Covalently attached metalloporphyrins in LBL self-assembled redox polyelectrolyte thin films

A formylporphyrin has been covalently bound to Poly (Allylamine Hydrochloride) (PAH) and electrostatically self-assembled polyelectrolyte films, containing the attached metalloporphyrin, have been constructed. The UV–vis absorption band at 390 nm has been followed as core porphyrin marker. The reflection–absorption IR spectra of the gold films modified with layer-by-layer (LBL) polyelectrolytes were recorded after 6 and 12 layers. Characteristic infrared absorbance bands of porphyrin, PAH and PVS became more evident on increasing the number of bilayers. The absorption bands at 750, 1214 and 2960 cm−1, attributed at ν(S–O), νs(SO3−) and ν(NH2+), respectively, showed a linear growth (R2 > 0.99) with the number of adsorbed layers. A lower correlation coefficient was observed for the band at 1585 cm−1 attributed to Fe-protoporphyrin. In order to evaluate the electron transfer (ET) rate, the ΔEp of the [Fe(CN)6]4−/[Fe(CN)6]3− couple in solution was measured after covering the electrode. A proportional increase of the ΔEp with the number of layers is observed up to the 4th layer. After the second bilayer, the magnitude of the peak separation is highly related to the charge of the topmost layer. The method allowed controlling the film thickness via the number of deposited layers (LBL). The electrode described, resulted in a good catalyst for O2 reduction and sulfite oxidation.