Imidazo[4,5-b]pyridine derived iminocoumarins as potential pH probes: Synthesis, spectroscopic and computational studies of their protonation equilibria

Boček, Ida; Hranjec, Marijana; Vianello, Robert (2022) Imidazo[4,5-b]pyridine derived iminocoumarins as potential pH probes: Synthesis, spectroscopic and computational studies of their protonation equilibria. Journal of Molecular Liquids, 355 . ISSN 01677322

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Abstract

We describe the synthesis, spectroscopic characterization and computational analysis of the protonation equilibria of several newly designed imidazo[4, 5-b]pyridine derived iminocoumarins to confirm their potential as pH sensing molecules in different solvents. The photophysical characterization and acid/base properties of these chromophores have been carried out in several polar and non-polar organic solvents as well as buffered aqueous solution with different pH values using UV–Vis and fluorescence spectroscopies. Obtained results revealed that both the solvent polarity and the electronic nature of substituents placed at the iminocoumarin and imidazo[4, 5-b]pyridine cores significantly influence spectral responses of studied systems. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are monoprotonated cations at neutral pH, while their transition to diprotonated forms occurs at pH values between 3.4 and 4.4, whereas they get reverted to neutral unionized molecules between 10.4 and 13.7. These small differences in narrow ranges of borderline pH values are predominantly brought about by variations in a single substituent on the iminocoumarin core, thereby allowing a simple strategy to further modify the observed sensing features and easily tune them for a specific application.

Item Type:	Article
Uncontrolled Keywords:	imidazo[4,5-b]pyridines; iminocoumarins; pH sensitivity; prototropic equilibrium; computational chemistry; DFT and TD-DFT calculations
Subjects:	NATURAL SCIENCES NATURAL SCIENCES > Chemistry NATURAL SCIENCES > Chemistry > Physical Chemistry NATURAL SCIENCES > Chemistry > Theoretical Chemistry NATURAL SCIENCES > Chemistry > Organic Chemistry
Divisions:	Division of Organic Chemistry and Biochemistry
Depositing User:	Robert Vianello
Date Deposited:	13 Feb 2024 09:03
URI:	http://fulir.irb.hr/id/eprint/8577
DOI:	10.1016/j.molliq.2022.118982

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