Investigation on the effect of connected bridge on thermally activated delayed fluorescence property for DCBPy emitter

Previously, extensive efforts have been devoted to designing highly performance TADF material via varying the electron-donator (D) and electron-acceptor (A) units and tried the best to find a matching combination of D and A units with high external quantum efficiency. In present work, we have investigated the effect of modifying the connected bridge between D and A units on their electronic properties. Based on the reported thermally activated delayed fluorescence (TADF) molecule DCBPy (compound 1), four compounds 2-5 have been designed by modifying the connected bridge between D and A units. For predicting the accurate singlet-triplet energy gap (ΔEST), the tuning range-separated functional has been utilized to calculate ΔEST. The calculated normal mode reorganization energy (λ) for the non-radiative decay process displays that the λ of compounds 2-5 in the high-frequency region is noticeably reduced compared with compound 1, suggesting that the high-frequency CO stretching vibration is hindered through modifying the connected bridge between D and A units. Moreover, the radiative decay rate constant (kr) values of compound 2-5 are one order of magnitude higher than that of pristine compound 1. Besides, for our designed molecules, modifying the connected bridges noticeably increase their spin-orbital coupling matrix element () values, although the ΔEST values of compound 2-5 are greater than that of compound 1. As a consequence, for this kind of DCBPy compounds, modifying the connected bridge between D and A units maybe a valid approach to improve their TADF performances.258