Metalation of Tetrakis(ethynylphenyl)porphyrin Films Grafted onto Glassy Carbon and Indium Tin Oxide Surfaces

Thin films of a free-base porphyrin were grafted onto glassy carbon (gc) or indium tin oxide (ITO) electrodes by anodic deposition of 5,10,15,20-tetrakis(ethynylphenyl)porphyrin, H 2 TEPP. Metalation of the porphyrin was carried out by soaking the electrode in an organic solvent containing a dissolved or suspended metal-halide or metal-acetate. Six metals (Mg, Cd, Zn, Co, Ni, and Cu) were tested, which gave relatively facile and complete conversion to the M(II) porphyrin, along with retention of the film thickness, which was generally in the range of one- to several-monolayers. The metalations carried out overnight at room temperature utilized MgBr 2 ·Et 2 O (in dichloromethane), CdI 2, or ZnCl 2, the latter two in diethyl ether. Those conducted at 353 K in DMF involved the M(II) acetate complexes of Co (for 1.3 h), Ni (2.5 h), and Cu (0.3 h). The metalated films were characterized by cyclic voltammetry on gc electrodes and by optical spectroscopy on ITO electrodes. Atomic force microscopy measurements on films of the free-base H 2 TEPP and the cobalt–metalated system showed that the latter retained the general morphology of globular-shaped units in the reaction process. The cobalt system was also characterized by X-ray photoelectron spectroscopy, which confirmed the presence of the Co(II) oxidation state for the CoTEPP film.