Carbonyl Activation and Heavy‐Atom Modulation of Spin–Orbit Coupling for Efficient Triplet Harvesting in Aromatic Phosphors

Bright room-temperature phosphorescence (RTP) and efficient triplet harvesting in purely organic systems remain fundamentally limited by weak spin-orbit coupling (SOC) and inefficient intersystem crossing (ISC). Herein, we report a two-step excited-state engineering strategy combining aromatic carbonyl activation and halogen heavy-atom modulation to achieve controllable triplet-dominated emission and enhanced RTP efficiency in aromatic systems. Aromatic carbonyl incorporation reconstructs the excited-state electronic manifold by converting intrinsic π → π* states into mixed n → π*/π → π* donor-acceptor configurations, markedly enhancing SOC and accelerated ISC. This enables efficient triplet population with triplet-emission contribution up to 82% in carbonyl-functionalized coronene derivatives (BCorP), while preserving efficient triplet harvesting in rigid polymer matrices. Further halogen substitution regulates spin dynamics through the internal heavy-atom effect without significantly altering the electronic structure. As a result, Br substitution affords the highest triplet-emission contribution (~52%), whereas Cl substitution achieves the highest photoluminescence quantum yield (~15%). This work provides a general strategy for triplet exciton engineering and offers design principles for high-performance organic RTP materials.