Metal-promoted intermolecular electron transfer in tetrathiafulvalene-thiacalix[4]arene conjugates and tetrachlorobenzoquinone.

In this work, two series of tetrathiafulvalene (TTF) and thiacalix[4]arene (TCA) conjugates (TTF-TCA) were designed by CuAAC click reactions. The results obtained from NMR and (1)H NMR NOE indicated that their conformations of thiacalix[4]arene framework may prefer to 1,3-alternate. The cyclic voltammograms of four TTF-TCA compounds containing electroactive TTF units were provided. Meanwhile, their intermolecular electron-transfer (ET) behaviors with tetrachlorobenzoquinone (Q) mediated by different metal ions, Sc(3+), Pb(2+), Ag(+), Cd(2+), and Zn(2+), in CH3CN-CH2Cl2 (V/V = 1:1) solution were studied and analyzed via UV-vis spectroscopy. It was determined that intermolecular ET between each TTF-TCA and Q ensemble was not observed without introduction of the metal ions mentioned above. The added specified metal ions most likely induced the intermolecular ET between TTF-TCA and Q ensemble, and the effects of Sc(3+) functions were the most imperative. The intermolecular ET also proved to be reliant on the structure of TTF-TCA, where TTF-TCA 7a and 7b were more effective than TTF-TCA 6a and 6b. The difference may be credited to TTF-TCA 7a or 7b possessing two independent TTF pendants and providing a more synergic coordination among the TTF radical cation and Q radical anion with a metal ion.