Unlocking Photocyclization via Hydrogen-Bond Disruption: A Theoretical Investigation of Esterification-Gated Diarylethene Switches

Diarylethene, as a classical photochromic molecule, often suffers from limitations in its reactive efficiency due to competitive nonradiative decay pathways. The competition between excited-state intramolecular proton transfer (ESIPT) and photocyclization is central to the function of the novel diarylethene derivative studied here. Incorporating an intramolecular hydrogen bond into the π-linker is found to advance ESIPT, which effectively suppresses photocyclization by providing a dominant nonradiative relaxation pathway. This mechanism is unraveled through systematic quantum chemical calculations of the ground- and excited-state potential-energy curves, with reaction barriers quantified by transition-state theory. The analyses of excited-state aromaticity and electronic structure provide a fundamental understanding of the reactivity and clarify the different properties and functions of molecules before and after cyclization. Disrupting the hydrogen bond via esterification conclusively validates the mechanism: it blocks the ESIPT pathway, turns off the nonradiative channel, and enables the efficient photocyclization and photochromic properties. This study elucidates a novel molecular-level strategy for modulating the photocyclization of diarylethene and establishes a foundational strategy for crafting intelligent photoresponsive materials.