Recently, the synthesis of the racemate of an overcrowded triply fused carbo[7]helicene of formula C₆₆H₃₆ with three carbo[7]helicenes fused within a central six-membered ring was described. This molecule was found to embed an extremely contorted central six-membered ring and two negative curvatures. We report herein the resolution of the corresponding enantiomers and their conformational, structural, photophysical, and chiroptical properties. The racemization of the triply fused carbo[7]helicene was determined to proceed at a rate of k_rac = 8.06 × 10^–4 s^–1 at 175 °C in ortho-dichlorobenzene, corresponding to a barrier to enantiomerization ΔG_enant^‡ = 140.4 kJ·mol^–1, a value significantly lower than for pristine carbo[7]helicene. Interestingly, the crystalline structures of the racemic and enantiopure materials show some differences regarding the molecular geometry, with an increased negative curvature in the latter cases. This unusual curved delocalized π-conjugated system afforded notably green fluorescence at room temperature and far-red phosphorescence at low temperature. Finally, electronic circular dichroism and circularly polarized luminescence responses of the enantiopure compounds have been measured and showed very close absorption and emission dissymmetry factors, g_abs and g_lum, respectively, of ca. 2.6 × 10^–3, indicating a similar chiral rigid geometry for both ground and excited states.

中文翻译：

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过度拥挤的三重稠合碳[7]螺烯的构象、结构和手性光学性质

_{最近，描述了式C 66} H ₃₆的过度拥挤三稠合碳[7]螺烯与稠合在中心六元环内的三个碳[7]螺烯的外消旋体的合成。人们发现该分子嵌入了一个极其扭曲的中心六元环和两个负曲率。我们在此报告了相应对映体的分辨率及其构象、结构、光物理和手性光学性质。_{三重稠合碳[7]螺烯的外消旋化在 175 ° C}的邻二氯苯中以k _rac = 8.06 × 10 ^–4 s ^–1的速率进行，对应于对映体化的障碍 Δ Genant ^‡ = 140.4 kJ·mol ^–1，该值明显低于原始碳[7]螺烯。有趣的是，外消旋和对映体纯材料的晶体结构在分子几何形状方面表现出一些差异，在后一种情况下负曲率增加。这种不寻常的弯曲离域π共轭系统在室温下提供显着的绿色荧光，在低温下提供远红磷光。最后，测量了对映体纯化合物的电子圆二色性和圆偏振发光响应，并显示出非常接近的吸收和发射不对称因子_{gabs 和 glum ，}分别约为约100%。2.6 × 10 ^–3，表明基态和激发态具有相似的手性刚性几何结构。