Orientation analysis by simulation of vibrational sum frequency generation spectrum: CH stretching bands of the methyl group

Hirose, Chiaki; Yamamoto, Hiroyoshi; Akamatsu, Naotoshi; Domen, Kazunari

doi:10.1021/j100141a028

Cited by 239 publications

(333 citation statements)

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“…Assuming C 2v symmetry for the methylene mode, the tensor elements can be related to the molecular hyperpolarizabilities. Within the limits of the bond polarizability derivative model [34][35] , we expect no strong symmetric vibration to appear in the χ yxx (2) and χ xyx (2) elements, whereas the contribution of the symmetric mode in χ xxy (2) is expected to be strong. 5 We indeed observe this trend for the 2954 cm…”

Section: Polarization-resolved Sfg Of the Carbon-hydrogen Stretching mentioning

confidence: 96%

Polarization-Sensitive Sum-Frequency Generation Microscopy of Collagen Fibers

Han

Hsu

et al. 2015

J. Phys. Chem. B

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Point-scanning sum-frequency generation (SFG) microscopy enables the generation of images of collagen I fibers in tissues by tuning into specific vibrational resonances of the polypeptide. It is shown that when collagen-rich tissues are visualized near the 2954 cm -1 stretching vibration of methylene groups, the SFG image contrast is higher compared to the contrast seen in nonresonant second-harmonic generation (SHG) imaging.Polarization and spectrally resolved analysis of the SFG signal as a function of fiber orientation in the CH-stretching range of the vibrational spectrum enabled a comparative characterization of the achiral tensor elements of collagen's second-order susceptibility. This analysis reveals that selected on-resonance tensor elements are enhanced over other elements, giving rise to a much stronger anisotropy ρ of the signal for SFG ( ρ≈15 ) compared to SHG ( ρ≈3 ). The improved anisotropy of the vibrationally resonant signal contributes to the higher contrast seen in the SFG tissue images.

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Section: Polarization-resolved Sfg Of the Carbon-hydrogen Stretching mentioning

confidence: 96%

Polarization-Sensitive Sum-Frequency Generation Microscopy of Collagen Fibers

Han

Hsu

et al. 2015

J. Phys. Chem. B

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“…Such average is performed by using the relationships connecting the molecular hyperpolarisability to the surface susceptibility as a function of the molecule orientation. [34][35][36] In principle, the four independent components of the susceptibility (ZZZ, XXZ, XZX, and ZXX) can be selectively probed with the four sets of polarisations, ppp, ssp, sps, and pss. However, on metallic surfaces, the electric field parallel to the surface is screened by the substrate electrons.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Orientational Analysis of Dodecanethiol and p‐Nitrothiophenol SAMs on Metals with Polarisation‐Dependent SFG Spectroscopy

Cecchet¹,

Lis²,

Guthmuller³

et al. 2010

ChemPhysChem

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“…20 To determine the tilt of the surface molecules, the macroscopic second-order nonlinear susceptibility has to be related to microscopic susceptibilities, . Here, we discuss only the ratio R ) A q (ssp, asymmetric)/A q (ssp, symmetric) for methyl groups which is independent of the Fresnel coefficients, refractive index, and the incident angles of the input beams.…”

mentioning

confidence: 99%

Molecular Structure of Hydrophobic Alkyl Side Chains at Comb Polymer-Air Interface

Gautam

Dhinojwala

2001

Macromolecules

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Introduction. Polymers with long side chains (comb polymers) provide unique opportunities to tailor surface properties of polymer films for applications in the areas of adhesion, friction, membrane transport, and biocompatibility. [1][2][3][4][5][6][7][8] In particular, polymers containing long alkyl or fluorinated alkyl side chains have been used to generate hydrophobic surfaces with surface energies that are comparable to those created by well-ordered self-assembled monolayers (SAM). 1-2,9-10 Comb copolymers with alkyl side chains typically show two thermal transitions: one associated with smectic liquid crystalline order where the d spacing is proportional to the length of the side groups 1,2 and the other associated with crystallization of the alkyl side chains. The surface energy of alkyl side chain comb polymers decreases with increase in the length of the alkyl side groups until a certain critical chain length, after which it asymptotes to a constant value. 1 These observations are reminiscent of results for SAM's where the length of the alkyl chains, packing, and mobility of the chains control the surface energies. 9,10 Although, considerable work has been done in the past in understanding the molecular ordering of SAM, very little is known about the molecular structure of alkyl chains at the comb polymer-air interface. 11 In this Communication, we report the first spectroscopic measurement of the molecular structure of octadecyl alkyl side chains at poly(vinyl octadecyl carbamatesco-vinyl acetate)-air interface (the polymer will be referred to as octadecyl polymer for simplicity) using the surface sensitive sum-frequency generation (SFG) technique. SFG involves mixing a visible high-intensity laser beam of frequency ω 1 , with a tunable infrared wavelength source of frequency ω 2 . According to the dipole approximation, generation of a SFG photon at (ω 1 + ω 2 ) is forbidden in the centrosymmetric bulk and is nonzero at interfaces where the inversion symmetry is broken. 12-16 SFG intensities are resonantly enhanced when ω 2 overlaps with the resonant frequency of a molecular vibrational mode that is both infrared and Raman active. The intensity, polarization, and resonance frequency of the SFG signal yield chemical and orientational information on molecules at interfaces. [12][13][14][15][16][17][18] Here, we compare the differences in the surface structure of 65 nm thick octadecyl polymer films prepared by spin-coating to a 7 nm polymer layer prepared by solution dipping on a mica substrate. In both cases, the SFG signals show strong methyl asymmetric and symmetric stretching vibrations indicating ordered methyl terminal groups. For the adsorbed octadecyl films, the SFG signal associated with methylene vibrations is higher indicating increased gauche defects in

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Orientation analysis by simulation of vibrational sum frequency generation spectrum: CH stretching bands of the methyl group

Cited by 239 publications

References 1 publication

Polarization-Sensitive Sum-Frequency Generation Microscopy of Collagen Fibers

Polarization-Sensitive Sum-Frequency Generation Microscopy of Collagen Fibers

Orientational Analysis of Dodecanethiol and p‐Nitrothiophenol SAMs on Metals with Polarisation‐Dependent SFG Spectroscopy

Molecular Structure of Hydrophobic Alkyl Side Chains at Comb Polymer-Air Interface

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