Photophysichochemical behavior of carbazole derivatized zinc phthalocyanine in the presence of ZnO microparticles and when embedded in electrospun fibers

Article abstract of DOI:10.1016/j.dyepig.2013.12.019

The synthesis of a zinc phthalocyanine complex tetrasubstituted with carbazole functionality at the peripheral position (complex 4) is reported. The singlet oxygen quantum yield of the complex was found to be 0.83 in dimethylformamide (DMF). The complex was subsequently conjugated to zinc oxide microparticles (ZnOMPs), the conjugation (formation of the amide bond) was confirmed by IR spectroscopy. The presence of ZnOMPs was found to reduce the singlet oxygen produced (Φ_Δ = 0.63) in DMF. Polystyrene electrospun fibers of complex 4 alone and its conjugate to ZnOMPs were found to be thermally stable. The singlet oxygen quantum yield of the modified electrospun fibers was determined in aqueous media with ADMA as a singlet oxygen quencher and were 0.25 and 0.20 for complex 4 and 4-ZnOMPs embedded in fibers, respectively.

Full text of DOI:10.1016/j.dyepig.2013.12.019

Accepted Manuscript
Photophysichochemical behavior of carbazole derivatized zinc phthalocyanine in the
presence of ZnO microparticles and when embedded in electrospun fibers
Phindile Khoza, Edith Antunes, Tebello Nyokong
PII:
S0143-7208(13)00496-8
10.1016/j.dyepig.2013.12.019
DYPI 4216
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 25 September 2013
Revised Date: 13 November 2013
Accepted Date: 18 December 2013
Please cite this article as: Khoza P, Antunes E, Nyokong T, Photophysichochemical behavior of
carbazole derivatized zinc phthalocyanine in the presence of ZnO microparticles and when embedded in
electrospun fibers, Dyes and Pigments (2014), doi: 10.1016/j.dyepig.2013.12.019.
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ACCEPTED MANUSCRIPT
Photophysichochemical behavior of carbazole
derivatized zinc phthalocyanine in the presence
of ZnO nanoparticles and when embedded in
electrospun fibers
Phindile Khoza, Edith Antunes, Tebello Nyokong
zinc phthalocyanice complex tetrasubstituted with
a carbazole functionality at the peripheral
position (complex 4) was conjugated to zinc oxide
nanoparticles (ZnONPs) and electrospun into
fibers. The singlet oxygen quantum yield values
obtained were 0.25 and 0.20 for complex 4 and 4-
ZnONPs, respectively.

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Photophysichochemical behavior of carbazole derivatized zinc phthalocyanine in the
presence of ZnO microparticles and when embedded in electrospun fibers
Phindile Khoza, Edith Antunes, Tebello Nyokong*
Department of Chemistry, Rhodes University, P.O. Box 94, Grahamstown, South Africa
Abstract
The synthesis of a zinc phthalocyanice complex tetrasubstituted with carbazole
functionality at the peripheral position (complex 4) is reported. The singlet oxygen
quantum yield of the complex was found to be 0.83 in dimethylformamide (DMF). The
complex was subsequently conjugated to zinc oxide microparticles (ZnOMPs), the
conjugation (formation of the amide bond) was confirmed by IR spectroscopy. The
presence of ZnOMPs was found to reduce the singlet oxygen produced (Φ∆=0.63) in
DMF. Polystyrene electrospun fibers of complex 4 alone and its conjugate to ZnOMPs
were found to be thermally stable. The singlet oxygen quantum yield of the modified
electrospun fibers was determined in aqueous media with ADMA as a singlet oxygen
quencher and were 0.25 and 0.20 for complex 4 and 4ꢀZnOMPs embedded in fibers,
respectively.
Keywords: zinc phthalocyanine, carbazole, polystyrene, ZnO microparticles, singlet
oxygen quantum yield
*Corresponding author. Tel.:+27ꢀ46ꢀ603 8260; fax: +27ꢀ46ꢀ622 5109. E-mail address:
t.nyokong@ru.ac.za (T. Nyokong).

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1.
Introduction
Metallophthalocyanine (MPc) complexes are being extensively researched for their
applications in for example electrocatalysis [1], nonlinear optics [2,3], chemical
sensors [4,5] and photovoltaic cells [6]. The physical, chemical, electrochemical and
other properties of these macrocycles are key to their suitability for the above
applications, and can be obtained by careful selection of the central metal, type and
position (peripheral and nonꢀperipheral) of the substituents on the MPc ring [7ꢀ9]. MPc
complexes are also well known as efficient photosensitizers in photodynamic therapy
(PDT) of cancer [10ꢀ13]. Singlet oxygen is the cytotoxic species is involved in PDT.
On the other hand ZnO nanoparticles (ZnONPs) [14] and microparticles (ZnOMPs) [15]
exhibit antimicrobial and anticancer activities through generation of reactive oxygen
species (ROS), mostly hydroxyl radicals, H2O2 and singlet oxygen [16,17]. Thus, linking
the MPc with ZnOMPs (as is the aim of this work) will result in combined generation of
ROS for improved antimicrobial and anticancer activities.
Zn phthalocyanine tetra substituted at the peripheral position with a carbazole
moiety (Scheme 1, complex 4) is employed in this work, and its suitability as a
photosensitizer examined. Carbazoles are also known to be good photosensitizers
[18,19]. Thus the combination of the carbazole skeleton with the phthalocyanine ring
is aimed at enhancing the photosensitizing activity of the Pc due to the synergistic
effect. To further enhance the photosensitizing ability, complex 4 will conjugated to

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ZnOMPs since both generate ROS. The conjugates of ZnOMPs with 4 will further be
embedded in polystyrene (PS) electrospun fibers, for ease of recovery of the catalyst
following future use in for example as antimicrobial agents. Electrospun fibers may be
suitably functionalized for specific purposes. Our group has successfully incorporated
phthalocyanines into a fiber mat for the photodegradation of organic pollutants in
water [20]. The photophysicochemical behavior of complex 4 in the presence of
ZnOMPs, in solution or when electrospun into fibers is investigated in this work. The
conjugate of complex 4 with ZnOMPs is represented as 4ꢀZnOMPs. The modified
electrospun polystyrene (PS) fibers are represented as 4/PS, ZnOMPs/PS and 4ꢀ
ZnOMPs/PS for 4 alone, ZnOMPs and 4ꢀZnOMPs, respectively.
2.
Experimental
2.1 Materials
Zinc acetate (99%), 1,8ꢀdiazabicyclo[5.4.0]undecꢀ7ꢀene (DBU), 4ꢀnitrophthalonitrile,
2ꢀhydroxycarbazole, zinc phthalocyanine, N,Nꢀdicyclohexylcarboiimide (DCC), Nꢀ
hydroxysuccinimide (NHS), anthraceneꢀ9,10–bisꢀmethylmalonate (ADMA), citric acid
and sodium hydroxide were purchased from Sigma Aldrich. Dimethylformamide (DMF),
potassium carbonate, methanol, ethanol, 1ꢀpentanol, acetone, diethyl ether and
tetrahydrofuran (THF) were obtained from SAARCHEM.
2.2 Equipment

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Ground state absorption spectra were recorded on a Shimadzu UVꢀ2550
spectrophotometer. Fluorescence excitation and emission spectra were recorded on a
Varian Eclipse spectrofluorimeter. Infrared spectra were recorded on a Perkin Elmer
1
Spectrum 100 FTꢀIR spectrometer, while H NMR spectra were recorded on a Bruker
AMX 600 NMR spectrometer.
Fluorescence lifetimes were measured using a time correlated single photon counting
(TCSPC) setup (FluoTime 200, Picoquant GmbH). The excitation source was a diode
laser (LDHꢀPꢀ670 driven by PDL 800ꢀB, 670 nm, 20 MHz repetition rate, 44 ps pulse
width, Picoquant GmbH). Details have been provided before [21].
Mass spectral data were collected with a Bruker AutoFLEX III Smart beam TOF/TOF
Mass spectrometer. The instrument was operated in positive ion mode using a m/z
range of 500–3000 amu as described before [21]. Xꢀray powder diffraction (XRD)
patterns were recorded on a Bruker D8 Discover XRD equipped with a Lynx Eye
Detector, using Cu Kα radiation (= 1.5405 Å, nickel filter). Details have been reported
before [22].
Scanning electron microscope (SEM) images of the fiber alone or for 4/PS, ZnOMPs/PS
and 4ꢀZnOMPs/PS were obtained using a JOEL JSM 840 scanning electron microscope.
Transmission electron microscope (TEM) images were obtained using a Carl Zeiss Libra
transmission electron microscope, at 100 kV accelerating voltage. Energy dispersive Xꢀ

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ray spectroscopy (EDX) was acquired on a INCA PENTA FET coupled to the VAGA TESCA
using 20 kV accelerating voltage. Fluorescence images of the fibers were taken with a
DMLS fluorescence microscope; the excitation source was a high voltage mercury
lamp.
Photoꢀirradiation for singlet oxygen quantum yield determinations for 4/PS,
ZnOMPs/PS and 4ꢀZnOMPs/PS in water were carried out using a General Electric
Quartz line lamp (300 W). A 600 nm glass cut off filter (Schott) and a water filter
were used to filter off ultraviolet and infrared radiations respectively. An
interference filter (Intor, 670 nm with a band width of 40 nm) was additionally placed
in the light path before the sample. Light intensity was measured with a POWER MAX
5100 (Molelectron detector incorporated) power meter, and was found to be 9.53 x
1018 photons s1cmꢀ2. The thermal degradation properties of polystyrene and
functionalized polystyrene electrospun fibers were studied using a thermogravimetric
analyser (TGA) Shimadzu simultaneous differential thermogravimetric analysis
o
thermal analyser (DTAꢀTG), at a heating rate of 10 C minꢀ1, under nitrogen
atmosphere, with a gas flow rate of 120 mL minꢀ1.
The phosphorescence of singlet oxygen at 1270 nm was used to determine the singlet
oxygen quantum yield of complex 4 and 4ꢀZnOMPs in DMF. For these studies, an ultraꢀ
sensitive germanium detector (Edinburgh Instruments, EIꢀP) combined with a 1000 nm
long pass filter (Omega, RD 1000 CP) and a 1270 nm bandꢀpass filter (Omega, C1275,

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BP50) were used. Experimental details have been provided before [23]. The singlet
oxygen phosphorescence signal was compared with that of the ZnPc standard.
2.3. Photophysical and photochemical parameters
2.3.1.Fluorescence quantum yield
Fluorescence quantum yields (Φf) were determined by the comparative method (Eq.
1)
where
and Fstd are areas under the fluorescence emission curves of the sample and
F
the standard, respectively. A and Astd are the absorbances of the analyte and the
standard at the excitation wavelength, respectively; n and nstd are refractive indices
of solvents used for samples and standard, respectively. ZnPc in DMF was used as a
standard, Φf = 0.30 [24], for the determination of fluorescence quantum yields. The
samples and the standard were both excited at the same relevant wavelength.
2.3.2.Singlet oxygen quantum yield (Φ∆)
The phosphorescence of single oxygen at 1270 nm was used to determine the singlet
oxygen quantum yields of complex 4 and 4ꢀZnOMPs in DMF. Equation 2 was employed
[25]:

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τ D
τ D
τT
τ D
[e−t / − e−t /
]
(2)
I(t) = B
τ T
−
1
1
where, I(t) is the phosphorescence intensity of O2 at time t, τD is the lifetime of O2
phosphorescence decay, τT is the triplet state lifetime of the standard or sample, and
B is a coefficient involved in sensitizer concentration and 1O2 quantum yield.
The singlet oxygen quantum yields (Φꢁ) of complex 4 and 4ꢀZnOMPs were determined
using Equation 3:
B
BStd
Φꢀ = ΦꢀStd
(3)
where ΦꢀStd is the singlet oxygen quantum yield of the standard ZnPc ( Std = 0.56 in
Φ
ꢀ
DMF [26]; B and BStd are the coefficients of the sample and standard, respectively.
A chemical method was used to determine singlet oxygen quantum yield for 4/PS and
4ꢀZnOMPs/PS. The studies were carried out in an aqueous solution, using ADMA
(concentration = 5.8 × 10ꢀ5 M). The decrease in the absorption for ADMA at 380 nm
was monitored. The modified fiber (10 mg) was suspended in the solution containing
ADMA and irradiated using the photolysis setup described above. The quantum yields
(ΦADMA) were calculated using equation (4), using the molar extinction coefficient of
ADMA in water, log (ε) = 4.1 [27].

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where Co and Ct are concentrations of ADMA before and after irradiation respectively;
Vt is the volume of the solution irradiated and Iabs is defined by equation 5.
where α = 1 ꢀ 10ꢀA(λ), A(λ) is the absorbance of the sensitizer at the irradiation
wavelength, A is the irradiation area (2.5 cm2), I is the intensity of light (9.53 ×1018
photons cmꢀ2 sꢀ1) and NA is the Avogadro’s constant. The absorbance used in equation
5 is that of complex 4 or 4ꢀZnOMPs on the fiber, determined by placing the fiber on a
glass plate. The light intensity measured refers to the light reaching the
spectrophotometer cell, and it is expected that some of the light may be scattered.
Therefore, Φ∆ values of complex 4 or 4ꢀZnOMPs on the fiber are estimates. The singlet
oxygen quantum yields (Φ∆) were calculated using equation 6 [28].
where kd is the decay constant of singlet oxygen and ka is the rate constant of the
reaction of ADMA with O2 (1∆g). The intercept obtained from the plot of 1/ΦADMA
versus 1/[ADMA] gives the Φ∆ values.
2.4. Synthesis

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2.4.1
4-(9H-carbazol-2-yloxy)-phthalonitrile (Scheme 1, complex 3)
A mixture of 2ꢀhydroxycarbazole (1, 1.00 g, 6.6 mmol) and 4ꢀnitrophthalonitrile (2,
1.1 g, 6.6 mmol) in DMSO (10 ml) was stirred under argon atmosphere at room
temperature. K2CO3 (10.07 g, 15 mmol) was added portionꢀwise to the reaction
mixture and the mixture was stirred for 48 h. The reaction mixture was poured into
ice water, and the precipitate was filtered off, washed with water and dried. The
crude product was recrystallized from an ethanol: water mixture and air dried.
Yield: 1.46 g (70 %). FT-IR/cm-1: 3078 (Ar–CH), 2961, 2834 (CH), 2230 (CN), 1579 (C C),
1
1475, 1456, 1442, 1383, 1325, (C-O-C), 1020, 1008, 962, 929, 792, 693. H NMR (DMSO-
d6): 11.46 (1H, s, NH), 8.27 (1H, J= 8.4 Hz, d, Ar–H), 8.19 (1H, J= 7.8 Hz, d, Ar–H), 8.12 (1H,
J= 8.8 Hz, d, Ar–H), 7.82 (1H, J= 9.4, 2.5 Hz,dd, Ar–H), 7.57 (1H, J= 8.1 Hz, d, Ar-H), 7.50 (1H,
J=8.8 Hz, dd, Ar-H), 7.43 (2H, m, Ar-H), 7.22 (1H,J=7.4, t, Ar-H), 7.03 (1H, J=8.4 Hz, dd, Ar-H).
Anal. C20H11N3O : Calc: C, 77.66; H, 3.58; N,13.58;. Found: C, 77.87; H, 4.21; N,13.07.
2.4.2. 2,(3)-Tetra(carbazol-2-yloxy)phthalocyaninatozinc(II) (Scheme 1, complex 4)
A mixture of zinc (II) acetate dihydrate (0.25 g, 1.1 mmol), 3 (1.36g, 4.4 mmol), DBU
o
(3 drops) and 1ꢀpentanol (10 mL) was stirred at 160 C for 5 h under nitrogen
atmosphere. After cooling, the solution was mixed with methanol. The green solid
product was precipitated and collected by centrifuging at 5100 rpm for 10 min. The

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crude product was washed with ethanol, acetone, nꢀhexane and diethyl ether. The
green product was further purified by passing through silica gel using THF as the
eluent.
Yield: 0.86 g (50 %). UV/vis (DMF): λmax nm (log ε); 680 (5.11), 612 (4.32 ), 362 (4.52).
FT-IR: (νmax/cm-1): 3200 (NH), 3161 (Ar-H), 1576, 1077, 1110 (C-O-C), 1559 (C=N), 1412
1H NMR (DMSO-d6): δ ppm 11.46-11.25 (4H, b, NH), 9.46-9.32(2H, b, Ar-H), 9.29-9.25 (1H,
b, Ar-H), 9.00-8.92 (3H, b, Ar-H), 8.39-8.11 (10H, b, Ar-H), 7.95-7.69 (4H, b, Ar-H), 7.65-7.17
(24H, b, Ar-H). Anal. C80H44N12O4Zn: Calc. : C, 73.76; H,3.40;N,12.90; Found: C, 73.06;
H,3.79; N, 12.88. MALDI TOF-MS (m/z): Calculated 1301; Found: 1302 [M+H]+.
2.4.3. Synthesis of MPc-ZnOMPs conjugate
Citric acid capped ZnOMPs were synthesized as reported in literature [29,30], Scheme
2. Conjugation of the ZnO microparticles (ZnOMPs) with complex 4 was achieved as
follows (Scheme 2). The carboxylic acid group of the citric acid capping of ZnO
microparticles (0.014 g/mL in DMF), was activated with DCC (0.019 mg, 0.094 mmol)
and NHS (3.62 mg, 0.031 mmol) for 16 h. Complex 4 (5 mg, 0.00384 mmol) dissolved
in DMF (1 mL), was added dropwise into the mixture, and the reaction was allowed to
continue for 24 h. The conjugate was purified by passing through a biobeads column
using DMF as an eluent.
2.4.4. Preparation of electrospun nanofibers

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The electrospinning technique (with or without MPc complexes) has been described
before [31,32]. Electrospun nanofibers were prepared as follows: A solution containing
2.5 g of polystyrene (PS), 3 mg of sample (complex 4, 4ꢀZnOMPs or ZnOMPs) and 10
mL DMF/THF(4:1) was stirred for 24 h to produce a homogeneous solution. The
solution was then placed in a syringe fitted with a capillary needle. A potential
difference of 20 kV was applied between the anode and cathode. The distance
between the cathode (static fiber collection point) and anode (tip of capillary needle)
was 15 cm. The pump rate was maintained at 0.05 mL/h.
3.
Results and Discussion
3.1. Synthesis and characterization of complex 4, ZnOMPs and 4-ZnOMPs
3.1.1.Complex 4
Complex 4 was prepared by the cyclotetramerization of the phthalonitrile (3) in the
presence of DBU and a metal salt. DBU acts as a neuclophilic base which allows for
the reaction to proceed under mild conditions, while preventing the formation of side
products (Scheme 1). A yield of 50% was obtained following repetitive purification by
column chromatography. For the confirmation of the predicted structure, complex 4
was characterized by IR, MS and elemental analysis. After purification, the elemental
analysis was in agreement with the proposed structure, confirming the purity of the
prepared complex. MS revealed the presence of a molecular ion peak at 1302 [M+H]+,
which further confirms the proposed structure. The higher Pc concentrations required

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1
for H NMR, and the presence of isomers complicates phthalocyanine spectra.
Nonetheless, the NMR spectrum of complex 4 showed aromatic peaks in the expected
regions, with all protons accounted for, as reported in the experimental section.
3.1.2.ZnOMPs
The synthesis of ZnOMPs was achieved by using a wellꢀestablished method reported by
Shaheer et al [30]. The particles obtained were microflakes as reported in literature
(Fig. 1a) [30]. The size of these microparticles ranged from 0.4 to 1.8 ꢂm, and their
size distribution is shown in Fig 1b. The purity and crystallinity of the formed ZnOMPs
were confirmed by the XRD, Fig. 2. The sharp, intense peaks in the XRD indicate that
the ZnOMPs are highly crystalline. The peaks in the XRD powder pattern were
observed at 2θ 31.95o, 34.56o, 36.40o, 47.68o, 56.830, 62.98o, 66.53o, 68.12o, 69.27o
and 76.97o and were indexed to the (100), (002), (101), (102), (110), (103), (200),
(112), (201), and (202) planes of the ZnO crystal respectively (as referenced by
standard data file JSPC card number 01ꢀ075ꢀ0576). The formation of a pure
hexagonalꢀwurtzite phase was confirmed by the XRD peaks at the (100), (002) and
(101) planes for the ZnO structure. In addition, the narrow peaks imply a large
particle size for the ZnOMPs, confirming the results obtained using SEM.
3.1.3.Complex 4-ZnNPs conjugate

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Conjugation of complex 4 to ZnOMPs was achieved by activating the carboxylic acid
functional group on the ZnOMPs with DCC which acts as a coupling agent (Scheme 2).
The amide bond was formed via a condensation reaction between the activated
carboxylic acid group on the ZnOMPs, and the secondary aromatic amine on the
carbazole derivatized ZnPc (4). The formation of the amide bond was confirmed by
the IR (Fig. 3), there is an appearance of a new peak at 1750 cmꢀ1, due to the C=O
stretching of the amide bond. The XRD pattern in Fig 2 shows the diffraction pattern
of complex 4 and that of 4 conjugated to ZnOMPs. The XRD of the conjugate shows
that the broad peak that is due to the Pc at 2θ = 20° is very weak [33], the broadness
is due to amorphous nature. The sharp peaks in the XRD pattern of the conjugate are
due to ZnOMPs. Thus, the XRD pattern of the conjugate clearly shows the presence of
highly crystalline ZnOMPs.
3.2. Ground state absorption spectra
One of the easiest ways of confirming the formation of metallophthalocyanines is
through their UVꢀVis spectra. Metallophthalocyanines exhibit two strong absorption
regions, the B band (~300 nm), and the intense Q band in the NIR region. The UVꢀVis
spectra of complex 4 in different solvents are shown in Fig. 4A. The absorption
spectrum of phthalocyanines is greatly influenced by the solvents basicity and the
refractive index [34]. The red shifts in the Q band in Fig. 4A follows the refractive
index of the solvents. Complex 4 was found to be soluble in most organic solvents,
and showed monomeric behavior, as evidenced by a single narrow Q band. Upon

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conjugating complex 4 to citric acid capped ZnOMPs, there was no significant shifting
of the Q band of complex 4 (Fig. 4B).
The onset of the absorption for bulk ZnO at room temperature has been reported to
be at 370 nm [35]. Citric acid capped ZnOMPs show a distinct absorption peak at ~ 340
nm (Fig. 5), the peak is blue shifted when compared to the bulk. The blue shift is due
to the nanosize regime occupied by the particles, exhibiting the quantum
confinement effect. The tailing of the absorption spectrum and the broadness of the
emission peak is due to poor size dispersity of the microparticles.
3.3. Photophysical and photochemical studies
3.3.1.Fluorescence studies
Fig. 6A shows the fluorescence emission, absorption and the excitation spectra of 4 in
DMF. The excitation and absorption spectra are the same and are both mirror images
of the emission spectra. The proximity (Table 1) of the Q band maxima of the
absorption and excitation spectra suggest that the nuclear configuration of the ground
state and excited state do not change upon excitation in all solvents. For the
conjugate of complex 4 with ZnOMPs, the excitation band is split, most likely due to
lowering of symmetry on excitation (Fig. 6B).
Fluorescence quantum yields (ΦF) represent the fraction of the excited molecules that
lose energy through fluorescence. The fluorescence quantum yields of the complexes
are shown in Table 2. The ΦF value of 4 was found to be 0.12 (Table 2), the ΦF

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calculated is lower than that of the unsubstituted ZnPc (ΦF = 0.30 [24]), implying that
the substituent has an effect on the photophysical behavior of the ZnPc, as reported
before [7]. The conjugate was found to give the same fluorescence quantum yield as
complex 4.
Fluorescence lifetime (τF) refers to the time a molecule spends in its excited state
before returning to the ground state. The fluorescence decay curve for 4 is shown in
Fig. 7a. A mono exponential decay curve was obtained for the Pc, further confirming
the purity of the prepared molecule. Due to the fluorescence quenching induced by
the substituent, the low fluorescence quantum yield of 4 was accompanied with a
short fluorescence lifetime when compared to the unsubsituted ZnPc in the same
solvent. The conjugate of complex 4 with ZnOMPs gave a double exponential decay,
with decrease in lifetime, Fig. 7b and Table 2. The presence or the evolution of two
fluorescence lifetimes has been attributed to the different orientations of the
phthalocyanines on the microparticles, with each orientation giving rise to a different
fluorescence lifetime [36].
3.3.2. Singlet oxygen quantum yield studies
Singlet oxygen quantum yield (Φ∆) is a measure of the efficiency of singlet oxygen
generation for a given photosensitizer. Singlet oxygen is the chief cytotoxic species
that is responsible for different applications. Singlet oxygen is formed via the
interaction of the triplet state of the photosensitizer with the ground state molecular

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oxygen. Factors which determine the magnitude of the singlet oxygen quantum yield
include, the triplet state energy, ability of the substituent and the solvent to quench
singlet oxygen, and the efficiency of the energy transfer between the triplet excited
state and the ground state molecular oxygen. Complex 4 showed a high singlet oxygen
quantum yield (Φ∆ = 0.83), proving its great potential for application as a
photosensitizer. The high singlet quantum yield can be attributed to the capabilities
of the carbazole ligand on its own to produce singlet oxygen. On conjugating complex
4 to ZnOMPs, there was a decrease in the amount of singlet oxygen produced (Φ∆ =
0.64). ZnOMPs have been reported to produce singlet oxygen. In this work, only the Q
band of the Pc was excited. Therefore, the value of singlet oxygen obtained does not
account for the singlet oxygen produced by ZnOMPs (which absorbs at higher energies
than the complex 4). Nonetheless, the presence of ZnOMPs quenched the singlet
oxygen produced by complex 4 alone.
3.4. Characterization of the electrospun fibers
3.4.1. Scanning electron microscopy
Functionalized electrospun PS fibers (4/PS, ZnOMPs/PS and 4ꢀZnOMPs/PS) were
characterized by the scanning electron microscopy. The electrospun fibers were
cylindrical and unꢀbranched with relatively smooth surfaces, Fig. 8. Electrospun
polystyrene alone gave diameter sizes in a range of 3–4 ꢂm (Fig 8a). The diameters
for 4/PS, ZnOMPs/PS and 4ꢀZnOMPs/PS ranged between 3 to 6 ꢂm. Functionalizing

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fibers with ZnOMPs produced nanofibers which showed “white spots” embedded
within (Fig. 8d). The spots were proven to be ZnO microparticles by EDX (Fig. 8e). The
EDX (Fig. 8e) shows the elemental composition of these spots, and clearly outlines the
high concentration of Zn and O as compared to neighboring areas (i.e. areas without
white spots (Fig. 8f). The idea behind electrospinning 4ꢀZnOMPs conjugate was to
obtain an optimal nanocomposite for various applications including waste water
disinfection. Nanofibers prepared are insoluble in water, making it easy to recover
the fiber after use. The insolubility of complex 4 and the conjugate in water is also an
advantage, as this implies that the content of the fiber will not leach out when used
in aqueous media.
3.4.2. Fluorescence microscopy
The ability of the nanofibers to emit light upon functionalization with complex 4 was
examined with the fluorescence microscopy. ZnOMPs/PS (Fig. 9a) showed fluorescent
spots, and the image correlates to that obtained from the SEM, further confirming
that the fluorescent spots, or the whitish spots observed on the SEM are ZnOMPs
embedded within the fiber. In the presence of complex 4, the fiber is observed to
have remarkable emission upon excitation (Fig. 9b). Similar fluorescence was
observed with excitation of the 4-ZnOMPs/PS (Fig.9c), albeit a weaker emission.
3.4.3.TGA/DTA

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The effect of heat on the prepared nanofibers was examined by thermal analysis.
Changes in weight with increase in temperatures were monitored by
thermogravimetric analysis (TGA). Fig. 10A shows that the modified fibers are slightly
more stable than polystyrene alone. Differential thermogravimetric analysis (DTA) was
acquired simultaneously with the thermogravimetric analysis; therefore, the results
obtained are comparable. DTA gives the apparent degradation temperature and the
derivative weight losses of the composites and polystyrene alone are shown in
Fig.10B. The DTA curve of ZnOMPs/PS is clearly shifted to higher temperatures,
indicating the greater thermal stability of the composite. The thermal stabilities of
complex 4/PS and 4ꢀZnOMPs/PS were found to be similar, and slightly improved when
compared to pristine polystyrene, as judged by the small shift to higher
temperatures.
3.4.4.UV-Vis spectra and XRD patterns
The fibers 4/PS, ZnOMPs/PS and 4ꢀZnOMPs/PS were not soluble in water but could be
dissolved in toluene, with the aim of examining the integrity of the components of the
modified fiber. UVꢀVis spectra of the fiber composites (in toluene) are shown in Fig.
11, with a characteristic Q band at 683 nm. The integrity of the components (complex
4 or 4ꢀZnOMPs) in the electrospun fiber are not compromised upon electrospinning,
since there were no changes in the Q band maxima. The XRD pattern of the
electrospun fibers is shown in Fig. 12. The XRD pattern of PS shows a broad peak at 2θ
= 20o, where phthalocyanines also show a peak [33] as observed in Fig. 2. This broad

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19
peak for PS is close to the 002 reflection peak for carbon [33]. The broadness of the
peak is an indication of the amorphous nature of polystyrene electrospun fibers.
Functionalization of polystyrene gave diffraction patterns that are mainly from
polystyrene, there were no significant changes on the diffraction pattern of
polystyrene upon functionalization (Fig 12).
3.4.5.Singlet oxygen quantum yield determination
The singlet oxygen generation abilities of 4/PS and 4ꢀZnOMPs/PS were determined
using the absolute method with ADMA as a quencher. Although the values obtained
are an estimate of the singlet oxygen produced by complex 4, they are extremely
useful for comparative purposes. Fig. 13 shows the degradation of ADMA in the
presence of 4/PS. There is evidence of photoꢀconversion of ADMA due to the singlet
oxygen produced by the phthalocyanine within the fiber. It is important to note that
complex 4 did not leach out into solution during photolysis (there is no Qꢀband
absorption). Singlet oxygen quantum yield values of 0.25 were obtained for 4/PS
while 4ꢀZnOMPs/PS gave a singlet oxygen value of Φ∆= 0.20, Table 2. These values
were found to be quite low, this is expected for experiments carried out in aqueous
media since water is known to quench singlet oxygen [34]. Although the Φ∆ values are
estimates, they do give an indication as to how effective the fiber will be as an
antimicrobial agent or a photocatalyst.
Conclusions

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Herein, we have reported on the synthesis and characterization of the carbazole
derivatized zinc phthalocyanine (complex 4). The complex showed remarkable
photochemical behavior in DMF, with singlet oxygen quantum yield of 0.83. Upon
conjugating the complex to ZnOMPs, the singlet oxygen quantum yield decreased
(0.63). The composites showed greater thermal stability than polystyrene alone. The
singlet oxygen quantum yields (in water) of the functionalized nanofibers were found
to be 0.25 and 0.20 for 4/PS and 4ꢀZnOMPs/PS respectively.
Acknowledgements
This work was supported by the Department of Science and Technology (DST)
Innovation and National Research Foundation (NRF), South Africa through DST/NRF
South African Research Chairs Initiative for Professor of Medicinal Chemistry and
Nanotechnology as well as Rhodes University and DST/Mintek Nanotechnology
Innovation Centre (NIC) – Sensors, South Africa

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Table 1:
Solvent
Q
abs (nm)
Qexc (nm)
Qemm (nm)
Stoke’s shift (nm)
THF
677
680
682
686
678
679
683
686
687
693
697
702
9
DMF
14
14
16
DMSO
Pyridine
Table 2:
τF (ns) a
Φ∆
Conjugate/Complex
ΦF
b
Complex 4
4-ZnOMPs
0.12 3.45 ± 0.03 (1.00) 0.83 (0.25)
0.12 2.82 ± 0.02 (0.80)
0.64 (0.20)
0.48 ± 0.02 (0.20)
ZnPc
0.30c
3.8c
0.56d
a
Abundances in brackets. b numbers in brackets are for modifies fibers. c Ref 24. d Ref 26.

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H
N
H
CN
CN
K2CO3
N
O
NO2
NC
NC
OH
DMF, 24 h
3
1
2
R
R
N
N
N
H
N
CN
O
N
Zinc acetate
Zn
N
N
N
DBU, 1-pentanol
CN
3
N
R
R
H
N
O
R =
4
Scheme 1

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28
OH
O
O
O
O
OH
O
HO
O
O
O
O
O
O
HO
OH
Zn
HO
OH
ZnO
O
+
NaOH
H3C
O
CH3
OH
O
O
water, 35 oC
OH
HO
DCC
NHS
1.
12 hrs
NH
2. Pc/DMF
36 hrs
NH
O
O
NH
O
O
O
N
N
N
N
OH
HO
O
N
M
N
O
O
N
N
N
N
N
O
N
ZnO
N
O
M N
N
O
O
N
N
N
OH
HO
HN
O
O
O
O
HN
HN
Scheme 2