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,N diphenylaniline (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/m 2 to 5000 cd/m 2 .