Conjugated polyelectrolyte with pendant carboxylate groups: Synthesis, photophysics, and pH responses in the presence of surfactants

Abstract

This article reports the synthesis, optical properties, and pH responses of a water-soluble poly(phenylene ethynylene) with pendant carboxylate groups. This conjugated polyelectrolyte, PPE-OBS, was prepared via a facile synthetic route, using 1,4-di(ethyl 4-oxy-butyrate)-2,5-diiodo-benzene as polymeric monomer and followed by the alkali induced saponification. PPE-OBS absorbs strongly in the blue region and emits a moderately intense fluorescence. However, it subjects to unstable emission in neutral aqueous media, which is believed to arise because the polymer tends to become more hydrophobic via protonation and to form much heavier aggregates (clusters). Subsequent studies on the interaction and stabilization of PPE-OBS with various surfactants indicate that its fluorescence stability can be largely improved in the presence of a small amount of surfactant. More interestingly, even at low pH, the surfactant-stabilized polyelectrolyte with its pendant groups being ACOOH rather than ACOO À remains water-soluble and emits efficiently, which is expected of great significance for the covalent linkage to bio-molecules. In addition, the sensitive pH response in emission spectrum of PPE-OBS/surfactant complex over a relatively wide range suggests surely a potential access to the fluorescent sensing of pH variation.

4,4′-[p-Phenylenebis(oxy)]dibutanoic acid

“…The title compound was synthesized according to the method of Zhang et al 2009. To a solution of p-dihydroxybenzene (0.01 mol) in acetonitrile (50 ml), anhydrous potassium carbonate (0.02 mol) and ethyl 4-bromobutanoate (0.01 mol) were mixed.…”

“…For related structures of multidentate O-donor ligands such as benzene-1,4-dioxydiacetic acid and benzene-1,4-dioxydibutanoic acid, see: Dai et al (2009);Zhu et al (2008); ; Yang et al (2010); Zhao (2011). For the synthesis of the title compound, see: Zhang et al (2009). For standard bond lengths, see: Allen et al (1987).…”

Highly Sensitive Fluorescence Detection of Hg2+ Based on a Water-soluble Conjugated Polymer with Carboxylate Groups

“…22 Unlike that of their small molecule counterparts, the unique π-π* conjugated electronic structure of CPs allows for rapid transfer of excitation along the entire backbone to energy/electron receptors, thereby resulting in a remarkable amplification of optical response. 23 Studies that detect metal ions with CPs in organic solvents have been proposed in the past 10 years. [24][25][26] However, toxic heavy metal ions mainly exist in aqueous solutions, and the quenching process of CPs and metal ions in aqueous solutions is rarely studied.…”

“…For example, Fan et al reported the synthetic route, optical properties, pH responses, and subsequent studies on the interaction and stabilization of poly(2,5-bis(sodium 4-oxybutyrate)-1,4-phenylethynylene-alt-1,4-phenyleneethynylene (PPE-OBS) with various surfactants. 23 Pei et al investigated an antioxidant probe based on a bimodal PPE-OBS-SO3. 31 A highselectivity and high-sensitivity fluorescent sensor for detecting highly toxic Hg 2+ was developed using PPE-OBS because of the good water solubility and considerable potential applications of PPE-OBS.…”

“…In the present work, PPE-OBS, which could be used to detect Hg 2+ in water samples, was synthesized according to a previous report. 23 When Hg 2+ is added, the coordination-induced aggregation and electron transfer between Hg 2+ and PPE-OBS results in the significant quenching of fluorescence and in a slight red shift. In particular, PPE-OBS exhibits better linear range, higher sensitivity, and higher selectivity for Hg 2+ than other metal ions used in other fluorescent sensing methods.…”