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Although many chiral molecules exhibiting circularly polarized luminescence (CPL) have been reported recently, few molecular design guidelines are known for increasing the dissymmetry factor for CPL (g lum). We demonstrate that a figure-eight-shaped molecule with D 2 symmetry has excellent chiroptical properties (Φf = 0.08, |g lum| = 1.5 × 10–2), which are attributed to the parallel arrangement of μ and m as well as a good |μ|/| m | ratio.

The effect of different substituents on the fluorescence properties of [5]helicene derivatives was investigated in terms of molecular orbital symmetry. Unsubstituted [5]helicene is nonemissive due to the symmetry-forbidden S → S transition. However, the fluorescence emission rate constant (k) of [5]helicenes is efficiently increased by removing the orbital degeneracy involved in the S → S transition. As a result, we achieved a [5]helicene derivative exhibiting a high fluorescence quantum yield (Φ = 0.23) and short emission lifetime (⟨τ⟩ = 1.5 ns), which is in marked contrast to unsubstituted [5]helicene (Φ = 0.04 and ⟨τ⟩ = 26 ns).

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Fluorescence behavior of 5,10-disubstituted [5]helicene derivatives is sensitive to the type of substituent and the motif of self-assembly in the solution phase.