Photoinduced intramolecular charge transfer in donor-acceptor substituted tetrahydropyrenes

Abstract

Two novel donor-acceptor-substituted tetrahydropyrene derivatives (1 and 2, Chart 1) were synthesized and photophysical properties investigated in solvents of different polarities. These studies revealed the existence of an intramolecular charge transfer (ICT) excited state in these molecules. The fluorescence lifetime and quantum yield measurements revealed that emission occurs from a planar ¹CT state in all the solvents. The solvent-dependent Stokes shift values for 1 and 2 were analyzed by the Lippert-Mataga equation and Liptay's modified equation to obtain the excited-state dipole moment values. The CT nature of the emitting states is further confirmed by studies in acidic medium. Change of pH results in well-separated LE and CT fluorescence and absorption bands. It is suggested that this property can be utilized for ph-sensing applications.