A fluorescent coumarin-thiophene hybrid as a ratiometric chemosensor for anions: Synthesis, photophysics, anion sensing and orbital interactions

Article abstract of DOI:10.1016/j.molstruc.2015.11.081

A colorimetric and fluorimetric fluorescent chemosensor (CT-2), having a coumarin ring as a signaling unit and an acetamido thiophene ring as an H-donor receptor, has been synthesized from amino derivative (CT-1) of CT-2 for the purpose of recognition of anions in DMSO. The absorption and emission maxima were both determined for the fluorescent dye in different solvents. Both hypsochromic shift at the absorption maximum, and quenching of fluorescence after interactions between the anions and the receptoric part, were observed. This phenomenon was explained using orbital interactions based on quantum chemical calculations. The selectivity and sensitivity of CT-2 for F^-, Cl^-, Br^-, I^-, AcO^-, CN^-, H₂PO₄^-, HSO₄^- and ClO₄^- anions were determined with spectrophotometric, fluorimetric and ¹H NMR titration techniques and it was found that CT-2 be utilized for the detection of CN^-, F^- and AcO^- in the presence of other ions as competitors. Color and fluorescence changes visible to the naked eye and under UV (365 nm) were observed upon addition of CN^-, F^- and AcO^- to the solution of chemosensor (CT-2) in DMSO. The sensor showed no colorimetric and fluorimetric response for the anions such as Cl^-, Br^-, I^-, H₂PO₄^-, HSO₄^-, and ClO₄^-. However, ¹H NMR titration shows that the chemosensor was more sensitive to CN^-, than F^- and AcO^- at the stochiometric ratio of 1:2.5 respectively. Additionally, the compounds CT-1 and CT-2 showed good thermal stability for practical applications.

Full text of DOI:10.1016/j.molstruc.2015.11.081

Journal of Molecular Structure 1108 (2016) 269e277
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
A fluorescent coumarin-thiophene hybrid as a ratiometric
chemosensor for anions: Synthesis, photophysics, anion sensing and
orbital interactions
*
Ufuk Yanar, Banu Babür, Damla Pekyılmaz, Issah Yahaya, Burcu Aydıner, Yavuz Dede ,
**
Zeynel Sefero gꢀ lu
Gazi University, Department of Chemistry, 06500 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 September 2015
Received in revised form
A colorimetric and fluorimetric fluorescent chemosensor (CT-2), having a coumarin ring as a signaling
unit and an acetamido thiophene ring as an H-donor receptor, has been synthesized from amino de-
rivative (CT-1) of CT-2 for the purpose of recognition of anions in DMSO. The absorption and emission
maxima were both determined for the fluorescent dye in different solvents. Both hypsochromic shift at
the absorption maximum, and quenching of fluorescence after interactions between the anions and the
receptoric part, were observed. This phenomenon was explained using orbital interactions based on
27 November 2015
Accepted 30 November 2015
Available online 11 December 2015
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
quantum chemical calculations. The selectivity and sensitivity of CT-2 for F , Cl , Br , I , AcO , CN ,
Keywords:
Coumarin
ꢀ ꢀ ꢀ
1
H PO , HSO and ClO anions were determined with spectrophotometric, fluorimetric and H NMR
2 4 4 4
ꢀ
ꢀ
ꢀ
titration techniques and it was found that CT-2 be utilized for the detection of CN , F and AcO in the
presence of other ions as competitors. Color and fluorescence changes visible to the naked eye and under
UV (365 nm) were observed upon addition of CN , F and AcO to the solution of chemosensor (CT-2) in
Coumarin-thiophene hybrid
Fluorescence chemosensor
Anion recognition
Frontier orbital
DFT
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
DMSO. The sensor showed no colorimetric and fluorimetric response for the anions such as Cl , Br , I ,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
H
2
PO
4
, HSO
4
, and ClO
4
. However, H NMR titration shows that the chemosensor was more sensitive to
ꢀ
CN , than F and AcO at the stochiometric ratio of 1:2.5 respectively. Additionally, the compounds CT-1
and CT-2 showed good thermal stability for practical applications.
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
on the functioning of the thyroid gland. Both excess and deficiency
of this anion affects the operation of the thyroid gland and can
cause serious illness [7,8]. Acetate anion plays a critical role in many
metabolic processes, and exhibits specific biochemical behavior on
antibodies and enzymes [9,10]. Cyanide ion is also vital as a raw
material in industrial process and it is also highly toxic for the
human body [11,12].
As a consequence, efforts have been made to determine fluoride,
chloride, bromide, iodide and other ions such as acetate, chlorate,
sulfate, phosphate and cyanide in real samples. The determination
of anions can be achieved by several methods including spectro-
scopic, chromatographic, electrochemical and analytical tech-
niques. However, the detection of anions with the use of simple
preparation and minimal instrumental assistance is desirable to-
ward practical applications. Colorimetric and fluorimetric chemo-
sensors are important alternatives to the traditional methods for
determination of anions. Therefore, synthesis of new additional
chemosensor is still required.
Anions are important in clinical, environmental, chemical and
industrial processes [1]. Drinking water is known to be the most
important source of fluoride and so is important for both human
body and bone growth [2]. Exposure to excess fluoride may cause
collagen break down, bone disorder, thyroid activity, and depres-
sion. Fluoride deficiency causes gum disease and osteoporosis,
while an excess (above 1.5 ppm) leads to fluorosis (fluoride
poisoning) because of its nephrotoxic effect [3,4]. High chlorine
concentration was determined in the sweat test used in the diag-
nosis of cystic fibrosis [5,6]. It is known that excess of bromide
causes severe irritation of the respiratory tract. Iodide has an effect
*
Corresponding author.
*
* Corresponding author.
E-mail addresses: dede@gazi.edu.tr (Y. Dede), znseferoglu@gazi.edu.tr
(
Z. Sefero gꢀ lu).
http://dx.doi.org/10.1016/j.molstruc.2015.11.081
022-2860/© 2015 Elsevier B.V. All rights reserved.
0

270
U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
The sensor (CT-2) reported here contains coumarin and
triplet, t; multiplet, m. Chemical shifts (d) are given in parts per-
thiophene unit as the main core. The coumarin ring is commonly
used as a fluorophore/chromophore in sensor systems because of
its high fluorescence quantum efficiency, large Stokes shift,
bright color under ambient light and ease of synthesis and
derivatization [13,14]. Thiophene derivatives are also valuable
compounds in heterocyclic chemistry due to its important optical
properties.
million (ppm) using the residue solvent peaks as reference relative
to TMS. ‘J’ values are given in Hertz (Hz). High resolution mass
spectra were recorded on a Waters-LCT-Premier-XE-LTOF (TOF-
MS), mass spectrometer operated in Electronionization (EI) mode
in m/z (rel. %) (Gazi University Laboratories, Department of Phar-
macological Sciences). The melting points were measured using
Electrothermal IA9200 apparatus and were uncorrected. Thermal
analyses were performed with a Shimadzu DTG-60H system, up to
In this work we chose coumarin as the fluorophore/chromo-
phore for signaling, and thiophene at the 3-position of the
coumarin ring to modify the fluorescence properties of the
coumarin core, in order to form a receptor for anions via an acet-
amide functional group. We first studied the photophysical prop-
erties of the fluorescence chemosensor (CT-2) and its starting
compound (CT-1). Afterwards, binding properties of the chemo-
ꢁ
ꢁ
ꢀ1
600 C (10 C min ) under a dynamic nitrogen atmosphere
(15 mL minꢀ1).
2.2. Spectrophotometric measurements
Ultravioletevisible (UVevis) absorption spectra were recorded
on Shimadzu Corporation, Kyoto Japan UV-1800 240 V spectro-
photometer (Gazi University, Department of Chemistry, Turkey) at
the wavelength of maximum absorption (lmax, in nm). Fluorescence
spectra were recorded on HITACHI F-7000 FL Spectro-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
sensor toward specific anions such as F , Cl , Br , I , AcO , CN ,
ꢀ
ꢀ
ꢀ
H
2
PO
4
, HSO
4
and ClO
4
was also investigated. Additionally, the
experimental results obtained were explained with theoretical
calculations. Thermal properties of CT-1 and CT-2 for optical usage
were also determined. CT-2 showed remarkable selectivity toward
fluorophotometer. All spectrophotometric measurements were
ꢀ
ꢀ
ꢀ
CN , F and AcO over other anions at the stochiometric ratio of 1:5
CT-2:Anion) respectively. However, the chemosensor was more
ꢁ
performed in thermostated quartz sample cells at 20 C, using
(
spectral grade solvents. The solution concentrations were 10
absorption spectroscopy and 1.0e5.0 M for fluorescence spec-
troscopy. Spectrophotometer slit widths were set to bandwidths of
nm for emission spectroscopy. The relative fluorescence quantum
yields, , were determined by standard methods [15,16] with
mM for
ꢀ
ꢀ
ꢀ
sensitive to CN , than F and AcO at the stochiometric ratio of
m
1
:2.5 respectively.
5
F
fl
2
. Experimental
Coumarin 153 (laser grade, Acros Organics,
a reference.
F
fl
¼ 0.38 in ethanol) as
2.1. Materials and instrumentations
All the chemicals used in the synthesis of the compounds were
2.3. Synthesis of 2-amino-4-(7-(diethylamino)-2-oxo-2H-
procured from Aldrich Chemical Company and were used without
further purification. The solvents used were of spectroscopic grade.
Thin-layer chromatography was carried out using precoated
aluminium-backed plates (Merck Silica Gel 60 F254) and visualised
chromen-3-yl)thiophene-3-carbonitrile (CT-1)
To a solution of C2 (2-(1-(7-(N,N-diethylamino)-2-oxo-2H-
chromen-3-yl)ethylidene)malononitrile) (10 mmol), elemental
sulfur (12 mmol), and triethylamine (1 mmol) in 30 mL ethanol,
were placed in a 100 mL round-bottom flask. The reaction
mixture was heated under reflux with stirring for 4 h. The
progress of the reaction was monitored by TLC (ethylacetate/n-
hexane 1:1). After cooling, the orange precipitate was filtrated
and product was washed with hot ethanol and dried. The pure
under UV light (
Mattson 1000 FT-IR spectrophotometer in KBr (
l
¼ 254e365 nm). FT-IR Spectra were recorded on a
ꢀ
1
y
are in cm ). NMR
spectra were run on a Bruker Avance 300 MHz instrument. NMR
samples were referenced against tetramethylsilane at 0.00 ppm for
1
H. Coupling constants (J) are given in hertz (Hz). Signals are
abbreviated as follows: singlet, s; doublet, d; doubletedoublet, dd;
Scheme 1. Synthetic pathway for CT-1 and CT-2.

U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
271
Table 1
Photophysical properties of CT-1 and CT-2.
CT-1
CT-2
Solvent
labs (nm)
l
fl
(nm)
Ф
fl
Stokes shift (nm)
labs (nm)
l
fl
(nm)
Ф
fl
Stokes shift (nm)
DMSO
MeOH
406
406
407
403
403
482
514
464
458
447
0.04
0.02
0.60
0.62
0.74
76
108
57
55
44
394
404
408
399
402
479
477
463
457
448
0.07
e
85
73
55
58
46
CH
2
Cl
2
0.33
0.34
e
THF
Toluene
Quantum yield (
Ф
fl
) of CT-1 and CT-2 are determined relative to the fluorescent standard coumarin 153a. a
(
Ф
fl.Cou. 153 ¼ 0.38 in ethanol).
Fig. 1. UVevis absorption spectra of CT-1 (left). Fluorescence emission spectra of CT-1 (right).
Fig. 2. UVevis absorption spectra of CT-2 (left). Fluorescence emission spectra of CT-2 (right).
product was obtained as a solid after crystallization from ethanol
2.4. Synthesis of N-(3-cyano-4-(7-(diethylamino)-2-oxo-2H-
chromen-3-yl)thiophen-2-yl)acetamide (CT-2)
ꢁ
ꢀ1
in 78% yield. Mp: 211e213 C. FT-IR (KBr,
y
max, cm ): 3395, 3322
(
1
NH ), 3045 (aromatic CeH), 2976 (aliphatic CeH), 2202 (CN),
687 (C]O, lactone), 1552 (C]C), 1252 (CeO); H NMR (DMSO-
2
1
To a solution of CT-1 (1.0 mmol), DMAP (1.7 mmol), and trie-
d
6
, 300 MHz):
d
H
8.00 (s, 1H), 7.47 (d, 1H, J ¼ 8.9 Hz), 6.72 (dd, 1H,
2 2
thylamine (2.5 mmol) in 10 mL CH Cl , placed in a 100 mL two-neck
J ¼ 2.2 Hz and J ¼ 8.8 Hz), 6.65 (s, 1H), 6.55 (d, 1H, J ¼ 2.0 Hz),
round bottomed flask, acetylchloride (1.15 mmol) was added. The
reaction mixture was stirred at room temperature for 18 h. The
progress of the reaction was monitored by TLC (ethylacetate/n-
hexane 1:1). After completion of the reaction, a yellow precipitate
13
3
d
.50 (q, 4H, J ¼ 6.8 Hz), 1.15 (q, 6H, J ¼ 6.9 Hz); C-APT (DMSO-
6
, 300 MHz):
d
C
12.8 (CH
3
), 23.5 (CH
3
), 44.9, 44.6 (CH
2
), 84.6
þ
(
CN), 165.7 (C]O); HRMS (m/z), (M þ H) : C18
13 3 2
H N O S, calcu-
lated: 340.1120; found: 340.1094.
was filtrated, washed with hot CH
in 74% yield. Mp: 340e341 C; FT-IR (KBr,
2
Cl
2
and dried. CT-2 was obtained
ꢁ
ꢀ1
ymax, cm ): 3395, 3322
2
(NH ), 3045 (aromatic CeH), 2976 (aliphatic CeH), 2202 (CN), 1687

272
U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
Fig. 6. Fluorescence emission titration spectra of CT-2 with TBACN (r:ratio).
Fig. 3. UVevis titration spectra of CT-2 with TBACN (r:ratio).
Fig. 7. Fluorescence emission titration spectra of CT-2 with TBAF (r:ratio).
Fig. 4. UVevis titration spectra of CT-2 with TBAF (r:ratio).
Fig. 8. Fluorescence emission titration spectra of CT-2 with TBAAcO (r:ratio).
Fig. 5. UVevis titration spectra of CT-2 with TBAAcO (r:ratio).

U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
273
Fig. 9. Absorption (left) and emission (right) titration spectra of CT-2 with all studied anions (r:ratio).
ꢀ
ꢀ
ꢀ
Scheme 2. Proposed binding mode of chemosensor CT-2 with CN , F and AcO in DMSO solution.
(
3
(
C]O, lactone), 1552 (C]C), 1252 (CeO); 1H NMR (DMSO-d
00 MHz)
8.02 (s, 1H), 7.45 (d, 1H, J ¼ 8.9 Hz), 7.24 (s, 1H), 6.75
dd,1H, J ¼ 2.0 Hz and J ¼ 8.9 Hz), 6.58 (d, 1H, J ¼ 2.0 Hz), 1.14 (q, 6H,
6
,
(C2) were prepared mainly by a previously reported procedure with
minor modifications (Pages S1 and S2 in Supplemantary
Information) [21]. The reaction of C2 with elemental sulfur in the
presence of a catalytic amount of triethylamine in ethanol gave the
fluorescent coumarin-thiophene hybrid CT-1. Reaction of CT-1 with
d
H
13
J ¼ 8.8 Hz); C-APT (DMSO-d
6 C 3 3
, 300 MHz): d 12.8 (CH ), 23.0 (CH ),
4
(
4.6 (CH ), 84.6 (CN), 160.2 (C]O), 169.2 (C]O); HRMS (m/z),
2
þ
M þ H) : C20
H
15
N
3
O
3
S, calculated: 382.1225; found: 382,1228.
2 2
acetylchloride in CH Cl using DMAP and triethylamine mixture
yielded the desired fluorescent chemosensor (CT-2) (Scheme 1).
Dyes CT-1 and CT-2 are colored, both in solid state and in so-
lution. In order to investigate the solvatochromic behavior, the
absorption and emission data of the dyes were determined in
various solvents with different dielectric constants (ε), i.e. DMSO
2
.5. Computational details
Geometry optimizations were performed using the density
functional theory (DFT) with the unrestricted formalism of B3LYP
hybrid functional [17a and b,18aef]. Pople's all-electron double-
basis including diffuse (þ) and polarization (d,p) functions (6-
(
(
46.45), MeOH (32.66), CH
Table 1).
2 2
Cl (8.93), THF (7.58), and toluene (2.38)
z
The compounds exhibited one absorption band in all the sol-
vents used and show absorption maxima ( max) ranging from 394
to 407 nm in the visible region. In addition, these dyes were found
to be fluorescent (with emission max 447e514 nm in all the solvent
3
1 þ G(d,p)) was used [19aee]. Harmonic vibrational frequencies
l
were computed at the level of geometry optimization and the
species reported herein were verified not to possess any imaginary
frequencies, and hence correspond to true minima. Only the singlet
state was considered. MO energies were reported in eV. Calcula-
tions were performed with Gaussian 09 suite of programs [20].
l
used). The compounds exhibited one emission band in all the sol-
vents used.
The Stokes shifts of CT-1 and CT-2 in various solvents varied
around 44e108 nm and 46e85 nm, respectively. Fluorescence
3
. Results and discussion
quantum yields (
vent used except MeOH and Toluene for CT-2 in the range of
.02e0.74 (relative to commercial reference standard Coumarin
53 (0.38) (Page S11 in Supplemantary Information) (Table 1)
Figs. 1 and 2).
fl
F ) of CT-1 and CT-2 were determined in all sol-
3.1. Synthesis and solvatochromic properties
0
1
(
3
-Acetyl-7-(diethylamino)-2H-chromen-2-one (C1) and 3-[7-
(N,N-diethylamino)-2-oxo-2H-chromen-3-yl]-3-oxopropanoate

274
U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
Fig. 10. 1H NMR (300 MHz) titration of CT-2 (1 ꢂ 10ꢀ2 M) with TBAF solution in DMSO-d
.
6
Fig. 11. Partial 1H NMR (300 MHz) titration of CT-2 (1 ꢂ 10ꢀ2 M) with studied anions (ranions
/
CT-2 ¼ 1:10) solution in DMSO-d
6
(r:ratio).

U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
275
3.2. UVevis absorption and fluorescence titrations of CT-2 with
the solution of CT-2 did not result in any significant changes in the
anions
absorption and emission spectra.
ꢀ
ꢀ
ꢀ
ꢀ
The interaction between CT-2 and the anions (F , Cl , Br , I ,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
The chemosensor performance of CT-2 was investigated using
UVevis absorption and fluorescence spectroscopy in DMSO against
HSO
4
, CN , AcO , H
2
PO
4
and ClO
4
) were probed with H NMR. CT-
ꢀ
1
2 and F showed a clear interaction in the H NMR titration of CT-2
with TBAF solution in DMSO. The free sensor CT-2 exhibited a sharp
singlet signal at 11.68 ppm, which was assigned to amide eNH (Hb).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
F , Cl , Br , I , AcO , CN , HSO
4
and ClO anions with tetrabuty-
4
lammonium (TBA) as the counter cation. The absorption maximum
of CT-2 was at 405 nm in DMSO (Fig. 3). This absorption band
shifted hypsochromically upon addition of one equiv of CN to the
ꢀ
Upon addition of 3 equiv of F to the solution of CT-2, the signal of
ꢀ
ꢀ
the amide eNH proton completely disappeared due to F inter-
solution of CT-2 and a new band at
l
¼ 392 nm was observed.
acting with the receptoric amide moiety (Scheme 2).
Upon addition of 7 equiv of F , the proton signals of the aromatic
3
thiophene ring (Ha) and acetyl CH shifted up-field from 7.27;
ꢀ
ꢀ
Aparently, the electrostatic interaction between CT-2 and CN
deprotonated the amide eNH function and negative charge accu-
mulated around the amide function giving rise to the observed
2.23 ppm to 6.64; 1.91 ppm, respectively, suggesting an accumu-
lation of negative charge on the amide nitrogen. Thus addition of 7
ꢀ
hypsochromic shift. The same results were observed for AcO and
ꢀ
ꢀ
F
(Figs. 4 and 5).
equiv of F resulted in deprotonation and led to an increase in the
To gain insight into the binding nature of CT-2 with anions,
electron density on the thiophene ring. Ha proton showed a drastic
fluorescence titrations were performed in DMSO with excitation
wavelength of 405 nm. Free sensor, CT-2 displayed an emission
maximum at 479 nm in DMSO with a high intensity. This UVevis
downfield shift due to the shielding effect of the negative electron
delocalization on the
p-conjugated thiophene framework. Most
importantly, a new signal at 15.55 ppm (JHF ¼ 121 Hz) after addition
ꢀ
ꢀ
ꢀ
ꢀ
study showed that, anions such as CN , F and AcO can remove
the eNH proton to form the corresponding anion in the ground
state. Therefore, these anions were expected to induce significant
of 7 equiv of F was observed indicating the creation of bifluoride
ꢀ
ꢀ
(FHF ) ion. Thus FHF was generated through abstraction of the
ꢀ
eNH proton by F (Fig. 10). The same deprotonation behaviour was
observed for AcO and CN , upon addition of 6 and 2.5 equiv of
ꢀ
ꢀ
ꢀ
fluorescence spectral changes in CT-2. Upon addition of CN (>1
equiv) to the solution of CT-2, the fluorescence intensity gradually
these anions respectively (Scheme 2). eNH (Hb) proton signal
ꢀ
ꢀ
decreased. Addition of 20 equiv of CN almost wiped out the
disappeared after the addition of 1 equiv of CN and 2 equiv of
ꢀ
ꢀ
fluorescence of CT-2 (Fig. 6). Similar results were observed for AcO
AcO . This difference is probably due to the basicity and molecular
ꢀ
ꢀ
ꢀ
ꢀ
and F (Figs. 7 and 8 in Supplemantary Information).
shape differences of AcO and CN compared to F (Figs. S15 and
S16 in Supplemantary Information).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
4
Interactions of CT-2 with Cl , Br , I , HSO
4
and ClO
anions
ꢀ
ꢀ
ꢀ
2 4 4 4
PO ),
, HSO- and ClO-
-
were also investigated by spectrophotometric and fluorimetric ti-
trations. As shown in Fig. 9, addition of 5 equiv of these anions to
For the rest of the anions (Cl , Br , I , H
even with 10 equiv, no significant changes were observed for the
-
Fig. 12. Frontier orbital energies (eV) and plots (isosurface at 0.03) of CT-2 and CT-2 at (U)B3LYP/6-31 þ G(d,p) level of theory. Hydrogens are excluded for clarity.

276
U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
aromatic thiophene proton signal (Ha). See Fig. 11 for a summary of
the associated spectral changes.
emission of CT-2, the donor to acceptor charge transfer transition
quenches the fluorescence.
3.3. Analysis of frontier molecular orbitals
3.4. Thermal stability of dyes
We have previously shown that molecular orbital (MO) analysis
is a very valuble tool to understand fluorescence switching [22].
The synthesized compounds in this study, CT-1 and CT-2, are
-
MOs for CT-2 and its unprotonated form (CT-2 ) are depicted in
fluorescently active dyes and have potential for usage as fluorescent
emitters. The light emitting potential of these dyes in the solid state
is linked to their thermal stability, thus CT-1 and CT-2 were sub-
jected to thermogravimetric analysis (TGA). The change in weight
of the compounds was measured as a function of temperature.
Fig. 12. (Fig. S17 in Supplemantary Information). It is clear that
without the abstraction of the amide proton, CT-2 undergoes a
coumarin based p/p* type of excitation. On the other hand, when
the reseptoric amide proton is transferred to fluoride, the remain-
ing negatively charged species is left with a large electron density
accumulating on the amide nitrogen and thiophene ring. This rise
Thermal stability of the dyes is shown in Fig. 13. The absence of
ꢁ
weight loss up to 80 C indicates that no water molecules are pre-
1
in electron density, is in perfect agreement with H NMR results,
sent in the solid state. The initial decomposition temperatures (T )
d
ꢁ
-
and switches the associated MO to be the HOMO in CT-2 instead of
for CT-1 and CT-2 were found to be 324 and 344 C respectively.
ꢁ
coumarin based HOMO in CT-2. Consequently while the
p/p*
Therefore, up to 320 C, both fluorescent dyes are fairly stable and
transition on coumarin is the electronic reason for fluorescent
hence promising in potential optical applications.
4. Conclusions
In this study, a novel coumarin-thiophene based colorimetric
and fluorimetric chemosensor (CT-2) was successfully synthesized
from coumarine-aminothiophene hybrid (CT-1) for ratiometric
ꢀ
ꢀ
ꢀ
sensing of CN , F and AcO . The results showed that strong, visible
colorimetric changes and emission quenching were observed in CT-
ꢀ ꢀ ꢀ
in the presence of CN , F and AcO in polar aprotic DMSO.
2
ꢀ
ꢀ
However, the chemosensor was more sensitive to CN , than F and
ꢀ
AcO at the stochiometric ratio of 1:2.5 respectively. The addition
ꢀ
ꢀ
ꢀ
of CN , F and AcO anions resulted in a light yellow-to-deep
yellow color change and emission quenched. Quantum chemical
calculations suggested that fluorescence quenching is due to
intramolecular charge transfer. No significant color or emission
changes were observed with the naked eye upon addition of the
rest of the ions (Figs. 14 and 15 ). Additionally, the TGA results show
that the dyes CT-1 and CT-2 have an enough thermal stability for
optical applications.
Fig. 13. TGA curves of CT-1 and CT-2.
Fig. 14. 1 ꢂ 10ꢀ M solutions of CT-2 in DMSO under ambient light, (rAnion/CT-2:10).
3
-3
Fig. 15. 1 ꢂ 10 M solutions of CT-2 in DMSO under UV light, 365 nm, (rAnion/CT-2:10).

U. Yanar et al. / Journal of Molecular Structure 1108 (2016) 269e277
277
Acknowledgements
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