A Strong Donor–Acceptor System Based on a Metal Chalcogenide

Article pubs.acs.org/IC

A Strong Donor−Acceptor System Based on a Metal Chalcogenide Cluster and Porphyrin Jing Xu, Li-Jun Xue, Jin-Le Hou, Zhong-Nan Yin, Xuan Zhang, Qin-Yu Zhu,* and Jie Dai* College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People’s Republic of China S Supporting Information *

ABSTRACT: Although great progress has been made for charge transfer (CT) compounds of various organic donor− acceptor systems, no CT compounds containing both inorganic chalcogenide cluster anions and organic porphyrin cations have been reported. Herein, a germanium chalcogenide cluster (Ge4S104−) is chosen as an electron donor and a methylated tetrakis(4-pyridyl)porphyrin (5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin, TMPyP) is selected as an electron acceptor to create chalcogenide cluster−porphyrin CT compounds (TMPyP-Ge4S10)·5H2O (1) and (MnTMPyPGe4S10)·13H2O (2). Their crystal structures have been characterized by single-crystal X-ray diffraction. Compound 1 is an ionic CT salt assembled through interion interactions, and compound 2 is a neutral CT dyad formed by metal−ligand axial coordination of the chalcogenide cluster with manganese porphyrin. The strong charge transfer properties are revealed by electronic spectra, theoretical calculations, 1H NMR, and ESR. The CT intensity of the chalcogenide cluster−porphyrin system can be modulated by metalation. The fluorescence and photocurrent response properties of 1 and 2 are related to the CT intensity.

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INTRODUCTION New approaches for the production of efficient, low-cost photovoltaic devices have been stimulated due to the requirement of developing inexpensive renewable energy sources.1 In recent years, interest has been drawn toward developing heterojunction organic solar cells which possess active layers of an electron donor (D) and an electron acceptor (A).2 Efficient photoinduced electron transfer (ET) or charge transfer (CT) occurs at the donor−acceptor (D-A) interface, and therefore, D-A conjugates are beneficial for efficient charge separation and charge transport as a means to generate appreciable photocurrent. An extensively conjugated π system with porphyrin electron donors is suitable for light-harvesting systems3 and for efficient electron transfer.4 Moreover, rich and extensive absorption features of porphyrinoid systems guarantee an efficient use of the solar spectrum.5 Therefore, electron D-A compounds involving porphyrins have been extensively investigated in the field of photonic wires,6 photoreaction centers,7 and photovoltaic cells.8 To date, the D-A systems have been mainly concerned with organic derivatives,9,10 such as porphyrin−C60 and porphyrin− perylenediimide. However, few reports have addressed an inorganic−organic D-A system with porphyrin derivatives. The electron-donating properties of porphyrins and metalloporphyrin complexes can be tuned as electron acceptors by introducing high-valent metal ions,11 protons,12 and strongly electron withdrawing substituents13 to the macrocycles. On the other hand, taking advantage of the electron-rich properties, © 2017 American Chemical Society

most inorganic chalcogenidometalate polyanions can act as electron donors to form D-A CT compounds or materials with photoactive metal−phenanthroline/bipyridine cations14 and an N,N′-dimethyl-4,4′-bipyridinium dication15 as electron acceptors. It is desirable and challenging to integrate the porphyrin acceptors with chalcogenidometalate donors to develop a new D-A charge transfer system with potential photoelectric-active applications. Herein, a germanium chalcogenide cluster (Ge4S104−) is chosen as an electron donor and a methylated tetrakis(4pyridyl)porphyrin (5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin, denoted as TMPyP; the four positive charges are not shown for brevity) (Chart 1) is selected as an electron acceptor to create chalcogenide cluster−porphyrin CT compounds. Although the CT compounds are well-known in various organic donor−acceptor systems, to the best of our knowledge, no charge-transfer compounds containing both chalcogenide cluster anions and porphyrin cations have been reported so far. Two D-A compounds, (TMPyP-Ge4S10)·5H2O (1) and (MnTMPyP-Ge4S10)·13H2O (2), have been obtained, and their crystal structures have been characterized by singlecrystal X-ray diffraction, which allows us to derive structure− activity relationships. The strong D-A interaction enhances the charge transfer between the anions and the cations, which has been studied comprehensively by electronic spectra, theoretical Received: March 24, 2017 Published: June 27, 2017 8036

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

Article

Inorganic Chemistry Chart 1. Structures of Ge4S104− (Left) and TMPyP (Right)

tube (0.7 cm diameter, 18 cm length) and quickly degassed with nitrogen. The sealed tube was heated under autogenous pressure at 100 °C for 7 days and then cooled to room temperature to yield dark green crystals of 2 suitable for X-ray crystallographic measurement. The crystals used for all other measurements were obtained as follows: TMPyP(PF6)4 (128 mg, 0.1 mmol), MnCl2·4H2O (80 mg, 0.4 mmol), and [(CH3)4N]4Ge4S10 (180 mg, 0.2 mmol) were mixed in 3 mL of CH3OH, 3 mL of DMF, and 3 mL of H2O. The mixed solution was placed in a double-neck round-bottom boiling flask, refluxed at 100 °C for 4 h under an argon atmosphere, and then cooled to room temperature. Small dark green crystals of 2 were filtered from the solution, washed with H2O and CH3OH, dried under vacuum, and preserved under a sealed and dry environment (71.1 mg, 45.1% yield based on TMPyP(PF6)4). Anal. Calcd for C44H62Ge4MnN8O13S10 (MW 1577.16): C, 33.51; H, 3.96; N, 7.10. Found: C, 33.38; H, 4.01; N, 7.07. ESI-MS: m/z 182.81 (corresponding to MnTMPyP with four positive charges). IR data (cm−1): 2978 (m), 2898 (m), 1635 (s), 1560 (w), 1541 (w), 1526 (w), 1508 (w), 1458 (s), 1406 (m), 1340 (m), 1207 (b), 1079 (m), 1029 (m), 1011 (s), 891 (m), 860 (w), 809 (w), 791 (s), 712 (m). X-ray Crystallographic Study. The measurement was carried out on a Xcalibur Atlas Geminin diffractometer for 1 and a Bruker APEXII CCD diffractometer for 2 at 223 K with graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. The structure was solved by direct methods using SHELXS-2016,18 and the refinement against all reflections of the compound was performed using SHELXL-2016.19 All of the non-hydrogen atoms were refined anisotropically, and hydrogen atoms were added theoretically. The solvent molecules of crystallization were identified and removed using the PLATON/ SQUEEZE procedure.20 Relevant crystal data, collection parameters, and refinement results can be found in Table S1 in the Supporting Information. CCDC: 1527247 for 1 and 1527248 for 2. Electrode Preparation and Photocurrent Measurement. The photoelectrodes of the compounds were prepared using the powdercoating method. As a typical procedure, the crystals (0.003 mmol) were ground and pressed uniformly on the cleaned ITO glass (50 Ω/ square). A 150 W high-pressure xenon lamp, located 20 cm away from the surface of the ITO electrode, was employed as a full-wavelength light source. The photocurrent experiments were performed on a CHI650E electrochemistry workstation in a three-electrode system, with the sample-coated ITO glass as the working electrode mounted on the window with an area of 0.385 cm2 (Φ = 0.7 cm), a Pt plate as the auxiliary electrode, and a saturated calomel electrode (SCE) as the reference electrode. The supporting electrolyte solution was a 0.1 mol L−1 sodium sulfate aqueous solution. The lamp was kept on continuously, and a manual shutter was used to block the exposure of the sample to the light. Theoretical Calculations. Density functional theory (DFT) calculations were carried out using the GAUSSIAN 09 program package at the B3LYP level.21 The basis set used for C, H, N, and S atoms was 6-31G, while effective core potentials with a LanL2DZ basis set were employed for Ge and Mn atoms.22 The crystal structures of 1 and 2, except for the cocrystallized water molecules, were used as the initial structures and optimized to the minimum energy configurations.

calculations, 1H NMR, and ESR. The metalation effect of a Mn(II) ion on the charge transfer is discussed. Photocurrent response properties of 1 and 2 were investigated.

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EXPERIMENTAL SECTION

General Remarks. The starting materials TMPyP(PF6)416 and [(CH3)4N]4Ge4S1017 were prepared according to the literature methods. All other analytically pure reagents were purchased commercially and used without further purification. Electrospray ionization mass spectra (ESI-MS) were carried out in the positive-ion mode on a Bruker micrOTOF-Q III instrument. The IR spectra were recorded using KBr pellets on a Nicolet Magna 550 FT-IR spectrometer. Elemental analyses of C, H, and N were performed using an VARIDEL III elemental analyzer. Solid-state room-temperature optical diffuse reflectance spectra of the microcrystal samples were obtained with a Shimadzu UV-2600 spectrometer. ESR spectra were recorded on a Bruker ER-420 spectrometer with a 100 kHz magnetic field in the X band at 110 K. Fluorescence was recorded on a Hitachi F2500 fluorescent photometer. The solution of MnTMPyP (the four positive charges are not presented for brevity) used in fluorescence spectra measurements was prepared by diluting the mixed solution of TMPyP and MnCl2 at a ratio of 1:4 as that of the synthesized product. 1H NMR spectra were recorded in d6-DMSO using tetramethylsilane, Si(CH3)4, as an internal standard on a UNITYNOVA-400 spectrophotometer. Preparation of Compounds. (TMPyP-Ge4S10)·5H2O (1). TMPyP(PF6)4 (3.2 mg, 0.0025 mmol) and [(CH3)4N]4Ge4S10 (4.5 mg, 0.005 mmol) were mixed in 0.2 mL of CH3OH, 0.2 mL of H2O, and 0.2 mL of DMF. The mixture was placed in a thick Pyrex tube (0.7 cm diameter, 18 cm length) and quickly degassed with nitrogen. The sealed tube was heated under autogenous pressure at 80 °C for 7 days and then cooled to room temperature to yield dark green crystals of 1 suitable for X-ray crystallographic measurement. The crystals used for all other measurements were obtained as follows: a solution of TMPyP(PF6)4 (128 mg, 0.1 mmol) in 3 mL of CH3OH and 3 mL of DMF was mixed with an aqueous solution (3 mL) of [(CH3)4N]4Ge4S10 (180 mg, 0.2 mmol). The mixed solution was placed in a double-neck round-bottom boiling flask, refluxed at 95 °C for 4 h under an argon atmosphere, and then cooled to room temperature. Small dark green crystals of 1 were filtered from the solution, washed with H2O and CH3OH, dried under vacuum, and preserved under a sealed and dry environment (69.3 mg, 51.6% yield based on TMPyP(PF6)4). Anal. Calcd for C44H48Ge4N8O5S10 (MW 1343.83): C, 38.29; H, 3.51; N, 8.12. Found: C, 38.43; H, 3.45; N, 8.21.ESI-MS: m/z 179.02 (corresponding to TMPyP·2H2O with four positive charges). 1H NMR (400 MHz, d6-DMSO, δ): 9.48 (d, 8H), 8.98 (d, 8H), 9.19 (s, 8H), 4.72 (s, 12H). IR data (cm−1): 2984 (w), 2916 (m), 2849 (m), 1624 (s), 1573 (s), 1541 (w), 1494 (s), 1466 (s), 1412 (m), 1320 (m), 1180 (s), 1080 (w), 1042 (m), 994 (s), 968 (w), 883 (w), 853 (w), 789 (s), 722 (w). (MnTMPyP-Ge4S10)·13H2O (2). TMPyP(PF6)4 (3.2 mg, 0.0025 mmol), MnCl2·4H2O (2.0 mg, 0.01 mmol), and [(CH3)4N]4Ge4S10 (4.5 mg, 0.005 mmol) were mixed in 0.1 mL of CH3OH, 0.2 mL of H2O, and 0.4 mL of DMF. The mixture was placed in a thick Pyrex

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RESULTS AND DISCUSSION

Synthesis and Crystal Structures. The dark green crystals of (TMPyP-Ge4S10)·5H2O (1) and (MnTMPyP-Ge4S10)· 13H2O (2) suitable for X-ray crystallographically measurement were obtained in a mixed solvent of H2O, CH3OH, and DMF under solvothermal conditions, but the yields were low and these crystals were too small to be collected. In order to obtain enough samples for all other measurements, an energy- and time-efficient procedure was used. The mixture of the reactants was refluxed under an argon atmosphere for 4 h to allow the reaction to proceed to completion, and the sparkling dark green crystals were filtered from the solution. The reactants [Ge4S10]4− ion and MnCl2 were water-soluble, and TMPyP8037

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry

Figure 1. (a) Molecular structure of compound 1. (b) Cluster anion Ge4S104− arrangement around the cation TMPyP. (c) Ion packing viewed along the c axis. Cocrystallized water molecules are omitted for clarity.

45.9(4)°, while adjacent pyrrole planes form dihedral angles of 44.6(4) and 48.1(4)°. One Ge4S104− anion is located almost right over the core of the TMPyP cation with one S5···N2 (3.223 Å) and two S6···C8 (3.484 Å) short contacts. In addition to the center Ge4S104− anion, each TMPyP cation is surrounded by four other Ge4S104− anions; those are located at the neighboring pyrrole ring through S1···C20 (3.238 Å) and S3···C16 (3.362 Å) short contacts (Figure 1b,c). These S···N and S···C short contacts are the pathway of the cation−anion charge transfer (discussed later). The crystal of compound 2 belongs to the Pbcn space group. The asymmetric unit is composed of one metalated TMPyP cation, MnTMPyP, one Ge4S104− T2 cluster anion, and 13 cocrystallized water molecules. The Mn(II) ion is fivecoordinated by four nitrogen atoms from the core pyrrole rings that constitute a square base of a tetragonal pyramid and one sulfur atom from one corner of the Ge4S104− cluster anion at the top position (Figure 2a). The Mn−S bond distance is

(PF6)4 can be dissolved in CH3OH; therefore, the product was washed with H2O and CH3OH in turns to ensure the purity. The purity of the bulky samples was confirmed by elemental analysis and by comparing the experimental XRD patterns with the calculated patterns from the crystal data (Figure S1 in the Supporting Information). Single-crystal X-ray diffractometry shows that compound 1 crystallized in the monoclinic P21/m space group. The asymmetric unit is composed of one TMPyP cation, one Ge4S104− anion, and five cocrystallized water molecules (Figure 1a). All of the four germanium atoms are each tetrahedrally coordinated by sulfur atoms and exhibit structural parameters of the T2-type Ge4S104− anion in agreement with the literature data.15a,23 The structure of the central macrocycle of the TMPyP cation has a nonplanar saddle conformation with the porphyrin pyrrole rings being alternately tilted up and down with respect to the least-squares plane of the porphyrin core. Opposite pyrrole planes form dihedral angles of 82.5(3) and 8038

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry

Figure 2. (a) Molecular structure of compound 2. (b) Pair arrangement showing Mn···C weak interaction. (c) Packing structure viewed along the a axis. Cocrystallized water molecules are omitted for clarity.

2.494(4) Å, which is consistent with a reported manganese(II) complex with a similar coordination environment.24 At the trans axial position, the weak interaction Mn1···C27 (3.636 Å) makes the coordination compound in a pair arrangement (Figure 2b). The metalated core adopts a domed conformation with the manganese ion deviating 0.648(2) Å from the plane of the four pyrrole nitrogen atoms toward the axial cluster Ge4S104−. Opposite pyrrole planes form dihedral angles of 8.8(5) and 14.5(4)°, while adjacent pyrrole planes form dihedral angles in the range of 4.7(4)−11.1(4)°. The short contacts S3···N8 (3.240 Å), S3···C36 (3.379 Å), S8···C25 (3.443 Å), and C44···C12 (3.286 Å) assemble the pairs in a supramolecular 2-D structure (Figure 2c). Charge Transfer Properties. Solid-state electronic spectra of 1 and 2 together with the starting materials TMPyP and Ge4S104− as used for comparison were measured at room temperature using BaSO4 as a standard reference (Figure 3). The Soret band of TMPyP is located at about 447 nm, and the Q bands are located at 522, 552, 589, and 644 nm. In comparison with the absorption curve of TMPyP, in the visible

Figure 3. Electronic spectra of 1 and 2 along with the starting materials TMPyP and [(CH3)4N]4Ge4S10 in the solid state.

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DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry and near-infrared range, a new broad absorption band appears for 1 and 2. The new band is so intense that the characteristic peaks of porphyrin only appear at shoulders, but it still can be seen that the Q bands of TMPyP are red-shifted for 1 and 2, from which it can be deduced that the Ge4S104− moiety has perturbation of the electronic structure centered on the TMPyP core. The molecular orbital analyses (Figure 4), obtained from

Figure 5. UV−vis absorption of compound 1 (1.0 × 10−5 mol L−1) in DMSO.

compound, a distinct upfield shift occurred, suggesting that the TMPyP is shielded by the electron-donating Ge4S104− anion. To further investigate whether an efficient charge transfer or partial electron transfer has happened, electron spin resonance (ESR) studies were carried out at 110 K (Figure 7). The solidstate ESR spectrum of 1 shows a sharp signal at g = 2.002, corresponding to the characteristics of the free radical signal of porphyrin,25 which indicates that partial electron transfer occurs in the ground state via an anion−cation interaction. The ESR spectrum of 2 displays a broadened signal with a center point located at g = 2.020, which is assigned to the unpaired electrons of the paramagnetic center of the Mn(II) atom. No charge transfer induced radical signal appears, which might be covered or coupled by the strong paramagnetic resonance.26 Fluorescence Properties. Taking advantage of the fluorescence-emission feature in the 570−800 nm spectral region that diamagnetic porphyrins display27 and fluorescence quenching resulting from electron transfer,28 the charge transfer properties can be studied quantitatively. Fluorescence spectra of TMPyP and MnTMPyP at the same molar concentrations (1.5 × 10−5 mol L−1) were recorded upon quantitative titration of the Ge4S10 cluster, and the results are given in Figure 8. A decrease in fluorescence was found for MnTMPyP (652 nm, 2649) (Figure 8a) in comparison with that of TMPyP (652 nm, 4288) (Figure 8b), which is attributed to the metalation effect of the porphyrin resulting from electron transfer.29 When an electron-donating Ge4S10 cluster is added, dramatic fluorescence quenching was found for both TMPyP and MnTMPyP with a 3 nm red shift of the peak (from 652 to 655 nm), which indicates that strong electron transfer occurs between TMPyP or MnTMPyP and Ge4S10. The intensity of the maximum peak at 652 nm of fluorescence spectra of TMPyP and MnTMPyP exhibits a linear decrease upon quantitative titration of Ge4S104− from 0 to 1 equiv of Ge4S10 in DMF. The changes are shown in Figure 9, and the corresponding emission quantum yields are given in Table 1. The linear fluorescence quenching rate of TMPyP is larger than that of MnTMPyP (see slopes in Figure 9) with the linear correlation coefficient R = 0.999 for TMPyP and 0.995 for MnTMPyP, which further confirms that the charge transfer between TMPyP and Ge4S10 is stronger than that between MnTMPyP and Ge4S10. On the basis of the results of structural analysis (discussed above), the electron pathways in 1 and 2 are different: namely, a short contact

Figure 4. Frontier molecular orbitals of 1 and 2 calculated using DFT B3LYP/6-31G/LanL2DZ methods.

B3LYP/6-31G/LanL2DZ calculations, show that the highest occupied molecular orbitals (HOMO and HOMO-1) of 1 are mainly localized on the Ge 4 S 10 4− moiety with small contributions of TMPyP. In contrast, the lowest unoccupied molecular orbitals (LUMO and LUMO+1) are totally localized on the TMPyP. This is taken as evidence that the observed new broad lowest energy band includes a contribution involving an interion charge transfer from the Ge4S104− moiety to the TMPyP, and therefore, 1 is a typical donor−acceptor compound. The result of molecular frontier orbital analyses of 2 is somewhat different from that of 1. The shift of the molecular population from the HOMOs to the LUMOs of 2 is not as obvious in comparison with that of 1. Furthermore, the energy gap (ΔE = ELUMO − EHOMO) of 2 is larger than that of 1 (Table S2 in the Supporting Information). The theoretical calculation results indicate that the intermolecular charge transfer property of 1, TMPyP-Ge4S10, is better than that of 2, MnTMPyP-Ge4S10, which is in accordance with the electronic spectra results, where the new CT band intensity of 1 is stronger than that of 2 and the band of 1 extends to the lower energy region as shown in Figure 3. The solution electronic spectra of crystals 1 and 2 together with the starting material TMPyP in DMSO were also recorded (Figure 5 and Figure S2 in the Supporting Information). The intensities of the Soret band for these three compounds are stronger than those of the Q bands, but no CT band appears due to the low solubility of 1 and 2. The CT interaction of 1 was also investigated by 1H NMR spectroscopy. Figure 6 shows a comparison of the partial 1H NMR spectra of TMPyP and 1 in d6-DMSO. The chemical shift of the H atoms of the pyridyl group (denoted as a and b) and of the pyrrole ring (denoted as c) are located at 9.53, 9.03, and 9.24 ppm, respectively. Upon the formation of the ionic CT 8040

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry

Figure 6. Partial 1H NMR spectra of TMPyP (bottom) and 1 (top) in d6-DMSO.

Figure 7. ESR spectra of 1 and 2 recorded at 110 K.

des, and the thickness of the active layer was about 100 μm. A 0.5 V bias was applied to the device, which facilitated the extraction of the charge carriers. The results are shown in Figure 11. Clear anodic photocurrent responses are observed on irradiation. The photocurrent intensity of 1 is 15 nA cm−2, more than two times that of 2 (6 nA cm−2). These results indicate that TMPyP-GeS is a photoelectroactive material. The results also reveal that charge transfer or charge separation of compound 1 is more effective than that of 2.

pathway for 1 and a metal coordination pathway for 2. In 1, Ge4S104− is located right over the core of TMPyP and the pathways are S···N and S···C short contacts between Ge4S104− and the core of TMPyP, while in 2, the pathway is the coordination interaction between Ge4S104− and the Mn(II) of MnTMPyP. Schematic diagrams of the energy states and electron transfer pathways for the fluorescence quenching can be found in Figure S3 in the Supporting Information. Photoelectric Response Properties. Considering the excellent photoelectric properties of porphyrin derivatives, we investigated the photocurrent responses of compounds 1 and 2, using a three-electrode photoelectrochemical cell with a microcrystal sample modified ITO working electrode (a more detailed description is given in the Experimental Section). No extra sacrificial reagent was added, and only a solution containing 0.1 mol L−1 sodium sulfate was used as the supporting electrolyte because these compounds are products of the coassembly of the photoactive electron acceptor porphyrin derivatives and the electron donor Ge4S104−. As shown in Figure 10, upon repetitive irradiation with xenon light on and off at 20 s intervals, clear photocurrent responses are observed. The anodic photocurrent was stable without a decrease in the intensity, providing an effective and repeatable photocurrent response. The photocurrent intensity of 1 is 1.5 μA cm−2 with 0 V bias potential and 9 μA cm−2 with 0.5 V bias potential, more than 2 times those of 2 and comparable with those of charge transfer systems of [MV]2Ge4S10·xSol compounds.15a On comparison of the J−t curves, the photocurrent response to the irradiation of 2 is faster than that of 1, because the photocurrent increases immediately. A simple Schottky-type device was also used to detect the photocurrent response properties of the two materials. The electroactive layer was sandwiched between two ITO electro-

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CONCLUSIONS A new type of chalcogenide cluster−porphyrin donor−acceptor dyad was obtained utilizing a germanium chalcogenide cluster as an electron donor and a methylated porphyrin as an electron acceptor. Single-crystal X-ray diffraction shows that compound 1 is an ionic salt assembled through interion interactions and compound 2 is a neutral dyad formed by metal−ligand axial coordination. The electronic spectra and theoretical calculation results show that the two compounds 1 and 2 are typical donor−acceptor dyads involving a charge transfer from the Ge4S104− moiety to the TMPyP and that the charge transfer properties of 1 are better than those of 2. 1H NMR and ESR results further confirm that an efficient charge transfer or partial electron transfer has occurred in 1. The fluorescence quenching of the TMPyP upon adding the cluster Ge4S104− is more efficient than that of MnTMPyP. The two compounds all show photocurrent response, and the order is 1 > 2. The results of fluorescence quenching and photocurrent response properties are in accordance with the strength of CT. These properties show that compounds 1 and 2, especially 1, are strong charge transfer dyads and will be promising systems for inorganic− organic photoelectronic devices. 8041

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry

Table 1. Emission Quantum Yields (Φ) of TMPyP and MnTMPyP in DMF with a Concentration of 1.5 × 10−5 mol L−1, upon Quantitative Titration of Ge4S104− from 0 to 1.0 equiva Φ amt of Ge4S10

4−

(equiv)

0.0 0.2 0.4 0.6 0.8 1.0 a

TMPyP

MnTMPyP

0.027 0.024 0.020 0.018 0.015 0.017

0.038 0.034 0.032 0.031 0.029 0.032

Anthracene in ethanol is used as a standard reference.

Figure 10. Photocurrent responses in the presence of a 0.1 mol L−1 Na2SO4 aqueous solution: with 0.5 V bias potential, black line for 1 and blue line for 2; with 0 V bias potential, olive line for 1 and red line for 2. Figure 8. Changes in the fluorescence spectra of (a) MnTMPyP and (b) TMPyP (λex 400 nm) in DMF with a concentration of 1.5 × 10−5 mol L−1, upon quantitative titration of Ge4S104−.

Figure 11. Photocurrent responses of crystals 1 and 2 measured as Schottky-type devices at 0.5 V bias potential.

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Figure 9. Comparison of the linear fluorescence quenching rates of the peak at 652 nm of fluorescence spectra of TMPyP and MnTMPyP in DMF with a concentration of 1.5 × 10−5 mol L−1, upon quantitative titration of Ge4S104− from 0 to 1.0 equiv.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00775. 8042

DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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Inorganic Chemistry

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Crystal data and structural refinement parameters for 1 and 2, energy of the frontier molecular orbitals of 1 and 2, experimental bulky sample powder XRD pattern and the calculated pattern from the crystal data of compounds 1 and 2, UV−vis absorption of compounds TMPyP(PF6)4 and 2 in DMSO, and schematic diagrams of the energy states and transfer pathways for the fluorescence quenching (PDF) Accession Codes

CCDC 1527247−1527248 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for Q.-Y.Z.: [email protected]. *E-mail for J.D.: [email protected]. ORCID

Qin-Yu Zhu: 0000-0003-1864-1175 Jie Dai: 0000-0002-3549-726X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support by the NSF of China (21571136 and 21171127), by the Priority Academic Program Development of Jiangsu Higher Education Institutions, and by the State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044

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DOI: 10.1021/acs.inorgchem.7b00775 Inorg. Chem. 2017, 56, 8036−8044