Thermal analysis study of 5,10,15,20-tetrakis (methoxyphenyl) porphyrins and their nickel complexes

Article abstract of DOI:10.1016/j.tca.2005.10.017

The thermal stability in air of 5,10,15,20-tetrakis (4-methoxyphenyl) porphyrin (4-TMPP), 5,10,15,20-tetrakis (3-methoxyphenyl) porphyrin (3-TMPP), and their nickel metallo-complexes (4-TMPP-Ni and 3-TMPP-Ni) has been investigated by thermogravimetry (TG). 4-TMPP and 4-TMPP-Ni exhibit higher thermal stability compared to 3-TMPP and 3-TMPP-Ni. Nickel complexes exhibit a little higher thermal stability than the corresponding porphyrins. The thermal behavior including melting temperature and enthalpy of fusion was determined by differential scanning calorimetry (DSC) and infrared spectra (IR). The activation energies of thermal decompositions of 4-TMPP-Ni and 3-TMPP-Ni were obtained by integral model-free method; the mechanism functions and pre-exponential factors were determined by master plots method. The kinetic models follow the same mechanism function, Avramie-Erofeev equations with integral forms g(α) = [-ln (l - α)]^0.278 and g(α) = [-ln (l - α)]^0.260, respectively.

Full text of DOI:10.1016/j.tca.2005.10.017

Thermochimica Acta 440 (2006) 181–187
Thermal analysis study of 5,10,15,20-tetrakis (methoxyphenyl)
porphyrins and their nickel complexes
Xiuhua Weia, Xiuhong Dub, Donghua Chena,∗, Zhangping Chenb
a Hubei Key Laboratory for Catalysis and Material Science, College of Chemistry and Material Science,
South-Central University for Nationalities, Wuhan 430074, Hubei, PR China
b College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, Hubei, PR China
Received 23 June 2005; received in revised form 12 September 2005; accepted 31 October 2005
Available online 7 December 2005
Abstract
The thermal stability in air of 5,10,15,20-tetrakis (4-methoxyphenyl) porphyrin (4-TMPP), 5,10,15,20-tetrakis (3-methoxyphenyl) porphyrin
(3-TMPP), and their nickel metallo-complexes (4-TMPP-Ni and 3-TMPP-Ni) has been investigated by thermogravimetry (TG). 4-TMPP and
4-TMPP-Ni exhibit higher thermal stability compared to 3-TMPP and 3-TMPP-Ni. Nickel complexes exhibit a little higher thermal stability
than the corresponding porphyrins. The thermal behavior including melting temperature and enthalpy of fusion was determined by differential
scanning calorimetry (DSC) and infrared spectra (IR). The activation energies of thermal decompositions of 4-TMPP-Ni and 3-TMPP-Ni were
obtained by integral model-free method; the mechanism functions and pre-exponential factors were determined by master plots method. The kinetic
models follow the same mechanism function, Avramie-Erofeev equations with integral forms g(α) = [−ln (l − α)]0.278 and g(α) = [−ln (l − α)]0.260
,
respectively.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Porphyrin; Nickel complexes; Infrared spectra; Thermal analysis
1. Introduction
transport of oxygen. Among different metalloporphyrins, nickel
(II) porphyrins are considered to be exemplary systems for spec-
troscopic studies because they display spectroscopic properties
of theoretical interest [7]. At present, most work of porphyrin
compound focus on the preparation technics, synthesis route and
application. Preparation technics and application condition are
restrictedby thermal propertiessuchasstability, meltingtemper-
ature. However, there are surprisingly very little thermochemical
data on 5,10,15,20-tetrakis (methoxyphenyl) porphyrin and their
nickel metallo-complexes. In view of this, we studied the ther-
mal behavior and thermal decomposition kinetics of this kind of
porphyrins.
This paper reports the thermal stability, melting tempera-
ture, enthalpy of fusion and thermal decomposition kinetics
of porphyrins and their nickel complexes. The thermal behav-
ior at lower temperature including melting temperature and
enthalpy of fusion has been investigated by differential scan-
ning calorimetry technology and infrared spectra. The thermal
stability and thermal decomposition kinetics have been studied
by thermogravimetry.
Photodynamic therapy (PDT) is a treatment that is used for
the destruction of certain types of tumours [1]. It is well known
that photodynamic therapy is based on the administration of a
photosensitizer that concentrates in tumor cells and, upon sub-
sequent irradiation with visible light in the presence of oxygen,
selectively destroys the cancerous cells [2]. Photodynamic stud-
ies, in model systems and biological media carried out with a
series of 5,10,15,20-tetrakis (methoxyphenyl) porphyrins, have
shown that these synthetic porphyrins are effective photosen-
sitizers that can be used as model compounds to investigate
the effects of photosensitizers used in PDT [3–6]. Metallo-
porphyrins are widely studied because they play an important
role in biology due to their crucial function in many biological
processes like photosynthesis, biological red-ox reactions, and
∗
Corresponding author. Tel.: +86 27 67841856; fax: +86 27 67842752.
E-mail address: chendh46@hotmail.com (D. Chen).
0040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2005.10.017

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X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
Scheme 1. The structures of the four samples.
2. Experimental
2.3. Thermogravimetry (TG) and FTIR spectra
measurements
2.1. Materials
TG measurements were carried out on a TGS-2 thermal-
balance (Perkin-Elmer Co., USA) in a static air atmosphere.
Dynamic experiments were performed at several heating rates:
5, 8, 10, 15, and 20 ◦C min−1 with sample size ranging from 1.50
to 2.50 mg. The dynamic results presented in the paper were cal-
culated from programs written by ourselves. According to the
onset temperature of DTG curve to evaluate the onset decompo-
sition temperature, sequentially estimate the thermal stability of
the four samples. The infrared spectra (NICOLET-NEXUS 470
Co., USA) were recorded for samples of 3-TMPP and 3-TMPP-
Ni at the given temperatures.
5,10,15,20-Tetrakis (4-methoxyphenyl) porphyrin (4-
TMPP), 5,10,15,20-tetrakis (3-methoxyphenyl) porphyrin
(3-TMPP), and their nickel metallo-complexes (4-TMPP-Ni
and 3-TMPP-Ni) were synthesized by the method described in
detail elsewhere [8,9]. Their structures were given in Scheme 1,
which have been characterized by MS, 1H NMR, FTIR
and UV.
2.2. Differential scanning calorimetry (DSC) measurements
The thermal behaviors including melting temperature and
enthalpy of fusion were determined with a computer controlled
METTLER-TOLEDO DSC822e (Co., Switzerland) under static
air atmosphere. The temperature and energy of instruments had
been calibrated by standard indium before all measurements.
Thereferencepanwaspurealuminumpan, whichmeltat660 ◦C,
so the highest measurement temperature is 600 ◦C. The thermal
behavior of each specimen was investigated during first and sec-
ond heating after cooling the sample from the melt at a cooling
rate 10 ◦C min−1. The DSC measurements on each sample were
repeated twice and values agreed within the experimental uncer-
tainties 0.5 Jg−1 for the enthalpy of fusion and 0.2 K for the
melting temperature.
3. Theoretical consideration
3.1. Calculation of activation energy Ea by integral
model-free method
The rate of solid-state non-isothermal decomposition reac-
tion is expressed as
ꢀ
ꢁ
ꢀ
ꢁ
dα
dT
A
β
−Ea
=
exp
f(α)
(1)
RT

X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
183
Rearranging Eq. (1) and integrating both sides of the equation
leads to the following expression:
ꢀ
ꢁ
ꢀ
ꢁ
AEa
ꢀ
ꢁ
ꢂ
ꢂ
T
T
A
β
−Ea
A
β
g(α) =
exp
dT ≈
ꢁ
RT
T0
0
ꢀ
ꢁ
ꢀ
−Ea
exp
dT =
P(u)
(2)
RT
βR
ꢃ
u
where P(u) = ∞ −(e−u/u2) du and u = Ea/RT. Unfortu-
nately, P(u) cannot be analytically integrated. To solve this
problem, an approximate formula [10] is introduced into Eq.
(2). Taking the logarithms of both sides, Eq. (3) is obtained as
ꢀ
ꢁ
ꢄ
ꢅ
β
AEa
ln
= ln
+ 3.635041
Fig. 1. TG/DTG and DSC curves for 4-TMPP with heating rate of 15 ◦C min−1
in air.
T1.894661
Rg(α)
1.001450Ea
− 1.894661 ln Ea −
(3)
RT
A group of lines were obtained by plotting ln [βR/Ea] − ln [P(u)]
against −ln [g(α)]1/n. The logarithmic value of pre-exponential
factor and the value of accommodate factor can be obtained from
the interception and the slope, respectively.
The plots of ln (β/T1.894661) versus 1/T give a group of straight
lines. The activation energy Ea can be obtained from the slope
−1.001450 Ea/R of the regression line.
4. Results and discussion
3.2. Determination of the kinetic model by master plots
method
4.1. Thermal decomposition process
Using a reference at point α = 0.5 and according to Eq. (2),
one gets
TGA is widely used for evaluating the thermal stability of
samples because it requires a small sample and the entire study
was over in a few hours. The TG/DTG and DSC curves of
the four samples are shown in Figs. 1–4. The phenomenolog-
ical aspects are illustrated in Table 1. From that we can see
they are all stable up approximately 350 ◦C, which illustrate
that all four samples have excellent stability. The DTG onset
temperature follow the order 4-TMPP-Ni > 4-TMPP > 3-TMPP-
Ni > 3-TMPP, which suggests that stability is 4-TMPP-Ni > 4-
TMPP > 3-TMPP-Ni > 3-TMPP. TheDTGpeaktemperaturefol-
low the order 3-TMPP-Ni > 4-TMPP-Ni > 3-TMPP > 4-TMPP,
which different from the DTG onset temperature order. It may
be because the thermal decomposition reaction rate (dα/dT) of
the four samples is greatly different at the same temperature.
ꢀ
ꢁ
AEa
βR
g(α) =
P(u0.5
)
(4)
When Eq. (2) is divided by Eq. (4), the following equation is
obtained:
g(α)
P(u)
=
(5)
g(0.5)
P(u0.5)
Plots of g(α)/g(0.5) against α correspond to theoretical master
plots of various g(α) functions [11,12]. To draw the exper-
imental master plots of P(u)/P(u0.5) against α from experi-
mental data obtained under different heating rates, an approx-
imate formula [13] of P(u) with high accuracy was used
P(u) = exp(−u)/[u(1.00198882u + 1.87391198)].
Eq. (5) indicates that, for a given α, the experimental value of
P(u)/P(u0.5) and theoretically calculated values of g(α)/g(0.5)
are equivalent when an appropriate kinetic model is used. Com-
paring the experimental master plots with theoretical ones can
conclude the kinetic model [14].
3.3. Estimation of the pre-exponential factor A and
accommodate factor n
Experimental data, the expression of the kinetic model and
the average activation energy predetermined are introduced into
Eq. (2). The following expression is obtained:
ꢄ
ꢅ
βR
Ea
− ln[P(u)] = ln A − n ln [g(α)]1/n
Fig. 2. TG/DTG and DSC curves for 4-TMPP-Ni with heating rate of
15 ◦C min−1 in air.
ln

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X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
Table 1
Phenomenological data for the thermal decomposition of TMPP and TMPP-Ni in air (β = 15 ◦C min−1
)
Sample
Stage
TG plateaux (◦C)
DTG peak (◦C)
DSC peak (◦C)
450
Mass loss (calculated, %)
Residue
4-TMPP
I
II
407–465
465–700
448
572
18.7 (16.9)
81.6 (83.1)
–
–
3-TMPP
I
II
365–474
474–650
453
597
454
16.7 (16.9)
84.1 (83.1)
4-TMPP-Ni
3-TMPP-Ni
I
II
130–210
410–550
180
464
175
475
1.5
88.6 (90.5)
NiO
NiO
I
375–610
480
486
88.1 (90.5)
due to the complete disintegration of the intermediate. Similar
phenomenon is observed in 3-TMPP.
Fig. 2 shows the TG/ DTG and DSC curves for 4-TMPP-
Ni. The weight loss of 1.5% observed between 130 and 210 ◦C
may be due to the elimination of small molecular impurity,
which corresponds to the 180 ◦C peak in DTG curve and 175 ◦C
exothermicpeakinDSCcurve. Theevidentweightlossof88.6%
is due to the complete decomposition of 4-TMPP-Ni and finally
nickel oxide is remained (the theoretical value of 90.5%). 3-
TMPP-Ni exhibits similar thermal decomposition process to that
of 4-TMPP-Ni, but it contains no impurity.
4.2. Thermal behavior at lower temperature
Fig. 3. TG/DTG and DSC curves for 3-TMPP with heating rate of 15 ◦C min−1
in air.
The thermal behavior at lower temperature obtained by DSC
with the heating rate of 10 ◦C min−1 is shown in Figs. 5–8. The
results obtained from DSC analysis are presented in Table 2.
All the temperatures here represent the peak onset temperature
of the DSC curves. The enthalpies (ꢀH) are the thermodynam-
ics parameter of these temperature variation processes, which
were estimated from each DSC peak area computed by standard
procedure in DSC apparatus, respectively.
As can be seen from the presented data, on heating and reheat-
ing 4-TMPP, an endothermic peak is observed at almost the
same temperature; on cooling it from the given temperature, an
exothermic peak is observed near the endothermic peak temper-
From the structures of these four samples, it also can be seen
that the conjugative effect existing in the systems of 4-TMPP
and 4-TMPP-Ni is better than that existing in the systems of 3-
TMPP and 3-TMPP-Ni, which makes 4-TMPP and 4-TMPP-Ni
have the better thermal stability than the other two.
Fig. 1 shows that the weight loss of 4-TMPP occurs in two
steps; at the end of the decomposition almost no residue is
remained. The initial weight loss (18.7%) observed between 407
and 465 ◦C is attributed to the remove of methoxy group (the the-
oretical value of 16.9%), correspondingly there is a 448 ◦C peak
in DTG curve and 450 ◦C exothermic peak in DSC curve; after
465 ◦C until 700 ◦C, the mass loss reaches 100.3%, which is
Fig. 5. DSC curves for 4-TMPP: (a) initial heating; (b) cooling; and (c) reheating
the same sample (heating rate/cooling rate: 10 ◦C min−1).
Fig. 4. TG/DTG and DSC curves for 3-TMPP-Ni with heating rate of
15 ◦C min−1 in air.

X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
185
Table 2
Extrapolated onset temperature and enthalpy change of peak in DSC curve
obtained by heating, cooling and reheating the samples
Sample
Ton (◦C)/ꢀH (J g−1
)
Heating
Cooling
Reheating
4-TMPP
4-TMPP-Ni
3-TMPP
190.29/4.06
275.75/19.00
351.90/91.03
363.97/79.81
188.36/−7.06
190.47/7.78
274.94/19.66
–
–
268.77/−19.57
–
–
3-TMPP-Ni
ature; the enthalpy change (ꢀH) observed on cooling is almost
equal to that observed on reheating. In addition, the endother-
mic peak in the DSC curve has no corresponding change in the
TG curve. Therefore, the endothermic peak observed in DSC
curve can clearly be attributed to fusion of 4-TMPP. Similar
phenomena are observed in 4-TMPP-Ni, but the melting point
of 4-TMPP-Ni is higher than that of 4-TMPP.
Fig. 6. DSC curves for 4-TMPP-Ni: (a) initial heating; (b) cooling; and (c)
reheating the same sample (heating rate/cooling rate: 10 ◦C min−1).
Figs. 7 and 8 show that on heating 3-TMPP and 3-TMPP-Ni
to 400 ◦C, a sharp endothermic peak is observed; on cooling and
reheating, nothing is observed; after the endothermic peak DSC
curve goes up rapidly. The results indicate that before the end
of fusion the decomposition has already started, which can be
confirmed by the infrared spectra (Figs. 9 and 10). The charac-
teristic peaks in the IR spectra of 3-TMPP (Fig. 9) after heating
to 300 ◦C is different from those of 3-TMPP heating to 360 ◦C.
The weak absorption band (ꢀ) at 1235 cm−1 observed in Fig. 9a
curve is assigned to the stretching vibration mode of ph O, how-
ever it does not exist in Fig. 9b curve. The IR spectrum provides
the evidence for the broken of ph O bond before 360 ◦C. From
Fig. 10, it also can be seen that the sharp absorption band (ꢀ) at
1229 cm−1 observed in Fig. 10a curve does not exist in Fig. 10b
curve, which indicate that the ph O bond has broken before
370 ◦C. Therefore, the decomposition temperature of 3-TMPP-
Niisbetween350and370 ◦C. TheresultsofIRanalysisconform
that the melting and decomposition processes of the two samples
occur almost simultaneously.
Fig. 7. DSC curves for 3-TMPP: (a) initial heating; (b) cooling; and (c) reheating
the same sample (heating rate/cooling rate: 10 ◦C min−1).
Fig. 8. DSC curves for 3-TMPP-Ni: (a) initial heating; (b) cooling; and (c)
reheating the same sample (heating rate/cooling rate: 10 ◦C min−1).
Fig. 9. FTIR spectra observed for 3-TMPP at: (a) 300 ◦C and (b) 360 ◦C.

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X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
Fig. 12. TG curves of 3-TMPP-Ni at different heating rates in air.
Fig. 10. FTIR spectra observed for 3-TMPP-Ni at: (a) 350 ◦C and (b) 370 ◦C.
hardly varies with the extent of conversion and the average acti-
vation energies are 125.81 and 120.30 kJ mol−1, respectively.
Little dependence of the activation energy on the extent of con-
version indicates that there is a high probability for the presence
of a single-step reaction.
Table 3
The activation energies of different extents of conversion
Conversion/α
Activation energies Ea (kJ mol−1
)
4-TMPP-Ni
3-TMPP-Ni
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Average
113.16
117.01
121.01
125.22
129.68
134.56
140.03
125.81
113.27
116.90
118.61
122.17
121.75
123.54
125.86
120.30
4.3.2. Determination of kinetic model and estimation of
pre-exponential factor A and accommodate factor n
The experimental master plots of P(u)/P(u0.5) against α con-
structed from experimental data of the thermal decomposition
of 4-TMPP-Ni under different heating rates and the theoretical
master plots of various kinetic functions are all shown in Fig. 13.
The experimental master plots of 3-TMPP-Ni and the theoreti-
cal master plots are shown in Fig. 14. The comparisons of the
experimental master plots with theoretical ones indicate that the
kinetic processes of the thermal decompositions of 4-TMPP-
Ni and 3-TMPP-Ni are all most probably described by the Am
model, g(α) = [−ln (l − α)]1/m, because the experimental master
plots lie between the theoretical master plots line 1 (A4) and line
2 (A3). The resulting logarithmic values of the pre-exponential
4.3. Kinetics analysis
4.3.1. Determination of activation energy Ea
The thermal decompositions of 4-TMPP-Ni and 3-TMPP-Ni
are selected for the kinetic study. The TG curves of 4-TMPP-
Ni and 3-TMPP-Ni at different heating rates are shown in
Figs. 11 and 12, respectively. When α = 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, and 0.8, the corresponding activation energies are shown
in Table 3. From Table 3 we can see that the activation energy
Fig. 13. Master plots of theoretical g(α)/g(0.5) against α for various reaction
models (solid curves represent 18 kinds of reaction models, curve 19 represents
function g(α) = [−ln (1 − α)]0.278) and experimental data (ꢁ) of 4-TMPP-Ni at
the heating rates of 5, 8,10, 15, and 20 ◦C min−1
.
Fig. 11. TG curves of 4-TMPP-Ni at different heating rates in air.

X. Wei et al. / Thermochimica Acta 440 (2006) 181–187
187
The activation energies Ea determined by integral model-free
method are 125.81 and 120.30 kJ mol−1. The resulting logarith-
mic values of the pre-exponential factor ln A (s−1) are 12.671
and 18.219.
Acknowledgements
The financial support from the Key Natural Science Fund of
Science and Technology Department of Hubei Province under
grant no. 2001ABA009 for this work is greatly appreciated.
References
[1] K.C. Ackroyd, N. Brown, M. Reed, Photochem. Photobiol. 74 (2001)
656–669.
[2] M. La Penna, M. Gabriela Alvarez, E. Ines Yslas, Viviana Rivarola,
E.N. Durantini, Dyes Pigments 49 (2001) 75–82.
[3] Z. Katona, A. Grofcsik, P. Baranyai, I. Bitter, G. Grabner, M. Kubinyi,
et al., J. Mol. Struct. 450 (1998) 41–45.
Fig. 14. Master plots of theoretical g(α)/g(0.5) against α for various reaction
models (solid curves represent 18 kinds of reaction models, curve 19 represents
function g(α) = [−ln (1 − ␣)]0.260) and experimental data (ꢂ) of 3-TMPP-Ni at
the heating rates of 5, 8,10, 15, and 20 ◦C min−1
.
[4] M.E. Milanesio, M.G. Alvarez, E.I. Yslas, C.D. Borsarelli, J.J. Silber,
V. Rivarola, et al., Photochem. Photobiol. 74 (2001) 14–21.
[5] M. La Penna, M.G. Alvarez, E.I. Yslas, V. Rivarola, E.N. Durantini,
Dyes Pigment 49 (2) (2001) 75–82.
[6] I. Yslas, M.G. Alvarez, C. Marty, G. Mori, E.N. Durantini, V. Rivarola,
Toxicology 149 (2000) 69–74.
factorln A(s−1)are12.671and18.219, theaccommodatefactors
n (1/m) are 0.278 and 0.260, respectively.
[7] P. Serguei, M.K. Pawel, Z.Z. Marek, J. Chem. Phys. 121 (2004) 3.
[8] A.D. Adler, F.R. Longo, J.D. Finarelli, J. Goldmacher, J. Assour, L.
Korsakoff, J. Org. Chem. 32 (1967) 476.
5. Conclusions
[9] A.D. Adler, F.R. Longo, F. Kampas, J. Kim, J. Inorg. Nucl. Chem. 32
(1970) 2443.
[10] T. Wanjun, L. Yuwen, Z. Hen, W. Cunxin, Thermochim. Acta 408 (2003)
39.
[11] F.J. Gotor, J.M. Criado, J. Malek, N. Koga, J. Phys. Chem. A 104 (2000)
10777.
[12] L.A. Perez-Maqueda, J.M. Criado, F.J. Gotor, J. Malek, J. Phys. Chem.
A 106 (2002) 2862.
[13] T. Wanjun, L. Yuwen, Z. Hen, W. Zhiyong, W. Cunxin, J. Therm. Anal.
Cal. 74 (2003) 309.
[14] W. Tang, Y. Liu, X. Yang, C. Wang, Ind. Eng. Chem. Res. 43 (2004)
2054–2059.
4-TMPP and 4-TMPP-Ni exhibit higher thermal stability
compared to 3-TMPP and 3-TMPP-Ni, but the melting point
is much lower than that of 3-TMPP and 3-TMPP-Ni, TMPP-
Ni exhibits higher thermal stability and melting point than
that of the corresponding TMPP. For 3-TMPP and 3-TMPP-
Ni, the melting and decomposition processes occur almost
simultaneously. Both of the decomposition kinetic models of
4-TMPP-Ni and 3-TMPP-Ni follow nucleation and growth
mechanism, Avrami-Erofeev equation with integral forms
g(α) = [−ln (1−α)0.278 and g(α) = [−ln (l − α)0.260, respectively