Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Organic Electronic Devices

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene (DTBDT) Kodai Iijima, Ryo Sanada, Dongho Yoo, Ryonosuke Sato, Tadashi Kawamoto, and Takehiko Mori ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b00416 • Publication Date (Web): 06 Mar 2018 Downloaded from http://pubs.acs.org on March 6, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Carrier Charge Polarity in Mixed-Stack ChargeTransfer Crystals Containing Dithienobenzodithiophene (DTBDT) †

†

†

†

†

Kodai Iijima, Ryo Sanada, Dongho Yoo, Ryonosuke Sato, Tadashi Kawamoto, and Takehiko Mori*,† †

Department of Materials Science and Engineering, Tokyo Institute of Technology, O-okayama,

Meguro-ku, Tokyo 152-8552, Japan

ABSTRACT:

Ditheno[2,3-d;2'3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT) forms mixed-stack chargetransfer complexes with fluorinated tetracyanoquinodimethanes (FnTCNQ, n = 0, 2 and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the FnTCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (teeff) is by more than ten times larger than the donor-to-donor hopping (theff). This is because the donor orbital next to the highest occupied molecular orbital (HOMO−1) makes a large contribution to the electron transport

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals.

KEYWORDS :

organic transistors, charge-transfer complex, ambipolar transistor, mixed

stack, single-crystal transistors

1. INTRODUCTION Donor–acceptor (D-A) polymers composed of electron-donating and electron-accepting components have been investigated extensively owing to the excellent properties in organic field-effect transistors and photovoltaics.1–16 In this connection, cocrystals of organic donor and acceptor molecules have attracted a great deal of attention due to the potential electronic and photonic applications.17-34 These charge-transfer complexes potentially enable both hole and electron transport, but they usually achieve unipolar transport. Accordingly, their conducting mechanism is a focus of increasing interest.35-43 Among small-molecule transistor materials, various thienoacenes have been investigated as hole-transporting materials,44,45 in which [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives are known to exhibit excellent mobility and high stability in organic transistors.46–48 BTBT also forms charge-transfer complexes such as (BTBT)2XF6 (X = P, As, Sb, and Ta), which show

very

high

conductivity

as

well

as

metallic

temperature

dependence.49-51

Tetracyanoquinodimethane (TCNQ) complexes of BTBT derivatives consist of alternating stacks of the donor and acceptor molecules.17-20 In such a case, hopping transport is supposed, where electrons transported from A to A have to overcome the donor potential. Nonetheless, singlecrystal transistors of these complexes exhibit electron mobilities of 0.4 cm2 V−1 s−1 in


2

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(CnBTBT)(F4TCNQ),18 0.19 cm2 V−1 s−1 in (BTBT)(F4TCNQ),21 and 0.097 cm2 V−1 s−1 in (DMeO-BTBT)(F2TCNQ),20 where CnBTBT and DMeO-BTBT are dialkyl- and dimethoxyBTBT, respectively.

Dibenzotetrathiafulvalene (DBTTF) complex of TCNQ has been

investigated for a long time,22-26 where change of carrier polarity has been reported, but in general charge-transfer salts containing TCNQ tend to show only electron transport irrespective of the donor strength.

When TCNQ is replaced by dimethyldicyanoquinonediimine

(DMDCNQI), ambipolar transport has been observed,27 but the acceptor strength of DMDCNQI is not largely different from TCNQ (Figure 1). Therefore, we cannot explain the charge polarity only from the donor and acceptor strengths. In (Perylene)n(TCNQ) (n = 1, 2, and 3), the charge polarity changes from electron transport, ambipolar, to hole transport with increasing n,28-31 so the steric factor, that realizes direct D-D and A-A interactions, seems important. However, FnTCNQ complexes of bulky coronene show only electron transport,32–34 and close investigation of intermolecular contacts reveals that it is difficult to account for the charge polarity only from the direct D-D and A-A interactions.20 Alternatively, charge polarity has been interpreted by the superexchange mechanism, where teeff and theff are respectively obtained from energy splittings of A-D-A and D-A-D triads,35,36 or from the partition technique.37 Simple perturbation theory, however, leads to the same hole and electron transfers, teeff = theff ~ t2/∆E. Here t is the transfer integral between the donor highest occupied molecular orbital (HOMO) and the acceptor lowest unoccupied molecular orbital (LUMO), and ∆E is the energy difference between these levels. Although this mechanism generally predicts ambipolar transport, unipolar transport is usually observed in many alternating-stack complexes.38–42

It has been recently suggested that

asymmetrical electron and hole transport appear when bridge orbitals other than HOMO and LUMO make an important contribution.37,43 Such discussion is also important because charge


3


Page 4 of 34

polarity of D-A polymers changes sensitively from hole transport to electron transport, as well as ambipolar transport in some occasions.1–16 Although many thienoacenes have been investigated,44-48 recently ditheno[2,3-d;2'3'd']benzo[1,2-b;4,5-b']dithiophene (DTBDT, Scheme 1) has attracted attention as a donor component in D-A polymers.52–55 The alkyl derivative (C6DTBDT) also shows as high mobility as 1.7 cm2 V−1 s−1.56

The TCNQ and F4TCNQ complexes have been reported,57 but the

transistor properties are not investigated. The present paper reports single-crystal transistors of (DTBDT)(FnTCNQ) (n = 0, 2 and 4) and (DTBDT)(DMDCNQI) together with the crystal structures. The dominance of electron transport is in agreement with the calculated teeff > theff, which comes from large mixing of the donor HOMO−1 to the acceptor LUMO. Carrier charge polarity is predicted satisfactory by investigating not only the HOMO-LUMO transfer but also the transfers to other bridge orbitals. R1

S S

S S

R2

NC

CN

NC

CN R2

R1

(DTBDT)(TCNQ) : R1 = R2 = H (DTBDT)(F2TCNQ) : R1 =H, R2 = F (DTBDT)(F4TCNQ) : R1 = R2 = F Me

S

CN

S N

S

S

N

NC Me (DTBDT)(DMDCQI)

Scheme 1. DTBDT complexes


4

Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2. EXPERIMENTAL SECTION DTBDT was prepared following the reported route.52

Single crystals of DTBDT were

prepared by the slow evaporation of the toluene solution. Although single-crystal growth of (DTBDT)(TCNQ) and (DTBDT)(F4TCNQ) by the physical vapor transport method was reported in Ref. 57, single crystals of DTBDT complexes were prepared by the simple slow evaporation method. Transistors were fabricated onto n-doped Si substrates with a thermally grown SiO2 dielectric layer (300 nm, C = 11.5 nF/cm2). For single-crystal transistors, the passivation layer polystyrene (PS, ε = 2.5) was deposited by spin coating (3000 rpm, and 30 sec) a solution of PS (20 mg) in toluene (1 mL) on the substrates with a thickness of 100 nm,58,59 where the calculated overall capacitance was 7.6 nF/cm2.60 Needle-like black crystals were put on the PS layer using ethanol.61 Carbon paste (DOTITE, XC-12) was deposited on two ends of a single crystal to make the source and drain electrodes, where the crystal long axis was oriented in the channel direction. The single-crystal X-ray diffraction indicates that the crystal long axis is parallel to the molecular stacking axis, along which the transistor properties were measured under the vacuum of 10−3 Pa by using a Keithley 4200 semiconductor parameter analyzer. The mobility was estimated from the saturated-region transfer characteristics. The molecular orbital calculations were performed with the PW91 functional and TZP basis set, using the the Amsterdam Density Functional (ADF) program.62


5


Page 6 of 34

3. RESULTS AND DISCUSSION 3.1. Energy Levels. Energy levels of BTDBT, FnTCNQ, and DMDCNQI are summarized in Figure 1. Oxidation potential of DTBDT is estimated to be +0.73 V vs. ferrocene/ferrocenium by cyclic voltammetry, from which the HOMO level is obtained to be −5.53 eV.52 Accordingly, DTBDT is a slightly stronger donor than BTBT (−5.6 eV).46-48

F4TCNQ and F2TCNQ are much stronger acceptor

than TCNQ (−4.6 eV). DMDCNQI is a slightly weaker acceptor than TCNQ. Although it is difficult to directly compare the calculated energy levels with the experimentally obtained energy levels, the calculated results are basically in agreement with the observations (Figure 1).

Figure 1. Energy levels of DTBDBT, FnTCNQ, and DMDCNQI. Red and blue solid lines are experimentally estimated HOMO and LUMO levels, respectively, and dashed lines are energy


6

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


levels obtained from molecular orbital calculations, among which HOMO and LUMO levels are indicated by red and blue colors.

3.2. Crystal structures Crystal data of FnTCNQ and DMDCNQI complexes of DTBDT are summarized in Table 1 together with those of neutral DTBDT. Crystal of neutral DTBDT consists of uniform stacks (Figure 2). The interplanar spacing (l) is 3.51 Å, which should be compared with 3.63 Å in C6DTBDT.14 All molecules are parallel in C6DTBDT with triclinic symmetry, but molecules in DTBDT are tilted alternately in opposite directions due to the monoclinic symmetry. From the lattice constant b and the interplanar spacing l, the tilt of the molecular plane from the normal to the stacking axis is estimated to be sin−1(l/b) = 37o, which is smaller than 47o in C6DTBDT. Crystal structures of (DTBDT)(TCNQ) and (DTBDT)(F4TCNQ) are identical to the previously reported results,57 but shown for the sake of comparison. (DTBDT)(F2TCNQ) and (DTBDT)(DMDCNQI) are essentially isostructural to these crystals (Figure 3).

These

complexes consist of alternating stacks of donor and acceptor molecules. The stacking direction is the b axis in the TCNQ and F2TCNQ complexes, but the a axis in the F4TCNQ and DMDCNQI complexes. The lattice constants a and b are very close. The a axis in the TCNQ complex is along the molecular short axis, which increases with the fluorine (or methyl in DMDCNQI) substitution. By contrast, b along the stacking axis decreases gradually. Then, the a and b axes exchange after the F4TCNQ complex. Donor and acceptor molecules are placed on an inversion center, and the half molecules are crystallographically independent. The donor and acceptor molecules overlap in a ring-over-bond manner (Figure 3(c)), where the molecular long axes are approximately parallel.

Reflecting the shrinkage of the stacking axis, the donor-


7


Page 8 of 34

acceptor interplanar spacing decreases as 3.38 Å, 3.37 Å, 3.31 Å, and 3.33 Å for the TCNQ, F2TCNQ, F4TCNQ, and DMDCNQI complexes, respectively. The tilt angles are obtained to be 32o, 32o, 32o, and 31o, similarly to DTBDT.

Short S–S contacts between the donors are

respectively 3.447(1), 3.481(3), 3.282(4), and 3.478(3) Å along the c axis, and 3.641(1), 3.728(3) Å (//a), 3.779(4), and 3.972(3) Å (//b). Charge transfer degrees estimated from bond lengths as well as the infrared C≡N stretching frequency are nearly zero (Supporting Information), indicating practically neutral character of these complexes. F4TCNQ is a strong acceptor with the LUMO level of −5.1 eV (Figure 1), but the DTBDT complex still shows a neutral character.


8

Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Crystallographic Data of DTBDT as well as FnTCNQ and DMDCNQI Complexes of DTBDT

C14H6S4

(DTBDT) (TCNQ) C26H10N4S4

302.44

506.63

DTBDT Formula Formula weight Crystal System Space Group Shape a (Å) b (Å) c (Å) α(deg.) β(deg.) γ(deg.) V (Å3) −3

ρ (g cm ) Z-value T (K) Total reflns. Unique reflns. (Rint) R1 [F2 > 2σ(F2)] wR2 [All reflns.] GOF Temperature (K)

(DTBDT) (DTBDT) (F2TCNQ) (F4TCNQ) C26H8N4F2S4 C26H6N4F4S4 542.61

monoclinic triclinic triclinic C2/c P–1 P–1 colorless black needle black needle plate 18.468(8) 7.5661(10) 7.689(5) 14.980(6) 7.9740(15) 7.978(6) 10.8786(16) 9.2855(15) 9.302(6) 90 101.154(15) 101.11(6) 96.04(3) 99.186(13) 99.66(5) 90 95.844(13) 96.12(6)

(DTBDT) (DMDCNQI) C24H14N4S4

578.59

486.64

triclinic P–1

triclinic P–1

black needle

black needle

7.8417(16) 7.8896(14)

7.730(4) 7.8084(13)

9.4489(14)

9.4033(14)

98.948(14) 100.39(2) 94.36(3)

108.145(12) 96.07(3) 94.06(3)

1207.8(11)

537.47(16)

546.3(7)

564.73(19)

533.1(3)

1.663 4 298 2227 1759 (0.0722)

1.565 1 298 3723 3137 (0.0201)

1.649 1 298 2451 1921 (0.0202)

1.701 1 298 3897 3284 (0.0360)

1.516 1 298 3076 1996 (0.0553)

0.0464

0.044

0.0521

0.0459

0.0921

0.1336

0.1168

0.1605

0.132

0.2872

1.042

1.003

1.011

1.009

1.005

298

298

298

298

298


9


Page 10 of 34

Figure 2. Crystal structure of DTBDT, (a) viewed along the c axis, and (b) along the b axis. The intrastack transfer integral is tb = 181 meV.


10

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Crystal structure of (DTBDT)(DMDCNQI), (a) viewed along the molecular short axis, (b) along the molecular long axis, and (c) along the a axis. (d) Molecular overlap viewed perpendicular to the molecular plane.


11


Page 12 of 34

3.3 Transistor Properties. Transistors of thermally evaporated DTBDT films were fabricated on hexamethyldisilazane (HMDS)-treated SiO2, and showed the hole mobility of 3.9×10–4 cm2 V–1 s–1 (Figure S9). Transfer and output characteristics of (DTBDT)(TCNQ) single-crystal transistors are shown in Figure 4. These complexes show electron transporting properties. From this, the transistor properties are extracted as listed in Table 2. (DTBDT)(TCNQ) exhibits a comparatively large mobility of 0.1 cm2 V−1 s−1.

This value is comparable to 0.19 cm2 V−1 s−1 in

(BTBT)(F4TCNQ),21 0.097 cm2 V−1 s−1 in (DMeO-BTBT)(F2TCNQ),20 and 0.4 cm2 V−1 s−1 in (CnBTBT)(F4TCNQ) single-crystal transistors.18 In the F2TCNQ and F4TCNQ complexes, the mobility decreases, but this is due to the successively decreasing on/off ratios (Figure S10). The "on" currents are approximately the same, but the "off" current increases from less than 10−10 A to more than 10−8 A.

The later corresponds to the bulk conductivity of 2.7×10–6 S/cm .

Although the bond lengths and the C≡N stretching frequency indicate basically neutral character of (DTBDT)(F4TCNQ), this result is not surprising based on the HOMO level (−5.53 eV) of DTBDT and LUMO level (−5.1 eV) of F4TCNQ (Figure 1). Although ambipolar transport has been reported in some DMDCNQI complexes,27 (DTBDT)(DMDCNQI) usually shows only electron transport. However, ambipolar transport is observed in some crystals (Figure 4c). These complexes do not form thin-film transistors probably due to the large difference of the evaporation temperatures of the donor and the acceptor molecules.


12

Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Transfer and (b) output characteristics of a single-crystal transistor of (DTBDT)(TCNQ). (c) Transfer characteristics of a single-crystal transistor of (DTBDT)(DMDCNQI).

Table 2.

Transistor Properties of Single-Crystal Transistors based on FnTCNQ and DMDCNQI

Complexes of DTBDT Compound

µe (cm2 V–1 s–1)

Vth (V)

on/off ratio

−32

8.2×103

0.1

2

7x102

(DTBDT)(F2TCNQ)

1.1×10−3

46

30

(DTBDT)(F4TCNQ)

9.8×10−3

−72

5

16

40

(−69)

(56)

DTBDT

a

3.9×10

(DTBDT)(TCNQ)

(DTBDT)(DMDCNQI)

–4 a

4.9×10

−4

(5.0×10−5) b a

Hole mobility in a thin-film transistor.

b

Hole mobility observed in some crystals.


13


Page 14 of 34

3.4 Transfer Integrals. In order to understand the observed carrier transport properties, transfer integrals are calculated on the basis of the crystal structures (Table 3). Intrastack transfers (t// ) between the donor HOMO and the acceptor LUMO are as large as 200 meV (first line in Table 3), which are comparable to 181 meV of the D-D transfer in the neutral DTBDT (Figure 2 caption). Interchain interactions between the donors coming from the short interchain S–S contacts (~24 meV) amount to one tenth of the intrachain interactions (Supporting Information), but the donordonor interaction does not seem to enhance the observed electron transport. Superexchange transfers estimated from the LUMO and LUMO+1 level splittings of the A-DA triads (teeff) are as large as > 50 meV, whereas those of the D-A-D triads (theff) are as small as < 4 meV (third and fourth lines in Table 3).35,36 teeff is by more than ten times larger than theff, and this accounts for the observed electron transport. Superexchange transfers of many TCNQ complexes have been calculated,35,36 but teeff is not always significantly larger than theff. Since reorganization energies of TCNQ are DTBDT are λ = 172 and 139 meV, respectively, these superexchange transfers account for the large difference of electron and hole mobilities (Table 3).63 From the second-order perturbation theory, hopping from A to A via D is given by teeff ~ t2/∆E. However, hopping from D to D via A (theff) is also given by the same form. Based on the resulting teeff ~ theff, ambipolar transport is universally expected.35,36 In the actual observations, however, unipolar transport is much more usual. By contrast, the present calculation affords largely different teeff and theff. Similar but smaller unbalance of teeff and theff has been observed in (DMeO-BTBT)(TCNQ) and (C8BTBT)(FnTCNQ).19,43


14

Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


When molecular orbital populations of a D-A pair are analyzed, the LUMO mainly comes from the acceptor LUMO (> 90% in Table 3), but more than 5% of the donor HOMO (or HOMO−1) is hybridized. In several complexes, mixing of HOMO−1 is more important than the HOMO mixing. In contrast, admixture of the acceptor LUMO to the HOMO is less than 2%. The mixing of the donor orbitals to the acceptor LUMO is different from the mixing of the acceptor orbitals to the donor HOMO, and this is the origin of the largely different teeff and theff. In order to investigate the asymmetrical transport, transfers from the transport orbitals to bridge orbitals are analyzed in Table 4 for (DTBDT)(TCNQ).35 Here, based on the second-order perturbation theory, the t2/∆E values are evaluated as well. Molecular orbitals with largely different energy levels are unimportant due to the large ∆E, so transfers to nearby energy levels are investigated. In addition to the direct transfer from the donor HOMO to the acceptor LUMO (187 meV), another transfer from the donor HOMO−1 to the acceptor LUMO (448 meV) is significant. The corresponding t2/∆E = 238 meV is larger than 67 meV for HOMO. Thus, the donor HOMO−1 makes a more important contribution to the electron transport than the donor HOMO.

For hole transport, however, the HOMO-LUMO transfer (67 meV) is the only

significant transfer, and the acceptor LUMO is the only potential hole pathway. Electrons located on the acceptor LUMO hops to the donor HOMO−1 rather than HOMO, where the large transfer (448 meV) is more important than the energy difference (∆E = 850 meV in comparison with 520 meV). Although HOMO and HOMO−1 are occupied levels, the hybridization to the acceptor LUMO (or tunneling using these orbitals) mediates the electron transport.35 In terms of the partition technique,37,64 this may be more appropriately interpreted as a tunneling phenomenon. By contrast, holes located on HOMO are not thermally excited to HOMO−1


15


Page 16 of 34

owing to this ∆E, and HOMO−1 does not participate in the hole transport. This is the mechanism of the asymmetrical carrier transport. The molecular orbitals of D-A pairs are depicted in Figure 5, where small contributions are emphasized by using a small isosurface level. The original molecular orbitals are also shown in Figure 6. The donor orbitals mixed to the acceptor LUMO have the same node structure as the acceptor LUMO. The acceptor LUMO has horizontal periodicity, and the donor HOMO−1 has similar symmetry. This is the origin of the large transfer between the acceptor LUMO and the donor HOMO−1.

Similar horizontal periodicity of HOMO−1 is in common with BTBT

derivatives.19,43 The F2TCNQ and the F4TCNQ complexes show the same tendency (Supporting Information), where t and t2/∆E to HOMO−1 are larger than those to HOMO (top two lines in Table 3). This is the origin of the predominant electron transport. In the DMDCNQI complex, the transfer to HOMO−1 is comparable to that to HOMO, and t2/∆E for HOMO−1 is smaller than that for HOMO. Then, theff is comparatively large (Table 3), and this is the origin of the ambipolar transport in the DMDCNQI complex. Here, mixing of the acceptor LUMO to the donor HOMO increases to 3.5% (Table 4), which is comparable to mixing of the donor HOMO to the acceptor LUMO (4.0%). It is noteworthy that the shape of the acceptor LUMO is obvious in Figure 5h. DMDCNQI complexes are more close to ambipolar transport because the direct HOMO-LUMO transfer is the principal carrier path, and the donor HOMO−1 participates less in the electron conduction. Carrier charge polarity is not always very clear only from teeff and theff. The present analysis makes bridge orbitals clear, and gives more insight in the inherently asymmetrical electron and hole transport in mixed-stack crystals. Transport properties of organic semiconductors and


16

Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


conductors have been discussed in view of transfer integrals,63,65 but transfer integrals are sensitive to the node structure of the molecular orbitals. If transfer integrals are estimated from the overlap of the molecular orbitals with the "frozen" orbital approximation, the transfer crosses zero when the transfer changes the sign. Since close intermolecular contacts exist even in these cases, it is questionable whether the nodes of the molecular orbitals lead to zero transfers and zero carrier transport in some particular geometries. Because this explicitly depends on the phase of the molecular orbitals, this is a kind of "quantum" effect. There is no unambiguous way to verify this kind of phase dependence in ordinary organic semiconductors. However, the present electron and hole asymmetry comes from the different HOMO and HOMO−1 transfers, which obviously stem from the node structure of the molecular orbitals. Therefore, electron and hole asymmetry in a mixed-stack charge-transfer crystal is a clear evidence of phase dependence of intermolecular transfers, and is a kind of "quantum" effect.


17


Page 18 of 34

Table 3. Estimations of Transfer Integrals (meV) based on Independent Molecules and Triads, together with Reorganization Energies (meV), Calculated Mobilities (cm2 V–1 s–1), and Populations of Bridge Orbitals in Diads Transfers

t//

(DTBDT) (TCNQ)

(DTBDT) (F2TCNQ)

(DTBDT) (F4TCNQ)

(DTBDT) (DMDCNQI)

HOMO/LUMO t (t2/∆E)

187 (67)

194 (90)

216 (123)

284 (124)

HOMO−1/LUMO t (t2/∆E)

448 (238)

424 (233)

415 (250)

−284 (81)

(A-D-A)

54

55

59

40

theff (D-A-D)

3.9

0.5

2.5

12

Electron

172

185

184

272

0.93

0.82

0.95

0.15

7.3 x10-3

1.2 x 10-4

3.0 x 10-3

0.070

A LUMO

91.8%

90.6%

89.0%

93.6%

D HOMO

2.2%

5.6%

4.2%

4.0%

D HOMO−1

5.3%

3.3%

6.3%

1.8%

D HOMO

94.4%

93.2%

90.8%

94.0%

D HOMO−1

1.4%

1.8%

3.3%

1.1%

D HOMO−2

2.1%

2.1%

2.8%

0.2%

A LUMO

1.3%

2.0%

2.1%

3.5%

a

Triad

b

λ

teeff

µ (cm2 V–1 s–1)

LUMO

Diad c HOMO

a

Electron Hole

Transfer integrals (meV) between the donor HOMO (or HOMO−1) and the acceptor LUMO.

The t2/∆E values in the parentheses are estimated similarly to Table 4. b

Superexchange transfers calculated from A-D-A and D-A-D triads.35-37

c

Populations of bridge orbitals in a D-A pair.37


18

Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 4. Energy Level Difference ∆E and Transfer Integrals t (meV) in (DTBDT)(TCNQ), together with t2/∆ ∆E (meV) in the Parentheses.

∆E from A LUMO ∆E from D HOMO

DTBDT

TCNQ HOMO

LUMO

−1080

520

HOMO−2

−1310

−170

−148 (19)

HOMO−1

−850

−49

−448 (238)

HOMO

−520

−23 (2)

187 (67)

LUMO

2170

80

−58 (2)

LUMO+1

3020

−217

−129 (10)


19


Page 20 of 34

Figure 5. Molecular orbitals of D-A pairs viewed perpendicular to the molecular plane (isosurface level: 0.008). (a) LUMO and (b) HOMO of (DTBDT)(TCNQ). (c) LUMO and (d) HOMO of (DTBDT)(F2TCNQ). (e) LUMO and (f) HOMO of (DTBDT)(F4TCNQ). (g) LUMO and (h) HOMO of (DTBDT)(DMDCNQI).


20

Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) DTBDT HOMO

(c) TCNQ LUMO

(b) DTBDT HOMO−1

(d) DMDCNQI LUMO

Figure 6. (a) HOMO and (b) HOMO−1 of DTBDT. (c) LUMO of TCNQ, and (d) LUMO of DMDCNQI.


21


Page 22 of 34

4. CONCLUSIONS DTBDT forms mixed-stack complexes with FnTCNQ and DMDCNQI. The single-crystal transistors show electron transporting properties, in which (DTBDT)(TCNQ) exhibits the electron mobility of 0.1 cm2 V−1 s−1. Mobility of the fluorinated complexes decreases mainly due to the increase of the "off" current. (DTBDT)(DMDCNQI) exhibits slight hole-transporting properties. Superexchange transfers estimated from the level splittings of A-D-A triads (teeff) are significantly larger than theff obtained from the D-A-D triads.

This is due to the large

participation of the donor HOMO−1 to the electron transport. Although similar electron and hole asymmetry has been pointed out,19,35,43 ten times different teeff and theff are remarkable in the present materials. In (DTBDT)(DMDCNQI), the electron path through the donor HOMO−1 is comparatively unimportant, and the direct HOMO-LUMO path is the main carrier path, so that this complex is more close to ambipolar transport.

Accordingly, the inherently asymmetrical

electron and hole transport in mixed-stack crystals is explained by analyzing the participating bridge orbitals.

ASSOCIATED CONTENTS Supporting Information The Supporting Information is available free of charge on the ACS Publication website at DOI: 10.1021/acs.acsami.xxxxxxx. Description of the single-crystal structure, intermolecular short contacts, degree of charge transfer, transistor characteristics, transfer integrals (PDF) Crystal data (CIF)


22

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected] Tel: +91-3-5734-2427.

ORCDI Takehiko Mori: 0000-0002-0578-5885 Dongho Yoo: 0000-0003-0886-7533 Tadashi Kawamoto: 0000-0002-5676-4013 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by JST ACT-C Grant Number JPMJCR12ZB, Japan, and by a JPSJ KAKENHI Grant Number 16K13974.


23


Page 24 of 34

REFERENCES (1)

Lucera, L.; Machui, F.; Kubis, P.; Schmidt, H. D.; Adams, J.; Strohm, S.; Ahmad, T.; Forberich, K.; Egelhaaf, H.-J.; Brabec, C. J. Highly Efficient, Large Area, Roll Coated Flexible and Rigid OPV Modules with Geometric Fill Factors up to 98.5% Processed with Commercially Available Materials. Energy Environ. Sci. 2016, 9, 89–94.

(2)

Zhao, Y.; Guo, Y.; Liu, Y. Recent Advances in n-Type and Ambipolar Organic FieldEffect Transistors. Adv. Mater. 2013, 25, 5372–5391.

(3)

Olivier, Y.; Niedzialek, D.; Lemaur, V.; Pisula, W.; Müllen, K.; Koldemir, U.; Reynolds, J. R.; Lazzaroni, R.; Cornil, J.; Beljonne, D. High-Mobility Hole and Electron Transport Conjugated Polymers: How Structure Defines Function. Adv. Mater. 2014, 26, 2119– 2136.

(4)

Choi, J.; Song, H.; Kim, N.; Kim, F. S. Development of n-Type Polymer Semiconductors for Organic Field-Effect Transistors. Semicond. Sci. Technol. 2015, 30, No. 64002.

(5)

Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L. Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115, 12666–12731.

(6)

Zhao, Z.; Yin, Z.; Chen, H.; Zheng, L.; Zhu, C.; Zhang, L.; Tan, S.; Wang, H.; Guo, Y.; Tang, Q.; et al. High-Performance, Air-Stable Field-Effect Transistors Based on Heteroatom-Substituted Naphthalenediimide-Benzothiadiazole Copolymers Exhibiting Ultrahigh Electron Mobility up to 8.5 cm2 V−1 s−1. Adv. Mater. 2017, 29, No. 1602410.

(7)

Kim, G.; Kang, S.-J.; Dutta, G. K.; Han, Y.-K.; Shin, T. J.; Noh, Y.-Y.; Yang, C. A Thienoisoindigo-Naphthalene Polymer with Ultrahigh Mobility of 14.4 cm2 /V·s That Substantially Exceeds Benchmark Values for Amorphous Silicon Semiconductors. J. Am. Chem. Soc. 2014, 136, 9477–9483.


24

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8)

Back, J. Y.; Yu, H.; Song, I.; Kang, I.; Ahn, H.; Shin, T. J.; Kwon, S.-K.; Oh, J. H.; Kim, Y.-H. Investigation of Structure–Property Relationships in Diketopyrrolopyrrole-Based Polymer Semiconductors via Side-Chain Engineering. Chem. Mater. 2015, 27, 1732– 1739.

(9)

Khim, D.; Cheon, Y. R.; Xu, Y.; Park, W.-T.; Kwon, S.-K.; Noh, Y.-Y.; Kim, Y.-H. Facile Route To Control the Ambipolar Transport in Semiconducting Polymers. Chem. Mater. 2016, 28, 2287–2294.

(10)

Kang, B.; Kim, R.; Lee, S. B.; Kwon, S.-K.; Kim, Y.-H.; Cho, K. Side-Chain-Induced Rigid Backbone Organization of Polymer Semiconductors through Semifluoroalkyl Side Chains. J. Am. Chem. Soc. 2016, 138, 3679–3686.

(11)

Bucella, S. G.; Luzio, A.; Gann, E.; Thomsen, L.; McNeill, C. R.; Pace, G.; Perinot, A.; Chen, Z.; Facchetti, A.; Caironi, M. Macroscopic and High-Throughput Printing of Aligned Nanostructured Polymer Semiconductors for MHz Large-Area Electronics. Nat. Commun. 2015, 6, No. 8394.

(12)

Wang, Y.; Hasegawa, T.; Matsumoto, H.; Mori, T.; Michinobu, T. D-A1-D-A2 Backbone Strategy for Benzobisthiadiazole Based N-Channel Organic Transistors: Clarifying the Selenium-Substitution Effect on the Molecular Packing and Charge Transport Properties in Electron-Deficient Polymers. Adv. Funct. Mater. 2017, 27, No. 1701486.

(13)

Wang, Y.; Nakano, M.; Michinobu, T.; Kiyota, Y.; Mori, T.; Takimiya, K. Naphthodithiophenediimide–Benzobisthiadiazole-Based Polymers: Versatile n-Type Materials for Field-Effect Transistors and Thermoelectric Devices. Macromolecules 2017, 50, 857–864.


25


(14)

Page 26 of 34

Wang, Y.; Hasegawa, T.; Matsumoto, H.; Mori, T.; Michinobu, T. Rational Design of High-Mobility Semicrystalline Conjugated Polymers with Tunable Charge Polarity: Beyond Benzobisthiadiazole-Based Polymers. Adv. Funct. Mater. 2017, 27, No. 1604608.

(15)

Wang, Y.; Kadoya, T.; Wang, L.; Hayakawa, T.; Tokita, M.; Mori, T.; Michinobu, T. Benzobisthiadiazole-Based Conjugated Donor–acceptor Polymers for Organic Thin Film Transistors: Effects of π-Conjugated Bridges on Ambipolar Transport. J. Mater. Chem. C 2015, 3, 1196–1207.

(16)

Wang, Y.; Masunaga, H.; Hikima, T.; Matsumoto, H.; Mori, T.; Michinobu, T. New Semiconducting Polymers Based on Benzobisthiadiazole Analogues: Tuning of Charge Polarity in Thin Film Transistors via Heteroatom Substitution. Macromolecules 2015, 48, 4012–4023.

(17)

Shibata, Y.; Tsutsumi, J.; Matsuoka, S.; Matsubara, K.; Yoshida, Y.; Chikamatsu, M.; Hasegawa, T. Uniaxially Oriented Polycrystalline Thin Films and Air-Stable n-Type Transistors Based on Donor-Acceptor Semiconductor (diC8BTBT)(FnTCNQ) [n = 0, 2, 4]. Appl. Phys. Lett. 2015, 106, No. 143303.

(18)

Tsutsumi, J.; Matsuoka, S.; Inoue, S.; Minemawari, H.; Yamada, T.; Hasegawa, T. NType Field-Effect Transistors Based on Layered Crystalline Donor–acceptor Semiconductors with Dialkylated Benzothienobenzothiophenes as Electron Donors. J. Mater. Chem. C 2015, 3 1976–1981.

(19)

Higashino, T.; Dogishi, M.; Kadoya, T.; Sato, R.; Kawamoto, T.; Mori, T. Air-Stable nChannel Organic Field-Effect Transistors Based on Charge-Transfer Complexes Including Dimethoxybenzothienobenzothiophene and Tetracyanoquinodimethane Derivatives. J. Mater. Chem. C 2016, 4, 5981–5987.


26

Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20)

Sato, R.; Dogishi, M.; Higashino, T.; Kadoya, T.; Kawamoto, T.; Mori, T. ChargeTransfer Complexes of Benzothienobenzothiophene with Tetracyanoquinodimethane and the n-Channel Organic Field-Effect Transistors. J. Phys. Chem. C 2017, 121, 6561–6568.

(21)

Ai, Q.; Getmanenko, Y. A.; Jarolimek, K.; Castañeda, R.; Timofeeva, T. V.; Risko, C. Unusual Electronic Structure of the Donor–Acceptor Cocrystal Formed by Dithieno[3,2a :2′,3′-c]Phenazine and 7,7,8,8-Tetracyanoquinodimethane. J. Phys. Chem. Lett. 2017, 8, 4510–4515.

(22)

Takahashi, Y.; Hasegawa, T.; Abe, Y.; Tokura, Y.; Nishimura, K.; Saito, G. Tuning of Electron Injections for n-Type Organic Transistor Based on Charge-Transfer Compounds. Appl. Phys. Lett. 2005, 86, No. 63504.

(23)

Takahashi, Y.; Hasegawa, T.; Abe, Y.; Tokura, Y.; Saito, G. Organic Metal Electrodes for Controlled p- and n-Type Carrier Injections in Organic Field-Effect Transistors. Appl. Phys. Lett. 2006, 88, No. 73504.

(24)

Shibata, K.; Ishikawa, K.; Takezoe, H.; Wada, H.; Mori, T. Contact Resistance of Dibenzotetrathiafulvalene-Based Organic Transistors with Metal and Organic Electrodes. Appl. Phys. Lett. 2008, 92, No. 23305.

(25)

Goetz, K. P.; Tsutsumi, J.; Pookpanratana, S.; Chen, J.; Corbin, N. S.; Behera, R. K.; Coropceanu, V.; Richter, C. A.; Hacker, C. A.; Hasegawa, T.; et al. Polymorphism in the 1:1 Charge-Transfer Complex DBTTF-TCNQ and Its Effects on Optical and Electronic Properties. Adv. Electron. Mater. 2016, 2, No. 1600203.

(26)

Fonari, A.; Sutton, C.; Brédas, J.-L.; Coropceanu, V. Impact of Exact Exchange in the Description of the Electronic Structure of Organic Charge-Transfer Molecular Crystals. Phys. Rev. B 2014, 90, No. 165205.


27


(27)

Page 28 of 34

Fujisue, C.; Kadoya, T.; Higashino, T.; Sato, R.; Kawamoto, T.; Mori, T. Air-Stable Ambipolar Organic Transistors Based on Charge-Transfer Complexes Containing Dibenzopyrrolopyrrole. RSC Adv. 2016, 6, 53345–53350.

(28)

Vermeulen, D.; Zhu, L. Y.; Goetz, K. P.; Hu, P.; Jiang, H.; Day, C. S.; Jurchescu, O. D.; Coropceanu, V.; Kloc, C.; McNeil, L. E. Charge Transport Properties of Perylene–TCNQ Crystals: The Effect of Stoichiometry. J. Phys. Chem. C 2014, 118, 24688–24696.

(29)

Hu, P.; Ma, L.; Tan, K. J.; Jiang, H.; Wei, F.; Yu, C.; Goetz, K. P.; Jurchescu, O. D.; McNeil, L. E.; Gurzadyan, G. G.; et al. Solvent-Dependent Stoichiometry in Perylene– 7,7,8,8-Tetracyanoquinodimethane Charge Transfer Compound Single Crystals. Cryst. Growth Des. 2014, 14, 6376–6382.

(30)

Hu, P.; Du, K.; Wei, F.; Jiang, H.; Kloc, C. Crystal Growth, HOMO–LUMO Engineering, and Charge Transfer Degree in Perylene-FxTCNQ (x = 1, 2, 4) Organic Charge Transfer Binary Compounds. Cryst. Growth Des. 2016, 16, 3019–3027.

(31)

Salzillo, T.; Masino, M.; Kociok-Köhn, G.; Di Nuzzo, D.; Venuti, E.; Della Valle, R. G.; Vanossi, D.; Fontanesi, C.; Girlando, A.; Brillante, A.; et al. Structure, Stoichiometry, and Charge Transfer in Cocrystals of Perylene with TCNQ-Fx. Cryst. Growth Des. 2016, 16, 3028–3036.

(32)

Wu, H.-D.; Wang, F.-X.; Zhang, M.; Pan, G.-B. Investigation of Transport Properties of coronene·TCNQ Cocrystal Microrods with Coronene Microrods and TCNQ Microsheets. Nanoscale 2015, 7, 12839–12842.

(33)

Zhang, J.; Liu, G.; Zhou, Y.; Long, G.; Gu, P.; Zhang, Q. Solvent Accommodation: Functionalities Can Be Tailored Through Co-Crystallization Based on 1:1 CoroneneF4TCNQ Charge-Transfer Complex. ACS Appl. Mater. Interfaces 2017, 9, 1183–1188.


28

Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34)

Kataeva, O.; Khrizanforov, M.; Budnikova, Y.; Islamov, D.; Burganov, T.; Vandyukov, A.; Lyssenko, K.; Mahns, B.; Nohr, M.; Hampel, S.; et al. Crystal Growth, Dynamic and Charge Transfer Properties of New Coronene Charge Transfer Complexes. Cryst. Growth Des. 2016, 16, 331–338.

(35)

Zhu, L.; Yi, Y.; Li, Y.; Kim, E.-G.; Coropceanu, V.; Brédas, J.-L. Prediction of Remarkable Ambipolar Charge-Transport Characteristics in Organic Mixed-Stack Charge-Transfer Crystals. J. Am. Chem. Soc. 2012, 134, 2340–2347.

(36)

Zhu, L.; Yi, Y.; Fonari, A.; Corbin, N. S.; Coropceanu, V.; Brédas, J.-L. Electronic Properties of Mixed-Stack Organic Charge-Transfer Crystals. J. Phys. Chem. C 2014, 118, 14150–14156.

(37)

Geng, H.; Zheng, X.; Shuai, Z.; Zhu, L.; Yi, Y. Understanding the Charge Transport and Polarities in Organic Donor-Acceptor Mixed-Stack Crystals: Molecular Insights from the Super-Exchange Couplings. Adv. Mater. 2015, 27, 1443–1449.

(38)

Zhang, J.; Xu, W.; Sheng, P.; Zhao, G.; Zhu, D. Organic Donor–Acceptor Complexes as Novel Organic Semiconductors. Acc. Chem. Res. 2017, 50, 1654–1662.

(39)

Zhang, J.; Jin, J.; Xu, H.; Zhang, Q.; Huang, W. Recent Progress on Organic Donor– acceptor Complexes as Active Elements in Organic Field-Effect Transistors. J. Mater. Chem. C 2018 DOI: 10.1039/c7tc04389a.

(40)

Qin, Y.; Cheng, C.; Geng, H.; Wang, C.; Hu, W.; Xu, W.; Shuai, Z.; Zhu, D. Efficient Ambipolar Transport Properties in Alternate Stacking Donor–acceptor Complexes: From Experiment to Theory. Phys. Chem. Chem. Phys. 2016, 18, 14094–14103.


29


(41)

Page 30 of 34

Hu, P.; Li, H.; Li, Y.; Jiang, H.; Kloc, C. Single-Crystal Growth, Structures, Charge Transfer and Transport Properties of Anthracene-F4TCNQ and Tetracene-F4TCNQ Charge-Transfer Compounds. CrystEngComm 2017, 19, 618–624.

(42)

Tu, Z.; Yi, Y.; Coropceanu, V.; Bredas, J.-L. Impact of Phonon Dispersion on Nonlocal Electron-Phonon Couplings in Organic Semiconductors: The Naphthalene Crystal as a Case Study. J. Phys. Chem. C 2017, 122, 44-49.

(43)

Zhu, L.; Geng, H.; Yi, Y.; Wei, Z. ChargeTransport in Organic Donor–Acceptor MixedStack Crystals: the Role of Nonlocal Electron–Phonon Couplings, Phys. Chem. Chem. Phys. 2017, 19, 4418–4425.

(44)

Kang, M. J.; Doi, I.; Mori, H.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H. Alkylated Dinaphtho[2,3-b:2′,3′-f]Thieno[3,2-b]Thiophenes (Cn-DNTTs): Organic Semiconductors for High-Performance Thin-Film Transistors. Adv. Mater. 2011, 23, 1222–1225.

(45)

Mitsui, C.; Okamoto, T.; Yamagishi, M.; Tsurumi, J.; Yoshimoto, K.; Nakahara, K.; Soeda, J.; Hirose, Y.; Sato, H.; Yamano, A.; et al. High-Performance Solution-Processable N-Shaped Organic Semiconducting Materials with Stabilized Crystal Phase. Adv. Mater. 2014, 26, 4546-4551.

(46)

Takimiya, K.; Ebata, H.; Sakamoto, K.; Izawa, T.; Otsubo, T.; Kunugi, Y. 2,7Diphenyl[1]benzothieno[3,2-b]benzothiophene, A New Organic Semiconductor for AirStable Organic Field-Effect Transistors with Mobilities up to 2.0 cm2 V−1 s−1. J. Am. Chem. Soc. 2006, 128, 12604–12605.


30

Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(47)

Amin, A. Y.; Khassanov, A.; Reuter, K.; Meyer-Friedrichsen, T.; Halik, M. Low-Voltage Organic Field Effect Transistors with a 2-Tridecyl[1]benzothieno[3,2b][1]benzothiophene Semiconductor Layer. J. Am. Chem. Soc. 2012, 134, 16548–16550.

(48)

Iino, H.; Usui, T.; Hanna, J.-I. Liquid Crystals for Organic Thin-Film Transistors. Nat. Commun. 2015, 6, No. 6828.

(49)

Kadoya, T.; Ashizawa, M.; Higashino, T.; Kawamoto, T.; Kumeta, S.; Matsumoto, H.; Mori, T. A Highly Conducting Organic Metal Derived from an Organic-Transistor Material: Benzothienobenzothiophene. Phys. Chem. Chem. Phys. 2013, 15, 17818–17822.

(50)

Kiyota, Y.; Kadoya, T.; Yamamoto, K.; Iijima, K.; Higashino, T.; Kawamoto, T.; Takimiya, K.; Mori, T. Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability. J. Am. Chem. Soc. 2016, 138, 3920–3925.

(51)

Higashino, T.; Kadoya, T.; Kumeta, S.; Kurata, K.; Kawamoto, T.; Mori, T. An Organic Metal Derived from a Selenium Analogue of Benzothienobenzothiophene. Eur. J. Inorg. Chem. 2014, 2014, 3895–3898.

(52)

Kim, J.; Han, A.-R.; Seo, J. H.; Oh, J. H.; Yang, C. β-Alkyl Substituted Dithieno[2,3d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene Semiconducting Materials and Their Application to Solution-Processed Organic Transistors. Chem. Mater. 2012, 24, 3464–3472.

(53)

Park, S.; Lim, B. T.; Kim, B.; Son, H. J.; Chung, D. S. High Mobility Polymer Based on a π-Extended Benzodithiophene and Its Application for Fast Switching Transistor and High Gain Photoconductor. Sci. Rep. 2014, 4, No. 5482.


31


(54)

Page 32 of 34

Tong, J.; Li, M.; An, L.; Li, J.; Xu, X.; Zhang, P.; Yang, C.; Wang, F.; Xia, Y. Synthesis of π-Extended Dithienobenzodithiophene-Containing Medium Bandgap Copolymers and Their Photovoltaic Application. J. Macromol. Sci. Part A 2015, 52, 934–941.

(55)

Lee, Y. S.; Song, S.; Yoon, Y. J.; Lee, Y.-J.; Kwon, S.-K.; Kim, J. Y.; Kim, Y.-H. Dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDAT)-Based Copolymers for High-Performance Organic Solar Cells. J. Polym. Sci. Part A Polym. Chem. 2016, 54, 3182–3192.

(56)

Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.; Baumgarten, M.; Pisula, W.; Müllen, K. Dithieno[2,3-d ;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene (DTBDT) as Semiconductor for High-Performance, Solution-Processed Organic Field-Effect Transistors. Adv. Mater. 2009, 21, 213–216.

(57)

Chernenkaya, A.; Morherr, A.; Backes, S.; Popp, W.; Witt, S.; Kozina, X.; Nepijko, S. A.; Bolte, M.; Medjanik, K.; Öhrwall, G.; et al. Microscopic Origin of the Charge Transfer in Single Crystals Based on Thiophene Derivatives: A Combined NEXAFS and Density Functional Theory Approach. J. Chem. Phys. 2016, 145, No. 34702.

(58)

Yoon, M.-H.; Yan, H.; Facchetti, A.; Marks, T. J. Low-Voltage Organic Field-Effect Transistors and Inverters Enabled by Ultrathin Cross-Linked Polymers as Gate Dielectrics. J. Am. Chem. Soc. 2005, 127, 10388–10395.

(59)

Tamura, S.; Kadoya, T.; Kawamoto, T.; Mori, T. Self-Contact Thin-Film Organic Transistors Based on Tetramethyltetrathiafulvalene. Appl. Phys. Lett. 2013, 102, No. 63305.


32

Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(60)

Baeg, K.-J.; Noh, Y.-Y.; Ghim, J.; Lim, B.; Kim, D.-Y. Polarity Effects of Polymer Gate Electrets on Non-Volatile Organic Field-Effect Transistor Memory. Adv. Funct. Mater. 2008, 18, 3678–3685.

(61)

Kawasugi, Y.; Yamamoto, H. M.; Hosoda, M.; Tajima, N.; Fukunaga, T.; Tsukagoshi, K.; Kato, R. Strain-Induced Superconductor/Insulator Transition and Field Effect in a Thin Single Crystal of Molecular Conductor. Appl. Phys. Lett. 2008, 92, No. 243508.

(62)

ADF2017.109; Scientific Computing & Modeling (SCM), Theoretical Chemistry, Vrije Universiteit: Amsterdam, The Netherlands (http://www.scm.com).

(63)

Kojima, H.; Mori, T. Dihedral Angle Dependence of Transfer Integrals in Organic Semiconductors with Herringbone Structures. Bull. Chem. Soc. Jpn. 2011, 84, 1049–1056.

(64)

Larsson, S. Electron Transfer in Chemical and Biological Systems. Orbital Rules for Nonadiabatic Transfer. J. Am. Chem. Soc. 1981, 103, 4034.

(65)

Mori, T.; Kobayashi, A.; Sasaki, Y.; Kobayashi, H.; Saito, G.; Inokuchi, H. The Intermolecular Interaction of Tetrathiafulvalene and Bis(ethylenedithio)tetrathiafulvalene in Organic Metals. Calculation of Orbital Overlaps and Models of Energy-Band Structures. Bull. Chem. Soc. Jpn. 1984, 57, 627–633.


33


Page 34 of 34

Table of Contents Graphic

LUMO

LUMO e

HOMO h HOMO−1


34

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals

Recommend Documents