Synthesis and photophysical properties of difluoroboron complexes of curcuminoid derivatives bearing different terminal aromatic units and a meso-aryl ring

Article abstract of DOI:10.1021/jo400389h

The synthesis of nine curcuminoids and their difluoroboron complexes is described, with seven of them containing a meso-phenyl ring. Dynamic ¹⁹F NMR confirmed the fact that rotation of that meso-aryl fragment is restricted in the latter systems at room temperature and become allowed at higher temperature (>45 C). The molecular structure of a meso-substituted derivative in the solid state showed that the phenyl ring lies in a highly twisted plane with respect to the mean curcuminoid plane. The photophysical properties of the nine compounds were investigated in solvents of different polarity. Meso-substitution with a phenyl ring has little influence on fluorescence emission properties in solution, radiative and nonradiative kinetic constants being similar for meso- and nonsubstituted compounds, which is in contrast to the case of BODIPY derivatives. However, introduction of an electron donor p-methoxy group at the meso-phenyl ring leads to small perturbation of the curcuminoid π-system fluorescence emission. We also report the influence of the meso-phenyl group on the emission properties of the aggregated solids.

Full text of DOI:10.1021/jo400389h

Article
pubs.acs.org/joc
Synthesis and Photophysical Properties of Difluoroboron Complexes
of Curcuminoid Derivatives Bearing Different Terminal Aromatic
Units and a meso-Aryl Ring
Abdellah Felouat, Anthony D’Aleo,* and Frederic Fages
́
́
́
Aix Marseille Universite, CNRS, CINaM UMR 7325, Campus de Luminy, Case 913, 13288 Marseille, France
S
* Supporting Information
ABSTRACT: The synthesis of nine curcuminoids and their difluoroboron
complexes is described, with seven of them containing a meso-phenyl ring.
Dynamic 19F NMR confirmed the fact that rotation of that meso-aryl fragment is
restricted in the latter systems at room temperature and become allowed at higher
temperature (>45 °C). The molecular structure of a meso-substituted derivative in
the solid state showed that the phenyl ring lies in a highly twisted plane with respect
to the mean curcuminoid plane. The photophysical properties of the nine
compounds were investigated in solvents of different polarity. Meso-substitution
with a phenyl ring has little influence on fluorescence emission properties in
solution, radiative and nonradiative kinetic constants being similar for meso- and
nonsubstituted compounds, which is in contrast to the case of BODIPY derivatives.
However, introduction of an electron donor p-methoxy group at the meso-phenyl
ring leads to small perturbation of the curcuminoid π-system fluorescence emission.
We also report the influence of the meso-phenyl group on the emission properties of the aggregated solids.
studies.24 Nevertheless, this study did not contain an in-depth
photophysical investigation of that compound.
INTRODUCTION
■
Since the first report on boron coordination compounds with
acetylacetonate (acacH),1 there has been a long-standing
interest in the spectroscopic properties of β-diketoboro-
nates.2−4 Currently, boron difluoride-containing molecules
represent a topical class of fluorophores that encompasses a
broad variety of chemical structures such as anils,5 2-(2′-
hydroxyphenyl)benzoxazole,6 quino[7,8-h]quinoline,7 anilido-
pyridine,8 chalcones,9 and 3-hydroxyflavones,10 with BODIPY11
and aza-BODIPY12 derivatives representing the most popular
dyes. These materials display outstanding electronic and optical
properties3,4 with applications in nonlinear optics,13 mechano-
chromism,3e organic photovoltaics,14 lasing,15 OLED dis-
play,3a,16 sensing,3f,17 photodynamic therapy,18 and cell
imaging.19
Curcuminoids are natural compounds featuring a π-
conjugated system and a central β-diketone unit.20 Their
optical properties21 and those of their metal complexes22 have
been investigated extensively. With boric acid, curcumin, the
main curcuminoid, has long been known to form a highly
colored dicurcuminatoboronium salt, the so-called rosocyanine,
that has been used for the colorimetric determination of
boron.23 Despite that work, the fluorescence emission proper-
ties and excited-state behavior of difluoroboron complexes of
natural and abiotic curcuminoids have far less been investigated.
Recently, Moore and co-workers reported the application of the
BF2 complex of 1,5-bis(N,N-dimethylaminostyryl)acacH as an
amyloid-β plaque-specific fluorescent probe providing a
promising near-infrared fluorescent dye for in vivo biological
In line with our ongoing work on hydroxychalcone−BF2
complexes,9 we decided to extend our investigation toward the
curcuminoid−BF2 counterparts. In particular, we wanted to
evaluate the influence of different aromatic groups placed at the
terminal positions or connected at the central carbon atom
(called meso in this paper) of the acac-BF2 moiety on solution
and solid-state optical properties. In the BODIPY series, the
fact that the meso-phenyl ring is either constrained or free to
rotate largely determines the efficiency of internal conversion
and in turn of fluorescence emission.25 To our knowledge,
while few examples of meso-aryl-substituted acacH derivatives
have been reported recently,26 there is no report in the
literature on meso-functionalized curcuminoids. Moreover, it
occurred to us that the presence of a meso-aryl substituent
could endow the flat, extended π-conjugated structures of
curcuminoids with enhanced solubility in organic solvents as
compared to the nonsubstituted analogues.
We present therein the synthesis of compounds 1−4 (Chart
1) and their electronic absorption and fluorescence emission
properties in organic solvents at room temperature. The data
are compared to those obtained for a series of model
compounds M1−M4 (Chart 2). The presence of the two
fluorine atoms allows dynamic 19F NMR studies with
compounds M1 and M2, which provides insight into the
dynamics around the aryl-acac single C−C bond in the ground
Received: March 4, 2013
© XXXX American Chemical Society
A
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Chart 1. Structure of the Compounds Investigated in This Study
Chart 2. Formulae of the Model Compounds
phenyl group on the emission properties of the aggregated
solids.
RESULTS AND DISCUSSION
■
Synthesis. The acacH ligand served as the main starting
building block toward compounds 1−4 and M1−M4 (Scheme
1). It is a very cheap and versatile compound that can easily be
substituted laterally (at the methyl carbon atoms) or centrally
(at the 3- or meso position). Meso substitution of acacH with
different aryl groups was performed straightforwardly by CuI-
catalyzed arylation of acetylacetone using the corresponding
iodoaryl precursors, as previously published.27 Lateral sym-
metric extension of π-conjugation leading to the introduction of
donor moieties was carried by an aldol-type condensation
reaction using the corresponding aldehydes (Scheme 1) and a
boronium intermediate obtained by the action of boric
anhydride on the acacH precursor.28 1,3-Diketodifluoroboro-
nate species were produced smoothly from the free ligands by
the action of boron trifluoride etherate in dichloromethane
state. The molecular structure of compound M4 in the solid
state is described which represents the first example of an X-ray
structure determination of a curcuminoid borondifluoride
complex. Furthermore, we report the influence of the meso-
Scheme 1. Synthetic Route to the 1,5-Distyrylacetylacetone Ligands and Their Boron Difluoride Complexes
B
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Figure 1. 19F NMR spectra of compounds (a) M1 and (b) M2 in CDCl3 at different temperatures.
(DCM) at reflux. Analytically pure samples of curcuminoids
containing the flat, extended aromatic units 2-methoxynaphth-
6-yl and N-methylcarbazol-4-yl were particularly difficult to
obtain because of the poor solubility of their BF2 complexes,
and they are not presented here. In contrast, the meso-phenyl
analogues 3 and 4 were quite soluble in organic solvents and
could be obtained with the high purity grade requested for
spectroscopic measurements. All compounds were found
chemically and photochemically stable in solution and in the
solid state. In particular, BF2 de-coordination was not observed
in all solvents used here, even in the presence of protic
solvents.9
a higher steric hindrance around the orthogonal C−C bond
when the phenyl ring is connected to the π-conjugated
curcuminoid skeleton. A consequence of the twisted geometry
for the meso-aryl substituent is a significant downfield shift (Δδ
= −0.20 ppm in 1-Ph vs 1-H) of the resonance of the olefinic
protons at positions α (C2 and C12, see Figure 2 for atom
numbering) to the acac C−O groups. This effect is consistent
with the location of these protons in the shielding cone of the
orthogonal aromatic group.
NMR Study. Except for M1 and M2, room-temperature 19
F
NMR spectra in CDCl3 solution show a single resonance peak
accompanied by a down-shielded satellite resonance due to the
isotope shift effect of the 18.8% naturally abundant 10B isotope.
As observed previously with diketonates,29 B-F coupling is not
observed. The m-methoxyphenyl-substituted compounds M1
and M2 give rise to a broadened multiplet in CDCl3 with a line
shape that is highly dependent on temperature (Figure 1). In
the high-temperature regime, above 320 K, a single resonance
line is observed for M1,30 while at low temperature, below 280
K, a well-resolved quadruplet clearly emerges along with the
down-shielded similar pattern stemming from 10B isotope effect
(Figure 1a). At 256 K, the spectrum clearly resembled that of
an AB spin system. This behavior reflects the dynamics of
internal rotation around the aryl-acac orthogonal C−C bond. In
the low-temperature regime, rotation is slowed down and
because of the presence of the m-methoxy group, the plane
containing the π-conjugated curcuminoid skeleton and the
boron atom is no longer a symmetry plane in M1. At low
temperature, the molecule belongs to the Cs symmetry point
group. As a result, the two fluorine atoms are chemically
nonequivalent. Assuming an AB spin pattern, Δν was found to
be 127 Hz and JAB (= JF−F) = 77 Hz, using 376.5 MHz 19F
NMR. At high temperature, rotation becomes allowed, NMR
peak coalescence is observed at 310 K, and on the NMR time
scale, M1 has the average C2v symmetry. Taking this value and
that of Δν, we obtain 282 s−1 and ca. 60 kJ mol−1 for the rate
constant and the activation barrier, respectively, for internal
rotation in M1 at 310 K in CDCl3. This value of the energy
barrier is in agreement with that determined experimentally for
biphenyl compounds.31 The 19F NMR spectrum of compound
M2 in CDCl3 exhibits a similar temperature dependence, but
coalescence is not observed below 318 K (Figure 1b) and is
believed to occur at higher temperature. This is an indication of
Figure 2. Molecular structure (ORTEP) of compound M4 with
displacement ellipsoids drawn at the 50% probability level.
Single-Crystal X-ray Analysis. X-ray quality crystals of M4
were grown by slow evaporation from ethyl acetate. A single
crystal was mounted on a glass fiber, and diffraction data were
acquired using a Mo Kα radiation source (λ = 0.71073 Å).
Detailed crystallographic parameters are included in Table 1.32
Figure 2 shows the molecular structure of M4 with the
displacement thermal ellipsoids drawn at the 50% probability
level. Compound M4 (P-1, Z = 2) crystallizes in a triclinic
crystal system with two independent molecules in the
asymmetric unit.
BF2 complexes of acacH have a large ground-state dipole
moment of about 6.7 D33 and thus behave like dipolar
chromophores in the crystal.34 Indeed, compound M4 exists as
stacks along the crystallographic a-axis (Figure 3) in which face-
to-face, antiparallel superimposition of π-conjugated systems
forms dimers with a short interplanar distance (3.65 Å). The
distance between adjacent molecules of two neighboring dimers
C
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width for 1-Ph in DCM) and can be attributed to a π−π*
transition. The spectrum of 1-Ph is red-shifted as compared to
that of 1-H, the bathochromic shift being nearly constant
irrespective of solvent nature (mean Δλ = +16 nm). The same
effect is also observed when passing from 2-H to 2-Ph, but the
mean bathochromic shift is larger (ca. Δλ = +20 nm in DCM).
This effect might stem from an increased planarity of the 1,5-
distyrylacetylacetone skeleton upon meso-functionalization with
the aryl group. The BF2 complexes of the curcuminoids are
fluorescent in the 540−650 nm region with fluorescence
quantum yields ranging from 40 to 60% in DCM. It is worth
noting that the highest value of 60% is obtained with the
carbazole-containing compound, giving a good brightness value
of ca. 42000 M−1 cm−1.
The solvent dependence of absorption and emission
properties was examined with the two series of compounds
1-H, 1-Ph and 2-H, 2-Ph in order to get better insight into the
influence of the meso-phenyl ring (Tables 3 and 4). Both
electronic absorption and fluorescence emission spectra of
these compounds show positive solvatochromism and lose their
vibronic structure in the more polar solvents (Figure 5). The
solvent-induced bathochromic shift of the absorption band
reaches 600 cm−1 within both series. The observation of a
positive solvatochromic effect allows to infer that vertical
absorption transition led to Franck−Condon S1 state that is
more polar than the ground state (vide supra).
Table 1. Selected Crystal Data for Compound M4
compound M4
formula
C29H25BF2O6
518.3
λ(Mo/Kα)/Å
T/K
Dc/g.cm−3
θ range/deg
hkl ranges
0.71073
293(2)
1.284
M/g
Size/mm3
crystal system
space group
0.30 × 0.26 × 0.2
triclinic
1.49−28.55
0, 11
P-1
−15, 15
−18, 17
346
a (Å)
b (Å)
c (Å)
8.448(1)
11.579(3)
14.093(4)
94.74(1)
102.62(2)
90.301(5)
1340.3(5)
2
variable
refln measured
refln I > 2σ(I)
R1 I > 2σ(I)
R1 all data
6349
3188
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
0.0831
0.1687
0.2305
0.309
wR2 I > 2σ(I)
wR2 all data
Δρ ( )/eÅ−3
0.667/−0.659
Plotting Stokes shift values for 1-H, 1-Ph and 2-H, 2-Ph
versus the polarity function Δf′ of the solvent gave linear plots
with positive slopes (Figures S36 and S37, Supporting
Information),35 which confirms the relaxation toward a
solvent-equilibrated singlet excited state with a charge-transfer
character and having an excited-state dipole moment larger
than that in the ground state. This behavior is in agreement
with that reported for diaroyl(methanato)boron difluoride
compounds4 and is related to the strong electron withdrawing
effect of the difluorodioxaborine chelate.3g The Stokes shift
values are observed to be smaller for the meso-substituted
compounds relative to the nonsubstituted ones. It is also worth
noting that solvatochromic shifts of the emission maximum are
smaller for curcuminoids than for diaroyl(methanato)boron
difluoride complexes.4 From these observations, one can infer
that the BF2-containing curcuminoid backbone undergoes a
limited nuclear reorganization accompanying excited-state
relaxation prior to emission because it can adopt a more
planar geometry in both ground and excited states,35 especially
in the case of dyes with the meso-phenyl ring as mentioned in
Figure 3. Crystal packing diagram of M4 down the b-axis direction,
illustrating π−π stacking interactions.
is significantly increased (4.15 Å). A torsion angle of 66.4° is
found between the planes of the meso-phenyl and dioxaborine
cycles, consistent with NMR data. We further observe that one
of the terminal anisole moiety is slightly twisted with respect to
the rest of the distyrylacetylacetone backbone. A torsion angle
of about 18° is measured between that phenyl ring and the
mean molecular plane.
Spectroscopic Properties. The electronic absorption and
fluorescence emission spectra were recorded in DCM (Figure
4), and the spectroscopic data are collected in Table 2. All
curcuminoids exhibit a strong absorption (ε > 50000 M−1
cm−1) with a similar band shape in the 500−570 nm range.
This band is rather narrow (ca. 80 nm, i.e., 3000 cm−1 at half-
Figure 4. a/Electronic absorption spectra (conc ≈ 10−5 M) and corrected fluorescence emission spectra (conc ≈ 10−6 M, λexc at the absorption
■
▲
▼
maximum) of 1-Ph (black , ), 2-Ph (blue , ), 3 (red , •), and 4 (green , ) in DCM at room temperature. All spectra are normalized.
D
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Table 2. Spectroscopic Data and Photophysical Properties of Compounds 1-H, 1-Ph, 2-H, 2-Ph, 3, and 4 in DCM at Room
a
Temperature
UV−vis
fluorescence
Φf x ε
compd
λabs
εmax
λem
ΔνST
Φf
τf
kf
knr
1-H
1-Ph
2-H
2-Ph
3
488
505
536
556
526
565
504
506
507
75480
78230
54470
57080
72120
69670
73200
74100
74770
538
554
616
633
600
636
556
571
557
1904
1751
2423
2188
2344
1976
1856
2250
1771
0.44
0.41
0.39
0.37
0.51
0.60
0.41
0.39
0.43
33211
32074
21243
21120
36781
41802
30012
28899
32151
1.30
1.35
1.96
1.91
1.86
2.15
1.32
1.31
1.34
3.4
3.0
2.0
1.9
2.7
2.8
3.2
3.0
3.4
4.3
4.4
3.1
3.3
2.6
1.9
4.5
4.7
4.3
4
M2
M3
M4
a
Absorption maximum wavelengths λabs (nm), molar absorption coefficients εmax (M−1 cm−1), fluorescence maximum wavelengths λem (nm), Stokes
shifts ΔνST (cm−1), fluorescence quantum yields Φf, brightness Φf × ε (M−1 cm−1), fluorescence lifetimes τf (ns), radiative kf (108 s−1) and
nonradiative knr = (1 − Φf)/τf (108 s−1) rate constants.
Table 3. Spectroscopic Data and Photophysical Properties of Compounds 1-H and 1-Ph in Solvents of Different Polarity at
a
Room Temperature
1-H
1-Ph
solvent
λabs
λem
ΔνST
Φf
τf
kf
knr
16
11
7.4
λabs
λem
ΔνST
Φf
τf
kf
knr
11
CCl4
477
475
480
488
483
483
492
497
515
538
534
549
639
930
0.20
0.24
0.35
0.44
0.45
0.51
0.50
0.70
0.88
1.30
1.49
1.55
4.0
3.5
3.9
3.4
3.0
3.3
493
491
496
505
500
500
515
520
534
554
549
564
870
1135
1435
1751
1785
2270
0.24
0.27
0.34
0.41
0.41
0.42
0.70
0.90
1.18
1.35
1.43
1.50
3.4
3.1
2.8
3.0
2.8
2.8
Et2O
8.1
5.6
4.4
4.2
3.9
AcOEt
DCM
acetone
ACN
1415
1905
1980
2490
4.3
3.7
3.2
a
Absorption maximum wavelengths λabs (nm), fluorescence maximum wavelengths λem (nm), Stokes shifts ΔνST (cm−1), fluorescence quantum
yields Φf, fluorescence lifetimes τf (ns), radiative kf (108 s−1) and nonradiative knr = (1 − Φf)/τf (108 s−1) rate constants; Et2O, ethylic ether; AcOEt,
ethyl acetate; DCM, dichloromethane; ACN, acetonitrile.
Table 4. Spectroscopic Data and Photophysical Properties of Compounds 2-H and 2-Ph in Solvents of Different Polarity at
a
Room Temperature
2-H
2-Ph
solvent
λabs
λem
ΔνST
Φf
τf
kf
knr
λabs
λem
ΔνST
Φf
τf
kf
knr
CCl4
523
516
524
536
532
530
561
587
590
616
622
651
1295
2344
2135
2423
2720
3507
0.23
0.29
0.31
0.39
0.21
0.12
1.18
1.34
1.51
1.96
1.03
0.65
2.0
2.1
2.1
2.0
2.1
1.9
6.5
5.3
4.5
3.1
7.7
542
540
542
556
549
550
577
583
603
633
631
649
1120
1365
1865
2190
2370
2775
0.23
0.29
0.32
0.37
0.22
0.12
0.94
1.12
1.28
1.91
1.02
0.63
2.4
2.6
2.5
1.9
2.2
1.8
8.3
6.3
5.3
3.3
7.6
Et2O
AcOEt
DCM
Acetone
ACN
13
14
a
Absorption maximum wavelengths λabs (nm), fluorescence maximum wavelengths λem (nm), Stokes shifts ΔνST (cm−1), fluorescence quantum
yields Φf, fluorescence lifetimes τf (ns), radiative kf (108 s−1) and nonradiative knr = (1 − Φf)/τf (108 s−1) rate constants; Et2O, ethylic ether; AcOEt,
ethyl acetate; DCM, dichloromethane; ACN, acetonitrile.
the NMR study. Compared to 1-H and 1-Ph, compounds with
the strong electron-donor aromatic groups, such as 2-H, 2-Ph,
3, and 4, give larger Stokes shift values.
observation indicates that there is no increase of fluorescence
transition moment with increasing polarity. This feature is
consistent with a limited nuclear reorganization in the relaxed
emitting state with respect to the Franck−Condon excited
state.36 The continuous decrease of knr values of 1-H and 1-Ph
with increasing solvent polarity indicates that nonradiative
processes are less efficient in polar solvents. In the case of 2-H
and 2-Ph, the decrease in knr was followed by an increase of
that parameter in highly polar solvents such as acetone and
acetonitrile. This effect might be associated to a change in
rotamer distribution associated with the terminal naphthalene
chromophores.
Kinetic constants were determined for radiative and
nonradiative deactivation pathways and are collected in Tables
2−4. Overall, kf values are in the same order of magnitude for
nonsubstituted and meso-substituted compounds, which in-
dicates that the emission probability is not significantly affected
by the presence of the meso-aryl group. The same observation
holds for knr values, showing that there is no significant energy
loss from the excited state via thermal deactivation pathways
that would arise from rotational motions of the phenyl
substituent. Such nonradiative deactivation due to meso-
substitution is classical in BODIPY derivatives.25 The radiative
constants kf are found to be insensitive to solvent polarity. This
Model compounds M2 and M4, with a meso-aryl group
containing an m-methoxy or p-carboxymethyl group, displayed
identical absorption and fluorescence emission spectra and
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Figure 5. Electronic absorption (a) and fluorescence emission (b) spectra of compound 4 in solvents of different polarity at room temperature (λexc
■
▲
▼
= 510 nm; carbon tetrachloride (, ), ethylic ether (red , •), ethyl acetate (blue , ), dichloromethane (green , ), acetone (pink ,
left-pointing triangle), and acetonitrile (gray , right-pointing triangle)).
photophysical properties (Table 2) with respect to compound
1-Ph. The presence of a meso-p-methoxyphenyl unit in M3,
however, affects significantly the fluorescence emission, but not
the electronic absorption properties. We notice a bathochromic
shift of the emission maximum wavelength (Δλ = +17 nm, i.e.,
Δν = 537 cm−1) with respect to 1-Ph along with a loss of the
vibronic structure that is already observable in weakly polar
solvents (Figure 6). The amplitude of the fluorescence
suspension that allowed recording fluorescence emission
spectra of the aggregated species (Figure 7).9 The four
compounds show solid-state emission spectra in the red to
near-infrared range, with the meso-phenyl-substituted dyes
exhibiting blue-shifted spectra relative to the meso-H analogues
(711 nm vs 679 nm for 1-H and 1-Ph, respectively, and 823 nm
vs 702 nm for 2-H and 2-Ph, respectively). This trend, opposite
to that noticed in solution, is consistent with the sterical
encumbrance of the meso-phenyl ring that tends to reduce the
interchromophoric π contact area in the solid state (Figure 3).
It is noteworthy that dynamic light scattering results indicate
that particle size distributions are very sensitive to the nature of
the donor group and to the presence of the meso aryl ring.37
Indeed, the latter leads to smaller size (Figures S38−S41,
Supporting Information), which correlates with the higher
solubility observed for the meso-phenyl-containing analogues.
CONCLUSION
■
We have synthesized BF2 complexes of a series of
curcuminoids. Within this series, those analogues that contain
a meso-aryl substituent are to date unprecedented structures.
The experimental observations obtained by dynamic 19F NMR
confirm the fact that rotation of the meso-aryl fragment is
restricted in the functionalized curcuminoids at room temper-
ature and become allowed at higher temperature (>45 °C). All
compounds give efficient fluorescence emission in solution.
Except for M3, meso- and nonsubstituted compounds exhibit
very close photophysical behavior showing no significant
influence of the meso-phenyl ring on S1 state dynamics, which
is in contrast with the behavior of BODIPY dyes. As a
consequence, the introduction of the axial phenyl group can be
exploited for endowing the curcuminoid unit with further
interesting features, such as enhanced solubility in common
organic solvents and modulated π−π stacking interaction,
without impeding fluorescence performance.
Figure 6. Normalized corrected fluorescence emission of compound
M3 (λexc = 480 nm) in solvents of different polarity at room
■
temperature (carbon tetrachloride (black , ), ethylic ether (red ,
▲
▼
•), ethyl acetate (blue , ), dichloromethane (green , ),
acetone (pink , left-pointing triangle), and acetonitrile (gray ,
right-pointing triangle)).
solvatochromic shift is also larger than for 1-Ph (Figures S36
and S37, Supporting Information). All together, these features
are indicative of the occurrence of a more polar excited π−π
state for the curcuminoid chromophore bearing the electron-
donor meso group. Although one may expect a rather weak
electronic communication between the meso-aryl ring and the
dioxaborine chelate, because of the large twist angle noticed
between these units in solution and the crystal, these
observations hint at some perturbation of the curcuminoid
excited-state properties by the meso-substituent in the case of
M3.
EXPERIMENTAL SECTION
■
General Experimental Methods. All solvents for synthesis were
of analytical grade. Spectroscopy measurements were carried out with
spectroscopic grade solvents. NMR spectra (1H, 13C, 19F) were
recorded at room temperature at 250, 62.5, and 235 MHz for 1H, 13C,
and 19F, respectively. Data are listed in parts per million (ppm) and are
reported relative to tetramethylsilane (1H and 13C); residual solvent
peaks of the deuterated solvents were used as an internal standard.
High-resolution mass spectra were recorded in positive electrospray
ionization mode using TOF analyzer.
By quick dilution of concentrated THF solutions of dyes 1-
H, 1-Ph, 2-H, and 2-Ph in water, we obtained stable colloids
F
dx.doi.org/10.1021/jo400389h | J. Org. Chem. XXXX, XXX, XXX−XXX

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■
Figure 7. Normalized corrected fluorescence emission of aggregated particles in water of compound (a) 1-H (black , ) and 1-Ph (red , •)
■
(λexc = 500 nm) and (b) 2-H (black , ) and 2-Ph (red , •) (λexc = 550 nm).
Syntheses. We used the following general procedure for the
synthesis of the compounds. In a 50 mL round-bottom flask, the
acetylacetonate derivative (1 molar equiv) and B2O3 (0.5 molar equiv)
were mixed in 15 mL of ethyl acetate and stirred at 60 °C for 30 min.
A solution of the appropriate aldehyde (2 molar equiv) and n-
tributylborane (2 molar equiv) in 10 mL of ethyl acetate was added,
and the mixture was stirred for 30 min at 60 °C. A catalytic amount of
butylamine (0.4 molar equiv) was then added to the solution, and the
reaction mixture was refluxed overnight. After the mixture was cooled
to 60 °C, 30 mL of 0.4 M HCl was added, and the resulting mixture
was stirred for 30 min. After cooling, the precipitate was filtered off
and dried in vacuo to yield ligands M4, 1-H, 2-H, and 3. The other
derivatives were further subjected to column chromatograhy on silica.
The free ligands were reacted with boron difluoride etherate to
produce the corresponding BF2 complexes as follows. In a 50 mL
round-bottom flask, the ligand (1 molar equiv) was solubilized in
dichloromethane (20 mL), and boron trifluoride etherate (1.3 molar
equiv) was added to this solution. The reaction mixture was refluxed
overnight. After being cooled to room temperature, the solvent was
evaporated and the resulting solid was suspended into diethyl ether.
The precipitate was filtered off, and the crude complex was purified by
column chromatography using silica gel when needed. In the latter
case, the chromatography conditions are specified for the compound.
(Z)-4-(Difluoroboryloxy)-3-(3-methoxyphenyl)pent-3-en-2-
one (M1). The free ligand (175 mg, 0.85 mmol) was reacted with
boron trifluoride etherate to afford the crude complex M1 that was
purified on silica using cyclohexane/DCM (3/1) as eluent. Slightly
yellow solid (198 mg, 92%): mp = 116−118 °C, 1H NMR (250 MHz,
1H NMR (250 MHz, CDCl3) δ = 8.03 (d, 3J = 15.5 Hz, 2H), 7.41 (m,
5H), 7.03 (dd, 3J = 8.3 Hz, 4J = 2.0 Hz, 1H), 6.85 (m, 6H), 6.39 (d, 3J
= 15.5 Hz, 2H), 3.86 (s, 3H), 3.83 (s, 6H); 13C NMR (62.5 MHz,
CDCl3) δ = 177.6, 162.7, 160.0, 147.1, 134.1, 131.3, 130.1, 127.3,
124.3, 117.8, 117.2, 117.0, 114.6, 114.5, 55.5; 19F NMR (235 MHz,
CDCl3) δ = −141.13 (10B-F, d, 2J = 152.7 Hz, 0.2F), −141.18 (11B-F,
2
2
d, J = 152.7 Hz, 0.8F), −141.41 (10B-F, d, J = 152.9 Hz, 0.2F),
2
−141.45 (11B-F, d, J = 152.9 Hz, 0.8F); LRMS (EI) (positive mode)
m/z 513.1 [M + Na]+, 529.1 [M + K]+; HRMS (ESI+) [M + Na]+
calcd for C28H25O5BF2Na+ 513.1660, found 513.1660.
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,4,7-tris(4-methoxy-
phenyl)hepta-1,4,6-trien-3-one (M3). The free ligand was
obtained as a yellow solid from meso-(p-methoxyphenyl)-acacH (314
mg, 1.52 mmol) and p-methoxybenzaldehyde (415 mg, 3.04 mmol)
and was filtered from ethyl acetate (350 mg, 52%): mp = 166−167 °C;
1H NMR (250 MHz, CDCl3) δ = 7.63 (d, 3J = 15.7 Hz, 2H), 7.30 (d,
3J = 8.6 Hz, 4H), 7.18 (d, 3J = 8.4 Hz, 2H), 6.97 (d, 3J = 8.4 Hz, 2H),
6.81 (d, 3J = 8.6 Hz, 4H), 6.38 (d, 3J = 15.7 Hz, 2H), 3.89 (s, 3H), 3.78
(s, 6H); 13C NMR (62.5 MHz, CDCl3) δ = 182.7, 161.1, 159.0, 140.4,
133.4, 129.8, 128,2, 127.7, 120.1, 115.3, 114.2, 113.9, 55.3; LRMS (EI)
(positive mode) m/z 443.1 [M + H]+, 441.3 [M + Na]+. Anal. Calcd
for C29H26O6: C, 76.00; H, 5.99. Found: C, 75.68; H, 5.60. This
compound (135 mg, 0.31 mmol) was reacted with boron trifluoride
etherate to afford the boron complex M3 as a red solid (150 mg,
1
quantitative): mp = 222−223 °C; H NMR (250 MHz, CDCl3) δ =
8.01 (d, 3J = 15.4 Hz, 2H), 7.37 (d, 3J = 8.6 Hz, 4H), 7.19 (d, 3J = 8.2
Hz, 2H), 7.02. (d, 3J = 8.2 Hz, 2H), 6.85 (d, 3J = 8.6 Hz, 4H), 6.39 (d,
3J = 15.4 Hz, 2H), 3.91 (s, 3H), 3.81 (s, 6H); 13C NMR (62.5 MHz,
3
CDCl3) δ = 7.39 (d, J = 7.8 Hz, 1H), 6.97 (m, 1H), 6.75 (m, 2H),
CDCl3) δ = 178.0, 162.7, 159.7, 147.0, 133.1, 131.3, 127.4, 124.7,
117.1, 115.1, 114.6, 114.5, 55.6; 19F NMR (235 MHz, CDCl3) δ =
−141.27 (10B-F, 0.2F), −141.33 (11B-F, 0.8F); LRMS (EI) (positive
mode) m/z 508.2 [M + NH4]+, 513.1 [M + Na]+; HRMS (ESI+) [M
+ Na]+ calcd for C28H25O5BF2Na+ 513.1660, found 513.1660.
Methyl 4-((1E,3Z,6E)-3-(difluoroboryloxy)-1,7-bis(4-methox-
yphenyl)-5-oxohepta-1,3,6-trien-4-yl)benzoate (M4). The free
ligand was obtained as a yellow solid from meso-(p-methylbenzoate)-
acacH (142 mg, 0.61 mmol) and p-methoxybenzaldehyde (165 mg,
1.21 mmol) and was filtered from ethyl acetate (117 mg, 41%): mp =
3.85 (s, 3H), 2.14 (s, 6H); 13C NMR (62.5 MHz, CDCl3) δ = 191.0,
160.3, 134.2, 130.6, 122.7, 116.3, 114.1, 55.3, 23.6; 19F NMR (235
MHz, CDCl3) δ = −138.14 (10B-F, 0.2F), −138.19 (11B-F, 0.8F),
−138.30 (10B-F, 0.2F), −138.34(11B-F, 0.8F); LRMS (EI) (positive
mode) m/z 272.1 [M + NH4]+, 277.0 [M + Na]+, (negative mode)
253.0 [M − H]−. Anal. Calcd for C12H13BF2O3: C, 56.74; H, 5.16.
Found: C, 57.03; H, 5.08.
(1E,4Z,6E)-5-(Ddifluoroboryloxy)-4-(3-methoxyphenyl)-1,7-
bis(4-methoxyphenyl)hepta-1,4,6-trien-3-one (M2). The free
ligand was obtained as a yellow solid from meso-(m-methoxyphenyl)-
acacH (253 mg, 1.23 mmol) and p-methoxybenzaldehyde (334 mg,
2.45 mmol) and was purified by column chromatography on silica
using cyclohexane/AcOEt (7/3 v/v) as eluent (76 mg, 14%): mp =
147 °C; 1H NMR (250 MHz, CDCl3) δ = 7.64 (d, 3J = 15.7 Hz, 2H),
7.36 (d, 3J = 8.0 Hz, 1H), 7.29 (d, 3J = 8.8 Hz, 4H), 6.96 (dd, 3J = 8.2
Hz, 4J = 2.5 Hz, 1H), 6.85 (m, 6H), 6.37 (d, 3J = 15.7 Hz, 2H), 3.83 (s,
3H), 3.78 (s, 6H); 13C NMR (62.5 MHz, CDCl3) δ = 182.4, 161.1,
140.6, 129.9, 129.5, 128.1, 124.8, 120.0, 117.5, 115.7, 114.2, 113.4,
55.3, 55.3; LRMS (EI) (positive mode) m/z 443.3 [M + H]+,
(negative mode) 441.4 [M − H]. Anal. Calcd for C29H26O6: C, 76.00;
H, 5.89. Found: C, 75.73; H, 5.60. This compound (38 mg, 0.086
mmol) was reacted with boron trifluoride etherate to afford the boron
complex M2 as a red solid (42 mg, quantitative): mp = 260−261 °C;
1
3
158−160 °C; H NMR (250 MHz, CDCl3) δ = 8.12 (d, J = 8.5 Hz,
2H), 7.66 (d, 3J = 15.7 Hz, 2H), 7.38 (d, 3J = 8.3 Hz, 2H), 7.27 (d, 3J =
8.8 Hz, 2H), 6.80 (d, 3J = 8.8 Hz, 2H), 6.28 (d, 3J = 15.5 Hz, 2H), 3.98
(s, 3H), 3.78 (6H); 13C NMR (62.5 MHz, CDCl3) δ = 182.2, 166.9,
161.3, 141.2, 140.9, 132.5, 129.9, 129.7, 129.4, 127.9, 119.5, 114.8,
114.3, 55.3, 52.2; LRMS (EI) (positive mode) m/z 471.3 [M + H]+,
493.2 [M + Na]+. Anal. Calcd for C29H26O6: C, 74.03; H, 5.57. Found:
C, 74.16; H, 5.60. This compound (77 mg, 0.16 mmol) was reacted
with boron trifluoride etherate to afford the boron complex M4 as a
1
red solid (85 mg, quantitative): mp = 229−230 °C; H NMR (250
3
3
MHz, CDCl3) δ = 8.18 (d, J = 8.5 Hz, 2H), 8.04 (d, J = 15.3 Hz,
2H), 7.40 (d, 3J = 8.5 Hz, 2H), 7.34 (d, 3J = 8.8 Hz, 2H), 6.84 (d, 3J =
3
8.8 Hz, 2H), 6.28 (d, J = 15.3 Hz, 2H), 3.99 (s, 3H), 3.81 (s, 6H);
13C NMR (62.5 MHz, CDCl3) δ = 177.4, 166.6, 162.9, 147.8, 137.9,
G
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Article
132.2, 131.6, 130.6, 130.2, 127.1, 116.4, 114.7, 55.5, 52.40; 19F NMR
(235 MHz, CDCl3) δ = −141.31 (10B-F, 0.2F), −141.37 (11B-F, 0.8F);
LRMS (EI) (positive mode) m/z 541.2 [M + Na]+, 557.2 [M + K]+.
Anal. Calcd for C29H25BF2O6·1/3CH2Cl2: C, 64.45; H, 4.73. Found: C,
64.09; H, 4.38.
and was filtered from ethyl acetate (319 mg, 44%): mp = 234−235 °C;
1H NMR (250 MHz, CDCl3) δ = 8.50 (d, 3J = 15.4 Hz, 2H), 8.26 (d,
3J = 8.3 Hz, 2H), 8.20 (d, 3J = 8.3 Hz, 2H), 7.47 (m, 10H), 6.72 (d, 3J
3
= 8.3 Hz, 2H), 6.53 (d, J = 15.4 Hz, 2H), 3.97 (s, 6H); 13C NMR
(62.5 MHz, CDCl3) δ = 182.5, 157.3, 137.6, 135.8, 132.6, 132.4, 128.6,
127.6, 127.4, 125.9, 125.5, 125.1, 123.2, 122.5, 122.4, 116.0, 103.8,
55.6; LRMS (EI) (positive mode) m/z 513.1 [M + H]+, (negative
mode) 511.2 [M − H]−. Anal. Calcd for C35H28O4: C, 82.01; H, 5.51.
Found: C, 81.83; H, 5.67. This compound (150 mg, 0.29 mmol) was
reacted with boron trifluoride etherate to afford the boron complex 2-
Ph as a red solid (164 mg, quantitative): mp = 299−301 °C; 1H NMR
(250 MHz, CDCl3) δ = 8.88 (d, 3J = 15.2 Hz, 2H), 8.25 (m, 4H), 7.56
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(4-methoxyphenyl)-
hepta-1,4,6-trien-3-one (1-H). The free compound38 (149 mg, 0.44
mmol) was reacted with boron trifluoride etherate to afford the crude
complex 1-H that was purified by column chromatography on silica
using Et2O/cyclohexane (1/1) as eluent. Red solid (170 mg, 74%):
1
3
mp = 247−249 °C; H NMR (250 MHz, CDCl3) δ = 7.98 (d, J =
15.4 Hz, 2H), 7.55 (d, 3J = 8.8 Hz, 4H), 6.92 (d, 3J = 8.8 Hz, 4H), 6.56
(d, J = 15.4 Hz, 2H), 5.98 (s, 1H), 3.84 (s, 6H); 13C NMR (62.5
3
3
3
(m, 9H), 7.37 (m, 2H), 6.76 (d, J = 8.4 Hz, 2H), 6.56 (d, J = 15.2
Hz, 2H), 4.00 (s, 6H); 13C NMR (62.5 MHz, CDCl3) δ = 177.4,
159.1, 143.6, 133.1, 132.9, 132.1, 129.1, 128.6, 128.2, 127.9, 129.0,
125.5, 124.1, 123.1, 122.7, 118.8, 104.0, 55.8; 19F NMR (235 MHz,
CDCl3) δ = −141.17 (10B-F, 0.2), −141.11 (11B-F, 0.8); LRMS (EI)
(positive mode) m/z 583.2 [M + Na]+, 599.2 [M + K]+; HR-MS (ESI
+) [M + Na]+ calcd for C35H27O4BF2Na+ 583.1869, found 583.1868.
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(6-methoxynaphtha-
len-2-yl)-4-phenylhepta-1,4,6-trien-3-one (3). The free ligand
was obtained as a yellow solid from meso-(phenyl)-acacH (224 mg,
1.27 mmol) and 6-methoxy-2-naphthaldehyde (474 mg, 2.54 mmol)
and was filtered from ethyl acetate (450 mg, 69%): mp = 278−279 °C;
1H NMR (250 MHz, CDCl3) δ = 7.83 (d, 3J = 15.6 Hz, 2H), 7.74 (s,
MHz, CDCl3) δ = 179.5, 162.8, 146.9, 131.2, 127.0, 119.1, 114.8,
101.6, 55.2; 19F NMR (235 MHz, CDCl3) δ = 140.96 (10B-F, 0.2F),
−141.08 (11B-F, 0.8F); LRMS (EI) (positive mode) m/z 407.1 [M +
Na]+, 423 [M + K]+; HRMS (ESI+) [M + Na]+ calcd for
C21H19O4BF2Na+ 407.1241, found 407.1238.
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(4-methoxyphenyl)-
4-phenylhepta-1,4,6-trien-3-one (1-Ph). The free ligand was
obtained as a yellow solid from meso-(phenyl)-acacH (350 mg, 1.99
mmol) and p-methoxybenzaldehyde (542 mg, 3.98 mmol) and was
purified by column chromatography on silica using cyclohexane/
1
AcOEt (1/9 v:v) as eluent (205 mg, 25%): mp = 171−172 °C; H
3
NMR (250 MHz, CDCl3) δ = 7.64 (d, J = 15.6 Hz, 2H), 7.43 (m,
3
3
3H), 7.27 (m, 6H), 6.80 (d, J = 8.8 Hz, 4H), 6.35 (d, J = 15.6 Hz,
1H), 3.78 (s, 6H); 13C NMR (62.5 MHz, CDCl3) δ = 182.5, 161.2,
140.6, 135.6, 132.3, 129.8, 128.5, 128.1, 127.6, 120.1, 115.9, 114.2,
55.3; LRMS (EI) (positive mode) m/z 413.2 [M + H]+, 435.2 [M +
Na]+, (negative mode): 411.3 [M − H]−. Anal. Calcd for C27H24O4:
C, 78.62; H, 5.86. Found: C, 78.27; H, 5.91.This compound (200 mg,
0.48 mmol) was reacted with boron trifluoride etherate to afford the
boron complex 1-Ph as a red solid (223 mg, quantitative): mp = 227−
229 °C; 1H NMR (250 MHz, CDCl3) δ = 8.02 (d, 3J = 15.3 Hz, 2H),
7.50 (m, 3H), 7.35 (d, 3J = 9.0 Hz, 4H), 7.28 (m, 1H), 6.84 (d, 3J = 9.0
3
3
2H), 7.69 (d, J = 8.9 Hz, 2H), 7.58 (d, J = 8.6 Hz, 2H), 7.48 (m,
3H), 7.34 (m, 4H), 7.11 (dd, 3J = 8.9 Hz, 4J = 2.4 Hz, 2H), 7.05 (d, 4J
3
= 2.4 Hz, 2H), 6.56 (d, J = 15.6 Hz, 2H), 3.90 (s, 6H); 13C NMR
(62.5 MHz, CDCl3) δ = 182.5, 158.8, 141.3, 135.5, 132.4, 130.7, 130.1,
129.9, 128.7, 128.6, 127.7, 127.3, 124.3, 121.4, 119.3, 116.3, 106.0,
55.4; LRMS (EI) (positive mode) m/z 513.1 [M + H]+, (negative
mode) 511.2 [M − H]−. Anal. Calcd for C35H28O4: C, 82.01; H, 5.51.
Found: C, 82.23; H, 5.60. This compound (118 mg, 0.23 mmol) was
reacted with boron trifluoride etherate to afford the boron complex 3
1
as a red solid (129 mg, quantitative): mp = 239−241 °C; H NMR
3
Hz, 4H), 6.35 (d, J = 15.3 Hz, 2H), 3.81 (s, 6H); 13C NMR (62.5
3
4
(250 MHz, CDCl3) δ = 8.20 (d, J = 15.4 Hz, 2H), 7.83 (d, J = 1.1
Hz, 2H), 7.72 (d, 3J = 9.0 Hz, 2H), 7.60 (d, 3J = 8.7 Hz, 2H), 7.55 (m,
3H), 7.35 (m, 4H), 7.14 (dd, 3J = 8.9 Hz, 4J = 2.4 Hz, 2H), 7.04 (d, 4J
MHz, CDCl3) δ 177.7, 162.7, 147.2, 132.8, 132.0, 131.3, 129.1, 128.7,
127.3, 117.0, 114.6, 55.5; 19F NMR (235 MHz, CDCl3) δ = −141.25
(10B-F, 0.2F), −141.31 (11B-F, 0.8F); LRMS (EI) (positive mode) m/z
483.1 [M + Na]+, 499.0 [M + K]+; HRMS (ESI+) [M + Na]+ calcd for
C27H23O4BF2Na+ 483.1555, found 483.1555.
3
= 2.3 Hz, 2H), 6.57 (d, J = 15.4 Hz, 2H), 3.90 (s, 6H); 13C NMR
(62.5 MHz, CDCl3) δ = 177.9, 159.7, 147.9, 136.5, 132.7, 132.3, 132.1,
130.7, 129.9, 129.2, 128.8, 128.6, 127.6, 124.3, 119.7, 118.4, 116.0,
106.2, 55.4; 19F NMR (235 MHz, CDCl3) δ = 140.95 (10B-F, 0.2),
141.01 (11B-F, 0.8); LRMS (EI) (positive mode) m/z 583.2 [M +
Na]+, 599.2 [M + K]+. Anal. Calcd for C35H28BF2O4·1/5CH2Cl2: C,
73.22; H, 4.78. Found: C, 73.59; H, 4.77.
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(4-methoxynaphtha-
len-1-yl)hepta-1,4,6-trien-3-one (2-H). The free ligand was
obtained as an orange solid from acacH (305 mg, 3.05 mmol) and
4-methoxy-1-naphthaldehyde (1.14 g, 6.11 mmol) and was filtered
from ethyl acetate (813 mg, 61%): mp = 233−234 °C; 1H NMR (250
MHz, CDCl3) δ = 8.48 (d, 3J = 15.5 Hz, 2H), 8.32 (dd, 3J = 8.3 Hz, 4J
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(9-methyl-9H-carba-
zol-3-yl)-4-phenylhepta-1,4,6-trien-3-one (4). The free ligand
was obtained as an orange-red solid from meso-(phenyl)-acacH (200
mg, 1.13 mmol) and N-methylcarbazole-3-carboxaldehyde (475 mg,
2.27 mmol) and was filtered from ethyl acetate (266 mg, 42%): mp =
3
3
= 1.0 Hz, 2H), 8.24 (d, J = 8.3 Hz, 2H), 7.79 (d, J = 8.2 Hz, 2H),
3
3
7.57 (m, 4H), 6.85 (d, J = 8.0 Hz, 2H), 6.66 (d, J = 15.5 Hz, 2H),
5.98 (s, 1H), 4.04 (s, 6H); 13C NMR (62.5 MHz, CDCl3): δ = 183.4,
157.4, 137.2, 132.6, 127.4, 125.8, 125.6, 125.6, 124.8, 124.2, 123.2,
122.6, 103.9, 101.7, 55.7; LRMS (EI): (positive mode) m/z 437.1 [M
+ H]+, 459.1 [M + Na]+, 478.1 [M + K]+. Anal. Calcd for C29H24O4:
C, 79.80; H, 5.54. Found: C, 79.79; H, 5.53. This compound (110 mg,
0.25 mmol) was reacted with boron trifluoride etherate to afford the
crude boron complex 2-H as a black solid that was purified by column
chromatography on silica using cyclohexane/DCM (2/3) as eluent (63
mg, 52%): mp = 309−311 °C; 1H NMR (250 MHz, CDCl3) δ = 8.88
1
4
256−258 °C; H NMR (250 MHz, CDCl3) δ = 8.07 (d, J = 1.3 Hz,
3
3
2H), 8.03 (d, J = 8.0 Hz, 2H), 7.93 (d, J = 15.5 Hz, 2H), 7.44 (m,
12H), 7.27 (m, 3H), 6.55 (d, J = 15.7 Hz, 2H), 3.81 (s, 6H); 13C
3
NMR (62.5 MHz, CDCl3) δ = 182.6, 142.2, 142.0, 141.4, 136.0, 132.6,
128.5, 127.5, 126.6, 126.2, 125.9, 123.2, 122.7, 121.3, 120.5, 119.6,
119.5, 115.8, 108.8, 108.7, 29.2; LRMS (EI) (positive mode) m/z
559.2 [M + H]+, (negative mode) 557.3 [M − H]−. Anal. Calcd for
C39H30N2O2: C, 83.85; H, 5.41; N, 5.01. Found: C, 84.07; H, 5.38; N,
4.86. This compound (111 mg, 0.20 mmol) was reacted with boron
trifluoride etherate to afford the boron complex 4 as a red solid (121
mg, quantitative): mp = 309−311 °C; 1H NMR (250 MHz, CDCl3) δ
3
3
(d, J = 15.3 Hz, 2H), 8.32 (m, 4H), 7.94 (d, J = 8.3 Hz, 2H), 7.60
(m, 4H), 6.90 (d, 3J = 8.5 Hz, 2H), 6.79 (d, 3J = 15.5 Hz, 2H), 6.12 (s,
1H), 4.08 (s, 6H); 13C NMR (62.5 MHz, CDCl3): Because of the
poor solubility of 2-H, a satisfactory 13C NMR spectrum could not be
obtained; 19F NMR (235 MHz, CDCl3) δ = −140.84 (10B-F, 0.2),
−140.90 (11B-F, 0.8); LRMS (EI) (positive mode) m/z 485.1 [M +
H]+, 507.1 [M + Na]+, 523.1 [M + K]+, 502.2 [M + NH4]+. Anal.
Calcd for C29H23BF2O4: C, 71.92; H, 4.79. Found: C, 72.12; H, 4.76.
(1E,4Z,6E)-5-(Difluoroboryloxy)-1,7-bis(4-methoxynaphtha-
len-1-yl)-4-phenylhepta-1,4,6-trien-3-one (2-Ph). The free ligand
was obtained as an orange solid from meso-(phenyl)-acacH (249 mg,
1.41 mmol) and 4-methoxy-1-naphthaldehyde (527 mg, 2.83 mmol)
3
4
3
= 8.29 (d, J = 15.4 Hz, 2H), 8.13 (d, J = 1.1 Hz, 2H), 8.05 (d, J =
9.0 Hz, 2H), 7.60 (m, 3H), 7.51 (m, 4H), 7.41 (m, 4H), 7.30 (d, 3J =
8.3 Hz, 4H), 6.54 (d, 3J = 15.4 Hz, 2H), 3.90 (s, 6H); 13C NMR (62.5
MHz, CDCl3) δ = 177.1, 148.7, 143.1, 141.3, 133.3, 132.3, 129.1,
128.6, 127.1, 126.6, 125.8, 123.4, 122.9, 122.6, 120.6, 120.2, 116.2,
113.5, 109.1, 109.0, 29.3; 19F NMR (235 MHz, CDCl3) δ = −140.95
(10B-F, 0.2), −141.01 (11B-F, 0.8); LRMS (EI) (positive mode) m/z
629.2 [M
+ +
Na]+, 645.2 [M K]+. Anal. Calcd for
H
dx.doi.org/10.1021/jo400389h | J. Org. Chem. XXXX, XXX, XXX−XXX

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Article
C39H29BF2N2O2·1/10CH2Cl2: C, 76.37; H, 4.79; N, 4.56. Found: C,
76.72; H, 4.65; N, 4.56.
Kawai, T. J. Am. Chem. Soc. 2011, 133, 9266−9269. (g) Fabian, J.;
Hartmann, H. J. Phys. Org. Chem. 2004, 17, 359−369. (h) Risko, C.;
Spectroscopy. Solid-state spectra were measured and corrected
for scattered light background by drop-casting the compound in dry
dichloromethane (DCM) on a quartz plate. Luminescence quantum
yields Φf were measured in diluted solution with an absorbance lower
than 0.1 at the excitation wavelength using the following equation Φfx/
Φfr = [Ar(λ)/Ax(λ)][Dx/Dr] where A is the absorbance at the
excitation wavelength (λ), and D the integrated luminescence
intensity. Subscripts “r” and “x” stand for reference and sample,
respectively. The luminescence quantum yields were not corrected by
the refractive indices. We used ruthenium trisbipyridine bischloride in
water (Φfr = 0.021) as reference compound. The luminescence
quantum yields were double-checked using chalcone boron difluoride
compounds previously reported.9 Luminescence lifetimes were
determined by a method adapted for time-correlated single-photon
counting. For these measurements, pulsed LEDs with the appropriate
wavelength were used. Emission was monitored perpendicular to the
excitation pulse.
X-ray Crystallography. The intensity data for the single-crystal X-
ray diffraction analysis of M4 were collected at room temperature on
diffractometer using Mo Kα radiation (λ = 0.71073 Å). Data collection
was performed with COLLECT,39 cell refinement and data reduction
with DENZO/SCALEPACK.40 The structure was solved with SIR9241
and SHELXL-9742 was used for full matrix least-squares refinement.
The H-atoms were then introduced at idealized positions and
constrained to their parent atom during the last refinements. Graphics
were generated with MERCURY 2.4.
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ASSOCIATED CONTENT
* Supporting Information
■
S
(12) (a) Killoran, J.; Allen, L.; Gallagher, J. F.; Gallagher, W. M.;
O’Shea, D. F. Chem. Commun. 2002, 1862−1863. (b) Gorman, A.;
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Proton and carbon NMR spectra of reported compounds. This
material is available free of charge via the Internet at http://
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AUTHOR INFORMATION
Corresponding Author
*E-mail: daleo@cinam.univ-mrs.fr.
■
(13) Hales, J. M.; Matichak, J.; Barlow, S.; Ohira, S.; Yesudas, K.;
́
Bredas, J.-L.; Perry, J. W. Science 2010, 327, 1485−1488.
(14) (a) Rousseau, T.; A. Cravino, A.; Ripaud, E.; Leriche, P.; Rihn,
S.; De Nicola, A.; Ziessel, R.; Roncali, J. Chem. Commun. 2010, 46,
Notes
The authors declare no competing financial interest.
5082−5084. (b) Bura, T.; Leclerc, N.; Fall, S.; Lev
Retailleau, P.; Rihn, S.; Mirloup, A.; Ziessel, R. J. Am. Chem. Soc. 2012,
134, 17404−17407. (c) Chambon, S.; DAleo, A.; Baffert, C.; Wantz,
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(15) Banuelos, J.; Martín, V.; Gomez-Duran, C. F. A.; Cor
A.; Pena-Cabrera, E.; García-Moreno, I.; Costela, A.; Per
́ ̂
eque, P.; Heiser, T.;
ACKNOWLEDGMENTS
Mass spectra and elemental analyses were realized in
Spectropole de Marseille (http://www.spectropole.fr/). The
́
■
́
́
́
doba, I. J.
ez-Ojeda, M.
̃
́
́
̃
́
authors thank Aix Marseille Universite and CNRS for financial
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E.; Arbeloa, T.; Arbeloa, I. L. Chem.Eur. J. 2011, 17, 7261−7270.
(16) Bonardi, L.; Kanaan, H.; Camerel, F.; Jolinat, P.; Retailleau, P.;
Ziessel, R. Adv. Funct. Mater. 2008, 18, 401−413.
support. Roseline Rosas and Michel Giorgi (Spectropole,
Marseille) are gratefully acknowledged for their technical help
with temperature-dependent NMR spectroscopy and X-ray
crystallography, respectively.
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