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Highly Stable and Strongly Emitting N-Heterocyclic Carbene Platinum(II) Biaryl Complexes


Suter, Dominik; van Summeren, Luuk T C G; Blacque, Olivier; Venkatesan, Koushik (2018). Highly Stable and Strongly Emitting N-Heterocyclic Carbene Platinum(II) Biaryl Complexes. Inorganic Chemistry, 57(14):8160-8168.

Abstract

C^C cyclometalated platinum(II) triplet emitters bearing electronically different N-heterocyclic carbenes—(1,3-diisopropyl-4-(trifluoromethyl)-imidazol-2-ylidene (d), 1,3-diisopropyl-benzimidazol-2-ylidene (e), and 1,3-diisopropyl-imidazol-2-ylidene (f))—as neutral ligands and biphenyl (bph) as well as its fluorinated derivative octafluorobiphenyl (oFbph) as dianionic cyclometalating ancillary ligand were synthesized and structurally characterized by 1H, 13C, 19F, and 195Pt NMR, single crystal X-ray diffraction, and HR-ESI-MS studies. Detailed photophysical investigations carried out reveal a strong influence on the excited-state properties exerted by the electronic nature of the N-heterocyclic carbenes as well as the fluorine functional groups on the ancillary biphenyl moiety. The solid-state structures of all complexes reveal a nearly planar and slightly distorted square planar geometry around the platinum center. Introduction of fluorine groups into the ligand framework leads to a less structured emission centered at 513 nm in poly(methyl methacrylate) (PMMA) thin films, compared to the highly structured emission profile of the bph analogues. Additionally, a hypsochromic shift of approximately 10–12 nm was found in the absorption as well as in the emission profiles and is attributed to the electron deficient nature of the oFbph ligand. Three wt % of the compounds doped in PMMA exhibit photoluminescence efficiencies as high as 92% in thin films. DFT and TD-DFT calculations on selected molecules revealed the charge transfer to be an admixture of intraligand (3ILCT) and metal-to-ligand charge transfer (3MLCT) and the frontier orbitals corresponding to the emission to be mainly localized on the bph and oFbph ligands, which is consistent with the observations from the photophysical investigations. The thermal stability of the complexes evaluated by thermogravimetric analysis (TGA) shows an enhanced thermal stability for the complexes bearing fluorine functional groups.

Abstract

C^C cyclometalated platinum(II) triplet emitters bearing electronically different N-heterocyclic carbenes—(1,3-diisopropyl-4-(trifluoromethyl)-imidazol-2-ylidene (d), 1,3-diisopropyl-benzimidazol-2-ylidene (e), and 1,3-diisopropyl-imidazol-2-ylidene (f))—as neutral ligands and biphenyl (bph) as well as its fluorinated derivative octafluorobiphenyl (oFbph) as dianionic cyclometalating ancillary ligand were synthesized and structurally characterized by 1H, 13C, 19F, and 195Pt NMR, single crystal X-ray diffraction, and HR-ESI-MS studies. Detailed photophysical investigations carried out reveal a strong influence on the excited-state properties exerted by the electronic nature of the N-heterocyclic carbenes as well as the fluorine functional groups on the ancillary biphenyl moiety. The solid-state structures of all complexes reveal a nearly planar and slightly distorted square planar geometry around the platinum center. Introduction of fluorine groups into the ligand framework leads to a less structured emission centered at 513 nm in poly(methyl methacrylate) (PMMA) thin films, compared to the highly structured emission profile of the bph analogues. Additionally, a hypsochromic shift of approximately 10–12 nm was found in the absorption as well as in the emission profiles and is attributed to the electron deficient nature of the oFbph ligand. Three wt % of the compounds doped in PMMA exhibit photoluminescence efficiencies as high as 92% in thin films. DFT and TD-DFT calculations on selected molecules revealed the charge transfer to be an admixture of intraligand (3ILCT) and metal-to-ligand charge transfer (3MLCT) and the frontier orbitals corresponding to the emission to be mainly localized on the bph and oFbph ligands, which is consistent with the observations from the photophysical investigations. The thermal stability of the complexes evaluated by thermogravimetric analysis (TGA) shows an enhanced thermal stability for the complexes bearing fluorine functional groups.

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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
Uncontrolled Keywords:Physical and Theoretical Chemistry, Inorganic Chemistry
Language:English
Date:16 July 2018
Deposited On:13 Dec 2018 13:04
Last Modified:13 Dec 2018 13:14
Publisher:American Chemical Society (ACS)
ISSN:0020-1669
OA Status:Closed
Publisher DOI:https://doi.org/10.1021/acs.inorgchem.8b00564
Project Information:
  • : FunderSNSF
  • : Grant ID200020_156967
  • : Project TitleNovel Organometallic Complexes and Polymers Based Luminescent Materials

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