Synthesis, Structures, Electrochemical and Optical Properties of Vinyl-Extended Tetrathiafulvalene Derivatives Functionalized with Two 2,6-Dicyano-⁵-Phosphinine Units

Derivatives of vinyl-extended tetrathiafulvalene (TTF) functionalized with two 2,6-dicyano-lambda(5)-phosphinine units (3 a-c) have been successfully synthesized. Cyclic voltammograms of all the derivatives are composed of three pairs of redox waves. The first and second redox waves correspond to one-electron transfer processes, in which the extended TTF moiety participated predominantly. The third redox wave corresponded to a two-electron transfer process, in which the two 2,6-dicyano-lambda(5)-phosphinine units were involved. The redox potentials at which the tetracations of 3 a-c were generated were considerably more negative than expected, probably due to the formation of stable closed-shell structures by conjugation between 2,6-dicyano-lambda(5)-phosphinine units. X-ray structural analyses of 3 b, 3 c, and (3b(2+))(Sb2Cl82-)(C6H5OCH3) revealed that the vinyl-extended TTF moiety in all the compounds adopts an almost planar structure, while the phosphinine units are significantly rotated relative to the extended TTF plane. The fluorescence spectroscopy revealed that the emission intensity of 3 b was very small in both the neutral and oxidized states.