Shifting Gears: Photochromic Metal–Organic Frameworks with Stimulus-Adaptable Performance

Abstract

The tunability of the reaction parameter space is probed in the presented work through photoswitch-directed energy and charge transfer pathways induced by organic chromophores, hierarchically organized within a well-defined, light-harvesting metal–organic framework. Unique matrix-imposed changes in photoswitch photophysical properties, including the first report of visible light-induced photoisomerization of a spiropyran derivative, illustrate the critical synergy between the selected matrix and the photoresponsive compound. Moreover, the confined space of the utilized porous matrix allowed for mimicking isomerization kinetics of integrated sterically demanding photochromic moieties in solution. More importantly, such photoisomerization suppresses the charge transfer processes in favor of resonance energy transfer pathways instead. The demonstrated ability to shift between multiple relaxation pathways (e.g., charge transfer, energy transfer, or photoluminescence) as a function of the excitation wavelength resulted in photoswitch-directed tailoring of model phosphinylation reaction outcomes. Thus, incorporating spiropyran moieties within the framework allows for visible light to be harvested and funneled toward either a ligand-based reactive center or an acceptor molecule such as a photochromic unit. Moreover, the framework’s chemical activity was promoted exclusively by organic linkers without the participation of metal nodes, the addition of (co)catalysts, or the use of harsh conditions at room temperature. Overall, this work paves the way for the development of stimulus-responsive platforms, for which chemical activity could be controlled through a photochromic moiety.