DOI: 10.1002/chem.201500681
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& p-Conjugated Molecules |Hot Paper|
Carboxylate-Driven Supramolecular Assemblies of Protonated meso-Aryl-Substituted Dipyrrolylpyrazoles Hiromitsu Maeda,*[a] Kengo Chigusa,[a] Ryohei Yamakado,[a] Tsuneaki Sakurai,[b, c] and Shu Seki[b, c] Abstract: Dipyrrolylpyrazole (dpp) derivatives possessing an aryl ring at the pyrazole 4-position were synthesized. Upon protonation, modified dpp derivatives formed a variety of assembled structures through complexation with carboxylates, as observed by single-crystal X-ray and synchrotron XRD analyses. In particular, the complexation of protonated dpp species possessing long alkyl chains with dicarboxylates
resulted in highly ordered assembled structures, the packing modes of which as lamellar structures were controlled by the lengths of the spacer units between two carboxylate moieties. The charge-carrier transporting properties of the solid materials were also controlled by bound anions, including dicarboxylates.
Introduction The location of p-electronic units in molecular assemblies determines their electronic properties because interactions between the constituting p systems control the mobility of charge carriers. A variety of noncovalent interactions, such as hydrogen-bonding and van der Waals interactions, often at the peripheral substituents, are effective for the arrangement of pelectronic units. In contrast to electronically neutral molecules, charged p-electronic species can use electrostatic force for assembly, and their arrangement is essential for the fabrication of functional electronic materials.[1, 2] In particular, electron-deficient cationic species behave as effective electron carriers for organic semiconductor devices owing to the formation of stacking structures. As a promising p-electronic cation, the protonated form of +2]3,5-dipyrrolylpyrazole (dpp; for example, 1)[3, 4] affords a [2+ type planar complex with trifluoroacetate (CF3CO2¢ ; Fig+2]-type ion-pairing complex is an attracure 1 a).[5] Such a [2+ tive scaffold for supramolecular assemblies and enables the formation of highly ordered organized structures by peripheral modifications of the dpp unit. The introduction of aryl moieties at the a positions of pyrrole, as seen in 2 a,b (Figure 1 a), re[a] Prof. H. Maeda, K. Chigusa, Dr. R. Yamakado College of Pharmaceutical Sciences, Ritsumeikan University Kusatsu 525-8577 (Japan) E-mail: [email protected] [b] Dr. T. Sakurai, Prof. S. Seki Department of Applied Chemistry, Graduate School of Engineering Osaka University, Suita 565-0871 (Japan) [c] Dr. T. Sakurai, Prof. S. Seki Department of Molecular Engineering Graduate School of Engineering, Kyoto University Kyoto 615-8510 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201500681. Chem. Eur. J. 2015, 21, 9520 – 9527
Figure 1. a) The dpp derivatives (left) and their [2+ +2]-type complexes with CF3CO2¢ in the protonated forms (right). TFA = trifluoroacetic acid. b) Synthesis of 3 a,b from the corresponding 2-arylmalonic acids.
sults in the formation of a 2D pattern at the solution–substrate (highly ordered pyrolytic graphite (HOPG)) interface, supramolecular gels, and mesophases based on [2+ +2]-type complexes with CF3CO2¢ .[4b, 6] Although a-aryl moieties were useful for installing various substituents on dpp, they interfered with stable complexation with CF3CO2¢ due to steric effects. Therefore, the formation of stable assembled structures comprising protonated dpp compounds and carboxylates requires the design and synthesis of dpp derivatives that possess an aryl substituent at a more suitable position. Potentially suitable motifs are the dpp derivatives with an aryl moiety at the pyrazole 4-position (meso position) because their protonated forms can provide functional assembled structures upon combination with a variety of carboxylate anions. Herein, we report on the synthesis of meso-aryl dpp derivatives and their ion-pairing dimension-controlled assembling modes of which in the proton-
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Full Paper ated forms were thoroughly examined by synchrotron XRD analysis.
Results and Discussion The dpp precursors, 2-aryl-substituted 1,3-dipyrrolyl-1,3-propanediones 3 a’,b’, were prepared by the treatment of 2-arylmalonic acids with thionyl chloride and subsequent reactions with pyrrole in 27 and 29 % yield (two steps), respectively.[7] The subsequent condensation reaction of 3 a’,b’ with hydrazine in acetic acid at reflux provided 3 a,b in 19 and 58 % yield, respectively (Figure 1 b). Currently, this procedure for 3 a,b, which includes the condensation of carbonyl and amino groups, is effective compared with cross-coupling. Structural elucidation of 3 a,b was carried out by using 1H NMR spectroscopy and MALDI-TOF MS. As seen in 1 and 2 a,b,[4] meso-aryl-substituted 3 a,b also showed singly pyrrole-inverted conformations with intramolecular hydrogen bonding between pyrrole NH and pyrazole N as stable optimized states (Figures S5 and S6 in the Supporting Information).[8] The singly inverted conformation of 3 a is more stable at 3.01 and 4.06 kcal mol¢1 than no inverted and doubly inverted conformations, respectively, at B3LYP/631G(d,p). In solution, the inverted pyrrole ring in 3 a,b is not fixed with NH tautomerism at the pyrazole N sites. Compound 3 b, which possesses long alkyl chains, formed a lamellar structure with a layer distance of 5.73 nm in the solid state, prepared from CH2Cl2/MeOH, as revealed by synchrotron XRD analysis at RT (Figure 2 a). The layer distance corresponded to the length of two molecules of 3 b, which suggested the formation of a dimeric structure of a singly pyrroleinverted conformation through hydrogen-bonding and dipole– dipole interactions (Figure S7 in the Supporting Information).[8] Polarized optical microscopy (POM) of 3 b revealed various textures upon cooling from an isotropic liquid (Iso), although differential scanning calorimetry (DSC) showed transitions at 57 and 47 8C upon first and second heating, respectively, and at 41 8C upon cooling, but no peaks that suggested the existence of mesophases (Figures S11 and S12 in the Supporting Information). After thermal annealing in Iso, compound 3 b exhibited a lamellar structure in the solid state with a layer distance of 3.40 nm, which was probably due to the formation of an interdigitating structure (Figure 2 b). Annealing as a process to form the solid in the absence of solvent would provide the condensed short layer structure. Compounds 3 a,b were converted into their protonated forms in solution upon the addition of TFA, as observed in the UV/Vis absorption and fluorescence emission spectral changes (Figures S8 and S9 in the Supporting Information). Protonation at the pyrazole N site in the dpp derivatives requires fairly strong acids, such as TFA. Compound 3 a formed a [2+ +2]-type complex with TFA in the solid state through N¢H···O hydrogen bonding with N(¢H)···O distances of 2.71 and 2.85 æ (Figure 3 a). In the solid state, the dihedral angle between the dpp pyrazole unit and meso-phenyl ring was estimated to be 63.08, and the steric effect of the meso-phenyl ring resulted in distortion of the planarity of the pyrrole rings, with dihedral angles of 12.2 and 19.78 to the pyrazole unit. These distortions were Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 2. i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of organized structures of 3 b a) as a precipitate (from CH2Cl2/ MeOH) at 25 8C and b) as a sample at 25 8C upon first cooling. The diffraction at 0.41 nm is derived from assembly of alkyl chains.
larger than those (1.2 and 8.18) in the [2+ +2]-type complex of 1·H +¢CF3CO2¢ .[4a] The [2+ +2]-type complex formed a herringbone-like packing structure with a dihedral angle of 100.08 for two dpp planes in neighboring columns, as observed in the TFA complex of 1.[4a] Furthermore, compound 3 b also formed a complex with TFA, 3 b·H +¢CF3CO2¢ , that could be purified by recrystallization from octane. POM revealed a broken fanlike texture from 69 8C to RT, whereas DSC results showed transitions only at 69 8C upon cooling and at 79 8C upon heating, due to the absence of mesophases (Figures S11 and S12 in the Supporting Information). The ion pair 3 b·H +¢CF3CO2¢ exhibited higher transition temperatures to and from the Iso by
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Full Paper 3 b due to more effective stacking as the assembled two units of 3 b·H + are bridged by CF3CO2¢ . It is notable that the protonation of dpp derivatives and ion pairing with carboxylate can control the stability of assembled structures. Synchrotron XRD measurements of the solid sample from octane at RT revealed a lamellar structure with a layer distance of 5.97 nm, which was slightly larger than that of 3 b, owing to complexation with TFA (Figure 3 b). After thermal annealing in Iso, the solid sample also exhibited a similar lamellar structure with a layer distance of 5.91 nm (Figure 3 c). The fairly sharp diffractions of the halo at around 0.4 nm at 60 8C and RT suggested the formation of a rigid packing structure. The small difference in the assembled structures of 3 b·H +¢CF3CO2¢ upon annealing is also in contrast to that in 3 b. Protonated dpp is an effective building subunit for the fabrication of highly organized structures, which are formed by bridging between components that possess multiple carboxylate moieties. In fact, single-crystal X-ray analysis revealed the assembly of parent dpp in the protonated form 1·H + with 0.5 equivalents of perfluorobutane dicarboxylate ((CF2)4(CO2¢)2 ;
Figure 3. a) Solid-state structure of 3 a·H +¢CF3CO2¢ as a [2+ +2]-type complex (left) and packing side-view diagram (right). i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of organized structures of 3 b·H +¢CF3CO2¢ as b) a precipitate (from octane) at 25 8C and c) a sample at 25 8C upon first cooling. The organized structures in part iii) of b) and c) are the same and are ascribable to almost no change in assembled structures upon annealing.
about 30 8C in comparison with 3 b with transitions at 47 and 41 8C upon heating and cooling, respectively. This observation suggested a more stable assembly for 3 b·H +¢CF3CO2¢ than Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 4. Solid-state structures of a) (1·H + )2¢(CF2)4(CO2¢)2 and b) (3 a·H + )2¢ (CF2)4(CO2¢)2 as i) hydrogen-bonding structures with a single dicarboxylate (left: top view and right: side view) and ii) packing structures.
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Full Paper Figure 4 a). In the solid state, protonated dpp 1·H + formed a herring-bone-like packing structure with a stacking p-plane distance of 3.46 æ, based on 3D networks forming the three hydrogen-bonding interactions between pyrrole/pyrazole-NH and carboxylate oxygen atoms with N(¢H)···O distances of 2.60–2.86 æ. The less effective interaction with carboxylate was observed for one of the pyrrole NH atoms. The observation of 1 by single-crystal X-ray analysis confirmed the expectation that the protonated form of dpp 3 a also formed supramolecular polymers with dicarboxylates. Similar to the assembly of (1·H + )2¢(CF2)4(CO2¢)2, the combination of 3 a·H + and (CF2)4(CO2¢)2 led to a solid-state assembled structure, as revealed by single-crystal X-ray analysis (Figure 4 b). The introduction of a phenyl moiety in 3 a·H + , with the dihedral angle of 64.18 to the dpp pyrazole unit, induced a stacking p-plane distance of 3.69 æ, which was slightly larger than that of (1· H + )2¢(CF2)4(CO2¢)2. Distortions of pyrrole rings in (3 a·H + )2¢ (CF2)4(CO2¢)2 of 9.0 and 15.88 are larger than those of (1·H + )2¢ (CF2)4(CO2¢)2 (5.3 and 5.88). The assembly was constructed by interactions not only between pyrrole/pyrazole-NH and carboxylate oxygen atoms, but also those between pyrrole CH and pyrrole/phenyl p planes, leading to larger p-plane distances. The solid-state structures were slightly different from regular +2]-type binding mode with carboxylate units, probably due [2+ to the preferred crystal-packing modes. However, the observations of the solid-state assembled structures consisting of dicarboxylates were valuable for the further design and preparation of highly ordered structures through the introduction of appropriate substituents to the dpp core unit. The long alkyl chains in 3 b can yield dimension-controlled organized structures based on van der Waals interactions between alkyl units supporting the stacking structures of the pelectronic moieties. Compound 3 b yielded precipitates of ionpairing assemblies from octane after mixing with 0.5 equivalents of (CF2)n(CO2H)2 (n = 4 and 8) in 1,2-dimethoxyethane (DME) and evaporation of the solvent, whereas it was difficult to obtain purified assemblies with (CF2)n(CO2H)2 (n = 6 and 10; Figure S10 in the Supporting Information). DSC results for (3 b·H + )2¢(CF2)n(CO2¢)2 (n = 4 and 8) revealed transitions to Iso at 98 and 73 8C, respectively, which suggested the absence of mesophases (Figure S11 in the Supporting Information).[9] The transition temperature of (3 b·H + )2¢(CF2)4(CO2¢)2 is 20 8C higher than that of 3 b·H +¢CF3CO2¢ (79 8C) probably because of the formation of the more stable assembly by tight binding of ionpairing moieties through perfluoroalkyl spacer units. Synchrotron XRD at 25 8C revealed the formation of lamellar structures in 3 b·H + as both (CF2)n(CO2¢)2 (n = 4 and 8) complexes in the solid state after melting to Iso (Figure 5 and Figure S13 in the Supporting Information). The complex containing (CF2)4(CO2¢)2 exhibited a layer distance of 5.91 nm (Figure 5 a), whereas the complex containing (CF2)8(CO2¢)2 exhibited a layer distance of 3.70 nm (Figure 5 b), which suggested that the difference in the alkyl chain lengths of the dicarboxylate could influence the organized structures formed by meso-modified dpp. Based on molecular modeling,[8] the dicarboxylate (CF2)4(CO2¢)2 has a short perfluoroalkyl chain, which may result in the formation of a lamellar structure of [2+ +2]-type supramolecular polymers Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 5. i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of the organized structures of 3 b·H + as a) (CF2)4(CO2¢)2 and b) (CF2)8(CO2¢)2 complexes (in a molar ratio of 2:1 for 3 b·H + and dicarboxylates) at 25 8C upon cooling from Iso.
with 3 b·H + or related carboxylate-binding structures with a repeat distance of 5.91 nm. On the other hand, the dicarboxylate (CF2)8(CO2¢)2 has a longer perfluoroalkyl moiety and enables the formation of a lamellar structure upon supramolecular polymerization with 3 b·H + by interdigitating into vacant areas between carboxylate complex units. Based on these results, the perfluoroalkyl moieties are essential for constructing different assembled structures in different forms. The complicated thermal transition behavior of (3 b·H + )2¢(CF2)8(CO2¢)2[9] can be ascribable to less effective packing than that of (3 b·H + )2¢ (CF2)4(CO2¢)2. Although the exact carboxylate binding mode cannot be elucidated by synchrotron XRD, the introduction of
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Full Paper aliphatic chains induced ordered structures owing to interactions between protonated 3 b and dicarboxylates. Currently, it is very challenging to reveal the assembling processes and mechanisms because they include the formation of solid states. On the other hand, the fairly disordered structures formed upon combination of 3 b with (CF2)n(CO2H)2 (n = 6 and 10) could be attributed to the nonideal lengths between two carboxylate moieties. The ion-pair-based assemblies of p-conjugated systems can control not only their structural order, but also their chargecarrier transporting properties. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements[10] were carried out to investigate the effect of the ion-pair-based directional assembly on the photoconductivity (Figure S14 in the Supporting Information). When photoexcited by a l = 355 nm laser pulse, thin films of 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢ (CF2)n(CO2¢)2 (n = 4 and 8) on quartz exhibited transient conductivity (fm), in which f and m represent the yield of charge-carrier generation and sum of the charge-carrier mobilities, respectively. We found the conductivity maxima, (fSm)max, to be around 1.6 Õ 10¢5, 1.7 Õ 10¢5, 1.9 Õ 10¢5, and 2.2 Õ 10¢5 cm2 V¢1 s¢1 for 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢ (CF2)n(CO2¢)2 (n = 4 and 8), respectively. The difference in (fSm)max between 3 b alone and the ion-pairing forms was small, probably because, upon dimerization, compound 3 b forms a mesoscopically ordered structure in its dimerized assembly. However, slight but significant differences in the photoconductivity were observed when coupled with dicarboxylates in the protonated form. We consider that the dicarboxylates are likely to promote supramolecular polymerization with protonated dpp units and suppress their dynamic motions, resulting in an advantage for the one-dimensional charge-carrier transporting event. In addition, ion pair (3 b·H + )2¢(CF2)8(CO2¢)2, the assembled structure of which is less thermally stable, has a slightly more effective pathway of charge carriers compared with (3 b·H + )2¢(CF2)4(CO2¢)2. The extremely long lifetime of the free charge carriers in the conductivity transient over 200 ms also supports the presence of a stable, isolated 1D pathway for the charge carriers.
Conclusion We synthesized dpp derivatives that possessed an aryl ring at the pyrazole 4-position. The modified dpp derivatives formed a variety of assembled structures based on [2+ +2]-type complexes upon combination with appropriate acids. In particular, complexation of protonated dpp derivatives with dicarboxylates resulted in highly ordered structures, the packing modes of which, along with thermal transition behavior, were controlled by the distances between two carboxylate moieties. This modulation also resulted in control of the charge-carrier transporting properties, as evidenced by electrodeless conductivity measurements. Planar ion-pairing complexes reported herein would afford various highly ordered assembled structures based on the combination of ionic species. One of the advantages in the ion-pairing assemblies is the control of packing structures and resulting properties by the constituting Chem. Eur. J. 2015, 21, 9520 – 9527
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ionic species. Further design and modification of dpp derivatives, as well as the synthesis of other new p-electronic systems, are currently ongoing in our laboratory in an effort to develop fascinating ion-based electronic materials.
Experimental Section General procedures Starting materials were purchased from Wako Pure Chemical Industries Ltd., Nacalai Tesque Inc, and Sigma–Aldrich Co., and used without further purification unless otherwise stated. UV/Vis spectra were recorded on a Hitachi U-3500 spectrometer. Fluorescence spectra were recorded on a Hitachi F-4500 fluorescence spectrometer for ordinary solutions. NMR spectra used in the characterization of products were recorded on a JEOL ECA-600 600 MHz spectrometer. All NMR spectra were referenced to residual solvent. MALDI-TOF MS was recorded on a Shimadzu Axima-CFRplus spectrometer. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was recorded on a Bruker solariX (Qh-FT-ICRMS) spectrometer and were carried out at the Joint Usage/Research Center (JURC) at the Institute for Chemical Research (ICR), Kyoto University. TLC analyses were carried out on aluminum sheets coated with silica gel 60 (Merck 5554). Column chromatography was performed on Sumitomo alumina KCG-1525, Wakogel C200, C-300, and Merck silica gel 60 and 60H.
2-Phenyl-1,3-dipyrrol-2-yl-1,3-propanedione (3 a’) Thionyl chloride (4 mL) was added slowly to a flask containing 3 a’’ (1.80 g, 10.0 mmol), and was stirred for 3 h at 50 8C. Excess thionyl chloride was removed under vacuum for several hours to give 2phenylmalonyl chloride as a yellow oil, which was immediately used in the next reaction without further purification. A solution of pyrrole (2 mL, 30 mmol) in CH2Cl2 (50 mL) was treated with 2-phenylmalonyl chloride at 0 8C and stirred for 3 h. After the consumption of the starting pyrrole was confirmed by TLC analysis, the mixture was washed with a saturated aqueous solution of Na2CO3 and water, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was then purified by column chromatography on a silica gel (eluent: 3 % MeOH/CH2Cl2) to give 3 a’ (746 mg, 2.68 mmol, 27 %) as a yellow solid. Rf = 0.37 (eluent: EtOAc/nhexane = 1:1). 1H NMR (600 MHz, CDCl3, 20 8C; the diketone is obtained as a mixture of keto and enol tautomers in the ratio of 1:0.17): keto form: d = 9.34 (br s, 2 H; NH), 7.54–7.28 (m, 5 H; Ar-H), 7.04–7.02 (m, 2 H; pyrrole-H), 7.01–7.00 (m, 2 H; pyrrole-H), 6.28– 6.27 (m, 2 H; pyrrole-H), 6.08 ppm (s, 1 H; CH); enol form: d = 18.57 (s, 1 H; OH), 9.34 (br s, 2 H; NH), 7.50–7.28 (m, 5 H; Ar-H), 6.90–6.89 (m, 2 H; pyrrole-H), 6.01–6.00 (m, 2 H; pyrrole-H), 5.19–5.18 ppm (m, 2 H; pyrrole-H); MALDI-TOF-MS: m/z (%): 279.1 (100) [M¢H] + .
4-Phenyl-3,5-dipyrrol-2-ylpyrazole (3 a) Following a procedure reported in the literature,[4] hydrazine monohydrate (300 mL, 6.17 mmol) was added to a solution of 3 a’ (55.3 mg, 0.20 mmol) in AcOH (2 mL) and stirred at reflux for 21 h. After monitoring the consumption of the starting diketone on TLC, the solvent was removed and then the reaction mixture was purified by column chromatography on silica gel (eluent: 3 % MeOH/ CH2Cl2), followed by evaporation, and recrystallization from CH2Cl2/ n-hexane to give 3 a (10.1 mg, 0.038 mmol, 19 %) as a white solid. Rf = 0.14 (eluent: 3 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C; pyrazole NH cannot be observed at this temperature): d =
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Full Paper 8.42 (br s, 2 H; pyrrole-NH), 7.50–7.42 (m, 5 H; Ar-H), 6.70–6.69 (m, 2 H; pyrrole-H), 6.14–6.13 ppm (m, 4 H; pyrrole-H); UV/Vis (CH2Cl2): lmax (e Õ 10¢4) = 277 nm (1.7 m¢1 cm¢1); fluorescence (CH2Cl2): lem (lex) = 391 nm (277 nm); MALDI-TOF-MS: m/z (%): 273.9 (100) [M]¢ .
1,2,3-Trihexadecyloxy-5-iodobenzene A mixture of 1,2,3-trihydroxy-5-iodobenzene[11] (3.35 g, 13.3 mmol), K2CO3 (12.9 g, 93.1 mmol), and 1-bromohexadecane (13.8 g, 45.2 mmol) in dry DMF (120 mL) was stirred at 80 8C for 3 d. After cooling, the solvent was evaporated. The crude product was dissolved in CHCl3, washed with water, dried over Na2SO4, and evaporated to dryness. The residue was then purified by column chromatography on silica gel (Wakogel C-300; eluent CH2Cl2/n-hexane = 1:4) to give 1,2,3-trihexadecyloxy-5-iodobenzene (11.1 g, 12.0 mmol, 90 %) as a white solid. Rf = 0.34 (eluent: CH2Cl2/nhexane = 1:4); 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.84 (s, 2 H; ArH), 3.91 (t, J = 6.0 Hz, 4 H; OCH2), 3.90 (t, J = 6.6 Hz, 2 H; OCH2), 1.80–1.70 (m, 6 H; OCH2CH2), 1.46–1.43 (m, 6 H; OC2H4CH2), 1.33– 1.25 (m, 72 H; OC3H6C12H24CH3), 0.89–0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 924.1 (100) [M¢H]¢ .
Di-tert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate Following a procedure reported in the literature,[6] a Schlenk tube containing [Pd2(dba)3] (dba = dibenzylideneacetone; 91.6 mg, 0.10 mmol), P(tBu)3 (40.5 mg, 0.20 mmol), tBuOK (247 mg, 2.2 mmol), and 1,2,3-trihexadecyloxy-5-iodobenzene (1.85 g, 2.0 mmol) was flushed with nitrogen and charged with anhydrous 1,4-dioxane (5.0 mL) and di-tert-butyl malonate (493 mL, 2.2 mmol). The mixture was heated at 80 8C for 12 h, cooled, and then partitioned between CH2Cl2, water and a saturated aqueous solution of NaCl. The combined extracts were dried over Na2SO4 and evaporated. The residue was then purified by column chromatography on silica gel (Wakogel C-300; eluent: CH2Cl2/n-hexane = 1:1) to give ditert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate (1.56 g, 1.54 mmol, 77 %) as a white solid. Rf = 0.35 (eluent: CH2Cl2/nhexane = 1:1); 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.56 (s, 2 H; ArH), 4.29 (s, 1 H; CH), 3.96–3.91 (m, 6 H; OCH2C15H31), 1.80–1.70 (m, 6 H; OCH2CH2C14H29), 1.46 (s, 18 H; tBu), 1.46–1.41 (m, 6 H; OC2H4CH2C13H27), 1.35–1.25 (m, 78 H; OCH2CH3 and OC3H6C12H24CH3), 0.89–0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 1013.9 (100) [M+ +H] + .
2-(3,4,5-Trihexadecyloxyphenyl)malonic acid (3 b’’) TFA (3.6 mL) was added to a solution of di-tert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate (1.56 g, 1.54 mmol) in CH2Cl2 (10 mL) and stirred at RT for 2 h. The reaction mixture was partitioned between CH2Cl2 and a saturated aqueous solution of NaHCO3. The aqueous phase was acidified with an aqueous solution of HCl, and then the product was extracted with diethyl ether. The combined extracts were dried over Na2SO4 and evaporated to give 3 b’’ (1.39 g, 1.54 mmol, quant) as a white solid. 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.57 (s, 2 H; Ar-H), 4.57 (s, 1 H; CH), 3.98–3.92 (m, 6 H; OCH2C15H31), 1.80–1.70 (m, 6 H; OCH2CH2C14H29), 1.47–1.42 (m, 6 H; OC2H4CH2C13H27), 1.33–1.21 (m, 72 H; OC3H6C12H24CH3), 0.89– 0.87 ppm (m, 9 H; OC15H30CH3); ESI-TOF-MS (FT-ICR): m/z (%): 899.8 (100) [M¢H]¢ . Chem. Eur. J. 2015, 21, 9520 – 9527
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2-(3,4,5-Trihexadecyloxyphenyl)-1,3-dipyrrol-2-yl-1,3-propanedione (3 b’) Thionyl chloride (3 mL) was added slowly to a flask containing 3 b’’ (571 mg, 0.63 mmol) and stirred for 1.5 h at 60 8C. Excess thionyl chloride was removed under vacuum for 1 h to give 2-(3,4,5-trihexadecyloxyphenyl)malonyl chloride as a yellow solid, which was used immediately in the next reaction without further purification. A solution of pyrrole (130 mL, 1.89 mmol) in CH2Cl2 (12 mL) was treated with 2-(3,4,5-trihexadecyloxyphenyl)malonyl chloride at RT and stirred for 30 min. After the consumption of the starting pyrrole was confirmed by TLC analysis, the mixture was washed with water and a saturated aqueous solution of NaCl, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was then purified by flash column chromatography on silica gel (eluent: 0.5 % MeOH/CH2Cl2) to give 3 b’ (143 mg, 0.14 mmol, 22 %) as a yellow solid. Rf = 0.24 (eluent: 0.5 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C): d = 9.29 (br s, 2 H; NH), 7.04–7.03 (m, 2 H; pyrrole-H), 7.00–6.98 (m, 2 H; pyrrole-H), 6.66 (s, 2 H; Ar-H), 6.28– 6.27 (m, 2 H; pyrrole-H), 5.94 (s, 1 H; CH), 3.97–3.89 (m, 6 H; OCH2C15H31), 1.78–1.68 (m, 6 H; OCH2CH2C14H29), 1.46–1.41 (m, 6 H; OC2H4CH2C13H27), 1.34–1.25 (m, 72 H; OC3H6C12H24CH3), 0.89– 0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 999.9 +H] + . (100) [M+
4-(3,4,5-Trihexadecyloxyphenyl)-3,5-dipyrrol-2-ylpyrazole (3 b) Following a procedure reported in the literature,[4] hydrazine monohydrate (240 mL, 4.94 mmol) was added to a solution of 3 b’ (56.8 mg, 0.057 mmol) in AcOH (1 mL), and stirred at reflux for 12 h. After monitoring the consumption of the starting diketone by TLC, the solvent was removed and then the reaction mixture was purified by flash column chromatography on silica gel (eluent: 2 % MeOH/CH2Cl2), followed by evaporation, and recrystallization from CH2Cl2/MeOH to give 3 b (32.7 mg, 0.033 mmol, 58 %) as a pale yellow solid. Rf = 0.22 (eluent: 2 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C): d = 8.47 (br s, 2 H; NH), 6.70 (br s, 2 H; pyrrole-H), 6.61 (s, 2 H; Ar-H), 6.22 (br s, 2 H; pyrrole-H), 6.16–6.15 (m, 2 H; pyrrole-H), 4.07 (t, J = 6.6 Hz, 2 H; OCH2C15H31), 3.90 (t, J = 6.6 Hz, 4 H; OCH2C15H31), 1.83–1.74 (m, 6 H; OCH2CH2C14H29), 1.55– 1.41 (m, 6 H; OC2H4CH2C13H27), 1.35–1.25 (m, 72 H; OC3H6C12H24CH3), 0.89–0.86 ppm (m, 9 H; OC15H30CH3); UV/Vis (CH2Cl2): lmax (e Õ 10¢4) = 273.5 nm (2.3 m¢1 cm¢1); fluorescence (CH2Cl2): lem (lex) = +H] + . 376 nm (274 nm); MALDI-TOF-MS: m/z (%):995.9 (100) [M+
Single-crystal X-ray analysis Crystallographic data for ion-pair complexes of dipyrrolylpyrazoles are summarized in Table 1. Single crystals of 3 a·H +¢CF3CO2¢ were obtained by vapor diffusion of n-hexane into a solution of 3 a and TFA in CH2Cl2 in a 1:1 molar ratio. The crystal was a colorless prism of approximate dimensions 0.40 Õ 0.10 Õ 0.10 mm. Complex (1·H + )2¢(CF2)4(CO2¢)2 was obtained by vapor diffusion of n-hexane into a solution of 1 and (CF2)4(CO2H)2 in a 2:1 molar ratio in DME. The data crystal was a colorless prism of approximate dimensions 0.20 Õ 0.20 Õ 0.10 mm. Single crystals of (3 a·H + )2¢(CF2)4(CO2¢)2 were obtained by vapor diffusion of n-hexane into a solution of 3 a and (CF2)4(CO2H)2 in a 2:1 molar ratio in CHCl3/DME. The crystal was a colorless prism of approximate dimensions 0.40 Õ 0.10 Õ 0.05 mm. Data were collected at 93 K on a Rigaku RAXIS-RAPID II diffractometer with graphite monochromated CuKa radiation (l = 1.54187 æ), and structures were solved by direct methods. The non-hydrogen atoms were refined anisotropically. The calculations were per-
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Full Paper Table 1. Crystallographic details for ion pairs 3 a·H +¢CF3CO2¢ , (1·H + )2¢(CF2)4(CO2¢)2, and (3 a·H + )2¢ (CF2)4(CO2¢)2.
formula Mr crystal size [mm] crystal system space group a [æ] b [æ] c [æ] a [8] b [8] g [8] V [æ3] 1calcd [g cm¢3] Z T [K] m(CuKa) [mm¢1] no. of reflns no. of unique reflns variables lCuKa [æ] R1 (I > 2s(I)) wR2 (I > 2s(I)) GOF
3 a·H +¢CF3CO2¢
(1·H + )2¢(CF2)4(CO2¢)2
(3 a·H + )2¢(CF2)4(CO2¢)2
C17H15N4·C2F3O2 388.35 0.40 Õ 0.10 Õ 0.10 monoclinic P21/a (no. 14) 16.5316(6) 5.9855(2) 17.8433(7) 90 91.687(2) 90 1764.83(11) 1.462 4 93(2) 1.023 14 369 3043 253 1.54187 0.0682 0.1057 1.000
2(C11H11N4)·C6F8O4 686.54 0.20 Õ 0.20 Õ 0.10 monoclinic C2/c (no. 15) 32.4979(6) 6.05510(10) 15.9142(3) 90 114.3858(9) 90 2852.18(9) 1.599 4 93(2) 1.278 13 033 2600 245 1.54187 0.0535 0.0954 1.067
2(C17H15N4)·C6F8O4 838.78 0.40 Õ 0.10 Õ 0.05 monoclinic P21/a (no. 14) 16.3472(5) 6.1376(2) 19.0404(5) 90 104.0875(16) 90 1852.92(10) 1.503 4 93(2) 1.101 17 619 3366 271 1.54187 0.0810 0.1867 1.075
formed by using the Crystal Structure crystallographic software package of the Molecular Structure Corporation.[12] CCDC-942381, 942382, and 942383 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
DFT and AM1 calculations Ab initio and semiempirical calculations of p-conjugated molecules were carried out by using the Gaussian 03 program[8] and an HP Compaq dc5100 SFF computer. The structures were optimized, and the total electronic energies were calculated at the B3LYP level by using a 6-31G(d,p) basis set for 3 a, 3 c (the derivative possessing methoxy substituents in place of hexadecyloxy moieties in 3 b), 3 a·H + , 3 c·H + , and 3 a·H +¢CF3CO2¢ and at AM1 level for 3 b and 3 b·H + .
The phase transition points were observed by using a differential scanning calorimeter (PerkinElmer Diamond DSC).
Polarizing optical microscopy (POM) POM measurements were carried out with a Nikon OPTIPHOT-POL polarizing optical microscope equipped with a Mettler FP82 HT hot stage.
Synchrotron XRD analysis High-resolution XRD analyses were carried out by using a synchrotron radiation X-ray beam with a wavelength of 1.00 æ on BL40B2 at SPring-8 (Hyogo, Japan). A large Debye–Scherrer camera with a camera length of 546.28 mm for XRD of 3 b (Figure 2), 3 b·H +¢ CF3CO2¢ (Figure 3), (3 b·H + )2 as a (CF2)4(CO2¢)2 complex (Figure 5 a www.chemeurj.org
Flash-photolysis time-resolved microwave conductivity (FPTRMC)
The charge-carrier mobility was measured by FP-TRMC technique. Complexes 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢(CF2)4(CO2¢)2, (3 b·H + )2¢(CF2)8(CO2¢)2 were mounted on a quartz plate, once heated up to the isotropic state, and then cooled to RT, to afford thin-film samples. Charge carriers were photochemically generated by using a third-harmonic generation (l = 355 nm) of a Spectra Physics model INDI-HG Nd:YAG laser with a pulse duration of 5– 8 ns. The photon density of a l = 355 nm pulse was 0.9 Õ 1016 photons per cm2. The microwave frequency and power were set at about 9.1 GHz and 3 mW, respectively. The TRMC signal, picked up by a diode (rise time < 1 ns), was monitored by means of a Tektronics model TDS3032B digital oscilloscope. The observed conductivities were normalized, given by a photocarrier generation yield (f) multiplied by sum of the charge carrier mobilities (Sm), according to the equation fSm = (1/eAI0Flight)(DPr/Pr), in which e, A, I0, Flight, Pr, and DPr were the unit charge of a single electron, the sensitivity factor (S¢1 cm), the incident photon density of the excitation laser (photon cm¢2), a correction (or filling) factor (cm¢1), and the reflected microwave power and its change, respectively. All experiments were carried out at RT in an ambient atmosphere.
Acknowledgements
Differential scanning calorimetry (DSC)
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and Figure S13 in the Supporting Information), and (3 b·H + )2 as a (CF2)8(CO2¢)2 complex (Figure 5 b and Figure S13 in the Supporting Information) with a quartz capillary and an imaging plate as a detector, for which the diffraction pattern was obtained with a 0.018 step in 2q. The exposure time to the X-ray beam was 10 to 60 s.
This work was supported by a Grants-in-Aid for Young Scientists (A) (no. 23685032) and Scientific Research (B) (no. 26288042) and on Innovation Areas (“Photosynergetics” Area 2606, no. 26107007) from the MEXT and Ritsumeikan R-GIRO project (2008–2013). We thank Prof. Atsuhiro Osuka and Hirotaka Mori, Kyoto University, for single-crystal X-ray analysis; Dr. Katsuhiro Isozaki and Prof. Hikaru Takaya, Kyoto University, for FT-ICR-MS measurements; Dr. Noboru Ohta, JASRI/SPring-8, for synchrotron XRD analysis; Prof. Kazuchika Ohta, Shinshu University, for the valuable discussion on the transition behavior; Prof. Tomonori Hanasaki, Ritsumeikan University, for DSC and POM measurements; and Prof. Hitoshi Tamiaki, Ritsumeikan University, for various measurements. T.S. thanks JSPS for a Research Fellowship for Young Scientists.
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Full Paper Keywords: heterocycles · ion pairs · polymers · self-assembly · supramolecular chemistry [1] a) A. Ciferri, Supramolecular Polymers, Marcel Dekker, New York, Basel, 2000; b) G. A. Ozin, A. C. Arsenault, Nanochemistry: A Chemical Approach to Nanomaterials, RSC, Cambridge, 2005; c) F. Wìrthner, Supramolecular Dye Chemistry, Topics in Current Chemistry, Springer, Berlin, 2005, 258, pp. 1 – 324. [2] For selected examples of ion-based assemblies, see: a) D. Wu, L. Zhi, G. J. Bodwell, G. Cui, N. Tsao, K. Mìllen, Angew. Chem. Int. Ed. 2007, 46, 5417 – 5420; Angew. Chem. 2007, 119, 5513 – 5516; b) H. Shimura, M. Yoshio, K. Hoshino, T. Mukai, H. Ohno, T. Kato, J. Am. Chem. Soc. 2008, 130, 1759 – 1765; c) M.-Y. Yuen, V. A. L. Roy, W. Lu, S. C. F. Kui, G. S. M. Tong, M.-H. So, S. S.-Y. Chui, M. Muccini, J. Q. Ning, S. J. Xu, C.-M. Che, Angew. Chem. Int. Ed. 2008, 47, 9895 – 9899; Angew. Chem. 2008, 120, 10043 – 10047; d) H. Shimura, M. Yoshio, A. Hamasaki, T. Mukai, H. Ohno, T. Kato, Adv. Mater. 2009, 21, 1591 – 1594; e) J. Fortage, F. Tuy¦ras, P. Ochsenbein, F. Puntoriero, F. Nastasi, S. Campagna, S. Griveau, S. Bedioui, I. Ciofini, P. P. Lain¦, Chem. Eur. J. 2010, 16, 11047 – 11063; f) T. Ichikawa, M. Yoshio, A. Hamasaki, J. Kagimoto, H. Ohno, T. Kato, J. Am. Chem. Soc. 2011, 133, 2163 – 2169; g) D. Wu, R. Liu, W. Pisula, X. Feng, K. Mìllen, Angew. Chem. Int. Ed. 2011, 50, 2791 – 2794; Angew. Chem. 2011, 123, 2843 – 2846; h) Y. Ren, W. H. Kan, M. A. Henderson, P. G. Bomben, C. P. Berlinguette, V. Thangadurai, T. Baumgartner, J. Am. Chem. Soc. 2011, 133, 17014 – 17026; i) T. Ichikawa, M. Yoshio, A. Hamasaki, S. Taguchi, F. Liu, X. B. Zeng, G. Ungar, H. Ohno, T. Kato, J. Am. Chem. Soc. 2012, 134, 2634 – 2643; j) Y. Ren, W. H. Kan, V. Thangadurai, T. Baumgartner, Angew. Chem. Int. Ed. 2012, 51, 3964 – 3968; Angew. Chem. 2012, 124, 4031 – 4035; k) J.-J. Lee, A. Yamaguchi, Md. A. Alam, Y. Yamamoto, T. Fukushima, K. Kato, M. Takata, N. Fujita, T. Aida, Angew. Chem. Int. Ed. 2012, 51, 8490 – 8494; Angew. Chem. 2012, 124, 8618 – 8622; l) B. Soberats, M. Yoshio, T. Ichikawa, S. Taguchi, H. Ohno, T. Kato, J. Am. Chem. Soc. 2013, 135, 15286 – 15289; m) M. Krikorian, S. Liu, T. M. Swager, J. Am. Chem. Soc. 2014, 136, 2952 – 2955; n) B. Soberats, E. Uchida, M. Yoshio, J. Kagimoto, H. Ohno, T. Kato, J. Am. Chem. Soc. 2014, 136, 9552 – 9555. [3] B. Oddo, C. Dainotti, Gazz. Chim. Ital. 1912, 42, 716 – 726. [4] a) H. Maeda, Y. Ito, Y. Kusunose, T. Nakanishi, Chem. Commun. 2007, 1136 – 1138; b) H. Maeda, K. Chigusa, T. Sakurai, K. Ohta, S. Uemura, S. Seki, Chem. Eur. J. 2013, 19, 9224 – 9233. [5] For reviews on ion-based assemblies comprised of anion complexes of p-conjugated molecules, see: a) B. Dong, H. Maeda, Chem. Commun. 2013, 49, 4085 – 4099; b) H. Maeda, Bull. Chem. Soc. Jpn. 2013, 86, 1359 – 1399.
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[6] Complementary hydrogen-bonding interactions are effective for the formation of soft materials: S. Mahesh, R. Thirumalai, S. Yagai, A. Kitamura, A. Ajayaghosh, Chem. Commun. 2009, 5984 – 5986. [7] 2-(3,4,5-Trihexadecyloxyphenyl)malonic acid was obtained by coupling of the corresponding aryl iodide and malonic acid tert-butyl ester and subsequent conversion from the ester; for the coupling, see: N. A. Beare, J. F. Hartwig, J. Org. Chem. 2002, 67, 541 – 555. [8] Molecular optimization was conducted by using the following program: Gaussian 03, Revision C.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wallingford CT, 2004. [9] Upon heating, complex (3 b·H + )2¢(CF2)8(CO2¢)2 exhibited two transitions at 47 and 73 8C, between which an exothermic process was observed. Synchrotron XRD at 51 8C showed a lamellar phase, and was similar to that of the solid state at RT. The gradual appearance of another crystal state upon annealing suggested a dual melting behavior. This complicated change of states can be correlated with an assembled structure comprised of multiple components, namely, cationic p-conjugated units and dicarboxylate in this study; the details will be discussed elsewhere. For double melting behavior, see: K. Ohta, H. Muroki, K. Hatada, I. Yamamoto, K. Matsuzaki, Mol. Cryst. Liq. Cryst. 1985, 130, 249 – 263. [10] a) A. Acharya, S. Seki, A. Saeki, Y. Koizumi, S. Tagawa, Chem. Phys. Lett. 2005, 404, 356 – 360; b) A. Saeki, S. Seki, T. Sunagawa, K. Ushida, S. Tagawa, Philos. Mag. 2006, 86, 1261 – 1276; c) S. Seki, A. Saeki, T. Sakurai, D. Sakamaki, Phys. Chem. Chem. Phys. 2014, 16, 11093 – 11113. [11] T. Cardolaccia, Y. Li, K. S. Schanze, J. Am. Chem. Soc. 2008, 130, 2535 – 2545. [12] CrystalStructure (Ver. 3.8), Single Crystal Structure Analysis Software, Rigaku/MSC and Rigaku Corporation, 2006. Received: February 16, 2015 Published online on May 26, 2015
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& p-Conjugated Molecules |Hot Paper|
Carboxylate-Driven Supramolecular Assemblies of Protonated meso-Aryl-Substituted Dipyrrolylpyrazoles Hiromitsu Maeda,*[a] Kengo Chigusa,[a] Ryohei Yamakado,[a] Tsuneaki Sakurai,[b, c] and Shu Seki[b, c] Abstract: Dipyrrolylpyrazole (dpp) derivatives possessing an aryl ring at the pyrazole 4-position were synthesized. Upon protonation, modified dpp derivatives formed a variety of assembled structures through complexation with carboxylates, as observed by single-crystal X-ray and synchrotron XRD analyses. In particular, the complexation of protonated dpp species possessing long alkyl chains with dicarboxylates
resulted in highly ordered assembled structures, the packing modes of which as lamellar structures were controlled by the lengths of the spacer units between two carboxylate moieties. The charge-carrier transporting properties of the solid materials were also controlled by bound anions, including dicarboxylates.
Introduction The location of p-electronic units in molecular assemblies determines their electronic properties because interactions between the constituting p systems control the mobility of charge carriers. A variety of noncovalent interactions, such as hydrogen-bonding and van der Waals interactions, often at the peripheral substituents, are effective for the arrangement of pelectronic units. In contrast to electronically neutral molecules, charged p-electronic species can use electrostatic force for assembly, and their arrangement is essential for the fabrication of functional electronic materials.[1, 2] In particular, electron-deficient cationic species behave as effective electron carriers for organic semiconductor devices owing to the formation of stacking structures. As a promising p-electronic cation, the protonated form of +2]3,5-dipyrrolylpyrazole (dpp; for example, 1)[3, 4] affords a [2+ type planar complex with trifluoroacetate (CF3CO2¢ ; Fig+2]-type ion-pairing complex is an attracure 1 a).[5] Such a [2+ tive scaffold for supramolecular assemblies and enables the formation of highly ordered organized structures by peripheral modifications of the dpp unit. The introduction of aryl moieties at the a positions of pyrrole, as seen in 2 a,b (Figure 1 a), re[a] Prof. H. Maeda, K. Chigusa, Dr. R. Yamakado College of Pharmaceutical Sciences, Ritsumeikan University Kusatsu 525-8577 (Japan) E-mail: [email protected] [b] Dr. T. Sakurai, Prof. S. Seki Department of Applied Chemistry, Graduate School of Engineering Osaka University, Suita 565-0871 (Japan) [c] Dr. T. Sakurai, Prof. S. Seki Department of Molecular Engineering Graduate School of Engineering, Kyoto University Kyoto 615-8510 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201500681. Chem. Eur. J. 2015, 21, 9520 – 9527
Figure 1. a) The dpp derivatives (left) and their [2+ +2]-type complexes with CF3CO2¢ in the protonated forms (right). TFA = trifluoroacetic acid. b) Synthesis of 3 a,b from the corresponding 2-arylmalonic acids.
sults in the formation of a 2D pattern at the solution–substrate (highly ordered pyrolytic graphite (HOPG)) interface, supramolecular gels, and mesophases based on [2+ +2]-type complexes with CF3CO2¢ .[4b, 6] Although a-aryl moieties were useful for installing various substituents on dpp, they interfered with stable complexation with CF3CO2¢ due to steric effects. Therefore, the formation of stable assembled structures comprising protonated dpp compounds and carboxylates requires the design and synthesis of dpp derivatives that possess an aryl substituent at a more suitable position. Potentially suitable motifs are the dpp derivatives with an aryl moiety at the pyrazole 4-position (meso position) because their protonated forms can provide functional assembled structures upon combination with a variety of carboxylate anions. Herein, we report on the synthesis of meso-aryl dpp derivatives and their ion-pairing dimension-controlled assembling modes of which in the proton-
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Full Paper ated forms were thoroughly examined by synchrotron XRD analysis.
Results and Discussion The dpp precursors, 2-aryl-substituted 1,3-dipyrrolyl-1,3-propanediones 3 a’,b’, were prepared by the treatment of 2-arylmalonic acids with thionyl chloride and subsequent reactions with pyrrole in 27 and 29 % yield (two steps), respectively.[7] The subsequent condensation reaction of 3 a’,b’ with hydrazine in acetic acid at reflux provided 3 a,b in 19 and 58 % yield, respectively (Figure 1 b). Currently, this procedure for 3 a,b, which includes the condensation of carbonyl and amino groups, is effective compared with cross-coupling. Structural elucidation of 3 a,b was carried out by using 1H NMR spectroscopy and MALDI-TOF MS. As seen in 1 and 2 a,b,[4] meso-aryl-substituted 3 a,b also showed singly pyrrole-inverted conformations with intramolecular hydrogen bonding between pyrrole NH and pyrazole N as stable optimized states (Figures S5 and S6 in the Supporting Information).[8] The singly inverted conformation of 3 a is more stable at 3.01 and 4.06 kcal mol¢1 than no inverted and doubly inverted conformations, respectively, at B3LYP/631G(d,p). In solution, the inverted pyrrole ring in 3 a,b is not fixed with NH tautomerism at the pyrazole N sites. Compound 3 b, which possesses long alkyl chains, formed a lamellar structure with a layer distance of 5.73 nm in the solid state, prepared from CH2Cl2/MeOH, as revealed by synchrotron XRD analysis at RT (Figure 2 a). The layer distance corresponded to the length of two molecules of 3 b, which suggested the formation of a dimeric structure of a singly pyrroleinverted conformation through hydrogen-bonding and dipole– dipole interactions (Figure S7 in the Supporting Information).[8] Polarized optical microscopy (POM) of 3 b revealed various textures upon cooling from an isotropic liquid (Iso), although differential scanning calorimetry (DSC) showed transitions at 57 and 47 8C upon first and second heating, respectively, and at 41 8C upon cooling, but no peaks that suggested the existence of mesophases (Figures S11 and S12 in the Supporting Information). After thermal annealing in Iso, compound 3 b exhibited a lamellar structure in the solid state with a layer distance of 3.40 nm, which was probably due to the formation of an interdigitating structure (Figure 2 b). Annealing as a process to form the solid in the absence of solvent would provide the condensed short layer structure. Compounds 3 a,b were converted into their protonated forms in solution upon the addition of TFA, as observed in the UV/Vis absorption and fluorescence emission spectral changes (Figures S8 and S9 in the Supporting Information). Protonation at the pyrazole N site in the dpp derivatives requires fairly strong acids, such as TFA. Compound 3 a formed a [2+ +2]-type complex with TFA in the solid state through N¢H···O hydrogen bonding with N(¢H)···O distances of 2.71 and 2.85 æ (Figure 3 a). In the solid state, the dihedral angle between the dpp pyrazole unit and meso-phenyl ring was estimated to be 63.08, and the steric effect of the meso-phenyl ring resulted in distortion of the planarity of the pyrrole rings, with dihedral angles of 12.2 and 19.78 to the pyrazole unit. These distortions were Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 2. i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of organized structures of 3 b a) as a precipitate (from CH2Cl2/ MeOH) at 25 8C and b) as a sample at 25 8C upon first cooling. The diffraction at 0.41 nm is derived from assembly of alkyl chains.
larger than those (1.2 and 8.18) in the [2+ +2]-type complex of 1·H +¢CF3CO2¢ .[4a] The [2+ +2]-type complex formed a herringbone-like packing structure with a dihedral angle of 100.08 for two dpp planes in neighboring columns, as observed in the TFA complex of 1.[4a] Furthermore, compound 3 b also formed a complex with TFA, 3 b·H +¢CF3CO2¢ , that could be purified by recrystallization from octane. POM revealed a broken fanlike texture from 69 8C to RT, whereas DSC results showed transitions only at 69 8C upon cooling and at 79 8C upon heating, due to the absence of mesophases (Figures S11 and S12 in the Supporting Information). The ion pair 3 b·H +¢CF3CO2¢ exhibited higher transition temperatures to and from the Iso by
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Full Paper 3 b due to more effective stacking as the assembled two units of 3 b·H + are bridged by CF3CO2¢ . It is notable that the protonation of dpp derivatives and ion pairing with carboxylate can control the stability of assembled structures. Synchrotron XRD measurements of the solid sample from octane at RT revealed a lamellar structure with a layer distance of 5.97 nm, which was slightly larger than that of 3 b, owing to complexation with TFA (Figure 3 b). After thermal annealing in Iso, the solid sample also exhibited a similar lamellar structure with a layer distance of 5.91 nm (Figure 3 c). The fairly sharp diffractions of the halo at around 0.4 nm at 60 8C and RT suggested the formation of a rigid packing structure. The small difference in the assembled structures of 3 b·H +¢CF3CO2¢ upon annealing is also in contrast to that in 3 b. Protonated dpp is an effective building subunit for the fabrication of highly organized structures, which are formed by bridging between components that possess multiple carboxylate moieties. In fact, single-crystal X-ray analysis revealed the assembly of parent dpp in the protonated form 1·H + with 0.5 equivalents of perfluorobutane dicarboxylate ((CF2)4(CO2¢)2 ;
Figure 3. a) Solid-state structure of 3 a·H +¢CF3CO2¢ as a [2+ +2]-type complex (left) and packing side-view diagram (right). i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of organized structures of 3 b·H +¢CF3CO2¢ as b) a precipitate (from octane) at 25 8C and c) a sample at 25 8C upon first cooling. The organized structures in part iii) of b) and c) are the same and are ascribable to almost no change in assembled structures upon annealing.
about 30 8C in comparison with 3 b with transitions at 47 and 41 8C upon heating and cooling, respectively. This observation suggested a more stable assembly for 3 b·H +¢CF3CO2¢ than Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 4. Solid-state structures of a) (1·H + )2¢(CF2)4(CO2¢)2 and b) (3 a·H + )2¢ (CF2)4(CO2¢)2 as i) hydrogen-bonding structures with a single dicarboxylate (left: top view and right: side view) and ii) packing structures.
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Full Paper Figure 4 a). In the solid state, protonated dpp 1·H + formed a herring-bone-like packing structure with a stacking p-plane distance of 3.46 æ, based on 3D networks forming the three hydrogen-bonding interactions between pyrrole/pyrazole-NH and carboxylate oxygen atoms with N(¢H)···O distances of 2.60–2.86 æ. The less effective interaction with carboxylate was observed for one of the pyrrole NH atoms. The observation of 1 by single-crystal X-ray analysis confirmed the expectation that the protonated form of dpp 3 a also formed supramolecular polymers with dicarboxylates. Similar to the assembly of (1·H + )2¢(CF2)4(CO2¢)2, the combination of 3 a·H + and (CF2)4(CO2¢)2 led to a solid-state assembled structure, as revealed by single-crystal X-ray analysis (Figure 4 b). The introduction of a phenyl moiety in 3 a·H + , with the dihedral angle of 64.18 to the dpp pyrazole unit, induced a stacking p-plane distance of 3.69 æ, which was slightly larger than that of (1· H + )2¢(CF2)4(CO2¢)2. Distortions of pyrrole rings in (3 a·H + )2¢ (CF2)4(CO2¢)2 of 9.0 and 15.88 are larger than those of (1·H + )2¢ (CF2)4(CO2¢)2 (5.3 and 5.88). The assembly was constructed by interactions not only between pyrrole/pyrazole-NH and carboxylate oxygen atoms, but also those between pyrrole CH and pyrrole/phenyl p planes, leading to larger p-plane distances. The solid-state structures were slightly different from regular +2]-type binding mode with carboxylate units, probably due [2+ to the preferred crystal-packing modes. However, the observations of the solid-state assembled structures consisting of dicarboxylates were valuable for the further design and preparation of highly ordered structures through the introduction of appropriate substituents to the dpp core unit. The long alkyl chains in 3 b can yield dimension-controlled organized structures based on van der Waals interactions between alkyl units supporting the stacking structures of the pelectronic moieties. Compound 3 b yielded precipitates of ionpairing assemblies from octane after mixing with 0.5 equivalents of (CF2)n(CO2H)2 (n = 4 and 8) in 1,2-dimethoxyethane (DME) and evaporation of the solvent, whereas it was difficult to obtain purified assemblies with (CF2)n(CO2H)2 (n = 6 and 10; Figure S10 in the Supporting Information). DSC results for (3 b·H + )2¢(CF2)n(CO2¢)2 (n = 4 and 8) revealed transitions to Iso at 98 and 73 8C, respectively, which suggested the absence of mesophases (Figure S11 in the Supporting Information).[9] The transition temperature of (3 b·H + )2¢(CF2)4(CO2¢)2 is 20 8C higher than that of 3 b·H +¢CF3CO2¢ (79 8C) probably because of the formation of the more stable assembly by tight binding of ionpairing moieties through perfluoroalkyl spacer units. Synchrotron XRD at 25 8C revealed the formation of lamellar structures in 3 b·H + as both (CF2)n(CO2¢)2 (n = 4 and 8) complexes in the solid state after melting to Iso (Figure 5 and Figure S13 in the Supporting Information). The complex containing (CF2)4(CO2¢)2 exhibited a layer distance of 5.91 nm (Figure 5 a), whereas the complex containing (CF2)8(CO2¢)2 exhibited a layer distance of 3.70 nm (Figure 5 b), which suggested that the difference in the alkyl chain lengths of the dicarboxylate could influence the organized structures formed by meso-modified dpp. Based on molecular modeling,[8] the dicarboxylate (CF2)4(CO2¢)2 has a short perfluoroalkyl chain, which may result in the formation of a lamellar structure of [2+ +2]-type supramolecular polymers Chem. Eur. J. 2015, 21, 9520 – 9527
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Figure 5. i) Synchrotron XRD patterns, ii) possible packing structures, and iii) illustration of the organized structures of 3 b·H + as a) (CF2)4(CO2¢)2 and b) (CF2)8(CO2¢)2 complexes (in a molar ratio of 2:1 for 3 b·H + and dicarboxylates) at 25 8C upon cooling from Iso.
with 3 b·H + or related carboxylate-binding structures with a repeat distance of 5.91 nm. On the other hand, the dicarboxylate (CF2)8(CO2¢)2 has a longer perfluoroalkyl moiety and enables the formation of a lamellar structure upon supramolecular polymerization with 3 b·H + by interdigitating into vacant areas between carboxylate complex units. Based on these results, the perfluoroalkyl moieties are essential for constructing different assembled structures in different forms. The complicated thermal transition behavior of (3 b·H + )2¢(CF2)8(CO2¢)2[9] can be ascribable to less effective packing than that of (3 b·H + )2¢ (CF2)4(CO2¢)2. Although the exact carboxylate binding mode cannot be elucidated by synchrotron XRD, the introduction of
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Full Paper aliphatic chains induced ordered structures owing to interactions between protonated 3 b and dicarboxylates. Currently, it is very challenging to reveal the assembling processes and mechanisms because they include the formation of solid states. On the other hand, the fairly disordered structures formed upon combination of 3 b with (CF2)n(CO2H)2 (n = 6 and 10) could be attributed to the nonideal lengths between two carboxylate moieties. The ion-pair-based assemblies of p-conjugated systems can control not only their structural order, but also their chargecarrier transporting properties. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements[10] were carried out to investigate the effect of the ion-pair-based directional assembly on the photoconductivity (Figure S14 in the Supporting Information). When photoexcited by a l = 355 nm laser pulse, thin films of 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢ (CF2)n(CO2¢)2 (n = 4 and 8) on quartz exhibited transient conductivity (fm), in which f and m represent the yield of charge-carrier generation and sum of the charge-carrier mobilities, respectively. We found the conductivity maxima, (fSm)max, to be around 1.6 Õ 10¢5, 1.7 Õ 10¢5, 1.9 Õ 10¢5, and 2.2 Õ 10¢5 cm2 V¢1 s¢1 for 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢ (CF2)n(CO2¢)2 (n = 4 and 8), respectively. The difference in (fSm)max between 3 b alone and the ion-pairing forms was small, probably because, upon dimerization, compound 3 b forms a mesoscopically ordered structure in its dimerized assembly. However, slight but significant differences in the photoconductivity were observed when coupled with dicarboxylates in the protonated form. We consider that the dicarboxylates are likely to promote supramolecular polymerization with protonated dpp units and suppress their dynamic motions, resulting in an advantage for the one-dimensional charge-carrier transporting event. In addition, ion pair (3 b·H + )2¢(CF2)8(CO2¢)2, the assembled structure of which is less thermally stable, has a slightly more effective pathway of charge carriers compared with (3 b·H + )2¢(CF2)4(CO2¢)2. The extremely long lifetime of the free charge carriers in the conductivity transient over 200 ms also supports the presence of a stable, isolated 1D pathway for the charge carriers.
Conclusion We synthesized dpp derivatives that possessed an aryl ring at the pyrazole 4-position. The modified dpp derivatives formed a variety of assembled structures based on [2+ +2]-type complexes upon combination with appropriate acids. In particular, complexation of protonated dpp derivatives with dicarboxylates resulted in highly ordered structures, the packing modes of which, along with thermal transition behavior, were controlled by the distances between two carboxylate moieties. This modulation also resulted in control of the charge-carrier transporting properties, as evidenced by electrodeless conductivity measurements. Planar ion-pairing complexes reported herein would afford various highly ordered assembled structures based on the combination of ionic species. One of the advantages in the ion-pairing assemblies is the control of packing structures and resulting properties by the constituting Chem. Eur. J. 2015, 21, 9520 – 9527
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ionic species. Further design and modification of dpp derivatives, as well as the synthesis of other new p-electronic systems, are currently ongoing in our laboratory in an effort to develop fascinating ion-based electronic materials.
Experimental Section General procedures Starting materials were purchased from Wako Pure Chemical Industries Ltd., Nacalai Tesque Inc, and Sigma–Aldrich Co., and used without further purification unless otherwise stated. UV/Vis spectra were recorded on a Hitachi U-3500 spectrometer. Fluorescence spectra were recorded on a Hitachi F-4500 fluorescence spectrometer for ordinary solutions. NMR spectra used in the characterization of products were recorded on a JEOL ECA-600 600 MHz spectrometer. All NMR spectra were referenced to residual solvent. MALDI-TOF MS was recorded on a Shimadzu Axima-CFRplus spectrometer. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was recorded on a Bruker solariX (Qh-FT-ICRMS) spectrometer and were carried out at the Joint Usage/Research Center (JURC) at the Institute for Chemical Research (ICR), Kyoto University. TLC analyses were carried out on aluminum sheets coated with silica gel 60 (Merck 5554). Column chromatography was performed on Sumitomo alumina KCG-1525, Wakogel C200, C-300, and Merck silica gel 60 and 60H.
2-Phenyl-1,3-dipyrrol-2-yl-1,3-propanedione (3 a’) Thionyl chloride (4 mL) was added slowly to a flask containing 3 a’’ (1.80 g, 10.0 mmol), and was stirred for 3 h at 50 8C. Excess thionyl chloride was removed under vacuum for several hours to give 2phenylmalonyl chloride as a yellow oil, which was immediately used in the next reaction without further purification. A solution of pyrrole (2 mL, 30 mmol) in CH2Cl2 (50 mL) was treated with 2-phenylmalonyl chloride at 0 8C and stirred for 3 h. After the consumption of the starting pyrrole was confirmed by TLC analysis, the mixture was washed with a saturated aqueous solution of Na2CO3 and water, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was then purified by column chromatography on a silica gel (eluent: 3 % MeOH/CH2Cl2) to give 3 a’ (746 mg, 2.68 mmol, 27 %) as a yellow solid. Rf = 0.37 (eluent: EtOAc/nhexane = 1:1). 1H NMR (600 MHz, CDCl3, 20 8C; the diketone is obtained as a mixture of keto and enol tautomers in the ratio of 1:0.17): keto form: d = 9.34 (br s, 2 H; NH), 7.54–7.28 (m, 5 H; Ar-H), 7.04–7.02 (m, 2 H; pyrrole-H), 7.01–7.00 (m, 2 H; pyrrole-H), 6.28– 6.27 (m, 2 H; pyrrole-H), 6.08 ppm (s, 1 H; CH); enol form: d = 18.57 (s, 1 H; OH), 9.34 (br s, 2 H; NH), 7.50–7.28 (m, 5 H; Ar-H), 6.90–6.89 (m, 2 H; pyrrole-H), 6.01–6.00 (m, 2 H; pyrrole-H), 5.19–5.18 ppm (m, 2 H; pyrrole-H); MALDI-TOF-MS: m/z (%): 279.1 (100) [M¢H] + .
4-Phenyl-3,5-dipyrrol-2-ylpyrazole (3 a) Following a procedure reported in the literature,[4] hydrazine monohydrate (300 mL, 6.17 mmol) was added to a solution of 3 a’ (55.3 mg, 0.20 mmol) in AcOH (2 mL) and stirred at reflux for 21 h. After monitoring the consumption of the starting diketone on TLC, the solvent was removed and then the reaction mixture was purified by column chromatography on silica gel (eluent: 3 % MeOH/ CH2Cl2), followed by evaporation, and recrystallization from CH2Cl2/ n-hexane to give 3 a (10.1 mg, 0.038 mmol, 19 %) as a white solid. Rf = 0.14 (eluent: 3 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C; pyrazole NH cannot be observed at this temperature): d =
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Full Paper 8.42 (br s, 2 H; pyrrole-NH), 7.50–7.42 (m, 5 H; Ar-H), 6.70–6.69 (m, 2 H; pyrrole-H), 6.14–6.13 ppm (m, 4 H; pyrrole-H); UV/Vis (CH2Cl2): lmax (e Õ 10¢4) = 277 nm (1.7 m¢1 cm¢1); fluorescence (CH2Cl2): lem (lex) = 391 nm (277 nm); MALDI-TOF-MS: m/z (%): 273.9 (100) [M]¢ .
1,2,3-Trihexadecyloxy-5-iodobenzene A mixture of 1,2,3-trihydroxy-5-iodobenzene[11] (3.35 g, 13.3 mmol), K2CO3 (12.9 g, 93.1 mmol), and 1-bromohexadecane (13.8 g, 45.2 mmol) in dry DMF (120 mL) was stirred at 80 8C for 3 d. After cooling, the solvent was evaporated. The crude product was dissolved in CHCl3, washed with water, dried over Na2SO4, and evaporated to dryness. The residue was then purified by column chromatography on silica gel (Wakogel C-300; eluent CH2Cl2/n-hexane = 1:4) to give 1,2,3-trihexadecyloxy-5-iodobenzene (11.1 g, 12.0 mmol, 90 %) as a white solid. Rf = 0.34 (eluent: CH2Cl2/nhexane = 1:4); 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.84 (s, 2 H; ArH), 3.91 (t, J = 6.0 Hz, 4 H; OCH2), 3.90 (t, J = 6.6 Hz, 2 H; OCH2), 1.80–1.70 (m, 6 H; OCH2CH2), 1.46–1.43 (m, 6 H; OC2H4CH2), 1.33– 1.25 (m, 72 H; OC3H6C12H24CH3), 0.89–0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 924.1 (100) [M¢H]¢ .
Di-tert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate Following a procedure reported in the literature,[6] a Schlenk tube containing [Pd2(dba)3] (dba = dibenzylideneacetone; 91.6 mg, 0.10 mmol), P(tBu)3 (40.5 mg, 0.20 mmol), tBuOK (247 mg, 2.2 mmol), and 1,2,3-trihexadecyloxy-5-iodobenzene (1.85 g, 2.0 mmol) was flushed with nitrogen and charged with anhydrous 1,4-dioxane (5.0 mL) and di-tert-butyl malonate (493 mL, 2.2 mmol). The mixture was heated at 80 8C for 12 h, cooled, and then partitioned between CH2Cl2, water and a saturated aqueous solution of NaCl. The combined extracts were dried over Na2SO4 and evaporated. The residue was then purified by column chromatography on silica gel (Wakogel C-300; eluent: CH2Cl2/n-hexane = 1:1) to give ditert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate (1.56 g, 1.54 mmol, 77 %) as a white solid. Rf = 0.35 (eluent: CH2Cl2/nhexane = 1:1); 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.56 (s, 2 H; ArH), 4.29 (s, 1 H; CH), 3.96–3.91 (m, 6 H; OCH2C15H31), 1.80–1.70 (m, 6 H; OCH2CH2C14H29), 1.46 (s, 18 H; tBu), 1.46–1.41 (m, 6 H; OC2H4CH2C13H27), 1.35–1.25 (m, 78 H; OCH2CH3 and OC3H6C12H24CH3), 0.89–0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 1013.9 (100) [M+ +H] + .
2-(3,4,5-Trihexadecyloxyphenyl)malonic acid (3 b’’) TFA (3.6 mL) was added to a solution of di-tert-butyl 2-(3,4,5-trihexadecyloxyphenyl)malonate (1.56 g, 1.54 mmol) in CH2Cl2 (10 mL) and stirred at RT for 2 h. The reaction mixture was partitioned between CH2Cl2 and a saturated aqueous solution of NaHCO3. The aqueous phase was acidified with an aqueous solution of HCl, and then the product was extracted with diethyl ether. The combined extracts were dried over Na2SO4 and evaporated to give 3 b’’ (1.39 g, 1.54 mmol, quant) as a white solid. 1H NMR (600 MHz, CDCl3, 20 8C): d = 6.57 (s, 2 H; Ar-H), 4.57 (s, 1 H; CH), 3.98–3.92 (m, 6 H; OCH2C15H31), 1.80–1.70 (m, 6 H; OCH2CH2C14H29), 1.47–1.42 (m, 6 H; OC2H4CH2C13H27), 1.33–1.21 (m, 72 H; OC3H6C12H24CH3), 0.89– 0.87 ppm (m, 9 H; OC15H30CH3); ESI-TOF-MS (FT-ICR): m/z (%): 899.8 (100) [M¢H]¢ . Chem. Eur. J. 2015, 21, 9520 – 9527
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2-(3,4,5-Trihexadecyloxyphenyl)-1,3-dipyrrol-2-yl-1,3-propanedione (3 b’) Thionyl chloride (3 mL) was added slowly to a flask containing 3 b’’ (571 mg, 0.63 mmol) and stirred for 1.5 h at 60 8C. Excess thionyl chloride was removed under vacuum for 1 h to give 2-(3,4,5-trihexadecyloxyphenyl)malonyl chloride as a yellow solid, which was used immediately in the next reaction without further purification. A solution of pyrrole (130 mL, 1.89 mmol) in CH2Cl2 (12 mL) was treated with 2-(3,4,5-trihexadecyloxyphenyl)malonyl chloride at RT and stirred for 30 min. After the consumption of the starting pyrrole was confirmed by TLC analysis, the mixture was washed with water and a saturated aqueous solution of NaCl, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was then purified by flash column chromatography on silica gel (eluent: 0.5 % MeOH/CH2Cl2) to give 3 b’ (143 mg, 0.14 mmol, 22 %) as a yellow solid. Rf = 0.24 (eluent: 0.5 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C): d = 9.29 (br s, 2 H; NH), 7.04–7.03 (m, 2 H; pyrrole-H), 7.00–6.98 (m, 2 H; pyrrole-H), 6.66 (s, 2 H; Ar-H), 6.28– 6.27 (m, 2 H; pyrrole-H), 5.94 (s, 1 H; CH), 3.97–3.89 (m, 6 H; OCH2C15H31), 1.78–1.68 (m, 6 H; OCH2CH2C14H29), 1.46–1.41 (m, 6 H; OC2H4CH2C13H27), 1.34–1.25 (m, 72 H; OC3H6C12H24CH3), 0.89– 0.87 ppm (m, 9 H; OC15H30CH3); MALDI-TOF-MS: m/z (%): 999.9 +H] + . (100) [M+
4-(3,4,5-Trihexadecyloxyphenyl)-3,5-dipyrrol-2-ylpyrazole (3 b) Following a procedure reported in the literature,[4] hydrazine monohydrate (240 mL, 4.94 mmol) was added to a solution of 3 b’ (56.8 mg, 0.057 mmol) in AcOH (1 mL), and stirred at reflux for 12 h. After monitoring the consumption of the starting diketone by TLC, the solvent was removed and then the reaction mixture was purified by flash column chromatography on silica gel (eluent: 2 % MeOH/CH2Cl2), followed by evaporation, and recrystallization from CH2Cl2/MeOH to give 3 b (32.7 mg, 0.033 mmol, 58 %) as a pale yellow solid. Rf = 0.22 (eluent: 2 % MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3, 20 8C): d = 8.47 (br s, 2 H; NH), 6.70 (br s, 2 H; pyrrole-H), 6.61 (s, 2 H; Ar-H), 6.22 (br s, 2 H; pyrrole-H), 6.16–6.15 (m, 2 H; pyrrole-H), 4.07 (t, J = 6.6 Hz, 2 H; OCH2C15H31), 3.90 (t, J = 6.6 Hz, 4 H; OCH2C15H31), 1.83–1.74 (m, 6 H; OCH2CH2C14H29), 1.55– 1.41 (m, 6 H; OC2H4CH2C13H27), 1.35–1.25 (m, 72 H; OC3H6C12H24CH3), 0.89–0.86 ppm (m, 9 H; OC15H30CH3); UV/Vis (CH2Cl2): lmax (e Õ 10¢4) = 273.5 nm (2.3 m¢1 cm¢1); fluorescence (CH2Cl2): lem (lex) = +H] + . 376 nm (274 nm); MALDI-TOF-MS: m/z (%):995.9 (100) [M+
Single-crystal X-ray analysis Crystallographic data for ion-pair complexes of dipyrrolylpyrazoles are summarized in Table 1. Single crystals of 3 a·H +¢CF3CO2¢ were obtained by vapor diffusion of n-hexane into a solution of 3 a and TFA in CH2Cl2 in a 1:1 molar ratio. The crystal was a colorless prism of approximate dimensions 0.40 Õ 0.10 Õ 0.10 mm. Complex (1·H + )2¢(CF2)4(CO2¢)2 was obtained by vapor diffusion of n-hexane into a solution of 1 and (CF2)4(CO2H)2 in a 2:1 molar ratio in DME. The data crystal was a colorless prism of approximate dimensions 0.20 Õ 0.20 Õ 0.10 mm. Single crystals of (3 a·H + )2¢(CF2)4(CO2¢)2 were obtained by vapor diffusion of n-hexane into a solution of 3 a and (CF2)4(CO2H)2 in a 2:1 molar ratio in CHCl3/DME. The crystal was a colorless prism of approximate dimensions 0.40 Õ 0.10 Õ 0.05 mm. Data were collected at 93 K on a Rigaku RAXIS-RAPID II diffractometer with graphite monochromated CuKa radiation (l = 1.54187 æ), and structures were solved by direct methods. The non-hydrogen atoms were refined anisotropically. The calculations were per-
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Full Paper Table 1. Crystallographic details for ion pairs 3 a·H +¢CF3CO2¢ , (1·H + )2¢(CF2)4(CO2¢)2, and (3 a·H + )2¢ (CF2)4(CO2¢)2.
formula Mr crystal size [mm] crystal system space group a [æ] b [æ] c [æ] a [8] b [8] g [8] V [æ3] 1calcd [g cm¢3] Z T [K] m(CuKa) [mm¢1] no. of reflns no. of unique reflns variables lCuKa [æ] R1 (I > 2s(I)) wR2 (I > 2s(I)) GOF
3 a·H +¢CF3CO2¢
(1·H + )2¢(CF2)4(CO2¢)2
(3 a·H + )2¢(CF2)4(CO2¢)2
C17H15N4·C2F3O2 388.35 0.40 Õ 0.10 Õ 0.10 monoclinic P21/a (no. 14) 16.5316(6) 5.9855(2) 17.8433(7) 90 91.687(2) 90 1764.83(11) 1.462 4 93(2) 1.023 14 369 3043 253 1.54187 0.0682 0.1057 1.000
2(C11H11N4)·C6F8O4 686.54 0.20 Õ 0.20 Õ 0.10 monoclinic C2/c (no. 15) 32.4979(6) 6.05510(10) 15.9142(3) 90 114.3858(9) 90 2852.18(9) 1.599 4 93(2) 1.278 13 033 2600 245 1.54187 0.0535 0.0954 1.067
2(C17H15N4)·C6F8O4 838.78 0.40 Õ 0.10 Õ 0.05 monoclinic P21/a (no. 14) 16.3472(5) 6.1376(2) 19.0404(5) 90 104.0875(16) 90 1852.92(10) 1.503 4 93(2) 1.101 17 619 3366 271 1.54187 0.0810 0.1867 1.075
formed by using the Crystal Structure crystallographic software package of the Molecular Structure Corporation.[12] CCDC-942381, 942382, and 942383 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
DFT and AM1 calculations Ab initio and semiempirical calculations of p-conjugated molecules were carried out by using the Gaussian 03 program[8] and an HP Compaq dc5100 SFF computer. The structures were optimized, and the total electronic energies were calculated at the B3LYP level by using a 6-31G(d,p) basis set for 3 a, 3 c (the derivative possessing methoxy substituents in place of hexadecyloxy moieties in 3 b), 3 a·H + , 3 c·H + , and 3 a·H +¢CF3CO2¢ and at AM1 level for 3 b and 3 b·H + .
The phase transition points were observed by using a differential scanning calorimeter (PerkinElmer Diamond DSC).
Polarizing optical microscopy (POM) POM measurements were carried out with a Nikon OPTIPHOT-POL polarizing optical microscope equipped with a Mettler FP82 HT hot stage.
Synchrotron XRD analysis High-resolution XRD analyses were carried out by using a synchrotron radiation X-ray beam with a wavelength of 1.00 æ on BL40B2 at SPring-8 (Hyogo, Japan). A large Debye–Scherrer camera with a camera length of 546.28 mm for XRD of 3 b (Figure 2), 3 b·H +¢ CF3CO2¢ (Figure 3), (3 b·H + )2 as a (CF2)4(CO2¢)2 complex (Figure 5 a www.chemeurj.org
Flash-photolysis time-resolved microwave conductivity (FPTRMC)
The charge-carrier mobility was measured by FP-TRMC technique. Complexes 3 b, 3 b·H +¢CF3CO2¢ , and (3 b·H + )2¢(CF2)4(CO2¢)2, (3 b·H + )2¢(CF2)8(CO2¢)2 were mounted on a quartz plate, once heated up to the isotropic state, and then cooled to RT, to afford thin-film samples. Charge carriers were photochemically generated by using a third-harmonic generation (l = 355 nm) of a Spectra Physics model INDI-HG Nd:YAG laser with a pulse duration of 5– 8 ns. The photon density of a l = 355 nm pulse was 0.9 Õ 1016 photons per cm2. The microwave frequency and power were set at about 9.1 GHz and 3 mW, respectively. The TRMC signal, picked up by a diode (rise time < 1 ns), was monitored by means of a Tektronics model TDS3032B digital oscilloscope. The observed conductivities were normalized, given by a photocarrier generation yield (f) multiplied by sum of the charge carrier mobilities (Sm), according to the equation fSm = (1/eAI0Flight)(DPr/Pr), in which e, A, I0, Flight, Pr, and DPr were the unit charge of a single electron, the sensitivity factor (S¢1 cm), the incident photon density of the excitation laser (photon cm¢2), a correction (or filling) factor (cm¢1), and the reflected microwave power and its change, respectively. All experiments were carried out at RT in an ambient atmosphere.
Acknowledgements
Differential scanning calorimetry (DSC)
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and Figure S13 in the Supporting Information), and (3 b·H + )2 as a (CF2)8(CO2¢)2 complex (Figure 5 b and Figure S13 in the Supporting Information) with a quartz capillary and an imaging plate as a detector, for which the diffraction pattern was obtained with a 0.018 step in 2q. The exposure time to the X-ray beam was 10 to 60 s.
This work was supported by a Grants-in-Aid for Young Scientists (A) (no. 23685032) and Scientific Research (B) (no. 26288042) and on Innovation Areas (“Photosynergetics” Area 2606, no. 26107007) from the MEXT and Ritsumeikan R-GIRO project (2008–2013). We thank Prof. Atsuhiro Osuka and Hirotaka Mori, Kyoto University, for single-crystal X-ray analysis; Dr. Katsuhiro Isozaki and Prof. Hikaru Takaya, Kyoto University, for FT-ICR-MS measurements; Dr. Noboru Ohta, JASRI/SPring-8, for synchrotron XRD analysis; Prof. Kazuchika Ohta, Shinshu University, for the valuable discussion on the transition behavior; Prof. Tomonori Hanasaki, Ritsumeikan University, for DSC and POM measurements; and Prof. Hitoshi Tamiaki, Ritsumeikan University, for various measurements. T.S. thanks JSPS for a Research Fellowship for Young Scientists.
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