Syntheses, electrochemistry and photophysical properties of a series of meso-pyridylpentafluorophenylporphyrins

Article abstract of DOI:10.1142/S108842461000280X

This work presents the synthesis and characterization of a series of substituted pyridylpentafluroporphyrins, including the separation of the cis- and trans-isomers, the latter being characterized by X-ray crystallography. The spectroscopic and electrochemical properties of the series are dependent on the number of electron withdrawing pentafluorophenyl substituent, but they do not depend on the symmetry of the molecule. Ongoing from the monosubstituted to the more substituted pentafluorophenyl porphyrin H₂(MPyTFPP) derivative, the Soret bands are slightly red-shifted and their quantum fluorescence yields range from 0.035 to 0.046, consistent with the value of 0.045 for the fully substituted 5,10,15,20-tetrapentafluorophenylporphyrin (dichloromethane solutions). The redox potentials of the reductive processes of monoanion and dianion formation are also sensitive to the number of pentafluoro substituents, shifting 180 mV to more positive values for the P⁰/P^-1 process ongoing from the monopentafluoro to the tris-pentafluorophenyl substituted derivative.

Full text of DOI:10.1142/S108842461000280X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 975–984
DOI: 10.1142/S108842461000280X
Published at http://www.worldscinet.com/jpp/
Syntheses, electrochemistry and photophysical properties of
a series of meso-pyridylpentafluorophenylporphyrins
a
a
a
Emmanuel Z. Moreira , Alba D.Q. Ferreira , Cláudio Roberto Neri ,
b
c
d
Sumitra Mukhopadhyay , Sérgio Dovidauskas , Sofia Nikolaou and
a
Yassuko Iamamoto*
a
Department of Chemistry, FFCLRP, University of São Paulo, Av. Bandeirantes 3900, Ribeirão Preto, 14040-901
SP, Brazil
b
Department of Chemistry, Massachusetts Institute of Technology (MIT), 77 Massachusetts Ave.,
Cambridge MA 02139-4307, USA
c
Adolfo Lutz Institute, Ribeirão Preto, São Paulo, Brazil
Department of Physics and Chemistry, FCFRP, University of São Paulo, Campus Universitário da USP,
d
Ribeirão Preto, 14040-903 SP, Brazil
Received 5 March 2010
Accepted 31 October 2010
ABSꢁRAcꢁ: This work presents the synthesis and characterization of a series of substituted
pyridylpentafluroporphyrins, including the separation of the cis- and trans-isomers, the latter being
characterized by X-ray crystallography. The spectroscopic and electrochemical properties of the series
are dependent on the number of electron withdrawing pentafluorophenyl substituent, but they do not
depend on the symmetry of the molecule. Ongoing from the monosubstituted to the more substituted
pentafluorophenyl porphyrin H (MPyTFPP) derivative, the Soret bands are slightly red-shifted and
2
their quantum fluorescence yields range from 0.035 to 0.046, consistent with the value of 0.045 for the
fully substituted 5,10,15,20-tetrapentafluorophenylporphyrin (dichloromethane solutions). The redox
potentials of the reductive processes of monoanion and dianion formation are also sensitive to the number
0
-1
of pentafluoro substituents, shifting 180 mV to more positive values for the P /P process ongoing from
the monopentafluoro to the tris-pentafluorophenyl substituted derivative.
KEYWoRꢂS: meso-pyridylpentafluorophenylporphyrins, spectroscopy, X-ray, isomerism, electro-
chemistry.
to this work are the porphyrins with coordinating sites
IꢀꢁRoꢂucꢁIoꢀ
such as the pyridyl group, since their introduction opens
the possibility of molecular expansion to a well-ordered
structure through further metal ion complexation leading
to supramolecular systems [7, 8].
Porphyrins are purple pigments, belonging to a class
of molecules that has been investigated with several pur-
poses such as the development of light harvesting sys-
tems, biomimetic systems, catalysis and material sciences
There are several applications for extended structures
presenting photoinduced charge and energy transfer
properties such as biosensors, DNA-binding agents and
photodynamic therapy sensitizers [9–12]. Several groups
are involved in the preparation of supermolecules derived
from porphyrins [13–18], via covalent or coordination
bonding of the desired components. In this way, one
expects to get new molecules capable of mimicking the
processes of charge transfer that happens in the natural
photosynthetic system [19–27].
[1–4]. For example, the introduction of electron with-
drawing substituents in the mesoaryl and/or β-pyrrolic
positions of the porphyrins has proved to be a successful
strategy for the preparation of more efficient and robust
catalysts for oxidation reactions [2, 5, 6]. Also of interest

SPP full member in good standing
*
Correspondence to: Yassuko Iamamoto, email: iamamoto@
usp.br, tel: +55 16-3602-3782, fax: +55 16-3602-4838
Copyright © 2010 World Scientific Publishing Company

976
E.Z. MOꢀEIꢀꢁ ꢀꢁ ꢂꢃ.
N
N
b
a
12
8
13
7
3
F
F
F
F
F
F
NH
N
N
NH
N
N
F
N
N
F
HN
HN
F
17
18
F
2
F
F
F
F
F
F
F
F
F
F
H2(MPyTFPP)
H (TPyMFPP)
2
N
N
F
F
F
F
F
F
F
F
NH
N
N
NH
N
N
N
F
F
F
HN
HN
F
F
F
F
F
F
F
N
F
trans-H2(BPyBFPP)
cis-H2(BPyBFPP)
Fig. 1. Schematic structure of the meso-pyridylpentafluorophenylporphyrins studied in this work, and their NMR labeling
Taking it into account, the series of free-base substi-
tuted pyridylpentafluoroporphyrins (Fig. 1) investigated
in this work are interesting because they present both
withdrawing and coordinating groups in their structure,
making then important candidates for catalytic studies
and as precursors for the development of supramolecu-
lar systems. With this concern, this piece of work deals
with an inedited and detailed description on the synthe-
sis, as well as the purification and characterization of this
important series of precursors, by means of spectroscopic
and electrochemical investigation.
tetrabutyl ammonium hexafluorophosphate (used as sup-
porting electrolyte for electrochemistry, Acros) and pyrrole
(Acros). Pyrrole and N,N′-dimethylformamide were dis-
tilled under reduced pressure immediately before use.
Syntheses
The series of meso-pyridylpentafluorophenylporphyrins:
5
,10,15,20-tetrapentafluorophenylporphyrin [H (TFPP)];
2
5
,10,15-tri-pentafluorophenyl-20-(4-pyridyl)porphyrin
[
H (MPyTFPP)]; 5,15-bis-pentafluorophenyl-10,20-bis-
2
(
4-pyridyl)porphyrin [trans-H (BPyBFPP)]; 5,10-bis-
2
pentafluorophenyl-15,20-bis-(4-pyridyl)porphyrin [cis-H2-
ExpERImEꢀꢁAl
(BPyBFPP)]; 5-pentafluorophenyl-10,15,20-tri-(4-pyridyl)-
porphyrin [H (TPyMFPP)] and 5,10,15,20-tetrapyridyl
2
porphyrin [H (TPyP)] was obtained using a modification
2
materiaꢃs
of the method described by Adler et al. [20, 28] for the
syntheses of meso-pyridylpentafluorophenylporphyrins
as described by Iamamoto et al. [30].
Two synthetic routes were accomplished, in which
the essential difference lays in the pyrrole/pentafluoro-
benzaldehyde/4-pyridinecarboxaldehyde molar ratio. The
first synthesis furnished the porphyrins with more pentaflu-
orophenyl substituents, whereas the second synthetic route
led to the porphyrins with more pyridyl substituents.
The following reagents were used: 5,10,15,20-tetra-
pentafluorophenylporphyrin (Midcentrury), 5,10,15,20-
tetrapyridylporphyrin (Aldrich), 4-pyridinecarboxaldehyde
(
Aldrich), pentafluorobenzaldehyde (Aldrich), propi-
onic acid (Aldrich), dichloromethane (Merck), acetone
Merck), acetronile (Merck), diethylether (Aldrich), etha-
nol (Merck), methanol (Merck), N, N′-dimethylformamide
Merck), (230–400 mesh) silica gel (Macherey-Nagel),
(
(
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 976–984

SꢂꢃꢄꢅESES, EꢆECꢄꢀOCꢅEMISꢄꢀꢂ ꢁꢃD PꢅOꢄOPꢅꢂSICꢁꢆ PꢀOPEꢀꢄIES
977
First synthesis. Freshly distilled pyrrole (5.6 mL,
0 mmol) was added to a solution of pentafluorobenzal-
was not precipitated in ethanol. However, when the pre-
cipitation was carried out, there was a considerable loss,
because the porphyrin was slightly soluble in this solvent.
However, this precipitation is advantageous because the
sludge is retained, so the purification becomes faster and
8
dehyde (4.7mL, 38mmol), and 4-pyridinecarboxal-
dehyde (4.0mL, 42mmol) in 200 mL of 99% propionic
acid, placed in a 500mL round bottom flask, fol-
lowed by reflux for 90min at 150 °C. The pyrrole/
pentafluorobenzaldehyde/4-pyridinecarboxaldehyde
molar ratio used was 4:1.9:2.1. The crude product was
initially purified by column chromatography on silica gel
using dichloromethane as eluent, followed by addition of
acetone until a ratio of 10/90 acetone/dichloromethane
was achieved. At the end of the elution, four violet spots
were detected and later purified separately.
1
viable. Elemental analyses, UV-vis and assigned H NMR
spectra are given as follows:
H (ꢁFpp) (midꢄentꢆry). UV-vis (CH Cl ): λmax, nm
2
2
2
(log ε) 412 (5.4), 506 (4.2), 541 (3.3), 583 (3.7), 649 (3.0).
H (mpyꢁFpp).Anal. calcd. for C F N H : C, 58.32;
2
43 15
5
14
H, 1.54; N, 7.91%. Found: C, 58.42; H, 1.55; N, 7.88%.
1
H NMR (500 MHz; CDCl ; Me Si): δ , ppm -2.90 (2H,
3
4
Η
s, pyrrole-NH), 8.87 (2H, m, pyrrole-H2,18), 8.92 (6H, s,
pyrrole-H3,7,8,12,13,17), 8.17 (2H, d, Pha), 9.07 (2H, d, Phb).
trans-H (BpyBFpp). Anal. calcd. for C F N H : C,
Separation of the first synthesis. The separation of
four violet components corresponding respectively to
H (TFPP) (R = 0.98), H (MPyTFPP) (R = 0.34), trans-
2
42 10
6
18
63.31; H, 2.28; N, 10.55%. Found: C, 63.67; H, 2.21; N,
2
f
2
f
1
H (BPyBFPP) (R = 0.15), [cis-H (BPyBFPP)]; (R = 0.08)
10.44%. H NMR (500 MHz; CDCl ; Me Si): δ , ppm
2
f
2
f
3
4
Η
were isolated. Each fraction was collected and chromato-
graphed once again to assure the purity of each of the
pyridylpentafluorophenylporphyrins, with the exception of
-2.92 (2H, s, pyrrole-NH), 8.86 (4H, m, pyrrole-H2,8,12,18),
8.92 (4H, m, pyrrole-H3,7,13,17), 8.19 (2H, d, Pha), 9.08
(2H, d, Phb).
thefractioncorrespondingtoH (TFPP).Theyieldofporphy-
cis-H (BpyBFpp) [32]. Anal. calcd. for C F N H :
2
2
42 10
6
18
rins was 1.3% H (MPyTFPP), 1.04% trans-H (BPyBFPP)
C, 63.33; H, 2.27; N, 10.55%. Found: C, 63.10; H, 2.37;
2
2
1
and 2.74% cis-H (BPyBFPP). In this first synthesis there
N, 10.10. H NMR (500 MHz; CDCl ; Me Si): δ , ppm
2
3
4
Η
was no formation of H (TPyMFPP) or H (TPyP). There-
-2.88 (2H, s, pyrrole-NH), 8.87 (2H, m, pyrrole-H2,13),
8.90 (2H, m, pyrrole-H3,12), 8.92 (2H, m, pyrrole-H7,8),
8.85 (2H, m, pyrrole-H17,18), 8.17 (2H, d, Pha), 9.08 (2H,
d, Phb).
2
2
fore, it was necessary to accomplish another synthesis.
Second synthesis. The second synthesis was carried
out by adding freshly distilled pyrrole (5.6mL, 80 mmol)
to a solution of pentafluorobenzaldehyde (3.7mL,
H (ꢁpymFpp)·2H o. Anal. calcd. for C F N H :
2
2
41
5
7
22
5
4
0 mmol) and of 4-pyridinecarboxaldehyde (4.8mL,
2 mmol) in 200mL of 99% propionic acid, placed in
C, 66.20 H, 3.53; N, 13.18%. Found: C, 65.56; H, 3.54;
1
N, 12.94%. H NMR (500 MHz; CDCl ; Me Si): δ ,
3
4
Η
a 500 mL round bottom flask, followed by reflux for
ppm -2.90 (2H, s, pyrrole-NH), 8.87 (6H, m, pyrrole-
9
4
0 min at 150 °C. The pyrrole/pentafluorobenzaldehyde/
-pyridinecarboxaldehyde molar ratio was: 4:1.5:2.5.
H2,8,12,13,17,18), 8.93 (2H, m, pyrrole-H ), 8.17 (2H, d, Pha),
9.08 (2H, d, Phb).
3,7
This time purification was accomplished in a different
way, by using a modification of the method described by
Engelmann et al. [31] for the purification of porphyrins.
Then, the solvent was almost completely removed in
the rotary evaporator and 200 mL of ethanol was added.
This was filtered and the solid was washed with the same
solvent until the filtrate became almost colorless. Wash-
ing with diethylether yielded 1.7 g of a violet solid.
Separation of the second synthesis. The separation of
H (ꢁpyp)(Aꢃdriꢄh). UV-vis(CH Cl ):λmax, nm(logε)
416 (5.4), 512 (4.2), 546 (3.6), 587 (3.7), 648 (3.2).
2
2
2
methꢅds
The UV-vis spectra were obtained in a HP-8453
diode-array spectrophotometer with 1 nm resolutions, in
the 190 to 1100 nm range, in dichloromethane. Samples
were run at room temperature in 1 cm quartz cuvettes.
1
H NMR were recorded on a Bruker Advanced DRX-500
the porphyrins was done as described above. The R value
f
MHz spectrometer using CDCL as the solvent and TMS
3
of the other porphyrins are: H (TPyMFPP) (R = 0.04),
2
f
as the internal standard.
H (TPyP) (R = 0.01), obtained in the same conditions
2
f
Electrochemistry was carried out in N, N′-dimethyl-
above.Theyieldofporphyrinswas0.5%trans-H (BPyBFPP)
2
®
formamide, using a AUTOLAB potentiostat/galva-
and 1.1% cis-H (BPyBFPP) and 2.2% H (TPyMFPP). The
2
2
nostat model PGSTAT 30, coupled with a compatible
microcomputer. A conventional cell consisting of a
platinum disk was used as working electrode. Potentials
were referenced to Ag/AgCl. The supporting electrolyte
was 0.1 M tetrabutylammonium hexafluorophosphate
main difference of this second syntheses was that there was
formation of H (TPyMFPP) and H (TPyP), and there was
2
2
no formation of H (TFPP) and H (MPyTFPP). The porphy-
2
2
rins H (TFPP) and H (TPyP) were not isolated because they
2
2
were not the objective of this work investigation.
(
TBAPF ) in N, N′-dimethylformamide. Ferrocene was
6
used as internal standard (0.548 V vs. SHE). All the
potentials were converted to SHE (standard hydrogen
electrode) scale by the addition of 0.222 V to the exper-
imental data obtained for all porphyrins, the experi-
mental value obtained for ferrocene in the system was
charaꢄterizatiꢅn
The first synthesis led to a larger overall porphyrin
yield than the second. This is because there was a differ-
ence in the purification process. In the first, the porphyrin
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 977–984

978
E.Z. MOꢀEIꢀꢁ ꢀꢁ ꢂꢃ.
0
.692 V (vs. SHE). To correct the obtained experimental
of Adler and Longo [28, 29]. The modifications to this
method were: the variation in the proportion of the
reagents and the use of other aldehydes for the reaction.
This synthesis involves the condensation reaction of pyr-
role, pentafluorobenzaldehyde and 4-pyridinecarboxal-
dehyde in propionic acid at 150 °C. The relative amount
of the porphyrin can be modulated by the variation of the
molar relation of the two aldehydes.
data, the value of 0.144 V was subtracted.
Theemission/excitationspectrawererecordedonaSpex
-6
Fluorolog-2 spectrophotometer, from 6 × 10 M dichlo-
romethane solutions, using quartz cells of 1.0 × 1.0 cm
path length. The fluorescence quantum yield were calcu-
lated from the comparison of the emission band intensity
of the studied porphyrins and that of the meso-tetra(phenyl)
porphyrin standard (H TPP), from spectra obtained under
the same conditions stated above. The equation below
was also used, and the standard quantum yield in dichlo-
The reaction was monitored by UV-visible spectros-
copy, from aliquots of the reaction media. Thus, it was
possible to verify the effective formation of the porphyrin
through the increase in the absorbance of the character-
istic Soret band.
2
romethane solution is Φ = 0.099:
fl
2
TPP
inx(x) abs(TPP) ν
abs(x) int(TPP)
Φ = Φ
.
.
.
(1)
x
TPP
2
x
ν
x-ray ꢄrystaꢃꢃꢅgraꢇhy
where, int(x) and int(H TPP) are the integrated area of the
2
To obtain the porphyrin crystals, a solution of the trans-
H (BPyBFPP) porphyrin at a concentration of 5.0 × 10 M
fluorescence emission bands, abs(x) and abs(H TPP) are
-3
2
2
the respective absorbance values at the excitation wave-
in a mixture of solvents (1 acetone:9 dichloromethane)
was prepared. The flask that contained the solution was
covered and small needles were introduced into the cover
so that the mixture of solvents could evaporate slowly,
leading to crystal formation in solution. The crystals
were collected and analyzed by crystallography. For the
2
2
lengths, and η and η
are the refraction indexes of
H TPP
2
x
2
2
the solution samples. In the present case, η = η
,
H TPP
2
x
since all the spectra were recorded in the same solvent.
Data for the trans-H (BPyBFPP) porphyrin crystal were
2
collected using a Bruker SMART CCD (charge coupled
device) based diffractometer equipped with a KRYOFLEX
BVT-AXS nitrogen cryostat operating at 173 K. Suitable
single crystal was chosen and mounted on a glass fiber
using Infineum V8512 oil (formerly called Paratone N
oil) and APIEZON-T grease. Data were measured using
omega scans of 0.3º per frame for 30 sec, so that a hemi-
sphere was collected. A total of 1271 frames were collected
with a maximum resolution of 0.75 Å. The first 50 frames
were recollected at the end of data collection, to monitor for
decay. The crystals used for the diffraction study showed
no decomposition during data collection.
isomeric form cis-H (BPyBFPP) the same procedure was
2
also adopted, but there was no formation of crystals.
The crystal structure of trans-H (BPyBFPP) is shown
2
in Figs 2 and 3. Table 1 depicts the crystallographic
parameters. The atomic positional parameters of the mol-
ecule are listed in Table 2. Table 3 presents the selected
bond distances and angles. trans-H (BPyBFPP) crystal-
2
lized in space group C2/c, with four porphyrin molecules
Cell parameters were retrieved using
SMART [33] software and refined using
SAINT [34] on all observed reflections.
Data reduction was performed using the
SAINT software, which corrects for Lp
and decay. The structure was solved by the
direct method using the SHELXS-97 pro-
gram [35] and refined by the least squares
method on F2, SHELXL-97 [36] incorpo-
rated in SHELXTL-PC V 5.10 [37]. All
non-hydrogen atoms were refined with
anisotropic thermal parameters. The posi-
tions of hydrogen atom were calculated
by geometrical methods and refined as a
riding model.
RESulꢁS Aꢀꢂ ꢂIScuSSIoꢀ
Syntheses
The syntheses of the molecules were
accomplished by the modified method
Fig. 2. The structure of trans-H (BPyBFPP)
2
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 978–984

SꢂꢃꢄꢅESES, EꢆECꢄꢀOCꢅEMISꢄꢀꢂ ꢁꢃD PꢅOꢄOPꢅꢂSICꢁꢆ PꢀOPEꢀꢄIES
979
In addition, Natash et al. suggested that weak π−π inter-
actions are likely if the distance between two parallel
porphyrin rings is near 7.5 Å [39].
ꢀmR sꢇeꢄtrꢅsꢄꢅꢇy
The series of the meso-pyridylpentafluorophenylpor-
phyrins were also structurally characterized in solution
1
by H NMR spectroscopy and the full assignment is
reported in the experimental section. The assignments
1
of the H NMR spectra were carried out by comparison
with parent porphyrins [32, 40] and, in most cases, it
is straightforward. In general, the β-pyrrole and inner ring
protons were found around 8.9 and -2.9 ppm, while Ha and
Hb protons were found around 8.2 and 9.1 (Fig. 5).
The great difficulty in the assignment of the signals
observed is in the differentiation of the isomeric cis-
Fig. 3. Unit cell diagram of trans-H (BPyBFPP)
2
in the unit cell. The two parallel molecules are 7.1 Å
apart (see Fig. 4). It is known that supramolecular por-
phyrinic self-assemble due to π-stacking when the dis-
tance between the two molecules is about 3.5 Å [38].
H (BPyBFPP) and trans-(BPyBFPP) forms. The expected
NMR pattern of the β-pyrrolic protons for the trans-
2
H (BPyBFPP) molecule [40] is the appearance of two
2
doublets, as it can be observed around δ = 8.90 (Fig. 5).
ꢁ
abꢃe 1. Crystal data and structure refinement for trans-H (BPyBFPP)
2
Identification code
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
trans-H (BPyBFPP)
2
C H F N
6
4
2
18 10
796.62
173(2)
0.71073
Crystal system
monoclinic
C2/c
Space group
Unit cell dimensions
a = 20.314(2) Å
b = 7.1098(7) Å
c = 23.597(2) Å
3407.8(6)
α = 90°
β = 90.752(3)°
γ = 90°
3
Volume, Å
Z
4
3
Density (calculated), Mg/m
Absorption coefficient, mm
F(000)
1.553
-1
0.132
1608
3
Crystal size, mm
0.30 × 0.20 × 0.08
1.73 to 28.27
-26<=h<=26,
θ range (data collection, º)
Index ranges
-9<=k<=9,
-31<=l<=30
Reflections collected
14600
Independent reflections [Rint]
Completeness to theta = 28.27°, %
Absorption correction
4043 [ 0.0585]
95.5
none
Full-matrix least-squares on F2
4043/0/266
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.070
Final R indices [I > 2σ(I)]
R = 0.0507,
1
wR = 0.1307
2
R indices (all data)
R = 0.0587,
1
wR = 0.1368
0.373 and -0.390
2
Largest diff. peak and hole, e.Å−
3
0.373 and -0.390
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 979–984

980
E.Z. MOꢀEIꢀꢁ ꢀꢁ ꢂꢃ.
4
ꢁ
abꢃe 2. Atomic coordinates (×10 ) and equivalent isotropic
ꢁabꢃe 3. Bond lengths (Å) and angles (°) for trans-
2
3
displacement parameters (Å × 10 ) for trans-H (BPyBFPP)
H (BPyBFPP)
2
2
U(eq) is defined as one third of the trace of the orthogonalized
F(1)-C(11)
N(2)-C(21)
N(2)-C(18)
F(5)-C(7)
1.3361(16)
1.3614(18)
1.3663(16)
1.3354(17)
1.3666(17)
1.3697(16)
1.321(2)
U tensor
ij
x
y
z
U(eq)
F(1)
1518(1)
93(1)
13591(1)
8226(2)
7820(2)
8515(2)
1650(2)
13994(2)
6512(2)
6750(2)
10475(2)
11361(2)
8986(2)
10708(2)
4597(2)
6193(2)
7699(2)
4939(2)
7021(2)
8262(2)
9373(2)
12255(2)
2757(2)
8234(2)
1350(2)
11141(2)
5808(2)
3424(2)
6736(2)
12482(2)
9580(2)
1654(1)
-663(1)
2230(1)
479(1)
49(1)
28(1)
51(1)
26(1)
33(1)
63(1)
28(1)
28(1)
28(1)
71(1)
26(1)
28(1)
25(1)
25(1)
28(1)
35(1)
25(1)
77(1)
34(1)
33(1)
34(1)
30(1)
38(1)
44(1)
39(1)
37(1)
40(1)
40(1)
44(1)
N(2)
F(5)
N(1)-C(1)
N(1)-C(4)
N(3)-C(15)
N(3)-C(16)
F(2)-C(10)
C(3)-C(2)
C(3)-C(4)
C(18)-C(12)
C(18)-C(19)
C(5)-C(1)
C(5)-C(21)#1
C(5)-C(6)
F(3)-C(9)
613(1)
N(1)
N(3)
F(2)
702(1)
2265(1)
2084(1)
1525(1)
522(1)
-663(1)
2677(1)
689(1)
1.323(2)
1.3396(18)
1.3586(19)
1.4235(18)
1.3995(18)
1.4529(19)
1.3931(18)
1.4044(18)
1.4893(18)
1.3296(18)
1.4289(17)
1.386(2)
C(3)
C(18)
C(5)
-690(1)
1336(1)
3482(1)
1005(1)
1904(1)
-395(1)
-264(1)
1136(1)
-631(1)
269(1)
716(1)
F(3)
1914(1)
937(1)
C(1)
C(6)
1033(1)
1417(1)
966(1)
C(13)
C(12)
C(2)
1458(1)
2023(1)
1047(1)
1175(1)
966(1)
C(1)-C(2)
C(6)-C(11)
C(6)-C(7)
C(14)
C(4)
1.389(2)
F(4)
3253(1)
2329(1)
2041(1)
-292(1)
-1174(1)
-435(1)
2976(1)
-1236(1)
-753(1)
-1537(1)
2565(1)
2857(1)
C(7)
C(11)
C(17)
C(21)
C(16)
C(9)
1418(1)
1245(1)
-225(1)
1683(1)
1628(1)
473(1)
C(19)
C(15)
C(20)
C(10)
C(8)
2426(1)
11(1)
1711(1)
1256(1)
1
On the other hand, the H NMR pattern of the β-pyrrole
protons for the molecule cis-H (BPyBFPP) [40] predicts
2
the appearance of two singlets and two doublets. However,
in our case there is an overlap of the singlets with the two
doublets, which can be observed at δ = 8.90 ppm and δ =
8
.87 ppm (Fig. 5). This fact, as pointed out elsewhere [32,
Fig. 4. π-stacking interactions between trans-H (BPyBFPP)
molecules
2
40], leads to a coalescence of the signal, whose multiplic-
ity resembles the profile of the β-pyrrolic protons of the
trans-isomer. In this regard, in the particular case of this
sort of cis-trans porphyrin isomerism, the NMR is not the
ideal tool to identify the isomeric species.
under investigation in this work. Figures 6 and 7 pres-
ent the electronic and fluorescence spectra of the series,
respectively.
The UV-visible absorption spectra of the meso-pyrid-
ylpentafluorophenylporphyrins were similar to the spec-
tra observed for other meso-substituted porphyrins, with
an intense Soret band around 415 nm and four Q-bands
Eꢃeꢄtrꢅniꢄ and ꢇhꢅtꢅꢇhysiꢄaꢃ ꢇrꢅꢇerties
Table 4 summarizes the spectroscopic data acquired
for the meso-pyridylpentafluorophenylporphyrins series
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 980–984

SꢂꢃꢄꢅESES, EꢆECꢄꢀOCꢅEMISꢄꢀꢂ ꢁꢃD PꢅOꢄOPꢅꢂSICꢁꢆ PꢀOPEꢀꢄIES
981
1
Fig. 5. H NMR spectra of the meso-pyridylpentafluorophe-
nylporphyrin series (region of pyridyl and β-pyrrole protons)
Fig. 6. UV-visible spectra of the meso-pyridylpentafluorophe-
around 510, 540, 580, and 650 nm (Table 4).Although the
meso-pyridylpentafluorophenylporphyrins studied here
are in general of low symmetry, their spectroscopic
behavior is similar since the pyridyl and the penta-
fluorophenyl peripheral rings are orthogonal to the
central plane and, therefore, do not interfere signifi-
cantly in the extended π-conjugation of the pyrrolic
central groups.
nylporphyrins series recorded from DCM solutions
In comparison with the 5,10,15,20-tetraphe-
nylporphyrin [H (TPP)], the main difference
2
observed for the meso-pyridylpentafluorophenylpor-
phyrins species is in the visible region of the spec-
tra. The spectrum of the H (TPP) species presents a
2
profile in which the Q-bands have a relative inten-
sity of IV > III > II > I, and this type of spectrum is
denominated etio [42]. In a case where the Q-bands
relative intensity is the opposite, i.e. IV > II > III > I,
one observes the phyllo type of spectrum. However,
-6
Fig. 7. Emission spectra recorded from 1.0 × 10 M DCM solutions
of the meso-pyridylpentafluorophenylporphyrins. λexc = 512 nm
ꢁabꢃe 4. Absorption and photophysical data collected for the meso-pyridylpentafluorophenylporphyrin
series, from dichloromethane solutions
−
1
−1
Molecule
Absorption data (λmax, nm (log ε , M .cm )
Q ( ) Q ( ) Q ( )
Soret
Q ( )
x 0,0
y
1,0
y
0,0
x
1,0
a
H (MPyTFPP)
413(5.4)
414(5.3)
415(5.4)
416(5.4)
508(4.3)
509(4.1)
509(4.2)
509(4.3)
540(3.4)
540(3.4)
541(3.4)
541(3.6)
583(3.8)
583(3.8)
583(3.7)
583(3.8)
649(3.2)
649(3.1)
649(2.8)
649(3.1)
2
b
trans-H (BPyBFPP)
2
b
cis-H (BPyBFPP)
2
a
H (TPyMFPP)
2
λemi, nm (λexc = 415 nm)
Q( )
Q( )
φfl
0
,0
0,1
a
H (MPyTFPP)
656
643
647
645
706
707
707
708
0.041
0.046
0.035
0.043
2
b
trans-H (BPyBFPP)
2
b
cis-H (BPyBFPP)
2
a
H (TPyMFPP)
2
a
b
Data collected in this work. Data from reference [32].
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 981–984

982
E.Z. MOꢀEIꢀꢁ ꢀꢁ ꢂꢃ.
tetraphenylporphyrins bearing halogen substituents
(the less symmetric ones). Experiments focusing solvent
dependence of the quantum yield values are underway in
our laboratories in order to verify the hypothesis raised
above.
(F, Cl, Br) in the ortho positions of the phenyl groups (as
in the case of the series presented in this work), display
absorption spectra with a significant intensity decrease in
bands III and I, being these bands practically bleached.
This has been assigned to a restriction in the rotation of
the phenyl groups due to the steric hindrance between the
ortho-substituted phenyl rings and the β-pyrrole hydro-
gen [41]. This rotation restriction also affects the extinc-
tion coefficient of the Q-bands slightly in comparison
with un-substituted porphyrins [41].
An interesting feature is observed regarding the λmax of
the Soret band. Along the series, this band presents a ten-
dency to be blue shifted with the increase in the number
of pentafluorophenyl substituents. This observation can
be rationalized in terms of the poor electron density of the
pentafluorophenyl group, which removes electronic den-
sity from the porphyrin central core, lowering the HOMO
energy and thus, increasing the Soret transition energy
Eꢃeꢄtrꢅꢄheꢈistry
Figure 8 presents the cyclic voltammograms of the
studied compounds. In the cathodic region, it is observed
that, with the exception of the meso-mono(4-pyridyl)-
tris(pentafluorophenyl)porphyrin, the other compounds
present two pairs of quasi-reversible waves, ascribed to
0
-1
the formation of the anion and dianion radicals (P /P
-1
-2
and P /P , Table 5) [47]. A shift of the redox potentials
to more positive values is observed as the number of
pentafluorophenyl substituents increased, reflecting the
electron withdrawing character of this group. In case of
meso-mono(4-pyridyl)-tris(pentafluorophenyl)porphy-
rin, a possible explanation to the occurrence of only the
first reduction process in the potential range investigated
is that the DMF solvent would provide some stabiliza-
tion to the monoanion radical, since in a control experi-
ment done in acetonitrile solution, the two reductions
processes were observed as a pair of reversible waves at
[43]. This behavior is consistent with the voltammetric
measurements, which have shown that the increase in the
number of the electron withdrawing groups implies in
more difficult oxidation of the porphyrin ring [44].
Free-base porphyrins usually display intense fluores-
cence emission in the visible region when excited in any
of their absorption bands, following Kasha’s rule [45].
The series presented here have two intense fluorescence
bands around 650nm and 710 nm (Fig. 7), assigned to
the transitions from the 0 vibrational component of the
first excited state to the 0 and 1 vibrational components
of the fundamental state.
-0.68 V and -1.10 V (vs. SHE).
It is important to point out the resemblance between
the redox potentials and the voltammogram profiles of
In order to rationalize the quantum yield values
observed in the series (Table 4), it is worth carrying out
a comparison with the quantum yield values of the sym-
metric H (TPP) (0.099) [45] and H (TFPP) (0.045, this
2
2
work) porphyrins.
In general, the porphyrins substituted with the
fluorophenyl groups present quantum yields ranging
from 0.035 to 0.046, about half of the typical values of
the phenyl porphyrin. Considering symmetry, fully sym-
metrical porphyrins (D h symmetry), such as H (TPP)
4
2
and H (TFPP), hold the above relation of φ , showing that
2
fl
the electron withdrawing property of the substituent plays
a role in diminishing the quantum yields. The next more
symmetric porphyrin in our series is the bi-substituted
trans-H (BPyBFPP), which has an φ value of 0.046,
2
fl
essentially equal to the value observed for H (TFPP).
2
The less symmetric molecules cis-H (BPyBFPP),
2
H (TPyMFPP), and H (MPyTFPP) present the lowest
2
2
quantum yield values. This kind of behavior has been
observed previously in a series of porphyrins substituted
with hydroxyl-phenyl groups [46]. One possible expla-
nation for the observed trends would be that, for sym-
metry reasons, the molecules polarity are different and
this aspect would imply in different solvation interac-
tions, favoring deactivation of the excited state by vibra-
tional pathways in the case of the more polar molecules
Fig. 8. Cyclic voltammograms in N,N′-dimethylformamide (tetra-
butylammonium perchlorate 0.1 M as supporting electrolyte) at
-1
2
00 mV.s (25 °C) of: (A) meso-mono(4-pyridyl)-tris(penta-
fluorophenyl)porphyrin; (B) meso-trans-bis(4-pyridyl)-bis(penta-
fluorophenyl)porphyrin; (C) meso-cis-bis(4-pyridyl)-bis(penta-
fluorophenyl)porphyrin; (D) meso-tris(4-pyridyl)-mono(penta-
-3
fluorophenyl)porphyrin. Porphyrins concentrations: 1.3 × 10 M
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 982–984

SꢂꢃꢄꢅESES, EꢆECꢄꢀOCꢅEMISꢄꢀꢂ ꢁꢃD PꢅOꢄOPꢅꢂSICꢁꢆ PꢀOPEꢀꢄIES
983
ꢁabꢃe 5. Redox potentials (V vs. SHE) of the meso-pyridylpen-
Sꢆꢇꢇꢅrting infꢅrꢈatiꢅn
tafluorophenylporphyrins, in DMF solution, tetrabutylammo-
nium perchlorate 0.1 M
Crystallographic data have been deposited at the Cam-
bridge Crystallographic Data Center (CCDC) under depo-
sition number CCDC 802070. Copies can be obtained on
request, free of charge, via www.ccdc.cam.ac.uk/conts/
retrieving.html or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK
-/2-
-/0
P+/0
Porphyrin
P
P
H (MPyTFPP)
not observed
-1.22
-0.60
-0.74
-0.74
-0.78
not observed
not observed
not observed
not observed
2
trans-H (BPyBFPP)
2
cis-H (BPyBFPP)
-1.22
2
(fax: +44 1223-336-033 or email: deposit@ccdc.cam.
H (TPyMFPP)
-1.24
2
ac.uk).
the cis- and trans-isomers. This fact has been observed
before by McDermot and Walker [48] in a series of sym-
metrically and antisymmetrically phenylsubstituted Zn-
tetraphenylporphyrins. They have concluded that the
distribution of the substituents produces a mean effect
in the central metal acidity and also over the porphyrin
core. Therefore, the observed behavior depends on the
electronic effects but do not depend on the symmetry dis-
tribution of the substituents.
Regarding the possible oxidation process P , it was
not observed in the compounds of this series, presumably
because the fluoro substituents make the porphyrinic core
so electron deficient, that the oxidation falls out of the
studied potential range.
REFEREꢀcES
1
. Milgrom LR. The Colours of Life, Oxford Univer-
sity Press: Oxford, 1997; pp 13–14.
2
. Vinhado FS, Martins PR and Iamamoto Y. Curr.
Top. Catal. 2002; 3: 199–213.
3
4
. Mansuy D. C. R. Chimie 2007; 10: 1–22.
. Bonnet R. Chemical Aspect of Photodynamic
Therapy, Gordon and Breach Science Publishers:
Amsterdam, 2000; Chapter 1.
+
/0
5
6
7
. Vinhado FS, Martins PR, Masson AP, Abreu DG,
Vidoto EA, Iamamoto Y and Nascimento OR.
J. Mol. Catal. A 2002; 188: 141–151.
. Skrobot FC, Rosa ILV, Marques APA, Martins PR,
Rocha J, ValenteAA and IamamotoY. J. Mol. Catal.
A 2005; 237: 86–92.
coꢀcluSIoꢀ
. Winnischofer H, Otake VY, Dovidauskas S, Naka-
mura M, Toma HE and Araki K. Electrochim. Acta
This work reported the synthesis and characterization
of a series of substituted pyridylpentafluroporphyrins,
2
004; 49: 3711–3718.
5
,10,15-tri-pentafluorophenyl-20-(4-pyridyl)-porphyrin
8
9
. Mayer I, Nunes GS, Toma HE and Araki K. Eur.
J. Inorg. Chem. 2006; 4: 850–856.
. Bonnett R. Chem. Soc. Rev. 1995; 24: 19–33.
[
H (MPyTFPP)]; 5,15-bis-pentafluorophenyl-10,20-bis-
2
(
4-pyridyl)porphyrin [trans-H (BPyBFPP)]; 5,10-bis-penta-
2
fluorophenyl-15,20-bis-(4-pyridyl)-porphyrin [cis-H (BPy-
2
1
0. Bonnett R, Charlesworth P, Djelal BD, Foley S,
McGarvey DJ and Truscott TGJ. Chem. Soc.-Perkin
Trans. 1999; 2: 325–328.
BFPP)]; 5-pentafluorophenyl-10,15,20-tri-(4-pyridyl)por-
phyrin [H (TPyMFPP)] and includes a description of
2
the separation of the cis- and trans-isomers. The latter
was characterized by X-ray crystallography, showing
the success of the chromatographic separation. On the
other hand, it was shown that the NMR analysis is not
the best tool for the identification of the isomeric cis-
H (BPyBFPP) and trans-H (BPyBFPP) derivatives, since
1
1
1
1. Nyman ES and Hynninen PH. J. Photoch. Photo-
bio. B 2004; 73: 1–28.
2. Langa K, Mosinger J and Wagnerová DM. Coord.
Chem. Rev. 2004; 248: 321–350.
3. Gust D, Moore TA, Moore AL, Seely G, Liddell P,
Barrett D, Harding LO, Ma XCC, Lee SJ and Gao
F. Tetrahedron 1989; 45: 4867–4891.
2
2
their spectral profiles are similar due to the coalescence
of the β-pyrrolic protons signal in the cis-isomer case.
The spectroscopic and electrochemical properties of the
series presented dependence on the number of with-
drawing pentafluorophenyl substituents, but they do not
depend on the symmetry of the molecule. On the other
hand, the trend followed by the fluorescence quantum
yields seems to depend on the molecule symmetry, being
higher for the more symmetric species.
1
1
1
4. Anderson HL and Sanders JKM. J. Chem. Soc.
-Perkin Trans. 1995; 1: 2223–2229.
5. Gust D, Moore TA and Moore AL. Pure Appl.
Chem. 1998; 70: 2189–2200.
6. OsukaA, Nakajima S, Okada T, Taniguchi S, Nozaki
K, Ohno T,Yamazaki I, NishimuraY and Mataga N.
Angew. Chem. Int. Ed. Engl. 1996; 35: 92–95.
7. OsukaA,Yamada H, Maruyama K, Mataga N,Asahi
T, Ohkouchi M, Okada T,Yamazaki I and Nishimura
Y. J. Am. Chem. Soc. 1993; 115: 9439–9452.
1
Aꢄknꢅwꢃedgeꢈents
This work was supported by the Brazilian agencies
Fundação de Amparo à Pesquisa do Estado de São Paulo,
FAPESP, and Conselho Nacional de Desenvolvimento
Científico e Tecnológico, CNPq.
18. Cho HS, Rhee H, Song JK, Min CK, Takase M,
Aratani N, Cho S, Osuka A, Joo T and Kim D. J.
Am. Chem. Soc. 2003; 125: 5849–5860.
19. Wasielewski MR. Chem. Rev. 1992; 92: 435–461.
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 983–984

984
E.Z. MOꢀEIꢀꢁ ꢀꢁ ꢂꢃ.
2
0. SteinbergYfrach G, Liddell PA, Hung SC, Moore
34. SAINT V 5.01 (NT) Software for the CCD Detector
System Bruker Analytical X-ray Systems, Madison,
WI, 1998.
AL, Gust D and Moore TA. Nature 1997; 385:
2
39–241.
2
2
2
2
1. Sessler JL, Wang B and Harriman A. J. Am. Chem.
Soc. 1995; 117: 704–714.
2. Kay A and Gratzel M. J. Phys. Chem. 1993; 97:
35. Sheldrick GM, SHELXS-97, Program for the Solu-
tion of Crystal Structure, University of Göttingen,
Germany, 1997.
36. Sheldrick GM, SHELXL-97, Program for the
Refinement of Crystal Structure, University of
Göttingen, Germany, 1997.
37. SHELXTL 5.10 (PC-Version), Program library for
Structure Solution and Molecular Graphics; Bruker
Analytical X-ray Systems, Madison, WI, 1998.
38. Balaban TS and Lehn JM. Eur. J. Org. Chem. 2000;
24: 4047–4057.
39. Nakash M, Clyde-Watson Z, Feeder N, Teat SJ and
Sanders JKM. Chem. Eur. J. 2000; 6: 2112–2119.
40. Meng GZG, James BR and Skov KA. Can. J. Chem.
1994; 72: 1894–1909.
6
272–6277.
3. Gust D, Moore TA and Moore AL. IEEE Eng. Med.
Biol. 1994; 1: 58–66.
4. Ramachandran GK, Tomfohr JK, Li J, Sankey OF,
Zarate X, Primak A, Terazono Y, Moore TA, Moore
AL, Gust D, Nagahara LA and Lindsay SM. J. Phys.
Chem. 2003; 25: 6162–6169.
2
2
2
5. Springer J, Kodis G, de la Garza L, Moore AL,
Moore TA and Gust D. J. Phys. Chem. 2003; 18:
3
567–3575.
6. Fungo F, Otero L, Durantini E, Thompson WJ, Sil-
ber JJ, Moore TA, Moore AL, Gust D and Sereno L.
Phys. Chem. Chem. Phys. 2003; 3: 469–475.
7. Moore TA, Moore AL and Gust Philo D. Philos.
Trans. R. Soc. London, Ser. B 2002; 1426:
41. Gianferrara T, Giust D, Bratsos I and Alessio E.
Tetrahedron 2007; 63: 5006–5013.
42. Wijesekera TP and Dolphin D. Metalloporphyrins,
Sheldon RA. (Ed.) Marcel Deker Inc.: New York,
1994; Chapter 7.
1
481–1489.
2
2
8. AdlerAD, Longo FR and Shergalis W. J. Am. Chem.
Soc. 1964; 86: 3145–3149.
43. Ner MM and Adler AD. J. Am. Chem. Soc. 1975;
97: 5107–5111.
9. Adler AD, Longo FR, Finarelli JD, Goldmacher J,
Assour J and Korsakoff L. J. Org. Chem. 1967; 32:
44. Kadish KM, Lin M, Van Caemlelbexhi E, De Ste-
fano G, Medforth CJ, Nurco DJ, Nelson NY, Krat-
tinger B, Muzzi CM, Jaquinod L, Xu Y, Shyr DC,
Smith KM and Shelnutt JA. Inorg. Chem. 2002; 41:
6673–6687.
4
76–476.
3
0. Prado-Manso CMC, Vidoto EA, Vinhado FS, Sacco
HC, Ciuffi KJ, Martins PR, Ferreira AG, Lindsay-
Smith JR, Nascimento OR and IamamotoY. J. Mol.
Catal. A 1999; 150: 251–266.
1. Engelmann FM, Losco P, Winnischofer H, Araki K
and Toma H. J. Porphyrins Phthalocyanines 2002;
45. Hochstrasser RM and Kasha M. Photochem. Photo-
biol. 1964; 3: 317–331.
3
46. Shi Y, Zheng W, Li Z, Wang X, Wang D, Qiu S and
Li X. Opt. Mater. 2006; 28: 1178–1186.
47. a) Araki K and Toma HE. J. Photochem. Photobiol.
A 1994; 83: 245–250. b) Caemelbecke EV, Kutner W
and Kadish KM. Inorg. Chem. 1993; 32: 438–444.
48. McDermott GA and Walker FA. Inorg. Chim. Acta
1984; 91: 95–102.
6
: 33–42.
3
3
2. Moreira EZ, Moraes LAB, Eberlin M, Iamamoto Y
and Nikolaou S. Polyhedron 2008; 27: 2721–2729.
3. SMART V 5.050 (NT) Software for the CCD
Detector System; Bruker Analytical X-ray Systems,
Madison, WI, 1998.
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 984–984