Functionalised 1,3-dithiole derivatives exhibiting intramolecular donor-acceptor properties
A variety of functionalised 1,3-dithiole derived donor-π-acceptor systems linked by an alkenic bridge have been synthesised, the acceptor units being dicyanomethylene and cyanoimine. They exhibit intramolecular electron transfer from the electron donor moiety to the electron acceptor moiety. The presence of electron donating substituents on the 1,3-dithiole ring increases the degree of overall charge transfer; this process has been studied by UV-VIS spectroscopy and X-ray crystallography. The latter technique indicates a significant amount of intramolecular electron transfer in the ground state. A selection of functionalised donor-π-acceptor systems linked by an anthracene spacer unit have been prepared which possess greater donor-Ti-acceptor characteristics; however, the degree of electron transfer measured by X-ray crystallography of one derivative appears to be less. The 1,3-diselenole donor unit has also been utilised as an electron donor unit in donor-π-acceptor systems however, for all derivatives the diselenole unit is inferior to the 1,3- dithiole unit. The linking of a 1,3-dithiole donor unit to two acceptor units produces charge transfer bands that are red shifted compared to the parent donor-π-acceptor systems. Exchange of one acceptor unit for a donor unit leads to a similar red shift. Solution electrochemical studies, non-linear optical properties, ultra-fast spectroscopy and solvatochromic analysis have been performed on a range of systems.