Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and 1 H-NMR spectroscopies

31 January 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Three anthraquinone-based chromophores (9,10-anthraquinone, alizarin, purpurin) are compared from the point of view of their experimental and computed NMR and UV-visible light absorption spectra. Using an hybrid (explicit/implicit) solvent model, each proton chemical shift can be reproduced with an error less than 7\%, even when such protons are engaged in inter-molecular hydrogen bonds with the solvent or when the analyzed sample contains a significant amount of impurities, for instance 9,10-anthraquinone in purpurin. All the steady-state UV-visible absorption spectra feature a significant vibrational progression in the first absorption band. The shape of the corresponding computed spectra, including vibronic couplings obtained with the Adiabatic Hessian approach and the Franck-Condon and Hertzberg-Teller approximation of the transition dipole, are in excellent agreement with the experimental one. The importance and the nature of the vibronic couplings are different for the three molecules, even if they only differ by the number of hydroxyl groups.

Keywords

Dyes
Hydroxy-anthraquinones
UV-visible
NMR
DFT
TD-DFT

Supplementary materials

Title
Description
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Title
Supplementary Information to "Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and 1H-NMR spectroscopies"
Description
9,10-anthraquinone, alizarin, purpurin tautomers and their free energy differences; natural transition orbital analysis; normal mode analysis; purpurin electrospray mass and 13-C NMR spectrum.
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