Accessing molecular memoryvia a disulfide switch

Herein we describe the results of a combined theoretical and spectroscopic investigation into the design of a simple molecular system intended to act as a memory storage bank. The main operating principle revolves around the two-electron reduction of an aryl disulfide bond. Addition of the first electron leads to elongation of the S–S bond but it breaks only if there is accompanying protonation. Adding a second electron causes S–S bond cleavage, with or without protonation. The structural changes have been assessed by way of quantum chemical calculations and molecular dynamics simulations. Electrochemical studies show that the two-electron reduced product can be re-oxidised at mildly anodic potentials and the cycle can be repeated many times. Both theory and experiment point towards pronounced potential inversion whereby the second reduction potential lies at a significantly more positive potential than that for the first step. Computer simulations of the cyclic voltammograms give rise to numerical values for the reduction potentials that are in quite good agreement with the computed values and also allow determination of the electrochemical rate constants and transfer coefficients. Accurate simulation of the experimental data can be realised only if one proton accompanies the second reduction step. The possibility to design an effective molecular-scale memory device around this system is discussed briefly.