Soft nanomaterials as plasmonic systems

Recently, attention has been paid to gold nanorods (GNRs) due to their unique shape-dependent properties, such as multiple plasmon bands that can be separately activated by incident light polarization [1]. However, for the maximum efficiency of a device based on the excitation of the GNRs localized surface plasmon resonance (LSPR), GNRs need to be well aligned. We show that using oriented linear arrays of smectic A defects, the so-called oily streaks, enables the orientation of GNRs for a large range of diameters and various ligands. Moreover, for the small GNRs, it enables oriented end-to-end chains of GNRs. We have characterized the orientation of single GNRs by spectrophotometry and Two-Photon Luminescence (TPL). Combining plasmonic absorption measurements, TPL measurements, and simulation of the plasmonic absorption, we show that the end-to-end GNR chains are either dimers, trimers, or quadrimers, all parallel to each other. A motion of the GNRs along the dislocations appears as a necessary ingredient for the formation of end-to-end GNR chains, the gap value being driven by the balance between the attracting Van der Waals interactions and the steric repulsion between the GNRs and leading to interdigitation of the neighboring ligands. Thus, we obtained electromagnetic coupling of nanorods, demonstrating it through light polarization [2]. [1] Perez-Juste J. et. al., Chem. Rev. 249, 1870 (2005). [2] Rožič, B. et. al., ACSNano 11, 6728 (2017).