Effect of Oriented External Electric Fields on the Photo and Thermal Isomerization of Azobenzene

Azobenzene is a prototype molecule with potential applications in molecular switches, solar thermal batteries, sensors, photoresponsive membranes, molecular electronics, data storage, and nonlinear optics. Photo and thermal isomerization pathways exhibit different charge-transfer character and dipole moments, implying that the use of electric fields can be used to modulate the reactivity of azobenzene. This article examines the differential effect of orientated electric fields on the rotation and inversion thermal and photoisomerization pathways of azobenzene to explore the feasibility of using electric fields in the design of azobenzene-based molecular devices. Our findings demonstrate that the application of orientated electric fields modifies the accessibility of the S₀/S₁ seam of electronic degeneracy, as well as changes the energetically favored relaxation pathway in the branching space to yield different photoproducts. In addition, we observed strong-field dipole-inversion effects that cause a topographical change in the response of the potential energy surface to the applied field and can result in geometric minima that do not exist under field-free conditions. On the S₀ surface, transition barriers can be modified on the order of ±10 kcal mol^-1, enabling control of thermal isomerization rates.