title: Blue-green iridium(III) emitter and comprehensive photophysical elucidation of heteroleptic cyclometalated iridium(III) complexes.
abstract: Synthesis and photophysical properties of the highly emissive complex [Ir(Fppy)2(dmb)](+) are reported along with those of additional heteroleptic cyclometalated Ir(III) complexes, [Ir(ppy)2(NN)](PF6): FppyH = 2-(2,4-difluorophenyl)pyridine; ppyH = 2-phenylpyridine; NN = 4,4'-dimethyl-2,2'-bipyridine (dmb), 1,10-phenanthroline (phen), or 4,7-diphenyl-1,10-phenanthroline (Ph2phen). TD-DFT calculations and Franck-Condon emission spectral band shape analyses show that the broad and structureless emission from [Ir(Fppy)2(dmb)](+) in acetonitrile at 298 K mainly arises from a triplet metal-to-ligand charge-transfer excited state, (3)MLCTIr(ppy)→NN. The emission maximum varies systematically with variations in electron-donating or -withdrawing substituents on both the NN and the Xppy ligands, and emission efficiencies are high, with an impressive ϕ ≈ 1 for [Ir(Fppy)2(dmb)](+). At 77 K in propionitrile/butyronitrile (4/5, v/v), emission from [Ir(Fppy)2(dmb)](+) is narrow and highly structured consistent with a triplet ligand-centered transition ((3)LCNN) and an inversion in excited-state ordering between the (3)MLCTIr(ppy)→NN and (3)LCNN states. In a semirigid film of the poly(ethyleneglycol)dimethacrylate with nine ethylene glycol spacers, PEG-DMA550, emission from [Ir(Fppy)2(dmb)](+) is MLCT-based. The thermal sensitivity of the photophysical properties of this excited state points to a possible application as a temperature sensor in addition to its more known use in light-emitting devices.
authors.affiliation: Laboratory of Photochemistry and Energy Conversion, Instituto de Química, Universidade de São Paulo - USP , Av. Prof. Lineu Prestes, 748, 05508-900, São Paulo, SP, Brazil.
authors.forename: Kassio P S
authors.initials: KP
authors.lastname: Zanoni
authors.forename: Bruna K
authors.initials: BK
authors.lastname: Kariyazaki
authors.forename: Akitaka
authors.initials: A
authors.lastname: Ito
authors.forename: M Kyle
authors.initials: MK
authors.lastname: Brennaman
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
authors.forename: Neyde Y
authors.initials: NY
authors.lastname: Murakami Iha