Influence of halogen atoms on a homologous series of bis-cyclometalated iridium(III) complexes

Research output: Contribution to journalArticlepeer-review

Authors

  • Etienne Baranoff
  • Basile F E Curchod
  • Filippo Monti
  • Frédéric Steimer
  • Gianluca Accorsi
  • Ivano Tavernelli
  • Ursula Rothlisberger
  • Rosario Scopelliti
  • Michael Grätzel
  • Md Khaja Nazeeruddin

Colleges, School and Institutes

External organisations

  • Ecole Polytechnique Federale de Lausanne
  • Molecular Photoscience Group
  • Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche , Via P. Gobetti 101, 40129 Bologna, Italy.
  • Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche (IPCF-CNR)
  • School of Basic Sciences
  • Laboratory of Computational Chemistry and Biochemistry

Abstract

A series of homologous bis-cyclometalated iridium(III) complexes Ir(2,4-di-X-phenyl-pyridine) 2(picolinate) (X = H, F, Cl, Br) HIrPic, FIrPic, ClIrPic, and BrIrPic has been synthesized and characterized by NMR, X-ray crystallography, UV-vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the p and m Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with FIrPic and ClIrPic, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of BrIrPic and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin-orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for ClIrPic and BrIrPic, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect.

Details

Original languageEnglish
Pages (from-to)799-811
Number of pages13
JournalInorganic Chemistry
Volume51
Issue number2
Publication statusPublished - 16 Jan 2012