Water‐Soluble Phosphonium Salts Enable Full‐Color Long‐Lived Phosphorescence in Polymer Matrix for Flexible Display and X‐Ray Imaging

Abstract The development of doped organic room‑temperature phosphorescent (RTP) polymers is hampered by the physicochemical incompatibility between hydrophilic hosts such as polyvinyl alcohol (PVA) and conventional hydrophobic phosphors. This mismatch triggers severe phase separation and lowers RTP performance. A molecular engineering strategy that addresses this challenge by introducing intrinsically water‑soluble phosphonium salt emitters is presented. The design combines a bromide counterion that enhances intersystem crossing with a bulky alkyl chain that suppresses aggregation‑induced quenching, while also guaranteeing seamless miscibility with PVA. This approach eliminates phase separation and yields highly efficient, full‑color RTP in doped films, with emissions tunable from 427 to 619 nm. The best performer shows an ultralong lifetime of 2.18 s and a quantum yield of 11.63%. Building on these properties, the versatility of the material in two key applications is demonstrated, namely high‑performance flexible displays and high‑resolution X‑ray imaging with a spatial resolution of 11.51 lp mm −1 .