Photoinduced optical anisotropy in films of photochromic liquid crystalline polymers

Fischer, Tony; Läsker, Lutz; Stumpe, Joachim; Kostromin, S. G.

doi:10.1016/1010-6030(94)01056-0

Cited by 122 publications

(94 citation statements)

References 9 publications

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“…In the process of reorientation of AZ-containing LCPs, important factors have been intensively studied, including the AZ contents, [ 106 ] enthalpy changes during phase transitions, [ 107 ] morphology of samples before irradiation, [ 108 ] intensity of actinic LPL, [109a] spacer length of side-chains in LCPs. [109b] In addition, structural effects of AZ moieties on photoalignment behavior have been systematically explored in a series of sidechain LCPs with different AZ moieties.…”

Section: Homopolymersmentioning

confidence: 99%

Photocontrollable Liquid‐Crystalline Actuators

2011

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Section: Homopolymersmentioning

confidence: 99%

Photocontrollable Liquid‐Crystalline Actuators

2011

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“…In the past years this spatial character of the photoinduced anisotropies has not received much attention and, until recently, it has been neglected in the bulk of experimental and theoretical studies of POA in azobenzene containing polymers [4,12,13,14,19,20,21,22,23,24]. On the other hand, the problems related to the 3D orientational structures in polymeric films are currently of considerable importance in the development of new compensation films for liquid crystal (LC) displays [25] and the pretilt angle generation by the use of photoalignment method of LC orientation [26].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation (angular redistribution of trans chromophores) or photoselection (angular selective trans-cis isomerization) mechanisms depending on the wavelength. At early stages of irradiation the films of both azopolymers are biaxial. This biaxiality disappears on reaching a state of photo-saturation. In the regime of photoselection the photo-saturated state of the film is optically isotropic. But, in the case of the photo-reorientation mechanism, anisotropy of this state is uniaxial with the optical axis dependent on the preferential alignment of azochromophores. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.

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“…This effect provides a means of having the lightcontrolled anisotropy and it makes the materials that exhibit POA very promising for use in many photonic applications [1,2]. Owing to extremely high efficiency of POA in side-chain polymers that contain covalently linked photochromic moieties such as azobenzene derivatives and are known as azopolymers, light induced ordering processes in these polymers have been the subject of intense experimental and theoretical studies in the last decade [2,3,4,5,6,7,8,9,10,11].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of photoinduced anisotropy in azopolymers: models and mechanisms

Kiselev

2002

J. Phys.: Condens. Matter

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We consider the effect of photoinduced optical anisotropy (POA) in azopolymers. Using a unified approach to the kinetics of photo-reorientation we discuss the assumptions underlying the known theoretical models of POA and formulate a tractable phenomenological model in terms of angular redistribution probabilities and order parameter correlation functions. The model takes into account biaxiality effects and long term stability of POA in azopolymers. It predicts that under certain conditions two different mechanisms, photoorientation and photoselection, will dominate POA depending on the wavelength of pumping light. By using available experimental data, we employ the model to compute dependencies of principal absorption coefficients on the illumination time. Our calculations clearly indicate the different regimes of POA and the numerical results are found to be in good agreement with the experimental data.

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Photoinduced optical anisotropy in films of photochromic liquid crystalline polymers

Cited by 122 publications

References 9 publications

Photocontrollable Liquid‐Crystalline Actuators

Photocontrollable Liquid‐Crystalline Actuators

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Kinetics of photoinduced anisotropy in azopolymers: models and mechanisms

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