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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Excition-Like and Charge-Transfer States in Cyanine-Oxonol Ion Paris. An Expeirmental and Theoretical Study
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Excition-Like and Charge-Transfer States in Cyanine-Oxonol Ion Paris. An Expeirmental and Theoretical Study

机译：花青-氧代酚离子巴黎的类似运动和电荷转移状态。实验和理论研究

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Absorption and fluorescence emission properties of cyanine—oxonol mixed dyes, i.e., salts formed by a cationic cyanine with an anionic oxonol as counterion, were investigated both theoretically and experimentally in order to probe the effects of ion pairing occurring in low-polarity solvents. We analyzed, in particular, three model systems (SI, S2, and S3) built combining thiacarbo- and thiadicarbocyanine (Cl, C2) with two vinylogous oxonol chromophores (Al/Al F, A2). In systems SI (Cl-Al) and 52 (C2-A2), where the visible absorption bands of the individual ions are almost superimposed, the formation of ion pairs gives rise to marked spectral alterations traceable to interchromophore resonance interactions. On the contrary, in system 53 (C2-AIF), whose components absorb widely apart, the spectrum of the contact ion pair and that of the dissociated form differ only for the relative band intensities. In both cases, however, contact ion pairing results in complete quenching of the emission of the chromophoric units. Such behaviors, emphasized by absorption and fluorescence emission and excitation spectra of both the mixed dyes and their components in solvents of different polarities, were the subject of a theoretical study based in particular on the calculation of structures and electronic spectra of the contac ion pairs. Molecular dynamics (MD) simulations and local full geometry optimizations led to two types of structures characterized by almost parallel and orthogonal arrangements of the long molecular axes. CS INDO SCI calculations using both arrangements emphasized the role of the exciton coupling between the local HOMO-LUMO excitations of the two chromophoric units. The ~most striking spectral characteristics in low-polarity solvent turned out to be explainable in terms of parallel type arrangements, even if an appreciable contribution of the orthogonal type structure was to be invoked for a complete interpretation of the S I spectral properties. In all contact ion pairs, independently of the structure, the lowest excited singlet is a forbidden anion-cation charge transfer (CT) state explainingwhy no fluorescence emission was observed in such systems.
机译：从理论上和实验上研究了花青-氧杂酚混合染料（即由阳离子花青与阴离子氧杂酚作为抗衡离子形成的盐）的吸收和荧光发射特性，以探究在低极性溶剂中发生的离子配对效应。我们特别分析了三个模型系统（SI，S2和S3），该模型系统是将硫杂碳酸酯和噻二碳环花菁（Cl，C2）与两个乙烯基含氧酚生色团（Al / Al F，A2）结合起来构建的。在系统SI（C1-A1）和52（C2-A2）中，各个离子的可见吸收带几乎重叠，离子对的形成引起可追溯到发色团间共振相互作用的明显光谱变化。相反，在系统53（C2-AIF）中，其组分吸收得很宽，接触离子对的光谱和解离形式的光谱仅在相对能带强度上有所不同。然而，在两种情况下，接触离子对都会导致发色单元的发射完全淬灭。混合染料及其组分在不同极性溶剂中的吸收，荧光发射和激发光谱强调了这种行为，这是理论研究的主题，尤其是基于接触离子对的结构和电子光谱的计算。分子动力学（MD）模拟和局部完整几何优化导致了两种类型的结构，其特征是长分子轴几乎平行和正交排列。使用两种布置的CS INDO SCI计算都强调了两个发色单元的局部HOMO-LUMO激发之间的激子耦合作用。事实证明，即使为了完全解释SI光谱性质而调用正交型结构的显着贡献，低极性溶剂中最显着的光谱特性也可以用平行型排列来解释。在所有接触离子对中，与结构无关，最低激发的单重态是禁止的阴离子-阳离子电荷转移（CT）状态，这解释了为什么在这种系统中未观察到荧光发射。

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