MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand 9054.
J Phys Chem A. 2012 Jun 7;116(22):5453-63. doi: 10.1021/jp301455r. Epub 2012 May 24.
The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.
一种高溶剂化变色的甲川菁染料，2-(3-氰基-5,5-二甲基-4-(3-(1-十八烷基吡啶-4(1H)-亚基)丙-1-烯基)呋喃-2(5H)-亚基)丙二腈（pyr3pi）的结构和电子性质已通过紫外-可见光谱、NMR、超拉曼散射和拉曼光谱进行了研究，并进一步使用计算化学进行了解释。光谱数据表明，pyr3pi 即使在低极性溶剂中也以两性离子形式存在，电子吸收光谱随着溶剂极性的增加而发生红移，并且 NMR 实验表明，随着温度的降低，在氯仿中两性离子结构越来越多。在极性逐渐增加的溶剂中，拉曼光谱显示结构的微小变化，与向具有更多两性离子特征的结构的变化一致。然而，计算的和实验的振动能和强度的比较以及 NMR 偶合常数与计算键序的比较表明，计算低估了在低极性溶剂中看到的电荷分离量。尽管对于该体系，密度泛函理论（DFT）计算和两态模型定性地再现了负溶剂化变色，但它们未能再现实验中观察到的超极化率趋势。这归因于溶剂场 DFT 计算低估了代表低极性溶剂的反应场中电荷分离的程度。
