Tunable Photocatalytic Singlet Oxygen Generation by Metal-Organic Frameworks via Functionalization of Pyrene-Containing Linkers

Metal-organic frameworks (MOFs) are highly versatilematerialsthat have shown great promise in chemical warfare agent (CWA) adsorptionand decontamination. Sulfur mustard has been one of the most prominentlyused CWAs over the last century; therefore, the development of effectivedetoxification strategies is of utmost importance. However, typicalroutes of detoxification are slow and/or result in the productionof harmful byproducts. NU-1000 has previously shown promise as a "soft"oxidizer that can readily detoxify sulfur mustard and its simulant2-chloroethyl ethyl sulfide (2-CEES) through the generation of singletoxygen in the presence of either UV (396 nm) or blue (465 nm) light.Several variants of NU-1000 were synthesized (MOF-R, R = -Cl,-NO2, -CH3) with functional groupspositioned either ortho or meta tothe carboxylic acid on the linker. NU-1000-o-(Cl)(4) and NU-1000-m-(Cl)(4) showed significantenhancement of photooxidation of 2-CEES due to spin-orbit coupling,enhancing the intersystem crossing into the MOF triplet (T-1) state. Furthermore, substitution of MOF linkers led to pyrene-phenylrotation. Linkers with substituents in the ortho-positionwere shown to have smaller pyrene-phenyl torsion angles, leadingto enhanced conjugation between the rings and a subsequent red shiftin the absorption spectra. This red shift leads to enhanced reactivityof NU-1000-o-(Cl)(4) under blue light conditionsand gives perspective on making materials with enhanced reactivityutilizing visible light.