Conformational Polymorphism of Octadehydrodibenzo[12]annulene with Dimethyl Phthalate Moieties

In this study, we found that an octadehydrodibenzo[12]annulene derivative with two dimethyl phthalate moieties yielded three polymorphic crystals I, II, and III, in which the annulene core arranges in herringbone, parallel-π-stacked, and zigzag-π-stacked fashion, respectively. This is the first example for dehydroannulenes to show polymorphic crystal structures. These polymorphs are brought from varied conformations of the dimethyl phthalate moieties because the direction of the carbonyl oxygen atoms in the phthalate affects the manner of CH/O interaction abundantly observed in the present systems. It is also revealed that the decomposition temperature of the polymorphic crystals varied over a wide range of values (112−163 °C), even though the crystals are composed of an identical molecule. This indicates that the molecular arrangement might have significant influence on the thermal stability and/or intermolecular reactivity of the annulene.

本研究中，我们发现一种带有两个邻苯二甲酸二甲酯（dimethyl phthalate）基团的十八脱氢二苯并[12]轮烯（octadehydrodibenzo[12]annulene）衍生物可生成三种多晶型晶体I、II与III，三类晶体中的轮烯核心分别采取人字排列、平行π堆叠以及之字形π堆叠的排布方式。这是脱氢轮烯类化合物呈现多晶型晶体结构的首例报道。该类多晶型体的差异源于邻苯二甲酸二甲酯基团的不同构象：邻苯二甲酸酯中羰基氧原子的取向，会对本体系中大量存在的CH/O相互作用（CH/O interaction）模式产生显著影响。研究同时发现，尽管这些晶体均由相同分子构成，但其分解温度分布于较宽区间（112−163 ℃）内。这表明分子排布方式可能对该轮烯类化合物的热稳定性及/或分子间反应活性具有显著影响。