SYNTHESIS AND INTRAMOLECULAR CHARGE-TRANSFER PROPERTIES OF NEW THIAFULVALENE-SIGMA-TETRACYANOANTHRAQUINODIMETHANE DIAD (TTF-SIGMA-TCNAQ) AND TRIAD (TTF-SIGMA-TCNAQ-SIGMA-TTF) MOLECULES

We report the use of functionalised electron acceptor tetracyanoanthra quinodimethane (TCNAQ) units in the synthesis of novel diad D-sigma-A compounds 6 and 7 [D = tetrathiafulvalenyl (TTF) and ferrocenyl] and t he triad TTF-sigma-TCNAQ-sigma-TTF assembly 8. Compounds 6-8 display a very weak, broad, low-energy intramolecular charge-transfer band in t he UV-VIS spectra. Nanosecond laser flash photolysis of compound 6 did not lead to any new transient absorptions in the 300-800 nm region, s uggesting that if a charge-separated species is formed upon excitation , then back electron transfer occurs very rapidly to regenerate the gr ound state. Cyclic voltammetry of compounds 6-8 shows that reversible oxidation processes occur for the TTF and ferrocene moieties, and a re versible two-electron reduction occurs for the TCNAQ moiety. Spectroel ectrochemical studies on compound 6 have enabled the redox processes t o be assigned to the sequential formation of the TTF radical cation an d dication upon oxidation, and the TCNAQ dianion upon reduction. Simul taneous electrochemistry and EPR (SEEPR) experiments provide further e vidence for intramolecular interaction between the TTF and TCNAQ moiet ies in compound 6. Quantum mechanical calculations on compound 6, perf ormed by the AM1 method, predict that in its minimum energy conformati on the TTF and TCNAQ moieties are approximately orthogonal to one anot her, with the TCNAQ unit folded into a butterfly conformation.