Synthesis and mesomorphism of tetraphenylporphyrin derivatives

Article abstract of DOI:10.1016/j.mencom.2008.11.013

Tetra-meso-phenylporphyrins with higher alkoxy substituents at 4-positions of 5,15- or 5,10,15,20-phenyl groups have been synthesised; their liquid-crystal properties have been studied, and compounds that can undergo vitrification with retention of the me

Full text of DOI:10.1016/j.mencom.2008.11.013

Mendeleev
Communications
Mendeleev Commun., 2008, 18, 324–326
Synthesis and mesomorphism of tetraphenylporphyrin derivatives
Irina N. Fedulova,*a Natalya A. Bragina,a Nikita V. Novikov,a Andrey F. Mironov,a
Venera V. Bykova,b Nadezhda V. Usol’tsevab and Galina A. Ananievab
a M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, 119571 Moscow, Russian Federation.
Fax: +7 495 936 8902; e-mail: in_fedulova@mail.ru
b Research Institute of Nanomaterials, Ivanovo State University, 153025 Ivanovo, Russian Federation.
Fax: +7 4932 37 0808; e-mail: usol@ivanovo.ac.ru
DOI: 10.1016/j.mencom.2008.11.013
Tetra-meso-phenylporphyrins with higher alkoxy substituents at 4-positions of 5,15- or 5,10,15,20-phenyl groups have been
synthesised; their liquid-crystal properties have been studied, and compounds that can undergo vitrification with retention of the
mesophase structure have been revealed.
Studies on the molecular design of mesogens have been developed
intensely since they can be used in the Langmuir–Blodgett
technology (sensors) and microelectronics (as structures with
one-dimensional conductivity), as well as in optical, photonic
and optoelectronic devices.1–3 For example, the field-induced
molecular reorientation in currently developed liquid-crystal
displays takes several milliseconds.4
Liquid crystals based on porphyrins belong to discotic
mesogens and are of considerable interest for optoelectronics
and display and data storage devices.5–8 Combination of a rigid
macrocycle with flexible aliphatic substituents facilitates self-
assembling of discotic molecules into a supramolecular ensemble
owing to plane–plane interactions.9 The size of aliphatic substi-
tuents plays a considerable role in the mesomorphic properties
of such compounds and in the formation of certain mesophases.7
Bulky aliphatic substituents at the porphyrin molecule can be
located either at outer β-carbon atoms or at the meso positions
of the macrocycle; in the latter case, they can be attached both
directly to carbon atoms 5, 10, 15 and 20, and to the phenyl
radicals located there. The latter variant allows porphyrins to
be synthesised from more accessible compounds (pyrrole and
substituted benzaldehydes) using efficient condensation tech-
niques. In this work, we synthesised similar porphyrins with
various long-chain substituents in order to study how the size and
number of these substituents affect the liquid-crystal properties
of porphyrins.
OR
OH
OR
N
RBr
H
Currently, the main method for the synthesis of meso-alkoxy-
substituted porphyrins involves the reaction of hydroxy-substi-
tuted tetraphenylporphyrin with alkyl bromides.11,12 We developed
another approach to synthesise lipoporphyrins, according to
which the residues of higher fatty alcohols are incorporated
into benzaldehyde derivatives at the first stage of the synthesis,
which is followed by condensation with pyrrole.13 Incorporation
of aliphatic substituents into a benzaldehyde molecule increases
its solubility in organic solvents, which results in more successful
condensations of benzaldehydes with pyrrole, shortens and
simplifies considerably the synthetic procedure, facilitates the
purification of the target products, and after all, provides higher
yields of lipoporphyrins. Porphyrins of two structural types were
synthesised by monopyrrole condensation (Type 1) and using
dipyrrolylmethanes (Type 2) in 36–44% yields (Scheme 1).†
Zinc and cobalt complexes 4, 5, 9–11 were obtained in 90–95%
CHO
RO
CHO
NH HN
N
H
OR
N
H
N
N
CHO
H
N
RO
OR
Type 1
RO
yields‡ from ligands 1,
6
and 7§ using conventional
techniques.14
The liquid crystal properties of porhyrins 1–11 were studied
by optical polarisation microscopy. Figure 1 shows the phase
transition temperatures of these porphyrins in the course of heating.
It was shown that five compounds could form a mesophase.
The thermotropic mesomorphism in the series of 5,15-di-
substituted tetraphenylporphyrin derivatives was observed for
5,15-di-(4-tetradecyloxyphenyl)-10,20-diphenylporphyrin 2 and
5,15-di-(4-hexadecyloxyphenyl)-10,20-diphenylporphyrin 3. An
increase in the substituent length in the series of compounds
1–3 decreases the melting point from 242.7° to 61.8 °C; 5,15-di-
N
H
N
N
H
N
OR
Type 2
Scheme 1 Synthesis of di- and tetrasubstituted tetraphenylporphyrins.
– 324 –
© 2008 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2008, 18, 324–326
transition. In the homologous series of 5,10,15,20-tetra(alkoxy-
crystal
mesophase
isotrope
phenyl)porphyrins, a narrow mesophase temperature range of
91.7–115 °C is observed only for compound 8, in which the
length of the peripheral substituent is 16 carbon atoms.
242.7
1
2
72.8
61.8
123.4
127
Incorporation of coordinatively unsaturated metals (Zn2+ and
Co2+) modifies considerably the properties of nonmesomorphic
ligand 1: zinc complex 4 shows the broadest range of meso-
phase existence (129.6 °C), while the cobalt complex forms
a mesophase in a high-temperature range (214.4–290.2 °C).
Porphyrins 6, 7 belonging to the first type do not show liquid-
crystal properties if a metal is incorporated. Thus, given equal
lengths of aliphatic substituents at the meso-position, liquid-
3
131.4
261
4
214.4
290.2
5
209.6
6
121.5
7
91.7 115
8
210.3
9
‡
General procedure for the synthesis of porphyrin metal complexes 4, 5,
227.1
10
11
9–11. A metal acetate (6 equiv.) in methanol was added to a porphyrin
(1 equiv.) in chloroform and the reaction mixture was stirred for 1 h.
The reaction mixture was concentrated, the residue was dissolved in
chloroform, inorganic salts were filtered off, and the product was crys-
tallised from heptane.
5,15-Bis(4-octyloxyphenyl)-10,20-diphenylporphyrin zinc complex 4.
Obtained from porphyrin 1 (20 mg, 0.023 mmol) and zinc acetate (25 mg,
0.138 mmol). Yield, 19 mg (90%). UV [lmax/nm (relative intensity)]:
423, 550.2, 590.4 (1:0.064:0.024).
5,15-Bis(4-octyloxyphenyl)-10,20-diphenylporphyrin cobalt complex
5. Obtained from porphyrin 1 (11 mg, 0.0127 mmol) and cobalt acetate
(20 mg, 0.0762 mmol). Yield, 10 mg (89%). UV [lmax/nm (relative
intensity)]: 414.4, 530 (1:0.078).
123
0
50
100
150
T/°C
200
250
300
Figure 1 Optical polarization microscopy data (the temperatures of phase
transitions in the course of heating).
(
4-octyloxyphenyl)-10,20-diphenylporphyrin 1 is non-mesomorphic.
For non-mesomorphic compounds, an increase in the substituent
length decreases the temperature of the crystal–isotrope phase
†
NMR spectra were recorded on a Bruker MSL-300 instrument with
a working frequency of 300 MHz; measurements were performed on a
d scale using TMS as an internal reference and CDCl3 as the solvent.
Electronic spectra were recorded in dichloromethane using a Jasco UV-7800
spectrophotometer. Elemental analyses were carried out with a FLASH
EA 112 Termo Finnigan C, H, N, S analyser.
Mesomorphic properties were studied by optical polarisation microscopy.
Thermotropic mesomorphism was studied with a Leitz Laborlux 12 Pol
optical thermopolarization microscope equipped with a Mettler FP 82
heating device.
General procedure for the synthesis of 5,15-disubstituted porphyrins
1–3. Boron trifluoride etherate (0.15 equiv.) was added to a solution of
dipyrrolylmethane (1 equiv.)10 and benzaldehyde (1.4 equiv.) in chloroform
at room temperature under argon. The reaction mixture was stirred for 1 h;
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (0.9 equiv.) was added and
the mixture was stirred for another 1 h at room temperature. The con-
densation products were separated by flash chromatography and the target
product was separated by column chromatography using chloroform–
hexane (4:1) for elution.
5,10,15,20-Tetra(4-octyloxyphenyl)porphyrin zinc complex 9. Obtained
from porphyrin 6 (25 mg, 0.133 mmol) and zinc acetate (30 mg). Yield, 21 mg
(90%). UV [lmax/nm (relative intensity)]: 423, 550, 590 (1:0.064:0.028).
5,10,15,20-Tetra(4-octyloxyphenyl)porphyrin cobalt complex 10. Obtained
from porphyrin 6 (20 mg, 0.13 mmol) and cobalt acetate (25 mg). Yield,
18 mg (90%). UV [lmax/nm (relative intensity)]: 415, 530 (1:0.08).
5,10,15,20-Tetra(4-tetradecyloxyphenyl)porphyrin zinc complex 11.
Obtained from porphyrin 7 (20 mg, 0.125 mmol) and cobalt acetate (30 mg).
Yield, 18 mg (92%). UV [lmax/nm (relative intensity)]: 423, 549, 591
(1:0.061:0.02).
§
General procedure for the synthesis of tetrasubstituted porphyrins 6–8.
Boron trifluoride etherate (0.1 equiv.) and a catalytic amount of anhydrous
ethanol were added to a solution of benzaldehyde (1 equiv.) and pyrrole
(1 equiv.) in dichloromethane at room temperature under argon. The
reaction mixture was stirred for 1 h in an inert gas stream at room
temperature; 2,3-dichloro-5,6-dicyano-1.4-benzoquinone (0.9 equiv.) was
added and the mixture was stirred for another 1 h. The reaction products
were separated by flash chromatography and eluted with chloroform.
The target product was purified by column chromatography and eluted
with chloroform. After that, it was crystallised from methanol.
5,15-Bis(4-octyloxyphenyl)-10,20-diphenylporphyrin 1. Obtained from
meso-(4-octyloxyphenyl)dipyrrolylmethane (0.400 g, 1.1 mmol) and benzal-
dehyde (0.150 g, 1.4 mmol). Yield, 0.170 g (36%), Rf 0.72 (CHCl3);
mp 242.7 °C. UV [lmax/nm (e×10–3)]: 418.0 (674), 515.2 (35), 550.8
(18.8), 590 (11.1), 646.2 (8.75). 1H NMR, d: –2.73 (s, 2H, NH), 0.9 (t,
6H, Me), 1.3 [m, 20H, (CH2)5], 2.02 (m, 4H, OCH2CH2), 4.28 (t, 4H,
OCH2, J 7 Hz), 7.75 [m, 10H, 10.20-(ArH)], 8.22 [m, 8H, 5.15-(ArH)],
8.87 (m, 8H, pyrrole). MS, m/z: 871.61 [M+ + 1]. Found (%): C, 82.94;
H, 7.21; N, 6.42. Calc. for C60H62N4O2 (%): C, 82.72; H, 7.17; N, 6.43.
5,15-Bis(4-tetradecyloxyphenyl)-10,20-diphenylporphyrin 2. Obtained
from meso-(4-tetradecyloxyphenyl)dipyrrolylmethane (0.330 g, 0.76 mmol)
and benzaldehyde (0.120 g, 1.14 mmol). Yield, 0.161 g (44%), Rf 0.68
(CHCl3). UV [lmax/nm (e×10–3)]: 418.0 (616), 515.2 (28.3), 550.6 (15.8),
5,10,15,20-Tetra(4-octyloxyphenyl)porphyrin 6. Obtained from 4-octyl-
oxybenzaldehyde (0.240 g, 1 mmol) and pyrrole (0.067 g, 1 mmol). Yield,
0.120 g (33%), Rf 0.9 (CHCl3). UV [lmax/nm (e×10–3)]: 418 (390), 519
1
(22.4), 556.2 (14.7), 591 (7.0), 646.6 (5.7). H NMR, d: –3.36 (s, 2H,
NH), 0.29 (t, 12H, Me), 1.02 [m, 40H, (CH2)5], 1.38 (m, 8H, OCH2CH2),
3.65 (t, 8H, OCH2CH2, J 7 Hz), 6.65–7.15 [m, 16H, meso-(ArH)],
8.25 (s, 8H, pyrrole). Found (%): C, 80.95; H, 8.40; N, 4.97. Calc. for
C76H94N4O4 (%): C, 80.81; H, 8.24; N, 4.86.
5,10,15,20-Tetra(4-tetradecyloxyphenyl)porphyrin 7. Obtained from
4-tetradecyloxybenzaldehyde (0.320 g, 1 mmol) and pyrrole (0.067 g,
1 mmol). Yield, 0.151 g (40%), Rf 0.9 (CHCl3). UV [lmax/nm (e×10–3)]:
418.2 (524), 515.4 (24.9), 550.4 (16.3), 590.6 (9.12), 646 (5.18). 1H NMR,
d: –3.36 (s, 2H, NH), 0.29 (t, 12H, Me), 1.04 [m, 88H, (CH2)11], 1.4 [m,
8H, OCH2CH2(CH2)11Me], 3.65 (t, 8H, OCH2, J 7 Hz), 6.65–7.15 [m,
16H, meso-(ArH)], 8.25 (s, 8H, pyrrole). Found (%): C, 83.03; H, 9.67;
N, 3.83. Calc. for C100H142N4O4 (%): C, 83.12; H, 9.64; N, 3.86.
5,10,15,20-Tetra(4-hexadecyloxyphenyl)porphyrin 8. Obtained from
4-hexadecyloxybenzaldehyde (0.350 g, 1 mmol) and pyrrole (0.067 g,
1 mmol). Yield, 0.102 g (39%), Rf 0.9 (CHCl3). UV [lmax/nm (e×10–3)]:
418.2 (623), 515.4 (21.9), 550.4 (15.3), 590.6 (9.1), 646 (7.8). 1H NMR,
d: –3.2 (s, 2H, NH), 0.31 (t, 12H, Me), 1.12 [br. m, 104H, (CH2)13], 1.4
(m, 8H, OCH2CH2CH2), 3.65 [t, 8H, OCH2(CH2)2, J 7 Hz], 7.53 [d, 8H,
2.6-(ArH)], 8.22 [d, 8H, 2.4-(ArH)], 8.9 (s, 8H, pyrrole). Found (%):
C, 82.28; H, 10.10; N, 3.55. Calc. for C108H158N4O4 (%): C, 82.12;
H, 10.14; N, 3.66.
1
590.4 (9.1), 646.2 (7.47). H NMR, d: –2.72 (s, 2H, NH), 0.91 (t, 6H,
Me), 1.31 [m, 44H, (CH2)11], 2.01 (m, 4H, OCH2CH2), 4.27 (t, 4H,
OCH2, J 7 Hz), 7.78 [m, 10H, 10.20-(ArH)], 8.23 [m, 8H, 5.15-(ArH)],
8.85 (m, 8H, pyrrole). MS, m/z: 1038.78 [M+]. Found (%): C, 83.22; H,
8.41; N, 5.41. Calc. for C72H86N4O2 (%): C, 83.19; H, 8.34; N, 5.39.
5,15-Bis(4-hexadecyloxyphenyl)-10,20-diphenylporphyrin 3. Obtained
from meso-(4-hexadecyloxyphenyl)dipyrrolylmethane (0.430 g, 0.9 mmol)
and benzaldehyde (0.130 g, 1.22 mmol). Yield, 0.189 g (38%), Rf 0.68
(CHCl3). UV [lmax/nm (e×10–3)]: 418.0 (610), 515.2 (27.2), 550.3 (14.6),
1
590.6 (8.3), 646.2 (7.45). H NMR, d: –2.72 (s, 2H, NH), 0.93 (t, 6H,
Me), 1.33 [m, 48H, (CH2)12], 1.61 [m, 4H, O(CH2)2CH2], 2.03 (m, 4H,
OCH2CH2), 4.25 (t, 4H, OCH2, J 7 Hz), 7.75 [m, 10H, 10.20-(ArH)],
8.22 [m, 8H, 5.15-(ArH)], 8.85 (m, 8H, pyrrole). Found (%): C, 83.42;
H, 8.71; N, 5.12. Calc. for C76H94N4O2 (%): C, 83.32; H, 8.65; N, 5.11.
– 325 –

Mendeleev Commun., 2008, 18, 324–326
the preceding mesophase packing [Figure 2(b)]. Various vitrifying
Table 1 Structures of the meso-alkoxyphenylporphyrins synthesised.
R1 R2
mesogens may find use in optical information recording, non-
linear optics, tunneling filters for optical communication, com-
pensators for optimizing the viewing angle of displays, solar
batteries and light-emitting diodes.
N
M
N
This study was supported by the Russian Foundation for
Basic Research (grant no. 07-03-00427) and the RF Mimistry
for Education and Science (grant no. RNP.2.2.1.1.7280).
N
N
References
R2
R1
R1
1
H. S. Nalwa, in Nonlinear Optics of Organic Molecules and Polymeric
Materials, eds. H. S. Nalwa and S. Miyata, CRC Press, Boca Raton,
1997, p. 617.
Compound
R2
M
2
J. H. Chou, in The Porphyrin Handbook, eds. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, New York, 2000, vol. 6,
p. 346.
M. Castella, F. Lopez-Calahorra and D. Velasco, Liq. Cryst., 2002,
29, 559.
N. V. Usol’tseva, V. V. Bykova and O. B. Akopova, in Uspekhi v
izuchenii zhidkokristallicheskikh materialov (Advances in Liquid
Crystal Materials), ed. N. V. Usol’tseva, IGU, Ivanovo, 2007 (in
Russian).
H. Eichhorn, J. Porphyrins Phthalocyanines, 2000, 4, 88.
C. Arunkumar, P. Bhyrappa and B. Varghese, Tetrahedron Lett., 2006,
47, 8033.
1
2
3
4
5
6
7
8
9
O(CH2)7Me
O(CH2)13Me
O(CH2)15Me
O(CH2)7Me
O(CH2)7Me
O(CH2)7Me
O(CH2)13Me
O(CH2)15Me
O(CH2)7Me
O(CH2)7Me
O(CH2)13Me
H
H
H
H
2H
2H
2H
Zn
Co
2H
2H
2H
Zn
Co
Zn
3
4
H
O(CH2)7Me
O(CH2)13Me
O(CH2)15Me
O(CH2)7Me
O(CH2)7Me
O(CH2)13Me
10
11
5
6
crystal properties are more likely in the case of 5,15-disub-
stituted porphyrins and the corresponding metal complexes.
The mesophase in all of the compounds is characterised by a
non-geometric grain structure presumably associated with a
column-type packing [Figure 2(a)].
Many photonics applications demand materials capable of
vitrification with preservation of the liquid-crystal order in a
solid phase without crystallisation.15 Thermotropic mesogens
2–5, 8 form a vitrified state on cooling with preservation of
7
8
9
M. Ichihara, M. Miida, B. Mohr and K. Ohta, J. Porphyrins Phthalo-
cyanines, 2006, 10, 1145.
J. M. Warman, J. E. Kroeze, P. G. Schouten and A. van de Craats, J.
Porphyrins Phthalocyanines, 2003, 7, 342.
N. V. Usoltseva, O. B. Akopova and V. V. Bykova, Zhidkiye kristally –
diskoticheskie mezogeny (Liquid crystals – Discotic Mesogenes), IGU,
Ivanovo, 2004, p. 128 (in Russian).
10 K. Ohta, N. Yamaguchi and I. Yamamoto, J. Mater. Chem., 1998, 8,
2637.
11 A. S. Semeykin, Zh. Obshch. Khim., 1984, 54, 1599 (in Russian).
12 L. Guo and Y. Liang, Spectrochim. Acta, Part A, 2003, 59, 219.
13 I. N. Fedulova, N. A. Bragina, N. V. Novikov, O. A. Ugol’nikova and
A. F. Mironov, Bioorg. Khim., 2007, 33, 635 (Russ. J. Bioorg. Chem.,
2007, 33, 589).
(a)
(b)
14 Porfiriny: struktura, svoistva, sintez (Porphyrins: Structure, Properties
and Synthesis), ed. N. S. Enikolopyan, Nauka, Moscow, 1987 (in Russian).
15 H. M. Chen, P. D. Katsis and S. H. Chen, Chem. Mater., 2003, 15,
2534.
Figure 2 Micrographs of (a) the texture of the thermotropic mesophase of
compound 3 in the course of heating, at 61.8 °C (crystal + isotrope); (b) the
vitrified state of the texture of the thermotropic mesophase of compound 3
on cooling, at 27.1 °C. The Nicols were crossed, ×250.
Received: 25th March 2008; Com. 08/3109
– 326 –