Temperature-Controlled Photooxygenation with Polymer Nanocapsules Encapsulating an Organic Photosensitizer.

A cross-linked poly- N-isopropylacrylamide (polyNIPAM) nanocapsule, TH@PC, containing thionine (TH), an organic photosensitizer, has been synthesized. This capsulated polymeric photosensitizer promotes a singlet oxygen oxygenation ( 1O 2) accurately controlled by temperature: it shows high oxygenation activity at low temperature, but shows activity decrease with a rise in temperature, resulting in almost zero activity at >40 °C. The clear on−off activity control is driven by a heat-induced structure change of the capsule from the swollensingle capsule to contractedstate, and then to aggregate, behaving as an intelligent 1O 2filter. At low temperature, the capsule exists as the swollen single capsule, which allows 1O 2diffusion to bulk water, resulting in high oxygenation activity. A rise in temperature leads to contraction of the capsule, reducing the mesh size of the capsule wall. This suppresses 1O 2diffusion to bulk water and shows decreased activity. Intercapsule aggregation at >30 °C further suppresses 1O 2diffusion and shows almost no activity. The capsule promotes reversible activity control regardless of the heating/cooling process and can be reused with a simple recovery process. [ABSTRACT FROM AUTHOR]