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Mysterious blue chemicals: Why are blue phthalocyanine compounds so special?
Phthalocyanine (Pc) is a large aromatic cyclic organic compound with a molecular structure of (C8H4N2)4H2, and is therefore highly valued in the fields of chemical dyes and optoelectronics. This compound is composed of four isoindole units connected by a nitrogen atom ring. Due to their extensive π-electron delocalization, phthalocyanines exhibit many useful properties and thus have great potential for applications in dyes and pigments. Phthalocyanine compounds derived from metal complexes are widely used in catalysis, solar cells and photodynamic therapy. Undoubtedly, these blue compounds have aroused the interest of scientists. How many unknown stories are hidden behind them?
Characteristics of Phthalocyanine
Phthalocyanine and its derived metal complexes (MPc) are usually aggregated and therefore have low solubility in common solvents. In the process of analyzing its characteristics, the researchers found that:
"At 40°C, benzene can dissolve less than 1 mg of H2Pc or CuPc."
On the contrary, the solubility of H2Pc and CuPc in sulfuric acid is significantly improved, which is due to the protonation of nitrogen atoms, which makes the connection of the pyrrole ring in their structure more stable. Most unsubstituted phthalocyanines have very high thermal stability and will not melt, but can sublime. Among them, CuPc can sublime above 500°C in an inert gas environment. Substituted phthalocyanine complexes tend to possess higher solubility, although their thermal stability is reduced.
Historical context
The history of phthalocyanine compounds dates back to 1907, when a blue compound was first reported. It was not until 1927 that Swiss researchers accidentally discovered copper phthalocyanine in the process of converting o-dibromobenzene to benzyl cyanide. Cyanine and its derivatives. They appreciated the stability of these compounds but did not explore it in depth. It was not until 1934 that Sir Patrick Linstead first characterized the chemical and structural properties of iron phthalocyanine. The discovery of these compounds and their potential applications have triggered a large number of subsequent studies.
Synthesis method
Phthalocyanine is usually synthesized through the cyclotetramerization reaction of different phthalic acid derivatives, including benzyl cyanide, diaminoisoindole, phthalic anhydride and phthalic amide. Alternatively, H2Pc can be generated by heating phthalic anhydride and urea. In 1985, the global production of various types of phthalocyanine was about 57,000 tons, indicating the considerable demand. Since metal phthalocyanines (MPcs) are more attractive for research, their synthesis is usually carried out in an environment containing metal salts.
Application Scope
Initially, the use of phthalocyanine was limited to dyes and pigments. With the deepening of research, the application scope of H2Pc and MPc has expanded to photovoltaics, photodynamic therapy, nanoparticle construction and catalysts. The electrochemical properties of MPcs make them efficient electron donors and acceptors, enabling the development of MPc-based organic solar cells with power conversion efficiencies at or below 5%. In addition, MPc has also been used for the oxidation catalysis of methane, phenol, alcohol, polysaccharide and olefin, and can even catalyze the formation of C-C bonds and various reduction reactions.
"Some metal phthalocyanines have been developed as photosensitizers for non-invasive cancer treatment."
Related compounds
The structure of phthalocyanine is closely related to other tetrapyrrolic macrocyclic compounds such as porphyrins and porphyrinoxines, which are characterized by four pyrrole-like subunits connected to form a 16-membered inner ring composed of alternating carbon and nitrogen. . In addition, larger analogs such as naphthalocyanines also exist. The pyrrole-like ring in phthalocyanine compounds is very similar to isoindole, and both porphyrin and phthalocyanine are planar tetradentate dianionic ligands that interact with metals through four inward-projecting nitrogen centers.
Soluble Phthalocyanine
Although the research value of soluble phthalocyanine is basic but its practical application is limited, researchers still develop soluble phthalocyanine by adding long alkyl chains to improve its solubility in organic solvents, or by introducing ionic or hydrophilic groups to impart water solubility. In addition, solubility can also be achieved through axial coordination, and optimization studies in this regard, such as the axial ligand functionalization of silicon phthalocyanine, have been widely explored.Toxicity and Hazards
Currently, there is no evidence that phthalocyanine compounds have acute toxicity or carcinogenicity. Their LD50 value (for rats, oral) is 10 g/kg, showing relative safety.
With the deepening of understanding of phthalocyanine compounds, the application of its various derivatives in different fields has received increasing attention. What unexpected discoveries and applications do you think these mysterious blue chemicals will have in the future?
