Determining the Orientation of Chemical Functional Groups on Metal Surfaces by a Combination of Homodyne and Heterodyne Nonlinear Vibrational Spectroscopy

Yang, Weichen; Hore, Dennis K.

doi:10.1021/acs.jpcc.7b09730

Cited by 16 publications

(16 citation statements)

References 41 publications

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“…For instance, metal surfaces like Au 66,67 or other interfaces that have been modified with dye molecules 68,69 or photoswitches 51,70 show strong 𝜒 𝑁𝑟𝑒𝑠 (2) contributions that can heterodyne the resonant 𝜒 𝑅 (2) signals due to the coherent overlap of 𝜒 𝑅 (2) and 𝜒 𝑁𝑟𝑒𝑠 (2) contributions (see equation ( 1)), as has been discussed in detail by Yang and Hore. 71 For example, optical transitions of the dye Rhodamine 6G are around 532 nm, and as was previously shown by Wang and co-workers 69 can lead to substance double resonance effects if similar wavelengths for the SFG or the visible pulses are chosen. In the present case of AAP-TB and Azo-TB at the air-water interface we have no direct optical resonances in our range of wavelength but with the SFG wavelengths in our experiments between 650 to 620 nm we are close to the optical transition of the photo-switches.…”

Section: Surface Excess and Molecular Ordermentioning

confidence: 84%

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

et al. 2020

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Arylazopyrazoles (AAPs) as substitutes for azo derivatives have gained considerable attention due to their superior properties offering E/Z photo-isomerization with high yield. In order to compare and quantify their performance, azobenzene tetraethylammonium (Azo-TB) and arylazopyrazole tetraethylammonium (AAP-TB) bromides were synthesized and characterized in the bulk (water) using NMR spectroscopy. At the air-water interface complementary information from vibrational sum-frequency generation (SFG) spectroscopy and neutron reflectometry (NR) has revealed the effects of E/Z isomerization in great detail. In bulk water the photostationary states of >89 % for E/Z switching in both directions were very similar for the surfactants, while their interfacial behavior was substantially different. In particular, the surface excess Γ of the surfactants changed drastically between E/Z isomers for AAP-TB (maximum change of Γ: 2.15 µmol/m²); for Azo-TB the change was only moderate (maximum change of Γ: 1.02 µmol/m²). Analysis of SFG spectra revealed that strong non-resonant contributions that heterodyned the resonant vibrational bands were proportional to Γ, enabling the aromatic C-H band to be interpreted as an indicator for changes in interfacial molecular order. Close comparison of Γ from NR with the SFG amplitude from the aromatic C-H stretch as a function of concentrations and E/Z conformation revealed substantial molecular order changes for AAP-TB. In contrast, only Γ and not the molecular order varied for Azo-TB. These differences in interfacial properties are attributed to the molecular structure of the AAP center that enables favorable lateral interactions at the air-water interface, causing closed-packed interfacial layers and substantial changes during E/Z photo-isomerization.

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Section: Surface Excess and Molecular Ordermentioning

confidence: 84%

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

et al. 2020

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“…The small phase change upon passing through the vibrational resonances is a result of the large nonresonant amplitude. The relationship between the phase and the amplitude ratio of resonance/nonresonance is discussed in detail by Hore et al 35…”

Section: Resultsmentioning

confidence: 99%

Phase-Sensitive Sum-Frequency Generation Measurements Using a Femtosecond Nonlinear Interferometer

et al. 2019

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Phase-sensitive sum-frequency spectroscopy is a unique tool to interrogate the vibrational structure of interfaces. A precise understanding of the interfacial structure often relies on accurately determining the phase of χ (2) , which has recently been demonstrated using a nonlinear interferometer in conjunction with a frequency-scanning picosecond laser system. Here, we implement nonlinear interferometry using a femtosecond laser system for broadband sum-frequency generation. The phase of the vibrational response from a self-assembled monolayer of octadecanethiol on gold is determined using the nonlinear femtosecond interferometer. The results are compared to those obtained using the more traditional heterodyne-detected phase measurements. Both methods give a similar phase spectrum and phase uncertainty. We also discuss the origin of the phase uncertainties and provide guidelines for further improvement.

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“…Generally, these components do not exhibit vibration modes over the probed infrared spectral range. The SFG spectra are then modelled by an effective susceptibility of the form [72,74]: For each vibration mode, the variation of the intensity from a visible wavelength to another is characteristic of electronic structure of the system (nanoparticles). (c) Unconventional use of SFG spectroscopy at variable visible wavelength.…”

Section: Ir Absorptionmentioning

confidence: 99%

A Unified Mathematical Formalism for First to Third Order Dielectric Response of Matter: Application to Surface-Specific Two-Colour Vibrational Optical Spectroscopy

Humbert

Noblet

2021

Symmetry

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To take advantage of the singular properties of matter, as well as to characterize it, we need to interact with it. The role of optical spectroscopies is to enable us to demonstrate the existence of physical objects by observing their response to light excitation. The ability of spectroscopy to reveal the structure and properties of matter then relies on mathematical functions called optical (or dielectric) response functions. Technically, these are tensor Green’s functions, and not scalar functions. The complexity of this tensor formalism sometimes leads to confusion within some articles and books. Here, we do clarify this formalism by introducing the physical foundations of linear and non-linear spectroscopies as simple and rigorous as possible. We dwell on both the mathematical and experimental aspects, examining extinction, infrared, Raman and sum-frequency generation spectroscopies. In this review, we thus give a personal presentation with the aim of offering the reader a coherent vision of linear and non-linear optics, and to remove the ambiguities that we have encountered in reference books and articles.

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Determining the Orientation of Chemical Functional Groups on Metal Surfaces by a Combination of Homodyne and Heterodyne Nonlinear Vibrational Spectroscopy

Cited by 16 publications

References 41 publications

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

Phase-Sensitive Sum-Frequency Generation Measurements Using a Femtosecond Nonlinear Interferometer

A Unified Mathematical Formalism for First to Third Order Dielectric Response of Matter: Application to Surface-Specific Two-Colour Vibrational Optical Spectroscopy

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