Unusually Large Band Gap Changes in Breathing Metal-Organic Framework Materials

Many of the potential applications for metal-organic frameworks (MOFs) focus on exploiting their porosity for molecular storage, release, and separation, where the functional behavior is controlled by a subtle balance of host-guest interactions. Typically, the host structure is relatively unperturbed by the presence of guests; however, a subset of MOFs exhibit dramatic phase-change behavior triggered by the adsorption of guests or other stimuli, for which the MIL-53 material is an archetype. In this work, we use density functional approaches to examine the electronic structure changes associated with changes of phase and density and find the associated change in band gaps can be larger than 1 eV for known MIL-53-type materials and hypothecated structures. Moreover, we show that internal pressure (via guest molecules) and external pressure can exert a major influence on the band gap size and gap states. The large response in electronic properties to breathing transitions in MOFs could be exploitable in future applications in resistive switching, phase-change memory, piezoresistor, gas-sensing and thermochromic materials.