Triplet Exciton Harvesting in Water by a Structurally Simple Organic Phosphor with Sustained Afterglow and Lifetime Tunability

Ultra-long room temperature phosphorescence (URTP) materials are extremely promising for applications in organic electronics. Creating materials with controlled photophysics to achieve this, however, is difficult due to the challenges in filling up and stabilizing the sensitive triplet excited states at ambient temperature. Herein, triplet excitons are harvested by an intuitively designed structurally simple organic phosphor in water under ambient conditions by using supramolecular host-guest chemistry with cucurbituril-7 (CB7) and sodium dodecyl sulphate (SDS), a negatively charged surfactant, with high photoluminescence (PL) quantum yields (PLQYs) (69% and 73% for CB7 and SDS, respectively) and phosphorescence lifetimes (12.52 and 12.42 ms for CB7 and SDS, respectively). A protective polyvinyl alcohol (PVA) film successfully controls the afterglow emission, excited state lifetime as well as PLQY in a single organic phosphor (CzPy24+). While a 1% concentration of CzPy24+ in the PVA film shows blue phosphorescence with 78.82% PLQY having a lifetime of 1.9 s, a 5% of CzPy24+ addition shows a green afterglow with 67.52% PLQY and a lifetime of 1.3 s. Similarly, yellow afterglow is achieved on adding 20% CzPy24+ to the PVA film with a PLQY of 40.88%. The findings are promising and helpful in constructing tunable phosphors for suitable applications. An intuitively designed organic phosphor could tune the ultra-long room temperature phosphorescence in aqueous environment under ambient conditions through imposed restrictions in the molecular dynamics.image