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

By connecting tercarbazole(3 Cz)and triphenyltriazine(TRz)units with a diphenyl ether group,we designed and synthesized a new donor-spacer-acceptor structure molecule9’-(4-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenoxy)phenyl)-9’H-9,3’:6’,9"-tercarbazole(3 Cz-o-TRz)as the multifunctional component of exciplex emitters.As expected,the intermolecular charge-transfer transition is dominant for3 Cz-o-TRz because of the space-enough and conjugation-forbidden linkage of the diphenyl ether group,increasing the intrinsic characteristics of the 3 Cz 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(B3 PyMPm),4,6-bis(3,5-di(pyridin-4-yl)phenyl)-2-methylpyrimidine(B4 PyMPm),and(1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-diyl)tris(diphenylphosphineoxide)(POT2 T))and three common electron donors(4,4’-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline)(TAPC),tris(4-(10 H-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 3 Cz-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:3 Cz-o-TRz-and 3 Cz-o-TRz:PO-T2 T-based OLEDs achieved desirable performance with maximum external quantum efficiencies(EQEs)around 12%.Moreover,a simple tandem OLED containing TAPC:3 Cz-o-TRz and 3 Czo-TRz:PO-T2 T emitters realized optimal performance with an ultralow turn-on voltage of 2.4 V and a maximum EQE of14.1%.These results indicate the great potential of the donorspacer-acceptor structure compounds in developing exciplex emitters.