Realizing metalloporphyrin functionalization of 4-vinylpyridine copolymer via axial coordination reaction

Article abstract of DOI:10.1142/S1088424610001957

Cobalt tetra(para-chlorophenyl)porphyrin (CoTCPP) and zinc tetraphenyl porphyrin (ZnTPP) were linked on the side chains of the copolymer of 4-vinylpyridine (4VP) and styrene (St), P(4VP-co-St), via axial coordination reactions, respectively, and the metalloporphyrin-functionalized macromolecules, CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), were prepared. Their chemical structures were characterized by FTIR and ¹H NMR. The spectral properties of the two macromolecular axial coordination complexes were mainly studied, and their photophysical behavior were discussed in depth. The experimental results show that the metalloporphyrin-functionalized macromolecules, CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), can be prepared favorably through axial coordination reaction with the side pyridine groups of the copolymer P(4VP-co-St) as ligands. The two complexes have characteristic spectra similar to that of the small molecular metalloporphyrins, CoTCPP and ZnTPP, respectively. At the same time, they also display the characteristic spectroscopic property of axial coordination complexes: the electronic adsorption spectra of CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St) red-shifted obviously as compared to that of CoTCPP and ZnTPP, and the fluorescence emission of ZnTPP-P(4VP-co-St) blue-shifted apparently with respect to that of ZnTPP. For CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), some polymer effects were found: (1) The bonding degree of the small molecular metalloporphyrin, CoTCPP or ZnTPP, on the side chains of the copolymer P(4VP-co-St) has a limit value because of the steric hindrance and there is a bonding degree difference between the actual value and the theoretical value; (2) For ZnTPP-P(4VP-co-St), slight energy transfer between adjacent ZnTPP units on an identical macromolecule occurs, leading to slight static quench of the fluorescence emission as the bonding density of ZnTPP units on the side chains of the copolymer P(4VP-co-St) reaches a certain value.

Full text of DOI:10.1142/S1088424610001957

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 235–243
DOI: 10.1142/S1088424610001957
Published at http://www.worldscinet.com/jpp/
Realizing metalloporphyrin functionalization of
4-vinylpyridine copolymer via axial coordination reaction
Baojiao Gao*, Ruixin Wang and Ruikui Du
Department of Chemical Engineering, North University of China, Taiyuan 030051, People’s Republic of China
Received 17 October 2009
Accepted 25 January 2010
ABSTRACT: Cobalt tetra(para-chlorophenyl)porphyrin (CoTCPP) and zinc tetraphenyl porphyrin
(ZnTPP) were linked on the side chains of the copolymer of 4-vinylpyridine (4VP) and styrene (St),
P(4VP-co-St), via axial coordination reactions, respectively, and the metalloporphyrin-functionalized
macromolecules, CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), were prepared. Their chemical
structures were characterized by FTIR and 1H NMR. The spectral properties of the two macromolecular
axial coordination complexes were mainly studied, and their photophysical behavior were discussed
in depth. The experimental results show that the metalloporphyrin-functionalized macromolecules,
CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), can be prepared favorably through axial coordination
reaction with the side pyridine groups of the copolymer P(4VP-co-St) as ligands. The two complexes
have characteristic spectra similar to that of the small molecular metalloporphyrins, CoTCPP and
ZnTPP, respectively. At the same time, they also display the characteristic spectroscopic property of axial
coordination complexes: the electronic adsorption spectra of CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-
co-St) red-shifted obviously as compared to that of CoTCPP and ZnTPP, and the fluorescence emission
of ZnTPP-P(4VP-co-St) blue-shifted apparently with respect to that of ZnTPP. For CoTCPP-P(4VP-co-
St) and ZnTPP-P(4VP-co-St), some polymer effects were found: (1) the bonding degree of the small
molecular metalloporphyrin, CoTCPP or ZnTPP, on the side chains of the copolymer P(4VP-co-St) has
a limit value because of the steric hindrance and there is a bonding degree difference between the actual
value and the theoretical value; (2) for ZnTPP-P(4VP-co-St), slight energy transfer between adjacent
ZnTPP units on an identical macromolecule occurs, leading to slight static quench of the fluorescence
emission as the bonding density of ZnTPP units on the side chains of the copolymer P(4VP-co-St)
reaches a certain value.
KEYWORDS: metalloporphyrin, 4-vinylpyridine copolymer, porphyrin-functionalization, axial
coordination.
redox, guest-binding, and catalytic entries. In present
INTRODUCTION
material science, to imitate the structure and function
Porphyrins and metalloporphyrins are an important
of natural porphyrins and to synthesize porphyrins and
class of macrocycle compounds that exist extensively
metalloporphyrins with different structures and functions
in nature and living bodies. The special chemical struc-
have become a very active study field. These mimetic
ture of porphyrins and metalloporphyrins affords them
porphyrins and metalloporphyrins are widely used in
unusual biological activity and physicochemical prop-
many scientific and technical fields, such as in medicine
erty, and they play very important roles in essential bio-
(photodynamic therapy), in material science (photoelec-
logical activities such as photoactive, oxygen-carrying,
tric materials), in biochemistry (molecular recognition),
in synthetic chemistry (biomimetic catalysis), in analyti-
cal chemistry (sensors), in energy science (solar energy
*Correspondence to: Baojiao Gao, email: gaobaojiao@126.
com, tel: +86 351-3921414, fax: +86 351-3922118
Copyright © 2010 World Scientific Publishing Company

236
B. GAO ET AL.
conversion), and in optical information technique (infor-
mation storage) [1–7].
porphyrin (ZnTPP), respectively, and the small molecular
metalloporphyrin was linked on the side chain of copoly-
mer P(4VP-co-St) via axial coordination reaction, result-
ing in the metalloporphyrin-functionalized polymers
CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St). The
spectral properties of the two functionalized polymers were
researched in depth. It is a particular and preferable route
to realize metalloporphyrin functionalization of polymers
that the polymers bearing ligands are allowed to coordinate
axially with metalloporphyrins. This synthesis route will
lead to a novel class of polymeric materials with optoelec-
tronic and redox properties. To our knowledge, no similar
studies have been reported. In fact, other methods of form-
ing porphyrin-polymer materials are increasingly being
developed. For example, Ikeda et al. made bis(imidazolyl)-
porphyrin to coordinate with cobalt ion to form a long poly-
meric array [19]; through electrostatic interactions, Xing
et al. made a cationic porphyrin and an anionic polymer to
form a complex in which a energy transfer phenomenon
can occur [20]; and Kokona et al. designed the binding of
basic peptides with anionic porphyrins, creating regulated
photoelectronically active biomaterials [21].
Natural porphyrins are always surrounded by some
natural macromolecules (for example, polypeptide). In this
special environment, natural porphyrins can fully play their
roles.At the same time, they are also protected by the macro-
molecular microenviroment, resulting in excellent chemical
stability [8]. For those small molecular porphyrins or metal-
loporphyrins mimetically synthesized, chemical stability is
lacking because there is no macromolecular microenviro-
ment surrounding them. Furthermore, those small molecular
porphyrins mimetically synthesized have no processability,
and they are used only as dopant. These factors limit the
applications of those synthesized small molecular porphy-
rins or metalloporphyrins greatly. For example, as porphy-
rins are used for preparing organic electroluminescence
materials, the doped porphyrins in the matrix not only eas-
ily produce concentrated quenching, but also heavily affect
the mechanical property of the material [9]. To overcome
the above drawbacks, it is an excellent strategy to realize
porphyrin functionalization of polymers. By adopting such
a method for porphyrins and metalloporphyrins, a special
microenvironment similar to polypeptide can be constructed
so as to enhance the chemical stability of porphyrins. At the
same time, it is beneficial to fully exert the property of por-
phyrins. In addition, because the polymers containing por-
phyrins have the processing properties, such as film-forming
and balling properties, it will extend the application range of
porphyrins and metalloporphyrins widely and will enhance
their application efficiency greatly. Therefore, it is significant
in material science to realize porphyrin functionalization of
polymers by well designing suitable chemical routes. How-
ever, so far, only a few studies on porphyrin functionalized
polymers have been reported [10, 11]. At present, in most
of the studies on porphyrin applications, the way of doping
small molecular porphyrins into matrix is adopted generally
[12, 13], for instance, doping-type nonlinear optical materi-
als [14] and doping-type membrane electrodes [15].
For natural enzymes containing metalloporphyrin which
acts as a cofactor, the axial coordination site, the fifth site,
is often occupied by N atom of amino acid residues. The
axial ligands have a strong influence on the spectral and
redox properties of metalloporphyrins. For reasons given,
chemists imitate the natural enzyme structure, prepare
axial coordination complexes of metalloporphyrins using
pyridine and imidazole as ligands, and research the effect
of the axial coordination ligands on the property of metal-
loporphyrins [16]. Experimental results show that the axial
coordination complexes of metalloporphyrins formed with
the ligands containing N, S or P atoms possess excellent
photophysical and photochemical characters as well as
chemical activity. These properties have important appli-
cation value in solar energy conversion, photodynamic
therapy and catalysis [17, 18]. In this work, the copolymer
of 4-vinylpyridine (4VP) and styrene (St), P(4VP-co-St),
was allowed to coordinate axially with cobalt tetra(para-
chlorophenyl)porphyrin (CoTCPP) and zinc tetraphenyl
EXPERIMENTAL
Materials and instruments
4-vinylpyridine (4VP, Acros Organics) was of ana-
lytical purity grade and was purified via vacuum distil-
lation before use; Styrene (St, Tientsin Denfen Chemical
Reagent Plant, Tientsin City, China) was of analytical
purity grade and was purified through vacuum distillation
prior to use; benzoyl peroxide (BPO, Beijing Chemical
Plant, Beijing, China) was of analytical purity grade and
was used as received; tetra(para-chlorophenyl)porphy-
rin (TCPP) and tetraphenyl porphyrin (TPP) was self-
synthesized through Alder method; toluene, chloroform
and N,N-dimethylformamide (DMF) as well as other
reagents used were all analytical pure commercial
reagents purchased from Chinese companies.
The instruments used in this study were as follows: Perki-
nElmer 1700 infrared spectrometer (FTIR, PerkinElmer
Company, USA), Unic UV/Vis-2602 spectrophotometer
(Unic Company, Shanghai, China), Hitachi F-2500 fluores-
cence spectrometer (Hitachi Company, Japan), Bruker drx
300 nuclear magnetic resonance spectrometer (1H NMR,
Bruker Company, Switzerland), Waters 2410 gel perme-
ation chromatograph (GPC, Waters Company, USA), and
Euro EA3000 element analyzer (EuroVector SpA, Italy).
Preparation of copolymer P(4VP-co-St)
Monomers 4VP and St as well as solvent toluene
with a given ratio were added into a four-necked flask
equipped with a mechanical agitator, a condenser and
an N2 inlet. The temperature was raised to 75 °C, and
initiator BPO (1% of the total monomer weight) was
Copyright © 2010 World Scientific Publishing Company
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REALIZING METALLOPORPHYRIN FUNCTIONALIZATION OF 4-VINYLPYRIDINE COPOLYMER
237
introduced. The solution polymerization was conducted
determination for CoTCPP-P(4VP-co-St) was not con-
ducted because of the paramagnetism of Co2+. (3) Deter-
mination of the bonding amount of metalloporphyrins in
the macromolecular axial coordination complexes. The
bonding amount of CoTCPP in CoTCPP-P(4VP-co-St)
macromolecules was determined with spectrophotometric
method. CoTCPP standard solutions of CHCl3 were pre-
pared, and the standard curve was plotted by determining
the absorbency at 528 nm. CoTCPP-P(4VP-co-St) sample
weighted accurately was dissolved in CHCl3, the absor-
bency at 552 nm (the characteristic absorption of CoTCPP
contained in CoTCPP-P(4VP-co-St) red shifts by 24 nm
with respect to CoTCPP) was determined, and the bond-
ing amount (g·g-1) of CoTCPP in CoTCPP-P(4VP-co-St)
was determined based on the standard curve. The bonding
amount of ZnTPP in ZnTPP-P(4VP-co-St) was also deter-
mined using the same method.
under N2 atmosphere with stirring at a constant tempera-
ture of 75 °C for 8 h. After ending the reaction, the copo-
lymer P(4VP-co-St) was precipitated out with petroleum
ether as precipitator, thoroughly washed with ethanol and
dried under vacuum to constant weight.
The copolymer P(4VP-co-St) was characterized suf-
ficiently: the infrared spectrum was determined with KBr
pellet method to confirm its structure, the N content was
determined with element analysis method to determine
the composition of the copolymer, and the molecular
weight of the copolymer was determined with GPC using
THF as mobile phase and polystyrene as standard sample.
The sample of the copolymer P(4VP-co-St) prepared and
used in this investigation had a 4VP unit content of 37%
(mol.%) and a relative molecular weight of 15100 (Mw).
Preparation of CoTPP and ZnTPP
Researching photophysical behaviors of CoTPP-
P(4VP-co-St) and ZnTPP-P(4VP-co-St)
0.5 g of TCPP was dissolved in 30 mL of DMF in a
three-necked flask. The content was heated to reflux tem-
perature (about 183 °C), and 1.25 g of cobalt chloride
was added. The mixture was allowed to be reacted for
100 min at the reflux temperature. The product mixture
was cooled to room temperature. Filtration yielded dark
red solid of CoTCPP. The solid CoTCPP was washed
with water repeatedly and dried. Similarly, solid ZnTPP
in brick red was also prepared according to the prepara-
tion process used for CoTCPP, except that zinc acetate
was used as a reaction reagent instead of cobalt chloride.
Measurement of electron absorption spectra: TPP,
CoTCPP and CoTCPP-P(4VP-co-St) solutions of CHCl3
were prepared and their UV-vis spectra were measured.
Similarly, the UV-vis spectra of ZnTPP and ZnTPP-
P(4VP-co-St) solutions of CHCl3 were also measured.
Measurement of fluorescence spectra: TPP, ZnTPP and
ZnTPP-P(4VP-co-St) solutions of CHCl3 were prepared
and the concentration of TPP unit in these solutions was
controlled at an order of magnitude of 10-5 M to avoid the
concentration quenching of TPP. The fluorescence emis-
sion spectra of these solution samples were determined
under excitation at 500 nm. The fluorescence spectrum
measurements for CoTCPP and CoTCPP-P(4VP-co-St)
solutions were not performed because they had no fluo-
rescence emission.
Preparation and characterization of axial coordina-
tion complexes
Preparation. 0.5 g of P (4VP-co-St) was added in a
three-necked flask of 100 mL containing 30 mL of CHCl3,
and the copolymer was dissolved. 1.5 unit of CoTCPP
(solid) based on the amount of 4VP unit was introduced
to the solution of P(4VP-co-St). The axial coordination
reaction was carried out at room temperature with stir-
ring for 24 h. At the end of the reaction, the product poly-
mer in red brown, macromolecular axial coordination
complex CoTCPP-P(4VP-co-St), was precipitated with
petroleum ether as precipitator, washed repeatedly with
petroleum ether until there was no CoTCPP in the filtrate
(detected with spectrophotometry), and dried. Similarly,
the macromolecular axial coordination complex ZnTPP-
P(4VP-co-St) in dark red was also prepared according to
the above procedure, except that ZnTPP was used as a
reaction reagent instead of CoTCPP.
Characterization. (1) Determination of FTIR spectrum.
The FTIR spectra of CoTCPP-P(4VP-co-St) and ZnTPP-
P(4VP-co-St) were determined by KBr pellet method, and
theirchemicalstructureswascharacterized.(2)Determina-
tion of 1H NMR. Using deuterated chloroform (CDCl3) as
solvent and tetramethylsilane (TMS) as internal standard,
1H NMR spectrum of ZnTPP-P(4VP-co-St) was recorded
and its structure was further confirmed. 1H NMR spectrum
RESULTS AND DISCUSSION
Axial coordination process of P(4VP-co-St) and
metalloporphyrins
The N atom of the side pyridine groups of P(4VP-
co-St) macromolecules contains lone-pair electron, and
the central cobalt ion, which has been coordinated by the
N atoms of porphyrin ring, has a still empty orbit. There-
fore, the side pyridine groups of P(4VP-co-St) macro-
molecules as the fifth ligand can coordinate to the cobalt
ion in the axial direction of the porphyrin ring plane. As a
consequence, CoTCPP is bonded on the side chains of the
copolymer P(4VP-co-St), and polymer CoTCPP-P(4VP-
co-St) is formed, namely, the copolymer P(4VP-co-St)
has been metalloporphyrin-functionalized. The axial
coordination process can be expressed schematically in
Scheme 1(A). For another metalloporphyrin-functionalized
polymer product, ZnTPP-P(4VP-co-St), there is a similar
coordination model shown in Scheme 1(B).
Copyright © 2010 World Scientific Publishing Company
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238
B. GAO ET AL.
Cl
Co
Cl
(A)
H2
C
H2
C
H C
2
H
C
N
N
CH
N
N
HC
Cl
Cl
+
N
P(4VP-co-St)
CoTCPP
H2
C
H2
C
H2C
H
C
CH
HC
N
Cl
Ph
N
N
Cl Ph
Co
Ph Cl
N
N
Ph Cl
CoTCPP-P(4VP-co-St)
(B)
H2
C
H2
C
H2C
H
C
N
N
N
N
CH
HC
Zn
+
N
P(4VP-co-St)
ZnTCPP
H2
C
H2
C
H2C
H
C
CH
HC
N
Ph
N
N
Ph
Zn
Ph
N
N
Ph
ZnTCPP-P(4VP-co-St)
Scheme 1. Schematic expression of the process to prepare CoTCPP-P(VP-co-St) and ZnTPP-P(VP-co-St)
Copyright © 2010 World Scientific Publishing Company
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REALIZING METALLOPORPHYRIN FUNCTIONALIZATION OF 4-VINYLPYRIDINE COPOLYMER
239
Characterization of CoTPP-P(4VP-co-St) and
ZnTPP-P(4VP-co-St)
small molecular metalloporphyrin, CoTCPP or ZnTPP,
has been produced, resulting in the formation of the
macromolecular axial coordination complex, CoTCPP-
P(4VP-co-St) or ZnTPP-P(4VP-co-St).
IR spectra. The spectra of P(4VP-co-St), CoTCPP-
P(4VP-co-St)andZnTPP-P(4VP-co-St)weredetermined,
respectively. In the spectrum of CoTCPP-P(4VP-co-St),
except those characteristic absorption bands of the copo-
lymer P(4VP-co-St) such as the skeletal vibration absorp-
tion of benzene ring at 1600 cm-1 for St units and the
vibrationabsorptionofC=Nbondsofsidepyridinegroups
at 1556 cm-1 for 4VP units, the characteristic absorption
bands of cobalt porphyrin appear at 1360, 1005, 802 and
708 cm-1. Among them, the band at 1005 cm-1 was attrib-
uted to the vibration absorption of N-Co bond. Besides,
for the side pyridine groups of the copolymer P(4VP-
co-St), the stretching vibration absorption of C=N bond
has shifted from 1556 cm-1 to 1527 cm-1. This red shift
is caused by the coordination of N atoms of the side
pyridine groups of P(4VP-co-St) with the central cobalt
ions. Similarly, in the spectrum of ZnTPP-P(4VP-co-St),
the characteristic absorption bands of zinc porphyrin
occur at 1350, 1066, 998, and 802 cm-1. Among them,
the bands at 1066 and 998 cm-1 are ascribed to the vibra-
tion absorption of N-Zn bond. Comparing the spectrum
of CoTCPP-P(4VP-co-St) or ZnTPP-P(4VP-co-St) with
that of P(4VP-co-St), the above spectrum variations con-
firmed that the coordination reaction between the side
pyridine groups of copolymer P(4VP-co-St) and the
1H NMR spectrum of ZnTPP-P(4VP-co-St). Figure
1 shows the 1H NMR spectrum of ZnTPP-P(4VP-co-St).
In this spectrum, all signals of the various protons of
ZnTPP-P(4VP-co-St) including the proton signals of
copolymer P(4VP-co-St) and metalloporphyrin ZnTPP
are displayed, and these protons are denoted in Fig. 1.
The signals of the various protons in the copolymer
P(4VP-co-St) of ZnTPP-P(4VP-co-St) are shown in Fig.
1 as follows: the chemical shifts at 0.8558, 0.8723 and
0.889 ppm (>CH-, a), the peaks at 1.2523 and 1.2777
ppm (-CH2-, b) and at 1.7297 ppm (-CH2-, c), the peak at
6.2641 ppm (-CH=N-, d), the peaks at 8.1318 and 8.1482
ppm (=CH- of pyridine, h), and the peaks 7.2519 and
7.2523 ppm (=CH- of benzene ring, e). Besides, for the
copolymer P (4VP-co-St), the signals of those protons
(k and l) of pyridine groups of 4VP unit which have par-
ticipated in the axial coordination are shifted to the left
owing to the axial coordination, and cannot be observed
due to overlapping with those singles of benzene ring
protons in 7–8 range.
The signals of the various protons of ZnTPP of ZnTPP-
P(4VP-co-St) are shown in Fig. 1 as follows: the peaks at
7.6528, 7.6717 and 7.6964 ppm (meta-8H and para-4H
of four benzene rings, f and g), the peaks at 8.1318 and
8.1482 ppm (ortho-8H of four benzene
rings, i) and the peak at 8.8492 ppm
(8H of four pyrrole rings, j).
1
The above data of H NMR spec-
trum once again prove that the axial
coordination reaction between the
copolymer P (4VP-co-St) and the zinc
porphyrin ZnTPP has occurred, and
that metalloporphyrin-functionalized
polymer, ZnTPP-P(4VP-co-St), has
been obtained.
Progress of axial coordination reac-
tion with time
The same copolymer P (4VP-co-St)
samples were used to axially coordi-
nate with CoTCPP and ZnTPP, respec-
tively. Figure 2 shows the variation
curve of the metalloporphyrin bond-
ing amount (BA, the definition of the
bonding amount (g·g-1) of metallopor-
phyrin in the macromolecular axial
coordination complexes can be found
in the Characterization section, but
then BA in Fig. 2 is transferred into
the form of the molar ratio of porphy-
rin to 4-vinylpyridine unit of P (4VP-
co-St), mol.mol-1, in order to observe
Fig. 1. 1H NMR spectrum of ZnTPP-P(4VP-co-St)
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B. GAO ET AL.
Fig. 2. Variation of bonding degree of CoTCPP or ZnTPP with
time
Fig. 3. Electronic absorption spectra of TCPP, CoTCPP and
CoTCPP-P(4VP-co-St) in CHCl3. Conc. of TCPP, CoTCPP and
CoTCPP contained in CoTCPP-P(4VP-co-St) = 4.37 × 10-5 M
the variation rule more clearly) with reaction time. It
can be seen that before 120 min, the bonding amount of
the metalloporphyrins increases rapidly with time, after
120 min, the variation of the bonding amount becomes
slow, and after 4 h, it almost does not vary anymore.
Here, the bonding amounts of CoTCPP and ZnTPP on
the macromolecules of P(4VP-co-St) are 0.66 mol.mol-1
and 0.73 mol.mol-1, respectively, and these amounts are
lower than the theoretical values (1 mol.mol-1). In fact,
the axial coordination reaction is easy to be carried out, so
at the beginning stage, the bonding amounts of CoTCPP
or ZnTPP increase sharply. However, as enough CoTCPP
or ZnTPP are bound to the side chains of the copolymer
P(4VP-co-St), bulky porphyrin rings will produce a
larger static hindrance, and this obstacle will enable the
axial coordination between CoTCPP or ZnTPP and the
side pyridine chains of P(4VP-co-St) to become more
and more difficult, leading to no variation in the bonding
amount after a certain period of time. Apparently, this is
a negative polymer effect.
As the central position of the porphyrin ring is occu-
pied by a metal ion and metalloporphyrin forms, the
metal ion accepts the lone-pair electrons of the N atoms
of the porphyrin ring, and the electrons of metal ion are
denoted to the porphyrin molecule, forming the delo-
calized π bond. The delocalized π bond will affect the
electron density of the metalloporphyrin [22]. How
the delocalized π bond changes the electron density of the
metalloporphyrin is dependant on the metal ion structure.
For cobalt porphyrin (Co2+ has d7 electron distribution),
its delocalized π bond decreases the average electron den-
sity of the metalloporphyrin, which increases the energy
available for electron transition. As a consequence, a blue
shift of the Soret bands occurred [22]. After four N atoms
in porphyrin ring coordinate with the central metal ion,
the D4h symmetry of the metal porphyrins forms instead
of the D2h symmetry of free-base porphyrins, and the
symmetry enhancement leads to degeneration of the Q
bands. For Co porphyrin, the Q band has only one peak
at 528 nm. [23].
The adsorption spectra of the functional macromol-
ecule CoTCPP-P(4VP-co-St) with that of CoTCPP have
some similar points, such as the decrease in the number
of Q bands and the blue shift of the Soret band relative
to TCPP. However, there are some important differences.
Different amounts of the copolymer P(4VP-co-St) sample
were added to the CoTCPP solution with a concentration
of 4.37 × 10-5 M and with a given volume, respectively,
and the axial coordination reactions were allowed to be
carried out for 4 h. The electronic absorption spectra
for these various reaction systems are shown in Fig. 4.
As shown, the absorbance of the Q band at 528 nm
decreases gradually when the concentration of the copo-
lymer increased, and a new peak at 552 nm appears and
its intensity increases continually. At the same time, there
appears a shoulder peak at 593 nm. An isosbestic point at
541 nm also appears clearly. The above-described varia-
tions of the electronic absorption spectra suggest that an
Electronic adsorption spectra of CoTCPP-P(4VP-
co-St) and ZnTPP-P(4VP-co-St)
The electronic adsorption spectra of TCPP, CoTCPP
and CoTCPP-P (4VP-co-St) are presented in Fig. 3. For
porphyrins, there are two energy levels with adjacent
energy on HOMO orbital, a1µ(π) and a2µ(π), and there
is a pair of degenerate energy levels, eg(π*), on LUMO
orbital. For TCPP, the band at 432 nm is assigned to the
Soret band arising from the transition of a1µ(π)→ eg(π*),
and the other four bands at 515, 550, 590 and 660 nm
are attributed to the Q bands corresponding to the transi-
tion of a2µ(π) → eg(π*) as shown in Fig. 3. When the Co
ion was inserted into the porphyrin core and CoTCPP is
formed, the Soret band blue shifts from 432 to 409 nm,
and the Q bands degenerate from 4 peaks to 1 peak at
528 nm. For these experimental results, some reasonable
interpretation can be given as follows.
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 240–243

REALIZING METALLOPORPHYRIN FUNCTIONALIZATION OF 4-VINYLPYRIDINE COPOLYMER
241
bands decreases from 4 to 2. For zinc porphyrin (Zn2+ has
d10 electron distribution), the delocalized π bond of the
Zn porphyrin increases the average electron density of
the metalloporphyrin and decreases the energy for elec-
tron transition, leading to a red shift in the Soret band
[19]. The two Q bands appear at 548 nm (the Q band with
high energy [24], i.e. Qβ band) and at 603 nm (the Q band
with low energy, i.e. Qα band).
Different amounts of the copolymer P(4VP-co-St)
sample were added to the ZnTPP solution with a concen-
tration of 4.37 × 10−5 M and with a given volume, respec-
tively, and the axial coordination reactions were also
allowed to be carried out for 4 h. The electronic absorp-
tion spectra for these various reaction systems are shown
in Fig. 6. It can be observed clearly that the spectrum
Fig. 4. Spectral evolution during addition of P(4VP-co-St) to
of ZnTPP is transformed gradually into that of ZnTPP-
P(4VP-co-St) when the amount of copolymer P(4VP-
co-St) increases. Comparing the adsorption spectrum of
ZnTPP-P(4VP-co-St) with that of ZnTPP, although there
are some similar points such as two peaks of the Q bands
and the red shift of the Soret band relative to TPP, there
are some differences. For example, the Q band of ZnT-
PP-P(4VP-co-St) appears at 564 nm, and red-shifts by
16 nm with respect to 548 nm of ZnTPP, displaying the
characteristic of the axial coordination complex.
CHCl3 solution of CoTPP. Conc. of CoTCPP = 4.37 × 10-5 M.
Conc. of P (4VP-co-St): (a) 2.67 × 10-5 M; (b) 10.86 × 10-5;
(c) 21.36 × 10-5; (d) 53.6 × 10-5; (e) 486 × 10-5; (f) 900 × 10-5
axial coordination complex has been formed, and that it
is the macromolecule CoTCPP-P(VP-co-St). Obviously,
the Q band of CoTCPP-P(VP-co-St) is at 552 nm, and
red-shifts by 24 nm with respect to CoTCPP, which is
characteristic of the axial coordination complex. The
N atoms of the side pyridine group of P(VP-co-St) are
electron-rich. When the axial coordination complex
CoTCPP-P(VP-co-St) is formed, a portion of the charge
of the N atom of the axial ligand, pyridine group, will
transfer to the porphyrin ring through the metal ion. This
will lead to an increase of the electron density of the
metalloporphyrin ring, and will reduce the gap between
a2µ(π) and eg(π*) energy levels [22], resulting in the red
shift of the Q band.
Fluorescence emission spectrum of ZnTPP-P(4VP-
co-St)
Porphyrins have the behavior of double fluorescence
emissions. The fluorescence emission caused by the tran-
sition of S2→S0 (from the second singlet-excited state to
the ground state) is at about 440 nm, corresponding to
the Soret band in the adsorption spectrum, the so-called
Soret emission band. The fluorescence emission arising
from the transition of S1→S0 (from the first excited state
to the ground state) is at about 660 nm, corresponding to
The electronic adsorption spectra of ZnTPP and ZnT-
PP-P(4VP-co-St) are presented in Fig. 5. In contrast with
CoTPP, after TPP is transformed to ZnTPP, the Soret band
red-shifts from 427 nm to 430 nm, and the number of Q
Fig. 6. Spectral evolution during addition of P(4VP-co-St) to
CHCl3 solution of ZnTPP. Conc. of ZnTPP = 4.33 × 10-5 M.
Conc. of P (4VP-co-St): (a) 2.67 × 10-5 M; (b) 5.34 × 10-5;
(c) 21.36 × 10-5; (d) 53.4 × 10-5; (e) 98.06 × 10-5; (f) 110 × 10-5
Fig. 5. Electronic absorption spectra of TPP, ZnTPP and
ZnTPP-P(4VP-co-St) in CHCl3. Conc. of TPP, ZnTPP and
ZnTPP contained in ZnTPP-P(4VP-co-St) = 4.37 × 10-5 M
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 241–243

242
B. GAO ET AL.
Fig. 8. Variation of fluorescence emission of ZnTPP-P(4VP-
co-St) during axial coordination process. Conc. of ZnTPP =
4.33 × 10-5 M; excitation at 550 nm
Fig. 7. Fluorescence emission spectra of TPP, ZnTPP and ZnT-
PP-P(4VP-co-St) in CHCl3. Conc. of TPP, ZnTPP and ZnTPP
contained in ZnTPP-P(4VP-co-St) = 4.33 × 10-5 M
the Q band in the adsorption spectrum, the so-called Q
emission band. Because the internal conversion of S2→S1
is very rapid [25], the Soret emission band is very weak,
so we will mainly discuss the Q emission band.
Solutions of TPP, ZnTPP and ZnTPP-P(4VP-co-St)
with an identical TPP concentration were prepared using
CHCl3 as solvent. Their fluorescence emission spectra
were measured with an excitation wave at 550 nm, and
are shown in Fig. 7. The Q emission band of TPP appears
at 653 nm, but those of ZnTPP appear at 602 nm and at
650 nm, exhibiting an obvious blue shift. This is consis-
tent with what was reported in literature [23, 26]. The
symmetry of the porphyrin was enhanced after incorpo-
ration of Zn2+, and the LUMO eg energy was increased,
resulting in the blue shift of the emission band.
Compared with the fluorescence emission spectrum
of ZnTPP, the emission bands of ZnTPP-P(4VP-co-St)
red-shift from 602 and 650 nm to 612 and 656 nm. The
possible reason for this is that the charge of the lone-
pair electrons of N atoms of the pyridine ligands of
ZnTPP-P(4VP-co-St) transfers to the metalloporphyrin
rings through the central metal ions, Zn2+. It will lead to
a reduction of the gap between the HOMO and LUMO
orbits, resulting in the red shift of the Q emission band
[25]. This once again displays the character of the axial
coordination complex.
Fig. 9. Plot of Q band at 612 nm vs. bound amount of ZnTPP
for ZnTPP-P(4VP-co-St). Conc. of ZnTPP = 4.33 × 10-5 M;
excitation at 550 nm
612 nm as a function of the bonding amount (BA) of
ZnTPP is shown in Fig. 9. The possible reason for that
variation is as follows. As the bonding density of ZnTPP
on the side chains of the copolymer P(4VP-co-St) devel-
ops to a certain extent, the energy transfer [27, 28]
between the adjacent zinc porphyrin units on one and
the same macromolecule chain will occur, and a slightly
static quenching phenomenon is produced possibly.
The CHCl3 solutions of the macromolecular axial
coordination complexes were prepared using different
ZnTPP-P(4VP-co-St) samples that have different bonding
amounts of ZnTPP; the concentration of the copolymer
P(4VP-co-St) in these solutions is the same. The fluores-
cence emission spectra of these solutions were determined
as shown in Fig. 8. It was found that the intensity of the
Q emission bands at 612 nm for these solution samples
first rises and then declines along with the increase of the
bonding amount (mol.mol-1) of ZnTPP although the vari-
ation extent is very small. In order to display this varia-
tion more clearly, the intensity of the Q emission bands at
CONCLUSION
In this investigation, the metalloporphyrin-functionaliza-
tion of the copolymer P(4VP-co-St) was realized success-
fully via the axial coordination reaction between the side
pyridine groups of P(4VP-co-St) and CoTPP or ZnTPP.
The prepared macromolecular axial coordination complex
CoTPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St) have the
spectral properties of the small molecular metalloporphy-
rins. At the same time, they exhibit the characteristics of
the axial coordination complexes. Due to the affording
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 242–243

REALIZING METALLOPORPHYRIN FUNCTIONALIZATION OF 4-VINYLPYRIDINE COPOLYMER
243
electron property of the N atom of the pyridine groups, the
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red shifts of the absorption bands of CoTPP-P(4VP-co-St)
and ZnTPP-P(4VP-co-St) have occurred to a great extent,
and the red shift of the emission band of ZnTPP-P(4VP-
co-St) can also be observed. For CoTPP-P(4VP-co-St) and
ZnTPP-P(4VP-co-St), some polymer effects were found:
(1) For the axial coordination reaction, the bonding degree
of the metalloporphyrins on the side chains of the copoly-
mer P(4VP-co-St) has a limit, (2)When the bonding density
of ZnTPP on the macromolecules of ZnTPP-P(4VP-co-St)
reaches a certain extent, the energy transfer between the
adjacent ZnTPP units on one and the same macromolecule
chain will occur, leading to slightly static quenching and
weakening of the fluorescence emission.
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