Synthesis, Photophysical Studies on Some Anthracene–based Ionic Liquids and their Application as Biofilm Formation Inhibitor

Imidazolium based monocationic and dicationic ionic liquids, with an anthracene moiety covalently attached to the imidazolium ions, via a methyl spacers, have been synthesized and their photophysical and biological studies have been carried out. Photophysical investigations have revealed that the monocationic anthracene based ionic liquid, AnILBr, exhibits a higher fluorescence quantum yield and average fluorescence lifetime compared to its parent fluorophore anthracene. For dication based systems (AnIL2Br2), the photophysical data have demonstrated that the attachment of two imidazolium cations on anthracene ring, leads to even further fluorescent enhancement. The quantum yield, average lifetime, red‐shifts of absorption and emission for AnIL2Br2 are observed to be relatively higher as compared to AnILBr. This observations illustrate that the imidazolium cation influences the electronic energy distribution in the fluorophore, in such a way, that it leads to enhancement of photoluminescence. Since ionic liquids have recently been shown to demonstrate anti‐biofilm activity, the potential of AnILBr, as a biofilm formation inhibiting agent has also been explored in details. The assay has revealed that addition of AnILBr up to 4 hours significantly inhibited the biofilm formed by both the strains, and this can be utilized to enhance the effectiveness of an antibacterial drug, when used along with AnILBr. Figure showing enhancement in fluorescent intensity of AnILBr as compared to anthracene and reduced intensity of violet colour of crystal violet in presence of AnILBr confirms the anti‐biofilm activity towards biofilm forming bacteria of Staphylococcus spp.