Photo- and Thermoresponsive Dehydration of Spiropyran-Functionalized Polymer Regulated by Molecular Recognition

The photo- and thermoresponse of poly(N-isopropylacrylamide) (pNIPAAm) functionalized with spiropyran chromophore is examined with respect to the influence of molecular recognition by cyclodextrin (CD). Characterization in aqueous solutions of spiropyran-functionalized poly(N,N-dimethylacrylamide) under coexistence of α-, β-, or γ-CD reveals that β-CD selectively includes the ring-closing isomer of the chromophore, which is dominant under light irradiation, while no inclusion is observed for the protonated ring-opening isomer, which is dominant in the dark before irradiation. As a result, it is shown that the selective inclusion of the chromophore at a polymer side chain is switched by light irradiation. Further, drastic photoresponsive dehydration of spiropyran-functionalized pNIPAAm is inhibited only by β-CD out of three examined CDs, demonstrating that the molecular recognition regulates the dehydration of the whole polymer triggered by the photoswitching of the chromophore introduced at only 1 mol% functionalization.