Excited-state dynamics in polar solvents of push-pull polyenes designed for nonlinear optics

Subpicosecond spectroscopy of push-pull polyenes, previously designed to ac hieve large optical nonlinearities, reveals an isosbestic point in the time -resolved gain band in polar solvents. The compounds possess a diethylthiob arbituric acid electron-withdrawing group and a dibutylaniline electron-rel easing group coupled by a pi-conjugated chain. The final gain peak exhibits a regular red shift with increasing chain length, whereas the ground-state absorption shift levels off. A fast photoinduced process toward a rigid, f ully conjugated cyanine-like structure is proposed. This observation suppor ts a recent proposal that a proper description of the excited-state dynamic s of these push-pull polyenes requires more than two valence bond states.