Design, Synthesis, and Properties of Azaporphyrin Phosphorus Complexes

[Design and Synthesis of Functional π Molecules and Their Application to Near-IR Materials]

　The combination of several aromatic rings and/or heterocycles can induce novel functions. This phenomenon is observed in porphyrin derivatives, commonly found in hemoglobin, in the active sites of P-450, etc. The ability of these structures to interact strongly with visible light accounts for today's increased interest in the development of rationally designed porphyrinoid-based optical materials. In the pharmaceutical sciences, designing near-IR materials can be a challenge due to the high transparency of near-IR light in biological samples. Phthalocyanines (Pcs) are robust organic dyes that are absorbed in visible light. A theoretical investigation of molecular orbitals of Pcs has revealed that the introduction of a phosphorus(V) atom into a macrocyclic core leads to a narrower highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Following these studies, we found that certain types of Pc phosphorus(V) complexes display main absorptions beyond 1000 nm. Additionally, phosphorus(V) complexes with other azaporphyrinoids have been designed and synthesized via a relatively simple procedure. These complexes showed novel optical properties which are potentially useful in the pharmaceutical and material sciences. Furthermore, we have overcome the problem of organic radicals and antiaromatic compounds, which are generally considered to be unstable, by using a combination of serendipitous synthetic methodologies and spectroscopic techniques. These novel azaporphyrin compounds are robust and free from transition metals. They are relatively easy to synthesize and also exhibit predictable properties.