Conjugated polyelectrolytes with guanidinium side groups. Synthesis, photophysics and pyrophosphate sensingElectronic supplementary information (ESI) available: Synthetic procedure of the monomer, NMR spectra of P1-Boc and P2-Boc, pH-dependent absorption and fluorescence spectra of P1, fluorescence quenching of P2 in methanol and fluorescence lifetime results. See DOI: 10.1039/c3pp50288k

Two cationic poly(phenylene ethynylene) conjugated polyelectrolytes (CPEs) featuring guanidinium side groups were the subject of investigation. Two polymers were examined, one is an alternating co-polymer (P1) in which the guanidinium groups are on every other repeat unit and the second is a homopolymer with the guanidinium groups on every repeat unit. The photophysical properties of the CPEs were investigated in CH 3 OH and H 2 O solution by absorption, steady-state fluorescence and fluorescence lifetime spectroscopy. The results indicate that P1 and P2 are molecularly dissolved in CH 3 OH solution; however, in water the polymers aggregate as evidenced by a substantial reduction in the fluorescence yield. Addition of the non-ionic surfactant (Triton X-100) into the weakly fluorescent aqueous solution of P1 increased the fluorescence by forming a polymer/surfactant complex. The fluorescence of the polymer/surfactant complex in aqueous solution was effectively quenched by the addition of pyrophosphate (PPi) with Stern-Volmer quenching constants ( K sv ) ∼ 1.7 × 10 5 M −1 ; the quenching occurs because PPi binds to the guanidinium groups and induces the aggregation of the polymer/surfactant complex. In addition, by using fluorescence correlation spectroscopy it was found that the diffusion time of the aggregated complex is increased 9-fold in comparison with the free CPE/surfactant complex. A sensor is developed utilizing the significant changes in fluorescence induced by the addition of PPi. Poly(phenylene ethynylene) conjugated polyelectrolytes with guanidinium solubilizing groups serve as a pyrophosphate sensor.