Plasmon-Enhanced Exciton Delocalization in Squaraine-Type Molecular Aggregates

Thomas Quenzel, Daniel Timmer, Moritz Gittinger, Jennifer Zablocki, Fulu Zheng, Manuela Schiek, Arne Lützen, Thomas Frauenheim, Sergei Tretiak, Martin Silies, Jin Hui Zhong, Antonietta De Sio, Christoph Lienau

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Enlarging exciton coherence lengths in molecular aggregates is critical for enhancing the collective optical and transport properties of molecular thin film nanostructures or devices. We demonstrate that the exciton coherence length of squaraine aggregates can be increased from 10 to 24 molecular units at room temperature when preparing the aggregated thin film on a metallic rather than a dielectric substrate. Two-dimensional electronic spectroscopy measurements reveal a much lower degree of inhomogeneous line broadening for aggregates on a gold film, pointing to a reduced disorder. The result is corroborated by simulations based on a Frenkel exciton model including exciton-plasmon coupling effects. The simulation shows that localized, energetically nearly resonant excitons on spatially well separated segments can be radiatively coupled via delocalized surface plasmon polariton modes at a planar molecule-gold interface. Such plasmon-enhanced delocalization of the exciton wave function is of high importance for improving the coherent transport properties of molecular aggregates on the nanoscale. Additionally, it may help tailor the collective optical response of organic materials for quantum optical applications.

Original languageEnglish
JournalACS Nano
DOIs
Publication statusPublished - 21 Feb 2022
Externally publishedYes

Keywords

  • excitons
  • molecular aggregates
  • squaraine
  • surface plasmon polariton
  • two-dimensional electronic spectroscopy
  • wave function delocalization

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