Photophysical studies of ligand photorelease from ruthenium-based complexes encapsulated within polyhedral zinc metal organic frameworks.

Delaney Sellers and Randy Larsen

University of South Florida

Metal organic framework materials (MOFs) are of interest due to their high porosity, large surface area, and substantial free volume making them advantageous in applications such as gas storage and delivery, light harvesting, sensing, and drug delivery. The large and tunable cavity sizes associated with MOFs are particularly attractive for biomolecular applications including light-activated drug delivery. The Ruthenium(II) bis(2,2’-bipyridine)L (RuBpyL) and ruthenium(II) bis(2,2’-bipyridine)L’2 (RuBpyL’2) complexes where L = sterically hindered bidentate ligand and L’ = monodentate ligands can serve as photo-releasable ‘cages’ for pharmaceutically active L and L’ ligands. These ruthenium-based complexes can be encapsulated in a variety of MOFs which provides an opportunity to develop light-activated pharmaceutical MOF materials. In these systems, photolysis of the RuBpyL@MOF or RuBpyL’2@MOF complexes releases the L or L’ ligands within the MOF cavities followed by diffusion into the bulk solvent. One of the challenges in developing these materials is to establish the parameters for effective photorelease of ligands. Here, the encapsulation of Ru(II)bis(2,2’-bipyridine) complexes with varying ligands in the two open coordination sites ((4,4’-Dmbpy), (4,4’-Dcbpy), (4-Amp)2, and (4-Mpy)2) are examined within two Zn-based polyhedral MOFs with differing cavity dimensions, MOF-5 and USF-2. Of specific interest are the photophysical properties of the encapsulated guests as well as the ability to photo-release both mono-dentate and bidentate ligands from the MOF cavities. The results indicate different photorelease mechanisms between the various complexes within the MOFs and cavity size selective ligand release. These results will be discussed within the context of broader MOF based photo-dynamic therapy applications.