Insights on Photochemical Processes in the Strong Coupling Regime by Atomistic Simulations*

Electronic excitations in molecules can be strongly coupled to electromagnetic modes of resonant cavities. The properties of the resulting hybrid states (polaritons) are different than those of the original electronic states. In particular, the resulting photochemistry depends on the features of the excited molecular states, and can therefore be modified by entering the strong coupling regime. As such, strong coupling is emerging as an elegant tool to manipulate the photochemistry (or rather the polaritonic chemistry) of molecules, elegant in that it is not relying on engineering of the molecule or of the solvent. In collaboration with the group of G. Granucci and M. Persico, we have developed an atomistic computational methodology [1] that extends to polaritonic chemistry a well-established semiclassical approach developed for photochemical processes [2]. We have applied it to azobenzene photoisomerization with a fully atomistic description of the molecule and of the surrounding environment to investigate how the mechanism and the yield of the reaction change entering the strong coupling regime [3,4]. The resulting picture is that of a complicated mechanism, where the modification of excited state lifetimes and effectiveness of vibrational energy redistribution play prominent roles [4]. Such mechanism could hardly be imagined a priori or on the basis of simplified theoretical models, showing the need of realistic simulations as a tool to discover and rationalize polaritonic chemistry mechanistic patterns to inspire experiments and further theoretical modeling.

[1] J. Fregoni, S. Corni, M. Persico, and G. Granucci. J. Comp. Chem. 41, 2033 (2020)
[2] G. Granucci, M. Persico, and A. Toniolo. J. Chem. Phys. 114, 10608 (2001)
[3] J. Fregoni, G. Granucci, E. Coccia, M. Persico, and S. Corni. Nat. Commun. 9, 4688 (2018)
[4] J. Fregoni, G. Granucci, M. Persico, and S. Corni. Chem 6, 250 (2020)