Photo-Induced Polymer Cyclization via Supramolecular Confinement of Cyanostilbenes.

Efficient synthesis of cyclic polymers has received much attention in polymer chemistry field. Although photochemical cycloaddition of terminal π-bonded units provides a plausible way toward cyclic polymerization, it remains challenging to avoid side reactions by manipulating the reaction selectivity. Herein supramolecular confinement has been developed as a promising strategy to address this issue, by introducing highly directional hydrogen bonds to the photo-reactive cyanostilbenes. The cyanostilbenes units on both ends of a telechelic macromonomer are orientationally aligned with high local concentrations, yielding [2+2] photo-cycloaddition products upon 430 nm light irradiation. It leads to the formation of cyclic polymers in the self-assembled state, in stark contrast to Z-E isomerization of cyanostilbenes in the monomeric state. Overall, supramolecular confinement effect exemplified in the current study provides new avenues toward cyclic topological polymers with high synthetic efficiency.