Dihydroazulene molecular switches: Via ultrafast Spectroscopy to the first bidirectional switch

We demonstrate by using ultrafast time resolved spectroscopy that the photoconversion from dihydroazulene (DHA) to vinylheptafulvene (VHF) is governed by two mechanisms: The ring opening proceeds on the excited energy surface on the picosecond time scale. It is followed by an internal conversion to the VHF ground state that is accelerated by the presence of a conical intersection in the case of cyclopenta-DHA. This conical intersection hinders the photoinduced back reaction from the final VHF products. However, we successfully photo-converted the cyanophenyl-VHF-cis back to the DHA in an experiment with two delayed pulses. This opens the route to the development of bistable dihydroazulene switches.