Azobenzene structure

The Sm-N distances are consistent with single a bonds suggesting the presence of a (C H NNC.H dianion. However, the 1.25(1) a NN distance is the same" as tire N=N double bond distances in a variety of azobenzene structures. The molecule also contains distorted N-C (phenyl) distances, which are stretched from a normal 1.42 8 distance to 1.56-1.61 8. In addition, the samarium atoms are displaced asymmetrically such that both come within 2.29-2.34 8 of the ortho hydrogens of a single phenyl ring in a bonafide agostic (6<0 Sm-H interaction. The ability of Sm(II) to structurally distort azobenzene in this way is remarkable. 

Moving from simple rod-like molecules, one arrives naturally at those amphiphiles which consist of a rod-like structure containing near its centre a cyclic group. A considerable amount of research has been devoted to the study of materials containing both the azobenzene structure and the closely related stilbene structure, which are illustrated in Figure 4.3. 

Name 2-Chloro-4 -n-butyl-4-(4-n-butoxybenzoyloxy) azobenzene Structure ... 

Chippendale et al.m studied 13C and 15N CP/MAS NMR of free acids and sodium salts of a series of sulfonated azobenzene dyestuffs (39). In solution the spectra of both free acid and salts are characteristic of /rani-azobenzene structures, as are the spectra of the solid samples of the salts. The spectra of the solid free acids are markedly different from those of the corresponding solid sodium salts (Tables 17 and 18) and exist as azonium tautomers (three resonance structures are shown for 39f). Solid-state structures of this type are probably stabilized by the formation of intermolecular bonds. 

Figure C2.4.6. Azobenzene structure modified with hydrocarbon chains [53, 54],... 

On the contrary, azobenzene structures with strong electron-donor and electron-acceptor groups on the para positions, which would have a higher dipole... 

One example is a copolymer of styrene, where azobenzene structures are attached in the comonomer to the benzene portion through amide linkages [210] ... 

Hydrazobenzenes with a chalcogenophosphoryl group were prepared by the reduction of 2-iodoazobenzene with hydrazine hydrate followed by a Pd(ii)-cata-lyzed cross-coupling with diphenylphosphine. The P(in) function was subsequently oxidised by hydrogen peroxide, sulfur and selenixun (Scheme 22) It was possible to restore the azobenzene structure by oxidation. The radical phosphination of aryl iodides by chlorodiphenylphosphine in the presence of tris(trimethylsilyl)silane, 1,1 -azobis(cyclohexane-l-carbonitrile) (V-40) and pyridine led to aryldiphenylphos-phines that were converted to the P-sulfides (Scheme 23). ... 

Molecular opto-electronic assemblies, which consist of a functionalized gold electrode with a photo-isomerizable redox-activated monolayer, enables amperometric transduction of the photonic information recorded by the interface. On-off operation of superstructure formation of hermaphroditic cyclodextrin derivatives is brought about by disturbing the monomer/dimer equilibrium of -azobenzene structures by photoisomerization. When the structures have the Z-form, the dimer dissociates. The thermal Z— isomerization can be enhanced by heating in favor of the dimer formation (Figure 89.8). ... 

All these examples demonstrate the possibiHty of manipulating self-assembHng structures of amphiphiles and artificial supramolecular structures, respectively, by reversible photoswitching between E- and Z-azobenzene structures. Advancements in the direction of real practical appHcations will depend on demonstrating the usefulness and stability of such systems. 

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