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, tau = 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. (C) 2011 Elsevier B.V. All rights reserved.