Construction and Photo-Responsiveness of Cyanostilbene-Based Supramolecular Polymers

The nucleation-elongation cooperative mechanism, as widely adopted by natural systems such as microtubules and actin filaments, exhibits superior properties for supramolecular systems in comparison to the isodesmic mechanism by avoiding the formation of short-ranged oligomers. In this study, a novel type of artificial supramolecular polymers with the nucleation-elongation mechanism have been constructed by incorporating hydrogen bonding recognition motifs adjacent to the cyanostilbene core. It facilitates the combination of hydrogen bonds and π-π stacking interactions between the neighboring monomers in a synergistic manner. The different hydrogen bonding units (urea versus amide) exert crucial impacts on the supramolecular polymerization behaviors, which can be qualified by the thermodynamic parameters of the self-assembly processes. Furthermore, supramolecular polymerization imparts confinement effect to the cyanostilbene unit, giving rise to the specific formation of 2+2 cycloaddition products under 430 nm photo-irradiation. It is in stark contrast to that in the monomeric state, which undergoes Z/E photoisomerization reactions under the same conditions. Overall, the current study provides new insights to modulate multi-path photochemical reactions in a precise manner.