Azobenzene optical data storage

FiaaHy, the use of photoreversible change of the circular dichroism for optical data storage is of iaterest. This technique offers an advantage over photochromic materials ia that the data can be read ia a way that does not damage the stored information. These chirooptic data storage devices have been demonstrated with the example of chiral peptides with azobenzene side groups (155). 

Weener et al. prepared photo-responsive monolayers from azobenzene modified polypropylene imine) dendrimers which also hold promise in the area of optical data storage [74], A fifth generation polypropylene imine) dendrimer was functionalized with equal amounts of palmitoyl and azobenzene containing alkyl chains, resulting in the formation of an amphiphilic copolymer with a random shell structure (Figure 16.5). 

Very recently, the azobenzene norbornene derivative XI (Scheme 2) was successfully prepared and polymerized with initiator 5 and 9, and it showed a nematic mesophase. The polymer was photo-switchable due to photo cisltrans-isomerization of the N=N double bond [65]. This is the first step towards ROMP-derived materials that may be used for optical data storage. 

PHOTOCHROMIC POLYMERS FOR OPTICAL DATA STORAGE AZOBENZENES AND PHOTODIMERS... 

This chapter discusses photochromic azobenzene polymers and photochromic molecules capable of undergoing photodimerization as materials for potential use in optical data storage applications. A brief introduction to photochromism, including recent examples of some photochromic systems, other than azobenzenes, based on variety of applications is presented at the outset. Thereafter, we shall focus on azobenzene photoaddressable polymers (PAPs) and [4 + 4]-photocycloaddition as materials for ultrahigh capacity optical data storage. 

We shall now embark on the main focus of this chapter photochromic azobenzene polymers and photochromic materials capable of undergoing photodimerization for potential use in optical data storage applications. Herein, the photochromic polymers described are those in which the photochromic molecule is covalently linked, either as part of the main chain or as a side-chain, to the polymeric system. 

Three-dimensional optical data storage using photochromic materials (spirobenzopyrans, dihetarylethenes, azobenzene derivatives 00CRV1777. 

For optical data storage, photosensitive hairy rod LBK structures can be constructed by incorporating photochromic molecules in the side chains [53-55]. The azobenzene molecules undergo transcis photoisomerization under irradiation of photoactive light with an appropriate wavelength, as detailed in the second section of this paper. This photochemical reaction has been shown to alter the structural properties of hairy rod LBK films, which have been investigated by using FT-IR and UV-VIS spectroscopies and X-ray reflectometry [54]. 

Thus, potential application of the ISA complexes for optical data storage has also been demonstrated. Photoreorientation of the induced optical structures in the complexes has been successfully achieved. Well-defined optical patterns were obtained when a second irradiation was applied through a standard photomask (Fig. 2.12c,d). Induction of optical phase gratings in films of the azobenzene-containing ISA complexes was also observed. A diffraction efficiency (DE) of approximately 7% was obtained on 100-nm thick films (calculated value of An that corresponds to this efficiency is 0.54) of the EO-FCigD complex after irradiation with two circularly polarized interfering beams of an Ar laser. 

Chaput F, Lahld K, Biteau J, BoUot J P, Darracq B, Levy Y, Peretti J, Safarov VI, Lehn J M, Fernandez Acebes A. 2000. Design of optical components and optical data storage in photochromic sol gel films containing dithienylethene or azobenzene derivatives. Proc SPIE 3943 32 37. 

Astrand PO, Ramanujam PS, Hvilsted S, Bak KL, Sauer SPA. 2000. Ab initio calculation of the electronic spectrum of azobenzene dyes and its impact on the design of optical data storage materials. J Am Chem Soc 122 3482 3487. 

Amorphous polymers with pendant azobenzene groups were demonstrated to be good candidates for optical data storage and other electrooptic applications. One such material can be illustrated as follows ... 

These modifications include variations on the length of the spacer which connects the azobenzene and the polymeric chain in side-chain azopolymers, or the electronic nature of substituents at the azobenzene moiety (Ruhmann, 1997). This requires the synthesis of appropriate monomers. Conventional techniques can be used for the polymerization of azobenzene monomers. For instance, step polymerization has been used by Hvilsted and co-workers to synthesize different series of liquid crystalline polyesters with potential applications in reversible optical data storage. These polyesters have a side-chain architecture, which synthesis is represented in Fig. 16.6 (Hvilsted et al, 1995). Being a modular synthetic approach, the influence of different structural parameters on the photoinduced optical properties can be evaluated in relatively simple manner. 

Other complex architectures, such as azobenzene star polymers (Angiolini et al, 2006) and molecular brushes (Lee et al, 2006a), have also been prepared, although their optical data storage capabilities have not yet been explored. Advances in these new macromolecular architectures are generally based on the combination of CRP and click chemistry reactions as a synthetic tool for achieving more complex smart polymers. 

Smart photoaddressable polymers containing azobenzene units have been actively investigated over more than two decades as media for optical data storage. Information can be recorded in these materials, through the effect of... 

Many studies have been directed toward utilizing azobenzene photochromism in optical data storage devices. However, thermal Z—isomerization limits the stability of the Z-isomer and causes information loss. Application of low temperatures is not an alternative for practical reasons. Embedding the photoactive molecules into more rigid matrices improves the stability of such photoswitches. Azobenzene included in microporous zeolites of different structures, such as AIPO4-5 and ZSM-5, shows reversible... 

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