Studies of photoinduced electron transfer and energy migration in a conjugated polymer system for fluorescence "turn-on" chemosensor applications.

A series of poly[p-(phenyleneethynylene)-alt-(thienyleneethynylene)] (PPETE) polymers with variable percent loadings of the N,N,N'-trimethylethylenediamino group on the polymer backbone were synthesized and fully characterized. Photophysical studies show that changes in the loading of the amino group receptor on the backbone do not affect the polymer electronic structure in either the ground or excited states. The fluorescence quantum yields were found to be directly related to the loading of the amino groups and can be modeled by a Stern-Volmer type relationship. Photophysical studies related the total quenching efficiency to the inherent rate of photoinduced electron transfer (PET), the lifetime of the exciton, the rate of excitation energy migration along the polymer backbone, and the total loading of the receptor on the polymer. The role of the loading dependence on the application of these polymers as fluorescence "turn-on" sensors for toxic metal cations in dilute solution was also studied. Results showed that the fluorescence enhancement upon binding various cations was maintained even when the amino receptor loading along the polymer backbone was reduced.