Changes in fluorescent emission of cationic fluorophores in the presence of n-alkanes and alcohols in different polarity solvents

► The effect of addition of nonfluorescent compounds, with low UV response, such as n-alkanes or alcohols, on emission properties of two cationic fluorophores, berberine and coralyne, are compared in solvents of different polarity, such as methanol, acetonitrile and dichloromethane. ► Results are also compared with previous work of us in Thin-Layer Chromatography, in which compounds were added to fluorophore-impregnated silica gel plates, a polar medium in the absence of solvent. ► Different mechanisms for fluorescence enhancement or quenching obtained in polar or apolar solvents are proposed here. Our results show that the effect of ion pairing between the cationic fluorophore and counterion (chloride or sulphate anion) should be taken into account in dichloromethane. In contrast, ion pairing is precluded by cationic fluorophore-solvent interaction in polar solvents methanol or acetonitrile. ► Based on the fluorescence intensity changes caused on the fluorophores studied here, this work may be useful to develop simple and high sensitive detection methods not only for alkanes or alcohols, but also for other kind of nonfluorescent compounds with a partially aliphatic structure, which is subject of current research in our laboratory, in the field of polymer science or compounds with biological interest.