The fluorescence of conjugated polyelectrolytes (CPEs) is quenched with very high efficiency by small molecule quenchers with opposite charges. This effect has been referred to as amplified quenching or superquenching. We study the profound correlation between the fluorescence quenching efficiency, CPE chain aggregation (induced by the addition of either Ca2+ or H2O to methanol solution), and quencher molecular size. We propose that the superlinear Stern-Volmer quenching behavior typically observed in CPE-quencher systems arises due to quencher-induced aggregation of the CPE chains.
For an example, two of the poly(phenyleneethynylene)-based CCPEs bearing cationic imidazolium groups synthesized in our lab showed excellent biocidal activity. These two polymers having same backbone differ only by the frequency of the imidazolium groups present on the chain, which in turn changes their solubility property in water. Addition of an anionic electron-acceptor like anthraquinone disulphate, even in a relatively low concentration to these CCPEs solution quenches their fluorescence via the amplified quenching effect. These CCPEs also display aggregation-induced fluorescence quenching property when exposed to pyrophosphates. Our investigation on their biocidal activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria in the dark and under blue-light-illumination revealed that these CCPEs are effective biocides, exhibiting greater than 3 log kill with 30-60 min of light exposure at concentrations of <10 mg mL-1.
ACS Appl. Mater. Interfaces, 2015, 7, 28027–28034.