High-efficiency blue hybridized local and charge-transfer fluorescent material affording OLEDs with external quantum efficiency exceeding 14 %

Hybridizezd local and charge-transfer (HLCT) materials are adaptable to the development of blue emissive materials for organic light-emitting diodes (OLEDs), while there is still a large room for performance improvement. In this work, we propose an effective strategy to design deep-blue/blue HLCT materials based on weak electron-donating carbazole donor (D) and electron-withdrawing dibenzoquinoxaline acceptor (A). The carbazole donor groups are substituted to the rigid dibenzoquinoxaline core in ortho-, meta-, to para-positions, resulting in HLCT materials O-2CzDQ, M-2CzDQ, and P-2CzDQ, respectively. With the D-A torsion angle gradually reduced, not only the molecular conjugation and planarity are extended, but also the LE composition and oscillator strength are increased, contributing to improved structural rigidity and enhanced photoluminescence efficiency in the para-substituted P-2CzDQ molecule. As expected, P-2CzDQ affords the best device performances such as a high external quantum efficiency of 14.6 % with blue emission, which is the highest efficiency reported amongst non-doped blue OLEDs based on HLCT materials.