Related Experiment Video
Updated: Jun 23, 2026
08:04
Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Elucidating the synergetic interplay between average intermolecular coupling and coupling disorder in short-time
Siwei Wang1, Guangming Liu1, Hsing-Ta Chen1
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46616, USA.
The Journal of Chemical Physics
|June 22, 2026
Summary
Short-time exciton transport in molecular aggregates is primarily governed by off-diagonal disorder, not diagonal disorder. This finding is crucial for optimizing organic optoelectronics and light-harvesting systems.
Area of Science:
- Physics
- Chemistry
- Materials Science
Background:
- Exciton transport is key to organic optoelectronics and light-harvesting.
- Research has focused on long-time dynamics, but ultrafast spectroscopy highlights short-time ballistic motion.
Purpose of the Study:
- Develop an analytical framework for short-time exciton dynamics.
- Investigate the roles of diagonal and off-diagonal disorder in exciton transport.
- Understand exciton behavior in disordered molecular aggregates.
Main Methods:
- Developed an analytical framework for short-time exciton dynamics in a 1D lattice.
- Incorporated both on-site energetic (diagonal) disorder and intermolecular coupling (off-diagonal) fluctuations.
- Used reciprocal-space analysis to derive closed-form expressions for spatial moments.
Main Results:
- Short-time ballistic exciton expansion is governed by off-diagonal disorder.
- Long-time exciton dynamics are influenced by diagonal disorder.
- A synergistic interplay exists between average and off-diagonal coupling disorder, contributing equally to short-time transport.
Conclusions:
- Off-diagonal disorder is the dominant factor in ultrafast exciton transport.
- The study provides a theoretical foundation for optimizing energy flow in disordered molecular systems.
- Findings are applicable to organic optoelectronics and light-harvesting technologies.
Related Concept Videos
01:27¹H NMR: Long-Range Coupling
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
01:22Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
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...
01:08Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
01:08NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
01:17Spin–Spin Coupling: One-Bond Coupling
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...