Supramolecular Assemblies by Complementary Hydrogen-Bonds and

Article pubs.acs.org/crystal

Nucleobase-Functionalized 1,6-Dithiapyrene-Type Electron-Donors: Supramolecular Assemblies by Complementary Hydrogen-Bonds and π‑Stacks Tsuyoshi Murata, Eigo Miyazaki, Kazuhiro Nakasuji, and Yasushi Morita* Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan S Supporting Information *

ABSTRACT: Synthesis, crystal structures and redox properties of 1,6-dithiapyrene (DTPY)-type electron-donors functionalized with nucleobases (uracil, cytosine and adenine) were investigated. The electrochemical measurements showed that the uracil-substituted derivatives were slightly stronger electron-donors than DTPY, and the cytosine- and adeninesubstitution caused a slight weakening of the electron-donating ability. In the crystal structures, DTPY-nucleobases constructed multidimensional assemblies by complementary hydrogen-bonds on the nucleobase moieties and π-stacks and S···S interactions on the DTPY skeleton. The uracil derivative formed two kinds of hydrogen-bonded pairs with different H-bonding modes (Watson−Crick and reverse Watson−Crick types), both of which were further linked through πstacks on the DTPY skeleton to construct one-dimensional alternating columns. In the CH2Cl2 solvated crystal, the uracil derivative built up a two-dimensional π-layer by the complementary hydrogen-bonds and π-stacks. In the cytosine derivative, the complementary hydrogen-bonded pair assembled by the π-stacks and S···S interactions of the DTPY skeleton constructed a twodimensional network. The adenine derivative formed a channel structure by the one-dimensional π-stack of complementary hydrogen-bonded pairs, where crystalline water molecules with a ladder-like hydrogen-bonded chain were included. Chargetransfer complexes of DTPY-nucleobases with tetracyanoquinodimethane possessed a neutral ground state and exhibited semiconductive behaviors with room temperature conductivities of 10−6 to 10−7 S cm−1.

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stacks.2 Such a self-assembling ability of nucleobases has been utilized in crystal engineering and supramolecular chemistry3 and has attracted much attention of materials chemists in the research fields of molecular magnets,4 conductors,5,6 etc. Author: For the exploration of charge-transfer (CT) complexes with new functions based on the structural modification7,8 and cooperation of proton- and electrontransfer,9 we investigated the H-bond incorporated CT complexes and salts for the exploration of new molecular conductors with well-defined assembled structures.10,11 In addition to the structural aspects, our investigation disclosed that the molecular recognition ability and high polarizability of H-bonds can modulate electronic structures and physical properties of CT complexes, demonstrating the new design strategies for conducting CT complexes.10a,d We also designed and synthesized tetrathiafulvalene (TTF) derivatives functionalized with nucleobases to develop organic conductors incorporated into biological self-assemblies.12−14 The complementary H-bonds inherent in nucleobases controlled the molecular arrangement to construct diverse supramolecular

INTRODUCTION

Supramolecular architectures in biomolecular systems such as peptide, enzyme, DNA, etc. have provided much inspiration for the development of various functional molecular materials.1 Nucleobases, adenine, thymine, guanine and cytosine (Chart 1), play an important role in the formation of double helical structure of DNA by forming selective complementary hydrogen-bonded (H-bonded) pairs and one-dimensional πChart 1. Chemical Structures of Nucleobases and ElectronDonor and -Acceptors in the Text

Received: September 27, 2012 Revised: October 19, 2012 Published: October 22, 2012 © 2012 American Chemical Society

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dx.doi.org/10.1021/cg301414s | Cryst. Growth Des. 2012, 12, 5815−5822

Crystal Growth & Design

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investigated their electrochemical behavior, crystal structures and CT complexes with tetracyanoquinodimethane (TCNQ). In the crystal structures, the cooperation of complementary Hbonds of nucleobases and strong π-stacks of DTPY moieties modulated the self-assembled structures.

architectures and yielded highly conductive CT complexes. Furthermore, the chemical modification on TTF-uracil derivatives, where the terminal vinyl group of TTF skeleton was substituted with ethylenedithio-15 or ethylenedioxygroup,16 highly affected the self-assembling ability of the TTF skeleton causing the increment of variation of molecular packing. 1,6-Dithiapyrene (DTPY) is a Weitz-type electron-donor molecule17,18 having an electron-donating ability comparable to that of TTF (Eox = −0.04 for DTPY and −0.08 V for TTF vs Fc/Fc+) and an 18π-electronic system larger than that of TTF (14π). The planar and extensive π-electronic system of DTPY often induces the formation of a one-dimensional column by strong π-stacks, being advantageous for a path for electrical conduction in CT complexes and salts. DTPY and its derivatives afforded CT complexes exhibiting metallic electrical conduction.17,18 In the present study, we have designed and synthesized DTPY derivatives substituted with nucleobase moieties (uracil, cytosine and adenine, 1−3 in Chart 2) and

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EXPERIMENTAL SECTION

Materials and Methods. The syntheses of DTPY,19 5-iodouracil derivatives 5,12a,15 1-n-butyl-5-iodo-4-(o-nitrophenoxyl)pyrimidine-2one 6,13 8-iodoadenosine derivative 7b14 are presented in our previous paper, and 9-n-butyl-8-iodoadenine (7a) was newly prepared by the literature method (see Supporting Information).20 TCNQ was purchased and purified by sublimation. Solvents were dried (drying agent in parentheses) and distilled under argon prior to use: THF (Na−benzophenone ketyl), toluene, DMF and CH2Cl2 (CaH2). All reactions requiring anhydrous conditions were conducted under an argon atmosphere. Rf values on TLC were recorded on E. Merck precoated (0.25 mm) silica gel 60 F254 plates. The plates were sprayed with a solution of 10% phosphomolybdic acid in 95% EtOH, and then heated until the spots became clearly visible. Silica gel 60 (100−200 mesh) deactivated by mixing with 6% water was used for column chromatography. Measurements. Melting points were measured with a hot-stage apparatus, Yanaco MP-J1, and uncorrected. 1H NMR spectra were obtained on a JEOL EX-270 with CDCl3 and DMSO-d6 using Me4Si as an internal standard. Infrared spectra (IR) were recorded on JASCO FT/IR-660M or Perkin-Elmer 1600 series using KBr plates (resolution 2 or 4 cm−1). Electronic spectra were measured by a Shimadzu UV3100PC spectrometer using KBr plates. EI-Mass spectra were taken at 70 eV by using a Shimadzu QP-5000 mass spectrometer, and FAB-MS spectra were recorded on a Shimadzu/KRATOS Concept 1S using 3nitrobenzylalcohol matrix. Elemental analyses were performed at the Graduate School of Science, Osaka University. Cyclic voltammetric measurements were made with an ALS Electrochemical Analyzer Model 612A. Cyclic voltammograms were recorded with a 1.6 mm diameter gold working electrode and a Pt wire counter electrode for 1 mM solutions of 1−3 in MeCN containing 0.1 M Et4NClO4 as the supporting electrolyte at room temperature. The experiments employed an Ag/AgNO3 reference electrode, and the final results

Chart 2. DTPY-Nucleobase Derivatives

Table 1. Crystallographic Data of DTPY-Nucleobases crystal formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g cm−3) μ (mm−1) temp (K) unique reflns reflns used (I > 2.0σ(I)) parameters R1 (I > 2.0σ(I)) wR2 (all data) GOF a

1a

1a·CH2Cl2

2a

3a·2H2O

C22H18N2O2S2 406.50 triclinic P1̅ 12.2288(2) 12.4347(3) 13.512(1) 92.751(6) 109.419(8) 106.704(7) 1832.4(1) 4 1.474 2.812a 150 6509 3233 532 0.0818 0.2648 0.983

C23H20Cl2N2O2S2 491.43 monoclinic P21/n 11.11(2) 8.731(7) 23.51(2) 90 98.59(5) 90 2254(4) 4 1.448 0.497b 150 4795 1559 280 0.1262 0.3777 0.985

C22H19N3O1S2 405.52 monoclinic P21/n 12.5214(9) 9.9250(3) 16.990(1) 90 111.766(8) 90 1960.9(2) 4 1.374 2.602a 150 3585 2776 253 0.0634 0.1875 1.054

C23H23N5O2S2 465.58 monoclinic P21/c 20.0919(7) 4.8285(1) 22.403(2) 90 101.226(7) 90 2131.8(2) 4 1.451 2.532a 200 3897 1914 305 0.0592 0.1251 0.920

Cu Kα radiation. bMo Kα radiation. 5816



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were calibrated with a ferrocene/ferrocenium (Fc/Fc+) couple. Temperature dependences of conductivity for compressed pellets were recorded by a two-probe method on a Fuso dc multichannel conductivity device HECS 944C type in a temperature range of 200− 300 K. X-ray Crystallographic Analysis. X-ray crystallographic measurements were made on a Rigaku Raxis-Rapid imaging plate with graphite monochromated Mo Kα (λ = 0.71075 Å) or Cu Kα (λ = 1.54187 Å) radiation. Empirical absorption corrections were applied. Structures were determined by a direct method using SHELXS-9721 or SIR2004.22 Refinements were performed by full-matrix least-squares on F2 using SHELXL-97.23 All non-hydrogen atoms were refined anisotropically. Positional parameters of hydrogen atoms were calculated with sp2 or sp3 configuration of the bonding carbon and nitrogen atoms, and hydrogen atoms were refined using the riding model. In the refinement procedures, isotropic temperature factors with magnitudes of 1.2 times of the equivalent temperature factors of the bonding atoms were applied for hydrogen atoms. In the cases of 2a, S1−C2 and S2−C14 disordered due to the reversal of DTPY skeleton. The siteoccupancy factors of 0.875 and 1.333 were applied for S and C atoms, respectively, which corresponds to the 8:2 probability of each conformation. Selected crystal data and data collection parameters are given in Table 1.

Information). The observed oxidation potentials are summarized in Table 2. The uracil substituted derivatives 1a and 1b Table 2. Redox Potentials (E) and Potential Gap (ΔE) of DTPY-Nucleobasesa 1a 1b 2a 2b 3a 3b DTPY

Eox1 (V)

Eox2 (V)

ΔE (V)

−0.05 −0.06 +0.02 +0.01 +0.05 +0.08 −0.04

b +0.21 +0.29 +0.28 b b +0.27

b 0.27 0.27 0.27 b b 0.31

a

Conditions: concentration of analyte, 1 mM; solvent, DMF (0.1 M Et4NClO4); scan rate, 10−100 mV/s; reference electrode, Ag/AgNO3 (0.01 M in MeCN); counter electrode, Pt wire; working electrode, Au disk; the results were calibrated with Fc/Fc+ couple. bIrreversible waves.

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show slightly more negative oxidation potentials (Eox1 = −0.05 and −0.06 V, respectively, vs Fc/Fc+) than that of DTPY (Eox1 = −0.04 V), indicating the electron-rich feature of uracil moiety. The cytosine substitution causes positive shifts of the oxidation potentials by 0.05−0.06 V for Eox1. Because of the electronwithdrawing feature of imino-skeleton in the purine-base, DTPY-adenine derivatives 3 exhibit the oxidation waves at the highest potentials (Eox1 = +0.05 and +0.08 V for 3a and 3b, respectively) among DTPY-nucleobases in the present study. The difference of the first and second oxidation potentials (ΔE = Eox2 − Eox1), a simple indicator of on-site Coulomb repulsion, slightly decreased due to the π-extension. These effects of substitution with nucleobases on the electron-donation abilities of electron-donors are very similar to those observed in the TTF-nucleobases.12−16 Crystal Structure of 1a. Single crystals of 1a suitable for the X-ray crystal structure analysis were obtained by the vapor diffusion method using ethyl acetate and hexane. The asymmetric unit is composed of two 1a molecules (1a-A and 1a-B). In the molecules of 1a-A and 1a-B, the DTPY and nucleobase skeletons are twisted by 4.4 and 14.5°, respectively, from each other. Notably, both molecules form pairs with different kinds of complementary H-bonds: Watson−Crick Hbonds (N···O distance, 2.96 Å) for 1a-A pair and reverse Watson−Crick type (2.87 Å) for 1a-B pair (Figure 1, panels a and b, respectively). Such a coexistence of two kinds of complementary H-bonds in one crystal structure has been occasionally reported in uracil derivatives.24 Both 1a molecules stack in a head-to-tail manner (interplanar distance: 1a-A−1aA; 3.54 Å, 1a-B−1a-B; 3.56 Å, respectively), connecting the Hbonded dimers to form one-dimensional alternating columns (Figure 1a,b). The π-stack dimers of 1a-A and 1a-B further stack alternately in a head-to-tail manner with a interplanar distance of 3.28−4.11 Å and tilt angle of 18.9°, forming a onedimensional (1a-A) 2−(1a-B)2 column along the [01̅1] direction (Figure 1c,d). It should be noted that, in the π-stacks of 1a-A−1a-A, 1a-B−1a-B and 1a-A−1a-B (Figure 1a−c), the electron-rich DTPY skeleton is placed over the electron-poor uracil moiety suggesting the importance of donor−acceptor interaction between DTPY and uracil moieties for the stabilization of these π-stacking structures. Crystal Structure of 1a·CH2Cl2. The vapor diffusion of 1a using CH2Cl2 and hexane afforded the CH2Cl2 solvated

RESULTS AND DISCUSSION Synthesis. Scheme 1 presents the synthetic procedures of DTPY-nucleobases. The key reaction is the Stille-type cross Scheme 1. Synthetic Procedures of DTPY-Nucleobases 1−3a

Reagents and conditions: (a) n-BuLi, THF, −78 °C; Bu3SnCl, −78 °C to rt, quantitative yield; (b) 10 mol % Pd(PPh3)4, 10 or 30 mol % CuI, toluene (reflux) or DMF (70 °C), 46% for 1a, 69% for 1b, 54% for 8, 20% for 3a and 30% for 3b; (c) NH3 aq or n-BuNH2, THF, rt, 57% for both 2a and 2b. a

coupling reaction between iodo-nucleobase derivatives 5−7 and tributylstannylated DTPY which was prepared by the lithiation of DTPY with n-BuLi followed by the treatment with Bu3SnCl. The cytosine derivatives 2a and 2b were prepared by the substituent exchange reaction of the o-nitrophenoxyl group of 8 with amino groups by the treatment with ammonia and nbutylamine, respectively. All these compounds are stable in air at room temperature. Because of the protection of N−H groups, they are soluble to common organic solvents (CH2Cl2, MeCN, THF, alcohols, etc.). Electrochemical Properties. Redox properties of DTPYnucleobases were evaluated by cyclic voltammetry in DMF at room temperature. All electron-donors exhibit two-stage oneelectron oxidation waves of the DTPY skeleton, although the second process (Eox2) for 1a, 3a and 3b is irreversible due to the insolubility of the dication species (Figure S1, Supporting 5817



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Figure 1. Crystal structure of 1a. (a and b) One-dimensional alternating columns of 1a-A and 1a-B formed by Watson−Crick and reverse Watson− Crick type H-bonds and π-stacks. (c) Overlap pattern in the 1a-A and 1a-B stack. (d) (1a-A)2−(1a-B)2 alternating column. Red lines show complementary H-bonds, and two-way arrows present the π-stacks.

Figure 2. Crystal structure of 1a·CH2Cl2. (a) Molecular packing viewed along the c-axis at c = 0 showing the two-dimensional π-layer by π-stacks and reverse Watson−Crick type H-bonds. Butyl groups are omitted for clarity. Red lines show complementary H-bonds, and two-way arrows present the π-stacks. (b) Overlap pattern within the π-layer. (c) The b-axis projection of molecular packing showing the alternating stack of the π-layer and Bu− CH2Cl2 layer.

crystals. One 1a and CH2Cl2 molecules are crystallographically independent within a unit cell. The twist angle of DTPY and uracil moieties is 2.2°, and 1a had a planar structure. Differently from the nonsolvated crystal, only the reverse Watson−Crick type H-bonds (N···O distance, 2.84 Å) are observed, and 1a molecules form a H-bonded pair (Figure 2a). π-Stacks of the pairs (interplanar distance: 3.35−3.56 Å) establish a twodimensional layer parallel to the ab-plane (Figure 2b). Similarly to the crystal structure of nonsolvated 1a (Figure 1a−c), the stacking between electron-rich DTPY and electron-poor uracil moieties is found in the π-layer (Figure 2b). The π-layer and hydrophobic layer comprised of the n-butyl group and CH2Cl2 are arranged alternately along the c-axis (Figure 2c). CO Stretching Modes in Vibration Spectra. Figure 3 illustrates the CO stretching modes (νCO) in the IR spectra of 1a, 1a·CH2Cl2 and 1b. The νCO frequency has been regarded as a useful probe to identify the complementary Hbonding modes of uracil derivatives.25 TTF-n-butyluracil derivative in the solution state (H-bond free) shows two

Figure 3. IR spectra of 1a·CH2Cl2, nonsolvated 1a and 1b in the C O stretching region.

νCO modes at 1716 and 1693 cm−1 (νCO(2) and νCO(4), respectively).12a A Watson−Crick type H-bonded pair in which the C4O group participates in the complementary H-bonds, 5818



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Figure 4. Crystal structure of 2a. (a) One-dimensional alternating column of 2a formed by complementary H-bonds. (b) Overlap pattern in a πstack dimer. (c) The c-axis projection of molecular packing showing a two-dimensional structure at c = 0. Red and green lines show complementary H-bonds and S···S contacts, respectively. Butyl groups are omitted for clarity in (c). Two-way arrows in (a) present the π-stacks, and gray two-way arrows in (c) show the edge-to-face interactions between DTPY and cytosine moieties.

Figure 5. Crystal structure of 3a·2H2O. (a) Molecular packing viewed along the b-axis showing the one-dimensional channel including water molecules. (b) Overlap pattern within the π-stacking column. (c) The π-stacking column and one-dimensional chain of water molecules. DTPY skeleton is shown in half-tone colors. Red thick and thin lines show Watson−Crick type H-bonds of the adenine moieties and H-bonds of water molecules, respectively.

the C4O bond softens to cause a low-frequency shift of νCO(4) band. The νCO(2) and νCO(4) modes of TTF-nbutyluracil forming the Watson−Crick type pairs are observed at 1702 and 1655 cm−1, respectively. In the case of TTFphenyluracil derivative which forms the reverse Watson−Crick type pairs, the νCO(2) mode shifts to a lower frequency region and appears at the same position of the νCO(4) mode (1697 cm−1).12c The 1a·CH2Cl2 crystal, exhibiting reverse Watson−Crick type H-bonds, shows a single band at 1684 cm−1 similar to that observed in TTF-phenyluracil. The nonsolvated 1a crystal shows three νCO modes at 1715, 1684, and 1660 cm−1, suggesting the coexistence of Watson−Crick and reverse Watson−Crick type H-bonds, well coinciding with the crystal structure. In the case of 1b, a single νCO mode was observed at 1714 cm−1 with a tailing down to ∼1650 cm−1 differently from the features of reverse Watson−Crick H-bonds. It has been known that the stabilization energies of Watson− Crick and reversed Watson−Crick type pairs of uracil are close to each other.26 In our previous studies on TTF-uracil derivatives, the complementary H-bond types are modulated by the subtle conditions such as substituent groups at the N1 atom,12c redox state of the TTF moiety12b and crystallization conditions.16 In the case of 1a, inclusion of CH2Cl2 highly affected the overall molecular packing and also two complementary H-bond types.

Crystal Structure of 2a. Single crystals of 2a suitable for Xray crystal structure analysis were prepared by vapor diffusion using toluene and Et2O. The asymmetric unit is composed of one 2a molecule, in which DTPY and cytosine moieties are nearly perpendicular to each other (twist angle, 79.2°). The N2−H···N3 double complementary H-bonds (N···N distance, 2.96 Å, Figure 4a) link the cytosine moieties to form a Hbonded pair. The similar H-bonded motif is observed in the TTF-cytosine system,13 suggesting the robustness of this Hbonding motif. The DTPY skeleton also forms a π-dimer through the small overlap (Figure 4b, interplanar distance =3.47 Å), and these interactions construct a one-dimensional alternating column (Figure 4a). Unlikely to 1a crystals, the cytosine moiety does not participate in the π-stacking motif probably due to the large torsion angle between DTPY and cytosine moieties, while the short edge-to-face C−H···π interactions (2.60 Å) are formed between electron-rich DTPY and electron-poor uracil moieties (gray arrows in Figure 4c). The S1···S1 interaction between adjacent DTPY skeletons (3.68 Å, slightly longer than the sum of van der Waals radius of S atoms, 3.60 Å27) links the alternating columns to build up a two-dimensional sheet parallel to the ab-plane (Figure 4c). Crystal Structure of 3a·2H2O. Single crystals of 3a suitable for the X-ray crystal structure analysis were prepared by the vapor diffusion using DMF and water. The asymmetric unit is composed of one 3a and two water molecules. DTPY and adenine moieties are twisted by 18.0° to each other. The 5819



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complementary N5−H···N4 H-bonds on the adenine moieties form a H-bonded pair of the Watson−Crick type (N···N distance, 2.97 Å, Figure 5a). The 3a molecules further stack with a slip-stack fashion (Figure 5b, interplanar distance, 3.56 Å) to build up a uniform one-dimensional column along the baxis (Figure 5c). Within a π-stack, adjacent DTPY skeletons are stacked to each other, and a small overlap between DTPY and adenine moieties are also found (Figure 5b). The crystalline water molecules form a one-dimensional ladder-like chain parallel to the π-stack column of 3a (Figure 5c, O···O distances, 2.79, 2.81, and 2.93 Å). The one-dimensional structures of 3a and water molecules are further linked through N2···H−O1 Hbonds (Figure 5c, N···O distance, 2.90 Å). Author: In the crystal structure of TTF-adenine derivative,14 a one-dimensional ribbon structure by the Hoogsteen type Hbonds is formed (Scheme 2), where π-stacks between adjacent Scheme 2. Watson−Crick and Hoogsteen Type H-bonded Motifs of Adenine

Figure 6. IR spectra (KBr pellet) of TCNQ complexes of 1−3 and related compounds in the CN stretching region.

neutral TCNQ and TCNQ radical anion species show b1u C N stretching mode at 2225 and 2195 cm−1, respectively. In the TCNQ complexes of 1−3, the bands are observed as weak shoulder peaks around 2207−2210 cm−1, from which ρ of TCNQ moieties are estimated to be −0.39 to −0.45.28 In the solid state electronic spectra (Figure 7), low energy absorption

TTF skeletons are not found; however, that between electronrich TTF and electron-poor adenine moieties is formed. The theoretical calculation indicates that the Watson−Crick and Hoogsteen type H-bonded pairs of adenine possess similar stabilization energies to each other.26 The stronger π-stacking ability of the DTPY skeleton to form a one-dimensional column probably controls the molecular packing and also modulates the H-bonding motif. Charge-Transfer Complexes with TCNQ. CT complexes were prepared by mixing the solutions of 1−3 and TCNQ. The selected physical properties of TCNQ complexes are summarized in Table 3. D−A ratios of the TCNQ complexes of 1a, 2a, 2b and 3a estimated by elemental analysis are 1:1, 3:2, 4:3 and 2:1, respectively. Figure 6 compares CN stretching modes in the IR spectra of TCNQ complexes with those of neutral and radical anion species of TCNQ. The b1u CN stretching frequency of TCNQ derivatives (νCN) is known to be sensitive to ionicity of TCNQ (ρ) and is used as a probe for the estimation.28 The

Figure 7. Electronic spectra of TCNQ complexes of 1−3 in KBr pellet. Arrows indicate the intermolecular CT absorption bands.

Table 3. Properties of TCNQ Complexes of 1−3a νCN/cm−1 [ρ]b (1a)(TCNQ) (2a)3(TCNQ)2 (2b)4(TCNQ)3 (3a)2(TCNQ)

2208 2210 2207 2207

[−0.43] [−0.39] [−0.45] [−0.45]

hvCTc/cm−1 6000 5300 6000 6200

bands assignable to the intermolecular CT between electrondonor and -acceptor molecules are observed at 5000−6000 cm−1.29 These observations indicate that the complexes are weak CT complexes having a neutral ground state (0 < |ρ| < 0.5) in agreement with the estimation of ρ values using CN stretching frequencies. In the electrical conductivity measurements using compressed pellets, although the individual components of the complexes, 1−3 and TCNQ, are insulators (room temperature conductivity (σRT) < 10−8 S cm−1), the complexes show semiconducting behaviors with σRT of 10−6 to 10−7 S cm−1.

σRTd/cm−1 [εa/meV] 2.3 2.5 3.7 3.4

× × × ×

10−6 10−7 10−6 10−7

[337] [312] [204] [e]

a

Molar ratios were estimated from the elemental analyses. Some complexes contained crystal water or crystal solvent. bρ values are estimated from CN stretching frequency in the IR spectra by the Chappell’s method.28 cThe lowest energy CT absorption bands in KBr pellets.29 dElectrical conductivity was measured by the two-probe method on a compressed pellet. eNot measured due to too high resistivity. 5820



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CONCLUSION We have synthesized new H-bonded electron-donors, where DTPY was functionalized with nucleobases, uracil, cytosine and adenine. The combination of complementary H-bonds of nucleobases and π-stacks on the DTPY skeleton constructed diverse supramolecular architectures. These observations indicate that the self-assembling ability of nucleobases and strong π-stacks of DTPY moiety are effective tools for the control of molecular arrangement in the future development of conducting CT complexes based on biological molecular systems. Furthermore, the present result serves as primary and important information in the development of novel molecular architectures with cooperative proton- and electron-transfer (PET) phenomena,9 for which the exploration of H-bonded CT complexes and salts is the most essential strategy.

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ASSOCIATED CONTENT

S Supporting Information *

Synthetic procedures and properties for identification and cyclic voltammograms of 1−3 in PDF format and X-ray crystallographic data for each structure in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Address: Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan. Phone: +81-6-6850-5393. Fax: +81-66850-5395. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partly supported by Grants-in-Aid for Scientific Research (23750039) from the Japan Society for the Promotion of Science, and for Scientific Research on Innovative Area (20110006) and Elements Science and Technology Project from the Ministry of Education, Culture, Sports, Sciences and Technology, Japan.

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