Leveraging P‐Reactivity and Ring Strain to Generate Molecular Diversity in Dithienylethenes‐Based Photochromes

We synthesized and studied phosphetene‐bridged dithienylethenes (DTEs), featuring 4‐membered P‐rings, exploring their P‐chemistry and ring strain reactivity that allowed us to isolate 5‐membered oxophospholenes. Experimental and density functional theory (DFT) studies revealed how these modifications influence photochromic properties, with an impact of the P‐environment on the photokinetic metrics, demonstrating the value of 4‐membered strained P‐rings for tunable photoresponse. These systems exhibit good fatigue resistance including in the solid‐state. This work highlights phosphorus‐based molecular engineering as a powerful strategy for designing advanced photochromic materials.