Dynamically Tunable Near-Infrared Photoluminescence with Long-Wavelength Energy Transfer Engineered by Multilevel Supramolecular Confinement

One of the major challenges in fabricating advanced optical materials is the achievement of efficient and tunable emission in the red to near-infrared range. To address this critical issue, a multilevel confinement strategy is employed to construct a supramolecular photoswitch, which is initially achieved by the formation of a unique 2:2 host-guest complex between cucurbit[8]uril and biphenyl-conjugated bipyridinium salt, followed by the intermolecular electrostatic wrapping with the negatively charged β-cyclodextrin-grafted hyaluronic acid. This two-stage assembling process can significantly immobilize the molecular conformation and potentiate the photoluminescence emission of the bipyridinium guest to ultimately induce a 40-fold enhancement of the red emission at 650 nm. The cyclodextrin units on the polysaccharide skeleton can further encapsulate adamantane-modified diarylethene, conferring the desired photoswitchable properties to the supramolecular assembly. The fluorescence emission can be reversibly regulated with a high photo-switching ratio and excellent fatigue resistance. Remarkably, near-infrared emission at 790 nm can be further achieved via Förster resonance energy transfer to Cy7. Benefiting from its photoswitching properties, the system is successfully applied in anti-counterfeiting and information encryption. This study establishes a versatile supramolecular engineering paradigm for constructing tunable red-to-near-infrared emission systems, which may open new avenues for designing dynamic optical and information encryption materials.