Electrochemical synthesis of novel π-extended phenoxazine derivatives of porphyrincatecholes

Article abstract of DOI:10.1016/j.electacta.2011.08.030

Three new functionalized phenoxazine-catechol porphyrins 7a-c have been synthesized by a green one-pot method and structurally characterized by spectroscopic analysis. The electro-oxidation of 5,10,15,20-tetrakis(2,3- dihydroxyphenyl) porphyrins(1a-c) wit

Full text of DOI:10.1016/j.electacta.2011.08.030

Electrochimica Acta 56 (2011) 9426–9432
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochemical synthesis of novel ␲-extended phenoxazine derivatives of
porphyrincatecholes
Samira Osati, Saied Saeed Hosseiny Davarani∗, Nasser Safari∗, Mohammad Hossein Banitaba
Department of Chemistry, Faculty of Science, Shahid Beheshti University, G.C, Evin, 1983963113 Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new functionalized phenoxazine-catechol porphyrins 7a–c have been synthesized by a green
one-pot method and structurally characterized by spectroscopic analysis. The electro-oxidation of
5,10,15,20-tetrakis(2,3-dihydroxyphenyl) porphyrins(1a–c) with four catechol units in the presence of
2-aminophenol 8 as bidentate nucleophile has been done and phenoxazine rings have been formed
by intermolecular and intramolecular Michael addition reactions. Spectroscopic characterization and
voltammetry results have allowed us to propose four independent ECEC mechanisms for the electrochem-
ical oxidation pathway. The functionalization of the porphyrins affected their photophysical properties.
Expansion of the UV–vis spectrum range and the decrease of the fluorescence intensity of the products
would support the energy transfer between the porphyrin core excited states to the four substitutions
as the electron acceptor subunits. SEM images indicate that this method produces regularly shaped
manganese porphyrin nano-particles 7c that possess a cubic nano structure.
Received 19 March 2011
Received in revised form 9 August 2011
Accepted 9 August 2011
Available online 19 August 2011
Keywords:
Porphyrins
Catechol
Phenoxazine
Electrosynthesis
Nanostructure
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Catecholes units in these compounds can be electrochemically oxi-
dized to very reactive forms of o-quinones with a total of eight
Porphyrins are macrocyclic compounds with highly ␲-
conjugated systems exhibiting intense absorption in the visible
region. They are also widely found in nature. They catalyze enzy-
matic reactions and transport oxygen in the human body [1] and
play an important role in photosynthesis. There has been continu-
ous interest in the synthesis of porphyrins because of their potential
applications in catalysis, medicine, photochemical energy conver-
sion, molecular switches, and molecular electronics [2–5].
More than 70 different metal ions can form complexes with
porphyrin rings and their physical and chemical properties can be
easily tuned by peripheral substituent modifications or metal com-
plexations. As a result, the diversity of synthetic routes towards
functionalized porphyrins has expanded rapidly [6–11].
Functionalization of porphyrins has been obtained via different
methods. We have endeavored to develop a synthetic strategy that
enables the use of readily prepared porphyrins that are capable
of being simply converted to a wide variety of functional groups.
The key to such a system is the use of a porphyrin with oxidiz-
able substituents as the starting material in the presence of diverse
nucleophiles, to provide a variety of functionalized porphyrins.
Electrosynthesis is perhaps the most selective, green and sim-
ple method. Tetra phenyl porphyrins with two adjacent hydroxyl
groups on each phenyl rings, actually have four units of catecholes.
electrophilic reactive sites that would be attacked by various nucle-
ophiles [12–18]. Using 2-aminophenol 8 as a bidentate nucleophile
leads to the formation of six member hetrocycles of phenox-
azine derivatives of porphyrins. Phenoxazine derivatives have been
widely investigated and have been shown to be an effective mate-
rial as antitumor, antileukemia, and antimicrobial drugs [19,20].
They have also been used as biological stains, laser dyes, indicators
and especially as chromospheres in antenna systems [21–25]. Since
hydroxyl-phenyl substituted porphyrins were developed as poten-
tial new photo sensitizers for photodynamic therapy, the joining of
four phenoxazine rings to the meso position of the porphyrins can
increase their applicability in cancer therapy [26].
We used water and ethanol as safe and environment-benign
solvents and designed an energy efficient process by performing
the reaction at ambient temperatures and pressures; therefore this
is a green synthetic method for porphyrin functionalization.
The present work develops a facile method for functionalizing
porphyrins and the synthesis of new phenoxazine-porphyrin cate-
chol derivatives (shown in Scheme 1) with good yields and purity.
These compounds display unique properties accounting for their
potential applications in chemistry, medicine, and physics.
2. Experimental
2.1. Apparatus and reagents
∗
Cyclic voltammetry and controlled potential coulometry
were performed using a ␮-Autolab potentiostat/galvanostat. The
Corresponding authors. Tel.: +98 2129902890; fax: +98 21 22403041.
E-mail address: n-safari@cc.sbu.ac.ir (N. Safari).
0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.08.030

S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
9427
O
O
HO
HO
O
O
N
N
N
N
HO
OH
-8e
N
N
N
N
M
M
-8H+
O
O
HO
OH
1a-c
O
O
OH
OH
2a-c
H2N
4eq
H
HO
N
HO
HO
H
N
8
-O
HO
HO
O
HO
HO
OH
HN
HO
OH
N
N
N
N
O
O-
M
HN
-O
OH
O
N
N
N
N
M
NH
OH
OH
OH
HO
NH
OH
O
OH
N
H
O-
N
H
3a-c
-8H+ -8e
H
4a-c
H
N
O
N
O
-O
O
HO
O
-O
O
O
HN
O
O
N
N
N
O
O
HN
O
OH
O
M
N
N
N
N
N
M
O-
NH
HO
NH
O-
O
O
O
O
OH
N
H
N
H
6a-c
5a-c
H
N
HO
HO
O
1a-7a: M= 2H
1b-7b: M= Zn
HO
OH
NH
HN
HO
O
N
N
N
M
N
1c-7c: M= Mn(OCOCH3)
O
OH
OH
OH
O
N
H
7a-c
Scheme 1. Synthetic route for preparing of 7a–c (proposed intermediates have been placed in brackets).
preparative electrolysis experiments were carried out with a Zah-
ner potentiostat/galvanostat. The working electrode used in the
voltammetry experiments was a glassy carbon disc (1.8 mm diam-
eter) and a platinum wire was used as the counter electrode. The
working electrode used in the controlled potential coulometry and
milli mole scale electrolysis was an assembly of four graphite rods
(10 mm diameter and 6 cm length) and a large surface platinum
gauze constituted the counter electrode (graphite rods from Azar
electrode, Uromieh, Iran and all other electrodes from Metrohm).
The working electrode potentials E were measured versus 3 M
Ag/AgCl as reference electrode. 1H NMR and 13C NMR spectra were
recorded using a 300 MHz Bruker instrument. Mass spectra were
obtained by a matrix assisted laser desorption ionization-time of
flight mass spectroscopy (MALDI-TOF-MAS) on a Kratos Kompakt
MALDI-TOF-MS in reflectron mode. UV–vis spectra were recorded
on a Shimadzu 2100 spectrophotometer using a 1 cm path-length
cell. Infrared spectra were obtained on a Bomem FT-IR 470 spec-
trophotometer. Fluorescence spectra were recorded on a Perkin
Elmer LS45 Fluorescence spectrometer.
All solvents and chemicals (pyrrole, BF3etherate, 2,3-
dimethoxybenzaldehyde, 3,4,5,6-tetrachloro-1,2-benzoquinone
(p-chloranil), manganese (III) acetate, zinc(II)acetate, boron

9428
S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
tribromide and 2-aminophenol 8) were reagent grade and pur-
chased from Merck. A solution of phosphate buffer in water/ethanol
(50/50, v/v) (0.1 M, pH = 7.5) was prepared.
5,10,15,20-Tetrakis (2,3-dihydroxyphenyl) porphyrin 1a,
5,10,15,20-tetrakis(2,3-dihydroxyphenyl) porphyrin zinc (II)
chloride
porphyrin manganese (III) acetate 1c were prepared by
demethylation reaction between their methoxy form
1b
and
5,10,15,20-tetrakis(2,3-dihydroxyphenyl)
(5,10,15,20-tetrakis(2,3-dimethoxyphenyl) porphyrin, 5,10,15,20-
tetrakis(2,3-dimethoxyphenyl) porphyrin zinc (II)) chloride and
5,10,15,20-tetrakis(2,3-dimethoxyphenyl) porphyrin manganese
(III) acetate and BBr3 according to literature [27,28].
Fig. 1. Cyclic voltammograms of: (a) 0.25 mmol dm−3 of 1c, (b) 1.0 mmol dm−3 of
compound 8 and (c) mixture of 1.0 mmol dm−3 8 and 0.25 mmol dm−3 of 1c at a
glassy carbon electrode (1.8 mm diameter) versus Ag/AgCl/3 M KCl as reference elec-
trode, in 0.1 M phosphate buffer in water/ethanol (50/50, v/v) (pH = 7.5) solution.
Scan rate = 100 mV s−1, t = ambient.
2.2. Electrosynthesis of 7a–c
A solution (ca. 100 cm3) of phosphate buffer in water/ethanol
(50/50, v/v) (0.1 M, pH = 7.5) containing 5,10,15,20-tetrakis(2,3-
dihydroxyphenyl)porphyrins (0.25 mmol) 1a–c and 8 (1 mmol),
was electrolyzed at 0.3 V versus 3 M Ag/AgCl in an undivided cell.
The electrolysis was terminated when the current decreased by
more than 95% of the initiated current. The process was interrupted
during the electrolysis and the graphite anode was washed in ace-
tone in order to reactivate it. At the end of the electrolysis, once
the completion of the reaction was indicated by TLC, a few drops of
phosphoric acid were added to the solution and the cell was placed
in a refrigerator overnight. The precipitated solid was separated
by filtration, washed with water and purified by recrystallization
in dichloromethane/ethanol. After purification, the products 7a–c
were characterized by UV–vis, IR, 1H NMR, 13C NMR, mass spec-
troscopy and elemental analysis.
(N-H), 6.15–7.7(aromatic-H), 9.4(phenolic OH), elemental analy-
sis Calc. for C70H43MnN8O14: C, 65.94; H, 3.40; N, 8.79; % Found
C, 65.98; H, 3.42; N, 8.75%. MALDI-TOF calcd m/z = 1215.21 [M-
acetate]+, found 1215.20.
3. Result and discussion
3.1. Electrochemical study of 1a–c in the presence of 8
The cyclic voltammogram of a 0.25 mM 1c in water/ethanol
(50/50) solution containing 0.1 M phosphate buffer (pH = 7.5), at
a bare glassy carbon electrode, showed an oxidation peak at 0.23 V
versus 3 M Ag/AgCl electrode. As can be seen in Fig. 1, curve a, a
cathodic peak C1 appeared in the reverse scan at −0.02 V vs. 3 M
Ag/AgCl, illustrating the partial reversibility of the eight electron
transfer process (four independent E mechanisms) that could be
assigned to the 1c and 2c redox complex.
2.3. Characteristic of 7a
Yield 66%, IR(KBr): 3375, 3304, 2958, 2586, 1603, 1511, 1462,
1402, 1282, 1267, 1217, 1141, 1082, 1029, 930, 760. UV–vis (DMF):
ꢀmax/nm (log ε): 415(5.6), 509(4.6), 584(4.1), 641(3.9). 1H NMR
(300 MHz, DMSO-d6, 25 ◦C): ı, ppm −2.84 (s, 2H, porphyrin N–H),
3.81 (s, 4H, N–H), 6.38(d, 4H, Ar–H), 6.98 (d, 4H, Ar–H), 7.21 (dd,
4H, Ar–H), 7.30 (dd, 4H, Ar–H), 7.69 (s, 4H, porphyrin Ar–H), 8.75(s,
8H, pyrrole-H), 9.51(s, 8H, OH). 13C NMR(75 MHz, DMSO-d6, 25 ◦C):
ı, ppm 180.4, 149.0, 148.2, 147.1, 142.1, 133.5, 128.7, 128.1, 125.2,
122.5, 116.0, 112.7, 112.1, 103.2, 98.3. Elemental analysis Calc. for
C68H42N8O12: C, 70.22; H, 3.64; N, 9.63; Found C, 70.19; H, 3.69; N,
9.68%. MALDI-TOF calcd m/z = 1162.29 [M]+, found 1162.25.
A
A peak current ratio (IpC1 /Ip ) of more than unity (about
1.2) could be considered as a criterion for the stability of o-
benzoquinone derivatives of 1c produced at the surface of the
electrode under the mentioned experimental conditions and partial
adsorption of 2c and/or 4c at the surface of electrode. It is note-
worthy that hydroxylation, ethoxylation [29,30], dimerization and
polymerization [31,32] reactions are too slow to be observed on the
time scale of cyclic voltammetry.
1
The electrooxidation of 1c in the presence of 8 as a nucleophile
was studied in some detail. Fig. 1, curve c shows the first cyclic
voltammogram obtained for a 0.25 mM solution of 1c in the pres-
ence of 1 mM of 8. The voltammogram exhibits two cathodic peaks
C1 and C0 (−0.35 V versus 3 M Ag/AgCl). In the second cycle (Fig. 2,
curve b) a new anodic peak (A0) appears with an Ep value of −0.32 V
versus 3 M Ag/AgCl. This new peak is related to the oxidation of
intermediate 4c via four nearly reversible two electron processes
(four independent E mechanisms). The decrease of peak C1 in the
cyclic voltammograms of 1c in the presence of 8 clearly indicated
that the electrochemical oxidation of 1c was followed by chemical
reactions with 8. In addition the increase of peak A1 in this voltam-
mogram is due to the overlap of the quasireversible oxidation peak
(A2) of 8 with porphyrin 1c oxidation peak. Fig. 1, curve b shows
the cyclic voltammogram of 8 for comparison.
It seems that in each electrochemical step of this study, the
second, third and fourth two-electron oxidations shift to lower
potentials (second, third and fourth electron transfers are assisted
by the previous steps). Hence the oxidation and reduction waves
now involving four merged waves; appear like a single two-
electron wave with respect to shape even although the height
corresponds to 8-electron process for each electrochemical step
[33,34].
2.4. Characteristic of 7b
Yield 60%, IR (KBr): 3410, 3302, 2924, 2852, 1654, 1590, 1493,
1464, 1422, 1393, 1269, 1200, 1169, 838, 756, 695, 581, 540, and
461. UV–vis (DMF): ꢀmax/nm (log ε): 414(5.5), 512(4.5), 544(4.11),
587(4.0), 642(3.70).1H NMR (300 MHz, DMSO-d6, 25 ◦C): 3.81 (s,
4H, N-H), 6.35(d, 4H, Ar–H), 6.83 (d, 4H, Ar–H), 7.38 (dd, 4H,
Ar–H), 7.48(dd, 4H, Ar–H), 7.71 (s, 4H, porphyrin Ar–H), 8.74(s, 8H,
pyrrole-H), 9.55(s, 8H, OH). 13C NMR(75 MHz, DMSO-d6, 25 ◦C): ı,
ppm 180.6, 149.3, 148.6, 147.8, 142.3, 134.1, 129.2, 128.4, 125.7,
123.1, 116.3, 113.2, 112.4, 103.8, 98.8. Elemental analysis Calc. for
C
68H40N8O12Zn: C, 66.59; H, 3.29; N, 9.14%; Found C, 66.55; H, 3.32;
N, 9.17%. MALDI-TOF calcd m/z = 1224.21 [M]+, found 1224.15.
2.5. Characteristic of 7c
Yield 57%, IR (KBr): 3410, 3304, 2922, 1652, 1600, 1497, 1466,
1424, 1271, 1201, 1170, 1112, 840, 757, 697, 582, 541, and 462.
UV–vis (DMF): ꢀmax/nm (log ε): 425(5.4), 473(5.1). Paramagnetic
1H NMR (300 MHz, DMSO-d6) ı, ppm −34.8 (␤-pyrolic-H), 3.82

S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
9429
Fig. 2. Multi-cyclic voltammograms of 0.25 mmol dm−3 1c in the presence of
1.0 mmol dm−3 8, at glassy carbon electrode (1.8 mm diameter) versus Ag/AgCl/3 M
KCl as reference electrode, in 0.1 M phosphate buffer in water/ethanol (50/50, v/v)
(pH = 7.5) solution. Scan rate = 100 mV s−1, t = ambient.
Fig. 4. Cyclic voltammograms of 0.25 mmol dm−3 1c in the presence of 1 mmol dm−3
8 in 0.1 mol dm−3 phosphate buffer (pH = 7.5) in water/ethanol (50/50, v/v) solution
at a glassy carbon electrode, during controlled potential coulometry at 0.3 V versus
Ag/AgCl/3 M KCl. After consumption of: (a) 0, (b) 22, (c) 45 (d) 78 (e) 171 (f) 185 C.
The effect of the potential scan rate on the shape of cyclic
voltammograms of 1c in the presence of 8 was also studied. It
can be seen that, proportional to the augmentation of the poten-
tial scan rate, the height of peak C1 increases (Fig. 3, curves: a–f).
A similar situation is observed when the 8 to 1c concentration
Inset: variation of peak current (IpA ) vs. charge consumed. Scan rate = 100 mV s
t = ambient.
,
−1
1
mechanisms (electrochemical/chemical/electrochemical/chemical
reactions) as illustrated in Scheme 1 [33].
ratio is decreased. A plot of the peak current ratio (IpC1 /Ip ) versus
A
1
On the basis of these observations one can suppose that
2a–c is formed from 1a–c by four E pathways, and then four
Michael-additions of nucleophile 8 at C-5 of o-benzoquinone occur
[15,35,36]. The formed o-diphenols in 4a–c are oxidized such as
1a–c in four E reactions to the o-benzoquinone 5a–c and four
intramolecular Michael-additions on this intermediate produces
benzoquinones in 2a–c (Scheme 1) seems to occur much faster
than other side reactions leading presumably to the intermediates
4a–c. The oxidation of the compounds 4a–c at the A0 peak poten-
tial followed by four intramolecular Michael additions [35–39] and
parallel two proton shifts and aromatization at each phenyl ring
(Scheme 1) lead to 7a–c as the final products. The Michael accep-
tors 2a–c are first attacked selectively by the –NH2 group of 8 which
has more nucleophilicity (not by oxygen) on the C-5 positions of the
phenyl ring that have less hindrance, then by –OH of 8 on the C-6
positions [12,13,17]. The successful synthesis of the target mate-
rials 7a–c was established via UV–vis, IR, 1H NMR, 13C NMR and
MALDI-mass spectroscopic methods.
the scan rate for a mixture of 1c and 8 confirms the reactivity of
o-benzoquinone derivatives of 1c, (2c) with 8, appearing as an
A
increase in the peak current ratio (IpC1 /Ip ) at higher scan rates
1
(Fig. 3, curve g). Furthermore, under these conditions, the current
function for A1 peak, (IpA1 /v1/2) changes only slightly when increas-
ing the scan rate (Fig. 3, curve h). Controlled potential coulometry
was performed in a water/ethanol (50/50) phosphate buffer solu-
tion (c = 0.1 M, pH = 7.5), containing 0.1 mmol of 1c and 0.4 mmol of
8 at 0.15 V versus 3 M Ag/AgCl. The monitoring of the electrolysis
progress was done using cyclic voltammetry, it could be clearly
observed that with the progress of the coulometry, anodic (A1)
and cathodic (C1) peaks disappeared when the charge consumption
became about 16 electrons per each molecule of 1c (Fig. 4). Similar
results were observed for the oxidation of 1a and 1b in the presence
of 8. Diagnostic criteria of cyclic voltammetry, the consumption of
16 electrons per molecules of 1a–c and the spectroscopic data of
the isolated product, indicated that the reaction mechanism of elec-
trooxidation of 1a–c in the presence of 8 is four independent ECEC
Fig. 3. Typical voltammograms of 0.25 mmol dm−3 1c in the presence of 1.0 mmol dm−3 8 in 0.1 mol dm−3 phosphate buffer (pH = 7.5) in water/ethanol (50/50, v/v) solution at
a glassy carbon electrode versus Ag/AgCl/3 M KCl as reference electrode and various scan rates. Scan rates from (a) to (f) are: 50, 100, 200, 400, 800, 1600 mV s−1, respectively.
A
Curve (g): variation of peak current ratio IpC /Ip vs scan rate. Curve (h): variation of peak current function (IpA /v1/2) vs scan rate, t = ambient.
1
1
1

9430
S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
where EO0X is the oxidation peak potential at pH = 0.0 and R, T and
F have their usual meanings [42]. This figure and Fig. 5c, curve I
also shows the (IpC1 /Ip ) decrease when the pH increases. This is
due to the coupling of monoanionic or dianionic forms of 1c with
their oxidized form 2c in a dimerization or polymerization reaction
[31,32]. The rate of the coupling reaction was pH dependent and
enhanced by the increasing of pH. The cyclic voltammograms of 1c
A
1
A
in the presence of 8 showed that the peak–current ratio (IpC1 /Ip
)
1
increased with the decreasing of pH (Fig. 5b and c, curve (II)).
This can be related to the protonation of the enolate form of 8
and its subsequent inactivation towards Michael addition reaction.
At pH = 7.5 the rate of dimerization and polymerization reaction is
A
decreased (peak current ratio IpC1 /Ip in the absence of 8 ∼1.25) and
1
the rate of the reaction between 8 and 2c and 4c is increased (peak
A
current ratio IpC1 /Ip in the presence of 8 ∼0.35), see Fig. 4, curves I
and II, respectively. Thus a solution of water/ethanol containing
0.1 M phosphate buffer (pH = 7.5) was the most suitable solvent
system for electrochemical study and synthesis in this work.
1
3.3. Spectroscopic characterization of 7a–c
The 1H NMR spectra of the products confirm their formation.
Assignments are made on the basis of previous assignments for
5,10,15,20-tetrakis (2,3-dihydroxyphenyl) porphyrin [34,43] and
Mn (III) tetraaryl porphyrin [44] complexes, relative intensity and
comparison with the pattern of signals in the starting materials.
Phenyl protons of 7a–b and 8 were split and were seen at 6.3–7.6.
Intensities of the phenyl signals relative to the pyrrole signals were
exactly 8–20 according to the related products. The disappearance
of the OH proton of 8 at 9.01 is another distinct reason for the occur-
rence of the cyclization reaction. Mn (III) porphyrins with unfilled
d shell of Mn (III) are paramagnetic. The observed chemical shifts
of protons in paramagnetic molecules are due to a combination
of diamagnetic and paramagnetic contributions. The paramagnetic
shifts are caused by spin delocalization from the unpaired electron
to the protons at the periphery of the molecule [45]. Paramagnetic
1H NMR of 7c shows ␤-pyrolic-Hs that appear at −34.8 ppm and
protons of the phenyls periphery appear as multiplet between 6.15
and 7.7 ppm [45].
The attachment of four units of 8 to porphyrin 7a and 7b pro-
duced 15 signals in the 13C NMR spectrum, while less symmetric
porphyrins with one, two or three units of 8 were expected to have
more signals. The signals related to C–OH carbons of 7a–b were seen
at 149.3 and 148.6 ppm, respectively. The FT-IR spectra of products
exhibit characteristic peaks of 1a–c and 8 according to literature
[34].
Fig. 5. (a) Cyclic voltammograms of 0.25 mmol dm−3 1c at different pHs versus
Ag/AgCl/3 M KCl. (b) Cyclic voltammograms of 0.25 mmol dm−3 1c in the presence of
A
1 mmol dm−3 8 at different pHs. (c) Curve (I), variation of peak–current ratio (IpC /Ip
)
1
1
of 1c in the absence of 8, curve (II), variation of peak current ratio (IpC /Ip ) of 1c in
A
1
1
the presence of 8 and curve (III), difference between peak–current ratio (IpC /Ip ) in
A
1
1
the presence and absence of 8.
3.3.1. UV–vis and fluorescence
3.2. The effect of pH
The absorption spectra of compounds 7a–c along with 1a–c
in methanol are shown in Fig. 6. Compound 8 does not have any
absorption in this region. The band at about 415 nm is the soret
band of the porphyrin moiety, which is an a1u (␲) → eg (␲*) electron
transition, assigned to the second excited state S2 generated by the
␲ → ␲* transition. The weak absorption bands between 500 nm and
660 nm are the Q bands of the porphyrin moiety and correspond
to an a2u (␲) → eg (␲*) electron transition, belonging to the first
excited state S1 generated by ␲ → ␲* transition [46,47]. The soret
absorption wavelength of 7a is almost identical with porphyrin 1a
but the intensity of the 7a soret band is stronger as a result of ␲ elec-
tron density extension of the HOMO ␲ system by the aminophenol
ring. Absorption spectrum of 1b has some differences relative to
7b. On the other hand, the soret band of 7b is stronger and blue-
shifted by 11 nm and its Q bands intensified compared to those of
the parent porphyrin. UV–vis spectrum of 7c is blue shifted about
50 nm and intensified compared to 1c. These blue shifts are more
The voltammetric behavior of catecholes at various pHs are well
known and were studied in various papers [40,41]. In this work the
electrochemical oxidation of 1c alone and in the presence of 8 were
studied in different pHs. As Fig. 5a shows, the peak potential for
peak A1 shifted to the negative potentials by increasing the pH. This
is expected because of the participation of protons in the oxidation
of 1c to 2c and 4c to 5c.
R − 8e− − mH+ ↔ O
where R stands for 1c and 4c, O stand for 2c and m is the number
of protons involved in the reactions. The oxidation peak potential
(for the A1 peak) Eox is given by:
ꢀ
ꢁ
2.303mRT
EOX = E0
−
pH
OX
8F

S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
9431
Fig. 7. Fluorescence spectra of compounds 1a, 8 and 7a in methanol at concentration
of 10−5 mol dm−3, ꢀexc = 400 nm.
the fluorophore near it via electron or energy transfer [51]. Thus the
order of fluorescence intensity of the porphyrins was 1a > 1b ꢀ 1c.
When 7b and 7c were excited at 400 nm the emission of the
porphyrins were quenched and had not been detected under the
particular experimental conditions used.
3.4. SEM
The synthetic versatility of porphyrins allows the preparation of
molecular units capable of assembling in ordered supramolecular
structures, characterized by different geometrical motifs [52–54].
The morphology and size of the samples were further investi-
gated using scanning electron microscopy (SEM). SEM images
indicate that this method produces regular shapes of manganese
porphyrin nano-particles and most of the crystals of 7c posses a
cubic nano structure with a dimension of about 100 nm (Fig. 8).
Synthesis of nanosized materials usually needs further treatment
such as hydrothermal and sonification [55–57] but in our work
nano-particles were deposited directly on the electrode during
electrosynthesis without using other techniques.
Fig. 6. UV–vis spectra of 1a–c and 7a–c in methanol at concentration of
10−5 mol dm−3
.
pronounced in 7c compared to 7b. The metallation of the free base
porphyrin by manganese results in considerable red shift due to the
effective ␲ interaction between metal d orbital’s and porphyrin ␲
system [48]. Blue shifts in 7b and 7c show that the effective inter-
action between metals and the porphyrin ligand is considerably
decreased due to the strong deformation of the porphyrins caused
by steric hindrance of the phenoxazine substitutions. Another fea-
ture of the UV–visible spectrum of 7c is its broadness that indicates
atropoisomerism resulting from bulky substitution on the phenyls
[49]. This indicates the substituent’s significantly affecting the pho-
tophysical nature of the metalloporphyrin core. The results of these
study show that electrosynthesized materials 7a–c could be bet-
ter candidate for designing light harvesting materials that operate
over a greater range of the solar spectrum compared to simple,
well-studied less functionalized porphyrin chromophores alone.
The fluorescence spectra of the 1a, 8 and 7a are shown in Fig. 7.
These compounds were excited at 400 nm, where the porphyrin
subunit absorbs strongly. The emission spectrum of 7a shows char-
acteristic luminescence of the metal-free porphyrin cores at 635 nm
and 690 nm that was quenched by 50% in comparison with 1a at
equal concentration. Compounds 8 and 1a show a very weak emis-
sion at about 460 nm that appears in the emission spectra of 7a
without any shift but notably decreases in intensity. This decrease
supports the energy transfer from the porphyrin core excited state
to the four 8 groups as the electron acceptor subunits in 7a [50].
Of the metalloporphyrins, the zinc porphyrin 1b emitted flu-
orescence; the emission peaks were situated at 580 and 635 nm
which was some 55 nm blue shifted compared to the metal-free
porphyrins. The fluorescence intensity of 1c is 15 times less than its
metal-free counterpart’s because MnIII is a paramagnetic ion with
an unfilled d shell and could strongly quench the fluorescence of
To the best of our knowledge, this is a novel method for the
synthesis of nano-sized structures of functionalized manganese
porphyrins during electrosynthesis.
Fig. 8. SEM image of 7c shows that most of crystals have cubic nano structures.

9432
S. Osati et al. / Electrochimica Acta 56 (2011) 9426–9432
4. Conclusion
[20] W. Muller, D.M. Crothers, Eur. J. Biochem. 54 (1975) 267.
[21] B.C. Channu, H.N. Kalpana, G.B. Eregowda, C. Dass, P.J. Houghton, K.N. Thimma-
iah, J. Pharm. Biomed. Anal. 21 (1999) 775.
In conclusion, the phenoxazine-porphyrin catechol com-
pounds were successfully synthesized and characterized. At first
porphyrin-catecholes 1a–c are oxidized to their respective o-
benzoquinones 2a–c. The formed o-benzoquinones are attacked by
four equivalent 8, via four independent ECEC mechanisms, includ-
ing two Michael addition reactions and two parallel or sequential
eliminations of hydrogen followed by intramolecular cyclization,
converted to 7a–c as the final products. The combination of the
novel properties of porphyrins, catecholes and phenoxazine and
the formation of ␲-extended heterocyclic fused porphyrins is the
major advantage of this research that can possibly create useful
properties. This strategy can be used for the synthesis of additional
new functionalized porphyrins.
[22] G.P. Moloney, Magn. Reson. Chem. 28 (1990) 824.
[23] F.P. Scheafer (Ed.), Dye Lasers, Springer-Verlag, Berlin, 1973.
[24] M. Pauchard, S. Huber, R. Meallet-Renault, H. Maas, R. Pansu, G. Calzaferri,
Angew. Chem. Int. Ed. 40 (2001) 2839.
[25] G. Calzaferri, H. Maas, M. Pauchard, M. Pfenniger, S. SonsMegelski, A. Devaux,
Advances in Photochemistry, vol. 27, John Wiley & Sons Inc., Hoboken, 2002, p.
1.
[26] A. Wiehe, E.J. Simonenko, M.O. Senge, B. Röder, J. Porphyrins Phthalocyanines
5 (2001) 758.
[27] S.A. Syrbu, A.S. Semeikin, Russ. J. Org. Chem. 35 (1999) 1236.
[28] D.A. James, D.P. Arnold, P.G. Parsons, Photochem. Photobiol. 59 (1994) 441.
[29] L. Papouchado, G. Petrie, J.H. Sharp, R.N. Adams, J. Am. Chem. Soc. 90 (1968)
5620.
[30] L. Papouchado, G. Petrie, R.N. Adams, J. Electroanal. Chem. 38 (1972) 389.
[31] R.E. Sioda, B. Frankowska, J. Electroanal. Chem. 568 (2008) 356.
[32] S.S. Hosseiny Davarani, N. Sheijooni Fumani, H. Arvin-Nezhad, F. Moradi, Tetra-
hedron Lett. 49 (2008) 710.
[33] A.J. Bard, L.R. Faulkner, Electrochemical Methods, 2nd ed., Wiley, New York,
2001, p. 469, 246, 497.
[34] P.R. Jamaat, S.S. Hosseiny Davarani, N. Sheijooni Fumani, L. Masoumi, N. Safari,
J. Porphyrins Phthalocyanines 12 (2008) 85.
[35] S.S. Hosseiny Davarani, N. Mashkouri Najafi, S. Ramyar, L. Masoumi, M. Sham-
sipur, Chem. Pharm. Bull. 54 (7) (2006) 959.
[36] D. Nematollahi, M. Hesari, J. Electroanal. Chem. 557 (2005) 197.
[37] M.R. Islami, Z. Hassani, H. Sheibani, B. Abdolahzadeh, N. Etminan, Tetrahedron
59 (2003) 4993.
Acknowledgements
This work was supported by the Iranian National Science Foun-
dation (INSF) and Shahid Beheshti University Research Affaires.
References
[38] D. Nematollahi, M. Rafiee, H.R. Khavasi, Bull. Chem. Soc. Jpn. 81 (11) (2008)
1505.
[1] K.M. Kadish, K.M. Smith, R. Guilard, The Porphyrin Handbook, vol. 3, Academic
Press, 2000 (Ch. 21).
[39] I. Yavari, M. Adib, L. Hojabri, Tetrahedron 58 (2002) 6895.
[40] D. Nematollahi, M. Rafiee, J. Electroanal. Chem. 566 (2006) 31.
[41] M. Rafiee, D. Nematollahi, J. Electroanal. Chem. 626 (2009) 36.
[42] H. Salehzadeh, D. Nematollahi, M. Rafiee, J. Electroanal. Chem. 650 (2011) 226.
[43] S. Osati, N. Safari, M. Kalate Bojdi, S.S. Hosseiny Davarani, J. Electroanal. Chem.
655 (2011) 120.
[2] D. Gust, T.A. Moore, A. Moore, Acc. Chem. Res. 42 (2009) 1890.
[3] N. Aratani, D. Kim, A. Osuka, Acc. Chem. Res. 42 (2009) 1922.
[4] C.L. Peng, P.S. Lai, C.C. Chang, P.J. Lou, M.J. Shieh, Dyes Pigments 84 (2010) 140.
[5] J.K. Park, J. Chen, H.R. Lee, S.W. Park, H. Hinokubo, T. Osuka, D. Kim, J. Phys.
Chem. 113 (2009) 21956.
[6] S. Zhao, M.G.P.M.S. Neves, A.C. Tome, A.M.S. Silva, J.A.S. Cavaleiro, M.R.M.
Domingues, A.J.F. Correia, Tetrahedron Lett. 46 (2005) 2189.
[7] N.M. Boyle, J. Rochford, M.T. Pryce, Coord. Chem. Rev. 254 (2010) 77.
[8] H. Boedigheimer, G.M. Ferrence, T.D. Lash, J. Org. Chem. 75 (2010) 2518.
[9] M. Zhu, M. Han, Y. Du, P. Yang, X. Wang, Dyes Pigments 86 (2010) 81.
[10] S. Osati, N. Safari, P.R. Jamaat, Inorg. Chim. Acta 363 (2010) 2180.
[11] N.K.S. Davis, A.L. Thompson, H.L. Anderson, J. Am. Chem. Soc. 133 (2011) 30.
[12] S.S. Hosseiny Davarani, A.R. Fakhari, N. Sheijooni Fumani, M. Kalate-bojdi, Elec-
trochem. Commun. 10 (2008) 1765.
[44] N. Safari, B. Notash, J. Mohammad Nezhad, H. Chiniforoshan, H. Hadadzadeh,
A.R. Rezvani, Inorg. Chim. Acta 358 (2005) 2967.
[45] E. Ben-Hur, W.S. Chan, K.M. Kadish, K.M. Smith, R. Guilard (Eds.), The Porphyrin
Handbook, vol. 5, 2003, p. 88, 157.
[46] J. Rodriguez, C. Kirmaier, D. Holten, J. Am. Chem. Soc. 111 (1989) 6500.
[47] S. Fukuzumi, Y. Endo, Y. Kashiwagi, Y. Araki, O. Ito, H. Imahori, J. Phys. Chem. B
107 (2003) 1979.
[48] K.M. Kadish, K.M. Smith, R. Guilard, The Porphyrin Handbook, vol. 3, Academic
Press, 2000, p. 59.
[13] M. Shamsipur, S.S. Hosseiny Davarani, M. Nasiri-Aghdam, D. Nematollahi, Elec-
trochim. Acta 51 (2006) 3327.
[14] A. Bayandori Moghaddam, F. Kobarfard, A.R. Fakhari, D. Nematollahi, S.S. Hos-
seiny Davarani, Electrochim. Acta 51 (2005) 739.
[15] S.S. Hosseiny Davarani, D. Nematollahi, M. Shamsipur, N. Mashkouri Najafi, L.
Masoumi, S. Ramyar, J. Org. Chem. 71 (2006) 2139.
[49] R.F. Beeston, S.E. Stitzel, M.A. Rhea, J. Chem. Educ. 74 (1997) 1468.
[50] X. Qiu, R. Lu, H. Zhou, X. Zhang, T. Xu, X. Liu, Y. Zhao, Tetrahedron Lett. 49 (2008)
7446.
[51] G. Szintay, A. Horvath, Inorg. Chim. Acta 324 (2001) 278.
[52] C.M. Drain, G. Smeureanu, S. Patel, X. Gong, J. Garno, J. Arijeloye, New J. Chem.
30 (2006) 1834.
[16] D. Nematollahi, A. Amani, E. Tammari, J. Org. Chem. 72 (2007) 3646.
[17] D. Nematollahi, D. Habibi, M. Rahmati, M. Rafiee, J. Org. Chem. 69 (2004)
2637.
[18] S.S. Hosseiny Davarani, S. Ramyar, L. Masumi, N. Sheijooni Fumani, A. Bayandori
Moghadam, J. Electrochem. Soc. 155 (2008) 120.
[53] X. Gong, T. Milic, C. Xu, J.D. Batteas, C.M. Drain, J. Am. Chem. Soc. 124 (2002)
14290.
[54] Z. Ou, H. Yao, K. Kimura, Photochem. Photobiol. A 189 (2007) 7.
[55] A. Gedanken, Ultrason. Sonochem. 11 (2004) 47.
[56] E. Lester, P. Blood, J. Denyer, D. Giddings, B. Azzopardi, M. Poliakoff, J. Supercrit.
Fluids 37 (2006) 209.
[19] A. Bolognese, G. Correale, M. Manfra, A. Lavecchia, O. Mazzoni, E. Novellino, V.
Barone, P. Colla, R. Loddo, J. Med. Chem. 45 (2002) 5217.
[57] H. Sadeghzadeh, A. Morsali, Ultrason. Sonochem. 18 (2011) 80.