Synthesis, spectroscopic, electrochemical and Pb2+-binding studies of tetrathiafulvalene acetylene derivatives

A series of tetrathiafulvalene acetylene derivatives, [TTF-CC-A] [A = C6H4N(CH3)(2)-4 (1), C6H4OCH3-4 (2), C6H5 (3), C6H4F-4 (4), C6H4NO2-4 (5), C5H4N-2 (6), C5H4N-3 (7), and C5H4N-4 (8)], have been designed and synthesized to provide insight into the nature of the donor-acceptor interaction via a pi-conjugated triple bond. The X-ray crystal structure of [TTF-(CC)-C6H4OCH3-4] (2) reveals that the phenyl ring linked by acetylene is almost coplanar to the plane of TTF with a dihedral angle of 3.6 degrees. The strong intermolecular C-H center dot center dot center dot O hydrogen bonding was found to direct the molecular helical assemblies with a screw pitch of 5.148 angstrom when viewed along the a-axis. Spectroscopic and electrochemical behaviors of the tetrathiafulvalene acetylene derivatives demonstrate that the TTF unit interacts with the electron-accepting group through the triple bond, thus leading to the intramolecular charge transfer. The pyridine-substituted TTF compounds 6-8 show remarkable sensing and coordinating properties toward Pb2+. Comparison of the spectroscopic and electrochemical properties and the calculation at the B3LYP/6-31G* level available in Gaussian 03 reveals that varying the bridged unit of the TTF-pi-A system from a double bond to a triple bond leads to positive shifts for the first and second oxidation potentials of the TTF moieties, while the extent of intramolecular charge transfer interactions through the pi-conjugated triple bond is smaller than that through the double bond.