In Situ Measurement of the Supramolecular Chirality in the Langmuir

Mar 10, 2014 - and Yuan Guo*. ,†. †. Beijing National Laboratory of Molecular Sciences, CAS Key Laboratory of Colloid, Interface and Thermodynamic...
0 downloads 0 Views 561KB Size
Download PDF
Article pubs.acs.org/JPCC

In Situ Measurement of the Supramolecular Chirality in the Langmuir Monolayers of Achiral Porphyrins at the Air/Aqueous Interface by Second Harmonic Generation Linear Dichroism Lu Lin,†,‡ Tianyu Wang,† Zhou Lu,† Minghua Liu,*,† and Yuan Guo*,† †

Beijing National Laboratory of Molecular Sciences, CAS Key Laboratory of Colloid, Interface and Thermodynamics, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ University of the Chinese Academy of Sciences, Beijing 100049, China S Supporting Information *

ABSTRACT: Chiral porphyrin assemblies are promising molecular materials because they possess unique biological compatibility and excellent electronic properties. Metal ions can strongly affect the formation of supramolecular chirality. In this paper, we investigated the effect of metal ions in the subphase on the supramolecular chirality of a porphyrin derivative with two long hydrophobic chains (TPPA2a) at the air/aqueous interfaces by means of second harmonic generation linear dichroism (SHGLD). It was found that TPPA2a can form chiral assemblies at the air/aqueous interface even though the molecule itself is achiral. Furthermore, metal ions added into the subphase have a considerable effect on the interfacial supramolecular chirality: Zn2+ inhibits the formation of supramolecular chirality, while Cu2+ promotes the formation. We suggest that the effect of metal ions on the supramolecular chirality is due to the coordination between the metal ions and TPPA2a molecules. To clarify the coordination mechanism, we also performed UV−vis measurements of TPPA2a Langmuir−Blodgett (LB) films and SHG-LD experiments on TPPA4, which is similar to TPPA2a but without ester groups. These results revealed that the metal ions did not interact with the central nitrogen of porphyrin rings, while the coordination between metal ions and the ester groups possibly affects the supramolecular chirality. This is a novel mechanism involving coordination between metal cations and side chains of porphyrin derivatives, and it may provide a deeper understanding of the supramolecular chirality of porphyrin assemblies.

■

ties.19−21 The porphyrin molecule consists of four pyrrole rings joined via their α-carbon atoms through four methine bridges. It has a rigid planar molecular conformation and π electrons delocalized over the whole molecular framework, which makes it an appropriate building block for selfassemblies. Furthermore, the porphyrin ring can be readily modified with hydrophilic functional groups or hydrophobic alkyl chains which facilitate the fabrication of Langmuir monolayers as well as Langmuir−Blodgett (LB) films from porphyrin derivatives. Various achiral free-base porphyrin derivatives could be fabricated into chiral assemblies at the air/water interface.13,22−35 In addition, free-base porphyrin can readily react with metal ions to form metalloporphyrin complexes and hence form assemblies with unique characteristics. It has been reported that the introduction of central metal ions has a major effect on the chirality of the assemblies. For example, our previous work demonstrated that when

INTRODUCTION Supramolecular chirality based on molecular self-assembly has received extensive research interest in the past few decades owing to its potential applications in molecular recognition,1−3 asymmetric catalysis,4−7 enantioselective separation,7−10 development of chiroptical devices, and other fields of research.11,12 Previous studies have revealed that three combinations of chiral and achiral molecules could possibly facilitate the chiral assemblies: from intrinsically chiral molecules, from achiral molecules on chiral templates, and from exclusively achiral molecules without chiral induction.13−15 The last case is of great importance because it involves spontaneous symmetry breaking, which may help explain the origin of the natural homochirality. We have shown that a variety of achiral molecules could possibly be fabricated into macroscopic chiral assemblies via interfacial noncovalent interactions such as π−π stacking, hydrogen bonds, and van der Waals interactions.13,16−18 Of all the achiral building blocks, porphyrin derivatives are particularly crucial because of their large π−π stacking ability, biological compatibility, and excellent electronic proper© 2014 American Chemical Society

Received: October 29, 2013 Revised: March 9, 2014 Published: March 10, 2014 6726

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

In SHG-LD experiments, the detection polarization is fixed, and the relationship between the incident polarization angle and the SH intensity can be expressed as48

spread on a pure water subphase the zinc porphyrin complex forms aggregates with no chirality, while the copper porphyrin complex shows strong chiral signals.36 However, most of these studies on the supramolecular chirality of porphyrin assemblies were performed in the LB films, which were obtained by transferring the Langmuir monolayers at the air/aqueous interface onto solid substrates. For supramolecular chiral assemblies fabricated from achiral molecular building blocks, some of the most important issues remain unknown. For example, are the chiral structures formed in situ in the Langmuir film or during the transfer process? Is there any effect of the metal ions in the aqueous subphase on the supramolecular chirality? To resolve these problems, it is necessary to unambiguously measure the supramolecular chirality in situ in the Langmuir films. Second-order nonlinear optical spectroscopic methods such as second harmonic generation (SHG) and sum frequency generation (SFG) have proven to be versatile tools for the in situ detection of interfacial chirality because of their inherent selectivity and sensitivity to interfaces and chirality.37−46 In the present work, we use SHG combined with linear dichroism (SHG-LD) to investigate the supramolecular chirality in the spreading Langmuir monolayers of a tetraphenylporphyrin (TPP) derivatives TPPA2a with two long alkyl chains and two ester groups. The introduction of an alkyl chain can increase the spreading ability of the porphyrin molecules to form a monolayer at the air/aqueous interface, while the shorter ester group can enhance the hydrophilicity of the molecule. We showed that TPPA2a can form chiral assemblies in situ at the air/aqueous interface, even though the molecule itself is achiral. Interestingly, when metal ions such as Zn2+ and Cu2+ are added into the subphase, the interaction with ions changes the supramolecular chirality dramatically. Zinc ions destroy the formation of supramolecular chirality of the TPPA2a monolayer, while copper ions promote it. To clarify the mechanism, UV−vis measurements of TPPA2a LB films and SHG-LD experiments of TPPA4, an analogue of TPPA2a, were also performed. The results provided a straightforward way of detecting chiral structures in situ in the spreading monolayers and a new insight into this chiral mechanism.

Is ∝ |χeff,45s sin 2α + χeff,chiral cos2 α|2

with χeff,45s = Lyy(2ω)Lzz(ω)Lyy(ω)sin βχyzy χeff,chiral = 2Lxx(2ω)Lyy(ω)Lzz(ω)sin β cos βχxyz

ΔI /I =

2(I −45◦ − I+45◦) (I −45◦ + I+45◦)

(4)

The physical meaning of DCE is that chiral enantiomer structures give rise to opposite signs of DCE. For porphyrin assemblies, the chirality originates from helical stacking of porphyrin molecules, and opposite helical directions will result in two different chiral states. By calculating the DCE, it can be determined whether the interface is predominantly in one chiral state or in the opposite chiral state, although the absolute chirality (helical direction) of the interface remains unknown. Nevertheless, the DCE value can still serve as a quantitative description of the interfacial chirality.

■

EXPERIMENTAL METHODS TPPA2a and TPPA4 were synthesized and purified according to the procedure in the literature.34 A chloroform solution of the TPPA2a (0.5 mM) was spread onto three different subphases, including pure water, the ZnCl2 aqueous solution, and the CuCl2 aqueous solution. Both the concentrations of Zn2+ and Cu2+ were 1 mmol/L. Before the SHG-LD detection, the solvent was evaporated from the air/water interface for more than 15 min to allow the porphyrin molecules to form monolayers and achieve thermodynamic equilibrium by means of free diffusion and intermolecular interactions. The surface pressure was detected by a normalized commercial pressure sensor (Nima PS4; Nima Technology Ltd.). For SHG-LD experiments, all the surface pressures were adjusted to 4 mN/ m. For UV−vis, circular dichroism, and AFM measurements, the films were transferred onto solid substrates at 4 mN/m by a vertical lifting method with the speed of 2 mm/min. The SHG-LD experimental setup was similar to what was previously reported.48,51 A mode-locked femtosecond Ti/ sapphire laser (Tsunami 3960C; Spectra-Physics) with a repetition rate of 82 MHz and a pulse width of 80 fs was used for the SHG-LD measurements. The laser beam was focused onto the interface by using an optical lens with a 10 cm focal length. The diameter of the laser spot is about 30 μm. The incident light wavelength was 800 nm with an incident angle of 70° and a typical laser power of 600 mW. The fundamental polarization angle was continuously adjusted using a rotating half-wave plate driven by a computer-controlled stepper motor, and the signal was collected by a high-gain photomultiplier tube

SHG-LD THEORY SHG-LD is based on the nonlinear optical method of second harmonic generation (SHG) spectroscopy with a linear polarized incident laser beam. By scanning the incident polarization angle, the variation of the second harmonic (SH) intensity can reveal the structural chirality at the interface. When a laser beam with a frequency of ω is incident onto the interface, a SH signal with a frequency of 2ω can be detected in the direction of reflection. The SH intensity is related to the effective second-order susceptibility of the interface by47 32π 3ω 2 sec 2 β (2) 2 2 |χ | I (ω) c03n12(ω)n1(2ω) eff

(3)

where the subscript s denotes polarization parallel to the interface and α is the polarization angle of the incident laser beam. L(ωi) is the local field factor tensor, and β is the incident angle of the laser beam. From eq 2, it can be deduced that the SH intensities are different at incident polarization angles of ±45° (−45° ≡ 135°) if the interface is chiral. To quantitatively characterize the interfacial chirality, the degree of chiral excess (DCE) has been introduced.48−50 It is defined as

■

I(2ω) =

(2)

(1)

where I denotes the SH intensity and χeff is the effective secondorder susceptibility. The susceptibility is a third-rank tensor with 27 elements, which can be reduced to four nonzero independent elements for isotropic chiral interfaces, namely, χzzz, χzxx = χzyy, χxzx = χxxz = χyzy = χyyz, and χxyz = χxzy = −χyzx = −χyxz. In the study of interfacial chirality of monolayers where the subphase is achiral, the last term originates exclusively from the interfacial chirality and is called χchiral. 6727

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

Figure 1. Polarization dependence curves of SH intensity from the TPPA2a monolayer on the pure water subphase at six different positions of the monolayer. The dots represent the experimental results, and the solid curves are fitting results with eq 2. All the SH intensity data have been normalized. The calculated DCE values are all negative, suggesting that TPPA2a molecules form a homochiral monolayer on the pure water subphase.

Figure 2. Polarization dependence curves of SH intensity from the TPPA2a monolayer on the ZnCl2 subphase at six different positions. The dots represent experimental results, and the solid curves are fitting results with eq 2. All the SH intensity data have been normalized. Both the positive and negative DCE values were found. Some of the positions are achiral because the SH intensities are almost the same at the incident polarization angles of ±45°. These results suggest that Zn2+ ions in the subphase inhibit the formation of chiral structures.

(Hamamatsu Photonics) and a single photon counting system (SR400; Stanford Research Systems) at different incident polarization angles. The sample stage could be translated horizontally so that different spots on the monolayer can be examined. In this way, we acquired dependence curves between the SH intensity and the incident polarization angle at different positions of the monolayers.

The polarization dependence curves of the TPPA2a Langmuir monolayer formed on the ZnCl2 aqueous solution subphase are shown in Figure 2. The signs of the DCE values are quite varied at different positions on the monolayer. On some spots (Figure 2A and B), the SH intensities are almost the same at the incident polarization angles of ±45°, and the DCE values equal zero, which means that no chiral structures or only racemic mixtures were formed. For some other spots, the SH intensities are different at the incident polarization angles of ±45°, and either the positive or negative DCE values are obtained, indicating the formation of heterochiral domains on the monolayer. Compared to the pure water subphase, the ZnCl2 aqueous solution subphase is unfavorable for the formation of chiral assemblies. To some degree, it even inhibits this chiral formation. In the case of the CuCl2 aqueous solution subphase (Figure 3), all the positions at the interface are chiral (I+45° ≠ I−45°), and the DCE values are positive except one position (Figure 3F). This is dramatically different from the uniformly negative DCE values for the TPPA2a monolayer on the pure water subphase

■

RESULTS AND DISCUSSION SHG-LD Results. The polarization dependence curves of the SH intensities from the TPPA2a Langmuir monolayer on the pure water subphase are shown in Figure 1. In each curve, the SH intensities are different at the incident polarization angles ±45°, indicating the formation of chiral assemblies in the monolayers. The chirality of the monolayer can be evaluated quantitatively by the DCE value, which is also shown in Figure 1. The calculated DCE values for six different positions are all below zero, indicating that homochiral assemblies are essentially formed. 6728

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

Figure 3. Polarization dependence curves of SH intensity from the TPPA2a monolayer on the CuCl2 subphase at six different positions. The dots represent experimental results, and the solid curves are fitting results with eq 2. All the SH intensity data have been normalized. The absolute values of DCE are greater than that of the TPPA2a monolayer on the pure water subphase, indicating that the Cu2+ ion in the subphase can promote the formation of chiral structures.

as shown in Figure 1. Since the nonzero χxyz originates from twisted packing of the chromophore,39,43,44 it can be concluded that the sign of χxyz, as well as the sign of DCE, was determined by the twist direction of the TPPA2a helix. Although it cannot be deduced from the DCEs whether TPPA2a formed a left- or right-handed helix on pure water, opposite signs of DCEs from water and CuCl2 subphases undoubtedly indicate enantiomerically different chiral assemblies. This means that the assemblies formed by TPPA2a molecules on the CuCl2 aqueous solution subphase are almost homochiral, and Cu2+ ions change the twist direction of the TPPA2a helix. Comparison of DCE Values. The DCE values are summarized in Figure 4. We first compare the absolute values

of DCE on different subphases. For monolayers on the pure water subphase, the absolute value of DCE ranges from 0.08 to 0.22, while for monolayers on CuCl2 and ZnCl2 aqueous solution subphases the ranges are 0.19−0.31 and 0.07−0.32, respectively. The largest range on the ZnCl2 solution subphase demonstrates the inhomogeneity of assemblies caused by Zn2+ ions. In contrast, monolayers on pure water and CuCl2 subphases are more homogeneous. We also compared the average DCE values for each subphase. For the pure water subphase, the average and standard deviations of the DCE values are 0.158 ± 0.002, while for the CuCl2 and ZnCl2 aqueous solution subphases the results are 0.242 ± 0.003 and 0.115 ± 0.014, respectively. The order of average DCE values is CuCl2 > H2O > ZnCl2. Comparing the DCE values obtained from pure water, the ZnCl2 aqueous solution, and the CuCl2 aqueous solution subphases, we can conclude that the ZnCl2 aqueous solution subphase hinders the formation of TPPA2a supramolecular chiral assemblies, while the CuCl2 aqueous solution indeed promotes it. These results indicate that Zn2+ and Cu2+ ions play different roles in the formation of TPPA2a supramolecular chiral assemblies. AFM Measurements. To compare the results obtained from TPPA2a Langmuir monolayers on different subphases with the corresponding LB films, we transferred TPPA2a monolayers onto mica surfaces and measured the morphologies of the samples by atomic force microscopy (AFM). The AFM images (Figure 5) show hierarchical structures at different length scales. TPPA2a assemblies obtained from the pure water subphase have lamella structures with an average height of 2.9 nm (Figure 5a). Assemblies obtained from the subphase containing Zn2+ have amorphous morphologies (Figure 5b), and assemblies obtained from the CuCl2 subphase have lamella structures with a height of about 3.3 nm. The morphologies of LB films deposited from subphases containing different metal ions seem to be related to the SHG-LD measurements on the corresponding TPPA2a Langmuir monolayers. From the DCE values and AFM images, assemblies obtained from water and the CuCl2 subphase possess strong supramolecular chirality and have ordered nanostructures, while assemblies from the ZnCl2 subphase show weak chirality and disordered structures. These results indicate that a compact stacking is essential for the

Figure 4. DCE values of TPPA2a monolayers on different subphases corresponding to the SH intensity polarization dependence curves presented above. On the pure water subphase (green), DCE values of different positions are of the same sign and are comparable with each other. On the ZnCl2 solution subphase (blue), DCE values of different positions are significantly different, indicating that TPPA2a forms nonuniform monolayers, while in the case of CuCl2 (red), the results are similar with that of the pure water subphase. 6729

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

Figure 5. AFM images of TPPA2a LB films deposited from (a) pure water, (b) ZnCl2 aqueous solution, and (c) CuCl2 aqueous solution subphases. The average height of the lamella structures is (a) 2.9 nm and (c) 3.3 nm, respectively.

formation of supramolecular chirality. Interestingly, when these LB films were subjected to circular dichroism spectral measurements, no Cotton effect was observed (Figure S3 in the Supporting Information), similar to the previous results.48 This may imply that the chirality of Langmuir monolayers is not always the same as that of the transferred LB films. Mechanism of Chiral Formation. In this section, we focus on the mechanism of the effect of metal ions on the chirality of porphyrin assemblies. This issue necessarily involves reactions of metal ions with porphyrin molecules. There are two possible reactions that could cause different ion effects on the chiral structures: the coordination of metal ions with the central nitrogen of TPPA2a to form metalloporphyrin derivatives and the coordination of metal ions to the oxygen atoms of the ester groups. It is known that the electronic absorption spectrum of a typical free-base porphyrin consists of one Soret band around 400 nm and four Q-bands in the visible region. If the porphyrin coordinated with metal ions from the central nitrogen, only two Q-bands could be obtained, and there would be some shift in the spectrum as compared to free-base porphyrins. To examine the first possibility, we recorded the UV−vis spectra of TPPA2a LB films deposited from the three different subphases as shown in Figure 6. This measurement showed four peaks without any peak shift for all three samples, indicating that metal ions do not interact with the central nitrogen of TPPA2a. The absence of metalloporphyrin formation at the air/ aqueous interface is likely due to the certain steric effects at the interface and the limited reaction time. Although free-base porphyrin easily reacts with a metal cation to form a metalloporphyrin, it generally occurs in solution and needs several hours to complete.52 Our SHG-LD measurements took less than 2 h. Such short time scales are possibly not enough to result in the reaction between metal cations and the porphyrin rings. Furthermore, the porphyrin rings are closely stacked, and the hydrophobicity pushes them away from the interface, making it difficult for the metal ions to approach inside. Next, we investigated the effects of metal ions on the supramolecular chirality of TPPA4 assemblies by SHG-LD measurements. The molecular structure of TPPA4 is similar to that of TPPA2a but does not contain ester groups (Scheme 1). Thus, this experiment will determine whether coordination of metal ions to the ester groups is a critical factor to affect the supramolecular chirality. The experimental procedure was the same as that for TPPA2a. The TPPA4 chloroform solutions were spread onto the three different subphases to form monolayers, and then SHG-LD measurements were taken. The results are shown in Figure 7. TPPA4 samples form chiral assemblies on all the subphases, with almost the same average

Figure 6. UV−vis spectra of TPPA2a LB films deposited from the three different subphases at the surface pressure of 4 mN/m. There are no significant differences between the curves, indicating no interaction between metal ions and porphyrin rings.

Scheme 1. Molecular Structure of TPPA2a (Left) and TPPA4 (Right)

DCE values (0.285 on pure water, 0.313 on ZnCl2, and 0.299 on CuCl2). Besides, unlike TPPA2a assemblies, the DCE values of TPPA4 assemblies on different subphases have the same sign. This means that metal ions in the subphases have little or no effect on the supramolecular chirality of TPPA4 assemblies. A comparison between TPPA2a and TPPA4 structures shows that these results must be due to the absence of ester groups in TPPA4. On the basis of the above experiments, we conclude that it is the coordination of metal ions in the subphase with the oxygen atoms of the ester groups that causes the different effects of 6730

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

Figure 7. Polarization dependence curves of SH intensity from the TPPA4 monolayer on pure water, ZnCl2, and CuCl2 aqueous solution subphases. The dots represent experimental results, and the solid curves are the fitting results with eq 2. All the SH intensity data have been normalized. For different subphases, the calculated DCE values are comparable, indicating negligible ionic effects on the formation of TPPA4 chiral assemblies.

through π−π stacking and hydrophobic interactions between the alkyl chains. When ZnCl2 is added into the subphase, Zn2+ ions disrupt the arrangement of TPPA2a molecules and hinder the formation of supramolecular chirality. In contrast, Cu2+ ions added into the subphase coordinate with TPPA2a molecules, and a more compact and twisted structure is formed.

metal ions on the formation of supramolecular chirality of the TPPA2a monolayer. The reasons for the above effects may be that Zn2+ ions prefer a tetrahedral mode, which may disturb the organization of porphyrin rings; Cu2+ ions adopt a squarecoordination mode, which helps pull porphyrin molecules together. The possible stacking of TPPA2a molecules on the three different subphases is illustrated in Figure 8. On the pure water subphase, TPPA2a molecules could form helical structures

■

CONCLUSIONS

We have presented an in situ SHG-LD study of the effects of metal ions on the supramolecular chirality of porphyrin derivative TPPA2a assemblies. Measurements of the polarization dependence curves of SH intensity from TPPA2a monolayers indicate that achiral TPPA2a molecules form supramolecular chiral assemblies on the pure water subphase. Zn2+ and Cu2+ added into the subphase cause a considerable variation of the interfacial chirality of TPPA2a assemblies: Zn2+ hinders the formation of supramolecular chiral assemblies, while Cu2+ promotes the formation. UV−vis spectra of TPPA2a LB films deposited from different subphases showed no significant difference, indicating that metal ions do not react with the central nitrogen of TPPA2a. SHG-LD measurements of the TPPA4 monolayer, which is similar to TPPA2a but without ester groups, on the pure water, Zn2+ aqueous solution, and Cu2+ aqueous solution subphases were also performed, and similar polarization dependence curves were obtained from different subphases. Thus, we concluded that the coordination reaction between metal ions in the subphase and the oxygen atoms of the ester groups in TPPA2a has a significant effect on the supramolecular chirality, and the different preferred coordination geometries of Zn2+ and Cu2+ ions give rise to significantly different chirality of the formed supramolecular assemblies.

Figure 8. Schematic illustration of the possible stacking of TPPA2a molecules on (A) pure water, (B) CuCl2 solution, and (C) ZnCl2 solution subphase. The green block represents the porphyrin ring. The blue and yellow lines represent hydrophobic and hydrophilic groups, respectively. The red balls in (B) represent Cu2+ ions, which make a more compact arrangement of TPPA2a molecules. The pale blue balls in (C) represent Zn2+ ions which disturb the organization of TPPA2a molecules. 6731

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

■

Article

(15) Gellman, A. J. Chiral Surfaces: Accomplishments and Challenges. ACS Nano 2010, 4, 5−10. (16) Chen, P. L.; Ma, X. G.; Liu, M. H. Optically Active Phthalocyaninato-Polysiloxane Constructed from Achiral Monomers: From Noncovalent Assembly to Covalent Polymer. Macromolecules 2007, 40, 4780−4784. (17) Zhang, Y. Q.; Chen, P. L.; Liu, M. H. Supramolecular Chirality from an Achiral Azobenzene Derivative through the Interfacial Assembly: Effect of the Configuration of Azobenzene Unit. Langmuir 2006, 22, 10246−10250. (18) Guo, Z. X.; Yuan, J.; Cui, Y.; Chang, F.; Sun, W. H.; Liu, M. H. Supramolecular Assemblies of a Series of 2-Arylbenzimidazoles at the Air/Water Interface: In situ Coordination, Surface Architecture and Supramolecular Chirality. Chem.Eur. J. 2005, 11, 4155−4162. (19) Pasternack, R. F.; Giannetto, A.; Pagano, P.; Gibbs, E. J. SelfAssembly of Porphyrins on Nucleic Acids and Polypeptides. J. Am. Chem. Soc. 1991, 113, 7799−7800. (20) Imahori, H.; Fukuzumi, S. Porphyrin- and Fullerene-Based Molecular Photovoltaic Devices. Adv. Funct. Mater. 2004, 14, 525− 536. (21) Elemans, J. A. A. W.; Van Hameren, R.; Nolte, R. J. M.; Rowan, A. E. Molecular Materials by Self-Assembly of Porphyrins, Phthalocyanines, and Perylenes. Adv. Mater. 2006, 18, 1251−1266. (22) Micali, N.; Engelkamp, H.; van Rhee, P. G.; Christianen, P. C. M.; Scolaro, L. M.; Maan, J. C. Selection of Supramolecular Chirality by Application of Rotational and Magnetic Forces. Nat. Chem. 2012, 4, 201−207. (23) de Miguel, G.; Hosomizu, K.; Umeyama, T.; Matano, Y.; Imahori, H.; Perez-Morales, M.; Martin-Romero, M. T.; Camacho, L. J-Aggregation of a Sulfonated Amphiphilic Porphyrin at the Air-Water Interface as a Function of pH. J. Colloid Interface Sci. 2011, 356, 775− 782. (24) Iavicoli, P.; Xu, H.; Feldborg, L. N.; Linares, M.; Paradinas, M.; Stafstrom, S.; Ocal, C.; Nieto-Ortega, B. L.; Casado, J.; Navarrete, J. T. L.; et al. Tuning the Supramolecular Chirality of One- and TwoDimensional Aggregates with the Number of Stereogenic Centers in the Component Porphyrins. J. Am. Chem. Soc. 2010, 132, 9350−9362. (25) Rosaria, L.; D’Urso, A.; Mammana, A.; Purrello, R. Chiral Memory: Induction, Amplification, and Switching in Porphyrin Assemblies. Chirality 2008, 20, 411−419. (26) Li, J. B.; An, Y. L.; Chen, X.; Xiong, D. A.; Li, Y.; Huang, N.; Shi, L. Q. Chiral Polymeric Micelles from Electrostatic Assembly between Achiral Porphyrins and Block Copolymers. Macromol. Rapid Commun. 2008, 29, 214−218. (27) El-Hachemi, Z.; Mancini, G.; Ribo, J. M.; Sorrenti, A. Role of the Hydrophobic Effect in the Transfer of Chirality from Molecules to Complex Systems: From Chiral Surfactants to Porphyrin/Surfactant Aggregates. J. Am. Chem. Soc. 2008, 130, 15176−15184. (28) Takeuchi, M.; Tanaka, S.; Shinkai, S. On the Influence of Porphyrin Pi-Pi Stacking on Supramolecular Chirality Created in the Porphyrin-Based Twisted Tape Structure. Chem. Commun. 2005, 5539−5541. (29) Kral, V.; Schmidtchen, F. P.; Lang, K.; Berger, M. AnionControlled Assembly of Porphyrin-Bicyclic Guanidine Conjugates. Org. Lett. 2002, 4, 51−54. (30) Rong, Y. L.; Chen, P. L.; Wang, D. G.; Liu, M. H. Porphyrin Assemblies through the Air/Water Interface: Effect of Hydrogen Bond, Thermal Annealing, and Amplification of Supramolecular Chirality. Langmuir 2012, 28, 6356−6363. (31) Qiu, Y. F.; Chen, P. L.; Liu, M. H. Interfacial Assemblies of Atypical Amphiphilic Porphyrins: Hydrophobicity/Hydrophilicity of Substituents, Annealing Effects, and Supramolecular Chirality. Langmuir 2010, 26, 15272−15277. (32) Zhang, Y. Q.; Chen, P. L.; Ma, Y. P.; He, S. G.; Liu, M. H. Acidification and Assembly of Porphyrin at an Interface: Counterion Matching, Selectivity, and Supramolecular Chirality. ACS Appl. Mater. Interfaces 2009, 1, 2036−2043.

ASSOCIATED CONTENT

S Supporting Information *

Surface pressure−area (π−A) isotherms, SHG-LD curves of TPPA2a at different pressures, circular dichroism spectra of TPPA2a LB films, and related discussions. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (M.L.). *E-mail: [email protected] (Y.G.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We acknowledge financial support from the National Natural Science Foundation of China (21073199, 91027042, and 21227802) and the National Key Basic Research Project of China (2013CB834504).

■

REFERENCES

(1) Mateos-Timoneda, M. A.; Crego-Calama, M.; Reinhoudt, D. N. Supramolecular Chirality of Self-Assembled Systems in Solution. Chem. Soc. Rev. 2004, 33, 363−372. (2) Hosseini, M. W. Molecular Tectonics: from Molecular Recognition of Anions to Molecular Networks. Coord. Chem. Rev. 2003, 240, 157−166. (3) Prins, L. J.; Huskens, J.; de Jong, F.; Timmerman, P.; Reinhoudt, D. N. Complete Asymmetric Induction of Supramolecular Chirality in a Hydrogen-Bonded Assembly. Nature 1999, 398, 498−502. (4) Li, S. S.; Northrop, B. H.; Yuan, Q. H.; Wan, L. J.; Stang, P. J. Surface Confined Metallosupramolecular Architectures: Formation and Scanning Tunneling Microscopy Characterization. Acc. Chem. Res. 2009, 42, 249−259. (5) Lee, S. J.; Lin, W. B. Chiral Metallocycles: Rational Synthesis and Novel Applications. Acc. Chem. Res. 2008, 41, 521−537. (6) de Jong, J. J. D.; Lucas, L. N.; Kellogg, R. M.; van Esch, J. H.; Feringa, B. L. Reversible Optical Transcription of Supramolecular Chirality into Molecular Chirality. Science 2004, 304, 278−281. (7) Lorenzo, M. O.; Baddeley, C. J.; Muryn, C.; Raval, R. Extended Surface Chirality from Supramolecular Assemblies of Adsorbed Chiral Molecules. Nature 2000, 404, 376−379. (8) Yuan, G. Z.; Zhu, C. F.; Xuan, W. M.; Cui, Y. Enantioselective Recognition and Separation by a Homochiral Porous Lamellar Solid Based on Unsymmetrical Schiff Base Metal Complexes. Chem.Eur. J. 2009, 15, 6428−6434. (9) Haq, S.; Liu, N.; Humblot, V.; Jansen, A. P. J.; Raval, R. Drastic Symmetry Breaking in Supramolecular Organization of Enantiomerically Unbalanced Monolayers at Surfaces. Nat. Chem. 2009, 1, 409− 414. (10) ten Cate, A. T.; Dankers, P. Y. W.; Kooijman, H.; Spek, A. L.; Sijbesma, R. P.; Meijer, E. W. Enantioselective Cyclization of Racemic Supramolecular Polymers. J. Am. Chem. Soc. 2003, 125, 6860−6861. (11) Mammana, A.; Carroll, G. T.; Areephong, J.; Feringa, B. L. A Chiroptical Photoswitchable DNA Complex. J. Phys. Chem. B 2011, 115, 11581−11587. (12) Canary, J. W.; Mortezaei, S.; Liang, J. A. Transition Metal-Based Chiroptical Switches for Nanoscale Electronics and Sensors. Coord. Chem. Rev. 2010, 254, 2249−2266. (13) Zhang, Y. Q.; Chen, P. L.; Liu, M. H. A General Method for Constructing Optically Active Supramolecular Assemblies from Intrinsically Achiral Water-Insoluble Free-Base Porphyrins. Chem. Eur. J. 2008, 14, 1793−1803. (14) De Feyter, S.; De Schryver, F. C. Two-Dimensional Supramolecular Self-Assembly Probed by Scanning Tunneling Microscopy. Chem. Soc. Rev. 2003, 32, 139−150. 6732

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733

The Journal of Physical Chemistry C

Article

(33) Zhang, L.; Liu, M. H. Supramolecular Chirality and Chiral Inversion of Tetraphenylsulfonato Porphyrin Assemblies on Optically Active Polylysine. J. Phys. Chem. B 2009, 113, 14015−14020. (34) Wang, T.; Liu, M. Langmuir-Schaefer Films of a Set of Achiral Amphiphilic Porphyrins: Aggregation and Supramolecular Chirality. Soft Matter 2008, 4, 775−783. (35) Chen, P. L.; Ma, X. G.; Duan, P. F.; Liu, M. H. Chirality Amplification of Porphyrin Assemblies Exclusively Constructed from Achiral Porphyrin Derivatives. ChemPhysChem 2006, 7, 2419−2423. (36) Yu, W.; Li, Z. S.; Wang, T. Y.; Liu, M. H. Aggregation and Supramolecular Chirality of Achiral Amphiphilic Metalloporphyrins. J. Colloid Interface Sci. 2008, 326, 460−464. (37) Fischer, P.; Hache, F. Nonlinear Optical Spectroscopy of Chiral Molecules. Chirality 2005, 17, 421−437. (38) Belkin, M. A.; Shen, Y. R. Non-linear Optical Spectroscopy as a Novel Probe for Molecular Chirality. Int. Rev. Phys. Chem. 2005, 24, 257−299. (39) Simpson, G. J. Molecular Origins of the Remarkable Chiral Sensitivity of Second-Order Nonlinear Optics. ChemPhysChem 2004, 5, 1301−1310. (40) Verbiest, T.; Kauranen, M.; Persoons, A.; Ikonen, M.; Kurkela, J.; Lemmetyinen, H. Nonliear-Optical Activity and Biomolecular Chirality. J. Am. Chem. Soc. 1994, 116, 9203−9205. (41) Byers, J. D.; Yee, H. I.; Petrallimallow, T.; Hicks, J. M. SecondHarmonic Generation Circular-Dichroism Spectroscopy from Chiral Monolayers. Phys. Rev. B 1994, 49, 14643−14647. (42) Haupert, L. M.; Simpson, G. J. Chirality in Nonlinear Optics. Annu. Rev. Phys. Chem. 2009, 60, 345−365. (43) Burke, B. J.; Moad, A. J.; Polizzi, M. A.; Simpson, G. J. Experimental Confirmation of the Importance of Orientation in the Anomalous Chiral Sensitivity of Second Harmonic Generation. J. Am. Chem. Soc. 2003, 125, 9111−9115. (44) Fujiwara, K.; Monjushiro, H.; Watarai, H. Non-Linear Optical Activity of Porphyrin Aggregate at the Liquid/Liquid Interface. Chem. Phys. Lett. 2004, 394, 349−353. (45) Fu, L.; Liu, J.; Yan, E. C. Y. Chiral Sum Frequency Generation Spectroscopy for Characterizing Protein Secondary Structures at Interfaces. J. Am. Chem. Soc. 2011, 133, 8094−8097. (46) Nagahara, T.; Kisoda, K.; Harima, H.; Aida, M.; Ishibashi, T. A. Chiral Sum Frequency Spectroscopy of Thin Films of Porphyrin JAggregates. J. Phys. Chem. B 2009, 113, 5098−5103. (47) Zhuang, X.; Miranda, P. B.; Kim, D.; Shen, Y. R. Mapping Molecular Orientation and Conformation at Interfaces by Surface Nonlinear Optics. Phys. Rev. B 1999, 59, 12632−12640. (48) Xu, Y. Y.; Rao, Y.; Zheng, D. S.; Guo, Y.; Liu, M. H.; Wang, H. F. Inhomogeneous and Spontaneous Formation of Chirality in the Langmuir Monolayer of Achiral Molecules at the Air/Water Interface Probed by In Situ Surface Second Harmonic Generation Linear Dichroism. J. Phys. Chem. C 2009, 113, 4088−4098. (49) Verbiest, T.; Kauranen, M.; Maki, J. J.; Teerenstra, M. N.; Schouten, A. J.; Nolte, R. J. M.; Persoons, A. Linearly Polarized Probes of Surface Chirality. J. Chem. Phys. 1995, 103, 8296−8298. (50) Maki, J. J.; Verbiest, T.; Kauranen, M.; VanElshocht, S.; Persoons, A. Comparison of Linearly and Circularly Polarized Probes of Second-Order Optical Activity of Chiral Surfaces. J. Chem. Phys. 1996, 105, 767−772. (51) Lin, L.; Liu, A. A.; Guo, Y. Heterochiral Domain Formation in Homochiral alpha-Dipalmitoylphosphatidylcholine (DPPC) Langmuir Monolayers at the Air/Water Interface. J. Phys. Chem. C 2012, 116, 14863−14872. (52) Kadish, K. M.; Smith, K. M.; Guilard, R. The Porphyrin Handbook: Inorganic, Organometallic and Coordination Chemistry; Academic Press: San Diego, 2003; Vol. 3.

6733

dx.doi.org/10.1021/jp4106579 | J. Phys. Chem. C 2014, 118, 6726−6733