Synthesis and Electronic Properties of Length-Defined 9,10

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Synthesis and Electronic Properties of LengthDefined 9,10-Anthrylene–Butadiynylene Oligomers Maiko Nagaoka, Eiji Tsurumaki, Mai Nishiuchi, Tetsuo Iwanaga, and Shinji Toyota J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00311 • Publication Date (Web): 18 Apr 2018 Downloaded from http://pubs.acs.org on April 18, 2018

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The Journal of Organic Chemistry

Synthesis and Electronic Properties of Length-Defined 9,10Anthrylene–Butadiynylene Oligomers Maiko Nagaoka†, Eiji Tsurumaki†, Mai Nishiuchi‡, Tetsuo Iwanaga‡, Shinji Toyota*† †

Department of Chemistry, School of Science, Tokyo Institute of Technology, 2–12–1 Ookayama, Meguro-ku, Tokyo 1528551, Japan ‡ Department of Chemistry, Faculty of Science, Okayama University of Science, 1–1 Ridaicho, Kita-ku, Okayama 700-0005, Japan Supporting Information Placeholder

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. Arylene 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 π-conjugation, 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 9,10-anthrylene 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(9anthryl)-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 having defined lengths. Therefore, we synthesized 9,10anthrylene–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 6mer.

Figure 1. Structures of 9,10-anthrylene ethynylene or butadiynylene linkers.

oligomers

with

Because our preliminary experiments revealed that substituent-free oligomers 4(H) were poorly soluble (see Experimental section), we introduced two t-butyl groups to each anthracene unit. We synthesized target oligomers 4 by the Pd/Cu-catalyzed oxidative coupling12 of 9,10diethynylanthracene 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 in from 5 and 6, respectively. Although the coupling reaction of

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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 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 (6-mer) with increasing chain length.

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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 increasing intensity as the number of anthracene units increased, even though the red-shift effect became gradually 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 shifts 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 non-radiative pathways, as reported for other diacetylene compounds.5,11d,18

Scheme 1. Synthesis of Oligomers 4

Figure 2. Two views of 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.

The X-ray structures of 4c are shown in Figure 2. The three anthracene planes are approximately coplanar along the linear 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 Sshaped 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)’ having SiMe3 terminal groups and no t-Bu groups. The optimized structures at the B3LYP/6-31G(d) level are shown in Figure 3 [4c(H)’] and Figures S7. In all the oligomers, the anthracene groups are coplanar, although the rotation along the acetylene axis requires a very small 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 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

LUMO –2.85 eV

HOMO –4.81 eV

Figure 3. Two views of calculated structure of 4c(H)’ (a SiMe3 derivative) at B3LYP/6-31G(d) level and its HOMO and LUMO plots. The data of other oligomers are given in Figure S7.

To investigate electrochemical redox properties, we carried out cyclic voltammetric measurements of 4a–d (Table 2 and Figure S6). Compound 4b exhibited two reversible oxidation waves Eox at +0.63 and +0.87 V, and 4c and 4d clearly showed


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The Journal of Organic Chemistry Table 1. Photophysical Properties of Oligomers 4 Measured in Toluene λmax (nm) (ε) a

λem (nm) b

Φf c

Stokes shift (eV)

Egmax (eV) d

Egonset (eV) e

EgDFT (eV) f

4a

440 (26000)

461

0.92

0.128

2.82

2.66

2.91

4b

524 (49600)

541

0.020

0.079

2.37

2.24

2.26

4c

570 (60400)

4d

582 (94500)

g

589

0.022

0.070

2.18

2.04

1.96

609

0.020

0.094

2.13

1.96

1.81

4e

585 (137000)

623

0.018

0.129

2.12

1.90

1.72

4f

588 (154000)

628

na

0.134

2.11

1.89

1.66

a. Wavelengths and molar extinction coefficients of the absorption maxima. b. Wavelengths of the emission maxima. c. Absolute fluorescence quantum yields. d. Energy gaps calculated from absorption maxima. e. Energy gaps calculated from absorption onset. f. Calculated HOMO-LUMO gap energies at B3LYP/6-31G(d) level for model compounds 4(H)’. g. A shoulder.

a. Conditions: Ag/AgCl working electrode (rod), Pt counter electrode (wire), supporting electrolyte 0.10 mol L–1 Bu4NClO4 in CH2Cl2. Scan rate 10 mV s–1. b. Differences between the first oxidation wave and the first reduction wave.

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.

three and four oxidation waves, respectively. These observations suggest that the oxidation proceeds in a stepwise manner and 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. Analogous pentacene oligomers showed multi-step 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

Table 2. Cyclic Voltammetry Data for 4a–d a Eox1 (V)

Eox2 (V)

Eox3 (V)

Eox4 (V)

Ered1 (V)

Ered2 (V)

∆E (eV) b

4a

+0.74

—

—

—

–2.08

—

2.82

4b

+0.63

+0.87

—

—

–1.73

–1.90

2.36

4c

+0.61

+0.77

+1.07

—

–1.58

–1.71

2.19

4d

+0.57

+0.70

+0.90

+1.06

–1.57

—

2.14

Conclusion In summary, 9,10-anthrylene–butadiynylene linear oligomers of up to 6-mer were successfully synthesized by a onepot 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. Experimental Section 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 FAB method with a quadrupole mass analyzer. IR spectra were recorded on a JASCO SC-100VIR 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. Column chromatography was carried out with Silica Gel 60 N (spherical, neutral) (40-50 mesh) (Kanto chemical). Typical Procedure for Synthesis of 9,10Diethynylanthracenes. 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 eq.) 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 eq.) 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,



4.68 mmol, 3.0 eq.) and nBuLi (1.6 mol L–1 solution in hexane, 3.0 mL, 4.68 mmol, 3.0 eq.) in another flask. To the solution of [(triisopropylsilyl)ethynyl]lithium was added 2,6-di-t-butyl9,10-anthraquinone21 (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 refluxed for 7 h. To the reaction mixture were added SnCl2.2H2O (1.77 g, 7.80 mmol, 5.0 eq.) and HCl (3 mol L–1, 4 mL), and then 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 by-products. 2,6-Di-t-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, 126.2, 126.2, 126.8, 130.9, 131.2, 132.1, 132.1, 148.9, 149.0; HRMS (FAB): m/z calcd for C38H54Si2 [M]+ 566.3764, found 566.3741. 2,6-Di-t-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-t-butyl-9,10bis[(trimethylsilyl)ethynyl]anthracene (6)22 was prepared in a similar manner from 2,6-di-t-butyl-9,10-anthraquinone and [(trimethylsilyl)ethynyl]acetylene. 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 eq.) 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 practically pure product as dark brown solid in quantitative yield, which was used for the next reaction without purification. 2,6-Di-t-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, 126.3, 126.3, 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-t-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 eq.) in THF (12 mL) were added PdCl2(PPh3)2 (10.5 mg, 15 µmmol, 0.15 eq.), CuI (1.5 mL of a 2.0 mg mL–1 solution in (i-Pr)2NH, 15 µmol, 0.15 eq.), I2 (19.9 mg, 78.4 µmol, 0.75 eq.), 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 ~ 0 : 1) followed by recrystallization from toluene/MeOH. 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%), and 4f (trace). See below, for the data of 4b–f. 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 eq.), CuI (1.5 mL of a 2.0 mg mL–1 (i-Pr)2NH solution, 15 µmol, 0.15 eq.), I2 (19.6 mg, 77.2 µmol, 0.75 eq.), 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 ~ 0 : 1) followed by recrystallization from toluene/MeOH. 4b: orange solid; yield 15.8 mg (30.8% based on 5); Rf 0.43 (hexane/CH2Cl2 = 20 : 1); mp 267–292 °C (dec.); 1H 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). 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


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The Journal of Organic Chemistry 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 (60700); FL (toluene, 1.5 × 10–5 mol L– 1 ): λmax = 589, 635 nm (λex 505 nm, Φf 0.022). 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). 4e: purple solid; 7.2 mg (6.9% based on 5); Rf 0.06; (hexane/CH2Cl2 = 20 : 1); mp 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), 1.58 (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). 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, 27H), 1.43 (s, 36H), 1.44 (s, 18H), 1.45 (s, 27H), 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 (MALDI-TOF): 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), 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 eq.) 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 eq.), CuI (4.1 mg, 22 µmol, 0.15 eq.), I2 (28 mg, 0.11 mmol, 0.75 eq.), and (iPr)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 ~ 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. 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 (125MHz, CDCl3): 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); FL (toluene): λmax = 535 nm (λex 485 nm, Φf 0.01). 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); FL (toluene): λmax = 582, 627 nm (λex 504 nm, Φf 0.01). 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 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 electrolyte. All potentials were measured with a Pt working electrode (rod) and a Pt counter electrode (wire) against an 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 10mV 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 with Saturn system equipped 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 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 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, P–1, 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.

ASSOCIATED CONTENT

Supporting Information The Supporting Information is available free of charge on the ACS Publications website. X-ray structures; UV-vis/FL spectra; CV data; DFT calculation data; Copy of 1H and 13C NMR spectra (PDF) Crystal data for 4c (CIF)

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]

ORCID Shinji Toyota: 0000-0002-1504-2030 Eiji Tsurumaki: 0000-0003-0536-3858 Tetsuo Iwanaga: 0000-0002-2224-3746

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was partly supported by JSPS KAKENHI for Scientific Research (C) Grant Number 26410060. The authors thank Professors 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 discussion, and Mr. Kenta Kawahata for his technical assistance.

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Synthesis and Electronic Properties of Length-Defined 9,10

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