Ambient Phosphor with High Efficiency and Long Lifetime in Poly(Methyl Methacrylate) Through Charge‐Transfer‐Mediated Triplet Exciton Formation for Photolithography Applications

Abstract Currently, purely organic compounds showing ambient phosphorescence with high efficiency ( Φ P ) and ultra‐long lifetime ( τ P ) are quite rare and often need to be achieved in hydrophilic poly(vinyl alcohol)‐based hosts. This severely limits their applications. Here, we provide a solution to this issue by constructing an ortho ‐linked donor‐acceptor (D−A) dyad whose D moiety has not only a long‐lived T 1 state to achieve a long τ P , but also a T n state that is close to the S 1 state of the dyad to trigger effective spin‐orbit charge transfer intersystem crossing (SOCT‐ISC). The rationality of this strategy was validated by a new phosphor OF‐BCz that is able to show a τ P of 1.92 s and a Φ P of 30 % even in a less rigid matrix of poly(methyl methacrylate) (PMMA). Excitingly, OF‐BCz exhibited its potential as both a photocuring initiator and an in situ quality indicator, allowing for the visual detection of defects in photolithographic patterning.