Biexcitons in mixed-stack charge-transfer solids, conjugated polymers, and molecular aggregates

Sumit Mazumdar, M. Chandross, Y. Shimoi, A. Chakrabarti, N. R. Armstrong, N. Peyghambarian

Research output: Contribution to journalConference article

Abstract

Ultrafast spectroscopic studies of organic solids reveal features unexpected within simple noninteracting models for these systems. We consider: (a) organic mixed-stack charge-transfer solids, (b) conjugated polymers, and (c) aggregates of metal-halogen phthalocyanines, and show that in all cases the photophysics is dominated by excitons and bound multiexciton states. Theoretical modeling is simplest for charge-transfer solids, where stable multiexcitons are verified by femtosecond pump-probe spectroscopy as well as two-photon absorption. In conjugated polymers, pump-probe spectroscopy reveals features due to biexcitons as well as a low energy charge-transfer exciton. In both charge-transfer solids and conjugated polymers the biexcitons are bound by electron-electron Coulomb interactions. In contrast, the exciton-exciton binding in molecular aggregates can originate from various sources and the magnitude of the biexciton binding energy in these systems is considerably smaller. No evidence for a biexciton in molecular aggregates have found to date. We present the first experimental evidence for a biexciton in the H-aggregate of a metal-halogen-phthalocyanine. Biexcitons, well-established in conventional semiconductors, are therefore characteristic elementary excitations of several different classes of organic solids.

Original languageEnglish (US)
Pages (from-to)69-80
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
Volume3145
DOIs
StatePublished - Dec 1 1997
EventOptical Probes of Conjugated Polymers - San Diego, CA, United States
Duration: Jul 28 1997Jul 30 1997

Keywords

  • Biexcitons in organic solids
  • Photophysics of organic solids

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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