Light-emitting iridium complexes with tridentate ligands

Abstract

Once the Cinderella amongst the Platinum Group Metals at the Photochemistry Ball, iridium has become of intense interest since the beginning of the decade. Complexes of iridium(III) can be prepared that are highly luminescent, with emission wavelengths tuneable over the whole of the visible region. Whilst most studies have focused on tris-bidentate complexes, a rich and varied chemistry is also possible using tridentate ligands. In this review, we discuss the synthesis and excited-state properties of such complexes, exploring in particular how the number of cyclometallating carbon atoms in the coordination sphere of the metal ion influences the luminescence. Moving from [IrN6]3+ to [IrN3X3] coordination via [IrN5X]2+ and cis/trans-[IrN4X2]+ complexes, where N is a heterocyclic nitrogen and X is an anionic ligand or cyclometallated carbon, a whole range of luminescence efficiencies are encountered, ranging from the barely detectable to room temperature quantum yields approaching unity. We consider the extent to which these profound differences, arising as a result of subtle changes in molecular structure, can be rationalised in terms of the nature of the frontier orbitals.

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, structural, photophysical and electrochemical studies of various d-metal complexes of btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] ligands that give rise to the formation of metallo-supramolecular gels

“…Giving that Ir(III) is isoelectronic to Ru(II) and its complexes have long been of interest, due to their emission properties, we decided to investigate their formation herein. 28 The d 8 octahedral Ni(II) complexes are isostructural to the octahedral d 6 metal complexes. Only one example of the interaction between the btp motif and the square planar d 8 Pt(II) 10 ion has been reported, where it was used in the formation of metallopolymers.…”

Bis-Tridentate Iridium(III) Phosphors Bearing Functional 2-Phenyl-6-(imidazol-2-ylidene)pyridine and 2-(Pyrazol-3-yl)-6-phenylpyridine Chelates for Efficient OLEDs

“…The precursor to the monoanionic tridentate chelate 4-(t-butyl)-2-(2,4-difluorophenyl)-6-(3-isopropyl-imidazol-2-ylidene)pyridine (phpyim-H 2 )PF 6 , was synthesized using a multi-step protocol (Scheme 1). First, treatment of 4-(t-butyl)-2,6-dichloropyridine and imidazole in the presence of tetrabutylammonium bromide (NBu 4 Br) as a phase transfer catalyst afforded the pyridine-imidazole derivative.…”

“…complexes, have met only with limited success, 6 among which [Ir(dpyx)(dppy)] (dppy = 2,6-diphenylpyridine) and [Ir(fpbpy)(dppy)] (fpbpy = 6-(5-trifluoromethylpyrazol-3-yl)-2,2′-bipyridine) provided the basic model, i.e. the need for a pair of monoanionic and dianionic chelates in assembling the charge-neutral bis-tridentate architecture (Chart 1).…”