Design of Robust Photochromic Silole-Fused Dithienylethenes and Computational Insights into Excited-State Reaction Pathways for Controllable Photoswitchable Materials

Abstract

Diarylethenes are widely recognized as promising candidates for applications in optical memory storage systems and photoswitchable molecular devices. In this study, we present a series of photochromic silole-fused dithienylethenes, and their electrochemical, photophysical and photochromic properties. These compounds exhibit high photoswitching efficiencies, excellent thermal irreversibility, and robust photofatigue resistance. The thermal backward reaction is found to be negligible even at 100 °C and the estimated half-life is around 776 days. Impressively, the compounds maintain photoreactivity with no apparent loss after at least five photoswitching cycles. Both the photocyclization and photocycloreversion quantum yields are found to be relatively high and comparable. Computational investigations of the excited-state reaction pathways provide mechanistic insights, suggesting that the predominant factors for achieving high photocycloreversion quantum yields in this class of compounds are associated with the less efficient S₁→S₀ nonradiative decay in the closed form and the more accessible pathway to the S₁/S₀ minimum energy conical intersection with small activation barrier slopes. Photochromism in rigid medium is also demonstrated by one of the compounds in polymethylmethacrylate (PMMA) thin film spin coated on a quartz plate, highlighting the potential use of these compounds in devices. These findings advance the rational design and mechanistic understanding of robust photochromic silole-based dithienylethenes and underscore their practical applications in high-performance optical memory devices.