Light-Controlled Interconvertible Self-Assembly of Non-Photoresponsive Suprastructures

Achieving light-induced manipulation of controlled self-assembly in nanosized structures is essential for developing artificially dynamic smart materials. Herein, we demonstrate an approach using a non-photoresponsive hydrogen-bonded (H-bonded) macrocycle to control the self-assembly and disassembly of nanostructures in response to light. The present system comprises a photoacid (merocyanine, 1-MEH), a pseudorotaxane formed by two H-bonded macrocycles, dipyridinyl acetylene, and zinc ions. The operation of such a system is examined according to the alternation of self-assembly through proton transfer, which is mediated by the photoacid upon exposure to visible light. The host-guest complexation between the macrocycle and bipyridium guests was investigated by NMR spectroscopy, and one of the guests with the highest affinity for the ring was selected for use as one of the components of the system, which forms the host-guest complex with the ring in a 2:1 stoichiometry. In solution, a dipyridine and the ring, having no interaction with each other, rapidly form a complex in the presence of 1-MEH when exposed to light and thermally relax back to the free ring without entrapped guests after 4 h. Furthermore, the addition of zinc ions to the solution above leads to the formation of a polypseudorotaxane with its morphology responsive to photoirradiation. This work exemplifies the light-controlled alteration of self-assembly in non-photoresponsive systems based on interactions between the guest and the H-bonded macrocycle in the presence of a photoacid.