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 CH3OH and H2O solution by absorption, steady-state fluorescence and fluorescence lifetime spectroscopy. The results indicate that P1 and P2 are molecularly dissolved in CH3OH 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 PI 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.
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