Switchable catalysis and CO2 sensing by reduction resistant, luminescent copper–thiolate complexes

Abstract

Metal–thiolate complexes have been the focus of research for several years because of their unique photophysical properties and their use as a precursor for synthesizing various well-defined metal nanoclusters. A rational understanding of their structure–property relationship is necessary to realize their full potential in practical applications. Herein, we demonstrate the synthesis of a unique copper–thiolate complex with reversibly switchable catalytic and photoluminescence (PL) properties. The as-synthesized complex at basic pH (Complex B) showed cyan PL with a strong peak at ∼488 nm (cyan) and a small shoulder peak at ∼528 nm (green). When the pH of the complex was changed to acidic (Complex A), the PL was switched to light green. Such pH-responsive PL properties were demonstrated to be useful for pH and CO₂ sensing. The switchable properties originate from their two distinct structural states at two different pHs. We found that Complex A was resistant to high concentrations of a strong reducing agent, and had an intermediate oxidation state of copper (Cu⁺) with good thermodynamic stability. Furthermore, the switchable catalytic property was investigated with a 4-nitrophenol reduction and 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation reaction. The reduction kinetics followed pseudo-first-order, where the catalytic activity was enhanced by more than 10³ times when Complex B was switched to Complex A. A similar trend was also observed for TMB oxidation. Our design strategy demonstrates that redox switchable metal–thiolate complexes could be a powerful candidate for a plethora of applications.