Highly phosphorescent iridium(III) complexes based on 2-(biphenyl-4-yl)benzo[d]oxazole derivatives: synthesis, structures, properties and DFT calculations

Five new bis-cyclometalated iridium(III) complexes, [(bpbo)2Ir(acac)] (3a), [(fbpbo)2Ir(acac)] (3b), [(Mebpbo)2Ir(acac)] (3c), [(3,5-f2bpbo)2Ir(acac)] (3d) and [(2,4-f2bpbo)2Ir(acac)] (3e) (bpbo = 2-(biphenyl-4-yl)benzo[d]oxazole, fbpbo = 2-(4′-fluoro-[biphenyl]-4-yl)benzo[d]oxazole, Mebpbo = (4′-methyl-[biphenyl]-4-yl)benzo[d]oxazole, 3,5-f2bpbo = 2-(3′,5′-difluoro-[biphenyl]-4-yl)benzo[d]oxazole, 2,4-f2bpbo = 2-(2′,4′-difluoro-[biphenyl]-4-yl)benzo[d]oxazole, acac = acetylacetone), have been synthesized and fully characterized. A single crystal X-ray diffraction study was carried out on complexes 3a–3d, which showed that each adopted the distorted octahedral coordination geometry with the cis-C,C′ and trans-N,N′ arrangement. All Ir(III) complexes are luminescent (560–566 nm) with quantum yields of 3.6–53.5% and lifetimes of 0.282–0.382 μs in solution at 298 K. The spectroscopic and redox characterisation of these complexes were complemented by DFT and TD-DFT calculations, supporting the assignment of 3MLCT/LC to the emissive character.

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