Conjugated, rigidified bibenzimidazole ancillary ligands for enhanced photoluminescence quantum yields of orange/red-emitting iridium(III) complexes

EZ-C acknowledges the University of St Andrews for financial support. We thank Umicore AG for the gift of materials. We would like to thank the Engineering and Physical Sciences Research Council for financial support for E.Z-C. (EP/M02105X/1) and for the studentship of A.H. (EP/J500549/1, EP/K503162/1, EP/L505097/1). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. We also would like to thank EaStCHEM and the School of Chemistry for supporting the computing facilities maintained by Dr. H. Früchtl.A series of six novel [Ir(C^N)2(N^N)](PF6) complexes (C^N is one of two cyclometalating ligands: 2-phenyl-4-(2,4,6-trimethylphenyl)pyridine, MesppyH, or 2- (napthalen-1-yl)-4-(2,4,6-trimethylphenyl)pyridine, MesnpyH; N^N denotes one of four neutral diamine ligands: 4,4’-di-tert-butyl-2,2’-bipyridine, dtbubpy, 1H,1’H-2,2’- bibenzimiazole, H2bibenz, 1,1’-(α,α’-o-xylylene)-2,2’-bibenzimidazole, o-Xylbibenz or 2,2’- biquinoline, biq) were synthesised and their structural, electrochemical and photophysical properties comprehensively characterised. The more conjugated MesnpyH ligands confer a red-shift in the emission compared to MesppyH but maintain high photoluminescence quantum yields due to the steric bulk of the mesityl groups. The H2bibenz and o-Xylbibenz ligands are shown to be electronically indistinct to dtbubpy but give complexes with higher quantum yields than analogous complexes bearing dtbubpy. In particular, the rigidity of the o-Xylbibenz ligand, combined with the steric bulk of the MesnpyH C^N ligands, give a red-emitting complex 4 (λPL = 586, 623 nm) with a very high photoluminescence quantum yield (ΦPL = 44%) for an emitter in that regime of the visible spectrum. These results suggest that employing these ligands is a viable strategy for designing more efficient orange-red emitters for use in a variety of photophysical applications.PostprintPeer reviewe

Conjugated, rigidified bibenzimidazole ancillary ligands for enhanced photoluminescence quantum yields of orange/red-emitting iridium(III) complexes

A series of six novel [Ir(C^N)2(N^N)](PF6) complexes (C^N is one of two cyclometalating ligands: 2-phenyl-4-(2,4,6-trimethylphenyl)pyridine, MesppyH, or 2- (napthalen-1-yl)-4-(2,4,6-trimethylphenyl)pyridine, MesnpyH; N^N denotes one of four neutral diamine ligands: 4,4’-di-tert-butyl-2,2’-bipyridine, dtbubpy, 1H,1’H-2,2’- bibenzimiazole, H2bibenz, 1,1’-(α,α’-o-xylylene)-2,2’-bibenzimidazole, o-Xylbibenz or 2,2’- biquinoline, biq) were synthesised and their structural, electrochemical and photophysical properties comprehensively characterised. The more conjugated MesnpyH ligands confer a red-shift in the emission compared to MesppyH but maintain high photoluminescence quantum yields due to the steric bulk of the mesityl groups. The H2bibenz and o-Xylbibenz ligands are shown to be electronically indistinct to dtbubpy but give complexes with higher quantum yields than analogous complexes bearing dtbubpy. In particular, the rigidity of the o-Xylbibenz ligand, combined with the steric bulk of the MesnpyH C^N ligands, give a red-emitting complex 4 (λPL = 586, 623 nm) with a very high photoluminescence quantum yield (ΦPL = 44%) for an emitter in that regime of the visible spectrum. These results suggest that employing these ligands is a viable strategy for designing more efficient orange-red emitters for use in a variety of photophysical applications

Dinuclear Ruthenium Complexes Containing the Hpbl Ligand: Synthesis, Characterization, Linkage Isomerism, and Epoxidation Catalysis

Three dinucleating Ru–Cl complexes containing the hexadentate dinucleating ligand [1,1′-(4-methyl-1<i>H</i>-pyrazole-3,5-diyl)­bis­(1-(pyridin-2-yl)­ethanol)] (Hpbl) and the meridional 2,2′:6′,2″-terpyridine ligand (trpy) have been prepared and isolated. These complexes include {[RuCl­(trpy)]₂(μ-pbl-κ-N³O)}⁺ (<b>1a</b>⁺), {[RuCl­(trpy)]₂(μ-Hpbl-κ-N³O)}²⁺ (<b>1b</b>²⁺), and {[RuCl­(trpy)]₂(μ-Hpbl-κ-N²O²)}²⁺ (<b>1c</b>²⁺) and were characterized by analytic and spectroscopic techniques. In addition, complexes <b>1b</b>²⁺ and <b>1c</b>²⁺ were characterized in the solid state by monocrystal X-ray diffraction analysis. The coordination versatility of the Hpbl ligand allows the presence of multiple isomers that can be obtained depending on the Ru oxidation state and were thoroughly characterized by electrochemical techniques, namely, cyclic voltammetry and coulometry. Finally, <b>1a</b>^<b>+</b> and its recently reported mononuclear analogue, <i>in</i>-[RuCl­(Hpbl)­(trpy)]⁺, have been tested as catalysts for epoxidation of <i>cis</i>-β-methylstyrene