Upcoming Seminar- Randy larsen

Date Published: 
Wednesday, January 23, 2013

Department of Chemistry, University of South Florida

“LIGHTING-UP METAL ORGANIC FRAMEWORKS: PHOTOCATALYTIC GUEST ENCAPSULATION IN METAL ORGANIC FRAMEWORKS”

Metal organic frameworks (MOFs) have emerged as an important class of porous materials noted for extremely high surface areas, functionalizable building blocks, and ease of synthesis. To date, a plethora of MOFs have now been synthesized and their physical properties examined with a focus on gas storage and separation. The catalytic diversity of MOFs, on the other hand, is emerging as an important area of MOF functionality with photo-catalysis a primary target of investigation. Two general strategies have been employed in the development of MOFs as photo-catalysts. The first utilizes the metal cluster building blocks and/or the ligands composing the framework as the photo-active component of the MOF. These photo-active framework MOFs typically contain lanthanide metal clusters or porphyrin based organic linkers which are both photo-chemically active. Alternatively, recent advances have been made in the development of MOFs in which the ligands connecting the metal clusters are composed of either free base or metallo-porphyrins. The advantages of this type of MOF photo-catalyst include a high density of available catalytic sites, ease of access of photochemical reactants and the ability to tune the framework to be selective for specific photo-chemical reactants. However, the drawbacks include non-specific photo-chemistry as the reactants can simply react with surface sites on the solid and difficulty in design of reactive cavities which can impart high selectivity.

Monday, January 28, 2013 @ 4:00 PM in Burson 115

Here we present photophysical studies of two well know metal organic frameworks (MOFs) (Zn HKUST-1 and USF2) containing either Ru(II)tris(2,2’ bipyridine) or Zn(II) tetrakis(N-methylpyridyl) porphyrin encapsulated within Zn-polyhedral MOFs. In addition, we present three new MOFs that have been templated using the photoactive Ru(II)tris(2,2’ bipyridine) cluster. In all cases, the results of our photophysical studies demonstrate the ability of the MOF framework to fine tune the photophysical properties of the guest molecules. In the case of the Ru(II)tris(2,2’bipyridine) materials, confinement in cavities with restricted space results in an increase in the non-radiative 3dd excited state thus increasing the observed lifetime of the 3MLCT excited state but to differing extents depending upon framework. For the Zn(II)-porphyrin system, confinement effects the porphyrin peripheral groups giving rise to triplet state perturbations. These studies suggest that photocatalytic properties of guest-based MOFs can be tuned to target specific catalytic processes.

Bio:
Dr. Larsen received his BS and then Ph.D. in chemistry from the University of New Mexico. He did his postdoctoral studies at CalTech before taking his first academic position at the University of Hawaii at Manoa. He is currently Professor and Chair of the Department of Chemistry at the University of South Florida.