Helical bis-Ruthenium Complex as Chiroptical Redox Switch

https://cesnet.zoom.us/j/98850077354

In this lecture, the synthesis of new aza[n]helicenes containing 4 – 7 aromatic benzene units will be described in detail together with their photophysical and chiroptical properties. The new compounds were prepared by a modified Mallory reaction using aromatic imines as precursors. The new, helical 2,2′-bipyridine ligands formed were coordinated to Ru(bipy)₂²⁺ units to form the [RuL (bipy)₂]²⁺ or [Ru₂L′(bipy)₄]⁴⁺ complexes where L and L ′ stands for new aza[n]helicenes. Coordination to Ru(bipy)₂²⁺ unit also resulted in the formation of diastereomerically and enantiomerically pure forms of complexes, which were studied from the topological and stereochemical point of view by X-ray crystallography. It is noteworthy that coordinating the helicene ligand to Ru²⁺allows for the formation of other helical structures at the helicene periphery containing the coordinated metal in its scaffold. These molecular fragments were entitled ruthena-helicenes. Subsequently, photophysical, chiroptical, and redox properties of these complexes were investigated. The finding that in the bis-ruthenium complex there is a significant change in the absorption of circularly polarized light between its oxidized and reduced form of Ru^3+/Ru²⁺ belonged among the most interesting results of this work. The largest change was observed at a wavelength of 290 nm when even the change in the sign takes place. The process is fully reversible as confirmed over 10 cycles without reducing the intensity of the response. Thus, the bis-ruthenium diaza[7]helicene complex exhibits a chiroptical Ru³⁺/Ru²⁺ redox-triggered switching activity.