The optical spectra of DMAC-based molecules for organic light-emitting diodes: Hybrid-exchange density functional theory study

Organic light-emitting diodes (OLED) have considerable advantages over the conventional counterpart. Molecular design by simulations is important for the discovery of new material candidate to improve the performance of OLED. Recently, thermally assisted delayed fluorescence OLED based on DMAC (9,9-dimethyl-9,10-dihydroacridine)-related molecules have been found to have superior performance. In this work, a series of first-principles calculations are performed on DMAC-DPS (diphenylsulfone, emission of blue-color light), DMAC-BP (benzophenone, green), DMAC-DCPP (dicyclohexylphosphonium, red), and the newly designed DMAC-BF (enaminone difluoroboron complexes, red) molecules, based on time-dependent density-functional theory, the hybrid-exchange density functional, and the long-range corrected hybrid-exchange density functional. By varying the percentage of Hartree-Fock (HF) exchange in the hybrid-exchange functional, the emission spectra can be over 97% fitted to the experimental results. We found that the fitted proportion of HF will increase as the wavelengths of the molecules decrease (30% for DPS, 20% for BP, and 10% for DCPP). By contrast, the long-range corrected hybrid-exchange density functional can lead to a good estimate on the absorption spectra. In addition, we have also applied our fitting computational procedure to the newly designed molecule. The molecular orbitals involved in the related excited states have also been investigated for these molecules, which show a common charge-transfer characteristic between the acceptor part (DPS/BP/DCPP/BF) and the donor (DMAC).