Strategic substitution of −OH/−NR 2 (R=Et, Me) imparts colorimetric switching between F − and Hg 2+ by salicyaldehyde/benzaldehyde‐quinoxaline conjugates

Bag, R. ORCID: https://orcid.org/0000-0001-8378-053X, Sikdar, Y. ORCID: https://orcid.org/0000-0002-1146-9950, Sahu, S., Bag, J. ORCID: https://orcid.org/0000-0002-7087-0867, Drew, M. G. B., Pal, K. ORCID: https://orcid.org/0000-0003-4422-6450 and Goswami, S. ORCID: https://orcid.org/0000-0002-1045-2508 (2022) Strategic substitution of −OH/−NR 2 (R=Et, Me) imparts colorimetric switching between F − and Hg 2+ by salicyaldehyde/benzaldehyde‐quinoxaline conjugates. ChemPhysChem, 23 (4). e202100718. ISSN 1439-7641 doi: 10.1002/cphc.202100718

Abstract/Summary

We herein report two salicyaldehyde-quinoxaline (HQS and HQSN) conjugates and a benzaldehyde-quinoxaline (QBN) conjugate to fabricate selective chemosensors for F− and Hg2+ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, −NEt2, in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F−, whereas HQSN and QBN are selective for Hg2+. In order to gain insights into the mechanism of sensing, geometry optimizations have been carried out on QS(−1), QS(−1)⋅⋅⋅HF, QSN(−1) and QSN(−1)⋅⋅⋅HF and the experimental data are validated in terms of free energy and pKa values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.