Emission from Charge Recombination between Radical Cations and Radical Anions of 9-Cyano-10-(p-substituted phenyl)anthracene Generated during Pulse Radiolysis

摘要

Emission from charge recombination between radical cations and anions of 9-cyano-10-(p-substi-tuted phenyl)anthracenes(RA,where R is 10-p-substituted phenyl:R = Phenyl(PA),anisyl(OA),p-N,N-dimethylaminophenyl(NA),N,N-di-p-anisylaminophenyl(DA)),as donor-acceptor type molecules,generated during the pulse radiolysis in benzene was measured together with the transient absorption of RA radical cations(RA~(centre dot+))and anions(RA~(centre dot-)).Based on the transient absorption and density functional theory(DFT-B3LYP/6-31G*)calculation,a twisted geometry is assumed for all RA in the ground state,RA~(centre dot+),and RA~(centre dot-).It is suggested that the positive charge of PA~(centre dot+),OA~(centre dot+),and NA~(centre dot+)is delocalized on two moieties,and that of DA~(centre dot+)is localized on the donor N,N-di-p-anisylaminophenyl moiety,while the negative charge of all RA~(centre dot-)is mainly on the acceptor 9-(10-cyano)anthracenyl moiety.When both RA~(centre dot+)and RA~(centre dot-)are generated with sufficiently high concentrations during the pulse radiolysis in benzene,the charge recombination between RA~(centre dot+)and RA~(centre dot-)occurred to give RA in the singlet excited state(~1RA*)as the emissive species,but not the excimers because of the twisted geometries of RA~(centre dot+)and RA~(centre dot-)with the large torsional angles between the 9-(10-cyano)anthracenyl and p-substituted phenyl moieties.Not only the fluorescence quantum yield of ~1RA* but also the energy differences between the annihilation enthalpy change and the excitation energy of ~1RA* are important factors for the radiolysis induced emission intensity of RA in benzene.