Ultrafast 2D IR microscopy

Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei

doi:10.1364/oe.22.018724

Cited by 75 publications

(67 citation statements)

References 32 publications

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“…The scattered light artifacts are eliminated, which permits the accurate determination of the time evolution of the 2D IR spectrum. The same polarizations and phase-cycling pulse sequence was recently used in a different application (2D IR microscopy) (19).…”

Section: Resultsmentioning

confidence: 99%

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Nishida

Tamimi

Fei

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

108

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The structural elasticity of metal-organic frameworks (MOFs) is a key property for their functionality. Here, we show that 2D IR spectroscopy with pulse-shaping techniques can probe the ultrafast structural fluctuations of MOFs. 2D IR data, obtained from a vibrational probe attached to the linkers of UiO-66 MOF in low concentration, revealed that the structural fluctuations have time constants of 7 and 670 ps with no solvent. Filling the MOF pores with dimethylformamide (DMF) slows the structural fluctuations by reducing the ability of the MOF to undergo deformations, and the dynamics of the DMF molecules are also greatly restricted. Methodology advances were required to remove the severe light scattering caused by the macroscopic-sized MOF particles, eliminate interfering oscillatory components from the 2D IR data, and address Förster vibrational excitation transfer.2D IR spectroscopy | metal-organic framework | UiO-66 MOF | ultrafast structural fluctuations | solvent confinement effect M etal-organic frameworks (MOFs) are molecular architectures in which metal clusters are connected by organic linkers to yield relatively regular 3D coordination polymers with nanometer-sized pores (1, 2). MOFs have been investigated for a wide variety of chemical applications, such as adsorption of gases (3) and heterogeneous catalysts (4). Among many types of porous materials, MOFs are unique because of their structural elasticity coexisting with a high degree of spatial regularity. In some sense, MOFs are like crystals and polymers. They have relatively regular structures like a crystal, but the metal clusters are joined by organic linkers that, in some systems, produce significant structural mobility. The elasticity of MOFs is intimately related to their physical properties and behavior (5).An important goal for understanding the nature of MOFs and how their chemical composition influences their properties and applications is to develop and apply an experimental method that can measure the ultrafast structural motions of MOFs. The relatively slow motions of the framework occurring in submicrosecond to millisecond scales have been studied by NMR and neutron scattering (6). However, until now, quantitative measurements that can characterize the time dependence of MOF structural motions in ultrafast regimes have not been possible because of the lack of appropriate techniques. Here, we have accomplished the goal by applying ultrafast 2D IR spectroscopy (7) to the study of MOF structural dynamics. 2D IR is akin to 2D NMR, but it operates on the ultrafast timescales necessary to characterize the time dependence of MOF structural motions. In addition, there is the important question of the effects on MOF dynamics when guest molecules fill the MOF nanopores. The guest molecules will affect the structural fluctuations of the framework by interacting with the linkers and the metal units. Furthermore, because of the confinement of guest molecules in MOF nanopores, the dynamics of these molecules are expected to be very different from t...

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Section: Resultsmentioning

confidence: 99%

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Nishida

Tamimi

Fei

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

108

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“…16 By spatially resolving interfaces and domains, microscopy could obtain domain specific knowledge and mitigate ensemble averaging. [17][18][19][20][21] Yet, in traditional optical microscopy, signals of non-centrosymmetric molecular interfaces and domains are often overwhelmed by those of isotropic bulk materials. Even-order nonlinear optical microscopy, such as second harmonic generation (SHG) microscopy, 22 has been a popular technique to image non-centrosymmetric systems and is widely implemented in biophysics.…”

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confidence: 99%

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

2017

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Vibrational sum frequency generation (VSFG) spectroscopy has been a powerful technique to probe molecular structures at non-centrosymmetric media. Recent developed heterodyne (HD) detection can further reveal spectral phase and molecular orientations. Adding imaging capability to an HD VSFG signal can bring spatial visualization capability into this non-linear optical technique. However, it has been a challenge to build an HD VSFG microscope that is both easy to align and has good spectral phase stability -two necessary criterions for the broad application of this technique into various areas of science. Here, we report a fully-collinear HD VSFG microscope, which meets both phase stability and optical alignment requirements that can spatially resolve images of molecular interfaces and domains, with chemical and structural sensitivities. The phase stability is more than nine times better than a Michelson Interferometric HD VSFG microscope. Using this HD VSFG microscope, we study the structures of molecular selfassembly films. Because of the superior phase sensitivity, we successfully identify two molecular domains with different molecular orientations, which we show is not possible to extract from an ensemble-averaged VSFG spectrum or homodyne-detected VSFG image.

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“…This eight-frame phase-cycling scheme is well known to be advantageous and has been used in other 2D spectroscopies. 28,38,39 …”

Section: Resultsmentioning

confidence: 99%

“…Taking the approach of Baiz et al, an image can be generated by scanning the sample to generate spatial resolution. 28 When point mapping, the detector is used to measure the spectrum of E sig rather than its spatial distribution. Wide-field imaging requires a different approach for detection because the detector measures an image and so cannot be used to measure the spectrum.…”

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confidence: 99%

Spatially Resolved Two-Dimensional Infrared Spectroscopy via Wide-Field Microscopy

et al. 2016

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We report the first wide-field microscope for measuring two-dimensional infrared (2D IR) spectroscopic images. We concurrently collect more than 16 000 2D IR spectra, made possible by a new focal plane array detector and mid-IR pulse shaping, to generate hyperspectral images with multiple frequency dimensions and diffraction-limited spatial resolution. Both frequency axes of the spectra are collected in the time domain by scanning two pairs of femtosecond pulses using a dual acousto-optic modulator pulse shaper. The technique is demonstrated by imaging a mixture of metal carbonyl absorbed polystyrene beads. The differences in image formation between FTIR and 2D IR microscopy are also explored by imaging a patterned USAF test target. We find that our 2D IR microscope has diffraction-limited spatial resolution and enhanced contrast compared to FTIR microscopy because of the nonlinear scaling of the 2D IR signal to the absorptivity coefficient for the vibrational modes. Images generated using off-diagonal peaks, created from vibrational anharmonicities, improve the molecular discrimination and eliminate noise. Two-dimensional wide-field IR microscopy provides information on vibrational lifetimes, molecular couplings, transition dipole orientations, and many other quantities that can be used for creating image contrast to help disentangle and interpret complex and heterogeneous samples. Such experiments made possible could include the study of amyloid proteins in tissues, protein folding in heterogeneous environments, and structural dynamics in devices employing mid-IR materials.

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Ultrafast 2D IR microscopy

Cited by 75 publications

References 32 publications

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

Spatially Resolved Two-Dimensional Infrared Spectroscopy via Wide-Field Microscopy

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