Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated polymers

Z. Shuai*, Jean-Luc Bredas, S. K. Pati, S. Ramasesha

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

18 Scopus citations

Abstract

The symmetrized density matrix renormalization group approach is applied within the extended Hubbard-Peierls model (with parameters U/t, V/t, and bond alternation δ) to study the ordering of the lowest one-photon (11Bu-) and two-photon (21Ag+) states as well as the lowest-lying triplet states in one-dimensional conjugated systems with chain lengths, N, up to N=80 sites. Three different types of crossovers are studied, as a function of U/t, δ, and N. The "U - crossover" and "δ crossover" are examined for long chains, which provide a sharp contrast to the situation found previously for short chains. The "N-crossover", which only occurs for realistic intermediate correlation strength, illustrates the more localized nature of the 2Ag excitation relative to the 1Bu excitation. We also apply the quantum-chemical Pariser-Parr-Pople (PPP) model with long-range Ohno potential to the polyene molecules. We find that the 2Ag state is always below the 1Bu state for chain lengths N=4 to 40. Most interestingly, the gap between 2Ag and 1Bu first increases for N up to 16, then levels off, and finally starts to decrease. Thus, extrapolations to long chain based on short polyene data are hazardous.

Original languageEnglish (US)
Pages (from-to)293-302
Number of pages10
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

  • Conjugated polymers
  • Density matrix renormalizatioin group
  • Electron correlation
  • Excited states
  • Photoluminescence
  • Polyene
  • Quantum confinement

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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