Rational Molecular Design of Germole-Fused Dithienylethenes with Tunable Photochromic Response, Reaction Pathway, and Switching Efficiency

A new series of photoswitchable organogermanium based on dithienylethenes with germole as the ethene bridge has been designed and synthesized. The rational designs of the germole-fused dithienylethene molecules allow fine-tuning of the optical band gaps, resulting in different photochromic responses upon photoexcitation at suitable wavelengths in the solution state and in PMMA thin films. The compounds exhibit robust photofatigue resistance with clean conversion between the open form and the closed form after 12 photoswitching cycles, as well as excellent thermal irreversibility with half-lives of up to 33 days even at 100 °C. High photoswitching efficiencies with balanced photocyclization and photocycloreversion quantum yields and a percentage conversion at photostationary state of up to 85% are also observed, rendering the germole-fused dithienylethenes attractive candidates as stable and efficient photoswitches for practical applications.