Efficient thermally activated delayed fluorescence carbazole derivatives with a cofacial acceptor/donor/acceptor chromophore: comparable luminescent properties to their counterparts with the opposite configuration of donor/acceptor/donor

Abstract

Four carbazole derivatives, PTBPAC, PTPAC, BPTBPAC and BPTPAC, are designed and synthesized for broadening the carbazole-containing thermally activated delayed fluorescence (TADF) materials. The compounds all contain a cofacial acceptor/donor/acceptor structural unit, in which two triphenyltriazine acceptors and one triphenylamine donor are fixed at the 1,9,8-positions of a single carbazole. The multiple π–π conjugations between the donor and acceptor powerfully restrict the mutual motion of the donor and acceptor, and thus create a firm sandwich structural TADF chromophore with intramolecular through-space charge transfer channels. Accordingly, the compounds exhibit high photoluminescence (PL) quantum yields of up to 91% and short delayed lifetimes of 4.4–5.5 μs with extremely small single–triplet splitting energies. Their solution-processed devices achieve excellent electroluminescent (EL) performances with the maximum external quantum efficiency of up to 18.4%, a low turn-on voltage and a relatively small efficiency roll-off. The PL and EL properties are comparable to those of their counterparts with a donor/acceptor/donor structural unit.