Using molecular vibrations to probe exciton delocalization in films of perylene diimides with ultrafast mid-IR spectroscopy

Eric R. Kennehan, Christopher Grieco, Alyssa N. Brigeman, Grayson S. Doucette, Adam Rimshaw, Kayla Bisgaier, Noel Christopher Giebink, John B. Asbury

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Ultrafast vibrational spectroscopy in the mid-infrared was used to directly probe the delocalization of excitons in two different perylenediimide (PDI) derivatives that are predicted to preclude the formation of excimers, which can act as trap sites for excited state energy in organic semiconductors. We identified vibrational modes within the conjugated C-C stretch modes of PDI molecules whose frequencies reported the interactions of molecules within delocalized excitonic states. The vibrational linewidths of these modes, which we call intermolecular coordinate coupled (ICC) modes, provided a direct probe of the extent of exciton delocalization among the PDI molecules, which was confirmed using X-ray diffraction and electro-absorption spectroscopy. We show that a slip-stacked geometry among the PDI molecules in their crystals promotes delocalized charge-transfer (CT) excitons, while localized Frenkel excitons tend to form in crystals with helical, columnar stacking geometries. Because all molecules possess vibrational modes, the use of ultrafast mid-infrared spectroscopy to measure ICC vibrational modes offers a new approach to examine exciton delocalization in a variety of small molecule electron acceptors for optoelectronic and organic photovoltaic applications.

Original languageEnglish (US)
Pages (from-to)24829-24839
Number of pages11
JournalPhysical Chemistry Chemical Physics
Volume19
Issue number36
DOIs
StatePublished - Jan 1 2017

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Perylene
Molecular vibrations
Infrared spectroscopy
excitons
vibration
Molecules
probes
spectroscopy
molecules
vibration mode
coupled modes
Vibrational spectroscopy
Crystals
Semiconducting organic compounds
Geometry
organic semiconductors
excimers
geometry
Absorption spectroscopy
Excited states

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Kennehan, Eric R. ; Grieco, Christopher ; Brigeman, Alyssa N. ; Doucette, Grayson S. ; Rimshaw, Adam ; Bisgaier, Kayla ; Giebink, Noel Christopher ; Asbury, John B. / Using molecular vibrations to probe exciton delocalization in films of perylene diimides with ultrafast mid-IR spectroscopy. In: Physical Chemistry Chemical Physics. 2017 ; Vol. 19, No. 36. pp. 24829-24839.
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Using molecular vibrations to probe exciton delocalization in films of perylene diimides with ultrafast mid-IR spectroscopy. / Kennehan, Eric R.; Grieco, Christopher; Brigeman, Alyssa N.; Doucette, Grayson S.; Rimshaw, Adam; Bisgaier, Kayla; Giebink, Noel Christopher; Asbury, John B.

In: Physical Chemistry Chemical Physics, Vol. 19, No. 36, 01.01.2017, p. 24829-24839.

Research output: Contribution to journalArticle

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