Computational Justification Towards Detection of Dual Anions on a Single Molecular Platform: The Role of Solvent in Decoration of Dual Channels

Abstract

Ratiometric optical detection of analytes is a convenient strategy as the technique is devoid of relative error and background correction. Herein, solvent-guided ratiometric optical recognition of fluoride and bisulfate anions by a low-cost, “off-the-shelf” bioactive molecule, harmane (HRH) is thoroughly explored. Interestingly, solvent plays a dynamic role in the selective recognition of the dual anions via the dual channels of HRH in an intelligent manner. The probe displays high-fidelity recognition behavior towards fluoride ion in an aprotic solvent (acetonitrile) and towards bisulfate ion in a protic environment (acetonitrile/water; 5:1; v/v). Both the channels of HRH are very selective for a particular anion (F⁻/HSO₄⁻) in a specific solvent. Organized and comprehensive theoretical calculation denotes that hydrogen bonding between the acidic pyrrolic proton of HRH and fluoride for the first channel and the acidic proton of bisulfate and the pyridinic nitrogen for the second channel of HRH led to the formation of a hydrogen-bonded ion pair (HBIP). Consequently, significant optical changes are observed in the visible region, which is convenient for real-life detection of F⁻ and HSO₄⁻ independently. The essential role of solvent in tuning the dual channels of HRH is an important artifact in the literature of fundamental photochemistry.