Abstract: In recent years, reversible excited-state photoacids have been exploited for high spatiotemporal sensing of local pH during electrochemical reactions, to study proton-coupled reaction mechanisms, to trigger processes in biological organisms relevant to energy transduction, and in the design of artificial light-driven proton pumps. Successful application of these photoacids in various systems requires non-trivial experimental quantification of accurate excited-state Brønsted-Lowry acidities (thermodynamics) and excited-state proton-transfer rate constants (kinetics). Traditional methods to quantify excited-state acidities of weak photoacids often result in incorrect values. In this talk, I will present a method to quantify accurate excited-state acidities of weak photoacids by analyzing rate constants for excited-state proton-transfer reactions from these photoacids to various proton-acceptors using driving-force-dependent kinetic theories. Furthermore, I will also set forth guidelines for the correct application of driving-force-dependent theories to relate thermodynamics and kinetics of proton-transfer reactions involving reversible excited-state photoacids.