Rationalizing the Unexpected Inefficiencies of 3D Porphyrin-MOFs as Singlet Oxygen Photosensitizers Against Botrytis cinerea

Abstract

Porphyrin-based MOFs (PMOFs) are known to be efficient photocatalysts and singlet oxygen (¹O₂) photosensitizers (PS) in solution, but their application in agriculture and food protection is practically unknown. In vitro tests on Botrytis cinerea using the renowned PCN-222 and PCN-224 reveal modest photo-antifungal activities at the solid–gas interface when compared to their standalone tetrakis(4-carboxyphenyl)porphyrin (TCPP) linker. This in-depth study examines the direct detection of ¹O₂(g) phosphorescence at the solid–air interface, binding of the PMOFs with the spores of B. cinerea by fluorescence microscopy, fluorescence quenching of the PMOFs by oxygen, and rates of exciton migration evaluated through the singlet-singlet annihilation process. The conclusion is that a significant proportion of ¹O₂ is unable to escape the porous materials before deactivation, or does so too late to then be able to reach, and that excitation migration is not efficient enough to generate significant amounts of ¹O₂ directly at the MOF surface. Given that TCPP is its own interface with the gas phase, it is not hindered by these factors, which explains its higher efficiency under these circumstances.