The synthesis, photophysical and electrochemical studies of symmetrical phthalocyanines linked thiophene substituents

Article abstract of DOI:10.1016/j.ica.2014.08.014

Tetrakis 4-(3-thienyl) and tetrakis 4-(5′-hexyl-2,2′- bithiophene) peripherally substituted zinc phthalocyanines were synthesized by using phthalonitrile derivatives. The phthalonitrile compounds were obtained through palladium catalyzed Suzuki-Miyaura cr

Full text of DOI:10.1016/j.ica.2014.08.014

Inorganica Chimica Acta 423 (2014) 139–144
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
The synthesis, photophysical and electrochemical studies of symmetrical
phthalocyanines linked thiophene substituents
Sadik Cogal a,d, Kasim Ocakoglu b,c, Aysegul Uygun Oksuz d,
⇑
a
Mehmet Akif Ersoy University, Faculty & Arts and Science, Department of Chemistry, 15030 Burdur, Turkey
Advanced Technology Research & Application Center, Mersin University, Ciftlikkoy Campus, 33343 Yenisehir, Mersin, Turkey
Mersin University, Tarsus Faculty of Technology, Department of Energy Systems Engineering, 33480 Mersin, Turkey
Suleyman Demirel University, Faculty of Arts and Science, Department of Chemistry, 32260 Isparta, Turkey
b
c
d
a r t i c l e i n f o
a b s t r a c t
0
0
Article history:
Received 25 June 2014
Received in revised form 12 August 2014
Accepted 13 August 2014
Available online 21 August 2014
Tetrakis 4-(3-thienyl) and tetrakis 4-(5 -hexyl-2,2 -bithiophene) peripherally substituted zinc phthalocy-
anines were synthesized by using phthalonitrile derivatives. The phthalonitrile compounds were
obtained through palladium catalyzed Suzuki–Miyaura cross-coupling reaction. The synthesized phthal-
1
ocyanines were characterized by FT-IR, H NMR and MALDI-TOF-MS methods. The absorption and emis-
sion properties were studied by using UV–Vis absorption and photoluminescence spectroscopies. The
electrochemical behaviors of compounds were also investigated using cyclic voltammetry (CV) measure-
ments. The 5 -hexyl-2,2 -bithiophene substituent shifted the absorption band to red region and decreased
the HOMO–LUMO energy gap of phthalocyanines.
Keywords:
Phthalocyanine
Thiophene
0
0
Ó 2014 Elsevier B.V. All rights reserved.
Phthalonitrile
1
. Introduction
Phthalocyanines (Pc) and metallophthalocyanines (MPc) have
areas. Özçe ßs meci et al. reported the synthesis and electrochemical
properties of phthalocyanines with ethynylthiophene substituent
on periphery position and found that the metal center of the
phthalocyanines affects the polymerization process [12]. Yavuz
et al. synthesized the tetrakis 4-(2,5-di-2-thiophene-2-yl-pyrrol-
1-yl) substituted nickel phthalocyanine (NiPc-SNS) and this mole-
cule was polymerized by electrochemical method [13]. Muto et al.
reported the synthesis of octabutoxyphthalocyanines having eight
received much attention as functional materials for various appli-
cations, including catalysis, photodynamic therapy, chemical sen-
sors, and solar cells [1–4]. Such applications are based on unique
optical, electrical, physical, chemical, and biological properties of
the phthalocyanines [5,6]. Furthermore, the properties of Pcs can
be altered by the introduction of appropriate substituents at the
periphery of the phthalocyanine and by metal insertion. Many dif-
ferent substituents and over seventy metals used to modify the
properties of phthalocyanine molecules and to enhance their
potential application areas [7,8]. However, much less effort has
been focused on the directly substitution of phthalocyanine at
the b positions with thiophene derivatives [9,10]. Thiophenes have
0
2-thienyl and [2,2 -bithiophene]-5-yl groups at b positions and
investigated their electrochemical and spectral features [10].
In this work, we have synthesized new symmetrical phthalocy-
0
0
anines linked 3-thienyl and 5 -hexyl-2,2 -bithiophene groups at
peripheral positions. The electrochemical behavior, absorption
and emission properties of the phthalocyanines were investigated
by using CV, UV–Vis and PL measurements.
been widely investigated
p-conjugated organic molecules due to
their stability and the fact that their synthetic chemistry has been
well-defined [11]. In addition, their structural planarity permits
strong electronic conjugation within the structure. For these rea-
sons, substitution of thienyl groups at the b positions of the Pc ring
2
. Experimental
2.1. Materials
could result in the extension and refinement of the p-systems [10].
On the other hand, if the 2 or/and 5 position of the thiophene moi-
ety is suitable, the phthalocyanine polymer films can be prepared
by electrochemical method on electrodes for various application
0
0
4
-Aminophthalonitrile, 3-thiopheneboronic acid, 5 -hexyl-2,2 -
bithiophene boronic acid pinacol ester, CHCl , THF, Hexane,
Pd(PPh , dimethoxy ethane (DME), 2-dimethylaminoethanol
DMAE), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU), zinc (II)
3
3 4
)
(
⇑
Corresponding author. Tel.: +90 2462114082.
E-mail address: ayseguluygun@sdu.edu.tr (A.U. Oksuz).
acetate were purchased from Aldrich; Silica Gel 60 (0.04–0.063)
was purchased from Merck.
http://dx.doi.org/10.1016/j.ica.2014.08.014
020-1693/Ó 2014 Elsevier B.V. All rights reserved.
0

1
40
S. Cogal et al. / Inorganica Chimica Acta 423 (2014) 139–144
Fig. 3. Q-Band absorption of ZnPc-1 in different solvents.
Fig. 1. Absorption spectra of ZnPc-1 and ZnPc-2 in THF.
ꢀ1
FTIR spectra were measured between 400 and 4000 cm from
KBr pellets on a Perkin Elmer Spectrum BX FTIR system (Beacons-
field, Buckinghamshire, HP91QA, England). The NMR (400 MHz)
spectra were recorded using a Bruker Ultrashield Plus Biospin
Table 1
UV–Vis absorption and emission spectral data of ZnPc-1 in different solvents at 25 °C.
kmax (nm) (
THF
e
, M 1 cm
ꢀ
ꢀ1
)
kmax (nm)
THF
3
GmbH spectrometer in CDCl . The absorption spectra were
DMF
CHCl
3
DMSO
recorded using Perkin Elmer Lambda 20 UV–Vis spectrometer.
The fluorescence spectra were measured on Varian Cary Eclipse
fluorescence spectrophotometer. Mass spectra were measured
using Bruker Microflex LT MALDI-TOF mass spectrometer.
ZnPc-1
ZnPc-2
360 (4.65)
366 (4.87)
623 (4.58)
691 (5.38)
362 (5.01)
632 (4.62)
697 (5.35)
359 (4.53)
625 (4.18)
693 (4.96)
357 (4.70)
638 (4.31)
700 (4.91)
367 (4.74)
626 (4.44)
696 (5.24)
–
697
6
6
21 (4.35)
88 (5.16)
355 (5.02)
724
6
6
34 (4.69)
96 (5.15)
2.2. Synthesis of 4-iodophthalonitrile (1)
This compound was synthesized as described in literature [14].
1
Yiled: 69%. H NMR (CDCl
(
3
, 400 MHz): d (ppm) = 8.17 (d, 1H), 8.12
13
dd, 1H, J = 8 Hz), 7.52 (d, 1H, J = 6.8 Hz).
3
C NMR (CDCl ,
4
00 MHz): d (ppm) = 142.48 (C-5), 142.07 (C-3), 134.01 (C-6),
1
17.04 (2C; CN), 114.94 (C-2), 113.85 (C-4), 99.69 (C-4). FTIR
ꢀ1
(
KBr) m (cm ): 3436, 3091, 3060, 3015, 2232 (–CN), 1946, 1811,
1
680, 1572, 1543, 1468, 1372, 1277, 1265, 1205, 1178, 1101,
1
071, 974, 907, 839, 581, 526, 475, 431, 410.
Fig. 4. Absorption spectra of ZnPc-1 in THF with different concentrations range
from 1.58 ꢁ 10ꢀ to 5.00 ꢁ 10 M.
6
ꢀ6
2.3. Synthesis of 4-(3-thienyl)phthalonitrile (2)
4
-Iodophthalonitrile (127 mg, 0.5 mmol), 3-thienylboronic acid
(
70.05 mg, 0.55 mmol) and tetrakis (triphenylphosphine) palla-
dium (0) (57.8 mg, 0.05 mmol) were dissolved in 20 ml of DME.
To this aqueous solution of sodium carbonate (26.5 mg, 0.25 mmol)
Fig. 2. Emission spectra of ZnPc-1 and ZnPc-2 in THF (Excitation: 600 nm).

S. Cogal et al. / Inorganica Chimica Acta 423 (2014) 139–144
141
The mixture was added by three drops of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) and heated at 130 °C under argon
atmosphere for 24 h. The reaction mixture was then allowed to
cool to room temperature and the product was filtered and solvent
was evaporated. The solid obtained was washed several times with
2
MeOH:H O (5:1) and the solid obtained was subjected to silica gel
column chromatography and eluted with hexane:ethyl acetate
ꢀ
1
(
5:2) to give green product. Yield: 71%. FTIR (KBr)
m
(cm ):
3
1
4
432, 3097, 2921, 2857, 2541, 1609, 1482, 1361, 1313, 1140,
1
095, 1062, 931, 859, 777, 746, 673, 624, 521. H NMR (CDCl
3
,
00 MHz): d (ppm) = 6.54–7.03 (12H, thienyl, Ar–H), 7.50–8.10
ꢀ
1
ꢀ1
(
12H, Ar–H). UV–Vis (THF): kmax, nm (log
e, M cm ) = 360
(
4.65), 621 (4.35) and 688 (5.16). MALDI TOF MS: m/z: calculated
9
06.43; found 905.96.
2.6. Synthesis of meso-tetrakis(5’-hexyl-2,2’-bithiophene)
phthalocyanine zinc(II) (ZnPc-2)
0
0
4
-(5 -hexyl-2,2 -bithiophene)phthalonitrile (94.15 mg, 0.25 mmol)
and zinc (II) acetate (12.61 mg, 0.069 mmol) were dissolved in
0 ml of DMAE. The mixture was added by three drops of 1,8-diaza-
Fig. 5. FTIR spectra of 4-(3-thienyl)phthalonitrile (a) and ZnPc-1 (b).
1
bicyclo[5.4.0]undec-7-ene (DBU) and heated at 130 °C under argon
atmosphere for 24 h. The reaction mixture was then allowed to cool
to room temperature and the product was filtered and solvent was
evaporated. The solid obtained was washed several times with
was added. The resultant reaction mixture was heated at 80 °C
under argon atmosphere for 16 h and then the reaction mixture is
allowed to cool to room temperature. The reaction mixture was fil-
tered and solvent was evaporated and the solid obtained was sub-
jected to silica gel column chromatography and eluted with
2
MeOH:H O (5:1) and the solid obtained was subjected to silica
gel column chromatography and eluted with hexane:THF (5:1) to
chloroform:hexane (3:1) mixture. Yield: 75%. 1H NMR (CDCl
3
,
ꢀ1
give green product. Yield: 62%. FTIR (KBr)
m
(cm ): 3634, 3435,
4
00 MHz): d (ppm) = 7.26 (m, 1H, Ar–H), 7.40 (m, 1H, Ar–H), 7.50
3
1
059, 2918, 2855, 1724, 1613, 1481, 1443, 1391, 1325, 1132,
094, 1055, 883, 785, 748, 733, 465. H NMR (CDCl , 400 MHz):
3
(
(
m, 1H, Ar–H), 7.67 (m,1H, Ar–H), 7.84 (m,1H, Ar–H), 7.91–8.00
1
1
3
m,1H, Ar–H).
3
C NMR (CDCl , 400 MHz): d (ppm) = 113.57,
d (ppm) = 0.91–2.84 (several m, 52H, alkyl), 6.54–7.33 (28H,
1
1
1
7
15.39, 115.50, 116.66, 124.26, 125.52, 128.14, 130.36, 131.07,
ꢀ1
ꢀ1
Ar–H). UV–Vis (THF): kmax, nm (log
4.69) ve 696 (5.15). MALDI TOF MS: m/z: calculated 1571.56; found
572.10.
e, M cm ) = 355 (5.02), 634
ꢀ1
34.08, 138.18, 140.78. FTIR (KBr)
m (cm ): 3102, 2230 (–CN),
(
1
654, 1594, 1523, 1423, 1353, 1264, 1216, 1089, 891, 846, 794,
02, 651, 584, 521.
0
0
3. Results and discussion
2
.4. Synthesis of 4-(5 -hexyl-2,2 -bithiophene)phthalonitrile (3)
0
0
The synthesis of symmetrical zinc phthalocyanines was illus-
trated in the Schema 1. The phthalonitrile compounds 2 and 3 were
obtained through Suzuki–Miyaura cross-coupling reaction of 4-
iodophthalonitrile with 3-thienylboronic acid and 5 -hexyl-2,2 -
bithiophene-5-boronic acid pinacol ester, respectively. ZnPc-1
and ZnPc-2 were prepared through 2 and 3, in DMAE solution in
the presence of DBU and zinc salt. Usually, the tetra-substituted
Pcs which are prepared from 4-substituted phthalonitriles give a
4
-Iodophthalonitrile (254 mg, 1 mmol), 5 -hexyl-2,2 -bithioph-
ene-5-boronic acid pinacol ester (414 mg, 1.1 mmol) and tetra-
kis(triphenylphosphine) palladium (0) (115.56 mg, 0,1 mmol)
were dissolved in 20 ml of DME. To this aqueous solution of
sodium carbonate (53 mg, 0.5 mmol) was added. The resultant
reaction mixture was heated at 80 °C under argon atmosphere
for 24 h and then the reaction mixture is allowed to cool to room
temperature. The reaction mixture was filtered and solvent was
evaporated and the solid obtained was subjected to silica gel col-
umn chromatography and eluted with chloroform:hexane (3:1)
0
0
s
mixture of four positional isomers with D2h, D4h, C2v and C sym-
metries [15]. Separation of these four isomers is extremely difficult
with common column chromatography or recrystallization. There-
fore, both ZnPc-1 and ZnPc-2 were obtained as a mixture of
isomers.
mixture. Yield: 58%. 1H NMR (CDCl
m, 3H, CH ), 1.36 (m, 2H, CH ), 1.42 (m, 2H, CH
CH2), 2.84 (m, 2H, CH ), 6.76 (m, 1H, Ar–H), 7.11 (m, 1H, Ar–H),
.29 (m, 1H, Ar–H), 7.79 (m, 1H, Ar–H), 7.80 (m, 1H, Ar–H), 7.86
3
, 400 MHz): d (ppm) = 0.94
), 1.72 (m, 2H,
(
3
2
2
2
7
(
(
13
m, 1H, Ar–H), 7.97 (m, 1H, Ar–H). C NMR (CDCl
ppm) = 14.07, 22.57, 28.74, 30.24, 31.54, 112.74, 115.24, 115.52,
3
, 400 MHz): d
3.1. Absorption and emission results
1
1
3
1
1
16.73, 124.33, 124.76, 125.22, 127.38, 128.71, 129.48, 132.44,
The absorption spectra of phthalocyanines are shown in Fig. 1.
ꢀ1
34.04, 136.88, 139.29, 141.76, 147.38. FTIR (KBr)
m (cm ):
The strong absorption of phthalocyanines in the visible region
106, 3067, 2954, 2920, 2841, 2229 (–CN), 1719, 1593, 1554,
495, 1446, 1439, 1411, 1369, 1314, 1280, 1219, 1202, 1175,
104, 1065, 905, 879, 837, 796, 777, 723, 521, 486, 430.
⁄
are assigned as the Q-band, which are attributed to the
p–p
tran-
sition between the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO) of the phthalocy-
anine ring [16]. ZnPc-1 and ZnPc-2 exhibited a strong absorption
peak at 688 and 696 nm, respectively. In addition, both phthalocy-
anines exhibited absorption band around 360 nm known as Soret
band. ZnPc-2, additionally present a weak absorption around
2.5. Synthesis of meso-tetrakis(3-thienyl)phthalocyanine zinc(II)
(ZnPc-1)
4
-(3-Thienyl)phthalonitrile (105 mg, 0.5 mmol) and zinc (II)
400 nm, which is assigned to the
tuent [17].
p-conjugated bithiophene substi-
acetate (25 mg, 0.136 mmol) were dissolved in 10 ml of DMAE.

1
42
S. Cogal et al. / Inorganica Chimica Acta 423 (2014) 139–144
S
NC
NC
NC
NC
NC
i
ii
+
2
(HO) B
NH
2
NC
I
2
S
1
O
B
NC
NC
+
S
S
ii
1
O
S
S
S
3
N
N
N
iii
N
S
N Zn
N
N
2
S
N
S
ZnPc-1
S
S
S
N
N
N
S
iii
N Zn
N
N
3
S
N
N
S
S
S
ZnPc-2
2 4 2 3 4 2 3 2
Scheme 1. Synthesis of phthalonitrile derivatives and phthalocyanines. (i) H SO , NaNO , KI. (ii) Pd(PPh ) , Na CO , DME, 80 C, 24 h. (iii) Zn(OAc) , DMAE, DBU 130 °C, 24 h.
Fluorescence spectra of ZnPc-1 and ZnPc-2 are shown in Fig 2.
The excitation wavelength is 600 nm. ZnPc-1 exhibited a maxi-
mum emission peak at 697 nm, while ZnPc-2 exhibited red shifted
emission peak at 724 nm. Conjugated bithiophene moiety shifted
the emission maxima to red region by 31 nm in ZnPc-2.
summarizes the UV–visible absorption spectral data of the com-
pounds at different solvents and emission data in THF.
The aggregation behaviors of the Pcs were investigated in THF.
Fig 4 shows the absorption spectra of ZnPc-1 at different concen-
trations. As shown in the figure, the intensity of absorption bands
increases with increasing concentration and no new bands were
observed signifying no aggregation behavior at these concentra-
tions. This is probably due to the bulky nature of the ring substit-
uents. The same behaviors were also observed for ZnPc-2.
Lambert–Beer’s law was observed for two complexes at the con-
The compounds ZnPc-1 and ZnPc-2 show an extended p-conju-
gation system, which produces a redshift in the absorption and
emission maximum, in comprasion with the unsubstituted zinc
phthalocyanine (ZnPc). ZnPc shows a Q-band absorption at
6
68 nm in THF [18], whereas ZnPc-1 and ZnPc-2 dyes show a max-
ꢀ6
imum absorbance at 688 and 696 nm, respectively. The use of con-
centrations less than 5 ꢁ 10 M [19].
0
0
jugated 3-thienyl and 5 -hexyl-2,2 -bithiophene substituents
enhanced the conjugation length of the phthalocyanine
macrocycle.
3.2. FTIR studies
Fig. 3 depicts the Q-band absorption of ZnPc-1 in different sol-
vents. Q-bands were red-shifted by about 3 nm, 5 nm and 8 nm by
Fig. 5 shows the FT-IR spectra of 4-(3-thienyl)phthalonitrile and
ZnPc-1. The characteristic CN stretching of phthalonitrile were
replacing THF with DMF, CHCl
3
and DMSO, respectively. Table 1
ꢀ1
observed at 2230 cm . The disappearance of the characteristic

S. Cogal et al. / Inorganica Chimica Acta 423 (2014) 139–144
143
ꢀ
1
3
067 cm and aliphatic C–H symmetric stretching at 2954, 2920
ꢀ
1
and 2851 cm which indicates the hexyl group. The aliphatic C–
stretching in ZnPc-2 was observed at 2952, 2918 and
H
2
ꢀ
1
855 cm . The C@C stretching of phthalonitrile and ZnPc-2 was
ꢀ
1
observed at 1593 and 1613 cm , respectively. The band at
ꢀ1
1
440 cm is assigned to the C@C stretching of bithiophene in
the both structure [21].
3.3. Electrochemical studies
The electrochemical behavior of the compounds was investi-
gated using cyclic voltammetry (CV). Fig. 7 shows the cyclic vol-
tammograms (CVs) of ZnPc-1 and ZnPc-2 in DMF solution
containing 0.1 M TBAPF6 as an electrolyte. ZnPc-1 shows a revers-
ible oxidation wave at 0.6 V (E1/2) which assigned to the phthalo-
cyanine ring. The onset oxidation and onset reduction potentials
are given in Table 2. The HOMO–LUMO level energy gap also
known as electrochemical band gap is estimated from the differ-
ence between the first oxidation and the first reduction potential
from cyclic voltammograms [10]. The HOMO energy level, LUMO
0
0
Fig. 6. FTIR spectra of 4-(5 -hexyl-2,2 -bithiophene)phthalonitrile (a) and ZnPc-2
b).
elec
energy level, and electrochemical band gap (E
g
) were calculated
(
as follows:
on
HOMO ¼ ꢀ½Eox ꢀ E1=2ðferroceneÞ þ 4:8ꢂeV;
on
red
LUMO ¼ ꢀ½E ꢀ E1=2ðferroceneÞ þ 4:8ꢂeV;
elec
g
E
¼ ðLUMO ꢀ HOMOÞeV;
where E1/2(ferrocene) is the ferrocene half-wave potential (0.57 mV),
on
ox
on
red
E
is the oxidation onset potential, E is the material reduction
onset potential, and 4.8 eV is the energy level of ferrocene below
the vacuum level. The HOMO–LUMO gaps obtained from the onset
oxidation–reduction potentials were calculated at 1.47 eV for ZnPc-
1
and 1.35 eV for ZnPc-2, respectively. In addition, both of the Pcs
showed oxidation over 1.2 V. The HOMO–LUMO gap of ZnPc-1
and ZnPc-2 decreased upon increasing the conjugation length
[
[
22],
in
comparison
with
the
unsubstituted
ZnPc
23]. Muto et al. reported the similar observation for 2-thienyl
0
and [2-2 -bithiophene]-5-yl substituted 1,4,8,11,15,18,22,25-octa-
8
butoxyphthalocyanines ((OBu) Pcs) [10]. The calculated HOMO
and LUMO energy levels of ZnPcs are summarized in Table 2.
4
. Conclusions
Fig. 7. Cyclic voltammograms of ZnPc-1 (a) and ZnPc-2 (b) in 0.1 M
TBAPF6 + DMF:DCM (1:1) on ITO working electrode. Scan rate: 25 mV/s.
In summary, the syntheses of two peripherally tetra-substituted
zinc phthalocyanines were presented. Spectral and electrochemical
0
0
characterizations were carried out. The 5 -hexyl-2,2 -bithiophene
substituent shifted the absorption band to red region and
decreased the HOMO–LUMO energy gap of phthalocyanine. It
was also found that the phthalocyanines have no aggregation in
low concentrations.
Table 2
Electrochemical and optical properties of ZnPc-1 and ZnPc-2.
on
ox
(V)a
on
red
(V)b HOMO (eV) LUMO (eV)
elec
E
E
E
g
(eV)
ZnPc-1 0.55 1.40
ZnPc-2 0.42 1.03 1.59 ꢀ0.93
ꢀ0.92
ꢀ4.78
ꢀ4.65
ꢀ3.31
ꢀ3.30
1.47
1.35
Acknowledgements
a
Oxidation onset potential.
Reduction onset potential vs. Ag/AgCl reference electrode.
b
This work was supported financially by the grant of Suleyman
Demirel University, Scientific Research Projects (2950-D-11).
CN band confirms the formation of phthalocyanine [20]. The bands
at around 3100 and 3097 cm are assigned to the aromatic C–H
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ꢀ1
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1
0
0
1
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ꢀ1
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