DMABI tripod structures with sensing capabilities: Synthesis, characterization and fluorescence analysis

Article abstract of DOI:10.1039/c5nj03613e

We present herein the synthesis, and the structural and spectroscopic analysis of a non-planar tripod-shaped p-(N,N′-dimethylamino)benzyliden-1,3-indandione (DMABI) chromophore. This novel molecule is composed of a Si core with three incorporated arms, each of them contains a 1,3-indandione derivative with an electron donating (-NMe₂) group, thus providing fluorescence capabilities. We prepared a DMABI arm by coupling a p-(N,N′-dimethylamino)benzaldehyde (DMAB) tripod substituted molecule with 1,3-indandione via aldol condensation. The structures of DMAB-tripods were confirmed by spectroscopic data and studied by quantum chemical calculations. Fluorescence spectroscopy was used for optical characterization. Quantum yields and the corresponding lifetimes reveal typical characteristics of conjugated derivatives. Finally, we monitored the enhancement in fluorescence intensity of compound 1 in the presence of 4-chloro-2,6-dinitroaniline (4CDNA) in the range between 0 and 20 mg L^-1. We justify this enhancement by calculated energies and the distribution of the HOMO and the LUMO for DMABI-tripod and 4CDNA.

Full text of DOI:10.1039/c5nj03613e

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DMABI tripod structures with sensing capabilities:
synthesis, characterization and fluorescence
analysis†
Cite this:DOI: 10.1039/c5nj03613e
Rafael Contreras-Caceres,a Manuel Dona,a Maria Rosa Lopez-Ramırez,b
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Manuel Algarra,c Jesus Hierrezuelo,a Miguel Angel Casado-Rodrıguez,a
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Maria Sanchez-Molina,a Amelia Dıaz,a Bruno B. Campos,d
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Joaquim C. G. Esteves da Silvad and Juan Manuel Lopez-Romero*a
´
We present herein the synthesis, and the structural and spectroscopic analysis of a non-planar tripod-shaped
p-(N,N0-dimethylamino)benzyliden-1,3-indandione (DMABI) chromophore. This novel molecule is composed
of a Si core with three incorporated arms, each of them contains a 1,3-indandione derivative with an electron
donating (ꢀNMe2) group, thus providing fluorescence capabilities. We prepared a DMABI arm by coupling
a p-(N,N0-dimethylamino)benzaldehyde (DMAB) tripod substituted molecule with 1,3-indandione via aldol
condensation. The structures of DMAB-tripods were confirmed by spectroscopic data and studied by
quantum chemical calculations. Fluorescence spectroscopy was used for optical characterization.
Quantum yields and the corresponding lifetimes reveal typical characteristics of conjugated derivatives.
Finally, we monitored the enhancement in fluorescence intensity of compound 1 in the presence of
4-chloro-2,6-dinitroaniline (4CDNA) in the range between 0 and 20 mg Lꢀ1. We justify this enhancement
by calculated energies and the distribution of the HOMO and the LUMO for DMABI-tripod and 4CDNA.
Received (in Montpellier, France)
18th December 2015,
Accepted 6th January 2016
DOI: 10.1039/c5nj03613e
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electron-donor and an electron-acceptor group connected by an
alkene bridge (push–pull chromophore).1–3 Consequently, DMABI
Introduction
During the last few years 1,3-indandiones have become an important chromophores possess excellent electrical, photoluminescence
group of molecules which have been extensively investigated as and optical properties, showing high dipolar photo-induced
chromophores in the field of optical sensing and for complexation electron transfer, which occurs in an intra-molecular and reversible
with transition metal ions.1 This b-diketone offers the possibility to fashion.4
be functionalized with different chemical groups in an easy and
In comparison with other organic or inorganic materials having
reproducible way, with the principal aim of increasing the solubility fluorescence capabilities, DMABI derivatives are easy to synthesize
of their derivatives as well as enhancing the fluorescence capability. (typically by aldol reaction). However, an important challenge is the
Among a great number of functional groups, an interesting improvement of their chemical and photochemical stability, which
alternative that satisfies the above mentioned assessments are is one of the principal motivations for the widespread application
molecules that contain a 2-(N,N0-dimethylamino)benzyliden- of these chromophores in the development of optoelectronic
1,3-indandione (DMABI) moiety. This derivative contains an devices with the aim to be implemented in biolabeling and
biomedicine purposes.5,6 An alternative to improve the optical
capabilities of these materials is the optimization of the chemical
a
structure and spectroscopic properties of the chromophores.7
In the case of DMABI, the optical properties can be optimized
by including different substituents in their structures or by the
modulation of their 3D structures. It has also been reported
that by increasing the molecular weight and the number of
phenyl groups in a molecule a better thermal sustainability can
be obtained.5,7 We have chosen tripodal oligo( p-phenylene)s
having a Si core as they have been used as ideal anisotropic
adsorbates in the generation of monolayers.8 The thin films
generated maintain the perpendicular orientation of the functional
´
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Dep. Quımica Organica, Facultad de Ciencias, Universidad de Malaga,
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Campus de Teatinos s/n, 29071 Malaga, Spain. E-mail: jmromero@uma.es;
Fax: +34 952 137383; Tel: +34 952 137383
b
c
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Dep. Quımica Fısica, Facultad de Ciencias, Universidad de Malaga,
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Campus de Teatinos s/n, 29071 Malaga, Spain
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Dep. Quımica Inorganica, Facultad de Ciencias, Universidad de Malaga,
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Campus de Teatinos s/n, 29071 Malaga, Spain
d
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Centro de Investigaçao em Quımica, Departamento de Quımica e Bioquımica,
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Faculdade de Ciencias da Universidade do Porto, Porto, Portugal
† Electronic supplementary information (ESI) available: Computed geometries,
1H and 13C NMR spectra and cartesian coordinates (x,y,z) of compounds 1 and 4.
See DOI: 10.1039/c5nj03613e
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Scheme 1 Synthetic strategy for obtaining the tripod-shaped 1. X = OR.
arm at the focal point of the tripod with respect to the surface.
This circumstance offers the possibility of fabricating solid
devices for the detection of molecules that interact with the
tripodal oligo(p-phenylene) compounds.
Scheme 2 Preparation of starting material.
Here we present the synthesis in good yields of a tripod-shaped
oligo-p-phenylene containing DMABI groups (compound 1,
Scheme 1). The synthesis of 1 was performed by sequentially
coupling phenyl units on the silicon core 2. We used the Suzuki–
Miyaura cross-coupling of tri( p-iodophenyl)-p-bromophenylsilane
(2, Scheme 1) with the corresponding phenylboronic acid (or ester)
derivative 3 as the key-step reaction.9–11
We also report the structural and spectroscopic characterization
of the tripod-shaped DMABI-substituted chromophore 1, and its
precursor 4 (see Scheme 3), a 2-(N,N0-dimethylamino)benzylidene
(DMAB) derivative, also with a non-planar tripod-shaped structure.
We present the analysis of the emission fluorescence spectra, the
intensity decay profiles and the corresponding lifetimes for both
tripod-shaped chromophores. We finally evaluate the possibility of
using compound 1 as a sensor by monitoring the fluorescence
enhancement using as a model probe 4-chloro-2,6-dinitroaniline
(4CDNA), a very well explosive component.
asymmetric tetraphenylsilane 29 and we chose the boronic acid
pinacol ester 3. Firstly, we studied the preparation of compound 5
as the key product (Scheme 2). We analyzed its synthesis by
following two different routes shown in Scheme 2. Both routes
start from 6, which was easily prepared by the bromination of
commercial 4-(N,N0-dimethylamino)benzaldehyde by treatment
with NBS. The first route (Scheme 2, Route I) presents as the first
step the aldol condensation of 1,3-indandione with 6 to give 7.
This reaction gave 7 in 67% yield. However, the treatment of 7
with bis(pinacolate)diboron and Pd(dppf)2Cl2 as a catalyst did
not produce 5, instead of that only the debromination product
was isolated. As a second option (Scheme 2, Route II), the
formation of the pinacolboronate 3a [X + X = OC(Me2)C(Me2)O]
was planned as an alternative in the first step of the synthesis,
followed by its aldol condensation with 1,3-indandione, likewise
yielding 5. Unfortunately, when 6 was treated with bis(pinacolate)-
diboron under the same conditions as above, only the debromina-
tion product of 6 was isolated. These results can be explained by
the steric hindrance of the N,N-dimethylamino group present in 6
and 7, which avoids the bulky pinacolboronate substitution.
Due to these negative results, we decided to prepare the
Results and discussion
Synthesis
The retrosynthetic analysis of compound 1 is shown in Scheme 1.
By this analysis, the starting materials are 1,3-indandione and the boronic acid of 3-bromo-4-(N,N0-dimethylamino)benzaldehyde
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Scheme 3 Synthesis of DMABI-tripod 1.
(3b, X = X = OH, Scheme 3) where steric hindrances are not so groups, and (ii) the repulsion between the o-hydrogen atoms of
strong. The successful synthesis of 3b was carried out by consecutive benzene rings, and between the o-hydrogen atoms
protecting the carbonyl group in 6 to obtain 8, followed by treatment and ꢀNMe2 groups, which tend to maintain the benzene rings in
with n-BuLi and trimethyl borate, as shown in Scheme 3. Compound orientations close to mutual perpendicularity.
3b was obtained with a 97% overall yield. This aldehyde 3b was
Extended electronic delocalization is manifested by the
then successfully coupled with compound 2 under Suzuki–Miyaura calculated values of the inter-ring C–C bond: 1.492 Å and
reaction conditions, obtaining the DMAB-tripod-shaped molecule 4 1.493 Å for molecules 4 and 1, respectively. These bonds have
in 87% yields.
lengths that lie between that of a pure single bond (ca. 1.53 Å)
Then, by the reaction of 4 with 1,3-indandione under aldol and that of a pure double bond (ca. 1.33 Å), also being greater
reaction conditions in the presence of piperidine, compound 1 than that for a non-substituted biphenyl group (1.486 Å). These
was finally obtained (Scheme 3). This compound presents three facts mean that electronic delocalization is not so effective in
DMABI moieties in its structure. By following this strategy, the molecules 4 and 1 as for biphenyl groups.12a
construction of the arms for the tripod and the chromophore
derivative was achieved simultaneously.
The calculated inter-ring torsion angles C–C–C–C for the
biphenyl moiety are 49.261 and 49.611 for 4 and 1, respectively.
The new compounds were characterized by their spectroscopic These values are slightly higher than the 38.41 inter-ring torsion
data (see Experimental). Compound 1 is a solid that shows a strong angle of biphenyl, calculated at the B3LYP/6-31G* level (the experi-
absorption at 470 nm in the UV spectrum in EtAcO solution, which mental gas-phase value of 44.4 ꢁ 1.21 was obtained from electron
gives the compound a strong orange colour. It is also worth diffraction measurements).12c
mentioning that chromophore 1 shows a high thermal stability
The clearly non-planar conformation in both molecules can
with a melting point of 287 1C without decomposition, which is be attributed to the ꢀNMe2 group in the DMABI molecules
much higher than that for pure DMABI molecules (231.7 1C)
replacing hydrogen, thus making the steric repulsion greater
than in the biphenyl group.
Structure analysis
It is important to remark that in molecule 1 the terminal benzene
The tripod-shaped structures were studied by quantum chemical ring of the biphenyl moiety and –CHQof the 1,3-indandione moiety
calculations (see Experimental for details). Molecules 4 and 1 are in the same plane. 1,3-Indandione was found to be a planar
display a tetrahedral symmetry around the silicon atom core, with molecule because of the expected conjugation between the –CQO
C–Si–C angles of 109.81 and 109.71, respectively (ESI,† Fig. S1A–D). bonds and the benzene ring.13 Consequently, in molecule 1
Compounds 4 and 1 present a non-planar relative position extended electronic delocalization is also to be expected between
of phenyl groups in each of the biphenyl moieties (torsion inter-ring the biphenyl moiety, the –CQC– double bond, the –CQO bonds
angle, C–C–C–C). This is known for non-substituted biphenyls, and the 1,3-indandione benzene ring.
being a determinant factor for the emitting light behaviour in
chromophores.12 The torsion inter-ring angle in compounds 4
Fluorescence measurements and 4CDNA sensing
and 1 depends on electronics and steric factors; (i) the stabilizing Fig. 1A shows the fluorescence spectra of both tripod-shaped
interaction between the p clouds of the benzene rings, leading to chromophores. Two emission maxima at about 543 nm for
the extension of electronic delocalization across them, which is compound 1 and 470 nm for compound 4 were obtained, when
clearly favoured by the planar arrangement of the biphenyl excited at 470 and 343 nm, respectively.
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Relevant information was obtained for compound 1 when (providing a red-shift as observed in the absorption spectra in
a marked shift to red was observed (73 nm) in compar- Fig. 1A).
ison to 4, providing 0.43 eV of stabilization. The terminal
The quantum yields (QY) of the fluorescence in a dilute
1,3-indandione moieties play an important role in 1, since it solution of ethyl acetate were calculated by using eqn (1) (see
provides additional stabilization energy when compared Experimental section) and were 0.16 and 0.38 for compounds 4
with the starting molecule 4. This additional stabilization is and 1, respectively. These data are in agreement with previously
attributed to the close plane-to-plane distance between the reported studies, which suggest that an increase in QYs is
neighbouring planar 1,3-indandione and benzene moieties, favoured by the rigidity of the molecular structure.14 The
resulting in suitably strong intermolecular p*–p* interactions photoluminescence features reveal typical characteristics of
conjugated derivatives.15 Intensity decay-time profiles of tripods
1 and 4 are shown in Fig. 1B, and the corresponding measured
lifetimes (t1 and t2) are shown in Table 1. One and two
component exponential-decay curves are detected for 1 and 4,
respectively, with lifetimes in the nanosecond range (parameters
B1, B2, A and w2 are fluorescence decay components in Table 1).
As a proof of concept, DMABI tripod 1 was assessed as a sensor
probe for 4-chloro-2,6-dinitroaniline (4CDNA), a nitro-derivative
compound which is used in the fabrication of explosive materials.16
Fig. 1C shows the emission spectra when DMABI tripod 1 (200 mL,
0.1 M) was exposed to increasing concentrations of 4CDNA, in the
range from 0 to 20 mg Lꢀ1. As can be observed, a remarkable
fluorescence enhancement at about 553 nm is produced, reaching
15 times higher when a concentration of 20 mg Lꢀ1 of 4CDNA was
used. A slightly small red shift (10 nm) was also observed, which
can be explained by the polar micro-environment produced by
ꢀNO2 substituents in 4CDNA. From the analysis of the fluores-
cence spectra (Fig. 1C), a linear dependence in the concentration
range 0–20 mg Lꢀ1 was observed. The fluorescence enhancement
versus 4CDNA concentration was successfully linearized (r = 0.98,
the inset in Fig. 1C), with a limit of detection (LD) of 1.92 mg Lꢀ1
(8.82 ꢂ 10ꢀ6 M) and an accuracy (as Relative Standard Deviation)
RSD = 1.92%. This fact opens up the possibility of sensing
of 4CDNA.
The enhancement in the fluorescence intensity and the
wavelength shift in the two emission maxima of compounds
4 and 1 can be explained by analysing their highest occupied
molecular orbital (HOMO) and their lowest unoccupied mole-
cular orbital (LUMO) energies and distributions by theoretical
calculations. As is well-known, HOMO and LUMO energies play
an important role in the chemical reaction mechanism, and a
number of studies revealed that the band gap between these
molecular orbital energies is an important stability indicator
for the molecules.17,18 A large band gap implies high stability
and a small gap implies low stability, thus providing high and
low chemical reactivity, respectively. Fig. 2 shows the structure
and contours of frontier orbitals HOMO–LUMO for 4CDNA,
Table 1 Lifetime intensity decays corresponding to compounds 1 and 4a
DMAB tripod-4
DMABI tripod-1
t1 (s)
t2 (s)
B1
5.74 ꢂ 10ꢀ10 (0.49)
1.48 ꢂ 10ꢀ10 (1.47)
Fig. 1 (A) Fluorescence intensity spectra of 4 (red line) and 1 (blue line) at
25 1C in ethyl acetate (1 : 50). (B) Fluorescence decay curves of 1 and 4 (for
compound 1: lex = 470 nm; lem = 543 nm, slit widths: 5.5 nm). (C) Fluorescence
spectra obtained when DMABI tripod 1 (200 mL, 0.1 M) was exposed to
increasing concentrations of 4CDNA: (a) 0.001; (b) 0.01; (c) 0.05; (d) 0.1;
(e) 0.75; (f) 2; (g) 5; (h) 10 and (i) 20 mg Lꢀ1, respectively. The inset shows
the obtained calibration curve.
2.79 ꢂ 10ꢀ9 (0.07)
—
0.023 (3.32 ꢂ 10ꢀ4
0.045 (3.30 ꢂ 10ꢀ4
4.28 (0.025)
)
)
37.11 (0.08)
—
17.04 (0.34)
1.61
B2
A
w2
1.32
a
In brackets the standard deviation of 3 measurements.
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Fig. 3 Frontier molecular orbital diagram and corresponding gaps of
calculated molecules at the B3LYP/6-31G* level of theory.
Table 2 Frontier molecular orbital energies (eV) and corresponding gaps
(eV) of calculated molecules at the B3LYP/6-31G* level of theory
Compound Compound Compound
4CDNA
4
1
1 + 4CDNA
Emin (Hartrees) ꢀ1156.201 ꢀ5222.267
ꢀ6484.069
ꢀ5.52
ꢀ7640.277
ꢀ5.35
EHOMO (eV)
ELUMO (eV)
GAP (eV)
ꢀ6.86
ꢀ3.36
3.50
ꢀ5.70
ꢀ1.50
4.19
ꢀ2.37
ꢀ3.42
3.14
1.93
can only occur when they have the correct symmetry, i.e., if
positive overlap can be achieved between the corresponding
HOMO and LUMO orbital of each molecule.19 Taking into
account the delocalization of these orbitals described above,
we were able to predict an energy favourable approximation of
the ꢀNO2 group of 4CDNA to the biphenyl group through one
of the leg of the compound 1 (Fig. 2).
Moreover, the strength of the interaction is directly related
to the HOMO–LUMO energy separation. In general, the smaller
the HOMO–LUMO separation, the stronger the interaction and
a more favoured reaction is produced. Considering the orbital
diagram of these molecules (Fig. 3), the energy difference of the
Fig. 2 3D Frontier molecular orbital contours of calculated molecules at
the B3LYP/6-31G* level of theory.
compound 4, compound 1 and the interaction between compound 1 HOMO of compound 1 and the LUMO of 4CDNA is only 2.16 eV,
and 4CDNA. Additionally the energies of these molecular orbitals are and consequently, the interaction (energetically favourable) can
shown in Fig. 3, whose specific values are shown in Table 2. It can be be performed. The interaction changes frontier orbital energies
observed in this table that the substitution of the biphenyl groups of the whole molecule leading to a decrease of the gap down to
reduces the energy gaps between the HOMO and the LUMO from 1.93 eV. This fact is confirmed by the optimized molecular
compound 4 (4.19 eV) to compound 1 (3.14 eV) explaining the red structure represented in Fig. 2, where it can be observed how
shift shown in Fig. 1A.
the –NO2 groups approximate to compound 1 through the
On the other hand, the energy gaps of 4CDNA and compound 1 biphenyl leg. Finally, a binding energy of 4.39 kcal molꢀ1 has
are quite similar. For 4CDNA the HOMO (lying at ꢀ6.86 eV) is been calculated for the interaction of 4CDNA and compound 1
delocalized along the aromatic ring and the –NO2 groups. In at the same level of theory.
contrast, for the LUMO (calculated at ꢀ3.36 eV) the delocalization
is produced over one of the ꢀNO2 groups (Fig. 2, above). For
compound 1 the delocalization of the HOMO orbital, calculated at
ꢀ5.52 eV, is centred in the biphenyl group of one leg. The LUMO
Conclusions
orbital, calculated at ꢀ2.37 eV, shows a delocalization along the We have developed the synthesis of tripod-shaped chromophores 4
whole leg, principally localized in the terminal 1,3-indandione and 1 in good yield. The key reactions are the Suzuki–Miyaura cross-
moieties, as can be observed in Fig. 2. Furthermore, the interaction coupling of an unsymmetrical tri(p-iodophenyl)-p-bromophenyl-
between frontier molecular orbitals of these two compounds silane as the core of the tripod with a phenyl substituted boronic
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acid derivative, followed by aldol condensation with 1,3-indandione.
Synthesis of 7. At rt, aromatic aldehyde 6 (13.4 mmol, 3.05 g)
Molecule 1 shows a high thermal stability.
was added to a solution of 1,3-indandione (13.5 mmol, 1.97 g)
The structure of both molecules has been established by in ethanol (100 mL), over a period of 3 min with constant
theoretical calculations, showing a tetrahedral symmetry around stirring. Then, 2–3 drops of piperidine were added to maintain
the Si core and a non-planar disposition of the phenyl groups in alkaline medium. The mixture was refluxed for 3 h. After this
each of the biphenyl moieties. The last can be explained by the period, the volume was reduced to half under vacuum and then
steric hindrance attributed to the presence of the bulky –NMe2. poured into crushed ice. The separated solid was filtered off and
The steric effect is predominant to electronic effects.
recrystallized from ethanol to give the desired 2-benzylidene-
1
Fluorescence spectroscopy was used for the optical characteriza- indandione derivative 7 (4.14 g, yield 87%). H-NMR (CDCl3) d
tion of 4 and 1. Fluorescence spectra of 1 and 4 show absorption (ppm) (400 MHz): 8.84 (s, 1H, Hvin), 8.36 (dd, J1 = 8.8 Hz, J2 = 2
maxima at 543 and 470 nm, respectively. Quantum yields were Hz, 1H, ArH), 7.94 (m, 2H, ArH), 7.77 (m, 2H, ArH), 7.70 (s, 1H,
obtained (4: 0.16 and 1: 0.38) and time-resolved fluorescence ArH), 7.04 (d, J = 8.8 Hz, 1H, ArH), 2.99 (s, 6H, –NMe2). 13C-NMR
measurements reveal typical characteristics of conjugated molecules. (CDCl3) d (ppm) (100 MHz): 190.6, 189.5 (2 ꢂ CQO), 155.9 (C–N),
Enhancement fluorescence values (up to 15 times higher) 145.3, 145.2, 142.5, 140.9, 140.1, 135.1, 127.6, 127.0, 123.2, 118.9,
were found when compound 1 was combined with 4-chloro-2,6- 115.2 (C–Br), 43.5 (–NMe2). MS (70 eV) m/z (%): 358 (17), 357 (92),
dinitroaniline. This interaction was linearized in the range of 0 355 (100), 354 (61).
to 20 mg Lꢀ1. This enhancement was explained by the calculation
Reaction of 6 or 7 with bis(pinacolate)diboron. Under an
of energies and the distribution of the HOMO and the LUMO for 1 Ar atmosphere, a degassed solution of 6 or 7 (1 eq.), bis-
and 4-chloro-2,6-dinitroaniline, and by the prediction of an energy (pinacolate)diboron (1.3 equiv.), Pd(dppf)2Cl2 (10% mol), and
favourable approximation of both compounds.
KAcO (4 eq.) in dry dimethoxyethane (10 mL) was heated under
The strong and sensitive fluorescence enhancement behavior of reflux for 18 h. After this period, the reaction was cooled to
the explosive 4-chloro-2,6-dinitroaniline towards 1 demonstrates room temperature, filtered, and diluted with CH2Cl2. The
that this tripod-shaped chromophore is a promising optical sensor organic solution was washed with water and brine, then dried
material for detecting nitro-containing explosives.
over MgSO4, and concentrated to dryness. The residue was
The results presented here are a part of ongoing research separated by SiO2 column chromatography eluting with EtOAc/
involving the synthesis of longer tripod-shaped oligo-p-phenylene cyclohexane, 1 : 1. Only debromination products of 6 or 7 were
chromophores, as well as the immobilization on solid substrates isolated, respectively.
(glass slides, optical fibers) for potential application as sensor
devices. Further work is in progress.
Synthesis of 2-(3-bromo-4-(N,N0-dimethylamino)-1-phenyl)-
1,3-dioxolane (8). To a solution of 6 (10.03 g, 44.2 mmol) in
toluene (80 mL), ethylene glycol (48.9 mL, 877 mmol) and
p-toluenesulfonic acid monohydrate (0.51 g, 2.6 mmol) were
added. The reaction was heated under reflux for 12 h while
removing water using a Dean–Stark apparatus. After this per-
iod, the solution was cooled to room temperature, aqueous
potassium carbonate 10% was added and then extracted with
EtAcO (3 ꢂ 20 mL). The organic phase was washed with brine
and water, dried over MgSO4 and concentrated under vacuum.
The product obtained (8) was used without purification in next
reactions (11.68 g, yield 98%).1H-NMR (CDCl3) d (ppm) (400 MHz):
7.66 (d, J = 2.0 Hz, 1H, ArH), 7.32 (dd, J1 = 8.4 Hz, J2 = 2.0 Hz, 1H,
ArH), 7.05 (d, J = 8 Hz, 1H, ArH), 5.70 (s, 1H, OCHO), 4.07 (m, 2H,
Experimental
Materials
The tri( p-iodophenyl)-p-bromophenylsilane (2) was prepared by
following the literature procedure.8 All reagents, including starting
materials, 1,3-indandione and p-(N,N0-dimethylamino)benzaldehyde
were purchased from Aldrich and used without further purification.
Deionized water was employed for all the experiments.
Synthetic procedures
Synthesis of 3-bromo-4-(N,N0-dimethylamino)benzaldehyde (6). OCH2), 3.97 (m, 2H, OCH2), 2.77 (s, 6H, –NMe2). 13C-NMR (CDCl3)
To a mixture of 4-(N,N0-dimethyl)aminobenzaldehyde (13.5 mmol, d (ppm) (100 MHz): 152.1 (C–N), 133.4 (C-1), 131.8, 126.2 (C-2, C-6),
2.01 g) and NH4OAc (10%) in CH3CN (75 mL) NBS (16 mmol, 120.0 (C-5), 109.2 (C–Br), 102.7 (OCO), 65.3 (2 ꢂ CH2), 43.3 (–NMe2).
2.90 g) was added and the mixture was stirred at room tempera-
Synthesis of 6-N,N0-dimethylamino-3-formyl-1-phenyl boronic
ture (rt) for 15 min. After completion of the reaction, as indicated acid (3b). Under Ar, to a solution of 2-(3-bromo-4-(N,N0-dimethyl-
by TLC, the mixture was concentrated under vacuum and amino)-1-phenyl)-1,3-dioxolane 8 (4.00 g, 14.7 mmol) in THF
extracted with EtOAc/H2O (1: 1) (3 ꢂ 50 mL). The organic portion (40 mL) cooled to ꢀ78 1C, n-BuLi (13.8 mL, 1.6 M, 22.05 mmol)
was then concentrated to dryness and subjected to column was added dropwise. The mixture was stirred for 5 min and
chromatography (SiO2, cyclohexane/EtOAc, 10 : 1) to obtain a trimethylborate (4.92 mL, 44.1 mmol) was added dropwise. The
pure compound 6 (2.69 g, yield 88%).1H-NMR (CDCl3) d (ppm) mixture was stirred at ꢀ50 1C for 2 h, then warmed up to room
(400 MHz): 9.79 (s, 1H, CHO), 8.01 (s, 1H, H-2), 7.72 temperature and stirred overnight. After this period, 1 M HCl
(dd, J1 = 8.4 Hz, J2 = 2 Hz, 1H, H-6), 7.06 (d, J1 = 8.4 Hz, 1H, H-5), solution (25 mL) was slowly added to the reaction mixture and
2.93 (s, 6H, NMe2). 13C-NMR (CDCl3) d (ppm) (100 MHz): stirred for 4 h. Then 10% K2CO3 solution (5 mL) was added to
189.5 (CQO), 156.9 (C–N), 135.9 (C-1), 130.9, 129.8 (C-2, C-6), the reaction mixture, adjusting the pH to 6–7. The solution was
119.3 (C-5), 116.4 (C–Br), 43.3 (–NMe2).
extracted with EtAcO and the organic phase was washed with
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water, brine and dried over MgSO4. The solution was filtered and and Perkin-Elmer 883 spectrophotometers. Mass spectrometry was
concentrated under vacuum. The residue was purified by SiO2 carried out on a Thermo Finnigan instrument using the direct
column chromatography using cyclohexane/EtAcO (1: 1) and injection and electron ionization (EI) modes. HRMS was recorded
1
then MeOH to obtain product 3b (2.21 g, yield 78%). H-NMR using a Micromass (Autospec-Q) spectrometer. 1H and 13C-NMR
(CDCl3) d (ppm) (400 MHz): 9.64 (s, 1H, CHO), 7.86 (s, 1H, H-2), spectra were recorded using a 400 MHz ARX 400 Bruker spectro-
7.61 (d, J = 8.8 Hz, 1H, H-6), 7.46 (d, J = 8.8 Hz, H-5), 6.70 meter by using the residual solvent peak in CDCl3 (dH 7.24 ppm for
(br s, B(OH)2), 2.87 (s, 6H, ꢀNMe2). 13C-NMR (CDCl3) d (ppm) 1H and dC = 77.0 ppm for 13C). TLC analyses were performed on
(100 MHz): 192.1 (CHO), 153.1 (C–N), 142.1 (C-6), 132.1 (C-4), Merck silica gel 60 F 254 plates, and column chromatography was
128.7, 124.0 (C-1, C-5), 116.0 (C-3), 42.1 (–NMe2). HRMS m/z (%): performed on silica gel 60 (0.040–0.063 mm). Emission spectra
C19H12BNO3 cal = 193.0910; exp = 193.0917. IR (KBr) n: excitation (295.3 to 671.7 nm) and emission (249.7 to 719.7 nm)
1715 cmꢀ1
.
spectra were obtained using a Spex 3D luminescence spectro-
Synthesis of 4. An oven-dried round-bottom flask was fitted photometer equipped with a Xenon pulse discharge lamp (75 W)
with a condenser, placed under an Ar atmosphere and charged and a CCD detector and 0.25 mm slits and 1 s integration times
with a mixture of solids: Cs2CO3 (206 mg, 0.6 mmol), 2 (250 mg, were used in scan mode at room temperature. Lifetime measure-
0.3 mmol) and Pd(PPh3)4 (36.4 mg, 0.03 mmol). The flask was ments were recorded using a Horiba Jovin Yvon Fluoromax 4
degassed with Ar. Then a degassed solution of 3b (202 mg, TCSPC using the following instrumental settings: 470 nm
1 mmol) in a mixture of toluene/MeOH (1 : 1, 25 mL) was added. NanoLED; time range, 1.6 ms; peak preset; 10 000 counts; repetition
The reaction mixture was refluxed for 18 h. After this period, rate, 500 kHz; synchronous delay, 25 ns; emission detection:
the inorganic solids were removed by filtration through Celite, 535 nm. Lifetime deconvolution analysis was performed using
and washed with CH2Cl2. Finally, the solvent was evaporated Decay Analysis Software, version 6.4.1 (Horiba JovinYvon). Fluores-
under vacuum and the residue was column chromatographied cence decays were interpreted in terms of a multi-exponential:
P
(SiO2, cyclohexane/EtOAc, 8/2) to give 4 as a white-yellow solid I(t) = A + Biexpꢀt/t, where A and Bi are the pre-exponential factors
i
(219 mg, yield: 87%). 1H-NMR (CDCl3) d (ppm) (400 MHz): 9.84 and ti the decay times.
(s, 3H, CHO), 7.75 (d, J = 8.4 Hz, 6H, ArH), 7.72 (d, J = 2.1 Hz,
Sensing experiments
3H, ArH) 7.65 (d, J = 8.4 Hz, 6H, ArH), 7.7–7.4 (m, 7H, ArH), 7.03
(d, J = 8.4 Hz, 3H, ArH), 2.72 (s, 18H, 3 ꢂ –NMe2). 13C-NMR For the sensing experiments between 4CDNA and compound 1
(CDCl3) d (ppm) (100 MHz): 190.6 (CHO), 156.0, 143.15, 140.1, different solutions of 4CDNA in EtOAc were prepared: 0.001;
137.9, 136.6, 134.2, 133.2, 132.1, 131.0, 130.7, 128.6, 127.9, 0.01; 0.05; 0.1; 0.75; 2; 5; 10 and 20 mg Lꢀ1. To these solutions
124.9, 116.3, 111.0, 42.9 (–NMe2). HRMS m/z (%): C51H46N3O3- an aliquot of 200 mL containing DMABI tripod 1 0.1 M was
SiBr cal = 855.2492; exp = 855.2500 (7%). ATR-IR n (cmꢀ1): 2923 added under mild magnetic stirring. Emission spectra were
(NMe), 2851 (QCH), 1680 (CHO), 1591, 1508, 729 (CBr). UV recorded as is detailed in the Instrumentation section.
(AcOEt) lmax (log e): 274 nm (4.51), 332 nm (4.45). EI-MS (70 eV)
DMABI-tripod structure calculations
m/z (%): 856 (5, M + 1), 224 (12), 158 (35), 96 (100).
Synthesis of 1. Under Ar, a solution of 4 (119 mg, 0.14 mmol, All calculations were performed using the Gaussian 09 series of
1 equivalent) in toluene (25 mL) was added over a stirred programs (Revision A.02).20 The geometries of molecules 1 and
solution of 1,3-indandione (180 mg, 1.23 mmol, 8.8 equiv.) in 4 were fully optimized using density functional theory (DFT)
EtOH (10 mL). 2–3 drops of piperidine were then added. The with the B3LYP three-parameter hybrid functional proposed by
reaction mixture was refluxed for 18 h. After completion of the Becke21 and the 6-31G(d) basis set.22,23 The B3LYP functional
reaction (TLC) the solvent was removed under vacuum and the comprises an exchange–correlation functional that mixes the
residue was separated by cc (SiO2, cyclohexane/EtOAc, 2/1) to non-local Fock exchange with the gradient-corrected form of
give 1 as an orange solid (50 mg, yield: 29%). Mp: 287–288 1C, Becke24 and adds the correlation functional proposed by Lee
1H-NMR (CDCl3) d (ppm) (400 MHz): 8.53 (s, 3H, Hvin), 8.45 et al.25 The optimum structures so obtained were further
(d, J = 8.8 Hz, 3H, ArH), 7.92 (m, 6H, ArH), 7.83 (s, 3H, ArH), certified as true minima by constructing and diagonalizing
7.73 (m, 6H, ArH), 7.69 (d, J = 8.0 Hz, 6H, ArH), 7.62 (d, J = the corresponding Cartesian Hessian matrix.
8.0 Hz, 6H, ArH), 7.57–7.54 (m, 4H, ArH), 7.02 (d, J = 8.8 Hz, 3H,
ArH), 2.79 (s, 18H, 3 ꢂ –NMe2).13C-NMR (CDCl3) d (ppm)
Quantum yield determination
(100 MHz): 190.1 (CO), 190 (CO), 155.5, 147.6, 143.2, 140.1, The quantum yield (QY) was determined using quinine sul-
138.2, 138.0, 137.9, 136.0, 135.9, 134.1, 132.5, 130.3, 130.3, phate as standard, which according to the literature has a QY of
129.7, 127.6, 126.9, 124.9, 43.9 (ꢀNMe2). HRMS m/z (%): 0.54 in sulphuric acid 0.1 M (n = 1.38), DMABI-tripod 1 was
C78H59N3O6SiBr cal = 1239.3378; exp = 1239.3348 (8%). ATR-IR dissolved in ethyl acetate. The calibration curve for quinine was
n (cmꢀ1): 2923, 2851, 1713, 1674 (CQO), 1595, 1555, 1508, 726 obtained. The integrated area under the fluorescence curves
(C–Br). UV (EtAcO) lmax (log e): 254 nm (4.90), 470 nm (4.68).
(excitation at 470 nm) was plotted versus the absorbance at
370 nm (after subtraction of the solvent absorbance) for different
concentrations. The same procedure was repeated for both the
´
Instrumentation
UV spectra were recorded using a Hewlett–Packard 8452A spectro- compounds (1 and 4) dissolved in ethyl acetate (n = 1.3720).
photometer, and IR spectra were recorded using Beckman Aculab IV The excitation intensity and slit width were held constant for
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(b) C. L. Ho and W. Y. Wong, New J. Chem., 2013, 37, 1665;
(c) M. A. R. Matos, M. S. Miranda, M. J. S. Monte, L. M. N. B.
F. Santos, V. M. F Morais, J. S. Chickos, P. Umnahanant and
J. F. Liebman, J. Phys. Chem. A, 2007, 111, 1115.
all measurements. The QY of DMABI-tripods 1 and 4 was obtained
from eqn (1):
ꢀ
ꢁꢂ
ꢃ
2
ðdI=dAÞCDs nCDs
QYCDs ¼ QYst
(1)
2
ðdI=dAÞst
nst
13 D. Katsis, Y. H. Geng, J. J. Ou, S. W. Culligan, A. Trajkovska,
S. H. Chen and L. J. Rothberg, Chem. Mater., 2002, 14, 1332.
14 V. Gulbinas, G. Kodis, S. Jursenas, L. Valkunas, A. Gruodis,
J. C. Mialocq, S. Pommeret and T. Gustavsson, J. Phys. Chem.
A, 1999, 103, 3969.
where I is the area under the fluorescence curves and A is the
corresponding absorbance.26
Acknowledgements
15 K. T. Wong, C. F. Wang, C. H. Chou, Y. O. Su, G. H. Lee and
S. M. Peng, Org. Lett., 2002, 4, 4439.
This work was funded by the Spanish Ministerio de Ciencia e
16 M. Algarra, B. B. Campos, M. S. Miranda and J. C. G. Esteves
da Silva, Talanta, 2011, 83, 1335.
´
´
Innovacion (Project Number CTQ2013-48418P) and Andalucıa
´
Tech program ‘‘U-mobility’’ co-financed by University of Malaga
17 Z. Zhou and R. G. Parr, J. Am. Chem. Soc., 1990, 112, 5720.
18 R. C. Haddon and T. Fukunaga, Tetrahedron Lett., 1980,
21, 1191.
and the European Community’s Seventh Framework Program
under Grant Agreement No. 246550.
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H. Zhang, W. Liu and J. Gao, New J. Chem., 2014, 38, 5754.
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Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
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A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada,
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J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
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