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Related Concept Videos

UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

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 of conjugation in the...
Molecular Spectroscopy: Absorption and Emission01:14

Molecular Spectroscopy: Absorption and Emission

Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational and vibrational energy levels. Each energy level is separated by an energy gap, with the gaps between adjacent electronic, vibrational, and rotational levels varying significantly. The three types of energy levels in a diatomic molecule are shown in Figure 1.
IR Absorption Frequency: Hybridization01:21

IR Absorption Frequency: Hybridization

Hydrocarbons such as alkanes, alkenes, and alkynes show characteristic C–H stretching absorption bands. These IR stretching frequencies depend on the hybridization of the involved carbon atom and can be explained in terms of the s character of each hybridized atomic orbital.
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that stretch at a...
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
UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this process,...
IR Absorption Frequency: Delocalization01:04

IR Absorption Frequency: Delocalization

Electron delocalization refers to the distribution of electrons across multiple atoms within a molecule rather than being confined to a single atom or bond. This phenomenon is common in systems with conjugated bonds—structures where alternating single and double bonds allow π-electrons to move freely across the network. The movement of electrons stabilizes the molecule and can affect various chemical properties, including vibrational frequencies observed in IR spectroscopy.
In IR spectroscopy,...

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Two-photon absorption in two-dimensional conjugated quadrupolar chromophores.

Aaron D Slepkov1, Frank A Hegmann, Rik R Tykwinski

  • 1Department of Physics, University of Alberta, Edmonton, Canada.

Optics Letters
|October 31, 2006
PubMed
Summary

This study reveals that all-donor substituted chromophores exhibit significantly higher two-photon absorption (TPA) cross sections than donor-acceptor species. This finding offers a more consistent understanding of TPA properties in conjugated systems.

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Area of Science:

  • Nonlinear Optics
  • Materials Science
  • Organic Chemistry

Background:

  • Two-photon absorption (TPA) is a crucial nonlinear optical phenomenon.
  • Understanding structure-property relationships in chromophores is key for developing new optical materials.
  • Previous studies often compared molecules with different symmetries (dipolar vs. quadrupolar), complicating direct comparisons.

Purpose of the Study:

  • To investigate the effect of donor/acceptor substitution on the TPA spectra of two-dimensionally conjugated quadrupolar chromophores.
  • To provide a more consistent evaluation of TPA properties by comparing molecules of the same symmetry.
  • To quantify the TPA cross sections of novel D/A and all-donor substituted chromophores.

Main Methods:

  • Ultrafast z-scan measurements were employed to determine TPA spectra.
  • The study focused on a pair of two-dimensionally conjugated quadrupolar chromophores.
  • Spectroscopic analysis was used to characterize the TPA cross sections.

Main Results:

  • The all-donor substituted chromophore exhibited a peak TPA cross section (sigma(2)) of 520±30 GM.
  • The donor/acceptor (D/A) chromophore displayed a lower peak TPA cross section of 240±20 GM.
  • The all-donor species showed a TPA cross section more than twice that of the D/A species.

Conclusions:

  • Donor substitution significantly enhances the two-photon absorption properties of quadrupolar chromophores.
  • Comparing quadrupolar molecules of similar conjugation provides a more reliable method for structure-property analysis.
  • These findings contribute to the design of advanced materials for nonlinear optical applications.