A Three-Pole Supramolecular Switch

A supramolecular system that switches reversibly, via three different states, through electrochemical adjustment of the guest properties of tetrathiafulvalene (TTF) has been developed. 1 H NMR, luminescence, and absorption spectroscopies, in conjunction with LSI mass spectrometry, X-ray crystallography, and cyclic/differential pulse voltammetries, established that the π -electron-accepting (EA) tetrathiafulvalenium dication (TTF 2+ ) binds strongly within the cavity of the π -electron-donating (ED) macrocyclic polyether 1,5-dinaphtho[38]crown-10 (1/5DN38C10), generating a host−guest complex that is stabilized by, inter alia, π − π stacking interactions. Comparable techniques have also demonstrated that neutral tetrathiafulvalene (TTF(0)) acts as an ED guest when it complexes with the EA tetracationic cyclophane cyclobis(paraquat- p -phenylene) (CBPQT 4+ ). On the other hand, the tetrathiafulvalenium radical cation (TTF +• ) is not bound by either of the hosts CBPQT 4+ or 1/5DN38C10. Electrochemical experiments revealed that the three-component mixture CBPQT 4+ −1/5DN38C10−TTF behaves as a reversible three-pole supramolecular switch, since, depending on the potential range, TTF can be (1) free (in the TTF +• state), (2) included within the cavity of CBPQT 4+ (as TTF(0)), or (3) complexed with 1/5DN38C10 (in the TTF 2+ state). The system's three-pole behavior has interesting implications in relation to the design of electrochromic displays and devices capable of controlling energy- or electron-transfer processes between selected components.