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Synthetic blue pigment from the group of phthalocyanine dyes

Copper phthalocyanine (CuPc), also called phthalocyanine blue, phthalo blue and many other names, is a bright, crystalline, synthetic blue pigment from the group of dyes based on phthalocyanines. 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.

The discovery of metal phthalocyanines can be traced to the observation of intensely colored byproducts from reactions of phthalic acid (benzene 1,2 dicarboxylic acid) or its derivatives with sources of nitrogen and metals. CuPc (copper phthalocyanine) was first prepared in 1927 by the reaction of copper(I) cyanide and o dibromobenzene, which mainly produces colorless phthalonitrile as well as an intensely blue by product. A couple of years later, workers at Scottish Dyes observed the formation of traces of phthalocyanine dyes in the synthesis of phthalimide by the reaction of phthalic anhydride and ammonia in the presence of metallic iron. In 1937, DuPont started producing copper phthalocyanine blue in the USA under the trade name Monastral Blue after it had been previously launched in Great Britain (ICI) and Germany (I. G. Farbenindustrie) in 1935. Difficulty was experienced in forming stable dispersions with the first alpha forms, especially in mixtures with rutile titanium, 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.

The substance, IUPAC name , is known by many names such 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, P. B.15.2, C. I. 74160, and British Rail Blue. Numerous other trade names and synonyms exist.

Metal phthalocyanines have long been examined as catalysts for redox reactions. Areas of interest are the oxygen reduction reaction and the sweetening of gas streams by removal of hydrogen sulfide.

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. All major artists' pigment manufacturers produce variants of copper phthalocyanine, designated color index PB15 (blue) and color indexes PG7 and PG36 (green). 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. It is present in a wide variety of products, such as color deposition hair conditioner, gel ink pens, eye patches, parfum, shampoo, skin care products, soap, sunscreen, tattoo ink, toothpaste, and even turf colorants.

CuPc has often been investigated in the context of molecular electronics. It is potentially 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 (buckminsterfullerene) 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 also been investigated as a component of organic field effect transistors. Copper Phthalocyanine (CuPc) has been suggested for data storage in quantum computing, due to the length of time its electrons can remain in superposition. CuPc can be easily processed into a thin film for use in device fabrication, which makes it an attractive qubit candidate.

Copper phthalocyanine is a complex of copper(II) 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 (< 0.1 g/100 ml at ), but soluble in concentrated sulfuric acid. The color is due to a π–π* electronic transition, with λmax ≈ 610 nm.

CuPc crystallizes in various forms (polymorphs). 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 (~3.8 Å) compared to the β phase (~4.8 Å).

The compound is non biodegradable, but not toxic to fish or plants. Oral LD50 in mammals is estimated to be greater than 5 g per kg, with no ill effects found at that level of ingestion,