- Email: [email protected]
Facile synthesis of isomeric fullerene derivatives as acceptors for high performance organic photovoltaic
Tetrahedron 71 (2015) 7998e8002
Contents lists available at ScienceDirect
Tetrahedron journal homepage: www.elsevier.com/locate/tet
Facile synthesis of isomeric fullerene derivatives as acceptors for high performance organic photovoltaic Guoming Lin a, b, Rongli Cui a, Huan Huang a, Xihong Guo a, Shangyuan Yang a, Cheng Li a, b, Jinquan Dong a, Baoyun Sun a, b, * a
CAS Key Lab for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing 100049, China University of Chinese Academy of Sciences, Beijing 100049, China
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 June 2015 Received in revised form 20 August 2015 Accepted 26 August 2015 Available online 9 September 2015
Two new isomeric fullerene derivatives, {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6] C61 and 1-(3(Benzoyl)propyl)-1-phenyl[6,6] C60, have been synthesized efficiently through a 1,3-dipolar cycloaddition of a tosylhydrazone to provide relatively high photovoltaic performances. A systematic study on the optical, electrochemical and photovoltaic properties of the fullerene derivatives has been performed. In particular, the polymer solar cell (PSC) based on {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6] C61 and poly(3-hexylthiophene) showed a power conversion efficiency of 2.81%, which is higher than that of PCBM (2.53%) under the same device conditions. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: Fullerene acceptor Isomer C60 Polymer solar cells
1. Introduction Organic solar cells have been attracting much attention around the world within recent years. The first semiconducting polymerfullerene bulk heterojunction (BHJ) solar cell was reported in 1993, which gave a power conversion efficiency (PCE) of 0.04%.1 Since then, the power conversion efficiency of single and tandem BHJ solar cells had achieved a significant 9.2%2 and a remarkable 10.6%,3 respectively, which was mainly ascribed to the design and synthesis of novel polymer donors4e6 and fullerene acceptors,7e11 the improvement of device processing12,13 and architectures.14,15 Due to their high electron affinity and high electron mobility, and tunable solubility, energy level and packing structure, numerous fullerene derivatives have been synthesized as acceptors for BHJ solar cells in the past decade. Since Hummelen et al. firstly synthesized [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in 1995,16 PCBM is still the most commonly used fullerene acceptor in the photovoltaic solar cells, which offer good solubility and high electron mobility. The structural modification on the substituent of PCBM could be a way to design various fullerene derivatives for investigating the relationship between the molecular structure of fullerene acceptor and photovoltaic properties in the BHJ solar cells.
* Corresponding author. Tel./fax: þ86 10 8823 3595; e-mail address: sunby@ihep. ac.cn (B. Sun). http://dx.doi.org/10.1016/j.tet.2015.08.064 0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.
The substituent of PCBM can normally be divided into four parts, a phenyl ring, a middle butyl chain, an ester group and a methyl end group. Hummelen et al. replaced the phenyl ring with a series of electron-donating or electron-withdrawing substituents, and indicated that raising the lowest unoccupied molecular orbital (LUMO) level of the acceptor fullerene does give a higher opencircuit voltage (Voc) in BHJ solar cell devices.17 Yang et al. reported the alkyl chain length on the side chain of the PCBM-like molecules significantly influence the photovoltaic performance of the fullerene derivatives.18 More researches focused on replacing the methyl end group with other groups such as octadecyl group19 or amine moiety,20 which was expected to result in better solubility, stronger absorption of the fullerene derivatives. However, research on replacing the ester group with other groups has been rarely reported. Li et al. converted the ester group into amide, which resulted in the ordered molecular aggregates because of the hydrogen-bonding interaction among amides and improved the performance of the PSCs.21 Echegoyen et al. recently described the synthesis of bisadducts of C60 and C70 using the same original substrate dibenzoyl propane. All synthesized bisadducts show higher LUMO level between 200 and 300 mV compared to the corresponding values for the pristine fullerenes, however their properties for the polymer solar cell is not investigated.22 Research on the relationship between structures and functions of fullerene derivatives provided new ideas for designing more efficient and stable organic photovoltaic devices.
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
7999
In this report, by replacing the ester group on PCBM with benzoyl to the get a more symmetrical fullerene acceptor, two isomeric fullerene derivatives, {6}-1-(3-(benzoyl)propyl)-{5}-1-phenyl[5,6] C61 (isomer 1) and 1-(3-(benzoyl)propyl)-1-phenyl[6,6]C60 (isomer 2), were synthesized through a 1,3-dipolar cycloaddition of a tosylhydrazone. Their optical and electrochemical properties were reported. The P3HT based BHJ solar cells were fabricated. The influence of isomers, the composition ratios of donor and acceptor, the thickness of BHJ films and additive on the photovoltaic properties was investigated with these fullerene derivatives. 2. Results and discussion The structure and synthesis of isomeric fullerene derivatives including intermediates were shown in Scheme 1. HPLC-spectra of two isomers on Buckyprep column show difference in retention time, which could be seen in Fig. S1. The FTIR spectra of isomer 1 and 2 had the C]O stretching band and the NMR data clearly showed the presence of the carbonyl carbon, which meant that the derivative group has been connected to C60. Isomer 1 showed 4 sp3carbons, and isomer 2 showed 6 sp3-carbons, which meant that isomer 1 was 5,6 adduct, and isomer 2 is 6,6 adduct. The functional C60 derivative isomers processed high solubility in toluene, chlorobenzene and o-dichlorobenzene (o-DCB), and could stable in air for a few months when stored away from light.
Fig. 1. UVevis absorption spectra for isomer 1, 2 and PCBM (as the comparison) in CH2Cl2 (105 mol L1).
reference PCBM were shown in Fig. 2. It could be seen that three cyclic voltammograms similarly exhibited tree reversible reduction/reoxidation processes over a negative potential range. Reduction potential, LUMO level and highest occupied molecular orbital (HOMO) level for isomer 1, 2 and PCBM were shown in Table 1. The first reduction potential of isomer 2 shifted toward more negative value for w15 mV with respect to isomer 1, because the two compounds had different numbers of p-electron (60 p-electrons for isomer 1, 58 p-electrons for isomer 2). According to the red1 þ 4:8Þ eV, HOMO levempirical equation: LUMO level ¼ ðE1=2 el¼LUMO levelEg,24 the LUMO values and the HOMO values of the three structures were calculated from CV data and the optical band gap values. The first reduction potential of isomer 2 shifted toward more negative value of w30 mV with respect to PCBM, which suggested benzoyl group the higher electron donating ability than the ester group. Both isomers showed higher LUMO level than PCBM, which implied a higher Voc in P3HT based BHJ devices.
Scheme 1. Synthesis routes and chemical structures of isomer 1 and isomer 2.
2.1. Optical property The UVevis absorption characteristics of isomer 1, 2 and the reference PCBM in CH2Cl2 solution with the same concentration of 1105 mol L1 were depicted in Fig. 1. Isomer 1 showed typical [5,6]-adduct absorption maxima in UVevis spectroscopy of 337 nm and 426 nm. Nevertheless, isomer 2 showed the characteristic absorption of the fullerene of [6,6]-adduct at 332 nm and 432 nm, similar to [6,6]-PCBM.16 Compared with isomer 2, the specific absorbing peak of isomer 1 at 337 nm and 426 nm had a red shift of 5 nm and blue shift of 6 nm, respectively. The onset peak of isomer 1, 2 and PCBM (Fig. S2) were calculated to be 750 nm from the UVevis absorption data, which suggested the similar optical band gap (Eg) values for these three fullerene derivatives.23 The UVevis absorption data in film, which could be seen in Fig. S3, showed no obviously different with those in solution.
Fig. 2. Cyclic voltammograms of isomer 1, 2 and the reference PCBM in a mixed solvent of o-DCB/MeCN (4:1 v/v) with 0.1 M TBAClO4 as supporting electrolyte at a scan rate of 100 mV/s. Ag/Agþ was used as quasi-reference electrode. Ferrocene was used as an internal standard.
2.2. Electrochemical property 2.3. Photovoltaic properties Electronic energy levels (especially the LUMO level) of the fullerene derivatives are crucial for their application in PSCs as acceptor, which can be measured by electrochemical cyclic voltammetry. The cyclic voltammograms of isomer 1, 2 and the
To evaluate the photovoltaic potential of the two isomers, PSCs with P3HT as electron donor and two isomeric fullerene isomers 1 or 2 as electron acceptors were fabricated with the structure of ITO/
8000
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
Table 1 Reduction potential, LUMO level and HOMO level for isomer 1, 2 and PCBM C60 derivative
PCBM Isomer 1 Isomer 2
red vs Fc/Fcþa E1=2
E1 (V)
E2 (V)
E3 (V)
1.122 1.138 1.153
1.524 1.535 1.546
2.023 2.013 2.034
LUMO Levelb(eV)
HOMO Levelc(eV)
3.68 3.66 3.65
5.38 5.36 5.35
a red ¼ ðEox þ Ered Þ=2 were measured versus Ag/Agþ Reduction potentials E1=2 p p quasi-reference electrode and standardized to Fc/Fcþ couple. b red þ 4:8ÞeV: Calculated from the following equation: LUMO level¼ðE1=2 c Calculated from the following equation: HOMO level¼LUMO levelEg, Eg is the optical band gap derived from absorption data.17
PEDOT: PSS (40 nm)/P3HT: isomer 1 (or isomer 2)/Ca (20 nm)/Al (100 nm). All of them were constructed with solvent annealing, thermal annealing at 130 C for 15 min. To get the optimized condition, the composite ratio of donor and acceptor was chosen as 1:0.75,1:1 and 1:1.25. We also varied the thickness of the active layer by varying the spin-coated speed (see details at Supplementary data Table S1e4). In our study, a 2% C60 was added to the bulk of active layer to improve the film forming process and device performance. Finally, the devices under the optimized processing condition (with the thickness of about 180 nm, 2% C60 additive and donor-acceptor ratio of 1:1) showed the highest PCE. Their current densityevoltage (JeV) curves were presented in Fig. 3. The details of the device performance could be seen in Table 2. The average and standard deviation for Voc, Jsc, FF and PCE could be seen in Table S5.
2.53% respectively), probably due to the highest fill factor (FF) (isomer 1>PCBM>isomer 2). The morphology of the photoactive layer is very important for the photovoltaic performance of PSCs. The surface morphology of the active layers of device under optimized processing conditions was characterized by atomic force microscopy (AFM). The scan range was 3 mm3 mm. The root mean square (rms) roughness of the active layer was 3.75 nm for isomer 1 and 5.41 nm for isomer 2 as shown in Fig. 4. The surface morphology seemed to show homogenous and clear phase separation. In general, smoother film means increased self-organization of active layer, which is favorable for higher exciton dissociation efficiency and charge collection efficiency.25,26 The rms roughness indicate that isomer 1 blending with P3HT shows better film-forming property than isomer 2, which may be the reason for the higher FF for isomer 1 than isomer 2. Therefore, though the Voc of isomer 1 was slightly lower than isomer 2, the overall performance was still better. The smoother surface based on isomer 1/P3HT shows the higher photovoltaic performance, implying that the better interfacial contact of fullerene acceptor and polymer donor is a key on the improvement of the PSCs performance. For comparison, the AFM height images of the corresponding active layer without C60 additive were shown in Fig. S4. The rms roughness of the active layer for isomer 1: P3HT and isomer 2: P3HT without 2% C60 additive were 4.31 nm and 6.21 nm. We found that by adding 2% C60 additive the active layer could be smoother and the device performance (particularly the FF) were highly improved. Recently, Jen et al. also reported the coassemblies of unfunctionalized C60 with C60 derivative into large crystalline domains, which allow the tuning of nanoscale parameters to optimize the macroscopic behavior.27
Fig. 4. Tapping mode AFM height images of active layer with best photovoltaic performance (a) P3HT: isomer 1 with C60 (b) P3HT: isomer 2 with C60. The scan range was 3 mm3 mm, and the scale bar was 20 nm for both height images. Fig. 3. The current densityevoltage (JeV) curves of the PSCs of P3HT: isomer 1, isomer 2 and PCBM.
Table 2 The best photovoltaic performance of P3HT: C60 derivatives based PSCs with 2% C60 as additive Acceptor
Jsc (mA cm2)
Voc (V)
FF (%)
PCE (%)
Isomer 1 Isomer 2 PCBM
7.32 7.35 7.21
0.60 0.62 0.59
63.8 56.2 60.1
2.81 2.57 2.53
Comparing the devices based on PCBM, devices based on isomer 1 and isomer 2 showed small-improved Voc, which was due to the slightly increased LUMOs. As the same kind of polymer donor was used, short-circuit current of isomer 1, isomer 2 and PCBM did not show significant difference. In sharp contrast, although the PSC based on isomer 1 showed a moderate Voc value of 0.60 V, the PCE was much higher (2.81%) than that of other two devices (2.57%,
3. Conclusions In conclusion, we have designed, synthesized and characterized two new isomeric PCBM-like fullerene derivatives, {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6]C61 and 1-(3-(Benzoyl)propyl)-1phenyl[6,6]C60. Polymer BHJ solar cells based on these two isomer accepters were demonstrated. In the BHJ PSC devices with P3HT as polymer donor, isomer 1 and isomer 2 showed the higher PCE than PCBM. Compared to isomer 2 (PCE¼2.57%), the isomer 1based device had increased PCE value (2.81%). The result indicated that the isomeric structures could influence the morphology of BHJ films and the performance of resulted devices.
4. Experimental section 4.1. Materials and measurement PCBM, P3HT and PEDOT: PSS were purchased from Nano-C, Rieke metals and Heraeus Germany, respectively. All chemicals
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
were utilized without further purification, except that pyridine and o-dichlorobenzene were distilled from calcium hydride. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III TM 500 MHZ spectrometer and referenced to the solvent peak. MALDI-TOF mass spectra were obtained in Bruker Autoflex with alphacyanocinnamic Acid (CCA) as matrix. Fourier-transform infrared (FTIR) spectra were recorded using Thermal Fisher Nicolet iN10 spectrometer. An Agilent Cary 5000 UV-Visible spectrophotometer was used for electronic absorption measurements. Tapping mode AFM was performed using a Bruker Dimension EDGE. A Hitachi s4800 Scanning Electron Microscope was used for cross-sectional analysis. The acceleration voltage was 5 kV. The solar cell characterizations were done using Keithley 4200 and San-Electric XES70S1 solar simulator under standard AM 1.5G illumination. The electrochemical measurements were performed using a CHI660D electrochemical analyzer with an o-DCB/acetonitrile (4:1) mixtures solution with tetrabutylammonium perchlorate (TBAClO4) (0.10 M) as the electrolyte at a scan rate of 100 mv/s; Glassy-carbon, platinum wire and Ag wire were used as working, counter, and quasireference electrodes, respectively; Ferrocene was employed as an internal standard. 4.2. Fabrication of PSCs ITO was purchased from Zhuhai Kaivo Co. Lit (15 U sq1), and was ultrasonically cleaned in detergent, distilled water, acetone, and isopropanol for 15 min, respectively. The cleaned ITO glasses were dried with high-pressure nitrogen gas and then on hot plate at 120 C for 20 min. The PEDOT: PSS was spin-coated (4000 rpm 60 s) on the cleaned ITO substrate after the ITO surface was exposed to UV-ozone for 30 min. The PEDOT: PSS layer was about 40 nm. The donor and acceptor were dissolved in o-DCB with a concentration of 34 mg/mL. The active layers were spin-coated on the PEDOT: PSS layer at 900 rpm to get about 180 nm thickness films. The active layer was slowly dried in glass Petri dishes. A thickness of 20 nm calcium and 100 nm aluminum top electrodes were deposited on the active layer under a vacuum of 3104 Pa in a thermal evaporator. The device area, as defined by the anodecathode overlap, was 0.06 cm2. All the procedures except for the casting of the PEDOT: PSS layer were processed in a nitrogen-filled glove box with oxygen and moisture levels <1 ppm. 4.3. Synthesis section 4.3.1. Synthesis of 1, 3-dibenzoylpropyl p-tosylhydrazone (DBPT). A catalytic amount of p-toluenesulfonic acid (p-TSA) and 1,3Dibenzoylpropane (2.00 g, 7.93 mmol) were dissolved in methanol (10 mL), and then p-toluenesulfonhydrazide (1.48 g, 7.93 mmol) was added. After refluxing for 1 h, the mixture was cooled to 0 C and filtrated to obtain a precipitate. The precipitate was washed by cold methanol for 3 times and purified by silica gel column chromatography with chloroform: ethyl acetate (20:1) as the eluent. Yield of white solid: 2.76 g (6.57 mmol, 89%). Characterization data of the compound. Mp: 140e143 C; 1H NMR (500 MHz, DMSO): d 10.70 (s, 1H), 7.94 (d, J¼7.2 Hz, 2H), 7.81 (d, J¼8.2 Hz, 2H), 7.67e7.64 (m, 3H), 7.54 (t, J¼7.7 Hz, 2H), 7.45e7.32 (m, 5H), 3.10 (t, J¼7.0 Hz, 2H), 2.83e2.64 (m, 2H), 2.36 (s, 3H), 1.70 (m, 2H). 13C NMR (126 MHz, DMSO): d 200.16, 155.92, 143.83, 137.01, 136.83, 136.70, 133.68, 130.01, 129.84, 129.22, 128.95, 128.28, 127.90, 126.58, 37.91, 26.45, 21.48, 20.88. HR-ESI-MS: calculated for C24H25N2O3S 421.1580, found 421.1587. 4.3.2. Synthesis of two C60 derivative isomers. Synthesis routes and chemical structures of isomer 1 and isomer 2 are presented in Fig. 1. Under N2 atmosphere, 1, 3-dibenzoylpropyl p-tosylhydrazone (700 mg, 1.67 mmol) and sodium methoxide (130 mg, 2.41 mmol)
8001
were dissolved in 15 mL dry pyridine (Py). After stirring for 15 min at 70 C, the rose-colored mixture was added into a solution of C60 (600 mg, 0.84 mmol) in o-DCB (150 mL) and stirred at 70 C for 7e8 h under N2 atmosphere. The solution was concentrated to 20 mL and recrystallized with 200 mL methanol to collect the crude product. The solid compound was purified by silica gel column chromatography with CS2 and followed with toluene: petroleum ether (1:1) as the eluents. HPLC (Japan Analytical Industry Co., Ltd) using a Buckyprep column (20 mm250 mm, Nacalai Co., Japan) with toluene as the mobile phase was used to separate the isomers, providing 240 mg (0.25 mmol, 30.1% based on the consumed C60) of adobe brown solid. Characterization data of isomer 1. Mp >300 C. 1 H NMR (500 MHz, CDCl3) d 8.00 (d, J¼7.9 Hz, 2H), 7.86 (d, J¼7.9 Hz, 2H), 7.62e7.50 (m, 3H), 7.43 (m, 3H), 2.79 (t, J¼7.1 Hz, 2H), 1.78e1.66 (m, 2H), 1.65e1.58 (m, 2H). 13C NMR (126 MHz, CDCl3, all signals represent 2C except noted) d 199.50 (COPH), 151.46 (1C), 147.42, 146.59, 145.21, 144.79, 144.52 (1C), 144.28, 144.00, 143.78, 143.69, 143.60, 143.17, 143.12, 143.10 (1C), 143.04, 142.75, 142.64 (1C), 142.58, 142.18, 142.16, 141.97, 141.90, 141.36, 141.04, 140.47, 139.94, 139.77, 138.84, 138.44, 138.20, 137.96, 136.80 (1C), 136.73 (1C), 135.11, 133.05 (1C), 130.85, 128.70, 128.59, 128.00, 127.77 (1C), 61.26 (1C), 38.49 (1C), 35.56 (1C), 19.07 (1C); MALDI-TOF: calculated for C77H16O 956.1, found 956.7. FTIR (microscope mode, cm1) 2956, 2922, 2852, 1737, 1685, 1261, 1092, 1021, 800. UVevis: (nm) 337, 426, 543. The isomerization of isomer 1 to isomer 2 was according to previously reported method14 by refluxing isomer 1 (60 mg, 0.06 mmol) in 20 mL o-DCB for 10 h. Purified by HPLC, and recrystallized by menthol, yield dark black solid (50 mg, 83.3% based on the consumed isomer 1). Characterization data of isomer 2. Mp >300 C. 1H NMR (500 MHz, CDCl3) d 7.96 (d, J¼7.7 Hz, 4H), 7.55 (t, J¼7.5 Hz, 3H), 7.46 (dd, J¼16.4, 8.5 Hz, 3H), 3.19 (t, J¼7.3 Hz, 2H), 3.02e2.94 (m, 2H), 2.33 (dd, J¼15.5, 7.3 Hz, 2H). 13C NMR (126 MHz, CDCl3 all signals represent 2C except noted) d 199.61(COPH), 148.82, 147.83, 145.81, 145.13 (4C), 145.08, 145.06, 144.98, 144.74, 144.65 (1C), 144.61, 144.45, 144.36, 143.95, 143.71 (4C), 143.06 (1C), 142.98, 142.94 (1C), 142.93, 142.87 (4C), 142.19, 142.14, 142.08, 142.05, 140.92, 140.70, 137.98, 137.51, 136.78, 136.67 (1C), 133.18 (1C), 132.13, 128.63, 128.42, 128.21 (1C), 128.00, 99.86 (1C), 79.85 (1C), 52.08 (1C), 38.40 (1C), 33.73 (1C), 21.45 (1C). HRESI-MS (MþHþ): calculated for C77H17O 957.1274, found 957.1279. MALDI-TOF: calculated for C77H17O 956.1, found 956.7. FTIR: (microscope mode, cm1) 2959, 2922, 2851, 1736, 1684, 1260, 1092, 1020, 800. UVevis: (nm) 332, 432, 695. The MALDI-TOF, 1H NMR and 13C NMR spectra of two isomers could be seen in Supplementary data Figs. S5e10. The HR-ESI-MS spectrum of isomer 2 could be seen in Fig. S11. Acknowledgements The research was supported by National Basic Research Program of China (973 Program) (2012CB932601), National Natural Science Foundation of China (21271174, Y5118Y005C). Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2015.08.064. These data include MOL files and InChiKeys of the most important compounds described in this article. References and notes 1. Sariciftci, N. S.; Braun, D.; Zhang, C.; Srdanov, V. I.; Heeger, A. J.; Stucky, G.; Wudl, F. Appl. Phys. Lett. 1993, 62, 585e587. 2. He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y. Nat. Photonics 2012, 6, 591e595. 3. You, J.; Dou, L.; Yoshimura, K.; Kato, T.; Ohya, K.; Moriarty, T.; Emery, K.; Chen, C.-C.; Gao, J.; Li, G.; Yang, Y. Nat. Commun. 2013, 4, 1e10.
8002
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
4. Chen, Y.-H.; Lin, L.-Y.; Lu, C.-W.; Lin, F.; Huang, Z.-Y.; Lin, H.-W.; Wang, P.-H.; Liu, Y.-H.; Wong, K.-T.; Wen, J.; Miller, D. J.; Darling, S. B. J. Am. Chem. Soc. 2012, 134, 13616e13623. 5. Sharma, G. D.; Mikroyannidis, J. A.; Singh, S. P. Org. Electron. 2012, 13, 252e263. 6. Yang, L.; Xiao, C.; Jiang, W.; Wang, Z. Tetrahedron 2014, 70, 6265e6270. 7. Li, Y. F. Chem.dAsian J. 2013, 8, 2316e2328. 8. Wang, N.; Bao, X.; Yang, C.; Wang, J.; Woo, H. Y.; Lan, Z.; Chen, W.; Yang, R. Org. Electron. 2013, 14, 682e692. 9. Chen, W.; Zhang, Q.; Salim, T.; Ekahana, S. A.; Wan, X.; Sum, T. C.; Lam, Y. M.; Cheng, A. H. H.; Chen, Y.; Zhang, Q. Tetrahedron 2014, 70, 6217e6221. 10. Miftakhov, M. S.; Mikheev, V. V.; Torosyan, S. A.; Biglova, Y. N.; Gimalova, F. A.; Menshov, V. M.; Mustafin, A. G. Tetrahedron 2014, 70, 8040e8046. 11. Lai, Y.-Y.; Cheng, Y.-J.; Hsu, C.-S. Energy Environ. Sci. 2014, 7, 1866e1883. 12. Zhou, H. Q.; Zhang, Y.; Seifter, J.; Collins, S. D.; Luo, C.; Bazan, G. C.; Nguyen, T. Q.; Heeger, A. J. Adv. Mater. 2013, 25, 1646e1652. 13. Zhang, Y. G.; Li, Z.; Ouyang, J. Y.; Tsang, S. W.; Lu, J. P.; Yu, K.; Ding, J. F.; Tao, Y. Org. Electron. 2012, 13, 2773e2780. 14. Zhang, H.; Xu, M. F.; Cui, R. L.; Guo, X. H.; Yang, S. Y.; Liao, L. S.; Jia, Q. J.; Chen, Y.; Dong, J. Q.; Sun, B. Y. Nanotechnology 2013, 24, 355e401. 15. Abdulrazzaq, O. A.; Saini, V.; Bourdo, S.; Dervishi, E.; Biris, A. S. Part. Sci. Technol. 2013, 31, 427e442. 16. Hummelen, J. C.; Knight, B. W.; Lepeq, F.; Wudl, F.; Yao, J.; Wilkins, C. L. J. Org. Chem. 1995, 60, 532e538.
17. Kooistra, F. B.; Knol, J.; Kastenberg, F.; Popescu, L. M.; Verhees, W. J. H.; Kroon, J. M.; Hummelen, J. C. Org. Lett. 2007, 9, 551e554. 18. Zhao, G. J.; He, Y. J.; Xu, Z.; Hou, J. H.; Zhang, M. J.; Min, J.; Chen, H. Y.; Ye, M. F.; Hong, Z. R.; Yang, Y.; Li, Y. F. Adv. Funct. Mater. 2010, 20, 1480e1487. 19. Johnson, B. H.; Allagoa, E.; Thomas, R. L.; Stettler, G.; Wallis, M.; Peel, J. H.; Adalsteinsson, T.; McNelis, B. J.; Barber, R. P. Sol. Energy Mater. Sol. Cells 2010, 94, 537e541. 20. Lv, M.; Lei, M.; Zhu, J.; Hirai, T.; Chen, X. ACS Appl. Mater. Interfaces 2014, 6, 5844e5851. 21. Liu, C.; Li, Y. J.; Li, C. H.; Li, W. W.; Zhou, C. J.; Liu, H. B.; Bo, Z. S.; Li, Y. L. J. Phys. Chem. C 2009, 113, 21970e21975. 22. Ceron, M. R.; Izquierdo, M.; Aghabali, A.; Valdez, J. A.; Ghiassi, K. B.; Olmstead, M. M.; Balch, A. L.; Wudl, F.; Echegoyen, L. J. Am. Chem. Soc. 2015, 137, 7502e7508. 23. Park, S. H.; Yang, C. D.; Cowan, S.; Lee, J. K.; Wudl, F.; Lee, K.; Heeger, A. J. J. Mater. Chem. 2009, 19, 5624e5628. 24. Zhang, C.; Chen, S.; Xiao, Z.; Zuo, Q.; Ding, L. Org. Lett. 2012, 14, 1508e1511. 25. Chen, L.-M.; Hong, Z.; Li, G.; Yang, Y. Adv. Mater. 2009, 21, 1434e1449. 26. Seo, J. H.; Nam, S. Y.; Lee, K. S.; Kim, T. D.; Cho, S. Org. Electron. 2012, 13, 570e578. 27. Zhang, J.; Li, C.-Z.; Williams, S. T.; Liu, S.; Zhao, T.; Jen, A. K. Y. J. Am. Chem. Soc. 2015, 137, 2167e2170.
Contents lists available at ScienceDirect
Tetrahedron journal homepage: www.elsevier.com/locate/tet
Facile synthesis of isomeric fullerene derivatives as acceptors for high performance organic photovoltaic Guoming Lin a, b, Rongli Cui a, Huan Huang a, Xihong Guo a, Shangyuan Yang a, Cheng Li a, b, Jinquan Dong a, Baoyun Sun a, b, * a
CAS Key Lab for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing 100049, China University of Chinese Academy of Sciences, Beijing 100049, China
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 June 2015 Received in revised form 20 August 2015 Accepted 26 August 2015 Available online 9 September 2015
Two new isomeric fullerene derivatives, {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6] C61 and 1-(3(Benzoyl)propyl)-1-phenyl[6,6] C60, have been synthesized efficiently through a 1,3-dipolar cycloaddition of a tosylhydrazone to provide relatively high photovoltaic performances. A systematic study on the optical, electrochemical and photovoltaic properties of the fullerene derivatives has been performed. In particular, the polymer solar cell (PSC) based on {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6] C61 and poly(3-hexylthiophene) showed a power conversion efficiency of 2.81%, which is higher than that of PCBM (2.53%) under the same device conditions. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: Fullerene acceptor Isomer C60 Polymer solar cells
1. Introduction Organic solar cells have been attracting much attention around the world within recent years. The first semiconducting polymerfullerene bulk heterojunction (BHJ) solar cell was reported in 1993, which gave a power conversion efficiency (PCE) of 0.04%.1 Since then, the power conversion efficiency of single and tandem BHJ solar cells had achieved a significant 9.2%2 and a remarkable 10.6%,3 respectively, which was mainly ascribed to the design and synthesis of novel polymer donors4e6 and fullerene acceptors,7e11 the improvement of device processing12,13 and architectures.14,15 Due to their high electron affinity and high electron mobility, and tunable solubility, energy level and packing structure, numerous fullerene derivatives have been synthesized as acceptors for BHJ solar cells in the past decade. Since Hummelen et al. firstly synthesized [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in 1995,16 PCBM is still the most commonly used fullerene acceptor in the photovoltaic solar cells, which offer good solubility and high electron mobility. The structural modification on the substituent of PCBM could be a way to design various fullerene derivatives for investigating the relationship between the molecular structure of fullerene acceptor and photovoltaic properties in the BHJ solar cells.
* Corresponding author. Tel./fax: þ86 10 8823 3595; e-mail address: sunby@ihep. ac.cn (B. Sun). http://dx.doi.org/10.1016/j.tet.2015.08.064 0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.
The substituent of PCBM can normally be divided into four parts, a phenyl ring, a middle butyl chain, an ester group and a methyl end group. Hummelen et al. replaced the phenyl ring with a series of electron-donating or electron-withdrawing substituents, and indicated that raising the lowest unoccupied molecular orbital (LUMO) level of the acceptor fullerene does give a higher opencircuit voltage (Voc) in BHJ solar cell devices.17 Yang et al. reported the alkyl chain length on the side chain of the PCBM-like molecules significantly influence the photovoltaic performance of the fullerene derivatives.18 More researches focused on replacing the methyl end group with other groups such as octadecyl group19 or amine moiety,20 which was expected to result in better solubility, stronger absorption of the fullerene derivatives. However, research on replacing the ester group with other groups has been rarely reported. Li et al. converted the ester group into amide, which resulted in the ordered molecular aggregates because of the hydrogen-bonding interaction among amides and improved the performance of the PSCs.21 Echegoyen et al. recently described the synthesis of bisadducts of C60 and C70 using the same original substrate dibenzoyl propane. All synthesized bisadducts show higher LUMO level between 200 and 300 mV compared to the corresponding values for the pristine fullerenes, however their properties for the polymer solar cell is not investigated.22 Research on the relationship between structures and functions of fullerene derivatives provided new ideas for designing more efficient and stable organic photovoltaic devices.
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
7999
In this report, by replacing the ester group on PCBM with benzoyl to the get a more symmetrical fullerene acceptor, two isomeric fullerene derivatives, {6}-1-(3-(benzoyl)propyl)-{5}-1-phenyl[5,6] C61 (isomer 1) and 1-(3-(benzoyl)propyl)-1-phenyl[6,6]C60 (isomer 2), were synthesized through a 1,3-dipolar cycloaddition of a tosylhydrazone. Their optical and electrochemical properties were reported. The P3HT based BHJ solar cells were fabricated. The influence of isomers, the composition ratios of donor and acceptor, the thickness of BHJ films and additive on the photovoltaic properties was investigated with these fullerene derivatives. 2. Results and discussion The structure and synthesis of isomeric fullerene derivatives including intermediates were shown in Scheme 1. HPLC-spectra of two isomers on Buckyprep column show difference in retention time, which could be seen in Fig. S1. The FTIR spectra of isomer 1 and 2 had the C]O stretching band and the NMR data clearly showed the presence of the carbonyl carbon, which meant that the derivative group has been connected to C60. Isomer 1 showed 4 sp3carbons, and isomer 2 showed 6 sp3-carbons, which meant that isomer 1 was 5,6 adduct, and isomer 2 is 6,6 adduct. The functional C60 derivative isomers processed high solubility in toluene, chlorobenzene and o-dichlorobenzene (o-DCB), and could stable in air for a few months when stored away from light.
Fig. 1. UVevis absorption spectra for isomer 1, 2 and PCBM (as the comparison) in CH2Cl2 (105 mol L1).
reference PCBM were shown in Fig. 2. It could be seen that three cyclic voltammograms similarly exhibited tree reversible reduction/reoxidation processes over a negative potential range. Reduction potential, LUMO level and highest occupied molecular orbital (HOMO) level for isomer 1, 2 and PCBM were shown in Table 1. The first reduction potential of isomer 2 shifted toward more negative value for w15 mV with respect to isomer 1, because the two compounds had different numbers of p-electron (60 p-electrons for isomer 1, 58 p-electrons for isomer 2). According to the red1 þ 4:8Þ eV, HOMO levempirical equation: LUMO level ¼ ðE1=2 el¼LUMO levelEg,24 the LUMO values and the HOMO values of the three structures were calculated from CV data and the optical band gap values. The first reduction potential of isomer 2 shifted toward more negative value of w30 mV with respect to PCBM, which suggested benzoyl group the higher electron donating ability than the ester group. Both isomers showed higher LUMO level than PCBM, which implied a higher Voc in P3HT based BHJ devices.
Scheme 1. Synthesis routes and chemical structures of isomer 1 and isomer 2.
2.1. Optical property The UVevis absorption characteristics of isomer 1, 2 and the reference PCBM in CH2Cl2 solution with the same concentration of 1105 mol L1 were depicted in Fig. 1. Isomer 1 showed typical [5,6]-adduct absorption maxima in UVevis spectroscopy of 337 nm and 426 nm. Nevertheless, isomer 2 showed the characteristic absorption of the fullerene of [6,6]-adduct at 332 nm and 432 nm, similar to [6,6]-PCBM.16 Compared with isomer 2, the specific absorbing peak of isomer 1 at 337 nm and 426 nm had a red shift of 5 nm and blue shift of 6 nm, respectively. The onset peak of isomer 1, 2 and PCBM (Fig. S2) were calculated to be 750 nm from the UVevis absorption data, which suggested the similar optical band gap (Eg) values for these three fullerene derivatives.23 The UVevis absorption data in film, which could be seen in Fig. S3, showed no obviously different with those in solution.
Fig. 2. Cyclic voltammograms of isomer 1, 2 and the reference PCBM in a mixed solvent of o-DCB/MeCN (4:1 v/v) with 0.1 M TBAClO4 as supporting electrolyte at a scan rate of 100 mV/s. Ag/Agþ was used as quasi-reference electrode. Ferrocene was used as an internal standard.
2.2. Electrochemical property 2.3. Photovoltaic properties Electronic energy levels (especially the LUMO level) of the fullerene derivatives are crucial for their application in PSCs as acceptor, which can be measured by electrochemical cyclic voltammetry. The cyclic voltammograms of isomer 1, 2 and the
To evaluate the photovoltaic potential of the two isomers, PSCs with P3HT as electron donor and two isomeric fullerene isomers 1 or 2 as electron acceptors were fabricated with the structure of ITO/
8000
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
Table 1 Reduction potential, LUMO level and HOMO level for isomer 1, 2 and PCBM C60 derivative
PCBM Isomer 1 Isomer 2
red vs Fc/Fcþa E1=2
E1 (V)
E2 (V)
E3 (V)
1.122 1.138 1.153
1.524 1.535 1.546
2.023 2.013 2.034
LUMO Levelb(eV)
HOMO Levelc(eV)
3.68 3.66 3.65
5.38 5.36 5.35
a red ¼ ðEox þ Ered Þ=2 were measured versus Ag/Agþ Reduction potentials E1=2 p p quasi-reference electrode and standardized to Fc/Fcþ couple. b red þ 4:8ÞeV: Calculated from the following equation: LUMO level¼ðE1=2 c Calculated from the following equation: HOMO level¼LUMO levelEg, Eg is the optical band gap derived from absorption data.17
PEDOT: PSS (40 nm)/P3HT: isomer 1 (or isomer 2)/Ca (20 nm)/Al (100 nm). All of them were constructed with solvent annealing, thermal annealing at 130 C for 15 min. To get the optimized condition, the composite ratio of donor and acceptor was chosen as 1:0.75,1:1 and 1:1.25. We also varied the thickness of the active layer by varying the spin-coated speed (see details at Supplementary data Table S1e4). In our study, a 2% C60 was added to the bulk of active layer to improve the film forming process and device performance. Finally, the devices under the optimized processing condition (with the thickness of about 180 nm, 2% C60 additive and donor-acceptor ratio of 1:1) showed the highest PCE. Their current densityevoltage (JeV) curves were presented in Fig. 3. The details of the device performance could be seen in Table 2. The average and standard deviation for Voc, Jsc, FF and PCE could be seen in Table S5.
2.53% respectively), probably due to the highest fill factor (FF) (isomer 1>PCBM>isomer 2). The morphology of the photoactive layer is very important for the photovoltaic performance of PSCs. The surface morphology of the active layers of device under optimized processing conditions was characterized by atomic force microscopy (AFM). The scan range was 3 mm3 mm. The root mean square (rms) roughness of the active layer was 3.75 nm for isomer 1 and 5.41 nm for isomer 2 as shown in Fig. 4. The surface morphology seemed to show homogenous and clear phase separation. In general, smoother film means increased self-organization of active layer, which is favorable for higher exciton dissociation efficiency and charge collection efficiency.25,26 The rms roughness indicate that isomer 1 blending with P3HT shows better film-forming property than isomer 2, which may be the reason for the higher FF for isomer 1 than isomer 2. Therefore, though the Voc of isomer 1 was slightly lower than isomer 2, the overall performance was still better. The smoother surface based on isomer 1/P3HT shows the higher photovoltaic performance, implying that the better interfacial contact of fullerene acceptor and polymer donor is a key on the improvement of the PSCs performance. For comparison, the AFM height images of the corresponding active layer without C60 additive were shown in Fig. S4. The rms roughness of the active layer for isomer 1: P3HT and isomer 2: P3HT without 2% C60 additive were 4.31 nm and 6.21 nm. We found that by adding 2% C60 additive the active layer could be smoother and the device performance (particularly the FF) were highly improved. Recently, Jen et al. also reported the coassemblies of unfunctionalized C60 with C60 derivative into large crystalline domains, which allow the tuning of nanoscale parameters to optimize the macroscopic behavior.27
Fig. 4. Tapping mode AFM height images of active layer with best photovoltaic performance (a) P3HT: isomer 1 with C60 (b) P3HT: isomer 2 with C60. The scan range was 3 mm3 mm, and the scale bar was 20 nm for both height images. Fig. 3. The current densityevoltage (JeV) curves of the PSCs of P3HT: isomer 1, isomer 2 and PCBM.
Table 2 The best photovoltaic performance of P3HT: C60 derivatives based PSCs with 2% C60 as additive Acceptor
Jsc (mA cm2)
Voc (V)
FF (%)
PCE (%)
Isomer 1 Isomer 2 PCBM
7.32 7.35 7.21
0.60 0.62 0.59
63.8 56.2 60.1
2.81 2.57 2.53
Comparing the devices based on PCBM, devices based on isomer 1 and isomer 2 showed small-improved Voc, which was due to the slightly increased LUMOs. As the same kind of polymer donor was used, short-circuit current of isomer 1, isomer 2 and PCBM did not show significant difference. In sharp contrast, although the PSC based on isomer 1 showed a moderate Voc value of 0.60 V, the PCE was much higher (2.81%) than that of other two devices (2.57%,
3. Conclusions In conclusion, we have designed, synthesized and characterized two new isomeric PCBM-like fullerene derivatives, {6}-1-(3-(Benzoyl)propyl)-{5}-1-phenyl [5,6]C61 and 1-(3-(Benzoyl)propyl)-1phenyl[6,6]C60. Polymer BHJ solar cells based on these two isomer accepters were demonstrated. In the BHJ PSC devices with P3HT as polymer donor, isomer 1 and isomer 2 showed the higher PCE than PCBM. Compared to isomer 2 (PCE¼2.57%), the isomer 1based device had increased PCE value (2.81%). The result indicated that the isomeric structures could influence the morphology of BHJ films and the performance of resulted devices.
4. Experimental section 4.1. Materials and measurement PCBM, P3HT and PEDOT: PSS were purchased from Nano-C, Rieke metals and Heraeus Germany, respectively. All chemicals
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
were utilized without further purification, except that pyridine and o-dichlorobenzene were distilled from calcium hydride. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III TM 500 MHZ spectrometer and referenced to the solvent peak. MALDI-TOF mass spectra were obtained in Bruker Autoflex with alphacyanocinnamic Acid (CCA) as matrix. Fourier-transform infrared (FTIR) spectra were recorded using Thermal Fisher Nicolet iN10 spectrometer. An Agilent Cary 5000 UV-Visible spectrophotometer was used for electronic absorption measurements. Tapping mode AFM was performed using a Bruker Dimension EDGE. A Hitachi s4800 Scanning Electron Microscope was used for cross-sectional analysis. The acceleration voltage was 5 kV. The solar cell characterizations were done using Keithley 4200 and San-Electric XES70S1 solar simulator under standard AM 1.5G illumination. The electrochemical measurements were performed using a CHI660D electrochemical analyzer with an o-DCB/acetonitrile (4:1) mixtures solution with tetrabutylammonium perchlorate (TBAClO4) (0.10 M) as the electrolyte at a scan rate of 100 mv/s; Glassy-carbon, platinum wire and Ag wire were used as working, counter, and quasireference electrodes, respectively; Ferrocene was employed as an internal standard. 4.2. Fabrication of PSCs ITO was purchased from Zhuhai Kaivo Co. Lit (15 U sq1), and was ultrasonically cleaned in detergent, distilled water, acetone, and isopropanol for 15 min, respectively. The cleaned ITO glasses were dried with high-pressure nitrogen gas and then on hot plate at 120 C for 20 min. The PEDOT: PSS was spin-coated (4000 rpm 60 s) on the cleaned ITO substrate after the ITO surface was exposed to UV-ozone for 30 min. The PEDOT: PSS layer was about 40 nm. The donor and acceptor were dissolved in o-DCB with a concentration of 34 mg/mL. The active layers were spin-coated on the PEDOT: PSS layer at 900 rpm to get about 180 nm thickness films. The active layer was slowly dried in glass Petri dishes. A thickness of 20 nm calcium and 100 nm aluminum top electrodes were deposited on the active layer under a vacuum of 3104 Pa in a thermal evaporator. The device area, as defined by the anodecathode overlap, was 0.06 cm2. All the procedures except for the casting of the PEDOT: PSS layer were processed in a nitrogen-filled glove box with oxygen and moisture levels <1 ppm. 4.3. Synthesis section 4.3.1. Synthesis of 1, 3-dibenzoylpropyl p-tosylhydrazone (DBPT). A catalytic amount of p-toluenesulfonic acid (p-TSA) and 1,3Dibenzoylpropane (2.00 g, 7.93 mmol) were dissolved in methanol (10 mL), and then p-toluenesulfonhydrazide (1.48 g, 7.93 mmol) was added. After refluxing for 1 h, the mixture was cooled to 0 C and filtrated to obtain a precipitate. The precipitate was washed by cold methanol for 3 times and purified by silica gel column chromatography with chloroform: ethyl acetate (20:1) as the eluent. Yield of white solid: 2.76 g (6.57 mmol, 89%). Characterization data of the compound. Mp: 140e143 C; 1H NMR (500 MHz, DMSO): d 10.70 (s, 1H), 7.94 (d, J¼7.2 Hz, 2H), 7.81 (d, J¼8.2 Hz, 2H), 7.67e7.64 (m, 3H), 7.54 (t, J¼7.7 Hz, 2H), 7.45e7.32 (m, 5H), 3.10 (t, J¼7.0 Hz, 2H), 2.83e2.64 (m, 2H), 2.36 (s, 3H), 1.70 (m, 2H). 13C NMR (126 MHz, DMSO): d 200.16, 155.92, 143.83, 137.01, 136.83, 136.70, 133.68, 130.01, 129.84, 129.22, 128.95, 128.28, 127.90, 126.58, 37.91, 26.45, 21.48, 20.88. HR-ESI-MS: calculated for C24H25N2O3S 421.1580, found 421.1587. 4.3.2. Synthesis of two C60 derivative isomers. Synthesis routes and chemical structures of isomer 1 and isomer 2 are presented in Fig. 1. Under N2 atmosphere, 1, 3-dibenzoylpropyl p-tosylhydrazone (700 mg, 1.67 mmol) and sodium methoxide (130 mg, 2.41 mmol)
8001
were dissolved in 15 mL dry pyridine (Py). After stirring for 15 min at 70 C, the rose-colored mixture was added into a solution of C60 (600 mg, 0.84 mmol) in o-DCB (150 mL) and stirred at 70 C for 7e8 h under N2 atmosphere. The solution was concentrated to 20 mL and recrystallized with 200 mL methanol to collect the crude product. The solid compound was purified by silica gel column chromatography with CS2 and followed with toluene: petroleum ether (1:1) as the eluents. HPLC (Japan Analytical Industry Co., Ltd) using a Buckyprep column (20 mm250 mm, Nacalai Co., Japan) with toluene as the mobile phase was used to separate the isomers, providing 240 mg (0.25 mmol, 30.1% based on the consumed C60) of adobe brown solid. Characterization data of isomer 1. Mp >300 C. 1 H NMR (500 MHz, CDCl3) d 8.00 (d, J¼7.9 Hz, 2H), 7.86 (d, J¼7.9 Hz, 2H), 7.62e7.50 (m, 3H), 7.43 (m, 3H), 2.79 (t, J¼7.1 Hz, 2H), 1.78e1.66 (m, 2H), 1.65e1.58 (m, 2H). 13C NMR (126 MHz, CDCl3, all signals represent 2C except noted) d 199.50 (COPH), 151.46 (1C), 147.42, 146.59, 145.21, 144.79, 144.52 (1C), 144.28, 144.00, 143.78, 143.69, 143.60, 143.17, 143.12, 143.10 (1C), 143.04, 142.75, 142.64 (1C), 142.58, 142.18, 142.16, 141.97, 141.90, 141.36, 141.04, 140.47, 139.94, 139.77, 138.84, 138.44, 138.20, 137.96, 136.80 (1C), 136.73 (1C), 135.11, 133.05 (1C), 130.85, 128.70, 128.59, 128.00, 127.77 (1C), 61.26 (1C), 38.49 (1C), 35.56 (1C), 19.07 (1C); MALDI-TOF: calculated for C77H16O 956.1, found 956.7. FTIR (microscope mode, cm1) 2956, 2922, 2852, 1737, 1685, 1261, 1092, 1021, 800. UVevis: (nm) 337, 426, 543. The isomerization of isomer 1 to isomer 2 was according to previously reported method14 by refluxing isomer 1 (60 mg, 0.06 mmol) in 20 mL o-DCB for 10 h. Purified by HPLC, and recrystallized by menthol, yield dark black solid (50 mg, 83.3% based on the consumed isomer 1). Characterization data of isomer 2. Mp >300 C. 1H NMR (500 MHz, CDCl3) d 7.96 (d, J¼7.7 Hz, 4H), 7.55 (t, J¼7.5 Hz, 3H), 7.46 (dd, J¼16.4, 8.5 Hz, 3H), 3.19 (t, J¼7.3 Hz, 2H), 3.02e2.94 (m, 2H), 2.33 (dd, J¼15.5, 7.3 Hz, 2H). 13C NMR (126 MHz, CDCl3 all signals represent 2C except noted) d 199.61(COPH), 148.82, 147.83, 145.81, 145.13 (4C), 145.08, 145.06, 144.98, 144.74, 144.65 (1C), 144.61, 144.45, 144.36, 143.95, 143.71 (4C), 143.06 (1C), 142.98, 142.94 (1C), 142.93, 142.87 (4C), 142.19, 142.14, 142.08, 142.05, 140.92, 140.70, 137.98, 137.51, 136.78, 136.67 (1C), 133.18 (1C), 132.13, 128.63, 128.42, 128.21 (1C), 128.00, 99.86 (1C), 79.85 (1C), 52.08 (1C), 38.40 (1C), 33.73 (1C), 21.45 (1C). HRESI-MS (MþHþ): calculated for C77H17O 957.1274, found 957.1279. MALDI-TOF: calculated for C77H17O 956.1, found 956.7. FTIR: (microscope mode, cm1) 2959, 2922, 2851, 1736, 1684, 1260, 1092, 1020, 800. UVevis: (nm) 332, 432, 695. The MALDI-TOF, 1H NMR and 13C NMR spectra of two isomers could be seen in Supplementary data Figs. S5e10. The HR-ESI-MS spectrum of isomer 2 could be seen in Fig. S11. Acknowledgements The research was supported by National Basic Research Program of China (973 Program) (2012CB932601), National Natural Science Foundation of China (21271174, Y5118Y005C). Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2015.08.064. These data include MOL files and InChiKeys of the most important compounds described in this article. References and notes 1. Sariciftci, N. S.; Braun, D.; Zhang, C.; Srdanov, V. I.; Heeger, A. J.; Stucky, G.; Wudl, F. Appl. Phys. Lett. 1993, 62, 585e587. 2. He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y. Nat. Photonics 2012, 6, 591e595. 3. You, J.; Dou, L.; Yoshimura, K.; Kato, T.; Ohya, K.; Moriarty, T.; Emery, K.; Chen, C.-C.; Gao, J.; Li, G.; Yang, Y. Nat. Commun. 2013, 4, 1e10.
8002
G. Lin et al. / Tetrahedron 71 (2015) 7998e8002
4. Chen, Y.-H.; Lin, L.-Y.; Lu, C.-W.; Lin, F.; Huang, Z.-Y.; Lin, H.-W.; Wang, P.-H.; Liu, Y.-H.; Wong, K.-T.; Wen, J.; Miller, D. J.; Darling, S. B. J. Am. Chem. Soc. 2012, 134, 13616e13623. 5. Sharma, G. D.; Mikroyannidis, J. A.; Singh, S. P. Org. Electron. 2012, 13, 252e263. 6. Yang, L.; Xiao, C.; Jiang, W.; Wang, Z. Tetrahedron 2014, 70, 6265e6270. 7. Li, Y. F. Chem.dAsian J. 2013, 8, 2316e2328. 8. Wang, N.; Bao, X.; Yang, C.; Wang, J.; Woo, H. Y.; Lan, Z.; Chen, W.; Yang, R. Org. Electron. 2013, 14, 682e692. 9. Chen, W.; Zhang, Q.; Salim, T.; Ekahana, S. A.; Wan, X.; Sum, T. C.; Lam, Y. M.; Cheng, A. H. H.; Chen, Y.; Zhang, Q. Tetrahedron 2014, 70, 6217e6221. 10. Miftakhov, M. S.; Mikheev, V. V.; Torosyan, S. A.; Biglova, Y. N.; Gimalova, F. A.; Menshov, V. M.; Mustafin, A. G. Tetrahedron 2014, 70, 8040e8046. 11. Lai, Y.-Y.; Cheng, Y.-J.; Hsu, C.-S. Energy Environ. Sci. 2014, 7, 1866e1883. 12. Zhou, H. Q.; Zhang, Y.; Seifter, J.; Collins, S. D.; Luo, C.; Bazan, G. C.; Nguyen, T. Q.; Heeger, A. J. Adv. Mater. 2013, 25, 1646e1652. 13. Zhang, Y. G.; Li, Z.; Ouyang, J. Y.; Tsang, S. W.; Lu, J. P.; Yu, K.; Ding, J. F.; Tao, Y. Org. Electron. 2012, 13, 2773e2780. 14. Zhang, H.; Xu, M. F.; Cui, R. L.; Guo, X. H.; Yang, S. Y.; Liao, L. S.; Jia, Q. J.; Chen, Y.; Dong, J. Q.; Sun, B. Y. Nanotechnology 2013, 24, 355e401. 15. Abdulrazzaq, O. A.; Saini, V.; Bourdo, S.; Dervishi, E.; Biris, A. S. Part. Sci. Technol. 2013, 31, 427e442. 16. Hummelen, J. C.; Knight, B. W.; Lepeq, F.; Wudl, F.; Yao, J.; Wilkins, C. L. J. Org. Chem. 1995, 60, 532e538.
17. Kooistra, F. B.; Knol, J.; Kastenberg, F.; Popescu, L. M.; Verhees, W. J. H.; Kroon, J. M.; Hummelen, J. C. Org. Lett. 2007, 9, 551e554. 18. Zhao, G. J.; He, Y. J.; Xu, Z.; Hou, J. H.; Zhang, M. J.; Min, J.; Chen, H. Y.; Ye, M. F.; Hong, Z. R.; Yang, Y.; Li, Y. F. Adv. Funct. Mater. 2010, 20, 1480e1487. 19. Johnson, B. H.; Allagoa, E.; Thomas, R. L.; Stettler, G.; Wallis, M.; Peel, J. H.; Adalsteinsson, T.; McNelis, B. J.; Barber, R. P. Sol. Energy Mater. Sol. Cells 2010, 94, 537e541. 20. Lv, M.; Lei, M.; Zhu, J.; Hirai, T.; Chen, X. ACS Appl. Mater. Interfaces 2014, 6, 5844e5851. 21. Liu, C.; Li, Y. J.; Li, C. H.; Li, W. W.; Zhou, C. J.; Liu, H. B.; Bo, Z. S.; Li, Y. L. J. Phys. Chem. C 2009, 113, 21970e21975. 22. Ceron, M. R.; Izquierdo, M.; Aghabali, A.; Valdez, J. A.; Ghiassi, K. B.; Olmstead, M. M.; Balch, A. L.; Wudl, F.; Echegoyen, L. J. Am. Chem. Soc. 2015, 137, 7502e7508. 23. Park, S. H.; Yang, C. D.; Cowan, S.; Lee, J. K.; Wudl, F.; Lee, K.; Heeger, A. J. J. Mater. Chem. 2009, 19, 5624e5628. 24. Zhang, C.; Chen, S.; Xiao, Z.; Zuo, Q.; Ding, L. Org. Lett. 2012, 14, 1508e1511. 25. Chen, L.-M.; Hong, Z.; Li, G.; Yang, Y. Adv. Mater. 2009, 21, 1434e1449. 26. Seo, J. H.; Nam, S. Y.; Lee, K. S.; Kim, T. D.; Cho, S. Org. Electron. 2012, 13, 570e578. 27. Zhang, J.; Li, C.-Z.; Williams, S. T.; Liu, S.; Zhao, T.; Jen, A. K. Y. J. Am. Chem. Soc. 2015, 137, 2167e2170.