Abstract: Selectivity in organic photo transformations continues to be one of the main topics of current interest^[1].Of the various approaches use of organized and const rained media had shown considerable promise^[2].Molecular-sieve zeolites represent a novel and unique class of materials^[3].This material may be regarded as open structures of silica in which silicon has been substituted by aluminum in a well-defined fraction of the tetrahe-dral sites.The frameworks thus obtained contain pores,channels,and cages of different dimensions and shapes.The pores and cages can accommodate,selectively according to size/shape,a variety of organic molecules of photochemical interest,and provide restrictions on the motions of the included guest molecules and reaction intermediates.For example,the internal surface of ZSM-5 consists of two types of pore systems (channels)^[3]:one is sinusoidal w ith a near circular cross section of ca.0.55 nm,and the other is straight and perpendicular to the sinusoidal channels.The straight channels are roughly elliptical with dimensions of ca.0.52?0.58 nm.Those channels of ZMS-5 can allow the adsorption of benzene and other molecules of similar molecular size,but prevent molecules which possess a larger size/shape from being sorbed into the internal framework.

Key words: selectivity in photochemical reaction, photosensitized oxidation of alkenes, trans, trans-1,4-diphenyl-1,3-butadiene, ZSM-5 zeolite