AFM Observation of Stimuli-Responsive Stretching Behavior for Spirobenzopyran/Crown-Ether Copolymer

• Published in: Bulletin of the Chemical Society of Japan 2011, Vol.84 (4), p.422-426
• Main Authors: Kado, Shinpei, Uehara, Kunika, Nakahara, Yoshio, Kimura, Keiichi
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Chains (polymeric); Copolymers; Crown ethers; Spirobenzopyran; Spiropyrans; Stimuli; Stretching
• ISSN: 0009-2673; 1348-0634; 1348-0634
• DOI: 10.1246/bcsj.20100289

We have observed stretching behavior of a stimuli-responsive polymer chain bearing two functional groups, spirobenzopyran (SP) and crown ether (CR), at the side chain (SP/CR copolymer) by atomic force microscopy (AFM). The spirobenzopyran side chain can undergo photoisomerization from its electrically neutral spiropyran form to zwitterionic merocyanine by UV irradiation. The crown ether side chain can complex with metal ions. These reactions in the side chains would cause changes in their geometric structure and/or physical properties, resulting in the enhanced bifunctionality of SP/CR copolymer based on their stimuli-responsive ability. In this study, SP/CR copolymer, which was adsorbed on mica substrate, was stretched by AFM tip, when external stimuli (i.e., photoirradiation or metal ion addition) were applied. The force–extension curves of SP/CR copolymer were then analyzed by curve fitting based on a theoretical model of polymer chain elasticity to elucidate the external-stimuli effect on the polymer stretching behavior at the single molecule level.