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

Spin–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...
1.1K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

1.9K
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...
1.9K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

2.9K
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...
2.9K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.3K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.3K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.1K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.1K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.9K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
1.9K

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Related Experiment Video

Updated: Aug 28, 2025

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
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Outsourcing Intersystem Crossing without Heavy Atoms: Energy Transfer Dynamics in PyridoneBODIPY-C60 Complexes.

Rachel K Swedin1, Andrew T Healy1, Jacob W Schaffner1

  • 1Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States.

The Journal of Physical Chemistry Letters
|September 16, 2022
PubMed
Summary

Researchers studied pyridone-BODIPY-fullerene complexes, revealing a ping-pong energy transfer mechanism. This process efficiently converts excited states (>85%) by utilizing fullerene intersystem crossing (ISC) and triplet-triplet energy transfer.

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Area of Science:

  • Photochemistry
  • Supramolecular Chemistry
  • Spectroscopy

Background:

  • Pyridone-BODIPY derivatives are strong chromophores.
  • Fullerenes are efficient electron acceptors and triplet sensitizers.
  • Understanding energy transfer in molecular complexes is crucial for optoelectronic applications.

Purpose of the Study:

  • To investigate the excited state dynamics of pyridone-BODIPY-fullerene complexes.
  • To elucidate the energy transfer mechanism between pyridone-BODIPY and fullerene.
  • To quantify the rates of energy transfer steps and identify factors influencing them.

Main Methods:

  • Time-resolved spectroscopy was employed to monitor excited state evolution.
  • Two distinct pyridone-BODIPY-fullerene complexes with varying bridge chemistries were synthesized and characterized.
  • Computational predictions were used to support experimental findings.

Main Results:

  • Photoexcitation of pyridone-BODIPY initiated a rapid energy transfer to fullerene.
  • Fullerene underwent intersystem crossing (ISC) to a triplet state, returning energy to pyridone-BODIPY via triplet-triplet energy transfer.
  • An efficient (>85%) ping-pong energy transfer mechanism was observed, enabling triplet sensitization of pyridone-BODIPY despite its lack of intrinsic ISC.
  • The N-methylpyrrolidine bridge slowed triplet-triplet energy transfer and final triplet state relaxation compared to an isoxazole bridge.

Conclusions:

  • The study demonstrates an efficient triplet sensitization strategy for chromophores with minimal spin-orbit coupling.
  • The ping-pong energy transfer mechanism is key to achieving high conversion efficiency.
  • Bridge chemistry significantly influences the kinetics of energy transfer processes in these complexes.