NEXMD Modeling of Photoisomerization Dynamics of 4-Styrylquinoline.

Isomerization of molecular systems is ubiquitous in chemistry and biology, and is also important for many applications. Atomistic simulations can help determine the tunable parameters influencing this process. In this paper, we use the Nonadiabatic EXcited state Molecular Dynamics (NEXMD) software to study the photoisomerization of a representative molecule, 4-styrylquinoline (SQ). trans-SQ transforms into dihydrobenzophenanthridine (DHBP) upon irradiation with laser light, with the cis conformer acting as an intermediate. We study how varying three different external stimuli (i.e., apolar versus polar solvent, low versus high photoexcitation energy, and vacuum versus a constant temperature thermostat) affects the trans-to- cis photoisomerization of SQ. Our results show that polarization effects due to implicit solvation and the thermostat play a crucial role in the isomerization process, whereas photoexcitation energy plays a lesser role on the outcome and efficiency. We also show that NEXMD captures the correct energy profile between the ground and first singlet excited state, showing that there are two distinct reaction pathways to the final stable product that vary by the number of photons absorbed, in agreement with experiment. Ultimately, NEXMD proves to be an effective tool for investigating excited state single molecule dynamics subject to various environments and initial conditions.