Control of Photochemical Reactions by Use of Complex Formation of Carbonyl Compounds with Cations

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The purposes of this investigation are clarification of the feature of the complex formation of excited carbonyl compounds with cation, Lewis acid, and protic acid, and evaluation of the possibility for controlling photoreactions by the complex formation.The results obtained are as follows :1. Interaction of the singlet excited states of various carbonyl compounds with cation, Lewis acid, and protic acid was observed in the fluorescence spectra. While 1:1 and 1:2 complex formation with cation was observed, only 1:1 complex formation with Lewis acid and protic acid was found. From the association constants for the complex formation obtained from the changes of the fluorescence spectra, the interaction seems to be stronger in order of cation, Lewis acid, and protic acid. No interaction of the ground state of the carbonyl compounds was observed in all cases.2. From the results of solvent effect and influence of cation, coordination of the cation to the singlet excited state of the carbonyl compounds seem to be responsible for the complex formation. Similar coordination may proceed with Lewis acid and proti cacid.3. The complex formation with cation decreased the quantum yield of the dimerization of an aromatic carbonyl compound which proceeded from the singlet excited state of the carbonyl compound, and suppressed also insertion reaction of alkenes into C-N bond of an aromatic imide which proceeded from the singlet excited state of the imide. Furthermore, remarkable acceleration effect of the complex formation with cation was observed in a photochemical electron-transfer reaction, in which the complex formation with cation prolonged the lifetime of the excited singlet state of the carbonyl compound. From the above results the complex formation with cation can be concluded to offer a useful method for controlling photoreactions. The complex formation with Lewis acid and protic acid was also found to be effective for controlling photoreactions.