INTRAZEOLITE PHOTOCHEMISTRY .13. PHOTOPHYSICAL PROPERTIES OF BULKY 2,4,6-TRIPHENYLPYRYLIUM AND TRITYLIUM CATIONS WITHIN LARGE-PORE AND EXTRA-LARGE-PORE ZEOLITES

The photophysical properties of 2,4,6-triphenylpyrylium (TPP+) and thr ee para-substituted tritylium ions encapsulated within Y, beta, and MC M-41 have been studied. It was found that TPP+ adsorbed within MCM-41 or silica only emits fluorescence (lambda(max) 470 nm), whereas when t his cation is incorporated within HY and LaY, simultaneous emission of fluorescence and room-temperature phosphorescence (lambda(max) 560 nm ) was observed. The fluorescence decay consists of two consecutive fir st-order processes and is dominated by the fast (0.2-0.7 ns) component . In addition to the prompt fluorescence, delayed emission observable 40 mu s after excitation was also detected for the three TPP+ samples. Weak fluorescence was observed for the series of tritylium ions embed ded within zeolites. The characteristic T-T absorption spectrum of the TPP+ triplet excited state has been detected using time-resolved diff use reflectance. Depending on the zeolite, shifts in the reflectance m aximum and changes in the extinction coefficient of the long-wavelengt h band have been noted. Similar transient spectra have also been obtai ned for the tritylium samples, which also show long-wavelength bands t hat are attributed to the corresponding triplet excited state.