Dual Macrocycle Strategy: CB[7]/CB[8] Encapsulation Unlocks Enhanced RTP in Aqueous Bromophenyl Pyridinium Cationic...

Developing efficient room-temperature phosphorescence (RTP) in aqueous, metal-free systems remains a significant challenge. This work demonstrates a supramolecular host-guest approach to activate and amplify RTP from a metal-free brominated pyridinium derivative (PTPyBr) in water, utilizing cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) as molecular containers. Encapsulation within these macrocycles fosters the formation of rigid assemblies that effectively inhibit molecular motions and quench vibrational dissipation. This confinement strategy substantially increases phosphorescence, exhibiting a 2.27-fold and 2.60-fold emission enhancement for the CB[7] and CB[8] complexes, respectively. Supramolecular encapsulation significantly prolongs the phosphorescence lifetime from 190 µs (free PTPyBr) to 390 µs with CB[7], and most notably, to 750 µs with CB[8], highlighting the exceptional efficacy of the CB[8] confinement. Encapsulation of an organic phosphor (PTPyBr) by CB[7]/[8] in 1:1 stoichiometry, confirmed by ¹H NMR titration, Job's plot, and isothermal titration calorimetry, provides exceptional stabilization and prolongs its phosphorescence lifetime. Accordingly, this study introduces a highly adaptable supramolecular methodology for generating robust, metal-free RTP in aqueous environments, for promising applications in bioimaging, sensing technologies, and luminescent materials.