Related Experiment Video
Updated: May 7, 2026
12:11
Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Ab initio calculation of molecular aggregation effects: a Coumarin-343 case study
Donghyun Lee1, Loren Greenman, Mohan Sarovar
1Department of Chemistry, University of California , Berkeley, California 94720, United States.
The Journal of Physical Chemistry. A
|September 19, 2013
Summary
We used time-dependent density functional theory to study how Coumarin-343 molecules aggregate. This helps in designing better sensors and light-harvesting devices by understanding quantum mechanical effects.
Area of Science:
- Computational Chemistry
- Materials Science
- Quantum Mechanics
Background:
- Chromophore aggregation influences optical and electronic properties.
- Developing new sensors and light-harvesting devices requires understanding these effects.
- Effective Hamiltonians can model excitonic properties in aggregate systems.
Purpose of the Study:
- Investigate quantum mechanical effects in Coumarin-343 aggregation.
- Develop and validate effective Hamiltonians for predicting excitonic properties.
- Assess accuracy of dipole-dipole approximation and Transition Density Cube (TDC) method.
Main Methods:
- Time-dependent density functional theory (TDDFT) calculations.
- Construction of effective Hamiltonians from single-chromophore data.
- Comparison of TDDFT dimer calculations with effective Hamiltonians and TDC method.
Main Results:
- Evaluated accuracy of dipole-dipole approximation and TDC method for dimer separation and orientation.
- Investigated the impact of Coulomb coupling terms in effective Hamiltonians.
- Examined orbital relaxation effects beyond current models.
Conclusions:
- Effective Hamiltonians can predict excitonic properties of aggregated chromophores.
- TDDFT provides a robust framework for studying quantum effects in aggregation.
- Accurate modeling requires considering Coulomb coupling and orbital relaxation.
Related Concept Videos
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
01:29UV–Vis Spectroscopy: Woodward–Fieser Rules
UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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...
01:27¹H 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.
01:18Aromatic Hydrocarbon Anions: Structural Overview
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
Due to the absence of continuous overlap of p...