TRANSIENT RESONANCE COHERENT ANTI-STOKES-RAMAN SCATTERING SPECTRA OF ION RADICALS OF ALL-TRANS-1,4-DIPHENYL-1,3-BUTADIENE

Transient CARS (coherent anti-Stokes Raman scattering) spectra of the photoinduced species of all-trans-1,4-diphenyl-1,3-butadiene (DPB) were observed in exciplex-forming systems: DPB/p-dicyanobenzene (DCNB) and DPB/N,N-dimethylaniline (DMA) in p-dioxane, and DPB alone in such polar solvents as acetone, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The transient species are ascribed to the DPB cation radical for the DPB/DCNB system and the anion radical for the DPB/DMA system, while either or both of DPB.+ and DPB.- were detected for the DPB solo solutions according to the change of electron-donating property of the polar solvents. The lifetimes of the photoproduced species in acetone and in the exciplex systems were much longer (approximately 500 ns for DPB in acetone, approximately 100 ns for DPB/DCNB, and approximately 130 ns for DPB/DMA in p-dioxane) than the reported fluorescence lifetime (less than 1 ns) of S1. The exciplex fluorescence spectra were also measured. A tentative assignment of the observed vibrational frequencies is given and trends concerning spectral characteristics and structures of the transient species for the series of shorter alpha,omega-diphenylpolyenes are briefly discussed.