Synthesis and photophysical properties of novel unsymmetrical metal-free and metallophthalocyanines

Article abstract of DOI:10.1016/j.jorganchem.2013.11.004

The synthesis of novel, unsymmetrical, octasubstituted metal-free and metallo phthalocyanines (zinc, manganese) bearing two ethynylthiophene moieties and six hexylthio substituents was achieved by a statistical condensation reaction of 4,5-di(hexylthio) p

Full text of DOI:10.1016/j.jorganchem.2013.11.004

Accepted Manuscript
Synthesis and Photophysical Properties of Novel Unsymmetrical Metal-free and
Metallophthalocyanines
İbrahim Özçeşmeci, Ayfer Kalkan Burat, Zehra Altuntaş Bayır
PII:
S0022-328X(13)00801-2
10.1016/j.jorganchem.2013.11.004
JOM 18348
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 25 July 2013
Revised Date: 4 October 2013
Accepted Date: 5 November 2013
Please cite this article as: İ. Özçeşmeci, A.K. Burat, Z.A. Bayır, Synthesis and Photophysical Properties
of Novel Unsymmetrical Metal-free and Metallophthalocyanines, Journal of Organometallic Chemistry
(2013), doi: 10.1016/j.jorganchem.2013.11.004.
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Graphical abstract Synopsis
Synthesis and Photophysical Properties of a Novel Unsymmetrical, Metal-free and
Metallophthalocyanines
İbrahim Özçeşmeci, Ayfer Kalkan Burat and Zehra Altuntaş Bayır*
Department of Chemistry, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
Graphical Abstract
Novel, unsymmetrical, octasubstituted phthalocyanines bearing two ethynylthiophene
moieties and six hexylthio substituents have been prepared and characterized. The
aggregation properties of these compounds were investigated. General trends for fluorescence
quantum yields and lifetimes of these phthalocyanines are also described. The fluorescence of
these compounds is effectively quenched by 1,4-benzoquinone.

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Graphical abstract

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Synthesis and Photophysical Properties of Novel Unsymmetrical Metal-free and
Metallophthalocyanines
İbrahim Özçeşmeci, Ayfer Kalkan Burat and Zehra Altuntaş Bayır*
*Istanbul Technical University, Faculty of Science and Letters, Department of Chemistry, 34469
Maslak, Istanbul, Turkey
Abstract
The synthesis of novel, unsymmetrical, octasubstituted metal-free and metallo
phthalocyanines (zinc, manganese) bearing two ethynylthiophene moieties and six hexylthio
substituents was achieved by a statistical condensation reaction of 4,5-di(hexylthio)
phthalonitrile with 4,5-bis(thiophen-3-ylethynyl)phthalonitrile in the presence of zinc and
manganese salts (without metal salt for metal-free phthlocyanine). 4,5-Bis(thiophen-3-
ylethynyl)phthalonitrile was obtained through Sonogashira coupling reaction. The new
compounds have been characterized by using elemental analyses, mass, proton nuclear
magnetic resonance (1H-NMR), fourier transform infrared spectroscopy (FT-IR) and
ultraviolet–visible spectroscopy (UV-vis) techniques. The aggregation properties of the
compounds were investigated in different concentrations in tetrahydrofuran before and after
addition of surfactant Triton X-100. General trends for fluorescence quantum yields and
lifetimes of unsymmetrical phthalocyanines (metal-free and zinc) are also described in
tetrahydrofuran (THF). The fluorescence of these compounds is effectively quenched by 1,4-
benzoquinone (BQ) in THF.
Keywords: Ethynylthiophene, manganese, phthalocyanine, Sonogashira-coupling,
unsymmetric, fluorescence.
*Corresponding author:Tel: +90 212 285 32 23; fax: +90 212 285 63 86.
E-mail address:bayir@ itu.edu.tr (Z. A. Bayır)
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1. Introduction
Phthalocyanines (Pcs) are an important class of organic materials. They have a
conjugated system of π-electrons and exhibit the ability to chelate metal ions at the center of
the ring [1-3]. Since their accidental discovery phthalocyanines have been used extensively as
dyes and pigments in indusrty due to their blue-green color [4, 5]. Phthalocyanines have
found widespread industrial and medical applications, namely, chemical sensors, display
devices, catalysts, data storage systems, and photosensitizers for photodynamic therapy (PDT)
[6-14].
Despite the variety of synthetic routes developed to prepare symmetrcally substituted
phthalocyanines, relatively few methods can be applied for preparing unsymmetrical
phthalocyanines [15]. More recently, particular attention has been paid to the development of
unsymmetrical phthalocyanines. This is because such phthalocyanines possess a number of
unique physicochemical properties and improved organization capabilities, which render
these compounds valuable applications in materials science, in particular in photodynamic
therapy and non-linear optics for optical limiting applications [8, 16, 17].
The random condensation of two differently substituted phthalonitriles A and B is the
most frequent method of the synthesis of unsymmetrical phthalocyanines. Although this
method has been widely used for the synthesis of A3B-type Pcs, it is often laborious, due to
difficulty in separating similar chemical structures [18]. The second method is ring expansion
of subphthalocyanines (SubPcs) developed by Kobayashi [19,20]. SubPcs are commonly used
to form the unsymmetrically substituted phthalocyanines by ring expansion employing
substituted phthalonitriles or diiminoisoindolines [21]. Good yields were obtained when the
SubPc was treated with phthalonitriles or diiminoisoindolinesin the presence of a strong base,
such as DBU, and a metal salt [22]. The last method is a polymer-support route in which one
of the Pc precursors is covalently attached to a polymer support prior to the synthesis of
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phthalocyanine [23]. Following the synthesis of macrocycle, the polymer-bound Pc is
obtained by filtration and the bond to the polymer is cleaved to yield pure 3:1
unsymmetrically substituted phthalocyanines. However, this method has not seen widespread
application and only a few examples have been reported to date.
We have previously reported the synthesis of different unsymmetrical pthalocyanines
bearing phenylethynyl [24], and morpholine groups [25] as peripheral substituents. In this
regard, we report herein the synthesis of A3B type unsymmetrically substituted metal-free (3)
and metallophthalocyanines (4, 5) carrying six hexylthio and two ethynylthiophene
substituents on the periphery. We also report spectroscopic characterization, aggregation
behavior as well as photophysical (fluorescence quantum yields and lifetimes) and quenching
properties of novel unsymmetrical, octasubstituted phthalocyanines complexes.
2. Experimental
All chemicals and reagents were purchased from major suppliers and used without any
1
further purification. All reported H NMR spectra were recorded on an Agilent VNMRS 500
MHz spectrometer. Chemical shifts (δ, ppm) were determined with TMS as the internal
reference. IR spectra were recorded on a Perkin-Elmer Spectrum One FT-IR (ATR sampling
accessory) spectrophotometer, electronic spectra were recorded on a Scinco LabProPlus
UV/Vis spectrophotometer. Fluorescence spectra were recorded on a Perkin-Elmer LS55
fluorescence spectrophotometer. Mass spectra were measured on a Bruker microflex LT
MALDI-TOF MS spectrometer and Perkin Elmer Clarus 500 mass spectrometer. The isotopic
patterns for all assigned signals are in agreement with the calculated natural abundance. Data
have been given for the most abundant isotope only. Silica gel (Kieselgel 60, 200–400 mesh)
was used in the separation and purification of compounds by column chromatography. The
homogeneity of the products was tested in each step by TLC. 4,5-Di(hexylthio)phthalonitrile
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(1) [26] and 4,5-bis(thiophen-3-ylethynyl)phthalonitrile (2) [27] were prepared according to
the reported procedures.
2.1 2,3,9,10,16,17-Hexakis(hexylthio)-23,24- bis(thiophen-3-ylethynyl)-29H, 31H-
phthalocyanine (3)
A mixture of dinitrile 1 (0.486 g, 1.45 mmol), dinitrile 2 (0.102 g, 0.30 mmol) and
o
lithium metal (1.5 mg, 0.5 mmol) in n-pentanol (1.5 mL) was heated at 145 C with stirring
for 2 h under N2. The resulting green suspension was cooled to ambient temperature. The
reaction mass was then dissolved in dimethylformamide (DMF) (1 mL) and poured into 200
ml ice-water mixture with the addition of 4 mL conc. hydrochloric acid (HCl). In this mixture,
the Li2Pcs formed was converted into H2Pcs. The precipitate was filtered off and washed with
cold methanol and then dried in vacuo. The purification was carried out by column
chromatography on silica gel using hexane/chloroform (CHCl3) (1:6) as the eluent to afford 3
o
as a green solid. The yield was 10.53 % (0.045 g). M.p.>200 C. IR, (cm-1): 3289 (N-H),
1
2955-2854 (Aliph.-H), 2206 (C≡C), 1260 (Ar-S-Aliph.), 741; H NMR (CDCl3-d6), δ, ppm:
8.38-7.18 (m, 14H, Ar-H), 3.47-3.01 (m, 12H, S-CH2), 1.59-1.25 (m, 48H, -CH2), 0.89 (b,
18H, -CH3), -5.00 (b, 2H, -NH); UV-Vis (tetrahydrofuran (THF)) : λmax/ nm (log ε, L. mol-1
cm-1): 282 (4.88), 327 (4.79), 700 (4.70), 723 (4.69); Anal. calc. for C80H94N8S8: C, 67.47; H,
6.65; N, 7.87. Found: C, 67.56; H, 6.60; N, 7.82; MS: m/z 1423.15 [M]+.
2.2 2,3,9,10,16,17-Hexakis(hexylthio)-23,24-bis(thiophen-3-ylethynyl)-29H, 31H-
phthalocyaninato zinc (II) (4)
A mixture of phthalocyanine (3) (0.100 g, 0.07 mmol) and anhydrous zinc(II)acetate
o
(Zn(CH3COO)2) ( 0.038 g, 0.21 mmol) in dried DMF (2 mL) was heated at 145 C with
stirring for 6 h under N2. The resulting blue suspension was cooled to ambient temperature.
The reaction mass was then poured into 100 mL ice-water mixture. The precipitate was
filtered off and washed with cold water, ethanol and hexane. After dried in vacuo, the
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purification was carried out by column chromatography on silica gel using hexane/THF (1:4)
o
as the eluent to afford 4 as a blue solid. The yield was 45.31 % (0.047 g). M.p.>200 C. IR,
1
(cm-1): 2953-2853 (Aliph.-H), 2206 (C≡C), 1259 (Ar-S-Aliph.), 740; H NMR (CDCl3-d6), δ,
ppm: 8.35–7.19 (m, 14H, Ar-H), 3.13-2.78 (m, 12H, S-CH2), 1.61-1.18 (m, 48H, -CH2), 0.81
(b, 18H, -CH3); UV-Vis (THF): λmax/ nm (log ε, L. mol-1 cm-1): 280 (4.79), 367 (4.90), 705
(5.31); Anal. calc. for C80H92N8S8ZnC, 64.59; H, 6.23; N, 7.53. Found: C, 64.56; H, 6.21; N,
7.55; MS: m/z 1485.57 [M]+.
2.3 2,3,9,10,16,17-Hexakis(hexylthio)-23,24- bis(thiophen-3-ylethynyl)-29H, 31H-
phthalocyaninatomanganese-(III)chloride (5)
A mixture of phthalocyanine (3) (0.100 g, 0.07 mmol) and manganese(II) chloride
o
(MnCl2) ( 0.026 g, 0.21 mmol) in dried DMF (2 mL) was heated at 145 C with stirring for 6
h under N2. The resulting brown suspension was cooled to ambient temperature. The reaction
mass was then poured into 100 mL ice-water mixture. The precipitate was filtered off and
washed with cold water, ethanol and hexane. After dried in vacuo, the purification was carried
out by column chromatography on silica gel using hexane/THF (1:3) as the eluent to afford 5
o
as a brown solid. The yield was 38.02 % (0.040 g). M.p.>200 C. IR, (cm-1): 2954-2852
(Aliph.-H), 2207(C≡C), 1261 (Ar-S-Aliph.), 741; UV-Vis (THF): λmax/ nm (log ε, L. mol-1
cm-1): 293 (5.24), 321 (5.14), 425 (4.90), 470 (4.87), 500 (4.81), 758 (5.13); Anal. calc. for
C80H92ClMnN8S8: C, 63.53; H, 6.13; N, 7.41. Found: C, 63.57; H, 6.16; N, 7.45; MS: m/z
1532.85 [M+Na]+, 1477.63 [M-Cl]+
3. Results and Discussion
3.1 Synthesis and characterization
There are three approaches for preparing unsymmetrically substituted
phthalocyanines: a statistical cyclization reaction of two different types of phthalonitriles [28],
a solid-state reaction of two types of phthalonitriles on macromolecular carriers [29] and a
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ring-expansion treatment of subphthalocyanine with diiminoisoindoline [30,31]. In this work
the statistical cyclization approach was used to synthesis of unsymmetrical Pcs. The rationale
behind this choice is that both nitriles significantly differ in polarity.
4,5-Di(hexylthio)phthalonitrile (1) and 4,5-bis(thiophen-3-ylethynyl)phthalonitrile (2)
were chosen as starting materials. It is well known that alkythio groups act as electron
releasing, enhance the solubility of phthalocyanine in common organic solvents and reduce
the aggregation of phthalocyanine. The insertion of alkylthio groups also facilitates the
isolation of the desired A3B product. The presence of ethynylthiophene moieties causes an
extended π- conjugation on phthalocyanine complexes. The combination of the sulfur atoms
and the alkynyl group influence the electronic spectra of Pcs and cause red shifting of the Q-
band. Compound 1 was prepared from 4,5-dichlorophthalonitrile and hexanethiol in DMF at
room temperature for 12 h. potassium carbonate (K2CO3) was used as the base for this
nucleophilic aromatic displacement [26]. The synthesis of nitrile 2 was accomplished in 35%
yield through Sonogashira cross-coupling reaction of 4,5-dichlorophthalonitrile with 3-
ethynylthiophene in triethylamine using bis(triphenylphosphine)palladium(II)chloride and
copper(I)iodide as catalysts [27]. The reaction was carried out 90 oC under N2 for 48 h.
The most usual method to prepare metal-free phthalocyanines is the
cyclotetramerisation of a phthalonitrile or diiminoisoindoline. A practical way of achieving
this goal is the treatment of a phthalonitrile with lithium alkoxide, giving rise to the
corresponding alkali metal phthalocyanines and it can be subsequently demetallated to the
metal-free phthalocyanine with a mineral acid. In the present work, the latter was chosen for
synthesising the A3B type metal-free phthalocyanine (3). The mixed condensation of 4,5-
di(hexylthio)phthalonitrile (1) with 4,5-bis(thiophen-3-ylethynyl)phthalonitrile (2) by using
lithium in 1-pentanol, and then acidification with HCl resulted with the formation of 3
(Scheme 1). A 3:1 ratio of the two precursors was used to modify the relative amounts of the
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individual species, which are present within the reaction mixture [32,33]. The reaction of
◦
metal-free phthalocyanine (3) with metal salts (Zn(CH3COO)2, MnCl2) in DMF at 145 C
under N2 led to the formation of desired unsymmetrical metallophthalocyanines (4 and 5),
respectively (Scheme 1). All of these new phthalocyanine compounds were purified by
column chromatography. They were obtained in moderate yields (11% for 3, 45.3 % for 4,
and 38% for 5) and were characterized by elemental analysis and by their spectral data (1H
NMR, IR, mass and UV-Vis spectra). The data are consistent with the assigned structures.
In the IR spectrum of compound 1 (and 2) the intense absorption band around 2233
cm−1 corresponding to C≡N vibrations, disappears after its conversion into the
phthalocyanines. The IR spectra of the phthalocyanines 3-5 are very similar, except the metal-
free (3), showing an NH stretching band peak at 3290 cm−1 in the inner core. The presence of
alkylthio side chains was confirmed by the observation of an intense aliphatic C-H stretching
around 2950-2850 cm-1 in the IR spectra of 3-5. The C≡C vibration was observed around
2200 cm-1.
The 1H NMR spectra of compounds 3 and 4 are consistent with the proposed structure.
1
In the H NMR spectrum of metal-free phthalocanine (3) in CDCl3 exhibited the aromatic
protons at around 8.38-7.18 ppm as multiplet, the aliphatic SCH2 and SCCH2 protons of
hexylthio group at 3.47 and 1.39 ppm as a triplet and a quintet, resectively, and the aliphatic
CH3 protons as a triplet at 0.89 ppm. The inner core protons of free-base phthalocyanine were
monitored at around −5.00 ppm. For compound 4, the aromatic protons of phthalocyanine
core appeared at 8.35–7.19 ppm, the SCH2 and SCCH2 protons at 3.13and 1.61 ppm,
respectively, and the CH3 protons at 0.81 ppm.
The elemental analysis and the mass spectra confirmed our structural assignment. The
peaks for the molecular ion were found at m/z= 1423.15 [M]+ for the phthalocyanine 3
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(Figure 1), 1485.57 [M]+ for 4, m/z= 1532.85 [M+Na]+ and m/z= 1477.63 [M-Cl]+ for 5
(Figure 1), respectively.
3.2 Ground state electronic absorption spectra
In substituted metal-free and MPcs, strong absorption bands are detected in the visible
region between the 600 and 700 nm, referred to as the Q band, and in the UV region between
300 and 350 nm, called the B (Soret) band [34-36]. The electronic absorption spectra of 4, 5
recorded in THF exhibit intense Q bands at 705 (4), and 758 nm (5) and the B bands in the
UV region, around 350 nm. The UV-Vis spectrum of manganese phthalocyanine 5 is clearly
different from the spectrum of the zinc phtalocyanine (4). The oxidation state of Mn in the
complex with Pc is +3, whereas the other metal Zn is in oxidation state +2. The Q band of
MnPc (5) is shifted by 30-50 nm compared the Q band of the other phthalocyanines 3 and 4.
Furthermore, MnPc 5 shows absorption at 425 nm, 470 nm and 500 nm which was interpreted
as a charge transfer absorption (phthalocyanine→metal, LMCT) [37-39]. For the metal-free
phthalocyanine 3 in THF, a split Q band observed at 700 nm and 723 nm, while the B-band
remained at 350 nm [40]. The UV-Vis spectra of compounds 3-5 in THF are shown in Figure
2. The presence of long hexylthio substituents in phthalocyanines 3–5 results in dramatic
increase of solubility of these compounds in various common organic solvents compared with
their symmetrical analogues which were synthesized in our recent work [27]. The Q bands of
these new species are shifted to the blue compared with their symmetrical analogues which
were synthesized in our recent work [27]. For the zinc (4) and mangenese (5)
phthalocyanines, the Q-band positions are 705 and 758 nm, respectively. However the Q-band
position of symmetrical analogues were observed around 722 nm for zinc and 775 nm for
manganese phthalocyanine. Zn (II) (4) and Mn (III) (5) phthalocyanines have the same blue
shifts (17 nm) compared with their symmetrical analogues [27].
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When we compare the absorption bands of current phthalocyanines (1-3) with
unsubstituted metal-free, Zn(II) and Mn(III) phthalocyanines [1], a significant red shift in Q
band wavelengths were observed. The Q bands of 1-3 are shifted bathochromically because of
the conjugation of the macrocyclic core and the ethynyl linkers [41]. The extension of the
aromatic system was found to causes a shift of the Q-band maximum of about 70–80 nm [1,
27]. In our case, the bathochromic shifts of Q bands were observed around 60 nm for 1, 40 nm
for 2 and 50 nm compound 3.
3.3 Aggregation Studies
Weaker absorptions of Pc’s compound on the lower wavelength side of Q bands
indicate the presence of aggregated species which are generally observed together with the
main Q bands essentially responsible for the intense absorption occurring due to the
monomeric species [42]. When the electronic spectra of the metal-free phthalocyanine (3) and
its metallo derivatives (4, 5) were examined, weak peaks were observed around 620-640 nm
just on the higher energy side of the strong Q band. In order to see whether these bands are a
consequence of aggregation or not has been investigated by measuring absorption spectra in a
concentration range [43]. In the concentration ranges studied (10 – 01 x 10-6 M) for 4 (Figure
3a ) and (20 - 1.25 x 10-6 M) for 5 (Figure 3b), no aggregation tendency has been discovered
as the appearance of the Q-band absorption maxima remained unchanged as the concentration
increases, as well as its apparent molar extinction coefficient remains almost constant
indicating purely monomeric form which obeyed the Beer–Lambert Law in the outlined range
of concentration (Figure 3c) [44]. In order to verify the presence of aggregation, Triton X, a
surfactant, has been added to the Pc solutions as given in Figure 3d, but the results indicate no
appreciable aggregation which can be decomposed by the addition of Triton X. By evaluating
these observations, it can be clearly concluded that the phthalocyanine derivatives (3-5) did
not show aggregation behaviour in THF at different concentrations [45].
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3.4 Fluorescence Spectra
The fluorescence behavior of zinc phthalocyanine complexes (3 and 4) was studied in
THF, upon excitation at the 670 nm Q-band vibration for 3 and excitation at the 635 nm Q-
band vibration for 4. Figure 4 shows the absorption, fluorescence emission and excitation
spectra for complex 3 and 4 in THF. Fluorescence emission peaks were observed at 736 nm
for 3 and 718 nm for 4 (Table 1). The observed Stokes shifts were within the region ∼10-15
nm observed for phthalocyanine complexes and they were typical of phthalocyanine
complexes [46]. Excition spectrum of 3 show two shoulder in the red spectral region and
emission maxima of 3 appears at lower energy than those of the corresponding metallo
derivative (4). It means that metal-free phthalocyanines shows red shift in emission maxima
compared to metallophthalocyanines because of symmetry lowering [47]. The proximity of
the wavelength of each component of the Q-band absorption to the Q-band maxima of the
excitation spectra for 4 suggest that the nuclear configurations of the ground and excited
states are similar and are not affected by excitation in THF.
Fluorescence quantum yields (ΦF) were determined by the comparative method (Eq.
(1)) [48]: ΦF = ΦF(Std) (FAStdη2 / FStdAη2
)
(1)
Std
where F and FStd are the areas under the fluorescence curves of phthalocyanines derivatives
and the standard, respectively. A and AStd are the respective absorbances of the sample and
standard at the excitation and η and ηStd are the refractive indices of solvents used for the
sample and standard, respectively. ZnPc was employed as a standard in DMF (ΦF = 0.23)
[49]. Both the sample and the standard were excited at the same wavelength. Radiative or
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natural lifetimes (τo) were estimated using PhotochemCAD program which uses the Strickler-
Berg equation [50]. Finally, the fluorescence lifetimes (τF) were calculated using the
following equation (Eq. (2)):
ΦF = τF / τo
(2)
The fluorescence quantum yields (ΦF) of 3 and 4 are given in Table 1. The measured
fluorescence quantum yields for 3 and 4 were lower than those for ZnPc, for which, in DMF
and unsubstituted ZnPc in THF [51], both quantum yield of 0.23 and 0.25 respectively at
room temperature. This implies that the presence of peripheral ethynylthiophene and
hexylthio substituents caused some fluorescence quenching of the parent 3 and 4. The ΦF
values of the Zn (II) Pc compound (4) are higher than for the metal-free Pc compound (3)
[52].
Fluorescence lifetime (τF) refers to the average time a fluorophore stays in its excited
state before fluorescing, and its value is directly related to that of fluorescence quantum yield.
Such factors include internal conversion and intersystem crossing shorten the fluorescence
lifetime of a fluorophore indirectly decreases the value of ΦF. As a result, the nature and the
environment of a fluorophore determine its fluorescence lifetime. The τF values of the Pc
complexes 3 and 4 (1.21 and 0.04 ns, respectively) are lower compared to unsubstituted ZnPc
complexes in THF [53], suggesting more quenching by substitution. The natural radiative
lifetime (τo) and the rate constants for fluorescence (kF) values were also shown in Table 1.
The kF values of studied phthalocyanine complexes (3 and 4) are higher than unsubstituted
ZnPc in THF.
3.5 Fluorescence quenching studies by 1,4-benzoquinone (BQ)
Fluorescence quenching experiments on phthalocyanine complexes (3 and 4) were
carried out by the addition of different concentrations of BQ to a fixed concentration of the
complex, and the concentrations of BQ in the resulting mixtures were 0, 0.01, 0.02, 0.03, 0.04
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and 0.05 M, respectively. The fluorescence spectra of compound 3-4 at each BQ
concentration were recorded, and the changes in fluorescence intensity related to BQ
concentration by the Stern–Volmer (SV) equation [54]:
(3)
where I0 and I are the fluorescence intensities of fluorophore in the absence and presence of
quencher, respectively. [BQ] is the concentration of the quencher and KSV is the Sterne-
Volmer constant which is the product of the bimolecular quenching constant (kq) and the τF
and is expressed in Eq. (4):
(4)
The ratios of I0/I were calculated and plotted against [BQ] according to Eq. (4), and
KSV is determined from the slope.
The fluorescence quenching of studied phthalocyanine complexes (3 and 4) by benzoquinone
(BQ) in THF was found to obey Stern-Volmer kinetics, which is consistent with diffusion-
controlled bimolecular reactions. Figure 5 shows fluorescence emission spectral changes of 3
and Figure 6 shows fluorescence emission spectral changes of 4 on addition of different
concentrations of BQ in THF. The Stern-Volmer plots for studied complexes (3 and 4) gave
straight lines, depicting diffusion controlled quenching mechanisms (Figure 5-6). The slope of
the plots shown at insert Figures 5 and 6 gave KSV values, listed in Table 1. The bimolecular
quenching constant (kq) values for the BQ quenching of phthalocyanine complexes in THF
are also listed in Table 1. The KSV values of the phthalocyanine complexes 3 and 4 are lower
than unsubstituted ZnPc in THF.
4. Conclusion
In this study, A3B type metal-free and metallophtalocyanines (3-5) wee successfully
prepared
from
4,5-di(hexylthio)phthalonitrile
(1)
and
4,5-bis(thiophen-3-
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ylethynyl)phthalonitrile (2). The statistical condensation reaction leads to a mixture of
variously substituted phthalocyanine products. Thereby, it turned out that the choice of the
phthalonitrile precursors having appropriate solubilizing groups plays a crucial role in the
separation of the desired 3:1 type Pc from the mixture of different Pcs formed during the
cyclotetramerization reaction. Desired A3B type phthalocyanines (3-5) have been obtained in
moderate yields after purifications. The synthesized, phthalocyanine complexes show very
good solubility in a number of solvents such as THF, CHCl3, dichloromethane. We show that
the presence of sulfur atoms and ethynylthiophene groups at the peripheral positions of the
phthalocyanine ring resulted in a shift of the Q-band to the near-IR region. The aggregation
behavior, photophysical and photochemical properties of these novel A3B type metal-free and
metallophtalocyanines (3-5) have been also investigated. The phthalocyanines 3 and 4 show
lower fluorescence quantum yields and shorter lifetimes when compared to unsubstituted zinc
phthalocyanine in THF. The fluorescence of 3 and 4 are effectively quenched by 1,4-
benzoquinone in THF.
Acknowledgements
This work was supported by the Research Fund of the Technical University of Istanbul.
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Table Captions
Table 1. Excitation spectra, emission spectra, photophysical and photochemical parameters
along with fluorescence quenching data for 3 and 4 in THF.
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Table(s)
Stokes
shift
(nm)
Excitation
λ Ex, (nm)
Emission
λ Em, (nm)
Comp.
ΦF
τF (ns) τo (ns)
kF (s-1)(x108)a
KSV
kq/ (x1011 s-1)
719
706
736
718
13
0.13
0.22
1.21
0.04
8.99
0.16
1.11
55.00
0.92b
17.34
43.12
48.48b
0.14
10.78
1.78b
3
4
12
7b
666b
673b
0.25b 2.72b 10.9b
ZnPcb
a kF is the rate constant for fluorescence. Values calculated using kF = ΦF/τF.
b Ref. [50].
Table 1.
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Figure and Scheme Captions
Figure 1.
Figure 2.
Figure 3.
Mass spectra of 3 and 5.
Absorption spectra of 3-5 in THF( 1.0 x 10-5 M).
Aggregation study of 3-5 in THF ( a- Aggregation behavior of 4 in THF at
different concentrations. b- Aggregation behavior of 5 in THF at different
concentrations. c- Plot of the Log ε of 3-5 against concentration. d- Changes in
the absorption spectra of 3 by the addition of Triton X-100 ( 1.0 x 10-5 M) ).
Excitation and emission spectra for compound 3 and 4 in THF. Excitation
wavelength = 670 nm for 3 and 635 nm for 4 in THF.
Figure 4.
Figure 5.
Fluorescence emission spectral changes of 3 (10-6 M) on addition of different
concentrations of benzoquinone (BQ) in THF. [BQ] = 0, 0.01, 0.02, 0.03, 0.04,
0.05 M. ( İnsert figure, Stern–Volmer plots for BQ quenching of 3. )
Fluorescence emission spectral changes of 4 (10-6 M) on addition of different
concentrations of benzoquinone (BQ) in THF. [BQ] = 0, 0.01, 0.02, 0.03, 0.04,
Figure 6.
0.05 M. ( İnsert figure, Stern–Volmer plots for BQ quenching of 4. )
o
.Scheme 1. The synthesis of phthalocyanine complexes (3-5). (i) Li, 1-pentanol, 140 C, 2
h, HCl ii) Zn(CH3COO)2, DMF, 140 oC, 6h iii) MnCl2, DMF, 140 oC, 6h. )
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Figures
Figure 1.
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Figure 2.
Figure 3.
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Figure 4.
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Figure 5.
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Figure 6.
Scheme
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S
S
S
CN
CN
NC
NC
+
A
B
S
i
S
S
S
S
S
S
N
N
N
N
N
Zn
N
N
S
S
S
ii
H
N
N
N
N
H
N
S
N
N
N
N
S
S
S
S
S
S
M= 2H (3)
M= Zn (4)
iii
S
S
S
N
N
N
Mn
N
S
S
Cl
N
N
N
N
S
S
S
M= Mn (5)
Scheme 1.
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Research Highlights
ꢀ Unsymmetrical phthalocyanines bearing ethynylthiophene moieties were synthesized.
ꢀ These phthalocyanines show the enhanced solubility in organic solvents.
ꢀ Aggregation properties of these compounds were investigated.
ꢀ Photophysical properties of these phthalocyanines have been investigated.
ꢀ The fluorescence quenching behaviour of these phthalocyanines were also reported.