Theoretical studies on electroluminescent mechanism of a series of thermally activated delayed fluorescence emitters possessing asymmetric-triazine-cored triads

Abstract

A series of thermally activated delayed fluorescence (TADF) emitters using asymmetric-triazine-cored triad as the electron-accepting unit have been investigated theoretically. Based on two experimentally reported TADF molecules (TPXZ-as-TAZ and oDPXZ-as-TAZ), two new molecules (mDPXZ-as-TAZ and pDPXZ-as-TAZ) have been designed to explore the isomeric effect on their TADF properties. The present results reveal that the absorption and emission spectra calculated by the time-dependent density functional theory (TD-DFT) method at the M06-2X level are match well the available experimental findings, and mDPXZ-as-TAZ and pDPXZ-as-TAZ are found to exhibit the same yellow emission as their analogue oDPXZ-as-TAZ. In addition, the rates of reverse intersystem crossing of mDPXZ-as-TAZ and pDPXZ-as-TAZ estimated by the semiclassical Marcus theory are 2.51 × 106 and 4.57 × 106 s−1, respectively, one order of magnitude larger than that of oDPXZ-as-TAZ (1.27 × 105 s−1), which suggests that our newly designed two molecules mDPXZ-as-TAZ and pDPXZ-as-TAZ can be also considered as potential yellow-light TADF emitters.