Photopolymerization and Formation of a Stable Purple Langmuir−Blodgett Film Based on the Gemini-Type Amphiphilic Diacetylene Derivatives

In this paper, we designed two gemini-type amphiphiles containing diacetylene units which were covalently linked through L-lysine or L-lysine ethyl ester moiety (abbreviated as TCDA-LysAc or TCDA-LysEs) as the spacer. These amphiphiles can be easily fabricated into organized molecular films though the Langmuir-Blodgett technique and the films showed an excellent photopolymerization ability. Upon photopolymerization, TCDA-LysEs formed a purple LB film with an excellent stability, while TCDA-LysAc formed the film with mixed blue, purple, and red phases. Aligned nanofibers were observed for the TCDA-LysEs film, while a mixed domain with short fiber and rotted wood structure was obtained for TCDA-LysAc. Different supramolecular chirality was obtained for the transferred LB films although both the compounds have spacers with similar chirality. It was suggested that the subtle change in the spacer structure led to different noncovalent interactions, which subsequently affected the polymerization. Through such a molecular design, we have successfully obtained the stable purple poly(diacetylene) film.