Electrochemical molecular recognition of silver cation by electropolymerised thieno[3 ',4 ': 5,6][1,4]dithiino[2,3-b]quinoxaline: a joint experimental and theoretical study

The novel annelated monomer thieno[3',4':5,6][1,4]dithiino[2,3-b]quinoxalin e 1 has been electropolymerised on a variety of electrodes, resulting in fi lms which are electroactive in non-aqueous and aqueous solution. The polyme r films exhibit a transformation in voltammetric response corresponding to a positive shift in redox potential in the presence of silver cation, the m aximum shift being ca. 150 mV in acetonitrile and ca. 400 epsilon mV in aqu eous LiClO4 solution. Mercury dication demonstrates a similar, but smaller (ca. 130 mV) shift in aqueous solution. Theoretical calculations clearly sh ow the potential of poly(1) as a metal complexation agent. The Ag+ ion coor dinates with 1 in two ways: (i) an apical conformation involving the two di thiine sulfurs and (ii) a lateral sigma -complex with a contribution from t he quinoxaline nitrogens. The Hg2+ ion prefers to coordinate with the sulfu r atoms. The calculations performed for the trimer illustrate that the meta l ions can be coordinated simultaneously by two repeat units in the polymer chain.