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.

Biocidal Activity of Cationic Conjuguated Polyelectrolytes (CCPEs) and Oligomers

Poly(phenyleneethynylene)-based CCPEs and oligomers bearing cationic functionality such as ammonium, DABCO and imidazolium groups synthesized in our lab showed excellent biocidal activity. These CCPEs are water-soluble and display very low cytotoxicity. Our investigation on their biocidal activity against various microorganisms such as Gram-negative and Gram-positive bacteria, and fungi planktonic cells and biofilms under visible-light-illumination revealed that these CCPEs are effective biocides at concentrations as low as 1 μM – 128 μM. The biocidal activity of these conjugated materials involves two main pathways: (1) the cationic segments in the side chains allow the CCPEs to electrostatically bind to the net-anionic membranes of the bacterial/fungi cell wall causing disruption, distortion and damage; and (2) upon irradiation with light, the conjugated backbone of CCPEs absorb light and photosensitize O₂ to produce reactive oxygen species (ROS), which readily react with the cell wall and other cellular components that lead to rapid cell inactivation.