Intramolecular end-to-end reactions of photoactive terminal groups linked by polymethylene chains

Abstract

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

Intramolecular excited state complexes in trichromophoric model compounds for polyesters derived from 2,6-naphthalenedicarboxylic acid and aliphatic glycols: experiment, rotational isomeric state model, and molecular dynamics

“…However, if the rings are both contributed by terminal naphthalene groups, they mainly give (if they exist) meta, and the contribution due to ortho and para increases with m. Complexes with simultaneous overlap of both rings are eclipsed and ortho. The geometry of the preferred complexes is quite different when they are formed from excited triplets, as shown by the work of Ashikaga et al on dibenz[b,f]azepine labels at the ends of polyethylene 28 or polyoxyethlene 29 chains. They described their preferred complexes of excited triplets as of the anti type, which approximates the para orientation of the excited singlets in the present work.…”

Stepwise Photopolymerization of Bichromophoric Chains by Cycloaddition of Dibenz[b,f]azepine Groups

“…If a linear dimer or trimer gives rise to intramolecular cyclization preferentially, the photopolymerization does not proceed. The intramolecular reaction in polymethylene systems 13 suggests that intramolecular cyclization occurs most easily for the linear trimer and that the linear trimer which has escaped from the intramolecular cycli- zation undergoes photopolymerization progressively. Therefore, the oligomers longer than the linear trimer preferentially undergo photopolymerization.…”

Spectral and photochemical properties of bifunctional compounds and their complexes

“…Change in the relative concentrations of components during photolysis of diaminobutane lb: Ib (1), 2b (L~, and 3b(3). 4.…”