Powder X-ray diffraction as a powerful tool to exploit in organic electronics: shedding light on the first N,N ',N ''-trialkyldiindolocarbazole

The first crystal structure of a fully N-alkylated diindolocarbazole derivative, namely, 5,8,14-tributyldiindolo[3,2-b;2',3'-h]carbazole (1, C36H39N3), has been determined from laboratory powder X-ray diffraction (PXRD) data. A complex trigonal structure with a high-volume unit cell of 12987 angstrom(3) was found, with a very long a(=b) [52.8790 (14) angstrom] and a very short c [5.36308 (13) angstrom] unit-cell parameter (hexagonal setting). The detailed analysis of the intermolecular interactions observed in the crystal structure of 1 highlights its potential towards the implementation of this core as a semiconductor in organic thin-film transistor (OTFT) devices. Since the molecule has a flat configuration reflecting its pi-conjugated system, neighbouring molecules are found to stack atop each other in a slipped parallel fashion via pi-pi stacking interactions between planes of ca 3.30 angstrom, with a centroid-centroid distance between the aromatic rings corresponding to the shortest axis of the unit cell (i.e. c). The alkylation of the three N atoms proves to be a decisive feature since it favours the presence of C-H center dot center dot center dot pi interactions in all directions, which strengthens the crystal packing. As a whole, PXRD proves to be a valuable option for the resolution of otherwise inaccessible organic crystal structures of interest in different areas.