Efficient, Persistent and Color‐Tunable Room‐Temperature Phosphorescence by a Protonation Strategy

Phenylpyridine derivatives (PPys) have no room‐temperature phosphorescence (RTP) intrinsically. How to transform PPys into persistent and efficient RTP remains challenging. To achieve this goal, we herein present a simple protonation strategy, utilizing phenylpyridine (PPy) derivatives as the guests and poly(acrylic acid) (PAA) as the host. In situ protonation of the PPy guest (proton acceptor) by PAA matrix (proton donor) markedly intensifies the intramolecular charge‐transfer (ICT) character and induces an excited‐state quinoidal resonance structure, which are favorable for promoting intersystem crossing and enhancing molecular rigidity. The PPyOMe@PAA doped film exhibits a remarkable phosphorescence lifetime of 1.54 s and a photoluminescence quantum yield of 45.9%. Theoretical calculations indicate that the protonation‐induced quinoidal structure facilitates the generation and accumulation of the triplet excitons. Intriguingly, the phosphorescence color can be easily tuned from blue to yellow by simply changing the substituents on the PPy moiety.