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

ABSTRACT

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.