Light‐ and Redox‐Gated Molecular Brakes Consisting of a Pentiptycene Rotor and an Indole Pad

Abstract

AbstractTwo photochemically and electrochemically active alkenes 3Me and 3An containing pentiptycene and indole groups have been synthesized and investigated as light and/or redox‐gated molecular brakes. The pentiptycene group functions as the four‐bladed rotor, the indole group as the brake pad, and the vinylene group as the switch module. The E configuration corresponds to the brake‐off state, in which the rotation of the rotor is free with a rotation rate of 108‐109 at ambient temperature according to DFT calculations. The Z configuration corresponds to the brake‐on state, in which the rotation rate is decreased to 101‐102, depending on the N‐substituent of indole, according to line‐shape analysis of variable temperature 13C NMR spectra. The overall braking effect reaches a factor of 106‐108. While the combined photochemical E → Z and electrochemical Z → E switching has a higher capacity than the two‐way photochemical switching in the case of 3Me, the switching capacity are comparable for the two methods in 3An. The results also show that photochemical E‐Z isomerization is much more reliable than the electrochemical counterpart, as the stability of the redox intermediates plays a critical role in determining the robustness of the molecular brakes via electrochemical switching.