Excited-state reactions acenaphthylene

The dimerisation of acenaphthylene has been used as a probe reaction to investigate the properties of the cavities of a zeolite.In solution acenaphthylene photodimerises to the syn and anti dimers (304) and (305) the singlet excited state yields the syn isomer exclusively, while the triplet excited state produces both the... 

In two cases, where the singlet- and triplet-state reactions have been carefully looked at and separated, this proves to be true. Thus coumarin 8.59, in the excited singlet state, dimerises to give only the HH dimer syn-8.60, but in the triplet state it gives both HH isomers syn-8.60 and anti-8.60, with only a trace of head-to-tail (HT) products.1119 Acenaphthylene also gives the syn dimer from the singlet-state reaction and a mixture of the syn and anti dimers from the triplet-state reaction.1120... 

The other reaction can be isolated by using air-saturated solutions or by adding cyclooctatetraene, without sensitisers it gives only iy/i-dimer. In the molten phase, this is the only reaction that has been observed . As to the mechanism of the two competing processes, it seems convenient to attribute the former to an excited triplet state of acenaphthylene, and the latter to the excited singlet state of a Tr-complex, that gives only syn adduct because of its initial geometry. 

Schenck et al. studied the photochemical reactions of the adducts of duroquinone with unsaturated compounds such as cyclic dienes, acenaphthylene, coumarin, and styrene (Scheme 12). Formation of both oxetanes and cyclobutanes was observed, depending on the substituents present in the quinone. From the theoretical and experimental investigations, p-benzoquinone reacts from its triplet mt excited state to yield exclusively oxetane adducts, while its tetramethyl or tetrachloro derivatives, duroquinone... 

The quenching of the trans dimer with oxygen and ferrocene indicates that this product is formed almost entirely from the triplet state. It is possible to calculate the amount of triplet-derived product in benzene by subtracting the amount of product obtained in the presence of oxygen from the amount of product obtained in the absence of oxygen. Such a calculation indicates that acenaphthylene triplets in benzene give both trans and cis dimers in the ratio of 74 26. The triplet state accounts for almost all of the trans product and about 10% of the cis product. The break in the slope of the Stem-Volmer plot for the trans dimer (Figure 10.3) may be attributed to the presence of two excited species which are quenched at different rates. These two species could be (a) two different monomeric acenaphthylene triplet states 7 and T2 or (b) a monomeric acenaphthylene triplet state 7 and a triplet excimer. This second triplet species is of relatively minor importance in the overall reaction since less than 5% of the total product in an unquenched reaction is due to this species. 

When xanthenethione (38) is excited to its ,7r -state, [2 + 2]cycloaddition proceeds with bis(alkylthio)ethyne. The cyclo-adduct [(42) or (43)] is in thermal equilibrium with its open isomer [(44) or (45)]. A similar reaction of (37) with acenaphthylene, indene, or A-phenylmaleimide affords a spirothietan derivative in good yield. Thioxanthenethione in the ,7r -state cyclo-adds to alkyl- or alkoxy-substituted butatrienes, giving the thietans (46)—(49). ... 

Haga, N., Nakajima, H., Takayanagi, H., and Tokumaru, K., Exclusive production of a cycloadduct from selective excitation of charge-transfer complex between acenaphthylene and tetracyanoethylene in crystalline state in contrast to failure of reaction in solution,/. Chem. Soc., Chem. Commun., 1171, 1997. 

Selective excitation of the CT complex between acenaphthylene 41 and tetracyanoethylene 42 in the crystaUine state exclusively affords the 1 1 [2+2]-cycloadduct 43, in contrast to the excitation in solu-tion. On irradiation of the complex of 41 and 42 with light of wavelength X > 500 nm, where neither 41 nor 42 is excited, 43 is obtained in 80% yield. Irradiation of an equimolar mixture of 41 and 42 in solution with X > 500 nm light induces no reaction. 

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