Intramolecular Radiative and Radiationless Charge Recombination Processes in Donor−Acceptor Carbazole Derivatives

Abstract

Photoinduced intramolecular charge transfer (ICT) in a series of N-bonded donor−acceptor derivatives of 3,6-di-tert-butylcarbazole containing benzonitrile, nicotinonitrile, or various dicyanobenzenes as an electron acceptor has been studied in solutions. The latter group of compounds, contrary to benzonitrile and nicotinonitrile derivatives, shows a well-separated low-energy CT absorption band which undergoes a distinct blue shift with increasing solvent polarity. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all of the compounds studied both in a polar and a nonpolar environment. An analysis of the CT fluorescence and absorption band shapes leads to the quantities relevant for the electron transfer in the Marcus inverted region. The values of the fluorescence rate constants (kf) and corresponding transition dipole moments (M) and their solvent polarity dependence indicate that the elec...