ABSTRACT
Conjugated polyelectrolytes (CPEs) are conjugated polymers (CPs) bearing ionic side groups. Due to the presence of these ionic side chains, CPEs are soluble in typical polar solvents like methanol and water. The first CPEs were reported by Wudl, Heeger, and coworkers in 1987, and these had a polythiophene backbone with ethylsulfonate and butylsulfonate anionic side chains.[ 1 ] These CPEs were synthesized 548by polymerization of their corresponding methyl sulfonate ester monomers, which were subsequently hydrolyzed to convert them to their respective water-soluble sodium salts. Ever since their inception, a multitude of CPEs with diverse backbone structures such as poly(para-phenylene) (PPP), poly(phenylene vinylene) (PPV), poly(phenylene ethynylene) (PPE), polythiophene (PTh) (Figure 14.1), and side chains were synthesized by several research groups around the world for applications such as sensing,[ 2 ] drug delivery,[ 3 ] bioimaging,[ 4 ] solar cells,[ 5 ] and organic light-emitting diodes (OLEDs).[ 6 ] The availability of various coupling reactions in the arsenal such as Suzuki coupling, Heck coupling, Sonagashira coupling, and Wittig-Horner coupling provides an opportunity for chemists to judicially choose a method to synthesize the corresponding polymers. In addition to these common methods, oxidative polymerization using FeCl3 and base-mediated Wessling reaction using sulfonium monomers and 1,4-photopolymerization were also employed to synthesize CPEs. In most cases, the synthetic pathway adopted to obtain a particular CPE depends on the nature of the polymeric backbone as required for the intended application. Over the past two decades tremendous effort has been made for obtaining CPEs of various structural diversities with improved processibility for a number of applications. Although numerous publications and patents on CPEs exist, it is important to highlight the various types of CPEs in general to give a perspective of the field. This chapter will begin with a discussion on various types of CPEs that have been reported, with several examples, that will be followed by the fluorescence properties of CPEs. The second section of the chapter will cover the biological applications of CPEs, in which biosensing, biocidal, and cell imaging properties will be described with specific examples. The goal of this chapter is not to provide an exhaustive review, but rather to give some useful examples that provide the reader with an overview of the field. Prototypical conjugated polymer backbone structures. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315159522/ab60430e-1b37-4c27-9089-7b3e8b4c996e/content/fig14_1_B.tif"/>
