No evidence has been reported for acute toxicity or carcinogenicity of phthalocyanine compounds. The dye derived from cobalt phthalocyanine and an amine is Phthalogen Dye IBN. Organic pigments such as diazo or phthalocyanine compounds feature conjugated systems of double bonds. Phthalocyanine blue is a complex of copper(II) with the conjugate base of phthalocyanine, i.e. CuPc. Similarly, a gold reflective layer does not guarantee use of phthalocyanine dye. Phthalonitrile is the precursor to phthalocyanine pigments, a very common organic pigment.. Contemporaneous reviews reported that discs made of phthalocyanine resulted in "barely discernible" images. Phthalocyanine blue is one such commonly used pigment. Substituted phthalocyanine complexes often have much higher solubility. Phthalocyanine complexes are an important class of pigments. In 1907, an unidentified blue compound, now known to be phthalocyanine, was reported. The other dyes used in CD-Rs are phthalocyanine and azo. Approximately 25% of all artificial organic pigments are phthalocyanine derivatives. Phthalocyanine green is derived from phthalocyanine blue by chlorination in the presence of aluminium trichloride. Phthalocyanine is also used on some recordable DVDs.