Photochromism Mechanism of N , C -Chelating Organoboron Compounds

Photochromic materials are valuable in the field of information storage and anticounterfeiting, but most of them require complex structures or ultraviolet (UV) irradiation that rely on significant structural changes or redox reactions. Here, we synthesized the N, C -chelating organoboron compound 5-Br-2-[2-(9-borabicyclo[3.3.1]-9-nonyl)-4-bromophenyl]pyridine ( BN-1 ) with highly efficient solid-state photochromic properties. BN-1 can change from colorless to pink under UV/visible irradiation in the solid state and then return to colorless when heated to 150 °C. The mechanistic study reveals a novel aggregation-activated mechanism, in which light triggers BBN substituent rocking, regulates the π–π stacking distance between aromatic rings, and promotes intermolecular charge transfer (CT) between 9-BBN and nitrogen-containing aromatic rings. This work unveils a novel noncovalent photochromism in BN-based molecules, providing insights for designing simple, visible-light-driven materials for anticounterfeiting and smart devices.