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

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.