Boron-containing Thermally Activated Delayed Blue Fluorescence Materials via Donor Tuning: a Theoretical Study

Based on the boron-containing thermally activated delayed fluorescence (TADF) compound p-AC (AC: acridine) 5, 9-dioxa-13b-boranaphtho 3, 2, 1-de] anthracene ( a ), a series of new TADF molecules b1 - b4 were designed via adding two nitrogen atoms at the AC donor part. Density functional theory and time-dependent density functional theory calculations were performed on the frontier orbital energy levels, emission spectra, singlet-triplet states energy gaps (\begin{document}$ \Delta E_{\rm{ST}} $\end{document}), reverse intersystem crossing (RISC) rate constant (\begin{document}$ k_{\rm{RISC}} $\end{document}) for compounds a and b1 - b4 . Our calculation results show that the maximum emission wavelengths of b1 - b4 are significantly blue-shifted by 47 - 125 nm compared with that of a . Molecules b1 and b3 exhibit dark-blue emission, while molecules b2 and b4 display light-blue emission, indicating that these four derivatives could be potential organic light-emitting diode (OLED) candidates with blue-light emitting. Moreover, we found the RISC processes in a , b2 , and b4 can occur not only from T₁ state to S₁ state, but also from T₂ state to S₁ state significantly, while the RISC processes in b1 and b3 mainly take place via the T₂→S₁ hot exciton way. Importantly, the T₁→S₁ \begin{document}$ k_{\rm{RISC}} $\end{document} values of b2 and b4 are predicted to be two to three times of that of a , indicating enhanced TADF property. Our results not only provide two promising boron-based TADF candidates ( b2 and b4 ), but also offer useful theoretical basis for the design of blue OLED materials.