A three-pole supramolecular switch

Abstract

A supramolecular system that switches reversibly, via three different states, through electrochemical adjustment of the guest properties of tetrathiafulvalene (TTF) has been developed. 1H 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 (TTF2+) 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 cyelophane cyclobis(paraquat-p-phenylene) (CBPQT4+). On the other hand, the tetrathiafulvalenium radical cation (TTF+-) is not bound by either of the hosts CBPQT4+ or 1/5DN38C10. Electrochemical experiments revealed that the three-component mixture CBPQT4+-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 CBPQT4+ (as TTF(0)), or (3) complexed with 1/5DN38C10 (in the TTF2+ 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.