Molecular junctions consisting of a monolayer of fluorene and 10 nm of TiO2 between conducting contacts exhibit a memory effect upon positive polarization of the of the TiO2 for a few milliseconds. The junction conductance increases for a period of several minutes, but can be “erased” by a millisecond negative bias pulse. This “memory” effect is attributed to a redox process in the TiO2 which generates TiIII and/or TiII, which have much higher conductance than TiO2 due to the presence of conduction band electrons. The redox process amounts to “dynamic doping” of the TiO2 layer by imposed electric field. The memory effect arises from a combination of the properties of the molecular and oxide layers, and is a special property of the molecular heterojunction configuration.