Probing the pH-Induced Spectral Modifications of NSAIDs for Designing Molecular Logic Gates and Combinational Logic Circuits

The current paper investigates the absorption and emission spectra of two non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen (N4HPA) and diclofenac (2DAPA), in aqueous solutions across different pH values. Both molecules exhibit significant changes in absorption and fluorescence spectra as a function of pH, which are attributed to the existence of these molecules in different forms (uncharged, anionic, and cationic) based on pH. The interpretation of these pH-dependent spectral behaviors in the presence or absence of the chemical inputs offers the possibility for the realization of a variety of unimolecular logic circuits, which are able to perform combinational logic operations. In this study, we aimed to implement two-input logic gates, namely, implication (IMP), inhibit (INH), and XNOR, using chemical inputs (H⁺ and OH⁻) and spectroscopic signals as outputs. Additionally, we have explored the design possibility of combinational logic circuits, namely, digital magnitude comparators and half-subtractor, by judiciously selecting positive or negative logic conventions for one or more output channels.