Two new self-assemblies of two zinc porphyrin with isonicotinic acid by metal-ligand axial coordination and their applications in supramolecular solar cell

Article abstract of DOI:10.1016/j.tetlet.2013.05.043

Two new self-assemblies based on two zinc porphyrins substituted at the meso-positions with different donor units (denoted as ZnP1 and ZnP2) and isonicotinic acid (A) by metal-ligand axial coordination have been designed and immobilized on the double-laye

Full text of DOI:10.1016/j.tetlet.2013.05.043

Tetrahedron Letters xxx (2013) xxx–xxx
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Two new self-assemblies of two zinc porphyrin with isonicotinic acid
by metal–ligand axial coordination and their applications in
supramolecular solar cell
a
b
c
Jing Cao a, Jia-Cheng Liu a, , Li-Wei Chen , Ren-Zhi Li , Neng-Zhi Jin
⇑
a Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education, Key Laboratory of Polymer Materials of Gansu Province, Key Laboratory
of Bioelectrochemistry & Environmental Analysis of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, PR China
b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China
c Gansu Computing Center, Lanzhou 730030, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new self-assemblies based on two zinc porphyrins substituted at the meso-positions with different
donor units (denoted as ZnP1 and ZnP2) and isonicotinic acid (A) by metal–ligand axial coordination
have been designed and immobilized on the double-layer nanostructured TiO2 film-coated highly trans-
parent FTO conducting glass electrode in a photosynthesis device. These cells were also measured under
irradiance of 100 mW cmÀ2 AM 1.5G sunlight. The results reveal that the performance of ZnP2-A outper-
forms that of ZnP1-A. The UV–vis absorption spectra, fluorescence spectra, molecular orbital (MO) pat-
terns, and HOMO–LUMO energy gaps of these assemblies were also investigated to further
demonstrate the photovoltaic behavior of these cells.
Received 8 March 2013
Revised 25 April 2013
Accepted 10 May 2013
Available online xxxx
Keywords:
Self-assembly
Zinc porphyrin
Solar cell
Ó 2013 Elsevier Ltd. All rights reserved.
Inspired by the model of the chromophores of bacterial photo-
synthetic reaction centers, utilization of the multiporphyrin-based
nor groups on the photoelectronic performance of their corre-
sponding cells, two different donor units (phenol and
benzimidazyl) of these assemblies were introduced. The UV–vis
absorption spectra, fluorescence spectra, molecular orbital (MO)
patterns, HOMO–LUMO energy gaps, and the photovoltaic perfor-
mance of these photosynthesis devices are also studied to further
understand these assemblies-sensitized solar cells.
The synthetic steps are shown in Supplementary data and ZnPx
are purple solids. The assembled processes of ZnPx-A on TiO2 sur-
face are as follows: A as anchoring unit was immobilized on the
surface of the double-layer nanostructured TiO2 film-coated highly
transparent FTO conducting glass electrode18 through carboxylic
groups, then the desired dye of ZnPx was bound to the anchoring
groups through coordination-bonded from porphyrin central Zn(II)
ions of ZnPx and the N atoms of A. The detailed assembly mode is
shown in Scheme 2.
self-assemblies formed by non-covalent interaction (such as
p–p
stacking and weak van der waals interaction) as sensitizers to mi-
mic the photoinduced energy and electron transfer processes in so-
lar cells have attracted increasing interests recently.1–6 For
example, several groups have constructed zinc(II) porphyrin-based
supramolecular assemblies by the coordination bonds of Zn-to-li-
gand to functionalize carbon nanotubes,7–9 gold electrode,10,11
and nanoparticles,12–15 with an ultimate goal of generating effi-
cient light-energy-harvesting devices employing these assemblies.
However, to the best of our knowledge, the reports about the
assembly architecture based on zinc porphyrin appended organic
acid via metal–ligand axial coordination approach immobilized
on nano-structured TiO2 substrates are very few.16,17
Herein, we report two new self-assemblies (described as ZnPx-
A, x = 1, 2) with two zinc porphyrins substituted at the meso-posi-
tions with different units (denoted as ZnPx, x = 1, 2, shown in
Scheme 1) and isonicotinic acid (denoted as A, shown in Scheme 1)
by metal–ligand axial coordination, wherein these assemblies were
immobilized directly on the double-layer nanostructured TiO2
film-coated highly transparent FTO conducting glass electrode in
a photosynthesis device. To probe into the impact of different do-
The parameters of UV–vis absorption and fluorescence spectra
of ZnPx in solid state and ZnPx-A on TiO2 thin film are summarized
in Table S1. As shown in Figure 1, these absorption maxima are dis-
played in the range of 400–480 nm for strong soret (B) bands and
550–630 nm for Q bands, respectively, ascribed to
p–
p⁄ transi-
tions.19 The absorption of ZnP2-A shows slight red-shift relative
to that of ZnP1-A, which showed good agreement with the varia-
tion of HOMO–LUMO gaps, probably assigned to the donoring abil-
ity of the phenol group over that of the benzimidazyl unit.
Interestingly, the absorption of ZnPx-A pronounces broadening
and red-shifts compared with that of ZnPx. Figure 2 compares
⇑
Corresponding author. Tel.: +86 9317971039; fax: +86 9317971989.
E-mail address: jcliu8@nwnu.edu.cn (J.-C. Liu).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.05.043
Please cite this article in press as: Cao, J.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.05.043

2
J. Cao et al. / Tetrahedron Letters xxx (2013) xxx–xxx
NH
NH
N
HO
N
N
O
NH
O
C
C
H
N
O
H
N
N
N
N
N
N
O
N
N
N
N
HO
N
NH
N
C
HN
C
Zn
C
N
N
OH
C
Zn
N
N
N
N
H
O
O
H
COOH
Anchoring
molecule (A)
C
O
HN
O
HN
N
N
OH
N
HN
ZnP2
ZnP1
Scheme 1. Structural diagram of ZnPx and anchoring molecule (A).
R
O
C
N
NH
N
(ZnP1)
R:
N
R
N
O
O
N
H
Z
n
N
N
R
N
HO
N
O
(ZnP2)
C
N
H
R
FTO/TiO2
Scheme 2. The detailed assembly approach of these assemblies on TiO2 electrode surface.
0.6
0.4
0.2
0.0
800
ZnP1
ZnP1
ZnP2
ZnP1-A
ZnP2-A
ZnP2
ZnP1-A
ZnP2-A
400
0
570
600
630
660
690
420
480
540
600
660
Wavelength/nm
Wavelength/nm
Figure 1. UV–visible spectra of ZnPx in solid state and ZnPx-A on TiO2 thin film.
Figure 2. Fluorescence spectra of ZnPx in solid state and ZnPx-A on TiO2 thin film.
the fluorescence spectra of ZnPx and ZnPx-A. The results reveal
that the latter show blue-shift than the former, especially, the shift
range between ZnP1 and ZnP1-A is longer than that of ZnP2 and
ZnP2-A, suggesting that the presence of J-aggregation16 of porphy-
rin assemblies for ZnPx-A devices on the TiO2 surface, and the
aggregation of ZnP1-A show more than that of ZnP2-A.
In order to further understand the electron density distribution
within the frontier and other neighboring orbitals of these assem-
blies, we performed calculations with density functional theory
(DFT) using the GAUSSIAN 09 program20 at the B3LYP/LanL2DZ level.
As shown in Figure S1, for ZnPx-A, the MO patterns of HOMOs are
mainly localized at porphyrin cores with slight delocalization to
the donor units, while the LUMOs show an electronic distribution
on isonicotinic acid groups, signifying the presence of excellent
electron-separated status for these assemblies-sensitized devices.
Figure 3 shows the energy-levels diagram of these assemblies
and TiO2. The energy gap between the HOMO and LUMO is
2.22 eV for ZnP1-A, and 2.15 eV for ZnP2-A, to some extent
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J. Cao et al. / Tetrahedron Letters xxx (2013) xxx–xxx
3
ZnP2-A
Dye
ZnP1-A
6
ZnP1-A
LUMO
ZnP1-A(d)
ZnP2-A
-3
-4
-5
ZnP2-A(d)
3
TiO2
CB
2.15
2.22
I-/I3-
Redox
0
HOMO
0.0
0.1
0.2
V/mV
0.3
0.4
Figure 3. Orbital energy-levels of these assemblies, TiO2, and electrolyte I3À/IÀ.
Figure 5. J–V characteristics of ZnPx-A-sensitized SC measured under irradiance of
100 mW cmÀ2 AM 1.5G sunlight (ZnPx-A) and in the dark (ZnPx-A(d)).
indicating that the assembly of ZnP2-A should have a higher effi-
ciency for corresponding device.21 Notedly, the LUMO levels of
these assemblies above that of the conducting band (CB) of TiO2,
and the HOMO levels below that of the electrolyte I3À/IÀ, suggest
that electron injection from LUMO of these assemblies to the CB
of TiO2 should be capable and feasible and the excited state of
these assemblies could be reduced smoothly by the electrolyte.
The self-assemblies of ZnPx-A were fabricated into DSSC de-
vices and tested their corresponding photovoltaic properties under
irradiance of 100 mW cmÀ2 AM 1.5G sunlight. The photovoltaic
parameters are listed in Table 1. The photocurrent action spectra
of ZnPx-A-sensitized solar cells in the wavelength range 300–
800 nm shown in Figure 4 are analogous to their respective UV–
vis spectra except for broader features, and consistent with the
variation of HOMO–LUMO gaps, demonstrating the responsibility
of photovoltaic behavior of these assemblies-sensitized solar cells.
The maximum value of ZnP2-A device approaching 60% is signifi-
cantly larger than that of the ZnP1-A device. As shown in Figure 5,
the short-circuit photocurrent density (Jsc), open-circuit photovolt-
lue of latter than the former to enhance the cell behavior of the lat-
ter. However, the larger Voc in ZnP1-A compared to ZnP2-A device
is observed, probably assigned to the effect of aggregation.22 Not-
edly, the poor efficiency of these assemblies may be assigned to
the inefficient absorption of porphyrin molecules on red-NIR opti-
cal range.
In summary, we have successfully designed and obtained two
new self-assemblies based on two zinc porphyrins ZnP1 and
ZnP2 bound to isonicotinic acid by metal–ligand axial coordina-
tion. The UV–vis absorption spectra, fluorescence spectra, and the
photovoltaic performance of these photosynthesis devices are also
described. Our results reveal that these photosynthesis devices en-
able attainment of impressive improvement in photocurrent re-
sponse, especially for ZnP2-A based on the substituent of phenol
over the ZnP1-A substituted with benzimidazyl. Additionally, the
molecular orbital (MO) patterns and HOMO–LUMO energy gaps
of these assemblies are also studied to further demonstrate these
experimental products. Further study about the construction of
similar assembly is on process.
age (Voc), fill factor (FF), and overall conversion efficient (g) are
found to be 4.03 mA cmÀ2, 0.40 V, 0.70, and 1.12% for ZnP1-A de-
vice; 4.98 mA cmÀ2, 0.30 mV, 0.69, and 1.34% for ZnP2-A device.
These results suggest that the phenol group increases the IPCE va-
Acknowledgements
The National Natural Science Foundation of China (No.
20871099) and Gansu provincial Natural Science Foundation of
China (No. 0710RJZA113) have supported this work. We are very
grateful to Professor Peng Wang (Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences) for supplying device fab-
rication and measurement of solar cell. We also thank the support
of Gansu Computing Center of China.
Table 1
Photovoltaic parameters of ZnP1-A/ZnP2-A-sensitized solar cells
Dye
Jsc (mA cmÀ2
)
Voc/V
FF
g (%)
ZnP1-A
ZnP2-A
4.03
4.98
0.40
0.30
0.70
0.69
1.12
1.34
Supplementary data
60
40
20
0
ZnP1-A
ZnP2-A
Supplementary data associated with this article can be found, in
the
online
version,
at
http://dx.doi.org/10.1016/
j.tetlet.2013.05.043.
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