPs to verify and compare their size distributions with the reported values. This is critical for reproducibility and assessing the uniformity of nanoparticle preparation.\n3. A dispersion stability test is necessary for the 3 nm AuNPs, as several conclusions hinge on their structural and optical integrity. Dynamic light scattering (DLS) over time or zeta potential measurements should be provided to support stability claims.\n4. The spectral splitting observed in Figure 1e (3 nm) but absent in Figures 1f-g (7 nm and 16 nm) raises questions. Were the surface areas of all nanoparticles normalized for chiral molecule adsorption? If yes, the authors should clarify why splitting occurs only for smaller nanoparticles. Provide a quantitative explanation, potentially involving localized surface plasmon resonance or molecular packing.\n5. The authors attribute the surface-enhanced Raman scattering (SERS) enhancement to CT excitation. However, contributions from local electromagnetic field effects cannot be ruled out. Raman spectra of the pure chiral molecules under identical excitation conditions should be included for comparison.\n6. Provide a more detailed analysis of how CT transitions lead to specific enhancements in SERS signals, including vibrational mode assignments.\n7. The rationale for using BDP3 as a chiral molecule is unclear, given its lack of orientational difference compared to BDP2. Explain its selection and its reduced chirality strength relative to BDP1 and BDP2. Additional molecular models or structural analysis supporting these differences would be beneficial.\n8. The difference in hot carrier lifetimes between AuNPs and the complexes is only marginally addressed. Include the full set of fitting timescales and associated errors for the transient absorption decay curves (Figure 3c) to provide quantitative evidence for chemical interface damping.\n9. If transient absorption spectra or other techniques detect features corresponding to reduced species, these should be explicitly discussed. This will strengthen claims regarding hot electron transfer.\n10. The possibility that plasmonic heating contributes to CD spectral broadening should be tested through temperature-dependent CD measurements of the chiral molecules. This would help disentangle thermal effects from CT contributions.\n11. The spectral splitting for complexes with different molecule-to-nanoparticle ratios may suggest aggregation. Perform DLS measurements both immediately after sample preparation and after 30 minutes to confirm aggregation behavior.\n12. The manuscript discusses Frenkel and CT mixing but lacks direct evidence linking these mechanisms to observed excitonic couplings. Provide additional data or calculations (e.g., molecular orbital overlap) to substantiate these claims.\nWhile the manuscript addresses a significant topic in plasmon-molecule interactions, its conclusions are undermined by gaps in experimental details and unclear mechanistic explanations. Addressing the points above will substantially strengthen the study's scientific rigor and clarity.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_4": "This manuscript extends the research by the authors into chirally-sensitive plasmonic nanoscale systems by investigating the role of charge transfer at the interface between the metal surface and adsorbed electronically resonant chromophores in the resonance enhancement of chiral spectroscopic signals. As the authors relate in the manuscript, the development of chiral nanoplasmonic materials promises great opportunities for controlling light-matter interactions at the molecular scale and so has generated much interest among scientists and technologists, but the complexity of the mechanisms involved have proven difficult to untangle. The potential mixing of electronic and vibrational states of analyte and reporter molecules with the oscillating intense electric fields of the plasmons and how these effect circularly polarized photons is a fascinating yet often-confusing field of research. New insights into the underlying mechanisms are valuable and noteworthy, and this manuscript is likely to be of great interest to other researchers in the field as well as the general scientist.\nThe work conducted describes a well thought-out strategy of multispectroscopic analyses with DFT calculations on related nanocomplexes. The application of CD obviously enables insights into the chiroptical responses of these complexes but it is notable that the authors support the CD measurements with SERS and transient absorption measurements to characterize the nanoparticle complexes. All measurements, and the DFT calculations, appear to be reliably performed and the analysis of the results leads to well supported conclusions. The methodology appears sound to me, and while interpretation of individual results can be complicated the combination of techniques used has allowed the authors to generate clear and useful conclusions. The extensive SI file should provide sufficient guidance for other researchers to attempt to replicate the results presented.\nHowever, the manuscript is not an easy read as the grammar and terminology used are dense in many places, which does not help to clarify this complex topic to the average reader. The standard of formal English in the manuscript is very high, but the descriptions used are very technical and are more relevant to a a more specialist journal than Nature Comms. The manuscript also seems to be quite long, over 5800 words, for a Nature Comms paper and we recommend reducing the length of this manuscript and simplification of some of the descriptions to improve readability for a broader audience. In particular, Figure 1 could potentially be moved into Supplementary Information along with the detailed attendant discussion. We recommend publication of this work as the research is important and will provide valuable guidance to other scientists in this field, but for Nature Communications the manuscript should be abbreviated and the descriptions should be simplified to make it more accessible to nonspecialists.", "reviewer_5": "In this study, Jiang and coworkers investigate the circular dichroism (CD) response of chiral molecule/plasmonic nanoparticle (NP) complexes to analyze the distinct roles played by near-field enhancement, NP/molecule charge transfer, and intermolecular exciton coupling.\nThese effects are challenging to disentangle. This study systematically addresses each of them by varying the properties of the metal/molecule complexes, such as NP size, adsorption orientation, and molecular concentration. The systems are characterized using optical and CD spectroscopy (including time-dependent evolution), Raman scattering, surface-enhanced Raman scattering (SERS), and transient-absorption spectroscopy. Additionally, density functional theory (DFT) calculations are performed for one of the three complexes under investigation, providing some theoretical support for the experimental results.\nThe CD signals of the molecule-metal complexes differ significantly from the sum of the signals of their individual components across all three cases. For complexes 1 and 2, this discrepancy arises primarily from molecule/NP charge transfer, with minimal contributions from local field enhancement. However, for complex 3, the CD signal is attributed to intermolecular excitonic coupling.\nDFT calculations, performed at the PBE level, corroborate these findings by demonstrating hybridization between the molecule and metal orbitals in complex 1.\nThe paper presents significant and relevant results, which merit publication in Nature Communications. However, the Authors should address the following points:\nMolecule/Metal Charge Transfer and Exciton Delocalization (Page 6):\nHow and why does molecule/metal charge transfer influence exciton delocalization? Could additional calculations clarify this mechanism?\nComplex 3: Charge Transfer:\nApparently charge transfer (CT) is either absent or ineffective for complex 3. Could the Authors confirm this observation with DFT calculations?\nCD Signal Origin in Complex 3:\nThe origin of the CD signal in complex 3 is not as thoroughly analyzed as in complexes 1 and 2. If the CD signal arises from intermolecular interactions, could this effect also be observed in the absence of Au NPs? Calculations or measurements of CD spectra of molecular assemblies without NPs could provide insight. Perhaps time-dependent density functional theory (TDDFT) calculations would be useful for addressing this point.\nFurther DFT Calculations for Complex 3:\nAs complex 3 displays a strikingly different behavior compared to the other systems, additional DFT calculations would be highly desirable to look at the differences with the other cases.", "reviewer_6": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "We sincerely appreciate your insightful feedback and suggestions below and apologize for the lack of clarity in the manuscript. We have carefully addressed your concerns regarding the strength of the study by incorporating substantially more theoretical calculations and experimental results. These new data, which are detailed in the revised manuscript and Supplementary Information, can significantly enhance the robustness of our conclusions. We have also comprehensively revised the manuscript, including the title, statement of the scientific questions, data discussions, and conclusions, to more clearly articulate the novel and original contributions of our research.\n[... point-by-point responses to all reviewers ...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed some of the comments, but not all of them. The key concern still remains in terms of the size-dependent, and laser excitation-dependent SERS results. The authors are suggested to re-visit their SERS results, and the corresponding discussions. More specifically,\n1. The authors should explain how the 16 nm AuNPs generate the SERS of their molecules. In theory, Au can only be a good plasmonic metal for SERS when the long wavelength (typically longer than 600 nm) is applied. It's a surprise that distinct SERS spectra were detected on 16 nm AuNPs at 532 nm, but not at 633 nm laser excitation. The authors are suggested to read the book chapter (Chapter 1.6-Choice of metals) in the book published by Elsevier (ISBN:978-0-12-821121-2). In this reviewers' opinion, the strong SERS signals detected at 532 nm are most likely from the chemical enhancement, rather electromagnetic mechanism.\n2. The authors need to explain the SERS shown in Fig. R15 and Fig. R16.\n3. In Fig. R17, there are no detectable SERS peaks of MBA on AuNPs for both 532 nm and 633 nm. It's acceptable that Au normally won't generate Raman enhancement at 532 nm. However, it's unclear why there were not any SERS peaks detected on AuNPs-MBA at 633 nm. It should be pointed out MBA is a very typical Raman-active molecules, and researchers have employed MBA as Raman reporter molecules for different applications.\n4. It's unclear what's the optimal size of AuNPs for SERS results. The suggestion to increase the nanoparticle sizes to 25 or even 50 nm was not well taken. The argument about the aggregation of large nanoparticles were not valid because the small AuNPs are not the optimal choice for SERS results. The authors should consider investigating larger size of AuNPs for their plasmonic effect, which could provide a clearer observation of plasmonic field enhancements and Stark effect variations.", "reviewer_2": "First, I would like to commend the authors for their thorough and thoughtful responses to my comments. Their effort is truly commendable. I recommend acceptance of the manuscript, pending the correction of a minor error.\n1. References 19 and 61 are identical. The authors should replace one of them with same groups recent manuscript, Plasmon-Induced Hot-Hole Generation and Extraction at Nano-Heterointerfaces for Photocatalysis, as its discussion on metal-molecule interfaces aligns well with the current work.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_5": "The manuscript has been thoroughly revised and the points raised by the Referees have been addressed providing many interesting additional measurements and calculations.\nOn my opinion the paper is now ready for publication."}, "author_response": "We sincerely appreciate the insightful comments. Note that our preliminary studies focused specifically on SERS characterization of 3 nm complexes. In response to your valuable feedback, we have conducted additional SERS investigations on 16 nm complexes. [...] We have also thoroughly reviewed and corrected the error [in references], followed by a comprehensive review of the entire document to prevent any recurrence of similar issues."}, {"round": 3, "reviewer_comments": {"reviewer_1": "The authors have addressed all the reviewers' comments. The manuscript reads publishable."}, "author_response": ""}, {"round": 4, "reviewer_comments": {"reviewer_7": "I have carefully read the author’s response letter as well the revised manuscript. This revised version includes updated data and discussion on BDP3. The authors have performed CD, Raman, TA spectroscopy, and DFT calculations on the new Complex 3 using standard and appropriate methodologies. In my view, this new set of results continues to support the existence of interface charge transfer.\nIn their response letter, the authors provided a clear, point-by-point comparison of the key data for the original BDP3 and the new molecule. Based on this comparison, I agree that the core conclusion—linking interface charge transfer to the observed chiroptical response—remains valid.\nThe interpretation of the TA data is also reasonable. A recent study (Nature Communications, 15, 445, 2024) reported a similar phenomenon in which interface charge transfer led to a shortened electron–phonon lifetime, consistent with the explanation offered here.\nAnother reviewer raised a valid concern that the TA results could be significantly affected by the solvent. On this point, I note that the fitted lifetimes for the control gold nanoparticles associated with the new Complex 3 differ considerably from those used with Complexes 1–2, particularly at 575 nm (Fig. 3d and 3f). This suggests that the authors likely considered solvent effects by employing nanoparticle controls dispersed in different solvents corresponding to each complex.\nSince the main text and Supporting Information specify that all new BDP3-based samples are dissolved in DMF, I recommend that the authors also indicate the solvent used for the corresponding nanoparticle controls (e.g., DMF or aqueous solution) in the figure captions for clarity.\nWith the addition of this minor clarification, I find the work sound and suitable for publication."}, "author_response": "Thank you for your insightful comment regarding the solvent details of nanoparticle controls in the figure captions. We have clarified the use of DMF as follows: 1) Added a statement in the caption of Figure 3. 2) Added a clarification in the relevant section of the Supplementary Information. [...] We confirm that the manuscript has been updated accordingly."}]

Decision letter