Photophysics of derivatives of all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH). Part 1.—Model involving fluorescence from S2 and S1 excited states

Absorption, fluorescence excitation and emission spectra have been measured for several derivatives of all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH) in several non-polar solvents over a range of temperatures. Emission is shown to occur from the low-lying 1A*g state (S1) and the 1B*u state (S2) which is at slightly higher energy. A model is proposed in which thermal repopulation of S2 from S1 proceeds at a rate which is comparable to radiative and non-radiative decay from S1.