In this presentation, we discuss enhancement of photo-orientation of azo-dye in films of polymer by surface enhanced visible absorption (SEVA) of the dye in the vicinity of Gold nanoantennas. The dye undergoes shape and orientation change; i.e. isomerization and reorientation, upon polarized light absorption; and the observation of enhanced photo-orientation by SEVA is done by photo-induced birefringence (PIB) experiments, since the signal detected from PIB experiments is directly proportional to the extinction coefficient of the dye. Both the dye’s absorption and photoorientation are enhanced by the presence of the plasmonic nanoantennas.
Materials which can be actuated by light have potential to lead to light fueled robots and machines. Such materials deform and move by the action of photo-active molecules; e.g. molecular machines. Azobenzene derivatives are such a molecules, and they undergo a high rate of light-induced cyclic molecular shape change from an elongated, trans form, to a more globular, cis form; a feature which imparts macroscopic motion into materials in the presence of intensity gradients. That is photoisomerization leads to matter motion in inhomogeneous irradiation light fields. In viscoelastic materials, matter motion, in concept, is due to competing forces, including viscous and photoisomerization forces, and possible radiation pressure and elastic forces, as well as random forces due to thermal fluctuations. In solid films of azopolymers, the photoisomerization force overcomes other forces due to softening and decrease of viscosity of the material by photoisomerization. In this paper, we give a brief overview of the theoretical concept of matter motion induced by photoisomerization; e.g. photochemical tweezing, and we show that light absorption provides the energy needed by the system for isomerization and matter motion.
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