An Air‐ and Water‐Stable B<sub>4</sub>N<sub>4</sub>‐Heteropentalene Serving as a Host Material for a Phosphorescent OLED
Junki Kashida, Yoshiaki Shoji, Yasuhiro Ikabata, Hideo Taka, Hayato Sakai, Taku Hasobe, Hiromi Nakai, Takanori Fukushima
Abstract
Abstract Replacement of the carbon–carbon bonds of antiaromatic compounds with polar boron–nitrogen bonds often provides isoelectronic BN compounds with excellent thermodynamic stability and interesting photophysical properties. By this element‐substitution strategy, we synthesized a new B 4 N 4 ‐heteropentalene derivative, 1 , which is fully substituted with mesityl groups. Owing to kinetic protection by the sterically bulky substituents, 1 is remarkably stable toward air and even water. Single‐crystal X‐ray analysis of 1 revealed the bonding characteristics of the B 4 N 4 ‐heteropentalene structure. In a glassy matrix, 1 emitted short‐wavelength phosphorescence with an onset at 350 nm, indicating that the triplet energy is substantially high. DFT calculations reasonably explained the ground‐ and excited‐state electronic structures of 1 as well as its emission properties. Motivated by the high‐energy triplet state of 1 , we used it as a host material to fabricate a phosphorescent organic light‐emitting diode with an external quantum efficiency of 15 %.