Abstract
Novel phenothiazine fluorophore containing two tricyanofuran-vinyl groups [tricyanofuran(TCF)-bearing phenothiazine(P); TCFP] as cyanide anion receptors was synthesized. TCFP demonstrated an intramolecular charge transfer (ICT) absorbance at 432 nm and fluorescence at 619 nm in acetonitrile. The absorbance and fluorescence peaks were monitored to decrease in a ratiometric mode upon titrating with various concentrations of CN
−
anions. Such optical responsiveness for CN
−
could be ascribed to nucleophile-based Michael addition of the CN
−
onto
α
-position of tricyanofuran-vinyl moieties in the TCFP molecular structure. Therefore, those electron deficient acceptors convert to anionic electron donors owing to the conjugate molecular system break down, which influence both ICT and fluorescence of TCFP. The results indicate that TCFP exhibits high sensitivity with a rapid responsiveness of less than 55 s. TCFP reaction mechanism with CN
−
was investigated by FT-IR,
1
H/
13
C NMR, and elemental analysis. As a result of the intramolecular charge transfer, the TCFP chromophore showed pronounced ionochromism relying on the solvent polarity demonstrating a colorimetric shift from light yellow to red. Owing to the existence of nitrogen-containing heterocyclic ring in its molecular structure, TCFP chromophore showed an antibacterial activity to
S. Aureus
,
E. Coli
and
C. Albican
. The cytotoxic action of the TCFP chromophore was evaluated. The current TCFP chromophore showed the lowest detection limit (1.1 × 10
–9
mol L
−1
) compared to previously reported chemosensors. This detection limit is below the allowed cyanide levels (1.9 × 10
–6
mol L
−1
) reported by WHO. Furthermore, cellulose test strips immobilized with TCFP were prepared for the detection of cyanide anion at different concentrations in aqueous solutions. The coloration measurements of the TCFP-immobilized cellulose dipstick were evaluated by CIE Lab parameters, coloration strength (
K/S
) and UV–Vis absorption spectra. Moreover, the TCFP-immobilized strip exhibits selectivity toward CN
−
with a limit of detection (LOD) at 25–100 ppb. Scanning electron microscope (SEM) was utilized to evaluate the morphologies of the TCFP-immobilized cellulose dipstick.