Ionic Engineering of Polymer-Based Room-Temperature Phosphorescence: Mechanistic Insights and TS-FRET-Enabled Multicolor Afterglow

Organic room-temperature phosphorescence (RTP) materials hold great promise for advanced optoelectronic applications. While ionic interactions have been shown to rigidify molecular matrices and enhance RTP, their application has largely been limited to small-molecule or crystalline systems. The mechanisms by which metal ion characteristics govern RTP in processable, amorphous polymers are still not well understood, hindering rational design of high-performance polymeric RTP materials. A series of ionic polymers are prepared by complexing poly(vinyl benzoic acid) (PVBA) with metal ions of different valences to obtain amorphous solid-state polymer materials with ion-dependent RTP properties. Valence-dependent coordination strengthens ionic cross-linking, increases chain rigidity, and suppresses nonradiative decay, thereby stabilizing triplet excitons for long-lived RTP. PVBA-Zn shows a phosphorescence lifetime of 1120 ms, a visible afterglow of ∼11 s, and a photoluminescence quantum yield (PLQY) of 18.9%, with an afterglow persisting under ambient conditions. Monovalent-ion-coordinated systems display markedly shorter lifetimes, whereas Fe 3+ coordination quenches both fluorescence and phosphorescence. Phosphorescence color is tuned by ion selection. To expand color diversity and improve PLQY, triplet-to-singlet Förster resonance energy transfer (TS-FRET) is realized by coupling long-lived PVBA-Li with Rhodamine B (RhB), yielding persistent luminescence with high PLQY (82.5%) and tunable emission color. This work provides an ion-regulated polymer platform for constructing long-lived and multicolor RTP materials.