Photoisomerization of azobenzene containing self-assembled monolayers investigated by Kelvin probe work function measurements

Photoisomerization of asymmetric azobenzene disulfide self-assembled monolayer (SAM) on gold was characterized by the Kelvin probe work function measurements in ambient atmosphere. The reversible changes in work function between trans and cis azobenzene SAMs are reasonably interpreted by the molecular dipole moments normal to the surface based on the molecular conformational models. The different para-substituents of azobenzene with electron donating and electron-withdrawing properties induce opposite responses in work function against UV-vis photoirradiation, which is a direct evidence of functional SAMs being effective for the energy-level alignment at the organic/electrode interface. The Kelvin probe measurements in atmosphere eventually provide the work function value equivalent to that determined by ultraviolet photoelectron spectroscopy (UPS) in ultrahigh vacuum in our previous study.