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Related Concept Videos

Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–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...
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.

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Related Experiment Video

Updated: Jul 16, 2026

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
10:51

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Published on: April 10, 2015

Switching Between ILCT and 3MLCT Excited States by Complex Formation in Ruthenium-Polypyridine Complex Containing

Sergey Tokarev1, Anatoly Botezatu1, Daria Kharkovskaya1

  • 1A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119334 Moscow, Russia.

Molecules (Basel, Switzerland)
|July 15, 2026
PubMed
Summary

Tuning ruthenium(II) complex photophysics is achieved by adding a second cation. This strategy modifies optical and electronic properties, enhancing phosphorescence quantum yields for advanced photosensitizers.

Keywords:
MLCTbimetallic complexcomplex formationimidazophenanthrolinephosphorescenceruthenium(II) complex

More Related Videos

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
09:45

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
06:44

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Published on: March 24, 2018

Related Experiment Videos

Last Updated: Jul 16, 2026

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
10:51

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Published on: April 10, 2015

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
09:45

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
06:44

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Published on: March 24, 2018

Area of Science:

  • Coordination Chemistry
  • Photophysics
  • Materials Science

Background:

  • Polypyridine ruthenium(II) complexes are crucial in photochemistry.
  • Tuning their photophysical properties is key for applications.
  • Controlling excited-state dynamics remains a challenge.

Purpose of the Study:

  • To demonstrate tuning photophysical properties of ruthenium(II) complexes.
  • To investigate the effect of second cation coordination on photophysics.
  • To explore rational design of photosensitizers.

Main Methods:

  • Synthesis of a novel ruthenium(II) complex with a thiacrown-ether fragment.
  • Spectroscopic (absorption, emission) and electrochemical studies.
  • Time-resolved luminescence and Density Functional Theory (DFT) calculations.

Main Results:

  • Selective binding of Ba2+, Cd2+, or Pb2+ to the thiacrown-ether fragment.
  • Suppression of intraligand charge transfer (ILCT) pathway upon cation binding.
  • Significant increase in phosphorescence quantum yields (up to 22.6%) via stabilized triplet metal-to-ligand charge transfer (3MLCT) pathway.
  • Conversion from biexponential to monoexponential luminescence decay.

Conclusions:

  • Second cation coordination effectively tunes photophysical properties of ruthenium complexes.
  • Cation binding alters electron density, stabilizing the 3MLCT pathway.
  • This approach offers a strategy for designing novel photosensitizers and photofunctional materials.