Experimental and Computational Investigation on the Origin of Inverted Solvatochromism in Cyanine and Cyanine Similar Compounds
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Date
2013-06-06
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Addis Ababa University
Abstract
Photophysical properties of the of methyl red, methyl orange, methyl violate and brilliant green molecules have been studied in solvents of varying polarity using steady-state fluorescence and UV-Vis spectroscopy. In addition computational technique has been applied to explain and verify the experimental result. The investigated molecules showed different solvatochromic shits. Attempt has been made to explain the different solvatochromisms, i.e. negative, positive and inverted solvatochromism. In all the studied compounds a strong solvent polarity dependent shift in absorption position was observed, except methyl violate, which did not show a significant solvent dependence. In methyl red a different situation was observed: in non polar to polar solvents a shift to lower λmax (positive solvatochromism), and in contrast, in polar to strong polar solvents negative solvatochromism was observed. This apparent reversal of solvatochromic behavior, which is commonly known as inverted solvatochromism, is against the theory of solvatochromism. In this work, the observed anomality is explained based on the existence of equilibrium structures each responsible to the resulting positive and negative solvatochromism. The computational results also support the existence of two mesomeric structures, namely polyene and zwitterionic structures.
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Keywords
Inverted Solvatochromism, Aggregation (Self Association), Methyl Red, Methyl Violate, Methyl Orange, Brilliant Green, TD-DFT