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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

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...
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–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...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–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,...
Valence Bond Theory02:42

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
Colors and Magnetism03:02

Colors and Magnetism

Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR 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...

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Updated: May 30, 2026

ARL Spectral Fitting as an Application to Augment Spectral Data via Franck-Condon Lineshape Analysis and Color Analysis
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Spin-orbit coupling in phosphorescent iridium(III) complexes.

Arthur R G Smith1, Paul L Burn, Ben J Powell

  • 1Centre for Organic Photonics and Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, QLD 4072, Australia.

Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry
|July 26, 2011
PubMed
Summary
This summary is machine-generated.

We calculated excited states of iridium(III) complexes for organic light-emitting diodes using TDDFT-ZORA. Relativistic effects significantly influence metal-to-ligand charge transfer states and optical properties.

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Area of Science:

  • Computational Chemistry
  • Materials Science
  • Quantum Chemistry

Background:

  • Iridium(III) complexes are crucial for organic light-emitting diodes (OLEDs).
  • Accurate theoretical modeling of excited states is essential for designing efficient OLED materials.
  • Relativistic effects play a significant role in the electronic structure of heavy metal complexes.

Purpose of the Study:

  • To investigate the excited states of two iridium(III) complexes, fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)3] and fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) [Ir(ptz)3].
  • To analyze the impact of scalar relativistic corrections and spin-orbit coupling (SOC) on their optical properties.
  • To compare the theoretical predictions with experimental data and predict differences in magnetic circular dichroism (MCD) spectra.

Main Methods:

  • Time-dependent density functional theory (TDDFT) calculations.
  • Zeroth-order regular approximation (ZORA) with perturbative spin-orbit coupling.
  • One-component and two-component relativistic formulations.

Main Results:

  • TDDFT-ZORA accurately reproduces experimental absorption spectra.
  • Scalar relativistic effects and SOC indirectly stabilize metal-to-ligand charge transfer (MLCT) states.
  • Relativistic effects enhance the hybridization of singlet and triplet states, influencing optical properties.

Conclusions:

  • The theoretical approach reliably models the excited states of iridium(III) complexes.
  • Indirect relativistic effects are crucial for understanding the photophysical properties of these OLED materials.
  • Despite similar electronic structures, the complexes are predicted to exhibit distinct MCD spectra.