Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 252, Nadia, West Bengal, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2012 Dec;99:37-45. doi: 10.1016/j.saa.2012.09.015. Epub 2012 Sep 10.
Interaction of a dye which is structurally similar to a ketocyanine dye with metal ions (alkali, alkaline earth and transition metal) has been studied by monitoring the electronic absorption, steady state and time resolved fluorescence parameters of the dye. The dye (S(0) state) forms a 1:1 complex with cations as indicated by the appearance of a new band at a longer wavelength. Equilibrium constant and other thermodynamic parameters for complexation have been determined. The interaction between the dye and the cation is mostly electrostatic in nature. Spectroscopic results have been supplemented by DFT calculation. For very low concentration of cations, where complexation is insignificant, the absorption band of the dye undergoes a slight blue shift. Enhancement of fluorescence intensity has been observed in the same concentration range. Both phenomena have been explained in terms of formation of a weak association complex where one/more cation replace equivalent solvent molecules in the cybotatic region around the dye. The binding constant of the weak association complex involving cation and the dye (S(1) state) has been determined and has been found to depend on the charge-to-size ratio of the cations. Measurement of fluorescence lifetime of the dye indicates that the association complex is slowly decaying relative to solvated dye. At higher concentration of metal ions, however, fluorescence of the dye is quenched by the metal ions. A red shift of fluorescence maximum has also been observed in this concentration range.
通过监测染料的电子吸收、稳态和时间分辨荧光参数，研究了一种与酮菁染料在结构上相似的染料与金属离子（碱金属、碱土金属和过渡金属）的相互作用。该染料（S(0) 态）与阳离子形成 1:1 配合物，这表现为在较长波长处出现新的带。已经确定了配合物的平衡常数和其他热力学参数。染料与阳离子之间的相互作用主要是静电性质的。光谱结果得到了 DFT 计算的补充。对于阳离子浓度非常低、配合作用不显著的情况，染料的吸收带会发生轻微的蓝移。在相同的浓度范围内观察到荧光强度增强。这两种现象都可以用形成弱缔合配合物来解释，其中一个/多个阳离子取代染料周围溶剂化区域中的等效溶剂分子。已经确定了涉及阳离子和染料（S(1) 态）的弱缔合配合物的结合常数，并且发现该结合常数取决于阳离子的电荷-尺寸比。染料荧光寿命的测量表明，缔合配合物相对于溶剂化染料的衰减速度较慢。然而，在较高浓度的金属离子下，染料的荧光被金属离子猝灭。在该浓度范围内，荧光的最大波长也发生红移。
