Optoelectronic characterization for some of the thermally activated delayed fluorescence (TADF) emitters using Density Functional Theory (DFT).

Materials that show thermally activated delayed fluorescence (TADF) mechanism are of great interest in the organic light-emitting diodes (OLEDs) due to their 100% external quantum efficiency (EQE) with no need to incorporate heavy atoms. Since blue emitting materials with high efficiency are still in high demand, the pyrazine core was used in this study because of its high energy of S1 along with its weak accepting ability. Therefore, pyrazine-based multi-carbazoles [1-3] were studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The compounds' simulated electronic and photophysical features agree with the experimental observations. All compounds show blue emission lies at 2.77, 2.68, and 2.62 eV, respectively. Replacing one biphenyl with carbazole (compound 2) decreases the ES1-T1 to 1.09 eV. Replacing two units of bi-phenyls with carbazoles (compound 3) reduces the ES1-T1 even further to 0.26 eV, facilitating the TADF mechanism. All compounds show mixed transitions of charge transfer and locally excited character due to the increase of the donation ability with the addition of carbazole units.