Related Experiment Video
Updated: Mar 31, 2026
10:03
Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
Published on: June 27, 2014
18.5K
Time-Resolved Twisting Dynamics in a Porphyrin Dimer Characterized by Two-Dimensional Electronic Spectroscopy
Franco V A Camargo1,2, Harry L Anderson3, Stephen R Meech1
1School of Chemistry, Norwich Research Park, University of East Anglia , Norwich NR4 7TJ, United Kingdom.
The Journal of Physical Chemistry. B
|October 27, 2015
Summary
Molecular twisting in porphyrin dimers was studied using two-dimensional electronic spectroscopy (2D ES). This technique revealed distinct ground and excited state twisting dynamics, crucial for understanding light-activated processes.
Area of Science:
- Photochemistry
- Spectroscopy
- Materials Science
Background:
- Molecular conformational changes in excited states are vital for light-activated processes.
- Intramolecular twisting in porphyrin oligomers affects energy and charge transport.
Purpose of the Study:
- To investigate the twisting reaction in both ground and excited states of a model porphyrin dimer.
- To differentiate ground and excited state dynamics using two-dimensional electronic spectroscopy (2D ES).
Main Methods:
- Utilized two-dimensional electronic spectroscopy (2D ES) to monitor molecular dynamics.
- Analyzed cross-peaks in excitation-detection frequency maps to identify twisting reactions.
- Examined spectral narrowing as an indicator of conformational disorder reduction.
Main Results:
- Observed a quasi-barrierless excited-state planarization on a picosecond timescale.
- Identified spectral narrowing in the excited state, suggesting reduced conformational disorder.
- Found the reverse twisting reaction suppressed in the excited state due to a high activation barrier.
- Detected both forward and reverse reactions in the ground state on a subnanosecond timescale due to a lower activation barrier.
Conclusions:
- Two-dimensional electronic spectroscopy (2D ES) effectively distinguishes ground and excited state twisting dynamics.
- Excited-state twisting is rapid and quasi-barrierless, while the reverse reaction is hindered.
- Ground-state twisting involves observable forward and reverse reactions within the thermal energy distribution.
Related Concept Videos
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
1.4K
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
1.4K
01:12Two-Dimensional (2D) NMR: Overview
1.8K
The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
1.8K
01:19Protein Dynamics in Living Cells
2.8K
Different fluorescence-based techniques are used to study the protein dynamics in living cells. These techniques include FRAP, FRET, and PET.
Fluorescent recovery after photobleaching (FRAP) is a fluorescent-protein-based detection technique used to quantify protein movement rates within the cell. This method exposes a small portion of the cell to an intense laser beam. The laser beam causes permanent photobleaching of the fluorophore-tagged proteins in the exposed region. As the bleached...
Fluorescent recovery after photobleaching (FRAP) is a fluorescent-protein-based detection technique used to quantify protein movement rates within the cell. This method exposes a small portion of the cell to an intense laser beam. The laser beam causes permanent photobleaching of the fluorophore-tagged proteins in the exposed region. As the bleached...
2.8K
01:16UV–Vis Spectroscopy: Molecular Electronic Transitions
3.5K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
3.5K
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.7K
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...
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...
1.7K
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
3.7K
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
3.7K