How Do Adsorbent Orientation and Direction of External Electric Field Affect the Charge-Transfer Surface-Enhanced Raman Spectra?

Ashtari-Jafari, Sahar; Jamshidi, Zahra

doi:10.1021/acs.jpcc.1c02319

Cited by 8 publications

(5 citation statements)

References 74 publications

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“…Comparison of experimental SERS results with the theoretically calculated spectra for flat and vertical configurations shows that we are simultaneously detecting both NHC configurations. Our combined results also showcase the strengths and weaknesses of SERS for molecular orientation studies. − Despite the flat configurations having lower calculated binding energies, SERS can detect even small populations of the less stable vertical configuration. Alternatively, a weakness of SERS for investigating molecular orientation lies in the reduced sensitivity to molecules with modes parallel with the surface.…”

mentioning

confidence: 56%

Using Surface-Enhanced Raman Spectroscopy to Unravel the Wingtip-Dependent Orientation of N-Heterocyclic Carbenes on Gold Nanoparticles

Thimes

Santos

Chen

et al. 2023

J. Phys. Chem. Lett.

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N-Heterocyclic carbenes (NHCs) are an attractive alternative to thiol ligands when forming self-assembled monolayers on noble-metal surfaces; however, relative to the well-studied thiol monolayers, comparatively little is known about the binding, orientation, and packing of NHC monolayers. Herein, we combine surface-enhanced Raman spectroscopy (SERS) and first-principles theory to investigate how the alkyl “wingtip” groups, i.e., those attached to the nitrogens of N-heterocyclic carbenes, affect the NHC orientation on gold nanoparticles. Consistent with previous literature, smaller wingtip groups lead to stable flat configurations; surprisingly, bulkier wingtips also have stable flat configurations likely due to the presence of an adatom. Comparison of experimental SERS results with the theoretically calculated spectra for flat and vertical configurations shows that we are simultaneously detecting both NHC configurations. In addition to providing information on the adsorbate geometry, this study highlights the extreme SERS enhancement of vibrational modes perpendicular to the surface.

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mentioning

confidence: 56%

Using Surface-Enhanced Raman Spectroscopy to Unravel the Wingtip-Dependent Orientation of N-Heterocyclic Carbenes on Gold Nanoparticles

Thimes

Santos

Chen

et al. 2023

J. Phys. Chem. Lett.

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“…A change in the chemical contribution to the SERS enhancement may be related to a change in the electronic structure of the SERS substrate or to a change in the interactions of the analyte with the SERS substrate. − In some cases, complexes may be formed from the analyte, coadsorbed species and the metal substrate which also influences the chemical contribution to the SERS enhancement factor . A change in the chemical contribution to the SERS enhancement is usually associated with significant changes of the recorded SERS spectra: one observes shift in the positions of SERS bands and changes in their relative intensities (example results how the electronic structure of the substrate influences the SERS spectra of pyridine can be found in refs − ). However, as can be seen in Figure , for all studied analytes, the change of the SERS substrate does not affect the “shape” of the SERS spectra, only their intensities.…”

Section: Resultsmentioning

confidence: 99%

“…A change in the SERS enhancement can be due to the change of the electromagnetic contribution to the SERS enhancement as well as due to the change of the so-called chemical (or charge transfer) contribution. A change in the chemical contribution to the SERS enhancement may be related to a change in the electronic structure of the SERS substrate or to a change in the interactions of the analyte with the SERS substrate. − In some cases, complexes may be formed from the analyte, coadsorbed species and the metal substrate which also influences the chemical contribution to the SERS enhancement factor . A change in the chemical contribution to the SERS enhancement is usually associated with significant changes of the recorded SERS spectra: one observes shift in the positions of SERS bands and changes in their relative intensities (example results how the electronic structure of the substrate influences the SERS spectra of pyridine can be found in refs − ).…”

Section: Resultsmentioning

confidence: 99%

GaN-Based Substrates as Surface-Enhanced Raman Scattering Sensors for Penicillin G: Does the Size of the Analyte Molecule Matter?

Michałowska,

Weyher,

Kudelski

2024

J. Phys. Chem. C

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Silver was deposited onto surfaces of GaN that were differently nanostructured (by formation of individual nanopillars, bunches of nanopillars, or hexagonal etch micropits). The different levels of surface-enhanced Raman scattering (SERS) activity of the nanomaterials obtained were compared by using them for the SERS detection of penicillin G in milk. The lowest limit of detection (LOD) of penicillin G was achieved for silver-covered GaN surfaces nanostructured with bunches of nanopillars (LOD = 1.1 × 10–9 M). The penicillin G LODs of other silver-covered GaN surfaces were higher, equal to 4.1 × 10–9 M for individual nanopillars, 7.3 × 10–8 M for hexagonal etch micropits, and 1.0 × 10–7 M for a flat GaN surface. SERS measurements carried out for analytes having significantly different sizes of molecules showed that the ratio of intensities of the SERS spectra measured on a layer of silver clusters deposited on a highly developed GaN surface or on a smooth GaN surface depends on the size of the analyte molecule and on the metal-analyte affinity. The larger the molecule, the smaller this ratio (for example, it was 9.5 for pyridine, 3.5 for penicillin G, and 1.5 for hemoglobin). These results show that some “SERS hot spots” cannot be reached by large molecules.

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“…In order to solve this inconsistency, recent works incorporate the intensity-borrowing effects due to the Herzberg–Teller (HT) mechanism, described by the so-called Placzek’s B, C, and D terms. The inclusion of HT terms could successfully explain the intensification of several bands. − Despite these results, invoking the perturbative HT approach does not appear to provide a fully robust framework for the estimation of enhancement factors due to the CT mechanism since Born–Oppenheimer (BO) approaches could break down when the CT state strongly couples with the plasmon, i.e., when the largest intensity borrowing is expected. Such a breakdown, which causes unreliable estimates of spectral intensities has been recently clearly shown in molecular systems for absorption and electronic circular dichroism spectroscopies, , and also RR .…”

Section: Introductionmentioning

confidence: 99%

Linear Vibronic Coupling Approach for Surface-Enhanced Raman Scattering: Quantifying the Charge-Transfer Enhancement Mechanism

García-González,

Otero,

Ávila Ferrer

et al. 2024

J. Chem. Theory Comput.

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The outstanding amplification observed in surfaceenhanced Raman scattering (SERS) is due to several enhancement mechanisms, and standing out among them are the plasmonic (PL) and charge-transfer (CT) mechanisms. The theoretical estimation of the enhancement factors of the CT mechanism is challenging because the excited-state coupling between bright plasmons and dark CT states must be properly introduced into the model to obtain reliable intensities. In this work, we aim at simulating electrochemical SERS spectra, considering models of pyridine on silver clusters subjected to an external electric field E ⃗ that represents the effect of an electrode potential V el . The method adopts quantum dynamical propagations of nuclear wavepackets on the coupled PL and CT states described with linear vibronic coupling models parametrized for each E ⃗ through a fragment-based maximum-overlap diabatization. By presenting results at different values of E ⃗ , we show that indeed there is a relation between the population transferred to the CT states and the total scattered intensity. The tuning and detuning processes of the CT states with the bright PLs as a function of the electric field are in good agreement with those observed in experiments. Finally, our estimations for the CT enhancement factors predict values in the order of 10 5 to 10 6 , meaning that when the CT and PL states are both in resonance with the excitation wavelength, the CT and PL enhancements are comparable, and vibrational bands whose intensity is amplified by different mechanisms can be observed together, in agreement with what was measured by typical experiments on silver electrodes.

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How Do Adsorbent Orientation and Direction of External Electric Field Affect the Charge-Transfer Surface-Enhanced Raman Spectra?

Cited by 8 publications

References 74 publications

Using Surface-Enhanced Raman Spectroscopy to Unravel the Wingtip-Dependent Orientation of N-Heterocyclic Carbenes on Gold Nanoparticles

Using Surface-Enhanced Raman Spectroscopy to Unravel the Wingtip-Dependent Orientation of N-Heterocyclic Carbenes on Gold Nanoparticles

GaN-Based Substrates as Surface-Enhanced Raman Scattering Sensors for Penicillin G: Does the Size of the Analyte Molecule Matter?

Linear Vibronic Coupling Approach for Surface-Enhanced Raman Scattering: Quantifying the Charge-Transfer Enhancement Mechanism

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