Electron Storage Capability and Singlet Oxygen Productivity of a Ru(II) Photosensitizer Containing a Fused Naphthaloylenebenzene Moiety at the 1,10‐Phenanthroline Ligand

As a novel rylene type dye a diimine ligand with a fully rigid and extended π‐system in its backbone was prepared by directly fusing a 1,10‐phenanthroline building block with 1,8‐naphthalimide. The corresponding heteroleptic ruthenium photosensitizer bearing one biipo and two tbbpy ligands was synthesized and extensively analyzed by a combination of NMR, single crystal X‐ray diffraction, steady‐state absorption and emission, time‐resolved spectroscopy and different electrochemical measurements supported by time‐dependent density functional theory calculations. The cyclic and differential pulse voltammograms revealed, that the naphthaloylenebenzene moiety enables an additional second reduction of the ligand. Moreover, this ligand possesses a very broad absorption in the visible region. In the Ru(II) complex this causes an overlap of ligand‐centered and metal‐to‐ligand charge transfer transitions. The emission of the complex is clearly redshifted compared to the ligand emission with very long‐lived excited states lifetimes of 1.7 and 24.7 μs in oxygen‐free acetonitrile solution. This behavior is accompanied by a surprisingly high oxygen sensitivity. Finally, this photosensitizer was successfully applied for the effective evolution of singlet oxygen challenging some of the common Ru(II) prototype complexes.