Abstract:

A series of thermally activated delayed fluorescence (TADF) materials (1-3) based on triphenylamine/diphenyl sulfone were synthesized by Suzuki cross-coupling reactions. The optical, electrochemical, delayed fluorescence, and thermal properties of these materials were characterized by UVVis spectroscopy, time-resolved fluorescence spectroscopic measurements, cyclic voltammetry (CV), theoretical calculations, thermal gravimetric analyses, and differential scanning calorimetry. Materials 1-3 are bipolar compounds based on intramolecular charge transfer (ICT), and they have small energy gaps between the singlet and triplet (ΔE_ST) of 0.46, 0.39, and 0.29 eV, respectively. The results of fluorescent quantum yields and fluorescent lifetime indicate that these materials can emit delayed fluorescence, and material 3 has the greatest potential as a TADF emitter among materials 1-3. The highest occupied molecular orbital (HOMO) energy levels of materials 1-3 were estimated to be -4.91, -4.89, and -4.89 eV, respectively. From the HOMO energy levels and the optical bandgap (E_g) values, the lowest unoccupied molecular orbital (LUMO) energy levels were estimated to be -1.74, -1.89, and -1.94 eV for materials 1-3, respectively. Thermal gravimetric analysis results reveal that materials 1-3 have high thermal decomposition temperatures (T_d), corresponding to 5% weight loss at 436, 387, and 310 ℃, respectively.

Key words: Triphenylamine, Diphenyl sulfone, Bipolar, Intramolecular charge transfer, Energy gap between singlet and triplet, Thermally activated delayed fluorescence