Photoinduced Intramolecular Charge Transfer in Diphenylamino-Substituted Triphenylbenzene, Biphenyl, and Fluorene

The photophysical properties of a diphenyl amino-substituted triphenylbenzene, (pEFTP), biphenyl (pEFBP), and fluorene (pEFF) derivative are compared. The similarity of the photophysical properties and their solvent dependence for the triphenylbenzene and the biphenyl model compound indicate the formation of a polar excited state, localized in one branch of pEFTP. Further comparison with the fluorene model compound suggests an excited state relaxation process of the biphenyl moiety in solvents of medium and high polarity toward a more planar geometry. The depopulation of the excited state is explained in the framework of the model developed to rationalize the photophysics of substituted biphenyl.