Synthesis and characterization of liquid crystalline unsymmetrically substituted phthalocyanines

Article abstract of DOI:10.1016/j.poly.2007.06.017

The synthesis of unsymmetrically substituted phthalocyanines bearing two p-tolyl-sulfonyl (tosyl)amido and six alkylthio moieties was achieved by cyclotetramerisation of two different phthalonitrile derivatives, namely 1,2-di(alkylthio)-4,5-dicyanobenzene

Full text of DOI:10.1016/j.poly.2007.06.017

Polyhedron 26 (2007) 4551–4556
www.elsevier.com/locate/poly
Synthesis and characterization of liquid crystalline
unsymmetrically substituted phthalocyanines
a
a
a,b,
*
Fatma Yuksel , Devrim Atilla , Vefa Ahsen
a
Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, Turkey
TUBITAK-Marmara Research Center, Materials Institute, P.O. Box 21, Gebze 41470, Turkey
b
Received 1 March 2007; accepted 9 June 2007
Available online 30 June 2007
Abstract
The synthesis of unsymmetrically substituted phthalocyanines bearing two p-tolyl-sulfonyl (tosyl)amido and six alkylthio moieties was
achieved by cyclotetramerisation of two different phthalonitrile derivatives, namely 1,2-di(alkylthio)-4,5-dicyanobenzene and 4,5-dicy-
ano-N,N0-ditosyl-o-phenylenediamine in the presence of an anhydrous metal salt and strong base. The new compounds were character-
ized by elemental analyses, UV/Vis, IR, NMR and mass spectra. The mesogenic properties of these new materials were studied by
differential scanning calorimetry (DSC) and polarizing optical microscopy. The mesogenic properties of these compounds were compared
to that of their symmetric analogous, octaalkythia substituted phthalocyanine derivatives.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Phthalocyanine; Asymmetric phthalocyanine; Liquid crystal; Metallomesogen
1. Introduction
substituted phthalonitriles or the corresponding 1,3-diimi-
noisoindolines [14,15]; reaction of a polymer-bonded
phthalonitrile or 1,3-diiminoisoindoline with excess of
another differently substituted one [16,17]; ring expansion
of a so-called sub-phthalocyanine with a substituted 1,3-
diiminoisoindoline [12,18–21] or phthalonitrile [11,22].
Each method has different advantages and disadvantages.
In general, the statistical condensation strategy is the most
widely preferred.
Pcs are known to form columnar liquid crystals. The
liquid crystalline properties of pcs depend on the number,
position and character of substituents, and the nature of
the central metal atom. It has been found that numerous
pc derivatives which are peripherally or non-pheripherally
octa- and tetra-substituted with alkyl- [23], alkoxy-
[24], alkoxymethyl- [25], oligo(ethyleneoxy) [5,26], alkylthia
[27,28], oligo (ethyleneoxy)thia [29] or even? crowned?
[30–32] groups exhibit thermotropic or lyotropic mesomor-
phism. Similar behaviour is demonstrated by asymmetri-
cally substituted pc derivatives. Contrary to symmetric
pcs, there are fewer studies on the liquid crystalline proper-
ties of asymmetric pcs [4–6].
Phthalocyanines (Pcs) have attracted great research
attention because of their fascinating electronic and optical
properties for many applications such as chemical sensors,
liquid crystals, catalysis and non-linear optics [1,2]. These
properties also strongly depend on the peripheral and axial
substitution pattern [1–3]. Upto now, a variety of symmet-
rical pcs have been reported [1–3], whilst there have been
only a limited number of reports on unsymmetrical pcs
because of synthesis and purification difficulties. Recent
researches have indicated that asymmetric pcs possess
interesting properties in various areas such as liquid crys-
tals [4–6], Langmuir Blodget (LB) film formation [7–9],
photodynamic therapy of cancer [10,11] and second-order
non-linear optics [12–14].
Different methods are known for the preparation of
asymmetric pcs: statistical condensation of two differently
*
Corresponding author. Address: Gebze Institute of Technology,
Department of Chemistry, P.O. Box 141, Gebze 41400, Turkey.
E-mail address: ahsen@gyte.edu.tr (V. Ahsen).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.06.017

4552
F. Yuksel et al. / Polyhedron 26 (2007) 4551–4556
Our previous studies have focused on the synthesis of
822e. The differential scanning calorimeter system was cal-
ibrated with indium from 3 to 4 mg samples under nitrogen
atmosphere.
new pcs exhibiting liquid crystal and gas sensor properties
[27–29,33–39]. The films of the pcs showing mesomorphic
properties at room temperature have been proven to be
used as photoconductors and gas sensors in molecular elec-
tronic devices. The ordered pc films obtained from liquid
crystalline pc compounds are more sensitive than
disordered pc films [28,39]. Recently, we have reported
the synthesis of peripherally symmetrical substituted octa
p-tolyl-sulfonyl (tosyl) amido pcs and their NMR and
UV spectra investigations in different solvents and pH
[40]. We have found that the hydrogen bonding capacity
and deprotonation of the tosylamido groups causes inter-
esting spectroscopic properties. Their potential application
as chemical gas sensor is being investigated. However, only
tosylamido substitution of the pc ring was not enough to
exhibit mesogenic properties. Therefore, we designed elec-
tron-with-drawing tosylamido and donor alkylthia substi-
tuted novel unsymmetrical pcs which are liquid crystals
owing to the alkyl chains. The synthesis, characterization
and investigation of mesogenic properties are reported
here. Also, the influence of the presence of the tosylamido
unit on the phthalocyanine core on the mesomorphic prop-
erties was determined.
3.1. Synthesis of asymmetric phthalocyanines
3.1.1. 2,3,9,10,16,17-Hexakis(hexylthio)-23,24-
bis(tosilamido)phthalocyaninato nickel(II) (3a)
A mixture of 1,2-di(hexylthio)-4,5-dicyanobenzene (2a)
(2 mmol),
4,5-dicyano-N,N0-ditosyl-o-phenylenediamine
(1) (1 mmol), anhydrous NiCl2 (1.5 mmol), 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU, 3 mmol) and 4 ml dried n-hex-
anol were heated to reflux for 18 h under an argon
atmosphere. After cooling to room temperature the mix-
ture was treated with ethanol (10 ml), filtered off and
washed several times with ethanol. The dark green product
was purified by preparative thin layer chromatography
(TLC) using a 5:2 CH2Cl2/n-hexane solvent system. Yield:
8%. Elemental Anal. Calc. for C82H102N10NiO4S8 (1605):
C, 61.29; H, 6.40; N, 8.72. Found: C, 61.10; H, 6.35; N,
8.70%. IR (KBr) mmax (cmꢀ1): 3258 (NH), 2956–2856
(CH2, CH3), 1599 (Car@N), 1350, 1163 (SO2), 560 (CS).
MS (ES–MS), m/z (%): 1606 (100) [M+H]+, 1607 (50)
[M+2H]+. 1H NMR (CDCl3) d: 0.94–1.18 (m, 18H,
CH3), 1.43–2.00 (m, 36H, CH2), 2.21 (t, 6H, Ar–CH3),
3.05–3.58 (m, 24H, CH2), 7.9–8.42 (m, 18H, NH, CHar).
13C NMR (CDCl3, Decoupled) d: 13.09 (CH3), 13.16
(CH3), 20.59 (CH2), 21.59 (CarCH3), 27.72–28.16 (CH2),
30.50–33.07 (CH2), 118.5 (CarH), 124.10 (CarH), 127.08
(CarH), 128.8 (Car), 129.85 (CarH), 132.05 (Car), 132.72
(Car), 134.7 (Car), 138.71 (Car), 139.11 (Car), 141.00 (Car),
143.01 (CN), 143.50 (CN).
2. Experimental methods
2.1. Materials
The 4,5-dicyano-N,N0-ditosyl-o-phenylenediamine (1)
[40] and 1,2-di(alkylthio)-4,5-dicyanobenzene derivatives
(2a–2c) [41,42] were synthesized according to published
procedures. All other reagents and solvents were reagent-
grade quality, obtained from commercial suppliers and
dried before use as described by Perrin and Armarego [43].
3.1.2. 2,3,9,10,16,17-Hexakis(dodecylthio)-23,24-
bis(tosilamido) phthalocyaninato nickel(II) (3b)
A mixture of 1,2-di(dodecylthio)-4,5-dicyanobenzene
(2b) (2 mmol), 4,5-dicyano-N,N0-ditosyl-o-phenylenedi-
amine (1) (1 mmol), anhydrous NiCl2 (1.5 mmol), 1,8-diaz-
abicyclo[5.4.0]undec-7-ene (DBU, 3 mmol) and 4 ml dried
n-hexanol were heated to reflux for 18 h under an argon
atmosphere. After cooling to room temperature the mix-
ture was treated with ethanol (10 ml), filtered off and
washed several times with ethanol. The dark green product
was purified by preparative thin layer chromatography
(TLC) using a 5:1 CH2Cl2/n-hexane solvent system. Yield:
7%. Elemental Anal. Calc. for C118H174N10Ni O4S8 (2110):
C, 67.11; H, 8.30; N, 6.63. Found: C, 67.00; H, 8.31; N,
6.70%. IR (KBr) mmax (cmꢀ1): 3263 (NH), 2957–2856
(CH2, CH3), 1598 (Car@N), 1348, 1164 (SO2), 559 (CS).
MS (ES–MS), m/z (%): 2111 (100) [M+H]+. 1H NMR
(CDCl3) d: 0.98–1.27 (m, 18H, CH3), 1.47-2.13 (m, 84H,
CH2), 2.32 (t, 6H, Ar–CH3), 3.10-3.65 (m, 48H, CH2),
7.8–8.62 (m, 18H, NH, CHar). 13C NMR (CDCl3, Decou-
pled) d: 13.08 (CH3), 13.24 (CH3), 20.59 (CH2), 21.52
(CarCH3), 27.80–28.32 (CH2), 30.56–33.12 (CH2), 118.67
(CarH), 124.32 (CarH), 127.12 (CarH), 127.54 (CarH),
128.8 (Car), 129.96 (CarH), 132.15 (Car), 132.87 (Car),
3. Measurements
Elemental analyses were obtained from Thermo Finni-
gan Flash 1112. Infrared spectra in KBr pellets were
recorded on a Bio-Rad FTS 175C FT IR spectrophotome-
ter. Optical spectra in the UV–Vis region were recorded
with a Shimadzu 2001 UV PC spectrophotometer using a
1 cm pathlength cuvette at room temperature The mass
spectra were recorded on a LCQ-ion trap (Thermofinnigan,
San Jose, CA,USA), equipped with an Electrospray (ES)
1
source. H and 13C NMR spectra were recorded in CDCl3
solutions on a Varian 500 MHz spectrometer. Thermo-
gravimetric analyses were carried out on Mettler Toledo
Stare Thermal Analysis System at a rate of 10 ꢁC minꢀ1in
a nitrogen flow (50 ml minꢀ1). The phase transition behav-
iour of these compounds was observed by means of a
polarizing microscope (Leitz Wetzler Orthoplan-pol.)
equipped with a hot stage (Linkam TMS 93) and tempera-
ture-controller (Linkam LNP). Transition temperatures
were determined with a scan rate of 10 ꢁC minꢀ1 using a
Mettler Toledo Stare Thermal Analysis System/DSC

F. Yuksel et al. / Polyhedron 26 (2007) 4551–4556
4553
134.75 (Car), 138.79 (Car), 139.31 (Car), 141.10 (Car), 143.01
(CN), 143.65 (CN).
preparation of the pcs, we tried two different methods: ring
expansion of corresponding sub-pc and statistical conden-
sation of the phthalonitriles. For the first method, the diim-
inoisondoline derivative of 1 is required. Probably due to
hydrolysis of the tosyl groups, it could not be obtained
according to the literature [45–47]. Therefore, we adopted
the second method (the statistical condensation method)
for the preparation of the asymmetric pcs (3a–3c). Mixed
condensation of 1,2-di(alkylthio)-4,5-dicyanobenzene (2a–
2c) and 4,5-dicyano-N,N0-ditosyl-o-phenylenediamin (1)
in the presence of anhydrous nickel (II) chloride, DBU as
a strong nitrogen base and n-hexanol as the solvent affor-
ded the asymmetric pcs (3a–3c). Generally, this method
predicts that the reaction of two different phthalonitriles
of the same reactivity in a 3:1 ratio will afford a mixture
of products in the following percentages: A4 33%, A3B
44%, other cross-condensation products 23% [44]. In our
case, the 1,2-di(alkylthio)-4,5-dicyanobenzene derivatives
(2a–2c) are much more reactive than 4,5-dicyano-N,N0-
ditosyl-o-phenylenediamine (1), therefore the symmetric
octaalkylthio phthalocyanine (A4) derivatives were found
to be more preferable than the asymmetric 3a–3c pcs
(A3B). To increase the yield of the asymmetric pcs (3a–
3c) we tried several experiments with different molar ratios,
and a 2:1 ratio of two dinitrile derivatives 2a–2c and 1 was
found to be the most appropriate. The asymmetric pcs (3a–
3c) were separated by preparative thin layer chromatogra-
phy from the corresponding symmetric octaalkylthio
substituted Ni(II) pc derivatives [NiPc(SR)8] and the other
products.
3.1.3. 2,3,9,10,16,17-Hexakis(hexadecylthio)-23,24-
bis(tosilamido)phthalocyaninato nickel(II) (3c)
A mixture of 1,2-di(hexadecylthio)-4,5-dicyanobenzene
(2c) (2 mmol), 4,5-dicyano-N,N0-ditosyl-o-phenylenedi-
amine (1) (1 mmol), anhydrous NiCl2 (1.5 mmol), 1,8-diaz-
abicyclo[5.4.0]undec-7-ene (DBU, 3 mmol) and 4 ml dried
n-hexanol were heated to reflux for 18 h under an argon
atmosphere. After cooling to room temperature the mix-
ture was treated with ethanol (10 ml), filtered off and
washed several times with ethanol. The dark green product
was purified by preparative thin layer chromatography
(TLC) using a 5:1 CH2Cl2/n-hexane solvent system. Yield:
6%. Elemental Anal. Calc. for C142H222N10NiO4S8 (2445):
C, 69.65; H, 9.16; N, 5.72. Found: C, 69.60; H, 9.20; N,
5.70%. IR (KBr) mmax (cmꢀ1): 3258 (NH), 2955–2851
(CH2, CH3), 1599 (Car@N), 1350, 1163 (SO2 ), 560 (CS).
MS (ES–MS), m/z (%): 2446 (40) [M+H]+. 1H NMR
(CDCl3) d: 0.97–1.29 (m, 18H, CH3), 1.37–2.17 (m, 108H,
CH2), 2.36 (t, 6H, Ar–CH3), 3.12–3.69 (m, 52H, CH2),
7.81–8.60 (m, 18H, NH, CHar). 13C NMR (CDCl3, Decou-
pled) d: 13.06 (CH3), 13.21 (CH3), 20.52 (CH2), 21.50
(CarCH3), 27.72–28.36 (CH2), 30.44-33.24 (CH2), 118.77
(CarH), 124.44 (CarH), 127.24 (CarH), 127.56 (CarH),
128.82 (Car), 129.76 (CarH), 132.21 (Car), 132.67 (Car),
134.70 (Car), 138.70 (Car), 139.21 (Car), 141.105 (Car),
143.01 (CN), 143.55 (CN).
4. Result and discussions
Elemental analysis results and the spectral data (1H
NMR, 13C NMR, FT IR, UV–Vis and MS) for the newly
synthesized pcs (3a–3c) were consistent with the assigned
formulations. The results are given in the experimental
section.
The IR spectral results of the pcs (3a–3c) are different
from the precursors 1 and 2a–2c, so the sharp peak for
the C”N vibrations around 2220–2240 cmꢀ1, associated
4.1. Synthesis and characterization
The synthetic route of the pcs is shown in Scheme 1. 1,2-
Di(alkylthio)-4,5-dicyanobenzenes (2a–2c) and 4,5-dicy-
ano-N,N0-ditosyl-o-phenylenediamin (1) were synthesized
according to the published procedures [40–42]. For the
RS
SR
N
H3C
CH3
O
O
N
N
N
H
N
S
RS
RS
H
N
N
CN
CN
RS
RS
CN
CN
S
(i)
O
+
O
N
Ni
N
O
O
S
N
H
S
N
H
N
1
O
H3C
O
2a R: C6H13
2b R: C12H25
2c R: C16H33
CH3
SR
RS
3a R: C6H13
3b R: C12H25
3c R: C16H33
Scheme 1. Synthesis of phthalocyanines 3a–3c (i) metal salt, DBU, n-hexanol, reflux.

4554
F. Yuksel et al. / Polyhedron 26 (2007) 4551–4556
with the nitrile groups, disappeared after conversion into
the pcs. The NH groups gave absorption bands at around
3260 cmꢀ1 and the characteristic vibration of SO2 groups
appeared at around 1340 and 1160 cmꢀ1 in the spectra of
all the pcs, and confirmed the presence of the tosylamido
groups. In addition, a group of intense absorption bands
was also seen in the range 2856–2957 cmꢀ1 in the IR spec-
tra of 3a–3c. These can be attributed to the C-H stretching
vibrations of the substituted alkyl chains.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
a
b
c
A close investigation of the mass spectra of 3a–3c con-
firmed the proposed structures. The mass spectra of these
compounds were obtained by the electron spray (ES) tech-
nique. We observed the molecular ion peaks of the pcs at
m/z: 1606 for 3a, m/z: 2111 for 3b and m/z: 2446 for 3c.
300
400
500
600
700
800
λ/nm
1
A common feature of the H NMR spectra of the pcs
Fig. 1. Visible absorption spectra of octahexzilthia Ni(II) phthalocyanine
(a), unsymmetrical substituted Ni(II) pc derivative (3a) (b) and octatos-
ilamido Ni(II) phthalocyanine (c) in chloroform. Concentration = 3.74 ·
(3a–3c) is the broad absorptions probably caused by the
aggregation of the pc, which is frequently encountered at
1
10ꢀ6 mol dmꢀ3
.
the concentrations used for NMR measurements. The H
NMR spectra of 3b and 3c are similar to that of 3a. The
1H NMR spectrum of 3a exhibits the aromatic and NH
protons at 7.90–8.42 ppm as multiplets, the aliphatic CH2
protons between 1.43 and 3.58 ppm as multiplets, CH3 pro-
tons at d 0.94–1.18 and ArC–CH3 protons at around
2.21 ppm. The ratio of aromatic to aliphatic protons
appears to show that the benzo groups with two different
substituents are present in a 3:1 ratio. The 13C NMR spec-
tral data of 3a–3c given in experimental section are also in
accord with the expected structures.
The blue-green pcs show typical electronic spectra with
two strong absorption bands: a Soret (B) band at around
300–350 nm and a Q band at around 600–700 nm. The
UV–Vis. spectra of 3a–c were obtained in chloroform
and the results are given in Table 1. All of these pcs gave
very similar spectra; they show the Q band at 697 nm
and the B band at 323 nm. Increasing the length of the
alkyl chain caused a decrease of the intensity of the Q band
as expected. The electronic spectrum is given for compound
3a (Fig. 1). In addition to this octatosylamido Ni(II) and
octahexilthia Ni(II) phthalocyanines are given in Fig. 1 to
compare the absorption bands. The electronic absorption
spectrum of octatosylamido Ni(II) phthalocyanine gave
two Q bands in chloroform: a monomeric Q band around
680 nm together with a blue-shifted intense band around
640 nm corresponding to aggregated species. No additional
band around 640 nm corresponding to aggregated species
was observed in the electronic spectra of the asymmetric
species (3a–3c). Octahexylthia substituted Ni(II) phthalo-
cyanine also a gave different electronic spectrum from its
asymmetric derivative (3a), with a Q band around
702 nm and a higher extinction coefficient than 3a.
4.2. Mesomorphic properties
The phase transition behaviours of the compounds 3a–
3c were determined by differential scanning calorimetry
(DSC) and polarizing microscopic observations. Phase
transition temperatures and enthalpy changes of these
products are presented in Table 2. The DSC-measurement
of compounds 3a–3c show a significant sharp peak in the
vicinity of 150 ꢁC, which relates to the melting transition.
Furthermore the DSC diagram of 3b and 3c depict a weak
peak at about 227 ꢁC and 205 ꢁC, respectively that belongs
to the clearing point. These investigations indicate that the
compounds exhibit a thermotropic liquid crystalline phase
between the melting and clearing point [25–28,32–34]. No
such additional peak is observed for compound 3a, which
excludes further phase transitions. Only the melting to
the mesophase is present. The phthalocyanine derivative
3a did not give any isotropic transition until 280 ꢁC. There-
fore the heating cycles were interrupted before reaching
any clearing point to avoid decomposition for 3a. The ther-
mal stability of the phthalocyanines (3a–3c) has been inves-
tigated by thermal gravimetric analysis (TGA). The initial
decomposition of the compounds 3a, 3b and 3c determined
Table 2
Phase transition temperatures and enthalpies for the compound 3a–3c as
determined by DSCa
Compound
Heating
Cooling
Table 1
C ! Colh ! I
165 (3.90)
161 (32.54)
144 (42.53)
I ! Colh ! C
not observed not observed 120 (4.06)
Electronic spectra of the phthalocyanines in chloroform
k )
max/nm (e/104 dm3 molꢀ1 cmꢀ1
3a
3b
3c
Compound
227 (1.19)
205 (6.17)
218 (2.96)
198 (5.52)
91 (21.11)
23 (50.59)
Soret band region
Q band region
3a
3b
3c
322.5(13.32) 413.0(3.64)
323.0(13.00) 414.0(3.22)
323.5(13.10) 413.5(3.50)
697.0(16.61)
697.5(15.82)
698.0(15.11)
Heating and cooling rates: 10 ꢁC, heating range: 0–280 ꢁC.
Phase nomenclature: Colh = discotic hexagonal columnar phase,
I = isotropic phase.
a

F. Yuksel et al. / Polyhedron 26 (2007) 4551–4556
4555
temperatures but decreases the clearing temperature. The
isotropic liquid phase was not observed for hexylthia and
dodecylthia substituted Ni(II) Pcs until 300 ꢁC in the liter-
ature [28], though isotropic transitions were observed for
the asymmetric derivatives (3b,3c) at 227 and 205 ꢁC
respectively. Furthermore, increasing the length of the
alkyl chain decreases the melting and isotropic phase tran-
sition temperatures of compounds 3a–3c.
5. Conclusions
Asymmetric mesogenic phthalocyanines are rather few.
In the present work, the synthesis of new asymmetric Ni(II)
phthalocyanines are described and characterized by stan-
dard methods (1H and 13C NMR, elemental analysis, IR,
UV/Vis and mass spectrometry). The asymmetric Ni(II)
phthalocyanine derivatives (3a–3c) exhibit a hexagonal
columnar (Colh) structure. The influence of nature of the
side chains upon the mesomorphic properties was com-
pared for the asymmetric pcs (3a–3c) and also with their
symmetric analogous without the tosylamido group
[NiPc(SR)8]. It could be seen that addition of the tosylam-
ido group to the phthalocyanine core increases liquid crys-
tal phase transition temperatures but decreases clearing
temperatures. In addition to this, increasing the length of
alkyl chain decreases the melting and isotropic phase tran-
sition temperatures of the compounds 3a–3c.
Fig. 2. Optical texture of 3b observed at 170 ꢁC (Magnification ·16).
Acknowledgements
The authors thank to Colette LEBRUN for ES
¨
mass spectra and Prof. Ayßse Gul GUREK for fruitful
¨
discussions.
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