journal menu
abstracts
CH/O interaction is recognized as a weak hydrogen bond with less directionality, compared with a strong hydrogen bond such as that between carboxylic acids. Therefore, the interaction does not seem to be suitable for precise design of crystal structures. In connection with this, however, we emphasized that the CH/O interaction, particularly that provided by methyl ester group, can utilize for affirmative generation of polymorphs of cyclic pi conjugated molecules. Since functionality of solid state materials based on pi conjugated molecules is crucially affected by their molecular arrangements, polymorphs are exactly appropriate systems to reveal the superstructure-dependent properties of such the materials, and therefore, affirmative preparation of polymorphs of pi conjugated molecules is challenging. Herein, we describe formation, crystallographic characterization, and superstructure-dependent properties of polymorphs of methyl ester functionalized dehydrobenzoannulenes (DBAs), a family of cyclic conjugated molecules consisted of benzene rings and acetylene units. We synthesized five DBA derivatives 1-5 with two types of annulene cores (octadehydrodibenzo[12]annulene and octadehydrotribenzo[14]annulene cores) and different number and position of methyl ester groups (Scheme1). These derivatives exhibit two to five polymorphic crystals with physical properties strongly depending with their supramolecular structures.[1-3] We believe that the present polymorph generation is exactly provided by rotationally flexible conformations of the ester groups and versatile ways of directionally tolerant CH/O interactions of the ester groups.
abstracts
Porous materials using organic molecules have attracted much attention due to their potential application such as gas absorption and so on. However, it is still difficult to construct porous structures from only simple organic molecules. Thus, we proposed a novel hierarchical method to construct porous structures. In this method, the first step is to build up molecular assemblies. These assemblies act to sustain porous structures with larger inclusion spaces. Then, the assemblies are accumulated by intermolecular interactions between assemblies to achieve both robustness and dynamics of the porous structures. We have previously reported organic salts composed of triphenylmethylamine (TPMA) and various sulfonic acid derivatives constructed unique molecular assemblies "supramolecular clusters" through cubic hydrogen-bonding networks. Here we demonstrate that TPMA and sulfonic acids having polyaromatic moieties give a new class of porous structures consisting of diamond networks, named as diamondoid porous organic salts (d-POSs). The supramolecular clusters are hierarchically accumulated by π–π interactions between the polyaromatic moieties to yield the d-POSs through formation of the diamond networks. Large steric hindrance of the clusters prevents the diamond networks from constructing highly interpenetrated structures, giving continuous open channels. It should be noted that the interpenetration degree of the diamond networks is controlled by tuning the bulkiness of the cluster with alteration of sulfonic acids.
