Exploring the Chemistry and Photophysics of Substituted Picolinates Positional Isomers in Iridium(III) Bisphenylpyridine Complexes

Abstract

2017) 'Exploring the chemistry and photophysics of substituted picolinates positional isomers in iridium(III) bisphenylpyridine complexes. ', Organometallics., 36 (15).The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. KEYWORDSPicolinate substitution, molecular building block, iridium, positional difference ABSTRACT: A simple and versatile route for modifying picolinate ligands coordinated to iridium is described. Reacting a µ-chloro iridium(C^N) dimer (where C^N is a phenylpyridine based ligand) with bromopicolinic acid (HpicBr) yields the corresponding iridium(C^N)2(picBr) complexes (1-4 and 11), which were readily modified by a Sonogashira reaction to give eight alkyne-substituted picolinate complexes (5-10, 12 and 13).The luminescent behaviour of these complexes shows that the position of substitution about the picolinate ring has both an effect on photophysical behaviour as well as the reactivity. and rely on dipole-dipole coupling between transition dipole moments of the donor and acceptor; 18 and ii) Dexter energy transfers, which involve the electron exchange between donor and acceptor. tend to favour conjugated tethers, but which can occur over a 20 Å distance between the sensitizer and emitter. 19 The most common approach to joining iridium sensitizers to an emitter is to attach the tether to the ancillary ligand of the iridium complex. This approach is favoured because the conditions required to coordinate the primary ligands are often harsh and lead to ligand exchange, but in contrast, the ancillary ligand coordinating conditions are typically mild, allowing for the ligand to be modified prior (or post) to coordination. The two most modified types of ancillary ligands are acetylacetonate (acac) and diimine ligands (e.g., 1,10phenanthroline [phen] or 2,2ˈ-bipyridine [bpy]). Acetylacetonate has been extensively modified at the beta methyl (β-methyl) positions with an assortment of aromatic and alkyl groups; 20-26 the unoccupied orbitals of acac tend to be high in energy and therefore have little involvement in the photophysics of the complexes. Recently, however, Zeissel et al., by substituting the central position with aromatic groups containing accessible triplet states, have demonstrated that it is possible to introduce an interligand energy transfer. 26,27 Diimine ligands tend to have low-lying π * orbitals, which result in the iridium complexes' lowest unoccupied molecular orbitals (LUMOs) being strongly diimine in character. These have been tethered by a variety of groups including alkanes and napthylene to lanthanide com...

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films

“…Because of its intrinsic accepting ability, the LUMO likely has high electron density on the picolinate ligand, as was previously described for very similar complexes of (ppy) 2 Ir(pic) derivatives. 24 Photoluminescence data support this hypothesis because emission energy should be lowered by increasing the accepting power of the LUMO-bearing moiety. 16 …”

Exploration of Bis(Arylimidazole) Iridium Picolinate Complexes

“…Planar 2-arylimidazole ligands are perpendicular with chelating nitrogen atoms opposite to each other, which is also observed in (ppy)2Ir(pic) complexes. 22,23 Bond angles and distances were typical of other Ir (III) structures in a distorted octahedral, with no significant steric interactions.…”

“…The PLQY measurements were performed relative to FIrPic in DCE (PLQY = 92%), as described previously 25,26. As has been described for a serious of recently published heteroleptic phenylpyridine acetylene-substituted picolinates, the observed PLQY values were much lower than those for FIrPic, but similar to those for Ir(ppy)2(pic) (14.7%) 23. Complex 12 exhibited the highest PLQY (24.7%) and complex 13 the lowest (6.4%).…”

“…25,26 As has been described for a serious of recently published heteroleptic phenylpyridine acetylene-substituted picolinates, the observed PLQY values were much lower than those for FIrPic, but similar to those for Ir(ppy)2(pic) (14.7%). 23 Complex 12 exhibited the highest PLQY (24.7%) and complex 13 the lowest (6.4%). Complex 10 displayed higher PLQY than complexes 9 and 11, and methoxy substituted complex 14.…”

The crystal structure of 5-bromopicolinic acid monohydrate, C6H6BrNO3

“…5-Bromopicolinic acid, one of the derivatives of picolinic acid, attracted attention over a long period of time and acted as organic ligand to form metal-organic complexes [5][6][7][8][9][10][11]. One of the derivatives, the methyl-5-bromo-6-methylpicolinate, has been reported as single crystal structure elsewhere [12].…”