The fluorescence quenching and photochemistry of 2-methyl-, 4-methyl-, and 6-methyl-1-naphthonitrile with tetramethylethylene have been studied in nonpolar solvents. Stern-Volmer constants (benzene solvent) are 10.1, 15.7, and 7.2 M-', respectively, showing that quenching is insensitive to the position of the methyl group. Exciplex emission was observed in each case, and exciplex lifetimes were measured by single photon counting techniques. The methylnaphthonitriles react with tetramethylethylene to give 1-cyano-7,7,8,8-tetramethyl-2,3-benzobicyclo[4.2.0] -2,4-octadiene derivatives, and limiting quantum yields were measured. In the case of 4-methyl-l-naphthonitrile, quenching with biacetyl showed that the exciplex is an intermediate in the cycloaddition reaction and no triplets are formed in the exciplex decay. Rates of exciplex collapse to cyclobutane products were derived. The bichromophoric molecules 1, 2, and 3, in which the chromophores are linked by a three-atom chain, were synthesized. All three show strong quenching of the monomer (naphthonitrile) fluorescence, and weak exciplex emission. Compounds 1,2, and 3 also react on irradiation, giving internal cycloaddition products. The structures of the latter were determined, and the structure work is described. Comparison of quantum yields for internal cycloaddition with limiting quantum yields for the bimolecular cases shows that the three-atom chain greatly facilitates collapse of the exciplexes to products in these systems. Exciplex formation and decay are discussed in terms of current theory. The structure of one photoproduct, 7-cyano-5,6,6-trimethyl-8,9-benzo-3-oxatricyclo[S.4.O.O1~5]-8,lO-undecadiene (lo), was determined by X-ray diffraction. and the structure is described.Exciplex formation was proposed some time ago by Hammond and co-workers2 to account for the quenching of fluorescence of aromatic compounds by dienes.2 The observation of exciplex fluorescence from 1 -naphthonitrile and electron-rich alkenes by Taylor3 showed that exciplexes are indeed formed in fluorescence quenching by ethylene derivatives. A kinetic analysis of the 1-naphthonitrile-olefin system has been carried o~t .~,~ Exciplex formation was found to be reversible, and rate constants for the ( I ) (a) Department

Sir:The aryl nitrile-olefm systems are interesting because they show exciplex fluorescence' as well as photoreactions. These allow Hamilton, Ontario, Canada U S 4Ml

Studies of the photocyclization of a-(0-tolyl)acetophenone dissolved in crosslinked ethylene -vinyl acetate beads show that quantum yields close to unity can be achieved, even in the solid polymer matrix. In preliminary experiments using solar radiation it was demonstrated that the rates of photochemical transformations are close to those calculated from the photon energy distribution of the solar spectrum.J . E. GUILLET, W. K. MACINNIS et A. E. REDPATH. Can. J . Chem. 63, 1333Chem. 63, (1985.Des Ctudes sur la photocyclisation de I'a-(0-tolyl)acttophCnone dissoute dans des billes d'un polymkre rCticulC d'Cthylkne et d'acttate de vinyle ont permis de montrer que I'on peut obtenir des rendements quantiques qui s'approchent de I'unitC, mCme dans la matrice solide d'un polymkre. Dans des experiences prkliminaires faisant appel a la radiation solaire, on a pu dCmontrer que les vitesses des transformations photochimiques se rapprochent de celles que I'on peut calculer en utilisant la distribution des Cnergies des photons du spectre solaire.[Traduit par le journal] Introduction The study of organic photochemistry has been an active field of research for many years. As a result of this work there is a wide variety of synthetic photochemical routes to the synthesis of novel organic compounds and intermediates. Surprisingly, very few applications of these synthetic routes have reached commercial practice, probably because of the high cost of using electrically driven lamps to provide the necessary photon energy. For a number of years, we have been interested in exploring the possible use of polymeric devices which could utilize natural sunlight to carry out photochemical processes in a manner which could be easily expanded to large-scale commercial production. In this paper we report a method of carrying out photochemical reactions in small crosslinked polymer beads. The beads can be supported on water which provides both a self-levelling support and a means of transporting the beads from the exposure area to a collection device.

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