Light‐Harvesting Supramolecular Phosphors: Highly Efficient Room Temperature Phosphorescence in Solution and Hydrogels

Abstract Solution phase room‐temperature phosphorescence (RTP) from organic phosphors is seldom realized. Herein we report one of the highest quantum yield solution state RTP (ca. 41.8 %) in water, from a structurally simple phthalimide phosphor, by employing an organic–inorganic supramolecular scaffolding strategy. We further use these supramolecular hybrid phosphors as a light‐harvesting scaffold to achieve delayed fluorescence from orthogonally anchored Sulforhodamine acceptor dyes via an efficient triplet to singlet Förster resonance energy transfer (TS‐FRET), which is rarely achieved in solution. Electrostatic cross‐linking of the inorganic scaffold at higher concentrations further facilitates the formation of self‐standing hydrogels with efficient RTP and energy‐transfer mediated long‐lived fluorescence.