Session: Inorganic Spectroscopy:

Metal organic frameworks (MOFs) are a class of nanoporous materials known for their exceptionally large surface area and pore volumes. Structural tuneability of MOFs allows for control over cavity size and topology leading to applications in gas storage and separation, sensing, catalysis, and drug delivery. The porosity of MOFs also allows for the encapsulation of photo active guests resulting in novel materials for photovoltaics, light activated drug delivery systems, photocatalysis and other light harvesting applications. Of particular interest as a photoactive guest is ruthenium (II) tris-(2,2’-bipyridine) (RuBpy) due to the complexes advantageous photophysics including long excited state lifetime (620 ns at 25 C) and a high luminescent quantum yield (Φ=0.09). In order to understand how nano-environments effect RuBpy photophysics, we have examined this complex in MOFs with systematically varied pore sizes. Specifically we have examined the photophysics of RuBpy non-covalently encapsulated within two distinct classes of Zr(IV)-based and Zn(II)-based MOFs. The Zr(IV)-based MOFs are known as the Uio series ( Uio-66, Uio-67, and Uio-68) and the analogous Zn(II)-based MOFs are MOF-5 and IRMOF-10 which all exhibit progressively larger cavity sizes while keeping similar topological features. The results support RuBpy encapsulation into the smaller cavities results in extended emission lifetimes as a result of deactivation of a higher energy ligand field state (³LF) while the progressively larger cavities leads to shorten lifetimes and photophysics consistent with RuBpy in solution.

Dr Randy William Larsen

Professor of Chemistry, University of South Florida

Appearances