Predicting and Designing Thermally Activated Delayed Fluorescence Molecules with Balanced ΔEST and Transition Dipole Moment

Abstract

AbstractThe investigations on the relationship between geometrical structures, excited state properties, and photophysical performance can accelerate the design of thermally activated delayed fluorescence (TADF) molecules. Herein, the photophysical properties of newly proposed organic TADF molecule: [4‐(9,9‐dimethyl‐9,10‐dihydroacridine) phenyl] (pyridin‐4‐yl)‐methanone (PyB‐DMAC), are theoretically investigated by using the quantum mechanics and molecular mechanics method. The photophysical performance dependency of PyB‐DMAC molecule on its geometrical and electronic structures, and aggregation effects are systematically analyzed. The calculated fluorescence quantum efficiencies are in good agreement with the experimental results, for instance, the calculated fluorescence efficiency of 61.2% (exp. 49%) for PyB‐DMAC molecule in the crystal phase. Based on these investigations, novel organic TADF molecules can be designed by balancing the singlet–triplet energy gap (ΔEST) and transition dipole moment. Sixteen unexplored candidates are screened with similar structures to PyB‐DMAC molecule, while two new TADF organic molecules (PyBF‐DMAC and OSOF‐DMAC) are selected with enhanced luminescence performance. The newly designed TADF molecules reveal lower reorganization energies and reduced nonradiative decay rates. The simulation results exhibit that their luminescence quantum efficiencies in toluene solvent and amorphous state are as high as 63.7%, 53.2% and 90%, 97.4%, respectively.