Metal-ion-promoted intermolecular electron transfer between anthraquinone-based tetrathiafulvalene derivative and p-chloranil

Based on copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, a novel anthraquinone-based tetrathiafulvalene (4) was synthesized through the reaction of the terminal alkyne compound (1), 1,8-dispropargyloxyanthraquinone and the terminal azide compound (3), 2-(2-azidoethylthio)-3,6,7-tris(methylthio)tetrathia-fulvalene in 52% yield. The compound 4 was characterized by 1H NMR, FT-IR, 13C NMR, MS and elemental analysis. The cyclic voltammogram of 4 shows as expected quasi-reversible redox behavior for anthraquinone and reversible redox for tetrathiafulvalene units. The fluorescence experiments have shown that compound 3 has a good selectivity with Al3+ and the complexation of 4 with Al3+ in a 1:1 complex mode gives an enhanced fluorescence change at 558 nm. In CHCl3–CH3CN (v:v = 1:1) solvent, the binding constant for the complex 4 and Al3+ is 3400 dm3 mol−1 at room temperature. Compound 4 may be used as a new fluorescent sensor for Al3+ ion. Meanwhile, the UV–vis spectra experiments show that many metal ions cannot oxidize the TTF units of 3 excluding Cu2+ and Hg2+ ions. Interestingly, the intermolecular electron transfer between 4 and p-chloranil (Q) did not apparently occur, however, the only two Al3+ and Pb2+ among tested metal ions may trigger the intermolecular electron transfer between 4 and Q, which may be ascribed to the synergic coordination of the radical anion of Q, nitrogen atoms of triazole and oxygen atoms of anthraquinone units in 4 with Al3+ or Pb2+ ions, whereas, the effects of Al3+ ion are obviously larger than that of Pb2+ ion.