Related Experiment Video
Updated: Jul 30, 2025
08:04
Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
8.5K
In-plane and out-of-plane excitonic coupling in 2D molecular crystals
Dogyeong Kim1, Sol Lee2,3, Jiwon Park1
1Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, Korea.
Nature Communications
|May 12, 2023
Summary
Researchers reveal the spatial evolution of molecular excitons in 2D perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) crystals. This study enhances understanding of excitonic coherence and charge transfer in low-dimensional molecular systems for advanced applications.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Photophysics
Background:
- Understanding molecular excitons in low-dimensional solids is crucial for photophysics and applications like energy harvesting and electronics.
- The precise spatial evolution of molecular excitons and their transition dipoles at molecular length scales remains challenging to characterize.
Purpose of the Study:
- To investigate the in-plane and out-of-plane excitonic evolution in two-dimensional (2D) perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) crystals.
- To determine the influence of crystal thickness and molecular coupling on exciton behavior and transition dipole moments.
Main Methods:
- Assembly growth of PTCDA crystals on hexagonal boron nitride (hBN) substrates.
- Polarization-resolved spectroscopy to analyze excitonic emissions.
- Electron diffraction to determine crystal lattice constants and molecular orientations.
Main Results:
- Complete lattice constants and orientations of herringbone-configured PTCDA molecules were determined.
- In single layers, Frenkel emissions showed Davydov splitting and temperature-dependent energy inversion, enhancing excitonic coherence.
- With increasing thickness, charge transfer excitons emerged and reoriented due to mixing with Frenkel states.
Conclusions:
- The study provides a detailed spatial anatomy of 2D molecular excitons in PTCDA crystals.
- Findings offer insights into excitonic coherence and coupling mechanisms in low-dimensional molecular systems.
- This work paves the way for deeper understanding and novel applications in molecular electronics and optoelectronics.
Related Concept Videos
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
43.3K
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
43.3K
02:58Crystal Field Theory - Octahedral Complexes
26.9K
Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
26.9K
01:20Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
1.1K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.1K
01:27¹H NMR: Long-Range Coupling
1.8K
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...
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...
1.8K
01:22Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)
1.1K
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...
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...
1.1K
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.1K
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...
1.1K