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Increased Light-Harvesting in Dye-Sensitized Solar Cells through Förster Resonance Energy Transfer within Supramolecular Dyad Systems Takahiro Kawata, Yoshiaki Chino, Nagao Kobayashi, and Mutsumi Kimura Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b01118 • Publication Date (Web): 01 Jun 2018 Downloaded from http://pubs.acs.org on June 1, 2018
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Increased Light-Harvesting in Dye-Sensitized Solar Cells through Förster Resonance Energy Transfer within Supramolecular Dyad Systems Takahiro Kawata, Yoshiaki Chino, Nagao Kobayashi, and Mutsumi Kimura* Department of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan Abstract: Novel pyridine-substituted subphthalocyanines were prepared for an additional harvesting of a green spectral region of the solar light spectrum for zinc phthalocyanine-based dye-sensitized solar cells. These compounds can bind with the central metal of zinc phthalocyanines to form the corresponding supramolecular complexes as monitored by the absorption and fluorescence spectral changes. The stability constants of these complexes were altered by the number and position of pyridine units in the pyridine-substituted subphthalocyanines. On the basis of fluorescence titration study, the complexes efficiently transfer energy from the subphthalocyanine to zinc phthalocyanine. The solar cells using TiO2 electrodes stained with the supramolecular complexes composed of zinc phthalocyanine sensitizer and pyridine-substituted subphthalocyanines showed panchromatic responses, and the photocurrent generation in the range of 500-600 nm is attributed to the efficient Förster resonance energy transfer from subphthalocyanine to zinc phthalocyanine on the TiO2 surface.
Introduction Considerable effort has been made to develop sensitizing dyes for efficient harvesting of solar light energy in dye-sensitized solar cells (DSSCs).1-3 Photo-excited dye adsorbed onto the surface of titanium oxide (TiO2) nanoparticles injects an electron into the conduction band of TiO2, and the oxidized dye is regenerated to the ground state by electron transfer from a redox shuttle in the electrolyte. π-Conjugated porphyrins and phthalocyanines (Pcs) have attracted a special attention because of their high extinction
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coefficients.4-9 However, these dyes lack absorption in a green spectral region of solar light between the Soret and Q bands. Therefore, co-sensitization by two dyes having complementary absorption spectra has been examined.10-12 Hardin et. al., successfully improved power conversion efficiency (PCE) of DSSCs sensitized with green-colored dye (TT1) by filling the absorption gap between the Soret and Q bands of TT1 using redox electrolyte containing red-colored perylene-3,4,9,10-tetracarboxylic diimide as an energy relay dye (ERD).13,14 Because the emission spectrum of ERD overlapped with absorption spectrum of TT1, the ERD in electrolyte could transfer its energy to TT1 anchored on the TiO2 through Förster resonance energy transfer (FRET). The FRET efficiency depends on the separation distance between the ERD and the sensitized dye. Dyad systems, in which two dyes were linked by covalent or non-covalent bonds, an enhanced photovoltaic performance in DSSCs by the improvement of FRET efficiency.15-21 Subphthalocyanines (SubPcs), in which three N-fused diiminoisoindole units are combined around a central boron atom, possess a smaller π electron system than 18π electron-conjugated Pcs.22,23 Absorption and fluorescent emission positions of SubPcs are complementally with those of Pcs. Hence, the SubPc-Pc dyads are expected to be efficient light-harvesting systems because of the efficient FRET through a good overlap between the emission of SubPc and the absorption of Pc together with a covering of absorption range in the visible light region.24-29 We have reported several approaches for improving PCEs of ZnPc-sensitized DSSCs such as steric prevention of aggregation, electronic push-pull structures, and optimization of adsorption sites.30-32 The structural
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optimization of peripheral bulky substituents and adsorption sites around the Pc core resulted in the significant improvement of incident photon-to-current efficiencies (IPCEs), and thereby achieved a PCE of 5.9% in PcS18 under one sun condition. Herein, we describe the harvesting of the green spectral region by the FRET process within the supramolecular
dyad
system
formed
by
the
coordination
bonding
of
SubPcs 1 and 2 with the central metal of PcS18 onto TiO2.
Experimental General. All chemicals purchased from commercial suppliers were used without further purification. Column chromatography was performed with silica gel (Wakogel C-200) or activated alumina (Wako, 200 mesh). Recycling preparative gel permeation chromatography was carried out by a JAI recycling preparative HPLC using CHCl3 as an eluent. NMR spectra were measured on a Bruker AVANCE 400 FT NMR spectrometer at 400.13 MHz for 1H in CDCl3 solution (chemical shifts are reported relative to internal TMS). High resolution mass spectra with atmospheric pressure chemical ionization were performed on a Bruker Daltonics micrOTOFII. DFT and TD-DFT calculations were carried out using the Coulomb-attenuating B3LYP (CAM-B3LYP) and 6-31G basis set as implemented in the Gaussian 09 software suit. UV-Vis spectra fluorescence spectra were obtained on a SHIMAZU UV2600 and a JASCO FP-750. Fabrication of DSSCs using PcS18 with SubPcs.31 Porous TiO2 electrodes (apparent surface area: 0.25 cm2 (0.5 x 0.5 cm), 15 µm-thick transparent layer + 6 µm-thick scattering layer) were prepared by printing on fluorine-doped tin oxide (FTO) glass substrates through the screen printing technique using two TiO2 nanoparticle pastes
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having different diameters of 15-20 and 400 nm. After sintering at 550 oC for 30 min in air, the TiO2 electrodes were treated with TiCl4. The dye adsorption of supramolecular complexes onto TiO2 films was achieved by immersion of electrodes into toluene solutions of mixed dyes (for 1 and PcS18-1 cells: [PcS18] = 50.0 µM, [1] = 16.7 µM; PcS18-2 cell: [PcS18] = 50.0 µM, [2] = 50.0 µM) for 32 hr at 25 oC. Dye-adsorbed electrode and Pt counter electrode were separated by a 50 µm thick hot melt ring DuPont), and sealed by heating. The space between two electrodes was filled with redox electrolytes (0.1 M LiI, 0.6 M 1,2-dimethyl-3-propylimidazolium iodide (DMPImI), 0.5 M tert-buthylpyridine (tBP), and 0.05 M I2 in dehydrated acetonitrile), and measured photovoltaic performance under one sun conditions (AM 1.5, 100 mW/cm2) by a solar simulator (Otenso-Sun 3SD, Bunko Keiki). Results and Discussion Scheme 1. Schematic diagram for the synthesis of SubPcs 1 and 2, and chemical structures of 6, 7 and PcS18.
a) 4-hexylphenol, pyridine, toluene, reflux; b) trimethyl(4-pyridyl)tin, Pd(PPh3)4, dry toluene, 95℃.
Iodine-containing SubPc was synthesized from 4-iodo-1,2-dicyanobenzene and and the symmetrical SubPc was separated from the resulting constitutional mixture by column chromatography according to the literature method.33 The axial chloride was
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converted to 6-hexylphenol, and the palladium-catalyzed Stille coupling reaction with trimethyl(4-pyridyl)tin afforded two pyridine-substituted SubPcs 1 (Scheme 1).34 The other SubPc 2 having one pyridine unit was synthesized by the mixed condensation between 4-iodo-1,2-dicyanobenzene and 1,2-dicyanobenzene in the presence of BCl3. While the 1H NMR spectrum of 1 revealed a simple pattern in accordance with the symmetry of the molecule (Fig. S8).33 All compounds showed a good solubility in toluene, CH2Cl2, THF, and DMF because of the introduction of an alkyl chain at the ligand as well as their non-plat bowl-shaped structure.
Figure 1 (a) Absorption spectra of 1 (solid line) and 2 (dotted line) in toluene. (b) DFT calculations of 1 (left) and 2 (right) by CAM-B3LYP/6-31G.
Table 1 Photo-physical and coordination properties of pyridine-substituted SubPcs, and solar cell performances using SubPc-ZnPc dyad systems.
1
Absorptiona [nm] (logε)
Fluorescencea [nm] (ΦF)
Kb x 10-4 [M-1]
Adsorption densityc x104 [mol cm-3]
Voce [mV]
Jsce,f [mA cm-2]
FFe
PCE [%]
580 (4.79)
587 (0.51)
14.0
1.1
589
11.6
0.73
5.0
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574 (4.69)
2
580 (0.47)
6.8
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1.0
a
585
7.1
0.77
3.2
b
Absorption and fluorescence spectra were measured in toluene solution. K is stability constants for 1:1 complex formation between SubPcs and 6. c Adsorption densities of PcS18 were determined by measuring the absorbance of dyes released from the TiO2 films after immersion into a solution of tetrabutylammonium hydroxide in THF. e Solar cell parameters of DSSCs were at the highest PCE in five cells. f Jsc values were in good agreement (within 5%) with the overlap integral of the photocurrent spectrum with standard global AM 1.5 solar spectrum.
Figure 1a shows UV-Vis spectra of 1 and 2in toluene. The Q band position of 1 is red-shifted by 16 nm compared to that of reference compound 6 lacking pyridine substituents (λmax = 564 nm)35, and the Q band of 2 was broadened relative to 1. In addition, the Q band intensity increased by increasing the number of pyridine To analyze the observed UV-Vis spectral differences between 1 and 2, we carried out density functional theory (DFT) and time-dependent DFT (TDDFT) calculations at the CAM-B3LYP/6-31G level.36 The optimized structure of 1 based on DFT calculation displayed
a
bowl-shaped
structure,
and
the
estimated
angle
(103o)
for
N(Pyrrole)-B-N(Pyrrole) was in fair agreement with the reported value of SubPc determined by single crystal X-ray analysis.37 Figure 1b shows the calculated energy level diagram of 1 and 2, and the frontier orbitals of HOMO, HOMO-3, LUMO and LUMO+1. The TDDFT calculations reproduced the spectral differences in 1 and 2. The calculated lowest-lying electronic transition of 1 was red-shifted compared with that of indicating the narrowing of the HOMO-LUMO band gap. The HOMO energy levels of and 2 were determined experimentally from the first oxidation potentials by means of a differential pulse voltammetry. The HOMO levels of 1 and 2 were 1.34 and 1.32 V vs. normal hydrogen electrode (NHE). The LUMO energy levels of 1 and 2 were -0.83 and -0.79 V vs. NHE calculated from HOMO and optical band gaps. The electron-withdrawing property of pyridine substituents in 1 can contribute to the
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stabilization of HOMO and LUMO energy levels, and the larger contribution for the stabilization of the LUMO energy level leads to a smaller HOMO-LUMO gap than that SubPc.
The
calculated
Q
bands
comprising
the
HOMO→LUMO
and
HOMO→LUMO+1 transitions for 2 split owing to the nondegeneracy of LUMO and LUMO+1 as a result of the introduction of the pyridine substituent into one portion of SubPc ring. The broadening of the Q band for 2 as observed in the UV-Vis spectrum can be explained by this splitting of Q bands. The fluorescence spectra of 1 and 2 have a at 590, 587 and 580 nm with the fluorescence quantum yields (ΦF) above 0.45 upon excitation at 520 nm in degassed toluene solution (Table 1).35 Highly-fluorescent 1 and 2 having coordination connection units can act as excellent antenna units for converting light energy in the 500-600 nm region through the formation of supramolecular complexes with ZnPcs.
b) ∆Abs.
Abs.
a)
Wavelength / nm
Mole fraction of 1
c)
d) F0/F
FL intensity / a.u.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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Wavelength / nm
[7] / µM
Figure 2 (a) Absorption spectral changes of 7 by the addition of
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SubPc(Py) in toluene. (b) Modified Job’s plot for the complexation of 7 and 1 in toluene by monitoring of the absorption intensity at 368nm. (c) Fluorescence spectral change of 1 by the addition of 7 ([7]/[1] = 0, 0.5, and 1] upon excitation at 520 nm. (d) Stern-Volmer plots for 1 (●), 2 (▲), and 6 (■) ([SubPc] = 4.0µM ) by the addition of 7 in toluene.
The
axial
ligations
of
zinc
2,3,9,10,16,17,23,24-octa(2’,6’-di-iso-propylphenoxy)phthalocyanine 738 with 1 and 2 were studied using the UV-Vis and fluorescence spectra. On the addition of pyridine, UV-Vis spectra of 7 in the range of 350-550 nm gradually changed, and the change showed clear isosbestic points in the range of 300-500 nm (Fig. S11). The stability constant K for the binding of pyridine with 7 was 4.2 x 105 M-1, which was evaluated from the absorption spectral change by using the Benesi-Hildebrand plot.26 This K value was much higher than the reported values for the complexation for zinc(II) tetra-tert-butylphthalocyanine with pyridine derivatives.26,39 According to the reported crystal structure of 7, the phthalocyanine core in 7 has a cone-shape with the central ion. This cone-shaped structure of phthalocyanine core may enhance the K value as compared to the plannar ZnPcs. Furthermore, the slope for the plot of log[(Aobs A0)/(Amax - Aobs)] vs. log[pyridine] (A0: the absorbance without pyridine, Aobs: the absorbance at an individual concentration of pyridine, Amax: the absorbance in the presence of a large excess of pyridine) was almost exactly 1.0, indicating the formation the 1:1 complexes of 7 and pyridine. While the UV-Vis spectral change of 7 with 2 was similar to that with pyridine (Figure 2a), the K value for the formation of 1:1 complex between 7 and 2 was about 1/6 that for pyridine (Table 1). The attachment of aromatic SubPc with the pyridine ring weakened the stability of metal-pyridine coordination
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because of the decreasing of electron density at the lone pair of nitrogen atom in In contrast, 1 having three pyridine rings showed higher K values than 2, suggesting electron densities of nitrogen atom in pyridine units for 1 as compared with 2. When the peak intensity at 368 nm was plotted against the mole fraction of 1, the Job’s plot a maximum at about 0.75 (Figure 2b). This supported the formation of a 3:1 complex between 1 and 7. Upon excitation of the mixed solution of 1 and 7 at 520 nm, where 1 absorbed, the fluorescence peak at 685 nm from 7 was observed, suggesting an FRET from 1 to 7 (Figure 2c).24-29 The excitation spectral shape of mixed solution was similar the ground-state absorption spectrum, revealing contributions from both dyes. The energy transfer efficiency from 1 to 7 was 41% estimated from the intensity ratio at the band of 1 between the absorption and excitation spectra.39 Figure 2d is the Stern-Volmer plots of four SubPcs in the presence of 7. The fluorescence quenching profiles strongly depended on the number and position of pyridine units in SubPcs. Although the Stern-Volmer plot for quenching of the fluorescence of 6 by the addition of 7 gave a straight line, the plots of 1 and 2 having pyridine units showed curves deviating largely upward from a straight line. The fluorescence of 1 substituted with three pyridine units was almost completely quenched at [7]/[1] = 3. These suggest the efficient energy/electron transfer between two macrocycles within the supramolecular complexes formed by the coordination bonding of pyridine-substituted 1 and 2 to the central metal ZnPc.
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Figure 3 (a) Absorption spectrum of dyad ([PcS18]/[1] = 3) adsorbed onto TiO2 surface. (b) Schematic representation of supramolecular dyad PcS18-1 adsorbed onto TiO2. (c) Photocurrent voltage obtained with a DSSC based on PcS18-1 under standard global AM 1.5 solar condition(●) and dark current（○）. The inset shows color difference between DSSCs based on PcS18-1 (right) and PcS18 (left). (d) IPCE spectrum for a DSSC based on PcS18-1(●) and PcS18 (▲). (e) Energy level diagrams of TiO2, PcS18, 1, and I-/I3-. The energy levels of PcS18 were determined from the oxidation potentials from DPVs and the optical band gaps using PcS18-1 stained TiO2 films.
The TiO2 films on a quartz substrate were immersed into mixed solutions of with 1 ([PcS18] = 50.0 µM, [1] = 16.7 µM) in toluene to obtain the absorption spectra dye-stained films. The absorption spectrum of dye-stained film prepared from the mixed solution of PcS18 and 1 showed two Q bands at 580 and 687 nm corresponding to and ZnPc, respectively (Figure 3a). The spectral shape of the dye-stained film was similar to that of the mixed solution, and the molar ratio between PcS18 and 1 was 3:1 estimated from the absorbance at two Q bands and their molar extinction Although several dyes having pyridine units have been used as sensitizers for DSSCs through the formation of coordination bonds with the TiO2 surface40-44, the TiO2 electrodes stained by only 1 and 2 showed a very light purple. This suggests that the
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binding of pyridine unit in 1 and 2 with the TiO2 surface pyridine is unstable. The dye density adsorbed onto the TiO2 films was determined from the absorbance at the Q band of PcS18 desorbed from the dye-stained TiO2 film by the treatment with tetrabutylammonium hydroxide methanoic solution (Table 1). The adsorption density of PcS18 with 1 was slightly lower than that of only PcS18 (1.3x10-4 mol/cm3)31, a loose packing of dyes onto the TiO2 surface. From these results, we suppose that the pyridine-substituted SubPcs form the supramolecular complexes with PcS18 in toluene, and the complexes adsorb onto the TiO2 surface using the carboxylic acid anchor group PcS18 (Figure 3b). Three DSSC cells (PcS18-1 and PcS18-2) using TiO2 electrodes stained by supramolecular dyads with electrolytes containing 0.6 M DMPImI, 0.1 M LiI, 0.05 M I2, and 0.5 M tBP in acetonitrile were fabricated, and the solar cell performances were measured under global AM 1.5 simulated solar conditions. Whereas the PcS18 cell had vivid green color, the PcS18-1 cell exhibited a dark blue as shown in the inset of Figure 3c. Table 1 summarized the short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), fill factor (FF), and PCE values for the three cells. The PcS18-1 cell exhibits a Jsc of 11.6 mA cm-2, a Voc of 589 mV, and a FF of 0.73, yielding a PCE of 5.0 % (Figure 3c), and the PCE value of PcS18-1 was better than PcS18-2. The PCE values of these cells using supramolecular dyad systems were inferior to only PcS18 cell (Jsc: 12.4 mA cm-2, Voc: 621 mV, FF: 0.75, PCE: 5.8 %). The inferior PCE of PcS18-1 cell was due to the lower Voc and Jsc values in comparison of the PcS18 cell. Furthermore, the number of pyridine units in SubPc also influenced the solar cell performance. The
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incident-photon to current conversion efficiency (IPCE) spectra of these cells exhibited the sum of two dyes, and the valley of IPCE response for PcS18 between the Soret and the Q bands was filled with the IPCE responses of SubPcs (Figure 3d). This demonstrate the energy-transfer-mediated electron injection from SubPcs to TiO2 within the supramolecular dyads adsorbed onto the TiO2 surface. However, the IPCE maximum at the Q band of PcS18 decreased from 74% to 62% by the complexing with 1. The LUMO energy level of 1 (-0.83 V vs. NHE) is lower than that of PcS18 adsorbed onto TiO2 (-0.97 V vs. NHE)32, suggesting the possibility of electron transfer from PcS18 to 1 (Figure 3e). This may lead to a loss of electron injection through unfavorable electron transfer from PcS18 adsorbed onto TiO2 to the SubPcs. This unfavorable electron transfer can be diminished by tuning energy levels and redox potentials of SubPcs through the introduction of different peripheral substituents.
Conclusions In summary, two SubPcs 1 and 2 possessing peripheral pyridine units have been synthesized and characterized. These dyes could form the supramolecular complexes with ZnPc through the coordination bonding of pyridines in 1 and 2 with the central metal of ZnPc. Pyridine-substituted SubPcs has a significant emission overlap with the absorption spectrum of ZnPc, and an efficient FRET between SubPcs to ZnPc was observed in the supramolecular complexes in solution. The incorporation of SubPcs bound to ZnPc sensitizer PcS18 leads to the panchromatic response in DSSCs, and the photocurrent generation in the range of 500-600 nm is attributed to the efficient FRET
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from SubPc to ZnPc on TiO2 surface. The solar cell performance for this supramolecular dyad system did not exceed that of PcS18 cell because of the poor adsorption density on the TiO2 surface and the electron transfer from PcS18 to SubPcs. Future supramolecular systems in DSSCs should be designed to create highly dense multiple layers composed of near-IR-absorbing acceptor dye and several antenna dyes by utilizing intermolecular non-covalent interactions onto the TiO2 surface. We will continue the construction of supramolecular multi-dye architectures having a spatial arrangement of energy relay dyes on the TiO2 surface to enhance the DSSC performance.
ASSOCIATED CONTENT Supporting Information 1
H NMR spectra of 1 in CDCl3; APCI-TOF-Ms spectra; Absorption and Fluorescence
spectra of 1, 2 and 6; Calculated absorption spectra and transition energies of 1, 2 and 6 Absorption spectral change of 6 by the addition of pyridine; Solar cell performance of PcS18 and PcS18-2. The Supporting Information is available free of charge on the ACS Publication website at DOI: ?????????. AUTHOR INFORMATION Corresponding Author *FAX: +81 268 21 5499. E-mail:
[email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work has been partially supported by Grants-in-Aid for Scientific Research (A) (No. 15H02172) from the Japan Society for the Promotion of Science of Japan.
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REFERENCES 1. O’Regan, B.; Grätzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films, Nature, 1991, 353, 737-740. 2. Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Dye-Sensitized Solar Cells, Chem. Rev. 2010, 110, 6595-6663. 3. Mishra, A.; Fischer, M. K. R.; Bäuerle, P. Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules, Angew. Chem. Int. Ed. 2009, 48, 2474-2499. 4. Imahori, H.; Umeyama, T.; Ito, S. Large πAromatic Molecules as Potential Sensitizers for Highly Efficient Dye-Sensitized Solar Cells, Acc. Chem. Res., 2009, 42, 1809-1818. 5. Urbani, M.; Grätzel, M.; Nazeeruddin, M. K.; Torres, T. Meso-Substituted Porphyrins for Dye-Sensitized Solar Cells, Chem. Rev. 2014, 114, 12330-12396. 6. Ladmenou, K.; Kitsopoulos, T. N.; Sharma, G. D.; Coutsolelos, A. G. The importance of various anchoring groups attached on porphyrins as potential dyes for DSSC applications, RSC Adv., 2014, 4, 21379-21404. 7. Higashino, T.; Imahori, H. Porphyrins as excellent dyes for dye-sensitized solar cells: recent developments and insights, Dalton Trans., 2015, 44, 448-463. 8. Ragoussi, M. –E.; Ince, M.; Torres, T. Recent Advances in Phthalocyanine-Based Sensitizers for Dye-Sensitized Solar Cells, Eur. J. Org. Chem., 2013, 6475-6489. 9. Singh, V. K.; Kanaparthi, R. K.; Giribabu, L. Emerging molecular design strategies for unsymmetrical phthalocyanines for dye-sensitized solar cell applications, RSC Adv., 2014, 4, 6970-6984. 10. Yella, A.; Lee, H. –W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W. –G.; Yeh, C. –Y.; Zakeeruddin, S. M.; Grätzel, M. Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency, Science, 2011, 334, 629-634. 11. Cid, J- J.; Yum, J. –H.; Jang, S. –R.; Nazeeruddin, M. K.; Martínez-Ferrero, E.; Palomares, E.; Grátzel, M.; Torres, T. Molecular Cosensitizatioin for Efficient Panchromatic Dye-Sensitized Solar Cells, Angew. Chem. Int. Ed., 2007, 46, 8358-8362. 12. Kimura, M.; Nomoto, H. Masaki, N. Mori, S. Dye Molecules for Simple Co-Sensitization Process: Fabrication of Mixed-Dye-Sensitized Solar Cells, Angew.
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Chem. Int. Ed. 2012, 51, 4371-4374. 13. Hardin, B. E.; Hoke, E. T.; Armstrong P. B.; Yum, J. –H.; Comte, P.; Torres, T.; Fréchet, J. M.; Nazeeruddin, M. K.; Grätzel, M.; McGehee, M. D. Increased light harvesting in dye-sensitized solar cells with energy relay dyes, Nat. Photo. 2009, 3, 406-411. 14. Yum, J. –H.; Hardin, B. E.; Hoke, E. T.; Baranoff, E.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Torres, T.; McGehee, M. D.; Grätzel, M. Incorporation Multiple Energy Relay Dyes in Liquid Dye-Sensitized Solar Cells, ChemPhysChem 2011, 12, 657-661. 15. Siegers, C.; Hohl-Ebinger, J.; Zimmermann, B.; Würfel, U.; Mülhaupt, R.; Hinsch, A.; Haag, R. A Dyadic Sensitizer for Dye Solar Cells with High Energy-Transfer Efficiency in the Device, ChemPhysChem 2007, 8, 1548-1556. 16. Park, J. K.; Chen, J.; Lee, H. R.; Park, S. W.; Shinokubo, H.; Osuka, A.; Kim, Dongho, Doubly β-Functionalized Meso-Meso Directly Linked Porphyrin Dimer Sensitizers for Photovoltaics, J. Phys. Chem. C 2009, 113, 21956-21963. 17. Mozer, A. J.; Griffith, M. J.; Tsekouras, G.; Wagner, P.; Wallace, G. G.; Mori, S.; Sunahara, K.; Miyashita, M.; Earles, J. C.; Gordon, K. C.; Du, L.; Kato, R.; Furube, A.; Officer, D. L. Zn-Zn Porphyrin Dimer-Sensitized Solar Cells, Toward 3-D Light Harvesting, J. Am. Chem. Soc. 2009, 131, 15621-15623. 18. Lee, C. Y.; Hupp, J. T. Dye Sensitized Solar Cells: TiO2 Sensitization with a Bodipy-Porphyrin Antenna System, Langmuir 2010, 26, 3760-3765. 19. Warnan, J.; Pellegrin, Y.; Blart, E.; Odobel, F. Supramolecular light harvesting antennas to enhance absorption cross-section in dye-sensitized solar cells, Chem. Commun. 2012, 48, 675-677. 20. Choi, H.; Cho, N.; Paek, S.; Ko, J. Direct Evidence of Förster Resonance Energy Transfer for the Enhanced Photocurrent Generation in Dye-Sensitized Solar Cell, J. Phys. Chem. C 2014, 118, 16319-16327. 21. Zhao, L.; Wagner, P.; van der Salm, H.; Clarke, T. M.; Gordon, K. C.; Mori, S.; Mozer, A. J. Dichromophoric Zinc Porphyrins: Filling the Absorption Gap between Soret and Q bands, J. Phys. Chem. C 2015, 119, 5350-5563. 22. Claessens, C. G.; González-Rodríguez, D.; Torres, T. Subphthalocyanines: Singular Nonplanar Aromatic Compounds – Synthesis, Reactivity, and Physical Properties, Chem. Rev. 2002, 102, 835-854.
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Page 16 of 19
23. Shimizu, S. Recent Advances in Subphthalocyanines and Triphyrin Analogues: Contracted Porphyrins Comprising Three Pyrrole Ringds, Chem. Rev., 2017, 117, 2730-2784. 24. González-Rodríguez, D.; Claessens, C. G.; Torres, T.; Liu, S.; Echegoyen, L.; Vila, N.; Nonell, S. Tuning Photoinduced Energy- and Electron-Transfer Events in Subphthalocyanine-Phthalocyanine Dyads, Chem. Eur. J., 2005, 11, 3881-3893. 25. Tolbin, A. Yu., Breusova, M. O.; Pushlarev, V. E.; Tomilova, L. G. Synthesis and spectroscopic properties of new boron subpthalocyanine complexes and a heteronuclear phthalocyanine complex, Russ. Chem. Bull., Int. Ed. 2005, 54, 2083-2086. 26. Xu, H.; Ng, D. K. P. Construction of Subphthalocyanine-Porphyrin and Subphthalocyanine-Phthalocyanine Heterodyads through Axial Coordination, Inorg. Chem. 2008, 47, 7921-7927. 27. Tolbin, A. Yu., Tomilova, L. G. Preparation of monohydroxyphthalocyanines and their use in the sunthesis of heteronuclear complexes, Mendeleev Commun. 2008, 18, 286-288. 28. Shibata,
N.;
Das,
B.;
Trifluoroethoxy-Coating
Tokunaga,
Improves
the
E.;
Shiro,
Axial
M.;
Ligand
Kobayashi,
N.
Substitution
of
Subphthalocyanine, Chem. Eur. J. 2010, 16, 7554-7562. 29. El-Khouly,
M.
E.
Electron
transfer
naphthalocyanine-subphthalocyanine
reaction
self-assembled
of
light-harvesting dyad:
zinc
spectroscopic,
electrochemical, computational, and photochemical studies, Phys. Chem. Chem. Phys. 2010, 12, 12746-12752. 30. Mori, S.; Nagata, M.; Nakahata, Y.; Yasuta, K.; Goto, R.; Kimura, M.; Taya, M. Enhancement
of
Incident
Photon-to-Current
Conversion
Efficiency
for
Phthalocyanine-Sensitized Solar Cells by 3D Molecular Structuralization, J. Am. Chem. Soc. 2010, 132, 4054-4055. 31. Kimura, M.; Nomoto, H.; Suzuki, H.; Ikeuchi, T.; Matsuzaki, H.; Murakami, T. N.; Furube, A.; Masaki, N.; Griffith, M. J.; Mori, S. Molecular Design Rule of Phthalocyanine Dyes for Highly Efficient Near-IR Performance in Dye-Sensitized Solar Cells, Chem. Eur. J. 2013, 19, 7496-7502. 32. Ikeuchi, T.; Nomoto, H.; Masaki, N.; Griffith, M. J.; Mori, S.; Kimura, M. Molecular engineering of zinc phthalocyanine sensitizers for efficient dye-sensitized
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Langmuir
solar cells, Chem. Commun. 2014, 50, 1941-1943. 33. Claessens, C. G.; Torres, T. Subphthalocyanine enantiomers: first resolution of a C3 aromatic compound by HPLC, Tetrahedron Lett. 2000, 41, 6361-6365. 34. Claessens, C. G.; Torres, T. Chiral Self-Discrimination in a M3L2 Subphthalocyanine Cage, J. Am. Chem. Soc. 2002, 124, 14522-14523. 35. Kobayashi, N. Synthesis and Spectroscopic Porperties of Phthalocyanine Analogs, in The Porphyrin Handbook (eds. K. M. Kadish, K. M. Smith, R. Guilard), Academic Press, 2003, Vol. 15, 161-262. 36. Gaussian 09, Revision D.01. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2009. 37. Kietaibl, H. The crystal and molecular structure of a new phthalocyanine-like boron complex, Monatsh. Chem. 1974, 105, 405-418. 38. McKeown, N. B.; Makhseed, S.; Msayib, K. J.; Ooi, L. –J.; Helliwell, M.; Warren, J. E. A Phthalocyanine Clathrate of Cubic Symmetry Containing Interconneted Solvent-Filled Voids of Nanometer Dimensions, Angew. Chem. Int. Ed., 2005, 44, 7546-7549. 39. Guldi, D. M.; Ramey, J.; Martínez-Díaz, M. V.; de la Escosura, A.; Torres, T.; Da Ros, T.; Prato, M. Reversible zinc phthalocyanine fullerene ensembles, Chem. Commun., 2002, 2774-2775. 40. Haugland, R. P.; Yguerabide, J.; Stryer, L. Dependence of the kinetics of siglet-singlet energy transfer on spectral overlap, Proc. Natl. Acad. Sci. U. S. A.,
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1969, 63, 23-30. 41. Ooyama, Y.; Inoue, S.; Nagano, T.; Kushimoto, K.; Ohshita, J.; Imae, I.; Komaguchi, K.; Harima, Y. Dye-Sensitized Solar Cells Based on Donor-Acceptor π-Conjugated Fluorescent Dyes with a Pyridine Ring as an Electron-Withdrawing Anchoring Group, Angew. Chem. Int. Ed. 2011, 50, 7429-7433. 42. Daphnomili, D.; Landrou, G.; Singh, S. P.; Thomas, A.; Yesudas, K.; K, B.; Sharma, G. D.; Coutsokelos, A. G. Photophysical, electrochemical and photovoltaic properties of dye sensitized solar cells using a series of pyridyl functionalized porphyrin dyes, RSC Adv. 2012, 2, 12899-12908. 43. Lu, J.; Xu, X.; Li, Z.; Cao, K.; Cui, J.; Zhang, Y.; Shen, Y.; Li, Y.; Zhu, J.; Dai, S.; Chen, W.; Cheng, Y.; Wang, M. Zinc Porphyrins with a Pyridine-Ring-Anchoring Group for Dye-Sensitized Solar Cells, Chem. Asian. J. 2013, 8, 956-962. 44. Stangel, C.; Bagaki, A.; Angaridis, P. A.; Charalambidis, G.; Sharma, G. D.; Coutsolelos, A, G. “Spider”-Shaped Porphyrins with Conjugated Pyridyl Anchoring Groups as Efficient Sensitizers for Dye-Sensitized Solar Cells, Inorg. Chem. 2014, 53, 11871-11881. 45. Ikeuchi, T.; Agrawal, S.; Ezoe, M.; Mori, S.; Kimura, M. Enhanced Charge Separation Efficiency in Pyridine-Anchored Phthalocyanine-Sensitized Solar Cells by Linker Elongation, Chem. Asian J. 2015, 10, 2347-2351.
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