Near‐Unity Intersystem Crossing Efficiency and Bright Polymer Phosphorescence Enabled by Charge‐Transfer Diarylketones

Abstract Bonding aromatic ring to carbonyl group is recognized as crucial for promoting intersystem crossing (ISC) owing to allowed 1 nπ* → 3 ππ* or 1 ππ* → 3 nπ* transition. The effect of charge transfer (CT) in such systems, however, is largely ignored for understanding ISC and phosphorescence efficiency. Here, we unveiled a principle for producing highly‐efficient room‐temperature phosphorescence (RTP) polymer where the role of CT in diarylketone phosphors was a prerequisite. Designed diarylketones with carbonyl group substituted by aromatic rings unsymmetrically achieved superior RTP quantum yield of >30% in copolymer. Detailed investigation indicated that 1 CT→ 3 LE (locally excited triplet state) transition with small energy gap (∆ E ST ) and strong spin‐orbit coupling underlies their ultrafast ISC, as recorded by femtosecond transient absorption (fs‐TA) spectroscopy. When single aromatic ring was bonded to carbonyl group, singlet (S 1 ) and triplet (T 1 ) states remained LE with large ∆ E ST and weak spin‐orbit coupling, leading to low RTP efficiency. Finally, manufacturing organic glass in presence of trace diarylketone monomers could generate shape‐rich three‐dimensional (3D) objects with intense afterglow under room lighting, even at high‐temperature and wet conditions. This work advances understanding on structure‐property relationship in popular aromatic ketone phosphors, and paves the way for producing afterglow materials with high brightness and stability.