A star-shaped bipolar host material based on carbazole and dimesitylboron moieties for fabrication of highly efficient red, green and blue electrophosphorescent devices

Abstract

A new bipolar host material based on carbazole and dimesitylboron moieties, 3,6-bis(dimesitylboryl)-9-(4-(dimesitylboryl)phenyl) carbazole (BDDPC), has been successfully synthesised and characterised by elemental analysis, nuclear magnetic resonance spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical and photophysical properties of BDDPC are studied by both experimental and theoretical methods. BDDPC exhibits excellent thermal stability (T_d = 234 °C), electrochemical stability, high fluorescence quantum yield (0.95) and high triplet energy (2.83 eV). A red phosphorescent organic light-emitting diode (PhOLED) device comprising BDDPC as the host material and Os(bpftz)₂(PPh₂Me)₂ as the dopant is fabricated and displays promising electrophosphorescence properties with a turn-on voltage of 3.0 V, a maximum brightness of 12 337 cd m⁻² and a maximum current efficiency of 11.04 cd A⁻¹. Similarly, BDDPC is used to fabricate a green PhOLED device with Ir(ppy)₂(acac) as the dopant, possessing a turn-on voltage of 2.5 V, a maximum brightness of 26 473 cd m⁻² and a maximum current efficiency of 38.60 cd A⁻¹. Furthermore, a blue PhOLED device with BDDPC as the host material and FIrpic as the dopant is fabricated with a turn-on voltage of 3.0 V, a maximum brightness of 7622 cd m⁻² and a maximum current efficiency of 7.39 cd A⁻¹. It is anticipated that BDDPC has great potential in manufacturing PhOLED devices for display or lighting applications.