Simultaneous Ring-Opening and Dehydrogenation of Diarylethene Induced by Tunneling Electrons.

Understanding the reversible transformation between two isomeric states of organic molecules under external stimulation is essential for advancing single-molecule device development. Photochromic diarylethene (DAE) derivatives are promising candidates for single molecular switching elements. This study investigates the single-molecule reactions of the closed-form isomer of a DAE derivative on Cu(111) using scanning tunneling microscopy (STM). A novel ring-opening pathway, distinct from the well-known photochromic isomerization, was discovered. Electron injection into the lowest unoccupied molecular orbitals induces the sequential anchoring of molecules to the substrate through the dehydrogenation of a methyl group at the 2-position of the thiophene ring. This mechanism was revealed by density functional theory calculations and STM simulations. The adsorption configurations for singly and doubly dehydrogenated DAEs were identified. Based on these findings, a new reaction mechanism extending beyond reversible isomeric reactions is proposed for DAE on Cu(111). The present work establishes a novel framework for future studies on single-molecule switching phenomena on metal substrates.