Highly Fluorescent [7]Carbohelicene Fused by Asymmetric 1,2-Dialkyl-Substituted Quinoxaline for Circularly Polarized Luminescence and Electroluminescence

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• 作者：Hayato Sakai ; Sho Shinto ; Jatish Kumar ; Yasuyuki Araki ; Tomo Sakanoue ; Taishi Takenobu ; Takehiko Wada ; Tsuyoshi Kawai ; Taku Hasobe
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：June 18, 2015
• 年：2015
• 卷：119
• 期：24
• 页码：13937-13947
• 全文大小：531K
• ISSN：1932-7455

文摘

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掳), 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 (桅_FL) of [7]Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference [7]Hl (桅_FL = 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_lum (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 脳 10^鈥?. The electroluminescence of an organic light-emitting diode utilizing [7]Hl-NAIQx was successfully observed.