Sky-Blue Thermally Activated Delayed Fluorescence with Intramolecular Spatial Charge Transfer Based on a Dibenzothiophene Sulfone Emitter

Intramolecular spatial charge transfer (ISCT) plays a critical role in determining the optical and charge transport properties of thermally activated delayed fluorescence (TADF) materials. Herein, a new donor/acceptor-type TADF compound based on rigid dibenzothiophene sulfone (DBTS) moiety, <b>STF-DBTS</b>, was designed and synthesized. Fluorene unit was used as a rigid linker to position the rigid acceptor and donor subunit in close vicinity with control over their spacing and molecular structure and to achieve high photoluminescence quantum yield (∼53%) and TADF property. For comparison purposes, we constructed the more flexible <b>STF-DPS</b> with a less rotationally constrained diphenylsulphone (DPS) acceptor instead of the rigid DBTS units, and <b>STF-DPS</b> showed no TADF properties and lower PLQY (16.0%). Organic light-emitting diodes (OLEDs) based on <b>STF-DBTS</b> achieve an external quantum efficiency (EQE) of 10.3% at 488 nm, which is a fivefold improvement in EQE with respect to <b>STF-DPS</b>.