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. 2023 Aug 23;13(1):13766.
doi: 10.1038/s41598-023-40905-z.

Ionic liquids with reversible photo-induced conductivity regulation in aqueous solution

Yige Zhang #  1 , Xiaowen Xie #  1 , Jianliang Liu #  1 , Boyuan Tang  2 , Can Fang  1 , Xiaoming Liu  3 , Zhifeng Dai  4   5 , Yubing Xiong  6   7
Affiliations

Ionic liquids with reversible photo-induced conductivity regulation in aqueous solution

Yige Zhang et al. Sci Rep. .

Abstract

Stimulus-responsive ionic liquids have gained significant attention for their applications in various areas. Herein, three kinds of azobenzimidazole ionic liquids with reversible photo-induced conductivity regulation were designed and synthesized. The change of electrical conductivity under UV/visible light irradiation in aqueous solution was studied, and the effect of chemical structure and concentration of ionic liquids containing azobenzene to the regulation of photoresponse conductivity were discussed. The results showed that exposing the ionic liquid aqueous solution to ultraviolet light significantly increased its conductivity. Ionic liquids with longer alkyl chains exhibited an even greater increase in conductivity, up to 75.5%. Then under the irradiation of visible light, the electrical conductivity of the solution returned to its initial value. Further exploration of the mechanism of the reversible photo-induced conductivity regulation of azobenzene ionic liquids aqueous solution indicated that this may attributed to the formation/dissociation of ionic liquids aggregates in aqueous solution induced by the isomerization of azobenzene under UV/visible light irradiation and resulted the reversible conductivity regulation. This work provides a way for the molecular designing and performance regulation of photo-responsive ionic liquid and were expected to be applied in devices with photoconductive switching and micro photocontrol properties.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Illustration of the photo-regulation aggregation of the ILs in water.
Figure 2
Figure 2
Synthesis of [AzoCnMIm]Br (n = 1, 2, 3) Ionic Liquids.
Figure 3
Figure 3
UV–vis spectra of azobenzene based ionic liquids: [AzoC2MIm]Br ((a) and (b)), [AzoC4MIm]Br ((c) and (d)) and [AzoC6MIm]Br (e and f) in aqueous solutions (3.3 × 10−5 mol L−1) under UV and visible light (indoor natural light) irradiations, respectively.
Figure 4
Figure 4
Reversible conductivity change of (a) [AzoC2MIm]Br, (b) [AzoC4MIm]Br, (c) [AzoC6MIm]Br aqueous solution (3.0 × 10−2 mol L−1) under alternating UV and visible light (indoor natural light) irradiation for 5 h at 25 °C.
Figure 5
Figure 5
The conductivity of azobenzene ionic liquids in aqueous solutions as a function of the concentration at 25 °C. (a) [AzoC2MIm]Br before UV irradiation; (b) [AzoC2MIm]Br after UV irradiation for 5 h; (c) [AzoC4MIm]Br before UV irradiation; (d) [AzoC4MIm]Br after UV irradiation for 5 h; (e) [AzoC6MIm]Br before UV irradiation; (f) [AzoC6MIm]Br after UV irradiation for 5 h.
Figure 6
Figure 6
The SEM images of freeze-dried [AzoC4MIm]Br powders with different concentrations and configurations: (a) 0.005 mol L−1 before UV irradiation ([AzoC4MIm]Br-trans); (b) 0.018 mol L−1 before UV irradiation ([AzoC4MIm]Br-trans); (c) 0.018 mol L−1 after UV irradiation ([AzoC4MIm]Br-cis); (d) 0.080 mol L−1 before UV irradiation ([AzoC4MIm]Br-trans); and (e) 0.080 mol L−1 after UV irradiation ([AzoC4MIm]Br-cis).
Figure 7
Figure 7
(a) Schematic illustration of the conductor and capacitor tests under UV/vis illumination. For the fabrication of capacitor, Ni and silicone were used as the electrodes and dielectric layer, respectively. (b) The change of resistance signal detected by PLA-IL sensor. (UV: λ = 365 nm, 30 mW cm−2; Vis: indoor natural light).
See this image and copyright information in PMC

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