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).
Highlights
Modern electronics, aiming to further material- and energyefficient miniaturization and the consequent cheapening of the electronic and optoelectronic devices increasingly dominant in our daily life, (e.g., TV, bank cards, computer screens, etc.), is increasingly focused on the use of properties and phenomena occurring in the ever growing group of diverse semi-conductive organic materials, which include both compounds with low molecular weight (‘‘small molecules’’, SM) and small oligomers, and macromolecular polymers [1, 2]
The bond lengths within carbazole skeletons of these molecules are in a good agreement with the corresponding distances in the unsubstituted carbazole [41], and the exceptions here are the lengths of the C2–C3 and C2–C3 and C6–C7 bonds; they are shorter by 0.017 (C2–C3 and C6–C7 in 1 and 2, respectively) and 0.019 Athan the corresponding distances in carbazole
The X-ray crystal structures of 3-chloro- and 3-bromo-9ethylcarbazole were described and compared with those of several of their simple analogs, including 9-ethylcarbazole, 9-methylcarbazole, unsubstituted carbazole and their mono- and di-substituted halogen derivatives. This comparison shows that modification of the molecular structure of the carbazole by replacing one of the C–H and N–H protons by Cl or Br atom and ethyl group, respectively, results in (i) an elimination of N–HÁÁÁp(5-membered ring), C1– H1ÁÁÁp(benzene ring) and C4–H4ÁÁÁp(benzene ring) interactions causing a typical herringbone arrangement of carbazole skeletons, (ii) associated with this a major decrease of proportion of CÁÁÁH/HÁÁÁC contacts, and (iii) an appearance of the HÁÁÁX/XÁÁÁH contacts and CÁÁÁC contacts corresponding to the slipped face-to-face pÁÁÁp interactions linking molecules into dimers
Summary
Modern electronics, aiming to further material- and energyefficient miniaturization and the consequent cheapening of the electronic and optoelectronic devices increasingly dominant in our daily life, (e.g., TV, bank cards, computer screens, etc.), is increasingly focused on the use of properties and phenomena occurring in the ever growing group of diverse semi-conductive organic materials, which include both compounds with low molecular weight (‘‘small molecules’’, SM) and small oligomers, and macromolecular polymers [1, 2]. Taking into account the fact that the typical herringbone (HB) packing of molecules in the solid-state structures of unsubstituted AHs and HHs is not very beneficial, especially in terms of electrical performance of OFETs (a measure of this performance is the mobility of the charge carriers) and high efficiency photovoltaic and solar cells, attempts to improve the arrangements of molecules through modifying the intermolecular interactions governing the solid-state packing, have been a field of intensive research in recent years [10,11,12,13,14,15,16,17,18] These attempts include the chemical modification of molecules of these hydrocarbons through the introduction of substituents on their periphery, and the construction of multicomponent molecular solids or co-crystals. Analyzing crystal structures of di-substituted naphthalene derivatives such as 1,3-, 1,6-, 1,7-, 2,3-, 2,6-, and 2,7dihydroxynaphthalene (CSD codes: HEGFAB [28], RIGMOK [29], LICKEO [30], VOGSEP [27], VOGSAL [27], and NPHLDL01 [31], respectively) and of 2-naphthol
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