Association behavior of porphyrin pendants in pH-sensitive water-soluble polymer
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A novel tripyridylporphyrin monomer, 5-[4-[2-(acryloyloxy)ethoxy]phenyl]-l0,l5,20-tris(4-pyridyl)porphyrin (TrPyP), was synthesized and polymerized with acrylamide (AM) to prepare the hydrophobically associating water-soluble polymer PAM-TrPyP. The aggregation behavior of porphyrin pendants was investigated by UV-Visible and fluorescence spectra. The polymer displays a strong tendency of hydrophobic association even in dilute solutions. With increasing the concentration, the maximum absorption wavelength of Soret band changes from 416 nm to 407 nm, and the fluorescence corrected for the inner filter effect exhibits moderate concentration quenching. All the results indicate that π-π interaction of porphyrin pendants plays a key role in association of PAM-TrPyP, and H-aggregates of porphyrins are mainly formed in the concentrated solution. On the other hand, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to follow the changes in size and structure of the macromolecular assemblies with the concentration increase. The polymer aggregation conformation changes from loose “vesicle-like” morphology to solid globule accordingly. When pH value of solution decreases to 4.3, pyridine moieties on porphyrin pendants could be protonated and the H-aggregates formed in macromolecular matrix are destroyed by electrostatic repulsion interactions.
KeywordsPorphyrin Water-soluble polymer π-π Interactions H-aggregate pH-sensitivity
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