Faculty of Chemistry, University of Wrocław , ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland.
J Phys Chem B. 2014 Jan 9;118(1):226-39. doi: 10.1021/jp408328h. Epub 2013 Dec 20.
In the present study the interaction of lanthanide β-diketonate complexes with polyvinylpyrrolidone (PVP) has been systematically investigated using fluorescence spectroscopy. The emission of terbium complexes with hexafluoroacetylacetone (hfa) ligands is almost completely quenched by PVP in the absence of H(+) ions, while it is enhanced by more than 30 times in the presence of H(+) ions. Conversely, the H(+) ions increase the quenching efficiency of terbium complex with acetylacetone ligands. The strikingly different behavior of complexes with fluorinated and nonfluorinated β-diketonates is accounted for by the interaction mechanism, in which the important role of hydrogen bonds is indicated. The proposed mechanism includes ion-dipol Coulombic interactions between negative charge localized on ligands O-C-CH2-C-O group and positive charge induced in N atom of PVP pyrrolidone group, as well as interactions through hydrogen bonds formed between ligand C-O groups and PVP, occurring directly or through solvent molecules. Additional stabilizing effect, significantly influencing the binding strength of ligands with PVP, results from hydrogen bonds formed by terminal (CF3 or CH3) substituents of ligands with C-O group of PVP. Importantly, the quenching and enhancement of luminescence of terbium complexes with hfa ligands in PVP solution is a reversible process. This enables one to obtain the emission switch-OFF-ON system triggered externally by H(+) ions, which can find possible application in the development of molecule-based devices.
在本研究中，使用荧光光谱法系统地研究了镧系β-二酮配合物与聚乙烯吡咯烷酮（PVP）的相互作用。在不存在 H(+)离子的情况下，六氟乙酰丙酮（hfa）配体的铽配合物的发射几乎完全被 PVP 猝灭，而在存在 H(+)离子的情况下，其发射强度增强了 30 多倍。相反，H(+)离子增加了乙酰丙酮配体的铽配合物的猝灭效率。氟化和非氟化 β-二酮配合物的明显不同行为归因于相互作用机制，其中氢键的重要作用得到了表明。所提出的机制包括配体 O-C-CH2-C-O 基团上的局部负电荷与 PVP 吡咯烷酮基团中诱导的正电荷之间的离子偶极库仑相互作用，以及通过配体 C-O 基团与 PVP 之间形成的氢键的相互作用，直接或通过溶剂分子发生。配体末端（CF3 或 CH3）取代基与 PVP 的 C-O 基团形成的氢键产生了额外的稳定效应，显著影响了配体与 PVP 的结合强度。重要的是，hfa 配体的铽配合物在 PVP 溶液中的荧光猝灭和增强是一个可逆过程。这使得人们能够获得由 H(+)离子外部触发的发光关闭-开启系统，这可能有助于开发基于分子的器件。
