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Issue 26, 2008
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Fluorenyl-substituted silole molecules: geometric, electronic, optical, and device properties

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A series of silole molecules with fluorenyl substituents at varying positions—1-(9,9-dimethylfluoren-2-yl)-1,2,3,4,5-pentaphenylsilole, 1-(fluoren-9-yl)-1,2,3,4,5-pentaphenylsilole, 1,1,3,4-tetraphenyl-2,5-bis(9,9-dimethylfluoren-2-yl)silole, and 1,1-diphenyl-2,3,4,5-tetrakis(9,9-dimethylfluoren-2-yl)silole—has been synthesized and compared to the previously reported compounds, 1,1,2,3,4,5-hexaphenylsilole and 1,1-bis(9,9-dimethylfluoren-2-yl)-2,3,4,5-tetraphenylsilole. The effect of fluorenyl substitution pattern on the geometric, thermal, electronic, optical, and electroluminescence properties was investigated both experimentally and theoretically. Analysis of the X-ray crystal packing diagrams for two new fluorenyl-substituted siloles indicates the presence of π–π stacking and CH⋯π interactions in the solid state. Across the series, excellent thermal and morphological stabilities are displayed. Photoelectron/inverse-photoelectron spectroscopy measurements and density functional theory (DFT) calculations suggest that increased conjugation length through substitution at the 2- and 5-positions plays a more significant role in tuning the ionization potentials and electron affinities of these siloles than do inductive effects through substitution of the silicon. The electronic structure (e.g., HOMO–LUMO gap) and, hence, the optical absorption and fluorescence properties are also sensitive to the positions at which the fluorenyl groups are introduced, with substitution at the 2,5-positions having the largest effect. Solution-processed electroluminescent devices fabricated with the fluorenyl-substituted siloles as the emissive layer have luminous efficiencies as high as 3.6 cd A−1.

Graphical abstract: Fluorenyl-substituted silole molecules: geometric, electronic, optical, and device properties

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Publication details

The article was received on 28 Feb 2008, accepted on 09 Apr 2008 and first published on 19 May 2008

Article type: Paper
DOI: 10.1039/B803470B
Citation: J. Mater. Chem., 2008,18, 3157-3166

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    Fluorenyl-substituted silole molecules: geometric, electronic, optical, and device properties

    X. Zhan, A. Haldi, C. Risko, C. K. Chan, W. Zhao, T. V. Timofeeva, A. Korlyukov, M. Yu. Antipin, S. Montgomery, E. Thompson, Z. An, B. Domercq, S. Barlow, A. Kahn, B. Kippelen, J. Brédas and S. R. Marder, J. Mater. Chem., 2008, 18, 3157
    DOI: 10.1039/B803470B

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