Date: Tuesday, March 17, 2015
Time: 11:00 am
Speaker: Alec Talin, Sandia National Laboratories (Livermore)
Title: Achieving Emergent Properties for Electronic and Energy Conversion Device Applications
Location: 67-3111 Chemla Room
Metal-organic frameworks (MOFs) are extended, crystalline compounds consisting of metal ions interconnected by organic ligands, forming scaffolding-like structures that are sometimes referred to as “molecular tinker toys”. MOFs have attracted considerable attention for traditional applications of microporous materials, such as gas storage and separation. In many of these cases, however, the interactions between the guest molecules (CO2, H2, etc.) and the framework are weak and do not constitute a chemical bond. In my talk I will discuss a rather different concept of Guest@MOF, one in which the interaction between the framework and the guest goes beyond the relatively weak physisorption and results in a new material with unique properties stemming from the strong MOF-guest interactions. The idea of Guest@MOFs emerging as a new class of materials was stimulated by our discovery that infiltrating HKUST-1 pores with TCNQ (an insulator in its pure state) increases the electrical conductivity of the insulating MOF by over seven orders of magnitude (from <10-8 S cm-1 to ~ 0.1 S cm-1 ). This emergent property results from a donor-bridge- acceptor geometry, in which TCNQ binds to two Cu(II) dimer units within the MOF pore. I will describe the synthesis, chemical, and electrical characterization of TCNQ@ HKUST-1, as well as first-principles electronic structure calculations that indicate that conductivity occurs via a hopping mechanism facilitated by the bridging TCNQ. I will also discuss recent thermoelectric measurements which suggest that Guest@MOF materials may be useful in waste heat recovery applications.