Antibonding Plasmon Modes in Colloidal Gold Nanorod Clusters

Abstract

The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies.

Functional Gold Nanorods: Synthesis, Self‐Assembly, and Sensing Applications

“…More controlled alignment of gold nanorods into chiral structures has been detailed by several groups. Grzelczak and coworkers formed ladder‐like rod assemblies which led to the presence of “anti‐bonding” modes in the optical spectrum and the suggestion that chiral structures could be formed using this method 251. True chiral rod assemblies were created by templating rods onto helical lipid structures and were characterized by circular dichroism spectroscopy (CD) and imaging 252.…”

Forming End-to-End Oligomers of Gold Nanorods Using Porphyrins and Phthalocyanines

“…11 These short oligomer species, primarily dimers and trimers, avoided the reduction in optical brightness found in longer chains. 8 However, the use of polymers, such as polystyrene and others, 12 for facilitating assembly required partially nonaqueous conditions for assembly and led to some undesirable side-byside assembly due to the length of even low-molecular-weight polymers, with a resultant decrease in the effective Raman enhancement of the active species. The problem we aim to solve, then, is how to reduce the inter-rod gap to create more intense hot spots while retaining oligomerization control to create increased proportions of dimers and trimers and how to do so in a simpler solvent system.…”

Salt-mediated kinetics of the self-assembly of gold nanorods end-tethered with polymer ligands

“…40,41 In addition, because of the asymmetric shape of the NRs, they can associate in a side-by-side, end-to-end, or ladder-like manner, thereby providing another degree of freedom in controlling optical properties of the system. [42][43][44][45][46] Here, we used gold NRs coated with hexadecyltrimethylammonium bromide along their long sides and tethered with thiol-terminated polystyrene (PS) at both ends. 23,24,47,48 The association of the NRs in an end-to-end manner was triggered by reducing the quality of the solvent for the PS tethers.…”