Synthesis and properties of 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido) phenyl]porphyrin and its metal complexes

Article abstract of DOI:10.2298/JSC110516190L

A novel 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]-porphyrin and its transition metal complexes are reported in this paper. Their molecular structures were characterized by elemental analysis as well as IR, ¹H-NMR and UV-Vis spectroscopy. Their spectroscopic properties were studied by Raman and fluorescence spectroscopy, and X-ray photoelectron spectroscopy (XPS). The fluorescence quantum yields were measured at room temperature. The fluorescence intensity of the porphyrin ligand was stronger than the intensity of the complexes. There were large differences in the Raman spectrum of the porphyrin ligand and those of the metal complexes due to changes in the symmetry of porphyrin plane. In the XPS spectra, the replacement of the free-base protons by a metal ion to form the metalloporphyrin not only increases the symmetry of the molecule, but also introduces an electron withdrawing group into the center of the porphyrin ligand, which increases the N_1S binding energy.

Full text of DOI:10.2298/JSC110516190L

J. Serb. Chem. Soc. 77 (3) 335–348 (2012)
JSCS–4272
UDC 547.979.733–034+543.428.3/.4:
535.375+535.372
Original scientific paper
Synthesis and properties of 5,10,15,20-tetrakis[4-(3,5-dioctyloxy-
benzamido)phenyl]porphyrin and its metal complexes
WENHUI LIAN, YUANYUAN SUN, BINBIN WANG, NING SHAN and TONGSHUN SHI*
College of Chemistry, Jilin University, Changchun 130023, P. R. China
(Received 16 May, revised 3 October 2011)
Abstract: A novel 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]-
porphyrin and its transition metal complexes are reported in this paper. Their
molecular structures were characterized by elemental analysis as well as IR,
1H-NMR and UV–Vis spectroscopy. Their spectroscopic properties were
studied by Raman and fluorescence spectroscopy, and X-ray photoelectron
spectroscopy (XPS). The fluorescence quantum yields were measured at room
temperature. The fluorescence intensity of the porphyrin ligand was stronger
than the intensity of the complexes. There were large differences in the Raman
spectrum of the porphyrin ligand and those of the metal complexes due to
changes in the symmetry of porphyrin plane. In the XPS spectra, the
replacement of the free-base protons by
a metal ion to form the
metalloporphyrin not only increases the symmetry of the molecule, but also
introduces an electron withdrawing group into the center of the porphyrin
ligand, which increases the N1s binding energy.
Keywords: porphyrin; transition metal complex; XPS spectra; Raman spectra;
fluorescence spectra.
INTRODUCTION
1,2
Recently, investigation of porphyrins has become of increasing interest.
Porphyrins and metalloporphyrins are functional molecules that are used for a va-
riety of applications and devices, such as optoelectronic, luminescent and, mole-
cular logic devices, supramolecular self-assembly, solar energy harvesting sys-
3–7
tems, photonic materials, and therapeutics. . These applications are affected by
the diverse electrochemical and photophysical properties of the porphyrins and
the ability to fine-tune these properties by the exocyclic substituents on the mac-
rocycle and via the choice of chelated metal ion.
Porphyrins have many desirable features, such as high stability, intense ab-
sorption of sunlight, a highly conjugated plane and a small gap between the high-
*Corresponding author. E-mail: wenhuilian1984@hotmail.com
doi: 10.2298/JSC110516190L
335
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336
LIAN et al.
est occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) energy level. The highly conjugated π-electron skeleton of a porphyrin
provides an adequate number of π electrons and π–π* transitions normally give a
8
strong absorption in the UV and visible regions of the spectrum. Metallopor-
phyrins generally have high thermal stability and show strong electronic transi-
tions in the visible and ultraviolet regions. In order to evaluate the applications of
metalloporphyrins, it is necessary to understand the electronic structure and pho-
tophysical properties. Raman spectroscopy, fluorescence spectra, X-ray photo-
electron spectroscopy, etc, have been widely used to study the porphyrin ligand
and metalloporphyrins, and the results could provide important information to
determine their electronic structure. X-Ray photoelectron spectroscopy (XPS) is
a powerful tool for the characterization of both the chemical composition and the
9–11
electronic environments of each atom in a molecular system.
To date, the synthesis and application of the substituent tetraphenylporphyrin
(TPP) bearing special functional groups have caused great interest, but those
bearing an amide group as side chains have been little reported. In this research, a
novel TPP derivative bearing an amide group and its transition metal complexes
were synthesized. The benzene core was replaced by a rigid porphyrin core,
which is linked via amide bonds to four triphenylenes. Since the porphyrin di-
mension is much larger than that of a benzene ring and the symmetry changes
from three-fold to four-fold, an entirely different self-assembly via hydrogen
bonding was to be expected. Their structures were characterized by their UV–
1
–Vis, IR and H-NMR spectra and the changes in the fluorescence, Raman spec-
tra and XPS behavior of these compounds were investigated.
RESULTS AND DISCUSSION
Physical, analytic and spectral data for 7a–7d
5,10,15,20-Tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7a). Purple
solid. Yield: 62.4 %; Anal. Calcd. for C
%. Found: C, 77.16; H, 8.48; N, 5.20 %. IR (KBr, cm ): 3314 (N–H, pyrrole),
H
N O : C, 77.12; H, 8.42; N, 5.26
136 178 8 12
–1
2925, 2855 (C–H), 1674 (C=O), 1523 (N–H, amide), 1245 (Ar–O–C), 966 (N–H,
1
pyrrole), 721 (–(CH ) –, n > 4). H-NMR (500MHz, CDCl , δ / ppm): 8.92 (8H,
2 n
3
s, pyrrole ring), 8.30 (4H, s, –NH–CO–), 8.20–8.26 (8H, d, J = 30 Hz, o–C H ),
6
4
8.08–8.03 (8H, d, J = 25 Hz, m-C H ), 6.98–7.04 (8H, d, J = 30 Hz, o–C H ),
6
4
6 3
6.64–6.69 (4H, d, J = 25 Hz, m–C H ), 4.10–4.22 (16H, m, –O–CH –), 1.78–1.98
6
3
2
(16H, m, –O–C–CH –), 1.49–1.64(16H, m, –CH –CH ), 1.21–1.40 (64H, m, –O–
2
2
3
C–C–(CH ) –C–CH ), 0.85–0.95 (24H, t, J = 25 Hz, –O–C–C–(C) –C–CH ),
2 4
3
4
3
–2.74 (2H, s, N–H, pyrrole). UV–Vis (CHCl , λ
/ nm): 425 (Soret band), 520,
3
max
555, 595, 650 (four Q bands).
Zinc 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7b).
Purple red solid. Yield: 90.5 %; Anal. Calcd. for C N O Zn: C, 74.93; H,
H
136 176
8 12
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
337
–1
8.35; N, 5.02 %. Found: C, 74.99; H, 8.30; N, 5.07 %. IR (KBr, cm ): 3285 (N–H,
imide), 2924, 2851 (C–H), 1664 (C=O), 1527 (N–H, amide), 1245 (Ar–O–C),
1
996 (N–Zn), 721 (–(CH ) –, n > 4). H-NMR (500 MHz ,CDCl , δ / ppm), 8.99
2 n
3
(8H, s, pyrrole ring), 8.12–8.30 (8H, d, J = 40 Hz, ο–C H ), 8.06 (4H, s,–CON–H),
6
4
7.95–7.96 (8H, d, J = 5 Hz, m–C H ), 7.26–7.27 (8H, d, J = 5 Hz, o–C H ),
6
4
6 3
6.96–6.87 (4H, t, J = 22.5 Hz, m-C H ), 3.92–4.03 (16H, t, J = 7.5 Hz, –O–CH –),
6
3
2
1.68–1.98 (16H, m, –O–C–CH –), 1.22–1.52 (80H, m, –C–C–(CH ) –CH ),
2
2 5
3
0.861–0.905 (24H, t, J = 11 Hz, –C–C–(C) –CH ). UV–Vis (CHCl , λ
/ nm):
5
3
3
max
425 (Soret band), 551, 592 (two Q bands).
Manganese 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]por-
phyrin (7c). Dark green solid. Yield: 82.4 %; Anal. Calcd. for C MnN O Cl:
H
136 176
8
12
–1
C, 74.12; H, 7.99; N, 5.04 %. Found: C, 74.07; H, 8.04; N, 5.08 %. IR (KBr, cm ):
3282 (N–H, imide), 2925, 2854 (C–H), 1677 (C=O), 1519 (N–H, amide), 1244
(Ar–O–C), 1008 (N–Mn), 721 (–(CH ) –, n > 4). UV–Vis (CHCl , λ / nm):
2 n
3
max
480 (Soret band), 585, 625 (two Q bands).
Cobalt 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamide)phenyl]porphyrin (7d).
Purple red solid. Yield: 85.7 %; Anal. Calcd. for C CoN O : C, 75.21; H,
H
136 176
8
12
–1
8.11; N, 5.09 %. Found: C, 75.14; H, 8.16 N, 5.15 %. IR (KBr, cm ) 3280 (N–H
(imide)), 2925, 2854 (C–H), 1658 (C=O), 1517 (N–H, amide), 1252 (Ar–O–C),
1000 (N–Co), 717 (–(CH ) –, n > 4). UV–vis (CHCl , λ / nm): 415 (Soret
2 n
3
max
band), 530, 675 (two Q bands).
UV–Vis spectra
The electronic absorption spectra of porphyrins result from electronic tran-
sitions from the ground state (S ) to the two lowest singlet excited states S and
0
1
S . The S →S transition gives rise to weak Q bands in the visible region while
2
0
1
12,13
the S →S transition produces a strong Soret band in the near UV region.
The absorption bands of 7a appear at 425, 520, 555, 595 and 650 nm. Compared
with the absorption bands of TPP, the absorption bands of 7a are red-shifted.
0
2
14
Possibly, this is because the substituent group on the phenyl group at the meso-
position of the porphyrin ring is an electron-donating group, thereby enabling the
electronic density on the phenyl ring to strengthen. Thus, the phenyl ring con-
jugates to a certain degree with the porphyrin macrocycle. This kind of conjuga-
tion action causes a reduction of the electron transition energy of the porphyrin
macrocycle, resulting in red shifts of the absorption bands.
When a metal atom is bonded to the central nitrogen atoms of a porphyrin,
the metal ion accepts the lone-pair-electrons of the N atoms of the pyrrole rings,
while the metal ion donates the electrons to the porphyrin molecule, forming de-
localized π bonds, which permit the easy flow of electrons within the delocalized
π system. In this work, the UV–Vis spectra of the metalloporphyrins exhibited
one Soret band and either one or two Q bands; the number of Q band decreases
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LIAN et al.
and the absorption frequencies shift. When the metal ion coordinates with por-
phyrin ligand, the symmetry of the molecule is changed from D to D , the
2h
4h
cleavage degree of the molecular orbital decreases and the degeneracy increases;
hence, the number of Q bands therefore decreases.
Infrared spectra
–1
The IR bands at 3314 and 966 cm of 7a are attributed to N–H stretching
and bending vibrations of the porphyrin ligand core, respectively, but they were
absent in the spectra of the complexes, because the hydrogen atom in the N–H
15
bond was replaced by a transition metal ion. In addition, a new band in the
–1
spectrum of 7b, 7c and 7d appeared at 996, 1008 and 1000 cm , respectively,
–1
which is characteristic of metalloporphyrins. The bands at about 3280–3285 cm
of the complexes are assigned to N–H stretching vibrations of the amide group
on the side chains, but in the spectrum of the porphyrin ligand, it overlapped the
N–H stretching vibration of the porphyrin core and could not be distinguished.
–1
The bands in the range of 1652–1670 cm are assigned to C=O stretching vib-
–1
ration (amide I). The bands at about 1517–1521 cm are assigned to N–H in-
–1
-plane bending and C–N stretching (imide II). The bands at about 1245–1252cm
–1
are assigned to Ar–O–C stretching vibrations. The bands at 717–721 cm are as-
signed to the methylene in-plane rocking vibration of a straight alkyl chain con-
taining more than four carbon atoms.
Fluorescence spectra
Excited-state processes in porphyrins are extremely important for their appli-
cation in molecular devices. The room temperature fluorescence spectra of the
–6
–1
porphyrin ligand and metalloporphyrins in chloroform (2×10 mol L ) were re-
corded. No fluorescence signal was detected for the metalloporphyrins 7c and 7d
Fig. 1. Excitation spectra of
7a and 7b in chloroform.
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
339
under the employed experimental conditions. The excitation spectra of 7a and 7b
are shown in Fig. 1. In the region of 350–700 nm, the excitation spectra are ap-
proximately mirror images of the absorption spectra, indicating that they corres-
pond to a similar electron transition process.
The emission spectra of 7a and 7b are shown in Fig. 2 for an excitation
wavelength of 420 nm. The emission spectra data of 7a and 7b are given in Table
I. Excitation to the S (B band) and the S (Q band) in porphyrin compounds re-
2
1
sults in fluorescence. The fluorescence of the S (B band) is attributed to the
2
transition from the second excited singlet state S to the ground state S , S →S ,
2
0
2
0
and it corresponds with the Soret band in the electronic absorption spectra. In
addition, fluorescence of the Q band is attributed to the transition from the lowest
excited singlet state S to the ground state S . The fluorescence of S →S was
1
0
2
0
too weak to be observed in this study, owing to light scattering and resorption of
strong Soret absorption band. It is well known that metal-free porphyrins usually
16
show two strong emission bands around 650 and 720 nm. The fluorescence
bands of 7a were at 653 and 716 nm. Compared with the fluorescent bands at 650
and 713 nm of TPP, the emission peaks of porphyrin ligand were red-shifted by 3
nm. The fluorescence bands of the Zn complex were at 597 and 644 nm, which
were red-shifted compared to ZnTPP (592 and 641 nm). These red shifts may be
due to the interaction of the arylamido group with the conjugated π-electron sys-
tem of the porphyrin macrocycle. The conjugation of the porphyrin macrocycle is
affected by the electronic donating groups. The conjugation is enhanced when the
alkylamide groups are linked on the phenyl group.
Fig. 2. Fluorescence spectra
of 7a and 7b in chloroform.
The quantum yield of porphyrin ligand and Zn complex were calculated
according to the following equation:
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LIAN et al.
F
A
sample
ZnTPP
φ
=
φ
ZnTPP
sample
F
A
ZnTPP sample
where F
and F
are the measured fluorescence integral areas of the
sample
ZnTPP
sample and the reference ZnTPP, respectively. A
and A
are the absor-
sample
ZnTPP
bance of the sample and the reference, respectively. φ
and φ
(φ
=
sample
ZnTPP ZnTPP
17
= 0.033) are the quantum yields of the sample and the reference ZnTPP at same
excitation wavelength. The quantum yields of the porphyrin ligand are much
18
lower than that of TPP (φ
= 0.11 ). As is known, porphyrins can be considered
TPP
as specific donor–acceptor systems, and the decrease in the fluorescence quan-
tum yields of the porphyrin ligand in comparison to that of TPP could be the re-
sult of intramolecular energy migration or electron transfer from the donor part of
the molecule to the acceptor part. The fluorescence quantum yields of 7a and 7b
were very small. Thus, the excited state S was primarily deactivated by radia-
1
tionless decay in porphyrins. This indicates fairly certainly that the spin forbid-
den process S →Tn is dominant for the radiationless deactivation of S in por-
1
1
phyrin compounds. The fluorescence yield of 7b was much smaller than that of
7a because zinc weakened the fluorescence radiation.
TABLE I. Emission spectra data and quantum yields (φf) of 7a and 7b
Compound
Q(0–0) / nm
Q(0–1) / nm
φf
7a
7b
653
597
716
644
0.064
0.032
Resonance Raman spectra
The resonance Raman spectra of the porphyrin ligand and complexes were
obtained by excitation at 514.5 nm. The important Raman frequencies and their
assignments are listed in Table II. The Raman spectra of the porphyrin ligand and
the Mn complex are shown in Fig. 3. The resonance Raman spectra of tetraphe-
19–21
nylporphyrin derivatives have been studied extensively.
Thus, the assign-
ments of Raman bands of porphyrin ligand and complexes are only discussed
briefly here.
TABLE II. Raman spectra and assignment of the porphyrin ligand and its complexes (vs: very
strong, s: strong, m: medium, w: weak)
Compound
Assigned
7a
7b
7c
7d
ν2, ν(CβCβ)
φ5, phenyl
ν3, ν(CαCm)
1553vs
1496m
1455s
1360m
1330m
1550s
1494m
1454w
1353s
–
1573vs
1497s
1456m
1372m
1341w
1561vs
1502m
1455w
1367s
–
ν4, ν(Cα–N) / ν(CαCβ)
ν20, ν(pyr. quarter-ring)
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
341
ν1, ν(Cm–Ph)
ν17, δ(Cβ–H)
ν15, ν(pyr. breath.) + phenyl
1240m
1081w
1002m
1242w
1067w
1008m
1241m
1086m
1002m
1242w
1076m
997w
TABLE II. Continued
Compound
Assigned
7a
963w
719w
7b
–
7c
–
7d
–
710w
395
312w
ν6, ν(pyrrole breath.)
π3, phenyl
717w
404w
–
713w
397w
313w
ν(M–N)
ν8, ν(pyr. translation)
335
Fig. 3. Raman spectra of the porphyrin ligand and the Mn complex.
–1
In the 900–1650 cm high-frequency region of the Raman spectra of por-
phyrin ligand and complexes, Raman bands generally arise from the totally sym-
metric vibrational modes, such as C C , C C , C C , pyrrole quarter-ring, and
β
β
α
β
α m
pyrrole half-ring stretching. The wavenumber positions of Raman bands in the
high-frequency region are sensitive to the core size, axial ligation and electron
–1
density of the central metal ion. In this region, the band at 1553 cm of porphy-
rin ligand was assigned to the C C stretch ν mode, which was up-shifted to
β
β
2
–1
–1
1573 cm in the Mn complex and to 1561 cm in Co complex, but it was down-
shifted to 1548 cm in the Zn complex. The ν mode was observed with en-
–1
2
hanced intensity in the complexes. In fact, it is one of the most intense bands in
–1
the high-frequency region. The band at 1496 cm of porphyrin ligand was as-
signed to the vibration of phenyl ring, and it was little shifted in the complexes,
which confirmed that the metal ion had little effect on the phenyl at the meso
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LIAN et al.
–1
positions. Raman bands in 1300–1450 cm were due to the out-of-phase coupled
–1
C C /C N stretching modes. The 1360 and 1330 cm bands of the porphyrin
α
β
α
ligand were assigned to the ν and ν mode, respectively. The ν mode of 7b, 7c
4
20
4
–1
and 7d appeared at 1353, 1372 and 1367 cm , respectively. The ν mode of 7c
20
–1
shifted to 1341 cm , while the ν mode of 7b and 7d were too weak to be
20
–1
observed in the present experiments. The 1240 cm band of the porphyrin ligand
–1
and the 1240–1242 cm band of the complexes were attributed to the Cm−ph
–1
stretching ν mode. The band at 1081 cm of the porphyrin ligand was assigned
1
to the vibrations of the pyrrole C –H stretching ν mode, which shifted to 1067,
β
9
–1
–1
1086 and 1076 cm in 7b, 7c and 7d, respectively. The band at 1002 cm of the
porphyrin ligand was assigned to the vibration of pyrrole breathing and phenyl
stretching ν mode, which did not shift in the Mn complex, but was up-shifted
15
–1
–1
to 1008 cm in the Zn complex and downshifted to 997 cm in the Co complex.
The band at 963 cm of the porphyrin ligand was assigned to pyrrole breathing
–1
ν mode, but it was absent in the spectra of the metalloporphyrins because the
6
hydrogen atom in the N−H bonding had been replaced by a metal ion. In the low-
-frequency region, the Raman bands of the metalloporphyrin complexes were
very different to those of the porphyrin ligand because the structures or vibratio-
nal dynamics, especially around the C C C bond-angles, were altered by the
α
m β
metal ions. For the porphyrin ligand, the only weak Raman band was observed at
–1
335 cm , which was assigned to the ν mode. The ν mode consists of the in-
8
8
-plane translational motion of the pyrrole, which can be described as a uniform
breathing of the whole porphine ring accompanied by an in-plane deformation of
22
C C C in the pyrrole ring.
α
m β
X-Ray photoelectron spectra
The XPS spectra of the porphyrin films were obtained. All elements of the
porphyrins, including C, N, O and different metals for the metalloporphyrins,
were found in the XPS spectra of their films grafted on Si (100). The X-ray pho-
toelectron spectra data of the porphyrin ligand and its complexes are given in
Table III. The XPS spectra of the N region are shown in Fig. 4.
1s
TABLE III. Binding energies (eV) of the porphyrin ligand and complexes obtained in the XPS
experiments
Compound
Signal
7a
397.65
399.75
–
285.03
–
7b
–
7c
7d
=N–
–
–
–NH–
–N–M–
C1s
M2p3/2
O1s
399.60
397.84
284.75
1021.10
532.95
399.85
398.65
284.69
642.40
532.95
399.49
398.70
284.60
780.08
532
532.9
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
343
Free base porphyrins exhibit two distinct N signals corresponding to the
1s
imine (–C=N–) nitrogen and the pyrrole (–NH–) nitrogen. The pyrrole nitrogen
23–26
usually has a higher N binding energy than the imine nitrogen.
The N
1s
1s
binding energies of these species were ≈400 and ≈397 eV, respectively, so that
they should have been readily resolved in the performed experiment. In the por-
phyrin ligand 7a, two N signals could be observed, one related to the N atoms of
unprotonated porphyrin rings (397.65 eV), and the other to the N atoms of pro-
tonated porphyrin-rings and the N atoms of the amide around the porphyrin-ring
(399.75 eV). The N spectra of the metalloporphyrins also exhibited two signals,
1s
the signal with the lower binding energy can be assigned to the metal-binding
nitrogen atoms. The binding energy of the protonated porphyrin-ring nitrogen co-
incides with the amide nitrogen, and their band energies were higher than for the
unprotonated porphyrin-ring. This is because of the protonation of the imine nit-
rogen atoms, which decreases the intensity of the N peak at the lower binding
1s
energy.
Fig. 4. N1s region of the porphyrin ligand and its complexes.
The metal ion region of the XPS spectra of the films of metalloporphyrins
7b, 7c, and 7d on the Si (100) surface are shown in Fig. 4. The metalloporphryins
exhibit a 2p signal. The M2p (M = Zn, Mn or Co) region of 7b, 7c and 7d
3/2
3/2
shows sharp peaks with bonding energy at 1021.10, 642.40 and 780.08 eV, res-
pectively, and it is lower than the M2p binding energy of corresponding metal
3/2
salt. This indicates that the metal atoms accept electrons from the porphyrin ring
when they generate complexes. The electrons of the porphyrin-ring nitrogens
transfer to an unoccupied metal orbital, i.e., they formed electron donor–acceptor
complexes.
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344
LIAN et al.
EXPERIMENTAL
General synthesis procedures
Chemicals and solvents were obtained from various commercial sources and used with-
out further purification unless otherwise stated. Pyrrole was freshly distilled before use. DMF
was pre-dried over activated 4Å molecular sieve and vacuum distilled from calcium hydride
(CaH2) prior to use. Dry CHCl3 and Et3N were obtained by redistillation from CaH2. Acetone
was dried with anhydrous magnesium sulfate. Anhydrous potassium carbonate was dried
under vacuum at 80 °C for 30 min.
The synthesis procedures are illustrated in Schemes 1 and 2. 5,10,15,20-Tetra-(4-nitro-
phenyl)porphyrin was synthesized through the reaction between pyrrole and p-nitrobenzal-
dehyde in the presence of lactic acid according to a published procedure.27 5,10,15,20-Tetra(4-
aminophenyl)porphyrin (TAPPH2) was prepared using SnCl2/HCl according to the method of
Kruper.28
Scheme 1. Synthetic route to 3,5-dioctyloxybenzoyl chloride.
Methyl 3,5-dioctyloxybenzoate (2). Compound 1 (3.36 g, 20.0 mmol), anhydrous potas-
sium carbonate (8.28 g, 60.0 mmol) and a catalytic amount of KI in acetone (150 ml) were
refluxed for 0.5 h and then 1-bromooctane (9.6 g, 50 mmol) was added in the solution. The
reaction mixture was gently refluxed for 36 h under an N2 atmosphere. The resulting mixture
was filtered to remove the impurities. The solution was evaporated to dryness. The solid
remaining was recrystallized from methanol to obtain 2 (m.p. 32 °C; yield: 89 %).
3,5-Dioctyloxybenzoic acid (3). It was synthesized according to a method similar to that
described in previous papers.29,30 The product was recrystallized from ethanol (m.p. 53 °C;
yield: 92 %).
3,5-Dioctyloxybenzoyl chloride (4). Compound 3 (3.78 g, 10.0 mmol) was dissolved in
20 ml thionyl chloride. The solution was refluxed for 12 h and then the solvent was evapo-
rated using a water vacuum pump.
Synthesis of the ligand 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7a)
A mixture of TAPPH2 (1.2 g, 1.8 mmol) and 3,5-dioctoxybenzoyl chloride (3.96 g, 10.0
mmol) was dissolved in 150 ml freshly distilled CHCl3 and then 3 ml triethylamine was added
into the system. The mixture was stirred at room temperature for 2 h, then refluxed for 10 h
and cooled to room temperature. The resulting mixture was poured into 150 ml distilled water,
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
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extracted four times with freshly distilled chloroform and then dried over anhydrous magne-
sium sulfate. The solvent was removed on a rotary evaporator. The residue was further puri-
fied by column chromatography (silica gel); the eluent was chloroform followed by chloro-
form/ethanol=50:1 (v:v). The first band was collected and evaporated to dryness to give a
purple solid, which was further recrystallized from chloroform/methanol.
Scheme 2. Synthetic route to the porphyrin ligand and its metal complexes.
Synthesis of zinc 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7b)
Compound 7a (80 mg) and ZnCl2 (100 mg) were dispersed in a mixture of CHCl3 and
methanol (2:1). The reaction mixture was refluxed for about 1.5 h. The progress of the reac-
tion was monitored by measuring the UV–Vis spectrum of the reaction solution. The resulting
mixture was washed with saturated aqueous NaCl solution and then concentrated. The product
was purified by column chromatography on silica gel; eluent: CHCl3/C2H5OH, 10:1 (v:v). The
second band was collected, dried under vacuum to give a purple red solid.
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LIAN et al.
Synthesis of manganese 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7c)
Complex 7c was prepared by reaction of 7a (100 mg) with MnCl2·4H2O (120 mg) in a
mixture of freshly distilled CHCl3 (10 ml) and dried DMF (15 ml) at 70 °C under an N2
atmosphere for about 4 h. The progress of the reaction was also monitored by measuring the
UV–Visible spectrum of the reaction mixture. After completion of the reaction, the resulting
mixture was cooled, extracted several times with CHCl3 and distilled water. Then the solvent
was removed to dryness, and the product was chromatographed on a silica gel column using
the eluent CHCl3/C2H5OH 10:1 (v:v).
Synthesis of cobalt 5,10,15,20-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]porphyrin (7d)
Compound 7d was synthesized in a similar manner to that described for 7c.
Characterization
1
The H-NMR spectra were acquired on a Varian Unity-500 (MHz) NMR spectrometer
using standard pulse sequences. The spectra were recorded at 298 K in CDCl3, unless other-
wise stated. Chemical shifts are reported on the δ scale relative to TMS. Elemental analyses
were performed on a Perkin-Elmer 240 C auto elementary analyzer. The infrared spectra were
obtained using a Nicolet 5PC-FT-IR spectrometer in the region of 4000–400 cm-1. The elec-
tronic absorption spectra were measured with a Shimadzu UV-3000 spectrometer. Steady-state
emission measurements were obtained on a Shimadzu RF-5301PC fluorescence spectrometer
with both the excitation and emission slit set at 5 nm. The resonance Raman (RR) spectra
were obtained using a Renishaw inVia microscopic instrument. Radiation of 514.5 nm was
obtained from an Ar+ laser. The chemical composition of the surface was investigated by
X-ray photoelectron spectroscopy using an ESCALAB Mark II spectrometer.
CONCLUSIONS
In this study, a novel meso-tetrakis[4-(3,5-dioctyloxybenzamido)phenyl]por-
phyrin and its transition metal complexes were synthesized and characterized.
Their properties were clearly influenced by the nature of the central transition
metal ions. Compared with the porphyrin ligand, the number of the electronic
absorption bands of the complexes decreased and exhibited some shifts. The
fluorescence results showed that the transition metal in the central porphyrin ring
quenched the fluorescence of porphyrin. From the XPS spectra, the information
concerning the character of the chemical bonding in the porphyrin ligand and its
complexes was obtained. In addition, the investigation could provide very useful
information for further study of these derivatives.
Acknowledgement. This work was supported by the National Natural Science Foundation
of the People’s Republic of China.
И З В О Д
СИНТЕЗА И СВОЈСТВА 5,10,15,20-ТЕТРАКИС[4-(3,5-ДИОКТИЛОКСИБЕНЗАМИДО)-
ФЕНИЛ]ПОРФИРИНА И ЊЕГОВИХ МЕТАЛНИХ КОМПЛЕКСА
WENHUI LIAN, YUANYUAN SUN, BINBIN WANG, NING SHAN и TONGSHUN SHI
College of Chemistry, Jilin University, Changchun 130023, P. R. China
Приказан је нови 5,10,15,20-тетракис[4-(3,5-диоктилоксибензамидо)фенил]порфирин и
његови комплекси са прелазним металима. Молекулске структуре окарактерисане су елемен-
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SYNTHESIS OF BENZAMIDOPHENYLPORPHYRIN AND ITS METAL COMPLEXES
1
347
талном анализом као и IR, H-NMR и UV–Vis спектрима. Спектроскопска својства проуча-
вана су раманском, флуоресцентном и фотоелектронском спектроскопијом Х-зрачења (XPS).
Квантни флуоресцентни приноси одређивани су на собној температури. Нађено је да је
интензитет флуоресценције за порфирински лиганд већи него за комплекс. Уочена је и већа
разлика између раманских спектара порфиринског лиганда и његових комплекса, што потиче
од симетрије порфиринске равни. Из XPS спектара произилази да замена протона металним
јоном у формирању метал-порфирина повећава молекулску симетрију и уводи у центар пор-
фирина електрон-привлачну групу, што повећава N1s енергију везивања.
(Примљено 16. маја, ревидирано 3. октобра 2011)
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