Photoinduced birefringence azobenzene polymers

C Wang, H Fei, Y Qiu, Y Yang, Z Wei, Y Tian, Y Chen, and Y Zhao, Photoinduced birefringence and reversible optical storage in liquid-crystalline azobenzene side-chain polymers, Appl. Phys. Lett., 74 19-21, 1999. 

The photoselection in azobenzene polymers (Figure 11) is rather a general phenomenon.77-84 Systematic studies have been conducted by Natansohn and coworkers on the photoinduced molecular reorientation of azobenzene units to induce birefringence and dichroism of thin films of acrylate amorphous polymers with Dispose Red (DR) pendant residues, which have been attracting extensive... 

Molecular glasses can be envisioned for the same applications as photoad-dressable polymers, but they have been studied far less extensively. It has been demonstrated that photoinduced birefringence can also be generated in thin films of azobenzene-based molecular glasses [54-58], Like homopolymers, they form SRGs in addition to gratings in the volume when illuminated with two interfering laser beams. 

Silva JR, Dall Agnol FF, Oliveira ON Jr., Giacometti JA. 2002. Temperature dependence of photoinduced birefringence in mixed Langmuir Blodgett (LB) films of azobenzene containing polymers. Pol5uner 43(13) 3753 3757. 

We have studied pMEA, pMAEA and pDRlM in comparison, in order to determine what is the importance of Rau s classification on the photoinduced birefringence. These three polymers have increasing dipole moments, and their comparison clearly indicate that the pseudostilbene -type azobenzenes are the best candidates for photoinduced orientation. Their absorbance in the visible range of the spectrum allows the use of lower power lasers (514 nm), the coincidental absorbances of the cis and trans isomers allows photoexcitation of both trans-cis and cis-trans isomerization processes. Both are necessary for orientation, and the lower the polarity of the azobenzene, the slower the cis-trans thermal isomerization process. The levels, rates and stabilities of the photoinduced birefringence, all are hi er for pDRlM in comparison with the other two, as is the efficiency of the process. Almost all our research is concentrated on the donor-acceptor substituted azobenzenes. 

In the case of pMNAP, the azobenzene group is tethered to the main chain by two bonds, and the spacer allowing some motion is much shorter than in all the previously analyzed polymers. Again, due to this structural feature, the Tg of the polymer is much higher, and so are the levels of photoinduced birefringence and its stability in the absence of light. 

This enzymatically synthesized azophenol polymer has an extremely high dye content (nearly 100%) and is soluble in most polar organic solvents. It forms good optical quality thin films. Polymer solutions show reversible trans to cis photoisomerizations of the azobenzene groups with long relaxation time. The poly(azophenol) films also exhibit photoinduced absorption dichroism and large photoinduced birefringence with unusual relaxation behavior. 

Yu, Fi. F. Kobayashi, T. Ge, Z. (2009c). Precise Control of Photoinduced Birefringence in Azobenzene-Containing Liquid-Crystalline Polymers by Post Functionalization" Macromol. Rapid Commun., 2009, 30,1725-1730. 

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