Synthesis and characterization of β-pyrrolic functionalized porphyrins as sensitizers for dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tetlet.2013.03.037

New β-pyrrolic functionalized porphyrins with donor-π-acceptor character were synthesized and characterized as dye sensitizers for dye-sensitized solar cells. Two types of π-conjugated spacers, namely benzene and thiophene rings, with cyanoacrylic acid as an acceptor were linked to the porphyrin ring at the β-pyrrolic position. These porphyrins showed high thermal and electrochemical stability. As sensitizers, the porphyrin dye bearing a thiophene ring as the π-conjugated spacer gave better cell performance with a short-circuit photocurrent density (J_sc) of 4.57 mA cm ^-2, an open-circuit voltage (V_oc) of 0.59 V, and a fill factor (ff) of 0.59, corresponding to an overall conversion efficiency (η) of 1.94%.

Full text of DOI:10.1016/j.tetlet.2013.03.037

Tetrahedron Letters 54 (2013) 2435–2439
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and characterization of b-pyrrolic functionalized porphyrins
as sensitizers for dye-sensitized solar cells
Kanokkorn Sirithip a, Somphob Morada a, Supawadee Namuangruk b, Tinnagon Keawin a,
Siriporn Jungsuttiwong a, Taweesak Sudyoadsuk a, Vinich Promarak c,
⇑
a Center for Organic Electronic and Alternative Energy, Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University,
Ubon Ratchathani 34190, Thailand
b National Nanotechnology Center (NANOTEC), 130 Thailand Science Park, Klong Luang, Pathumthani 12120, Thailand
c School of Chemistry and Center for Innovation in Chemistry, Institute of Science, Suranaree University of Technology, Muang District, Nakhon Ratchasima 30000, Thailand
a r t i c l e i n f o
a b s t r a c t
Article history:
New b-pyrrolic functionalized porphyrins with donor–
characterized as dye sensitizers for dye-sensitized solar cells. Two types of
benzene and thiophene rings, with cyanoacrylic acid as an acceptor were linked to the porphyrin ring at
the b-pyrrolic position. These porphyrins showed high thermal and electrochemical stability. As sensitiz-
p
–acceptor character were synthesized and
-conjugated spacers, namely
Received 19 October 2012
Revised 22 February 2013
Accepted 8 March 2013
Available online 15 March 2013
p
ers, the porphyrin dye bearing a thiophene ring as the
with a short-circuit photocurrent density (Jsc) of 4.57 mA cmꢀ2, an open-circuit voltage (Voc) of 0.59 V,
and a fill factor (ff) of 0.59, corresponding to an overall conversion efficiency ( ) of 1.94%.
p-conjugated spacer gave better cell performance
Keywords:
Porphyrin
b-Pyrrolic position
g
Ó 2013 Elsevier Ltd. All rights reserved.
Donor–p–acceptor
Thiophene
Dye-sensitized solar cell
Dye-sensitized solar cells (DSSCs) have attracted considerable
and sustained attention as they offer the possibility of low-cost
conversion of photoenergy.1 To date, DSSCs with a validated
efficiency record of >11% have been obtained with Ru complex
dyes.2 More recently, a DSSC submodule of 17 cm2 consisting of
eight parallel cells with conversion efficiency of >9.9% was fabri-
cated by Sony.3 Though there is still room for improvement of
the efficiency of Ru-based DSSCs, Ru dyes are nevertheless costly,
hard to obtain, and normally have moderate absorption
intensity.2,4 Significant effort is being dedicated to develop new
and efficient dyes being suitable for their modest cost, ease of
synthesis and modification, large molar extinction coefficients,
framework.8 Furthermore, its inherent LUMO level is situated
above the conduction band of TiO2, and its HOMO level is below
the redox couple of the electrolyte solution required for charge
separation at the semiconductor-dye-electrolyte surface, which
makes it a good donor moiety.9 A large number of porphyrins have
been developed as sensitizers for DSSCs such as carboxyphenyl
metalloporphyrins,10 thiophene-, olefin-, and acetylene-linked
porphyrins,11 quinoxaline-fused porphyrins,12 a Zn–Zn porphyrin
dimer,13
bacteriochlorin.15
oligo(phenylethynyl)-linked
porphyrins,14
and
From the Goutermann orbital model of porphyrin (Fig. 1), in the
ground state, the HOMOs (a1u or a2u) have the orbital density
mostly on the porphyrin meso-positions and the nitrogens with a
small amount of electron density on the b-pyrrolic positions. In
the excited state, the electrons go into the LUMO orbitals (Eg)
which have electron density on the b-pyrrolic and meso-positions.
This means that a porphyrin functionalized at the b-pyrrolic
positions would be expected to show strong excited state commu-
and long-term stability.5 Organic dyes with donor–
(D– –A) character meet all these criteria. Remarkable progress
p–acceptor
p
has been made in the pursuit of organic dyes as sensitizers for
DSSCs6 and efficiencies exceeding 11% have been achieved.7 Most
of the efficient dyes have a cyanoacrylic acid unit as acceptor and
anchoring groups.6
Among these dyes, porphyrin has attracted a great deal of
attention because of its natural role in photosynthesis, its intense
absorption in the visible region, its high stability and the relative
ease with which functional groups can be attached to its
nication. Therefore, incorporation of p-conjugated spacers with
cyanoacrylic acid as an acceptor at the b-pyrrolic position of
porphyrin would potentially offer strong excited state electron
transfer from the porphyrin dye to TiO2, consequently resulting
in a highly efficient dye for DSSCs.
In this work, we present the synthesis and characterization of
⇑
new functionalized porphyrins bearing two types of
spacers, namely benzene and thiophene rings, with cyanoacrylic
p-conjugated
Corresponding author. Tel.: +66 44 224 207; fax: +66 44 224 185.
E-mail address: pvinich@sut.ac.th (V. Promarak).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.03.037

2436
K. Sirithip et al. / Tetrahedron Letters 54 (2013) 2435–2439
To gain insight into the geometrical and electronic properties of
these functional porphyrins, quantum chemistry calculations were
performed using the PCM-TD-B3LYP/6-31+G(d)//B3LYP/6-31G(d)
method.18 The calculated molecular structures, in the ground-state
of dyes 6 and 7, revealed that the plane of the 30,50-di-tert-butyl-
phenyl ring was aligned nearly orthogonal to the porphyrin plane
due to steric interactions between the b-pyrrolic and aryl ring pro-
tons. The resulting bulky structures of both dyes could help to pre-
N
N
N
N
N
N
N
N
N
N
N
N
eg
LUMO
a2u
a1u
HOMO
vent effectively the close
molecules. It is known that a major factor for low conversion effi-
p p aggregation between the dye
ꢀ
= electron density
Figure 1. The Gouterman orbital models for the HOMO and LUMO orbitals of
ciencies of many organic dyes in DSSCs is the occurrence of dye
porphyrin.
aggregation on the TiO2 surface.19 The benzene
p
-conjugated
spacer in 6 (dihedral angle = 65.39°) adopted a less planar confor-
mation than that of the thiophene -conjugated spacer in 7 (dihe-
dral angle = 39.97°). This suggests that the excited -electrons
p
acid as an acceptor unit linked to the porphyrin ring at the
b-pyrrolic position. An investigation of the physical and photo-
physical properties, and their applications as sensitizers in DSSCs
are also reported.
p
from the porphyrin donor moiety can delocalize effectively to the
acrylic acid acceptor in 7, which subsequently transfer to the con-
duction band of TiO2. The electron distributions of the HOMO and
LUMO levels of 6 and 7 are shown in Figure 2. To create an efficient
charge-transfer transition, the HOMO must be localized on the do-
nor unit, and the LUMO on the acceptor unit.20 In the HOMOs, elec-
trons are delocalized over the porphyrin moiety, while in the
Scheme 1 outlines the synthesis of the designed b-pyrrolic func-
tionalized porphyrin dyes. We began with selective bromination of
5,10,15,20-tetrakis(30,50-di-tert-butylphenyl)porphyrin (1)16 at the
b-pyrrolic position with NBS in a mixed solvent of CHCl3/AcOH to
give 1-bromo-1,5,15,20-tetrakis(30,50-di-tert-butylphenyl)porphy-
rin (2) in a moderate 45% yield. To facilitate the metal-catalyzed
coupling reaction the bromo porphyrin 2 was first chelated with
zinc by heating a solution of 2 in CH2Cl2/MeOH with Zn(OAc)2ꢁ2H2O
to give zinc 1-bromo-5,10,15,20-tetrakis(30,50-di-tert-butylphenyl)-
porphyrin (3) in quantitative yield. Cross-coupling of 3 with either
4-formylphenylboronic acid or 5-formyl-2-thiopheneboronic acid
catalyzed by Pd(PPh3)4/Na2CO3 (aq) in THF gave the corresponding
aldehydes 4 and 5 in yields of 65% and 59%, respectively. Final Knoe-
venagel condensation of these aldehydes with cyanoacrylic acid in
the presence of a catalytic amount of piperidine in CHCl3 at reflux
afforded (E)-3-[4-{5,10,15,20-tetrakis(30,50-di-tert-butylphenyl)-
porphyrin-1-yl}phenyl]-2-cyanoacrylic acid (6) and (E)-3-[5-{5,10,
15,20-tetrakis(30,50-di-tert-butylphenyl)porphyrin-1-yl}thiophen-2
-yl]-2-cyanoacrylic acid (7) as dark red solids in fairly good yields of
86% and 72%, respectively. The structures of all the dye molecules
were characterized unambiguously by 1H NMR and 13C NMR spec-
troscopy as well as by high-resolution mass spectrometry.17 These
compounds show good solubility in organic solvents allowing dye
adsorption on TiO2 film, and thus fabrication of DSSCs could be
performed.
LUMOs, the excited electrons are delocalized across the
p-conju-
gated spacers and cyanoacrylic acid, indicating donor– –acceptor
p
character in both dyes. The results suggest that the HOMO ? LU-
MO transition can be considered as an intramolecular charge-
transfer (ICT) transition.
In a CH2Cl2 solution, the absorption spectra of both dyes 6 and 7
showed characteristic absorptions due to the porphyrin, which
consist of two sets of bands, namely an intense B band (the Soret
band) in the range of 400–430 nm and weaker Q bands in the range
of 550–650 nm (Fig. 3a). These characteristic absorption spectra
arise due to the configurational interaction of two porphyrin
p-
p
⁄ electronic transitions a1u ), a2u
(
p
(p
) ? Eg(p⁄). The constructive
interaction corresponds to a strong allowed transition giving rise
to the Soret band, whereas the destructive interaction corresponds
to a weak disallowed transition giving rise to the Q bands at longer
wavelength. In most porphyrins, in response to the absorption of
light, rapid population of the lowest energy excited singlet state
occurs due to fast nonradiative transitions. The absorption spectra
of 6 and 7 adsorbed on TiO2 films showed broader absorption
peaks than those in solution. Such a phenomenon is commonly ob-
served in the spectral response of other organic dyes, which may
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
4-formylphenylboronic acid
Pd(PPh3)4, 2 M Na2CO3
N
H
N
M
N
N
Zn
N
NBS, CHCl3 /AcOH
45%
N
N
N
N
N
N
THF, heat, 65%
H
N
Br
Ar
CHO
1
2
4
M = 2H
Zn(OAc)2 2H2O,
5-formyl-2-thiopheneboronic acid
Pd(PPh3)4, 2 M Na2CO3
THF, heat, 59%
CH2Cl2/MeOH, heat, 98%
3 M = Zn
CNCH2COOH,
piperidine, CHCl3, 86%
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
CNCH2COOH,
N
Zn
N
N
N
piperidine, CHCl3
N
N
N
Zn
N
N
N
Zn
N
N
72%
S
S
CN
COOH
CHO
Ar
Ar
Ar
Ar
COOH
NC
Ar = 3,5-di-tert-butylphenyl
Scheme 1. Synthesis of b-pyrrolic functionalized porphyrins 6 and 7.
5
7
6

K. Sirithip et al. / Tetrahedron Letters 54 (2013) 2435–2439
2437
LUMO
LUMO
HOMO
HOMO
6
7
Figure 2. HOMO and LUMO orbitals of 6 and 7 calculated using the PCM-TD-B3LYP/6-31+G(d)//B3LYP/6-31G(d) method.
6
(a) 1
(b)
7 in CH2Cl2
6 in CH2Cl2
7 on TiO2
6 on TiO2
7
6
4
2
0
-2
-4
-6
0
300
400
500
600
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Wavelength (nm)
Potential vs Ag/Ag+ (V)
Figure 3. (a) Absorption spectra of 6 and 7 in CH2Cl2 and adsorbed on TiO2 films. (b) CV curves of 6 and 7 measured in CH2Cl2 at a scan rate of 50 mV/s.
Table 1
Device characteristics of DSSCs fabricated with 6 and 7 as dye sensitizers
Dye
Abs (nm)a
E1/2 versus Ag/Ag+ (V)b
HOMO (eV)c
LUMO (eV)c
Eg (eV)c
IPCEmax (%)
Jsc (mA/cm2)
Voc (V)
ff
g (%)
6
7
428, 555, 594
428, 557, 597
ꢀ1.69, ꢀ1.43, 0.72, 1.00, 1.37
ꢀ1.65, ꢀ1.38, 0.74, 1.02
ꢀ5.08
ꢀ5.10
ꢀ3.21
ꢀ3.10
1.87
2.00
34
70
2.62
4.57
0.59
0.59
0.57
0.59
1.13
1.94
a
Measured in CH2Cl2.
Measured by CV using a glassy carbon working electrode, a Pt counter electrode and an Ag/Ag+ reference electrode with 0.1 M n-Bu4NPF6 as the supporting electrolyte in
b
CH2Cl2.
À
Á
À
Á
c
ox
onset
re
onset
Calculated by HOMO ¼ ꢀ 4:44 þ E
; LUMO ¼ ꢀ 4:44 þ E
; Eg = HOMOꢀLUMO.
be ascribed to the interaction of the anchoring groups of the dyes
with the surface of TiO2.21 The wide absorption spectrum is an
advantageous spectral property for light-harvesting of the solar
spectrum.
A cyclic voltammetry (CV) study on 6 and 7 revealed quasi-
reversible oxidation and reduction waves (Fig. 3b). The first and
second oxidation potentials (0.70–0.72 and 1.00–1.02 V) of 6 and
7 are nearly the same, and they are assigned to removal of elec-
trons from the porphyrin ring resulting in porphyrin radical cations
and dications, respectively. The first reduction wave of 6 and 7 is
assigned to the reduction of the porphyrin to form an anion radical,
while the second reduction wave is assigned to the reduction of the
cyanoacrylic acid moiety. Multiple CV scans of both 6 and 7 dis-
played unchanged CV curves indicating electrochemically stable
molecules. The HOMO and LUMO levels of 6 and 7 were calculated
to be ꢀ5.08 and ꢀ3.21 eV, and ꢀ5.10 and ꢀ3.10 eV, respectively
(Table 1). From these CV results, it was found that substitution at
the b-pyrrolic position of the porphyrin ring with either phenyl
cyanoacrylic acid or thiophen-2-yl cyanoacrylic acid had a major
effect on the excited state (reduction) of the porphyrin ring, while

2438
K. Sirithip et al. / Tetrahedron Letters 54 (2013) 2435–2439
(a) 80
60
(b)
5
4
3
2
1
0
7
6
7
6
40
20
0
0.0
0.2
0.4
0.6
400
500
600
700
Voltage (V)
Wavelength (nm)
Figure 4. (a) IPCE spectra and (b) I–V characteristics of the fabricated DSSCs.
a weak effect was found in the ground state (oxidation). This is in
agreement with the Gouterman orbital models (Fig. 1) and the
quantum chemical calculations (Fig. 2). Thermogravimetric analy-
sis (TGA) revealed that 6 and 7 were thermally stable with a 5%
weight loss (T5d) at a temperature well over 500 °C.
The photovoltaic properties of 6 and 7 as sensitizers for
dye-sensitized nanocrystalline anatase TiO2 solar cells (DSSCs)
were investigated. Cells with an effective area of 0.25 cm2
from the porphyrin to the acceptor, and the efficiency of porphy-
rin-based solar cells are dependent upon the degree of co-planarity
between the porphyrin ring and the linker. Further structural mod-
ification of porphyrin 7 to widen the absorption spectrum and in-
crease the molar extinction coefficient would be anticipated to give
even better cell performance.
Acknowledgements
(0.5 ꢂ 0.5 cm) were fabricated with an 11
lm (9.5 lm transpar-
ent + 1.5 m scattering) thick TiO2 working electrode, a platinum
l
This work was supported financially by the National Science
and Technology Development Agency [SPA A5: Solar Cell
(10ISRA05)], Center for Innovation in Chemistry, and the Strategic
Scholarships for Frontier Research Network for Research Groups
(CHE-RES-RG50) from the Office of Higher Education Council. We
acknowledge the scholarship support for Miss K. Sirithip from
the Strategic Scholarships for Frontier Research Network for the
Joint Ph.D. Program Thai Doctoral degree from the Office of the
Higher Education Commission.
(Pt) counter electrode, and an electrolyte composed of 0.03 M I2/
0.6 M LiI/0.1 M guanidinium thiocyanate/0.5 M tert-butylpyridine
in a 15/85 (v/v) mixture of benzonitrile/acetonitrile. For the deter-
mination of the photovoltaic performance, five cells were prepared
and measured under standard conditions. The corresponding cur-
rent density–voltage (J–V) characteristics and the incident mono-
chromatic photon-to-current conversion efficiency (IPCE) plots
are shown in Figure 4, respectively, and the resulting photovoltaic
parameters (average values) are summarized in Table 1. The IPCE
spectra of sensitizers 6 and 7 plotted as a function of excitation
wavelength were coincident with their absorption spectra. The
IPCE spectrum of porphyrin 7 showed a high maximum value of
70%, which was higher than the IPCE value of 6 (34%). Under stan-
dard AM 1.5G 100 mW cmꢀ2 illumination, the porphyrin 7-based
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solar cell gave
a short-circuit photocurrent density (Jsc) of
4.57 mA cmꢀ2, an open-circuit voltage (Voc) of 0.59 V, and a fill fac-
tor (ff) of 0.59, corresponding to an overall conversion efficiency
(g
) of 1.94%, while the porphyrin 6-based cell showed a lower Jsc
of 2.62 mA cmꢀ2 resulting in a lower conversion efficiency, (
) of
1.13%. The better solar cell performance (high IPCE, and Jsc) of
7 could be rationalized by the more efficient electron transfer from
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the quantum chemical calculations.
In summary, we have designed and synthesized b-pyrrolic func-
tionalized porphyrins as sensitizers for dye-sensitized solar cells.
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p-conjugated spacers, namely ben-
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and electrochemical stability. DSSCs fabricated using these
porphyrins as sensitizers exhibited efficiencies ranging from
1.13–1.94% under AM 1.5G illumination. The porphyrin dye bear-
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performance among both dyes with a maximum IPCE value of
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Characterization data for 6: mp >250 °C; 1H NMR (300 MHz, CDCl3) d 8.89–8.75
(m, 8H), 8.09–8.06 (m, 6H), 7.85–7.69 (m, 8H), 7.51 (d, 2H, J = 7.2 Hz), 7.37
(s,1H), 1.51 (s, 54H), 1.35 (s, 18H) ppm; 13C NMR (75 MHz, CDCl3) d 169.13,
151.24, 150.41, 150.30, 150.25, 150.21, 150.14, 148.28, 148.23, 148.19, 147.57,
145.93, 145.40, 144.32, 142.44, 142.39, 142.35, 141.6, 135.95, 132.63, 131.94,
131.40, 130.77, 129.94, 129.67, 129.57, 129.41, 122.81, 122.03, 121.63, 120.91,
120.46, 118.68, 34.97, 34.73, 31.76, 31.69 ppm; HRMS m/z calcd for
14. Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C
2009, 113, 755–764.
15. (a) Wang, X.-F.; Kitao, O.; Zhou, H.; Tamiaki, H.; Sasaki, S. J. Phys. Chem. C 2009,
113, 7954–7961; (b) Wang, X.-F.; Kitao, O.; Zhou, H.; Tamiaki, H.; Sasaki, S.
Chem. Commun. 2009, 1523–1525.
16. Promarak, V.; Burn, P. L. J. Chem. Soc., Perkin Trans. 1 2001, 14–20.
17. Characterization data for 3: mp >250 °C; 1H NMR (300 MHz, CDCl3) d 9.15 (s,
1H), 8.99 (m, 6H), 8.12 (s, 4H), 8.08 (d, 2H, J = 1.5 Hz), 7.95 (d, 2H, J = 1.5 Hz),
7.82 (s, 4H), 1.55 (s, 72H) ppm; 13C NMR (75 MHz, CDCl3) d 151.30, 150.87,
150.73, 150.68, 150.35, 148.69, 148.53, 147.87, 143.04, 141.83, 140.61, 136.91,
132.88, 132.40, 132.35, 132.27, 131.70, 129.61, 129.42, 129.20, 129.07, 122.88,
122.29, 121.97, 121.23, 121.12, 121.05,120.98, 120.79, 119.23, 35.05,
31.77 ppm; HRMS m/z calcd for C76H91BrN4Zn, 1202.5719; found, 1203.5797
[M+H] and 1225.5616 [M+Na].
C
86H97N5O2Zn, 1295.6934; found, 1295.6831 [M+] and 1318.6954 [M+Na].
Characterization data for 7: mp >250 °C; 1H NMR (300 MHz, CDCl3) d 9.13–8.84
(m, 8H), 8.44 (s, 1H), 8.13 (d, 6H, J = 6.6 Hz), 7.95 (s, 2H), 7.83 (s, 2H), 7.74 (s,
1H), 7.54 (d, 2H, J = 21.0 Hz), 6.79 (s, 1H), 1.55 (s, 54H), 1.43 (s, 18H) ppm; 13
C
NMR (75 MHz, CDCl3) d 169.41, 151.51, 150.96, 150.94, 150.90, 150.84, 150.64,
150.42, 148.62, 148.58, 148.09, 147.29, 145.75, 141.73, 141.53, 141.18, 137.64,
136.91, 136.58, 135.05, 133.22, 132.45, 131.80, 130.03, 129.59, 123.09, 122.68,
122.65, 122.36, 121.87, 120.85, 118.28, 123.09, 122.68, 122.65, 122.36, 121.87,
120.85, 118.28, 35.07, 34.80, 31.79, 31.77 ppm; HRMS m/z calcd for
C84H95N5O2SZn, 1301.6498; found, 1302.6576 [M+H] and 1324.6396 [M+Na].
Characterization data for 4: mp >250 °C; 1H NMR (300 MHz, CDCl3) d 9.99 (s,
1H), 9.09 (d, 2H, J = 3.6 Hz), 9.07 (s, 2H), 9.02 (d, 1H, J = 4.5 Hz), 8.99 (s, 1H),
8.87 (d, 1H, J = 4.8 Hz), 8.21 (d, 2H, J = 1.5 Hz), 8.18 (d, 2H, J = 1.5 Hz), 8.15 (d,
2H, J = 1.5 Hz), 7.90 (d, 2H, J = 1.5 Hz), 7.85–7.83 (m, 3H), 7.72 (d, 2H,
J = 8.1 Hz), 7.67 (d, 2H, J = 8.1 Hz), 7.40 (s, 1H), 1.54 (s, 54H), 1.40 (s, 18H)
ppm; 13C NMR (75 MHz, CDCl3) d 191.97, 151.49, 150.87, 150.73, 150.67,
150.54, 148.64, 148.60, 147.78, 146.61, 146.03, 145.40, 141.88, 141.77, 141.05,
135.87, 133.46, 132.83, 132.44, 132.37, 132.28, 131.79, 130.96, 130.48, 129.86,
129.59, 129.50, 128.59, 126.65, 123.19, 122.74, 122.37, 122.12, 121.30, 120.87,
35.07, 34.75, 31.77, 31.61 ppm; HRMS m/z calcd for C83H96N4OZn, 1228.6876;
found, 1229.6954 [M+H] and 1251.6773 [M+Na].
18. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.;
Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven,
T.; Montgomery, Jr., J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.;
Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.;
Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas,
Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. GAUSSIAN, Inc.: Wallingford,
CT, 2009.
19. Fink, R. F.; Seibt, J.; Engel, V.; Renz, M.; Kaupp, M.; Lochbrunner, S.; Zhao, H. M.;
Pfister, J.; Wurthner, F.; Engels, B. J. Am. Chem. Soc. 2008, 130, 12858–12859.
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21. (a) Thomas, K. R. J.; Hsu, Y. C.; Lin, J. T.; Lee, K. M.; Ho, K. C.; Lai, C. H.; Cheng, Y.
M.; Chou, P. T. Chem. Mater. 2008, 20, 1830–1840; (b) Lu, M.; Liang, M.; Han, H.-
Y.; Sun, Z.; Xue, S. J. Phys. Chem. C 2011, 115, 274–281.
Characterization data for 5: mp >250 °C; 1H NMR (300 MHz, CDCl3) d 9.83 (s,
1H), 9.06–9.02 (m, 3H), 8.96 (d, 2H, J = 4.7 Hz), 8.40 (d, 2H, J = 4.7 Hz), 8.13 (d,
2H, J = 1.5 Hz), 8.11 (d, 2H, J = 1.5 Hz), 8.09 (d, 2H, J = 1.5 Hz), 7.93 (d, 2H,
J = 1.6 Hz), 7.81 (d, 3H, J = 1.6 Hz), 7.53 (s, 1H), 7.39 (d, 1H, J = 3.8 Hz), 6.80 (d,
1H, J = 3.8 Hz), 1.53 (s, 54H), 1.41 (s, 18H) ppm; 13C NMR (75 MHz, CDCl3) d
182.74, 151.65, 151.46, 151.03, 150.96, 150.88, 150.41, 148.65, 148.04, 147.15,
145.51, 142.12, 141.66, 141.60, 141.17, 137.59, 136.63, 136.16, 133.13, 132.52,
131.87, 130.18, 129.86, 129.72, 129.59, 129.53, 35.07, 34.82, 31.77, 31.64 ppm;
HRMS m/z calcd for C81H94N4OSZn, 1234.6440; found, 1235.6518 [M+H] and
1257.6338 [M+Na].