The influence of alkyl chain substitution pattern on the

Liquid Crystals

ISSN: 0267-8292 (Print) 1366-5855 (Online) Journal homepage: http://www.tandfonline.com/loi/tlct20

The influence of alkyl chain substitution pattern on the two- and three-dimensional self-assembly of truxenone discogens Peng Ruan, Bo Xiao, Hai-Liang Ni, Ping Hu, Bi-Qin Wang, Ke-Qing Zhao, QingDao Zeng & Chen Wang To cite this article: Peng Ruan, Bo Xiao, Hai-Liang Ni, Ping Hu, Bi-Qin Wang, Ke-Qing Zhao, Qing-Dao Zeng & Chen Wang (2014) The influence of alkyl chain substitution pattern on the two- and three-dimensional self-assembly of truxenone discogens, Liquid Crystals, 41:8, 1152-1161, DOI: 10.1080/02678292.2014.909538 To link to this article: http://dx.doi.org/10.1080/02678292.2014.909538

Published online: 16 Apr 2014.

Submit your article to this journal

Article views: 167

View related articles

View Crossmark data

Citing articles: 2 View citing articles

Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tlct20 Download by: [Sichuan Normal University]

Date: 04 November 2015, At: 00:21

Liquid Crystals, 2014 Vol. 41, No. 8, 1152–1161, http://dx.doi.org/10.1080/02678292.2014.909538

The influence of alkyl chain substitution pattern on the two- and three-dimensional self-assembly of truxenone discogens Peng Ruana, Bo Xiaoa,b, Hai-Liang Nia, Ping Hua*, Bi-Qin Wanga, Ke-Qing Zhaoa*, Qing-Dao Zengb and Chen Wangb* a

College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, P. R. China; bNational Center for Nanoscience and Technology (NCNST), Beijing, P. R. China

Downloaded by [Sichuan Normal University] at 00:21 04 November 2015

(Received 10 February 2014; accepted 25 March 2014) The synthesis of new discotic liquid crystals and the study of self-assembly behaviours are important for the supramolecular chemistry and organic electronics. Six new truxenone discogens 7a–f with different alkyl chain substitution patterns were synthesised and all exhibited only one three-dimensional ordered hexagonal columnar mesophase with wide temperature ranges including room temperature, which were characterised with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. The self-assembly behaviours in solutions were studied by using concentration-variation 1H NMR and scanning electron microscopy. The twodimensional ordered self-assembly of 7c and 7f on the liquid–solid interface of highly oriented pyrolytical graphite were imaged by scanning tunnelling microscopy, and the results showed that the two-dimensional monolayer selfassembled structures on the atomically flat surfaces can be controlled by the peripheral alkyl chain substitution patterns. Keywords: truxenone; liquid crystal; self-assembly; nanostructure; scanning tunnelling microscopy; scanning electron microscopy

Introduction Discotic liquid crystals (DLCs) are among the most important molecular materials in organic electronics, [1–12] as they can self-organise into three-dimensional (3D) ordered columnar mesophases and display high charge carrier mobility along the columnar axis.[13–22] DLCs usually consist of a polycyclic aromatic core and six to eight peripheral flexible chains, show good solubility in common organic solvents, and can be fabricated into electronic devices by solution-processing or printing technique with the cost-effective advantage. Now DLC semiconductors are attractive materials in organic fieldeffect transistors (OFETs),[6,7] organic photovoltaic (OPV) solar cells,[23–25] organic light-emitting diodes (OLEDs),[26,27] and sensors [28] for the assay of organic explosive nitro compounds [29,30] and volatile organic compounds.[31,32] Among the DLCs reported, truxene derivatives have shown interesting polymesomorphism and inverted phase sequences.[33–38] In the 3D selfassembled columnar mesophase, the columns formed by the π–π stacking truxene aromatic cores are semiconducting and electrons and holes hop in the columns with high mobility rates, which have been demonstrated by the time-of-flight (TOF) measurement technique [39–42] and field-effect transistor device

performance.[43] However, the mesomorphism of truxenone DLCs has not been reported from our knowledge though the merits of higher chemical stability and the n-type semiconducting characteristic are expected. Understanding and controlling the self-assembly of discotic materials are essentially important for their application.[10] Rod-like liquid crystalline molecules spontaneously organise to orientation-ordered configuration and this orientation can be controlled by external electric field. This property of the rod-like liquid crystals has been widely applied in the flat panel liquid crystal displays, and the techniques to control the self-organisation of rod-like liquid crystals are well developed. However, controlling the selfassembly of DLCs is still a challenge.[10] For fully realising the electronic and optical functionality of DLCs, it is necessary to understand and control the self-assembly of semiconducting discogens in solutions and on the interfaces of different substrates.[44–49] Here we report the synthesis and characterisation of six new 2,3,7,8,12,13-hexakis(alkoxy)truxenone discogens with different peripheral alkyl chain substitution patterns. Their self-assembly behaviours in solutions were studied with concentration-variation 1H NMR and scanning electron microscopy (SEM). The two-dimensional (2D) ordered monolayer structures on the liquid–solid

*Corresponding author. Email: [email protected] (Ke-Qing Zhao); (Chen Wang) © 2014 Taylor & Francis

[email protected] (Ping Hu); [email protected]


Liquid Crystals

1153

Scheme 1. The synthesis of 2,7,12-tris(decanoxy)-3,8,13-tris(alkoxy)-5,10,15-truxenones.

interface of highly oriented pyrolytical graphite (HOPG) were imaged with scanning tunnelling microscopy (STM). The influence of alkyl chain substitution pattern on the 2D and 3D selfassembly has been compared and discussed. Scheme 1 shows the synthetic route for the new truxenone DLCs.

Results and discussion

Photophysical property: UV–Vis absorption and photoluminescent spectra The application of DLCs in devices is strongly dependent on their photo-physical properties. We measured the UV–Vis absorption spectra and the emission spectra of 7a and 7f in dilute solution (1 × 10–5 M) of CH2Cl2, the results shown in Figure 1. Both of the UV–Vis absorption spectra display three peaks at 270, 332, and 372 nm. For the emission spectra measuring, the samples were excited with light of 370 nm,

Synthesis and characterisation For the study of the influence of peripheral chain on mesomorphism and self-assembly behaviour, we designed the target molecules with truxenone core and two different substitution patterns. The 2,7,12-tris(decanoxy)-3,8,13-tris(hydroxy)truxene 6 is the key intermediate and it was synthesised by the cyclic self-condensation trimerisation of indanone.[42] The target compounds 7a–f were synthesised through the Williamson ether reaction of 6 with various 1-bromoalkane producing hexakis(alkoxy)truxenes, and then followed airoxidation of the truxene to truxenone. The total synthetic yields of the last two steps are as high as 65%. The new truxenones 7a–f were characterised with 1H-NMR, 13C-NMR, IR, and micro-analysis. The results are in good agreement with their molecular structures.

Figure 1. (colour online) UV–V is absorption and photoluminescent (PL) spectra (normalised) of 7a and 7f in CH2Cl2 solution (1 × 10–5 M) at room temperature.

1154

P. Ruan et al.

and the emitting spectra peaked at 570 nm. The absorption and emission spectra of 7a and 7f are almost identical and they are green light emitters. This result has demonstrated that hexakis(alkoxy) truxenone is a green light emitting aromatic framework and the peripheral chain length difference has no influence on their photophysical properties.


Mesomorphism: POM textures We observed the textures of the discogens 7 under a polarising optical microscope (POM) with a hotplate and a temperature controller. The samples between two untreated glass slides between crossed polarisers show identifiable birefringence in very wide temperature ranges. The POM photomicrographs of the truxenones 7 have been shown in Figure 2. The optical textures of these discogens contain typical dendritic, fan-shaped, or ‘medal ribbon’ appearance of a mosaic texture of discotic columnar mesophase.[1,2] The compounds showed some degrees of face-on (homeotropic) alignment behaviours (the dark areas on the

photos) between two untreated glass slides, which is a merit for the TOF charge mobility measurement and practical applications of the discogens in OLED and OPV. The mesomorphism: DSC results The phase transition temperatures and enthalpy changes of the discogens were tested with differential scanning calorimetry (DSC). The DSC traces of the six truxenones were combined in Figure 3 and the phase transition temperatures and enthalpy change data have been summarised in Table 1. The DSC trace for each compound exhibited two peaks on heating: the lower temperature peak presented the transition from polycrystalline to mesophase, and the higher temperature peak from mesophase to isotropic liquid. On cooling, two peaks appeared as well, which presented the reversed phase transitions of the heating process. Compound 7c possesses six identical alkyl chains and exhibited mesophase between 20°C and 323°C on

Figure 2. (colour online) Polarising optical microscopic textures of the truxenone discogens. The microphotos from (a)–(f) corresponding to the textures of 7a–f.

Liquid Crystals

1155

(7d, 7e, and 7f), the melting points were increased and the clearing points decreased, so the mesophase ranges narrowed. It was noticed that 7a had the lowest melting point of −37°C and the highest clearing point of 347°C, with the widest mesophase range near 400°C. The unsymmetrical substitution pattern of peripheral chain can be applied for the controlling of phase transition temperatures and mesophase ranges. The broad mesophase ranges including room temperature make these truxenone DLCs attractive for the practical application study.


Mesomorphism: XRD results

Figure 3. DSC traces of hexakis(alkoxy)truxenone DLCs 7a–f. (a) The first cooling runs; (b) the second heating runs. Scanning rate: 10 K/min.

heating, with mesophase range in excess of 300°C. Comparing the phase transition temperatures of 7c with the other five discogens which possess two different alkyl chains, we discovered the influence of alkyl chain length on mesomorphism: To the discogens with shorter chains (7a and 7b), the melting points were decreased and the clearing points increased, and the mesophase ranges were widened; On the contrary, to the discogens with longer chains

Compounds 7a–f possess similar chemical structures and showed only one stable columnar mesophase identified from the DSC and POM. We further studied this discotic mesophase in detail by using the temperature-variation X-ray diffraction (XRD). Compound 7f has been selected for the XRD study as it had the lowest clearing point of 264°C among the six discogens here, which advantaged its thermal stability. Figure 4 shows its XRD patterns from 20°C to 270°C. For the measurement, sample was first heated to isotropic liquid and slowly cooled to the testing temperatures. The XRD patterns of 7f showed typical feature for the discotic ordered hexagonal columnar (Colho) mesophase: at the low-angle region, a set of diffractions corresponding to d100, d110, and d200 with spacing ratios of 1: 1/√3: 1/2 were observed. The result proves that the discotic columns are arranged in a hexagonal pattern. There were another two diffraction peaks at the wide-angle region: the broad peak at 4.5 Å represents the distance among the liquid-like alkyl chains surrounding the rigid truxenone cores; the peak at 3.4 Å reflects the ordered π–π stacking of the aromatic cores and the core-core distance in the columns. The temperature-variation XRD results further support the conclusion that 7f exhibits the Colho mesophase with the lattice parameter a value of 3.15 nm (at 20°C). The self-assembly behaviour: the concentration dependent 1H NMR The wide columnar mesophase ranges with high thermal stability for discogens 7a–f demonstrate that the hexakis(alkoxy)truxenones have strong π–π intermolecular interactions and self-assemble into highly ordered discotic columns in the pure bulk form. We further investigated the self-assembly behaviours of the compounds in solution by using concentrationvariation 1H NMR. Figure 5 shows a part of proton NMR signals of 7c: the signals of both Ha and Hb at

1156

P. Ruan et al. Table 1. Thermotropic phase behaviours of truxenone discogens. Mesophases, transition temperature, and enthalpy changes Compound

Second heating/°C (ΔH, kJ/mol)

7a (C6) 7b (C8) 7c (C10) 7d (C12) 7e (C14) 7f (C16)

Cry −37 (16.2) Colho 347 (7.5) Iso Cry −10 (30.1) Colho 334 (8.8) Iso Cry 20 (24.4) Colho 323 (6.7) Iso Cry 8 (40.2) Colho 303 (6.4) Iso Cry 18 (52.6) Colho 280 (5.5) Iso Cry 25 (52.2) Colho 264 (7.8) Iso

First cooling/°C (ΔH, kJ/mol) Iso Iso Iso Iso Iso Iso

345 336 319 300 278 262

(7.8) (8.8) (8.7) (7.8) (6.3) (8.2)

Colho Colho Colho Colho Colho Colho

−39 (9.6) Cry −14 (28.1) Cry −4 (32.9) Cry 4 (39.1) Cry 10 (53.5) Cry 16 (53.2) Cry

Note: Cry, crystal state; Colho, hexagonal columnar phase; Iso, isotropic liquid.


b a

a

b

15.12 mM 10.08 mM 5.04 mM 8

7

6

5

4

ppm

Figure 5. The concentration-variation 1H NMR spectra of 7c (in CDCl3). The concentration increased from 5.04 to 15.12 mM.

due to the π–π facial interactions of the polycyclic aromatic units.[38] Figure 4. (colour online) XRD pattern of 7f at different temperatures.

8.8 and 7.0 ppm shift up-field as its concentration in CDCl3 is increasing from 5.04 to 15.12 mM at room temperature. The signal at 4 ppm corresponding to the first methylene of alkoxyl closing to the aromatic core also shows similar up-field shift with concentration increasing. The up-field shifting of the two protons on the truxenone core and the proton of OCH2– closing to the core with the concentration increasing reflects that the discotic compounds aggregate face to face in solution, and the proton signals are affected by the neighbouring aromatic ring electricity. The concentration-variation 1H NMR results demonstrate that the truxenones have self-aggregations in CDCl3

The self-assembly in solutions: SEM study In addition, we further explored the self-organisation of the truxenones with the SEM. The samples were first dissolved in organic solvents in 1 mg/ml, and then small amount of solution was drop on the SEM sample wafers and let the solvent evaporating slowly. After that, the samples were measured under SEM. The images of the self-organised microstructures for 7a, 7c, and 7f in ethyl acetate (solvent 1), dioxane (solvent 2), and methanol (solvent 3) are shown in Figure 6. It is noticed that 7a, 7c, and 7f display different morphologies in solvents. In ethyl acetate with a concentration of 1 mg/mL, 7a, 7c, and 7f all formed microscale spherical particles, and 7a looked more obvious. In dioxane with a


Liquid Crystals

1157

Figure 6. SEM images of Truxenone 7a, 7c, and 7f assembled in the solvent of ethyl acetate (1), dioxane (2), and methanol (3). Scale bars: 50 µm.

concentration of 1 mg/mL, 7a and 7c formed grapeshaped morphology, but 7f got small-sized particles. However, the solution in CH2Cl2 dropped to methanol, 7a, and 7c, no ordered assembled structures were observed. From the primary SEM results, we understand that the self-assembly tendencies of hexakis(alkoxy)truxenones to ordered structures in solvents are weak compared with the reported lessalkyl chain containing truxene or truxenones or their electronic donor–acceptor systems.[38,50–52] Hexakis(alkoxy)truxenones studied here possess six long alkyl chains, and they show higher solubility in solvents due to the stronger van der Waals interactions between the solvent and solute molecules, which may disrupt the ordered assembly of the discogens into long fibres. The self-assembly on substrate: STM investigation The 7a–f self-organise into 3D Colho mesophase with high thermal stability. The result cannot directly transfer to the 2D monolayer structures of

the discogens on the interface of solution–substrate. As the so-called 2D crystal engineering results are much more complicated, and the results are strongly affected by the intermolecular interactions of the adsorbate–substrate, adsorbate–adsorbate, and adsorbate–solvent. Understanding and controlling the self-assembly behaviours of the organic semiconducting molecules on solvent–substrate interface are important for surface science and technology of organic electronics and nanoscale materials.[44–49] Truxene and truxenone are polycyclic aromatics consist of four benzene rings and three cyclopentadiene rings and cyclopentadienone ring, respectively. They are good building blocks for the STM images of the nanoscale construction of various buildings.[53–58] However, truxenone with long alkyl chains are not reported from the best of our knowledge, especially for the comparative study of the 2D STM monolayer assembly behaviour with that of the 3D mesomorphic property presented by the bulk sample.


1158

P. Ruan et al.

The 2D self-assembly behaviours of two samples (7c and 7f) were investigated with STM. The truxenone samples were dissolved in toluene with concentration less than 1.0 × 10–4 M. A droplet of solution (0.4 μL) containing 7c or 7f was deposited onto the freshly cleaved HOPG (grade ZYB, Advanced Ceramics Inc., Cleveland, OH, USA). After evaporation of the toluene, a droplet of n-octylbenzene was used to cover the sample and then studied with STM. STM investigation was performed with a Nanoscope IIIa scanning probe microscope system (Bruker, Camarillo, CA, USA) under atmosphere conditions. All STM images provided are raw data and are acquired in constant current mode using a mechanically formed Pt/Ir (80/20) tip. The drift for all presented STM images is calibrated by using the underlying graphite lattice as a reference. Besides, all of the molecular models are built with a HyperChem software package (Hypercube, Inc., Gainsville, FL, USA). The alkyl chains play an important role in the solubilising of the discogens in organic solvents and the creation of a well-ordered adlayers on HOPG.[45,46] STM images of the aromatic core are brighter and the alkyl chains darker. Compound 7c and 7f displayed different self-assembly structures (see Figures 7 and 8). The highest occupied molecular

(a)

orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a truxenone were computerised and the results shown in Figure S1 (Supplementary Information). Comparing the electronic density of the frontier molecular orbitals of HOMO and LUMO and the STM images we knew that the bright triangular-shaped spots in the STM images look more like the shape of the LUMO. Figure 7 illustrates the current STM images of 7c in the thin film and the model for the molecular selfassembly. The discotic molecules assembled periodically on the surface as a hexagonal geometry with lattice constant of a = 2.6 nm, and θ = 120°. The 2D assembly results coincided with the 3D Colho mesophase arrangement (with comparable lattice parameter of 3.15 nm). Figure 8 displays the STM images and the selfassembly model of 7f. The molecules of 7f arrange in row periodically and form dimers on the liquid– HOPG interface, with the cell lattice constants of a = 1.7 and b = 6.3 nm, and θ = 82°. The dimeric row arrangement of 7f resulted in by the strong interaction between the alkyl chains. The alkyl chain interdigitating of the neighbouring molecules occurred on the graphite surface as 7f possesses two different kinds of alkyl chain of C10 and

(b)

(c)

a

a

θ

θ

5 nm

10 nm

Figure 7. (colour online) STM images of 7c and the self-assembly model. A unit cell for 7c is outlined with the parameters of a = 2.6 ± 0.1 nm, θ = 120° ± 2°. (a) Large-scale STM image (51 nm × 51 nm) of a self-assembled monolayer of 7c on an HOPG surface. The imaging conditions: Itip = 389 pA, Vbias = 480 mV. (b) High-resolution STM image (15 nm x 15 nm) of the self-assembled 7c. The imaging conditions: Itip = 358 pA, Vbias = 489 mV. (c) Structure model for the self-assembly 7c.

(a)

(b) a )θ

(c) b

b a 25 nm

)θ

5 nm

Figure 8. (colour online) STM imagines of 7f and the self-assembly model. A unit cell for 7f is outlined with the parameters of a = 1.7 ± 0.1 nm, b = 6.3 ± 0.1 nm, θ = 82° ± 3°. (a) Large-scale STM image (120 nm × 120 nm) of a self-assembled monolayer of 7f on an HOPG surface. The imaging conditions: Itip = 283 pA, Vbias = 580 mV. (b) High-resolution STM image (26 nm × 26 nm) of 7f self-assembly. The imaging conditions: Itip = 342 pA, Vbias = 675 mV. (c) Structure model for 7f self-assembly.


Liquid Crystals C16. The 2D monolayer structure of 7f on HOPG is different from its 3D Colho mesophase structure. Summarising the influence of unsymmetrical alkyl chain substitution pattern on the self-assembly behaviours of the truxenone discogens, it is first noticed that the type of mesophase is not affected, but the phase transition temperatures and mesophase ranges are varied obviously. The strong π–π intermolecular interactions dominate the 3D selfassembly of the Colho mesophase arrangement, and the truxenone cores are rotating fast around the columnar axis while the peripheral chains are in the liquid-like molten state. However, for the 2D monolayer molecular self-assembly, the π–π interaction of the aromatic core and the van der Waals interaction of the alkyl chains with graphite are strong and anchor the discotic molecules on the surface of HOPG, so the influence of alkyl chain length difference and the unsymmetrical substitution pattern is more obvious and the 2D molecular self-assembly pattern is changed.

Conclusion In conclusion, six new 2,3,7,8,12,13-hexakis(alkoxy) truxenone discogens with two different peripheral alkyl chain substitution patterns have been synthesised, and they have shown only one Colho mesophase with very broad mesophase ranges including room temperature. The change of the alkyl chain substitution pattern on the truxeneone core has different impacts on the 3D self-organisation property of columnar mesophase and the 2D selfassembly behaviour of STM: all compounds exhibit only one 3D Colho mesophase, however at least two different 2D self-assembly monolayer structures. We anticipate that this phenomenon exists in the other discotic systems, and hope to make this discovery to be used for the 3D mesophase controlling and performance improvement of the DLC electronic devices.

Funding The research was supported by the National Natural Science Foundation of China (NSFC) [grant number 51273133], [grant number 51073112], [grant number 50973076].

Supplemental data The experimental; synthesis and characterisations of the intermediates and target compounds; 1H NMR and 13C NMR spectra; The HOMO and LUMO of the hexakis (methoxy)truxenone. Supplemental data for this article can be accessed here.

1159

References [1] Kumar S. Chemistry of discotic liquid crystals: from monomers to polymers. Boca Raton (FL): Taylor & Francis; 2011. [2] Pal SK, Setia S, Avinash BS, Kumar S. Triphenylenebased discotic liquid crystals: recent advances. Liq Cryst. 2013;40:1769–1816. doi:10.1080/02678292.2013. 854418 [3] Bushby RJ, Kawata K. Liquid crystals that affected the world: discotic liquid crystals. Liq Cryst. 2011;38:1415–1426. doi:10.1080/02678292.2011.603262 [4] Laschat S, Baro A, Steinke N, Giesselmann F, Hägele 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. doi:10.1002/anie.200604203 [5] Sergeyev S, Pisula W, Geerts YH. Discotic liquid crystals: a new generation of organic semiconductors. Chem Soc Rev. 2007;36:1902–1929. doi:10.1039/ b417320c [6] Shimizu Y, Oikawa K, Nakayama K, Guillon D. Mesophase semiconductors in field effect transistors. J Mater Chem. 2007;17:4223–4229. doi:10.1039/ b705534j [7] Funahashi M. Development of liquid-crystalline semiconductors with high carrier mobilities and their application to thin-film transistors. Polym J. 2009; 41:459–469. doi:10.1295/polymj.PJ2008324 [8] Pisula W, Zorn M, Chang JY, Mullen K, Zentel R. Liquid crystalline ordering and charge transport in semiconducting materials. Macromol Rapid Commun. 2009;30:1179–1202. doi:10.1002/marc. 200900251 [9] Kato T, Yasuda T, Kamikawa Y, Yoshio M. Selfassembly of functional columnar liquid crystals. Chem Commun. 2009;729–739. doi:10.1039/B816624B [10] Kaafarani BR. Discotic liquid crystals for optoelectronic applications. Chem Mater. 2011;23:378– 396. doi:10.1021/cm102117c [11] Bushby RJ, Lozman OR. Discotic liquid crystals 25 years on. Curr Opin Colloid Interface Sci. 2002;7:343– 354. doi:10.1016/S1359-0294(02)00085-7 [12] Bushby RJ, Lozman OR. Photoconducting liquid crystals. Curr Opin Solid State Mater Sci. 2002;6:569–578. doi:10.1016/S1359-0286(03)00007-X [13] Adam D, Schuhmacher P, Simmerer J, Häussling L, Siemensmeyer K, Etzbachi KH, Ringsdorf H, Haarer D. Fast photoconduction in the highly ordered columnar phase of a discotic liquid crystal. Nature. 1994;371:141–143. doi:10.1038/371141a0 [14] Feng X, Marcon V, Pisula W, Hansen MR, Kirkpatrick J, Grozema F, Andrienko D, Kremer K, Müllen K. Towards high charge-carrier mobilities by rational design of the shape and periphery of discotics. Nat Mater. 2009;8:421–426. doi:10.1038/nmat2427 [15] Demenev A, Eichhorn SH, Taerum T, Perepichka DF, Patwardhan S, Grozema FC, Siebbeles LDA, Klenkler R. Quasi temperature independent electron mobility in hexagonal columnar mesophases of an H-bonded benzotristhiophene derivative. Chem Mater. 2010; 22:1420–1428. doi:10.1021/cm902453z [16] Chen S, Raad FS, Ahmida M, Kaafarani BR, Eichhorn SH. Columnar mesomorphism of fluorescent board-shaped quinoxalinophenanthrophenazine

1160

[17]

[18]

[19]


[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

P. Ruan et al.

derivatives with donor-acceptor structure. Org Lett. 2013;15:558–561. doi:10.1021/ol303375x García-Frutos EM, Pandey UK, Termine R, Omenat A, Barberá J, Serrano JL, Golemme A, Gómez-Lor B. High charge mobility in discotic liquid-crystalline triindoles: just a core business? Angew Chem Int Ed. 2011;50:7399–7402. doi:10.1002/anie.201005820 Jankowiak A, Pociecha D, Szczytko J, Monobe H, Kaszyński P. Photoconductive liquid-crystalline derivatives of 6-oxoverdazyl. J Am Chem Soc. 2012; 134:2465–2468. doi:10.1021/ja209467h Jankowiak A, Pociecha D, Monobe H, Szczytko J, Kaszyński P. Thermochromic discotic 6-oxoverdazyls. Chem Commun. 2012;48:7064–7066. doi:10.1039/ c2cc33051b Nekelson F, Monobe H, Shiro M, Shimizu Y. Liquid crystalline and charge transport properties of doubledecker cerium phthalocyanine complexes. J Mater Chem. 2007;17:2607–2615. doi:10.1039/b616848p Sienkowska MJ, Monobe H, Kaszynski P, Shimizu Y. Photoconductivity of liquid crystalline derivatives of pyrene and carbazole. J Mater Chem. 2007;17:1392– 1398. doi:10.1039/b612253a Yasuda T, Shimizu T, Liu F, Ungar G, Kato T. Electro-functional octupolar π-conjugated columnar liquid crystals. J Am Chem Soc. 2011;133:13437– 13444. doi:10.1021/ja2035255 Schmidt-Mende L, Fechtenkotter A, Mullen K, Moons E, Friend RH, MacKenzie JD. Self-organized discotic liquid crystals for high-efficiency organic photovoltaics. Science. 2001;293:1119–1122. doi:10.1126/ science.293.5532.1119 Kang SJ, Ahn S, Kim JB, Schenck C, Hiszpanski AM, Oh S, Schiros T, Loo Y, Nuckolls C. Using selforganization to control morphology in molecular photovoltaics. J Am Chem Soc. 2013;135:2207–2212. doi:10.1021/ja308628z Hori T, Miyake Y, Yamasaki N, Yoshida H, Fujii A, Shimizu Y, Ozaki M. Solution processable organic solar cell based on bulk heterojunction utilizing phthalocyanine derivative. Appl Phys Express. 2010;3:101602–101603. doi:10.1143/APEX.3.101602 Hassheider T, Benning SA, Kitzerow HS, Achard MF, Bock H. Color-tuned electroluminescence from columnar liquid crystalline alkyl arenecarboxylates. Angew Chem Int Ed. 2001;40:2060–2063. doi:10.1002/1521-3773(20010601)40:113.0.CO;2-H Diring S, Camerel F, Donnio B, Dintzer T, Toffanin S, Capelli R, Muccini M, Ziessel R. Luminescent ethynylpyrene liquid crystals and gels for optoelectronic devices. J Am Chem Soc. 2009;131:18177–18185. doi:10.1021/ja908061q Boden N, Bushby RJ, Clements J, Movaghar B. Device applications of charge transport in discotic liquid crystals. J Mater Chem. 1999;9:2081–2086. doi:10.1039/a903005k Bhalla V, Singh H, Kumar M, Prasad SK. Triazolemodified triphenylene derivative: self-assembly and sensing applications. Langmuir. 2011;27:15275–15281. doi:10.1021/la203774p Bhalla V, Gupta A, Kumar M, Rao DSS, Prasad SK. Self-assembled pentacenequinone derivative for trace detection of picric acid. ACS Appl Mater Interfaces. 2013;5:672–679. doi:10.1021/am302132h

[31] Bayn A, Feng X, Müllen K, Haick H. Field effect transistors based on polycyclic aromatic hydrocarbons for the detection and classification of volatile organic compounds. ACS Appl Mater Interfaces. 2013;5:3431– 3440. doi:10.1021/am4005144 [32] Zilberman Y, Tisch U, Pisula W, Feng X, Müllen K, Haick H. Spongelike structures of hexa-peri-hexabenzocoronene derivatives enhance the sensitivity of chemiresistive carbon nanotubes to nonpolar volatile organic compounds of cancer. Langmuir. 2009;25: 5411–5416. doi:10.1021/la8042928 [33] Destrade C, Gasparoux H, Babeau A, Tinh NH, Malthete J. Truxene derivatives: a new family of disclike liquid crystals with an inverted nematic-columnar sequence. Mol Cryst Liq Cryst. 1981;67:37–47. doi:10.1080/00268948108070873 [34] Foucher P, Destrade C, Tinh NH, Melthete J, Levelut AM. Hexaalkoxytruxenes, a new series of disc-like mesogens. Mol Cryst Liq Cryst. 1984;108:219–229. doi:10.1080/00268948408078675 [35] Tinh NH, Foucher P, Destrade C, Levelut AM, Malthete J. Reentrant mesophases in disc-like liquid crystals. Mol Cryst Liq Cryst. 1984;111:277–292. doi:10.1080/00268948408072438 [36] Warmerdam TW, Nolte RJM, Drenth W, Van Miltenburg JC, Frenkel D, Zijlstra RJJ. Discotic liquid crystals. Physical parameters of some 2,3,7,8,12,13hexa(alkanoyloxy)truxenes. Observation of a reentrant isotropic phase in a pure disc-like mesogen. Liq Cryst. 1988;3:1087–1104. doi:10.1080/ 02678298808086564 [37] Li LL, Hu P, Wang BQ, Yu WH, Shimizu Y, Zhao KQ. Synthesis and mesomorphism of ether–ester mixed tail c3-symmetrical truxene discotic liquid crystals. Liq Cryst. 2010;37:499–506. doi:10.1080/ 02678290903215337 [38] Gomez-Esteban S, Pezella M, Domingo A, Hennrich G, Gómez-Lor B. Solvent-dependent truxene-based nanostructures. Chem Eur J. 2013;19:16080–16086. doi:10.1002/chem.201301069 [39] Isoda K, Yasuda T, Kato T. Truxene-based columnar liquid crystals: self-assembled structures and electroactive properties. Chem Asian J. 2009;4:1619–1625. doi:10.1002/asia.200900038 [40] Zhao KQ, Chen C, Monobe H, Hu P, Wang BQ, Shimizu Y. Three-chain truxene discotic liquid crystal showing high charged carrier mobility. Chem Commun. 2011;47:6290–6292. doi:10.1039/c1cc10299k [41] Monobe H, Chen C, Zhao KQ, Hu P, Miyake Y, Fujii A, Ozaki M, Shimizu Y. Bipolar carrier transport in tri-substituted octyloxy-truxene DLC. Mol Cryst Liq Cryst. 2011;545:149/[1373]–155/[1379]. doi:10.1080/ 15421406.2011.568891 [42] Ni HL, Monobe H, Hu P, Wang BQ, Shimizu Y, Zhao KQ. Truxene discotic liquid crystals with two different ring substituents: synthesis, mesomorphism and high charged carrier mobility. Liq Cryst. 2013;40:411–420. doi:10.1080/02678292.2012.755224 [43] Sun Y, Xiao K, Liu Y, Wang J, Pei J, Yu G, Zhu D. Oligothiophene-functionalized truxene: star-shaped compounds for organic field-effect transistors. Adv Funct Mater. 2005;15:818–822. doi:10.1002/adfm.200400380 [44] Bai C, Liu M. From chemistry to nanoscience: not just a matter of size. Angew Chem Int Ed. 2013;52:2678– 2683. doi:10.1002/anie.201210058


Liquid Crystals [45] Katsonis N, Marchenko A, Fichou D. Substrateinduced pairing in 2,3,6,7,10,11-hexakis-undecalkoxytriphenylene self-assembled monolayers on au(111). J Am Chem Soc. 2003;125:13682–13683. doi:10.1021/ ja0375737 [46] Wu P, Zeng Q, Xu S, Wang C, Yin S, Bai CL. Molecular superlattices induced by alkyl substitutions in self-assembled triphenylene monolayers. Chem Phys Chem. 2001;2:750–754. doi:10.1002/1439-7641 (20011217)2:123.0.CO;2-9 [47] Ma XJ, Yang YL, Deng K, Zeng QD, Wang C, Zhao KQ, Hu P, Wang BQ. Identification of a peripheral substitution symmetry effect in self-assembled architectures. Chem Phys Chem. 2007;8:2615–2620. doi:10.1002/cphc.200700424 [48] Ma X, Yang Y, Deng K, Zeng Q, Zhao KQ, Wang C, Bai C. Molecular miscibility characteristics of selfassembled 2D molecular architectures. J Mater Chem. 2008;18:2074–2081. doi:10.1039/b713426f [49] Zhang X, Wang H, Wang S, Shen Y, Yang Y, Deng K, Zhao KQ, Zeng Q, Wang C. Triphenylene substituted pyrene derivative: synthesis and single molecule investigation. J Phys Chem C. 2013;117:307–312. doi:10.1021/jp3095616 [50] Wang J, Yan J, Ding L, Ma Y, Pei J. One-dimensional microwires formed by the co-assembly of complementary aromatic donors and acceptors. Adv Funct Mater. 2009;19:1746–1752. doi:10.1002/adfm.200900093 [51] Luo J, Chen L, Wang JY, Lei T, Li LY, Pei J, Song YA. A co-assembly system of an aromatic donor and acceptor: charge transfer, electric bistability and photoconductivity. New J Chem. 2010;34:2530–2533. doi:10.1039/c0nj00536c [52] Wang JY, Yang J, Li Z, Han JM, Ma Y, Bian J, Pei J. Isomeric effect on microscale self-assembly:

[53]

[54]

[55]

[56]

[57]

[58]

1161

interplay between molecular property and solvent polarity in the formation of 1D n-type microbelts. Chem Eur J. 2008;14:7760–7764. doi:10.1002/ chem.200800396 Yang ZY, Tao Y, Chen T, Yan HJ, Wang ZX. Hydrogen bonding network of truxenone on a graphite surface studied with scanning tunneling microscopy and theoretical computation. Phys Chem Chem Phys. 2013;15:2105–2108. doi:10.1039/ c2cp42828h Chen F, Hu Z, Ji Y, Zhao A, Wang B, Yang J, Hou JG. Interactions in different domains of truxenone supramolecular assembly on Au(111). Phys Chem Chem Phys. 2012;14:3980–3986. doi:10.1039/ c2cp23190e Liu J, Zhang X, Yan HJ, Wang D, Wang JY, Pei J, Wan LJ. Solvent-controlled 2D host−guest (2,7,12-trihexyloxytruxene/coronene) molecular nanostructures at organic liquid/solid interface investigated by scanning tunneling microscopy. Langmuir. 2010;26:8195– 8200. doi:10.1021/la904568q Liu J, Wang D, Wang JY, Pei J, Wan LJ. Scanning tunneling microscopy investigation of copper phthalocyanine and truxenone derivative binary superstructures on graphite. Chem Asian J. 2011;6:424–429. doi:10.1002/asia.201000628 Liu J, Zhang X, Wang D, Wang JY, Pei J, Stang PJ, Wan LJ. Shape-persistent two-component 2D networks with atomic-size tunability. Chem Asian J. 2011;6:2426–2430. doi:10.1002/asia.201100431 Liu J, Chen T, Deng X, Wang D, Pei J, Wan LJ. Chiral hierarchical molecular nanostructures on two-dimensional surface by controllable trinary selfassembly. J Am Chem Soc. 2011;133:21010–21015. doi:10.1021/ja209469d