Optical and electrochemical properties of soluble donor-π-donor compounds as potential molecular wires and electrochemically-triggered optical switches

With the aim of designing molecular wires operating at easily accessible potentials, a series of soluble bis-donor polyenic compounds (up to 3.2 nm long) has been prepared. Their optical and electrochemical properties have been investigated. These model compounds were shown to exhibit a reversible two-electron oxidation process at low potential (which further decreases with increasing polyenic chain length). The oxidized dicationic species combine convenient stability and solubility. Interestingly, these species also show reduced bond length alternation along the polyenic chain, consistent with a significant red-shift of their absorption band to the NIR region. Such behaviour is expected to lead to a dramatic enhancement of the third-order nonlinear optical responses of the polyenic molecules upon oxidation, opening the way to optical switches. Hence, such molecules represent promising model compounds for molecular wires but also open an innovative route towards voltage-driven optical switches.