Abstract
Azobenzene (AZO) has attracted increasing interest due to its reversible structural change upon a light stimulus. However, poor fatigue durability and the photobleaching phenomenon restricts its further application. Herein, the AZO domain as a pendent group, was incorporated into copolymers, which was synthesized by radical copolymerization in the research. Structure-properties of synthesized copolymer can be adjusted by monomer ratios. Emphatically, responsive properties of copolymer in different solutions were investigated. In the DMSO solution, copolymer exhibited effective structural change, stable rapid responsive time (1 min) upon UV light at room temperature, stable relative acceptable recovery time (100 min) upon white light at room temperature, and good fatigue resistance property. In an aqueous solution, even more controllable responsive properties and fatigue resistance properties for copolymer were verified by results. More pervasively, the recovery process could be controlled by light density and temperature. In order to clarify reasons for the difference between the AZO molecule and the AZO domain of copolymer, energy barrier or interactions between single atoms or even structural units was calculated using the density functional theory (DFT). Furthermore, the status of copolymer was characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Finally, copolymer was further functionalized with bioactive protein (concanavalin, ConA) to reduce the cytotoxicity of the AZO molecule.
Highlights
Effective structural change, stable rapid responsive time, stable enough/controllable operation time and fatigue resistance are all desirable properties for a photo switch. These results revealed that the synthesized copolymer in the dimethyl sulfone (DMSO) solution exhibited typical characteristics of photo switch, which was superior to an unmodified AZO small molecule with an obvious photobleaching phenomenon and an uncontrollable response/recovery process according to our previous research (Pang et al, 2018)
AZO-HEMA-NVP-NAS copolymers were successfully synthesized by radical copolymerization with controllable domain content by monomer ratios
Fatigue resistance was observed, which further confirmed the excellent performance of copolymer as a photo switch
Summary
Photo molecular switches can reversibly exhibit different properties due to their structural changes upon a light stimulus, making them new favorites in recent decades in fields that require switching effects, such as information science and chemical sensing (Sun et al, 2012; Yuan et al, 2014; Chiang and Chu, 2015; Kim et al, 2015; Bian et al, 2016a). Besides the above-mentioned performance in the DMSO solution, effects of light density and temperature on cis-to-trans recovery time was tracked and recorded. 2,455 1,588 1,299 blue shifted from 360 to 346 nm which might be attributed to the copolymer structural response upon UV light stimulations, since the phenomenon was not found in AZO small molecules according to our previous research (Pang et al, 2018).
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