Bis‐NHC‐Diarylethene Palladium Complexes: Dynamic Behavior and Self‐Tuning Photoswitching

Abstract Light offers a unique means of controlling matter with high precision, yet the development of robust photoresponsive transition‐metal complexes remains a challenge. Here we report a self‐tuning photochromic system based on a diarylethene‐derived bis‐NHC‐palladium complex. The trans‐anti complex ( 1 oo ) undergoes efficient stepwise photocyclization as well as unprecedented light‐induced trans/cis isomerization at the metal center. Isolation and crystallographic characterization of the cis‐anti isomer ( 2 oo ) reveal a thermodynamically more stable structure with enhanced photochromic performance and reversible multistate switching. Thermal studies uncover interconversion with additional rotamer, establishing a dynamic equilibrium among several photoactive palladium species. Spectroscopic and computational investigations elucidate the electronic transitions that drive both diarylethene cyclization and Pd─NHC geometric rearrangements. We demonstrate that the catalytic activity in the Suzuki‐Miyaura coupling reaction can be reversibly switched by light, with the photocyclized catalyst forms showing negligible catalytic activity, while the open forms achieve high efficiency. This establishes a direct link between photoisomerization and predicted catalytic performance. Pre‐catalyst evolution demonstrates that the geometry of the complex controls the balance between nanoparticle‐mediated and homogeneous reactivity, delineating a novel strategy for adaptive catalysis.