Revisiting the Ullman's Radical Chemistry for Phthalocyanine Derivatives

Article abstract of DOI:10.1002/chem.201704903

Phthalocyanine derivatives do not cease to gain attention due to their numerous properties and applications (e.g., sensor, PDT). This makes them a unique scaffold for the design of new material. In this context, we were interested to develop the synthesis of an imino nitroxide-substituted phthalocyanine by Ullman's procedure; a challenge due to the intrinsic low solubility of most phthalocyanine derivative in much solvents. To overcome this solubility problem, we designed a phthalocyanine with bulky neopentyl substituents in peripheral positions as counterpart to the imino nitroxide moieties. The imino nitroxide-substituted phthalocyanine was obtained by condensation of a monoformyl-substituted phthalocyanine with 2,3-bis(hydroxylamino)-2,3-dimethylbutane in refluxing THF–MeOH (2:1) mixture in the presence of p-toluenesulfonic acid monohydrate, follow by oxidation with PbO₂. Characterization was performed by electrochemistry, UV/Vis and EPR spectroscopy in solution as well as SQUID in solid state.

Full text of DOI:10.1002/chem.201704903

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Title: Revisiting the Ullman's Radical Chemistry for Phthalocyanine
Derivatives
Authors: catherine Hirel, Ismail Fidan, Dominique Luneau, and Vefa
Ahsen
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Chemistry - A European Journal
10.1002/chem.201704903
Revisiting the Ullman’s Radical Chemistry for Phthalocyanine Derivatives
a
b
a
a
Ismail Fidan , Dominique Luneau ,Vefa Ahsen* , Catherine Hirel*
a
Gebze Technical University, Faculty of Science, Department of Chemistry, Gebze, 41400 Kocaeli, Turkey
Université Claude Bernard Lyon 1, Laboratoire des Multimatériaux et Interfaces (UMR 5615), Campus de La
b
Doua, 69622 Villeurbanne Cedex, France
chirel@gtu.edu.tr
In the memory of Paul Rey
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Abstract
Phthalocyanine derivatives do not cease to arouse attention due to their numerous properties and
applications (e.g., sensor, PDT). This makes them unique scaffold for the design of new material.
In this expectative, we were interested to develop the synthesis of an imino nitroxide-substituted
phthalocyanine via the Ullman’s procedure; a challenge due to the intrinsic low solubility of
most phthalocyanine derivative in much solvents. To overcome this solubility problem we
designed a phthalocyanine with bulky neopentyl substituents in peripheral positions as
counterpart to the imino nitroxide moieties. The imino nitroxide-substituted phthalocyanine was
obtained by condensation of a monoformyl-substituted phthalocyanine with 2,3-
bis(hydroxylamino)-2,3-dimethylbutane in refluxing THF-MeOH (2:1) mixture in the presence
of p-toluenesulfonic acid monohydrate, follow by oxidation with PbO . Characterization was
2
performed by electrochemistry, UV-Vis and EPR spectroscopy in solution as well as SQUID in
solid state.
Keyword: Imino nitroxide, radical, Ullman’s synthesis, formyl-substituted phthalocyanine
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Introduction
Among open-shell molecules, imino and nitronyl nitroxide free-radical derivatives are one of the
most represented family due to their high stability and versatile synthesis. They have been
[
1,2]
essentially famous as building blocks in magnetic materials.
A renewed interest in their
chemistry has come in the spotlight because of their involvement in organic electrode-active
[
3]
[4]
materials or fluorophore-nitroxide hybrid probe. Imino and nitronyl nitroxide radical
[
5]
derivatives are classically obtained by the Ullman procedure involving the condensation of 2,3-
bis(hydroxylamino)-2,3-dimethylbutane (6) with an appropriate aldehyde in methanol to
generates the 1,3-dihydroxyimidazolidine derivative. For aromatic aldehyde condensation takes
hours at reflux. However, in some cases the reaction goes further and the 1,3-
[
6]
dihydroxyimidazolidine derivative undergoes dehydration to 1-hydroxy-2-imidazoline. In very
[
7]
exceptional case dehydration takes place even at room temperature. Condensation products
suffer from low solubility. Consequently, their purification and characterization are always a
difficult task and the Ullman’s synthesis is generally continued without further purification.
Oxidation of 1,3-dihydroxyimidazolidine or 1-hydroxy-2-imidazoline condensation product can
be carried out by employing various oxidants such as NaIO , PbO , MnO , or even air to afford
4
2
2
the corresponding nitronyl nitroxides(Way I) and imino nitroxide (Way II) respectively. In case
[
8]
[2]
of excess of oxidant or if the solution is acidic, nitronyl nitroxides are converted
spontaneously to imino nitroxide in a non-reversible way (Way III), as described in scheme 1.
Noteworthy that purity of 2,3-bis(hydroxylamino)-2,3-dimethylbutane (6) have a direct impact
[
9]
on the success.
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Scheme 1: Syntheses of nitronyl nitroxide and imino nitroxide free-radicals.
Although imino and nitronyl nitroxide free-radical derivatives are obtained satisfactorily with
numerous substituents, the Ullman route suffers from major drawbacks in the case of highly
aromatic aldehyde which require multi-step synthesis. Their low solubility in methanol as well as
the stabilization of the aldehyde function by resonance prevents the condensation with 6 in an
appropriate manner. Despite these constraints, the Ullman radicals were introduced in numerous
[
10]
[11]
[12]
[13]
[14]
molecules like pyrene, quinolone, 1,2,4-triazole, calixarene or ferrocene or even in
[15]
the axial position of tetraphenylporphinatozinc(II) coordinated by p-pyridyl nitronyl nitroxide.
Our interest in the phthalocyanine dyes as a promising group of fluorophore derivatives with
high quantum yield, used in numerous applications (chemical sensor, solar cell, PDT, etc.),
prompted us to investigate the synthesis of a phthalocyanine covalently link to an imino nitroxide
moiety. This has been a real challenge and motivation to revisit the Ullman’s radical chemistry
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owing to the low solubility of the phthalocyanines. It follows, there are at each step synthetic
problems that need to be specifically taken with care and into a better consideration than normal;
i) get the key precursor 2,3-bis(hydroxylamino)-2,3-dimethylbutane (6) and (ii) formyl-
substituted phthalocyanine in pure and good yield, also iii) optimize the condensation and the
oxidation step conditions in efficient way. These problems are probably the cause of the lack of
phthalocyanines bearing Ullman’s radical. Step i) was not a problem for us as the synthesis of 6
has been for long mastered in our laboratory. Step ii) and iii) required reconsideration.
To have an acceptable solubility we restricted our investigation to a mono imino nitroxide-
substituted phthalocyanine and ancillary bulky neopentyl substituents on other peripheral
positions. Synthesis of the mono formyl-substituted phthalocyanine was thus a prerequisite. In
the literature, there are only few reports about monoformyl-substituted phthalocyanine based on
two strategies: post-modification of a pre-formed macrocycles to introduce formyl group or
protection of the formyl group at the phthalonitrile level. By the former method formyl group is
[
16]
obtained by oxidative cleavage reaction of the monovinyl-substituted phthalocyanine
or
[
17, 18]
oxidation of hydroxymethyl-substituted phthalocyanine.
As the formyl group is fragile and
will not withstand the harsh Rosenmund-von Braun cyanation or phthalocyanine formation
conditions, its protection is indispensable. Indeed, cyanation via Rosenmund-von Braun takes
place at elevated temperatures which may lead to decomposition of aldehyde. To stand on the
safe side, aldehyde group was protected prior to cyanation process. Ethylene glycol was reported
to protect the formyl function to form a dioxalane derivative that is easily deprotected after
phthalocyanine formation by cleavage with 2 N hydrochloric acid in THF at room temperature.
In this article we describe the first synthesis of a metal-free phthalocyanine macrocycle
bearing one imino nitroxide radical as substituent (10) which has been fully characterized (see
scheme 2). This comprises an alternative synthesis to monoformyl-substituted phthalocyanine by
the protection/deprotection pathway and a detail optimization of the key steps aforementioned
condensation and oxidation for the imino nitroxide formation.
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Scheme 2: The Ullman’s synthetic route to metal-free phthalocyanine macrocycle bearing
one imino nitroxide radical as substituent (10).
Results and discussion
The monoformyl phthalocyanine: As stated above, our strategy to obtain a phthalocyanine
bearing one imino nitroxide radical (10) is based on the Ullman’s route whose unavoidable
precursor should be a formyl group. Therefore, we sought to synthesis an asymmetric A B-type
3
phthalocyanine bearing in one hand a protected formyl group and on the other hand neopentyl
bulky group substituents at the peripheral positions (5) to reduce aggregation and increase the
solubility in organic solvents. A B-type phthalocyanine classical synthetic methodology consists
3
[
19]
on the statistically crossover condensation
of two appropriate phthalonitrile precursors in
different ratio; in our case 4,5-dineopentoxyphthalonitrile (2) and 4-(5,5-dimethyl-1,3-dioxane-2-
yl)-phthalonitrile (1). The synthesis of phthalonitrile 2 was carried out on the basis of Leznoff’s
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10.1002/chem.201704903
[
20]
[21]
procedure with substantial modifications (SI, scheme S1). Catechol was brominated firstly,
thus 1,2-dibromo-4,5-dihydroxybenzene was treated with hexamethylphosphoramide, KOH,
tetraheptylammonium bromide, and neopentyl tosylate to give 1,2-dibromo-4,5-
dineopentoxybenzene. The conversion of it to 2 was achieved by the Rosenmund-von Braun
reaction under microwave irradiation in NMP which makes possible to obtain a cleaner product
[
22]
with a better yield in a shorter time.
The synthesis of 1 is inspired by the procedure of
[
23]
Hanack’s, only by modifying the nature of the protecting group. 2,2-dimethylpropan-1,3-diol,
a vicinal diol that could be used without further purification, was preferred to ethylene glycol due
to its ease of handling (SI, scheme S1). 3 was obtained by overnight reflux of 2 and 1 in
pentanol under template effect of metallic lithium, in the ratio 6/1 to afford the mixture of the
symmetric 2,3,9,10,16,17,23,24-octaneopentoxyphthalocyanine (4) and the asymmetric 3 in 23%
yield which have been isolated easily through column chromatography on silica gel eluting with
dichloromethane-hexane mixture (scheme 2). 3 and 4 were identified by MALDI-TOF mass
+
spectroscopy, which show [M+H] ion peaks at m/z =1204 and m/z = 1146, respectively (SI,
figures S18, S20).
The cleavage of the dioxalane group performed in F CCOOH-CH Cl (1/1) mixture at room
3
2
2
temperature allows to obtain 5 almost quantitatively (scheme 2). 5 was characterized by FT-IR,
1
13
H NMR, C NMR, MALDI MS (SI, figures S21-24) and elemental analyses (see experimental
−
1
section) by the typical carbonyl stretching of aldehyde at 1693 cm and the characteristic formyl
+
resonance at δ= 10.40 ppm corroborated by the ion peak at m/z = 1060 [M+H] . The production
of 5 in sufficient quantity is important to guarantee the optimization work required during the
following condensation and oxidation steps.
Condensation optimization: The condensation step between 6 and aldehyde derivative is
classically carried out by refluxing them in methanol. The use of methanol is a crucial parameter
as i) 6 is very soluble in it, and ii) it acts also as a catalyst by its slightly acidity. But this could be
also a major drawback when aldehydes are not or only partially soluble in it. In these cases, the
condensation conditions need to be addressed specifically. A co-solvent may be required to
[
24]
overcome the aldehyde solubility obstacle
or an alternative catalyst TsOH in high boiling
[25]
[26]
point solvent may force the condensation reaction . Solvent free condensation is also one
possibility even if it is little used as it appears from the literature. Table 1 reports the
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experimental condensation reaction conditions tested due to the lack of solubility of 5 in
methanol.
Table 1: Optimization of condensation reaction conditions.
Entry
Solvent
Temperature Catalyst Time
(days)
Result
1
CH Cl -MeOH (2:1)
RT
RT
reflux
RT
-
7
7
3
7
No reaction
No reaction
No reaction
No reaction
2
2
[
[
[
a]
a]
a]
2
3
4
CH Cl -MeOH (2:1)
TsOH
TsOH
TsOH
2
2
CH Cl -MeOH (2:1)
2
2
PhMe-MeOH
2:1)
PhMe-MeOH
2:1)
(
[
a]
5
reflux
TsOH
3
Small amount formed
but not finish
No reaction
No reaction
No reaction
Small amount formed
but not finish
Product formed
No reaction
(
6
THF-MeOH (2:1)
THF-MeOH (2:1)
THF-MeOH (2:1)
THF-MeOH (2:1)
RT
RT
50 °C
50 °C
-
7
7
7
7
[
a]
7
TsOH
-
TsOH
8
[
a]
9
[
a]
1
0
THF-MeOH (2:1)
Solvent free
reflux
RT
RT
TsOH
-
TsOH
2
7
7
1
2
1
[
a]
1
Solvent free
No reaction
General optimization reaction conditions: Monoformyl-substituted phthalocyanine (5) (10.7 mg, 1 eq.) and 6 (14.8
mg, 10 eq.) were stirred in 2 mL of methanol and 4 mL of co-solvent under argon atmosphere. Progress of the
reaction was monitored by TLC analysis.
[a]
6
eq of TsOH (11.4 mg, 6 eq.) was added as catalyst.
The best condensation conditions for the phthalocyanine derivative were observed in refluxing
THF-MeOH (2:1) mixture during two days in the presence of TsOH as catalyst. On these bases,
solely 1-hydroxy-2-imidazoline derivative (8) instead of the anticipated 1,3-
dihydroxyimidazolidine derivative (7) was obtained as confirmed by MALDI-TOF mass
+
spectroscopy which present an ion peak at m/z =1171 [M] (SI, figure S26).
The dehydration of 7 seems to be promoted not only by high reflux temperature but also
combined with the use of an excess of TsOH. Further optimizations are still in progress to find
the balance of the TsOH ratio which may give accessibility to 7. Taking these facts into account,
solely imino nitroxide-substituted phthalocyanine 10 could be accessed by the oxidation.
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Oxidation optimization: MnO , PbO , NaIO , or bubbling of the air in a NH OH (aq.)/MeOH/
2
2
4
4
Cu(OAc) mixture are among the commonly oxidants utilized in the Ullman pathway. Each
2
oxidation conditions were tested in order to find the best oxidative conditions. The suspension of
[
27]
[28]
an excess of MnO2
or PbO2
in solvent like CH Cl , CHCl or toluene allow a
2 2 3
heterogeneous oxidation, whereas oxidation by a drop by drop addition of NaIO (aq.) need a bi-
4
phasic solution of a water-immiscible solvent such as CH Cl or diethyl ether and saturated
2
2
[
2]
NaHCO (aq.) solution vigorously stirred. Bubbling of air into a NH OH (aq.)/MeOH/
3
4
Cu(OAc) mixture was less common. The experiments achieved were tabulated in Table 2.
2
Table 2: Optimization of oxidation conditions.
Entry Oxidant Solvent
Time
3 days
Result
[
a]
1
NaIO4
CH Cl -
Reaction very slow and even never complete
2
2
NaHCO3(aq.)
CH Cl
[
[
[
b]
c]
d]
2
3
4
PbO2
MnO2
Air
2 days
2 days
3 days
8 is completely consumed - Product formed
Phthalocyanine decomposed
Reaction very slow, By-products formed
2
2
2
CH Cl
2
THF-MeOH,
NH OH
4
(aq.)
General optimization reaction conditions: 8 (11.7 mg, 1 eq.) was suspended in 30 mL of organic solvent. The
mixtures were stirred vigorously at room temperature for 3 days in dark. Progress of the reaction was monitored by
TLC.[a] Addition of saturated NaHCO (aq.) solution (20 mL) and NaIO (21.4 mg, 10 eq.) dissolved in H O (5 mL);
3
4
2
[
b]
[c]
[d]
PbO (480 mg, 200 eq.); Activated MnO (174 mg, 200 eq.);
NH OH
(10 mL) and Cu(OAc) (catalytic
2
2
4
(aq.)
2
amount) were added. Air was bubbled through the solution
The oxidation of 8 was achieved efficiently only by the use of PbO in CH Cl at room
2
2
2
temperature. After two days of stirring at RT, a green solution corresponding to the imino
nitroxide-substituted phthalocyanine derivative 10 was obtained and isolated as a green solid in
3
8% yield (scheme 2).
1
0 was characterized unambiguously with a rich array of analyses such as FT-IR, MALDI-TOF
MS, elemental analysis, UV-Vis, CV, EPR, demonstrating the strength and the universality of
the Ullman method in obtaining nitroxide radicals, even with extreme solubility conditions.
UV-Visible spectroscopy: To gain first insight into electronic interactions between the radical
and phthalocyanine moieties, the absorption and emission spectra of 4 and 10 were recorded in
THF and presented in Figure 1. 4 and 10 were soluble in organic solvents such as DCM or THF
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−
6
in which the Beer−Lambert Law was observed for both compounds in the range of 10 M to
−
5
1
0 M (SI, figures S29-33, S54-55). 4 and 10 show the typical split Q band characteristic of
2
0
free-based phthalocyanines. In contrast, the low symmetry of 10 leads to a closer Q bands. B
bands around 350 nm are almost identical to each other. Noteworthy that the extension of the
conjugation pathway introduced by the imino nitroxide radical moiety of 10 (λmax= 441 nm) lead
to a 11 nm red shift of the charge transfer band in comparison to that of 4 (λmax= 430 nm). In the
7
visible range, the specific weak transitions of imino nitroxide radical at~ 450 nm are simply
overshadowed by those of phthalocyanine. Both molecules exhibit one main fluorescence
emission band at 699 nm, but as anticipated the introduction of the radical moiety decreased 8-
fold the fluorescence intensity. Fluorescence quantum yield in THF were found to be ΦF(4)= 0.25
and ΦF(10)= 0.03 for 4 and 10, respectively, thus confirming the quenching of the fluorescence.
Figure 1: UV-Vis and fluorescence spectra of 4 and 10 in THF.
EPR spectroscopy: The typical seven-line splitting pattern with the relative intensity
1
:1:2:1:2:1:1 presented in figure 2, proves the radical existence of 10. The seven-line spectrum
1
4
reasoned by the interaction of the unpaired electron (S=1/2) with two unequivalent N nitrogen
atoms (nuclear spin I=1) in the imidazoline ring. This spectrum was simulated with Jeol IsoSimu
computer program. Best fitting parameters are found as g = 2.0088, aN1 = 9.3 G, aN2 = 4.2 G,
ΔHp−p = 2.1 G.
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-4
Figure 2: EPR Spectra of the Radical 10 at 293 K at 10 M in Dichloromethane-toluene (1:1)
Mixture.
Electrochemical measurements: The electrochemical behavior of imino nitroxide-substituted
phthalocyanine 10 was investigated by cyclic voltammetry. 10 showed an irreversible oxidation
wave at 1.260 V vs. SCE and a reversible reduction one at −0.886 V (see Figure 3). Noteworthy
+
that potentials were referenced to ferrocene/ferrocenium couple by taking E1/2 (Fc/Fc ) = 0.480 V
[
28]
vs. SCE in dichloromethane with 0.1 M n-Bu NClO as supporting electrolyte.
The redox
4
4
characteristics and the observed potentials is another way to demonstrate the radical character of
imino nitroxide-substituted phthalocyanine 10.
Figure 3: Cyclic Voltammogram of Phthalocyanine 10 Recorded at rt in Dichloromethane, 0.1
M n-Bu NClO as Supporting Electrolyte, Scan Rate of 100 mV/s.
4
4
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Magnetic study: The magnetic measurements that were performed on different samples have
revealed that compound 10 is diamagnetic in the solid state. Such an unexpected magnetic
behavior while EPR spectroscopy in solution shows that compound 10 is unambiguously an
imino nitroxide free-radical has to be ascribed to intermolecular antiferromagnetic interaction.
Strong ferro- or antiferromagnetic intermolecular interactions are not uncommon. Nitronyl or
imino nitroxide free radical in the solid state may present either a direct interaction between the
[
30]
[31]
N-O group or a McConnell type interaction.
In the present case and without any crystal
structure it is not easy to have a straight opinion of the interaction pathway. However, owing to
the bulky neopentyl substituents a McConnel type interaction is unlikely because this required
that phenyl come close. We favor a direct interaction of the N-O group in a head-to-tail mode
(Figure 4) that generally results in strong antiferromagnetic interaction and a diamagnetic
behavior as is observed here for 10.
Figure 4: Representation of N-O group in a head-to-tail mode.
Conclusion
An imino nitroxide radical moiety covalently bonded to phthalocyanine macrocycle was
successfully synthesized for the first time in spite of the phthalocyanine inherent problems, i.e.
their high aromaticity and their insolubility in methanol which prevents condensation with 2,3-
bis(hydroxylamino)-2,3-dimethylbutane. The use of a co-solvent associating with TsOH as
catalyst in the condensation step and PbO as oxidant were the best conditions. 10 was obtained
2
in good yield according to the multi-step synthesis. As expected, the fluorescence intensity and
the quantum yield of 10 were very low compare to the symmetrical counterpart 4. Potentialities
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of this new optimized pathway are promising for the synthesis of novel highly aromatic
nitroxides. Especially, fluorophore link to nitroxide are promising candidate for sensor
application based principally on OFF-ON principle.
Experimental Section
The following abbreviations were used in this article and in the figures: N-methyl-2-pyrrolidone
(NMP), dichloromethane (DCM), dimethylformamide (DMF), tetrahydrofuran (THF), p-
toluenesulfonic acid (TsOH), hexamethylphosphoramide (HMPA), tetraheptylammonium
bromide (Hep NBr).
4
General. All reagents, purchased from fine chemical suppliers Aldrich, Merck, Alfa Aesar and
Fluka, were used without further purification unless otherwise stated. Zinc phthalocyanine
(ZnPc) as reference standard was purchased from Aldrich. Solvents were either used as
commercially supplied, or purified by standard techniques. Anhydrous THF was freshly distilled
over sodium/benzophenone media.
Methods. Non-aqueous reactions were performed in oven-dried glassware under argon
atmosphere at reported temperature. Microwave reactions were carried out in Milestone Start S
Microwave Labstation for Synthesis which operates at fixe frequency (2450 MHz). The
equipment can control the temperature (up to 250 ºC) in a range of power values from 0 to 1000
Watt. The reactions were carried out either in reagent grade solvents or in dry solvents if
necessary. The reactions were monitored by thin layer chromatography on Merck silica gel 60
F254 precoated aluminum sheets. Spots were visualized either by UV 254 nm light or by staining
with acidic ninhydrin solution. Column chromatography was performed on Merck silica gel 60
(230−400 mesh size) using the appropriate solvent system as eluent. Distilled technical solvents
were used as eluent for column purifications.
Melting Points. Melting points were obtained using Stuart SMP3 melting point apparatus and
were uncorrected.
Elemental Analysis. Elemental Analysis was performed on Thermo Finnigan Flash 1112 Series
Elemental Analyzer operated at The Scientific and Technological Research Council of Turkey
(TUBITAK), Marmara Research Center, Institute of Chemical Technology.
Infrared Spectroscopy. Infrared spectra were recorded on a Perkin-Elmer Spectrum 100 FT-IR
spectrometer with an attenuated total reflection (ATR) accessory featuring diamond/ZnSe plate.
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Samples were deposited as neat on ATR module and absorption maxima (νmax) were quoted in
-1
-1
wavenumbers (cm ) in the range of 4000-650 cm . Intensities of absorptions are abbreviated as
s:strong, m:medium, and w:weak.
1
13
NMR Spectroscopy. H and C nuclear magnetic resonance spectra were taken on either Varian
Unity INOVA 500 MHz or Bruker Ultrashield Plus 400 MHz FT-NMR spectrometer. Deuterated
solvents were used in all NMR measurements. Chemical shifts (δ) are reported in parts per
1
13
million (ppm) relative to residual solvent peaks as an internal reference for H- C nuclei.
Assignments were determined either on the basis of unambiguous chemical shift or coupling
patterns. Peak multiplicities are defined as s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet, br = broad and coupling constants (J) are reported in Hz.
Mass Spectra. Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass
spectra were recorded on a BRUKER Microflex LT spectrometer using reported matrixes.
Absorption Spectroscopy. Absorption spectra were recorded at room temperature on a
Shimadzu UV-2600 UV-Vis spectrometer using a 1 cm path length quartz cuvette between 200
and 900 nm. Solutions were prepared in spectro-grade solvents. Molar extinction coefficients (Ɛ)
were determined by measurement of the absorption of at least six solutions of differing
concentration for each radical, followed by determination of the slope.
Electrochemical Analyses. Electrochemical measurements were carried out on CH Instruments
8
42B model work station. The setup was conventional three-electrode cell equipped with glassy
carbon working electrode, platinum wire counter electrode, and Ag/AgNO reference electrode.
3
The glassy carbon electrode was polished routinely with 0.05 micron alumina powder/water
slurry on pads before running experiments. All measurements of samples were recorded as
reported analyte concentration in 0.1 M n-Bu NClO electrolyte solutions of dichloromethane.
4
4
Solutions were deaerated with argon purge for 5 minutes and kept under blanket of argon during
the experiments. All electrochemical measurements were performed at ambient temperature.
Ferrocene was used as internal reference and all potentials were referenced to
+
ferrocene/ferrocenium (Fc/Fc ) redox couple (E : 0.480 V vs. SCE). All potentials as E : (Epa
1
/2
1/2
+
Epc)/2 were reported versus Saturated Calomel Electrode (SCE). Scan rate was 100 mV/s for
all Cyclic Voltammetry (CV) experiments. 3 mm-diameter glassy carbon working electrode
+
(
CHI104), non-aqueous Ag/Ag reference electrode with porous teflon tip (CHI112), platinum
wire counter electrode (CHI115) and electrode polishing kit (CHI120) were purchased from CH
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Instruments. Supporting electrolyte, n-Bu NClO was purchased from Aldrich and dried at 40°C
4
4
under vacuum for days. Ferrocene was supplied by Fluka, AgNO by Carlo Erba, and anhydrous
3
dichloromethane by Aldrich.
Electron Paramagnetic Resonance (EPR) Spectroscopy. The EPR solution spectra were
recorded with Jeol JES FA 300 X-band (9.6 GHz) spectrometer, with 100 kHz magnetic field
modulation. Modulation amplitude was kept below of the estimated peak-to-peak width for all
spectra. Spectra were simulated using Jeol IsoSimu computer program to obtain the value of g,
isotropic hyperfine coupling constants (a ) and linewidth (H ). Typical concentration of the
N
p-p
-4
radicals is 10 M in dichloromethane-toluene (1:1) mixture. Solutions in spectro-grade solvent
mixture were degassed by bubbling argon through the solutions for 30 minutes. Spectra for
degassed solutions of the radicals were recorded at reported temperature.
Steady-State Luminescence Emission. Steady-state luminescence emission was recorded on a
Fluorolog-3 from Horiba-Jobin Yvon with a Time Correlated Single Photon Counting (TCSPC)
system.
Fluorescence Quantum Yield Determinations.
Fluorescence quantum yield values (F) were calculated by the comparative William’s method.
[
32]
Absorbance and luminescence spectra of the sample and a reference standard were measured
under identical conditions (absorbance at both the excitation wavelengths were 0.05). In our
study, zinc phthalocyanine (ZnPc) which have a F= 0.18 in DMSO was used as reference
standard.
Magnetic Measurements. Magnetic susceptibility data were tentatively collected on different
polycrystalline sample on a Quantum Design MPMS-XL SQUID magnetometer under an
applied magnetics field of 0.1 T and temperature range 2-300 K. All data were not significant
and of the order of magnitude of the sample holder contribution on the all temperature range
evidencing diamagnetism.
Syntheses.
The synthetic procedures for 1, 2, and 6 are provided in SI.
2
-(5,5-Dimethyl-1,3-dioxane-2-yl) -9,10,16,17,23,24-hexaneneopentoxyphthalocyanine (3):
Metallic lithium was dissolved in pentanol (50 mL) and stirred for 1 hour. Phthalonitrile 1 (1 eq.,
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Chemistry - A European Journal
10.1002/chem.201704903
0
.002 mol, 0.484 g) and phthalonitrile 2 (6 eq., 0.012 mol, 3.600 g) were added to the solution
and refluxed overnight. The intense green solution was cooled to ambient temperature and added
drop by drop into water-ethanol mixture to formed a green precipitate was collected by suction
filtration, washed with water and ethanol, to be finally dried under air stream to afford 3.800 g of
a crude green waxy solid. Crude product was purified by column chromatography on silica gel
eluting with dichloromethane-hexane mixture. Column purification gave two major products;
1
.680 g of the symmetric 2,3,9,10,16,17,23,24-octaneopentoxyphthalocyanine (4) as a green
waxy solid and 0.527 g of asymmetric 3 as green powder in 23% yield.
−
1
Phthalocyanine 4: FT-IR (ATR, νmax, cm ) : 3295w, 3077w, 2954s, 2906s, 2867m, 1600m,
1
1
491s, 1465s, 1444s, 1419m, 1391s, 1362s, 1325s, 1275s, 1260s, 1211s, 1197s, 1170m, 1098s,
053s, 1014s, 917m, 866s, 852s, 806s, 748s, 723m, 709s, 693m. MALDI-TOF MS (2,5-
+
dihydroxybenzoic acid, m/z): C H N O [calculated] 1203, [found] 1204 [M + H] .
72
98
8
8
−
1
Phthalocyanine 3: FT-IR (ATR, νmax, cm ) : 3296w, 3032w, 2956m, 2914m, 2869m, 1546s,
1
1
534s, 1471s, 1454s, 1408s, 1394s, 1378s, 1340s, 1280m, 1261s, 1218m, 1170s, 1133s, 1096s,
050m, 1018s, 850s, 799s, 766s, 742s, 647m. MALDI-TOF MS (2,5-dihydroxybenzoic acid,
+
m/z): C H N O [calculated] 1145, [found] 1146 [M + H] .
68
88
8
8
2
-(Formyl)-9,10,16,17,23,24-hexaneneopentoxyphthalocyanine (5): 3 (0.46 mmol, 0.527 g)
was stirred in F CCOOH-CH Cl mixture (40 mL-40 mL) at room temperature overnight. Green
3
2
2
mixture was poured into water. The organic phase was extracted and washed with saturated
NaHCO (aq.) solution (5 X 100 mL), then with water (10 X 100 mL), to be finally dried over
3
Na SO . Crude product was purified by column chromatography on silica gel eluting with
2
4
dichloromethane-hexane mixture (5:1). Column purification gave 0.477 g of 5 as green powder
−
1
in 98% yield. FT-IR (ATR, νmax, cm ) : 3296w, 3077w, 2954s, 2907m, 2868m, 1693s, 1607m,
1
1
1
1
583m, 1490s, 1474s, 1450s, 1393s, 1363s, 1342s, 1280m, 1260s, 1235s, 1205s, 1158s, 1132m,
1
095s, 1068s, 1049s, 1017s, 921s, 854s, 830s, 739s, 715s, 691s. H NMR (500 MHz, CDCl ): δ
3
0.40 (s, 1H, -CHO), 8.93 (s, 1H, aromatic −CH), 8.53 (d, J = 5 Hz, 1H, aromatic −CH), 8.41 (s,
H, aromatic −CH), 8.29 (s, 1H, aromatic −CH), 8.10 (m, 2H, aromatic −CH), 7.96 (s, 1H,
aromatic −CH), 7.56 (m, 2H, aromatic −CH), 4.33 (s, 2H, -CH O-), 4.31 (s, 2H, -CH O-), 4.20
2
2
(
s, 2H, -CH O-), 4.07 (s, 2H, -CH O-), 3.92 (s, 2H, -CH O-), 3.90 (s, 2H, -CH O-), 1.48 (s, 18H,
2 2 2 2
neopentyl -CH ), 1.45 (s, 9H, neopentyl -CH ), 1.41 (s, 9H, neopentyl -CH ), 1.38 (s, 18H,
3
3
3
1
3
neopentyl -CH ), -3.92 (s, 2H, -NH) ppm. C NMR (125 MHz, CDCl ): δ 192.79, 152.66,
3
3
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Chemistry - A European Journal
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1
1
7
52.48, 152.28, 152.22, 151.96, 151.93, 141.99, 137.96, 135.69, 133.20, 133.16, 129.46, 126.93,
26.72, 126.06, 126.01, 123.05, 122.21, 106.08, 105.96, 103.75, 103.54, 102.62, 102.45, 79.14,
8.83, 78.75, 78.49, 78.48, 77.73, 32.76, 32.63, 32.56, 32.53, 27.35, 27.29, 27.19 ppm. MALDI-
TOF MS (2,5-dihydroxybenzoic acid, m/z): C H N O [calculated] 1059, [found] 1060 [M +
6
3
78
8
7
+
H] . Elemental Analysis for C H N O [calculated]: C, 71.43; H, 7.42; N, 10.58. [found]: C,
6
3
78
8
7
6
9.81; H, 7.78; N, 9.23.
2
-(1-Oxyl-4,4,5,5-tetramethyl-2-imidazoline-2-yl)-9,10,16,17,23,24-
hexaneopentoxyphthalocyanine (10) : 5 (1 eq., 0.075 mmol, 0.079 g), 2,3-bis(hydroxylamino)-
,3-dimethylbutane (6) (40 eq., 3 mmol, 0.444 g), and TsOH (6 eq., 0.45 mmol, 0.086 g) were
2
charged into 25 mL flask. The reaction solution was refluxed at 70 °C under argon in a THF (10
mL) and MeOH (5 mL) mixture for two days. The reaction mixture was evaporated to dryness.
The green residue was dissolved in CH Cl (150 mL) and washed firstly with 10% ethanol-water
2
2
mixture (2 X 100 mL), then with saturated NaHCO (aq.) solution (1 X 100 mL), finally with
3
water (3 X 100 mL) and then dried over Na SO , evaporated to dryness under vacuum to give a
2
4
green powder. FT-IR and MALDI-TOF MS analyses of the green powder (as crude product)
confirm the identity of as 2-(1-hydroxy-4,4,5,5-tetramethyl-2-imidazoline-2-yl)-
8
−
1
9
3
1
,10,16,17,23,24-hexaneneopentoxyphthalocyanine . FT-IR (ATR, νmax, cm ) of compound 8:
296w, 3081w, 2954s, 2907m, 2868m, 1607m, 1488s, 1474s, 1451s, 1393s, 1363s, 1329s,
279s, 1260s, 1208s, 1173s, 1096s, 1047s, 1015s, 920s, 855s, 811m, 788m, 742s, 716s, 698s.
MALDI-TOF MS (trans-2-[3-(4-tert -butylphenyl)-2-methyl-2-propenylidene]-malononitrile,
+
m/z): C H N O [calculated] 1171, [found] 1171 [M] .
69
90 10
7
The crude product of 8 was subjected to PbO oxidation without further purification. 8 was
2
suspended in CH Cl (250 mL) in 1 L flask and PbO (200 eq., 3.6 g) was added as a suspension.
2
2
2
The mixture was stirred vigorously at room temperature for 3 days in the dark. It was filtered on
Celite-plug and washed with CH Cl . The green solution was evaporated to dryness. Crude
2
2
product was purified with plaque chromatography on silica gel eluting with dichloromethane-
methanol mixture (200:1). The plaque purification gave 0.033 g of 10 as green powder in 38%
−
1
yield (from aldehyde). FT-IR (ATR, νmax, cm ): 3296w, 3081w, 2955s, 2925m, 2867m, 1736w,
1
1
608w, 1491s, 1474s, 1451s, 1393s, 1363s, 1329m, 1279s, 1260s, 1209m, 1171s, 1097s, 1049s,
016s, 920m, 873s, 855s, 796s, 743s, 717s, 698s. MALDI-TOF MS (trans-2-[3-(4-tert -
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Chemistry - A European Journal
10.1002/chem.201704903
butylphenyl)-2-methyl-2-propenylidene]-malononitrile, m/z): C H N O [calculated] 1170,
69
89 10
7
+
[
found] 1171 [M+H] . Elemental Analysis for C H N O [calculated]: C, 70.80; H, 7.66; N,
69 89 10 7
1
1.97. [found]: C, 71.70; H, 7.98; N, 11.62.
Acknowledgement
The authors acknowledge the Scientific and Technical Research Council of Turkey (TÜBİTAK)
through the project 114Z767 and the COST action CM1305 “ECOSTBio” for their financial
support
Conflict of interest
The authors declare no conflict of interest.
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Graphical abstract:
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