Polymer Chain Length Dependence of Amplified Fluorescence Quenching in Conjugated Polyelectrolytes

This paper reports the synthesis and photophysical study of a series of anionic, carboxylate-substituted poly(phenylene ethynylene)-based conjugated polyelectrolytes (CPEs) with variable chain lengths. These CPEs are of interest as they allow the study of the effect of chain length on amplified fluorescence quenching. The CPEs were synthesized via organic soluble ester precursor polymers. The degree of polymerization of the precursor polymers was controlled by addition of a monofunctional “end-cap” to the polymerization reaction. The CPEs were obtained postpolymerization by base-promoted hydrolysis of the ester protecting groups. Stern−Volmer fluorescence quenching of the CPEs in methanol with monovalent electron-transfer quenchers (MV⁺ and HV⁺) show that the Stern−Volmer quenching constant (K_SV) increases with polymer chain length reaching a maximum of ca. 2 × 10⁵ M⁻¹ at a degree of polymerization of 49. The results indicate that a maximum quenching amplification factor of 53 is attained under conditions where monovalent quencher ions interact with nonaggregated (single) polymer chains.