Electrochemical and spectroscopic investigation of neutral, oxidized and reduced double-decker lutetium(III) phthalocyanines

The double-decker lutetium(III) phthalocyanine [(C₆H ₁₃S)₈Pc]₂Lu was investigated by electrochemical and spectroelectrochemical methods and comparisons made to previously investigated [(C₁₂H₂₅S)₄Pc] ₂Lu and (Pc)₂Lu under the some experimental conditions. All three compounds undergo a single reversible one-electron oxidation and up to four reversible one-electron reductions in CH₂Cl₂ containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The octa- and tetra substituted phthalocyanine derivatives exhibit one oxidation and three or four reductions in solution while five reductions can be detected for the two compounds in a gel-like cast film membrane of tetraoctylphosphonium bromide (4C₈P⁺Br^-) at a basal plane pyrolytic graphite electrode which was immersed in aqueous 0.5 M KCl. The half-wave potentials of these SR substituted complexes in CH₂Cl₂ are negatively shifted by 210-490 mV from E_1/2 values for the same compounds in the aqueous 4C₈P⁺Br^- matrix and five reductions of these compounds are observed under the latter experimental conditions. The UV-visible spectra of the compounds were measured in five different oxidation states and ESR spectra were also characterized for the neutral and doubly reduced complexes. As was expected, [(Pc)₂Lu]^-, {[(C ₆H₁₃S)₈Pc]₂Lu}^- and {[(C₁₂H₂₅S)₄Pc]₂Lu}^- are ESR silent while electrogenerated [(Pc)₂Lu]^2-, {[(C ₆H₁₃S)₈Pc]₂Lu}^2- and {[(C₁₂H₂₅S)₄Pc]₂Lu}^2- show broad strong signals at g = 2.0046, 2.0041 and 2.0034 with linewidths of 13.9, 16.1 and 12.9, respectively. These signals are indicative of organic free radicals where the unpaired electrons of the dianion are delocalized over two macrocycles.