New 2,3-diphenylquinoxaline containing organic D-A-π-A dyes with nickel oxide photocathode prepared by surfactant-mediated synthesis for high performance p-type dye-sensitized solar cells

Article abstract of DOI:10.1016/j.dyepig.2018.12.042

Dye-sensitized solar cells (DSSCs) are one of the most promising organic photovoltaics. The optimized efficiency of a tandem cell combined with both n- and p-type DSSCs was theoretically predicted to be 43%. The bottleneck for reaching the optimized performance is limited by the p-type half-cell, particularly the lacking of an appropriate semiconducting material as the photocathode. In this regard, we report the surfactant-mediated synthesis of nickel oxide nanomaterial using a chemical co-precipitation method. The new material was fully characterized by XRD, SEM, XPS, EDS, and BET. The BET result indicates the nickel oxide nanoparticles synthesized with surfactant attain higher surface area than the conventional one. In addition, the new organic dyes with electron-deficient diphenylquinoxaline incorporated within the molecular structure were prepared for p-type dye-sensitized solar cells with the newly prepared NiO as the photocathode. The new organic dyes consist of carboxylic acid as the anchoring group, triphenylamine as the electron donor, 2,3-diphenylquinoxaline as the auxiliary acceptor moiety, 2-methylenemalononitrile as electron acceptor, connected with thiophene, 3,4-ethylenedioxythiophene, and 2,2′-bithiophene as the π-spacer. Sensitizers with mono-anchoring group (EH166, EH122, and EH174) performed better than their corresponding double-anchoring sensitizers (EH162, EH126, and EH170). Among these, dye EH174 exhibited the best conversion efficiency up to 0.207% with a short-circuit photocurrent density of 4.84 mAcm^?2, an open-circuit photovoltage of 137 mV, and a fill factor of 0.312. The current results indicate that the combination of electron-deficient quinoxaline motif with suitable π-linker in a D-A-π-A molecular structure is a promising design of p-type sensitizers for NiO-based p-DSSCs.

Full text of DOI:10.1016/j.dyepig.2018.12.042

Accepted Manuscript
New 2,3-diphenylquinoxaline containing organic D-A-π-A dyes with nickel oxide
photocathode prepared by surfactant-mediated synthesis for high performance p-type
dye-sensitized solar cells
Hulugirgesh Degefu Weldekirstos, Ming-Chung Kuo, Sie-Rong Li, Wei-Lin Su,
Mekonnen Abebayehu Desta, Wen-Ti Wu, Chun-Hong Kuo, Shih-Sheng Sun
PII:
S0143-7208(18)32144-2
https://doi.org/10.1016/j.dyepig.2018.12.042
DYPI 7247
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 27 September 2018
Revised Date: 12 November 2018
Accepted Date: 19 December 2018
Please cite this article as: Weldekirstos HD, Kuo M-C, Li S-R, Su W-L, Desta MA, Wu W-T, Kuo C-H,
Sun S-S, New 2,3-diphenylquinoxaline containing organic D-A-π-A dyes with nickel oxide photocathode
prepared by surfactant-mediated synthesis for high performance p-type dye-sensitized solar cells, Dyes
and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2018.12.042.
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ACCEPTED MANUSCRIPT
New 2,3-Diphenylquinoxaline Containing Organic D-A-π-A Dyes with
Nickel Oxide Photocathode Prepared by Surfactant-Mediated Synthesis
for High Performance p-type Dye-Sensitized Solar Cells
a, b,c
a
a
a
Hulugirgesh Degefu Weldekirstos,
Ming-Chung Kuo,
Sie-Rong Li, Wei-Lin Su,
a
a
a
a
Mekonnen Abebayehu Desta, Wen-Ti Wu, Chun-Hong Kuo,* and Shih-Sheng Sun*
a
Institute of Chemistry, Academia Sinica, Taipei, 115, Taiwan, R.O.C
b
Molecular Science and Technology, Taiwan International Graduate Program, Taipei, 10617,
Taiwan, R.O.C
c
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan, R.O.C
Corresponding Authors Emails: sssun@chem.sinica.edu.tw (S.-S. Sun),
chunhong@gate.sinica.edu.tw (C.-H. Kuo)
ABSTRACT
Dye-sensitized solar cells (DSSCs) are one of the most promising organic photovoltaics. The
optimized efficiency of a tandem cell combined with both n- and p-type DSSCs was theoretically
predicted to be 43%. The bottleneck for reaching the optimized performance is limited by the p-
type half-cell, particularly the lacking of an appropriate semiconducting material as the
photocathode. In this regard, we report the surfactant-mediated synthesis of nickel oxide
nanomaterial using a chemical co-precipitation method. The new material was fully
characterized by XRD, SEM, XPS, EDS, and BET. The BET result indicates the nickel oxide
nanoparticles synthesized with surfactant attain higher surface area than the conventional one. In
addition, the new organic dyes with electron-deficient diphenylquinoxaline incorporated within
the molecular structure were prepared for p-type dye-sensitized solar cells with the newly
prepared NiO as the photocathode. The new organic dyes consist of carboxylic acid as the
anchoring group, triphenylamine as the electron donor, 2,3-diphenylquinoxaline as the auxiliary
acceptor moiety, 2-methylenemalononitrile as electron acceptor, connected with thiophene, 3,4-
ethylenedioxythiophene, and 2,2'-bithiophene as the π-spacer. Sensitizers with mono-anchoring
1

ACCEPTED MANUSCRIPT
group (EH166, EH122, and EH174) performed better than their corresponding double-anchoring
sensitizers (EH162, EH126, and EH170). Among these, dye EH174 exhibited the best
-2
conversion efficiency up to 0.207% with a short-circuit photocurrent density of 4.84 mAcm , an
open-circuit photovoltage of 137 mV, and a fill factor of 0.312. The current results indicate that
the combination of electron-deficient quinoxaline motif with suitable π-linker in a D-A-π-A
molecular structure is a promising design of p-type sensitizers for NiO-based p-DSSCs.
Graphic abstract:
Keywords: surfactant, nickel oxide, quinoxaline, p-type sensitizers, p-type dye-sensitized solar
cells
1
. Introduction
Solar energy is largely abundant, exceeding our current global annual energy needs. The
total solar energy absorbed by earth's atmosphere, oceans and land masses is approximately 3.85
2
4
×
10 joules per year[1]. Radical improvements in device manufacture led to a remarkable
increase in solar energy conversion efficiencies and significant price cuts [2]. The dye-sensitized
solar cell (DSSC) is one type of organic photovoltaics mimicking the process of natural
photosynthesis [3]. Up to date, the majority of the research efforts on DSSCs has been focused
on the development of n-type DSSCs (n-DSSCs) with the highest efficiency up to 14% [4, 5].
The interest in studying p-type DSSCs (p-DSSCs) [6] as an important component for the
construction of tandem DSSCs (t-DSSCs) with n-DSSCs and for potential solar fuel with dye-
2

ACCEPTED MANUSCRIPT
sensitized photoelectrochemcial cells has been a focus recently[7-9]. Theoretical prediction for
the t-DSSC is projected to 43% when all components in the cell are optimized [10].
Compared to n-DSSCs, nevertheless, much less studies have been reported on the
sensitization of p-DSSCs with wide band gap p-type semiconductors [11]. The highest efficiency
of p-DSSC with iodide/triiodide based redox electrolyte is 0.61% using the sensitizer, TPA-6T-
PMI (triphenylamine-sexithiophene-perylene monoimide), with a push-pull structural design
[12]. The efficiency of TPA-6T-PMI sensitized p-DSSC was boosted to 1.3% with the cobalt
based redox mediator and registered the highest open circuit voltage of 709 mV[13]. Recently,
the efficiency of p-DSSC was further raised to a record high of 2.51% for the same sensitizer via
iron based redox mediator[14]. The best efficiency for pn t-DSSC achieved 4.1% with a TiO2
photoanode sensitized by dye D35 and a NiO photocathode sensitized by a diketopyrrolopyrrole
dye [15].
The most commonly used photocathode material for p-DSSCs is NiO, which possesses a
wide band gap of 3.5 eV with excellent chemical and thermal stability. However, NiO suffers
significant drawbacks as the photocathode because of 1) small energy gap between the valence
-
-
band of NiO and commonly used I /I redox couple that results in low photovoltage and 2)
3
limited thickness due to the weak mechanical strength of NiO that reduces the amount of dye
loading and lowers down the light harvesting ability, and 3) low intrinsic conductivity of NiO
that slows down the hole mobility and reduces the charge collection efficiency and fill factor. In
order to boost p-DSSCs with better performance, investigations have been carried out on both
novel p-type semiconductors and light harvesting dyes[16-20]. The criteria for appropriate p-type
semiconductors include good hole collection efficiency and better mechanical strength in
comparison with conventional NiO [21-28]. The strategy of designing p-type photosensitizers
aims at superior light harvesting efficiency, suitable energy level alignment with both the valence
band of p-type semiconductor and the redox potential of redox mediator, and effective charge
separation to suppress charge recombination[29-36].
Hole transport in the mesoporous film is one of the limiting factors to the performance of
p-DSSCs, pointing out the need to improve the hole conductivity of the nickel oxide based
electrode[37]. As yet, the efficiency of p-type system is limited by the intrinsically low open
circuit potential caused by the small difference in potential between the quasi-Fermi level in the
3

ACCEPTED MANUSCRIPT
semiconductor and the electrochemical potential of the redox mediator [38]. In addition, low
photocurrent density due to fast charge recombination between the reduced dye and the holes
generated in the nickel oxide as well as the low light-harvesting efficiency (LHE) resulting from
the limited dye loading on the nickel oxide film all lead to low efficiencies [39-42].
In this work, we report the synthesis of dodecyltrimethylamonium bromide (DTAB)
mediated nickel oxide with a uniform particle size and excellent morphology for photocathode
material of p-DSSCs. Six new organic p-type sensitizers with a D–A–
prepared with triphenylamine (TPA) as a donor, an electron deficient 2,3-diphenylquinoxaline as
the auxiliary acceptor, various thiophene derivatives as the -linkers, methylene malonitrile as
π–A framework were
π
the electron acceptor, and carboxylic acid as the anchoring group. The molecular structures of
these dyes are shown in Fig 1. Organic dyes with electron-deficient quinoxaline incorporated
within a D–A–
π–A framework have been widely employed as photosensitizers for n-DSSCs [43-
4
9]. Our findings here along with the literature report confirm that quinoxaline unit could also be
an effective auxiliary acceptor for p-DSSCs [50].
NC
NC
NC
NC
NC
S
NC
O
S
S
S
O
N
N
N
N
N
N
HO
O
HO
O
HO
O
N
N
N
N
N
N
NC
N
S
NC
N
S
NC
N
S
CN
CN
S
CN
O
CN
O
EH122
EH166
EH174
O
O
O
NC
HO
HO
HO
HO
NC
CN
NC
CN
S
S
S
S
N
N
N
O
N
N
N
N
O
N
N
HO
HO
O
O
O
EH126
EH162
EH170
Fig. 1: Molecular structures of p-type sensitizers EH122, EH126, EH162, EH166, EH170 and
EH174
4

ACCEPTED MANUSCRIPT
2
. Experimental Section
.1 Materials and Characterization Methods
2
All reagents are commercially available unless otherwise noticed. Powder X-Ray
diffraction patterns were recorded 2 in the range of 20-90º using a Brüker D8 Advance
θ
diffractometer (Cu Ka, 40 kV, 40 mA). Morphology of nanoparticle and surface of the thin film
analysis done by field-emission scanning electron microscope with model (ULTRA PLUS, a
member of Carl Zeiss). The Brunauere-Emmete-Teller (BET) specific surface area
measurements were carried out with a micrometrics ASAP 2020 surface area and porosity
analyzer instrument using N as gas analyzer. Elemental analysis was done using energy
2
dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). Work
function measurements were done on an AC-2 model photoelectron spectrometer (Riken Keiki).
The film thickness of each working electrodes were measured by surface profilometer-Dectack
5
0. Photocurrent–voltage characteristics of p-type solar cell devices were measured by using a
-2
LSQE-IV Class AAA solar simulator (SAN-EL Electric Co.) at a light intensity of 100 mWcm
and calibrated by using an Oriel reference solar cell (Oriel 91150, New port S). Intensity-
modulated photovoltage spectroscopy (IMVS) was carried out by using an electrochemical
workstation (Zahner, Zennium) equipped with a frequency-response analyzer under an intensity-
-
2
modulated (10 to 300 Wm ) white-light-emitting diode. The frequency range was set from 1
kHz to 100 mHz. Cyclic voltammetry experiments were performed using a CH Instruments
electro-chemical workstation (model 660A). The experiments were carried out under N2
atmosphere in DMF solution containing 0.1 M tetrabutylammonium hexafluorophosphate (n-
Bu NPF ) as a supporting electrolyte at a scan rate of 100 mV/s. The potentials are quoted
4
6
against the ferrocene standard. UV-visible absorption spectroscopy measurements were carried
out using Varian Cary 300 type UV-Vis spectrophotometer.
2
.2 Surfactant mediated synthesis of nickel oxide
The surfactant mediated synthesis of nickel oxide was carried out according to the
following procedure. The hexahydrate nickel(II) chloride (1 g) and DTAB (1 g) were dispersed
and stirred in 40 mL of deionized (DI) water at room temperature. Subsequently, a sodium
5

ACCEPTED MANUSCRIPT
hydroxide solution (0.94 g in 40 mL DI water) was added slowly to the nickel(II) chloride
solution [42]. The combined solution was kept for 1 h with constant stirring before being
centrifuged and washed with DI water to purify from spectator ions. The residue was dried at 90
°
2
C to remove the solvent and produced the green nickel hydroxide (Ni(OH) ). The thus obtained
nickel hydroxide was calcined at 350 °C for 2 h to yield the desired NiO.
2
.2 Synthesis of organic compounds
The synthetic procedures for precursors and sensitizers are depicted in Scheme S1-S3 in
Supporting Information. Compounds
according to the literature procedures.
7 [51], Q [52], 5 [53], TPA2 [54] were synthesized
2
.2.1 5'-(8-bromo-2,3-diphenylquinoxalin-5-yl)-[2,2’-bithiophene]-5-carbaldehyde (Q-BT)
A mixture in a 250-mL flask containing compound
7 (1.00 g, 4.76 mmol), compound Q
(
4.19 g, 9.52 mmol), Pd(PPh ) Cl (0.17 g, 0.24 mmol), Na CO (1.77 g, 16.66 mmol) and 100
3
2
2
2
3
mL THF/H O mixed solvent (v/v = 4/1) was refluxed for 8 h. The solvent was evaporated and
2
the residue was extracted with DCM and water. The organic layer was collected and dried over
MgSO . Solvent evaporation afforded the crude compound 8, which was dissolved in 7 mL
4
DMF. To this DMF mixture was dropwisely added POCl (6.6 mL) in an ice bath. The mixture
3
was heated to reflux for 8 h and cooled to room temperature. The solution was neutralized by an
aqueous NaHCO in an ice bath followed by extraction with DCM/H O. The organic layer was
3
2
collected and dried over MgSO
4
. The desired product Q-BT was obtained by column
1
chromatography flashed with EA/hexane (1/5) as a red solid (1.87 g, 71%). H NMR (400 MHz,
CDCl
Hz, 1H), 7.74-7.69 (m, 5H), 7.47-7.36 (m, 7H), 7.32 (d,
CDCl , ppm): = 182.5, 153.5, 152.7, 147.5, 141.7, 139.5, 139.2, 138.8, 138.2, 138.0, 137.51,
37.48, 133.1, 131.7, 130.5, 130.3, 129.5, 128.39, 128.35, 127.5, 126.8, 125.7, 124.0, 123.3.
3
, ppm):
δ
= 9.89 (s, 1H), 8.08 (d,
J
= 8.0 Hz, 1H), 8.01 (d,
J = 8.0 Hz, 1H), 7.85 (d, J = 4.0
1
3
J
= 4.0 Hz, 1H). C NMR (125 MHz,
δ
3
1
+
HRMS (FAB) m/z: calcd for C H BrN OS : 553.0044; [M+H] found: 553.0046.
2
9
18
2
2
2
.2.2 7-(8-bromo-2,3-diphenylquinoxalin-5-yl)-2,3-dihydrothieno[3,4b][1,4]dioxine-5-
carbaldehyde (Q-EDOT)
A mixture in a 250-mL flask containing compound
5
(1.00 g, 5.88 mmol), compound
Q
(5.17 g, 11.75 mmol), Pd(OAc)
2
(0.21 g, 0.94 mmol), Na
2 3
CO (2.18 g, 20.57 mmol) and 100 mL
6

ACCEPTED MANUSCRIPT
DMF solvent was refluxed for 8 h. The solvent was evaporated and the residue was extracted
with DCM and water. The organic layer was collected and dried over MgSO . The desired
4
product Q-EDOT was obtained by column chromatography flashed with EA/hexane (1/5) as a
1
red solid (1.40 g, 45%). H NMR (400 MHz, CDCl
3
, ppm):
δ
= 10.01 (s, 1H), 8.49 (d,
J
= 8.0
1
3
Hz, 1H), 8.08 (d,
J
= 8.4 Hz, 1H), 7.72-7.67 (m, 4H), 7.42-7.34 (m, 6H), 4.46 (s, 4H). C NMR
(125 MHz, CDCl
3
, ppm): =180.6, 153.4, 152.7, 147.6, 140.0, 138.5, 138.2, 137.8, 132.9, 130.5,
δ
1
30.3, 129.9, 129.6, 129.5, 129.4, 128.4, 128.3, 123.9, 123.0, 119.9, 64.9, 64.8. HRMS (FAB)
+
m/z: calcd for C H BrN O S: 529.0222; [M+H] found: 529.0233.
2
7
18
2
3
2
.2.3 Methyl 4-(bis(4-bromophenyl)amino)benzoate (12)
To a 250-mL flask containing compound 11 (1.00 g, 2.24 mmol) was added 100 mL of
2 4
methanol and 2 mL H SO . The solution was heated to reflux for 8 h before being cooled to
room temperature. The mixture was extracted with water/DCM. The organic layer was collected
and dried over MgSO
4
. A white solid of 12 (1.02 g, 99%) was obtained after solvent evaporation.
= 7.88 (d, = 8.4 Hz, 2H), 7.41 (d, = 8.4 Hz, 4H), 7.00-
.97 (m, 6H), 3.88 (s, 3H). C NMR (125 MHz, CDCl , ppm): = 166.8, 151.2, 145.6, 132.9,
1
H NMR (400 MHz, CDCl , ppm):
δ
J
J
3
1
3
6
1
δ
3
31.2, 127.0, 123.6, 121.1, 117.5, 52.1. HRMS (FAB) m/z: calcd for C20
H15Br
2
NO2: 458.9470;
+
M found: 458.9481.
2
.2.4 Dimethyl4,4’-((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)
azanediyl)
benzoate (TPA1)
To a 250-mL flask containing compound 12 (1.26 g, 2.73 mmol), bis(pinacolato)diboron
1.46 g, 5.74 mmol), Pd(dppf)Cl (0.20 g, 0.27 mmol), and KOAc (0.67 g, 6.83 mmol) was
(
2
added 60 mL of 1,4-dioxane. The mixture was heated to reflux under nitrogen atmosphere for 12
h. After cooling to room temperature, the mixture was extracted with water/DCM. The organic
layer was collected and dried over MgSO . The desired product of TPA1 was obtained as a
4
1
white solid (0.80 g, 53%) by column chromatography eluted with EA/hexane (1/20). H NMR
(
400 MHz, CDCl
3
, ppm):
δ
= 7.87 (d,
J
= 8.8 Hz, 2H), 7.72 (d,
J
= 8.4 Hz, 4H), 7.11-7.04 (m,
= 166.9, 151.5,
1
3
6
H), 3.88 (s, 3H), 1.34 (s, 24H). C NMR (125 MHz, CDCl , ppm):
δ
3
7

ACCEPTED MANUSCRIPT
1
49.4,136.3, 131.0, 124.4, 123.7,122.3, 83.9, 60.5, 52.0, 25.0. HRMS (FAB) m/z: calcd for
+
C H B NO 555.2963; M found: 555.2970.
32
39
2
6:
2
.2.5 Methyl 4-(bis(4-(8-(5-formylthiophen-2-yl)-2,3-diphenylquinoxalin-5-yl)phenyl)amino)
benzoate (17)
To a 100-mL flask containing Q-T (1.00 g, 2.12 mmol), TPA1 (0.59 g, 1.06 mmol),
3 2 2 2 3 2
Pd(PPh ) Cl (0.08 g, 0.11 mmol), and Na CO (0.56 g, 5.3 mmol) was added a 50 mL TH/H O
mixed solvent (v/v = 4/1). The mixture was heated to reflux under nitrogen atmosphere for 8 h
before being cooled to room temperature. The solution was evaporated to dryness and the residue
4
was extracted with DCM and water. The organic layer was collected and dried over MgSO . The
desired product of 17 was obtained as a red solid (0.44 g, 38%) by column chromatography
1
eluted with EA/hexane (1/1). H NMR (400 MHz, CDCl
3
, ppm):
= 8.8 Hz, 4H), 7.84 (d,
H), 7.62-7.60 (m, 4H), 7.43-7.39 (m, 10H), 7.36-7.28 (m, 8H), 3.92(s, 3H). C NMR (150
, ppm): = 183.4, 166.8, 152.3, 152.2, 151.6, 148.5, 146.6, 145.1, 140.1, 138.7,
38.6, 138.3, 137.5, 135.7, 133.4, 132.1, 131.0, 130.4, 130.3, 130.1, 129.4, 129.2, 128.5, 128.3,
δ
= 10.0 (s, 2H), 8.27 (d,
J =
7
4
.6 Hz, 2H), 7.98-7.92 (m, 6H), 7.88 (d,
J
J = 4.0 Hz, 2H), 7.76-7.73 (m,
1
3
MHz, CDCl
3
δ
1
1
1
46 5 4 2
27.1, 126.1, 125.5, 124.7, 123.5, 122.0, 51.9. HRMS (FAB) m/z: calcd for C70H N O S :
+
084.2991; [M+H] found: 1084.3000.
2
.2.6 4-(bis(4-(8-(5-formylthiophen-2-yl)-2,3-diphenylquinoxalin-5-yl)phenyl)amino)benzoic
acid (18)
To a 50-mL flask containing 17 (200 mg, 0.18 mmol) and LiOH (31 mg, 0.74 mmol)
was added 21 mL of THF/MeOH/H O (v/v/v = 5/1/1) mixed solvent and the mixture was heated
2
to reflux for 8 h. After cooling to room temperature, the solution was neutralized by dilute HCl.
The precipitate was collected, washed with water, and dried under vacuum to afford a dark red
1
solid of compound 18 (195 mg, 99%). H NMR (400 MHz, CDCl
3
, ppm):
= 4.0 Hz, 2H), 7.94 (d,
= 8.8 Hz, 2H), 7.76-7.73 (m, 4H), 7.62-7.60 (m, 4H), 7.43-
δ
= 10.0 (s, 2H), 8.27
(d,
J
= 8.0 Hz, 2H), 8.02 (d,
.89 (d, = 8.4 Hz, 4H), 7.85 (d,
.41 (m, 10H), 7.36-7.29 (m, 8H). C NMR (125 MHz, CDCl , ppm):
J
= 8.8 Hz, 2H), 7.97 (d,
J
J
= 7.6 Hz, 2H),
7
7
1
J
J
1
3
δ
= 183.5, 170.8, 152.4,
3
52.3, 152.2, 148.4, 146.4, 145.0, 140.0, 138.7, 138.6, 138.3, 137.5, 135.7, 133.7, 132.1, 131.7,
8

ACCEPTED MANUSCRIPT
1
30.4, 130.3, 130.1, 129.43, 129.39, 129.2, 128.5, 128.3, 128.2, 127.1, 125.0, 122.0, 121.5.
+
HRMS (MALDI) m/z: calcd for C H N O S : 1070.2835; [M+H] found: 1070.2828.
6
9
44
5
4 2
2
.2.7 4-(bis(4-(8-(5-(2,2-dicyanovinyl)thiophen-2-yl)-2,3-diphenylquinoxalin-5-
yl)phenyl)amino) benzoic acid (EH122)
To a 50-mL flask containing 18 (100 mg, 0.09 mmol) and malononitrile (14 mg, 0.21
mmol) was added 20 mL DCM. The solution was stirred at room temperature for 2 h.
Subsequently, the mixture was concentrated to ~5mL followed by adding large amount of
hexane to crash a red solid. The dark red solid was collected, washed with hexane, and dried
1
under vacuum to afford EH122 (48 mg, 44%). H NMR (400 MHz, CDCl
3
, ppm):
= 8.4 Hz, 4H), 7.86 (s, 2H),
= 4.4 Hz, 2H), 7.82-7.80 (m, 4H), 7.63-7.61 (m, 4H), 7.45-7.41 (m, 10H), 7.36-7.30
δ = 8.33 (d, J
=
8.0 Hz, 2H), 8.01 (d,
J = 8.8 Hz, 2H), 7.96-7.94 (m, 4H), 7.90 (d, J
7
.84 (d,
J
1
3
(
m, 8H). The C NMR spectrum was not obtained because of very low solubility of EH122.
+
HRMS (FAB) m/z: calcd for C H N O S : 1166.3059; [M+H] found: 1166.3054.
7
5
44
9
2 2
2
.2.8 Dimethyl 4,4’-((4-(8-(5-formylthiophen-2-yl)-2,3-diphenylquinoxalin-5-yl) phenyl)
azanediyl) dibenzoate (19)
To a 100-mL flask containing Q-T (1.00 g, 2.12 mmol), TPA2 (1.03 g, 2.11 mmol),
Pd(PPh ) Cl (0.08 g, 0.11 mmol) and Na CO (0.79 g, 7.43 mmol) was added 50 mL THF/H O
3
2
2
2
3
2
mixed solvent (v/v = 4/1). The mixture was refluxed under nitrogen atmosphere for 8 h. After
cooling the solution to room temperature, the mixture was extracted with DCM and water. The
organic layer was collected and dried over MgSO . The desired product of 19 was obtained as a
4
1
red solid (1.05 g, 66%) by column chromatography eluted with EA/hexane (1/1). H NMR (400
MHz, CDCl , ppm):
δ
= 10.00 (s, 1H), 8.27 (d,
.6 Hz, 1H), 7.87-7.83 (m, 3H), 7.75-7.72 (m, 2H), 7.60-7.58 (m, 2H), 7.43-7.41 (m, 3H), 7.37
d, = 7.2 Hz, 1H), 7.33 (d, = 7.6 Hz, 2H), 7.29 (d, = 8.4 Hz, 2H), 7.22 (d, = 8.8 Hz, 4H),
.92 (s, 6H). C NMR (150 MHz, CDCl , ppm): = 183.4, 166.6, 152.3, 152.2, 151.0, 148.4,
J = 8.0 Hz, 1H), 7.98-7.95 (m, 5H), 7.92 (d, J =
3
7
(
J
J
J
J
1
3
3
1
1
δ
3
46.0, 145.1, 139.9, 138.62, 138.59, 138.3, 137.5, 135.7, 134.2, 132.3, 131.1, 130.5, 130.4,
30.1, 129.5, 129.4, 129.2, 128.5, 128.3, 128.2, 127.2, 125.2, 124.6, 123.1, 52.0. HRMS (FAB)
+
m/z: calcd for C H N O S: 752.2219; [M+H] found: 752.2229.
4
7
34
3
5
9

ACCEPTED MANUSCRIPT
2
.2.9 4,4’-((4-(8-(5-formylthiophen-2-yl)-2,3-diphenylquinoxalin-5-yl) phenyl) azanediyl)
dibenzoic acid (20)
Compound 20 was synthesized followed the same procedures for compound 18. A dark
1
red solid was obtained in a yield of 99%. H NMR (400 MHz, DMSO-d6, ppm):
δ
= 10.00 (s,
= 8.4 Hz,
= 7.2 Hz, 2H), 7.47-7.44 (m, 3H),
1
2
7
H), 8.63 (d,
H), 7.90 (d,
J
= 8.0 Hz, 1H), 8.25 (d,
= 8.4 Hz, 4H), 7.69-7.66 (m, 2H), 7.56 (d,
= 8.4 Hz, 2H), 7.16 (d, = 8.8 Hz, 4H). C NMR (100 MHz,
= 184.6, 166.8, 152.1, 151.6, 150.2, 146.4, 145.5, 145.0, 138.9, 138.3, 138.0,
37.8, 137.0, 136.4, 133.5, 132.3, 131.0, 130.1, 129.8, 129.33, 129.28, 129.1, 128.5, 128.3,
28.1, 127.7, 125.1, 124.8, 122.8. HRMS (FAB) m/z: calcd for C H N O S: 724.1906; [M+H]
J = 4.4 Hz, 1H), 8.12-8.08 (m, 2H), 7.98 (d, J
J
J
1
3
.43-7.34 (m, 3H), 7.30 (d,
, ppm):
J
J
DMSO-
d
6
δ
1
1
4
5
30
3
5
+
found: 724.1898.
2
.2.10 4,4’-((4-(8-(5-(2,2-dicyanovinyl)thiophen-2-yl)-2,3-diphenylquinoxalin-5 yl) phenyl)
azanediyl) dibenzoic acid (EH126)
To a 50-mL flask containing 20 (100 mg, 0.14 mmol) and malononitrile (11 mg, 0.17
mmol) was added 20 mL DCM and 5 mL EtOH. The solution was stirred at room temperature
for 2 h. Subsequently, the mixture was concentrated to ~5mL followed by adding large amount
of hexane to crash a red solid. The red solid was collected, washed with hexane, and dried under
1
vacuum to afford EH126 (67 mg, 63%). H NMR (400 MHz, DMSO-
d
6
, ppm):
= 8.0 Hz, 1H), 8.02 (d,
= 8.8 Hz, 4H), 7.77-7.75 (m, 2H), 7.59-7.57 (m, 2H),
δ
= 8.70 (s, 1H),
8
1
7
.68 (d,
H), 7.95 (d,
.42-7.34 (m, 6H), 7.27 (d,
J
= 7.6 Hz, 1H), 8.30 (d,
= 8.4 Hz, 2H), 7.88 (d,
= 8.8 Hz, 2H), 7.12 (d,
J
= 4.0 Hz, 1H), 8.09 (d,
J
J
= 4.8 Hz,
J
J
1
3
J
J = 8.8 Hz, 4H). The C NMR spectrum
was not obtained because of very low solubility of EH126. HRMS (FAB) m/z: calcd for
+
C
48
H
30
N
5
O
4
S
:
772.2019; [M+H] found: 722.2009.
2
.2.11 Methyl4-(bis(4-(8-(7-formyl-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenyl
quinoxalin-5-yl)phenyl)amino)benzoate (21)
To a 100-mL flask containing Q-EDOT (1.00 g, 1.89 mmol), TPA1 (0.52 g, 0.94
mmol), Pd(PPh ) Cl (0.07 g, 0.10 mmol), and Na CO (0.50 g, 4.72 mmol) was added a 50 mL
3
2
2
2
3
2
TH/H O mixed solvent (v/v = 4/1). The mixture was heated to reflux under nitrogen atmosphere
for 8 h before cooling to room temperature. The solution was evaporated to dryness and the
1
0

ACCEPTED MANUSCRIPT
residue was extracted with DCM and water. The organic layer was collected and dried over
MgSO . The desired product of 21 was obtained as a red solid (0.46 g, 41%) by column
4
1
chromatography eluted with EA/hexane (1/1). H NMR (400 MHz, CDCl , ppm):
δ
= 10.03 (s,
= 8.0 Hz, 2H), 7.88 (d, = 8.4
Hz, 4H), 7.77-7.75 (m, 4H), 7.62-7.60 (m, 4H), 7.42-7.38 (m, 10H), 7.35-7.29 (m, 8H), 4.49 (s,
3
2
H), 8.71 (d,
J
= 8.0 Hz, 2H), 7.96 (d,
J
= 8.8 Hz, 2H), 7.92 (d,
J
J
1
3
8
1
1
3
H), 3.92 (s, 3H); C NMR (125 MHz, CDCl , ppm): δ = 180.6, 166.9, 151.9, 151.7, 151.5,
47.8, 146.4, 139.8, 139.1, 138.8, 138.3, 138.2, 137.7, 133.6, 132.2, 132.1, 131.0, 130.5, 130.1,
29.8, 129.4, 129.3, 129.1, 128.8, 128.6, 128.4, 128.3, 124.7, 121.9, 119.5, 65.0, 64.8, 51.9.
+
HRMS (FAB) m/z: calcd for C74
H
50
N
5
O
8
S
2
: 1200.3108; [M+H] found: 1200.3105.
2
.2.12 4-(bis(4-(8-(7-formyl-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenylquinoxalin-
-yl)phenyl)amino)benzoic acid (22)
5
Compound 22 was synthesized followed the same procedures as compound 18. A dark
1
red solid was obtained in a yield of 99%. H NMR (600 MHz, CDCl , ppm):
δ
= 10.02 (s, 2H),
= 8.0 Hz, 2H), 7.87 (d, = 8.5 Hz,
H), 7.77-7.75 (m, 4H), 7.61-7.59 (m, 4H), 7.42-7.38 (m, 10H), 7.34-7.28 (m, 8H), 4.48 (s, 8H).
3
8
.70 (d,
J
= 8.0 Hz, 2H), 8.00 (d,
J
= 9.0 Hz, 2H), 7.90 (d,
J
J
4
1
3
3
CNMR (125 MHz, CDCl , ppm): δ = 180.7, 171.0, 152.3, 151.7, 151.3, 147.9, 146.1, 139. 9,
1
1
38.7, 138.20, 138.16, 137.5, 133.7, 132.1, 131.7, 130.5, 130.1, 129.6, 129.3, 129.2, 129.1,
28.7, 128.4, 128.3, 124.9, 123.9, 122.0, 121.3, 119.4, 116.7, 64.9, 64.7. HRMS (FAB) m/z:
+
calcd for C73
H
48
N
5
O
8
S
2
: 1186.2944; [M+H] found: 1186.2936.
2
.2.13 4-(bis(4-(8-(7-(2,2-dicyanovinyl)-2,3-dihydrothieno[3,4-b]
[1,4]
dioxin-5-yl)-2,3-
diphenyl quinoxalin-5-yl) phenyl) amino) benzoic acid (EH166)
To a 50-mL flask containing 22 (118 mg, 0.10 mmol) and malononitrile (15 mg, 0.23
mmol) was added 20 mL DCM. The solution was stirred at room temperature for 2 h.
Subsequently, the mixture was concentrated to ~5mL followed by adding large amount of
hexane to crash a red solid. The dark red solid was collected, washed with hexane, and dried
1
under vacuum to afford EH166 (64 mg, 50%). H NMR (400 MHz, CDCl
3
, ppm):
δ = 8.77 (d, J
=
8.4 Hz, 2H), 8.00 (d,
J
= 8.4 Hz, 2H), 7.95 (s, 2H), 7.90 (d,
J
= 8.0 Hz, 2H), 7.88-7.83 (m, 6H),
1
3
7
.62 (d, = 6.8 Hz, 4H), 7.44-7.37 (m, 10H), 7.31-7.28 (m, 8H), 4.47 (s, 8H). The C NMR
J
1
1

ACCEPTED MANUSCRIPT
spectrum was not obtained because of very low solubility of EH166. HRMS (MALDI) m/z:
+
calcd for C H N O S : 1281.3085; M found: 1281.3065.
7
9
47
9
6 2
2
.2.14 Dimethyl 4,4'-((4-(8-(7-formyl-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenyl
quinoxalin-5-yl)phenyl)azanediyl)dibenzoate (23)
To a 100-mL flask containing Q-EDOT (1.00 g, 1.89 mmol), TPA1 (0.92 g, 1.89
3 2 2 2 3
mmol), Pd(PPh ) Cl (0.07 g, 0.10 mmol), and Na CO (0.70 g, 6.61 mmol) was added a 50 mL
TH/H O mixed solvent (v/v = 4/1). The mixture was heated to reflux under nitrogen atmosphere
2
for 8 h before cooling to room temperature. The solution was evaporated to dryness and the
residue was extracted with DCM and water. The organic layer was collected and dried over
MgSO . The desired product of 23 was obtained as a red solid (1.04 g, 68%) by column
4
1
chromatography eluted with EA/hexane (1/1). H NMR (400 MHz, CDCl
3
, ppm):
= 8.0 Hz, 1H), 7.86 (d,
Hz, 2H), 7.77-7.74 (m, 2H), 7.60-7.57 (m, 2H), 7.42-7.40 (m, 3H), 7.36 (d, = 7.2 Hz, 1H), 7.32
= 8.8 Hz, 4H), 4.48 (s, 4H), 3.91 (s, 6H).
= 180.6, 166.7, 152.0, 151.6, 151.0, 147.8, 145.8, 139.9,
δ
= 10.02 (s,
1
H), 8.70 (d,
J
= 8.0 Hz, 1H), 7.96 (d,
J
= 8.8 Hz, 4H), 7.89 (d,
J
J
= 8.4
J
(d,
J = 7.6 Hz, 2H), 7.28 (d, J = 8.4 Hz, 2H), 7.21 (d, J
1
3
C NMR (150 MHz, CDCl , ppm):
δ
3
1
1
38.7,138.3, 138.2, 137.7, 134.4, 132.3, 131.1, 130.5, 130.1, 129.8, 129.4, 129.3, 129.2, 129.0,
28.4, 128.3, 125.2, 124.6, 124.0, 123.0, 119.5, 65.0, 64.8, 52.0. HRMS (FAB) m/z: calcd for
+
C H N O S: 810.2274; [M+H] found: 810.2280.
49
36
3
7
2
.2.15 4,4'-((4-(8-(7-formyl-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenylquinoxalin-
-yl) phenyl)azanediyl)dibenzoic acid (24)
5
Compound 24 was synthesized followed the same procedures as compound 18. A dark
1
red solid was obtained in a yield of 99%. H NMR (600 MHz, DMSO-d6, ppm):
δ
= 9.97 (s, 1H),
8
4
1
4
1
1
.82 (d,
H), 7.60 (d,
H), 7.37-7.34 (m, 2H), 7.28 (d,
J
= 7.8 Hz, 1H), 8.10 (d,
= 7.2 Hz, 2H), 7.55 (d,
= 8.4 Hz, 2H), 7.12 (d,
, ppm):
J
= 8.4 Hz, 1H), 7.94 (d,
= 7.2 Hz, 2H), 7.47-7.43 (m, 3H), 7.39 (d,
= 8.4 Hz, 4H), 4.56 (d,
J
= 8.4 Hz, 2H), 7.88 (d,
J
J
J
= 8.4 Hz,
= 7.8 Hz,
= 5.4 Hz,
J
J
J
J
1
3
H). C NMR (125 MHz, DMSO-
d
6
δ
= 180.1, 166.8, 151.8, 150.2, 148.4, 145.5, 140.4,
38.4, 137.9, 137.8, 137.6, 136.7, 133.6, 132.4, 131.1, 130.1, 129.8, 129.7, 129.5, 129.3, 129.1,
28.2, 128.1, 125.1, 124.9, 122.8, 121.7, 118.4, 65.0, 64.9. HRMS (ESI) m/z: calcd for
-
C
47
H
30
N
3
O
7
S: 780.1804; [M-H] found: 780.1795.
1
2

ACCEPTED MANUSCRIPT
2
.2.16 4,4'-((4-(8-(7-(2,2-dicyanovinyl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenyl
quinoxalin-5-yl)phenyl)azanediyl)dibenzoic acid (EH162)
To a 50-mL flask containing 24 (100 mg, 0.13 mmol) and malononitrile (10 mg, 0.15
mmol) was added 20 mL DCM and 5 mL EtOH. The solution was stirred at room temperature
for 2 h. Subsequently, the mixture was concentrated to ~5mL followed by adding large amount
of hexane to crash a red solid. The dark red solid was collected, washed with hexane, and dried
1
under vacuum to afford EH162 (69 mg, 65%). H NMR (400 MHz, DMSO-d6, ppm):
δ
= 8.89
= 8.4 Hz, 2H), 7.87 (d,
.8 Hz, 4H), 7.77-7.74 (m, 2H), 7.58-7.56 (m, 2H), 7.42-7.35 (m, 6H), 7.26 (d, = 8.4 Hz, 2H),
= 8.8 Hz, 4H), 4.56 (s, 4H). The C NMR spectrum was not obtained because of very
(d,
J
= 8.0 Hz, 1H), 8.25 (s, 1H), 8.11(d,
J
= 8.0 Hz, 1H), 7.94 (d,
J
J =
8
7
J
1
3
.11 (d,
J
+
32 5 6
low solubility of EH162. HRMS (FAB) m/z: calcd for C50H N O S: 830.2073; [M+H] found:
8
30.2081.
2
.2.17 Methyl4-(bis(4-(8-(5'-formyl-[2,2’-bithiophen]-5-yl)-2,3-diphenyl quinoxalin-5-yl)
phenyl) amino)benzoate (25)
To a 100-mL flask containing Q-BT (1.00 g, 1.81 mmol), TPA1 (0.50 g, 0.90 mmol),
3 2 2 2 3
Pd(PPh ) Cl (0.06 g, 0.09 mmol), and Na CO (0.48 g, 4.52 mmol) was added a 50 mL
THF/H O mixed solvent (v/v = 4/1). The mixture was heated to reflux under nitrogen
2
atmosphere for 8 h before cooling to room temperature. The solution was evaporated to dryness
and the residue was extracted with DCM and water. The organic layer was collected and dried
over MgSO . The desired product of 25 was obtained as a red solid (0.45 g, 40%) by column
4
1
chromatography eluted with EA/hexane (2/1). H NMR (600 MHz, CDCl
3
, ppm):
= 7.8 Hz, 2H), 7.88 (d,
J = 3.6 Hz, 2H), 7.63-7.61 (m,
δ
= 9.89 (s,
2
H), 8.24 (d,
Hz, 4H), 7.85 (d,
H), 7.46-7.41 (m, 8H), 7.39 (d,
125 MHz, CDCl , ppm): = 182.5, 166.9, 152.1, 151.7, 151.6, 147.9, 146.4, 141.5, 140.4,
38.8, 138.7, 138.6, 138.5, 137.6, 137.0, 133.6, 132.0, 131.0, 130.8, 130.5, 130.1, 129.6, 129.3,
J
= 7.8 Hz, 2H), 7.96 (d,
= 4.2 Hz, 2H), 7.79-7.77 (m, 4H), 7.72 (d,
= 8.4 Hz, 4H), 7.37-7.27 (m, 10H), 3.92 (s, 3H). CNMR
J
= 9.0 Hz, 2H), 7.91 (d,
J
J
= 8.4
J
13
4
J
(
δ
3
1
1
29.1, 128.3, 127.0, 126.6, 125.7, 124.8, 123.8, 123.2, 121.8, 51.9. HRMS (FAB) m/z: calcd for
+
C
78
H
50
N
5
O
4
S
4
: 1248.2746; [M+H] found: 1248.2751.
1
3

ACCEPTED MANUSCRIPT
2
.2.18 4-(bis(4-(8-(5'-formyl-[2,2’-bithiophen]-5-yl)-2,3-diphenylquinoxalin-5-yl)phenyl)
amino) benzoic acid (26)
Compound 26 was synthesized followed the same procedures as compound 18. A dark
1
red solid was obtained in a yield of 98%. H NMR (500 MHz, CDCl , ppm):
δ
= 9.90 (s, 2H),
= 8.0 Hz, 2H), 7.90 (d, = 8.5 Hz,
= 4.0 Hz, 2H), 7.64-7.62 (m, 4H),
3
8
2
7
.26 (d,
J
= 8.0 Hz, 2H), 7.98 (d,
J
= 9.0 Hz, 2H), 7.93 (d,
J
J
J
H), 7.87 (d,
J
= 4.0 Hz, 2H), 7.80-7.78 (m, 4H), 7.73 (d,
1
3
.47-7.40 (m, 12H), 7.38-7.28 (m, 10H). The C NMR spectrum was not obtained because of
+
47 5 4 4
very low solubility of 26. HRMS (FAB) m/z: calcd for C77H N O S :1234.2589; [M+H]
found: 1234.2593.
2
.2.19 4-(bis(4-(8-(5'-(2,2-dicyanovinyl)-[2,2'-bithiophen]-5-yl)-2,3-diphenylquinoxalin-5-yl)
phenyl) amino) benzoic acid (EH174)
To a 50-mL flask containing 26 (100 mg, 0.08 mmol) and malononitrile (12 mg, 0.18
mmol) was added 20 mL DCM and 5 mL EtOH. The solution was stirred at room temperature
for 2 h. Subsequently, the mixture was concentrated to ~5mL followed by adding large amount
of hexane to crash a red solid. The dark red solid was collected, washed with hexane, and dried
1
under vacuum to afford EH174 (49 mg, 45%). H NMR (500 MHz, DMF-
d
7
, ppm):
δ
= 8.63 (d,
J
= 7.5 Hz, 2H), 8.18 (d,
H), 7.61 (d, = 3.5 Hz, 2H), 7.56-7.50 (m, 6H), 7.46-7.40 (m, 10H), 7.27 (d,
C NMR (100 MHz, DMF- 7, ppm): = 168.1, 160.5, 153.4, 152.6, 152.5, 152.3, 147.3, 141.5,
J
= 4.0 Hz, 2H), 8.14-8.10 (m, 8H), 7.90-7.88 (m, 6H), 7.75-7.73 (m,
= 6.0 Hz, 4H).
6
J
J
1
3
d
δ
1
1
1
1
40.5, 140.2, 139.6, 139.4, 139.0, 138.8, 137.6, 135.1, 134.9, 133.4, 132.8, 132.2, 131.9, 131.7,
31.2, 130.41, 130.35, 130.1, 129.4, 129.3, 128.8, 127.8, 125.7, 125.4, 124.8, 122.7, 118.0,
+
17.7, 81.5. HRMS (FAB) m/z: calcd for C H N O S : 1330.2814; [M+H]
found:
8
3
48
9
2 4
330.2799.
2
.2.20 Dimethyl4,4'-((4-(8-(5'-formyl-[2,2'-bithiophen]-5-yl)-2,3-diphenyl quinoxalin-5-yl)
phenyl) azanediyl)dibenzoate (27)
To a 100-mL flask containing Q-BT (1.00 g, 1.81 mmol), TPA2 (0.88 g, 1.81 mmol),
Pd(PPh ) Cl (0.06 g, 0.09 mmol), and Na CO (0.67 g, 6.32 mmol) was added a 50 mL
3
2
2
2
3
2
THF/H O mixed solvent (v/v = 4/1). The mixture was heated to reflux under nitrogen
atmosphere for 8 h before cooling to room temperature. The solution was evaporated to dryness
1
4

ACCEPTED MANUSCRIPT
and the residue was extracted with DCM and water. The organic layer was collected and dried
over MgSO . The desired product of 27 was obtained as a red solid (1.02 g, 68%) by column
4
1
chromatography eluted with EA/hexane (2/1). H NMR (400 MHz, CDCl , ppm):
δ
= 9.89 (s,
= 8.0 Hz, 1H), 7.88-7.84
= 4.0 Hz, 1H), 7.61-7.59 (m, 2H), 7.46-7.42 (m, 4H), 7.37
= 7.5 Hz, 1H), 7.34-7.32 (m, 3H), 7.29 (d, = 8.5 Hz, 2H), 7.22 (d, = 9.0 Hz, 4H), 3.92 (s,
= 182.7, 166.9, 152.3, 151.8, 151.2, 148.0, 146.0,
3
1
H), 8.24 (d,
m, 3H), 7.79-7.77 (m, 2H), 7.72 (d,
d,
J = 8.0 Hz, 1H), 7.96 (dd, J = 7.0, 2.0 Hz, 4H), 7.90 (d, J
(
(
J
J
J
J
1
3
6
1
1
H). C NMR (125 MHz, CDCl , ppm):
δ
3
41.7, 140.5, 139.1, 138.9, 138.8, 138.64, 138.59, 137.7, 137.2, 134.6, 132.4, 131.3, 131.2,
30.7, 130.3, 129.9, 129.5, 129.4, 128.5, 127.3, 126.8, 125.9, 125.5, 124.7, 124.0, 123.2, 52.2.
+
HRMS (FAB) m/z: calcd for C H N O S : 833.2018; M found: 833.2014.
5
1
35
3
5 2
2
.2.21 4,4'-((4-(8-(5'-formyl-[2,2'-bithiophen]-5-yl)-2,3-diphenylquinoxalin-5-
yl)phenyl)azanediyl)dibenzoic acid (28)
Compound 28 was synthesized followed the same procedures as compound 18. A dark
1
red solid was obtained in a yield of 99%. H NMR (400 MHz, DMSO-
d
6
, ppm):
δ
= 9.91 (s, 1H),
= 8.0 Hz, 2H),
8
7
3
.57 (d,
.89 (d,
J
J
= 8.4 Hz, 1H), 8.15 (d,
J
= 4.0 Hz, 1H), 8.07-8.04 (m, 2H), 7.97 (d,
J
= 8.8 Hz, 4H), 7.76-7.73 (m, 3H), 7.60-7.57 (m, 3H), 7.50-7.47 (m, 3H), 7.42-7.37 (m,
1
3
H), 7.29 (d,
J = 8.4 Hz, 2H), 7.15 (d, J = 8.4 Hz, 4H). C NMR (125 MHz, DMSO-d6, ppm): δ
=
184.2, 167.3, 152.4, 151.6, 150.7, 146.5, 145.8, 141.5, 139.7, 139.3, 138.9, 138.8, 138.4,
1
1
38.2, 138.0, 136.3, 134.2, 132.7, 131.5, 130.7, 130.4, 130.3, 130.2, 129.8, 129.6, 128.68,
28.65, 128.4, 127.4, 126.7, 125.5, 125.4, 125.2, 123.2. HRMS (FAB) m/z: calcd for
+
C
49
H
32
N
3
O
5
S
2
: 806.1783; [M+H] found: 806.1773.
2
.2.22 4,4'-((4-(8-(5'-(2,2-dicyanovinyl)-[2,2'-bithiophen]-5-yl)-2,3-diphenylquinoxalin-5-yl)
phenyl) azanediyl)dibenzoic acid (EH170)
To a 50-mL flask containing 28 (100 mg, 0.15 mmol) and malononitrile (10 mg, 0.15
mmol) was added 20 mL DCM and 15 mL EtOH. The solution was stirred at room temperature
for 2 h. Subsequently, the mixture was concentrated to ~5mL followed by adding large amount
of hexane to crash a red solid. The dark red solid was collected, washed with hexane, and dried
1
under vacuum to afford EH170 (74 mg, 70%). H NMR (600 MHz, DMSO-d6, ppm):
δ
= 8.46
= 7.2
(
s, 1H), 8.38 (d, J = 7.8 Hz, 1H), 7.95 (s, 1H), 7.88-7.84 (m, 6H), 7.74 (s, 1H), 7.64 (d, J
1
5

ACCEPTED MANUSCRIPT
Hz, 2H), 7.59 (s, 1H), 7.51 (d,
m, 2H), 7.33-7.30 (m, 3H), 7.18 (d,
MHz, DMSO- 6, ppm): = 167.2, 152.4, 152.1, 151.3, 150.7, 149.2, 145.8, 143.1, 140.3, 138.9,
38.4, 138.2, 138.0, 137.9, 136.1, 134.0, 133.6, 132.6, 131.5, 130.7, 130.2, 130.1, 130.0, 129.8,
J
= 7.2 Hz, 2H), 7.48 (s, 1H), 7.44 (d,
J = 7.2 Hz, 2H), 7.41-7.37
1
3
(
J
= 7.8 Hz, 2H), 7.11 (d, = 8.4 Hz, 4H). C NMR (150
J
d
δ
1
1
29.6, 128.8, 128.6, 128.2, 127.5, 127.1, 125.6, 125.2, 125.0, 123.2, 115.3, 114.5, 73.8. HRMS
+
(MALDI) m/z: calcd for C52
H
32
N
5
O
4
S
2
: 854.1890; [M+H] found: 854.1899.
2
.3 Solar cell device fabrication and measurements
For the preparation of nickel oxide film, the nickel oxide paste prepared by mixing 1 g of
NiO, 2.7 mL ethanol, 0.342 g ethyl acetate, and 6 mL α-terpinol for each powders and then
nickel oxide film was made using doctor blade method with two steps on FTO glass and sintered
at 450 ºC for 30 minutes. The film thickness and working area of each working electrodes were
measured by a surface profilometer. Then the prepared NiO films were soaked in a 0.3 mM dye
solution for 24 h. Platinized counter electrode was prepared by spraying H PtCl on predrilled
2
6
and cleaned FTO glass, followed by drying at 70 ºC and sintered at 500 ºC for 1 h. The dyed NiO
working electrode was assembled face-to-face with platinized counter electrode in the presence
3
0 µm surlyn outside the hole. The electrolyte was injected through the hole and covered with a
microscopic glass and surlyn. The electrolyte is a combination of 0.6 M DMPII, 0.03 M I , 0.1 M
2
GuSCN, 0.5 M TBP, and 0.05 M LiI in a dry acetonitrile. The amount of dye loading was
determined by desorption of adsorbed dye on NiO with DMF. The concentration of dye in the
desorption solution was determined by absorption spectrophotometry.
3
. Results and Discussion
3
.1 Synthesis and characterization of surfactant mediated nickel oxide photocathode materials
Here we used the cationic surfactant, DTAB, which has not been reported previously for
the synthesis of nickel oxide. The synthetic procedures are shown in Scheme 1. Hexahydrate
nickel (II) chloride (NiCl •6H O) was stirred with DTAB in a basic solution following the
2
2
literature procedure with modifications [42]. The green nickel hydroxide, Ni(OH) , was collected
2
by centrifugation. The desired nickel oxide nanoparticles were obtained after calcination. The
powder X-ray diffraction (PXRD) patterns of nickel oxide nanoparticles prepared without and
with DTAB as the surface-active agent are plotted in Fig.2. It can be seen that both samples
1
6

ACCEPTED MANUSCRIPT
show the same XRD patterns with high crystallinity. There exist five diffraction peaks at 2
θ
position of 37.1, 43.4, 62.7, 76.5, and 79.3°, which are indexed to (111), (200), (220), (311), and
222) of the cubic nickel oxide, respectively.
(
Scheme 1. Synthesis rout for nickel oxide nanoparticles
Fig. 2. XRD patterns for the nickel oxide nanoparticles prepared with and without DTAB.
The SEM images of the as-synthesized NiO nanoparticles without and with DTAB do not
exhibit significant difference in their particle uniformity (Fig. S1). However, very distinct results
were obtained in their annealed films. Fig. 3 shows the SEM images of NiO films prepared
without (a, c) and with DTAB (b, d) on an ITO conductive substrate acquired from a top (a, b)
and a cross-section view (c, d). From the top-view images, the NiO film in (a) formed with
apparently smaller agglomerates of NiO nanoparticles compared with those on the film in (b). It
indicates that the energy from input heat for preparation of a NiO film easily overcame inter-
particle affinity, and hence drove lateral diffusion of NiO nanoparticles without DTAB.
1
7

ACCEPTED MANUSCRIPT
Conversely, the existence of DTAB elevates inter-particle affinity so as to result in big chunks of
NiO nanoparticle assemblies. From the cross-section images, it is clear in both cases that a thin
annealed NiO films were formed homogeneously at the interfaces between ITO substrates and
NiO chunks. The result infers the strong interaction between NiO and ITO. On the base film,
agglomerates of NiO nanoparticles are short without DTAB and tall with DTAB, corresponding
with those in top-view images. Hence, it is very likely the big NiO chunks came from DATB-
modified surface property before annealing. Such difference by treating with DTAB induces
rough surface morphologies of annealed NiO film that increases dye-loading quantity (Table 1).
It is well known that the short-circuit current density is highly determined by the initial number
of photo-generated charges. Here, the initial number of photo-generated charges could be
significantly affected by differently structured films where the amount of light-harvesting dyes is
different. The amount of dye adsorbed on nickel oxide surfaces was determined using UV-vis
-2
absorption spectroscopy and estimated to be 17.9 and 11.6 nmolcm for DTAB treated and
untreated NiO, respectively, with Coumarin 343 (C343) as the p-type sensitizer (Table 1). The
increase in dye loading originated from morphology difference of the DTAB assisted synthesis
of nickel oxide nanoparticles which is responsible for enhancing the number of photo-generated
charges.
Fig. 3. SEM images with the top views (a, b) and cross-section views (c, d) of NiO surfaces.
NiO prepared without (a, c) and with DTAB (b, d).
1
8

ACCEPTED MANUSCRIPT
Different physical parameters of nickel oxide nanoparticles including Fermi level,
average particle size, and surface area are collected in Table 1. The Fermi level of the NiO
nanoparticles was determined from the work function measurement of the thin film. The average
particle size of nickel oxide nanoparticles estimated from SEM images from Figure S1 is about
1
2 nm for nickel oxide prepared from surfactant-assisted synthesis whereas the NiO particles
prepared without surfactant are not well dispersed due to the agglomeration. DTAB-assisted
synthesis of nickel oxide film resulted in enhanced dye loading by about 35% which leads to
improved light harvesting ability.
Table 1. Physical Parameters of Nickel Oxide Nanoparticles
Parameters
NiO
NiO-DTAB
5.3
Work function /eV from vacuum level 5.3
-
2
Dye loading/nmol cm
11.6
41.5
17.9
2
Surface area, BET (m /g)
56.8
The influence of DTAB on the different oxidation states of nickel in nickel oxide and the
defect site on oxygen was studied by XPS spectra as illustrated in Fig. 4, which plotted at the Ni
2
p and O 1s edge. All three satellites with fitting at the binding energy indicated in the inset of
2
+
3+
Fig. 4 in both samples are characteristic peaks of Ni and Ni oxidation states in NiO thin films
24]. This result confirms the addition of DTAB does not significantly affect the oxidation state
[
of nickel in nickel oxide because the binding energies of the satellites are numerically close.
Energy dispersive X-ray spectroscopy (EDS) data was also studied for further elemental analysis.
The percentage atomic composition of nickel and oxygen in two materials is shown in Fig. 5. It
turns out that the compoistions of NiO nanoparticles with and without DTAB are pretty
consistent, indirectly confiming the auxiliary role of DTAB only to assist the dispersion of
nanoparticles.
1
9

ACCEPTED MANUSCRIPT
Fig. 4. XPS study nickel oxide samples synthesized with and without DTAB.at the Ni 2p, O 1s
edge
Fig. 5. EDS of nickel oxide samples synthesized with and without DTAB.
3
.1.1 p-DSSC Performance Study
The newly synthesized NiO was evaluated as the photocathode material for p-DSSC. The
photocurrent density versus photovoltage curve and the corresponding IPCE plots of the devices
sensitized with C343 are shown in Fig.6 for both NiO nanoparticles. Among the two, the device
with NiO prepared with DTAB produced better photocurrent density, photovoltage, and fill
factor than the other. The DTAB-assisted synthesized NiO film with C343 achieved higher
power conversion efficiency of 0.0418%, with a short-circuit current density (J ) of 0.963
sc
2
0

ACCEPTED MANUSCRIPT
–
2
mAcm and an open circuit potential (
Voc) of 121 mV. The detailed photovoltaic data are
summarized in Table 2.
Fig. 6. (a) Current voltage characteristic curves and (b) IPCE plots for p-DSSCs sensitized by
C343 for two different NiO films
a
Table 2. Photovoltaic Performance of p-DSSCs Sensitized by C343
C343 (NiO)
0.112
C343 (NiO-DTAB)
0.121
Voc/V
Jsc/mAcm
FF
-
2
0.621
0.963
0.364
0.359
ƞ
(%)
0.0253
0.0418
a
The cells were composed of 4 µm thick NiO. The electrolyte used was a mixture of 0.6 M
DMPII, 0.03 M iodine, 0.1 M GuSCN, 0.5 M TBP and 0.05 M LiI in a dry acetonitrile.
Fig. 7 displays the results of intensity-modulated photovoltage spectroscopy (IMVS)
measurements (a) and charge extraction analysis (b) to assess the detail information of the hole
lifetime, Fermi level with photovoltage and also the hole density [55]. The results in Fig. 7(a)
show that the hole lifetime in NiO nanoparticle prepared using DTAB is longer than that
prepared without DTAB. The charge concentration as a function of open-circuit potential
induced by various illumination intensities is shown in Fig. 7(b), in which the hole density of
2
1

ACCEPTED MANUSCRIPT
NiO film prepared with DTAB is higher than that prepared without DTAB. It is clearly
demonstrated here that the NiO prepared from morphology-directing surfactant does produce
more effective photocathode than the one with unmodified NiO.
Fig. 7. (a) Hole lifetime versus open circuit voltage and (b) charge density versus open circuit
voltage
3
.2 Design and Synthesis of Organic Dyes
Six new organic dyes with a general D-A-π-A framework were designed with the
carboxylic acid as the anchoring group, triphenylamine as the electron donor, 2,3-
diphenylquinoxaline as the auxiliary acceptor moiety, 2-methylenemalononitrile as the electron
acceptor and various thiophene derivatives as the π-spacers. These dyes are classified into two
categories: the mono-anchoring dyes (EH122
EH126 EH162, and EH170). The detail synthetic procedures are illustrated in Scheme 2
whereas for compounds TPA1 and TPA2 reported in supporting information (Scheme S1).
, EH166, and EH174) and di-anchoring dyes
(
,
5, 7,
In general, the synthesis of these dipolar organic dyes involved multiple synthetic steps including
bromination, Miyaura borylation, condensation, and Suzuki coupling [53, 54, 56]. The purity and
identity of these dyes were fully characterized by NMR spectroscopy and high-resolution mass
spectrometry.
2
2

ACCEPTED MANUSCRIPT
Br
Br
HO
S
N
N
B
HO
7
a
d
S
Q
5
Br
S
S
Br
N
N
c
N
N
b
O
S
4
O
Br
8
S
O
S
N
N
Br
S
Br
N
N
O
N
N
O
Q-T
Q-BT
Q-EDOT
CN
CN
CN
R
N
R
N
Bpin
Bpin
O
NC
O
R
R
O
O
R
N
R
O
Br
R
g
h
f
O
O
N
N
N
N
N
N
N
+
N
N
N
N
N
N
N
N
O
OH
TPA1
O
O
S
HO
O
S
S
R
R
=
=
=
=
Q-T
R
S
EH122
EH166
S
17; R
=
18; R
22;
=
=
S
Q-EDOT
Q-BT
O
S
S
R
R
O
O
=
=
R
2
1; R
O
O
O
S
O
O
R
=
S
EH174
=
S
S
S
2
5; R
26; R
=
S
S
S
O
O
O
O
O
HO
OH
O
O
O
R
O
Br
O
R
O
CN
CN
j
N
N
R
k
i
N
Bpin
+
N
R
N
N
N
N
N
N
N
N
S
HO
O
O
O
O
TPA2
OH
S
S
=
S
S
Q-T
R
R
1
9;
R
=
=
20;
24;
=
=
R
R
R
R
=
=
EH126
EH162
S
S
S
Q-EDOT
Q-BT
=
=
O
2
3;
R
R
O
O
O
O
O
O
O
S
R
S
2
7;
=
28;
=
S
S
EH170
R
=
S
R
S
S
S
Scheme 2: Synthetic strategy of sensitizers’: EH122, EH126, EH162, EH166, EH170 and
EH174 Reagents and conditions: a, d, f, i) Pd(PPh ) Cl , Na CO , THF:H O (4:1), reflux, 8 h; b,
3
2
2
2
3
2
o
e) DMF, POCl
3
, CH
2
Cl
2
, 65 C, 8 h; c) Pd(OAc)
2
, Na
2
3
CO , DMF, reflux, 8 h; g, j) LiOH,
THF:MeOH:H O (5:1:1), reflux, 8 h; h, k) pepperdine, malononitrile, CH Cl , rt, 2 h.
2
2
2
3
.2.1 Photophysical and Electrochemical Properties
The UV-vis absorption spectra of all six sensitizers in DMF solutions and adsorbed on
NiO films are depicted in Fig.8 and the data are summarized in Table 3. In general, the spectral
coverages for all six new dyes reach nearly 600 nm. Two absorption bands were observed in
solution for each case (Fig. 8(a)). The absorption band between 290-370 nm is assigned to a π-π*
2
3

ACCEPTED MANUSCRIPT
transition and the other band located in the visible region between 450-600 nm is attributed to an
intramolecular charge-transfer (ICT) transition. The extinction coefficients of mono-anchoring
dyes (EH174
, EH122 and EH166) are greater than those of with double anchoring groups
(
EH126 EH162 and EH170). EH174 and EH166 with the bithiophene and EDOT π-linkers,
,
-1
-1
respectively, exhibited the molar extinction coefficients over 40000 M cm on both bands,
signifying their excellent light harvesting ability. The absorption bands become broad over the
range from 400 to 650 nm when these dyes are adsorbed onto NiO film indicative of some
degree of dye aggregation on NiO surface. The optical band gaps (E0-0) of all the new sensitizers
were determined by the intersection of normalized absorption and emission spectra. The band
gaps of EH dyes are comparable and ranged from 2.15-2.24 V as shown in Table 3.
Fig. 8. (a) UV-Vis absorption spectra of EH dyes in DMF solutions and (b) adsorbed on nickel
oxide films.
a
Table 3. Photophysical Parameters of EH Dyes
4
-1
-1
b
Dye
λ
max, nm (
ε
× 10 , M cm )
λem, nm
E , eV
0-0
EH122
EH126
EH166
EH162
EH174
323 (5.41), 474 (3.40)
323 (3.61), 468 (1.84)
315 (5.53), 497 (4.59)
322 (3.85), 487 (2.31)
345 (8.36), 474 (4.38)
338 (3.32), 501 (2.22)
711
657
660
652
660
653
2.15
2.24
2.19
2.21
2.22
2.17
EH170
a
b
The absorption and emission spectra were measured in DMF solutions. E0-0 was calculated
2
4

ACCEPTED MANUSCRIPT
from the intersection of normalized absorption and emission spectra (E0-0 = 1240 / λ).
Cyclic voltammograms of six dyes were measured in DMF solutions to access the
relative energy levels and feasibility of hole injection from the excited dyes into the valence band
of NiO and electron transfer from the reduced dyes to redox couples in the electrolyte. The
+
details of electrochemical parameters such as oxidation potential (E (S /S)), reduction potential
ox
-
-
(
Ered (S/S )), and exited state reduction potential (E *(S*/S )) are summarized in Table 4. The
red
relative energy levels of all sensitizers, the valence band position of nickel oxide, and the redox
mediator are depicted in Fig.9. The potential differences between the Fermi level of NiO and the
HOMOs of sensitizers range from 0.89 to 1.03 V indicative of a sufficient driving force for hole
injection. The high energy levels of LUMOs of these dyes also ensure favorable dye
regeneration.
a
Table 4. Electrochemical Potentials of EH Dyes
+
-
b
Dye
E (S /S), V
E (S/S ), V
E *, V
red
ox
red
EH122
EH126
EH166
EH162
EH174
1.27
1.32
1.28
1.18
1.13
-0.70
-0.70
-0.67
-0.62
-0.68
-0.69
1.45
1.54
1.52
1.59
1.54
EH170
1.02
1.48
a
+
-
Oxidation potential (Eox(S /S)) and reduction potential (Ered (S/S )) were measured in DMF
solutions with tetrabutylammonium hexafluorophosphate (0.1 M) as the supporting electrolyte.
b
The potentials were calibrated with ferrocene/ferrocenium vs NHE. The excited-state reduction
-
potential (E *) was calculated by E (S/S ) + E
red
red
0-0
2
5

ACCEPTED MANUSCRIPT
Fig. 9. The energy levels of EH-series sensitizers relative to the valence band potential of nickel
oxide and oxidation potential of the redox mediator
3
.2.2 Theoretical Calculations
Theoretical studies based on density functional theory (DFT) calculations using the
Gaussian 09 [57] program package at the mPW1K[58] /6-31G*[59] level of theory were carried
out in the SMD [60] solvation model (DMF) for the six dyes to construct their geometries. The
0 1 0 2
electron density difference maps of S to S and S to S transitions for the six dyes obtained by
time-dependent density functional theory (TD-DFT) were calculated and the results are
presented in Fig. 10. The molecular orbitals of HOMO and LUMO were depicted in Fig. S2 in
supplementary information. The calculated absorption spectra and the transitions involved are
also summarized in Figure S3 and Table S1 in supplementary information. The electron density
of the HOMOs is mostly localized on the triphenylamine donor moiety with some charge
diffusion towards the quinoxaline moiety, whereas the electron density of the LUMOs is
delocalized from quinoxaline to the π-spacer and 2-methylenemalononitrile acceptor. Upon light
excitation, the hole generated from charge transfer transition would be effectively injected into
the valence band of NiO via the terminal anchoring groups. Sensitizers with bithiophene and
thiophene π-spacers showed better charge separation than EDOT π-spacer resulted from the
presence of less electron-rich group capable of facilitating charge separation. For the mono-
anchoring sensitizers, EH122 and EH174, the electron densities in the auxiliary fragments
2
6

ACCEPTED MANUSCRIPT
(diphenylquinoxaline) further shift to the acceptor group. As a result, EH122 and EH174 have
less charge retention on the 2,3-diphenylquinoxaline that results in a significant charge
separation.
Sensitizers
EH122
S0 → S1
S0 → S2
EH166
EH174
EH126
EH162
2
7

ACCEPTED MANUSCRIPT
EH170
Fig. 10. Geometry-optimized structures of the six new dyes and the electron density distributions
of frontier molecular orbitals from TD-DFT calculations. The yellow and red colors represent
increase of electron density and decrease of electron density, respectively.
3
.2.3 Photovoltaic Performance
The performances of p-DSSCs sensitized with six new dyes using DTAB mediated
–
–
3
nickel oxide nanoparticles as photocathode and I /I as the redox couple were measured under
–
2
standard AM 1.5G condition (100 mWcm ). The photocurrent density/voltage curves and the
incident photon-to-electron conversion efficiency (IPCE) plots for the DSSCs sensitized by six
dyes are depicted in Fig. 11. The detailed photovoltaic data are summarized in Table 5. The
device sensitized by the standard p-type sensitizer, P1, measured under the same experimental
conditions is also included for comparison purpose [61]. In general, the mono-anchoring dyes
displayed higher short-circuit current density (J ), likely due to the nearly twice as high as the
sc
molar extinction coefficients than their corresponding di-anchoring congeners. Sensitizers with
bithiophene linker showed slightly larger open-circuit photovoltage (V ) than dyes with
oc
thiophene and EDOT linkers. Among the dyes investigated, the p-DSSC sensitized by EH174
with a bithiophene π-linker and with one anchoring group exhibits the highest power conversion
–
2
efficiency of 0.207% with a J of 4.84 mAcm , a V of 0.137 V and a fill factor of 0.312.
sc
oc
Whereas the EH162 with an EDOT π-linker and double anchoring groups displays the lowest
cell performance of all. The cell performance follows the order of EH174 EH122 EH170
EH126 EH166 EH162. The recorded IPCE values are over 25% between 450-550 nm for
>
>
>
>
>
dyes EH174 and EH122. The higher photocurrent densities from devices sensitized by EH174
and EH122 than others can be considered the results of higher effective chromophores adsorbed
on NiO. The amount of dye adsorbed on NiO for the mono-anchoring dyes is comparable to that
of bi-anchoring dyes despite the larger molecular sizes of the mono-anchoring dyes. In other
words, a more compact dye block layer on NiO for mono-anchoring dyes than their respective
2
8

ACCEPTED MANUSCRIPT
bi-anchoring dyes is expected, which may contribute to more effective suppression of the charge
recombination between the injected holes and the reduced form of redox mediators. The
photovoltages of devices sensitized by EH sensitizers follow the order of
EH170
~EH174~EH122 > EH166 > EH126 > EH115. A similar trend for the dark current was
also recorded.
Fig. 11. (a) Current voltage characteristic curves and (b) IPCE plots of p-DSSCs sensitized by
EH dyes
Dye loading,
-2
Sensitizers
Voc/V
Jsc/mAcm
FF
ƞ (%)
-
2
nmolcm
EH122
EH126
EH166
EH162
EH174
EH170
P1
0.134±0.005 4.39±0.05
0.122±0.006 3.93±0.02
0.131±0.003 3.47±0.01
0.115±0.006 1.79±0.02
0.137±0.008 4.84±0.03
0.139±0.012 3.47±0.03
0.303±0.004 0.178±0.020 31.4
0.304±0.003 0.146±0.006 37.4
0.284±0.003 0.129±0.005 22.1
0.304±0.007 0.062±0.004 34.3
0.312±0.006 0.207±0.014 29.4
0.315±0.007 0.152±0.007 29.1
0.123
2.57
0.294
0.093
a
Table 5. Photovotaic Parameters of the EH Dyes
2
9