A New Class of Iridium Complexes Suitable for Stepwise Incorporation into Linear Assemblies: Synthesis, Electrochemistry, and Luminescence

Abstract

A new family of cationic iridium(III) complexes is reported that contain two cyclometalating terdentate ligands. The complex [Ir(N--C--N-dpyx)(N--N--C-phbpy)]+ (1) contains one N--C--N-coordinating ligand, cyclometalating through the central phenyl ring, and one N--N--C-coordinated ligand, cyclometalated at the peripheral phenyl ring [dpyxH = 1,3-di(2-pyridyl)-4,6-dimethylbenzene; phbpyH = 6-phenyl-2,2'-bipyridine]. This binding mode dictates a mutually cis arrangement of the cyclometalated carbon atoms: the complexes are thus bis-terdentate analogues of the well-known [Ir(N--C-ppy)2(N--N-bpy)]+ family of complexes, which similarly contain a cis-C2N4 coordination environment. The dpyx ligand can be brominated regioselectively at the carbon atom para to the metal under mild conditions. Starting from a modified complex, [Ir(N--C--N-dpyx)(N--N--C-mtbpy-phi-Br)]+ (2), which incorporates a pendent bromophenyl group, a sequential cross-coupling-bromination-cross-coupling strategy can be applied for the stepwise introduction of aryl groups into the ligands, using in situ palladium-catalyzed Suzuki reactions with arylboronic acids [mtbpyH-phi-Br = 4-(p-bromophenyl)-6-(m-tolyl)bipyridine]. Dimetallic complexes 6 and 7 have similarly been prepared by a palladium-catalyzed reaction of complex 2 with 1,4-benzenediboronic acid and 4,4'-biphenyldiboronic acid, respectively. All five monometallic complexes and both dimetallic systems are luminescent in solution, emitting around 630 nm in MeCN at 298 K, with quantum yields in the range of 0.02-0.06, superior to [Ir(ppy)2(bpy)]+. The luminescence, electrochemistry, and singlet-oxygen-sensitizing abilities of the new family of complexes are discussed in the context of the tris-bidentate analogues and related bis-terdentate compounds that contain a trans arrangement of cyclometalated carbon atoms.

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[92][93][94][95] In addition to the complexes bearing three bidentate ligands, the analogous compounds containing two tridentate ligands [96] (e.g., 2,2 0 :6 0 ,2 00 -terpyridine, 2,6-diaryl-pyridine, and their derivatives) have recently gained more attention as potential candidates for applications in areas such as luminescent sensors or materials for directional energy and electron transfer. [97][98][99][100][101][102][103][104] A detailed review about this concept has recently been published by Williams et al [105] Iridium(III) mono-terpyridine complexes decorated with electron-donor or -acceptor groups have furthermore been employed as asymmetric chromophores in nonlinear optics. [106,107] By introducing strong ligand-field-stabilizing ligands, such as CN À or CO, the energy gap between the HOMO and LUMO can be significantly increased resulting in anionic or cationic iridium(III) complexes with bright blue emission.…”

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

“…1, 2 and 3 ( Figure 1). [18][19][20][21][22][23][24][25][26][27][28][29] Consequently, for luminescence applications research has primarily concentrated on monoiridium complexes. 30,31 Nevertheless, the study of phosphorescent diiridium complexes is a rapidly expanding topic and a range of complexes with various conjugated bridging ligands have been reported to possess efficient photo-(PL) and electroluminescence (EL).…”

Theoretical study on the electronic structures and phosphorescent properties of a series of iridium(III) complexes with the different positional N-substitution in the pyridyl moiety

“…complexes have attracted considerable attention as the emitting layers in organic light-emitting diodes (OLEDs) because of their good color purity, high phosphorescence emission quantum yields, short excited triplet state lifetime, and high photochemical stability [1][2][3][4][5][6][7][8]. Especially, phosphorescent Ir(III) complexes have been extensively investigated due to their good phosphorescent emission properties since the pioneering works were performed by Thompson and coworkers [9][10][11].…”