Electronic structure and solvatochromism of merocyanines: NMR spectroscopic point of view

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• 作者：Andrii V. Kulinich ; Alex ; er A. Ishchenko ; Ulrich M. Groth
• 关键词：Merocyanine ; Electronic structure ; Positive and negative solvatochromism ; NMR spectroscopy
• 刊名：Spectrochimica Acta Part A ; Molecular and Biomolecular Spectroscopy
• 出版年：2007
• 期刊代码：99_13861425
• 类别：ch
• 出版时间：September 2007
• 卷：68
• 期：1
• 页码：6-14
• 文件大小：198 K

摘要

¹H and ¹³C NMR spectra of two series of malononitrile-based merocyanines, which possess positive and negative solvatochromism have been in detail investigated in low polar chloroform and polar dimethyl sulfoxide (DMSO). Careful attribution of signals in spectra has been made with the help of two-dimensional NMR experiments (COSY, NOESY, HMBC, and HMQC). Hence, the dependence of merocyanines electronic structure on their chemical structure and solvent nature has been studied by this powerful method. It has been shown that there exists a good correlation between the calculated charges on carbon atoms of a polymethine chain and their chemical shifts in ¹³C NMR spectra. The influence of solvent polarity on bond orders for dyes with positive and negative solvatochromism is also observed. The comparison of ¹³C NMR spectra of merocyanines and corresponding parent ionic dyes allows to determine their sign of solvatochromism irrespectively of electronic spectra, and also to find the key atoms of chromophore whose signals in ¹³C NMR spectra are most informative.