Bottom-up Design of Hybrid Polymer Nanoassemblies Elucidates Plasmon-Enhanced Second Harmonic Generation from Nonlinear Optical Dyes

Abstract

Flexible design of hybrid polymer nanoassemblies consisting of nonlinear optical (NLO) polymer nanosheets and gold nanoparticle alignment was done to elucidate near-field effects of localized surface plasmon (LSP) coupling, which was generated from coupled gold nanoparticles, on enhanced second harmonic generation (SHG) from nonlinear optical (NLO) dyes in hybrid nanoassemblies. Structurally well-defined hybrid polymer nanoassemblies comprising NLO polymer nanosheets and aligned gold nanoparticles were fabricated using bottom-up approaches: Langmuir-Blodgett (LB) technique and nanoparticle adsorption. Two hybrid polymer nanoassembled structures were particularly examined: a single-layer NLO polymer nanosheet and gold nanoparticle monolayer (single-layer structure) exhibiting intralayer LSP coupling, and a single-layer NLO polymer nanosheet sandwiched between two-layer gold nanoparticle monolayers (sandwich structure). The latter enables interlayer LSP coupling between the two gold nanoparticle monolayers. Dependence of SHG intensity on the distance between the NLO layer and nanoparticle layer was examined according to the LB layer structure and gold nanoparticle size variation. The SH light intensity from the NLO polymer nanosheet decreased almost exponentially with increasing spacer distance between the NLO polymer nanosheet and gold nanoparticle monolayer in both single-layer and sandwich structures. The decay length depends strongly on the gold nanoparticle size, indicating effective spatial distance for enhanced SHG from NLO polymer nanosheets. Theoretical calculations were used to study the enhancement mechanism. Finite difference time domain (FDTD) calculations reproduced the exponential behavior of SH light intensity as a function of separation distance, which confirmed the importance of coupled gold nanoparticle formation and parallel geometry of near-field coupling of the coupled gold nanoparticles with NLO polymer nanosheets for efficient SHG enhancement. Dipole-type LSP coupling along the long axis of adjacent gold nanoparticles at the fundamental frequency dominates enhancement of SHG from NLO dyes oriented parallel to the long axis of LSP coupling, which occurs at the center of the Au NPs.

Optical Properties of Hybrid Organic‐Inorganic Materials and their Applications

“…[521] Multilayers systems can be an alternative to control interactions between metal NPs and luminescent polymers. [513,[522][523][524] M. Mitsuishi et al used also hybrid polymer approach combining polymer nanosheets nanoassemblies through LangmuirBlodgett technology and introduced metal nanoparticles layers. [522,523] The polymer layer part included chromophores (for luminescence or NLO), and the distance to the nanoparticles deposited on the films or between two films was controlled by the length and the thickness of the polymers.…”

“…The SHG enhancement was dominated by the dipole LSP coupling (confirmed by FDTD calculations) and controlled at the nanometer scale. [522] Scattering of nanoparticles can be efficiently used to enhance the absorption of devices, in particular in the field of photovoltaics. [525] Future applications of polymer-metal NPs interaction in solar cells are thus extremely promising, and can for instance be used to increase drastically the light absorption of the organic photovoltaic device through the local field enhancement.…”

Luminescence Properties of Platinum Porphyrin Embedded in Multilayered Polymer Nanosheets

“…The monolayer is easily transferable on solid supports as Y-type LB films over 700 layers. [2] A diverse range of molecules have been successfully incorporated in ultrathin polymer films at the monolayer level: e.g., organometallic complexes, [3] aromatic hydrocarbons, [4][5][6] redox active groups, [7,8] thermosensitive groups, [9] nonlinear optical active groups, [10][11][12] ferroelectric polymers, [13] and polyhedral oligomeric silsesquioxane. [14,15] The ultrathin polymer films act as a nanoruler manipulating nanomaterials systematically with nanoscale precision.…”

“…[14,15] The ultrathin polymer films act as a nanoruler manipulating nanomaterials systematically with nanoscale precision. [12,16] After demonstrating the versatility of acrylamide-based polymer LB films in terms of surface coating at the nanometer level, we designated polymer LB films as "polymer nanosheet". [17] We are interested in bottom-up design of polymer nanoassemblies with wide variety of nanomaterials.…”

Probing the linear and nonlinear optical properties of nitrogen-substituted carbon nanotube

“…In order to get considerable NLO response, not only various mechanisms and phenomena have been investigated, but also the prediction and design of molecules with large (hyper)polarizabilities have received much attention [10][11][12][13][14]. Generally speaking, inorganic and organic materials [15][16][17][18][19] are the two main types of nonlinear optical (NLO) materials. Traditionally, inorganic NLO crystals such as lithium niobate (LiNbO 3 ) and potassium dihydrogen phosphate (KH 2 PO 4 ) are known to exhibit second harmonic generation (SHG) effect.…”