Near-Unity Intersystem Crossing Efficiency and Bright Polymer Phosphorescence Enabled by Charge-Transfer...

Bonding aromatic ring to carbonyl group is recognized as crucial for promoting intersystem crossing (ISC) owing to allowed ¹nπ* → ³ππ* or ¹ππ* → ³nπ* 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 ¹CT→³LE (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 (S₁) and triplet (T₁) 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.