Alkynyl substituted phthalocyanine derivatives as targets for optical limiting

Article abstract of DOI:10.1039/b210707d

One of the key issues in the development of efficient optical limiters is the search for appropriate materials with improved nonlinear absorption. Phthalocyanine materials are among the most promising nonlinear absorbers described in the literature. Ethyn

Full text of DOI:10.1039/b210707d

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Alkynyl substituted phthalocyanine derivatives as targets for optical
limiting
Eva M. Garc´ıa-Frutos,a Sean M. O’Flaherty,b Eva M. Maya,a Gema de la Torre,b
Werner Blau,a Purificacio´n Va´zqueza and Toma´s Torres*a
aDepartamento de Qu´ımica Orga´nica, Facultad de Ciencias, Universidad Auto´noma de
Madrid, Cantoblanco, 28049 Madrid. E-mail: tomas.torres@uam.es
bMaterials Ireland Polymer Research Centre, Department of Physics, Trinity College Dublin,
Dublin 2, Republic of Ireland
Received 30th October 2002, Accepted 10th January 2003
First published as an Advance Article on the web 25th February 2003
One of the key issues in the development of efficient optical limiters is the search for appropriate materials with
improved nonlinear absorption. Phthalocyanine materials are among the most promising nonlinear absorbers
described in the literature. Ethynyl and butadiynyl-bridged bisphthalocyanines and related ethynyl-containing
mononuclear compounds have been synthesized and experimentally studied using the z-scan technique with
nanosecond pulses at 532 nm. We intend to ascertain the effect of the electronic interaction between
macrocycles in the optical limiting performance of phthalocyanines.
explored. It has been demonstrated that the insertion of heavy
atoms into the phthalocyanine ring, such as indium9–11 and
lead,12 causes
significant improvement in the reverse
saturable absorption behaviour, owing to an increased rate
of inter-system crossing from the lowest excited singlet state to
the strongly absorbing triplet state. Axial substitution over
indium phthalocyanines has been shown to be effective in
improving OL capabilities.10,11 On the other hand, the effect of
the peripheral substituents is less clear.13–15
Determining the rationale of the influence of the electronic
interactions between macrocycles on the nonlinear absorption
of Pc-based systems is also an appealing task that has not been
addressed previously. Recently, we have prepared homo- and
heterodimetallic ethynyl- and butadiynyl-bridged bisphthalo-
cyaninato complexes using metal-mediated coupling meth-
odologies.16 It has been recognized that ethyne and butadiyne
linkages are ideal for enabling electronic interactions between
chromophores. For this reason we have performed Z-scan
measurements on a series of ethynyl-substituted mononuclear
Pcs and ethynyl- and butadiynyl-bridged binuclear phthalo-
cyanines 1–6 in order to ascertain the effect of the electronic
communication between macrocycles on the nonlinear absorp-
tion properties of phthalocyanines, as well as the role of the
substituents and central atoms in these molecular structures.
Introduction
Optical limiters are materials that are fairly transparent at
normal ambient light intensities but strongly attenuate intense
optical beams. These are of great interest1 since they can
protect optical sensors and the human eye from intense light
sources such as lasers. Passive optical limiting (OL) usually
relies on two non-linear effects: non-linear absorption and/or
refraction. Nonlinear refraction means that the refractive index
of a material varies under the influence of the incident light.
This index variation forms a lens that can defocus the beam and
deflects a fraction of the light into the wings of the beam, where
it is blocked by a properly located aperture. Materials with a
positive nonlinear absorption coefficient are often said to
exhibit reverse saturable absorption (RSA), where a decrease of
transmittance is observed at high illumination levels. This is the
most common effect that takes place in optical limiting
processes. Mechanistically, RSA occurs when the incident
light is intense enough to provide a significant population in the
excited state and the excited state absorption cross-section (sex)
is larger than that of the ground state (so). Thus, an ideal
material would have both a weak ground-state absorption and
a large excited-state absorption, in addition to a long excited
state lifetime, over a wide spectral width.
a
Over the last decade, many scientists have been concerned
with the search of materials with improved optical limiting
capabilities.2 Phthalocyanines3 (Pcs) have emerged as very
promising materials for OL4–8 because of their unique
electronic absorption features, allowing high linear transmis-
sion in the spectral window between the main two absorption
Soret and Q bands, and their chemical, optical and thermal
stability. They show strong excited-state absorption and long
excited-state lifetimes, which can vary over orders of magni-
tude depending on the central atom. Another advantage this
family offers is a tremendous architectural flexibility, which
allows the tailoring of their electronic structure and physical
properties over a wide range of structural modifications, such
as attaching peripheral groups to the periphery of the
macrocycle, incorporating many different metal ions into the
ring and attaching axial substituents to this metal. Thus, for
example, the role of the central metal atom has been widely
Results and discussion
Synthesis and characterization
The synthesis of ethynyl-containing phthalocyanines 1 and 2
was attempted by two different procedures. The first route
involves mixed condensation of 4-(3-hydroxy-3-methyl-1-
butynyl)phthalonitrile, prepared by Shonogashira coupling
between the 4-iodophthalonitrile and 2-methyl-3-butyn-2-ol,17
with 3 equivalents of 4-tert-butylphthalonitrile in the presence
of a metal(II) salt (Scheme 1, route 1), as previously described.16
After isolation of the desired phthalocyanine from the
statistical mixture by column chromatography (24% yield for
8a and 21% yield for 8b), the protecting group of the ethynyl
function was removed by treatment with sodium hydroxide in
toluene to give 1 and 2 in 74 % yield.
DOI: 10.1039/b210707d
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Scheme 1 Synthesis of ethynyl-containing phthalocyanines 1 and 2 by two different routes.
give rise to similar overall yields of the resulting phthalocyanine
1 (14%), the latter proceeds in only two steps and the
intermediate iodophthalocyanine 7a is also the starting
compound for the synthesis of the butadiynyl-linked dimer 5
in high yields, as we will see below.
The preparation of ethynyl-bridged phthalocyanines 3 and
4,16 has been previously reported. Metal mediated cross-
coupling between the ethynyl-containing phthalocyanines 1 or
2 and the unsymmetrycally substituted iodophthalocyanine 7a
affords the homo- and heterodimetallic ethynyl-bridged
bisphthalocyanines 3 and 4 (Scheme 2).
Butadiynyl-bridged bisphthalocyanine 5 and 6 were pre-
pared following procedures described earlier.16 They were
synthesized by oxidative homocoupling of the terminal alkynes
1 or 2 in the presence of copper(II) acetate monohydrate in a
mixture of dry pyridine and dry methanol (Scheme 2) in ca.
60% yield. Compound 5 was also prepared in 84% yield by
reaction of iodophthalocyanine 7a with tributyl(ethynyl)tin
and catalytic amounts of tetrakis(triphenylphosphine)palla-
dium(0) in refluxing toluene. One should note that the
application of different temperatures to the same mixture of
reactants can provide either the mononuclear ethynyl-contain-
ing phthalocyanine 1 or the butadiynyl-linked binuclear
compound 5. Once again, the application of Stille conditions
to the cobalt derivative 7b for the synthesis of compound 6 was
unsuccessful.
The optical features of the binuclear chromophoric systems
3–6 differ from that of the corresponding unsymmetrically
substituted parent alkynes 1, 2 (Fig.1). In general, both the
ethynyl- and the butadiynyl-bridged binuclear phthalocyanines
show broad Q bands that are red-shifted with regard to their
mononuclear counterparts. This shift to the red could be
attributed to the enlargement of the p-conjugated system. The
broadening and splitting of the Q band as a consequence of the
splitting of the energetic levels must be due to electronic
coupling between the two halves of the molecule more than to
an intermolecular effect, since the spectra remain invariable
when changing the concentration.
The second approach involves the preparation of the
iodophthalocyanines 7a–b by mixed condensation of
4-iodophthalonitrile18 with 4-tert-butylphthalonitrile19 in the
presence of the corresponding metallic salt (15% yield)
(Scheme 1, route 2).16 The zinc(II) derivative 7a yields the
Stille coupling product 1 by reaction with tributyl(ethynyl)tin
and a catalytic ratio of tetrakis(triphenylphosphine)palla-
dium(0) in toluene (70 uC) in 92% yield. However, a Stille
reaction with the cobalt(II) complex 7b gives rise to a complex
mixture of products (including homocoupling compounds of
the starting iodophthalocyanine 7b and demetallated deriva-
tives), from which the desired phthalocyanine 2 could not be
isolated.
Z-scan measurements
Regarding the synthesis of the zinc(II) derivative 1, one can
compare the overall yield for the two experimental procedures
starting from 4-iodophthalonitrile. Even though both routes
The open-aperture Z-scan experiment20 is a very convenient
method to evaluate the optical limiting properties of materials.
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Fig. 2 Schematic diagram of the open aperture Z-scan apparatus.
Loge½1zq0(z)ꢀ
q0(z)
Tnorm(z)~
where q0(z) is given by
q0(z)~
,
(1)
q00
ꢀ
ꢁ
2
,
(2)
z
1z
=
z0
z0 is the is the diffraction length of the beam and q00
b
~
effI0Leff, where Leff ~ [12exp(2a0L)]/a0. beff is the effective
intensity dependent nonlinear absorption coefficient, I0 is the
intensity of the light at focus. Leff is known as the effective
length of the sample, defined in terms of the linear absorption
coefficient, a0, and the true optical path length through the
sample, L. These equations were incorporated into a computer
code and a least squares regression algorithm was used to fit
this to the experimental data.
The imaginary third-order optical susceptibility Im{x(3)} is
directly related to the intensity dependent absorption coeffi-
cient bI and is expressed as
Scheme 2 Synthesis of ethynyl- and butadiynyl-linked dimers 3–6.
n20e0clbI
2p
È
É
Im x(3)
~
,
(3)
where no is the linear refractive index, eo is the permittivity of
free space, c is the speed of light and l is the wavelength of the
incident light. The relationship between Im{x(3)} and the
second order molecular hyperpolarizability (c) is defined as:
È
É
Im x(3)
f 4cmolNA
c~
,
(4)
2
where f ~ (n0 1 2)/3 is the Lorentz local field enhancement
factor, n0 is the linear refractive index of the sample, cmol is the
molar concentration and NA is Avogadro’s number.
The open aperture z-scan experiments were performed using
0.5 g L21 solutions of phthalocyanines 1–6 in toluene,
measuring the sample transmission at 532 nm. All the
compounds exhibited a reduction in the transmission about
the focus of the lens, which is indicative of positive nonlinear
absorption attributed to reverse saturable absorption. Non-
linear absorption coefficients bI (Table 1) were calculated from
the data by least squares fitting of equations 1 and 2 with the
waist radius of the beam treated as a free parameter. One
should note that these nonlinear coefficients are not stationary
with respect to the focus intensity since they reduce in
magnitude with increasing focal intensity indicating that they
Fig. 1 UV-vis spectra in toluene of compounds 1 (c ~ 5.5 6 1027 M)
(solid line) and 5 (c ~ 4.4 6 1026 M) (broken line).
This technique measures the total transmittance through the
sample as a function of incident laser intensity while the sample
is gradually moved along the optical axis of a convex lens. The
set-up is shown schematically in Fig. 2. The normalized
transmittance Tnorm(z) as a function of the position along
the z axis is given by
Table 1 Experimentally determined optical coefficients
Compound
a0/cm21
I0/GW cm22
bI/cm W21
Im{x(3)
}
eff/ESU
ceff/ESU
Fsat/J cm22
k (sex/s0)
1
2
3
4
5
6
1.95
1.76
1.06
1.22
1.19
1.60
0.5
2.0
0.2
0.5
0.5
0.5
(3.5 ¡ 0.7)e208
(1.4 ¡ 0.3)e209
(1.2 ¡ 0.2)e208
(5.6 ¡ 1.1)e209
(2.3 ¡ 0.5)e208
(3.5 ¡ 0.7)e208
(1.3 ¡ 0.2)e211
(5.1 ¡ 1.0)e213
(4.6 ¡ 0.8)e212
(2.1 ¡ 0.4)e212
(8.7 ¡ 1.6)e212
(1.3 ¡ 0.2)e211
(8.3 ¡ 1.6)e233
(3.2 ¡ 0.6)e234
(5.8 ¡ 1.1)e233
(2.6 ¡ 0.5)e233
(1.1 ¡ 0.2)e232
(1.7 ¡ 0.3)e232
14 ¡ 0.7
70 ¡ 30
1.9 ¡ 0.1
1.3 ¡ 0.1
3.9 ¡ 0.3
9.5 ¡ 0.2
8.9 ¡ 0.3
3.3 ¡ 0.8
3.0 ¡ 0.1
1.8 ¡ 0.1
5.4 ¡ 0.2
11.0 ¡ 0.1
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are comprised of contributions from third and higher order odd
terms. Effective third order nonlinear absorption coefficients bI
were estimated using data interpolation at the focal intensities
given in Table 1. Im{x(3)} and c were also calculated and are
quoted in Table 1. It can be seen that the effective nonlinear
absorption coefficient bI ranges from values of the order of
1029 to 1028 cm W21, which corresponds to effective second
order molecular hyperpolarizabilities ranging from orders of
10234 to 10232 esu.
After manipulating the open aperture spectra, the normal-
ised transmission (Tnorm) was plotted against the incident
energy density per pulse (F) to further investigate the optical
limiting. The nonlinear absorption coefficient given by
equation 5 was derived using laser rate equations21 and applied
in a static state approximation, fitted using least squares
regression. Fsat is the energy density at which the output
reaches its saturated value. k is the excited to ground state
absorption cross-section ratio (sex/s0). The parameters k
(realistically sex as a0 was measured) and Fsat were both
treated as free constants in the fitting algorithm. The a0, k and
Fsat values for each compound are also presented in Table 1.
Fig. 5 Plots of normalized transmission against incident pulse energy
density for butadiynyl-bridged bisphthalocyanines 5 and 6. The solid
lines are theoretical curve fits.
The optical limiting response of the ethynyl-bridged
bisphthalocyanines 3 and 4 is presented in Fig. 4. The zinc
dimer 3 exhibits a larger optical limiting response than that of
the cobalt compound 4. The k coefficient exhibited by 4 is the
lowest in the study at k # 1.8 ¡ 0.1 and it also exhibits the
ꢂ
ꢃ
a0
F
aðF,Fsat,kÞ~
1zk
,
(5)
F
sat
1z F
Fsat
lowest saturation energy density at Fsat # (1.3 ¡ 0.1) J cm22
.
Compound 3 saturated at 1.9 J cm22 and exhibited a k
coefficient y1.8 times that of 4 (k # 3.0 ¡ 0.1).
In Fig. 3 normalized transmission against incident pulse
energy density is plotted for the mononuclear phthalocyanines
1 and 2. The solid lines are the theoretical curve fits. The zinc
centered Pc (1) is the strongest nonlinear absorber of the
mononuclear compounds. It also exhibits the largest excited to
singlet state absorption cross section ratio k and the lowest
Plots of normalized transmission against incident pulse
energy density for the butadiynyl-bridged bisphthalocyanines
5 and 6 are presented in Fig. 5, where again the solid lines are
the theoretical curve fits. It is very interesting that in this case
the cobalt dimer 6 exhibits a much larger nonlinear absorption
than the zinc dimer 5. This contradicts the trend in the
associated mononuclear analogues 1 and 2. The cobalt dimer 6
displayed the largest k coefficient in the study at k # 11.0 ¡
0.1, approximately twice that of 5. It can also be noted that 6
exhibited a much higher saturation energy density, by a factor
y2.4, than that of 5.
saturation energy density Fsat
.
In summary, the mononuclear cobalt derivative is a weaker
nonlinear absorber than its zinc counterpart. In contrast,
the cobalt dimer 6 exhibits the largest bI response of all the
binuclear derivatives. One can note that in the zinc series, the
nonlinear absorption, the saturation energy density Fsat and
also the k coefficients decrease in the order 3 v 5 v 1. One
would expect that electronic interaction between the two
chromophores would be maximum for 3 as the spatial
separation of the macrocycles is less than that for 5. The
trends in the data therefore imply that the derivative with the
highest degree of electronic interaction between the two
chromophores (3) is the weakest nonlinear absorber. On the
other hand, intermolecular interactions seem to positively
affect the nonlinear response in the cobalt series since the
cobalt dimer 6 has the largest bI of all the compounds presented
in this study. This is surprising since the cobalt(II) mononuclear
derivative 2 is a poorer optical limiter as compared to the ZnII
compound (1). These results seem to indicate that there is an
inseparable link between the peripheral structure and the
central metal in this type of system. Thus, one cannot
separately tune the nonlinear optical response by changing
either the main structure or the central metal of the
chromophore because both factors are inextricably inter-
twined. However, the knowledge of the fundamental photo-
physical properties (quantum yields and excited state lifetimes)
of these derivatives could provide additional information for
the understanding of these observable facts. All dimers exhibit
lower Fsat than their mononuclear parent compounds, but the
cobalt dimer 6 has the highest of the four bridged dimers.
Notably this compound also exhibits the largest k coefficient of
the seven compounds studied, with k # (11.0 ¡ 0.1).
Fig. 3 Plots of normalized transmission against incident pulse energy
density for mononuclear phthalocyanines 1 and 2. The solid lines are
theoretical curve fits.
Fig. 4 Plots of normalized transmission against incident pulse energy
density for ethynyl-bridged bisphthalocyanines 3 and 4. The solid lines
are theoretical curve fits.
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with water. The green solid was purified by column chromato-
graphy on silica gel, using a mixture of hexane–dioxane (2 : 1)
as eluent. Yield: 84%. Mp w 250 uC. IR (KBr): n(CMCH) 3428,
n(CMC) 2556 cm21. 1H NMR (CDCl3, 300 MHz) d 9.5–7.2 (m,
24H, ar.), 1.6 (bs, 54H, C(CH3)3). UV-vis (CHCl3), lmax (log e/
dm3 mol21 cm21): 709 (4.7), 675 (4.7), 350 (4.6) nm. MS
(MALDI-TOF, dithranol), m/z (%): 1539–1535 (isotopic
pattern) (100) [M 1 H]1.
Conclusions
In conclusion, these compounds do not exhibit, in general, high
magnitude nonlinear absorption. It was found that putting
cobalt into the central cavity of mononuclear phthalocyanines
produces undesirable effects from the point of view of optical
limiting as it reduces the magnitude of the nonlinear
absorption. However, the cobalt(II) phthalocyaninate-based
dimer 6 shows good nonlinear absorption coefficients and k
values, thus indicating that the presence of cobalt could be
desirable in structures which can give rise to intermolecular
electronic interactions. The other remarkable feature is that the
other bridged binuclear derivatives 3–5 are promising when one
would require low Fsat properties for practical optical limiters.
Acknowledgements
The Spain group was supported by CICYT (Spain), Comuni-
dad de Madrid (Spain) and the European Union through
grants BQU2002-04697, 07N/0030/2002 and HPRN-CT-2000-
00020, respectively. The Dublin group would like to acknow-
ledge the support of Enterprise Ireland and the Irish Higher
Education Authority (HEA).
Experimental section
Melting points were determined on a Bu¨chi apparatus and are
uncorrected. 1H-NMR spectra were recorded on a Bruker AC-
300 (300 MHz). UV-vis spectra were recorded on a Perkin-
Elmer 8453 spectrophotometer. Mass spectra were determined
on a VG AutoSpec spectrometer. The starting 4-iodophthalo-
nitrile18 and 4-tert-butylphthalonitrile19 were prepared following
described procedures.
All z-scan experiments were performed using 6 ns pulses
from a Q-switched Nd:YAG laser. The beam was spatially
filtered to remove higher order modes and tightly focused with
a 9 cm focal length lens. The laser was operated as its second
harmonic, 532 nm, with a pulse repetition rate of 10 Hz.
Samples were prepared by dissolving the compound in toluene
at 0.5 g L21 followed by gentle agitation for approximately
30 min in a low-power (60 W) sonic bath. All measurements
were performed in quartz cells with a 1mm through path
length.
References
1
2
L. Tutt and T. F. Boggess, Prog. Quant. Electron., 1993, 17, 299.
Nonlinear Optics of Organic Molecules and Polymers, ed.
H. S. Nalwa and S. Miyata, CRC Press, Boca Raton, FL, 1997.
G. de la Torre, M. Nicolau and T. Torres in Supramolecular
Photosensitive and Electroactive Materials, ed. H. R. Nalwa,
Academic Press, New York, 2001, p. 1.
3
4
5
6
J. A. Armstrong, J. Appl. Phys., 1965, 36, 471.
F. Gires and F. Combaud, J. Phys. Chem., 1965, 26, 325.
H. S. Nalwa and J. S. Shirk in Phthalocyanines. Properties and
Applications, ed. C. C. Leznoff and A. B. P. Lever, VCH,
Cambridge, 1996, vol 4, p. 79.
7
J. W. Perry in Nonlinear Optics of Organic Molecules and
Polymers, ed. H. S. Nalwa and S. Miyata, CRC Press, Boca
Raton, FL 1997, p. 813.
8
9
G. de la Torre, P. Vazquez, F. Agullo-Lopez and T. Torres, J. Mat.
Chem., 1998, 8, 1671.
J. W. Perry, K. Mansour, I.-Y. S. Lee, X.-L. Wu, P. V. Bedworth,
C.-T. Chen, D. Ng, S. R. Marder, P. Miles, T. Wada, M. Tian and
H. Sasabe, Science, 1996, 273, 1533.
2-Ethynyl-9,16,23-tri-tert-butylphthalocyaninate zinc(II) (1)
A mixture of tri-tert-butyliodophthalocyaninate zinc(II) 7a16
(22 mg, 0.025 mmol), Pd(PPh3)4 (1.3 mg, 0.001 mmol) and
tributyl(ethynyl)tin (0.025 mmol) in dry toluene was heated at
60 uC for 4 h under an argon atmosphere. After the solvent had
been removed, the crude was extracted with CH2Cl2 and
washed with water. The blue solid was purified by column
chromatography on silica gel, using a mixture of hexane–
dioxane (4 : 1) as eluent. Yield: 92%. Mp w 250 uC. IR (KBr):
10 J. S. Shirk, R. G. S. Pong, S. R. Flom, H. Heckman and
M. Hanack, J. Phys. Chem. A, 2000, 104, 1438.
11 M. Hanack, T. Schneider, M. Barthel, J. S. Shirk, S. R. Flom and
R. G. S. Pong, Coord. Chem. Rev., 2001, 219-221, 235.
12 J. S. Shirk, R. G. S. Pong, F. J. Bartoli and A. W. Snow, Appl.
Phys. Lett., 1993, 63, 880.
13 F. Z. Henari, J. Callaghan, W. J. Blau, P. Haisch and M. Hanack,
Pure Appl. Opt., 1997, 6, 741.
14 M. Sanghadasa, I.-S. Shin, R. D. Clark, H. Guo and B. G. Penn,
J. Appl. Phys., 2001, 90, 31.
n(CMCH) 3495, n(CMC) 2103 cm21
.
1H NMR (CDCl3, 300
MHz) d 9.0–7.5 (m, 12H, ar.), 3.40 (s, 1H, CMCH), 1.6 (bs, 27H,
C(CH3)3). UV-vis (CHCl3), lma´x (log e/dm3 mol21 cm21): 684
(5.4), 612 (4.7), 350 (5.1) nm. MS (FAB, NOBA), m/z (%): 769
(100) [M 1 H]1, 753 (26)[M 2 CH3]1.
15 A. W. Snow, J. S. Shirk and R. G. S. Pong, J. Porphyrins
Phthalocyanines, 2000, 4, 518.
16 E. M. Maya, P. Vazquez and T. Torres, Chem. Eur. J., 1999, 5,
2004.
17 E. M. Maya, P. Va´zquez and T. Torres, Chem. Commun., 1997,
1175.
18 S. M. Marcuccio, P. I. Svirskaya, S. Greenberg, A. B. P. Lever and
C. C. Lexnoff, Can. J. Chem., 1985, 63, 3057.
19 B. W. Larner and A. T. Peters, J. Am. Chem. Soc., 1952, 680.
20 M. Sheik-Bahae, A. A. Said, T.-H. Wei, D. J. Hagan and E. W. Van
Stryland, IEEE J. Quant. Elec., 1990, 26, 760.
21 S. M. O’Flaherty, S. V. Hold, M. J. Cook, T. Torres, Y. Chen,
M. Hanack and W. J. Blau, Adv. Mater., 2002, 15, 19.
Bis[(tri-tert-butylphthalocyaninate)cobalt(II)]butadiyne (5)
A mixture of tri-tert-butyliodophthalocyaninate zinc(II) 7a16
(63 mg, 0.072 mmol), Pd(PPh3)4 (15 mg, 0.013 mmol) and
tributyl(ethynyl)tin (0.083 mmol) in dry toluene was refluxed
for 9 h under an argon atmosphere. After the solvent had been
removed, the crude was extracted with CH2Cl2 and washed
J. Mater. Chem., 2003, 13, 749–753
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