Self-Assembled Monolayers of C60–Triphenylamine Dyads as Photo-Switched Interfacial Layers for Potential Application in Photovoltaic Cells

C60–Triphenylamine dyads were synthesized for incorporation as photoswitched interfacial layers in organic photovoltaic (OPV) cells. Self-assembled monolayers (SAMs) of these dyads on gold (through S–Au and C60–Au interactions) were prepared through one or two adsorption processes, and their packing densities were fully characterized. Analysis using quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS) measurements indicated that all SAMs exhibit dense coverage on the gold surfaces. Electrochemical desorption in KOH confirmed that the cis-1 dyad is anchored to the gold surface through its thiol group. Impedance measurements in the absence and presence of UV irradiation were performed to observe the photoswitched properties of these surface confined dyads. Upon UV light exposure of the SAMs, the charge-transfer resistance decreased when Fe(CN)6 3–/4– was used as the probe redox couple and increased with Ru(NH3)6 3+/2+, confirming the generation of positive charges on the surface upon UV irradiation.