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Mesomorphism and Luminescence Properties of Platinum(II) Complexes with Tris(alkoxy)phenyl-Functionalized Pyridyl Pyrazolate Chelates

Authors

  • Ching-Ting Liao,

    1. Department of Chemistry, Tamkang University, 151, Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137 (R.O.C.), Fax: (+886) 02-26209924
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  • Dr. Hsiu-Hui Chen,

    1. Department of Chemistry, Tamkang University, 151, Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137 (R.O.C.), Fax: (+886) 02-26209924
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  • Prof. Hsiu-Fu Hsu,

    Corresponding author
    1. Department of Chemistry, Tamkang University, 151, Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137 (R.O.C.), Fax: (+886) 02-26209924
    • Department of Chemistry, Tamkang University, 151, Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137 (R.O.C.), Fax: (+886) 02-26209924
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  • Anurach Poloek,

    1. Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan (R.O.C.), Fax: (+35) 711-082
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  • Hsiu-Hsuan Yeh,

    1. Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan (R.O.C.), Fax: (+35) 711-082
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  • Prof. Yun Chi,

    Corresponding author
    1. Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan (R.O.C.), Fax: (+35) 711-082
    • Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan (R.O.C.), Fax: (+35) 711-082
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  • Kang-Wei Wang,

    1. Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
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  • Dr. Chin-Hung Lai,

    1. Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
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  • Gene-Hsiang Lee,

    1. Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
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  • Chun-Wei Shih,

    1. Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
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  • Prof. Pi-Tai Chou

    Corresponding author
    1. Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
    • Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.), Fax: (+886) 02-23695208
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Abstract

A series of new mesomorphic platinum(II) complexes 14 bearing pyridyl pyrazolate chelates are reported herein. In this approach, pyridyl azolate ligands have been strategically functionalized with tris(alkoxy)phenyl groups with various alkyl chain lengths. As a result, they are ascribed to a class of luminescent metallomesogens that possess distinctive morphological properties, such as their intermolecular packing arrangement and their associated photophysical behavior. In CH2Cl2, independent of the applied concentration in the range 10−6–10−3M, all PtII complexes exhibit bright phosphorescence centered at around 520 nm, which is characteristic for monomeric PtII complexes. In stark contrast, the single-crystal X-ray structure determination of [Pt(C4pz)2] (1) shows the formation of a dimeric aggregate with a notable Pt⋅⋅⋅Pt contact of 3.258 Å. Upon heating, all PtII complexes 14 melted to form columnar suprastructures, for which similar intracolumnar Pt⋅⋅⋅Pt distances of approx. 3.4–3.5 Å are observed within an exceptionally wide temperature range (>250 °C), according to the powder XRD data. Upon casting into a neat thin film at RT, the luminescence of 14 is dominated by a red emission that spans 630–660 nm, which originates from the one-dimensional, chainlike structure with Pt–Pt interaction in the ground state. Taking complex 4 as a representative, the emission intensity and wavelength were significantly decreased and blueshifted, respectively, on heating from RT to 250 °C. Further heating to liquefy the sample alters the red emission back to the green phosphorescence of the monomer. The results highlight the pivotal role of tris(alkoxy)phenyl groups in the structural versus luminescence behavior of these PtII complexes.

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