Fluorescence of derivatives of all-trans-1,6-diphenyl-1,3,5-hexatriene

Abstract Fluorescence quantum yields and lifetimes have been measured for ring-substituted derivatives of all-trans-1,6-diphenyl-1,3,5-hexatnene in several non-polar solvents over a range of temperature. The fluorescence quantum yields were high in all non-polar solvents and showed small decreases with increasing temperature. The fluorescence lifetimes varied with the nature of the substituent group and showed a marked solvent dependence. The results are interpreted in terms of a model in which thermal repopulation of S 2 from S 1 proceeds at a rate which is comparable to radiative and non-radiative decay from S 1 . It is shown that neglect of Franck-Condon packing strain effects leads to overestimates of the true S 2 -S 1 energy differences. Significant S 2 -S 0 emission can interfere with attempts to quantify enhancement of the S 1 -S 0 transition by intensity borrowing from the S 2 -S 0 transition, leading to serious overestimates of vibronic coupling matrix elements.