Enhanced Near-Infrared Emission from Carbon Dots by Surface Deprotonation - Liu et al. - 2021 - Unknown

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pubs.acs.org/JPCLLetterEnhancedNear-InfraredEmissionfromCarbonDotsbySurfaceDeprotonation##EnshanLiu,TaoLiang,ElenaV.Ushakova,BingzheWang,BohanZhang,HuiqunZhou,GuichuanXing,ChunmingWang,ZikangTang,*SongnanQu,*andAndreyL.RogachCiteThis:J.Phys.Chem.Lett.2021,12,604−611ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Carbondots(CDs)withefficientexcitationandemissionindeep-red/near-infrared(NIR)spectralrangeareimportantforbioimagingapplications.Herein,wedevelopasimpleandeffectivemethodtosignificantlyenhanceboththeabsorptionandemissionofCDsindeep-red/NIRbysuppressingnonradiativechargerecombinationviadeprotonationoftheCDsurface.Ascomparedtoaqueoussolutionsatroomtemperature,NIRemissionofCDsinN,N-dimethylformamideandglycerolexperiencea50-and70-foldincreaseat−20°C,respectively,duetoenhanceddeprotonationabilityandviscosity.OnthebasisoftheadjustableNIRfluorescenceintensityofCDs,multileveldataencryptionintheNIRregionisrealizedbycontrollingthehumidityandthetemperatureofaCD-inkstampedpaper.wingtotheirattractiveopticalproperties,lowcostandphotothermalconversionefficiency,leadingtolowPLQYinO5,14−16biocompatibility,luminescentcarbondots(CDs)havetheNIRregion.Therefore,itisofprimaryimportancetoemergedaspromisinglight-emittingmaterialsforvariousstudyandunderstandthefactorsaffectingthePLemissionand12applicationssuchasoptoelectronics,photocatalysis,biosens-thephotothermalconversionofCDsinthedeep-red/NIR3,4ingandbioimaging.TherehavebeenalotofreportsonCDsregion,inordertodesignCDswithenhancedemissioninthiswithahighphotoluminescencequantumyield(PLQY)inthespectralrange,andtosuppresstheenergylossesinthe1,2,4visiblespectralregion.Longerwavelengthemissioninsamples.ItisknownthatthesurfaceofCDsoftencontainsdeep-redandnear-infrared(NIR)spectralregionsareessentialabundant−OHgroups,buttherewereonlyafewstudiesforinvivobiologicalimaging,wherebothtissueautofluor-concerningtheimpactsoftheprotonationprocessatCDescenceandlightscatteringareminimized,thusimprovingsurfaceontheirenergystructure.175,6DownloadedviaBUTLERUNIVonMay16,2021at14:10:43(UTC).bothimagingcontrastandspatialresolution.SeveralgroupsRecently,wereportedthesynthesisofNIRemissiveCDshavereportedonCDswithadeep-redand/orNIRemissions,throughasolvothermalreactionindimethylsulfoxide7−9whichwereexcitedbylightinthegreenspectralregion.(DMSO)fromtwocommonprecursorscitricacidandurea,Heteroatomdoping,sizecontrol,surfaceengineering,andwhichexhibitedadominantabsorptionbandat605nmwithacontrolofthechemicalenvironmentofCDswereusedtoshoulderat650nm.5Under655nmexcitation,theaqueousSeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.modulateabsorptionbandsandNIRemissionofCDs.Bietal.solutionoftheseCDsshowedaNIRemissionpeakat720nmhavereportedafull-rangeUV−Vis−NIRemissiveCDsbywithaverylowPLQYof0.2%.Inthiswork,wereportasimple10performingFandNcodoping;theiroptimumexcitationandeffectivemethodtosignificantlyenhanceboththewavelengthwasaround550nmwithPLQYof9.8%.ChaoetabsorptionandemissionoftheseCDsindeep-red/NIRregional.synthesizedCDsfromo-phenylenediaminethroughaone-bysuppressingnonradiativechargerecombinationviastephydrothermaltreatment,whichshowedmulticolordeprotonationoftheCDsurface,whichhasbeenaccom-emissionwithanexcitation-independentbehaviorindifferentplishedbychangingthesolventdeprotonationabilityand11solvents.Ourgrouprealizedfull-coloremissiveCDsbyviscosity.Theemergeddominantabsorptionbandat650nmemployingthreedifferentsolvents,wheretheemissioncolorandenhancedNIRemissionwithPLQYreachingupto4%12wascorrelatedtotheCDsize.WehavealsodemonstratedNIRabsorptionandenhancedNIRemissionofCDswhichhasbeenrealizedthroughthesurfaceadsorptionofelectron-Received:November12,2020acceptorgroups.13However,thereisstillalackofefficientAccepted:December23,2020syntheticmethodstomovethemainabsorptionbandofCDsPublished:December31,2020todeep-redorNIRregionsandtorealizeanefficientdeep-redorNIRlightexcitedNIRemission.Furthermore,mostofthereportedCDswithdeep-redorNIRabsorptionexhibitedhigh©2020AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.jpclett.0c03383604J.Phys.Chem.Lett.2021,12,604−611

1TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure1.(a)Absorptionand(b)PLspectra(excitationat655nm)ofdiluteaqueoussolutionsofCDsatdifferentpHvalues(concentration:50ppm).Thedashedlinein(b)showsthepositionofthePLpeakinH2OatpH=7.(c)FT-IRspectraofCDsatdifferentpHvalues.(d)TemperatureevolutionsoftheaqueoussolutionsofCDs(100μg·mL−1)atdifferentpHvaluesunder655nmlaserirradiationatapowerdensityof1W·cm−2.Figure2.Schematicillustrationoftheprotonation/deprotonationoftheCDsurface.and6%weredetectedintheCDsglycerolandDMSOaqueoussolution,CDsexhibitthemainabsorptionbandatsolutionsatroomtemperature,respectively.ComparedtoCD605nmwithashoulderbandat665nm,andaNIRemissionaqueoussolutionatroomtemperature,a50-and70-foldpeakedat715at655nmexcitation.Inacidicaqueoussolution,increaseoftheNIRemissionhasbeenobservedfortheCDsintheshapeoftheabsorptionspectrumoftheCDsisnearlytheN,N-dimethylformamide(DMF)andglycerolsolutionsatsame,whiletheintensitiesofboththemainabsorptionband−20°C,respectively.BasedontheenvironmentcontrollableandNIRemissionareweakened.Incontrast,inalkalineNIRemissionofCDs,multilevelfluorescenceencryptionwasaqueoussolution,theabsorptionintensityoftheCDsisrealizedbychangingthehumidityandtemperatureintheCD-increasedandthemainabsorptionbandbecomesred-shiftedinkstampedpaper.to645nm,whiletheNIRemissionisalsoenhancedbutCDsweresynthesizedaccordingtothepreviouslypublishedslightly(∼10nm)blue-shifted.TofurtherverifythepHeffectprocedure,fromcitricacidandureaviathesolvothermalontheCDsurfacechemicalgroups,FT-IRspectrawere5methodinDMSO.AsdemonstratedbyX-rayphotoelectronmeasuredonsamplesobtainedbyfreeze-dryingofCDaqueousspectroscopy(XPS)andFourier-transforminfrared(FT-IR)solutionsatpH=7andpH=9.AsshowninFigure1c,themeasurements,theseCDscontainedhydroxyl,amide,carbon-broadbandat3000−3500cm−1consistsof2peaksataboutyl,andaminegroupsatthesurface,whicharesensitivetopH3430and3200cm−1,whichcanbeassignedtoν(O−H)andνinaqueoussolutionduetotheprotonation/deprotonation(N−H)vibrationsinthearomaticring,respectively.Theprocesses.Astheprotonationanddeprotonationcanincreaseintenseandbroadpeakataround1650cm−1canbeattributedordecreasethepopulationofthe-NH2and−OHgroupsattotheamidegroupatthesurface,andν(C−N)andν(C−C)theCDsurface,respectively,potentialchangesofopticalvibrationsinthearomaticring.ComparedtoCDsatpH=7,propertiesofCDsindiluteaqueoussolutionsatdifferentpHtheabsorptionbandofCDsatpH=9at3430cm−1isvaluesweretested.Figure1aandFigure1bshowabsorptionincreased,whilethebandat3200cm−1isdecreased,suggestingandPLspectra(at655nmexcitation)ofCDsinaqueousthattheincreaseofpHresultsindeprotonationofCDsurfacesolutionsatthreedifferentpHvaluesof5,7,and9.InaneutralwhichinturnleadstoimprovementofthePLsignal.Asshown605https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

2TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetteraTable1.OpticalCharacteristicsofCDsinDiluteH2O,Glycerol,Ethanol,DMSO,andDMFSolventssolventprotic/aproticrelativepolarityabspeak(nm)PLpeak(nm)PLlifetime(ns)PLQY(%)viscosity(10−3Pa·s,25°C)H2O16657100.800.20.89glycerolprotic0.8126707051.284.0934ethanolprotic0.6546606901.782.21.07DMSOaprotic0.4446706852.325.91.99DMFaprotic0.3866656852.424.90.79aThemassconcentrationoftheCDsinallmeasurementswere0.05mg/mL.Figure3.(a)UV−visibleabsorptionand(b)PLspectra(excitedat655nm)ofCDsinH2O,glycerol,ethanol,DMSO,andDMFsolvents(concentration:50ppm).ThegapinthePLspectraofethanol,glycerol,andH2O)at650−670isduetosubtractionofthepeakfromtheexcitationsource.(c)PLdecaycurvesofCDsinH2O,glycerol,ethanol,DMSO,andDMF,monitoredat700nmunder640nmexcitation.IRFstaysforinstrumentalresponsefunction.(d)Peakpositionsofthelowestenergyabsorption(solidsquares)andPL(solidcircles)ofCDsderivedfromthedataprovidedinframes(a)and(b),withthesamecolorcodingfordifferentsolvents.Thedashedlinesareguidesfortheeye.(e)PLQY(solidtriangles)andPLlifetimes(hollowtriangles)ofCDsplottedvstherelativesolventpolarity,thecolorcodingindicatetherespectivesolvent.(f)NIRfluorescenceimages(under655nmexcitation,top)andbrightfieldimages(bottom)underdaylightofCDsindifferentsolvents.inFigure2,atacidicpH,theprotonationrendersthesurfaceofability,polarity,andviscosity.Thedataobtained,alongsidetheCDswithlesselectron-richgroups,whileatthebasicpH,withthecharacteristicsofthesolventsused,aresummarizedinthedeprotonationprocessleadstotheappearanceofmoreTable1.PanelsaandbofFigure3showabsorptionandelectron-richsurfacegroups.emissionspectraofCDsindifferentsolventsatroomAswasreportedinourpreviouswork,theCDsexhibithightemperature.UponchangingsolventsfromH2OtoDMF,photothermalconversionefficiencyinneutralaqueousbothabsorptionandPLspectrabecomebetterstructured,5solution,equalto59%.ThephotothermalbehaviorofCDswhichagreeswiththeobservationsfortheorganicdyes,whereinaqueoussolutionsatdifferentpHvaluesweretestedandareboththeH-bondingandtheprotonationoftheluminophore’ssummarizedinFigure1d.Under655nmlaserirradiationatagroupsmaycausebroadeningandblurringofpeaksinthepowerdensityof1W·cm−2for10min,thefinaltemperatureofabsorptionandemissionspectra.18Inproticsolvents(glycerolthe100ppmofCDaqueoussolutionsatpHequal5,7,and9andethanol),thePLQYsofCDsreach2.2%and4.0%,haveincreasedfrom27°Cto63,61,and53°C,respectively,respectively,whichismorethan20-foldenhancementoftheirindicatingdecreasedphotothermalperformancewithincreas-PLQYinH2O(0.2%).BothDMFandDMSOareaproticingpH.ConsideringthatthemaindifferenceoftheCDsurfacesolventswithgooddeprotonationabilityduetotheirelectron-atlowandhighpHvaluesisthepopulationoftheamine,acceptorgroupsCO/SO;theNIRemissionofCDsincarbonylgroups,andH-bonding,itcanbeinferredthatthethesetwosolventsisfurtherenhanced,withPLQYsreachingdecreasedH-bondinganddeprotonationprocessofCDsat4.9%inDMFand5.9%inDMSO.ThePLdecaycurvesforbasicpHresultsinalowervibrationalenergydissipation,NIRemissionoftheCDsindifferentsolventsmonitoredatwhichmightbethereasonfortheenhancedNIRemission.700nmunder640nmexcitationareshowninFigure3c.TheTofurtherrevealthedetailsofinteractionofCDswiththeaveragePLlifetimeofCDsinaproticsolvents(DMFanddifferentchemicalenvironments,theiropticalresponseswereDMSO)islongerthaninproticsolvents(ethanolandmeasuredinasetofsolventswhichdifferindeprotonationglycerol),whichwellcoincideswiththeobservationthat606https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

3TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure4.ProposedenergydiagramsoftheCDs:(a)duringprotonation/deprotonation,(b)withtheeffectofsolventpolarity,(c)inH2Osolution,and(d)inDMFsolution.S*coreandS*surfareenergystatescorrespondingofthecore(I1inFigure5a−c)andsurface(I2inFigure5a−c)absorptionbands,respectively.Abs,Fluo,andknrdesignateabsorption,emission,andnonradiativedissipationofenergy,respectively,withthelastshownbydashedlines.Theinternalconversionisshownbywavylines.Thethicknessofthelinescorrespondstotheanticipatedintensityofthetransitions.Figure5.AbsorptionspectraofCDs(50ppmconcentration)in(a)H2O,(b)DMF,and(c)glycerolatdifferenttemperatures.Dashedlinesindicatethepositionsoftwomajorabsorptionpeaks(I1at∼605nmandI2at∼665nm).(d)I2/I1ratioagainsttemperatureforthe50ppmofCDsinH2O,DMF,andglycerol.PLspectraof50ppmofCDsin(e)H2O,(f)DMF,and(g)glycerolatdifferenttemperatures,measuredat655nmexcitation.(h)TemperaturedependenceoftheNIRemissionintensityof50ppmofCDsinH2O,DMF,andglycerol.deprotonationoftheCDsurfaceresultsinincreasedPLAtthesametime,acleartrendofshiftingthePLpeakofintensity.AplausibleenergystructureofCDsdependingonCDstowardlowerenergieswithincreasingsolventpolarityistheprotonation/deprotonationprocessispresentedinFigureobservedinFigure3d,whichisdifferentfromanalmost4a.Theexcitedstateofthesurface(S*surf)canbeshiftedtounchangedpositionoftheirabsorptionpeak.Thisimpliesthatlowerorhigherenergyduringtheprotonationordeprotona-thepolarityofthesolventaffectsthelowestexcitedstatefrom18tionprocess,respectively.DuringtheCDsurfacedeproto-whichtheradiativerecombinationoccurs,whichisillustratednation,theenergygapbetweentheexcitedstateofthecoreintheenergystructurediagrampresentedinFigure4b.After(S*core)andtheexcitedstatesofthesurface(whicharerelatedabsorptionofthephoton,arapidinternalconversionoccurstotothesolventchange)decreasestogetherwithnonradiativethelowestexcitedenergystate,S*surf.Theexcitedstateisthenenergydissipation,resultingintheincreaseofPLQYaswasstabilizedbythepolarsolventmoleculesthroughreorientationobservedforCDsinaproticsolvents(Figure3e).oftheirdipolesandrelaxationaroundtheexcitedstate,which607https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

4TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure6.TAspectraofCDsin(a)H2Oand(b)DMFatindicatedtimesdelays,afterexcitationatλpump=400nm(1kHz,50fs)withanexcitationdensityof5.0μJcm−2.BleachsignalkineticsoftheCDsin(c)HOand(d)DMFforλ=400nmandprobewavelengthsof600nm(black2pumpsymbols/lines)and680nm(redsymbols/lines).Dotsareexperimentalpoints,andsolidlinesarefittinglines.resultsinthedecreaseoftheenergyoftheexcitedstatealmostunchangedabsorption(Figure5d).Itisworth(S*surf).Withtheincreaseofthesolventpolarity,thiseffectmentioningthatforCDsinglycerolsolution,themainPLbecomesstronger,leadingtotheobservationofthePLpeakshiftsfrom705to685nmupondecreasingtemperature,18emissionatlowerenergies.BothPLQYandtheaveragePLwhichisaccompaniedbyanalmost8-foldenhancementandlifetimeofCDsexhibitalineardependenceonthesolventappearanceofthelowerenergybandintheemissionspectrum,polarity,asshowninFigure3e.ItisworthmentioningthatforwhichthenhasashapesimilartothatofCDsinproticCDsinglycerolsolutionthePLQYbreaksoutfromtheabove-solvents.Theseobservationsarecorrelatedwiththosementionedlineardependenceandislargerthanexpectedobservedfororganicfluorophores,whoseemissionsshiftto18accordingtothePLlifetimevalue.Thisobservationcanbeshorterwavelengthswithatemperaturedecrease.Attheexplainedbytakingintoaccountthelargevalueoftheglycerolsametime,asatlowertemperatures,thesolventsbecomemoreviscosity(Table1),whichfavorssuppressionofthevibrationalviscous(FigureS1),thetimeforthesolventreorientationmotionsand,hence,nonradiativelossesinthesample.Thisincreases,andtherateKSinFigure4bdecreases,whichmayresultsintheincreaseofthePLQYofCDinglycerol.Figure3falsoaffecttheenergystructureofCDs.ThiseffectissimilartoshowsthebrightfieldandNIRimagesoftheCDsindifferentthedecreaseofthesolventpolarity,whichisinagreementwithsolvents,whicharewellconsistentwithvaluesofPLQYshownchangesofabsorptionandthePLpeakpositionsshownininFigure3e.Figure3d.SincethevibrationsofsurfacegroupsofCDs,suchasamine,Theexcited-statedynamicsofCDsinteractingwithdifferentcarbonyl,andamide,andtheirinteractionswithsolventaresolventswerefurtherinvestigatedviatransientabsorptionsensitivetothetemperatureoftheenvironment,temperature-(TA)spectroscopymeasurementsperformedunderfemto-dependentmeasurementsoftheabsorptionandNIRemissionsecondpulseexcitationat400nm.Inaqueoussolution,CDsspectraofCDsinH2O,glycerol,andDMFwerecarriedoutexhibitasingleground-statebleach(GSB1)peakcenteredat(Figure5).FortheCDsinH2O,uponincreasingthe600nmwhichisrelatedtotheI1absorptionband(Figure6a).temperaturefrom10to80°C,theabsorptionbandI1atFollowingthetimeprofileat600nm,asshowninFigure6c,605nmgraduallydecreased,whiletheabsorptionbandI2atthisinitiallypopulatedstatetheexcitedstateoftheinner665nmincreased,whichsomewhatcontradictsthecommoncarboncoredeactivatesrapidlywithin1.54±0.52ps,andobservationthatthePLintensitytendstodecreaseathigharound90%ofitsinitialpopulationdepopulatesthrough19temperatures.ThereasoncouldbethattheH-bondingnonradiativerelaxation,i.e.,thevibrationalmotions.TheweakbetweenH2Omoleculesandthesurfacecarbonylgroupsoflong-livedstatewithalifetimeof804.00±247.71psisCDsmaybecomeweakenedathighertemperatures,leadingtoassignedtotheexcitedstateoftheCDsurface(I2absorptionalowerdegreeoftheprotonationoftheCDsurface,whichisband).AsfortheCDsinDMF,asshowninFigure6b,afterthenaccompaniedbyanincreaseoftheabsorptionbandat665theinitialexcitationoftheCDinnercore(GSB1at600nm),anm,andtherelatedNIRemissionat705nm.TheI2/I1ratioofbleachingfeaturearound680nm(GSB2)ascribedtoCDtheabsorptionpeaksat665nm/605nmisgiveninFigure5d.surfacestatearisesduetotheenergytransferprocessfromtheFortheCDsinDMFandglycerolsolvents,theoppositeeffectexcitedstateofthecore(I1absorptionband).Thisenergyisobserved:theNIRemissionintensityincreasedwithtransferprocessisratherfast,withalifetimeof0.38±0.01ps.decreasingthetemperature(Figure5h),accompaniedbyThebleachingfeatureoftheinnercarboncore(GSB1)608https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

5TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure7.(a)SchematicdiagramofthemultilevelencryptionsystembasedontheCDink.(b)Brightfield(iandv)andNIRfluorescenceimages(ii−iv,vi−viii)oftheCDpatternexcitedat655nm.Imagesweretakenwithout(i−iv)andwith(v−viii)coverpaper.deactivatestothegroundstatein457.19±185.23ps,andtowhichisduetotheefficientpenetrationofNIRemissionfromthesurfacestate(GSB2)in192.83±9.12ps,asshownintheCDink,whichconstitutesthefirstleveloftheencryption.Figure6d.ThelatterprocesscorrespondstotheenhancedAftersprayingwateronthepatternedpaper(Figure7b-iiiandNIRemission.TheassignmentoftheGSB2tothesurfacestateFigure7b-vii),theNIRemissionfromthepatternisagreeswellwiththesteady-statespectralmeasurementsshownsignificantlyweakenedandcannotbedetectedthroughtheinFigure1a,Figure3a,andFigure5,sincetheabsorptionpeakcoverpaper,whichisduetothequenchingofCDNIRat660−670nmishighlysensitivetothechemicalenviron-emissionbyH2O.TheNIRemissionoftheCDpatternment:H-bonding,protonation/deprotonation,andsolventsensitivetohumiditycanbeencryptedonthesecondlevel.polarity.First,asdemonstratedabove,loweringthetemperaturecanEnergydiagramssummarizingtheproposedmechanismsofincreasetheviscosityofglycerolandincreasetheNIRemissionthephotophysicalprocessestakingplaceintheCDsinintensity.Toprovethis,theCD-inkstampedpaperwasmovedaqueousandDMFsolutionsarepresentedinFigure4c,d,toarefrigeratorandheldat−20°Cfor10min,afterwhichtherespectively.Intheaqueoussolution,afterthefastabsorptionpatterncouldbeagainrecognizedthroughthecoverpaper,astotheexcitedcorestate(S*core),theenergyrapidlydissipatesshowninFigure7b-ivandFigure7b-viii.Thisisthesecondtothegroundstatenonradiatively;onlyasmallpartoftheleveloftheencryption.Thus,multileveldataencryptionbasedenergytransferstothesurfacestate(S*surf)followedbyontheadjustableNIRemissionofCDsbycontrollingrelaxationtothelowestenergystatefromwhichbothradiativehumidityandtemperatureoftheenvironmenthasbeenandnonradiativeenergydissipationsmayoccur.Theradiativerealized.recombinationissuppressedbyvibrationalmotionsandInsummary,wedevelopedasimpleandeffectivemethodtoprotonationoftheCDsurface.FortheCDsinDMFsolution,significantlyenhanceboththeabsorptionandemissionofCDsafterabsorptiontothehighestenergylevels,theexcitationinthedeep-red/NIRregionbysuppressingnonradiativeundergoesatransfertotheS*surfenergylevel,andfromthereitchargerecombinationviadeprotonationoftheCDsurface,dissipatestothelowestexcitedstate,whichliesslightlyhigherwhichhasbeenaccomplishedbychangingthesolventthanthatfortheCDsinaqueoussolutionduetothelowerdeprotonationabilityandviscosity.TheabsorptionbandatpolarityofDMFanditsstrongerdeprotonationability.From630−700nmincreased,andthePLQYoftheNIRemissionthelowestexcitedstate,excitonsrelaxradiativelygivingrisetoreached4%and6%forCDsdissolvedinglycerolandDMSOtheNIRemissionwithalmost25-foldenhancementcomparedsolutionsatroomtemperature,respectively,whichisalargetothatoftheCDaqueoussolution,whichindicatestronglyimprovementcomparedtoonly0.2%PLQYinaqueoussuppressednonradiativerelaxation.solution.ThetemperaturedecreaseledtofurtherenhancementThepeculiarNIRemissionpropertiesofCDsindifferentoftheNIRemissionduetotheincreasedviscosityofthesolventsofferthepossibilityoftheirapplicationinmultilevelsolvent,whichresultedinloweringenergylossesattheCDinformationencryption.Here,theCDssolutioninglycerolwassurface.AscomparedwithCDaqueoussolutionsatroomusedasaninktostampluminescentpatternsonacommercialtemperature,theintensityoftheNIRemissionofCDsinDMFprintingpapertorealizemultipleluminescence-basedandglycerolsolutionsat−20°Cincreased50-and70-fold,encryptions,asillustratedinFigure7a.AsshowninFigurerespectively.Inourspectroscopydataanalysis,weascribe7b,aluminescentpatternofthe“UniversityofMacau”inabsorptionbandsat520−630and630−700nmasbelongingChinesecharactersstampedbytheCDinkcanbeobservedtotheCDinnercorestateandsurfacestate,respectively,withunderdaylightbutitnaturallybecomescompletelyinvisiblethemaincontributiontotheNIRemissioncomingfromthewhencoveredwithaprintingpaper.Under655nmexcitation,surfacestate.OnthebasisofthechangesoftheNIRemissionthepatterncanbeeasilyobservedthroughthecoverpaper,ofCDsdeterminedbychangingenvironment,multilevel609https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

6TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterfluorescenceencryptionwasrealizedbyvaryinghumidityandEngineering,UniversityofMacau,Taipa999078,MacautemperatureoftheCD-inkstampedpaper.OurstudyopensupSARafacileroutetoenhancementoftheCDemissionofCDsandTaoLiang−JointKeyLaboratoryoftheMinistryofprovidesanewprospectforfuturepracticalapplicationsofEducation,InstituteofAppliedPhysicsandMaterialsCDsindataencryption.Engineering,UniversityofMacau,Taipa999078,MacauSAR■CHEMICALSANDMATERIALSElenaV.Ushakova−DepartmentofMaterialsScienceandEngineeringandCentreforFunctionalPhotonics(CFP),CityCitricacid,urea,DMF,DMSO,ethanol,andglycerolwereUniversityofHongKong,Kowloon999077,HongKongpurchasedfromAladdin.H2OwasdeionizedandpurifiedonaSAR;CenterofInformationOpticalTechnologies,ITMOLabconcoWaterProspurificationsystem.AllreagentshadatUniversity,SaintPetersburg197101,Russia;orcid.org/leastanalyticalgradepurityandwereusedasreceivedwithout0000-0001-6841-6975furtherpurification.BingzheWang−JointKeyLaboratoryoftheMinistryof■Education,InstituteofAppliedPhysicsandMaterialsSYNTHESISOFCDSEngineering,UniversityofMacau,Taipa999078,MacauFirst,citricacid(2g)andurea(6g)werereactedat160°CforSAR4hundersolvothermalconditionsin30mLofDMSOandBohanZhang−JointKeyLaboratoryoftheMinistryofthencooledtoroomtemperature.TheacquireddarksolutionEducation,InstituteofAppliedPhysicsandMaterialswasmixedwithtwiceitsvolumeofethanolandthenEngineering,UniversityofMacau,Taipa999078,Macaucentrifugedat8000rmin−1for5min.TheprecipitatewasSARcollectedandfreeze-dried.HuiqunZhou−StateKeyLaboratoryofQualityResearchinChineseMedicine,InstituteofChineseMedicalSciences,■CHARACTERIZATIONUniversityofMacau,Taipa999078,MacauSARUV−visabsorptionspectrawerecollectedonaShimadzuUV-GuichuanXing−JointKeyLaboratoryoftheMinistryof2600spectrophotometer.Steady-statePLspectrawereEducation,InstituteofAppliedPhysicsandMaterialsmeasuredonanOceanOpticsQEpro,andtime-resolvedPLEngineering,UniversityofMacau,Taipa999078,Macauspectra,onaLifeSpec-IIlifetimespectrometer(EdinburghSAR;orcid.org/0000-0003-2769-8659Instruments).FT-IRspectrawereperformedonaBrukerChunmingWang−StateKeyLaboratoryofQualityResearchTensor27FT-IRspectrometer.TAmeasurementswereinChineseMedicine,InstituteofChineseMedicalSciences,performedonanUltrafastSystemHELIOSspectrometerinUniversityofMacau,Taipa999078,MacauSARanondegeneratepump−probeconfiguration.ThelasersourceAndreyL.Rogach−DepartmentofMaterialsScienceandwastheCoherentLegendregenerativeamplifier(100fs,1EngineeringandCentreforFunctionalPhotonics(CFP)andkHz,400nm)seededbyaCoherentVitesseoscillator(100fs,ShenzhenResearchInstitute,CityUniversityofHongKong,80MHz).ThepHvaluesoftheCDaqueoussolutionswereKowloon999077,HongKongSAR;orcid.org/0000-adjustedwithHClorNaOHaqueoussolutionbyprecisepH0002-8263-8141Meter(PHS-25,China).TheviscositydataofallsolventswasCompletecontactinformationisavailableat:collectedonaDiscoveryHR-2hybridrheometer.Thehttps://pubs.acs.org/10.1021/acs.jpclett.0c03383photoluminescencequantumyieldofallnanomaterialswascollectedatroomtemperatureonanEdinburghFS5AuthorContributionsspectrophotometer.#E.S.LiuandT.Liangcontributedequallytothiswork.■AuthorContributionsASSOCIATEDCONTENTS.N.Qudesignedtheexperiments.E.S.LiuandT.Liang*sıSupportingInformationperformedthesynthesisandcharacterizations.B.Z.WangTheSupportingInformationisavailablefreeofchargeatperformedthetransientabsorptionmeasurements.S.N.Qu,Z.https://pubs.acs.org/doi/10.1021/acs.jpclett.0c03383.K.Tang,G.C.Xing,E.S.Liu,E.V.Ushakova,H.Q.Zhou,B.Viscosityevolutions(PDF)H.ZhangandC.M.Wangparticipatedinthedataanalysis.E.S.Liu,T.Liang,S.N.Qu,E.V.Ushakova,B.Z.Wang,andA.■L.Rogachwrotethepaper.AllauthorscontributedtotheAUTHORINFORMATIONmanuscript.CorrespondingAuthorsNotesSongnanQu−JointKeyLaboratoryoftheMinistryofTheauthorsdeclarenocompetingfinancialinterest.Education,InstituteofAppliedPhysicsandMaterialsEngineering,UniversityofMacau,Taipa999078,Macau■SAR;orcid.org/0000-0003-4159-096X;ACKNOWLEDGMENTSEmail:songnanqu@um.edu.moThisworkwassupportedbytheNationalNaturalScienceZikangTang−JointKeyLaboratoryoftheMinistryofFoundationofChina(61922091and91733302),theScienceEducation,InstituteofAppliedPhysicsandMaterialsandTechnologyDevelopmentFund,MacauSAR(0040/Engineering,UniversityofMacau,Taipa999078,Macau2019/A1,0073/2019/AMJ,FDCT/199/2017/A3,andSAR;Email:zktang@um.edu.moFDCT/013/2017/AMJ),theFundfromtheUniversityofMacau(SRG2019-00163-IAPME),theResearchandDevelop-AuthorsmentGrantforChairProfessorFundfromtheUniversityofEnshanLiu−JointKeyLaboratoryoftheMinistryofMacau(CPG2020-00026-IAPME),ResearchGrantEducation,InstituteofAppliedPhysicsandMaterials(MYRG2019-00103-IAPME)fromtheUniversityofMacau,610https://dx.doi.org/10.1021/acs.jpclett.0c03383J.Phys.Chem.Lett.2021,12,604−611

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