Related Experiment Video
Updated: May 9, 2026
14:44
Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
Published on: December 16, 2013
Disentangling electronic and vibronic coherences in two-dimensional echo spectra
Christoph Kreisbeck1, Tobias Kramer, Alán Aspuru-Guzik
1Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
The Journal of Physical Chemistry. B
|July 25, 2013
Summary
Long-lasting signals in light-harvesting complexes arise from both electronic coherences and spectral features. Two-dimensional echo spectroscopy may overestimate electronic coherence lifetimes by obscuring energy transport pathways.
Area of Science:
- Spectroscopy
- Quantum Biology
- Physical Chemistry
Background:
- Two-dimensional (2D) echo spectroscopy reveals long-lasting oscillatory signals in light-harvesting complexes.
- The origins of these signals, whether electronic coherences or vibronic spectral features, are actively researched.
Purpose of the Study:
- To investigate the interplay between electronic coherences and vibronic spectral density in generating oscillatory signals.
- To develop methods for disentangling these contributions in spectroscopic data.
Main Methods:
- Utilized 2D echo spectroscopy to probe light-harvesting complexes.
- Introduced a time-windowed Fourier transform to analyze signal amplitude.
- Differentiated between electronic and vibronic contributions to spectral oscillations.
Main Results:
- Identified intertwined contributions of electronic coherences and narrow vibronic spectral bands to oscillatory signals.
- Demonstrated that 2D spectra can be influenced by excitation pathways not involved in excitonic energy transport.
- Found that 2D spectroscopy may underestimate the actual lifetime of electronic coherences.
Conclusions:
- The interpretation of oscillatory signals in 2D echo spectroscopy requires careful consideration of both electronic and vibronic effects.
- Standard 2D spectral analysis may not accurately reflect the dynamics of excitonic energy transport due to competing signal contributions.
Related Concept Videos
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
01:12Double Resonance Techniques: Overview
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
01:27π Electron Effects on Chemical Shift: Overview
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...