Photophysical and photochemical behavior of electrospun fibers of a polyurethane polymer chemically linked to lutetium carboxyphenoxy phthalocyanine

Article abstract of DOI:10.1039/c1nj20126c

A phthalocyanine complex of lutetium substituted with four peripherally substituted 4-carboxyphenoxy groups was synthesized using cyclotetramerisation reaction. Its structure was elucidated using conventional spectroscopic methods and elemental analysis. The spectral behavior of the complex was studied in DMF solution and in a solid polyurethane fiber matrix. The UV-Visible spectrum showed a red shift in its Q-band maximum absorption within the fiber as compared to that in solution. The triplet quantum yield in DMF was determined to be 0.51 with a lifetime of 2.7 μs and a singlet oxygen quantum yield of 0.33 with a lifetime of 19.85 μs in the same solvent. The functionalized phthalocyanine fiber could be a promising fabric material for applications such as self-disinfecting in wound dressing. A method based on the conversion of ADMA was used to estimate the singlet oxygen quantum yield of the Pc in the hybrid fiber. An estimated singlet oxygen quantum yield value of 0.11 in aqueous medium was obtained. The fluorescence quantum yield of the Pc was found to be 0.01 with a lifetime of 3.20 ns in DMF.

Full text of DOI:10.1039/c1nj20126c

New Journal of Chemistry
A journal for new directions in chemistry
www.rsc.org/njc
Volume 35 | Number 8 | August 2011 | Pages 1565–1760
ISSN 1144-0546

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Cite this: New J. Chem., 2011, 35, 1588–1595
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PAPER
Photophysical and photochemical behavior of electrospun fibers
of a polyurethane polymer chemically linked to lutetium
carboxyphenoxy phthalocyanine
Ruphino Zugle, Christian Litwinski, Nelson Torto and Tebello Nyokong*
Received (in Montpellier, France) 16th February 2011, Accepted 18th April 2011
DOI: 10.1039/c1nj20126c
A phthalocyanine complex of lutetium substituted with four peripherally substituted
4
-carboxyphenoxy groups was synthesized using cyclotetramerisation reaction. Its structure
was elucidated using conventional spectroscopic methods and elemental analysis. The spectral
behavior of the complex was studied in DMF solution and in a solid polyurethane fiber matrix.
The UV-Visible spectrum showed a red shift in its Q-band maximum absorption within the fiber
as compared to that in solution. The triplet quantum yield in DMF was determined to be
0
.51 with a lifetime of 2.7 ms and a singlet oxygen quantum yield of 0.33 with a lifetime
of 19.85 ms in the same solvent. The functionalized phthalocyanine fiber could be a promising
fabric material for applications such as self-disinfecting in wound dressing. A method based on
the conversion of ADMA was used to estimate the singlet oxygen quantum yield of the Pc in the
hybrid fiber. An estimated singlet oxygen quantum yield value of 0.11 in aqueous medium
was obtained. The fluorescence quantum yield of the Pc was found to be 0.01 with a lifetime
of 3.20 ns in DMF.
1
6,17
Introduction
the phthalocyanine being maintained in the solid fiber core.
7
Mosinger and co-workers reported that a ZnPc anchored on
a polyurethane polymer fiber led to a red shifted Q-band
compared with those recorded in solution. The theory of
molecular exciton is widely used to rationalize the differences
Phthalocyanines have applications in a wide variety of fields
3
1
including as dyes and pigments, in catalysts, deodorants,
2
4
5
photovoltaic cells and photodynamic therapy (PDT). In
applications such as in PDT, phthalocyanines are usually in
solution. However, some applications of phthalocyanines are
between the optical spectra in the liquid phase and those in the
18–20
solid state.
It is therefore important to determine precisely
6
preferable in their solid state as in read–write compact discs
or when incorporated into solid support systems as in nanofabrics.
the electronic absorption spectral behavior of phthalocyanines
within such solid support systems.
7
Such support systems offer comparably better advantages such
as ease of recovery of the phthalocyanine during photosensitized
Equally important is the fact that the inherent photophysical
and photochemical properties of the phthalocyanines can be
altered when on supports since they are constrained within the
environment of a polymeric matrix and therefore the photo-
activity of the resulting material cannot be directly extra-
8
reactions as well as helping in the photodynamic targeting of
the photosensitiser to specific sites such as blood components
9
using biocompatible supports. Support systems such as
1
0
11
12
amberlite, zeolite and polycrystalline titanium dioxide
have been reported for catalysis.
19
polated from the known behavior in a solution.
In this work, we report for the first time on the synthesis,
characterization as well as spectral, photophysical and photo-
sensitization behavior of 2(3), 9(10), 16(17), 23(24)-(tetracarboxy-
phenoxyphthalocyaninato) lutetium(III) acetate (LuTCPPc) in
solution and in a solid polyurethane (PUR) polymer fiber core.
Lutetium was chosen as a central metal because of its diamagnetic
nature as well as its large size that could enhance intersystem
crossing to the triplet excited state of the phthalocyanine
complex. This could then possibly lead to a large singlet
oxygen quantum yield upon interaction with ground state
molecular oxygen, which is implicated in photocatalysed
reactions. The ring substituent was chosen to allow for chemical
linking of the amino group of the polyurethane (PUR) fiber
Recently, new polymeric materials with photodynamic activity
have been employed for the fabrication of intraocular lenses
1
3,14
having bactericidal surfaces
1
and nanofabrics for wound
Such self-disinfecting nanofabrics are equally
5
dressing.
promising materials for water filters and for other hetero-
geneous photo-sensitized catalytic conversions.
Incorporation of phthalocyanines into electrospun solid
polymer fibers has been reported with the functionality of
Department of Chemistry, Rhodes University, Grahamstown 6140,
South Africa. E-mail: t.nyokong@ru.ac.za; Fax: +27 46 6225109;
Tel: +27 46 6038260
1
588 New J. Chem., 2011, 35, 1588–1595
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

with the carboxylic acid group of LuTCPPc. This is the first
time that a phthalocyanine is chemically linked to a polymer
for the formation of electrospun fibers. The aim is to develop
fibers modified with phthalocyanines for use in photocatalytic
reactions such as degradation of pollutants. The fibers containing
phthalocyanines are expected to be re-used for these types of
applications.
were treated using Eva (evaluation curve fitting) software.
Baseline correction was performed on each diffraction pattern
by subtracting a spline fitted to the curved background and the
full-width at half-maximum values used in this study were
obtained from the fitted curves.
Time resolved phosphorescence of singlet oxygen at 1270 nm
was used to determine the singlet oxygen quantum yield of
LuTCPPc in DMF. The dynamic phosphorescence decay of
1
singlet oxygen ( O ) was demonstrated using its phosphorescence
2
Experimental
at 1270 nm. For these studies an ultra sensitive germanium
detector (Edinburgh Instruments, EI-P) combined with a 1000 nm
long pass filter (Omega, RD 1000 CP) and a 1270 nm band-pass
Materials
The following chemicals were purchased from SAARCHEM;
1
filter (Omega, C1275, BP50) was used to detect O
2
phosphores-
1
-pentanol, n-hexane, dimethylsulfoxide (DMSO), N,N-dimethyl-
formamide (DMF). Zinc phthalocyanine (ZnPc), 1,8-diazabicyclo-
5.4.0]undec-7-ene (DBU), dicyclohexylcarbodiimide (DCC)
9%, anthracene-9,10-bis-methylmalonate (ADMA), polyurethane
cence under the excitation using a Quanta-Ray Nd:YAG laser
providing 400 mJ, 9 ns pulses of laser light at 10 Hz pumping a
Lambda-Physik FL3002 dye (Pyridine 1 dye in methanol),
with a pulse period of 7 ns and a repetition rate of 10 Hz. The
near-infrared phosphorescence of the samples was focused
onto the germanium detector by a lens (Edmund, NT 48–157)
with the detection direction perpendicular to the excitation
laser beam. The detected signals were averaged with a digital
[
9
ꢀ
3
7
(PUR, density 1.4 g cm , estimated average molecular weight ),
potassium carbonate, 4-hydroxybenzoic acid, lutetium(III) acetate
and sodium azide 99% were from Sigma Aldrich. 4-Nitro-
phthalonitrile (1) and 4-(4-carboxyphenoxy) phthalonitrile (2)
21–23
were synthesized according to literature procedures.
Column
oscilloscope (Tektronics, TDS 360) to show the dynamic decay
1
of O
chromatography was performed on silica gel 60 (0.04–0.063 mm)
and preparative thin layer chromatography was performed on
2
. The data obtained were analysed using ORIGIN Pro 8
software. The singlet oxygen phosphorescence signal was
compared with the ZnPc standard in the determination of
singlet oxygen quantum yield of LuTCPPc in DMF solution.
Fluorescence excitation and emission spectra were recorded
on a Varian Cary Eclipse spectrofluorimeter. Fluorescence
lifetimes of the LuTCPPc were measured using a time correlated
single photon counting (TCSPC) setup (Fluo Time 200,
Picoquant GmbH) with a diode laser as an excitation source
(LDH-P-670 driven by PDL 800-B, 670 nm, 20 MHz repetition
rate, Picoquant GmbH). Fluorescence was detected under the
magic angle with a peltier cooled photomultiplier tube (PMT)
(PMA-C 192-N-M, Picoquant GmbH) and integrated electronics
(PicoHarp 300E, Picoquant GmbH). A monochromator with
a spectral width of about 4 nm was used to select the required
emission wavelength. The response function of the system,
which was measured with a scattering Ludox solution (DuPont),
had a full width at half-maximum (FWHM) of about 300 ns.
The ratio of stop to start pulses was kept low (below 0.05) to
ensure good statistics. The luminescence decay curve was
measured at the maximum of the emission peak. The data
were analyzed with the program FluoFit (Picoquant GmbH).
silica gel 60 P F254
.
Equipment
Infrared (IR) spectra were recorded on a Perkin-Elmer Fourier
transform–IR (FT-IR) SPECTRUM 2000 spectrometer using
potassium bromide (KBr) disks. UV-Vis absorption spectra
were recorded on a Cary 500 Vis/NIR spectrophotometer.
Samples of LuTCPPc for solid state UV-Vis spectra were
prepared by depositing a solution of the LuTCPPc in DMF
on a glass plate and allowing it to dry. The modified fiber
was directly placed on the glass plate and the spectra recorded.
1
H-NMR spectra were recorded on a Bruker AMX600 MHz
in deuterated DMSO. Microanalyses were performed using a
Vario-Elementar Microcube ELIII. Mass spectral data were
recorded on an ABI Voyager De-STR Maldi TOF instrument
at University of Stellenbosch, South Africa, using 2,5-dihydroxy
benzoic acid as a matrix. Scanning electron microscope (SEM)
images were obtained using a JEOL JSM 840 scanning
electron microscope.
Irradiations for singlet oxygen studies were performed using
a General Electric Quartz lamp (300 W), 600 nm glass (Schott)
and water filters, to filter off ultra-violet and far infrared
radiations respectively. An interference filter, 670 nm with a
band of 40 nm, was placed in the light path just before the cell
containing the sample.
2
4
The support plane approach was used to estimate the errors
of the decay times.
Triplet state yields and lifetimes
The triplet quantum yield was determined for LuTCPPc in
2
5
A Bruker Vertex 70-Ram II Raman spectrometer (equipped
with a 1064 nm Nd:YAG laser and a liquid nitrogen cooled
germanium detector) was used to collect Raman data.
X-Ray powder diffraction patterns were recorded on a
DMF using a comparative method, eqn (1), with ZnPc as the
standard.
Std
T
DATe
Std
FT ¼ FT
ð1Þ
Std
Bruker D8 Discover equipped with a proportional counter,
˚
DAT eT
a
using Cu–K radiation (l = 1.5405 A, nickel filter). Data were
Std
collected in the range from 2y = 51 to 601, scanning at
T T
where DA and DA
are the changes in the triplet state
absorbances of LuTCPPc and the standard, respectively.
ꢀ
1
1
a slit width of 6.0 mm. Samples were placed on a zero back-
1 min with a filter time-constant of 2.5 s per step and
Std
eT and eT are the triplet state molar extinction coefficients
Std
for LuTCPPc and the standard, respectively. FT is the triplet
ground silicon wafer slide. The X-ray diffraction (XRD) data
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1588–1595 1589

Std
T
quantum yield for the standard, ZnPc (F
= 0.58 in
using aqueous solutions of ADMA (absorbance = 0.54 at
380 nm). The modified fiber (PUR/LuTCPPc) was suspended
as small pieces within the solution containing ADMA. The
solution was irradiated using the set-up described above. The
ADMA quantum yield FADMA was calculated using eqn (5)
and the extinction coefficient of AMDA in water, log(e) = 4.1
2
6
DMF). The triplet lifetime was determined by exponential
fitting of the kinetic curve using the program ORIGIN Pro 8.
Fluorescence quantum yield
The fluorescence quantum yield (F ) was determined in DMF
F
2
by the comparative method, eqn (2)
7
31
at 380 nm.
FAStdn2
ðC0 ꢀ CtÞVR
Std
FF ¼ FF
FStdAn2
ð2Þ
FADMA ¼
ð5Þ
Iabst
Std
where C and C are the ADMA concentrations prior to and
0
F and FStd are the areas under the fluorescence emission
curves of LuTCPPc and the standard, respectively. A and AStd
are the respective absorbances of the sample and standard
at the excitation wavelength. The same solvent was used
for the sample and standard. Unsubstituted ZnPc in DMF
t
after irradiation, respectively; VR is the solution volume; t is
the irradiation time per cycle and Iabs is defined by eqn (6).
aAI
NA
Iabs ¼
ð6Þ
Std
28
F
(F = 0.3) was employed as the standard. Both the sample
ꢀ
A(l)
where a = 1–10
the irradiation wavelength, A is the irradiated area (2.5 cm ),
, A(l) is the absorbance of the sensitizer at
2
and standard were excited at the same wavelength of 612 nm
and emission spectra were recorded from 630–790 nm. The
absorbances of the solutions at the excitation wavelength were
about 0.05 to avoid any inner filter effects.
1
6
ꢀ2 ꢀ1
s ) and
I is the intensity of light (4.52 ꢂ 10 photons cm
is Avogadro’s constant. The absorbance used for eqn (6) is
N
A
that of the LuTCPPc on the fiber (not in solution) measured as
described above. The light intensity measured refers to the
light reaching the spectrophotometer cells, and it is expected
Singlet oxygen quantum yields
Time resolved phosphorescence of singlet oxygen at 1270 nm
was used to determine the singlet oxygen quantum yield of
LuTCPPc in DMF. Eqn (3) as theoretically described in the
D
that some of the light may be scattered, hence the F value of
the LuTCPPc in the fiber is an estimate.
2
9
D
The singlet oxygen quantum yield (F ) was calculated using
32
eqn (7)
literature was employed.
tD
tT ꢀ tD
where, I(t) is the phosphorescence intensity of O
½eꢀ
t=tT
ꢀ eꢀt=tD
ꢁ
ð3Þ
IðtÞ ¼ B
1
1
1 kd
1
¼
þ
ð7Þ
FADMA
FD FD ka ½ADMAꢁ
1
2
at time t,
1
t
D
is the lifetime of O
2
phosphorescence decay, t
T
is the triplet
state lifetime of the standard or sample and B is a coefficient
where kd is the decay constant of singlet oxygen in the
respective solvent and k is the rate constant of the reaction
a
1
involved in sensitizer concentration and O
1
2
quantum yield.
of LuTCPPc in DMF,
of ADMA with O ( D ). The intercept obtained from the plot
2
g
1
The singlet ( O
2
) quantum yield, F
was then determined using eqn (4):
D
of 1/FADMA versus 1/[ADMA] gives FD.
Synthesis of LuTCPPc (Scheme 1)
BAStd
BStdA50
Std
FD ¼ FD
ð4Þ
A mixture of anhydrous lutetium(III) acetate (134 mg, 0.38 mmol)
and 4-(4-carboxyphenoxy)phthalonitrile (2) (981 mg, 0.76 mmol)
in 1-pentanol (2.5 ml) was refluxed for 7 h under a nitrogen
atmosphere using DBU as a catalyst. After cooling, the crude
product was precipitated with n-hexane, filtered and washed
with excess n-hexane and then dried in air. Column chromato-
graphy (silica gel) was employed using DMF as the eluting
Std
where F
standard ZnPc (F
coefficients involved in sensitizer concentration and O
D
is the singlet oxygen quantum yield for the
Std
30
Std
D
= 0.56 in DMF). B and B refer to
1
2
quantum
Std
yield for the sample and standard respectively; and A and A
to the absorbances of the sample and standard, respectively, at
the excitation wavelength.
ꢀ1
solvent to purify the product. Yield: 10%. IR [KBr, n/cm
]
A chemical method was employed for the estimation of
singlet oxygen quantum yield determination of the LuTCPPc
modified fiber in water using ADMA as a quencher in water. The
748, 802, 862, 880, 969, 1024 (Pc skeleton), 1248, 1324, 1482
(C–O–C), 1656.17 (CQO), 2855.69, 2926.58 (C–H, aromatic),
3503.79 (O–H). UV-Vis (DMF): lmax/nm (log e) 345 (5.02),
D
singlet oxygen quantum yield (F ) determinations were carried out
35 8
610 (4.61), 678 (5.31), calcd for C62H N O14Lu; C 57.68,
Scheme 1 Synthetic route for LuTCPPc.
1
590 New J. Chem., 2011, 35, 1588–1595
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

1
H 2.73, N 8.68. Found C 57.23, H 3.10, N 9.04%; H NMR
(
DMSO-d
6
): d, ppm 10.81 (4, s carboxylic acid), 8.00–8.10
(
acetate-CH ). MS (MALDI-TOF) (m/z): calc. 1291; found:
12, m, Pc-H), 6.58–7.87 (16 m, Phenyl-H), 2.09 (3-H, s,
3
+
293 [M + 2H ].
1
Preparation of PUR/LuTCPPc and fibers
A solution of LuTCPPc was prepared by dissolving 20 mg in
1
0 ml of DMF. Then 0.5 g of dicyclohexylcarbodiimide (DCC)
was added and the resulting solution stirred for four days. This
was done to enhance the electrophilicity of carbonyl of the
carboxylic acid functional group for amide bond formation
with the polyurethane polymer. In order to prepare 7.5%
polymer solution, 0.75 g of polyurethane was then added to
the solution containing LuTCPPc and stirred for a further
four days and the resulting solution electro-spun into fibers
using the following conditions. The voltage was set at +20 kV
and ꢀ10 kV with the flow rate of the solution set at 1 ml hꢀ
and the distance between the cathode (static fiber collection
point) and anode (tip of capillary needle) was 15 cm.
1
Fig. 2 Fluorescence decay profile of LuTCPPc in DMF.
are similar and not affected by excitation in DMF. The Stokes
34
shift of 11 nm is typical of MPc complexes.
Results and discussions
Fluorescence quantum yield and lifetimes. The fluorescence
quantum yield of LuTCPPc was determined to be 0.01 in
Characterization of LuTCPPc
DMF using a comparative method. The low Q value could be
F
Spectroscopic characterization. The LuTCPPc was charac-
1
terized by several techniques including H NMR, mass, IR
attributed to the heavy atom effect of the central metal, which
encourages intersystem crossing to the triplet state. A similar
argument has also been suggested for hafnium phthalo-
and UV-Vis spectroscopies as well as elemental analyses.
LuTCPPc showed a molecular ion peak corresponding to a
+
protonated species [M + 2H] at 1293 amu.
3
5
cyanines which do not fluoresce at all.
The fluorescence lifetime was determined in DMF to be
3.20 ns using a technique based on time correlated single
photon counting. The fluorescence decay profile, Fig. 2, for
the phthalocyanine is characterized by a one exponential decay
process. This suggests that one molecular species is present in
the solution.
The IR spectra of LuTCPPc showed a broad peak around
3
functional group; the peaks at 2927 and 2856 cm are due to
ꢀ
1
504 cm due to the O–H stretch of the carboxylic acid
ꢀ1
ꢀ1
C–H stretches; the sharp intense peak at 1656 cm could be
assigned to the CQO group of the carboxylic acid; the peaks
at 1499, 1439, 1403 and 1383 cm are due to phthalocyanine
ꢀ
1
ꢀ
1
C–N vibrations; 1254 and 1221 cm are due to the ether
ꢀ
1
C–O–C) bond while those at 1148, 1087 and 1060 cm could
Triplet quantum yield and lifetime. The ability of an excited
state phthalocyanine to go from the singlet state to the triplet
state is a prerequisite for it to generate singlet oxygen from
ground state molecular oxygen. The triplet state quantum
(
3
3
be assigned to phenyl vibrations. The UV-Vis spectrum of
LuTCPPc, Fig. 1a, is typical of metallated phthalocyanines,
with a Q-band absorption maximum of 678 nm in DMF.
Fig. 1 shows that the fluorescence spectrum is a mirror image
of the excitation spectrum. The proximity of the Q band maxima
of the absorption and excitation spectra for the complex suggests
that the nuclear configurations of the ground and excited states
yield (F ) of LuTCPPc was determined to be 0.51 in DMF
T
and the corresponding lifetime 2.7 ꢃ 0.01 ms. The triplet decay
curve is shown in Fig. 3 and is consistent with first order
kinetics. The triplet state quantum yield of 0.51 offers a good
possibility of singlet oxygen generation.
Singlet oxygen quantum yield and lifetime. An optical
technique based on phosphorescence decay of singlet oxygen
at 1270 nm was employed in DMF, Fig. 4, using zinc
phthalocyanine as the standard. The singlet oxygen quantum
yield was determined to be 0.33 with a lifetime of 19.85 ꢃ 0.09 ms
in DMF after duplicate measurements.
For phthalocyanines with central metals that have closed
1
shell electron configuration, quantum yields of O
2
formation
3
4
D
(F ) between 0.2 and 0.6 have been reported. Higher singlet
oxygen quantum yields of metallophthalocyanines have also
Fig. 1 Absorption (a), excitation (b) and emission (c) spectra for
been reported for other metals with closed shell electron
36
LuTCPPc in DMF.
configurations. In our case, lutetium is a closed shell diamagnetic
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1588–1595 1591

of various functional groups of polyurethane and LuTCPPc.
Fig. 6 shows the FT–IR spectra of LuTCPPc powder (Fig. 6a),
polyurethane fibers (Fig. 6b) and the LuTCPPc functionalized
ꢀ1
fiber (Fig. 6c) recorded from 4000 to 650 cm
The IR spectra of the PUR fiber (Fig. 6b) showed the
.
ꢀ
1
following peaks: 3316 cm is due to weak N–H stretching
ꢀ
1
of a secondary amine; 2932, 2851 and 2790 cm are due to
ꢀ
1
C–H stretches, 1704 cm is due to the CQO stretch of the
amide; 1525 1444 and, 1365 cm are due to C–N stretches;
ꢀ
1
ꢀ
1
33
peak at 1224 cm could be assigned to C–O–C stretching.
In the case of the hybrid fiber (Fig. 6c), the disappearance of
ꢀ1
the broad band at about 3504 cm in Fig. 6a (for LuTCPPc
alone) suggests the cleavage of the hydroxyl group of the
acid functional group of LuTCPPc on covalent amide bond
formation with some N–H groups of PUR. Also the shift of
ꢀ1
ꢀ1
the carbonyl peak at 1656 cm of LuTCPPc and 1704 cm
ꢀ
1
for PUR to 1699 cm in the hybrid fiber suggests an electronic
interaction involving the carbonyl group of LuTCPPc due
to amide bond formation. This is supported by the shift of
Fig. 3 Triplet decay curve of LuTCPPc in DMF at 500 nm. Excitation
wavelength 675 nm.
ꢀ
1
the N–H peak position in the hybrid fiber from 3316 cm
ꢀ
1
for PUR) to 3322 cm (PUR/LuTCPPc hybrid). The rest of
(
the existing peaks in Fig. 6a and b especially those of the
phenyl groups have their positions and intensities slightly
shifted in the hybrid fiber. These are indications that LuTCPPc
molecules are embedded in the hybrid fiber and that there is
electronic interaction between the two components. The strong
ꢀ1
new peak at 2116 cm for the PUR/LuTCPPc fiber (Fig. 6c)
is attributed to the NQCQN stretch originating from
3
7
some residual bound dicyclohexylcarbodiimide in the hybrid
fiber.
XRD spectra. The crystalline nature of the hybrid fiber was
assessed using X-ray diffraction. The technique also further
confirmed that the phthalocyanine, LuTCPPc, is embedded
within the fiber matrix. Fig. 7 shows the XRD patterns of
the hybrid fiber and that of LuTCPPc alone. The peak at
2y = 24.11 was the only pronounced peak on the XRD spectrum
Fig. 4 Singlet oxygen phosphorescence decay profile of LuTCPPc
of 3 (Fig. 7b). This peak is close to the (002) reflection of
in DMF.
3
carbon. The broad nature of this peak underlines the
8
3
9
substantial amorphous nature of LuTCPPc. The peak for
LuTCPPc is slightly shifted in the conjugate due to the
possible binding interaction between LuTCPPc and PUR.
large atom and as such the observed quantum yield is
expected.
Scanning electron microscopy characterization
of the PUR/LuTCPPc conjugate
UV-Visible spectra. Fig. 8 shows the spectra of LuTCPPc in
DMF (Fig. 8b), PUR/LuTCPPc fiber (Fig. 8c) and LuTCPPc
as powder (Fig. 8d). The Q-band of LuTCPPc in DMF
The conjugate was formed by the formation of the amide bond
between the NH group of PUR and the carboxylic group of
the LuTCPPc, Scheme 2.
(
Fig. 8b) occurs at 678 nm with a vibronic band at 610 nm,
while a B-band maximum occurs at 345 nm. The Q band of the
LuTCPPc in the solid state (Fig. 8d) is slightly broader and
red-shifted, as is typical of solid state spectra. The absorption
spectrum of the phthalocyanine in the functionalized fiber
Fig. 5a shows the SEM image of the electrospun fiber mat of
the PUR/LuTCPPc hybrid. The fibers are randomly aligned
and are more or less a network of random diameters ranging
from 187–5734 nm under the operating conditions. The SEM
of PUR alone shows a more defined structure in Fig. 5b, than
for the PUR/LuTCPPc hybrid.
(
Fig. 8c) has an even more red-shifted Q-band. The spectral
difference between the phthalocyanine in the powder form and
in the fiber can be attributed to the bonding interactions
between the phthalocyanine and the polymeric support rather
than interactions among the phthalocyanine moieties. Similar
observation and explanation have been put forward by
Spectroscopic characterization of the PUR/LuTCPPc
conjugate
4
0
FTIR spectra. Covalent attachment of LuTCPPc on the
polyurethane polymer was assessed by observing conversions
Bourdelande et al. As expected, the electronic spectrum of
the polyurethane fiber alone (Fig. 8a) has no obvious bands.
1
592 New J. Chem., 2011, 35, 1588–1595
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

Scheme 2 Formation of an amide bond between LuTCPPc and PUR.
Fig. 5 Fiber mat of (a) PUR/LuTCPPc composite and (b) PUR alone.
Fig. 6 FT-IR spectra of various samples. (a) LuTCPPc, (b) PUR fiber, and (c) LuTCPPc/PUR hybrid fiber.
The interpretation of solid state spectra of phthalocyanine is
4
interaction between adjacent molecules although it could be
42
extended to molecules of infinite stacks. When the exciton
1
commonly performed by the theory of exciton coupling. In a
very simplified form, the theory is said to be based on the
interaction involves two non-cofacial but edge-to-edge arranged
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 1588–1595 1593

Fig. 9 Raman spectrum of PUR/LuTCPPc.
The much more red shift in the Q-band of LuTCPPc within
the fiber core than in its powder form could be attributed to
the covalent attachment of the Pc to the polymer further
enhancing the non-planar nature of LuTCPPc.
Fig. 7 X-Ray diffraction patterns of hybrid LuTCPPc/PUR fiber
a) and of LuTCPPc (b).
(
Raman spectra. In addition, Raman spectroscopy was
employed to characterize the PUR/LuTCPPc conjugate. Fig. 9
shows the Raman spectra of PUR/LuTCPPc with amide I,
ꢀ1
amide II and amide III bands at 1591, 1452 and 1294 cm
low intensity), respectively, confirming the linkage between
the LuTCPPc and PUR. The amide bands are in agreement
(
4
6,47
with what has been observed elsewhere for amides.
Singlet oxygen generation. Singlet oxygen quantum yield
of the functionalized fiber was determined by using ADMA as
a quencher with the fiber suspended as small pieces in solution.
Fig. 10 shows the spectral changes of ADMA during the
photolysis. There is evidence of photo-conversion of the ADMA
due to singlet oxygen production of the phthalocyanine within
the fiber matrix, though a long period (75 min at 100 W) of
irradiation was required. The value of singlet oxygen quantum
Fig. 8 UV-Vis absorbance spectra of PUR fiber solid alone (a),
ꢀ3
ꢀ
6
4
.85 ꢂ 10 mol dm LuTCPPc in DMF (b), PUR/LuTCPPc (solid)
(
c) and LuTCPPc solid (d).
phthalocyanines, the theory predicts a red-shifted Q-band. In
4
3
this regard Sharp and Abkowitz have reported a red-shift in
the Q-band of metallophthalocyanines in their solid state, as
observed in this work for LuTCPPc in its powder form and in
4
4
the solid polyurethane polymer fiber core. Mizuguchi et al.
have also given an alternative explanation to the optical behavior
of solid state metallophthalocyanines. They explained that the
red-shift of the Q band of non-planar metallophthalocyanines
is influenced by the molecular distortion on the approach of
ring moieties due to p–p interaction along the stacks. This kind
4
5
of behavior has been reported by other researchers. In our
case, the tetra-p-carboxyphenoxy phthalocyanine complex of
lutetium would be non-planar due to the large Lu central metal,
thus the observed solid state spectral behavior of LuTCPPc
could also be explained in the context of its non-planar shape.
Fig. 10 UV-Vis spectral changes observed on photolysis of
PUR/LuTCPPc in the presence of ADMA in water. (a) Starting
spectrum of ADMA, (f) spectrum after 75 min of photolysis, starting
ADMA concentration = 5.53 ꢂ 10ꢀ mol dm
5
ꢀ3
.
1
594 New J. Chem., 2011, 35, 1588–1595
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

yield was estimated to be 0.11. The yield is quite low, as expected
13 S. M. McGlinchey, C. P. McCoy, S. P. Gorman and D. S. Jones,
Expert Rev. Med. Devices, 2008, 5, 581–590.
2
8
for aqueous media, since water quenches singlet oxygen, but
the value is still significant in showing the singlet oxygen
generating ability of the modified fiber. It is important to note
that during photophysical or photochemical studies, the
LuTCPPc did not leach out into solution since there is no
observed Q-band absorption corresponding to the phthalo-
cyanine. This is desirable and suggests that the functionalized
fiber could possibly be applied in real-life involving aquatic
systems without loss of phthalocyanine within the fiber matrix.
1
4 C. Brady, S. E. J. Bell, C. Parsons, S. P. Gorman, D. S. Jones and
C. P. McCoy, J. Phys. Chem. B, 2007, 111, 527–534.
1
5 J. Mosinger, O. Jirsak, P. Kubat, K. Lang and B. Mosinger Jr.,
´
´
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1, 1928–1935.
In this work we have demonstrated that a covalently bound
LuTCPPc to a polyurethane polymer can be spun into fibers.
The UV-visible spectral features of the phthalocyanine show
a red shift within the fiber matrix as compared to that in DMF
solution. It was further shown that the phthalocyanine is a
promising photo-sensitizer with triplet quantum yield of 0.51
and a corresponding lifetime of 2.7 ms in DMF. The singlet
oxygen quantum yield was determined to be 0.33 and a lifetime
of 19.85 ms in DMF. The photoactivity of the phthalocyanine
was also found to be maintained within the polymer fiber
matrix with an estimated singlet oxygen quantum yield of 0.11
in water.
2
2
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Acknowledgements
This work was supported by the Department of Science and
Technology (DST) and National Research Foundation (NRF)
of South Africa through DST/NRF South African Research
Chairs Initiative for Professor of Medicinal Chemistry and
Nanotechnology and Rhodes University.
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New J. Chem., 2011, 35, 1588–1595 1595