Intense chiroptical switching in a dicationic helicene-like derivative: exploration of a viologen-type redox manifold of a non-racemic helquat.

Two-step redox switching in enantiopure helquat system [P-1](2+) ⇌ [P-1](•+) ⇌ [P-1](0) is demonstrated. The viologen-type electroactive unit embedded directly in the helical scaffold of 1 is responsible for the prominent chiroptical switching at 264 nm. This process is associated with a marked sign-reversal of Cotton effect ramping between Δε = +35 M(-1) cm(-1) for [P-1](2+) and Δε = -100 M(-1) cm(-1) for [P-1](0). This helically chiral system features the most intense chiroptical switch response documented in the field of helicenoids.