Topological Control of Columnar Stacking Made of Liquid-Crystalline Thiophene-Fused Metallonaphthalocyanines.

The spontaneous organization of two-dimensional polyaromatic molecules into well-defined nanostructures through noncovalent interactions is important in the development of organic-based electronic and optoelectronic devices. Two regioisomers of thiophene-fused zinc naphthalocyanines ZnTNcendo and ZnTNcexo have been designed and synthesized to obtain photo- and electroactive liquid crystalline materials. Both compounds exhibited liquid crystalline behavior over a wide temperature range through intermolecular π-π interactions and local phase segregation between the aromatic cores and peripheral side chains. The structural differences between ZnTNcendo and ZnTNcexo affected the stacking mode in self-assembled columns, as well as symmetry of the two-dimensional rectangular columnar lattice. The columnar structure in liquid crystalline phase exhibited an ambipolar charge-transport behavior.

Introduction

Spontaneous organization of two‐dimensional polyaromatic molecules into well‐defined nanostructures through noncovalent interactions has been intensively explored, to realize organic‐based electronic and optoelectronic devices.1, 2, 3 The decoration of polyaromatic cores with flexible alkyl chains results in the formation of liquid‐crystalline phases, which correspond to one‐dimensional columnar stacks of polyaromatic molecules driven by the intermolecular π–π interactions and the local phase segregation between the flat rigid aromatic cores and peripheral side chains.4, 5 The intermolecular π–π overlap among polyaromatic molecules within the columns provides a transport pathway for charge or energy along the columnar axis. The charge carrier mobilities and semiconductivities can be tailored by designing polyaromatic cores and controlling the self‐organization of molecules in the bulk.

Metallophthalocyanines (MPcs) and their analogs have been widely used as molecular materials in applications from organic pigments to semiconductors for electronic devices because of their unique optical properties and thermal stability.6, 7 Since the first report of liquid crystalline Pc by Piechocki and Simon8, liquid crystalline MPcs have been modified to control the self‐organized nanostructures, and applied as molecular components in organic thin‐film transistors (OTFTs) and solar photovoltaics (OPVs).9, 10 The optical and electronic properties of MPcs strongly depend on the size of the π‐system.11 The expansion of the phthalocyanine π‐system has been achieved by condensation of fused polyaromatic precursors.12, 13, 14, 15, 16, 17, 18 The size and geometry of the annulated aromatic residues on the tetraazaporphyrin core affects the position of the Q band, as well as the HOMO and LUMO energy levels. Moreover, the expansion of the π‐system enhances the tendency for π‐stacking. Although various ring‐expanded MPcs with alkyl chains have been synthesized, and their self‐assembly properties in solution or on substrates investigated, there have been few reports on the spontaneous organization of liquid crystalline ringexpanded MPcs into nanostructures.19, 20, 21, 22

In this paper, we report the syntheses of two isomeric, thiophene‐fused zinc naphthalocyanines (Nc), ZnTNc and ZnTNc, decorated with sixteen dodecyl chains, and their self‐organization properties. Thiophene‐fused polyaromatic molecules display excellent performance in OTFT and OPV, due to the formation of three‐dimensional molecular stacks through sulfur–sulfur contact between thiophene segments.23, 24 We hoped to control the organized structure of ring‐expanded MPcs and enhance the charge mobilities by fusing with thiophene rings at the peripheral positions of the Nc ring. The physical properties and self‐organized structures in the liquid crystalline phase, and the carrier mobilities of the two isomers were compared with each other.

Results and Discussion

Thiophene‐fused ZnNc derivatives were synthesized from 4,5‐dithienylphthalonitrile by Yan et al., and they studied their aggregation behavior in solution.25 In this paper, we designed and synthesized two isomers, ZnTNc and ZnTNc, possessing sixteen dodecyl chains, in which flexible dodecyl chains were attached to the two positions of the peripheral thiophene rings.

Regioisomers of thiophene‐fused phthalonitriles 6 and 7 were synthesized from 2‐bromo‐4,5‐didodecylthiophene as a starting material (Scheme 1). 2‐Bromo‐4,5‐didodecylthiophene was prepared from 3‐bromothiophene according to the procedure reported by Kuo et al.26 Compound 2 was synthesized from 2‐bromo‐4,5‐didodecylthiophene by the selective lithiation at the α‐hydrogen of the thiophene ring using n‐butyllithium, followed by reaction with 2‐isopropoxy‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane.27 The other isomer 3 was prepared in two synthetic steps: isomerization of 2‐bromo‐4,5‐didodecylthiophene with lithium diisopropylamide (LDA),28, 29 and the palladium‐catalyzed Miyaura borylation reaction with bis(pinacolato)diboron.30, 31 Phthalonitrile precursors 4 and 5 were synthesized by the Suzuki–Miyaura coupling reaction of 4,5‐dichlorophthalonitrile with 2 or 3 in the presence of a palladium catalyst using S‐Phos ligand.32 The two thiophenes in 4 and 5 were fused by FeCl3‐mediated oxidative cyclization.28, 29 Phthalonitriles 6 and 7, in which two thiophenes are annealed at different positions, were isolated as yellow solids, and unambiguously characterized by NMR spectroscopy, FT‐IR, and matrix‐asssited laser desorption ionization–time‐of‐flight mass spectrometry (MALDI‐TOF MS).

Scheme 1

Syntheses of ZnTNcendo and ZnTNcexo. Reagents and conditions: a) LDA, THF, rt, 12 h, 80 %; b) i) 1.6 m nBuLi, THF, −78 °C, 1 h; ii) 2‐isopropoxy‐4,4,5,5‐tetramethyl‐ 1.3.2‐dioxaborolane, rt, 12 h, 72 %; c) bis(pinacolato)diboron, Pd(dppf)Cl2 ⋅CH2Cl2, KOAc, 1,4‐dioxane, 80 °C, 6 h, 44 %; d) 4,5‐dichlorophthalonitrile, Pd(OAc)2, S‐Phos, K3PO4, toluene, DME, H2O, 85 °C, 12 h, 61 %; e) FeCl3, CH3NO2, CH2Cl2, 0 °C, 0.5 h, 86 %; f) Zn(OAc)2, DBU, 1‐pentanol, 140 °C, 12 h, 50 %.

Figure 1 a shows the absorption and fluorescence spectra of 6 and 7 in CH2Cl2. The shapes of the absorption spectra of 6 and 7 were different, and the emission maximum of 7 was red‐shifted relative to that of 6. Density functional theory (DFT) calculations were conducted for 6 and 7, in order to gain insight into the equilibrium geometries and electronic structures of the frontier orbitals of the compounds. The transitions calculated by time‐dependent (TD) DFT agreed well with the experimental absorption spectra of 6 and 7 (Figure S3). While 7 has a planar geometry, the other isomer 6 shows a less planar structure as shown in Figure 1 b. The steric hindrance arising from the methyl units of two different thiophenes in 7 induces strain in the thiophene‐fused phthalonitrile. The differences in the absorption and fluorescence spectra of 6 and 7 can be explained by a change in conjugation caused by the strain of the aromatic rings.33

Figure 1

a) Absorption and fluorescence spectra of 6 (black line) and 7 (red line) in CH2Cl2. b) Optimized structures of 6 and 7 (methyl‐substituted analogs) obtained by DFT at the B3LYP/6‐31G(d) level.

The syntheses of ZnTNc and ZnTNc decorated with sixteen alkyl chains were achieved by heating 6 or 7 with 1,8diazabicyclo[5.4.0]undec‐7‐ene (DBU) and zinc acetate in n‐pentanol.34, 35 Both complexes were characterized by NMR spectroscopy and MALDI‐TOF MS, and were found to be highly soluble in many organic solvents except for acetone and alcohols. Phthalocyanine analogs exhibit a strong absorption band (Q band) in the near‐infrared (IR) region, and the Q band position can be shifted to longer wavelengths with increasing size of the π‐system.11 However, ZnTNc and ZnTNc showed sharp Q bands at 775 and 778 nm in tetrahydrofuran (THF, Figure 2 a and Table 1), and the positions of the Q band in ZnTNc and ZnTNc are equal to that of zinc(II) tetra(tert‐butyl)naphthalocyanine (Zn(tBu)Nc) lacking fused thiophene rings (λ max=778 nm).36 The fluorescence spectra of ZnTNc and ZnTNc have a peak at 783 nm with a near mirror image of the Q band and a very small Stoke‐shift. The optical HOMO–LUMO band gaps (E g) for ZnTNc and ZnTNc were determined to be 1.6 eV from the crossing point of the normalized absorption and fluorescence spectra. The electron density distributions of the HOMO and LUMO calculated by DFT are mainly populated over the Nc skeleton within ZnTNc and ZnTNc (Figure 2 b and S4). While the Q band position of phthalocyanine can be shifted to the near‐IR by linear annulation, to form Nc and further to further anthracocyanine, the angular annulation does not result in a red‐shift of the Q band.11, 37 The fusing of thiophene rings at the angular positions of Nc in ZnTNc and ZnTNc does not effect a shift of the Q band as well as the change of E g.

Figure 2

a) Absorption and fluorescence spectra of ZnTNc (black line) and ZnTNc (red line) in THF. b,c) HOMO/LUMO orbitals and optimized structures of ZnTNc and ZnTNc (methyl‐substituted analogs) obtained by DFT at the B3LYP/6‐31G(d) level.

Table 1

Photochemical, electrochemical, and thermal analysis data of ZnTNc and ZnTNc.

	λabs [a] [nm]	ɛmax×10−5 [M−1 cm−1]	λfl [a] [nm]	E g opt[b] [eV]	HOMO[c] [eV]	LUMO[c] [eV]	T (ΔH)[d] [°C (kJ mol−1)]	T d [e] [°C]
ZnTNcendo	775	3.72	783	1.6	−4.8	−3.2	−5.5 (8), 257 (6)	259
ZnTNcexo	778	3.55	782	1.6	−4.7	−3.1	5.1 (16), 204 (12)	245

[a] Measured in THF. [b] Estimated from cross point of normalized absorption and fluorescence spectra. [c] HOMO and LUMO energy levels were determined by HOMO=−(4.8+E ox 1/2 (vs. Fc/Fc+) and LUMO=HOMO+E g opt. [d] Phase transition temperatures and their enthalpies determined by differential scanning calorimetry (DSC). [e] Temperature of starting weight loss determined by thermogravimetric analysis (TGA).

According to the equilibrium geometries calculated by DFT (Figure 2 c), the peripheral two thiophene rings in ZnTNc are twisted, due to the steric repulsion of neighboring alkyl groups. The molecular dimensions of ZnTNc and ZnTNc were estimated from the analysis of the surface pressure versus area (π–A) isotherm on pure water as the subphase (Figure S5 in the Supporting Information).38 The limiting surface areas per molecule of ZnTNc and ZnTNc were estimated to be 1.47 and 1.10 nm2, respectively, determined by extrapolating the slope of the π–A isotherm in the liquid‐condensed region to zero pressure. The observed area of ZnTNc was larger than that of ZnTNc, suggesting a larger stacking distance between the thiophene‐fused Nc rings within the edge‐on stacks on water by distortion of the structure from planarity in ZnTNc.

The HOMO energy levels of ZnTNc and ZnTNc were determined from the first oxidation potential (E ox) by differential pulse voltammetry measurements in dry dichloromethane containing 0.1 m nBu4NClO4 as a supporting electrolyte. Both complexes exhibited one oxidation peak for the oxidation of the naphthalocyanine ring (ZnNc(−1)/ZnNc(−2)) at −0.02 and −0.15 V vs. the ferrocene/ferrocenium couple (Fc/Fc +), which were negative relative to the E ox of Zn(tBu)Nc (Table 1).36 The HOMO energy levels of ZnTNc and ZnTNc were estimated to be −4.8 and −4.7 eV, respectively, from E ox calibrated by the Fc/Fc + redox potential vs. vacuum. The HOMO and LUMO energy levels of ZnTNc and ZnTNc were higher than those of Zn(tBu)Nc, indicating that the fusing of thiophene rings with the Nc ring leads to the destabilization of HOMO and LUMO energy levels.36

The thermal phase transition behavior of ZnTNc and ZnTNc was investigated by a combination of differential scanning calorimetry (DSC) and temperature‐controlled polarizing optical microscopy (TPOM). The DSC profile of ZnTNc showed two reversible transitions at 5 and 204 °C upon heating (Table 1). In thermogravimetric analysis (TGA) curves, ZnTNc exhibited an onset of weight loss above 240 °C, suggesting that decomposition does not occur at the transition point, as observed in the DSC. Under TPOM, a birefringent dendritic texture appeared at 190 °C on cooling from the isotropic melt, and remained without any change until room temperature (Figure 3 a). This texture is typical of columnar liquid crystalline materials.39, 40 To confirm the self‐organized structure of ZnTNc in the liquid crystalline state, temperature‐controlled X‐ray diffraction (XRD) measurements were performed. The XRD profile of ZnTNc at 100 °C revealed a set of diffraction peaks corresponding to a d spacing of 30.0, 24.5, 12.5, 10.1, and 8.46 Å, which were indexed in sequence as (100), (200), (320), (330), and (340) of a rectangular columnar (Colr) lattice with lattice parameters of a=49.0 and b=38.7 Å, and with the number of molecules in the unit cell Z=2. The rectangular lattice has a P21/a symmetry, as shown in Figure 4 a. Moreover, the XRD profile in the wide‐angle region showed only a broad halo around d=4.6 Å, and did not exhibit reflections corresponding to the stacking periodicity in the columnar assemblies. While the other isomer ZnTNc also exhibited a columnar liquid crystalline phase, the transition temperature of ZnTNc from the liquid crystalline state to the isotropic melt was 53 °C higher than that of ZnTNc. The texture of ZnTNc in the liquid crystalline state under TPOM was also different from ZnTNc (Figure 3 b). The XRD reflections of ZnTNc were fitted to a two‐dimensional Colr lattice with P2m symmetry (Figure 4 b and S6 in the Supporting Information).

Figure 3

X‐ray diffraction (XRD) patterns of a) ZnTNc at 100 °C and b) ZnTNc at 160 °C. The insets show crossed polarized optical micrographs of ZnTNc at 190 °C and ZnTNc at 240 °C, and d‐spacing values for ZnTNc and ZnTNc. c) Absorption spectra of ZnTNc (black line) and ZnTNc (red line) in their liquid crystalline states on quartz plates.

Figure 4

Schematic illustrations of two‐dimensional columnar packing symmetry and one‐dimensional molecular stacking feature of a) ZnTNc and b) ZnTNc.

Figure 3 c shows UV/Vis spectra of thin films of ZnTNc and ZnTNc in the liquid crystalline state on quartz plates. UV/Vis spectra provide information on the type of aggregated structures, such as face‐to‐face, edge‐to‐edge, and herringbone arrangements.41, 42 The maximum of the Q band for the film of ZnTNc in the liquid crystalline phase was found to be 737 nm, and the blue shift of the Q band compared with the solution spectrum indicates the formation of stacks having a face‐to‐face arrangement. On the other hand, the ZnTNc film showed a red shift of the Q band position relative to the solution spectrum, suggesting that the aromatic planes in ZnTNc were stacked in an eclipsed conformation within the one‐dimensional stacks (Figure 4 a). The tilted angle of the aromatic plane of ZnTNc in the stacks was estimated to be 16 degrees from the horizontal axis, based on the lattice parameters in the XRD analysis and the molecular dimensions from the DFT calculations. Liquid crystalline Pc and benzoporphyrins substituted with alkyl chains at the lateral positions also showed an eclipsed conformation with a tilt angle to the columnar axis.43, 44, 45 The lateral alkyl chains located at the crowded bay areas of ZnTNc reduce the strength of intermolecular interactions between the aromatic cores due to the steric repulsion of alkyl chains arranged out of the core plane. Recently, Aida and coworkers reported liquid crystalline behavior of propeller‐shaped fused oligothiophenes.29 They found the formation of long‐range columnar assemblies of oligothiophenes through well‐organized intermolecular sulfur–sulfur contacts. The transition enthalpy of ZnTNc from the Colr to the isotropic phase was larger than that of ZnTNc. The peripheral sulfur atoms in ZnTNc can interact with the other molecules in the neighboring column, and the sulfur–sulfur interaction may stabilize the intercolumnar assemblies in the Colr phase. However, we do not have data to support the formation of intermolecular sulfur–sulfur interactions at this stage.

The well‐organized columnar nanostructures made from liquid crystalline π‐conjugated polyaromatic materials can create long‐range pathways for mobile charge carriers.46 The carrier mobilities of liquid crystalline materials have been measured by time‐of‐flight (TOF) and radiolysis‐time resolved microwave conductivity.47, 48, 49, 50 The TOF method gives mobilities of more than micrometer‐scale distance in bulk materials. To evaluate the mobilities of ZnTNc and ZnTNc, TOF measurements were performed for ZnTNc and ZnTNc in the liquid crystalline states. Since the onset of the thermal decomposition of ZnTNc is very close to the melting point, the carrier mobility μ of ZnTNc could not be obtained because of the decomposition during the preparation of measurement cell. In contrast, the other isomer ZnTNc showed transient photocurrents in the Colr phase of ZnTNc at 50 and 150 °C under different applied biases at ±65 and ±80 V. Compound ZnTNc exhibited an ambipolar carrier transport behavior (Figure S7 in the Supporting Information). The hole and electron mobilities are calculated to be 7×10−2 and 8×10−2 cm2 V−1 s−1, and the mobilities are independent of electrical field as well as temperature. Because ZnTNc formed multidomains with imperfect alignment of columns between two electrodes, the hole and electron mobilities of ZnTNc are slightly lower than the reported values of liquid crystalline Pcs.51

In conclusion, we have designed and synthesized two structural regioisomers of near‐IR light‐absorbing ZnTNc and ZnTNc decorated with sixteen long alkyl chains. We have elucidated the influence of the molecular structural differences in the two isomers on their self‐organizing behavior and photoconductivity. Ring‐expanded ZnTNc and ZnTNc assemble into one‐dimensional columnar nanostructures over a wide temperature range from room temperature. TOF experiments have revealed that the organized ZnTNc shows a wellbalanced ambipolar carrier transport behavior, with carrier mobilities of the order of 10−2 cm2 V−1 s−1. Spontaneous alignment of columnar assemblies on substrates is a key issue for improving the carrier mobilities. Work is underway in our laboratory to control the columnar alignment on the substrate by structural elaboration of thiophene‐fused naphthalocyanines.

Experimental Section

General procedures

NMR spectra were recorded on a Bruker AVANCE 400 FT NMR spectrometer (Billerica, MA, USA) at 399.65 MHz and 100.62 MHz for 1H and 13C in CDCl3 solution. Chemical shifts are reported relative to internal tetramethylsilane (TMS). IR spectra were obtained on a SHIMAZU IR Prestige‐21 with DuraSample IR II (Kyoto, Japan). Absorption spectra were measured on a SHIMAZU UV‐2600. MALDI‐TOF mass spectra were obtained on a Bruker Autoflex spectrometer with dithranol as matrix.

All chemicals were purchased from commercial suppliers and used without further purification. 2‐Bromo‐4,5‐didodecylthiophene was synthesized according to the literature method.26 Column chromatography was performed with activated alumina (Wako, 200 mesh) or silica gel (Wakogel C‐200). Recycling preparative gel permeation chromatography was carried out by a JAI recycling preparative HPLC using CHCl3 as an eluent. Analytical thin layer chromatography was performed with commercial Merck plates coated with silica gel 60 F254 or aluminum oxide 60 F254.

Syntheses

Replacement of substitution position28, 29

3‐Bromo‐4,5‐didodecylthiophene (1): To a solution of diisopropylamine (1.43 mL, 10.2 mmol) in THF (60 mL) was slowly added n‐BuLi (1.6 m in hexanes, 4.5 mL, 7.20 mmol), and the reaction kept for 30 min at 0 °C under an Ar atmosphere. A solution of 2‐bromo‐4,5‐didodecylthiophene (3.0 g, 6.00 mmol) in THF (15 mL) was added, and the mixture stirred for 12 h at rt, then the reaction mixture poured into H2O and extracted with n‐hexane. The organic layer was washed with saturated aqueous NH4Cl (3×100 mL) and H2O (3×100 mL), and dried over Na2SO4. The residue was purified by column chromatography on silica gel by eluting with n‐hexane, to give 1 as a colorless liquid (2.41 g, 80 %); 1H NMR (CDCl3, 400.13 MHz): δ=6.95 (1 H, s, ArH), 2.72 (2 H, t, J=7.2 Hz, CH 2), 2.53 (2 H, t, J=7.6 Hz, CH 2), 1.57–1.65 (2 H, m, CH 2), 1.45–1.52 (2 H, m, CH 2), 1.26–1.32 (36 H, m, CH 2), 0.88 ppm (6 H, t, J=6.4 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ=140.2, 136.7, 119.1, 112.9, 32.5, 32.1, 30.5, 30.3, 30.2, 30.1, 30.0, 29.9, 29.4, 28.4, 23.3, 14.6 ppm.

Attachment of borate ester

2‐(4,4,5,5‐Tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐4,5‐didodecylthiophene (2):26 To a solution of 2‐bromo‐4,5‐didodecylthiophene (4.0 g, 8.01 mmol) in THF (100 mL) was added dropwise n‐BuLi (1.6 m in hexanes, 6.0 mL, 9.61 mmol) at −78 °C under an Ar atmosphere, and the mixture stirred for 1 h at the same temperature under an Ar atmosphere. To this reaction mixture was slowly added 2‐isopropoxy‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (1.79 g, 9.62 mmol), and the reaction mixture stirred o/n at rt. The reaction was quenched by adding a small amount of MeOH and ether added to the mixture. The organic layer was washed with brine (3×100 mL), H2O (3×100 mL), dried over Na2SO4, and the solvent evaporated. The residue was purified by column chromatography on silica gel by eluting with EtOAc/n‐hexane (1:10 v/v), to give 2 as a colorless liquid (3.17 g, 72 %); 1H NMR (CDCl3, 400.13 MHz): δ)=7.37 (1 H, s, ArH), 2.73 (2 H, t, J=7.2 Hz, CH 2), 2.49 (2 H, t, J=7.6 Hz, CH 2), 1.54–1.66 (4 H, m, CH 2), 1.26–1.41 (36 H, m, CH 2), 1.23 (12 H, s, CH 3), 0.88 ppm (6 H, t, J=6.4 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ=147.5, 140.0, 139.6, 84.1, 32.4, 32.1, 31.2, 30.2, 30.1, 30.0, 29.9, 29.8, 29.7, 28.6, 28.5, 25.2, 25.1, 23.2, 14.5 ppm.

3‐(4,4,5,5‐Tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐4,5‐didodecylthiophene (3):30, 31 To a solution of 1 (1.0 g, 2.00 mmol) in 1,4‐dioxane (10 mL) were added bis(pinacolato)diboron (0.762 g, 3.00 mmol), [1,1′‐bis(diphenylphosphino)ferrocene]dichloropalladium(II), complex with dichloromethane [Pd(dppf)Cl2⋅CH2Cl2] (0.163 g, 0.200 mmol), and KOAc (0.589 g, 6.00 mmol). The reaction mixture was stirred at 80 °C for 6 h under an Ar atmosphere, then the reaction quenched by adding H2O, and extracted with ether (3×50 mL). The organic layer was washed with brine (3×100 mL) and H2O (3×100 mL), dried over Na2SO4, and the solvent evaporated. The residue was purified by column chromatography on silica gel by eluting with EtOAc/n‐hexane (1:3 v/v), to give 3 as a colorless liquid (0.480 g, 44 %); 1H NMR (CDCl3, 400.13 MHz): δ=7.65 (1 H, s, ArH), 2.69–2.74 (4 H, m, CH 2), 1.58–1.65 (2 H, m, CH 2), 1.42–1.50 (2 H, m, CH 2), 1.29 (12 H, s, CH 3), 1.27–1.37 (36 H, m, CH 2), 0.88 ppm (6 H, t, J=6.4 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ=143.3, 140.0, 134.3, 83.4, 32.6, 32.4, 32.1, 30.3, 30.2, 30.1, 29.9, 29.8, 28.5, 28.5, 28.1, 25.2, 23.2, 14.6 ppm.

Suzuki–Miyaura coupling reaction32

1,2‐Dicyano‐4,5‐bis(4,5‐didodecyl‐2‐thienyl)benzene (4): To a solution of 4,5‐dichlorophthalonitrile (90.1 mg, 0.457 mmol) and 2 (1.00 g, 1.83 mmol) in a mixed solvent of toluene (2.0 mL), 1,2‐dimethoxyethane (DME, 2.0 mL) and H2O (1.0 mL) were added Pd(OAc)2 (1.03 mg, 4.59 μmol), 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (S‐Phos) (3.75 mg, 9.13 μmol) and K3PO4(0.397 g, 1.83 mmol), and the reaction mixture stirred at 85 °C for 12 h under an Ar atmosphere. After cooling to rt, the reaction mixture was poured into H2O (50 mL), and extracted with CH2Cl2 (3×30 mL). The organic layer was dried over MgSO4, and the solvent evaporated. The residue was purified by column chromatography on silica gel by eluting with CH2Cl2/n‐hexane (1:1 v/v) and recycling preparative HPLC, to give 4 as a pale yellow oily liquid (0.269 g, 61 %); 1H NMR (CDCl3, 400.13 MHz): δ=7.81 (2 H, s, ArH), 6.72 (2 H, s, ArH), 2.69 (4 H, t, J=7.6 Hz, CH 2), 2.43 (4 H, t, J=7.2 Hz, CH 2), 1.55–1.63 (4 H, m, CH 2), 1.44–1.49 (4 H, m, CH 2), 1.26–1.33 (72 H, m, CH 2), 0.88 ppm (12 H, t, J=6.8 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ 143.6, 139.4, 139.3, 135.5, 134.2, 131.2, 115.8, 113.6, 32.6, 32.2, 31.2, 30.2, 30.1, 30.0, 29.9, 29.8, 29.7, 28.5, 28.3, 23.1, 14.5 ppm.

1,2‐Dicyano‐4,5‐bis(4,5‐didodecyl‐3‐thienyl)benzene (5): Compound 5 was synthesized from 4,5‐dichlorophthalonitrile (66.1 mg, 0.335 mmol) and 3 (0.737 g, 1.35 mmol) by the same procedure as for 4, affording a yellow oily liquid (217 mg, 67 %); 1H NMR (CDCl3, 400.13 MHz): δ=7.75 (2 H, s, ArH), 6.68 (2 H, s, ArH), 2.67 (4 H, t, J=7.6 Hz, CH 2), 2.18 (4 H, t, J=6.4 Hz, CH 2), 1.58 (4 H, t, J=7.2 Hz, CH 2), 1.26–1.37 (76 H, m, CH 2), 0.879 ppm (12 H, t, J=7.2 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz, ppm): δ=143.4, 141.5, 138.4, 136.1, 135.6, 122.6, 115.8, 114.1, 32.4, 32.2, 31.0, 30.1, 30.0, 29.9, 29.8, 29.7, 29.6, 29.4, 28.7, 27.3, 23.1, 21.7, 14.5 ppm.

FeCl3‐mediated oxidative cyclization28, 29

8,9‐Dicyano‐2,3,4,5‐tetradodecyl‐naphtho[1,2‐: To a CH2Cl2 solution (50 mL) of 4 (0.269 g, 0.307 mmol) was added a CH3NO2 solution (10 mL) of FeCl3 (0.226 g, 1.39 mmol) at 0 °C under an Ar atmosphere, and the resulting solution stirred at rt for 30 min. The reaction was quenched by adding MeOH (25 mL), and an organic extract washed with brine (3×50 mL) and saturated aqueous NH4Cl (3×50 mL), dried over Na2SO4, and the solvent evaporated. The residue was purified by column chromatography on silica gel by eluting with CH2Cl2/n‐hexane (1:1 v/v) and recrystallization from acetone, to give 6 as a pale yellow solid (0.193 g, 72 %); mp: 53 °C; 1H NMR (CDCl3, 400.13 MHz): δ=8.42 (2 H, s, ArH), 2.97–3.05 (8 H, m, CH 2), 1.75–1.82 (4 H, m, CH 2), 1.17–1.46 (76 H, m, CH 2), 0.85–0.89 ppm (12 H, m, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ=144.5, 137.5, 136.2, 133.8, 130.8, 127.7, 116.6, 109.6, 32.4, 32.0, 30.4, 30.2, 30.1, 30.0, 29.9, 29.8, 29.7, 23.1, 14.5 ppm;. IR (ATR): =2228 cm−1 (CN); UV/Vis (CH2Cl2): λ (log ɛ/M−1 cm−1)=336 nm (4.76); MALDI‐TOF MS (dithranol) m/z [M+H]+ calcd for C64H102N2S2: 962.75, found: 962.08.

5,6‐Dicyano‐2,3,8,9‐tetradodecyl‐naphtho[2,1‐: Compound 7 was synthesized from 5 (0.216 g, 0.224 mmol) and FeCl3 (0.181 g, 1.12 mmol) by the same procedure as for 6 to yield a pale yellow solid (0.185 g, 86 %); mp: 57 °C; 1H NMR (CDCl3, 400.13 MHz): δ=8.78 (2 H, s, ArH), 3.03 (4 H, t, J=6.8 Hz, CH 2), 2.93 (4 H, t, J=7.6 Hz, CH 2), 1.73–1.81 (4 H, m, CH 2), 1.26–1.67 (76 H, m, CH 2), 0.878 ppm (12 H, t, J=7.2 Hz, CH 3); 13C NMR (CDCl3, 100.61 MHz): δ=141.6, 136.2, 134.6, 131.0, 130.5, 129.6, 116.9, 108.6, 32.4, 30.1, 30.0, 29.9, 29.8, 29.7, 29.4, 29.2, 23.1, 14.5 ppm; IR (ATR): =2228 cm−1 (CN); UV/Vis (in CH2Cl2): λ (log ɛ/M−1 cm−1)=285 (4.80), 317 (4.67), 395 nm (4.03); MALDI‐TOF MS (dithranol) m/z [M+H]+ calcd for C64H102N2S2: 962.75, found: 962.28.

Teteracyclization of 6 and 734, 35

ZnTNc: A mixture of 6 (100.0 mg, 0.104 mmol), 1,8‐diazabicyclo[5.4.0]‐7‐undecene (DBU) (15.5 μL, 0.104 mmol), and Zn(OAc)2 (4.76 mg, 25.9 μmol) in 1‐pentanol (1.0 mL) was stirred at 140 °C for 12 h under an Ar atmosphere. After cooling to rt, the reaction mixture was poured into H2O and extracted with CH2Cl2 (3×30 mL). The organic layer was washed with H2O (3×50 mL), dried over Na2SO4, and the solvent evaporated. The residue was purified by column chromatography on activated alumina by eluting with n‐hexane and recycling preparative HPLC, to give ZnTNc as a dark green solid (51.8 mg, 51 %); 1H NMR (CDCl3, 400.13 MHz): δ=9.33 (8 H, brs, ArH), 2.79–3.53 (32 H, br, CH 2), 1.28–2.09 (320 H, br, CH 2), 0.82–0.89 ppm (48 H, br, CH 3); UV/Vis‐NIR (THF): λ (log ɛ/M−1 cm−1)=363 (5.13), 452 (4.83), 692 (4.84), 740 (4.83), 775 nm (5.57); MALDI‐TOF MS (dithranol) m/z [M+H]+ calcd for C256H408N8S8Zn: 3914.92, found 3914.91.

ZnTNc: ZnTNc was synthesized from 7 (80 mg, 83.0 μmol), DBU (12.4 μL, 20.8 μmol), and Zn(OAc)2 (3.81 mg, 83.0 μmol) by the same procedure as for ZnTNc to yield a dark green solid (41.0 mg, 50 %); 1H NMR (CDCl3, 400.13 MHz): δ=10.86 (8 H, brs, ArH), 2.51–4.41 (32 H, br, CH 2), 0.48–2.34 ppm (368 H, br, CH 2, CH 3); UV/Vis‐NIR (THF): λ (log ɛ/M−1 cm−1)=353 (5.24), 475 (4.26), 692 (4.85), 739 (4.81), 778 nm (5.55); MALDI‐TOF MS (dithranol) m/z [M+H]+ calcd for C256H408N8S8Zn: 3914.92, found: 3914.44.

Time‐of‐flight measurements52, 53

Measurement cells for TOF were composed of two Indium tin oxide (ITO) patterned glass substrates and a silicon spacer containing silica beads with 15 μm diameter. The effective area of the cells was 0.25 cm2. Powdered samples of ZnTNc or ZnTNc (∼5 mg) were put on the bottom ITO substrate, and the cells placed in a vacuum oven. After evacuation, the oven was filled with Ar and heated at 210 or 260 °C for ZnTNc and ZnTNc, respectively. The area between the two ITO electrodes was filled with melted ZnTNc or ZnTNc by injection from the cell slit through capillary action, and the cell was then cooled to rt at 1 °C min−1 inside the oven, to achieve the formation of large‐area domains. The transient photocurrents were detected using a digital oscilloscope after light irradiation with a 377 nm N2‐pulse laser having a pulse width of 800 ps under various electric fields. An electric field was created in the cell using a DC power supply. The temperature of the cells was controlled within 0.2 K using a temperature controller and a hot stage. Carrier (hole or electron) mobility μ was calculated from the following equation, μ=d /(V t) where d is the sample thickness, V is the applied bias, and t is the transit time of the photo‐generated carriers traversing the sample layer. The t values of the photo‐generated carriers in the material were determined from an inflection point on the double logarithmic plot of the transient photocurrent decay curves.

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Supplementary

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