Pd(II)-directed layer-by-layer assembly and characterization of zinc tetrapyridylporphyrin-linked poly(4-vinylpyridine) multilayers on substrate surfaces

Polymeric zinc porphyrin derivatives have been synthesized through an axial coordination reaction of zinc tetra(pyridylporphyrin) chloride tetrakis(methochloride) (ZnTMPyP) with poly(4-vinylpyridine) (PVP). The molar fractions of ZnTMPyP relative to pyridyl substituents of PVP in the as-prepared ZnTMPyP-PVP polymers were 1:30 and 1:250. Palladium (II) directed Pd/ZnTMPyP-PVP coordination polymer multilayers were constructed on the quartz and gold substrate surfaces by the layer-by-layer (LBL) method with the use of Na2PdCl4 as the connector and the polymeric zinc porphyrins as the linkers. Compositions, film structure and morphologies of the LBL multilayers were characterized by using UV–vis absorption, X-ray photoelectron spectroscope, scanning electron microscope and atomic force microscope. The fluorescence emission properties of the porphyrins in the LBL multilayers were similar to those in the methanol solutions. The emission lifetime was about 1.36 and 0.16 ns for the zinc porphyrins in the ZnTMPyP-PVP30 solution and LBL multilayers, respectively. It was revealed that the present Pd/ZnTMPyP-PVP LBL multilayers could be used as heterogeneous photocatalyst for the degradation of methyl orange under irradiation at room temperature. Because the multilayers were anchored on the substrate surface through covalent and coordinative bonding, they were of high stability, good recyclability, and facile separation from the reaction system.

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► Two polymeric zinc porphyrins were synthesized.
► Metal-mediated Pd/ZnTMPyP-PVP multilayers were constructed and characterized.
► Immobilized Pd/ZnTMPyP-PVP multilayers were used as heterogeneous photocatalyst.