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Visual detection: cyclo-Bis(urea-3,6-dichlorocarbazole) (1), the first anion receptor bearing urea, displays a fluorescence quenching effect with pyrophosphate and fluoride ions. Its deprotonated form (12−) acts as a new fluorescent probe that can selectively detect metal cations (Zn2+ and Cu2+) by means of colorimetric changes.
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Ahmed et al. (2011) studied this question.
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