Luminescence mechanism analysis of a TADF molecule showing peculiar thermal behavior

• Published in: Faraday discussions 2024-03, Vol.25, p.233-25
• Main Authors: Tsuchiya, Youichi, Mizukoshi, Keito, Saigo, Masaki, Ryu, Tomohiro, Miyata, Kiyoshi, Onda, Ken, Adachi, Chihaya
• Format: Article
• Language: English
• Subjects: Carbazoles; Decay; Electrons; Fluorescence; Luminescence; Molecular orbitals; Temperature dependence; Thermodynamic properties
• ISSN: 1359-6640; 1364-5498
• DOI: 10.1039/d3fd00151b

In recent years, much attention has been paid to the development of thermally activated delayed fluorescence (TADF) materials with short delayed-fluorescence lifetimes to improve the device performances of OLEDs. In principle, by reducing the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) overlap, while the energy difference between S 1 -T 1 (Δ E ST ) and activation energy ( E a ) can be reduced, and the reverse intersystem crossing rate constant ( k RISC ) can be accelerated, a decrease in the radiative rate constant happens, necessitating an advanced molecular design. Furthermore, a molecule based on heptazine as a parent skeleton has recently been found to have a peculiar temperature dependence of luminescence decay, suggesting a negative gap (NG) material. In this report, we show that 9-[1,4]benzoxaborino[2,3,4- kl ]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9 H -carbazole (TMCz-BO), a donor-acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of NG materials based on the temperature dependence of its luminescence decay in solution. 9-[1,4]Benzoxaborino[2,3,4- kl ]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9 H -carbazole, a donor-acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of negative gap materials.