Acid-Base Strength and Acidochromism of Some Dimethylamino-Azinium Iodides. An Integrated Experimental and Theoretical Study

Enrico Benassi, Benedetta Carlotti, Cosimo G. Fortuna, Vincenzo Barone, Fausto Elisei, Anna Spalletti

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

The effects of pH on the spectral properties of stilbazolium salts bearing dimethylamino substituents, namely, trans isomers of the iodides of the dipolar E-[2-(4-dimethylamino)styryl]-1-methylpyridinium, its branched quadrupolar analogue E,E-[2,6-di-(p-dimethylamino)styryl]-1-methylpyridinium, and three analogues, chosen to investigate the effects of the stronger quinolinium acceptor, the longer butadiene π bridge, or both, were investigated through a joint experimental and computational approach. A noticeable acidochromism of the absorption spectra (interesting for applications) was observed, with the basic and protonated species giving intensely colored and transparent solutions, respectively. The acid-base equilibrium constants for the protonation of the dimethylamino group in the ground state (pKa) were experimentally derived. Theoretical calculations according to the thermodynamic Born-Haber cycle provided pKa values in good agreement with the experimental values. The very low fluorescence yield did not allow a direct investigation of the changes in the acid-base properties in the excited state (pKaa∗) by fluorimetric titrations. Their values were derived by quantum-mechanical calculations and estimated experimentally on the basis of the Förster cycle. (Figure Presented).

Original languageEnglish
Pages (from-to)323-333
Number of pages11
JournalJournal of Physical Chemistry A
Volume119
Issue number2
DOIs
Publication statusPublished - 15 Jan 2015
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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