title: Charged bis-cyclometalated iridium(III) complexes with carbene-based ancillary ligands.
abstract: Charged cyclometalated (C(^)N) iridium(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C(^)N ligands, in contrast to the classical design of charged complexes where N(^)N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C(^)N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C(^)C:) and four different pyridine-carbene (N(^)C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C(^)C: complexes show much larger photoluminescence quantum yields (ΦPL) of ca. 30%, compared to the N(^)C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly(methyl methacrylate) matrix, ΦPL 30-60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N(^)C:-type complexes possess a low-lying triplet metal-centered ((3)MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C(^)C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N(^)C: and :C(^)C: complexes.
authors.affiliation: Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche , Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Monti
authors.forename: Florian
authors.initials: F
authors.lastname: Kessler
authors.forename: Manuel
authors.initials: M
authors.lastname: Delgado
authors.forename: Julien
authors.initials: J
authors.lastname: Frey
authors.forename: Federico
authors.initials: F
authors.lastname: Bazzanini
authors.forename: Gianluca
authors.initials: G
authors.lastname: Accorsi
authors.forename: Nicola
authors.initials: N
authors.lastname: Armaroli
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Bolink
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí
authors.forename: Rosario
authors.initials: R
authors.lastname: Scopelliti
authors.forename: Md Khaja
authors.initials: MK
authors.lastname: Nazeeruddin
authors.forename: Etienne
authors.initials: E
authors.lastname: Baranoff