Anion Sensing by Novel Triarylboranes Containing Boraanthracene: DFT Functional Assessment, Selective Interactions,...

Analytical methods often involve expensive instrumentation and tedious sample pretreatment for an analyte detection. Being toxic and detrimental to human health, sensing of cyanide (CN^-), fluoride (F^-), chloride (Cl^-), bromide (Br^-), nitrate (NO₃ ^-), acetate (CH₃COO^-), and bisulfate (HSO₄ ^-) is performed by a boron-based molecular receptor, N,N,N,3,5-pentamethyl-4-{2-thia-9-boratricyclo[8.4.0.0^3,8]tetradeca-1(10),3(8),4,6,11,13-hexaen-9-yl}anili-nium (1), and the three newly designed receptors from it. Thermodynamics, electronic structure, and photophysical properties are computed by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to explore selective sensing of these anions and its mechanism. Free-energy changes (ΔG) and binding energies (ΔE) suggest that among these anions, only binding of CN^- and F^- is thermodynamically feasible with a very strong binding affinity with the receptors. Boron atoms containing positive natural charges act as the electrophilic centers to bind the anions involving a 2p-2p orbital overlap resulting in charge transfer. In the receptor-analyte complexes with CN^- and F^-, fluorescence is quenched due to the intramolecular charge transfer transitions (π-π* transitions in the case of the receptors lead to fluorescence), internal conversion, and associated configurational changes. Among the six tested functionals, CAM-B3LYP/6-31G(d) is found to be the most accurate one. The designed receptors are better fluorescent probes for F^- and CN^-, demonstrating their importance for the practical utility.