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The triplet-sensitized photochemical reaction using a series of poly(oxyethylene) chains with a pair of photoactive terminal groups, dibenz[b,f]azepine (DBA) chromophores (DBA–COCH2CH2(OCH2CH2)nOCH2CH2CO–DBA, n=0–10) was examined. The photoirradiation of bichromophoric compounds caused either intra- or intermolecular reactions. These reactions were kinetically analyzed by two different methods: the measurement of deactivation processes of the reaction intermediates (excited triplet state of DBA) by nanosecond laser photolysis and the quantitative analysis of the reaction products by GPC. The intramolecular deactivation rate constant, kintra, showed a remarkable chain-length dependence; the maximum kintra value appeared at n=5 and it was found to be 5.9×104 s−1. On the other hand, the intramolecular cyclization rate also depends on the chain length; the maximum quantum yield, φdintra, was given at n=7 (φdintra=0.51). The chain length for the maximum cyclization yield shifted slightly to the longer region than that for the maximum kintra value due to the restriction of the terminal structure (anti-configuration). The results obtained for this reaction system are compared with those obtained for the previously reported polymethylene system and the effect of chain flexibility on the intramolecular ring-closure reaction is discussed.

diated on a merry-go-round apparatus at 25 OC. Direct irradiations were carried out through a K2C0, ( 1.3%)-K2Cr04 (0.13%) filter solution (mainly 3 13 nm). Benzophenone-sensitized irradiations were done through a phenanthrene solution (5 g/L) in methanol (>350 nm) or through a glass filter (Riko U-360, mainly 366 nm). The reaction mixtures were analyzed by HPLC, using naphthalene or m-terphenyl as the internal standard. A small amount of isomeric olefin impurities involved in the starting material was carefully checked by HPLC: the purities of the rt-and t-isomers were >99.99% and those of the other isomers were >99.4%. When necessary, corrections were made in the calculation of the quantum yields. In all cases the reaction was stopped at a small conversion (<4%). Two parallel runs for quantum yield measurements agreed within experimental error (&5%). The transcis isomerization of r-S was used for actinometry (adim = Pns = C~.50~~).Abstract: Intramolecular end-to-end reactions of a pair of photoactive terminal groups, dibenz[bflazepine (DBA) chromophores, linked by a series of polymethylene chains (DBA-CO(CH,),CO-DBA, n = 2-30) were studied by two different approaches. One approach is to measure the intramolecular deactivation rate constants of the excited triplet state of terminal DBA groups by the nanosecond laser photolysis and the other is to measure the intramolecular photocyclization rates of these bichromophoric compounds by the quantitative product analysis with GPC. The excited triplet state of the DBA group is the intermediate of the reaction. The intramolecular deactivation rate constant, k'""", of each compound showed a pronounced chain length dependence, while the intermolecular deactivation rate constant, kintCr, was independent of its chain length within the range