Synthetic Control of Photophysical Process and Circularly Polarized Luminescence of Carbohelicene Derivatives Substituted by Maleimide Units
journal contributionposted on 27.03.2016, 00:00 by Hayato Sakai, Takako Kubota, Junpei Yuasa, Yasuyuki Araki, Tomo Sakanoue, Taishi Takenobu, Takehiko Wada, Tsuyoshi Kawai, Taku Hasobe
A series of carbohelicene derivatives substituted by electron-withdrawing maleimide and electron-donating methoxy, such as maleimide-substituted 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 carbohelicene derivatives were performed by comparing with the structural isomers: picene derivatives. Introduction of an electron-withdrawing maleimide group onto a carbohelicene core contributes to the stabilized LUMO state in HeliIm as compared to that of 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 (ΦFL) of HeliIm (0.37) largely increased as compared to carbohelicene, Heli (0.04), whereas ΦFL 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 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 glum were estimated to be ∼2.4 × 10–3 and ∼2.3 × 10–3, relatively. This is the first observation of CPL in carbohelicene derivatives.
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CPLenergy levelHeliIm skeletonpicene derivativesspectroscopic measurementselectrochemical propertiesanisotropy factor g lumTheses photophysical processesΦ FLfluorescence quantumSynthetic ControlPhotophysical ProcessLUMO statecircularlyMaleimide Unitselectrochemical measurementsDFT calculationsHOMO statecarboheliceneluminescenceCircularly Polarized Luminescence