Trialkyltetrathiafulvalene-sigma-tetracyanoanthraquinodimethane (R3TTF-sigma-TCNAQ) diads: Synthesis, intramolecular charge-transfer properties, and X-ray crystal structure

We report the use of the electron-donating 4,5-dipentyl-4'-methyl-TTF (TTF = tetrathiafulvalene) moiety in combination with the electron acceptor 11,1 1,12,12-tetracyanoanthraquinodimethane (TCNAQ) unit in the novel D-sigma -A diad molecules 11, 17, and 18. These compounds display a weak, broad, low- energy intramolecular charge-transfer (ICT) band in the W-vis spectra (lamb da (max) 430-450 nm). Cyclic voltammetric studies show two reversible one-e lectron oxidation processes for the R3TTF moiety, and a reversible two-elec tron reduction process for the TCNAQ moiety. The electron affinity of TCNAQ is significantly enhanced by the electron-withdrawing sulfonamide and sulf onic ester groups (compounds 17 and 18, respectively). Simultaneous electro chemistry and EPR (SEEPR) experiments show no significant intramolecular in teraction between the R3TTF and TCNAQ moieties in compounds 11 and 18. X-ra y crystallographic data are presented for 5, 11, and 20. The structure of 5 reveals hydrogen-bonded dimers. In molecule 11 the bond lengths and confor mations of both donor and acceptor moieties are typical for neutral species . Compound 20 is an unusual calcium complex of TCNAQ derivative obtained by dicyanomethylation of anthraquinone-2-carboxylic acid.