Colorimetric fluoride ion sensors based on dipyrrolic and bipyrrolic compounds: Synthesis and anion recognition

abstract

The synthesis and spectroscopic studies of four sensors for fluoride chromogenic sensing are described. The new compounds were prepared by the Knoevenagel condensation of diformyl-substituted bipyrrolic and dipyrrolic synthons ([2,2 '-bipyrrole]-5,5 '-dicarbaldehyde and dipyrromethane-1,9-dicarbaldehyde moieties) with malononitrile or indane-1,3-dione. They strongly absorb in the visible region and significant color changes occur in the presence of fluoride anions. Acetate and dihydrogenphosphate anions also induce observable colorimetric changes, albeit to a lesser extent. These changes, which are visible to the unaided eye, are associated with NH- bonding interactions that are unique to each anion. Non-linear regression analysis of the ground- and excited- state changes revealed anion recognition in a 2:1 stoichiometry (Host:Guest), where the electronegative character of the substituents (malononitrile or indane-1,3-dione residues) controls the sensitivity of the binding. The proposed systems all feature exceptional anion receptors that display an impressive chromogenic response through NH-bonding. Among these, compound 3 stands out with exceptionally high affinity constants of up to 7.39x109 M-2, as well as an extremely low limit of detection at 92 ppm. NMR spectroscopy and mass spectrometry confirmed the structures of the synthesized compounds, with increased complexity in the NMR spectra due to the presence of malononitrile and indane-1,3-dione moieties. These findings highlight the potential of incorporating highly conjugated push-pull chromophores into bipyrrolic and dipyrrolic synthons for improved fluoride sensing performance in terms of both binding and signaling.

keywords

PROBES; CHEMOSENSORS; CHROMOPHORES; DERIVATIVES; PORPHYRINS; WATER

subject category

Chemistry; Engineering; Materials Science

authors

Figueira, F; Farinha, ASF; Santana, A; Vrouwenvelder, JS; Tomé, AC; Chernyshov, D; Paz, FAA; Cavaleiro, JAS; Tomé, JPC

Groups

G1 - Porous Materials and Nanosystems

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020), & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), LAQV-REQUIMTE (LA/P/0008/2020, UIDP/50006/2020 and UIDB/50006/2020), CQE (UIDB/00100/2020 and UIDP/00100/2020) and IMS (LA/P/0056/2020) research units, financed by national funds through the FCT/MCTES (PIDDAC). The research contract of FF (REF-168-89-ARH/2018) is funded by national funds (OE), through FCT, in the scope of the framework contract foreseen in Nos. 4, 5 and 6 of article 23 of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. We thank the European Synchrotron Research Facility (ESRF) for approving the research proposal CH-5240.