Light-Tunable Plasmonic Nanoarchitectures Using Photosensitive Gold-Surfactant Complexes

Liudmila Lysyakova Department of Experimental Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Department of Soft Matter Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Nino Lomadze Department of Experimental Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Alexey Kopyshev Department of Experimental Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Ksenia Maximova LP3 UMR 7341, Aix Marseille University, CNRS, Marseille, France Andrei Kabashin LP3 UMR 7341, Aix Marseille University, CNRS, Marseille, France Dieter Neher Department of Soft Matter Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Svetlana Santer Department of Experimental Physics, Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany

Surfactant molecules carrying photosensitive azobenzene units have attracted considerable interest due to their versatile applications in the field of light controlled shape and functionality of soft nano-objects.^1,2 Azobenzenes are known to undergo trans-cis isomerization under irradiation with light, serving therefore a photo-trigger for the hydrophobicity of the surfactant. In this work we demonstrate how azobenzenes offer controllable plasmonic response in "hard" nano-objects.

Here, we present the results of a comprehensive study of the optical and structural properties of complexes formed between gold nanoparticles (10 nm average diameter) and azobenzene-containing cationic surfactant molecules, employing UV-Vis absorption spectroscopy, dynamic light scattering and electron microscopy. Depending on gold-surfactant molar ratios, three different constitutions of the nanoparticle-surfactant complexes were identified, where nanoparticles are represented either by negatively (region I) or positively (region III) charged single specimens, or by clusters in the intermittent region II.

We show that UV light illumination enables nanoaggregation into spherical gold nanoclusters of around 100nm in diameter, exhibiting visible change in solution color from red to blue. We also find that the presence of gold nanoparticles accelerates the cis-trans isomerization rate of the adsorbed azobenzenes, probably due to electron transfer. Finally, decorated with azobenzene-containing molecules gold nanoparticles from region III are applied to form plasmonic nanowires.

[1] Zakrevskyy, Y.; Cywinski, P.; Cywinska, M.; Paasche, J.; Lomadze, N.; Reich, O.; Löhmannsröben, H.-G.; Santer, S. The Journal of Chemical Physics, 140 (2014), 044907.

[2] Zakrevskyy, Y.; Kopyshev, A.; Lomadze, N.; Morozova, E.; Lysyakova, L.; Kasyanenko, N.; Santer, S. Phys Rev E, 84 (2011), 021909.

lysyakov@uni-potsdam.de