Highly fluorescent [7]carbohelicene fused by asymmetric 1,2-dialkyl-substituted quinoxaline for circularly polarized luminescence and electroluminescence

Hayato Sakai, Sho Shinto, Jatish Kumar, Yasuyuki Araki, Tomo Sakanoue, Taishi Takenobu, Takehiko Wada, Tsuyoshi Kawai, Taku Hasobe

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Abstract

A new 1,2-dialkylquinoxaline-fused [7]carbohelicene ([7]Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused [7]carbohelicene ([7]Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, [7]Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of [7]Hl-NAIQx were significantly red-shifted compared to those of [7]Hl-Qx and [7]carbohelicene ([7]Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (Φ<inf>FL</inf>) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (Φ<inf>FL</inf> = 0.02). Such a large enhancement of the fluorescence of [7]Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor g<inf>lum</inf> (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10<sup>-3</sup>. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.

Original languageEnglish
Pages (from-to)13937-13947
Number of pages11
JournalJournal of Physical Chemistry C
Volume119
Issue number24
DOIs
Publication statusPublished - 2015 Jun 18

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quinoxalines
Quinoxalines
Electroluminescence
electroluminescence
Luminescence
phenanthrene
Fluorescence
luminescence
Alkylation
Dichroism
Organic light emitting diodes (OLED)
Quantum yield
Light polarization
Torsional stress
fluorescence
Density functional theory
Anisotropy
Single crystals
alkylation
polarized light

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

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Highly fluorescent [7]carbohelicene fused by asymmetric 1,2-dialkyl-substituted quinoxaline for circularly polarized luminescence and electroluminescence. / Sakai, Hayato; Shinto, Sho; Kumar, Jatish; Araki, Yasuyuki; Sakanoue, Tomo; Takenobu, Taishi; Wada, Takehiko; Kawai, Tsuyoshi; Hasobe, Taku.

In: Journal of Physical Chemistry C, Vol. 119, No. 24, 18.06.2015, p. 13937-13947.

Research output: Contribution to journalArticle

Sakai, Hayato ; Shinto, Sho ; Kumar, Jatish ; Araki, Yasuyuki ; Sakanoue, Tomo ; Takenobu, Taishi ; Wada, Takehiko ; Kawai, Tsuyoshi ; Hasobe, Taku. / Highly fluorescent [7]carbohelicene fused by asymmetric 1,2-dialkyl-substituted quinoxaline for circularly polarized luminescence and electroluminescence. In: Journal of Physical Chemistry C. 2015 ; Vol. 119, No. 24. pp. 13937-13947.
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abstract = "A new 1,2-dialkylquinoxaline-fused [7]carbohelicene ([7]Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused [7]carbohelicene ([7]Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, [7]Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of [7]Hl-NAIQx were significantly red-shifted compared to those of [7]Hl-Qx and [7]carbohelicene ([7]Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (ΦFL) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (ΦFL = 0.02). Such a large enhancement of the fluorescence of [7]Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor glum (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10-3. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.",
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T1 - Highly fluorescent [7]carbohelicene fused by asymmetric 1,2-dialkyl-substituted quinoxaline for circularly polarized luminescence and electroluminescence

AU - Sakai, Hayato

AU - Shinto, Sho

AU - Kumar, Jatish

AU - Araki, Yasuyuki

AU - Sakanoue, Tomo

AU - Takenobu, Taishi

AU - Wada, Takehiko

AU - Kawai, Tsuyoshi

AU - Hasobe, Taku

PY - 2015/6/18

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N2 - A new 1,2-dialkylquinoxaline-fused [7]carbohelicene ([7]Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused [7]carbohelicene ([7]Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, [7]Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of [7]Hl-NAIQx were significantly red-shifted compared to those of [7]Hl-Qx and [7]carbohelicene ([7]Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (ΦFL) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (ΦFL = 0.02). Such a large enhancement of the fluorescence of [7]Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor glum (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10-3. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.

AB - A new 1,2-dialkylquinoxaline-fused [7]carbohelicene ([7]Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused [7]carbohelicene ([7]Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, [7]Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of [7]Hl-NAIQx were significantly red-shifted compared to those of [7]Hl-Qx and [7]carbohelicene ([7]Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (ΦFL) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (ΦFL = 0.02). Such a large enhancement of the fluorescence of [7]Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor glum (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10-3. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.

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