Palladium-mediated stepwise assembly of three-dimensional organized multiporphyrin arrays directly on solid substrates

A palladium-mediated assembling strategy was developed to construct organized, three-dimensional multiporphyrin arrays, wherein layers of multiporphyrin arrays can be embedded via a Py-Pd-Py coordination unit directly on solid substrates. Multilayers of the multiporphyrin arrays were characterized by use of X-ray photoelectron, UV-vis, and fluorescence spectroscopy. A linear increase was observed for the absorption intensity of the Soret band of porphyrins or the pi-pi* charge transition with the layer numbers of porphyrins or palladium ions assembled. The surface density of (Zn)TPyP molecules in one layer of multiporphyrin arrays was estimated to be in the range of 1.9-2.4 x 10(-10) mol/cm(2). The orientation angle of the porphyrin macrocycles was in the range of 55-60degrees. A schematic model for the multiporphyrin arrays was proposed based on the spectral analysis, orientation angle, and film thickness from atomic force microscopy measurement. These Pd-mediated multiporphyrin arrays showed high thermal and chemical stability. They were stable in air and commonly used organic solvents. Moreover, no significant absorption spectral change was recorded in a temperature up to 150 degreesC and in an aqueous solution with pH < 2.