Structure–Property Relationship of Triscarbazole-diphenyltriazine-type Blue Thermally Activated Delayed Fluorescent Emitters

9-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-9 ',9 ''-dip henyl9H,9 ' H,9 '' H-3,3 ':6 ',3 ''-tercarbazole (1TCzTrz) and 9,9 ''-bis(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9 '-phenyl-9H,9 ' H,9 '' H-3,3 ':6 ',3 ''-tercarbazole (13TCzTrz) derived from a triscarbazole donor and a diphenyltriazine acceptor were developed as blue fluorophores to study the structure-property relationship in thermally activated delayed fluorescence compounds. 1TCzTrz had one acceptor unit attached to the triscarbazole donor, whereas 13TCzTrz had two acceptor units attached to the triscarbazole donor. The 1TCzTrz emitter worked efficiently relative to the 13TCzTrz emitter because of the high photoluminescence efficiency. The 1TCzTrz device delivered an external quantum efficiency of 23.4% compared with 19.6% of the 13TCzTrz device. However, the 13TCzTrz device was advantageous to increase horizontal emitting dipole orientation.