Reaction-based colorimetric and ratiometric fluorescence sensor for detection of cyanide in aqueous media

Article abstract of DOI:10.1002/asia.201200578

A stilbene-based compound (1) has been prepared and was highly selective for the detection of cyanide anion in aqueous media even in the presence of other anions, such as F^-, Cl^-, Br^-, I ^-, ClO₄^-, H₂PO₄ ^-, HSO₄^-, NO₃^-, and CH₃CO₂^-. A noticeable change in the color of the solution, along with a prominent fluorescence enhancement, was observed upon the addition of cyanide. The color change was observed upon the nucleophilic addition of the cyanide anion to the electron-deficient cyanoacrylate group of 1. The spectral changes induced by the reaction were analyzed by comparison with two model compounds, such as compound 2 with dimethyl substituents and compound 3 without a cyanoacrylate group. An intramolecular charge-transfer (ICT) mechanism played a key role in the sensing properties, and the mechanism was supported by DFT/TDDFT calculations. Sense and sensitivity: A highly efficient and selective colorimetric and ratiometric fluorescent sensor for detection of cyanide in aqueous media has been developed. This sensor exhibits a distinctive color change upon reaction with cyanide, along with significant fluorescence amplification. The sensing mechanism is discussed with the aid of spectral analyses and DFT/TDDFT calculations. Copyright

Full text of DOI:10.1002/asia.201200578

DOI: 10.1002/asia.201200578
Reaction-Based Colorimetric and Ratiometric Fluorescence Sensor for
Detection of Cyanide in Aqueous Media
Yan-Duo Lin,[a] Yung-Shu Pen,[b] Weiting Su,[c] Kang-Ling Liau,[d] Yun-Sheng Wen,[a]
Chin-Hsin Tu,[b] Chia-Hsing Sun,[b] and Tahsin J. Chow*[a]
Abstract: A stilbene-based compound
(1) has been prepared and was highly
selective for the detection of cyanide
anion in aqueous media even in the
presence of other anions, such as Fꢀ,
addition of cyanide. The color change
was observed upon the nucleophilic ad-
dition of the cyanide anion to the elec-
tron-deficient cyanoacrylate group of 1.
The spectral changes induced by the
reaction were analyzed by comparison
with two model compounds, such as
compound 2 with dimethyl substituents
and compound 3 without a cyanoacry-
late group. An intramolecular charge-
transfer (ICT) mechanism played a key
role in the sensing properties, and the
mechanism was supported by DFT/
TDDFT calculations.
ꢀ
ꢀ
ꢀ
Clꢀ, Brꢀ, Iꢀ, ClO4 , H2PO4 , HSO4 ,
ꢀ
ꢀ
NO3 , and CH3CO2 .
A noticeable
Keywords: anions
eter cyanides
sensors
·
chemodosim-
fluorescence ·
change in the color of the solution,
along with a prominent fluorescence
enhancement, was observed upon the
·
·
Introduction
rivatives, and the attachment with quantum dots, etc.[4,5] Re-
action-based chemosensors for cyanide anion were also used
by taking advantage of their high selectivity over other
anions, especially in aqueous solutions. This chemosensor
can effectively reduce the interference of hydrogen bonding
and the acidity of the media. Effective sensors have been
designed using squaraine,[6] acridium salts,[7] oxazines,[8] tri-
fluoroacetophenone derivatives,[9] benzyl derivatives,[10] and
dicyanovinyl derivatives.[11]
Among the various signals for detection, fluorescence
emission is regarded to be the most efficient owing to its
high sensitivity and easy implementation under diversified
environmental conditions.[12] Usually, fluorescence detection
depends on the intensity change at a single wavelength. The
signal output could be easily overshadowed by the back-
ground noise of the sample media. To overcome this short-
coming, ratiometric fluorescent sensing is used, and this
allows the measurement of relative fluorescence intensities
at two different wavelengths.[13] The proportional ratio be-
tween the two different emissions can serve as an internal
reference for self-correction, therefore the reliability of the
measurements is substantially enhanced.[12b,14] To date, only
limited examples of ratiometric fluorescent chemosensors of
cyanide have been reported.[15]
Anions play important roles in the chemistry of biology,
medicine, and catalysis.[1] Among them, the cyanide ion is
unique owing to its lethal effect on living organisms and the
influence it has on our environment.[2] Nevertheless, cyanide
is widespread in industrial processes, including gold mining,
electroplating, metallurgy, and the synthesis of fibers and
resins.[3] The accidental or intentional release of toxic chemi-
cals can contaminate drinking water and become a serious
threat to the environment. Therefore, the detection of cya-
nide has become a subject of much attention in recent years.
Versatile methods for the detection of cyanide have been
developed, such as those based on hydrogen-bonding inter-
actions, complex formations with metal ions and boron de-
[a] Dr. Y.-D. Lin, Y.-S. Wen, Prof. Dr. T. J. Chow
Institute of Chemistry
Academia Sinica
Taipei 115 (Taiwan)
Fax : (+886)2-27884179
E-mail: chowtj@gate.sinica.edu.tw
[b] Dr. Y.-S. Pen, C.-H. Tu, Prof. Dr. C.-H. Sun
Department of Chemistry
Soochow University
To design a ratiometric probe that functions at two differ-
ent wavelengths, either a fluorescence resonance energy
transfer (FRET) or an intramolecular charge transfer (ICT)
mechanism can be adopted.[15] Herein we report a high-per-
formance colorimetric and ratiometric fluorescent chemo-
sensor (1) for cyanide that is based on the ICT mechanism.
This sensor works effectively in aqueous media with a dis-
tinctive visual color change and a large signal amplification
(2250 fold) upon fluorescence; uses an electron-rich trans-4-
(N,N-diphenylamino)stilbene (3) as a fluorescence emitter[16]
Taipei 111 (Taiwan)
[c] W. Su
Department of Chemistry
National Taiwan University
Taipei 106 (Taiwan)
[d] Dr. K.-L. Liau
Department of Chemistry
National Central University
Chung-Li 320 (Taiwan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200578.
Chem. Asian J. 2012, 00, 0 – 0
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Scheme 2. Synthesis of compound 2.
and a 2-cyanoacrylate as a detecting unit (Scheme 1). Upon
photoexcitation, compound 1 displays a strong ICT absorp-
tion. However, the fluorescence quantum yield is relatively
Figure 1. The X-ray crystal structures of 1 with displacement atomic ellip-
soids drawn at the 30% probability level.
Scheme 1. Synthesis of compound 1 and the reaction of 1 with the cya-
nide anion for the formation of 1-CN.
low owing to polarity quenching of the charge-separated
state. The sensing mechanism is recognized by a nucleophilic
addition of cyanide to the b-position of 2-cyanoacrylate.[11e]
The interruption in the p-conjugation between the stilbene
and the carboxylate, therefore terminates the ICT. As a con-
sequence, the color of the solution fades (blue shift in the
UV region), and at the same time a strong p–p* fluores-
cence from the stilbene chromophore emerges. The detec-
tion of the cyanide ion can be clearly observed by a discerni-
ble color change in both the absorption and emission spec-
tra.
stilbene moiety. Such planar conformation provides efficient
p-conjugation and favors the efficient ICT transition be-
tween the donor and the acceptor groups. Another structur-
al feature worth noting is the planar conformation of the
substituents around the nitrogen atom. The sum of the bond
angles (q) around the nitrogen atom is about 3558, thereby
indicating that the three phenyl substituents are in an ideal
trigonal planar arrangement. This ensures an effective deloc-
alization of the amine lone pair to the adjacent p-systems.[20]
A strong dipole is therefore expected in the ICT state upon
photoexcitation.
Results and DiscussionSynthesis and Crystal
Structure
Colorimetric and Absorption Spectral Response
The photophysical properties of the compounds 1–3 and 1-
CN in water/tetrahydrofuran (THF) solutions are summar-
ized in Table 1. The sensing properties of 1 were examined
in water/THF solutions (30:70 (v/v)) by the addition of the
tetrabutylammonium (TBA) salt of various anions such as
The synthesis of compounds 1 and 2 are outlined in
Schemes 1 and 2. The synthesis of 3,[16a] 4,[17] 5,[18] and 6[17]
have been previously reported. The synthesis of 1 was ach-
ieved readily through condensation of aldehyde 4[17] with
ethyl cyanoacetate in the presence of acetic acid. Compound
6[17] was coupled with 4-bromo-2,6-dimethyl-benzaldehyde
through a Heck-type reaction to afford 7, followed by
a Knoevenagel reaction with ethyl cyanoacetate to afford
the desired compound 2.
A single crystal of compound 1 was resolved by X-ray dif-
fraction analyses, and its molecular structure is shown in
Figure 1.[19] From the side view it is clearly observed that the
2-cyanoacrylic acid ethyl ester group is coplanar with the
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4 , H2PO4 , HSO4 , NO3 , CH3CO2 ,
and with and without CNꢀ (Figure 2a). In the UV/Vis ab-
sorption spectrum, the solution of 1 showed two distinct ab-
sorption bands at 310 and 446 nm. The former is attributed
to the p–p* transition and the latter to an ICT transition.
Upon addition of 30 equivalents of various anions except
for CNꢀ ion, the absorption spectra of sensor 1 did not ex-
hibit any significant change. However, upon addition of
CNꢀ ion, both absorption bands diminished with concomi-
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Fluorescence Sensor for Detection of Cyanide in Aqueous Media
Table 1. Maxima of UV/Vis absorption (labs), fluorescence (lf), fluores-
cence decay times (tfl), 0,0 transition (l0,0), and fluorescence quantum
yields (Ffl) for compounds 1–3 and 1-CN in water/THF solutions.
Compound
labs [nm]
lf [nm]
l0ꢀ0 [nm][a]
tfl
Ffl
1
310, 446
296, 373
305, 394
296, 366
460, 676
460
500, 655
455
533
419
474
405
2.48[b]
n.d[c]
0.012
0.66
0.031
0.89
1-CN
2
3
2.90[b]
2.41[d]
[a] The value of l0ꢀ0 was obtained from the intersection of normalized
absorption and fluorescence spectra. [b] The value of tfl was determined
with excitation around the spectral maxima and emission around 460 nm
for 1 and 500 nm for 2. [c] Not determined. [d] The value of tfl was deter-
mined with excitation and emission around the spectral maxima.
Figure 3. a) Time-dependent absorption spectra of sensor 1 (3ꢂ10ꢀ5 m)
upon the addition of CNꢀ (10 equiv) in a water/THF (30:70, v/v) solution.
The arrows indicate the change in incubation time from 0 to 14 mins.
b) Time-dependent absorption intensity of sensor 1 at 446 nm (&) and
373 nm (~) in the presence of CNꢀ (10 equiv).
Figure 2. a) Absorption spectra of 1 in a water/THF (30:70, v/v) solution
ꢀ
(3ꢂ10ꢀ5 m), and Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4ꢀ, H2PO4ꢀ, HSO4ꢀ, NO3ꢀ, CH3CO2
with and without CNꢀ (30 equiv each); b) Absorption titration spectra of
1 with different concentrations of CNꢀ (0ꢂ30 equiv at 2.0 equiv inter-
vals).
Figure 4. Jobꢁs plot of 1 in a water/THF (30:70, v/v) solution showing the
1:1 stoichiometry of the reaction with CNꢀ. The total concentration of
1 and CNꢀ is 10ꢀ5 molLꢀ1. Absorbance is recorded at 373 nm.
tant growth of two new bands at 296 and 373 nm (Fig-
ure 2b). The time-dependence changes in the absorption
spectra of sensor 1 upon the addition of cyanide were
almost completed within 14 min, as indicated in Figure 3.
The presence of three clear isosbestic points at 305, 338, and
397 nm implies its clean transformation into a new species
(Figure 2b). This is in good agreement with a 1:1 binding
stoichiometry by Jobꢁs plot of the UV/Vis absorption
(Figure 4). The significant changes in the color can be per-
ceived clearly by the naked eye (Figure 5). The color change
is attributed to the nucleophilic addition of CNꢀ to the b-po-
sition of 2-cyanoacrylic acid ethyl ester, thereby leading to
tonation of CNꢀ (Figure S11, see the Supporting Informa-
tion).
Fluorescence Behavior
When compound 1 was photoexcited, a weak red fluores-
cence centered at 676 nm was observed (Ff =0.012, excited
at the isosbestic point 338 nm). Along with this major emis-
sion band, a minor emission band centered at 460 nm can
also be observed (Figure 6a). The ICT nature of compound
1 at the 676 nm band is unambiguously supported by the sol-
vent-polarity dependent spectral shift, as depicted in Fig-
a
significant blue shift in the absorption wavelength
(Scheme 1). The spectral response is predictable in neutral
and basic solutions, yet in an acidic solution (pHꢁ5), the
detecting sensitivity is substantially reduced due to the pro-
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pound 2, by using DFT calculations (Figure S8, see the Sup-
porting Information), the dihedral angle between the 2-cya-
noacrylate and the adjacent phenyl group was twisted to ap-
proximately 508 in its lowest energy state. The presence of
dual fluorescence of 2 at 500 and 655 nm in aqueous solu-
tion resembles closely to that of 1 (Figure 7). The intensity
of the 500 nm emission of 2 was found to be higher than the
Figure 5. a) Color changes of 1 (3ꢂ10ꢀ5 m) after addition of Fꢀ, Clꢀ, Brꢀ,
Iꢀ, ClO4ꢀ, H2PO4ꢀ, HSO4ꢀ, NO3ꢀ, CH3CO2ꢀ, and CNꢀ (30 equiv, respec-
tively) in water/THF (30:70, v/v); b) fluorescence change of 1 (3ꢂ10ꢀ5 m)
ꢀ
ꢀ
ꢀ
ꢀ
after addition of Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4
, H2PO4 , HSO4 , NO3 ,
ꢀ
CH3CO2 and CNꢀ (30 equiv, respectively) in water/THF (30:70, v/v)
upon excitation at 365 nm with a laboratory UV lamp.
Figure 7. Normalized fluorescence spectra of 1 and 2 in a water/THF
(30:70, v/v) solution.
460 nm emission of 1, as a result of a higher population of
the twist conformation. The excitation spectrum of 2 coin-
cides with the absorption maximum of 3 (Figure S7b, see
the Supporting Information). The lifetime of the 500 nm
emission (tf =2.41 ns) of 2 was also quite close to that of
1 at 460 nm. All of this information supports the conclusion
that the minor emission band of 1 is derived from a twisted
conformational isomer, which forms an equilibrium with the
major planar conformational isomer.[15f,21]
Anions-Induced Fluorescence Spectral Response
ꢀ
ꢀ
Upon the addition of Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4 , H2PO4 ,
ꢀ
ꢀ
ꢀ
HSO4 , NO3 , and CH3CO2 , no significant change was ob-
served in the emission spectra of 1. The only prominent re-
sponse appeared when CNꢀ was added (Figure 8a), while
fluorescence was observed at 460 nm and the band at
676 nm diminished. The blue shift induced by the addition
of CNꢀ was very large (216 nm) with a clear isoemissive
point at 643 nm. The intensive blue fluorescence can be
easily observed by the naked eye (Figure 5b). The ratio of
fluorescence intensities at 460 nm and 676 nm (I460/I673) ex-
hibited a 2.25ꢂ103 fold in enhancement, that is, from 0.08 to
180 (Ff =0.66) before and after the addition of CNꢀ
(30 equiv), respectively. To further elucidate the effective-
ness of sensor 1 under harsher conditions, a competitive ex-
periment was examined in a water/THF solution in the pres-
Figure 6. a) Normalized fluorescence spectra of 1 and 3 in a water/THF
(30:70, v/v) solution; b) Normalized fluorescence spectra of sensor 1 in
cyclohexane, toluene, ethyl acetate, THF, and water/THF (30:70, v/v).
ure 6b. The emission band at 460 nm is most likely derived
from the trans-4-(N,N-diphenylamino) stilbene moiety (c.f.,
compound 3 at lmax 455 nm Figure 6a), as the result of an
out-of-plane twist between the stilbene and 2-cyanoacrylate
moieties. The excitation spectra were also obtained by moni-
toring the emission at 460 nm, and the excitation spectra of
1 was in good agreement with the absorption spectra of 3,
thereby suggesting that the emission of 1 at 460 nm is de-
rived from a similar chromophore to that of 3 (Figure S7a,
see the Supporting Information). The fluorescence lifetime
(tf) of 1 at 460 nm (tf =2.48 ns) is also close to that of 3 at
455 nm (tf =2.90 ns). To shed more light on the origin of the
dual fluorescence, a dimethyl-substituted derivative 2 was
synthesized for comparison. In a simulated structure of com-
ꢀ
ence of the following anions: Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4 ,
ꢀ
ꢀ
ꢀ
ꢀ
H2PO4 , HSO4 , NO3 , and CH3CO2 (30 equiv each). The
color of the solution changed from orange to colorless upon
the addition of CNꢀ in the same manner as those by adding
each anion alone (Figure 2a). The strong fluorescence en-
hancement was not affected either by the presence of all
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Fluorescence Sensor for Detection of Cyanide in Aqueous Media
Figure 9. a) The fluorescence intensity of sensor 1 (3ꢂ10ꢀ5 m) incubated
with CNꢀ (6ꢂ10ꢀ4 m) for 0–3 min. b) Pseudo-first-order kinetic plot of
the reaction of 1 (3ꢂ10ꢀ5 m) incubated with CNꢀ (6ꢂ10ꢀ4 m) in a water/
Figure 8. a) Fluorescence titration spectra of 1 (3ꢂ10ꢀ5 m in water/THF
30:70, v/v) in solution with different concentrations of CNꢀ (0ꢂ30 equiv
at 2.0 equiv interval). Inset: ratio of fluorescent intensities at 676 and
460 nm as a function of CNꢀ concentration; b) The fluorescence ratio in-
tensity of 1 (3ꢂ10ꢀ5 m) at 460 nm and 673 nm in the presence of various
analytes (30 equiv) in a water/THF (30:70, v/v) solution.
THF (30:70, v/v) solution. Slope=ꢀ0.396 minꢀ1
.
of the line provides the pseudo-first-order rate constant for
CNꢀ: k’=0.396 minꢀ1.
1H NMR Titration Experiments
anions together (Figure 8b). These experiments not only
confirmed the excellent selectivity of 1 for the cyanide
anion, but also illustrated its high potential for practical ap-
plications.
1
The product 1-CN was analyzed by H NMR spectroscopy.
A solution of 1 in [D8]THF solution was monitored by grad-
ual addition of tetrabutylammonium cyanide (Figure 10).
The increase in cyanide concentration resulted in a dimin-
ished vinylic proton signal (Ha) at 8.24 ppm, until it com-
pletely disappeared with the addition of 1 equiv of cyanide
anion. A new signal appeared at 5.04 ppm, which corre-
sponds to the b-proton of cyanoacrylate. Meanwhile, the
two sets of aromatic protons (Hc and Hd in the styrene
moiety) are shifted to higher field with respect to the ethyl-
ene protons. These observations are consistent with the pro-
Kinetic Studies
The reaction rate constant of 1 (3ꢂ10ꢀ5 m) with CNꢀ (6ꢂ
10ꢀ4 m) was estimated under a pseudo-first-order approxima-
tion (Figure 9). The reaction of sensor 1 (3ꢂ10ꢀ5 m) with
CNꢀ (6ꢂ10ꢀ4 m) in a water/THF (30:70, v/v) solution was
monitored by using the fluorescence intensity at 460 nm
(Figure 9a). The reaction was carried out at room tempera-
ture. The pseudo-first-order rate constant for the reaction
was determined by fitting the fluorescence intensities of the
samples to the pseudo-first-order equation (1):
ln ½ðFmaxꢀFtÞ=Fmaxꢃ ¼ ꢀk0t
ð1Þ
where Ft and Fmax are the fluorescence intensities at
460 nm at time t and the maximum value obtained after the
reaction was completed. k’ is the pseudo-first-order rate con-
stant. The pseudo-first-order plot for the reaction of 1 with
CNꢀ (6ꢂ10ꢀ4 m) is shown in Figure 9b. The negative slope
Figure 10. 1H NMR spectral changes of 1 in [D8]THF upon the addition
of CNꢀ anion.
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Table 2. Calculated TDDFT excitation energies (E), oscillator strengths
(f), MO compositions, and characters for 1 and 1-CN.
posed mechanism shown in Scheme 1. However, no signal
was observed that corresponds to the a-proton of the ethyl-
ene moiety due to the persistence of a stabilized enolate
anion.[4d] In addition, the formation of cyanide adduct 1-CN-
H (i.e., neutral form of anion 1-CN) was further confirmed
by high-resolution FAB-MS, where a peak at m/z 498.2190
is assigned to [1-CN + 2H]+ (Figure S9, see the Supporting
Information).
Dye
n[a] E (ev, nm)
f
Composition
Character
1
1
2
6
1
5
6
2.37 (524)
3.33 (372)
3.70 (335)
2.99 (414)
3.93 (315)
3.93 (315)
1.00 98% HOMO!LUMO
0.99 82% HOMO-1!LUMO
CT
p–p* (1)
0.13 93% HOMO!LUMO+3 p–p* (2)
1-CN
1.06 97% HOMO!LUMO
0.16 95% HOMO!LUMO+3 p–p* (1)
0.60 93% HOMO-1!LUMO p–p* (2)
CT
[a] Sequence of calculated transitions in order of energy.
Molecular Orbital Calculations
To gain further insight into the mechanism of the color
bleaching and fluorescence enhancement of 1 in the pres-
ence of CNꢀ, molecular modeling was performed by using
the density function theory with B3LYP using 6-31GACTHUNTGRNEUNG(d,p)
basis sets implanted in a Gaussian 03 program.[22] The opti-
mized geometries of 1 and 1-CN are shown in Figure 11.
The optimized geometry of sensor 1 was in good agreement
with the experimental crystal structures shown in Figure 1.
The major chromophore adopts a nearly planar conforma-
tion, extending from the 2-cyanoacrylate acceptor to the stil-
bene moiety. The three aromatic substituents around the N
atom maintain an ideal trigonal planar shape (q=3608). The
ground-state geometry undergoes an apparent twist upon
the addition of CNꢀ, while the p-conjugation between the 2-
cyanoacrylate and the stilbene was interrupted. The inter-
ruption of the p-conjugation resulted in a substantial blue
shift in the absorption spectrum, and decreased the ICT
character.
Detailed information about the marked absorption in the
blue shift upon nucleophilic cyanide addition with 1 can be
obtained from time-dependent DFT (TDDFT) calculations
as well. The results of transitions with an oscillator strength
above 0.1 are summarized in Table 2. The calculated absorp-
tion wavelengths of 1 and 1-CN were 524 nm and 414 nm,
respectively, with oscillator strengths of 1.00 and 1.06. The
calculated hypsochromic shift is in good agreement with ex-
perimental results. The simulated spectra of 1 and 1-CN are
shown in Figure S10 (See the Supporting Information).
The calculated electron distributions in the frontier mo-
lecular orbitals of 1 and 1-CN are shown in Figure 12. For
comparison, the corresponding data for 3 are also included
Figure 12. The HOMO and LUMO energy levels and the orbitals of 1, 1-
CN and 3.
in Figure 12. In the case of 1, the electron density in the
HOMO is localized mainly on the triphenylamine (TPA)
moiety, while the LUMO is localized on the 2-cyanoacrylic
acid ethyl ester. A charge separation is expected to be pro-
duced while an electron is promoted from the HOMO to
the LUMO. However, the electron distribution in 1-CN, par-
ticularly in the LUMO, is different from that of 1. Because
of the saturation of a C=C bond, the electron population in
the LUMO of 1-CN is confined on the stilbene moieties,
without involving the cyanoacrylate. The electronic configu-
ration of 1-CN is analogous to that of 3, as well as their high
fluorescence quantum efficiencies.[16] The calculated elec-
tronic nature of 1 complies nicely with the experimental ob-
servations (Figure 5).
Conclusions
A
stilbene-based sensor for
CNꢀ in an aqueous THF solu-
tion displayed a remarkable se-
lectivity in the presence of
other anions. A large blue shift
(73 nm) was observed in the
absorption spectra in response
to CNꢀ. A ratiometric dual
fluorescence was also detected
with an intensity enhancement
of I460/I673 up to 2.25ꢂ103 fold.
The dual fluorescent nature
was found to be a result of an
Figure 11. The optimized structures of 1 and 1-CNꢀ.
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Fluorescence Sensor for Detection of Cyanide in Aqueous Media
123.05, 20.72 ppm; FAB-HRMS calcd for C29H26NO [M+H+] 404.2014,
found 404.2025.
equilibrium between two conformational isomers. This phe-
nomenon can be explained explicitly with the aid of DFT/
TDDFT calculations, the spectral blue shift was caused by
diminishing the ICT character, therefore inhibiting the fluo-
rescence quenching mechanism.
2-Cyano-3-{4-[2-(4-diphenylamino-phenyl)-vinyl]-2,6-dimethyl-phenyl}-
acrylic acid ethyl ester (2)
An acetic acid solution of 7 (0.85 g, 2.1 mmol), ethyl cyanoacetate (2.4 g,
21 mmol), and ammonium acetate (0.04 g, 0.53 mmol) was stirred at
908C for 24 h. The organic layer was separated and dried over MgSO4.
After the solvent was removed under reduced pressure, the crude prod-
uct was recrystallized in CH2Cl2/MeOH to afford the desired product 2
Experimental Section
1
(0.66 g, 63%) as light-orange solid. M.p. 161–1628C; H NMR (400 MHz,
General Information
CDCl3): d=8.51 (s, 1H), 7.39 (d, J=8.4 Hz, 2H), 7.29–7.24 (m, 6H),
7.14–7.03 (m, 9H), 6.92 (d, J=16.0 Hz, 1H), 4.41 (q, J=7.1 Hz, 2H),
1.43 ppm (t, J=7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=161.54,
157.38, 147.72, 147.45, 139.34, 136.71, 130.98, 130.35, 129.71, 129.30,
127.53, 126.01, 125.82, 124.63, 123.29, 123.17, 114.44, 110.60, 62.76, 20.48,
14.11 ppm; FAB-HRMS calcd for C34H31N2O2 [M+H+] 499.2385, found
499.2398.
1H and 13C NMR spectra were recorded on a Bruker 400 MHz spectrom-
eter. Fast atom bombardment (FAB) mass spectra were recorded on
a Jeol JMS 700 double-focusing spectrometer. UV spectra were measured
on a Jasco V-530 double-beam spectrophotometer. Fluorescence spectra
were recorded on a Hitachi F-4500 fluorescence spectrophotometer. Ab-
sorption and fluorescence sensing measurements were performed in 3ꢂ
10ꢀ5 m water/THF (30:70, v/v) solutions in all cases. The aliquots of
a freshly prepared anion solution (0.03M) at defined increments were
added to an optical cell containing compound 1 (2 mL) and a magnetic
stir bar. Solutions were allowed to equilibrate for 15 min before taking
each measurement. Experiments with longer equilibration times did not
produce noticeable differences. A nitrogen bubbled solution of anthra-
cene (Ff =0.27 n-hexane)[23] was used as a standard for the fluorescence
quantum yield determinations. An error of 10% is estimated for the fluo-
rescence quantum yields. Fluorescence lifetimes were also measured at
room temperature by using a Edinburgh FLS920 spectrometer. The in-
strument response function was calibrated by a scatter solution using
a gated hydrogen arc lamp. The goodness of the nonlinear least-squares
fit was judged by the reduced c2 value (<1.2 in all cases), the randomness
of the residuals, and the autocorrelation function. Solvents of reagent
grade were used for syntheses, and those of spectroscopy grade for spec-
tra measurements. Compounds purchased from commercial sources were
used as received. The syntheses of compounds 5[18] and 6[17] have been re-
ported previously.
Quantum Chemistry Computation
Computations were performed using the Gaussian 03 program pack-
age.[22] The geometry was optimized by using B3LYP (Becke three pa-
rameters hybrid functional with Lee–Yang–Parr correlation functionals)
with the Pople 6–31GACTHNUTRGNEUNG
(d,p) atomic basis set.[22b,c]
Acknowledgements
Financial support was provided in part by the National Science Council
of the Republic of China. We thank Professor J.-S. Yang for the lifetime
measurements.
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2-Cyano-3-{4-[2-(4-diphenylamino-phenyl)-vinyl]-phenyl}-acrylic acid
ethyl ester (1)
An acetic acid solution of
4 (0.5 g, 1.30 mmol), ethyl cyanoacetate
(0.2 mL, 13.40 mmol), and ammonium acetate (0.03 g, 0.33 mmol) was
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J=8.4 Hz, 2H), 7.48 (d, J=8.4 Hz, 2H), 7.36 (d, J=16.4 Hz, 1H), 7.28–
7.24 (m, 4H), 7.14 (d, J=16.4 Hz, 1H), 7.11 (d, J=8.4 Hz, 2H), 7.05–7.01
(m, 5H), 4.32 (q, J=7.1 Hz, 2H), 1.35 ppm (t, J=7.1 Hz, 3H); 13C NMR
(100 MHz, [D8]THF): d=163.35, 154.36, 149.35, 148.63, 144.16, 132.80,
132.62, 132.03, 131.58, 130.33, 128.98, 127.78, 126.42, 125.79, 124.36,
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C32H27N2O2 [M+H+] 471.2072, found 471.2079.
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A
ACHTUNGTRENNUNG
and 6 (2.23 g, 8.2 mmol) under argon were heated at 808C for 18 h. The
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Tahsin J. Chow et al.
FULL PAPER
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Received: June 28, 2012
Published online: && &&, 0000
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

FULL PAPER
Fluorescent Sensors
Yan-Duo Lin, Yung-Shu Pen,
Weiting Su, Kang-Ling Liau,
Yun-Sheng Wen, Chin-Hsin Tu,
Chia-Hsing Sun,
Tahsin J. Chow*
&&&& — &&&&
Sense and sensitivity: A highly effi-
cient and selective colorimetric and
ratiometric fluorescent sensor for
detection of cyanide in aqueous media
has been developed. This sensor exhib-
its a distinctive color change upon
reaction with cyanide, along with sig-
nificant fluorescence amplification.
The sensing mechanism is discussed
with the aid of spectral analyses and
DFT/TDDFT calculations.
Reaction-Based Colorimetric and
Ratiometric Fluorescence Sensor for
Detection of Cyanide in Aqueous
Media
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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