Novel diyne-bridged dyes for efficient dye-sensitized solar cells

Materials Chemistry and Physics 195 (2017) 1e9

Contents lists available at ScienceDirect

Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys

Novel diyne-bridged dyes for efficient dye-sensitized solar cells Jing-Kun Fang a, *, Tengxiao Sun a, Yi Tian b, Yingjun Zhang c, **, Chuanfei Jin c, Zhimin Xu a, Yu Fang a, Xiangyu Hu a, Haobin Wang a a

Department of Chemistry, School of Chemical Engineering, Nanjing University of Science and Technology, Xiaolingwei Street No. 200, Nanjing, 210094, China b Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan c HEC Pharm Group, HEC R&D Center, Dongguan, 523871, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Diyne-bridge was introduced into dye molecules by a transition-metalfree protocol.
Power conversion efficiency grows from 1.55% to 3.12% by replacing monoyne unit with diyne unit.
FSD101 with diyne unit shows the highest electron lifetime resulting in a higher Voc.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 September 2016 Received in revised form 22 March 2017 Accepted 25 March 2017 Available online 5 April 2017

Three new metal free organic dyes (FSD101-103) were synthesized to investigate the influence of diyne unit on dye molecules. FSD101 and FSD102 with diyne unit and FSD103 with monoyne unit were applied as sensitizers in the dye-sensitized solar cells (DSSCs). The optical and electrochemical properties, theoretical studies, and photovoltaic parameters of DSSCs sensitized by these dyes were systematically investigated. By replacing the monoyne unit with a diyne unit, FSD101 exhibited broader absorption spectrum, lower IP, higher EA, lower band gap energy, higher oscillator strength, more efficient electron injection ability, broader IPCE response range and higher te in comparison with FSD103. Hence, DSSC sensitized by FSD101 showed higher Jsc and Voc values, and demonstrated a power conversion efficiency of 3.12%, about 2-fold as that of FSD103 (1.55%). FSD102 showed similar results as FSD101, with a power conversion efficiency of 2.98%, despite a stronger electron withdraw cyanoacrylic acid group was introduced. This may be due to the lower efficiency of the electron injection from dye to TiO2 and lower te of FSD102 than that of FSD101. These results indicate that the performance of DSSCs can be significantly improved by introducing a diyne unit into this type of organic dyes. © 2017 Elsevier B.V. All rights reserved.

Keywords: Dye-sensitized solar cells Organic dyes Diyne Anthracene Photovoltaic performances

1. Introduction

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J.-K. Fang), [email protected] (Y. Zhang). http://dx.doi.org/10.1016/j.matchemphys.2017.03.047 0254-0584/© 2017 Elsevier B.V. All rights reserved.

€tzel and Dye-sensitized solar cells (DSSCs), first reported by Gra coworker in 1991 [1], are breakthrough in the photovoltaic field. In addition to conventional Ru-complex sensitizers [2e4], various organic dyes have also been investigated in DSSCs [5e7]. Organic dye based DSSCs have several advantages as sensitizers compared

2

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

to the metal complex analogs: low cost, environmental safe, larger absorption coefficients due to intramolecular p-p* transitions and a large variety of available structures due to ease of preparation. Most of the organic dyes contain a Donor-p bridge- Acceptor (Dp-A) structure [8,9] since the D-p-A can reduce the intra-molecular charge recombination to improve the power conversion efficiency. Typically, a wider absorption spectra and high intramolecular charge transfer efficiency are essential for high performance dyes [10]. To maximize the photo activity of organic dyes, a common strategy is to combine different functional groups into one dye molecule. Additionally, both double bonds and triple bonds are widely applied to bridge the different functional groups as conjugating units to increase the range of absorption [11,12]. In many cases, the triple bond incorporation shows advantages compared to double bond, since 1) triple bond, with a linear structure, has no cis/ trans isomers as double bond has [13] and 2) the carbon atoms of a triple bond are sp hybridization and the more negative feature can influence the distribution of electrons. A significant bathochromic shift has been observed for the absorption spectra by replacing C] C unit with C^C unit [14]. Further, acetylene-bridged dyes were reported to exhibit higher open circuit potential (Voc), electron transfer efficiencies and power conversion efficiencies for DSSCs due to their higher electron transfer efficiency [15,16]. Based on these results, several properties such as the absorption on TiO2 [17], the range of p electron conjugation [18], and the energy level of front orbitals [19], etc can be modified by incorporate C^C unit. Most of the excellent efficiency DSSCs with organic dyes reported recently are sensitized by dyes with C^C units [20e22]. We have reported that molecules with diyne unit can greatly increase the life time (t) and decrease the sum of radiative and nonradiative rates (kr and knr), both of which can benefit the power conversion efficiency of DSSCs [23,24]. Giving these results and the significance of incorporation of a C^C unit mentioned above, we asked whether dye molecules containing diyne unit can exhibit beneficial properties. In this paper, we report the synthesis and characterizations of 3 novel dyes, FSD101-103, withFSD101 and FSD102 containing a diyne unit, and FSD103 with a monoyne unit. The structures of the dyes are shown in Scheme 1. Anthracene moiety was selected to increase the Voc of the DSSCs by suppressing charge recombination [14]. The optical and electrochemical properties of the three dyes and their application as sensitizers in DSSCs were evaluated. 2. Results and discussion 2.1. Design and synthesis of dyes Scheme 2 depicts the synthetic routes for FSD101-103. Hexyloxy groups attached triphenylamine was selected as the donor unit because of its excellent electron donating property and the advantage on preventing the aggregation of the dyes on the TiO2 surface. Intermediate 1a and 1b were synthesized by Suzuki cross coupling reaction between (4-(bis(4-(hexyloxy)phenyl)amino) phenyl)boronic acid and functionalized bromoanthracene. 1a was converted to 2a by oxidation and 1b was converted to 2b by removing the trimethylsilyl protecting group. The monoyne or diyne units containing intermediate 3 and 4 were synthesized by a double elimination or by a Sonogashira cross coupling reaction [23,24], respectively. Carboxylic acid groups were formed by oxidation of the aldehyde group or its precursor and cyanoacrylic acid group was synthesized by Knoevenagel reaction to give the desired dyes FSD101-103 [25]. All of the synthetic steps produced the desired products in moderate to high yield. FSD101-103 were fully characterized with 1H NMR, 13C NMR, and HRMS (see the Experimental Section).

Scheme 1. Molecular structures of dyes FSD101-103.

2.2. UVeVIS absorption spectra As mentioned above, there are significant correlations between absorption spectra and light harvesting capabilities of dyes. Consequently, the absorption spectra of the dyes were measured to investigate their light harvesting capabilities. The UVevis absorption spectra of dyes FSD101-103 in dichloromethane (DCM) solutions at a concentration of 1.5  105 M and adsorbed on 2 mm transparent TiO2 films are shown in Fig. 1. The corresponding data are listed in Table 1. Strong absorption maxima of dyes FSD101-103 in the visible region were observed, which can be ascribed to transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) [26]. The absorption spectrum of FSD103 showed an absorption maximum (lmax) at 439 nm. Compared to FSD103, the absorption spectrum of FSD101 was bathochromic shifted 9 nm corresponding to a 0.06 eV decrease in energy, with lmax appearing at 448 nm for the sake of the introduction of an extra triple bond. FSD102 was obtained by replacing carboxylic acid group with a stronger electron withdraw group, cyanoacrylic acid group. A further bathochromic shift of 13 nm was observed in the absorption spectrum of FSD102, which indicates that the cyanoacrylic acid group is a more efficient group than carboxylic acid group for the intramolecular charge transfer from the donor unit to the acceptor unit. By attaching dyes on TiO2 films, hypsochromic shift was usually observed for the absorption spectra caused by the deprotonation of the anchoring group and H-aggregation state of the dyes on semiconductor surface. The absorption maxima for FSD101, FSD102 and FSD103 on 2 mm TiO2 transparent films were 428, 441 and 419 nm, respectively. All exhibited hypsochromic shift of 20 nm equally compared to their corresponding absorption spectra in the DCM solution, which means these 3 dyes show similar

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

3

Scheme 2. Synthetic routes of the dyes FSD101-103.

a

40000

b

FSD101 FSD102 FSD103

30000

FSD101 FSD102 FSD103

2.0

Absorbance

20000

ε (L/M

-1

·cm-1)

1.5

10000

1.0

0.5

0 300

400

500

600

Wavelength / nm

0.0 350

400

450 500 Wavelength / nm

550

600

Fig. 1. UVeVis absorption spectra of dyes FSD101-103 in DCM solution (a) and adsorbed on 2 mm TiO2 transparent films (b).

characteristic on TiO2 films. 2.3. Electrochemical properties The Cyclic voltammetry was performed to investigate the redox behavior of dyes FSD101-103 as well as to evaluate the possibilities

of electron injection from the excited dyes into the conduction band of TiO2 and dye regeneration by redox electrolytes. The cyclic voltammograms are represented in Fig. 2 and the corresponding data are summarized in Table 1. The oxidation potential (Eox) (refers to the HOMO level) of dyes FSD101-103 were 0.75, 0.83 and 0.85 V, respectively. The results are

4

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

Table 1 Optical and electrochemical data of dyes FSD101-103. Dye FSD101 FSD102 FSD103

lmaxa

lTiO2b (nm)

Eoxc (eV)

E0-0d (eV)

Erede (eV)

IP (eV)

EA (eV)

Eexc (eV)

f

(nm) 448 461 439

428 441 419

0.75 0.83 0.85

2.28 2.15 2.38

1.53 1.32 1.53

5.74 7.53 6.18

1.20 1.73 0.22

2.13 1.75 2.22

0.21 0.27 0.15

Fermi level of TiO2 (0.5 V vs. NHE), providing the thermodynamic feasibility of electron injection from the excited dye molecules into the conduction band of the TiO2 semiconductor. These results clearly demonstrate that the dyes FSD101-103, especially for the diyne containing dyes FSD101 and FSD102 with lower band gap energy, could be potentially efficient sensitizers to be used in DSSCs.

a

Absorption maximum in CH2Cl2 solution. Absorption maximum on 2 mm TiO2 transparent films. c First oxidation potentials (Eox) (vs. NHE) were calibrated with ferrocene (0.63 V vs. NHE). d E0-0 transition energy measured at the onset of absorption spectra. e Ered ¼ Eox - E0-0. b

80 FSD-101 FSD-102 FSD-103

Current / μA

60

40

20

0

-20 0.0

0.5 1.0 Potential / V (vs. Ag/AgCl)

1.5

Fig. 2. CV plots of dyes FSD101-103.

summarized in energy band diagrams of FSD101-103 in Fig. 3. The values were more positive than the I- 3/I- redox potential value (0.4 V vs. NHE), which guarantees efficient dye regeneration of the oxidized dyes by the electrolyte [27]. The band gap energies (E0-0) of FSD101-103 were 2.28, 2.15 and 2.38 V, respectively, which were estimated from the onset wavelengths in the absorption spectra of the dyes in DCM [28]. Ered (refers to the LUMO level) can be calculated from Eox - E0-0. The Ered of dyes FSD101-103 (1.53, 1.32 and 1.53 V, respectively) were sufficiently more negative than the

2.4. Theoretical calculation To gain a deeper insight into the effect of molecular structures and electron distributions of FSD101-103 on the performance of DSSCs, the geometries and energies of FSD101-103 were optimized by density functional theory (DFT) calculations with the B3LYP exchange correlation functions under the 6-31G (d) basis set implemented in the Gaussian 09 program. Geometry optimizations were followed by single-point TD-DFT calculations to obtain the vertical excitation energy (Eexc.) and oscillator strength (f). The cation (Mþ) and anion (M) energies of each compound (M) were calculated by using the optimized ground-state structures as initial structures. Hence, vertical ionization potential (IP ¼ EMþ - EM) and vertical electron affinity (EA ¼ EM - EM-) values were determined. The detailed data are listed in Table 1. The computed electronic distribution of the frontier molecular orbitals (HOMOs and LUMOs) of the dyes is shown in Fig. 4, with the isodensity surface values fixed at 0.02. The optimized geometries of FSD101-103 showed that the phenyl rings of the donor attached to anthracene core were perpendicular to the anthracene moieties, which may suppress the dye aggregation on TiO2 and improve their photovoltaic performances [28]. FSD101-103 exhibited a typical D-p-A architecture with the HOMO orbitals mainly located on the triphenylamine moieties with a little contribution from the anthracene core, while the LUMOs all delocalized over the anthracene core and carboxylic or cyanoacrylic acid acceptors. Thus, the electrons from donor part could efficiently transfer to the acceptor part and leading to efficient electron injection from the excited dyes into the acceptor group-connected semiconductor. The lower IP value of FSD101 with diyne unit revealed that the entrance of holes from the TiO2 to the hole transport layer is easier compared to FSD103 with monoyne unit. The higher EA value of

-2.5 -2.0

Potential Vs NHE / V

-1.5

-1.53

-1.32

-1.53

LUMO

-1.0 -0.5

2.28

2.15

TiO2

2.38

CB

0.0

I-/I3-

0.5

0.75

0.83

0.85

1.0

FSD101

FSD102

FSD103

-0.5 0.4

HOMO

1.5 2.0 Fig. 3. The energy band diagram of FSD101-103.

Fig. 4. The electron distribution of the HOMO and LUMO of FSD101-103.

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9 Table 2 Calculated MO transition data of the three dye-(TiO2)8. Species

IPCEmax.(nm)

f

Main MO transition

FSD101-(TiO2)8 FSD102-(TiO2)8 FSD103-(TiO2)8

682 757 592

0.28 0.84 0.32

HOMO - 1 / LUMO þ 2 (96.5%) HOMO - 1 / LUMO þ 1 (99.4%) HOMO - 1 / LUMO þ 4 (97.6%)

FSD101 revealed that the entrance of electrons from cathode to the electron transport layer is easier compared to FSD103. Thus, FSD101 showed better balanced electronehole creation compared to FSD103 because of the a diyne unit [29]. The Eexc according to single-point TD-DFT calculations (2.13, 1.75 and 2.22 eV for FSD101103, respectively) showed good coincidence with the E0-0 estimated from the onset of absorption spectra (2.28, 2.15 and 2.38 eV for FSD101-103, respectively). FSD101 showed lower Eexc compared with FSD103. Conjugation extent enlarged by introducing diyne unit resulted in a wider range of absorption spectrum which is essential for high performance dyes. FSD102 showed much lower Eexc value as expected by replacing the carboxylic acid group to cyanoacrylic acid group. Both the diyne featuring dyes FSD101 and FSD102 showed a higher oscillator strength (f) compared with that of FSD103, which could benefit the light harvesting efficiency leading to higher power conversion efficiency [30]. To further understand the charge transfer nature of the photoexcited compounds upon adsorption on TiO2, we performed DFT calculations for dye-(TiO2)8 complexes. The geometries of those complexes were first optimized at the same level of theory as for the isolated compounds mentioned above, and then single-point TD-DFT calculations were performed to estimate the optical properties. The absorption maximum of the incident photon to current conversion efficiency spectra (IPCEmax) and the relevant data are listed in Table 2. FSD103-(TiO2)8 showed the shortest IPCEmax among these dye-(TiO2)8 complexes, mainly due to its MO transition is from HOMO - 1 to LUMO þ 4 requiring more energy compared with the others. The IPCEmax of FSD101-(TiO2)8 with diyne unit is bathochromic shifted significantly (90 nm) compared that of FSD103-(TiO2)8 with monoyne unit. These data indicate that DSSC sensitized by FSD101 could utilize a wider range of solar

a

radiation spectrum, resulting in a higher power conversion efficiency, and the results are consistent with the experimental data (see below). The spatial extent of the HOMO - 1 was similar in these 3 dye(TiO2)8 complexes. In all complexes, it extended primarily to the dye molecules. However, the nature of the excited state orbitals of FSD101-(TiO2)8 (LUMO þ 2) was significantly different from the other two complexes: it is totally localized in the (TiO2)8 moiety, while in FSD102-(TiO2)8 and FSD103-(TiO2)8, it is delocalized over the electron accepting part of the dyes and the (TiO2)8 moieties. A three dimensional representation of the frontier orbitals in the 3 complexes is shown in Fig. 5. The main conclusion from the above results is that the electron injection from dye to TiO2 is more efficient for FSD101, thus leading to a higher power conversion efficiency. 2.5. Photovoltaic properties The monochromatic incident photon to current conversion efficiency (IPCE) spectra of the DSSCs in the region (350e700 nm) based on the three dyes are shown in Fig. 6a. The highest IPCE values were observed with the maximum values of 80% at 460 nm for FSD101, 75% at 450 nm for FSD102 and 72% at 430 nm for FSD103. The onsets of the IPCE spectra for FSD101-103 were at 630, 660 and 580 nm, respectively. The broader IPCE response range and higher IPCE values of FSD101 and FSD102 compared with those of FSD103 explained the higher Jsc value of FSD101 and FSD102 from the J-V measurement, resulting in better photovoltaic performances of FSD101 and FSD102, which is in agreement with the absorption spectrum of the dye. These results indicate that by introducing a diyne unit to the dyes as in FSD101 and FSD102, the IPCE response range and values of DSSCs increased significantly compared to that of FSD103. Fig. 6b shows the current densityevoltage (JeV) curves of the cells sensitized with different dyes under AM 1.5G irradiation (1 sun, 100 mW cm2). Their corresponding photoelectrode chemical properties, short-circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency (h) data are listed in Table 3. The solar cell based on dye FSD101 with diyne unit

c

b

HOMO-1

LUMO+2

5

HOMO-1

LUMO+1

HOMO-1

LUMO+4

Fig. 5. (a) HOMO - 1 and LOMO þ 2 of FSD101-(TiO2)8 complex. (b) HOMO - 1 and LOMO þ 1 of FSD102-(TiO2)8 complex. (c) HOMO - 1 and LOMO þ 4 of FSD103-(TiO2)8 complex.

6

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

b 10 80 FSD101 FSD102 FSD103

IPCE (%)

60

4.5

40

3.0

20

1.5

0 400

500 600 Wavelength / nm

Integrated Jsc

6.0

FSD-101 FSD-102 FSD-103

8

Current density (mA/cm-2)

a

6

4

2

0 0.0

0.0 700

0.2

0.4

0.6

0.8

Potential / V

Fig. 6. Monochromatic incident photon-to-electron conversion efficiency (IPCE) spectra of DSSCs based on FSD101-103 (a) and J-V curves of DSSCs based on FSD101-103 (b).

Table 3 Photovoltaic performances parameters and simulated EIS data of DSSCs based on FSD101-103. Dye

Jsc (mA/cm2)

Voc (V)

FF

h/%

G (M/cm2)

te (ms)

Rs(U)

RCE(U)

Rrec(U)

FSD101 FSD102 FSD103

6.97 6.95 3.76

0.61 0.59 0.56

0.738 0.731 0.740

3.12 2.98 1.55

2.6  108 4.3  108 6.6  108

356.8 17.6 2.5

24.77 16.12 13.30

1.19 0.27 0.21

120.1 116.5 175.8

exhibits a short-circuit photocurrent density (Jsc) of 6.97 mA/cm2, which is almost double the value of the cell based on dye FSD103 with monoyne unit (3.76 mA/cm2). Similar Jsc was observed for FSD102 by replacing carboxylic acid group with cyanoacrylic acid group. The open circuit voltage (Voc) of the cells based on FSD101 and FSD102 also give higher value (0.61 V and 0.59 V, respectively) than the cell based on dye FSD103 (0.56 V). Consequently, the cells based on FSD101 and FSD102 exhibit better power conversion efficiency (3.12% and 2.98%, respectively) than the cell based on dye FSD103 (1.55%). Typically, the amount of dye molecules loading on TiO2 (G) is consistent with the trend in Jsc for the same dye sensitizer [31]. The contrary tendency of dye loading for FSD101-103 demonstrate that dyes with diyne unit would give high Jsc values despite of low dye loading. It’s worth noting that FSD102 shows no further performance improvement compared with FSD101 even though FSD102

a

70

FSD101 FSD102 FSD103

60

shows wider range of absorption and lower Eexc by replacing carboxylic acid group with cyanoacrylic acid group. It is probably because that the electron injection from dye to TiO2 is more efficient for FSD101 compared with FSD102 (Fig. 5). Based on these results, the performance of DSSCs could be significantly improved by introducing a diyne unit to the dye sensitizer.

2.6. Electrochemical impedance spectroscopy To investigate the differences of the photovoltage between these dyes, electrochemical impedance spectroscopy (EIS) of the DSSCs in dark under an applied dc voltage equivalent to Voc of the device were measured. Nyquist plots and Bode phase plots of DSSCs based on FSD101-103 are shown in Fig. 7. In the Nyquist plots, the series resistance (Rs) values of these three cells (24.77 U for FSD101, 16.12 U for FSD102 and 13.30 U for

b

FSD101 FSD102 FSD103

35 30 Phase / degree

50 -Z'' / ohm

40

40 30 20 10

25 20 15 10 5

0 0

20

40

60

80 100 120 140 160 180 200 220 240 Z' / ohm

0 0

2

4 6 lg (frequency)

Fig. 7. Nyquist plots (a) and Bode plots (b) of the DSSCs based on FSD101-103.

8

10

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

FSD103) are similar due to using the same electrode material and electrolyte. The small charge transfer resistances at the interface of Pt/electrolyte (RCE) values (1.19 U for FSD101, 0.27 U for FSD102 and 0.21 U for FSD103) mean the rapid reduction of I- 3 ions at Pt counter electrode [32]. The semicircles of Nyquist plots are assigned to interface of TiO2/dye/electrolyte (Rrec), which give information about the charge recombination resistance of TiO2/Dye/ Electrolyte interface arising from charge recombination from TiO2 CB to Dye HOMO and Redox Couple oxidation potential. Large Rrec values of these three cells (120.1 U for FSD101, 116.5 U for FSD102 and 175.8 U for FSD103) guarantee there high Voc. The Rrec trend of FSD101-103 appeared inconsistent with the order of their Voc. Thus, we studied the electron lifetime (te) to further elucidate this phenomenon. te can be estimated from the peak frequency (f) at lower frequency region (4.5  102 Hz for FSD101, 9.0  103 Hz for FSD102 and 6.4  104 Hz for FSD103) corresponds to the TiO2/dye/electrolyte interface, in the Bode phase plots according to te ¼ 1/2pf [28]. In general, the Voc is dependent on the electron lifetime in the TiO2 conduction band. Thus, higher te value would lead to increasing of Voc. te of FSD101 (356.8 ms) is remarkably higher than te of FSD103 (2.5 ms). As a result, a higher Voc is observed for DSSCs based on FSD101. In other words, the back electron recombination can be suppressed efficiently by introducing of a diyne unit into dye molecules.

3. Experimental 3.1. Reagents and materials All reagents obtained from commercial sources were used as received, unless otherwise noted. Tetrahydrofuran was dried over sodium/benzophenone and distilled before used. Other solvents such as toluene, diisopropylamine were distilled from CaH2. FTO conductive glasses (sheet resistance of <14 U/sq, 2.2 mm thick) were used for DSSCs fabrication.

3.2. Instruments and characterization Melting points were measured on an X-4A apparatus. 1H NMR and 13C NMR spectra were recorded at room temperature on Bruker DRX300 or Bruker AVANCE III 500 instruments and calibrated with tetramethylsilane (TMS) as an internal reference. HRMS were recorded by Waters Q-TOF Micro™. UVeVis absorption spectra were recorded by THERMO FISHER EVOLUTION220 at room temperature. Cyclic voltammetry measurements of dyes were carried out with a Versa STAT3 electrochemical workstation in tetrahydrofuran (THF) (1.0  103 M) containing 0.1 M Bu4NPF6 as the supporting electrolyte, and a three-electrode system (glassy carbon as the working electrode, platinum wire as the counter electrode, and Ag/AgCl as reference electrode). Ferrocene was used as the external standard. The scan rate was 50 mV/s. The incident photonto-current efficiencies (IPCE) were measured with mono-chromatic incident light under 100 mW cm2 with bias light in DC mode (Newport monochromator, using a 450 W xenon lamp). Current density-voltage measurements were carried out using simulated 1.5 AM sunlight with an output power of 100 mW cm2. Electrochemical impedance spectroscopy (EIS) were measured by Zahner Zennium Impedance Analyzer in the frequency range of 101105 Hz under 1 sun bias illumination under an open-circuit condition. The amount of dye load was measured by desorbing the dye from the films with 0.1 M Tetrabutylammonium Hydroxide in THF/ H2O (1:1) and measuring the corresponding UVevis spectrum.

7

3.3. Synthesis of sensitizers All reactions were carried out under an atmosphere of nitrogen with freshly distilled solvents unless otherwise noted. (4-(bis(4(hexyloxy)phenyl)amino)phenyl)boronic acid and 2-(4-((phenylsulfonyl)methyl)phenyl)-1,3-dioxolane were synthesized according to the literature [33,34]. 3.3.1. 3-(10-{4-[Bis-(4-hexyloxy-phenyl)-amino]-phenyl}anthracen-9-yl)-prop-2-yn-1-ol (1a) (4-(bis(4-(hexyloxy)phenyl)amino)phenyl)boronic acid (240 mg, 0.49 mmol), 3-(10-Bromo-anthracen-9-yl)-prop-2-yn-1ol (152 mg, 0.49 mmol), Pd(PPh3)4 (28 mg, 0.024 mmol), aqueous K2CO3 (2 M, 10 mL) and toluene (10 mL) were added to a flask under argon and the mixture was stirred at 80  C overnight. Then the reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, PE/EA, 5:1) to give 1a as yellow solid (215 mg, 65% yield). M.p: 45e46  C. 1H NMR (300 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 6.9 Hz, 6H), 1.35 (t, J ¼ 3.3 Hz, 8H), 1.42e1.51 (m, 4H), 1.74e1.83 (m, 4H), 1.93 (s, 1H), 3.95 (t, J ¼ 6.6 Hz, 4H), 4.85 (d, J ¼ 4.8 Hz, 2H), 6.89 (d, J ¼ 9 Hz, 4H), 7.09 (d, J ¼ 8.4 Hz, 2H), 7.18 (t, J ¼ 8.7 Hz, 6H), 7.40 (t, J ¼ 7.5 Hz, 2H), 7.56 (t, J ¼ 6.6 Hz, 2H), 7.84 (d, J ¼ 8.7 Hz, 2H), 8.60 (d, J ¼ 8.7 Hz, 2H). 13C NMR (75 MHz, CDCl3) d (ppm): 13.98, 22.51, 25.64, 29.19, 31.48, 51.87, 68.12, 82.43, 98.59, 115.26, 116.11, 119.22, 125.23, 126.21, 126.59, 126.83, 127.46, 129.23, 129.96, 131.58, 132.37, 138.80, 140.45, 148.14, 155.46. 3.3.2. (10-{4-[Bis-(4-hexyloxy-phenyl)-amino]-phenyl}-anthracen9-yl)-propynal (2a) Compound 1a (398 mg, 0.59 mmol), Manganese dioxide (512 mg, 5.9 mmol) and CH2Cl2 (10 mL) were added to a flask and the mixture was stirred at room temperature overnight. Then the manganese dioxide was removed by filtration through a short plug of Celite, which was washed with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, PE/CH2Cl2, 3:2) to give 2a as red solid (302 mg, 76% yield). M.p: 88e89  C. 1H NMR (300 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 6.9 Hz, 6H), 1.35 (t, J ¼ 3.6 Hz, 8H), 1.42e1.49 (m, 4H), 1.74e1.83 (m, 4H), 3.96 (t, J ¼ 6 Hz, 4H), 6.90 (d, J ¼ 9 Hz, 4H), 7.10 (d, J ¼ 6 Hz, 2H), 7.19 (t, J ¼ 7.5 Hz, 6H), 7.46 (t, J ¼ 8.7 Hz, 2H), 7.66 (t, J ¼ 6.9 Hz, 2H), 7.90 (d, J ¼ 8.7 Hz, 2H), 8.62 (d, J ¼ 8.7 Hz, 2H), 9.75 (s, 1H). 13C NMR (75 MHz, CDCl3) d (ppm): 13.98, 22.51, 25.66, 29.20, 31.49, 68.06, 92.80, 99.88, 111.80, 115.27, 118.79, 125.64, 125.96, 127.02, 127.68, 127.98, 128.18, 129.93, 131.32, 134.16, 140.16, 143.31, 148.56, 155.71, 176.08. 3.3.3. Synthesis of [4-(10-ethynyl-anthracen-9-yl)-phenyl]-bis-(4hexyloxy-phenyl)-amine (2b) (4-(bis(4-(hexyloxy)phenyl)amino)phenyl) boronic acid (1.465 g, 3 mmol), (10- Bromo-anthracen-9-ylethynyl)-trimethylsilane (1.057 g, 3 mmol), Pd(PPh3)4 (173 mg, 0.15 mmol), aqueous K2CO3 (2 M, 10 mL) and toluene (25 mL) were added to a flask under argon. The reaction mixture was heated to reflux and stirred for 12 h and then cooled to room temperature. The reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was added K2CO3 (2.439 g, 17.6 mmol), THF (10 mL) and MeOH (10 mL) and the mixture was stirred at room

8

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

temperature for 2 h. Then the reaction mixture was poured into water and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, the solvent was removed in a rotary evaporator. The crude product was subjected to column. Chromatography (SiO2; eluent, PE/CH2Cl2, 5:1) to give 2b as red sticky oil (1.117 g, 98% yield). 1 H NMR (300 MHz, CDCl3) d (ppm): 0.90 (t, J ¼ 6.9 Hz, 6H), 1.34 (t, J ¼ 3.3 Hz, 8H), 1.41e1.51 (m, 4H), 1.73e1.82 (m, 4H), 3.94 (t, J ¼ 6.6 Hz, 4H), 4.00 (s, 1H), 6.88 (d, J ¼ 9 Hz, 4H), 7.09 (d, J ¼ 8.7 Hz, 2H), 7.18 (t, J ¼ 8.7 Hz, 6H), 7.40 (t, J ¼ 7.5 Hz, 2H), 7.57 (t, J ¼ 6.6 Hz, 2H), 7.85 (d, J ¼ 8.7 Hz, 2H), 8.64 (d, J ¼ 8.7 Hz, 2H). 13C NMR (75 MHz, CDCl3) d (ppm): 14.04, 22.61, 25.76, 29.32, 31.60, 68.21, 80.68, 88.22, 115.34, 115.69, 119.32, 125.36, 126.47, 126.64, 126.98, 127.65, 127.94, 129.30, 130.07, 131.65, 132.92, 139.34, 140.56, 148.34, 155.67.

3.3.4. (4-{10-[4-(4-[1,3]dioxolan-2-yl-phenyl)-buta-1,3-diynyl]anthracen-9-yl}-phenyl)-bis-(4-hexyloxy-phenyl)-amine (3) Compound 2a (220 mg, 0.33 mmol), 2-(4-((phenylsulfonyl) methyl)phenyl)-1,3-dioxolane (120 mg, 0.39 mmol) and THF (8 mL) were added to a flask and stirred at room temperature under argon. Then diethyl chlorophosphate was added at 0  C. The reaction mixture was stirred for 5 min and then Lithium bis(trimethylsilyl) amide was added. The reaction mixture was stirred at room temperature overnight. Then the reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, PE/CH2Cl2, 3:2) to give 3 as red solid (200 mg, 75% yield). M.p: 54e55  C. 1H NMR (300 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 6.6 Hz, 6H), 1.35 (t, J ¼ 3.3 Hz, 8H), 1.42e1.49 (m, 4H), 1.74e1.83 (m, 4H), 3.96 (t, J ¼ 6.3 Hz, 4H), 4.04e4.10 (m, 2H), 4.11e4.17 (m, 2H), 5.85 (s, 1H), 6.89 (d, J ¼ 8.7 Hz, 4H), 7.09 (d, J ¼ 8.7 Hz, 2H), 7.19 (t, J ¼ 8.7 Hz, 6H), 7.42 (t, J ¼ 7.8 Hz, 2H), 7.51 (d, J ¼ 8.1 Hz, 2H), 7.57e7.66 (m, 4H), 7.86 (d, J ¼ 8.7 Hz, 2H), 8.64 (d, J ¼ 8.4 Hz, 2H). 13 C NMR (75 MHz, CDCl3) d (ppm): 14.03, 22.58, 25.72, 29.27, 31.56, 65.30, 68.15, 75.00, 79.51, 84.00, 84.71, 103.05, 115.28, 119.12, 122.71, 125.52, 126.57, 126.88, 126.97, 127.36, 127.84, 128.95, 130.08, 131.55, 132.41, 133.79, 138.93, 140.09, 140.40, 148.35, 155.64.

3.3.5. Synthesis of 4-(10-{4-[bis-(4-hexyloxy-phenyl)-amino]phenyl}-anthracen-9-ylethynyl)-benzaldehyde (4) Compound 2b (442 mg, 0.69 mmol), 4-iodo-benzaldehyde (175 mg, 0.754 mmol), Pd(PPh3)2Cl2 (24 mg, 0.034 mmol), CuI (7 mg, 0.037 mmol), diisopropylamine (3 mL) and toluene (6 mL) were added to the flask and the mixture was stirred at room temperature overnight. Then the reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, the solvent was removed in a rotary evaporator. The crude product was subjected to column chromatography (SiO2; eluent, PE/CH2Cl2, 2:1) to give 4 as yellow solid (421 mg, 82% yield). M.p: 152e153  C. 1H NMR (300 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 6.9 Hz, 6H), 1.35 (t, J ¼ 3.6 Hz, 8H), 1.42e1.49 (m, 4H), 1.74e1.83 (m, 4H), 3.96 (t, J ¼ 6.6 Hz, 4H), 6.89 (d, J ¼ 8.7 Hz, 4H), 7.11 (d, J ¼ 8.7 Hz, 2H), 7.19e7.22 (m, 6H), 7.44 (t, J ¼ 7.4 Hz, 2H), 7.62 (t, J ¼ 6.9 Hz, 2H), 7.87e7.99 (m, 6H), 8.69 (d, J ¼ 8.7 Hz, 2H), 10.08 (s, 1H). 13C NMR (75 MHz, CDCl3) d (ppm): 14.03, 22.59, 25.74, 29.30, 31.57, 68.19, 90.97, 99.87, 115.32, 115.84, 119.19, 125.45, 126.51, 126.62, 126.98, 127.80, 129.06, 129.64, 129.88, 130.16, 131.61, 131.94, 132.55, 135.32, 139.89, 140.45, 148.37, 155.66, 191.24.

3.3.6. 4-[4-(10-{4-[Bis-(4-hexyloxy-phenyl)-amino]-phenyl}anthracen-9-yl)-buta-1,3-diynyl]-benzoic acid (FSD-101) Compound 4 (818 mg, 1 mmol), p-toluenesulfonic acid (190 mg, 1 mmol) and THF (16 ml) were added to a flask and the mixture was stirred at room temperature overnight. Then aqueous hydrogen peroxide (30%, 0.8 mL, 8 mmol), aqueous KOH (50%, 0.3 mL, 4 mmol), methyl alcohol (4 mL) were added to the flask. The reaction mixture was heated to reflux and stirred for 12 h and then cooled to room temperature. Then the reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, CH2Cl2/CH3OH, 30:1) to give FSD-101 as dark red solid (427 mg, 54% yield). M.p: 192e193  C. 1H NMR (500 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 7.0 Hz, 6H), 1.34e1.36 (m, 8H), 1.44e1.50 (m, 4H), 1.76e1.82 (m, 4H), 3.96 (t, J ¼ 6.5 Hz, 4H), 6.89 (d, J ¼ 8.5 Hz, 4H), 7.10 (d, J ¼ 8.5 Hz, 2H), 7.17e7.21 (m, 6H), 7.43 (t, J ¼ 7.5 Hz, 2H), 7.62 (t, J ¼ 7.0 Hz, 2H), 7.72 (d, J ¼ 8.0 Hz, 2H), 7.87 (d, J ¼ 9.0 Hz, 2H), 8.14 (d, J ¼ 7.5 Hz, 2H), 8.63 (d, J ¼ 9.0 Hz, 2H). 13C NMR (125 MHz, CDCl3) d (ppm): 14.03, 22.60, 25.75, 29.31, 31.59, 68.27, 77.83, 81.19, 83.24, 84.40, 114.73, 114.86, 115.38, 119.19, 125.59, 126.51, 127.03, 127.57, 127.95, 128.96, 129.48, 130.17, 131.59, 132.37, 133.94, 140.49, 148.46, 155.71, 171.18. HRMS (ESI, m/z): Calcd for [MH]- C55H50NO 4: 788.3745, found: 788.3755. 3.3.7. 3-{4-[4-(10-{4-[Bis-(4-hexyloxy-phenyl)-amino]-phenyl}anthracen-9-yl)-buta-1,3-diynyl]-phenyl}-2-cyano-acrylic acid (FSD-102) Compound 4 (180 mg, 0.22 mmol), cyanoacetic acid (35.6 mg, 0.42 mmol), ammonium acetate (41 mg, 0.53 mmol) and acetic acid (10 mL) were added to a flask under argon and the reaction mixture was heated to reflux and stirred for 5 h. Then the reaction mixture was cooled to room temperature. Then the reaction mixture was poured into water and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, CH2Cl2/ CH3OH, 30:1) to give FSD-102 as dark red solid (168 mg, 91% yield). M.p: 187e189  C. 1H NMR (500 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 7.0 Hz, 6H), 1.34e1.37 (m, 8H), 1.44e1.50 (m, 4H), 1.76e1.82 (m, 4H), 3.96 (t, J ¼ 6.5 Hz, 4H), 6.89 (d, J ¼ 8.5 Hz, 4H), 7.10 (d, J ¼ 8.0 Hz, 2H), 7.20 (t, J ¼ 8.5 Hz, 6H), 7.44 (t, J ¼ 7.5 Hz, 2H), 7.62 (t, J ¼ 7.0 Hz, 2H), 7.75 (d, J ¼ 8.0 Hz, 2H), 7.88 (d, J ¼ 9.0 Hz, 2H), 8.06 (d, J ¼ 8.5 Hz, 2H), 8.30 (s, 1H), 8.63 (d, J ¼ 8.5 Hz, 2H). 13C NMR (125 MHz, CDCl3) d (ppm): 14.03, 22.59, 25.73, 29.28, 31.58, 68.26, 79.24, 82.25, 83.24, 84.43, 102.50, 114.48, 114.86, 115.36, 119.16, 125.63, 126.43, 127.00, 127.16, 127.73, 127.99, 128.82, 130.08, 131.12, 131.28, 131.58, 132.97, 133.97, 140.44, 140.80, 148.46, 154.89, 155.66, 167.06. HRMS (ESI, m/z): Calcd for [M-CO2H]- C57H51N2O 2: 795.3956, found: 795.3965. 3.3.8. 4-(10-{4-[Bis-(4-hexyloxy-phenyl)-amino]-phenyl}anthracen-9-ylethynyl)-benzoic acid (FSD-103) Compound 3 (750 mg, 1 mmol), aqueous hydrogen peroxide (30%, 0.8 mL, 8 mmol), aqueous KOH (50%, 0.3 mL, 4 mmol) and methyl alcohol (4 mL) were added to a flask. The reaction mixture was heated to reflux and stirred for 12 h and then cooled to room temperature. Then the reaction mixture was poured into saturated NH4Cl and extracted with CH2Cl2, the organic layer was washed with saturated brine and dried over MgSO4. After filtration, solvents were removed by rotary evaporation. The crude product was subjected to column chromatography (SiO2; eluent, CH2Cl2/CH3OH, 30:1) to give FSD-103 as red solid (483 mg, 63% yield).

J.-K. Fang et al. / Materials Chemistry and Physics 195 (2017) 1e9

M.p: 87e88  C. 1H NMR (300 MHz, CDCl3) d (ppm): 0.91 (t, J ¼ 6.6 Hz, 6H), 1.29e1.35 (m, 8H), 1.42e1.49 (m, 4H), 1.77e1.81 (m, 4H), 3.96 (t, J ¼ 6.3 Hz, 4H), 6.90 (d, J ¼ 8.7 Hz, 4H), 7.11 (d, J ¼ 8.4 Hz, 2H), 7.21 (t, J ¼ 8.4 Hz, 6H), 7.44 (t, J ¼ 7.8 Hz, 2H), 7.62 (t, J ¼ 7.5 Hz, 2H), 7.88 (d, J ¼ 8.4 Hz, 4H), 8.21 (d, J ¼ 8.1 Hz, 2H), 8.71 (d, J ¼ 8.4 Hz, 2H). 13C NMR (125 MHz, CDCl3) d (ppm): 14.03, 22.60, 25.76, 29.32, 31.60, 68.28, 90.42, 99.94, 115.39, 116.05, 119.32, 125.46, 126.61, 126.99, 127.81, 128.57, 129.26, 129.35, 130.22, 130.29, 131.52, 131.68, 132.58, 139.75, 140.57, 148.39, 155.69, 171.52. HRMS (ESI, m/z): Calcd for [MH]- C53H50NO 4 : 764.3745, found: 764.3752. 3.4. Fabrication of DSSCs Working electrodes (an 8 mm thick transparent TiO2 layer with a 3 mm thick TiO2 scattering layer) were dipped in a freshly prepared TiCl4 aqueous solution at 70  C for 30 min. The electrode was then flushed with de-ionized water, ethanol, and dried with an air flow. Electrodes were then sintered at 500  C for 30 min. After being cooled to 80  C, the electrodes were immersed in the dye solutions (0.3 mM in CHCl3) for 24 h. The films were flushed with CHCl3 and dried in air for use. The counter electrodes were prepared by casting H2PtCl6 solution on clean FTO glass and sintered at 450  C for 30 min. Two electrodes were sandwiched using a 45 mm thick hot-melt ring (Surlyn, DuPont). The internal space was filled with liquid electrolytes, which consists of 0.04 M LiI, 0.06 M I2, 0.053 M 4-tert-butylpyridine, 0.9 M DMPII and 0.08 M GuSCN in acetonitrile, using a vacuum back filling system through pre-drilled holes on the counter electrode. The holes were sealed with a Surlyn sheet and a thin glass cover. 4. Conclusions In summary, three novel organic dyes were designed and synthesized to investigate the effects of the diyne-bridge on the lightharvesting, electrochemical properties and performance of DSSCs. Compared to the reference dye FSD103 with monoyne unit, FSD101 with diyne unit exhibits broader absorption spectrum, lower IP, higher EA, lower band gap energy, higher oscillator strength, more efficient electron injection ability, broader IPCE response range and higher te which led to a higher Jsc and Voc for DSSC and resulted in a higher power conversion efficiency (3.12% compared with 1.55% for FSD103). FSD102 showed similar results as FSD101, but its power conversion efficiency was slightly decreased (2.98%) even though a stronger electron withdraw group cyanoacrylic acid group is introduced, which is probably due to the lower efficient of the electron injection from dye to TiO2 and lower te of FSD102. Based on these results, we conclude that the performance of DSSCs can be significantly improved by introducing a diyne unit into this type of organic dyes. Acknowledgment This work was supported by the Natural Science Foundation of Jiangsu Province (BK20140780).

9

References [1] B. Oregan, M. Gr€ atzel, Nature 353 (1991) 737e740. €tzel, Acc. Chem. Res. 42 (2009) 1788e1798. [2] M. Gra [3] M.K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Mueller, P. Liska, €tzel, J. Am. Chem. Soc. 115 (1993) 6382e6390. N. Vlachopoulos, M. Gra [4] M.K. Nazeeruddin, P. Pechy, T. Renouard, S.M. Zakeeruddin, R. HumphryBaker, P. Comte, P. Liska, L. Cevey, E. Costa, V. Shklover, L. Spiccia, G.B. Deacon, €tzel, J. Am. Chem. Soc. 123 (2001) 1613e1624. C.A. Bignozzi, M. Gra [5] G.L. Zhang, H. Bala, Y.M. Cheng, D. Shi, X.J. Lv, Q.J. Yu, P. Wang, Chem. Commun. 16 (2009) 2198e2200. [6] K. Hara, Z.S. Wang, T. Sato, A. Furube, R. Katoh, H. Sugihara, Y. Dan-Oh, C. Kasada, A. Shinpo, S. Suga, J. Phys, Chem. B 109 (2005) 3907e3914. [7] E.A. Pidko, P. Mignon, P. Geerlings, R.A. Schoonheydt, R.A. Van Santen, J. Phys. Chem. C 112 (2008) 5510e5519. [8] M.F. Xu, S. Wenger, H. Bala, D. Shi, R.Z. Li, Y.Z. Zhou, S.M. Zakeeruddin, €tzel, P. Wang, J. Phys. Chem. C 113 (2009) 2966e2973. M. Gra [9] Z.S. Wang, N. Koumura, Y. Cui, M. Takahashi, H. Sekiguchi, A. Mori, T. Kubo, A. Furube, K. Hara, Chem. Mater 20 (2008) 3993e4003. [10] X. Yang, J.K. Fang, Y. Suzuma, F. Xu, A. Orita, J. Otera, S. Kajiyama, N. Koumura, K. Hara, Chem. Lett. 40 (2011) 620e622. [11] H.N. Tian, X.C. Yang, R.K. Chen, A. Hagfeldt, L.C. Sun, Energy Environ. Sci. 2 (2009) 674e677. [12] J.K. Fang, X. Yu, X. Yang, W.F. Li, D.L. An, Chin. J. Org. Chem. 32 (2012) 1261e1269. [13] Y. Hu, A. Abate, Y. Cao, A. Ivaturi, S.M. Zakeeruddin, M. Gra€tzel, N. Robertson, J. Phys. Chem. C 120 (2016) 15027e15034. [14] C. Teng, X. Yang, C. Yang, S. Li, M. Cheng, A. Hagfeldt, L. Sun, J. Phys. Chem. C 114 (2010) 9101e9110. [15] C.L. Mai, T. Moehl, Y. Kim, F.Y. Ho, P. Comte, P.C. Su, C.W. Hsu, F. Giordano, A. Yella, S.M. Zakeeruddin, C.Y. Yeh, M. Gr€ atzel, RSC Adv. 4 (2014) 35251e35257. [16] C. Teng, X. Yang, C. Yang, H. Tian, S. Li, X. Wang, A. Hagfeldt, L. Sun, J. Phys. Chem. C 114 (2010) 11305e11313. [17] C.W. Lee, H.P. Lu, C.M. Lan, Y.L. Huang, Y.R. Liang, W.N. Yen, Y.C. Liu, Y.S. Lin, E.W. Diau, C.Y. Yeh, Chem. Eur. J. 15 (2009) 1403e1412. [18] M.E. Ragoussi, J.J. Cid, J.H. Yum, G. Torre, D.D. Censo, M. Gr€ atzel, M.K. Nazeeruddin, T. Torres, Angew. Chem. Int. Ed. 51 (2012) 4451e4454. [19] M.E. Ragoussi, G. Torre, T. Torres, Eur. J. Org. Chem. 2013 (2013) 2832e2840. [20] A. Yella, H.W. Lee, H.N. Tsao, C. Yi, A.K. Chandiran, M.K. Nazeeruddin, €tzel, Science 334 (2011) E.W.G. Diau, C.Y. Yeh, S.M. Zakeeruddin, M. Gra 629e634. [21] S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B.F.E. Curchod, N. Ashari€tzel, Nat. Astani, I. Tavernelli, U. Rothlisberger, M.K. Nazeeruddin, M. Gra Chem. 6 (2014) 242e247. [22] Z. Yao, H. Wu, L. Yang, J. Wang, J. Zhang, M. Zhang, Y. Guo, P. Wang, Energy Environ. Sci. 8 (2015) 3192e3197. [23] J.K. Fang, D.L. An, K. Wakamatsu, T. Ishikawa, T. Iwanaga, S. Toyota, S.I. Akita, D. Matsuo, A. Orita, J. Otera, Tetrahedron 66 (2010) 5479e5485. [24] J.K. Fang, D.L. An, K. Wakamatsu, T. Ishikawa, T. Iwanaga, S. Toyota, D. Matsuo, A. Orita, J. Otera, Tetrahedron Lett. 51 (2010) 917e920. [25] Y.J. Guo, J.L. Su, Z.W. An, X.B. Chen, P. Chen, J. Mol. Struct. 1094 (2015) 195e202. [26] J. Lin, A. Elangovan, T. Ho, J. Org. Chem. 70 (2005) 7397e7407. [27] R. Misra, R. Maragani, D. Arora, A. Sharma, G.D. Sharma, Dyes Pigments 126 (2016) 38e45. [28] X. Qian, L. Shao, H.M. Li, R.C. Yan, X.Y. Wang, L.X. Hou, J. Power Sources 319 (2016) 39e47. [29] A.S. Shalabi, A.M. El Mahdy, M.M. Assem, H.O. Taha, K.A. Soliman, J. Nanopart. Res. 16 (2014) 2579. [30] W. Fan, W. Deng, Commun. Comput. Chem. 1 (2013) 152e170. [31] W. Li, Z. Liu, H. Wu, Y.-B. Cheng, Z. Zhao, H. He, J. Phys. Chem. C 119 (2015) 5265e5273. [32] F. Zhang, J. Fan, H. Yu, Z. Ke, C. Nie, D. Kuang, G. Shao, C. Su, J. Org. Chem. 80 (2015) 9034e9040. [33] M.Z. Yigit, H. Bilgili, E. Sefer, S. Demic, C. Zafer, M. Can, S. Koyuncu, Electrochim 147 (2014) 617e625. [34] A. Orita, F.G. Ye, G. Babu, T. Ikemoto, J. Otera, Can. J. Chem. 83 (2005) 716e727.