Synthesis and the electrochemical and fluorescence properties of new cyclophane-derivatized oligothiophenes

Several new oligothiophenes blocked by cyclophane end groups with 2, 3, 4 or 6 thiophene rings in the chain have been prepared and studied by electrochemistry and by UV-visible and fluorescence spectroscopy. Both radical cations and dications are stable, even for the bithiophene compound; besides the stabilization induced by the blocking of the reactive alpha positions, this strongly suggests electronic connection between the cyclophanes and the oligothiophene chains, especially for the shorter compounds. All the molecules are strongly fluorescent with increasing quantum yields up to 4 thiophene rings. The assumption of a conjugation between the cyclophane end groups and the oligothiophene main chain is also supported by the UV-visible and fluorescence results, since the spectroscopic data correlate well with (n+2)(-1) instead of n(-1), with n representing the number of thiophene rings in the oligomer.