Synthesis and photophysical properties of annulated dinuclear and trinuclear phthalocyanines

Article abstract of DOI:10.1002/chem.200500617

Metal-free mononuclear, dinuclear and trinuclear phthalocyanines were prepared by a mixed cyclotetramerisation of a 1,2,4,5-tetracyanobenzene derivative and 4,5-bis(2,6-dimethylphenoxy)phthalonitrile. For the first time, a π-electron-conjugated tri-nuclea

Full text of DOI:10.1002/chem.200500617

DOI: 10.1002/chem.200500617
Synthesis and Photophysical Properties of Annulated Dinuclear and
Trinuclear Phthalocyanines
Sergey Makarov,[a, c] Christian Litwinski,[b] Eugeny A. Ermilov,[b] Olga Suvorova,[c]
Beate Rçder,*[b] and Dieter Wçhrle*[a]
Abstract: Metal-free mononuclear, di-
nuclear and trinuclear phthalocyanines
were prepared by a mixed cyclotetra-
merisation of a 1,2,4,5-tetracyanoben-
zene derivative and 4,5-bis(2,6-dime-
thylphenoxy)phthalonitrile. For the
first time, a p-electron-conjugated tri-
nuclear phthalocyanine was synthesised
with phthalocyanine units connected by
common annulated benzene rings. The
Q band of the trinuclear compound in
solution occurs at l=944 nm whereas
those of the dinuclear and mononu-
clear compounds are at l=853/830 and
701/664 nm, respectively. Fluorescence
quantum yields, fluorescence lifetimes
and singlet-oxygen quantum yields of
the compounds were determined.
Keywords: fluorescence ·
N
ligands
properties
UV/Vis spectroscopy
·
photophysical
·
phthalocyanines
·
Introduction
high extinction coefficients e>105 mÀ1 cmÀ1. Substituted Pcs,
especially those containing electron-donating substituents
such as alkoxy groups in positions 1, 4, 8, 11, 14, 18, 22 and
25, exhibit a bathochromic shift of their Q band up to l
ꢀ760 nm.[7] By annulation of further benzene rings at the Pc
moiety the p system is extended, and strong redshifts of the
Q band are observed for naphthalocyanines (Nc) at lꢀ740–
810 nm and anthracocyanines (Ac) at lꢀ830–860 nm that
are dependent on the substituents on the naphthalene or an-
thracene rings.[8] A great disadvantage is the decreasing sta-
bility of the compounds going from Pc to Nc and then to
Ac. Anthracocyanines are particularly unstable in solution
and also in the solid state.[8b]
Another possibility to extend the p-electron system and
thus to shift the Q band into the NIR region is the dimerisa-
tion of Pcs and related macrocycles through a common an-
nulated benzene ring or another fully conjugated linker.
Conjugated dimers and oligomers are well known in the por-
phyrin family and are of special interest as potential molecu-
lar wires and photosynthetic antenna models.[9] Some exam-
ples are known among phthalocyanines and related porphyr-
azine derivatives: Pc–Pc, Pc–Nc, Pc–pyrazinoporphyrazine
dimers sharing a common benzene ring; Pc–Pc sharing a
common naphthalene ring; dimeric Pc fused with anthraqui-
none.[10] Their Q bands are shifted up to lꢀ850 nm into the
NIR region, thus indicating the extension of the p-electron
system. Besides electronic absorption spectra, the dinuclear
compounds were characterized by magnetic circular dichro-
ism (MCD) spectra,[10a,c,d] electrochemical redox behav-
Some of the most important applications of phthalocyanines
(Pcs) are based on the interaction of visible light with the
chromophore: dyes and pigments,[1] photoconductors in
laser printers,[2] photosensitisers in the photodynamic thera-
py of cancer[3] and degradation of pollutants of waste and
natural water.[4] Pcs as thin films or adsorbed on inorganic
semiconductors have potential applications in photovoltaic
or dye-sensitised solar cells.[5] Based on these applications
and taking into account the increasing interest in near-infra-
red (NIR) absorbing systems,[6] it is important to make com-
pounds with absorptions over a broad region of visible light
down to the NIR region.
Most dissolved monomolecular metal-free or metal-con-
taining Pcs have a Q-band absorption at lꢀ680 nm with
[a] S. Makarov, Prof. Dr. D. Wçhrle
Institut für Organische und Makromolekulare Chemie
Universität Bremen, P.O. Box 330440, 28334 Bremen (Germany)
Fax : (+49)421-218-4935
E-mail: woehrle@chemie.uni-bremen.de
[b] C. Litwinski, Dr. E. A. Ermilov, Prof. Dr. B. Rçder
Institut für Physik, Photobiophysik
Humboldt-Universität zu Berlin
Newtonstr. 15, 12489 Berlin (Germany)
Fax : (+49)30-2093-7666
E-mail: roeder@physik.hu-berlin.de
[c] S. Makarov, Dr. O. Suvorova
G. A. Razuvaev Institute of Organometallic Chemistry
Russian Academy of Sciences, Nizhny Novgorod (Russia)
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FULL PAPER
iour,[10a,d] time-resolved electron paramagnetic resonance
(TREPR),[10b] mesophase behaviour[10g] and molecular orbi-
tal calculations.[10a,c,d]
In this paper, the synthesis and photophysical properties
of a metal-free dinuclear phthalocyanine H2Pc–H2Pc 4 and
its mononuclear analogue H2Pc 3 are presented and com-
pared. To the best of our knowledge, the synthesis of a tri-
nuclear phthalocyanine H2Pc–H2Pc–H2Pc 5 is described here
for the first time. All annulated Pcs containing the same
bulky substituents are bridged through shared benzene rings
and consist of extended p-electron systems. This structural
situation allows the comparison of their photophysical prop-
erties such as fluorescence quantum yields, fluorescence life-
times and singlet-oxygen quantum yields.
Scheme 1. Synthesis of 4,5-bis(2,6-dimethylphenoxy)phthalonitrile (2).
cyanobenzene and an alkoxy-substituted phthalonitrile.[10,15]
Annulated phthalocyanines studied in this work were pre-
pared by a method for binuclear porphyrazines described by
Hoffmann et al.[16] As shown in Scheme 2, the employed
method is based on a mixed cyclotetramerisation of the bis-
(diiminoisoindoline) 1 and the substituted phthalonitrile 2 in
a molar ratio of 1:7, with magnesium butoxide in boiling bu-
tanol. Attempts to use other molar ratios of 1 and 2 were
unsuccessful for the isolation of the trinuclear compound 5.
For example, the theoretical molar ratio of 1:4 for synthesis-
ing 5 led to a larger amount of higher oligomeric phthalo-
cyanines thus preventing the isolation of the trinuclear Pc.
Resulting mixtures of magnesium phthalocyanines were de-
metallated with trifluoroacetic acid. The obtained mixture
of metal-free phthalocyanines was separated by chromatog-
raphy on silica gel. As main products, an octasubstituted
mononuclear phthalocyanine H2Pc 3 (24% yield) and an an-
nulated dinuclear phthalocyanine H2Pc–H2Pc 4 (11% yield)
Results and Discussion
Synthesis: 4,5-Bis(2,6-dimethylphenoxy)phthalonitrile (2) as
one precursor for the synthesis of the phthalocyanines was
synthesized according to a well-known method[11] (aromatic
nucleophilic substitution) from 4,5-dichlorophthalonitrile
and 2,6-dimethylphenol (Scheme 1). Introducing bulky sub-
stituents onto the phthalocyanine ring is a common method
used to increase the solubility, reduce aggregation and allow
easier chromatographic separation of the phthalocyanines.
In comparison with monosubsti-
tuted (e.g., tert-butyl- or neopen-
toxy-[12]) phthalonitriles, phthalo-
cyanines formed from 4,5-or 3,6-
disubstituted phthalonitriles exist
as single isomers, with the advan-
tages of easier separation and
characterisation. In contrast to
alkoxy[13] and most other types of
substituents,[14] phenoxy groups
can be introduced into phthalo-
nitrile by a simple one-step proce-
dure starting from commercially
available compounds. Thus, the
2,6-dimethylphenoxy group was
found to be a suitable peripheral
substituent. The bis(diiminoisoin-
doline) compound 1 of 1,2,4,5-tet-
racyanobenzene was prepared as
described in the literature[10d] and
used directly in the phthalocya-
nine synthesis without further pu-
rification. The yield of 1 was
quantitative, but the mass spec-
trum indicated traces of alkoxy-
iminoisoindolenines.
On the whole, annulated phtha-
locyanine dimers are prepared by
mixed condensation of two diimi-
noisoindoline derivatives, ob-
tained by reaction of 1,2,4,5-tetra-
Scheme 2. Synthesis of mononuclear, dinuclear and trinuclear phthalocyanines 3, 4 and 5 by mixed conden-
sation of 1 and 2.
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1469

B. Rçder, D. Wçhrle et al.
were isolated. The linear, annulated trinuclear phthalocya-
nine H2Pc–H2Pc–H2Pc 5 showed a small peak near l=
950 nm in the UV/Vis spectrum of the obtained phthalocya-
nine mixture. Compound 5 was eluted from the chromato-
graphic column in a mixture with 4, and then isolated by re-
crystallisation from toluene (0.2% yield). In the reaction
mixture an additional peak near l=900 nm was also seen,
but the corresponding compound expected to be a G-type
trimer was not isolated. Compound 5 is the first example of
a conjugated trinuclear Pc–Pc–Pc compound bridged by
common annulated benzene rings. Favoured by the bulky
substituents, all phthalocyanines are soluble in several or-
ganic solvents (CHCl3, aromatics and THF, but not in alco-
hols or hexane), with an aggregation tendency low enough
for chromatographic separation and NMR characterisation
(see below). In the solid state the phthalocyanines are inten-
sively green coloured. In solution, 3 is intensively green col-
oured whereas 4 and 5 of the same concentration exhibit
only a weak yellow-green colour as a result of their low ab-
sorption intensities in the visible region (Figure 2, see
below).
Figure 1. 1H NMR spectrum of 5 in CDCl3.
clear and trinuclear phthalocyanines, the most downfield-
shifted signals are those of the protons on the common
bridging benzene rings. They appear as singlets near d=
11 ppm, which is comparable to what was previously ob-
served for dinuclear Pc[10g] and subphthalocyanine.[19] For 4
and 5 the signals of the pyrrole protons are less upfield-
shifted than those in 3 which indicates the deshielding effect
of the neighbouring phthalocyanine rings. The NMR spec-
trum is a rather clear proof that the trinuclear Pc 5 has a
linear annulated and not a rectangular annulated structure.
The NMR spectra of 5 does not contain the pattern of other
phthalocyanines such as 3 and 4. For tert-butyl-substituted
metal-free phthalocyanines (Pc), naphthalocyanine (Nc) and
anthracocyanine (Ac), the pyrrole protons are less upfield-
shifted with increasing size of the macrocycle, which indi-
cates that the ring current decreases the larger the macrocy-
cle.[8b]
The NIR-absorbing 4 and 5 exhibit, in contrast to other
NIR-absorbing phthalocyanine analogues like Nc and Ac in
air and daylight, good stability in the solid state and in solu-
tion which enables their chromatographic purification. Acs
decompose quickly even during chromatography, which is
necessary for their purification.[8b] Solid CoAc can be stored
in the dark whereas solid H2Ac decomposes within a few
days even if stored in the dark under nitrogen. The photo-
oxidative stabilities of ZnAcs and ZnNcs are one and a half
and one order of magnitude lower than ZnPcs, respective-
ly.[17]
The phthalocyanines exhibit molecular-ion peaks in their
mass spectra (electrospray ionization (ESI) for 3 and 4 and
matrix-assisted laser desorption/ionization (MALDI) for 5)
without significant fragmentation. The MALDI spectrum of
trinuclear 5 contains no peaks of mononuclear 3 and dinu-
clear 4, which is a sign of the good purity of 5.
1H NMR spectra of metal-free phthalocyanines 3, 4 and 5
were recorded in CDCl3 at room temperature. They show
no evidence of aggregation (broadening of the signals of Pc
aromatic protons) at the concentrations used (10À4 m). All
phthalocyanines show relatively simple 1H NMR spectra
due to their high symmetry. The aromatic protons of 2,6-di-
methylphenoxy substituents give broad, nonresolved multip-
lets for all compounds. For 5, two broad peaks with a 1:3
ratio (at d=7.48–7.53 and 7.32–7.44 ppm, respectively) can
be assigned to the substituents at central and side phthalo-
cyanine rings, respectively. The chemical shifts of aromatic
protons on phthalocyanine rings, pyrrole protons and methyl
protons are shown in Table 1. In the symmetrical mononu-
clear compound 3, both methyl and Pc aromatic protons
give one singlet each. In the dinuclear compound 4, three
types of methyl groups and four types of Pc aromatic pro-
tons lead, as expected, to separate singlets taking into ac-
count ring-current effects. The protons closer to the centre
of the molecule are deshielded by the ring currents of both
phthalocyanine subunits and their signals are more down-
field-shifted. In the trinuclear compound 5, four types of
methyl groups and five types of Pc aromatic protons are
clearly resolved in the spectrum (Figure 1). In both dinu-
Photophysical properties: The UV/Vis-NIR spectra of 3, 4
and 5 in solution are shown in Figure 2, and values are given
in Table 2. The two most intense Q bands (Q1 and Q2) are
bathochromically shifted going from the mononuclear 3 (l=
664/701 nm) to the dinuclear 4 (l=830/853 nm) and to the
trinuclear 5 (l=944 nm), which clearly reflects the exten-
sion of the p-electron system
by the three connected phtha-
Table 1. 1H NMR chemical shifts (d in ppm) for the phthalocyanines 3, 4 and 5 in CDCl3.
locyanines rings.[8b,10c,16] Sur-
prisingly, two-dimensional poly-
(phthalocyanines) show no
Methyl protons
Pc aromatic protons
Pyrrole protons
3 (M=2H)
4 (M=2H)
5 (M=2H)
2.43
8.18
À0.76
À0.04
2.38, 2.48, 2.62
2.37, 2.49, 2.60, 2.64
8.15, 8.29, 9.06, 11.14
8.16, 8.29, 9.06, 9.15, 11.12
apparent redshift of the
Q
0.01, 0.65
band which may due to some
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Phthalocyanines
FULL PAPER
phyrazine dimer absorbing at l=730 nm a shift of only
900 cmÀ1 with respect to the corresponding Pc monomer ab-
sorbing at l=685 nm and a further shift of only 450 cmÀ1
from the dimer to a Pc–triazolehemiporphyrazine–Pc trimer
absorbing at l=755 nm are observed.[20] The reason for this
is that the bridging hemiporphyrazine is nonaromatic thus
giving only a weak contribution to the extension of the con-
jugated p-electron system. A Pc dimer connected by a dehy-
dro[12]annulene fragment shows only a 1550 cmÀ1 redshift
of the Q band compared with its monomeric analogue.[21]
Triphthalocyaninodehydro[18]annulenes exhibit no pro-
nounced long wavelength shift of the Q band.[21] Therefore,
using a benzene ring as a linker provides the best conjuga-
tion between Pc rings.
Compounds 3, 4 and 5 additionally exhibit small absorp-
tion bands (Q3, Q4, Q5) of low extinctions outside the main
Q-band region (Q1, Q2) due to normal vibrational splitting
and (for 4 and 5) electronic
Figure 2. Absorption spectra of the phthalocyanines 3, 4 and 5 in toluene
(a.u.=arbitrary units).
splitting of Q bands.[10c] For all
Table 2. Absorption bands [nm] of phthalocyanines 3, 4 and 5 in toluene; values in parentheses are given in
cmÀ1
.
compounds 3–5 the change of
the Soret (B) band position
around l=360 nm is very
small compared with that of
the Q bands (Tables 2 and 3).
The very small shift of the B
band indicates that linking of
Q1
Q2
Q3
Q4
Q5
B
3
4
5
701 (14250)
853 (11750)
944 (10600)
664 (15050)
830 (12050)
–
647 (15450)
745 (13400)
887 (11300)
636 (15700)
–
833 (12000)
601 (16650)
–
760 (13150)
353 (28350)
358 (27800)
362 (27600)
defects in the structure of the polymer, but this is still a
point of discussion.[18] Taking the centre between the maxi-
mum of the Q1 and Q2 bands of 3 and 4, and the maximum
of the Q1 band of 5, the bathochromic shift decreases from
2750 cmÀ1 going from 3 to 4 to 1300 cmÀ1 going from 4 to 5
(Table 3). The first value is comparable with 2700 cmÀ1 re-
two or three Pcs results only in a weak perturbation of the
high excited singlet states of the Pc moiety.[10c,16]
The extinction coefficients are 1.38”105 mÀ1 cmÀ1 (l=
707 nm, in toluene) for 3, 1.65”105 mÀ1 cmÀ1 (l=853 nm, in
toluene) for 4 and 3.00”105 mÀ1 cmÀ1 (l=944 nm, in THF)
for 5. For tert-butyl-substituted metal-free Pc, Nc and Ac
the extinction coefficients of the longest wavelength Q
bands in pyridine are 1.41”105 (l=698 nm), 2.04”105 (l=
784 nm) and only 0.89”105 mÀ1 cmÀ1 (l=858 nm), respecti-
vely.[8b] Surprisingly, the extinction coefficient of H2Ac is
lower than that of H2Nc. The values of 3, 4 and 5 increase
with extension of the p-electron system which is a usual
effect of increasing transition dipole moment.
Table 3. Shifts [cmÀ1] between absorption bands of the phthalocyanines
3, 4 and 5 in toluene.
B band
Q band
3–4
4–5
550
200
2750 (Q1/Q2 for 3 and Q1/Q2 for 4)
1300 (Q1/Q2 for 4 and Q1 for 5)
As metal-free Pcs have a D2h symmetry, the Q band of
the mononuclear Pc 3 is split into two sub-bands Q1 and Q2
with an energetic distance of 800 cmÀ1 (Table 2). A small
(300 cmÀ1) splitting of the main peak in Q band was also ob-
served for the dinuclear Pc 4, probably due to the presence
of isomers with different positions of inner hydrogen
atoms[10c] (this splitting is solvent-dependent and absent, for
instance, in DMF). The Q1 band of the trinuclear phthalo-
cyanine Pc 5 shows no visible splitting (Figure 2). For metal-
free Pcs and their analogues it was found that the splitting
of the Q band decreases with increasing absorption wave-
length.[8b,22]
The fluorescence spectra of compounds 3, 4 and 5 are
shown in Figure 3. The maximum of the fluorescence spec-
trum of the mononuclear Pc 3 at l=706 nm shifts to l=
860 nm for the dinuclear Pc 4 and to l=956 nm for the tri-
nuclear Pc 5 (Table 4). The Stokes shifts between the
maxima of the lowest energetic absorption and fluorescence
ported for similar mono-and dinuclear metalf-ree Pcs (with
other substituents).[10c] Also, for tert-butyl-substituted metal-
free phthalocyanine (Pc), naphthalocyanine (Nc) and an-
thracocyanine (Ac) absorbing at l=664/698, 784 and
858 nm, respectively, the Q bands are observed at longer
wavelengths with increasing number of annulated benzene
rings on the macrocycles.[8b] The shift of the Q bands on
going from H2Pc to H2Nc and to H2Ac are 1939 and
1100 cmÀ1, respectively. Therefore the extension of the p-
electron system by annulation of phthalocyanines bridged
by benzene rings leads to a larger bathochromic shift than
the annulation of benzene rings at the phthalocyanine. An
interesting long wavelength shift was also observed for an-
nulated subphthalocyanines (lmax =575 (monomer), 693
(dimer), 755 nm (trimer)[19a]).[19] For a Pc–triazolehemipor-
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1471

B. Rçder, D. Wçhrle et al.
1270 nm.[26,27] For the mononuclear 3, the FD value of 0.10 is
in good agreement with the values known for other metal-
free phthalocyanines.[26] Due to the low triplet energy of di-
nuclear 4 and trinuclear 5, the signal of singlet-oxygen lumi-
nescence was below the resolution of the measurement
setup (<0.02) for these compounds (Table 4).
Conclusion
The mixed cyclotetramerisation of the bis(diiminoisoindo-
line) compound 1 from 1,2,4,5-tetracyanobenzene and 4,5-
bis(2,6-dimethylphenoxy)phthalonitrile (2) in nBuOH in the
presence of magnesium butoxide with a precursor molar
ratio of 1:7 is suitable to isolate the mononuclear H2Pc 3
and the dinuclear H2Pc-H2Pc 4, in addition to the trinuclear
H2Pc-H2Pc-H2Pc 5 in a low yield. The phthalocyanine rings
in 4 and 5 are connected by common annulated benzene
rings. To the best of our knowledge, a trinuclear benzo-
bridged p-electron conjugated phthalocyanine is described
here for the first time. UV-visible-NIR spectra in solution
document a very strong extension of the conjugated p-elec-
tron system by a shift of the Q bands at l=664/701 nm for
H2Pc 3 to l=830/853 nm for H2Pc–H2Pc 4 and then to l=
944 nm for H2Pc–H2Pc–H2Pc 5. Furthermore, the extinction
coefficients increase with molecular extension. In the series
of mononuclear Pc 3 to dinuclear Pc 4 and then to trinuclear
Pc 5, the fluorescence quantum yields, fluorescence lifetimes
and singlet-oxygen quantum yields decrease. Work is now in
progress to synthesise metal complexes of mononuclear, di-
nuclear and trinuclear phthalocyanines connected either by
annulated benzene rings or by single bonds in order to study
the influence of the binding type on the photophysical prop-
erties in more detail.
Figure 3. Fluorescence spectra of the phthalocyanines 3, 4 and 5 in tolu-
ene.
Table 4. Photophysical properties of the phthalocyanines 3, 4 and 5 in
toluene.
Fluorescence band[a]
Stokes shift
Ffl
tfl
FD
[cmÀ1
]
[ns]
3
4
5
706 (14150)
860 (11600)
956 (10450)
100
100
150
0.33
0.04
<0.02
6.2
0.8
0.4
10
<0.02
<0.02
[a] Fluorescence in nm; values in parentheses are given in cmÀ1
.
band are comparably low for 3, 4 and 5, which is usual for
such rigid molecules like Pcs and their analogues.
The fluorescence quantum yield (Ffl) of the mononuclear
Pc 3 is 0.33, of the dinuclear Pc 4 0.04 and for the trinuclear
Pc 5 less than 0.02 (Table 4). The fluorescence lifetime (tfl)
of 3 is 6.2 ns compared with 0.8 ns for 4 and 0.4 ns for 5. The
values of the fluorescence quantum yield of the dinuclear
and trinuclear Pcs are reduced compared with that of the
mononuclear Pc. The reduction is in good agreement with
the decrease of the fluorescence lifetime. Similarly, for a dif-
ferently substituted metal-free Pc and an analogously substi-
tuted metal-free Nc with an enlarged p-electron system, a
decrease of the fluorescence quantum yield from 0.85 to
0.14 and a decrease of the fluorescence lifetime from 7.2 to
3.2 ns was reported.[23] This usual effect is due to the de-
crease of the HOMO–LUMO gap and a more extended vi-
brational level structure of larger molecules, thus increasing
the probability of nonradiative decay.
Experimental Section
Measurements: IR spectra were recorded on a Perkin–Elmer Spectrum
1000 FTIR spectrometer, 1H NMR spectra were recorded on a Bruker
Avance DPX-200 (200 MHz), MS MALDI-TOF spectra were recorded
on a Applied Biosystems Voyager System 6033, MS-ESI spectra were re-
corded on a Bruker Esquire LC and MS-EI spectra were recorded on a
Finnigan MAT 95.
1
Singlet oxygen (1O2, Dg) is generated by energy transfer
Steady-state absorption and fluorescence: The ground-state absorption
spectra were recorded at room temperature by using the Shimadzu
UV160 A spectrophotometer. The emission spectra were recorded at
room temperature in optical quartz cells (1”1 cm) using a xenon lamp
(OSRAM) with monochromator for excitation and a polychromator with
a cooled charge coupled device (CCD) matrix for detection (LOT-Oriel,
Instaspec IV).[28] The mononuclear Pc 3 and binuclear Pc 4 were mea-
sured relative to pheophorbide a in ethanol (Ffl =0.28).[29] The fluores-
cence quantum yield of the trinuclear compound 5 was estimated by
comparison with the dye IR140 in dimethyl sulfoxide (DMSO).[30]
from the excited triplet state of a sensitiser molecule to the
ground-state triplet oxygen (3O2, ꢀg ). As the O2 state lies
0.98 eV above the triplet ground state, the energy difference
between T1 and S0 of a sensitiser should be above or around
this value to allow the generation of singlet oxygen.[23,24]
This prerequisite holds for 5,10,15,20-tetraphenylporphyrins
with a triplet energy (ET) of ꢀ1.59 eV and phthalocyanines
with ET of ꢀ1.2 eV.[25] For ZnPc and H2Pc singlet-oxygen
quantum yields (FD) of 0.55 and 0.13, respectively, were
found.[26] The triplet energy of Ncs is ꢀ0.94 eV, thus below
0.98 eV.[23a] The singlet-oxygen quantum yields of 3, 4 and 5
were determined by time-resolved measurement of the pho-
tosensitised-generated singlet-oxygen luminescence at l=
3
À
1
Time-resolved fluorescence: The time-resolved fluorescence decays were
obtained by using a time-correlated single-photon-counting technique
(TCSPC) (Becker & Hickl GmbH, SPC 600) with frequency-doubled
pulses of a Ti:sapphire laser (Coherent Mira 900, 350–460 nm, FWHM
120 fs) for excitation. The response function of the system, which was
measured with a scattering Ludox solution (Aldrich), had a full width at
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Phthalocyanines
FULL PAPER
half-maximum height (FWHM) of spectral peak of about 60 ps. The
setup was previously described in reference [31].
Compound 5: Green powder, yield: 2.0 mg (0.2%); 1H NMR (200 MHz,
CDCl3, 258C, TMS): d=11.12 (s, 4H), 9.15 (s, 4H), 9.06 (s, 4H), 8.29 (s,
4H), 8.16 (s, 4H), 7.48–7.53 (brm, 12H), 7.32–7.44 (brm, 36H), 2.64 (s,
24H), 2.60 (s, 24H), 2.49 (s, 24H), 2.37 (s, 24H), 0.65 (brs, 2H),
0.01 ppm (brs, 4H); UV/Vis (THF): lmax (e)=944 (300000), 890 (73000),
836 (88000), 754 (69000), 661 (40000), 608 (36000), 355 nm
(177000mÀ1 cmÀ1) (see Table 2); MS (MALDI-TOF): m/z: 3306 [M+C].
Time-resolved singlet-oxygen detection: Photosensitised-generated sin-
glet-oxygen luminescence (SOLM) was measured time-resolved at
1270 nm. A nanosecond Nd-YAG laser (BMI) was used to excite the
samples at l=355 nm and the luminescence signal was recorded by using
a germanium pin diode (Northcoast). For calculating the singlet-oxygen
quantum yield of both samples the solution of the H2TPP in toluene was
used as reference (FD =0.68).[27] The setup and details are described else-
where.[26]
Acknowledgements
Materials: 4,5-Dichlorophthalonitrile (Aldrich), 2,6-dimethylphenol (Al-
drich), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Aldrich), magnesium
turnings (Merck) and anhydrous potassium carbonate (Merck) purchased
in the highest available purity were used without further purification.
The bis(diiminoisoindoline) compound 1 was prepared as described[10d]
from 1,2,4,5-tetracyanobenzene.[32] The solvents used for the preparations
(reagent grade) were dried, distilled and stored under dry conditions. All
syntheses were carried out under dry high purity nitrogen. Silica gel 60
(40–63 mm; Merck) was used for chromatographic analyses.
This research was partly supported by the VolkswagenFoundation under
the grant Az/78 204 (S.M.) and the Hanse Institute for Advanced Study
(Delmenhorst, Germany; O.S.). B.R. and E.A.E. thank the DFG for fi-
nancial support (grant RO1042/9-3). We thank Dr. Matthias Ganschow
(Clariant GmbH, Germany) for the MALDI-TOF mass spectra, Dr.
Thomas Dülcks (Universität Bremen) for ESI and EI mass spectra and
Mrs. Gisela Wçhlecke (Humboldt-Universität zu Berlin) for the technical
support.
4,5-Bis(2,6-dimethylphenoxy)phthalonitrile (2): 4,5-Dichlorophthaloni-
trile (4.0 g, 20 mmol) and 2,6-dimethylphenol (14.6 g, 120 mmol) in dry
DMSO (40 mL) were stirred under dry nitrogen at 958C. Dry potassium
carbonate (5”12 g) was added (every 5 min) and the solution was stirred
at 958C for an additional 1.5 h, then cooled and poured into ice–water
(400 mL). The sticky precipitate was filtered, washed with cold water,
ethanol, and then dissolved in dichloromethane and precipitated with
ethanol with subsequent evaporation of dichloromethane. The precipitate
was filtered and vacuum-dried to give white crystals (5.77 g, 77%).
1H NMR (200 MHz, CDCl3, 258C, TMS): d=7.20 (brs, 6H), 6.74 (s, 2H),
2.19 ppm (s, 12H); MS (EI, 70 eV): m/z (%): 368 (100) [M+C], 105 (55)
[R+] (see Scheme 2).
[1] P. Erk, H. Hengelsberg in The Porphyrin Handbook, Vol. 19 (Eds.:
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sumed). Compounds 1 (prepared from 101 mg (0.57 mmol), 1,2,4,5-tetra-
cyanobenzene)[10d] and 2 (1.47 g, 4 mmol) were added to this cooled sus-
pension and the mixture was heated under reflux for 48 h. After the reac-
tion mixture had been cooled, methanol (200 mL) was added and the re-
sulting mixture was stirred for 1 h. The precipitate was collected by cen-
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toluene. After evaporation of toluene the solid was dissolved in trifluoro-
acetic acid (25 mL) and stirred in the dark for 1 h. The solution was
poured into ice–water (100 mL), the precipitate collected, washed succes-
sively with water, 5% NaHCO3, water and methanol, then dried under
vacuum, extracted with toluene/hexanes (4:1 v/v) and subjected to chro-
matography on silica gel eluting with toluene/hexanes gradually reducing
the hexanes content from 20 to 5 vol%. From the first green fraction
containing 3 the solvents were evaporated, and the resulting solid was re-
crystallised from toluene. From the main (front) part of the second green
fraction the solvents were evaporated and the solid 4 was reprecipitated
from toluene with hexanes. From the tail of the second fraction a part
having an absorption peak near 950 nm in the UV-visible-NIR spectrum
was collected and the solvents were evaporated; the solid was recrystal-
lised twice from toluene. Thus 5 was obtained. Solids 3, 4 and 5 were
then dried under vacuum (10À2 mbar) at 608C.
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Green crystals; yield: 0.36 g (24%); 1H NMR (200 MHz, CDCl3, 258C,
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À
(brs, 2H); IR (KBr): n˜ =3296 (N H), 3024, 2952, 2922, 2854, 1612, 1588,
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708, 696 cmÀ1; UV/Vis: see Table 2; MS (ESI, positive mode): m/z: 1475
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Compound 4: Green powder; yield: 0.15 g (11%); 1H NMR (200 MHz,
CDCl3, 258C, TMS): d=11.14 (s, 2H), 9.06 (s, 4H), 8.29 (s, 4H), 8.15 (s,
4H), 7.32–7.44 (brm, 36H), 2.62 (s, 24H), 2.48 (s, 24H), 2.38 (s, 24H),
À
À0.04 ppm (brs, 4H); IR (KBr): n˜ =3296 (N H), 3024, 2952, 2922, 2854,
1612, 1588, 1470, 1446, 1398, 1352, 1328, 1274, 1222, 1186, 1092, 1058,
1012, 880, 764, 706, 694 cmÀ1; UV/Vis: see Table 2; MS (ESI, positive
mode): m/z: 2390 [M+C]; MS (ESI, negative mode): m/z: 2389 [MÀÀH].
Chem. Eur. J. 2006, 12, 1468 – 1474
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www.chemeurj.org
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Received: June 1, 2005
Published online: November 25, 2005
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