Hydrogen Bonding-Induced Assembled Structures and Photoresponsive Behavior of Azobenzene Molecule/Polyethylene Glycol Complexes

Abstract

We investigated the self-assembled structures and photoresponsive and crystallization behaviors of supramolecules composed of 4-methoxy-4′-hydroxyazobenzene (Azo) molecules and polyethylene glycol (PEG) that were formed through hydrogen-bonding interactions. The Azo/PEG complexes exhibited the characteristics of photoresponse and crystallization, which originated from Azo and PEG, respectively. When Azo/PEG complexes were dissolved in solvents, hydrogen-bonding interaction hindered the rotation and inversion of mesogens, causing a reduction in the photoisomerization rate compared with the photoisomerization rate of the neat Azo. The confinement of Azo/PEG complexes in thin films further resulted in a substantial decrease in the photoisomerization rate but an increase in the amounts of H-aggregated and J-aggregated mesogens. Regarding PEG crystallization, ultraviolet irradiation of Azo/PEG complexes increased the quantity of high-polarity cis isomers, which improved the compatibility between mesogens and PEG, subsequently increasing the crystallization temperature of PEG. Moreover, the complexation of Azo and PEG induced microphase separation, forming a lamellar morphology. Within the Azo-rich microphases, mesogens aggregated to form tilted monosmectic layers. By contrast, PEG crystallization within the PEG-rich microphases was hard confined, indicating that the domain size of the lamellar morphology was unchanged during PEG crystallization.

Photoinduced Alignment under Solvent Vapor Annealing (PA-SVA): Enhanced Ordering and Patterning in Block Copolymer Films

“…Figures e and f display the FTIR spectra of the PS- b -PEO/4AzOH complexes with various 4AzOH contents (molar ratio of EO to 4AzOH). When the amount of 4AzOH increases, the transmittance at the wavenumber of 1066 cm –1 shifts to the wavenumber of 1102 cm –1 , caused by the supramolecular interactions (hydrogen bonding) between the ether groups of PEO chains and the phenol groups of the 4AzOH molecules . The formation of hydrogen bonds also cause the peak shift to a higher frequency (from 5.3 to 5.5 ppm) in NMR spectra due to the deshielding effect, as shown in Figure S1 …”

“…When the amount of 4AzOH increases, the transmittance at the wavenumber of 1066 cm −1 shifts to the wavenumber of 1102 cm −1 , caused by the supramolecular interactions (hydrogen bonding) between the ether groups of PEO chains and the phenol groups of the 4AzOH molecules. 18 The formation of hydrogen bonds also cause the peak shift to a higher frequency (from 5.3 to 5.5 ppm) in NMR spectra due to the deshielding effect, as shown in Figure S1. 19 XPS measurements are performed to study the differences in binding energies between the neat PS-b-PEO, 4AzOH, and PSb-PEO/4AzOH complexes.…”

Polymeric Self-Assemblies Based on tetra-ortho-Substituted Azobenzene as Visible Light Responsive Nanocarriers

“…The spectra of the self-assemblies (both micelles and vesicles) aqueous dispersions showed a blue shift of the π-π* band maximum from 360 nm to 320 nm indicative of the prevalent formation of H-aggregates of azobenzene units (Figure 2). Moreover, two weak shoulders were observed, one at 360 nm associated to the non-aggregated azobenzenes and one at 375 nm arising the formation of J-aggregates [19,[33][34][35][36][37]. Upon UV illumination, a decrease on the intensity of the π-π* band with a concurrent increase in the absorbance at 450 nm was monitored and associated to the trans-cis photoisomerization and changes of the azobenzene aggregation.…”

Strategies for Incorporating Graphene Oxides and Quantum Dots into Photoresponsive Azobenzenes for Photonics and Thermal Applications

“…Azobenzene moieties, like most other chromophores with an extended π system, are sensitive to packing and aggregation effects due to chromophore-chromophore intermolecular interactions [89,90]. The nature of these interactions and the packing arrangement of the chromophores depend on the structure and physical properties of the chromophores as well as on their local environment [91]. Proximity of the chromophores to one another leads to extensive changes in their electronic transition energies.…”