Luminescent biscyclometalated arylpyridine iridium(III) complexes with 4,4’-bi-1,2,3-triazolyl ancillary ligands

The synthesis, characterization and photophysical investigation of complexes of the form [Ir(R-ppy)2(btz)]PF6 (1 to 3) are reported (btz = 1,1’-dibenzyl-4,4’-1,2,3-triazolyl, R-ppy = 4-(pyrid-2-yl)benzaldehyde (1), 2-phenylpyridine (2) and 2-(2,4-difluorophenyl)pyridine (3)). Complexes 1, 2 and 3 are luminescent and exhibit structured emission bands with vibronic progressions at 532 & 568 nm, 476 & 508 nm and 454 & 483 nm respectively. The structuring of these emission bands is indicative of cyclometalate ligand centred emissive states and is further corroborated by the nearly identical emission spectra for 2 and 3 to previously reported analogous complexes with 4-(pyrid-2-yl)-1,2,3-triazole based ancillary ligands. Computational density functional theory calculations on these complexes show that the LUMOs of 2 and 3 are largely btz-centred but with some cyclometalate pyridine π* character. The LUMO of 1 on the other hand is localized primarily on the cyclometalate ligands. Spin population analysis of the lowest lying triplet excited states for these complexes indicate significant spin population over the iridium centres and the aryl and pyridyl moieties in these complexes with virtually no localization of unpaired electrons over the btz ancillary ligands. This is therefore in agreement with the assignment of the emissive state having largely cyclometalate 3LC character and being independent of the ancillary ligand.