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Related Concept Videos

Van der Waals Interactions01:24

Van der Waals Interactions

Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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 π orbitals.
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Intermolecular Forces and Physical Properties02:56

Intermolecular Forces and Physical Properties

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Second-order dispersion interactions in π-conjugated polymers.

William Barford1, Nattapong Paiboonvorachat, David Yaron

  • 1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom. william.barford@chem.ox.ac.uk

The Journal of Chemical Physics
|June 28, 2011
PubMed
Summary
This summary is machine-generated.

We calculated dispersion interactions in parallel π-conjugated polymers. Ground-state interactions depend on chain length and separation, while excited-state interactions show complex behavior and are sensitive to density fluctuations.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Chemistry

Background:

  • Dispersion interactions are crucial for understanding the behavior of conjugated polymers.
  • Accurate calculations of these interactions are essential for designing new materials with specific electronic properties.

Purpose of the Study:

  • To calculate the ground and excited state second-order dispersion interactions between parallel π-conjugated polymers.
  • To investigate the dependence of these interactions on chain length, inter-chain separation, and excitation level.
  • To explore the implications of these interactions for polymer properties and their sensitivity to density fluctuations.

Main Methods:

  • Utilized the Pariser-Parr-Pople model with Configuration Interaction Singles (CI-singles) theory to compute unperturbed eigenstates and energies.
  • Employed large-scale calculations using trans-polyacetylene as a model system.
  • Applied dimensional analysis to derive scaling relationships for dispersion interactions.

Main Results:

  • Derived distinct scaling laws for ground-state dispersion interactions (ΔE(GS)) based on inter-chain separation (R) and chain length (L): ΔE(GS)∼L(2)/R(6) for L ≪ R and ΔE(GS)∼L/R(5) for R ≪ L.
  • Identified a crossover in excited-state screening interactions (ΔE(n)) with increasing R, transitioning from monopole-line dipole to dipole-dipole or line dipole-line dipole interactions.
  • Observed that ΔE(n) increases with excitation level (n), with significant energy shifts for higher excitons (e.g., ΔE(n=3) ≃ 1.2 eV for poly(para-phenylene)).
  • Demonstrated a strong dependence of ΔE(n) on density fluctuations, with a 10% fluctuation causing shifts of tens of meV for common light-emitting polymers.

Conclusions:

  • The study provides fundamental insights into inter-chain dispersion interactions in conjugated polymers.
  • The derived scaling laws offer a predictive framework for understanding these interactions.
  • The sensitivity of excited-state interactions to density fluctuations highlights their importance in disordered polymer systems and devices.