Sulphonated phthalocyanines as effective oxidation photocatalysts for visible and UV light regions

Article abstract of DOI:10.1016/j.molcata.2007.03.024

Attention was paid to the synthesis, chemical modification (sulphonation), characterisation and practical catalytic utilisation of metal free phthalocyanine and a series of phthalocyanines (PHCs) with Zn, Al, Si, Co, Ni, Cu and Ti central atoms. These organometallic compounds are referred to as highly active species due to their ability to produce singlet oxygen upon energy absorption. Photocatalytic efficiency of the prepared PHCs was tested in a model oxidation of 4-chlorophenol under illumination with visible and UV light in agreement with location of their distinctive absorption bands in both these regions. It was shown that different types of phthalocyanines revealed very different photocatalytic activities and only those with a long life-time of the excited triplet states (ZnPHC, SiPHC, AlPHC) effectively interacted with molecular oxygen to form the reactive singlet oxygen. The indispensable role of constant pH (～10) was also clarified in separate experiments. Determined values of quantum yields for reactions carried out in the UV region were always higher than for reactions induced by the visible light.

Full text of DOI:10.1016/j.molcata.2007.03.024

Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
Sulphonated phthalocyanines as effective oxidation photocatalysts
for visible and UV light regions
P. Klusona,∗, M. Drobeka, T. Strasaka, J. Krysaa, M. Karaskovab, J. Rakusanb
a Institute of Chemical Technology Prague, Technicka 5, 166 28 Prague 6, Czech Republic
b Research Institute for Organic Syntheses, Pardubice-Rybitv´ı 532 18, Czech Republic
Received 6 February 2007; received in revised form 7 March 2007; accepted 8 March 2007
Available online 15 March 2007
Abstract
Attention was paid to the synthesis, chemical modification (sulphonation), characterisation and practical catalytic utilisation of metal free
phthalocyanine and a series of phthalocyanines (PHCs) with Zn, Al, Si, Co, Ni, Cu and Ti central atoms. These organometallic compounds are
referred to as highly active species due to their ability to produce singlet oxygen upon energy absorption. Photocatalytic efficiency of the prepared
PHCs was tested in a model oxidation of 4-chlorophenol under illumination with visible and UV light in agreement with location of their distinctive
absorption bands in both these regions. It was shown that different types of phthalocyanines revealed very different photocatalytic activities and
only those with a long life-time of the excited triplet states (ZnPHC, SiPHC, AlPHC) effectively interacted with molecular oxygen to form the
reactive singlet oxygen. The indispensable role of constant pH (∼10) was also clarified in separate experiments. Determined values of quantum
yields for reactions carried out in the UV region were always higher than for reactions induced by the visible light.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Phthalocyanines; 4-Chlorophenol; Photocatalysis; Quantum yield; Singlet oxygen
1. Introduction
species such as a superoxide radical [9]. The former is usually
being considered as the prominent active species in a majority of
photo-induced reactions with PHCs as photocatalysts [10–16].
However, it is rather correct that the mechanisms are compet-
itive and the appearance of the prevalence form depends upon
the photophysical properties of the particular phthalocyanine.
Nevertheless, it is generally known [9] that the active singlet
oxygen form occurs when porphyrine with longer life-time of
the excited triple state is involved. It must be noted that PHCs
with a completely occupied valence sphere or d-orbitals are such
structures [17–19]. On the other hand, PHCs containing metal
ions with not fully occupied d-orbitals (e.g. Co2+, Cu2+, Ni2+)
tend toward rapid extinction of their excited triple states with
consequences in a lower number of formed active species. More
details on these aspects are given elsewhere [9,20–29].
Photo-induced reactions involving phthalocyanines and
focused on environmental applications may specifically come
into account due to negligible toxicity of PHCs and their high
activity toward oxidative decomposition of majority of typ-
ical organic pollutants appearing in drinking, industrial and
waste water [10,11,18,30–35]. However, very low solubility of
the PHC molecule in polar and non-polar solvents requires its
Syntheticmacrocycliccompoundsknownasphthalocyanines
(PHCs) are derived from the basic structure of porphyrine [1]
(Fig. 1). They differ in a character of the central atom, which is
usually represented by an atom of metal with direct implication
in their physical and chemical properties. It must be noted that
also various phthalocyanines are synthetically simply available.
Because of their characteristic light absorption in the well-
defined region of the visible part of the spectrum they have been
used as common industrial colorants, such as pigments, direct
dyes, reactive dyes, solvent dyes and vat dyes [1,2]. Also, many
other applications have appeared recently including the photo-
dynamic therapy, gas sensors, solar cells technology, catalysis
and photocatalysis [3–8]. These applications arise from the abil-
ity of most of the PHCs to produce highly active oxygen either in
the form of singlet 1O2 or in the form of various reactive oxygen
∗
Corresponding author. Tel.: +420 220 444 158; fax: +420 220 441 968.
E-mail address: P.Kluson@seznam.cz (P. Kluson).
URL: http://www.vscht.cz/kot/en/list/petr kluson.html (P. Kluson).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.03.024

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P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
Fig. 1. Basic structure of porphyrin (A), metal free phthalocyanine (B), metal phthalocyanine (C) and sulphonated metal phthalocyanine (D).
tion of Al3+ (aluminium acetate, Aldrich), were of chloride
origin (all p.a., Fluka). Other chemicals, such as 4-chlorophenol,
quinoline, acetone, methanol, 1,1-dioxothiolan, urea and chloro-
sulphonic acid were of analytical grades and were received from
Aldrich.
chemical modification. For aqueous solutions it is necessary to
introduce specific chemical functional groups to benzene rings
ofthebasicPHCskeleton. Themostfrequentchemicalmodifica-
tions are sulphonated [24,36] or carboxylated [29,37] derivatives
already well soluble in water, but, tending to aggregate [25]. For
the sulphonated molecules of PHCs it was found that higher
the content of more sulphonated individual derivatives, higher
the tendency for aggregation [18,36,25]. On the other hand, mix-
turesofderivativesofPHCsatdifferentsulphonationstageswere
not seriously affected by aggregation [24]. Also some additives,
such as surfactants or certain alcohols may limit this undesired
phenomenon [33,38]. Another possibility to prepare active, sta-
ble and non-aggregated phthalocyanines could be based on their
heterogenisation [39,40].
2.2. Preparation of PHCs
Phthalocyanines used in this work were produced either in a
solvent (metal free PHC, SiPHC, ZnPHC, TiPHC) or by means
of the solvent free method (AlPHC, CoPHC, NiPHC, CuPHC).
2.2.1. Synthesis in a solvent (batch process)
In this paper, we report on preparation, chemical modification
(sulphonation), characterisation and practical catalytic utilisa-
tion of metal free phthalocyanine and phthalocyanines with Zn,
Al, Si, Co, Ni, Cu and Ti central atoms in 4-chlorophenol oxida-
tion under UV and visible light activation. The role of pH is also
discussed. To the best of our knowledge, such a comparison for
both distinctive light regions and for such an extended series of
PHCs has not been published yet.
Metal free PHC (MeFPHC): o-Phthalodinitrile + quinoline
(solvent) mixed for 8 h at 473 K and 10 MPa of hydrogen, then
refined from acetone.
SiPHC: o-Cyanobenzamide (produced from o-phthalodini-
trile, acetic acid and acetanhydride) + quinoline + o-dichloro-
benzene, stirred under nitrogen with slow addition of SiCl4 at
483 K for 2 h, filtered and washed with hot quinoline, pyridine,
acetic acid and ethanol.
ZnPHC: o-Pthalodinitrile + ZnCl2 + nitrobenzene (solvent),
ammonium molybdenate (catalyst), ammonia. This mixture
was stirred for 6 h, refluxed and stripped with ammonia, fil-
tered and washed with methanol and finally precipitated from
96% sulphuric acid.
2. Experimental
2.1. Chemicals
o-Pthalodinitrile was used for preparation of various PHCs
and it was supplied by BASF, all metal ions (Zn2+, Si4+, Co2+,
Ni2+, Cu1+, Ti4+) appearing in the PHCs skeletons, with excep-
TiPHC: o-Cyanobenzamide (produced from o-phthalodi-
nitrile, acetic acid and acetanhydride) + quinoline + o-
dichlorobenzene, stirred under nitrogen with slow addition

P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
215
of TiCl4 at 483 K, filtered and washed with hot quinoline,
pyridine, acetic acid and ethanol.
by HPLC (Shimadzu LC 20A Prominence) with LiChrosper
100 RP-18 (5 ␮m) column and methanol/water mobile phase
(40/60). Content of PHCs in withdrawn samples of reaction
mixtures was verified spectrally (UV–vis spectrometer, Cecil
Instruments)withintherange250–800 nm. Thesameinstrumen-
tation was also used for characterisation of absorption intervals
of the produced chemically modified mixtures of PHCs deriva-
tives (cPHC = 1.4 × 10−5 mol/dm3). In experiments, constant pH
was established and maintained (NaOH solution) by means of
the automatic titration equipment Titrator Manager TIM 856
(TitraLab) with a combined pH electrode (Radiometer).
2.2.2. Solvent free synthesis
AlPHC: Phthalanhydride + urea mixed with aluminium
acetate, sodium sulphate and ammonium molybdenate, stirred
in a batch reactor at 463 K, then precipitated from 96% sul-
phuric acid.
CoPHC: Phthalanhydride + urea mixed with CoCl2 dihydrate,
sodium sulphate and ammonium molybdenate (catalyst), reac-
tion carried out in continuous stirred tank reactor (CSTR) at
463 K, then it was precipitated from 96% sulphuric acid.
NiPHC: Phthalanhydride + ureamixedwithNiCl2, sodiumsul-
phate and ammonium molybdenate, carried out in CSTR at
463 K and then precipitated from 96% sulphuric acid.
CuPHC: Phthalanhydride + urea mixed with Cu2Cl2, sodium
sulphate and ammonium molybdenate, carried out in CSTR at
463 K and then precipitated from 96% sulphuric acid.
2.5. Quantum yields
Values of quantum yields φ were evaluated for all studied
reactions. The quantum yield (%, Eq. (1)) represents a basic
kinetic parameter of a photophysical and/or photochemical pro-
cess reflecting the quantitative relationship between the number
of involved (reacting) molecules and the number of involved
photons:
2.3. Chemical modification of PHCs
Vcik
φ =
100
(1)
JhνA
Sulphonations were carried out either in fuming sulphuric
acid (AlPHC, CoPHC, NiPHC, CuPHC) or in 1,1-dioxothiolan
with chlorosulphonic acid (ZnPHC, MeFPHC, TiPHC). Reac-
tions in fuming sulphuric acid were performed in atmosphere
of carbon dioxide. The extent of sulphonation, representation
of mono, di, tri and tetra-sulphonated derivatives, was managed
in both reaction systems by means of reaction temperature and
reaction time. Composition of the prepared mixtures of deriva-
tives was characterised by thin layer chromatography (TLC)
together with quantitative elemental (C, N, H, S) analysis (Ele-
mentar Vario EL III).
in which Jhν is the incident photon flux intensity (Ein-
stein s−1 m−1, Eq. (2)), V represents the reaction volume (m3),
ci the initial concentration of 4-chlorophenol (mol/m3), A the
illuminated area (m2) and k is the rate constant (s−1). For deter-
mination of rate constants k the first order kinetics was assumed
for all reactions.
λPf
Jhν
=
(2)
hγNA
where Pf is the experimentally measured irradiation intensity
(W/m), λ the maximum wavelength of the used illumination
source, h the Planck constant 6.626 × 10−34 J s, γ the light
velocity in vacuum (3 × 108 m/s) and NA denotes the Avogadro
number (6.022 × 1023 mol−1).
2.4. Photocatalytic experiments
These experiments were carried out in a magnetically stirred
batch reactor (300 ml, reaction mixture volume 200 ml, satu-
rated with air) illuminated with well-defined sources of light in
the UV and visible regions. For the visible light measurements
three fluorescent tubes Narva Yellow Special 016 (emission
interval 500–700 nm, maximum at 580 nm, verified on spec-
trofluorometer Fluoromax 2, Jobin Yvon) with nominal output
18 W each were fitted exactly 100 mm above the level of the
reaction mixture. The irradiation intensity measured at this
level was 1.52 mW/cm2 (determined with help of a Si photo-
diode Hamamatsu S1337-BQ). Experiments in the UV region
were carried out with three Narva Blacklight Blue 073 lamps
(emission interval 330–400 nm, verified on spectrofluorometer
Fluoromax 2, Jobin Yvon) with nominal output 18 W each. The
irradiation intensity measured at a level of the reaction mixture
was 1.29 mW/cm2 (determined with help of UV Light Meters,
Mannix Interstate). 4-Chlorophenol solved in high pressure liq-
uid chromatography (HPLC) grade water was employed as a
model compound (1 × 10−4 mol/l). Water solution of PHC in the
form of sodium salt of its sulphoacid was introduced as a catalyst
(7 × 10−6 mol/l). Samples of reaction mixtures were analysed
3. Results and discussion
The principal property of a PHC molecule comprises its
ability to absorb photons in two distinctive and well-separated
regions. The major absorbance band, which is associated with
the visible colour properties of PHCs, is located inside of the
interval 500–700 nm and it is usually referred to as the Q band.
Significant light absorption below 400 nm denotes then for
interactions with highly energetic photons in the UV region.
Absorption spectra recorded for a series of eight PHCs used
in this work are shown in Fig. 2a–d. The multimodal course
(bimodal) of absorption bands in both regions is a characteristic
feature revealed by all chemically modified PHCs due to their
aggregation tendency. It should be noted that besides monomers
mostly dimeric forms appear and their absorption bands are
those shifted toward energetically more abundant region. For
the modified PHCs it was observed that the higher the content
(HPLC) of more sulphonated individual derivatives, the higher
was the tendency for their aggregation. On the other hand,

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P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
Fig. 2. (a) Absorption spectra of sulphonated Zn and AlPHC, cPHC = 1.4 × 10−5 mol/dm3. (b) Absorption spectra of sulphonated Si and TiPHC,
cPHC = 1.4 × 10−5 mol/dm3. (c) Absorption spectra of sulphonated Co and NiPHC, cPHC = 1.4 × 10−5 mol/dm3. (d) Absorption spectra of sulphonated Cu and
MeFPHC, cPHC = 1.4 × 10−5 mol/dm3.
mixtures of derivatives of PHCs at different sulphonation
stages were not seriously affected by this phenomenon and
mostly dimers appeared along with the monomeric forms. This
finding also described in literature [24] rendered possible to use
mixtures of sulphonated derivatives rather than pure individual
derivatives obtainable by tedious chromatography separation.
An essential part of this work was focused on activity tests of
the prepared and chemically modified PHCs. These tests were
accomplished as the homogeneous photocatalytic decomposi-
tion of 4-chlorophenol (4CP) in aqueous solution using low
intensity visible (500–700 nm) and UV (330–400 nm) light. The
model reactant 4-chlorophenol was chosen because of its antic-
ipated simple decomposition mechanism (Fig. 3) and it also
represented a characteristic trace pollutant of drinking water
processed by chlorination. Forming intermediates and reaction
products were identified by HPLC and LC–MS techniques.
However, for the kinetic data treatment only the change of the
relative concentration of 4-chlorophenol as a function of time
was used and the raw experimental results were plotted as a
dependency of natural logarithm of a relative concentration of
4CP on time. Initially, some effort had been spent to describe
the progress of the reaction without any catalyst (PHC), only
with UV–vis light and 4-chlorophenol. It must be noted that 4-
chlorophenol was found completely photo-inactive (under used
experimental conditions) and the indispensable role of UV–vis
light was also proofed by excluding it in reactions involving only
PHCs and 4-chlorophenol (no transformation of 4CP). Monitor-
ing of the photocatalytic reaction embodied the periodic sample
Fig. 3. Oxidation mechanism of 4CP.

P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
217
Fig. 4. Photooxidation of 4CP catalysed by sulphonated phthalocya-
nines with different central metal atoms in the visible light region
(c4CP(initial) = 1 × 10−4 mol/dm3, cPHC = 7 × 10−6 mol/dm3, pH 10).
Fig. 5. Photooxidation of 4CP catalysed by sulphonated AlPHC in the vis-
ible light region (c4CP(initial) = 1 × 10−4 mol/dm3, pH 10), variable conc. of
AlPHC—different amount of the catalyst.
of dissolved oxygen molecules in the reaction mixture at high
PHC concentrations.
withdrawal, theHPLCanalysisandtheverificationspectralanal-
ysis on the content of PHC. With the used concentrations and
sources of photon flux a typical reaction run took about 200 min.
The first set of experiments was carried out at pH 10 and with
photons emitted in the visible region. It was evident (Fig. 4)
that sulphonated phthalocyanines of Si and Al significantly sur-
passed the remaining members of the series. ZnPHC revealed
moderate photocatalytic activity and the other used PHCs could
be referred to as not active. These findings were in compliance
withtheprominentconceptofthesingletoxygengenerationonly
by certain PHCs with a specific electronic molecular structure.
The exited triplet states with longer life-time are characteristic
for porphyrins involving metal ions with completely occupied
d-orbitals (e.g. AlPHC, SiPHC, ZnPHC). In such cases, prob-
ability of interactions of the lower active triplet oxygen with
molecular oxygen yielding the active singlet oxygen was much
higher. On the other hand, CoPHC, NiPHC, CuPHC and TiPHC
contained ions with not fully occupied d-orbitals. Thus, these
molecules upon photon flux absorption tended toward rapid
extinction of their excited triple states with consequences in a
lower number of formed active species (singlet oxygen) and thus
also in much lower observed photocatalytic activity. Negligible
photocatalytic activity observed for metal free phthalocyanine
(MefreePHC) could beascribed toasimilarphenomenon despite
no metal ion was present in its molecule (incompletely occupied
valence sphere).
To elucidate the photostability of AlPHC, ZnPHC and SiPHC
constrained to the duration of a typical reaction run these pho-
tocatalysts were exposed to standard experimental conditions
(without 4CP) and the mixtures were analysed on their content
periodically. Decomposition of the three active phthalocyanines
induced by photons emitted inside of the Q-band was insignifi-
cant as indicated in Fig. 6 (diminution of the relative absorbance
as a function of time). After an initial decline down the level
of ∼90% (25 min) the parameter of relative absorbance (A/A0)
remained already constant.
The pH value as one of the most important parameters affect-
ing rate of the studied photocatalytic reaction was optimised
separately for AlPHC and SiPHC. The positive role of the more
basic reaction environment is shown in Fig. 7 for the pH inter-
val 7.5–10. By increasing the pH value of the reaction mixture
the tendency of the Lewis type acids Al(III) or Si(IV) to coor-
dinate OH− ions also increased. Due to this coordination the
discussed phenomenon of aggregation was significantly limited
As expected, experiments with variable load of PHC (vari-
able initial concentration of PHC in water) revealed more rapid
decomposition of 4CP with increased initial concentration of
PHC as shown in Fig. 5 for AlPHC. However, this trend was
not linear, especially at higher concentrations of AlPHC. The
interpretation might be sought both in terms of the “light trans-
port” effects causing that the activating photons still available in
high abundance were, however, absorbed by only some of the
PHC molecules despite vigorous mixing and potentialy also by
their increased tendency to aggregate (typical at high concen-
trations). Another possible reason might be seen in a deficiency
Fig. 6. Diminution of the relative absorbance of phthalocyanine in time
(cPHC(initial) = 7 × 10−5 mol/dm3).

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P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
Fig. 7. Photooxidation of 4CP catalysed by sulphonated AlPHC in the visible
light region (c4CP(initial) = 1 × 10−4 mol/dm3, cPHC = 7 × 10−6 mol/dm3), differ-
ent values of pH.
Fig. 8. Photooxidation of 4CP catalysed by sulphonated phthalocya-
nines with different central metal atoms in the UV light region
(c4CP(initial) = 1 × 10−4 mol/dm3, cPHC = 7 × 10−6 mol/dm3, pH 10).
and only sulphonated PHC monomers and dimers were spec-
trally detected. Larger aggregates appearing at pH values closer
to the neutral region were found much less active. It must also
be noted that, specifically for 4CP, in basic reaction environ-
ment more molecules of 4-chlorophenol were transformed to
phenolates with lower redox potential and thus it was easier
to oxidise them. At higher pH values 4-chlorophenol was oxi-
dised stepwise with formation of various intermediates. Among
them p-benzoquinone (in equilibrium with hydroquinone) dom-
inated. Due to high pH of the solution further oxidation lead
especially to formation of sodium salts of maleic and fumaric
acids. Such reaction products and intermediates caused rapid
decline of pH, consequent aggregation of PHC and then a drop
of its photoactivity. To avoid these unfavourable effects con-
stant pH was established and maintained (NaOH solution) by
means of the automatic titration equipment combined with a pH
electrode.
Similar experimental setup (pH 10) with exception of the
source of the photon flux was used to inspect the photocatalytic
properties of the series of sulphonated PHCs in the UV region.
As clearly evidenced in Fig. 8 again only AlPHC, SiPHC and
ZnPHC might be referred to as photoactive species. This find-
ing was not very surprising because the same mechanism as
previously was being considered responsible for their enhanced
photocatalytic activity. Despite presence of energetically more
abundant photons the three active PHCs were again found very
stable under experimental conditions.
obtained (3.93 × 10−9 Einstein s−1 cm−2/UV and 7.39 × 10−9
Einstein s−1 cm−2/VIS). Such a distinction might be theoreti-
cally attributed to the fact that the light source in the visible
region emitted more photons than that emitting in UV. In the
UV region photons were, on the other hand, more abundant in
energy. Regarding the studied photocatalytic transformation of
4CP the key parameter was represented rather by the number
of photons than their energies because of the accepted the-
oretical stoichiometry, one incident photon = one transformed
molecule. Accordingly, the reactions in the visible regions
should be favoured, however, as it is evident form Table 1 that
rate constants and calculated quantum yields were much higher
for reactions carried out with UV light. Emission spectrum of
the lamp in the UV region covered perfectly the very strong
absorbance band of the three active PHCs (AlPHC, SiPHC,
ZnPHC). It might be expected that most of the incident pho-
tons were effectively absorbed. On the other hand maximum of
the emission spectrum of the visible light source was shifted
slightly toward the yellow colour comparing with the maximum
of absorption bands of PHCs. In this case, it might be expected
that only a certain proportion of incident photons was effectively
absorbed with direct implications in the values of the rate con-
Table 1
RateconstantsandquantumyieldsforreactionswithAlPHC, SiPHCandZnPHC
The first order kinetics of the 4CP decomposition is explicit
from the previously discussed graphs and thus the slopes of the
lines could be identified with the rate constants k. These val-
ues are listed in Table 1 for the UV and visible regions together
with quantum yields and corresponding pH values for AlPHC,
SiPHC and ZnPHC. The parameter of quantum yield φ reflected
the quantitative relationship between the number of reacting
molecules of 4CP and the total number of involved photons in
the particular region of the lamp emission. Irradiation intensities
in the UV and visible regions were very similar, 1.29 × 10−2
and 1.52 × 10−2 W/cm2, respectively. However, when photon
flux intensities were inferred values differing significantly were
pH
Visible region
UV region
k (min−1 Φ4CP (%) k (min−1
)
)
Φ4CP (%)
AlPHC(SO3Na)mix 10
1.1 × 10−2 0.53
3.4 × 10−3 0.16
3.3 × 10−3 0.16
2.5 × 10−2 2.25
2.3 × 10−2 2.03
1.0 × 10−2 0.91
9
8
SiPHC(SO3Na)mix 10
9.5 × 10−3 0.45
3.9 × 10−3 0.19
5.4 × 10−4 0.02
9
8
ZnPHC(SO3Na)mix 10
5.0 × 10−3 0.24
1.9 × 10−3 0.09
5.0 × 10−4 0.02
9
8

P. Kluson et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 213–219
219
stants and quantum yields. Thus, the evaluated quantum yields
in the visible region must be referred to only as apparent due
to a limited number of absorbed photons and their comparison
with formally similar values for the UV region must be carried
out with precaution.
The indispensable role of constant pH value carefully opti-
mised (∼10) in the experiments with visible light is also evident
from Table 1. Only a fractional decline below the optimised level
was immediately reflected in lower values of rate constants and
apparent quantum yields.
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A series of phthalocyanines with different central atoms
including the metal free phthalocyanine were successfully syn-
thesised. These structures were chemically modified by means
of sulphonation with fuming sulphuric acid or chlorosulphonic
acid in the organic solvent sulpholane. The prepared derivatives,
mostly in monomeric and dimeric forms, were characterised
spectrally and then used in photochemical reactions. Due to their
significant absorption in visible and UV regions the experiments
were also carried out in two well-separated regions with two
1
distinctive sources of photons. The singlet oxygen O2, which
was generally accepted as the active species in such reaction,
was identified sufficiently abundant only for phthalocyanines
with completely occupied d-orbitals. AlPHC, SiPHC, ZnPHC
revealed much longer life-time of the excited triple-states in
comparison with CoPHC, NiPHC, CuPHC, TiPHC, MefreePHC
and yielding effectively upon their contact with molecular oxy-
gen its active singlet form. Determined values of quantum yield
for reactions carried out in the UV region were always higher
than for reactions induced by the visible light. The effectiveness
of the studied photoreaction was also strongly dependent on the
pH value. It was optimised in a set of experiments in the visi-
ble region and then kept constant (∼10). In neutral or less basic
reaction environment molecules of PHCs tend to aggregate with
consequences in diminishing their photocatalytic activity.
[31] V. Iliev, L. Prahov, L. Bilyarska, H. Fischer, G. Schultz-Ekloff, D. Wohrle,
L. Petrov, J. Mol. Catal. A 151 (2000) 161.
Acknowledgements
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Khim. 70 (2000) 133.
Authors wish to thank to Ministry of Education of the Czech
Republic, project NanoPin No. 1M4531433201 and to Grant
Agency of Academy of Sciences of the Czech Republic, project
HNPM No. KAN400720701, for funding this research. M.D.
also thanks to Grant Agency of the Czech Republic for funding
partly his Ph.D. (Doctoral Grant No. 203/03/H140).
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