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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. 

A series of tungsten cyclopentadienyl carbonyl complexes were prepared and characterized to quantify their thermochemical properties and explore their reactivity. The PR3 ligand was systematically varied across a series of CpW(CO)2PR3H metal hydride complexes, where PR3 = P(OEt)3, P(Bu)3, and P(Cy)3. These complexes are known to undergo multiple proton, electron, and proton-coupled electron transfer reactions to access a variety of species including [CpW(CO)2PR3]–, [CpW(CO)2PR3(CH3CN)]+, and [CpW(CO)2PR3]2. Cyclic voltammograms of the CpW(CO)2PR3H•+/0 and [CpW(CO)2PR3]•0/– couples are chemically irreversible, indicating chemical reactivity upon oxidation; the anodic peak potential shifts to lower potentials as the donating ability of phosphine is increased, agreeing with previous literature on similar complexes. Additionally, voltammograms of [CpW(CO)2P(Cy)3]– become chemically reversible at scan rates above 500 mV/s, indicating that the dimerization of the [CpW(CO)2PR3]• product, formed by the oxidation of [CpW(CO)2PR3]–, is slower with the sterically bulky phosphine P(Cy)3, and at high scan rates the species can be reduced before dimerization occurs. Further, as the donating ability of the phosphine increases, the pKa of the CpW(CO)2PR3H complexes increases. This work shows how ligand sterics and electronics can tune the thermochemical properties that underpin proton, electron, and proton-coupled electron transfer reactivity of these complexes. 

Ligand-to-metal charge transfer (LMCT) excited states are capable of undergoing a wide array of photochemical reactions, yet receive minimal attention compared to other charge transfer excited states. This work provides general criteria for designing transition metal complexes that exhibit low energy LMCT excited states and routes to drive photochemistry from these excited states. General design principles regarding metal identity, oxidation state, geometry, and ligand sets are summarized. Fundamental photoreactions from these states including visible light-induced homolysis, excited state electron transfer, and other photoinduced chemical transformations are discussed and key design principles for enabling these photochemical reactions are further highlighted. Guided by these fundamentals, this review outlines critical considerations for the future design and application of coordination complexes with LMCT excited states. 

A need for enhanced access to formal electrochemistry training has led to the launch of several standalone workshops, including Cyclic Voltammetry Boot Camp. In this article, we describe the history of Cyclic Voltammetry Boot Camp, its scope and mission, the structure and content covered during the three-day workshop, and the impact the workshop has had on participants. The workshop is also contextualized through a brief summary of related workshops.