Publications

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 ( 1oo) 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 (2oo) 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.

Single-atom catalysts (SACs) represent a pinnacle of atomic efficiency and catalytic precision. Their remarkable activity and selectivity arise from isolated, low-coordinate metal centers that engage directly in bond-forming events. However, under realistic reaction conditions, SACs are far from static. Increasing evidence reveals that single atoms undergo dynamic evolution over the reaction time. In this perspective, we challenge the conventional dichotomy that views SACs and nanoparticles (NPs) as fundamentally distinct catalytic systems. We propose that NPs, rather than acting as parallel or cooperative catalysts, may function as catalytic poisonants for SACs by trapping active metal atoms. This transformation results in loss of activity, reduced selectivity, and degradation of the catalytic system. Drawing on mechanistic studies, thermodynamic data, and experimental observations across diverse reaction classes, including hydrogenation, oxidation, and cross-coupling, we show that the aggregation of SACs into NPs is not merely a side process but rather a limitation to their stability and utility. We further outline thermodynamic and kinetic strategies to suppress this deactivation pathway and propose design principles that elevate NP suppression from a synthetic challenge to a foundational criterion in catalyst development. This perspective reframes the SAC–NP relationship as a dynamic continuum and emphasizes the importance of stabilizing isolated active sites in next-generation catalytic technologies.