Hybrid sensor materials based on tin(IV) oxide and crown-containing 4-amino-1,8-naphthalimides

Article abstract of DOI:10.1016/j.mencom.2011.01.005

The cation-dependent spectral properties of crown-containing 4-aminonaphthalimide derivatives have been studied in an acetonitrile solution and within hybrid materials based on tin dioxide; these compounds can be of interest for producing fluorescent sensors for metal ions.

Full text of DOI:10.1016/j.mencom.2011.01.005

Mendeleev
Communications
Mendeleev Commun., 2011, 21, 12–14
Hybrid sensor materials based on tin(iv) oxide and
crown-containing 4-amino-1,8-naphthalimides
Pavel A. Panchenko,*a Yury V. Fedorov,a Olga A. Fedorova,a Boris A. Izmailov,a Valery A. Vasnev,a
Vladislav V. Istratov,a Ekaterina A. Makeeva,b Marina N. Rumyantsevab and Alexander M. Gaskovb
a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 499 135 5085; e-mail: pavel@ineos.ac.ru
b Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation
DOI: 10.1016/j.mencom.2011.01.005
The cation-dependent spectral properties of crown-containing 4-aminonaphthalimide derivatives have been studied in an acetonitrile
solution and within hybrid materials based on tin dioxide; these compounds can be of interest for producing fluorescent sensors for
metal ions.
The rapid development of nanotechnologies and supramolecular
chemistry has led to the creation of hybrid organo-inorganic
materials.1,2 This type of materials is of interest not only for
fundamental studies but also for the development of principally
new devices because a combination of organic and inorganic
compounds expands the functional capabilities of these devices.3
Hybrid organo-inorganic materials play an important role in
the detection of metal cations in solutions. The operating principle
of such materials is based on combining a synthetic receptor (a
fluorophore functionalised by an ionophore) and a semiconductor
oxide that serves as the support. The binding of cations changes
the ability of a fluorophore to undergo photoinduced processes
such as electron transfer, charge transfer or energy transfer. A
semiconductor oxide modified by a fluorophore also changes
its electric characteristics such as electrical conductivity and
ability to generate photo-emf, which allows these materials to
be integrated in automatic instruments.
The derivatives of naphthalic acid imide (1,8-naphthalimide)
are efficient organic luminophores, and they often play a role of
signal elements in sensor-type optical molecular devices.4,5 Here
we examined the use of 4-aminonaphthalimide derivatives 1 and 2
containing benzo-15-crown-5 and N-phenylaza-15-crown-5 ether
substituents, respectively (Scheme 1),† as fluoroionophores for
hybrid organo-inorganic materials based on quasi-one-dimen-
sional single crystals of tin dioxide. First, the photophysical
properties of compounds 1 and 2 were studied in acetonitrile
solutions in the presence and absence of alkaline-earth metal
cations.
The spectral characteristics of compounds 1 and 2 and their
complexes with magnesium and calcium cations are presented in
Table 1.‡ The long-wavelength band in the absorption spectra of
4-aminonaphthalimides 1 and 2 is due to charge transfer from
the electron-donating amino group at the 4-position of the naph-
thalene ring to the carbonyl groups of the carboxyimide moiety10
(Scheme 1). As an example, Figure 1 shows the absorption and
fluorescence spectra of benzo-crown ether derivative 1.
Table 1 indicates that the nature of the crown ether substituent
does almost not affect the positions of absorption and emission
20
1.0
2
15
10
5
0.8
0.6
0.4
1
0.2
0.0
0
300
400
500
600
700
l/nm
Figure 1 (1) Absorption and (2) fluorescence spectra of compound 1 in
acetonitrile.
‡
Spectroscopic studies were performed using acetonitrile for spectro-
photometry (Aldrich). Absorption spectra were measured with a Varian-
Cary two-channel spectrophotometer. Fluorescence spectra were recorded
using a FluoroMax-3 spectrofluorimeter. The observed fluorescence was
detected at right angle relative to the excitation beam. All measured fluore-
scence spectra were corrected for the nonuniformity of detector spectral
sensitivity. Fluorescence quantum yields were determined in air-saturated
solutions at 20 1°C with respect to the following standards: quinine
sulfate in 1 n sulfuric acid (jfl = 0.55)7 and Rhodamine 6G in ethanol
(jfl = 0.95).8 The quantum yields were calculated using the equation9
O
O
O
O
O
1 Ar =
O
N
N
O
Ar
H2N
O
O
O
O
D0
2
^
h
1
10- Sin0
-
-
jifl jfl
,
2
2 Ar =
=
0
Di
1
10- S0ni
^
h
where jifl and j0fl are the quantum yields of the test solution and
the standard; Di and D0 are the absorptions of the test solution and the
standard, Si and S0 are areas underneath the fluorescence spectrum curves
for the test solution and the standard, ni and n0 are refraction factors of
solvents of the test compound and the standard compound, respectively.
Scheme 1
† Compound 1 was obtained previously;6 the synthesis of aza-crown ether
naphthalimide derivative 2 will be published elsewhere.
© 2011 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2011, 21, 12–14
Table 1 Absorption and emission maxima, fluorescence quantum yields
solutions in acetonitrile. As can be seen, spectral changes were
most significant in the case of aza-crown derivative 2.
and stability constants of compounds 1, 2 and complexes [1]·Mg2+, [2]·Ca2+
in acetonitrile at 293 K.
Based on spectrofluorimetric titration data for azacrown deriva-
tive 2, the stability constant of the resulting 1:1 complex was
determined (Table 1).§ In the case of benzocrown-containing
naphthalimide 1, the constant cannot be calculated because of
very small changes in the absorption and fluorescence spectra upon
complex formation.As reported previously,11 the stability constant
for N-acetylamino-substituted analogue of 1 is logK = 5.33 0.02.
Apparently, the value of log K for compound 1 will differ only
slightly from the above value since changes in the electronic
structure of the naphthalimide moiety due to the replacement of
an amino group by an acetylamino group should not affect con-
siderably the ionophoric N-aryl moiety.
Hybrid sensor materials were obtained using SnO2 single
crystal belts a few micrometers thick (whiskers) that were grown
from a gas phase and characterised by IR spectroscopy and X-ray
diffraction.12 To obtain a uniform surface coating on the semi-
conductor oxide and ensure the maximum bonding of fluorophore
molecules to it, organosilicon compounds (3-glycidyloxypropyl-
trimethoxysilane 3 and polyvinyldimethylsilazane 4) were used
as linkers (Scheme 2).
Compound lambasx/nm (lg el)
lfml ax/nm
jfl
lg K
1
414 (4.14)
417 (4.15)
415 (4.17)
420 (4.16)
519
521
518
520
0.43
0.59
0.0024
0.43
—
[1]·Mg2+
2
not determined
—
4.94 0.02
[2]·Ca2+
bands, but it affects considerably the fluorescence quantum yield.
Compound 1 demonstrates intense fluorescence, whereas the
fluorescence quantum yield of aza-crown ether derivative 2 is a
few thousandth.
As noted previously,6,11 the presence of electron-donating
alkoxy or dialkylamino substituents at the N-aryl ring results in
fluorescence quenching of the naphthalimide chromophore. This
effect can be explained by the existence of a nonradiative process
related to electron transfer from the N-aryl substituent to the naph-
thalimide residue, which competes with fluorescence. The lower
quantum yield of compound 2 is most likely related to the higher
electron-donating properties of the nitrogen atom in the aza-crown
ether ring in comparison with the oxygen atoms of the crown ether
in compound 1, which are in conjugation with the benzene ring.
The complexation of compounds 1 and 2 with magnesium
and calcium cations resulting in a decrease in the electron-donating
properties of the oxygen and nitrogen atoms bound to the benzene
ring was accompanied by a fluorescence enhancement. These
cations were selected because they can form stable complexes of
1:1 stoichiometry upon coordination with 15-crown-5 and aza-
15-crown-5. Figure 2 shows changes in the fluorescence spectra
of crown-containing derivatives 1 and 2 that occurred upon gradual
addition of magnesium perchlorate or calcium perchlorate to their
OMe
MeO Si
O
OMe
O
3
Me
H
N
H2N
Si
HN
Si NH Si NH
H
NH
Me
Si
H2N
n
4
(a)
5.0
Scheme 2
100 equiv. Mg2+
4.0
The technique of fluorophore immobilization on SnO2 surfaces
involved the following steps. First, a covalent bond was formed
between the fluorophore and linker 3 by heating the components
in a butyl acetate or toluene solution (Scheme 3). Tin dioxide
whiskers previously mounted on the edges of a glass plate were
immersed in the resulting solution and then dried in air. To obtain
a uniform coating, this operation was repeated several times.
3.0
2.0
0 equiv. Mg2+
1.0
0.0
450 500 550 600 650 700
O
l/nm
O
O
N
O
Ar
+
BuOAc
H2N
(b)
140 °C,
20 min
1.0
0.8
0.6
(MeO)3Si
1.0
3
0.4
0.2
0.8
[Ca2+]
(MeO)3Si
0.0
O
N
O
0.6
0
20 40 60 80 100
Ca2+ (equiv.)
O
Ar
0.4
0.2
0.0
HO
HN
Scheme 3
450 500 550 600 650 700 750 800
Afterwards, the plate with the whiskers was dried for 1.5 h at
100°C. At this step, the linkers were bound to the SnO2 surface
via the OH groups located on it (Scheme 4). Note that the addi-
l/nm
Figure 2 Spectrofluorimetric titration of (a) compound 1 with magnesium
perchlorate and (b) compound 2 with calcium perchlorate in acetonitrile.
§
The stability constant of the complex [2]·Ca2+ was determined according
(a) CL = 1.3×10–5 mol dm–3, lexcit = 365 nm; (b) CL = 5.0×10–6 mol dm–3
,
to the general procedure used previously for benzocrown-containing
naphthalimide derivatives.11
l
excit = 420 nm; the insert shows the dependence of fluorescence intensity at
the maximum on the number of Ca2+ equivalents added.
– 13 –

Mendeleev Commun., 2011, 21, 12–14
(a)
(a)
(b)
(b)
40 µm
40 µm
60 µm
60 µm
(c)
300
250
200
150
100
50
Figure 3 Micrographs of band-shaped SnO2 crystals: (a) clean specimen
(optical micrograph); (b) specimen coated with a polymeric organosilicon
film containing functionalized fluorophore 1 (fluorescent micrograph).
2
tion of silazane 4 to the working solution favoured the formation
of a cross-linked polymeric coating and improved the binding
quality of the fluorophore with the surface.
1
0
+
+
MeOH
OH
MeO Si
O
Si
SnO2
SnO2
Scheme 4
550
600
650
700
750
800
l/nm
Figure 5 Sensor properties of single crystal whiskers of SnO2 modified by
fluorophore 2. Fluorescent micrographs of the hybrid material (a) before
and (b) after treatment with 0.1 m solution of Ca(ClO4)2 in acetonitrile.
(c) Fluorescence spectra of the specimen surface: (1) original specimen and
(2) specimen treated with 0.1 m solution of Ca(ClO4)2 in acetonitrile.
The materials obtained by this procedure were analysed using
a Nikon Digital Eclipse C1 laser scanning confocal microscope
connected to an Avantes 2040 fibre-optic spectrofluorimeter.
Figure 3 exhibits the micrographs of SnO2 whiskers modified by
benzocrown-containing derivative 1.
The treatment of surfaces of the hybrid materials modified
by fluorophores 1 and 2 with a 0.1 m solution of magnesium or
calcium perchlorate in acetonitrile was accompanied by a fluore-
scence enhancement (Figures 4 and 5). The subsequent water
treatment of the surface led to the cation wash-out from the crown
ether cavity resulting in a fluorescence intensity decrease to the
original level [Figure 4(c)].
Thus, we found that crown-containing naphthalimide deriva-
tives 1 and 2 are fluorescent sensors for metal cations in aceto-
nitrile solutions and in composite hybrid materials. The covalent
binding of fluorophores to the surface of single crystal SnO2 whiskers
does not result in a loss of their sensor properties. Since the
interaction of metal ions with the crown ether moiety is reversible,
the materials can be used for creation of sensitive optical sensors
selective for Mg2+ and Ca2+ cations.
This study was supported by the Russian Foundation for Basic
Research (grant nos. 09-03-00047 and 09-03-91136).
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1
3
0
550
600
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700
750
800
l/nm
Figure 4 Sensor properties of single crystal SnO2 whiskers modified by
fluorophore 1. Fluorescent micrographs of the hybrid material (a) before
and (b) after treatment with a 0.1 m solution of Mg(ClO4)2 in acetonitrile.
(c) Fluorescence spectra of the specimen surface: (1) original specimen and
(2), (3) specimens treated with 0.1 m solution of Mg(ClO4)2 in acetonitrile
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Received: 25th June 2010; Com. 10/3548
– 14 –