Hexadecapropyloxy-substituted diphthalocyanine complexes of rare-earth elements: Synthesis, spectroscopic and electrochemical studies

Article abstract of DOI:10.1023/A:1026036100317

Hexadecapropyloxy-substituted diphthalocyanine complexes of rare-earth elements (REE = Lu, Tm, Sm) were synthesized. The new symmetrically substituted diphthalocyanine complexes prepared starting from 4,5- dipropyloxyphthalodinitrile (phthalogen) are char

Full text of DOI:10.1023/A:1026036100317

Russian Chemical Bulletin, International Edition, Vol. 52, No. 8, pp. 1709—1714, August, 2003
1709
Hexadecapropyloxyꢀsubstituted diphthalocyanine complexes
of rareꢀearth elements: synthesis, spectroscopic and electrochemical studies
a
I. P. Kalashnikova,a I. V. Zhukov,a L. G. Tomilova,b and N. S. Zefirov
ꢀ
aInstitute of Physiologically Active Compounds, Russian Academy of Sciences,
142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (095) 913 2113
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (095) 939 0290. Eꢀmail: tom@org.chem.msu.su
Hexadecapropyloxyꢀsubstituted diphthalocyanine complexes of rareꢀearth elements (REE =
Lu, Tm, Sm) were synthesized. The new symmetrically substituted diphthalocyanine comꢀ
plexes prepared starting from 4,5ꢀdipropyloxyphthalodinitrile (phthalogen) are characterized
by better solubilities compared to the known hexadecamethylꢀsubstituted diphthalocyanine
complexes of the same REE. Spectral and electrochemical characteristics of the complexes
were studied. The compounds can be used as materials for highꢀcontrast electrochromic
devices.
Key words: diphthalocyanines, rareꢀearth elements, complexes, electrochemistry, elecꢀ
tronic absorption spectra.
Scheme 1
Recently, phthalocyanines and their complexes with
various metals have attracted considerable attention beꢀ
cause of their distinct electrochromic and semiconductor
properties and unique spectral characteristics that open
up new fields of application.1—7 Many of these characterꢀ
istics are particularly pronounced with diphthalocyanine
complexes. This makes the synthesis of new, functionally
substituted diphthalocyanine complexes topical.
The subject of our earlier studies8,9 were tertꢀbutylꢀ
substituted diphthalocyanines. In this work we report on
the synthesis of hexadecapropyloxyꢀsubstituted diphthaloꢀ
cyanine complexes of some rareꢀearth elements (REE =
Lu, Tm, Sm). With 4,5ꢀdipropyloxyphthalodinitrile (1)
as the phthalogen, we prepared a number of new, symꢀ
metrically substituted diphthalocyanine complexes charꢀ
acterized by higher solubilities compared to the known
hexadecamethylꢀsubstituted diphthalocyanine complexes
of the same REE.10,11
Synthesis of complexes. The starting phthalodinitrile 1
was obtained from 4,5ꢀdibromopyrocatechol (2) syntheꢀ
sized by treating pyrocatechol with bromine in AcOH 12
(Scheme 1). The reaction of nꢀpropyl bromide with
dibromide 2 at 20 °C resulted in 1,2ꢀdibromoꢀ4,5ꢀ
dipropyloxybenzene (3). The product yield exceeded 70%.
Cyanation of dibromide 3 was accomplished by heating it
with excess CuCN under reflux for 8 h in DMF.13,14
Phthalodinitrile 1 was obtained after recrystallization from
EtOH in 68% yield.
Lutetium, thulium, and samarium diphthalocyanine
complexes (4—6, respectively) were prepared by treating
the REE acetates or formates with an eightꢀfold excess of
phthalodinitrile 1 in amyl alcohol under reflux in the
presence of DBU in an inert atmosphere. The reaction
mixtures were heated until disappearance of the starting
phthalodinitrile (TLCꢀmonitoring).
The diphthalocyanine complexes 4—6 were separated
and purified by column chromatography (Al2O3, with
CHCl3—MeOH (10 : 1) as eluent) and finally obtained in
61 to 66% yields. Compounds 4—6 are water insoluble
but readily soluble in most of organic solvents (CHCl3,
CH2Cl2, C6H6, Me2CO). Both TLCꢀmonitoring and
the electronic absorption spectra (EAS) showed that
the reaction mixtures contained not only the target
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1621—1626, August, 2003.
1066ꢀ5285/03/5208ꢀ1709 $25.00 © 2003 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 52, No. 8, August, 2003
Kalashnikova et al.
products 4—6 but also small amounts of phthalocyanine 7
(Scheme 2).
(complex 6), the main absorption maximum is shifted
toward the longꢀwavelength region (680 nm). The EAS of
all the complexes synthesized in this work exhibit maxima
in the region 460—480 nm. This is yet another characterꢀ
istic feature of the REE diphthalocyanine complexes,
which appears due to the presence of the unpaired elecꢀ
tron since these compounds are stable radicals. On going
from lutetium phthalocyanine to samarium phthalocyaꢀ
nine this maximum behaves similarly to the main absorpꢀ
tion maximum, namely, it experiences a bathochromic
shift, while its intensity increases (probably, due to an
increase in the distance between the phthalocyanine rings).
Electrochemical studies. The electrochemical properꢀ
ties of the hexadecapropyloxyꢀsubstituted diphthaloꢀ
cyanine complexes of Lu, Tm, and Sm were studied by
cyclic voltammetry (CV) in oꢀdichlorobenzene (DCB).
Three reversible redox transitions were detected for the
complexes, one in the oxidation region and the other two
in the reduction region (Fig. 1). The potentials of the
redox transitions are listed in Table 1.
Scheme 2
Electrochemical measurements were carried out using
a working electrode made of a graphiteꢀlike material with
highly developed surface (pyrolyzed polyacrylontrile, PA).
This allowed operation at lower concentrations of the
compounds under study compared to the measurements
with compact platinum electrodes.11,13 This is of considꢀ
erable importance for the electrochemical studies of phꢀ
thalocyanine complexes, since many of them are poorly
soluble in most of organic solvents used for electrochemiꢀ
cal measurements. The PA electrode is characterized by a
10–5 A
–0.5
0
0.5
1.0
–E/V
Ln = Lu (4), Tm (5), Sm (6); X = OCHO, OAc; R = PrO
The absorption spectra of complexes 4—6 follow an
identical pattern and exhibit a characteristic maximum in
the region 660—680 nm and a Soret band near 320 nm.
For the diphthalocyanine complexes of the late REE (4, 5)
the Qꢀband position varies only slightly (660 and 662 nm).
As the ionic radius of the central metal ion increases
Fig. 1. Cyclic voltammogram of complex 4 (graphite electrode;
DCB; 0.15 M Bun4NBF4; Ag|AgCl|KCl; v = 200 mV s–1; 20 °C).

Substituted diphthalocyanine complexes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 8, August, 2003
1711
Table 1. Potentials of redox transitions of complexes 4—6a
E1/2/V
6
Ox1
1
Complex
Eb/V
5
4
0.4
0.2
0.874 V Å–1
R = 0.9931
Oxidation
Reduction
4
4c
5
0.38
0.39
0.42
0.50
–0.02
–0.02
0.02
–0.97
–0.99
–1.02
–0.98
6
2
6
0.10
5
Red1
0.874 V Å–1
R = 0.9931
4
a Graphite electrode; DCB; 0.15 M Bun4NBF4; Ag|AgCl|KCl;
v = 200 mV s–1; 20 °C.
0
b Arithmetic mean of the direct and reverse peaks.
c Pt electrode.
–0.2
–0.4
–0.6
–0.8
–1.0
higher signalꢀtoꢀnoise ratio compared to the smooth Pt
electrode and, hence, provides better results despite the
increase in the surface area of the Pt electrode. The poꢀ
tentials measured with the PA electrode and the smooth
Pt electrode are very close (see Table 1), which allows a
comparison of the results obtained using the two elecꢀ
trodes.
The potentials of the first redox transitions of the comꢀ
plexes studied in this work are in good agreement with the
published data13 for the REE diphthalocyanines containꢀ
ing pentyloxy groups in the same positions of phthaloꢀ
cyanine macrocycles (0.39—0.50 V for oxidation and
–0.06—0.05 V for reduction). The propyloxyꢀsubstituted
complexes are characterized by small narrowing of the
electrochemical gap (G = E Ox – ERed) from 0.45 to 0.40 V.
Earlier,13,15—17 it was shown that, depending on substituꢀ
ents, the G value for the substituted diphthalocyanine
complexes of REE can vary from 0.33 to 0.54 V.
4
6
3
Red2
5
1.00
1.04
1.08
1.12
R
3+/Å
Fig. 2. Effect of the REE ionic radius on the potentials of the
first oxidation transition (1) and of the first (2) and second (3)
reduction transitions of complexes 4—6.
The potentials of the first redox transitions of the comꢀ
plexes correlate with the REE ionic radii (R = 0.9931,
see Fig. 2), which is due to π—πꢀinteraction between
phthalocyanine rings.18 The slopes of the correspondꢀ
ing straight lines (0.874 V A–1) are somewhat larger
than those obtained for pentyloxyꢀsubstituted complexes
course of electrolysis. The positions of the absorption
maxima in the EAS of the neutral, reduced, and oxidized
forms of the complexes are listed in Table 2. In Fig. 3 we
present the EAS of the neutral, reduced, and oxidized
forms of diphthalocyanine 5 obtained by bulk electrolysis.
The pattern of the EAS of the redox forms of the comꢀ
plexes is typical of the REE diphthalocyanine complexes20
and indicate that the first redox processes involve one
electron and localization of electronic changes on the
phthalocyanine macrocycles.18,21—23
Comparison of the spectral parameters of the redox
forms of the complexes studied in this work reveals a
bathochromic shift of the absorption bands with an inꢀ
crease in the radius of the central metal ion (see Table 2).
This is a characteristic feature of diphthalocyanine comꢀ
plexes of REE.9 The red shift of the absorption bands of
the redox forms compared to the unsubstituted complexes
(see Table 2) is due to the presence of electronꢀdonor
nꢀpropyloxy groups, which is in agreement with the pubꢀ
lished data.13,24 The complexes exhibit high color conꢀ
trast between the neutral, reduced, and oxidized redox
forms (see Table 2), which can be assessed as arrangeꢀ
ments of hues in the equally contrast Munsell color circle.
(0.798 V A–1 13
and are characteristic of the diphthaloꢀ
)
cyanine complexes of REE.13,15,19 Thus, enhancement of
the effect of the REE ionic radius on the first redox poꢀ
tentials and the narrowing of the electrochemical gap for
the REE diphthalocyanine complexes occur simultaꢀ
neously. A similar trend was also observed earlier (see,
e.g., Ref. 13). The effect of the REE ionic radii on the
second reduction potentials of the complexes is much less
pronounced (see Fig. 2).
Both the first redox and the second reduction potenꢀ
tials of the complexes studied in this work also correlate
with the sums of the Hammett constants of substituents
(quantitative characteristic of electronic changes due to
the presence of substituents in the phthalocyanine rings).13
The spectral and electrochemical properties of the
complexes were studied using a quartz cell, which alꢀ
lowed the detection of spectral changes directly in the

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Kalashnikova et al.
Table 2. Maxima of the electronic absorption spectra of the
neutral, reduced, and oxidized forms of complexes 4—6 and
Pc2Lu in DCB and colors of the corresponding solutions
alcohol ("pure" grade) and propyl bromide ("chemically pure"
grade) were distilled prior to use; DMF and DMSO (both of
"chemically pure" grade) were vacuum distilled over BaO;
oꢀdichlorobenzene (DCB) of "chemically pure" grade was passed
through a column with neutral Al2O3 immediately prior to use;
and Bun4NBF4 (Aldrich) was twice recrystallized from propanꢀ
2ꢀol ("extra pure" grade) and then vacuum dried at 110 °C.
Phthalocyanines were synthesized from the corresponding lanꢀ
thanide formates and acetates (analytical grade).
NMR spectra were recorded on a Bruker DPXꢀ200 specꢀ
trometer (200 MHz) in CDCl3, containing Me4Si (0.05%) as
internal reference. Absorption spectra were recorded on a
Specord Mꢀ800 spectrophotometer in the region 200—800 nm.
4,5ꢀDibromopyrocatechol (2). To a solution of pyrocatechol
(44 g, 0.4 mol) in AcOH (150 mL), a solution of Br2 (135.8 g,
0.85 mol) in AcOH (100 mL) was added dropwise with stirring
and cooling with ice—water mixture. Once bromine was added,
the mixture was allowed to stand for 12 h at ca. 20 °C. Then the
solvent was partially distilled off and the residue was poured into
ice—water mixture (1.2 L). The white precipitate that formed
was filtered off, dried in air, and recrystallized from CHCl3 to
give compound 2 (80.1 g, 89%), m.p. 119—120 °C (cf. Ref. 12:
119—120 °C).
Compꢀ R3+
λ
a/nm
max
lex
/A
[xPc2Ln]–
[xPc2Ln]0
[xPc2Ln]+
4
0.99 361, 570 sh,
624, 702
367, 481,
576 sh, 600,
634 sh, 664
(green)
387, 499,
632 sh, 697
(orange)
(blue)
5
6
1.04 363, 596 sh,
626, 700
369, 480,
581 sh, 603,
640 sh, 666
(green)
374, 494,
586 sh, 613,
643 sh, 674
(green)
339, 459,
573 sh, 596,
629 sh, 659
(green)
389, 502,
634 sh, 701
(orangeꢀ
pink)
391, 520,
640 sh, 724
(pink)
(blue)
1.13 365, 583 sh,
634, 684
(blue)
Pc2Lub 0.99 333, 560 sh,
616, 690
350, 477,
623, 693
(orange)
(dark blue)
1,2ꢀDibromoꢀ4,5ꢀdipropyloxybenzene (3). To a stirring mixꢀ
ture of KOH powder (11.11 g, 0.198 mol) in anhydrous DMSO
(50 mL), 4,5ꢀdibromopyrocatechol (2; 6.63 g, 0.025 mol) and
nꢀpropyl bromide (12.18 g, 0.099 mol) were added at 20 °C and
the reaction mixture was stirred for 1.5 h. The resulting mixꢀ
ture was poured into water—ice mixture (200 mL), extracted
with CH2Cl2 (4×30 mL), washed with dilute NaOH solution
(2×30 mL), water, and dried over MgSO4. The orange oil obꢀ
tained after removal of the solvent was dissolved in benzene and
the product was separated by column chromatography (Al2O3,
with C6H6 as the eluent). Dibromide 3 (6.34 g, 73%) was obꢀ
tained as colorless crystals, m.p. 60—61 °C. Found (%): C, 40.90;
H, 4.53; Br, 45.45. C12H16Br2O2. Calculated (%): C, 40.94;
a The most intense absorption bands are underlined.
b DCB—MeCN (1 : 1).
Thus, these compounds can be used as materials for
electrochromic devices.
Experimental
The starting pyrocatechol of "purum" grade was used as reꢀ
ceived. 4,5ꢀDibromopyrocatechol (2) was synthesized following
the known procedure12 that was modified in some way. Amyl
A
2
1.0
1
2
3
1
0.5
3
3
1
2
25
20
15
ν•10–3/cm–1
Fig. 3. Electronic absorption spectra of the neutral (1), reduced (2), and oxidized (3) forms of complex 5 generated at potentials of
–0.5 and +1.0 V (vs. Ag|AgCl|KCl) at the Pt electrode in DCB with 0.15 M Bun4NBF4 as the background electrolyte.

Substituted diphthalocyanine complexes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 8, August, 2003
1713
H, 4.58; Br, 45.39. 1H NMR (CDCl3, J/Hz), δ: 1.02 (t, 6 H,
2 Me, J = 6.7); 1.85 (m, 4 H, 2 CH2); 3.90 (t, 4 H, 2 CH2,
J = 6.7); 7.04 (s, 2 H, C6H2).
The concentrations of solutions of the complexes under study
ranged from 7•10–5 to 1•10–4 mol L–1
.
The electrochemically generated redox forms used in the
spectroelectrochemical studies of phthalocyanine complexes
were obtained in the potentiostatic mode in a tailorꢀmade quartz
cell with anodic and cathodic compartments separated by a
porous glass membrane at 20 °C. The cell was connected to the
potentiostat by the threeꢀelectrode scheme. The working elecꢀ
trode was a Pt grid with a surface area of nearly 9.7 cm2 (estiꢀ
mated by comparing the electrochemical responses of ferrocene
at the Pt grid and at a Pt electrode of a simple shape), the
supporting electrolyte was 0.15 M Bun4NBF4, and the auxiliary
electrode was a Pt plate. The potentials were measured vs. an
AgCl electrode. DCB was used as the solvent. The concentraꢀ
tions of solutions of the complexes under study ranged from
2•10–5 to 3•10–5 mol L–1. Passing dry argon stream was used
both to remove oxygen prior to the experiments and to stir the
solutions in the cell. The electronic spectra of the electrochemiꢀ
cally generated redox forms of the complexes were recorded on a
Specord UVꢀVIS spectrophotometer (Carl Zeiss) immediately
in the quartz cell in the range 30000—13500 cm–1 (333—800 nm)
with 0.15 M Bun4NBF4 in the same solvent as the reference
solution.
4,5ꢀDipropyloxyphthalodinitrile (1). A mixture of 1,2ꢀdiꢀ
bromoꢀ4,5ꢀdipropyloxybenzene (3; 6.34 g, 0.018 mol) and CuCN
(4.84 g, 0.054 mol) in anhydrous DMF (80 mL) was refluxed
for 8 h. After cooling the solvent was evaporated in vacuo, CH2Cl2
(80 mL) and 30% aqueous ammonia (150 mL) were added to the
residue, and the resulting mixture was vigorously stirred for 24 h.
The aqueous layer was extracted with CH2Cl2, the organic layer
was washed with water, and the combined organic extracts were
dried over MgSO4. The solvent was removed in vacuo and the
residue was recrystallized from EtOH to give compound 1 (2.71 g,
68%) as colorless crystals, m.p. 151—152 °C. Found (%):
C, 68.81; H, 6.58; N, 11.27. C14H16N2O2. Calculated (%):
C, 68.83; H, 6.60; N, 11.47. 1H NMR (CDCl3, J/Hz), δ: 1.09 (t,
6 H, 2 Me, J = 6.7); 1.90 (m, 4 H, 2 CH2); 4.02 (t, 4 H, 2 CH2,
J = 6.7); 7.10 (s, 2 H, C6H2).
Bis(octapropyloxyphthalocyanine)lutetium(III) (4). A mixture
of 4,5ꢀdipropyloxyphthalodinitrile (3; 340 mg, 1.4 mmol),
Lu(OCHO)3•2H2O (60 mg, 0.17 mmol), and DBU (106 mg,
0.70 mmol) was refluxed in amyl alcohol (5 mL) for 8 h in Ar
atmosphere. After cooling the solvent was removed in vacuo,
the residue was reprecipitated with water from DMF, washed
with aqueous MeOH, and dried in air. After separation with
column chromatography (Al2O3, with CHCl3—MeOH (10 : 1)
as the eluent) diphthalocyanine 4 (182 mg, 61%) was obꢀ
tained as darkꢀgreen fineꢀcrystalline powder. Solubility (benꢀ
zene) 1.41•10–2 mol L–1. Found (%): C, 63.44; H, 6.29;
N, 10.18. C112H128LuN16O16. Calculated (%): C, 63.18; H, 6.06;
N, 10.53.
Bis(octapropyloxyphthalocyanine)thulium(III) (5) was syntheꢀ
sized similarly from dinitrile 3 (250 mg, 1 mmol) and
Tm(OAc)3•4H2O (53 mg, 0.13 mmol). Diphthalocyanine 5
(180 mg, 66%) was obtained as darkꢀgreen powder. Found (%):
C, 63.52; H, 6.44; N, 10.21. C112H128N16O16Tm. Calculated (%):
C, 63.36; H, 6.08; N, 10.55.
Bis(octapropyloxyphthalocyanine)samarium(III) (6) was synꢀ
thesized similarly from dinitrile 3 (370 mg, 1.5 mmol) and
Sm(OAc)3 (75 mg, 0.19 mmol). Diphthalocyanine 6 (247 mg,
62%) was obtained as darkꢀgreen fineꢀcrystalline powder.
Found (%): C, 63.54; H, 6.44; N, 10.93. C112H128N16O16Sm.
Calculated (%): C, 63.91; H, 6.13; N, 10.65.
This work was carried out with the financial support of
the Russian Foundation for Basic Research (Project No.
00ꢀ03ꢀ32658) and the International Scientific and Techꢀ
nical Center (Project No. 1526).
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Received December 30, 2002;
in revised form April 23, 2003