0000000000171838
AUTHOR
Silvia Dobis
Intramolecular photocycloaddition of anthracene and benzene ring systems
Abstract The anthracenes 3a – c , substituted in the 9-position with 3,5-dialkoxybenzyloxymethyl groups exhibit, in diluted solutions, intramolecular [4π+4π] photocycloaddition reactions to the polycyclic compounds 4a – c . The quantitative processes are completely reversible by heating, unless acid-catalyzed cleavages lead to thermally stable mono- and diketones: 4a – c → 5a – c → 6 .
Structure Determination of Photoproducts of Anthracenes with (Arylmethoxymethyl) Sidechains
Irradiation of 9-(arylmethoxymethyl)anthracenes 3 leads either to a cyclomer and cyclodimer mixture (3a 4a,5a), to selectively formed dimers (3b 5b), or a selectively formed cyclomer (3c 4c). The [4π+4π]cyclodimerization is under the conditions used a regioselective head-to-tail process. In the crystals of the dimers 5a,b, the sidechains are attached in an antiperiplanar position related to the CC bonds generated in the dimerization. In solutions, however, the structures consist of three rotamers the equilibration of which was studied by temperature-dependent NMR spectra. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Rearrangement of the carbon skeleton in the intramolecular photoadduct of anthracene and benzene rings
Abstract The effectivity of optical switching between anthracene derivatives 3a,b and their intramolecular photocycloadducts 4a,b is impaired by traces of acid. The systematic treatment of 4a,b with an increasing excess of formic acid revealed that—apart from the normal enolether cleavage 4a,b → 6a,b → 7a,b —a cleavage with rearrangement of the carbon skeleton can occur: 5b → 6b′ . The driving force is a stability enhancement of the involved carbenium ions 5b → 5b′ . A further increased excess of formic acid leads finally to a competitive ether cleavage in the tetrahydrofuran ring 5b → 8 .
Optical Switching and Antenna Effect of Dendrimers with an Anthracene Core
Dendrimers 6G(i) (i=1-4) consisting of an anthracene core and Fréchet dendrons which are attached via a CH(2)OCH(2) chain in the 9-position undergo quantitative and completely reversible intramolecular [4pi+4pi] cycloaddition. The process can be monitored by absorption and fluorescence measurements. The Fréchet dendrons act as an energy funnel that collects and focuses the photon energy but does not change the photostationary states, which for both directions are completely on the product side when the separate chromophores are selectively irradiated. The quantum yields of anthracene fluorescence and of singlet energy transfer from the dendrons to the core were studied as a function of dend…