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Host–Guest Interactions of Phosphorescent Molecular Tweezers Based on an Alkynylplatinum(II) Terpyridine System with Polyaromatic Hydrocarbons

Authors

  • Dr. Yuya Tanaka,

    1. Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P.R. China)
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  • Dr. Keith Man-Chung Wong,

    1. Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P.R. China)
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  • Prof. Dr. Vivian Wing-Wah Yam

    Corresponding author
    1. Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P.R. China)
    • Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P.R. China)
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Abstract

Host–guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D 1H NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host–guest interactions. The binding constants (KS) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 104M−1 for coronene to no observable interaction for benzene, indicating that the π-surface area is important for such host–guest interactions. The substituent effect on the host–guest interaction based on the guest series of 9-substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron-donating groups, although steric and π-conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) admixture band upon addition of various guest molecules to 1, whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host–guest interaction.

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