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Related Concept Videos

Deactivation Processes: Jablonski Diagram01:25

Deactivation Processes: Jablonski Diagram

605
Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
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meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H

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All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
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Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

2.9K
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...
2.9K
ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

5.5K
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
5.5K
The Electron Transport Chain01:30

The Electron Transport Chain

16.3K
The electron transport chain or oxidative phosphorylation is an exothermic process in which free energy released during electron transfer reactions is coupled to ATP synthesis. This process is a significant source of energy in aerobic cells, and therefore inhibitors of the electron transport chain can be detrimental to the cell's metabolic processes.
Inhibitors of the electron transport chain
Rotenone, a widely used pesticide, prevents electron transfer from Fe-S cluster to ubiquinone or Q...
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Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

2.4K
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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Facile Preparation of 4-Substituted Quinazoline Derivatives
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Non-Radiative Deactivation in Isolated Quinoline.

Floriane Sturm1, Christoph Herok1, Ingo Fischer1

  • 1Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.

The Journal of Physical Chemistry. A
|September 20, 2024
PubMed
Summary

The photophysics of quinoline

Area of Science:

  • Photochemistry
  • Molecular Spectroscopy
  • Physical Chemistry

Background:

  • Polycyclic aromatic nitrogen-containing hydrocarbons (PANHs) are crucial in atmospheric and combustion chemistry.
  • Understanding the excited-state dynamics of PANHs like quinoline is essential for predicting their environmental fate and reactivity.
  • Previous studies have explored quinoline's photophysics, but detailed picosecond dynamics remain less understood.

Purpose of the Study:

  • To investigate the excited-state photophysics of the S2 1(ππ*) state of quinoline.
  • To determine the deactivation pathways and lifetimes of the S2 state using advanced spectroscopic techniques.
  • To elucidate the role of internal conversion and intersystem crossing in quinoline's relaxation dynamics.

Main Methods:

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  • Picosecond time-resolved photoelectron imaging spectroscopy.
  • Multiphoton ionization spectroscopy in a free jet expansion.
  • Excitation of quinoline's S2 state across a range of wavelengths (312.2–279.7 nm).

    • Main Results:

    • The S2 origin was identified at ~32,200 cm−1 with associated vibronic structure.
    • Time-resolved images revealed a short-lived component (ps lifetime) and a long-lived component with an offset.
    • Lifetimes of the S2 state decreased from 45 ps at the origin to 11 ps at higher energies, indicating rapid deactivation.

    Conclusions:

    • The short-lived component is attributed to the S2 1(ππ*) state.
    • The long-lived component with an offset is assigned to ionization from the triplet manifold (T1 state).
    • Deactivation likely proceeds via internal conversion to the S1 1(nπ*) state, followed by intersystem crossing to the triplet state.