Journal of Chemical Sciences

, Volume 129, Issue 5, pp 647–656 | Cite as

Bis(pyrrole-benzimidazole) conjugates as novel colorimetric sensor for anions

Regular Article


Novel bis(pyrrole-benzimidazole) (PYBI) conjugates were investigated as colorimetric anion recognition motif by employing multiple donor sites. In this regard, PYBI derivatives where pyrrole unit is connected to the C2 position of benzimidazole via its \(\alpha \)-position were synthesized and their anion recognition behavior were evaluated by UV-Vis, fluorescence and \(^{1}\hbox {H NMR}\) spectroscopy. PYBI selectively interacts with fluoride ion, whereas introduction of nitro group on the benzimidazole moiety enhances the binding affinity by at least one order, albeit at the expense of the selectivity. Bridging of two PYBIs led to interesting cooperative effect between the two subunits, which gets enhanced upon changing the spacer between the two from non-conjugating type \(({ sp}^{3}\hbox {-C})\) to conjugating one (quinoxaline). This also affects the way they interact with anions, with the latter moiety displaying very interesting stepwise double deprotonation of benzimidazole protons upon addition of fluoride ions with strong colorimetric as well as fluorometric response. Further, acidity of the H-bond donor sites was found to play pivotal role in the anion complexation mechanism and selectivity.

Graphical abstract 

SYNOPSIS Novel bis(pyrrole-benzimidazole) (PYBI) conjugates where pyrrole units are connected to the C2 position of benzimidazole via its \(\alpha \)-position were synthesized and their anion recognition behavior were evaluated. Anion selectivity and mode of interaction was found to depend on the nature of the substituent and the spacer between the two PYBI units.


Pyrrole benzimidazole anion recognition cooperative proton migration 



This work is supported by Council of Scientific & Industrial Research (CSIR), India project No. 01(2449)/10/EMR-II (P K P) and the Department of Science & Technology (DST), Government of India project No. SB/FT/CS-090-2014 (S. P. M.).

Supplementary material

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Supplementary material 1 (docx 4400 KB)


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Copyright information

© Indian Academy of Sciences 2017

Authors and Affiliations

  1. 1.Department of Chemical SciencesTezpur UniversityNapaamIndia
  2. 2.School of ChemistryUniversity of HyderabadHyderabadIndia

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