5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,20-triphenylporphyrin

Article abstract of DOI:10.1142/S1088424612004501

The new triazene-porphyrin dye 5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)- 10,15,20-triphenylporphyrin, encompassing a reactive protonated triazene moiety, was prepared starting from meso-tetraphenylporphyrin (H₂TPP), first converting it to the

Full text of DOI:10.1142/S1088424612004501

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 200–209
DOI: 10.1142/S1088424612004501
Published at http://www.worldscinet.com/jpp/
5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,20-
triphenylporphyrin: a new triazene-porphyrin dye and its
spectroelectrochemical properties
Bernardo A. Iglesiasa, Manfredo Hörnerb, Henrique E.Tomaa and Koiti Araki*a◊
a Universidade de São Paulo, Departamento de Química Fundamental, Instituto de Química, CEP 05508-000, São
Paulo, SP Brazil
b Universidade Federal de Santa Maria, Departamento de Química, CEP 97105-900, Rio Grande do Sul, RS, Brazil
Received 5 October 2011
Accepted 11 November 2011
ABSTRACT: The new triazene-porphyrin dye 5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,20-
triphenylporphyrin, encompassing a reactive protonated triazene moiety, was prepared starting from
meso-tetraphenylporphyrin (H2TPP), first converting it to the 5-(4-nitrophenyl)-10,15,20-triphenyl-
porphyrin, then reducing to the 5-(4-aminophenyl)-10,15,20-tri(phenyl)porphyrin intermediate, and
reacting with the diazonium salt of 4-nitroaniline; and characterized by spectroscopic and electrochemical
methods. The absorption spectrum of the neutral species resembled the sum of H2TPP and of 1,3-bis(4-
nitrophenyl)triazene spectrum, but the deprotonated anionic species showed more delocalized frontier
orbitals, behaving as a push-pull system exhibiting triazenide-to-porphyrin charge-transfer transitions.
KEYWORDS: triazene-porphyrins, spectroelectrochemistry, push-pull system.
compounds are important and stable intermediates for the
INTRODUCTION
preparation of that class of bioactive molecules.
Porphyrins are particularly interesting and versatile
Nevertheless, reports describing the electronic,
building-blocks for the preparation of supramolecular and
electrochemical and binding properties of triazene
hybrid nanomaterials aiming a wide range of applications.
derivatives are rather scarce. Only few works describing
For example, well-designed porphyrin derivatives have
their physico-chemistry, particularly substituent effects
been proposed as models in natural photosynthetic
and acid-catalyzed decomposition properties, were found
systems [1–4], molecular switches [5–7] and organic
in the literature [16]. The main focus at this moment
semiconductors [8–10]. In this context, triazenes are
seems to be on their biological activity, especially as new
special diazoamino compounds which have been
targeting factors for receptor-RNAs [17]. Also, Daasbjerg
employed as dyes and pigments, in advanced materials
et al. [18–20] reported an interesting electrografting
and as biologically active compounds [11, 12]. They are
method based on aryldiazonium salts, generated by
susceptible to photoinduced cis-trans isomerization and
in situ acid catalyzed decomposition of a triazene,
can act as charge-transfer site in suitable donor-acceptor
involving the covalent bond of tethering aryl groups to
systems [13]. Recently, the synthesis of benzotriazoles
via cyclization of substituted triazenes followed by
various conducting materials. On the other hand, Lu et al.
[21] described a new method for direct covalent grafting
palladium(II) catalyzed intramolecular amination
of molecules onto semiconductor and metal surfaces
reaction was described [14, 15], showing that those
(GaAs, Si and Pd) based on a triazene-porphyrin offering
a very attractive and simple route for the preparation of
highly passivating and robust molecular mono and multi-
layers on those materials. That water soluble porphyrin
SPP full member in good standing
derivative was synthesized by Pd-catalyzed cross-
coupling reaction of 1-diethyl-3-(4-iodophenyl)triazene
*Correspondence to: Koiti Araki, email: koiaraki@iq.usp.br,
tel: +55 11-3091-8513, fax: +55 11-3815-5579
Copyright © 2012 World Scientific Publishing Company

5-(1-(4-PHENYL)-3-(4-NITROPHENYL)TRIAZENE)-10,15,20-TRIPHENYLPORPHYRIN
201
with 5,10,15-tris{4-{2-[2-(2-methoxy-ethoxy)-ethoxy]-
The triazene-porphyrin H2MTTPP was prepared
from H2TPP, according to the route depicted in
Scheme 1, by reacting H2MATPP with freshly prepared
4-nitrophenyldiazonium salt for 30 min. Then, the
reaction mixture was neutralized with ammonia aqueous
solution until the typical green color of the ring-
protonated porphyrin changed to the red color of the
respective free-base species. A dark red solid, exhibiting
a consistent elemental and spectroscopic analysis, was
isolated after workup (yield: 15%).
ethoxy}}phenyl-20-(4-trimethylsilanylethynyl)phenyl-
porphyrin, the sole triazene-porphyrin found in the
literature, after deprotecting the ethenyl group with
tetrabutylammonium fluoride. Thus, pursuing new
synthetic approaches on porphyrin supramolecular
chemistry [22–24], here we report the synthesis of the
5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,20-
triphenylporphyrin species (H2MTTPP, Scheme 1),
a new triazene-porphyrin, by direct coupling of
5-(4-aminophenyl)-10,15,20-triphenylporphyrin
the diazonium salt of 4-nitroaniline, in addition to its
spectroscopic and electrochemical properties.
with
The 1H NMR spectrum of the triazene-porphyrin
species is compared with those of H2MNTPP and
1,3-bis(4-nitrophenyl)triazene, TriazNO2, in Fig. 1. The
incorporation of a substituent in the para-position of one of
the meso-phenyl rings removed the four-fold rotation axis
of H2TPP, decreasing the molecular symmetry to C2v. Thus,
the b-pyrrolic protons are no longer equivalent because a
plane of symmetry divides the molecule in two halves, and
the protons next to the substituted phenyl ring tend to be
more influenced by the substituent. Thus, the H2MTTPP
exhibited the b-pyrrolic protons (H1, H2 and H3) as a
broadened singlet and a doublet at 8.85 (6H) and 8.87 (2H)
ppm. The signals of the ortho-phenyl protons are shifted to
lower fields by the stronger current effect of the porphyrin
ring; and the “a” and “d” protons should appear as a doublet
at lower field (8.22 ppm, 6H) as compared with the “b”, “c”,
“e” and “f” protons, that appeared as a multiplet at 7.79 ppm
(9H). The inner ring protons were found at -2.78 ppm.
The TriazNO2 species showed only a pair of doublets
at 7.56 and 8.06 ppm, as expected for a molecule in a more
symmetric trans–trans conformation. The N–H proton
RESULTS AND DISCUSSION
The nitration of H2TPP can take place at the beta-
pyrrolic or at the meso-phenyl positions depending on
the nitration method employed. Reactions carried out
using fuming HNO3 involve the NO2 radical species,
thus favoring the beta-pyrrolic substitution, as described
by Ostrowski et al. [25]. On the other hand, reactions
carried out with NaNO2 in strongly acidic conditions
(in our case, TFA was used), i.e. using the nitronium
ion as the reactive species, as well as the consequent
protonation of the porphyrin ring deactivating the beta-
pyrrolic positions, favor the nitration at the meso-phenyl
substituents. The last method was used for the nitration
reaction and the spectroscopic properties found for the
porphyrin precursors H2MNTPP and H2MATPP were
consistent with those described [26, 27], thus confirming
the mono-substitution at the meso-(4-phenyl) position.
1
could not be observed in the H NMR spectrum due to
N
N
H
H
NaNO2, TFA
SnCl2·2H2O, HCl
N
N
N
N
H
N
H
N
NO2
H2MNTPP
e
f
c
d
1
b
a
N
H
1. NaNO2, HCl, -5 °C
N
H
2. NH4OH
1
N
N
N
N
NO2
H
N
H
N
4
H2N
5
2
3
NO2
N
N
H
NH2
N
H2MATPP
H2MTTPP
7
6
Scheme 1. Scheme showing the synthetic route of the triazene-porphyrin H2MTTPP from H2TPP
Copyright © 2012 World Scientific Publishing Company
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202
B.A. IGLESIAS ET AL.
the relatively high acidity and consequent faster exchange
with the solvent. Four signals are expected for the H4–H7
protons. Interestingly, though only two doublets (7.56
(4H) and 8.30 ppm (4H), J = 9.0 Hz) were found for the
nitrophenyl (H6, H7) and bridging phenyl (H4, H5) protons
in the triazene-porphyrin. This accidental coincidence was
confirmed by the COSY 1H–1H correlation spectrum (see
Supporting information section), such that each signal
corresponds to 4H instead of 2H.
Absorption and fluorescence spectra
The UV-vis absorption spectrum of the H2MNTPP
and H2MATPP species are very similar to that of the
H2TPP precursor [28], exhibiting the characteristic
Soret and the Q-bands respectively at 418, 516, 552,
591, 646 nm and 420, 518, 554, 592 and 648 nm. Note
that the presence of a nitro or amino group at the phenyl
para-position only slightly perturbed the electronic states
inducing a bathochromic shift of the absorption bands, as
expected for electron withdrawing groups, indicating that
the H2MATPP species probably is protonated.
Interestingly, the diazoamino group can be easily
deprotonated (TriazNO2, pKa ≈ 9.5, in aqueous solution)
[16] to the triazenide anion, leading to dramatic changes
in the electronic spectrum, as shown in Figs 2a and 2b.
Fig. 1. Comparative 1H NMR spectra of the TriazNO2,
H2MTTPP and H2MNTPP species, in CDCl3
Fig. 2. Experimental (violet line) absorption spectra and deconvoluted bands (dotted lines) of (a) TriazNO2, (b) TriazNO2- anion,
(c) H2MTTPP and (d) H2MTTPP- anion, in DMF solution. The triazenide species were obtained by deprotonating the respective
triazene derivatives with a potassium hydroxide solution in methanol
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 202–209

5-(1-(4-PHENYL)-3-(4-NITROPHENYL)TRIAZENE)-10,15,20-TRIPHENYLPORPHYRIN
203
The deprotonated species is known to be a planar
In order to improve the understanding on the
triazenide porphyrin species, its geometry was optimized
based on iterative molecular mechanics (MM+ method),
and the electronic structure and electronic density
distribution calculated using the ZINDO/S semi-
empirical method. The optimized geometry found for the
triazenide porphyrin anion is illustrated in Fig. 3. Note
that the bridging phenyltriazenide substituent is almost
coplanar but makes a ~45º angle with the porphyrin
ring and with the nitrophenyl group. Similar optimized
geometry was obtained for the protonated species,
however the frontier orbitals were more localized on the
meso-tetraphenylporphyrin or on the 1-(µ-4-phenyl)-3-
(4-nitrophenyl)triazene moiety. In fact, in this case, the
modeled electronic spectrum was consistent with the sum
of the spectrum of those components, in agreement with
the experimental result. However, a significant degree of
delocalization of the frontier orbitals is apparent in the
triazenide porphyrin species (Fig. 3).
According to the theoretical calculations, the two
frontier HOMO levels, represented by MO-143 and
MO-142, are delocalized on the 5-(1-(4-phenyl)-3-(4-
nitrophenyl)triazenide)-10,15,20-triphenylporphyrin
chromophore. The next HOMO level MO-141, as
well as the two lowest energy LUMO levels (MO-
144, MO-145) is essentially localized on the porphyrin
center, while the electronic density of MO-146 is mainly
concentrated on the peripheral (4-nitrophenyl)triazenide
group. The theoretical spectrum consisted of a strong
band at 530 nm (oscillator strength 1.16) associated with
delocalized molecule, in which the triazenide group
behaves as a much better electron donor than the triazene
itself. In fact, the strong band at 391 nm in the neutral
species was replaced by a broad structured set of bands
with maximum at 531 nm (see the deconvoluted band),
that was previously assigned to a triazenide-to-NO2(p*)
charge-transfer transition, while a weak band around 440
nm can be assigned to a charge-transfer transition from the
triazenide to phenyl ring p* orbitals, based on resonance
Raman evidences [29].
The UV-vis spectrum of the H2MTTPP species in
DMF solution (Fig. 2c) exhibited a typical free-base
porphyrin spectrum with an intense Soret band at 419 nm
(loge=5.31)andtheQ-bandsat515,552,591and648nm,
except for a broad shoulder at 383 nm (log e = 4.89),
that was assigned to a charge-transfer transition centered
at the nitrophenyltriazene moiety. The deprotonation
promoted by the addition of a methanolic KOH solution
led to the formation of the anionic H2MTTPP- species,
which exhibited the four Q-bands superimposed to
a broad asymmetric set of bands centered at ~566 nm
(log e = 4.58) and a weak broad band at 649 nm (Fig. 2d).
This spectral pattern is analogous to that observed for the
symmetric 1,3-bis(4-nitrophenyl)triazenide anion, as
shown in Figs 2b and 2d. Surprisingly though the Soret
band was only slightly blue shifted and the shoulder at
378 nm, which now can be assigned to a triazenide to
phenyl ring charge-transfer transition, remained almost
unchanged.
Fig. 3. Electronic density distributions (green shadow) on the H2MTTPP- species major HOMO and LUMO levels, determined by
theoretical ZINDO/S calculations
Copyright © 2012 World Scientific Publishing Company
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B.A. IGLESIAS ET AL.
the MO-143→MO-146 transition, mainly involving
the nitrophenyltriazenide chromophore, with a small
porphyrin-to-nitrophenyl charge-transfer contribution.
The position of this band practically coincided with
the experimentally observed transition (l = 531 nm)
assigned to the (4-nitrophenyl)triazenide moiety
(Fig. 3b). An additional band is theoretically expected
at 632 nm (oscillator strength 0.40) involving the
MO-143→MO-145 transition. This band approached
the band around 648 nm (Fig. 3a), and involves a charge-
transfer transition from the triazenide to the porphyrin
center through the phenyl bridge. The HOMO-LUMO
transition (MO-143→MO-144) is theoretically predicted
as a weak band at 460 nm (oscillator strength 0.11), also
exhibiting a strong charge-transfer character. This band
is probably masked by the strong bands around 440 nm,
corresponding tothe theoretical transitions from MO-(142,
141) to MO-(144, 145), consistent with a porphyrin p→p*
(Soret) band. Thus, considering the molecular structure
and theoretical calculation results, the compound can
be better described as a push-pull system, since the
(4-nitrophenyl)triazenide moiety tends to behave as a
donor and the phenyl group as a good molecular bridge,
delocalizing the electronic density on both chromophores.
The fluorescence emission spectrum of H2MTTPP,
in argon-saturated CH2Cl2 solution (Fig. 4), presented
strong fluorescence bands at 656 nm and 716 nm when
excited at the Soret (lexc = 418 nm) and the Q-bands, in
analogy to other meso-substituted free-base porphyrins.
The H2MNTPP and H2MATPP precursors, as well as
the H2TPP standard, presented similar emission spectra
and fluorescence quantum yields, as shown in Table 1.
In addition, the excitation spectrum reproduced the
corresponding absorption spectrum pattern, clearly
showing the Soret and Q-bands (Fig. 4). This result
confirmed that the lowest excited state is localized at
the porphyrin ring in all those species. However, the
fluorescence spectrum of the deprotonated H2MTTPP-
species could not be registered because the luminescence
efficiency was too low.This means that F0fl (lexc = 418 nm)
should be lower than ~1 × 10-4 and the triazenide group is
a good quencher, probably by redox mechanism.
Fig. 4. Emission (black line, lexc = 418 nm) and excitation (red
line, lem = 716 nm) spectra of H2MTTPP in argon-saturated
CH2Cl2 solution
was assigned to the reduction of the diazoamino proton to
hydrogen gas, generating the respective triazenide anion.
This was followed by two reversible processes tentatively
assigned to the first monoelectronic porphyrin ring
reduction and to the reduction of the triazenide moiety
(see Supporting information section). This process was
shifted 70 mV to more negative potentials as compared
to the corresponding process in 1,3-bis(4-nitrophenyl)
triazene, as expected for the less electronegative character
of the porphyrin ring as compared to the nitro group. The
redox potentials of the 1,3-bis(4-nitrophenyl)triazene and
triazene porphyrin species were compiled in Table 2. The
assignments of the redox processes were based on the
spectroelectrochemistry results, as described below for
the H2MTTPP species.
Spectroelectrochemistry
Spectroelectrochemical studies were carried out
with a 2 × 10-4 M solution of H2MTTPP in DMF for
reduction and in CH2Cl2 for oxidation processes. The
spectroelectrochemistry results, in the 0.0 to 2.1 V range,
are shown in Fig. 6. The CVs in the same potential range
were included to facilitate the correlation of those data
with the electrochemistry results discussed in the previous
section. The oxidation in the 0.0 to 1.50 V range (Fig. 6a)
Electrochemistry
Table 1. Fluorescence emission bands and fluorescence
quantum yields of the H2MNTPP, H2MATPP and H2MTTPP
species in argon-saturated CH2Cl2 solution, exciting at the Soret
band (lexc = 418 nm). A solution of H2TPP in CH2Cl2 was used
as standard
The cyclic voltammograms of H2MTTPP and
TriazNO2 in anhydrous DMF are shown in Fig. 5. Three
irreversible processes were observed at Epa equal to 1.27,
1.70and1.85V,whentheelectrodepotentialswasscanned
from 0.70 to 2.0 V. The first process was assigned to the
monoelectronic oxidation of the porphyrin ring, while
the following two oxidation processes were tentatively
assigned to the oxidation of the triazene substituent bound
at the meso-phenyl position. In contrast, an irreversible
and two reversible processes were observed at Epc equal to
-0.73, -0.94 and -1.25V. The first one, also observed in the
CV of 1,3-bis(4-nitrophenyl)triazene in DMF solution,
Compound
F0fl (lexc = 418 nm)
Emission bands, nm
H2TPP
0.150
0.099
0.083
654, 714
654, 714
660, 718
H2MNTPP
H2MATPP
H2MTTPP
0.110
656, 716
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5-(1-(4-PHENYL)-3-(4-NITROPHENYL)TRIAZENE)-10,15,20-TRIPHENYLPORPHYRIN
205
Fig. 5. Cyclic voltammograms of a 2 × 10-3 M (a) H2MTTPP porphyrin and (b) TriazNO2 solution in DMF, 0.1 M TBAClO4, using
platinum disk electrode, at scan rate of 100, 80 and 50 mV.s-1
Table 2. Redox potentials of the 5-(1-(4-phenyl)-3-(4-nitrophenyl))-
triazene-10,15,20-triphenylporphyrin and 1,3-bis(4-nitrophenyl)triazene,
in DMF solution
the triazenide anion to the triazenide dianion
were observed. This was characterized by the
disappearance of the bands around 390, 450
and 560 nm, concomitantly with the increase of
the absorption at 300 and 810 nm, as shown in
Fig. 7c.
-/2-
Redox process
P0/+
P+/2+
T0/+
T0/- (H+)
P0/-
T
a
a
a
H2MTTPP
TriazNO2
1.27 V 1.70 V 1.85 V -0.73 V -0.94 Vb -1.25 Vb
a
—
—
~1.20 V -0.66 V
—
t-1.04 V
The
spectroelectrochemical
behavior
of TriazNO2 was studied for comparison
purposes.Theprotonof1,3-bis(4-nitrophenyl)-
a = anodic peak and b = cathodic peak potential.
triazene species is relatively acidic due to the strong
electron withdrawing character of the nitro group. Thus,
one can perceive the presence of a low intensity band at
581 nm, attributed to a triazenide-to-nitrophenyl charge-
transfer transition, indicating that the compound is
partially deprotonated (Fig. 8a) in DMF solution. This
was confirmed by reducing the compound at -0.90 V,
where the broad band at 581 nm (Fig. 8b) was strongly
intensified, confirming the formation of the triazenide
anion as H+ is reduced to H2. In fact, the amount of
triazenideinthatDMFsolutionwasestimatedasbeing8%.
The subsequent reduction of that species to the triazenide
dianion at -1.30 V, led to the shift of the 581 nm band to
670 nm (Fig. 8c). This process is electrochemically and
chemically reversible, as confirmed by the presence of
several well defined isobestics points and the regeneration
of the initial spectrum when the potential was reverted to
-0.90 V. This behavior parallels the one observed for the
triazene-porphyrin species, as discussed above.
Then, the solution was renewed before exploring the
oxidation processes, in order to avoid contamination. It is
interesting to note that the application of 1.0 V led to the
rise of a new band at 494 nm and the disappearance of
the 581 nm band concomitantly with the decrease of the
408 nm band. This indicates that the irreversible oxidation
peak at 0.75 V can be assigned to the oxidation of the
1,3-bis-(4-nitrophenyl)triazenide anion present in small
amount (~8%), but not to the oxidation of the triazene
species which should be oxidized at higher potentials
led to the bathochromic shift of the Soret band from 419
to 442 nm and to the appearance of two new bands at
657 and 885 nm, while the Q-bands faded. These spectral
changes can be attributed to the monoelectronic oxidation
of the porphyrin ring to the p-radical cation species [30].
When the potential was shifted from 1.50 to 1.80 V, the
intensity of the Soret and 657 nm bands decreased while
there was an increase of absorbance at 469 nm, indicating
the occurrence of the second monoelectronic oxidation
of the porphyrin ring (Fig. 6b) [31, 32]. Finally, when the
applied potential was increased to 2.10 V, the absorbance
at 219 nm, assigned to the n → p* and p → p* transitions
of triazene (that started to rise at 1.80V), increased further
(Fig. 6c) suggesting the oxidation of the triazene moiety.
Moving to the negative potential side, the reduction of
the triazene-porphyrin in the 0.0 to -0.80 V range (Fig. 7a)
led to the appearance of the characteristic broad charge-
transfer band at 566 nm, clearly indicating the formation of
thetriazenidespeciesduetothereductionofthediazoamino
protontohydrogengas,whiletheporphyrinbandsremained
almost unchanged. Then, the disappearance of the Soret
band was observed at -1.10 V (Fig. 7b), concomitantly
with an increase of the absorbance at 439 nm and the rise
of the absorption in the 630–915 nm range. These spectral
changes can be attributed to the monoelectronic reduction
of the porphyrin ring to the p-radical anion species. Finally,
when the potential was shifted to -1.50 V, spectral changes
that can be assigned to the monoelectronic reduction of
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B.A. IGLESIAS ET AL.
Fig. 6. Spectroelectrochemistry of a 2 × 10-4 M H2MTTPP solution in CH2Cl2, 0.1 M TBAClO4, in the (a) 0.0 V to 1.50 V, (b) 1.50 V
to 1.80 V and (c) 1.80 V to 2.10 V range, respectively. The CVs of a 2 × 10-3 M solution of H2MTTPP (v = 50, 80 and 100 mV.s-1)
in the same solvent and 0.1 M TBAClO4 are also shown in the upper left corner
(~1.20 V). This fact was confirmed by applying an initial
potential of -0.90 V, enough to promote the reduction
of H+ to H2 and consequent formation of the TriazNO2-
species, before the oxidation at 1.00 V.
(5.43), 516 (4.13), 552 (3.78), 591 (3.57) and 646
(3.39). H NMR (500 MHz, CDCl3): d, ppm -2.70 (s,
1
2H), 7.12 (d, 2H, J = 9.0 Hz), 7.83 (m, 9H), 8.05 (d, 2H,
J = 9.0 Hz), 8.28 (m, 6H), 8.88 (s, 6H), 9.00 (s, 1H).
13C NMR (150 MHz, CDCl3): d, ppm 146.5, 145.9,
140.1, 138.2, 135.3, 132.0, 131.2, 128.8, 127.9, 127.4,
121.1, 118.8, 115.0, 111.4. MS (ESI): m/z 660.5 (calcd.
for [M + H]+ 660.5).Yield 0.075 g (70%). Anal. calcd. for
C44H29N5O2.0.5H2O; C: 79.02%; H, 4.52%; N, 10.47%.
Found: C, 79.10%; H, 4.50%; N, 10.36%.
5-(4-aminophenyl)-10,15,20-triphenylporphyrin
(H2MATPP). UV-vis (CH2Cl2): lmax, nm (log e) 420
(5.44), 518 (4.12), 554 (3.90), 592 (3.64) and 648 (3.61).
1H NMR (500 MHz, CDCl3): d, ppm -2.75 (s, 2H), 4.24
(broad s, 2H), 7.07 (d, 2H, J = 9.0 Hz), 7.75 (m, 9H),
7.99 (d, 2H, J = 9.0 Hz), 8.22 (m, 6H), 8.85 (s, 6H), 8.95
(s, 2H). 13C NMR (150 MHz, CDCl3): d, ppm 146.1,
145.2, 140.0, 138.3, 134.9, 132.2, 131.2, 128.7, 127.4,
127.2, 121.3, 118.0, 114.9, 110.8. MS (ESI): m/z 630.5
(calcd. for [M + H]+ 630.5). Yield 0.054 g (54%). Anal.
calcd. for C44H31N5; C, 83.92%; H, 4.96%; N, 11.12%.
Found: C, 83.50%; H, 4.92%; N, 11.15%.
EXPERIMENTAL
Synthesis of 5-(4-nitrophenyl)-10,15,20-triphenylpor-
phyrin, H2MNTPP, and 5-(4-aminophenyl)-10,15,20-
triphenylporphyrin, H2MATPP
H2MNTPPandH2MATPPwerepreparedaccordingto
themethoddescribedbySmithetal.[27].Thefirstonewas
prepared by the reaction of meso-tetraphenylporphyrin,
H2TPP, and sodium nitrite, in trifluoroacetic acid,
TFA. Then, the nitro group of H2MNTPP was reduced
with stannous chloride dihydrate, in concentrated HCl,
at 65 °C, for 2 h, to get the respective 4-aminophenyl
derivative, H2MATPP, as a purple solid, after workup.
5-(4-nitrophenyl)-10,15,20-triphenylporphyrin
(H2MNTPP). UV-vis (CH2Cl2): lmax, nm (log e) 418
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5-(1-(4-PHENYL)-3-(4-NITROPHENYL)TRIAZENE)-10,15,20-TRIPHENYLPORPHYRIN
207
Fig. 7. Spectroelectrochemistry of a 2 × 10-4 M H2MTTPP solution in DMF, 0.1 M TBAClO4, in the (a) 0.0 V to -0.80 V, (b) -0.80 V
to -1.10 V and (c) -1.10 V to -1.50 V range, respectively. The CVs of a 2 × 10-3 M solution of H2MTTPP (v = 50, 80 and 100 mV.s-1)
in the same solvent and 0.1 M TBAClO4, are also shown in the upper left corner
Synthesis of 5-(1-(4-phenyl)-3-(4-nitrophenyl)triaz-
ene)-10,15,20-triphenylporphyrin, H2MTTPP
7.79 (m, 9H), 8.22 (d, 6H, J = 9.0 Hz), 8.30 (d, 4H, J =
9.0 Hz), 8.85 (broad s, 6H), 8.87 (broad s, 2H). 13C NMR
(150 MHz, CDCl3): d, ppm 192.6, 163.1, 162.9, 148.9,
146.8, 144.2, 141.1, 136.3, 135.2, 130.9, 131.7, 128.3,
127.7, 126.9, 121.3, 118.2, 115.0, 110.7. MS (ESI): m/z
779.5 (calcd. for [M + H]+ 779.5). Yield 0.010 g (15%).
Anal. calcd. for C50H34N8O2.7H2O; C, 66.36%; H, 5.35%;
N, 12.38%. Found: C, 66.36%; H, 5.31%; N, 12.41%.
H2MTTPP was synthesized as follows. First, 0.087 g
(0.63 mmol) of 4-nitroaniline was dissolved in a mixture
of 20 mL of HCl and 5 mL of water, cooled to -5 °C, and
a sodium nitrite solution (0.045 g; 0.66 mmol in 5 mL of
water) slowly added to get the respective diazonium salt.
Then, a solution of H2MATPP (0.040 g; 0.063 mmol) in
glacial acetic acid (10 mL) was poured into that solution
under stirring. After 30 min, the reaction mixture was
neutralized with ammonium hydroxide, extracted with
CH2Cl2 (3 × 50 mL) and the solvent removed in a flash
evaporator. The crude solid was purified by silica-gel
(200–400 mesh, 60 Å, Aldrich) column chromatography,
using CH2Cl2/hexane (1:1) as eluent. A dark-red solid
was obtained after recrystallization from a CH2Cl2/
MeOH mixture.
Synthesis of 1,3-bis(4-nitrophenyl)triazene, TriazNO2
The symmetric TriazNO2 was prepared in a similar
way, according to the conventional method described in
the literature [33].
1,3-bis(4-nitrophenyl)triazene (TriazNO2). UV-vis
(DMF): lmax, nm (log e) 233 (4.25), 272 (3.84), 320
1
(4.00) and 391 (4.68). H NMR (200 MHz, CDCl3): d,
ppm 7.56 (d, 4H, J = 9.0 Hz), 8.06 (d, 4H, J = 9.0 Hz).
13C NMR (75 MHz, CDCl3): d, ppm 192.9, 163.6, 162.7,
149.6. MS (ESI): m/z 288.2 (calcd. for [M + H]+ 288.1).
Yield 14.9 g (67.5%). Anal. calcd. for C12H9N5O4; C,
50.18%; H, 3.16%; N, 24.38%. Found: C, 50.40%; H,
3.18%; N, 24.20%.
5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,
20-triphenylporphyrin (H2MTTPP). UV-vis (DMF):
l
max, nm (log e) 383 (4.89), 419 (5.31), 515 (4.03), 552
1
(3.86), 591 (3.61) and 648 (3.48). H NMR (500 MHz,
CDCl3): d, ppm -2.78 (s, 2H), 7.56 (d, 4H, J = 9.0 Hz),
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 207–209

208
B.A. IGLESIAS ET AL.
Fig. 8. Spectroelectrochemistry of a 2 × 10-3 M TriazNO2 solution in DMF, 0.1 M TBAClO4, in the (a) 0.0 to 1.00 V, (b) 0.0 to
-0.90 V and (c) -0.90 to -1.30 V range, respectively. Figure 5c was included in the upper left corner to facilitate the correlation of
those data with the electrochemistry behavior discussed in a previous section
All reagents and solvents were of analytical grade and
employed without further purification, unless otherwise
specified.TheUV-visspectrawererecordedonaHP-8453A
diode-array spectrophotometer, in the 190 to 1100 nm
range, in CH2Cl2 or DMF, using a 10.0 mm quartz cuvette.
The emission and excitation spectra were recorded on a
Photon Technology Inc., model LS100 spectrofluorimeter,
AgNO3, in acetonitrile) reference electrode and a coiled
platinum wire auxiliary electrode. The redox potentials
were converted to the SHE scale by adding 0.503 V to the
experimental data. The spectroelectrochemistry data were
collected using a previously described homemade thin-
layer cell [30], a PAR model 283 potentiostat/galvanostat
and the HP-8453A spectrophotometer.
1
using N2 gas purged CH2Cl2 solutions. The H NMR
spectra were recorded on a Bruker APX200 or DRX500
spectrophotometer, using CDCl3 as solvent. Chemical
shifts were presented in ppm using tetramethylsilane
(TMS) as internal reference. Electrospray ionization mass
spectra (ESI-MS) were registered in a Bruker Daltonics
Esquire 3000 Plus using the following conditions:
capillary voltage 3.0 kV, sample cone 30 V, extraction
cone 3.0 V, source temperature 100 °C, desolvation
was carried out with N2 gas at 100 °C and flow rate of
400 mL.min-1. The electrochemical experiments were
carried out in anhydrous CH2Cl2 and DMF (Aldrich) as
solvent, and anhydrous TBAClO4 (Aldrich) as electrolyte,
using an AutoLab PGStat30 potentiostat/galvanostat
and a conventional electrochemical cell consisting of
a platinum disk working electrode, Ag/Ag+ (0.010 M
Theoretical calculations
Theoretical quantum chemical calculations were
carried out at the semi-empirical level using the
HyperChemTM 8.0 program. Molecular structures were
derived by full geometry optimization using a modified
MM2 force field and the charge distributions calculated
by the semi-empirical ZINDO/S method. A conjugate
gradient of 10-3 kcal.Å-1.mol-1 was set as a convergence
criterion using a conjugate gradient algorithm. The
SCF convergence tolerance was 10-5 kcal.mol-1 in all
RHF calculations. Electronic properties and molecular
orbitals were then computed using the ZINDO/S method,
assuming an orbital criterion involving the 10 highest
occupied and the 10 lowest unoccupied levels.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 208–209

5-(1-(4-PHENYL)-3-(4-NITROPHENYL)TRIAZENE)-10,15,20-TRIPHENYLPORPHYRIN
209
9. Schaming D, Farha R, Xu HL, Goldmann M and
CONCLUSION
Ruhlmann L. Langmuir 2011; 27: 132–143.
The 5-(1-(4-phenyl)-3-(4-nitrophenyl))triazene-10,15,
20-triphenylporphyrin species was successfully pre-
pared by the direct reaction of 5-(4-aminophenyl)-
10,15,20-triphenylporphyrin with the diazonium salt
of 4-nitroaniline, and characterized by spectroscopic
and electrochemical, as well as molecular modeling
techniques. The triazene porphyrin exhibited an
electronic spectrum that resembled the sum of H2TPP
and 1,3-bis(4-nitrophenyl)triazene, but the deprotonated
triazenide species showed much more delocalized
frontier orbitals, accounting for the appearance of
triazenide-to-porphyrin charge-transfer transitions. Also
exhibited a series of six redox processes centered at the
porphyrin ring and the triazene moiety, as confirmed
by spectroelectrochemistry. The 5-(1-(4-phenyl)-3-
(4-nitrophenyl))triazene-10,15,20-triphenylporphyrin
represents the first of a series of porphyrin derivatives
possessing peripheral coordinating and reactive groups,
that are being pursued as porphyrin building-blocks of
supramolecular materials for sensor applications.
10. Tour JM. J. Org. Chem. 2007; 72: 7477–7496.
11. Priya B, Uma L, Ahamed AK, Subramanian G and
Prabaharan D. Biores. Tech. 2011; 102: 7218–7223.
12. Ono RJ, Suzuki Y, Khramov DM, Ueda M, Ses-
sler JL and Bielawski CW. J. Org. Chem. 2011; 76:
3239–3245.
13. Tabone R and Barra M. Dyes Pigm. 2011; 88:
180–186.
14. Zhou J, He JJ, Wang BJ, Yang WJ and Ren HJ.
J. Am. Chem. Soc. 2011; 133: 6868–6870.
15. Zhang Y and Wang JB. Eur. J. Org. Chem. 2011:
1015–1026.
16. Chen N, Barra M, Lee I and Chahal N. J. Org.
Chem. 2002; 67: 2271–2277.
17. Larroque-Lombard AL, Todorova M, Golabi N,
Williams C and Jean-Claude BJ. J. Med. Chem.
2010; 53: 2104–2113.
18. Kongsfelt M, Vinther J, Malmos K, Ceccato M,
Torbensen K, Knudsen CS, Gothelf KV, Pedersen
SU and Daasbjere K. J. Am. Chem. Soc. 2011; 133:
3788–3791.
19. Ceccato M, BousquetA, Hinge M, Pedersen SU and
Daasbjerg K. Chem. Mater. 2011; 23: 1551–1557.
20. Hinge M, Goncalves ES, Pedersen SU and Daasb-
jerg K. Surface Coat Tech. 2010; 205: 820–827.
21. Lu M, Chen B, He T, Li Y and Tour JM. Chem.
Mater. 2007; 19: 4447–4453.
Acknowledgements
The authors are grateful to Fundação de Amparo
à Pesquisa do Estado de São Paulo (FAPESP) for the
financial support.
Supporting information
22. Martins PR, Popolim WD, Nagato LAF, Takemoto
E, Araki K, Toma HE, Angnes L and Penteado
MDC. Food Chem. 2011; 127: 249–255.
23. de Paula LR, Parussulo ALA, Araki K and Toma
HE. Sens. Actuators B-Chem. 2011; 156: 325–331.
24. Toma HE and Araki K. Prog. Inorg. Chem. 2009;
56: 379–485.
Figures S1–S8 are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
REFERENCES
1. Krayer M, Yang EK, Kim HJ, Kee HL, Deans
RM, Sluder CE, Diers JR, Kirmaier C, Bocian DF,
Holten D and Lindsey JS. Inorg. Chem. 2011; 50:
4607–4618.
2. Ballut S, Naud-Martin D, Loock B and Maillard P.
J. Org. Chem. 2011; 76: 2010–2028.
25. Ostrowski S, Szerszen D and Ryszczuk M. Synthe-
sis-Stuttgart 2005: 819–823.
26. Carofiglio T, Schlorlin M and Tonellato U. J. Por-
phyrins Phthalocyanines 2007; 11: 749–754.
27. Luguya R, Jaquinod L, Fronczek FR, Vicente AGH
and Smith KM. Tetrahedron 2004; 60: 2757–2763.
28. Bajema L, Gouterman M and Meyer B. J. Molec.
Spectros. 1968; 27: 225.
3. Inoue H, Funyu S, Shimada Y and Takagi S. Pure
Appl. Chem. 2005; 77: 1019–1033.
4. Gunderson VL, Wilson TM and Wasielewski MR.
J. Phys. Chem. C 2009; 113: 11936–11942.
5. Merino E. Chem. Soc. Rev. 2011; 40: 3835–3853.
6. Trabolsi A, Khashab N, Fahrenbach AC, Friedman
DC, Colvin MT, Coti KK, Benitez D, Tkatchouk E,
Olsen JC, Belowich ME, Carmielli R, Khatib HA,
Goddard WA, Wasielewski MR and Stoddart JF.
Nature Chem. 2010; 2: 42–49.
7. Tanaka K, Kohayakawa K, Iwata S and Irie T.
J. Org. Chem. 2008; 73: 3768–3774.
8. Ayyildiz E, Boyarbay B, Cetin H and Uygun A.
Appl. Phys. a-Mater. Sci. Proces. 2011; 103: 89–96.
29. Ando RA, dos Santos APV, Horner M and Santos
PS. J. Raman Spectros. 2008; 39: 607–610.
30. Engelmann FM, Losco P, Winnischofer H, Araki K
and Toma HE. J. Porphyrins Phthalocyanines 2002;
6: 33–42.
31. Kruger RA, Terpstra AS and Sutherland TC. Can.
J. Chem-Rev. Can. Chim. 2011; 89: 214–220.
32. Formiga ALB, Nogueira AF, Araki K and Toma HE.
New. J. Chem. 2008; 32: 1167–1174.
33. Horner M, Bresolin L, Bordinhao J, Hartmann
E and Strahle J. Acta Cryst. Sec. C-Cryst. Struc.
Commun. 2003; 59: O426–O427.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 209–209

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