Aggregation effects on electrochemical and spectroelectrochemical properties of [2,3,9,10,16,17,23,24-octa(3,3-dimethyl-1-butynyl)phthalocyaninato]cobalt(II) complex

The title complex, [Co(odmbpc)], which is a single isomer and is highly soluble in common organic solvents, has been prepared and investigated electrochemically and spectroelectrochemically in dichloromethane solutions. The cyclic voltammograms of this complex at a concentration of ca. 6x10(-5) mol dm(-3) exhibited two reversible reduction waves at E-1/2 = -0.67 V (vs. ferrocenium+/ferrocene) and -1.74 V, which were attributed to cobalt-centered and triple-bond-centered (in a peripheral substituent) reductions, respectively, and three quasi-reversible oxidation waves at 0.26, 0.46, and 0.74 V, the former two and the latter one of which were attributed to phthalocyanine-chromophore-centered and cobalt-centered oxidations, respectively. Some of these assignments were supported by the electronic absorption spectra of the electro-generated species. The first reduction wave was not observed at 6x10(-4) mol dm(-3) until the applied potential was swept to the second reduction wave. Nevertheless, under the same conditions, the controlled-potential electrolyses in an optically transparent thin-layer electrode at potentials around the first reduction wave gave rise to drastic spectral changes without any preliminary electrolysis at potentials around the second reduction wave. Such strange phenomena are discussed in terms of molecular aggregation of the complexes in solutions. The peripheral alkynyl group has been found to be slightly electron-donating.