Electron transfer through molecular bridges between reducible pentakis(thiophenyl)benzene subunits

"Dimers" 3, 4 and 7 which consist of two reducible pentakis(thiophenyl)benz ene subunits linked by different molecular structures, have been synthesise d as model compounds for reducible molecular-wire-type synthons to represen t differences in the electron-transfer ability as a function of the bridgin g structure. The bridging units consist of para-divinylbenzene in 3, bis-hy drazone in 4 and diacetylene in 7. Their ability to transfer electrons from one reducible subunit to the other was investigated by electrochemical and spectroelectrochemical methods and, in the case of 4 and 7 the solid-state structures support the experimental findings. The para-divinylbenzene brid ge in 3 was found to completely isolate the reducible structures (Class I s ystem). In contrast, the diacetylene bridge in 7 electronically connects th e two reducible structures (ClassIII system) and, thus, demonstrates its po tential application as a "molecular wire" The bis-hydrazone-linked compound 4 displayed only a low level of electronic connection between the subunits and was only observed in the spectroelectrochemical investigation.