Revisiting the BODIPY-borane dyad for the design of efficient aqueous phase molecular probes for anion recognition: A DFT/TD-DFT study

Abstract

Fluoride (F−), cyanide (CN−) etc. ions have important roles in various chemical and biological applications. But their excessive use can lead to severe health issues like kidney, gastric etc. Generally analytical methods with costly instruments and laborious treatment are involved for the detection of such analytes. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) studies suggest that BODIPY-TAB dyad (where BODIPY implied boron dipyrrometehene and TAB is triarylborane) molecular receptor, 1 and the four newly designed receptors 2–5 have selective binding feasibility with CN−, F− and chloride (Cl−) among F−, CN−, Cl−, bromide (Br−), acetate (CH3COO−), nitrate (NO3−), sulphate (SO4−) and bisulphate (HSO4−) via computing thermodynamic energy viz free energy changes, ΔG and binding energies, ΔE. The NPA show the analyte binding at boron atoms of TAB moieties making them the electrophilic centers. The change in optical properties (fluorescence quenching) in the receptor-analyte complexes of CN−, F− and Cl− involve intramolecular charge transfer (ICT) between BODIPY and TAB moieties, associated configurational changes and internal conversion (while π-π* transitions in the receptors make them fluorescent). CAM-B3LYP/6-31G(d) model chemistry provides best results among all the twelve tested functionals. Keeping in view the practical importance, the designed receptors will be improved fluorescent probes for CN−, F− and Cl−. Due to the increased Stokes shifts in case of aqueous medium, 1–5 act as best receptors for CN−, F− and Cl− recognition in aqueous medium in comparison to tetrahydrofuran and dichloromethane.