Tetracene Hybrid Flowerlike

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Supramolecular Synthesis of Fullerene/Tetracene Hybrid Flowerlike Microstructures of Nanoplates via the Charge-Transfer Interactions Lang Wei,†,‡ Yishi Wu,† Lanfen Wang,† Hongbing Fu,*,† and Jiannian Yao† † ‡

Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 The Graduate University of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China

bS Supporting Information ABSTRACT: A supramolecular method had been developed for the fabrication of C60/tetracene hybrid flowerlike microstructures built of nanoplates. Sequential control of the nucleation and growth of tetracene and C60 components generated first disklike nanocrystals of tetracene about 5 nm in diameter, which then act as seeds for further growth of C60 molecules at its periphery driven by directional CT interactions. As a consequence, embedment of 5 nm tetracene disks in a polycrystalline C60 matrix gives rise to the composite structures of nanoplates, which can interconnect with each other and form complex 3D microspheres. The complete quenching of tetracene fluorescence suggested a highly efficient electron transfer process from tetracene to C60 in flowerlike microstructures. Upon heating to 330 °C, sublimation of tetracene components results in fcc C60 microstructures with the same shape and size as hybrid C60/tetracene microspheres. Moreover, thin films made of either C60/tetracene or fcc C60 flowerlike microstructures featured water-repellent superhydrophobicity with a water contact angle of 150.2 and 156.3°, respectively.

’ INTRODUCTION Fullerene (C60)-based materials have been a subject under intensive investigation in the past decades because of their potential applications in various devices, such as photovoltaic cells,1 field-effect transistors,2 and electrochemical sensors.3 The performances of these devices, particularly the bulk heterojunction (BHJ) solar cells comprising bicontinuous polymer donor and fullerene acceptor phases, depend sensitively on the size, morphology, and connection of C60 crystalline grains in the photoactive layer.4 Consequently, considerable effort has been dedicated to controlled fabrication of fullerene nano- and microstructures with well-defined sizes and shapes. So far, the morphological control and modulation of C60 nano- and microstructures has been achieved mainly via three strategies, that is, the solvent-dependent crystallization or precipitation,5,6 the supramolecular self-assembly,7 and the physical vapor deposition (PVD).8 For example, 1D nanowires9 and rods10 were formed upon crystallization induced by spontaneous solvent evaporation, whereas liquid liquid interface precipitation generated 1D whiskers6 and 2D hexagonal nanosheets.11 Recently, Choi and coworkers reported a highly selective synthesis of 2D disks on graphite substrate by using the PVD method.8 Furthermore, 3D flowerlike12 and 1D ribbon-like13 supramolecular assemblies were also prepared by using chemically modified C60 derivatives through amphiphilic and hydrogen-bonding interactions, respectively. Nonetheless, controlled fabrication of crystalline hybrid nano- and microstructures comprising C60 acceptor and molecular donor materials had been met with limited success.14 r 2011 American Chemical Society

Molecular donors, such as linear acenes,15 have been widely used in bilayer planar heterojunction solar cells,16 which are generally prepared by vacuum deposition because most highperformance molecular semiconductors are insoluble in common solvents. For example, Yang and coworkers reported a power conversion efficiency of 2.3% for C60/tetracene bilayer heterojunction solar cells.17 Because the exciton dissociation process is confined to the donor acceptor interfacial zone, the performances of bilayer heterojunctions are limited by the short exciton diffusion length (typically 10 20 nm) in organic semiconductors. In this regard, hybrid molecular BHJ structures, in which polydisperse polymers are replaced by soluble, conjugated molecules as donor materials have recently given rise to a burst of interest,18 however, remain a formidable task. Herein, we report a solution-based supramolecular synthesis of C60/tetracene hybrid flowerlike microstructures of nanoplates based on a hightemperature reprecipitation method. HRTEM and XRD results verify that flowerlike microstructures of nanoplates are actually nanocomposite materials with disklike tetracene nanocrystals of 5 10 nm in diameter embedded in a continuous polycrystalline matrix of fcc C60. A complete quenching of tetracene fluorescence was observed in hybrid flowerlike microstructures, suggesting a highly efficient electron transfer process from tetracene to C60 components. Upon heating to 330 °C, sublimation of Received: June 29, 2011 Revised: October 3, 2011 Published: October 04, 2011 21629

dx.doi.org/10.1021/jp206155q | J. Phys. Chem. C 2011, 115, 21629–21634

The Journal of Physical Chemistry C

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tetracene components left C60 microspheres with the fcc crystal structure retaining the same size and shape as those of hybrid flowerlike microstructures. Moreover, thin films made of either hybrid or fcc C60 flowerlike microstructures featured waterrepellent superhydrophobicity with a water contact angle of 150.2 and 156.3°, respectively. These results might be helpful for achieving rational design and synthesis of molecular BHJ structures.

’ EXPERIMENTAL SECTION Materials. Fullerene (C60, 99.5%) was obtained from Aldrich Chemical and was used directly without further purification. Tetracene was obtained from TCI and was used directly without further purification. 1,2,4-Trimethylbenzene (TMB) was purchased from ACROS. Ethanol was provided by the Beijing Chemical Agent China. Preparation. In a typical synthesis, 9 mg of C60 (0.0125 mmol), 2.5 mg of tetracene (0.011 mmol), and 2.5 mL of TMB were loaded into a reaction flask. The mixture was purged by bubbling N2 for 30 min, and then was heated slowly to the boiling point of TMB (168 °C) under N2 flow. The mixture turned optical transparent at 168 °C, from which tetracene fluorescence is still observed. After removing the heating device, 5 mL of ethanol (EtOH) was injected in the transparent solution as soon as possible (within 1 min) at 160 °C under the protection of refluxing. The temperature decreased rapidly to 90 °C after finishing the injection of EtOH. Finally, the whole mixture was cooled to room temperature slowly at a rate of 2 °C/min. The dark-brown precipitates were centrifugally separated from the suspension and washed twice with ethanol prior to vacuum drying. Characterization Techniques. The morphologies and sizes of the sample were examined using field emission scanning electron microscopy (FESEM, Hitachi S-4800) at acceleration voltages of 10 15 kV. Prior to analysis, the samples were coated with a thin platinum layer using an Edwards Sputter Coater. TEM images were collected by a JEOL JEM-2100 transmission electron microscopy (TEM). One drop of the as-prepared colloidal dispersion was deposited on a carbon-coated copper grid and left to dry under high vacuum; then, observation was performed at room temperature at an accelerating voltage of 200 kV. The diffusion reflectance spectrum was obtained from Shimidzu UV-3600. FTIR spectrum was obtained with KBr pellet on a Bruker Tensor 27. The Raman scattering spectrum was recorded on a Bruker RFS 100 Raman spectrometer with a laser of 1064.4 nm at power density of 50 mW 3 mm 2. X-ray diffraction (XRD) patterns were measured by a D/max 2500 X-ray diffractometer with Cu Kα radiation (λ = 1.54050 Å) operated in the 2θ range from 5 to 40°. The steady-state fluorescence spectroscopy was performed on a Hitachi F-4500 fluorescence spectrophotometer. All spectroscopic measurements were carried out at room temperature if no further notification. The picosecond time-resolved fluorescence apparatus has been described as below: The excitation laser pulses (470 nm) were supplied by an optical parametric amplifier (OPA-800CF, Spectra Physics), which was pumped by a regenerative amplifier (Spitfire, Spectra Physics). The excitation energy at the sample was ∼100 nJ/pulse. Fluorescence collected with the 90° geometry was dispersed by a polychromator (250is, Chromex) and detected with a streak camera (C5680, Hamamatsu Photonics). The spectral resolution was 0.2 nm, and the temporal resolution was ∼20 ps on the measured delay-time-range setting.

Figure 1. Typical (a) SEM, (b) TEM, and (c) magnified SEM images of C60/tetracene flowerlike microstructures. (d) TEM image, (e) SAED pattern, and (f,g) HRTEM images of one C60/tetracene nanoplate with nanocomposite structure.

Thermogravimetric analysis (TGA) was carried on SII TG/ DTA 6300. The sample was heating from 25 to 800 °C with heating rate of 10 °C/min. The whole measurement was under nitrogen protection Theoretical Calculation. Geometry optimization for tetracene-C60 complex was performed using MPWB95, a hybrid meta density functional theory (DFT), on the basis set of 6-31G(d) level. All DFT calculations were carried out using Gaussian03 program.

’ RESULTS AND DISCUSSION Scanning electron microscopy (SEM) images shows that flowerlike microspheres were obtained with a diameter of 5 10 μm (Figure 1a), also confirmed by TEM measurement (Figure 1b). The high-magnification SEM image of Figure 1c depicts that each flowerlike microstructure is uniformly built by interconnected nanoplates, which have clear and smooth outer surfaces with a thickness of 30 ( 5 nm. To investigate further the internal structure, we dispersed the flowerlike microspheres into ethanol and obtained separated nanoplates upon ultrasonic treatment. Figure 1d shows the low-resolution TEM image of a single nanoplate. Figure 1e shows the selected area electron diffraction (SAED) pattern, recorded by directing the electron beam perpendicular to the flat surface of the nanoplate. The observed multiple diffraction rings suggest that the nanoplate is polycrystalline in nature. Interestingly, middle-resolution TEM image of Figure 1f reveals that the nanoplate is actually composed of quasi-spherical disklike nanocrytals with clearly resolved lattice about 7.2 ( 3.2 nm in diameter (labeled by white circles in Figure 1f) surrounded by a continuous solid matrix. Figure 1g displays the high-resolution TEM image of a single disklike nanocrystal in the nanoplate. Two kinds of fringe with a separation angle of 86.3° can be indentified with interplanar distances of 3.0 and 3.9 Å, respectively, which are in agreement with the known values for the (020) and (200) planes of the triclinic tetracene crystal structure (a = 7.9 Å, b = 6.03 Å, c = 13.53 Å, α = 100.3°, β = 113.2°, γ = 86.3°, Figure S1a of the Supporting Information).19 Thereby, the flat surfaces of disklike tetracene nanocrystals are bound by (001) facets. 21630

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Figure 2. (a) IR spectrum and (b) Raman spectrum of fcc C60 powder, triclinic tetracene powder, and C60/tetracene flowerlike microstructures.

Figure 3. (a) XRD patterns, (b) TG analysis, and (c) diffuse reflectance spectrum of fcc C60 powder, triclinic tetracene powder, and C60/ tetracene flowerlike microstructures. (d) Graph of the FL kinetics at wavelength of 490 600 nm.

To investigate the composition of flowerlike microspheres, we measured Fourier transform infrared (FTIR) spectra, as shown in Figure 2a. For comparison, FTIR spectra of the pristine C60 and tetracene powder were also included. It can be seen that the FTIR spectra of flowerlike microspheres are factually a combination of C60 and tetracene components. Besides the peaks labeled by triangles for tetracene, four strong and sharp peaks at 1428, 1182, 576, and 526 cm 1 labeled by white circles in the FTIR spectrum of flowerlike microspheres (Figure 2a) are the characteristic bands of C60.20 Besides, no new absorption bands and frequency shifts that result from polymerization of C60 have been observed.21 This is also confirmed by Raman spectroscopy measurement, in which the Ag(2) pentagonal pinch modes are found at 1468 cm 1 for both the flowerlike microsphere and the pristine C60 samples (Figure 2b).5 That is, the C60 components in flowerlike microspheres are monomeric molecules. In another part, only three single peaks attribute to the hydrogen in tetracene were observed in 1H NMR spectroscopy (Figure S2 of the Supporting Information) of our complex microstructure, further confirming the purity of tetracene after hybridization. Additionally, absorption peaks of TMB are not found in all FTIR, Raman, and NMR spectra, indicating that no solvent molecules remain in the hybrid microspheres. We also performed XRD measurement to characterize the crystalline nature of the hybrid flowerlike microstructures. Figure 3a presents the XRD patterns of the hybrid flowerlike microstructures, the pristine powder of fcc phase C60, and triclinic phase tetracene. The XRD peaks of the composite microspheres (middle curve) are much broader than those of the pristine C60 and tetracene powder. On the one hand, three peaks labeled by circles can be assigned to Bragg diffractions from (001), (002), and (110) crystal planes of triclinic phase tetracene.19 The appearance of {00l} peaks with l = 1, 2 indicates that tetracene nanocrystals adopt a lamellar structure with the crystal (001) plane parallel to the substrate (Figure 3a), consistent with the HRTEM observation. We calculated the crystal dimension according to Scherrer equation, τ = Kλ/β cos θ, where τ is the mean of crystal dimension, K is the shape factor which has a typical value of about 0.9, λ is the X-ray wavelength of

1.54 Å, β is the line broadening at half the maximum intensity in radians, and θ is the Bragg angle.22 The result shows that the average size of tetracene crystal grain is ∼9.8 nm, in good agreement with the appearance size of 7.2 ( 3.2 nm determined by TEM in Figure 1f. On the other hand, three peaks labeled by triangles can be assigned to Bragg diffractions from (111), (220), and (311) crystal planes of fcc phase C60.20 Combining HRTEM and XRD results together, one can conclude that flowerlike microspheres of nanoplates adopt hybrid nanocomposite structures with small disklike tetracene nanocrystals embedded in a polycrystalline matrix of fcc phase C60. It should be noted that the peak indexed to (111) of fcc C60 in the XRD pattern of hybrid microstructures (middle line in Figure 3a) is blue-shifted by a value of 0.5° from that in the XRD pattern of the pristine C60 powder (top line in Figure 3a). This suggests that the interplanar distance of d(111) is little larger in hybrid structures (8.58 Å) than that in the pristine C60 powder (8.11 Å). Figure 3b presents TGA curves of the pristine tetracene and fullerene powder as well as the hybrid microspheres. In the TGA curve of C60/tetracene flowerlike microstructures (top line), there were three weight-loss processes in a step function at 300, 330, and 600 °C, respectively. The weight loss around 300 °C can be attributed to tetracence components,23 whereas the one around 600 °C is due to the degradation of C60 compounds. Furthermore, an additional endothermic peak at 330 °C, unobservable in both the pristine C60 and tetracene powder, is clearly resolved in the TGA curve of the hybrid microstructures. As above-mentioned, signals from polymerized tetracene or fullerene are not detected in the IR, Raman, and NMR spectra. Therefore, we speculate that those tetracene molecules at the periphery of disklike nanocrystals might interact strongly with the fcc C60 matrix and distort the interplanar distance of d(111). The charge-transfer (CT) interactions in C60/ polyacenes photovoltaic systems had been theoretically studied by several groups.24,25 In our system, three possible configurations for C60/tetracene complexes are optimized by using MPWB95/6-31G(d) method, including face-to-face, edge-toedge, and side-to-side configurations (Figure S6 of the Supporting Information). All three configurations show that the HOMO 21631



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Figure 5. Water contact angle (CA) of the layer composed of (a) C60/ tetracene flowerlike microstructure and (b) fullerene flowerlike microstructure.

Figure 4. (a) SEM and (b) magnified SEM images of C60 flowerlike microstructures. (c)TEM, (f) HRTEM images and SAED pattern of the edge of C60 flowerlike microstructures. (e) XRD patterns of (1) fcc C60, (5) triclinic tetracene, (4) C60/tetracene flowerlike microstructures, and C60/tetracene flowerlike microspheres after 2 h of heating at (3) 200 and (2) 330 °C.

is mainly distributed in tetracene unit and the LUMO is contributed by C60 unit, verifying the CT interactions in the C60/ tetracene complex. This is consistent with the previously reported result of edge-to-edge C60/pentacene complex using the time-dependent long-range corrected density functional theory.25 Moreover, our results (Figure S6 of the Supporting Information) reveal that the binding energy of face-to-face C60/ tetracene configuration is 0.154 eV, larger than those of side-toside and edge-to-edge configurations (∼0.05 eV).25 Combining the TGA and calculational results together, we conclude that the endothermic peak at 330 °C in Figure 3b is due to the formation of CT complex at the interface between tetracence disklike nanocrystals and the fcc C60 matrix in hybrid microspheres. According to the percentages of weight loss at 300, 330, and 600 °C (Figure S3 of the Supporting Information), the weight percentages of tetracene and C60 are determined to be 24 and 76%, respectively, in hybrid structures. Figure 3c shows the diffuse reflectance spectra of the pristine tetracene and fullerene powder as well as the hybrid microspheres. It can be seen that hybrid microspheres present a broad absorption covering both the features of tetracene and C60. Moreover, as compared with the pristine C60 powder (blue line), the low-energy absorption tail of hybrid microspheres is redshifted from 760 to 800 nm. Recently, Sathish and coworkers prepared C60 3 (Ferrocene)2 cocrystallized nanosheets and reported a CT band of C60/Ferrocene at 782 nm.11 Note that the CT process from tetracene to C60 is energetically favorable (Figure S4 of the Supporting Information).17 Therefore, the red-shifted absorption tail of hybrid microstructures should result from the formation of CT complex at the interface between tetracence disklike nanocrystals and the fcc C60 matrix in hybrid microspheres. As a matter of fact, the green fluorescence observed for the pristine tetracene powder (Figure S5 of the Supporting Information) was almost completely quenched in hybrid microstructures. Figure 3d shows the time-resolved fluorescence spectra for both the tetracene powder and hybrid flowerlike microstructures. The pristine tetracene powder (black curve) exhibits a biexponential fluorescence decay with a short component of 74 ( 6 ps (92%) and a much longer component of hundreds of nanoseconds (8%, not included in Figure 3d), consistent with the previous reports.26 Remarkably, the fluorescence of the hybrid microstructures decays single exponentially

with a time constant of 6 ( 0.2 ps (red curve), much faster than that of the pristine powder. This is probably because the comparable size of tetracene nanocrystals (7.2 ( 3.2 nm) to the exciton diffusion length (10 20 nm) facilitates the CT process from tetracene to C60 components in hybrid nanocomposite microstructures. In this regard, the charge separation efficiency (Φcs) is evaluated to be 92 ( 3%, according to Φcs = [(1/τ) (1/τ0)]/(1/τ),27 where τ = 6 ps and τ0 = 74 ps represent the measured lifetime of tetracene fluorescence for the C60/tetracene flowerlike microstructures and the pristine tetracene powder, respectively. As shown in Figure 3b, tetracene components can be removed from the hybrid microstructures through the sublimation procedure above 330 °C. Figure 4a,b presents SEM images of the thermal decomposition products of C60/tetracene flowerlike microstructures upon heating at 330 °C for 2 h. It can be seen that the flowerlike morphology is retained after the heat treatment; in addition, the size is almost unchanged. However, the surfaces of the nanoplates that build up the flowerlike morphology become rough (Figure 4b). The TEM image (Figure 4c), taken at the edge of a single nanoplate, clarifies that the treated nanoplate is porous with holes ranging from 5 to 10 nm in diameter, probably left behind by vaporized tetracene nanocrystals. Figure 4d shows the SAED pattern of a single porous nanoplate with regular hexagonal diffraction spots, which can be indexed to (111) and (220) Bragg diffractions of fcc C6028 corresponding to the lattice spacing of 8 and 5 Å, respectively, as determined by HRTEM in Figure 4f. Therefore, hybrid C60/ tetracene microstructures are successfully converted to porous fcc C60 microstructures by the heat treatment, with the size and flowerlike morphology being retained. We also monitored the thermal decomposition process by XRD (Figure 4e). Upon heating the hybrid structures at 330 °C: (i) The tetracene (001), (110) peaks vanish (see the spectra 5, 4, and 3 in Figure 4e). (ii) Meanwhile, the blue-shifted (111) peak of fcc C60 observed in hybrid structures also decreases concurrently with the appearance of a new peak, which matches exactly with fcc C60 powder and becomes dominant in the treated samples (see the spectra 4, 3, 2 and 1). These results are consistent with electron microscopy observations and solidify our previous assignment that the blue-shifted fcc C60 (111) peak in hybrid structures are due to the partial penetration of tetracene molecules into the (111) crystal plane of fcc C60. It is known that hydrophobicity is an important aspect of materials in industrial and biological applications. For a particular material, the hydrophobicity is generally associated with the surface roughness.29 We prepared uniform films composed of either C60/tetracene or fcc C60 flowerlike microstructures by using the air water interface transfer technique (Figure S7 of the Supporting Information). The water contact angle (CA) of C60/ tetracene and fcc C60 flowerlike microstructure films is measured 21632



Figure 6. Schematic illustration of the formation process of C60/ tetracene hybrid flowerlike microstructures of nanoplates.

to be 150.2 and 156.3°, respectively (Figure 5), indicating their super water-repellent properties. To probe the formation mechanism of C60/tetracene flowerlike microstructures, we systematically adjusted the loading molar ratio (NT:NC60) between the tetracene and the fullerene molecules. When tetracenes were excessive (NT:NC60 4:1), SEM and fluorescence microscopy results (Figure S8a and inset image of the Supporting Information) indicated that serious phase segregation took place: tetracene rods and fullerene microparticles were obtained, and flowerlike structures were not observed. However, under conditions of excessive fullerene (NT:NC60 1:4), C60/tetracene flowerlike microstructures were also generated along with fullerene microparticles (Figure S8b of the Supporting Information). According to these observations, the crystallization of tetracene seems to occur prior to the crystallization of C60, suggesting a lower nucleation threshold concentration of tetracene than that of fullerene in this TMB system. Figure 6 proposes a growth mechanism to describe the formation of hybrid flowerlike microstructures. The whole procedure includes three steps: the formation of tetracene nanocrystals (Step I), the growth of nanocomposite plate structures (Step II), and the evolution of the final flowerlike morphology (Step III). The driving force for crystallization is generally expressed as Δμ/ kBT,30 where Δμ is the difference in chemical potential between the growth units in the crystal and the liquid phase, kB is the Boltzmann’s constant, T is the absolute temperature, and Δμ can be expressed in terms of the supersaturation σ, according to Δμ = kBT ln(σ) and σ = C/Ceq, where C and Ceq represent the actual concentration and the equilibrium concentration (or the nucleation threshold concentration) of growth units in the coexistence phase.31 Note that both tetracene and C60 are poorly dissolved in common solvents at room temperature. At an elevated temperature of 165 °C, both tetracene and C60 molecules are welldissolved in TMB (the top left image), leading to high values of C. Upon injection of the poor solvent of EtOH into the TMB solution, the changing of the solvent surroundings as well as the sudden temperature drop from 160 to 90 °C lowers the values of Ceq. As Ceq(tetracene) < Ceq(C60), the nucleation of tetracene driven by supersaturation might take place prior to the nucleation of C60. Because of the strong 2D π π interactions within the ab plane of triclinic tetracene crystal,32 thin disklike nanocrystals about 5 10 nm in size are formed in a lamellar structure with tetracene molecules packing parallel to side faces and perpendicular to top and bottom faces (Step I, Figure S1b of the Supporting Information). Note that the majority of C60 molecules might be still be left in the liquid phase in this stage, probably due to the higher nucleation threshold concentration of C60 crystallization. With further decrease in temperature in the

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subsequent cooling process, the as-formed tetracene nanocrystals are capable of serving as the high-energy “seeds” for further growth of C60 molecules via the directional CT interactions (the top middle image). Therefore, secondary nucleation of C60 molecules is prompted by its preferential adhesion to the side faces of disklike tetracence nanocrystals bound by {hkl} facets with l = 0. Moreover, the dynamic exchange on and off the tetracene seeds helps the growth of C60 molecules along the 2D directions defined by the preformed tetracene disklike nanocrystals.33 Although it has not yet been fully understood, composite nanoplate structures might form via an oriented-attachment mechanism,34 which involves the spontaneous self-organization of adjacent particles of hybrid C60/tetracence nanocrystals to share a common crystallographic plane, such as the (111) of fcc C60, and subsequent fusing of these particles into plate structures (Step II). Indeed, 2D sheets were occasionally observed by casting the sample at 90 °C directly on a Si substrate (Figure S9 of the Supporting Information). We did not observe the rolling up procedure12 in each nanoplate during the formation C60/tetracence flowerlike products. Instead, the nanoplates composed of flowerlike microstructures are very thin and rigid, similar to those obtained in the oriented-attachment mechanism.21 Therefore, we speculate that these nanoplates provide a platform for the growth of other plates perpendicular to the initial one (the top right image); finally, complex flowerlike microstructures of nanoplates are generated.21

’ CONCLUSIONS The fabrication of C60/tetracene hybrid flowerlike microstructures that are built by nanoplates has been developed through supramolecular method. Sequential control of the nucleation and growth of tetracene and C60 components generated first disklike nanocrystals of tetracene about 5 nm in diameter, which then act as seeds for further growth of C60 molecules at its periphery driven by directional CT interactions. As a result, embedment of 5 nm tetracene disks in a polycrystalline C60 matrix builds up the composite structures of nanoplates, which can interconnect with each other and form complex 3D microspheres. The complete quenching of tetracene fluorescence suggested a highly efficient electron transfer process from tetracene to C60 in flowerlike microstructures. After heating to 330 °C, sublimation of tetracene components results in fcc C60 microstructures with the same shape and size as hybrid C60/ tetracene microspheres. Moreover, thin films made of either C60/ tetracene or fcc C60 flowerlike microstructures featured waterrepellent superhydrophobicity with a water contact angle of 150.2 and 156.3°, respectively. Our work might be helpful for achieving rational design and synthesis of fullerene-based molecular BHJ structures ’ ASSOCIATED CONTENT

bS

Supporting Information. Schematic crystal structure of tetracene, H1 NMR spectra and TGA of C60/tetracene flowerlike microstructures, band diagram between tetracene and fullerene, steady-state fluorescence spectra of tetracene pristine powder, SEM image and fluorescence image details of C60/ tetracene film, and calculated configurations for C60/tetracene complex. This material is available free of charge via the Internet at http://pubs.acs.org.

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’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT This work has been supported by the grants-in-aid from the Natural Science Foundation of China (nos. 90301010, 20873163, 20803085, 20925309), the Chinese Academy of Sciences (‘‘100 Talents’’ program), and the National Research Fund for Fundamental Key Project 973 (2011CB808402).

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