Systematic Synthesis of Tetrathia[8]circulenes: The Influence of

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Systematic Synthesis of Tetrathia[8]circulenes: The Influence of Peripheral Substituents on the Structures and Properties in Solution and Solid States Shohei Kato, Shuhei Akahori, Yuma Serizawa, Xu Lin, Mitsuaki Yamauchi, Shiki Yagai, Tsuneaki Sakurai, Wakana Matsuda, Shu Seki, Hiroshi Shinokubo, and Yoshihiro Miyake J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01655 • Publication Date (Web): 12 Aug 2019 Downloaded from pubs.acs.org on August 12, 2019

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The Journal of Organic Chemistry

Systematic Synthesis of Tetrathia[8]circulenes: The Influence of Peripheral Substituents on the Structures and Properties in Solution and Solid States Shohei Kato,† Shuhei Akahori,† Yuma Serizawa,† Xu Lin,‡ Mitsuaki Yamauchi,‡ Shiki Yagai,# Tsuneaki Sakurai,§ Wakana Matsuda,§ Shu Seki,§ Hiroshi Shinokubo,† and Yoshihiro Miyake*,† †

Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Furo-cho, Chikusa-ku, Nagoya University, Nagoya, 464-8603, Japan. ‡

Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan. #

Institute for Global Prominent Research (IGPR), Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.

§

Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan. E-mail: [email protected] Systematic synthesis of tetrathia[8]circulenes R R R

Bpin S

S

S

direct C–H borylation

Bpin pinB

S

S

S

S

S

R S pinB

S

S

S

R

R S

S

S R R

R S R Peripheral substituents

R

R Packing structures Self-assembly Charge carrier mobility

ABSTRACT: We developed the diversity-oriented approach for the synthesis of tetrathia[8]circulenes with a variety of peripheral substituents. Iridium-catalyzed direct C–H borylation of tetrathienylene provided 1,4,7,10-tetraboryltetrathienylene as a major product. 1,4,7,10-Tetraboryltetrathienylene served as an a key intermediate to achieve the selective synthesis of octasubstituted or tetrasubstituted tetrathia[8]circulenes via rhodium-catalyzed annulation with symmetric internal alkynes or sequential Sonogashira–Hagihara coupling and base-promoted intramolecular cyclization. A variety of substituents were installed at the peripheral positions of tetrathia[8]circulenes systematically. The self-assembling behavior of tetrathia[8]circulenes was investigated using 1H NMR and AFM measurements. The number and the chain length of alkyl groups exerted a significant influence on the aggregation ability and the crystal packing structures of tetrathia[8]circulenes both in solution and solid states. We also found that the molecular arrangement of the self-assembled tetrathia[8]circulene molecules affected the hole mobility assessed by the FP-TRMC method. the molecular stacking into one-dimensional columns in the solid INTRODUCTION state, offering preferred charge carrier transporting pathways. Polycyclic aromatic hydrocarbons (PAHs) and heteroatomIntroduction of peripheral substituents in disk-shaped molecules containing PAHs have attracted considerable attention as key modulates electronic and photophysical properties as well as components for the organic electronic devices.1-4 In addition, disksolubility and aggregation properties in solid and liquid crystals. shaped PAHs represent a series of organic semiconductors with Consequently, diversity-oriented approaches which enable the controllable self-assembly and anisotropic transporting properties efficient synthesis of disk-shaped molecules with a variety of because of their highly symmetric, rigid, and planar structures.5,6 substituents are highly desirable. The large intermolecular overlap between their π-planes induces

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The Journal of Organic Chemistry 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

[n]Circulenes are representative PAHs, in which n-membered rings are surrounded by n fused benzene units.7-11 Numbers of fused-benzene rings have a significant impact on the structures of [n]circulenes. For example, [8]circulenes adopt saddle-shaped conformation.11 Hetero[n]circulenes are heteroatom analogues of [n]circulenes. Replacement of benzene rings in [n]circulenes with heteroles such as furan, pyrrole, and thiophene dramatically alters their electronic properties. Recently, hetero[8]circulenes are expected to be applicable for the organic electronic materials based on the effective electronic perturbation by heteroatoms.12-21 Because of the electron-donating character of thiophenes, annulation of thiophene units to π-conjugated systems significantly affects their electronic nature. Thiophene-fused ladder-shaped compounds have been extensively studied as p-type semiconductors. However, the synthesis of disk-shaped molecules annulated by thiophenes are quite limited.4,20b,22 Octathia[8]circulene and tetraselenatetrathia[8]circulene are a class of thiophene-annulated hetero[8]circulenes, which exhibit excellent charge transporting properties (Figure 1).16,17 However, the lack of peripheral substituents in octathia[8]circulene and tetraselenatetrathia[8]circulene cause low solubility in common organic solvents, hampering fine-tuning of photophysical and electrochemical properties and controlling packing structures in the solid state. In 2015, Wong and co-workers have reported the first successful synthesis of tetrathia[8]circulene as a new entry of thiophene-fused [8]circulenes. Unfortunately, the peripheral substituents were limited to eight methoxy groups (Scheme 1a).15 This methodology requires each tetraphenylene precursor with a specific alkoxy group for the synthesis of each substituted tetrathia[8]circulene. Independently, we have developed the diversity-oriented approach for the synthesis of tetrathia[8]circulenes 1 with various peripheral substituents. This strategy employs tetraborylated tetrathienylene 3 as a common building block, which was readily prepared from tetrathienylene 2 via direct C–H borylation (Scheme 1b).18 In this article, we describe the systematic synthesis of 1 and the effect of the number and chain length of alkyl groups in 1 on their intrinsic properties such self-association in solution and hole mobility in solid. R Y S

S

R

S

S

R

R

Y

Y

R S

Y

R S

S

S R

Y = S: octathia[8]circulene Y = Se: tetraselenatetrathia[8]circulene

R

tetrathia[8]circulene 1

Figure 1. Hetero[8]circulenes annulated by thiophenes.

Page 2 of 10

(a) Previous Method (ref. 10) MeO

OMe

MeO Br Br

MeO

OMe

MeO

OMe MeO

bromination

OMe

S 1) lithiation, S

MeO MeO

MeO

OMe

Br Br MeO

Br Br OMe

OMe S

MeO

OMe Bpin S

direct C–H borylation

S Bpin

pinB S

S

OMe

OMe S

(b) This Work S S

OMe

S

MeO MeO

2) Cu

OMe Br Br

S

S

2 R

R

S

3

pinB R S

R

S

S

S

S

R R

R

R S

S

R

R R R Systematic Synthesis of Tetrathia[8]circulenes 1

RESULTS AND DISCUSSION We investigated iridium-catalyzed direct C–H borylation of tetrathienylene 2 (Scheme 2).23,24 Treatment of 2 with 8 equiv of pinacolborane (HBpin) in the presence of 2.5 mol% of [Ir(OMe)(cod)]2 (cod = 1,5-cyclooctadiene) and 5 mol% of 4,4'di-tert-butyl-2,2'-bipyridyl (dtbpy) in hexane at 10 °C for 90 h afforded a mixture of 1,4,7,10-tetraboryltetrathienylene 3 and its regioisomers in 62% total yield. The content percentage of 3 in the mixture was 80%. After recrystallization from heptane, 3 was isolated as a white solid in 33% yield. The reaction temperature is an important factor for controlling the distribution of the products. In fact, when the borylation reaction of 2 was performed at 60 °C, the percentage of 3 decreased to 50%. Separately, we conducted the density functional theory (DFT) calculations at the B3LYP/631G(d) level on 3 and its regioisomers. The calculations show that 3 is energetically the most stable isomer among the tetraborylated compounds. Considering these experimental and theoretical results, we concluded that 3 is one of the thermodynamically favorable products. Scheme 2. Direct C–H Borylation of Tetrathienylene 2.

Scheme 1. Synthesis of Tetrathia[8]circulenes S

S

+ S

S

HBpin (8 equiv)

[Ir(OMe)(cod)]2 (2.5 mol%) dtbpy (5 mol%) hexane

Bpin S

S Bpin

pinB S

2

S pinB

3

temperature (°C)

time (h)

yield of a mixture of regioisomers (%)

percentage of 3 (%)b

10 60

90 18

62 (33)a 75

80 50


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The Journal of Organic Chemistry a

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Isolated yield of 3 after recrystallization. bDetermined by 1H NMR.

(a)

The use of rhodium catalyst [Cp*RhCl2]2 (Cp*: h -C5Me5) enables successful annulation of 3 with internal alkynes leading the octasubstituted tetrathia[8]circulenes 1a–1i (Scheme 3).18,25 Various symmetric alkynes participated in this annulation to allow the introduction of a variety of aryl and alkyl groups to the eightperipheral positions. Unfortunately, the reaction with 1-phenyl-1hexyne afforded a mixture of regioisomeric tetrathia[8]circulenes. Scheme 3. Annulation of 3 with Internal Alkynes to Octasubstituted Tetrathia[8]circulenes. 5

Bpin S pinB S

R

R R (4: 5 equiv) [Cp*RhCl2]2 (20 mol%) S R Bpin Cu(OAc)2•H2O (1 equiv) LiOAc (4 equiv) R

pinB

S

3

S R R

DMF, air 100 °C, 2 h

S

R

S

R R 1f (R = C7H15): 25% 1g (R = C8H17): 20% 1h (R = C9H19): 20% 1i (R = C12H25): 16%

1a (R = 4-tBuC6H4): 27% 1b (R = 3,5-(tBu)2C6H3): 26% 1c (R = 4-nBuOC6H4): 23% 1d (R = C2H5): 33% 1e (R = C6H13): 33%

Tetraboryltetrathienylene 3 also serves as a common building block for the synthesis of tetrasubstituted tetrathia[8]circulenes (Scheme 4). The boryl groups of 3 was easily transformed into iodo groups by the reaction with CuI and N-iodosuccinimide (NIS).19a,26 The Sonogashira–Hagihara coupling reaction of tetraiodotetrathienylene 5 with terminal alkynes 6 yielded the corresponding tetraalkynyl tetrathienylene 7 quantitatively. Subsequent fourfold intramolecular cyclization of 7 was successfully promoted with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base27 to provide the corresponding circulenes 1j–1l in moderate yields. The synthetic procedures shown in Schemes 2-4 provide efficient methodologies for the selective synthesis of octasubstituted and tetrasubstituted tetrathia[8]circulenes, thus enabling the convenient installation of various peripheral substituents. Scheme 4. Synthesis of Tetrasubstituted Tetrathia[8]circulenes. Bpin S

I S

S Bpin ref. 20a

pinB S H R (6: 6 equiv) PdCl2(PPh3)2 (10 mol%) R CuI (10 mol%) Et3N 60 °C, 3 h

S I

I S

S 3

pinB

S 5

I R

S

R S

S

S

S

S

DBU R R (5 equiv.) S

S R

7

(b)

S

NMP reflux, 12 h

R

R 1j (R = C4H9): 54% 1k (R = C7H15): 43% 1l (R = C12H25): 41%

Figure 2. Packing structures of (a) 1d (ref. 19) and (b) 1j. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are set to 50% probability.

Recrystallization of tetrasubstituted tetrathia[8]circulene 1j (odichlorobenzene/acetonitrile) afforded single crystals suitable for X-ray diffraction analysis. The tetrathia[8]circulene core in 1j adopted a planar structure, which is similar to those in 1b and 1d. In the packing structure of 1b, no significant intermolecular interactions are observed due to the steric hindrances of the peripheral aryl groups on 1b. In contrast, the molecules of 1d are arranged in a face-to-face stacking manner in a one-dimensional columnar structure, in which the distance between the π-planes is 3.461 Å (Figure 2a).18 The molecules of 1j are also stacked in a face-to-face manner with an interplanar distance of 3.539 Å. However, the overlapped area of the π-surface in the packing structure of 1j is significantly smaller than that of 1d (Figure 2b). Figure 3 shows the electronic absorption spectra of octaaryl circulene 1b, octaheptyl circulene 1f, and tetraheptyl circulene 1k in CHCl3. The feature of the spectrum of 1b was similar to those of 1f and 1k. As compared to 1f and 1k, the low energy absorption bands of 1b were red-shifted because of the expansion of πconjugation with the peripheral aryl groups. On the other hand, a distinct difference among the absorption spectra of 1b, 1f, and 1k in the solid state was observed. The longest-wavelength absorption band of 1f and 1k in the solid state exhibits a bathochromic shift as compared with those in the CHCl3 solution (Figures 4b and 4c). The red shift is probably originated from J-aggregate-like assembly of alkylated tetrathia[8]circulenes in the solid state. In contrast, the solid state absorption spectrum of 1b was almost identical with the absorption spectrum of 1b in solution, indicating the lack of significant intermolecular interactions in the solid state due to eight bulky aryl groups (Figure 4a).


The Journal of Organic Chemistry 120000

of 1k was enthalpy driven probably due to favorable interactions between the slipped stacked dimer.

ε / M–1 cm–1

100000 80000

𝐾" =

60000 40000 20000 0 250

[(𝟏𝐤)" ] [𝟏𝐤]"

δ = δ, + (δ. − δ, ) 01 +

(1)

1 − 28𝐾" 𝐶 + 1 7 4𝐾" C

(2)

Scheme 5. Self-Association of 1k. 300 350 400 wavelength/nm

450

500

(a)

(b)

(c)

Normalized absorbance

Normalized absorbance

Figure 3. Absorption spectra of 1b (black), 1f (red), and 1k (blue) in CHCl3. Normalized absorbance

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 4 of 10

350 400 450 500 wavelength/nm


R

R R

S

S

S

S R

Ha 1k: R = C7H15


Figure 4. Absorption spectra in solid (red) and in CHCl3 (black) of 1b (a), 1f (b), and 1k (c).

The values of NICS(0) and NICS(1) at the center of eightmembered ring in tetrathia[8]circulene core are +6.78 and +3.97 (B3LYP/6-31G(d) level) and they may indicate antiaromatic nature (Figure 8x). However, the 1H NMR spectra of tetraalkyl circulenes 1j, 1k and 1l display one singlet around the aromatic region (7.6-8.0 ppm) assignable to the protons of benzene ring in 1j, 1k and 1l. These results clearly suggest that the structural contribution of aromatic benzene in tetrathia[8]circulene core is predominant and the antiaromartic nature of central eightmembered ring is negligible. Interestingly, the 1H NMR spectra of tetraheptyl circulene 1k in CDCl3 at 20 °C indicated distinguishable concentration dependence (Figure 5a). The signal assigned to the aromatic proton (Ha) at the benzene rings in 1k varied from 8.034 ppm to 7.678 ppm as the concentration of 1k increased from 0.265 mM to 10.0 mM in CDCl3 (Scheme 5). This phenomenon is likely due to self-association of 1k in a CDCl3 solution. The upfield shift indicates that the molecules in the aggregates accumulate in a Jaggregate-like slipped stacking arrangement. The association constant (K2) of 1k was determined by assuming a monomer– dimer equilibrium.28,29 The least-squares curve fitting with eqs 1 and 2 determined K2, where dm, dd, and C denote the chemical shift of monomer 1k, the chemical shift of dimer (1k)2, and the total concentration of the substrate, respectively. The dilution curve for 1k is shown in Figure 6. K2 was estimated to be 63.6 ± 1.63 M–1. The 1H NMR spectra of 1k were also dependent on temperatures. Thermodynamic parameters were determined by applying the association constants at various temperatures to the van't Hoff plot (Figure S2). Thermodynamic parameters DG, DH, and DS at 298 K were estimated to be –9.95 kJ mol–1, –20.1 kJ mol–1, and –34.0 J mol–1 K–1, respectively. These values indicated that the dimerization

K2 R

R

S R

R S

S S

S R S

S R

S R

R

(1k)2

In sharp contrast, octasubstituted circulene octaheptyl circulene 1f exhibited different behavior in solution. The solution of 1k in CDCl3 at 5 mM was clear, while a precipitate formed from the CDCl3 solution of 1f at the similar concentration (Figures 5b and 5c). In addition, we observed gel formation of 1f in non-polar solvents. Octasubstituted circulene 1f was dissolved in methylcyclohexane (MCH, 3 mM) at 50 °C. The subsequent cooling of the solution to room temperature resulted in formation of a gel (Figure 5d). In contrast, no gelation was observed in the case of tetraheptyl circulene 1k. The xerogel of 1f showed tetragonal packing in its X-ray diffraction (XRD) (Figure S3), where the distinct peaks at the spacing d = 20.0, 14.1, 9.9, and 8.9 Å were assigned to (100), (110), (200), and (210) of a tetragonal 2D packing, respectively. With the information of the molecular size of 1f (~28 Å), we concluded that 1f self-assembles into a tetragonal columnar structure via π–π stacking with interdigitation of heptyl chains to form 1D fibers. The fibers are further entangled into networked structures to form a gel. To obtain insights into the structure of the aggregates promoting the gelation behavior, the morphology of micro/nano aggregates of 1f was traced by atomic force microscopy (AFM). For this purpose, a dilute MCH solution of 1f was prepared by heating-cooling procedure and the resulting homogeneous solution was spincoated onto a highly oriented pyrolytic graphite (HOPG) substrate. AFM images thus obtained visualized plate-like nanoaggregates forming step-terrace structures with a periodic thickness of 21 Å (Figure 7). These structures indicate the high crystallinity of 1f and interdigitation of heptyl chains. The presumed nanostructures from these AFM images are compatible to the kinetic formation of onedimensional aggregates of 1f.


Page 5 of 10 Ha

(a)

CHCl3

Figure 7. (a,b) AFM height images of nanoaggregates of 1f cast from a MCH solution (100 mM) onto HOPG by spin-coating. (c) Crosssectional analysis along the white line in (b) to show the thickness of plate-like aggregates.

(b)

10.0 mM 7.52 mM 5.64 mM 4.23 mM (c) 2.12 mM 1.06 mM 0.529 mM 0.265 mM 8.2 8.0

7.8 7.6 7.4 δ/ppm

7.2 7.0

(d) cooling heating

rt

50 °C

Figure 5. (a) 1H NMR spectra of 1k in CDCl3 at 20 °C at various concentrations. (b) Photo of the tube containing 1k in CDCl3 at 5 mM. (c) Photo of a tube containing 1f in CDCl3 at 5 mM. (d) Photos of the tube containing 1f in methylcyclohexane at 3 mM at 50 °C and rt. 8.1

10 ℃ 15 ℃ 20 ℃ 30 ℃ 40 ℃ 50 ℃

8.0

chemical shift (ppm)

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


7.9

7.8

7.7

The strong intermolecular interactions observed for octaheptyl circulene 1f motivated us to investigate its charge transport property within the one-dimensional columnar structure with sufficient structural stabilization via inter-columnar interactions. Both of drop-casting and spin-coating of 1f yielded no films but ununiform powders on quartz substrates, which is unsuitable for spectroscopic assessments. Consequently, the vacuum deposition method was employed to obtain smooth thin films for octaethyl circulene 1d, octaheptyl circulene 1f, and tetrabutyl circulene 1j. The temperature of the quartz substrates during vacuum deposition (Tsub) was set at r.t. or 80 °C. The change of Tsub has a possibility of well-controlled aggregation rate of conjugated molecules with strong-stacking tendency.30 The XRD patterns of the vapor-deposited film of 1f (Tsub = r.t.) showed a set of diffraction peaks at d = 19.2, 13.8, and 9.7 Å in small angle region (Figure S4), which were assignable to those from (100), (110), and (200) planes of a tetragonal columnar packing, respectively. Several unassignable minor diffractions were also observed in a wide angle region, which may be ascribable to intracolumnar periodicity. This packing structure is almost identical to that observed for the xerogel of 1f, indicating that 1f strongly self-assembles into a tetragonal columnar crystalline phase during deposition on the substrate. The vacuum-deposited films on the quartz plates were subjected to flash-photolysis time-resolved microwave conductivity (FPTRMC) technique, a contactless microwave-probing method of photo-injected charge carriers.31 All the films of 1d, 1f, and 1j exhibited typical decay profiles of transient conductivity upon photoexcitation at 355 nm (Figure 8a), where 1f showed particularly large maximum values (fSμ)max. For the detailed assessment of the photo-injected charge carrier density/species, transient absorption spectroscopy (TAS) of these films was performed. The film of 1f (Tsub = 80 °C) showed clear transient absorption at around 435 nm (Figure 8b and S3), which is in line with the absorption of radical cations of tetrathia[8]circulenes (435 nm, e ~6500 M–1 cm–1).19 The charge carrier generation yield f was estimated from the following equation,

φ=

7.6 0

2

4 6 8 concentration (mM)

10

Figure 6. Concentration dependence of the 1H NMR chemical shift of 1k in CDCl3 at various temperature.

ΔO.D. ε I 0 FTAS

(3)

where, O.D. e, I0, and FTAS represent optical density of the photoinduced transient species at 435 nm, absorption coefficient of the transient species (e435 nm ~6500 M–1 cm–1), incident photon density of excitation laser (cm–2), and correction factor depending on the geometry and thickness of the sample films (mol), respectively. For the estimation of Sµ (~µh), the values of (f∑µ)0.2 µs from FPTRMC and f0.2 µs from TAS at 0.2 µs were used to remove the contribution of fluorescence strongly appeared at ~0 µs, and the obtained values are summarized in Table 1. The estimated hole mobility for 1f marks the highest value in the range of 10–3 cm2 V–1 s–1, while those for 1d and 1j are in the range of 10–4 cm2 V–1 s–1 and 10–5 cm2 V–1 s–1, respectively; the alkyl length and substitution patterns play a key role in the observed hole mobility. On the other hand, no obvious effect of Tsub on the values of µh was confirmed (Table 1), though 1d and 1j showed changes in the XRD patterns depending on the Tsub (Figure S4). These results implied that 1d



and 1j form crystalline films but the crystal structures are not so much stable–easily transformed to other polymorphs by elevating the temperature. On the other hand, 1f showed tetragonal packing patterns with large intensities of XRD peaks and the patterns are almost identical between Tsub = r.t. and 80 °C. Considering all these observations, we concluded that regulation of thermal fluctuation in the columnar structure of 1f by the strong interdigitation of its heptyl chains resulted in the observed larger hole mobility than those of 1d and 1j.

Page 6 of 10

Hagihara coupling and base-promoted intramolecular cyclization furnished octasubstituted tetrathia[8]circulenes. These systematically synthetic approach for tetrathia[8]circulenes enables to clarify the relationship between the properties and peripheral substituents. 1H NMR and AFM measurements revealed that the aggregation abilities and crystallinity of tetrathia[8]circulenes in solution and solid states depend on the number and the chain length of alkyl groups. The FP-TRMC method elucidated that the crystal packing structure of tetrathia[8]circulenes affected charge carrier mobilities and octasubstituted tetrathia[8]circulenes exhibited higher charge carrier mobilities than those of tetrasubstituted tetrathia[8]circulenes.

EXPERIMENTAL SECTION

Figure 8. (a) Kinetic traces of photoconductivity transients observed for vacuum-deposited films of 1d (red, orange), 1f (blue, turquoise), and 1j (green, lime) upon photoexcitation at 355 nm. Tsub represents the temperature of quartz substrates during vacuum deposition. Photon density was set at 4.6 × 1015 cm–2 for 1d and 1f, and 9.1 × 1015 cm–2 for 1j. (b) Kinetic traces of photoconductivity transient (red) and transient absorption at 435 nm (blue) for vacuum-deposited film of 1f (Tsub = 80 °C). The spike at around 0 µs in TAS originates from fluorescence of 1f.

Table 1. Summary of the evaluated maximum conductivity ((f∑ µ)max) and conductivity at 0.2 µs (f∑µ)0.2 µs in FP-TRMC, charge generation efficiency (f) at 0.2 µs in TAS, and estimated hole mobility (µh) for vacuum-deposited thin films of 1. Sample

(fSµ) max/ 2

–1 –1

(fSµ)0.2 µs / 2

f0.2 µs a

µh / cm2V–1s–1

–1 –1 a

cm V s

cm V s

1f (Tsub = r.t.)

8.9 × 10–5

6.7 × 10–5

6.3 × 10–2

1.1 × 10–3

1f (Tsub = 80 °C)

2.2 × 10–4

1.7 × 10–4

6.9 × 10–2

2.5 × 10–3

1d (Tsub = r.t.)

3.5 × 10–5

1.6 × 10–5

7.0 × 10–2

2.3 × 10–4

1d (Tsub = 80 °C)

5.7 × 10–5

4.6 × 10–5

1.1 × 10–1

4.2 × 10–4

1j (Tsub = r.t.)

1.7 × 10–5

8.4 × 10–6

9.7 × 10–2

8.6 × 10–5

1j (Tsub = 80 °C)

1.2 × 10–5

4.9 × 10–6

7.7 × 10–2

6.3 × 10–5

fmax was difficult to determine due to the overlap of a spike peak by fluorescence from films of 1. Thus µh was calculated by the quotient of the conductivity at 0.2 µs, (fSµ)0.2 µs, from FP-TRMC and charge generation efficiency at 0.2 µs, f0.2 µs, from TAS measurements. a

CONCLUSION In summary, we have developed the synthesis of tetrasubstituted and octasubstituted tetrathia[8]circulenes 1 with a variety of substituents. 1,4,7,10-Tetraboryltetrathienylene 3, obtained from C–H borylation of tetrathienylene, was employed as a common intermediate for both tetrasubstituted and octasubstituted tetrathia[8]circulenes. Rhodium-catalyzed annulation of 3 with symmetric internal alkynes afforded octasubstituted tetrathia[8]circulenes, while the combined use of Sonogashira–

General Methods. 1H NMR (500 MHz) and 13C{1H} NMR (126 MHz) spectra were recorded on a Bruker AVANCE III HD spectrometer, and chemical shifts were reported as the delta scale in ppm relative to CHCl3 (δ = 7.260 ppm) for 1H NMR and CDCl3 (δ = 77.0 ppm) for 13C NMR. UV/vis absorption spectra were recorded on a Shimadzu UV-2550 or JASCO V670 spectrometer. Mass spectra were recorded on a Bruker microTOF using positive mode ESI-TOF and APCI-TOF method for acetonitrile solutions. Melting points were measured by an SRS MPA100 OptiMelt Automated Melting Point System. Gel permeation chromatography (GPC) was performed using a JAI model LC-928 recycling preparative HPLC equipped either with JAIGEL-2H-40 and JAIGEL-2.5H-40 columns (40 × 600 mm × 2) with CHCl3 as eluent. Solvents were dried by the general methods and degassed before use. Unless otherwise noted, materials obtained from commercial suppliers were used without further purification. Tetraboryl tetrathienylene 3,18 and tetraiodo tetrathienylene 519 were prepared according to the literature procedures. Synthesis of tetrathia[8]circulenes 1a-1i has been reported.18 Pd-Catalyzed Coupling Reaction of 5 with terminal alkynes. Typical procedure for the palladium-catalyzed coupling reaction of 5 with terminal alkyne 6a is described below. In a 20 mL Schlenk flask were placed 5 (40.0 mg, 48.1 μmol), PdCl2(PPh3)2 (3.4 mg, 10 mol%), and CuI (1.8 mg, 20 mol%) under N2. 1-Hexyne 6a (33.2 µL, 6.0 equiv) and triethylamine (1 mL) were added to a solution and the mixture was heated at 60 °C for 3 h. After cooling to room temperature, water (5 mL) was added. The resulting mixture was extracted with chloroform (10 mL × 3). The combined organic layer was dried over Na2SO4, and the organic solvent was removed in vacuo. The crude product was purified by column chromatography (SiO2) with hexane/CHCl3 to give 7a (31.2 mg, 48.1 μmol, quantitative yield) as a yellow oil. 7a: quantitative. A yellow oil. 1H NMR (CDCl3) δ 7.24 (s, 4H), 2.34 (t, J = 7.3 Hz, 8H), 1.51 (quint, J = 7.3 Hz, 8H), 1.39 (sext, J = 7.3 Hz, 8H), 0.92 (t, J = 7.3 Hz, 12H). 13C NMR (CDCl3) δ 138.8, 134.9, 125.5, 122.0, 96.2, 73.9, 30.7, 22.1, 19.6, 13.8. HRMS (APCI) Calcd. for C40H41S4 [M+H]: 649.2086. Found: 649.2085. 7b: quantitative. A yellow oil. 1H NMR (CDCl3) δ = 7.24 (s, 4H), 2.33 (t, J = 7.0 Hz, 8H), 1.51 (quint, J = 7.0 Hz, 8H), 1.32 (m, 32H), 0.91 (t, J = 7.0 Hz, 12H). 13C NMR (CDCl3) δ = 138.8, 134.9, 125.5, 122.0, 96.2, 74.0, 32.0, 29.0, 28.6, 22.8, 19.9, 14.3. HRMS (APCI) Calcd. for C52H65S4 [M+H]: 817.3964. Found: 817.3930. 7c: quantitative. A yellow oil. 1H NMR (CDCl3) δ = 7.24 (s, 4H), 2.33 (t, J = 6.9 Hz, 8H), 1.51 (quint, J = 6.9 Hz, 8H), 1.28 (m,


Page 7 of 10 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


72H), 0.89 (t, J = 6.9 Hz, 12H). 13C NMR (CDCl3) δ = 138.8, 134.9, 125.5, 122.0, 96.2, 74.0, 32.1, 29.84, 29.78, 29.5, 29.3, 29.1, 28.6, 22.9, 19.9, 14.3. HRMS (APCI) Calcd. for C72H105S4 [M+H]: 1097.7094. Found: 1097.7063. Cyclization of 7. Typical procedure DBU-mediated cyclization of 7a is described below. In a 20 mL Schlenk flask was placed 7a (31.2 mg, 48.1 μmol) under N2. 1,8-Diazabicyclo[5.4.0]undec-7ene (DBU, 36.0 µL, 5.0 equiv) and N-methylpyrrolidone (1 mL) were added and the reaction mixture was refluxed for 3 h. After cooling to room temperature, water (5 mL) was added. The resulting mixture was extracted with chloroform (10 mL × 3). The combined organic layer was dried over Na2SO4, and the organic solvent was removed in vacuo. The residue was purified by column chromatography (SiO2) with hexane/CHCl3 to give a yellow solid. After recrystallization from CHCl3/hexane, 1j was obtained (16.9 mg, 26.0 μmol, 54% yield). 1j: 54% yield. A yellow solid. 1H NMR (CDCl3) δ = 7.95 (s, 4H), 3.17 (t, J = 7.6 Hz, 8H), 1.98 (quint, J = 7.6 Hz, 8H), 1.60 (sext, J = 7.6 Hz, 8H), 1.07 (t, J = 7.6 Hz, 12H). 13C NMR (CDCl3) δ = 137.41, 137.36, 135.0, 130.7, 129.3, 120.5, 34.6, 31.2, 23.0, 14.2. HRMS (APCI) Calcd. for C40H41S4 [M+H]: 649.2086. Found: 649.2060. 1k: 43% yield. A yellow solid. 1H NMR (CDCl3) δ = 7.92 (s, 4H), 3.14 (t, J = 7.5 Hz, 8H), 1.59-1.34 (m, 32H), 0.92 (t, J = 7.5 Hz, 12H). 13C NMR (CDCl3) δ = 137.4, 137.3, 134.9, 130.7, 129.3, 120.4, 34.9, 32.0, 29.9, 29.4, 29.0, 22.9, 14.3. HRMS (APCI) Calcd. for C52H65S4 [M+H]: 817.3964. Found: 817.3947. 1l: 41% yield. A yellow solid. 1H NMR (CDCl3) δ = 7.88 (s, 4H), 3.10 (t, J = 7.4 Hz, 8H), 1.96 (quint, J = 7.4 Hz, 8H), 1.58-1.28 (m, 72H), 0.88 (t, J = 7.4 Hz, 12H). 13C NMR (CDCl3) δ = 137.4, 137.3, 134.9, 130.7, 129.3, 120.3, 34.9, 32.1, 30.0, 29.9, 29.83, 29.76, 29.5, 29.0, 22.6, 14.3. HRMS (APCI) Calcd. for C72H105S4 [M+H]: 1097.7094. Found: 1097.7132.

ASSOCIATED CONTENT Supporting Information Spectroscopic data, CIF files, and X-ray data. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *[email protected]

Funding Sources No competing financial interests have been declared.

ACKNOWLEDGMENT This work was supported by Grant-in-Aids for Scientific Research on Innovative Areas “pi-System Figuration (No. 2601)” (JSPS KAKENHI Grants 26102003, 26102011 and 26102001) and “Precisely Designed Catalysts with Customized Scaffolding (No. 2702)”(JSPS KAKENHI Grant 16H01013) from MEXT, Japan.

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Systematic synthesis of tetrathia[8]circulenes R R R

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Systematic Synthesis of Tetrathia[8]circulenes: The Influence of

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