Synthesis and spectroscopic-voltammetric behaviors of silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole

Article abstract of DOI:10.1016/j.dyepig.2013.08.010

In the present work, 2,5-diphenylthiazolo[5,4-d]thiazole (DTT) and silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole complex(Ag₂DTT) were synthesized, and then their spectroscopic and voltammetric behaviors were investigated. The DTT was obtained b

Full text of DOI:10.1016/j.dyepig.2013.08.010

Accepted Manuscript
Synthesis and spectroscopic-voltametric behaviors of silver(I) 2,5-
diphenylthiazolo[5,4-d]thiazole
Uğursoy Olgun, Mustafa Gülfen
PII:
S0143-7208(13)00308-2
10.1016/j.dyepig.2013.08.010
DYPI 4057
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 15 March 2013
Revised Date: 12 July 2013
Accepted Date: 12 August 2013
Please cite this article as: Olgun U, Gülfen M, Synthesis and spectroscopic-voltametric behaviors
of silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole, Dyes and Pigments (2013), doi: 10.1016/
j.dyepig.2013.08.010.
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ACCEPTED MANUSCRIPT
Synthesis and spectroscopic-voltametric behaviors
of silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole
Uğursoy Olgun* and Mustafa Gülfen
Department of Chemistry, Faculty of Arts and Sciences, Sakarya University,
TR-54187, Sakarya, Turkey
*
Corresponding author: Dr. Uğursoy Olgun
Sakarya University
Faculty of Arts and Sciences
Department of Chemistry
TR-54187, Sakarya, TURKEY
uolgun@sakarya.edu.tr
Tel: +90 264 2956060
Fax: +90 264 2955950
1

ACCEPTED MANUSCRIPT
Synthesis and spectroscopic-voltametric behaviors
of silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole
Uğursoy Olgun* and Mustafa Gülfen
Department of Chemistry, Faculty of Arts and Sciences, Sakarya University,
TR-54187, Sakarya, Turkey
Abstract
In the present work, 2,5-diphenylthiazolo[5,4-d]thiazole (DTT) and silver(I)
2
,5-diphenylthiazolo[5,4-d]thiazole complex (Ag
spectroscopic and voltametric behaviors were investigated. The DTT was obtained by the
reaction of rubeanic acid and benzaldehyde. Then the Ag DTT was prepared using AgNO
and DTT in DMSO. The DTT and Ag DTT were examined by FT-IR, UV-vis. absorption and
fluorescence spectroscopy. The UV-vis. measurements showed the formation of M L type
complex. The molar absorptivity coefficients (ε) of DTT and Ag DTT at 420 nm were found
as 11952 and 21747 L/cm.mol in DMSO, and 11062 and 13861 L/cm.mol in CH CN,
respectively. In addition, the electrochemistry of both DTT and Ag DTT was performed using
2
DTT) were synthesized, and then their
2
3
2
2
2
3
2
2
cyclic voltametry. The HOMO-LUMO band gaps of DTT and Ag DTT were calculated as
3
.26 and 2.96 eV, respectively. The fluorescence measurements showed that both DTT and
Ag DTT have fluorescence emissions at 451 nm in DMSO with the excitation at 380 nm. The
2
metal complexes of 2,5-diphenylthiazolo[5,4-d]thiazole can be useful for various electronic
and optical applications.
Keywords: 2,5-diphenylthiazolo[5,4-d]thiazole; silver complex; UV-vis.; FTIR; cyclic
voltametry; band gap
2

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1
. Introduction
In recent years, the scientific aspects of new thiazolo[5,4-d]thiazole derivatives have been
studied in different fields and the obtained results are receiving attention due to their
interesting electro-optic, non-linear optic, liquid crystalline, fluorescence and
semiconductivity properties. Thiazolo[5,4-d]thiazoles are an important class of bicyclic
aromatic molecule with two fused thiazole rings. Studies of the structure [1], spectroscopic
properties [2, 3], liquid crystallinity [4, 5], conductivity properties [6], fluorescent dyes [7, 8],
non-linear optical properties [9] and biological activities [10] of some thiazolo[5,4-d]thiazole
derivatives have already been reported [7].
Thiazolo[5.4,d]thiazole and 2,5-diphenyl-thiazolo[5.4,d]thiazole (DTT) were synthesized
previously by Ephraim and Johnson et. al. [11, 12, 13]. 2,5-diphenyl-thiazolo[5,4-d]thiazole
(Fig. 1a), which is a derivative molecule of thiazolo[5,4-d]thiazole (Fig. 1b) can be
synthesized by the reaction of dithiooxamide (rubeanic acid) and benzaldehyde [7, 9, 12, 14].
It has polarizability since it contains conjugated electron-donor thiazole and electron-
withdrawing benzene groups [7]. Depending on the type of solvent, the maximum absorbance
in the electronic absorption spectrum of DTT is observed at around 350-400 nm and the
fluorescence emission is found at about 410 nm [2, 7, 9]. A number of commercial fluorescent
dyes and brighteners bearing the thiazole unit have been produced worldwide [7].
Thiazolo[5,4-d]thiazole derivatives were also patented for various applications [15-17].
Only limited number of metal complexes of DTT derivatives was studied in the literature.
For example, the copper and ruthenium complexes of 2,5-di(2-pyridyl)thiazolo[5,4-d]thiazole
were studied by Zampese et al. [18]. In another study, the fluorescent boron complexes of
thiazolo[5,4-d]thiazole were prepared by Li et al. [19]. The color former nickel complex of
2
,5-bis(o-hydroxyphenyl)-thiazolo[5,4,d]thiazole was reported by Jubran [17]. The
coordination polymers of thiazolo[5,4-d]thiazole-2,5-dicarboxylic acid with Ag(I), Mn(II),
Co(II), Zn(II) and Cu(II) were investigated by Apre et al. [20]. Polymeric solar cells using
thiazolo[5,4-d]thiazole groups were were also reported by Helgesen et al.[21] and Lee et al.
[
22]. Recently, 2,5-diarylthiazolo[5,4-d]thiazole derivatives bearing ethylene oxide was used
3
+
3+
as fluorescent chemosensors for Cr and Al [23].
3

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Coordination complexes of DTT and derivative molecules with different properties such
as biological activity, photosensivity, liquid crystalinity and semi conductivity have not been
examined enough. In this study, the synthesis, electronic and vibrational spectroscopy, and
2
cyclic voltametry of both DTT ligand and Ag DTT complex have been investigated. The
molar absorptivity coefficients, the HOMO and LUMO energy levels, and the band gaps of
DTT and Ag DTT were calculated by using electronic spectroscopy and cyclic voltametry.
2
2
. Experimental Procedure
2
.1. Synthesis of 2,5-diphenylthiazolo[5,4-d]thiazole (DTT)
2
,5-diphenylthiazolo[5,4-d]thiazole can be synthesized by the reaction of rubeanic acid
(dithiooxamide) and benzaldehyde [12, 18, 24]. In our study, 2,5-diphenylthiazolo[5,4-
d]thiazole (DTT) was prepared in 30 mL ethanol solution of 0.92 g (10 mmol) rubeanic acid
and 2.12 g (20 mmol) benzaldehyde by adding 0.5 M NaOH up to the formation of dark red
color under boiling conditions. After a 60 minute reaction period under boiling condition, 30
2
mL H O was added to the mixture and then it was heated for another 60 min. The mixture was
acidified by adding 0.5 M HCl solution. The product was extracted into ethylacetate phase
and the solvent was removed in a rotary evaporator. A 100 mg product of 2,5-
diphenylthiazolo[5,4-d]thiazole was obtained as yellow powder.
2
2
.2. Synthesis of silver(I) 2,5-diphenylthiazolo[5,4-d]thiazole complex (Ag DTT)
0
.0282 g (0.1 mmol) 2,5-diphenylthiazolo[5,4-d]thiazole (DTT) in 10 mL CH
3
CN and
DTT
0
.0340 g (0.2 mmol) AgNO in 10 mL CH CN solutions were mixed for the Ag
3
3
2
complex formation at room temperature. The solvent was evaporated off in a rotary
2
evaporator and the dark brown product was obtained. The prepared Ag DTT complex was
characterized using spectroscopic and electrochemical methods.
4

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2
2
.3. Measurements and apparatus
.3.1. UV-vis. spectroscopy
Electronic absorption UV–vis. spectra were recorded on a Shimadzu UV-vis. 2401 PC
model spectrophotometer with a photodiode array detector, double beam system and scanning
between 200-800 nm. A 1 cm square quartz cuvette was used for measurements of solutions.
The UV-vis. measurements of 2,5-diphenyl-thiazolo[5,4-d]thiazole and silver 2,5-
diphenyl-thiazolo[5,4-d]thiazole complex were taken in DMSO and CH CN solutions. 0.354
3
mM 2,5-diphenyl-thiazolo[5,4-d]thiazole ligand and 0.354 mM silver nitrate solutions were
prepared in DMSO. A 0.5 mL of DTT solutions were placed in six different test tubes and the
various amounts of silver solutions were added to the tubes such that the final M/L mole
ratios are 1/3, 1/2, 1/1, 2/1, 3/1, 4/1, and 5/1. The UV-visible measurements of prepared silver
complex and the solutions of DTT have been carried out within 30 minutes after mixing. The
2 3
molar absorptivity coefficients of DTT and Ag DTT were calculated in DMSO and CH CN
from the slope of the calibration plots.
2
.3.2. FT-IR spectroscopy
The FTIR measurements were recorded on a Shimadzu IRPrestige-21 FTIR-8400S
model spectrophotometer equipped with a diamond ATR unit. Ag DTT was synthesized in
CH CN at 2/1 mole ratio of Ag(I) to the ligand. The solvent was evaporated off and the dried
powder was used in the measurements.
2
3
2
.3.3. Cyclic voltametry
To examine the electrochemical properties of Ag DTT, the solutions of 0.00354 M
2
AgNO
measurements, LiClO
.05 M. The cyclic voltametric measurements of AgNO , DTT and Ag DTT were performed
3
2 3
, 0.00177 M DTT and 0.00177 M Ag DTT in CH CN were prepared. During the
4
solution was added as an electrolyte to achieve a concentration of
0
3
2
at 100 mV/s on Gamry 750 EQCM model voltammeter between -2.0 and 2.0 volts. The
measurements were done with Ag/AgCl reference electrode (E= +0.197 V) and two platinum
electrodes as working and counter electrodes. The HOMO energy levels for the synthesized
5

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DTT and Ag
2
DTT were calculated using the data obtained from the cyclic voltammograms
according to the literature [25].
2
.3.4. Selectivity
3
+
2+
+
2+
2+
2+
The selectivity of DTT to Fe , Cu , Ag , Zn , Co and Ni ions was examined
using UV-vis. spectroscopy. A 0.1 mM solution of each metal ion including 0.05 mM DTT
M/DTT ratio = 2/1; M DTT) was prepared in DMSO. The UV-vis. spectra of prepared
(
2
solutions were measured in the range of 200-800 nm and the maximum absorbance values
were compared with each other.
2
.3.5. Fluorescence spectroscopy
2
The fluorescence measurements of DTT and Ag DTT samples were performed in DMSO.
The fluorescence properties of 0.4 mM DTT and 0.4 mM Ag DTT solutions in DMSO were
2
tested by the excitations at 380 nm and 420 nm wavelengths. The measurements were taken
by using Hithachi F-2710 model fluorescence spectrophotometer.
3
. Results and Discussion
3
2
.1. UV-vis. spectroscopy of DTT and Ag DTT
The UV-vis. spectrum of synthesized DTT was measured in acidic and basic conditions
and the results are shown in Fig. 2. At first, the UV-vis. spectrum was measured in DMSO
for the acidic and the basic forms of DTT. As can be seen from Fig. 2, a new absorption
maximum at 420 nm, which is related to the deprotonated form of DTT was recorded. The
protonation-deprotonation equilibrium of DTT is also demonstrated in Fig. 3. After 0,1 M
NaOH addition, a new band at 420 nm was observed and it was attributed to the n-π*
transition of the paired electrons of nitrogen atoms. A bathochromic shift in the spectrum of
DTT in DMSO solution was observed after the base addition.
6

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DTT ligand is expected to the form silver complex with N and S donor atoms because
of soft-soft acid-base principle suggested by Pearson [26]. Therefore, the silver complex
formation of the DTT has been studied. The UV-vis. spectra of prepared silver(I) 2,5-
diphenylthiazolo[5,4-d]thiazole complexes were performed at different M/L mole ratios in
3 2 3
acidic and basic media in DMSO. The spectra of DTT, ML , ML, M L and M L solutions are
given in Fig. 4. It was found that the absorbance increased gradually up to M L mole ratio and
2
then it started to decrease at M
DTT form M L type complex in DMSO as the solvent. The proposed structure of Ag
given in Fig. 5.
3
L. From these observations, it was concluded that silver and
2
2
DTT is
The molar absorptivity coefficients of both DTT and Ag
solvents were calculated from the UV-vis spectrophotometric measurements at the maximum
wavelengths. The obtained results are given in Table 1. In CH CN, the maximum absorbance
2 3
DTT in DMSO and CH CN
3
of DTT was observed at 380 nm (Fig. 2). As can be seen from Table 1, the absorptivity
coefficients of DTT at 380 nm in CH CN and DMSO were calculated as 874 and 1383
3
3
(L/cm.mol), respectively. Base addition increased the molar absorptivity of DTT in CH CN
from 874 to 3598 (L/cm.mol). This is due to deprotonation and the transitions of n electrons.
The molar absortivity coefficients increased significantly from 11062 to 13861 (L/cm.mol)
3 2
CH CN and from 11952 to 21747 (L/cm.mol) in DMSO after the formation of Ag DTT. The
increase of the molar absorptivities also confirms the formation of silver complex.
The HOMO–LUMO gap defines the band gap energy (E ) of the molecule. It can be
g
calculated from UV-vis spectra. Here, in this study, using the UV-vis. spectra of the
compounds, the HOMO-LUMO energy band gaps of DTT and Ag
.26 and 2.96 eV, respectively. It was seen that the UV-vis. spectrum of DTT after silver
complex formation, shifted to red with the formation of lower band gap energy structure. In
previous work of Pinto et al. [7], the SoꢀS transition energy was calculated as 3.3308 eV,
2
DTT were calculated as
3
1
which is close to the 3.26 eV found in our study. The small change in the transition energy
was attributed to the protonation of DTT ligand.
7

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3
2
.2. FT-IR spectroscopy of DTT and Ag DTT
The FTIR spectra of rubeanic acid, benzaldehyde and 2,5-diphenylthiazolo[5,4-
d]thiazole are shown in Fig. 6. The vibration frequencies of functional groups were also listed
in Table 2. When Fig. 6 is examined, it can be seen that some functional group peaks of
rubeanic acid and benzaldehyde have changed significantly with the formation new different
peaks of 2,5-diphenylthiazolo[5,4-d]thiazole. In the spectrum of rubeanic acid, the C=S peak
-1
-1
at 1576 cm was disappeared and the N-H peaks of primer amine group at 3127-3281 cm
changed. In the spectrum of benzaldehyde, two C-H peaks of aromatic aldehyde at 2737 and
-1
-1
2
818 cm and the C=O peak of aromatic aldehyde at 1695 cm were disappeared. The strong
-1
C-C peak (Aryl C-C) at 1202 cm was shifted. In the spectrum of the synthesized 2,5-
-1
diphenylthiazolo[5,4-d]thiazole, strong peak at 1687 cm for the C=N bond of thiazole ring
-1
was observed. The C=C and C-S peaks of thiazole ring at 1494 and 912 cm , respectively
were also assigned. The C-H peaks (in plane and out of plane stretching vibrations of
-1
monosubstitued aromatic ring) at 1167, 1072, 743 and 687 cm in the spectrum of
-1
benzaldehyde have changed to the new peaks at around 1101 and 692 cm in the spectrum of
2
3
3
,5-diphenylthiazolo[5,4-d]thiazole. The N-H vibration peaks of primer amine group at 3127-
-1
281 cm in the spectrum of rubeanic acid changed to the peaks of imino groups at 3348 and
-1
377 cm for the thiazole ring in the 2,5-diphenylthiazolo[5,4-d]thiazole. The C=N vibration
-1
-1
2
frequency of DTT ligand at 1687 cm is shifted to 1662 cm in the spectrum of Ag DTT
-1
complex. Also, the C-S peak of DTT at 912 cm changed. The FTIR analysis results
confirmed that Ag(I) ions was coordinated by electron donating N and S atoms of DTT [7, 27,
2
8].
3
2
.3. Cyclic voltametry of DTT and Ag DTT
The cyclic voltammograms of AgNO
3 2 3
, DTT and Ag DTT were recorded in CH CN
solutions including 0.05 M LiClO as the electrolyte. The results of CV measurements are
4
given in Fig 7. The peaks of AgNO
3
at -0.5423, 0.4111 and 1.173 V were shifted to -0.6524,
0
.5827 and 1.108 V, respectively. The reversible anodic and cathodic peaks of fused thiazole
ring of DTT were disappeared due to the complexation of silver to the thiazole groups. The
anodic peak in the voltammogram of DTT at -1.508 V was observed at 1.482 V for the
Ag
2
DTT. New waves in the voltammogram of Ag
2
DTT occurred at -1.020 V and -0.3486 V.
8

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2
According to Fig. 7, it is concluded that Ag DTT complex was formed between DTT and
silver ions.
The HOMO energy levels can be estimated from the electrochemical data. Here, the
HOMO energy levels of DTT and Ag DTT were calculated using the values in the cyclic
voltammograms according to the previous literature [19, 25]. It was found that the HOMO
energy levels of DTT and Ag DTT were -5.68 and -5.65 eV, respectively. Then band gap
2
2
energies were also calculated from the UV-vis absorption values. The obtained results are
given in Table 3.
3
.4. Selectivity of DTT to other metal ions
3
+
2+
+
2+
2+
2+
The selectivity of DTT to Fe , Cu , Ag , Zn , Co and Ni ions was measured by
UV-vis spectrophotometer using 0.05 mM DTT solutions containing 0.1 mM of each metal
ion in DMSO. The obtained results showing the increases in absorbance values after the
3+
2+
+
addition of Fe , Cu and Ag ions are given in Fig. 8. As shown in UV-vis spectra, the DTT
2
+
2+
2+
did not have any selectivity to Zn , Co and Ni ions. DTT molecule has different
3+
2+
+
selectivity values to Fe , Cu and Ag at 295 nm, 380 nm and 460 nm. It was found that the
3+
2+
+
3+
+
2+
order of absorbance values were Fe > Cu > Ag at 295 nm, Fe > Ag > Cu at 380 nm
+
2+
3+
3+
and Ag > Cu > Fe at 460 nm. The relatively high selectivity was observed to Fe at 295
2
+
+
and 380 nm, Cu at 295 nm and Ag at 380 and 460 nm.
.5. Fluorescence spectroscopy of DTT and Ag2DTT
3
-5
The fluorescence property of DTT was studied previously in DMSO solutions (10 M) using
50 nm excitation wavelength and the fluorescence emission was observed at 417.6 nm with a
quantum yield of 0.16 [7]. In our study, the fluorescence spectra of 0.4 mM DTT and 0.4 mM
Ag DTT solutions in DMSO were tested by excitation at 380 nm wavelength and the results
are demonstrated in Fig. 9. Both DTT and Ag DTT showed fluorescence emissions at 451
nm. The fluorescence emission of Ag DTT at 451 nm is similar to DTT with slightly decrease
in fluorescence intensity. In addition, the fluorescence measurements of both DTT and
Ag DTT were also performed at 420 nm excitation wavelength. At 420 nm excitation
3
2
2
2
2
wavelength, although DTT molecule has not exhibited any florescence emission, the Ag
complex has a florescence emission at 451 nm.
2
DTT
9

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4
. Conclusions
The present work described the synthesis and spectroscopic-voltametric behaviors of
,5-diphenylthiazolo[5,4-d]thiazole (DTT) ligand and silver(I) 2,5-diphenylthiazolo[5,4-
2
d]thiazole (Ag
2
DTT) complex. It was found from the measurements with UV-vis. that
L type complex. The molar absorptivities (ε) of DTT and Ag DTT at
20 nm were found as 11952 and 21747 L/cm.mol in DMSO, and 11062 and 13861 L/cm.mol
silver(I)-DTT formed M
2
2
4
3 2
in CH CN, respectively. The HOMO-LUMO band gap energies of DTT and Ag DTT were
also calculated as 3.26 and 2.96 eV from UV-vis. spectroscopy. The HOMO levels of DTT
and Ag DTT were -5.68 and -5.65 eV from the CV measurements. By the excitation at 380
nm, the fluorescence emissions of DTT and Ag DTT are observed at 451 nm. It is concluded
2
2
that DTT is a potential ligand for many metal ions and its metal complexes needs to be
studied for different applications.
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1
2

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Figure Captions
Fig. 1. a) 2,5-diphenyl-thiazolo[5,4-d]thiazole b) Thiazolo[5,4-d]thiazole.
Fig. 2. UV-vis. spectra of 2,5-diphenyl-thiazolo[5,4-d]thiazole in DMSO.
Fig. 3. Protonation equilibrium of 2,5-diphenyl-thiazolo[5,4-d]thiazole.
2
Fig. 4. UV-vis. spectra of DTT and Ag DTT at different M/L mole ratios in a) acidic b) basic
DMSO solutions (M:Ag, L:DTT).
Fig. 5. Silver complexation equilibrium of 2,5-diphenyl-thiazolo[5,4-d]thiazole.
Fig. 6. FT-IR spectra of benzaldehdye, rubeanic acid, DTT and Ag DTT.
Fig. 7. Cyclic voltammograms of AgNO , DTT and Ag DTT.
2
3
2
Fig. 8. UV-vis. absorption spectra showing the selectivity of DTT to different metal ions in
DMSO.
Fig. 9. UV-vis. absorption (normalized) and fluorescence spectra of DTT (λem = 452 nm) and
2
Ag DTT (λem = 451 nm) in DMSO (λex = 380 nm).

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Table 1.
Molar absorptivity coefficients of DTT and Ag DTT
2
DMSO
CH
3
CN
ε (L/cm.mol)
λ (nm)
ε (L/cm.mol)
λ (nm)
Sample
Ag DTT (Basic)
DTT (Acidic)
420
380
21747
1383
11952
295
380
295
13861
874
11062
3598
2
420
DTT (Basic)
3
80

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Table 2.
FTIR peaks of rubeanic acid, benzaldehyde and DTT
Rubeanic acid
Frequency
Benzaldehyde
Frequency
2,5-Diphenylthiazolo[5,4-d]thiazole (DTT)
Group
Group
Frequency
Group
+
N-H (Primer
amine)
N-H (Primer
amine)
N-H (Primer
amine)
N-H (C=N(H )- (Protonated imino
goup)
N-H (C=N(H )-( Protonated imino
3
3
3
281
204
127
3063
2818
2737
C-H (Aromatic)
3377
+
C-H (Aldehyde)
C-H (Aldehyde)
3265
3057
goup)
C-H (Aromatic)
1
1
576
423
C=S
C-N
1695
1583
C=O (Aldehyde)
C=C (Aromatic)
1654
1593
C=N
C=C (Aromatic)
1
196
C-C
1454
C=C (Aromatic)
1494
C=C (Thiazolo ring)
8
6
27
96
C=S stretching
1202
1167
C-C (Aryl-aldehyde)
C-H (Aromatic in plane,
monosubstitue)
1472
1176
C-C
C-H (Aromatic in plane,
monosubstitue)
C-H (Aromatic in plane,
monosubstitue)
C-H (Aromatic out of plane,
monosubstitue)
C-H (Aromatic out of plane,
monosubstitue)
C-H (Aromatic in plane,
monosubstitue)
C-H (Aromatic out of plane,
monosubstitue)
6
21
NH
2
twisting
1072
1028
744
7
6
43
87
731
C-S
C-H (Aromatic out of plane,
monosubstitue)
6
84

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Table 3.
HOMO, LUMO and band gap energies of DTT and Ag DTT
2
Material
HOMO, eV
LUMO eV
Band gap (HOMO-LUMO), eV
DTT
-5.68
-5.65
-2.42
-2.69
3.26
2.96
Ag
2
DTT

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