Tetra-(benzo-24-crown-8)-phthalocyanines as a platform for supramolecular ensembles: Synthesis and interaction with viologen

Article abstract of DOI:10.1142/S1088424620500297

The synthesis of a series of novel tetra-(benzo-24-crown-8)-phthalocyanines (Mg(II), Ni(II) and Co(II)) as well as a modified procedure for the free-base ligand and its Zn(II) and Cu(II) complexes are reported. The tendency of these phthalocyanines to und

Full text of DOI:10.1142/S1088424620500297

Published at https://www.worldscinet.com/jpp/
Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2020; 24: 1083–1092
DOI: 10.1142/S1088424620500297
Tetra-(benzo-24-crown-8)-phthalocyanines as a platform
for supramolecular ensembles: Synthesis and interaction
with viologen
Evgeniya A. Safonovaa, Jennifer A. Wytko*b◊, Jean Weissb◊,
Elena A. Ugolkovac, Nikolay N. Efimovc, Vadim V. Mininc,
Yulia G. Gorbunova*a,c◊ and AslanYu.Tsivadzea,c
aA.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 119071, Leninsky pr., 31,
building 4, Moscow, Russia
bInstitut de Chimie de Strasbourg, UMR 7177, CNRS, Université de Strasbourg, 4 Rue Blaise Pascal, 67008
Strasbourg, France
cN.S. Kurnakov Institute of General and Inorganic Chemistry RAS, 119991, Leninsky pr., 31, Moscow, Russia
Received 4 May 2020
Accepted 18 June 2020
ABSTRACT: The synthesis of a series of novel tetra-(benzo-24-crown-8)-phthalocyanines (Mg(II),
Ni(II) and Co(II)) as well as a modified procedure for the free-base ligand and its Zn(II) and Cu(II)
complexes are reported. The tendency of these phthalocyanines to undergo supramolecular cofacial
dimerization induced by interaction with a viologen (N,N-di(but-3-ynyl)-4,4′-bipyridinium) was
investigated by UV-vis absorption and EPR spectral studies in solution. The nature of the metal cation in
phthalocyanine, the concentration, as well as the solvent all influenced the assembly processes.
KEYWORDS: phthalocyanine, crown ether, viologen, supramolecular assembly, UV-vis absorption,
EPR spectroscopy.
spectral range and remarkable photochemical and redox
INTRODUCTION
properties [4, 12, 13].
The development of molecular machines and switches
Initially designed for the recognition of alkali and
is on the foremost edge of today’s science [1–5].
alkaline-earth metal ions, crown ethers have shown
Applications of such molecular devices include multiple
strong affinities for ammonium- and pyridinium-based
aspects of modern life [6], medicine [7, 8] and electronics
organic cations and thus have also often been used
[9, 10], as well as artificial small-molecule robots [11].
for molecular machine development [14–17]. Crown-
Conceptually, it should be possible to develop materials
substituted tetrapyrrolic macrocycles [18–20] that
for information recording and storage with unique
integrate the features of both classes of substances may
density, where one molecule bears one information bit,
be interesting platforms for the construction of novel
or for the control of drug delivery with target carriers.
molecular machines. For example, tetra-(benzo-24-
Tetrapyrrolic macrocycles are very promising scaffolds
crown-8)-phthalocyanine has been used as a versatile
for the formation of molecular machines and switches
building block for the design of a fourfold rotaxane
because of their chemical and thermal stability along
consisting of cofacially stacked homo- or heteronuclear
with their intense absorbance in the UV and visible
phthalocyanine (Pc)–porphyrin (Por) dimers [21–24].
Switchable spin–spin interactions in such rotaxanes
have been induced by supramolecular interactions
between crown ethers appended to phthalocyanines and
◊ SPP full member in good standing.
protonated amino groups of a neighboring porphyrin
molecule. More complex trinuclear porphyrin-Pc
*Correspondence to: Jennifer Wytko, email: jwytko@unistra.
fr, Yulia Gorbunova, email: yulia@igic.ras.ru.
Copyright © 2020 World Scientific Publishing Company

1084 E. A. SAFONOVA ET AL.
assemblies have been designed by three approaches. The
first strategy was the introduction of additional porphyrin
molecules as the third deck in the rotaxane structure
using specific recognition due to ionic interactions [25].
The second approach involved the assembly of two
phthalocyanine molecules onto a porphyrin template
containing eight amino-groups to form a heterotrimer
H2Por-Cu(II)Pc-Cu(II)Pc [26]. The last approach was
the design and synthesis of another type of triple-decker
assembly, namely a multiply interlocked catenane with
a novel molecular topology, in which four peripheral
crown ethers were quadruply interlocked with a cofacial
porphyrin dimer bridged with four alkylammonium
chains [27].
Today, no examples of scaffolds built on phthalocy-
anines have been reported in the literature. This work
reports the design of a new type of molecular device
based on tetra-(benzo-24-crown-8)-phthalocyanine 8M
in which the crown ether ring could bind positively
charged viologens to form cofacial dimers (Fig. 1). Since
viologens can exist in three distinct redox states, the
electrochemical control of the dynamic states could be
used for the further design of a device constructed on the
basis of such supramolecular assemblies [28–30]. The
ethynyl groups of the viologens offer the future possibility
of locking the dimeric structure by a click reaction with
bulky azide stoppers. In this work, the synthesis of tetra-
(benzo-24-crown-8)-substituted phthalocyanine and its
metal complexes 8M (Mg(II), Ni(II), Co(II)), Zn(II)
and Cu(II)) as well as their supramolecular interactions
with a viologen (N,N-dibutynyl-4,4′-bipyridinium) are
described. The formation of supramolecular cofacial
dimers in solution is investigated in detail by UV-vis and
EPR spectroscopy.
fluorophosphate (9) were synthesized by previously
reported procedures [31–33].
Triethyleneglycol (1), p-toluenesulphonylchloride
(TsCl), NaOH, K2CO3, catechol, N-bromosuccinimide
(NBS), I2, imidazole, triphenylphosphine (PPh3), Cs2CO3,
.
Zn(CN)2, Pd2(dba)3, dppf, Cu(OAc)2, Zn(OAc)2 2H2O
.
.
Mg(OAc)2 H2O, Mg, Co(OAc)2 4H2O, Ni(acac)2,
CF3COOH, 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU)
and the solvents (tetrahydrofuran (THF), N,N-dimethyl-
formamide (DMF), N,N-dimethylacetamide (DMA),
pentanol,dichlorobenzene,dichloromethane,chloroform,
ethanol and methanol) were acquired from commercial
suppliers (Acros, Merck, Aldrich, and Sigma). Pentanol
was distilled over magnesium under argon. DBU was
distilled over CaH2 under reduced pressure, and stored
under argon. Chloroform (stabilized with 0.6–1%
ethanol) was dried over CaCl2 and distilled over NaHCO3.
Other reagents were used without additional purification.
Neutral alumina (Merck) and silica gel (Macherey Nagel,
Kieselgel 60) were used for column chromatography. Bio-
Beads SX-1 (BIO-RAD) were used for size-exclusion
chromatography.
NMR spectra were recorded on Bruker Avance 600
and Bruker Avance 300 spectrometers. NMR spectra
were referenced to the residual solvent signals [27].
UV-vis spectra were measured with a Thermo Evolution
210 spectrometer in quartz cells with a 1 cm and 0.1 cm
optical path equipped with a Peltier thermostating
accessory.
Matrix-assisted laser desorption ionization time-of-
flight mass spectra (MALDI-TOF MS) were measured
on a Bruker Daltonics Ultraflex spectrometer with
2,5-dihydroxybenzoic acid as the matrix. High-resolution
mass spectrometry (HRMS) experiments were performed
on a Bruker Daltonics microTOF spectrometer (Bruker
Daltonik GmgH, Bremen, Germany) by the Service de
Spectrométrie de Masse de la Fédération de Chimie
“Le Bel” (FR 2010). X-Band EPR spectra were measured
at a 9.8 GHz microwave frequency on a Bruker Elexsys
E-680X radiospectrometer at 90 K. Resulting EPR
spectra of 8Co and 8Cu were described using rhombic
spin Hamiltonian with Zeeman, hyperfine and super
hyperfine interactions (Equation 1).
EXPERIMENTAL
Materials and equipment
Triethyleneglycol monotosylate (2), 1,2-bis-2′-[2′′-
(2′′′-hydroxyethoxy)-ethoxy]-ethoxy}-benzene (3) and
1,1′-di(but-3-ynyl)-4,4′-bipyridine-1,1′-diium bis(hexa-
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
O
N
N
N
N
M
N
N
O
O
O
O
O
O
Phthalocyanine
O
O
O
O
O
O
O
8M
O
O
+
O
N
N
Viologen
9
Fig. 1. Viologen-induced formation of cofacial dimers of 8M.
Copyright © 2020 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2020; 24: 1084–1092

TETRA-(BENZO-24-CROWN-8)-PHTHALOCYANINES AS A PLATFORM FOR SUPRAMOLECULAR ENSEMBLES 1085
at room temperature. A saturated aqueous solution of
Na2SO3 was added. The reaction mixture was filtered
and the solvent was evaporated from the filtrate. The
resulting compound was purified by chromatography
on silica by gradient elution with a mixture of hexane-
CH2Cl2–EtOH (1:1:0–0:95:5), yielding 2.67 g of 4 as
H = gzbHzSz + gxbHxSx + gybHySy + AIzSz + BIxSx + CIySy +
(gzazaSzIza + gxaxaSx Ixa + gyayaSyIya )
b
∑
α
(1)
Here gz, gx, gy –z, x, y are components of the g-tensor,
1
a yellowish oil (86%). H NMR (600 MHz, CDCl3) d
A, B, C–z, x, y are components of the HFS tensor, Sz, Sx and
Sy are projections of the spin operator onto coordination
axes, S = 1/2, Iz, Ix and Iy are projections of nuclear spin
operators onto coordination axes, ICu = 3/2, ICo = 7/2.
Ii = 1 is the nuclear spin of nitrogen and az, ax and ay are
components of super hyperfine tensors in Gauss.
The resulting EPR spectrum of 8Cu + viologen is the
sum of the dimer spectrum with S = 1 and the monomer
spectrum with S = 1/2 and was described using spin
Hamiltonian with fine interactions for S = 1 (Equation 2).
7.15 (s, 1H, HAr), 4.15–4.18 (m, 2H, a1), 3.84–3.93 (m,
2H, a2), 3.73–3.77 (m, 4H, a3,a4), 3.68–3.72 (m, 2H, a5),
3.62–3.64 (m, 2H, a6).
Preparation of 4,5-bis-2′-[2′′-(2′′′-iodoethoxy)-
ethoxy]-ethoxy}-1,2-dibromobenzene (5). PPh3 (2.33 g,
9.1 mmol) and I2 (2.22 g, 8.7 mmol) were dissolved in
85 mL of CH2Cl2 (freshly distilled over CaCl2) and then
imidazole (1.16 g, 17.0 mmol) was added. The mixture
was stirred for 10 min and then 1 (0.968 g, 18.2 mmol)
was added. The reaction mixture was stirred for 2 h at
room temperature, then a solution of Na2SO3 (0.97 g,
7.7 mmol) in 15 mL of water was added. The organic
layer was separated and the solvent was evaporated.
The resulting compound was purified by column
chromatography on silica by gradient elution with a
mixture of hexane-CH2Cl2-EtOH (1:1:0–0:95:5) to afford
H = b(gxSx Hx + gySyHy + gzHzSz )
(2)
+ D(Sz2 − S(S +1) / 3)
Where D is the component of the fine interaction
tensor.
The parameters of EPR spectra were found using the
best approximation method, which minimizes the error
function (Equation 3).
1
0.84 g of 5 as a yellow oil (61%). H NMR (600 MHz,
CDCl3) d, ppm: 7.15 (s, 1H, HAr), 4.14 (t, J = 4.9 Hz, 2H,
a1), 3.86 (t, J = 4.9 Hz, 2H, a2), 3.76 (t, J = 6.8 Hz, 2H, a3),
3.72 (m, 2H, a4), 3.68 (m, 2H, a5), 3.26 (t, J = 6.8 Hz, 2H,
a6). 13C-NMR (151 MHz, CDCl3) d, ppm: 149.0, 119.4,
115.6, 72.2, 71.1, 70.5, 69.9, 69.5, 3.1. HRMS ESI: m/z
calculated for C18H26Br2I2O6 [M + NH4]+ – 769.8504, m/z
found [M + NH4]+ – 769.8511; m/z calculated for
[M + Na]+ – 774.8058, m/z found [M + Na]+ – 774.8079;
m/z found for C18H26Br2I2O6 [M + K]+ – 790.7798, m/z
found [M + K]+ – 790.7799.
Preparation of 4′,5′-dibromodibenzo-24-crown-8-
ether (6). A solution of 5 (1.20 g, 1.6 mmol) and cate-
chol (0.17 g, 1.6 mmol) in 10 mL of DMF was added
by syringe pump over 10 h to a suspension of Cs2CO3
(2.60 g, 8.0 mmol) in 50 mL of DMF at 80°C in argon.
Then reaction mixture was stirred for 2 h and cooled to
room temperature. The resulting mixture was filtered and
the solvent was evaporated from the filtrate. The resulting
compound was purified by chromatography on silica in a
mixture of CH2Cl2–EtOH (95:5) to yield 0.52 g of 6 as a
colorless solid (54%). M.p.. = 101–104°C. 1H NMR (600
MHz, CDCl3) d, ppm: 7.06 (s, 1H, a-HAr), 6.85–6.91 (m,
2H, b,g-HAr), 4.13–4.16 (m, 2H, CH2), 4.09–4.11 (m, 2H,
CH2), 3.87–3.92 (m, 4H, CH2), 3.81 (dd, J = 6.5, 2.0 Hz,
4H, CH2). 13C-NMR (151 MHz, CDCl3) d, ppm: 149.1,
149.0, 121.6, 118.6, 115.4, 114.3, 71.5, 71.4, 70.1, 70.0,
69.8, 69.5.
F =
(YT −Y E )2 / N
i i
(3)
∑
i
Here YE is the array of the observed intensities of
i
EPR signals at different values of magnetic field H, YT
i
represents the theoretical values of intensities at the same
values of magnetic field H and N indicates the number
of points.
Theoretical spectra were plotted according to a
previously reported procedure [34]. Line shapes were
described using Gaussian and Lorentzian functions [35].
The line widths were parameterized using relaxation
theory [36] (Equation 4).
σk = ak + bkmI + gkmI2
(4)
Here mI is the projection of nuclear spin on the
magnetic field direction and k = x, y, z, ak, bk, gk represent
broadening parameters in corresponding orientations.
Minimization of error function implied variation of
g-factors, HFS and super hyperfine constants, line widths
and shapes.
Synthesis
Preparation of 8′,9′-benzo-24-crown-8-phthalonit-
rile (7). To a degassed mixture of 6 (270 mg, 450 mmol),
Zn(CN)2 (84 mg, 710 mmol), Pd2(dba)3 (20 mg, 30 mmol)
and dppf (21 mg, 37 mmol), 4 mL of DMA were added.The
mixture was refluxed for 2 h, cooled to room temperature,
diluted with CH2Cl2 and filtered over a pad of alumina.
Preparation of 4,5-bis-2′-[2′′-(2′′′-hydroxyethoxy)-
ethoxy]-ethoxy}-1,2-dibromobenzene (4). A solution of
NBS (2.29 g, 16.4 mmol) in 20 mL of DMF was added
to a solution of 3 (2.19 g, 7.5 mmol) in 20 mL of DMF.
The reaction mixture was stirred for 3 days open to air
Copyright © 2020 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2020; 24: 1085–1092

1086 E. A. SAFONOVA ET AL.
The solvent was evaporated and the resulting product was
purified by column chromatography on alumina (CH2Cl2–
EtOH (95:5)) to yield 0.204 mg of 7 as a brownish solid
(91%). M.p. = 104–107°C. 1H NMR (600 MHz, CDCl3)
d, ppm: 7.11 (s, 1H, a-HAr), 6.83–6.92 (m, 2H, b,g-HAr),
4.17–4.23(m, 2H, CH2), 4.10–4.16 (m, 2H, CH2), 3.87–
3.97 (m, 4H, CH2), 3.81 (s, 4H, CH2). 13C-NMR (151
MHz, CDCl3) d, ppm: 152.5, 149.0, 121.7, 116.5, 115.8,
114.2, 109.1, 71.7, 71.4, 70.7, 70.2, 70.1, 69.4.
Preparation of Mg[(B24C8)4Pc] (8Mg). Method 1.
A mixture of phthalonitrile 7 (200 mg, 402 mmol),
Mg(OAc)2 (28 mg, 201 mmol) and DBU (60 ml, 400 mmol)
in 5 mL of pentanol was refluxed overnight under argon.
The reaction mixture was cooled to room temperature
and poured into hexane. The resulting precipitate was
filtered, washed with hexane and dissolved in CHCl3. The
solvent was evaporated under vacuum. The product was
purified by size-exclusion chromatography on a column
packed with Bio-Beads SX-1 in CHCl3 + 2.5 vol %
MeOH yielding 80 mg of green solid (39%).
Method 2. A mixture of phthalonitrile 7 (200 mg,
402 mmol), and metallic Mg (19 mg, 804 mmol) in
10 mL of pentanol was refluxed overnight under argon.
The reaction mixture was cooled to room temperature
and poured into hexane. The resulting precipitate was
filtered, washed with hexane and dissolved in CHCl3.
The solvent was evaporated under vacuum. The product
was purified by size-exclusion chromatography with
Bio-Beads SX-1 in CHCl3 + 2.5 vol % MeOH to yield
130 mg of 8Mg as a green solid (64%). HRMS ESI, m/z:
calculated for C104H120MgN8O32 — 2017, 7884, found —
2017.7847. 1H NMR (600 MHz, CDCl3) d, ppm: 8.93 (s,
1H, a-HAr), 6.78–6.85 (m, 2H, b,g-HAr), 4.67–4.73 (bs,
2H, CH2), 3.72–4.23 (m, 10H, CH2). UV-vis (CHCl3),
l, nm (log(e)): 678 (5.30), 613 (4.53), 360 (4.92), 283
(5.08).
Preparation of Zn[(B24C8)4Pc] (8Zn). A mixture of
phthalonitrile 7 (100 mg, 200 µmol), and Zn(OAc)2 2H2O
.
(19 mg, 100 mmol) in 7 mL of pentanol was heated to
reflux and then DBU (30 ml, 200 µmol) was added. The
reaction mixture was refluxed overnight under argon,
then cooled to room temperature and poured into hexane.
The resulting precipitate was filtered, washed with
hexane and dissolved in CHCl3. Solvent was evaporated
under vacuum. The product was purified by size-
exclusion chromatography (Bio-Beads SX-1 in CHCl3 +
2.5 vol % MeOH) to yield 90 mg of 8Zn as a green solid
(87%). HRMS ESI, calculated for C104H120ZnN8O32
—
1
2058.7317, found — 2058.7306. H NMR (300 MHz,
CDCl3) d, ppm: 8.87 (s, 1H, a-HAr), 6.79–6.88 (m, 2H,
b,g-HAr), 4.74 (bs, 2H, CH2), 4.16–4.24 (m, 4H, CH2),
4.01–4.06 (m, 2H, CH2), 3.92–4.00 (m, 4H, CH2). UV-vis
(CHCl3), l, nm (log(e)): 680 (5.14), 614 (4.71), 358
(4.24).
Preparation of Ni[(B24C8)4Pc] (8Ni). A mixture of
8H2 (50 mg, 25 mmol) and Ni(acac)2 (13 mg, 50 mmol)
in 10 mL of dichlorobenzene was refluxed for 15 min
under argon. The reaction mixture was cooled to room
temperature and poured into hexane. The resulting
precipitatewasfiltered, washedwithhexaneanddissolved
in CHCl3. The solvent was evaporated under vacuum. The
product was purified by size-exclusion chromatography
(Bio-Beads SX-1 in CHCl3 + 2.5 vol % MeOH) to yield
42 mg of 8Ni bluish green solid (82%). HRMS ESI m/z:
calculated for C104H120NiN8O32 — 2051.7389, found —
2051.7342. 1H NMR (600 MHz, CDCl3) d, ppm: 8.18 (s,
1H, a-HAr), 6.75–6.84 (m, 2H, b,g-HAr), 4.65–4.72 (bs,
2H, CH2), 4.23–4.32 (bs, 2H, CH2), 4.14–4.21 (m, 2H,
CH2), 4.05–4.10 (m, 2H, CH2), 3.96–4.02 (m, 4H, CH2).
UV-vis (CHCl3), l, nm (log(e)): 668 (5.22), 604 (4.49),
407 (4.46), 310 (4.83), 286 (4.90).
Preparation of Co[(B24C8)4Pc] (8Co). A mixture of
8H2 (30 mg, 15 mmol), Co(OAc)2 (5 mg, 30 mmol), and
DBU (5 ml, 15 mmol) in 10 mL of DMF was refluxed for
30 min under argon. The reaction mixture was cooled to
room temperature and poured into water. The resulting
precipitate was filtered, washed with water and dissolved
in CHCl3. The solvent was evaporated under vacuum. The
product was purified by size-exclusion chromatography
(Bio-Beads SX-1 in CHCl3 + 2.5 vol % MeOH) to
yield 24 mg of 8Co as a bluish green solid (78%).
Preparation of H2[(B24C8)4Pc] (8H2). CF3COOH
(0.5 mL, 650 mmol) was added to a solution of 8Mg
(77 mg, 38 mmol) in 12 mL of CHCl3 and the reaction
mixture was refluxed for 10 min. The mixture was cooled
to room temperature and neutralized with Et3N (1 mL,
650 mmol). Solvents were removed under vacuum. The
resulting product was dissolved in CHCl3 and washed
with water. The organic layer was dried with Na2SO4 and
the solvent was evaporated. Column chromatography
over alumina in a CH2Cl2/MeOH mixture (95:5) afforded
a green compound, which was further purified by
repetitive size-exclusion chromatography (Bio-Beads
SX-1 in CHCl3 + 2.5 vol % MeOH). Yield: 63 mg (80%).
HRMS ESI m/z: calculated for C104H120CoN8O32
—
1
2052.7368, found — 2052.7366. found — 2052.7. H
NMR (600 MHz, CDCl3) d, ppm: 10.66 (s, 1H, a-HAr,
6.78–6.87 (bs, 2H, b,g-HAr), 4.98–5.07 (bs, 2H, CH2),
4.54–4.62 (bs, 2H, CH2), 4.23–4.31 (m, 4H, CH2), 4.05–
4.17 (m, 4H, CH2). UV-vis (CHCl3), l, nm (log(e)): 670
(5.06), 606 (4.49), 402 (4.33), 298 (4.87).
MALDI-TOF MS, m/z: calculated for C104H122N8O32
—
1
1995.82, found — 1995.8. H NMR (600 MHz, CDCl3)
d, ppm: 8.58 (s, 1H, a-HAr), 6.77–6.86 (m, 2H, b,g-HAr),
4.72–4.77 (bs, 2H, CH2), 4.23–4.33 (m, 2H, CH2), 4.15–
4.21 (m, 2H, CH2), 4.05–4.09 (m, 2H, CH2), 3.96–4.02
(m, 4H, CH2). UV-vis (CHCl3), l, nm (log(e)): 701
(5.10), 663 (5.02), 602 (4.39), 420 (4.56), 348 (4.90),
294 (4.75).
Preparation of Cu[(B24C8)4Pc] (8Cu). Phthalocy-
anine 8H2 (48 mg, 24 mmol), was dissolved in 8 mL
of DMF and heated to reflux under argon, then
.
Cu(OAc)2 2H2O (22 mg, 98 mmol) was added in
two portions and the mixture was refluxed for 105 min.
Copyright © 2020 World Scientific Publishing Company
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TETRA-(BENZO-24-CROWN-8)-PHTHALOCYANINES AS A PLATFORM FOR SUPRAMOLECULAR ENSEMBLES 1087
The reaction mixture was cooled to room temperature and
poured into water. The resulting precipitate was filtered,
washed with water and dissolved in CHCl3. The solvent
was evaporated under vacuum. Column chromatography
on alumina in a CH2Cl2/MeOH (95:5) mixture afforded a
green compound which was further purified by repetitive
size-exclusion chromatography (Bio-Beads SX-1 in
CHCl3 + 2.5 vol % MeOH). Yield: 36 mg (72%). HRMS
ESI, m/z: calculated for C104H120CoN8O32 — 2057.7332,
found — 2057.7302. UV-vis (CHCl3), l, nm (log(e)):
678 (5.26), 611 (4.51), 412 (4.46), 341 (4.84).
was carried out to give compound 5 in moderate yield.
In addition, use of a Pd-catalyzed cyanation in the last
step instead of a classical Rosenmund–Braun reaction
increased the yield of 6 from 55 to 91% [37].
The target metal complexes were synthesized using a
template approach (8Mg and 8Zn) or by metalation of
free-base phthalocyanine 8H2 with the corresponding
metal salts (8Co, 8Cu or 8Ni) (Scheme 1). Thus,
complex 8Mg was obtained by template condensation
of phthalonitrile 7 with Mg(OAc)2 in the presence of
DBU with a quite low, 39%, yield. Interestingly, the
replacement of Mg(OAc)2 and DBU with metallic Mg
in the template reaction increased the yield up to 64%.
Using the template method for the synthesis of the
previously described 8Zn afforded this product with
a 2.6 times higher yield (87%) than by using the two-
step procedure (synthesis of free base ligand 8H2 and its
metalation, 33%) [22].
RESULTS AND DISCUSSION
Synthesis and characterization
The benzo-24-crown-8-phthalonitrile — precursor 7
[37] of the target phthalocyanines — was synthesized by
a modified six-step method as shown in Scheme 1. Instead
of the previously described tosylation of 4, iodination
Phthalocyanine 8H2 was obtained by demetallation of
8Mg with trifluoroacetic acid. This two-step synthesis of
Scheme 1. Synthesis of di-(benzo-24-crown-8)-phthalonitrile 7 and tetra-(benzo-24-crown-8)-phthalocyanines 8M (M=Mg(II),
Zn(II), Co(II), Cu(II), Ni(II), H2).
Copyright © 2020 World Scientific Publishing Company
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1088 E. A. SAFONOVA ET AL.
8H2 in 51% yield appeared to be more efficient than the
previously described synthesis, with a reported yield of
34% starting from phthalonitrile [21]. Complexes 8Co,
8Ni and 8Cu were synthesized from phthalocyanine
8H2 by metalation with the corresponding metal salts
and were isolated with reasonably high yields (78, 82
and 72%, respectively). The metalated compounds
were purified by column chromatography on alumina
followed by repetitive size-exclusion chromatography
on columns packed with Bio-Beads SX-1. All products
were characterized by NMR (Fig. 2, Figs S1–S10 in
the Supporting information), UV-vis (Fig. 3, Figs S11–
S14), HR ESI MS (Figs S15–S20), and EPR (Figs 4–6)
spectroscopies.
The molecular structure of the 8Ni complex was
confirmed by its1H NMR spectrum in CDCl3 which shows
two resonance signals of aromatic protons at 8.27 and
6.75–7.84 ppm and five signals of crown ether protons
in the aliphatic region of 3.80–4.80 ppm (Fig. 2). The 1H
NMR spectra of 8H2 and 8Zn (Figs S8–S10) are similar,
with the same set of the signals. In contrast, the spectrum
of complex 8Mg consists of broad signals that suggest
aggregation processes in solution. Surprisingly, despite
the paramagnetic nature of the Co(II) nucleus of 8Co, it
was possible to obtain an informative 1H NMR spectrum
which displayed a broad signal at low field centered at
10.64 ppm for the phthalocyanine aromatic protons and
four sets of signals for the crown ether protons (Fig. 2).
by a well-resolved vibrational satellite at 601 nm and
a B band at 348 nm that are typical for monomeric
phthalocyanines (Fig. 3, Figs S11–S14, Table 1) [38].
The broad band at 420 nm corresponds to a charge
transfer band from lone pairs of oxygen atoms to the
phthalocyanine aromatic system [39]. Due to the higher
symmetry of the metal complexes, only one Q band, in
the 668–681 nm region, is observed in the spectra of 8M
solutions, as shown for 8Ni in Fig. 3.
EPR investigations
Due to the paramagnetic nature of the Co(II) and
Cu(II) complexes, 8Co and 8Cu were also characterized
by EPR spectroscopy. The spectrum of complex 8Cu was
recorded in frozen CH2Cl2 at 90 K. Pyridine was added
to the solution to prevent aggregation. The spectrum
displays hyperfine interaction of spin S = 1/2 with
the nuclear spin of copper I = 3/2 and super hyperfine
interaction with four equivalent nitrogen nuclei IN
=
1 (Fig. 4). The parameters (gz = 2.152, gx = 2.033, gy =
2.037, A = 1.932 × 10-2 cm-1, B = 2.067 × 10-3 cm-1, C =
2.011 × 10-3 cm-1, az(Pc) = 14.82 Gs, ax(Pc) = 16.33 Gs,
ay (Pc) = 16.96 Gs) are typical for species of this type
(Fig. 3) [40,41].
The EPR spectrum of 8Co in CHCl3 (Fig. 5) reveals
hyperfine structure from interaction of spin S = 1/2 with
the nuclear spin of cobalt I = 7/2 with parameters: gz =
1.990, gx = 2.352, gy = 2.410, A = 1.156 × 10-2 cm-1,
B = 5.325 × 10-3 cm-1, C = 8.168 × 10-3 cm-1. It is very
important to mention that 4.8% of 8Co is coordinated
to O2. The parameters for the 8Co-O2 complex are:
gz = 1.985, gx = 1.995, gy = 2.058, A = 1.007 × 10-3 cm-1,
UV-vis properties
The UV-vis spectrum of 8H2 in CHCl3 at c ≈ 10-5 M
displays two intense Q bands at 663 and 701 nm followed
Fig. 2. 1H-NMR spectra of 8Ni (top) and 8Co (bottom) in CDCl3.
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TETRA-(BENZO-24-CROWN-8)-PHTHALOCYANINES AS A PLATFORM FOR SUPRAMOLECULAR ENSEMBLES 1089
Fig. 3. Normalized UV-vis spectra of 8Ni (left) and 8H2 (right) in CHCl3.
Table 1. The wavelengths of the Q and B bands of 8M in the UV-vis spectra in CHCl3.
8H2
8Mg
8Zn
8Ni
8Co
8Cu
Q-band, nm (log(e)) 663 (5.02), 701 (5.10) 678 (5.30)
680 (5.14) 668 (5.22)
670 (5.06) 678 (5.26)
B-band, nm (log(e)) 348 (4.90)
283 (5.08), 360 (4.92) 358 (4.24) 286 (4.90), 310 (4.83) 298 (4.87) 341 (4.84)
Fig. 5. EPR spectrum of 8Co in CHCl3 at 90 K (b) and
theoretical spectra of 8Co (a) and 8Co-O2 (c).
Fig. 4. EPR spectra of 8Cu in CH2Cl2-pyridine (9:1) at 90 K:
experimental (violet) and theoretical (grey).
10 times — up to 53.9%. This increase is similar to results
described earlier for cobalt(II) phthalocyanine [34]. New
parameters for monomeric 8Co are gz = 2.003, gx = 2.229,
gy = 2.216, A = 9.690 × 10-3cm-1, B = 2.390 × 10-3 cm-1, C =
2.400 × 10-3 cm-1, az(Pyr) = 17.40 Gs, ax(Pyr) = 6.99 Gs, ay
(Pyr) = 7.75 Gs and for 8Co-O2 complex, the parameters
are gz = 1.999, gx = 2.009, gy = 2.061, A = 1.053 ×
10-3 cm-1, B = 1.069 × 10-3 cm-1 and C = 1.974 × 10-3 cm-1.
B = 1.694 × 10-3 cm-1, C = 2.344 × 10-3 cm-1. In addition,
the observation of a prohibited transition signal in the
spectrum of 8Co in CHCl3 at 1600 Gs provided evidence
for partial aggregation of the complex.
Addition of pyridine to the 8Co solution led to
significant changes in the EPR spectrum (Fig. 6). The
disappearance of the signal at 1600 Gs signified the
suppression of the aggregation process. On the other
hand, super hyperfine interactions with the coordinated
pyridine nitrogen nucleus IN = 1 appeared. The amount
of 8Co-O2 complex in the mixture increased more than
The host-guest interactions of MPc with viologen
Next, the interaction of tetra-(benzo-24-crown-8)-
phthalocyanine and its host–guest complexes with
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1090 E. A. SAFONOVA ET AL.
an important role. Thus, it was demonstrated that acetone
was more efficient than acetonitrile for dimerization of Pc
(Fig. 7a) probably due to the lower polarity of the acetone
compared to acetonitrile. Furthermore, the amount
of polar solvent should not be higher than 20% in the
final solution. Further increases of the amount of polar
solvent led to aggregation of the starting compound and
dimerization was not observed. Additionally, increasing
the concentration of 8Ni from 10-5 up to 10-4 M led to
more efficient supramolecular assembly (Fig. S23).
The partial aggregation of 8Ni due to p–p stacking at
higher concentration could lead to preorganization of
the molecules which would facilitate the formation of
cofacial dimers. Dilution studies showed that deviation
from the Beer–Lambert–Bouguer law in the spectra of
8Ni in CH2Cl2 solutions starts at concentrations above
10-6 (Fig. S24). Unfortunately, the ratio of dimers and
monomers in the solution could not be determined from
the UV-vis spectra because of overlapping of their low
energy absorption bands.
Fig. 6. EPR spectrum of 8Co in frozen CHCl3-pyridine mixture
(4:1) at 90 K (b) and theoretical spectra of Py-8Co (a) and
Py-8Co-O2 (c).
Furthermore, the nature of the central metal cation
appeared to play a crucial role in supramolecular
processes. Addition of viologen 9 to solutions of 8H2
and 8Cu led to changes in UV-vis spectra similar
to those observed for 8Ni (Figs S25–26). However,
complexes 8Zn, 8Mg and 8Co demonstrated completely
different behavior upon addition of viologen. Only
minor bathochromic shifts of the Q band were observed,
suggesting the formation of other types of supra-
molecular aggregates (Fig. 7 right, Figs S27–S28). This
phenomenon can be explained by the difference in the
coordination environment of the central metal atoms.
It is well known that cations such as Zn(II), Mg(II) and
Co(II) coordinated in a phthalocyanine are able to bind
additional axial ligands [43, 44]. EPR studies in this
work demonstrated that 8Co can easily form complexes
with axially coordinated O2. Earlier it was shown that
H2O molecules as an axial ligands on Mg(II) and Zn(II)
viologen 9 (N,N-dibutynyl-4,4′-bipyridinium) [33] was
investigated by UV-vis and EPR spectroscopy. Unfor-
tunately, NMR spectroscopy was not informative,
probably due to the presence of several different aggre-
gated forms in solution (Fig. S21).
Complex 8Ni was chosen as the main object of the
supramolecular assembly investigation because of the
absence of axial ligands on the central nickel cation that
should prevent formation of cofacial dimers. The addition
of viologen 9 in acetone or MeCN to a CH2Cl2 solution
of 8Ni led to significant hypochromic and hypsochromic
shifts (56 nm) of the Q band in the UV-vis spectra,
which are typical for the formation of cofacial Pc dimers
[40, 42] (Fig. 7 left). Surprisingly, these changes were
not observed in the case of CHCl3 solution (Fig. S22);
thus, it seems that solvent plays a very important role in
the supramolecular aggregation [40]. On the other hand,
the solvent in which the viologen was dissolved also plays
Fig. 7. UV-vis spectra of 8Ni (left) and 8Mg (right) in CH2Cl2 (c = 10-4 M) upon addition of viologen (2 eq.) in MeCN (orange
spectrum) or acetone (blue spectra).
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TETRA-(BENZO-24-CROWN-8)-PHTHALOCYANINES AS A PLATFORM FOR SUPRAMOLECULAR ENSEMBLES 1091
8Zn and 8Co, where axial ligands probably prevent this
process due to steric hindrance. The important role of
solvent and concentration in supramolecular aggregation
was also demonstrated. Preorganization of the Pc
molecules by p–p stacking seems to be necessary for
further supramolecular dimerization. EPR spectroscopy
was shown to be efficient in determining the monomer/
dimer ratio in assemblies of 8Cu and viologen 9. These
results could be useful for further application of tetra-
(benzo-24-crown-8)-substituted phthalocyanines as a
platform in the design of a supramolecular devices and
switches.
Acknowledgments
Fig. 8. EPR spectrum of 8Cu in CH2Cl2 (violet) and after
addition of viologen 9 (2 eq.) in acetone (orange) at 90 K.
The authors are grateful to the Russian Science
Foundation (Grant #18-73-00249). Measurements were
performed using equipment of CKP FMI IPCE RAS
and IGIC RAS. JAW and JW gratefully acknowledge
phthalocyanines can sterically hinder the formation of
the CNRS and the University of Strasbourg for financial
cofacial dimers [43].
support.
Due to the paramagnetic nature of the Cu(II) atom,
EPR spectroscopy can be used as an additional method
to investigate the supramolecular behavior of 8Cu in the
Supporting information
presence of viologen 9. The cobalt complex 8Co was
not investigated because the UV-vis study demonstrated
that cofacial dimers were not observed upon addition of
viologen. The addition of a solution of viologen in acetone
com/jpp/jpp.shtml.
to a solution of 8Cu in CH2Cl2 led to the appearance
Figures S1–S29, including spectral data, are given in
the supplementary material. This material is available
free of charge via the Internet at http://www.worldscinet.
in the EPR spectrum at 90 K of two additional signals
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