Novel donor-spacer-acceptor compound as the multifunctional component of exciplexes for efficient organic light-emitting diodes

Abstract

By connecting tercarbazole (3Cz) and triphenyltriazine (TRz) units with a diphenyl ether group, we designed and synthesized a new donor-spacer-acceptor structure molecule 9′-(4-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenoxy) phenyl)-9′H-9,3′:6′,9″-tercarbazole (3Cz-o-TRz) as the multifunctional component of exciplex emitters. As expected, the intermolecular charge-transfer transition is dominant for 3Cz-o-TRz because of the space-enough and conjugation-forbidden linkage of the diphenyl ether group, increasing the intrinsic characteristics of the 3Cz and TRz moieties in its single-molecule state. Accordingly, three common electron acceptors (4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (B3PyMPm), 4,6-bis(3,5-di(pyridin-4-yl)phenyl)-2-methylpyrimidine (B4PyMPm), and (1,3,5-triazine-2,4,6-triyl) tris(benzene-3,1-diyl)tris(diphenylphosphineoxide) (POT2T)) and three common electron donors (4,4′-(cyclohexane-1,1-diyl)bis(N, N-di-p-tolylaniline) (TAPC), tris(4-(10H-phenoxazin-10-yl)phenyl)amine (TPA-PXZ), and N1-phenyl-N4, N4-bis(4-(phenyl(m-tolyl)amino)phenyl)-N1-(m-tolyl)benzene-1,4-diamine (m-MTDATA)) were chosen to construct six exciplex emitters with 3Cz-o-TRz. In the organic light-emitting diodes (OLEDs), the emission spectra of these exciplex emitters could be gradually modulated from 510 to 590 nm. In addition, TAPC:3Cz-o-TRz- and 3Cz-o-TRz:PO-T2T-based OLEDs achieved desirable performance with maximum external quantum efficiencies (EQEs) around 12%. Moreover, a simple tandem OLED containing TAPC:3Cz-o-TRz and 3Cz-o-TRz:PO-T2T emitters realized optimal performance with an ultralow turn-on voltage of 2.4 V and a maximum EQE of 14.1%. These results indicate the great potential of the donor-spacer-acceptor structure compounds in developing exciplex emitters.