Alkylated Dinaphtho[2,3‐b:2′,3′‐f]Thieno[3,2‐b]Thiophenes (C_n‐DNTTs): Organic Semiconductors for High‐Performance Thin‐Film Transistors

Abstract

Organic thin-fi lm transistors (OTFTs) have attracted great interest for their potential use in several electronic applications, including active-matrix displays, electronic paper, and chemical sensors. [ 1 ] Among the many semiconducting materials evaluated in the TFT confi guration, pentacene is the best as it shows the highest fi eld-effect mobility ( > 3.0 cm 2 V − 1 s − 1 ). [ 2 , 3 ] On the other hand, new organic semiconductors are being actively investigated to further improve the performance of OTFTs. In fact, superior unconventional organic semiconductors used to produce high-performance OTFTs have been recently reported, including picene (3.2 cm 2 V − 1 s − 1 ), [ 4 ] [ 6 ] and hexamethylene-tetrathiafulvalene (HMTTF, 6.9 cm 2 V − 1 s − 1 . [7] We have also developed several new heteroarenebased organic semiconductors that show high mobility in the TFT confi guration: 2,7-diphenyl[1]benzothieno[3,2-b ]benzothiophene (DPh-BTBT, 2.0 cm 2 V − 1 s − 1 ), [ 8 ] dinaphtho[2,3-b :2 ′ ,3 ′ -f ] thieno[3,2-b ]thiophene (DNTT, 2.9 cm 2 V − 1 s − 1 ), [ 9 ] and alkylatedBTBTs (C n -BTBTs, 3.9 cm 2 V − 1 s − 1 ). [ 10 ] Intrinsically, carrier transport in organic molecular solids is governed by the extent of intermolecular orbital coupling (transfer integrals), where larger orbital coupling can afford higher mobility. [ 11 ] One of the promising approaches to enhance orbital coupling is to use highly π -extended molecules: high-performance OTFTs based on picene, DTTE, or DNTT [ 12 ] that have highly π -extended structure are an example. Another effective approach is to use the self-organizing nature of organic molecules: this is exemplifi ed by DTBDT or C n -BTBTbased OTFTs, in which long alkyl groups can act as the driving force for molecular ordering in the solid state owing to the van der Waals intermolecular interaction between the alkyl groups, or the so-called molecular fastener effect, [ 13 ] that renders the semiconducting core to pack tightly, thereby enhancing carrier mobility. With these molecular design strategies for enhancing TFT performance, we focused on alkylated DNTTs (C n -DNTTs, Scheme 1 ) as new promising molecular semiconductors. In this paper, we report their synthesis, characterization, and OTFT devices that show very high fi eld-effect mobility close to 8.0 cm 2 V − 1 s − 1 .The syntheses of C n -DNTT ( n = 6, 8, 10, 12) were carried out with the same strategy as that for the parent DNTT. Starting from 6-alkyl-2-naphthaldehyde, introduction of methylthio moiety at the 3-position via the selective o -lithiation with lithium N,N,N ′ -trimethylethylenediamide and excess n-BuLi gave 3-methylthio-6-alkyl-2-naphthaldehyde in moderate yields. Low-valent titanium-mediated dimerization of the aldehyde functionality readily gave the olefi ne precursor, which was fi nally converted into C n -DNTTs in moderate to good yields via the idodine-promoted ring closing reaction (Scheme 1 ).[ 9 ] C nDNTTs are stable yellow compounds and their characterization was accomplished by spectroscopic and combustion ...

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

“…[4][5][6][7][8] Along with improving device performance, underlying charge transport mechanism has been extensively studied because it is closely related to device key parameters such as mobility, threshold voltage, subthreshold swing, and electrical and environmental stability. Charge transport of organic transistors using single crystals and thin-films has been studied from temperature (T)-dependent transistor characteristics.…”

Liquid crystalline organic semiconductors for organic transistor applications

“…100°C in dialkyl BTBTs. 4 The adoption of larger core systems such as DNTT 5 and DNBDT 7 unfortunately always result in poor solubility because of a trade-off between the solubility in solvents and the melting point, so that it is quite difficult to satisfy both requirements. …”

Organic Field-effect Transistors Based on Alkylphenyl-substituted Dinaphtho[2,1-b:2′,1′-f]thieno[3,2-b]thiophenes

“…The two approaches to enhance orbital coupling, which can afford high mobility are as follows: to develop molecules with highly conjugated O-systems and to introduce long alkyl substituents that facilitate molecular ordering in the solid state. 12 In this study, we have synthesized isomers of alkylphenyl-substituted dinaphtho[2,1-b:2B,1B-f ]thieno [3,2-b]thiophenes called 4,4B-nP-21DNTT and 6,6B-nP-21DNTT ( Fig. 1) and characterized the organic thin-film transistors based on these newly developed materials.…”

“…11 One of the possible reason is expanded conjugated O-systems allow to enhance orbital coupling, and the other is the strong molecular fastener effect -molecular ordering promoted by van der Waals intermolecular interactions among the substituent n-alkyl groups-can render the core structures of 21DNTT to pack tightly, thereby enhancing carrier mobility. 12 …”