The solvent relaxation response to the solute out of equilibrium is central in determining kinetic and energetic of any physicochemical process in solution. [Kumpulainen2017, Carter91] Changes of the local environment (solute–solvent interactions) which follow the charge redistribution of the system in its excited state, can significantly influence the photophysical properties and chemical reactivity. [Petrone2014] Thanks to the fast development of ultrafast spectroscopies in the last decades, [Bolzonello2018, Rondi2015, Kumpulainen2017] more and more refined information on the role played by the solvent on the ultrafast dynamics of photo-excited states can be accessed. Experimental research has been supported by theoretical calculations capable to disclose atomistic insights into the solvent rearrangements, suggesting the idea of a rather complex solvent response dynamics, [Kundu2019] with the solvent as a principal actor in the modification of the solute’s excited state charge distribution, often through the formation or breaking of strongly interacting solute-solvent clusters. Solvation dynamics is crucial when the timescales of bonding and medium organization are comparable to those of the processes involved, and, as a matter of fact, such events take place on a rather wide time scale, ranging from femtoseconds to nanoseconds.
From the theoretical and computational point of view, in the past decades, the problem of studying an evolving mutual interaction between an electronically excited solute and its solvent environment has been tackled at an increasing level of complexity, [Nogueira2018, Shi2018] allowing the treatment of the dynamics of non-adiabatic states, [Falahati2018, Borrego-Varillas2018, Pápai2019, Barbatti2014] photo-reactivity, [Goyal 2017, Houari2014] solvation dynamics. [Laage2017, Prampolini2019] Urgent challenges include, advanced non-equilibrium molecular dynamics approaches, [Post2019] accuracy of the potentials, the description of the effect of mutual polarization of solute and solvent, [Widman2018] the necessity to cover different length and time scales and the development of possible strategies to merge a quantum description of the solute nuclear motions with explicit solvent models. [Cerezo2018] In this field a close synergy between theoretical/computational and experimental research is essential to open the door toward novel approaches and applications.
To the best of our knowledge, although both nonequilibrium quantum process and solvent effects on photochemistry and photophysics have been the focus of previous CECAM workshops, the topics of nonequilibrium environment effects on excited state lifetime and reactivity has not been developed yet. This workshop aims at filling this gap, bringing together leading scientists from theory and experiment to push forward the discussion on nonequilibrium solvent effects on excited states. It will cover state dynamics in complex environments, advanced transient spectroscopies, energy and charge transfer processes, nonadiabatic transitions at conical intersections, solvent response dynamics, excited state reactivity (PT and PCET etc.) and cutting-edge methodological developments in the framework of solvent description.