Intrazeolite photochemistry .12. Ship-in-a-bottle synthesis and control of the photophysical properties of 9-(4-methoxyphenyl)xanthenium ion imprisoned into large-pore zeolites

The 9-(4-methoxyphenyl)xanthylium ion (AnX(+)), a bulky cation that according to molecular modeling simulations cannot enter through the 7.4 Angstrom pore opening of tridirectional large-pore zeolites Y and beta, has been prepared by ship-in-a-bottle synthesis within the supercages of these two zeolites. The synthetic procedure involves two steps: (i) generation of xanthylium cation (X(+)) adsorbed within the zeolite by treatment of xanthydrol onto the H+ form of these solids; (ii) electrophilic attack of the cation to anisole within the framework of the zeolite. Carrying out the same procedure using toluene or benzene or using an alternative process involving the reaction of xanthone with anisole, led to the corresponding 9-arylxanthylium ions together with some unidentified adventitious material. Textural and acidic properties of these composites were tested using a-methylstyrene dimerization and were found to be very similar to the original HY or H beta zeolites, thus indicating an internal location for AnX(+). Entrapment within the zeolite framework restricts AnX(+) conformational mobility, thwarting the deactivation pathway occurring in solution. This has allowed for the first time characterization of its tripler excited state as a long-lived transient species (tens of microseconds), as well as the observation of room-temperature fluorescence in the nanosecond range.