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Spectroscopic and Computational Study of the Protonation Equilibria of Amino-Substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as Novel pH-Sensing Materials

Perin, Nataša; Babić, Darko; Kassal, Petar; Čikoš, Ana; Hranjec, Marijana; Vianello, Robert (2022) Spectroscopic and Computational Study of the Protonation Equilibria of Amino-Substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as Novel pH-Sensing Materials. Chemosensors, 10 (1). ISSN 2227-9040

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Abstract

We present the synthesis and analytical, spectroscopic and computational characterization of three amino-substituted benzo[b]thieno[2, 3- b]pyrido[1, 2-a]benzimidazoles as novel pH probes with a potential application in pH-sensing materials. The designed systems differ in the number and position of the introduced isobutylamine groups on the pentacyclic aromatic core, which affects their photophysical and acid- base properties. The latter were investigated by UV-Vis absorption and fluorescence spectroscopies and interpreted by DFT calculations. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are unionized at neutral pH, while their transition to monocationic forms occurs at pH values between 3 and 5, accompanied by substantial changes in spectroscopic responses that make them suitable for detecting acidic conditions in solutions. Computations identified imidazole imino nitrogen as the most favorable protonation site, further confirmed by analysis of perturbations in the chemical shifts of 1H and 13C NMR, and showed that the resulting basicity emerges as a compromise between the basicity-reducing effect of a nearby nitrile and a favorable contribution from the attached secondary amines. With this in mind, we designed a system with three amino substituents for which calculations predict pKa = 7.0 that we suggest as an excellent starting point for a potential pH sensor able to capture solution changes during the transition from neutral towards acidic media.

Item Type: Article
Uncontrolled Keywords: benzo[b]thieno[2, 3-b]pyrido[1, 2-a]benzimidazoles ; DFT calculations ; TD-DFT calculations ; pH sensitivity ; acid-base chemistry ; NMR chemical shifts
Subjects: NATURAL SCIENCES > Chemistry
Divisions: Division of Organic Chemistry and Biochemistry
Division of Physical Chemistry
NMR Center
Projects:
Project titleProject leaderProject codeProject type
Dizajn, sinteza i računalna analiza novih optičkih kemijskih pH osjetilnih derivata benzazolaVianello, RobertIP-2020-02-8090HRZZ
Depositing User: Sofija Konjević
Date Deposited: 19 Jan 2022 13:19
URI: http://fulir.irb.hr/id/eprint/6887
DOI: 10.3390/chemosensors10010021

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