1st reduction 2nd reduction The cyclic voltammetry for L 1 in solution follows diffusion control. For solid-state 1 and 2 a different response might be anticipated. If the MOF were to interact strongly with the electrode surface, for example through chemical modification then the current would be proportional to scan rate and DE (= Ep a -Ep c ) = 0 V and a pseudo capacitive response would be observed. This is not observed for the experiments with 1 or 2. Plots of Ip c or Ip a versus the square root of scan rate and DE > 0 V might indicate that the electrochemical response has a diffusive component (Fig. ). However, unlike standard diffusion dependent solution phase behaviour, the behaviour observed for the MOFs, a 'diffusion-like' response, may result from either exchange-like electron hopping, as observed in high porosity MOFs featuring large apertures, or counter-ion motion. By comparison with the response for the Fc + /Fc couple, in solution, under these conditions, we note that DE (= Ep a -Ep c ) for the MOFs is larger, and increases with increasing scan rate suggesting that the couples all have a component of kinetic control (Fig. ). It is likely that the electrochemical response results from electron transfers between PDIs located close to the surface, in close proximity to the electrode. The current response to reduction and re-oxidation appears to correlate with the square root of scan rate and this may result from slow electron hopping between PDIs separated by insulating 'metal' layers; although the slow diffusion of electrolyte through the pores of the MOFs, as a result of ionic interactions, blocked pores or extended pathways, may also contribute to this response. Figure shows the initial profile and the final profile of the voltammograms demonstrating a change between the initial and final experiments. We assign this difference to the material not being stabilised on the substrate at the onset of the experiment but stability is achieved after a few cycles to produce the familiar profile of PDI-based redox processes (Fig. ).