Induction of Molecular Chirality by Circularly Polarized Light in Cyclic Azobenzene with a Photoswitchable Benzene Rotor

Abstract

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.

Toward the Rational Design of Galactosylated Glycoclusters That Target Pseudomonas aeruginosa Lectin A (LecA): Influence of Linker Arms That Lead to Low‐Nanomolar Multivalent Ligands

“…Introduction of ag lycol moiety between the aromatic ring and the anomeric carbon atom (Scheme 1) was achievedb yg alactosylation of nitrophenoxyethanols 2a-c readily obtained by alkylation from ethylene carbonate of the corresponding phenols 1a-c. [52][53][54] Galactosides 3a-c werec onverted into the de- Authors 37 10 Chabre et al [51] 5.8 0 Cecioni et al [31] 4.2 11 Kadam et al [13] 4.2 11 Kadam et al [48] 6.3 2 Rodrigue et al [49] [a] The K d valuesw ere measured by using ITC.…”

Light‐Gated Molecular Brakes Based on Pentiptycene‐Incorporated Azobenzenes

“…[7,[10][11][12][13][14][15][16][17][18][19] One such prototypei s" molecular brakes", which possess two or more states that differ in the rotationr ate of ar igid subunit (rotor) about as ingle bond;t hese states could be interconverted by using external stimuli (fuels). [19][20][21][22][23][24] Among the various forms of fuel, light has the advantages of rapid input, remote control, and no waste deposition. However,l ight gating often suffers from incomplete switching.…”

Reactive molecular dynamics simulations of switching processes of azobenzene-based monolayer on surface

“…The geometrically extended trans isomer is usually slightly lower in energy than the compact cis isomer. The photochemically and thermally reversible conversation between these two isomers, coupled with dramatically different physical and chemical properties, 1-3 is expected to have broad applications in liquid crystal, [4][5][6][7][8][9][10][11] photoswitching biomaterials, 12 molecular machines, [13][14][15][16][17] and photonic nanoscale devices. [18][19][20][21][22][23][24] Rational design of azobenzene-based molecular devices has attracted extensive interest from both the experimental and theoretical chemists for many years.…”