Arrangement Modulation of π-Stacked Columnar Assemblies of

Article pubs.acs.org/crystal

Arrangement Modulation of π‑Stacked Columnar Assemblies of Octadehydrodibenzo[12]annulene: Substituent Effects of Peripheral Thienyl and Phenyl Rings Ichiro Hisaki,*,† Keisuke Osaka,† Nobuaki Ikenaka,† Akinori Saeki,‡ Norimitsu Tohnai,† Shu Seki,‡,⊥ and Mikiji Miyata§ †

Department of Material and Life Science, and ‡Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan § The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki Osaka 567-0047, Japan S Supporting Information *

ABSTRACT: Introduction of rigid aryl substituents into the periphery of a π-conjugated molecule changes its assembly manner from that of the parent compound, resulting in drastic changes of optical and electrical properties of the assembly. In this study, we revealed that ortho-thienyl substituted octadehydrodibenzo[12]annulene derivative 2 yielded two types of crystal structures with zigzag and one-dimensionally (1D) π-stacked motifs. Their thermal, optical, and electrical properties were investigated. Furthermore, we demonstrate that although the phenyl- and thienyl-substituted derivative (1 and 2, respectively) yielded closely resembled 1D π-stacked columns in their crystals (1-column and 2-II, respectively), arrangements of the columns are completely different due to subtle differences of the substituents. Such differences in the arrangements drastically affect the lifetime of charge carrier generated in crystals, although the intensity of the photoconductivity is almost the same in both crystals. These results can provide a new insight for tuning of the assembly’s properties by changing the peripheral aryl substituents of π-conjugated molecules.

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INTRODUCTION Regulation and fine-tuning of a stacking manner of πconjugated molecules is necessary for developing molecular electronic materials.1−6 To modulate and control a stacking manner of π-conjugated cores, introduction of rigid aryl groups into the periphery of the core is one of the effective approaches because of the following two aspects. (1) Intermolecular interactions among the peripheral aryl groups can force the πconjugated cores to be packed into specific structures which are not achieved by the parent compounds themselves.7 (2) The sterically hindered aryl substituents can provide an inclusion space capable of accommodating guest species, which can contribute to achieve versatile arrangements of the core.8,9 A representative example of the steric effects of peripheral aryl groups is rubrene which crystallizes into a widely overlapped πstacking structure10 to achieve high charge carrier mobility,11,12 even though its parent compound tetracene crystallizes into a herringbone structure with less overlap of π-conjugated planes.13,14 Moreover, Fukushima, Aida and co-workers nicely demonstrated that two phenylene groups attached to one side of the periphery of a hexabenzocoronene molecule were crucial to form the exotic graphene tube.15 In connection with the guest accommodation, Moorthy and co-workers, for example, © XXXX American Chemical Society

demonstrated that tetraarylpyrene forms various solvates and co-crystals, in which the guest molecules, accommodated in the void spaces composed of the aryl groups, play a role to yield versatile arrangements of the pyrene core.8,9 We also reported that aryl-substituted C3 symmetric π-conjugated systems such as dehydrobenzoannulene derivatives formed crystalline supramolecular architectures possessing a large inclusion space accommodative for guest species,16−18 and that ortho-phenyl substituted octadehydrodibenzo[12]annulene ([12]DBA) 1 (Chart 1) gave 12 inclusion or guest-free crystals that can be classified into four types of frameworks of the [12]DBA core, exhibiting structure-dependent properties.19 In addition to a phenyl or phenylene group, a thienyl group, another common aryl substituent, has also been introduced into the periphery of a π-conjugated system such as acene and other polycyclic aromatic hydrocarbons (PAHs).20−27 Compared with a phenyl ring, a thienyl ring has a dipole moment, different electrostatic potential surface, and slightly smaller dimension (Figure 1). Because of such differences, thienylReceived: September 2, 2015 Revised: November 11, 2015

A

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monochromated by the fixed exit Si (111) double crystal. The cell refinements were performed with HKL2000 software.28 Direct methods (SIR-2008,29 SIR-2011,30 or SHELXL201331) were used for the structure solution of the crystals. All calculations were performed with the observed reflections [I > 2σ(I)] with the program CrystalStructure crystallographic software packages,32 except for refinement, which was performed using SHELX97 or SHELXL2013.31 All non-hydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were placed in idealized positions and refined as rigid atoms with the isotropic displacement parameters. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement.33,34 Nanosecond laser pulses from a Nd:YAG laser (third harmonic generation, THG (355 nm) from Spectra Physics, INDI, fwhm 5−8 ns) were used as excitation sources. The incident photon density of the laser was set at 9.1 × 1015 photons/cm2/pulse. For TRMC measurements, the microwave frequency and power were set at ∼9.1 GHz and 3 mW, respectively, so that the motion of the charge carriers was not disturbed by the low electric field of the microwaves. The TRMC signal picked up by a diode (rise time 2σ(I)) Rw (all data) GOF T/K CCDC nos.37

576.76 monoclinic P21/c 11.4496(3) 15.9082(3) 7.2775(2) 90 98.9246(12) 90 1309.49(6) 2 8391 2343 0.074 1.463 0.0487 0.1336 1.052 93 1419483

2-II(DMF)

2-II(THF)

2-II(NitroBn)

2-II(CHCl3)

(C36H16S4) (C3H7NO) 649.86 monoclinic P21/c 23.4485(4) 14.1029(2) 9.02150(10) 90 92.0021(6) 90 2981.52(7) 4 19222 5376 0.042 1.448 0.0443 0.1330 1.115 93 1419485

(C36H16S4) (C4H8O) 648.87 monoclinic I2/a 9.1266(4) 13.9281(3) 23.45470(10) 90 91.7250(11) 90 2980.12(15) 4 9585 2556 0.043 1.446 0.0876 0.3036 1.601 93 1419482

(C36H16S4) (C6H5NO2)0.5 638.32 triclinic P1̅ 9.2729(2) 13.4411(2) 14.0205(3) 115.3210(8) 98.8230(12) 105.2480(16) 1451.45(6) 2 8952 5047 0.028 1.460 0.0909 0.2390 1.296 93 1419486

(C36H16S4) (CHCl3) 696.14 monoclinic P21/c 9.16050(10) 13.8914(2) 23.4141(4) 90 91.6680(7) 90 2978.23(7) 4 20015 5771 0.044 1.552 0.0588 0.1504 1.045 93 1419484

J1 13

= 0.8 Hz, J2 = 2.0 Hz, 4H), 7.38−7.36 (m, 8H), 7.25 (s, 4H) ppm. C NMR (150 MHz, DMSO-d6 50 °C): δ 140.5, 137.1, 131.8, 129.1, 128.8, 127.6, 126.0 ppm. HR-MS(MALDI-TOF): calcd for C36H16S4 [M]+ 576.0135; found 576.0190. 7: mp (dec.) 196 °C. 1H NMR (600 MHz, CDCl3 40 °C): δ 7.77 (dd, J1 = 1.2 Hz, J2 = 3.0 Hz, 6H), 7.57 (s, 6H), 7.50 (dd, J1 = 1.2 Hz, J2 = 4.8 Hz, 6H), 7.45 (dd, J1 = 3.0 Hz, J2 = 4.8 Hz, 6H) ppm. 13C NMR (150 MHz, DMSO-d6, 50 °C): δ 138.6, 138.4, 130.4, 127.9, 126.2, 125.1, 122.0, 81.7, 80.9 ppm. HR-

A mixture of the precursor (500 mg, 1.72 mmol) CuCl (200 mg, 2.02 mmol) in CH2Cl2 (280 mL) was stirred for 20 min at room temperature. N,N,N′,N′-Tetramethylethylenediamine (TMEDA) (5.95 mL, 1.13 mL) was added dropwise to the solution and stirred for 3 h at room temperature. The reaction mixture was filtrated and washed with MeOH and CH2Cl2 to give dimer 2 (351 mg, 72%) as a yellow solid. To the filtrate was added excess MeOH and resulting insoluble solid was filtrated to give trimer 7 (24.8 mg, 5%) as a pale yellow solid. 2: mp (dec.) 161 °C. 1H NMR (600 MHz, CDCl3, 40 °C): δ 7.64 (dd, C

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MS(MALDI-TOF): calcd for C54H24S6 [M ]+ 864.0202; found 864.0477.

Table 2. Dihedral Angles between Substituted Thienyl Groups and the [12]DBA Core

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RESULTS AND DISCUSSION Preparation and Crystallization of [12]DBA 2. [12]DBA 2 was synthesized according to Scheme 1a. Suzuki-Miyaura cross-coupling reaction of 1,2,3,4-tetrabromobenzene (3)35,36 with 3-thienyl boronic acid (4) gave 1,4-disubstituted product 5 in 55% yield. Reaction of 5 with trimethylsilylacetylene in the presence of Pd(0) and CuI at 100 °C gave diethynyl derivative 6 in 30% yield. Desililation of 6, followed by Hay oxidation coupling, gave dimer 2 together with trimer 7 in 72% and 5% yields, respectively. [12]DBA 2 was crystallized by using various solvents readily available, and totally five crystal structures were successfully solved (Scheme 1b). Their crystal data are listed in Table 1. Compared to the phenyl-substituted derivative 1, which yields four kinds of different molecular packings (Figure S1),19 the present thienyl-substituted derivative 2 resulted in two types of crystal structures with zigzag and 1D π-stacked motifs. Guest-free crystal 2-I(GF) with the zigzag π-stacked motif tends to be obtained by slow evaporation of a THF solution at room temperature. On the other hand, solventincluded crystals 2-II(DMF), 2-II(THF), 2-II(NitroBn), and 2-II(CHCl3) with 1D π-stacked motifs were obtained by relatively rapid evaporation of the solutions of DMF, THF, nitrobenzene, and chloroform, respectively. In all crystal structures, the four thienyl groups are rotationally disordered more or less. Therefore, structural refinement was conducted taking into account this point, although only major conformations are shown because of a clarity reason. The details of the structures are described as follows. Molecular Conformation. Regarding the conformation of the peripheral four thienyl groups, totally four types of conformation were observed in the obtained crystals as shown in Figure 2 and Table 2. Crystal 2-I(GF) has the

twisted anglea/°

crystal 2-I(GF) 2-II(DMF) 2-II(THF) 2-II(NitroBn) 2-II(CHCl3) 2(calcd.) a

A: 41.7, A: 33.6, A: 33.1, A: 37.5, A: 35.3, (37.5)

B: B: B: B: B:

41.6, 35.2, 34.4, 39.2, 33.7,

C: C: C: C: C:

41.6, 30.3, 33.1, 37.6, 36.9,

D: D: D: D: D:

point group 41.7, 36.5, 34.4, 31.1, 33.5,

(41.7) (33.9) (33.8) (36.4) (34.9)

Ci C1 C2 C1 C1

Averaged values are shown in parentheses.

The rotational conformations of the thienyl groups are very sensitive for guest species. Molecular Arrangement in 2-I(GF). [12]DBA 2 crystallized into space group of P21/c by slow evaporation of a THF solution, giving guest-free crystal 2-I(GF) as shown in Figure 3.

Figure 3. Crystal structure of 2-I(GF) viewed from the (a) c and (b) a axes. [12]DBA cores and the thienyl rings are colored with gray and green, respectively, except for S atoms, which are highlighted with orange. Although all thienyl rings of 2 are rotationally disordered, major conformers are presented and minors are omitted for clarity.

The [12]DBA cores are stacked with a zigzag fashion through π/π interactions between the annulated benzene rings (the closest stacking distance: ca. 3.37 Å). This zigzag-stacked layer structure was also observed in the case of the previously reported phenyl-substituted systems, such as 1-III′(THF) as shown in Figure S1d,19 although in the case of 1-III′(THF) solvent molecules (THF) were accommodated between the zigzag motifs. In the following part, we will refer to 1III′(THF) as 1-zigzag and compare the crystal structures of 2I(GF) and 1-zigzag. Structural Comparison of 2-I(GF) and 1-zigzag. To evaluate a substituent effect of the aryl groups (i.e., phenyl and thienyl groups), crystal structures of 1-zigzag and 2-I(GF) were compared from a viewpoint of the aryl−aryl interactions of the substituents as shown in Figure 4. In the case of 1-zigzag, the phenyl groups (i) and (ii) within the zigzag motif are arranged into face-to-edge manner via favorable CH/π interactions (distance of C−H···π-plane: 2.79 Å) (Figure 4b), while no

Figure 2. Conformation of [12]DBA 2 in crystals 2-I(GF), 2II(DMF), 2-II(THF), and 2-II(NitroBn). The anisotropic displacement ellipsoids were drawn with 50% probability. Thienyl groups are colored green, except for S atoms which are in orange. Since the thienyl groups are disordered, major conformations are shown for clarity.

largest dihedral angle of the thienyl groups and the [12]DBA core (i.e., 41.7°) among the obtained crystals. Those of crystals 2-II(DMF), 2-II(THF), 2-II(NitroBn), and 2-II(CHCl3) range from 31.1° to 39.2°. Since crystal 2-II(CHCl3) is an isostructure with 2-II(DMF), the structure of only 2II(DMF) is shown as a representative example in the latter part. It is remarkable that crystals 2-II(DMF), 2-II(THF), and 2-II(NitroBn) have different versatile conformers, although they have quite similar molecular packing as described below. D

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guest molecules between the motifs, and that the motif composed of 2 can be less stable, and therefore, shows no tolerance toward guest species. Crystal Structures of 2-II. Recrystallization of [12]DBA 2 from solutions of DMF, THF, nitrobenzene, and chloroform yielded the corresponding solvent-included crystals 2-II(DMF), 2-II(THF), 2-II(NitroBn), and 2-II(CHCl3), respectively. They have the closely resembled columnar motifs, in which [12]DBA cores are π-stacked with an AB manner. On the other hand, symmetry and rotational conformation of the peripheral thienyl rings are different in 2-II(DMF), 2-II(THF), and 2II(NitroBn), except for 2-II(CHCl3) which is basically same with 2-II(DMF) (Table 2, Figure 5, and Figure S2). Crystal 2-II(DMF) belongs to space group P21/c (Figure 5a). The [12]DBA core forms 1D π-stacked columnar motif along the c axis with an interplanar distance of 3.60 Å. Peripheral thienyl rings made both intercolumnar and intracolumnar face-to-edge contacts with the dihedral angle from 66.7° to 68.2°(Figure 5b,c). Discrete inclusion space surrounded by the thienyl rings were formed along the c axis, and DMF molecules are accommodated in the space with a 1:1 host/guest ratio. This type of molecular arrangement was also observed in 2-II(CHCl3) as shown in Figure S2. Crystal 2II(THF) belongs to space group I2/a (Figure 5d). The [12]DBA core again forms 1D π-stacked columnar motif along the c axis with interplanar distance of 3.57 Å. Peripheral thienyl rings made both intercolumnar and intracolumnar face-to-edge contacts with the dihedral angle of 66.5° (Figure 5e,f). Since 1D thienyl chains formed through face-to-edge contacts align with an offset fashion (Figure 5f), infinite inclusion channel formed along the c axis, and THF molecules are accommodated in the channel with a 1:1 host/guest ratio. Crystal 2II(NitroBn) belongs to space group P1̅ (Figure 5g). The framework is desymmetrized presumably so as to accommodate relatively large guest species, nitrobenzene. However, π-stacked columnar motif has basically the same structure with that of 2II(DMF) and 2-II(THF): interplanar distance: 3.40 Å, dihedral

Figure 4. Structural comparison between 1-zigzag (a−c) and 2-I(GF) (d−f). (a, d) Molecular packing. (b, e) Edge-to-face arrangements of the aryl groups (i) and (ii) within the zigzag layer motif. (c, f) Parallel arrangements of the aryl groups bound to the adjacent layers. THF molecules included in 1-zigzag crystal are colored in yellow.

significant interaction could be observed between the phenyl groups (ii) and (iii) (Figure 4c). Similarly, 2-I(GF) has a faceto-edge arrangement of the thienyl groups (i) and (ii) (Figure 4e). In this case, however, the distance of the C−H···π-plane (3.17 Å) is too long to show an attractive interaction. On the other hand, the thienyl groups (ii) and (iii) are stacked (interplanar distance: 3.85 Å) with antiparallel fashion, which is a favorable arrangement for two neighboring dipole moments (Figure 4f). These results imply that the zigzag motif composed of 1 can be stable and be robust enough to include various

Figure 5. Crystal structures of (a−c) 2-II(DMF), (d−f) 2-II(THF), and (g−i) 2-II(NitroBn). (a, d, g) Packing diagrams. (b, e, h) Edge-to-face contacts of thienyl rings formed between the adjacent columnar motifs. (c, f, i) Inclusion spaces surrounded by the thienyl rings. The [12]DBA cores and included solvent molecules are colored with gray and yellow, respectively. The thienyl rings are colored with green, except for S atoms, which are highlighted with orange. Although all thienyl rings of 2 in these crystals are rotationally disordered, major conformers are presented and minors are omitted for clarity. Included nitrobenzene molecules in 2-II(NitroBn) are disordered. E

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thienyl groups, the [12]DBA cores chose the arrangement as observed in 2-II(THF) (Figure 6d). Additionally, it would subtly affect the arrangement that the slightly electrostatically negative sulfur atom faces the aromatic hydrogen atom (C− H···S interaction). These results imply that even slight differences in molecular size, electrostatic potential surface, and dipole moment would dominate arrangements of the [12]DBA cores critically. Thermal Stability of the Crystals. Crystals 2-I(GF), 2II(DMF), 2-II(THF), and 2-II(NitroBn) are subjected to differential scanning calorimetry (DSC) analysis. 2-I(GF) shows exothermic peaks at 164 °C. Inclusion crystals 2II(DMF) and 2-II(THF) show weak endothermic peaks at 108 and 96 °C, respectively, and exothermic peaks at 166 and 160 °C respectively (Figure S3), while 2-II(NitroBn) shows no endothermic peaks before an exothermic peak appeared at 216 °C. Thermal gravimetric (TG) analysis indicates that crystals 2II(DMF) and 2-II(THF) experienced weight loss corresponding to the accommodated solvent molecules [2-II(DMF): 11.6% (11.1% assuming for a 1:1 host/guest ratio), 2-II(THF): 10.7% (11.2% assuming for a 1:1 host/guest ratio)] (Figure S4). Furthermore, powder X-ray diffraction (PXRD) patterns of the crystals after endothermic process agreed with that of 2I(GF) (Figure S5), indicating that the inclusion channels formed in the crystals 2-II(DMF) and 2-II(THF) were unable to maintain their space after removal of the solvent molecules and the crystal structures transformed into more stable 2I(GF). TG analysis of 2-II(NitroBn) also showed a weight loss of 10.3%, which corresponds to the accommodated nitrobenzene molecules (9.6% assuming for a 2:1 host/guest ratio). 2-II(NitroBn) experienced guest desorption and decomposition of the crystals simultaneously at around 200 °C. The exothermic multistep peaks of the DSC curve at 160 to 250 °C are probably attributed to thermally induced irreversible reaction such as polymerization,39−43 although the resultant black materials show no PXRD signals and were insoluble in common organic solvents, preventing the solution NMR analysis. To our surprise, the reaction occurred at a significantly lower temperature compared with the phenyl-substituted derivative 1 (ca. 300 °C). Structure Dependent Optical and Electrical Properties of the Crystals. Theoretical calculation of [12]DBAs 1 and 2 show quite similar energy levels of the frontier molecular orbital (Figure S6). Their UV−vis spectra in chloroform solution also show a similar profile with almost the same absorption edges (ca. 465 nm for 1 and ca. 480 nm for 2) (Figure S7). Additionally, their fluorescence spectra in chloroform show exactly the same profiles (Figure S7). These results imply that electronic property of the DBA core is not affected significantly by substituent groups. On the other hand, optical property of [12]DBA 2 depends on molecular arrangements in the crystalline state (Figure 7, Table 3). Fluorescence spectrum of crystal 2-I(GF) has an obvious vibrational structure with λemmax = 579 nm [ϕF = 1.2%], where λemmax, and ϕF denote wavelength at fluorescence maximum and fluorescence quantum yield, respectively. Crystal 2II(DMF), on the other hand, shows structureless and redshifted spectra with λemmax = 614 nm ϕF = 1.1%], indicating that the molecular arrangements of the crystals 2-II provide more stable excited state compared with the crystals 2-I(GF). Next, we investigated an anisotropic photoconductivity of 2II(THF) and 1-column by flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement.33,34 As

angle of the thienyl rings: 68.1−76.8°. Discrete inclusion space is also similar to that of 2-II(DMF) (Figure 5i), and the nitrobenzene molecule is included with a 2:1 host/guest ratio. The 1D π-stacked columnar structure in the 2-II crystals was also observed in the previously reported phenyl-substituted systems such as 1-IV(DCM), as shown in Figure S1e.19 In the following part, we will refer to 1-IV(DCM) as 1-column and compare the crystal structures of 2-II(DMF) and 1-column. Structural Comparison of 2-II and 1-column. As reported previously,19 the 1D π-stacked columnar structure observed in the 2-II crystals was also formed in crystal 1column as shown in Figure 6a, although the arrangement of the

Figure 6. Comparison of the columnar motif’s arrangements of 2-II and 1-column. (a) Packing diagram of 1-column. (b) The peripheral phenyl groups of 1-column in nearly ideal face-to-edge geometries to maximize CH/π interactions. (c) Edge-to-edge contact of [12]DBA cores in 1-column. (d) Offset arrangements of the [12]DBA cores in 2-II(THF). Guest molecule, dichloromethane, is colored in yellow in (a).

columnar motif is different from each other. To reveal effects of the substituted aryl groups, the crystal structures of 2-II(THF) and 1-column were compared and interpreted in the terms of interaction of the aryl groups as follows. In the case of 1column, the peripheral phenyl groups are arranged with an edge-to-face fashion (Figure 6b). Particularly, the contact angle is nearly 90°, which maximizes CH/π interaction to give very stable and robust frameworks.38 The neighboring [12]DBA cores of 1 are contacted with an edge-to-edge fashion so as to fit the asperity of the molecular edges (Figure 6c). However, contact between electrostatically positive hydrogen atoms has no significant contribution to stabilize the molecular assembly. These results indicate that the crystal structure of 1-column is governed by favorable packing of the peripheral phenyl groups. The thienyl group, however, is smaller than phenyl group, and therefore, is unable to form face-to-edge contacted array if the [12]DBA cores are aligned in the edge-to-edge fashion same as 1-column. To achieve a face-to-edge contacted array of the F

DOI: 10.1021/acs.cgd.5b01273 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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is 2.6 times larger than those in the orthogonal axis (ϕΣμ = 1.8 × 10−5 cm2/(V s)). Anisotoripic behavior of charge carrier mobility is often observed in such 1D π-stacked systems.44−47 The present values are in good agreement with those previously reported.19 The crystal 2-II(THF) also exhibited moderate photoconductivity (ϕΣμ = 4.8 × 10−5 cm2/(V s)) along the crystallographic a axis, which is 5.5 times larger than those in the orthogonal axis (ϕΣμ = 8.7 × 10−6 cm2/(V s)). These values are quite similar to those of 1-column, which is natural because the crystals have 1D π-stacked columnar motifs that closely resemble each other. On the other hand, it is noteworthy that arrangements of the columnar motifs crucially affected the decay profiles of the generated charge carrier. Namely, the transient profile of 1-column rapidly decayed and nearly disappeared within 2 μs, while that of 2-II(THF) showed no decay and maintained the original intensity even after 8 μs. In 1-column, the generated charge carrier can migrate among the adjacent columns contacted, resulting in frequent quenching such as trapping at defect and charge recombination. On the other hand, the isolation of the πstacked columns in 2-II(THF) prevents intercolumnar hopping of the charge carrier to allow a longer lifetime.48−50

Figure 7. Fluorescence spectra of bulk crystals of 2-I(GF) and 2II(DMF), as well as 2 in chloroform. Excitation wavelengths for 2I(GF), 2-II(DMF), and the solution were 365, 365, and 341 nm, respectively.

Table 3. Fluorescence Properties of 2-II(GF) and 2II(DMF) λem 2-I(GF) 2-II(DMF) 2 in chloroform

max/nm

579 614 557

ΦF

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1.2% 1.1% 0.1%

CONCLUSION In this study, we synthesized novel ortho-3-thienyl substituted [12]DBA 2, revealed two types of crystals of 2 (i.e., 2-I(GF) and 2-II(solv.), and investigated their thermal, optical, and electrical properties. Furthermore, comparison of crystal structures of 2 with those of phenyl-substituted derivative 1 demonstrated that structural differences of the aryl group strongly affects arrangements of the π-conjugated core. Particularly in the crystals 1-column and 2-II(THF), closely resembled 1D π-stacked columnar motifs are formed, while the columns arranged in a different manner in the crystals due to subtle differences of the substituents, causing significant differences in the lifetime of charge carrier generated in crystals, although the intensity of the photoconductivity is almost same in both crystals. These results can provide new insight for tuning of the assembly’s properties by changing the peripheral aryl substituents of π-conjugated molecules.

described above, these two crystals have closely resembled πstacked columnar motifs of [12]DBA cores, which are, on the other hand, arranged in a different way, allowing us to reveal the effects of arrangement of the 1D π-stacked columns on the charge carrier behaviors. Photoconductivity of anisotoropically oriented bulk crystals were recorded along the columnar axis direction and the orthogonal direction as shown in Figure 8. The crystal 1-column exhibited moderate photoconductivity (ϕΣμ = 4.7 × 10−5 cm2/(V s), where ϕ and Σμ denote photocarrier generation yield and the sum of the charge carrier mobilities, respectively) along the crystallographic a axis, which corresponds to π-stacked direction of the [12]DBA. The value

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01273. 1 H and 13C NMR Spectra of the synthesized compounds, crystal structure of 2-II (CHCl3), thermal analyses, optical properties, theoretical calculation, and summarized crystal structures of 1 (PDF) Accession Codes

CCDC 1419482−1419486 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Figure 8. Photo conductivity transient curves of oriented bulk crystals of (a) 1-column and (c) 2-II(THF) along the columnar axis direction (red curve) and its orthogonal direction (light blue line).

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. G

DOI: 10.1021/acs.cgd.5b01273 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto-shi, Kyoto 615-8510, Japan. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Grant-in-Aid for Scientific Research (C) (T15K04591) and for Scientific Research on Innovative Areas: π-System Figuration (15H00998) from MEXT Japan. We thank Dr. S. Mori at Ehime University for his fruitful advice about a structural refinement of disordered molecules. Crystallographic data was collected using a synchrotron radiation at the BL38B1 in the SPring-8 with approval of JASRI (Proposal No. 2014A1252, 2014B1168, and 2015A1174).

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DOI: 10.1021/acs.cgd.5b01273 Cryst. Growth Des. XXXX, XXX, XXX−XXX