Charge Transport within Metal-Organic Frameworks: The Role of Topologically Controlled Charge Hopping Process

Metal-organic frameworks (MOFs), assembled from redox active building blocks such as metalloporphyrins, have defined these 3D crystalline porous molecular assemblies as emerging compositions for energy conversion. In this regards, it was established that MOF-modified working electrodes can provide a high surface concentration of electrocatalytic species that do not need to diffuse in/out. Electrocatalytic conversions involving multi-electron redox activation, such as porphyrinatoiron mediated CO2 reduction, require efficient charge transport process within the framework. However, the potentiometric difference between the metalloporphyrin based catalytic linkers and metal-oxo nodes enforces a hopping type charge transport processes. Analysis of the electron transfer processes within the framework of the Marcus theory suggests that besides the unique reorganization energy required in the porous composition, the initial-state/final-state electronic coupling term (i.e. the charge-transfer integral, HDA ) will play a critical role in such redox hopping process as this term exponentially dependent on the modular molecular geometry, particularly the distance (r) between the donor (D) and acceptor (A). This paper will discuss how the charge-hopping process is inherently controlled by the modular geometries defined by the underlined topological network of the MOF compositions.