Role of the Alkylation Patterning in the Performance of OTFTs: The Case of Thiophene-Functionalized Triindoles

Abstract

Organic semiconductors have emerged as potential alternatives to conventional inorganic materials due to their numerous assets and applications. In this context, the star-shaped triindole core stands as a promising system to design new organic materials with enticing charge-transporting properties. Herein, we present the synthesis of three thiophene-containing triindole derivatives that feature N-alkyl chains of different lengths, from methyl to decyl. The impact of the alkylation patterning on the crystallinity of the thin films and their resultant performance as semiconductor have been analyzed. All derivatives displayed p-type semiconductor properties, as demonstrated via both TOF measurements and integration in organic thin-film transistor (OTFT) devices. The attachment of longer alkyl chains and the functionalization of the silicon substrate with octadecyltrichlorosilane (OTS) prompted better OTFT characteristics, with a hole mobility value up to 5 × 10−4 cm2 V−1 s−1. As elucidated from the single crystal, this core is arranged in a convenient cofacial packing that maximizes the π-overlapping. The analysis of the thin films also corroborates that derivatives possessing longer N-alkyl chains confer a higher degree of order and a more adequate morphology.

Confronting Positions: Para- vs. Meta-Functionalization in Triindole for P-Type Air-Stable Otfts

“…The presence of sulfur slightly ameliorated the charge carrier mobility, which goes in accordance with the relevance of sulfurated semiconductors in organic electronics [28][29][30][31]. Secondly, the length of the N-alkyl chains was studied in 10,15-dihydro-3,8,13-tris (5-methylthien-2-yl)-5H-diindolo[3,2-a:3′,2′-c]carbazole, which pointed out the relevance of medium-to-long alkyl chains over shorter ones in this particular system [27]. Albeit the aliphatic units exert a rather limited impact to the properties of the main core, they are decisive in determining the arrangement and morphology in the solid state.…”

“…Scheme 1 compiles the synthesis of the meta-substituted triindoles 2a,b. Compounds 1a [27] and 1b [26] have been synthesized analogously, as described in the literature. Commercially available 6-bromoisatin was N-alkylated to compound 3 with 1-bromohexane in anhydrous DMF, using K 2 CO 3 as base.…”

“…1, these functionalization points encompass three different kind of substitution motifs, which involve: positions 3,8,13 (referred as para with respect to the nitrogens), 2,7,12 (analogously denoted as meta) and the nitrogen heteroatoms. This topic has been explored in our research group, analyzing different structural modifications and functionalization patterns to optimize the semiconductor properties of the triindole core [26,27]. Fig.…”

“…Further insight will be acquired by means of the single-crystal structures and X-ray diffraction patterns of the films. The interest in the triindole core also resides on the notoriously long lifetime periods it displays as the active layer of a device [17,18,26,27], claiming a highly sought-after feature that is often hastily monitored in the existing literature. Therefore, this factor is likewise analyzed in this work.…”

Programming Positive Mechanofluorescence in Liquid Crystalline Elastomers

“…Carbazole is a recurrent and highly versatile scaffold within chemistry, biomedicine, and materials science because of its attractive luminescent and semiconductor properties, which can be fine-tuned through not only the subtle and rational modification of its molecular structure but also imparting control over the interactions established with the environment at the supramolecular level. − …”