Synthesis, Aggregation Behavior, and Electronic Properties of some Metallophthalocyanines with 2-Isopropyl-5-methylphenoxy Substituents

Article abstract of DOI:10.1002/zaac.201500121

The aim of this study was to perform facile synthesis of novel phthalocyanines with high solubility. The synthesis and characterization of 2-isopropyl-5-methylphenoxy substituted copper, zinc, nickel, and cobalt phthalocyanines are reported. The compounds

Full text of DOI:10.1002/zaac.201500121

Journal of Inorganic and General Chemistry
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500121
Synthesis, Aggregation Behavior, and Electronic Properties of some
Metallophthalocyanines with 2-Isopropyl-5-methylphenoxy Substituents
M. Salih Ag˘ırtas,*[a] Ceyhun Karatas,[a] and Selçuk Gümüs[a]
¸
¸
¸
Keywords: Phthalocyanine; Facile synthesis; Characterization; Electronic structure; Aggregation
Abstract. The aim of this study was to perform facile synthesis of isopropyl-5-methylphenoxy substituted phthalocyanine complexes do
novel phthalocyanines with high solubility. The synthesis and charac-
not have any aggregation behavior for the concentration range of
terization of 2-isopropyl-5-methylphenoxy substituted copper, zinc, 1ϫ10–5 to 1ϫ10–6 m in THF. Additionally, the ground-state geome-
nickel, and cobalt phthalocyanines are reported. The compounds were tries of the complexes were optimized using density functional theory
characterized by using electronic absorption, nuclear magnetic reso-
nance spectroscopy, infrared and elemental analysis. The aggregation
investigations carried out in different concentrations indicate that 2-
methods at B3LYP/6-31G (d, p) level in order to obtain information
about the 3D geometries and electronic structure.
1 Introduction
2 Experimental Section
2.1 General
Phthalocyanines (Pcs) exhibit salient properties like intense
brightness, high thermal, chemical stability, and high effi-
ciency in electron transfer.[1,2] The applicability of these com-
pounds has been investigated in different areas, in therapeutic
medicine, in photodynamic therapy and antioxidant,[3] in mate-
rials science, including nonlinear optics,[4,5] liquid crystals,[6,7]
semiconductors,[8] solar cells,[9] chemical sensor,[10] ink-jet
printing,[11] Langmuir-Blodgett films,[12] optical read-write
discs,[13] and catalysis.[14] Similar to other tetrapyrrolic macro-
cycles, phthalocyanines in water have a strong tendency for
aggregate to form dimer and high order oligomers, induced by
the tendency of the hydrophobic skeleton to avoid the contact
with water.[15] Aggregation decreases photosensitizing effi-
cacy.[16] Such a widespread diversity of possible applications
is due to high stability of many phthalocyanine and a
possibility of tailoring their properties by modification of
central atoms and appropriate substitution with peripheral
groups.[17,18]
ZnCl2, CuCl2, CoCl2, NiCl2, K2CO3, CHCl3, THF, DMSO, and DBU
were purchased from Merck. The solvents were purified according to
standard procedure[19] and stored over molecular sieves (4 Å). All re-
actions were carried out in a dry nitrogen atmosphere. Melting points
were measured with an electrothermal apparatus. Electronic spectra
were recorded with a Hitachi U-2900 Spectrophotometer (Van YYU,
Central Laboratory, Turkey). Routine FT-IR spectra were recorded
with a Thermo Scientific FT-IR (ATR sampling accessory) spectropho-
tometer (Van YYU, Central Laboratory, Turkey). 1H NMR spectra
were recorded with a Bruker 300 MHz spectrometer (Malatya IBTAM,
Central Laboratory, Turkey) with tetramethylsilane as internal stan-
dard.
2.2 Synthesis of 4-(2-Isopropyl-5-methylphenoxy)phthalo-
nitrile (3)
A mixture of thymol (5-methyl-2-isopropylphenol) (2) (0.7511 g,
5 mmol) and 4-nitrophthalonitrile (1) (0.865 g, 5 mmol) in dimethyl-
formamide (25 mL, DMF) was stirred at room temperature in a nitro-
gen atmosphere. After stirring for 15 min, K2CO3 (2.2 g, 16 mmol)
In this study, the synthesis and characterization of phthalo- was added into the mixture over a period of 2 h. The reaction mixture
was further stirred for 24 h, and poured into cold water (200 mL) and
cyanines bearing 2-isopropyl-5-methylphenoxy substituents on
stirred. The precipitate was filtered off, washed with water to neu-
the peripheral positions are described. This designed combina-
tralize it, and dried. The residue was recrystallized from ethanol. The
tion for the synthesis may improve the solubility of the systems
in organic solvents such as DMF, THF, CHCl3, CH2Cl2, and
product is soluble in ethyl acetate, acetonitrile, CH2Cl2, CHCl3, DMF,
and DMSO. Yield 0.838 g (63%). Mp: 116 °C. C18H16N2O: calcd. C
78.24; H 5.84; N 10.14%; found C 78.17; H 5.86; N 10.19%. 1H
NMR (300 MHz, [D6]DMSO): δ = 8.08, 7.74, 7.37, 7.25, 7.14, 6.90
(m, Ar-H), 4.36, 3.34, 2.95, 2.94, 2.51, 2.28, 1.21, 1.12, 1.06 (CH3)
ppm. FT-IR ν˜ = 3086 (Ar–CH), 2970 (CH3), 2225 (CN), 1593, 1563,
1481, 1458, 1246, 1195, 1165, 1083, 1060, 960 cm–1.
DMSO, and add interesting chemical, biological, and elec-
tronic properties.
* Dr. M. S. Ag˘ırtas¸
2.3 Synthesis of 2,10,16,24-Tetrakis(2-isopropyl-5-methyl-
phenoxy phthalocyaninato) Copper(II) (4)
Fax: +90-432-225-1802
E-Mail: salihagirtas@hotmail.com
[a] Department of Chemistry, Faculty of Science
Yüzüncü Yıl University
A
mixture of 4-(2-isopropyl-5-methylphenoxy) phthalonitrile (3)
65080, Van, Turkey
(0.100 g, 0.36 mmol) and CuCl2 (0.020 g) was powdered in a quartz
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crucible and heated in a sealed glass tube for 8 min in a nitrogen atmo-
The time-dependent density functional theory (TD-DFT) calculation
sphere at 200 °C. After cooling to room temperature, the product was was used to obtain the vertical excitation energies, oscillator strengths
washed with cold, hot ethanol and n-hexane, and filtered. The product
was dissolved in THF to remove impurities. Afterwards, THF was
evaporated to dryness to obtain final product. The product is soluble
in DMF, THF, CHCl3, CH2Cl2 and DMSO. The yield was 0.038 g
(36%). C72H64CuN8O4: calcd. C 73.98; H 5.52; N 9.59%; found: C
73.87; H 5.55; N 9.51%. UV/Vis (THF) λmax (log ε) = 676(5.32),
608(4.77), 344(5.05). FT-IR ν˜ = 3080 (Ar–CH), 2958, 2870 (CH3),
1612, 1573, 1504, 1465, 1246, 1222, 1091, 1053, 956, 813,
744 cm–1.
(f) and excited state compositions in terms of excitations between the
occupied and virtual orbitals for metal complexes.[22,23] In this study,
the TD-DFT method with the same basis set was performed to obtain
absorption wavelengths and the oscillation strength (f) within visible
to near-UV region.
3 Results and Discussion
3.1 Synthesis and Characterization
The synthesis route and structures of the 4-(2-isopropyl-5-
methylphenoxy) phthalonitrile (3) and metallophthalocyan-
ines( 4–7) are shown in Scheme 1. The 4-(2-isopropyl-5-meth-
ylphenoxy)phthalonitrile (3) was prepared by a base catalyzed
nucleophilic aromatic nitro displacement reaction between 5-
methyl-2-isopropylphenol (2) and 4-nitrophthalonitrile (1) in
the presence of dry K2CO3 in dry DMF in a nitrogen atmo-
sphere at room temperature for 1 d. The phthalocyanines
(4–7) were synthesized by the reaction of the 4-(2-isopropyl-
5-methylphenoxy) phthalonitrile (3) with CuCl2, ZnCl2,
NiCl2, CoCl2 in a nitrogen atmosphere. The characterization of
the compounds was carried out by the combination of several
methods, including elemental analysis, IR, 1H NMR, and
UV/Vis spectra. The structures of the compounds were con-
firmed by the results of these analyses.
2.4 Synthesis of 2,10,16,24-Tetrakis(2-isopropyl-5-methyl-
phenoxy phthalocyaninato) Zinc(II) (5)
The procedure was similar to the synthesis of compound 4 from 3,
except using ZnCl2 and 7 min reaction time. The product is soluble
in DMF, THF, CHCl3, CH2Cl2, and DMSO. The yield was 0.041 g
(39%).C72H64N8O4Zn: calcd. C 73.87; H 5.51; N 9.57%; found: C
73.91; H 5.49; N 9.60%. 1H NMR ([D6]DMSO): δ = 8.34; 7.55; 7.32;
6.87–6.66 (A–Hr); 3.36(CH); 2.39; 1.38–1.13 (CH3) ppm. UV/Vis
(THF) λmax (log ε) = 676 (5.32), 610 (4.76) 350 (5.08). FT-IR ν˜ =
3086 (Ar–CH), 2962, 2916, 2870 (CH3), 1608, 1573, 1504, 1261,
1215, 1087, 1041, 956, 806, 744 cm–1.
2.5 Synthesis of 2,10,16,24-Tetrakis(2-isopropyl-5-methyl-
phenoxy phthalocyaninato) Nickel(II) (6)
The procedure was similar to the synthesis of compound 4 from 3,
except using NiCl2. The product is soluble in DMF, THF, CHCl3,
CH2Cl2, and DMSO. The yield was 0.035 g (33%).C72H64N8NiO4:
calcd. C 74.29; H 5.54; N 9.63%; found: C 74.18; H 5.67; N 9.55%.
1H NMR ([D6]DMSO): δ = 8.07–6.91 (A–Hr), 3.34 (CH3); 2.94
(CH3); 1.21 (CH3); 1.12 (CH3) ppm. UV/Vis (THF) λmax (log ε) =
672 (5.33), 606 (4.82), 330 (4.95). FT-IR ν˜ = 3070 (Ar–CH), 2962,
2924 (CH3), 1612, 1573, 1535, 1469, 1408, 1249, 1222, 1091, 1056,
960, 813, 748 cm–1.
2.6 Synthesis of 2,10,16,24-Tetrakis(2-isopropyl-5-methyl-
phenoxy phthalocyaninato) Cobalt(II) (7)
The procedure was similar to the synthesis of compound 4 from 3,
except using CoCl2 and 7 min reaction time. The product is soluble in
DMF, THF, CHCl3, CH2Cl2, and DMSO. The yield was 0.037 g
(35%). C72H64CoN8O4: calcd. C 74.28; H 5.54; N 9.62%; found: C
74.13; H 5.61; N 9.72%. UV/Vis (THF) λmax (log ε) = 664(5.29),
602(4.79), 328(5.20). FT-IR ν˜ = 3095 (Ar–CH), 2958, 2927, 2866
(CH3), 1612, 1573, 1523, 1469, 1246, 1222, 1091, 1056, 960,
748 cm–1.
2.7 Computational Method
Three-dimensional structures of the compounds were obtained by ge-
ometry optimization using density functional theory at B3LYP/6-
31G(d,p) level with no symmetry restrictions. Gaussian 09 and Spar-
tan14 package programs were used to perform all computational calcu-
lations.[20,21] The frequency analysis for each metal phthalocyanine did
not yield any imaginary frequencies, indicating that the structure of
each molecule corresponds to at least a local minimum on the potential
energy surface. The normal mode analysis was performed for 3N-6
vibrational degrees of freedom, N being the number of atoms forming
the phthalocyanine molecule.
Scheme 1. Route for the synthesis of compounds 3–7.
1
The structure of compound 3 is confirmed by H NMR for
the 4-(2-isopropyl-5-methylphenoxy) phthalonitrile through
aromatic ring protons in its respective regions. In the 1H NMR
spectrum of compound 3 in [D6]DMSO, aromatic protons ap-
pear at 8.08–6.90 (Ar–H), aliphatic protons at 4.36, 3.34, 2.52,
and 1.12 (CH3). In the 1H NMR spectrum of compound 5
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within [D6]DMSO, aromatic protons appear at 8.34–6.66 and (b) two methyl and two isopropyl substituents up. The
(A–Hr) and aliphatic protons at 3.36, 2.51, 2.39, 1.38, and 1.13 comparison of the electronic energy data suggest that these two
(CH3) ppm. 1H NMR measurement of compounds 4 and 7
1
were excluded due to their paramagnetic properties. In the H
NMR spectrum of compound 6 in [D6]DMSO, aromatic pro-
tons appear at 8.07–6.91 (A–Hr), aliphatic protons at 3.34,
2.94, 2.51, 1.21 and 1.12 (CH3) ppm.
Comparison of the IR spectroscopic data clearly indicated
the formation of compound 3 by the appearance of new ab-
sorption bands at 3086 (Ar–CH), 2970 (CH3), 2225 (CN),
1595–1536 (C=C), 1246 (Ar–O–Ar). After conversion of the
phthalonitrile derivative 3 into Pcs 4–7, the sharp peak for the
(CN) vibrations disappeared. The IR spectra of compounds
4–7 displayed aromatic CH peaks at 3070–3095 cm–1,
aliphatic CH peaks at 2958–2962 cm–1, C=C (in phenyl rings)
peaks at 1612–1573 cm–1, and Ar–O–Ar peaks at 1246–
1261 cm–1.
Figure 1 and Figure 2 show representative geometry opti-
mized structure of compound 6 and the Mulliken charge[24]
distribution in the center of the presented complexes, respec-
tively. The optimization procedure was applied to two possible
orientation of the substituents: (a) all methyl substituents up,
Figure 3. Three-dimensional electrostatic potential map for Zn and Ni
complexes.
Figure 1. Top and side view of geometry optimized structure for Ni
complex 6. (a) Four methyl substituents up. (b) Two methyl and two
isopropyl substituents up.
Figure 4. Computed UV/Vis spectra of Zn (5) and Ni (6)
complexes.
Figure 2. Mulliken charge distribution for present metallocyanines.
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orientations possess almost equal stability with the latter hav- donation from coordinating nitrogens. All the coordinating do-
ing 0.3 kJ·mol–1 lower energy. The geometry optimized struc- nor nitrogen atoms have been calculated to develop negative
tures of the complexes 4–7 indicate square-planar arrangement charges. The coordinating nitrogen atoms are more negative
at the parent phthalocyanine moiety at the center; however, the than the connecting nitrogen atoms, which might be a conse-
orientation of the peripheral substituents found perpendicular quence of lack of imino hydrogen atom. Upon coordination to
to the main circuit and positioned almost parallel to one an- the central metal atom the expected –1 formal charge on these
other for all cases. Figure 2 shows a representative charge dis- atoms decreased absolutely to –0.688. The three-dimensional
tribution model in the heart of the complexes. The charge dis- electrostatic potential maps for 5 and 6 complexes are given
tribution depends on the type of the metal. As seen in Figure 2, in Figure 3. The positive charge development was indicated by
the formal charge +2 of the central metal atom decreased to blue and green area, whereas red and yellow area shows the
the net charge ranging from +1.014 to +0.889, due to charge negative charge.
Figure 5. Frontier molecular orbital schemes and molecular orbital energy levels of Zn (5) and Ni (6) phthalocyanines.
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The electronic spectra are the best indication for the phthalo-
cyanine compounds, which show characteristic Q band and B
bands in UV/Vis spectra. Also, a close investigation of the UV/
Vis spectra of the phthalocyanines 4–7 confirmed the proposed
structures. The electronic absorption data of all these phthalo-
cyanines were measured in THF at a concentration of
1ϫ10–5 mol·L–1. The phthalocyanines showed characteristic
absorptions in the Q band region at 676 nm for compound 4,
676 nm for compound 5, 672 nm for compound 6, and 664 nm
for 7. These Q band absorptions were attributed to the π–π*
transition from the highest occupied molecular orbital
(HOMO) to the lowest unoccupied molecular orbital (LUMO)
of the Pcs ring and the other visible region at about 344 nm for
compound 4, 350 nm for compound 5, 330 nm for compound 6
and 328 nm for compound 7 B band, which represents
Figure 7. Aggregation behavior of phthalocyanine 5.
transition from the deeper
respectively.
π levels to the LUMO,
Secondly, the structures obtained from geometry optimiza-
tions were subjected to TD-DFT calculations at the same basis
set (B3LYP/6-31G(d,p)) to predict the electronic spectra of the
phthalocyanine compounds. Transition energies and molecular
orbital energies and schemes were predicted for singlet state
excitations. Molecular orbital energies indicate that transitions
from HOMO to LUMO are responsible for the Q band of the
experimental spectrum. Calculated UV/Vis spectra and three-
dimensional HOMO and LUMO molecular orbital schemes for
compounds 5 and 6 are shown in Figure 3 and Figure 4,
respectively. The absorption bands on the UV/Vis spectra may
slightly differ from the experimental data due to the fact that,
the computations were performed for isolated molecule,
whereas experimental data obtained for the bulk
system[25] (Figure 4). The carbon and nitrogen atoms of the
central periphery contribute both HOMO and LUMO of the
complexes with little contributions from the outer atoms (Fig-
ure 5).
Figure 8. Aggregation behavior of phthalocyanine 6.
Aggregation behaviors of compounds 4–7 investigated in
THF at different concentrations range are presented in Fig-
ure 6, Figure 7, Figure 8, and Figure 9.
Figure 9. Aggregation behavior of phthalocyanine 7.
4 Conclusions
This study aimed to develop soluble and non-aggregate
phthalocyanines bearing 2-isopropyl-5-methylphenoxy substit-
Figure 6. Aggregation behavior of phthalocyanine 4.
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tries and important electronic data of the present structures.
These phthalocynanine compounds can be used in application
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Acknowledgements
This study was supported by the Research Fund of Yüzüncü Yıl Uni-
versity (2015-FBE-D041).
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