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

• Published in: Chemistry : a European journal Vol. 26; no. 71; pp. 17027 - 17034
• Main Authors: Yang, Yingya, Brückmann, Jannik, Frey, Wolfgang, Rau, Sven, Karnahl, Michael, Tschierlei, Stefanie
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 18.12.2020; John Wiley and Sons Inc
• Subjects: Absorption; Acetonitrile; Charge transfer; Chemistry; Density functional theory; Electrochemistry; electron storage; Emission measurements; Emissions; excited state properties; extended π-systems; Ligands; NMR; Nuclear magnetic resonance; Oxygen; Ruthenium; ruthenium photosensitizers; Single crystals; Singlet oxygen; singlet oxygen evolution; Spectroscopy; Time dependence
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202001564

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 RuII 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 RuII prototype complexes. The constant evolution of phenanthroline leads to a new type of a polycyclic, fully conjugated, and rigid diimine ligand with a naphthaloylenebenzene moiety in the back. The so‐called biipo ligand enabled a RuII photosensitizer, which has an excited state lifetime of up to 24.7 μs and is active for the light‐driven singlet oxygen production.