Callaghan Innovation Research Papers

Back to Research Papers

TitleTesting computational models of hyperpolarizability in a merocyanine dye using spectroscopic and DFT methods
Publication TypeJournal Article
Year of Publication2012
AuthorsReish, M.E., Kay A.J., Teshome A., Asselberghs I., Clays K., and Gordon K.C.
JournalJournal of Physical Chemistry A
Pagination5453 - 5463
Date Published2012
ISSN10895639 (ISSN)
KeywordsBond orders, Charge separations, Computational model, Density functional theory, Density functional theory calculations, DFT calculation, DFT method, Electronic absorption spectra, Electronic properties, Hyper Rayleigh scattering, Hyper-polarizability, Hypsochromic shifts, Malononitriles, Merocyanine dye, NMR coupling, nuclear magnetic resonance spectroscopy, Organic solvents, Polar solvents, Raman spectroscopy, Reaction fields, Separation, Small variations, Solvatochromic, Solvatochromisms, Solvent polarity, Solvents, Spectroscopic data, Two-state model, Vibrational energies, Zwitterionic forms, Zwitterionic structure
AbstractThe 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. © 2012 American Chemical Society.

Back to top