An unusual behaviour has been observed in the photo-indueed response of an azobenzene side chain liquid erystalline polyester (P6d4). Room temperature irradiation with linearly polarised 488 nm light does not induce any birefringence (An) in films of this polymer that have been quenehed from the isotropie state. However, using the same irradiation conditions An is indueed in quenehed films that have been kept in darkness for a few minutes. Besides, no photo-induced An is observed in films irradiated with 488 nm light that have been previously irradiated with UV light. In this ease, An can be reeorded if the UV irradiated films have been kept in darkness for several hours. In another set of experiments performed with the P6d4 polymer, irradiation with high intensity linearly polarised 488 nm light induces an initial increase of An and then it goes back to zero. Subsequent irradiation with linearly polarised 633 nm light induces an orientation of the azobenzene ehromophores perpendicular to the polarisation of the 488 nm light and independent of the 633 nm light polarisation direetion. These results are very different from those obtained lis other side chain polyesters whieh only differ from P6d4 in the end substituent. The anornalous behaviour of P6d4 is discussed in terms of a supercooling effect of the isotropic phase, the trans to cis back isomerization, the trans aggregation kinetics and a memory effect associated with the main ehain orientation.
|Journal||European Polymer Journal|
|Publication status||Published - 2006|
- Azobenzene, Polyesters, Photo-induced optical anisotropy