Perspective: Mechanistic investigations of photocatalytic processes with time-resolved optical spectroscopy.

Rational design and optimization of photocatalytic systems can only be achieved through understanding the reaction mechanisms involved. Time-resolved optical spectroscopy has been employed to resolve the complexities involved in photocatalytic reaction systems by identifying transient reaction intermediates and measuring the key kinetic parameters. In this Perspective, we showcase three systems that were systematically investigated as examples to demonstrate that well-designed time-resolved spectroscopic experiments can play a vital role in mechanistic investigations of photocatalytic systems while it is necessary to combine them with other analytical methods to fully resolve the complexities in these reaction processes. We summarize the commonly used methodologies and indicate the critical dynamic information that should be addressed in spectroscopic analysis. We also discuss the utilization of mechanistic insights to improve reaction performances and inspire the invention of novel photocatalysts. We foresee that the close collaboration of physical, synthetic, and materials chemists will mutually promote progress in the rapidly developing fields of photocatalysis and spectroscopy.