Nonequilibrium thermodynamics of light-induced reactions

TL;DR

This paper extends nonequilibrium thermodynamics to include incoherent light as a free-energy source, deriving new thermodynamic potentials and forces for light-induced chemical reactions, and analyzing two key photochemical mechanisms.

Contribution

The authors develop a theoretical framework incorporating incoherent light into nonequilibrium thermodynamics of chemical reactions, expanding beyond chemostats as energy sources.

Findings

Derived chemical potential of photons relative to systems.

Identified thermodynamic forces for light-driven reactions.

Connected theoretical results to measurable quantities like quantum yields.

Abstract

Current formulations of nonequilibrium thermodynamics of open chemical reaction networks only consider chemostats as free-energy sources sustaining nonequilibrium behaviours. Here, we extend the theory to include incoherent light as a source of free energy. We do so by relying on a local equilibrium assumption to derive the chemical potential of photons relative to the system they interact with. This allows us to identify the thermodynamic potential and the thermodynamic forces driving light-reacting chemical systems out of equilibrium. We use this framework to treat two paradigmatic photochemical mechanisms describing light-induced unimolecular reactions -- namely the adiabatic and diabatic mechanisms -- and highlight the different thermodynamics they lead to. Furthermore, using a thermodynamic coarse-graining procedure, we express our findings in terms of commonly measured experimental quantities such as quantum yields.