A theoretical investigation on the thermally activated delayed fluorescence characteristics of the isomers of DTCBPy

It has been reported that 3, 5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-phenyl)(pyridin-4-yl)meth (DTCBPy) is an efficient thermally activated delayed fluorescence (TADF) molecule. We designed a series of the isomeric molecules (2–5) of DTCBPy (1) by changing the position of nitrogen atom in the acceptor and the substituent position of donor units. The highest occupied molecular orbitals (HOMO) of 1–5 are all delocalized over the donor units, and the lowest unoccupied molecular orbitals (LUMO) are located on the acceptor unit. As expected from frontier molecular orbital analysis, the singlet-triplet energy splitting (ΔEST) values of 1–5 are in a small range from 0.087 to 0.147 eV, indicating the easy realization of reverse intersystem crossing from the lowest triplet to singlet excited states. However, the structural modification has a significant influence on the fluorescence radiative rate (kr), which varies from 3.49× 106 to 2.04 × 107 s−1 for 1–5. This work is expected to provide valuable information for synthesizing highly efficient TADF materials based on DTCBPy. In this work, based on DTCBPy (1), four isomeric TADF molecules (2–5) have been designed by changing the position of the nitrogen atom in the acceptor unit and the substituent position of donor units. Using density functional theory calculation, the structure-property relationship has been revealed. The calculated results indicate that 1–5 show a noticeable HOMO and LUMO separation. As expected from the HOMO and LUMO distributions, the singlet-triplet energy splitting (ΔEST) values of 1–5 are very small, which are in a range from 0.087 to 0.147 eV. Such small ΔEST is advantage for the realization of reverse intersystem crossing from the lowest triplet to singlet excited states. [Display omitted] •Four isomeric molecules (2–5) of DTCBPy (1) have been designed.•HOMO of 1–5 are delocalized over the donor units, and the LUMOs are located on the acceptor unit.•ΔEST values of 1–5 are very small, indicating an efficient T1→S1 RISC.•kr values of 1–5 vary from 3.49 × 106 to 2.04 × 107 s−1.