Red-emitting cationic fluorophore as a probe for anionic surfactants

A water soluble N-methylpyridinium dye (DABP) was synthesized and investigated as a fluorescence probe for the detection of anionic surfactants. DABP shows strong solvatochromism with emission at 685 nm in water. The probe-surfactant interaction induces distinct color changes and optical properties. In the presence of anionic surfactants such as SDS, AOT and zwitterionic surfactant such as CHAPS, a multi-fold intensity enhancement is observed but not with positively charged surfactant, CTAB indicating the selectivity for negatively charged surfactants. This is ascribed to the electrostatic attraction between the negatively charged surfactant head group and the positively charged pyridinium ring of the diarylbutadiene chromophore. Such distinguishable emission behavior may be of interest for designing fluorogenic sensors for targeted detection.