Oxidized Bis(indolyl)methane Derivatives with Diverse Signaling Units: An Excitation-Dependent Fluorescence Response toward Heavy Metal Pollutants in an Aqueous Medium
Rikitha S. Fernandes, Nilanjan Dey
Abstract
Herein, we have designed and synthesized two oxidized bis(indolyl)methane derivatives with pyrene and anthracene as signaling moieties. Both the amphiphilic compounds exhibited microenvironment-sensitive (pH, temperature, polarity, etc.) nanoscopic aggregate formation in an aqueous medium. It has been observed that the excitation of either monomer species or aggregates is possible by choosing a suitable excitation channel. Upon photoexcitation, the monomer species showed a turn-off response specifically for Hg 2+ ions. On the other hand, Hg 2+ -coordination promotes the aggregation of probe molecules in an aqueous medium, leading to the enhancement of aggregate fluorescence. Further, it was observed that the relative response of pyrenylated and anthracenyl probes toward Hg 2+ ions was dependent on excitation wavelength. This might be due to differences in the conformation of these molecules, the p K a of indolyl nitrogen ends, and the amphiphilicity (propensity of aggregation). The sensory system was further utilized to quantify Hg 2+ in natural water samples. In addition, we have prepared dye-coated paper strips for rapid on-location analysis of Hg 2+ ions without engaging any sophisticated instruments or trained technicians.