Phototaxis of Oil Droplets Comprising a Caged Fatty Acid Tightly Linked to Internal Convection

• Published in: Chemphyschem 2016-08, Vol.17 (15), p.2300-2303
• Main Authors: Suzuki, Kentaro, Sugawara, Tadashi
• Format: Article
• Language: English
• Subjects: active matter; droplets; photolysis; phototaxis; self-assembly
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201600273

We found that novel sub‐millimeter‐sized photoactive oil droplets of oleic acid bearing a photolabile protecting group, 2‐nitrobenzyl oleate (NBO), in basic water exhibited unidirectional motion toward a UV light source. This unidirectional motion can be explained by anisotropic photolysis on a surface of the NBO droplet with low permeability for UV light. Time‐dependent changes of the movement under UV irradiation occurred in a cascade manner (still‐standing, induction, and active stages). The velocity of the UV‐irradiated droplet in the induction stage was small, but it was accelerated sixteen times by the presence of an inner convection structure, which was created by continued photolysis. This characteristic dynamics, which is derived from a supramolecular machinery system towards the external stimulus, may be similar to the phototaxis of a living cell. A photoactive oil droplet is prepared from a newly synthesized caged oleic acid. The droplet exhibits unidirectional motion toward a UV light source. The velocity of the UV‐irradiated droplet increases non‐linearly as a result of the formation of an inner convection structure during prolonged photolysis.