Monocyano-monosubstituted dihydroazulenes: from energy storage to fast-responsive materials

The aim of this research is to study the influence of substituents on C-1 of the dihydroazulene scaffold (DHA) on the lifetime of the corresponding vinylheptafulvenes (VHF) and on the energy storage capacities of the DHA/VHF pair. The DHA/VHF system is a T-type photoswitch based on the light- or thermal-induced interconversion between the DHA and the VHF components, and is characterized by the presence of two cyano groups in position 1 of DHA. So far, alternative functionalizations at C-1 have attracted little attention, considering the two nitriles essential for the photochromic properties of the system. We experienced a peculiar reactivity of one of the two nitriles towards 2-aminothiols and explored the removal of this functional group for energy storage purposes. In this communication, we will describe the one-step syntheses from the parent DHA of a selection of monocyano-monosubstituted DHAs, together with the stereochemical outcome of the reactions, and the influence of the nature of the new substituents on the lifetimes of the corresponding VHFs.