Phthalocyanine and Related Analogues

Phthalocyanine (Pc) has been one of the most important industrial dyes exhibiting lasting blue or green color and used in various research fields including not only organic electronics but also biomedical field. The aim of this chapter is to overview the chemistry of Pc and its ring contracted analogue, subphthalocyanine (SubPc), with an emphasis on their syntheses and optical properties from a viewpoint of molecular symmetry–property relationships. A basic theoretical description of the absorption properties of Pc and SubPc, which is referred to as Gouterman's four orbital theory, is introduced. In addition, magnetic circular dichroism (MCD) spectroscopy, a powerful spectroscopic tool to analyze the absorption spectra of Pc, SubPc, and related analogues, is briefly described. Finally, recent advances in the synthesis of new Pc-based NIR chromophores will also be covered.