Gelation or crystallization? Subtle balance of structural factors for assembly of DBA derivatives with methyl esters

Abstract

Morphology of molecular aggregates is crucially affected by molecular shape and intermolecular interactions. In 2009, we reported the unusual gelation behaviour of a curved-butadiynyl-bridged cyclic pi-conjugated molecule, octadehydrodibenzo[12]annulene ([12]DBA), possessing two methyl ester groups in noncentrosymmetric positions. Aggregation of the [12]DBA derivative occurred anisotropically to give crystalline nanofibers, which finally formed an organogel. To investigate the aggregation behaviour of the related analogues, we synthesized octadehydrotribenzo[14]annulene ([14]DBA) derivatives with two and four methyl ester groups and revealed that the [14]DBAs gave not gels but crystals, in which the molecules are stacked not in a unidirectional manner but in an alternating way. The results indicate that the gelation and crystallization of the present molecular system is derived from the subtle balance of molecular shape and intermolecular interactions.