AMINO DERIVATIVES OF SYMMETRICAL 1,3,5-TRIPHENYLBENZENE - NATURE OF THE POLAR SINGLET EXCITED-STATE

The solvent dependence of the fluorescence spectra of (dialkylamino) a nd (diarylamino) substituted triphenylbenzene derivatives indicates th at the emission occurs from a highly polar excited state. The exponent ial fluorescence decays, obtained with time correlated single photon t iming, suggest that equilibration between the different excited specie s occurs within the time resolution of the experimental set-up. For ie thylamino)phenyl)-N,N,N',N'-tetrakisethyl-(1,1': 3,1''-terphenyl)-3,3' '-diamine the size of the excited state dipole moment excludes the for mation of a TICT state. For -ethylphenyl)(1,1':3',1''-terphenyl)-4,4'' -diamine the large fluorescent rate constant in polar solvents suggest s the formation of a conjugated intramolecular charge transfer state. Only for trakis-ethyl-(1,1':3',1''-terphenyl)-4,4''-diamine the experi mental evidence does not allow to exclude either the formation of a TI CT state or a delocalized ICT state.