High‐Mobility Regioisomeric Thieno[f,f′]bis[1]benzothiophenes: Remarkable Effect of Syn/Anti Thiophene Configuration on Optoelectronic Properties, Self‐Organization, and Charge‐Transport Functions in Organic Transistors

Abstract

π‐Conjugated thienoacene‐based organic semiconductors with high charge carrier mobility and processability have been intensively pursued for electronic device applications, including organic field‐effect transistors (OFETs). Their charge carrier mobility is an important figure of merit, and is influenced not only by the intrinsic electronic structure at molecular level, but also by the molecular packing arrangement and crystallinity in the solid state. In this work, the focus is on a unique regioisomeric thienoacene system involving dialkyl‐thieno[f,f′]bis[1]benzothiophene isomers having different syn/anti thiophene configurations (syn‐ and anti‐TBBT‐8). The effects of these regioisomeric structures on the physicochemical properties, self‐organization behavior, and charge‐transport functions are systematically investigated using experimental and theoretical analyses. The structural analyses indicate that the syn‐ and anti‐TBBT‐8 isomers self‐organize into completely different packing arrangements, in the form of solution‐crystallized microribbons and thin films. The resulting charge‐transport properties are strongly dependent on the syn/anti thiophene configurations. Remarkably, solution‐processed OFETs using the syn‐TBBT‐8 isomer show high hole mobilities of up to 10.1 cm2 V−1 s−1, which are more than one order of magnitude higher than those of the anti‐TBBT‐8 isomer. This work highlights the importance of the regioisomeric molecular configuration of thienoacene‐based organic semiconductors for developing high‐performance electronic devices.

Solution-Processable Organic Semiconductors Featuring S-Shaped Dinaphthothienothiophene (S-DNTT): Effects of Alkyl Chain Length on Self-Organization and Carrier Transport Properties

“…A similar dominant uniaxial orientation of single-crystalline domains has also been achieved with other alkylated thienoacenes in their dip-coated thin films. 45,46 In the POM under the crossed Nicols condition, the birefringence of the dip-coated film of S-DNTT-10 was extinguished when the pulling direction was aligned with the polarizer or analyzer and was maximally bright when the film sample was rotated by 45°( Figure 8f), verifying a high degree of crystallographic alignment on a macroscopic scale. 45,62 ■ CONCLUSIONS…”

“…As for S-DNTT-8 and -10, relatively large values of transition enthalpies (ΔH = 26−27 kJ mol −1 ) and entropy changes (ΔS = 56−58 J mol −1 K −1 ) in their LC-to-isotropic phase transition and vice versa imply the formation of a highorder smectic LC phase. 38,46 Despite the lowering of T i , the total ΔS appears to increase with elongation of the alkyl chains (Figure 2c), suggesting that greater intramolecular forces could be preserved in the crystalline phases of S-DNTTs with longer alkyl chains (for 4 ≤ n ≤ 10) through the molecular fastener effect.…”

“…Motivated by the excellent performance of S-DNTT-10 in vacuum-deposited OFETs, we then investigated the performance of its solution-processed OFETs manufactured by dip-coating. ,,− This technique can typically provide higher film quality and better control of the morphology than vacuum deposition as well as spin-coating. The bare Si/SiO 2 substrates were dipped into a toluene solution (1.0 g L –1 ) at 50 °C and lifted out at a constant pulling rate (4 μm s –1 ) to obtain uniformly grown continuous thin films of S-DNTT-10 with a thickness of 30–50 nm (corresponding to approximately 10–16 monolayers).…”

“…Particularly, OFETs based on S-DNTT-10 with two decyl chains exhibited exceptionally high hole mobilities exceeding 10 cm 2 V –1 s –1 and sufficient operational and environmental stabilities. Replacing common linear thienoacenes with crooked π-cores − is no longer a trivial modification but rather an effective strategy that can open a new prospect in the design of solution-processable organic semiconductors with both excellent charge-transport and physicochemical properties.…”

Synthesis and Physicochemical Properties of 2,7-Disubstituted Phenanthro[2,1-b:7,8-b’]dithiophenes

“…Recently, thiophene-containing fused molecules have played an important role in the progress of OFETs [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. For instance, [ 1 ]benzothieno [3,2- b ][ 1 ]benzothiophene (BTBT) [ 43 ], dinaphtho[2,3- b :2′,3′- f ]thieno[3,2- b ]thiophene (DNTT) [ 44 ], and their dialkyl derivatives formed a herringbone packing structure showing hole mobilities higher than 1 cm 2 V −1 s −1 .…”