Evolutions of Singlet Excited-State Absorption and Fluorescence of all-trans-1,6-Diphenyl-1,3,5-hexatriene in the Picosecond Time Domain

Temporal behaviors of singlet excited-state absorption and fluorescence of all-trans-1,6-diphenyl-1,3,5-hexatriene in solution are reported in the picosecond time domain. Contrary to an earlier study, the absorbance ratio at the two λmax (∼460 and ∼650 nm) is time (∼10 ps resolution) and, except for small shifts, temperature (238−298 K) independent. Similarly, in contrast to an earlier report, identical time evolution of fluorescence intensity is found at short (405 ± 10 nm) and long (≥500 nm) λ. We conclude that the initially formed 1Bu state completely relaxes to a 11Bu/21Ag equilibrium mixture within our time resolution (∼10 ps). Since the latter is favored overwhelmingly, all transient absorption is assigned to n 1Bu ← 21Ag transitions, consistent also with small red shifts in λmax with increased medium polarizability. We discern no spectral manifestations of phenyl−vinyl torsional motions, or any associated stabilization of the 11Bu state, at times longer than 10 ps.