Porphyrin is a general term for homologues and derivatives formed by substitution of different substituents at positions where the outer ring of the porphin can be substituted. A porphyrin ligand refers to a ligand containing a porphyrin ring in a molecular structure. Phthalocyanine is a generic term for homologues and derivatives formed by replacing four median carbon atoms of a porphin ring with a nitrogen atom and then replacing it with four different benzene rings on the outer side of the four pyrrole rings. A phthalocyanine ligand refers to a ligand containing a phthalocyanine ring in a molecular structure. Both the porphyrin ligand and the phthalocyanine ligand belong to the large π conjugated system composed of 18 electrons, and thus have similarities in physicochemical properties. In general, porphyrin ligands and phthalocyanine ligands are solids with higher melting points and darker colors, and are relatively stable to light, heat, and strong acids and bases. Their most prominent chemical properties are the ability to react with metal ions to form complexes. The properties of the complexes formed are also varied depending on the metal ion radius, valence, and coordination number.
Figure 1. Porphyrin ligand
Figure 2. Phthalocyanine ligand
Due to its unique structure, porphyrin ligands and phthalocyanine ligands have superior physicochemical and optical characteristics, making porphyrin ligands and phthalocyanine ligands widely used in materials science, organic synthesis and biomedicine.
- Material chemistry: The metal complexes formed by porphyrin ligands and metals are widely used in material chemistry. In the case of organic solar cells, the porphyrin metal complex acts as a photosensitizer to increase the photoelectric conversion. Porphyrin metal complexes can also be prepared to require special molecular materials that are commonly used for energy conversion, optical communication, and data storage. In addition, porphyrin ligands have important applications in liquid crystal materials, organic electroluminescence and photoconductive materials. Like porphyrin ligands, phthalocyanine ligands are also very powerful in materials chemistry. The phthalocyanine ligand has liquid crystal properties, exhibits anisotropic conductivity and light conductivity, and thus can be used for preparing a liquid crystal display material. The phthalocyanine ring is a highly conjugated large π system with excellent chemical stability and excellent photoconductivity, making it a non-linear optical material with excellent performance. The introduction of different rare earth metal ions into the phthalocyanine macrocyclic ligand can produce an organic ferromagnetic substance, which can be used to prepare molecular magnets. Many phthalocyanine ligands have electrochromic properties, especially the sandwich-type rare earth metal phthalocyanine, which can be used as a gas sensor or detector. In addition, phthalocyanine ligands play an important role in sensitive devices, solar cell materials, and electrophotographic materials in chemical sensors.
- Organic Synthesis: Metalloporphyrin complexes not only have extremely high surface area and porosity, but also are easy to regulate the framework structure, can mimic the biological tissue model of proteins such as peroxidase and cytochrome P450, and are a kind of homogeneous catalyst and bionics. Metalloporphyrin complexes are capable of catalyzing many reactions such as oxidation reactions, substitution reactions, coupling reactions, cycloaddition reactions, and polymerization reactions.
- Biology and medicine: Metal complexes in which porphyrin ligands can form with certain metal ions are active substances widely present in the biological world, such as chlorophyll and heme, which are typical representatives. Chlorophyll and heme are used as metal complexes of porphyrin ligands with magnesium and iron to promote plant photosynthesis and hemoglobin synthesis, respectively. In addition, since porphyrin ligands and metal complexes have good affinity for many cancer cells, they can be selectively retained in tumor cells after being introduced into tumor cells. Tumor cells can be well detected and killed using their special photon absorption and emission properties. Metal complexes of phthalocyanine ligands with metals such as zinc and aluminum can be used as drugs for tumor photodynamic therapy.
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