Heterosupramolecular chemistry: An approach to modulating function in molecular devices

Linked viologen-anthraquinone molecules are attached to TiO2 nanocrystallites supported on a conducting glass substrate. The resulting assembly is incorporated as the working electrode in an electrochemical cell. Under open-circuit conditions, band-gap excitation of the semiconductor nanocrystallite results in viologen-mediated electron transfer to anthraquinone. Prior application of a negative potential step, which results in 2e(-)/2H(+) reduction of anthraquinone, permits electron transfer only to viologen. At positive applied potentials, electron transfer following band-gap excitation is largely suppressed. Some implications of these findings for modulation of Function in molecular devices are considered.