Molecular switching in phospholipid-azobenzene mixed monolayers by photoisomerization

Abstract

Molecular switching in phospholipid and azobenzene mixed monolayers on a water surface was examined by Maxwell displacement current (MDC) measurements coupled with surface–pressure measurements. MDC and thermally stimulated current (TSC) measuring techniques also examined molecular switching in these monolayers on a solid substrate. It was found that the molecular aggregation of pure azobenzene monolayers in both Langmuir (L) and Langmuir–Blodgett (LB) films is reduced by the introduction of phospholipids possessing unsaturated long alkyl chains (DOLPC) or saturated long alkyl chains (DPPC), and that the cis–trans photoisomerization in a mixed monolayer is accelerated. However the contribution of the two kinds of lipids in mixed monolayers was found to be different. The temperature dependence of charge induced across these mixed LB films, due to photoisomerization, corresponded well with that of 4-octyl-4′-(5-carboxyl-pentamethyleneoxy)-azobenzene (8A5H) LB films. Finally it was concluded that the cis-state 8A5H molecules, in monolayers, return to the trans-state during heating.