Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy

Heejae Chung, Tomoyuki Narita, Jaesung Yang, Pyosang Kim, Masayoshi Takase, Masahiko Iyoda*, Dongho Kim

*Corresponding author for this work

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

We have investigated the photophysical properties of star-shaped oligothiophenes with three terthiophene arms (meta to each other, S3) or six terthiophene arms (ortho-, meta-, and para-arranged, S6) connected to an ethynylbenzene core to elucidate the relationship between their molecular structure and electronic properties by using a combination of ensemble and single-molecule spectroscopic techniques. We postulate two different conformations for molecules S3 and S6 on the basis of the X-ray structure of hexakis(5-hexyl-2-thienlyethynyl)benzene and suggest the coexistence of these conformers by using spectroscopic methods. From the steady-state spectroscopic data of compound S6, we show that the exciton is delocalized over the core structure, but that the meta-linkage in compound S3 prevents the electronic communication between the arms. However, in single-molecule spectroscopic measurements, we observed that some molecules of compound S3 showed long fluorescence lifetimes (about 1.4 ns) in the fluorescence-intensity trajectories, which indicated that π electrons were delocalized along the meta linker. Based on these observations, we suggest that the delocalized exciton is intensely sensitive towards the dihedral angle between the core and the adjacent thiophene ring, as well as to the substituted position of the terthiophene arms. Our results highlight that the fluorescence lifetimes of compounds S3 and S6 are strongly correlated with the spatial location of their excitons, which is mainly affected by their conformation, that is, whether the innermost thiophene rings are facing each other or not. More interestingly, we observed that the difference between the degrees of ring-torsional flexibility of compounds S3 and S6 results in their sharply contrasting fluorescence properties, such as a change in fluorescence intensity as a function of temperature. Written in the stars: The electronic nature of star-shaped oligothiophenes can be controlled by increasing the number of branched arms (see figure), because these structural modifications lead to differences in the ring-torsional flexibility, which determines the degree of exciton delocalization throughout the core structure.

Original languageEnglish (US)
Pages (from-to)9699-9709
Number of pages11
JournalChemistry - A European Journal
Volume19
Issue number29
DOIs
StatePublished - Jul 15 2013

Fingerprint

Stars
Excitons
Fluorescence
Spectroscopy
Molecules
Thiophenes
Thiophene
Conformations
Molecular electronics
Dihedral angle
Benzene
Electronic properties
Molecular structure
Trajectories
X rays
LDS 751
Electrons
Communication
alpha-terthienyl
Temperature

Keywords

  • delocalization
  • electronic structure
  • oligothiophenes
  • single-molecule studies
  • time-resolved spectroscopy

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

Cite this

Chung, Heejae ; Narita, Tomoyuki ; Yang, Jaesung ; Kim, Pyosang ; Takase, Masayoshi ; Iyoda, Masahiko ; Kim, Dongho. / Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy. In: Chemistry - A European Journal. 2013 ; Vol. 19, No. 29. pp. 9699-9709.
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Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy. / Chung, Heejae; Narita, Tomoyuki; Yang, Jaesung; Kim, Pyosang; Takase, Masayoshi; Iyoda, Masahiko; Kim, Dongho.

In: Chemistry - A European Journal, Vol. 19, No. 29, 15.07.2013, p. 9699-9709.

Research output: Contribution to journalArticle

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T1 - Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy

AU - Chung, Heejae

AU - Narita, Tomoyuki

AU - Yang, Jaesung

AU - Kim, Pyosang

AU - Takase, Masayoshi

AU - Iyoda, Masahiko

AU - Kim, Dongho

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