As society moves away from fossil fuels being the predominant energy source, emerging prospects for the generation of clean energy from abundant feedstocks such as sunlight and carbon dioxide (CO2) have increased in prominence. This need introduces challenges in precision control over the coupling of photon absorption events to subsequent dynamics of electrons and protons. With accurate knowledge of rate constants for each elementary reaction step, light-absorbing catalysts can be designed to steer reactivity as desired for high activity and selectivity. The techniques and analyses described herein were aimed at attaining this important information as it applies to several classes of light-absorbing molecules whose light-driven charge transfer events drive reactions pertinent to renewable energy generation and solar fuels catalysis. In Chapter 1, I present a modification to an established method of electrochemical analysis, foot-of-the-wave analysis, to determine rate constants of regeneration of excited-state electron-transfer dyes bound to mesoporous thin films (dye-sensitized photovoltaics) through interfacial reductive electron transfer from redox shuttles. While foot-of-the-wave analysis has been used for quantification of rate constants in homogeneous solution catalysis, I demonstrate using spectroelectrochemistry the ability to determine interfacial electron-transfer rate constants for reactions involving a dye bound to a thin film and a redox mediator donor substrate in solution. In Chapters 2 and 3, I present the use of photoacids as dye sensitizers that use light to sense and vary the local concentration of protonic species. Upon absorption of light, photoacids exhibit a reversible decrease in their acid dissociation constants, enabling excited-state proton transfer to a proton acceptor, followed by subsequent regeneration of the photoacid in the ground state via proton transfer from a proton donor to the ground-state conjugate base. Photoacids can be used toward control of local pH conditions that can dictate reaction selectivity for electrochemical CO2 reduction, and by monitoring their photoluminescence they serve the dual role of molecular sensors to garner information about local concentrations of protonic species. In Chapter 2, I demonstrate the sensing capabilities of photoacids for aqueous proton acceptors including water, hydroxide, (bi-)carbonate, acetate and formate using steady-state and nanosecond time-resolved photoluminescence spectroscopies. In Chapter 3 I characterize photoacid ground-state regeneration toward control of local concentrations of protonic species. Using nanosecond transient absorption spectroscopy, I confirm that the charge-separated state of the deprotonated ground-state photoacid and hydronium can persist for up to tens of microseconds, and uniquely tune whether ground-state reprotonation occurs from either hydronium or water. This was possible by careful control over photon fluence, dye concentration, and dye pKa, and comparing an analytical model for reversible proton-transfer events with experimental data as a function of aqueous pH. The research presented herein aims to contribute to the fundamental photochemical knowledge of proton and electron transfer reactions that serve as foundations for control over their reactivities.