Dialkylated Dihydroazulene and Vinylheptafulvene Derivatives – Synthesis and Switching Properties.

Functionalization of molecular photoswitches at specific positions offers a way of tuning their switching properties. The work presented here describes the development of a new protocol towards the synthesis and functionalization of the dihydroazulene/ vinylheptafulvene (DHA/VHF) photo-/thermoswitch. The key step is a facile condensation reaction using a functionalized tropone derivative, and the new synthetic method was employed in the regioselective preparation of a novel dimethyl-substituted DHA photoswitch. This compound presents the first accessible derivative with alkyl groups on the seven-membered ring of the system — at positions C5 and C7. From experimental and theoretical kinetics studies on the thermal VHF-to-DHA electrocyclic reaction, the influence of the electron-donating methyl groups was elucidated. In addition, we subjected a small selection of 4,8a-dialkylated compounds to a computational study to elucidate how steric interactions can alter the relative DHA–VHF stabilities. The synthetic methodology offers access to novel DHA scaffolds and substitution patterns, which in turn can lead to systems that can help to address broader questions concerning the potential applicability of the DHA/VHF system in the context of solar-thermal energy- storage systems or other photochromic applications. [ABSTRACT FROM AUTHOR]