The effect of porphyrins suspended with different electronegative moieties on the photovoltaic performance of monolithic porphyrin-sensitized solar cells with carbon counter electrodes

Article abstract of DOI:10.1039/c4nj02186j

Three D-π-A porphyrin sensitizers with different electronegative moieties (2,4,6-triphenyl-1,3,5-triazine, carbazole and triphenylamine) attached at the meso-position were designed and synthesized for monolithic dye-sensitized solar cells based on mesoscopic carbon counter electrodes. The effects of these different electronegative moieties on the photophysical, electrochemical and accordingly photovoltaic performance of the corresponding devices were investigated systematically. Electrochemical measurements indicate that the HOMO and LUMO energy levels could be tuned through the introduction of different electronegative groups onto the backbone of D-π-A porphyrin molecules. Current-voltage characteristics indicate that the J_sc and V_oc of the DSSCs based on WH-C3, WH-C4 and WH-C5 increase as the electron-donating ability of their donors enhance in the order of WH-C3 < WH-C4 < WH-C5 and WH-C5-sensitized cells showed the best photovoltaic performance: a short circuit photocurrent density (J_sc) of 11.43 mA cm^-2, an open circuit voltage (V_oc) of 633.84 mV, and a fill factor (FF) of 0.69, corresponding to an overall conversion efficiency (η) of 5.00%.

Full text of DOI:10.1039/c4nj02186j

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The effect of porphyrins suspended with different electronegative moieties on the
photovoltaic performance of monolithic porphyrin-sensitized solar cells with
carbon counter electrodes

Jiangzhao Chen, Songguk Ko, Linfeng Liu, Yusong Sheng, Hongwei Han, Xiong Li
Michael Grätzel Center for Mesoscopic SolarCells, Wuhan National Laboratory for Optoelectronics,
Huazhong University of Science and Technology,Wuhan 430074,Hubei, P. R. China

Correspondence to: Xiong Li (Email address: lxwhu2008@hotmail.com)
Tel: +86 27 87793027; fax: +86 27 87793027
Abstract
Three D-π-A porphyrin sensitizers attached with different electronegative
moieties (2,4,6-triphenyl-1,3,5-triazine, carbazole and triphenylamine) at the
meso-position were designed and synthesized for monolithic dye-sensitized solar cells
based on mesoscopic carbon counter electrodes. The effects of these different
electronegative moieties on the photophysical, electrochemical and accordingly
photovoltaic performance of the corresponding devices were investigated
systematically. Electrochemical measurement indicates that the HOMO and LUMO
energy levels could be tuned through introducing different electronegative groups
onto the backbone of D-π-A porphyrin molecules. Current–voltage characteristics
indicate that the Jsc and Voc of the DSSCs based on WH-C3, WH-C4 and WH-C5
increase as electron-donating ability of their donors enhance in the order of WH-C3 <
WH-C4 < WH-C5 and WH-C5-sensitized cell showed the best photovoltaic
-
2
performance: a short circuit photocurrent density (Jsc) of 11.43 mA cm , an open
1

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circuit voltage (Voc) of 633.84 mV, and a fill factor (FF) of 0.69, corresponding to an
overall conversion efficiency (η) of 5.00%.
Keywords: Porphyrin dyes; Different electronegative moieties; Monolithic
dye-sensitized solar cells; Carbon counter electrodes
1
. Introduction
With the depletion of fossil fuels and exacerbation of pollution problems,
dye-sensitized solar cells (DSSCs) as a promising photovoltaic device have attracted
extensive attention owing to their high power conversion efficiency, ease of
fabrication and potential low cost compared with traditional silicon-based solar
1
-5
cells.
It is well known that DSSCs are principally composed of dye-sensitized
working electrodes (WE), electrolytes, and counter electrodes (CEs)，where the dyes
play a crucial role in determining the power conversion efficiencies (PCEs) of the
6
-9
devices. In the past two decades, Rupolypyridyl sensitizers with PCEs of over 11%
have been demonstrated to be very efficient due to their broad absorption spectrum
through metal-to-ligand charge transfer (MLCT), longer exciton lifetime, and
2
, 5, 10
long-term chemical stability.
However, several drawbacks, which include the
high cost of noble metal ruthenium, the requirement for careful synthesis, tricky
1
0-12
purification steps and low molar extinction coefficient,
and so on, restrict
Rupolypyridyl sensitized DSSCs towards commercial viability. Seeking alternative
snsetizers seems to be a solution to these problems, which is an intensive research
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topic of high priority.
As a promising substitute for the Rupolypyridyl dye in DSSCs, porphyrins have
been widely investigated because of their low cost, high molar extinction coefficients
1
3-19
and structural diversity.
Great progress has been made in the past few years and a
record efficiency as high as 12.3% has been achieved by molecular engineering
methodology based on cosensitization of porphyrinYD2-o-C8 with organic dye Y123
2
0
and a Cobalt (II/III) redox electrolyte. Additionally, the solar cell cosensitized by
organic dye C1 and the porphyrin XW4 with an extended conjugation framework and
a carbazole donor exhibited a high PCE of 10.45% with an improved current density
2
1
(
Jsc) and an open-circuit voltage (Voc) values. Recently, through inserting a
benzothiadiazole unit between the porphyrin ring and benzoic acid accepter, an
structure-optimized dye SM315 was obtained and produced a world record efficiency
2
2
of 13% in the field of DSSCs.
As similar as the structures of the most organic dyes, the porphyrin dyes are
designed according to basic structures of Donor- π-conjugated bridge-Acceptor
(simplified as D-π-A) which are beneficial to intramolecular electron transportation.
In case of organic dyes, the donor is of great importance in determining the
photovoltaic performance of DSSCs through influencing the photophysical and
electrochemical properties of the sensitizers. Hence, various kinds of organic groups,
2
3, 24
25, 26
27, 28
29, 30
such as triphenylamine,
carbazole,
coumarin,
indoline,
3
1-33
phenothiazine,
and so on, have been extensively applied as donors in organic dyes
for DSSCs over the past two decades. On the contrary, literature investigating the
3

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influence of different donors on the photovoltaic performance of porphyrin-sensitized
3
4
DSSCs was limited.
In order to improve further the performance of porphyrin sensitized solar cells,
more insight should be devoted into the structure-property relationships of this kind of
dye. Herein, we designed and synthesized a serials of porphyrin dyes through
incorporating different electronegative organic moieties (2,4,6-triphenyl-1,3,5-triazine,
triphenylamine and carbazole) onto the dye molecule. Accordingly, the influence of
different donors on the photophysical and electrochemical characteristics of porphyrin
sensitizers were systematically investigated. It was found that different
electronegative organic moieties significantly influence the HOMO, LUMO levels
and molar absorption ability of porphyrin molecules. To further scrutinize the
relationship between the electronegativity of organic moieties and the photovoltaic
performance of DSSCs sensitized by the corresponding porphyrin dyes, a fully
printable low-cost monolithic architecture with mesoscopic carbon counter electrodes
was utilized to fabricate the complete DSSC devices. Thereinto, utilizing the
porphyrin dye molecule (coded as WH-C5) attached with triphenylamine as donor
afforded DSCs exhibiting a open circuit voltage (Voc) of 633.84 mV, short-circuit
-
2
current density (Jsc) of 11.43 mA cm , fill factor (FF) of 0.69 and the best PCE of 5%.
2
2
. Results and discussion
.1. Synthesis
In the present work, three porphyrin dyes with different electronegative moieties
(2,4,6-triphenyl-1,3,5-triazine, carbazole and triphenylamine) at the meso-position
4

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opposite to the anchoring benzoic acid group were designed and synthesized for
monolithic DSSCs based on carbon/graphite counter electrodes, coded as WH-C3,
WH-C4 and WH-C5, respectively. The structures of the dyes and the synthetic
scheme are shown in Fig. 1 and in Scheme 1, respectively. The detailed synthetic
procedures are presented in the experimental section. The molecular structures of all
1
13
target porphyrins and intermediates were confirmed by H NMR, C NMR and
APCI/ESI-MS, which are given in the experimental section.
Fig. 1 Molecular structures of sensitizers in this study.
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Scheme 1. Synthetic route of WH-C3, WH-C4 and WH-C5. Reaction conditions: a)
KI, KIO3, CH3COOH, 118℃; b) CuI, NaI, ethylenediamine, dioxane, 110 °C , 24 h; c)
bromoethane, KOH, DMF; d) HCHO,CF3COOH, RT, 15min; e) 1-Bromooctane,
K2CO3, acetone, 60℃, 4d; f) (ⅰ) n-butyllithium, TMEDA, THF, 0℃, 3h; (ⅱ) DMF,
RT, 2h; g) (ⅰ) 5 , CF3COOH, CH2Cl2, RT, 4h; (ⅱ) DDQ, 1h; h) NBS, pyridine,
CHCl3, 0 ℃ , 0.5h; i) Zn(OAc)2·2H2O, Methanol/CH2Cl2, RT, 3h; j)
(
triisopropylsilyl)acetylene, Pd(PPh ) Cl , CuI, triethylamine, THF, 65℃, 6h; k) (ⅰ)
3 2 2
TBAF in THF, THF, RT, 0.5h; (ⅱ) 1/2/4, 4-Iodobenzoic acid, Pd2(dba)3, AsPh3,
triethylamine, THF, 65℃, 5-8h.
6

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2
.2. Optical properties
The UV-vis absorption spectra of WH-C3, WH-C4 and WH-C5 in THF solution
are depicted in Fig. 2. The corresponding peak positions and molar absorption
coefficients (ε) of Soret and Q bands are listed in Table 1. As shown in Fig. 2, the
three sensitizers exhibit typical porphyrin absorption characteristics with a strong
Soret band appearing in the range of 400-500nm and mild Q bands appearing in the
longer wavelength range of 600-700nm, which is attributed to π-π* charge transfer
transitions of the conjugated molecule and intramolecular charge transfer (ICT)
3
5
transitions of the D-π-A conjugated backbone. According to the absorption data in
Table 1, it is observed obviously that the Soret band and Q band peak positions for
WH-C4 and WH-C5 are red-shifted in comparison with WH-C3, which may be
ascribed to stronger electron-donating ability of carbazole and triphenylamine
corresponding to the band gap (E0-0) of three porphyrin dyes. Compared with WH-C3
and WH-C5, it is clear that the maximum molar extinction coefficients of Soret band
-
1
-1
of WH-C4 is the highest reaching 444300 M cm which is roughly double that of
WH-C5. Meanwhile, Fig. 3 presents the UV-visible absorption spectra of the
sensitizers adsorbed on TiO2 films. In comparison with the absorption spectra in
solution, the trend of the Soret and Q bands in the absorption spectra is similar to
when the sensitizers are adsorbed on TiO2 films. Nevertheless, the Soret and Q
absorption bands are broadened and red-shifted conspicuously. This phenomenon is
1
3, 27, 36
proposed to result from the formation of J-aggregation.
Additionally, the
fluorescent emission spectra were measured in THF and are shown in Fig. 4. For the
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fluorescence spectra, major emission bands are observed at 668, 671 and 673 nm for
WH-C3, WH-C4 and WH-C5, respectively, which are similar to the trend of the
Soret band absorption spectra. Therefore, it can be concluded that porphyrin dye
molecules with different kinds of donors possess significantly different optical
properties.
Fig. 2 UV-visible absorption spectra of sensitizers in THF solvent.
Fig. 3 UV-visible absorption spectra of the sensitizers adsorbed on TiO films.
2
8

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Fig. 4 Emission spectra of sensitizers in THF solvent.
Table 1. Photophysical and electrochemical properties of the sensitizers.
a
b
c
d
Dye
λmax /nm
Emission Eox /V(vs.
E0-0
ELUMO /V(
Dye
4
-1
-1
a
e
-7
(
ε/10 M cm )
λmax /nm
NHE)
/V(vs.
NHE)
1.985
1.920
1.915
vs. NHE)
loading /10
-
2
molcm
WH-C3
WH-C4
WH-C5
453(26.35),660(4.21)
456(44.43),660(7.59)
457(22.31),661(4.39)
668
671
673
0.956
0.861
0.660
-1.029
-1.059
-1.255
0.32
0.37
0.37
a
Absorption and emission data were measured in THF at 25 ℃ . Excitation
b
wavelengths: 453 nm (WH-C3), 456 nm (WH-C4), 457nm (WH-C5). The first
porphyrin-ring oxidation was performed at 25℃ with each porphyrin (0.5 mM) in
THF containing TBAPF6(0.1M) under N2 condition with a GC working electrode, a Pt
-
1 c
counter electrode, and a Ag/AgCl reference electrode with a scan rate of 50 mV s .
E0–0 was estimated from the intersection wavelengths of the normalized UV/Vis
d
e
absorption and fluorescence spectra. ELUMO = Eox - E0-0. The amount of porphyrin
dyes were carried out through the desorption of a 5 um thick TiO2 film sensitized by
9

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dye in the 0.05 M solution of NaOH in THF/EtOH/H2O(v/v/v, 1:1:1) for 2 days.
2
.3. Electrochemical properties
In order to investigate the feasibility of electron injection and dye regeneration
processes in DSSCs, Cyclic voltammetry measurements for the three dyes were
performed in water-free THF containing 0.1 tetrabutylammonium
M
hexafluorophosphate (TBAPF6) as the supporting electrolyte at room temperature and
cyclic voltammograms are presented in Fig. 5. It is observed that the electrochemical
data for the three dyes displays quasi-reversible couples. The highest-occupied
molecular orbitals (HOMOs) of dyes corresponding to the first redox potential were
calculated to be 0.956, 0.861 and 0.660V for WH-C3, WH-C4 and WH-C5,
respectively. Practically, it was confirmed thatηinj with unit efficiency requires
approximately 0.2 V of over-potential (-ΔG) between the TiO2 conduction band (CB)
and lowest unoccupied molecular orbital (LUMO) level of the dye, and 0.3 V of –ΔG
between the highest occupied molecular orbital (HOMO) level of the dye and redox
potential of the electrolyte, to create a sufficient driving forces for the electron
5
, 37
injection from the dye to the CB of TiO2 and the regeneration of oxidized dye.
It is
observed that the HOMO levels of the three porphyrin dyes are sufficiently more
3
8
positive than the iodine/iodide redox potential value (0.4 V vs. NHE), guaranteeing
-
the efficient regeneration of oxidized dye through I presented in the electrolyte of the
DSSCs. The zero–zero excitation energies (E0–0) were calculated to be 1.985V
(WH-C3), 1.920V (WH-C4) and 1.915V (WH-C5) by the intersection of the
normalized UV-vis absorption spectrum and steady-state fluorescence emission
1
0

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spectrum. The lowest-unoccupied molecular orbitals (LUMOs) levels of all porphyrin
sensitizers were determined according to the expression of LUMO = HOMO - E0–0
and the corresponding level values are summarized in Table 1. Obviously, the LUMO
levels of all dyes are sufficiently more negative compared with the conduction band
edge level (Ecb) of the TiO2 electrode (-0.5 V vs. NHE), which means that electron
injection from the excited dye into the conduction band of TiO2 is thermodynamically
feasible. Therefore, the three dyes are properly used as sensitizers for DSSCs.
Fig. 5 Cyclic voltammograms of sensitizers in THF at a scan rate of 50
mV/s
at
room
temperature
with
0.1
M
tetra-n-butylammoniumhexafluorophosphate(TBAPF6) as the supporting electrolyte.
GC working electrode, Pt wire counter electrode, and Ag/AgCl reference electrode
were used.
2
.4. Photovoltaic performance of DSSCs
In this work, we synthesized three porphyrin dyes with the incorporation of three
different donors to investigate the effect of different donors on photovoltaic
performance of monolithic dye-sensitized solar cells with mesoscopic carbon counter
1
1

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electrodes. Compared with the conventional DSSC, this monolithic DSSC permits
printing paste layer by layer on a single FTO glass substrate by screen-printing
technique, which makes large scale commercial production possible. Furthermore,
carbon black/graphite composite used as counter electrodes in this study is an
abundantly available and low-cost material compared with high cost metallic CE,
3
9-41
which have been applied successfully in DSSCs.
Monochromatic incident photon-to-current conversion efficiency (IPCE) for
5
, 42
DSSCs is expressed as follows:
IPCE(λ) =ηLHEηinjηcc
Where ηLHE is the light harvesting efficiency, ηinj is the electron injection yield from
the photo-excited dye into TiO2, and ηcc is the charge collection efficiency at the
electrodes. Among them, ηLHE and ηinj contribute to the improvement of IPCE greatly.
In the past, it was demonstrated that the molecular structures of sensitizers have a
significant influence on the photovoltaic performance of ηLHE and ηinj through
influencing their Photophysical and electrochemical properties. The IPCEs for DSSCs
based on the three dyes are presented in Fig. 6. As shown in Fig. 6, it is observed
obviously that two peaks are located in the range of 400-500nm and 600-700nm,
respectively, which is consistent with UV-visible absorption spectra of the three dyes.
1
2

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Fig. 6 Action spectra of monochromatic incident photon-to-current conversion
efficiency (IPCE) for DSSCs based on WH-C3, WH-C4 and WH-C5. Black:
WH-C3, red: WH-C4, and blue: WH-C5.
It is clear that WH-C4 and WH-C5 possess two nearly strong IPCEs values
corresponding to Soret and Q absorption bands. In contrast, the maximum IPCE value
of the Soret band of WH-C3 is approximately three times as large as that of Q
absorption band. It was explained by the fact that the introduction of strong
electron-withdrawing 2,4,6-triphenyl-1,3,5-triazine is unfavourable to intramolecular
charge transfer from HOMO to LUMO. As a matter of fact, the conclusion was
demonstrated through utilizing a similar acceptor-π-donor-π-acceptor structure.
LW12 and LW13 with the symmetrical acceptor-π-donor-π-acceptor structure
showed inferior power conversion efficiencies compared to LD14 with D-π-A
4
3
structure. Compared with WH-C3, the maximum IPCEs of Soret bands of WH-C4
and WH-C5 dye were increased by 291% and 229%, respectively. Additionally,
although WH-C5 dye has the weakest absorption at Soret and Q absorption bands in
comparison with WH-C3 and WH-C4, the DSSCs based on WH-C5 exhibit optimal
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3

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IPCE. It may be caused by the higher ηinj resulting from a higher LUMO level.
The current density-voltage (I-V) characteristic of the DSSCs sensitized by
WH-C3, WH-C4 and WH-C5 is displayed in Fig. 7 with the corresponding detailed
photovoltaic performance parameters listed in Table 2. Under standard global air mass
1
.5 solar conditions, the WH-C3 sensitized cell gave a short circuit photocurrent
-
2
density (Jsc) of 2.50 mA cm , an open circuit voltage (Voc) of 514.57 mV, and a fill
factor (FF) of 0.75, corresponding to an overall conversion efficiency (η) of 0.97%.
The low Jsc of WH-C3 might be attributed to the following three reasons: Firstly, the
low dye absorbed amount for WH-C3 should be mainly responsible for the low IPCE
and Jsc. Secondly, the WH-C3 molecule with planar 2,4,6-triphenyl-1,3,5-triazine
moiety is liable to aggregate and form self-quenching, leading to the low ηLHE and
IPCE. Finally, acceptor- π -donor- π -acceptor structure of WH-C3 with
electron-withdrawing groups on both sides of porphyrin ring was thought to be
detrimental to intermolecular charge transfer and eventually influenced electron
injection efficiency, which resulted in low IPCE and short circuit current. Actually, the
fact that D-π-A structure is superior to A-π-A structure in porphyrin dye molecules
has been demonstrated through theoretical calculations at the density functional
4
4, 45
B3LYP level.
Under the same conditions, the DSSCs for WH-C4 and WH-C5
with incorporation of carbazole and triphenylamine as additional donor at the
meso-position opposite to the anchoring benzoic acid group showed Jsc of 10.07 and
-
2
1
1.43 mAcm ,Voc of 609.81 and 633.84 mV, and FF of 0.72 and 0.69, corresponding
to η of 4.40% and 5.00%, respectively. Apparently, Jsc of DSSCs based on the three
1
4

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sensitizers increases with electron-donating ability of groups suspending at the
meso-position opposite to anchoring group in the order of WH-C3 < WH-C4 <
4
6
WH-C5, which is consistent with the trend of IPCEs. In comparison with WH-C3,
the Jsc of WH-C4 and WH-C5-sensitized solar cells is enhanced by 303% and 357%,
respectively. So it has been well documented that the incorporation of
electron-donating donor is beneficial to intramolecular charge transfer and improves
the short circuit current dramatically. At the same time, the higher dye loading amount
of WH-C4 and WH-C5 could be another cause of their higher Jsc. In addition，as seen
from Table 2 and Fig. 7, the Voc of the devices sensitized by the three porphyrin dyes
follows the order：Voc（WH-C5）> Voc(WH-C4) > Voc(WH-C3).
Fig. 7 Current-voltage characteristics of DSSCs sensitized with WH-C3, WH-C4 and
-
2
WH-C5 under AM 1.5 G simulated solar light (100 mW cm ). Black: WH-C3, red:
WH-C4, and blue: WH-C5.
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Table 2. The photovoltaic performance parameters of the DSSCs employing WH-C3,
-
2
WH-C4 and WH-C5 under AM 1.5 G simulated solar light (100 mW cm ).
-
2
Dye
Voc/mV Jsc/mA·cm
FF
η/%
0.97
4.40
5.00
Rrec/Ω τe/ms
14.26 2.04
WH-C3 514.57
WH-C4 609.81
WH-C5 633.84
2.50
10.07
11.43
0.75
0.72
0.69
17.75 27.99
39.41 37.97
From the perspective of molecular structure, the different Voc may be ascribed to vast
differences between donor structures. Planar 2,4,6-triphenyl-1,3,5-triazine in WH-C3
not only easily aggregates, but also weakly suppresses charge recombination between
-
the electron injected into the conduction band of TiO2 and I3 at the vicinity of TiO2.
By contrast, carbazole and triphenylamine have a larger steric hindrance, preventing
electron recombination which results in their higher Voc.
2
.5. Electrochemical impedance spectroscopy (EIS)
To further investigate and elucidate the photovoltaic results and obtain more
interfacial charge transfer information of the DSSC with the different dyes,
electrochemical impedance spectroscopy (EIS) was also performed in the dark under
a forward bias of -0.6V. The Nyquist and Bode plots for WH-C3, WH-C4 and
WH-C5 are shown in Fig. 8. From the Nyquist plots (Fig. 8(a)), in the high frequency
6
range over 10 Hz, the impedance is dominated by the ohmic serial resistance (Rs) of
the dummy cell owing to the square resistance of FTO glass substrate, where the
5
, 40
phase is zero.
As seen in Fig. 8(a), the first semicircle is assigned to impedances
related to charge transport at the electrolyte/counter electrode interface. In the middle
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frequency range, the large semicircle is ascribed to the electron recombination
4
7, 48
resistance (Rrec) and chemical capacitance at the working electrode /electrolyte.
It
is obvious that the semicircle based on different dyes is in the order of WH-C3 <
WH-C4 < WH-C5, indicating that the electron recombination resistance augments
5
from WH-C3 to WH-C5. It is well known that the photovoltage of a DSSC is
intrinsically determined by the potential difference between the quasi Fermi level of
4
9
TiO2 and the redox potential of the electrolyte. As a matter of fact, the Voc can be
affected by following two factors: a) the shift of the TiO2 conduction band edge; b)
4
9
the degree of electron recombination reaction. Based on the above conclusions, the
order of the Voc(WH-C3 < WH-C4 < WH-C5) could be attributed to different
electron recombination resistances caused by different donors. The larger the
semicircle is, the slower the recombination kinetics is. It is observed that the WH-C5
with classical triphenylamine donor presented the highest recombination resistance. In
the Bode phase plots Fig. 8(b), the middle-frequency peak stands for the
charge-transfer process of injected electrons in TiO2 corresponding to the first
semicircle in Nyquist plots. The Bode phase plots likewise demonstrate the
differences in the Rrec. Electron lifetime calculated through the relation τe = 1/(2πf) (f
5
0
is the peak frequency of middle-frequency range in EIS Bode plot) can effectively
explain the higher Voc of WH-C5-sensitized solar cells compared with that of
WH-C3 and WH-C4. Electron lifetime τe was determined to be 2.04, 27.99 and 37.97
ms, for WH-C3, WH-C4 and WH-C5, respectively. The higher electron lifetime τe
observed from WH-C5 indicated more effective repression of the charge
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recombination back reaction, which could be reflected in the improvements of Voc,
resulting in improved device efficiency. To summarise, it has been demonstrated that
the incorporation of triphenylamine donor can act as blocking layer through
suppression of recombination reaction between the electron injected into the
-
conduction band of TiO2 and I3 at the vicinity of TiO2.
Figure 8. Electrochemical impedance spectroscopy (EIS) for DSSCs based on the
sensitizers. (a) Nyquist plots; (b) Bode phase plots in the dark under a forward bias of
-
0.6 V.
. Conclusions
In conclusion, three push-pull porphyrins with different electron-donating ability
3
donors were designed and synthesized for monolithic dye-sensitized solar cells based
on carbon/graphite counter electrodes. We have systematically investigated the effect
of different electron-donating ability organic groups on the photovoltaic performance
of the porphyrin-sensitized solar cells through photophysical, electrochemical,
photocurrent -voltage curve, monochromatic incident photon-to-current conversion
efficiency curve and electrochemical impedance spectroscopy characterization
1
8

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methods. The open circuit voltage and short circuit photocurrent density of the
devices sensitized by the three porphyrin dyes follows the order：WH-C5 > WH-C4 >
WH-C3. Under standard global air mass 1.5 solar conditions, the highest power
conversion efficiency was achieved by the WH-C5 sensitized solar cell, which gave a
-
2
short circuit photocurrent density (Jsc) of 11.43 mA cm , an open circuit voltage (Voc)
of 633.84 mV, and a fill factor (ff) of 0.69, corresponding to an overall conversion
efficiency (η) of 5.00%. In a word, it has been demonstrated that the incorporation of
different donors can have a profound impact on the photovoltaic performance of the
porphyrin-sensitized solar cells. The present study could provide guidance role for the
rational design of highly efficient porphyrin sensitizers.
4
4
. Experimental
.1. Materials
All reagents and solvents were obtained from commercial sources and used
without further purification unless otherwise noted. THF and toluene was dried over
sodium/benzophenone and freshly distilled before use. DMF used for formylation was
dried over enough P2O5 for several hours and distilled under reduced pressure.
Column chromatography of all the products was performed on silica gel (Kanto,
Silica Gel 60N, spherical, 200–300 mesh), and some were further purified by
recrystallization.
4
.2. Preparation of platinized carbon paste
Platinized carbon paste was prepared as described elsewhere. 2 g carbon black
powders (particle size: 30 nm) and H2PtCl6 (Sigma) with a predetermined Pt/carbon
4
0
1
9

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black weight ratio were added into 20 ml isopropanol solution (Sigma) under continue
stirring for 30 min, and then the paste was sintered for 30 min at 380 ◦C in furnace to
thermally deposit the Pt nanoparticles on the surface of carbon black, followed by
mixing with graphite powders (particle size: 1.3 μm) with a predetermined
graphite/carbon black weight ratio. Finally, 1 g of 20 nm ZrO2 nanopowders (Sigma)
and 1 g of hydroxypropyl cellulose (Sigma) were added into a 30 ml terpineol
solution. The platinized carbon material paste was obtained after stirring vigorously
using ball milling for 2 h.
4
4
.3. Synthesis
-iodo-N,N-diphenylaniline (1)
5
1, 52
Compound 1 was prepared according to literature procedure.
To the solution
of triphenylamine(1g, 4mmol) in 100mL HOAc were KI(0.332g, 2mmol) and
KIO3(0.428g, 2mmol) and was refluxed under dinitrogen for 14 h. The progress of the
reaction was monitored with TLC. After finishing reacting, saturated NaHSO (aq)
3
were added slowly into the reaction flask until the reaction solution turned from
reddish brown to colourless. After extraction with DCM, The combined extracts were
dried over anhydrous MgSO4and the solvent was removed under reduced pressure.
The residue was purified by column chromatography (silica gel) using petroleum
1
ether as eluent to give a white solid 1(1.128g, 76%). HNMR (CDCl3, 600MHz) δH
7
.49 (d, J = 8.82Hz, 2H), 7.25 (t, J = 7.89Hz, 4H), 7.07 (d, J = 7.62Hz, 4H), 7.03 (t, J
1
3
=
7.35Hz, 2H), 6.82 (d, J = 8.76Hz, 2H). C NMR (CDCl3, 600 MHz) δC 147.3,
1
38.0, 129.4, 129.2, 125.3, 124.2, 123.3. APCI-MS: m/z calcd for C18H14IN 371,
2
0

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+
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found 371 [M] .
2
-(4-iodophenyl)-4,6-diphenyl-1,3,5-triazine (2)
Compound 2 was prepared according to literature procedure. A Schlenk tube
charged with CuI (11mg, 0.058mmol, 5.0 mol%),
5
3
was
2
2
0
-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine(450mg, 1.159mmol), NaI (347mg,
.318mmol), briefly evacuated and backfilled with argon. Ethylenediamine(8 µL,
.116mmol, 10 mol%) and dioxane (2.0 mL)were added under argon. The Schlenk
tube was sealed with a Teflon valve and the reaction mixture was stirred at 110 °C for
2
3
4 h. The resulting suspension was allowed to reach room temperature, diluted with
0% aq ammonia (5 mL), poured into water (20 mL), and extracted with
dichloromethane (3×20 mL).The combined organic phases were dried over Na2SO4
and the solvent was removed under reduced pressure. The residue was purified by
column chromatography (silica gel) using petroleum ether as eluent to give a white
1
solid 2 (356mg, 70.6%). H NMR (CDCl , 600 MHz) δ 8.77 (d, J = 7.1 Hz, 4H),
3
H
8
7
1
9
.65 (d, J = 8.5 Hz, 2H), 7.72 (d, J = 8.5 Hz, 2H), 7.65 (t, J = 7.2 Hz, 2H), 7.60 (t, J =
1
3
.3 Hz, 4H). C NMR (CDCl3, 600 MHz) δC 171.7, 170.8, 136.0, 135.2, 132.7, 131.9,
+
30.5, 129.0, 128.7, 127.5. APCI-MS: m/z calcd for C21H14IN3 435, found 435 [M] .
-ethyl-9H-carbazole (3)
Compound 3 was prepared according to modified conditions of literature
5
4
procedure. Potassium hydroxide (42 g, 750mmol) was dissolved in DMF (200 ml)
for 20min and then carbazole (19.8g, 120mmol) was added into the above solution
and stirred for 40min. Subsequently, bromoethane (19.62 g, 180mmol) in 50ml DMF
2
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was stepwise added into the above solution and stirred overnight at RT. After being
poured into 1L deionized water, the white precipitate appeared, stilled for 30 min,
filtered and washed several times with cool water. The resulting precipitate was
subjected to recrystallization from ethanol, giving white solid (21.36 g, 92.4%).
1
HNMR (CDCl3, 400MHz) δH 8.06 (d, J = 7.76 Hz, 2H), 7.42 (t, J = 8.2 Hz, 2H),
7
7
1
3
.33(d, J = 8.2 Hz, 2H), 7.19 (t, J = 7.88 Hz, 2H), 4.25 (q, J = 7.2 Hz, 2H), 1.34 (t, J =
1
3
.24 Hz, 3H). C NMR (CDCl3, 400 MHz) δC 140.1, 125.7, 123.1, 120.5, 118.9,
+
08.5, 37.6, 13.9. APCI-MS: m/z calcd for C14H13N 195, found 195 [M] .
-iodo-9-ethyl-9H-carbazole (4)
A procedure similar to 1 was employed for the synthesis of 4 (1.137g,70.8%)
1
from 3 (1g, 5mmol). HNMR (CDCl3, 600MHz) δH 8.40 (s, 1H), 8.04 (d, J = 7.74 Hz,
1
7
H), 7.71 (d, J = 8.52 Hz, 1H), 7.49 (t, J = 7.68 Hz, 1H), 7.40 (d, J = 8.22 Hz, 1H),
.24 (d, J = 7.5 Hz, 1H), 7.20 (d, J = 8.52 Hz, 1H), 4.34 (q, J = 7.26 Hz, 2H), 1.41 (t,
1
3
J = 7.29 Hz, 3H). C NMR (CDCl , 600 MHz) δ 139.9, 139.0, 133.8, 129.3, 126.4,
3
C
1
25.5, 121.7, 120.6, 119.3, 110.5, 108.7, 81.2, 37.6, 13.8. APCI-MS: m/z calcd for
+
C14H12IN 321, found 321 [M] .
dipyrromethane (5)
4
3, 55
Compound 5 was prepared by adapting the literature procedure.
Solid
paraformaldehyde (3g, 90mmol) was added to pyrrole (150 mL, 2.16mol) and the
solution degassed by stirring under reduced pressure and flushing with N2. TFA (0.81
mL, 10.9 mmol) was added with vigorous stirring, and the reaction was allowed to
proceed for 15 min at room temperature before NaOH (0.2M×100 mL). The product
2
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was extracted by DCM and washed with water (3×100 mL). The combined extracts
were dried over anhydrous MgSO4. After removal of DCM under diminished pressure,
excess pyrrole was distilled out under reduced pressure. And then the crude product
was purified by column chromatography eluted with ethyl acetate and petroleum ether
1
mixture, giving the product as a colourless crystalline solid (6.97g, 53%). H NMR
(CDCl3, 400 MHz) δH 7.54 (br. s, 7.54), 7.19 (s, 2H), 6.54 (m, 2H), 6.13 (m, 2H), 6.01
1
3
(
m, 2H), 3.87 (s, 2H). C NMR (CDCl3, 400 MHz) δC 129.2, 117.5, 108.3, 106.6,
+
2
6.4. APCI-MS: m/z calcd for C9H10N2 146, found 146 [M] .
1
,3-Dioctoxybenzene (6)
2
0
Compound 6 was prepared according to literature procedure. A mixture of
resorcinol (11 g, 0.1 mol), 1-bromooctane (69.6mL, 0.4mol) and K2CO3(69g, 0.5mol)
was refluxed for 4 days in dry acetone (500mL).The solvent was removed under
reduced pressure and extracted with EtOAc (3×100mL). The combined extracts were
washed with water and dried over anhydrous MgSO . After removal of solvent under
4
reduced pressure, the product was purified by column chromatography eluting with
1
hexanes to give 1,3-di(octyloxy)benzene (26.5g, 79%). H NMR (CDCl3, 400 MHz)
δH 7.13 (t, J = 8.4 Hz, 1H), 6.46 (m, 3H), 3.92 (t, J = 6.6 Hz, 4H), 1.79-1.72 (m, 4H),
1
3
1
.47-1.40 (m, 4H), 1.35-1.23 (m, 16H), 0.88 (t, J = 6.7 Hz, 6H). C NMR (CDCl3,
4
00 MHz) δC 160.4, 129.7, 106.7, 101.5, 68.0, 31.8, 29.4, 29.3, 29.2, 26.1, 22.7, 14.1.
+
APCI-MS: m/z calcd for C22H38O2 335, found 336 [M+1] .
2
,6-Dioctoxybenzenaldehyde (7)
Compound 7 was prepared according to literature procedure. A three-neck flask
2
0
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3

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was equipped with an additional funnel and charged with compound 9 (10 g, 0.03 mol)
and tetramethylethylenediamine (TMEDA) (1.15 mL) in 84 mL of tetrahydrofuran.
The solution was degassed with dinitrogen for 15 min and cooled to 0oC, and then
n-butyllithium (22.4 mL, 1.6 M solution in hexanes 0.036 mol) was added dropwise
over 20 min and allowed to stir for 3 h. After warming to room temperature,
dimethylformamide (DMF) (4.38 mL, 0.06 mol) was added dropwise, and the
reaction was stirred for an additional 2 h. The reaction was quenched with water, and
the mixture was extracted with ether (3×80 mL), dried over anhydrous MgSO4, and
the solvent was removed under reduced pressure. The product was recrystallized from
1
hexanes to yield a white solid (8.67 g, 80% yield). H NMR (CDCl3, 400 MHz) δH
1
4
6
2
0.54 (s, 1H), 7.37 (t, J = 8.4 Hz, 1H), 6.52 (d, J = 8.5 Hz 2H), 4.01 (t, J = 6.5 Hz,
H), 1.85-1.78 (m, 4H), 1.50-1.43 (m, 4H), 1.36-1.28 (m, 16H), 0.88 (t, J = 6.9 Hz,
1
3
H). C NMR (CDCl3, 400 MHz) δC 189.2, 161.7, 135.5, 114.8, 104.5, 68.9, 31.8,
9.3, 29.2, 29.1, 26.0, 22.6, 14.1. APCI-MS: m/z calcd for C H O 362, found 363
2
3
38
3
+
[
M+1] .
,15-Bis(2,6-dioctoxyphenyl)porphyrin (8)
Compound 8 was synthesized according to literature procedure. To a degassed
5
2
0
solution of dipyrromethane (6.04 g, 41.4 mmol) and compound 7 (15 g, 41.4 mmol) in
DCM (5.4 L) was added trifluoroacetic acid (2.75 mL, 37.3 mmol). After the
solution was stirred at 23 °C under dinitrogen for 4 h, DDQ (14.1 g, 62.1 mmol) was
added and the mixture was stirred for an additional 1 h. The mixture was basified with
Et3N (7 mL) and filtered through silica. The solvent was removed under reduced
2
4

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pressure and the residue was purified by column chromatography (silica gel) using
DCM/hexanes = 1/2 as eluent. The product was recrystallized from MeOH/CH2Cl2 to
1
give the product (6.07 g, 30.1%) as a purple powder. H NMR (CDCl3, 400 MHz) δH
1
2
0.12 (s, 2H), 9.24 (d, J = 4.6 Hz, 4H), 8.96 (d, J = 4.5 Hz, 4H), 7.68 (t, J = 8.4 Hz,
H), 7.00 (d, J = 8.5 Hz, 4H), 3.82 (t, J = 6.4 Hz, 8H), 0.95-0.87 (m, 8H), 0.85-0.78
1
3
(
m, 8H), 0.66-0.59 (m, 8H), 0.56-0.50 (m, 28H), 0.48-0.40 (m, 8H), -2.99 (s, 2H). C
NMR (CDCl3, 400 MHz) δC 160.2, 147.7, 145.0, 130.8, 130.4, 130.0, 120.1, 111.6,
1
9
5
05.4, 103.9, 68.8, 31.3, 28.6, 25.3, 22.3, 13.8. APCI-MS: m/z calcd for C64H86N4O4
+
75, found 976 [M+1] .
,15-Dibromo-10,20-bis(2,6-dioctoxyphenyl)porphyrin (9)
5
6, 57
Compound 9 was synthesized according to literature procedure.
Compound
8
(4.836g,4.96mmol) was dissolved in chloroform (300mL) with pyridine (2.6mL).A
solution of NBS (1.768g, 9.92 mmol) in chloroform (100mL) and pyridine (1.4 mL)
was added dropwise at 0℃ over 30min. The reaction was stirred for 15min and then
quenched with acetone (10mL). The solvents were removed under reduced pressure
and the residue was purified by column chromatography (silica gel) using
DCM/hexanes = 1/4(volume ratio) as eluent. The product was recrystallized from
1
THF/MeOH to give the product (5.18g, 92.2%) as a purple powder. H NMR (CDCl3,
4
00 MHz) δH 9.50 (d, J = 4.8 Hz, 4H), 8.78 (d, J = 4.6 Hz, 4H), 7.69 (t, J = 8.4 Hz,
H), 6.97 (d, J = 8.4 Hz, 4H), 3.83 (t, J = 6.4 Hz, 8H), 0.98–0.91 (m, 8H), 0.84–0.76
2
(
m, 8H), 0.69–0.56 (m, 8H), 0.53–0.48 (m, 28H), 0.46–0.37 (m, 8H), -2.59 (s, 2H).
1
3
C NMR (CDCl3, 400 MHz) δC 160.0, 151.5, 149.8, 132.9, 130.1, 120.8, 115.0,
2
5

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1
05.2, 104.0, 68.6, 31.3, 28.6, 25.3, 22.2, 13.8. APCI-MS: m/z calcd for
+
C64H84Br2N4O4 1133, found 1133 [M] .
[5,15-Dibromo-10,20-bis(2,6-di-octoxyphenyl)porphinato] zinc(II) (10)
2
0
Compound 10 was prepared under modified conditions of literature procedure.
A suspension of 9 (4g, 3.52 mmol) and Zn(OAc)2•2H2O (6.476g, 35.2mmol) in a
mixture of DCM (400mL) and MeOH (200 mL) was stirred at RT overnight. The
reaction was quenched with water (100 mL), and the mixture was extracted with
DCM (2×100mL). The combined extracts were washed with water and dried over
anhydrous MgSO4. The solvent was removed under reduce pressure to give the
1
product (3.92g, 93.1%). H NMR (CDCl3, 400 MHz) δH 9.62 (d, J = 4.6 Hz, 4H), 8.88
(d, J = 4.6 Hz, 4H), 7.69 (t, J = 8.4 Hz, 2H), 6.99 (d, J = 8.4 Hz, 4H), 3.83 (t, J = 6.4
Hz, 8H), 0.97–0.91 (m, 8H), 0.86–0.74 (m, 8H), 0.61–0.54 (m, 8H), 0.53–0.41 (m,
1
3
2
1
8H), 0.39–0.32 (m, 8H). C NMR (CDCl3, 400 MHz) δC 159.9, 151.4, 149.7, 132.8,
30.0, 120.7, 114.9, 105.2, 103.9, 68.6, 31.3, 28.6, 25.2, 22.2, 13.8. APCI-MS: m/z
+
calcd for C64H82Br2N4O4Zn1197, found 1197 [M+1] .
[5,15-Bis(2,6-di-octoxyphenyl)-10,20-Bis[(triisopropylsilyl)ethynyl]-porphinato]
zinc(II) (11)
2
0
Compound 11 was prepared according to literature procedure. A mixture of the
zinc complex of 10 (0.910g, 0.81 mmol), (triisopropylsilyl)acetylene (0.906mL, 4.08
mmol), Pd(PPh3)2Cl2 (0.220g, 0.32 mmol), CuI (0.094g, 0.48 mmol), THF (60 mL)
and NEt3 (10mL) was refluxed at 65℃ for 4 h under dinitrogen. The solvent was
removed under vacuum. The residue was purified by column chromatography(silica
2
6

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gel) using DCM/hexanes = 1/20 to as eluent to give the product (0.97 g, 85.7%) as a
1
purple solid. H NMR (CDCl3, 400 MHz) δH 9.66 (d, J = 4.6 Hz, 4H), 8.86 (d, J = 4.6
Hz, 4H), 7.66 (t, J = 8.4 Hz, 2H), 6.98 (d, J = 8.4 Hz, 4H), 3.81 (t, J = 6.4 Hz, 8H),
1
0
1
2
1
.48–1.41 (m, 42H), 0.99–0.86 (m, 8H), 0.79–0.70 (m, 8H), 0.58–0.51 (m, 8H),
1
3
.51–0.45 (m, 28H), 0.44–0.33 (m, 8H). C NMR (CDCl3, 400 MHz) δC 159.9, 152.0,
50.7, 131.7, 130.9, 130.8, 121.0, 114.9, 110.1, 105.4, 100.2, 96.5, 68.8, 31.2, 28.5,
5.2, 22.1, 19.1, 13.7, 11.9. APCI-MS: m/z calcd for C86H124N4O4Si2Zn 1399, found
+
400 [M+1] .
Compound WH-C3
5
6-58
Compound WH-C3 was prepared according to literature procedure.
To a
solution of porphyrin 11 (98 mg, 0.07 mmol) in dry THF (20 mL) was added TBAF
1M in THF, 0.57 mL, 0.57 mmol). The solution was stirred at room temperature for
.5 h. The mixture was concentrated and then extracted with CH2Cl2/H2O. The
(
0
organic layer was dried over anhydrous MgSO and the solvent was removed under
4
vacuum. The residue, 2-(4-iodophenyl)-4,6-diphenyl-1,3,5-triazine (33.5mg,
0
.077mmol, 1.1eq), and 4-iodobenzoic acid (17 mg, 0.07mmol, 1.0eq) were dissolved
in a mixture of THF (20 mL) and Et3N (4 mL) and degassed with N2 for 10 min, and
then Pd2(dba)3 (33 mg, 0.036 mmol) and AsPh3 (88 mg, 0.29mmol) were added to the
mixture. The solution was refluxed for 5 h under N2 and the solvent was removed
under reduced pressure. The residue was purified on a column chromatography (silica
gel) using CH2Cl2/CH3OH = 20/1 as eluent. Recrystallization from CH2Cl2/EtOH
1
gave a green solid (32.8mg, 31%). H NMR (CDCl3/pyridine-d5, 600 MHz) δH 9.61
2
7

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(
d, J = 4.4 Hz, 4H), 8.89 (d, J = 4.2 Hz, 2H), 8.87 (d, J = 4.6 Hz, 2H), 8.86 (d, J = 4.4
Hz, 2H), 8.84 (d, J = 4.7 Hz, 4H), 8.30 (dd, J = 3.8 Hz, 4H), 8.02 (t, J = 6.2 Hz, 4H),
.95 (d, J = 7.8 Hz, 2H), 7.73 (d, J = 8.6 Hz, 2H), 7.71 (d, J = 8.6 Hz, 2H), 7.63 (d, J
9.1 Hz, 4H), 7.60 (d, J=6.4 Hz, 2H), 7.50 (t, J=7.6 Hz, 2H), 7.04 (t, J=8.6 Hz,8H),
.87 (t, J = 6.4 Hz, 8H), 1.33–1.19 (m, 8H), 0.98–0.86 (m, 8H), 0.74–0.72 (m, 8H),
7
=
3
0
1
1
1
2
1
3
.65–0.56 (m, 28H), 0.46–0.42 (m, 8H). C NMR (CDCl3/pyridine-d5, 400 MHz) δC
59.9, 151.5, 151.3, 150.7, 150.6, 150.5, 136.1, 132.5, 131.6, 131.5, 131.3, 131.0,
30.9, 130.3, 130.1, 129.9, 129.8, 129.7, 129.6, 129.0, 128.9, 128.6, 128.5, 127.8,
24.7, 123.4, 121.3, 121.2, 115.3, 115.0, 105.1, 99.7, 94.9, 94.7, 93.9, 68.5, 31.4, 29.2,
8.7, 28.6, 25.2, 22.3, 13.8. ESI-MS: m/z calcd for C96H101N7O6Zn: 1514; found 1514
+
[
M] .
Compound WH-C4
Compound WH-C4 was synthesized from 3-iodo-9-ethyl-9H-carbazole (25mg,
0
.077mmol, 1.1eq) according to the procedure as described above for synthesis of
1
WH-C3, giving a green solid (37.6mg, 38.4%). H NMR (CDCl3/pyridine-d5, 600
MHz) δH 9.70 (d, J = 4.3 Hz, 2H), 9.60 (d, J = 4.3 Hz, 2H), 8.84 (d, J = 4.4 Hz, 4H),
8
.70 (s, 1H), 8.52 (s, 1H), 8.29 (d, J = 8.0 Hz, 2H), 8.24 (d, J = 7.6 Hz, 1H), 8.08 (d, J
8.2Hz, 1H), 8.02 (d, J = 8.0 Hz, 2H), 7.71 (t, J = 8.6 Hz, 2H), 7.53 (t, J = 8.4 Hz,
H), 7.46 (d, J = 8.1 Hz, 1H), 7.03 (d, J = 8.6 Hz, 4H), 4.43 (q, J = 7.2 Hz, 2H), 3.87
=
2
(t, J = 6.4 Hz, 8H), 1.49 (t, J = 7.2 Hz, 3H), 1.32–1.21 (m, 8H), 0.99–0.86 (m, 8H),
1
3
0
.77–0.69 (m, 8H), 0.63–0.57(m, 28H), 0.48-0.46 (m, 8H).
C NMR
(CDCl3/pyridine-d5, 600 MHz) δC 160.0, 151.7, 151.4, 150.6, 150.4, 140.4, 139.5,
2
8

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1
1
2
31.7, 131.3, 130.9, 130.4, 130.0, 129.9, 129.6, 129.3, 126.0, 123.8, 123.4, 122.7,
21.5, 120.7, 119.3, 114.9, 108.7, 105.2, 101.1, 98.2, 97.0, 96.7, 68.5, 37.7, 31.4,
8.7, 28.6, 28.5, 25.3, 22.3, 17.8, 13.9. ESI-MS: m/z calcd for C89H99N5O6Zn: 1400;
+
found 1400 [M] .
Compound WH-C5
Compound WH-C5 was synthesized from 4-iodo-N,N-diphenylaniline (29mg,
0
.077 mmol, 1.1eq) according to the procedure as described above for synthesis of
1
WH-C3, giving a green solid (41 mg, 40.6%). H NMR (CDCl3/pyridine-d5, 600
MHz) δH 9.60 (dd, J = 4.4, 4.3 Hz, 4H), 8.85 (d, J = 4.4 Hz, 2H), 8.83 (d, J = 4.3 Hz,
2
H), 8.28 (d, J = 7.7 Hz, 2H), 8.00 (d, J = 7.7 Hz, 2H), 7.80 (d, J = 8.1 Hz, 2H), 7.71
t, J = 8.4 Hz, 2H), 7.31 (t, J = 7.5 Hz, 4H), 7.24 (d, J = 5.8 Hz, 2H), 7.20 (d, J = 7.7
Hz, 4H), 7.18 (d, J = 7.9 Hz, 2H), 7.09 (t, J = 7.3 Hz, 2H), 7.03 (d, J = 8.5 Hz, 2H),
(
3
0
1
1
6
1
4
.87 (t, J = 6.2 Hz, 8H), 1.30–1.26 (m, 8H), 0.98–0.94 (m, 8H), 0.80–0.77 (m, 8H),
1
3
.65–0.60 (m, 28H), 0.50–0.44 (m, 8H). C NMR (CDCl /pyridine-d , 600 MHz) δ
C
3
5
59.8, 151.5, 151.2, 150.5, 150.4, 149.6, 147.6, 147.2, 132.3, 130.8, 130.3, 129.8,
29.7, 129.4, 124.8, 123.4, 123.3, 122.6, 121.0, 115.0, 105.0, 100.5, 98.6, 94.9, 92.9,
8.4, 31.4, 28.7, 28.6, 28.5, 25.2, 22.3, 13.9. ESI-MS: m/z calcd for C93H101N5O6Zn:
+
450; found 1450 [M] .
.4. Spectral and electrochemical measurements
UV-visible spectra were performed on PerKinElmer Lambda 950
1
13
spectrophotometer. H NMR and C NMR spectra were recorded on Bruker-AV400
spectrometers with 400MHz. The chemical shifts were recorded in parts per million
2
9