| Popis: |
The photochemical reactions of 4-acylstyrenes (1a–e; acyl = acetyl, benzoyl, 1-naphthoyl, 2-naphthoyl, and 9-phenanthrylcarbonyl, respectively) were investigated, and their excited state behavior and photoreactivities are discussed in relation to the aryl ketone structures. Photoirradiation of 1a–e in benzene gave two isomeric cyclodimers of trans- and cis-1,2-bis(4-acylphenyl)cyclobutanes(2a–e and 3a–e) as main products, accompanied by the formation of some oligomers and polymers. The fractions of the trans-form in the cyclodimers were ca. 80%; this indicated that the cyclodimerization proceeded via the π,π* triplet state. The quantum yields of the photodimerization for 1a–e were almost the same irrespective of the acyl substituents (Φ = 0.03–0.04 at [1a–e] = 0.1 mol dm−3). Phosphorescence spectra of 1c (τ = 0.48 s) and 1d (τ = 0.91 s) observed in a rigid solution at 77 K, which coincided with those of the respective model aryl ketones, were ascribed to the low-lying excited π,π* triplet states localized... |
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