367-35-1Relevant articles and documents
Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor
Hashim,Thomas, Reji,Tamaoki, Nobuyuki
supporting information; experimental part, p. 7304 - 7312 (2011/08/05)
New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3′-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed. Copyright
Controlling catenations, properties and relative ring-component movements in catenanes with aromatic fluorine substituents
Ballardini, Roberto,Balzani, Vincenzo,Credi, Alberto,Brown, Christopher L.,Gillard, Richard E.,Montalti, Marco,Philp, Douglas,Stoddart, J. Fraser,Venturi, Margherita,White, Andrew J. P.,Williams, Brian J.,Williams, David J.
, p. 12503 - 12513 (2007/10/03)
Four new fluorine-containing macrocyclic polyethers based on bis-p- phenylene-34-crown-10 have been synthesized and subsequently catenated, separately, with cyclobis(paraquat-p-phenylene). The efficiencies of the catenations are strongly influenced by the aromatic ring templates in the macrocyclic polyethers. Incorporation of fluorine atom substituents into one of the hydroquinone rings in bis-p-phenylene-34-crown-10 had only a small effect on the percentage yields, whereas employing bis-p-phenylene-34-crown- 10 derivatives, in which both hydroquinone rings have been at least partially fluorinated, resulted in a dramatic decrease in catenation yields. In [2]catenanes incorporating macrocyclic polyethers containing one hydroquinone and one fluorinated hydroquinone ring, in both the solution (1H and 19F NMR, and UV-vis spectroscopies, electrochemical studies and molecular modeling) and solid (X-ray crystallography and molecular modeling) states, by far the major translational isomers observed were the ones with the hydroquinone ring located 'inside' the cavity of the tetracationic cyclophane. The diminished strength of the noncovalent interactions arising as a result of aromatic fluorine substituents is also reflected in the rates of the movements of the two ring components (dynamic NMR spectroscopy). As well as their electron-withdrawing effect, the fluorine substituents have a pronounced effect (UV-vis spectroscopy, electrochemical studies and molecular modeling) on the geometry of the ArO-CH2 bonds within the (fluorinated) hydroquinone rings.
