The oxidized bisindolyl-based amphiphilic, chromogenic probe has been synthesized that can form nanoscopic aggregates in the aqueous medium. Along with solvent polarity and pH of the medium, it was observed that the addition of heavy metal pollutants, like Hg2+ can cause significant alteration in the charge transfer state. This resulted in the immediate change in the solution color from yellow to orange. Additionally, we could excite either the monomer species or the aggregates of the probe by choosing the proper excitation wavelength. Upon exciting at 390 nm, the compound exhibited a broad fluorescence spectrum with maxima at 450 nm, presumably due to twisted state charge transfer. On the contrary, the aggregated species (λex = 465 nm) displayed a comparatively weaker fluorescence band centered at 565 nm. Interestingly, the fluorescence intensity at the 450 nm band experience fluorescence quenching in the presence of Hg2+ ion, while the aggregate emission band remained unaffected. Finally, the present system was utilized for detection of mercury ions in natural water samples.
Keywords: Bisindolyl probe; Dual-mode sensing; Excitation channel; Heavy metal pollutants; Twisted intramolecular charge transfer.
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