Creation via Hybridization: Highly Efficient Switch of Water-Insoluble Azobenzene on Gold Nanoparticle Surface in Aqueous Media
Photoswitchable molecules, which can be reversibly switched between two states by light, have been a highly topical research field due to their great potential in a wide range of applications.[1] Azobenzenes displaying reversible trans-cis photoisomerization represent a classical type of photoswitches[2] and have been explored for regulating assembly/disassembly of gold nanoparticles in organic solvents, displaying versatile functions in re-writeable materials,[3] trapping of molecules[4] as well as catalysis[4]. However, many practical applications, especially those related to biological processes, requires water, instead of an organic solvent, as a media. Hybridization between different components offers the possibility for the maximum optimization of the materials properties. Here, in this work, water-insoluble azobenzene thiol ligands and water-soluble background ligands were co-immobilized onto the surfaces of 2.5 nm-sized gold nanoparticles. The obtained hybrid monolayer protected gold nanoparticles show excellent water solubility even when the surface coverage of azobenzene is as high as 36%, 60%, and 85% for the azobenzenes bearing an alkyl chain, an oligo(ethylene glycol) chain, and an alkyl chain and a cationic charge, respectively. Upon irradiation with low-intensity UV light (< 0.7 mW/cm2) for less than 10 min, the azobenzene reaches the photo stationary state consisting more than 90% cis-isomer and less than 10% trans-isomer. Subsequent illumination of the sample with visible or blue light can generate ca. 15% cis-isomer and 85% trans-isomer. The photo-switchability doesn’t show any decay even after 10 reversible cycles. It was observed that the half-life of the cis-isomer can be tuned by two orders of magnitudes by just altering the background thiol ligands.
References
[1] A. H. Gelebart, et al., Nature 2017, 546, 632.
[2] R. Klajn, et al., Chem. Soc. Rev. 2010, 39, 2203.
[3] R. Klajn, et al., Angew. Chem. Int. Ed. 2009, 48, 7035.
[4] R. Klajn, et al., Nat. Nanotech. 2016, 11, 82.
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