Original polymorphism in a naphthalene bisimide π-conjugated organogelator: a complex interplay between hydrogen bonding and heterocycle π-stacking. Issue 42 (9th October 2019)

• Record Type: Journal Article
• Authors: Diebold, Morgane; Christ, Elliot; Biniek, Laure; Karmazin, Lydia; Heinrich, Benoît; Contal, Christophe; Ghosh, Suhrit; Mesini, Philippe J.; Brinkmann, Martin
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 42(2019)
• Page Start: 13120
• Page End: 13129
• Publication Date: 2019-10-09
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9tc04402g
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : A naphthalene bisimide organogelator forms different supramolecular assemblies in the gel phase and in the solid states; the structures of these different polymorphs have been uncovered by electron and X-ray diffraction, UV and FTIR spectroscopies. 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.