Notable Third-Order Optical Nonlinearities Realized in Layer-by-Layer

Sep 22, 2016 - Their third-order nonlinear optical properties were studied by Z-scan measurement with laser pulse duration of 6–7 ns at a wavelength...
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Notable Third-Order Optical Nonlinearities Realized in Layer-byLayer Assembled Composite Films by Intercalation of Porphyrin/ Polyoxometalate into Layered Double Hydroxide Guanying Zhu, Yi Long, Haizhou Ren, Yunshan Zhou,* Lijuan Zhang,* Zonghai Shi, Farooq K. Shehzad, and Hafiz Muhammad Asif State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China S Supporting Information *

ABSTRACT: A series of uniform and smooth (TCPP/LDH)n films and (TCPP/P5W30/LDH)n films were fabricated with meso-tetrakis(p-carboxyphenyl)porphyrin (TCPP), Preysslertype polyoxometalate K 12.5 Na 1.5 [NaP 5 W 30 O 110 ]·15H 2 O (P5W30), and exfoliated Mg2Al−NO3 layered double hydroxide (LDH) monolayer nanaosheets by layer-by-layer assembly technique. The resulting films were characterized by UV− visible spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and fluorescence spectroscopy. Their third-order nonlinear optical properties were studied by Z-scan measurement with laser pulse duration of 6− 7 ns at a wavelength of 532 nm. The (TCPP/LDH)n films exhibit notable self-defocusing effect and saturated absorption effect which is different from TCPP solution. The optical nonlinearity of films becomes larger with the increase of the number of bilayers. The third-order nonlinear optical coefficient χ(3) of (LDH/TCPP)50/LDH is calculated to be (6.4 ± 0.18) × 10−11 esu. Remarkably, experimental results showed that the (LDH/P5W30/LDH/TCPP)n/LDH films exhibit much larger nonlinearity than that of the (LDH/TCPP)n/LDH films when n is the same, which is thought to result from the interlayered charge/energy transfer between porphyrin and polyoxometalate although the LDH sheet is electron-inert material.

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saturation effect in respect to optical nonlinearity.12 Another choice is to form a donor−acceptor system with other materials13 like graphene14−16 and carbon nanotubes,17,18 which can take advantage of constituents to enhance the nonlinear optical effect with a simple procedure and wide range of raw materials; however, organic nonlinear optical materials normally have low melting point, low thermostability, and poor transparency, which inhibit their practical application. In this context, polyoxometalate (POM), a kind of inorganic metal− oxygen cluster19,20 having good stability and solubility, can act as an excellent electron acceptor because the transition metal atoms in the clusters are at the highest valence.21,22 Some theoretical23,24 and experimental25−28 researches have shown that when donor−acceptor systems are formed between POM acting as electron acceptor and porphyrin acting as electron donor, charge transfer and/or energy transfer can occur, resulting in enhanced/tuned nonlinear optical responses. However, highly negatively charged POMs anions can only combine positively charged porphyrins via electrostatic

INTRODUCTION Nonlinear optical materials are the physical embodiment of nonlinear optics, with which the frequency, amplitude, and phase of beam can be modulated, and hence can find many significant applications in laser modulation, optical communication, optical calculation, laser protection, nanometer laser devices, and so on.1 Porphyrins constitute a kind of organic molecule possessing a highly delocalized aromatic π-electron system, large nonlinear coefficient, fast response speed, narrow linear absorption range, and stable structure which can also be finely modified, and thus exhibit great potential for practical application. Extensive studies in the early stage were mainly conducted on simple monomeric porphyrin systems by insertion of different metals in the porphyrin core or by addition of suitable substituents to form asymmetrically substituted push−pull porphyrin in order to improve optical nonlinearities of porphyrins.2 Later, one new strategy is proven effective to improve the nonlinear optical effect of porphyrin, namely, getting multiple porphyrins with further π-extensions such as porphyrin di-, tri-, nona-, and dendramers,3−11 but their successful synthesis normally is very tedious with difficult separation/purification procedures; especially, these large π-conjugated porphyrin systems show © XXXX American Chemical Society

Received: July 31, 2016 Revised: September 12, 2016

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DOI: 10.1021/acs.jpcc.6b07695 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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Chart 1. Structure Diagram of TCPP (a), [NaP5W30O110] Anion (Color Code: Na+, Pink; P−O Tetrahedron, Blue; W−O Octahedron, Aqua) (b), and Mg2Al−NO3 LDH (c) Used in This Study

Isis 300 attachment. Quartz glass, ordinary glass, and silicon slices were used for film fabrication and characterization. AFM images were investigated using a Bruker AFM Mutimode 8 atomic force microscope in Scan Asyst mode. Fluorescence spectra were obtained on an F-7000 fluorospectrophotometer. The third-order nonlinear optical properties were studied by using an EKSPLA NL303 Q-switched Nd:YAG laser at 532 nm with a pulse duration of 6−7 ns and a repetition rate of 10 Hz. The laser beam was focused on the sample by a lens, and the waist radius was 23 μm. The linear transmittance of the aperture was 0.25. All the reagents used were analytically pure and were not further purified before use. TCPP was synthesized according to the literature;34 P5W30 was synthesized according to the literature.35 The synthesis and exfoliation of Mg2Al−NO3 LDH was realized according to the literature.36 The substrates used (quartz glass, ordinary glass, silicon slice) were cleaned as follows: After immersion of substrates into H2SO4/H2O2 (7:3, v/v) mixture for 30 min, the substrates were rinsed with bulk of deionized water and dried with nitrogen. The surfaces of the cleaned substrates were hydrophilic and electronegative. Preparation of the Stock Solutions. TCPP solution (0.1 mM) was prepared by dissolving 0.0024 g of TCPP powder into 30 mL of deionized water with pH value being 8.0 adjusted by diluted NaOH solution. The 1.0 mM P5W30 solution was prepared by dissolving 0.247 g of P5W30 powder into 30 mL of deionized water. Poly(allylamine hydrochloride) (PAH) solution (0.01 M) was prepared by dissolving 0.0114 g of PAH into 20 mL of deionized water with pH 8.0 adjusted by diluted NaOH solution. The poly(styrenesulfonate) (PSS) solution (0.01 M) was prepared by adding 0.0823 g of PSS into 40 mL of deionized water. An amount of 0.1 g of Mg2Al−NO3 LDH in a flask containing 100 mL of formamide under sealed N2 atmosphere was vigorously stirred for 48 h at room temperature, resulting in exfoliated Mg2Al−NO3 colloidal suspension. The exfoliated Mg2Al−NO3 colloidal solution was centrifuged for 10 min with 5000 rpm before use. Fabrication of (LDH/TCPP)n/LDH Films. The cleaned substrate was dipped into exfoliated LDH solution for 20 min, rinsed with water, and dried in N2 flow. After that, it was dipped into TCPP solution for 20 min, then rinsed and dried in the same way. Thus, one layer of LDH/TCPP film was deposited on the substrate. By repeating those procedures above for n times, the (LDH/TCPP)n/LDH films were obtained. Fabrication of (LDH/P5W30)n/LDH Films. The films were fabricated in the same approach as that for (LDH/TCPP)n/ LDH films. Briefly, the substrate was dipped into P5W30 solution and exfoliated LDH solution alternately, for 10 min, and then rinsed with water and dried in N2 flow, respectively.

interaction, and the negatively charged porphyrins which compose a wide arrange of high-potential nonlinear optical (NLO) materials are excluded due to the negative−negative repulsion interaction between negatively charged POMs anions and negatively charged porphyrins. Thus, no effort has been paid to understand influence of negatively charged polyoxometalate anions on the nonlinear optical response of negatively charged porphyrins. Layered double hydroxide (LDH) is a kind of anionic clay with positively charged nanosheets/layers and the balancing anions located in the interlayer region.29 In recent years, with the improvement of exfoliation methods, transparent positively charged nanosheets of LDH can easily be obtained30 and have been used as building units for engineering organic/inorganic or inorganic/inorganic composite materials by layer-by-layer assembly technique with the nanosheets and functional molecules. It has been reported that assembly of exfoliated LDH with porphyrin can form film where negatively charged porphyrins are immobilized with suppressed aggregation and enhanced uniformity and stability.31 Intercalation of POM anions into LDH layers resulting in insoluble product in aqueous media have also been reported, 32 where the polyoxoanions intercalated between the LDH layers may be even more stabilized than free ones.33 These interesting works imply that LDH can offer the opportunity to get negatively charged porphyrins and negatively charged polyoxoanions integrated. Taking the above into account, in this article, we selected meso-tetrakis(p-carboxyphenyl)porphyrin (TCPP) as a prototype, exfoliated Mg2Al−NO3 LDH monolayer nanosheets, and Preyssler-type POM K12.5Na1.5[NaP5W30O110]·15H2O (P5W30) which has a high reduction potential (Chart 1) as building blocks to prepare (LDH/TCPP)n/LDH and (LDH/P5W30/ LDH/TCPP)n/LDH ultrathin films. The composition and morphology of films were characterized by UV spectroscopy, energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The third-order nonlinear optical property of them was determined by the Z-scan method. Experimental results showed that the nonlinearity of porphyrin can be modulated/tuned by combination with LDH nanosheets and can be further enhanced by incorporation of POM.

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EXPERIMENTAL DETAILS Instruments and Materials. UV−vis absorption spectra were determined with a Shimadzu UV-2550 spectrophotometer with the slit width of 1.0 nm. SEM images and EDX spectra were determined using an SEM Hitachi S-3500 scanning electron microscope equipped with an EDX Oxford Instrument B

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Figure 1. UV−vis absorption spectra of (LDH/TCPP)n/LDH (n = 1−7) films (a) (the red dotted line shows the spectrum of 1 × 10−7 mol·L−1 aqueous TCPP solution) and (LDH/P5W30/LDH/TCPP)n/LDH (n = 1−7) films (c). The insets show the plot of the absorbance vs number of bilayers at 418 nm (a) and 213 and 418 nm (c), respectively. Digital photo of (LDH/TCPP)n/LDH films (top) and (LDH/P5W30/LDH/TCPP)n/ LDH films (bottom) with n = 10, 20, and 50, respectively, highlighting color change with increasing layer number n (b).

Figure 2. SEM images of (LDH/P5W30/LDH/TCPP)20/LDH (a, top view; b, side view) and (LDH/TCPP)n/LDH film (c, top view with n = 50; d, side view with n = 10−50, respectively).

Fabrication of PAH/PSS/(LDH/PSS)n/LDH Films. The films were fabricated according to a literature.37 Briefly, the clean substrate was dipped into PAH solution for 20 min, and was rinsed by abundant deionized water and dried in N2 flow. Then, the substrate was dipped into PSS solution for 20 min, rinsed by abundant deionized water and dried with nitrogen. The precoated substrate was dipped into exfoliated LDH solution for 10 min and PSS solution for 15 min and was then rinsed and dried, respectively. Repeating the above last two procedures for n times resulted in formation of PAH/PSS/ (LDH/PSS)n/LDH films. Fabrication of (LDH/P5W30/LDH/TCPP)n/LDH Films. The clean substrate was dipped into exfoliated LDH solution for 20 min, followed by rinsing with water and drying in N2 flow. Then, it was dipped into P5W30 solution for 20 min and rinsed and dried. Then, it was dipped into exfoliated LDH solution for 10 min and was rinsed and dried in the same way.

By repeating those procedures above for n times, the (LDH/ P5W30/LDH/TCPP)n/LDH films were prepared.

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RESULTS AND DISCUSSION Preparation and Characterization of the Films. The growth of films of different compositions on a quartz plate in this work was monitored by measuring the ultraviolet−vis (UV−vis) spectra of the components after each deposition process. It was found that intensities of the characteristic absorption bands of TCPP, viz., the strong absorption band around 418 nm (Soret band) corresponding to the S0−S2 transition and the four absorption bands in the range of 500− 700 nm (Q-band) corresponding to the S0−S1 transition, increase linearly with the increase of the number of bilayers in the (LDH/TCPP)n/LDH (n = 1−7) films (Figure 1a). This shows that the films grow uniformly and the content of porphyrin deposited within each layer is the same. However, when compared with TCPP solution, the Soret band of C

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Figure 3. AFM image (a and c) and the corresponding 3D image (b and d) of (LDH/TCPP)50/LDH film (a and b) and (LDH/P5W30/LDH/ TCPP)20/LDH film (c and d), respectively.

porphyrin in the films gets broadened and red-shifted, a phenomenon also found in other porphyrin-intercalated LDH composites, which may be related to the space constraint from LDH sheets and stacking of porphyrin.38 UV−vis absorption spectra of (LDH/P5W30/LDH/TCPP)n/LDH films are shown in Figure 1c. It was found that the absorbance at 418 nm assigned to the Soret band of TCPP and the absorbance at 213 and 418 nm assigned to O → W charge transition in P5W3039 increase linearly as the number of layers increase, which proves the films grow uniformly. That the shape and position of the absorption bands are nearly the same as that of the TCPP solution shows that porphyrin molecules in between the LDH layers are not aggregated.40 The linear growth of the (LDH/TCPP)n/LDH and (LDH/ P5W30/LDH/TCPP)n/LDH films with increasing layer number n can be also proved by observing the color of films (Figure 1b). It was found that the films on the substrate show homogeneous color, good transparency, and the color of films darkens with the increase of the number of bilayers, indicating increase of the number of porphyrin molecules. From the SEM images of the (LDH/P5W30/LDH/TCPP)20/ LDH and (LDH/TCPP)50/LDH films (Figure 2), selected as representatives, it is known that the films are continuous, smooth, homogeneous, and uniform (Figure 2, parts a and c). Considering the thickness of (LDH/TCPP)n/LDH films (Figure 2d), the thickness of LDH nanosheets being ca. 1.0

nm, and the thickness of (LDH/P5W30/LDH/TCPP)20/LDH film measured to be 74 nm (Figure 2b), the height of the interlayer of P5W30 is calculated to be about 0.93 nm, implying that P5W30 anions are arranged in the interlayer with the C5 rotation axis perpendicular to the LDH sheet. In order to get the more detailed information on the surface of films, the AFM technique was used. It was found that the film (LDH/TCPP)50/LDH, selected as a representative, is quite smooth and homogeneous (Figure 3, parts a and b) with root-mean-square roughness being 10.6 nm. After insertion of P5W30, the resulting (LDH/P5W30/LDH/TCPP)n/LDH films become a little rough (Figure 3, parts c and d) as compared with (LDH/TCPP)n/LDH films which is known by considering the root-mean-square roughness being 16.9 nm of (LDH/ P5W30/LDH/TCPP)20/LDH film selected as a representative. The increased roughness may result from the interaction between LDH and POM bearing 13 negative charges which is stronger than that between LDH and TCPP bearing four negative charges, thus resulting in formation of more particles on the surface of the film. However, (LDH/P5W30/LDH/ TCPP)n/LDH films are still thought to be relatively smooth in view of the thickness of films. All the films have a good transparency, which is important in view of their application in optics. Third-Order Optical Nonlinearities of the Films. The Zscan curves along with corresponding fits for (LDH/TCPP)n/ D

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Figure 4. Open-aperture curves (a and c) and pure refraction curves (b and d) for (LDH/TCPP)n/LDH films (n = 10−50) (a and b) and aqueous TCPP solution (1 × 10−4 mol·L−1) (c and d), respectively. Scatter points are the experimental data; the solid curves are the theoretical fitting results (n = 10, black; 20, orange; 30, green; 40, pink; 50, blue).

Table 1. Third-Order Nonlinear Optical Parameters of TCPP/LDH Films and TCPP/P5W30/LDH Films samples TCPP solution (LDH/TCPP)10/LDH (LDH/TCPP)20/LDH (LDH/TCPP)30/LDH (LDH/TCPP)40/LDH (LDH/TCPP)50/LDH (LDH/P5W30/LDH/TCPP)10/LDH (LDH/P5W30/LDH/TCPP)20/LDH

β × 10−7 (esu) 15.9 −4.93 −6.24 −11.69 −25.56 −31.61 −5.70 −6.96

± ± ± ± ± ± ± ±

0.48 0.11 0.16 0.12 0.77 0.47 0.06 0.11

LDH films (n = 10, 20, 30, 40, 50) are shown in Figure 4. Reasonably good matches between the observed experimental data and the theoretical curves are observed. This result suggests that the experimentally detected NLO effects have an effective third-order characteristic. All of the films have notable nonlinear saturable absorption under the open-aperture configuration corresponding to a negative nonlinear absorption coefficient (Figure 4a). Each of the closed-aperture Z-scan curves for the films have a peak−valley configuration corresponding to a negative nonlinear refractive index and a characteristic self-defocusing behavior of the propagating wave in the films (Figure 4b). In order to investigate the contribution of LDH and TCPP in the films to the third-order NLO response of the hybrid films, Z-scan curves of the multilayer films PAH/PSS/(LDH/PSS)20/LDH were obtained (Figure S3). It was found that both the open-aperture curve and pure refraction curve are almost straight lines, indicating that the third-order optical nonlinearity of LDH nanosheets themselves

n2 × 10−11 (esu) −8.89 −0.67 −8.59 −16.94 −27.79 −40.14 −11.51 −14.24

± ± ± ± ± ± ± ±

0.26 0.01 0.17 0.17 0.80 0.60 0.13 0.14

χ(3) × 10−12 (esu) 12.69 1.26 13.62 27.00 44.37 64.03 18.34 22.68

± ± ± ± ± ± ± ±

0.38 0.05 0.27 0.24 1.33 0.96 0.22 0.23

is negligible even if they are assembled with PSS. So, the observed third-order optical nonlinearities for the (LDH/ TCPP)n/LDH films can only come from the intercalated TCPP molecules. However, it was found that the TCPP solution shows a notable reverse saturation absorption property (Figure 4c) originating from the occurrence of intersystem crossing from the lowest excited singlet state to the lowest triplet state and the subsequent increase in the population of the strongly absorbing triplet state with nanosecond dynamics, respectively. The transformation in the nonlinear absorption from nonlinear reverse saturation absorption for TCPP solution to nonlinear saturable absorption for the (LDH/TCPP)n/LDH films under the open-aperture configuration should be attributed to the surface effect of the ultrathin hybrid film due to strong interaction between negatively charged TCPP and positively charged LDH, i.e., the excited electrons introduced by laser E

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Figure 5. Open-aperture curves (a) and pure refraction curves (b) for (LDH/TCPP)n/LDH films (n = 10, black; 20, green) and (LDH/P5W30/ LDH/TCPP)n/LDH films (n = 10, orange; 20, pink). Scatter points are the experimental data; the solid curves are the theoretical fitting results.

would be trapped by the surface state in the film rather than the excited state.27,41,42 According to Sheik-Bahae et al.’s theoretical equations,43 the nonlinear refractive index n2, nonlinear absorption coefficient, and the resulting third-order optical nonlinear susceptibility χ(3) are calculated (see Table 1). It is found that the magnitude of χ(3) (esu) for (LDH/TCPP)n/LDH films (n = 10, 20, 30, 40, 50) increases with increasing layer number n of films, i.e., the optical nonlinear susceptibility χ(3) is dependent on the amount of NLO-active component TCPP. Likewise, (LDH/P5W30/LDH/TCPP)10/LDH films exhibit nonlinear saturated absorption and self-defocusing NLO properties, and the nonlinearity of them increases as the number of layers increase, the same trend as that for (LDH/ TCPP)n/LDH films. Importantly, it was found that the (LDH/ P5W30/LDH/TCPP)n/LDH films have much larger optical nonlinearity than the (LDH/TCPP)n/LDH (Figure 5, Table 1) when the number n of layers is the same. Because neither P5W30 solution (Figure S4) nor (LDH/P5W30)n/LDH films (Figure S5) show obvious third-order nonlinear optical response under the same experimental conditions, and the contents of TCPP are approximately the same in the films when n is the same known from the absorption intensity of the band appearing at 421 nm that is attributed to Soret band of TCPP (Figure 6), obviously, the above results demonstrate that the incorporation of P5W30 can enhance the nonlinear optical response of TCPP in the films. In order to understand the nonlinear optical response enhancement caused by insertion of P5W30, the energy levels of

the frontier molecular orbitals of TCPP and P5W30 were obtained and compared. On the basis of the cyclic voltammogram (Figure 7a) and UV−vis absorption spectrum (Figure 7b), the energy gap corresponding to the difference of the energy level of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of TCPP can be calculated with the formula Eg = 1240/λ = 1.87 eV. The first onset oxidation potential of TCPP (Eox = 1.07 V) can be obtained from the cyclic voltammetry of TCPP. According to the formula EHOMO (eV) = −e(4.8 − EFOC + EOX) (EFOC = 0.47 V, Ag/AgCl electrode used as reference), the energy level of the HOMO of TCPP can be obtained as EHOMO = −5.40 eV. Thus, the LUMO energy level of TCPP is obtained as ELUMO = EHOMO + Eg = −3.53 eV.44 It is found that the LUMO energy level of P5W30 (ELUMO = −4.75 eV)45 is lower than that of TCPP as depicted in Figure 8a. Thus, it may be deduced that, under the irradiation of laser, electrons in the porphyrin are excited and transit from their HOMO to LUMO orbits. The electrons in the LUMO of porphyrin can easily transit to the low-energy LUMO of P5W30 and lead to expanded flow range of electrons, consequently resulting in the enhancement of nonlinearity of porphyrin. In addition, from the fluorescence emission spectra of (LDH/TCPP)20/LDH and (LDH/P5W30/LDH/TCPP)20/ LDH films where the content of porphyrin is approximately the same (Figure 8a), it is known that the fluorescence intensity of the peak at 632 nm for (LDH/P5W30/LDH/TCPP)20/LDH films is lower by 14.2% than that for (LDH/TCPP)20/LDH films (Figure 8b). The fluorescence quenching further confirms that charge or energy transfer can occur between the POM moiety acting as electron acceptor and porphyrin moieties acting as electron donor which are separated by exfoliated LDH nanosheets, although the LDH sheet is an electron-inert material.46

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CONCLUSIONS Transparent (LDH/TCPP)n/LDH films and (LDH/P5W30/ LDH/TCPP)n/LDH films, which are homogeneous, smooth, and ultrathin, were successfully prepared by layer-by-layer assembly technique and characterized. All the resulting films exhibit saturated absorption and self-defocusing effect. The third-order nonlinear optical effect can be regulated by controlling the number of layers. Importantly, the nonlinearity of porphyrin can be improved by the incorporation of POMs, which may result from the energy transfer between POMs and porphyrin in different interlayers. In perspective, given the large

Figure 6. UV−vis absorption spectra of (LDH/TCPP)n/LDH films (black, a, n = 10; b, n = 20) and (LDH/P5W30/LDH/TCPP)n/LDH films (red, c, n = 10; d, n = 20). F

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Figure 7. Cyclic voltammetry of 1 mM TCPP solution in DMF solution containing 0.1 M tetrabutylammonium hexafluorophosphate used as supporting electrolyte (a), and UV−vis absorption spectra of 0.1 mM TCPP solution in DMF (b).

Figure 8. Energy diagram of the frontier molecular orbitals of TCPP and P5W30 (a) and fluorescence emission spectra of (LDH/TCPP)20/LDH film (black) and (LDH/P5W30/LDH/TCPP)20/LDH film (red) excited at 418 nm (b).

number of negatively charged porphyrins, LDHs, and polyoxometalates of various structures, constitutes, and properties reported in the literature, the present results may provide us with a new guide to design and explore porphyrin-based NLO materials possessing excellent optical nonlinear responses by proper combination with polyoxometalates and LDH of different compositions, structures, and chemophysical properties.

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ACKNOWLEDGMENTS

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REFERENCES

The authors thank the Natural Science Foundation of China and open projects fund of Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences for financial support. Professor Xue Duan of Beijing University of Chemical Technology is greatly acknowledged for his kind support.

ASSOCIATED CONTENT

(1) Zyss, J. Molecular Nonlinear Optics: Materials, Physics and Devices; Academic Press: Boston, MA, 1994. (2) Senge, M. O.; Fazekas, M.; Notaras, E. G. A.; Blau, W. J.; Zawadzka, M.; Locos, O. B.; Ni Mhuircheartaigh, E. M. Nonlinear Optical Properties of Porphyrins. Adv. Mater. 2007, 19, 2737−2774. (3) Hu, X.; Xiao, D.; Keinan, S.; Asselberghs, I.; Therien, M. J.; Clays, K.; Yang, W.; Beratan, D. N. Predicting the Frequency Dispersion of Electronic Hyperpolarizabilities on the Basis of Absorption Data and Thomas-Kuhn Sum Rule. J. Phys. Chem. C 2010, 114, 2349−2359. (4) Imahori, H. Giant Multiporphyrin Arrays as Artificial LightHarvesting Antennas. J. Phys. Chem. B 2004, 108, 6130−6143. (5) Xu, Y.; Liu, Z.; Zhang, X.; Wang, Y.; Tian, J.; Huang, Y.; Ma, Y.; Zhang, X.; Chen, Y. A Graphene Hybrid Material Covalently Functionalized with Porphyrin: Synthesis and Optical Limiting Property. Adv. Mater. 2009, 21, 1275−1279. (6) Jiang, N.; Zuber, G.; Keinan, S.; Nayak, A.; Yang, W.; Therien, M. J.; Beratan, D. N. Design of Coupled Porphyrin Chromophores with Unusually Large Hyperpolarizabilities. J. Phys. Chem. C 2012, 116, 9724−9733. (7) Ogawa, K.; Kobuke, Y. Construction and Photophysical Properties of Self-Assembled Linear Porphyrin Arrays. J. Photochem. Photobiol., C 2006, 7, 1−16. (8) Tanaka, T.; Osuka, A. Conjugated Porphyrin Arrays: Synthesis, Properties and Applications for Functional Materials. Chem. Soc. Rev. 2015, 44, 943−969.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b07695. UV−vis absorption spectra of (LDH/P5W30)n/LDH (n = 1−7) and PAH/PSS/(LDH/PSS)n/LDH (n = 1−7) films, third-order nonlinear optical measurements and calculation methods, and open-aperture and closedaperture curves for PAH/PSS/(LDH/PSS)20/LDH, P 5 W 30 aqueous, and (LDH/P 5 W 30 ) 25 /LDH films (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Phone: +86 18511945529. *E-mail: [email protected]. Phone: +86 13717916378. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. G.Z. and Y.L. contributed equally. Notes

The authors declare no competing financial interest. G

DOI: 10.1021/acs.jpcc.6b07695 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.jpcc.6b07695 J. Phys. Chem. C XXXX, XXX, XXX−XXX