A novel fluorescent sensor for Cr3+ based on rhodamine-cored poly (amidoamine) dendrimer

Article abstract of DOI:10.1016/j.saa.2011.08.006

A novel poly (amidoamine) (PAMAM) dendrimer, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, has been synthesized and characterized. The dendrimer shows dramatic increase in its fluorescence intensity in t

Full text of DOI:10.1016/j.saa.2011.08.006

Spectrochimica Acta Part A 83 (2011) 149–154
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A novel fluorescent sensor for Cr3+ based on rhodamine-cored poly (amidoamine)
dendrimer
Yonglin Lei∗, Yuanqiang Su, Jichuan Huo
State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, School of Material Science and Engineering, Southwest University of Science and Technology,
621010 Mianyang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel poly (amidoamine) (PAMAM) dendrimer, comprising rhodamine B unit in the core and 1-phenyl-
3-methyl-5-pyrazolone unit at the periphery, has been synthesized and characterized. The dendrimer
shows dramatic increase in its fluorescence intensity in the presence of proton and metal cations, espe-
cially in the presence of Cr3+. The complex formed by dendrimer and Cr3+ in ethanol solution has also
been studied, considering the potential application for Cr3+ fluorescent sensor. The influence of the unique
chemical structure and resulted photoinduced electron transfer, as well as spirolactam ring-opening on
the photophysical properties of the product has been investigated.
Received 24 March 2011
Received in revised form 15 July 2011
Accepted 7 August 2011
Keywords:
Poly (amidoamine) dendrimer
Rhodamine B
1-Phenyl-3-methyl-5-pyrazolone
Ring opening
© 2011 Elsevier B.V. All rights reserved.
Photoinduced electron transfer
1. Introduction
foreign ions and low fluorescence quantum yield. As few fluores-
cent PAMAM derivatives for Cr3+ ions were reported, the design of
Trivalent chromium ion plays an important role as a neces-
sary trace element in human nutrition. Chromium deficiency can
increase the risk of getting diabetes and cardiovascular diseases.
In addition, chromium is a well-known environmental pollutant
which accumulates due to agricultural and industrial activities.
Due to the vital importance of chromium in biological system and
industry, a narrow window of concentration between essentiality
and toxicity warrants the determination of chromium. Although
sophisticated analytical techniques, such as ICP-AES, X-ray flu-
orescence, HPLC and DPP, have been employed for trace level
determination, they are of high cost and inconvenient for routine
analysis. Therefore, it is important to develop a more convenient,
faster, and lower cost method for trace Cr3+ determination, for
instance, analyzing by ion-selective sensors [1–6].
PAMAM-based fluorescent sensors for Cr3+ ion is still an attractive
prospect.
Rhodamine based chemodosimetric sensors are popular for
their excellent photophysical properties, such as low excitation
energy, high fluorescence quantum yield, large extinction coef-
ficient and their spirolactam ring-opening reaction, which can
provide a strong fluorescence emission and a distinct color upon
selective opening of rhodamine spirolactam ring in the presence
of specific metal cations [17–22]. Several successful attempts have
been made to develop selective sensors for Cr3+ ion based on rho-
damine [6]. Thus, in our work, rhodamine B was chosen as the
fluorophore component in the dendrimer core in view of its pecu-
liar merit of high fluorescence efficiency [23] and its ring-opening
process in PAMAM-based PET sensors [24].
A
review of literature revealed that poly (amidoamine)
Of particular interest, the PET fluorescent sensors are designed
so that the electron transfer occurs between the fluorophore
(signaling unit) and the receptor (“switch” of the fluorescence
intensity) [25–27]. The receptor unit with shorter wavelength
absorption has been connected chemically to fluorophore, where
the PET between them is occurred effectively [28–30]. Therefore, an
electron-donating compound, which can absorb short wavelength
light and chelate with metal ions effectively, was chosen as the
receptor unit. As a strong UV absorption chromophore, 1-phenyl-
3-methyl-5-pyrazolone can transfer electron easily and chelate to
Cr3+ ion effectively [31]. It is a good candidate for the receptor
unit. Keeping this in mind, we have designed a chemosensor by
(PAMAM) dendrimer can act as effective photoinduced electron
transfer (PET) fluorosensors for metal cations and proton [7–11].
Furthermore, it was reported that PAMAM functionalized den-
drimers possessing 1,8-naphthalimides at the periphery might
enhance their selectivity towards some specific metal cations
[12–16], such as Li+ and Cu2+. However, better design of such kind
of sensors is still needed due to their bad anti-jamming ability to
∗
Corresponding author. Tel.: +86 0816 2419209.
E-mail address: leiyonglin@163.com (Y. Lei).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.08.006

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Y. Lei et al. / Spectrochimica Acta Part A 83 (2011) 149–154
Bruker AV II spectrometer, operating at 400 MHz for 1H using CDCl3
as solvent. The chemical shifts were referenced to tetramethyl-
silane (TMS). The IR spectra were measured on a Spectrum One
(Version BM) FTIR spectrometer with 2 cm−1 resolution using KBr
pellet method.
The effect of the metal cations and proton on the fluorescence
intensity was examined by adding a few ␮L of stock solution of
metal cations to a fixed volume of dendrimer solution (3 mL). The
addition amount of the cations solution was limited to 0.08 mL
to make sure the dilution effect was insignificant. The pH was
adjusted by addition of HCl or NaOH into 3 mL of solvent. All
spectral measurements in this study were performed at room
temperature.
2.3. Synthesis of new dendrimer G3
Dendrimer G3 was readily prepared according to Scheme 2.
Step one: diamine (0.03 mol) was dissolved in 50 mL of ethanol,
and then rhodamine B (0.01 mol) and thionyl chloride (0.5 mL)
were added dropwise under vigorous stirring at room temperature
within 30 min. The mixture solution was heated at 75 ◦C for 5 h
under vigorous stirring. The solvent was removed by distillation
under the vacuum of 0.093 MPa at 75 ◦C. The obtained product was
named with “compound 1” which had a yield of 87.4%. It was puri-
fied by double re-crystallization with ethanol and dried in vacuum
at room temperature.
Scheme 1. Chemical structures of dendrimer G3.
Step two: compound 1 (0.005 mol), methylacrylate (0.02 mol)
and methanol (50 mL) were mixed and stirred at 0 ◦C under a nitro-
gen atmosphere for 24 h. Then, the mixture was distilled under
the vacuum of 0.093 MPa at 0 ◦C, and the residue was washed by
methanol. The obtained product was named with “compound 2”
which had a yield of 74%. Subsequently, 0.002 mol compound 2 was
reacted with 0.02 mol of ethylene diamine in 50 mL of methanol
under nitrogen atmosphere for 24 h at room temperature. The sol-
vent was removed by vacuum distillation of 0.093 MPa at 75 ◦C, and
the residue was dried in vacuum at 25 ◦C. The obtained product was
named with “compound 3” which had a yield of 68%.
linking 1-phenyl-3-methyl-5-pyrazolone as an appended group to
the PAMAM periphery, and expect it could give the dendrimer
desired fluorescent properties and transmit the recognition sig-
nal.
In the present work, we designed and synthesized a novel
PAMAM dendritic polymer (dendrimer G3, as shown in Scheme 1).
Rhodamine B unit in the core of PAMAM and 1-phenyl-3-methyl-
5-pyrazolone fluorescent unit performed as fluorophore reporter
and receptor, respectively. By introducing typical photoactive units
both in and outside of PAMAM, unique properties, such as inter-
esting PET process and ring opening process of rhodamine were
expected. Furthermore, according to the simultaneous effect of
PET and ring-opening mechanism, we first designed a Cr3+ sensor
containing photoactive PAMAM structure, which simultaneously
contained rhodamine and pyrazolone units. In this work, the
photophysical properties of the obtained dendrimers have been
investigated in detail, and their relationship with the PET and ring-
opening effect was also discussed.
The same procedure was conducted for the synthesis of com-
pound 5. It was produced from compound 3 using the above
mentioned “step two”. Finally, 0.001 mol of compound 5, 0.004 mol
of 1-phenyl-3-methyl-5-pyrazolone and 30 mL of ethanol were
heated and refluxed for 6 h. Then, the solvent was removed under
vacuum condition. With these efforts, the final product den-
drimer G3 was obtained after solvent removal, and purified by
column chromatography using silica gel as stationary phase and
dichloromethane methanol (12:1) mixture as mobile phase. The
yield of dendrimer G3 was of 71.6%, and the corresponding FT-
2. Experimental
IR and 1H NMR data were listed as follows. FT-IR (KBr), cm−1
:
2.1. Materials
3428, 3063.8, 2961.9, 2925, 2797, 1948, 1713.7, 1657.7, 1621.6,
1596.4, 1499.1, 1457.4, 1436.8, 1403, 1361.4, 1320.2, 1262.1,
1099.4, 1028.5, 905.7, 800.1, 756.9, 692.1, 662.1, 505.0; 1H NMR
(CDCl3, 400 MHz, ppm): 1.14 (t, 12H, CH3CH2N), 1.246 (s, 12H,
CH3CNN), 1.408 (m, 8H, NCCH2C), 2.006 (m, 4H, OCCH2CH2N),
2.093 (m, 8H, OCCH2CH2N), 2.207 (m, 4H, OCCH2CH2N), 2.240
(m, 8H, OCCH2CH2N), 2.335 (m, 2H, NCH2CH2NH), 2.376 (m,
4H, CONHCH2CH2N), 2.605 (m, 8H, CONHCH2CH2N), 2.855 (m,
2H, ArCONHCH2CH2N), 2.937 (m, 4H, (CH3)2NCH2CH2NH), 3.187
(m, 8H, CNCH2CH2N), 3.420 (q, 8H, CH3CH2N), 7.174 (m, 2H,
C6H3), 7.193 (m, 2H, C6H3), 7.215 (m, 2H, C6H3), 7.255 (br s, 4H,
CONHCH2CH2N), 7.313 (s, 4H, C6H5), 7.332 (s, 4H, C6H5), 7.352 (d,
4H, C6H5), 7.403 (d, 1H, C6H5), 7.421 (d, 1H, C6H5), 7.625 (s, 1H,
C6H4), 7.644(br s, 2H, CONHCH2CH2N), 7.831 (m, 1H, C6H4), 7.914
(m, 1H, C6H4), 7.966 (br s, 1H, ArCONHCH2CH2N), 8.235 (m, 1H,
C6H4). Analysis: C100H129ClN24O8, Calcd: C 65.30, H 7.51; N 18.27,
Found: C, 65.61; H, 7.10; N, 18.36.
1-Phenyl-3-methyl-5-pyrazolone, rhodamine B, ethylene
diamine, thionyl chloride, and methylacrylate were purchased
form Shanghai Chemical Reagents (Shanghai). All organic solvents
(including methanol, ethanol) used in this study were of analytical
reagent grade. Cr(NO3)3·9H2O, Cu(NO3)2·3H2O, Zn(NO3)2·4H2O,
Fe(NO3)3, Ba(NO3)2, SrCl2·2H2O, Al(NO3)3, Hg(NO3)2, Ni(NO3)2,
CaCO3, KCl were the metal cation sources and were obtained from
Chengdu Chemical Reagent Factory (Chengdu).
2.2. Methods
UV–vis spectrophotometric investigations were performed on
a UV-3150 spectrophotometer with the solution concentration of
1 × 10−5 mol L−1. The fluorescence spectra were recorded by a PE
LS55 spectrofluorimeter. The NMR spectra were obtained by a

Y. Lei et al. / Spectrochimica Acta Part A 83 (2011) 149–154
151
Scheme 2. Synthesis route of dendrimer G3.
showed that it was quite different of the two compounds’ fluo-
rescence behavior. The pH titration control experiments revealed
that the compound 1 did not show any obvious fluorescence emis-
sion when the pH value was between 5 and 9. However, it had a
strong fluorescence response in acid media (pH 3–4). These changes
are similar to most rhodamine-based spirolactam chemosensors,
which attribute to the ring opening of spirolactam in acid media (pH
3–4) and the formation of a highly delocalized conjugated structure.
However, the dendrimer G3 shows weak fluorescence when the
pH value was between 5 and 9. In this pH range, the spirolactam ring
of dendrimer G3 was closed like compound 1. But for the effect of
steric hindrance, the molecular distortion of dendrimer G3 was less
than that of compound 1, and the delocalized conjugated degree of
dendrimer G3 was larger. Thus, a weak fluorescence emission was
observed.
Compared to compound 1, a stronger fluorescence response of
dendrimer G3 was also observed in acid media (pH 3–4), which
could be explained by the ring-opening mechanism (Scheme 3).
Moreover, in acid media (pH 3–4), the fluorescence response of
dendrimer G3 was much weaker than that of compound 1 at the
same pH. This fluorescence response may be caused by electronic
transfer from the nitrogen of PAMAM part and terminal pyrazolone
moieties of dendrimer G3 to the rhodamine core, which leads to a
decreased fluorescence intensity of rhodamine core.
Fig. 1. pH vs. fluorescence intensity of the dendrimer G3 in ethanol at concentration
of 10−5 mol L−1
.
3. Results and discussion
3.1. Influence of proton on the fluorescence properties of
dendrimer G3
3.2. Influence of metal cations on the fluorescence properties of
dendrimer G3
Fig. 1 presents the fluorescence response of the dendrimer G3
and compound 1 in ethanol solution with various pH values. The
experiments were carried out in a pH range of 3–9. The result
The supramolecular fluorescence properties of dendrimer G3
in the presence of different metal cations (Cr3+, Ba2+, Ca2+, Sr2+
,

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Y. Lei et al. / Spectrochimica Acta Part A 83 (2011) 149–154
Scheme 3. The reaction scheme of dendrimer with H+.
Fig. 2. Fluorescence enhancement of G3 in the presence of different metal cations
(C = 1 × 10−5 mol L−1) in ethanol. The dendrimer G3 concentration in the solution is
Fig. 3. Fluorescence enhancement of rhodamine B in the presence of different metal
cations (C = 1 × 10−5 mol L−1) in ethanol. The rhodamine B concentration in the solu-
C = 1 × 10−5 mol L−1
.
tion is C = 1 × 10−5 mol L−1
.
the Cr3+ ion. These results indicated that the presented dendrimer
G3 could be used as an efficient sensor for Cr3+ ion.
Fe3+, Al3+, Zn2+, Hg2+, Ni2+, Cu2+ and K+) have been studied with
regard to their application as sensors for these cations. The ability
of dendrimer G3 to detect metal cations has been tested in ethanol
solution by monitoring the changes of fluorescence spectrum in the
presence of these cations.
Fig. 3 shows the FE data of rhodamine B. Almost no change of the
fluorescence enhancement could be observed even in the presence
of the same cations. This phenomenon can be reasonably explained
by the ring-opening of spirolactam of rhodamine B. Thus, the inter-
action between rhodamine B and these metal cations cannot affect
the delocalized conjugated degree of rhodamine B molecular. The
comparative experiment indicated that the Cr3+ ion selectivity of
dendrimer G3 is better than that of rhodamine B.
The fluorescence response of the guest metal cations in the G3
solution is signaled quantitatively by fluorescence enhancement
factor (FE, FE = I/I0). Herein, “I” represents the fluorescence inten-
sity after addition of guest metal ions, and “I0” is the fluorescence
intensity without metal ions. Fig. 2 presents the dependence of fluo-
rescence enhancements of dendrimer G3 in ethanol solution on the
above mentioned metal cations. The result showed that the highest
FE value of dendrimer G3 could be observed in the presence of Cr3+
ion. The FE value for Cr3+ ions used in this study was very good, since
at least a 20-fold increase in fluorescence intensity is found. The FE
value for Cr3+ ion was 21.08, which was 4 times larger than that for
To confirm the Cr3+ recognition ability of dendrimer G3, fur-
ther investigation was carried out by mixing Cr3+ ion with other
background metal cations. As shown in Fig. 4, the Cr3+ fluorescence
response of dendrimer G3 was barely affected by the background
metal cations. The results indicated that dendrimer G3 had remark-
able selectivity for Cr3+ ion and could be used as a high sensitive
sensor for Cr3+ ion.
Ca2+. While other metal cations, such as Ba2+, Ca2+, Sr2+, Fe3+, Al3+
,
Zn2+, Hg2+, Ni2+, Cu2+ and K+, provided weaker spectral response
than Cr3+ ion did in parallel condition. The unique selectivity for
Cr3+ ion is probably a result of simultaneous effect of some factors,
such as suitable coordination geometry conformation of the recep-
tor, radius of the Cr3+ ion and the amide deprotonation ability of
3.3. Study on the complexation behavior between Cr3+ and
dendrimer G3
The complexation behavior between dendrimer and different
concentrations of Cr3+ ion has been tested in ethanol solution by

Y. Lei et al. / Spectrochimica Acta Part A 83 (2011) 149–154
153
Scheme 4. The reaction scheme of dendrimer G3 with Cr3+
.
Fig. 4. The fluorescence responses of dendrimer G3 to 10−5 mol L−1 Cr3+ in the pres-
ence of other selected metal cations (C = 1 × 10−5 mol L−1) in ethanol. The dendrimer
Fig. 5. Fluorescence spectra of dendrimer G3 in ethanol at different concentra-
tions of Cr3+ cations (0–1.2 × 10−4 mol L−1). The dendrimer G3 concentration in the
G3 concentration in the solution is C = 1 × 10−5 mol L−1
.
solution is C = 1 × 10−5 mol L−1
.
C = 1.0 × 10−5–1.0 × 10−4 mol L−1). The possible mechanism for
these fluorescence responses is shown in Scheme 4. According
to some reported rhodamine-based chemosensors similar to
our compound in literatures [19,32], the nitrogen and amide
oxygen atoms of spirolactam will combine with nearby nitrogen
and amide oxygen atoms to form a nice binding pocket for the
complexation of metal ion. Thus, we supposed that the recognition
of Cr3+ in our case has the similar mechanism, i.e. one nitrogen
atom and two amide oxygens provide a nice binding pocket
for the complexation of Cr3+, which will induce ring-opening of
spirolactam and lead to the fluorescence enhancement of den-
drimer G3 as shown in Scheme 4. When the concentration of Cr3+
is more than 1.0 × 10−5 mol L−1, the fluorescence enhancement
most likely attributes to the complexation of Cr3+ with some
other part of dendrimer G3. This complexation will block the PET
process and increase the fluorescence intensity. The ring-opening
process was supported by the fact that the fluorescence intensity
of dendrimer G3 (1 equiv.) induced by Cr3+ ion (1 equiv.) cannot
be further suppressed by adding excess chelator (e.g. EDTA).
It suggests an irreversible sensing process of dendrimer G3 to
Cr3+ ion. Besides, the PET process was further confirmed by the
fact that the fluorescence intensity of dendrimer G3 (1 equiv.)
induced by Cr3+ ion (10 equiv.) can change into the one induced
by 1 equiv. of Cr3+ ion by adding excess chelator (e.g. EDTA). This
suggests a reversible sensing process of dendrimer G3 to Cr3+
ion.
monitoring the fluorescence spectral changes. In ethanol solution
the dendrimer was colorless with the fluorescence maximum at
ꢀF = 571 nm which is caused by ␲–␲* transition of the limited
extent of delocalization in the xanthene moiety of core group-
rhodamine B.
Fig. 5 shows the fluorescence spectrum of dendrimer G3 with
various Cr3+ concentrations (i.e. 0–1.2 × 10−4 mol L−1). The effect
of Cr3+ ion on the fluorescence intensity of dendrimer G3 was also
plotted in the figure. It clearly showed that the fluorescence inten-
sity at 571 nm dramatically increased with the increase of Cr3+
which was exited at 548 nm. We noticed that, when the concentra-
tion of Cr3+ reached to a certain limit (i.e. 1.0 × 10−5 mol L−1), the
dendrimer G3 solution turned to red, and the fluorescence intensity
increased slowly with the increase of Cr3+. Finally, the fluores-
cence intensity remained constant and the curve turned to a plateau
when the concentration of Cr3+ was above 1.0 × 10−4 mol L−1. These
results indicated that 10 equiv. of Cr3+ and 1 equiv. of dendrimer G3
could quickly react and reach the equilibrium with the formation
of a dendrimer G3/Cr3+ complex stoichiometrically.
3.4. Binding model of the complexes
The photophysical properties revealed that 1:10 com-
plex was formed between dendrimer G3 and Cr3+ ion. But
the sensor gave different fluorescence responses in differ-
ent Cr3+ concentration ranges (C = 0–1.0 × 10−5 mol L−1 and

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4. Conclusion
[6] Y. Wan, Q.J. Guo, X.F. Wang, A.D. Xia, Anal. Chim. Acta 665 (2010) 215–220.
[7] I. Grabchev, D. Staneva, R. Betcheva, Polym. Degrad. Stabil. 91 (2006)
2257–2264.
The third generation of poly (amidoamine) dendrimer with 1-
phenyl-3-methyl-5-pyrazolone fluorescent unit as periphery and
rhodamine B unit as core has been synthesized and characterized
for the first time. The obtained dendrimer G3 showed a consid-
erable fluorescence intensity increase in acidic solution and in
presence of metal cations. Among the tested metal cations, Cr3+ ion
provided the strongest enhancement of the fluorescence intensity.
The formation of a dendrimer G3/Cr3+ complex with stoichio-
metric proportion of 1:10 was proved. The particular interesting
photophysical properties of the dendrimer significantly depended
on the spirolactam ring-opening process and photoinduced elec-
tron transfer effect. Moreover, the novel synthesized dendrimer is
proved to be a much better sensor for Cr3+ ion than rhodamine B
only. On the basis of this present investigation, the produced den-
drimer G3 shows a potential to be applied in fluorescent sensor of
Cr3+ ion in the environmental and biological system.
[8] Q.Q. Chen, L. Lin, H.M. Chen, S.P. Yang, L.Z. Yang, X.B. Yu, J. Photochem. Photobiol.
A: Chem. 180 (2006) 69–74.
[9] V.B. Bojinov, N.I. Georgiev, P.S. Nikolov, J. Photochem. Photobiol. A: Chem. 193
(2008) 129–138.
[10] N.I. Georgiev, V.B. Bojinov, N. Marinova, Sens. Actuators B: Chem. 150 (2010)
655–666.
[11] N.I. Georgiev, V.B. Bojinov, Dyes Pigments (2010) 249–256.
[12] I. Grabcheva, X.H. Qian, V.B. Bojinovc, Y. Xiao, W. Zhang, Polymer 43 (2002)
5731–5736.
[13] I. Grabchev, P. Bosch, M. McKenna, A. Nedelcheva, Polymer (2007) 1–8.
[14] I. Grabchev, S. Dumas, J.M. Chovelon, Tetrahedron 64 (2008) 2113–2119.
[15] I. Grabchev, D. Staneva, V.B. Bojinov, R. Betcheva, V. Gregoriou, Spectrochim.
Acta A 70 (2008) 532–536.
[16] I. Grabchev, S. Dumas, J.M. Chovelon, Dyes Pigments 82 (2009) 336–340.
[17] J.Y. Kwon, Y.J. Jang, Y.J. Lee, K.M. Kim, M.S. Seo, W. Nam, J. Yoon, J. Am. Chem.
Soc. 127 (2005) 10107–10111.
[18] Y.K. Yang, K.J. Yook, J. Tae, J. Am. Chem. Soc. 127 (2005) 16760–16761.
[19] M.H. Lee, J.S. Wu, J.W. Lee, J.H. Jung, J.S. Kim, Org. Lett. 9 (2007) 2501–2504.
[20] S. Bae, J. Tae, Tetrahedron Lett. 48 (2007) 5389–5392.
[21] J.H. Soh, K.M.K. Swamy, S.K. Kim, S. Kim, S.H. Lee, J. Yoon, Tetrahedron Lett. 48
(2007) 5966–5969.
[22] M.H. Lee, H.J. Kim, S. Yoon, N. Park, J.S. Kim, Org. Lett. 10 (2008) 213–216.
[23] S. Yokoyama, T. Nakahama, A. Otomo, S. Mashiko, Colloids Surf. A 198–200
(2002) 433–438.
Acknowledgement
[24] V.B. Bojinov, A.I. Venkova, N.I. Georgiev, Sens. Actuators B: Chem. 143 (2009)
42–49.
[25] B. Ramachandram, J. Fluoresc. 15 (2005) 71–83.
[26] V.B. Bojinov, T.N. Konstantinova, Sens. Actuators B: Chem. 123 (2007)
869–876.
This work was supported by a grant from the National High
Technology Research and Development Program of China (863 Pro-
gram) (No. 2009AA035002).
[27] V.B. Bojinov, I.P. Panova, Dyes Pigments 80 (2009) 61–66.
[28] V.B. Bojinov, N.I. Georgiev, P.S. Nikolov, J. Photochem. Photobiol. A: Chem. 197
(2008) 281–289.
[29] V.B. Bojinova, I.P. Panovaa, D.B. Simeonovb, N.I. Georgieva, J. Photochem. Pho-
tobiol. A: Chem. 210 (2010) 89–99.
References
[1] V.K. Gupta, A.K. Jain, P. Kumar, S. Agarwal, G. Maheshwari, Sens. Actuators B:
Chem. 113 (2006) 182–186.
[2] H.A. Zamani, G. Rajabzadeh, M.R. Ganjali, Sens. Actuators B: Chem. 119 (2006)
41–46.
[30] V.B. Bojinov, N.I. Georgiev, N.V. Marinova, Sens. Actuators B: Chem. 148 (2010)
6–16.
[3] A.K. Singh, V.K. Gupta, B. Gupta, Anal. Chim. Acta 585 (2007) 171–178.
[4] A.J. Weerasinghe, C. Schmiesing, E. Sinn, Tetrahedron Lett. 50 (2009)
6407–6410.
[31] Y. Akama, T. Iwadate, A. Tong, Y. Takahashi, S. Tanaka, J. Chromatogr. A 789
(1997) 479–483.
[32] A.B. Othman, J.W. Lee, J.S. Wu, J.S. Kim, R. Abidi, P. Thuéry, J.M. Strub, A.V.
Dorsselaer, J. Vicens, J. Org. Chem. 72 (2007) 7634–7640.
[5] H.W. Wang, Y.Q. Feng, C. Chen, J.Q. Xue, Chin. Chem. Lett. 20 (2009) 1271–1274.