Synthesis of perialkynylated tetrapyrazinoporphyrazines and its optical properties

Article abstract of DOI:10.3184/030823409X449473

Some phthalocyanines soluble in organic solvents have been developed by peripheral introduction of substituent groups. We report a new method for preparation of the polyphenyl-substituted dicyanopyrazines based on the [2 + 4] Diels-Alder cycloaddition of

Full text of DOI:10.3184/030823409X449473

312 RESEARCH PAPER
MAY, 312–316
JOURNAL OF CHEMICAL RESEARCH 2009
Synthesis of perialkynylated tetrapyrazinoporphyrazines and its optical
properties
Chun Keun Jang and Jae Yun Jaung*
Department of Fiber and Polymer Engineering, Hanyang University 17 Haengdang-dong, Seongdong-gu, Seoul, 133791, Korea
Some phthalocyanines soluble in organic solvents have been developed by peripheral introduction of substituent
groups. We report a new method for preparation of the polyphenyl-substituted dicyanopyrazines based on the [2 + 4]
Diels–Alder cycloaddition of the tetraphenylcyclopentadienone to an ethynyl compound. The synthesised
tetrapyrazinoporphyrazinato metal complexes were characterised by UV-visible spectroscopy, MALDI-TOF-Ms
(matrix-assisted laser desorption ionisation time-of-flight mass) spectroscopy, and 1H NMR spectroscopy.
Keywords: porphyrazine, spectral change, aggregation, fluorescence, perialkynyl substituent
Phthalocyanine derivatives have found wide applications as
traditional dyes1 in liquid crystallinity,2 chemical sensors,3 and
non-linear optical materials.4 In addition, they can be applied
to the electronics industry. For instance, they may be used for
optical data storage, colour display technology, and biological
technology (e.g. photodynamic tumour therapy (PDT)).5-6
The properties of phthalocyanines are influenced by the
nature of the peripheral substituents and the central metal
ion. Unsubstituted phthalocyanine has poor solubility.
However, alkyl chain substituents can increase the solubility
in common organic solvents and facilitate the formation
of discotic mesophases. It promises high potential for high
charge mobilities in sufficiently ordered rod-like structures.
The phthalocyanine transferred films or patterning have been
actively researched. Zangmeister et al. transferred peripherally
ethylene oxide substituted copper phthalocyanines to bilayer
films by Langmuir–Blodgett (LB) films.7,8
Faust et al. researched phthalocyanines or tetrapyrazino-
porphyrazines that contained acetylene groups as their
peripheral substituents. Peripheral alkynyl substitution of
strongly absorbent chromophores, such as porphyrins and
phthalocyanines, is becoming an increasingly popular strategy
for the design of functional dyes.
We now report a general synthesis of 2,3-dicyanopyrazines
and their conversion to tetrapyrazinoporphyrazines equipped
with polyphenyl dendrons. The perialkynyl substituent
can modify the chromophores in two different ways. First,
it can cause bathochromic shifts in the electron absorption
and emission spectra, due to the expansion of the p-electron
systems of the chromophores. Second, it can act as a monomer
and can be linked to form delocalised multichromophore
chains or two-dimensional polymer networks.9,10
Result and discussion
Synthesis
The preparation method of 1-bromo-4-(4-(octyloxy)styryl)
benzene (1) has been described in previous literature.11,12
1-(4-Bromophenyl)-2-[4-(octyloxy)phenyl]ethane-1,2-dione
(2) was prepared by refluxing 1 in dimethyl sulfoxide (DMSO)
and 0.4 equiv. of iodine with a 69% yield. 1-[4-(Octyloxy)
phenyl]-2-[4-((trimethylsilyl)ethynyl)phenyl]ethane-1,2-
dione (3) was synthesised by palladium-catalysed ethynylation
in triethylamine. Scheme 1 shows these steps for preparing an
acetylene group containing an a-diketone.
Compound 3 can be a precursor of various compounds,
which are used for preparing peripheral substituents of
phthalocyanines, as shown in Scheme 2. The reaction of 3 with
2,3-diaminomaleonitrile (DAMN) in ethanol, in the presence
of p-toluenesulfonic acid produced the 2,3-dicyanopyrazine
derivative 4.
Treatment of 4 with tetrabutylammonium fluoride in
THF, under mild conditions, with subsequent removal of
the triisopropyl silyl group resulted in a high conversion to
5-(4-ethynylphenyl)-6-(4-(octyloxy)phenyl)pyrazine-2,3-
dicarbonitrile (5).
The compounds 6 were prepared by the condensation
between dibenzyl ketone and a-diketones, in the presence
of potassium hydroxide in ethanol.13 However, the reaction
conditions were highly basic and this meant that the reaction
rate was too fast. A low yield, with various by-products,
O
Br
Br
I2 / DMSO
O
O(CH2)7CH3
1
H3C(H2C)7O
2
O
N(Et)3
Si
O
1) Pd(OAc)2 / PPH3
2)
Si
H3C(H2C)7O
3
Scheme 1 Synthesis method of acetylene-containing a-diketone.
* Correspondent. E-mail: jjy1004@hanyang.ac.kr

JOURNAL OF CHEMICAL RESEARCH 2009 313
H
NC
NC
NH2
NH2
O
Si
Si
NC
NC
N
N
NC
NC
O
N
N
THF
Bu4NF-
MeOH
O(CH2)7CH3
O(CH2)7CH3
H3C(H2C)7O
4
5
3
O
O
Benzyltrimethylammonium hydroxide
tert-butyl alcohl
O(CH2)7CH3
Si
6
SO2(CH2)2CH(CH3)2
H
O
NC
NC
SO2(CH2)2CH(CH3)2
N
N
NC
NC
N
N
OCH3
O(CH2)7CH3
H3CO
7
O(CH2)7CH3
5
Scheme 2 Preparation of 2,3-dicyanopyrazines.
resulted. But in an improvement the base and solvent used
were benzyltrimethyl ammonium hydroxide and tert-butyl
alcohol respectively and as a result even though the reaction
rate was slightly slower a more favourable yield (72%)
resulted. A[2 + 4] Diels–Alder cycloaddition reaction between
tetraphenylcyclopentadienone 6 and the acetylene-group-
containing compound 5 was used, and the polyphenylene
substituent-containing 2,3-dicyanopyrazine 7 was created by
refluxing in degassed p-xylene, followed by the elimination
of carbon monoxide. The advantage of this cycloaddition is
that it is practically free of side reactions, and the equilibrium
is shifted toward the products due to the irreversible loss of
CO and the formation of a benzene ring. Therefore, a retro
Diels–Alder reaction cannot occur.14
butoxide emulsion to afford magnesium complexes 8 and 10.
The magnesium derivatives were demetallised by stirring
them with excess p-toluenesulfonic acid in THF at room
temperature for 30 min to produce 9 and 11, as shown in
Scheme 3.
UV-visible spectra
The maximum absorption wavelength and molar absorptivity
(e) values for compounds 8–11 are shown in Table 1. The
typical B-band (Soret band, around 400nm), and Q-band (in
600–700nm region) of phthalocyanines were identified in this
study. The metal-free tetrapyrazinoporphyrazine generally
have two narrow splitting Qx/Qy bands. These are not related
to their peripheral substituents.
The synthesised 2,3-dicyanopyrazine compounds
and 7 are precursors of tetrapyrazinoporphyrazines. 2,3-
Dicyanopyrazines undergo cyclotetramerisation with
magnesium metal ion, which was prepared from a magnesium
4
The compound 8 shows the highest molar absorptivity of all
of the products. Even if compounds 8 and 9 have only TIPS
groups attached, the wavelengths of the Q-bands are almost
the same as those for 10 and 11, which have polyphenylene
a
SO2(CH2)2CH(CH3)2
OCH3
H3C(H2C)7O
Si
H3C(H2C)7O
OCH3
(H3C)2HC(H2C)2O2S
N
N
N
C
N
Si
C
O(CH2)7CH3
C
C
O(CH2)7CH3
N
C
N
C
N
N
N
C
N
N
N
N
N
N
N
C
N
N
M
N
N
M
N
C
N
C
N
C
C
N
N
N
H3C(H2C)7O
C
N
C
N
N
N
H3C(H2C)7O
C
N
C
Si
N
SO2(CH2)2CH(CH3)2
OCH3
O(CH2)7CH3
H3CO
Si
O(CH2)7CH3
8 : M = Mg
9 : M = 2H
10 : M = Mg
11 : M = 2H
(H3C)2HC(H2C)2O2S
Scheme 3 Structure of tetrapyrazinoporphyrazines.

314 JOURNAL OF CHEMICAL RESEARCH 2009
Table 1 Absorption and molar absorptivity of tetrapyrazino-
porphyrazines
Compd. Solvent
lmax(nm)
e( l/mol∙cm)a
Soret band
(B-band)
Q-band
8
9
CHCl3
THF
383
385
380
379
373
374
384
380
381
377
371
374
667
3.68 ¥ 105
3.77 ¥ 105
2.79 ¥ 105
8.98 ¥ 104
7.55 ¥ 104
4.45 ¥ 104
7.20 ¥ 104
9.16 ¥ 104
4.53 ¥ 104
1.55 ¥ 105
1.49 ¥ 105
1.24 ¥ 105
661
CCl4
666
CHCl3
THF
CCl4
CHCl3
THF
CCl4
CHCl3
THF
CCl4
650, 679
650, 673
681
10
11
662
660
661
650,679
679,673
649, 679
Fig 2 Effect of concentration on the absorption spectra of
compound 8 (solid line: 2.8 ¥ 10-5 M, dashed line: 2.8 ¥ 10-6 M,
dotted line: 0.7 ¥ 10-6 M).
aMolar absorptivity of Q-band or Qy band.
groups attached as their peripheral substituents.
which was added to the nonaqueous solvents in the form of
tetra-n-butylammonium salts. The spectra were found to
rapidly change. Previous researchers showed that the fluoride
anion can bind within the cores of metallophthalocyanines.
Strictly speaking, it forms F- coordinated complexes15 or
causes deprotonation of the proton on the pyrrole group of
metal-free phthalocyanines.16 In our case, Figure 3 shows
the UV-visible spectral changes of 10 and 11 upon adding
tetrabutylammonium fluoride monohydrate (TBAF). The
spectra showed a sharp peak in the Q-band and the molar
absorptivity was higher than that for the initial solution.
The aggregation behaviour of phthalocyanines is a specific
property due to the intermolecular stacking of the planar
and rigid core structures of the molecules. Sometimes
this can become a significant problem for their various
applications. The synthesised products aggregated in solution,
and this tendency was varied by controlling the products'
environments, such as the solvents, their concentration and
the basicity. Figure 1 shows spectra of compounds 8 and 9
in CCl4, chloroform, and THF all at the same concentration.
Spectra of 10 and 11 show almost the same behaviour. The
absorbance of the spectra was significantly decreased in
CCl4. Especially comparing with 9 and 11, spectral peaks of
compound 10 were severely broadened. However, spectral
peaks of compound 11 remain as narrow peaks, although the
absorptivity is decreased. It is assumed that the rigidity of the
phthalocyanine structure is decreased because of the out-of-
twisted peripheral phenyl components.
Fluorescence property
Tetrapyrazinoporphyrazine derivatives show fluorescence
properties which vary according to different environments
around the molecule. The excitation wavelengths used in the
experiments were the lmax of B and Q-bands.
The aggregation behaviour of 8 was investigated at different
concentrations in CHCl3. In CHCl3, as the concentration was
decreased, the intensity of absorption of the Q-band increased
as shown in Fig. 2, because of reduction of aggregation.
There has been a great deal of research focusing on the
optical sensitivity of phthalocyanines due to their acidic
or basic properties. In this paper, the synthesised products
also experience an anion effect, especially with the F- anion,
Fig.1 Absorption spectra of 8 (A, 4.4 ¥ 10-6 M) and 9 (B, 1.78
¥ 10-5 M) in CCl4 (dot line), tetrahydrofuran (dashed line), and
chloroform (solid line).
Fig.3 UV-vis absorption spectral change upon adding a base
to 10 (1.74x10-5 M) and 11 (1.75x10-5 M).

JOURNAL OF CHEMICAL RESEARCH 2009 315
Fig. 4 Fluorescence spectra in chloroform (solid line) and THF (dashed line) at the same concentration (8: 2.6 ¥ 10-7 M, 9:2.6 ¥ 10-7 M,
10:1.74 ¥ 10-7M, 11:1.75 ¥ 10-7 M).
Fig. 5 Fluorescence change upon adding a base to 8 (8:TBAF = 1:0 (solid line), 8:TBAF = 1:108 (dashed line) mol ratio), and
9 (9:TBAF = 1:0 (solid line), 9:TBAF = 1:150 (dashed line) mol ratio).
points were obtained with a capillary melting point apparatus and
are uncorrected. 1H NMR spectra were recorded on a VARIAN
UnityInova 300 MHz FT-NMR Spectrometer. UV-visible and
fluorescence spectra were measured using a SCINCO S-4100 and
a SHIMADZU RF-5301PC spectrophotometer. MALDI-TOF-Ms
(matrix-assisted laser desorption ionisation time-of–flight mass)
spectra were obtained on a Waters Limited MALDI-TOF spectrometer
with dithranol as a matrix. All chemicals were used of reagent grade
without further purification unless otherwise specified.
Figure 4 shows fluorescence spectra of the synthesised
products in chloroform and THF, from the emission peak in
the B-band. Generally, the emission peak around 450–550 nm
was more intense in chloroform. However, the emission peak
around 650–750 nm which shows a red fluorescence, was
significantly more intense in THF than in chloroform.
The appearance of the long wavelength region can be
examined by the fluorescence quenching effect, due to the
intermolecular p-p interaction relatively decreasing in
solution.
Tetrapyrazinoporphyrazinato magnesium complex (8)
A suspension of Mg turning (200 mg, 8.4 mmol), one small crystal
of iodine and n-butanol 20 mL were heated under reflux for 4 h.
The reaction mixture was then cooled to room temperature, and
dicyanopyrazine 4 (1.2 g, 2.1 mmol) was added in one portion.
The reaction mixture was quickly reheated to reflux for 1 h. After
approximately 10 min, the reaction mixture had become dark green.
The mixture was cooled and the solvent was removed in vacuo,
yielding crude product as a dark green solid. The crude product was
purified using chloroform/methanol (30/1) as an eluent. 8 (dark green
solid, 48%): m.p >300°C; 1H NMR (300 MHz, CDCl3) d : 0.40–
1.85 (m, –CH3, 12H), 1.08–1.55 (m, –Si–C–CH3, 72H; methylene,
40H; –Si–CH, 12H), 1.90–2.21 (m, –O–C–CH2, 8H,), 3.90–4.38
(m, O–CH2, 8H,), 6.6–8.3 (m, aryl protons, 32H); MALDI-TOF
mass-spectra: m/z 2387.1 (Calcd 2387.8)
Figure 5 displays the emission spectra of compounds 8 and
9 when tetra-n-butylammonium fluoride (TBAF) was added
in chloroform. The Fmax was significantly changed and Fig. 5
also shows the strong fluorescence in the 650–750nm region.
Conclusion
In this study, the peripheral acetylene group was successfully
attached in the pyrazine unit, and it could be used as a
precursor of various compounds by using condensation and
cycloaddition reactions. We also designed and synthesised
metal and metal-free tetrapyrazinoporphyrazines, which show
that the polyphenylene dendrimers increase the solubility of
porphyrazines in common organic solvents. The aggregation
behaviour in solution was investigated through their absorption
and emission spectra.
Demetallised tetrapyrazinoporphyrazine (9)
p-Toluenesulfonic acid (0.81 g, 4.23 mmol) was added to a
solution of Mg tetrapyrazinoporphyrazine 8 (200 mg, 0.08 mmol)
in tetrahydrofuran (THF, 10 mL) and the reaction mixture was
stirred at room temperature for 30 min. The solvent was removed in
vacuo, yielding the crude product as a dark green solid. The crude
product was purified by column chromatography on silica gel using
chloroform/methanol (30/1) as an eluent. 9 (dark green solid, 58%):
Experimental
General
Compounds were identified and their properties were measured using
the following techniques. Flash chromatography was performed
with Merck-EM type 60 (230–400 mesh) silica gel (flash). Melting
1
m.p >300°C; H NMR (300 MHz, CDCl3) d : –0.80 (s, N–H, 2H),
0.98–1.08 (m, CH3, 12H), 1.20 (s, –Si–C–CH3, 72H), 1.36–1.58 (m,

316 JOURNAL OF CHEMICAL RESEARCH 2009
methylene, 40H), 1.59–1.68(m, –Si–CH, 12H), 1.83–2.13 (m, –O–
C–CH2, 8H), 3.90–4.20 (m, O–CH2, 8H), 6.92–7.05 (m, ArH, 8H),
7.62–7.80 (m, ArH, 16H), 7.87–8.10(m, ArH, 8H); MALDI-TOF
mass-spectra: m/z 2364.9 (Calcd 2365.51)
This study was supported by a grant from the Fundamental
R&D Program (M200701004) for Core Technology of
Materials funded by the Ministry of Commerce, Industry and
Energy, and a grant No. R01-2006-000-10489-0 from the
Basic Research Program of the Korea Science and Engineering
Foundation and BK21 project in Republic of Korea.
Tetrapyrazinoporphyrazinato magnesium complex (10)
This compound was prepared by the procedure described for 8 but
from magnesium (0.11 g, 4.5 mmol), 10 mL of n-butanol and 7
(0.72 g, 0.75 mmol). The mixture was cooled and the solvent was
removed in vacuo, yielding crude product as a dark green solid.
The crude product was purified using chloroform/methanol (30/1)
as an eluent. 10 (dark green solid, 59%): m.p >300°C; 1H NMR
Received 1 July 2008; accepted 28 July 2008
Paper 08/5298A doi: 10.3184/030823409X449473
Published online: 20 May 2009
1
(300 MHz, CDCl3) H NMR (300 MHz, CDCl3) d : 0.80–1.08 (m,
References
–CH3, 36 protons), 1.22–1.53 (m, methylene, 40H), 1.53–1.75
(m, O–C–CH2, 8H), 1.80–2.20 (m, –S–C–CH2–CH, 12H), 2.90–3.10
(m, –S–CH2, 8H), 3.62–3.80 (m, –O–CH3, 12 protons), 4.00–4.24
(m, –O–CH2, 8H), 6.2–8.2 (m, Aryl protons, 108H); MALDI-TOF
mass-spectra: m/z 3841.4 (Calcd 3845.16)
1
2
3
4
5
C.C. Lenzoff and A.P.F. Lever, Phthalocyanine-properties and
applications, VCH, New York, 1996, Vol. IV.
C. Piechoki, J. Simon, A. Skoulious, D. Gullion and P. Weber, J. Am.
Chem. Soc., 1982, 104, 5245.
A.W. Snow, W.R. Barger, M. Klusty, H. Wohltjen and N.L. Jarvis,
Langmuir, 1986, 2, 513.
A. Grund,A. Kaltbeitzel,A. Mathy, R. Schwarz, C. Bubeck, P. Vernmehren
and M. Hanack, J. Phys. Chem., 1992, 96, 7450-4.
I. Okura. Photosensitisation of porphyrins and phthalocyanines, Taylor &
Francis, 2001.
H. Ali and J.E. van Lier, Chem. Rev., 1999, 99, 2379-2450.
P. Smolenyak, R. Peterson, K. Nebesny, M. Toerker, D. O'Brien and
N.R. Armstrong, J. Am. Chem. Soc., 1999, 12, 8628.
R.A.P. Zangmeister, D.F. O'Brien and N.R. Armstrong, Adv. Funct. Mater.,
2002, 12, 179-186.
Demetallised tetrapyrazinoporphyrazine (11)
This compound was prepared by the procedure described for 9 but
from compound 10 (100 mg, 0.04 mmol), p-toluenesulfonic acid
(0.4 g, 2.12 mmol). The solvent was removed in vacuo, yielding the
crude product as a dark green solid. The crude product was purified
by column chromatography on silica gel using chloroform/methanol
(30/1) as an eluent. 11 (dark green solid, 70%): m.p >300°C;
1H NMR (300 MHz, CDCl3) d : –0.64 (s, N–H, 2H), 0.90–1.00 (m,
CH3, 36H), 1.25–1.50 (m, methylene, 40H), 1.53–1.65 (m, O–C–CH2,
8H),1.80–2.00(m,–S–C–CH2–CH,12H),2.90–3.02(m,–S–CH2,8H),
3.62 (s, –O–CH3, 12 protons), 4.08–4.15 (m, –O–CH2, 8H), 6.46 (d,
J = 9.0 Hz, ArH, 8H), 6.53 (d, J = 9.0 Hz, ArH, 8H), 6.71 (d,
J = 9.0 Hz, ArH, 8H), 6.77 (d, J = 9.0 Hz, ArH, 8H), 6.90–7.05
6.46(m, ArH, 30H), 7.09 (d, J = 9.0 Hz, ArH, 8H), 7.20 (s, ArH, 4H),
7.35 (d, J = 9.0 Hz, ArH, 8H), 7.47 (d, J = 9.0 Hz, ArH, 8H), 7.53 (d,
J = 9.0 Hz, ArH, 8H), 7.77(d, J = 12.0 Hz, ArH, 4H), 7.95–8.03 (m,
ArH, 6H); MALDI-TOF mass-spectra: m/z 3822.7 (Calcd 3822.87)
6
7
8
9
R. Faust and C. Weber, J. Org. Chem., 1999, 64, 2571.
10 R. Faust, Eur. J. Org. Chem., 2001, 15, 2797-2803.
11 W. Pisula, F. Dierschke and K. Müllen, J. Mater. Chem., 2006, 16, 4068-
4064.
12 B.H. Lee and J.Y. Jaung, Dyes Pigments, 2003, 59, 135-142.
13 M. Wehmeier, M. Wagner and K. Müllen, Chem. Eur. J., 2001, 7, 2197-
2205.
14 U.M. Wiesler, A.J. Berresheim, F. Morgenroth, G. Leser and K. Müllen,
Macromolecules 2001, 34,187-199.
15 Z. Ou, J. Shen and K.M. Kadish, Inorg. Chem., 2006, 45, 9569-79.
16 H. Weitman, S. Schatz, H.E. Gottlieb, N. Kobayashi and B. Ehrenberg,
Photochem. Photobiol., 2001, 73, 473-481.