Photoinduced cooperative molecular reorientation on azobenzene side-chain-type copolymers

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 183; no. 3; pp. 273 - 279
• Main Authors: Fukuda, Takashi, Kim, Jun Young, Barada, Daisuke, Yase, Kiyoshi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.10.2006
• Subjects: Azobenzene copolymer; Holographic data storage; Molecular reorientation; Photoinduced birefringence; Photoinduced cooperative motion; Photoinduced cooperative motion; Photoinduced birefringence; Molecular reorientation; Azobenzene copolymer; Holographic data storage
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2006.06.012

In order to improve the value of photoinduced birefringence and the long-term stability of azobenzene copolymer, two series of azobenzene side-chain-type copolymers consisting of two repeating units, one bearing cyanoazobenzene (or cyanoazopyridine) and the other bearing a long π-conjugated chromophore (bisazobenzene), have been synthesized and compared with respect to their photoinduced birefringence characteristics. Consequently, a fairly large value (observed highest value was 0.244) and superior stability (initial relaxation value was less than 0.2%) of photoinduced birefringence have been achieved. Furthermore, unusual behavior of the photoinduced birefringence depending on the copolymerization ratio of the two chromophores has been found, i.e., a sharp peak of the photoinduced birefringence has been observed at a copolymerization ratio of around 50:50 mol%. This phenomenon could be attributed to mutual promotion of the photoinduced molecular reorientation process, that is cooperative molecular motion, taking place at a specific stoichiometric composition ratio of the two chromophores.