Molecules Containing Azobenzene Units

Many substituted azobenzenes belong to the azobenzene type, as well. Substitution may shift the n —> it band from 440 nm (azobenzene), to 465 nm (hexamethylazobenzene), to 480 nm (2,2 -dimethyl-4,6,4 ,6 -tetra-tert.butylazobenzene), and even to 520 nm (hexaphenylazobenzene). Hydrocarbon, halogen, nitro, carboxy, acetyl, hydroxy, m-amino" and even 2,2 4,4 ,6,6 hexaphenyl substitution— influences the (7i,7t )-(n,7i ) state energy gap, but not so much as to shift the molecule into the aminoazobenzene group. In the context of this book, it is important that the long-chain and polymeric molecules containing azobenzene units coupled by means of hydroxy and carboxy substituents are of the azobenzene type. 

On the other hand, azobenzene can quench the fluorescence of other moleetdes. This has been investigated in molecules containing both a fluorescing and an azobenzene unit. It was found that the E-form is about 3 times, or even up to 13 times, as effective a quencher as the Z-form. The influence of the environment on such bichromophoric molecules was studied by Eisenbach et al. ... 

In this paper we describe two newly developed conductive LB films an LB film with metallic conductivity using transition metal complexes [23], and a photochemical switching LB film using a TCNQ radical salt, containing an azobenzene unit in the hydrophobic part of the amphiphilic molecule [13]. 

Polymer or SiUca Film Photoresponsive Molecules Containing an Azobenzene Unit... 

The majority of the systems outlined in this monograph contain the azobenzene moiety as the photoswitchable unit. Therefore, the first chapter of this monograph deals with the properties of this simple molecule and its simple derivatives. Applications for various purposes are covered in some of the following chapters. 

Monolayers with much higher coverage were reported to form from the fi-aminocyclodextrin derivative containing only one disulphide-terminated alkane chain attached to the amino group of the 6-deoxyaminoglucose unit. These layers were shown to bind naphthalenesulphonic acids" ". A similar monolayer selectively binds a trans-azobenzene derivative" " . /3-Cyclodextrin modified layers also show selective transport of ferrocene carboxyhc acid and hydroxyquinone. The selective transport can be controlled by blocking the /3-cyciodextrin cavities with some guest molecules such as cyclohexanol, borneol and ursodeoxycholic acid . ... 

The synthesis and gelation properties of compounds 52-55, containing aromatic chromophores, were reported (Scheme 21). The central unit A of gela-tor 52 is based on two azobenzene chromophores that are connected by a central flexible diamino chain [76]. This compound was observed to gelate various organic solvents, such as 1-hexanol, 1-octanol, toluene, m-xylene, and p-xylene, under 1.0-5.0wt%. As observed in the case of ALS systems, CD spectroscopy pointed to the chiral orientation of 52 molecules within the gel aggregate and TEM photographs showed the occurrence of helical fibers. 

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