Covalent Synthesis of Two Hybrids Composed of Dawson-Type

Article pubs.acs.org/IC

Covalent Synthesis of Two Hybrids Composed of Dawson-Type Polyoxometalate and Porphyrin with Remarkable Third-Order Optical Nonlinearities Reflecting the Effect of Polyoxometalates Hafiz Muhammad Asif, Yunshan Zhou,* Lijuan Zhang,* Nusrat Shaheen, Di Yang, Jiaqi Li, Yi Long, Arshad Iqbal, and Yanqin Li State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology, Beijing 100029, P. R. China S Supporting Information *

ABSTRACT: Two new porphyrin-polyoxometalate hybrids, namely, [(C4H9)4N]10H2[{COHNC(CH2O)3P2V3W15O59}2C44N4H28]·CH3CN 1, bearing two covalent-bonded Wells− Dawson-type polyoxometalates (POMs), and [(C4H9)4N)]5H[COHNC(CH2O)3P2V3W15O59{C44H29N4}]·CH3CN 2, bearing one covalent-bonded POM, have been synthesized and thoroughly characterized by means of elemental analysis, powder XRD, FT-IR, 1H (31P, 51V) NMR, MALDI-TOF-MS, UV−vis spectra, and cyclic voltammetry measurement. Experimental results demonstrate that while all the compounds show remarkable third-order optical nonlinearities, the hybrids 1 and 2 are superior to their corresponding porphyrin precursors (molecular second hyperpolarizability γ = 8.0 × 10−28 esu for 54-N-N′(1,3-tetrahydroxy-2-(dihydroxymethyl)propan-4-diyl)benzdiamide,10,15,20-triphenyl porphyrin that is the precursor for the hybrid 1, γ = 2.6 × 10−28 esu for 54-N-(1,3-dihydroxy-2(hydroxymethyl)propan-2-yl)benz-amide,10,15,20-triphenyl porphyrin that is the precursor for the hybrid 2), and the hybrid 1 (γ = 12.9 × 10−28 esu) is superior to the hybrid 2 (γ = 12.2 × 10−28 esu) reflecting more POM moieties covalently bonded to the porphyrin moiety exerting more significant influence on the third-order optical nonlinearities. Meanwhile, attachment of POMs on the porphyrin results in significant fluorescence quenching (fluorescence intensity is decreased 97% for the hybrid 1 and 80% for the hybrid 2 with respect to that of their corresponding porphyrin precursors) indicating strong electron transfer from porphyrin moiety to the polyoxometalate moiety. Lower transition energy, small energy difference between singlet and triplet excited states, and faster intersystem crossing (ISC) process of the hybrids are favorable to enhance the NLO responses of hybrids 1 and 2 resulting from the facile electron transfer from the porphyrin moiety to the Dawson POM moiety when the hybrids are subjected to laser irradiation, which is thought to be responsible to the superior of the hybrid 1 to hybrid 2 and the superior of the hybrids to their corresponding porphyrin precursors as well.

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INTRODUCTION Nonlinear optical materials with large third-order optical susceptibility have numerous applications, including optical memory devices and fabrication,1 two-photon photodynamic therapy,2 optical limiting,3 optical communications,4 optical switching,5 electro-optical signal processing,6,7 and so on. The greater value of nonlinear refraction (n2) leads to scope for ultrafast optical signal processing8 and two photon absorption controlled by imaginary component Imχ(3) is useful for optical limiting.1 In this context, while highly conjugated materials normally possess strong third-order optical nonlinearity,3,9−11 porphyrins exhibit distinctive features which execute their superiority as NLO materials12 because of their large polarizable π-conjugated system with their optical properties being customized by altering the metal center of different oxidation state, the axial ligands, or the nature of the substituents at the peripheral positions of macrocycle, apart © 2017 American Chemical Society

from their ease of fabrication and high thermal stability, which is also important in view of their practical applications.13−18 Recently, new approaches have also been applied, such as designing symmetric porphyrins,19 asymmetric porphyrins,20 porphyrins-based hybrids,21 etc., to tune the NLO properties. It is found that the peculiar derivatives of porphyrins which may be aromatic, nonaromatic and antiaromatic22−24 having more than one accessible and well-defined substituents exhibit exceptional optoelectronic and excellent redox properties. Of particular interest, it is found that porphyrins attached to different electron acceptor or electron donor moieties at its different positions (meso or β25 and cis or trans26,27) can greatly enhance the optical nonlinearity. Throughout the course, a theory of charge transfer28,29 was proposed based Received: December 23, 2016 Published: August 10, 2017 9436

DOI: 10.1021/acs.inorgchem.6b03155 Inorg. Chem. 2017, 56, 9436−9447

Article

Inorganic Chemistry Scheme 1. Schematic Illustration of the Synthetic Route of Hybrids 1 and 2

their NLO properties is necessary in both theoretical and practical point of view. In the present work, we report the synthesis and thorough characterizations of two new hybrids derived by grafting different number of vanadium capped Wells−Dawson-type cluster P2W15V3O629− onto a porphyrin moiety, namely, [(C 4 H 9 ) 4 N] 1 0 H 2 [{COHNC(CH 2 O) 3 P 2 V 3 W 1 5 O 5 9 } 2 C 44 N 4 H 28 ]·CH 3 CN 1 and [(C 4 H 9 ) 4 N)] 5 H[C OHNC(CH2O)3P2V3W15O59{C44N4H29}]·CH3CN 2, to scrutinize the structure-NLO property relationship and obtain more promising third-order NLO materials, which are synthesized by reacting [N(C4H9)4]5[H4P2W15V3O62] (denoted parent Dawson POM) with 54-N-N′(1,3-tetrahydroxy-2-(dihydroxymethyl)propan-4-diyl)benz-diamide,10,15,20-triphenyl porphyrin (denoted TPP-di-Tris) and 54-N-(1,3-dihydroxy-2(hydroxymethyl)propan-2-yl)benz-amide,10,15,20-triphenyl porphyrin (denoted TPP-Tris), respectively (Scheme 1). Importantly, it is found that while all the compounds show remarkable third-order optical nonlinearities, the hybrids are superior to their corresponding porphyrin precursors and the hybrid 1 is superior to the hybrid 2 reflecting more POM moieties covalent-bonded to the porphyrin moiety exert more significant influence on the third-order optical nonlinearities.

on a lot of experiments and theories, stating that a donor and acceptor in a conjugated molecular system can facilitate the charge/energy transfer from donors to acceptors which is beneficial to NLO enhancement. As polyoxometalates are excellent electron acceptors, efforts have been driven to bond the polyoxometalate with porphyrins to get excellent nonlinear responses.30−39 Studies on the nonlinearity of a series of Keggin polyoxometalate-porphyrin sandwich compounds have informed that the auxiliary electron acceptors on the porphyrin ring cause to enhance the value of second order polarziability.31 Recently, our group32,34−36,38,39 has been interested in exploring third-order NLO properties of new porphyrin-polyoxometalates hybrid systems formed either by electrostatic or covalent bonding, and the results imply that such kind of hybrids are promising candidate materials for device applications in photonics and optoelectronics and high potential as lower power optical limiting materials. The hybrids composed of one Dawson POM anion moiety and one porphyrin moiety bonded by covalent interaction through aromatic ring substituents was found to exhibit much remarkable enhancement in NLO response.34 It is also concluded that the hybrid wherein Anderson type POM is coupled covalently to porphyrin through shorter bridge has an NLO response superior to the hybrid, wherein Anderson type POM is bonded via longer bridge to porphyrin, and the hybrid having two porphyrins connected to Anderson type POM shows more enhancement than the hybrid having single porphyrin fused to Anderson type POM.32 Notably, the previous study showed that polyoxometalate having lower LUMO level (versus LUMO of porphyrin moiety) can act as electron acceptor making easy the transfer of electrons from porphyrin moieties (acting as electron donor to polyoxometalates),32−35,38,39 and the resulting hybrids exhibit better optical nonlinearities. While the previous work is fruitful and interesting, the study on this new emerging porphyrinpolyoxometalates hybrid system is still quite limited and well understanding remains a challenge in view of structure− property relationship, therefore more effort in designing and synthesizing more new hybrids of different structures to study

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EXPERIMENTAL DETAILS

Reagents and Chemicals. Parent Dawson POM,40 TPP-Tris32,41 (see Supporting Information). and 5,15-bis(4-phenyl)-10,20-bis(4carboxymethylphenyl)porphyrin42 were prepared and characterized according to the literatures. All solvents used for the synthesis were freshly distilled prior to use. Other chemicals were purchased commercially and used without further purification. Instruments and Measurements. Elemental analyses for C, H, and N were performed on a PerkinElmer Vario El element analyzer. Analyses for P, W, and V was conducted on a Spectro Arcos inductively coupled plasma atomic emission spectrometer (ICP-AES) after the samples were destroyed in mixture of HNO3 (conc.)/CH3CN and then diluted with deionized water. UV−vis. spectra were recorded with a UV-2550 spectrophotometer (Shimadzu). Infrared spectra were recorded at room temperature on a Nicolet 470 FT−IR spectrophotometer as KBr pellet in the 4000−400 cm−1 region. Peak intensities are indicated by the following abbreviations: weak (w), medium (m), 9437


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Inorganic Chemistry

Figure 1. Integrated 1H NMR spectra of TPP-di-Tris (a) and TPP-Tris (b) and hybrids 1 (d) and 2 (e) recorded in DMSO and CD3CN, respectively, with labeled partial 1H−1H NOESY NMR spectrum of TPP-di-Tris (c) (600 MHz, DMSO-d6, 298 K) recorded in DMSO. and sharp (s). The 1H NMR and 31P NMR spectra were recorded on a Bruker AV 400 spectrometer in DMSO and CD3CN at room temperature for ligands and hybrids, respectively. The 51V NMR spectra were recorded on a Bruker AV 600 spectrometer in CD3CN for hybrids at room temperature. Multiplicities are indicated by the following abbreviations: s = singlet, d = doublet, t = triplet, dd = doublet of doublets, m = multiple, br = broad for 1H NMR. Thin-layer chromatography (TLC) was performed using precoated silica gel 60 F254. Silica gel (zcx II, 100−200 mesh) was used for column chromatography with suitable solvents as the eluent. Cyclic voltammograms were obtained on a CHI660B electrochemical analyzer in dry DMF/CH3CN at room temperature under nitrogen atmosphere at the rate of 10 mV/s in the presence of 0.1 M (n-Bu4N)PF6 as a supporting electrolyte. The scan range of the CV were selected carefully from the wide range (+3 V to −3 V) to narrow range. A glassy carbon electrode was used as a working electrode, Ag/AgCl as a reference electrode and a Pt wire as an auxiliary electrode. Powder X-ray diffraction (PXRD) measurements of the samples were obtained using a Rigaku-Dmax 2500 diffractometer at a scanning rate of 15° per minute in the 2θ range from 3° to 55° using a graphite monochromatized Cu Kα radiation with wavelength λ = 0.15405 nm. Electron spray ionization mass spectra (ESI-MS) were recorded by using the waters ACQUITY UPLC and Xevo G2 Qtof MS systems. MALDI-TOF-MS measurements were conducted by using the Shimadzu Biotech Performance 2.9.3, mode linear, power 76, blanked systems. The observed

experimental values were consistent, within the experimental values with accuracy of ±2 in the m/z range of 400−3500 in ESI-MS and m/ z 4500−13 000 for MALDI-TOF-MS. Measurements of the thirdorder nonlinear optical properties of all the compounds were done at room temperature using an EKSPLA NL303 Q-switched Nd:YAG laser with a wavelength of λ = 532 nm, a pulse duration of τ = 6 ns, and a repetition rate of 10 Hz with intensity of light at the focus E0 of 4.2 μJ employed as the light source. 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 laser beam (i.e., GAUSSIAN light beam), after being focused by a 20 cm focal length lens into the sample placed in an L = 1 mm path-length quartz cell, was passed through a large-area beam splitter. Before the measurements, the system was calibrated using CS2 in a quartz cell as reference. Photoluminescence (fluorescence and phosphorescence) measurements were recorded at room temperature by using a Hitachi F-7000 FL fluorescence spectrophotometer with both excitation and emission slits of 5 nm, using a xenon arc lamp as the light source (150w), the photomultiplier tube voltage was 400 V, the scan speed was 1200 nm·min−1. Synthesis of TPP-di-Tris. 5,15-Bis(4-phenyl)-10,20-bis(4carboxymethylphenyl)porphyrin (1 mmol), K2CO3 (0.083 g, 2 mmol), and tris-hydroxylaminomethane (2 mmol) were introduced in a 2 mL flask. DMSO (2 mL, dried on molecular sieves) was added, and the mixture was protected from light and stirred for 17 h under 9438


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Figure 2. 51V NMR spectra of hybrid 1 (a), hybrid 2 (b), and parent Dawson POM (c) recorded in CD3CN (600 MHz) at room temperature.

Figure 3. 31P NMR spectra of hybrids 1 and 2 (a) and parent Dawson POM (b) recorded in CD3CN (400 MHz) at room temperature. nitrogen at 85 °C. The mixture was poured in cold distilled water (100 mL), the resulting precipitate is collected by simple filtration, adsorbed on silica gel and purified by flash chromatography, elution with a gradient from methanol + ethyl acetate (1:2) to yield the expected product as a violet powder (0.295 g, 50% yield). Elemental analysis (%) calcd. for C52H46N8O8 (908.34 g/mol): C 68.56, H 5.09, N 12.30; found C 68.44, H 5.15, N 11.4. (ESI-MS) m/z 909.35 (M + 1)+. 1H NMR (400 MHz; DMSO-d6): δ = 8.86−7.84 [all phenyl + pyrrole “H”], 7.71 (s, 2H, NH), 4.91 (s, 6H, OH), 3.87 (s, 12H, −CH2), −2.89 (s, 2H, −NH). FT-IR (KBr): νmax = 3409 (νO−H, m, br), 3323 (νN−H, m, br), 2933, 2860 (ν C−H, w), 1729 (w), 1651 (νCO, vs), 1605 (m), 1536 (s), 1493 (m), 1475 (νC−H, sh), 1404 (sh), 1356 (m), 1226 (w), 1183 (m), 1158 (w), 1046 (s), 1015 (m), 971 (s), 866 (m), 804 (vs), 798 (vs), 737 (s), 704 (s), 568 (sh) cm−1. UV−vis spectrum (λmax (nm) in DMF/CH3CN: 415, 513, 547, 588, and 644. Synthesis of Hybrid 1. Parent Dawson POM (500 mg, 2 mmol) and TPP-di-Tris (0.070 g, 1 mmol) were introduced in a Schlenk bottle under nitrogen atmosphere. N,N-Dimethylacetamide (2 mL, dried on molecular sieve) was added, and the resulting suspension was

protected from light and heated at 80−90 °C under nitrogen for 6 days. The mixture was cooled to room temperature and added dropwise to diethyl ether (50 mL). The precipitate was collected by simple filtration and then dissolved in small amount (3 mL) of CH3CN and precipitated again in diethyl ether. Filtration and precipitation were repeated thrice to get the pure product. The resulting hybrid was obtained as a purple powder (0.23 g, 75% yield). Elemental analysis (%) calcd. for [(C4H9)4N]10H2[{COHNC(CH2O)3P2V3W15O59}2C44N4H28]·CH3CN: C 23.16, H 3.63, N 2.13; found C 23.50, H 3.90, N 2.10. ICP analyses (%) calcd. for [(C 4 H 9 ) 4 N] 10 H 2 [{COHNC(CH 2 O) 3 P 2 V 3 W 15 O 59 } 2 C 44 N 4 H 28 ]· CH3CN: P 1.08, W 48.21, V 2.67%; found P 1.01, W 48.80, V 2.50. 1H NMR (400 MHz; CD3CN): δ = 8.94−7.63 [all phenyl + pyrrole “H”], 7.01 (s, 2H, NH),6.03 (s, 12H, OCH2), 3.12 (m, 80H, NCH2, TBA+), 1.62 (m, 80H, TBA+), 1.40 (m, 80H, TBA+), 0.97 (t, 120H, TBA+), −2.87(s, 2H, NH). 31P NMR (400 MHz, CD3CN): δ = −13.45, −7.32. 51V NMR (600 MHz, CD3CN): δ = −541.10. MS (MALDITOF) m/z: observed for [(C 4 H 9 ) 4 N] 10 H 2 [{HNC(CH 2 O) 3 P2V3W15O59(CO)}2C44N4H2]·CH3CN, [M − TBAH2]+ = 10954.70. 9439


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Inorganic Chemistry Table 1. FT-IR Data of the TPP-di-Tris, TPP-Tris, Hybrid 1, Hybrid 2 and Parent Dawson POM parent Dawson POM 3375 2958, 2947, 2884

TPP-di-Tris 3409 3323 2933, 2860 1651 1596, 1570, 1536 1404, 1356 1046 1073 971 798 737

956, 907,830 599

TPP-Tris 3402 3324 2946 2894 1644 1597, 1531, 1498 1448, 1348 1052 960 804 737

assignmentsa

hybrid 1

hybrid 2

3462 2966, 2940, 2880

3475 2970, 2940, 2886

1664 1593, 1541, 1486 1388, 1314 1089 1022

1677 1599, 1543, 1472 1382, 1313 1082 1021

ν(−HN−CO) phenyl ν(Pyr half- ring)psym ν(C−O) ν(Pyr halfδ(Pyr breath)d/δ(Pyr breath)p+ phenyl δ(Pyr def)dasym/δ(Pyr def)pasym

956, 910 824

963, 917 818

ν(WO) ν(br.W−O−W)

ν(br. O−H) ν(N−H) phenyl and ν(CH)∼TBAa

a ν = stretching, a = tetra-butyl ammonium, δ = in-plane bending, γ = out-of-plane bending modes, subscripts sym = symmetric, subscripts asym = asymmetric modes, def = deformation, and pyr = pyrrole, superscript p = protonated pyrrole, superscript d = deprotonated pyrrole.

Characteristic FT-IR (KBr) bands: νmax = 3462 (w), 2966, 2940, 2880 (νC−H, s),1664 (νCO, s), 1605(sh), 1593 (w), 1486 (νC−H, br), 1388 (sh), 1314 (m), 1321 (m), 1266 (sh), 1151(sh), 1089 (vs), 948 (vs), 956 (br), 824 (νW−O−W, vs), 725 (νW−O−W, s), 523 (sh) cm−1. UV−vis spectrum (λmax (nm) in DMF/CH3CN: 417, 514, 546, 590, and 645. Synthesis of Hybrid 2. Same procedure for the synthesis of hybrid 1 was used but with some modifications where Parent Dawson POM (250 mg, 1 mmol) and TPP-Tris (0.058 g, 1 mmol) were used for the synthesis of hybrid 2. The resulting hybrid was obtained as a purple powder (0.23 g, 75% yield). Elemental analyses (%) calcd. for [(C 4 H 9 ) 4 N)] 5 H[HNCO(CH 2 O) 3 CP 2 V 3 W 15 O 59 {C 44 H 29 N 4 }]: C 27.00, H 4.10, N 2.62; found C 27.34, H 4.73, N 2.58. ICP analyses (%) calcd. for [(C4 H9) 4 N)] 5 H[HNCO(CH2 O)3 CP2 V3W 15O59{C44H29N4}]: P 1.04, W 46.49, V 2.58; found P 1.06 W 46.30 V 2.35. 1H NMR (400 MHz; CD3CN): δ = 8.94−7.63 [all phenyl + pyrrole ‘H’], 7.01 (s, 1H, NH), 6.03 (s, 6H, OCH2), 3.12 (m, 40H, NCH2, TBA+), 1.62 (m, 40H, TBA+), 1.40 (m, 40H, TBA+), 0.97 (t, 60H, TBA+), −2.87 (s, 2H, NH). 31P NMR (400 MHz, CD3CN): δ = −13.32, −7.43. 51V NMR (600 MHz CD3CN): δ = −541.10. MS(MALDI-TOF)m/z: observed for [(C 4H 9) 4 N)] 5H[HNCO(CH2O)3CP2V3W15O59{C44H29N4}]·CH3CN, [M + H]+ = 5929.86. Characteristic FT-IR (KBr) bands: νmax = 3475 (w), 2970, 2940, 2886 (ν C−H, s), 1677 (νCO, s),1599(sh), 1543 (w), 1472 (νC−H, br),1407 (m), 1382 (sh), 1352 (m), 1313 (m), 1267 (br), 1153 (m),1082 (vs), 963 (sh), 917 (br), 818 (νW−O−W, vs), 725 (νW−O−W, s), 596 (m), 525 (sh) cm−1. UV−vis spectrum (λmax (nm) in DMF/ CH3CN: 416, 513, 547, 589, and 644.

Figure 4. FT-IR spectra of TPP-di-Tris, TPP-Tris, hybrid 1, hybrid 2, and parent Dawson POM.

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RESULTS AND DISCUSSION IR, NMR (1H NMR, 51V NMR, 31P NMR), ESI-MS, MALDITOF-MS, UV−visible spectroscopy, and elemental analysis techniques have been used to characterize the given compounds. Powder X-ray diffraction studies show that the as-prepared compounds are lack of good crystallinity (Figure S1) and attempt to try to get single crystals of high quality is failed and given up. For TPP-di-Tris, the characteristics chemical shifts for aliphatic protons appear at 3.87 ppm for −CH2− as singlet, for −OH proton, the δ is 4.92 ppm also singlet because both neighboring protons of CH2 and OH do not couple due to less J value, by which there is no observable splitting.41,43 and most important chemical shift for linker amide proton is at 7.71 ppm which is in downfield region because of electron-withdrawing effect of amide functionality attached with phenyl ring of porphyrin as shown in the Figure 1a. 2D NOESY NMR spectrum as shown in Figure 1c, is recorded in DMSO-d6 to find the conformations in TPP-di-Tris

Figure 5. UV−visible spectra of TPP-di-Tris, TPP-Tris, hybrids 1 and 2, and the parent Dawson POM in the mixture of DMF/CH3CN (v/v = 1:1). (All compounds have concentration of 1.0 × 10−5 M with 1 cm optical path length.)

having functionality at trans position.44 This 2D NMR technique is used to identify spin undergoing cross-relaxation. Cross relaxation rates are also measured by 2D NOESY NMR technique. If the distance between two protons is less than 5 Å then the signal is observed.45 TPP-di-Tris having functional groups at trans position, exhibited a strong correlation between the amide proton (Hd) and (Hc) as compare to Hd and Ha suggesting the trans functionality is the coconformation for TPP-di-Tris. For TPP-Tris, the characteristics chemical shifts for aliphatic protons appear at 3.87 ppm for −CH2− as doublet, for −OH proton, the δ is 4.92 ppm triplet because both neighboring protons of −CH2− and OH couple as shown in Figure 1b, and most important chemical shift for linker amide 9440


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moiety. There is a shifting of signal for amide link from 7.74 to 6.98 ppm for hybrid 1 and 7.71 to 6.93 ppm for hybrid 2 due to decrease in electron withdrawing effect of amide functionality. The signals at 4.92 ppm for hydroxyl of the porphyrin TPP-diTris and TPP-Tris have been vanished in the hybrids due to attachment with the cap of the POM anion. Another significant shifting of the signal is from 3.87 to 6.02 ppm for −CH2 proton of the linker in hybrid 1 from upfield to downfield due to neighboring caped vanadium atoms of the POM anion. Similarly this shifting of −CH2 protons for hybrid 2 is from 3.88 to 6.00 ppm. This is shown in the Figure 1d and e. 51V NMR spectra show one broad peak at −585.48 ppm for parent Dawson POM but when porphyrin molecules are attached covalently then peaks appeared at −540.45 and 542.25 ppm for hybrids 1 and 2 (Figure 2), respectively. 31P NMR spectra show two peaks at δ = [−14.04, −7.07] ppm for parent Dawson POM, but when porphyrin molecules are bonded covalently then peaks fluctuates from [−14.04, −7.07] ppm (parent Dawson POM) to [−13.43, −7.32] and [−13.32, −7.43] ppm for hybrids 1 and 2 (Figure 3), respectively,31 all match well to earlier work40,41,46 not only indicating the substitution of six and three μ-alkoxy groups of TPP-di-Tris and TPP-Tris, respectively, over vanadium cap in the parent Dawson POM anion but also proving the intactness/stability of the POM moiety within the hybrids 1 and 2. From the FT-IR spectra of parent Dawson POM, TPP-diTris, TPP-Tris, and hybrids 1 and 2 and data listed in Table 1 for the observed IR bands and their assignments along with their mode numbers, it is known that the peaks at 3323 and 3324 cm−1 were assigned to stretching vibration of the amino group of amide link ν(−NH) for TPP-di-Tris and TPP-Tris, respectively. The peaks appeared at 2933, 2860 and 2946, 2894 cm−1 were attributed to stretching vibration of ν(−CH) benzene ring of porphyrins of TPP-di-Tris and TPP-Tris, respectively.41 The strong peak at 1651 and 1644 cm−1 are mentioned to ν(C = O) in TPP-di-Tris and TPP-Tris, respectively. The peaks at 798 and 804 cm−1 are attributed to ν(C−H) out-plane bending vibration in pyrrole of TPP-di-Tris and TPP-Tris, respectively. Similarly, for the hybrids 1 and 2, the characteristics peaks appear at 3462 and 3475 cm−1 for ν(N−H) respectively. The bands at 2966, 2940, and 2880 cm−1 are attributed to [Bu4N]+ of hybrid 1. Similarly, for hybrid 2 the peaks for [Bu4N]+ can be seen at 2970, 2940, and 2886.40,47−49

Table 2. Electronic Absorption Spectral Data of Parent Dawson POM, TPP-di-Tris, TPP-Tris, Hybrid 1, and Hybrid 2 in the Mixture of DMF/CH3CNa entry compounds 1 2

TPP-diTris TPP-Tris

3

hybrid 2

4

hybrid 1

5

parent Dawson POM

absorptions: λmax (nm), (ε, M− cm−) 270(5.47 × 105), 415(2.14 × 106), 513(1.20 × 105), 547(9.50 × 104), 587(4.7 × 104), 644(3.57 × 104) 272(3.00 × 105), 415(2.06 × 106), 512(3.33 × 104), 548(1.67 × 104), 589(1.33 × 104), 645(1.35 × 104) 261(−1.82 × 106), 417(4.64 × 105), 514(−2.72 × 104), 550(−2.27 × 104), 590 (−1.82 × 104), 647(−1.82 × 104) 261(−1.00 × 105), 416(1.15 × 104), 514(−5.17 × 104), 548(−4.27 × 104), 590(−3.44 × 104), 645(−3.44 × 104) 282(1.06 × 106)

a All compounds have concentration of 10−5 M with 1 cm optical path length.

Figure 6. Emission fluorescence spectra of 10−5 M solutions of TPPdi-Tris and TPP-Tris, hybrid 1, and hybrid 2 in DMF/CH3CN (v/v = 1:1) at the excitation wavelength λexc= 315, 322, 331, and 328 nm, respectively. Photograph of the solutions of TPP-di-Tris (a), TPP-Tris (b), hybrid 2 (c), and hybrid 1 (d) compounds are drawn under UV illumination.

proton is at 7.72 ppm, which is in downfield region due to electron withdrawing effect of amide functionality attached with phenyl ring of porphyrin41 as shown in Figure 1b. The 1H NMR spectra of hybrids 1 and 2 (Figure 1d, e) show clearly resolved signals, all of which can be unambiguously assigned. In hybrid 1, the signals for aromatic protons for porphyrin appear from 7.63 to 8.95 ppm. The most important shifts are in the linker between porphyrin moiety and POM

Figure 7. Z-scan curves for TPP-di-Tris, TPP-Tris, hybrid 1, and hybrid 2 in DMF/CH3CN (v/v = 1:1) (all the compounds have the concentrations of 3.25 × 10−4 M) under open (a) and closed (b) aperture at 532 nm. The symbols indicate the measured data and the solid lines represent the theoretical fits. 9441


Article

E(CS) = E(oxidation of porphyrin) − E(reduction of POM) (eV), where porphyrin = TPP-di-Tris and TPP-Tris. Compd 1 = (Bu4N)4K2[{C52H32N5O2ZnHNC(CH2O)3P2V3W15O59]·2(C4H9NO),34 compd 2 = (Bu4N)4K2[{C52H32N5O2}HNC(CH2O)3P2V3W15O59]·3(C4H9NO).34

−1.66 −0.03

The linker ν(CO) peaks have been appeared at 1664 and 1677 cm−1 for hybrids 1 and 2 respectively.41 Other important strong peaks for ν(C−H) have been shown at 1486 and 1472 cm−1 for hybrids 1 and 2 respectively. Very strong bands appearing in the low wavenumber region at 824, 725 and 818, 725 cm−1 are assigned for ν(W−O−W) hybrids 1 and 2, respectively.40 IR studies prove the covalent bonding between porphyrin moieties and POM moiety in the hybrids 1 and 2. In addition to the above characterization, ESI-MS and MALDI-TOF-Mass studies are also used to strongly prove the successful formation of the hybrids 1 and 2, TPP-di-Tris, and TPP-Tris, respectively. The TPP-di-Tris (C54H48N6O8, Fw = 908) (Figure S2a) and TPP-Tris (C49H39N5O4, Fw = 761) (Figure S2b) have molecular ion peak at 909.6 [M + H]+ and 762.6 [M + H]+, respectively. Incorporation of the porphyrin moieties at the POM’s cap was evidenced by MS (MALDITOF) m/z for hybrid 1 (Figure S3a) calcd = [M − TBAH2]+ = 10957.70, observed = [M − TBAH2]+ = 10954.54; for hybrid 2 (Figure S3b) calcd = [M + H]+ = 5929.86, observed = [M + H]+ = 5929.96, respectively. It should be mentioned that porphyrin molecules TPP-diTris and TPP-Tris possess two and one triol moieties, respectively. There is a substitution of three μ2-oxo ligands of the {V3} cap in the parent Dawson Polyoxometalate by the three μ2-alkoxy groups of the two and one triol moieties of porphyrin molecules in hybrids 1 and 2, respectively,50−53 and the alkoxo ligand should bridge between V centers of POMs and porphyrin molecules via sigma bonds. Besides, depending upon the configuration of amide linkage it can be deduced that the POM moiety shall direct to the opposite side in hybrid 1, away from the porphyrin moiety due to local C3v symmetry,40,41 and the conformational flexibility can afford a stable structure as a local minimum. UV−vis Spectroscopy Studies. The linear electronic properties of the compounds were studied by UV−vis spectroscopy in DMF/CH3CN as shown in Figure 5 and data summarized in Table 2.54 TPP-di-Tris in the mixture of DMF/CH3CN shows absorption bands (also called Soret band or B-band) at 415 nm ascribed to π → π* transition (attributed S0 − S2 transition) and four weak Q-bands at 513, 547, 588, and 644 nm (correspond to S0−S1 transition). Similarly, the strong absorption band of TPP-Tris appear at 415 nm, and four weak Q-bands appear at 512, 548, 589, and 645 nm) (Table 2).41,55,56 Both the porphyrin molecules show typical features of metal free in their electronic absorption spectra, revealing their nonaggregated molecular spectroscopic nature. Though the electronic absorption spectra of hybrids 1 and 2 are different from corresponding parent compounds (Figure 5), wherein the TPP-di-Tris and TPP-Tris exhibited intense soret bands at 415 nm,41 there is only a slight red-shift from 415 to 417 nm for the hybrids with respect to TPP-di-Tris and TPP-Tris. One reason for this may be because strong substitution effects in tetrapyrroles of porphyrin core are directly associated with the meso position,57 while in the current work substituents are bonded at para position of phenyl ring which is at the meso position of porphyrin core so substituents are indirectly attached at the meso position of porphyrin core typically exert weaker influence over the porphyrin core.57,58 On the basis of the results, it is concluded that there is a weaker electronic interaction in the ground state between TPP moieties and POM moiety in the hybrids. Generally, polyoxometalates show absorption in ultraviolet region due to LMCT O → metal transition,59 and may show absorption in

a

−1.64

E(CS) E(*T)

−0.04

−0.020 −0.015 −0.016 −0.025

E(*S1) (ev) Eg (ev)

1.88 1.86 1.89 1.87 1.86 1.87 4.38 8.01 12.91 2.60 12.22 0.59 0.51 1.59 2.56 0.52 2.43 0.38 0.33 0.93 3.73 0.48 3.37 2.29 2.05 TPP-di-Tris hybrid 1 TPP-Tris hybrid 2 compd 134 compd 234 parent DawsonPOM

0.72 2.90 0.37 2.62 1.80 1.60

−1.04 −1.67 −0.34 −1.58 −0.20 −0.17

−1.58 −2.53 −0.51 −2.40 −0.30 −0.26

γ (esu) × 10−28 χ(3) (esu) × 10−10 Reχ(3) (esu) × 10−10 Imχ(3) (esu) × 10−11 n2 (esu) × 10−9 β (esu) × 10−5 compds

Table 3. Z-Scan Data for the Compounds at a Concentration of 0.1 mM in DMF/CH3CN at 532 nm with I0 being 4.20 × 1011 W/m2 and the Obtained HOMO−LUMO gaps Eg, Singlet Excited States E(*S1), Triplet Excited States E(*T), and Energy Levels of the Charge Separated States E(CS)a

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Figure 8. Cyclic voltammograms of ferrocene (a), dawson POM (b), TPP-di-Tris (c), and TPP-Tris (d) in DMF/CH3CN (v/v = 1:1). (All the compounds have the concentrations of 1 mM in the presence of 0.1 M (n-Bu4N)PF6 as a supporting electrolyte.)

4.2 μJ employed as the light source) to monitor the color change. Fluorescence Studies. Fluorescence measurements are performed on TPP-di-Tris, TPP-Tris, and hybrids 1 and 2 at very low concentration (10−5 M in DMF/CH3CN) to prevent them from self-quenching. TPP-di-Tris, TPP-Tris, and hybrids 1 and 2 exhibit the emission peak at 651 nm as shown in Figure 6 as they are excited at 315, 322, 331, and 328 nm, respectively. However, it is found that attachment of POMs on the porphyrin results in significant fluorescence quenching (fluorescence intensity is decreased 97% for the hybrid 1 and 80% for the hybrid 2 with respect to that of their corresponding ligand precursor TPP-di-Tris, TPP-Tris, showing that Dawson polyoxometalate moiety is a strong quencher. This quenching phenomenon not only suggests the formation of hybrids 1 and 2 via covalent bonding interaction by reacting TPP-di-Tris and TPP-Tris with the parent Dawson POM but also indicates the favored photoinduced electron transfer from porphyrin moiety acting as an electron donor to Dawson POM moiety acting as an electron acceptor54,62−65 in such an intramolecular donor− acceptor structural system of molecules of hybrids 1 and 2, respectively. As it is known that fluorescence intensity strongly depends upon the molar extinction coefficient and that greater the value of extinction coefficient, the higher will be the intensity of fluorophore. TPP-di-Tris having greater molar extinction coefficient value (2.14 × 10 6 M − cm) exhibits higher fluorescence emission intensity.52,66−68 In the case of hybrid 1, there is more fluorescence quenching than hybrid 2 hence, there is more photo induced electron transfer from the porphyrin moieties to whole Dawson POM moiety,50−52 leading to that quenching of porphyrin emission in hybrid 1 is more effective than in hybrid 2.

Figure 9. Energy level diagram assumed for the covalent hybrids 1 and 2: photon absorption generates the doublet and singlet excited-state of porphyrin molecules which interconverts to the triplet state by intersystem crossing (ISC). In general, the radiative decay of the triplet state to the ground state is in competition with two other processes: nonradiative decay (NR) and electron transfer (ET) to the charge separated state.

the visible region leading to color change when intervalence charge transfer takes place within the POM anions in the presence of electron donors.60,61 Based on the following fluorescence quenching result and the enhancement of NLO response after attachment of POMs on the porphyrin moiety, we believe that photoinduced electron transfer occurs from the porphyrin moiety to the Dawson-type POM moiety in the hybrids, which may result in reduction of partial WVI to WV under laser irradiation and consequent appearance of absorption around 650 nm. However, this process is too fast (a wavelength of λ = 532 nm, a pulse duration of τ = 6 ns, and a repetition rate of 10 Hz with intensity of light at the focus E0 of 9443


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Inorganic Chemistry Nonlinear Optical Properties. Single-beam Z-scan technology is a prominent and efficient technique to measure the third-order nonlinear optical properties of compounds.69−71 It is an efficient and customary technique for the determination of the nonlinear optical parameters of materials, providing simultaneously the third-order nonlinear susceptibilities, the magnitude of nonlinear absorption as well as sign of the nonlinear refraction. The third order nonlinear optical properties of TPP-di-Tris, TPP-Tris, hybrids 1, 2, and Parent Dawson POM (0.1 mM) were measured in mixture of DMF/ CH3CN. The Z-scan curves {i.e., open aperture (OA) and closed aperture (CA)} along with the corresponding fits72,73 for the compounds are shown in Figure 7a and b. Reasonably, good matches between the experimental data and the theoretical curves are observed indicating that the experimentally detected NLO effects have an efficient third-order characteristic. As shown in Figure 7a and b, all of the samples have notable nonlinear reverse saturated absorption under the open-aperture configuration corresponding to a positive nonlinear absorption coefficient (β), an intrinsic property of a material that is widely applicable in the protection of optical sensors. As peak and valley configuration corresponding to the characteristic behavior of self-defocusing of propagating waves74,75 occurs in the closed aperture curves of TPP-diTris, TPP-Tris, and hybrids 1 and 2, which corresponds to the negative refractive index in TPP-di-Tris, TPP-Tris, and hybrids 1 and 2. (Note: The solution of Parent Dawson POM shows negligible NLO response.) According to the theoretical equations given by Sheik-Bahae et al. and Wang et al., the nonlinear refractive index n2, nonlinear absorption coefficient β, resulting third-order optical nonlinear susceptibility Imχ(3), Reχ(3), and χ(3) and the molecular second hyperpolarizability γ are calculated (Table 3). From data listed in Table 3, it is found that the molecular second hyperpolarizability (γ), n2, β, Imχ(3), Reχ(3), and χ(3) all follow the order of hybrid 1 > hybrid 2 > TPP-di-Tris > TPP-Tris in view of their magnitude. While the porphyrin molecules TPP-di-Tris (γ = 2.60 × 10−28 esu) and TPP-Tris (γ = 8.01 × 10−28 esu) show high second hyperpolarizability, the massive enhancement for the “γ” in hybrids 1 and 2 over the porphyrin molecules is realized, showing that grafting POM clusters on the porphyrin molecules is an efficient way to improve the NLO response.30,65 It is well-known that electronic structure of porphyrins will be perturbed by the presence of strong electron-with drawing groups,76−79 and consequently molecular second hyperpolarizability (γ) values can be influenced by perturbing the charge density in the porphyrin core because of external substituents. When the structures of the compounds are compared, it can be seen that TPP-di-Tris has two electron withdrawing groups (tris-hydroxylaminomethane) at the trans position of highly conjugated porphyrin making stronger overlapping between two π electronic systems of peripheral carbonyl functionality and porphyrin core π electrons in TPP-di-Tris, while TPP-Tris has only one electron withdrawing attached with the phenyl which is at the meso position of porphyrin in TPP-Tris. The two electron-withdrawing groups in TPP-di-Tris can pull the electrons toward themselves more strongly than one electron withdrawing group in TPP-Tris.76 Similarly, when polyoxometalates (powerful electron accepting groups) has been bonded covalently with the porphyrin via tris alkoxo bridge, the hybrid 1 has two Dawson POM anion at trans position while hybrid 2 has one Dawson POM anion covalently bonded with porphyrin. The two POM moieties in hybrid 1 can pull the

electrons toward themselves more strongly than one POM moiety in hybrid 2. Because the Dawson type polyoxometalate moiety is a more powerful electron accepting group than trishydroxylaminomethane, the electron/charge density in the porphyrin core will be perturbed much significantly via electron/charge transfer through the overlapping area of pπ orbitals of terminal oxygen atoms of porphyrin molecules and dπ orbitals of vanadium more effectively in the hybrids 1 and 2 than that in the TPP-Tris and TPP-di-Tris, that is, electron transfer from porphyrin moiety77,78 to polyoxometalate moiety promotes the polarziability of the hybrid molecules. In addition, the strong polar organic solvents DMF/CH3CN used to dissolve the hybrids 1 and 2 in our experiments can further improve the polarity of hybrids 1 and 2.35,64 As a consequence, molecular polarization occurs more easily and efficiently in the hybrids under laser irradiation thus leading to enhanced NLO response than that in the porphyrin precursor molecules. It should be mentioned that the molecular second hyperpolarizability γ of the hybrids 1 and 2 is found to be ca. 6 times greater than the reported hybrids named (Bu 4 N) 4K 2 [{C52 H32N5O2Zn}HNC(CH2O)3P 2V3W15O59]·2(C4H9NO) and (Bu4N)4K2[{C52H32 N5O2}HNC(CH2O)3P2V3W15O59]· 3(C4H9NO), where much longer linker was used to link the Dawson POM with porphyrin.34 Obviously, this result is matching well with our previous observation32 found during the study of NLO properties of a series of hybrids composed of Anderson type polyoxometalate and porphyrin where both the number of Anderson type polyoxometalate moiety and the distance between porphyrin and POM moieties were studied as variables. In addition, it is also found that the molecular second hyperpolarizability γ of the hybrid 2 is ∼5 times larger than that of (N(C 4 H 9 ) 43 C 44 H 29 N 4 CONHC(CH 2 O) 3 Mn Mo 6 O 18 (OCH2)3CCH3·CH3C(O)N(CH3)232 containing one Anderson polyoxometalate and one porphyrin moiety the same as that in the hybrid 2, reflecting the remarkable difference of POM types on the NLO properties. As it is well-known that NLO property is related to the values of transition energy.80,81 The HOMO−LUMO gap (Eg) values for TPP-di-Tris, TPP-Tris, and hybrids 1, 2 have been calculated from the absorption edges of UV−visible spectra by Eg = 1240/λ (λ is absorption edge are shown in the Figure S4).82,83 From the calculated data listed in Table 3, it is known that the Eg values of the compounds decrease in the following order: Eg(POM) > Eg(TPP‑Tris) > Eg(TPP‑di‑Tris) > Eg(hybrid2) > Eg(hybrid 1), while the second hyperpolarizability increases as follows: TPP-Tris < TPP-di-Tris < hybrid 2 < hybrid 1. Lower Eg value of the compounds is showing the ease of electrons transition from HOMO levels to LUMO levels when compounds are subjected to laser irradiation. On the other hand, hybrid 1 and 2 possess singlet excited state energies about −0.015 eV for hybrid 1, −0.025 eV for hybrid 2 and triplet excited state energies −0.04 eV for hybrid 1, −0.03 eV for hybrid 2, respectively. Their energy level of charge separated state is estimated as −1.64 eV for hybrid 1 and −1.66 eV for hybrid 2 (Table 3, Supporting Information). It is well-known that porphyrins possess very strong excited state absorption from both the triplet as well as the singlet states, singlet excited state has a shorter lifetime and transfers the excited state energy to triplet state through inter system crossing (ISC).41 Porphyrin molecules typically emit in the 600−700 nm range due to radiative relaxation.84,85 However, after attachment of POM on porphyrin molecules, energy difference of singlet and triplet excited states of hybrids 1 and 2 are very small which 9444


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speed up the ISC process,41,86,87 consequently enhance the optical nonlinearities of the resulting hybrids86,88 while the luminescence is quenched by rapid photo induced electron transfer from triplet excited state porphyrin molecules to Dawson POMs (Figure 9).

ACKNOWLEDGMENTS The authors thank the Natural Science Foundation of China for financial support. Prof. Xue Duan of Beijing University of Chemical Technology is greatly acknowledged for his kind support.

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CONCLUSION Two covalently bonded hybrids composed of porphyrin moiety and Wells-Dawson type polyoxometalate moiety are synthesized and thoroughly characterized. Remarkable enhancement of the nonlinearity of the hybrids over their corresponding porphyrin precursors is observed, which is thought to be because of lower LUMO level of the POM than that of the porphyrin favoring the easy charge transfer from porphyrin to polyoxometalates when compounds are subjected to laser irradiation. Hybrid 1 has shown greater NLO response than hybrid 2, reflecting the effect of (different number of) polyoxometalates wherein more POM moiety in hybrid 1 is thought to be more favorable for charge transfer from porphyrin to polyoxometalates. Considering the fact that electronic structures of porphyrins of various structures can be well tuned by attaching polyoxometalates of different structure with various properties in various manners, as a consequence NLO properties can be well modulated/tuned accordingly to meet requirements. Obviously, the result is instructive for future exploration of porphyrin- polyoxometalate hybrid systems with remarkable NLO response.

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REFERENCES

(1) Ehrlich, J.; Wu, X.; Lee, I. Y.; Hu, Z. Y.; Röckel, H.; Marder, S.; Perry, J. Two-Photon Absorption and Broadband Optical Limiting with Bis-Donor Stilbenes. Opt. Lett. 1997, 22, 1843−1845. (2) Bhawalkar, J.; Kumar, N.; Zhao, C. F.; Prasad, P. Two-Photon Photodynamic Therapy. J. Clin. Laser. Med. Sur. 1997, 15, 201−204. (3) Kawata, S.; Sun, H. B.; Tanaka, T.; Takada, K. Finer Features for Functional Microdevices. Nature 2001, 412, 697−698. (4) Zyss, J. Molecular Nonlinear Optics: Materials, Physics, and Devices; Academic Press, 2013. (5) Chen, Y. C.; Raravikar, N.; Schadler, L.; Ajayan, P.; Zhao, Y. P.; Lu, T. M.; Wang, G. C.; Zhang, X. C. Ultrafast Optical Switching Properties of Single-Wall Carbon Nanotube Polymer Composites at 1.55 Mm. Appl. Phys. Lett. 2002, 81, 975−977. (6) Chen, C. T.; Liu, G. Z. Recent Advances in Nonlinear Optical and Electro-Optical Materials. Annu. Rev. Mater. Sci. 1986, 16, 203− 243. (7) Avalos, M.; Babiano, R.; Cintas, P.; Jiménez, J.; Palacios, J. C. Nonlinear Stereochemical Effects in Asymmetric Reactions. Tetrahedron: Asymmetry 1997, 8, 2997−3017. (8) Hales, J. M.; Zheng, S.; Barlow, S.; Marder, S. R.; Perry, J. W. Bisdioxaborine Polymethines with Large Third-Order Nonlinearities for All-Optical Signal Processing. J. Am. Chem. Soc. 2006, 128, 11362− 11363. (9) Coulter, D. R.; Miskowski, V. M.; Perry, J. W.; Wei, T. H.; Van Stryland, E. W.; Hagan, D. J. In Optical Limiting in Solutions of MetalloPhthalocyanines and Naphthalocyanines, 1989 Orlando Symposium; International Society for Optics and Photonics, 1989; pp 42−51. (10) Wei, T.; Hagan, D.; Sence, M.; Van Stryland, E.; Perry, J.; Coulter, D. Direct Measurements of Nonlinear Absorption and Refraction in Solutions of Phthalocyanines. Appl. Phys. B: Lasers Opt. 1992, 54, 46−51. (11) Perry, J. W.; Alvarez, D.; Choong, I.; Mansour, K.; Marder, S. R.; Perry, K. J. Enhanced Reverse Saturable Absorption and Optical Limiting in Heavy-Atom-Substituted Phthalocyanines. Opt. Lett. 1994, 19, 625−627. (12) Ravikanth, M.; Ravindra Kumar, G. Nonlinear Optical Properties of Porphyrins. Curr. Sci. 1995, 68, 1010−1017. (13) Rao, D.; Aranda, F. J.; Roach, J. F.; Remy, D. E. Third-Order, Nonlinear Optical Interactions of Some Benzporphyrins. Appl. Phys. Lett. 1991, 58, 1241−1243. (14) Guha, S.; Roach, J. F.; Aranda, F. J.; Rao, D.; Remy, D. E.; Kang, K.; Porter, P. Third-Order Optical Nonlinearities of Metallotetrabenzoporphyrins and a Platinum Poly-Yne. Opt. Lett. 1992, 17, 264−266. (15) Anderson, H. L. Conjugated Porphyrin Ladders. Inorg. Chem. 1994, 33, 972−981. (16) Zojer, E.; Beljonne, D.; Pacher, P.; Brédas, J. L. Two-Photon Absorption in Quadrupolar π-Conjugated Molecules: Influence of the Nature of the Conjugated Bridge and the Donorhird-Order Optical Non. Chem. - Eur. J. 2004, 10, 2668−2680. (17) Kato, S. I.; Matsumoto, T.; Ishi-i, T.; Thiemann, T.; Shigeiwa, M.; Gorohmaru, H.; Maeda, S.; Yamashita, Y.; Mataka, S. Strongly Red-Fluorescent Novel Donor−π-Bridge−Acceptor−π-Bridge−Donor (D−π−a−π−D) Type 2, 1, 3-Benzothiadiazoles with Enhanced TwoPhoton Absorption Cross-Sections. Chem. Commun. 2004, 2342− 2343. (18) Abbotto, A.; Beverina, L.; Bozio, R.; Facchetti, A.; Ferrante, C.; Pagani, G. A.; Pedron, D.; Signorini, R. Novel Heteroaromatic-Based Multi-Branched Dyes with Enhanced Two-Photon Absorption Activity. Chem. Commun. 2003, 2144−2145. (19) 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.; et al.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b03155. Powder XRD pattern of hybrids 1 and 2 with parent Dawson POM; ESI-MS spectra of TPP-di-Tris and TPPTris; MALDI-TOF-MS spectra of hybrids 1 and 2; UV− vis. spectra of Dawson POM, TPP-di-Tris, TPP-Tris, hybrid 1, and hybrid 2 in DMF/CH3CN; phosphorescence spectra of 10−5 M solutions of hybrids 1 and 2 in DMF/CH3CN (v/v = 1:1) at the excitation wavelength λexc= 331 and 328 nm, respectively; calculation of the estimated energy level of the singlet excited state, triplet excited states, and charge-separated state and cyclic voltammograms of hybrids 1 and 2 in DMF/CH3CN; and primary equations used to find the important parameters of third-order nonlinear optical properties (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yunshan Zhou: 0000-0003-0143-7370 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest. 9445


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Covalent Synthesis of Two Hybrids Composed of Dawson-Type

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