Selective fluoride ion recognition by a thiourea based receptor linked acridinedione functionalized gold nanoparticles

Article abstract of DOI:10.1016/j.jphotochem.2010.10.025

The design and synthesis of acridinedione functionalized gold nanoparticles based PET anion sensor 6 is described. The sensor 6 employs simple aromatic thiourea as anion receptors and the fluorophore is the acridinedione moiety, which were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), UV-vis, steady-state and time-resolved fluorescence techniques. Upon selective recognition of F^- in acetonitrile, the fluorescence emission of 6 was quenched with significant changes in the absorption spectrum. These changes are ascribed due to the hydrogen bonding and deprotonation of the thiourea receptor of ADDTU-GNPs.

Full text of DOI:10.1016/j.jphotochem.2010.10.025

Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Selective fluoride ion recognition by a thiourea based receptor linked
acridinedione functionalized gold nanoparticles
R. Velu, V.T. Ramakrishnan, P. Ramamurthy∗
National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai 600113, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The design and synthesis of acridinedione functionalized gold nanoparticles based PET anion sensor 6
is described. The sensor 6 employs simple aromatic thiourea as anion receptors and the fluorophore is
the acridinedione moiety, which were characterized by transmission electron microscopy (TEM), Fourier
transform infrared (FT-IR), UV–vis, steady-state and time-resolved fluorescence techniques. Upon selec-
tiverecognitionofF− in acetonitrile, the fluorescence emissionof 6 wasquenchedwith significant changes
in the absorption spectrum. These changes are ascribed due to the hydrogen bonding and deprotonation
of the thiourea receptor of ADDTU-GNPs.
Received 26 February 2010
Received in revised form 12 May 2010
Accepted 28 October 2010
Available online 4 November 2010
Keywords:
Acridinedione
Photoinduced electron transfer
Fluorescence
© 2010 Elsevier B.V. All rights reserved.
Sensors
Gold nanoparticles
1. Introduction
ous colorimetric anion receptors containing NH binding sites and
demonstrated that the deprotonation trend is enhanced by the
The design and synthesis of systems that are capable of sensing
various biologically and chemically important anions are cur-
rently of major interest, because anions play a fundamental role in
chemical and biological processes [1–4]. Among various important
anionic analytes, the fluoride ion is one of the most significant due
to its role in dental care [5] and treatment of osteoporosis [6]. In
order to selectively differentiate between biologically interesting
anionic substrates of similar basicity and surface charge density,
such as F−, CH3COO−, and H2PO4−, considerable efforts have been
made to develop hydrogen-bonding donors/receptors containing
urea [5], thiourea [6], amide [7–9], phenol [10–12], imidazole
[13], or pyrrole [14] subunits involving different kinds of signaling
mechanisms including internal charge transfer (ICT) [15,16], pho-
toinduced electron transfer (PET) [17,18], metal-to-ligand charge
transfer (MLCT)[19], excimer/exciplex formation [20], and tuning
proton transfer [21] for fluorescence chemosensors.
increase in the acidity of the hydrogen-bond donors and basicity
of the anions [27–29]. As the smallest and the most electronega-
tive atom, the fluoride ion shows a very high affinity toward the
N–H fragments of receptors containing a urea subunit and allows
N–H deprotonation. Moran and co-workers, Gale and co-workers
have reported acridinone-based anion sensors [30,31].
Acridinedione dyes (ADDs) have been reported as a new class of
laser dyes with lasing efficiency comparable to that of coumarin-
102 [32,33]. Interestingly, these dyes have been shown to mimic the
NADH analogues to a greater extent because of their tricyclic struc-
ture, which is capable of protecting the enamine moiety [34]. It has
been reported earlier by us that acridinedione thiourea chemosen-
sor was excellent in specificity toward AcO−, H2PO4−, and F−
over other anions [35]. In this paper, we report the fluorescent
chemosensor, thiourea based receptor linked acridinedione func-
tionalized gold nanoparticles (ADDTU-GNPs). This chromophore,
operated by PET mechanism, exhibits excellent specificity toward
F− over other anions.
In particular, the neutral anion receptors embracing the
hydrogen-donor urea group have been extensively studied [22–26],
in which the NH-anion hydrogen bond or anion-induced depro-
tonation of the NH groups was observed. To gain an insight into
hydrogen-bond formation and neat proton transfer existing in the
anion recognition process, Fabbrizzi et al. have investigated vari-
2. Experimental
2.1. Materials
All chemicals used were of the highest purity available. Sol-
vents used were of HPLC grade obtained from Qualigens (India)
Ltd. All the anions used in this assay were in the form of their tetra-
butylammonium (TBA) salts. Dimedone, 1, 2 phenylenediamine,
∗
Corresponding author. Tel.: +91 44 24547190; fax: +91 44 24546709.
E-mail addresses: prm60@hotmail.com, perumal ramamurthy@yahoo.co.in
(P. Ramamurthy).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.10.025

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R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
Scheme 1. Schematic illustration of synthesis and assembly of ADDTU-GNPs (6) via the reaction of HAuCl4 with ADDTU (5).
lipoic acid, DCC, sodium borohydride (NaBH4), and tetrachloroauric
acid (HAuCl4·3H2O) were purchased from Sigma–Aldrich Chemi-
cals Pvt., Ltd.
2.3.1. Preparation of 2,2ꢀ-(4-nitrobenzylidene) bis
(5,5-dimethylcyclohexane-1,3-dione) (1)
To a mixture of dimedone (5.0 g, 36 mmol in aq. methanol)
was added 4-nitrobenzaldehyde (2.7 g, 18 mmol) and the mix-
ture was warmed until the solution became cloudy. The
(4-nitrobenzylidene)bis dimedone started to separate out. The
reaction mixture was diluted with water (250 mL) and allowed to
stand overnight; the tetraketone 1 was collected by filtration, dried
and recrystallised from methanol.
2.2. Experimental methods
Absorption spectra were recorded on a Agilent 8453 diode
array spectrophotometer. Fluorescence spectral measurements
were carried out using a Perkin-Elmer MPF-44B fluorescence
spectrophotometer, interfaced with PC through RISHCOM-100
multimeter. 1H NMR, 13C NMR spectra were recorded with
BRUKER-SF300 (300 MHz) instrument, with TMS as internal stan-
dard (chemical shift in ␦ ppm). Elemental analysis was carried
out using a EURO EA Elemental analyzer. For HR-TEM studies, a
drop of dilute suspension was placed on a carbon-coated cop-
per grid and the solvent was allowed to evaporate. Specimens
were imaged on a JEOL 300 kV high resolution transmission elec-
tron microscopy. FT-IR spectra were recorded with NICOLET-6700
instrument.
Yield: 6.9 g (94%).
M.P.: 182–184 ◦C (Lit. [17] M.P. 188–190 ◦C).
2.3.2. N-[4-{3,3,6,6-Tetramethyl-10-(2-thioctinoylamino
phenyl)-3,4,6,7,9,10-hexahydro-1,8 (2H,
5H)-acridinedione-9-yl}-phenyl]-Nꢀ-phenyl thiourea (5)
A mixture of aminoacridinedione 4 (1.0 g, 1.55 mmol) and
phenyl isothiocyanate (0.037 g, 2.7 mmol) in dry dichloromethane
(20 mL) was refluxed for 24 h under nitrogen atmosphere. After
completion of the reaction, as indicated by TLC, the mixture was
concentrated and the solid obtained was filtered and dried under
vacuum. The thiourea derivative 5 was purified by column chro-
matography over silica gel using 2% methanol in chloroform as an
eluent.
2.3. Synthesis of acridinedione thiourea derivative (ADDTU)
The synthetic procedure is shown in Scheme 1. The reaction of
tetraketone 1 and 1,2-phenylenediamine in acetic acid on reflux
afforded nitroacridinedione 2. A mixture of 2 and lipoic acid in dry
dichloromethane with dicyclohexylcarbodiimide (DCC) on reflux,
afforded the acridinedione derivative 3. A mixture of 3, Zn-dust
and CaCl2 in ethanol on reflux, afforded the amino acridinedione
derivative 4 [36]. An equimolar mixture of 4 and phenyl isoth-
iocyanate in dichloromethane on reflux, afforded acridinedione
thiourea derivative (ADDTU) 5. The residue was recrystallised from
a mixture (9:1) of CHCl3 and methanol to yield yellow crystals of
ADDTU.
Yield: 0.90 g (75%), M.P. 172–174 ◦C.
IR (KBr) cm−1: 3244, 3309, 2923, 1625, 1494.
1H
NMR
(DMSO-d6,
300 MHz):
ı
(in ppm)
1.08
and 1.10 (2 s, 12H, gem-dimethyl), 1.35–1.71 (m, 6H,
S–CH–CH2–CH2–CH2–CH2–CO–), 1.81 (m, 1H, S–CH–), 2.15–2.20
and 2.60–2.65 (2d, 4H, J = 16.1 Hz, C4 and C5–CH2), 2.24 (t, 2H,
S–CH–CH2–CH2–CH2–CH2–CO–), 2.20 (s, 4H, C2 and C7–CH2), 2.30
(t, 2H, S–CH2-), 3.30 (m, 2H, S–CH2–CH2–CH–CH2), 5.81 (s, 1H,
C9–H), 6.80–7.50 (m, 12H, Ar-H), 9.10 (s, 1H, NH), 9.79 and 9.85
(2 s, 2H, 2 NH thiourea) [Fig. S1].

R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
315
Fig. 1. FT-IR spectra of (5) ADDTU, (6) ADDTU-gold nanoparticles (No S–H stretching band at ca. 2560 cm−1 can be observed in the IR spectrum of 6). A comparison of the
FT-IR spectra of ADDTU-GNPs resembles that of 5. NaBH4 reduces the disulfide moieties of lipoic acid as well as enables the formation of metallic gold nuclei, which leads to
the formation of S–Au bond to produce 6.
13C NMR (DMSO-d6, 300 MHz): ı (in ppm) 21.6, 22.6, 24.5, 26.3,
27.2, 27.9, 29.3, 30.6, 32.3, 49.6, 54.4, 112.3, 112.9, 120.4, 122.4,
123.5, 124.3, 125.1, 128.4, 128.5, 135.9, 144.3, 149.1, 168.0, 179.5,
195.1 [Fig. S2].
Analysis: Found (calculated for C44H50N4O3S3): C, 67.71 (67.83),
H, 6.51 (6.46), N, 7.29 (7.19) EI-MS: 797[M+H2O+H].
exhibits a band at 360 nm in acetonitrile Fig. 2A. The anion-binding
ability of ADDTU (5) with the anions F−, Cl−, Br−, I−, HSO4−, ClO4
,
−
AcO−, H2PO4−, and BF4 in acetonitrile were investigated using
UV–vis and steady-state fluorescence techniques. It can be noted
that, upon the addition of anions (except F−), no noticeable absorp-
−
tion spectral changes occurred Fig. 2B (AcO−, H2PO4 (inset)). On
−
the other hand, upon addition of F−, the absorption spectrum is
dramatically affected (Fig. 2C) due to the deprotonation of the
ADDTU thioctic amide hydrogen with associated enhancement in
the push-pull character of the ICT transition, which is reflected
in the increased absorbance at 375 nm. A similar result with OH−
ion confirms the deprotonation of ADDTU thioctic amide hydrogen
providing evidence for the above observation. The inset of Fig. 2C
represents a lower concentration of F−, no significant change was
observed.
2.3.3. Synthesis of gold nanoparticles capped with ADDTU
(ADDTU-GNPs) (6)
The synthesis of monolayer-protected clusters (MPCs) adopts
modification of the method reported by Brust et al. [37]. To
a stirred solution of tetraoctylammonium bromide (0.068 g,) in
toluene (5 mL) was added dropwise an aqueous solution of
hydrogentetrachloroaurate-(III) hydrate (11 mg, 0.028 mmol), and
the mixture was stirred for 20 min. The reaction mixture was
washed with distilled water (10 mL) several times, and the organic
layer was separated. A solution of ADDTU (10 mg, 0.0072 mmol)
in toluene (2 mL) was added to the above solution, and the result-
ing mixture was stirred for 30 min. An aqueous solution (3 ml) of
sodium borohydride (11 mg, 0.28 mmol) was added dropwise, and
the mixture was stirred for a further period of 3 h. The organic layer
was washed with water and diluted with methanol (250 mL). It
was kept in a refrigerator, and the precipitate obtained was further
purified by dispersion in toluene and then centrifugation after the
addition of methanol (10 mL). This process was repeated twice to
remove any unbound thiol. The residue obtained was redispersed
in 5 mL of toluene and used as stock solution. No S–H stretching
band at ca. 2560 cm−1 can be observed in the IR spectrum of 6. A
comparison of the FT-IR spectra of ADDTU-GNPs resembles that of
5 (Fig. 1) as reported by Yan-Li et al. [38] and Velu et al. [39].
3.2. Emission spectral studies of ADDTU (5) with anions
The relative decrease in the fluorescence intensities without
shift in the emission maximum of an acetonitrile solution of the
ADDTU scaffolds in the presence of various anions are represented
in (Fig. 3). The hydrogen bonding interaction of the AcO−, H2PO4
,
−
and F− with thiourea (TU) brings out a decrease in the oxidation
potential of the receptor, which triggers the PET from TU to the
relatively electron deficient ADD moiety, and this causes the fluo-
rescence to be quenched [19]. It can be noted that, upon addition of
all other the anions, no noticeable spectral changes were observed
(Fig. S3).
3.3. Time-resolved fluorescence studies of ADDTU with anions
3. Results and discussion
The complexation between anions and ADDTU has been inves-
tigated by the time-resolved fluorescence technique. Figs. S4–S6
present the fluorescence decay of ADDTU at different concentration
of anions was monitored at 430 nm, respectively, in acetonitrile. In
the absence of anion, ADDTU (5) exhibited triexponential decay
with lifetimes of 0.52, 0.91 and 3.1 ns (with amplitudes of 16%, 70%
and 14%, respectively). The triexponential decay data suggests th−e
presence of three distinct species. Upon the addition of F−, H2PO4
and AcO− to ADDTU, The fluorescence decay exhibited triexpo-
nential behaviour with decreasing lifetimes of 0.25, 1.2 and 3.0 ns
3.1. Absorption studies
The absorption and emission maximum of acridinedione dyes in
acetonitrile solution are centered around 380 and 430 nm, respec-
tively. The peak at 380 nm is attributed to the intramolecular charge
transfer from the nitrogen to the carbonyl oxygen in the acridine-
dione moiety and the emission at 430 nm to that of the local excited
(LE) state [32–34,40–42]. In this study, acridinedione thiourea (5)

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R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
Fig. 2. The absorption spectra in acetonitrile of (A) ADDTU; (B) upon addition of AcO− (the inset of B represents addition of H2PO4−, where no significant change was
observed). (C) Upon addition of F−
.
for F− (wi−th amplitudes of 5%, 71% and 24%); 0.24, 1.2 and 3.1 ns
for H2PO4 and 0.26, 1.2 and 3.2 (for AcO− at monitored 430 nm−).
The relative abundance of all these species (ADDTU with H2PO4
and AcO−) remained more or less unaffected. The decrease in the
lifetime was attributed to the PET between the TU and ADD in
ADDTU–anions complex. The variation in the fluorescence lifetime
of ADDTU on addition of anions, in acetonitrile, was observed as
presented in Table ST1.
is 32.15 nm2. Using the hexagonally close packed surface density
of nanogold (13.89 atoms/nm2); we could estimate the number of
gold atoms on the surface of nanogold to be 566. (Detailed calcula-
tion and data given in the supplementary data.)
3.5. Absorption studies of ADDTU-GNPs (6)
In general, the absorption and emission maxima of acridine-
dione dyes in acetonitrile solution are centered around 380 and
430 nm, respectively. In this study, acridinedione thiourea-GNPs
exhibited two sets of bands; absorption band in the UV region is
characteristic of functionalized ADDTU molecules (360 nm) in ace-
tonitrile and a broad band in the visible region (529 nm), which is
attributed to the surface plasmon resonance (SPR) absorption for
the stabilized gold nanoparticles 6 (Fig. 5A).
3.4. HR TEM studies
The HR TEM sample of 6 was prepared by drop-casting a
dilute suspension on a carbon-coated copper grid. Images are pre-
sented in (Fig. 4). Three-dimensional approach in TEM images
indicates that ADDTU (5) is anchoring on the surface of the gold
nanoparticles (GNPs). The size of GNPs was found to be an aver-
age diameter of 3.2 nm. The GNPs are assumed to be spherical;
the number of ADDTU molecules capping with one gold nanopar-
ticle of size 3.2 nm can be estimated, if the foot print area of the
ADDTU molecule is 0.657 nm2. This shows that forty-nine ADDTU
molecules are capping with the nanogold particle having a total
surface area of 32.15 nm2. In this study, it has been estimated that
the number of gold atoms in the nanoparticle as 992.55 using
the density of nanogold (58.01 atoms/nm3) by adopting a tight-
packed spherical model suggested by Murray and co-workers [43].
The surface area of the nanogold particle obtained in our study
3.6. Selective fluorescence signaling of fluoride anion by
ADDTU-GNPs (6)
The ability of the ADDTU-GNPs to sense anions AcO−, H2PO4
−
and F− was investigated. No significant change was observed in
the longer wavelength absorption and emission spectra of ADDTU-
GNPs on the addition of AcO− and H2PO4− in acetonitrile as shown
in Figs. 5B, 7A and S7A. This indicates that there is no interaction
between these anions and ADDTU-GNPs in the ground state and
excited state. On the other hand, upon addition of F− the absorp-

R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
317
12000000
10000000
8000000
6000000
4000000
2000000
0
A
B
10000000
No F-
0M
No H2PO4-
8000000
6000000
4000000
2000000
0
increasing [F-]
2.4x10-3M
increasing [ H2PO4-]
400
450
500
550
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
10000000
8000000
6000000
4000000
2000000
0
C
No AcO-
Increasing [AcO-]
400
450
500
550
Wavelength (nm)
Fig. 3. The fluorescence emission spectra of 5 upon addition of (C) F−, (D) H2PO4−, (E) AcO− (0–2.4 × 10−3 M) in acetonitrile, showing the quenching of fluorescence emission
upon anions recognition.
tion spectrum is dramatically affected. The absorption at 300 nm
decreases with the appearance of a new band centered at 375 nm
with an isosbestic point at 321 nm (Fig. 6). The inset of Fig. 6 rep-
resents at lower concentration of F−, where no significant change
was observed.
Excitation at the isosbestic point shows fluorescence quenching
(Fig. 7) with the increase in the concentration of F−. The quench-
ing of fluorescence in the presence of F− is due to the photoinduced
electron transfer (PET), which takes place between the anion recep-
tor and the ADD moiety in the fluorophore. At lower concentration
Fig. 4. Typical HR-TEM images of compound 6.

318
R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
0.7
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
A
B
0.6
0.5
0.4
[AcO-]
ADDTU-GNPs
0.3
0.2
0.1
0.0
300
400
500
600
700
300
400
500
600
700
Wavelength, nm
Wavelength, nm
−
Fig. 5. UV–vis spectral changes observed for (A) ADDTU and (B) ADDTU-GNPs with addition of AcO−, H2PO4 (inset)(0–2.4 × 10−3 M) in acetonitrile.
of F− (0–6.6 × 10−5 M), the hydrogen-bonding interaction predom-
inates, while at higher concentration (6.6 × 10−5–2.4 × 10−3 M) the
deprotonation occurs at thiourea (TU) moiety in the fluorophore.
Both the processes bring out a decrease in the oxidation potential
of TU receptor, which triggers the PET from TU to the relatively
electron deficient ADD moiety, and this causes the fluorescence
quenching (Fig. 7B). Fig. 8 depicts the plot for the selectivity of 6
towards the anions. To confirm the hydrogen bonding interaction
and deprotonation of ADDTU with F−, the 1H-NMR titration was
carried out in CDCl3 + DMSO-d6 (Fig. S8) at 25 ◦C. At lower con-
centration of F− broadening with shift of the signals (–NH) were
observed, which indicate the hydrogen bonding interaction of F−
with ADDTU; at higher concentration the complete disappearance
of amide–NH proton peaks was observed similar to that of the ear-
lier investigation [44,45]. The up-field shift of the aromatic proton
attributed to the decrease in ring current by anion recognition [17].
When the ADDTU molecules were functionalized on gold
nanoparticles, it was found that approximately 49 ADDTU
molecules were bound to single nanoparticles. The presence of such
a large number of molecules hinders, the approach of larger anions
like phosphate and acetate, sterically. This facilitates the selectiv-
ity of the F− ion interaction with ADDTU-GNPs as shown in the
Scheme 2.
1.0
0.8
0.6
0.4
0.2
0.0
6.6x10-5 M
0 M
2.1x10-3 M
Wavelength, nm
[F-]
0M
No F-
300
350
400
450
500
550
600
650
700
Wavelength, nm
Fig. 6. UV–vis spectral changes observed for ADDTU-GNPs 6 with addition of fluo-
ride anion (0–2.4 × 10−3 M) in acetonitrile.
9x106
5000000
A
B
N o F
8x106
4000000
7x106
[AcO- ]
6x106
5x106
4x106
3x106
2x106
Increasing [F
]
3000000
2000000
1000000
0
1x106
0
400
450
500
550
500
400
4 0
5
550
Wavelength (nm)
Wavelength (nm)
Fig. 7. (A) Addition of AcO− did not alter the emission in acetonitrile. (B) Fluorescence emission spectra of 6 upon addition of fluoride anion (2.4 × 10−3 M), showing the
fluorescence emission being quenched upon F− recognition.

R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
319
10000
No F
1.0
0.9
0.8
0.7
0.6
0.5
1000
increasing [F - ]
100
10
1
H2PO4-
AcO-
F-
3
8
13
18
23
28
33
38
Time, ns
Fig. 9. Fluorescence decay profile of ADDTU-GNPs (6) with different concentration
of F− in acetonitrile; ꢀexc = 375 nm and concentrations of F− 0–1.3 mM. Fluorescence
decay was monitored at 430 nm (A) in acetonitrile.
acetonitrile. In the absence of anion, ADDTU-GNPs (6) exhibited
triexponential decay with lifetimes of 0.44, 1.20 and 4.22 ns (with
amplitudes of 27%, 50% and 23%, respectively). The triexponential
decay data suggests the presence of three distinct species. Upon the
addition of AcO− and H2PO4− to ADDTU-GNPs, there was no signif-
icant change in the fluorescence lifetime. On the other hand, upon
addition of F−, the fluorescence profile exhibited triexponential
decay at lower and higher concentrations of F−. The fluorescence
decay exhibited triexponential behaviour with decreasing lifetimes
of 0.25, 1.19 and 3.69 ns (with amplitudes of 25%, 50% and 25%,
respectively, at monitored 430 nm). The relative abundance of
both these species (free ADDTU-GNPs and ADDTU-GNPs with F−)
remained more or less unaffected. The decrease in the lifetime was
0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007
[Anion M]/6
Fig. 8. Plot of I/I0 versus the [anion]: 6, which illustrates the selectivity for F−, over
H2PO4 and AcO− ions.
−
3.7. Time-resolved fluorescence studies
The complexation between anions and ADDTU-GNPs has been
investigated by the time-resolved fluorescence technique. Fig. 9
presents the fluorescence decay of ADDTU-GNPs at different
concentration of F− was monitored at 430 nm respectively in
−
Scheme 2. The possible mechanism of the phenomenon of binding of the free ADDTU-GNPs with F−, AcO− and H2PO4
.
Table 1
Fluorescence lifetime of ADDTU-GNPs on the addition of F− in acetonitrile.
[F−] (×10−5 M)
ꢁ1 (ns)
ꢁ2 (ns)
ꢁ3 (ns)
B1 (%)
B2 (%)
B3 (%)
ꢂ2
0
98
130
170
190
0.44
0.25
0.25
0.25
0.25
1.20
1.16
1.08
1.19
1.16
4.22
3.5
3.12
3.69
3.4
27
22
28
25
33
50
50
43
50
45
23
28
29
25
22
1.24
1.20
1.40
1.38
1.00

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R. Velu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 313–320
attributed to the PET between the TU and ADD in ADDTU-GNPs–F−
complex. The variation in the fluorescence lifetime of ADDTU-GNPs
on addition of F−, in acetonitrile, was observed as presented in
Table 1.
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4. Conclusion
In summary, the chemosensors ADDTU and ADDTU-GNPs have
TU receptor site, which play a key role in the selective fluorescence
anion sensing. This inve−stigation represents a ADDTU derivative as
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Acknowledgments
R.V. thanks University of Madras for the University Research Fel-
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