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. 2020 Mar 4;5(10):4787–4797. doi: 10.1021/acsomega.9b03408

Single-Component Polycondensation of Bis(alkoxycarbonyldiazomethyl)aromatic Compounds To Afford Poly(arylene vinylene)s with an Alkoxycarbonyl Group on Each Vinylene Carbon Atom

Hiroaki Shimomoto †, Taka-aki Moriya †, Takeshi Mori †, Tomomichi Itoh †, Shinji Kanehashi ‡, Kenji Ogino ‡, Eiji Ihara †,*
PMCID: PMC7081273  PMID: 32201764

Abstract

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The original synthetic strategy for a new type of poly(arylene vinylene) (PAV) is presented, where the C=C-bond-forming coupling of bis(alkoxycarbonyldiazomethyl)aromatic compounds is utilized as propagation. The strategy is unique in that the resulting PAVs have an alkoxycarbonyl group as an electron-withdrawing substituent on each vinylene carbon atom in the polymer main chain. Among the transition-metal catalysts examined in this study, RuCl(cod)Cp* (cod = 1,5-cyclooctadiene, Cp* = pentamethylcyclopentadienyl) is the most efficient, affording PAVs from a series of bis(alkoxycarbonyldiazomethyl)aromatic compounds with a high trans-C=C-forming selectivity of up to 90%. A PAV sample with a fluorenylene framework as an arylene moiety prepared by the Ru catalyst exhibited a hole mobility of 4 × 10–6 cm2 V–1 s–1.

Introduction

Polymerization using diazocarbonyl compounds as monomers has attracted much attention recently.1,2 In particular, Pd- and Rh-initiated polymerization of diazoacetates has been demonstrated to be an effective method for C–C main-chain polymer syntheses, where the main-chain framework is constructed from one carbon unit, alkoxycarbonylmethylene, derived from the monomer after N2 elimination. In addition to the C–C main-chain polymer syntheses, the reactivity of diazocarbonyl groups can be utilized in the polycondensation of bis(diazocarbonyl) compounds, which can afford a variety of unique polymer structures (Scheme 1).3−9 For example, we have succeeded in developing a novel three-component polycondensation of bis(diazoketone), diol or dicarboxylic acid, and tetrahydrofuran (THF), affording a new type of poly(ether ketone) (Scheme 1A) or poly(ester ether ketone) (Scheme 1B), respectively.4,5 In the polycondensation, whereas the initially anticipated propagation was the well-established Rh-catalyzed insertion of a diazocarbonyl group into an O–H group of diol or dicarboxylic acid, we unexpectedly found that 1 equiv of THF employed as a solvent was inserted with its ring-opening between the diazo-bearing carbon and the hydroxyl oxygen atoms of each bifunctional monomer, resulting in the formation of the unique polymer main-chain structures. Quite recently, we further applied the polycondensation to an enol form of bis(1,3-diketone) as one of the substrates, demonstrating that the resulting poly(β-keto enol ether)s can be efficiently degraded into well-defined low-molecular-weight products under mildly acidic conditions (Scheme 1C).9 In addition, we reported Ru-catalyzed polycondensation of bis(diazocarbonyl) compounds with aromatic diamine, affording a new type of polyamine, without the insertion of ring-opened THF in this case (Scheme 1D).8

Scheme 1. Previous Polycondensation of Bis(diazocarbonyl) Compounds.

Scheme 1

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Meanwhile, as another mode of polycondensation of bis(diazocarbonyl) compounds, Liu’s and our groups independently demonstrated that C=C-forming coupling reactions of bis(diazoacetate)s can be utilized as propagation, yielding unsaturated polyesters.6,7 In the course of investigating the C=C-forming polycondensation, we happened to notice that, with the appropriate design of a monomer structure, the reaction can be utilized for the preparation of poly(arylene vinylene)s (PAVs), where an alkoxycarbonyl group (ester) as an electron-withdrawing group (EWG) is located on each vinylene carbon atom (Scheme 2). Although the fundamental concept of forming PAVs with phenyl-substituted vinylene carbons from bis(diazoarene)s via C=C-forming coupling was proposed and examined in 1969 by De Koninck and Smets to yield the products with Mn of 3000–5000,3,10 the preparation and use of the unstable bis(diazoarene) monomers would be somewhat troublesome, in particular compared to the relatively stable bis(diazocarbonyl) compounds employed in this study.

Scheme 2. C=C-Bond-Forming Coupling of Bis(alkoxycarbonyldiazomethyl)aromatic Compounds To Afford PAV with an Alkoxycarbonyl Group on Each Vinylene Carbon Atom.

Scheme 2

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PAVs are one of the most important π-conjugated polymers and have been widely utilized as materials for optical and electronic applications.11 Accordingly, the synthetic strategy for PAV has been extensively explored, and various methods have been achieved for preparing PAVs with a variety of chemical structures with respect to arylene structures (Ar), cis–trans compositions, and substituents on arylene and vinylene frameworks.11 From these studies, some general principles for improving properties of PAVs have been established, and one of them is the introduction of EWGs on vinylene carbon atoms. Indeed, poly(phenylene vinylene)s (PPVs) with EWGs on their vinylene carbon atoms have recently been demonstrated to exhibit extremely high electron mobility (>1 cm2 V–1 s–1),12,13 to which the high planarity of the π-conjugation systems in the polymer structures could contribute the most though. However, to the best of our knowledge, a general synthetic method for incorporating EWGs (e.g., CN, F, CO2R) on all of the vinylene carbons in PAV has not been achieved so far and has remained an unrealized objective. In this context, our new synthetic strategy proposed in Scheme 2 is quite promising as a method for realizing the substitution pattern of vinylene carbons. Furthermore, another advantage of this method is the latitude in the choice of the Ar structures because practically any bis(halomethyl)aromatic compound can be transformed into its corresponding bis(alkoxycarbonyldiazomethyl)aromatic compound as a monomer for the polymerization.

In this paper, we will report the preparation of a series of bis(alkoxycarbonyldiazomethyl)aromatic compounds and attempt to polymerize the monomers with transition metal catalysts for preparing a new type of PAV. In addition, some photophysical properties of the resulting polymers will be reported.

Results and Discussion

Model Reaction Using Methyl 2-Diazo-2-phenylacetate (1)

As a model reaction for the polycondensation to obtain PAVs from bis(alkoxycarbonyldiazomethyl)aromatic compounds, we chose a transition-metal-catalyzed C=C-forming coupling reaction of methyl 2-diazo-2-phenylacetate (1) (Scheme 3). As transition metal catalysts, we first employed Cu(acac)2 and Rh2(OAc)4, which have been reported to be effective for the coupling reactions of diazocarbonyl compounds such as diazoketones, diazoacetates, and diazomalonates.7,14,15 For example, when 1 was reacted with Cu(acac)2 with a feed ratio of [1]/[Cu] = 50 in CH2Cl2 at room temperature (RT), the desired coupling products were obtained as a mixture of cis-2 and trans-2 in a ratio of [cis-2]/[trans-2] = 5:3 in high yield (run 1 in Table 1), where each isomer was identified according to the data reported in the literature.16 The 1H NMR spectrum of the isolated product mixture revealed the presence of another minor compound, whose MeO signal appeared at a different chemical shift than the corresponding signals for cis-2 and trans-2. According to the literatures,17−19 the structure of the compound was revealed to be azine 3 containing an =N–N= framework between two units derived from 1 as a result of a coupling reaction with the release of only 1 equiv of N2 from two molecules of 1; the content of 3 was determined to be 12 mol % based on relative signal intensities in the 1H NMR spectrum. A significant decrease in the 3 content was observed in the reaction in toluene, particularly at 100 °C, down to 2% (runs 2 and 3 in Table 1). It was interesting to note that when Rh2(OAc)4 was used as a catalyst in place of Cu(acac)2 under the same conditions, while the product mixture was obtained in high yield (>90%), the main product was azine 3 (runs 4–6 in Table 1) and the selectivity of the products was highly dependent on the solvent employed for the reaction (CH2Cl2 or toluene) as well.

Scheme 3. Transition-Metal-Catalyzed C=C Formation of Methyl 2-Diazo-2-phenylacetate (1).

Scheme 3

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Table 1. Transition-Metal-Catalyzed Coupling of 1a.

run catalyst solvent temp. total yield (%)b cis-2/trans-2/3 (mol %)c
1 Cu(acac)2 CH2Cl2 RT 92 55:33:12
2 Cu(acac)2 toluene RT 66 47:47:6
3 Cu(acac)2 toluene 100 °C 85 40:58:2
4 Rh2(OAc)4 CH2Cl2 RT 94 3:4:93
5 Rh2(OAc)4 toluene RT 97 18:20:62
6 Rh2(OAc)4 toluene 100 °C 92 20:16:64
7 Grubbs first CH2Cl2 RT n.d.d n.d.d
8 Grubbs first toluene 100 °C 45 50:34:16
9 RuCl(cod)Cp* CH2Cl2 RT 57 11:87:2
10 RuCl(cod)Cp* CH2ClCH2Cl 60 °C 88 2:96:2
11 RuCl(cod)Cp* toluene 100 °C 57 4:94:2
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a

Reaction period = 17 h, [1]/[catalyst] = 50 (runs 1–3), 100 (runs 4–8), or 20 (runs 9–11).

b

Total yield was 100 × [weight of PhCO2(Me)C in all of the products]/[weight of PhCO2(Me)C in the starting 1].

c

mol % ratios were determined from 1H NMR spectra.

d

Not determined.

As for Ru complexes as a catalyst, whereas Grubbs catalysts were effective for the analogous polycondensation of bis(diazoacetate)s having H at their diazo-bearing carbons to yield unsaturated polyesters via C=C-forming coupling in our previous publication,7 the Grubbs first catalyst did not efficiently catalyze the coupling of 1, probably because the reactivity of diazoacetates considerably differs depending on the substituent (H or Ph) at their diazo-bearing carbons; while the catalyst gave a complex mixture at room temperature in CH2Cl2, the product was obtained in moderate yield (45%) at 100 °C in toluene (runs 7 and 8 in Table 1). In the meantime, because we have found that RuCl(cod)Cp (cod = 1,5-cyclooctadiene, Cp = cyclopentadienyl) can catalyze the coupling of 1 efficiently under a certain condition in the literature,20 we employed a more convenient and commercially available Ru complex with a similar structure, RuCl(cod)Cp* (Cp* = pentamethylcyclopentadienyl), for the model reaction. As listed in runs 9 and 10 in Table 1, while the reaction in CH2Cl2 at room temperature gave the products in moderate yield (57%) with high trans-C=C selectivity (87%), both the yield and trans-C=C selectivity improved significantly in 1,2-dichlorethane as the solvent at 60 °C to 88 and 96%, respectively. The high trans-C=C selectivity was retained when the reaction was conducted in toluene at 100 °C, although the yield became moderate (57%) (run 11 in Table 1). It is noteworthy that the azine 3 formation was suppressed to 2 mol % in these RuCl(cod)Cp*-catalyzed reactions. The results for the model reaction described above indicated that with the appropriate choice of the catalyst and reaction conditions, it would be possible to prepare well-defined PAVs having an alkoxycarbonyl group at each vinylene carbon atom by single-component polycondensation of bis(alkoxycarbonyldiazomethyl)aromatic compounds.

Monomer Syntheses

Syntheses of bis(alkoxycarbonyldiazomethyl)aromatic compounds employed as monomers in this study are outlined in Scheme 4 and Scheme S1. By a three-step process, the starting bis(halomethyl)aromatic compounds were transformed into bis(alkoxycarbonylmethyl)aromatic compounds, which were then subjected to a diazo-transfer reaction to yield a series of monomers with biphenylene (4a and 4b), phenylene (5), and di(n-octyl)fluorenylene (6) frameworks as the aromatic moieties. In each monomer structure, linear alkyl side chains (C6, C8, or C12) were incorporated for improving the solubility of the resulting polymers.

Scheme 4. Syntheses of Bis(alkoxycarbonyldiazomethyl)aromatic Compounds.

Scheme 4

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Polymerization of Bis(alkoxycarbonyldiazomethyl)aromatic Compounds

RuCl(cod)Cp*-Catalyzed Polymerization

With the use of RuCl(cod)Cp* exhibiting high trans-C=C selectivity in the aforementioned model reaction, we first examined the polymerization of a biphenyl-type monomer 4a to optimize the reaction conditions (runs 1 and 2 in Table 2 and Scheme 5). While the reaction of 4a with RuCl(cod)Cp* in CH2Cl2 (room temperature) or in toluene (room temperature and 50 °C) gave ill-defined polymeric products in low yield in contrast to the successful results of the model reactions at these temperatures, increasing the reaction temperature to 100 °C in toluene turned out to be effective for affording a relatively well-defined polymer in a feed ratio of [4a]/[Ru] = 25 (run 1 in Table 2). In the 1H NMR spectrum of the product in run 1 (Figure S1), a predominant signal for −CO2CH2– in the alkoxycarbonyl moiety appears corresponding to the trans-C=C framework based on the comparison with the spectrum of the model reaction products 2. However, along with the signals assignable to cis-C=C and azine frameworks, there exist some other unassignable minor signals in this region. After examining various reaction conditions to improve the polymerization behavior, we have found that increasing the amount of the catalyst with respect to 4a is crucial for obtaining more well-defined polymers in this polymerization. Thus, the reaction with a feed ratio of [4a]/[Ru] = 10 was conducted in toluene at 100 °C (run 2 in Table 2), and the 1H NMR spectrum of the product (size-exclusion chromatography (SEC)-estimated Mn = 20 800) obtained in 51% yield is shown in Figure 1. In contrast to the spectrum of the product in run 1, the intensities of unidentified signals except for −CO2CH2– signals of trans- (4.0 ppm) and cis-C=C (4.2 ppm) and azine (4.4 ppm) frameworks became diminished, and the composition of the three components could be calculated based on the relative signal intensities to be cis/trans /azine = 6:90:4. Likewise, the polymerization of 4b with a longer ester substituent (n-dodecyl) proceeded to give a relatively well-defined polymer in a lower yield of 25% with a slightly diminished trans-C=C selectivity (87%) (run 3 in Table 2; 1H NMR spectrum in Figure S2). When phenylene-bridged 2,6-bis(n-hexyloxycarbonyldiazomethyl)benzene 5 was employed as a monomer, the same reaction condition as the above afforded a relatively well-defined polymer despite a lower trans-C=C selectivity (84%) (run 4 in Table 2; 1H NMR spectrum in Figure S3). The polymerization of the monomer 6 with a di-n-octyl-substituted fluorenylene framework gave a polymer in 67% yield with high trans-C=C selectivity (90%) (run 5 in Table 2). Along with the 1H NMR analysis (Figure 2), the polymer structure including the azine composition was confirmed from the elemental analysis results in this case; the expected values calculated based on the (cis + trans)/azine ratio determined from the 1H NMR spectrum is C 80.36, H 9.92, and N 0.23, which agreed well with the observed values of C 79.02, H 9.37, and N 0.50. These results demonstrate that the polycondensation with the Ru catalyst can indeed afford PAVs with an alkoxycarbonyl group on each vinylene carbon atom with a relatively high trans-C=C selectivity, although a small amount of azine framework exists in the polymer main chain.

Table 2. Transition-Metal-Catalyzed Polymerization of Bis(alkoxycarbonyldiazomethyl)aromatic Compoundsa.
run catalyst (cat.) monomer (M) solvent temp. [M]/[cat.] yield (%)b Mn × 10–3 Mw/Mn cis/trans/azine unit%c
1 RuCl(cod)Cp* 4a toluene 100 °C 25 38 8.6 1.4 9:80:11
2 RuCl(cod)Cp* 4a toluene 100 °C 10 51 20.8 2.2 6:90:4
3 RuCl(cod)Cp* 4b toluene 100 °C 10 25 27.9 2.3 7:87:6
4 RuCl(cod)Cp* 5 toluene 100 °C 10 39 8.9 1.3 11:84:5
5 RuCl(cod)Cp* 6 toluene 100 °C 10 67 11.3 1.6 4:90:6
6 Cu(acac)2 4a toluene 100 °C 25 63 56.8 2.7 41:48:11
7 Cu(acac)2 4a toluene 100 °C 10 35 90.8 3.1 38:55:7
8 Cu(acac)2 5 toluene 100 °C 25 53 8.9 1.4 47:45:8
9 Cu(acac)2 5 toluene 100 °C 10 26 24.6 2.3 45:50:5
10 Rh2(OAc)4 4a CH2Cl2 RT 50 83 40.0 2.7 9:12:79
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a

Reaction period = 17 h.

b

Polymer yield was 100 × [weight of C, H, O in the product]/[weight of C, H, O in the monomer].

c

Unit% ratios were determined from 1H NMR spectra.

Scheme 5. Transition-Metal-Catalyzed Polycondensation of Bis(alkoxycarbonyldiazomethyl)aromatic Compounds.

Scheme 5

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Figure 1.

Figure 1

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1H NMR spectrum of PAV obtained from 4a by RuCl(cod)Cp* (run 2 in Table 2).

Figure 2.

Figure 2

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1H NMR spectrum of PAV (poly6′) obtained from 6 by RuCl(cod)Cp* (run 5 in Table 2).

Even though we have succeeded in obtaining relatively well-defined trans-C=C-rich PAVs from the Ru-catalyzed polycondensation, the products contained the azine framework and unidentified structural defects even, to a small extent, in the main chain, which would bring about a moderate performance in the hole mobility measurement for a polymer sample obtained from 6 described in a later section below.

Cu(acac)2- and Rh2(OAc)4-Catalyzed Polymerization

In a manner similar to that observed in the previous section of RuCl(cod)Cp*-catalyzed reactions, the polymerization of 4a with Cu(acac)2 in CH2Cl2 at room temperature, which was a suitable condition for the model reaction of 1, did not afford a well-defined polymer. However, the use of toluene as a solvent at 100 °C again was quite effective to give relatively well-defined polymers with the catalyst. As shown in run 6 in Table 2, the reaction with a feed ratio of [4a]/[Cu] = 25 afforded a high-molecular-weight polymer with Mn = 56 800 in moderate yield (63%). As clearly observed in the 1H NMR spectrum of the product (Figure 3A), the selectivities of cis- and trans-C=C (41 and 48%, respectively) were low, as expected from the results in the model reaction of 1 (run 3 in Table 1), while the composition of the azine framework (11%) is higher in the polymerization than that observed in the model reaction (2%). The increase of the amount of the catalyst to [4a]/[Cu] = 10 resulted in both a higher Mn (90 800) and a higher trans selectivity (55%), despite the lower polymer yield (35%) (run 7 in Table 2). Phenylene-bridged monomer 5 was also polymerized under the same conditions to give polymers with a lower Mn, yield, and trans-C=C selectivity (runs 8 and 9 in Table 2 and Figure S4) compared to the polymerization of 4a. Interestingly, Rh2(OAc)4-catalyzed polymerization of 4a in CH2Cl2 at room temperature afforded a high Mn polymer (Mn = 40 000), where the azine framework is predominant (selectivity = 79%, run 10 in Table 2 and Figure 3B) in accordance with the result of the model reaction.

Figure 3.

Figure 3

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1H NMR spectra of the PAV obtained from 4a by (A) Cu(acac)2 (run 6 in Table 2) and (B) Rh2(OAc)4 (run 10 in Table 2).

Optoelectronic Properties of PAVs with a Fluorenylene Framework

Preliminary measurements were carried out to estimate the optoelectronic properties of PAV (poly6′) with a fluorenylene framework obtained from 6. Figure 4 shows UV–vis absorption and photoluminescence (PL) spectra of a poly6′ sample (Mn = 10 900, Mw/Mn = 1.73) in a CHCl3 solution (10 mg/L) (a) and in the film state (b). In the solution, compared with the reported data of a conventional poly(9,9-dialkylfluorenylene-2,7-vinylene) (PFV) with unsubstituted olefinic double bonds,21 a significant blue-shift (45 nm) was observed in the UV–vis spectrum of poly6′ [absorption maximum (λmax) = 345 nm], which indicated that the steric hindrance of alkoxycarbonyl groups and/or structural defects may impede the coplanar structure of the backbone or decrease the effective π-conjugation length. In addition, a significantly red-shifted emission (540 nm of emission maximum) was observed in the poly6′ solution compared with that in the PFV solution (450 nm of emission maximum), resulting in a much larger Stokes shift of poly6′ [195 nm (poly6′) vs 60 nm (PFV)]. This larger Stokes shift of poly6′ could be ascribed to the significant conformational change in an excited state in the solution, resulting in variations in the twist angle between neighboring fluorene rings.22

Figure 4.

Figure 4

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UV–vis absorption and photoluminescence spectra of PAV obtained from 6 by RuCl(cod)Cp* (Mn = 10 900, Mw/Mn = 1.73) in a CHCl3 solution (10 mg/L, λex = 345 nm) (a) and the film state (b).

As for the UV–vis absorption spectrum in the film state (Figure 4b), no bathochromic shift was observed (λmax = 345 nm) in comparison with the solution state, suggesting that polymer-chain aggregation was restricted in the solution owing to the long alkyl chains both in fluorenylene and ester moieties. A blue emission peak (425 nm of emission maximum) with shoulders derived from vibronic bands was observed in the film state, and the Stokes shift (80 nm) was similar to that of the conventional PFV (60 nm).

Since semiconducting materials have been applied to electroluminescent and photovoltaic devices in a diode geometry, it is important to evaluate their mobility in the direction perpendicular to the substrate. As the results of such a mobility evaluation for the poly6′ sample, Figure S5 shows current density (J)–voltage (V) curves for a hole-only device with the configuration of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/PAV/Au (a) and their log–log plots (b); in the latter plot, as expected, regions with a slope of 2 were observed for all devices examined. Therefore, the space-charge-limited current (SCLC) mobility of poly6′ was estimated to be 4 × 10–6 cm2 V–1 s–1 (the mean value for three devices). Although this value was lower than those reported for regioregular poly(3-hexylthiophene)23 and its homologues,24 it was in the same order of conventional poly(dialkoxy-p-phenylene vinylene).25 More importantly, the relatively low planarity in the structure of poly6′ could be the critical reason for the low hole mobility, in comparison to the reported much higher mobility of polymers with high planarity.12,13 With the higher structural integrity achieved on the PAV framework and the higher planarity imparted with the appropriate design of monomer structures, we can expect a significant improvement in the photophysical properties of the PAVs prepared by this new synthetic strategy.26

Conclusions

We have succeeded in establishing a new synthetic method for PAVs bearing an alkoxycarbonyl group on each vinylene carbon atom, utilizing transition-metal-catalyzed C=C-forming coupling reactions of a series of bis(alkoxycarbonyldiazomethyl)aromatic compounds. In particular, we have demonstrated that the Ru-catalyzed polymerization can afford PAVs with high trans-C=C selectivity. The synthetic strategy for PAVs is totally new, and the resulting polymer structures cannot be prepared by any other synthetic method for PAVs reported so far. Furthermore, because the presence of EWG groups on the vinylene carbon atoms in PAV has been reported to enhance the photophysical performances and since there is high latitude in the arylene structure variation, the method could bring about new PAV-based polymeric materials, although the PAV obtained from 6 showed moderate hole mobility at present. Further investigation for improving the structural integrity of the PAVs and evaluating properties of the resulting polymers for a variety of applications is underway in our groups.

Experimental Section

Materials

Tetrahydrofuran (THF) and toluene were dried over a Na/K alloy and Na, respectively, and distilled before use. CH2Cl2 was dried over CaH2 and used without further purification. Cu(acac)2 (TCI; >97%), Rh2(OAc)4 (AZmax; 99%), RuCl(cod)Cp* (Sigma-Aldrich), Grubbs first catalyst (Sigma-Aldrich; 97%), 1-hexanol (TCI; >98.0%), diisopropyl azodicarboxylate (Wako; >90%), triphenylphosphine (Nacalai; >98.0%), MgCl2 (Nacalai; >97.0%), 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) (Nacalai; >97.0%), and 1-dodecanol (TCI; >99.0%) were used as received without further purification. Tosyl azide,27 4,4′-biphenylenediacetic acid,28 1,4-phenylenediacetic acid,28,29 and 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetonitrile30 were prepared following the procedures reported in the literatures. Methyl 2-diazo-2-phenylacetate17 was prepared using tosyl azide as a diazo transfer agent following a reported general procedure for this type of diazoketones. Caution! Extra care must be taken for the preparation and handling of the diazoacetates because of their potential explosiveness.

Synthesis

Di-n-hexyl 4,4′-Biphenylenediacetate

Under a N2 atmosphere, a toluene (50 mL) solution of 4,4′-biphenylenediacetic acid (3.41 g, 12.6 mmol), 1-hexanol (4.0 mL, 32 mmol), and diisopropyl azodicarboxylate (5.8 mL, 30 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After a toluene (35 mL) solution of triphenylphosphine (7.96 g, 30.3 mmol) was added dropwise from the dropping funnel, the reaction mixture was stirred overnight at room temperature. To remove the resulting triphenylphosphine oxide as an insoluble salt, MgCl2 (5.77 g, 60.6 mmol) was added and the mixture was stirred for 2 h at 60 °C. The resulting solid was removed by filtration, and the filtrate was washed with H2O and dried over Na2SO4. After Na2SO4 was removed by filtration, volatiles were removed from the solution by evaporation under reduced pressure. The residue was purified by silica gel chromatography with a mixed solvent (CHCl3/hexane = 4:1) as an eluent to give the product in 58% yield as a colorless solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.53 (d, J = 8.4 Hz, 4H, Ph–H), 7.35 (d, J = 8.0 Hz, 4H, Ph–H), 4.10 (t, J = 6.6 Hz, 4H, −CO2–CH2−), 3.65 (s, 4H, Ph–CH2–CO2), 1.62 (q, J = 7.0 Hz, 4H, CO2–CH2–CH2−), 1.38–1.21 (m, 12H, −[CH2]3–CH3), 0.87 (t, J = 6.6 Hz, 6H, −CH3).

Di-n-hexyl 4,4′-Biphenylenebis(diazoacetate) (4a)

Under a N2 atmosphere, an acetonitrile (40 mL) solution of di-n-hexyl 4,4′-biphenylenediacetate (3.06 g, 6.98 mmol) and tosyl azide (3.30 g, 16.7 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After an acetonitrile (20 mL) solution of DBU (2.8 mL, 19 mmol) was added dropwise from the dropping funnel, the mixture was stirred overnight at room temperature. On the addition of 60 mL of H2O to the resulting mixture, an insoluble solid appeared, and the solid was separated by filtration and washed with H2O. Purification of the solid by silica gel chromatography with a mixed solvent (CHCl3/hexane = 3:1) as an eluent gave the product in 60% yield as an orange solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.63 (d, J = 8.8 Hz, 4H, Ph–H), 7.55 (d, J = 8.4 Hz, 4H, Ph–H), 4.29 (t, J = 6.4 Hz, 4H, −CO2–CH2−), 1.72 (q, J = 7.0 Hz, 4H, CO2–CH2–CH2−), 1.47–1.27 (m, 12H, −[CH2]3–CH3), 0.91 (t, J = 6.4 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 165.3 (−CO2−), 137.6 (Ph–C), 127.3 (Ph–C), 124.7 (Ph–C), 124.3 (Ph–C), 65.2 (−CO2–CH2−), 63.5 (C=N2), 31.4, 28.8, 25.6, and 22.6 (−[CH2]4–CH3), 14.0 (−CH3). Anal. calcd for C28H34N4O4: C, 68.55; H, 6.99; N, 11.42. Found: C, 68.84; H, 6.84; N, 11.34.

Di-n-dodecyl 4,4′-Biphenylenediacetate

Under a N2 atmosphere, a THF (28 mL) solution of 4,4′-biphenylenediacetic acid (3.28 g, 12.1 mmol), 1-dodecanol (6.0 mL, 27 mmol), and diisopropyl azodicarboxylate (5.2 mL, 27 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After a toluene (16 mL) solution of triphenylphosphine (6.98 g, 26.6 mmol) was added dropwise from the dropping funnel, the reaction mixture was stirred overnight at room temperature. After volatiles were removed under reduced pressure, MgCl2 (5.77 g, 60.6 mmol) and toluene (45 mL) were added and the mixture was stirred for 2 h at 60 °C. The resulting solid was removed by filtration, and the filtrate was washed with H2O and dried over Na2SO4. After Na2SO4 was removed by filtration, volatiles were removed from the solution by evaporation under reduced pressure. The residue was purified by silica gel chromatography with CHCl3 as an eluent to give the product in 57% yield as a colorless solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.54 (d, J = 8.4 Hz, 4H, Ph–H), 7.35 (d, J = 8.0 Hz, 4H, Ph–H), 4.10 (t, J = 6.6 Hz, 4H, −CO2–CH2−), 3.65 (s, 4H, Ph–CH2–CO2), 1.62 (q, J = 7.0 Hz, 4H, CO2–CH2–CH2−), 1.36–1.18 (m, 36H, −[CH2]9–CH3), 0.88 (t, J = 6.8 Hz, 6H, −CH3).

Di-n-dodecyl 4,4′-Biphenylenebis(diazoacetate) (4b)

Under a N2 atmosphere, an acetonitrile (9 mL) solution of di-n-dodecyl 4,4′-biphenylenediacetate (2.44 g, 4.02 mmol) and tosyl azide (1.92 g, 9.74 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After a toluene (4 mL) solution of DBU (1.6 mL, 11 mmol) was added dropwise from the dropping funnel, the mixture was stirred overnight at room temperature. On the addition of 15 mL of H2O to the resulting mixture, an insoluble solid appeared, and the solid was separated by filtration and washed with H2O. Purification of the solid by silica gel chromatography with a mixed solvent (CHCl3/hexane = 4:1) as an eluent gave the product in 43% yield as a yellow solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.63 (d, J = 7.6 Hz, 4H, Ph–H), 7.55 (d, J = 8.0 Hz, 4H, Ph–H), 4.29 (t, J = 6.8 Hz, 4H, −CO2–CH2−), 1.72 (q, J = 7.0 Hz, 4H, CO2–CH2–CH2−), 1.47–1.15 (m, 36H, −[CH2]9−), 0.88 (t, J = 6.8 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 165.4 (−CO2−), 137.7 (Ph–C), 127.3 (Ph–C), 124.7 (Ph–C), 124.4 (Ph–C), 65.2 (−CO2–CH2−), 32.0, 29.7 (2C), 29.6, 29.5, 29.4, 29.3, 28.8, 25.9, and 22.7 (−[CH2]10–CH3), 14.2 (−CH3). The signal for the diazo-bearing carbon atom cannot be identified, probably because of its broadness. Anal. calcd for C40H58N4O4: C, 72.91; H, 8.87; N, 8.50. Found: C, 72.39; H, 9.13; N, 8.50.

Di-n-hexyl 1,4-Phenylenediacetate

Under a N2 atmosphere, a THF (22 mL) solution of 1,4-phenylenediacetic acid (1.07 g, 5.51 mmol), 1-hexanol (1.6 mL, 13 mmol), and diisopropyl azodicarboxylate (2.4 mL, 12 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After a THF (14 mL) solution of triphenylphosphine (3.20 g, 12.2 mmol) was added dropwise from the dropping funnel, the reaction mixture was stirred overnight at room temperature. After insoluble solids were removed by filtration, volatiles were removed under reduced pressure. The residue was purified by using preparative recycling gel permeation chromatography (GPC) to give the product in 64% yield as a colorless solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.24 (s, 4H, Ph–H), 4.08 (t, J = 6.6 Hz, 4H, −CO2–CH2−), 3.59 (s, 4H, Ph–CH2–CO2), 1.60 (q, J = 6.8 Hz, 4H, CO2–CH2–CH2−), 1.37–1.19 (m, 12H, −[CH2]3–CH3), 0.88 (t, J = 6.2 Hz, 6H, −CH3).

Di-n-hexyl 1,4-Phenylenebis(diazoacetate) (5)

Under a N2 atmosphere, an acetonitrile (40 mL) solution of di-n-hexyl 1,4-phenylenediacetate (1.29 g, 3.56 mmol) and tosyl azide (1.57 g, 7.96 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After an acetonitrile (20 mL) solution of DBU (1.4 mL, 9.4 mmol) was added dropwise from the dropping funnel, the mixture was stirred overnight at room temperature. On the addition of 60 mL of H2O to the resulting mixture, an insoluble solid appeared, and the solid was separated by filtration and washed with H2O. Purification of the solid by silica gel chromatography with a mixed solvent (CHCl3/hexane = 2:1) as an eluent gave the product in 57% yield as an orange solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.50 (s, 4H, Ph–H), 4.27 (t, J = 6.6 Hz, 4H, −CO2–CH2−), 1.70 (q, J = 7.0 Hz, 4H, CO2–CH2–CH2−), 1.46–1.22 (m, 12H, −[CH2]3–CH3), 0.90 (t, J = 6.8 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 165.3 (−CO2−), 124.4 (Ph–C), 122.8 (Ph–C), 65.2 (−CO2–CH2−), 63.4 (C=N2), 31.4, 28.8, 25.5, and 22.5 (−[CH2]4–CH3), 14.0 (−CH3). Anal. calcd for C22H30N4O4: C, 63.75; H, 7.30; N, 13.52. Found: C, 64.22; H, 7.26; N, 13.52.

2,2′-(9,9-Dioctyl-9H-fluorene-2,7-diyl)diacetic Acid

A mixture of 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetonitrile (0.761 g, 1.62 mmol), EtOH (20 mL), and 4 M KOH aqueous solutions (20 mL) was placed in a round-bottomed flask equipped with a reflux condenser, and the mixture was refluxed for 24 h. After the mixture was cooled to room temperature, a 1 N HCl aqueous solution was added dropwise until the pH of the mixture became 1. The mixture was transferred into a separatory funnel, and the organic layer was separated with the use of 150 mL of CHCl3. The organic layer was washed with 300 mL of H2O, dried over Na2SO4, and concentrated under reduced pressure to give a crude product of 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetic acid almost quantitatively, which was used for the next step without further purification. 1H NMR (400 MHz, dimethyl sulfoxide (DMSO)-d6), δ (ppm): 11.5–13.0 (br, 1H, CO2H), 7.68 (d, J = 7.6 Hz, 2H, Ar–H), 7.28 (s, 2H, Ar–H), 7.20 (d, J = 8.0 Hz, 2H, Ar–H), 1.91 (m, 4H, −CH2−), 1.19 (quint, J = 6.8 Hz, 4H −CH2−), 0.95–1.10 (m, 16H, −CH2−), 0.79 (t, J = 7.2 Hz, 6H, −CH3), 0.54 (br, 4H, −CH2−).

Di-n-hexyl 2,2′-(9,9-Dioctyl-9H-fluorene-2,7-diyl)diacetate

Under a N2 atmosphere, a toluene (4.3 mL) solution of 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetic acid (0.313 g, 0.618 mmol), 1-hexanol (0.27 mL, 2.2 mmol), and diisopropyl azodicarboxylate (0.31 mL, 1.6 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After a toluene (3.1 mL) solution of triphenylphosphine (0.397 g, 1.51 mmol) was added dropwise from the dropping funnel, the reaction mixture was stirred overnight at room temperature. After MgCl2 (0.30 g, 3.2 mmol) was added and the mixture was stirred for 2 h at 60 °C. The resulting solid was removed by filtration, and the filtrate was washed with H2O and dried over Na2SO4. After Na2SO4 was removed by filtration, volatiles were removed from the solution by evaporation under reduced pressure. The residue was purified by silica gel chromatography with a mixed solvent of hexane/CH2Cl2 as an eluent to give the product in 68% yield as an orange viscous oil. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.60 (d, J = 8.4 Hz, 2H, Ar–H), 7.23 (s, 2H, Ar–H), 7.22 (d, J = 8.4 Hz, 2H, Ar–H), 4.08 (t, J = 7.0 Hz, 4H, −CO2–CH2−), 1.91 (m, 4H, −CH2−), 1.51 (quint, J = 7.2 Hz, 4H, −CH2−), 1.25–1.35 (m, 6H, −CH2−), 1.21 (quint, J = 7.2 Hz, 4H, −CH2−), 1.05–1.15 (m, 8H, −CH2−), 1.03 (br, 8H, −CH2−), 0.87 (t, J = 6.8 Hz, 6H, −CH3), 0.82 (t, J = 7.2 Hz, 6H, −CH3), 0.62 (br, 4H, −CH2−). Anal. calcd for C45H70O4: C, 80.07; H, 10.45. Found: C, 80.14; H, 11.14.

Di-n-hexyl 2,2′-(9,9-Dioctyl-9H-fluorene-2,7-diyl)bis(diazoacetate) (6)

Under a N2 atmosphere, an acetonitrile (4.2 mL) solution of di-n-hexyl 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetate (0.508 g, 7.53 mmol) and tosyl azide (0.532 g, 2.70 mmol) was placed in a round-bottomed flask equipped with a dropping funnel. After an acetonitrile (2.8 mL) solution of DBU (3.1 mL, 21 mmol) was added dropwise from the dropping funnel, the mixture was stirred overnight at room temperature. After the addition of 10 mL of H2O to the resulting mixture, the mixture was transferred to a dropping funnel, with which the organic layer was separated with the use of 300 mL of CHCl3, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by silica gel chromatography with a mixed solvent (CH2Cl2/hexane = 1:1) as an eluent, giving the product in 68% yield as a reddish-orange solid. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.65 (d, J = 8.0 Hz, 2H, Ar–H), 7.49 (s, 2H, Ar–H), 7.37 (d, J = 8.0 Hz, 2H, Ar–H), 4.29 (t, J = 6.6 Hz, 4H, −CH2–O−), 1.94 (m, 4H, −CH2−), 1.72 (quint, J = 7.0 Hz, 4H, −CH2−), 1.19 (m, 4H, −CH2−), 1.00–1.15 (m, 16H, −CH2−), 0.91 (t, J = 6.4 Hz, 6H, −CH3), 0.81 (t, J = 7.0 Hz, 6H, −CH3), 0.63 (br s, 4H, −CH2−). 13C NMR (100 MHz, CDCl3), δ (ppm): 165.5 (−CO2−), 151.5 (Ar), 138.6 (Ar), 123.8 (Ar), 122.5 (Ar), 120.0 (Ar), 118.5 (Ar), 65.1 (−CO2–CH2−), 64.1 (C=N2), 55.4 (n-Oct2C), 40.2 (n-C7H15–CH2−), 31.8, 31.4, 29.9, 29.2, 29.1, 28.8, 25.6, 23.7, 22.6, and 22.5 (−[CH2]6–CH3 and −[CH2]4–CH3), 14.0 and 13.9 (−CH3). Anal. calcd for C45H66N4O4: C, 74.34; H, 9.15; N, 7.71. Found: C, 74.51; H, 9.63; N, 7.81.

Model Reaction Procedure

A typical procedure for the model reaction of 1 using RuCl(cod)Cp* (run 11 in Table 1) as a catalyst is described as follows: Under a N2 atmosphere, RuCl(cod)Cp* (8.1 mg, 0.021 mmol) and 1 (74.9 mg, 0.425 mmol) were placed in a Schlenk tube. After toluene (4.3 mL) was added to the mixture, it was heated to 100 °C and stirred for 17 h at the temperature. After the mixture was cooled to room temperature, a 1 N HCl aqueous solution (10 mL), a 1 N HCl/MeOH solution (10 mL), and CHCl3 (15 mL) were added, and the organic layer was separated using a separatory funnel. The organic layer was washed with the 1 N HCl aqueous solution (50 mL) and saturated NaCl aqueous solution (50 mL) and dried over Na2SO4. After the volatiles were removed under reduced pressure from the organic layer, the residue was purified using preparative SEC with CHCl3 as an eluent to give the product as a mixture of cis, trans, and azine forms. The composition of the cis/trans/azine form was determined by 1H NMR analysis to be 4:94:2. The yield (57%) was calculated from the equation of 100 × [weight of PhCO2(Me)C in all of the products]/[weight of PhCO2(Me)C in the starting 1].

Polymerization Procedure

As a typical example, the polymerization procedure for run 5 in Table 2 is described as follows. Under a N2 atmosphere, RuCl(cod)Cp* (15.3 mg, 0.0403 mmol) and 6 (0.294 g, 0.0403 mmol) were placed in a Schlenk tube. Toluene (8.1 mL) was added at room temperature, and the resulting solution was heated at 100 °C for 17 h. After the mixture was cooled to room temperature, a 1 N HCl/MeOH solution (10 mL), a 1 N HCl aqueous solution (10 mL), and CHCl3 (15 mL) were added, and the mixture was transferred to a separatory funnel to separate the organic layer. The aqueous layer was extracted with CHCl3 trice (total amount of CHCl3 was 60 mL), and the combined organic layer was washed with the 1 N HCl aqueous solution (50 mL) and saturated NaCl solution (50 mL), dried over Na2SO4, and concentrated under reduced pressure. The residual solid was subjected to purification by preparative SEC using CHCl3 as an eluent to afford the product in 67% yield.

Measurements

The number-average molecular weight (Mn) and polydispersity ratio [weight-average molecular weight/number-average molecular weight (Mw/Mn)] were measured by means of SEC on a Jasco-ChromNAV system equipped with a differential refractometer detector using THF as eluent at a flow rate of 1.0 mL/min at 40 °C, calibrated with six poly(methyl methacrylate) (PMMA) standards (Shodex M-75; Mp = 2400–212 000, Mw/Mn < 1.1) and dibutyl sebacate (molecular weight = 314.5). The columns used for the SEC analyses were a combination of Styragel HR4 and HR2 (Waters; exclusion limit molecular weight = 600 and 20 kDa for polystyrene, respectively; column size = 300 mm × 7.8 mm i.d.; average particle size = 5 μm). Purification by preparative SEC was performed on a JAI LC-918R equipped with a combination of columns of JAIGEL-3H and JAIGEL-2H (Japan Analytical Industry; exclusion limit molecular weight = 70 and 5 kDa for polystyrene, respectively; column size = 600 mm × 20 mm i.d.) using CHCl3 as the eluent at a flow rate of 3.8 mL/min at room temperature. 1H (400 MHz) and 13C (100 MHz) NMR spectra were recorded on a Bruker Avance 400 spectrometer at room temperature (monomers) or at 50 °C (polymers). Elemental analysis was performed on YANAKO CHN Corder MT-5. UV–vis absorption spectra for PAV were obtained on a JASCO V560 or V-570 spectrophotometer, and photoluminescence (PL) spectra were obtained on a JASCO FP-6500 or FP8300 spectrophotometer with an excitation at the absorption maximum for a chloroform solution and for the film state. The film was fabricated via a spin-coating process using a chloroform solution (10 mg/mL) on a quartz plate. Hole-only devices with the configuration of ITO/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (40 nm)/PAV (150 nm) (run 5 in Table 2)/Au (100 nm) were fabricated with 0.1 cm2 of the active layer. All of the spin-coating processes and current density–voltage measurements were carried out at room temperature in a glove box under a nitrogen atmosphere for three devices utilizing a Keithley 2400 sourcemeter. The hole mobility was determined with eq 1, taking the series resistance (20 Ω) into consideration and assuming that the built-in voltage is close to zero due to the small difference of work functions for both electrodes

graphic file with name ao9b03408_m001.jpg 1

where J is the hole current density, μh the hole mobility, εr the relative permittivity of the material (3.0), ε0 the permittivity of vacuum, L the thickness of the active layer (650–700 nm), and V the voltage drop across the device.

Acknowledgments

This work was financially supported by a Grant-in-Aid for Young Scientists (B) (JSPS KAKENHI Grant Number 16K17916), a Grant-in-Aid for Scientific Research (B) (JSPS KAKENHI Grant Number 18H02021), a Grant-in-Aid for Scientific Research (C) (JSPS KAKENHI Grant Number 19K05586), a Grant-in-Aid for Challenging Exploratory Research (JSPS KAKENHI Grant Number 19K22219), Sasakawa Scientific Research Grant (The Japan Science Society), and a Research Fellowship Grant (The Kyoto Technoscience Center). The authors thank Applied Protein Research Laboratory in Ehime University for its assistance in NMR and Advanced Research Support Center in Ehime University for its assistance in elemental analysis.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.9b03408.

  • Scheme of monomer syntheses, 1H NMR spectra of PAV, current density–voltage characteristics, and UV–vis absorption and photoluminescence spectra of PAV (PDF)

Author Contributions

The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Supplementary Material

ao9b03408_si_001.pdf (736.3KB, pdf)

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