Light- and Electric-Field-Induced Switching of Thiolated Azobenzene Self-Assembled Monolayer

The reversible isomerization of the azobenzene (AZO) based self-assembled monolayers (SAMs) under external stimuli is the key to their application as molecular switches. To establish the relationship between electronic structure and switching function, AZO and its derivatives with electron donating (NH2) and withdrawing (NO2) terminal groups, respectively, are investigated in the light and electric field triggered configuration changes by using density functional theory (DFT) and molecular dynamics (MD) simulation. Using the modified force field, whose parameters are taken from DFT calculations on the ground and first excited states, the non-equilibrium molecular dynamics simulations show the collective structural transitions in Au(111) surface supported AZO SAMs under ultraviolet–visible light and external electric field stimulation. Along MD trajectories, an index function, S, is then defined to depict the SAM switching dynamics between “on” (S = 1) and “off” (S = 0) states. The charge transfer between SAM and surface and dipole interactions under the external electric field are revealed. The joint configuration changes of the AZO molecules in the SAM are also displayed to be able to lift the alkythiol coated mercury droplet in the Au(111)–SAMAZO//SAMC12–Hg junction model, in agreement with experimental observations on the photoswitching of the current in molecular junction. In addition to the manipulation of switching by light irradiation, it is predicted that the AZO SAMs, with or without substitutions, may also work as a molecular cargo lifter under the electric field.