Unusual behavior in di-substituted piperidine and piperazine anthraquinones upon protonation – Spectral, electrochemical, and quantum chemical studies

The objective of the study is to determine the influence of a substituent on the spectroscopic and electrochemical properties of a series of novel 9,10‑anthraquinone piperidine and piperazine derivatives. We conducted UV–Vis spectroscopy, pH-spectroscopic titration, and cyclic voltammetry measuremen...

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Bibliographic Details
Published in:Journal of molecular liquids 2019-04, Vol.279, p.154-163
Main Authors: Wcisło, Anna, Dąbkowska, Iwona, Czupryniak, Justyna, Ossowski, Tadeusz, Zarzeczańska, Dorota
Format: Article
Language:English
Subjects:
Aminoanthraquinone
Electrochemistry
Intramolecular charge transfer
Protolytic forms
Spectroscopy
TD-DFT
Theoretical UV–Vis spectra
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Summary:The objective of the study is to determine the influence of a substituent on the spectroscopic and electrochemical properties of a series of novel 9,10‑anthraquinone piperidine and piperazine derivatives. We conducted UV–Vis spectroscopy, pH-spectroscopic titration, and cyclic voltammetry measurements with an interesting phenomenon observed in the case of di-substituted quinones. Compounds with substituents in position 1 and 8 exhibit a significant increase in the absorption intensity of the monoprotonated form. Spectroscopic studies in the conjunction with time-dependent density functional theory (TD-DFT) calculations were employed to explore the unusual behavior. The state-of-the-art quantum chemistry calculations including bulk solvent in the polarizable continuum model (PCM) enabled the study of prototropic tautomerization and its influence on the position of absorption bands. The results of cyclic voltammetry measurements allowed us to determine the deciding factor influencing the reduction – the number of substituents and the possibility of the hydrogen bond formation of the charged states. [Display omitted] •Eight piperidine and piperazine derivatives of 9,10-anthraquinone were investigated.•1,8 substituted derivative exhibits unique spectral changes upon protonation.•The TD-DFT calculations assigned unusual spectral changes to the enol tautomers.•For all derivatives an additional reduction anodic peak on CV voltammograms was seen.
ISSN:0167-7322
1873-3166
DOI:10.1016/j.molliq.2019.01.115