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Cis–Trans Isomerization of Azopolyimides in the Solid State
Published in Andreea Irina Barzic, Neha Kanwar Rawat, A. K. Haghi, Imidic Polymers and Green Polymer Chemistry, 2021
Photoisomerization is a photoinduced reversible transformation of the structure of a chemical compound, associated with a change in the energy state of the molecule due to excitation through the absorption of electromagnetic waves. The consequence of excitation is a change in both spectral and physicochemical properties. Irradiation of compound A with the light of wavelength λ1, another structurally different compound B is formed. The return of compound B to A can occur spontaneously, as a result of thermal relaxation (kT) or as a result of irradiation with radiation of wavelength λ2.10,11 The isomerization process is schematically shown in Figure 3.1.
Ultrafast phenomena: Experimental
Published in Guo-ping Zhang, Georg Lefkidis, Mitsuko Murakami, Wolfgang Hübner, Tomas F. George, Introduction to Ultrafast Phenomena from Femtosecond Magnetism to high-harmonic Generation, 2020
Guo-ping Zhang, Georg Lefkidis, Mitsuko Murakami, Wolfgang Hübner, Tomas F. George
As mentioned in Chapter 1, rhodopsin is the key molecule for our vision. Rhodopsin is not only found in mammals, but also in bacteria. Bacteriorhodopsin is an example, with 15 carbons forming the backbone of the molecule, in contrast to rhodopsin which has 13. Photoisomerization refers to the photon-induced molecular structural change without change in constituents. The molecule may have multiple structures (called isomers), which have different total energies and are on different points on potential energy surfaces.
Preparation and drug release application of pH and light dual-stimuli- responsive nanocarrier based on mesoporous silica nanoparticles
Published in Journal of Dispersion Science and Technology, 2019
Si Chen, Jin Hu, Feng Wang, Hui Liu
Inspired by the above discussions and combined with our previous works,[42–44] we design a light and pH dual-stimuli-responsive drug delivery system based on mesoporous silica nanoparticles which are used to encapsulate doxorubicin hydrochloride (DOX·HCl). DOX·HCl is a typical anticancer drug and it is usually used as the drug model. Initiated group modified MSNs are grafted with photo- and pH-sensitive random copolymer P(SPMA-co-MAA) via surface-initiated atom transfer radical polymerization (SI-ATRP) and chemical hydrolysis.[45–47] The photosensitive SPMA group would undergo the photoisomerization process under the irradiation of ultraviolet (UV) light at 365 nm, leading to the switch from hydrophobic spiropyran (SP) form into hydrophilic merocyanine (MC) form. In neutral or alkaline conditions, the MAA unit chains would be in the swollen state. On the contrary, the polymer wall would be collapsed under acidic environments.
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 photoresponsive properties of the iodine-bonded samples were initially investigated in liquid crystal cells and then in solutions upon irradiation of UV light at 365 nm (80 mW/cm2). As shown in Figure 6(a), the initial POM image was a bright view with a highly birefringent SmA phase at approximately 41°C. Upon photo-irradiation, the small domain of the focal conic fan textures first disappeared, followed by the disappearance of the large intact texture, and finally, only a dark image was observed after 3 s (Figure 6(b)). This indicates the occurrence of a photoinduced phase transition from the liquid crystal to the isotropic phase, which was caused by the photoisomerization of the azopyridine molecules. In other words, the trans form of the azopyridine derivatives have a rodlike shape, which stabilised the liquid crystal phase (Figure 6(a), inset), while the bent-shaped cis isomer of the azopyridine derivatives tends to destabilise the ordered liquid crystal phase [46]. As a result, the liquid crystal phase vanished in response to UV irradiation (Figure 6(b), inset). After withdrawing the UV light, the sample reverted to the original texture of the liquid crystal phase (Figure 6(c)).
Light intensity as mechanical potential: a symmetry-based approach
Published in Liquid Crystals, 2019
Tianyi Guo, Xiaoyu Zheng, Peter Palffy-Muhoray
The responsible physical mechanism here is selective absorption and random orientational diffusion [24]. Azo dyes absorb selectively when the orientation of the absorption moment is parallel to the incoming electric field orientation; this leads to photoisomerization from the elongated trans isomer to the more compact cis form. The cis isomers readily diffuse in orientation space, and decay to the lower energy trans state. Although the detailed dynamics can again be modelled, the simpler symmetry arguments can also be used. Using the same definitions as above, the light-induced torque can be constructed as