Knowledge Bank

One photon fluorescence excitation spectra, fluorescence spectra, and single vibrational level decay kinetics have been measured for $diphenylbutadiene1$ (DPB) and $diphenylhexatriene2$ (DPH) seeded in supersonic helium expansions. In each case a long lived (52.8 nsec for DPB and 90.7 nsec for DPH) doubly excited $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Ag\ast$ state is located well below the lowest singly excited state $(11Bu\ast )$. The $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Ag\ast$ to $11Bu\ast$ energy gap is $1150cm-1$ for DPB and $3400cm-1$ for DPH. All of the observed vibrational states have odd inversion symmetry and are coupled to the $11Bu\ast$ state. Emission produced by excitation of this $11Bu\ast$ state emanates not from this state but from vibrationally excited levels of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Ag$ state which are isoenergetic with the initially prepared state. Comparisons of the gas phase data obtained here with that obtained in low temperature matrices provides a clearer picture of the photodynamics and electronic structure of diphenylpolyenes than was previously available.