光化學(xué)與光功能材料課件

上次課的內(nèi)容光子和分子之間的相互作用（光的吸收過程)躍遷發(fā)生的條件：對稱性；軌道重疊；自選反轉(zhuǎn)激發(fā)態(tài)單線態(tài)和三線態(tài)激發(fā)態(tài)和基態(tài)性質(zhì)之間的區(qū)別3.4激發(fā)態(tài)的失活過程ChemicalreactionDecayofexcitedstatesPhysicalProcessChemicalProcessIntramolecularprocessIntermolecularProcessRadiativeProcessNon-radiativeprocessEnergytransferElectrontransferFluorescencePhosphorescenceInternalconversionIntersystemcrossing3.4激發(fā)態(tài)的失活過程-單分子(分子內(nèi)）反應(yīng)非輻射失活-產(chǎn)生熱熒光(S1-S0)系間竄越(ISC)磷光熒光的定義:磷光的定義:EExcitationNon-radioactive

processFluorescenceS0S1T1ISCPhosphorescenceICS1-S0T1-S0FluorescencespectraandStoke’sShiftStock’sshiftwasaffectedby:

2.…….PhosphorescenceIntensityQuantumyieldLonglifetime;lowquantumyield;

3.4激發(fā)態(tài)的失活過程-雙分子或多分子的過程Excimer(基激締合物)和Exciplex(基激復(fù)合物)A*+A=(AA)*A*+B=(AB)*由于生成的這兩種復(fù)合物,和單獨(dú)的一個(gè)處于激發(fā)態(tài)的分子相比,其更穩(wěn)定.從而發(fā)射譜的峰值位于長波方向,由于結(jié)構(gòu)的柔性,導(dǎo)致發(fā)射峰很寬.生成Excimer和Exciplex的條件:

溶液的濃度足夠大;分子之間具有很強(qiáng)的相互作用;分子是平面的分子.3.4.2.

能量傳遞(energytransfer)D*+A=D+A*Donor;Acceptor3.4激發(fā)態(tài)的失活過程

-雙分子或多分子的過程PerylenediimideZinc(II)PhthalocyanineDonorAcceptor重疊積分——Overlapintegral(J)wherefDisthenormalizeddonoremissionspectrum,andεAistheacceptormolarextinctioncoefficient

NDIPorTheenergytransferefficiency(Ent)

wherekEntistherateofenergytransfer,kftheradiativedecayrateandthekiaretherateconstantsofanyotherde-excitationpathway.Whereristhedonor-to-acceptorseparationdistance,R0beingtheF?rsterdistanceofthispairofdonorandacceptor,i.e.thedistanceatwhichtheenergytransferefficiencyis50%.(臨界距離：1-10nm)where0isthefluorescencequantumyieldofthedonorintheabsenceoftheacceptor,κ2isthedipoleorientationfactor,nistherefractiveindexofthemedium,NA

isAvogadro‘snumber,andJisthespectraloverlapintegral.κ2=2/3isoftenassumed.

Thisvalueisobtainedwhenbothdyesarefreelyrotatingandcanbeconsideredtobeisotropicallyorientedduringtheexcitedstatelifetime.Ifeitherdyeisfixedornotfreetorotate,thenκ2=2/3willnotbeavalidassumption.

Inmostcases,however,evenmodestreorientationofthedyesresultsinenoughorientationalaveragingthatκ2=2/3doesnotresultinalargeerrorintheestimatedenergytransferdistanceduetothesixthpowerdependenceofR0onκ2.Evenwhenκ2isquitedifferentfrom2/3theerrorcanbeassociatedwithashiftinR0andthusdeterminationsofchangesinrelativedistanceforaparticularsystemarestillvalid.Fluorescentproteinsdonotreorientonatimescalethatisfasterthantheirfluorescencelifetime.Inthiscase0≤κ2≤4.

CalculationofEnergytransferefficiency()andRateconstant(k)Whereisthefluorescencelifetimeofdonorinthepresenceofacceptor;0isthefluorescencelifetimeofdonorwithoutacceptor;fisthefluorescencequantumyieldofdonorinthepresenceofacceptorand

f0isthefluorescencequantumyieldofdonorwithoutofacceptor3.4.3.光致電子轉(zhuǎn)移(photoinducedelectrontransfer)D*+A=D++A-.D+A*=D++A-.能量關(guān)系:

EDAHOMOLUMOHOMOLUMOeEHOMOLUMOHOMOLUMOeeDAElectrontransferHoletransfer

ElectrontransferHoletransfer3.4.4.光致電子轉(zhuǎn)移(photoinducedelectrontransfer)的理論Rehm-Weller公式:

共價(jià)鍵相聯(lián)的Donor-Acceptor體系Marcus

電子轉(zhuǎn)移理論----解釋ErG活化能>0GG活化能=0活化能>0lgk-G,自由能變正常區(qū)翻轉(zhuǎn)區(qū)激發(fā)態(tài)的壽命:激發(fā)態(tài)分子失活到原來的1/e時(shí)所需要的時(shí)間;e為自然對數(shù)的底(2.718)數(shù)學(xué)定義:

=1/kf+1/kic+1/knr+1/ket+1/kent……各種失活過程的速率常數(shù)的倒數(shù)的和激發(fā)態(tài)的壽命不僅和分子的結(jié)構(gòu)有關(guān),同時(shí)和分子所處的環(huán)境很大的關(guān)系,譬如:溶劑的極性;溫度和壓力等.人們在這個(gè)領(lǐng)域已經(jīng)積累了豐富的理論和實(shí)際的經(jīng)驗(yàn).激發(fā)態(tài)壽命的測定作為一種分析手段,已經(jīng)廣泛應(yīng)用于生物體系,材料領(lǐng)域,超分子化學(xué),膠體與界面化學(xué)和環(huán)境化學(xué)等領(lǐng)域.

3.5激發(fā)態(tài)的壽命Franck-CondonPrincipleClassically,theFranck–Condonprincipleistheapproximationthatanelectronictransitionismostlikelytooccurwithoutchangesinthepositionsofthenucleiinthemolecularentityanditsenvironment.TheresultingstateiscalledaFranck–Condonstate,andthetransitioninvolved,averticaltransition.Thequantummechanicalformulationofthisprincipleisthattheintensityofavibronictransitionisproportionaltothesquareoftheoverlapintegralbetweenthevibrationalwavefunctionsofthetwostatesthatareinvolvedinthetransition.

—IUPACCompendiumofChemicalTerminology,2ndEdition(1997)

EnergydiagramillustratingtheFranck-Condonprincipleappliedtothesolvatio