Tetrahedron Letters,Vol.31,No.l,pp47-50,199O 0040-4039/90 $3.00 +.oo Printed in Great Britain Pergamon Press plc Modification of Photochemical Reactivity by Zeolites: Cation Controlled

Abstract: Photolyses of accnaphthylene included in WY zeolites gave the corresponding cis and trans dimcrs. The ratio of the dimers formed depends on the type of cation present in the supercage. Dimerization is believed to originate from the excited singlet state in the case of lower atomic weight cations and from the triplet state in the case of higher atomic weight cation exchanged zeolites. Dimerization provides insight into the distribution and migration of molecules within the zeolite internal structures. The internal surfaces of zeolites have recently been demonstrated to exert significant influence on the unimolecular photoreactivity of included molecules. 1 However, no such effect on bimolecular photoreactions of guests within zeolite frameworks has yet been reported. We present here our preliminary results on a study of a photochemical bimolecular reaction, the dimerization of acenaphthylene, within a zeolite framework. Further, we also show that the multiplicity of the reactive state can be controlled by careful choice of the exchangeable cations that are present within the supercage. &