Electrochemistry of zinc tetraarylporphyrins containing fused butano and benzo groups. Effect of solvent and substituents on spectra, potentials and mechanism in nonaqueous media

Article abstract of DOI:10.1142/S1088424618501067

Two series of zinc tetraarylporphyrins containing four β,β′-pyrrole fused butano or benzo groups were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in nonaqueous media. The examined compounds are represented as butano(Ar)₄PorZn and benzo(Ar)₄PorZn, where Por is the porphyrin dianion and Ar is a p-CH₃Ph, Ph or p-ClPh substitutent on meso-positions of the macrocycle. Each Zn(II) butano-And benzoporphyrin undergoes two one-electron reductions to give a p-Anion radical and dianion in CH2Cl2. In contrast, three reductions were observed for the benzoporphyrin derivatives in pyridine, the third of which is assigned as electron addition to a benzophlorin anion generated from the doubly reduced benzoporphyrin. Two overlapped one-electron oxidations were observed for the butanoporphyrins in CH2Cl2, a result not previously observed for any other zinc porphyrin. The electrochemically measured HOMO-LUMO gap of the benzoporphyrins ranges from 1.89 to 1.90 V in CH2Cl2 and from 1.93 to 1.95 V in pyridine. Both values are smaller than the gaps of butanoporphyrins at 2.11-2.13 V in CH_2Cl2 and 2.07.2.09 V in pyridine.

Full text of DOI:10.1142/S1088424618501067

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2018; 22: 1–14
DOI: 10.1142/S1088424618501067
Published at http://www.worldscinet.com/jpp/
Electrochemistry of zinc tetraarylporphyrins containing fused
butano and benzo groups. Effect of solvent and substituents
on spectra, potentials and mechanism in nonaqueous media
a,b
b
c◊
b,c
b◊◊
LinaYe , Yuanyuan Fang* , Zhongping Ou , Liping Wang , Songlin Xue ,
b
c◊
Jing Sun and Karl M. Kadish*
a
College of Computer, Jilin Normal University, Siping 136000, P. R. China
b
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China
Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
c
Received 1 October 2018
Accepted 24 October 2018
ABSTRACT: Two series of zinc tetraarylporphyrins containing four b,b′-pyrrole fused butano or benzo
groups were synthesized and characterized as to their electrochemical and spectroelectrochemical
properties in nonaqueous media. The examined compounds are represented as butano(Ar) PorZn and
4
benzo(Ar) PorZn, where Por is the porphyrin dianion and Ar is a p-CH Ph, Ph or p-ClPh substitutent on
4
3
meso-positions of the macrocycle. Each Zn(II) butano- and benzoporphyrin undergoes two one-electron
reductions to give a p-anion radical and dianion in CH Cl . In contrast, three reductions were observed
2
2
for the benzoporphyrin derivatives in pyridine, the third of which is assigned as electron addition to a
benzophlorin anion generated from the doubly reduced benzoporphyrin. Two overlapped one-electron
oxidations were observed for the butanoporphyrins in CH Cl , a result not previously observed for any
2
2
other zinc porphyrin. The electrochemically measured HOMO–LUMO gap of the benzoporphyrins
ranges from 1.89 to 1.90 V in CH Cl and from 1.93 to 1.95 V in pyridine. Both values are smaller than
2
2
the gaps of butanoporphyrins at 2.11–2.13 V in CH Cl and 2.07–2.09 V in pyridine.
2
2
KEYWORDS: synthesis, porphyrinoids, electrochemistry, spectroelectrochemistry, substituent effect.
UV-vis spectral and electrochemical properties as
compared to the parent porphyrins lacking the b,b′-
pyrrole fused benzo groups [26–32].
INTRODUCTION
The properties of synthetic zinc porphyrins have
been examined in numerous publications related to solar
cells [1–5], nanomaterials [6, 7], photoinduced electron
transfer and biohydrogen production [8–10], self-
assembled arrays [11, 12], molecular recognition [13]
and supramolecular assemblies [10, 14–18].
Among the many examined porphyrins which are
relevant to studies of catalysis, medicine and material
science [19, 20], are the tetrabenzoporphyrins which
possess an extended p conjugated system [19, 21–25],
display a high chemical stability and also have unique
Zinc tetrabenzoporphyrin is one of the earliest electro-
chemically examined porphyrins with an extended
p-system [33–36]. The zinc tetraphenyltetrabenzo-
porphyrin, benzo(Ph) PorZn was previously synthesized
4
andcharacterized[32, 37]butitselectrochemicalproperties
and that of the zinc tetraaryltetrabutanoporphyrins have
not, to the best of our knowledge, been reported in the
literature. This is addressed in the present manuscript,
where two series of zinc tetraarylporphyrins containing
four fused b,b′-butano or b,b′-benzo rings were
synthesized and characterized as to their electrochemistry
and spectroelectrochemistry in nonaqueous media. The
◊
SPP full member in good standing
◊◊
examined compounds are represented as butano(Ar) PorZn
SPP student member
4
*
Correspondence to: Yuanyuan Fang, email: 170173915@
and benzo(Ar) PorZn, where Por is a dianion of the
4
qq.com; Karl M. Kadish, email: kkadish@uh.edu.
porphyrin and Ar is a p-CH Ph, Ph, or p-ClPh substitutent
3
Copyright © 2018 World Scientific Publishing Company

2
L. YE ET AL.
H C
CH3
Cl
3
Cl
Cl
N
N
N
Zn
N
N Zn N
N Zn N
N
N
N
N
CH3
H C
3
Cl
(
CH Ph) PorZn (1a)
(Ph) PorZn (1b)
(ClPh) PorZn (1c)
4
3
4
4
Cl
Cl
H C
3
CH3
N
N
N
N Zn N
N Zn N
N
N Zn N
N
N
Cl
butano(Ph) PorZn (2b) butano(ClPh) PorZn (2c)
CH3
Cl
H C
3
butano(CH Ph) PorZn (2a)
3
4
4
4
H C
3
CH3
Cl
Cl
N
N
N
N Zn N
N
N Zn N
N
N Zn N
N
CH3
Cl
Cl
H C
3
benzo(CH Ph) PorZn (3a)
benzo(Ph) PorZn (3b)
benzo(ClPh) PorZn (3c)
4
3
4
4
Chart 1. Structures of examined zinc porphyrins
on each of the four meso-positions of the macrocycle.
Structures of the examined butano and benzoporphyrins
are shown in Chart 1 which also includes structures of
Zn(OAc) in a mixed solvent of CHCl and CH OH
(v/v = 9/1) with a yield of 46–73%.
2
3
3
The zinc tetrabenzotetraarylporphyrins 3a–3c were
synthesized via a reaction between zinc phenylacetate
or para-substituted phenylacetate and phthalimide as
shown in Scheme S1b, with the yield ranging from 3–8%.
Each synthesized zinc porphyrin was characterized by
the related tetraarylporphyrins, (Ar) PorZn. The effects
4
of solvent and fused b,b′-butano or b,b′-benzo groups on
the UV-vis spectra and redox potentials of the porphyrins
are discussed.
1
mass spectrometry and H NMR, and the data are given
in Figs S1–S3.
RESULTS AND DISCUSSION
UV-vis spectra of the zinc porphyrins were
measured in CH Cl and pyridine, and examples of the
2
2
spectra are shown in Fig. 1 for the meso-tetraphenyl
derivatives 1b, 2b and 3b. As seen in the figure, the
parent tetraphenylporphyrin 1b is characterized in
CH Cl by a sharp Soret band at 419 nm and two low
intensity Q bands at 548 and 585 nm, while the related
butanoporphyrin 2b possesses a Soret band at 435 nm
along with a single Q band at 565 nm under the same
solution conditions. The Soret band of 2b at 435 nm is
red-shifted by 16 nm as compared to the band of 1b at
419 nm.
Synthesis and UV-vis spectra
The tetraarylporphyrins 1a–1c were synthesized using
literature methods [29] and synthetic routes to obtain
butano(Ar) PorZn 2a–2c and benzo(Ar) PorZn 3a–3c
2
2
4
4
are shown in Scheme S1. The free-base tetrabutanotetra-
arylporphyrinsweresynthesizedfromtetrahydroisoindole
and arylaldehyde using literature methods [38, 39] and
the desired zinc butanoporphyrins 2a–2c were then
obtained via a reaction between butano(Ar) PorH and
4
2
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ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
3
Fig. 1. UV-vis spectra of (Ph) PorZn 1b, butano(Ph) PorZn 2b and benzo(Ph) PorZn 3b in (a) CH Cl and (b) pyridine, 0.1 M TBAP
4
4
4
2
2
A more significant red-shift in lmax is seen for the
benzoporphyrin 3b which has a Soret band at 455 nm,
an intense Q band at 650 nm and a weaker Q band at
because of an increased conjugation between the four
fused benzo groups and the porphyrin macrocycle.
These results are consistent with what has earlier been
reported for benzoporphyrins containing other central
metal ions, namely Pt(II), Cu(II), Co(II) or Fe(III) [21,
22, 30, 31, 38].
6
04 nm in CH Cl (see bottom spectrum in Fig. 1a). The
2 2
red-shift in the Soret band of 3b amounts to 36 nm, while
the Q bands are red-shifted by 56–65 nm as compared to
the corresponding zinc tetraphenylporphyrin 1b.
Similar UV-vis spectral changes with changes in the
macrocyclic structure occur in pyridine where the Soret
bands of 2b and 3b are red-shifted by 23 and 44 nm,
respectively, as compared to the soret band of 1b (Fig. 1b).
Similar red-shifted bands can also be seen in the spectra
of the other examined butano and benzoporphyrins in
both CH Cl and pyridine and these spectra are illustrated
Electrochemistry
Each porphyrin was examined in CH Cl and pyridine
2
2
containing 0.1 M TBAP. A summary of the measured
reduction and oxidation potentials in these two solvents
is given in Table 1 and a discussion of the data is given
below, first for the butanotetraarylporphyrins and then for
benzotatraarylporphyrins.
2
2
in Fig. S4.
It is known that zinc tetraarylporphyrins can axially
bind one pyridine ligand to form a five-coordinate species
in solution [40–42] and this coordination leads to a red-
shift in both the Soret and Q bands [43–46]. Red shifts
Butano(Ar) PorZn. Two overlapping one-electron
4
oxidations are observed for the butano(Ar) PorZn
4
derivatives 2a–2c in CH Cl as seen in Fig. 2a. This is
2
2
unlike the (Ar) PorZn complexes 1a–1c which undergo
4
in the absorption bands are seen for butano(Ar) PorZn
two well-defined one-electron oxidations with the
4
2
a–2c and benzo(Ar) PorZn 3a–3c in pyridine, and this
separation in potential (listed as D E
in Table 1)
(ox –ox )
1
4
2
is consistent with the formation of butano(Ar) PorZn(Py)
ranging from 0.27 to 0.31 V in CH Cl containing 0.1 M
4
2 2
and benzo(Ar) PorZn(Py) under the given solution
conditions.
TBAP (Fig. S5). An overlapping 2-electron oxidation
has not been seen for other zinc porphyrins, but similar
overlapping oxidations have been reported for the
structurally related cobalt butanoporphyrins under
similar solution conditions [30].
4
It should be pointed out that the Q(0,0) bands of the
three benzoporphyrins in Figs 1 and S4 have a relatively
high intensity in both CH Cl and pyridine. This is
2
2
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L. YE ET AL.
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ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
5
Fig. 3. Cyclic voltammograms showing reductions of
butano(CH Ph) PorZn 2a in (a) CH Cl and (b) pyridine cont-
3
4
2
2
aining 0.1 M TBAP at a scan rate of 0.10 V/s
after the first oxidation and first reduction of 2a–2c are
shown in Fig. 4. The applied oxidation and reduction
potentials are indicated in the figure and were in each case
sufficiently positive or negative potentials for the specific
redox couple to enable a complete conversion of the
neutral porphyrin to its singly reduced or doubly oxidized
form (where the two oxidation processes are overlapped).
As seen in the figure, the three butanoporphyrins exhibit
similar spectral changes, independent of the specific
meso-substituents on the porphyrin macrocycle. The
Soret and Q bands both decrease significantly in intensity
during the first oxidation and first reduction, which are
consistent with formation of a porphyrin dication and
p-anion radical, respectively.
Fig. 2. Cyclic voltammograms showing oxidations of
butano(Ar) PorZn 2a–2c in (a) CH Cl and (b) pyridine, 0.1 M
TBAP
4
2
2
Figure 2b illustrates cyclic voltammograms for
oxidation of the same three butanoporphyrins in pyridine,
0
.1 M TBAP. Two well-separated reversible one-electron
transfers are observed for 2a and 2b, while the oxidation
of 2c involves two overlapping one-electron transfers
at the same potentials. The easiest first oxidation of the
butanoporphyrins occurs for the meso-CH Ph derivative
3
2
a, while the hardest first oxidation is seen for the meso-
Figure 5 shows the spectral changes obtained for
ClPh compound 2c. The substituent effect of the meso-
butano(CH Ph) PorZn 2a during the oxidations and
3 4
CH Ph group on the E1/2 of the second oxidation is
almost the same as that of the meso-Ph group and thus
reductions in pyridine. Because the central zinc metal
ion is redox inactive, both oxidations of the compounds
can only be porphyrin ring-centered and lead to spectra
consistent with formation of porphyrin p-cation radicals
and dications. The reductions are also porphyrin ring-
3
a similar DE(
value is seen for 2a and 2b (0.14 and
.13 V). However, the meso-ClPh substituent has almost
ox –ox )
2
1
0
no effect on the second oxidation potential and this
results in an overlapping of the two oxidation processes
centered electron transfers, leading in the first step to the
-
(DE(
= 0.0 V) for 2c.
formation of a stable [butano(CH
the second to an unstable [butano(CH
3
Ph)
4
PorZn(py)] and in
ox –ox )
2
1
2
-
Figure 3 shows cyclic voltammograms of butano-
3
Ph)
4
PorZn(py)]
(
CH Ph) PorZn 2a in CH Cl and pyridine, 0.1 M TBAP.
product. Similar spectral changes are observed for other
two butanoporphyrins 2b and 2c during the oxidations
(Fig. S7) and reductions (Fig. S8), indicating that
these compounds have similar spectroelectrochemical
properties as compared to compound 2a under the same
solution conditions.
3
4
2
2
This butanoporphyrin undergoes two major reductions,
the first of which is reversible and located at E1/2 = -1.65V
in CH Cl and -1.64V in pyridine. The second reduction is
irreversible in both solvents and located at E = -1.98 and
-
2
2
pc
2.01 V, respectively, for a scan rate of 0.10 V/s. This
reduction is coupled with one or two re-oxidations on the
return potential sweep. Similar electrochemical behavior
is seen for butano(Ph) PorZn 2b and butano(ClPh) PorZn
Benzo(Ar)
derivatives 1a–1c, the benzoporphyrins 3a–3c undergo
two reversible one-electron oxidations in CH Cl and
4
PorZn. Similar to the parent (Ar) PorZn
4
4
4
2
2
2
c in CH Cl and pyridine (Fig. S6).
pyridine. The DE(ox –ox ) value between the first two
2
2
2
1
Thin-layer UV-vis spectroelectrochemistry of each
butanoporphyrin was carried out in CH Cl containing
0
oxidations of 3a in CH Cl is 0.19 V (Fig. 6a), which is
2 2
similar to the DE1/2 value (0.16 V) of (DPP)Zn (DPP =
dianion of dodecaphenylporphyrin) in the same solvent
2
2
.1 M TBAP. Examples the spectra obtained before and
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L. YE ET AL.
Fig. 4. UV-vis spectra of (a) butano(CH Ph) PorZn 2a, (b) butano(Ph) PorZn 2b and (c) butano(ClPh) PorZn 2c obtained before
3
4
4
4
(
solid line) and after (dashed line) the first controlled potential oxidation and reduction in CH Cl containing 0.1 M TBAP
2 2
Fig. 5. Thin-layer UV-vis spectral changes of butano(CH Ph) PorZn 2a during the controlled potential (a) oxidations and
3
4
(
b) reductions in pyridine containing 0.1 M TBAP
[
47], but much smaller than that of compounds 1a–1c
E1/2 = -1.47 V (3a) to -1.40 V (3c), while the second is
quasi-reversible and located at -1.69 V (3a), -1.67 V (3b)
and -1.59 V (3c) at a scan rate of 0.10 V/s.
where the two oxidations are separated by 0.27 to 0.31 V
in CH Cl (Fig. S5).
2
2
A smaller potential separation between the two
oxidations is seen for the benzoporphyrins 3a–3c in
pyridine as compared to that for the same compounds
Thin-layer spectral changes were monitored during
the first one-electron oxidation and first one-electron
reduction of the three benzoporphyrins in CH Cl and
2
2
in CH Cl . The DE
in pyridine is 0.14 V for 3a,
(ox –ox )
2 1
this data is seen in Fig. 8. The Soret and Q bands all
decrease in intensity during the first controlled potential
oxidation, indicating formation of porphyrin p -cation
2
2
0
.15 V for 3b and 0.08 V for 3c (Fig. 6b).
The benzoporphyrins 3a–3c undergo two one-electron
+
·
reductions in CH Cl containing 0.1 M TBAP. As seen in
radicals of the form [benzo(Ar) PorZn] . As expected,
2
2
4
Fig. 7, the first reduction is reversible and ranges from
the Soret and Q bands also decrease in intensity upon the
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ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
7
Fig. 6. Cyclic voltammograms showing oxidations of benzo(Ar) PorZn 3a–3c in (a) CH Cl and (b) pyridine, 0.1 M TBAP
4
2
2
is reversible (E1/2 = -1.43 V), but the second is irreversible
(
E = -1.83 V) and coupled with two re-oxidation peaks
pc
at E = -0.36 and -0.62 V on the return scan. The peak
pa
currents of the two re-oxidations also increases in
intensity when the reduction potential is held at -1.90 V
for 30 s before the potential scan being reversed. The
electroreduction behavior of 3b and 3c in pyridine is
similar to that of 3a (see Fig. S9) and the results are
consistent with a chemical reaction following the second
one-electron addition to the macrocycle leading to an
electroactive porphyrin dianion.
It was earlier reported that generation of a phlorin
anion may occur in nonaqueous media after generation
of a porphyrin dianion [43, 48–50]. The electrochemical
behavior of the benzoporphyrins 3a–3c in pyridine
suggests that a phlorin anion is generated from the doubly
reduced benzoporphyrin, with the proposed mechanism
being given in Scheme 1.
Figure 10 shows the spectral changes obtained during
the first two reductions of benzo(Ar) PorZn 3a–3c in
pyridine containing 0.1 M TBAP. As seen in the figure,
the initial Soret band at 474–476 nm and Q bands between
4
Fig. 7. Cyclic voltammograms showing the reductions of
benzo(Ar) PorZn 3a–3c in CH Cl containing 0.1 M TBAP at a
scan rate of 0.10 V/s.
4
2
2
6
8
15–661 nm for each compound were red-shifted by
–10 nm after the first controlled potential reduction.
one-electron addition, indicating formation of porphyrin
These changes, illustrated in the top of Fig. 10, suggest
the formation of porphyrin anion radicals after the first
one-electron addition [48]. The products generated after
the second reduction of 3a–3c have a split Soret band at
483–486 and 516–518 nm along with a broad Q band at
-·
p-anion radicals of the form [benzo(Ar) PorZn] .
4
Different reduction behavior is seen for the
benzoporphyrins in pyridine and an example of which is
given in Fig. 9 for 3a. The first reduction of this porphyrin
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L. YE ET AL.
Fig. 8. Thin-layer UV-vis spectral changes of (a) benzo(CH Ph) PorZn 3a, (b) benzo(Ph) PorZn 3b and (c) benzo(ClPh) PorZn 3c
3
4
4
4
during the first controlled potential oxidation and reduction in CH Cl containing 0.1 M TBAP
2
2
Ar
Ar
Ar
2
—
N
N
N
N
+e
N
N
N
N
+e
N
N
N
N
Zn
Py
Ar
Ar
Zn
Py
Ar
Ar
Zn
Ar
Ar
-1.25 V
-1.60 V
Py
Ar
Ar
Ar
_
Ar
Ar
2—
N
N
N
N
H
+
e
N
N
N
N
H
Ar
Zn
Zn
Ar
Ar
Ar
Py
-1.88 V
Py
Ar
Ar
Scheme 1. Proposed reduction mechanism of benzo(Ar) PorZn 3a–3c in pyridine, 0.1 M TBAP (potentials in Scheme are for 3c)
4
8
18–822 nm (see bottom spectra in Fig. 10). The results
benzoporphyrins in pyridine containing 0.1 M TBAP. The
spectral changes are shown in Fig. S10 for 3b and 3c. The
results are consistent with the generation of porphyrin
p-cation radicals and dications under the given solution
conditions.
are consistent with formation of benzotetraphenylphlorin
anions under the given solution conditions [48–50].
Controlled potential oxidations and spectral monito-
ring of the products were carried out for the Zn(II)
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ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
9
Fig. 9. Cyclic voltammograms showing reductions of benzo(CH Ph) PorZn 3a in pyridine containing 0.1 M TBAP at a scan rate of
3
4
0
.10 V/s
Fig. 10. Thin-layer UV-vis spectral changes of (a) benzo(CH Ph) PorZn 3a, (b) benzo(Ph) PorZn 3b and (c) benzo(ClPh) PorZn 3c
3
4
4
4
during the first two controlled potential reductions in pyridine containing 0.1 M TBAP
Effect of Substituents
of the macrocycle may have a significant effect on the
electrochemical properties [19, 20, 51–54]. This is
also the case for the currently investigated b,b′-pyrrole
substituted butano- and benzotetraarylporphyrins. As
It has long been known that modification of a porphyrin
structure by addition of electron-withdrawing or electron-
donating substituents on the meso- and/or b -positions
seen in Fig. 11, the first oxidation of butano(Ph) PorZn
4
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1
0
L. YE ET AL.
Fig. 11. (a) Cyclic voltammograms showing the oxidation and reduction of compounds 1b, 2b and 3b in CH Cl , 0.1 M TBAP and
2
2
(
b) graphical presentation of HOMO-LUMO gap for the three zinc(II) porphyrins
2
b is negatively shifted by 230 mV (easier oxidation)
Benzo(Ph) PorZn 3b has the smallest HOMO–LUMO
4
as compared to (Ph) PorZn 1b in CH Cl , while the first
gap which is 1.90 V in CH Cl (Fig. 11) and 1.95 V in
4
2
2
2
2
reductioninthissolventundergoesa290mVnegativeshift
harder reduction) as compared to the parent porphyrin
without the fused benzo groups. An easier oxidation and
pyridine (Fig. 12).
(
Similar HOMO–LUMO gaps are seen for a nonplanar
zinc tetraphenylporphyrin with eight b-phenyl rings
on the pyrrole positions, (DPP)Zn (DE1/2 = 1.82 V) [47]
and for the benzoPorZn derivative (DE1/2 = 1.86 V) [33]
under similar solution conditions. As seen in Table 1,
the HOMO–LUMO gap of the investigated tetrabutano-
porphyrins ranges from 2.11 to 2.13 V in CH Cl and
harder reduction is also seen for benzo(Ph) PorZn 3b as
4
compared to its parent compound 1b.
A significant effect of the b,b′-fused butano and
benzo groups on the redox potentials is also seen when
pyridine is used as the solvent. Comparisons of the first
oxidation and first reduction potentials for compounds
2
2
from 2.07 to 2.09 V in pyridine, while the gap of the
benzo(Ar) PorZn derivatives is 1.89–1.90 V in CH Cl
2
1
b, 2b and 3b in pyridine are shown in Fig. 12. The
4
2
b,b′-fused tetrabenzo groups effect not only the
individual reduction and oxidation potentials but also
the HOMO–LUMO gap (DE ) of the porphyrins.
and 1.93–1.95 V in pyridine. The smaller HOMO–LUMO
gaps of the benzoporphyrins suggest that these compounds
might possess nonplanar macrocycles [32].
1
/2
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ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
11
Fig. 12. (a) Cyclic voltammograms showing the first oxidation and first reduction of butano(Ph) PorZn 2b, (Ph) PorZn
4
4
1
b and benzo(Ph) PorZn 3b in pyridine, 0.1 M TBAP and (b) graphical presentation of HOMO–LUMO gap for the three
4
metalloporphyrins
overlapped one-electron oxidations are observed for the
zinc butanoporphyrins in CH Cl while three reductions
CONCLUSION
2
2
The four b,b′-fused butano or benzo-rings on the zinc
porphyrins have a significant effect on UV-vis spectra,
reduction-oxidation potentials and the HOMO–LUMO
gap of the investigated compounds. The Soret band is red-
shifted by ~17 and ~36 nm for the tetrabutanoporphyrins
and tetrabenzoporphyrins, respectively, as compared
to the related non-b-substituted porphyrins. Two
are observed for the benzoporphyrin derivatives, the
last of which involves a product generated in solution
after formation of the porphyrin dianion. The Zn(II)
benzotetraarylporphyrinshaveasmallestHOMO–LUMO
gap (1.89–1.90V in CH Cl and 1.93–1.95V in pyridine),
2
2
as compared to that of butanotetraarylporphyrins and
tetraarylporphyrins.
Copyright © 2018 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2018; 22: 11–14

1
2
L. YE ET AL.
(
m, 8H), 7.78–7.72 (m, 8H). MS (MALDI-TOF): m/z
EXPERIMENTAL SECTION
+
calcd for [M] 812.005, found: 814.237.
Instrumentation
Synthesis of zinc butanoporphyrins
Cyclic voltammetry was carried out at 298 K by
using an EG&G Princeton Applied Research (PAR) 173
potentiostat/galvanostat or CHI-730C Electrochemical
Workstation. A homemade three-electrode cell was used
for all electrochemical measurements. A three-electrode
system was used in each case and consisted of a glassy
carbon working electrode. A platinum wire served as
the auxiliary electrode and a saturated calomel electrode
Free-base butano(Ar) PorH (0.04 mmol) was
4
2
dissolved into a mixed CHCl /CH OH (v/v 9:1) solvent
3
3
containing excess Zn(OAc) ·2H O (0.4 mmol). The
2
2
mixture was stirred at room temperature for 15 min.
After the starting compound was completely comsumed,
the solution was washed by water and the product
extracted by CH Cl . After drying with Na SO , the
2
2
2
4
solvent was removed under reduced pressure and then
chromatographed on a neutral Al O column (200–300
(
SCE) as the reference electrode, which was separated
2
3
from the bulk of the solution by means of a salt bridge
of low porosity which contained the solvent/supporting
electrolyte mixture. All experiments were carried out
under room temperature.
Thin-layerUV-visspectroelectrochemicalexperiments
were performed with a home-built thin-layer cell which
has a light transparent platinum net working electrode or
a screen printed working electrode (Pine Instruments).
Potentials were applied and monitored with an EG&G
PAR Model 173 potentiostat. Time-resolved UV-visible
spectra were recorded with a Hewlett-Packard Model
mesh) using CH Cl as eluent. The green fraction was
2
2
collected and evaporated to dryness.
Butano(CH Ph) PorZn 2a. Yield: 15 mg (40%);
3
4
UV-vis (pyridine): lmax, nm (log e) = 348 (4.30), 455
1
(
5.40), 587 (3.96), 635 (3.59); H NMR (400 MHz, CDCl )
3
d 7.98 (d, J = 7.3 Hz, 8H), 7.46 (d, J = 7.3 Hz, 8H), 2.67 (s,
1
2H), 2.39 (s, 16H), 1.50 (s, 16H); MS (MALDI-TOF):
+
m/z calcd for [M–Zn] 886.497, found: 887.811.
Butano(Ph) PorZn 2b. Yield: 16 mg (45%); UV-vis
4
(
(
pyridine): lmax, nm (loge) = 348 (4.30), 453 (5.20), 585
1
3.96), 631 (3.53); H NMR (400 MHz, CDCl ) d 8.15 (d,
3
8
453 diode array spectrophotometer. High purity N was
2
J = 6.4 Hz, 8H), 7.70 (d, J = 7.1 Hz, 12H), 2.40 (s, 16H),
.53 (s,16H); MS (MALDI-TOF): m/z calcd for [M–Zn]
usedtodeoxygenatethesolutionandkeptoverthesolution
during each electrochemical and spectroelectrochemical
experiment. MALDI-TOF mass spectra were taken on a
Bruker BIFLEX III ultra-high resolution instrument using
alpha-cyano-4-hydroxycinnamic acid as the matrix.
+
1
8
30.435, found: 831.731.
Butano(ClPh) PorZn 2c.Yield: 22 mg (55%); UV-vis
4
(
(
(
(
pyridine): lmax, nm (loge) = 349 (4.31), 456 (5.17), 587
1
3.99), 633 (3.60); H NMR (400 MHz, CDCl ) d 8.07
3
s, 8H), 7.69 (s, 8H), 2.41 (s, 16H), 1.28 (s, 16H); MS
MALDI-TOF): m/z calcd for [M–Zn] 968.276, found:
Chemicals
+
9
69.630.
Dichloromethane (CH Cl , ≥99.8%) was purchased
2
2
from EMD Chemicals Inc. and pyridine (Py, ≥99.9%)
was purchased from Sigma-Aldrich and used as received.
Tetra-n-butylammonium perchlorate (TBAP, ≥99.0%)
was purchased from Sigma-Aldrich Co. and used as
received. Reagents and solvents (Sigma-Aldrich, Fluka
or Sinopharm Chemical Reagent Co.) for synthesis
and purification were of analytical grade and used as
received.
Synthesis of benzoporphyrins
The para-substituted phenylacetate (8.5 g, 57 mmol)
was dissolved in ~250 mL NaOH (2.3 g, 58 mmol)
solution and the pH adjusted to 8.0 by diluting with HCl.
In another beaker ZnCl (4.1 g, 30 mmol), was dissolved
2
in water and the pH was adjusted to 3.0 by diluting with
HCl. ZnCl was then added into the sodium substituted
2
phenylacetate solution after which the white precipitate
was filtered and dried to give the zinc substituted
phenylacetate with a yield of ~80%.
Synthesis of zinc porphyrins
The (Ar) PorZn complexes were synthesized accor-
4
ding to a procedure in the literature [29].
The zinc substituted phenylacetate (7.9 g, 36.8 mmol)
and phthalimide (5.5 g, 37.4 mmol) were mixed and
pulverized in a mortar. The mixture was then transferred
into a crucible and heated at 340°C in a muffle furnace for
1.5 h. After cooling to room temperature and dissolving in
(
CH Ph) PorZn 1a. UV-vis (CH Cl ): l
= 421,
3
4
2
2
max
1
5
8
1
49 nm. H NMR (400 MHz, CDCl ), d 8.96 (s, 8H),
3
.10 (d, J = 7.7 Hz, 8H), 7.55 (d, J = 7.6 Hz, 8H), 2.71 (s,
+
2H). MS (MALDI-TOF): m/z calcd for [M] 732.223,
found: 732.402.
Ph) PorZn 1b. UV-vis (CH Cl ): l = 419, 548 nm.
CH Cl , the raw products were obtained. The solvent was
removedunderreducedpresure,andthenchromatographed
on a silica gel column (200–300 mesh) using a hexane/
2 2
(
4
2
2
max
1
H NMR (400 MHz, CDCl ), d 8.99 (s, 8H), 8.30–8.22
3
(
m, 8H), 7.86–7.73 (m, 12H). MS (MALDI-TOF): m/z
CH
was collected and evaporated to dryness.
Benzo(CH Ph) PorZn 3a. Yield: 257.3 mg, 3%.
2 2
Cl mixture (v/v 1:1) as eluent. The first green fraction
+
calcd for [M] 676.161, found: 676.226.
(
ClPh) PorZn 1c. UV-vis (CH Cl ): l
= 420, 548
3
4
4
2
2
max
1
nm. H NMR (400 MHz, CDCl ), d 8.94 (s, 8H), 8.16–8.10
UV-vis (pyridine): l max, nm (loge) = 317 (4.37), 475
3
Copyright © 2018 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2018; 22: 12–14

ELECTROCHEMISTRY OF ZINC TETRAARYLPORPHYRINS CONTAINING FUSED BUTANO AND BENZO GROUPS
13
1
(
5.50), 615 (4.30), 658 (4.62); H NMR (400 MHz,
11. Ogawa K and Kobuke Y. J. Photochem. Photobio.
C: Photochem. Rev. 2006; 7: 1–16.
12. Aratani N and Osuka A. Bull. Chem. Soc. Jpn 2001;
74: 1361–1379.
CDCl ) d 8.16 (d, J = 7.4 Hz, 8H), 7.67 (d, J = 7.3 Hz,
H), 7.27 (br m, 10H), 7.24–7.18 (m, 6H), 2.82 (s, 12H).
MS (MALDI-TOF): m/z calcd for [M] 932.286, found:
3
8
+
9
32.520.
13. Weiss J. J. Inclu. Pheno. Macrocycl. Chem. 2001;
40: 1–22.
Benzo(Ph) PorZn 3b [32, 37]. Yield: 644.9 mg, 8%.
4
UV-vis (pyridine): l max, nm (loge) = 317 (4.37), 474
14. Hagfeldt A, Gratzel M, Nogueria AF, Furtado
LFO, Formiga ALB, Nakamura M, Araki K, Toma
HE, Panigrahi S and Pal T. Chemtracts 2004; 17:
175–182.
15. Joe O. Trends Phys. Chem. 2001; 8: 61–72.
16. Prodi A, Indelli MT, Kleverlaan CJ, Alessio E and
Scandola F. Coord. Chem. Rev. 2002; 229: 51–58.
17. Satake A and Kobuke Y. Tetrahedron 2005; 61:
13–41.
18. Xu C, Li D, Guo Y and Wang E. Chin. Sci. Bull.
2001; 46: 1061–1066.
19. Kadish KM, Van Caemelbecke E and Royal G. In
The Porphyrin Handbook (Eds. Kadish KM, Smith
KM and Guilard R), Academic Press: San Diego,
1
(
5.39), 615 (4.30), 658 (4.66); H NMR (400 MHz,
CDCl ) d 8.33–8.26 (m, 8H), 7.94 (t, J = 7.8 Hz, 4H),
3
7
.87 (t, J = 7.3 Hz, 8H), 7.27 (br m, 4H), 7.26–7.24 (m,
J = 6.4 Hz, 4H), 7.16 (m, 8H). MS (MALDI-TOF): m/z
calcd for [M] 876.223, found: 876.416.
+
Benzo(ClPh) PorZn 3c. Yield: 466.4 mg, 5%. UV-vis
4
(
(
4
1
pyridine): lmax, nm (loge) = 317 (4.32), 476 (5.37), 618
1
4.20), 661 (4.56); H NMR (400 MHz, CDCl ) d 8.49 (s,
3
H), 8.24 (s, 4H), 7.87 (s, 6H), 7.52 (s, 2H), 7.39 (br m,
2H), 7.20–7.05 (m, 4H). MS (MALDI-TOF): m/z calcd
+
for [M] 1014.064, found: 1013.756.
Acknowledgments
2
000; 8: 1–114.
We gratefully acknowledge support from the National
Natural Science Foundation of China (Grants 21501070),
Jiangsu University Foundation (Grant 15JDG131), China
Postdoctoral Science Foundation (Grant 2017M611707)
and the Robert A. Welch Foundation (K.M.K., Grant
E-680).
2
0. Kadish KM, Royal G and Van Caemelbecke E. In
The Porphyrin Handbook (Eds. Kadish KM, Smith
KM and Guilard R), Academic Press: San Diego,
2
000; 9: 1–219.
2
1. Armaroli N, Chambron JC, Collin JP, Dietrich-
Buchecker C, Flamign L, Kern JM, Sauvage JP.
Elect. Trans. Chem. 2001; 3: 582–654.
Supporting information
22. Aratani N and OsukaA. Bull. Chem. Soc. Jpn. 2001;
4: 1361–1379.
7
Figures S1–S10 are given in the supplementary
material. This material is available free of charge via the
Internet at http://www.worldscinet.com/jpp/jpp.shtml.
2
3. Ye LN, Ou ZP, Fang YY, Xue SL, Song Y, Wang
LP, Wang ML and Kadish KM. RSC Adv. 2015; 5:
7
7088–77096.
2
2
4. Chen P, Finikova OS, Ou ZP, Vinogradov SA and
Kadish KM. Inorg. Chem. 2012; 52: 6200–6210.
5. Okujima T, HashimotoY, Jin G,Yamada H and Ono
N. Heterocycle 2009; 77: 1235–1248.
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