Imidazo[1,2-b]pyridazine as Building Blocks for Host Materials for High-Performance Red-Phosphorescent Organic Light-Emitting Devices

Abstract

A novel electron-transporting unit, imidazo [1,2-b]pyridazine (IP), was first reported for developing host materials. The IP moiety possesses excellent electron-transporting ability and great thermal stability. Using carbazole as p-type units and IP as n-type units, several bipolar host materials, namely, IP6Cz, IP68Cz, IP36Cz, and IP368Cz, were developed through altering the substitution site of the IP core. Among these four materials, 6-site-substituted IP6Cz and 6,8-sitesubstituted IP68Cz exhibit the best electroluminescence (EL) performance. IP6Cz-and IP68Cz-based red phosphorescent organic light-emitting diodes using Ir(pq) 2 acac as the emitter exhibit extremely high EL efficiency with the maximum external quantum efficiency (η ext,max ) of 26.9 and 25.2% and an insignificant efficiency roll-off. Moreover, IP6Cz-and IP68Cz-based deep-red devices doped by Ir(piq) 2 acac also show satisfactory EL performance with a η ext,max of 20.5 and 19.9%, respectively. The influence of different substitution sites of the IP core on the photophysical and electrochemical properties was systematically investigated. This study demonstrates that IP could be a first-rate electron-transporting unit for bipolar materials for red-emitting devices.

Synthesis and Functionalization of Imidazo[1,2‐b]Pyridazine by Means of Metal‐Catalyzed Cross‐Coupling Reactions

“…This new series of host materials 54-57 for high-performance red phosphorescent organic light-emitting devices was prepared using Suzuki-Miyaura cross-coupling method (scheme 27). [101] The reactions were performed employing Pd(PPh 3 ) 4 as catalyst with (9-phenyl-9H-carbazol-3-yl)boronic acid and specific halogenated imidazo[1,2-b]pyridazines 53(a-d) in the presence of K 2 CO 3 in THF/H 2 O at reflux for 24 h. The arylated imidazo[1,2-b]pyridazines 54-57 were obtained in good yields (scheme 27).…”

Are pure hydrocarbons the future of host materials for blue phosphorescent organic light-emitting diodes?

“…Chart 1: Selected examples of state of the art of heteroatoms-based host materials. [4][5][6][7][8][9][10] Second, regarding the stability, it has been shown that the C-N, C-P and C-S bonds, particularly in their excited states, can be easily broken by the energy of excitons formed in blue PhOLEDs (which is around 3 eV). [31][32][33] Indeed, the dissociation energies of the C-N, C-P or C-S bonds in common building units used in host materials lies in this range.…”

A meta-linkage strategy towards high-performance hosts for efficient blue thermally activated delayed fluorescence OLEDs

“…[1][2][3][4][5] To suppress exciton annihilation and concentration quenching in emitting layers, generally, these triplet-excited-state-involved emitters have to be doped into suitable host materials. [6][7][8][9][10][11] The triplet energy of the host must be higher than that of the emitter to ensure efficient exothermic energy transfer from the host to the guest molecule and to confine the triplet excitons within the emitting layers. [12][13][14] In the case of blue emitters, the lowest triplet state (T 1 ) energy level of the host should be at least 2.9 eV.…”