# Photokinetics of Mixtures of Independent Photoreactions

## TL;DR

This paper introduces a new method to study and quantify the behavior of multiple simultaneous photochemical and photothermal reactions under light exposure.

## Contribution

A holistic approach is proposed to analyze mixtures of independent photoreactions using an extended integrated rate-law formula.

## Key findings

- The explicit formula successfully fits kinetic traces of binary and ternary photoreactive mixtures.
- The method quantifies the effects of initial concentration changes and inert molecules in the reactor.
- The approach is shown to be efficient and applicable to a wide range of photothermal systems.

## Abstract

The photokinetic behavior of concomitant and independent photo- and photothermal reactions exposed to monochromatic or polychromatic irradiation, has not yet been described in photochemistry literature. The occurrence of such mixtures is reported in a wide range of fields, from living species to technologically designed devices. To address the lack of investigative tools that facilitate better understanding, quantification, and control of such parallel-reaction systems, a new holistic approach is proposed in the present study. It contributes to an effort dedicated to rationalizing photokinetics along the same criteria required for thermal kinetics. The methodology builds on a previously introduced general explicit integrated rate-law formula for single-reaction systems (whose integro-differential rate-equation is not solvable). The extension of its field of applicability to multi-component photoreactive mixtures is demonstrated in the present paper. For this purpose, a large number of combinations of both photo- and photothermal individual reactions, possessing distinctly different features, were studied in binary and ternary mixtures. The data of reactions/mixtures were generated by a fourth-order Runge–Kutta numerical integration. An excellent fitting of the species’ kinetic traces by the adapted explicit formula was obtained for all mixtures. Also, the quantification of the effects of the variation in the initial concentration of one component of the mixture, and/or the presence of inert spectator molecules in the reactor, was successfully performed. The investigative photokinetic tools proposed here are shown to be handy, efficient, and useful. The findings of the present study are also thought to expand the application possibilities of reactive photothermal systems in mixtures.