Effect of number of donor-acceptor repeat units and macrocyclic configuration on excited state properties in TADF emitters: A multiscale theoretical study

Thermally Activated Delayed Fluorescent (TADF) molecules with Donor (D) -Acceptor (A) -Donor-Acceptor pi-Conjugated Macrocycle structures have broad application potential in organic light-emitting diodes. In this paper, three D - A line type and one D - A - D - A pi-Conjugated Macrocycle molecules with same donor and acceptor groups are investigated using polarizable continuum model (PCM) combined with density functional theory (DFT) and time-dependent functional theory (TD-DFT) in solvent and film. It is found that the macrocyclic structure has a smaller energy gap (Delta EST) between the first singlet excited state (S1) and the first triplet excited state (T1) than the linear structure. The TADF efficiency is also analyzed based on the calculation of spin-orbit coupling (SOC) and the (reverse) intersystem crossing (RISC) rates between S1 and T1. The macrocyclic molecules have larger SOC and faster RISC rates, which also well explains the experimental predictions and results.