Besides light emitting diodes, photovoltaic devices, and field effect transistors, recently, conjugated organic materials displaying memory effects have received considerable attention.
Memory effects can be driven by several physical phenomena. Here, we refer to organic based devices in which the memory effect is induced by an electrical stimulus. In these devices, two stable conducting states (hereafter labeled OFF and ON states) exist at the same applied voltage, and one can switch from one state to the other by applying a suitable voltage. Once the device is in the ON state, for instance, it retains its high conductivity until a specific action (reset) is taken by a reverse voltage that erases the ON state and returns the device in its OFF state. In some cases there is strong evidence that the mechanism is intrinsic, driven by the nature of the organic material. In some cases, it has been explained in terms of structural rearrangements (conformational changes), or electronic changes induced by redox reactions, or both. One such example is Rose Bengale (RB). Among molecular systems, diphenyl bithiophene (DPBT) derivatives have been shown to display electrical bistability. The simplest organic molecule displaying electrical memory behavior is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).
Among the processes governing the electrical (or resistive) memory function in molecular materials, we consider the efficiency of carrier injection into the organic material at the electrode/organic interface and the charge transport within the organic semiconductor as factors limiting the current.
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2) S. Di Motta, E. Di Donato, F. Negri, G. Orlandi, D. Fazzi, C. Castiglioni, “Resistive molecular memories: influence of molecular parameters on the electrical bistability”, J. Am. Chem. Soc., 131, (2009), 6591-6598.
3) D. Fazzi, C. Castiglioni, F. Negri, “Resistive Memories Based on Rose Bengal and Related Xanthene Derivatives: Insights from Modeling Charge Transport Properties”, Phys. Chem. Chem. Phys., 12, (2010), 1600-1609.
