Synthesis, optical, and conductive properties of long oligothiophenes and their utilization as molecular wires

This account reviews the current development of extraordinarily long oligot hiophenes involving the 48-mer and 72-mer, which correspond to mono-dispers e polymers. The systematic studies of the homologous series have provided v aluable information on the optical and conductive properties of alpha -conj ugated thiophene systems: an effective conjugation length extends to around 20 thiophene units in the neutral state and around 30 thiophene units in t he oxidation state; this length plays a critical role in determining the el ectronic structures and conductivities. In addition, the active charge carr ier species are both pi -dimers and chain dimers, and charge transport occu rs through the transfiguration of both species. This account also describes how useful oligothiophenes are as molecular wires allowing photoinduced el ectron- and/or energy-transfer. The molecular-wire behaviors of sophisticat ed oligothiophenes that are functionalized with a donor unit and an accepto r unit at the terminal alpha -positions are demonstrated.