Development of Organic Conductors with Self-Assembled Architectures of Biomolecules: Synthesis and Crystal Structures of Nucleobase-Functionalized Tetrathiafulvalene Derivatives

Supramolecular assemblies and charge-transfer complexes of new nucleobase-functionalized tetrathiafulvalene (TTF) derivatives were investigated. Stille-type cross-coupling reaction between tributylstannylated TTF and iodinated nucleobase derivatives yielded mono- and bisnucleobase-substituted TTF derivatives. The electrochemical measurements revealed that the uracil- and cytosine-substituted derivatives possessed strong electron-donating abilities comparable to that of pristine TTF, and the electron-deficient features of adenine and guanine caused high potential shifts of the oxidation waves. In the solution-state electronic spectra, the intramolecular charge-transfer absorption bands were observed at a low-energy region. In the crystal structures, the donor molecules constructed supramolecular polymers by the complementary hydrogen-bonds inherent in nucleobases; a one-dimensional zigzag chain in the adenine-substituted derivative and a linear chain in the bis(uracil)-substituted derivative. The tetracyanoquinodimethane complexes of uracil- and cytosine-substituted derivatives possessed a mixed valence state exhibiting high conductivities (room-temperature conductivities = 10(-2)-10(-1) S cm(-1)). In the cyananilic acid complexes, cytosine- and adenine-substituted TTF acted as electron-donors and proton-acceptors to yield simultaneous charge- and proton-transfer complexes.