Thermal amplification of photoinduced optical anisotropy of <i>p</i>-cyanoazobenzene polymer films monitored by temperature scanning ellipsometry

Kidowaki, Masatoshi; Fujiwara, Takenori; Morino, Shin’ya; Ichimura, Kunihiro; Stumpe, Joachim

doi:10.1063/1.126037

Cited by 48 publications

(44 citation statements)

References 12 publications

(16 reference statements)

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“…3 exhibits a high thermal stability up to 280°C due to its high glass-transition temperature. 23 Photopatterning dichroic dye molecules onto the photoalignment azobenzene-containing layer can fabricate a polarizer film.…”

Section: ç Photoalignment For Liquid Crystalsmentioning

confidence: 99%

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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Photosensitive materials for photoalignment of liquid crystals (LCs) and photoinduced molecular reorientation are described, especially focusing on azobenzene-containing materials and photocrosslinkable polymers. All the materials generate photoinduced optical anisotropy by means of linearly polarized (LP) light exposure. The large optical anisotropy is induced when the axis-selective photoreaction is accompanied by molecular reorientation. Ç IntroductionDue to practical applications of the alignment layer of functional materials such as low-molecular-weight liquid crystals (LCs), photoalignment and photoinduced molecular reorientation of photosensitive films have received much attention. 13 Additionally, these films have been investigated for molecularly oriented birefringent devices due to the absence of mechanical damage, absence of electric charge, and patterning ability.13 Photoinduced optical and physical anisotropies can be generated in a photoreactive polymeric film by light exposure because the photoreaction changes the inherent refractive index of the molecules. Irradiating with linearly polarized (LP) light causes the photosensitive molecules parallel to the polarization (E) of LP light (y axis) to preferentially photoreact (Figure 1). This axis-selective photoreaction leads to optical anisotropy (birefringence) between the y axis and xz plane if the photoreaction changes the inherent refractive indices of the molecules.To obtain uniaxial alignment of LCs on thin polymeric films, the LC photoalignment layer should exhibit optical or physical anisotropy. Under this circumstance, a large molecular orientation of the film is unnecessary. The anisotropic interaction between the photoalignment layer and LC molecules induces uniaxially oriented LC molecules.1 Because the axis-selective photoreaction induces a small change in the refractive index of the photoalignment layer, 4 a thick film is necessary for optically anisotropic devices such as a birefringent film. Consequently, a large optical anisotropy in the photoreacted film is generated when molecular reorientation occurs during an anisotropic photoreaction. 3Various types of materials that undergo an axis-selective photoreaction to generate photoinduced optical anisotropy have been investigated, including azobenzene-containing polymers 2,57 and photocrosslinkable polymers. 1,3,4 For the azobenzene molecules, axis-selective photoisomerization is generated when the film is irradiated with linearly polarized (LP) light (Figure 2a). Similarly, irradiating with LP ultraviolet (LPUV) light induces both axis-selective [2 + 2] photo/cycloaddition (photocrosslinking) reaction and photoisomerization for cinnamic ester derivatives (Figure 2b). Low-molecular LC molecules easily align on these anisotropically photoreacted films. When an axis-selective photoreaction occurs without generating molecular reorientation, the photoinduced birefringence (¦n) is less than 0.01. 4 An anisotropic photoreaction combined with molecular motion may generate a large optica...

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Section: ç Photoalignment For Liquid Crystalsmentioning

confidence: 99%

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Kawatsuki¹

2011

Chemistry Letters

116

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“…[6][7][8][9][10][11][12][13][14][15] High and stable values of birefringence have been obtained in liquid crystalline homopolymers with azobenzene side units due to the strong interaction between chromophores. 8,9 In spite of these good properties, the use of these liquid crystalline materials is inherently limited to thin grating recording. This limitation is due to the fact that liquid crystalline microdomains produce light scattering, decreasing the optical quality of films as thickness increases.…”

Section: Pulsed Recording Of Anisotropy and Holographic Polarization mentioning

confidence: 99%

“…[1][2][3][4][5] The interaction of light with properly engineered azobenzene containing materials has demonstrated to be an effective and elegant tool to modulate their optical and mechanical properties. [6][7][8][9][10][11][12][13][14][15][16][17][18] In particular, an intense investigation has been performed on the optical anisotropy induced by polarized light in azobenzene side chain polymers, due to its potential application in reversible optical storage technologies. Linearly polarized light in the bluegreen region selectively induces isomerization of azo molecules with their absorption transition dipole moment having a component parallel to the light polarization direction.…”

Section: Pulsed Recording Of Anisotropy and Holographic Polarization mentioning

confidence: 99%

Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

Forcén

Oriol

Sánchez

et al. 2008

Journal of Applied Physics

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Recording of anisotropy and holographic polarization gratings using 532 nm, 4 ns light pulses has been carried out in thin films of polymers with the same azobenzene content ͑20 wt % ͒ and different molecular architectures. Random and block copolymers comprising azobenzene and methylmethacrylate ͑MMA͒ moieties as well as statistical terpolymers with azobenzene, biphenyl, and MMA units have been compared in terms of recording sensitivity and stability upon pulsed excitation. Photoinduced anisotropy just after the pulse was significantly higher in the case of the block copolymers than in the two statistical copolymers. The stability of the recorded anisotropy has also been studied. While a stationary value of the photoinduced anisotropy ͑approximately 50% of the initial photoinduced value͒ is reached for the block copolymer, photoinduced anisotropy almost vanished after a few hours in the statistical copolymers. Polarization holographic gratings have been registered using two orthogonally circularly polarized light beams. The results are qualitatively similar to those of photoinduced anisotropy, that is, stability of the registered grating and larger values of diffraction efficiency for the block copolymer as compared with the random copolymers. The recording of holographic gratings with submicron period in films several microns thick, showing both polarization and angular selectivity, has also been demonstrated. Block copolymers showed a lamellar block nanosegregated morphology. The interaction among azo chromophores within the nanosegregated azo blocks seems to be the reason for the stability and the photoresponse enhancement in the block copolymer as compared with the statistical ones.

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“…[12][13][14] Furthermore, by annealing at elevated temperatures, the orientational order of the films is often enhanced. [11,[13][14][15] In contrast, we have studied thermally enhanced molecular reorientation in PLC films with a photo-cross-linkable 4-cinnamoyloxyethoxybiphenyl (4CEB) mesogenic side group by irradiating with a linearly polarized ultraviolet (LPUV) light and subsequent annealing. [16][17][18][19][20] Unlike the reorientation behavior of PLC with azobenzene groups, PLC with 4CEB generates an in-plane reorientation parallel to E. Thus a thermally stable birefringent film can be achieved because of its cross-linked structure.…”

Section: Introductionmentioning

confidence: 95%

Control of In‐Plane and Out‐Of‐Plane Reorientation in Photo‐Cross‐Linkable Copolymer Liquid‐Crystal Films by Irradiation with Linearly Polarized Ultraviolet Light and Annealing

Kawatsuki

Furuso

Uchida

et al. 2002

Macro Chemistry & Physics

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This paper describes thermally enhanced in‐plane and out‐of‐plane reorientation of mesogenic groups in copolymer liquid‐crystal (CPLC) films that have a photo‐cross‐linkable 4‐(4′‐methoxycinnamoyl)biphenyl (MCB) side group and a 4‐methoxybiphenyl (4MB) side group. The side groups are cross‐linked by irradiation with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Due to axis‐selective photo‐cross‐linking, a small negative optical anisotropy is observed for all CPLCs after exposure to LPUV light. When the composition of the 4MB comonomer is less than 45 mol‐%, thermal treatment in the liquid‐crystalline temperature range causes in‐plane reorientation of the film and results in an in‐plane order parameter of 0.71. In contrast, when the composition of the 4MB is increased, out‐of‐plane reorientation is generated. Three‐dimensional molecular reorientation and inclined out‐of‐plane reorientation are achieved by adjusting the exposure angle. Angular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.magnified imageAngular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.

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Thermal amplification of photoinduced optical anisotropy of p-cyanoazobenzene polymer films monitored by temperature scanning ellipsometry

Cited by 48 publications

References 12 publications

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

Control of In‐Plane and Out‐Of‐Plane Reorientation in Photo‐Cross‐Linkable Copolymer Liquid‐Crystal Films by Irradiation with Linearly Polarized Ultraviolet Light and Annealing

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