Synthetic Control of Photophysical Process and Circularly Polarized Luminescence of [5]Carbohelicene Derivatives Substituted by Maleimide Units

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• 作者：Hayato Sakai ; Takako Kubota ; Junpei Yuasa ; Yasuyuki Araki ; Tomo Sakanoue ; Taishi Takenobu ; Takehiko Wada ; Tsuyoshi Kawai ; Taku Hasobe
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：April 14, 2016
• 年：2016
• 卷：120
• 期：14
• 页码：7860-7869
• 全文大小：520K
• 年卷期：0
• ISSN：1932-7455

文摘

A series of [5]carbohelicene derivatives substituted by electron-withdrawing maleimide and electron-donating methoxy, such as maleimide-substituted [5]carbohelicene (HeliIm) and methoxy-substituted HeliIm (MeO-HeliIm), were newly designed and synthesized to examine the electrochemical properties, excited-state dynamic and circularly polarized luminescence (CPL). First, electrochemical measurements and DFT calculations of [5]carbohelicene derivatives were performed by comparing with the structural isomers: picene derivatives. Introduction of an electron-withdrawing maleimide group onto a [5]carbohelicene core contributes to the stabilized LUMO state in HeliIm as compared to that of [5]carbohelicene (Heli), whereas the energy level of HOMO state in MeO-HeliIm increases by introducing electron-donating methoxy (MeO) groups onto a HeliIm skeleton. The HOMO–LUMO gap of MeO-HeliIm is smaller than those of HeliIm and Heli, which is similar to the steady-state spectroscopic measurements. The absolute fluorescence quantum yield (Φ_FL) of HeliIm (0.37) largely increased as compared to [5]carbohelicene, Heli (0.04), whereas Φ_FL of MeO-HeliIm (0.22) was slightly smaller than that of HeliIm. Theses photophysical processes including intersystem crossing are successfully explained by the kinetic discussions. Since [5]carbohelicene derivatives show the chirality, measurements of circular dichroism (CD) and circularly polarized luminescence (CPL) were successfully performed. In particular, HeliIm and MeO-HeliIm have provide excellent circularly polarized luminescence (CPL) and the values of the anisotropy factor g_lum were estimated to be ∼2.4 × 10^–3 and ∼2.3 × 10^–3, relatively. This is the first observation of CPL in [5]carbohelicene derivatives.