Stabilizing Indigo Z‐Isomer through Intramolecular Associations of Redox‐Active Appendages

Abstract Photoswitchable small molecules, such as N,N’ ‐disubstituted indigos, have received great interest within fields such as pharmacology, energy storage, and functional materials, as they represent key building blocks for reversible and non‐invasive control of chemical processes. However, to ensure applicability of photochromic systems it is of paramount importance to manipulate the photostationary state. In this work, we achieved this by tethering two redox‐active indenofluorene‐extended tetrathiafulvalene units to an N,N’ ‐disubstituted indigo photoswitch. Upon two‐electron oxidation, we observe significantly enhanced stability of the Z ‐isomer, compared to the neutral compound, illustrated by a substantial increase in the half‐life from 0.48 seconds to 22 hours. This remarkable stabilization is ascribed to formation of strong, intramolecular π‐dimers between the oxidized subunits.