Meta-Pyridyl Substitution for New Blue Host Materials with Enhanced Thermal Stability and Electron-Injection Properties

Two new host materials, 3-(3-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)phenyl)pyridine (TDBA-Py) and 3,3′-(5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-1,3-phenylene)dipyridine (TDBA-dPy), were designed and synthesized by introducing one pyridine unit at the meta position and two pyridine units at the 3,5-positions, respectively, of the terminal phenyl ring of the TDBA core, a 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DOBNA)-based multiple-resonance framework, and the resulting changes in their properties were analyzed. By controlling the number of pyridine substituents at the meta positions of a single phenyl ring, the extension of intramolecular conjugation was suppressed, which maintained a high triplet energy (T1 ≥ 2.76 eV) and the emission wavelength and simultaneously improved the electron-injection properties. In the devices employing ν-DABNA as the dopant, the TDBA-Py-based device exhibited a low turn-on voltage of 2.5 V, a maximum power efficiency (PEmax) of 10.9 lm W−1, and a maximum current efficiency (CEmax) of 12.5 cd A−1, which can be attributed to its lowered lowest unoccupied molecular orbital (LUMO) level. These results demonstrate that introducing appropriate electron-accepting character through single pyridine substitution is an effective host-design strategy for improving device efficiency.