Chiral nanomaterials attract broad attention, as they offer new possibilities of modulation of optical properties and dissymmetry factors outperforming organic materials. Among various nanoparticles, plasmonic bipyramids present numerous advantages as building blocks of chiral nanomaterials (well-defined modulation of optical properties with the morphology of nanoparticles, narrow optical resonances, and high size and shape uniformity of synthesized particles). We study different possible orientations of gold bipyramids with respect to each other in dimers obtained by wet chemistry methods. For circularly polarized incident light we evaluate linear optical cross sections and plasmonic local field enhancement using COMSOL Multiphysics. We observe coupling of the nanoparticles’ local fields and thus changes in extinction spectra, which modulate chiroptical properties of dimers. To assess the chirality of various arrangements, we note differences in cross sections for left- and right-handed polarized light which we further evaluate as the dissymmetry g -factor. Our results provide BPs configurations with dissymmetry factor as high as −0.3.

The nonlinear optical effect of second harmonic generation can be very strong when originating from nanoplasmonic structures, due to enhancement of the surrounding material's intrinsic non-linear optical properties or due to its occurrence as a result of the plasmonic structure. However, manufacturing of large-scale three dimensional nanoplasmonic structures is still a challenge. Here, we demonstrate the two-photon luminescence and second-harmonic generation in a Bi2O3-Ag eutectic-based metamaterial exhibiting a hierarchic structure of nano- and micro-sized silver precipitates. The investigations employed a microscope system combined with polarimetric analysis. It appears that the second-harmonic-generation arises from the silver plasmonic structure rather than from the nonlinear effects of the bismuth oxide matrix. Both quadrupolar and dipolar modes of polarization are observed.

The design of two-photon absorbing azobenzene (AB) derivatives has received much attention; however, the two-photon absorption (2PA) properties of bis-conjugated azobenzene systems are relatively less explored. Here, we present the synthesis of six azobenzene derivatives and three bis-azobenzenes substituted (or not) at para position(s) with one or two amino group(s). Their linear and nonlinear absorption properties are studied experimentally and theoretically. The switching behavior and thermal stability of the Z -isomer are studied for unsubstituted mono- ( 1a , 2a ) and bis-azobenzene ( 3a ) compounds, showing that when the length of the π system increases, the half-life of the Z -isomer decreases. Moreover, along with the increase of π-conjugation, the photochromic characteristics are impaired and the photostationary state (PSS) related to E – Z photoisomerization is composed of 89% of the Z -isomer for 2a and 26% of the Z -isomer for 3a . Importantly, the 2PA cross-section increases almost five-fold on extending the π-conjugation ( 2a vs 3a ) and by about one order of magnitude when comparing two systems: the unsubstituted π-electron one ( 2a , 3a ) with D-π-D ( 2c , 3c ). This work clarifies the contribution of π-conjugation and substituent effects to the linear and nonlinear optical properties of mono- and bis-azobenzene compounds based on the experimental and theoretical approaches.