Helical Nanostructures Self-Assembled from Optically Active


Mar 10, 2010 - Effect of central metal ion on the morphology, dimension, and handedness. Ranran Sun , Liang Wang , Jing Tian , Xiaomei Zhang , Jianzhu...
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Helical Nanostructures Self-Assembled from Optically Active Phthalocyanine Derivatives Bearing Four Optically Active Binaphthyl Moieties: Effect of Metal-Ligand Coordination on the Morphology, Dimension, and Helical Pitch of Self-Assembled Nanostructures Lizhen Wu,† Quanbo Wang,† Jitao Lu,† Yongzhong Bian,‡ Jianzhuang Jiang,*,†,‡ and Xiaomei Zhang*,† †

Department of Chemistry, Shandong University, Jinan 250100, China, and ‡Department of Chemistry, University of Science and Technology Beijing, Beijing 100083, China Received November 9, 2009. Revised Manuscript Received February 19, 2010

(R)- and (S)-Enantiomers of optically active metal free tetrakis[11,12:13,14-di(10 ,20 -naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-trieno]-phthalocyanine and their zinc complexes, (R)- and (S)-H2Pc (1) and (R)- and (S)-ZnPc (2), were prepared from the tetramerization of corresponding phthalonitriles, (R)- and (S)-2,3-(40 ,50 -dicyanobenzo)11,12:13,14-di(10 ,20 -naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene, in the absence and presence of Zn(OAc)2 3 2H2O template, respectively, promoted by organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Their selfassembly behavior in the absence and presence of 4,40 -bipyridine has been comparatively investigated by electronic absorption and circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) technique, and X-ray photoelectron spectroscopy (XPS). The metal free phthalocyanine self-assembles into highly ordered fibrous nanostructures (ca. 3 μm length, 70 nm width, and 125 nm helical pitch) with left-handed and right-handed helicity for (R)-1 and (S)-1, respectively, through the hierarchical manner via one-dimensional helices with chirality determined by the optically active binaphthyl side chains. In contrast, self-assembly of the phthalocyaninato zinc analogue leads to the formation of nanoparticles. However, in the presence of 4,40 -bipyridine, additionally formed metal-ligand Zn-N4,40 -bipyridine coordination bonds between the nitrogen atoms of additive 4,40 -bipyridine molecule and the zinc center of (R)- and (S)-2 molecules together with π-π interaction and chiral discrimination of chiral side chains induce a right-handed and left-handed helical arrangement in a stack of (R)and (S)-2 molecules, respectively, which further hierarchically packs into highly ordered fibrous nanostructures of average tens of micrometers in length, 30 nm width, and 106 nm helical pitch with the same helicity to the stack, revealing the effect of metal-ligand coordination bonding interaction on the morphology, dimension, handedness, and helical pitch of self-assembled nanostructures.

Introduction Chirality is one of the most fascinating and complicated features commonly found in nature.1 Inspired by the elegance of biological supramolecular structures, numerous artificial helical supramolecular structures with controlled helicity have been developed depending on various noncovalent interactions.2 In recent years, precise control over the helical packing of π-conjugated molecules has attracted increasing attention owing to their ability to mimic *To whom correspondence should be addressed. E-mail: [email protected], [email protected]; [email protected] (1) (a) Garoff, R. A.; Litzinger, E. A.; Connor, R. E.; Fishman, I.; Armitage, B. A. Langmuir 2002, 18, 6330–6337. (b) Wang, M.; Silva, G. L.; Armitage, B. A. J. Am. Chem. Soc. 2000, 122, 9977–9986. (c) Pasternack, R. F.; Giannetto, A.; Pagano, P.; Gibbs, E. J. J. Am. Chem. Soc. 1991, 113, 7799–7780. (d) Hannah, K. C.; Armitage, B. A. Acc. Chem. Res. 2004, 37, 845–853. (e) Chen, X.; Liu, M. J. Inorg. Biochem. 2003, 94, 106–113. (2) (a) Schmuck, C. Angew. Chem., Int. Ed. 2003, 42, 2448–2452. (b) Nelson, J. C.; Saven, J. G.; Moore, J. S.; Wolynes, P. G. Science 1997, 277, 1793–1796. (c) Cornelissen, J. J. L. M.; Fisher, M.; Sommerdijk, N. A. J. M.; Nolte, R. J. M. Science 1998, 280, 1427–1430. (d) Oda, R.; Schmutz, M.; Candau, S. J.; MacKintosh, F. C. Nature 1999, 399, 566–569. (e) Hirschberg, J. H. K. K.; Brunsveld, L.; Ramzi, A.; Vekemans, J. A. J. M.; Sijbesma, R. P.; Meijer, E. W. Nature 2000, 407, 167–170. (f) Berl, V.; Huc, I.; Khoury, R. G.; Krische, M. J.; Lehn, J.-M. Nature 2000, 407, 720– 723. (g) Zubarev, E. R.; Pralle, M. U.; Sone, E. D.; Stupp, S. I. J. Am. Chem. Soc. 2001, 123, 4105–4106. (h) Sone, E. D.; Zubarev, E. R.; Stupp, S. I. Angew. Chem., Int. Ed. 2002, 41, 1706–1709. (i) Fenniri, H.; Deng, B.-L.; Ribbe, A. E. J. Am. Chem. Soc. 2002, 124, 11064–11072. (j) Giorgi, T.; Lena, S.; Mariani, P.; Cremonini, M. A.; Masiero, S.; Pieraccini, S.; Rabe, J. P.; Samori, P.; Spada, G. P.; Gottarelli, G. J. Am. Chem. Soc. 2003, 125, 14741–14749. (k) Xiao, J.; Xu, J.; Cui, S.; Liu, H.; Wang, S.; Li, Y. Org. Lett. 2008, 10, 645–648.

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biomacromolecules with potential applications in chemical sensors, catalysts, and chiroptical devices.3 Due to the unique planar and rigid molecular geometry and aromatic electronic feature delocalized over the molecular frame, phthalocyanines often exhibit intriguing, peculiar, and tunable spectroscopic, photophysical, and photochemical properties.4 As a consequence, these tetrapyrrole derivatives have received extensive research interest as ideal building blocks for the construction of noncovalent linked supramolecular assemblies with motivation for preparing molecular-based electronic and optical devices such as electronic wires, switches, electroluminescence devices, field-effect transistors, and photovoltaic devices.5 Actually, a lot of well-defined, discrete supramolecular assemblies with (3) (a) Ishi-I, T.; Kuwahara, R.; Takata, A.; Jeong, Y.; Sakurai, K.; Mataka, S. Chem.;Eur. J. 2006, 12, 763–776. (b) Roman, A. E.; Nolte, R. J. M. Angew. Chem., Int. Ed. 1998, 37, 63–68. (c) Yashima, E.; Maeda, K.; Okamoto, Y. Nature 1999, 399, 449–451. (d) Pantos, G. D.; Wietor, J. L.; Sanders, J. K. M. Angew. Chem., Int. Ed. 2007, 46, 2238–2240. (e) Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M. Chem. Rev. 2001, 101, 4039–4070. (f) Palmans, A. R. A.; Vekemans, J. A. J. M.; Havinga, E. E.; Meijer, E. W. Angew. Chem., Int. Ed. 1997, 36, 2648–2651. (g) Stupp, S. I.; LeBonheur, V.; Walker, K.; Li, L. S.; Huggins, K. E.; Keser, M.; Amstutz, A. Science 1997, 276, 384–389. (h) Prins, L. J.; Huskens, J.; F. Jong, D.; Timmerman, P. Nature 1999, 398, 498–502. (4) (a) Lever, A. B. P.; Leznoff, C. C. Phthalocyanine: Properties and Applications; VCH: New York, 1989-1996; Vols. 1-4. (b) McKeown, N. B. Phthalocyanines Materials: Synthesis, Structure and Function; Cambridge University Press: New York, 1998. (c) Kadish, K. M.; Smith, K. M.; Guilard, R. The Porphyrin Handbook; Academic Press: San Diego, 2000-2003; Vols. 1-20.

Published on Web 03/10/2010

DOI: 10.1021/la100061e

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elaborately designed phthalocyanine building blocks have been fabricated thus far. Among which, helical supramolecular architectures fabricated from optically active phthalocyanine compounds attracted widespread research interest in association with their potential applications in the fields of smart soft nanomaterials for data storage and processing, using chiral architectures as template for helical crystallization of proteins, chiral sensing, optobioelectronics, chiroptical devices, catalysis, and biochemistry.6 As a natural result, a relatively a large number of phthalocyanine compounds with chiral substituents have been synthesized and tried to be fabricated into supramolecular architectures.7 However, it is worth noting that installing stereocenters onto the periphery of a phthalocyanine molecule just provides a possibility toward fabrication of helical supramolecular structures. Actually, at the molecular level, quite a large number of phthalocyanine compounds with peripheral subsitutents containing stereocenters even do not display any CD signal in the whole phthalocyanine absorption range due to the weak perturbation from the peripheral substituents with stereocenters to the phthalocyanine core.6b,g,7b,c In a similar manner, many phthalocyanine derivatives bearing peripheral chiral subsitutents with stereocenters could only form normal supramolecular structures without exhibiting helicity.7 Obviously, the delicate interplay of intrinsic intermolecular π-π interaction with additionally introduced intermolecular noncovalent interactions including chiral information discrimination of phthalocyanine compounds should play an important role in forming artificial supramolecular architectures with helicity. Kimura and collaborators prepared chiral fibrous assemblies of phthalocyaninato zinc complexes carrying chiral diol or chiral branched alkyl chains.6g Very recently, this group revealed the formation of elemental one-dimensional helices from an optically active phthalocyanine compound bearing four peripheral chiral menthol side groups.7b Side on aggregation of these helices in turn leads to highly ordered fibrous nanostructures with both right-handed and left-handed helicity. In addition, additives were also revealed to be able to induce the formation of chiral aggregates.8 For example, a phthalocyaninato magnesium compound decorated with eight chiral thioether units did not show any CD signal in toluene solution, which however became CD active in toluene with addition of PdCl2 due to the formation of a twisted H-type dimer depending on the Pd-S coordination bond formed between the introduced palladium ion and sulfur atom of thioether side chains with the help of π-π interaction between neighboring phthalocyanine molecules.9 Nevertheless, a nonoptically active phthalocyanine derivative substituted with thioether groups was revealed to exhibit optical (5) (a) Kimura, M.; Narikawa, H.; Ohta, K.; Hanabusa, K. Chem. Mater. 2002, 14, 2711–2717. (b) Huang, X.; Zhao, F.; Li, Z.; Tang, Y.; Zhang, F.; Tung, C. Langmuir 2007, 23, 5167–5172. (c) de la Escosura, A.; Díaz, M. V. M.; Thordarson, P.; Rowan, A. E.; Nolte, R. J. M.; Torres, T. J. Am. Chem. Soc. 2003, 125, 12300–12308. (d) Chen, P.; Ma, X.; Liu, M. Macromolecules 2007, 40, 4780–4784. (6) (a) Kobayashi, N. Coord. Chem. Rev. 2001, 219-221, 99–123. (b) Liu, H.; Liu, Y.; Liu, M.; Chen, C.; Xi, F. Tetrahedron Lett. 2001, 42, 7083–7086. (c) Liu, H.; Chen, C.; Ai, M.; Gong, A.; Jiang, J.; Xi, F. Tetrahedron Asymmetry 2000, 11, 4915–4922. (d) Kobayashi, N. Chem. Commun. 1998, 487–488. (e) Kobayashi, N.; Kobayashi, Y.; Osa, T. J. Am. Chem. Soc. 1993, 115, 10994–10995. (f) Kimura, M.; Ueki, H.; Ohta, K.; Shirai, H.; Kobayashi, N. Langmuir 2006, 22, 5051–5056. (g) Kimura, M.; Kuroda, T.; Ohta, K.; Hanabusa, K.; Shirai, H.; Kobayashi, N. Langmuir 2003, 19, 4825–4830. (7) (a) Engelkamp, H.; Middelbeek, S.; Nolte, R. J. M. Science 1999, 284, 785– 788. (b) Lv, W.; Wu, X.; Wu; Bian, Y.; Jiang, J.; Zhang, X. ChemPhysChem 2009, 10, 2725–2732. (c) Rai, R.; Saxena, A.; Ohira, A.; Fujiki, M. Langmuir 2005, 21, 3957– 3962. (8) (a) John, G.; Jung, J. H.; Minamikawa, H.; Yoshida, K.; Shimizu, T. Chem.;Eur. J. 2002, 8, 493–497. (b) Thomas, B. N.; Lindemann, C. M.; Corcoran, R. C.; Cotant, C. L.; Kirshch, J. E.; Persichini, P. J. J. Am. Chem. Soc. 2002, 124, 1227– 1233. (c) Svenson, S.; Messersmith, P. B. Langmuir 1999, 15, 4464–4471. (9) Adachi, K.; Chayama, K.; Watarai, H. Langmuir 2006, 22, 1630–1639. (10) Adachi, K.; Chayama, K.; Watarai, H. Chirality 2006, 18, 599–608.

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Wu et al. Scheme 1. Schematic Molecular Structures of Phthaolcyanine Derivatives (R)-/(S)-H2Pc (1), (R)-/(S)-ZnPc (2), and 4,40 -Bipyridine

chirality after adding the chiral Pd(II)-BINAP complex.10 However, it must be emphasized that, despite the extensive studies over the self-assembled nanostructures with controlled helicity, fabrication of functional molecules into a prerequisite nanostructure with desirable morphology, dimension, and handedness through tuning the intermolecular interaction via chemical modification and additive still remains a great challenge for molecular materials with a conjugated electronic structure including phthalocyanines. In the present paper, we describe the design and synthesis of optically active tetrakis[11,12:13,14-di(10 ,20 -naphtho)-1,4,7,10,15, 18-hexaoxacycloeicosa-2,11,13-trieno]-phthalocyanine derivatives, (R)- and (S)-MPc (M = 2H, Zn) (1, 2) (Scheme 1). Their selfassembly behavior in the absence and presence of 4,40 -bipyridine was comparatively investigated, revealing the effect of metal-ligand coordination bonding interaction on the morphology, dimension, handedness, and actually the helical pitch of self-assembled nanostructures. The present results will be helpful in providing new insight into chiral information transfer and expression for synthetic conjugated systems at the supramolecular level.

Experimental Section General. 1-Pentanol was freshly distilled just before use. Column chromatography was carried out on silica gel (Merck, Kieselgel 60, 200-300 mesh) with the indicated eluents. Optically pure (R)- and (S)-2,20 -dihydroxy-1,10 -binaphthyl (>99% ee) were obtained from Dalian Reagent Company. All other solvents were used as received without further treatment. (R)- and (S)-Tetrakis[11,12:13,14-di(10 ,20 -naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-trieno]-phthalocyanine, (R)- and (S)-H2Pc (1) together with (R)- and (S)-2,3-(40 ,50 -dicyanobenzo)-11,12:13,14-di(10 ,20 naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene were prepared according to the published procedures.6c Nanostructure Fabrication. The self-assembled nanofibers fabricated from the (R)- or (S)-ZnPc (2) with addition of 4,40 bipyridine were prepared by the solution mixture method according to the following procedure.11 An equal volume of n-hexane (11) (a) Balakrishnan, K.; Datar, A.; Oitker, R.; Chen, H.; Zuo, J.; Zang, L. J. Am. Chem. Soc. 2005, 127, 10496–10497. (b) Su, W.; Zhang, Y.; Zhao, C.; Li, X.; Jiang, J. ChemPhysChem 2007, 8, 1857–1862. (c) Lu, G.; Zhang, X.; Cai, X.; Jiang, J. J. Mater. Chem. 2009, 2417–2424. (d) Gong, X.; Milic, T.; Xu, C.; Batteas, J. D.; Drain, C. M. J. Am. Chem. Soc. 2002, 124, 14290–14291. (e) Lu, G.; Chen, Y.; Zhang, Y.; Bao, M.; Bian, Y.; Li, X.; Jiang, J. J. Am. Chem. Soc. 2008, 130, 11623–11630. (f) Gao, Y.; Zhang, X.; Ma, C.; Li, X.; Jiang, J. J. Am. Chem. Soc. 2008, 130, 17044–17052.

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Figure 1. Electronic absorption and circular dichroism (CD) spectra for (R)- and (S)-H2Pc (1) together with their self-assembled nanostructures. CD spectra of (R)- and (S)-1 in dilute chloroform solution (A); electronic absorption spectra of H2Pc (1) in dilute chloroform solution (dashed line) and nanostructures of H2Pc (1) dispersed in n-hexane (solid line) (B); CD spectra of nanostructures of (R)- and (S)-1 dispersed in n-hexane (C); nanofibers fabricated from (R)- and (S)-1 observed by TEM (D) and SEM (E); high-magnification SEM image of structures fabricated from (R)- and (S)-1 indicating the bunchy growth (e); high-magnification SEM image of structures fabricated from (R)-1 showing left-handed fibrous nanostructure (F); high-magnification SEM image of structures fabricated from (S)-1 showing right-handed fibrous nanostructure (G).

solution (4 mL) was injected into a homogeneous chloroform solution (4 mL) containing (R)- or (S)-2 (0.48 mg, 5  10-5 M) and 4,40 -bipyridine (0.04 mg, 6  10-5 M). After the solution was allowed to equilibrate at ambient temperature for 2 days, loose aggregates were observed. These precipitates were then transferred to the carbon-coated grid by pipetting for TEM and SEM observations. The nanoparticles and nanofibers fabricated from (R)-/(S)-2 and (R)-/(S)-1, respectively, were prepared by the same method without adding 4,40 -bipyridine. The experimental results were stable and reproducible under the experimental conditions described above. Measurements. 1H NMR spectra were recorded on a Bruker DPX 300 spectrometer (300 MHz) in CDCl3 using the residual solvent resonance of CHCl3 at 7.26 ppm relative to SiMe4 as internal reference. Fourier transform infrared spectra (IR) were recorded in KBr pellets with 2 cm-1 resolution using an RALPHAT spectrometer. MALDI-TOF mass spectra were taken on a Bruker BIFLEX III ultrahigh resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer with Rcyano-4-hydroxycinnamic acid as matrix. Elemental analyses were performed on an Elementar Vavio El III instrument. Transmission electron microscopy (TEM) images were measured on a JEOL100CX II electron microscope operated at 100 kV. Scanning electron microscopy (SEM) images were obtained using a JEOL JSM-6700F field-emission scanning electron microscope. For TEM imaging, a drop of sample solution was cast onto a carbon copper grid and flushed with methanol. For SEM imaging, Au (1-2 nm) was sputtered onto the grids to prevent charging effects and to improve the image clarity. Circular dichroism (CD) measurement and electronic absorption spectra were carried out on a JASCO J-810 spectropolarimeter. X-ray photoelectron spectroscopy (XPS) was carried out on PHI 5300 ESCA system (PerkinElmer). The excitation source is Al KR radiation. Low-angle X-ray diffraction (XRD) measurements were carried out on a Rigaku D/ max-γB X-ray diffractometer.

Preparation of (R)- and (S)-Tetrakis[11,12:13,14-di(10 ,20 naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-trieno]phthalocyaninato Zinc Complexes (R)- and (S)-ZnPc (2). A mixture of (R)- or (S)-2,3-(40 ,50 -dicyanobenzo)-11,12:13,14-

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di(10 ,20 -naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene (0.1365 g, 0.23 mmol), Zn(OAc)2 3 2H2O (0.0128 g, 0.058 mmol), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU; 0.004 g, 0.023 mmol) in n-pentanol (4 mL) was heated to reflux under nitrogen for 56 h. Then the reaction mixture was cooled to room temperature, and methanol (20 mL) was added. The crystalline residue was collected by filtration, washed with methanol, and purified by silica gel column chromatography with chloroform/methanol [100:3 (v/v)] as eluent. The crude product was purified by repeated chromatography followed by recrystallization from chloroform and n-hexane. Yield for (R)- or (S)-ZnPc (2): 0.0699 g (50%), green solid. 1H NMR data recorded by 300 MHz in CDCl3: 3.72-4.18 (br m, 64H, CH2), 7.12-7.82 (br m, 56H, ArH). MS: calcd for C144H120N8O24Zn (M)þ, 2411.9; found, m/z 2411.0. Anal. calcd (%) for C144H120N8O24Zn 3 0.5CHCl3: C, 70.22; H, 4.91; N, 4.53. Found: C, 70.09; H, 5.21; N, 4.24.

Results and Discussion Molecular Design, Synthesis, and Characterization. Because of the dominant intermolecular π-π interaction between phthalocyanine molecules with large conjugated electronic structure, one-dimensional supramolecular structures are usually prepared from the self-assembling process of phthalocyanine derivatives. Incorporating chiral groups (actually chiral discrimination information) onto the peripheral positions of the phthalocyanine ring therefore provides the possibility to fabricate helical supramolecular structures. In comparison with the chiral side chains containing chiral carbons, peripherally attached optically active aromatic substituents often show intensified asymmetric perturbation to the phthalocyanine chromophore. With this idea in mind, optically active binaphthayl units were chosen to be incorporated onto the peripheral positions of the phthalocyanine ligand via the crown ether unit. Meanwhile, the hexa-coordination preferred zinc ion is introduced into the central hole of the phthalocyanine ligand, which is expected to provide an additional chance to tune the morphology and dimension of chiral aggregates based on the formation of axial metal-ligand coordination bonds. DOI: 10.1021/la100061e

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Figure 2. Electronic absorption and circular dichroism (CD) spectra for (R)- and (S)-ZnPc (2) together with their self-assembled nanostructures. CD spectra of (R)- and (S)-2 in dilute chloroform solution (A); electronic absorption spectra of ZnPc (2) in dilute chloroform solution (dashed line) and nanostructures fabricated from (R)- and (S)-2 in the absence of 4,40 -bipyridine dispersed in n-hexane (solid line) (B); CD spectra of nanostructures fabricated from (R)- and (S)-2 in the absence of 4,40 -bipyridine dispersed in n-hexane (C); CD spectra of (R)and (S)-2 in dilute chloroform solution (D); electronic absorption spectra of ZnPc (2) in dilute chloroform solution (dashed line) and nanostructures fabricated from (R)- and (S)-2 in the presence of 4,40 -bipyridine dispersed in n-hexane (solid line) (E); CD spectra of nanostructures fabricated from (R)- and (S)-2 in the presence of 4,40 -bipyridine dispersed in n-hexane (F); nanoparticles fabricated from 2 in the absence of 4,40 -bipyridine observed by TEM (G) and SEM (H); nanofibers fabricated from 2 in the presence of 4,40 -bipyridine observed by TEM (I) and SEM (J); high-magnification TEM image of structures fabricated from (R)-2 in the presence of 4,40 -bipyridine showing lefthanded fibrous nanostructure (K); high-magnification TEM image of structures fabricated from (S)-2 in the presence of 4,40 -bipyridine showing right-handed fibrous nanostructure (L).

Metal free (R)- and (S)-tetrakis[11,12:13,14-di(10 ,20 -naphtho)1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-trieno]-phthalocyanine compounds, (R)- and (S)-H2Pc (1), were prepared according to a published procedure.6c The corresponding phthalocyaninato zinc complexes (R)- and (S)-ZnPc (2) were obtained in good yield from the cyclic tetramerization of corresponding phthalonitriles, (R)and (S)-2,3-(40 ,50 -dicyanobenzo)-11,12:13,14-di(10 ,20 -naphtho)1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene6c with Zn(OAc)2 3 2H2O as template in the presence of DBU in refluxing n-pentanol. Satisfactory elemental analysis results were obtained for the newly prepared zinc complexes after repeated column chromatography followed by recrystallization. The MALDI-TOF mass spectra of these complexes clearly showed an intense signal for the molecular ion (M)þ. The enantiomeric zinc complexes were also characterized with a range of spectroscopic methods. The 1H NMR spectra of (R)- or (S)-2 were recorded in CDCl3 at room temperature. All the signals can be readily assigned; see Figure S1 in the Supporting Information. Electronic Absorption and Circular Dichroism (CD) Spectroscopy. The electronic absorption and circular dichroism (CD) spectra of both phthalocyanine derivatives (R)-/(S)-H2Pc (1) and (R)-/(S)-ZnPc (2) in CHCl3 were recorded, and the data are compiled in Table S1 in the Supporting Information. As expected, 1 and 2 showed typical features of metal free and phthalocyaninato metal compounds,12 respectively, in their electronic absorption spectra, revealing the nonaggregated molecular spectroscopic nature of both compounds in CHCl3. As shown in Figure 1B, the absorption around 338 nm for 1 can be attributed to the phthalocyanine Soret band, while two strong split absorpt(12) (a) Li, R.; Zhang, X.; Zhu, P.; Ng, D. K. P.; Kobayashi, N.; Jiang, J. Inorg. Chem. 2006, 45, 2327–2334. (b) Bian, Y.; Li, L.; Dou, J.; Cheng, D. Y. Y.; Li, R.; Ma, C.; Ng, D. K. P.; Kobayashi, N.; Jiang, J. Inorg. Chem. 2004, 43, 7539–7544.

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ions at 646 and 682 nm with two weak shoulders at 589 and 624 nm are assigned to the phthalocyanine Q bands. The weak absorption around 415 nm is common for alkoxyl-substituted phthalocyanines due to an nfπ* transition.13 Upon complexation with the zinc metal ion, the increase in the molecular symmetry from C2h for H2Pc (1) to C4h for ZnPc (2) induces the change in the electronic absorption spectrum from a typical feature for metal free phthalocyanine to that for a typical phthalocyaninato metal species (Figure 2B or E).14 The phthalocyanine Soret band is observed at 352 nm, and the Q absorption appears at 661 nm as a very strong band with a weak vibronic shoulder at 559 nm for 2 in CHCl3. The weak absorption at 420 nm is also due to the nfπ* transition. It is noteworthy that the intense absorption below 300 nm appearing in the electronic absorption spectra of both compounds is attributed to the absorption of binaphthyl groups, which is supported by the corresponding CD signals for (R)-/(S)-1 and (R)-/(S)-2 in the same region in their CD spectra (Figures 1A and 2A or D).14 It can be seen from the CD spectra that introduction of the optically active binaphthyl moieties via a crown ether unit onto the peripheral positions of phthalocyanine ligand induces the appearance of CD signals in both the Soret and Q absorption regions of the two phthalocyanine derivatives, indicating the effective chiral information transfer from the optically active binaphthyl moieties to the phthalocyanine chromophore at the molecular level. In detail, for (R)-1 and (R)-2, the sign of the CD is (13) (a) Zhang, Y.; Zhang, X.; Liu, Z.; Bian, Y.; Jiang, J. J. Phys. Chem. A 2005, 109, 6363–6370. (b) Sheng, N.; Li, R.; Choi, C.-F.; Su, W.; Ng, D. K. P.; Cui, X.; Yoshida, K.; Kobayashi, N.; Jiang, J. Inorg. Chem. 2006, 45, 3794–3802. (14) In order to clearly compare the electronic absorption and circular dichroism spectra of the (R)- and (S)-ZnPc (2) in dilute chloroform with their aggregates fabricated from (R)- and (S)-2 with and without the addition of 4,40 -bipyridine, the electronic absorption and circular dichroism spectra of (R)- and (S)-2 in dilute chloroform are shown in Figure 2B, E, A, and D.

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mainly positive over the main Soret and Q bands, while conversely (S)-1 and (S)-2 show a mainly negative CD sign. According to the chiral exciton theory,15 (R)-1 and (R)-2 are right-handed while (S)1 and (S)-2 left-handed on the basis of the CD pattern in the range of 250-300 nm. The electronic absorption and CD spectra of the aggregates formed from (R)- and (S)-H2Pc (1) in n-hexane as well as those from (R)- and (S)-ZnPc (2) in the absence and presence of 4,40 bipyridine are also recorded and shown in Figures 1B,C and 2B,C, E, and F, respectively, which are different from the spectra of corresponding compounds in CHCl3. As shown in Figure 1B, when metal free phthalocyanine 1 self-assembles into aggregates, both the Soret and Q bands for 1 lose some intensity. In particular, the Soret band for the aggregates takes a slight redshift with the maximum at 344 nm. Meanwhile, the well-defined Q bands of metal free phthalocyanine 1 at 646 and 682 nm disappear and a very broad absorption band appears in the lower energy side of (646 þ 682)/2 = 664 nm with the maximum at 672 nm in the aggregate electronic absorption spectrum. In comparison with the electronic absorption spectrum of 2 in dilute chloroform solution, the main phthalocyanine Q band at 661 nm in CHCl3 for 2 was found to be broadened in its aggregate electronic absorption spectrum in n-hexane with the maximum red-shifting to 682 nm (Figure 2B). In addition, the phthalocyanine Soret band at 352 nm blue-shifts to 341 nm. In contrast, addition of 4,40 bipyridine during the self-assembly process of 2 induces a slight blue-shift for the main phthalocyanine Q absorption with the maximum at 659 nm and a relatively significant blue-shift for phthalocyanine Soret band with the maximum at 345 nm (Figure 2E), revealing the enhanced intermolecular interaction due to the additionally introduced metal-ligand Zn-N4,40 -bipyridine coordination bonds. On the basis of Kasha et al.’s exciton theory,16 a red-shift in the main absorption bands of H2Pc (1) and ZnPc (2) upon aggregation in the absence of any additive reveals that the phthalocyanine molecules self-assemble into J aggregates with a head-to-tail molecular arrangement in their nanostructures. In contrast, the blue-shifted absorption bands in the electronic absorption spectra of aggregates of 2 formed in the presence of 4,40 -bipyridine are typically a sign of the effective π-π interaction between the ZnPc molecules, indicating the formation of H aggregates and revealing a face-to-face molecular arrangement in these nanostructures. Comparison with the electronic absorption spectrum of 1 in n-hexane, the larger degree of redshift in the main absorption bands of 2 upon aggregation in the absence of 4,40 -bipyridine observed indicates a stronger interaction between ZnPc molecules in aggregates because of the formation of additional metal-ligand (Zn-Ocrown ether) coordination bonds between the crown ether substituents of one phthalocyaninato zinc molecule and central zinc ion of neighboring molecule.17 Furthermore, observation of the change from redshift of the main absorption bands for 2 upon aggregation in the absence of 4,40 -bipyridine to blue-shift for the same complex in the presence of 4,40 -bipyridine reveals the effect of Zn-N4,40 -bipyridine coordination bonding interaction formed between the central metal ion of phthalocyaninato zinc molecule and nitrogen atom of added 4,40 -bipyridine molecule on tuning the molecular packing mode and in turn the aggregate morphology. These (15) (a) Harada, H.; Nakanishi, K. Circular Dichroic Spectroscopy, Exciton Coupling in Organic Stereochemistry University Science Books: New York, 1983. (b) Kobayashi, N. Chem. Commun. 1998, 487–488. (16) Kasha, M.; Rawls, H. R.; EI-Bayoumi, M. A. Pure Appl. Chem. 1965, 11, 371–392. (17) Gao, Y.; Chen, Y.; Li, R.; Bian, Y.; Li, X.; Jiang, J. Chem.;Eur. J. 2009, 15, 13241–13252.

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results are in line with the morphology of the aggregates and the X-ray photoelectron spectroscopic results as detailed below. In the CD spectra of aggregates fabricated from (R)- and (S)H2Pc (1) as well as (R)- and (S)-ZnPc (2) in the absence and presence of 4,40 -bipyridine (Figures 1C and 2C, F), perfect mirroring Cotton effects were observed, indicating the successful chiral expression on the phthalocyanine chromophore at the supramolecular level. According to the semiempirical method developed by Nakanishi and co-workers,18 the given sign of coupling and the direction of dipole moments can be used to determine the chirality of stacked phthalocyanine molecules in aggregates. In general, the CD spectrum featuring a bisignate Cotton effect showing a positive feature at longer wavelength and a negative one at shorter wavelength indicates the right-handed chirality of the dipole moments (positive chirality), while conversely left-handed chirality (negative chirality). In the present case, all the phthalocyanine derivatives display two strong bisignated (with the same direction of dipole moments) Cotton effects, with a crossover at 351 and 607 nm for (R)- and (S)-H2Pc (1) aggregates formed in the absence of 4,40 -bipyridine, 351 and 642 nm for (R)- and (S)-ZnPc (2) aggregates formed in the absence of 4,40 -bipyridine, and 347 and 628 nm for (R)- and (S)-2 aggregates formed in the presence of 4,40 -bipyridine, corresponding to the Soret and Q bands of 1, 2, and 2/4,40 -bipyridine aggregates. As a consequence, the negative chirality of (S)-1, (R)-2, and (R)-2/4,40 bipyridine aggregates corresponds to a left-handed helical arrangement, and the positive chirality of (R)-1, (S)-2, and (S)-2/ 4,40 -bipyridine aggregates indicates a right-handed helical arrangement of corresponding molecules in a stack of corresponding phthalocyanine derivative in aggregates, respectively. The formation of the supramolecular helicity, revealed by CD spectroscopy, is further unequivocally confirmed by SEM and TEM analysis of aggregates as detailed below. Morphology of the Aggregates. The morphology of the aggregates formed was examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Samples were prepared by casting a drop of sample solution onto a carboncoated grid. When injecting an equal volume of n-hexane solution in a homogeneous chloroform solution containing corresponding phthaolcyanine derivatives, nanostructures were obtained when the mixture solvent was equilibrated for 2 days. As can be found in Figure 1D and E, both (R)- and (S)-H2Pc (1) enantiomers selfassemble into long, twisted fibrous nanostructures, which are approximately 70 nm in width and 3 μm in length. In a highmagnification SEM image (Figure 1e), it is clearly shown that these fibers consist of bundles of single, twisted strands. Careful inspection indicates that these nanofibers with left-handed and right-handed helicity were formed from (R)- and (S)-1 enantiomers, respectively, which were clearly revealed by two highmagnification SEM images, chosen simultaneously from (R)and (S)-1 aggregates, respectively (Figure 1F and G). Analysis of a single fibrous nanostructure fabricated from (R)- and (S)-1 enantiomers shows the average helical pitch is about 125 nm, with an angle (the angle of the groove with respect to the main fiber axis) of about 46°. As discussed above, the CD signal demonstrated that a right-handed and left-handed helical arrangement was formed from (R)- and (S)-1 enantiomers in a stack of the metal free phthalocyanine molecules in aggregates, respectively. (18) (a) Berova, N.; Nakanishi, K.; Woody, R. CircularDichroism: Princples and Applications, 2nd ed.; Wiley-VCH: New York, 2000; pp 337-382. (b) Hofacker, A. L.; Parquette, J. R. Angew. Chem., Int. Ed. 2005, 44, 1053–1057. (c) Balaz, M.; Holmes, A. E.; Benedetti, M.; Rodriguez, P. C.; Berova, N.; Nakanishi, K.; Proni, G. J. Am. Chem. Soc. 2005, 127, 4172–4173. (d) Borovkov, V. V.; Lintuluoto, J. M.; Fujiki, M.; Inoue, Y. J. Am. Chem. Soc. 2000, 122, 4403–4407.

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Figure 3. XRD profile of the nanostructures of H2Pc (1) (A); schematic representation of a H2Pc (1) molecule (B); XRD profile of the nanostructures fabricated from ZnPc (2) in the presence of 4,40 -bipyridine (C); schematic representation of a ZnPc (2) molecule, a 4,40 bipyridine molecule, and a ZnPc (2)/4,40 -bipyridine polymer (D).

However, observation of nanostructures with just opposite helicity to the stack fabricated from either (R)- or (S)-1 enantiomer according to the SEM result clearly reveals the hierarchical selfassembly nature of this metal free phthalocyanine compound. In detail, the (R)-1 molecules first self-assemble into one-dimensional right-handed helices with positive chirality (Figure 1C), which act as elementary building blocks and further stack into highly ordered fibrous nanostructures with left-handed helicity (Figure 1F). In the case of the (S)-1 enantiomer, the left-handed helices with negative chirality (Figure 1C) are formed at the first stage of aggregation and then stack into highly ordered nanofibers with right-handed helicity (Figure 1G). In comparison with metal free phthalocyanine, self-assembly of the phthalocyaninato zinc complex in the absence of 4,40 -bipyridine leads to the formation of large scale nanoparticles with the average particle radius of 1.25 μm (Figure 2G and H). However, in the presence of 4,40 -bipyridine, the morphology of nanostructures for both (R)- and (S)-ZnPc (2) was changed. Figure S2 in the Supporting Information shows the quantitative effect of 4,40 bipyridine on the aggregated morphology of (R)- and (S)-2. As can be found, when the molecular ratio between 4,40 -bipyridine and (R)-/(S)-2 was below 1, short nanofibers and nanoparticles were obtained. However, when the ratio between 4,40 -bipyridine and (R)-/(S)-2 reached or became larger than 1, only nanofibers were observed. Further careful inspection over these nanofibers fabricated from (R)- and (S)-2 revealed that the dimension of these one-dimensional nanostructures remains almost unchanged along with the change in the molecular ratio between 4,40 bipyridine and (R)- or (S)-2 with tens of micrometers in length and ca. 30 nm width [Figures 2 and S2 (Supporting Information)], indicating the effect of added 4,40 -bipyridine on the dimension of nanofibers formed. In high-magnification TEM images (Figure 2K and L), it can be seen that these one-dimensional nanostructures are formed by twisting together several single helical fibers with left-handed helicity for (R)-2/4,40 -bipyridine and right-handed helicity for (S)-2/4,40 -bipyridine. Further careful analysis of a single fibrous nanostructure fabricated from (R)and (S)-2/4,40 -bipyridine reveals a smaller average angle (the 7494 DOI: 10.1021/la100061e

angle of the groove with respect to the main fiber axis, 34°, and a relatively shorter helical pitch length, ca. 106 nm, in comparison with that formed from metal free phthalocyanine 1, 46° and 125 nm). In comparison with the aggregates formed from 1 in n-hexane, stronger intermolecular interaction between ZnPc molecules in aggregates, fabricated in the absence of 4,40 -bipyridine, was observed due to the formation of metal-ligand (Zn-Ocrown ether) coordination bonds as mentioned in the electronic absorption section. However, the formation of Zn-Ocrown ether coordination bonds also leads to a decreased distance between neighboring phthalocyaninato zinc molecules, resulting in an increased steric hindrance between bulky side chains of neighboring molecules. This in turn prevents phthalocyaninato zinc molecules from packing into a long-range ordering and finally induces the formation of nanoparticles. In contrast, in the presence of 4,40 -bipyridine, formation of metalligand (Zn-N4,40 -bipyridine) coordination bonds between additionally introduced 4,40 -bipyridine and central zinc ion of 2 enhances the intrinsic π-π interaction between neighboring ZnPc molecules, resulting in one-dimensional helical nanostructures with fibrous morphology. In addition, in line with the metal free analogues, both (R)- and (S)-2 enantiomers self-assemble into the one-dimensional helical nanostructures with fibrous morphology also in a hierarchical manner. According to the CD spectroscopic results (Figure 2F), in the presence of 4,40 -bipyridine, (R)- and (S)-2 first form the onedimensional helices with left-handed and right-handed helical arrangement, respectively, which act as elementary building blocks and further stack into highly ordered fibrous nanostructures with the same helicity (Figure 2K and L). At the end of this section, it is noteworthy that left-handed and right-handed helical arrangements were also revealed in the stack of phthalocyaninato zinc molecules in the aggregates formed from (R)- and (S)-2, respectively, in the absence of 4,40 -bipyridine according to CD spectroscopy results. X-ray Diffraction Patterns of the Aggregates. The internal structure of self-assembled nanostructures was further investigated by X-ray diffraction (XRD) technique. Figure 3 exhibits the diffraction patterns of the self-assembled nanostructures formed from H2Pc (1) in the absence of 4,40 -bipyridine and ZnPc (2) in the presence of 4,40 -bipyridine. As can be seen from Figure 3A, the Langmuir 2010, 26(10), 7489–7497

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XRD diagram of H2Pc nanofibers shows one broad diffraction peak at 2θ = 3.08° (corresponding to 2.87 nm) in the low angle range and two relatively weak peaks at 2θ = 10.48 and 21° (corresponding to 0.84 and 0.42 nm) in the wide angle range, originating from the (010), (001), and (002) planes. Among which, the diffraction peaks at 2.87 and 0.84 nm correspond to the length and height of a H2Pc molecule according to the geometry optimization and energy minimized molecular structure of metal free phthalocyanine 1 using the Gaussian 98 program at the B3LYP/6-31G(d) level19 (Figure 3B). In addition, the H2Pc nanofibers present another sharp refraction at 0.32 nm in the wide angle region due to the stacking distance between neighboring phthalocyanine rings along the direction perpendicular to the phthalocyanine rings, in line with previous investigation results.20 In the low angle range of the XRD diagram (Figure 3C), the nanofibers formed from ZnPc (2) in the presence of 4,40 -bipyridine show a strong refraction peak at 2θ = 1.30° (6.80 nm) and two relatively weak refractions at 1.94° (4.53 nm) and 2.60° (3.40 nm), which are ascribed to the refractions from the (002), (003), and (004) planes. In addition, the XRD pattern also displays another broad peak at 3.00° (2.95 nm) originating from the (010) plane. On the basis of the geometry optimization and energy minimized molecular structure of 2 using the Gaussian 98 program at the B3LYP/6-31G(d) level,19 the dimensional size for a phthalocyaninato zinc molecule is about 2.95 nm (both length and width), while for a 4,40 -bipyridine molecule the size is about 0.71 nm (length) (Figure 3D). Considering the average Zn-N4,40 -bipyridine coordination bond distance, 0.21 nm, revealed by single crystal X-ray diffraction analysis,21 the sharp peaks observed at 3.40, 4.53, and 6.80 nm in the XRD diagram of nanofibers of 2 formed in the presence of 4,40 -bipyridine can therefore be assigned to the length from the central zinc ion of the first phthalocyaninato zinc molecule to the central zinc ion of the fourth, fifth, and seventh phthalocyaninato zinc molecules, respectively, as shown in Figure 3D. In the meantime, the diffraction peak at 2.95 nm corresponds to the length of a ZnPc (2) molecule. It is noteworthy that, due to the limitation of the diffraction angle range during the lower angle X-ray diffraction measurement, the refraction from the (001) plane was not detected. However, observation of the higher order refraction peak of the (001) plane suggests the high molecular ordering nature of this nanostructure along this direction. This result is in line with the speculated assembly mechanism as detailed below. (19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.05; Gaussian, Inc.: Pittsburgh, PA, 2003. (20) (a) Janczak, J.; Idemori, Y. M. Inorg. Chem. 2002, 41, 5059–5065. (b) Gardberg, A. S.; Yang, S.; Hoffman, B. M.; Ibers, J. A. Inorg. Chem. 2002, 41, 1778–1781. (21) (a) Soldatov, D. V.; Tinnemans, P.; Enright, G. D.; Ratcliffe, C. I.; Diamente, P. R.; Ripmeester, J. A. Chem. Mater. 2003, 15, 3826–3840. (b) Litvinov, A. L.; Konarev, D. V.; Kovalevsky, A. Yu.; Neretin, I. S.; Coppens, P.; Lyubovskaya, R. N. Cryst. Growth Des. 2005, 5, 1807–1819. (c) Shukla, A. D.; Dave, P. C.; Suresh, E.; Das, A.; Dastidar, P. J. Chem. Soc., Dalton Trans. 2000, 4459–4463. (d) Haas, M.; Liu, S.-X.; Neels, A.; Decurtins, S. Eur. J. Org. Chem. 2006, 5467–5478. (e) Zeng, Q.; Wu, D.; Wang, C.; Lu, J.; Ma, B.; Shu, C.; Ma, H.; Li, Y.; Bai, C. CrystEngComm 2005, 7, 243–248. (f) Geiss, A.; Vahrenkamp, H. Inorg. Chem. 2000, 39, 4029–4036.

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Figure 4. Schematic illustration for the hierarchical formation of helical nanostrucutres fabricated from (R)- and (S)-H2Pc (1).

XPS Analysis. To confirm the existence of Zn-Ocrown ether coordination bonds between the crown ether unit of the phthalocyaninato zinc molecule and zinc center of neighboring molecules in the aggregates of 2 formed in the absence of 4,40 -bipyridine and Zn-N4,40 -bipyridine coordination bonds between the zinc center and added 4,40 -bipyridine in the aggregates of 2 formed in the presence of 4,40 -bipyridine, X-ray photoelectron spectroscopy (XPS) was employed to detect the zinc ion circumstance. Figure S3 in the Supporting Information displays the XPS spectra of 2 in chloroform and aggregates formed from 2 in the absence and presence of 4,40 -bipyridine. As expected, all the three samples show typical signals for the Zn2þ ion in their XPS spectra.22 However, the Zn2þ signals in the XPS spectra of both aggregates of 2 formed in the absence and presence of 4,40 -bipyridine obviously shift to the lower bonding energy direction in comparison with those of 2 in chloroform, indicating the change of Zn2þ circumstance after the self-assembly process due to the formation of Zn-Ocrown ether and Zn-N4,40 -bipyridine coordination bonds in the aggregates of ZnPc (2) formed in the absence and presence of 4,40 -bipyridine. Assembly Mechanism. According to Nolte and co-workers,7a three types of helical structures could be imagined in the helical arrangement of optically active phthalocyanine derivatives. First, the phthalocyanine molecules are arranged in a “spiral-staircaselike” manner. Second, the rings may be positioned on top of each other but with a nearly constant staggering angle between neighboring phthalocyanines and always in the same direction. Third, the normal of the plane of each phthalocyanine ring may be tilted and gradually rotated along the stacking axis. If structures of the first and third type were formed in the self-assembly process of (R)- or (S)-H2Pc (1), the stacking distance observed via the X-ray reflection would be much shorter than that of the second type. As described above, a stacking distance of 0.32 nm was revealed for nanostructures of 1 according to the X-ray diffraction analysis, which corresponds well with that revealed for selfassembled nanostructures formed from normal phthalocyanine (22) (a) Hunsicker, R. A.; Klier, K. Chem. Mater. 2002, 14, 4807–4811. (b) Gaskell, K. J.; Starace, A.; Langell, M. A. J. Phys. Chem. C 2007, 111, 13912– 13921. (c) Mielczarski, J. A.; Cases, J. M.; Alnot, M.; Ehrhardt, J. J. Langmuir 1996, 12, 2531–2543.

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Figure 5. Schematic illustration for the hierarchical formation of helical nanostructures fabricated from (R)- and (S)-ZnPc (2) in the presence of 4,40 -bipyridine.

derivatives.6g,f,7 This result therefore suggests that (R)- and (S)-1 self-assemble into helical structures most likely according to the second type manner (Figure 4). This is also true for the selfassembly of (R)- and (S)-ZnPc (2) in the presence of 4,40 bipyridine (Figure 5). As revealed by the XPS and XRD techniques, Zn-N4,40 -bipyridine coordination bonds exist in the aggregates of ZnPc (2) formed in the presence of 4,40 -bipyridine. Considering the average Zn-N4,40 -bipyridine coordination bond distance, 0.21 nm, and the length of the 4,40 -bipyridine molecule, 0.71 nm, the stacking distance between the neighboring 2 molecules in the nanostructures of 2 formed in the presence of 4,40 bipyridine is about 0.21  2 þ 0.71 = 1.13 nm. This distance is even much larger than the average stacking distance, 0.32 nm, revealed for nanostructures of H2Pc (1), suggesting the second type nanostructures of 2 formed in the presence of 4,40 -bipyridine. As observed from the TEM and SEM images, the helical nanostructures fabricated from (R)-/(S)-1 in the absence of 4,40 bipyridine and (R)-/(S)-2 in the presence of 4,40 -bipyridine are composed of several single-helices. In order to maximize the van der Waals interaction between single helixes, each helix has to bend over in order to fit into the groove of the other one. Nolte and co-workers used an equation,7a shown in eq S1 in the Supporting Information, to calculate the staggering angle (the angle between two phthalocyanine molecules) and evaluate the handedness of supercoils formed according to the crossing angles (the tilting angle between the two fibers which is double the angle of the groove with respect to the stacking axis). In this equation, R is the crossing angle, d the interplanar stacking distance, D the diameter, and Φ the staggering angle in radians. For (R)- and (S)1, the diameter is 2.87 nm and interplanar stacking distance revealed by X-ray diffraction is 0.32 nm. According to eq S1 in the Supporting Information, if the staggering angle is larger than 12.8°, the crossing angle becomes larger than 90° and in turn the supercoiled structure formed would have a helical sense opposite to that of the original helix. It is also true for the nanostructures formed from (R)- and (S)-2 with the help of 4,40 -bipyridine if the staggering angle is larger than 43.9° obtained from calculation using eq S1 in the Supporting Information. For (R)- and (S)-1, based on the crossing angle measured in the SEM images of 92°, a 7496 DOI: 10.1021/la100061e

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staggering angle of 13.2° could be estimated. However, in the case of (R)- and (S)-2/4,40 -bipyridine, a staggering angle of 29.6° is estimated according to the crossing angle measured in the TEM images, 68°. It is noteworthy that, in the case of (R)- and (S)-2/ 4,40 -bipyridine, according to the calculated staggering angle between two phthalocyaninato molecules of 29.6°, the fourth phthalocyaninato zinc molecule will rotate roughly 90° and the seventh molecule about 180° within a stack of phthalocyaninato zinc molecules, just corresponding to the quarter and half length of the helical cycle, respectively. This analysis is in good accordance with the X-ray diffraction results as detailed above, further verifying the higher ordering of the nanostructures formed from ZnPc (2) in the presence of 4,40 -bipyridine along the stacking axis direction. On the basis of the experimental results described above, the formation mechanism of helical nanostructures from (R)-/(S)H2Pc (1) in the absence of 4,40 -bipyridine and (R)-/(S)-ZnPc (2) in the presence of 4,40 -bipyridine was proposed (Figures 4 and 5). For (R)- and (S)-1, the metal free phthalocyanine molecules first self-assemble into one-dimensional right-handed and left-handed helices, respectively, which act as elementary building blocks and further stack into highly ordered fibrous nanostructures with opposite helicity (Figure 4). In the case of (R)- and (S)-2/4,40 bipyridine, the left-handed and right-handed helices are formed, respectively, at the first stage of aggregation and then stack into highly ordered nanofibers with the same helicity (Figure 5). IR Spectra. The IR spectra of these two phthalocyanine derivatives and their self-assembled nanostructures obtained are shown in Figures S4 and S5 in the Supporting Information. The similar feature in the IR spectra of the nanostructures to that of corresponding compounds for both (R)- and (S)-H2Pc (1) as well as (R)- and (S)-ZnPc (2) unambiguously confirms the composition of nanostructures from corresponding phthalocyanine compounds.

Conclusion In the present paper, two enantiomers of an optically active metal free phthalocyanine and their zinc complexes were designed and synthesized. The self-assembly behavior of these phthalocyanine derivatives in the absence and presence of 4,40 -bipyridine has been comparatively studied. (R)- and (S)-H2Pc (1) hierarchically self-assemble into highly ordered fibrous nanostructures of average 3 μm length, 70 nm width, and 125 nm helical pitch with lefthanded helicity for (R)-1 and right-handed helicity for (S)-1 via one-dimensional helices with chirality determined by the chiral side chains. Both (R)- and (S)- ZnPc (2) self-assemble into nanoparticles. With addition of 4,40 -bipyridine, the additionally formed metal-ligand (Zn-N4,40 -bipyridine) coordination bonding interaction between the nitrogen atom of additive 4,40 -bipyridine molecule and the zinc center of ZnPc (2) together with π-π interaction and chiral discrimination of chiral side chains during the self-assembly process dominates a left-handed and righthanded helical arrangement of (R)- and (S)-2 in a stack of corresponding phthalocyanine molecules, respectively, which then further hierarchically self-assemble into highly ordered fibrous nanostructures of average tens of micrometers in length, 30 nm width, and 106 nm helical pitch with the same helicity as that of the original phthalocyanine stack. The present results not only reveal the effect of additionally formed metal-coordination bonds on the morphology, dimension, handedness, and helical pitch of selfassembled nanostructures formed but also are helpful in providing new insight into chiral information transfer and expression for synthetic conjugated systems at the supramolecular level. Langmuir 2010, 26(10), 7489–7497

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Acknowledgment. Financial support from the Natural Science Foundation of China (Grant Nos. 20931001 and 20801031), Ministry of Education of China, and Shandong Province (Grant No. Q2008B01) is gratefully acknowledged. Supporting Information Available: 1H NMR spectrum of (R)-/(S)-ZnPc (2) in CDCl3; electronic absorption spectral data for (R)-/(S)-H2Pc (1) and (R)-/(S)-ZnPc (2) dissolved in CHCl3 and their aggregates fabricated from (R)- and (S)-1, (R)- and (S)-2 in the absence of 4,40 -bipyridine, and (R)- and (S)-2 in the presence of 4,40 -bipyridine dispersed in hexane; TEM images of self-assembled nanostructures fabricated from (R)- and (S)-2 in the presence of 4,40 -bipyridine with

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different molecular ratio; X-ray photoelectron spectra for (R)- and (S)-2 (dotted line), nanostructures of (R)- and (S)-2 in the absence of 4,40 -bipyridine (dashed line), and nanostructures of (R)- and (S)-2 in the presence of 4,40 -bipyridine (solid line) deposited on silicon surface; the calculation equation; IR spectra of (R)- and (S)-1 (A) and nanostrucutres of (R)- and (S)-1 (B) in the region of 400-4000 cm-1 with 2 cm-1 resolution; IR spectra of (R)- and (S)-2 (A), nanostrucutres of (R)- and (S)-2 in the absence of 4,40 -bipyridine (B), and nanostrucutres of (R)- and (S)-2 in the presence of 4,40 -bipyridine (C) in the region of 400-4000 cm-1 with 2 cm-1 resolution. This material is available free of charge via Internet at http://pubs.acs.org.

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