Small Molecular Glasses Based on Multiposition Encapsulated Phenyl Benzimidazole Iridium(III) Complexes: Toward Efficient Solution-Processable Host-Free Electrophosphorescent Diodes

Abstract

Three electrophosphorescent small molecular Ir(3+) complexes, Ir(HexPhBI)(3) 1 (HexPhBI = 1-Hexyl-2-phenyl-1H-benzo[d]imidazole), Ir(CzPhBI)(3) 2 (CzPhBI = 9-(6-(2-phenyl-1H-benzo[d]imidazol-1-yl)hexyl)-9H-carbazole), and Ir(Cz(2)PhBI)(3) 3 (Cz(2)PhBI = 9-(6-(4-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo[d]imidazol-2-yl)phenoxy)hexyl)-9H-carbazole), were synthesized in which 3 was designed with the structure of multiposition encapsulation. Compared to the hexyl-substituted 1, 2 and 3 end-capped with the conjugated carbazole moieties have improved thermal stability. X-ray diffraction analysis proved the amorphous state of 2 and 3. High-photoluminescent efficiencies of 3 are achieved as 72% in solution and 61% in solid. It indicates that the peripheral carbazoles not only facilitate the separation of triplet-emission cores and reduce the intermolecular aggregation but also supply a routine for the intermolecular energy transfer. Electrochemical analysis showed the more oxidation states of 3, which might be anticipated to make it superior to 1 and 2 in hole injection and transporting. The important role of the peripheral carbazole moieties in carrier injection/transporting and the optical properties of the complexes were further investigated by Gaussian simulation. A dramatic electroluminescent (EL) performance, including external quantum efficiency of nearly 6%, low turn-on voltage of 2.5 V, and high brightness over 6000 cd m(-2), from the host-free spin-coated device of 3 was achieved. The superiority of multiencapsulation in EL was proved by comparing the EL performance of 2 and 3. By making comparison between the host-free and phosphor-doping devices, it indicated that the combined modification of the aliphatic chains and functional groups in multipositions is a feasible approach to realize the high-efficiency small molecular phosphorescent materials.

Synthesis of cationic iridium(III) complexes with high quantum yield via enhancing the steric hindrance of ligands

“…Successful example of enhancing the efficiency of Ir(III) complexes by introducing bulky side groups into ligands has also reported by Xu and his-cowokers [39,40]. However, there were few reports about improvement of quantum efficiency for cationic Ir(III) complexes by increasing the steric hindrance of complexes [41e46], especially through grafting the rigid ring end-capped aliphatic chains, such as carbazole-9-yln-butyl group (here, abbreviated as 'CZB'), on the biscyclometalated ligands and/or ancillary ligands of cationic Ir(III) complexes.…”

Direct imaging of biological sulfur dioxide derivatives in vivo using a two-photon phosphorescent probe

“…The cyclometalated iridium(III) chloro-bridged dimers were synthesized according to a procedure described in the literature [30,32] …”

Synthesis, structure, photophysical and electroluminescent properties of a blue-green self-host phosphorescent iridium(III) complex

“…The absorption band at 264 nm is assigned to the singlet pep * charge transition in the main ligand 2-phenylbenzimidazole. The above absorption bands are similar to the main ligand CzPhBI [10]. The band at 380e490 nm is ascribed to the triplet exciton transition from the metal to ligand charge transition ( 3 MLCT).…”

“…Yue et al [10] have reported a series of green iridium(III) complexes with hole-transporting carbazole group as its side chain that could act as single emitting layer. With the introduction of carbazole group, good electroluminescent performances have been achieved with a high luminance over 6000 cd m À2 .…”