Fluorescence, Metal Ion Binding, and Viscosity Properties of Poly[2- and 4-vinylpyridine N-oxide]s in Aqueous Solution

Abstract

Poly(2-vinylpyridine N-oxide) (P2VPNO) and poly(4-vinylpyridine N-oxide) (P4VPNO) were synthesized by the oxidation of the corresponding poly(vinylpyridine)s. They are soluble in water and have a characteristic fluorescence in aqueous solutions. The fluorescence intensities of P2VPNO were over 3 times that of P4VPNO in 10-2 M aqueous solutions at ambient temperature, which was accounted for by the difference in the microenvironment of the pyridine N-oxide fluorophore. The N-oxide polymers formed strong complexes with Tb3+ in aqueous solution, and the fluorescence intensities of Tb3+ were greatly enhanced upon complex formation. The increase in fluorescence intensity is due both to the replacement of inner-coordinated water molecules of Tb3+ by N-oxide polymers and to a ligand-to-metal energy transfer. P4VPNO is a better complexing agent for Tb3+ than P2VPNO. The reduced viscosity of P4VPNO increased sharply at polymer concentrations smaller than 1.0 g/dL, as in polyelectrolytes. However, in the case of P2VPNO, the concentration dependence of the reduced viscosity was similar to that of nonionic polymers. These differences are due to the position of the N−O group. P2VPNO and P4VPNO have a charge separation across the N+−O- bond with a large dipole moment. P4VPNO forms a partial complex with water which transforms the N−O group into a weak acid. The complex then behaves like a polyelectrolyte, and upon dilution, the reduced viscosity increases due to chain expansion. In the case of P2VPNO, the N−O group is close to the polymer backbone, which sterically decreases the formation of the water complex, and its reduced viscosity then behaves like that of nonionic polymers. Although P2VPNO does not behave like a polyelectrolyte, addition of Tb3+ reduces the solution viscosity due to a complexation of Tb3+ with the ligands.

Characterization of poly(4‐vinylpyridine 1‐oxide) by free‐solution capillary electrophoresis and micellar electrokinetic chromatography

“…In this concern, the results obtained by FSCE agreed with those previously reported using viscosity, light scattering, conductivity and acid-base studies [22][23][24]. The results are also consistent with the presence of at least two forms of the polymer in aqueous solutions, likely one of them constituted by free chains (unimers) and the other one by aggregates.…”

“…This charge separation has been also demonstrated in PVP-NO [22]. According to viscosity and light scattering measurements in solution, PVP-NO has been shown to behave like a polyelectrolyte, rather than as a noncharged polymer [22,23].…”

“…This charge separation has been also demonstrated in PVP-NO [22]. According to viscosity and light scattering measurements in solution, PVP-NO has been shown to behave like a polyelectrolyte, rather than as a noncharged polymer [22,23]. This behavior has been attributed to the presence of strong interparticle forces, which result from the charge separation across the N-O bond [23].…”

“…Further, PVP-NO solutions in water have a non-zero electrical conductivity (2.8610 -7 -3.4610 -6 S/cm), which contrasts with the electrically insulating properties of the corresponding non-oxidated poly(4-vinylpyridine) (,10 -14 S/cm) [24]. Finally, purified PVP-NO fractions gave solutions with pHs as low as 3.4-4.5 when solved in water, which was attributed to the formation and subsequent ionization of a PVP-NO/ water complex [22].…”

Efficient Donor for Terbium Luminescence Based on Polymer Ligand Containing Quinolinone Fluorophore

“…In our preliminary study [12][13][14] we replaced the lowmolecular-weight pyridine cryptands with poly(2-and 4-vinylpyridine)s or poly(2-and 4-vinylpyridine N-oxide)s. The fluorescence of the polymer ligand (donor) was overlapped by the absorption of the terbium ion (acceptor) and a ligand-to-metal energy transfer was observed. The increase in Tb 3þ luminescence intensity was due to both the replacement of the inner-coordinated solvent (water or methanol) molecules and ligand-to-metal energy transfer.…”