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Original polymorphism in a naphthalene bisimide π-conjugated organogelator: a complex interplay between hydrogen bonding and heterocycle π-stacking

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Abstract

This study focuses on the structure of different supramolecular assemblies formed in the gel phase and in the solid state by a naphthalene-bisimide organogelator: N,N′-di(2-(3,4,5-trioctyloxybenzamido))eth-1-yl naphthalene-1,4,5,8 tetracarboxylic acid bisimide (NDI2). This molecule is formed by a naphthalene bisimide core with symmetric dendrons composed of a flexible alkyl linker, an amide group and a trialkoxyphenyl group. The structure, especially the original polymorphism of this molecule, was correlated with optical and electronic properties in the solid state. Four polymorphs have been prepared in pure form: a dried gel phase, a quenched metastable liquid crystalline phase, a crystalline phase and its sister phase with molten alkyl side chains. The molecular packing of those phases was determined by X-ray diffraction, electron diffraction and high resolution TEM. UV-vis and infrared spectroscopy of the polymorphs uncover the nature of intermolecular π-stacking and H-bonding interactions. In the fibrils of the gel phase, NDI2 molecules form columnar stacks and the fiber axes correspond to the direction of H-bonds between amide groups. The crystalline phase shows an unusual packing where each NDI is π-stacked between two phenyl groups of the adjacent NDI2 molecules. In the metastable LC phase NDI2 molecules assemble into 6/1 supramolecular helices grouped in a frustrated trigonal unit cell. Temperature-dependent TEM, UV-vis and FTIR helped to unveil the molecular reorganization upon transformation between these different polymorphs. Finally, a global phase diagram has been obtained.

Graphical abstract: Original polymorphism in a naphthalene bisimide π-conjugated organogelator: a complex interplay between hydrogen bonding and heterocycle π-stacking

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Publication details

The article was received on 09 Aug 2019, accepted on 29 Sep 2019 and first published on 09 Oct 2019


Article type: Paper
DOI: 10.1039/C9TC04402G
J. Mater. Chem. C, 2019, Advance Article

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    Original polymorphism in a naphthalene bisimide π-conjugated organogelator: a complex interplay between hydrogen bonding and heterocycle π-stacking

    M. Diebold, E. Christ, L. Biniek, L. Karmazin, B. Heinrich, C. Contal, S. Ghosh, P. J. Mesini and M. Brinkmann, J. Mater. Chem. C, 2019, Advance Article , DOI: 10.1039/C9TC04402G

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