Design Strategy of Decorating Phenylcarbazole with a Donor and Acceptor for Blue-Shifted Emission in Thermally Activated Delayed Fluorescent Emitters.

A series of blue thermally activated delayed fluorescent (TADF) emitters of 1''-(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9''-diphenyl-9H,9''H-3,3':9',4''-tercarbazole (TrzCz1) and 3',6'-di-tert-butyl-1-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-4,9'-bicarbazole (TrzCz2) were synthesized through a molecular design approach to decorate phenylcarbazole with a donor and an acceptor. The 1- and 4-positions of the phenylcarbazole core were modified with a diphenyltriazine acceptor and a bicarbazole or tert-butylcarbazole donor, respectively, through a synthetic strategy to introduce Br at the 1-position and F at the 4-position. The TrzCz1 and TrzCz2 emitters showed maximum photoluminescence emission bands at λ=443 and 433 nm, which were blueshifted relative to those of the corresponding TADF emitters with the same donor and acceptor, respectively. In the device application, the TrzCz1 emitter showed a maximum external quantum efficiency of 22.4 %, with a color coordinate of (0.16, 0.21), and the TrzCz2 emitter showed a maximum external quantum efficiency of 9.9 %, with a color coordinate of (0.14, 0.09). This work proved that the design strategy of decorating phenylcarbazole with a donor and an acceptor is effective at blueshifting the emission of TADF emitters.