Tetraalkoxyphenanthrene-Fused Hexadecadehydro[20]- and

Article pubs.acs.org/joc

Tetraalkoxyphenanthrene-Fused Hexadecadehydro[20]- and Tetracosadehydro[30]annulenes: Syntheses, Aromaticity/ Antiaromaticity, Electronic Properties, and Self-Assembly Nobutaka Takahashi,† Shin-ichiro Kato,†,§ Minoru Yamaji,† Masahiko Ueno,† Ryunosuke Iwabuchi,† Yui Shimizu,† Masashi Nitani,‡ Yutaka Ie,‡ Yoshio Aso,‡ Takeshi Yamanobe,† Hiroki Uehara,† and Yosuke Nakamura*,† †

Division of Molecular Science, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan ‡ The Institute of Scientific and Industrial Research (ISIR), Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan S Supporting Information *

ABSTRACT: Tetraalkoxyphenanthrene-fused hexadecadehydro[20]- and tetracosadehydro[30]annulenes possessing octatetrayne linkages were synthesized and their properties together with those of phenanthrene-fused octadehydro[12]and dodecadehydro[18]annulenes have been investigated. Various spectroscopic and electrochemical measurements as well as quantum chemical calculations support that planar [20]- and [30]annulenes are weakly antiaromatic and nonaromatic, respectively. The detailed concentration- and temperature-dependent 1H NMR and UV−vis data of present dehydroannulenes provided evidence for the enhancement of π−π stacking interactions by extension of the acetylenic linkages. Dehydroannulenes formed self-assembled clusters and their morphology and crystallinity proved to depend on the length of acetylenic linkages, the shape of dehydroannulene core, and the bulkiness of alkoxy groups appended to the phenanthrene moieties.

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INTRODUCTION Highly conjugated organic molecules have been recognized as ideal materials for electronic and photonic applications due to their ease of structural fine-tuning for enhancing specific properties of specialized applications. Fully π-conjugated cyclic oligomers with nondeformable backbone, namely, shapepersistent macrocycles (SPMs) constituted the important class of compounds among various π-conjugated systems, because they show intriguing optoelectronic properties based on the infinite π-conjugation and are capable of building up highly ordered 1D, 2D, and 3D supramolecular nano- and microstructures.1 Dehydro[n]annulenes and dehydrobenzo[n]annulenes ([n]DBAs), in which n denotes the number of carbon atoms in the cyclic pathway, have been investigated extensively since 1960s in connection with validation of Hückel rule concerning aromaticity/antiaromaticity of cyclic πconjugated systems.2 Over the last two decades, however, dehydro[n]annulenes and [n]DBAs have been the subjects of renewed intense interest because of their aspects as SPMs and substructures of 2D carbon networks (e.g., graphyne and graphdiyne).3,4 Due to the recent development of synthetic methodologies using transition-metal catalysts, the synthesis and investigation of increasingly larger and synthetically more complex systems, such as multiple-fused [n]DBA derivatives, have been achieved. Just as a recent example, Shimizu, Seki, © 2017 American Chemical Society

Kamada, Moore, Tobe, and co-workers synthesized the largest graphyne fragments, namely, trigonally expanded tetrakis[12]DBAs,4 which exhibit large two-photon absorption cross sections and high charge-carrier mobility; the compounds with alkoxycarbonyl groups were found to display liquid-crystalline phases.4e,5 One of the rational design strategies to create dehydro[n]annulene-based π-functional materials should be the appropriate annulation of aromatic and conjugated heterocycles larger than benzene to a dehydro[n]annulene ring, because the structural and electronic features of the annulated moiety have potential to bring about fascinating electronic and selfassembling properties in the resulting molecules.6−13 In line with this strategy, we have recently designed and synthesized octadehydro[12]annulene 1a and dodecadehydro[18]annulene 2a that consist of 2,3,6,7-tetrakis(decyloxy)phenanthrene moieties and butadiyne linkages (Chart 1).14 By investigating their properties with [12]- and [18]DBA derivatives, the annulation of phenanthrene into a dehydroannulene ring enhances the tropicities and decreases the HOMO−LUMO gaps of the molecules relative to the benzannulation, because the higher bond order of the 9−10 bond of phenanthrene than Received: May 12, 2017 Published: August 7, 2017 8882

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

Article

The Journal of Organic Chemistry

clarification of the impact of extending acetylenic linkages from butadiyne to octatetrayne units on the overall properties of our tetraalkoxyphenanthrene-fused dehydroannulene systems. For instance, we had the following questions with respect to the structure−property relationships: (1) Do 3 and 4 still show distinct tropicity in spite of their large dehydroannulene rings? (2) How does the extension of acetylenic linkages from 1 and 2 to 3 and 4 alter the optoelectronic properties (e.g., HOMO− LUMO gaps) and self-assembling properties? The syntheses of acetylenic macrocycles possessing oligoyne linkages that are longer than butadiyne linkages are challenging, because an increase in the number of the conjugated CC−C bonds decreases the stability in the resulting molecules. Only a limited number of dehydroannulenes and DBAs possessing octatetrayne linkages have been reported so far.17 Hence, there still remains the elucidation of the effects of incorporation of an octatetrayne unit into dehydroannulene and DBA systems on various properties as an important issue from the point of both fundamental and materials science aspect of the annulene chemistry. In this article, we describe the synthesis, characterization, and unique properties of hitherto unknown 3 and 4, which are so stable that they are isolable in the solid state. The tropicity and physicochemical properties of 3 and 4 were assessed by various spectroscopies, cyclic and differential-pulse voltammetry (CV and DPV), and quantum chemical calculations and compared with those of reference compounds 1 and 2. Concentrationand temperature-dependent 1H NMR and UV−vis spectroscopies were applied for the quantitative analysis for the selfassociation of 1−4; this is the first example of thermodynamic study on the self-association processes of conjugated macrocycles possessing octatetrayne linkages. The formation of selfassembled clusters from 1−4 was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and wide-angle X-ray diffraction (WAXD). These results highlight the significance of the incorporation of oligoyne linkages into the annulenic systems for the creation of πfunctional systems.

Chart 1. Structures of Phenanthrene-Fused Dehydroannulenes 1a,b, 2a,b, 3a,b, and 4b

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RESULTS AND DISCUSSION Syntheses. The synthetic route to dehydro[20]- and [30]annulenes 3a,b and 4b is outlined in Scheme 1. We planned to introduce decyloxy or 2-ethylhexyloxy groups to phenanthrene-fused dehydroannulenes because the bulkiness of alkoxy groups was anticipated to affect the solubility and selfassembling behavior of the compounds.18 Intramolecular oxidative cyclization of benzils 5a,b with MoCl5/TiCl4 mixture in CH2Cl2 afforded diketones 6a,b. The addition of the lithiated acetylide of trimethylsilylacetylene (TMSA) to 6a,b, followed by the treatment with (MeO)2SO2 gave methyl ethers 7a,b. Desilylation of the TMS groups of 7a,b with K2CO3 afforded 8a,b, which were then subjected to the Cadiot−Chodkiewicz coupling reaction condition with (2-bromoethynyl)triisopropylsilane to give 9a,b. Reductive aromatization of 9a,b with SnCl2·2H2O in THF in the presence of H2SO4 smoothly proceeded to afford 10a,b. Removal of the triisopropylsilyl groups of 10a,b with tetrabutylammonium fluoride (TBAF) gave the key intermediates 11a,b, which were immediately subjected to macrocyclization reaction; terminal alkynes 11a,b were unstable in contrast to 10a,b. First, the Hay coupling reaction of 11a by using CuCl and N,N,N′,N′-tetramethylethylenediamine (TMEDA) in CH2Cl2 was examined. 1H NMR and mass spectrometric analyses of the

the carbon−carbon bond of benzene causes high extent of πconjugation in the annulenic moieties. Various spectroscopic measurements of 1a established its noticeable degree of antiaromaticity; afterward, several research groups reported that the annulation of phenanthrene into an antiaromatic 4nπ system is an efficient way for developing highly antiaromatic yet stable compounds.15,16 Both 1a and 2a were also found to exhibit self-association properties in solution through π−π stacking interactions resulting from their extended π-surfaces and to produce 1D self-assembled clusters with high aspect ratio. In view of the appealing optoelectronic and self-assembling properties of 1a and 2a, we were motivated to prepare their higher analogs, namely, hexadecadehydro[20]- and tetracosadehydro[30]annulene derivatives 3 and 4 possessing octatetrayne linkages (Chart 1). We were interested in the 8883

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

Article

The Journal of Organic Chemistry Scheme 1. Synthesis of Dehydroannulenes 3b and 4ba

Reagents and conditions: (a) TiCl4, MoCl5, CH2Cl2, 0 °C to RT; (b) (1) Me3Si−CCLi, THF, − 78 °C to RT; (2) (MeO)2SO2, THF, − 78 °C to RT; (c) K2CO3, THF/MeOH (1:1 v/v), RT; (d) (i-Pr)3Si−CCBr, NH2OH·HCl, n-BuNH2, CuCl, CH2Cl2/H2O (1:1 v/v), 30 °C; (e) SnCl2· 2H2O, H2SO4, THF, reflux; (f) TBAF, THF, 0 °C; (g) Condition A: CuCl, TMEDA, CH2Cl2, RT; Condition B: [PdCl2(PPh3)2], CuI, Et3N, THF, RT. TBAF = tetrabutylammonium fluoride. TMEDA = N,N,N′,N′-tetramethylethylenediamine. a

in 3b and 4b may contribute to their exceptional solid-state stability electronically and kinetically, respectively. Thermal gravimetric analyses (TGA) under nitrogen atmosphere showed that the 5% weight loss occurred at 328 and 273 °C for 3b and 4b, respectively, indicative of their high thermal stability (Figure S1). As reference compounds of 3b and 4b, dehydro[12]- and [18]annulenes 1b and 2b were also prepared in similar manners for the synthesis of 1a and 2a, respectively (Scheme S1).14 1 H NMR Spectra and NICS Calculations. To gain insight into the structures of the dehydroannulenes, we optimized ground-state structures of 1′−4′, in which the 2-ethylhexyloxy groups in 1b−4b were replaced with methoxy groups, at the B3LYP/6-31G(d) level of theory.20 The optimized structures of 1′ and 3′ have planar D2h symmetry, whereas 2′ and 4′ are also planar with D3h symmetry. The partial 1H NMR spectra of 3b, 4b, and acyclic 10b in CDCl3 are shown in Figure 1. Dehydroannulenes 3b and 4b exhibit very simple NMR signals, namely a pair of two singlets in the aromatic region owing to their highly symmetrical structures. For the assignment of the 1 H NMR signals of the aromatic protons in 1b−4b, the GIAO calculations for 1′−4′ at the B3LYP/6-311++(2d,2p)// B3LYP/6-31G(d) level were conducted. The experimental and theoretical 1H NMR chemical shifts are listed in Table 1; there is the semiquantitative accordance between the theoretical chemical shifts of 1′−4′ and the corresponding 1b−4b.

resulting material indicated the formation of 3a, however, its isolation and full characterization could not be accomplished due to the severe insolubility in organic solvents. Next, we performed the Hay coupling reaction of 11b, and gratifyingly isolated 3b in 56% yield together with 4b in 5% yield, over two steps from 10b. Dehydroannulenes 3b and 4b are red solids that are readily soluble in common organic solvents, such as hexane, toluene, and CHCl3, in sharp contrast to 3a due to the bulky 2-ethylhexyloxy groups appended to the phenanthrene moieties in 3b and 4b. The Pd-mediated oxidative coupling reaction of 11b with [PdCl2(PPh3)2] and CuI under air was also performed, and 4b was obtained in 16% yield. The formation of 3b was not detected by the thin-layer chromatography (TLC) and the 1H NMR spectroscopic analysis of the reaction mixture. The preferential formation of 4b by the Pd-mediated homocoupling reaction of 11b should reflect the difference of mechanism between the Cu- and Pdmediated diyne-formation reactions.19 Dehydroannulenes 3b and 4b were undoubtedly identified by MALDI-TOF-MS analyses together with their highly symmetric 1H NMR spectra as described below. Neither 3b nor 4b shows any sign of decomposition when kept in the solid state for over a year. The solid-state stability of 3b and 4b is quite remarkable, because macrocycles possessing octatetrayne units are known to be generally unstable in neat form; for instance, hexadecadehydrodibenzo[20]- and tetracosadehydrotribenzo[30]annulenes synthesized by us decompose in the solid state.17d The phenanthrene moieties and the bulky 2-ethylhexyloxy groups 8884

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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(Table 1). The moderate NICS values of 3′ imply borderline character of 3b between antiaromaticity and nonaromaticity. The NICS(0) (and NICS(1)) values of 4′ (−0.8 (−0.8)) are less negative than those of 2′ (−2.3 (−2.1)) and close to zero, indicating the lack of aromaticity of 4b. Electronic and Photophysical Properties. Figure 2 shows the absorption and emission spectra of 1b−4b, 10b, Figure 1. Partial 1H NMR spectra of (a) 10b, (b) 3b (3.56 × 10−4 mol L−1), and (c) 4b (1.68 × 10−4 mol L−1) in CDCl3 at 20 °C. Peaks attributed to the impurity by CDCl3 are labeled with asterisks.

Table 1. Observed and Calculated 1H NMR Chemical Shifts and NICS Values for 1b−4b, 10b, and 12b Ha δobs 1b 2b 3bd 4be 10b 12b

Hb

a

δcalcd

7.52 7.83 7.56 7.68 7.68 7.70

7.55 8.19 7.49 8.01 7.89 7.84

b

δobs

a

7.00 8.06 7.19 7.71 7.68 7.79

δcalcdb

NICS(0)c

NICS(1)c

6.94 8.84 7.00 8.37 7.97 8.10

+10.8 −2.3 +6.0 −0.8 N/A N/A

+9.5 −2.1 +5.4 −0.8 N/A N/A

a In CDCl3 at 25 °C. bCalculated by using GIAO/B3LYP/6-311+ +G(2d,2p)//B3LYP/6-31G(d) for 1′−4′, 10b′, and 12b′, where the 2-ethylhexyloxy and TIPS groups in 1b−4b, 10b, and 12b were replaced with methoxy and the TMS groups, respectively. cCalculated by using GIAO/B3LYP/6-311++G(2d,2p)//B3LYP/6-31G(d) for 1′−4′. d[3b] = 3.56 × 10−4 mol L−1. e[4b] = 8.43 × 10−4 mol L−1.

Planar dehydro[20]- and [30]annulenes 3b and 4b are formally antiaromatic and aromatic, respectively. The 1H NMR chemical shifts are a good measure for the elucidation of tropicity, namely paratropicity or diatropicity. Thus, we compared the changes in the resonances (Δδ) of the aromatic protons Ha and Hb in 3b and 4b from those signals in 10b. The resonances of the aromatic protons for 3b are upfield shifted relative to 10b by Δδ = 0.12 and 0.49 ppm for Ha and Hb, respectively. Considering that Hb in 3b is closer to the dehydroannulene ring than Ha, the larger Δδ value of Hb than Ha implies the ring current of dehydro[20]annulene moiety, that is, the paratropicity of 3b. The resonances of the aromatic protons for 4b are almost unchanged relative to 10b by Δδ = 0 and 0.03 ppm for Ha and Hb, respectively, suggesting the atropicity of 4b. The observed chemical shift changes from 10b to 3b and 4b are apparently small as compared to those from 12b to 1b and 2b (Chart 2); the Δδ values are 0.18 and 0.79

Figure 2. UV−vis and/or fluorescence spectra of 1b, 2b, 3b, 4b, 10b, and 12b in CHCl3 at 25 °C, and phosphorescence spectrum of 12b in MTHF at −196 °C. Fluorescence from 1b and 3b in CHCl3 at 25 °C, and phosphorescence from 1b−4b, and 10b in MTHF at −196 °C were absent.

and 12b. The longest wavelength absorption maxima (λmaxabs) and the molar absorption coefficients (ε) of these compounds are listed in Table 2. The absorption bands of 1b−4b are located in the longer wavelength region than those of the corresponding 10b and 12b, reflecting the formation of the dehydroannulene moieties. These observations indicate the extended π-conjugation of 1b−4b compared with 10b and 12b. The longest λmaxabs value of 3b (552 nm) is closely located to that of 1b (560 nm), although the number of the tethering C C−C bonds differs from four to two. This similarity in the longest λmaxabs values is originated from the combination of the extension of π-electron systems and the weakened antiaromaticity from 1b to 3b, which was recognized by the NMR spectroscopic investigations (vide supra). In contrast, the longest λmaxabs value of 4b (504 nm) is red-shifted compared to that of 2b (456 nm) apparently due to the extension of πconjugation. Interestingly, the longest λmaxabs value of 3b is redshifted relative to that of 4b although the conjugation pathway of 3b is shorter than that of 4b. The difference in the longest λmaxabs values between 3b and 4b may be derived from the distortion of the octatetrayne unit and/or the antiaromaticity in 3b.22

Chart 2. Structure of Reference Compound 12b

ppm for 1b and 0.13 and 0.27 ppm for 2b with respect to the signals of 12b. These results clearly indicate the decrease of the tropicity of 3b and 4b relative to 1b and 2b, respectively. Indeed, the nucleus-independent chemical shift (NICS) (0) (and NICS(1))21 values of 3′ at the GIAO/B3LYP//6-311+ +G(2d,2p)// B3LYP/6-31G(d) level are calculated to be +6.0 (+5.4), which are less positive than those of 1′ (+10.8 (+9.5)) 8885

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry Table 2. Photophysical Data of 1b−4b, 10b, and 12b 1b 2b 3b 4b 10b 12b

λmaxabs [nm]a (ε [L mol−1 cm−1])

λmaxfl [nm]a

Φfa,b

τf [ns]a,c

kf [107 s−1]a,d

knr [107 s−1]a,e

560 (1600) 456 (101000) 552 (7400) 504 (102200) 426 (11400) 397 (6900)

N.D. 509 N.D. 535 454 419

∼0 0.20 ∼0 0.005 0.77 0.54

N/A 7.7 N/A 1.7 9.7 6.9

N/A 10.4 N/A >330 2.9 5.9

In CHCl3 at 25 °C. bAbsolute fluorescence quantum yields. cLifetime of fluorescence. dFluorescence rate constant estimated by kf = Φfτf−1. Nonradiative rate constant estimated by knr = (1−Φf)τf−1.

a e

Fluorescence from 1b and 3b in CHCl3 at 25 °C was absent, which is rationalized by considering the forbidden HOMO− LUMO transition characteristic of 4nπ-electron systems as revealed by quantum chemical calculations (vide inf ra). Fluorescence quantum yields (Φf) and lifetimes (τf) for 2b, 4b, 10b, and 12b were determined, and based on these values, the fluorescence rates (kf) and nonradiative rates (knr) were evaluated; these photophysical data are listed in Table 2. The Φf values of 2b and 4b are lower than those of 10b and 12b. The kf values of 2b and 4b are in the same magnitude of order as those of 10b and 12b, whereas the knr of 4b is substantially greater than those of 2b, 10b, and 12b. Noticeably, 10b possessing butadiyne units provides high Φf value of 0.77; aromatic compounds having butadiyne units are generally less fluorescent.23 Very weak phosphorescence from 12b was observed in 2-methyltetrahydrofuran (MTHF) at −196 °C, while that from 1b−4b and 10b was absent. Observation of phosphorescence from 12b indicates that intersystem crossing from the lowest excited singlet (S1) state to the triplet (T1) state is operative. Conversely, there would be two plausible explanations for the absence of phosphorescence in 1b−4b and 10b. One is that the deactivation of the S1 state is governed by internal conversion to the ground state. The other is that the T1 state is nonphosphorescent in nature. To make clear this issue, laser flash photolysis of 1b−4b and 10b using a 266 nm laser pulse was carried out to understand the photophysical and photochemical features of the triplet states. Figure 3 shows a transient absorption spectrum obtained upon 266 nm laser pulsing in CHCl3 solution of 3b. The absorption spectrum is located from UV−vis to NIR region.

The intensities of the absorption at 535 and 700 nm decreased with a rate of 2.1 × 105 s−1. In the presence of oxygen, the decay was accelerated, indicating that the obtained transient signal is due to the triplet state; the transient signal data for 1b, 2b, 4b, 10b, and 12b are deposited in Figures S6−S10 in the Supporting Information. Based on the facts of being quenched by the dissolved oxygen, these transient signals for 1b, 2b, 4b, and 10b were also assigned to the triplet states. The transient signal for 12b was not affected by the presence of the dissolved oxygen. Hence, the transient species observed for 12b may be formed by a chemical reaction in the S1 state, although it is not identified yet. From the results of transient absorption measurements, it is inferred that the nonradiative process of the S1 states involves the intersystem crossing to the T1 state of 1b−4b and 10b and a chemical reaction for 12b under the experimental conditions applied. Consequently, we concluded that the T1 states of 1b−4b and 10b are nonphosphorescent, and that the knr values for 2b, 4b, and 10b are substantially due to intersystem crossing from the S1 to the T1 states. Quantum chemical calculations for 3′ and 4′ were performed to investigate the electronic properties. The calculated surfaces of the molecular orbitals are depicted in Figure 4. The energy levels of HOMO and HOMO−1 for 2′ and 4′ are similar to each other, as are those of LUMO and LUMO+1. It can be seen for 1′−4′ that the calculated electronic distribution is delocalized on the dehydroannulene moieties. These results indicate that the extension of the oligoyne linkage does not inherently affect the delocalization of the electronic distribution on the studied molecular orbitals. The HOMOs and LUMOs of 1′ and 3′ are found to be of ungerade. From this result, it is inferred that the transition between HOMO and LUMO for 1′ and 3′ is symmetrically forbidden as seen for 4nπ-electron systems. By contrast, as for 2′ and 4′, the HOMO−1s and HOMOs are of gerade, and the LUMOs and LUMO+1s are of ungerade. The transitions between HOMO or HOMO−1 and LUMO or LUMO+1 are symmetrically allowed. These considerations for the transition probability are supported from the viewpoint of the oscillator strength ( f). The f values of the HOMO → LUMO transitions for 1′ and 3′ were calculated to be 0 with the longest absorption maxima (λmaxcalcd) of 716 and 783 nm for 1′ and 3′, respectively, as listed in the Table S1. By contrast, the f values of HOMO−1 → LUMO+1, HOMO− 1 → LUMO, HOMO → LUMO, and HOMO → LUMO+1 for 2′ and 4′ were calculated to be 1.23 (λmaxcalcd = 463 nm) and 1.36 (λmaxcalcd = 552 nm), respectively (Table S1); these f values are for allowed transitions. Electrochemical Properties. The electrochemical properties of 1b−4b, 10b, and 12b were examined by using CV and DPV in o-dichlorobenzene (o-DCB), and their oxidation onset (Eonsetox) and reduction onset (Eonsetred) are summarized in Table 3. Acyclic 12b displayed one irreversible oxidation step,

Figure 3. A transient absorption spectrum at 100 ns upon 266 nm laser pulsing in Ar−purged CHCl3 solution of 3b at 25 °C. Inset; traces at 535 nm (upper) and at 700 nm (lower). 8886

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry

Figure 4. (Black) Energy diagrams and frontier molecular orbital (FMO) plots of 1′−4′ by using the B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) method, and their transitions estimated by TD-DFT calculations at B3LYP/6-31G(d)//B3LYP/6-31G(d). (Gray) HOMO and LUMO levels of 1b−4b deduced from the oxidation onset (Eonsetox) and reduction onset (Eonsetred) values according to the following equation: HOMO = −(4.8 + Eonsetox) eV, LUMO = −(4.8 + Eonsetred) eV.

Table 3. Oxidation and Reduction Potentials of 1b−4b, 10b, and 12b,a Theoretically Calculated HOMO and LUMO Levels, Electrochemical Gaps, and Optical Gaps Eonsetox (Epa) [V] 1b 2b 3b 4b 10b 12b

e

e

+0.39 (+0.51) (+0.77) +0.55 (+0.68)e (+0.93)e (+1.15)e +0.59 (+0.72)e (+0.87)e +0.62 (+0.79)e (+0.95)f +0.44 (+0.78)f (+1.33)f +0.63g

Eonsetred (Epc) [V] −1.74 −1.92 −1.51 −1.59 N.D. N.D.

e

e

(−1.90) (−2.15) (−2.10)f (−2.33)g (−1.72)e (−1.76)e (−1.95)e (−2.19)e

HOMO [eV]b

LUMO [eV]b

ΔEredox [V]c

ΔEcalcd [eV]b

ΔEopt [eV]d

−4.91 −5.13 −5.12 −5.24 −5.43 −5.40

−2.56 −2.30 −2.98 −2.81 −2.21 −1.75

2.13 2.47 2.10 2.21 N.A. N.A.

2.35 2.83 2.14 2.43 3.22 3.65

2.21 2.72 2.25 2.46 2.91 3.12

a Measuring by using CV in o-DCB (0.1 mol L−1 n-Bu4NPF6). All the potentials are given versus the Fc+/Fc couple as an external standard. Scan rate = 100 mV s−1. bCalculated by using B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) for 1′−4′, 10′, and 12′, where the 2-ethylhexyloxy and TIPS groups in 1b−4b, 10b, and 12b were replaced with methoxy and TMS groups, respectively. cThe electrochemical gap (ΔEredox) is defined as the potential difference between Eonsetox and Eonsetred. dThe optical gap (ΔEopt) is defined as the longest maximal absorption wavelength. eReversible wave. f Quasireversible wave. gIrreversible wave.

for 1b and 2b. The observed potential shifts should reflect the stronger electron-withdrawing ability of an octatetrayne unit than a butadiyne unit.25 From 1b to 3b, the positive shift of the Eonsetox values is almost the same as that of the Eonsetred values, and thus the potential difference (ΔEredox) between the Eonsetox and Eonsetred values of 1b and 3b is similar to each other. On the other hand, from 2b to 4b, the positive shift of the Eonsetred value is pronounced relative to that of the Eonsetox value, and hence the ΔEredox of 4b is smaller than that of 2b. A good correlation exists between the optical gaps (ΔEopt) and the ΔEredox in 1b−4b suggesting that the same orbitals, namely HOMO and LUMO, are involved in both optical and electrochemical gaps for 1b−4b. Thus, the oxidation and reduction of 1b−4b occurred on their dehydroannulene moieties, which is supported by the finding that their HOMOs and LUMOs have large contribution from the dehydroannulene rings (vide supra). The ΔEredox values for

and 10b displayed two reversible oxidation waves (Figure 5); neither 12b nor 10b showed reduction wave. Dehydroannulenes 1b−4b displayed amphoteric multiredox behavior within the available potential window (Figure 5). The redox processes for 1b−4b were reversible except for the reduction processes for 2b, whereas the redox processes for 1a and 2a were irreversible. This indicates that the cationic and anionic species of phenanthrene-fused dehydroannulenes become kinetically stable by replacement of the linear decyloxy groups with the branched 2-ethylhexyloxy groups.24 The oxidation potentials (Epa) and reduction potentials (Epc) measured by CV matched the corresponding Epa and Epc measured by DPV (see Figure S11 and Table S7 in the Supporting Information). The Eonsetox values for both 1b and 2b are more negative than that for 12b, while the Eonsetox values for both 3b and 4b are more positive than that for 10b. Both the Eonsetox and Eonsetred values for 3b and 4b are positively shifted as compared to those 8887

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry

Figure 5. Cyclic voltammograms of (a) 1b, (b) 2b, (c) 3b, (d) 4b, (e) 10b, and (f) 12b measured in o-DCB (0.1 mol L−1 n-Bu4NPF6) at scan rate of 100 mV s−1. The peaks attributed to the decomposed species formed by reduction are labeled with asterisks. Neither 10b nor 12b showed reduction wave within the potential window of o-DCB.

Figure 6. (a) Partial 1H NMR spectra of 3b in CDCl3 in various concentrations at 20 °C and (b) the corresponding nonlinear curvefitting plots of the concentration dependence of the chemical shifts of the aromatic protons.

1b−4b match the calculated gaps (ΔEcalcd) for the corresponding 1′−4′. An analysis of the influence of electron-donating 2ethylhexyloxy groups on the Epa values of 1b−4b gives a deeper insight into the antiaromatic characteristic of 1b and 3b. Going from 1b and 3b to 2b and 4b, the number of 2ethylhexyloxy groups increases from 8 to 12, however, both the first and second Epa values of 1b and 3b are more negative than those of 2b and 4b, respectively. Thus, it seems that the antiaromatic character of 1b and 3b provides an explanation for the observed readiness to release electrons as compared to the corresponding 2b and 4b; it is easier to withdraw two electrons from antiaromatic 4nπ systems. The difference of the first Epa values between 3b and 4b (0.07 V) is smaller than that between 1b and 2b (0.17 V), suggesting the weaker antiaromaticity of 3b than 1b; this is in good agreement with the finding that the NICS values of 3′ are less positive than that of 1′ as described above. Self-Association. We have recently demonstrated that 1a and 2a aggregate in CDCl3 by effective π−π interactions.14 In order to elucidate the effects of the bulkiness of alkoxy groups on the phenanthrene moieties and the length of oligoyne linkages on the self-association behavior of dehydroannulenes, the 1H NMR spectral measurements of 1b−4b in CDCl3 were carried out at the concentration of 10−2−10−5 mol L−1. Unlike 1a and 2a, the resonances of the aromatic protons in 1b and 2b were almost independent of concentrations, indicating that 1b and 2b are mainly present as a monomer under these conditions, which should be attributed to the bulky 2ethylhexyloxy groups. Noticeably, in contrast to 1b and 2b, the 1H NMR signals of 3b and 4b are concentration-dependent with aromatic proton signals moving upfield upon increasing concentrations as shown in Figure 6 (Figure S13 for 4b). This demonstrates that 3b and 4b form stacked aggregates by π−π interactions and the extension of the oligoyne linkages apparently enhances the self-association ability. The diffusion coefficients (D) for 3b and 4b were almost independent of the concentrations on the basis of the diffusion NMR experiments,

suggesting that a monomer−dimer equilibrium predominantly exists. The plots of the chemical shifts of the aromatic protons vs the concentrations of 3b and 4b were fitted to a curve for the monomer−dimer model,26 which produced the self-association constants (K) of 3b and 4b to be 9 and 62 L mol−1, respectively (Table 4). The larger K value of 4b than 3b should reflect the larger number of phenanthrene moieties of the former than the latter. It is well-known that the self-association behavior of πconjugated compounds is highly solvent-dependent.27 We analyzed the self-association behavior of 1b−4b in nonpolar methylcyclohexane (MCH) by 1H NMR spectroscopy at the concentration of 10−2−10−5 mol L−1. Unlike in the case in CDCl3, the 1H NMR signals of 1b and 2b in MCH were concentration-dependent; their aromatic proton signals shifted upfield with increasing the concentrations. This indicates the occurrence of self-association of 1b and 2b, which hints a solvophobic contribution of MCH to their self-association. The K value of 2b (16 L mol−1), which was determined on the basis of the isodesmic model, is smaller than that of 1b (400 L mol−1), although the π framework of the former is larger than the latter. According to the PM7 calculations for 1b′ and 2b′,28 in which the 2-ethylhexyloxy groups in 1b and 2b were replaced with the hexyloxy groups, there is steric hindrance from the alkoxy groups in 2b′ in contrast to 1b′ (Figure S4), which should result in the smaller K value of 2b than 1b. Pronounced concentration-dependent 1H NMR chemical shift changes were observed for 3b; the K value of 3b in MCH was estimated to be 2200 L mol−1. Dehydroannulene 4b showed considerably broad proton signals even at the dilute concentration of 2.19 × 10−6 mol L−1, representing a high degree of self-association of 4b as compared to 1b−3b, however, the determination of the K value of 4b in MCH was not possible. Therefore, we investigated the self-association behavior of 1b−4b in MCH by UV−vis spectroscopy in the concentration 8888

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The Journal of Organic Chemistry Table 4. Association Constants and Thermodynamic Parameters of 1b−4b CDCl3a −1 c

1b 2b 3b 4b

−1

K [L mol ]

ΔH [kJ mol ]

∼0 ∼0 9 62

N.D. N.D. −8.8 −19

methylcyclohexaneb ΔS [J K

−1

−1

mol ]

N.D. N.D. −12 −32

−1

K [L mol ]

ΔH [kJ mol−1]

ΔS [J K−1 mol−1]

400c,d 16c,d 1400c,e (1600)f 43000c,e (33000)f

−23d −25d −68e −75e

−26d −60d −170e −167e

Monomer−dimer model. 1H NMR experiments (concentration dependence). bIsodesmic model. cAt 20 °C. d1H NMR experiments (concentration dependence). eUV−vis experiments (temperature dependence). fUV−vis experiments (concentration dependence) at 25 °C.

a

region of ca. 10−3−10−7 mol L−1; wide concentration ranges are accessible by UV−vis spectroscopy relative to NMR spectroscopy. The UV−vis spectra of 1b and 2b were almost concentration-independent, indicating that 1b and 2b mainly exist as monomeric species under the dilute conditions measured. In stark contrast, the absorption bands of 3b and 4b became red-shifted through several isosbestic points upon increasing concentrations as shown in Figure 7 (Figure S15 for

(Figure 7 and Figure S15). The analyses of the temperaturedependent UV−vis spectral change of 3b and 4b afforded the K values to be 1400 and 43000 L mol−1, respectively, which are reasonably comparable to the values obtained by concentrationdependent UV−vis spectroscopic measurements. We investigated the thermodynamics of the self-association behavior of 1b−4b. The van’t Hoff plots gave the thermodynamic parameters, namely enthalpic term (ΔH) and entropic term (ΔS), for the self-association as summarized in Table 4. In any cases, both the ΔH and ΔS values are negative, illustrating that their self-association processes are enthalpydriven and entropy-opposed. The self-association of 3b and 4b is enthalpically more favored than that of 1b and 2b, respectively; the ΔH values of 1b−4b are −23, − 25, − 68, and −75 kJ mol−1, respectively. This suggests that the extension of oligoyne linkages from butadiyne to octatetrayne units enhances the π−π stacking interactions. The well-known polar/π model predicts that the introduction of electron-withdrawing substituents reduces the electron density of the π-system and thus decreases the electrostatic repulsion between π-electrons and promotes πstacking interactions.29,30 To examine the electronic effect of the oligoyne linkages on the self-association of dehydroannulenes, the electrostatic-potential surface (ESPs) and molecular electrostatic potentials (MEPs) of 1′ and 3′ at the B3LYP/631+G(d,p)//B3LYP/6-31G(d) level were calculated (Figure S3). The MEPs at 2 Å above the center of the benzene rings of phenanthrene moieties are −10.7 and −11.3 kcal mol−1 for 1′ and −8.1 and −8.0 kcal mol−1 for 3′. These results indicate a less-negative character for the phenanthrene moieties of 3b than 1b. Accordingly, it is likely that the self-association of 3b and 4b is greatly facilitated relative to 1b and 2b, respectively, due to the strong electron-withdrawing effect of octatetrayne linkages in 3b and 4b, which is in good agreement with the polar/π model. Dehydroannulenes 3b and 4b show large negative ΔS values compared to 1b and 2b, respectively; the ΔS values are −26, − 60, − 170, and −167 J K−1 mol−1 for 1b, 2b, 3b, and 4b, respectively. Interestingly, the trend of the ΔS values for 1b−4b follows that of their ΔH values, and thus the enthalpy−entropy compensation seems to apply. This finding supports that the molecular motion of 3b and 4b in the aggregates is restricted relative to that of 1b and 2b, respectively, reflecting the more effective π−π stacking interactions in the former than the latter. The more negative ΔH values of 2b and 4b than 1b and 3b, respectively, suggest that strong π−π stacking interactions are operative in 2b and 4b relative to 1b and 3b, respectively, which is probably due to larger π-electron systems of the former than the latter. The self-association of 3b and 4b in MCH is enthalpically more favored but entropically less favored than that in CDCl3. The enthalpic contributions are involved in desolvation as well as attractive electrostatic forces. A well-solvated solute

Figure 7. UV−vis spectra at various concentration of (a) 3b ([3b] = 5.48 × 10−6−3.87 × 10−3 mol L−1) in methylcyclohexane. Arrows indicate the spectral changes with increasing concentration. Inset; Fitting of the change in the molar absorptivity at 484 nm to the isodesmic model. UV−vis spectra of (b) 3b (2.04 × 10−3 mol L−1) in methylcyclohexane at various temperatures. Arrows indicate the spectral changes with decreasing temperature. Inset; Fitting of the change in the molar absorptivity at 543 nm to the isodesmic model.

4b). These results indicate that 3b and 4b produce J-type assemblies by self-associations and equilibrate with their stacked assemblies. The K values of 3b and 4b were estimated to be 1600 and 33000 L mol−1, respectively, according to the isodesmic model, and found to be hundreds of times as high as the K values in CDCl3. The UV−vis spectra of 3b and 4b were also sensitive to temperature, and thus the λmaxabs values were blue-shifted upon warming the solution from 5 to 60 °C 8889

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry commonly receives small enthalpic contribution during its association, because the desolvation of the solvent and the solute has to pay a large enthalpic cost. We observed that 3b and 4b together with 1b and 2b are highly soluble in CHCl3 relative to MCH, which should rationalize the finding that the ΔH values of 3b and 4b in MCH are significantly negative relative to those in CHCl3. Self-Assembled Structures. We have recently found that 1a and 2a formed 1D superstructures with high aspect ratio by self-assembly driven by π−π interactions; microbelts with lengths of >300 μm and widths of 0.2−1 μm were obtained from 1a, and nanofibers with lengths of >1 μm and widths of 0.05−0.1 μm were obtained from 2a.14 We became interested in the elucidation of the influence of the bulkiness of alkoxy groups appended to the phenanthrene moieties and the size of the dehydroannulene moiety on the morphology of superstructures and hence carried out the fabrication of selfassembled structures of 1b−4b through a phase-transfer method.31 Thus, to a solution of 1b−4b in CHCl3 (5 × 10−3 mol L−1), ca. 80 vol% EtOH was slowly added so that two phases can be maintained. The resulting mixtures were allowed to stand at room temperature for a day to afford the aggregates, which were visualized by SEM as shown in Figure 8.

Figure 9. SEM images of (a) 1b, (b) 2b, (c) 3b, and (d) 4b obtained from methylcyclohexane/EtOH system.

obtained from a CHCl3/EtOH system. Noticeably, the morphology of self-assembled clusters of 4b obtained from MCH/EtOH system is quite different from that obtained from CHCl3/EtOH system. Thus, helically twisted microrods with lengths of 10−20 μm and widths of 0.5−3 μm were observed together with microspheres (Figure 9d), and a straight microrod formed from CHCl3/EtOH system was no longer observable. These results suggest that the self-assembling processes of 4b in MCH/EtOH system are distinct from those in CHCl3/EtOH system. Ostwald’s rule of order states that the less stable (namely metastable) polymorph forms first and then gets converted to a more stable polymorph;32 it is possible that the initially formed metastable polymorph converts to the more stable one directly and/or by repetition of dissolution and adhesion of the molecules. From a closer inspection of the images obtained for 4b (Figure 10), it is considered that the morphological changes

Figure 8. SEM images of (a) 1b, (b) 2b, (c) 3b, and (d) 4b obtained from CHCl3/EtOH system.

Dehydroannulene 1b formed microrods, namely prismatic structures with lengths of 5−100 μm and widths of 1−10 μm, while 2b produced large platelet structures with lengths of 1−2 mm and widths of 100−200 μm. The lower self-association ability of 1b and 2b than 1a and 2a may give rise to the lower aspect ratio of self-assembled structures of the former than the latter. Dehydroannulenes 3b and 4b were found to form more flexible superstructures than 1b and 2b. Thus, 3b produced slightly twisted microbelts with lengths of 10−1000 μm and widths of 0.3−3 μm. A number of microrods with lengths of 5− 50 μm and widths of 0.3−2 μm also coexisted. Dehydroannulene 4b formed microrods with lengths of 5−10 μm and widths of 0.5−1 μm and 0D microspheres with diameters of 4−10 μm. The microsphere was connected to the neighboring one or microrod to form irregular clusters. Solvent is an important factor for molecular self-assembly in the solution-based process. Therefore, we conducted the fabrication of self-assembled clusters for 1b−4b by replacement of the good solvent from CHCl3 to MCH. As shown in Figure 9, the morphology of superstructures of 1b, 2b, and 3b obtained from MCH/EtOH system is essentially similar to that

Figure 10. Different regions of the SEM images of superstructures of 4b: (a−d) obtained from CHCl3 /EtOH system and (e−h) methylcyclohexane/EtOH system.

of 4b are as follows. In CHCl3/EtOH system, molecules of 4b formed metastable 0D microspheres at the beginning, which radiate to produce radially connected, straight 1D microrods (Figure 10a−d), while in MCH/EtOH system initially formed microspheres deform elliptically (Figure 10e,f) and subsequently evolve into helically twisted microrods (Figure 10g,h). The observed supramolecular organization of 4b depending on the solvents used, i.e., supramolecular polymorphism, is considered to stem from a combination of the difference of polarity between CHCl3 and MCH and the difference of the solubility of 4b toward CHCl3 and MCH; however, the reason 8890

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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possible stacking modes: one is stacking of same-side phenanthrene moieties, and the other is alternative stacking of opposite-side phenanthrene moieties (Figure S19). The former arrangement gives the smaller periodicity similar to the lateral size of the molecule, and the latter arrangement almost doubles the lateral periodicity. The set of 2θ = 5° and 9° (dspacings of 18 and 10 Å) seems to agree with this speculation for assembled 1b. In the case of assembled 3b, the extension of acetylenic linkages enlarges the lateral dimension into the set of 2θ = 4° and 8° (d-spacings = 22 and 11 Å). The other set of assembled 2b and 4b mainly displays three peaks in the region of 2θ = 3−9°. The triangular shape of 2b and 4b allows three types of stacking mode: the first is matching of all three apexes of triangle, and the second or third is two- or one-apex matching (Figure S20). Here, the assembled 2b exhibits the three strong peaks at 2θ = 4°, 6°, and 8° (d-spacings of 22 Å, 15 Å, and 11 Å). Among these arrangements, the two-apex matching is most probable; a parallelogram topology is composed of two triangular molecules.17d,36 Such parallel arrangement in 2b should enhance the lateral growth of the self-assembled cluster into the large and square platelets as depicted in Figure 11b. The diffraction pattern of the assembled 4b is broader than that of the assembled 2b, indicating that the lateral periodicity in the former is restricted relative to that in the latter. Hence, the oneapex matching for 4b may be prevalent, giving the strongest peak at 2θ = 2° (d-spacing = 44 Å). The other two peaks at 2θ = 4° and 6° (d-spacings = 22 and 15 Å) for the assembled 4b are situated in the low-angle region compared to those for the assembled 2b. The 2θ values for 4b are rather similar to those for the assembled 1b and 3b, however, the difference lies in the reduced intensity at 2θ = 4° for the assembled 4b. Overall, it is likely that the restricted anisotropic growth of the assembled 4b gives the granular morphology as depicted in Figure 10. The WAXD patterns of the superstructures of 1b, 2b, and 3b obtained from MCH/EtOH system are quite similar to the patterns of the corresponding superstructures obtained from CHCl3/EtOH system in a whole region (Figure S18). This demonstrates that the molecular arrangement and the crystallinity of the superstructures of 1b, 2b, and 3b are almost independent of the good solvents used for self-assembly as expected from the SEM observations. Interestingly, the assembled 4b also afforded similar diffraction patterns irrespective of solvents, suggesting that the molecular arrangement in the clusters of 4b obtained from MCH/EtOH system resembles that obtained from CHCl3/EtOH system in spite of the drastically different morphology depending on the solvents.

why only 4b showed marked polymorphism is not clear at present. It is pointed out that the rapid precipitation of compounds from the molecularly dispersed solutions tends to afford kinetically trapped aggregates.33,34 The morphology of the drop-casted films of 1b−4b from MCH solutions (1 × 10−4 mol L−1) on SiO2 has been visualized by AFM (Figure S17). Interestingly, the AFM image for 4b exhibited the appearance of globular aggregates uniformly, supporting the formation of microspheres from 4b at the initial stage of self-assembly by the phase-transfer method. The images of 1b, 2b, and 3b showed the presence of needle-like aggregates as expected from the SEM images of their superstructures. The self-assembled clusters of 1b−4b were further investigated by WAXD measurements. The WAXD patterns of the superstructures obtained from CHCl3/EtOH system were shown in Figure 11. The effects of the length of oligoyne

Figure 11. WAXD profiles of superstructures of (a) 1b, (b) 2b, (c) 3b, and (d) 4b obtained from CHCl3/EtOH solvent system at 25 °C.

linkages and the topology of the dehydroannulene moieties on the crystallinity of the self-assembled clusters are visible from inspection of the peaks around 2θ = 23° (d spacing = 3.8 Å), which corresponds to π−π stacking distance along the growth direction of the cluster, and the results are generally consistent with the SEM measurements. The diffraction pattern of assembled 1b showed sharp peaks at 2θ = 24.9°, 22.0°, and 20.9° (d-spacing = 3.6, 4.0., and 4.2 Å, respectively). The assembled 2b exhibited peaks at 2θ = 25.0° and 21.1° (dspacing = 3.6 and 4.2, respectively). As compared to the assembled 1b, the WAXD pattern of the assembled 3b displayed broad peaks at 2θ = 24.1°, 21.6°, and 20.7° (dspacing = 3.7, 4.1, and 4.3 Å). The assembled 4b showed a significantly broad peak at 2θ = 19−25°. The overall results suggest that the extension of oligoyne linkages decreases the crystallinity of the self-assembled clusters, and the dehydro[12]and [20]annulene moieties with ellipsoidal shape are responsible for the high crystallinity of the superstructures relative to the dehydro[18]- and [30]annulene moieties with triangular shape, respectively.35 A number of peaks with strong intensity were also observed in the region of 2θ = 3−9°. There are some common features, i.e., two strong peaks for assembled 1b and 3b with ellipsoidal shape, but three for assembled 2b and 4b with triangle moiety. The corresponding d-spacing is 10−29 Å, which is attributable to the lateral dimension of the cluster molecules. Given that the π−π stacking is predominant for 1b and 3b, there are two

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CONCLUSIONS We have synthesized tetraalkoxyphenanthrene-fused dehydro[20]- and [30]annulenes 3b and 4b possessing octatetrayne linkages together with dehydro[12]- and [18]annulenes 1b and 2b possessing butadiyne linkages. Dehydroannulenes 3b and 4b are remarkably stable enough to be readily handled in a neat form, which is in stark contrast to the previously reported macrocycles with octatetrayne units. The tropicity was shown to decrease by expanding the dehydroannulene core with the acetylenic linkages on going from butadiyne to octatetrayne units. Thus, 3b and 4b are considered to be weakly antiaromatic and nonaromatic, respectively. Both the HOMO and LUMO levels of 3b and 4b become lower than those of 1b and 2b reflecting the stronger electron withdrawing effect of an octatetrayne unit than a butadiyne unit. Dehydroannulenes 3b 8891

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry

UV−vis transitions are vertical. The NMR properties were calculated using the GIAO method at B3LYP/6-311++G(2d,2p) level of theory. The ESPs and MEPs were calculated at the B3LYP/6-31+G(d,p) level of theory. PM7 optimization was performed using MOPAC2012.39 Preparation of Dione 6b. To a solution of benzil 5b (4.04 g, 5.58 mmol) in CH2Cl2 was added TiCl4 (2.45 mL, 22.3 mmol) at 0 °C under argon atmosphere and the resulting mixture was stirred for 5 min. MoCl5 (3.35 g, 12.29 mmol) was added and the mixture was stirred for 10 min at room temperature, and then an ice-cold H2O was added. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was washed with H2O, dried over anhydrous MgSO4, and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/ethyl acetate, 1:30 to 1:1) to afford 6b (2.24 g, 3.10 mmol, 55%) as deeply red solids. Mp 113−116 °C; 1H NMR (CDCl3, 600 MHz): δ 0.90 (t, 6H, J = 7.2 Hz), 0.90 (t, 6H, J = 6.9 Hz), 0.94 (t, 6H, J = 7.2 Hz), 0.98 (t, 6H, J = 7.5 Hz), 1.31−1.58 (m, 32H), 1.75− 1.84 (m, 4H), 3.90−3.96 (m, 4H), 4.07 (d, 4H, J = 5.4 Hz), 7.10 (s, 2H), 7.51 (s, 2H); 13C NMR (CDCl3, 150 MHz): δ 11.3, 11.5, 14.2, 23.16, 23.18, 24.1, 29.21, 29.28, 30.70, 30.75, 39.54, 39.64, 71.57, 71.73, 106.9, 112.8, 124.5, 131.3, 149.9, 156.0, 179.4 (21 signals out of 23 expected); UV−vis (CH2Cl2): λmaxabs (relative intensity) = 293 (0.91, sh), 300 (1.00), 367 (0.29), 518 (0.02) nm; MALDI-TOF-MS (dithranol, positive): 743.2 [M+Na]+; Anal. Calcd for C46H72O6: C 76.62; H 10.06. Found: C 76.27; H 9.83. Preparation of Methyl Ether 7a. To a solution of trimethylsilylacetylene (TMSA) (1.00 mL, 7.05 mmol) in THF (15 mL) was added dropwise a n-BuLi hexane solution (2.69 mol L−1, 2.49 mL, 6.72 mmol) at −78 °C under argon atmosphere. After stirring at room temperature for 30 min, a solution of dione 6a (1.40 g, 1.68 mmol) in THF (10 mL) was added dropwise to the mixture at −78 °C. After stirring at room temperature for 40 min, (MeO)2SO2 (1.11 mL, 11.8 mmol) was added dropwise to the mixture at −78 °C. After the mixture was stirred at room temperature for 15 h, the resulting mixture was diluted with H2O. The organic phase was separated, and the aqueous phase was extracted with ethyl acetate. The combined organic phase was washed with H2O, dried over anhydrous MgSO4, and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/CH2Cl2, 1:1) to afford 7a (1.18 g, 1.12 mmol, 66%) as yellow oil. 1H NMR (CDCl3, 300 MHz): δ 0.32 (s, 18H), 0.90 (t, 12H, J = 6.6 Hz), 1.30−1.51 (m, 56H), 1.81−1.92 (m, 8H), 3.17 (s, 6H), 4.09 (t, 8H, J = 6.3 Hz), 7.17 (s, 2H), 7.47 (s, 2H); 13C NMR (CDCl3, 75 MHz): δ 0.2, 14.2, 22.80, 22.84, 26.2, 29.52, 29.60, 29.76, 29.81, 31.7, 32.1, 52.3, 69.1, 70.1, 81.0, 94.6, 102.5, 110.7, 115.8, 124.7, 125.4, 147.9, 149.6 (23 signals out of 31 expected); UV−vis (CH2Cl2): λmaxabs (relative intensity) = 252 (1.0) 320 (0.51) nm; MALDI-TOF-MS (dithranol, positive): m/z 1056.7 [M]+; Anal. Calcd for C66H112O6Si2: C 74.94; H 10.67. Found: C 74.69; H 10.73. Preparation of Methyl Ether 7b. To a solution of TMSA (1.01 mL, 7.21 mmol) in THF (15 mL) was added dropwise a n-BuLi hexane solution (2.65 mol L−1, 2.61 mL, 6.93 mmol) at −78 °C under argon atmosphere. After stirring at −78 °C for 30 min, a solution of dione 6b (1.00 g, 1.38 mmol) in THF (15 mL) was added dropwise to the mixture. After stirring at room temperature for 90 min, (MeO)2SO2 (0.89 mL, 9.70 mmol) was added dropwise to the mixture at −78 °C. After the mixture was stirred at room temperature for 15 h, the resulting mixture was diluted with H2O. The organic phase was separated, and the aqueous phase was extracted with CHCl3. The combined organic phase was washed with H2O, dried over anhydrous MgSO4, and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/ethyl acetate, 40:1 to 30:1) to afford 7b (1.10 g, 1.16 mmol, 84%) as yellow oil. 1H NMR (CDCl3, 400 MHz): δ 0.29 (s, 18H), 0.87−0.98 (m, 24H), 1.27−1.54 (m, 32H), 1.75−1.83 (m, 4H), 3.15 (s, 6H), 3.93−3.96 (m, 8H), 7.12 (s, 2H), 7.43 (s, 2H); 13C NMR (CDCl3, 75 MHz): δ 0.2, 11.37, 11.43, 14.3, 22.8, 23.3, 24.1, 29.27, 29.33, 30.74, 30.80, 31.8, 39.7, 39.8, 52.4, 71.6, 72.3, 81.0, 94.6, 102.6, 110.3, 115.7, 124.5, 125.3, 148.2, 150.0; UV−vis (CH2Cl2): λmaxabs (relative intensity) = 253 (1.0), 322 (0.28) nm; MALDI-TOF-MS (dithranol, positive): m/z

and 4b were found to self-associate more strongly than 1b and 2b. The detailed thermodynamic study on self-association behavior of conjugated macrocycles possessing octatetrayne linkages was carried out for the first time. The more negative ΔH values for the self-association of 3b and 4b than 1b and 2b clearly demonstrate that the octatetrayne linkages effectively promote π−π stacking interactions due to their electronwithdrawing ability, which accords to the polar/π model. An increase in the enthalpic contribution is counterbalanced by increasing the entropic cost, that is, enthalpy−entropy compensation is applicable. Dehydroannulenes 1b−4b produced self-assembled clusters, which differ in the morphology and the crystallinity depending on the length of the acetylenic linkages, the shape of dehydroannulene core, and the bulkiness of alkoxy groups appended to the phenanthrene moieties. The intriguing supramolecular organization of 4b depending on the solvent polarity was observed. We believe that the present study provides valuable information on developing strategies for new π-functional acetylenic macrocycles. Further extension of the acetylenic linkages in tetraalkoxyphenanthrene-fused dehydroannulenes is currently underway in our laboratory.

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EXPERIMENTAL SECTION

General Experimental Methods. Commercially available reagents were used as received. Caution! Dimethyl sulfate should be used in a well-ventilated hood, since it is hazardous and volatile. THF, CH2Cl2, CHCl3, o-dichlorobenzene (o-DCB), and methylcyclohexane (MCH) were distilled from relevant drying agents prior to use. Compounds 5a14,37 and 5b38 were prepared according to the literature procedures. Column chromatography and plug filtrations were carried out with SiO2. Thin-layer chromatography (TLC) was conducted on aluminum sheets coated with SiO2 60 F254. Melting points (Mp) were measured with a hot-stage apparatus and are uncorrected. Recycling gel-permeation chromatography was performed with UV detectors using 1H and 2H polystyrene columns. 1H and 13C NMR spectra were recorded on a spectrometer at 300, 400, or 600 MHz for 1H and 75 or 150 MHz for 13C. Residual and deuterated solvent signals in the 1H and 13C NMR spectra were used as an internal reference, respectively (CDCl3, 1H: δ 7.26; 13C: δ 77.16). MALDI-TOF-MS spectra and HRFAB-MS spectra were recorded with dithranol and 3-nitrobenzyl alcohol as a matrix, respectively. UV−vis spectra were recorded in CH2Cl2 or CHCl3 at 10−5−10−7 mol L−1. All peaks followed Beers law, which confirms that the absorption is intrinsic to molecules rather than aggregation. UV−vis spectroscopic measurements in MCH at various temperature were carried with Peltier-type temperature controller. The absolute fluorescence quantum yields were determined by an integrating sphere system. Cyclic voltammetry and differential pulse voltammetry were performed by using a cell equipped with a platinum as working electrode, a platinum wire as counter electrodes, and Ag/ AgNO3 as a referential electrode. All electrochemical measurements were performed in o-DCB solution (ca. 5 × 10−4 mol L−1) containing 0.1 mol L−1 n-Bu4NPF6 at RT. All potentials are referenced to the ferrocenium/ferrocene (Fc+/Fc) couple, used as a standard. For SEM measurements, a Pt−Pd coating was applied using an ion sputterer. WAXD measurements for the materials from 1b−4b through a phase transfer method were performed on an X-ray diffractometer for which a Cu−Kα radiation (λ = 1.54 Å) was used. The obtained WAXD patterns were recorded using a cooled CCD camera with an image intensifier. For AFM measurements, compounds were drop-casted from a MCH solution on the SiO2 surface. TG-DTA was performed at heating and cooling rates of 10 °C min−1. Theoretical calculations were performed using the Gaussian 09 program package.20 Geometry optimization of 1′−4′ was performed with restricted Becked hybrid (B3LYP) at the 6-31G(d) basis set. Further single-point calculations were performed at the 6-31+G(d,p) basis set to obtain the molecular orbital energies. TD calculations were performed at the B3LYP/6-31G(d) level of theory. The calculated 8892

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

Article

The Journal of Organic Chemistry 944.8 [M]+; Anal. Calcd for C58H96O6Si2: C 73.67; H 10.23. Found: C 73.37; H 10.55. Preparation of Butadiynyl-Substituted Dihydrophenanthrene 9a. A mixture of methyl ether 7a (800 mg, 0.76 mmol) and K2CO3 (209 mg, 1.51 mmol) in THF/MeOH (1:1, 10 mL) was stirred at room temperature for 30 min. After the mixture was diluted with CH2Cl2, the insoluble material was removed by filtration and the filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (acetone) to give desilylated alkyne 8a. To a suspension of CuCl (75 mg, 0.76 mmol) and n-BuNH2 (2.61 mL, 26.4 mmol) in H2O (20 mL) and CH2Cl2 (20 mL) was added NH2OH·HCl (7 mg, 0.1 mmol) at 0 °C. A solution of 8a and (2bromoethynyl)triisopropylsilane (885 mg, 3.39 mmol) in CH2Cl2 (10 mL) was then added dropwise to the mixture. After the mixture was stirred at 30 °C for 15 h, H2O was added to the resulting mixture. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/CH2Cl2, 1:0 to 1:1) to afford 9a (877 mg, 0.70 mmol, 92%) as yellow oil. 1H NMR (CDCl3, 600 MHz) δ 0.89 (t, 6H, J = 6.9 Hz), 0.89 (t, 6H, J = 7.2 Hz), 1.13 (brs, 42H), 1.24−1.40 (m, 48H), 1.46−1.52 (m, 8H), 1.82−1.87 (m, 8H), 3.17 (s, 6H), 4.07−4.14 (m, 8H), 7.15 (s, 2H), 7.37 (s, 2H); 13 C NMR (CDCl3, 150 MHz): δ 11.5, 14.3, 18.7, 22.9, 26.18, 26.23, 29.50, 29.52, 29.55, 29.59, 29.62, 29.76, 29.81, 29.83, 32.08, 32.09, 52.9, 69.3, 70.0, 73.8, 75.0, 81.7, 85.3, 89.4, 110.5, 116.1, 123.9, 125.2, 148.1, 150.0 (30 signals out of 34 expected); UV−vis (CH2Cl2): λmaxabs (relative intensity) = 260 (1.0), 321 (0.35) nm; MALDI-TOF-MS (dithranol, positive): 1273.9 [M+H]+; Anal. Calcd for C82H136O6Si2: C 77.30; H 10.76. Found: C 77.18; H 11.13. Preparation of Butadiynyl-Substituted Dihydrophenanthrene 9b. A mixture of methyl ether 7b (1.11 g, 1.17 mmol) and K2CO3 (325 mg, 2.35 mmol) in THF/MeOH (1:1, 10 mL) was stirred at room temperature for 30 min. After the mixture was diluted with CH2Cl2, the insoluble material was removed by filtration and the filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (acetone) to give desilylated alkyne 8b. To a suspension of CuCl (116 mg, 1.17 mmol) and n-BuNH2 (4.07 mL, 41.1 mmol) in H2O (5 mL) and CH2Cl2 (5 mL) was added NH2OH·HCl (12 mg, 0.2 mmol) at 0 °C. A solution of 8b and (2bromoethynyl)triisopropylsilane (1.22 g, 4.70 mmol) in CH2Cl2 (5 mL) was then added dropwise to the mixture. After the mixture was stirred at 30 °C for 15 h, H2O was added to the resulting mixture. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/CH2Cl2, 1:1) to afford 9b (1.20 g, 1.03 mmol, 88%) as yellow solids. Mp 88−90 °C; 1 H NMR (CDCl3, 300 MHz) δ 0.91−0.98 (m, 24H), 1.12 (brs, 42H), 1.32−1.59 (m, 32H), 1.72−1.82 (m, 4H), 3.18 (s, 6H), 3.96 (d, 4H, J = 5.5 Hz), 3.97 (d, 4H, J = 5.4 Hz), 7.13 (s, 2H), 7.35 (s, 2H); 13C NMR (CDCl3, 150 MHz): δ 11.5, 14.3, 18.7, 23.23, 23.25, 24.04, 24.09, 29.23, 29.26, 29.34, 29.39, 30.74, 30.80, 30.83, 39.71, 39.79, 53.0, 71.57, 71.68, 72.23, 72.27, 73.9, 75.0, 81.8, 85.2, 89.4, 110.2, 115.8, 123.6, 125.1, 148.4, 150.33, 150.36; UV−vis (CH2Cl2): λmaxabs (relative intensity) = 260 (1.0), 332 (0.35) nm; MALDI-TOF-MS (dithranol, positive): 1161.8 [M+H]+; Anal. Calcd for C74H120O6Si2: C 76.49; H 10.41. Found: C 76.43; H 10.41. Preparation of Butadiynyl-Substituted Phenanthrene 10a. To a suspension of butadiynyl-substituted dihydrophenanthrene 9a (1.30 g, 1.02 mmol) and SnCl2·H2O (1.14 g, 5.10 mmol) in THF (20 mL) was added H2SO4 (0.5 mol L−1, 10 μL) under argon atmosphere. After the mixture was refluxed for 15 h, H2O was added to the resulting mixture. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column (hexane/CH2Cl2, 2:1) to afford 10a (1.00 g, 0.82 mmol, 81%) as yellow solids. Mp 85−88 °C; 1H NMR (CDCl3, 400 MHz): δ 0.88 (t, 12H, J = 6.6 Hz), 1.15−1.16 (m, 42H), 1.28− 1.45 (m, 48H), 1.51−1.58 (m, 8H), 1.89−1.97 (m, 8H), 4.21 (t, 4H, J

= 6.6 Hz), 4.22 (t, 4H, J = 6.6 Hz), 7.70 (s, 2H), 7.71 (s, 2H); 13C NMR (CDCl3, 75 MHz): δ 11.5, 14.3, 18.8, 22.9, 26.21, 26.31, 29.28, 29.44, 29.56, 29.66, 29.78, 29.83, 32.1, 69.1, 69.6, 73.8, 83.1, 90.0, 90.6, 105.1, 108.7, 120.9, 124.6, 126.2, 149.8, 150.6 (26 signals out of 33 expected); UV−vis (CH2Cl2): λmaxabs (relative intensity) = 256 (0.53), 291 (1.0), 306 (0.89), 318 (0.60), 375 (0.43), 395 (0.60), 423 (0.19) nm; MALDI-TOF-MS (dithranol, positive): 1212.0 [M+H]+; Anal. Calcd for C80H130O4Si2: C 79.27; H 10.81. Found: C 79.20; H 10.77. Preparation of Butadiynyl-Substituted Phenanthrene 10b. To a suspension of butadiynyl-substituted dihydrophenanthrene 9b (1.05 g, 0.90 mmol) and SnCl2·H2O (1.01 g, 4.51 mmol) in THF (10 mL) was added H2SO4 (0.5 mol L−1, 10 μL) under argon atmosphere. After the mixture was refluxed for 21 h, H2O was added to the resulting mixture. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column (hexane/CH2Cl2, 2:1) to afford 10b (840 mg, 0.76 mmol, 84%) as yellow solids. Mp 113−118 °C; 1H NMR (CDCl3, 400 MHz): δ 0.92 (t, 12H, J = 7.0 Hz), 0.99 (t, 6H, J = 7.4 Hz), 1.00 (t, 6H, J = 7.6 Hz), 1.15 (brs, 42H), 1.30−1.64 (m, 32H), 1.83−1.93 (m, 4H), 4.05−4.12 (m, 8H), 7.69 (s, 4H); 13C NMR (CDCl3, 75 MHz): δ 11.4, 11.6, 14.3, 18.8, 23.3, 24.2, 29.27, 29.35, 30.9, 39.4, 39.7, 71.4, 71.8, 73.9, 83.1, 90.1, 90.6, 104.7, 108.3, 120.8, 124.6, 126.1, 150.1, 151.0 (24 signals out of 29 expected); UV−vis (CHCl3): λmaxabs (ε) = 292 (62300), 307 (55300), 319 (36700), 376 (27200), 396 (37700), 426 nm (11400 L mol−1 cm−1); MALDI-TOFMS (dithranol, positive): 1098.9 [M]+; Anal. Calcd for C72H114O4Si2: C 78.63; H 10.45. Found: C 78.40; H 10.84. Preparation of Hexadecadehydro[20]- and Tetracosadehydro[30]annulenes 3b and 4b (Cu-Mediated Method). To a solution of 10b (300 mg, 0.27 mmol) in THF (15 mL) was added dropwise a TBAF THF solution (1 mol L−1, 1.36 mL, 1.36 mmol) at 0 °C. After the mixture was stirred for 15 min at 0 °C, the resulting mixture was diluted with CH2Cl2 (20 mL). The mixture was concentrated under reduced pressure to approximately 1 mL. The resulting mixture was purified by silica gel column chromatography (CH2Cl2) to give a yellow solution of desilylated diyne 11b, which was used in the next coupling reaction without further purification due to the instability. To a solution of 11b in CH2Cl2 (27 mL) were added CuCl (135 mg, 1.36 mmol) and TMEDA (0.21 mL, 1.36 mmol) at room temperature. After the mixture was stirred at room temperature for 4 h under air, the suspension was filtrated through a bed of silica gel. The filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (CH2Cl2/hexane, 1:4) and subsequent recycling gel-permeation chromatography eluting with CHCl3 to afford 3b (120 mg, 0.076 mmol, 56%) and 4b (11 mg, 0.0046 mmol, 5%) as red solids. 3b: Mp 188 °C (decomp.); 1H NMR (CDCl3, 600 MHz, 2.11 × 10−2 mol L−1): δ 0.91 (t, 12H, J = 6.9 Hz), 0.92 (t. 12H, J = 6.6 Hz), 0.97 (t, 12H, J = 7.5 Hz), 0.99 (t, 12H, J = 7.5 Hz), 1.35−1.61 (m, 64H), 1.81−1.87 (m, 8H), 3.94−3.99 (m, 8H), 4.07 (d, 8H, J = 5.4 Hz), 7.16 (s, 4H), 7.54 (s, 4H); 13C NMR (CDCl3, 150 MHz): δ 11.47, 11.53, 14.3, 23.3, 24.1, 24.2, 29.33, 29.38, 30.83, 30.88, 39.58, 39.61, 68.9, 71.1, 71.6, 72.3, 83.2, 85.3, 104.2, 107.6, 124.69, 124.79, 125.1, 150.1, 151.3 (25 signals out of 27 expected); IR (KBr) ν 2958, 2926, 2872, 2857, 2178, 2109, 1734, 1614, 1508, 1455, 1382, 1314, 1259, 1182, 1087, 1033 cm−1; UV−vis (CHCl3): λmaxabs (ε) = 262 (122900), 279 (168800), 298 (155000), 337 (53000), 362 (80700), 390 (83700), 493 (41100), 552 nm (7400 L mol−1 cm−1); MALDITOF-MS (dithranol, positive): 1569.5 [M]+; Anal. Calcd for C108H144O8: C 82.61; H 9.24. Found: C 82.85; H 9.36. 4b: Mp 223 °C (decomp.); 1H NMR (CDCl3, 600 MHz, 2.69 × 10−3 mol L−1): δ 0.93 (t, 18H, J = 6.9 Hz), 0.97 (t, 18H, J = 6.9 Hz), 1.03 (t, 18H, J = 7.2 Hz), 1.04 (t, 18H, J = 7.2 Hz), 1.26−1.64 (m, 96H), 1.89−1.92 (m, 12H), 4.09 (brs, 12H), 4.13 (d, 12H, J = 5.4 Hz), 7.61 (s, 6H), 7.65 (s, 6H); 13C NMR (CDCl3, 150 MHz): δ 11.6, 14.3, 14.3, 23.27, 23.33, 24.20, 24.25, 29.40, 29.46, 31.0, 39.6, 39.7, 65.7, 70.7, 71.2, 71.7, 76.3, 83.1, 104.6, 107.8, 120.9, 124.8, 126.1, 150.4, 151.4 (25 signals out of 27 expected); IR (KBr) ν 2957, 2926, 2857, 2182, 2095, 1612, 1504, 1456, 1433, 1379, 1260, 1186, 1120, 1053 cm−1; UV−vis (CHCl3): λmaxabs (ε) = 290 (183800), 462 (98600), 504 nm (102200 L 8893

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

Article

The Journal of Organic Chemistry mol−1 cm−1); MALDI-TOF-MS (dithranol, positive): 2353.8 [M]+; Anal. Calcd for C162H216O12: C 82.61; H 9.24, Found: C 82.35; H 9.37. Preparation of Tetracosadehydro[30]annulene 4b (Pd-Mediated Method). To a solution of 10b (300 mg, 0.27 mmol) in THF (15 mL) was added dropwise a TBAF THF solution (1 mol L−1, 1.36 mL, 1.36 mmol) at 0 °C. After the mixture was stirred for 15 min at 0 °C, the resulting mixture was concentrated under reduced pressure to approximately 1 mL. The resulting mixture was purified by silica gel column chromatography (THF) to give a yellow solution of desilylated diyne 11b, which was used in the next coupling reaction without further purification due to the instability. [PdCl2(PPh3)2] (191 mg, 0.27 mmol), CuI (26 mg, 0.13 mmol), and Et3N (0.15 mL, 1.09 mmol) were added to a solution of 11b in THF (9 mL). The resulting mixture was stirred at room temperature for 3 h. After the solvent was removed under reduced pressure, the residue was purified by silica gel column chromatography (CH2Cl2/hexane, 1:2) and recycling gelpermeation chromatography (CHCl3) to give 4b (34 mg, 14.4 μmol, 16%) as yellow solids. We confirmed that the 1H NMR data of the material are in agreement with those of 4b synthesized by the Cumediated method. Preparation of Ethynyl-Substituted Phenanthrene 12b. To a suspension of ethynyl-substituted dihydrophenanthrene 7b (380 mg, 0.40 mmol) and SnCl2·2H2O (452 mg, 2.00 mmol) in THF (20 mL) was added H2SO4 (0.5 mol L−1, 0.03 mL) under argon atmosphere. After the mixture was refluxed for 11 h, brine was added into the mixture. The organic phase was separated, and the aqueous phase was extracted with CH2Cl2. The combined organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column (hexane/CH2Cl2, 5:1) to afford 12b (300 mg, 0.76 mmol, 84%) as yellow oil. 1H NMR (CDCl3, 300 MHz): δ 0.37 (s, 18H), 0.92 (t, 12H, J = 7.0 Hz), 0.99 (t, 6H, J = 7.6 Hz), 1.00 (t, 6H, J = 7.4 Hz), 1.32−1.64 (m, 32H), 1.85−1.92 (m, 4H), 3.99−4.07 (m, 4H), 4.11 (d, 4H, J = 6.0 Hz), 7.70 (s, 2H), 7.79 (s, 2H); 13C NMR (CDCl3, 150 MHz): δ 0.4, 11.3, 11.5, 14.3, 23.25, 23.29, 24.19, 29.22, 29.35, 30.85, 30.93, 39.5, 39.7, 71.4, 71.8, 103.2, 103.3, 104.8, 108.8, 120.7, 124.2, 125.6, 149.8, 150.4 (24 signals out of 26 expected); UV−vis (CHCl3): λmaxabs (ε) = 267 (62800), 298 (40800), 305 (42900), 345 (19600), 360 (25300), 397 nm (6900 L mol−1 cm−1); MALDI-TOF-MS (dithranol, positive): 883.9 [M+H]+; HR-FAB-MS (3-nitrobenzyl alcohol, positive): m/z calcd for C56H90O4Si2+ 882.6378, found 882.6366 [M]+. Preparation of Octadehydro[12]- and Dodecadehydro[18]annulenes 1b and 2b (Cu-Mediated Method). A mixture of ethynyl-substituted phenanthrene 12b (130 mg, 0.14 mmol) and K2CO3 (101 mg, 0.73 mmol) in THF/MeOH (1:1, 10 mL) was stirred at room temperature for 30 min. After the mixture was concentrated under reduced pressure to approximately 1 mL, the resulting mixture was purified by silica gel column chromatography (THF) to give a colorless solution of desilylated diyne 13b. The solvent was replaced with CH2Cl2 by evaporation followed by dilution, and the solution was used in the next reaction immediately. CuCl (72 mg, 0.73 mmol) and TMEDA (0.1 mL, 0.73 mmol) were added to a solution of 13b in CH2Cl2 (28 mL). The resulting mixture was refluxed for 5 h under a supply of air. After the solvent was removed under reduced pressure, the residue was suspended with CHCl3, and the resulting mixture was washed with H2O. The organic phase was dried over anhydrous MgSO4 and evaporated under reduced pressure. The residue was purified by silica gel column chromatography (CHCl3/hexane = 1:4) and recycling gel-permeation chromatography eluting with CHCl3 to give 1b (57 mg, 0.038 mmol, 55%) as red solids and 2b (5 mg, 2.26 × 10−3 mmol, 5%) as yellow solids. 1b: Mp 188− 190 °C; 1H NMR (CDCl3, 600 MHz): δ 0.91 (t, 12H, J = 7.0 Hz), 0.94 (t, 12H, J = 6.5 Hz), 0.97 (t, 12H, J = 7.5 Hz), 0.99 (t, 12H, J = 7.5 Hz), 1.32−1.62 (m, 64H), 1.81−1.88 (m, 8H), 3.94−4.00 (m, 8H), 4.07 (d, 8H, J = 5.5 Hz), 7.01 (s, 4H), 7.53 (s, 4H); 13C NMR (CDCl3, 150 MHz): δ 11.4, 11.5, 14.26, 14.29, 23.25, 23.28, 24.19, 24.22, 29.36, 29.40, 30.84, 30.91, 39.66, 39.71, 71.2, 71.7, 88.4, 93.9, 104.4, 107.8, 124.5, 124.7, 126.7, 150.8, 151.0; IR (KBr) ν 2959, 2925, 2857, 2174, 1615, 1509, 1455, 1379, 1275, 1257, 1221, 1197, 1177,

1037 cm−1; UV−vis (CHCl3): λmaxabs (ε) = 275 (85000), 306 (79700), 332 (59800), 347 (86700), 387 (12700), 405 (14300), 473 (26300), 560 nm (1600 L mol−1 cm−1); MALDI-TOF-MS (dithranol, positive): 1473.1 [M]+; Anal. Calcd for C100H144O8: C 81.47; H 9.85. Found: C 81.35; H 9.76. 2b: Mp 101−104 °C; 1H NMR (CDCl3, 600 MHz): δ 0.88 (t, 18H, J = 7.2 Hz), 0.94 (t, 18H, J = 7.1 Hz), 1.04 (t, 18H, J = 7.4 Hz), 1.05 (t, 18H, J = 7.1 Hz), 1.30−1.68 (m, 96H), 1.87 (sep, 6H, J = 6.0 Hz), 1.93 (sep, 6H, J = 6.1 Hz), 4.18 (d, 12H, J = 5.4 Hz), 4.28 (d, 12H, J = 3.6 Hz), 7.83 (s, 6H), 8.07 (s, 6H); 13C NMR (CDCl3, 150 MHz): δ 11.6, 11.9, 14.22, 14.30, 23.3, 24.2, 24.4, 29.40, 29.50, 31.0, 31.10, 31.12, 39.7, 71.6, 71.7, 82.7, 83.3, 104.9, 109.6, 120.8, 124.7, 126.0, 150.0, 151.4; IR (KBr) ν 3463, 2959, 2928, 1615, 1505, 1456, 1376, 1261, 1194, 1029 cm−1; UV−vis (CHCl3): λmaxabs (ε) = 275 (128000), 405 (88900), 426 (92300), 441 (81400) 458 nm (101000 L mol−1 cm−1); MALDI-TOF-MS (dithranol, positive): 2209.8 [M]+; Anal. Calcd for C150H216O12: C 81.47; H 9.85. Found: C 81.18; H 10.04. Preparation of Dodecadehydro[18]annulene 2b (Pd-Catalyzed Method). A mixture of ethynyl-substituted phenanthrene 12b (224 mg, 0.25 mmol) and K2CO3 (175 mg, 1.26 mmol) in THF/MeOH (1:1, 10 mL) was stirred at room temperature for 30 min. After the mixture was concentrated under reduced pressure to approximately 1 mL, the resulting mixture was purified by silica gel column chromatography (THF) to give a colorless solution of desilylated diyne 13b. The solvent was replaced with CH2Cl2 by evaporation followed by dilution, and the solution was used in the next reaction immediately. Et3N (25 mL) was added to a solution of 13b in THF (25 mL), and the resulting solution was bubbled with argon with stirring for 30 min. [PdCl2(PPh3)2] (17 mg, 0.025 mmol), CuI (9 mg, 0.050 mmol), and p-benzoquinone (24 mg, 0.22 mmol) were added to the solution. After the mixture was stirred at 70 °C for 2 h, the suspension was filtered through a bed of silica gel, and the filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (CH2Cl2/hexane = 1:3) and recycling gelpermeation chromatography eluting with CHCl3 to give 2b (20 mg, 9.04 μmol, 10%) as yellow solids. We confirmed that the 1H NMR data of the material are in agreement with those of 2b synthesized by the Cu-mediated method.

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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.7b01165. Synthetic procedures, thermal analyses, theoretical data, photophysical data, electrochemical data, MALDI-TOFMS spectra, concentration- and temperature-dependent 1 H NMR and/or UV−vis spectra, and WAXD profiles and 1H and 13C NMR spectra of new compounds (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel: +81-277-30-1310; Fax: +81-277-30-1314; E-mail: [email protected] ORCID

Minoru Yamaji: 0000-0001-9963-2136 Yosuke Nakamura: 0000-0002-6047-1336 Present Address §

Department of Materials Science, School of Engineering, The University of Shiga Prefecture, 2500 Hassaka-cho, Hikone, Shiga 522-8533, Japan Notes

The authors declare no competing financial interest. 8894

DOI: 10.1021/acs.joc.7b01165 J. Org. Chem. 2017, 82, 8882−8896

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The Journal of Organic Chemistry

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ACKNOWLEDGMENTS This work was financially supported by Grants-in-Aid for Scientific Research from MEXT, Japan (No. JP15K05415, JP15K05416, JP25870112). This work was performed under the Cooperative Research Program of “Network Joint Research Center for Materials and Devices” (Osaka University, Kyushu University). S.K. thanks the Tokuyama Science Foundation for financial support. Quantum chemical calculations were performed in the Research Center for Computational Science, Japan. We thank Ms. Yumi Hirose (Osaka University) for the helpful assistance of AFM measurements.

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