Electric field effects on a single carotene molecule

The behavior of two isomers (cis/trans) of carotene subject to the effects of an electric field has been theoretically investigated by means of quantum chemical calculations. The calculations indicate that the trans isomer is stabilized at positive biases and destabilized at negative biases, whereas the cis isomer is destabilized at either bias. This result has been interpreted by considering the different molecular symmetries of the isomers under study. Furthermore, an n-alkanedithiol molecule of comparable length is slightly stabilized at either bias. This difference in response, with respect to carotenes, is attributed to the lack of π-electrons in n-alkanedithiols. The present study is expected to shed some light on the discrepancies observed in recent electron transport experiments performed on metal–carotene–metal junctions.