Excited state properties, fluorescence energies, and lifetime of a poly(fluorene-pyridine) copolymer, based on TD-DFT investigation

Rungtiwa Chidthong, Supa Hannongbua, Adelia J.A. Aquino, Peter Wolschann, Hans Lischka

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15 Scopus citations

Abstract

The structural and electronic properties of the fluorene-pyridine copolymer (FPy)n (n = 1-4) were investigated theoretically by means of quantum mechanical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) using the B3LYP functional. Geometry optimizations of these oligomers were performed for the ground state and the lowest excited state. It was found that (FPy)n is nonplanar in its ground state, whereas a more pronounced trend toward planarity is observed in the S 1 state. Absorption and fluorescence energies have been extrapolated to infinite chain length making use of their good linearity with respect to 1/n. An extrapolated value of 2.64 eV is obtained for vertical excitation energy. The S1←S0 electronic excitation is characterized as a highest occupied molecular orbital to lowest unoccupied molecular orbital transition and is dominating in terms of oscillator strength. Fluorescence energies and radiative lifetime were calculated as well. The obtained results indicate that the fluorescence energy and radiative lifetime of (FPy) n are 2.16 eV and 0.38 ns, respectively. The decrease of fluorescence energy and radiative lifetime with the increase in the chain length is discussed.

Original languageEnglish
Pages (from-to)1735-1742
Number of pages8
JournalJournal of Computational Chemistry
Volume28
Issue number10
DOIs
StatePublished - Jul 30 2007

Keywords

  • Excited state
  • Fluorene-pyridine copolymer
  • Fluorescence energy
  • Ground state
  • Lifetime
  • TD-DFT
  • Vertical excitation energy

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