Synthesis and electronic absorption studies of novel (trifluoromethyl) phenoxy-substituted phthalocyanines

Article abstract of DOI:10.1007/s00706-011-0614-3

The reaction of 4-[4-(trifluoromethyl)phenoxy]phenol with 4-nitrophthalonitrile in the presence of K₂CO₃ leads to formation of 4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]phthalonitrile. Tetrakis[4-[4-(trifluoromethyl)phenoxy]phenoxy]-substituted metal-free phthalocyanine was achieved by tetramerization of the phthalonitrile in 2-(dimethylamino)ethanol, whereas metallophthalocyanines were prepared in the presence of zinc, cobalt, or copper salts. These compounds show high solubility in weakly and medium polar solvents, in strongly polar solvents (dimethylformamide, dimethylsulfoxide), and in aromatic hydrocarbons (toluene, benzene). The new phthalocyanines were characterized by elemental analyses, ¹H nuclear magnetic resonance (NMR), ¹³C NMR, ¹⁹F NMR, ultraviolet-visible (UV-Vis), Fourier-transform infrared (FT-IR), and mass spectroscopic methods.

Full text of DOI:10.1007/s00706-011-0614-3

Monatsh Chem (2012) 143:437–442
DOI 10.1007/s00706-011-0614-3
ORIGINAL PAPER
Synthesis and electronic absorption studies of novel
(trifluoromethyl)phenoxy-substituted phthalocyanines
¨
•
•
Ayfer Kalkan Burat Zeliha Pınar Oz
Zehra Altuntas¸ Bayır
Received: 19 July 2010 / Accepted: 5 August 2011 / Published online: 3 September 2011
Ó Springer-Verlag 2011
Abstract The reaction of 4-[4-(trifluoromethyl)phen-
oxy]phenol with 4-nitrophthalonitrile in the presence of
K2CO3 leads to formation of 4-[4-[4-(trifluoromethyl)phen-
oxy]phenoxy]phthalonitrile. Tetrakis[4-[4-(trifluoromethyl)
phenoxy]phenoxy]-substituted metal-free phthalocyanine
was achieved by tetramerization of the phthalonitrile in
2-(dimethylamino)ethanol, whereas metallophthalocya-
nines were prepared in the presence of zinc, cobalt, or copper
salts. These compounds show high solubility in weakly and
medium polar solvents, in strongly polar solvents (dimeth-
ylformamide, dimethylsulfoxide), and in aromatic hydro-
carbons (toluene, benzene). The new phthalocyanines were
[9], nonlinear optics [10], solar energy conversion [11], and
electrochromism [12, 13].
Most notable among the uses of phthalocyanines is as
photosensitizers in photodynamic therapy (PDT) [14–16].
Zinc phthalocyanines in particular are well known for their
photosensitizing abilities, while unmetallated phthalocya-
nine derivatives show very little PDT effect [17, 18]. Also
metallophthalocyanine derivatives act as photosensitizers
for different reactions including transformation of alkenes
and alkanes [19] and degradation of pollutants [20].
The specificity of applications of phthalocyanines can be
modified by both changes in the phthalocyanine p-conju-
gation or changes in the central metals. Unsubstituted
phthalocyanines and their metal-ion-containing derivatives
are characterized by strong intermolecular cohesion, which
results in nonmelting, insoluble solids. Peripheral or non-
peripheral attachment of bulky or long-chain groups to the
phthalocyanine greatly increases the solubility of these
complexes in common organic solvents due to enhanced
disaggregation over that observed for other phthalocyanine
complexes in solution. Among these, we may cite alkoxy
[21–24], aryloxy [25–28], alkylsulfanyl [29, 30], aryl-
sulfanyl [31], and bulky groups [32, 33]. The introduction
of amino, pyridyl, or carboxy groups gives water-soluble
products [34–36]. Also these substituents offer a useful
way of regulating the wavelength of the Q band. Although
phthalocyanines carrying electron-donating substituents
have frequently been described, those with electron-with-
drawing groups have not been extensively studied,
especially those containing fluorine atoms. Recently, sev-
eral workers reported the synthesis and properties of some
fluoroalkoxy-substituted phthalocyanines [37–39].
1
characterized by elemental analyses, H nuclear magnetic
resonance (NMR), 13C NMR, 19F NMR, ultraviolet-visible
(UV-Vis), Fourier-transform infrared (FT-IR), and mass
spectroscopic methods.
Keywords Aggregation Á Metals Á Phthalocyanines Á
Phenoxy Á Solubility
Introduction
Phthalocyanines have been investigated in detail for many
years with respect to their attractive optical and electrical
properties combined with thermal and chemical stability
[1, 2]. In addition to their use as blue/green colorants,
phthalocyanines have been recently expanding into applied
fields such as catalysts [3, 4], photocatalysts [4, 5], sensors
[6], optical data storage [7], liquid crystals [8], xerography
¨
A. K. Burat Á Z. P. Oz Á Z. A. Bayır (&)
Fluorine compounds are known to enhance the solubility
of phthalocyanine in polar, aprotic solvents [40]. Intro-
ducing electron-withdrawing fluorine substituents to the
Department of Chemistry, Istanbul Technical University,
Maslak, Istanbul 34469, Turkey
e-mail: bayir@itu.edu.tr
123

438
A. K. Burat et al.
Scheme 1
phthalocyanines shifts the redox processes towards positive
potentials [41]. Phthalocyanines are shown to catalyze
reactions such as the reduction and/or oxidation of some
special species, oxygen, carbon dioxide, and formic acid
[42, 43]. Fluorinated phthalocyanines and porphyrin
derivatives provide some advantages over nonfluorinated
derivatives as photosensitizers [44–47]. The influence of
the trifluoromethyl group in biologically active molecules
is associated with the increased lipophilicity that this sub-
stituent imparts [48].
During the last few years we have focused on the prepa-
ration and study of phthalocyanines and related compounds.
The introduction of functional groups on the phthalocyanine
improves its solubility and enhances electrochemical and
optical properties of the phthalocyanines [49–51]. The prime
objective of the present work is the synthesis and charac-
terization of new readily soluble phthalocyanines with
strong electron-withdrawing substituents. The catalytic
efficiency of phthalocyanine complexes depends on their
aggregation state and the influence of the medium on sta-
bilization of the catalytically active coordination forms [52].
In this connection, the aggregation behavior of the synthe-
sized complexes was studied by electronic spectroscopy in
different solvents and over a wide concentration range.
Scheme 2
experimental conditions that may vary from one complex to
another, was efficient. The phthalocyanines were isolated by
column chromatography on silica gel.
Results and discussion
Tetrasubstituted phthalocyanines, synthesized from
3- and 4-substituted phthalonitrile or other ortho-disubstituted
phenyl derivatives, are obtained as mixtures of four
structural isomers with D2h, C4h, C2v, and Cs symmetries,
respectively [56]. These isomers are rarely separable, but it
was shown to be possible by high-performance liquid
chromatography (HPLC) techniques [57]. No attempt was
made to separate the isomers of 5–7.
The 1H NMR, 13C NMR, 19F NMR, FT-IR, UV-Vis, and
MS spectral data for the newly synthesized compounds
were consistent with the assigned formulation. The results
are given in the experimental section.
A convenient route is to synthesize tetrasubstituted pht-
halonitriles through reactions between 4-nitrophthalonitrile
and donor groups, and the prepared phthalonitriles undergo
cyclotetramerization to give the corresponding phthalocy-
anines [53–55].
Starting from 4-nitrophthalonitrile (1) and 4-[4-(trifluo-
romethyl)phenoxy]phenol (2), compound 3 was obtained
by a base-promoted nucleophilic aromatic displacement.
The reaction was carried out at 30 °C in dry N,N-dimeth-
ylformamide (DMF) with K2CO3 as the base. The synthetic
route is shown in Scheme 1.
Template cyclotetramerization of dinitrile derivative 3 in
the presence of anhydrous metal salts [Zn(CH3COO)2,
CoCl2, CuCl2] gave the tetrasubstituted phthalocyanine
derivatives as shown in Scheme 2. Metal-free phthalocya-
nine 4 was obtained directly by refluxing 3 in 2-(dimethyl-
amino)ethanol. Column chromatographic purification, with
The infrared (IR) spectral results of the metallopht-
halocyanines 5–7 are different from compound 3, so the
sharp peak for the C:N vibration at 2,233 cm-1, associ-
ated with the nitrile group, disappeared after conversion
1
into the phthalocyanines. H NMR spectra of 3 in CDCl3
showed only the signal due to the aromatic ring protons at
123

Synthesis and electronic absorption studies
439
d = 7.75–7.07 ppm. 19F NMR spectroscopy is a very
useful technique for investigating the fluorinated com-
pound. The 19F NMR spectrum of 3 showed a peak at
-64.66 ppm.
The IR spectra of metal-free phthalocyanine 4 show an
NH stretching band at 3,287 cm-1 due to the inner core
imino group. These protons are also very well character-
1
ized by the H NMR spectrum, which shows a peak at
d = -6.08 ppm as a result of the aromatic 18 p-electron
system of the phthalocyanine ring.
1H NMR spectra of ZnPc 5 provided the characteristic
chemical shifts for the structure expected. The aromatic
protons appeared between 7.55 and 6.98 ppm. The IR
spectrum of ZnPc exhibits two bands at 3,111 and
3,063 cm-1 assigned to the symmetric and asymmetric
stretching vibration of -CH in the aromatic ring, and at
two bands 1,407 and 1,251 cm-1 assigned to the aromatic
C–H bending vibrations.
Fig. 1 Electronic spectra of 4–7 in chloroform; c = 6 9 10-6
M
interactions between the aromatic macrocycles. Aggrega-
tion is easily detected from optical absorption studies. Any
increase in concentration results in aggregation of phtha-
locyanine molecules which is accompanied by a blueshift of
the Q band with some decrease in intensity [59]. The
aggregation behavior of the phthalocyanine complexes was
investigated in different solvents. The optical absorption
spectra of compound 4 depend on the solvent type. It has
been concluded that aggregation is enhanced by solvent
polarity. The tendency to form aggregates increases in
the order: tetrahydrofuran \ chloroform \ dimethylform-
amide \ dichloromethane \ ethyl acetate \ dimethylsulf-
oxide for metal-free phthalocyanine 4 (Fig. 2).
Phthalocyanines show typical electronic spectra with
two strong absorption regions, one of them in the UV
region at about 300–400 nm (B-band) arising from the
deeper p-levels ? lowest unoccupied molecular orbital
(LUMO) transition and the other in the visible region at
600–700 nm (Q band) attributed to the p-p* transition
from the highest occupied molecular orbital (HOMO) to
the LUMO of the phthalocyanine ring [58]. The UV-Vis
spectrum of metal-free phthalocyanine in chloroform dis-
played two characteristic absorption bands in the visible
region at 666 and 702 nm.
In this work, the aggregation behavior of the complexes
4–7 was examined in two different concentration ranges in
chloroform (Fig. 3, for complex 5 as an example). In the
concentration range of 4.00 9 10-6 to 14.00 9 10-6 M,
the intensity of absorption of the Q band increased in par-
allel with the increase in the concentration and there were
no new bands (normally blueshifted) due to the aggregated
species [1, 36]. This means that the phthalocyanine
The UV spectra of ZnPc, CuPc, and CoPc show the
typical absorptions of phthalocyanines, mainly the p-p*
transitions within the heteroaromatic p system. The UV-Vis
spectrum of ZnPc 5 in CHCl3 exhibited a typical B-band at
351 nm and a Q band at 680 nm with a weak band at
612 nm. The UV-Vis spectra of CoPc 6 and CuPc 7 were
very similar to that of ZnPc, and the data are given in Fig. 1.
Cobalt phthalocyanine 6 displays a Q band around 671 nm
in chloroform, whereas zinc and copper phthalocyanines
show nearly the same values around 680 nm and illustrate
*9 nm bathochromic shifts according to the cobalt
phthalocyanine analog. The introduction of CF3 groups at
the para-positions of phenoxy groups in phthalocyanines
4–7 resulted in very good solubility of these macrocycles in
most organic solvents, including acetone. The newly pre-
pared phthalocyanines 4–7 displayed high solubility in
various organic solvents such as toluene, chloroform, tetra-
hydrofuran (THF), ethyl acetate, and acetone.
Aggregation is usually depicted as a coplanar association
of rings progressing from monomer to dimer and higher-
order complexes. It is dependent on the concentration,
nature of the solvent, nature of the substituents, complexed
metal ions, and temperature. For phthalocyanines, the
aggregation behavior in solution is a good indication of
Fig. 2 Electronic spectra of 4 in a toluene, b tetrahydrofuran, c ethyl
acetate, d dimethylsulfoxide, e dimethylformamide, f dichlorometh-
ane; c = 6 9 10-6
M
123

440
A. K. Burat et al.
Fig. 3 Aggregation behavior of 5 in chloroform at different concentrations: a 14 9 10-6 M, b 12 9 10-6 M, c 10 9 10-6 M, d 8 9 10-6 M,
e 6 9 10-6 M, and f 4 9 10-6
M
Conclusions
The main aim of the work is to synthesize new highly
soluble phthalocyanine complexes with strong electron-
withdrawing substituents on the periphery of the macro-
cyclic ligand. These novel complexes possessed excellent
solubility in various organic solvents such as CH2Cl2,
THF, DMF, DMSO, toluene, and acetone. Catalytic prop-
erties of these novel fluorinated phthalocyanines will be
investigated.
Experimental
Fig. 4 Electronic spectra of
5
in chloroform: a
1 9 10-4 M,
b 5 9 10-5 M, c 1 9 10-5 M, d 5 9 10-6 M, and e 1 9 10-6
M
IR spectra were recorded on a PerkinElmer Spectrum One
FT-IR (ATR sampling accessory) spectrophotometer,
and electronic spectra on a Scinco Neosys-2000 double-
derivatives 4–7 did not show aggregation in chloroform in
this concentration range and the Beer–Lambert law was
obeyed for all of these compounds. The aggregation
behavior of the phthalocyanine complex 5 was also inves-
tigated for the concentrations ranging from 1.00 9 10-6 to
1.00 9 10-4 M (Fig. 4). At the lower concentration side
(10-6 M), the Q band of the phthalocyanine complex 5 is
the major band in the long-wavelength region and Q band
corresponding to monomeric species appeared around
670–680 nm. When the concentration of the compound was
raised to 10-4 M, Q band absorptions for monomeric spe-
cies and aggregated ones become almost equally intense;
i.e., the aggregated form of the phthalocyanine molecules
has taken the priority at these concentrations.
1
beam UV-Vis spectrophotometer. H NMR spectra were
recorded on a Bruker 250 MHz spectrometer using tetra-
methylsilane (TMS) as internal reference. 13C NMR and
19F NMR spectra were recorded on a Varian Unity Inova-
500 MHz NMR spectrometer. Mass spectra were per-
formed on a Varian 711 mass spectrometer. All reagents
and solvents were of reagent-grade quality, obtained from
commercial suppliers. The homogeneity of the products
was tested in each step by thin-layer chromatography
(TLC). All solvents were dried and purified as described by
Perrin and Armarego [60]. The solvents were stored over
molecular sieves. 4-Nitrophthalonitrile [61] was prepared
by reported procedures.
123

Synthesis and electronic absorption studies
441
4-[4-(Trifluoromethyl)phenoxy]phenoxy]phthalonitrile
(3, C21H11F3N2O2)
2,9,16,23-Tetrakis[4-[4-(trifluoromethyl)phenoxy]-
phenoxy]phthalocyaninatozinc(II) (5, C84H44F12N8O8Zn)
Compound 3 (0.20 g, 0.52 mmol) and 0.024 g Zn(CH3
COO)2 (0.13 mmol) were mixed in 1 cm3 dry 2-(dimethyl-
amino)ethanol in a glass tube. The mixture was sealed and
heated at 150–160 °C for 24 h under N2 to give the desired
substituted phthalocyanine. After being cooled, the reaction
mixture was poured into 50 cm3 ice-water mixture and the
bluish-green precipitate was separated by filtering and
washed several times with hot hexane. Finally the solid
was dried and purified by column chromatography on silica
gel using THF as eluent. Yield 0.050 g (24%); m.p.:
[200 °C; 1H NMR (250 MHz, CDCl3): d = 7.55-6.98 (m,
44H, Ar–H) ppm; 13C NMR (500 MHz, CDCl3): d = 175.44
(2C, pyrrole C), 160.65 (2C, pyrrole C), 158.13 (2C, pyrrole
C), 153.14 (4C, aromatic C–O), 151.62 (4C, aromatic C–O),
149.59 (8C, aromatic C–O), 137.64 (2C, pyrrole C), 130.64
(4C, aromatic C), 127.25 (4C, aromatic C), 126.32 (8C,
aromatic C), 125.13 (4C, C–F), 124.83 (4C, aromatic C),
122.00 (8C, aromatic C), 121.50 (2C, aromatic C), 120.93
(4C, aromatic C), 118.93 (4C, aromatic C), 117.48 (16C,
aromatic C), 110.65 (2C, aromatic C) ppm; IR: vꢀ = 3,111–
3,063 (Ar–H), 1,612, 1,493, 1,470, 1,407, 1,320 (C–F),
1,251, 1,220, 1,158, 1,061, 946, 830, 748 cm-1; UV-Vis
(CHCl3, c = 6Á10-6 mol dm-3): kmax (e) = 351 (83,333),
612 (33,333), 680 (178,333) nm (mol-1 dm3 cm-1).
4-Nitrophthalonitrile (1, 0.5 g, 2.89 mmol) was dissolved in
20 cm3 dry DMF. To this was added 1.47 g 4-[4-(trifluoro-
methyl)phenoxy]phenol (2, 5.78 mmol). After stirring for
15 min, 1.79 g dry and finely powdered potassium carbonate
(13 mmol) was added portionwise over 2 h with efficient
stirring. The reaction mixture was stirred under nitrogen at
room temperature for 48 h. After 2 days, the reaction
mixture was poured into a mixture of ice-water (400 cm3)
and the creamy precipitate that formed was filtered and
washed several times with water until the washing became
neutral. Finally the white compound was crystallized from
petroleum ether. Yield 0.89 g (81%); m.p.: 113 °C; 1H NMR
(250 MHz, CDCl3): d = 7.75 (d, 1H, Ar–H), 7.62 (d, 2H,
Ar–H), 7.28 (d, 2H, Ar–H), 7.15-7.07 (m, 6H, Ar–H) ppm;
13C NMR (125 MHz, APT, CDCl3): d = 162.61 (aromatic
C–O), 155.57 (aromatic C–O), 149.86 (aromatic C–O),
135.43 (aromatic CH), 127.31 (aromatic CH), 126.09
(aromatic C), 125.13 (C–F), 121.55 (aromatic CH), 121.32
(aromatic CH), 118.43 (aromatic C), 118.27 (aromatic CH),
115.53 (C:N), 115.49 (C:N), 109.71 (aromatic C) ppm;
19F NMR (470 MHz, CDCl3): d = -64.66 (CF3) ppm; IR:
vꢀ = 3,111 (Ar–H), 2,233 (C:N), 1,598, 1,501, 1,480, 1,322
(C–F), 1,235 (C–O–C), 1,063, 950, 833 cm-1
.
2,9,16,23-Tetrakis[4-[4-(trifluoromethyl)phenoxy]-
2,9,16,23-Tetrakis[4-[4-(trifluoromethyl)phenoxy]-
phenoxy]phthalocyanine (4, C84H46F12N8O8)
phenoxy]phthalocyaninatocobalt(II) (6, C84H44CoF12N8O8)
A mixture of 0.25 g 3 (0.65 mmol) and 0.021 g anhydrous
CoCl2 (0.16 mmol) was refluxed in 1 cm3 DMAE with
stirring for 24 h under N2. The resulting suspension was
cooled to room temperature, and the crude product was
precipitated by addition of a mixture of ice-water. It was
centrifuged off and washed first with water and then with hot
hexane. The blue product was obtained on silica gel with
toluene:THF (5:1) as eluent. Yield 0.080 g (31%); m.p.:
[200 °C; IR: vꢀ = 3,058 (Ar–H), 1,611, 1,495, 1,470, 1,408,
1,323 (C–F), 1,190, 1,064, 956, 835, 750 cm-1; UV-Vis
(CHCl3, c = 6Á10-6 mol dm-3): kmax (e) = 324 (80,000),
607 (38,333), 671 (136,666) nm (mol-1 dm3 cm-1).
Compound 3 (0.30 g, 0.79 mmol) was heated in 1 cm3 2-
(dimethylamino)ethanol (DMAE) at 150 °C for 24 h in a
sealed glass tube under nitrogen. After cooling to room
temperature, the reaction mixture was diluted with meth-
anol until the crude product completely precipitated. The
blue precipitate was centrifuged off and washed with hot
methanol and then dried in vacuo. The resulting solid was
purified by column chromatography on silica gel using
chloroform:cyclohexane (5:1) as eluent. Yield 0.09 g
(30%); m.p.: [200 °C; 1H NMR (250 MHz, CDCl3):
d = 7.65–6.82 (m, 44H, Ar–H), -6.08 (br s, 2H, NH)
ppm; 13C NMR (500 MHz, CDCl3): d = 175.21 (2C,
pyrrole C), 160.64 (2C, pyrrole C), 158.00 (2C, pyrrole
C), 154.41 (4C, aromatic C–O), 151.71 (4C, aromatic C–O),
149.98 (8C, aromatic C–O), 137.20 (2C, pyrrole C), 131. 14
(4C, aromatic C), 127.30 (4C, aromatic C), 126.29 (8C,
aromatic C), 125.22 (4C, C–F), 124.80 (4C, aromatic C),
123.06 (8C, aromatic C), 121.64 (2C, aromatic C), 121.10
(4C, aromatic C), 118.99 (4C, aromatic C), 117.51 (16C,
aromatic C), 110.50 (2C, aromatic C) ppm; IR: vꢀ = 3,287
(NH), 3,058 (Ar–H), 1,611, 1,494, 1,472, 1,423, 1,321
(C–F), 1,216, 1,189, 1,160, 1,090, 1,063, 1,008, 925, 833,
740 cm-1; UV-Vis (CHCl3, c = 6Á10-6 mol dm-3): kmax
(e) = 341 (91,666), 605 (40,000), 639 (61,666), 666
(161,666), 702 (190,000) nm (mol-1 dm3 cm-1).
2,9,16,23-Tetrakis[4-[4-(trifluoromethyl)phenoxy]-
phenoxy]phthalocyaninatocopper(II)
(7, C84H44CuF12N8O8)
Compound 3 (0.30 g, 0.79 mmol) was dissolved in 2 cm3
DMAE, and 0.026 g anhydrous CuCl2 (0.20 mmol) was
added to this solution. The reaction mixture was stirred at
reflux temperature for 24 h. The blue mixture was cooled
to room temperature and precipitated with a mixture of ice-
water. The precipitate was filtered off and washed first with
water and then with hexane. The desired compound was
purified by column chromatography on silica gel with
dichloromethane:hexane (3:1) as eluent. Yield 0.044 g
123

442
A. K. Burat et al.
25. Derkacheva VM, Luk’yanets EA (1980) Zhurnal Obs Khim
50:2313
(14%); m.p.: [200 °C; IR: vꢀ = 3,058 (Ar–H), 1,611,
1,495, 1,470, 1,408, 1,323 (C–F), 1,190, 1,064, 956, 835,
750 cm-1; UV-Vis (CHCl3, c = 6Á10-6 mol dm-3): kmax
(e) = 339 (68,333), 613 (40,000), 680 (143,333) nm
(mol-1 dm3 cm-1); MS (FAB): m/z = 1,585 (M ? 1).
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Acknowledgment This work was supported by the Research Fund
˙
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