No abstract

Ladder-type molecules, which possess an extended aromatic backbone, are particularly sought within the optoelectronic field. In view of the potential of the 14H-bis[1]benzothieno[3,2-b:2’,3’-h]carbazole core as a p-type semiconductor, herein we studied a set of two derivatives featuring a different alkylation patterning. The followed synthetic route, involving various sulfurated carbazole-based molecules, also resulted in a source of fluorophores with different emitting behaviors. Surprisingly, the sulfoxide-containing fluorophores substantially increased their blue fluorescence with respect to the nearly non-emitting sulfur counterparts. On this basis, we could shed light on the relationship between their chemical structure and their emission as an approach for future applications. Considering the performance in organic thin-film transistors, both bisbenzothienocarbazole derivatives displayed p-type characteristics, with hole mobility values up to 1.1 × 10−3 cm2 V−1 s−1 and considerable air stability. Moreover, the role of the structural design has been correlated with the device performance by means of X-ray analysis and the elucidation of the corresponding single crystal structures.

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.

No abstract

Encouraged by the outstanding performance of pentacene, the perspective over enhanced organic semiconductors has been focused on studying analogous ladder-type materials. In this context, the case of the diindolo­[3,2-b:2′,3′-h]­carbazole core is a promising example of a semiconductor with improved stability. Herein, we report the synthesis of five diindolo­[3,2-b:2′,3′-h]­carbazole derivatives displaying different alkylation patterning, as well as their integration in organic thin-film transistors. The elucidation of the single-crystal structures of three of the derivatives, accomplished by means of powder X-ray diffraction (PXRD), provided further insight into the intermolecular disposition of this core. As a result, the relationship between the structural design and the performance of the final devices could be analyzed. Globally, a scope of mobility values from 10–6 to 10–3 cm2 V–1 s–1 was achieved by just fine-tuning the length of the alkyl chains and the type of passivation layer applied onto the SiO2 surface. Remarkably, all the fabricated devices excel in terms of temporal and air stability with a shelf lifetime up to years, a coveted feature in organic electronics that confirms the potential of this core.