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

Abstract

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 Å3 was found, with a very long a(=b) [52.8790 (14) Å] and a very short c [5.36308 (13) Å] 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 π-conjugated system, neighbouring molecules are found to stack atop each other in a slipped parallel fashion via π–π stacking interactions between planes of ca 3.30 Å, 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...π 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.

Insight into the Diindolo[3,2-b:2′,3′-h]carbazole Core as an Air-Stable Semiconductor for OTFTs

“…Indeed, this approach was confirmed as a convenient procedure for determining the crystal structure of the tributylated derivative 1b. 35 On the basis of these initial results, the aforementioned protocol also succeeded in the elucidation of two additional structures, that is, derivatives 1a and 1d. estimated density value of 1.2 Mg/m 3 , the number of molecules in the unit cell was calculated to be Z = 16 for 1a and Z = 4 for 1d.…”

“…Consequently, we attempted the elucidation of their crystal structures from powder X-ray diffraction (PXRD). Indeed, this approach was confirmed as a convenient procedure for determining the crystal structure of the tributylated derivative 1b . On the basis of these initial results, the aforementioned protocol also succeeded in the elucidation of two additional structures, that is, derivatives 1a and 1d .…”

“…This element also plays a key role in determining the performance of the final device. − In order to get further insight into the role of these structural features and the main core design, the elucidation of the crystal structures represented a crucial step. In this context, the resolution via powder X-ray diffraction (PXRD) proved as a valuable support for the interpretation of derivatives 1a , 1b, and 1d , which represent the only reported crystal structures of N -trialkylated diindolocarbazole derivatives to date. The notorious stability of these materials as p-type semiconductors in OTFT devices, which extends to periods up to years, definitely fosters the potential of this core.…”