Interaction of a Disaccharide, Lactose With Resorcinol-Based Acridinedione Dyes in Water: A Combined Study Involving Photophysical, Electrochemical, and Theoretical Approach

The interaction of lactose with two structurally distinct resorcinol-based acridinedione (AD-res) dyes accompanied with variation in their photophysical properties was carried out in aqueous solution. The introduction of lactose to ADR1 dye hardly influenced the intramolecular charge transfer (ICT) absorption maxima; however, a clear isosbestic point exists between the dye and disaccharide elucidating a ground state complex formation. The ground state characteristics of ADR2 dye in the presence of lactose are entirely different from those of ADR1 dye. In the case of ADR1 dye, fluorescence enhancement (FE) occurs, and fluorescence quenching (FQ) occurs in the case of ADR2 dye. Lactose in aqueous solution promotes multiple microenvironments that differ in hydrogen-bonding patterns, such that a formidable variation in the fluorescence lifetime was observed. The variation in the microenvironment is due to the presence of more water molecules with fewer numbers of lactose surrounding the dye and vice versa, ascertained through fluorescence lifetime studies. Similarly, in electrochemical studies, the introduction of lactose results in a shift in the oxidation and reduction potentials of both ADR1 and ADR2 dyes. This shift correlates with combined conventional hydrogen bonding (cHB) and hydrophobic interactions, supporting the variation in the excited-state nature of the AD-res dyes.