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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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
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Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

5.7K
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
5.7K
UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

7.3K
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent...
7.3K
UV–Vis Spectroscopy: Woodward–Fieser Rules01:29

UV–Vis Spectroscopy: Woodward–Fieser Rules

25.4K
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...
25.4K
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
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.4K
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.
2.4K

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Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera
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Positional Isomeric Thiophene-Based π‑Conjugated Chromophores: Synthesis, Structure, and Optical Properties.

Huan Yi1, Xi Qin1, Lei Zhai1

  • 1Department of Chemistry and Chemical Engineering, Chongqing University of Science and Technology, Chongqing 401331, P.R. China.

Precision Chemistry
|August 29, 2025
PubMed
Summary

Synthesized thiophene-based chromophores (TC) show tunable optical properties. The para-isomer (p-TC) exhibits superior UV-vis absorption and fluorescence, with all isomers displaying strong electrochemiluminescence.

Keywords:
DFT simulationsECL propertiesFluorescence emissionPositional isomersSingle-crystal structureUV−vis absorption

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photophysics

Background:

  • Thiophene-based oligomers are crucial in organic electronics.
  • Understanding structure-property relationships is key for designing new materials.

Purpose of the Study:

  • To synthesize and characterize positional isomers of thiophene-based chromophores (TC).
  • To investigate the impact of isomerism on optical and electrochemical properties.
  • To explore potential applications in optoelectronics.

Main Methods:

  • Divergent synthesis of ortho- (o-TC), meta- (m-TC), and para- (p-TC) isomers.
  • Single-crystal X-ray diffraction for structural analysis.
  • UV-vis absorption and fluorescence spectroscopy in various solvents.
  • Density Functional Theory (DFT) calculations.
  • Electrochemical measurements.

Main Results:

  • Synthesized three positional isomers of TC with thiophene moieties and π-conjugated bridges.
  • Observed a unique zipper-like packing in the solid state for m-TC.
  • p-TC displayed the most intense UV-vis absorption, fluorescence, and highest photoluminescence quantum yield.
  • DFT calculations elucidated the electronic structure and absorption origins of p-TC.
  • All isomers demonstrated strong and stable electrochemiluminescence (ECL).

Conclusions:

  • Positional isomerism significantly influences the photophysical properties of TC chromophores.
  • p-TC is a promising candidate for applications requiring intense luminescence.
  • The observed ECL properties of all isomers broaden the scope of thiophene-based materials in optoelectronics.