19 September 2011 Theoretical study of the origin of the large difference in the visible absorption spectra of organic dyes containing a thienylmethine unit and differing by the methine unit position
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Abstract
We analyze the origin of the large (about 128 nm) difference in the maximum of the visible absorption spectrum of dyes 2-Cyano-3-[5'-(4''-(N,N-dimethylamino) phenyl) thiophen-2'-yl] acrylic acid and Cyano-[5-(4-(N,Ndimethyl-amino) benzylidene)-5H-thiophen -2-ylidene]-acetic acid which differ by the position of the methine unit that was observed in an acetonitrile solution. We perform an ab initio analysis of possible factors such as (non-)planarity of the molecule, isomerization, and solvent effects as well as of the influence of computational parameters. Ground state calculations failed to account for the difference in transition energies, but excited state optimization of deprotonated dyes in solution resulted in values comparable to the experiment. We conclude that the most likely explanation for the difference is different stabilization of the LUMO by the polar solvent.
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Sergei Manzhos, Makoto Komatsu, Jotaro Nakazaki, Hiroshi Segawa, Koichi Yamashita, "Theoretical study of the origin of the large difference in the visible absorption spectra of organic dyes containing a thienylmethine unit and differing by the methine unit position", Proc. SPIE 8109, Solar Hydrogen and Nanotechnology VI, 810908 (19 September 2011); doi: 10.1117/12.893262; https://doi.org/10.1117/12.893262
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