Photo- and Thermal Interconversion of Multiconfigurational Strained Hydrocarbons Exhibiting Completely Switchable Oxidation to Stable Dicationic Dyes

Highly strained hydrocarbons with two di/tribenzocycloheptatriene units were designed as electrochromic overcrowded ethylenes that undergo reversible interconversion with stable dicationic dyes. Due to severe steric repulsion, two configurational isomers (anti,anti-folded and syn,anti-folded forms) were isolated as stable entities. Photo- and thermal interconversion of these isomers proceeded cleanly: one-way photoisomerization occurred from anti,anti- to syn,anti-form and one-way thermal isomerization was observed from syn,anti- to anti,anti-form. Even though both isomers undergo two-electron oxidation into the same twisted dications, quite different oxidation potentials enable completely selective oxidation of syn,anti-isomers. Thus, the present multiconfigurational strained hydrocarbons are capable of switching of activation/deactivation of their electrochromic properties by light/heat.