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Aggregation-Enhanced Two-Photon Absorption of Anionic Conjugated Polyelectrolytes.

Silvano R Valandro1, Pradeepkumar Jagadesan1, Fude Feng2

  • 1Department of Chemistry, University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States.

The Journal of Physical Chemistry Letters
|September 10, 2020
PubMed
Summary

Anionic conjugated polymers show enhanced two-photon excited fluorescence (2PEF) and two-photon cross section (σ₂) when aggregated in solution. Aggregation effects are independent of the polyvalent cation used, driven by increased charge transfer.

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Area of Science:

  • Materials Science
  • Photochemistry
  • Polymer Chemistry

Background:

  • Conjugated polymers are crucial for advanced optical applications.
  • Understanding two-photon absorption (2PA) is key to developing new photonic materials.
  • Poly(phenylene ethynylene)s offer tunable electronic and optical properties.

Purpose of the Study:

  • To investigate the two-photon absorption (2PA) properties of anionic poly(phenylene ethynylene)-type conjugated oligo- and polyelectrolytes.
  • To compare 2PA properties in molecularly dissolved versus aggregated states.
  • To determine the influence of polyvalent cations on aggregation-induced 2PA enhancement.

Main Methods:

  • Synthesis of anionic poly(phenylene ethynylene)-type conjugated oligo- and polyelectrolytes.
  • Induction of aggregation using various polyvalent cations in aqueous solution.
  • Spectroscopic characterization of two-photon excited fluorescence (2PEF) and two-photon cross section (σ₂).

Main Results:

  • Aggregated forms of the conjugated materials exhibit significantly enhanced 2PEF and σ₂ compared to dissolved states.
  • The nature of the polyvalent cation used for aggregation does not affect the observed enhancement.
  • Enhanced σ₂ is attributed to an increased difference dipole moment (Δμ) in the aggregates.

Conclusions:

  • Aggregation of anionic conjugated polymers leads to improved two-photon absorption properties.
  • The enhancement mechanism involves increased charge transfer character in the excited state of the aggregates.
  • These findings are valuable for designing advanced materials for nonlinear optics and photonics.