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Pyrene-Based Asymmetric Supramolecule: Kinetically Controlled Polymorphic Superstructures by Molecular Self-Assembly

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journal contribution
posted on 13.02.2017, 00:00 by Minwook Park, Won-Jin Yoon, Dae-Yoon Kim, Yu-Jin Choi, Jahyeon Koo, Seok-In Lim, Dong-Gue Kang, Chih-Hao Hsu, Kwang-Un Jeong
To understand the kinetically controlled polymorphic superstructures of asymmetric supramolecules, a pyrene-based asymmetric supramolecule (abbreviated as Py3M) was newly synthesized by connecting two pyrene headgroups (Py) to a biphenyl-based dendritic tail (3M) with an iso­phthala­mide connector. On the basis of thermal, microscopic, spectroscopic, and scattering results, it was realized that Py3M exhibited the monotropic phase transition between a stable crystalline phase (K1) and a metastable crystalline phase (K2). This monotropic phase transition behavior was mainly originated from the competitions of intra- and intermolecular interactions (π–π interactions and hydrogen bonds) as well as from the nanophase separations. From the two-dimensional (2D) wide-angle X-ray diffraction patterns and transmission electron microscopy images of the self-assembled Py3M superstructures, it was found that Py3M formed two synclinically tilted crystalline superstructures: the 6.75 and 4.4 nm periodicities of layered structures for K1 and K2 phases, respectively. The stable K1 phase was predominantly induced by the π–π interactions between pyrenes, while the intermolecular hydrogen bonds between iso­phthala­mides were the main driving forces for the formation of the metastable K2 phase. Ultraviolet–visible and photoluminescence experiments indicated that the photophysical properties of Py3M were directly related to their molecular packing superstructures.