Analytical chemistry, multidimensional spectral signatures, and the future of coherent multidimensional spectroscopy

Abstract

Spectroscopy is a dominant measurement methodology because it resolves molecular level details over a wide concentration range. Its limitations, however, become challenged when applied to complex materials. Coherent multidimensional spectroscopy (CMDS) is the optical analogue of multidimensional NMR and like NMR, its multidimensionality promises to increase the spectral selectivity of vibrational and electronic spectroscopy. This article explores whether this promise can make CMDS a dominant spectroscopic method throughout the sciences. In order for CMDS to become a dominant methodology, it must create multidimensional spectral fingerprints that provide the selectivity required for probing complex samples. Pump-CMDS probe methods separate the pump's measurement of dynamics from a multidimensional and selective probe. Fully coherent CMDS methods are ideal multidimensional probes because they avoid relaxation effects, spectrally isolate the output signals, and provide unique and invariant spectral signatures using any combination of vibrational and electronic quantum states.

Interference among Multiple Vibronic Modes in Two-Dimensional Electronic Spectroscopy

“…Two-dimensional electronic spectroscopy (2D ES) is the ultimate four-wave mixing spectroscopy method because it can provide maximum resolution of the underlying nonlinear optical signal pathways [20][21][22][23]. In the most prevalent implementation of 2D ES measurements, three femtosecond laser pulses focus on a sample, from which they produce a four-wave mixing signal, which is a laser beam emitted by the sample that is subsequently detected by a spectrometer [24].…”

Coherent two-dimensional Fourier transform spectroscopy using a 25 Tesla resistive magnet

“…Two-dimensional Fourier transform (2DFT) spectroscopy based on the coherent FWM signal has more recently emerged [49][50][51][52][53][54] and has been successfully applied to III-V semiconductors [55][56][57][58][59][60][61][62][63] , diamond nitrogenvacancy center 64 , biological photosynthetic centers [65][66][67][68][69][70] , peptides 52,71,72 , and two-dimensional materials [73][74][75] , providing important insights difficult to access using traditional time-integrated and spectrally resolved FWM spectroscopy. The advantages of 2DFT spectroscopy over traditional one-dimensional FWM have been well documented in the literature 51,[76][77][78][79][80][81][82] . The correlated nature of the frequency axes can reveal underlying physics in the FIG.…”

“…In 2DFT spectroscopy, two time delays are monitored simultaneously and the phase of an induced nonlinear signal is explicitly tracked. This leads to a twodimensional time-domain data set, which is converted to a two-dimensional spectrum by a Fourier transform, analogous to the extension of nuclear magnetic resonance from one to two dimensions 51,[76][77][78][79][80][81][82] . However, performing these measurements in the near infrared and visible spectral range has been difficult, due to the phase stability needed.…”

Fundamental Studies of Relationships between Experimental Nonlinear Coherent Vibrational Spectroscopies

“…These pathways are particularly useful because the output signal can be spectrally resolved from the excitation frequencies so single-photon detection becomes possible. 35 Because the pathways are fully coherent, they are immune to population relaxation. The coupled quantum states create multidimensional molecular fingerprints.…”

“…The coupled quantum states create multidimensional molecular fingerprints. 35 Complications from relaxation effects are avoided because relaxation collapses the entangled Schrodinger cat states and destroys the emission. The coupling between quantum states manifests through the requirement that the pathways involve an overtone and combination band state in an infrared or Raman transition.…”