Surface potential of photochromic poly(L-lysine) monolayers

The surface potentials of monolayers of two polymers containing azobenzene-substituted sidechains have been measured. The measurements were made on the ''dark'' (100% trans) and ''UV irradiated'' (90% cis, 10% trans) forms of the polymers, which were a 100% and a 43% azobenzene-substituted poly(L-lysine), respectively. The results were applied to the Demchak and Fort electrostatic model of a monolayer and to the inverted cone model first described by Oliveira et al. to determine the angle of inclination of the dipole moment of the azobenzene cis isomer in the ''UV irradiated'' monolayer. Our estimates for this angle suggest that the cis isomer in both polymers lies approximately perpendicular to the interface.