Naphthalimide-Linked Carbazole Derivative: Synthesis, Gelation and Naked Eye Detection of Cu2+ and Fe3+-Ions Under Different Conditions

Abstract

Naphthalimide-labeled carbazole derivative NC has been synthesized, characterized, and tested for sensing of metal ions in different conditions. Compound NC acts as Low Molecular Weight Gelator (LMWG) and exhibits gelation from aqueous DMF, DMSO, and 1,4-dioxane. Morphologies of the gels are fibrous and their packing varies with the nature of the gelling solvent. All the gels reveal good viscoelastic response. Based on the different morphologies, the rheological behavior of gels differs. DMSO/H2O and DMF/H2O gels with lower tan delta values intimate considerable mechanical strength. As an application, the brown gel derived from DMF: H2O (1:1, v/v) is Cu2+ and Fe3+ responsive involving a gel-to-sol conversion, and validates the naked eye detection. The Fe3+broken gel is is sharply distinguished from the Cu2+-broken gel by adding F- ions. In CH3CN, compound NC also shows interaction with Cu2+ and Fe3+ ions through a color change (yellow to colorless) and fluorescence quenching. The metal ions are fluorimetrically differentiated in aqueous CH3CN using F- ions although compound NC was incapable of showing selectivity in aqueous CH3CN. The detection limits for Cu2+ and Fe3+ ions are calculated using emission data as 2.02 x 10- 7M and 2.09 x 10- 7 M, respectively. Compound NC also recognizes Cu2+ and Fe3+ ions through paper strips under UV light and the ions are distinguished by F- solution. The binding and spectroscopic observations are explained by theoretical calculations. The structure of the copper complex as obtained from single crystal x-ray analysis gives additional support to the observation.