A Porphyrin-Bridged Pd Dimer Complex Stabilizes Gold Nanoparticles

A porphyrin-bridged bimetallic palladium(II) diphenylacetylide complex and the oligomer with 3-5 repeat units have been prepared and spectroscopically characterized. The porphyrin-bridged Pd complex has been used for the stabilization of gold nanoparticles, thus giving rise to unexpected stable structures with no evidence of covalent bonds between the porphyrin and the gold nanoparticles. The morphology investigated by TEM analysis shows that gold nanoparticles with a mean diameter of about 5 nm have been obtained. UV/Vis spectra reveal the achievement of stabilized gold nanoparticles through the presence of the plasmon resonance at 500 nm together with the absorption features of the porphyrin molecule at 436 and 620 nm (Q band). Photoluminescence spectra exhibit an emission feature centred at 572 nm with a shoulder at 325 nm with no quenching effects. XPS measurements at the Au 4f core level suggest an electronic interaction between the gold atoms of the nanoparticle surface and the porphyrin-based complex; NMR spectroscopic studies indicate that interactions and assemblies also occur that involve the porphyrin rings. Elemental analysis suggests that about 120 tilted porphyrins are physisorbed onto the Au core.