Design, Synthesis, and Crystallization-Induced Emission of Boron Difluorides β-Ketoiminates

Article abstract of DOI:10.1002/cplu.201800069

A series of new nitrogen-containing analogues of boron difluoride benzoylacetonates with hydrogen and methyl substituents at the nitrogen atom have been synthesized. A comparative study of boron difluoride β-ketoiminates and their oxygen-containing analogues by means of luminescence and IR spectroscopic methods as well as quantum chemistry simulations was also performed.

Full text of DOI:10.1002/cplu.201800069

Accepted Article
Title: Synthesis, molecular design and crystallization-induced emission
of novel boron difluorides β-ketoiminates
Authors: Elena Fedorenko, Anatolii Mirochnik, Anton Beloliptsev,
Galina Tretyakova, and Irina Svistunova
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Synthesis, molecular design and crystallization-induced emission
of novel boron difluorides β-ketoiminates
Elena V. Fedorenko,[a] Anatolii G. Mirochnik,[a] Anton Yu. Beloliptsev,[a] Irina V. Svistunova,[b] and
Galina O. Тretyakova*[a,b]
Abstract: A series of new nitrogen-containing analogs of boron
difluoride benzoylacetonates with hydrogen and methyl substituents
at the nitrogen atom have been synthesized. The comparative study
of boron difluoride β-ketoiminates and their oxygen-containing
analogs by the methods of luminescence and IR spectroscopy and
quantum chemistry simulation has been performed.
properties such as large molar absorption coefficients and high
fluorescence quantum yields in the solid state.[14] Moreover, boron
difluoride ketoiminates could be a promising structure for
receiving aggregation-induced emission (AIE), crystallization-
induced
emission
(CIE)
and
mechanofluorochromism
properties.[14,18,19]
It is well known that the fluorescence intensity of organic
luminophores in the crystal state usually weakens as compared
to that of dilute solutions because of aggregation-caused
quenching (ACQ) process brought about by formation of
delocalized excitons and excimers in aggregated state.[20]
However, at the same time the aggregation processes can restrict
intramolecular rotation which are the cause of the nonradiative
transitions.[21-23] Aggregation-induced emission, which special
case is crystallization-induced emission is a key phenomenon for
overcoming of ACQ effect and obtaining efficient luminophores in
the crystal state. However although the number of the
luminophores capable of AIE ang CIE is rather limited,[12,14,22,24-26]
interest to study of such luminophores grows due to possibility of
their use as optoelectronic devices,[22,26] luminescent
sensors,[22,25,26] biomedical imaging [22,25,26] and smart materials.[22]
Within the scopes of the present work, the synthesis of a series
of new nitrogen-containing analogs of boron difluoride
benzoylacetonates with small-size substituents at the nitrogen
atom (Н, СН3) has been performed. The luminescence properties
and molecular structure features of these compounds have been
investigated by the methods of IR, UV-vis and luminescence
spectroscopy and quantum chemistry simulation. The
comparative investigation of the luminescence properties of boron
difluoride β-ketoiminates with hydrogen and methyl substitutes
and respective boron difluoride β-diketonates was carried out.
Introduction
Boron difluoride β-diketonates exhibit intensive luminescence in
both solution and crystals that determined growing interest to
[1]
study of their photophysical and photochemical properties due to
possibility of their use in organic light-emitting diodes,[2,3]
molecular probes,[4,5] semiconductors,[6] oxygen sensors
and
[7]
mechanical sensors.[8] Attention to boron difluoride β-diketonates
is also attracted by ability of this class of compounds to
phosphorescence at the room temperature and to reversible
thermo- and mechanochromism.[8-10] Boron difluoride β-
ketoiminates are structure and electron analogs of boron
difluoride β-diketonates. It was show by recent investigation that
nitrogenous analogs of boron difluoride β-diketonates
(ketoiminates and diiminates) are characterized with a relatively
low luminescence in dilute solutions [11-13] while in the crystal state
their luminescence is intensive.[12-15] The group of studied boron
difluoride ketoiminates is rather limited: mostly, luminescence
properties of the compounds containing bulky substituents by the
nitrogen atom (phenyl, tret-butyl, p-bromphenyl, and p-
methoxyphenyl) have been described.[11,16] At the same time, it
was shown on the example of boron difluoride
enaminedibenzoylmethanates that addition of small substitutes to
the nitrogen atom considerably changes the molecular structure
and its luminescence properties as compared to the β-diketonate
analogs.[14,17] Boron difluoride ketoiminates are an important
class of organoboron dyes because they possess prominent optic
Results and Discussion
Earlier we synthesized boron difluoride β-ketoiminates and
studied their luminescence properties.[17,27] To reveal the
relationship between luminescence properties and the features
of the molecular structure of boron difluoride β-ketoiminates, the
range of ligands was extended significantly. The general method
of synthesis of boron difluoride β-ketoiminates is shown on the
Scheme 1.
Ligands were obtained through interaction of the respective
boron difluoride β-diketonate with ammonia or methylamine.
According to [28], the interaction of ammonia and primary amines
with boron difluoride β-diketonates causes the selective
substitution of the oxygen atom at the methyl group by the amine
group.
[a]
E.V. Fedorenko, A.G. Mirochnik, A.Yu. Beloliptsev, G.O. Тretyakova
Institute of Chemistry, Far Eastern Branch of the Russian Academy
of Sciences Department
Prosp. 100 letiya Vladivostoka, 159, Vladivostok (Russian
Federation)
E-mail: tretyakova_galin@list.ru, tretyakova.go@dvfu.ru
I.V. Svistunova, G.O. Тretyakova,
[b]
Far Eastern Federal University
Sukhanova Str., 8, Vladivostok (Russian Federation)
Supporting information for this article is given via a link at the end of
the document.
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R1
CH3
R2
R1
substituent (3a-е) proceeds under more severe conditions as a
result of the decrease of the reactivity of the respective enamine
because of the increase of the electron-donor capacity of the
substituent at the nitrogen atom. In the case of the compound 3а
instead of tributoxyborane calcium carbonate was used, which is
a stronger proton acceptor. [27] The synthesis of similar complexes
with the developed π-system in the α-position of the chelate cycle
(3b-e) proceeds in toluene at heating up to 80 °C.
R1
CH3
R2
CH3
NH2R2
[BF3]
O
N
O
N
O
O
B
B
F
F
F
F
1 a-e
2 a-e, 3 a-e
β-Diketonate
β-Ketoiminate
R1
R2 = H R2 =CH3
-C6H5
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
-4-Me-O-C6H5
-C6H4-4-C6H5
naphtyl
As was earlier established for the compounds 2a and 3a, the
substitution of one of oxygen atoms in boron difluoride β-
diketonate (1а) proceeds selectively for the oxygen atom next to
the methyl group, which was corroborated by the X-ray data.[27,34]
antronyl
1
Analysis of the H NMR data for the compounds 2a-e and 3a-e
Scheme 1. General method of synthesis of boron difluoride β-ketoiminates
corroborates the selective substitution of the oxygen atom next to
the methyl group: the position of the signal of methyl group
hydrogen atoms in the chelate ring α-position around 2.29–2.39
ppm corresponds to the signal from hydrogen atoms of the methyl
group conjugated with the С=N fragment.
As was earlier found for the compounds 2a [27] and 3a [34] by the
X-ray data, unlike the respective β-diketonate analog (1a), one
observes the disorder of the quasi-aromaticity of the chelate
cycle: the С–С bond by the nitrogen atom is longer than that by
the oxygen atom, the С–N bond length corresponds to that of the
double bond, and the С–О bond length is equal to that of the
single bond. Disorder of the quasi-aromaticity is observed for
Interaction of respective ligand with boron trifluoride etherate in
toluene at heating results in formation of ketoiminate complexe
(2а) with high yield.[27] However, at interaction of boron trifluoride
etherate with β-ketoimines having a hydrogen substituent at the
nitrogen atom and a developed π-system in the α-position of the
chelate ring (2b-e), a side reaction of oxidation of the formed
boron difluoride β-ketoiminate into the β-diketonate complex
observes (Scheme 2).
R1
R1
CH3
CH3
[O]
nitrogen-containing
analogs
of
boron
difluoride
O
N
dibenzoylmethanate as well.[14,17,34] These data allow us to
conclude that there is a diene structure in the chelate cycle of
boron difluoride β-ketoiminates.[14,17,27,34]
O
O
B
B
H
F
F
F
F
IR spectra of the compounds 2a-е and 3a-е contain the
absorption bands in the ranges 1612–1637 cm-1 and 1566–1544
cm-1, whereas IR spectra of β-diketonate complexes contain a
unified absorption band of conjugated С=О and С=С bonds at
1540 cm-1 (Figure 1).[35-42] According to quantum chemistry
calculations of IR spectra of the compound 1а, this absorption
band is the result of flat bending vibrations of the chelate ring with
participation of stretching C–C and С–О vibrations (Figure 2a).
The reason of the above differences consists in disorder of the
quasi-aromaticity of the chelate cycle for all the boron difluoride
β-ketoiminates under study.
Scheme 2. Side reaction of boron difluoride β-ketoiminate oxidation
As a rule, boron difluoride β-diketonates and β-ketoiminates are
synthesized at prolonged heating (from 3 to 16 hours) in different
solvents (chloroform, methylene chloride, toluene).[14,16,29-31]
Depending on the ligand activity, the synthesis can take place in
the presence of different bases.[29,31,32] Earlier we synthesized the
simplest of nitrogen-containing boron difluoride benzoylacetonate
derivative (2а) at boiling in toluene with tributoxyborane (yield
82 %).[27]
The IR spectrum of 2a contains an absorption band of a middle
intensity at 1636 cm-1 and a broad intensive band at 1537 cm-1
(Figure 1). According to the quantum chemistry calculations data,
the absorption band with a maximum at 1636 cm-1 is the result of
a plane deformation of the chelate ring, bending vibrations of the
methyl group, and stretching vibrations of C=C and C=N bonds of
the chelate cycle (Figure 2b), whereas the band with a maximum
at 1537 см-1 – of planar bending vibrations of the chelate ring with
participation of stretching C–C vibrations in the chelate cycle
(Figure 2c).
Attempts to obtain other β-ketoiminate complexes with the
hydrogen substituents at the nitrogen atom (2b-e) at boiling in
toluene were accompanied with a side reaction of oxidation into
[33]
boron difluoride β-diketonates (Scheme 2). The authors of
described the mechanochemical synthesis of boron difluoride β-
diketonates with high yields. However, when the attempt was
made to spread this synthesis method to ketoiminates, the
respective β-diketonate complex was isolated in the individual
form instead of the compound 2b. Individual boron difluoride β-
ketoiminates (2b-e) were synthesized under mild conditions: by
stirring respective ligands with boron trifluoride etherate in
methylene chloride under low heating (25–30 °C) for 4–8 h. Thus,
convenient technique of obtaining boron difluoride β-ketoiminates,
which allows avoiding the formation of oxidation products even
without application of an inert gas, was suggested.
Unlike the synthesis of boron difluoride β-ketominiates with the
hydrogen substituent, the synthesis of complexes with the methyl
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Here, according to quantum chemistry calculations (Table 1), the
geometric structures of 2a-c and 3a-c molecules undergo, upon
excitation, substantial changes: one observes the decrease of the
С2–С3 bond lengths, the increase of the С3–С4, С2–N, and С4–О
ones, and a substantial shortening of lengths of the С4–С5 bonds
between the chelate cycle and the aromatic substituent. At
transition of molecules of 2a-c and 3a-c into the excited
structurally relaxed state (ESRS), there occurs a transformation
of the phenyl ring into the quinoid one described earlier for 2а
(scheme 3).[27] It is worth mentioning that in case of the
compounds 2d,e and 3d,e the transition into the excited state is
accompanied with some other geometry changes: in the ESRS,
the lengths of С2–N and С4–О bonds increase significantly, while
changes in the С2–С3 and С3–С4 bonds lengths are smaller. Note
that in some cases (compounds 2a-c and 3a-c) the increase of
the length of the С3–С4 bond is so substantial that one can
conclude that in the excited state the length of this bond
corresponds ordinary to the length of the ordinary С–С bond.[43]
As was shown by quantum chemistry calculations, the different
character of changes in the molecular geometry of boron
difluoride β-ketoiminates 2,3а-с and 2,3d,e at transition from the
ground to the excited state was caused by the peculiarities of
redistribution of the electron density during the HOMO–LUMO
transition (Figure 3). As seen from Figure 3, in case of the
compounds 2a-c, during the HOMO–LUMO transition one
observes an insignificant redistribution of the electron density
between the aromatic α-substituent and the chelate cycle.
However, in case of the compounds 2d,e and 3d,e, the HOMO–
LUMO transition is accompanied with a significant transfer of the
electron density from the aromatic substituent to the chelate cycle.
100
%T
90
1
8
6
4
2
80
70
60
1a
2a
50
1800 1600 1400 1200 1000
800
600
400
1/cm
Figure 1. Fragment of IR spectra of compounds 1a and 2a
H3C
HN
H3C
HN
O
O
B
B
F F
F F
Scheme 3. Geometry changes in the molecule of 2a at transition into the excited
state [27]
As was shown by quantum chemistry calculations and the IR
spectroscopy and X-ray data, in the molecules of boron difluoride
β-ketoiminates, one observed a clearly expressed disorder of the
quasi-aromaticity of the chelate cycle. In view of the above, there
emerges a question: how the disorder of the quasi-aromaticity is
reflected in the compounds luminescence properties? To get an
answer to this question, the spectral characteristics of solutions
and crystals of boron difluoride β-ketoiminates under study (2a-e
and 3a-e) and their oxygen-containing analogs (1a-e) (Table 2)
were investigated.
Figure 2. Atomic displacements of 1a in the mode at 1540 cm-1 (a), and 2a in
the modes at 1636 cm-1 (b) and 1537 cm-1 (c)
As follows from the data of quantum chemistry calculations of the
geometry of molecules of boron difluoride β-ketoiminates (2a-e
and 3a-e) in the ground state, in all β-ketoiminate complexes one
observes a disorder of the chelate cycle symmetry (Table 1),
which is in good agreement with the X-ray data of compounds 2a
and 3a.[27,34] The data of Table 1 clearly demonstrate that while
C–C and C–O bonds of molecules of all the β-diketonate
complexes under study (1a-e) are pairwise equaled, in the
compounds 2a-e and 3a-e the lengths of C2–C3 bonds are
significantly larger than those of C3–C4 bonds, and the C2–N bond
lengths are significantly larger than those of С4–О bonds.
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Table 1. Some calculated bond lengths (Å) of compounds 1a-3e in the geometry of the ground and excited structurally relaxed states
Ground state
C4-C5
1.476
1.481
1.481
1.467
1.473
1.472
1.473
1.477
1.476
1.475
1.478
1.478
1.485
1.489
1.489
ESRS
C4-C5
C2-C3 [a]
1.391
1.409
1.415
1.388
1.405
1.412
1.390
1.406
1.414
1.390
1.408
1.415
1.392
1.411
1.417
C3-C4
1.401
1.387
1.382
1.405
1.392
1.386
1.402
1.391
1.383
1.402
1.389
1.383
1.399
1.385
1.379
C4-O
1.291
1.301
1.304
1.292
1.302
1.305
1.291
1.300
1.304
1.291
1.302
1.305
1.289
1.301
1.305
C2-N/O
1.289
1.314
1.316
1.291
1.317
1.319
1.290
1.317
1.317
1.290
1.315
1.317
1.290
1.315
1.317
C2-C3
1.389
1.388
1.386
1.404
1.394
1.383
1.396
1.398
1.395
1.391
1.401
1.405
1.401
1.409
1.413
C3-C4
1.507
1.491
1.480
1.424
1.464
1.478
1.404
1.440
1.449
1.395
1.391
1.388
1.378
1.375
1.377
C4-O
1.292
1.298
1.301
1.318
1.312
1.309
1.320
1.310
1.307
1.329
1.332
1.334
1.350
1.355
1.345
C2-N/O
1.304
1.343
1.353
1.303
1.342
1.357
1.305
1.334
1.342
1.313
1.342
1.345
1.337
1.367
1.358
1a
2a
3a
1b
2b
3b
1c
2c
3c
1d
2d
3d
1e
2e
3e
1.402
1.413
1.415
1.450
1.420
1.411
1.463
1.429
1.421
1.468
1.464
1.460
1.497
1.490
1.492
[a] Numbering of atoms in molecules of boron difluoride β-ketoiminates
C3
(H3C)C1
C5(R1)
C4
O
C2
N/O
B
R2
F
F
As follows from the luminescence data shown in Table 2, the
absorption and excitation spectra of boron difluoride β-
ketoiminates are not identical, unlike the case of their oxygen-
containing analogs. The authors of [27] related this discrepancy to
substantial differences in the structures of the complex in ground
and excited states.
The luminescence spectra of diluted solutions of boron difluoride
β-ketoiminates are virtually identical or slightly bathochromically
shifted relatively to spectra of respective β-diketonate analogs
(Table 2). It is worth mentioning that the largest Stokes shift
(7100–8080 cm-1) is observed for the compounds 2d,e and 3d,e,
which is explained by significant redistribution of the electron
density between the aromatic α-substituent and the chelate cycle
at transition to the excited states as compared to the compounds
2а-с and 3а-с (1800 – 6490 cm-1) (Figure 3).
Figure 3. Frontier molecular orbitals of compounds 2a-е in the ground state
geometry
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significantly (up to 1.507 Å) and it virtually becomes an ordinary
bond. Here, the quantum yield of luminescence of 1а is negligibly
small (φ = 0.001) (Table 2). However, in compounds, whose
geometries of the ground and excited states differ insignificantly,
the quantum yield of luminescence is rather high. For example, in
case of the compound 1с (φ = 0.75) (Table 2), changes in lengths
of the С2–С3 and С3–С4 bonds at transition from the ground to the
excited state are insignificant (Table 1).
Evidently, differences in the character of changes in the molecular
geometry of boron difluoride β-ketoiminates and their oxygen-
containing analogs are caused by peculiarities of their molecular
structure. It is well-known that one of the factors responsible for
radiationless transitions in boron difluoride β-diketonates consists
in rotation of the aromatic substituent around the С4–С5 bond,
Table 2. Spectral characteristics of solutions and crystals of boron
difluoride β-diketonates and their nitrogen-containing analogs
Solutions
Crystals
∆ST[d]
[cm-1]
[a]
[b]
[c]
λabs
λex
λlum
λex
[nm]
λlum
[nm]
φ[e]
φ[d]
[nm]
[nm]
[nm]
1a
2a
3a
1b
2b
3b
1c
2c
3c
1d
2d
3d
1e
2e
3e
330
330
335
360
350
350
360
350
350
380
330
350
440
385
385
340
370
370
365
360
380
360
360
360
380
345
350
450
385
385
400
420
420
385
390
430
425
415
420
440
450
420
535
530
535
5300
6490
6040
1800
2930
5320
4250
4480
4760
3590
8080
4760
4040
7100
7280
0.001
0.07
0.002
0.04
0.02
0.09
0.75
0.02
0.03
0.53
0.16
0.01
0.09
0.05
0.03
380
470
380
445
380
380
450
350
380
485
430
385
500
450
425
440
485
430
480
475
465
505
450
450
515
515
465
555
520
485
0.29
0.11
0.08
0.26
0.13
0.27
0.14
0.02
0.12
0.28
0.01
0.18
0.05
0.03
0.07
which
was
demonstrated
for
boron
difluoride
dibenzoymethanate.[44,45] The rotation blocking at the transition to
the excited state for boron difluoride β-diketonates and β-
ketoiminates is realized due to the increase of the order of the
bond between the chelate cycle and the aromatic substituent (S1–
S1' transition, Figure 4). For a most of boron difluoride β-
diketonates (1b-e), for which quasi-aromaticity of the chelate
cycle is observed, the transition of molecule to the optimal
geometry of the excited state (S1', Figure 4) requires less
significant restructuring of the molecule geometry, which is
responsible for quantum yield of luminescence. In opposite, in
case of boron difluoride β-ketoiminates (2,3а-е), the molecule
transition to an optimal geometry requires a substantial molecule
restructuring for transition to the S1' state that takes place within
a longer period of time. Thus, only a small part of molecules 2,3а-
е are capable to attain the optimal excited state and luminesce in
the S0' state (Figure 4), whereas for a most of molecules the
process of dissipation of the electron excitation energy on
torsional vibrations of the substituent takes place. Such
peculiarities of changes in the geometry of molecules 2,3а-е at
transition from the ground to the excited state are responsible for
low quantum yield of luminescence of these compounds in
solutions.
[a] Absorption wavelength;[b] Excitation wavelength; [c] Emission
wavelength; [d] Stokes shift; [e] Quantum yield determined in solution, using
naphthalene as a reference (φ = 0.12); [d] Quantum yield of crystals,
determined using the integrated sphere method
Note that substitution of the oxygen atom by that of nitrogen
results in the decrease of the quantum yield of luminescence
(Table 2). Here, in the series of boron difluoride β-ketoiminates,
the quantum yield of luminescence increases along with the
increase of donor properties of the substituent in the α-position of
the chelate cycle (the largest value of quantum yield of
luminescence is observed for the compound 2d having the
naphtyl α-substituent (φ = 0.16). Interestingly, the quantum yield
of luminescence for β-ketoiminates and their oxygen-containing
analogs depends on the degree of chelate cycle conjugation. In
case of boron difluoride β-diketonates and β-ketoiminates, in
molecules of which, at transition from the ground state to the
excited state take place a significant change in the lengths of the
C-C bonds in the chelate cycle (see the quantum chemistry
calculations data, Table 1), the value of quantum yield of
luminescence is low. For example, according to the data of
quantum chemistry calculations for the compound 1а, in the
ground state the length of the С2–С3 bond is equal to 1.391 Å
while that of the С3–С4 bond – to 1.401 Å (Table 1). At transition
to the excited state, the length of the С3–С4 bond increases
Figure 4. Basic illustration of energy-level diagram and effects of the boron β-
ketoiminates
It is evident that blocking of radiationless transitions of
compounds 2,3а-е through slowing down of the substituent
rotation around the С4–С5 bond facilitates the molecules transition
to the excited state, which determines the ability of compounds of
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this class to crystallization- and aggregation-induced emission. [14,
boron difluoride β-ketoiminates with the methyl substituent at the
nitrogen atom (3a-е), as compared to respective β-diketonates, is
caused by the monomeric nature of luminescence of nitrogen-
containing complexes. Indeed, as seen from Figure 6 and Table
3, for the compounds 3а-е one observes coincidence or small
bathochromic shift of the spectra of luminescence and excitation
of crystals relatively to spectra of diluted solutions.
46-50]
Figure 5 clearly demonstrates the difference in luminescence
properties of boron difluoride β-ketoiminates and β-diketonates.
Boron difluoride β-ketoiminates (2,3a-e) are characterized with
low-intensity luminescence of solutions and bright one of crystals.
A
majority of boron difluoride β-diketonates (1b-e) are
characterized with intensive luminescence in both solutions and
crystals.
Figure 6. Luminescence (solid lines) and excitation (dotted lines) spectra of
crystals (black) and solutions (CHCl3, C = 1·10-5 mol/L) (blue) of 3a-d
Another picture is observed for boron difluoride β-ketoiminates
with the hydrogen substituent (2a-e) that does not create
substantial steric hindrances. In some cases of boron difluoride β-
ketoiminates with the hydrogen substituent at the nitrogen atom,
similarly to β-diketonate complexes, a bathochromic shift of the
luminescence spectra of crystals relatively to spectra of solutions
observes (Table 3, Figure 7). The compound 2е is here an
Figure 5. Images of solutions and crystals of 1-3a-e under UV light
Here, unlike solutions, in case of crystals one observes a reverse
dependence: the luminescence spectra of β-ketoiminate
complexes are hypsochromically shifted relatively to spectra of
oxygen-containing analogs. Evidently, the observed difference in
the spectra of boron difluoride β-diketonates and β-ketoiminates
are related to peculiarities of their crystal structure.
exception characterized with
a
hypsochromic shift of
luminescence and excitation spectra at transition from solutions
to crystals.
It is well-known that the luminescence of boron difluoride β-
diketonates is an excimer one,[39, 51-54] and the bathochromic shift
of the luminescence spectra maximums at transition from diluted
solutions (monomeric luminescence) to crystals could attain 100
nm.[54,55] In the excitation spectra of boron difluoride β-diketonates,
one observes a narrow band of excitation of J-aggregates.[56] The
excimer formation requires the presence of pre-excimer sites
comprising parallel molecules with a substantial degree of
overlapping.[51-54] The optimal condition for excimer formation
would consist in the existence of pairs of molecules with
sufficiently high degree of overlapping and subsequent formation
of J-aggregates from these molecules pairs comprising excimer
traps.[17, 51-54]
In the compounds 3a-е, the presence of the methyl group at the
nitrogen atom creates steric hindrances at formation of excimers
in crystals. Here, the crystals excitation spectrum corresponds to
excitation of the monomeric luminescence (Figure 6). Thus, the
observed hypsochromic shift in the luminescence spectra of
Figure 7. Luminescence (solid lines) and excitation (dotted lines) spectra of
crystals (black) and solutions (CHCl3,C = 1·10-5 mol/l) (blue) of 2a,b,c,e
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One can see from Table 2 and Figure 5 that for most of boron
difluoride β-ketoiminates (2,3a-e) the quantum yield of
luminescence of the crystals is higher that of the solutions that
lets to say about ability of these complexes to CIE. Basing on the
previously studies crystal structure of the compound 1а-е,[51, 57-59]
significant, the dissipation of the energy of the excited state is
mainly realized through radiationless processes caused by
rotation of the aromatic substituent, which results in the decrease
of the quantum yield of luminescence (0.001–0.06). For the
compounds with insignificant differences in geometries of the
ground and excited states, the quantum yield of luminescence is
high (0.2–0.7).
[27]
[34]
2а
и 3а
as well as on the analysis of the luminescence
properties of boron difluoride β-ketoiminates (2,3a-e) and their
oxygen-containing analogs (1a-e) (Table 2) one can reveal the
main factors which influence on intensity of emission in solid state.
The data of Table 2 show that in case of boron difluoride β-
ketoiminates with hydrogen substitute at the nitrogen atom (2а-е),
at the transition from solutions to the solid state one can observe
insignificant increase of the quantum yield of luminescence. We
consider that it is determined by the two competitive processes:
restriction of intramolecular rotation of the α-substitute resulting in
CIE and formation of the excimers between the molecules with a
considerable degree of overlap which causes ACQ. Really, at
transition from the solutions to the crystals the quantum yield of
luminescence in most cases either does not change (for 2с φsolv
= 0.02, φcryst = 0.02) or slightly rises (e.g. for 2b φsolv = 0.02, φcryst
= 0.13). Another picture is observed for boron difluoride β-
ketoiminates with methyl substitute at the nitrogen atom (3а-е):
the quantum yield of luminescence is much more than that of the
solutions (e.g. for 3b φsolv = 0.09, φcryst = 0.27) that is connected
with nothing but the restricted processes of the α-substitute
rotation.
The transition of boron difluoride β-ketoiminates to the crystalline
state blocks rotations of the aromatic substituent, which is
responsible for the ability of this class of compounds to
crystallization-induced emission.
Experimental Section
Instrumentation: 1H (400 MHz) and 13C (100 MHz) NMR spectra were
recorded using Bruker WH 400 spectrometers. In the 1H and 13C NMR
spectra, tetramethylsilane (TMS) was used as an internal standard in
CDCl3. UV-visible absorption spectra were recorded using
a
spectrophotometer 2550 (Shimadzu-UV) with a quartz cuvette (path length
1 cm). Fluorescence emission and excitation spectra were recorded using
a spectrofluorimeter RF5301 (Shimadzu) with a quartz cuvette (path length
1 cm). A solution of naphthalene in ethanol was used as a standard for
measuring the fluorescence quantum yield (φ
= 0.12). Absolute
fluorescence quantum yields of crystals were measured with a Horiba
Fluorolog 3 spectrometer (integrating sphere method). IR spectra (KBr
disks, oil) were recorded on the Shimadzu IR Prestige-21. Mass spectra
were recorded in the positive and negative ion modes (electrospray
ionization ESI, a Shimadzu LCMS 2010EV mass spectrometry detector);
the samples were injected in the system acetonitrile – water (9 : 1).
Conclusions
Materials:
A series of new nitrogen-containing analogs of boron difluoride
benzoylacetonates with hydrogen and methyl substituents at the
nitrogen atom have been synthesized. The comparative study of
luminescence properties and molecular structures of boron
difluoride β-ketoiminates and their oxygen-containing analogs has
been performed by the methods of luminescence and IR
spectroscopy and quantum chemistry simulation.
Boron difluoride benzoylacetonate (1a) was synthesized from
benzoylacetone according to the reported method.[32] Boron difluoride 3-
amino-1-phenyl-2-buten-1-onate (2a) and boron difluoride 3-methylamino-
1-phenyl-2-buten-1-onate (3a) was obtained according to the procedure
described earlier.[27] Boron difluoride 1-(4-methoxyphenyl)butane-1,3-
dionate (1b) was synthesized according to the reported method. [57] Boron
difluoride 1-(biphenyl-4-yl)butane-1,3-dionate (1c) was obtained according
to the procedure described earlier.[58] Boron difluoride 1-(naphthalen-2-
yl)butane-1,3-dionate (1d) was synthesized according to the reported
method.[58] Boron difluoride 1-(anthracen-9-yl)butane-1,3-dionate (1e) was
synthesized according to the reported method.[51] Solvents were obtained
from EKOS-1 and used without additional purification.
It has been established that the crystals luminescence has the
monomeric nature in boron difluoride β-ketoiminates with the
methyl substituent at the nitrogen atom. For boron difluoride β-
ketoiminates with the hydrogen substituent not creating
substantial steric hindrances, the crystals luminescence is caused
by the luminescence of excimers and aggregates on their basis.
Quantum chemistry calculations, the IR spectroscopy and X-ray
data demonstrated that in case of boron difluoride β-ketoiminates
(unlike boron difluoride β-diketonates) one observes a clearly
expressed disorder of the quasi-aromaticity of the chelate cycle.
It has been established that the substitution of the oxygen atom
by that of nitrogen results in the decrease of the quantum yield of
luminescence. For the studied boron difluoride β-diketonates and
β-ketoiminates, the transition of molecules from the ground to the
excited states yields changes in the molecular geometry
accompanied with the increase of the order of the bond between
the chelate cycle and the aromatic substituent resulting in
blocking of rotation of the aromatic substituent. In case of boron
difluoride β-diketonates and β-ketoiminates, for which differences
in the geometries of the ground and the excited states are
Synthesis of 2b:
Synthesis
of
3-amino-1-(4-methoxyphenyl)-but-2-en-1-one:
The
compound 1b (1 g, 4.2 mmol) was dissolved in acetonitrile (25 mL) at
heating. Thereafter, the reaction mixture was gradually added with an
aqueous solution of ammonia (25 %, 3.2 mL, 21 mmol). The reaction
mixture was stirred at heating up to 60 °C for 12 hours (the reaction
completion was controlled by the thin-layer chromatography (TLC)). The
reaction mixture was extracted with methylene chloride and washed with
water. The organic mixture was dried with sodium sulfate and the solvent
was evaporated. The formed precipitate was recrystallized from
1
isopropanol (yield 0.4 g, 40 %). H NMR (400 MHz, CDCl3): δ = 2.03 (s,
3H; CH3), 3.84 (s, 3H; O-CH3), 5.70 (s, 1H; ChH (hydrogen atom at the
central carbon atom of the chelate cycle)), 6.89-6.93 (m, 2H; ArH), 7.85-
7.88 (m, 2H; ArH), 10.13 ppm (s, 2H; NH2). 13C NMR (100 MHz, CDCl3):
δ = 22.81, 55.26, 91.69, 113.31, 128.90, 132,76, 161.73, 188.46 ppm. IR
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(oil): 3290 (νN-H),1639 (C=N),1600 (νC=O), 1566 (νC=C) cm-1. MS: m/z
calculated for C11H13NO2 191.22, found: 190.0 [M-1]. The elemental
analysis calculated data (%) for C11H13NO2: C 69.09; H 6.85; N 7.32;
found: C 69.35; H 6.51; N 6.98.
84 %). 1H NMR (400 MHz, CDCl3): δ = 2.06 (s, 3H; CH3), 5.78 (s, 1H;
ChH), 7.25-7.97 (m, 9H; ArH), 10.24 ppm (s, 2H; NH2). 13C NMR (100 MHz,
CDCl3): δ = 22.87, 92.31, 126.89, 127.16, 128.78, 138.95, 140.44, 143.49,
162.83, 188.94 ppm. IR (oil): 3285 (νN-H), ~1620 (shoulder) ν (C=N,) 1598
(νC=O), 1537 (νC=C) cm-1. MS: m/z calculated for C16H15NO 237.30,
found: 236 [M-1]. Elemental analysis calculated (%) for C16H15NO: C
80.98; H 6.37; N 5.90; found: C 80.66; H 6.05; N 6.21.
Synthesis of boron difluoride 3-amino-1-(4-methoxyphenyl)-but-2-en-1-
onate (2b): The mixture of 3-amino-1-(4-methoxyphenyl)-but-2-en-1-one
(0.37 g, 1.94 mmol) with boron trifluoride etherate (1 mL, 3.87 mmol) in
methylene chloride (10 mL) was stirred using a magnetic stirrer upon
heating up to 30 °C for 5 h. Thereafter, the reaction mixture was washed
with water, and filled with a drier. The solvent was evaporated, and the
formed precipitate was recrystallized from an isopropanol–acetonitrile
mixture (yield 0.26 g, 57 %), m.p. 134-136 °C. 1H NMR (400 MHz, CDCl3):
δ = 2.29 (s, 3H; CH3), 3.85 (s, 3H; O-CH3), 5.98 (s, 1H; ChH), 6.91-6.94
(m, 2H; ArH), 7.89-7.91 ppm (m, 2H; ArH). 13C NMR (100 MHz, CDCl3): δ
= 23.92, 55.47, 92.63, 114.02, 129.59, 163.26, 172.57 ppm. IR (oil): 3348
(νN-H), 1622 (νC=N), 1543 (νC=C) cm-1. MS: m/z calculated for
C11H12BF2NO2 239.02, found: 238.0 [M-1]. Elemental analysis calculated
(%) for C11H12BF2NO2: C 55.27; H 5.06; N 5.86; found: C 55.21; H 6.15; N
5.68.
Synthesis of boron difluoride 3-amino-1-(biphenyl-4-yl)but-2-en-1-onate
(2c): The compound 2c was prepared from 3-amino-1-(biphenyl-4-yl)but-
2-en-1-one (0.35 g, 1.47 mmol) according to the method for 2b. The crude
product was purified by silica gel chromatography (benzene) to produce
2c as a light-beige solid (yield 0.18 g, 43%), m.p. 205-207 °C. 1H NMR
(400 MHz, CDCl3): δ = 2.34 (s, 3H; CH3), 6.13 (s, 1H; ChH), 7.39-8.03
ppm (m, 9H; ArH). 13C NMR (100 MHz, CDCl3): δ = 24.16, 93.74, 118.96,
127.18, 128.08, 128.94, 139.73, 145.31, 173.02 ppm. IR (KBr): 3344 (νN-
H), 1631 (νC=N), 1547 (νC=C). MS: m/z calculated for
C16H14BF2NO 285.10, found: 284.0 [M-1]. Elemental analysis calculated
(%) for C16H14BF2NO: C 67.41; H 4.95; N 4.91; found: C 67.28; H 5.63; N
5.51.
Synthesis of 3b:
Synthesis of 3с:
Synthesis of 3-methylamino-1-(4-methoxyphenyl)-but-2-en-1-one: The
compound 1b (0.5 g, 2.08 mmol) was dissolved at heating in acetonitrile
(20 mL). Thereafter, the reaction mixture was added with an aqueous
solution of methylamine (40 %, 0.85 mL, 10.41 mmol). The reaction
mixture was stirred using a magnetic stirrer at heating up to 30 °C for 12 h
(the reaction completion was controlled using the TLC method). The
reaction mixture was extracted by methylene chloride and washed with
water. The organic layer was dried by sodium sulfate and the solvent was
evaporated. The formed light-yellow precipitate was recrystallized from
isopropanol (yield 0.28 g, 68 %). 1H NMR (400 MHz, CDCl3): δ = 2.03 (s,
3H; CH3), 2.98 (s, 3H; N-CH3), 3.81 (s, 3H; O-CH3), 5.63 (s, 1H; ChH),
6.87-6.89 (m, 2H; ArH), 7.81-7.83 (m, 2H; ArH), 11.21 ppm (s, 1H, N-H).
13C NMR (100 MHz, CDCl3): δ = 19.18, 29.55, 55.24, 91.35, 113.29,
128.58, 133.13, 161.48, 165.19, 186.88 ppm. IR (oil): 1635 (C=N),1612
(νC=O), 1572 (νC=C) cm-1. MS: m/z calculated for C12H15NO2 205.25,
found: 204 [M-1]. Elemental analysis calculated (%) for C12H15NO2: C
70.22; H 7.37; N 6.82; found: C 71.26; H 6.83; N 6.61
Synthesis
of
3-methylamino-1-(biphenyl-4-yl)but-2-en-1-one:
3-
Methylamino-1-(biphenyl-4-yl)but-2-en-1-one was prepared from 1c (1g,
3.49 mmol) according to the method for 3-methylamino-1-(4-
methoxyphenyl)-but-2-en-1-on. The formed green precipitate was
recrystallized from isopropanol (yield 0.61 g, 70 %). 1H NMR (400 MHz,
CDCl3): δ = 2.07 (s, 3H; CH3), 3.03 (s, 3H; N-CH3), 5.73 (s, 1H; ChH),
7.25-7.94 (m, 9 H; ArH), 11.37 ppm (s, 1H, N-H). 13C NMR (100 MHz,
CDCl3): δ = 19.24, 29.68, 91.97, 126.81, 127.10, 127.32, 128.74, 139.19,
140.49, 142.99, 165.89, 187.02 ppm. IR (oil):1620 (νC=N),1603 (νC=O),
1541 (νC=C) cm-1. MS: m/z calculated for C17H17NO 251.32, found: 250
[M-1]. Elemental analysis calculated (%) for C17H17NO: C 81.24; H 6.82; N
5.57; found: C 81.36; H 6.31; N 5.43.
Synthesis of boron difluoride 3-methylamino-1-(biphenyl-4-yl)but-2-en-1-
onate (3c): The compound 3c was prepared from 3-methylamino-1-
(biphenyl-4-yl)but-2-en-1-one (0.25 g, 1.0 mmol) according to the method
for 3b. The formed white precipitate was recrystallized from isopropanol
(yield 0.19 g, 66 %), m.p. 207-209 °C. 1H NMR (400MHz, CDCl3): δ = 2.26
(s, 3H; CH3), 3.25 (s, 3H; N-CH3), 6.06 (s, 1H; ChH), 7.25-7.98 ppm (m, 9
H; ArH). 13C NMR (100 MHz, CDCl3): δ = 20.56, 32.83, 95.56, 118.95,
127.13, 128.90, 139.84, 144.66, 168.43, 171.00 ppm. IR (oil): 1630 (νC=N),
1537 (νC=C). MS: m/z calculated for C17H16BF2NO 299.12, found: 298.0
[M-1]. Elemental analysis calculated (%) for C17H16BF2NO: C 68.26; H
5.39; N 6.61; found: C 68.49; H 5.04; N 6.37.
Synthesis of boron difluoride 3-methylamine-1-(4-methoxyphenyl)-but-2-
en-1-onate (3b): A mixture of 3-amino-1-(4-methoxyphenyl)-but-2-en-1-
one (0.23 g, 1.12 mmol) with boron trifluoride etherate (0.6 mL, 2.2 mmol)
in toluene (5 mL) was stirred using a magnetic stirrer at heating up to 80 °C
for 16 h. Thereafter, the reaction mixture was extracted with methylene
chloride, washed with water, and filled with drier. The solvent was
evaporated and the formed precipitate was recrystallized from an
isopropanol–acetonitrile mixture (yield 0.17 g, 61 %), m.p. 141-142 °C. 1H
NMR (400 MHz, CDCl3): δ = 2.22 (s, 3H; CH3), 3.21 (s, 3H; N-CH3), 3.84
(s, 3H; O-CH3), 5.93 (s, 1H; ChH), 6.90-6.92 (m, 2H; ArH), 7.84-7.87 ppm
(m, 2H; ArH). 13C NMR (100 MHz, CDCl3): δ = 20.49, 32.61, 55.43, 94.37,
113.91, 188.94, 129.06, 162.77, 168,62, 170.68 ppm. IR (oil): 1632 (νC=N),
1541 (νC=C) cm-1. MS: m/z calculated for C12H14BF2NO2 253.05, found:
252.0 [M-1]. Elemental analysis calculated (%) for C12H14BF2NO2: C 56.96;
H 5.58; N 5.54; found: C 57.24; H 5.41; N 5.73.
Synthesis of 2d:
Synthesis of 3-amino-1-(naphthalen-2-yl)but-2-en-1-one: 3-Amino-1-
(naphthalen-2-yl)but-2-en-1-one was prepared from 1d (1 g, 3.8 mmol)
according to the method for 3-amino-1-(4-mehtoxyphenyl)-but-2-en-1-one.
The formed yellow precipitate was recrystallized from isopropanol (yield
0.75 g, 94 %). 1H NMR (400 MHz, CDCl3): δ = 2.08 (s, 3H; CH3), 5.89 (s,
1H; ChH), 7.25-8.38 (m, 7H; ArH), 10.28 ppm (s, 2H; NH2). 13C NMR (100
MHz, CDCl3): δ = 22.89, 92.53, 124.16, 126.19, 127.15, 127.60, 129.16,
132.84, 137.50, 162.88, 189.28 ppm. IR (oil): 3395 (νN-H),1614 (νC=N),
1595 (νC=O),1529 (νC=C) cm-1. MS: m/z calculated for C14H13NO 211.26,
found: 212 [M+1]. Elemental analysis calculated (%) for C14H13NO: C
79.59; H 6.20; N 6.63; found: C 79.32; H 6.41; N 6.39.
Synthesis of 2с:
Synthesis of 3-amino-1-(biphenyl-4-yl)but-2-en-1-one: 3-Amino-1-
(biphenyl-4-yl)but-2-en-1-one was prepared from 1c (0,55 g, 1.9 mmol)
according to the method for 3-amino-1-(4-methoxyphenyl)-but-2-en-1-one.
The formed precipitate was recrystallized from isopropanol (yield 0.38 g,
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Synthesis of boron difluoride 3-amino-1-(naphthalen-2-yl)but-2-en-1-onate
(2d): The compound 2d was prepared from 3-amino-1-(naphthalen-2-
yl)but-2-en-1-one (0.71 g, 3.36 mmol) according to the method for 2b. The
formed yellow precipitate was recrystallized from a mixture isopropanol–
acetonitrile (yield 0.55 g, 63 %), m.p. 136-138 °C. 1H NMR (400MHz,
CDCl3): δ = 2.24 (s, 3H; CH3), 6.32 (s, 1H; ChH), 7.25-8.55 ppm (m, 7H;
ArH). 13C NMR (100 MHz, CDCl3): δ = 25.93, 41.81, 97.02, 123.20, 126.85,
127.67, 128.39, 129.39, 132.68, 135.20, 183.06.190.04, 193.84 ppm. IR
(oil): 3341 (νN-H),1634 (νC=N), 1543 (νC=C). MS: m/z calculated for
C14H12BF2NO 259.06, found: 258 [M-1]. Elemental analysis calculated
(%) for C14H12BF2NO: C 64.91; H 4.67; N 5.41; found: C 64.62; H 4.81;
N 5.28.
126.96, 128.55, 129.58, 130.97, 173.47, 175.83 ppm. IR (oil): 3358 (νN-
H),1616 (νC=N), 1539 (νC=C). MS: m/z calculated for C18H14BF2NO
309.12, found: 309 [M]. Elemental analysis calculated (%) for
C18H14BF2NO: C 69.94; H 4.56; N 4.53; found: C 69.71; H 4.73; N 4.81.
Synthesis of 3e:
Synthesis
of
3-methylamino-1-(anthracen-9-yl)but-2-en-1-one:
3-
methylamino-1-(anthracen-9-yl)but-2-en-1-one was prepared from 1e (0.7
g, 2.25 mmol) according to the method for 3-methylamino-1-(4-
methoxyphenyl)-but-2-en-1-one. The formed yellow-brown precipitate was
recrystallized from a mixture isopropanol–water (yield 0.49 g, 79 %). 1H
NMR (400MHz, CDCl3): δ = 2.03 (s, 3H; CH3), 3.11 (s, 3H; N-CH3), 5.39
(s, 1H; ChH), 7.24-8.39 (m, 9H; ArH), 11.51 ppm (s, 1H, N-H). 13C NMR
(100 MHz, CDCl3): δ = 18.95, 29.81, 99.39, 118.89, 125.07, 125.49,
126.10, 128.22, 131.24, 138.27,165.52, 192.35 ppm. IR (oil): 1620 (νC=N),
1597 (νC=O), 1550 (νC=C) cm-1. MS: m/z calculated for C19H17NO 275.35,
found: 275 [M]. Elemental analysis calculated (%) for C19H17NO: C 82.88;
H 6.22; N 5.09; found: C 82.59; H 6.41; N 5.27.
Synthesis of 3d:
Synthesis of 3-methylamino-1-(naphthalen-2-yl)but-2-en-1-one: 3-
methylamino-1-(naphthalen-2-yl)but-2-en-1-one was prepared from 1d
(1.1 g, 4.23 mmol) according to the method for 3-methylamino-1-(4-
methoxyphenyl)-but-2-en-1-one. The formed green precipitate was
recrystallized from isopropanol (yield 0.91 g, 96 %). 1H NMR (400MHz,
CDCl3): δ = 2.06 (s, 3H; CH3), 3.01 (s, 3H; N-CH3), 5.83 (s, 1H; ChH),
7.25-8.36 (m, 7H; ArH), 11.40 ppm (s, 1H, N-H). 13C NMR (100 MHz,
CDCl3): δ = 19.20, 29.64, 92.19, 124.05, 127.50, 129.0, 134.33, 137.68,
165.95, 187.26 ppm. IR (oil): ~1620 (shoulder) (νC=N), 1598 (νC=O), 1552
(νC=C) cm-1. MS: m/z calculated for C15H15NO 225.29, found: 224 [M-1].
Elemental analysis calculated (%) for C15H15NO: C 79.97; H 6.71; N 6.22;
found: C 79.82; H 6.93; N 6.38.
Synthesis boron difluoride 3-methylamino-1-(anthracen-9-yl)but-2-en-1-
onate (3e): The compound 3e was prepared from 3-methylamino-1-
anthronyl-4-but-2-en-1-on: (0.35 g, 1.27 mmol) according to the method
for 3b. The formed brown precipitate was recrystallized from a mixture
isopropanol–acetonitrile (yield 0.21 g, 51 %), m.p. 183-185 °C. 1H NMR
(400MHz, CDCl3): δ = 2.29 (s, 3H; CH3), 3.37 (s, 3H; N-CH3), 5.80 (s, 1H;
ChH), 7.45-8.49 ppm (m, 9H; ArH). 13C NMR (100 MHz, CDCl3): δ = 33.02,
44.84, 104.09, 118.95, 125.24, 125.39, 126.73, 128.46, 129.25, 130.96,
171.15, 193.07 ppm. IR (oil): 1633 (νC=N), 1562 (νC=C). MS: m/z
calculated for C19H16BF2NO 323.14, found: 323,0 [M]. Elemental analysis
calculated (%) for C19H16BF2NO: C 70.62; H 4.99; N 4.33; found: C 70.31;
H 5.18; N 4.62.
Synthesis of boron difluoride 3-methylamino-1-(naphthalen-2-yl)but-2-en-
1-onate (3d): The compound 3d was prepared from 3-methylamino-1-
(naphthalen-2-yl)but-2-en-1-one (0.85 g, 3.77 mmol) according to the
method for 3b. The formed precipitate was recrystallized from a mixture
isopropanol–acetonitrile (yield 0.71 g, 70 %), m.p. 140-141 °C. 1H NMR
(400 MHz, CDCl3): δ = 2.25 (s, 3H; CH3), 3.25 (s, 3H; N-CH3), 6.13 (s, 1H;
ChH), 7.25-8,50 ppm (m, 7H; ArH). 13C NMR (100 MHz, CDCl3): δ = 20.49,
32.81, 92.27, 95.92, 123.06, 126.74, 129.25, 132.78, 134.97, 168.49,
171.10, 193.06 ppm. IR (oil): 1638 (νC=N), 1539 (νC=C). MS: m/z
calculated for C15H14BF2NO 273.08, found: 272,0 [M-1]. Elemental
analysis calculated (%) for C15H14BF2NO: C 65.97; H 5.17; N 5.13; found:
C 65.74; H 5.31; N 5.27.
Computational details
Quantum chemistry simulations of electron absorption spectra of
compounds in different conformations were performed in a cluster
approximation using GAMESS program complexes.[60] The structural
parameters, energy characteristics, and electron structures of compounds
were determined at full geometry optimization in the basis 6-311G (d,p) by
the nonempirical method and the density functional method with the
exchange-correlation potential B3LYP. The compounds electron
absorption spectra with taking into account excited singlet and triplet states
were calculated by the TDDFT method in the basis 6-311G(d, p) with the
potential B3LYP.
Synthesis of 2e:
Synthesis of 3-amino-1-(anthracen-9-yl)but-2-en-1-one: 3-Amino-1-
(anthracen-9-yl)but-2-en-1-one was prepared from 1e (0.7 g, 2.2 mmol)
according to the method for 3-amino-1-(4-methoxyphenyl)-but-2-en-1-one.
The formed yellow-brown precipitate was recrystallized from a mixture
isopropanol–water (yield 0.43 g, 73 %). 1H NMR (400 MHz, CDCl3): δ =
2.00 (s, 3H; CH3), 5.44 (s, 1H; ChH), 7.25-8.41 (m, 9H; ArH), 10.43 ppm
(s, 2H; NH2). 13C NMR (100 MHz, CDCl3): δ = 22.55, 99.59, 118.93,
125.15, 125.93, 128.31, 131.23, 138.19, 162.53, 194.81 ppm. IR (oil):
3358 (νN-H), 1616 (νC=N), ~1600 (shoulder) (νC=O), 1539 (νC=C) cm-1.
MS: m/z calculated for C18H15NO 261.32, found: 260 [M-1]. Elemental
analysis calculated (%) for C18H15NO: C 82.73; H 5.79; N 5.36; found: C
82.48; H 5.93; N 5.62.
Acknowledgements
Studies were supported by the „Far East“ Program for
Fundamental Studies of the Far Eastern Branch of the Russian
Academy of Sciences (Grant № 18-3-027). We are grateful
Shimadzu for their equipment providing an opportunity to conduct
research at a very high scientific level. The authors are grateful to
PhD (Phys.-Math.) A.A. Sergeev (Institute of Automation and
Control Processes Far Eastern Branch of the Russian Academy
of Sciences) for determining of the absolute fluorescence
quantum yields of crystals.
Synthesis of boron difluoride 3-amino-1-(anthracen-9-yl)but-2-en-1-onate
(2e): The compound 2e was prepared from 3-amino-1-(anthracen-9-yl)but-
2-en-1-one (0.35 g, 1.34 mmol) according to the method for 2b. The
formed yellow precipitate was recrystallized from a mixture isopropanol–
acetonitrile (yield 0.24 g, 58 %), m.p. 197-199 °C. 1H NMR (400MHz,
CDCl3): δ = 2.39 (s, 3H; CH3), 5.90 (s, 1H; ChH), 7.48-8.53 ppm (m, 9H;
ArH). 13C NMR (100 MHz, CDCl3): δ = 24.04, 102.45, 125.10, 125.49,
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Keywords: boron difluoride β-ketoiminate • boron difluoride β-
diketonate • luminescence • quantum chemistry modeling •
crystallization-induced emission
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FULL PAPER
Elena V. Fedorenko,
Anatolii G. Mirochnik, Anton Yu.
Beloliptsev, Irina V. Svistunova,
Galina O. Тretyakova*
Page No. – Page No.
Synthesis, molecular design and
crystallization-induced emission of
novel boron difluorides β-
ketoiminates
A series of new nitrogen-containing analogs of boron difluoride benzoylacetonates
with hydrogen and methyl substituents at the nitrogen atom have been synthesized.
It is established that the luminescence of crystals of boron difluoride β -ketoiminates
depends essentially on the nature of the substituent at the nitrogen atom: the
luminescence of complexes with a methyl substituent has the monomeric nature,
but for boron difluoride β-ketoiminates with the small hydrogen substituent the
crystals luminescence is caused by the luminescence of excimers and aggregates
on their basis.
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