INTRAZEOLITE PHOTOCHEMISTRY .14. PHOTOCHEMISTRY OF ALPHA,OMEGA-DIPHENYL ALLYL CATIONS WITHIN ZEOLITES

1,3-Diphenylpropenylium (DP3(+)) and 1,5-diphenylpentadienylium (DP5()) ions have been generated within acid ZSM-5 and mordenite zeolites a s persistent species by adsorption of alpha,omega-disubstituted alpha, omega-diphenylalkanes. It was found that besides alpha,omega-diacetate s, alpha,omega-dichlorides and alpha,omega-diols are also convenient p recursors, Irradiation of these allylic cations embedded within zeolit es led to cis-trans isomerization as the only observable process. Mole cular modeling suggests that there is enough space in the intersection of the channels in HZSM-5 to accommodate both the planar E,E-DP3(+) a nd the nonplanar E,Z-DP3(+) stereoisomers. Fluorescence emissions foll ow a near-first-order decay, with a dominant short and a minor long co mponent; the latter having a lifetime close to that reported for DP5() in solution at low temperatures. Z-E isomerization led to a blue-shi ft in the absorption spectra together with an increase in the apparent extinction coefficient, while emission maxima also appeared at longer wavelengths exhibiting distinctive decays. Evidence for the tripler e xcited states has been obtained by time-resolved diffuse reflectance s pectroscopy. Estimated lifetimes obtained from the best first-order fi t are in the tens of microseconds range. Weak delayed emission associa ted to the triplet excited state has also been observed.