Mode Switching of a Self-Propelled Camphor Disk Sensitive to the Photoisomerization of a Molecular Layer on Water

A simple self-propelled motor on a 4-[[(dodecyloxy)benz-4-yl]azo]benzoic acid (DBA) molecular layer was investigated from the viewpoint of motor control depending on the molecular structure. The nature of the self-motion of a camphor disk on the DBA molecular layer changed depending on the surface pressure (pi)-area (A) isotherm of DBA, which in turn changed by the photoisomerization between UV and green lights. The characteristic motion of the camphor disk is discussed in relation to the pi-A isotherm of DBA, which changes depending on the photoisomerization as the driving force of motion.