Spectral and redox properties of zinc porphyrin core dendrimers with triarylamines as dendron

Article abstract of DOI:10.1039/c0dt00199f

The first and second generation of zinc porphyrin core dendrimers (3 and 4) with triarylamine as dendron have been synthesized via Ullmann coupling reaction. Their absorption and emission spectra indicate that there are strong interactions between zinc porphyrin core and triarylamine dendrons. Zinc porphyrin links with triarylamine causes Soret band broadening and Q band shift as compared with ZnTPP. Because of the antenna effect on these dendrimers, the fluorescence quantum yields were strongly enhanced when more triarylamine moieties were linked. Cyclic voltammetry and spectroelectrochemical methods were used to investigate the redox properties of dendrimers. Axial ligation of zinc porphyrin with N-methylimidazole is useful in differentiating the oxidation site of dendrimers. For the first generation dendrimer (3), porphyrin ring oxidation potential shifts cathodically because the periphery dendrons are strong electron-donating groups. On the other hand, the dendrons of the second generation (4) are oxidized first and generate an atmosphere of eight positive charges. The porphyrin ring core is then oxidized with an anodic shift in potential due to the electron-withdrawing effect of the oxidized substituents.

Full text of DOI:10.1039/c0dt00199f

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Spectral and redox properties of zinc porphyrin core dendrimers with
triarylamines as dendron†
Chih-Yen Huanga and Yuhlong Oliver Su*a,b
Received 24th March 2010, Accepted 17th June 2010
First published as an Advance Article on the web 6th August 2010
DOI: 10.1039/c0dt00199f
The first and second generation of zinc porphyrin core dendrimers (3 and 4) with triarylamine as
dendron have been synthesized via Ullmann coupling reaction. Their absorption and emission spectra
indicate that there are strong interactions between zinc porphyrin core and triarylamine dendrons. Zinc
porphyrin links with triarylamine causes Soret band broadening and Q band shift as compared with
ZnTPP. Because of the antenna effect on these dendrimers, the fluorescence quantum yields were
strongly enhanced when more triarylamine moieties were linked. Cyclic voltammetry and
spectroelectrochemical methods were used to investigate the redox properties of dendrimers. Axial
ligation of zinc porphyrin with N-methylimidazole is useful in differentiating the oxidation site of
dendrimers. For the first generation dendrimer (3), porphyrin ring oxidation potential shifts
cathodically because the periphery dendrons are strong electron-donating groups. On the other hand,
the dendrons of the second generation (4) are oxidized first and generate an atmosphere of eight
positive charges. The porphyrin ring core is then oxidized with an anodic shift in potential due to the
electron-withdrawing effect of the oxidized substituents.
We report here the study of porphyrin-triarylamine dendrimers.
Introduction
The spectral and electrochemical properties of first and sec-
ond generation (3 and 4) are analyzed. As compared to the
previous study in porphyrin-carbazole dendrimers,13 porphyrin-
triarylamine dendrimers show stronger electronic interactions
between porphyrin and dendrons, and the intramolecular energy
transfer from dendrons to the zinc porphyrin core is observed.
Scheme 1
Porphyrin is a p-conjugated macromolecular with unique pho-
tophysical and electrochemical properties. These properties can
be fine tuned and controlled by bonding with proper functional
groups at the meso and b positions on the macrocycle.1 In the past
decades, artificial metalloporphyrins have played an important
role in biological applications, for example, to mimic the catalytic
reactions of cytochromes.2 Subsequently, metalloporphyrin core
dendrimers have been synthesized, which show reversible O2
binding,3 good regioselectivity for the substrate and a more
stable catalytic active center in the catalytic reaction.4 Moreover,
porphyrin core dendrimers with a large number of chromophores
at the branches or periphery are appropriate to mimic the antenna
effect of light-harvesting photosynthetic complexes.5
Triphenylamine (TPA)-based derivatives are widely investigated
in the application to optoelectronic materials such as hole
transporting materials in organic light emitting diode (OLED),6
dyes in dye-sensitized solar cells (DSSCs)7 and electrochromic
polymer.8 Recently, hybridization of porphyrin and TPA have
attracted much attention.9–12 Cheng’s group first reported the
electrochemistry of triarylamine-porphine hybrid conjugates.9
Yeh’s group is engrossed in the porphyrin-triarylamine conjugates
link via ethynyl linkage to enhance the electronic interaction.10–11
Both of their investigations show strong electronic interactions
between two entities, including the decrease in HOMO–LUMO
gap, the potential shift of porphyrin ring oxidation and the charge
transfer from triarylamine to porphyrin.
Scheme 1 Zinc porphyrin core dendrimers and relative compounds.
aDepartment of Applied Chemistry, National Chi Nan University, 1, Univer-
sity Rd., Puli, Nantou County, 54561, Taiwan. E-mail: yosu@ncnu.edu.tw;
Fax: +886-49-2917956; Tel: +886-49-2910960 ext: 4150
Results and discussion
Spectral properties
bDepartment of Chemistry, National Chung Hsing University, 250, Kuo
Kuang Rd., Taichung, 402, Taiwan
Absorption spectra of zinc porphyrins are shown in Fig. 1.
Zinc porphyrin core dendrimers 3 and 4 exhibit very different
shapes of the spectra as compare to ZnTPP. These observations
† Electronic supplementary information (ESI) available: 1H NMR spectra,
excitation spectra and tables of calculated numbers of electron transferred.
See DOI: 10.1039/c0dt00199f
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Table 1 Absorption spectral lmax (nm), full width at half maximum height
(fwhm, cm-1) and oscillator strength (f )a of zinc porphyrins in CH2Cl2
Table 2 Half-wave potentials (E1/2 vs. Ag/AgCl(saturated))c and peak
potentials (Ep) of zinc porphyrins and dendrons
Compound Soret band
max, fwhm, f
Q(0,1)
max, fwhm, f
Q(0,0)
max, fwhm, f
Q band
f total
Compound Ox 4
Ox 3
Ox 2
Ox 1
Red 1
Red 2
b
l
l
l
ZnTPP
—
—
—
+0.96
+1.42a
+1.00
+1.13
+1.42a
+0.87b
+0.71
+0.73b
+0.82
+0.78
+0.66b
+0.38
+0.42b
-1.31
—
-1.36
—
-1.82a
—
ZnTPP
3
4
419, 573, 1.98 548, 704, 0.079 586, 614, 0.009 0.088
445, 3684, 1.33 558, 993, 0.050 604, 903, 0.051 0.101
419, 1132, 1.54 561, 1347, 0.058 610, 1047, 0.070 0.128
1
3
2
4
—
+1.35a
—
-1.81a
—
+1.43a
-1.36
-1.84a
a Oscillator strength (f ). f = 4.319 ¥ 10-9A/n, where A = integrated area of
peak and n = reflection index of solvent. Using the plot of (e vs. cm-1) to
a Peak potential of an irreversible wave. b Multiple electrons transfer
obtain each absorption peak’s integrated area (A) in the spectrum. b f total
=
involved. c E1/2 of Fc/Fc+ is +0.54 V vs. Ag/AgCl(saturated).
f Q(0,1) + f Q(0,0)
.
Fig. 2 Fluorescence spectra of compounds. ZnTPP, 1 and 3 were excited
at 419, 301, 301 nm in CH2Cl2 respectively. 2 and 4 were excited at 313 nm
in toluene. The concentration of 1 and 2 were 8.0 ¥ 10-6 M, 3 and 4 were
2.0 ¥ 10-6 M.
Fig. 1 Absorption spectra of 2.0 ¥ 10-6 M ZnTPP, 3 and 4 in CH2Cl2.
include the specific absorption of dendrons in UV region, the
broadening and splitting of Soret bands, and bathochromic shift of
Q bands. These phenomena indicate that there is strong electronic
interaction between dendron and zinc porphyrin. The results
are similar to the previous studies in triarylamine-porphyrin
conjugates.9–10 Maximum absorption wavelength (lmax), full width
at half maximum height (fwhm) and oscillator strength (f ) of peaks
are summarized in Table 1. In this study, the Q band oscillator
strength becomes more intense as more electron-donating groups
bond with porphyrin. We find the dendritic zinc porphyrin 4 has
the most intense Q band in these three zinc porphyrins. According
to the four-orbital-model theory,14 the intensity of Q band depends
on the energy difference between a2u and a1u orbitals. Previous
studies have indicated that the energy of a2u is higher than a1u
in tetraphenylporphyrin.14,15 The bonding of electron-donating
group at the meso position of porphyrin ring will raise the energy
of a2u orbital, and then result in a larger energy difference between
a2u and a1u.
set to 0.11.16 Values obtained for ZnTPP, 3 and 4 are 0.037, 0.130
and 0.163 respectively.17 It shows an enhanced quantum efficiency
when triarylamine dendrons are bonded to the zinc porphyrin
core.
Cyclic voltammetry
Cyclic voltammograms (CV) and half-wave potentials (E1/2) of
ZnTPP and 1–4 are shown and listed in Fig. 3 and Table 2. ZnTPP
can undergo two ring oxidations to radical cation and dication at
E1/2 = +0.82 and +1.13 V, respectively. Compound 1 can reversibly
be oxidized at E1/2 = +0.78 V, followed by an irreversible oxidation
wave at Epa = +1.42 V. There is a new and small oxidative wave
The fluorescence spectra of ZnTPP and 1–4 are shown in Fig. 2,
where 1 and 2 were excited at 301 and 313 nm respectively. The
emission peaks are at 389 nm for 1 and 423 nm for 2, respectively.
When dendritic zinc porphyrin 3 is excited at wavelength of Soret
band, it exhibits one emission peak at 635 nm. Interestingly, while
3 is excited at 301 nm, there is no peak found in the region of 350–
550 nm and instead, it emits at 635 nm. Similar results also can be
found in 2 and 4, where the emission peak of 4 is at 632 nm. These
phenomena indicate that an intramolecular energy transfer occurs
between dendron and zinc porphyrin core. The antenna effect of
triphenyamine bound zinc porphyrin has been reported before.9
In this study, the quantum efficiency of 3 and 4 are also measured
by using H2TPP as standard. The quantum yield of H2TPP was
Fig. 3 Cyclic voltammograms of ZnTPP and 1–4 in CH2Cl2 containing
0.1 M TBAP. Scan rate: 0.1 V s-1. Molar concentrations of compounds:
1.0 ¥ 10-3 M.
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Table 3 Half-wave potentials (E1/2), peak-to-peak separations (DEp) and
peak currents (ip) of each redox in the cyclic voltammogram of zinc
porphyrin 4
at about +1.00 V in the second cyclic scan when scan potential is
over +1.42 V. The new wave is suggested to be the oxidation of the
carbazole derivative, which is generated from an unstable 12+.18 It
can be observed in Fig. 3 that there are multiple redox couples
overlapping in the potential range of +0.5 to +1.2 V in the CV of
3. According to the structural relations and oxidation potentials
between ZnTPP, 1 and 3, it is reasonable to predict that the CV
of 3 could have total 6e- oxidations involved.
Zinc porphyrin (4)
1/2/V
Ox 3
Ox 2
Ox 1
Red 1
E
+1.00
0.13
8.6
+0.73b
0.23
37.1
+0.42b
0.22
37.0
-1.36
0.12
9.2
DEp/V
ip/mAa
a These values are referring to anodic and cathodic peak currents for
oxidative and reductive reactions respectively. b Multiple electrons transfer
involved.
The literature has reported that axial ligation to zinc porphyrin
could tune the redox potentials of zinc porphyrin.19 Imidazole
ligation would cause a cathodic shift in potential for first zinc
porphyrin oxidation and an anodic shift for the second oxidation.
In this study, we use N-methylimidazole (N-MeIm) as the axial
ligand to deconvolute the overlapping oxidation waves. Fig. 4(A)
is the CV of 3 in the presence of N-MeIm. In the potential range
of +0.5 to +0.8 V, as N-MeIm is added to the solution, one
redox couple at Epa = +0.56 V appears while other redox waves
have little change in potential. It gradually separated into two
redox couples when the concentration of N-MeIm reaches one
equivalent of 3 (Fig. 4(A)(e)). According to the axial ligation effect
on zinc porphyrin, the first oxidation of 3 is thus assigned to the
oxidation at the porphyrin ring, and the second one is assigned
to one of the four triarylamines. During the N-MeIm titration,
the redox reactions in the region of +0.8 to +1.2 V were getting
closer and became one redox with a peak-to-peak separation of
0.19 V. The results suggest that 4e- transfer is involved in this redox
including 1e- oxidation of porphyrin radical cation to dication and
3e- oxidation of three triarylamine moieties. Further confirmation
will be conducted by spectroelectrochemical method.
peak separation (DEp) of Red 1 are 9.2 mA and 0.12 V respectively.
As compared with Red 1, the first and second oxidative redox
reactions (Ox 1 and Ox 2) have larger ip and DEp (Table 3). The
third oxidative redox (Ox 3) has about the same current value with
Red 1 can be assigned as a 1e- transfer electrochemical reaction.
The ip of Ox 3 is smaller than that of Red 1 by about 6%. The
large positive charge (9+) apparently exhibits significant effect in
association with electrolyte during the diffusion process. As shown
in Table 3, the values of ip and DEp in Ox 1 and Ox 2 are almost
equal. So we infer that both Ox 1 and Ox 2 involved 4e- transfers.
Using N-MeIm as axial ligand to probe the oxidation sites of 4.
The CV of 4 in the presence of N-MeIm is shown in Fig. 4(B). Only
Ox 3 was cathodically shifted by 0.06 V when N-MeIm ligated to
4. It indicates that Ox 3 is the porphyrin ring oxidation of 4. It is
interesting to note that the dendrons at the periphery of 4 bearing
8+ charges causes the porphyrin ring to be harder to oxidize by
0.18 V as compared with ZnTPP, and that imidazole ligation
makes the porphyrin ring oxidation easier by 0.06 V.
In the discussion above, we conclude the Ox 1 and Ox 2 of 4 are
the removal of the first and second electron from each of the four
dendrons to form 44+ and 48+, respectively. Subsequently, Ox 3 is
the first porphyrin ring oxidation to form 49+.
UV/Vis/NIR spectroelectrochemistry
The studies of electron interaction between dendron and zinc
porphyrin core and further confirmation of the oxidative sites on
zinc porphyrins were carried out by UV/Vis/NIR spectroelectro-
chemistry. The spectral changes upon applied potentials of 1 and 3
are in Fig. 5. The radical cation of compound 1 exhibits absorption
peaks at 372, 582 and 756 nm. Owing to the overlapped multiple
redox reactions in CV, the spectroelectrochemical investigation
of 3 were performed by small increments of potential from
+0.45 to +1.04 V. According to the trend of spectral change,
the spectra were divided into five diagrams (Fig. 5(B)–(F)). In
Fig. 5(B), the diminished Soret band at 445 nm indicates that the
porphyrin ring is oxidized. This result is consistent with what
we inferred from cyclic voltammetry (Fig. 4(A)). It is worth
noting that during the process of 3 to 3+, the absorption band
of triarylamine moieties at 301 nm also decreases, accompanied
by forming new bands at 780 and 1418 nm, which are due to
the specific absorption of triarylamine radical cation and the
charge transfer between triarylamines and zinc porphyrin core.9–10
A reasonable explanation for this phenomenon is that electron-
rich triarylamines transfer its electrons to the porphyrin ring,
which lacks an electron after 1e- removal. Fig. 5(C) represents
the formation of 32+, which is assigned as the oxidation of one
Fig. 4 Cyclic voltammograms of zinc porphyrins (A) 3; (B) 4 in CH2Cl2
containing 0.1 M TBAP. Scan rate: 0.1 V s-1. Molar concentrations of 3
and 4 are both 1.0 ¥ 10-3 M; [N-MeIm]: (a) 0; (b) 2.5 ¥ 10-4; (c) 5.0 ¥ 10-4;
(d) 7.5 ¥ 10-4; (e) 1.0 ¥ 10-3 M.
The CV of 2 exhibited two reversible redox reactions at E1/2
=
+0.38 and +0.71 V and a subsequent irreversible oxidative wave
at +1.42 V. It is noteworthy that there is a new wave produced at
+1.12 V in the second cyclic scan when the scan potential is over
+1.42 V. The new wave is assigned as the oxidation of benzidine,
which is the dimerization product of 23+. This phenomenon is
similar to the dimerization of triphenylamine and oligo(N-phenyl-
m-aniline)s.20 There are four reversible redox reactions in the CV
of 4 and may have nine electrons involved in the three oxidative
couples. The redox couple at E1/2 = -1.36 V (Red 1) is a 1e-
reduction of the porphyrin ring. Peak current (ip) and peak-to-
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Fig. 5 Spectral changes of 1 and 3 in CH2Cl2 containing 0.1 M TBAP at various applied potentials.
triarylamine moiety. The absorbance of triarylamine decreases
and the charge transfer band at NIR region continues to grow.
Fig. 5(D)–(F) are the spectra at applied potentials from +0.78
to +1.04 V, as we inferred in cyclic voltammetry that there
should be a total of 4e- oxidations within this potential region.
In Fig. 5(D), the absorption of neutral triarylamine is totally
diminished and the extinction coefficient (e) of the new absorption
band formed at 756 nm is about three times as compared with
that of 1+. It indicates the four triarylamines were all oxidized
to radical cations at +0.90 V. The oxidation state in here is
assigned as 35+, including 1e- removed from the porphyrin ring
and 4e- from the triarylamine moieties. Because all redox centers
in this molecule were oxidized, there is only small absorbance
present in NIR region. Furthermore, one band with a high e
value (150 000 dm3 mol-1 cm-1) and a quite narrow bandwidth
appeared at 430 nm. This band is like a Soret band of neutral
porphyrin. This “Soret band-like” absorption probably resulted
from the resonance of electrons from four triarylamine radical
cations to the periphery of porphyrin ring, and then causes
an increased electron density in porphyrin ring. The spectral
changed at +0.90 V to +1.02 V become more irregular and more
complicated (Fig. 5(E) and (F)). The potential applied at +1.04 V
leads to the decomposition of the zinc porphyrin.
During the process of 2 oxidized to 2+, three new bands appeared
at 438, 768 and 1356 nm (Fig. 6(A)). The bands in NIR are known
as intervalence charge transfer (IVCT) band. The spectral pattern
Fig. 6 Spectral changes of 2 and 4 in CH2Cl2 containing 0.1 M TBAP at various applied potentials.
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of 2+ is similar to the triamine radical cation in the previous
study.21 Because the electron-donating effect of methoxy groups
on 2+, the new peaks were located at lower energy (22 831, 13 016,
7375 cm-1) as compared to the peaks of triamine radical cation
(23 040, 14 350, 8117 cm-1).21 The intensity of the IVCT band is
increased and blue shift to 1182 nm during the oxidation process
of 2+ to 22+ (Fig. 6(B)). Moreover, absorption bands at 294 and
438 nm were diminished and one band appeared at 590 nm. The
spectral recoveries are both quantitative for monocation 2+ and
dication 22+, when they returned to their former oxidation state. It
shows that these two oxidation products are very stable.
ZnTPP. Consequently an electron-lacking environment around
the porphyrin ring was therefore created. The oxidized dendrons
just like electron-withdrawing groups, which causes an anodic shift
in potential of the first porphyrin ring oxidation of 4. The charge
transfer bands which appeared in NIR in the oxidation process of
3 indicates the significant interaction between dendrons and zinc
porphyrin core. In the oxidation process of 4, the IVCT bands
are resulted from the charge transfer between nitrogen atoms
within each dendron substituent, not through the zinc porphyrin
bridge. Further studies in catalytic reactions by using these two
macrocycles with electro-active metals are in progress.
The first oxidative redox in the CV of 4 was examined by
spectroelectrochemistry with applied potentials from 0.00 V to
+0.55 V. In Fig. 6(D), the spectral shape in 650 to 2200 nm at
+0.55 V is similar to the spectrum of 2+, and no other new bands
appear in this region. The e of the IVCT band at 1354 nm is
almost four times as large as that of 2+ at 1356 nm. Furthermore,
the number of electrons transferred in this oxidation process is
about 1 for each dendron.22 This evidence indicates that there is
no charge transfer from the dendron moieties to the zinc porphyrin
core. The electrochemical behaviour of dendrons are independent
and the intervalence charge transfer occurs within each of four
single dendron moieties. Because of the spectral overlapping, the
Soret band has a red shift from 419 to 426 nm with increased
absorbance by about 18%. Furthermore, the spectrum of 44+ at
+0.55 V is very similar to the sum of the spectrum of neutral state
of ZnTPP and four times of 2+ (Fig. 6(C)). Similar phenomena
are occurring at the process of the oxidation of 44+ to 48+, where
the e of the band at 1172 nm is also almost four times to that of
22+ at 1182 nm (Fig. 6(E)). During the process of 48+ to 49+, the
Soret band at 426 nm and the Q band at 554 nm are decreasing
and is accompanied by an increasing of absorbance in 550–700 nm
(Fig. 6(F)). This is a typical absorption spectrum of the formation
of porphyrin radical cation.23 Absorption band at NIR region
just has slightly changed in absorbance, which shows there has
quite small amount of charge transfer between dendron and zinc
porphyrin core via the phenyl bridging.
Experimental
General
1H and 13C NMR spectra were obtained from Varian Unity
Inova 300 WB spectrometers. Varian Cary-50 scanning UV/Vis
spectrometer was used to determine extinction coefficients of zinc
porphyrins and to obtain absorption spectra with 1 cm cuvette.
Mass spectra were obtained with Applied Biosystem Voyager-
DETM Pro spectrometer. Fluorescence spectra, excitation spectra
and fluorescence quantum yields measurement were finished
with Varian Cary Eclipse spectrometer. For electrochemical
studies, CHI 700A electroanalytical workstation was used in
cyclic voltammetry and conducted with a three-electrode cell.
Glassy carbon electrode (area = 0.07 cm2) was used as working
electrode. The auxiliary and reference electrodes were platinum
wire and Ag/AgCl(KCl saturated) respectively. Spectroelectro-
chemistry was performed with JASCO V-570 UV/Vis/NIR
spectrometer and Bioanalytical System Model SP-2 potentiostat.
Platinum gauze, platinum wire and Ag/AgCl(KCl saturated) were
used as working, auxiliary and reference electrode respectively
in a spectroelectrochemical cell with an 1 mm optical path
length.
Materials
Zinc tetraphenylporphyrin (ZnTPP) and zinc meso-tetra(p-
aminophenyl)porphyrin (ZnTAPP) were synthesized from lite-
rature methods,24,25 and follow by metallating with zinc
acetate dihydrate in CH2Cl2–CH3OH. N,N-Di-(4-methoxy-
phenyl)phenylamine (1) and N,N-di-(4-methoxy-phenyl)-4¢-
iodophenylamine (I-TPA-(OCH3)2) were obtained according to
the literature methods.26,27 Other chemicals were all commercially
available. Organic solvents that were used in electrochemical stud-
ies were dried and distilled before use. Tetra-n-butylammonium
perchlorate (TBAP) were recrystallized twice from ethyl acetate
and dried before use.
Conclusions
The first synthesis of porphyrin-triarylamine conjugated den-
drimers is reported here. As compared with those porphyrin-
carbazole dendrimers,13 bonded triarylamine dendrons greatly
affect the electronic configuration of porphyrin. These phenomena
are reflected in the electronic spectra of 3 and 4. In the emission
spectroscopy study, the intramolecular energy transfer is found in
both 3 and 4. Dendrons absorb the UV light and then transfer the
energy to the porphyrin core. Fluorescence in the visible region
subsequently is emitted from porphyrin. Due to the antenna effect
found in these dendrimers, 3 and 4 exhibit an enhancement in
quantum efficiency.
4,4¢-Di-[N,N-di(4-methoxyphenyl)amino]triphenylamine (2)31
From cyclic voltammetry and spectroelectrochemistry studies,
we have analyzed the electron transfer reactions for each redox
couples of 3 and 4. Owing to the strong electron-donating N,N-
di-(p-methoxyphenyl)amino groups bonded to the zinc porphyrin,
the potential of the first porphyrin ring oxidation of 3 was
cathodic shifted about 0.20 V as compared to ZnTPP.30 It
is worth noting that the same substituent effect on 4 is not
observed because the dendrons of 4 are easier to oxidize than
The precursor 4,4¢-diaminotriphenylamine was synthesized by
modifying the literature method,28 in which 3,4-dimethylaniline
was replaced by aniline. Compound 2 was obtained by reacting
4,4¢-diaminotriphenylamine and 4-iodoanisole with Ullmann cou-
pling reaction. 4,4¢-Diaminotriphenylamine (0.39 g, 1.42 mmol)
and 4-iodoanisole (6.80 g, 29.05 mmol) were dissolved in 1,2-
dichlorobenzene (10 ml) containing K2CO3 (1.57 g, 11.36 mmol),
Cu powder (0.72 g, 11.36 mmol) and 18-crown-6 (1.13 g,
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4.26 mmol). The reaction mixture was heated to reflux with stirring
for 48 h. When the mixture was cooled to room temperature,
50 ml CH2Cl2 was added and then filtrated. The filtrate was
passed through a silica gel column with CH2Cl2 as eluent. Yield:
0.35 g, 35%. UV/Vis lmax(CH2Cl2)/nm 313 (e/dm3 mol-1 cm-1 38
600), 1H NMR dH(300 MHz, d6-DMSO) 7.19 (2 H, t, J 7.6, Ar–
H), 6.97 (8 H, d, J 8.8, Ar–H), 6.87 (15 H, m, Ar–H), 6.74 (4
H, d, J 8.8, Ar–H), 3.71 (12 H, s, OCH3); EA found: N, 5.70;
C, 78.55; H, 6.10. Calc. for C46H41N3O4: N, 6.00; C, 78.95; H,
5.91%.
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Compound 3 was synthesized by modifying the literature
method.29 ZnTAPP (0.15 g, 0.20 mmol) and 4-iodoanisole (3.80 g,
16.30 mmol) were dissolved in 1,2-dichlorobenzene (2 ml) contain-
ing K2CO3 (2.25 g, 16.30 mmol), Cu powder (1.04 g, 16.30 mmol)
and 18-crown-6 (0.16 g, 0.60 mmol). The reaction mixture was
heated to reflux with stirring for 24 h. When the mixture was
cooled to room temperature, 50 ml CH2Cl2 was added and then
filtrated. The filtrate was passed through a silica gel column with
CH2Cl2 as eluent. Yield: 0.25 g, 78%. UV/Vis lmax(CH2Cl2)/nm
301 (e/dm3 mol-1 cm-1 69 800), 408 (82 500), 445 (123 000), 558
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1
(15 900), 604 (17 000); H NMR dH(300 MHz, CDCl3) 9.09 (8
H, s, pyrrolic-H), 8.01 (8 H, d, J 8.5, Ar–H), 7.36 (16 H, d, J 9.0,
Ar–H), 7.31 (8 H, d, J 8.5, Ar–H), 6.96 (16 H, d, J 9.0, Ar–H),
3.84 (24 H, s, OCH3); 13C NMR dC(75.47 MHz, CDCl3) 156.0,
150.4, 148.1, 141.2, 135.3, 134.9, 131.8, 126.9, 121.1, 118.3, 114.9,
55.5; MS(MALDI-TOF): m/z calcd for C100H80N8O8Zn: 1587.14,
found: 1587.17.
Zinc meso-tetra-4-[N¢,N¢-di-4-[(N,N-di(4-methoxylphenyl)-
amino)phenyl]amino]phenylporphyrin (4)
The synthetic method of 4 is similar to 3. ZnTAPP (0.065 g,
0.09 mmol) and I-TPA-(OCH3)2 (3.04 g, 7.04 mmol) were dis-
solved in 1,2-dichlorobenzene (2 ml) containing K2CO3 (0.97 g,
7.04 mmol), Cu powder (0.45 g, 7.04 mmol) and 18-crown-6
(0.07 g, 0.26 mmol). The reaction mixture was heated to reflux
with stirring for 96 h. When the mixture was cooled to room
temperature, 50 ml CH2Cl2 was added and then filtrated. The
filtrate was passed through a column (silica gel) with CH2Cl2 as
eluent to carry out unreacted reactants and 1,2-dichlorobenzene.
Then CH2Cl2 : EA = 1 : 1 was used as eluent to get the target
compound. Yield: 0.19 g, 68%. UV/Vis lmax(CH2Cl2)/nm 313
(e/dm3 mol-1 cm-1 140 800), 332 (133 800), 419 (247 900), 561
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1
(16 800), 610 (20 700); H NMR dH(300 MHz, CDCl3) 9.06 (8
H, s, pyrrolic-H), 8.03 (8 H, d, J 8.1, Ar–H), 7.40 (8 H, d, J 7.8,
Ar–H), 7.25 (16 H, d, overlap with solvent peak, Ar–H), 7.11 (32
H, d, J 8.6, Ar–H), 7.01 (16 H, d, J 8.6, Ar–H), 6.84 (32 H, d, J 8.7,
Ar–H), 3.78 (48 H, s, OCH3); 13C NMR dC(75.47 MHz, CDCl3)
155.7, 150.5, 147.9, 144.6, 141.5, 141.3, 135.5, 135.4, 132.0, 127.1,
126.2 122.6, 121.2, 119.4, 114.8, 55.6; MS(MALDI-TOF): m/z
calc. for C204H168N16O16Zn: 3165.00, found: 3165.17.
Acknowledgements
This work was supported by the National Science Council of the
Republic of China.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 8306–8312 | 8311
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8312 | Dalton Trans., 2010, 39, 8306–8312
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The Royal Society of Chemistry 2010
©