Synthesis and spectral characteristics of phthalocyanines of unsymmetrical structure containing fragments of 3,6-didecyloxyphthalonitrile and 2-methyl-5,6-dicyanobenzimidazole

Article abstract of DOI:10.1134/s1070428008020073

By alkylation of 3,6-dihydrooxyphthalonitrile with 1-bromodecane and by reaction of 4,5-diaminophthalodinitrile with acetic acid were synthesized respectively 3,6-didecyloxyphthalonitrile (A) and 2-methyl-5,6- dicyanobenzimidazole (B). The random condensation of the dinitriles obtained provided unsymmetrical phthalocyanines of A ₃ B, AABB, and AB ₃ type. Their spectral characteristics were investigated.

Full text of DOI:10.1134/s1070428008020073

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 2, pp. 225−230. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © N.E. Galanin, E.V. Kudrik, G.P. Shaposhnikov, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 2,
pp. 234−239.
Synthesis and Spectral Characteristics of Phthalocyanines
of Unsymmetrical Structure Containing Fragments
of 3,6-Didecyloxyphthalonitrile
and 2-Methyl-5,6-dicyanobenzimidazole
N. E. Galanin, E. V. Kudrik, and G. P. Shaposhnikov
Ivanovo State University of Chemical Engineering, Ivanovo, 153000 Russia
e-mail: ttoc@isuct.ru
Received May 10, 2007
Abstract—By alkylation of 3,6-dihydrooxyphthalonitrile with 1-bromodecane and by reaction of 4,5-di-
aminophthalodinitrile with acetic acid were synthesized respectively 3,6-didecyloxyphthalonitrile (A) and 2-methyl-
5,6-dicyanobenzimidazole (Β). The random condensation of the dinitriles obtained provided unsymmetrical
phthalocyanines of A3Β, AAΒΒ, and AΒ3 type. Their spectral characteristics were investigated.
DOI: 10.1134/S1070428008020073
Phthalocyanines belong to aromatic macrorings
possessing a number of unique characteristics governing
the range of their application. These compounds are used
as valuable dyes [1], catalysts of various redox processes
[2] etc. A special place in the series of this class
compounds belongs to phthalocyanines of unsymmetrical
structure where alternation occurs of nonuniformly
substituted isoindole fragments bound by bridging nitro-
gen atoms. These compounds proved to be very promising
as materials for nonlinear optics [3], liquid crystals
substances [4, 5], and as compounds capable of providing
highly regular monomolecular layers. Therefore the
synthesis of these compounds is an essential problem.
the target substances in organic solvents. It was previous-
ly established [6] that 3,6-didecyloxyphthalonitrile (I)
at heating with lithium 1-pentanolate in 1-pentanol was
not capable to form a symmetrical octaalkoxyphthalo-
cyanine due to sterical hindrances. In order to increase
the selectivity of the random condensation nitrile I
(component A) was also used in this study. It was prepar-
ed by alkylating 3,6-dihydroxyphthalonitrile (II) with
1-bromodecane in the presence of potassium carbonate.
OH
OC10H21
CN
CN
CN
K2CO3
C10H21Br
CN
OC10H21
According to the generally applied classification the
unsymmetrical phthalocyanines are subdivided in three
types: A3Β, AΒAΒ, and AAΒΒ, where A and Β are various
peripheral fragments of the phthalocyanine molecule.
Note that unlike the symmetrical analogs the phthalo-
cyanines of unsymmetrical structure are relatively poorly
documented. It is due to the difficulties met in their
preparation, isolation, and purification.
OH
II
I
Our procedure is distinguished from that of [7] by
the use of DMF instead of acetone as solvent. Therefore
we were able to carry out the alkylation at 100°C and
thus to reduce the process time ftom 56 to 20 h and to
increase the yield of dinitrile I from 65 to 95%. Its
composition and structure were confirmed by elemental
analysis and IR spectrum. IR spectrum of compound I
contained absorption bands in the region 3032–2936 cm–
1 cor-responding to the stretching vibrations of the C–H
bonds in the alkyl groups, and also a band at 2304 cm–1
from the stretching vibrations of cyano groups. The bands
Several methods exist for the synthesis of unsym-
metrical phthalocyanines. However the most convenient
procedure of preparation of these compounds is the
random condensation of two different dinitriles or
1,3-diiminoisoindolines where one of the components
contains bulky substituents providing for solubility of
225

GALANIN et al.
226
at 1116 and 1080 cm–1 originate from the stretching
vibrations of the CAr–O and CAlk–O bonds of the alkoxy
substituents.
isolated from the mixture obtained by column chromato-
graphy. It turned out unexpectedly that phthalocyanine
of the AΒAΒ structure did not form in significant amount
in the course of the synthesis. It is evidently due to the
more planar structure of the cis-isomer VI and therefore
to its higher thermodynamic stability.
We employed as component B 2-methyl-5,6-dicyano-
benzimidazole (III). The compounds containing benz-
imidazole structure attract interest for the benzimidazole
heterocycle sometimes imparts to these compounds
fluorescence property [8]. Besides the presence in the
imidazole ring of pyrrole and pyridine type nitrogen
atoms capable of entering into hydrogen bonds should
favor formation of supermolecular aggregates arising in
the course of crystallization or association. In their turn
the supermolecular aggregates underlie the formation of
columnar mesophases [9], and therefore the alkoxy-
substituted phthalocyanine containing imidazole frag-
ment can be promising for preparation of liquid crystal
materials.
The homogeneity and structure of obtained phthalo-
cyanines was proved by TLC, elemental analysis, vibra-
tion, 1H NMR, and electronic spectroscopy.
In the IR spectra of obtained phthalocyanines V–VII
a number of common bands is present. For instance,
absorption bands in the region 3300–3286 cm–1 char-
acterize the vibrations of N–H bonds in the imidazole
rings, the bands at 3081–3076 cm–1 belong to the
vibrations of N–H bonds of the endocyclic imino groups,
the strong bands at 2954–2853 cm–1 correspond to the
vibrations of C–H bonds of alkyl moieties. The strong
bands at 1767, 1728, 1726, 1504, 1270 cm–1 characterize
the vibrations of C = C and C = N bonds in the macroring
and the benzimidazole structures. The bands at 1120 and
1179 cm–1 correspond to the vibrations of CAr–O bonds,
those at 1060 and 1058 cm–1, to CAlk–O bonds.
The synthesis of nitrile III was performed by the
reaction of 4,5-diaminophthalonitrile (IV) prepared as
described in [10] with excess acetic acid.
H2N
CN
NC
N
MeCO2H
1
In the H NMR spectra of phthalocyanines V–VII
Me
five groups of signals are observed characterizing the
proton resonances of endocyclic N–H groups, of
oxydecyl substituents, of methyl groups from imidazole
fragments, of aromatic protons of benzene rings, and of
proton signals of N–H groups in the imidazole rings.
Therewith in going from compound V to compound VII
the positions of the signals change insignificantly, only
their intensity varies. For instance, in phthalocyanine V
the proton peak of the N–H group in the imidazole ring
appears as a singlet at 8.97 ppm, two protons of the
benzene ring from the benzimidazole structure are
observed as a singlet at 8.51 ppm, the six protons from
the decyloxy-substited benzene rings give a multiplet in
the region 6.90–7.10 ppm. In a stronger field at 4.01–
3.95 ppm appears a triplet corresponding to 12 protons
of the α-methylene groups of the oxydecyl substituents.
The multiplet in the region 2.60–2.45 belongs to three
protons of the methyl group at the imidazole fragment,
the broadened singlet in the region 2.05–1.55 ppm char-
acterizes the resonance of 96 protons of the 48 methylene
groups of the oxydecyl, and the singlet at 0.88 ppm
corresponds to 18 protons of the six terminal methyl
groups of the same substituents. The most upfield singlet
at –0.67 ppm belongs to two protons of the endocyclic
imino groups. In the 1H NMR spectra of compounds VI
and VII the relative intensity of signals corresponding
to the protons of CH3 and N–H groups of the imidazole
N
H
H2N
CN
NC
IV
III
Compound III is a light-yellow powder soluble in
hot water, DMF, aceton, dilute water solutions of mineral
acids and alkali. Its composition and structure were con-
firmed by elemental analysis, IR and mass spectrum
(ionization by electron impact). In the IR spectrum of
dinitrile III the band at 3416 cm–1 corresponds to the
vibrations of the N–H bond of the imidazole ring, in the
region 2936 cm–1 appeared the bands of the stretching
vibrations of the C–H bonds in the methyl group, the
band at 2232 cm–1 belonds to the vibrations of cyano
groups.
The mass spectrum of compound III contains the
peak of the molecular ion of m/z 182 [M]+, and also of
its fragmentation products of m/z 167 [M – CH3]+ and
154 [M – HCN]+.
The random condensation of nitriles I and III by
heating with lithium butanolate in butanol followed by
demetallation of the obtained dilithium phthalocyanines
with acetic acid led to the formation of a mixtur of
unsymmetrically substituted phthalocyanines V–VIII in
keeping with Scheme 1.
Phthalocyanines A3Β (V), AAΒΒ (VI), and AΒ3 (VII)
due to their high solubility in organic solvents were
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SYNTHESIS AND SPECTRAL CHARACTERISTICS OF PHTHALOCYANINES
227
Scheme 1.
H21C10O
OC10H21
OC10H21
(1) BuOLi,
BuOH
OC10H21
CN
N
N
N
N
(2) MeCO2H,
H2O
NC
NC
N
N
NH
Me
Me
HN
N
H
N
H
CN
OC10H21
N
N
III
OC10H21
I
H21C10O
OC10H21
V
H21C10O
OC10H21
OC10H21
H21C10O
OC10H21
N
N
N
N
N
N
N
N
N
N
N
Me
Me
NH
NH
HN
HN
Me
N
N
N
H
H
H
N
N
N
N
OC10H21
Me
HN
N
HN
N
NH
N
Me
VI
Me
VII
N
N
N
N
N
N
Me
NH
HN
Me
N
H
N
H
N
N
HN
N
Me
VIII
fragments increased, and insignificant upfield shift of
the proton peaks of the endocyclic imino groups was
observed. This fact suggests that the molecules of
compounds VI and VII have more planar structure.
The electron absorption spectra of phthalocyanines
V–VII contain strong absorptions corresponding to π−
π* transitions in the visible (Q-bands) and UV region
(Β-bands).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 2 2008

GALANIN et al.
228
the AAΒΒ type compared with the compounds of the A3Β
D
1
1.5
1.0
0.5
type can be understood involving a four-orbital model
of Gouterman [13]. In keeping with this model the
longwave bands in the electron absorption spectra of
symmetrical phthalocyanines are regarded as electron
transition from the a1u orbital to two normal to each other
2
3
degenerate orbitals e*. In event of unsymmetrically sub-
g
stituted phthalocyanines the degeneration is removed,
and the Q-band splits in two components of close
intensity. The splitting in accordance with the theoretical
prediction should be the least for compound of the AAΒΒ
type. In our case we observe just this pattern.
0.0
As to the electronic spectrum of compound VII
(Fig. 1, 3), its character as expected is similar to that of
the spectrum of phthalocyanine V. The Q-band is also
split in three components with the maxima at 738, 708,
and 669 nm, thus compared with the spectrum of
compound V the maxima of bands suffer blue shift by
29, 16, and 20 nm respectively. This fact may be attribut-
ed to the decrease in the energy of HOMO a1u under the
effect of three moieties of 2-methylbenzimidazole acting
as electron-acceptor substituents.
400
500
600
700
800
λ, nm
Fig. 1. Electron absorption spectra in CHCl3. (1) compound
V; (2) compound VI; (3) compound VII.
In the electron absorption spectrum of phthalocyanine
V (Fig. 1, 1) the Q-band is split in three components
with the maxima at 767, 724, and 689 nm. Three-band
spectrum in the longwave region is one of the
characteristic features of metal-free phthalocyanines of
the A3Β type, and the most longwave component
corresponds to the charge transfer from the donor part
of the molecule to the acceptor one [11], whose role play
here the fragments of 2-methylbenzimidazole. A similar
spectral pattern was previously observed for a phthalo-
cyanine of the A3Β type containing three fragments of
3,6-dipentoxyphthalonitrile and one of unsubstituted
phthalonitrile [12].
The spectra of compounds V–VII contain broadened
bands in the region 401–463 nm that we believe to be
the bands of charge-transfer from the donor to the
acceptor part of the molecule.
The imidazole fragments included in the molecules
of phthalocyanine V–VII are of amphotheric character
and are capable of reacting with acids and bases. For
instance, these reactions of compound V can be
represented by Scheme 2.
In the electron absorption spectrum of compound VI
(Fig. 1, 2) the Q-band is split in two components with
the maxima at 755 and 675 nm. The decrease in the
number of bands in the spectrum of phthalocyanines of
These properties of the imidazole fragments suggest
that the electronic spectra of the synthesized phthalo-
cyanines should suffer significant changes depending on
Scheme 2.
H21C10O
OC10H21
OC10H21
H21C10O
OC10H21
OC10H21
N
N
N
N
N
N
N
N
+
OH _
NH
N
H+
NH
NH
HN
Me
V
HN
Me
_
N
N
H
N
N
N
N
OC10H21
OC10H21
H21C10O
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 2 2008
H21C10O
OC10H21
OC10H21

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF PHTHALOCYANINES
229
the pH of the environment. Actually, the electron absorp-
tion spectrum of compound V registered in chloroform
with added diethylamine (Fig. 2, 1) contains a Q-band
with the maxima at 751 and 671 nm, therefore a blue
shift of the maxima by 16–18 nm occurs compared with
their position in the pH-neutral solvent. Besides the
spectrum becomes two-band, and this may be ascribed
to increased symmetry of the molecule. Evidently here
considerably decreased the electron-acceptor capacity of
the Β fragment leading to diminished polarization of the
whole molecule.
Another pattern was observed on registering the
electron absorption spectrum of compound V in chloro-
form acidified with HCl (Fig. 2, 2). In this case a red
shift of the Q-band maxima was observed to 865 and
751 nm, namely, by 98 and 62 nm. This may be due to
the increase in the acceptor properties of fragment Β and
consequently the higher degree of the molecule polariza-
tion. This assumption is supported by the considerably
increased relative intensity of the absorption band at
545 nm that is a charge-transfer band.
Fig. 2. Electron absorption spectra of compound V. (1) in
CHCl3 + NHEt2, (2) in CHCl3 + HCl.
3,6-Didecyloxyphthalonitrile (I). A mixture of
10.0 g (0.0625 mol) of 3,6-dihydroxyphthalonitrile (II),
55.2 g (0.25 mol) of 1-bromodecane, 34.5 g (0.25 mol)
of K2CO3, and 50 ml of DMF was stirred at 100°C for
20 h. On completion of the reaction the reaction mixture
was cooled, diluted with water, and the separated
precipitate was filtered off. The reaction product obtained
was recrystallized from petroleum ether and DMF,
washed with 50 ml of acetone, and dried at room
temperature. Yield 26 g (95%), white powder, mp 148°C,
well soluble in benzene, chloroform, insoluble in water,
sparingly soluble in DMF and acetone. IR spectrum, ν,
cm–1: 3096, 3032, 2936, 2304, 1528, 1416, 1336, 1220,
1116, 1080, 832. Found, %: C 76.91; H 10.26; N 6.14.
C28H44O2N2. Calculated, %: C 76.32; H 10.06; N 6.36.
The electron absorption spectrum of phthalocyanine
VII in the acidified chloroform contains a broadened
Q-band with the maxima at 859 and 770 nm cor-
responding to the red shift of the band by 105 nm. The
diffuse character of the band suggests a strong association
of compound VII in solution. The band at 558 nm is also
a charge-transfer band. As to the Soret band, it also
undergoes the red shift by 40 nm.
Unlike compound V, the electronic spectrum of
compound VI does not suffer considerable changes on
adding to the chloroform solution of diethylamine.
Evidently the formation of phthalocyanine VI dianion
does not affect significantly the dipole moment of the
molecule that governs the spectral characteristics of
compound VI.
2-Methyl-5,6-dicyanobenzimidazole (III). A mix-
ture of 1.0 g (6.3 mmol) of 4,5-diaminophthalonitrile
(IV) and 10 ml of acetic acid was heated to boiling and
maintained at this temperature for 2 h, then the reaction
mixture was cooled and poured into 50 ml of ice-water
mixture. The separated precipitate was filtered off,
washed with water, recrystallized from water, and dried.
Yield 0.86 g(75%), light-yellow powder, mp 245°C,
soluble in hot water, acetone, DMF, in dilute water
solutions of mineral acids and alkali. IR spectrum, ν,
cm–1: 3416, 2936, 2232, 1664, 1600, 720. Mass spectrum
(electron impact), m/z (Irel, %): 182 [M]+ (10), 167 [M –
CH3]+ (100), 154 [M – HCN]+ (25). Found, %: C 65.11;
H 3.50; N 30.59. C10H6N4. Calculated, %: C 65.93; H 3.32;
N 30.75.
EXPERIMENTAL
Electron absorption spectra of compounds obtained
were measured on a spectrophotometer Hitachi UV-2001,
1H NMR spectra in CDCl3, on a spectrometer Bruker
AMD-200 (200 MHz, internal reference TMS), IR
spectra, on spectriohotometer Avatar 360 FT-IR in the
range 400–4000 cm–1 from thin films, mass spectra were
registered on a GC-MS instrument Varian Saturn 2000R.
Elemental analysis was carried out on a FlashEA 1112
CHNS-O Analyzer.
Condensation of 3,6-didecyloxyphthalonitrile (I)
with 2-methyl-5,6-dicyanobenzimidazole (III). Into
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GALANIN et al.
230
a solution of lithium 1-butanolate in 1-butanol prepared
from 0.2 g of lithium and 30 ml of anhydrous 1-butanol
was charged 1.0 g (2.3 mmol) of compound I, and the
mixture was kept at reflux for 1 h, then 0.7 g (4.0 mmol)
of compound III was added, and the mixture was heated
at reflux for 3 h more. The reaction mixture was cooled,
and 10 ml of acetic acid and 20 ml of water was added,
the separated precipitate was filtered off, washed on the
filter with 30 ml of acetone, and dried. The residue was
dissolved in benzene and subjected to chromatography
on a column packed with silica gel 60 (eluent toluene–
acetone, 10:1 v/v). Therewith the mixture separated into
three zones containing phthalocyanines V, VI, and VII
respectively.
1,4-Didecyloxytri[2,3-(2-methylimidazolo)]-
phthalocyanine (VII) (AB3). Yield 0.12 g (5%), violet
powder, well soluble in benzene, chloroform, sparingly
soluble in acetone, insoluble in water. Electron absorption
spectrum, λmax, nm (D/Dmax), (CHCl3): 738 (1.00), 708
(0.58), 669 (0.33), 401 (0.32), 331 (0.48). IR spectrum,
λ, cm–1: 3301, 3086, 2952, 2928, 2859, 1766, 1477, 1455,
1
1271, 1222, 1168, 1052, 755, 576. H NMR spectrum,
δ, ppm: –0.92 s (2H), 0.83 s (6H), 1.65–2.05 s (32H),
2.50–2.55 m (9H), 4.15–4.25 t (4H), 6.95–7.00 m (2H),
8.54 s (6H), 8.95 s (3H). Found, %: C 71.01; H 6.05;
N 18.55. C58H64N14O2. Calculated, %: C 70.42; H 6.52;
N 19.82.
REFERENCES
1,4,8,11,15,18-Hexadecyloxy-2,3-(2-methyl-
imidazolo)phthalocyanine (V) (A3B). Yield 0.09 g
(8%), green powder, well soluble in benzene, chloroform,
insoluble in acetone and water. Electron absorption
spectrum, λmax, nm (D/Dmax), (CHCl3): 767 (1.00), 724
(0.51), 689 (0.36), 426 (0.23). 334 (0.55); (CHCl3 +
NHEt2): 751 (1.00), 674 (0.41), 463 (0.22), 330 (0.68);
(CHCl3 + HCl): 864 (1.00), 751 (0.68), 547 (0.34), 335
(0.77). IR spectrum, ν, cm–1: 3286, 3081, 2954, 2923,
2853, 1728, 1599, 1504, 1377, 1270, 1182, 1121, 1060,
966, 889, 807, 760, 722, 597. 1H NMR spectrum, δ, ppm:
–67 s (2H), 0.88 s (18H), 1.55–2.05 s (96H), 2.45–2.60 m
(3H), 3.95–4.01 t (12H), 6.90–7.10 m (6H), 8.51 s (2H),
8.97 s (1H). Found, %: C 75.01; H 9.15; N 8.64.
C94H140N10O6. Calculated, %: C 74.96; H 9.37; N 9.30.
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2. Tarasevich, M.S. and Radyushkina, K.A., Kataliz i
elektrokataliz metalloporfirinami (Catalysis and
Electrocatalysis with Metalloporphyrins), Moscow:
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Akad. Nauk, Ser. Khim., 2000, vol. 12, p. 2062.
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Vysokomol. Soedin. B, 1988, vol. 30, p. 286.
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Serano, J.L., Ed., Weinheim: VCH, 1996, 498 p.
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Obshch. Khim., 1999, vol. 69, p. 1372.
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Rizzoli, C., Gaberkorn, A., and Stuzhin, P.A., Mendeleev
Commun., 2001, vol. 2, p. 45.
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Spectr., 1969, vol. 11, p. 108.
cis-1,4,8,11-Tetradecyloxydi[2,3-(2-methylimid-
azolo)]phthalocyanine (VI) (AABB). Yield 0.08 g (6%),
violet powder, well soluble in benzene, chloroform,
insoluble in acetone and water. Electron absorption
spectrum, λmax, nm (D/Dmax), (CHCl3): 754 (1.00), 674
(0.31), 463 (0.18), 331 (0.49); (CHCl3 + HCl): 859 (1.00),
770 (0.91), 558 (0.52), 370 (1.55). IR spectrum, ν, cm–1:
3300, 3081, 2954, 2924, 2853, 1767, 1726, 1614, 1499,
1467, 1367, 1278, 1216, 1179, 1058, 945, 823, 748, 640,
1
581. H NMR spectrum, δ, ppm: –0.75 s (2H), 0.85 s
(12H), 1.65–2.08 s (64H), 2.45–2.68 m (6H), 3.93–
4.00 t (8H), 6.90–7.10 m (4H), 8.58 C (4H), 8.95 s (2H).
Found, %: C 81.50; H 4.75; N 7.00. C76H102N12O4.
Calculated, %: C 73.16; H 8.24; N 13.47.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 2 2008