Stabilization of ultra-small gold nanoparticles in a photochromic organic cage: modulating photocatalytic CO2 reduction by tuning light irradiation.

Synthesis and stabilization of ultra-small metal nanoparticles (MNPs) composed of a few atoms are of paramount importance in modulating their material properties based on quantum confinement effects. The highly reactive surface of small MNPs tends to aggregate, resulting in bigger particles and subsequent deterioration of the catalytic activity. In this work, we exploited a dithienylethene (DTE) based photochromic organic cage (TAE-DTE) for the in situ stabilization of ultra-small Au NPs (Au@TAE-DTE) (<2 nm) through a unique "reverse double-solvent approach (RDSA)". The Au@TAE-DTE showed similar photochromic properties to the TAE-DTE and shuttled between two metastable photoisomers, Au@TAE-DTE-O and Au@TAE-DTE-C, based on DTE ring opening and closing upon treating with visible and UV-light, respectively. The Au@TAE-DTE hybrid showed visible light (λ = 400–750 nm) driven catalytic activity for photochemical CO₂ reduction to CO. Importantly, irradiating with light of the full range (λ = 250–750 nm) allowed for co-existence of both photoisomers which thereby showed wide spectrum absorption as compared to individual photoisomers, consequently displaying substantially enhanced performance for the photocatalytic CO₂ reduction. Further, the real-time progress of the CO₂ reduction reaction and corresponding reaction intermediates was detected by an in situ DRIFT experiment. [ABSTRACT FROM AUTHOR]