Design of ortho -Substituted Donor-Acceptor Molecules as Highly Efficient Green Thermally Activated Delayed Fluorescent Emitters

The ortho-substituted donor-acceptor molecules 2-(4,6-diphenyl-1, 3, 5-triazin-2-yl)-N,Ndiphenylaniline (DPA-o-Trz) and 2-(4,6-diphenyl-1, 3, 5-triazine-2-yl)-N,N-di-p-tolylaniline (MPA-o-Trz) were designed, synthesized, and found to exhibit green fluorescence characteristics. Notably, the singlet-triplet energy gap was less than 0.1 eV, indicating that reverse intersystem crossing gave rise to thermally activated delayed fluorescence (TADF). The organic light-emitting device performance of MPA-o-Trz showed a high external quantum efficiency of 16.3% and good color stability from 0.1 cd/m2 to 5000 cd/m2.