A new insight into the mechanism of influence of different inorganic salts on optical properties of water-soluble cationic conjugated polymers

摘要

The water-soluble conjugated polyelectrolyte poly{2,5-bis[3-(N,N,N-triethylammoniumbromide)-1-oxapropyl]-1,4-phenylenevinylenej (P2) was synthesized and the influences of different inorganic salts on the optical properties of the polyelectrolyte were studied. New absorption and emission peaks at longer wavelength can be observed in the case of P2 with addition of different concentrations of Cl~- or NO_3~-, whereas addition of l~- or ClO_4~- only induces a red shift. Interestingly, addition of SO_4~(2-) or F~- does not result in considerable changes in optical spectra. Through UV-visible spectrometry, photolu-minescence, ~1H NMR and cyclic voltammetry, we showed that the nature of the inorganic salts brings these different changes. The special structure of the Π_4~6 bond of NO_3~- and the large electronegativity of chlorine lead to an electron transfer between the conjugated polymer and the negative ions. The large radius of l~- and the weak electron withdrawing ability of CIO_4~- only bring a red shift of optical spectra. In addition, SO_4~(2-) and F~ do not affect the spectra significantly, except that the fluorescence intensity falls slightly indicating that P2 is not sensitive to these ions.