Electrostatic Investigation of 4-Dicyanomethylene-2,6-dimethyl-4H-pyran (DDP) Dye with Amide Derivatives in Water.

Abstract

Cyclic voltammetry (CV) studies of 4-dicyanomethylene-2,6-4H-pyran (DDP) dye with alkyl-substituted amides were carried out in an aqueous solution. Formamide and substituted amide interaction with DDP dye were characterized by fluorescence spectral techniques in an aqueous solution, but the electrochemical nature and the interaction at the interface region between dye–amide remains largely unexplored. The introduction of formamide to DDP dye exhibits an increase in the peak current accompanied with potential values gradually shifting more toward a less positive region. A large variation in the current–potential characteristics is observed in alkyl-substituted amides. The cyclic voltammograms of alkyl amides are found to be entirely different from each other. The role of alkyl substitution in the amide molecular framework influences the reduction potential of the dye in an aqueous medium. The mode of interaction of the dye with alkyl-substituted amides is predominantly due to the electrostatic behavior, even though hydrogen-bonding interactions coexist throughout the aqueous phase. The binding constant parameter (K), free-energy changes (ΔG), and the variation in the potential behavior of the dye in the presence of formamide and alkyl amides authenticate that the nature of interaction operates by both hydrogen-bonding mode and electrostatic interactions. Electrochemical techniques when coupled with fluorescence methods provide an efficient method of determining the interaction at the bulk and the interface regions of a water-soluble dye with nonfluorophoric solutes.