China
Africa
Explore chapters and articles related to this topic
Photoresponsive Polymers
Published in Asit Baran Samui, Smart Polymers, 2022
Under UV irradiation the rod-like trans-azobenzene moieties, fitting within the LC polymer arrangement, undergo isomerization to the cis-form. This causes disruption of the homogeneous arrangement and strains the system. The incident light is absorbed by only a thin surface layer with high azobenzene concentration, and the resultant strain is asymmetric as only the surface layer creates strain. This type of strain forces the sample to bend toward the light source for in-plane-aligned mesogens. Continuous irradiation results in photo-induced unbending because the loss of the asymmetric strain after the photostationary state in the cis-azobenzene concentration is reached throughout the film.34 Visible light can also result in unbending via back-isomerization of cis- to trans form. A single nanosecond pulse is enough to bend the sample, with corresponding response below one millisecond duration.
Metal-Containing Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Christopher M. Brown, Michael O. Wolf
Upon excitation with 410 nm light (a wavelength that will not promote the trans-to-cis isomerization of the azobenzene unit), polymers 54a–d all showed fluorescence at λmax = 453, 483, 455, and 454 nm, respectively when dissolved in DMF with an emission attributed to the ILCT band involving the PE and Zn-tpy moieties. The isomerization of 54c to the cis-configuration was achieved in DMF solution by irradiating with light λex = 365 nm and the photostationary state reached after 150 s. Reversing to the trans form on illuminating λex = 455 nm over the same time scale could be achieved over many repetitions with no appreciable degradation seen.
Crystalline Colloidal Array Photonic Crystal Optical Switching
Published in Anwar Sohail, Raja M Yasin Anwar Akhtar, Raja Qazi Salahuddin, Ilyas Mohammad, Nanotechnology for Telecommunications, 2017
Upon UV irradiation, the diffraction blueshifts 5 nm, and additional irradiation with visible light causes an additional 9 nm blueshift (Maurer et al. 2005). Starting at the dark equilibrium state and applying visible light results in the same photostationary state with a 14 nm diffraction blueshift. Irradiating this system with UV light redshifts the diffraction 9 nm (Figure 8.11). This suggests that the concentration of the closed form in the UV photostationary state is between the closed spiropyran-dominated visible photostationary state and the open merocyanine-dominated dark equilibrium state.
Non-linear disulphide-centred S-shaped oligomers with inner and outer spacers connected by aromatic azo moieties
Published in Liquid Crystals, 2023
Pui-Wing Yap, Faridah Osman, Guan-Yeow Yeap, Yoshiyuki Nakamura, Kazuyoshi Kaneko, Akio Shimizu, Masato M Ito
The absorption spectra of 7f recorded under the UV light from 0 s (in the absence of UV light) to 1620 s are shown in Figure 7(a) while the time dependent photoisomerisation curve of compound 7f showing the photostationary state from trans to cis isomer within 1620 s in the presence of UV irradiation is shown in Figure 7(b). Inspection on Figure 7(a) shows that the intensity of absorption band for compound 7f at 325 nm gradually decreases whereas the absorption at 447 nm increases from 0 to 1020 s. At the stationary state, the absorption spectrum shows two maxima at 325 and 447 nm as well as two isobestic points at 270 and 405 nm. The results can be attributed to the trans-to-cis photoisomerisation of the oligomer which absorbs at 365 nm. It can also be generalised from Figure 7(b) that the absorbance of compound 7f decreases within 1620 s when the time increases.
Langmuir and Langmuir–Blodgett films of aromatic amphiphiles
Published in Soft Materials, 2022
Dodero and coworkers have reported a simple azoamphiphile 74 with a nonionic head-group – hydroxyl triethyleneglycol .[127] In the solution phase, 74 exists as a 95:5 (trans:cis) isomeric mixture which on UV irradiation (360 nm) converted to a 10:90 (trans:cis) mixture at photostationary state. Both of these isomeric mixtures formed stable Langmuir films. The trans-rich 74 achieved a greater πc (53 mN/m) compared to the cis-rich isomer (42 mN/m) but had similar Ac value (23 Å2/molecule). BAM imaging revealed that the trans-rich type formed more solid-like monolayer compared to its cis-rich counterpart. The isotherm profile was also studied in the presence of a complex biomimetic membrane lipid (Lipoid s75) which contains 75% phosphatidylcholine (PC). The pure Lipoid s75 had a lower compressibility modulus (45 mN/m) compared to that of a mixture of 74:Lipoid s75 (1:4) (70 mN/m) implying that 74 molecules imparted a more condensed character to the membrane lipid. Photoisomerization proceeded smoothly in vesicles prepared from 20 mol % of 74 in Lipoid s75. DSC and POM studies showed that the vesicles became more condensed during the trans-to-cis photoisomerization step.
Photoresponsive iodine-bonded liquid crystals based on azopyridine derivatives with a low phase-transition temperature
Published in Liquid Crystals, 2019
Meiling Du, Luhai Li, Jingting Zhang, Kexuan Li, Meijuan Cao, Lixin Mo, Guosheng Hu, Yinjie Chen, Haifeng Yu, Huai Yang
The UV-vis absorption spectra of the complex I-A12AzPy before and after UV irradiation in its cyclohexane solution are shown in Figure 7. The absorption peaks of the I-A12AzPy are located at 350 nm due to the π–π* transition and approximately 450 nm due to the n–π* transition before UV irradiation. As shown in Figure 7(a), the absorbance peaks of the π–π* band decreased dramatically, and the n–π* band increased obviously (Figure 4(a) (inset)) upon photo-irradiation for 1 s, indicating the occurrence of an efficient trans-cis photoisomerization. Continuing this light irradiation, there are no significant changes in the UV-vis absorption spectra, indicating that the photostationary state of the trans-cis isomerization was obtained after 3 s of UV irradiation. When the irradiated sample was kept in dark at room temperature, the absorbance peaks were slowly restored because of the cis-trans back-isomerization, as shown in Figure 7(b) [47,48].