Highly Charge Transport Thermally Activated Delayed Fluorescence Host Materials Based on Phenyl-Biscarbazolyl Derivatives.

Abstract

We designed novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence by combining the electron donor 1,3-Bis(N-carbazolyl)benzene (mCP) unit and the electron acceptor diphenylphosphine oxide-4-(triphenylsilyl) phenyl (TSPO1) unit in a single molecule based on density functional theory. We obtained the energies of the first singlet (S1) and the first triplet (T1) excited states of the TADF materials by performing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the large separation between the HOMO and LUMO caused a small difference in energy (ΔEST) between the S1 and T1 states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results showed that these molecules are promising TADF host materials because they have a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔEST.