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Monocyclometalated Gold(III) Complexes Bearing π-Accepting Cyanide Ligands: Syntheses, Structural, Photophysical, and Electrochemical Investigations


Szentkuti, Alexander; Garg, Jai Anand; Blacque, Olivier; Venkatesan, Koushik (2015). Monocyclometalated Gold(III) Complexes Bearing π-Accepting Cyanide Ligands: Syntheses, Structural, Photophysical, and Electrochemical Investigations. Inorganic Chemistry, 54(22):10748-10760.

Abstract

The synthesis, structural, photophysical, and electrochemical investigations of a series of gold(III) monocyclometalated complexes bearing ancillary ligands with π-accepting properties is reported. Complexes of the type [(C∧N)Au(C≡N)2] [C∧N = 2-phenylpyridine (ppy) (1), 2-(p-tolyl)pyridine (tpy) (2), 2-(2-thienyl)-pyridine (thpy) (3), 2-(5-methyl-2-thienyl)pyridine (5m-thpy) (4), 1-phenylisoquinoline (piq) (5)], and [(N∧N)Au(C≡N)2] [N∧N = 3,5-bis(phenyl)-2-(2′-pyridyl)pyrrole (pyrpy) (6)] were prepared, and the influence of both the cyanide as an ancillary ligand as well as the different electronic properties of the cyclometalating ligands (1–5) and the chelating bidentate (6) on the triplet emission properties were studied. The physicochemical properties were evaluated by a variety of physical methods, and the structure of selected complexes was further confirmed by X-ray diffraction studies. Complexes 1–5 display long-lived emission in solution, neat solid, spin coated PMMA films, and at 77 K in 2-MeTHF. The emission energies were strongly dictated by the cyclometalating ligands independent of the cyanide ligand, which is in quite a contrast to the previously reported dicyano complexes of iridium(III) and the isoelectronic platinum(II) complexes. The nonemissive behavior of complex 6 in any medium further highlights the importance that the good σ-donating properties of the cyclometalating ligand alone is not decisive in rendering the gold complexes emissive, but also the appropriate placement of the energy level of the ligand orbitals is also important. Detailed photophysical studies in conjunction with density functional theory and time-dependent density functional theory calculations support the origin of the emission to be a metal perturbed intra ligand 3IL (π–π*) delocalized over the cyclometalating ligand. The stability of the complexes combined with good emission quantum yields and tunability of the emission energies makes these complexes suitable alternatives to the relatively less stable monocyclometalated gold(III) diaryl or dialkyne complexes for organic light emitting device applications.

Abstract

The synthesis, structural, photophysical, and electrochemical investigations of a series of gold(III) monocyclometalated complexes bearing ancillary ligands with π-accepting properties is reported. Complexes of the type [(C∧N)Au(C≡N)2] [C∧N = 2-phenylpyridine (ppy) (1), 2-(p-tolyl)pyridine (tpy) (2), 2-(2-thienyl)-pyridine (thpy) (3), 2-(5-methyl-2-thienyl)pyridine (5m-thpy) (4), 1-phenylisoquinoline (piq) (5)], and [(N∧N)Au(C≡N)2] [N∧N = 3,5-bis(phenyl)-2-(2′-pyridyl)pyrrole (pyrpy) (6)] were prepared, and the influence of both the cyanide as an ancillary ligand as well as the different electronic properties of the cyclometalating ligands (1–5) and the chelating bidentate (6) on the triplet emission properties were studied. The physicochemical properties were evaluated by a variety of physical methods, and the structure of selected complexes was further confirmed by X-ray diffraction studies. Complexes 1–5 display long-lived emission in solution, neat solid, spin coated PMMA films, and at 77 K in 2-MeTHF. The emission energies were strongly dictated by the cyclometalating ligands independent of the cyanide ligand, which is in quite a contrast to the previously reported dicyano complexes of iridium(III) and the isoelectronic platinum(II) complexes. The nonemissive behavior of complex 6 in any medium further highlights the importance that the good σ-donating properties of the cyclometalating ligand alone is not decisive in rendering the gold complexes emissive, but also the appropriate placement of the energy level of the ligand orbitals is also important. Detailed photophysical studies in conjunction with density functional theory and time-dependent density functional theory calculations support the origin of the emission to be a metal perturbed intra ligand 3IL (π–π*) delocalized over the cyclometalating ligand. The stability of the complexes combined with good emission quantum yields and tunability of the emission energies makes these complexes suitable alternatives to the relatively less stable monocyclometalated gold(III) diaryl or dialkyne complexes for organic light emitting device applications.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:16 November 2015
Deposited On:13 Jan 2016 15:48
Last Modified:05 Apr 2016 19:53
Publisher:American Chemical Society (ACS)
ISSN:0020-1669
Publisher DOI:https://doi.org/10.1021/acs.inorgchem.5b01762

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