Solution Properties and Effect of Anions on Third-Order Optical

Article pubs.acs.org/JPCC

Solution Properties and Effect of Anions on Third-Order Optical Nonlinearity of Porphyrin−Heteropolyoxometalate Hybrid System Zonghai Shi,† Yunshan Zhou,*,†,‡ Lijuan Zhang,*,† Sadaf ul Hassan,† and Ningning Qu† †

State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology, Beijing 100029, P. R. China ‡ Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China S Supporting Information *

ABSTRACT: The investigation on interactions between tetraphenylporphyrin (TPP) and α-Keggin-type heteropolyoxometalates (POMs) (POMs sequentially refer to H5PMo10V2O40·36H2O (PMoV), H 3 PMo 12 O 40 ·14H 2 O (PMo), H 4 SiMo 12 O 40 ·xH 2 O (SiMo), and H4SiW12O40·xH2O (SiW)) in THF reveals that TPP evolves into a monosalt and successively into a disalt by accepting protons from POMs and that the 2:1 hybrid between PMoV and TPP and the 1:1 hybrids between TPP and PMo, SiMo, and SiW are formed in the THF solution. The reaction equilibrium constants calculated for the 1:1 complexes are quite large, indicative of strong interaction between TPP and POMs. When the concentration of the reactants were simply increased, four hybrids [H2TPP][H4PMo10V2O40]2·6C4H4O·H2O (1), [H2TPP][HPMo12O40]· 5C4H8O·5H2O (2), [H2TPP][H2SiMo12O40]·3C4H8O·3H2O (3), and [H2TPP][H2SiW12O40]·4C4H8O·8H2O (4) were isolated and characterized. Z-scan measurement showed that POMs themselves had negligible nonlinear optical response, whereas they imposed remarkable effect on the third-order nonlinear optical properties of resulting TPP−POM hybrid systems. It is found that the second hyperpolarizability values of compounds 1−4 are inversely proportional to the highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO− LUMO) gaps of these compounds and directly proportional to the discrepancy between the LUMO levels of TPP and POMs, i.e., the low-lying LUMO level of the POMs is important for the improved second hyperpolarizability value of the compounds. porphyrin arrays,25−28 and porphyrin-based hybrids.29−32 Nevertheless, as far as we know, no investigation about the effect of anions on the nonlinearity of porphyrin has been reported to date. Polyoxometalates (POMs) are inorganic metal−oxygen clusters formed by the early transition metals, incorporating nearly every element of the periodic table. They exhibit remarkable structural diversity and chemical composition variety, have shown unique physicochemical properties, and are used in various applications.33,34 In particular, POM anions are a kind of good electron acceptor and able to exchange many electrons without changing their structure. This remarkable property makes them fascinating building blocks which can play an important role in supramolecular and optical fields.35−41 Because the diverse chemical and physical properties of porphyrins and POMs are in many ways complementary rather than overlapping,42,43 there are a few reports on the activity of materials containing both types of molecules which mainly focus on their catalytic and photoelectrochemical proper-

1. INTRODUCTION Third-order nonlinear optical (NLO) materials have attracted attention because of their potential utilization in photonic applications such as ultrafast optical switching and modulations.1−3 Various types of organic compounds have been studied to obtain materials with improved NLO properties.4−7 It has been generally accepted that highly delocalized πconjugated systems can give rise to a strong NLO response.8,9 Among the NLO materials concerned, porphyrins, which are composed of four pyrrole units linked together through their αpositions by methine bridges, are promising candidates because of the large π-conjugated system, their versatile structural modifications, high stability and flexibility of excited state properties as well as remarkable NLO response, which can be easily modulated through conformational design, molecular symmetry, metal complexation, orientation and strength of the molecular dipole moment, size and degree of conjugation of the π-systems, and appropriate donor−acceptor substituents.9 They have gained intense attention in the field of nonlinear optics. The current strategies adopted on porphyrin-based materials for improving and optimizing NLO properties have mainly focused on symmetric porphyrins,10−13 asymmetric porphyrins,14−17 porphyrin oligomers,18−22 expanded porphyrins,23,24 © 2014 American Chemical Society

Received: December 20, 2013 Revised: February 24, 2014 Published: February 27, 2014 6413

dx.doi.org/10.1021/jp412500r | J. Phys. Chem. C 2014, 118, 6413−6422

The Journal of Physical Chemistry C

Article

Figure 1. UV−vis spectral titrations of TPP with (A) PMoV, (B) PMo, (C) SiMo, and (D) SiW. Insert charts (a) are the plots of A415 nm versus [POM]/[Porphyrin]; insert charts (b) are the magnified spectra of the spectral titrations at 550−720 nm (the concentrations of PMoV is increased in the unit of 6.4 × 10−7 M, while the concentration of PMo, SiMo, and SiW is increased in the unit of 3.2 × 10−7 M from the black to the purple line).

ties.44−59 So far, two articles are reported about their secondorder NLO properties where the porphyrin−POM hybrids are found to possess remarkably large static second-order polarizabilities47,60 due to charge transfer between TPP and POMs. This further illustrates that the hybrids between porphyrins and POMs are expected to become a new type of excellent NLO material. However, to the best of our knowledge, no studies about the third-order NLO properties of such porphyrin−POM hybrids have been reported. Inspired by the above analysis, herein the solution properties of the hybrid system consisting of tetraphenylporphyrin (TPP, see Figure S1A of Supporting Information) selected as a protype and α-Keggin-type POMs61 (POMs sequentially refer to H5PMo10V2O40·36H2O (PMoV), H3PMo12O40·14H2O (PMo), H4SiMo12O40·xH2O (SiMo), and H4SiW12O40·xH2O (SiW), see Figure S1B of Supporting Information) were studied by a spectroscopic titration method in THF. Four porphyrin− heteropolyoxometalate hybrids [H2TPP][H4PMo10V2O40]2· 6C4H4O·H2O (1), [H2TPP][HPMo12O40]·5C4H8O·5H2O (2), [H 2 TPP][H 2 SiMo 12 O 40 ]·3C 4 H 8 O·3H 2 O (3), and [H2TPP][H2SiW12O40]·4C4H8O·8H2O (4) comprising TPP cations and POM anions via electrostatic forces were isolated by simply increasing the concentration of the reactants and characterized by standard methods including infrared spectroscopy and thermogravimetric (TG) and elemental analyses. The third-order NLO properties of the hybrid system were studied by Z-Scan technique, and the effect of POM anions on the third-order nonlinearity of porphyrin was addressed for the first time.

2. EXPERIMENTAL SECTION 2.1. Materials and Instruments. TPP,62 PMoV,63 and SiMo64 were prepared according to literature methods. All the other chemicals were purchased from Aladdin, were of analytical grade, and were used without further purification. Solvents were used as received or dried using standard procedures. IR spectra were recorded on a Nicolet 6700 spectrophotometer with KBr pellet in the range of 400−4000 cm−1. The UV−vis spectra were recorded with a Shimadzu UV-2550 spectrophotometer in the range of 200−800 nm. Thermogravimetric analyses were carried out on a TGAQ50 instrument at a heating rate of 10 °C/min under air atmosphere. Elemental analyses for C, H, and N was performed on an 1106 type analytical instrument. Cyclic voltammograms (CV) were obtained on a CHI660B electrochemical analyzer in dry DMF at room temperature at the rate of 10 mV/s in the presence of 0.1 M [(n-butyl)4N]PF6 (TBAPF6) as a supporting electrolyte. A glassy carbon electrode was used as a working electrode, Ag/AgCl as a reference electrode, and a Pt wire as an auxiliary electrode. NLO properties were performed by using an EKSPLA NL303 Q-switched Nd:YAG laser at 532 nm with a pulse duration of 20 ps, a repetition rate of 10 Hz, and the intensity of the light at focus E0 being 2.3 uJ. The waist ω0 was measured to be 19 μm. The linear transmittance of the far-field aperture S (defined as the ratio of the pulse energy passing through the aperture to the total pulse energy) was measured to be 0.25. The linear absorption coefficient α0 was measured to be 0.55 cm−1 at 532 nm, and the linear refractive index n0 was measured to be ca.1.429 for all the samples. 2.2. Investigation Method of Solution Properties of Porphyrin−Heteropolyoxometalate Hybrid Systems. 6414



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Figure 2. Plot of (A − A0)/(A∞ − A) vs ([POM] - α[porn]) of (A) 2, (B) 3, and (C) 4 at 415 nm.

444 nm for SiW) appear and their intensities increase with increasing POM concentration in the solution. The peaks at around 235 and 310 nm in Figure 1A−C are assigned to charge-transfer absorption band of M ← Od and M ← Ob, c, respectively.66 When the UV−vis spectra of parent POMs in THF are compared (Figure S3 of Supporting Information), the charge-transfer absorption bands have a red-shift or blue-shift indicating the strong interaction between POMs and TPP in the solution. The difference for titration of SiW is the W ← Ob, c absorption band appearing at 276 nm and the M ← Od band is absent in this spectrum (Figure 1D) because of the low wavelength of its location.67 The band at 276 nm also showed a red-shift. The new peak at 444 nm in Figure 1 increases with increasing POM concentration in the solution, indicating the existence of [H4TPP]2+ in the form of J-aggregates formed by accepting two H from POMs.68 The peak intensity increasing at ca. 656 nm with increasing POM concentration is also evidence of the existence of J-aggregates.68 The red-shift of this band indicates the presence of TPP monosalt in the solution, and the TPP free base evolves into a monosalt by accepting a H proton from POM and then into a disalt during titration of POMs.69 The float of the isosbestic point in the region 555−615 nm is also powerful proof of the existence of a monosalt (inset charts marked (b) in Figure 1).69 The peaks at 512, 545, and 589 nm gradually disappear when the POM concentration in THF is big enough. The observed pattern of electronic absorption bands can be explained on the basis of increased symmetry of disalt [H4TPP]2+ (S4) compared to that of free base (D2h) because of addition of two protons at the nitrogen atoms of the pyrrole rings. Precipitate of compounds 1−4 will be found when the concentration of TPP and POMs in THF is increased. As shown in the insert chart (a) of Figure 1A, PMo10V2O405− has linear hypochromophores effect on TPP when the concentration of PMo10V2O405− is less than two times the concentration of TPP. An obvious turning point at 2:1 stoichiometry of [PMo10V2O405−]/[TPP] indicates that the 2:1 complex is formed between PMo10V2O405− and TPP in the solution. The 1:1 complexes are formed between TPP and PMo, SiMo, and SiW (panels B, C, and D of Figure 1, respectively),43 which is in agreement with the results obtained from elemental analyses. The equilibrium constant K for the 2:1 complex was not calculated because of the formation of an unclear intermediate product during reaction. The equilibrium constants K for the 1:1 complexes were calculated by eqs 1−4.70

The solution properties of porphyrin−heteropolyoxometalate hybrid systems were studied in THF by a spectroscopic titration method and performed in a quartz cell (1 cm optical path length). Titrations were achieved by successive addition of THF solutions of POMs (the concentration of POMs was continuously increased in the unit of 6.4 × 10−8 M) into a TPP solution with fixed concentration (2.5 × 10−6 M). The UV−vis spectrum was recorded for each titration process until the absorption peak at 415 nm disappeared completely. 2.3. Preparation of Compounds 1−4. [H 2 TPP][H4PMo10V2O40]2·6C4H8O·H2O (1). TPP (0.18 g) and PMoV (0.21 g) were dissolved separately in 20 mL of tetrahydrofuran (THF) solution. A green powder solid appeared instantaneously after the two concentrated solutions were mixed under stirring. The product was collected by vacuum filtration, washed with 40 mL of THF four times, and air-dried. Yield: 0.19 g (70% based on PMoV). Elemental analyses (%) calcd.: C 17.81, N 1.20, H 2.01. Found: C, 17.38; N, 1.18; H, 1.93. [H2TPP][HPMo12O40]·5C4H8O·5H2O (2). The synthetic procedure was similar to that used for 1, except that PMo was used instead of PMoV. Yield: 0.27 g (85% based on PMo). Elemental analyses (%). Calcd.: C, 26.61; N, 1.94; H, 2.87. Found: C, 26.18; N, 1.91; H, 2.66. [H2TPP][H2SiMo12O40]·3C4H8O·3H2O (3). The synthetic procedure was similar to that used for 1, except that SiMo was used instead of PMoV. Yield: 0.26 g (83% based on SiMo). Elemental analyses (%). Calcd.: C, 24.68; N, 2.05; H, 2.42. Found: C, 25.24; N, 1.92; H, 2.56. [H2TPP][H2SiW12O40]·4C4H8O·8H2O (4). The synthetic procedure was similar to that used for 1, except that SiW was used instead of PMoV. Yield: 0.23 g (80% based on SiW). Elemental analyses (%). Calcd.: C, 18.02; N, 1.45; H, 1.92. Found: C, 18.31; N, 1.43; H, 2.08.

3. RESULTS AND DISCUSSION 3.1. Solution Properties of Porphyrin−Heteropolyoxometalate Hybrid Systems. The solution properties of porphyrin−heteropolyoxometalate hybrid systems were studied by a spectroscopic titration method in THF as shown in Figure 1 (Figure S2 of Supporting Information). As compared with the absorption of free TPP which are mostly confined to B (415 nm) and Q (512, 545, 589, 644 nm) bands,65 the B band and Q band of TPP reduce gradually with the increase of POM concentration in the solution with three isosbestic points (the isosbestic points appeared at 389, 424, and 501 nm for titrations of PMoV; 359, 424, and 490 nm for PMo; 384, 424, and 497 nm for SiMo; and 354, 424, and 496 nm for SiW). Three new absorption peaks at 236, 303, and 444 nm for titration of PMoV (the new peaks are located at 240, 312, and 444 nm for PMo; 241, 303, and 444 nm for SiMo; and 276 and

K

[por] + [POM] ⇔ [Conc] 6415

(1)



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Table 1. IR Data of TPP and Compounds 1−4a TPP (cm−1)

1 (cm−1)

2 (cm−1)

3 (cm−1)

4 (cm−1)

assignment

3321 3091/3078 3134/3108 1599 1442 1351 1001/989 978/965 887/875 851/830 699

3314 3070 3102 1599 1442 1289 1002 985 880 850 706 1059 (1066) 959 (962) 875 (865) 797 (782)

3309 3069 3106 1599 1440 1293 1011 992 884 858 712 1062 (1066) 958 (960) 878 (869) 797 (779)

3310 3080 3094 1599 1442 1291 1002 983 875 846 707 973 (981) 919 (926) 885 (882) 795 (782)

3316 3073 3099 1599 1442 1293 1020 1007 890 856 711 954 (956) 904 (907) 868 (858) 795 (782)

ν(N−H) ν(Cβ−H)dsym/ν(Cβ−H)psym ν(Cβ−H)dasym/ν(Cβ−H)pasym phenyl Phenyl ν(pyr half-ring)psym ν(pyr half-ring)dasym + phenyl/ν(pyr half-ring)dasym δ(pyr breath)d/δ(pyr breath)p + Phenyl δ(pyr def)dsym/δ(pyr def)dsym δ(pyr def)dasym/δ(pyr def)dasym γ(Cβ−H)sym + phenyl M−Oa M−Od M−Ob−M M−Oc−M

a Annotation: ν, δ, γ denote stretching, in-plane bending, and out-of-plane bending modes, respectively. The subscripts sym and asym represent the symmetric and asymmetric modes, respectively. Def and pyr represent deformation and pyrrole, respectively. Superscript p and d denote protonated and deprotonated pyrrole, respectively. The data in the parentheses are IR data of the corresponding parent POMs (PMoV, PMo, SiMo, SiW).

K=

[Conc] [por][POM]

(A − A 0 ) = K ([POM] − α[por]) (A ∞ − A ) α=

(A − A 0 ) (A ∞ − A 0 )

symmetry.71 However, for the porphyrin−POM hybrids 1−4, the vibrations of B2u and B3u symmetries merge together to give vibrations at 3069−3080 and 3094−3106 cm−1 in the form of single peak due to the [H2TPP]2+ formation in the porphyrin− POM hybrids, respectively. The downshift in these modes (B2u and B3u) is due to formation of dication [H2TPP]2+, which causes a decrease in the electron density on Cβ atoms of pyrrole (Figure S1A of Supporting Information).71 The phenyl ring modes of TPP are observed at 599 and 1442 cm−1, which do not show any shift in wavenumber in the porphyrin−POM hybrids corresponding to the reference report.71 In the lowwavenumber region of the spectra of TPP, we observe pairs of bands due to the in-plane bending, out-of-plane bending, ring rotation, and ring torsion modes of the porphyrin skeleton, which can be assigned to the vibrational mode of B2u and B3u symmetry.71 For TPP, these pair of bands can be seen at 830 and 851 cm−1, 875 and 887 cm−1, 965 and 978 cm−1, and 989 and 1001 cm−1. For the porphyrin−POM hybrids, these pairs of bands collapse to single bands. Corresponding bands are now observed at 846−858, 875−890, 983−1007, and 1002− 1020 cm−1 for compounds 1, 2, 3, and 4, respectively. Observation of single bands for the porphyrin−POM hybrids in place of pairs of bands can be explained by an increase in the symmetry of the porphyrin molecule from 2-fold (D2h for TPP) to 4-fold (S4 for [H2TPP]2+), a result that matches well with the UV−vis spectral analyses. All of the above discussion can prove that the TPP exists in the form of a dication in the porphyrin− POM hybrids. When IR spectra of compounds 1−4 are compared with those of POMs (Figure S5 of Supporting Information) in the range of 700−1100 cm−1, four characteristic vibration patterns derived from α-Keggin-type heteropolyoxoanions are observed and the vibrational band of the M− Oa, M−Od bond has a red-shift while the vibrational bands of the M−Ob−M, M−Oc−M bond have a blue shift indicating that the M−Oa, M−Od bonds are weakened while the M−Ob− M, M−Oc−M bonds are strengthened in the porphyrin−POM hybrids.64,72 The structure of POM anions remains intact in the porphyrin−POM hybrids and has a large distorting effect due to the drastic interaction between the [H2TPP]2+ cations and POM anions.37

(2)

(3)

(4)

where A is the absorption of the solution at 415 nm and A0 and A∞ are the initial and final absorption at the same wavelength in the absence and presence of a large excess of POMs, respectively; [por] is the concentration of TPP, [POM] the concentration of POM, and [Conc] the concentration of 1:1 complex. According to eq 3, a plot of (A − A0)/(A∞ − A) versus ([POM] − α[por]) in Figure 2 gives a linear correlation constant, and the equilibrium constants K are determined from the slopes to be K(2) = 2.03 × 107, K(3) = 1.12 × 106, and K(4) = 1.38 × 107 for compounds 2, 3, and 4, respectively. The equilibrium constants of three kinds of 1:1 supramolecular compounds are very large, which explains the experimental phenomena that the solid appears instantaneously after mixing the concentrated THF solution of TPP and POMs. 3.2. IR Spectra. The IR spectra of TPP and compounds 1− 4 are shown in Figure S4 of Supporting Information. The observed IR bands and their assignments along with mode number are listed in Table 1. All the C−H and CC stretching vibration of benzene ring, CN stretching vibration of pyrrole ring, as well as the CC stretching vibration are found in the IR spectra of compounds 1−4, indicting that the structure of TPP remains intact in the resulting porphyrin−POM hybrids. The N−H stretching bands are observed at 3321 cm−1 for TPP and 3309−3316 cm−1 for compounds 1−4. Downward shift in the wavenumber of this band is assigned to cation [H2TPP]2+ in the hybrids formed by accepting two protons from POMs; the electron density of the [H2TPP]2+ is decreased at the pyrrole N or H atoms compared to that of neutral TPP.71 The doublet bands observed at 3078/3091 cm−1 and 3108/3134 cm−1 in TPP spectra are assigned to the skeletal modes which are split into B2u and B3u symmetries due to 2-fold D2h 6416



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Figure 3. Z-scan curves of compounds 1−4 and TPP in DMF (all the compounds have the concentration 3.25 mM). (A) open-aperture curves; (B) closed-aperture curves. The open triangles indicate the measured data; the solid curves are theoretical fits. Color code: green, 1; black, 2; red, 3; purple, 4; pink, TPP.

Figure 4. Z-Scan curves of POMs (3.25 mM, in DMF) and DMF. (A) open-aperture curves; (B) closed-aperture curves. Color code: black, PMoV; red, PMo; green, SiMo; blue, SiW; pink, DMF).

3.3. Thermogravimetric Analyses for Compounds 1− 4. To confirm the molecule formulas of compounds 1−4 given by elemental analyses, we performed thermogravimetric analyses. The TG curves of compounds 1−4 are shown in Figure S6 of Supporting Information. Compounds 1−4 lose all of the organic part, lattice solvent, and water molecules in one step. Compound 1 loses 22.48% in weight in the range of 45− 440 °C, corresponding to loss of one TPP, one lattice water, and six lattice THF (calculated value, 22.61%); from 45 to 490 °C, the weight loss of compound 2 is 36.18%, which corresponded to five lattice waters, five lattice THF, and one TPP (calculated value, 36.85%). Compound 3 loses 32.25% in weight in the range of 45−475 °C, corresponding to loss of one TPP, three lattice waters, and three lattice THF (calculated value, 33.07%); from 45 °C to 550 °C, the weight loss of compound 4 is 26.66%, which corresponded to eight lattice waters, four lattice THF, and one TPP (calculated value, 26.68%). The molecules of compounds 1−4 obtained here match well with the elemental analysis results. 3.4. Nonlinear Optical Properties and the Effect of POM Anion. The Z-scan curves along with the corresponding fits for compounds 1−4 and TPP are shown in Figure 3. 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 compounds and TPP have notable nonlinear reverse saturated absorption under the open-aperture configuration corresponding to a positive nonlinear absorption coefficient β (Figure 3A), a property that is widely applicable in the protection of optical sensors.73 Each of the closed-aperture Z-scan curves for compounds 1−4 and TPP have a peak-valley configuration corresponding to a negative nonlinear refractive index and a characteristic selfdefocusing behavior of the propagating wave in the compounds

and in TPP (Figure 3B). The Z-scan curve of DMF was obtained under the same experimental conditions to check the effect of DMF on third-order NLO properties of compounds 1−4 (Figure 4). The result reveals that DMF has negligible nonlinear optical absorption and self-focusing nonlinear optical properties. Hence, the solvent contribution has no considerable effect on the nonlinear optical absorption while reducing the actual nonlinear refractive index n2 of compounds 1−4 to the same extent because the same concentration and amount of compounds 1−4 and TPP are used in the Z-scan measurements. The nonlinear refractive index values for the samples are actually higher than those calculated and presented here.74 The following formulas are used to calculate the third-order nonlinear refractive index n2 (electrostatic unit), the nonlinear absorption coefficient β (electrostatic unit), and the third-order optical nonlinear susceptibility χ(3) (electrostatic unit).75 ΔTP−V = 0.406(1 − S)0.25 |Δϕ0|

(5)

Δϕ0 = kLeff γI0

(6)

Leff = (1 − e−α0L)/α0

(7)

n2(esu) =

cn0 γ(m 2/W) 40π

(8)

where ΔTP−V is the normalized peak-valley difference, Δφ0 the phase shift of the beam at the focus, K = 2π/λ the wave vector, I0 (watts per square meter) the intensity of the light at the focus, Leff the effective length of the sample defined in terms of the linear absorption coefficient α0 and the true optical path length through the sample, n0 the linear refractive index, and γ the optical Kerr constant. The conversion can be realized between n2 (electrostatic unit) and γ (square meters per watt) by eq 8. 6417



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Table 2. Third-Order Nonlinear Parameters Obtained by Z-Scan Measurements, HOMO−LUMO Gaps Eg, LUMO Energy Levels, and ΔE(TPP−POM) compound TPP 1 parent 2 parent 3 parent 4 parent a

β × 10−6 (esu)

n2 × 10−11 (esu)

χ(3) × 10−12 (esu)

γ × 10−30 (esu)

Eg (eV)

ELUMO (eV)

1.89 2.31

−3.19 −4.72

5.41 7.75

0.84 1.20

1.88 1.83

−3.44

ΔE (TPP−POM)a 1.32

−4.76a

PMoV 2.22

−3.45

5.96

0.92

1.85

1.14 −4.58a

PMo 2.18

−2.99

5.33

0.83

1.86

1.03 −4.47a

SiMo 1.55

−1.60

3.13

0.49

1.87

0.49 −3.93a

SiW

ΔE(TPP−POM) = ELUMO(TPP) − ELUMO(POM).

Figure 5. CV spectra of parent (A) TPP, (B) PMoV, (C) PMo, (D) SiMo, (E) SiW and (F) ferrocene in dry DMF (all the compounds have the concentration of 1 mM).

When the sample is measured under open aperture, the normalized transmittance T (z, s = 1) can be expressed as ∞

T (z , s = 1) =

∑ m=0

The Z-scan curves of POMs show that the POMs have negligible nonlinear optical absorption and self-focusing nonlinear optical properties (Figure 4) under the same experimental conditions. The nonlinear refractive indexes n2 of PMoV, PMo, SiMo, and SiW obtained by eq 8 are 9.78 × 10−11, 9.81 × 10−11, 9.84 × 10−11, and 9.88 × 10−11 esu, respectively. It is not difficult to see that the POMs have a nonlinear refractive index n2 that is almost the same as that of DMF (9.83 × 10−11 esu), indicating that POMs have only negligible nonlinear refractive effects and that the observed closed-aperture signals come from DMF. It can be concluded that the observed NLO properties of resulting porphyrin− POM hybrids mainly come from TPP. Using eqs 8−11, the nonlinear refractive index n2, nonlinear absorption coefficient β, third-order optical nonlinear susceptibility χ(3), and second hyperpolarizability γ are calculated (Table 2). Obviously, it can be deduced that the type of POMs has a notable influence on the third-order NLO property in our studied porphyrin−POM systems. When compared with the NLO properties of TPP, the second hyperpolarizability γ values of compounds 1 and 2 (γ(1) and γ(2)) are improved whereas the second hyperpolarizability γ value of compounds 3 (γ(3)) almost has not changed and the second hyperpolarizability γ value of compound 4 (γ(4)) is reduced. The second

[−q0(z)]m (m + 1)3/2

(9)

where q0(z) = (βI0Lef f)/(1 + z2/z20) and β is the nonlinear absorption coefficient. From eq 9, we can get β. From eq 10, we can get the thirdorder optical nonlinear susceptibility χ(3). χ

(3)

=

2 ⎛ cn0 ⎞2 ⎛ cβn03λ ⎞ ⎜ ⎟ γ⎟ + ⎜ 3 ⎝ 160π 2 ⎠ ⎝ 64π ⎠

(10)

The molecular second hyperpolarizability γ of the samples was calculated using the following equation:76

γ=

χ (3) NcL

(11)

where n0 is the linear refractive index of the sample, Nc the molecular number density per cubic centimeter, and L the local-field correction factor, which may be approximated by [(n02+2)/3]4.76 6418



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hyperpolarizability γ values of compounds 1−4 and TPP are in the following order: γ(1) > γ(2) > γ(TPP) ≈ γ(3) > γ(4). It is well-know that the NLO property is related to the values of the transition energy.77,78 The HOMO−LUMO gap Eg values of compounds 1−4 and TPP were derived from the absorption edges of the spectra by equation Eg = 1240/λ (λ is absorption edge, Figure S7 of Supporting Information) (Table 2).79 From the data in Table 2, we can see that the Eg values of compounds 1−4 increase in following order: Eg(1) < Eg(2) < Eg(3) < Eg(4) while the second hyperpolarizability γ values decrease accordingly as follows: γ(1) > γ(2) > γ(3) > γ(4); in other words, the second hyperpolarizability γ values are inversely proportional to the HOMO−LUMO gap Eg. In order to get insight into the effect of POM anions on the third-order NLO properties of the porphyrin−POM hybrids, the molecular orbital levels of parent TPP and parent POMs were calculated by cyclic voltammetry spectra (Figure 5). The lowest unoccupied molecular orbital level of TPP was obtained by ELUMO (eV) = −e (4.8 − EFOC + Eox) + Eg (Eox is the onset of oxidation potential of TPP, EFOC = (Eox + Ered)/2 the energy level of ferrocene used as a standard, and Eg the HOMO− LUMO gap of TPP); the LUMO levels of the POMs were obtained by ELUMO (eV) = −e (4.8 − EFOC + Ered) (Ered is the onset of reduction potential of POMs).79,80 The scan ranges of the CV were selected carefully from the wide range (+3 V to −3 V) to a narrow range (presented in the paper) to ensure the peak used for calculating the HOMO or LUMO levels is the onset peak. As the LUMO level of the POMs is lower than that of the TPP demonstrated in Table 2, some excited electrons could inject from the TPP to the POMs. The energy level and electron-transfer processes are schematically illustrated in Figure 6. The excited electron transfer can make the resulting

compounds 1 and 2 are improved by 1.43 and 1.11 times, whereas the values had little change for compound 3 and reduced for compound 4. This result indicates that an energy discrepancy ΔE(TPP−POM) of 1.03 eV (like the case for TPP-SiMo) is the threshold for the improvement of third-order NLO properties of TPP by forming porphyrin−POM hybrids. Therefore, improvement of third-order NLO properties of TPP can be achieved by forming a hybrid with POM which has a lower LUMO level. Obviously, a porphyrin-based supramolecular system incorporating heteropolyoxometalate can enhance the third-order NLO susceptibility of porphyrin. The charge transfer from porphyrin to heteropolyoxometalate plays the key role in the enhancement of the NLO response. A low-lying LUMO level of POM is the principal factor for the improved second hyperpolarizability γ value. Although the second hyperpolarizabilities presented here are not big enough for practical applications, the effect of heteropolyoxometalate anions on the NLO properties of porphyrin provides us with a new guide for exploring the NLO materials of porphyrin−POM hybrids with higher second hyperpolarizabilities.

4. CONCLUSIONS We have reported for the first time the solution properties of TPP and POMs in THF and studied the effect of heteropolyoxometalate anion on the third order NLO properties of TPP. Z-scan results show that combination of heteropolyoxometalate and porphyrin forming porphyrin− heteropolyoxometalate hybrids can enhance its third-order NLO susceptibility. The charge transfer from TPP to POMs in the hybrids plays the key role in the enhancement of NLO response, and the low-lying LUMO level of POM is the principal factor for improved second hyperpolarizability γ value. The present paper provides important insight into the NLO properties of a new type of porphyrin−POM hybrids, and it is hoped that the results will provides us with a new guide for exploring the NLO materials of porphyrin−POM hybrids with higher second hyperpolarizabilities.

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ASSOCIATED CONTENT

S Supporting Information *

Structure of tetraphenylporphin and α-Keggin-type polyoxometalate; UV−vis spectral titrations of TPP with POMs; UV− vis spectra of POMs in THF; IR spectra of compounds 1−4, TPP, and POMs; TG curves of compounds 1−4; and UV−vis spectra of compounds 1−4 and TPP in DMF. This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 6. Energy level and electron-transfer processes diagram of TPP and POM molecules. Color code: blue, LUMO level; black, HOMO level.

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porphyrin−POM hybrids more activated when exposed to the laser, corresponding to smaller HOMO−LUMO gaps Eg, which results in the enhancement of nonlinear response. The discrepancy between LUMO levels of TPP and that of POMs ΔE(TPP−POM) (Table 2) decrease in the following order: ΔE(TPP−PMoV) > ΔE(TPP−PMo) > ΔE(TPP−SiMo) > ΔE(TPP−SiW), while the second hyperpolarizability γ values decrease accordingly as follows: γ(1) > γ(2) >γ(3) > γ(4). The second hyperpolarizability γ values are proportional to the discrepancy of LUMO levels ΔE(TPP−POM). Hence, in these porphyrin−POM systems, low-lying LUMO levels of POMs are thought to be the principal factors for the improved second hyperpolarizability γ value. Compared with third-order NLO properties of TPP, the second hyperpolarizability γ values of

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-10-64414640. Fax: +86-10-64414640. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The financial support of the NSFC (Grants 20541001, 20771012, and 21371020) and PCSIRT (IRT1205) is greatly acknowledged. Y.Z. thanks Prof. Enbo Wang for his kind instruction and prompting and dedicates this paper to him. Prof. Xue Duan of Beijing University of Chemical Technology is greatly acknowledged for his kind support. 6419



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(22) Taylor, P. N.; Wylie, A. P.; Huuskonen, J.; Anderson, H. L. Enhanced Electronic Conjugation in Anthracene-Linked Porphyrins. Angew. Chem., Int. Ed. 1998, 37, 986−989. (23) Yoon, Z. S.; Kwon, J. H.; Yoon, M. C.; Koh, M. K.; Noh, S. B.; Sessler, J. L.; Lee, J. T.; Seidel, D.; Aguilar, A.; Shimizu, S.; Suzuki, M.; Osuka, A.; Kim, D. Nonlinear Optical Properties and Excited-State Dynamics of Highly Symmetric Expanded Porphyrins. J. Am. Chem. Soc. 2006, 128, 14128−14134. (24) Sessler, J. L.; Seidel, D. Synthetic Expanded Porphyrin Chemistry. Angew. Chem., Int. Ed. 2003, 42, 5134−5175. (25) Rubtsov, I. V.; Susumu, K.; Rubtsov, G. I.; Therien, M. J. Ultrafast Singlet Excited-State Polarization in Electronically Asymmetric Ethyne-Bridged Bis [(porphinato) zinc (II)] Complexes. J. Am. Chem. Soc. 2003, 125, 2687−2696. (26) Tsuda, A.; Nakano, A.; Furuta, H.; Yamochi, H.; Osuka, A. Doubly meso-β-Linked Diporphyrins from Oxidation of 5, 10, 15Triaryl-Substituted NiII- and PdII- Porphyrins. Angew. Chem., Int. Ed. 2000, 39, 558−561. (27) Matsuzaki, Y.; Nogami, A.; Iwaki, Y.; Ohta, N.; Yoshida, N.; Aratani, N.; Osuka, A.; Tanaka, K. Quantum-Chemical Investigation of the Electroabsorption Spectra of Directly Meso−Meso-Linked Porphyrin Arrays: Essential Role of Charge-Transfer Excited States Accidentally Overlapping with Soret Bands. J. Phys. Chem. A 2005, 109, 703−713. (28) Matsuzaki, Y.; Nogami, A.; Tsuda, A.; Osuka, A.; Tanaka, K. A. Theoretical Study on the Third-Order Nonlinear Optical Properties of π-Conjugated Linear Porphyrin Arrays. J. Phys. Chem. A 2006, 110, 4888−4899. (29) Guo, Z.; Du, F.; Ren, D. M.; Chen, Y. S.; Zheng, J. Y.; Liu, Z. B.; Tian, J. G. Covalently Porphyrin-functionalized Single-walled Carbon Nanotubes: A Novel Photoactive and Optical Limiting Donor− Acceptor Nanohybrid. J. Mater. Chem. 2006, 16, 3021−3030. (30) Ryppa, C.; Niedzwiedzki, D.; Morozowich, N.; Srikanth, R.; Zeller, M.; Frank, H.; Brückner, C. Stepwise Conversion of Two Pyrrole Moieties of Octaethylporphyrin to Pyridin-3-ones: Synthesis, Mass Spectral, and Photophysical Properties of Mono and Bis(oxypyri)porphyrins. Chem.Eur. J. 2009, 15, 5749−5762. (31) Tanaka, T.; Lee, B. S.; Aratani, N.; Yoon, M. C.; Kim, D.; Osuka, A. Synthesis and Properties of Hybrid Porphyrin Tapes. Chem.Eur. J. 2011, 17, 14400−14412. (32) Liu, Z. B.; Xu, Y. F.; Zhang, X. Y.; Zhang, X. L.; Chen, Y. S.; Tian, J. G. Porphyrin and Fullerene Covalently Functionalized Graphene Hybrid Materials with Large Nonlinear Optical Properties. J. Phys. Chem. B 2009, 113, 9681−968. (33) Hill, C. Introduction: PolyoxometalatesMulticomponent Molecular Vehicles to Probe Fundamental Issues and Practical Problems. Chem. Rev. 1998, 98, 1−2. (34) Long, D. L.; Burkholder, E.; Cronin, L. Polyoxometalate Clusters, Nanostructures and Materials: From Self-Assembly to Designer Materials and Devices. Chem. Soc. Rev. 2007, 36, 1050−121. (35) Liu, C. G.; Guan, W.; Song, P.; Su, Z. M.; Yao, C.; Wang, E. B. Second-Order Nonlinear Optical Properties of Trisubstituted Keggin and Wells−Dawson Polyoxometalates: Density Functional Theory Investigation of the Inorganic Donor-Conjugated Bridge-Acceptor Structure. Inorg. Chem. 2009, 48, 8115−8119. (36) Liu, C. G.; Guan, W.; Yan, L. K.; Su, Z. M.; Song, P.; Wang, E. B. Second-Order Nonlinear Optical Properties of Transition-MetalTrisubstituted Polyoxometalate-Diphosphate Complexes: A Donor− Conjugated Bridge−Acceptor Paradigm for Totally Inorganic Nonlinear Optical Materials. J. Phys. Chem. C. 2009, 113, 19672−19676. (37) Niu, J. Y.; You, X. Z.; Duan, C. Y.; Fun, H. K.; Zhou, Z. Y. A Novel Optical Complex between an Organic Substrate and a Polyoxometalate. Crystal and Molecular Structure of α-H4SiW12O40· 4HMPA·2H2O (HMPA = Hexamethylphosphoramide). Inorg. Chem. 1996, 35, 4211−4217. (38) Compain, J. D.; Mialane, P.; Dolbecq, A.; Marrot, J.; Proust, A.; Nakatani, K.; Yu, P.; Sécheresse, F. Second-Order Nonlinear Optical Properties of Polyoxometalate Salts of a Chiral Stilbazolium Derivative. Inorg. Chem. 2009, 13, 6222−6228.

REFERENCES

(1) Prasad, P. N., Williams, D. J. Introduction to Nonlinear Optical Effects in Molecules and Polymers; Wiley: New York, NY, 1991. (2) Zyss, J. Molecular Nonlinear Optics: Materials, Physics and Devices; Academic Press: Boston, MA, 1994. (3) Bosshard, C.; Sutter, K.; Prêtre, P.; Hulliger, J.; Flörsheimer, M.; Kaatz, P.; Günter, P. Organic Nonlinear Optical Materials; Gordon and Breach: Amsterdam, Netherlands, 1995. (4) Chemla, D. S.; Zyss, J. Nonlinear Optical Properties of Organic Molecules and Crystals; Academic Press: Orlando, FL, 1987. (5) Hann, R. A.; Bloor, D. Organic Materials for Nonlinear Optics II; Royal Society of Chemistry: London, U.K., 1991. (6) Ashwell, G. J.; Bloor, D. Organic Materials for Nonlinear Optics III; Royal Society of Chemistry: London, U.K., 1993. (7) Nalwa, H. S. Organic Materials for Third-Order Nonlinear Optics. Adv. Mater. 1993, 5, 341−358. (8) Tillekaratne, A. D.; Silva, R. M. D.; Silva, K. M. N. D. Push−pull Porphyrins as Non-linear Optical Materials: Ab Initio Quantum Chemical Calculations. J. Mol. Struct. 2003, 638, 169−176. (9) Senge, M. O.; Fazekas, M.; Notaras, E. G. A.; Blau, W. J.; Zawadzka, M.; Locos, O. B.; Mhuircheartaigh, E. M. N. Nonlinear Optical Properties of Porphyrins. Adv. Mater. 2007, 19, 2737−2774. (10) Blau, W.; Byrne, H.; Dennis, W. M.; Kelly, J. M. Reverse Saturable Absorption in Tetraphenylporphyrins. Opt. Commun. 1985, 56, 25−29. (11) Humphrey, J.; Kuciauskas, D. Charge-Transfer States Determine Iron Porphyrin Film Third-Order Nonlinear Optical Properties in the near-IR Spectral Region. J. Phys. Chem. B 2004, 108, 12016−12023. (12) Kiran, P. P.; Reddy, D. R.; Maiya, B. G.; Dharmadhikari, A. K.; Kumar, G. R.; Rao, D. N. Nonlinear Absorption Properties of ‘AxialBonding’ Type Tin (IV) Tetratolylporphyrin Based Hybrid Porphyrin Arrays. Opt. Commun. 2005, 252, 150−161. (13) Kandasamy, K.; Shetty, S. J.; Puntambekar, P. N.; Srivastava, T. S.; Kundu, T.; Singh, B. P. Effects of Metal Substitution on ThirdOrder Optical Non-linearity of Porphyrin Macrocycle. J. Porphyrins Phthalocyanines 1999, 3, 81−87. (14) Morotti, T.; Pizzotti, M.; Ugo, R.; Quici, S.; Bruschi, M.; Mussini, P.; Righetto, S. Electronic Characterisation and Significant Second-Order NLO Response of 10,20 Diphenylporphyrins and Their ZnII Complexes Substituted in the meso Position with π-Delocalised Linkers Carrying Push or Pull Groups. Eur. J. Inorg. Chem. 2006, 2006, 1743−1757. (15) Zhang, T. G.; Zhao, Y. X.; Song, K.; Asselberghs, I.; Persoons, A.; Clays, K.; Therien, M. J. Electronic Modulation of Hyperpolarizable (Porphinato)zinc(II) Chromophores Featuring Ethynylphenyl-, Ethynylthiophenyl-, Ethynylthiazolyl-, and Ethynylbenzothiazolyl-Based Electron-Donating and -Accepting Moieties. Inorg. Chem. 2006, 45, 9703−9712. (16) Beratan, D. N. Predicting the Frequency Dispersion of Electronic Hyperpolarizabilities on the Basis of Absorption Data and Thomas−Kuhn Sum Rules. J. Phys. Chem. C 2010, 114, 2349−2359. (17) Reeve, J. E.; Collins, H. A.; Mey, K. D.; Kohl, M. M.; Thorley, K. J.; Paulsen, O.; Clays, K.; Anderson, H. L. Amphiphilic Porphyrins for Second Harmonic Generation Imaging. J. Am. Chem. Soc. 2009, 131, 2758−2759. (18) Anderson, H. L.; Martin, S. J.; Bradley, D. D. C. Synthesis and Third-Order Nonlinear Optical Properties of a Conjugated Porphyrin Polymer. Angew. Chem., Int. Ed. Engl. 1994, 33, 655−657. (19) Anderson, H. L. Supramolecular Orientation of Conjugated Porphyrin Oligomers in Stretched Polymers. Adv. Mater. 1994, 6, 834−836. (20) Thorne, J. R. G. S.; Kuebler, M.; Denning, R. G.; Blake, I. M.; Taylor, P. N.; Anderson, H. L. Degenerate Four-Wave Mixing Studies of Butadiyne-Linked Conjugated Porphyrin Oligomers. Chem. Phys. 1999, 248, 181−193. (21) Screen, T. E. O.; Thorne, J. R. G.; Denning, R. G.; Bucknall, D. G.; Anderson, H. L. Two Methods for Amplifying the Optical Nonlinearity of a Conjugated Porphyrin Polymer: Transmetallation and Self-assembly. J. Mater. Chem. 2003, 13, 2796−2808. 6420



Article

(39) Yang, G. H.; Guan, W.; Yan, L. K.; Su, Z. M.; Xu, L.; Wang, E. B. Theoretical Study on the Electronic Spectrum and the Origin of Remarkably Large Third-Order Nonlinear Optical Properties of Organoimide Derivatives of Hexamolybdates. J. Phys. Chem. B 2006, 110, 23092−23098. (40) Zhang, L. J.; Zhou, Y. S.; Li, Y. H. Surface Modification with Multiphilic Ligands at Detectable Well Defined Active Positions of Nano-Object of Giant Wheel Shaped Molybdenum Blue Showing Third-Order Nonlinear Optical Properties. J. Mol. Struct. 2010, 969, 69−74. (41) Geletii, Y. V.; Hill, C. L.; Atalla, R. H.; Weinstock, I. A. Reduction of O2 to Superoxide Anion (O2− ) in Water by Heteropolytungstate Cluster-Anions. J. Am. Chem. Soc. 2006, 128, 17033−17042. (42) Fang, X.; Hill, C. L. Multiple Reversible Protonation of Polyoxoanion Surfaces: Direct Observation of Dynamic Structural Effects from Proton Transfer. Angew. Chem., Int. Ed. 2007, 46, 3877− 3880. (43) Liu, S. Q.; Xu, J. Q.; Sun, H. R.; Li, D. M. meso-Tetrakis(4-Nbenzylpyridyl)porphyrin and Its Supramolecular Complexes Formed with Anionic Metal−Oxo Cluster: Spectroscopy and Electrocatalytic Reduction of Dioxygen. Inorg. Chim. Acta 2000, 306, 87−93. (44) Harriman, A.; Elliott, K. J. Intramolecular Electron Transfer Reactions Observed for Dawson-Type Polyoxometalates Covalently Linked to Porphyrin Residues. J. Phys. Chem. C 2009, 113, 5834− 5842. (45) Yang, Y. B.; Xu, L.; Li, F. Y.; Du, X. G.; Sun, Z. X. Enhanced Photovoltaic Response by Incorporating Polyoxometalate into a Phthalocyanine-Sensitized Electrode. J. Mater. Chem. 2010, 20, 10835−10840. (46) Costa-Coquelard, C.; Sorgues, S.; Ruhlmann, L. Photocatalysis with Polyoxometalates Associated to Porphyrins under Visible Light: An Application of Charge Transfer in Electrostatic Complexes. J. Phys. Chem. A 2010, 114, 6394−6400. (47) Yao, C.; Yan, L. K.; Guan, W.; Liu, C. G.; Song, P.; Su, Z. M. Prediction of Second-Order Optical Nonlinearity of Porphyrin− Metal−Polyoxometalate Sandwich Compounds. Dalton Trans. 2010, 39, 7645−7649. (48) Fan, D. W.; Li, G. B.; Hao, J. C. Fabrication and Electrocatalytic Activities of Porphyrin and 12-molybdophosphoric Acid hybrid Films. J. Colloid Interface Sci. 2010, 351, 151−155. (49) Schaming, D.; Allain, C.; Ruhlmann, L. Synthesis and Photocatalytic Properties of Mixed Polyoxometalate-Porphyrin Copolymers Obtained from Anderson-Type Polyoxomolybdates. Langmuir 2010, 26, 5101−5109. (50) Schaming, D.; Costa-Coquelard, C.; Sorgues, S.; Ruhlmann, L.; Lampre, I. Photocatalytic Reduction of Ag2SO4 by Electrostatic Complexes Formed by Tetracationic Zinc Porphyrins and Tetracobalt Dawson-Derived Sandwich Polyanion. Appl. Catal., A 2010, 373, 160− 167. (51) Schaming, D.; Farha, R.; Ruhlmann, L. Formation and Photocatalytic Properties of Nanocomposite Films Containing both Tetracobalt Dawson-Derived Sandwich Polyanions and Tetracationic Porphyrins. Langmuir 2011, 27, 132−143. (52) Yokoyama, A.; Kojima, T. Remarkable Enhancement of Catalytic Activity of a 2:1 Complex between a Non-Planar Mo(V)Porphyrin and a Ruthenium-Substituted Keggin-Type Heteropolyoxometalate in Catalytic Oxidation of Benzyl Alcohols. Dalton Trans. 2012, 41, 10006−10013. (53) Ahmed, I.; Wang, X. X.; Ruhlmann, L. Photocatalytic Synthesis of Silver Dendrites Using Electrostatic Hybrid Films of PorphyrinPolyoxometalate. Appl. Catal., A 2012, 447−448, 89−99. (54) Zou, C.; Zhang, Z. J.; Wu, C. D. A Multifunctional Organic− Inorganic Hybrid Structure Based on MnIII-Porphyrin and Polyoxometalate as a Highly Effective Dye Scavenger and Heterogenous Catalyst. J. Am. Chem. Soc. 2012, 134, 87−90. (55) Nagai, M.; Sanpei, H.; Shirakura, M. Cobalt PorphyrinTungsten Polyoxometalate Anion as Non-Noble Metal Cathode Catalyst in a Fuel cell. J. Mater. Chem. 2012, 22, 9222−9229.

(56) Araghi, M.; Mirkhani, V.; Moghadam, M. Synthesis and Characterization of a New Porphyrin−Polyoxometalate Hybrid Material and Investigation of Its Catalytic Activity. Dalton Trans. 2012, 41, 3087−3094. (57) Ahmed, I.; Farha, R.; Goldmann, M.; Ruhlmann, L. A Molecular Photovoltaic System Based on Dawson Type Polyoxometalate and Porphyrin Formed by Layer-by-Layer Self-Assembly. Chem. Commun. 2013, 49, 496−498. (58) Allain, C.; Schaming, D.; Karakostas, N.; Erard, M.; Gisselbrecht, J. P.; Sorgues, S.; Lampre, I.; Ruhlmann, L.; Hasenknopf, B. Synthesis, Electrochemical and Photophysical Properties of Covalently Linked Porphyrin-Polyoxometalates. Dalton Trans. 2013, 42, 2745−2754. (59) Ahmed, I.; Farha, R.; Ruhlmann, L. Porphyrin−Polyoxometalate Hybrids Connected via a Tris-Alkoxo Linker for the Generation of Photocurrent. Electrochim. Acta 2013, 110, 726−734. (60) Zhang, T.; Ma, N. N.; Yan, L. K.; Wen, S. Z.; Ma, T. Y.; Su, Z. M. Theoretical Exploration to Second-Order Nonlinear Optical Properties of New Hybrid Complexes via Coordination Interaction between (Metallo)porphyrin and [MSiW11O39]3− (M = Nbv or Vv) polyoxometalates. J. Mol. Graphics Modell. 2013, 46, 59−64. (61) Chen, W. L., Wang, E. B. Polyoxometalate Chemistry; Science Press: Beijing, China, 2013. (62) Adler, A. D.; Longo, F. R.; Finarlli, J. D. A Simplified Synthesis for meso-Tetraphenylporphin. Inorg. Chem. 1967, 32, 476. (63) Pettersson, L.; Andersson, I.; Selling, A.; Grate, J. H. Multicomponent Polyanions. 46. Characterization of the Isomeric Keggin Decamolybdodivanadophosphate Ions in Aqueous Solution by 31 P and 51V NMR. Inorg. Chem. 1994, 33, 982−993. (64) Rocchiccioli-Deltcheff, C.; Fournier, M.; Franck, R.; Thouvenot, R. Vibrational Investigations of Polyoxometalates. 2. Evidence for Anion−Anion Interactions in Molybdenum(VI) and Tungsten(VI) Compounds Related to the Keggin Structure. Inorg. Chem. 1983, 22, 207−216. (65) Meot-Ner, M.; Adler, A. D. Substituent Effects in Noncoplanar π Systems. ms-Porphins. J. Am. Chem. Soc. 1975, 97, 5107−5111. (66) So, H.; Pope, M. T. Origin of Some Charge-Transfer Spectra. Oxo Compounds of Vanadium, Molybdenum, Tungsten, and Niobium Including Heteropoly Anions and Heteropoly Blues. Inorg. Chem. 1972, 11, 1441−1143. (67) Gao, Y. Z.; Xu, Y. Q.; Han, Z. G.; Li, C. H.; Cui, F. Y.; Chi, Y. N.; Hu, C. W. Syntheses, Structures and Properties of 3D InorganicOrganic Hybrid Frameworks Constructed from Lanthanide Polymer and Keggin-Type Tungstosilicate. J. Solid State Chem. 2010, 183, 1000−1006. (68) Barber, D. C.; Freitag-Beeston, R. A.; Whitten, D. G. Atropisomer-Specific Formation of Premicellar Porphyrin J-Aggregates in Aqueous Surfactant Solutions. J. Phys. Chem. 1991, 95, 4074−4086. (69) Aronoff, S. Perchloric Acid Titrations of Porphyrins in Nitrobenzene. J. Phys. Chem. 1958, 62, 428−431. (70) Fukuzumi, S.; Kondo, Y.; Mochizuki, S.; Tanaka, T. Complex Formation between NADH Model Compounds and Metalloporphyrins. J. Chem. Soc., Perkin Trans. 1989, 2, 1753−1761. (71) Saini, G. S. S.; Sharma, S.; Kaur, S.; Tripathi, S. K.; Mahajan, C. G. Infrared Spectroscopic Studies of Free-Base Tetraphenylporphine and Its Dication. Spectrochim. Acta, Part A 2004, 61, 3070−3076. (72) Tsigdinos, G. A.; Hallada, C. J. Molybdovanadophosphoric Acids and Their Salts. I. Investigation of Methods of Preparation and Characterization. Inorg. Chem. 1968, 7, 437−441. (73) Norman, T. Conference on Laser and Electro-Optics, OSA Technical Digest Series; Optical Society of America: Washington, DC, 1993. (74) Rao, S. V.; Anusha, P. T.; Giribabu, L.; Tewari, S. P. Picosecond Optical Nonlinearities in Symmetrical and Unsymmetrical Phthalocyanines Studied Using the Z-scan Technique. Pramana J. Phys. 2010, 75, 1017−1023. (75) Sheik-Bahae, M.; Said, A.; Wei, T.; Hagan, D.; Stryland, E. V. Sensitive Measurement of Optical Nonlinearities Using a Single Beam. IEEE J. Quantum Electron. 1990, 26, 760−769. 6421



Article

(76) Wang, S. F.; Huang, W. T.; Zhang, T. Q.; Gong, Q. H.; Okuma, Y.; Horikiri, M.; Miura, Y. F. Third-Order Nonlinear Optical Properties of Didodecyldi-Methylammonium-Au(dmit)2. Appl. Phys. Lett. 1999, 75, 1845−1847. (77) Yang, G. C.; Guan, W.; Yan, L. K.; Su, Z. M. Theoretical Study on the Electronic Spectrum and the Origin of Remarkably Large Third-Order Nonlinear Optical Properties of Organoimide Derivatives of Hexamolybdates. J. Phys. Chem. B 2006, 110, 23092−23098. (78) Victor, M. G.; Christoph, L.; Jean-Luc, B. Origin of High Second- and Third-Order Nonlinear Optical Response in Ammonio/ Borato Diphenylpolyene Zwitterions: The Remarkable Role of Polarized Aromatic Groups. J. Am. Chem. Soc. 2003, 125, 15651− 15658. (79) Sun, X. B.; Liu, Y. Q.; Chen, S. Y.; Qiu, W. F.; Gui, Y.; Ma, Y. Q.; Qi, T.; Zhang, H. J.; Xu, X. J.; Zhu, D. B. X-Shaped Electroactive Molecular Materials Based on Oligothiophene Architectures: Facile Synthesis and Photophysical and Electrochemical Properties. Adv. Funct. Mater. 2006, 16, 917−925. (80) Hyun, B. R.; Zhong, Y. W; Bartnik, A. C.; Sun, L. F.; Abrun, H. D.; Wise, F. W.; Goodreau, J. D.; Matthews, J. R.; Leslie, T. M.; Borrelli, N. F. Electron Injection from Colloidal PbS Quantum Dots into Titanium Dioxide Nanoparticles. ACS Nano 2008, 2, 2206−2212.

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Solution Properties and Effect of Anions on Third-Order Optical

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