Anion Sensing by Novel Triarylboranes Containing Boraanthracene: DFT Functional Assessment, Selective Interactions, and Mechanism Demonstration

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 (NO 3 - ), acetate (CH 3 COO - ), and bisulfate (HSO 4 - ) 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 (Δ G ) and binding energies (Δ E ) 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.