Synthesis and investigation of spectral and electrochemical properties of alkyl-substituted planar binuclear phthalocyanine complexes sharing a common naphthalene ring

Article abstract of DOI:10.1016/j.ica.2010.02.011

Hexa-tert-butyl and dodeca-n-butyl-substituted planar binuclear phthalocyanines sharing a common naphthalene ring with Mg as a central metal were synthesized with high yields and characterized by UV/Vis spectra, luminescence spectra, NMR, electrochemical,

Full text of DOI:10.1016/j.ica.2010.02.011

Inorganica Chimica Acta 363 (2010) 1869–1878
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and investigation of spectral and electrochemical properties
of alkyl-substituted planar binuclear phthalocyanine complexes sharing
a common naphthalene ring
b
a
b
Tatiana V. Dubinina a,b, , Aleksey V. Ivanov , Natalia E. Borisova , Stanislav A. Trashin ,
*
Stanislav I. Gurskiy a, Larisa G. Tomilova a,b, Nikolay S. Zefirov a
a Chemistry Department, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, 119991 Moscow, Russia
b Institute of Physiologically Active Compounds, 1 Severny Proezd, 142432 Chernogolovka, Moscow Region, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Hexa-tert-butyl and dodeca-n-butyl-substituted planar binuclear phthalocyanines sharing a common
naphthalene ring with Mg as a central metal were synthesized with high yields and characterized by
UV/Vis spectra, luminescence spectra, NMR, electrochemical, and spectroelectrochemical measurements.
On the base of these complexes, the metal-free phthalocyanine ligands and the series of binuclear phtha-
locyanine complexes of rare earth elements (REE) were synthesized.
Received 23 December 2009
Received in revised form 8 February 2010
Accepted 11 February 2010
Available online 16 February 2010
All compounds obtained revealed an intensive near IR-absorption reaching 855 nm for trinuclear
phthalocyanine. A crucial increase in NMR spectra resolution was achieved by the addition of ethylene
glycol as a disaggregating agent. Spectroelectrochemical measurements during oxidation showed revers-
ible changes of absorbance at 709 and 800 nm.
Keywords:
Binuclear phthalocyanines
UV/Vis spectroscopy
Fluorescence spectroscopy
Voltammetry
Ó 2010 Elsevier B.V. All rights reserved.
Spectroelectrochemistry
1. Introduction
nificant progress was achieved in this area [1,7]. Thus, the data
obtained for this type of binuclear phthalocyanine are unclear
The use of phthalocyanines in numerous applications has ex-
panded rapidly [1–4] in the last decade. This has inspired investi-
gators to synthesize new analogues and then to determine the
‘‘structure–properties” correlationship, and novel compounds with
modulated properties have also been obtained.
and contradictory [1,5,7]. Moreover, to our knowledge, no electro-
chemical and spectroelectrochemical investigations have been per-
formed for planar binuclear phthalocyanines sharing a common
naphthalene ring, although such data were obtained in the case
of analogues with a common benzene ring [8,9].
Planar binuclear phthalocyanines are of increasing importance
due to their potential use in non-linear optical [1] and data storage
devices, and as laser dyes [5]. In previous work [6] we have re-
ported intensive absorption in the near IR-region and 200 nm red
shift of the Q-band for planar binuclear phthalocyanines sharing
a common benzene ring compared with corresponding monopht-
halocyanines. These peculiarities are due to the extended aromatic
system and allow the use of planar binuclear phthalocyanines as
effective solid and liquid phase colour filters as well as IR-labels.
The first attempt to increase the aromatic bridge from benzene
to naphthalene was realized by Yang et al. [5]. However, the target
compound was obtained in only 6% yield, while absorption in the
near IR-region was not revealed. In subsequent researches no sig-
The main purpose of the current work was the synthesis of new
alkyl-substituted planar binuclear phthalocyanines sharing a com-
mon naphthalene ring and investigation of their properties.
2. Experimental
UV/Vis spectra were recorded using a Helios-
a spectrophotom-
eter in quartz cells (0.5 Â 1 cm) using pyridine, DMSO, CH3CN,
C6H6, and THF as solvents. The fluorescence spectra were recorded
on a Perkin–Elmer LS 55 (xenon discharge lamp, U = 775 V) spec-
trometer in quartz cells (1 Â 1 cm). 1H and 13C NMR spectra were
recorded on a Bruker ‘‘Avance 400” spectrometer (400.13 and
100.61 MHz, respectively) using CDCl3, DMSO-d6, and Py-d5 as sol-
vents at 20 °C (if not additionally specified). Chemical shifts are gi-
ven in ppm relative to SiMe4. Coupling constants, J, are given in Hz.
The column chromatography was performed using Lancaster Silica
Gel 60 (0.060–0.200 mm) and Merck Silica Gel 40 (0.063–
0.200 mm). Preparative TLC was performed using flexible plates
Merck Silica Gel 60 F254 and Merck Aluminium Oxide F254 neutral.
* Corresponding author. Address: Chemistry Department, M.V. Lomonosov
Moscow State University, 1 Leninskie Gory, 119991 Moscow, Russia. Tel.: +7 495
939 1243; fax: +7 495 939 0290.
E-mail addresses: dubinina.t.vid@gmail.com (T.V. Dubinina), tom@org.chem.
msu.ru (L.G. Tomilova).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.02.011

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T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
The gel permeation chromatography was performed using Bio
Beads SX-1 (Bio Rad). The CHN analysis was carried out using a
CHNOS Elemental Analyzer vario MICRO. Mass-spectra were re-
corded on a Finnigan MAT INSOC-50 (EI 70 eV) and a VISION-
2000 (MALDI-TOF). IR-spectra were recorded on a spectrophotom-
eter SPECORD M-70 b SPECORD UR-20 in liquid paraffin and using
KBr discs.
89%), m.p. 317 °C (in the sealed capillary), Rf = 0.51 (Al2O3, C6H6).
1H NMR (400.13 MHz, CDCl3, 20 °C): d = 8.24 (s, 2H, HAr – 1, 4);
8.29 (s, 2H, HAr – 5, 8). 13C NMR (100.61 MHz, (CD3)2SO, 20 °C):
d = 110.10 (s, C2, C3); 116.04 (s, CN); 126.86 (s, C6, C7); 132.37
(s, C9, C10); 133.17 (s, C1, C4); 135.57 (s, C5, C8). Anal. Calc. for
C12H4Br2N2: C, 42.90; H, 1.20; N, 8.34. Found: C, 42.77, 42.66; H,
1.25; 1.38; N, 8.11, 8.12%.
The salts, Mg(OAc)2Á4H2O, Ni(OAc)2Á4H2O, Lu(OAc)3Á4H2O,
Er(OAc)3Á4H2O, and Gd(OAc)3Á3H2O, were dried under vacuum at
100 °C for 4 h immediately before use. 4,5-Dibutyl-phthalonitrile
[10] and 4-tert-butyl-phthalonitrile [11] were synthesized accord-
ing to the published procedures. The magnesium complex of
2(3),9(10),16(17),23(24)-tetra-tert-butylphthalocyanine (tBuPcMg)
was obtained as a by-product of 6a synthesis and was separated
by gel permeation chromatography.
Electrochemical measurements were carried out with an IPC-
Pro potentiostat (Econix, Moscow, Russia). Cyclic voltammetry
was performed in a conventional three electrode cell using Pt-disk
(2.0 mm in diameter) working and Pt-foil counter electrodes. The
Ag|AgCl reference electrode was connected to the solution through
a salt-bridge and a Luggin capillary, whose tip was placed close to
the working electrode. The junction potentials were corrected by
ferrocenium+/ferrocene (Fc+/Fc) couple. 0.1 mol/l solution of
Bu4NBF4 (Sigma–Aldrich, recrystallized and dried under vacuum
at +70 °C) in o-dichlorobenzene (DCB, 99% Sigma–Aldrich, HPLC-
grade) containing 1–5 Â 10À4 M of sample was bubbled with argon
for 20 min before measurements were taken.
Spectroelectrochemical experiments were performed with a
quartz electrochemical cell composed of three separated compart-
ments. The 9.3 mm path-length rectangular compartment con-
tained a Pt-net working electrode, which was placed near the
sidewall to avoid an influence on the light beam. A Luggin capillary
and a capillary for argon bubbling were close to the working elec-
trode. A reference Ag|AgCl electrode was connected to the cell
through a salt-bridge. A Pt-counter electrode with a surface area
larger than the area of the working electrode was in a separate
compartment connected to the working space through a glass tube
with a frit. Pure argon was used to remove oxygen from sample
solutions and for gentle stirring during the electrolysis. To measure
equilibrium potentials at different stages of electrolysis, the open
circuit potential was recorded until a stable value was reached.
2.1.3. Naphthalene-2,3,6,7-tetracarbonitrile 4
6,7-Dibromonaphthalene-2,3-dicarbonitrile 3 (2.23 g, 6.60 mmol)
and CuCN (2.98 g, 33.00 mmol) were stirred in DMF (45 mL) under
reflux in the flux of argon for 5 h (TLC-control: Al2O3, C6H6:CH3CN
(10:1 V/V)). The reaction mixture was cooled to room temperature
and the saturated aqueous solution of FeCl3Á6H2O was added. The
black precipitate was filtered and washed with NH3aq. Then the pre-
cipitate was dissolved in CH3CN and heated to reflux. The insoluble
admixtures were filtered. The filtrate was evaporated and the result-
ing solid was additionally purified using column chromatography
(SiO2, acetone: C6H6 (1:15 V/V)) to give 4 (1.028 g, 68%), Rf = 0.70
(Al2O3, C6H6:CH3CN (10:1 V/V)). The compound is decomposed under
melting (360 °C). 1H NMR (400.13 MHz, (CD3)2SO, 20 °C): d = 9.01 (s,
4H, HAr – 1, 4, 5, 8). IR (liquid paraffin): m mC„N). MS
max/cmÀ1 2255 (
(EI) m/z: 228 (M+). Anal. Calc. for C14H4N4: C, 73.68; H, 1.77; N,
24.55. Found: C, 73.77, 73.44; H, 1.88, 1.75; N, 24.05, 24.67%.
2.1.4. Isoindolo[5,6-f]isoindole-1,3,6,8(2H,7H)-tetraimine 5
Naphthalene-2,3,6,7-tetracarbonitrile 4 (100 mg, 0.40 mmol)
was stirred in MeONa–MeOH solution (7.0 mg Na in 10 mL MeOH)
under cooling for 4 h with dry NH3 bubbled through the solution
(TLC-control: Al2O3, C6H6:CH3CN (10:1 V/V)). The IR-spectrum of
the target compound did not exhibit nitrile absorption observed
for the starting nitrile at 2255 cmÀ1
(mC„N). The brown precipitate
was filtered and washed by MeOH and Et2O to give 5 (80 mg, 70%),
Rf = 0 (Al2O3, F254, C6H6:CH3CN (10:1 V/V)). IR (liquid paraffin):
m
max/cmÀ1 1650 (
mC@N), 1210–1030 (mC–H, Ar), 735 (mN–H).
2.2. Synthesis of binuclear phthalocyanine complexes
2.2.1. Reaction in DMAE
2.2.1.1.
7,12,17,22-tetraazaporphyrino)[b,g]
(Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
naphthalene)
dimagnesium
6a. The mixture of 5 (64 mg, 0.30 mmol), 4-tert-butylphthalonitri-
le (920 mg, 5.00 mmol), and Mg(OAc)2Á4H2O (180 mg, 0.80 mmol)
in DMAE (10 mL) was heated to reflux under argon for 17 h. The
reaction mixture was cooled to room temperature and the mixture
MeOH:H2O (1:1 V/V) was added. The blue precipitate was filtered
and washed by water and MeOH. The target compound 6a
(19 mg, 6%) was separated using gel permeation chromatography
(C6H6). 1H NMR (400.13 MHz, Py:CDCl3 (1:7 V/V), 20 °C):
d = 1.95–2.19 (m, 54H, HBt u); 8.29–8.55, 9.45–10.03 (m, HAr);
10.56–11.03 (br s, HNph). MS (MALDI-TOF), m/z: 1381 [M]+, 2763
2.1. Synthesis of isoindolo[5,6-f]isoindole-1,3,6,8(2H,7H)-tetraimine
2.1.1. 1,2-Dibromo-4,5-bis(dibromomethyl)benzene 2
1,2-Dibromo-4,5-dimethylbenzene (6.60 g, 25.00 mmol) was
dissolved in CCl4 (38 mL) under reflux. Bromine (5 mL, 0.1 mol)
was then slowly added dropwise to the stirring solution under irra-
diation with a 300 W lamp for 7 h (TLC-control: silica gel, n-hex-
ane). The reaction mixture was cooled to room temperature and
washed by an aqueous solution of Na2S2O3. The organic layer
was dried with CaCl2. The solvent was evaporated and the resulting
solid was recrystallized from n-hexane: ethyl acetate (1:1 V/V) to
give white crystals of 2 (9.74 g, 67%), m.p. 131.8 (lit. 132 °C [12]),
Rf = 0.38 (silica gel, n-hexane).
2Á[M]+, 4144 3Á[M]+. UV/Vis (THF) kmax/nm (log
e
): 358 (5.13);
709 (5.06); 743 (5.12); 789 (5.52). IR (KBr):
m
max/cmÀ1 3081,
3058, 3024 (
mC–H); 1582, 1600 (mC@N); 1392, 1362 (ratio of intensity
1:2, C(CH3)3).
m
The 2(3),9(10),16(17)-tri-tert-butyl-25,26-dicyano-phthalocya-
nine magnesium 8 (20 mg, 10%) was separated using column chro-
matography (Al2O3, CHCl3: EtOH (100:1 V/V)), and then
additionally purified using gel permeation chromatography
(C6H6). MS (MALDI-TOF), m/z: 823 [M]+, 810 [MÀMe]+, 795
[MÀ2Me]+. UV/Vis (THF) kmax/nm: 355, 634, 674, 700.
2.1.2. 6,7-Dibromonaphthalene-2,3-dicarbonitrile 3
1,2-Dibromo-4,5-bis(dibromomethyl)benzene
2
(16.68 g,
29.00 mmol), fumaronitrile (3.40 g, 44.00 mmol) and sodium io-
dide (14.0 g, 93.00 mmol) was stirred in DMF (153 mL) at 70 °C
for 4.5 h (TLC-control: Al2O3, C6H6). The reaction mixture was
cooled to room temperature and water was added. The product
was collected by filtration and washed by aqueous solution of
Na2S2O3. Then the precipitate was recrystallized from CCl4. Addi-
tional purification was carried out using sublimation (290 °C, p
= 10 mm Hg). Complex 3 was obtained as white crystals (8.69 g,
2.2.2. Reaction in i-AmOH
2.2.2.1. (Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-7,12,
17,22-tetraazaporphyrino)[b,g] naphthalene) dimagnesium 6a. A
mixture of
5 (48 mg, 0.18 mmol), 4-tert-butylphthalonitrile

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1871
(673 mg, 4.00 mmol), and Mg(OAc)2Á4H2O (157 mg, 0.73 mmol) in
2.4.2. (Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene) dilutetium
diacetate 10a
i-AmOH (12 mL) in the presence of DBU (0.5 mL) was heated to re-
flux under argon for 8 h. The reaction mixture was cooled to room
temperature and the mixture MeOH:H2O (1:1 V/V) was added. The
blue precipitate was filtered and washed by water and MeOH. The
target compound 6a (49 mg, 19.5%) was separated using gel per-
meation chromatography (C6H6). The characteristics of the com-
pound obtained were identical with those obtained by method a.
The trinuclear magnesium complex 9 (29 mg, 8%) was sepa-
rated using gel permeation chromatography. 1H NMR
(400.13 MHz, Py: MeOD (40:1 V/V), 20 °C): d = 0.87–2.22 (m, 72H,
HtBu); 6.57–6.88 (m, 24H, HAr); 7.27–7.44 (m, 8H, HNph). MS (MAL-
DI-TOF), m/z: 2003 [M]+. UV/Vis (THF) kmax/nm: 356; 809; 832;
855.
Yield 7.0 mg (98%). MS (MALDI-TOF), m/z: 1936
[MÀ2OAc+2HY]+, 1338 [MÀ2Lu+4HÀ2OAc]+. UV/Vis (THF) kmax
/
nm: 350; 704; 749; 791.
2.4.3. (Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene) dierbium diacetate
10b
Yield 6.7 mg (90%). MS (MALDI-TOF), m/z: 1975
[MÀ2OAc+2HY]+, 1679 [MÀ21MeÀ2OAc+2HY]+. UV/Vis (THF)
kmax/nm: 355; 703; 749; 790.
2.4.4. (Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene) digadolinium
diacetate 10c
2.2.3. (Bis(92,102,142,152,192,202-hexa-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene) dimagnesium 6b
The mixture of 5 (16 mg, 0.040 mmol), 4-tert-butylphthalonitri-
le (240 mg, 0.83 mmol), and Mg(OAc)2Á4H2O (157 mg, 0.73 mmol)
in i-AmOH (12 mL) in the presence of DBU (0.5 mL) was heated
to reflux under argon for 33 h. The reaction mixture was cooled
to room temperature and the mixture MeOH:H2O (1:1 V/V) was
added. The blue precipitate was filtered and washed by water
and MeOH. The target compound 6b (16 mg, 22.2%) was separated
using gel permeation chromatography (C6H6:pyridine (100:1)). 1H
NMR (400.13 MHz, Py-d5+1 eq of ethylene glycol, 20 °C): d = 0.85
(t, JH,H = 7.34 Hz, 12H, CH3); 0.87 (t, JH,H = 7.34 Hz, 12 H, CH3);
0.88 (t, JH,H = 7.34 Hz, 12 H, CH3); 1.30 (m, JH,H = 7.34, 3.20, Hz, 24
H, CH2); 1.49 (tt, JH,H = 7.34, 3.20 Hz, 24H, CH2); 2.67 (t,
JH,H = 7.34 Hz, 24 H); 7.89 (with pyridine residual protons, 12H,
HAr) 9.68 (br s, 4 H, HNph). MS (MALDI-TOF), m/z: 1718 [M]+. UV/
Vis (THF) kmax/nm: 360; 709; 751; 800.
Yield 6.0 mg (94%). MS (MALDI-TOF), m/z: 2675
2Á[MÀ2Gd+4HÀ2OAc]+,
1935
[MÀ2OAc+2HY]+,
1338
[MÀ2Gd+4HÀ2OAc]+. UV/Vis (THF) kmax/nm: 350; 702; 751; 790.
2.4.5. (Bis(92,102,142,152,192,202-hexa-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] dilutetium diacetate 10d
Yield 8.5 mg (97%). MS (MALDI-TOF), m/z: 1684
[MÀ6BuÀ2OAc]+. UV/Vis (THF) kmax/nm: 353; 707; 759; 803.
2.4.6. (Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene) dinickel 10e
Yield 5.7 mg (98%). MS (MALDI-TOF), m/z: 1450 [M]+, 2900
2Á[M]+, 4351 3Á[M]+, 5804 4Á[M]+. UV/Vis (TCB) kmax/nm: 332,
707, 753, 796.
2.3. Synthesis of metal-free binuclear phthalocyanines
3. Results and discussion
2.3.1. Bis(9(10)2,14(15)2,19(20)2-tri-tert-butyltribenzo [i,n,s]-
7,12,17,22-tetraazaporphyrino)[b,g] naphthalene 7a
3.1. Synthesis of binuclear phthalocyanines
The binuclear phthalocyanine 6a (40 mg, 0.030 mmol) was dis-
solved in concentrated sulfuric acid (4 mL). This solution was
poured into the ice. At the same time the green precipitate was
formed. This precipitate was filtered and washed by MeOH to give
The statistical condensation between bis(diiminoisoindoline)
derivative and corresponding alkyl-substituted phthalonitriles
was chosen for synthesis of planar binuclear phthalocyanines shar-
ing a common naphthalene ring. The possibility of increasing
yields of target compounds due to the simplicity of the synthetic
procedure is an important advantage of this method in comparison
with the reaction using the unsymmetrical substituted phthalocy-
anines [7]. Moreover, it is possible to carry out the experiment un-
der mild conditions in contrast to the solid phase method [13].
Bis(diiminoisoindoline) derivative forming the naphthalene
bridge was obtained according to Scheme 1.
Free radical bromination of 4,5-dibromo-o-xylene 1 under UV-
irradiation conditions gave compound 2. Further treatment with
NaI eliminated bromine gave an intermediate o-quinodimethane
derivative, which was intercepted by a Diels-Alder reaction with
fumaronitrile and produced compound 3. Compound 4 was ob-
tained by cyanation of 3 under Rosenmund-von Braun conditions.
This synthetic approach is the most preferable for 4, because the
standard method described in Ref. [14] led to a low yield of 4
(the authors [14] used 4,5-dimethyl-phthalonitrile as a starting
compound). The reproduction of this literature route showed that
bromination of 4,5-dimethyl-phthalonitrile gave less brominated
products which were difficult to separate. So the target compound
was obtained with a low yield (33%) [14] and the authors could not
give the exact characteristics of the compound synthesized. The
approach used in the present paper allowed the yield of 4 to be in-
creased to 68%.
7a (38 mg, 99%). MS (MALDI-TOF), m/z: 1338 [M]+ UV/Vis (TCB)
.
kmax/nm: 348; 700; 725; 764; 802. IR (KBr):
1599 ( C@N); 937–1296 ( C–H).
m
max/cmÀ1 1512,
m
m
2.3.2. Bis(92,102,142,152,192,202-hexa-butyltribenzo [i,n,s]-7,12,17,22-
tetraazaporphyrino)[b,g] naphthalene 7b
The binuclear phthalocyanine 6b (56 mg, 0.030 mmol) was dis-
solved in concentrated sulfuric acid (5 mL). This solution was
poured into the ice. At the same time the green precipitate was
formed. This precipitate was filtered and washed by MeOH to give
7b (54 mg, 99%). 1H NMR (400.13 MHz, Py-d5, 20 °C): d = 0.58–1.12
(m, 3H, CH3); 1.15–1.50 (m, 4H, CH2); 2.72 (m, 2H, CH2). MS (MAL-
DI-TOF), m/z: 1674 [M]+. UV/Vis (THF) kmax/nm: 335; 693; 721.
2.4. Synthesis of binuclear phthalocyanine complexes of the REE and Ni
2.4.1. General procedure
The metallation of binuclear phthalocyanine ligands
7
(0.004 mmol) was realized by heating to reflux in i-AmOH (5 mL)
for 2–3 min in the presence of M(OAc)mÁnH2O (0.04 mmol, M = Lu
(10a and 10d), Er (10b), Gd (10c), Ni (10e)), and lithium methylate
(2.0 mg, 53.00 mmol). The solvent was evaporated and the residue
obtained was dissolved in THF. The insoluble admixtures of inor-
ganic compounds were filtered. The evaporation of THF gave the
corresponding compound 10 as dark-greenish powders.
To increase the reactivity in phthalocyanine synthesis, tetranit-
rile 4 was converted to bis(diiminoisoindoline) derivative 5 by

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T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
NC
Br
Br
CHBr2
CHBr2
Br
Br
NaI
Br2, hν
Br
Br
CHBr
CHBr
CN
1
2
HN
HN
HN
NH
NH
NH
NH3
NC
CN
CN MeONa/MeOH
Br
Br
CN
CuCN
NC
CN
4
5
3
Scheme 1. Synthesis of bis(diiminoisoindoline) derivative 5.
analogy with the published procedure for synthesis of bis(1,3-dii-
minoisoindoline) [8,15].
The metal-free binuclear phthalocyanines 7 were obtained
upon treatment of magnesium complexes 6 with concentrated sul-
phuric acid using a standard technique [16]. Subsequent metalla-
tion of 7a by REE and nickel acetates produced a series of
complexes 10 in almost quantitative yields (Scheme 4). Dodeca-
n-butyl-substituted binuclear phthalocyanine lutetium complex
10d was synthesized by analogy with Scheme 4.
The binuclear phthalocyanines 10a–10d bear the extra-ligands
and consequently may exist in both syn and anti isomeric forms,
which however cannot be separated using chromatographic meth-
ods [17].
Template assembling of magnesium complexes and their further
demetallation gave the metal-free phthalocyanines (Scheme 2).
The magnesium complexes 6 were synthesized by statistical
condensation in boiling solvent under argon. The formation of
symmetrical substituted phthalocyanine as by-products was
found, which is typical for these types of reactions [6,15].
When using DMAE mentioned in the literature [5] as a solvent
and a ratio of 5: 4-tert-butylphthalonitrile (1:5), the low yield of
6a was caused by incomplete cyclization (Scheme 3). To favour for-
mation of 6a by completing cyclization of the second ring at 8, the
ratio of initial compounds was changed to 1:20 although the prod-
uct yield was not increased significantly (Table 1).)
3.2. Spectral properties of binuclear phthalocyanines
Further optimization of reaction conditions has shown that
employment of isoamyl alcohol–DBU system leads to the highest
yield of 6a, while trinuclear phthalocyanine 9 was obtained as a
by-product (Scheme 3).
To avoid the formation of an isomers mixture (of which the
highest possible quantity in the case of tert-butyl-substituted pla-
nar binuclear phthalocyanines can be 36), for ease of interpretation
of NMR spectra, a magnesium complex 6b was synthesized starting
from 4,5-dibutylphthalonitrile (Scheme 2).
In Refs. [6,18] it was mentioned that planar binuclear phthalo-
cyanines sharing a common benzene ring have a tendency to
aggregation in non-coordinating solvents. In the case of the mag-
nesium complexes 6, broadening of the Soret (B) band and the Q-
band (700–850 nm) and also a significant fall in the Q-band inten-
sity were observed in non-coordinating solvents (CHCl3, C6H6). The
increase in solvent polarity improves spectrum resolution. Thus, in
DMSO, pyridine, and THF an intensive absorption maximum was
observed in the near IR-region, and the Soret band became sharp.
R
CN
CN
CN
2
2
, Mg(OAc) *4H O
, Mg(OAc)2*4H2O
R'
CN
DBU, -AmOH
5
i
DB U, -AmOH
i
R'
N
R
R'
R
N
N
N
N
N
R'
R
N
N
R
N
N
N
N
N Mg N
N
N MgN
N
N Mg N
N
N
N Mg N
R'
N
N
N
N
N
N
N
N
R
R'
R R'
6a
H2SO4
6b: R = R' = Bu
H
2SO4
R'
R
R'
N
R
N N
N
N
N
N
N
N
N
N
N
R'
R
R
NH HN
N
NH HN
N
N
NH HN
N
NH HN
R'
N
N
N
N
N
N
N
N
R
R'
R
R'
7a
R = R' = Bu
7b:
Scheme 2. Synthesis of binuclear phthalocyanine magnesium complexes and metal-free binuclear phthalocyanines.

T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
1873
i
Mg(OAc)2*4H2O, DBU, -AmOH
Mg(OAc)2*4H2O, DMAE
CN
CN
5
+
+
C
NH
NH
NH
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C
6a
+
Mg
Mg
N
Mg
Mg
6a
N
N
N
N
N
N
N
N
N
N
N
N
C
9
8
Scheme 3. Formation of complexes 8 and 9.
Table 1
Synthetic conditions for compound 6a.
with ones for monophthalocyanines [19] but by an order of magni-
tude greater than that for the planar binuclear phthalocyanines de-
scribed in literature [17,20].
It is noteworthy that the structure of the UV/Vis spectrum of
metal-free binuclear phthalocyanine becomes clear and has the
best resolution in o-DCB (Fig. 2).
In the case of REE phthalocyanines 10 the character of the cen-
tral metal did not influence the Q-band position, and this was also
observed for monophthalocyanines but not for diphthalocyanines
[16]. However, a noticeable red shift going from 10a to 10d was ob-
served. This effect can be explained by strengthening of the donor
properties of substituents.
Solvent/base
Ratio
Time of
reaction (h)
Yield (%)
5: 4-tert-butylphthalonitrile
DMAE
1:5
61
17
8
2
6
19.5
1:20
1:20
i-AmOH/DBU
These changes can be explained by extra-coordination of solvent
molecules to the magnesium ion, which prevents -stacking inter-
p
By the example of UV/Vis spectra of binuclear phthalocyanine
complexes of REE it was clearly shown that three main absorption
bands were observed in the region 700–800 nm (Fig. 3). A less
intensive absorption band in the near IR-region for REE complexes
in comparison with magnesium complexes seems to be caused by
stronger aggregation due to a high coordination number of REE.
In order to unambiguously interpret absorption bands in UV/Vis
spectra, the fluorescence spectra were investigated for compounds
6a (Fig. 4) and 7a.
action between binuclear phthalocyanine molecules in solution
suppressing the aggregation. The typical changes in UV/Vis spectra
are shown in Fig. 1 on an example of 6a.
When comparing the spectra of tert-butyl-substituted (6a) and
butyl-substituted (6b) magnesium complexes, 2 and 11 nm red
shifts going from 6a to 6b were observed (Table 2) for the B- and
Q-bands respectively. In comparison with binuclear magnesium
complexes, an additional extension of the
p-electron system for
trinuclear phthalocyanine 9 gives a larger bathochromic shift of
In the case of 6a THF solution (Fig. 5), the Stoke shift was not
observed for the absorption band at k = 709 nm. The Stoke shift
of the absorption band at k = 789 nm was 11 nm. Thus, due to
the fluorescence spectra, these bands can be attributed to Q-bands.
the Q-band.
It was determined that compound 6a (THF) conformed to Beer’s
law for concentrations less than 10À5 M with the extinction coeffi-
cient of 3.3 Â 105 MÀ1 cmÀ1 (k = 789 nm). This value is comparable
OAc
OAc
N
N
N
N
N
N
N
Ln
N
N
Ln
N
Ln(OAc)3*nH2O
N
N
N
MeOLi, AmOH
N
N
i-
N
a: R = tBu, R' = H, Ln = Lu
b: R = tBu, R' = H, Ln = Er
c: R = tBu, R' = H, Ln = Gd
e: R = tBu, R' = H
10a - 10c
7a
N
N
Ni(OAc)2*4H2O
N
N
N
Ni
N
N
Ni
N
N
N
N
N
MeOLi, AmOH
i-
N
N
N
N
10e
Scheme 4. Metallation of metal-free ligands 7a.

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T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
λ
Fig. 3. UV/Vis spectra of 10a (solid line) and 10d (dashed line) in THF.
Fig. 1. UV/Vis spectra of 6a in THF (solid line) and C6H6 (dashed line) (C = 2.27 lM).
scribed in Ref. [8]. These data predict the splitting of the Q-band
due to the independent nature of the two phthalocyanine rings.
Moreover, in comparison with planar binuclear phthalocyanine
sharing a common benzene ring, the hypsochromic shift of the
Q-band is expected due to the increase in the HOMO–LUMO dis-
tance for planar binuclear phthalocyanine sharing a common
naphthalene ring.
Table 2
Absorption bands of phthalocyanine complexes in THF.
Compound k (I/Imax), nm
Compound k (I/Imax), nm
6a
6b
9
358(0.54); 709(0.42);
10a
10b
10c
10d
350(1.00); 704(0.78);
743(0.48); 789(1.00)
360(0.94); 709(0.83);
751(0.55); 800(1.00)
356(1.00); 809(0.71);
832(0.56); 855(0.54)
749(0.54); 791(0.85)
355(1.00); 703(0.90);
749(0.39); 790(0.53)
350(1.00); 702(0.97);
748(0.48); 790(0.32)
353(1.00); 707(0.57);
759(0.35); 803(0.38)
3.3. 1H NMR spectroscopy of planar binuclear phthalocyanine
complexes
A number of problems accompany the NMR study of planar
binuclear phthalocyanines. The authors of Ref. [17] note that 1H
NMR spectra of planar binuclear phthalocyanines sharing a com-
mon naphthalene ring are characterized by broad signals in the
aromatic area. However, deep insight into the nature of this phe-
nomenon is not discussed. Thus, it is very important to consider
the influence of solvent nature and temperature on the character
of 1H NMR spectra in order to find optimum NMR conditions for
these types of complexes.
The absorption band at k = 743 nm is reflected relative to the axis
which passes across the intersection of the absorption and fluores-
cence spectra and was consequently attributed to a vibrational
satellite.
In the case of metal-free binuclear phthalocyanine, the absorp-
tion bands at k = 725 nm and k = 802 nm were attributed to Q-
bands and the absorption bands at k = 700 nm and k = 764 nm
were attributed to vibrational satellites (Fig. 6). The Stoke shift
was not observed in the case of the absorption band at
k = 725 nm; however the Stoke shift of the absorption band at
k = 802 nm was 14 nm.
When 1H NMR spectra of the complexes are observed in non-
coordinating solvents, only broad signals are observed, probably
due to the aggregation phenomenon. Compounds bearing tert-bu-
tyl-substituents, which cause the signals of binuclear phthalocya-
nine complex isomers to be unequal, hinder the correlation of
the spectrum in the aliphatic region, but compound 7b possesses
low solubility. Due to the mentioned restrictions, we chose com-
pound 6b for detailed NMR investigation.
The results obtained could be interpreted well with molecular
orbital calculations for the planar binuclear phthalocyanines de-
Preliminary investigation of the 1H NMR spectrum of the n-bu-
tyl-substituted magnesium complex of binuclear phthalocyanine
6b was carried out in pyridine-d5. However, even in highly polar
pyridine, solvent signals of aromatic protons HAr were not ob-
served due to the aggregation of the phthalocyanine. This can be
explained by strong
p-stacking interactions between phthalocya-
nine molecules in solution. In order to examine this hypothesis
several experiments at elevated temperature were carried out.
The values of T2 are diminished by the temperature rise (see Table
1 in Supplementary material), which supports the hypothesis of
the aggregation of the phthalocyanine moiety. This observation
correlates well with previous findings. A crucial increase in spectra
resolution was achieved by the addition of a drop of ethylene gly-
col, a good coordination molecule for the oxophilic magnesium cat-
ion. The tertiary complex formation between magnesium,
phthalocyanine, and ethylene glycol was confirmed by DOSY
experiment (Fig. 7). Almost the same diffusion coefficient for
phthalocyanine 6b and coordinated ethylene glycol supports the
tertiary complex formation. Moreover, the complex showed a clear
λ
Fig. 2. UV/Vis spectra of 7a in o-DCB (solid line) and in THF (dashed line).

T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
1875
THF
DMSO
THF
C6H6
DMSO
C6H6
λ
λ
Fig. 4. UV/Vis (A) and fluorescence spectra (B) (kex = 355 nm) of 6a (C = 2.20 lM)
Fig. 5. UV/Vis (solid line) and fluorescence (dashed line) spectra (kex = 355 nm) of
6a in THF (C = 2.20 M).
l
Fig. 7. DOSY-spectrum of phthalocyanine 6b in the presence of ethylene glycol.
3.4. Electrochemistry
3.4.1. Cyclic voltammetry
The redox proprieties of phthalocyanines were studied using
cyclic voltammetry (CV) on a platinum electrode. DCB was chosen
as a solvent due to the good solubility of the binuclear phthalocy-
anines and the great convenience of this solvent for electrochemi-
cal measurements according to our previous experience. Fig. 8
shows cyclic voltammograms of 6a, 6b, and tBuPcMg (as a mon-
ophthalocyanine control) with the half-wave potentials of redox
couples listed in Table 3. tBuPcMg gave three quasi-reversible re-
Fig. 6. UV/Vis (solid line) and fluorescence (dashed line) spectra (kex = 355 nm) of
7a in o-DCB.
NMR spectrum for phthalocyanine moiety and T2 values for all of
the aliphatic protons were diminished to a magnitude of about
1.8 Hz. These clearly show that the broadening of the signals orig-
inally observed originated from the molecules approaching aggre-
gation, which is eliminated by coordination of extra-ligands to the
metal ion.
dox-processes (
D
Ep < 0.15 V, ip,a = ip,c, ip ꢀ v
0.5) at potentials which
are in good agreement with previously published data for tBuPcCu
[21]. Compound 6a showed a slight anodic shift of the potential of
red1 and the same value of red2 compared with the potentials of
couples for monophthalocyanine. CV of 6b revealed a splitting of

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T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
simultaneous chemical reaction [22,23]. However, while the
nature of this reaction is not clearly understood, aggregation be-
tween the oxidized form (as electron acceptor) and native form
(as electron donor) seems to be the most probable process. Sand-
wich-like aggregates with an oxidized phthalocyanine in the mid-
dle can show a low rate of reduction on the back scan. High scan
rates do not provide sufficient time for aggregates formation or
reorganization, and thus the current of the peak increases on the
back scan. Additional evidences of high ability to aggregation in
DCB are (i) broadened Q-bands in the electronic spectrum of 6a
and (ii) deviation from Beer’s law at concentrations above
7 Â 10À6 M (data not shown).
Oxidation of 6b was more irreversible compared with 6a, and
only a minor current was observed on the back scan even at high
scan rates. This result is also in agreement with the assumption
of aggregation as the chemical process, since Bu-substituted
phthalocyanines with six butyl groups form aggregates more easily
than tBu-substituted ones, which have only four tert-butyl groups.
As a feature of 6b, an additional irreversible peak at a potential of
0.96 V was observed in the anodic area.
The previously described binuclear phthalocyanine sharing a
common benzene ring gave a splitting of all redox couples with
D
Esplit = 0.24 V. In the case of the naphthalene bridge, a smaller
value is expected due to the increase in distance between mono-
mer centres. In fact, only 6b showed the splitting for one of the
redox couples. The peak separation in the other cases is probably
not sufficient to be resolved in CV. However, the splitting of 6b
could also arise due to a strong
p-stacking interaction because
of aggregation [24,25]. As a result, the approximate redox poten-
tials and kinetic restrictions of back reduction from the oxidized
state of the binuclear phthalocyanines were determined using
CV experiments.
3.5. Spectroelectrochemistry
In order to obtain information on the thermodynamic revers-
ibility of the oxidation and electrochromic properties of binuclear
phthalocyanines, spectroelectrochemical investigation of 6a was
performed. Open circuit potentials and electronic spectra were
measured during the electrolysis to relate an equilibrium potential
to changes in the phthalocyanine. While two bands at k = 709 and
800 nm decreased when oxidation was started (Fig. 9A), new bands
at k = 520 and 865 nm appeared according to the formation of a
cation radical [16,26]. However, absorbance of the Q-band fell un-
evenly. The graph of dependence of the absorbance at k = 709 and
800 nm on the potential is shown in Fig. 10. In the potential win-
dow between 0.2 and 0.45 V the absorbance at k = 800 nm rapidly
and reversibly changed. In contrast, the absorbance at k = 709 nm
mostly changed at potentials between 0.50 and 0.75 V. Thus, the
spectroelectrochemical investigation has clearly revealed two
stages of the oxidation of 6a. A distance between the waves of
the absorbance-potential curves (Fig. 10) was 0.20–0.25 V, which
is close to the expected splitting of two one-electron oxidation
steps for binuclear phthalocyanines [8]. Spectroelectrochemical
study of the previously described binuclear phthalocyanine shar-
ing common benzene ring [8] has not shown a two-stage drop in
Q-bands, but independent changes have been noted in the band
at k = 865 nm, attributed to distortion of the planar structure of
binuclear phthalocyanine. Thus, our studies have demonstrated,
for the first time, two-stage changes in the Q-bands of binuclear
phthalocyanine. In the back reduction from the totally oxidized
form to the initial form, the complex was fully regenerated
(Fig. 9B). This clearly demonstrates thermodynamic reversibility
of the oxidation process of 6a, whereas cyclic voltammetry showed
sufficient kinetic restrictions of the back reduction.
Fig. 8. Cyclic voltammograms for 6a (A), 6b (B), and tBuPcMg (C) in DCB. The
numbers near the curves denote scan rates in V sÀ1; the currents for 0.05 V sÀ1 were
multiplied by 2 for scaling. The insert shows the dependence of the ratio between
peaks of current in the direct and back scans on the scan rate for the oxidation
process of 6a.
Table 3
Half-wave potentials for phthalocyanines derivatives in DCB.a
Phthalocyanine
E1/2 (red2)/V
E1/2 (red1)/V
E1/2 (ox1)/V
tBuPcMg
tBuPc2Mg2 (6a)
BuPc2Mg2 (6b)
À1.45 (À2.08)
À1.46 (À2.09)
À
À1.02 (À1.65)
À0.98 (À1.61)
À0.97 (À1.60)b
0.60 (À0.03)
0.49 (À0.14)
0.49 (À0.14)c
Values with respect to Fc+/Fc couple are given in brackets.
a
b
c
Mean potential of the splitting with
DEsplit = 0.19 V.
An additional irreversible redox-process with E1/2 = 0.96 V was observed.
the couple red1 with
DEsplit = 0.19 V and a middle value of the
potentials almost equal to the potential of red1 for 6a. However,
the couple red2 of 6b was missing, probably because it was outside
the voltage range.
In contrast to monophthalocyanines, only an irreversible redox
wave of ox1 appeared for binuclear phthalocyanines at the poten-
tial of 0.49 V that is, 0.11 V less positive than that for tBuPcMg. The
cathodic peak on the back scan was much lower than the anodic
peak on the direct scan, but the ratio between them increased with
the scan rate and reached a value of 0.5–0.6 at the scan rate of
0.5 V sÀ1 (see inset in Fig. 8). Such electrochemical behaviour is
probably due to coupling of the electrochemical process with

T.V. Dubinina et al. / Inorganica Chimica Acta 363 (2010) 1869–1878
1877
Fig. 9. Electronic spectra of 6a obtained at different degrees of oxidation (A) and back reduction from the oxidized state (B). Equilibrium potentials of the working electrode
(in V) from up to down (A): 0.2, 0.35, 0.41, 0.49, 0.61, 0.66, 0.68, 0.70, 0.73, 0.75; (B): 0.73, 0.69, 0.63, 0.50, 0.35, 0.26, 0.2.
Acknowledgements
This study was supported by the Russian Foundation for Basic
Research (grant no. 08-0300753) and the programme of the Presi-
dium of the Russian Academy of Science ‘‘Development of a strat-
egy of organic synthesis and creation of compounds with valuable
and applied proprieties”.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.02.011.
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