Photoinduced Modulation of Rectification and Charge Transport in Diarylethene-Viologen Molecular Junction

Abstract

Large-area molecular junctions combining photochromic and redox-active functionalities provide an attractive platform for controlling charge transport by light. In this work, we study Au/DAEVIO/Ti/Au molecular junctions incorporated with electro-grafted layers of diarylethene-viologen with thicknesses of 12-16 nm. In the initial OFF state, the junctions exhibit low current densities and strong rectification, with a rectification ratio of 300 at 1V. Temperature-dependent measurements reveal a thermally assisted contribution at higher temperatures and a much weaker temperature dependence below 160-180K, consistent with multistep charge transport through molecular and/or interfacial states rather than direct coherent tunneling across the entire molecular layer. Under continuous in situ 385 nm irradiation, the electrical response is strongly and asymmetrically modified. The current density at +1V increases by a factor of 200, while the negative-bias current is only weakly modified, reducing the rectification ratio from 300 to 2. Illumination also produces a nonzero short-circuit current density of + 0.006mA cm-2 and an open-circuit voltage of -0.45V. These results indicate that irradiation simultaneously modifies molecular charge transport and generates a measurable photoelectric response. This behavior is consistent with light-induced changes in electronic coupling associated with DAE photocyclization, combined with photoinduced charge generation and field-dependent charge separation involving the redox-active viologen units and asymmetric electrode interfaces.