Visible-Light-Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex

• Published in: Angewandte Chemie (International ed.) Vol. 54; no. 39; pp. 11457 - 11461
• Main Authors: Wezenberg, Sander J., Chen, Kuang-Yen, Feringa, Ben L.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 21.09.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: alkenes; Chemistry; Chemistry, Multidisciplinary; Contraction; Coordination; Fjords; Isomerism; Isomerization; Ligands; Light; Magnetic resonance spectroscopy; Mathematical analysis; metal-ligand interactions; Molecular motors; Motors; NMR; NMR spectroscopy; Nuclear magnetic resonance; Olefins; Photochemical; Photochemical Processes; Photochemicals; photochromism; Physical Sciences; Proton Magnetic Resonance Spectroscopy; Rotation; Ruthenium; Ruthenium compounds; Ruthenium Compounds - chemistry; Science & Technology; Spectrophotometry, Ultraviolet; Steric hindrance; Thermodynamic properties; Ultraviolet radiation; photochromism; alkenes; molecular motors; ACCELERATION; ruthenium; metal-ligand interactions; SWITCHES; UNIDIRECTIONAL ROTATION; AZOBENZENE; PHOTOCHEMISTRY; STRUCTURAL MODIFICATION; ENERGY-TRANSFER; ROTARY MOTION; FLUOROAZOBENZENES
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201505781

Toward the development of visible‐light‐driven molecular rotary motors, an overcrowded alkene‐based ligand and the corresponding ruthenium(II) complex is presented. In our design, a 4,5‐diazafluorenyl coordination motif is directly integrated into the motor function. The photochemical and thermal isomerization behavior has been studied by UV/Vis and NMR spectroscopy. Upon coordination to a RuII bipyridine complex, the photoisomerization process can be driven by visible (λmax=450 nm) instead of UV light and furthermore, a large increase of the speed of rotation is noted. DFT calculations point to a contraction of the diazafluorenyl lower half upon metal‐coordination resulting in reduced steric hindrance in the “fjord region” of the molecule. Consequently, it is shown that metal‐ligand interactions can play an important role in the adjustment of both photophysical and thermodynamic properties of molecular motors. A positive spin: A molecular motor containing a 4,5‐diazafluorenyl ligation motif can be coordinated to ruthenium(II) ions (see figure). After complexation, the photoisomerization process can be driven by visible instead of UV light. Unexpectedly, a large enhancement of the speed of rotation was observed, which can be ascribed to contraction of the diazafluorenyl unit upon metal coordination.