Triarylmethylium Cations Encapsulated within Zeolite Supercages

A series of substituted triarylmethylium cations, including malachite green, tris(4-methoxyphenyl)methylium, and bis(4-methoxyphenyl)phenylmethylium cations, has been prepared adsorbed on tridirectional large pore zeolites Y and β in their H+ or La3+ form, as well as within the novel mesoporous aluminosilicate MCM-41, by ship-in-a-bottle synthesis from the corresponding benzaldehyde and N,N-dimethylaniline or anisole. The resulting composites exhibit diffuse reflectance and IR spectra characteristic of these trityl dyes. The cation content was determined by thermogravimetry−differential scanning calorimetry. Preparation of these triarylmethylium cations exclusively on the external surface of ZSM-5, a medium pore zeolite whose internal voids are too small to accommodate these cations, is also possible. Therefore, the methodology based in the diffusion of smaller precursors does not guarantee itself the intrazeolite location of the synthesized guests. In this work, we have experimentally determined that the dyes are blocked in the interior of the faujasite pores. Thus, direct evidence showing the location of the organic material inside the zeolite supercages was obtained using X-ray diffraction and X-ray photoelectron spectroscopy. These dyes incorporated within microporous solids can act as heterogeneous photosensitizers to promote the sensitized dimerization of 1,3-cyclohexadiene.