Design and synthesis of novel stimuli-responsive supramolecular and mechanically interlocked molecular systems and the study of their molecular switching behavior

Integrating photo- and pH-active units into molecules to construct stimuli-responsive smart materials that can be reversibly controlled is a challenging and vibrant area of research field. Light as a stimulus seems to be ideal for dynamically controlling the morphology and functionality of supramolecular assemblies, which is not chemically destructive and can be delivered with high spatiotemporal precision. It also allows remote, localized activation and does not cause the formation of waste products in the system. Recently, we developed a photo-responsive supramolecular gelator comprised of a light-active stiff-stilbene core and a calix[4]arene macrocycle unit and an acid-base switchable multi-responsive rotaxane-based molecular machine composed of a photochromic diarylethene (DAE) containing an axle and a macrocycle connected to an aggregation-induced emission (AIE)-active tetraphenylethene (TPE). The supramolecular gelator was first synthesized as a single isomer of cis-stiff stilbene-bridged biscalix[4]arene via a systematic approach and could be efficiently converted to its trans-isomer with UV light irradiation. The trans-isomer was found to be an excellent supergelator in some non-polar organic solvents and exhibited interesting morphological transitions. The rotaxane showed multi-responsive dynamic behaviors such as aggregation-induced emission, which could be slightly affected by acid-base stimuli-induced changes, and Förster resonance energy transfer efficiency from TPE to DAE can be changed by controlling the ring opening and closing of the DAE unit with light irradiation. Moreover, the rotaxanes exhibited remarkable photochromic and fluorescent characteristics in solution, making them suitable for applications in reversible photo-patterning and information storage. All the responses found in both studies were well-investigated by various spectroscopic techniques.
Overall, this research will provide insights into the systematic design, synthesis, and applications of switchable molecular systems, with the potential to contribute to the development of new functional materials and technologies in the fields of nanotechnology, biology, and materials science.