Charged bis-cyclometalated iridium(III) complexes with carbene-based ancillary ligands

Research output: Contribution to journalArticlepeer-review

Authors

  • Filippo Monti
  • Florian Kessler
  • Manuel Delgado
  • Julien Frey
  • Federico Bazzanini
  • Gianluca Accorsi
  • Nicola Armaroli
  • Henk J Bolink
  • Enrique Ortí
  • Rosario Scopelliti
  • Md Khaja Nazeeruddin

Colleges, School and Institutes

External organisations

  • Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche , Via P. Gobetti 101, 40129 Bologna, Italy.

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.

Details

Original languageEnglish
Pages (from-to)10292-305
Number of pages14
JournalInorganic Chemistry
Volume52
Issue number18
Publication statusPublished - 16 Sep 2013