The synthesis and spectral properties of amber phthalocyanines

Novel antimony(V)-phthalocyanine complexes, [Sb(tObpc)(OH) ₂]⁺, [Sb(tppc)(OH)₂]⁺, and [Sb(tppc)Cl₂]⁺ (where tObpc and tppc denote tetra(n-butoxy)phthalocyaninate, C₄₈H₄₈N₈O ₄^2-, and tetrakis(2′,6′-dimethylphenoxy) phthalocyaninate, C₆₄H₄₈N₈O₄ ^2-, respectively) were synthesized by oxidizing the corresponding antimony(III) derivatives either with tert-butyl perbenzoate or sulfuryl chloride. The compounds are dissimilar to conventional phthalocyanines in that they are of amber color in solution. Optical properties were studied by absorption and magnetic circular dichroism spectroscopy. The amber color was attributed to a combination of an intense absorption band (Q-band; log(ε/M^-1 cm^-1) = ca. 5) at ∼735-760 nm, which was red-shifted by ∼1000-1200 cm^-1 compared to conventional phthalocyanines and a less intense (log(ε) = ca. 4) but broad band at ∼400-500 nm, which is not observed for conventional phthalocyanines. The additional band at ∼400-500 nm was considered to be a red-shifted Soret band.