Ranran
Wang
,
Ke
Shi
,
Kang
Cai
,
Yikun
Guo
,
Xiao
Yang
,
Jie-Yu
Wang
,
Jian
Pei
* and
Dahui
Zhao
*
National Laboratory for Molecular Sciences, Centre for Soft Matter Science and Engineering and the Key Laboratory of Polymer Chemistry and Physics of the Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China. E-mail: dhzhao@pku.edu.cn; jianpei@pku.edu.cn
First published on 15th October 2015
Using readily available aryl glyoxylic acids and arylene diacetic acids as starting materials, a series of polycyclic aromatic molecules bearing two phthalimide functional groups are synthesized via Perkin condensation followed by intramolecular cyclization reactions. Two different cyclization methods, photo-oxidation and Heck cross-coupling, are employed, both of which effectively accomplish the transformations from diaryl maleic anhydride or maleimide to polycyclic aromatic phthalimide functionality. The photocyclization protocol conveniently allows direct bridging of two plain aromatic C–H sites linked by a maleic anhydride group and uniquely produces the more twisted polycyclic framework as the major product, whereas the Heck coupling approach can typically afford more extended polycyclic skeletons. Thionation reactions are then carried out for the obtained polycyclic diimide molecules using Lawesson's reagent. For all isolated stable products, partial thionation occurs. The prepared polycyclic diimide compounds possess relatively low LUMO levels, and thionation further decreases the LUMO energy of the molecules by 0.2–0.3 eV. Electron-transporting properties are characterized by using solution-processed OFET devices, and an electron mobility of 0.054 cm2 V−1 s−1 is demonstrated by a selected compound. Such semiconducting performance promises great potentials of this class of compounds as useful electron-accepting and transporting building blocks in developing various new semiconductive materials.
Here, we report the syntheses and properties of a series of polycyclic aromatic molecules bearing phthalimide functional groups, which are potentially suitable building blocks of new electron-accepting or transporting materials. Specifically, eight different PAI compounds are obtained, each containing 5 to 7 fused benzene rings decorated with two phthalimide units (Chart 1). Among various available synthetic strategies,7 we select Perkin condensation to assemble a series of different diaryl maleic anhydrides, which serve as effectual precursors to the target PAI molecules. Great merits of Perkin condensation are its facile synthetic procedures and readily available substrates. The starting materials used in the current work are phenyl and naphthyl glyoxylic acids along with various arylene diacetic acids. Two annulation methods, the intramolecular Heck coupling8 and photo-oxidation cyclization,9–11 are employed to accomplish different polycyclic aromatic scaffolds (Scheme 1). In all the prepared PAIs, branched alkyl side groups are attached to the imide nitrogen atoms, which help in ensuring adequate solubility of the products in common organic solvents.3,4,12 Electrochemical characterization shows that these PAI molecules possess relatively low LUMO levels at −3.4 to −3.7 eV. As an effort to further lower the LUMO levels, thionation of the carbonyl groups is then carried out for the PAI compounds using Lawesson's reagent (Scheme 2). Interestingly, for all isolated stable products, partial yet regio-selective thionation occurs. That is, only one of the two carbonyl groups in every dicarboximide unit gets thionated (Chart 1). Compared to their oxo-counterparts, these thio-substituted PAI derivatives exhibit further decreased LUMO energy levels at −3.8 to −3.9 eV. Subsequently, for molecules suitable for fabricating solution-processed organic field effect transistors (OFETs), the electron-transporting ability is evaluated. An electron mobility of 0.054 cm2 V−1 s−1 is determined for one of the PAI molecules. Such semiconducting properties promise this class of compounds as potentially useful subunits for developing new electron-accepting and transporting (polymer) materials.
Upon further examination, the final PAI products derived from dianhydride 9 were a mixture of two different molecules, regio-isomers 1 and 2, which could be separated and characterized respectively. Although the 1H NMR spectra offered certain evidence for differentiating 1 and 2, unambiguous structural identifications were realized only after isomer 2 was independently prepared via a different synthetic route (Scheme 1). In this alternative pathway, 2,2′-(2,5-dibromo-1,4-phenylene)diacetic acid was subjected to Perkin condensation conditions and coupled with two equivalents of phenylglyoxylic acid, affording a dibromo-substituted bis-maleic anhydride. Imidization was then carried out and offered intermediate 11 with improved solubility, which allowed proper conduction of subsequent intramolecular Heck cross coupling,8 yielding exclusively diimide 2.
After identifying the structures of 2, the helicene-type isomer 1 was found to be the major product from the photo-oxidation reaction, along with byproduct diimide 2 having a relatively extended polycyclic skeleton formed in <5% yield. Such a regio-selectivity of the photocyclization protocol was consistent with the results previously reported by Frimer et al.10 On the other hand, with an overall yield of >40% over three steps, the route harnessing the Heck coupling was apparently a more favorable synthetic path for PAI 2, although it required the pre-installation of bromine atoms at specific positions. Nonetheless, the photocyclization method uniquely generated diimide 1 with a helicene-type scaffold, which was difficult to attain from alternative approaches.
When similar photocyclization procedures followed by an imidization process were applied to bis-maleic anhydride 10, again a pair of regio-isomer PAI products was produced. Distinct 1H NMR spectra clearly identified and differentiated 3 and 4, because 3 had an asymmetric polycyclic backbone, while 4 featured a mirror-plane symmetry. Moreover, PAI 3 was found to be the major component in the final product mixture, indicating that the main product yielded from photocyclization of 10 was the asymmetric dianhydride structure.9,10 This result was also in accordance with previous observations made with photocyclization of 1,3-distyrylbenzene derivatives.13 From the above results, it was clear that such photo-induced oxidative couplings preferentially happened to arene C–H sites with two ortho-substitutions.10,13
To further explore the substrate scope of the photocyclization protocol, we then used naphthylenediacetic acids as the central moiety to prepare PAI molecules with larger aromatic skeletons. When 2,2′-(naphthalene-2,6-diyl)diacetic acid was employed as a reactant to couple with phenylglyoxylic acid, only diimide 5 was isolated upon a series of reactions including Perkin condensation, photocyclization and imidization. No other regio-isomer involving photo-cyclization on the β-positions of naphthylene was detected. This result was not surprising since the α-position of naphthalene was commonly more reactive than the β-position. When phenylglyoxylic acid was subjected to reaction with 2,2′-(naphthalene-1,5-diyl)diacetic acid, PAI 6 was formed as the only product after photocyclization and imidization procedures. It is noteworthy that a prolonged irradiation time was necessary for the 1,5-naphthylene-derived substrate 13 than corresponding 2,6-substituted analogue 12. Presumably this was also because the reactivity of the β-positions of naphthalene was much lower compared to the α-positions in the photocyclization.
We then employed another dianhydride substrate 14, which was obtained from Perkin condensation between 1,4-phenylenediacetic acid and 1-naphthylglyoxylic acid. As expected, PAI 7 was formed as the major product, with a minimal byproduct of isomer 8. Evidently, the same regio-selectivity was manifested here as in the reaction generating PAI 1. Meanwhile, following the route of Perkin condensation, imidization, and Heck coupling, PAI 8 was obtainable in a more favorable yield from dianhydride intermediate 15, prepared from 2,5-dibromo-1,4-phenylenediacetic acid and 1-naphthylglyoxylic acid as the substrates.
Φ | E g /eV | LUMOc/eV | HOMOd/eV | |
---|---|---|---|---|
a Fluorescence quantum yields measured in chloroform. b Band gap values estimated from the absorption onset. c From the onset of the first reduction wave in CV. d Calculated from Eg and the LUMO. | ||||
1 | 0.10 | 2.64 | −3.51 | −6.15 |
2 | 0.21 | 2.50 | −3.56 | −6.06 |
3 | 0.01 | 2.66 | −3.41 | −6.07 |
4 | 0.25 | 2.63 | −3.49 | −6.12 |
5 | 0.15 | 2.51 | −3.41 | −5.92 |
6 | 0.21 | 2.58 | −3.40 | −5.98 |
7 | 0.15 | 2.44 | −3.54 | −5.98 |
8 | 0.14 | 2.23 | −3.67 | −5.90 |
6-S | <0.01 | 2.00 | −3.76 | −5.76 |
7-S | <0.01 | 1.99 | −3.83 | −5.82 |
8-S | <0.01 | 1.85 | −3.90 | −5.75 |
Most of the prepared PAI molecules were moderately fluorescent (Fig. 3), showing fluorescence quantum yields ranging from 0.10 to 0.25 (Table 1).15 Nonetheless, the Φ value of 3 (∼0.01) was significantly lower than those of other PAIs, which was likely a result from its twisted polycyclic backbone. The steric hindrance between the imide carbonyl and the aromatic backbone possibly caused additional non-radiative decay in the excited state of 3. All three thionated compounds 6-S, 7-S and 8-S were nearly non-fluorescent, reflecting a significant emission quenching effect of the sulfur atoms.
In subsequent electrochemical characterization, PAIs 1–8 all showed two reversible reductive waves in their cyclic voltammograms (CVs) (Fig. 4).16 Estimated from the potential onset of the first reduction peaks, the LUMO energy levels of 1–7 were all in the range of −3.40 to −3.56 eV, while PAI 8 exhibited a lower LUMO at −3.67 eV (Table 1). Specifically, among regio-isomers 1–4, PAI 2 having an extended benzo[k]tetraphene-5,6,12,13-tetracarboxydiimide backbone displayed the lowest LUMO level and the narrowest band gap, whereas molecule 3 featuring an asymmetric benzo[c]chrysene-1,2,7,8-tetracarboxydiimide displayed the highest LUMO and the most widened band gap. Such electronic properties of 3 could as well be related to its twisted polycyclic framework, which frustrated electron delocalization over the conjugated aromatic skeleton. This assumption was confirmed by density functional theory (DFT) calculations, which revealed that molecule 3 had a non-planar polycyclic backbone due to the steric interference between one of the terminal benzene rings and a nearby imide carbonyl group (Fig. S1, ESI†). As a result, the LUMO of 3 was localized to part of the polycyclic backbone, covering only one of the two dicarboximide moieties. In contrast, the LUMOs of all other three isomers were delocalized over the entire polycyclic scaffolds.
With additional benzene rings fused to the polycyclic frameworks, the HOMO levels of 5–8 were noticeably boosted relative to those of 1–4 (Table 1). While regio-isomers 5 and 6 possessed similar LUMOs at −3.4 eV, much lowered LUMOs were detected with 7 and 8. Particularly, compound 8 manifested the lowest LUMO at −3.67 eV among all herein studied PAIs.
Partial thionation of the dicarboximide groups brought about conspicuous decrease in the LUMO levels of these polycyclic diimide molecules. According to the CV data, the LUMOs of 6-S, 7-S and 8-S were all lowered by 0.2 to 0.3 eV relative to their respective oxo- analogues 6–8. Such a pronounced effect of carbonyl thionation was also consistent with the DFT calculation results, which showed that thiocarbonyl moieties made substantial contributions to the LUMOs of the molecules (Fig. S2, ESI†).
In addition to the melting points, the device performance of solution-processed semiconductors was also sensitive to the crystallinity of the active materials. Most of the prepared PAI molecules exhibited evident tendency to crystallize under solution processing conditions, rendering them unsuitable for solution-processed OFET characterization. An electron mobility of ∼10−3 cm2 V−1 s−1 was observed for PAI 2. Such a mobility value most likely suffered from the high tendency of compound 2 to crystallize under the device fabrication conditions, since discontinuous crystalline domains were perceivable with the semiconductive layer. Atomic force microscopy (AFM) and X-ray diffraction (XRD) provided supportive evidence for the high crystallinity of 2 in the thin-film state (Fig. S3 and S4, ESI†). In comparison, PAI 8 exhibiting a suitable melting point and more favorable film morphology displayed a much more desirable electron mobility of 0.054 cm2 V−1 s−1 under ambient conditions (Fig. 6).
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Fig. 6 The transfer (a) and output (b) profiles of 8 measured in solution-processed OFET under ambient conditions. |
Owing to the electron-withdrawing effect of the dicarboximide groups, all the prepared polycyclic aromatic dicarboximide molecules show relatively low LUMOs at −3.4 to −3.7 eV, and the LUMOs of partially thionated molecules are typically further lowered by 0.2 to 0.3 eV relative to their respective oxo- analogues. An electron mobility of 0.054 cm2 V−1 s−1 is observed in a solution-processed field effect transistor with a selected structure 8 having suitable melting point and film morphology. Such semiconductive performance demonstrates great promise of this class of compounds as useful electron-accepting and transporting building blocks in developing new semiconductive materials. The thionated derivatives with lower LUMOs are especially attractive subunit structures.
1: 1H NMR (400 MHz, CDCl3) δ 9.12 (s, 2H), 9.09 (m, 2H), 8.08 (m, 2H), 7.65 (m, 2H), 7.27 (m, 2H), 3.72 (d, J = 7.2 Hz, 4H), 1.99 (br, 2H), 1.41–1.22 (m, 64H), 0.86–0.83 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 169.7, 169.5, 133.7, 130.3, 129.5, 128.7, 128.5, 127.4, 127.1, 126.2, 125.4, 125.1, 42.4, 37.3, 31.9, 31.6, 30.05, 30.02, 29.68, 29.65, 29.60, 29.3, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C66H93N2O4 (M + H+): 977.7130; found: 977.7103. Elem. anal.: calcd for C66H92N2O4: C, 81.10%; H, 9.49%; N, 2.87%; found: C, 81.02%; H, 9.51%; N, 2.91%. m.p.: 109.6 °C.
2: 1H NMR (300 MHz, CDCl3) δ 10.10 (s, 2H), 9.04 (d, J = 7.5 Hz, 2H), 8.76 (d, J = 7.5 Hz, 2H), 7.85–7.76 (m, 4H), 3.60 (d, J = 7.5 Hz, 4H), 1.95 (br, 2H), 1.40–1.20 (m, 64H), 0.86–0.83 (m, 12H). 13C NMR (75 MHz, CDCl3) δ 169.0, 168.9, 132.0, 130.1, 129.5, 128.5, 127.9, 125.9, 124.5, 123.6, 123.2, 119.4, 41.9, 37.4, 31.92, 31.89, 31.5, 30.1, 29.72, 29.67, 29.4, 26.4, 22.7, 22.6, 14.1. HR-ESI MS: calcd for C66H93N2O4 (M + H+): 977.7130; found: 977.7152. Elem. anal.: calcd for C66H92N2O4: C, 81.10%; H, 9.49%; N, 2.87%; found: C, 80.97%; H, 9.68%; N, 2.85%. m.p.: 137.0 °C.
3: 1H NMR (400 MHz, CDCl3) δ 9.28 (s, 1H), 9.26 (s, 1H), 9.18 (d, J = 8.0 Hz, 1H), 8.80 (d, J = 9.2 Hz, 1H), 8.76 (m, 1H), 8.37 (d, J = 8.0 Hz, 1H), 7.91–7.87 (m, 2H), 7.76 (t, J = 7.6 Hz, 1H), 7.56 (t, J = 7.6 Hz, 1H), 3.73 (d, J = 6.8 Hz, 2H), 3.56–3.42 (m, 2H), 1.97 (br, 1H), 1.86 (br, 1H), 1.43–1.22 (m, 64H), 0.89–0.83 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 170.0, 169.63, 169.60, 168.1, 135.3, 134.9, 132.9, 130.7, 130.3, 130.2, 129.8, 129.4, 128.7, 128.5, 127.9, 127.5, 126.22, 126.20, 126.1, 125.80, 125.76, 125.5, 125.3, 124.1, 123.4, 120.0, 116.4, 42.3, 37.34, 37.29 31.9, 31.6, 31.5, 30.1, 30.0, 29.63, 29.57, 29.3, 26.6, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C66H93N2O4 (M + H+): 977.7130; found: 977.7154. Calcd for C66H92N2O4: C, 81.10%; H, 9.49%; N, 2.87%; found: C, 81.05%; H, 9.62%; N, 2.90%. m.p.: 100.2 °C.
4: 1H NMR (300 MHz, CDCl3) δ 10.33 (s, 1H), 9.38 (s, 1H), 8.98 (d, J = 3.9 Hz, 2H), 8.61 (d, J = 3.9 Hz, 2H), 7.75–7.72 (m, 4H), 3.62 (d, J = 4.5 Hz, 4H), 1.97 (br, 2H), 1.48–1.22 (m, 64H), 0.86–0.81 (m, 12H). 13C NMR (75 MHz, CDCl3) δ 169.6, 169.2, 132.4, 131.4, 129.4, 128.9, 128.1, 127.2, 126.8, 125.5, 124.1, 123.9, 123.0, 116.7, 42.4, 37.2, 31.9, 31.6, 30.1, 29.9, 29.7, 29.3, 26.5, 22.7, 14.1. HR-ESI MS: calcd for C66H93N2O4 (M + H+): 977.7130; found: 977.7152. Calcd for C66H92N2O4: C, 81.10%; H, 9.49%; N, 2.87%; found: C, 80.99%; H, 9.52%; N, 2.83%. m.p.: 86.6 °C.
5: 1H NMR (300 MHz, CDCl3) δ 9.13 (d, J = 8.1 Hz, 2H), 8.83 (d, J = 8.7 Hz, 2H), 8.66 (d, J = 8.7 Hz, 2H), 8.62 (d, J = 8.1 Hz, 2H), 7.77–7.66 (m, 4H), 3.56 (d, J = 7.2 Hz, 4H), 1.94 (br, 2H), 1.38–1.22 (m, 64H), 0.87–0.82 (m, 12H). 13C NMR (75 MHz, CDCl3) δ 169.7, 169.4, 132.3, 131.2, 130.9, 129.0, 128.8, 128.2, 127.4, 126.6, 125.8, 124.5, 122.2, 42.1, 37.2, 31.9, 31.5, 30.0, 29.9, 29.63, 29.58, 29.5, 29.3, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C70H95N2O4 (M + H+): 1027.7286; found: 1027.7284. Elem. anal.: calcd for C70H94N2O4: C, 81.82%; H, 9.22%; N, 2.73%; found: C, 81.75%; H, 9.35%; N, 2.70%.
6: 1H NMR (300 MHz, CDCl3) δ 9.34 (d, J = 9.0 Hz, 2H), 9.30 (m, 2H), 8.75 (m, 2H), 8.71 (d, J = 9.0 Hz, 2H), 7.85–7.80 (m, 4H), 3.68 (d, J = 7.5 Hz, 4H), 1.99 (br, 2H), 1.46–1.13 (m, 64H), 0.88–0.82 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 169.69, 169.67, 133.6, 133.0, 131.8, 129.8, 129.7, 128.9, 128.8, 128.0, 126.3, 126.0, 123.6, 119.7, 42.6, 37.2, 31.9, 31.7, 30.1, 29.70, 29.65, 29.6, 29.4, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C70H95N2O4 (M + H+): 1027.7286; found: 1027.7274. Elem. anal.: calcd for C70H94N2O4: C, 81.82%; H, 9.22%; N, 2.73%; found: C, 81.65%; H, 9.21%; N, 2.55%. m.p.: 106.5 °C.
7: 1H NMR (400 MHz, CDCl3) δ 9.94 (d, J = 4.0 Hz, 2H), 9.47 (s, 2H), 7.87 (d, J = 8.0 Hz, 2H), 7.83 (d, J = 8.0 Hz, 2H), 7.76 (t, J = 12.0 Hz, 2H), 7.54–7.46 (m, 4H), 3.75 (d, J = 8.0 Hz, 4H), 2.04 (br, 2H), 1.41–1.22 (m, 64H), 0.86–0.82 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 169.3, 169.1, 135.4, 132.7, 130.7, 130.2, 129.5, 129.0, 128.5, 127.7, 127.62, 127.59, 126.9, 126.8, 125.2, 42.9, 37.2, 31.9, 31.7, 30.1, 30.0, 29.7, 29.66, 29.60, 29.3, 26.5, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C74H97N2O4 (M + H+): 1077.7443; found: 1077.7445. Elem. anal.: calcd for C74H96N2O4: C, 82.48%; H, 8.98%; N, 2.60%; found: 82.24%; H, 8.86%; N, 2.54%. m.p.: 98 °C.
8: 1H NMR (400 MHz, CDCl3) δ 10.51 (s, 2H), 9.45 (d, J = 8.0 Hz, 2H), 8.86 (d, J = 8.0 Hz, 2H), 8.16 (d, J = 12.0 Hz, 2H), 8.00 (d, J = 8.0 Hz, 2H), 7.77–7.69 (m, 4H), 3.56 (d, J = 8.0 Hz, 4H), 1.97 (br, 2H), 1.39–1.18 (m, 64H), 0.84–0.79 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 169.0, 168.8, 133.14, 133.09, 131.3, 130.8, 129.9, 129.7, 128.8, 127.8, 127.7, 127.5, 126.4, 124.2, 123.8, 121.1, 120.7, 42.5, 37.1, 31.93, 31.91, 31.6, 30.2, 29.74,29.72, 29.68, 29.0, 29.37, 26.4, 22.7, 14.1. HR-ESI MS: calcd for C74H97N2O4 (M + H+): 1077.7443; found: 1077.7466. Elem. anal.: calcd for C74H96N2O4: C, 82.48%; H, 8.98%; N, 2.60%; found: C, 82.41%; H, 8.99%; N, 2.52%. m.p.: 195.6 °C.
6-S: 1H NMR (400 MHz, CDCl3) δ 10.13 (m, 2H), 9.21 (d, J = 8.0 Hz), 8.80 (m, 2H), 8.71 (d, J = 8.0 Hz, 2H), 7.85–7.79 (m, 4H), 4.05 (d, J = 8.0 Hz, 4H), 2.17 (br, 2H), 1.37–1.22 (m, 64H), 0.87–0.82 (m, 12H). 13C NMR (120 MHz, CDCl3) δ 197.9, 171.1, 134.0, 133.5, 132.1, 130.8, 130.1, 129.3, 129.0, 128.0, 127.0, 123.8, 122.9, 119.3, 100.0, 45.5, 36.5, 31.9, 31.8, 30.1, 29.7, 29.6, 29.6, 29.3, 26.4, 22.7, 14.1. Calcd for C70H95N2O2S2 (M + H+): 1059.6830; found: 1059.6839. m.p.: 75.0 °C.
7-S: 1H NMR (400 MHz, CDCl3) δ 9.97 (d, J = 2.8 Hz, 2H), 9.68 (d, J = 8.0 Hz, 2H), 7.78–7.67 (m, 6H), 7.34–7.24 (m, 4H), 4.03 (t, J = 8.0 Hz, 4H), 2.18–2.14 (m, 2H), 1.39–1.20 (m, 64H), 0.86–0.81 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 196.6, 170.4, 134.9, 132.8, 131.5, 130.4, 129.1, 129.1, 128.5, 128.3, 127.7, 127.7, 127.6, 126.6, 126.4, 125.2, 125.0, 45.7, 36.6, 31.95, 31.93, 31.7, 30.2, 30.1, 29.74, 29.73, 29.70, 29.68, 29.66, 29.40, 29.39, 26.4, 22.7, 14.2. Calcd for C74H97N2O2S2 (M + H+): 1109.6986; found: 1109.6952. Elem. anal.: calcd for C74H96N2O2S2: C, 80.09%; H, 8.72%; N, 2.52%; found: C, 79.94%; H, 8.87%; N, 2.41%. m.p.: 65.7 °C.
8-S: 1H NMR (400 MHz, CDCl3) δ 10.39 (s, 2H), 8.93 (d, J = 8.0 Hz, 2H), 7.93 (d, J = 8.0 Hz, 2H), 7.95–7.67 (m, 4H), 7.60–7.54 (m, 4H), 3.54 (d, J = 8.0 Hz, 4H), 1.96 (br, 2H), 1.37–1.20 (m, 64H), 0.85–0.82 (m, 12H). 13C NMR (100 MHz, CDCl3) δ 196.1, 170.3, 133.3, 133.0, 131.9, 131.2, 129.7, 129.3, 128.6, 127.7, 127.4, 125.9, 125.0, 124.1, 123.0, 122.9, 121.1, 45.1, 36.5, 32.0, 31.9, 31.7, 30.2, 29.78, 29.76, 29.7, 29.43, 29.40, 26.4, 22.72, 22.70, 14.1. Calcd for C74H97N2O2S2 (M + H+): 1109.6986; found: 1109.6949. Elem. anal.: calcd for C74H96N2O2S2: C, 80.09%; H, 8.72%; N, 2.52%; found: C, 80.12%; H, 8.87%; N, 2.51%. m.p.: 137.0 °C.
Footnote |
† Electronic supplementary information (ESI) available: Complete synthetic details, NMR spectra and DFT calculation results. See DOI: 10.1039/c5nj01849h |
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