Two novel compounds, 4-(pyren-1-ylimino)methylphenol and 4-[(triisopropylsilyl)oxy]phenylmethylenepyren-1-amine) were synthesized. Solutions of 4-(pyren-1-ylimino)methylphenol in dimethyl sulfoxide (DMSO) are colorless, but on addition of cyanide and fluoride they become colored due to the deprotonation of the chemosensor. The system is highly selective toward cyanide with the addition of water. This compound can be solubilized in water with addition of cetyltrimethylammonium bromide above its critical micellar concentration. The pKa of the compound in water was determined as 10.49 ± 0.02 and this value is lowered in micellar medium to 7.49 ± 0.02, which means that only cyanide is sufficiently basic to achieve the deprotonation of the compound. Solutions of 4-[(triisopropylsilyl)oxy]phenylmethylenepyren-1-amine) in DMSO are colorless, but they are colored in the presence of cyanide and fluoride and only cyanide could be detected in DMSO-water mixture. The nucleophilic attack of the anions on the silicon center of the compound releases colored 4-(pyren-1-ylimino)methylphenolate, enabling the detection of nucleophilic analytes.

A two-step experiment is proposed for a third year class in experimental organic chemistry. Over a period of five weeks, the students synthesized calix[4]pyrrole, a receptor that is highly selective for fluoride, and a pyridinium N-phenolate dye. Subsequently, the students used the synthesized compounds to investigate a displacement assay on the basis of the competition in acetonitrile between fluoride and the dye for calix[4]pyrrole. The experiment increased the students' skills in organic synthesis and in the characterization of organic compounds, provided a very attractive and accessible illustration of important supramolecular phenomena, and allowed the study of a chromogenic chemosensor.

O composto 4-(4-nitrobenzilidenoamino)fenol foi utilizado em duas estratégias que permitem uma detecção altamente seletiva de F- e CN-. Primeiramente, observou-se que o composto em acetonitrila age como um quimiossensor cromogênico devido ao fato de que ânions básicos levam ao seu desprotonamento (solução incolor), resultando numa solução colorida contendo fenolato. A detecção seletiva de CN- sobre F- foi obtida adicionando-se 1,4% de água ao sistema: a água solvata preferencialmente o F-, enquanto o CN- fica relativamente livre para desprotonar o composto fenólico. Outra estratégia envolveu um ensaio de competição do fenolato e do analito pelo calix[4]pirrol em acetonitrila, um receptor altamente seletivo para F-. O fenolato e o calix[4]pirrol formam um complexo por ligação de hidrogênio, com mudança na cor do meio. Dentre diversos ânions, somente o F- foi capaz de restaurar a cor original correspondendo ao fenolato, pelo fato do ânion deslocá-lo do sítio de complexação.

4-(4-Nitrobenzylideneamine)phenol was used in two strategies allowing the highly selective detection of F- and CN-. Firstly, the compound in acetonitrile acts as a chromogenic chemosensor based on the idea that more basic anions cause its deprotonation (colorless solution), generating a colored solution containing phenolate. The discrimination of CN- over F- was obtained by adding 1.4% water to acetonitrile: water preferentially solvates F-, leaving the CN- free to deprotonate the compound. Another strategy involved an assay comprised of the competition between phenolate dye and the analyte for calix[4]pyrrole in acetonitrile, a receptor highly selective for F-. Phenolate and calix[4]pyrrole form a hydrogen-bonded complex, which changes the color of the medium. On the addition of various anions, only F- was able to restore the original color corresponding to phenolate in solution due to the fact that the anion dislodges phenolate from the complexation site.