Two isostructural halogen derivatives of 9-ethylcarbazole: Crystal structure, Hirshfeld surface analysis, and structural comparison with other simple analogs

Abstract

This article describes a detailed study of the molecular packing and intermolecular interactions in crystals of two derivatives of 9-ethylcarbazole, i.e., 3-chloro- and 3-bromo-9-ethylcarbazole (1 and 2, respectively). A significance of this study lies both in the comparison drawn between the crystal structures of these compounds and those of several of their simple analogs [i.e., 3,6-dibromo-9-ethylcarbazole (3), 3,6-dibromo-9-methylcarbazole (4), 3,6-dibromocarbazole (5), 3-bromocarbazole (6), 3,6-diiodocarbazole (7), 9-ethylcarbazole (8), 9-methylcarbazole (9) and carbazole (10)], and in the preliminary assessment of their suitability as active materials for organic electronics. This comparison shows a close similarity in the packing of molecules of three of them (i.e., 3, 4, 6) that form the π-stacks along the shortest crystallographic axes, with a substantial spatial overlap between adjacent molecules in the stacks, depending mainly on the length of substituent at position 9 of carbazole skeleton and on the ratio of (%C⋯H)/(%C⋯C) interactions. Similar to them, in the crystal structures of 1 and 2 there is slipped face-to-face π⋯π interaction, but in contrast this interaction connects two molecules of these compounds into the dimers that are further connected by C-H⋯π interaction. The molecular packing in crystals of these compounds is intermediate between the arrangement of molecules of 3, 4, and 6, where the slipped π-stacking is predominant, and the typical herringbone packing in compounds 5 and 7-10. Thus, it can be supposed that out of ten compounds analyzed here, only 3, 4, and 6 will turn to be the most promising materials for device applications (particularly for field-effect transistors).