Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2a and 2b, respectively), recently synthesized using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone via a vinyl bridge, are presented in detail. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV-vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in neutral and oxidized states ([2a]·+, [2b]·+, and [2b]2+) are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation between Ru centers and helicenic ligandsfacilitated by the vinyl moiety, clearly visible in the electronic structures of 2a,b, introduces new active bands in the ECD spectra that lead in consequence to a significant increase in optical rotation of Ru-vinylhelicenes compared to the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2a,b is examined in detail using ECD spectroscopy. The modifications of the ECD spectra in the UV-vis and NIR region are well reproduced and rationalized by theory.