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+) reversible arrow [P-1](center dot) reversible arrow [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 Delta epsilon = +35 M-1 cm(-1) for [P-1](2+) and Delta epsilon = -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.