Dynamical Friction Effects on the Photoisomerization of a Model Protonated Schiff Base in Solution

Abstract

Photoisomerization involving a conical intersection (CI) for a model protonated Schiff base (PSB) in modeled water and acetonitrile solvents is examined with the inclusion of energy- and momentum-transfer effects described via a generalized Langevin equation (GLE) frictional approach and surface-hopping dynamics. Short-time GLE frictional effects on the model's three coordinates, the intramolecular bond length alternation and torsional PSB coordinates and a solvent coordinate, eliminate several unphysical features associated with a no-friction inertial description and have the general feature of accelerating nonadiabatic transitions to the ground electronic state. The inertial prediction of equal probability formation of ground-state trans and cis isomer products subsequent to the Franck-Condon excitation of the ground cis isomer is replaced by the GLE prediction of a preferential higher proportion of ground-state trans isomer, that is, a successful cis to trans photoreaction. This preference is solvent-dependent and is enhanced in water solvent with its higher friction intensity and short time scales. For the fast water solvent motion, the nonadiabatic transitions to the S(0) ground state are centered around the CI seam (which is due to the solvent coordinate's role as a tuning coordinate), facilitating direct transitions to the ground-state trans isomer. In contrast, for the slower acetonitrile solvent motion, the decay occurs, on average, away from the CI seam in regions with a finite free-energy gap between the excited and ground states, resulting in reduced trans isomer production. Some directions for the extension of the model description are also discussed.

Molecular Mechanism of Diaminomaleonitrile to Diaminofumaronitrile Photoisomerization: An Intermediate Step in the Prebiotic Formation of Purine Nucleobases

“…[17,[21][22][23] Different behavior was reported for protonated Schiff bases (PSBs), in which bond alternation is the predominant molecular coordinate that lifts the degeneracy at the 1 pp*/S 0 conical intersection. [24][25][26] The pyramidalization coordinate was found not to play any significant role in the singlet cis-trans isomerization mechanism of PSBs.…”

Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: Sequential, concerted, and complex branching mechanisms

“…In principle, the intramolecular coordinates could be treated with Langevin dynamics as well if they are coupled to the solvent. 52 The quantitative accuracy of this approach may be limited by the approximations associated with a dielectric continuum representation of the solvent, linear response theory, and surface hopping. Nevertheless, this approach is expected to capture the qualitative aspects of photoinduced PCET processes.…”

Solvation Dynamics in Liquid Water. 1. Ultrafast Energy Fluxes

“…The closest solvation dynamicsreaction rate connection is for low barrier electron 2,5,35,36 and proton transfers 37 , with a partial connection for other reaction classes [38][39][40] . There is however another potential solvation dynamics connection which is relatively little explored, i.e.…”