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 fluorescenc e 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 absor bance ratio at the two lambda(max) (similar to 460 and similar to 650 nm) is time (similar to 10 ps resolution) and, except for small shifts , temperature (238-298 K) independent. Similarly, in contrast to an ea rlier report, identical time evolution of fluorescence intensity is fo und at short (405 +/- 10 nm) and long (equal to or greater than 500 nm ) lambda. We conclude that the initially formed 1(1)B(u) state complet ely relaxes to a 1(1)B(u)/2(1)A(g) equilibrium mixture within our time resolution (similar to 10 ps). Since the latter is favored overwhelmi ngly, all transient absorption is assigned to n(1)B(u) <-- 2(1)A(g) tr ansitions, consistent also with small red shifts in lambda(max) with i ncreased medium polarizability. We discern no spectral manifestations of phenyl-vinyl torsional motions, or any associated stabilization of the 1(1)B(u) state, at times longer than 10 ps.