Azobenzene-Incorporated Single- and Double-Stranded Polynorbornenes: Facile Synthesis and Diverse Photoresponsive Property

Double-stranded polymeric ladderphane using azobenzene as linkers and the single-stranded polynorbornene with azobenzene pendants are synthesized by the ring-opening metathesis polymerization using Grubbs ruthenium-based catalyst. Hydrolysis of these as-prepared polynorbornenes gives the corresponding isotactic single-stranded polynorbornene having similar polydispersity and degree of polymerization as those of the original polymers. The photosensitive property of double-stranded ladderphane indicates significant interactions between adjacent chromophores. These single- and double-stranded polynorbornenes incorporating azobenzene chromophores exhibit distinct photoresponsive performance in the dilute solutions. The rate of photoisomerization for double-stranded ladderphane is found to be from 6 to 9 times slower than that obtained for single-stranded polymer. This is ascribed to the differences in structure of polymers and the interaction between azobenzene chromophores in the polymers.