|Name||Mr. Abdulaziz Alanazi|
|Organization or Institution||University of South Florida|
The encapsulation of reactive guest molecules including free-base and metalloporphyrins within two CdII-carboxylate MOFs
Abdulaziz A. Alanazi, Randy W. Larsen* and, Lukasz Wojtas
University of South Florida
Metal−organic frameworks (MOFs) are functional porous materials with wide-ranging applications. The versatility of MOFs can be expanded through the encapsulation of reactive guest molecules including free-base and metalloporphyrins. Recently, tetra (N-methyl-4-pyridyl)-21H,23H porphine (T4MPyP) encapsulated within two CdII-carboxylate MOFs has been reported. The T4MPyP@MOM-11 exhibits porphyrin molecules encapsulated within square windows while the T4MPyP@MOM-12 has porphyrin molecules encapsulated within hexagonal cavities. Here, the photophysical properties of the encapsulated porphyrins are examined in order to understand the effects of confinement on the porphyrin electron structure. The Soret absorption bands display a large bathochromic shift of T4MPyP@MOM-11 and CdT4MPyP@MOM-12 (49 nm and 58 nm respectively) relative to the T4MPyP in solution (Soret maximum ∼ 426 nm). A similar bathochromic shift is also observed in the steady-state emission spectra. The T4MPyP@MOM-11 and T4MPyP@MOM-12 exhibit emission maximum at 683 nm and 695 nm, respectively, while the TMPyP in solution exhibits a maximum peak at 659 nm with a shoulder at 721 nm. Transient absorbance data reveal porphyrin triplet state lifetimes that are an order of magnitude longer than that observed in solution (τ≈ 0.03 ms for T4MPyP and τ≈ 0.3 ms for both T4MPyP@MOM-11 and T4MPyP@MOM-12) which likely arises from changes in the intersystem crossing (ISC) coupling between the excited triplet and singlet ground states.