Construction of 3, 7-Dithienyl Phenothiazine-Based Organic Dyes via

Article pubs.acs.org/joc

Cite This: J. Org. Chem. 2018, 83, 8114−8126

Construction of 3,7-Dithienyl Phenothiazine-Based Organic Dyes via Multistep Direct C−H Arylation Reactions Wen Wang,† Xiaoyu Li,‡ Jingbo Lan,*,† Di Wu,† Ruilin Wang,*,§ and Jingsong You† †

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Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China ‡ Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory, Southwest University of Science and Technology, Mianyang 621010, China § College of Materials Science and Engineering, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China S Supporting Information *

ABSTRACT: Herein, an effective and feasible approach to prepare 3,7-dithienyl phenothiazine-based organic dyes has been developed. In this synthetic procedure, the Pd-catalyzed multistep direct C−H arylation of thiophene derivatives with phenothiazine bromides was employed for the first time to construct the 3,7dithienyl phenothiazine core scaffold, which greatly streamlines access to this class of organic dyes. 3-Thienyl phenothiazine-based dyes were also synthesized via the direct C−H arylation of thiophenes as references. Most of the 3,7-dithienyl phenothiazine-based dyes exhibit better photovoltaic performances than the 3thienyl phenothiazine-based dyes. Among these organic dyes, the solar cell device based on 6d exhibits the highest conversion efficiency of 8.9%. Compared with 6d, organic dyes with longer π-conjugation, also including bithiophene as the π-spacer, show dramatically reduced conversion efficiencies of cell devices. The introduction of the more electron-rich 3,4-ethylenedioxythiophene to the C3- and/or C7position of phenothiazine instead of thiophene does not significantly improve the photoelectric conversion performance. The highly efficient synthetic strategy herein developed and these primary results may be helpful to design and synthesize a variety of new 3,7-dithienyl phenothiazine-based organic dyes.

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INTRODUCTION

In recent years, organic dyes based on a phenothiazine electron donor and a thiophene π-spacer have been developed and exhibit promising performances.6b,8 Traditional methods to connect the phenothiazine unit and the thiophene unit mainly rely on Stille or Suzuki coupling reaction.8 These methods generally suffer from limitations, including tedious synthetic steps to prepare organoboron or organotin reagents, using highly toxic trimethyltin chloride or tributyltin chloride, and a stoichiometric amount of toxic byproducts. Undoubtedly, transition-metal-catalyzed direct C−H arylation is an ideal strategy to accomplish the coupling between phenothiazine and thiophene.9 This strategy avoids the time-consuming prefunctionalization of thiophene, including the regioselective halogenation, the lithiation, as well as the subsequent reaction with borate esters or trialkyltin chlorides, and thus greatly simplifies the operation processes and reduces the unnecessary wastes. The effect of various thiophene π-spacers, including thiophene, bithiophene, 3,4-ethylenedioxythiophene (EDOT), etc., on DSSC performances has not been studied systematically so far, due to the lack of rapid, general routes to connect phenothiazine with thiophene. Once a concise and reliable pathway toward the connection between phenothiazine and

Metal-free organic dyes for dye-sensitized solar cells (DSSCs) have gained widespread attention in recent years due to their low cost, easy preparation and purification, and structural flexibility.1 The construction of a donor−π−acceptor (D−π− A) structure is a common principle in the design of organic dyes for DSSCs, in which a 2-cyanoacrylic acid or rhodanine unit usually renders the acceptor functionality and furthermore is used as an anchoring group.1f,2 Most of the electron-rich units can be employed as electron donors. Phenothiazine possesses a nonplanar heteroanthracene structure with a butterfly conformation, which can serve to inhibit the dye aggregation and the excimer formation.3 Moreover, the electron-rich sulfur and nitrogen atoms located in the middle ring endow phenothiazine a strong electron-donating ability.4 Therefore, phenothiazine has been widely used as an electron donor to develop organic dyes in recent years.5 In addition, it is well-known that the selection of a suitable π-conjugated spacer between the donor and the acceptor is very important in the design of organic dyes.6 Thiophenes possess thermal stability, aromaticity, and a slightly electron-rich characteristic and thus are widely employed as π-spacers in organic dyes, which are usually preferable to extend π-conjugation and promote the efficient intramolecular charge transfer (ICT).6,7 © 2018 American Chemical Society

Received: April 11, 2018 Published: May 31, 2018 8114

DOI: 10.1021/acs.joc.8b00915 J. Org. Chem. 2018, 83, 8114−8126

Article

The Journal of Organic Chemistry Scheme 1. Synthetic Routes to 3,7-Dithienyl Phenothiazine-Based Organic Dyesa

Reaction conditions: (i) Pd(OAc)2, PCy3·HBF4, PivOH, K2CO3, toluene, 110 °C, 24 h; (ii) N-bromosuccinimide, DMF, 0−25 °C, 12 h; (iii) Pd(OAc)2, PCy3·HBF4, PivOH, K2CO3, toluene, 110 °C, 24 h; (iv) cyanoacetic acid, piperidine, chloroform, 80 °C, 6 h. Cy = cyclohexyl, DMF = N,N-dimethyl formamide, PivOH = pivalic acid. a

Table 1. Optimization of the Direct C−H Arylation of 2a with 1aa

entry

catalyst

ligand

base

solvent

1 2 3 4b 5 6 7 8 9 10 11 12 13c 14 15

PdCl2 Pd(PPh3)2Cl2 Pd(OAc)2 Pd(OAc)2 Pd(TFA)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2

PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 P(t-Bu)3·HBF4 PPh3 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4 PCy3·HBF4

K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 Cs2CO3 Na2CO3 NaOAc K2CO3 K2CO3 K2CO3 K2CO3 K2CO3

toluene toluene toluene toluene toluene toluene toluene toluene toluene toluene dioxane DMF toluene toluene toluene

temperature 110 110 110 110 110 110 110 110 110 110 110 110 110 100 120

°C °C °C °C °C °C °C °C °C °C °C °C °C °C °C

yield (%) 62 5 89 60 65 48 42 30 11 3 54 59 66 82 64

a

Reaction conditions: 3-bromo-10-hexyl-10H-phenothiazine (1a, 0.5 mmol, 1.0 equiv), thiophene-2-carbaldehyde (2a, 0.75 mmol, 1.5 equiv), catalyst (5 mol %), ligand (10 mol %), base (0.75 mmol, 1.5 equiv), PivOH (30 mol %), solvent (1.5 mL), 110 °C, 24 h. Isolated yield. bIn the absence of pivalic acid. cBase (1.5 mmol, 3.0 equiv).

as an additive under a N2 atmosphere (Table 1, entry 3). In the absence of pivalic acid, 3a could be obtained with a yield of 60% (Table 1, entry 4). Upon addition of 30 mol % pivalic acid to this catalytic system with an excess of potassium carbonate, 3a was obtained in 89% yield (Table 1, entry 3), where potassium pivalate could be generated in situ. The pivalate might serve as a soluble proton transfer agent from the thiophene and palladium catalyst to the insoluble carbonate salt.12 Therefore, we deduced that the concerted metalation−deprotonation (CMD) pathway promoted by pivalate might result in the increased reactivity. Under the optimal conditions, 5-(10-hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (3a), 5-(10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (3b), and 5′-(10-hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (3c) were synthesized through the direct C−H arylation reaction as dye precursors for further modifications (Scheme 2). It is worth noting that 3a could be obtained not only with a yield of 89% by loading 0.5 mmol of 1a but also with a high yield of 83% on a gram scale (12.0 mmol). Replacing brominated phenothiazine with brominated triphenylamine and carbazole, the direct C−H arylation

thiophene has been established, it would provide opportunities for the rapid construction of a series of various phenothiazine− thiophene D−π−A structures for screening high performance organic dyes. Following our continuing interest in C−H bond activation and functionalization,10,11 we herein present the first example of the Pd-catalyzed multistep direct C−H arylation of thiophene derivatives to prepare the organic dyes based on 3,7dithienyl phenothiazine D−π−A structures and the investigation of their photophysical, electrochemical, and photovoltaic properties (Scheme 1).

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RESULTS AND DISCUSSION Our investigation began with the direct C−H arylation of thiophene-2-carbaldehyde (2a) with 3-bromo-10-hexyl-10Hphenothiazine (1a) by using PdCl2 in conjunction with PCy3· HBF4 ligand (Table 1, entry 1). Delightedly, the direct arylation product 3a was obtained in 62% yield. After screening other catalysts, ligands, bases, solvents, additives, and reaction temperatures, the best result was obtained in toluene at 110 °C for 24 h with 5 mol % Pd(OAc)2 as a catalyst, PCy3·HBF4 as a ligand, K2CO3 as a base, and pivalic acid (PivOH, 30 mol %) 8115


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The Journal of Organic Chemistry

the Knövenagel condensations of 5 with cyanoacetic acid were performed in the presence of piperidine in CHCl3 to prepare the 3,7-dithienyl phenothiazine-based organic dyes (6a−6l) (Scheme 5). 3-Thienyl phenothiazine-based organic dyes 6m and 6n were also synthesized as references. With a divergent library of 3,7-dithienyl phenothiazine-based organic dyes in hand, we subsequently investigated their photophysical and electrochemical properties. Figure 1 shows the UV−vis absorption spectra of each dye in dichloromethane solution (2 × 10−5 M) and adsorbed on TiO2 film, and the detailed parameters including the wavelength of maximum absorption (λmax), the molar extinction coefficient (ε), and the absorption onset (λonset) of these dyes are summarized in Table 2. The UV−vis absorption spectra of these organic dyes in CH2Cl2 (2 × 10−5 M) exhibit two absorption bands, appearing at 300−410 and 410−600 nm, which are assigned to the localized π−π* transitions of the chromophores and the charge-transfer (CT) transition from the donor to the acceptor, respectively (Figure 1a). Compared with 3-thienyl phenothiazine-based organic dyes (6m and 6n), the short-wavelength absorption of the π−π* transitions of 3,7-dithienyl phenothiazine-based dyes (6a−6l) is enhanced due to the extended conjugation length. The dye 6n shows higher extinction coefficients in CT absorption than 6m due to the extended conjugation length. The dyes 6a−6l show lower molar extinction coefficients in CT transitions than 6n, which might be attributed to the nonplanarity of the additional donor including triphenylamine and carbazole that enhances geometric twisting of molecules.13 In 6a−6l, the molar extinction coefficients of the CT transition of dyes are slightly enhanced with an increased electron-donating capability of π-spacer or an extended π-conjugation length (for example, the molar extinction coefficients: 6b > 6a, 6f > 6e > 6d, 6h > 6g, and 6k > 6j). When these dyes are adsorbed on TiO2 films, although the wavelengths of maximum absorptions are slightly blue-shifted with respect to their solutions due to the deprotonation of carboxylic acids, their absorption thresholds are remarkably red-shifted to above 650 nm, which matches well with the visible region of the solar spectrum (Figure 1b). The electrochemical properties of these organic dyes (6a− 6n) were investigated via cyclic voltammetry to evaluate the possibility of the electron injection from the photoexcited dyes to the conduction band (CB) of TiO2 and the dye regeneration (Table 2 and Figure S1). Most of the dyes show more than one oxidation potential due to the presence of an additional donor, and the first and second oxidation potentials of dyes are listed in Table 2. The first oxidation potentials (Eox) of 6a−6n range from 0.72 to 0.89 V (vs NHE), which correspond to the highest occupied molecular orbital (HOMO) of molecules. Their zero−zero band gaps (E0−0) were estimated from the onset of the absorption spectra, which are between 1.90 and 2.01 eV. The excited-state oxidation potentials (Eox*), calculated from Eox − E0−0, correspond to the lowest unoccupied molecular orbital (LUMO), which ranges from −1.12 to −1.23 V. The HOMO levels of all of these dyes are much more positive than the iodine/iodide redox potential value (0.42 V vs NHE), ensuring that the oxidized dyes can be regenerated by the I−/ I3− electrolyte. Similarly, the LUMO levels of 6a−6n are sufficiently more negative than the conduction-band-edge energy level (ECB) of the TiO2 photoanode (−0.5 V vs NHE), implying the feasibility of electron injection from the photoexcited dyes into the CB of TiO2.

Scheme 2. Synthesis of Thienyl Phenothiazine, Triphenylamine, and Carbazole Derivatives via the Direct C−H Arylation of Thiophenesb

a

Gram scale. bReaction conditions: 1 (0.5 mmol, 1.0 equiv), 2 (0.75 mmol, 1.5 equiv), Pd(OAc)2 (5 mol %), PCy3·HBF4 (10 mol %), PivOH (30 mol %), K2CO3 (0.75 mmol, 1.5 equiv), toluene (1.5 mL), 110 °C, 24 h under a N2 atmosphere. Isolated yield.

reaction still worked well, affording N,N-diphenyl-4-(thiophen2-yl)aniline (3d) and 9-hexyl-3-(thiophen-2-yl)-9H-carbazole (3e) in good yields. Next, the bromination of 3-thienyl phenothiazines was carried out. Owing to the absence of the competitive reaction of the C2-position of thienyl groups, the bromination reaction mainly took place at the C7-position of phenothiazines, providing the brominated 3-thienyl phenothiazine derivatives 4a, 4b, and 4c in 78, 75, and 68% yields, respectively (Scheme 3). Utilizing the direct C−H arylation of thiophenes once again, a series of 3,7-dithienyl phenothiazine derivatives (5a−5l) were obtained in moderate to good yields (Scheme 4). Subsequently, Scheme 3. Bromination of 3-Thienyl Phenothiazinesa

a Reaction conditions: 3 (8 mmol, 1.0 equiv), N-bromosuccinimide (NBS, 8.8 mmol, 1.1 equiv), DMF (45 mL), 0−25 °C, 12 h. Isolated yield.

8116


Article

The Journal of Organic Chemistry Scheme 4. Synthesis of 3,7-Dithienyl Phenothiazine Derivatives via the Direct C−H Arylation of Thiophenesa

Reaction conditions: 4 (0.5 mmol, 1.0 equiv), 2 or 3 (0.75 mmol, 1.5 equiv), Pd(OAc)2 (5 mol %), PCy3·HBF4 (10 mol %), K2CO3 (0.75 mmol, 1.5 equiv), PivOH (30 mol %), toluene (2 mL), 110 °C, 24 h. Isolated yield. a

Scheme 5. Preparation of 3,7-Dithienyl Phenothiazine-Based Organic Dyes via Knövenagel Condensationa

a Reaction conditions: 3 or 5 (0.25 mmol, 1.0 equiv), cyanoacetic acid (0.75 mmol, 3.0 equiv), piperidine (0.75 mmol, 3.0 equiv), CHCl3 (2 mL), reflux, 6 h. Isolated yield.

cm−2), and the photocurrent−voltage (J−V) plots are shown in Figure 2a. The solar cell of 3-thienyl phenothiazine-based organic dye 6m exhibits a relatively low conversion efficiency of 5.25%.15 Replacing thiophene with bithiophene to extend the π-bridge, the conversion efficiency of the cell based on 6n increases to 6.91%. Introducing electron-donating units, such as 5-(4-(diphenylamino)phenyl)thiophen-2-yl, 5-(9H-carbazol-9yl)thiophen-2-yl, 5-(9H-carbazol-9-yl) 3,4-ethylenedioxythiophen-2-yl, 5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl, 3,4-ethyl-

The DSSCs with an active area of 0.4 × 0.4 cm2 were fabricated using TiO2 photoanodes sensitized with organic dyes (6a−6n), electrodeposited platinum counter electrodes, and an I−/I3− redox couple as the electrolyte. Considering that the solvent may make a difference for the photovoltaic properties of DSSC devices,14 the optimization of the device fabrication process with different solvents is provided in the Supporting Information (section II). The photovoltaic parameters were measured under an irradiance of AM 1.5G sunlight (100 mW 8117


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Figure 1. Absorption spectra of 6a−6n (a) in CH2Cl2 (2 × 10−5 M) and (b) anchored on 3 μm transparent TiO2 films.

Table 2. Photophysical and Electrochemical Properties of 6a−6n dyes 6a 6b 6c 6d 6e 6f 6g 6h 6i 6j 6k 6l 6m 6n

λmax (nm) (ε × 104 M−1 cm−1)a 370 376 381 361 369 388 365 368 364 362 372 361 373

(3.80) (3.76) (3.27) (2.45) (2.13) (2.06) (2.89) (2.36) (3.38) (1.94) (1.52) (2.26) (1.46)

470 (1.75) 484 (2.24) 481 495 467 490 498 462 480 486 490 478 490

(2.19) (2.51) (2.57) (2.50) (2.78) (2.06) (1.71) (1.97) (2.01) (2.20) (3.14)

λonsetb (nm)

Eoxc (V)

642 630 634 627 632 616 638 643 633 641 652 653 636 642

0.81 0.75 0.72 0.81 0.78 0.89 0.77 0.80 0.78 0.73 0.72 0.77 0.78 0.80

1.24 1.27 1.32 1.03 1.04 1.01 1.02 1.03 1.00 1.02 1.02 1.35 1.04

E0−0d (eV)

Eox* e (V)

1.93 1.97 1.96 1.98 1.96 2.01 1.94 1.93 1.96 1.93 1.90 1.90 1.94 1.93

−1.12 −1.22 −1.23 −1.17 −1.18 −1.12 −1.17 −1.13 −1.18 −1.20 −1.18 −1.13 −1.16 −1.13

Absorption maxima (λmax) and molar extinction coefficients (ε) were measured in CH2Cl2 (2 × 10−5 M). bAbsorption onset (λonset) of sensitizers. Oxidation potential was measured in DMSO containing 0.1 M n-Bu4NPF6 with a scanning rate of 50 mV s−1 (vs NHE). dE0−0 = 1240/λonset. eEox* = Eox − E0−0. a c

Figure 2. (a) J−V plots under simulated AM 1.5G irradiation. (b) IPCE curves.

V, FF = 0.727), which approximates to the efficiency of the N719-based device (9.63%) under the same conditions. These results demonstrate that the introduction of the more electronrich EDOT to the C3- and/or C7-position of phenothiazine instead of thiophene cannot significantly improve the photovoltaic performance of the resulting organic dyes. Moreover, compared with 6d, 6e, 6g, and 6h, the organic dyes 6a, 6b, 6c, and 6f with longer π-conjugation show dramatically reduced conversion efficiencies of solar cells, indicating that a greater length of conjugation may induce larger dispersion forces between the dyes and the acceptors, leading to short electron lifetimes and thus lower Voc. In addition, the dyes with a greater length of conjugation might form less trimly packed dye layers, resulting in uncovered TiO2 areas and low dye loads.16

enedioxythiophen-2-yl (EDOT), and 5-hexyl-EDOT, to the C7-position of the phenothiazine of 6m results in increased conversion efficiencies in varying degrees (Table 3, 6a, 6d, 6g, 6i, 6j, and 6l). However, introducing the same electrondonating units, such as 5-(4-(diphenylamino)phenyl)thiophen2-yl and 5-(9H-carbazol-9-yl)thiophen-2-yl, to the C7-position of the phenothiazine of 6n leads to slightly reduced conversion efficiencies (Table 3, 6c and 6f). Furthermore, replacing the thiophene at the C3-position of the phenothiazine of 6a, 6d, 6g, and 6j with EDOT, the resulting dyes 6b, 6e, 6h, and 6k exhibit slightly reduced efficiencies of solar cells, except for 6h. The conversion efficiency of the solar cell based on 6h is higher than that based on 6g but slightly lower than that based on 6e. Among these dyes, the cell based on 6d exhibits the highest conversion efficiency of 8.9% (Jsc = 15.91 mA cm−2, Voc = 0.770 8118


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The Journal of Organic Chemistry Table 3. Photovoltaic Performance of DSSC Devicesa dyes 6a 6b 6c 6d 6e 6f 6g 6h 6i 6j 6k 6l 6m 6n N719b

Voc (V) Jsc (mA cm−2) 0.726 0.727 0.670 0.770 0.784 0.726 0.736 0.755 0.694 0.737 0.667 0.748 0.678 0.750 0.764

12.66 12.15 13.69 15.91 14.79 13.10 14.72 15.67 13.59 13.48 14.38 13.90 11.83 14.36 18.24

FF

PCE (%)

Rrec (Ω)

τe (ms)

0.724 0.734 0.661 0.727 0.735 0.719 0.711 0.706 0.632 0.724 0.660 0.714 0.655 0.642 0.690

6.66 6.48 6.07 8.90 8.53 6.85 7.70 8.36 6.05 7.19 6.33 7.42 5.25 6.91 9.63

46 54 31 70 77 46 58 64 45 59 25 62 63 64

6.1 8.5 4.3 20.1 23.1 6.7 9.4 18.4 5.5 9.9 3.5 13.3 4.9 16.9

Nyquist plots. In general, the larger radius of the semicircle means larger Rrec and smaller electron recombination rate.17 As shown in Table 3, the order of Rrec is consistent with the order of Voc. 6e exhibits the largest Rrec and thus the largest Voc. From the peak frequency (f) in the lower frequency region in EIS Bode phase plots (Figure 3b), the effective electron lifetime (τe) is obtained by τe = 1/(2πf) (Table 3).18 Longer lifetime means smaller electron recombination rate. The results of the electron lifetime are consistent with the values of Voc of devices.

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CONCLUSION In summary, we have developed an efficient and stepeconomical synthetic route to prepare phenothiazine-based organic dyes by Pd-catalyzed multistep direct C−H arylation of thiophene derivatives. On the basis of this synthetic strategy, a class of 3,7-dithienyl phenothiazine core scaffolds were constructed successfully. 3-Thienyl phenothiazine-based dyes 6m and 6n were also synthesized as references. The photophysical, electrochemical, and photovoltaic properties of the resulting organic dyes (6a−6n) were systematically investigated. The incorporation of electron-donating units to the C7-position of the phenothiazine of 6m results in an increase in the conversion efficiency of DSSCs. Among these dyes, the solar cell device based on 6d exhibits the highest conversion efficiency of 8.9% (Jsc = 15.91 mA cm−2, Voc = 0.770 V, FF = 0.727), which approximates to the efficiency of the N719-based device (9.63%) under the same conditions. The introduction of the more electron-rich EDOT to the C3- and/ or C7-position of phenothiazine instead of thiophene cannot significantly improve the photoelectric conversion performance. Compared with 6d, organic dyes with longer π-conjugation show dramatically reduced conversion efficiencies, indicating that a great length of conjugation may induce a large dispersion force between the dye and the acceptor, or a less trimly packed dye layer, thus leading to low Voc and/or Jsc. We hope that the highly efficient synthetic strategy herein developed and these primary results will be helpful to design and synthesize a variety of new 3,7-dithienyl phenothiazine-based organic dyes.

a J−V characteristics were measured under standard AM 1.5G irradiation (100 mW cm−2) with an effective working area of 0.4 × 0.4 cm2 at room temperature. TiO2 photoanode was dipped in 0.5 mmol/L dye solution (DCM/THF 9/1) for 12 h. TiO2 photoanode: 14 μm thick of 20 nm sized TiO2 transparent film with 5 μm thick of 400 nm sized TiO2 light scattering layer. The electrolyte was composed of 1.0 M DMPII, 0.1 M LiI, 0.05 M I2, and 0.5 M TBP with CH3CN as solvent. EIS was measured in dark conditions under a forward bias of −0.70 V, and Rrec was fitted by Z-View software. bThe TiO2 photoanode was dipped in the solution of N719 (0.5 mmol/L) in CH3CN/t-BuOH (1:1) for 12 h.

The incident photo-to-current conversion efficiencies (IPCE) of the DSSC devices are shown in Figure 2b. The IPCE curves of photosensitizers demonstrate that the light ranging from 350 to 650 nm can be converted to photocurrent effectively, which is consistent with the UV−vis absorption spectra of the dyes adsorbed on TiO2 films. The maximum values of the IPCE of all sensitizers exceed 60%. Among these, 6d exhibits the highest IPCE value of 87% and exceeds 80% in the spectra of 400−560 nm. To get an elucidation of the difference of open-circuit photovoltages in DSSCs based on these dyes, electrochemical impedance spectroscopy (EIS) was performed in dark conditions under a forward bias of −0.70 V. Figure 3a shows the Nyquist plots of the DSSCs and their charge transfer resistance (Rrec) values are listed in Table 3, which are fitted by Z-View software according to a circuit diagram. The interfacial charge recombination reaction at the TiO2/dye/electrolyte interface can be described by Rrec, which corresponds to the larger semicircle (occurs in the middle frequency range) of the

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EXPERIMENTAL SECTION

General Information. 1H (400 MHz) and 13C (100 MHz) NMR spectra were obtained on a Bruker AV II-400 MHz or an Agilent 400MR DD2 spectrometer. The 1H NMR chemical shifts were measured relative to CDCl3 or DMSO-d6 as an internal reference (CDCl3, δ = 7.26 ppm; DMSO-d6, δ = 2.50 ppm). The 13C NMR chemical shifts were given using CDCl3 or DMSO-d6 as an internal standard (CDCl3, δ = 77.16 ppm; DMSO-d6, δ = 39.52 ppm). High-resolution mass spectra (HRMS) were obtained with Waters-Q-TOF-Premier (ESI). Cyclic voltammetry (CV) was performed on LK2005A. UV−vis-NIR

Figure 3. Electrochemical impedance spectroscopy (EIS) for DSSCs: (a) Nyquist plots; (b) Bode phase plots. 8119


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over 20 min. The mixture was then allowed to warm to room temperature and then heated to reflux for 2 h. After being cooled to room temperature, the mixture was poured into sodium acetate aqueous solution. After stirring for 10 min, dichloromethane was added to the mixture. The organic layer was washed with brine, dried over anhydrous Na2SO4, and concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether/acetone = 6/1, V/V). 3,4-Ethylenedioxythiophene-2-carbaldehyde was afforded as a white solid (3.3 g, 70% yield). 1H NMR (400 MHz, CDCl3): δ = 4.26−4.28 (m, 2H), 4.35−4.37 (m, 2H), 6.80 (s, 1H), 9.90 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 64.5, 65.4, 111.0, 118.6, 141.9, 148.6, 180.3 ppm. Synthesis of [2,2′-Bithiophene]-5-carbaldehyde (2b).22 [2,2′Bithiophene]-5-carbaldehyde was synthesized with a procedure similar to that of 3,4-ethylenedioxythiophene-2-carbaldehyde, and 2,2′bithiophene (8.9 g, 53.3 mmol) was used as substrate to obtain [2,2′-bithiophene]-5-carbaldehyde as a green solid (5.6 g, 54% yield). 1 H NMR (400 MHz, CDCl3): δ = 7.06−7.08 (m, 1H), 7.25 (d, J = 4.0 Hz, 1H), 7.35−7.37 (m, 2H), 7.67 (d, J = 4.0 Hz, 1H), 9.86 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 124.4, 126.3, 127.2, 128.5, 136.1, 137.6, 141.7, 147.3, 182.7 ppm. Synthesis of 9-Thiophen-2-yl-9H-carbazole (2c).23 In a Schlenk flask (250 mL), a mixture of 9H-carbazole (5.0 g, 30 mmol), 2-bromothiophene (7.3 g, 45 mmol), CuI (450 mg, 2.4 mmol), KI (7.5 g, 45 mmol), K2CO3 (24.9 g, 90 mmol), and L-proline (350 mg, 3.1 mmol) was dissolved in DMF (150 mL), heated to reflux, and kept strring for 48 h under a nitrogen atmosphere. After being cooled to room temperature, the mixture was dissolved in dichloromethane and washed with water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether) to afford 2c as a white powder (4.8 g, 65% yield). 1H NMR (400 MHz, CDCl3): δ = 7.18−7.22 (m, 2H), 7.30−7.34 (m, 2H), 7.38−7.40 (m, 1H), 7.42−7.48 (m, 4H), 8.12 (d, J = 7.6 Hz, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ = 110.3, 120.3, 120.7, 123.6, 124.4, 125.0, 126.3, 126.4, 138.9, 142.1 ppm. Synthesis of 9-(3,4-Ethylenedioxythiophen-2-yl)-9H-carbazole (2d).24,25 In a Schlenk flask (250 mL), EDOT (10 g, 7.52 mL) was dissolved in a solution of THF/HOAc (90 mL/90 mL) and cooled to 0 °C. Then, NBS (12.5 g dissolved in THF) was added dropwise. The mixture was allowed to warm to room temperature and keep stirring for 2 h. The mixture was dissolved in ethyl acetate and washed with water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether), and 2-bromo-3,4ethylenedioxythiophene was afforded as a pale yellow oil (14.3 g, 92% yield). Immediately, in a Schlenk flask (250 mL), a mixture of 2-bromo3,4-ethylenedioxythiophene (7.2 g, 32.3 mmol), 9H-carbazole (6 g, 35.5 mmol), CuI (6.2 g, 32.3 mmol), and K2CO3 (5.8 g, 42.2 mmol) was dissolved in nitrobenzene (180 mL), and then, the mixture was refluxed under nitrogen for 36 h. The nitrobenzene was removed by distillation under a vacuum, and the residue was dissolved in 300 mL of CHCl3. Then, 100 mL of H2O and 150 mL of saturated NH4OH aqueous solution were added to the residue and the mixture was stirred for 2 h. The organic layer was washed with water and brine and dried over anhydrous Na2SO4, concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether/ethyl acetate 10/1, V/V). After being recrystallized, 2d was afforded as a white solid (3.2 g, 30% yield). M.p.: 132−138 °C. 1H NMR (400 MHz, CDCl3): δ = 4.19−4.21 (m, 2H), 4.27−4.29 (m, 2H), 6.43 (s, 1H), 7.28−7.32 (m, 2H), 7.37−7.40 (m, 2H), 7.43−7.47 (m, 2H), 8.086−8.090 (m, 1H), 8.10−8.11 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 64.8, 65.0, 97.5, 110.5, 120.4, 120.6, 123.7, 126.2, 137.5, 140.9, 141.8 ppm. HRMS (ESI+): calcd for C18H14NO2S [M + H]+ 308.0740, found 308.0744. General Procedure for the Preparation of 3 by Direct C−H Arylation. In a Schlenk tube, a mixture of 3-bromo-10-hexyl-10Hphenothiazine (1a, 181.1 mg, 0.5 mmol, 1.0 equiv), thiophene-2carbaldehyde derivatives (2, 0.75 mmol, 1.5 equiv), Pd(OAc)2 (5.6

absorption spectra were recorded on a SHIMADZU UV-3600 spectrophotometer. Photoelectrochemical characterizations on the solar cells were performed by employing an Oriel Class AAA solar simulator (Oriel 94023A, Newport Corp.). Photocurrent−voltage characteristics of the DSSCs were obtained by a potentiostat/galvanostat (Keithley Series 2400 SourceMeter, Keithley Instruments, Inc.) at a light intensity of 100 mW cm−2 calibrated by an Oriel reference solar cell (Oriel 91150V, Newport Corp.). An IPCE test was performed by using a Qtest Station 1000AD (Crowntech, Inc.) which has a xenon light source and a monochromator (Czerny-Turner). The system is equipped with a NIST traceable Si detector as a reference. A short circuit photocurrent spectrum was recorded with a Keithley 2000 multimeter. Electrochemical impedance spectroscopy (EIS) was recorded by a Solotron 1260 and 1287. Unless otherwise noted, all reagents were obtained from commercial suppliers and used without further purification. The Pt-counter electrode and two types of TiO2 films were purchased from OPV Tech (China). A 3 μm thick film of transparent TiO2 films as the absorbing layer coated on a FTO glass substrate with dimensions of 1.0 × 1.0 cm2 was used to test UV−vis spectra. A 14 μm thick of 20 nm sized TiO2 transparent film with 5 μm thick of 400 nm sized TiO2 light scattering layer coated on a FTO glass substrate with dimensions of 0.4 × 0.4 cm2 was used to assemble DSSCs. Synthesis of 3-Bromo-10-hexyl-10H-phenothiazine (1a).19 In a Schlenk flask (250 mL), phenothiazine (10.4 g, 52.2 mmol) and KOH (4.4 g, 78.3 mmol) were dissolved in DMSO (120 mL). After the mixture was stirred for 1 h at room temperature, 1-bromohexane (9.3 mL, 62.7 mmol) was added by means of a syringe, and the solution was stirred for 12 h. The mixture was dissolved in ethyl acetate and washed with water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under a vacuum. The residue was purified by column chromatography (silica gel, petroleum ether). 10Hexyl-10H-phenothiazine was afforded as a colorless oil (13.3 g, 90% yield). 1H NMR (400 MHz, CDCl3): δ = 0.88 (t, J = 7.2 Hz, 3H), 1.28−1.32 (m, 4H), 1.40−1.47 (m, 2H), 1.77−1.82 (m, 2H), 3.84 (t, J = 7.2 Hz, 2H), 6.85−6.92 (m, 4H), 7.12−7.17 (m, 4H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.8, 27.0, 31.6, 47.6, 115.5, 122.4, 125.0, 127.3, 127.5, 145.5 ppm. In a Schlenk flask (250 mL), 10-hexyl-10H-phenothiazine (7.5 g, 26.5 mmol) was stirred in DMF (70 mL) and cooled to 0 °C. NBromosuccinimide (NBS) (4.7 g dissolved in 30 mL of DMF) was added dropwise. Then, the mixture was allowed to warm to room temperature and keep stirring overnight. The mixture was dissolved in ethyl acetate and washed with water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether) to afford 3-bromo-10-hexyl-10H-phenothiazine as a colorless oil (7.0 g, 72.9% yield). 1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 7.2 Hz, 3H), 1.26−1.28 (m, 4H), 1.37−1.43 (m, 2H), 1.73−1.80 (m, 2H), 3.79 (t, J = 7.2 Hz, 2H), 6.68−6.70 (m, 1H), 6.83−6.86 (m, 1H), 6.90−6.94 (m, 1H), 7.10−7.17 (m, 2H), 7.21−7.25 (m, 2H) ppm. Synthesis of 4-Bromo-N,N-diphenylaniline (1b).20 In a Schlenk flask (250 mL), triphenylamine (6.08 g, 24.8 mmol) was dissolved in DMF (50 mL) and cooled to 0 °C and NBS (4.41 g, 24.8 mmol dissolved in 40 mL DMF) was added dropwise. Then, the mixture was allowed to warm to room temperature and keep stirring overnight. The mixture was dissolved in ethyl acetate and washed with water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under a vacuum. The residue was purified by silica gel column chromatography (petroleum ether) to afford 4-bromo-N,Ndiphenylaniline as a white solid (7.2 g, 89% yield). 1H NMR (400 MHz, CDCl3): δ = 6.95 (d, J = 8.8 Hz, 2H), 7.04 (t, J = 7.4 Hz, 2H), 7.08 (d, J = 8.0 Hz, 4H), 7.26 (t, J = 7.8 Hz, 4H), 7.33 (d, J = 8.8 Hz, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ = 114.9, 123.4, 124.5, 125.3, 129.5, 132.3, 147.2, 147.5 ppm. Synthesis of 3,4-Ethylenedioxythiophene-2-carbaldehyde (2a).21 3,4-Ethylenedioxythiophene (EDOT) (3 mL, 28 mmol) and dry DMF (2.2 mL, 28 mmol) were stirred in dry dichloroethane (15 mL) and cooled to 0 °C, and POCl3 (2.6 mL, 28 mmol) was added dropwise 8120


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The Journal of Organic Chemistry mg, 0.025 mmol, 0.05 equiv), PCy3·HBF4 (18.4 mg, 0.05 mmol, 0.1 equiv), K2CO3 (103.6 mg, 0.75 mmol, 1.5 equiv), PivOH (15.2 mg, 0.15 mmol, 0.3 equiv), and toluene (1.5 mL) was stirred at 110 °C under a nitrogen atmosphere for 24 h. The reaction mixture was then cooled to room temperature, diluted with dichloromethane, filtered through a Celite pad, and washed with dichloromethane. The combined filtrate was concentrated, and the residue was purified by column chromatography on silica gel. 5-(10-Hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (3a).8b Purification by column chromatography on silica gel (petroleum ether/acetone = 10/1, v/v) afforded 3a as a red oil (175 mg, 89% yield; 3.9 g, 83% yield for gram scale). 1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 6.6 Hz, 3H), 1.30−1.32 (m, 4H), 1.40−1.48 (m, 2H), 1.78−1.85 (m, 2H), 3.86 (t, J = 7.2 Hz, 2H), 6.86 (t, J = 7.8 Hz, 2H), 6.94 (t, J = 7.6 Hz, 1H), 7.15 (dd, J = 7.6 Hz, 16.8 Hz, 2H), 7.28 (d, J = 4.0 Hz, 1H), 7.40−7.45 (m, 2H), 7.70 (d, J = 4.0 Hz, 1H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.7, 26.9, 31.6, 47.8, 115.6, 115.7, 123.0, 123.2, 123.9, 125.0, 125.68, 125.72, 127.4, 127.62, 127.64, 137.8, 141.7, 144.5, 146.5, 153.8, 182.8 ppm. 5-(10-Hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (3b).8b Purification by column chromatography on silica gel (petroleum ether/acetone = 5/1, v/v) afforded 3b as a yellow solid (185.0 mg, 82% yield). 1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 6.4 Hz, 3H), 1.30−1.31 (m, 4H), 1.39−1.47 (m, 2H), 1.76−1.84 (m, 2H), 3.84 (t, J = 7.2 Hz, 2H), 4.36−4.40 (m, 4H), 6.84 (t, J = 8.6 Hz, 2H), 6.92 (t, J = 7.6 Hz, 1H), 7.10−7.16 (m, 2H), 7.52 (d, J = 8.4 Hz, 1H), 7.59 (s, 1H), 9.90 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.8, 26.9, 31.6, 47.8, 64.7, 65.3, 115.0, 115.3, 115.6, 122.9, 124.1, 125.2, 125.7, 126.1, 127.5, 127.6, 128.6, 137.2, 144.6, 145.7, 149.2, 179.6 ppm. 5′-(10-Hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (3c).26 Purification by column chromatography on silica gel (petroleum ether/acetone = 10/1, v/v) afforded 3c as a red oil (190.3 mg, 80% yield). 1H NMR (400 MHz, CDCl3): δ = 0.88 (t, J = 7.0 Hz, 3H) 1.30−1.32 (m, 4H), 1.40−1.44 (m, 2H), 1.77−1.85 (m, 2H), 3.85 (t, J = 7.2 Hz, 2H), 6.83−6.88 (m, 2H), 6.91−6.96 (m, 1H), 7.12− 7.18 (m, 3H), 7.23 (d, J = 4.0 Hz, 1H), 7.30 (d, J = 3.6 Hz, 1H), 7.35− 7.38 (m, 2H), 7.67 (d, J = 4.0 Hz, 1H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.8, 26.8, 26.9, 31.6, 47.7, 115.6, 122.8, 123.4, 123.9, 124.0, 124.6, 125.0, 125.6, 127.3, 127.5, 127.6, 127.9, 134.3, 137.7, 141.4, 144.8, 145.4, 145.5, 147.5, 182.6 ppm. N,N-Diphenyl-4-(thiophen-2-yl)aniline (3d).27 Purification by silica gel column chromatography (petroleum ether/dichloromethane = 10/ 1, V/V) afforded 3d as a white solid (83.4 mg, 51% yield). 1H NMR (400 MHz, CDCl3): δ = 7.01−7.13 (m, 9H), 7.21−7.28 (m, 6H), 7.46−7.48 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ = 122.4, 123.2, 123.9, 124.1, 124.6, 126.9, 128.1, 128.7, 129.4, 144.4, 147.4, 147.6 ppm. 9-Hexyl-3-(thiophen-2-yl)-9H-carbazole (3e).27 Purification by silica gel column chromatography (petroleum ether/dichloromethane = 10/1, V/V) afforded 3e as a pale green oil (76.7 mg, 46% yield). 1H NMR (400 MHz, CDCl3): δ = 0.86−0.89 (m, 3H), 1.26−1.41 (m, 6H), 1.83−1.91 (m, 2H), 4.28 (t, J = 7.4 Hz, 2H), 7.10−7.12 (m, 1H), 7.23−7.27 (m, 2H), 7.34−7.35 (m, 1H), 7.37−7.41 (m, 2H), 7.46− 7.50 (m, 1H), 7.72−7.74 (m, 1H), 8.14 (d, J = 7.6 Hz, 1H), 8.33 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.7, 27.1, 29.1, 31.7, 43.3, 109.0, 109.1, 118.0, 119.1, 120.6, 122.1, 122.9, 123.4, 123.7, 124.4, 125.7, 126.0, 128.1, 140.1, 141.0, 146.0 ppm. HRMS (ESI+): calcd for C22H23NNaS [M + Na]+ 356.1449, found 356.1452. General Procedure for Bromination of 3. A 100 mL flask with a magnetic stirring bar was charged with 3 (8 mmol, 1.0 equiv) and DMF (30 mL). The solution was stirred at 0 °C, and NBS (1.56 g, 8.8 mmol, 1.1 equiv) dissolved in DMF (15 mL) was added dropwise. The mixture was allowed to warm to room temperature and keep stirring overnight. The mixture was extracted by ethyl acetate (60 mL × 3); the combined organic layer was washed by water and brine, respectively, and dried over anhydrous Na2SO4 and then concentrated under a vacuum. The crude product was purified by column chromatography on silica gel to afford 4.

5-(7-Bromo-10-hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (4a).28 Purification by column chromatography on silica gel (petroleum ether/acetone = 10/1, v/v) afforded 4a as a red solid (2.9 g, 78% yield). M.p.: 74 °C. 1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 6.4 Hz, 3H), 1.29−1.31 (m, 4H), 1.39−1.46 (m, 2H), 1.74−1.82 (m, 2H), 3.81 (t, J = 7.2 Hz, 2H), 6.70 (d, J = 8.0 Hz, 1H), 6.85 (d, J = 8.8 Hz, 1H), 7.23−7.26 (m, 2H), 7.29 (d, J = 4.0 Hz, 1H), 7.38 (brs, 1H), 7.43−7.45 (m, 1H), 7.70 (d, J = 4.0 Hz, 1H), 9.86 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.7, 26.7, 26.8, 31.5, 47.9, 115.1, 115.8, 116.8, 123.3, 125.0, 125.1, 126.0, 126.2, 127.7, 129.8, 130.3, 137.8, 141.8, 143.7, 146.0, 153.4, 182.8 ppm. 5-(7-Bromo-10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (4b).8b Purification by column chromatography on silica gel (petroleum ether/acetone = 5/1, v/v) afforded 4b as a yellow solid (3.2 g, 75% yield). M.p.: 85 °C. 1H NMR (400 MHz, CDCl3): δ = 0.86 (t, J = 6.8 Hz, 3H), 1.27−1.29 (m, 4H), 1.36− 1.41 (m, 2H), 1.71−1.79 (m, 2H), 3.78 (t, J = 7.2 Hz, 2H), 4.35−4.39 (m, 4H), 6.67 (d, J = 8.4 Hz, 1H), 6.80 (d, J = 8.8 Hz, 1H), 7.20−7.23 (m, 2H), 7.49−7.51 (m, 1H), 7.549−7.552 (m, 1H), 9.88 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.6, 26.8, 31.5, 47.8, 64.7, 65.3, 115.0, 115.2, 115.5, 116.7, 124.4, 125.8, 126.2, 126.38, 126.41, 128.2, 129.8, 130.2, 137.3, 143.8, 145.3, 149.1, 179.6 ppm. 5′-(7-Bromo-10-hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (4c).26 Purification by column chromatography on silica gel (petroleum ether/acetone = 10/1, v/v) afforded 4c as a red solid (3.0 g, 68% yield). M.p.: 77−80 °C. 1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 7.0 Hz, 3H), 1.28−1.31 (m, 4H), 1.38−1.46 (m, 2H), 1.74−1.81 (m, 2H), 3.80 (t, J = 7.2 Hz, 2H), 6.70 (d, J = 9.2 Hz, 1H), 6.83 (d, J = 8.4 Hz, 1H), 7.15 (d, J = 4.0 Hz, 1H), 7.22−7.26 (m, 3H), 7.30 (d, J = 4.0 Hz, 1H), 7.32 (d, J = 2.0 Hz, 1H), 7.36−7.38 (m, 1H), 7.67 (d, J = 4.0 Hz, 1H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.7, 26.8, 31.5, 47.8, 114.9, 115.8, 116.7, 123.5, 124.0, 124.6, 124.9, 125.2, 126.3, 127.3, 128.3, 129.8, 130.2, 134.5, 137.6, 141.5, 143.9, 145.0, 145.2, 147.4, 182.6 ppm. General Procedure for the Preparation of 5 by Direct C−H Arylation. In a Schlenk tube, a mixture of 4 (0.5 mmol, 1.0 equiv), 2 or 3 (0.75 mmol, 1.5 equiv), Pd(OAc)2 (5.6 mg, 0.025 mmol, 0.05 equiv), PCy3·HBF4 (18.4 mg, 0.05 mmol, 0.1 equiv), K2CO3 (103.6 mg, 0.75 mmol, 1.5 equiv), PivOH (15.2 mg, 0.15 mmol, 0.3 equiv), and toluene (2 mL) was stirred at 110 °C under a nitrogen atmosphere for 24 h. The reaction mixture was then cooled to room temperature, diluted with dichloromethane, filtered through a Celite pad, and washed with dichloromethane. The combined filtrate was concentrated, and the residue was purified by column chromatography on silica gel. 5-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl-10Hphenothiazin-3-yl)thiophene-2-carbaldehyde (5a). Purification by column chromatography on silica gel (petroleum ether/acetone = 10/ 1, v/v) afforded 5a as a red solid (183.3 mg, 51% yield). M.p.: 92 °C. 1 H NMR (400 MHz, CDCl3): δ = 0.89 (t, J = 6.2 Hz, 3H), 1.32−1.33 (m, 4H), 1.43−1.47 (m, 2H), 1.81−1.84 (m, 2H), 3.86 (t, J = 7.2 Hz, 2H), 6.84−6.86 (m, 2H), 7.03−7.08 (m, 4H), 7.12−7.17 (m, 6H), 7.28−7.29 (m, 5H), 7.36−7.48 (m, 6H), 7.70−7.71 (m, 1H), 9.86 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.8, 26.7, 26.9, 31.6, 47.9, 115.5, 115.8, 123.21, 123.25, 123.4, 123.8, 124.3, 124.4, 124.6, 124.8, 125.0, 125.1, 125.8, 126.4, 127.5, 128.4, 129.5, 129.6, 137.8, 141.6, 141.7, 143.1, 143.4, 146.0, 147.4, 147.6, 153.6, 182.8 ppm. HRMS (ESI+): calcd for C45H39N2OS3 [M + H]+ 719.2219, found 719.2215. 5-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl-10Hphenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (5b). Purification by column chromatography on silica gel (petroleum ether/acetone = 4/1, v/v) afforded 5b as a red solid (217.6 mg, 56% yield). M.p.: 120 °C. 1H NMR (400 MHz, CDCl3): δ = 0.88 (t, J = 7.0 Hz, 3H), 1.30−1.32 (m, 4H), 1.40−1.44 (m, 2H), 1.77−1.84 (m, 2H), 3.84 (t, J = 7.2 Hz, 2H), 4.36−4.40 (m, 4H), 6.82 (dd, J = 2.4 Hz, 8.8 Hz, 2H), 7.01−7.07 (m, 4H), 7.10−7.16 (m, 6H), 7.24−7.26 (m, 3H), 7.28 (s, 1H), 7.33−7.34 (m, 1H), 7.35−7.38 (m, 1H), 7.45−7.47 (m, 2H), 7.50−7.53 (m, 1H), 7.58 (d, J = 2.0 Hz, 1H), 9.89 (s, 1H) ppm. 13 C NMR (100 MHz, CDCl3): δ = 14.1, 22.8, 26.7, 26.9, 31.6, 47.8, 8121


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The Journal of Organic Chemistry 64.7, 65.3, 115.0, 115.3, 115.6, 123.2, 123.4, 123.8, 124.3, 124.4, 124.5, 124.6, 124.7, 125.7, 126.16, 126.19, 126.4, 128.4, 128.5, 129.4, 137.3, 141.7, 143.1, 143.6, 145.2, 147.4, 147.6, 149.2, 179.6 ppm. HRMS (ESI+): calcd for C47H41N2O3S3 [M + H]+ 777.2274, found 777.2272. 5′-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl-10Hphenothiazin-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (5c). Purification by column chromatography on silica gel (petroleum ether/ acetone = 10/1, v/v) afforded 5c as a red solid (200.2 mg, 50% yield). M.p.: 126 °C. 1H NMR (400 MHz, CDCl3): δ = 0.89 (t, J = 6.8 Hz, 3H), 1.32−1.34 (m, 4H), 1.43−1.47 (m, 2H), 1.79−1.86 (m, 2H), 3.85 (t, J = 7.2 Hz, 2H), 6.83 (d, J = 8.0 Hz, 2H), 7.02−7.08 (m, 4H), 7.12−7.16 (m, 7H), 7.23−7.25 (m, 2H), 7.29−7.31 (m, 4H), 7.35− 7.40 (m, 4H), 7.47 (d, J = 8.8 Hz, 2H), 7.66 (d, J = 3.6 Hz, 1H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.8, 26.8, 26.9, 31.6, 47.8, 115.55, 115.65, 123.2, 123.38, 123.43, 123.8, 124.0, 124.3, 124.5, 124.57, 124.64, 124.8, 124.9, 125.1, 126.4, 127.3, 128.0, 128.4, 129.38, 129.45, 134.4, 137.6, 141.4, 141.7, 143.0, 143.8, 144.9, 145.4, 147.35, 147.43, 147.6, 182.6 ppm. HRMS (ESI+): calcd for C49H41N2OS4 [M + H]+ 801.2096, found 801.2096. 5-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (5d). Purification by column chromatography on silica gel (petroleum ether/acetone = 6/1, v/v) afforded 5d as a yellow solid (237.1 mg, 74% yield). M.p.: 90−94 °C. 1 H NMR (400 MHz, CDCl3): δ = 0.88−0.89 (m, 3H), 1.33−1.34 (m, 4H), 1.43−1.51 (m, 2H), 1.80−1.87 (m, 2H), 3.88 (t, J = 7.2 Hz, 2H), 6.86−6.89 (m, 2H), 7.15 (d, J = 3.6 Hz, 1H), 7.25 (s, 1H), 7.28−7.34 (m, 3H), 7.39−7.47 (m, 6H), 7.54 (d, J = 8.0 Hz, 2H), 7.70 (d, J = 4.0 Hz, 1H), 8.10−8.12 (m, 2H), 9.86 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.7, 26.9, 31.6, 47.9, 110.2, 110.4, 115.6, 115.8, 120.4, 120.8, 121.2, 123.2, 123.7, 124.58, 124.60, 124.9, 125.1, 125.9, 126.0, 126.4, 127.6, 129.2, 137.3, 137.7, 141.6, 141.8, 142.0, 144.0, 145.9, 153.5, 182.7 ppm. HRMS (ESI + ): calcd for C39H33N2OS3[M + H]+ 641.1750, found 641.1746. 5-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (5e). Purification by column chromatography on silica gel (petroleum ether/ acetone = 3/1, v/v) afforded 5e as a red solid (192.2 mg, 55% yield). M.p.: 159−164 °C. 1H NMR (400 MHz, CDCl3): δ = 0.87−0.91 (m, 3H), 1.31−1.34 (m, 4H), 1.42−1.47 (m, 2H), 1.79−1.87 (m, 2H), 3.87 (t, J = 7.2 Hz, 2H), 4.38−4.42 (m, 4H), 6.85−6.88 (m, 2H), 7.15 (d, J = 4.0 Hz, 1H), 7.24−7.25 (m, 1H), 7.30−7.33 (m, 2H), 7.39− 7.47 (m, 4H), 7.52−7.55 (m, 3H), 7.61 (d, J = 2.0 Hz, 1H), 8.11 (d, J = 7.6 Hz, 2H), 9.90 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.8, 26.7, 26.9, 31.6, 47.9, 64.7, 65.3, 110.4, 115.1, 115.4, 115.7, 120.4, 120.8, 121.1, 123.6, 124.4, 124.6, 124.7, 125.0, 125.8, 126.0, 126.2, 126.3, 126.4, 128.3, 129.0, 137.2, 137.3, 141.7, 142.0, 144.1, 145.1, 149.2, 179.6 ppm. HRMS (ESI+): calcd for C41H35N2O3S3 [M + H]+ 699.1804, found 699.1807. 5′-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (5f). Purification by column chromatography on silica gel (petroleum ether/acetone = 10/ 1, v/v) afforded 5f as a red solid (213.3 mg, 59% yield). M.p.: 179− 182 °C. 1H NMR (400 MHz, CDCl3): δ = 0.90 (t, J = 7.0 Hz, 3H), 1.33−1.34 (m, 4H), 1.43−1.46 (m, 2H), 1.80−1.87 (m, 2H), 3.87 (t, J = 7.0 Hz, 2H), 6.84−6.88 (m, 2H), 7.15 (t, J = 3.4 Hz, 2H), 7.23 (d, J = 4.0 Hz, 1H), 7.25−7.26 (m, 1H), 7.30−7.48 (m, 9H), 7.53−7.55 (m, 2H), 7.66 (d, J = 4.0 Hz, 1H), 8.11 (d, J = 7.6 Hz, 2H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.2, 22.8, 26.7, 26.9, 31.6, 47.9, 110.4, 115.6, 115.7, 120.4, 120.8, 121.1, 123.5, 123.6, 124.0, 124.56, 124.59, 124.7, 124.8, 125.07, 125.12, 126.0, 126.4, 127.3, 128.2, 128.9, 134.4, 137.2, 137.6, 141.5, 141.7, 142.0, 144.3, 144.8, 145.3, 147.4, 182.6 ppm. HRMS (ESI+): calcd for C43H35N2OS4 [M + H]+ 723.1627, found 723.1619. 5-(7-(5-(9H-Carbazol-9-yl)-3,4-ethylenedioxythiophen-2-yl)-10hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (5g). Purification by column chromatography on silica gel (petroleum ether/ acetone = 5/1, v/v) afforded 5g as a yellow solid (262.1 mg, 75% yield). M.p.: 147 °C. 1H NMR (400 MHz, CDCl3): δ = 0.89 (t, J = 7.0 Hz, 3H), 1.31−1.34 (m, 4H), 1.42−1.49 (m, 2H), 1.79−1.87 (m, 2H), 3.86 (t, J = 7.2 Hz, 2H), 4.24−4.26 (m, 2H), 4.38−4.40 (m, 2H),

6.84−6.87 (m, 2H), 7.27−7.32 (m, 3H), 7.40−7.47 (m, 6H), 7.50 (dd, J = 2.0 Hz, 10.8 Hz, 1H), 7.58 (d, J = 2.4 Hz, 1H), 7.69 (d, J = 4.0 Hz, 1H), 8.09−8.11 (m, 2H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.8, 26.7, 26.8, 31.6, 47.9, 64.8, 65.0, 110.5, 110.6, 114.2, 115.5, 115.6, 120.4, 120.7, 123.2, 123.8, 124.1, 125.07, 125.08, 125.2, 125.4, 125.8, 126.3, 127.5, 127.6, 136.9, 137.78, 137.85, 141.7, 143.0, 146.0, 153.7, 182.8 ppm. HRMS (ESI + ): calcd for C41H35N2O3S3 [M + H]+ 699.1804, found 699.1806. 5-(7-(5-(9H-Carbazol-9-yl)-3,4-ethylenedioxythiophen-2-yl)-10hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (5h). Purification by column chromatography on silica gel (petroleum ether/acetone = 3/1, v/v) afforded 5h as a red solid (200.6 mg, 53% yield). M.p.: >200 °C. 1H NMR (400 MHz, CDCl3): δ = 0.89 (t, J = 6.4 Hz, 3H), 1.32−1.34 (m, 4H), 1.43−1.45 (m, 2H), 1.81−1.84 (m, 2H), 3.85 (t, J = 7.0 Hz, 2H), 4.24−4.25 (m, 2H), 4.37−4.38 (m, 6H), 6.83−6.86 (m, 2H), 7.28−7.32 (m, 2H), 7.42− 7.57 (m, 8H), 8.10 (d, J = 7.6 Hz, 2H), 9.90 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.8, 26.7, 26.8, 31.6, 47.8, 64.6, 64.8, 65.0, 65.3, 110.4, 110.6, 114.3, 115.0, 115.2, 115.5, 120.4, 120.7, 123.8, 124.3, 124.5, 125.1, 125.3, 125.7, 126.1, 126.2, 126.3, 127.5, 128.4, 136.8, 137.3, 137.8, 141.7, 143.1, 145.3, 149.2, 179.6 ppm. HRMS (ESI+): calcd for C43H37N2O5S3 [M + H]+ 757.1859, found 757.1860. 5-(10-Hexyl-7-(5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)-10Hphenothiazin-3-yl)thiophene-2-carbaldehyde (5i). Purification by column chromatography on silica gel (petroleum ether/dichloromethane = 1/1, v/v) afforded 5i as a red solid (217.5 mg, 60% yield). M.p.: 87−92 °C. 1H NMR (400 MHz, CDCl3): δ = 0.85−0.91 (m, 6H), 1.29−1.43 (m, 12H), 1.80−1.92 (m, 4H), 3.87 (t, J = 7.2 Hz, 2H), 4.30 (t, J = 7.4 Hz, 2H), 6.84−6.87 (m, 2H), 7.21 (d, J = 3.6 Hz, 1H), 7.28−7.30 (m, 2H), 7.39−7.51 (m, 8H), 7.69 (d, J = 4.0 Hz, 1H), 7.73 (dd, J = 2.0 Hz, 8.8 Hz, 1H), 8.14 (d, J = 7.6 Hz, 1H), 8.32 (d, J = 1.6 Hz, 1H), 9.86 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.17, 14.18, 22.7, 22.8, 26.7, 26.9, 27.1, 29.1, 31.6, 31.7, 43.4, 47.9, 109.0, 109.1, 115.5, 115.8, 117.6, 119.2, 120.6, 122.9, 123.0, 123.2, 123.4, 123.5, 124.0, 124.29, 124.33, 124.8, 125.0, 125.1, 125.6, 125.8, 126.1, 127.4, 129.8, 137.8, 140.1, 141.0, 141.1, 141.7, 143.3, 144.8, 146.0, 153.7, 182.8 ppm. HRMS (ESI+): calcd for C45H45N2OS3 [M + H]+ 725.2689, found 725.2683. 5-(7-(3,4-Ethylenedioxythiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)thiophene-2-carbaldehyde (5j). Purification by column chromatography on silica gel (petroleum ether/acetone = 5/1, v/v) afforded 5j as a red solid (146.7 mg, 55% yield). M.p.: 154 °C. 1H NMR (400 MHz, CDCl3): δ = 0.86 (t, J = 7.0 Hz, 3H), 1.27−1.31 (m, 4H), 1.38−1.42 (m, 2H), 1.75−1.83 (m, 2H), 3.82 (t, J = 7.2 Hz, 2H), 4.21−4.23 (m, 2H), 4.28−4.30 (m, 2H), 6.24(s, 1H), 6.80−6.82 (m, 2H), 7.25 (d, J = 2.0 Hz, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.39−7.46 (m, 2H), 7.48 (d, J = 2.4 Hz, 1H), 7.67 (d, J = 4.0 Hz, 1H), 9.83 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.8, 26.7, 26.8, 31.6, 47.8, 64.6, 64.9, 97.1, 115.4, 115.5, 116.4, 123.1, 123.9, 124.9. 125.0, 125.1, 125.2, 125.7, 127.3, 128.3, 137.8, 141.6, 142.3, 142.6, 146.1, 153.7, 182.8 ppm. HRMS (ESI+): calcd for C29H27NNaO3S3 [M + Na]+ 556.1045, found 556.1046. 5-(7-(3,4-Ethylenedioxythiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophene-2-carbaldehyde (5k). Purification by column chromatography on silica gel (petroleum ether/ acetone = 3/1, v/v) afforded 5k as a red solid (147.9 mg, 50% yield). M.p.: 107 °C. 1H NMR (400 MHz, CDCl3): δ = 0.88 (t, J = 6.0 Hz, 3H), 1.30−1.32 (m, 4H), 1.42−1.44 (m, 2H), 1.76−1.84 (m, 2H), 3.83 (t, J = 7.0 Hz, 2H), 4.23−4.24 (m, 2H), 4.29−4.30 (m, 2H), 4.36−4.39 (m, 4H), 6.24 (s, 1H), 6.81 (d, J = 8.8 Hz, 2H), 7.44−7.53 (m, 3H), 7.58 (s, 1H), 9.89 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 26.7, 26.8, 31.6, 47.8, 64.60, 64.63, 64.9, 65.3, 97.0, 114.9, 115.2, 115.4, 116.5, 124.0, 124.5, 124.8, 125.1, 125.7, 126.0, 126.1, 128.2, 128.5, 137.2, 137.8, 142.3, 142.7, 145.4, 179.6 ppm. HRMS (ESI+): calcd for C31H30NO5S3 [M + H]+ 592.1281, found 592.1280. 5-(10-Hexyl-7-(5-hexyl-3,4-ethylenedioxythiophen-2-yl)-10Hphenothiazin-3-yl)thiophene-2-carbaldehyde (5l). Purification by column chromatography on silica gel (petroleum ether/acetone = 5/1, v/v) afforded 5l as a red oil (188.4 mg, 61% yield). 1H NMR (400 8122


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The Journal of Organic Chemistry MHz, CDCl3): δ = 0.86−0.91 (m, 6H), 1.30−1.32 (m, 10H), 1.57− 1.65 (m, 4H), 1.77−1.84 (m, 2H), 2.62−2.66 (m, 2H), 3.84 (t, J = 7.2 Hz, 2H), 4.20−4.22 (m, 2H), 4.27−4.28 (m, 2H), 6.79−6.83 (m, 2H), 7.26−7.28 (m, 1H), 7.38−7.39 (m, 1H), 7.40−7.41 (m, 1H), 7.42− 7.43 (m, 1H), 7.457−7.463 (m, 1H), 7.69 (d, J = 4.0 Hz, 1H), 9.85 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 14.2, 22.7, 25.9, 26.7, 26.9, 29.0, 30.6, 31.6, 31.7, 47.8, 64.5, 65.0, 111.9, 115.3, 115.6, 116.4, 123.1, 123.8, 124.6, 124.8, 125.0, 125.2, 125.7, 127.2, 128.7, 137.7, 137.8, 138.0, 141.6, 142.0, 146.3, 153.8, 182.7 ppm. HRMS (ESI+): calcd for C35H40NO3S3 [M + H]+ 618.2165, found 618.2163. General Procedure for Knö venagel Condensations of 3 or 5 with Cyanoacetic Acid. In a Schlenk tube, a mixture of 3 or 5 (0.25 mmol, 1.0 equiv) and cyanoacetic acid (64 mg, 0.75 mmol. 3.0 equiv) was dissolved in CHCl3 (2 mL) and then piperidine (74 μL, 0.75 mmol, 3.0 equiv) was added. The mixture was heated to reflux under a nitrogen atmosphere and kept stirring for 6 h. Then, the mixture was cooled to room temperature and diluted by dichloromethane (20 mL). Then, HCl (1 M, 10 mL) was added and kept stirring at room temperature for 1 h. After separation of the CH2Cl2 layer, the aqueous layer was extracted with CH2Cl2 (2 × 10 mL). The combined organic phase was washed with water and brine, respectively, and dried over Na2SO4. After removal of the solvent under reduced pressure, the residue was purified by silica gel column chromatography to afford 6. 3-(5-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6a). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6a as a dark red solid (141.5 mg, 72% yield). M.p.: >280 °C. 1H NMR (400 MHz, DMSOd6): δ = 0.78 (brs, 3H), 1.19 (brs, 4H), 1.33 (brs, 2H), 1.62 (brs, 2H), 3.80 (brs, 2H), 6.93−7.07 (m, 10H), 7.27−7.53 (m, 13H), 7.70 (brs, 1H), 8.16 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.8, 22.1, 25.8, 26.1, 30.8, 46.7, 116.1, 116.2, 119.0, 123.1, 123.3, 123.38, 123.43, 123.6, 123.8, 123.9, 124.0, 124.2, 124.6, 125.4, 126.2, 127.2, 127.6, 128.5, 129.6, 135.2, 136.7, 140.6, 141.4, 141.8, 143.0, 144.6, 146.7, 146.8, 148.0, 164.1 ppm. HRMS (ESI + ): calcd for C48H40N3O2S3 [M + H]+ 786.2277, found 786.2281. Anal. Calcd for C48H39N3O2S3 (%): C, 73.35; H, 5.00; N, 5.35; S, 12.24. Found: C, 73.28; H, 5.03; N, 5.27; S, 12.31. 3-(5-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophen-2-yl)-2-cyanoacrylic Acid (6b). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6b as a dark red solid (145.6 mg, 69% yield). M.p.: 238−245 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.84−0.85 (m, 3H), 1.23−1.25 (m, 4H), 1.39−1.40 (m, 2H), 1.69−1.72 (m, 2H), 3.91 (brs, 2H), 4.44−4.46 (m, 4H), 6.98−7.12 (m, 10H), 7.31−7.64 (m, 12H), 8.13 (s, 1H) ppm. HRMS (ESI+): calcd for C50H42N3O4S3 [M + H]+ 844.2332, found 844.2326. Anal. Calcd for C50H41N3O4S3 (%): C, 71.15; H, 4.90; N, 4.98; S, 11.39. Found: C, 71.04; H, 4.91; N, 4.88; S, 11.50. 3-(5′-(7-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-10-hexyl10H-phenothiazin-3-yl)-[2,2′-bithiophen]-5-yl)-2-cyanoacrylic Acid (6c). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6c as a dark red solid (172.6 mg, 80% yield). M.p.: 266−269 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.79 (t, J = 7.0 Hz, 3H), 1.20−1.22 (m, 4H), 1.32−1.36 (m, 2H), 1.61−1.68 (m, 2H), 3.83 (t, J = 6.0 Hz, 2H), 6.94−7.07 (m, 10H), 7.28−7.34 (m, 5H), 7.39−7.45 (m, 8H), 7.53 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 4.0 Hz, 1H), 8.16 (s, 1H) ppm. 13C NMR (100 MHz, DMSOd6): δ = 13.9, 22.1, 25.8, 26.1, 30.8, 46.7, 69.8, 107.4, 116.0, 116.2, 118.8, 123.1, 123.4, 123.5, 123.6, 124.0, 124.2, 124.36, 124.41, 124.5, 124.9, 126.2, 127.1, 127.5, 127.6, 128.3, 129.6, 133.9, 135.3, 137.1, 140.6, 141.8, 142.0, 143.2, 143.9, 146.7, 146.8 ppm. HRMS (ESI+): calcd for C52H42N3O2S4 [M + H]+ 868.2154, found 868.2154. Anal. Calcd for C52H41N3O2S4 (%): C, 71.94; H, 4.76; N, 4.84; S, 14.77. Found: C, 71.88; H, 4.78; N, 4.72; S, 14.82. 3-(5-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6d). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6d as a dark red solid (132.7 mg, 75% yield). M.p.: 266−270 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.83 (t, J = 7.0 Hz,

3H), 1.22−1.26 (m, 4H), 1.37−1.44 (m, 2H), 1.67−1.74 (m, 2H), 3.92 (t, J = 6.8 Hz, 2H), 7.08−7.11 (m, 2H), 7.31−7.35 (m, 2H), 7.38 (d, J = 3.6 Hz, 1H), 7.46−7.54 (m, 6H), 7.57−7.60 (m, 3H), 7.68 (d, J = 4.4 Hz, 1H), 7.94 (d, J = 4.0 Hz, 1H), 8.23 (d, J = 7.6 Hz, 2H), 8.42 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.8, 26.1, 30.8, 46.9, 110.2, 116.4, 116.5, 116.9, 120.6, 121.0, 122.3, 123.0, 123.5, 123.7, 123.8, 124.42, 124.44, 125.1, 126.1, 126.6, 126.8, 126.9, 128.3, 134.0, 136.0, 140.5, 141.1, 141.2, 143.4, 145.3, 163.7 pm. HRMS (ESI+): calcd for C42H34N3O2S3 [M + H]+ 708.1808, found 708.1801. Anal. Calcd for C42H33N3O2S3 (%): C, 71.26; H, 4.70; N, 5.94; S, 13.59. Found: C, 71.21; H, 4.72; N, 5.82; S, 13.68. 3-(5-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophen-2-yl)-2-cyanoacrylic Acid (6e). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6e as a dark red solid (160.8 mg, 84% yield). M.p.: 235−240 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.82−0.85 (m, 3H), 1.22−1.27 (m, 4H), 1.37−1.42 (m, 2H), 1.68−1.73 (m, 2H), 3.91 (t, J = 6.2 Hz, 2H), 4.44−4.50 (m, 4H), 7.08−7.12 (m, 2H), 7.32−7.35 (m, 2H), 7.38−7.39 (m, 1H), 7.46− 7.60 (m, 9H), 8.18 (s, 1H), 8.24 (d, J = 8.0 Hz, 2H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.7, 26.0, 30.8, 46.8, 64.8, 65.6, 108.2, 110.1, 112.4, 116.2, 116.4, 117.4, 120.6, 120.9, 122.2, 122.9, 123.2, 123.4, 123.7, 124.6, 125.0, 125.5, 126.2, 126.5, 126.7, 128.2, 136.0, 137.8, 140.4, 141.0, 143.4, 144.6, 164.0 ppm. HRMS (ESI+): calcd for C44H36N3O4S3 [M + H]+ 766.1862, found 766.1856. Anal. Calcd for C44H35N3O4S3 (%): C, 69.00; H, 4.61; N, 5.49; S, 12.56. Found: C, 68.92; H, 4.72; N, 5.38; S, 12.63. 3-(5′-(7-(5-(9H-Carbazol-9-yl)thiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophen]-5-yl)-2-cyanoacrylic Acid (6f). Purification by column chromatography on silica gel (dichloromethane/ methanol = 20/1, v/v) afforded 6f as a dark red solid (156.0 mg, 79% yield). M.p.: 254−260 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.79 (t, J = 7.0 Hz, 3H), 1.18−1.23 (m, 4H), 1.31−1.36 (m, 2H), 1.61− 1.68 (m, 2H), 3.83 (t, J = 6.0 Hz, 2H), 6.95−7.00 (m, 2H), 7.29−7.34 (m, 3H), 7.41−7.50 (m, 11H), 7.54 (d, J = 4.0 Hz, 1H), 7.70 (d, J = 4.0 Hz, 1H), 8.18−8.22 (m, 3H) ppm. 13C NMR (100 MHz, DMSOd6): δ = 13.9, 22.1, 25.8, 26.1, 30.8, 46.7, 69.8, 110.1, 116.1, 116.2, 118.7, 120.6, 120.9, 122.1, 122.9, 123.63, 123.64, 124.38, 124.45, 124.9, 126.4, 126.7, 127.2, 127.5, 128.0, 133.9, 135.1, 135.8, 137.5, 140.5, 141.0, 141.8, 142.3, 143.3, 143.7, 143.9, 163.81, 163.83 ppm. HRMS (ESI+): calcd for C46H36N3O2S4 [M + H]+ 790.1685, found 790.1691. Anal. Calcd for C46H35N3O2S4 (%): C, 69.93; H, 4.47; N, 5.32; S, 16.23. Found: C, 69.98; H, 4.49; N, 5.24; S, 16.31. 3-(5-(7-(5-(9H-Carbazol-9-yl)-3,4-ethylenedioxythiophen-2-yl)10-hexyl-10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6g). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6g as a dark red solid (158.9 mg, 83% yield). M.p.: 225−230 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.80 (brs, 3H), 1.22 (brs, 4H), 1.36 (brs, 2H), 1.66 (brs, 2H), 3.84 (brs, 2H), 4.29 (brs, 2H), 4.43 (brs, 2H), 7.00−7.03 (m, 2H), 7.28− 7.31 (m, 2H), 7.40−7.52 (m, 8H), 7.63 (brs, 1H), 7.93 (brs, 1H), 8.19 (d, J = 8.0 Hz, 2H), 8.43 (s, 1H) ppm. 13C NMR (100 MHz, DMSOd6): δ = 13.9, 22.1, 25.8, 26.1, 30.8, 46.8, 64.6, 65.0, 97.8, 108.9, 110.5, 112.6, 116.2, 116.3, 116.7, 120.5, 120.8, 122.99, 123.01, 123.6, 124.0, 124.3, 124.4, 125.2, 126.0, 126.5, 126.7, 127.0, 133.8, 137.3, 138.1, 140.9, 141.5, 142.4, 145.3, 146.5, 152.0, 163.8 ppm. HRMS (ESI+): calcd for C44H36N3O4S3 [M + H]+ 766.1862, found 766.1870. Anal. Calcd for C44H35N3O4S3 (%): C, 69.00; H, 4.61; N, 5.49; S, 12.56. Found: C, 68.95; H, 4.66; N, 5.44; S, 12.67. 3-(5-(7-(5-(9H-Carbazol-9-yl)-3,4-ethylenedioxythiophen-2-yl)10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophen-2-yl)2-cyanoacrylic Acid (6h). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6h as a dark red solid (166.8 mg, 81% yield). M.p.: 195−200 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.82 (t, J = 7.2 Hz, 3H), 1.23−1.26 (m, 4H), 1.34−1.41 (m, 2H), 1.64−1.71 (m, 2H), 3.86 (t, J = 7.0 Hz, 2H), 4.29−4.30 (m, 2H), 4.43−4.48 (m, 6H), 7.05 (d, J = 8.8 Hz, 2H), 7.28−7.32 (m, 2H), 7.42−7.54 (m, 8H), 8.17−8.21 (m, 3H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.2, 25.8, 26.1, 30.9, 46.8, 64.6, 64.8, 65.0, 65.7, 108.2, 108.9, 110.5, 112.6, 116.0, 116.3, 117.3, 8123


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7.68 (brs, 1H), 7.96 (brs, 1H), 8.46 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.8, 26.1, 30.8, 46.7, 97.8, 116.1, 116.2, 116.7, 122.5, 123.0, 124.28, 124.34, 124.4, 125.9, 126.6, 127.2, 127.9, 133.8, 141.6, 143.8, 145.8, 146.5, 152.1, 163.8 ppm. HRMS (ESI+): calcd for C26H25N2O2S2 [M + H]+ 461.1352, found 461.1357. Anal. Calcd for C26H24N2O2S2 (%): C, 67.80; H, 5.25; N, 6.08; S, 13.92. Found: C, 67.69; H, 5.35; N, 5.99; S, 14.04. 3-(5′-(10-Hexyl-10H-phenothiazin-3-yl)-[2,2′-bithiophen]-5-yl)-2cyanoacrylic Acid (6n). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6n as a dark red solid (103.1 mg, 76% yield). M.p.: 200−212 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.81 (t, J = 7.0 Hz, 3H), 1.22−1.25 (m, 4H), 1.35−1.39 (m, 2H), 1.63−1.68 (m, 2H), 3.86 (t, J = 7.0 Hz, 2H), 6.93−6.97 (m, 1H), 7.00−7.02 (m, 2H), 7.14−7.16 (m, 1H), 7.18− 7.22 (m, 1H), 7.47−7.51 (m, 3H), 7.54 (d, J = 4.0 Hz, 1H), 7.57−7.58 (m, 1H), 7.94 (d, J = 4.4 Hz, 1H), 8.45 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.8, 26.2, 30.8, 46.6, 116.0, 116.1, 116.8, 122.8, 123.7, 124.4, 124.6, 124.8, 125.0, 127.18, 127.23, 127.8, 128.3, 133.3, 133.8, 144.1, 144.5, 144.8, 145.6, 163.7 ppm. HRMS (ESI+): calcd for C30H27N2O2S3 [M + H]+ 543.1229, found 543.1221. Anal. Calcd for C30H26N2O2S3 (%): C, 66.39; H, 4.83; N, 5.16; S, 17.72. Found: C, 66.30; H, 4.88; N, 5.05; S, 17.64. Measurement of CV Curves. In consideration of the solubility of dyes, we used DMSO instead of DCM as solvent for measurement of CV curves. Cyclic voltammetry (CV) was measured in DMSO with 0.1 M tetra-n-butylammonium hexafluorophosphate (TBAPF6) as a supporting electrolyte (scanning rate, 50 mV s−1; counter electrode, a platinum wire; working electrode, a platinum plate; reference electrode, Ag/Ag+ (0.01 M AgNO3 in acetonitrile)) and ferrocene/ ferricenium (Fc+/Fc) as an external standard at 0.63 V (vs NHE).29 The value of the ground oxidation potential was calculated according to Eox (vs NHE) = Eox + 0.63 V. Fabrication of DSSC Devices. Dyes 6a−6n (0.01 mmol) were dissolved in a mixture of CH2Cl2/THF (9/1, 20 mL) and kept stirring for 1 h at room temperature. After fitration of the mixture by a microporous filtering film, the TiO2 photoanode (0.4 cm × 0.4 cm) was immersed in the dye solution for 12 h and then rinsed with CH2Cl2/THF (9/1) and dried by air flow. The TiO2 photoanode was clipped onto the Pt-counter electrode with a small gap caused by a 30 μm parafilm (Sigma-Aldrich) between these two electrodes. The I−/ I3− electrolyte (1.0 M DMPII, 0.1 M LiI, 0.05 M I2, 0.5 M TBP in CH3CN) was then syringed into the gap between these two electrodes.

120.5, 120.8, 122.9, 123.0, 123.1, 124.0, 124.6, 125.2, 125.8, 126.6, 127.0, 137.3, 137.8, 138.1, 140.9, 142.4, 144.7, 149.3, 164.2 ppm. HRMS (ESI+): calcd for C46H38N3O6S3 [M + H]+ 824.1917, found 824.1908. Anal. Calcd for C46H37N3O6S3 (%): C, 67.05; H, 4.53; N, 5.10; S, 11.67. Found: C, 66.98; H, 4.62; N, 5.03; S, 11.78. 3-(5-(10-Hexyl-7-(5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6i). Purification by column chromatography on silica gel (dichloromethane/ methanol = 10/1, v/v) afforded 6i as a dark red solid (162.6 mg, 82% yield). M.p.: 167−175 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.77−0.82 (m, 6H), 1.18−1.38 (m, 12H), 1.67−1.76 (m, 4H), 3.87− 3.90 (m, 2H), 4.36−4.39 (m, 2H), 7.03−7.06 (m, 1H), 7.20−7.24 (m, 1H), 7.45−7.49 (m, 4H), 7.54−7.67 (m, 5H), 7.72−8.05 (m, 4H), 8.22−8.26 (m, 1H), 8.35−8.38 (m, 1H), 8.42−8.52 (m, 1H) ppm. HRMS (ESI+): calcd for C48H45N3NaO2S3 [M + Na]+ 814.2566, found 814.2572. Anal. Calcd for C48H45N3O2S3 (%): C, 72.79; H, 5.73; N, 5.31; S, 12.14. Found: C, 72.68; H, 5.80; N, 5.25; S, 12.23. 3-(5-(7-(3,4-Ethylenedioxythiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6j). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6j as a dark red solid (118.6 mg, 79% yield). M.p.: >280 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.79−0.82 (m, 3H), 1.22−1.23 (m, 4H), 1.35−1.36 (m, 2H), 1.64−1.68 (m, 2H), 3.85 (brs, 2H), 4.23−4.31 (m, 4H), 6.55 (s, 1H), 7.00−7.02 (m, 2H), 7.40−7.42 (m, 2H), 7.50−7.52 (m, 2H), 7.59−7.60 (m, 1H), 7.80− 7.81 (m, 1H), 8.26 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.8, 26.1, 30.9, 46.7, 64.2, 64.8, 97.4, 114.8, 116.1, 116.2, 118.2, 122.9, 123.6, 123.7, 124.0, 124.2, 124.8, 125.7, 127.0, 127.7, 134.7, 138.0, 138.7, 142.1, 142.2, 143.3, 145.0, 149.5, 163.9 ppm. HRMS (ESI+): calcd for C32H29N2O4S3 [M + H]+ 601.1284, found 601.1296. Anal. Calcd for C32H28N2O4S3 (%): C, 63.98; H, 4.70; N, 4.66; S, 16.01. Found: C, 63.89; H, 4.77; N, 4.54; S, 16.23. 3-(5-(7-(3,4-Ethylenedioxythiophen-2-yl)-10-hexyl-10H-phenothiazin-3-yl)-3,4-ethylenedioxythiophen-2-yl)-2-cyanoacrylic Acid (6k). Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6k as a dark red solid (128.5 mg, 78% yield). M.p.: 252−254 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.81 (t, J = 6.6 Hz, 3H), 1.22−1.23 (m, 4H), 1.34−1.35 (m, 2H), 1.64−1.67 (m, 2H), 3.82 (brs, 2H), 4.226−4.234 (m, 2H), 4.30−4.31 (m, 2H), 4.42−4.45 (m, 4H), 6.55 (s, 1H), 7.00 (t, J = 8.4 Hz, 2H), 7.39−7.42 (m, 2H), 7.47−7.50 (m, 2H), 8.15 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 22.1, 25.8, 26.0, 30.8, 46.7, 64.2, 64.8, 65.4, 69.8, 97.4, 108.5, 114.8, 115.9, 116.1, 118.3, 122.8, 123.1, 123.5, 124.4, 124.7, 125.6, 125.9, 127.7, 137.6, 138.0, 142.0, 142.2, 144.4, 147.8 ppm. HRMS (ESI+): calcd for C34H30N2NaO6S3 [M + Na]+ 681.1158, found 681.1158. Anal. Calcd for C34H30N2O6S3 (%): C, 61.99; H, 4.59; N, 4.25; S, 14.60. Found: C, 61.89; H, 4.58; N, 4.13; S, 14.69. 3-(5-(10-Hexyl-7-(5-hexyl-3,4-ethylenedioxythiophen-2-yl)-10Hphenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6l). Purification by column chromatography on silica gel (dichloromethane/ methanol = 20/1, v/v) afforded 6l as a dark red solid (137.0 mg, 80% yield). 1H NMR (400 MHz, DMSO-d6): δ = 0.79−0.86 (m, 6H), 1.21−1.30 (m, 12H), 1.48−1.52 (m, 2H), 1.63−1.68 (m, 2H), 2.57 (t, J = 7.6 Hz, 2H), 3.85 (t, J = 6.6 Hz, 2H), 4.21−4.29 (m, 4H), 6.98− 7.04 (m, 2H), 7.35−7.37 (m, 2H), 7.51−7.55 (m, 2H), 7.64 (d, J = 4.0 Hz, 1H), 7.92 (d, J = 4.4 Hz, 1H), 8.39 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = 13.9, 14.0, 22.09, 22.12, 25.2, 25.8, 26.1, 28.2, 29.9, 30.8, 31.0, 46.7, 64.2, 64.9, 110.6, 114.96, 114.97, 116.1, 116.2, 117.0, 122.8, 123.3, 123.7, 124.2, 126.7, 128.0, 134.0, 137.9, 138.2, 141.5, 145.4, 151.5, 163.8 ppm. HRMS (ESI + ): calcd for C38H41N2O4S3 [M + H]+ 685.2223, found 685.2225. Anal. Calcd for C38H40N2O4S3 (%): C, 66.64; H, 5.89; N, 4.09; S, 14.04. Found: C, 66.52; H, 5.99; N, 4.01; S, 13.98. 3-(5-(10-Hexyl-10H-phenothiazin-3-yl)thiophen-2-yl)-2-cyanoacrylic Acid (6m).15 Purification by column chromatography on silica gel (dichloromethane/methanol = 20/1, v/v) afforded 6m as a dark red solid (93.3 mg, 81% yield). M.p.: 160−165 °C. 1H NMR (400 MHz, DMSO-d6): δ = 0.81 (brs, 3H), 1.23 (brs, 4H), 1.37 (brs, 2H), 1.66 (brs, 2H), 3.87 (brs, 2H), 6.96−7.21 (m, 5H), 7.55 (brs, 2H),

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b00915. Cyclic voltammograms of organic dyes (6a−6n), optimization of DSSC fabrication, and copies of 1H NMR and 13C NMR spectra of key intermediates and final products (PDF)

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AUTHOR INFORMATION

Corresponding Authors

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

Jingbo Lan: 0000-0001-5937-0987 Jingsong You: 0000-0002-0493-2388 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by grants from the National NSF of China (Nos. 21672154, 21432005, and 21772133) and 8124


Article


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Comprehensive Training Platform of Specialized Laboratory, College of Chemistry, Sichuan University.

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