Mix and Match Tuning\nof the Conformational and Multistate\nRedox Switching Properties of an Overcrowded Alkene

Overcrowded alkenes\nhave received considerable attention\nas versatile\nstructural motifs in a range of optical switches and light-driven\nunidirectional motors. In contrast, their actuation by electrochemical\nstimuli remains underexplored, even though this alternative energy\ninput may be preferred in various applications and enables additional\ncontrol over molecular switching states and properties. While symmetric\nbistricyclic overcrowded enes (BAEs) containing two identical halves\nbased on either thioxanthene (TX) or acridine (Acr) motifs are known\nto be reversible conformational redox switches, their redox potentials\nare generally too high or low, respectively, thereby preventing wider\napplications. Herein, we demonstrate that the “mixed”\nTX-Acr switch possesses redox properties that lie between those of\nits parent symmetric analogs, enabling interconversion between three\nstable redox and conformational states at mild potentials. This includes\nthe neutral <i>anti-</i>folded, the dicationic orthogonal,\nand a unique twisted monoradical cation state, the latter of which\nis only accessible in the case of the mixed TX-Acr switch and in a\npathway-dependent manner. Consequently, with this multistate redox\nswitch, a myriad of molecular properties, including geometry, polarity,\nabsorbance, and fluorescence, can be modulated with high fidelity\nand reversibility between three distinct stable states. More generally,\nthis study highlights the versatility of the “mix and match”\napproach in rationally designing redox switches with specific (redox)\nproperties, which in turn is expected to enable a myriad of applications\nranging from molecular logic and memory to actuators and energy storage\nsystems.