Redox active cyclophanes and donor-acceptor systems from new TTFAQ building blocks
The saddle-shaped electron donor 9,10-his(l,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ) 49, which oxidises in a single, quasi-reversible, two-electron wave, accompanied by a dramatic conformational change, has been incorporated into donor-acceptor system 130. However, no significant charge-transfer interaction was observed. Pyrrolo-annelated TTFAQ derivatives 173 and 174 were synthesised, and donor-acceptor dyads, which showed intramolecular charge-transfer interactions, derived. TTFAQ cyclophanes 206 and 207 were synthesised in good yields, paving the way for the incorporation of more elaborate functionalities into TTFAQ cyclophanes, as exemplified by the synthesis of a TTFAQ- phenanthroline cyclophane with potential use as an electroactive sensor. A new methodology for the synthesis of TTFAQ derivatives has been developed, allowing the synthesis of cyanoethyl protected TTFAQ thiolate derivatives. These derivatives afforded several TTFAQ cyclophanes, of which the most interesting were the double-bridged cyclophanes 291 and 292. Due to the rigidity imposed by the two bridges, little conformational change is possible upon oxidation, which for the first time allowed us to study the elusive TTFAQ cation radical using cyclic voltammetry and spectroelectrochemistry, since 291 and 292 are oxidised in two, reversible, one-electron waves. The X-ray crystal structures of numerous new TTFAQ derivatives are also presented.