Charge Transfer Mediated Spin‐Flipping for Harvesting Triplet Exciton in D‐A Corannulene Dyes

Abstract Corannulene ( Cor ) possesses an unique curved conjugated structure and remarkable photoelectric properties, yet its application is hindered by low triplet exciton utilization and unclear decay pathway regulation. This study proposes a strategy to regulate the spin‐flipping process by precisely alignment of charge transfer (CT) state energy levels for enhancing triplet excitons harvesting in Cor . An electron donor−acceptor dye ( Cor‐PTZ ) with phenothiazine (PTZ) donor and Cor acceptor is constructed. Cor‐PTZ demonstrates thermally activated delayed fluorescence (TADF) emission with a small singlet‐triplet energy gap, enabling fast spin‐flipping for harvesting triplet excitons to support a maximum external quantum efficiency of 18.5% in OLEDs. Selective sulfur oxidation in Cor‐PTZ yields Cor‐PTZ‐O _X (X = 1, 2) , which show elevated CT energy levels. This elevation suppresses reversed intersystem crossing, switching the dominant emission pathway from TADF to room‐temperature phosphorescence (RTP). Nanosecond transient absorption spectroscopy and density functional theory calculation confirm that the low‐lying triplet states are delocalized ³ CT state in Cor‐PTZ whereas the localized triplet state on Cor unit in Cor‐PTZ‐O _X (X = 1, 2) . This work reveals that the energy positioning of CT states dictates the spin‐flipping, offering a general molecular design strategy for efficient triplet exciton utilization in curved polycyclic aromatic hydrocarbon systems.