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Broadening of van Hove Singularities Measured by Photoemission Spectroscopy of Single and Mixed Chirality Single-Walled Carbon Nanotubes
摘要： The occupied valence electronic states of single walled carbon nanotubes (SWCNTs) are responsible for their optoelectronic properties and are unique for each SWCNT chirality. Photoemission spectroscopy (PES) is one of the few methods capable of directly measuring the electron density in the valence states of materials but there are only few reports which have observed the valence states of SWCNTs and no examples for single-chirality SWCNTs. Here we prepare single and mixed chirality SWCNT films and characterise their valence states using PES. Chirality pure SWCNTs were isolated using both gel permeation chromatography and ssDNA facilitated aqueous two phase extraction from starting materials consisting of mixed chirality species. Chirality separation and purity was confirmed with UV-Vis-nIR absorption spectroscopy. SWCNT films were prepared for the single chirality species (10,3), (7,6), (7,3), (6,5), (8,3), (9,1) along with SWCNT chirality mixture of metallic and semiconducting SWCNTs, and as-synthesised mixtures possessing a range of SWCNT diameter. PES using synchrotron radiation was completed for all samples with survey and C 1s core level spectra obtained to confirm SWCNT coverage, defect level and purity. Valence band PES was obtained to characterise the valence electronic states and showed significant broadening of the signal, in comparison to calculated density of states, which could not be accounted for by instrument resolution. An inverse diameter dependence of the broadening was observed with greater broadening for smaller diameter SWCNTs. The broadening is hypothesised to be related to the photohole lifetime which was found to be significantly longer for wide diameter SWCNTs. The diameter dependence of the broadening and photohole lifetimes is discussed in terms of both Tomonaga-Luttinger and Landau theory of Fermi liquids.
关键词： chirality,valence electronic states,single-walled carbon nanotubes,van Hove singularities,photoemission spectroscopy
更新于2025-09-16 10:30:52
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Observation of persistent orientation of chiral molecules by a laser field with twisted polarization
摘要： Molecular chirality is an omnipresent phenomenon of fundamental significance in physics, chemistry, and biology. For this reason, the search for various techniques for enantioselective control, detection, and separation of chiral molecules is of particular importance. It has been recently predicted that laser fields with twisted polarization may induce a persistent enantioselective field-free orientation of chiral molecules. Here, we report an experimental observation of this phenomenon using propylene oxide molecules (CH3CHCH2O, or PPO) spun by an optical centrifuge—a laser pulse—whose linear polarization undergoes an accelerated rotation around its propagation direction. We show that PPO molecules remain oriented on a timescale exceeding the duration of the centrifuge pulse by several orders of magnitude. The demonstrated long-time field-free enantioselective orientation may open new avenues for optical manipulation, discrimination, and, potentially, the separation of molecular enantiomers.
关键词： enantioselective control,persistent orientation,optical centrifuge,molecular chirality,propylene oxide
更新于2025-09-16 10:30:52
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Local Optical Chirality Induced by Near-Field Mode Interference in Achiral Plasmonic Metamolecules
摘要： When circularly polarized light interacts with a nanostructure, the optical response depends on the geometry of the structure. If the nanostructure is chiral (i.e. it cannot be superimposed on its mirror image) then its optical response, both in near-field and far-field, depends on the handedness of the incident light. In contrast, achiral structures exhibit identical far-field responses for left- and right-circular polarization. Here, we show that a perfectly achiral nanostructure, a plasmonic metamolecule with trigonal D3h symmetry, exhibits a near-field response that is sensitive to the handedness of light. This effect stems from the near-field interference between the different plasmonic modes sustained by the plasmonic metamolecule under circularly polarized light excitation. The local chirality in a plasmonic trimer is then experimentally evidenced with nanoscale resolution using a molecular probe. Our experiments demonstrate that the optical near-field chirality can be imprinted into the photosensitive polymer, turning the optical chirality into a geometrical chirality that can be imaged using atomic force microscopy. These results are of interest for the field of polarization-sensitive photochemistry.
关键词： circular polarization,plasmonic metamolecules,Chirality,chiral plasmonics,photopolymers
更新于2025-09-12 10:27:22
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The Effect of Chiral Ligand Concentration and Binding Mode on Chiroptical Activity of CdSe/CdS Quantum Dots
摘要： Chiroptically active fluorescent semiconductor nanocrystals, quantum dots (QDs), are of high interest from a theoretical and technological point of view as they are promising candidates for a range of potential applications. Optical activity can be induced in QDs by capping them with chiral molecules, resulting in circular dichroism (CD) signals in the range of the QD UV-Vis absorption. However, the effects of the chiral ligand concentration and binding modes on the chiroptical properties of QDs are still poorly understood. In the present study, we report the strong influence of the concentration of a chiral aminoacid (cysteine) on its binding modes upon the CdSe/CdS QD’s surface, resulting in varying QD chiroptical activity and corresponding CD signals. Importantly, we demonstrate that the increase of cysteine concentration is accompanied by the growth of the QD CD intensity, reaching a certain critical point after which it starts to decrease. The intensity of the CD signal varies by almost an order of magnitude across this range. NMR and FTIR data, supported by DFT calculations, reveal a change in the binding mode of cysteine molecules from tridentate to bidentate when going from low to high concentrations, which results in a change in the CD intensity. Hence, we conclude that the chiroptical properties of QDs are dependent on the concentration and binding modes of the capping chiral ligands. These findings are very important for understanding chiroptical phenomena at the nanoscale and for the design of advanced optically active nanomaterials.
关键词： cysteine,chiroptical activity,density functional theory,quantum dots,chirality,ligand concentration,binding mode
更新于2025-09-12 10:27:22
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Reconfigurable Plasmonic Diastereomers Assembled by DNA Origami
摘要： Herein, we reported self-assembled reconfigurable plasmonic diastereomers based on DNA nanotechnology. Up to three plasmonic chiral centers were organized by dynamic DNA origami platforms. Meanwhile, each chiral center could be individually controlled to switch between left-handed and right-handed states. Thus, complex and reconfigurable chiral plasmonic diastereomers with eight plasmonic stereoisomers were achieved, driven by programmed DNA reactions. With this plasmonic diastereomers, we demonstrated the existence of strong cross-talk near-filed coupling among chiral centers, and the coupling of chiral centers could substantially contribute to the overall CD signals. Our work provides an important bottom-up approach for building complex and dynamic chiral plasmonics and for probing the interactions of plasmonic chiral centers.
关键词： DNA origami,self-assembly,plasmonic chirality,chiral centers,diastereomers
更新于2025-09-12 10:27:22
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Photo-controlled chirality transfer and FRET effects based on pseudo[3]rotaxane
摘要： The use of light to regulate the chirality of supramolecular assemblies in a non-invasive manner remains a challenge. Herein, we report a novel photochromic pseudo[3]rotaxane based on a (R/S)-2,20-binaphthyl secondary ammonium salt guest (2) and anthracene-bridged bis(dibenzo-24-crown-8) (1), which features a chirality transfer and fluorescence resonance energy transfer (FRET) from 2 to 1. Benefiting from the photo-oxidation of anthracene, the induced circular dichroism (ICD) signals of (R/S)-2@1 can be switched off/on by irradiation with 365 nm UV light and heating. This noncovalent supramolecular assembly strategy provides us with unique opportunities to design and construct further smart photo-responsive chiral molecular switches.
关键词： circular dichroism,supramolecular assemblies,FRET,chirality transfer,photo-oxidation
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Electric-Dipole Based Chiral Sensitivity in High Harmonic Generation by Dynamical Symmetry Breaking Spectroscopy
摘要： Chirality is a fundamental asymmetry property that appears abundantly in nature [1]. A system is chiral if and only if it is distinct from its mirror image (its opposite handedness chiral-partner), e.g. circularly polarized light or chiral molecules. Such systems are unique in that their properties are completely independent of their handedness up until the moment they interact with another chiral object. For instance, partner chiral molecules have identical cross-sections for absorption of linearly-polarized light, but not for absorption of circularly polarized light, leading to circular dichroism (CD) [1]. Standardly, chirality is analyzed by chiroptical techniques that measure the medium’s response to elliptically polarized light. However, such techniques rely on magnetic-dipole or higher electric-moment transitions, because electric-dipole interactions average-out to zero in isotropic media (circularly polarized light has a helical pitch that is negligible in the dipole approximation) [1]. Consequently, standard chiroptical approaches lead to very weak signals, especially in the gas phase. In recent years, several seminal electric-dipole based methods were developed that lead to much larger chiral signals, including photoelectron CD [1–4], coulomb explosion imaging [5], and microwave three-wave mixing [6]. Importantly, high harmonic generation (HHG) was shown to be chirality-sensitive, leading to relatively large (up to 10%) femtosecond-resolved chiral signals [7,8]. Still, the chiral signal in HHG is based on magnetic-dipole interactions (same as in the standard techniques), and the signal is relatively large only due to the non-perturbative nature of the process. Extending HHG to produce an electric-dipole chiral response could open-up many possibilities for optically exploring ultrafast chirality and weakly-chiral systems. Here we propose and theoretically explore a novel HHG-based chiroptical approach that relies solely on electric-dipole interactions. The method is implemented through bi-chromatic non-collinear HHG, where the beams’ properties are chosen from group theory symmetry-based considerations to exhibit reflection or inversion dynamical symmetries (DSs) [9]. This scheme leads to forbidden harmonic selection rules from isotropic achiral media which are broken in chiral media, because it does not exhibit reflection and inversion symmetries. As a result, ‘forbidden’ harmonics are emitted only if the medium is chiral, and their intensity is correlated to the enantiomeric excess (ee), providing a single-shot background free signal. We analytically derive the general conditions that allow an electric-dipole based chiral response, and numerically demonstrate several feasible geometries [10]. For instance, using DS group theory considerations [9], we numerically demonstrate that the bi-chromatic non-collinear chiral HHG scheme presented in Fig. 1(a) – two intense non-collinear bi-chromatic (3:5 carrier frequency ratios), counter rotating, elliptically polarized beams propagate with a relative opening angle of 2α – leads to an electric-dipole based ‘forbidden harmonic’ signal. When this field interacts with an achiral medium (e.g. a non-oriented racemic mixture of chiral molecules), even harmonic emission is forbidden due to a dynamical inversion symmetry selection rule (the pump is invariant under the DS: (cid:1870)?→-(cid:1870)?, t→t+T/2) [9]. However, when this field interacts with a chiral medium, even harmonics are emitted in all polarizations, and the electric-dipole response does not average-out to zero [10]. This results from the medium breaking the pump’s inversion DS; hence, the intensity of the even harmonics is correlated to the ee, while the odd harmonics are chirality-independent and can be used as a reference (see Fig. 1(c)). This scheme leads to a nearly background free chiral/achiral signal, reaching as high as 97% for the normalized harmonic response from chiral media compared to achiral media (Fig. 1(d)).
关键词： Electric-Dipole,Dynamical Symmetry Breaking Spectroscopy,Chirality,High Harmonic Generation
更新于2025-09-11 14:15:04
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Helicity of harmonic generation and attosecond polarization with bichromatic circularly polarized laser fields
摘要： We theoretically investigate the high-order harmonic generation (HHG) of helium atom driven by bichromatic counter-rotating circularly polarized laser fields. By changing the intensity ratio of the two driving laser fields, the spectral chirality of the HHG can be controlled. As the intensity ratio increases, the spectral chirality will change from positive- to negative-value around a large intensity ratio of the two driving fields when the total laser intensity keeps unchanged. However, the sign of the spectral chirality can be changed from positive to negative around a small intensity ratio of the two driving fields when the total laser intensity changes. At this time, we can effectively control the helicity of the harmonic spectrum and the polarization of the resulting attosecond pulses by adjusting the intensity ratio of the two driving laser fields. As the intensity ratio and the total intensity of the driving laser fields increase, the relative intensity of either the left-circularly or right-circularly polarized harmonic can be enhanced. The attosecond pulses can evolve from being elliptical to near linear correspondingly.
关键词： spectral chirality,attosecond polarization,high-order harmonic generation,bichromatic circularly polarized laser fields
更新于2025-09-11 14:15:04
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Out of plane stacking of InSe-based heterostructures towards high performance electronic and optoelectronic devices using a graphene electrode
摘要： Supramolecular chirality has attracted significant attention because of its critical roles in the life and material sciences. In this study, a natural triterpenoid-tailored amphiphilic molecule C4-MOP was designed and synthesized, in which the pyridinium head group was modified on the skeleton of triterpenoid through an alkyl linker. The introduction of pyridinium not only offers a hydrophilic cation to promote the assembly process but also renders itself as the nucleation point to adsorb silica precursors. The results showed that by adjusting the solvent compositions and the concentration of C4-MOP, well-ordered helical nanoribbons with both right- and left-handedness were fabricated by the assembly of C4-MOP, where the hydrophilic pyridinium cations were helically displayed on the surface of ribbons. Subsequently, by taking advantage of electrostatic interactions between pyridinium and the silica precursor, the supramolecular chirality of C4-MOP was successfully imprinted onto the silica nanostructures using the gel–sol mineralization process. Our work provides a simple yet useful strategy to prepare chiral silica, which could promote the applications of chiral natural products in material science.
关键词： triterpenoid,helical ribbons,silica,biomineralization,supramolecular chirality
更新于2025-09-11 14:15:04
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Plasmonic Properties and Optical Activity of a Three-Dimensional Six-Blade Windmill Nanostructure
摘要： Two exchangeable LSPR modes with different coupling field are observed in calculating magnetic field intensity in accordance with adjusting geometrical parameters. Compared with planar nanostructures, three-dimensional windmills show stronger optical activity, and the maximum value of the asymmetry g-factor was 0.6. The numerical simulation results in this paper also contain the optimal geometrical parameters to achieve the best circular dichroism effect at different resonance modes. The results give a contribution to the design of novel chiral optical nanostructures.
关键词： chirality,surface plasmon resonance,optical activity,surface-enhanced spectroscopy
更新于2025-09-11 14:15:04