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Many transition metal coordination complexes are known to undergo a structural change in response to a stimulus, like light, which can have a debilitating impact on properties of interest (e.g., quantum yield, stability, reactivity, etc.). This is particularly true for Cu(I) coordination complexes that suffer from short, excited-state lifetimes due to D2d to D2 distortion and solvent coordination. Here, we investigate the impact of strategic surface binding and the role of the surface binding motif on the excited state lifetime of Cu(I) complexes with carboxylate-functionalized N-phenylpyridin-2-ylmethanimine ligands. Relative to the solution, the excited state lifetime for the ZrO2-bound complexes increases 7-fold when either one ligand is bound or both ligands are bound through a flexible linker but 17-fold when both ligands are rigidly bound to the surface. With support from theoretical calculations, we attribute the dramatic increase in lifetime for the latter to the rigid binding strategy inhibiting the planarizing distortion and possible quenching via solvent coordination. These results lend further support to the idea that molecular immobilization via strategic surface binding is an effective strategy for inhibiting undesired molecular distortion. 

Understanding the landscape of molecular photocatalysis is vital to enable efficient conversion of feedstock molecules to targeted products and inhibit off-cycle reactivity. In this study, the light-promoted reactivity of [RuCp*2]+ was explored via electronic structure, photophysical, and photostability studies and the reactivity of [RuCp*2]+ within a photocatalytic hydrogen evolution cycle was assessed. TD-DFT calculations support the assignment of a low-energy ligand-to-metal charge transfer transition (LMCT) centered at 500 nm, where an electron from a ligand-based orbital delocalized across both Cp* ligands is promoted to a dx2–y2-based β-LUMO orbital. Upon irradiating the LMCT absorption feature, ultrafast transient absorption spectroscopy measurements show that an initial excited state (τ1 = 1.3 ± 0.1 ps) is populated, which undergoes fast relaxation to a longer-lived state (τ2 = 12.0 ± 0.9 ps), either via internal conversion or vibrational relaxation. Despite the short-lived nature of these excited states, bulk photolysis of [RuCp*2]+ demonstrates that photochemical conversion to decomposition products is possible upon prolonged illumination. Collectively, these studies reveal that [RuCp*2]+ undergoes light-driven decomposition, highlighting the necessity to construct molecular photocatalytic systems resistant to off-cycle reactivity in both the ground and excited states.