Phthalocyanine building block is a building block that uses phthalocyanine as a raw material to achieve specific functions. Phthalocyanine is a type of macrocyclic conjugated compound with a planar structure of 18 π electrons. Its structure is similar to that of porphyrin found in nature. Phthalocyanine has a darker color, a higher melting point, and strong stability to light and heat. Because there are sixteen positions on the benzene ring around the phthalocyanine, substitution reactions occur, and there are many types of groups that can participate in the substitution to form a variety of substituted phthalocyanines. In addition, phthalocyanine easily reacts with metal ions. Due to the difference in metal valence, radius and coordination number, the formed metal compounds are various.
Figure 1. Phthalocyanine molecule
Phthalocyanine itself has excellent thermal stability and chemical stability, and has strong absorption in infrared and near infrared. At the same time, due to its diverse stereo configuration and self-assembly characteristics, phthalocyanine compounds were carried out functional design, so that it has more properties. Therefore, phthalocyanine compounds show good application performance in the fields of organic catalysis, nonlinear optics, sensors and photodynamic therapy (PDT).
- Organic catalysis: Metal phthalocyanine complex (M-Pc) has the advantages of low cost, easy availability, good thermal stability and good chemical stability, and is often used as an important catalyst for organic reactions. At present, metal phthalocyanine compounds are mainly used to catalyze oxidation reactions. For example, Cu-Pc and Co-Pc catalyze the oxidation of phenols, and Fe-Pc catalyzes the oxidation-aromatization reaction of unsaturated ketones and hydrazine hydrate. In addition, metal phthalocyanine compounds are also used in other types of catalytic reactions. For example, Cu-Pc catalyzes the cyclopropanation of olefins, and Fe-Pc and Mg-Pc catalyze the cycloaddition of CO2 and cyclopropane.
- Material: The unique hollow structure of carbon nanotubes makes it have high elasticity and better shaping, so it can be used as the skeleton structure of composite materials. The adsorption of phthalocyanine molecules on the surface of carbon nanotubes by physical and chemical reactions can improve the performance of carbon nanotubes and play a greater application value in the field of materials. The composite formed by the combination of metal phthalocyanine and carbon nanotubes has very wide applications in photovoltaic materials, chemical sensors, and dielectric materials.
Figure 2. Carbon nanotubes modified by phthalocyanine
- Other fields: In addition to the above application fields, phthalocyanine building blocks also play a huge application value in many other fields. For example, photodynamic therapy is a new method for treating tumors. The key to this therapy is photosensitizers. Because there are many similarities between the structure and performance of phthalocyanine and porphyrin, people have studied the application of phthalocyanine compounds in the medical field. The Zn2+ and Al3+ compounds of sulfophthalocyanine entered the clinical trial stage as photosensitizers. In addition, in the field of dyes, copper phthalocyanine pigments are widely used for the coloration of inks, coatings, and leather because of their excellent chemical stability, bright color, strong tinting strength, and low production cost.
Figure 3. Phthalocyanine dye
Phthalocyanine does not exist in nature, but is prepared by artificial synthesis. Currently, there are three main methods for preparing phthalocyanine.
- Phthalonitrile route: So far, the most commonly used method for preparing phthalocyanine in the laboratory is to use the phthalonitrile method. This preparation method has the advantages of high yield, relatively mild reaction process and easy purification. The specific operation process of this method is to heat the substituted phthalonitrile derivative in a high-boiling solvent (such as n-pentanol, quinoline, etc.) containing a catalyst to form phthalocyanine by cyclization.
- Phthalic anhydride-urea route: Currently, the main method used in the industry to prepare phthalocyanine is the phthalic anhydride-urea method. This method contains two types, namely the solid phase method and the liquid phase method. The liquid phase method uses ammonium molybdate as a catalyst, adding metal salts, urea and phthalic anhydride to the trichlorobenzene solvent to prepare phthalocyanine. The solid phase method is to heat all the reaction raw materials to a molten state to react, thereby preparing the desired phthalocyanine.
- 1,3-Diiminoisoindoline route: This method is to mix 1,3-diiminoisoindoline with N, N-dimethylethanolamine and other substances that can provide hydrogen, and then heat to a certain temperature to prepare phthalocyanine.
- Guo Y S. (2009), "Comparative study on carbon cathodes with and without cobalt phthalocyanine in Li /(SOCl2+BrCl) cells." J Power Sources 194(1), 508-514.
- SAKA E T，C. (2017). "New Co(Ⅱ) and Cu(Ⅱ) Phthalocyanine Catalysts Reinforced by Long Alkyl Chains for the Degradation of Organic Pollutants." Catalysis Letters 147(6),1471-1477.
- Wang B. (2012), "Lead phthalocyanine modified carbon nanotubes with enhanced NH3 sensing performance." Sensors and Actuators B:Chemical 171 /172, 398-404.