Optical suppression of ferroelectricity in polysiloxane copolymers with chiral and photochromic side groups

• Published in: Polymers for advanced technologies Vol. 9; no. 10-11; pp. 665 - 671
• Main Authors: Meier, Johann Georg, Stumpe, Joachim, Fischer, Birgit, Thieme, Cathrin, Fischer, Thomas M., Kremer, Friedrich, Öge, Tanja, Zentel, Rudolf
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-10-1998
• Subjects: azobenzene; ferroelectricity; light-induced phase transition; photochromic polysiloxane; photoisomerization
• ISSN: 1042-7147; 1099-1581
• DOI: 10.1002/(SICI)1099-1581(1998100)9:10/11<665::AID-PAT839>3.0.CO;2-W

The ferroelectricity of surface‐stabilized aligned films of polysiloxane copolymers containing chiral esters and photochromic azobenzene moieties within the side groups is suppressed on UV irradiation and is rebuilt on visible irradiation. The liquid crystalline polymer (Sc* 64 SA 80 i) shows ferroelectric behavior below 64°C. The photoinduced modification of supramolecular order and the corresponding changes in its dynamics are studied by polarized UV/vis spectroscopy and broad band dielectric spectroscopy (10−2–105 Hz). The dielectric measurements show that UV irradiation causes a loss of ferroelectricity within an interval of 10 K below the phase transition temperature. The photochemical change of intermolecular interactions results in the disappearance of the Sc* phase and the Goldstone mode. Polarized absorption spectroscopy indicates the degree of order, the orientational direction as well as the establishment of different steady states of the EZ photoisomerization by UV and visible exposure. The photoisomerization of only a small amount of azobenzene moieties causes a decrease of the phase transition temperature between the ferroelectric Sc* and the nonferroelectric SA mesophase. This is connected with a reversible modification of the degree of order and of the director orientation characteristic for the Sc* and SA phases. Thus, the photoinduced modification of the intermolecular interactions results in an opto‐dielectric effect. © 1998 John Wiley & Sons, Ltd.