Metallophthalocyanines

Metallophthalocyanines are coordination compounds in which a metal atom is bound to a phthalocyanine ligand, a highly conjugated macrocycle formed by four isoindole units. In the classic species, the metal resides at the center of a square-planar M–N4 core formed by the four inner nitrogen atoms of the macrocycle. The macrocycle is highly aromatic and provides tunable electronic properties. Metallophthalocyanines are typically prepared by metallation of metal-free phthalocyanine or by direct synthesis from metal salts under high-temperature conditions; axial ligands can be bound in some cases, leading to coordinations beyond the planar M–N4 core.

Properties of metallophthalocyanines include high thermal and chemical stability and vivid colors, making them important pigments and dyes. They exhibit strong electronic absorption, with intense Q-band bands in the visible region and often substantial near-infrared absorption, depending on the central metal and substituents. The compounds are generally air-stable and display redox activity, enabling catalytic and electrochemical uses. In the solid state, molecules often stack through pi–pi interactions, influencing electronic and optical behavior.

Applications span pigments for coatings and inks, and catalysts for chemical transformations. They serve in oxidation reactions, electrocatalysis such as oxygen reduction and hydrogen evolution, and as components in chemical sensors and organic electronic devices, including solar cells and field-effect transistors. They are also investigated as photosensitizers in photodynamic therapy due to their visible-light activity and singlet oxygen generation. Common metals used include Fe, Co, Ni, Cu, Mn, and Zn, with research exploring other metals and extensive peripheral substitution to tune properties and solubility.