Synthesis and structure of molecules containing linked donor and acceptor units, new tellurium-TTF derivatives and their charge transfer complexes

Our efforts in designing, synthesizing and characterizing organic conducting materials have been focused primarily on the preparation and structure determination of D-A-D (D = donor, A = acceptor) and A-D-A molecular units in which donors and acceptors are chemically attached via bridging atoms or groups. The strategy that motivates the synthetic work is aimed at gaining control over the architectural features of the solid state structures of the materials, since gaining control over the three-dimensional structure is a vital pre-condition for achieving electrical conductivity in organic materials. Construction of such molecular units predetermines the D-A molar ratio as well as the maximum degree of charge transfer. Moreover, we have already shown that this molecular motif has a high propensity to crystallize in the desired crystallographic arrangement, characterized by segregated stacks of both donors and/or acceptor, with significant overlap between adjacent units in the stack. Following this approach we have synthesized two types of molecules; one contains two donors attached to one acceptor via -CH₂- or S atom bridges, and in the other, two acceptors are linked to one donor via methylene bridges. In addition, the importance of introducing heavy atoms in charge-transfer complexes has long been recognized. Consequently, extensive work has been carried out on the synthesis of various TTF derivatives, in which Se and Te atoms replace sulfur or hydrogen atoms in TTF. Recently, we have synthesized new compounds in which two TTF molecules are linked via tellurium atoms, TTF-Te-TTF and TTF-Te-Te-TTF, and prepared their complexes with TCNQ. They all exhibit conductivity at r.t.