Article pubs.acs.org/JPCC
Angle-Dependent Photoluminescence Spectroscopy of SolutionProcessed Organic Semiconducting Nanobelts Mao Wang,† Yi Gong,† Francesc Alzina,‡ Clivia M. Sotomayor Torres,‡ Hongxiang Li,§ Zhiliang Zhang,† and Jianying He*,† †
NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim 7491, Norway ‡ Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC, Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, Barcelona 08193, Spain § Key Laboratory of Synthetic and Self-assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, CAS, Shanghai 200032, China S Supporting Information *
ABSTRACT: We report an anomalous anisotropy in photoluminescence (PL) from crystalline nanobelt of an organic small-molecule semiconductor, 6,13-dichloropentacene (DCP). Large-area well-aligned DCP nanobelt arrays are readily formed by self-assembly through solution method utilizing the strong anisotropic interactions between molecules. The absorption spectrum of the arrays suggests the formation of both intramolecular exciton and intermolecular exciton. However, the results of angle-dependent PL spectroscopy indicate that the PL arises only from the relaxation of intramolecular exciton, which has an optical transition dipole moment with an angle of 115° with the long-axis of the nanobelts. The angular dependence of PL signals follows a quartic rule (IPL(θ) ∝ cos4(θ − 115)) and agrees well with the optical selection rule of individual DCP molecules. The measured polarization ratio ρ from the individual nanobelts is on average 0.91 ± 0.02, superior to that of prior-art organic semiconductors. These results provide new insights into exciton behavior in 1D π−π stacking organic semiconductors and demonstrate DCP’s great potential in the photodetectors and optical switches for large-scale organic optoelectronics.
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selectivity and sensitivity in response to polarized light.7,13 Compared with numerous studies on the electrical properties, less effort has been made on the optical properties from the 1D π−π stacking system.8 In our previous reports, a new pentacene derivative with 6,13 positions functionalized with chlorine groups (6,13-dichloropentacene: DCP, molecular structure in Figure 1a) is found to exhibit excellent semiconducting properties.14,15 The introduction of chlorine groups changes the 2D herringbone structure into 1D slipped face-to-face arrangement at aggregation state and leads to the enhancement of charge diffusion along the π−π stacking direction.15,16 The hole mobility of the field-effect transistor based on DCP nanoribbon (obtained by physical vapor transport (PVT) method) reaches ∼9.0 cm2V−1 s−1 along crystal growth direction (π−π stacking direction).14 Besides the enhanced uniaxial electrical performance, the anisotropic optical properties are anticipated because of the strong π−π interactions along quasi-1D cofacial stacking orientation.
INTRODUCTION Organic crystalline semiconductors have drawn enormous attention for their promising application as various organic optoelectronics as well as the intriguing physical characteristics related to exciton formation, transport, and dissipation.1−3 The bulk properties of organic molecular crystals are determined by the interplay between the intrinsic electronic properties of molecule units and the intermolecular interactions between these units.4,5 In particular, the self-assembly of organic semiconducting molecules with large π-conjugated structures often leads to the formation of well-defined 1D micro/ nanostructures driven by the columnar π−π stacking between the molecular cores.6,7 The electronic delocalization and energy transfer caused by the highly anisotropic interactions in these systems often result in the anisotropic electrical and optical properties.8,9 Taking advantages of the 1D enhanced exciton and charge diffusion along the π−π stacking direction, these organic semiconducting micro/nanostructures show promising potential for flexible optoelectronics with performance enhancement and size miniaturization.10−12 The uniaxial semiconducting properties coupling to highly anisotropic optical properties will lead to a new generation of optical sensors, switches, and other optoelectronics with better © XXXX American Chemical Society
Received: March 28, 2017 Revised: May 21, 2017 Published: May 23, 2017 A
DOI: 10.1021/acs.jpcc.7b02958 J. Phys. Chem. C XXXX, XXX, XXX−XXX
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The Journal of Physical Chemistry C
Figure 1. (a) Molecular structure of 6,13-dichloropentacene. (b) Optical microscopic image of DCP nanobelt arrays. The scale bar length is 20 μm. (c) Thin-film XRD spectrum of DCP nanobelt arrays. (d) Unit cell of DCP single crystals with (020) surface highlighted. (e) AFM image (left) and its 3D view (right) of the top surface of individual DCP nanobelt. The scale bar length is 200 nm.
emission spectra were measured with HITACHI U-3900 UV− vis spectrophotometer and HITACHI F-2700 FL spectrophotometer (excitation wavelength: 532 nm), respectively. For nanobelt arrays on quartz, the absorption spectra were taken with the HITACHI U-3900 UV−vis spectrophotometer. Optical polarization microscopy was performed on an Olympus BX 51 microscope with two crossed polarizers. Thin-film X-ray diffraction (XRD) measurements were carried out in the reflection mode using Bruker D8 Advance DaVinci1-diffractometer with monochromatic Cu Kα1 as radiation source. The surface morphology was investigated with AFM (Veeco) under ambient condition. Angle-Dependent PL Characterization. The HORIBA T64000 spectrometer system with a liquid-nitrogen cooled CCD detector served as the instrument for the polarizationrelated PL measurements of DCP nanobelts. The PL spectrum of DCP is very sensitive to laser exposure. To compare with the absorption spectrum of DCP nanobelt arrays obtained at r.t., we measure the PL spectrum under vacuum at r.t. with 3s exposure time for the whole range from 550 to 800 nm. For angle-dependent PL, the sample was placed in a vacuumed (∼7 × 10−3 mbar) cryostat that was cooled by a closed-cycle liquidnitrogen system (∼77 K). A 532 nm diode laser was used as the excitation source. A rotatable half-wave plate was inserted between the laser source and samples to adjust the polarization of incident light to the desired angle in the horizontal plane.19,20 The PL emission from the sample was collected by the objective lens with backscattering mode and then passed again through the same half-wave plate where the polarization was counter-rotated by the same angle. The analyzer, installed before the entrance slit and monochromator, was fixed to only pass the E-field component of light which was parallel to the incident laser. By using this configuration, the polarization of the emitted light entering the spectrometer was always kept the same, thus avoiding the polarization effects from the grating. The laser was focused on the samples with a spot of diameter ∼2 μm through a long working distance microscope objective
Herein we report a systematic investigation on the optical properties of the well-aligned DCP crystalline nanobelts obtained with optimized solution processing methods (droplet-pinned crystallization).17 The absorption spectrum clearly exhibits the coexistence of intermolecular exciton (dimer or excimer) and intramolecular exciton, which is common for nanostructures with strong π−π interaction between adjacent molecules.18 The angle-dependent PL spectra show a quartic pattern (I(θ) ∝ cos4(θ − 115)) when changing the polarization angle θ. (θ is the angle between the polarization direction of incident light and the long-axis of DCP nanobelt.) Moreover, the PL signal reaches the maximum when the polarization angle matches the direction of optical transition dipole moment of individual DCP molecules and therefore verifies that the PL emission is only related to the relaxation of intramolecular exciton despite the strong π−π interaction of adjacent molecules.
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MATERIALS AND METHODS Nanobelt Arrays Preparation and Characterization. DCP was synthesized following the same method described in our previous work.15 The SiO2/Si and quartz substrates were cleaned in hot Piranha solution to remove the organic contamination, then cleaned with deionized water, acetone, and isopropyl alcohol in ultrasound, respectively, and at last dried with N2 flow. Before deposition, the substrates were further processed in oxygen plasma for 3 min. Solutions of DCP in o-dichlorobenzene at a concentration of ∼1.0 mg/mL were dropcast onto the substrate on a hot plate held at ∼140 °C. A piece of silicon wafer was used as the pinner to steady the receding line. After deposition, samples were covered with a Petri dish to control solvent evaporation. Within 2 to 3 min, large-area well-aligned DCP nanobelts with controlled growth direction appeared, followed by an annealing procedure at 150 °C for 10 min. Optical Properties and Structure Characterization. For dilute DCP solution in chlorobenzene, the absorption and B
DOI: 10.1021/acs.jpcc.7b02958 J. Phys. Chem. C XXXX, XXX, XXX−XXX
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Figure 2. (a) Absorption (Abs) spectra of DCP in dilute chlorobenzene solution (0.1 mg/mL) and solution-processed DCP nanobelt arrays. (b) Molecular arrangement on crystallographic (a, c) plane with optical transition dipole moments of intermolecular and intramolecular excitons. (c) Fluorescence of DCP in dilute chlorobenzene solution (0.1 mg/mL) and the PL spectrum of individual DCP nanobelt. Absorption spectrum of DCP arrays is included to clearly show the overlap between A0′ and B1′. The excitation wavelength is 532 nm.
of the b axis (18.72 Å) of the DCP unit cell (Figure 1d). It indicates that DCP molecules assemble themselves in the ordered manner with b axis perpendicular and (a, c) plane parallel to the substrate surface. Moreover, the atomic force microscope (AFM) images (Figure 1e) show the terrace morphology of the nanobelts top surface with a step distance of 9.3 ± 0.5 Å (equal to single molecular layer), which is close to the calculated d spacing from the XRD results, and further prove DCP’s well-organized structure. The high quality of obtained crystalline structures, as well as the convenient solution-processed method, indicates DCP’s promising application for the up-scale production of optoelectronics. Optical Properties. The optical properties of organic crystals, such as refractive index, absorption, and PL properties, strongly depend on the molecular packing and the orientation of the molecular optical transition dipole moment.24,25 Polarized optical microscopy (POM) is employed to clarify the optical anisotropy of DCP nanobelts, as shown in the Supplementary Figure S1. Clear birefringence phenomenon is found when rotating under the crossed polarizers as the nanobelt arrays change from bright to dark alternatively. This is caused by the anisotropic refraction index along different crystallographic axes arising from the well-organized 1D cofacial arrangement of DCP molecules. All of the nanobelts in the image follow the same changing behavior, indicating that the DCP molecules share the same packing pattern through the whole nanobelt arrays. Figure 2a displays the normalized UV absorption and emission spectra of DCP solution and nanobelt arrays. The absorption spectrum of DCP in chlorobenzene (regarded as the state of individual DCP molecules) exhibits three well-resolved bands at 610, 562, and 523 nm, which correspond to the vibronic S1 ← S0 0−0 (labeled as A1), S1 ← S0 0−1 (A2), and S1 ← S0 0−2 (A3) transitions, respectively. The associated vibrational energy (ω0) between A1 and A2 (A2 and A3) is ∼1333 cm−1 (0.17 eV) which arises from the ring-breathing vibrations from carbon−carbon conjugated skeleton.26 For the absorption spectrum of DCP in the aggregation state (Figure 2a), a new bathochromic-shifted absorption peak appears at 650 nm (A0′), together with two overlapped peaks at 601 (A1′) and 566 nm (A 2 ′). Previous studies on 6,13-bis(triethylsilylethynyl)pentacene (TES-PEN) possessing a similar chromophore (five conjugated benzene rings) with DCP have assigned such an emergent bathochromic-shifted absorption peak as the signature for induced delocalized intermolecular exciton because its optical transition dipole moment is oriented close to the pentacene−pentacene core-stacking direction.27 In DCP crystals, the intermolecular distance between adjacent
(50× and NA. 0.55). The light intensity on the sample surface was kept lower than 0.7 mW (checked by a photodiode) to avoid potential sample damage. For one set of data, the laser spot was fixed at the same place for the different polarization angles. Five sets of data were collected from different nanobelts, and all of the angle-dependent PL showed the same pattern as described in the main text. A detailed schematic setup is shown in Scheme S1. Confocal Fluorescence Microscopy. Fluorescence images at different polarization angles were obtained by twophoton excitation with a LSM 800 confocal scanning microscope (Zeiss) in a reflection mode and with a 40× objective (NA. 0.8). The excitation laser was a pulsed (80 MHz) TiSp-laser MIRA-900-F from Coherent. The excitation wavelength was 780 nm. A rotatable half-wave plate was inserted between the laser source and objective to adjust the incident polarization angle. The emitted fluorescence signals from the sample were directed through beam splitter and bandpass filters (569−676 nm) to the detector.
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RESULTS AND DISCUSSION Controlled Nanobelt Arrays Formation. Solution processability of organic semiconductor has always been regarded as the key character for achieving low-cost manufacturing of large-area and flexible optoelectronic.21 The chlorine groups at 6,13 positions improve pentacene core’s solubility in organic solvents, remarkably enhance DCP’s stability against oxidation, and thus enable it with various solution processing methods.15 DCP tends to form 1D nanostructures along the π−π stacking direction owning to the strong face-to-face interaction between the planar cores. We obtain large-area well-aligned DCP nanobelt arrays by maintaining a steady receding line at the solution/substrate/ air three-phase contact interface with droplet-pinned crystallization method.17,22 Continuous, uniform, and well-defined nanobelt arrays are formed on the plasma-processed SiO2/Si substrate (Figure 1b and Figure S1). The whole process takes 4 μm), thus enabling us to study the emission from single DCP nanobelt. As shown in Figure 4b,d, almost no PL signal is detected when polarization angle θ equals 0°, and as θ approaches ∼115°, the PL signal reaches the maximum. The PL intensities change with polarization angle as IPL(θ) ∝ cos4(θ − 115). The maximum/minimum intensity ratio (Imax/Imin) is as high as ∼22 ± 5, and the polarization ratio ρPL=(I115 − I0)/(I115 + I0) is extremely high over most of the energy range of the PL peaks (on average 0.91 ± 0.02). As far as we know, this value is one of the highest polarization ratio reported for organic smallmolecule semiconductors, which is comparable to that obtained for the highly PL polarized single-crystalline InP nanowires.13 The PL properties of organic semiconducting crystals are decided by the microscopic arrangement of molecules and the interactions between each other.24,32,33 With our experimental configuration (Figure 4a), the incident laser illuminates perpendicularly on the (a, c) plane of an individual nanobelt. It is found that the short axes (same direction as the optical transition dipole moment) of both DCP molecules (M1 and M2) from the same unit cell are parallel to each other and form the same angle of ∼115° with the crystallographic a axis (Figure 4c). In any other configurations, the direction of the two optical transition dipole moments from M1 and M2 would be different and result in complex angular-dependent optical properties. This coincidence allows us to study the correlation of angle-dependent PL and the transition dipole moment of DCP molecules in the nanobelts. Assuming that the PL emission arises from the individual DCP molecules, the intramolecular dipole moment forms an angle of ∼115° with the long axis of nanobelts. When linearly polarized light interacts with the dipole transition moment of the individual D
DOI: 10.1021/acs.jpcc.7b02958 J. Phys. Chem. C XXXX, XXX, XXX−XXX
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Figure 4. (a) Schematic of the PL measurement configuration. θ is the polarization angle and φ is the angle between optical dipole moment and the long axis of nanobelt. (b) PL spectra of different polarization angles. (c) Schematic showing the interaction of laser with DCP molecules in the nanobelts, where the red arrows indicate the optical transition dipole moment of the molecule M1 and M2 in the same unit cell. (d) Angulardependent PL of intensity of peak at ∼656 nm (1.89 eV) in Supporting Figure S2 and the fitting lines of the quartic function.
ization-sensitive nanoscale photodetectors and optical switches for large-scale flexible organic electronics. Beyond that, because the 1D π−π stacking arrangement is ubiquitous for organic semiconductors, our work opens an avenue for the exploration of extraordinary optical and optoelectrical properties of a family of organic semiconducting materials.
molecules, both the absorption and emission rates share the same orientation-dependent rule: I(θ) ∝ cos2(θ − 115). Therefore, the resultant angular PL pattern can be fit by a cosine function raised to the fourth power, which agrees well with our experimental findings (Figure 4d). The angledependent PL unambiguously verifies that the emission arises merely from the intramolecular exciton. As for the intermolecular exciton, it may dissipate in other nonemissive ways, such as internal conversion, intersystem crossing, and thermal dissipation. The acenes and their derivatives are the typical systems for which singlet fission (SF) occurs because of the small exchange energy between singlet excitation state and triplet excitation state,34,35 so one of the possible relaxation paths for the intermolecular exciton in DCP nanobelts is that the singlet state of one excited dimer quickly splits into two excited triplets, which are spin-forbidden from emitting light. However, further experiments and calculations need to be conducted to verify this assumption.
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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.jpcc.7b02958. Detailed description of the angle-dependent PL setup. Polarized optical microscope of DCP nanobelt arrays. The PL spectrum (deconvoluted with Gaussian method) from individual DCP nanobelt. (PDF)
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AUTHOR INFORMATION
Corresponding Author
CONCLUSIONS We report the anisotropic optical properties of solutionprocessed DCP nanobelt arrays directed by the strong 1D π−π coupling between adjacent molecular cores. With angledependent PL spectroscopy, we demonstrate that the PL spectra of the DCP nanobelts arise only from the relaxation of intramolecular exciton despite the coexistence of intermolecular exciton. On average, the polarization ratio reaches 0.91 ± 0.02, which is among the highest range for organic semiconducting structures. This intrinsic giant anisotropy as well as the convenient solution-processability for large-area well-aligned nanobelt arrays demonstrate DCP’s great potential in polar-
*E-mail:
[email protected]. ORCID
Clivia M. Sotomayor Torres: 0000-0001-9986-2716 Jianying He: 0000-0001-8485-7893 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is financially supported by NTNU, The Research Council of Norway, Det Norske Oljeselskap ASA and Wintershall Norge AS via WINPA project (Grant No. E
DOI: 10.1021/acs.jpcc.7b02958 J. Phys. Chem. C XXXX, XXX, XXX−XXX
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(19) Livneh, T.; Zhang, J.; Cheng, G.; Moskovits, M. Polarized Raman Scattering from Single GaN Nanowires. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 035320. (20) Duesberg, G. S.; Loa, I.; Burghard, M.; Syassen, K.; Roth, S. Polarized Raman Spectroscopy on Isolated Single-Wall Carbon Nanotubes. Phys. Rev. Lett. 2000, 85, 5436−5439. (21) Diao, Y.; Tee, B. C. K.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C. B.; Bao, Z. Solution Coating of Large-Area Organic Semiconductor Thin Films with Aligned Single-Crystalline Domains. Nat. Mater. 2013, 12, 665− 671. (22) Li, H.; Tee, B. C. K.; Giri, G.; Chung, J. W.; Lee, S. Y.; Bao, Z. High-Performance Transistors and Complementary Inverters Based on Solution-Grown Aligned Organic Single-Crystals. Adv. Mater. 2012, 24, 2588−2591. (23) Hatcher, P. V.; Reibenspies, J. H.; Haddon, R. C.; Li, D.; Lopez, N.; Chi, X. A Polymorph of the 6,13-Dichloropentacene Organic Semiconductor: Crystal Structure, Semiconductor Measurements and Band Structure Calculations. CrystEngComm 2015, 17, 4172−4178. (24) Bao, Q.; Goh, B. M.; Yan, B.; Yu, T.; Shen, Z.; Loh, K. P. Polarized Emission and Optical Waveguide in Crystalline Perylene Diimide Microwires. Adv. Mater. 2010, 22, 3661−3666. (25) James, D. T.; Kjellander, B. K. C.; Smaal, W. T. T.; Gelinck, G. H.; Combe, C.; McCulloch, I.; Wilson, R.; Burroughes, J. H.; Bradley, D. D. C.; Kim, J.-S. Thin-Film Morphology of Inkjet-Printed SingleDroplet Organic Transistors Using Polarized Raman Spectroscopy: Effect of Blending TIPS-Pentacene with Insulating Polymer. ACS Nano 2011, 5, 9824−9835. (26) Spano, F. C. The Spectral Signatures of Frenkel Polarons in Hand J-Aggregates. Acc. Chem. Res. 2010, 43, 429−439. (27) James, D. T.; Frost, J. M.; Wade, J.; Nelson, J.; Kim, J.-S. Controlling Microstructure of Pentacene Derivatives by Solution Processing: Impact of Structural Anisotropy on Optoelectronic Properties. ACS Nano 2013, 7, 7983−7991. (28) Ostroverkhova, O. Organic Optoelectronic Materials: Mechanisms and Applications. Chem. Rev. 2016, 116, 13279−13412. (29) Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J.-L. Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926−952. (30) Tiago, M. L.; Northrup, J. E.; Louie, S. G. Ab initio Calculation of the Electronic and Optical Properties of Solid Pentacene. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 67, 115212. (31) Wong, C. Y.; Cotts, B. L.; Wu, H.; Ginsberg, N. S. Exciton Dynamics Reveal Aggregates with Intermolecular Order at Hidden Interfaces in Solution-Cast Organic Semiconducting Films. Nat. Commun. 2015, 6, 5946. (32) Huang, L.; Tam-Chang, S. W.; Seo, W.; Rove, K. Microfabrication of Anisotropic Organic Materials via Self-Organization of an Ionic Perylenemonoimide. Adv. Mater. 2007, 19, 4149−4152. (33) Huang, L.; Catalano, V. J.; Tam-Chang, S.-W. Anisotropic Fluorescent Materials via Self-Organization of Perylenedicarboximide. Chem. Commun. 2007, 2016−2018. (34) Wilson, M. W. B.; Rao, A.; Ehrler, B.; Friend, R. H. Singlet Exciton Fission in Polycrystalline Pentacene: From Photophysics toward Devices. Acc. Chem. Res. 2013, 46, 1330−1338. (35) Zimmerman, P. M.; Bell, F.; Casanova, D.; Head-Gordon, M. Mechanism for Singlet Fission in Pentacene and Tetracene: From Single Exciton to Two Triplets. J. Am. Chem. Soc. 2011, 133, 19944− 19952.
Nano2021 and Petromaks2 234626/O70). The Research Council of Norway is acknowledged for the support to the Norwegian Micro- and Nano-Fabrication Facility, NorFab (197411/V30).
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REFERENCES
(1) Anthony, J. E. Organic Electronics: Addressing Challenges. Nat. Mater. 2014, 13, 773−775. (2) Giri, G.; Verploegen, E.; Mannsfeld, S. C. B.; Atahan-Evrenk, S.; Kim, D. H.; Lee, S. Y.; Becerril, H. A.; Aspuru-Guzik, A.; Toney, M. F.; Bao, Z. Tuning Charge Transport in Solution-Sheared Organic Semiconductors Using Lattice Strain. Nature 2011, 480, 504−508. (3) Zhang, Y.; Dong, H.; Tang, Q.; Ferdous, S.; Liu, F.; Mannsfeld, S. C. B.; Hu, W.; Briseno, A. L. Organic Single-Crystalline p−n Junction Nanoribbons. J. Am. Chem. Soc. 2010, 132, 11580−11584. (4) Yang, J. L.; Yan, D. H.; Jones, T. S. Molecular Template Growth and Its Applications in Organic Electronics and Optoelectronics. Chem. Rev. 2015, 115, 5570−5603. (5) Mishra, A.; Bäuerle, P. Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology. Angew. Chem., Int. Ed. 2012, 51, 2020−2067. (6) Zheng, Y. Q.; Wang, J. Y.; Pei, J. One-Dimensional (1D) Micro/ Nanostructures of Organic Semiconductors for Field-Effect Transistors. Sci. China: Chem. 2015, 58, 937−946. (7) Min, S.-Y.; Kim, T.-S.; Lee, Y.; Cho, H.; Xu, W.; Lee, T.-W. Organic Nanowire Fabrication and Device Applications. Small 2015, 11, 45−62. (8) Kim, F. S.; Ren, G.; Jenekhe, S. A. One-Dimensional Nanostructures of π-Conjugated Molecular Systems: Assembly, Properties, and Applications from Photovoltaics, Sensors, and Nanophotonics to Nanoelectronics. Chem. Mater. 2011, 23, 682−732. (9) Che, Y.; Datar, A.; Yang, X.; Naddo, T.; Zhao, J.; Zang, L. Enhancing One-Dimensional Charge Transport through Intermolecular π-Electron Delocalization: Conductivity Improvement for Organic Nanobelts. J. Am. Chem. Soc. 2007, 129, 6354−6355. (10) Garcia-Frutos, E. M. Small Organic Single-Crystalline OneDimensional Micro- and Nanostructures for Miniaturized Devices. J. Mater. Chem. C 2013, 1, 3633−3645. (11) El Gemayel, M.; Treier, M.; Musumeci, C.; Li, C.; Müllen, K.; Samorì, P. Tuning the Photoresponse in Organic Field-Effect Transistors. J. Am. Chem. Soc. 2012, 134, 2429−2433. (12) Huo, N.; Yang, S.; Wei, Z.; Li, S.-S.; Xia, J.-B.; Li, J. Photoresponsive and Gas Sensing Field-Effect Transistors based on Multilayer WS2 Nanoflakes. Sci. Rep. 2015, 4, 5209. (13) Wang, J.; Gudiksen, M. S.; Duan, X.; Cui, Y.; Lieber, C. M. Highly Polarized Photoluminescence and Photodetection from Single Indium Phosphide Nanowires. Science 2001, 293, 1455−1457. (14) Wang, M.; Li, J.; Zhao, G.; Wu, Q.; Huang, Y.; Hu, W.; Gao, X.; Li, H.; Zhu, D. High-Performance Organic Field-Effect Transistors Based on Single and Large-Area Aligned Crystalline Microribbons of 6,13-Dichloropentacene. Adv. Mater. 2013, 25, 2229−2233. (15) Li, J.; Wang, M.; Ren, S.; Gao, X.; Hong, W.; Li, H.; Zhu, D. High Performance Organic Thin Film Transistor Based on Pentacene Derivative: 6,13-Dichloropentacene. J. Mater. Chem. 2012, 22, 10496− 10500. (16) Zhang, X.; Yang, X.; Geng, H.; Nan, G.; Sun, X.; Xi, J.; Xu, X. Theoretical Comparative Studies on Transport Properties of Pentacene, Pentathienoacene, and 6,13-Dichloropentacene. J. Comput. Chem. 2015, 36, 891−900. (17) Li, H.; Tee, B. C. K.; Cha, J. J.; Cui, Y.; Chung, J. W.; Lee, S. Y.; Bao, Z. High-Mobility Field-Effect Transistors from Large-Area Solution-Grown Aligned C60 Single Crystals. J. Am. Chem. Soc. 2012, 134, 2760−2765. (18) Datar, A.; Balakrishnan, K.; Yang, X.; Zuo, X.; Huang, J.; Oitker, R.; Yen, M.; Zhao, J.; Tiede, D. M.; Zang, L. Linearly Polarized Emission of an Organic Semiconductor Nanobelt. J. Phys. Chem. B 2006, 110, 12327−12332. F
DOI: 10.1021/acs.jpcc.7b02958 J. Phys. Chem. C XXXX, XXX, XXX−XXX
