Synthesis and properties of a highly soluble dihydoxo(tetra-tert-butylphthalocyaninato)antimony(V) complex as a precursor toward water-soluble phthalocyanines

The title complex cation, [Sb(tbpc)(OH)2]+ (where tbpc denotes tetra(tert  -butyl)phthalocyaninate, C48H48N82-), has been prepared by oxidizing [Sb(tbpc)]I3 with tert-butyl perbenzoate in CH2Cl2, CHCl3, o-dichlorobenzene and also without solvent in the range of 20–80 °C. This species has been isolated as I3- salt and characterized by elemental analysis, ESI-MS, FT-IR, optical absorption and emission, and magnetic circular dichroism spectroscopy. This compound is quite well soluble in common polar organic solvents (e.g., CH2Cl2, acetonitrile, acetone) without detectable aggregation at least up to ca. 10−4 M while much less soluble (e.g., benzene, chloronaphthalene) or insoluble (hexane) in non-polar solvents. Although this compound is insoluble in water, it makes hydrophilic colloids in acetone–water mixtures. The most intense absorption band (Q-band) in a specific solvent red-shifts with an increase in the refractive index of the solvent. However, considerable deviation of the Q-band positions in donor-solvents from linear correlation between the positions and Onsager’s solvent polarity function suggests that there are significant specific chemical interactions between the axial hydroxyl groups and the surrounding donor molecules. The low fluorescence quantum yield (ca. 0.01) for [Sb(tbpc)(OH)2]+ suggests that the singlet excited state of this species is considerably quenched by the presence of antimony ion in the chromophore.