(Phthalocyaninato)(porphyrinato) - American Chemical Society

Jan 5, 2010 - attracted great attention over the past century due to their potential applications in molecular electronics and magnets.12. In particul...
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J. Phys. Chem. B 2010, 114, 1233–1240

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Organic Nanostructures with Controllable Morphology Fabricated from Mixed (Phthalocyaninato)(porphyrinato) Europium Double-Decker Complexes Xiaomei Zhang,† Quanbo Wang,† Lizhen Wu,† Wei Lv,† Jitao Lu,† Yongzhong Bian,‡ and Jianzhuang Jiang*,†,‡ Department of Chemistry, Shandong UniVersity, Jinan 250100, China, and Department of Chemistry, UniVersity of Science and Technology Beijing, Beijing 100083, China ReceiVed: July 17, 2009; ReVised Manuscript ReceiVed: October 29, 2009

The self-assembly behavior of two sandwich-type mixed (phthalocyaninato)(porphyrinato) europium doubledecker complexes, namely Eu(Pc)(TClPP) [Pc ) phthalocyaninate; TClPP ) meso-tetrakis(4-chlorophenyl)porphyrinate] (1) and optically active (R)- and (S)-EuH[Pc(OBNP)2](TClPP)] [Pc(OBNP)2 ) phthalocyaninate with two aromatic chiral binaphthayl units attached at the nonperipheral positions] (2), has been comparatively studied. In addition, a hydrophilic additive with intense adhesive ability, sodium carboxymethylcellulose (CMC), was also introduced onto the sandwich-type self-assembly systems to combine with double-decker molecules to induce additional hydrophilic/hydrophobic interaction. In the absence of the additive CMC, the double-decker molecules of 1 self-assemble into nanobelts in mixed solvent of chloroform and methanol. Introduction of two aromatic chiral binaphthayl units onto the nonperipheral positions of phthalocyanine ligand in the sandwich-type mixed double-decker complex 2 leads to the formation of tubal nanostructures. Observation of significant difference in the circular dichroism (CD) spectra of (R)- and (S)-2 in chloroform from their aggregates dispersed in methanol confirms the effective intermolecular interaction due to the interplay of π-π interaction between adjacent double-decker molecules with chiral discrimination among chiral side chains at supramolecular level. With addition of CMC, cooperation of intrinsic intermolecular π-π interaction with additionally introduced hydrophilic/hydrophobic interaction between adjacent doubledecker molecules induces the formation of nanoscale hollow spheres at 45 °C during the self-assembly process of 1 and 2. Introduction Controlled self-assembly of elaborately designed molecules is a challenging topic for interdisciplinary research in the fields of chemistry, biology, and materials science because it provides spontaneous nanostructures with well-defined discrete morphology, whose property exhibits significant dependence on their morphology.1 The major driving forces operating in these precisely controlled nanoscopic architectures are various noncovalent interactions such as π-π, van der Waals, hydrogen bonding, hydrophilic/hydrophobic, electrostatic, and metal-ligand coordination bonding. On the basis of the interplay of these noncovalent interactions, many self-assembled organic nanostructures with different morphology including nanowires,2 nanotubes,3 nanovesicles,4 and nanobelts5 have been fabricated. Due to the rich optical, electronic, and magnetic properties, synthetic conjugated molecular systems containing various functional groups have been recognized as attractive building blocks for supramolecular self-assemblies toward construction of functional nanodevices.6 Over the past decade, great efforts have been devoted to design synthetic conjugated molecules containing various functional group(s) and fabricate them into different nanostructures with specific shape and novel functionalities. For example, Ajayaghosh and co-workers have found that intermolecular π-π interaction of the bis(hydroxymethyl)oligo(p-phenylenevinylene) (OPV), with two cholesterol units * To whom correspondence should be addressed. E-mail: jzjiang@ sdu.edu.cn, [email protected]. † Shandong University. ‡ University of Science and Technology Beijing.

attached at the two oxygen atoms of the hydroxyl groups, led to the formation of twisted helical assemblies. However, incorporation of one cholesterol unit onto one of the two hydroxyl groups of the bis(hydroxymethyl)-OPVs induced the formation of a coiled helical assembly due to the synergistic interplay of hydrogen bonding interaction between the remaining hydroxyl groups of two neighboring OPV molecules with intrinsic intermolecular π-π interaction.7 Systematic studies revealed that metal free 5,15-di[4-(5-acetylsulfanylpentyloxy)phenyl]porphyrin H2[DP(CH3COSC5H10O)2P] self-assembled into nanoscale hollow spheres and nanoribbons in MeOH and n-hexane, respectively, depending on the intermolecular π-π interaction. In contrast, introduction of additional Zn-O coordination bond for its zinc congener Zn[DP(CH3COSC5H10O)2P] induces competition with intermolecular π-π interaction, resulting in nanostructures with nanorod and hollow nanosphere morphology in MeOH and n-hexane.8 Nevertheless, additives have also been revealed effective in tuning the morphology of self-assembled nanostructures of conjugated molecular systems through changing the hydrophobic/ hydrophilic nature of original molecular materials via combination with conjugated molecules.9 Investigation over the selfassembly behavior of the optically active phthalocyanine decorated with chiral binaphthyl group revealed that the phthalocyanine molecules could self-assemble into nanoparticles. In contrast, with the addition of cetyltrimethylammonium bromide (CTAB), the hydrophilic property of the assembled system was improved, and the whole system become amphiphilic, resulting in the hollow spherical nanostructures with

10.1021/jp9067608  2010 American Chemical Society Published on Web 01/05/2010

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Zhang et al.

Figure 1. Schematic molecular structures of mixed (phthaloycaninato)(porphyrinato) europium double-decker complexes 1, (R)- or (S)-2, and sodium CMC.

potential application as drug delivery agents.10 In addition, the length and aspect ratio of the nanoprisms fabricated from tetrakis(4-pyridyl)porphyrinato zinc complex (ZnTPyP) with the addition of CTAB could also be tuned by changing the stioichiometric ratio of ZnTPyP over CTAB.11 As the typical representative of functional molecular materials with large conjugated electronic molecular structure, sandwich phthalocyaninato and/or porphyrinato rare earth complexes have attracted great attention over the past century due to their potential applications in molecular electronics and magnets.12 In particular, their sandwich molecular structure with two or three tetrapyrrole ligands connected by one or two rare earth metal ion(s) renders it possible to incorporate various functional groups onto the peripheral positions of one, two, or even three tetrapyrrole ligands, providing enough room to introduce various noncovalent interactions to tune the intermolecular interaction of sandwich complexes and in turn the morphology of selfassembled nanostructures. Very lately, incorporation of different number of hydroxyl groups onto the meso-substituted phenyl groups of porphyrin ligand in mixed (phthalocyaninato)(porphyrinato) europium triple-decker complexes has been revealed to induce additional hydrogen bonding interaction between neighboring triple-decker molecules in addition to intermolecular π-π interaction, which in turn results in the formation of nanostructures with different morphology.13 However, fabrication of functional tetrapyrrole derivatives into a prerequisite nanostructure with desirable dimension and morphology through intramolecular modification and intermolecular regulation still remains a great challenge in this field. In the present paper, we describe the self-assembly properties of two mixed (phthalocyaninato)(porphyrinato) europium doubledecker complexes with and without addition of the additive sodium carboxymethylcellulose (CMC), namely Eu(Pc)(TClPP) (1) and optically active (R)- and (S)-EuH[Pc(OBNP)2](TClPP)] (2) (Figure 1). In the absence of CMC, double-decker complex 1 self-assembles into nanobelts. Introduction of two aromatic chiral binaphthayl units onto the nonperipheral positions of phthalocyanine ligand in the sandwich-type mixed double-decker complex 2 induces effective interplay of the π-π interaction between adjacent double-decker molecules with the chiral discrimination among chiral side chains, which in turn leads to the formation of tubal nanostructure. With addition of CMC, cooperation of intrinsic intermolecular π-π interaction with additional introduced hydrophilic/hydrophobic interaction between adjacent molecules of 1 and 2 induces the formation of nanoscale hollow spheres at 45 °C during their self-assembly process. This represents part of our continuous efforts toward understanding the relationship between synergistic interplay of noncovalent interactions and corresponding nanostructures of tetrapyrrole derivatives with large conjugated π system through intramolecular modification and intermolecular regulation.

Experimental Section Measurements. Electronic absorption spectra were recorded on a Schimadzu UV-1650 PC spectrometer. Fourier transform infrared spectra were recorded in KBr pellets with 2 cm-1 resolution using a R ALPHA-T spectrometer. Circular dichroism (CD) measurements were carried out on a JASCO J-810 spectropolarimeter. X-ray diffraction (XRD) measurements were carried out on a Rigaku D/max-cB X-ray diffractometer. Transmission electron microscopic (TEM) images were collected on a JEOL-100CX II electron microscope operated at 100 KV. High-resolution TEM (HRTEM) measurement was performed with a JEOL-2010 working at 200 KV. Scanning electron microscopic images were obtained on a JEOL JSM-6700F. For TEM imaging, a drop of sample solution was cast onto a carbon copper grid. For scanning electron microscopy (SEM) imaging, Au (1-2 nm) was sputtered onto these grids to prevent charging effects and to improve image clarity. Chemicals. Eu(Pc)(TClPP) (1) and its optically active doubledecker analogue (R)- and (S)-2 were synthesized and purified according to the published procedure.14,15 The compounds were characterized by 1H NMR spectroscopy, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy, and elemental analysis. CMC was purchased from Tianjian Chemical Co and used without further purification. Both chloroform and methanol (HPLC grade) were purchased from Tianjin Kermel Co. All the other chemicals were of reagent grade form and used as received without further purification. Nanostructure Fabrication. The self-assembled nanosacle hollow spheres of complexes 1 and 2 with addition of CMC were fabricated by the solution mixture method according to the following procedure.16 A volume of methanol solution (10 mL) was injected into a homogeneous chloroform solution (10 mL) containing 1 (5.94 mg) or 2 (5.94 mg) and CMC (1 mg). After the solution was allowed to equilibrium at 45 °C for 1 h, precipitates were observed in the solution, and the solvent became colorless. These precipitates were transferred to the carbon-coated grid by pipetting for the TEM and SEM observations. Nanobelts or nanotubes were prepared by the same method except taking out CMC and decreasing the temperature to 0 °C. The experimental results were stable and reproducible under the experimental conditions described above. Results and Discussion Molecular Design, Synthesis, and Characterization. Mixed (phthalocyaninato)(porphyrinato) rare earth complexes with special sandwich molecular structure are of typical large conjugated molecular electronic structure. As expected, the dominant intermolecular interaction among sandwich tetrapyrrole rare earth molecules is π-π interaction. Tuning the intermolecular interaction of sandwich-type tetrapyrrole rare earth molecules can therefore be reached by introducting

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Figure 2. The electronic absorption spectrum of 1 in dilute chloroform solution (solid line), nanobelt aggregates (dashed line), and nanoscale hollow spheres (dotted line) fabricated from 2/CMC dispersed in methanol.

additional intermolecular noncovalent interaction through incorporating functional groups onto the peripheral positions of phthalocyanine and/or porphyrin ring or adding the additive into the self-assembly system. On the basis of these considerations, aromatic chiral binaphthayl units were chosen to be attached onto the nonperipheral positions of phthalocyanine ligand of mixed (phthalocyaninato)(porphyrinato) europium molecule to tune the morphology of self-assembled nanostructures depending on the synergistic interplay of chirality discrimination among chiral binaphthayl units with intrinsic intermolecular π-π interaction between neighboring double-decker molecules at the supramolecular level. Nevertheless, the strong asymmetric perturbation of chiral binaphthayl units to the phthalocyanine and/or porphyrin chromophores in the sandwich double-decker molecules revealed previously renders it possible to investigate the intermolecular interaction in the nanostructures via CD technique in addition to the sole traditional electronic absorption spectroscopy.15 For the purpose of comparative studies, mixed ring europium analogue with unsubstituted phthalocyanine ligand was also synthesized, and its self-assembly behavior investigated. 1 was derived from previous studies.14 The optically active double-decker compound (R)- and (S)-2 was prepared according to a published procedure.15 These compounds were characterized by 1H NMR spectroscopy, MALDI-TOF mass spectroscopy, and elemental analysis. Electronic Absorption and CD Spectroscopy. The electronic absorption spectra of 1 and 2 in CHCl3 and the CD spectra of optically active double-decker enantiomers (R)-2 and (S)-2 are recorded and shown in Figures 2 and 3. As can be seen, in line with analogous M(Pc)(TClPP) (M ) Y, La-Lu except Ce and Pm)17 and MIIIH[Pc(R-OC5H11)4](TClPP) [M ) Y, Sm, Eu; Pc(ROC5H11)4 ) 1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninate],17a both 1 and 2 show typical molecular electronic absorption spectrum of neutral and protonated mixed (phthalocyaninato)(porphyrianto) rare earth double-decker complexes, respectively, revealing their nonaggregated molecular spectroscopic nature in CHCl3. As shown in Figure 2, the absorption spectrum of Eu(Pc)(TClPP) shows two strong absorption bands at about 335 and 411 nm due to the Soret bands of the phthalocyanine and porphyrin ligands, respectively. The absorptions at 481 and 996 nm are due to electronic transitions involving the semioccupied orbital, which have a higher Pc character. Furthermore, an additional characteristic near-IR band for tetrapyrrole-radical anions at 1169 nm can also be observed

Figure 3. CD spectra of (R)- and (S)-2 in dilute chloroform solution (A) and their nanotube aggregates dispersed in methanol (C) together with the electronic absorption spectrum of (R)- and (S)-2 in dilute chloroform solution (solid line), nanotube aggregates (dashed line), and nanoscale hollow spheres (dotted line) fabricated from 2/CMC dispersed in methanol (B).

for the trivalent europium double-decker complex 1. As shown in Figure 3B, the electronic absorption spectrum of the protonated double-decker 2 resembles those of mixed ring double-deckers containing two dianionic ligands such as [CeIV(Pc)(TPP)]18 and Li[MIII(Pc)-(TPyP)] (M ) Eu, Gd).17d The spectrum shows medium to strong phthalocyanine and porphyrin Soret bands at 332 and 415 nm, respectively, and several Q bands at 562, 615, and 848 nm. The spectrum also displays a band with medium intensity at 484 nm, which is attributed to a transition involving a delocalized orbital.19,20 An additional marker band for single-hole doubledeckers in the near-IR region, characteristic of the nonprotonated complexes, was not detected for 2, indicating the “reduced” nature of the double-decker 2. Corresponding to the electronic absorption spectra, in the CD spectra of optically active double-decker complex 2 (Figure 3A) the two enantiomers show perfect mirror-image CD spectra of each other in the whole spectral region, indicating effective chiral information transfer from aromatic chiral binaphthayl units linked at the nonperipheral positions of phthalocyanine ligand of sandwich mixed (phthalocyaninato)(porphyrinato) europium molecule to the phthalocyanine chromophore and further to the porphyrin chromophore at the molecular level. The aggregate electronic absorption spectra of 1 and 2 dispersed in methanol with and without addition of additive CMC and the CD spectra of aggregates fabricated from optically active double-decker enantiomers (R)-2 and (S)-2 without addition of CMC are also recorded and given in Figures 2 and

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3, respectively, which are different from the spectra of corresponding compounds 1 and 2 in CHCl3. As shown in Figure 2, the phthalocyanine Soret band at 335 nm in CHCl3 for 1 takes a slight blue shift to 332 nm, the Q absorptions at 558 and 608 nm in chloroform disappear, and a new absorption peak appears at 575 nm in the methanol solution of aggregates 1 formed without addition of CMC. In the meantime, the low energy absorption band appearing at 1168 nm in chloroform was blueshifted to 1157 nm. When CMC was introduced into the selfassembly system of double-decker complex 1, aggregation of the 1/CMC complex experiences similar electronic absorption spectroscopic change with the phthalocyanine Soret bands further blue-shifting to 330 nm, one new Q absorption band appearing at 576 nm, and the low energy absorption band appearing at 1154 nm (Figure 2), indicating intensified intermolecular interaction among the double-decker molecules due to the interplay of π-π stacking between the double-decker molecules with additionally introduced hydrophilic/hydrophobic interaction between the 1/CMC complexes. In contrast to 1, significant red-shift was observed upon aggregation in all the Soret and Q absorptions from 332, 415, 484, 562, 615, and 848 nm for 2 in CHCl3 to 336, 422, 489, 575, 629, and 995 nm for its aggregates formed without addition of CMC in the methanol (Figure 3B), indicating the significant effect of chiral discrimination among chiral binaphthayl units at the nonperipheral positions of phthalocyanine ligand of double-decker molecules on tuning the molecular packing mode. This was further supported by the CD spectroscopic and XRD results as detailed below. With the addition of CMC, aggregation of 2 induces further red shift for all the Q absorption bands to 491, 614, 676, and 997 nm (Figure 3C), indicating again the intensified intermolecular interaction of double-decker 2 due to the interplay of chiral discrimination among chiral binaphthayl units with additionally introduced hydrophilic/hydrophobic interaction. On the basis of Kasha’s exciton theory,20 blue-shifts in the main absorption bands of double-decker 1 upon aggregation is typically a sign of the effective π-π interaction between double-decker molecules, indicating the formation of H aggregate from this compound with and without the addition of CMC, revealing the face-to-face molecular arrangement in the nanoaggregates. In contrast, the red-shifted absorption bands in the electronic absorption spectra of double-decker 2 with and without the addition of CMC upon aggregation, imply the J aggregation mode with a head-to-tail molecular arrangement employed by double-decker molecules of this complex in the nanostructures formed. In line with the CD spectra of optically active double-decker 2 in chloroform, aggregates formed from the two enantiomers with or without addition of CMC also show perfect mirrorimage CD spectra of each other in the whole spectral region (Figure 3C and Supporting Information, Figure S1), indicating the just same molecular arrangement and intermolecular interaction in the aggregates formed from the two enantiomers of this double-decker compound. In addition, both the relatively significant and slight change in the CD spectra of the nanostructures formed without and with addition of CMC, respectively, in comparison with those in chloroform solution was observed. For example, both the phthalocyanine and porphyrin Soret bands of double-decker 2 shift from 294-395 and 395-421 nm in chloroform to ca. 308-361, 295-373, and 361-463, 373-420 nm in the aggregates formed without and with the addition of CMC, respectively. Meanwhile, the lowest energy absorption band at 421-678 nm in chloroform for double-decker 2 appears to extend further into longer wavelength

Zhang et al. at 463-747 and 420-686 nm in the aggregates formed without and with the addition of CMC. These shifts are caused by exciton coupling between neighboring molecules 2 in a stack, suggesting the presence of a right-handed or left-handed helical arrangement of the transition dipole of the molecule of 2 within a stack of double-decker molecules in aggregates. In addition, these changes reveal the effect of chiral discrimination between neighboring double-decker molecules on chiral information transfer from aromatic chiral binaphthayl units linked at the nonperipheral positions of phthalocyanine ligand of sandwich mixed (phthalocyaninato)(porphyrinato) europium molecule to the phthalocyanine chromophore and porphyrin chromophore at molecular and supramolecular levels. IR Spectra. To further confirm the composition of the nanostructures formed from corresponding double-decker complexes, IR spectroscopy was employed. The IR spectra of the two double-decker complex themselves, aggregates formed with and without addition of additive CMC are shown in Figures S2 and S3 (Supporting Information). The similar feature in the IR spectra of the nanostructures to that of corresponding compounds for both double-decker 1 and 2 unambiguously confirms the composition of nanostructures from corresponding porphyrin compounds. For example, compound 1 shows an intense band at 1315 cm-1 due to the phthalocyanine π-radical anion (Figure S2, Supporting Information).14,21,22 A similar band at ca. 1316 and 1313 cm-1 was observed in the IR spectra of nanoscale hollow spheres and nanobelts fabricated from doubledecker 1 with and without CMC, respectively, revealing the neutral bis(tetrapyrrole) rare earth(III) molecular nature of 1 in the nanostructures formed. This is also true for the protonated reduced bis(tetrapyrrole) rare earth(III) molecular nature of 2 by the observation of phthalocyanine dianion absorption band at 1323, 1319, and 1320 cm-1 in the IR spectra of 2, nanoscale hollow spheres, and nanotubes fabricated from 2 with and withoutCMC,respectively(FigureS3,SupportingInformation).14,21,22 XRD Patterns. The internal structure of self-assembled nanostructures was further investigated by XRD technique. Figure 4 exhibits the diffraction patterns of the self-assembled nanostructures formed from 1 and 2 without and with the addition of CMC, respectively. As can be seen from Figure 4A, in the low angle range, the XRD diagram of the nanobelts formed from 1 without addition of CMC shows two relatively broad refraction peaks at 1.32 and 1.00 nm, respectively, originating from the (001) and (010) planes. According to the single crystal XRD analysis result of a similar compound, Gd(Pc)(TClPP),14 the length of the molecule is ca. 1.32 nm, and the height from the top-most carbon atom of the benzene ring of porphyrin ring to the isoindole N4 plane of the phthalocyanine ring of the double-decker is ca. 0.58 nm (Figure S4, Supporting Information). Considering the average stacking distance between neighboring isoindole N4 planes of the phthalocyanine rings of the adjacent double-decker molecules (0.42 nm) obtained on the basis of single crystal XRD analysis result,14,17 the sharp peak observed at 1.00 nm in the nanobelts can therefore be assigned to the one layer height of the lamellar structure of the nanobelts (Figure S4B). These results confirm the formation of the ordered H-type aggregates, revealing the face-to-face molecular arrangement in the nanobelts of 1 depending mainly on the π-π stacking between the neighboring molecules. Similar to the aggregates 1 formed without addition of CMC, the XRD diagram of the nanoscale hollow spheres formed from 1 with addition of CMC also displays two refraction peaks at 1.32 and 0.99 nm, respectively, indicating the almost same

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Figure 4. XRD profile of the aggregates fabricated from 1 without (A) and with (B) the help of CMC, and XRD profile of the aggregates fabricated from (R)-2 without (C) and With (D) the help of CMC.

molecular stacking mode in these two aggregates. However, the layer height in the aggregates of 1/CMC is a bit of shorter than that of 1, indicating the relatively intensified π-π stacking between neighboring 1/CMC units due to the introduction of additionally introduced hydrophilic/hydrophobic interaction. This is in good accordance with that revealed by electronic absorption spectroscopic results for this complex as detailed above. Furthermore, in the wide-angle region, the XRD pattern also presents two refractions at 0.41 and 0.28 nm, respectively, which might be attributed to the distance of interisoindole N4 planes between the phthalocyanine rings of neighboring mixed ring double-decker molecules and the intraisoindole N4 planes between the porphyrin and phthalocyanine rings of doubledecker molecule, as shown in Figure S5 (Supporting Information). In line with the electronic microscopic result, a different XRD diagram was obtained for the aggregates formed from 2 (Figure 4C). From the diagram, it can be seen that, in the low-angle range, the XRD diagram of the nanotubes formed from 2 without addition of CMC shows a weak refraction peak at 2θ ) 2.56° (corresponding to 3.45 nm) and two conjoint refraction peaks at 2.07 and 1.96 nm, which are ascribed to the refractions from the (001), (010), and (100) planes, respectively. The (001) plane gives its higher order refractions at 1.73 (002) and 1.15 (003) nm, respectively. In addition, the XRD pattern also displays one well-defined peak at 0.98 nm, which can be assigned to the higher order refractions of the (100) plane. These diffraction results could be assigned to the refractions from a parallelepipedal lattice with cell parameters of a ) 3.45 nm, b ) 2.07 nm, and c ) 1.96 nm (Figure 5). As can be seen from Figure 5A,B, the dimensional size for a double-decker molecule 2 is 2.15 nm (length) × 1.24 nm (width) × 1.07 nm (height) according to the geometry optimization and energy minimized molecular structure of 2 using the Gaussian 98 program at the B3LYP/6-31G(d) level.23 From these experimental results, the unit cell consisting of two molecules with a head-to-tail molecular arrangement is given for double-decker molecule 2 (Figure 5C). In comparison with the XRD pattern of self-assembled nanotubles formed from 2, the XRD pattern of self-assembled

Figure 5. Schematic representation of the unit cell in the aggregate of (R)-2.

nanoscale hollow spheres formed from complex 2 with addition of CMC shows three relatively strong diffraction peaks at 2.15, 1.24, and 1.07 nm in the low angle region, just corresponding to the molecular length, width, and height (Figures 4D, 5A, and 5B). These results imply different molecular packing models in these two corresponding nanostructures. In addition, in the wide-angle region, the XRD pattern also presents one refraction peak at 0.28 nm, assigned to the distance of the intraisoindole N4 planes between porphyrin and phthalocyanine rings in the double-decker molecule. In addition, in the wide-angle region, the XRD pattern also presents one refraction peak at 0.28 nm, assigned to the distance of intraisoindole N4 planes between porphyrin and phthalocyanine rings in the double-decker molecule. Aggregate Morphology. When methanol was injected into a solution of complex 1 or 2 in chloroform, self-assembled

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Figure 6. (A) TEM image of the self-assembled nanobelts fabricated from 1. (B) Low-magnification TEM image of the self-assembled nanotubes fabricated from (R)-2. (b) High-magnification TEM image of nanotubes fabricated from (R)-2, indicating hollow structures. (C) Low-magnification SEM image of the self-assembled nanotubes fabricated from (R)-2. (c) high-magnification SEM image fabricated from (R)-EuH[Pc(OBNP)2](TClPP) (2), showing the hollow tubal structure; (D) HR-TEM image of the self-assembled nanotubes fabricated from (R)-2, and the arrow is the nanotube axis. (E) Lowmagnification SEM image of the self-assembled nanoscale hollow spheres fabricated from (R)-2. (e) High-magnification SEM image showing the hollow spherical structure fabricated from (R)-2. (F) Lowmagnification SEM image of the self-assembled nanoscale hollow spheres fabricated from (R)-2.

nanostructures of double-decker compounds were formed when the ratio of chloroform/methanol reaches 1:1 (V/V) at 0 °C. The morphologies of these nanostructures were examined by SEM and TEM. As shown in Figure 6A, depending mainly on the intermolecular π-π interaction, molecules of double-decker complex 1 self-assemble in methanol into nanostructures with beltlike morphology with several micrometer long and ca. 300 nm width. However, as displayed in Figure 6B,b,C,c, with the introduction of aromatic chiral binaphthayl units onto the nonperipheral positions of the phthalocyanine ligand of a sandwich mixed (phthalocyaninato)(porphyrinato) europium compound, molecules of optically pure enantiomers of 2 selfassemble into nanostructures with tubelike morphology as a result of the interplay of chiral discrimination with the van der Waals interaction among chiral binaphthayl units of adjacent double-decker molecules. As clearly shown in Figure 6B, these three-dimensional nanoscale tubes display uniform size with length in the range of 1.5-5 µm, diameter of 200-300 nm, and wall thickness of approximately 50 nm. In addition, the

Zhang et al. images shown in Figure 6b,c reveal the open, uneven, and multilayer nature of these nanotubes. This is also confirmed by the HRTEM observation result (Figure 6D). As can be seen from this figure, the well-ordered multilayer structure of these nanotubes indicates the highly ordered stacking of the doubledecker molecules in the nanostructures. Furthermore, the disklike molecules were found to be parallel to the longer axis of the tubes, reflecting the head-to-tail molecular arrangement in the nanoaggregates. At the end of this paragraph, it is worth noting that, unlike pure (R)- or (S)-2, the racemic mixture composed of the same amount of (R)- and (S)-2 was found to form two-dimensional structures with nanobelt morphology (Figure S6, Supporting Information), confirming the importance of chiral discrimination on tuning the intermolecular interaction and, in turn, the molecular packing mode of mixed ring doubledecker complexes. Along with the increase in the temperature until 45 °C, nanoparticles instead of the nanobelts or nanotubes were revealed to be formed from the self-assembly of the doubledecker molecules of 1 and 2 (Figure S7, Supporting Information), indicating the effect of temperature on the morphology of nanostructures. However, with the addition of a small amount of CMC into the self-assembly system, both double-decker complexes were found to form nanoscale hollow spheres in chloroform/methanol (1:1) at 45 °C, indicating the dominant hydrophobic/hydrophilic interaction between 1/CMC or 2/CMC units associated with the nature transform of the self-assembly system due to the combination of the additive molecules with the conjugated double-decker molecules. Figure 6E displays a typical SEM image of the nanostructures with hollow sphere morphology formed from (R)-2 with addition of CMC. As can be found, large-scale particles having average diameter of about 150 nm with well-defined three-dimensional spherical structure were obtained, most of which remain intact, and only a few spheres are deformed or cracked. Nevertheless, the hollow structure of these nanospheres is clearly revealed from a typical broken spherical image of a zoom-in image of a piece of nanoparticles shown in Figure 6e. Further evidence for the hollow structure of these nanostructures comes from their TEM image (Figure 6F). In this image, the presence of circular rings of several spheres with a cavity confirms the hollow structure nature of these nanostructures. Furthermore, a strong contrast difference for all the spheres with dark ring and bright inner shell gives additional support for their hollow structure nature. The formation of these nanoscale hollow spheres would normally belong to the superstrong segregation limit. Owing to the different solubility of the hydrophilic and hydrophobic units of the amphiphilic molecular system, in selective solvents, they can fabricate into hollow spherical supramolecular structures.24 First, CMC adheres to the double-decker compounds, form stable supramolecular structures depending mainly on the hydrophobic interaction between hydrophobic moieties of CMC and the double-decker molecules together with hydrogen bonding formed between the nitrogen/oxygen atoms of the double-decker molecules and hydrophilic portions of CMC.25 Due to the combination of the hydrophobic double-decker molecules of compound 1 or 2 with hydrophilic CMC molecules, the formed supramolecular structure 1/CMC or 2/CMC exhibits amphiphilic nature, which then self-assembles into hollow spheres in the chloroform/methanol mixed-solvent system in a manner similarto that of a typical amphiphilic molecular system.24

Organic Nanostructures of Pc-TClPP Eu Complexes Conclusion To summarize briefly, the self-assembly behavior of two sandwich-type mixed (phthalocyaninato)(porphyrinato) europium double-decker complexes with and without addition of the additive CMC have been comparatively and systematically studied. Investigation results reveal that competition and/or cooperation of intermolecular hydrophilic/hydrophobic interaction and chiral discrimination with the π-π interaction between the double-decker molecules leads to different molecular packing conformation and, in turn, different nanostructure morphology in the self-assembly process. The π-π interaction dominates the formation of nanobelts for compound 1, while the cooperation of intermolecular chiral discrimination with the π-π interaction leads to the nanotubles for 2. The interplay of intermolecular hydrophilic/hydrophobic interaction with the π-π interaction among the double-decker molecules induces the formation of nanoscale hollow spheres for 1 and 2 in the presence of additive CMC. The present result represents part of our continuous efforts toward understanding the relationship between synergistic interplay of noncovalent interactions and corresponding nanostructures of tetrapyrrole derivatives with large conjugated π system through intramolecular modification and intermolecular regulation. Owing to the rich optical, electrical, and chemical properties together with the special electronic structure of sandwich-type tetrapyrrole rare earth complexes, these nanostructures are expected to have applications in diverse fields, including nanoelectronics. 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: CD spectra of (R)- and (S)-2 in dilute chloroform solution and their nanoscale hollow spheres fabricated from (R)- and (S)-2 with CMC dispersed in methanol. Low-magnification TEM image of the self-assembled nanobelts of symmetric 2, SEM image of the self-assembled nanobelts of symmetric 2, and high-magnification SEM image of symmetric 2, showing the terminal belt structure. TEM spectra of nanoparticles fabricated from (R)-2 at 45 °C. Molecular size of 1 obtained from the crystal structure of a similar compound, GdPc(TClPP) and schematic representation of a dimer formed from compound 1. Molecular size of 1 obtained from the crystal structure of a similar compound, GdPc(TClPP) and schematic representation of a dimer formed from 1/CMC complex;. IR spectra of nanoscale hollow spheres fabricated from 1/CMC complex, double-decker 1, and nanobelts fabricated from 1 in the region of 400-1800 cm-1 with 2 cm-1 resolution. IR spectra of nanoscale hollow spheres fabricated from 2/CMC complex, double-decker 2, and nanotubes fabricated from 2 in the region of 400-1800 cm-1 with 2 cm-1 resolution. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) (a) Lehn, J. M. Supramolecular Chemistry, Concepts and PerspectiVes; VCH Press: New York, 1995. (b) Fo¨rster, S.; Plantenberg, T. Angew. Chem., Int. Ed. 2002, 41, 688–714. (c) Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M. Chem. ReV. 2001, 101, 4039–4070. (d) Tao, F.; Bernasek, S. L. Chem. ReV. 2007, 107, 1408– 1453. (e) Ryu, J.-H.; Tang, L.; Lee, E.; Kim, H.-J.; Lee, M. Chem.sEur. J. 2008, 14, 871–881. (2) Gan, H.; Liu, H.; Li, Y.; Zhao, Q.; Li, Y.; Wang, S.; Jiu, T.; Wang, N.; He, X.; Y, D.; Zhu, D. J. Am. Soc. Chem. 2005, 127, 12452–12453.

J. Phys. Chem. B, Vol. 114, No. 3, 2010 1239 (3) (a) Yan, D. Y.; Zhou, Y. F.; Hou, J. Science 2004, 303, 65–67. (b) Shimizu, T.; Masuda, M.; Minamikawa, H. Chem. ReV. 2005, 105, 1401– 1444. (c) Zhi, L.; Gorelik, T.; Wu, J.; Kolb, U.; Mu¨llen, K. J. Am. Chem. Soc. 2005, 127, 12792–12793. (d) Liu, Q.; Li, Y.; Liu, H.; Chen, Y.; Wang, X.; Zhang, Y.; Li, X.; Jiang, J. J. Phys. Chem. C. 2007, 111, 7298–7301. (4) Vriezema, D. M.; Hoogboom, J.; Velonia, K.; Takazawa, K.; Christianen, P. C. M.; Maan, J. C.; Rowan, A. E.; Nolte, R. J. M. Angew. Chem., Int. Ed. 2003, 42, 772–776. (5) Balakrishnan, K.; Datar, A.; Naddo, T.; Huang, J.; Oitker, R.; Yen, M.; Zhao, J.; Zang, L. J. Am. Chem. Soc. 2006, 128, 7390–7398. (6) (a) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. ReV. 2005, 105, 1491–1546. (b) Ajayaghosh, A.; Praveen, V. K. Acc. Chem. Res. 2007, 40, 644–656. (c) Wu, J.; Watson, M. D.; Zhang, L.; Wang, Z.; M|Aaullen, K. J. Am. Chem. Soc. 2004, 126, 177– 186. (d) Palmans, A. R. A.; Meijer, E. W. Angew. Chem., Int. Ed. 2007, 46, 8948–8968. (7) Ajayaghosh, A.; Vijayakumar, C.; Varghese, R.; George, S. J. Angew. Chem., Int. Ed. 2006, 45, 456–460. (8) Gao, Y.; Zhang, X.; Ma, C.; Li, X.; Jiang, J. J. Am. Chem. Soc. 2008, 130, 17044–17052. (9) (a) Brizard, A.; Aime´, C.; Labrot, T.; Huc, I.; Berthier, D.; Artzner, F.; Desbat, B.; Oda, R. J. Am. Chem. Soc. 2007, 129, 3754–3762. (b) John, G.; Jung, J. H.; Minamikawa, H.; Yoshida, K.; Shimizu, T. Chem.sEur. J. 2002, 8, 493–497. (c) 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. (d) Svenson, S.; Messersmith, P. B. Langmuir 1999, 15, 4464– 4471. (10) Lv, W.; Zhang, X.; Lu, J.; Zhang, Y.; Li, X.; Jiang, J. Eur. J. Inorg. Chem. 2008, 4255–4261. (11) Hu, J.; Guo, Y.; Liang, H.; Wan, L.; Jiang, L. J. Am. Chem. Soc. 2005, 127, 17090–17095. (12) (a) Jiang, J.; Ng, D. K. P. Acc. Chem. Res. 2009, 42, 79–88. (b) Jiang, J.; Bao, M.; Rintoul, L.; Arnold, D. P. Coord. Chem. ReV. 2006, 250, 424–448. (c) Jiang, J.; Kasuga, K.; Arnold, D. P. In Supramolecular PhotosensitiVe and ElectroactiVe Materials; Nalwa, H. S., Ed.; Academic Press: New York, 2001; Chapter 2, pp 113-210. (d) Ng, D. K. P.; Jiang, J. Chem. Soc. ReV. 1997, 26, 433–442. (e) Yoshimoto, S.; Sawaguchi, T.; Su, W.; Jiang, J.; Kobayashi, N. Angew. Chem., Int. Ed. 2007, 46, 1071– 1074. (f) Ye, T.; Takami, T.; Wang, R.; Jiang, J.; Weiss, P. S. J. Am. Chem. Soc. 2006, 128, 10984–10985. (13) Lu, G.; Chen, Y.; Zhang, Y.; Bao, M.; Bian, Y.; Li, X.; Jiang, J. J. Am. Chem. Soc. 2008, 130, 11623–11630. (14) Lu, F.; Sun, X.; Li, R,; Liang, D.; Zhu, P.; Choi, C.-F.; Ng, D. K. P.; Fukuda, T.; Kobayashi, N.; Bai, M.; Ma, C.; Jiang, J. New. J. Chem. 2004, 28, 1116–1122. (15) Zhang, X.; Muranaka, A.; Lv, W.; Zhang, Y.; Bian, Y.; Jiang, J.; Kobayashi, N. Chem.sEur. J. 2008, 14, 4667–4674. (16) (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. (17) (a) Wang, R.; Li, R.; Zhang, Y. X.; Zhu, P.; Lo, P.-C.; Ng, D. K. P.; Pan, N.; Ma, C.; Kobayashi, N.; Jiang, J. Chem.sEur. J. 2006, 12, 1475– 1485. (b) Chabach, D.; Tahiri, M.; De Cian, A.; Fischer, J.; Weiss, R.; El Malouli, M. Bibout. J. Am. Chem. Soc. 1995, 117, 8548–8556. (c) Jiang, J.; Liu, W.; Sun, X.; Ng, D. K. P. Chem. Res. Chin. UniV. 2001, 17, 134– 142. (d) Jiang, J.; Mak, T. C. W.; Ng, D. K. P. Chem. Ber. 1996, 129, 933–936. (18) (a) Lachkar, M.; De Cian, A.; Fischer, J.; Weiss, R. New J. Chem. 1988, 12, 729–731. (b) Tran-Thi, T.-H.; Mattioli, T. A.; Chabach, D.; Cian, A. De.; Weiss, R. J. Phys. Chem. 1994, 98, 8279–8288. (19) (a) Kadish, K. M.; Moninot, G.; Hu, Y.; Dubois, D.; Ibnlfassi, A.; Barbe, J.-M.; Guilard, R. J. Am. Chem. Soc. 1993, 115, 8153–8166. (b) Guilard, R.; Barbe, J.-M.; Ibnlfassi, A.; Zrineh, A.; Adamian, V. A.; Kadish, K. M. Inorg. Chem. 1995, 34, 1472–1481. (20) Kasha, M.; Rawls, H. R.; EI-Bayoumi, M. A. Pure Appl. Chem. 1965, 11, 371–392. (21) (a) Buchler, J. W.; Ng, D. K. P. In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds; Academic Press: San Diego, 2000; Vol. 3, pp 245-294. (b) Jiang, J.; Liu, W.; Arnold, D. P. J. Porphyrins Phthalocyanines 2003, 7, 459–473. (22) (a) Jiang, J.; Arnold, D. P.; Yu, H. Polyhedron 1999, 18, 2129– 2139. (b) Lu, F.; Bao, M.; Ma, C.; Zhang, X.; Arnold, D. P.; Jiang, J. Spectrochim. Acta, Part A 2003, 3273–3286. (c) Bao, M.; Pan, P.; Ma, C.; Arnold, D. P.; Jiang, J. Vib. Spectrosc. 2003, 32, 175–184. (d) Bao, M.; Bian, Y.; Rintoul, L.; Wang, R.; Arnold, D. P.; Ma, C.; Jiang, J. Vib. Spectrosc. 2004, 34, 283–291. (23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, Jr. 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.;

1240

J. Phys. Chem. B, Vol. 114, No. 3, 2010

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.

Zhang et al. (24) (a) Li, Y.; Li, X.; Li, Y.; Liu, H.; Wang, S.; Gan, H.; Li, J.; Wang, N.; He, X.; Zhu, D. Angew. Chem., Int. Ed. 2006, 45, 3639–3643. (b) Antonietti, M.; Fo¨rster, S. AdV. Mater. 2003, 15, 1323–1333. (25) (a) Reis, E. A. O.; Caraschi, J. C.; Carmona-Ribeiro, A. M.; Petri, D. F. S. J. Phys. Chem. B 2003, 107, 7993–7997. (b) Castro, L. B. R.; Soares, K. V.; Naves, A. F.; Carmona-Ribeiro, A. M. D.; Petri, F. S. Ind. Eng. Chem. Res. 2004, 43, 7774–7779. (c) Kwak, J. C. T. PolymerSurfactant Systems; Surfactant Science Series 77; Marcel Dekker: New York, 1998. (d) Anghel, D. F.; Winnik, F. M.; Galatanu, N. Colloids Surf., A 1999, 149, 339–345. (e) Bai, D.; Khin, C. C.; Chen, S. B.; Tsai, C.-C.; Chen, B.-H. J. Phys. Chem. B 2005, 109, 4909–4916.

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