Unexpected Emission Behaviors of Rhodamine Derivatives in PVA After UV‒Green Light Excitation

Abstract Rhodamine derivatives are a class of common fluorescent dyes and are usually co‐doped with room temperature phosphorescence (RTP) polymers for tuning colors; here, their unusual luminescence properties in polyvinyl alcohol are first disclosed. The doped polyvinyl alcohol (PVA) films are photo‐excited for 0.5‒1 min and emit orange and red afterglows with lifetimes of over 1 s at room temperature. More unexpectedly, the respective prompt and delayed room temperature emission colors and spectra are identical, and the red‐shifted afterglows are observed in liquid nitrogen, indicating that room temperature afterglow is thermally activated delayed fluorescence (TADF). Their molecular structure features and quantum chemical calculations support this inference. Impressively, the room temperature afterglows are visible light excitable up to 540 nm since the maximal and strong absorption bands are in green regions. Hence, this work discloses unknown excitation and emission properties of rhodamine derivatives and provides the really visible light excited yet intrinsic red TADF afterglows for the first time.