Boron-based TADF emitters with improved OLED device efficiency roll-off and long lifetime

A class of four-coordinate boron complexes is reported that contain both electron-rich and electron-poor functional groups. Judicious selection of donor and acceptor moieties with the use of a boron atom as a separating node yields charge transfer complexes capable of thermally activated delayed fluorescence (TADF). Complexes were prepared by a modular method providing access to a wide range of emission colors. The singlet (S1) and triplet (TI) energies are independently tuned to achieve a small S-1-T-1 gap. Raising and lowering of S-1 and T-1 states can be predicted using cyclic voltammetry, NTO analysis, and spin density distribution as determined using Density Functional Theory; separation of the hole and electron wavefunction for S-1 excitation and delocalization of spin density distribution in the T-1 state can help in achieving negligible S-1-T-1 gap. Although photoluminescent quantum yields of the boron complexes in a host matrix are less than 65%, OLED device external quantum efficiencies of up to 8.1% have been achieved at a luminance of 1000 cd/m(2). Selection of a boron emitter with a gap of less than 0.01 eV between the singlet and triplet excited state enables the fabrication of a device with low efficiency roll off and long lifetime. (C) 2017 Elsevier Ltd. All rights reserved.