High-Efficiency Dicyanobenzene-Based Organic Light-Emitting Diodes Exhibiting Thermally Activated Delayed Fluorescence

Abstract

We have designed novel thermally activated delayed fluorescence (TADF) materials, 2DMACPN and 2DMACTPN, with 9,9-dimethyl-9,10-dihydroacridine (DMAC) as an electron donor and dicyanobenzene as an electron acceptor. We obtain the zero-zero transition energies of the first excited singlet (S1) and first triplet excited (T1) states of TADF materials by performing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the ground state using a dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. The calculated ΔEST values of 2DMACPN (0.019 eV) and 2DMACTPN (0.023 eV) were smaller than those of 2CzPN (0.363eV) and 2CzTPN (0.178eV) because of the large dihedral angles between the plane of DMAC and the connected phenyl rings of PN and TPN. We show that 2DMACPN would have the highest TADF efficiency among the four compounds because it has the largest dihedral angle, which creates a small spatial overlap between the HOMO and the LUMO, and consequently the smallest ΔEST.