Glasses, molecular, azobenzene-containing

Holographic Gratings and Data Storage in Azobenzene-Containing Block Copolymers and Molecular Glasses... 

Azobenzene-containing materials can be classified into two groups polymer-based systems and molecular glasses. Azobenzene chromophore units, which are the optically addressable moiety, can be incorporated into polymer systems in several ways, as is schematically illustrated in Fig. 3. 

Fig. 3 Schematic representation of different polymer materials and molecular glasses containing azobenzene moieties. Azobenzene chromophore units (shaded circles) non-absorbing repeating units of the polymer (open circles) azobenzene-containing molecular glasses (shaded circles enclosing Y )...

Fig. 8 Schematic structure of different topologies of photoaddressable azobenzene containing molecular glasses with two, three, and four azobenzene moieties (open circles) core (filled rectangles) azobenzene chromophore units...

Fig. 11 DSC curves of azobenzene-containing molecular glasses 2-4. Second heating curves at a rate of 10 K min-1 under N2...

Fig. 21 Chemical structures of azobenzene-containing molecular glasses 9a-e based on tripheny-lamine and their glass transition temperatures...

Fig. 22 Temporal evolution of the diffraction efficiency 7] (t) during hologram inscription on a thin film of the azobenzene-containing molecular glass 9b. Writing was performed with the laser polarization configuration 45°. The black triangles corresponds to measured data, whereas the curve represents the fit of (3). In the first few seconds, the diffraction efficiency due to reorientation of the chromophores in the bulk is visible (see inset), later-on the influence of the SRG dominates. (Reprinted with permission from [71]. Copyright 2009 American Chemical Society)...

Assuming the influence of the electric field to be constant and comparing different azobenzene-containing molecular glasses at one given polarization setting, then only the material susceptibility % influences fx. The optical susceptibility can be written as... 

For a comparison of azobenzene-containing molecular glasses three molecular parameters are important absorption coefficient, susceptibility, and volume of the chromophore. The glass transition temperature Tg of the investigated materials has no measurable influence on the formation of SRGs. The Tg values of all materials differ by only 30°C and are well above room temperature, e.g., the lowest Tg was determinded to 89°C for compound 9d. 

We have demonstrated that azobenzene-containing materials can efficiently form holographic SRGs and volume gratings for various kinds of applications. Two material classes, azobenzene-containing block copolymers and molecular glasses, were designed and synthesized and they can find applications in different fields. 

A nnmber of studies probing the underlying physics behind the fight-indnced volume transition of supramolecular azobenzene-containing polymers have been carried out in an attempt to nnderstand the molecular orientation of macromolecnles far below their glass transition temperatures. These theories are beyond the scope of this chapter and for an example of such work, the reader is directed elsewhere." ... 

Audorff, H., Kreger,K., Walker, R., Haarer, D., Kador L. and Schmidt, H. -W. (2010) Holographic gratings and data storage in azobenzene-containing block copolymers and molecular glasses , Adv. Polym. ScL, 228,59-121. 

In order to obtain stable amorphous states of organic materials, the glass transition temperature (Tg) of the materials should be higher than room temperature. Molecular motion is frozen at temperatures below Tg, and crystal growth is suppressed. The Tg of la was found to be lower than room temperature. Although several photochromic amorphous materials containing azobenzene unit have been synthesized, the practical use of amorphous azobenzenes is limited because of thermal instability of the cis-isomer and low reactivity in the solid state. Figure 17.3 shows some molecular structures... 

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