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Many researchers have reported dibenzo b , d furan segment as a building block of organic light-emitting diode (OLED) materials because it has high thermal stability and triplet energy. However, most of the research has focused on symmetrically substituting the same functional groups at 2-position due to easy functionalization or substituting the same functional groups at different positions of dibenzo b , d furan. Herein, we design and synthesize three new hole blocking materials based on asymmetrically difunctionalized dibenzo b , d furan, diphenyl (2-(pyridin-3-yl)dibenzo b , d furan-6-yl)phosphine oxide (DBFPO-Py), diphenyl(2-(pyrimidin-5-yl)dibenzo b , d furan-6-yl)phosphine oxide (DBFPO-Pyr), and diphenyl(2-(4-(triphenylsilyl)phenyl)dibenzo b , d furan-6-yl)phosphine oxide (DBFPO-Si) for high-performance phosphorescent OLEDs. Phosphine oxide, tetraphenylsilane, pyridine, and pyrimidine segments are successfully introduced into the asymmetric position of a dibenzo b , d furan. It is found that DBFPO-Py, DBFPO-Pyr, and DBFPO-Si possess high thermal stability; high triplet energies of 2.96, 2.98, and 2.80 eV; and deep highest occupied molecular orbital (HOMO) energy levels of −7.13, −7.23 and −7.07 eV; respectively. Blue phosphorescent OLEDs with DBFPO-Py, DBFPO-Pyr, and DBFPO-Si show low turn-on voltages, high current and power efficiencies, and superior external quantum efficiencies. Blue phosphorescent OLEDs with DBFPO-Py and DBFPO-Pyr showed improved performance in terms of current and power efficiencies, etc, compared with the device with 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB), which is commonly used as a hole blocking layer. More importantly, the blue phosphorescent OLEDs with DBFPO-Pyr showed the best performance with maximum external quantum efficiency of 23.6%, current efficiency of 29.8 cd A−1, power efficiency of 26.0 lm W−1, and low efficiency roll-off of 6.38%. Novel hole blocking materials based on asymmetrically difunctionalized dibenzo b , d furan are expected to make a significant contribution to the development of blue phosphorescent OLEDs. Image 1 • HBMs based on asymmetrically difunctionalized dibenzo b , d furan were synthesized. • HBMs possessed high triplet energy (2.96 eV) and deep HOMO energy level (−7.13 eV). • Blue PhOLEDs with HBMs showed superior external quantum efficiency (23.6%). • Blue PhOLEDs showed current and power efficiencies (29.8 cd A−1, and 26.0 lm W−1). [ABSTRACT FROM AUTHOR]

Novel n-type host materials based on tricyclic aromatic compounds, dibenzo b , d furan and dibenzo b , d thiophene (2Trz6CNDBF and 2Trz6CNDBT), have been successfully synthesized and characterized for high-performance blue thermally activated delayed fluorescence (TADF) organic light-emitting devices (OLEDs). Dibenzo b , d furan and dibenzo b , d thiophene were utilized as central molecular building blocks to achieve excellent thermal stability and high triplet energy (E T). Nitrile and diphenyltriazine functional groups were introduced at the 6- and 2- positions of the central building blocks to achieve low-lying lowest unoccupied molecular orbital (LUMO) energy levels, high E T , and excellent electron transport properties. UV–Vis absorption, low-temperature photoluminescence, and ultraviolet photoelectron spectroscopy analysis showed that 2Trz6CNDBF and 2Trz6CNDBT possessed high E T (2.95 and 2.88 eV) and low-lying LUMO energy levels (−3.43 and −3.16 eV) that were well-matched with a blue TADF emitter, 5CzCN. Moreover, the electron-only device (EOD) result revealed that 2Trz6CNDBF and 2Trz6CNDBT had excellent electron transport properties. Blue TADF OLEDs fabricated with a p-type host material, m CBP, and n-type host, 2Trz6CNDBF or 2Trz6CNDBT, exhibited lower driving voltages (3.34 and 3.26 V, respectively) than a TADF OLED with only a p-type host material, m CBP (3.83 V). Blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT exhibited superior external quantum efficiency (η ext , 15.6 and 14.7%), current efficiency (η ce , 33.8 and 32.7 cd A−1), and power efficiency (η pe , 25.6 and 25.7 lm W−1), respectively. The η ext and η ce of blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT increased by more than 70% and η pe by approximately 150% compared to those of the TADF OLED with a single p-type host, m CBP. In addition, the device lifetimes of blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT increased by more than 1000%. The efficient electron injection by the low-lying LUMO energy level, effective exciton confinement by high E T , and high thermal stability of the film morphology provided the enhanced efficiency and lifetime for blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT. Image 1 • n-Type hosts based on tricyclic aromatic compounds, dibenzo b , d furan and dibenzo b , d thiophene, were synthesized for blue TADF devices. • n-Type hosts, 2Trz6CNDBF and 2Trz6CNDBT, possessed high triplet energies (2.95 and 2.88 eV) and low-lying LUMO energy level (−3.43 and −3.16 eV). • External quantum efficiencies of blue TADF devices with n-type hosts increased by more than 70%. • Device lifetimes of blue TADF devices with n-type hosts enhanced by more than 1,000%. [ABSTRACT FROM AUTHOR]