Phthalocyanine Blue BN, also called by many names, is a bright, crystalline, synthetic blue pigment from the group of phthalocyanine dyes. Its brilliant blue is frequently used in paints and dyes. It is highly valued for its superior properties such as light fastness, tinting strength, covering power and resistance to the effects of alkalis and acids. It has the appearance of a blue powder, insoluble in most solvents including water.
History
CuPc was first prepared in 1927 by the reaction of copper cyanide and o-dibromobenzene, with the apparent intent of preparing phthalonitrile. A couple of years later, workers at Scottish obtained CuPc, FePc, and NiPc from reactions of phthalic anhydride and ammonia. Specifically at the ICI phthalimide plant, a blue contaminant was traced to a byproduct formed when the phthalimide reacted with trace amounts of iron from the metal reactor. The chemist took samples of this blue and using sulfuric acid as a solvent, managed to produce a workable pigment. These leads led to the blue pigment sold under the trade name Monastral. Industrial production commenced in 1935 at ICI, I.G. Farbenindustrie, and DuPont. Difficulty was experienced in forming stable dispersions with the first alpha forms, especially in mixtures with rutiletitanium, where the blue pigment tended to flocculate. The beta form was more stable, as was the improved stabilized alpha form. Today, there are even more isomeric forms available.
Synonyms and trade names
The substance, chemical namecopper, is also known as monastral blue, phthalo blue, helio blue, thalo blue, Winsor blue, phthalocyanine blue, C.I. Pigment Blue 15:2, copper phthalocyanine blue, copper tetrabenzoporphyrazine, Cu-phthaloblue, PB-15, PB-36, C.I. 74160, and British Rail Blue. Numerous other trade names and synonyms exist. The abbreviation "CuPc" is also used.
Due to its stability, phthalo blue is also used in inks, coatings, and many plastics. The pigment is insoluble and has no tendency to migrate in the material. It is a standard pigment used in printing ink and the packaging industry. Industrial production was of the order of 10,000 tonnes per annum in the 1980s and 1990s in Japan alone. The pigment is the highest volume pigment produced. All major artists' pigment manufacturers produce variants of copper phthalocyanine, designated and . A common component on the artist's palette, phthalo blue is a cool blue with a bias towards green. It has intense tinting strength and easily overpowers the mix when combined with other colors. It is a transparent staining color and can be applied using glazing techniques. This colour is also present in Lidl's Dentalux Total Care Plus toothpaste, listed as the final ingredient.
Research
Although never commercialized, CuPc has often been investigated in the context of molecular electronics. It is well suited for organic solar cells because of its high chemical stability and uniform growth. CuPc usually plays the role of the electron donor in donor/acceptor based solar cells. One of the most common donor/acceptor architectures is CuPc/C60 which rapidly became a model system for the study of small organic molecules. Photon to electron conversion efficiency in such system reaches approximately 5%. CuPc has been investigated as a component of organic field-effect transistors. Copper Phthalocyanine has been suggested for data storage in quantum computing, due to the length of time its electrons can remain in superposition. The compound has also been investigated in the context of quantum computing. CuPc can be easily processed into a thin film for use in device fabrication, which makes it an attractive qubit candidate.
CuPc derivatives
Approximately 25% of all artificial organic pigments are phthalocyanine derivatives. Copper phthalocyanine dyes are produced by introducing solubilizing groups, such as one or more sulfonic acid functions. These dyes find extensive use in various areas of textile dyeing, for spin dyeing and in the paper industry. Direct blue 86 is the sodium salt of CuPc-sulfonic acid, whereas direct blue 199 is the quaternary ammonium salt of the CuPc-sulfonic acid. The quaternary ammonium salts of these sulfonic acids are used as solvent dyes because of their solubility in organic solvents, such as Solvent Blue 38 and Solvent Blue 48. The dye derived from cobalt phthalocyanine and an amine is Phthalogen Dye IBN. 1,3-Diiminoisoindolene, the intermediate formed during phthalocyanine manufacture, used in combination with a copper salt affords the dye GK 161. Phthalocyanine Blue BN is also used as a source material for manufacture of Phthalocyanine Green G.
Structure, reactivity and properties
Phthalocyanine blue is a complex of copper with the conjugate base of phthalocyanine, i.e. Cu2+Pc2−. The description is analogous to that for copper porphyrins, which are also formally derived by double deprotonation of porphyrins. CuPc belongs to the D4h point group. It is paramagnetic with one unpaired electron per molecule. The substance is practically insoluble in water, but soluble in concentrated sulfuric acid. Density of the solid is ~1.6 g/cm3. The color is due to a π–π* electronic transition, with λmax ≈ 610 nm.
Crystalline phases
CuPc crystallizes in various forms. Five different polymorphs have been identified: phases α, β, η, γ and χ. The two most common structures in CuPc are the β phase and the metastable α phase. Those phases can be distinguished by the overlap of their neighboring molecules. The α phase has a larger overlap and thus, a smaller Cu-Cu spacing compared to the β phase.
Toxicity and hazards
The compound is non-biodegradeable, but not toxic to fish or plants. No specific dangers have been associated with this compound. Oral LD50 in mammals is estimated to be greater than 5 g per kg, with no ill effects found at that level of ingestion, for chronic ingestion estimated dose of low concern was 0.2 mg/kg per day in rats. No evidence indicates carcinogenic effects. Sulfonated phthalocyanine has been found to cause neuroanatomical defects in developing chicken embryos when injected directly into incubating eggs.
