Cruciform Molecules Bearing Bis(phenylsulfonyl)benzene Moieties for High‐Efficiency Solution Processable OLEDs: When Thermally Activated Delayed Fluorescence Meets Mechanochromic Luminescence

Four crucifix-shaped molecules, named TPA-BPSB, DMAc-BPSB, MTPA-BPSB and MDMAc-BPSB, bearing the same acceptor fragment of bis(phenylsulfonyl)benzene (BPSB) and different donor segments (TPA and MTPA are the diphenylamine derivatives while DMAc and MDMAc are the 9,9-dimethylacridine derivatives) are synthesized and characterized by NMR, mass spectra, and single crystal X-ray crystallography. The molecular structure-property relationship of these crucifix-shaped molecules is systematically explored. All compounds display thermally activated delayed fluorescence (TADF) in the region of 500-550 nm. In addition, charming mechanochromic luminescence properties are observed for all these TADF molecules under external stimuli, such as grinding and exposure to CH2Cl2 vapor. Four TADF molecules are used as the emitters in organic light-emitting diodes (OLEDs) fabricated via solution process. MTPA-BPSB-based device presents a best performance with a highest external quantum efficiency of approximate to 21%, which is among the highest efficiencies for reported BPSB-based solution-processable OLEDs so far. This research has an important significance in designing high-efficiency multifunctional TADF molecules.