Syntheses, Unique Strained Molecular Structures, and Unusual Transannular Electronic Interactions of a Series of Crisscross-Overlapped Tetrathiafulvalenophanes

A series of novel tetrathiafulvalenophanes has been synthesized, in which two tetrathiafulvalenes (TTF) are linked in a crisscross-overlapped arrangement by four alkylenedithio bridges. Their molecular structures were elucidated by X-ray crystal analyses, being characterized by the bent TTF skeletons as well as the unique stacking mode. The degree of the bend largely depends on both the length and conformational rigidity of the alkylenedithio chains. The short and rigid chains induce severe bending, which brings about a hypsochromical effect in the electronic absorption spectra. On the other hand, the long and flexible chains reduce the strain and make an inside cavity large enough to include a guest molecule. In addition, the less strained compounds can effect an intramolecular transannular Coulombic interaction between their two TTF units in solution, as demonstrated by multistage redox waves in the cyclic voltammograms. All the radical cation salts formed from these tetrathiafulvalenophanes have conductivities of the same order of 10^-6-10^-7 S cm^-1, which are apparently independent of the donor and the counterion species.