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.
Highlights
The molecular design and synthesis of multifunctional polymeric materials have received much attention because of their favorable properties in a variety of fields [1,2,3,4,5,6]
Depicts the Fouriertransform transform infrared infrared (FTIR) spectra of azobenzene monomer 4-methoxy-40 -hydroxyazobenzene (Azo)/polyethylene glycol (PEG) complexes with various Azo contents, which are Discussion presented in weight percentage
When the Azo/PEG complex was dissolved in benzene, toluene, and CH2 Cl2, the photoisomerization rate of the Azo/PEG complex decreased compared with that of the neat Azo in these solvents. Such behavior was attributed to the hydrogen-bonding interaction between Azo and PEG, which hindered the rotation and inversion of azobenzene molecules, thereby reducing the photoisomerization rate of the complex
Summary
The molecular design and synthesis of multifunctional polymeric materials have received much attention because of their favorable properties in a variety of fields [1,2,3,4,5,6]. Photoinduced properties of azobenzene-containing polymers originate from the photoisomerization of azobenzene mesogens. When azobenzene-containing polymers are irradiated with ultraviolet (UV) light, the trans-to-cis isomerization of mesogens is triggered. Cis-to-trans isomerization can be induced with visible light irradiation. Photoisomerization simultaneously changes the molecular shape of mesogens, which in turn alters the dipole moments of azobenzene-containing materials [12]. The alignment of azobenzene mesogens in mesophases may be achieved by applying linearly polarized light [13,14,15,16]. The absorbance of azobenzene-containing polymers strongly depends on the aggregation state of azobenzene chromophores.
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