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Tuning the luminescent properties of PT(II) acetylide complexes through varying the electronic properties of N-heterocyclic carbene ligands


Zhang, Y; Clavadetscher, Jessica; Bachmann, Michael; Blacque, Olivier; Venkatesan, Koushik (2014). Tuning the luminescent properties of PT(II) acetylide complexes through varying the electronic properties of N-heterocyclic carbene ligands. Inorganic Chemistry, 53(2):756-771.

Abstract

This Article reports the synthesis, structural characterization, electrochemistry, and photophysical investigations of five groups of luminescent Pt(II) alkynyl complexes bearing N-heterocyclic carbene (NHC) ligands with varying electronic properties. Complexes of the type [Pt(pmdb)(C≡CR)2] 1a–c, [Pt(pm2tz)(C≡CR)2] 2a–d, [Pt(pm3tz)(C≡CR)2] 3a–c, [Pt(ppim)(C≡CR)2] 4(a, b, e), and [Pt(ppbim)(C≡CR)2] 5(a, b, e), where pmdb =1,1′-dipentyl-3,3′-methylene-dibenzimidazoline-2,2′-diylidene, pm2tz = 1,1′-dipentyl-3,3′-methylene-di-1,2,4-triazoline-5,5′-diylidene, pm3tz = 1,1′-dipentyl-3,3′-methylene-di-1,3,4-triazoline-5,5′-diylidene, ppim = 3-pentyl-1-picolylimidazoline-2-ylidene, and ppbim = 3-pentyl-1-picolylbenzimidazoline-2-ylidene, and R = 4-C6H4F, C6H5, 4-C6H4OMe, SiMe3, and 4-C6H4N(C6H5)2, were prepared, and the consequences of the electronic properties of the NHC ligands on the phosphorescent emission efficiencies were studied. Moreover, the emission quantum efficiencies of the previously reported complexes [Pt(pmim)(C≡CR)2] where pmim = 1,1′-dipentyl-3,3′-methylene-diimidazoline-2,2′-diylidene and R = 4-C6H4F 6a, C6H5 6b, and 4-C6H4OMe 6c were also recorded in neat solid and in 10 wt % PMMA film. The square planar coordination geometry with the alkynyl ligands in cis configuration was corroborated for selected complexes by single crystal X-ray diffraction studies. The observed moderate difference in emission efficiencies of the bis-carbene complexes 6a–c, 1a–c, 2a–c, and 3a–c in conjunction with the decreasing electron-donating nature of the NHC ligands, pmim > pmdb > pm2tz ≈ pm3tz, can be attributed to the slight modification of the triplet emission parentage among the different complexes. The quantum efficiencies of complexes 4(a, b) and 5(a, b) bearing pyridyl-NHC ligand were significantly low in comparison to the bis-carbene complexes owing to the significant change in the charge transfer character of the triplet manifold. Complexes 4e and 5e bearing diarylamine phenylacetylenes display high ϕem of 27% and 33% in 10 wt % PMMA film, respectively.

Abstract

This Article reports the synthesis, structural characterization, electrochemistry, and photophysical investigations of five groups of luminescent Pt(II) alkynyl complexes bearing N-heterocyclic carbene (NHC) ligands with varying electronic properties. Complexes of the type [Pt(pmdb)(C≡CR)2] 1a–c, [Pt(pm2tz)(C≡CR)2] 2a–d, [Pt(pm3tz)(C≡CR)2] 3a–c, [Pt(ppim)(C≡CR)2] 4(a, b, e), and [Pt(ppbim)(C≡CR)2] 5(a, b, e), where pmdb =1,1′-dipentyl-3,3′-methylene-dibenzimidazoline-2,2′-diylidene, pm2tz = 1,1′-dipentyl-3,3′-methylene-di-1,2,4-triazoline-5,5′-diylidene, pm3tz = 1,1′-dipentyl-3,3′-methylene-di-1,3,4-triazoline-5,5′-diylidene, ppim = 3-pentyl-1-picolylimidazoline-2-ylidene, and ppbim = 3-pentyl-1-picolylbenzimidazoline-2-ylidene, and R = 4-C6H4F, C6H5, 4-C6H4OMe, SiMe3, and 4-C6H4N(C6H5)2, were prepared, and the consequences of the electronic properties of the NHC ligands on the phosphorescent emission efficiencies were studied. Moreover, the emission quantum efficiencies of the previously reported complexes [Pt(pmim)(C≡CR)2] where pmim = 1,1′-dipentyl-3,3′-methylene-diimidazoline-2,2′-diylidene and R = 4-C6H4F 6a, C6H5 6b, and 4-C6H4OMe 6c were also recorded in neat solid and in 10 wt % PMMA film. The square planar coordination geometry with the alkynyl ligands in cis configuration was corroborated for selected complexes by single crystal X-ray diffraction studies. The observed moderate difference in emission efficiencies of the bis-carbene complexes 6a–c, 1a–c, 2a–c, and 3a–c in conjunction with the decreasing electron-donating nature of the NHC ligands, pmim > pmdb > pm2tz ≈ pm3tz, can be attributed to the slight modification of the triplet emission parentage among the different complexes. The quantum efficiencies of complexes 4(a, b) and 5(a, b) bearing pyridyl-NHC ligand were significantly low in comparison to the bis-carbene complexes owing to the significant change in the charge transfer character of the triplet manifold. Complexes 4e and 5e bearing diarylamine phenylacetylenes display high ϕem of 27% and 33% in 10 wt % PMMA film, respectively.

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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:2014
Deposited On:20 Feb 2015 10:13
Last Modified:05 Apr 2016 18:56
Publisher:American Chemical Society
ISSN:0020-1669
Publisher DOI:https://doi.org/10.1021/ic401841n

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