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Hierarchical Self-Assembly of Disc-Rod Shape Amphiphiles Having Hexa-peri-hexabenzocoronene and a Relatively Long Rod Kehua Gu, Meng-Yao Zhang, Yu Zhou, Mengying Han, Wei Zhang, Zhihao Shen, and Xing-He Fan Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b00456 • Publication Date (Web): 16 Mar 2017 Downloaded from http://pubs.acs.org on March 19, 2017

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Hierarchical Self-Assembly of Disc-Rod Shape Amphiphiles Having Hexa-peri-hexabenzocoronene and a Relatively Long Rod Kehua Gu, Mengyao Zhang, Yu Zhou, Mengying Han, Wei Zhang, Zhihao Shen,* and Xinghe Fan

Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, and College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.

Abstract: Two disc-rod shape amphiphiles consisting of hexa-peri-hexabenzocoronene (HBC) and a nano-sized rod-like mesogen were designed and synthesized. Thermotropic phase behaviors were carefully studied. Despite significant steric mismatch between the discs and rods, hierarchical structures were observed for both disc-rod shape amphiphiles at ambient temperature and upon heating. Molecular packing schemes were proposed and confirmed by the reconstructed electron density maps, molecular dynamics simulation, and direct observation by transmission electron microscope. The results demonstrate that the shape effect is of great importance in the self-assembly of shape amphiphiles.

Introduction 1 ACS Paragon Plus Environment

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The molecular shape is of great importance in the self-assembly of supramolecular systems. For instance, rod-like liquid crystalline (LC) molecules usually form nematic or smectic phases, while disc-like LC molecules generally form columnar phases.1 Furthermore, shape amphiphiles, constructed by molecular building blocks with distinct shapes, are featured by the ability to form a variety of sophisticated hierarchical structures.2-3 Cheng et al. reported a sphere-cubic shape amphiphile composed of a [60] fullerene (C60) and a polyhedral oligomeric silsesquioxane (POSS). The dyad can crystalize into two different crystalline structures, an orthorhombic unit cell and a hexagonal structure, depending on the different packing orientations of the cubic-like POSS.4 Glotzer et al. predicted the formation of lamellar, hexagonal, and cubic phases by different kinds of “tethered nanoparticle” shape amphiphiles using computer simulation.5

In 1970, Freiser theoretically predicated the existence of the biaxial nematic phase by mixing rod-like molecules and disc-like molecules.6 To prevent the mixture of disc-like and rod-like molecules from phase separation, disc-like and rod-like molecules were covalently linked, forming disc-rod shape amphiphiles.7 Disc-rod shape amphiphiles are reported to form ordinary nematic phases

8-9

and biaxial nematic phases.7,

10

Up to now, several high-ordered

self-assembling structures have been obtained.11-13 However, there are still few reports about the formation of hierarchical structures by disc-rod shape amphiphiles.

Herein, we report two newly designed and synthesized disc-rod shape amphiphiles with flexible

spacers

of

different

lengths.

The

disc-rod

dyads

are

composed

of

a

hexa-peri-hexabenzocoronene (HBC) and a rod-like mesogen. HBC derivatives are well-known 2 ACS Paragon Plus Environment

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for the high charge carrier mobility and the stable hexagonal columnar (Colh) phases.14 A rod-like mesogen was introduced in an asymmetric molecular structure to change the shape of the dyad and break the six-fold symmetry of the disc-like HBC. The disc-rod shape amphiphile was supposed to form a complex hierarchical structure because of the low symmetry and incompatiblity between the two mesogens.11 It turns out that well-ordered hierarchical structures are formed both at low temperatures and upon heating. This is the first example that the rod-like mesogen of disc-rod shape amphiphiles form ordered structures upon heating rather than pack randomly around the HBC supramolecular columns.15-16 The shape amphiphiles were characterized by combining techniques of polarized light micrscopy (PLM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), one-dimensional (1D) wide angle X-ray diffraction (WAXD) two-dimensional (2D) WAXD, and transmission electron microscopy (TEM). Reconstruction of electron density maps and molecular dynamics annealing were used to determine the exact molecular packing schemes in the unit cell.

Experimental Section

Materials: Tetrahydrofuran (THF) and dichloromethane (CH2Cl2) were purified with the M.Braun SPS-800 solvent purification system. Triethylamine was distilled over CaH2 prior to use. 1,4-Dioxane (99.5%, superdry), iron(III) chloride, lithium aluminium hydride (1.0 M solution in THF), and tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4) were purchased from J&K Chemical, and dicobalt octacarbonyl stabilized with 1−5% hexane was purchased 3 ACS Paragon Plus Environment

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from TCI Chemicals. All other chemicals were commercially available and were used as received. Analytical thin-layer chromatography (TLC) was performed on 0.2 mm silica gel-coated glass slides with an F254 indicator.

Instruments: NMR spectra were obtained on a Bruker-400 (400 MHz) or Bruker-500 (500 MHz) spectrometer. Chemical shifts are reported in parts per million (ppm) down-field from tetramethylsilane (TMS) used as an internal reference, and coupling constants are reported in hertz (Hz). Electron ionization (EI) mass spectra were recorded on a ZAB-HS magnetic mass spectrometer. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra were acquired on a Bruker Autoflex III MALDI-TOF spectrometer with

α-cyano-4-hydroxycinnamic acid (CCA) served as the matrix. Elemental analysis was carried out on a Vario EL element analyzer. Thermogravimetric analysis (TGA) was carried out on a TA Instrument Q600 analyzer under N2 (10 oC/min). Differential scanning calorimetry (DSC) examination was carried out on a TA DSC Q100 calorimeter with nitrogen as the purge gas. Polarized light microscopy (PLM) observation was performed on a Nikon DS-Ri1 microscope. An Instec HCS302 hot stage was used for controlling the temperature. Small-angle X-ray scattering (SAXS) experiments were carried out on an X-ray scattering instrument (SAXSess mc2, Anton Paar) equipped with line collimation (Cu-Kα, λ = 0.154 nm). The working voltage and current were 40 kV and 40 mA, respectively. SAXS measurements were also performed in the transmission mode with synchrotron radiation at Beamline BL16B1 of Shanghai Synchrotron Radiation Facility (SSRF) and at beamline 1W2A at Beijing Synchrotron Radiation Facility 4 ACS Paragon Plus Environment

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(BSRF) (λ = 0.124 nm).17 The scattering vector q is defined as q = 4πsinθ/λ, where the scattering angle is 2θ, and the d-spacing is given by 2π/q. Two-dimensional (2D) wide-angle X-ray diffraction (WAXD) patterns were acquired on a Bruker D8 Discover diffractometer with a GADDS as a 2D detector. The bright-field image was obtained on a JEM 2100 transmission electron microscopy (TEM) with an accelerating voltage of 200 kV. Thin sections of samples were conducted on a Leica EM UC6 ultramicrotome.

Sample preparation: The detailed synthetic procedures of the intermediates and the shape amphiphiles are described in the supporting information (SI). The shape amphiphiles were cooled from the isotropic state at a constant rate of 0.1 oC/min before the powder SAXS measurements. Two-dimensional WAXD experiments were performed on sheared samples, and the incident beam is perpendicular to the sheared sample. Thin slices of the bulk samples suitable for TEM experiments were obtained using a Leica EM UC6 ultramicrotome at ambient temperature, and then transferred to carbon-coated copper grids for TEM experiments.

Density measurement: The samples were placed in a tube with water. Afterwards, air bubbles were carefully removed by sonication. Saturated potassium iodide aqueous solution was added dropwise to the tube for HBC-C4-Rod, while methanol was added for HBC-C11-Rod. The density of the sample was equal to the solution when the sample was suspended in the middle of the solution.

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Reconstruction of electron density maps: Reconstruction of the electron density maps was based on the following formula for 2D ordered structures:

∑ =∑

ρ ( xy ) =

hk

hk

F ( hk ) exp[2π i ( hx + ky )] I ( hk ) exp[2π i ( hx + ky ) + iφ ( hk )]

I is the intensity of the (hk) reflection and Φ(hk) is the phase of the (hk) reflection.18 Fourier Filtering: A circular mask of a radius of 0.0641 nm1 was applied to the central peak in the frequency domain, and circular masks of radius of 0.0322 nm1 were applied to the diffraction peaks. All unmasked Fourier spectrum terms were set to zero. Inversed fast Fourier transform (IFFT) on the processed Fourier spectrum yields the filtered spatial image.3

Molecular dynamics simulation: Molecular dynamics simulation was carried out on Materials Studio (Accelrys Inc.) using the Forcyte Module following the procedure described by Prof. Ungar.19 The structures were obtained after 30 temperature cycles of constant volume dynamics between 300 K and 700 K with the 3D periodic boundary conditions equal to the calculated unit cell parameters a, b, c, and γ.

Results and Discussion

Synthesis and structural characterization of the shape amphiphiles. The shape amphiphiles HBC-C4-Rod and HBC-C11-Rod were synthesized from hydroxyl HBC derivatives 1a and 1b through esterification (Scheme 1) with the rod-like molecule 4, respectively. Mono-functional HBCs were prepared following the reported procedure of our group (Scheme S1 in SI).20 All 6 ACS Paragon Plus Environment

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intermediates and final products were purified using column chromatography and unambiguously characterized by 1H and

13

C NMR, mass spectra, and element analysis. Figures

S1 and S2 in SI show the MALDI-TOF MS spectra of the shape amphiphiles, confirming the chemical structures of the shape amphiphiles.

Scheme 1. Synthetic route of the disc-rod shape amphiphiles.

Thermotropic phase behaviours. Thermotropic phase behaviours of the shape amphiphiles were carefully studied by TGA, DSC and PLM. The TGA results show that both shape amphiphiles

exhibit good thermal stabilities with 5% weight loss temperatures over 400 °C

(Figure S3 in SI). DSC experiments were carried out to study the bulk phase transitions. For HBC-C4-Rod, an endothermic peak in the DSC curve is observed at 73.0 oC on heating, while the isotropization occurs at 136.5 oC (the black line in Figure 1a). The typical columnar fan texture was observed at 90 oC during the cooling process under PLM, indicating the formation of a columnar phase (Figure 1b). HBC-C11-Rod with a much longer spacer exhibits a pretty complex DSC profile (the red line in Figure 1a). For the PLM textures of HBC-C11-Rod (ColII 7 ACS Paragon Plus Environment

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phase) observed during the cooling process from the isotropic state, it is a fan texture with dark bands (Figure 1c) at 90 oC, while it is a columnar fan texture (Colob phase) at 145 oC (Figure 1d). For smectic liquid crystals, the anisotropic lattice contraction during the transition from the hexagonal smectic B (SB) phase to the orthorhombic SE phase usually results in a fan texture with dark bands in the SE phase.21-22 The dark bands in the fan texture of HBC-C11-Rod (Figure 1c) may be rationalized in terms of contractions of the lattice in different directions during the transition from the Colob phase to the ColII phase upon cooling.

Figure 1. First-cooling and second-heating DSC traces of HBC-C4-Rod and HBC-C11-Rod at a rate of 10 oC/min under nitrogen (a), with transition temperatures (oC), enthalpic changes in parentheses (kJ/mol), and phases indicated (K = supramolecular crystalline phase; Colob = oblique columnar phase; Iso = isotropic phase); PLM micrographs of the textures exhibited by


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the Colob phase of HBC-C4-Rod at 90 oC (b) and by the ColI phase at 90 oC (c) and the ColII phase at 145 oC (d) of HBC-C11-Rod.

Self-assembled structures at ambient temperature. In order to determine the phase structures of the shape amphiphiles at ambient temperature, powder SAXS and 2D WAXD experiments on sheared samples were performed. In Figures 2a and 2b, the powder SAXS profiles of HBC-C4-Rod and HBC-C11-Rod show a series of sharp reflection peaks in the low-angle region. 2D WAXD patterns on sheared samples (parts c and d in Figure 2) show that all the low-angle reflections are along the shear direction. And the high-angle reflections are perpendicular to the shear direction. Considering the strong π-π interaction between HBCs, the shape amphiphiles tend to form supramolecular columns. Thus, the low-angle reflections are attributed

to

the

2D

inter-columnar

packing,

while

the high-angle reflections are

attributed to face-to-face stacking of the shape amphiphiles. With combination of the powder SAXS and 2D WAXD results, the reflections in the SAXS profile can be properly indexed. On the basis of the assignment of the reflections, the HBC-C4-Rod is

supramolecular

crystal (K phase) of

calculated to be monoclinic, and the space group is determined to be P2/m. In

addition, the cell parameter c is determined from the reflections in the high-angle region (Figure 2a). Measured and calculated q and d-spacing values are listed in Tables S1 in SI. The cell parameters are a = 5.94 nm, b = 2.33 nm, c = 0.468 nm, and γ = 98.0o. Similarly, on the basis of the SAXS and 2D WAXD results of HBC-C11-Rod (parts b and d in Figure 2), the lattice parameters of ColI phase are a = 7.08 nm, b = 2.36 nm, γ = 101.1o (Table S2 in SI). The value of 9 ACS Paragon Plus Environment

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c is about 0.434 nm, which is calculated from the scattering halo centred at 14.5 nm−1 in Figure 2b. The numbers of molecules in the unit cell are calculated according to the measured density and the cell volume (Table S3 in SI). There are two molecules in a unit cell for both HBC-C4-Rod and HBC-C11-Rod.

Electron density maps of HBC-C4-Rod and HBC-C11-Rod were reconstructed with the Miller indices and normalized intensities of the low-angle reflections to determine the exact positions of the HBC cores and the rod-like segments in the unit cell23 (Tables S1 and S2 in SI). In the electron density maps, red represents the highest electron density, and dark blue the lowest. The reconstructed electron density maps of HBC-C4-Rod (Figure 2e) and HBC-C11-Rod (Figure 2f) show similar alternating stacks of discs and rods at ambient temperature. The HBC cores form a bilayer lamella, and the rods are packed parallel in dimers (parts e and f of Figure 2) according to the proposed packing schemes.


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Figure 2. Powder SAXS profile (a: HBC-C4-Rod, K phase; b: HBC-C11-Rod, ColI phase), 2D WAXD pattern on a sheared sample (c: HBC-C4-Rod, K; d: HBC-C11-Rod, ColI), and


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reconstructed electron density maps (e: HBC-C4-Rod, K; f: HBC-C11-Rod, ColI) of HBC-C4-Rod and HBC-C11-Rod.

As shown in Figure 3a, a TEM bright-field image of a microtomed thin-sectioned HBC-C4-Rod sample shows the structure along the direction, and its fast Fourier transform (FFT) pattern is shown in the inset of Figure 3a. The dark parts in the figure representing high electron density regions are attributed to the disc-like and rod-like mesogens. Fourier filtering treatment3 provides a clear image along the direction (Figure 3b). The magnified image (inset of Figure 3b) clearly shows the exact positions of discs and rods in the unit cell,

matching well

with

the reconstructed

electron density map of HBC-C4-Rod

(Figure 2e). The TEM image along the supramolecular columns (Figure 3c) with a periodicity of 2.4 nm is in accordance with the cell parameter b. The TEM bright-field image of HBC-C11-Rod and its FFT pattern also confirm the self-assembled structure (Figure S4 in SI). The calculated periodicity of about 2.3 nm agrees with the spacing between two HBC supramolecular columns.


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Figure 3. TEM bright-filed image along the direction of HBC-C4-Rod in the K phase (a: inset, the FFT pattern of the image) and Fourier filtering pattern of the TEM image (b: inset,


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magnification of the image), and the TEM image showing the parallel supramolecular columns of HBC-C4-Rod in the K phase (c: inset, magnification of the image).

Figure 4. Powder SAXS profile of HBC-C4-Rod (a) and HBC-C11-Rod (b); reconstructed electron density maps of HBC-C4-Rod (c) and HBC-C11-Rod (d) in their Colob phases.


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Self-assembled structures upon heating. When HBC-C4-Rod is heated to 90 oC, it forms a Colob phase according to the powder SAXS (Figure 4a) and 2D WAXD (Figure S5a in SI) results. The calculated 2D lattice parameters are a = 6.29 nm, b = 2.89 nm, γ = 98.9o (Table S4 in SI). The scattering halo centred at 23o (inset of Figure 4a) indicates the distance of π-π stacking c = 0.38 nm. There should be two molecules in a unit cell according to the measured density. The reconstructed electron density map (Figure 4c) and the snapshot after molecular dynamics (MD) annealing (Figure 5a) by Materials Studio18-19 show that the HBC cores form a quasi-rhombic packing in the lamella with an inter-disc distance of about 2.9 nm. The simulated SAXS profile obtained from the MD result is consistent with the experimental SAXS result (Figure 5c).24 These results strongly support the molecular packing scheme we proposed.

Figure 5. Snapshots of HBC-C4-Rod (a) and HBC-C11-Rod (b) after MD annealing in the Colob phases, with HBC cores in red, rod-like mesogens in orange, and alkyl chains in green; experimental (black) and simulated (red) SAXS profiles of HBC-C4-Rod (c) and HBC-C11-Rod (d) in the Colob phases. 15 ACS Paragon Plus Environment

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Similarly, cell parameters of HBC-C11-Rod in the Colob phase at 145 oC are a = 7.39 nm, b = 5.91 nm, c = 0.38 nm, γ = 95.4o (Table S5 in SI) from the powder SAXS (Figure 4b), WAXD (inset of Figure 4b), and 2D WAXD (Figure S5b in SI) results. The number of molecules in a unit cell is 4. The reconstructed electron density map (Figure 4d) and the MD simulation result of the Colob phase (Figure 5b) reveal the similar bilayer molecular structure with HBC-C4-Rod. Nevertheless, the unit cell of HBC-C11-Rod is nearly two times the size of HBC-C4-Rod. Figure 5d shows the simulated SAXS profile obtained from the snapshot by Materials Studio. There is a little difference between the simulated and experimental profiles, because the experimental profile is a time-space averaged result of the annealing system.

Although several ordered structures have been reported for HBC-rod shape amphiphiles in bulk, such self-assembled hierarchical structures are rare. Even in most studies on shape amphiphiles, hierarchical structures are seldom reported. It is reported that the HBC-pyrene dyad, which has a similar topological structure with the HBC-rod dyads, forms a Colh phase upon heating.15 The pyrenes were packed randomly around the HBC supramolecular columns in the Colh phase. In sharp contrast, the synthesized shape amphiphiles in this work are able to form well-ordered hierarchical structures upon heating, which displays reflections with high Miller indices. The different lattice structures are owing to the spacers of different lengths. We propose that the driving force for the rod-like mesogens to be packed regularly is the excluded volume effect.25-27 The effect, which is basically of entropy origin, is attributed to the ordering force which makes the rod-like molecules form the parallel arragement. In such an arrangement, the 16 ACS Paragon Plus Environment

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rod-like molecules can translate more easily along the oriented direction than in a disordered state, which increases the translational entropy that overwhelms the orientational entropy. The large aspect ratio of the rods in this work greatly enhances the excluded volume effect, which forces the rods to be packed parallel and maximize the space filling.

Conclusions

In conclusion, two shape amphiphiles are designed and synthesized. The self-assembly of the shape amphiphiles at different temperatures are studied by combining techniques of SAXS, 2D-WAXD, TEM, reconstructed electron density maps, and MD. No matter at low temperatures or upon heating, the two disc-rod shape amphiphiles form alternating lamellae of discs and rods through nanophase-separation. In the HBC lamella, the disc-like HBC cores are packed closely with a thermodynamically stable quasi-rhombic lattice, while the rods are packed parallel. Parallel packing of the rods is attributed to the exclusive volume effect. This work demonstrates the importance of the shape effect in self-assembling supramolecular structures. In addition, it reveals that the enhancement of the excluded volume effect of the rod-like mesogen and the symmetry breaking strategy can facilitate the formation of well-ordered hierarchical structures.

ASSOCIATED CONTENT

Supporting information: Detailed synthetic procedures, TGA diagram, MALDI-TOF mass spectra, 2D WAXD patterns, experimental and calculated d-spacing of the shape amphiphiles. This material is available free of charge via the Internet at http:// pubs.acs.org. 17 ACS Paragon Plus Environment

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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

ACKNOWLEDGMENT The authors thank Prof. Wenbin Zhang for his helpful discussion in the subject of shape amphiphiles and Prof. Shuang Yang for advices about reconstruction of electron density maps. The authors also gratefully acknowledge the scientists at beamline 1W2A at Beijing Synchrotron Radiation Facility (BSRF) and at beamline BL16B1 at Shanghai Synchrotron Radiation Facility (SSRF) for their helpful assistance on the synchrotron-radiation SAXS experiments. This work was supported by the National Natural Science Foundation of China (Grant 21674004).

REFERENCES (1) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hagele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Discotic liquid crystals: From tailor-made synthesis to plastic electronics, Angew. Chem. Int. Ed. 2007, 46, 4832-4887. (2) Zhang, W. B.; Yu, X. F.; Wang, C. L.; Sun, H. J.; Hsieh, I. F.; Li, Y. W.; Dong, X. H.; Yue, K.; Van Horn, R.; Cheng, S. Z. D. Molecular nanoparticles are unique elements for macromolecular science: from "nanoatoms" to giant molecules, Macromolecules 2014, 47, 1221-1239.


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(3) Huang, M. J.; Hsu, C.; Wang, J.; Mei, S.; Dong, X.; Li, Y.; Li, M.; Liu, H. L.; Zhang, W.; Aida, T.; Zhang, W. B.; Yue, K.; Cheng, S. Z. D. Selective assemblies of giant tetrahedra via precisely controlled positional interactions, Science 2015, 348, 424-428. (4) Sun, H. J.; Tu, Y. F.; Wang, C. L.; Van Horn, R. M.; Tsai, C. C.; Graham, M. J.; Sun, B.; Lotz, B.; Zhang, W. B.; Cheng, S. Z. D. Hierarchical structure and polymorphism of a sphere-cubic shape amphiphile based on a polyhedral oligomeric silsesquioxane-[60]fullerene conjugate, J. Mater. Chem. 2011, 21, 14240-14247. (5) Glotzer, S. C.; Horsch, M. A.; Iacovella, C. R.; Zhang, Z. L.; Chan, E. R.; Zhang, X. Self-assembly of anisotropic tethered nanoparticle shape amphiphiles, Curr. Opin. Colloid Interface Sci. 2005, 10, 287-295. (6) Freiser, M. J. Ordered States of a Nematic Liquid, Phys. Rev. Lett. 1970, 24, 1041-1043. (7) Hunt, J. J.; Date, R. W.; Timimi, B. A.; Luckhurst, G. R.; Bruce, D. W. Toward the biaxial nematic phase of low molar mass thermotropic mesogens: Substantial molecular biaxiality in covalently linked rod-disk dimers, J. Am. Chem. Soc. 2001, 123, 10115-10116. (8) Kouwer, P. H. J.; Mehl, G. H. Full miscibility of disk- and rod-shaped mesogens in the nematic phase, J. Am. Chem. Soc. 2003, 125, 11172-11173. (9) Kouwer, P. H. J.; Mehl, G. H. Multiple levels of order in linked disc-rod liquid crystals, Angew. Chem. Int. Ed. 2003, 42, 6015-6018. (10) Jeong, K.-U.; Jing, A. J.; Mansdorf, B.; Graham, M. J.; Yang, D.-K.; Harris, F. W.; Cheng, S. Z. D. Biaxial molecular arrangement of rod-disc molecule under an electric field, Chem. Mater. 2007, 19, 2921-2923. 19 ACS Paragon Plus Environment

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(11) Jeong, K.-U.; Jing, A. J.; Monsdorf, B.; Graham, M. J.; Harris, F. W.; Cheng, S. Z. D. Self-assembly of chemically linked rod-disc mesogenic liquid crystals, J. Phys. Chem. B 2007, 111, 767-777. (12) Wang, S.; Doessel, L.; Mavrinskiy, A.; Gao, P.; Feng, X.; Pisula, W.; Muellen, K. Self-Assembly and Microstructural Control of a Hexa-peri-hexabenzocoronene-Perylene Diimide Dyad by Solvent Vapor Diffusion, Small 2011, 7, 2841-2846. (13) Dössel, L. F.; Kamm, V.; Howard, I. A.; Laquai, F.; Pisula, W.; Feng, X.; Li, C.; Takase, M.; Kudernac, T.; De Feyter, S.; Müllen, K. Synthesis and controlled self-assembly of covalently linked hexa-peri-hexabenzocoronene/perylene diimide dyads as models to study fundamental energy and electron transfer processes, J. Am. Chem. Soc. 2012, 134, 5876-5886. (14) Schmidt-Mende, L.; Fechtenkötter, A.; Müllen, K.; Moons, E.; Friend, R. H.; MacKenzie, J. D. Self-organized discotic liquid crystals for high-efficiency organic photovoltaics, Science 2001, 293, 1119-1122. (15) Tchebotareva, N.; Yin, X. M.; Watson, M. D.; Samorì, P.; Rabe, J. P.; Müllen, K. Ordered architectures of a soluble Hexa-peri-hexabenzocoronene-pyrene dyad: Thermotropic bulk properties and nanoscale phase segregation at surfaces, J. Am. Chem. Soc. 2003, 125, 9734-9739. (16) Mativetsky, J. M.; Kastler, M.; Savage, R. C.; Gentilini, D.; Palma, M.; Pisula, W.; Müllen, K.; Samorì, P. Self-assembly of a donor-acceptor dyad across multiple length scales: Functional architectures for organic electronics, Adv. Funct. Mater. 2009, 19, 2486-2494. (17) Li, Z.; Wu, Z.; Mo, G.; Xing, X.; Li, P. A small-angle x-ray scattering station at Beijing Synchrotron Radiation Facility, Instrum Sci. Technol. 2014, 42, 128-141. 20 ACS Paragon Plus Environment

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(18) Prehm, M.; Liu, F.; Baumeister, U.; Zeng, X. B.; Ungar, G.; Tschierske, C. The Giant-Hexagon cylinder network - A liquid-crystalline organization formed by a T-shaped quaternary amphiphile, Angew. Chem. Int. Ed. 2007, 46, 7972-7975. (19) Kim, H. J.; Liu, F.; Ryu, J. H.; Kang, S. K.; Zeng, X.; Ungar, G.; Lee, J. K.; Zin, W. C.; Lee, M. Self-organization of bent rod molecules into hexagonally ordered vesicular columns, J. Am. Chem. Soc. 2012, 134, 13871-13880. (20) Zhou, Y.; Zhang, M. Y.; Gu, K. H.; Zhu, Y. F.; Fan, X. H.; Shen, Z. Facile Synthesis and Phase Behaviors of Monofunctionalized Hexa-peri-hexabenzocoronenes, Asian J. Org. Chem. 2015, 4, 746-755. (21) Coates, D.; Harrison, K. J.; Gray, G. W. Studies of mesophase transformations for certain schiff's base esters, Mol. Cryst. Liq. Cryst. 1973, 22, 99-122. (22) Sackmann, H.; Demus, D. The problems of polymorphism in liquid crystals, Mol. Cryst. Liq. Cryst. 1973, 21, 239-273. (23) Glettner, B.; Liu, F.; Zeng, X. B.; Prehm, M.; Baumeister, U.; Walker, M.; Bates, M. A.; Boesecke, P.; Ungar, G.; Tschierske, C. Liquid-crystalline kagome, Angew. Chem. Int. Ed. 2008, 47, 9063-9066. (24) Zeng, X. B.; Liu, F.; Fowler, A. G.; Ungar, G.; Cseh, L.; Mehl, G. H.; Macdonald, J. E. 3D Ordered gold strings by coating nanoparticles with mesogens, Adv. Mater. 2009, 21, 1746-1750. (25) Onsager, L. The Effects of Shape on the Interaction of Colloidal Particles, Ann. N.Y. Acad. Sci. 1949, 51, 627-659.


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(26) Kim, Y. H.; Pincus, P. Nematic Polymers - Excluded-Volume Effects, Biopolymers 1979, 18, 2315-2322. (27) Frenkel, D. Columnar Ordering as an Excluded-Volume Effect, Liq. Cryst. 1989, 5, 929-940.


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TOC Entry for

Hierarchical

Self-Assembly

of

Disc-Rod

Shape

Amphiphiles

having

Hexa-peri-hexabenzocoronene and a Relatively Long Rod

Kehua Gu, Mengyao Zhang, Yu Zhou, Mengying Han, Wei Zhang, Zhihao Shen,* and Xinghe Fan

Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry Education, Center for Soft Matter Science and Engineering, and College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

Two disc-rod shape amphiphiles were designed and synthesized. Hierarchical structures were observed. Both disc-rod dyads form similar well-ordered alternating bilayer stacks of disc-like segments and rod-like segments at low temperatures and upon heating. 23 ACS Paragon Plus Environment

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Scheme 1 55x37mm (300 x 300 DPI)

ACS Paragon Plus Environment

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Figure 1 85x86mm (300 x 300 DPI)


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Figure 2 189x433mm (300 x 300 DPI)


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Figure 3 182x541mm (300 x 300 DPI)


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Figure 4 152x277mm (300 x 300 DPI)


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Figure 5 65x53mm (300 x 300 DPI)


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TOC 32x18mm (300 x 300 DPI)


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Hierarchical Self-Assembly of Disc-Rod Shape ... - ACS Publications

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