Light-Controlled Macrocyclic Supramolecular Assemblies and Luminescent Behaviors

Abstract

Intelligent supramolecular assemblies can respond well to external stimuli such as pH, temperature, light, electricity, magnetism, and enzymes to achieve not only reversible topological morphology changes and assembly/disassembly processes but also special physical and chemical properties, which are successfully applied to biological imaging, cancer treatment, luminescent materials, anticounterfeiting, sensing, molecular switch in chemical, materials, as well as biological research fields. Among all stimuli-responsive supramolecular assemblies, light-controlled supramolecular assemblies have always attracted intense attention because light is a kind of clean and eco-friendly energy. In this Account, we focus on light-controlled supramolecular assemblies formed by four types of photoresponsive molecules and macrocyclic hosts such as cucurbit[n]urils, cyclodextrins, and crown ethers, and their regulations in luminescent materials and bioimaging. The assemblies and cascade assemblies between photoisomerization or photoreaction molecules and macrocyclic hosts mainly include: 1) light-controlled supramolecular assemblies based on macrocycles and diarylethene. As molecular switches, the open-ring and closed-ring configurations of diarylethenes can be reversibly controlled to achieve tunable fluorescence resonance energy transfer (FRET) process and further regulate luminescent behaviors to construct intelligent response cell-imaging, anticounterfeiting, and multicolor luminescence systems. 2) Light-controlled supramolecular assemblies based on macrocycles and spiropyran. Different from the diarylethenes, spiropyran can converse between positive charges in the ring-open merocyanie (MC) state, which is amphiphilic and easy to bond with macrocycles like cucurbit[n]urils, and neutral/negative charges in the ring-closed spiropyran (SP) state, which is more likely to self-assemble. Therefore, the differentiation of bonding affinities with macrocycles between MC and SP can achieve light-driven molecular machines. 3) Light-controlled supramolecular assemblies between macrocycles and azobenzene, whether azobenzene is modified to the macrocyclic hosts or functional guests, supramolecular assemblies are formed through host–guest interactions, and the topological morphology and luminescence behavior of the assemblies can be regulated by photoisomerization to apply in catalytic activity modulation, induction of microtubule (MT) assembly/disassembly, drug delivery, and others. 4) Light-controlled supramolecular assemblies based on macrocycles and anthracene, in which different bonding affinities between anthracene before and after photooxidation and macrocyclic hosts, as well as reversible dimerization, not only change the topological morphologies but also drive fluorescence phosphorescence dual imaging and the construction of photostimuli-driven luminescent lanthanide molecular switch. With the creation of macrocycles with novel building units and different modifications of photoresponsive molecules, we consider that the innovation and growth of light-controlled intelligent supramolecular materials should be more widely used in tunable material topological morphology conversion, real-time cell imaging, targeted drug delivery, organic optoelectronic materials, molecular machines, and photocatalysis reactions.