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Crystal Engineering of Dibenzothiophenothieno[3,2‑b]thiophene (DBTTT) Isomers for Organic Field-Effect Transistors Hung-Yang Chen,*,† Guillaume Schweicher,*,‡ Miquel Planells,† Sean M. Ryno,§ Katharina Broch,∥ Andrew J. P. White,† Dimitrios Simatos,‡ Mark Little,† Cameron Jellett,† Samuel J. Cryer,†,# Adam Marks,† Michael Hurhangee,† Jean-Luc Bred́ as,§ Henning Sirringhaus,‡ and Iain McCulloch†,⊥ †

Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K. Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K. § Solar and Photovoltaics Engineering Research Center, Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia ∥ Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany ⊥ King Abdullah University of Science and Technology (KAUST), Kaust Solar Center (KSC), Thuwal 23955-6900, Saudi Arabia # Department of Chemistry, University College London, London WC1H 0AJ, U.K.

Chem. Mater. 2018.30:7587-7592. Downloaded from pubs.acs.org by UNIV OF RHODE ISLAND on 11/30/18. For personal use only.

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S Supporting Information *

ABSTRACT: Three thiophene ring-terminated benzothieno[3,2-b]benzothiophene (BTBT) derivatives, C-C6-DBTTT, C-C12-DBTTT, and L-C12-DBTTT, were designed and synthesized, differing in the isomerization of alkyl chain position as well as aromatic core construction. A study of crystal structure and electronic properties combined with a theoretical investigation was performed to understand the structure− property relationships for the application of these molecules in organic field-effect transistors (OFETs). Different crystal packing structures were observed for these three isomers by single-crystal X-ray diffraction as a result of a crystal engineering molecular design approach. The highest charge-carrier mobility was observed for the isomer with a collinear core, L-C12-DBTTT. Preliminary results demonstrated a promising hole mobility of 2.44 cm2 V−1 s−1, despite the polymorphism observed in ambient conditions.

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INTRODUCTION Organic field-effect transistors (OFETs) have sparked intensive interest in both the academic and industrial fields due to their application in low-cost and flexible electronics. Charge carrier mobility μ (cm2 V−1 s−1), defined as the drift velocity of the charge carrier (cm s−1) per unit of applied electric field (V cm−1), is a key figure of merit for these OFET devices. The past three decades have witnessed a tremendous improvement in the charge carrier mobility in both conjugated polymer and small-molecule organic semiconductors. Mobilities of >1−10 cm2 V−1 s−1 have been achieved in both p-type and n-type1 transport through intensive materials development and device optimization, exceeding amorphous silicon-based FETs (0.5−1.0 cm2 V−1 s−1).2 Thienoacene-based polymers3 and small molecules4 have been prominent in the materials classes as p-channel semiconductors for OFETs due to their high chemical stability and potential for optimal electronic intermolecular coupling. For example, benzothieno[3,2-b]benzothiophene (BTBT) is one of the most studied molecular cores in small molecule OFETs. Owing to its poor filmforming property and high ionization potential (IP) (5.8 eV),4 © 2018 American Chemical Society

structural modifications on the parent BTBT core have been necessary to successfully achieve high mobility in OFET devices. Two main approaches for the molecular design of BTBT-based small molecule OFETs have been applied: first, grafting of aromatic rings or long hydrocarbon chains on the 2,7-positions of the BTBT core and, second, π-conjugation extension. 2,7-Diphenyl[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) was the first reported high mobility BTBT analogue with mobility up to 2.0 cm2 V−1 s−1 achieved in a vapor-processed OFET device.5 DPh-BTBT exhibits a reduced IP of 5.6 eV compared to that of the parent BTBT, which is beneficial for hole injection from electrodes and can be attributed to the extension of its π-conjugation. The substitution of long hydrocarbon chains does not adversely affect the intermolecular packing of the BTBT core structure; rather, these chains induce closer packing for the molecules due to the van der Waals intermolecular interaction between Received: June 30, 2018 Revised: October 23, 2018 Published: October 25, 2018 7587

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Figure 1. (a) Molecular structures of different DBTTT derivatives. (b) Side view of the packing structure highlighting the side-chain behavior. (c) Lattice parameters of the crystalline structure [Å]. (d) Packing of the aromatic cores underscoring the formation of a classical herringbone motif for DBTTT and L-C12-DBTTT, a slipped cofacial packing for C-C6-DBTTT, and a slipped-stack sandwich packing for C-C12-DBTTT (side chains are omitted for clarity).

demonstrate the crystal engineering of three thiophene ringterminated BTBT derivatives for OFET applications by varying the isomerism of the alkyl side chain and the aromatic core.

alkyl groups. This enhanced packing also results in significantly smaller IPs of 5.3 eV for alkylated BTBT molecules (CnBTBT).6 Illustrating the π-conjugation extension approach, several highly π-extended molecules based on the BTBT core, such as DNTT,7 DATT,8 BBTBDT,9 BNTBDT,9 and BBTNDT,10 have also demonstrated high charge carrier mobility, with values in excess of 1.0 cm2 V−1 s−1. One of the crucial factors in the high charge carrier mobility of these BTBT derivatives is their herringbone molecular packing, realizing a two-dimensional (2D) electronic structure in the thin film morphology. This can be attributed to their effective intermolecular interactions through short S−S contacts by sulfur atoms in the central thienothiophene moiety of the BTBT core. Recently, extending the π-conjugation of BTBT core was achieved by adding thiophene rings as the terminal ring, dibenzothiopheno[6,5-b:6′,5′-f ]thieno[3,2-b]thiophene (DBTTT),11 to further enhance S−S and S−C interactions, thus increasing the compactness of the packing. Compared with its electronically equivalent benzene analogue, DNTT, DBTTT molecules showed shorter intermolecular π−π distance and higher packing density, demonstrating a high mobility of 19.3 cm2 V−1 s−1 in a polycrystalline thin-film transistor. Previously, we have also reported a new polymer containing a repeat unit based on the BTBT core with two thiophene rings as the terminal rings, tetradodecylthieno[3′,2′:6,7][1]benzothieno[3,2-b]-thieno[3,2-g][1]benzothiophene (DTBTBT), which shows a mobility of 0.1 cm2 V−1 s−1 when copolymerized with thiophene.12 The crystal packing and OFET performance for the core structure of DTBTBT were not explored; therefore, we designed and synthesized three isomers of DTBTBT by varying the alkyl side chain position (changing from the lateral position to the axial position) and the position of the terminal thiophene rings (from a curved core to a linear core). In this work, we

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RESULTS AND DISCUSSION

The chemical structures of the investigated three isomers are presented in Figure 1a. For consistency, two different aromatic cores are both denoted as DBTTT with C- and L- representing curved and linear cores, respectively. The reported nonalkylated DBTTT (dibenzothiopheno[6,5-b:6′,5′-f ]thieno[3,2b]thiophene) is also included for comparison. Three alkylated DBTTT isomers were obtained according to the synthetic routes outlined in Schemes S1−S3 of the Supporting Information. The two curved DBTTT isomers (C-C6DBTTT and C-C12-DBTTT) were synthesized from the same core structure, 2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene, with different substituents (compounds 2 and 9 in Schemes S1 and S2) to afford the final products, respectively. Compounds 2 and 9 were separately synthesized from Negishi and Stille coupling reactions in good yields, respectively. C-C6-DBTTT was obtained by the palladium (Pd)-catalyzed double cross-coupling bis-annulation reaction13 via the tetrabromo-tetraaryl compound 2 and vic-diborylated tetradec-7-ene compound 3. C-C12-DBTTT was synthesized from a platinum (Pt)-catalyzed intramolecular cyclization of two alkyne groups on the thieno[3,2-b]thiophene derivative 9. The synthesis of the linear DBTTT isomer, L-C12-DBTTT, was performed following a literature procedure.11 The key step in preparing L-C12-DBTTT employed an acid-catalyzed intramolecular cyclodehydration (i.e., hetero-Bradsher reaction14) from dicarboxaldehyde compound 13, which was obtained in three steps starting from the commercially available thieno[3,2-b]thiophene. The full synthetic procedures 7588

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aromatic cores in two dimensions, a key component for good charge transport properties. Crystallographic information files (CIFs) for different DBTTT derivatives are available in the Supporting Information [these data can also be obtained free of charge from The Cambridge Crystallographic Data Centre; CCDC 1590306 (C-C6-DBTTT), CCDC 1590307 (C-C12DBTTT), and CCDC 1590308 (L-C12-DBTTT)]. To have a clear quantitative and visual insight into the intermolecular interactions, Hirshfeld surfaces of the DBTTT derivatives and their relative 2D fingerprints were calculated using Crystal Explorer (Figure S6). Interestingly, the derivatives C-C6-DBTTT and C-C12-DBTTT do not present the dominant interactions found in DBTTT and L-C12DBTTT (S···S, C···S, and C−H···π), as seen in the Hirshfeld surfaces as bright red areas (shorter contacts). A look at the 2D fingerprint plots (Figure S7) clearly reveals that the packing environment is completely different for the three observed molecular packings. The C−H···π hydrogen bonds in DBTTT and L-C12-DBTTT appear as a pair of wings of almost equal length in the (di, de) regions of (1.8 Å, 1.2 Å) and (1.2 Å, 1.8 Å). The absence of such distinct features in C-C6-DBTTT and C-C12-DBTTT points to the lack of such strong directional interactions. The presence of C−H···S interactions is manifested in the form of two spikes appearing in the (di, de) regions at (1.9 Å, 1.2 Å) and (1.2 Å, 1.9 Å) in the fingerprint plots. These C−H···S interactions act as additional reinforcements within the π-stacked columns of C-C6-DBTTT and C-C12-DBTTT, with the π−π interactions visible in the regions of di = de = 2.0 Å. A look at the relative contributions of the various close intermolecular contacts for the different alkylated DBTTT derivatives (Figure S7) highlights the driving role of the alkyl chains in the crystal packing of the alkylated DBTTT derivatives since the H···H contacts account for ∼70% of the Hirshfeld surface area. The C···H contacts, corresponding to C−H···π interactions, vary significantly, from 5.8% in C-C6-DBTTT to 15.1% in L-C12-DBTTT due to the herringbone packing in the latter case. Moreover, the C···C contacts, corresponding to π···π interactions, are as low as 0.1% in L-C12-DBTTT. The ionization potentials (IPs) of the three investigated isomers, estimated using photoelectron spectroscopy in air (PESA), are 5.49, 5.34, and 5.17 eV for C-C6-DBTTT, C-C12DBTTT, and L-C12-DBTTT, respectively. Despite the same conjugated core in the case of C-C6-DBTTT and C-C12DBTTT, the different IP values arise from different molecular packing patterns and intermolecular interactions. Compared with the IP of non-alkylated DBTTT (5.32 eV),11 the smaller IP for L-C12-DBTTT may imply that long hydrocarbon chains induce a more closely packed molecular arrangement, which enhances intermolecular electronic coupling interactions between adjacent molecules. This difference is consistent with those observed in BTBT/Cn-BTBT and DNTT/CnDNTT molecules.4 To further reinforce this idea, we performed theoretical calculations to determine the molecular ionization energies and electronic polarization energies (P+).19 The gas-phase IEs suggest an ordering similar to the PESA measurements of 7.00, 6.67, and 6.63 eV for C-C6-DBTTT, CC12-DBTTT, and L-C12-DBTTT, respectively. However, the IE differences between the molecules are largely different from those of the experimental values, and as the packing changes between each of the molecules the local molecular environment is expected to be different for each of the systems. The electronic polarization energies were calculated to be 0.97,

are detailed in the Supporting Information. These three isomers exhibit significantly different solubility in common organic solvents at room temperature, in descending order of solubility: C-C6-DBTTT > C-C12-DBTTT > L-C12-DBTTT. The thermotropic behaviors of the three DBTTT isomers were investigated by differential scanning calorimetry (DSC) (Figure 2). All isomers exhibit good thermal stability with

Figure 2. DSC curves of the three alkylated DBTTT isomers. Inset shows polarized optical microscope (POM) images of the liquid crystal phases of C-C12-DBTTT and L-C12-DBTTT.

thermal decomposition temperature (Td) higher than 400 °C. Interestingly, DSC scans of these isomers highlight several phase transitions in the range 25−300 °C. Both C-C12DBTTT and L-C12-DBTTT exhibit more than one phase transition, including the presence of liquid-crystal (LC) phases. As examined under a polarized optical microscope (POM), a nematic LC phase was observed after the isotropic to LC crystallization at 176 °C during the cooling scan for C-C12DBTTT. L-C12-DBTTT presents several crystalline phases differentiated by small enthalpy energies below the LC to crystal transition taking place at 267 °C.15 Between 267 and 280 °C, a LC phase assigned as a SmA phase16 persists before the isotropic melt at 282 °C. C-C6-DBTTT shows a sharp melting peak at 175 °C during the heating scan and exhibits unresolved crystallization events during the cooling scan. The strong difference of thermotropic behavior of the investigated isomers is mainly attributed to the various anchored positions of alkyl chains. The LC phases of C-C12-DBTTT and L-C12DBTTT arise from their rodlike molecular shapes with alkyl chains anchored axially to the rigid aromatic core. This tends to self-align molecules and induce a long-range directional order with their long axis roughly parallel. A similar phenomena was also observed recently in didodecyl[1]benzothieno[3,2-b][1]benzothiophene isomers.17 Single crystals of the different DBTTT derivatives were grown by slow recrystallization from a saturated 1,2dichlorobenzene solution. Structure determination was realized by single-crystal X-ray diffraction, and the complete crystal data are available in the Supporting Information (the crystal structure of DBTTT has previously been solved by Lee and coworkers11). L-C12-DBTTT, the axial alkylated version of DBTTT, adopts a classical layer-by-layer herringbone packing motif mostly stabilized by CH···π interactions (like DBTTT, see Figure 1). In comparison, cofacial interdigitated structures dominated by π−π interactions are observed for C-C6DBTTT and C-C12-DBTTT that differ by the number of alkyl substitutions and the position of their lateral thiophene unit on the aromatic core. C-C6-DBTTT and C-C12-DBTTT exhibit a slipped cofacial packing and a slipped-stack sandwich packing, respectively.18 The shortest stacking distance between molecular planes, 3.59 Å, is obtained for C-C12-DBTTT. Table S1 highlights the different distances of stacking and slippage from the structures. DBTTT and L-C12-DBTTT present consequently favorable close contacts between the 7589

DOI: 10.1021/acs.chemmater.8b02757 Chem. Mater. 2018, 30, 7587−7592

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Chemistry of Materials 0.85, and 1.05 eV for C-C6-DBTTT, C-C12-DBTTT, and LC12-DBTTT, respectively, suggesting that the environment of charge carriers in L-C12-DBTTT is more stabilizing than either C-C6-DBTTT or C-C12-DBTTT and possibly due to denser packing of L-C12-DBTTT. Correcting the values of the molecular IEs with the calculated polarization energies gives final IE values of 6.03, 5.82, and 5.58 eV for C-C6-DBTTT, CC12-DBTTT, and L-C12-DBTTT, respectively, in excellent agreement with the IE differences from PESA. Density function theory (DFT) calculations at the ωB97XD/aug-cc-pvdz level was performed to understand the electronic interactions between adjacent π-systems of three DBTTT isomers to collect the theoretical estimates of two important energetic parameters for charge transport: (i) the charge transfer integral (J) and (ii) the reorganization energy (λ). Figure 3 shows the corresponding indexation of the

ization of polycrystalline bottom-gate top-contact organic fieldeffect transistors (OFETs; 20 nm thick evaporated films, substrates kept at room temperature). Figure 4 shows

Figure 3. Top view of the packing structures showing the indexation of the molecules used for calculations of the transfer integrals and their related values [meV] (side chains are omitted for clarity). Negligible couplings have been omitted for clarity. Calculations at the ωB97X-D/aug-cc-pvdz level.

Figure 4. (a) Transfer characteristics measured in the linear and saturation regime (logarithmic scale). (b) Output characteristics. (c) Transfer characteristics in the linear and saturation regime (linear and square root scale respectively). (d) Gate-voltage dependence of the linear and saturation mobility for L-C12-DBTTT OFETs (L = 100 μm, W = 700 μm) presenting F4-TCNQ and MoO3 doped contacts. (e) Transfer characteristics measured in the saturation regime. (f) Gate-voltage dependence of the saturation mobility for C-C6DBTTT, C-C12-DBTTT, and L-C12-DBTTT OFETs (L = 100 μm, W = 700 μm) using MoO3 doped contacts.

molecules within the bulk single-crystal phase. Among three isomers, L-C12-DBTTT presents the most balanced transfer integrals along three directions (92, 59, and 17 meV) within a molecular layer compared with the other two isomers wherein couplings are only significant along one direction. This is due to its herringbone packing that favors a 2D charge transport compared to the 1D slip-stack packing present in C-C6DBTTT. Moreover, the transfer integral along the edge-toedge pair (the a-axis) is significantly larger in L-C12-DBTTT (92 meV) than in the well-known, high-performant C12-BTBT (79 meV) under the same calculations. This may be attribute to the extended π-conjugation for L-C12-DBTTT that enhances the intermolecular orbital overlap.4 For C-C6DBTTT and C-C12-DBTTT, significant transfer integrals are calculated only along the π−π stacking axis, which means the spatial overlaps of HOMO wave functions between molecular columns are extremely small. In particular, C-C12-DBTTT shows a distinct larger transfer integral (149 meV) along the π−π stacking axis among three isomers due to its smaller displacement between adjacent molecules and shorter π−π stacking distance (Table S1). The reorganization energies were calculated to compare the core structures, with the linear isomer L-DBTTT (261 meV) presenting a smaller energy than the curved isomer C-DBTTT (336 meV). The smaller reorganization energy of the linear isomer combined with large electronic coupling could indicate an increased likelihood of bandlike transport. The first assessment for the performance of the alkylated DBTTT derivatives has been performed through the character-

representative characteristics of 100 μm long and 700 μm wide channel devices of the three alkylated DBTTT derivatives (forward and backward sweeps are always displayed to highlight the presence of any hysteresis). Thienoacenes are known to exhibit injection issues because of their deep IPs;20,21 therefore, F4-TCNQ and MoO3 doped contacts were used for L-C12-DBTTT to assess our device architecture (Figure 3a− d). The characteristics of the MoO3 doped contacts devices of L-C12-DBTTT exhibit relatively ideal behavior through hysteresis-free, acceptable level of threshold voltage (∼−25 V), linearity of the output characteristics at small drain voltages, and the establishment of a stable mobility over the whole ON-state gate voltage range. On the contrary, F4TCNQ doped contacts devices present less ideal characteristics (small hysteresis, large threshold voltage (∼−55 V), presence of a “hump” nonlinearity in the subthreshold regime, incoherence between the linear and saturation regime), attributed to a larger contact resistance: 1.1 and 4.6 kΩ cm for MoO3 and F4-TCNQ doped contacts, respectively, evaluated by transfer line measurement (L = 50 and 100 μm; Figure S8). MoO3 doped contacts were thus selected to investigate the performance of the other two derivatives. Transfer characteristics measured in the saturation regime and relative gate-voltage dependence of the saturation mobility of C-C6-DBTTT, C-C12-DBTTT, and L-C12-DBTTT are 7590

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Table 1. OFET Performances in the Linear and Saturation Regime for the Different DBTTT Derivatives in Devices Presenting a Bottom-Gate Top-Contact Architecture with a 100 μm Long and 700 μm Wide Channel material

regime a

C-C6-DBTTT

C-C12-DBTTTa L-C12-DBTTTb L-C12-DBTTTa

linear saturation linear saturation linear saturation linear saturation

μhole (cm2 V−1 s−1) 0.03 0.02 0.003 0.002 1.13 1.76 2.39 2.44

± ± ± ± ± ± ± ±

Vth (V) −79.7 −76.9 −74.1 −71.5 −54.8 −57.2 −29.5 −21.9

0.01 0.01 0.001 0.001 0.08 0.12 0.05 0.06

± ± ± ± ± ± ± ±

Ion/Ioff ∼1 × 106 ∼7 × 105 ∼4 × 104 ∼4 × 104 ∼4 × 107 ∼7 × 106 ∼2 × 108 ∼1 × 108

4.0 3.8 2.3 2.3 2.9 1.4 2.0 0.8

a

Injection layer: MoO3. bInjection layer: F4-TCNQ.

presented in Figure 3e,f for comparison (see Figures S9 and S10 for the individual characteristics of C-C6-DBTTT and CC12-DBTTT). At first observation, it is clear that these two derivatives exhibit poor performance, leading to highly nonideal devices: hysteresis, extremely large threshold voltage (∼−75 V), nonlinearity of the characteristics, and incoherence between the linear and saturation regime. This is most probably the result of a deeper IP combined with a molecular packing less optimal for charge transport. The hole transport in the linear and saturation regime from OFET devices is presented in Table 1. It is worth noting that despite extraction of parameters for the less ideal devices, these values should be viewed with caution. Indeed, only ideal devices can provide unambiguous information regarding the charge transport properties of a new material. The good agreement between the linear and saturation mobilities supports, however, the reliability of the extracted values for our MoO3 doped contact devices of L-C12-DBTTT. All depositions were performed at room temperature. Large grain size could be expected by performing the thermal evaporation at elevated temperature. X-ray reflectivity (XRR) and grazing-incidence X-ray diffraction (GIXRD) performed at room temperature on thin films of the different DBTTT derivatives highlight, however, the presence of polymorphism for each molecule. The films consist of a mixture of two polymorphs for C-C12-DBTTT and L-C12-DBTTT while only one polymorph is present for C-C6-DBTTT (see Figure S11 and also extra information in the XRD section of the Supporting Information). This polymorphic behavior is most likely the result of the stabilization within the thin film geometry of polymorphs present in the thermotropic behavior of the different derivatives (all molecules present several solid−solid transitions as seen in the DSCs22,23). Polymorphism most likely impacts charge transport and leads to trapping effects in our films. Atomic force microscopy (AFM) images confirm (see AFM section of the Supporting Information) that the morphology is not impacting the charge transport performance in our devices. Despite larger domains, C-C12-DBTTT exhibits the poorest transport properties while C-C6DBTTT, presenting smaller domains, has slightly better performance. In summary, we have designed and synthesized three isomers of thiophene-ring terminated BTBT derivatives with varying isomerism of the alkyl side chain and the aromatic core. Our combined theoretical and experimental study demonstrated an effective crystal engineering approach for the design of thiophene-ring terminated BTBT molecules in OFET applications. The isomer with the linear aromatic core, L-C12-DBTTT, shows the most optimal molecular packing for

two-dimensional charge transport, with a herringbone arrangement. Evaluation of the charge transport properties of L-C12DBTTT shows promising semiconducting behavior despite polymorphism under the conditions used.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.8b02757.

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Materials, characterization, and synthesis, crystallography and crystal analysis, fabrication of organic field-effect transistors (OFETs), computational methodologies, Xray reflectivity (XRR) and grazing-incidence X-ray diffraction (GIXRD) (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Hung-Yang Chen: 0000-0001-8426-4254 Iain McCulloch: 0000-0002-6340-7217 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.-Y.C. acknowledges postdoctoral fellowship support from Ministry of Science and Technology in Taiwan. G.S. acknowledges postdoctoral fellowship support from the Wiener-Anspach Foundation and The Leverhulme Trust (Early Career Fellowship supported by the Isaac Newton Trust). We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities, and we thank Dr. Raja Znaiguia and Dr. Francesco Carla for assistance in using beamline ID03. K.B. acknowledges financial support from the Institutional Strategy of the University of Tuebingen (Deutsche Forschungsgemeinschaft ZUK63). I.M., S.C., C.J., and M.L. acknowledge EC FP7 SC2 (610115), EC H2020 (643791), and EPSRC Projects EP/G037515/1 EP/ M024873/1 and EP/M005143/1.

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REFERENCES

(1) Holliday, S.; Donaghey, J. E.; McCulloch, I. Advances in Charge Carrier Mobilities of Semiconducting Polymers Used in Organic Transistors. Chem. Mater. 2014, 26, 647−663.

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DOI: 10.1021/acs.chemmater.8b02757 Chem. Mater. 2018, 30, 7587−7592

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Chemistry of Materials (2) Sirringhaus, H. 25th Anniversary Article: Organic Field-Effect Transistors: The Path Beyond Amorphous Silicon. Adv. Mater. 2014, 26, 1319−1335. (3) Chen, H.; Hurhangee, M.; Nikolka, M.; Zhang, W.; Kirkus, M.; Neophytou, M.; Cryer, S. J.; Harkin, D.; Hayoz, P.; Abdi-Jalebi, M.; McNeill, C. R.; Sirringhaus, H.; McCulloch, I. Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors. Adv. Mater. 2017, 29, 1702523. (4) Takimiya, K.; Osaka, I.; Mori, T.; Nakano, M. Organic Semiconductors Based on [1]Benzothieno[3,2-b][1]Benzothiophene Substructure. Acc. Chem. Res. 2014, 47, 1493−1502. (5) Takimiya, K.; Ebata, H.; Sakamoto, K.; Izawa, T.; Otsubo, T.; Kunugi, Y. 2,7-Diphenyl[1]Benzothieno[3,2-b]Benzothiophene, a New Organic Semiconductor for Air-Stable Organic Field-Effect Transistors with Mobilities Up to 2.0 cm2V−1s−1. J. Am. Chem. Soc. 2006, 128, 12604−12605. (6) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. Highly Soluble [1]Benzothieno[3,2-b]Benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 15732−15733. (7) Yamamoto, T.; Takimiya, K. Facile Synthesis of Highly piExtended Heteroarenes, Dinaphtho[2,3-b:2’,3′-f ]Chalcogenopheno[3,2-b]Chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224−2225. (8) Niimi, K.; Shinamura, S.; Osaka, I.; Miyazaki, E.; Takimiya, K. Dianthra[2,3-b:2’,3′-f ]Thieno[3,2-b]Thiophene (DATT): Synthesis, Characterization, and FET Characteristics of New pi-Extended Heteroarene with Eight Fused Aromatic Rings. J. Am. Chem. Soc. 2011, 133, 8732−8739. (9) Yamamoto, T.; Nishimura, T.; Mori, T.; Miyazaki, E.; Osaka, I.; Takimiya, K. Largely pi-Extended Thienoacenes with Internal Thieno[3,2-b]Thiophene Substructures: Synthesis, Characterization, and Organic Field-Effect Transistor Applications. Org. Lett. 2012, 14, 4914−4917. (10) Mori, T.; Nishimura, T.; Yamamoto, T.; Doi, I.; Miyazaki, E.; Osaka, I.; Takimiya, K. Consecutive Thiophene-Annulation Approach to pi-Extended Thienoacene-Based Organic Semiconductors with [1]Benzothieno[3,2-b][1]Benzothiophene (BTBT) Substructure. J. Am. Chem. Soc. 2013, 135, 13900−13913. (11) Park, J.-I.; Chung, J. W.; Kim, J.-Y.; Lee, J.; Jung, J. Y.; Koo, B.; Lee, B.-L.; Lee, S. W.; Jin, Y. W.; Lee, S. Y. Dibenzothiopheno[6,5b:6’,5′-f ]Thieno[3,2-b]Thiophene (DBTTT): High-Performance Small-Molecule Organic Semiconductor for Field-Effect Transistors. J. Am. Chem. Soc. 2015, 137, 12175−12178. (12) Biniek, L.; Schroeder, B. C.; Donaghey, J. E.; Yaacobi-Gross, N.; Ashraf, R. S.; Soon, Y. W.; Nielsen, C. B.; Durrant, J. R.; Anthopoulos, T. D.; McCulloch, I. New Fused Bis-Thienobenzothienothiophene Copolymers and Their Use in Organic Solar Cells and Transistors. Macromolecules 2013, 46, 727−735. (13) Shimizu, M.; Nagao, I.; Tomioka, Y.; Hiyama, T. PalladiumCatalyzed Annulation of Vic-Bis(Pinacolatoboryl)Alkenes and -Phenanthrenes with 2,2’-Dibromobiaryls: Facile Synthesis of Functionalized Phenanthrenes and Dibenzo[g,p]Chrysenes. Angew. Chem., Int. Ed. 2008, 47, 8096−8099. (14) Ahmed, M.; Ashby, J.; Ayad, M.; Meth-Cohn, O. The Direct Bradsher Reaction. Part I. Synthesis of Thiophen Analogues of Linear Polycyclic Hydrocarbons. J. Chem. Soc., Perkin Trans. 1 1973, 0, 1099−1103. (15) Leroy, J.; Boucher, N.; Sergeyev, S.; Sferrazza, M.; Geerts, Y. H. Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes: Convenient Synthesis and Transition-Temperature Engineering. Eur. J. Org. Chem. 2007, 2007, 1256−1261. (16) Iino, H.; Usui, T.; Hanna, J.-I. Liquid Crystals for Organic Thin-Film Transistors. Nat. Commun. 2015, 6, 6828. (17) Tsutsui, Y.; Schweicher, G.; Chattopadhyay, B.; Sakurai, T.; Arlin, J.-B.; Ruzié, C.; Aliev, A.; Ciesielski, A.; Colella, S.; Kennedy, A. R.; Lemaur, V.; Olivier, Y.; Hadji, R.; Sanguinet, L.; Castet, F.; Osella, S.; Dudenko, D.; Beljonne, D.; Cornil, J.; Samori, P.; Seki, S.; Geerts,

Y. H. Unraveling Unprecedented Charge Carrier Mobility Through Structure Property Relationship of Four Isomers of Didodecyl[1]Benzothieno[3,2-b][1]Benzothiophene. Adv. Mater. 2016, 28, 7106− 7114. (18) Desiraju, G. R.; Gavezzotti, A. From Molecular to CrystalStructure - Polynuclear Aromatic-Hydrocarbons. J. Chem. Soc., Chem. Commun. 1989, 0, 621−623. (19) Ryno, S. M.; Lee, S. R.; Sears, J. S.; Risko, C.; Brédas, J.-L. Electronic Polarization Effects Upon Charge Injection in Oligoacene Molecular Crystals: Description via a Polarizable Force Field. J. Phys. Chem. C 2013, 117, 13853−13860. (20) Rolin, C.; Kang, E.; Lee, J.-H.; Borghs, G.; Heremans, P.; Genoe, J. Charge Carrier Mobility in Thin Films of Organic Semiconductors by the Gated Van Der Pauw Method. Nat. Commun. 2017, 8, 14975. (21) Schweicher, G.; Lemaur, V.; Niebel, C.; Ruzié, C.; Diao, Y.; Goto, O.; Lee, W.-Y.; Kim, Y.; Arlin, J.-B.; Karpinska, J.; Kennedy, A. R.; Parkin, S. R.; Olivier, Y.; Mannsfeld, S. C. B.; Cornil, J.; Geerts, Y. H.; Bao, Z. Bulky End-Capped [1]Benzothieno[3,2-b]Benzothiophenes: Reaching High-Mobility Organic Semiconductors by Fine Tuning of the Crystalline Solid-State Order. Adv. Mater. 2015, 27, 3066−3072. (22) Jones, A. O. F.; Chattopadhyay, B.; Geerts, Y. H.; Resel, R. Substrate-Induced and Thin-Film Phases: Polymorphism of Organic Materials on Surfaces. Adv. Funct. Mater. 2016, 26, 2233−2255. (23) Diao, Y.; Lenn, K. M.; Lee, W.-Y.; Blood-Forsythe, M. A.; Xu, J.; Mao, Y.; Kim, Y.; Reinspach, J. A.; Park, S.; Aspuru-Guzik, A.; Xue, G.; Clancy, P.; Bao, Z.; Mannsfeld, S. C. B. Understanding Polymorphism in Organic Semiconductor Thin Films Through Nanoconfinement. J. Am. Chem. Soc. 2014, 136, 17046−17057.

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DOI: 10.1021/acs.chemmater.8b02757 Chem. Mater. 2018, 30, 7587−7592