Nano-photomechanical motion of small particles induced by switching photon force through photochemical processes

In the present study, we propose a combined (hybrid) approach of optical manipulation and photochemical reactions for achieving nano-photomechanical motions with small particles. Aa photochemical reactions, we have employed P-type and T-type photochromic reactions of diarylethene (DAE) and pyranoquinazoline (PQ) derivatives, respectively. Single polymer particle containing each of the photochromic compounds was optically trapped in water with a CW visible laser. At this stage, the particle experienced mainly gradient force and was trapped at the focal point of the CW laser. The absorption force was negligible because most of the photochromic molecules in the particle were in the colorless form. UV exposure induced the photoisomerization of the photochromic molecules, resulting in the increase in the number of colored forms. As a result, the absorption force acting on the particle increased and, the position of the particle shifted towards the light propagation direction depending on experimental condition. After turning the UV light off, the particle went back to the original position. The trapped particle thus underwent reciprocal motion synchronizing with the change of photo-response due to the photochromic reactions.