A Red-Light-Driven CO-Releasing Complex: Photoreactivities and Excited-State Dynamics of Highly Distorted Tricarbonyl Rhenium Phthalocyanines.

A complex comprising one [Re(CO) 3 ] + unit and a phthalocyanine (Pc) ligand (Re 1 Pc) is shown to function as a photo-induced CO-releasing molecule (photoCORM) in the presence of O 2 and a coordinative solvent under irradiation with red light, which can deeply penetrate living tissues. Transient absorption spectroscopic measurements indicate very short excited-state lifetimes and ultrafast intersystem crossing for Re 1 Pc and Re 2 Pc, which contains two [Re(CO) 3 ] + units. The excited-state properties are ascribed to efficient spin-orbit coupling and large Franck-Condon factors originating from the complexes' distorted structures, that is, unsymmetric coordination of [Re(CO) 3 ] + unit(s), one of which was confirmed by single-crystal X-ray analysis of a symmetrically substituted Pc with two [Re(CO) 3 ] + units. Re 1 Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.