Photoinduced Three-dimensional Structures in Amorphous and LC Polymers

Jung, Carl Christoph; Rutloh, Michael; Stumpe, Joachim

doi:10.1080/10587250210553

Cited by 5 publications

(9 citation statements)

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“…The mean absorbance A m decreases for all absorbances with a transition moment parallel to the segmental axis, e.g., ν(C⋮N) absorption band (see Figure a), and increases in the case of bands with a perpendicular transition moment such as the ν(CH 2 ) or ν(CO) bands (not shown here) compared to the isotropic initial state. This is in agreement with the population of a non-rotationally symmetric orientational plane perpendicular to the electric field vector of the incident light at 488 nm, as proposed by other studies, which have applied null ellipsometry and waveguide spectroscopy to study the conventional photoorientation process after laser irradiation. , Or in other words, this means optically that the light-induced order of the film is characterized by two different long axes perpendicular to the E-vector and one short axis parallel to the E-vector (biaxial oblate order).…”

Section: Resultssupporting

confidence: 90%

“…In addition to the orientational direction, the three-dimensional structure of the order photogenerated by the two processes is also different. While the spectral data confirm a uniaxial prolate order as a result of the HeNe laser irradiation, a biaxial oblate order with a preferential out-of-plane component was found in the case of the conventional photoorientation process in the glassy state, which is in agreement with the order detected by waveguide spectroscopy . The difference in the three-dimensional order seems to influence the stability of the induced order.…”

Section: Discussionsupporting

confidence: 79%

“…While the spectral data confirm a uniaxial prolate order as a result of the HeNe laser irradiation, a biaxial oblate order with a preferential out-of-plane component was found in the case of the conventional photoorientation process in the glassy state, which is in agreement with the order detected by waveguide spectroscopy. 34 The difference in the three-dimensional order seems to influence the stability of the induced order. As shown earlier, 2,3 any anisotropy can be erased by heating the sample above the clearing temperature.…”

Section: Discussionmentioning

confidence: 99%

“…This is in agreement with the population of a non-rotationally symmetric orientational plane perpendicular to the electric field vector of the incident light at 488 nm, as proposed by other studies, which have applied null ellipsometry and waveguide spectroscopy to study the conventional photoorientation process after laser irradiation. 33,34 Or in other words, this means optically that the light-induced order of the film is characterized by two different long axes perpendicular to the E-vector and one short axis parallel to the E-vector (biaxial oblate order). Therefore, eq 6 and its assumptions are not valid for the observed orientational state.…”

Section: Uv-vis Spectroscopic Characterization Of Thementioning

confidence: 99%

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Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Zebger¹,

Rutloh²,

Hoffmann³

et al. 2003

Macromolecules

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In contrast to the conventional photoorientation process with blue light, an orientation of 4-cyano-4′-alkoxyazobenzene side groups parallel to the electric field vector of the incident light is generated upon irradiating films of a liquid-crystalline side-chain polymer with linearly polarized red light. The polyester is characterized by smectic and nematic phases g24S X26SA34N46i and a strong tendency to form J-aggregates. The process requires a photochemical pretreatment by irradiation with UV light or an exposure to visible light of high power density to produce a certain concentration of the Z-isomer, which destroys any initial orientational order and J-aggregates. The orientation process is cooperative, whereas the light-induced orientation of the photochromic moiety causes an ordering of the alkylene spacers and even of the main-chain segments into the same direction. The most probable mechanism of this two-step process is the angular-selective transformation of the bulky Z-isomers to the rodlike E-isomeric formed by the red light. The aligned E-azobenzene side groups become strongly J-aggregated. Very high values of dichroism of about 0.8 and birefringence of about 0.3 were generated as a result of this combination of the photoinduced orientation process and the thermotropic selforganization, which take place simultaneously under the irradiation conditions. The process results in a uniaxial prolate order of the film, whereas conventional photoorientation leads to a biaxial oblate order. These two different three-dimensional orders have been characterized by FTIR polarization spectroscopy and exhibit also varying intermediate thermal stabilities.

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Section: Resultssupporting

confidence: 90%

Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Uv-vis Spectroscopic Characterization Of Thementioning

confidence: 99%

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Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Zebger¹,

Rutloh²,

Hoffmann³

et al. 2003

Macromolecules

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“…This corresponds to the induction of an oblate order in the film, i.e. the azobenzene groups are preferably oriented in a plane perpendicular to the electric field vector of the incident light [19].…”

Section: Photoorientation In Polymer F Ilmsmentioning

confidence: 99%

Photoinduced Optical Anisotropy in New Polymers containing Azobenzene Side Groups

Sava¹,

Brumă²,

Köpnick³

et al. 2007

High Performance Polymers

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A series of new photosensitive polymers have been synthesized by polycondensation reaction of 2,2-bis{3-amino-4-[( p-oxyhexyloxy- p'-butoxy)azobenzene]-phenylene}-hexafluoropropane or 2,2-bis{3-amino-4-[( p-oxybutyloxy- p'-phenyl)azobenzene]-phenylene}-hexafluoropropane with hexafluoroisopropylidene diphthalic anhydride or with a diacid chloride containing hexafluoroisopropylidene or dimethylsilane groups. These amorphous polymers have good solubility in organic solvents and good film-forming properties. The irradiation of polymer films with linearly polarized visible light causes a reorientation of the azobenzene groups by angular-selective E/Z photoisomerization. Thus, optical anisotropy is induced in the initially isotropic films. The photoinduced dichroism in the films was measured and the results are discussed with respect to the polymer structure.

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The Generation of Three-dimensional Anisotropies in Thin Polymer Films by Angular Selective Photoproduct Formation and Annealing

et al. 2005

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Linearly polarized light can induce an order parallel to the polarization direction of light in polymer films containing different photochromic groups. In principle, this offers the possibility to generate prolate in-plane orders in polymer films. Two such photochemical processes are investigated in this paper. One of them is the irradiation of azobenzene-containing polymer films with linearly polarized red light after an unpolarized UV preirradiation step. The other one is the angular selective photocycloaddition of cinnamate-containing polymer films induced by linearly polarized UV light. Because in both cases the order is low after the irradiation, the liquid crystalline polymer films are annealed in their mesophase to modify the photoinduced order by thermotropic self-organization. The resulting threedimensional indicatrices, as determined by waveguide spectroscopy, are found to be prolate in-plane, biaxial, or homeotropic in dependence on the polymer structures, preparation conditions, and irradiation conditions of the films.

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Photoinduced Three-dimensional Structures in Amorphous and LC Polymers

Cited by 5 publications

References 0 publications

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Photoinduced Optical Anisotropy in New Polymers containing Azobenzene Side Groups

The Generation of Three-dimensional Anisotropies in Thin Polymer Films by Angular Selective Photoproduct Formation and Annealing

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