Synthesis and photophysical properties of alkoxysilyl derivatives of dibenzoylmethanatoboron difluoride

Article abstract of DOI:10.1002/hc.21091

Alkoxysilyl derivatives of dibenzoylmethanatoboron difluoride (DBMBF ₂) are synthesized by the hydrosilylation reaction of the corresponding O-allyl derivatives of DBMBF₂ with triethoxysilane. The photophysical properties of the synt

Full text of DOI:10.1002/hc.21091

Heteroatom Chemistry
Volume 00, Number 0, 2013
Synthesis and Photophysical Properties
of Alkoxysilyl Derivatives of
Dibenzoylmethanatoboron Difluoride
Yuriy N. Kononevich,1 Ivan B. Meshkov,1 Natalia V. Voronina,1
Nikolay M. Surin,1 Viacheslav A. Sazhnikov,2 Andrei A. Safonov,2
Alexander A. Bagaturyants,2 Mikhail V. Alfimov,2
and Aziz M. Muzafarov1
1N. S. Enikolopov Institute of Synthetic Polymeric Materials, Russian Academy of Sciences,
117393 Moscow, Russian Federation
2Photochemistry Center, Russian Academy of Sciences, 119421 Moscow, Russian Federation
Received 19 June 2012; revised 17 March 2013
derivatives can be adequately explained by the over-
lapping of two absorption bands. 2013 Wiley Peri-
ABSTRACT: Alkoxysilyl derivatives of dibenzoyl-
ꢀC
methanatoboron difluoride (DBMBF2) are synthesized
by the hydrosilylation reaction of the corresponding
O-allyl derivatives of DBMBF2 with triethoxysilane.
The photophysical properties of the synthesized O-allyl
and alkoxysilyl derivatives are investigated. It is found
that the absorption and fluorescence spectra of the
DBMBF2 derivatives essentially depend on the position
of the O-allyl or O-propyl alkoxysilyl substituent. The
highest fluorescence quantum yield is obtained for the
para-position, whereas the substitution at the meta-
position gives the largest bathochromic shift in the
fluorescence spectrum. Density functional theory cal-
culations of the structures and time-dependent density
functional theory calculations of the gas-phase excita-
tion and emission energies of alkoxysilyl derivatives
are performed at the PBE0/SVP level of theory. Some
spectral features of para-, ortho-, and meta-substituted
odicals, Inc. Heteroatom Chem 00:1–12, 2013; View
this article online at wileyonlinelibrary.com. DOI
10.1002/hc.21091
INTRODUCTION
Recently, interest in the synthesis and study of di-
fluoroboron β-diketonates (BF2bdks) has increased
because of useful photophysical and photochemical
properties of these compounds [1–7]. BF2bdks ex-
hibit large extinction coefficients, large two-photon
absorption cross section, intense fluorescence with
high quantum yields, and high photostability. The
fluorescence properties of many BF2bdks have been
studied in solution and in crystal state [8–19].
The introduction of these compounds into a
polymer gives rise to new optical materials with in-
teresting fluorescence properties [20]. In particular,
polylactide modified by BF2bdk [21–23] can be used
for biological visualization, sensing, and photody-
namic therapy because of high biocompatibility of
polylactide polymers [24–26].
Correspondence
to:
Yuriy
N.
Kononevich;
e-mail:
kononevich.yuriy@gmail.com.
Contract grant sponsor: Russian Ministry for Science and Edu-
cation.
Contract grant numbers: 02.527.11.0009 and 16.523.11.3015.
Contract grant sponsor: Russian Foundation for Basic Research.
Contract grant number: 12-03-01103a.
BF2bdks in their singlet-excited state undergo
photocycloaddition with alkenes and arenes; there-
fore, they can serve as starting compounds for the
Supporting Information is available in the online issue at wiley-
onlinelibrary.com.
ꢀC
2013 Wiley Periodicals, Inc.
1

2
Kononevich et al.
synthesis of 1,5-diketones [27–34]. BF2bdks are used
in the design of a new polymethine dye with intense
long-wavelength absorption [35,36].
A distinctive feature of BF2bdks is their ability
to form exciplexes in the first excited singlet states
with aromatic hydrocarbons that have strong fluo-
rescence with a fluorescence maximum shifted to
longer wavelengths [37–42]. The magnitude of the
shift depends on the electron-donating ability of
the hydrocarbon. The stronger the electron-donating
properties of a hydrocarbon, the larger the shift of
the fluorescence maximum to longer wavelengths.
This feature allows BF2bdks to be used as chemi-
cal sensors for aromatic hydrocarbons [43,44]. Silica
in its various forms is one of the most promising sub-
strates for the deposition of molecular systems with
sensing capabilities. It is widely used in a variety of
sensing systems. The immobilization of BF2bdks on
the surface of silica particles is relevant and promis-
ing. The functionalization of BF2bdks to form silyl-
functionalized derivatives is an optimal solution to
this problem.
SCHEME 2 Synthesis of β-diketonatoboron difluorides 6a–
6c.
and 1b, respectively, in the presence of sodium hy-
dride in benzene. For the synthesis of β-diketone 3c,
ethyl benzoate 4 and 4-O-allylacetophenone 5 were
used. The yield of products was 68%–76%.
Boron difluoride complexes 6a–6c were ob-
tained by the reaction of the corresponding β-
diketones 3a–3c with boron trifluoride diethyl ether-
ate in dichloromethane (Scheme 2). The reaction
proceeded to completion in 1 h at room tempera-
ture. After completion of the reaction, the solvent
was removed in vacuo and the residue was recrystal-
lized from toluene. A crystalline substance with an
intense yellow color was formed. The product yield
was 59%–64%.
In this article, we describe the synthesis and pho-
tophysical properties of dibenzoylmethanatoboron
difluoride (DBMBF2) derivatives containing a spacer
with a terminal alkoxysilyl group.
The
obtained
boron
complexes
were
modified to form alkoxysilyl derivatives by the
hydrosilylation of O-allyl derivatives of boron diflu-
oride β-diketonates 6a–6c with triethoxysilane in
the presence of a platinum catalyst. The reaction was
carried out in tetrahydrofurane (THF) in the pres-
ence of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane
platinum (Scheme 3). The reaction was completed
in 8 h at room temperature, as evidenced by
the complete disappearance of signals of allylic
protons in the 1H NMR spectrum. It was found
that the reduction of the double bond proceeded
in parallel with hydrosilylation with a yield of
15%–25%, depending on the isomer. The formation
of side products of this kind is typical for the
hydrosilylation reaction [45]. The reaction products
were separated by gel permeation chromatography
(GPC).
RESULTS AND DISCUSSION
Synthesis
The general pathway for the synthesis of alkoxysi-
lyl derivatives of boron difluoride β-diketonates is
shown in Scheme 1. O-Allyl derivatives were ob-
tained by the known method involving the inter-
action of boron trifluoride etherate with the corre-
sponding diketones [13].
The synthesis of O-allyl derivatives of β-
diketones 3a–3c was carried out by the Claisen con-
densation (Scheme 1). β-Diketones 3a and 3b were
obtained by the reaction of acetophenone 2 and
methyl esters of 2- and 3-O-allyl benzoic acids 1a
To investigate the photophysical properties
of the synthesized boron difluoride β-diketonate
derivatives 7a–7c, containing a spacer with the ter-
minal alkoxysilyl group, the absorption and fluores-
cence spectra of corresponding model compounds
9 (Fig. 1) and 6a–6c were measured in THF solu-
tions and compared with the corresponding spectra
of alkoxysilyl derivatives.
UV–Vis and Fluorescence Studies
Photographs of the fluorescence of synthesized com-
pounds 6a–6c are shown in Fig. 2.
SCHEME 1 Synthesis of 1,3-diaryl-propane-1,3-diones 3a–
3c.
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Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride
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a = ortho, b = meta, c = para
SCHEME 3 Hydrosilylation of β-diketonatoboron difluorides.
two peaks at 288 and 272 nm (the wavenumber sep-
aration about 2040 cm−1). The fluorescence peaks
of 9 are centered at 400, 420, and 445 nm (25,000,
23,810 and 22,470 cm−1, respectively). Thus, the
wavenumber separations between the peaks of ab-
sorption and fluorescence bands are about 1150 and
1300 cm−1, which seems to correspond to a usual vi-
brational progression. As has been shown previously
[47], the shapes of the better resolved absorption
(320–400 nm) and fluorescence (400–500 nm) bands
of DBMBF2 in hexane can be adequately described
as a superposition of vibronic bands with vibrational
FIGURE 1 Model compound 9.
frequencies of 1200–1300 cm−1
.
The substitution of the O-allyl group for the
methyl group at the para-position leads to a ba-
tochromic shift (∼10 nm) of the absorption bands.
The fluorescence band of 6c is also redshifted as
compared to 9 but does not reveal any visible vi-
bronic structure.
Figure 4 shows that the absorption bands of or-
tho (6a) or meta (6b) O-allyl substituted derivatives
are slightly blueshifted and broadened compared to
6c, whereas their broad fluorescence bands are sig-
nificantly redshifted. It should also be noted that 6a
exhibits a well-resolved and relatively intense peak
at about 343 nm.
FIGURE 2 Photographs of solutions of 6a–6c in THF excited
with black light at 365 nm (from left to right: 6a, 6b, and 6c,
respectively).
Figure 5 shows that the spectral properties of
7a–c are very similar to those of 6a–6c.
As seen in Table 1, there is a very strong de-
pendence of the molar extinction coefficients and
quantum yields on the substituent position. In par-
ticular, the para-substitution (compounds 6c and
7c) leads to near-unity quantum yields whereas the
quantum yields of only 0.3 (comparable with that of
9) are obtained for meta-substututed derivatives (6b
and 7b). Ortho-substituted 6a exhibits a somewhat
higher quantum yield (about 0.6).
Thus, the absorption and fluorescence spectra
of 6a–6c depend significantly on the position of the
O-allyl substituent. Further support for this state-
ment is the fact that the photophysical properties of
β-diketonatoboron difluorides 7a–7c, containing a
spacer with a terminal alkoxysilyl group, are almost
identical to the photophysical properties of 6a–6c.
The molar absorption coefficient was deter-
mined for solutions with a concentration of 5 ×
10−5 mol/L. A solution of rhodamine 6G was used
as a standard for measuring the fluorescence quan-
tum yield (ꢀF = 0.94–0.96) [46]. The energy of the
purely electronic 0–0 transition was determined by
the intersection of the normalized absorption and
emission spectra.
The absorption and fluorescence emission spec-
tra of the studied compounds are shown in Figs. 3–5,
and spectral characteristics are given in Table 1.
As can be seen in Fig. 3, the long-wavelength ab-
sorption band of 9 consists of two resolved peaks
at 386 and 370 nm and a low-intensity shoulder at
about of 353 nm (25,900, 27,030 and 28,330 cm−1
,
respectively). The second absorption region includes
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Kononevich et al.
FIGURE 3 Absorption and fluorescence emission spectra of β-diketonatoboron difluorides 9 and 6c.
FIGURE 4 Absorption and fluorescence emission spectra of β-diketonatoboron difluorides 6a–6c.
It can be suggested that the observed changes
in photophysical properties and the difference in
the calculated spectra of different isomers (com-
pounds 6a–6c) are attributable to the difference in
the mesomeric and inductive effects of the oxygen
atom in the ortho, meta, and para-positions. Thus,
it was shown in [48] that the substitution effect of
the methoxy group depends on its position in the
phenyl ring: In ortho- or para-positions, it acts as
a mesomeric electron donor whereas it acts as an
inductive electron acceptor in meta-positions.
Density Functional Theory Results
To provide an assignment of the observed spectra,
the geometrical structures and electronic absorption
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Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride
5
and fluorescence emission spectra of compounds 9
and 6a–6c were studied theoretically by quantum-
chemical density functional theory (DFT) and time-
dependent density functional theory (TDDFT) calcu-
lations (details are described in the Experimental).
As an example, the calculated optimized geome-
tries for 9 in the ground and the first excited states
are shown in Fig. 6. The results for compounds 6a–
6c are given in Fig. S1 and Table S1 (in the Support-
ing Information).
As seen in Fig. 6, the excitation of 9 involves the
following conformation changes: an increase (∼7◦)
in the dihedral angle between BF2 fragment and the
plane of the central ring, a decrease (∼6◦) in the
torsion angles between the phenyl rings and the cen-
tral ring, a shortening of the C C bonds connect-
ing these rings, and some changes in the C C bond
lengths of phenyl rings.
It was found that similar changes in geome-
tries are also characteristic of compounds 6a–6c
(Table S1 in the Supporting Information), despite
of the fact that they have different equilibrium
structures.
The energies of the frontier molecular orbitals
for the ground and first excited states of the stud-
ied compounds are presented in Table 2. The verti-
cal electronic transition energies for absorption and
emission, oscillator strengths, main configurations,
and configuration interaction (CI) coefficients of the
low-lying electronically excited states are listed in
Table 3.
TDDFT calculations, in agreement with the ex-
perimental data, indicate that for 9 there is only
one long-wavelength absorption peak in the region
of 320–400 nm. The nature of this intense band is
mainly due to the electronic HOMO → LUMO transi-
tion (f = 0.880, CI = 0.998). The calculated transition
energy 3.65 eV (339 nm) for 9 is somewhat higher
than the experimental value of 3.21 eV (386 nm).
The calculated transition energy for emission is
also overestimated (by 0.35 eV), but the calculated
Stokes shift (1600 cm−1) matches well the experi-
mental value of 900 cm−1. Table 3 shows that for 9
the calculated emission wavelength of 359 nm cor-
responds to experimental one at 400 nm. Thus, it
is seen that conformational transformations in the
S1 state lead mainly to a considerable (by ∼0.2 eV)
increase in the HOMO orbital energy. It should be
noted that the decrease in the HOMO—LUMO en-
ergy gap is approximately equal to the calculated
difference in the vertical excitation and emission
transitions.
FIGURE 5 Absorption and fluorescence emission spectra of
β-diketonatoboron difluorides: (a) 6a and 7a; (b) 6b and 7b;
(c) 6c and 7c.
The calculated HOMO and LUMO orbitals of
9 involved in the vertical transitions, correspond-
ing orbital energies and wavelengths of vertical
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Kononevich et al.
TABLE 1 Optical Properties of 9, 6a–6c, and 7a–7c
Absorbance
Fluorescence
Compound
λabs (nm)
ε (M−1 cm−1
)
λem (nm)
ꢀF (%)
0–0 Transition Energy, Е00 (eV)
6a
6b
6c
7a
7b
7c
9
395
385
397
396
367
398
370
26,820
32,680
47,380
17,710
26,880
42,770
43,900
456
485
426
458
488
429
400
57
34
96
29
24
86
30
2.99
3.02
3.04
2.97
2.99
3.02
3.16
lying transition (4.21 eV, f = 0.22), which can be
related to HOMO-2 → LUMO transition.
It is well known that methoxy (or the like)
groups have a stronger electron-donating ability
than methyl groups. Therefore, it may be expected
that the substitution of a methyl group for an alkoxy
group in the para-position can result in redshifts of
calculated absorption and emission bands.
The most favorable calculated structures and the
corresponding HOMOs and LUMOs of isomers 6c,
6a, and 6b (ground state geometry) are shown in
Figs. 8–10.
Figures 8–10 show that the frontier MOs in-
volved in the vertical transitions for absorption and
emission in 6a–6c are significantly different from
those of 9. In all the cases, the introduction of an oxy-
gen atom leads to a significant change in the electron
density distribution in the ground state and to elec-
tron density transfer from the oxygen atom to con-
jugated rings upon excitation. As can be seen, these
effects are most pronounced for meta-substituted
compound 6b.
Table 2 shows that the oxygen lone pair affects
significantly the orbital energy levels, thus changing
the energy gaps. For example, the energies of HOMO
and LUMO for 6c (–6.82 and –2.72 eV, respectively)
are higher than those for HOMO and LUMO of 9 (–
7.10 and –2.85 eV). As a result, the calculated absorp-
tion transition is redshifted by 10 nm (Table 2), in
good agreement with the experimental data (Fig. 3).
In addition, this leads to an increase in the oscillator
strength up to unity, which may explain the greater
extinction coefficient and the higher quantum yield
for 6c (47,380 M−1 cm−1; 0.96) as compared to 9
(43,900 M−1 cm−1; 0.30).
Table 2 shows that ortho and meta substitutions
lead to additional upward shifts of the energy lev-
els of the HOMO and especially HOMO-1 orbitals
(see Fig. S2 in the Supporting Information). This
leads to a stronger interaction between the HOMO →
LUMO and HOMO-1 → LUMO transitions in 6a and
6b. As a consequence, the second transition in 6a is
FIGURE 6 Calculated equilibrium configurations of 9 in the
(top) ground and (bottom) first excited states.
transitions (Table 3) are dramatically illustrated in
Fig. 7.
It should be noted that the second calculated
transition for 9 at 4.18 eV (296 nm) has a small oscil-
lator strength (0.013) and corresponds to HOMO-1
→ LUMO (S0 → S2) transition. It may be attributed
to the observed weak absorption band at 288 nm. In
the 300-nm region, calculations reveal a third close-
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Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride
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TABLE 2 Molecular Orbital Energies (eV) of 9 and 6a–
6c in the Ground and Relaxed S1 States Calculated at the
PBE0/SVP Level of Theory.
Compound State LUMO HOMO HOMO-1 HOMO-2
9
S0
S1
S0
S1
S0
S1
S0
S1
–2.85
–2.88
–2.72
–2.73
–2.73
–2.74
–2.88
–2.96
–7.10
–6.89
–6.82
–6.64
–6.88
–6.68
–6.80
–6.53
–7.79
–7.83
–7.52
–7.47
–7.29
–7.25
–7.31
–7.31
–7.85
–7.95
–7.78
–7.91
–7.74
–7.87
–7.80
–7.89
6c
6a
6b
redshifted and their intensity increases in compar-
ison with 6c and for 6b this transition exhibits
a greater intensity as compared to the HOMO →
LUMO transition. This statement is strikingly illus-
trated in Fig. S3 (in the Supporting Information).
It is interesting to note that these results pro-
vide a possible explanation for main features of the
absorption and fluorescence of compounds 6a and
6b. The observed small blueshits and a broadening
of their absorption bands, as well as the appearance
of a peak at 343 nm in the absorption spectrum of
6a may be a consequence of the contribution of the
second HOMO-1 → LUMO transition to combined
absorption in the 300–400 nm wavelength region.
At the same time, the fluorescence bands of 6a and
6b corresponding to the LUMO → HOMO transi-
tions exhibit redshifted wavelengths, weaker oscil-
lator strengths and, consequently, smaller quantum
yields as compared to 6c, which correlates well with
the experimental data.
FIGURE 7 Frontier molecular orbitals involved in the vertical
excitation and emission of 9. The dotted arrows represent
conformational transformations.
sities of the first transitions due to conformation
strains or solvent effects.
CONCLUSIONS
Thus alkoxysilyl derivatives of boron difluoride
β-diketonates have been synthesized by the hy-
drosilylation reaction of the corresponding O-
allyl derivatives of boron difluoride β-diketonates
with triethoxysilane. The hydrosilylation reaction is
accompanied by the reduction of the double bond
in the O-allyl substituent with a yield of 15%–25%,
depending on the O-allyl position in the phenyl
ring. The absorption and fluorescence spectra of
boron difluoride β-diketonates essentially depend on
An alternative explanation, of course, may in-
volve the redistrubution of relative vibronic inten-
TABLE 3 Electronic Excitation and Emission Energies, Oscillator Strengths (f), Main Configurations, and Configuration Inter-
action (CI) Coefficients of the Low-Lying Electronically Excited States for 9 and 6a–6c
Compound
Transition
Energy (eV/nm)
f
Composition
CI
9
S0 → S1
S0 → S2
S1 → S0
S0 → S1
S0 → S2
S1 → S0
3.65/339
4.18/296
3.45/359
3.54/350
4.23/293
3.39/366
0.880
0.013
0.861
1.000
0.035
0.989
HOMO → LUMO
HOMO-1 → LUMO
HOMO-2 → LUMO
HOMO → LUMO
HOMO-1 → LUMO
HOMO-1 → LUMO
HOMO → LUMO
HOMO → LUMO
HOMO-1 → LUMO
HOMO-1 → LUMO
HOMO → LUMO
HOMO → LUMO
HOMO-1 → LUMO
HOMO-1 → LUMO
HOMO → LUMO
0.998
0.816
0.184
0.994
0.081
0.909
0.065
0.980
0.172
0.970
0.181
0.986
0.113
0.985
0.125
6c
6a
6b
S0 → S1
S0 → S2
S1 → S0
3.48/357
3.89/319
3.30/376
0.445
0.295
0.499
S0 → S1
S0 → S2
S1 → S0
3.31/375
3.77/329
2.97/417
0.194
0.660
0.128
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Kononevich et al.
FIGURE 8 Optimized structure and molecular orbitals
(HOMO and LUMO) of compound 6c.
FIGURE 10 Optimized structure and molecular orbitals
(HOMO and LUMO) of compound 6b.
toxide. Methyl esters of 2- and 3-O-allyl benzoic acids
1a,b, respectively, and 4-O-allylacetophenone 5 were
prepared using methods described in the literature
[49, 50]. All other purchased reagents were used
without further purification. The reactions were
monitored by thin-layer chromatography using
Fluka silica gel (60 F 254) plates (0.25 mm). Col-
umn chromatography was carried out using Merck
60 (230–400 mesh) silica gel. Visualization was made
with UV light. Melting points of synthesized com-
pounds were taken on a melting point tube. In-
frared spectra were recorded on Bruker Equinox
55/S spectrometer (Germany). 1Н NMR spectra
were recorded on a Bruker WP 250 SY spectrom-
eter (250.13 MHz; Germany). 13C, 19F, and 29Si
NMR spectra were recorded on a Bruker DRX500
spectrometer (Germany). Chemical shifts are re-
ported relative to chloroform (δ = 7.25 ppm) or
dimethyl sulfoxide (δ = 2.50 ppm) for 1Н NMR,
chloroform (δ = 77.00 ppm) for 13C NMR. High-
resolution mass spectra (HRMS) were measured us-
ing a Bruker micrOTOF II instrument (Germany)
with electrospray ionization (ESI). The absorp-
tion spectra were recorded on a Shimadzu UV-
25001PC spectrophotometer (Japan) in THF solu-
tion. The fluorescence spectra were measured on
the scanning spectrofluorimeter developed and con-
structed at Institute of Synthetic Polymeric Mate-
rials, Russian Academy of Sciences, Moscow, Rus-
sian Federation, equipped with a 150-W arc xenon
lamp as the pumping source, two Seya-Namioka-
type monochromators and two photoelectronic
multipliers [51].
FIGURE 9 Optimized structure and molecular orbitals
(HOMO and LUMO) of compound 6a.
the position of the O-allyl or O-propyl alkoxysilyl
substituent. In particular, the highest fluorescence
quantum yield and the greatest long-wavelength
shift of the fluorescence spectrum are attained in the
cases of para- and meta-positions, respectively. The-
oretical calculations of the absorption and emission
spectra at the TDDFT–PBE0/SVP level are in satis-
factory agreement with the obtained experimental
data. However, a more detailed analysis of the vi-
bronic structure of the absorption and fluorescence
bands of different derivatives would provide a better
understanding of its origin. This work is currently in
progress.
EXPERIMENTAL
General Methods
Computational Details
All solvents were purified before use. THF and ben-
zene were distilled from sodium/benzophenone, and
dichloromethane was distilled over phosphorus pen-
Geometry optimization for the ground electronic
state was performed by DFT with the Perdew-
Burke-Ernzerhof (PBE) functional and Ahlrichs’
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Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride
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93.3, 112.9, 118.0, 119.2, 119.7, 127.1, 128.7, 129.6,
132.4, 132.8, 135.4, 137.0, 158.8, 185.4, 185.7. IR
(CsI): 3076, 2981, 2845, 1604, 1576, 1489, 1257,
1203, 1028, 920, 764, 683 cm−1. UV–vis (THF) λ =
357 nm (ε = 26,000 L/mol*cm). HRMS (ESI) m/z
calcd. for C18H16NaO3 [(M + Na)+]: 303.0992, found
303.0988. Elemental analysis calcd. for C18H16O3:
C, 77.12; H, 5.75. Found: C, 77.16; H, 5.77.
double-zeta polarized Split Valence Polarization
(SVP) basis set using the ORCA program [52]. Struc-
tures in the excited electronic state, which are re-
sponsible for the fluorescence spectra, were op-
timized using the time-dependent DFT (TDDFT)
method with the Becke-Half-and-Half-Lee-Yang-
Parr (BH and HLYP) functional and the SVP basis
set.
At the optimized geometries, the absorption
and fluorescence spectra were calculated using the
TDDFT method with the PBE0 functional and the
SVP basis set. TDDFT calculations were performed
using the Firefly program [53], which is partially
based on the GAMESS (US) [54] source code.
1-Phenyl-3-[4-(prop-2-en-1-yloxy)phenyl]propane-
1,3-dione, 3c. Yield: 76%, mp 48–50◦C. 1H NMR
(300 MHz, DMSO-d6): δ 4.69 (d, 2H, J = 4.9 Hz,
O
CH2), 5.27–5.46 (m, 2H, C CH2), 5.98–6.14 (m,
1H, CH C), 7.10 (d, 2H, J = 8.6 Hz, Ar), 7.29 (s,
1H, CO CH CO), 7.52–7.66 (m, 3H, Ar), 8.14–8.18
(m, 4H, Ar), 15.10 (s, 1H, OH). 13C NMR (75 MHz,
CDCl3): δ 68.9, 92.3, 114.6, 118.2, 127.0, 128.2,
128.6, 129.3, 132.1, 132.5, 135.5, 162.2, 184.0, 186.1.
IR (CsI): 3078, 2929, 1605, 1510, 1259, 1176, 1014,
922, 841, 766 cm−1. UV–vis (THF) λ = 353 nm
(ε = 23,180 L/mol*cm). HRMS (ESI) m/z calcd.
for C18H16NaO3 [(M + Na)+]: 303.0992, found
303.0992. Elemental analysis calcd for C18H16O3: C,
77.12; H, 5.75. Found: C, 77.15; H, 5.78.
General Procedure for the Synthesis of
1,3-Diaryl-propane-1,3-diones (3a–3c)
The solution of ketone (0.05 mol) and ester
(0.05 mol) in dry benzene (30 mL) was added to sus-
pension of sodium hydride (1.32 g, 0.055 mol) in dry
benzene (20 mL) under inert atmosphere. The result-
ing mixture was heated at reflux for 8 h. Suspension
was cooled to room temperature and poured into
dilute HCl (5%, 100 mL). An organic layer was iso-
lated with a separating funnel and washed with aque-
ous Na2CO3, then H2O. After drying over Na2SO4,
the solvent was evaporated in vacuo. The resid-
ual product was purified by recrystallization from
isopropanol.
General Procedure for the Synthesis of
β-Diketonatoboron difluorides (6a–6c)
To
a
solution of 1,3-diaryl-propane-1,3-dione
(0.01 mol) in dry dichloromethane (30 mL), boron
trifluoride-diethyl etherate (0.012 mol) was added.
The reaction mixture was stirred for 1 h at room
temperature. After removing the solvent by evapora-
tion in vacuo, the residue was purified by recrystal-
lization from toluene.
1-Phenyl-3-[2-(prop-2-en-1-yl-oxy)phenyl]propane-
1,3-dione, 3a. Yield: 68%, mp 55–57◦C. 1H NMR
(300 MHz, CDCl3): δ 4.67 (d, 2H, J = 5.3 Hz,
O
CH2), 5.33–5.54 (m, 2H, C CH2), 6.08–6.20 (m,
1H, CH C), 6.98 (d, 1H, J = 8.2 Hz, Ar), 7.07 (t, 1H,
J = 7.3 Hz, Ar), 7.27 (s, 1H, CO CH CO), 7.42–7.56
(m, 4H, Ar), 7.94–7.99 (m, 3H, Ar). 13C NMR (75
MHz, CDCl3): δ 69.4, 98.6, 112.9, 118.3, 121.0, 125.0,
127.2, 128.4, 128.5, 128.6, 130.3, 132.2, 132.6, 133.0,
135.9, 157.5, 183.8, 185.6. IR (CsI): 3082, 1606, 1564,
1275, 1244, 1009, 937, 760 cm−1. UV–vis (THF) λ =
356 nm (ε = 22,960 L/mol*cm). HRMS (ESI) m/z
calcd. for C18H16NaO3 [(M + Na)+]: 303.0992, found
303.0989. Elemental analysis calcd. for C18H16O3:
C, 77.12; H, 5.75. Found: C, 77.29; H, 5.75.
2,2-Difluoro-4-phenyl-6-[2-(prop-2-en-1-yloxy)
phenyl]-1,3,2-(2H)-dioxaborine, 6a. Yield: 59%, mp
219–221◦C. 1H NMR (300 MHz, DMSO-d6): δ 4.84 (d,
2H, J = 5.5 Hz, O CH2), 5.36–5.56 (m, 2H, C CH2),
6.13–6.29 (m, 1H, CH C), 7.20 (t, 1H, J = 7.3 Hz,
Ar), 7.34 (d, 1H, J = 8.6 Hz, Ar), 7.64–7.85 (m, 4H,
Ar), 7.91 (s, 1H, CO CH CO), 8.03 (d, 1H, J = 7.9
Hz, Ar), 8.14 (d, 2H, J = 7.3 Hz, Ar). 13C NMR (75
MHz, CDCl3): δ 69.8, 98.8, 113.0, 119.6, 121.1, 121.4,
128.9, 129.0, 131.9, 132.0, 132.4, 134.9, 136.4, 159.8,
180.9, 182.6. 19F NMR (282 MHz, CDCl3): δ –139.59
(24%, 10B–F), –139.66 (76%, 11B–F). IR (CsI): 1603,
1547, 1489, 1367, 1225, 1097, 1041 cm−1. UV–vis
(THF) λ = 394 nm (ε = 26,860 L/mol*cm). HRMS
(ESI) m/z calcd. for C18H15BF2NaO3 [(M + Na)+]:
351.0978, found 351.0973. Elemental analysis calcd
for C18H15BF2O3: C, 65.89; H, 4.61; B, 3.29; F, 11.58.
Found: C, 66.01; H, 4.65; B, 3.28; F, 11.57.
1-Phenyl-3-[3-(prop-2-en-1-yl-oxy)phenyl]propane-
1,3-dione, 3b. Yield: 72%, mp 40–42◦C. 1H NMR
(300 MHz, CDCl3): δ 4.61 (d, 2H, J = 4.9 Hz,
O
CH2), 5.30–5.48 (m, 2H, C CH2), 6.00–6.16 (m,
1H, CH C), 6.83 (s, 1H, CO CH CO), 7.09–7.13
(m, 1H, Ar), 7.38 (t, 1H, J = 7.9 Hz, Ar), 7.45–7.57
(m, 5H, Ar), 7.98 (d, 2H, J = 6.7 Hz, Ar), 11.49
(s, 1H, OH). 13C NMR (75 MHz, CDCl3): δ 68.9,
Heteroatom Chemistry DOI 10.1002/hc

10 Kononevich et al.
2,2-Difluoro-4-phenyl-6-[3-(prop-2-en-1-yloxy)
(m, 4H, Ar), 7.85 (s, 1H, CO CH CO), 8.09 (d, 2H,
J = 7.0 Hz, Ar), 8.22 (d, 1H, J = 8.2 Hz,). 13C NMR
(75 MHz, CDCl3): δ 6.9, 18.3, 23.1, 58.5, 71.21, 98.7,
112.9, 121.1, 128.8, 129.1, 132.0, 134.6, 136.4, 160.5,
181.3, 182.7. 19F NMR (282 MHz, CDCl3): δ –140.94
(22%, 10B–F), –141.01 (78%, 11B–F). 29Si NMR (59
MHz, CDCl3): δ –46.45. IR (CsI): 2927, 1601, 1535,
phenyl]-1,3,2-(2H)-dioxaborine, 6b. Yield: 64%, mp
1
127–129◦C. H NMR (300 MHz, DMSO-d6): δ 4.72
(d, 2H, J = 5.5 Hz, O CH2), 5.28–5.48 (m, 2H,
C CH2), 6.01–6.16 (m, 1H, CH C), 7.40–7.44 (m,
2H, Ar), 7.56–7.71 (m, 3H, Ar), 7.81–7.90 (m, 2H,
Ar), 7.96–7.99 (m, 2H, Ar, CO CH CO), 8.40 (d,
2H, J = 7.3 Hz, Ar). 13C NMR (75 MHz, CDCl3):
δ 68.7, 94.7, 114.7, 117.8, 121.9, 122.4, 129.4 (d, J
= 2.8 Hz), 130.6, 131.2, 132.7, 133.2, 135.9, 158.7,
182.4, 182.8. 19F NMR (282 MHz, CDCl3): δ –136.86
(21%, 10B–F), –136.92 (79%, 11B–F). IR (CsI): 1541,
1485, 1379, 1363, 1263, 1047, 773 cm−1. UV–vis
(THF) λ = 384 nm (ε = 32,660 L/mol*cm). HRMS
(ESI) m/z calcd. for C18H15BF2NaO3 [(M + Na)+]:
351.0978, found 351.0967. Elemental analysis calcd
for C18H15BF2O3: C, 65.89; H, 4.61; B, 3.29; F, 11.58.
Found: C, 65.84; H, 4.61; B, 3.34; F, 11.51.
1491, 1375, 1198, 1165, 1101, 1078, 1045, 958 cm−1
.
UV–vis (THF) λ = 396 nm (ε = 17,660 L/mol*cm).
HRMS (ESI) m/z calcd. for C24H31BF2NaO6Si [(M
+ Na)+]: 515.1848, found 515.1844. Elemental
analysis calcd for C24H31BF2O6Si: C, 58.54; H, 6.35;
B, 2.20; F, 7.72; Si, 5.70. Found: C, 56.33; H, 5.46; B,
1.75; F, 6.59; Si, 6.02.
2,2-Difluoro-4-phenyl-6-[3-(3-(triethoxysilyl)
propoxy)phenyl]-1,3,2-(2H)-dioxaborine,
7b.
Yield: 75%. 1H NMR (300 MHz, DMSO-d6): δ
0.79 (m, 2H, CH2Si), 1.23 (t, 9H, J = 6.7 Hz,
2,2-Difluoro-4-phenyl-6-[4-(prop-2-en-1-yloxy)
Si O C CH3), 1.94 (m, 2H, O C CH2 C), 3.85
phenyl]-1,3,2-(2H)-dioxaborine, 6c. Yield: 61%, mp
(q, 6H, J = 7.3 Hz, Si
6.7 Hz, Ar
CO CH CO), 7.21 (dd, 1H, J1 = 2.4 Hz, J2
O
CH2 ), 4.03 (t, 2H,
1
203–205◦C. H NMR (300 MHz, DMSO-d6): δ 4.77
J
=
O CH2 ), 7.17 (s, 1H,
(d, 2H, J = 5.5 Hz, O CH2), 5.30–5.47 (m, 2H,
C CH2), 6.0–6.15 (m, 1H, CH C), 7.22 (d, 2H, J
= 9.2 Hz, Ar), 7.65 (t, 2H, J = 7.9 Hz, Ar), 7.80
(t, 1H, J = 7.3 Hz, Ar), 7.86 (s, 1H, CO CH CO),
8.33–8.42 (m, 4H, Ar). 13C NMR (75 MHz, CDCl3): δ
69.2, 92.5, 115.3, 118.7, 124.2, 128.6, 129.0, 131.6,
131.9, 132.2, 134.7, 164.7, 181.4, 182.2. 19F NMR
(282 MHz, CDCl3): δ –140.18 (19%, 10B–F), –140.24
(81%, 11B–F). IR (CsI): 1595, 1541, 1491, 1365,
1317, 1244, 1190, 1043, 999, 775, 559 cm−1. UV–vis
(THF) λ = 398 nm (ε = 46,600 L/mol*cm). HRMS
(ESI) m/z calcd. for C18H15BF2NaO3 [(M + Na)+]:
351.0978, found 351.0963. Elemental analysis calcd
for C18H15BF2O3: C, 65.89; H, 4.61; B, 3.29; F, 11.58.
Found: C, 65.75; H, 4.57; B, 3.24; F, 11.63.
=
8.5 Hz, Ar), 7.43 (t, 1H, J = 7.9 Hz, Ar), 7.55 (t, 2H, J
= 7.9 Hz, Ar), 7.63–7.72 (m, 3H, Ar), 8.15 (d, 2H, J =
7.3 Hz, Ar). 13C NMR (75 MHz, CDCl3): δ 6.5, 18.3,
22.7, 58.5, 70.3, 93.6, 114.0, 121.2, 122.1, 128.9,
129.2, 130.1, 132.0, 133.3, 135.2, 159.7, 183.2, 183.3.
19F NMR (282 MHz, CDCl3): δ –140.68 (22%, 10B–F),
–140.74 (78%, 11B–F). 29Si NMR (59 MHz, CDCl3):
δ –45.60. IR (CsI): 2929, 1599, 1545, 1487, 1377,
1263, 1167, 1101, 1078, 1045, 960 cm−1. UV–vis
(THF) λ = 367 nm (ε = 26,840 L/mol*cm). HRMS
(ESI) m/z calcd. for C24H31BF2NaO6Si [(M + Na)+]:
515.1848, found 515.1875. Elemental analysis calcd
for C24H31BF2O6Si: C, 58.54; H, 6.35; B, 2.20; F,
7.72; Si, 5.70. Found: C, 55.53; H, 5.22; B, 1.80; F,
6.52; Si, 6.93.
General Procedure of the Hydrosilylation of
β-diketonatoboron Difluorides
2,2-Difluoro-4-phenyl-6-[4-(3-(triethoxysilyl)
propoxy)phenyl]-1,3,2-(2H)-dioxaborine,
7c.
To a suspension of β-diketonatoboron difluoride
(0.003 mol) and triethoxysilane (0.0032 mol) in dry
THF (30 mL) under argone, 30 μL of a Pt catalyst
was added. The reaction mixture was stirred for 8 h
at room temperature. After GPC (eluent THF), the
product was obtained as a yellow oil.
Yield: 85%. 1H NMR (300 MHz, DMSO-d6): δ
0.77 (m, 2H, CH2Si), 1.23 (t, 9H, J = 7.0 Hz,
Si
O C CH3), 1.94 (m, 2H, O C CH2 C), 3.84
(q, 6H, J = 6.9 Hz, Si
O CH2 ), 4.06 (t, 2H, J
= 6.4 Hz, Ar OCH2 ), 6.99 (d, 2H, J = 9.2 Hz,
Ar), 7.08 (s, 1H, CO CH CO), 7.51 (t, 2H, J = 7.3
Hz, Ar), 7.64 (t, 1H, J = 7.3 Hz, Ar), 8.10 (m, 4H,
Ar). 13C NMR (75 MHz, CDCl3): δ 6.5, 18.3, 22.6,
58.5, 70.4, 92.4, 115.1, 116.3, 123.8, 128.6, 129.0,
131.7, 131.9, 132.3, 134.6, 165.4, 181.2, 182.2. 19F
NMR (282 MHz, CDCl3): δ –141.64 (21%, 10B–F),
–141.70 (79%, 11B–F). 29Si NMR (59 MHz, CDCl3): δ
–45.97. IR (CsI): 2927, 1599, 1543, 1493, 1373, 1269,
1238, 1176, 1103, 1078, 1047, 958 cm−1. UV–vis
2,2-Difluoro-4-phenyl-6-[2-(3-(triethoxysilyl)
propoxy)phenyl]-1,3,2-(2H)-dioxaborine, 7a. Yield:
82%. 1H NMR (300 MHz, CDCl3): δ 0.80 (m, 2H,
CH2Si), 1.18 (t, 9H, J = 6.7 Hz, Si
2.08 (m, 2H, O
CH2 C), 3.77 (q, 6H, J =
6.7 Hz, Si
CH2 ), 4.17 (t, 2H, J = 6.7 Hz,
Ar CH2 ), 7.01–7.12 (m, 2H, Ar), 7.51–7.69
O C CH3),
C
O
O
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride 11
[23] Zhang, G.; Chen, J.; Payne, S. J.; Kooi, S. E.; Demas,
(THF) λ = 398 nm (ε = 42,760 L/mol*cm). HRMS
(ESI) m/z calcd. for C24H31BF2NaO6Si [(M + Na)+]:
515.1848, found 515.1825. Elemental analysis calcd
for C24H31BF2O6Si: C, 58.54; H, 6.35; B, 2.20; F,
7.72; Si, 5.70. Found: C, 56.98; H, 6.08; B, 1.82; F,
6.69; Si, 6.11.
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