Functionalization of rho-ZMOF with photosensitizers for singlet oxygen generation

Abstract

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.