Note pubs.acs.org/joc
Cite This: J. Org. Chem. 2018, 83, 5784−5790
Synthesis and Electronic Properties of Length-Defined 9,10Anthrylene−Butadiynylene Oligomers Maiko Nagaoka,† Eiji Tsurumaki,† Mai Nishiuchi,‡ Tetsuo Iwanaga,‡ and Shinji Toyota*,† †
Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan
‡
S Supporting Information *
ABSTRACT: Linear π-conjugated oligomers consisting of anthracene and diacetylene units were readily synthesized by a one-pot process that involved desilylation and oxidative coupling from appropriate building units. We were able to isolate length-defined oligomers ranging from 2-mer to 6-mer as stable and soluble solids. The bathochromic shifts in the UV−vis spectra suggested that the π-conjugation was extended with elongation of the linear chain. Cyclic voltammetric measurements showed characteristic reversible oxidation waves that were dependent on the number of anthracene units.
A
rylene oligomers composed of ethynylene or butadiynylene linkers offer versatile molecular designs for the construction of novel π-conjugated compounds.1 The structures and properties of such compounds are modified by varying the kind and number of arene units, the substitution position, and the kinds of linkers.2 Fundamental oligomers consisting of phenylene units have been extensively studied from various aspects, and their shapes are strongly dependent on the substitution positions. 3 Because 1,4-phenylene oligomers have characteristic rod shapes and extended πconjugation, many derivatives have been synthesized to produce functional oligomers such as electronic devices and wires.4 In the linear oligomers, the use of other arene units can widen the scope of the molecular design to accumulate the properties of each arene unit. For example, Tykwinski et al. connected four pentacene units with butadiynylene linkers to realize a small HOMO−LUMO gap.5 Regarding 9,10anthrylene oligomers,6 anthrylene−ethynylene 3-mers 1 (hereinafter, n-mer refers to an oligomer consisting of n aromatic units) were investigated as organic semiconductors (Figure 1).7,8 In addition, 1,4-di(9-anthryl)-1,3-butadiyne derivatives 2, namely, anthrylene−butadiynylene 2-mers, were applied to two-photon adsorption materials and biochemical fluorescent dyes.9 Swager et al. reported the synthesis of a series of anthrylene−butadiynylene polymers 3 as low band gap materials.10 Although they provided spectroscopic and electrochemical data, they used a mixture of polymers for their measurements. In order to analyze the effects of the chain length on the properties of such oligomers, we need to obtain stable and soluble oligomers with defined lengths. Therefore, we synthesized 9,10-anthrylene−butadiynylene oligomers 4 in pure forms for systematic analysis based on synthetic techniques accumulated from previous researches on anthracene−acetylene oligomers.11 We herein report the synthesis, structures, and properties of these novel π-conjugated rod-type oligomers up to 6-mer. © 2018 American Chemical Society
Figure 1. Structures of 9,10-anthrylene oligomers with ethynylene or butadiynylene linkers.
Because our preliminary experiments revealed that substituent-free oligomers 4(H) were poorly soluble (details in the Experimental Section), we introduced two tert-butyl groups to each anthracene unit. We synthesized target oligomers 4 by the Pd/Cu-catalyzed oxidative coupling12 of 9,10-diethynylanthracene 8 and singly silylated compound 7 as internal and terminal units, respectively (Scheme 1). We prepared 7 and 8 by desilylation of the trimethylsilyl groups from 5 and 6, respectively. Although the coupling reaction of isolated 7 and 8 gave the desired oligomers, their overall yields were not high because of the unstable nature of the terminal alkynes. Therefore, we integrated the two steps by a one-pot process technique.13 A mixture of 5 and 6 was treated with K2CO3 in THF/MeOH in a flask, into which reagents and a base for the Pd/Cu-catalyzed oxidative coupling were added. The reaction mixture instantly turned deep purple as a result of the formation of a mixture of oligomers. The products were Received: February 2, 2018 Published: April 18, 2018 5784
DOI: 10.1021/acs.joc.8b00311 J. Org. Chem. 2018, 83, 5784−5790
Note
The Journal of Organic Chemistry Scheme 1. Synthesis of Oligomers 4
separated by chromatography on silica gel to give 2-mer to 6mer (4b−f) in isolated yields, as shown in Scheme 1. These oligomers were characterized by NMR spectroscopy and mass spectrometry. In the 13C NMR spectra, the signals due to the diyne carbons were observed at δ 83 and 86 for 4b−d, these values being typical for diarylbutadiynes. These oligomers were stable in solid or solutions when they were handled under room light and air or under conditions for conventional spectroscopic measurements. The long oligomers are reasonably soluble in toluene. Their colors range from orange (2-mer) to purple (6mer) with an increasing chain length. The X-ray structures of 4c are shown in Figure 2. The three anthracene planes are approximately coplanar along the linear
Figure 3. Two views of the calculated structure of 4c(H)′ (a SiMe3 derivative) at the B3LYP/6-31G(d) level and its HOMO and LUMO plots. The data of other oligomers are given in Figure S7. Figure 2. Two views of the X-ray structure of 3-mer 4c. One of the two independent molecules in an asymmetric unit is shown. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are set at 50% probability.
although the rotation along the acetylene axis requires very little energy. For example, the calculation revealed that the rotation of the central anthracene unit in 3-mer required an energy of less than 0.5 kJ mol−1.15 In these coplanar conformations, the molecular orbitals spread over the acetylene and anthracene moieties at the HOMO and LUMO levels, as reported for 1,4-phenylene−butadiynylene and related oligomers.16 The HOMO−LUMO gaps decrease with an increasing chain length (Table 1 and Figure S8). The UV−vis and fluorescence spectra of 4 were measured in toluene (Figure 4). Selected data are listed in Table 1. In the UV−vis spectra, the absorption band at the longest wavelength was observed at 524 nm for 4b, which was red-shifted by 84 nm relative to that of 4a. The corresponding absorptions shifted toward the long wavelength region to 588 nm with an increasing intensity as the number of anthracene units increased, even though the red-shift effect became gradually
molecular axis where t-Bu groups are arranged in an alternate fashion. The distance between the terminal Si atoms is ca. 3.0 nm. The side view shows that the molecule is slightly S-shaped although the deformation at each sp carbon atom is insignificant (bond angles 175.2−177.4°). Such deformations are rather usual for acetylene-containing molecular rods in the solid state due to packing interactions.5,14 The molecular structures were calculated by the DFT method for model compounds 4a−f(H)′ containing SiMe3 terminal groups and no t-Bu groups. The optimized structures at the B3LYP/631G(d) level are shown in Figure 3 [4c(H)′] and Figure S7. In all of the oligomers, the anthracene groups are coplanar, 5785
DOI: 10.1021/acs.joc.8b00311 J. Org. Chem. 2018, 83, 5784−5790
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The Journal of Organic Chemistry Table 1. Photophysical Properties of Oligomers 4 Measured in Toluene λmax (nm) (ε)a 440 523 570 582 585 589
4a 4b 4c 4d 4e 4f
λem (nm)b
Φfc
Stokes shift (eV)
Egmax (eV)d
Egonset (eV)e
EgDFT (eV)f
461 541 589 609 623 629
0.92 0.020 0.022 0.020 0.018 na
0.128 0.079 0.070 0.094 0.129 0.134
2.82 2.37 2.18 2.13 2.12 2.11
2.66 2.24 2.04 1.96 1.90 1.89
2.91 2.26 1.96 1.81 1.72 1.66
(25900) (49500) (60400)g (94500) (135000) (151000)
a Wavelengths and molar extinction coefficients of the absorption maxima. bWavelengths of the emission maxima. cAbsolute fluorescence quantum yields. dEnergy gaps calculated from absorption maxima. eEnergy gaps calculated from absorption onset. fCalculated HOMO−LUMO gap energies at the B3LYP/6-31G(d) level for model compounds 4(H)′. gA shoulder.
Analogous pentacene oligomers showed multistep reduction waves and rather ambiguous oxidation waves.5 Therefore, the anthracene oligomers are able to tolerate electrochemical oxidation compared with the pentacene oligomers. As shown in Table 2, the longer the oligomer chain, the easier both oxidation and reduction occur. The electrochemically determined band gaps decrease with increasing the chain length from 2.82 to 2.14 eV. These band gap values are in good agreement with those estimated from the maximum of the absorption spectrum rather than the calculated HOMO− LUMO gaps (Table 1). These results suggest that diacetylene linkers effectively mediate electronic communication between aromatic units by mixed valence contributions of the oxidized and reduced species, as pointed out for other redox systems.19 In summary, 9,10-anthrylene−butadiynylene linear oligomers of up to 6-mer were successfully synthesized by a one-pot process. Because of the reasonable solubility and stability of these length-defined oligomers, we could evaluate their properties by spectroscopic and electrochemical measurements with the aid of DFT calculations. The π-conjugation is extended in long oligomers, leading to a characteristic deep color. These oligomers will be attractive as core units in the molecular design of linear π-conjugated compounds for functional dyes and electronic devices. In order to realize these potential applications, the synthesis of oligomers having various terminal groups and longer oligomers is in progress.
Figure 4. UV−vis (a) and fluorescence (b) spectra of 4 in toluene. Spectra of 4b in various solvents (Figure S3) show small solvent effects.
small. A plot of the energy gaps obtained from the absorption onset Egonset (eV) against the minimum number of multiple bonds between the terminal sp carbons x afforded the following relationship: Egonset = 3.77 (1/x) + 1.73 (Figure S5).17 The value for 4f (1.89 eV) is comparable to that of an anthracene− diacetylene polymer (1.9 eV), the average degree of polymerization of which is ca. 130-mer.10 A similar bathochromic shift of the emission wavelengths was observed in the fluorescence spectra, from 461 nm (4a) to 628 nm (4f). Although 4a was highly emissive, the longer oligomers gave weak emissions of Φf of ca. 0.02. These observations indicate that the presence of diacetylene moieties facilitates quenching via nonradiative pathways, as reported for other butadiyne compounds.5,11d,18 To investigate electrochemical redox properties, we carried out cyclic voltammetric measurements of 4a−d (Table 2 and
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General. All chemical materials and solvents were purchased from commercial sources and used without further purification unless otherwise noted. Melting points are uncorrected. Elemental analyses were performed with an elementar vario MICRO cube analyzer. NMR spectra were measured on a JEOL Resonance ECZ500 spectrometer (1H 500 MHz, 13C 125 MHz). Low-resolution MALDI-TOF mass spectra were measured on a SHIMADZU AXIMA Confidence spectrometer. High-resolution mass spectra were measured on a JEOL MStation-700 spectrometer by the FAB method with a quadrupole mass analyzer. IR spectra were recorded on a JASCO SC-100-VIR spectrometer. UV spectra were measured on a JASCO V670 spectrophotometer with a 10 mm cell. Fluorescence spectra were measured on a JASCO FP-6500 spectrofluorometer with a 10 mm cell. Fluorescence lifetimes were measured on a time-correlated singlephoton counting system (HORIBA Fluoro Cube) with a NanoLED laser (444 nm). Column chromatography was carried out with silica gel 60 N (spherical, neutral) (40−50 mesh) (Kanto chemical). Typical Procedure for the Synthesis of 9,10-Diethynylanthracenes. This compound was prepared in a one-pot process.11c,18a,20 To a solution of (triisopropylsilyl)ethyne (0.39 mL, 1.72 mmol, 1.1 equiv) in Et2O (10 mL) cooled to 0 °C was added nBuLi (1.6 mol L−1 in hexane, 1.08 mL, 1.72 mmol, 1.1 equiv) under N2 gas. This solution was stirred at 0 °C for 30 min and then at room temperature for 1 h. A solution of [(trimethylsilyl)ethynyl]lithium in Et2O was similarly prepared from (trimethylsilyl)acetylene (0.65 mL,
Table 2. Cyclic Voltammetry Data for 4a−da
4a 4b 4c 4d
Eox1 (V)
Eox2 (V)
+0.74 +0.63 +0.61 +0.57
+0.87 +0.77 +0.70
Eox3 (V)
+1.07 +0.90
Eox4 (V)
Ered1 (V)
Ered2 (V)
ΔE (eV)b
−1.90 −1.71
+1.06
−2.08 −1.73 −1.58 −1.57
2.82 2.36 2.19 2.14
EXPERIMENTAL SECTION
a
Conditions: Ag/AgCl working electrode (rod), Pt counter electrode (wire), supporting electrolyte 0.10 mol L−1 of Bu4NClO4 in CH2Cl2. Scan rate = 10 mV s−1. bDifferences between the first oxidation wave and the first reduction wave.
Figure S6). Compound 4b exhibited two reversible oxidation waves Eox at +0.63 and +0.87 V, and 4c and 4d clearly showed three and four oxidation waves, respectively. These observations suggest that the oxidation proceeds in a stepwise manner and that even multiply oxidized species are relatively stable. For the reduction, 4a and 4b gave one and two waves, respectively, whereas 4c and 4d gave one or two irreversible waves. 5786
DOI: 10.1021/acs.joc.8b00311 J. Org. Chem. 2018, 83, 5784−5790
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The Journal of Organic Chemistry 4.68 mmol, 3.0 equiv) and nBuLi (1.6 mol L−1 solution in hexane, 3.0 mL, 4.68 mmol, 3.0 equiv) in another flask. To the solution of [(triisopropylsilyl)ethynyl]lithium was added 2,6-di-tert-butyl-9,10anthraquinone21 (501 mg 1.56 mmol), and then the reaction mixture was stirred at room temperature for 1 h. To the reaction mixture was added the solution of [(trimethylsilyl)ethynyl]lithium, and then the mixture was refluxed for 7 h. To the reaction mixture were added SnCl2·2H2O (1.77 g, 7.80 mmol, 5.0 equiv) and HCl (3 mol L−1, 4 mL), and then the mixture was stirred room temperature for 15 h. The reaction mixture was quenched with NaHCO3 (20 mL), and the organic materials were extracted with Et2O (20 mL × 4). The combined organic solution was washed with H2O (10 mL × 3), dried over Na2SO4, and evaporated. The residue was purified by chromatography on silica gel with hexane to give the desired product as a yellow green solid. Symmetrically substituted derivatives 6 (210 mg, 28%) and 4a were also obtained as byproducts. 2,6-Di-tert-butyl-9[(triisopropylsilyl)ethynyl]-10-[(trimethylsilyl)ethynyl]anthracene (5): yield 464 mg (52%); Rf 0.45 (hexane); mp 150−155 °C; 1H NMR (500 MHz, CDCl3) δ 0.43 (s, 9H), 1.28 (s, 3H), 1.30 (s, 18H), 1.47 (s, 9H), 1.49 (s, 9H), 7.70 (dd, J = 9.5, 2.0 Hz, 1H), 7.71 (dd, J = 9.5, 2.0 Hz, 1H), 8.51 (d, J = 2.0 Hz, 1H), 8.52 (d, J = 9.0 Hz, 1H), 8.56 (d, J = 9.0 Hz, 1H), 8.56 (d, J = 1.5 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 0.2, 11.5, 18.9, 29.7, 30.8, 31.0, 35.2, 101.9, 103.7, 104.0, 107.4, 117.3, 118.0, 121.5, 121.6, 126.18, 126.23, 126.8, 130.9, 131.2, 132.05, 132.09, 148.9, 149.0; HRMS (FAB) m/z calcd for C38H54Si2 [M]+ 566.3764, found 566.3741. 2,6-Di-tert-butyl-9,10bis[(triisopropylsilyl)ethynyl]anthracene (4a): yellow solid, yield 30 mg (3%); Rf 0.58 (hexane); mp 260−265 °C; 1H NMR (500 MHz, CDCl3) δ 1.28 (s, 6H), 1.29 (s, 36H), 1.48 (s, 18H), 7.70 (dd, J = 9.5, 2.0 Hz, 2H), 8.57 (d, J = 2.0 Hz, 2H), 8.57 (d, J = 9.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 29.7, 31.0, 35.2, 103.8, 103.9, 117.8, 121.7, 126.2, 126.8, 131.2, 132.1, 149.0; HRMS (FAB) m/z calcd for C44H66Si2 [M]+ 650.4703, found 650.4684; IR (ATR) 2955, 2923, 2862, 2126, 1625, 1461, 1374, 880, 714, 680, 646 cm−1; UV−vis (toluene, 3.0 × 10−5 mol L−1) λmax (ε) 382 (7340), 393 (8990), 415 (20300), 440 nm (25900); FL (toluene, 3.0 × 10−5 mol L−1) λmax 461, 494 nm (λex 415 nm, Φf 0.92, τ 5.64 ns). Elemental analysis calcd for C44H66Si2: C, 81.16; H, 10.22. Found: C, 81.19; H, 10.06. 2,6-Di-tertbutyl-9,10-bis[(trimethylsilyl)ethynyl]anthracene (6)22 was prepared in a similar manner from 2,6-di-tert-butyl-9,10-anthraquinone and [(trimethylsilyl)ethynyl]acetylene. Compound 6: yellow green solid, yield 87%; Rf 0.32 (hexane); mp 232−234 °C; 1H NMR (500 MHz, CDCl3) δ 0.44 (s, 18H), 1.50 (s, 18H), 7.72 (dd, J = 9.0, 2.0 Hz, 2H), 8.51 (d, J = 2.0 Hz, 2H), 8.52 (d, J = 9.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 0.2, 30.8, 35.2, 101.9, 107.5, 117.5, 121.5, 126.2, 126.8, 130.8, 132.1, 149.0; HRMS (FAB) m/z calcd for C32H42Si2 [M]+ 482.2825, found 482.2802. Typical Procedure for Desilylation Reactions. Compound 5 (57.1 mg, 0.10 mmol) was stirred with K2CO3 (70.7 mg, 0.51 mmol, 5.1 equiv) in MeOH (6 mL) and THF (6 mL) in the dark at room temperature for 1.5 h. The mixture was quenched with water (40 mL), and the organic materials were extracted with hexane (20 mL × 4). The combined organic solution was dried over Na2SO4. The evaporation gave a practically pure product as a dark brown solid in a quantitative yield, which was used for the next reaction without purification. 2,6-Di-tert-butyl-9-ethynyl-10-[(triisopropylsilyl)ethynyl]anthracene (7): Rf 0.57 (hexane/CH2Cl2 = 10:1); 1H NMR (500 MHz, CDCl3) δ 1.27 (s, 3H), 1.28 (s, 18H), 1.47 (s, 9H), 1.48 (s, 9H), 4.05 (s, 1H), 7.69 (dd, J = 5.5, 2.5 Hz, 1H), 7.71 (dd, J = 5.5, 1.5 Hz, 1H), 8.48 (d, J = 1.5 Hz, 1H), 8.51 (d, J = 9.5 Hz, 1H), 8.57 (d, J = 2.5 Hz, 1H), 8.58 (d, J = 9.5 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 29.7, 30.3, 30.9, 35.2, 80.7, 89.2, 103.6, 104.2, 116.2, 121.3, 121.8, 126.26, 126.32, 126.6, 126.9, 131.1, 131.3, 132.0, 132.3, 149.1, 149.3; HRMS (FAB) m/z calcd for C35H46Si [M]+ 494.3369, found 494.3332. 2,6-Di-tert-butyl-9,10-diethynylanthracene (8): Rf 0.43 (hexane/CH2Cl2 = 10:1); 1H NMR (500 MHz, CDCl3) δ 1.48 (s, 18H), 4.06 (s, 2H), 7.70 (dd, J = 9.0, 2.0 Hz, 2H), 8.49 (d, J = 2.0 Hz, 2H), 8.52 (d, J = 9.0 Hz, 2H); HRMS (FAB) m/z calcd for C26H26 [M]+ 338.2035, found 338.2000.
Oligomerization. To a solution of 7 (51.0 mg, 0.103 mmol) and 8 (35.2 mg, 0.104 mmol, 1.0 equiv) in THF (12 mL) were added PdCl2(PPh3)2 (10.5 mg, 15 μmmol, 0.15 equiv), CuI (1.5 mL of a 2.0 mg mL−1 solution in (i-Pr)2NH, 15 μmol, 0.15 equiv), I2 (19.9 mg, 78.4 μmol, 0.75 equiv), and (i-Pr)2NH (10.5 mL) in the dark under air. The reaction mixture was stirred at room temperature for 2 h. After the mixture was quenched with aq NH4Cl (10 mL), the organic materials were extracted with toluene (10 mL × 3). The combined organic solution was dried over Na2SO4 and evaporated. The crude product was purified by chromatography on silica gel with hexane/ toluene (20:1 to 0:1) followed by recrystallization from toluene/ MeOH. The following are yields of 4 based on 7: 4b 14.7 mg (28.9%), 4c 6.0 mg (8.7%), 4d 4.1 mg (4.8%), 4e 3.3 mg (3.2%), 4f (trace). For the data of 4b−f, see below. One-Pot Oligomerization. A mixture of 5 (58.7 mg, 0.104 mmol) and 6 (50.0 mg, 0.104 mmol) was treated with K2CO3 (144 mg, 1.04 mmol) in THF (12 mL) and MeOH (12 mL) at room temperature for 1.5 h in the dark. To the solution were added PdCl2(PPh3)2 (10.8 mg, 15 μmol, 0.15 equiv), CuI (1.5 mL of a 2.0 mg mL−1 (i-Pr)2NH solution, 15 μmol, 0.15 equiv), I2 (19.6 mg, 77.2 μmol, 0.75 equiv), and (i-Pr)2NH (10.5 mL) under air. After the reaction mixture was stirred at room temperature for 2 h, the solvents were evaporated. The crude product was purified by silica gel column chromatography with hexane/toluene (20:1 to 0:1) followed by recrystallization from toluene/MeOH. Compound 4b: orange solid; yield 15.8 mg (30.8% based on 5); Rf 0.43 (hexane/CH2Cl2 = 20:1); mp 267−292 °C (dec); 1 H NMR (500 MHz, CDCl3) δ 1.28 (s, 6H), 1.29 (s, 36H), 1.49 (s, 18H), 1.54 (s 18H), 7.75 (dd, J = 9.5, 1.5 Hz, 2H), 7.78 (dd, J = 9.5, 1.5 Hz, 2H), 8.57 (d, J = 1.5 Hz, 2H), 8.60 (d, J = 9.0 Hz, 2H), 8.61 (d, J = 1.5 Hz, 2H), 8.64 (d, J = 9.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 29.7, 30.96, 31.00, 35.3, 82.9, 86.4, 103.6, 105.1, 116.0, 119.1, 121.3, 122.0, 126.5, 126.7, 126.7, 127.1, 131.2, 132.10, 132.12, 133.1, 149.4, 149.8; HRMS (FAB) m/z calcd for C70H90Si2 [M]+ 986.6581, found 986.6600; IR (ATR) 2960, 2864, 2125, 1372, 1250, 885, 817, 714, 671, 617, 606 cm−1; UV−vis (toluene, 2.0 × 10−5 mol L−1) λmax (ε) 388 (10600), 474 (41600), 487 (40400), 523 nm (49500); FL (toluene, 2.0 × 10−5 mol L−1) λmax 541, 572 nm (λex 474 nm, Φf 0.020). Compound 4c: red solid; yield 12.9 mg (18.7% based on 5); Rf 0.26 (hexane/CH2Cl2 = 20:1); mp 300−315 °C (dec); 1H NMR (500 MHz, CDCl3) δ 1.28 (s, 6H), 1.29 (s, 36H), 1.49 (s, 18H), 1.54 (s, 18H), 1.56 (s, 18H), 7.75 (dd, J = 9.0, 2.0 Hz, 2H), 7.78 (dd, J = 9.5, 2.0 Hz, 2H), 7.82 (dd, J = 9.0, 1.5 Hz, 2H), 8.57 (d, J = 1.0 Hz, 2H), 8.59−8.61 (m, 6H), 8.64 (d, J = 9.0 Hz, 2H), 8.67 (d, J = 9.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 29.7, 30.96, 30.98, 31.00, 35.27, 35.31, 83.8, 83.5, 86.3, 87.2, 103.6, 105.3, 115.8, 117.2, 119.2, 121.3, 121.6, 122.1, 126.5, 126.7, 126.8, 127.0, 127.1, 131.2, 132.09, 132.11, 132.2, 133.1, 133.2, 149.4, 149.8, 150.1; HRMS (FAB) m/z calcd for C96H114Si2 [M]+ 1322.8459, found 1322.8470; IR (ATR) 3065, 2952, 2865, 2366, 2130, 1626, 1459, 1368, 885, 818, 714, 671, 649 cm−1; UV−vis (toluene, 1.5 × 10−5 mol L−1) λmax (ε) 390 (17700), 503 (58800, sh), 540 (79000), 570 nm (60400, sh); FL (toluene, 1.5 × 10−5 mol L−1) λmax 589, 635 nm (λex 505 nm, Φf 0.022). Compound 4d: deep red solid; 11.0 mg (12.7% based on 5); Rf 0.13 (hexane/CH2Cl2 = 20:1); mp 233−260 °C (dec); 1H NMR (500 MHz, CDCl3) δ 1.29 (s, 6H), 1.30 (s, 36H), 1.50 (s, 18H), 1.55 (s, 18H), 1.57 (d, J = 1.0 Hz, 36H), 7.76 (dd, J = 9.0, 1.5 Hz, 2H), 7.80 (dd, J = 9.0, 2.0 Hz, 2H), 7.84 (dd, J = 9.5, 2.0 Hz, 2H), 7.85 (dd, J = 9.5, 2.0 Hz, 2H), 8.58 (d, J = 2.0 Hz, 2H), 8.61 (d, J = 9.0 Hz, 2H), 8.62 (d, J = 2.0 Hz, 2H), 8.63 (d, J = 2.0 Hz, 4H), 8.64 (d, J = 9.5 Hz, 2H), 8.69 (d, J = 9.0 Hz, 4H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 29.7, 31.0, 35.28, 35.32, 82.8, 83.4, 83.6, 86.3, 87.1, 87.3, 103.6, 105.3, 115.8, 117.1, 117.4, 121.3, 121.6, 121.7, 122.1, 125.3, 126.5, 126.7, 126.8, 126.97, 127.02, 127.2, 128.2, 129.0, 131.2, 132.09, 132.11, 132.2, 133.1, 133.1, 133.2, 149.4, 149.9, 150.1, 150.2; HRMS (FAB) m/z calcd for C122H139Si2 [M]+ 1660.0415, found 1660.0400; IR (ATR) 3066, 2953, 2865, 2131, 1625, 1461, 1368, 1250, 884, 817, 715, 674, 649 cm−1; UV−vis (toluene, 6.0 × 10−6 mol L−1) λmax (ε) 391 (22600), 548 (112000), 582 nm (94500); FL (toluene, 6.0 × 10−6 mol L−1) λmax 609 nm (λex 508 nm, Φf 0.020). Compound 4e: purple solid; 7.2 mg (6.9% based on 5); Rf 0.06 (hexane/CH2Cl2 = 20:1); mp 5787
DOI: 10.1021/acs.joc.8b00311 J. Org. Chem. 2018, 83, 5784−5790
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The Journal of Organic Chemistry 312−318 °C (dec); 1H NMR (500 MHz, CDCl3) δ 1.29 (s, 6H), 1.30 (s, 36H), 1.50 (s, 18H), 1.55 (s, 18H), 1.58 (s, 18H), 1.58 (s, 18H), 1.59 (s, 18H), 7.76 (dd, J = 9.5, 1.5 Hz, 2H), 7.80 (dd, J = 9.0, 2.0 Hz, 2H), 7.84 (dd, J = 9.5, 2.0 Hz, 2H), 7.85 (dd, J = 9.5, 1.5 Hz, 2H), 7.86 (dd, J = 9.0, 1.5 Hz, 2H), 8.59 (d, J = 2.0 Hz, 2H), 8.61 (d, J = 9.0 Hz, 2H), 8.62 (d, J = 1.5 Hz, 2H), 8.63 (d, J = 1.5 Hz, 2H), 8.64 (d, J = 2.0 Hz, 2H), 8.65 (d, J = 9.0 Hz, 2H), 8.70 (d, J = 8.0 Hz, 4H), 8.70 (d, J = 9.5 Hz, 4H); HRMS (FAB) m/z calcd for C148H162Si2 [M]+ 1995.2215, found 1995.2241; IR (ATR) 3066, 2952, 2864, 2131, 1625, 1459, 1369, 1252, 884, 816, 716, 679 cm−1; UV−vis (toluene, 8.1 × 10−6 mol L−1) λmax (ε) 392 (29300), 558 (138000), 585 nm (135000); FL (toluene, 8.1 × 10−6 mol L−1) λmax 624 nm (λex 513 nm, Φf 0.018). Compound 4f: purple solid; trace; Rf 0.01 (hexane/toluene = 20:1); mp 254−256 °C (dec); 1H NMR (500 MHz, C6D6) δ 1.35− 1.38 (m, 42H), 1.41 (s, 18H), 1.43 (s, 36H), 1.44 (s, 18H), 1.45 (s, 36H), 7.58 (dd, J = 9.0, 2.0 Hz, 2H), 7.59−7.62 (m, 8H), 7.65 (dd, J = 9.5, 2.0 Hz, 2H), 8.88 (d, J = 9.0 Hz, 2H), 8.90 (dd, J = 9.0, 2.0 Hz, 8H), 8.93 (d, J = 2.0 Hz, 2H), 8.99−9.00 (m, 12H); MS (MALDITOF) m/z calcd for C174H186Si2 [M]+ 2331.4093, found 2331.4119; IR (ATR) 3650, 3063, 2954, 2864, 2130, 1625, 1459, 1367, 1249, 884, 817, 714, 649 cm−1; UV−vis (toluene, 4.8 × 10−6 mol L−1) λmax (ε) 373 (18800), 393 (32000), 429 (29400), 554 (142000), 589 (151000) nm; FL (toluene, 4.8 × 10−6 mol L−1) λmax 629 nm (λex 552 nm). Synthesis of Oligomers 4b(H). A mixture of 9[(triisopropylsilyl)ethynyl]-10-[(trimethylsilyl)ethynyl]anthracene23 (5(H), 66.5 mg, 0.146 mmol) and 9,10-bis[(trimethylsilyl)ethynyl]anthracene22 (6(H), 54.2 mg, 0.146 mmol) was treated with K2CO3 (201 mg, 1.46 mmol, 10 equiv) in THF (16 mL) and MeOH (16 mL) at room temperature for 1.5 h in the dark. To the solution were added PdCl2(PPh3)2 (15.5 mg, 22 μmol, 0.15 equiv), CuI (4.1 mg, 22 μmol, 0.15 equiv), I2 (28 mg, 0.11 mmol, 0.75 equiv), and (i-Pr)2NH (16 mL) under air. After the reaction mixture was stirred at room temperature for 4 h, the solvents were evaporated. The crude product was purified by silica gel column chromatography with hexane/toluene (20:1 to 0:1) followed by recrystallization from toluene/MeOH to give pure 2-mer and 3-mer; 4-mer was inseparable and checked only by TLC and mass spectrometry. Compound 4b(H): orange solid; yield 18.1 mg (32.5% based on 5(H)); Rf 0.48 (hexane/toluene = 20:1); mp 243−245 °C; 1H NMR (500 MHz, CDCl3) δ 1.28 (s, 6H), 1.29 (s, 36H), 7.65 (dt, J = 7.5, 1.0 Hz, 2H), 7.66 (dt, J = 7.5, 1.0 Hz, 2H), 7.68 (dt, J = 7.5, 1.0 Hz, 2H), 7.69 (dt, J = 7.5, 1.0 Hz, 2H), 8.69 (d, J = 8.5 Hz, 4H), 8.71 (d, J = 8.0 Hz, 4H); 13C NMR (125 MHz, CDCl3) δ 11.5, 18.9, 82.7, 86.6, 103.2, 106.2, 116.7, 120.1, 127.1, 127.1, 127.4, 127.5, 132.4, 133.4; HRMS (FAB) m/z calcd for C54H58Si2 [M]+ 762.4077, found 762.4044; UV−vis (toluene, 1.3 × 10−5 mol L−1) λmax (ε) 384 (8720), 401 (9450), 440 (25800, sh), 468 (53100), 483 (49600), 521 (53400) nm; FL (toluene) λmax 535 nm (λex 485 nm, Φf 0.01). Compound 4c(H): black solid; yield 12.9 mg (17.9% based on 5(H)); mp 300−305 °C (dec); Rf 0.20 (hexane/ toluene = 20:1); 1H NMR (500 MHz, CDCl3) δ 1.28 (s, 6H), 1.30 (s, 36H), 7.66 (dt, J = 8.8, 1.0 Hz, 2H), 7.67 (dt, J = 8.8, 1.0 Hz, 2H), 7.70 (dt, J = 8.8, 1.0 Hz, 2H), 7.71 (dt, J = 8.8, 1.0 Hz, 2H), 7.76 (dq, J = 6.5, 3.0 Hz, 4H), 8.70 (d, J = 8.5 Hz, 4H), 8.73 (d, J = 9.0 Hz, 4H), 8.77 (dq, J = 7.0, 3.5 Hz, 4H); 13C NMR (125 MHz, CDCl3): 11.5, 18.9, 82.6, 83.4, 86.5, 87.5, 103.2, 106.3, 116.6, 118.1, 120.3, 127.05, 127.14, 127.4, 127.5, 127.6, 127.7, 132.4, 133.4, 133.5; HRMS (FAB) m/z calcd for C72H66Si2 [M]+ 986.4703, found 986.4700; UV−vis (toluene, 1.0 × 10−5 mol L−1) λmax (ε) 387 (12600), 421 (18200), 503 (65800, sh), 538 (82700), 568 (51300, sh) nm; FL (toluene) λmax 582, 627 nm (λex 504 nm, Φf 0.01). Compound 4d(H): trace; Rf = 0.12 (hexane/toluene = 20:1); MS (MALDI-TOF) m/z calcd for C90H74Si2 [M]+ 1210.532, found 1210.439. DFT Calculations. Calculations were carried out with the Gaussian 09 (version C.01) program24 on a Windows computer. The structures were optimized by the hybrid DFT method at the B3LYP/6-31G(d) level. The frequency analysis was performed for each optimized structure, and no imaginary frequency was obtained in each structure. In order to reduce the calculation costs, we adopted model compounds 4(H)′, where t-butyl groups on anthracene moieties
were omitted and terminal triisopropylsilyl groups were replaced by trimethylsilyl groups. Cyclic Voltammogram Measurements. CV measurements were performed on a Hokuto Denko HSV-110 automatic polarization system. The data were collected in CH2Cl2 solution at room temperature together with 0.10 mol L−1 of Bu4NClO4 as an electrolyte. All potentials were measured with a Pt working electrode (rod) and a Pt counter electrode (wire) against Ag/AgCl/NaCl in a Luggin capillary, and the values were converted to the potentials vs Fc/Fc+ under the identical conditions. The scan rate was 10 mV s−1. No reliable voltammograms of 4e and 4f were obtained due to the low solubility. X-ray Crystallographic Analysis of 4c. A single crystal of 4c was obtained by recrystallization from CH2Cl2/ethyl acetate. Diffraction data were collected on a Rigaku Varimax unit with a Saturn system equipped with a Rigaku GNNP low temperature device using Mo Kα radiation (λ = 0.71075 Å) to a maximum 2θ value of 55.0° at −150 °C. Equivalent reflections were merged, and the images were processed with the Rigaku CrysAlisPro program. The structure solution was performed using the Yadokari-XG25 program as a graphical user interface with SHELX-201326 as a set of structure determination programs. The structure was solved by the direct method and refined by the full-matrix least-squares method. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in fixed positions. Crystallographic data: formula C96H114Si2; C4H8O2; CH2Cl2, M = 1324.14, triclinic, P1, a = 13.0957(4), b = 19.0281(7), c = 19.8599(6) Å, α = 68.022(3)°, β = 88.534(3)°, γ = 87.009(3)°, V = 4582.8(3) Å3, Z = 2, Dc = 1.083 g cm−3, (Mo Kα) = 0.143 mm−1. Number of data 13509, number of data used 14215 [I > 2.0σ(I)], R1 = 0.0992, wR2 = 0.3037, GOF = 1.010, CCDC1582756. The data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html. The structures of two independent molecules and the packing diagrams are shown in Figure S1.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b00311.
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X-ray structures, UV−vis/fluorescence spectra, CV data, DFT calculation data, and copies of 1H and 13C NMR spectra (PDF) Crystal data for 4c (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Eiji Tsurumaki: 0000-0003-0536-3858 Tetsuo Iwanaga: 0000-0002-2224-3746 Shinji Toyota: 0000-0002-1504-2030 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
This work was partly supported by JSPS KAKENHI for Scientific Research (C) Grant no. 26410060. The authors thank Professor Osamu Ishitani and Professor Nobuharu Iwasawa of Tokyo Institute of Technology for the measurements of fluorescence spectra and cyclic voltammetry, Professor Kan Wakamatsu of Okayama University of Science and Dr. Masashi Hasegawa of Kitasato University for helpful discussions, and Mr. Kenta Kawahata for his technical assistance. 5788
DOI: 10.1021/acs.joc.8b00311 J. Org. Chem. 2018, 83, 5784−5790
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The Journal of Organic Chemistry
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