Strategic Substitution of -OH/-NR 2 (R=Et, Me) Imparts Colorimetric Switching between F - and Hg 2+ by Salicyaldehyde/Benzaldehyde-Quinoxaline Conjugates.

We herein report two salicyaldehyde-quinoxaline (HQS and HQSN) conjugates and a benzaldehyde-quinoxaline (QBN) conjugate to fabricate selective chemosensors for F - and Hg 2+ in the micromolar range. This work demonstrates how sensing outcomes are affected by modulating proton acidity by introducing an electron donating group, -NEt 2 , in the probe backbone. Interestingly, the un-substituted probe HQS can selectively detect F - , whereas HQSN and QBN are selective for Hg 2+ . 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 pK a values. Detailed DFT and TD-DFT analyses provide ample support towards the mechanism of sensing of the analytes.