Recently, chiral metal‐organic coordination materials have emerged as promising candidates for a wide range of applications in chiroptoelectronics, chiral catalysis, and information encryption, etc. Notably, the chiroptical effect of coordination chromophores makes them appealing for applications such as photodetectors, OLEDs, 3D displays, and bioimaging. The direct synthesis of chiral coordination materials using chiral organic ligands or complexes with metal‐centered chirality is very often tedious and costly. In the case of ionic coordination materials, the combination of chiral anions with cationic, achiral coordination compounds through noncovalent interactions may endow molecular materials with desirable chiroptical properties. The use of such a simple chiral strategy has been proven effective in inducing promising circular dichroism and/or circularly polarized luminescence signals. This concept article mainly delves into the latest advances in exploring the efficacy of such a chiral anion strategy for transforming achiral coordination materials into chromophores with superb photo‐ or electro‐chiroptical properties. In particular, ionic small‐molecular metal complexes, metal clusters, coordination supramolecular assemblies, and metal‐organic frameworks containing chiral anions are discussed. A perspective on the future opportunities on the preparation of chiroptical materials with the chiral anion strategy is also presented.
Unraveling the origin of chirality from plasmonic nanoparticle-protein complexes
Plasmon-coupled circular dichroism has emerged as a promising approach for ultrasensitive detection of biomolecular conformations through coupling between molecular chirality and surface plasmons. Chiral nanoparticle assemblies without chiral molecules present also have large optical activities. We apply single-particle circular differential scattering spectroscopy coupled with electron imaging and simulations to identify both structural chirality of plasmonic aggregates and plasmon-coupled circular dichroism induced by chiral proteins. We establish that both chiral aggregates and just a few proteins in interparticle gaps of achiral assemblies are responsible for the ensemble signal, but single nanoparticles do not contribute. We furthermore find that the protein plays two roles: It transfers chirality to both chiral and achiral plasmonic substrates, and it is also responsible for the chiral three-dimensional assembly of nanorods. Understanding these underlying factors paves the way toward sensing the chirality of single biomolecules.
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- Award ID(s):
- 1903980
- NSF-PAR ID:
- 10166490
- Date Published:
- Journal Name:
- Science
- Volume:
- 365
- Issue:
- 6460
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 1475 to 1478
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Plasmon-phonon coupling between metamaterials and molecular vibrations provides a new path for studying mid-infrared light-matter interactions and molecular detection. So far, the coupling between the plasmonic resonances of metamaterials and the phonon vibrational modes of molecules has been realized under linearly polarized light. Here, mid-infrared chiral plasmonic metasurfaces with high circular dichroism (CD) in absorption over 0.65 in the frequency range of 50 to 60 THz are demonstrated to strongly interact with the phonon vibrational resonance of polymethyl methacrylate (PMMA) molecules at 52 THz, under both left-handed and right-handed circularly polarized (LCP and RCP) light. The mode splitting features in the absorption spectra of the coupled metasurface-PMMA systems under both circular polarizations are studied in PMMA layers with different thicknesses. The relation between the mode splitting gap and the PMMA thickness is also revealed. The demonstrated results can be applied in areas of chiral molecular sensing, thermal emission, and thermal energy harvesting.
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Chiral transition-metal complexes are of interest in many fields ranging from asymmetric catalysis and molecular materials science to optoelectronic applications or fundamental physics including parity violation effects. We present here a combined theoretical and experimental investigation of gas-phase valence-shell photoelectron circular dichroism (PECD) on the challenging open-shell ruthenium( iii )-tris-(acetylacetonato) complex, Ru(acac) 3 . Enantiomerically pure Δ- or Λ-Ru(acac) 3 , characterized by electronic circular dichroism (ECD), were vaporized and adiabatically expanded to produce a supersonic beam and photoionized by circularly-polarized VUV light from the DESIRS beamline at Synchrotron SOLEIL. Photoelectron spectroscopy (PES) and PECD experiments were conducted using a double imaging electron/ion coincidence spectrometer, and compared to density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The open-shell character of Ru(acac) 3 , which is not taken into account in our DFT approach, is expected to give rise to a wide multiplet structure, which is not resolved in our PES signals but whose presence might be inferred from the additional striking features observed in the PECD curves. Nevertheless, the DFT-based assignment of the electronic bands leads to the characterisation of the ionized orbitals. In line with other recent works, the results confirm that PECD persists independently on the localization and/or on the achiral or chiral nature of the initial orbital, but is rather a probe of the molecular potential as a whole. Overall, the measured PECD signals on Ru(acac) 3 , a system exhibiting D 3 propeller-type chirality, are of similar magnitude compared to those on asymmetric-carbon-based chiral organic molecules which constitute the vast majority of species investigated so far, thus suggesting that PECD is a universal mechanism, inherent to any type of chirality.more » « less
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Post-synthetic phase transfer ligand exchange has been established as a simple, reliable, and versatile method for the synthesis of chiral, optically active colloidal nanocrystals displaying circular dichroism (CD) and circularly polarized luminescence (CPL). Herein we present a water-free and purification-free cyclohexane → methanol ligand exchange system that led to the synthesis of stable, non-aggregating chiral and fluorescent cadmium sulfide quantum dots (CdS QDs). Absorption and emission studies revealed that the carboxylate capping ligands can tune the band gap by up to 65 meV as well as control the band gap and deep trap emission pathways. The CD data revealed that the addition of a 2nd stereogenic center did not automatically lead to an increase of the CD anisotropy of QDs, but rather match/mismatch cooperativity effects must be considered in the transfer of the chirality from the capping ligands to the achiral nanocrystals. Variation in position of the functional groups as well as the chemical identity of the functional groups impacted both the shape and anisotropy of the induced CD spectra and revealed the importance of the functional groups’ coordination and polarity on the binding geometry and induced chiroptical properties. Finally, we describe the first example where CD spectra of QDs capped with the same ligand and dissolved in the same solvent displayed very different spectral profiles. This work provides deeper insight into induced CD of QDs and paves the path to rational design of chiral nanomaterials.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/science.aax5415
