Noble-metal nanoparticles [1] with localized surface-plasmon resonances (LSPR) have been recently used to prepare new materials with improved optical circular dichroism.[2] This interest stems from a wide range of applications in biology and physics, including the structural determination of proteins and DNA [3] and the pursuit of negative refraction.[4] Surfaceplasmon-mediated circular dichroism (SP-CD) in solution has been explored to date using small spherical metal particles, invariably resulting in moderate signals over a narrow spectral range. [5][6][7][8][9][10] In contrast, we present herein a novel class of metamaterial consisting of gold nanorods (NRs) organized in three-dimensional (3D) chiral structures and yielding a record circular dichroism anisotropy factor for metal nanoparticles (> 0.02) across visible and near-infrared (Vis-NIR) wavelengths (600-900 nm). The fabrication process can be easily upscaled, as it involves the self-assembly of gold nanorods on a fiber backbone with chiral morphology. Our measurements are fully supported by theoretical modeling based on coupled dipoles, unraveling the key role of gold nanorods in the chiroptical response.Three major strategies have been considered for the generation of SP-CD responses: synthesis of metal clusters with an intrinsically chiral surface, [11,12] adsorption of chiral molecules onto achiral metal nanoparticles, [5,13] and organization of nanoparticles into three-dimensional chiral arrangements.[5-10] Herein, we present a record level of optical activity with a chiral assembly of NRs, which we interpret as SP-CD. Known as plasmonic nanoantennas, [14] these particles are characterized by the resonant collective interaction of their conduction electrons with light in the form of both scattering and absorption, with resonance frequencies that can be tuned across the Vis-NIR spectrum by simply changing the aspect ratio of the nanocrystals.[15] Moreover, the LSPR of NRs is very sensitive to the presence and relative orientation of neighboring particles.[16] These two properties combined make NRs promising building blocks for intense and tunable SP-CD. We have designed a new nanocomposite using a self-assembly strategy [17] with NRs adsorbed onto a scaffold of supramolecular fibers with chiral morphology through specific non-covalent interactions.NRs with an average length of 45 nm and average width of 17 nm were prepared by a seeding growth method, [18] and subsequently coated with the amphiphilic polymer poly(vinylpyrrolidone) (PVP) in ethanol. [19] Fibers having a chiral morphology were obtained by adding water to a DMF/ ethanol solution of anthraquinone-based oxalamide 1 (Figure 1 a), [20] forming a fluid dispersion (see the Supporting Information for experimental details). In Figure 1 b,c, we present scanning electron microscopy (SEM) images of twisted fibers with right-(P) and left-handedness (M), corresponding to (R)-1 and (S)-1, respectively, with widths in the hundred-nanometer range and lengths of several micrometers.For the preparation o...

Noble-metal nanoparticles [1] with localized surface-plasmon resonances (LSPR) have been recently used to prepare new materials with improved optical circular dichroism.[2] This interest stems from a wide range of applications in biology and physics, including the structural determination of proteins and DNA [3] and the pursuit of negative refraction.[4] Surfaceplasmon-mediated circular dichroism (SP-CD) in solution has been explored to date using small spherical metal particles, invariably resulting in moderate signals over a narrow spectral range. [5][6][7][8][9][10] In contrast, we present herein a novel class of metamaterial consisting of gold nanorods (NRs) organized in three-dimensional (3D) chiral structures and yielding a record circular dichroism anisotropy factor for metal nanoparticles (> 0.02) across visible and near-infrared (Vis-NIR) wavelengths (600-900 nm). The fabrication process can be easily upscaled, as it involves the self-assembly of gold nanorods on a fiber backbone with chiral morphology. Our measurements are fully supported by theoretical modeling based on coupled dipoles, unraveling the key role of gold nanorods in the chiroptical response.Three major strategies have been considered for the generation of SP-CD responses: synthesis of metal clusters with an intrinsically chiral surface, [11,12] adsorption of chiral molecules onto achiral metal nanoparticles, [5,13] and organization of nanoparticles into three-dimensional chiral arrangements.[5-10] Herein, we present a record level of optical activity with a chiral assembly of NRs, which we interpret as SP-CD. Known as plasmonic nanoantennas, [14] these particles are characterized by the resonant collective interaction of their conduction electrons with light in the form of both scattering and absorption, with resonance frequencies that can be tuned across the Vis-NIR spectrum by simply changing the aspect ratio of the nanocrystals.[15] Moreover, the LSPR of NRs is very sensitive to the presence and relative orientation of neighboring particles.[16] These two properties combined make NRs promising building blocks for intense and tunable SP-CD. We have designed a new nanocomposite using a self-assembly strategy [17] with NRs adsorbed onto a scaffold of supramolecular fibers with chiral morphology through specific non-covalent interactions.NRs with an average length of 45 nm and average width of 17 nm were prepared by a seeding growth method, [18] and subsequently coated with the amphiphilic polymer poly(vinylpyrrolidone) (PVP) in ethanol. [19] Fibers having a chiral morphology were obtained by adding water to a DMF/ ethanol solution of anthraquinone-based oxalamide 1 (Figure 1 a), [20] forming a fluid dispersion (see the Supporting Information for experimental details). In Figure 1 b,c, we present scanning electron microscopy (SEM) images of twisted fibers with right-(P) and left-handedness (M), corresponding to (R)-1 and (S)-1, respectively, with widths in the hundred-nanometer range and lengths of several micrometers.For the preparation o...

The photoinduced gelation system based on 1 (non-gelling) to 2 (gelling) molecular photoisomerization in water results by microspheres (1) to gel fibers (2) transformation at the supramolecular level.

Bis(LeuOH) (1a), bis-(ValOH) (2a) and bis(PhgOH) (5a) (Phg denotes (R)-phenylglycine) oxalyl amides are efficient low molecular weight organic gelators of various organic solvents and their mixtures as well as water, water/DMSO, and water/DMF mixtures. The organisational motifs in aqueous gels are dominated primarily by lipophilic interactions while those in organic solvents are formed by intermolecular hydrogen bonding. Most of the gels are thermoreversible and stable for many months. However, 2a forms unstable gels with organic solvents which upon ageing transform into variety of crystalline shapes. For some 1a/alcohol gels, a linear correlation between alcohol dielectric constants (epsilon) and gel melting temperatures (Tg) was found. The 1H NMR and FTIR spectroscopic investigations of selected gels reveal the existence of temperature dependent network assembly/dissolution equilibrium. In the 1H NMR spectra of gels only the molecules dissolved in entrapped solvent could be observed. By using an internal standard, the concentration of dissolved gelator molecules could be determined. In FTIR spectra, the bands corresponding to network assembled and dissolved gelator molecules are simultaneously present. This enabled determination of the Kgel values by using both methods. From the plots of InKgel versus 1/T, the deltaHgel values of selected gels have been determined (-deltaHgel in 10-36 kJ mol(-1) range) and found to be strongly solvent dependent. The deltaHgel values determined by 1H NMR and FTIR spectroscopy are in excellent agreement. Crystal structures of 2a and rac-5a show the presence of organisational motifs and intermolecular interactions in agreement with those in gel fibres elucidated by spectroscopic methods.