Photochromic Heterocycle-Fused Thieno[3,2‑b]phosphole Oxides as Visible Light Switches without Sacrificing Photoswitching Efficiency

A series of novel photochromic thieno­[3,2-b]­phosphole oxides has been shown to demonstrate photochromism without the need for the use of high-energy ultraviolet (UV) light irradiation while maintaining promising photochromic properties such as excellent thermal irreversibility, robust fatigue resistance, and high photoswitching efficiency. Promising visible light-induced photochromic properties have been realized by the new molecular design, in which various π systems have been incorporated into the weakly aromatic phosphole backbone instead of the conventional modification of the peripheral diaryl units that usually leads to a drastic reduction of the photochromic quantum yields (ϕO→C and ϕC→O O→C = 0.87 and ϕC→O = 0.44), rendering it a new promising candidate as visible light photoswitches for various potential applications.