Free jet excitation and emission spectra of diphenylbutadiene.

Highly resolved emission and one-photon fluorescence excitation spectra for 1,4-diphenyl-1,3-butadiene seeded in a supersonic expansion of helium have been measured. The spectra show a long-lived (52.8 nsec for excitation at the 0-0) state at 29,652.5 cm(-1), approximately 1,150 cm(-1) below the well-characterized (1)B(u) state, which is assigned as (1)A(g)-i.e., we have directly observed a polyene (1)A(g) state in the gas phase. Emission spectra and decay times for the (1)A(g) state were measured at a number of different excitation energies. These data clarify the ordering of excited singlet states and the photophysical behavior of diphenylbutadiene.