Functionalization of rho-ZMOF with photosensitizers for singlet oxygen generation

Here we report the functionalization of a zeolite-like-metal organic framework of RHO topology with two cationic photosensitizers, methylene blue (MB+) and phenosafranine (PS+). The spectroscopic properties of encapsulated MB+ are strongly influenced by host–guest interactions. At low MB+ loading levels, the photo-sensitizer remains monomeric and exhibits absorption and emission spectra that are red-shifted with respect to MB+ spectra in aqueous solution. Strong interactions between MB+ and the framework are clearly evident from the long fluorescence lifetime of the functionalized material, τ = 3.2 ns, that is nearly an order of magnitude longer relative to MB+ in aqueous solutions. Unlike MB+, the larger diameter of PS+ dye prevents its incorporation within the ZMOF framework and PS+ molecules weakly bind to the external surface of the framework and exhibit absorption and emission properties similar to those measured for PS+ in methanolic solution. The immobilized photosensitizers partially preserve their capacity to generate singlet oxygen as determined indirectly using diphenylanthracene as a chemical trap.