New crown annelated tetrathiafulvalenes: Synthesis, electrochemistry, self-assembly of thiol derivatives, and metal cation recognition

The synthesis of new S2O4-crown annelated tetrathiafulvalene (TTF) derivati ves substituted with one terminal thiol group is described. Self-assembled monolayers (SAMs) of these compounds have been assembled on gold and platin um surfaces, the latter substrate giving improved quality films. SAMs of TT F derivative 16b are the most stable of those we have studied. Electrochemi cal data for SAMs of 5a, 5b, 8, 16a, and 16b in acetonitrile reveal two rev ersible one-electron waves, typical of the TTF system; the current increase d linearly with scan rate, indicating a surface wave response. SAMs of 8, 1 6a, and 16b exhibited an electrochemical response in aqueous electrolytes, which was observed between 50 and 100 cycles. Moreover, if the potential sc anned was limited to the first TTF oxidation, the cyclic voltammetry respon se was observed fbr at least 1000 cycles. Metal complexation by the crown i onophore of the SAMs in acetonitrile has been monitored by a positive shift in the first oxidation potential of the TTF unit (maximum DeltaE(1)(1/2) = 80 mV for Ag+). We also report the X-ray crystal;structure of TTF-crown de rivative 21 bearing two hydroxymethyl substituents, synthesized during the course of this work. The structure is characterized by infinite chains of m olecules Linked by strong intrachain hydrogen bonds between the terminal hy droxy groups.