Syntheses, properties, and photoreactions of the hybrid molecules consisting of a Co(II) mononuclear complex and porphyrins.

New hybrid molecules consisting of mononuclear Co(II) complexes and porphyrin moieties were synthesized and their new photoreactions were examined. Three porphyrins with different meso-substituents (2,6-dimethoxyphenyl, 3,5-di-tert-butylphenyl, and 2,6-difluorophenyl groups) were used to change the redox potentials of the hybrid compounds. The hybrid molecules were prepared by the stepwise condensation of amide bonds. The cyclic voltammograms of these hybrid molecules showed the redox processes of both the cobalt and porphyrin moieties. The redox potentials of the porphyrins showed a systematic change that was consistent with the electronic effects of the meso-substituents. The emission spectra only showed fluorescence of the porphyrins with slightly decreased intensities. When a solution of the hybrid molecule, durohydroquinone, and N,N-diisopropylethylamine in CHCl(3)/MeCN was irradiated with visible light (>580 nm), durohydroquinone was converted into duroquinone with the concurrent formation of the reduced product of CHCl(3). The hydroquinone was employed as an electron donor capable of reversible redox reactions, which is in contrast to conventional sacrificial reagents such as EDTA. The course of the photoreaction was followed by (1)H NMR spectroscopy and the amount of produced duroquinone was between 50-60% after 600 min. We propose that the photoreaction involves a photoinduced electron transfer from the hydroquinone to the excited porphyrin, followed by the formation of a Co(I) intermediate by charge shift, thus leading to the reaction with CHCl(3).