N,O π-Conjugated 4-Substituted 1,3-Thiazole BF2 Complexes: Synthesis and Photophysical Properties

Article abstract of DOI:10.1021/acs.joc.7b02239

A series of 1,3-thiazole-based organoboron complexes has been designed and synthesized by acylation of 2-amino 4-subsituted 1,3-thiazoles with (4-dimethylamino)benzoyl chloride and the subsequent BF₂ complexation reaction. The influence of substituents in position 4 of the thiazole ring on photophysical properties of the complexes has been investigated. Synthesized thiazolo[3,2-c][1,3,5,2]oxadiazaborinines mainly showed intensive fluorescence in solutions. Complex with a 4,5-unsubstituted thiazole unit demonstrated an aggregation induced emission (AIE) effect and a very high fluorescent quantum yield (94%) in the solid state because of the inhibition of π-π/π-n interactions in the molecular packing.

Full text of DOI:10.1021/acs.joc.7b02239

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Article
N,O #-Conjugated 4-Substituted-1,3-Thiazole BF2
Complexes: Synthesis and Photophysical Properties
Mykhaylo A. Potopnyk, Roman Lytvyn, Yan Danyliv, Magdalena Ceborska,
Oleksandr Bezvikonnyi, Dmytro Volyniuk, and Juozas Vidas Grazulevicius
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b02239 • Publication Date (Web): 04 Jan 2018
Downloaded from http://pubs.acs.org on January 4, 2018
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N,O π-Conjugated 4-Substituted-1,3-Thiazole BF2 Complexes: Synthesis and Photophysical
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Properties
Mykhaylo A. Potopnyk,*,† Roman Lytvyn,‡,# Yan Danyliv,‡ Magdalena Ceborska,§ Oleksandr
Bezvikonnyi,‡ Dmytro Volyniuk,‡ and Juozas Vidas Gražulevičius*,‡
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†Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01ꢀ224, Warsaw, Poland, eꢀmail:
potopnyk@gmail.com
‡Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl. 19, LTꢀ50254
Kaunas, Lithuania
#Department of Organic Chemistry, Ivan Franko National University of Lviv, Kyryla and Mefodia St. 6, 79005
Lviv, Ukraine
§Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01ꢀ224, Warsaw, Poland
Abstract:
A
series of 1,3ꢀthiazole based
organoboron complexes have been designed and
synthesized by acylation of 2ꢀaminoꢀ4ꢀsubsitutedꢀ
1,3ꢀthiazoles
with
(4ꢀdimethylamino)benzoyl
chloride, and the subsequent BF2 complexation
reaction. The influence of substituents in position 4
of the thiazole ring on photophysical properties of
the complexes has been investigated. Synthesized
thiazolo[3,2ꢀc][1,3,5,2]oxadiazaborinines
mainly
showed intensive fluorescence in solutions.
Complex with 4,5ꢀunsubstituted thiazole unit
demonstrated aggregation induced emission (AIE)
effect and very high fluorescent quantum yield (94%) in the solid state, because of the inhibition
of π−π/π−n interactions in the molecular packing.
Introduction
The evolution of new technologies entails an intensive scientific research in the area of photoꢀ
and electroactive organic materials. The development of luminescent compounds, which can
serve as components of various optoelectronic devices such as organic lightꢀemitting diodes
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(OLEDs)1ꢀ5 or lightꢀemitting electrochemical cells (OLECs),6,7 optical sensing materials in
biological8ꢀ10 and supramolecular11ꢀ13 systems is one of the biggest scientific challenges.
In this context, organoboron complexes have many advantages compared to other fluorophores
(porphyrins, metal complexes, etc.) including strong absorption bands in UV and visible regions,
high fluorescent quantum yields, photostability, relatively long excitedꢀstate lifetime (1–5 ns),
good solubility in common organic solvents; insensitivity to the environment e.g. pH.14
Currently, the most investigated organoboron compounds are boronꢀdipyrromethene (BODIPY)
derivatives.15,16 Unfortunately, despite the intensive fluorescence of BODIPY dyes in solution,
their emission in the solid state is usually weak, which limits optoelectronic applications.17
In the last few years, a study of different boron (III) organic complexes, including other than
pyrrole heterocyclic units, was the subject of great research interest.17 They are very attractive
because of their optical variability and synthetic convenience. However, in contrast to boron
complexes with N,Nꢀchelating ligands,18ꢀ25 N,Oꢀanalogues were little investigated. Mainly those
based on phenolic26ꢀ37 or βꢀketoiminate38ꢀ43 ligands were reported, while the complexes formed
from amid group containing ligands are presented only as pyridine and 1,8ꢀnaphthyridine
derivatives.18,43ꢀ47 The use of N,O πꢀconjugated ligands with carbonyl Oꢀ and heterocyclic Nꢀ
coordinating centers can opens the way to obtain various new boron (III) complexes with
interesting properties. The design of the donorꢀacceptor type systems can lead to attractive
electronic properties, such as chromism, charge transporting properties, πꢀconjugated electronic
states recombination.48ꢀ50
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In this article we report on the synthesis and photophysical properties of thiazolo[3,2ꢀ
c][1,3,5,2]oxadiazaborinine derivatives.
Results and Discussion
Synthesis of Boron Complexes
Our strategy involves the incorporation of electron donating and accepting groups into the
complex structure, which is anticipated to result in a donorꢀacceptor system. We have chosen
2,2ꢀdifluoroꢀ1,3,5,2ꢀoxadiazaborinine unit as previously known acceptor.43ꢀ47 On the other hand,
4ꢀdimethylaminophenyl group has been used as effective donor. To investigate the influence of
substituents at the position 4 of the thiazole ring on photophysical properties of these boron dyes,
we designed compounds with corresponding groups.
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In order to realize this idea, we developed a simple synthetic way for the preparation of such
complexes. 4ꢀRꢀthizolꢀ2ꢀamines were selected as useful building blocks for construction the
complexes. Unsubstituted thiazolꢀ2amine (2a) is commercial available. 4ꢀMethylthiazolꢀ2ꢀamine
(2b) was prepared by reaction between acetone (1b), iodine, and thiourea in 37% yield. The
other 4ꢀRꢀthizolꢀ2ꢀamines (2c–g) were obtained by the Hantzsch thiazole reaction of 2ꢀ
bromoketones (1c–g) with thiourea in 68–97% yields. To prepare the N,O ligands, 4ꢀsubstituted
thiazolꢀ2ꢀamines 2a–g were acylated by (paraꢀdimethylamino)benzoyl chloride 3 in the basic
conditions in refluxing 1,4ꢀdioxane to provide amides 4a–g in 46–80% yields. Ligands 4a–g
were transformed into boron complexes 5a–g by the treatment with boron trifluoride in the
presence of diisopropylethylamine (DIPEA) in fair to good (48−77%) yields (Scheme 1). Such
obtained complexes have different substitutes at position 4 of the thiazole ring, including donor
and acceptor groups. All the synthesized compounds were characterized by highꢀresolution mass
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spectrometry and the IR and NMR analysis (1H and C for amines 2b–g and ligands 4a–g; and
1H, 13C, and 19F for complexes 5a–g). In addition, the structures of 5a and 5c–e were further
confirmed by singleꢀcrystal Xꢀray analysis (Figure 1–4 and Tables S1–S4 in the Supporting
Information).
Scheme 1. Synthesis of Complexes 5a–g
X-Ray Analysis
Xꢀray analysis of complexes 5a and 5c–4e confirmed that, the boron atom is coordinated in a
tetrahedral geometry by nitrogen, oxygen and two fluorine atoms. In the solid state, compound
5a has definitely nonꢀplanar geometry. Dimetylaminophenyl group is twisted against thiazoloꢀ
oxadiazaborinine unit: the torsion angle of C3−C4−C9−N2 is 24.2° (Figure 1).
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Figure 1. ORTEP diagram of complex 5a. The ellipsoid contour of probability level is 50%.
On the other hand, complex 5c exhibits almost planar structure, including ester group at the
thiazole unit (the torsion angles of C7−C6−C9−N2 and O2−C13−C10−N3 are 4.0° and 5.1°,
respectively) (Figure 2). Another situation is observed in the case of compounds 5d and 5e: the
main part of the molecules remain flat; however, the aryl substituents at position 4 of thiazole
ring are twisted to the rest of the molecules. For complex 5d, the torsion angles of
C16−C11−C10−N2 and C6−C1−C7−N1 are 4.3° and 59.2°. While, the value of the
corresponding angles of dye 5e (C5−C6−C9−N4 and C18−C13−C12−N2) are 3.4° and 58.1°,
respectively (Figure 3 and 4).
Figure 2. ORTEP diagram of complex 5c. The ellipsoid contour of probability level is 50%.
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Figure 3. ORTEP diagram of complex 5d. The ellipsoid contour of probability level is 50%.
Figure 4. ORTEP diagram of complex 5e. The ellipsoid contour of probability level is 50%.
Electrochemical Properties
The cyclic voltammetry technique was used to explore the redox behavior of dyes 5a–g. The
oxidation and reduction scans were performed in deoxygenated dichloromethane solution at
room temperature with tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting
electrolyte. Onset reduction and onset oxidation potentials, as well as, the electron affinities
(EAs) and the ionization potentials (IPs) of complexes are summarized in Table 1 and cyclic
voltammograms are shown in Figures S1–S7 in the Supporting Information. The values of IP are
mostly contained in a narrow range from 5.03 to 5.08 eV; however for compound with additional
donor (4ꢀdimethylaminophenyl) substituent at thiazole ring (5e) the corresponding value is
smaller (4.76 eV). Electron affinity is changing from 2.20–2.35 eV for compounds 5a–d, and 5f
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to 2.59 eV for 5e, and is increasing significantly to 2.95 eV for complex with 4ꢀnitrophenyl
substituent at thiazole ring (5g).
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Table 1. Onset Reduction and Onset Oxidation Potentials, Electron Affinities and
Ionization Potentials of Complexes 5a–g
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Compound
Eredonset, V
ꢀ2.112
ꢀ2.203
ꢀ2.056
ꢀ2.133
ꢀ1.810
ꢀ2.046
ꢀ1.454
Eoxonset, V
0.674
0.636
0.663
0.647
0.355
0.676
0.625
EA, eV
2.29
2.20
2.34
2.27
2.59
2.35
2.95
IP, eV
5.07
5.04
5.06
5.05
4.76
5.08
5.03
5a
5b
5c
5d
5e
5f
5g
Photophysical Characterization of Complexes 5a–g in Solutions
Having established a structural and electrochemical data of boron complexes 5a–g, we
evaluated their photophysical properties. The absorption and fluorescence spectra of the
solutions of compounds 5a–g are demonstrated in Figure 5. The obtained data are summarized in
Table S5 in the Supporting Information. The characteristic absorption peak, with the maximum
absorption wavelengths at 402–417 nm, showed almost no variation with changing solvent
polarity. The molar absorption coefficient values are changed from the minimum for complex 5e
(46,700–50,600 Mꢀ1cmꢀ1) to maximum for 5g (60,100–67,600 Mꢀ1cmꢀ1).
The dilute solutions of 5a–d,f–g show one very similar emission band centered with the
maxima in toluene at 437–448 nm, in DCM at 453–456 nm, in THF at 453–462 nm, and in
acetonitrile at 453–477 nm; while compound 5e is characterized by bathochromic shift (emission
maximum in toluene at 518 nm, in DCM at 590 nm, and in THF at 616 nm). In acetonitrile,
complex 5e does not show essential fluorescence. The solvent effect on the fluorescence
properties of 5a–g is manifested in increasing the value of λem and Stokes shift with the increase
of the solvent polarity, while fluorescence quantum yields are decreased. These observations
indicate that the fluorescence emission of dyes 5a–g was partially or fully originated from
photoinduced intramolecular charge transfer (ICT) state.
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Figure 5. Absorption (solid lines) and emission (dashed lines) spectra of 5a–g recorded in
different solvents
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Complexes 5a–d,f showed very high fluorescent quantum yields in nonꢀpolar solvents, while
these parameters in acetonitrile are weak. Another properties were observed for complexes 5e
and 5g. Complex 5e showed comparatively good quantum yield in toluene (0.66), but very small
in DCM, THF and MeCN. Complex 5g exhibited very weak emission in every investigated
solvent. For the THF solutions of the investigated complexes, the lifetimes of excited state were
measured (Table 2). It is worth noting that value of the lifetime of compound 5e (0.21 ns) is
considerably smaller that for the rest of complexes (1.39–2.24 ns).
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Table 2. Lifetime of the Excited State of Complexes 5a–g in THF
Compound
5a
5b
5c
5d
5e
5f
5g
τ, ns
2.22
2.24
2.10
2.06
0.21
1.39
1.64
Quantum Chemical Calculation
To understand the absorption properties of the synthesized complexes, density functional
theory (DFT) calculations were performed using the Gaussian 09 software package.51 All
geometrical structures are optimized and molecular orbitals calculated at the B3LYP/6ꢀ31G*
level. The calculated HOMOꢀLUMO plots are given in Figure 6.
In compounds 5d–g, the aryl groups at position 4 of the thiazole ring are twisted in the ground
state, what is agreed with Xꢀray analysis of 5d and 5e (Figures 3 and 4). Thus, these substituents
are deconjugated with the rest of the molecule. The electron distribution of the HOMOs and
LUMOs for 5a–g is subjected to the general rule that the HOMO electrons are predominantly
located on the dimethylaminophenyl group while LUMO electrons are mainly located on
thiazoloꢀoxadiazaborinine moiety. The exceptions are compounds with weak emission properties
(5e and 5g). In the case on complex 5e, there are two donor (dimethylaminophenyl) groups and
in HOMO the electron distribution are shifted to donor substituent at thiazole ring, while
HOMOꢀ1 is very similar to HOMO of compounds 5a–d and 5f–g. The specific situation is
observed for compound 5g: LUMO is shifted from fluorophore unit and preferably located on
nitroꢀphenyl group. However, LUMO+1 has an analogical shape comparably with LUMO of the
rest of complexes.
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Figure 6. Frontier molecular orbitals of complexes 5a–g.
To calculate singlet transitions timeꢀdependent DFT (TDꢀDFT) computations were also
performed at the B3LYP/6ꢀ31G* level, using previously obtained optimized structures. The
calculated excitation energies for the six lowest singlet excited state, maximum absorption
wavelengths (λmax), oscillator strengths (f) and molecular contribution of the leading
configurations are shown in Table S6 in the Supporting Information.
For compounds 5a–d,f the excitation to the first singlet excited state (S0→S1) is preferable (f ~
1, λmax = 381–391 nm). Then, these complexes exhibit the reverse transition S1→S0, which is
accompanied by light emission. On the other hand, compound 5e absorbs light preferably by
transition S0→S2 (f = 1.1481, λmax = 380 nm), when electron moves from HOMOꢀ1 to LUMO.
For compound 5g, the excitation also occurs dominantly by S0→S2 transition (f = 1.1688, λmax
=
393 nm). However, in this case electron moves from HOMO to LUMO+1. Probably, the deꢀ
excitation of molecules 5e and 5g includes several transitions (S2→S1/S2→T1 and following
S1→S0/T1→S0), which finally provide to the quenching of fluorescence.
Photophysical Characterization of Complexes 5a–g in the Solid State
To study the solidꢀstate photophysical properties of the synthesized complexes, the thin films
were obtained by spinꢀcasting technique from DCM solutions. The emission maxima of the solid
samples of all the studied thiazoleꢀboron complexes are redꢀshifted with respect to those of the
corresponding solutions (Figure 7, Table 3). The films of most of the synthesized dyes showed
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relatively weak fluorescence quantum yields (Ф = 0.07–0.25), which were apparently
predetermined by aggregation induced quenching. Compound 5g in the solid state as well as in
the dilute solution was almost nonꢀemissive (Ф < 0.01). In contrast, the thin film of 5a exhibited
very high fluorescence quantum yield (0.94), which is comparative with that of dilute solutions
in nonpolar solvents (toluene, DCM and THF).
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Figure 7. Overlaid normalized emission spectra of 5a–g in the solid state.
Table 3. Photophysical Data of Complexes 5a–g in the Solid Samples
Compound
λem, nm
512
Ф
τ, ns
0.94
0.12
0.09
0.25
0.10
0.07
<0.01
2.08, 8.83
1.56, 5.66
1.85, 8.79
0.73, 7.51
1.62, 6.11
1.33, 6.35
1.94, 10.27
5a
5b
5c
5d
5e
5f
473
502
513
554
514
468
5g
The value of fluorescent quantum yield in the solid state largely depends on interactions
between the molecules in the crystal packing. In this context, π−π intermolecular interactions can
inhibit the fluorescence.39
To consider the differences the quantum yield, we carefully analyzed the molecular packing of
complexes 5a, c–e. As shown on Figure 8, molecules 5c are linked by CH–O (2.93 Å) and CH–F
(3.48 Å) hydrogen bonds forming the dimers in the top view. On the other hand, these molecules
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are organized in the dimers by π−π and π−n interactions (C−C: 3.43−3.59 Å; C−N: 3.42−3.65 Å)
in the side view. Additionally, π−π/π−n interactions were observed for each of these dimers
(C−C: 3.41−3.65 Å; C−N: 3.47−3.66 Å), forming stoking columns. Because of the relatively
effective π−π/π−n interactions, compound 5c exhibit weak fluorescent quantum yield (9%) in the
solid state.
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Figure 8. Molecular packing of complex 5c: (a) top view; (b) side view; (c) list of intermolecular
interactions. Greenꢀ and light blueꢀdotted lines show π−π and π−n interactions; blueꢀdotted lines
show hydrogen bonds.
Complex 5e also exhibits wellꢀordered packing. The molecules form a netꢀtype structure by
connection via CH–N (3.50 Å), CH–S (3.80 Å), and two CH–F (3.21 and 3.44 Å) hydrogen
bonds. Moreover, the dimethylaminophenyl groups at the position 4 of the thiazole ring
demonstrate π−π and π−n interactions (C–C: 3.35–3.59 Å; C–N: 3.36–3.67 Å) (Figure 9). As
result, in this case the relatively strong π−π/π−n interactions provide to the weak fluorescence in
the solid state (Ф = 10%).
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Figure 9. Molecular packing of complex 5e: (a) top view; (b) side view; (c) list of intermolecular
interactions. Greenꢀ and light blueꢀdotted lines show π−π and π−n interactions; magentaꢀ, blueꢀ,
and redꢀdotted lines show hydrogen bonds.
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As shown on Figure 10, boron derivative 5d form layers consisting of dimers interacting via a
parallel CH−π interactions (CH–C: 3.33–3.49 Å). However, in this structure, effective π−π/π−n
interactions do not observed (Figure 12). Therefore, compound 5d is considered to have weaker
intermolecular interactions than 5c and 5e, and the slightly higher fluorescent quantum yield of
5d (Ф = 25%) is probably owing to the nonꢀavailability π−π and π−n interactions.
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Figure 10. Molecular packing of complex 5d: (a) top view; (b) side view; (c) list of
intermolecular interactions. Greenꢀdotted lines show CH−π interactions in dimers.
For complex 5a, the molecular packing is definitely different than for dyes 5c–e (Figure 11). In
this case, neighboring molecules are connected by weak CH–F hydrogen bonds (3.04 and
3.31 Å). The dimethylaminophenyl groups are twisted and orientated at some angle towards each
other. The molecules do not make any effective π−π or π−n interactions. Because of the
inhibition of effective π−π/π−n interactions, the quantum yield of complex 5a in the solid state is
very high (94%).
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Figure 11. Molecular packing of complex 5a: (a) top view; (b) side view; (c) list of
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intermolecular interactions. Blueꢀdotted lines show hydrogen bonds.
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Water-Induced Aggregation of Complexes 4a in THF
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Additionally, the fluorescence properties of 5a were investigated in THFꢀwater mixtures of
various ratios (5a is soluble in THF but not soluble in water). The fluorescence intensity
decreased with increasing water content to 80%. However, when the water content was increased
to 90%, the dramatic increase of the fluorescence intensity and the change of emission colour
from blue (λem = 454 nm) to green (λem = 508 nm) were observed (Figure 12). These changes
resulted from the formation of aggregates in the THFꢀwater mixtures, which definitely indicates
the effect of aggregation induced emission (AIE)52 for dye 5a.
Figure 12. (A) Emission spectra of 5a in THF/water mixture with different fraction of water and
(B) change of emission intensity of 5a with water fraction.
Analogical investigation of emission activity of complex 5d (Ф = 25% in the solid state) in
THF/H2O solutions demonstrated missing of the AIE effect (Figure 13). This can by explain by
molecular packing. Probably, the reason of the deficiency of AIE effect in this case is formation
of the dimer molecules 5d in the solid state (Figure 10), which is not observed for boron complex
5a (Figure 11).
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Figure 13. (A) Emission spectra of 5d in THF/water mixture with different fraction of water and
(B) change of emission intensity of 5d with water fraction.
Conclusions
In conclusion, we developed new N,O πꢀconjugated donorꢀacceptor organoboron complexes
containing thiazole building blocks. Compound with unsubstituted thiazole unit (5a) exhibits
very high emission in the solutions. The influence of the substitute at position 4 of the thiazole
ring on electronic and photophysical properties was investigated. The incorporation of methyl or
ethoxycarbonyl groups into the molecular structure (compounds 5b,c) does not affect
significantly on the photophysical parameters in the solution. The aryl groups at position 4 of the
thiazole ring are twisted against fluorophore (thiazoloꢀoxadiazaborinine) unit. As the result,
depending on donor/acceptor strength, these substituents can cause the changes in the excitation
transitions, which can provide to the fluorescence quenching. In the solid state, most of the
synthesized boron complexes showed relatively weak fluorescence quantum yields (7–12%),
which were apparently predetermined by aggregation induced quenching. The thin film of
complex 5d exhibited higher fluorescence quantum yield (25%), because of the nonꢀavailability
π−π and π−n intermolecular interactions in the solid state. In contrast, besause of the unusual
molecular packing and inhibition of π−π/π−n interactions, complex 5a exhibited very high
fluorescence quantum yield (94%) in the solid state, and demonstated aggregation induced
emission effect.
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Experimental Section
General
All chemicals [including 1ꢀ(4ꢀ(dimethylamino)phenyl)ethanꢀ1ꢀone, ethyl bromopyruvate (1c),
2ꢀbromoacetophenone (1d), 4ꢀ(2ꢀbromoacetyl)benzonitrile (1f), 2ꢀbromoꢀ1ꢀ(4ꢀnitrophenyl)ethanꢀ
1ꢀone (1g), and thiazolꢀ2ꢀamine (2a)] were received from commercial sources (Aldrich, Alfa
Aesar, TCI or Acros Organics) and used without further purification. All reported NMR spectra
were recorded with Varian Mercury 400 MHz (at 400 MHz, 100 MHz, and 375 MHz for 1H, 13C,
and 19F NMR spectra, respectively), Varian VNMRS 500 MHz (at 500 MHz, 125 MHz, and 470
MHz for 1H, 13C, and 19F NMR spectra, respectively) or Varian VNMRS 600 MHz (at 150 MHz
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for C NMR spectra) spectrometers for solutions in CDCl3 or DMSOꢀd6 and TMS as the internal
standard. Infrared (IR) spectra were recorded as a solid using attenuated total reflectance (ATR)
method or as a film (CH2Cl2) with a Jasco FT/IRꢀ6200 spectrometer in the 4000–400 cmꢀ1
region. Mass spectra were recorded with Synapt G2ꢀS HDMS (Waters Inc) mass spectrometer
equipped with an electrospray ion source and qꢀTOF type mass analyzer. The instrument was
controlled and recorded data were processed using MassLynx V4.1 software package (Waters
Inc). Thin layer chromatography (TLC) was performed on silica gel plates coated with
fluorescent indicator. Colunm chromatography was performed on silica gel (Merck, 230ꢀ400
mesh). Melting points were measured on Automatic Melting Point System (OptiMelt, Stanford
Research Systems).
UV/Vis spectra of 10ꢀ5 M solutions of the compounds were recorded in quartz cells using
Perkin Elmer Lambda 35 spectrometer. Photoluminescence (PL) spectra of 10ꢀ5 M solutions of
the compounds were recorded using Edinburgh Instruments' FLS980 Fluorescence Spectrometer.
Thin solid films for recording of PL spectra were prepared by using spinꢀcoating technique
utilizing SPSꢀEurope Spin150 Spin processor using 2.5 mg/ml solutions of the compounds in
DCM on the preꢀcleaned quartz substrates. Fluorescence quantum yields of the solutions and of
the solid films were estimated using the integrated sphere method. An integrating sphere
(Edinburgh Instruments) coupled to the FLS980 spectrometer was calibrated with two standards:
quinine sulfate in 0.1 M H2SO4 and rhodamine 6G in ethanol. Each quantum yield measurement
was repeated 5 times and the error corridor was estimated. Fluorescence decay curves of the
samples were recorded using a timeꢀcorrelated single photon counting technique utilizing the
PicoQuant PDL 820 picosecont diode laser as an excitation source. Electrochemical
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measurements were carried out using mAUTOLAB Type III apparatus, glassy carbon electrode
(diam. 2 mm), platinum coil and silver wire as working, auxiliary and reference electrode,
respectively and the scan rate at 100mV/s. Potentials are referenced with respect to ferrocene
(Fc), which was used as the internal standard. Cyclic voltammetry experiments were conducted
in a standard oneꢀcompartment cell, in DMF (SigmaꢀAldrich, HPLC grade), under argon. 0.1M
Bu4NPF6 (SigmaꢀAldrich, 99%) was used as the supporting electrolyte. The concentration of
compounds was equal 0.1·mmol/dm3. Deaeration of the solution was achieved by a nitrogen
bubbling through the solution for about 10 min before measurement. All electrochemical
experiments were carried out under ambient conditions. Ionization potentials (IP) and electron
affinities (EA) were determinate from the onset oxidation potentials (Eoxonset) and the onset
reduction potentials (Eredonset), respectively: IP = Eoxonset + 4.4; EA = Eredonset + 4.4 (Table 1).
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X-ray Diffraction
Crystals of compounds 5a and 5c–e were obtained by the slow evaporation of their solution in
DCM/hexane (1:1). The Xꢀray measurements were performed at 100 K on SuperNova Agilent
diffractometer using MoKα (λ = 0.71073 Å) and CuKα (λ = 1.54184 Å) radiation. Data
reduction and analysis were carried out with CrysAlisPro (Agilent Technologies, CrysAlisPro,
Version 1.171.35.21b). The structures were solved by direct methods and refined using SHELXL
Software Package (Sheldrick, G.M. Acta Cryst. 2008, 64a, 112). Crystals of 5a were of very low
quality allowing structure confirmation but not enabling good quality refinement.
Crystallographic data for 5a, 5c–e have been deposited with the Cambridge Crystallographic
Data Centre. Copies of the data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: +44(0)ꢀ1223ꢀ336033 or eꢀmail:
deposit@ccdc.cam.ac.uk].
Synthesis
4-Methylthiazol-2-amine (2b) was synthesized using a modified literature procedure.53 To a
solution of thiourea (1.00 g, 13.14 mmol) in acetone (1.5 mL) was added iodine (1.67 g,
6.57 mmol) and the reaction mixture was heated under reflux for 4h. After cooling, the solvent
was removed by vacuum. The reaction mixture was poured onto ice cold water (15 mL) and
adjusted to pH ~ 8 with ammonium hydroxide (25% aqueous solution). The water layer was
extracted with ether (5×30 mL), the organic phase was dried (Na2SO4) and concentrated. The
crude product 2b was purified by column chromatography (hexanes/AcOEt = 2:1 to 1:2, v/v) to
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afford pure yellow oil in 37% yield (0.56 g). H NMR (400 MHz, CDCl3): δ = 6.05 (1H, d, J =
1.0 Hz, thiazoleꢀH), 5.31 (2H, s, NH2), 2.21 (3H, d, J = 1.0 Hz, CH3) ppm; 13C NMR (100 MHz,
CDCl3): δ = 167.5, 148.5, 102.4, 17.1 ppm. IR (film): 3435, 3294, 3114, 2979, 2949, 2917,
1620, 1520, 1442, 1378, 1332, 1144, 1107, 1035, 969, 841 cmꢀ1.
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Synthesis of 4-R-thiazol-2-amines 2c,d,f,g (General procedure A) was based on a previous
literature procedure.53 A mixture of 2ꢀhalogenoketone 1c,d,f,g (1 eq.) and thiourea (1 eq.) in
ethanol (15 mL) was refluxed for 4h. After cooling, water (30 mL) was added, next, ammonium
hydroxide (25% aqueous solution) was added dropwise to pH ~ 8. The product was filtered,
dried and used in the next step without further purification.
Ethyl 2-aminothiazole-4-carboxylate (2c) was obtained in 94% yield (523 mg) using general
procedure A from ethyl bromopyruvate (1c, 628 mg, 3.21 mmol) and thiourea (245 mg,
3.21 mmol). Mp. 142.5–144.2 °C, white powder. 1H NMR (400 MHz, DMSOꢀd6): δ = 8.31 (2H,
s, NH2), 7.59 (1H, s, thiazoleꢀH), 4.25 (2H, q, J = 7.2 Hz, CH2), 1.26 (3H, t, J = 7.2 Hz, CH3)
ppm; 13C NMR (100 MHz, DMSOꢀd6): δ = 168.9, 159.0, 136.0, 117.5, 61.1, 14.1 ppm. IR (film):
3437, 3254, 3125, 2988, 2897, 1691, 1617, 1538, 1368, 1337, 1239, 1076, 1021, 960, 875, 784,
748 cmꢀ1. HRMS (ESIꢀTOF) calcd for C6H8N2O2SNa [M + Na]+: 195.0204, found: 195.0197.
4-Phenylthiazol-2-amine (2d) was obtained in 97% yield (431 mg) using general procedure A
from 2ꢀbromoacetophenone (1d, 500 mg, 2.51 mmol) and thiourea (191 mg, 2.51 mmol). Mp.
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149.1–150.3 °C (lit.54 150–151 °C), white powder. H NMR (400 MHz, DMSOꢀd6): δ = 7.79
(2H, d, J = 8.0 Hz, ArꢀH), 7.35 (2H, dd, J = 8.0 Hz, J = 7.6 Hz, ArꢀH), 7.25 (1H, t, J = 7.6 Hz,
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ArꢀH), 7.03 (2H, s, NH2), 6.98 (1H, s, thiazoleꢀH) ppm; C NMR (100 MHz, DMSOꢀd6): δ =
168.2, 149.8, 134.9, 128.4 (2C), 127.1, 125.5 (2C), 101.4 ppm. IR (film): 3436, 3255, 3157,
3114, 1596, 1531, 1517, 1482, 1441, 1389, 1332, 1307, 1283, 1200, 1070, 1038, 1021, 909, 845,
771, 713 cmꢀ1. HRMS (ESIꢀTOF) calcd for C9H9N2S [M + H]+: 177.0486, found: 177.0485.
4-(2-Aminothiazol-4-yl)benzonitrile (2f) was obtained in 98% yield (443 mg) using general
procedure A from 4ꢀ(2ꢀbromoacetyl)benzonitrile (1f, 502 mg, 2.24 mmol) and thiourea (171 mg,
2.24 mmol). Mp. 242.4–244.2 °C, white powder. 1H NMR (400 MHz, DMSOꢀd6): δ = 7.96 (2H,
d, J = 8.4 Hz, ArꢀH), 7.80 (2H, d, J = 8.4 Hz, ArꢀH), 7.29 (1H, s, thiazoleꢀH), 7.16 (2H, s, NH2)
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ppm; C NMR (100 MHz, DMSOꢀd6): δ = 168.5, 148.1, 138.9, 132.5 (2C), 126.1 (2C), 119.0,
109.2, 105.4 ppm. IR (ATR): 3381, 3305, 3115, 2778, 2229, 1644, 1604, 1542, 1482, 1410,
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1343, 1284, 1196, 1174, 1133, 1044, 1012, 839, 742, 710 cmꢀ1. HRMS (ESIꢀTOF) calcd for
C10H8N3S [M + H]+: 202.0439, found: 202.0435.
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4-(4-Nitrophenyl)thiazol-2-amine (2g) was obtained in 93% yield (583 mg) using general
procedure A from 2ꢀbromoꢀ1ꢀ(4ꢀnitrophenyl)ethanꢀ1ꢀone (1g, 505 mg, 2.07 mmol) and thiourea
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(158 mg, 2.07 mmol). Mp. 284.3–285.7 °C (lit.54 285–286 °C), yellow powder. H NMR (400
MHz, DMSOꢀd6): δ = 8.29 (2H, d, J = 8.8 Hz, ArꢀH), 8.01 (2H, d, J = 8.8 Hz, ArꢀH), 7.55 (1H,
s, thiazoleꢀH), 6.73 (2H, s, NH2) ppm; 13C NMR (100 MHz, DMSOꢀd6): δ = 170.0, 147.0, 139.5,
136.0, 126.8 (2C), 124.2 (2C), 107.3 ppm. IR (ATR): 3399, 3306, 3146, 3115, 1644, 1594, 1539,
1519, 1504, 1411, 1334, 1204, 1110, 1077, 1039, 852, 844, 715 cmꢀ1. HRMS (ESIꢀTOF) calcd
for C9H8N3O2S [M + H]+: 222.0337, found: 222.0332.
Synthesis of 4-(4-(dimethylamino)phenyl)thiazol-2-amine (2e).
1ꢀ(4ꢀ(Dimethylamino)phenyl)ethanꢀ1ꢀone (1.00 g, 6.16 mmol) was dissolved in concentrated
H2SO4 (25 mL) and the solution was cooled to 0 °C. Bromine (0.98 g, 6.16 mmol) was added
dropwise over 1h. The reaction mixture was stirred for 2h and poured in ice water (~ 100 mL).
Saturated aqueous solution of K2CO3 was added to pH ~ 8 and the mixture was extracted with
DCM (3×100 mL). The organic layer was dried with Na2SO4, filtered, and concentrated. The
resulting crude product was purified by column chromatography (hexanes/ethyl acetate = 9:1,
v/v) to give 2ꢀbromoꢀ1ꢀ(4ꢀ(dimethylamino)phenyl)ethanꢀ1ꢀone (1e) (1.28 g, 86%). Mp. 90.5–
92.1 °C (lit.55 91–92 °C), green powder. H NMR (400 MHz, CDCl3): δ = 7.88 (2H, d, J = 8.9
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Hz, ArꢀH), 6.65 (2H, d, J = 8.9 Hz, ArꢀH), 4.35 (2H, s, CH2), 3.07 (6H, s, 2 × CH3) ppm; C
NMR (100 MHz, CDCl3): δ = 189.3, 153.8, 131.3 (2C), 121.7, 110.7 (2C), 40.0 (2C), 30.7 ppm.
2ꢀBromoꢀ1ꢀ(4ꢀ(dimethylamino)phenyl)ethanꢀ1ꢀone (1e, 700 mg, 2.89 mmol) was dissolved in
EtOH (30 mL). Thiourea (220 mg, 2.89 mmol) was added and the reaction mixture was refluxed
for 4h. After cooling, ethanol was removed by vacuum. The reaction mixture was poured onto
ice cold water (15 mL) and adjusted to pH ~ 8 with ammonium hydroxide (25% aqueous
solution). The water layer was extracted with DCM (3×30 mL), the organic phase was dried
(Na2SO4) and concentrated. The product 2e was purified by column chromatography
(DCM/MeOH = 100:0 to 99:1, v/v) to afford solid in 68% yield (430 mg). Mp. 188.0–190.3 °C,
yellow powder. 1H NMR (400 MHz, DMSOꢀd6): δ = 7.61 (2H, d, J = 8.9 Hz, ArꢀH), 6.90 (2H, br
s, NH2), 6.69 (2H, d, J = 8.9 Hz, ArꢀH), 6.65 (1H, s, thiazoleꢀH), 2.91 (6H, s, 2 × CH3) ppm; 13C
NMR (100 MHz, DMSOꢀd6): δ = 167.8, 150.4, 149.5, 126.4 (2C), 123.5, 112.0 (2C), 97.3, 40.0
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(2C) ppm. IR (ATR): 3456, 3357, 3264, 3118, 3090, 2925, 2806, 1638, 1609, 1542, 1514, 1496,
1442, 1359, 1336, 1228, 1199, 1168, 1126, 1065, 1040, 1002, 946, 817, 736 cmꢀ1. HRMS (ESIꢀ
TOF) calcd for C11H14N3S [M + H]+: 220.0908, found: 220.0909.
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Synthesis of ligands 4a–g (General procedure B). To a solution of amine 2a–g in 1,4ꢀdioxane
(20 mL) were added 4ꢀ(dimethylamino)benzoyl chloride (3, 1 eq.), distillated trimethylamine (3
eq.) and DMAP (0.05 eq.). The reaction mixture was refluxed for 24h. After cooling, a saturated
aqueous solution (50 mL) of NaHCO3 were added and the mixture was extracted with DCM (3 ×
40 mL). The combined organic layers were dried over Na2SO4, filtered and concentrated. The
product was purified by column chromatography (DCM/MeOH = 100:0 to 99:1, v/v).
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4-(Dimethylamino)-N-(thiazol-2-yl)benzamide (4a) was obtained in 72% yield (105 mg) using
general procedure B from 2a (59 mg, 0.59 mmol) and 3 (108 mg, 0.59 mmol). Mp. 163.0–
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165.2 °C, white powder. H NMR (400 MHz, CDCl3): δ = 12.33 (1H, s, NH), 7.97 (2H, d, J =
9.0 Hz, ArꢀH), 7.25 (1H, d, J = 3.8 Hz, thiazoleꢀH), 6.91 (1H, d, J = 3.8 Hz, thiazoleꢀH), 6.70
(2H, d, J = 9.0 Hz, ArꢀH), 3.06 (6H, s, 2 × CH3) ppm; 13C NMR (100 MHz, CDCl3): δ = 165.4,
160.9, 153.2, 136.9, 129.8 (2C), 118.8, 112.8, 111.1 (2C), 40.0 (2C) ppm. IR (ATR): 3300, 3159,
2938, 1655, 1601, 1535, 1440, 1374, 1320, 1286, 1194, 1167, 1127, 1062, 944, 891 829, 745 cmꢀ
1. HRMS (ESIꢀTOF) calcd for C12H13N3OSNa [M + Na]+: 270.0677, found: 270.0672.
4-(Dimethylamino)-N-(4-methylthiazol-2-yl)benzamide (4b) was obtained in 66% yield (115
mg) using general procedure B from 2b (76 mg, 0.67 mmol) and 3 (122 mg, 0.67 mmol). Mp.
214.4–216.1 °C, white powder. 1H NMR (400 MHz, CDCl3): δ = 10.88 (1H, s, NH), 7.81 (2H, d,
J = 9.0 Hz, ArꢀH), 6.66 (2H, d, J = 9.0 Hz, ArꢀH), 6.50 (1H, d, J = 1.0 Hz, thiazoleꢀH), 3.04 (6H,
s, 2 × CH3), 2.15 (3H, d, J = 1.0 Hz, thiazoleꢀCH3) ppm; 13C NMR (100 MHz, CDCl3): δ =
164.8, 159.3, 153.2, 146.9, 129.4 (2C), 118.6, 111.0 (2C), 107.8, 40.0 (2C), 16.80 ppm. IR
(film): 2921, 2812, 1653, 1604, 1526, 1442, 1371, 1290, 1195, 1135, 1064, 978, 944, 895, 827,
758, 724 cmꢀ1. HRMS (ESIꢀTOF) calcd for C13H15N3OSNa [M + Na]+: 284.0834, found:
284.0829.
Ethyl 2-(4-(dimethylamino)benzamido)thiazole-4-carboxylate (4c) was obtained in 46% yield
(117 mg) using general procedure B from 2c (138 mg, 0.80 mmol) and 3 (147 mg, 0.80 mmol).
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Mp. 163.5–165.2 °C, white powder. H NMR (400 MHz, CDCl3): δ = 10.03 (1H, s, NH), 7.84
(1H, s, thiazoleꢀH), 7.80 (2H, d, J = 9.2 Hz, ArꢀH), 6.69 (2H, d, J = 9.2 Hz, ArꢀH), 4.33 (2H, q, J
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= 7.2 Hz, CH2), 3.06 (6H, s, 2 × CH3), 1.36 (3H, t, J = 7.2 Hz, CH2CH3) ppm; C NMR (100
MHz, CDCl3): δ = 164.6, 161.6, 159.0, 153.4, 141.6, 129.2 (2C), 122.1, 117.5, 111.1 (2C), 61.3,
40.0 (2C), 14.3 ppm. IR (film): 3115, 2930, 1717, 1655, 1604, 1529, 1442, 1370, 1330, 1290,
1198, 1136, 1096, 1022, 945, 898, 826, 756 cmꢀ1. HRMS (ESIꢀTOF) calcd for C15H17N3O3SNa
[M + Na]+: 342.0888, found: 342.0880.
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4-(Dimethylamino)-N-(4-phenylthiazol-2-yl)benzamide (4d) was obtained in 70% yield (133
mg) using general procedure B from 2d (103 mg, 0.58 mmol) and 1 (107 mg, 0.58 mmol). Mp.
195.0–196.4 °C, white powder. 1H NMR (400 MHz, CDCl3): δ = 10.00 (1H, s, NH), 7.80 (2H, d,
J = 8.0 Hz, ArꢀH), 7.77 (2H, d, J = 8.8 Hz, ArꢀH), 7.37 (2H, dd, J = 7.2 Hz, J = 8.0 Hz, ArꢀH),
7.27 (2H, t, J = 7.2 Hz, ArꢀH), 7.13 (1H, s, thiazoleꢀH), 6.60 (2H, d, J = 8.8 Hz, ArꢀH), 3.01 (6H,
s, 2 × CH3) ppm; 13C NMR (100 MHz, CDCl3): δ = 164.5, 159.0, 153.2, 149.9, 134.5, 129.1
(2C), 128.6 (2C), 127.8, 126.0 (2C), 118.0, 111.0 (2C), 107.6, 39.9 (2C) ppm. IR (film): 3234,
3106, 3059, 2915, 1653, 1604, 1526, 1482, 1442, 1372, 1327, 1282, 1197, 1173, 1137, 1062,
1027, 946, 893, 825, 776, 758, 722 cmꢀ1. HRMS (ESIꢀTOF) calcd for C18H18N3OS [M + H]+:
324.1171, found: 324.1167.
4-(Dimethylamino)-N-(4-(4-(dimethylamino)phenyl)thiazol-2-yl)benzamide
(4e)
was
obtained in 80% yield (148 mg) using general procedure B from 2e (110 mg, 0.50 mmol) and 3
(110 mg, 0.50 mmol). Mp. 209.4–211.0 °C, green powder. 1H NMR (400 MHz, CDCl3): δ = 9.99
(1H, s, NH), 7.83 (2H, d, J = 9.0 Hz, ArꢀH), 7.69 (2H, d, J = 8.8 Hz, ArꢀH), 6.91 (1H, s,
thiazoleꢀH), 6.73 (2H, d, J = 8.8 Hz, ArꢀH), 6.66 (2H, d, J = 9.0 Hz, ArꢀH), 3.03 (6H, s, 2 ×
CH3), 2.97 (6H, s, 2 × CH3) ppm; 13C NMR (100 MHz, CDCl3): δ = 164.3, 158.7, 153.2, 150.4,
150.3, 139.1 (2C), 127.0 (2C), 123.3, 118.4, 112.4 (2C), 111.2 (2C), 104.4, 40.4 (2C), 40.0 (2C)
ppm. IR (ATR): 3108, 2896, 2803, 1649, 1609, 1524, 1495, 1441, 1368, 1331, 1283, 1231, 1197,
1133, 1064, 947, 892, 823, 758 cmꢀ1. HRMS (ESIꢀTOF) calcd for C20H23N4OS [M + H]+:
367.1593, found: 367.1593.
N-(4-(4-Cyanophenyl)thiazol-2-yl)-4-(dimethylamino)benzamide (4f) was obtained in 50%
yield (87 mg) using general procedure B from 2f (100 mg, 0.50 mmol) and 3 (91 mg,
0.50 mmol). Mp. 230.1–232.4 °C, yellow powder. 1H NMR (400 MHz, CDCl3): δ = 9.96 (1H, s,
NH), 7.87 (2H, d, J = 8.6 Hz, ArꢀH), 7.79 (2H, d, J = 9.0 Hz, ArꢀH), 7.61 (2H, d, J = 8.6 Hz, Arꢀ
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H), 7.27 (1H, s, thiazoleꢀH), 6.64 (2H, d, J = 9.0 Hz, ArꢀH), 3.05 (6H, s, 2 × CH3) ppm; C
NMR (100 MHz, CDCl3): δ = 164.5, 159.5, 153.3, 147.9, 138.5, 132.4 (2C), 129.2 (2C), 126.4
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(2C), 118.9, 117.7, 111.0 (2C), 111.0, 110.5, 40.0 (2C) ppm. IR (ATR): 3340, 3105, 2925, 2856,
2226, 1748, 1655, 1608, 1532, 1445, 1374, 1323, 1278, 1194, 1091, 1056, 944, 890, 850, 825,
752, 712 cmꢀ1. HRMS (ESIꢀTOF) calcd for C19H16N4OSNa [M + Na]+: 371.0943, found:
371.0936.
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4-(Dimethylamino)-N-(4-(4-nitrophenyl)thiazol-2-yl)benzamide (4g) was obtained in 62%
yield (113 mg) using general procedure B from 2g (110 mg, 0.50 mmol) and 3 (91 mg,
1
0.50 mmol). Mp. 276.2–277.1 °C, yellow powder. H NMR (400 MHz, DMSOꢀd6): δ = 12.39
(1H, s, NH), 8.29 (2H, d, J = 8.0 Hz, ArꢀH), 8.19 (2H, d, J = 8.0 Hz, ArꢀH), 8.04 (2H, d, J = 8.4
Hz, ArꢀH), 7.94 (1H, s, thiazoleꢀH), 6.75 (2H, d, J = 8.4 Hz, ArꢀH), 3.01 (6H, s, 2 × CH3) ppm;
13C NMR (100 MHz, DMSOꢀd6): δ = 164.8, 159.6, 153.0, 146.7, 146.3, 140.5, 129.8 (2C), 126.5
(2C), 124.1 (2C), 117.6, 112.5, 110.8 (2C), 39.6 (2C) ppm. IR (ATR): 3426, 3104, 2907, 2819,
1645, 1603, 1526, 1505, 1433, 1371, 1333, 1269, 1190, 1108, 1060, 945, 873, 824, 758, 726 cmꢀ
1. HRMS (ESIꢀTOF) calcd for C18H17N4O3S [M + H]+: 369.1021, found: 369.1014.
Synthesis of complexes 5a–g (General procedure C). To a solution of compound 4a–g in dry
DCM (20 mL) were added BF3·Et2O (10 eq.) and distillated N,Nꢀdiisopropylethylamine (20 eq.)
under an argon atmosphere. The reaction mixture was stirred for 24h at room temperature and
then washed with water. The organic phase was dried over anhydrous Na2SO4, and filtered. The
solvent was removed under reduced pressure and the crude product was purified by column
chromatography (hexanes/dichloromethane from 1:1 to 0:1, v/v).
4-(1,1-Difluoro-1H-1λ4,8λ4-thiazolo[3,2-c][1,3,5,2]oxadiazaborinin-3-yl)-N,N-
dimethylaniline (5a) was obtained in 58% yield (51 mg) using general procedure C from ligand
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4a (74 mg, 0.30 mmol). Mp. 245.2–246.8 °C, yellow powder. H NMR (400 MHz, CDCl3): δ =
8.18 (2H, d, J = 9.2 Hz, ArꢀH), 7.46 (1H, d, J = 4.4 Hz, thiazoleꢀH), 6.95 (1H, d, J = 4.4 Hz,
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thiazoleꢀH), 6.67 (2H, d, J = 9.2 Hz, ArꢀH), 3.09 (6H, s, 2 × CH3) ppm; C NMR (100 MHz,
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CDCl3): δ = 173.9, 167.0, 154.2, 132.3 (2C), 129.6, 117.4, 112.3, 110.9 (2C), 40.0 (2C) ppm; F
NMR (375 MHz, CDCl3): δ = –136.63 (d, J = 11.4 Hz), –136.69 (d, J = 11.4 Hz) ppm. IR (film):
3156, 3121, 2920, 2852, 1615, 1556, 1538, 1499, 1463, 1423, 1363, 1276, 1227, 1183, 1127,
1063, 940, 911, 874, 860, 820, 761, 724, 702 cmꢀ1. HRMS (ESIꢀTOF) calcd for
C12H12BN3OF2SNa [M + Na]+: 318.0660, found: 318.0654.
4-(1,1-Difluoro-7-methyl-1H-1λ4,8λ4-thiazolo[3,2-c][1,3,5,2]oxadiaza-borinin-3-yl)-N,N-
dimethylaniline (5b) was obtained in 51% yield (48 mg) using general procedure C from ligand
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4b (79 mg, 0.30 mmol). Mp. 224.0–226.3 °C, yellow powder. H NMR (400 MHz, CDCl3): δ =
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8.18 (2H, d, J = 9.2 Hz, ArꢀH), 6.67 (2H, d, J = 9.2 Hz, ArꢀH), 6.50 (1H, d, J = 0.7 Hz, thiazoleꢀ
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H), 3.08 (6H, s, 2 × CH3), 2.49 (3H, d, J = 0.7 Hz, thiazoleꢀCH3) ppm; C NMR (100 MHz,
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CDCl3): δ = 173.6, 166.2, 154.1, 141.9, 132.2 (2C), 117.5, 110.9 (2C), 106.9, 40.0 (2C), 14.9
ppm; 19F NMR (375 MHz, CDCl3): δ = –133.77 (d, J = 13.0 Hz), –133.84 (d, J = 13.0 Hz) ppm.
IR (film): 3114, 2911, 1609, 1573, 1567, 1488, 1451, 1402, 1370, 1285, 1227, 1192, 1135, 1056,
1000, 929, 897, 850, 822, 743, 708 cmꢀ1. HRMS (ESIꢀTOF) calcd for C13H15BN3OF2S [M + H]+:
310.0997, found: 310.0991.
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Ethyl
3-(4-(dimethylamino)phenyl)-1,1-difluoro-1H-1λ4,8λ4-thiazolo[3,2-
c][1,3,5,2]oxadiazaborinine-7-carboxylate (5c) was obtained in 48% yield (51 mg) using
general procedure C from ligand 4c (92 mg, 0.29 mmol). Mp. 193.6–195.4 °C, yellow powder.
1H NMR (500 MHz, CDCl3): δ = 8.19 (2H, d, J = 9.2 Hz, ArꢀH), 7.75 (1H, s, thiazoleꢀH), 6.67
(2H, d, J = 9.2 Hz, ArꢀH), 4.43 (2H, q, J = 7.5 Hz, CH2), 3.10 (6H, s, 2 × CH3), 1.42 (3H, t, J =
13
7.2 Hz, CH3) ppm; C NMR (125 MHz, CDCl3): δ = 174.8, 167.1, 157.3, 154.4, 136.2, 132.7
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(2C), 120.5, 116.7, 110.9 (2C), 62.3, 40.0 (2C), 14.0 ppm; F NMR (470 MHz, CDCl3): δ = –
131.57 (d, J = 6.6 Hz), –131.63 (d, J = 10.8 Hz) ppm. IR (film): 3133, 2922, 1730, 1606, 1562,
1530, 1495, 1455, 1407, 1369, 1288, 1218, 1190, 1131, 1058, 930, 822, 757, 734 cmꢀ1. HRMS
(ESIꢀTOF) calcd for C15H17BN3O3F2S [M + H]+: 368.1052, found: 368.1043.
4-(1,1-Difluoro-7-phenyl-1H-1λ4,8λ4-thiazolo[3,2-c][1,3,5,2]oxadiaza-borinin-3-yl)-N,N-
dimethylaniline (5d) was obtained in 58% yield (64 mg) using general procedure C from ligand
1
4d (96 mg, 0.30 mmol). Mp. 221.1–222.4 °C, yellow powder. H NMR (400 MHz, CDCl3): δ =
8.18 (2H, d, J = 9.2 Hz, ArꢀH), 7.68 (2H, dd, J = 8.4 Hz, J = 2.0 Hz, ArꢀH), 7.43–7.48 (3H, m,
ArꢀH), 6.76 (1H, s, thiazoleꢀH), 6.67 (2H, d, J = 9.2 Hz, ArꢀH), 3.07 (6H, s, 2 × CH3) ppm; 13C
NMR (100 MHz, CDCl3): δ = 174.2, 166.3, 154.2, 146.1, 132.3 (2C), 131.0, 126.2 (2C, t, JCꢀF
=
5.6 Hz), 129.1, 128.3 (2C), 117.3, 110.9 (2C), 109.1, 40.0 (2C) ppm; 19F NMR (375 MHz,
CDCl3): δ = –130.47 (d, J = 10.0 Hz), –130.53 (d, J = 10.0 Hz) ppm. IR (film): 3136, 2923,
1610, 1562, 1543, 1480, 1404, 1369, 1334, 1286, 1227, 1186, 1137, 1046, 934, 886, 823, 751
cmꢀ1. HRMS (ESIꢀTOF) calcd for C18H16BN3OF2SK [M + K]+: 410.0712, found: 410.0704.
4,4'-(1,1-Difluoro-1H-1λ4,8λ4-thiazolo[3,2-c][1,3,5,2]oxadiazaborinine-3,7-diyl)bis(N,N-
dimethylaniline) (5e) was obtained in 77% yield (89 mg) using general procedure C from ligand
4e (102 mg, 0.28 mmol). Mp. 206.2–208.4 °C, yellow powder. 1H NMR (500 MHz, CDCl3): δ =
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8.19 (2H, d, J = 9.2 Hz, ArꢀH), 7.58 (2H, d, J = 8.9 Hz, ArꢀH), 6.75 (2H, d, J = 8.9 Hz, ArꢀH),
6.67 (2H, d, J = 9.2 Hz, ArꢀH), 6.65 (1H, s, thiazoleꢀH), 3.08 (6H, s, 2 × CH3), 3.01 (6H, s, 2 ×
CH3) ppm; 13C NMR (125 MHz, CDCl3): δ = 173.9, 165.9, 154.0, 151.0, 147.0, 132.2 (2C),
130.0 (2C), 118.5, 117.5, 111.5 (2C), 110.9 (2C), 107.2, 40.2 (2C), 40.1 (2C) ppm; 19F NMR
(470 MHz, CDCl3): δ = –130.50 (d, J = 10.1 Hz), –130.55 (d, J = 8.8 Hz) ppm. IR (film): 2893,
2808, 1609, 1560, 1484, 1445, 1404, 1368, 1338, 1228, 1195, 1137, 1048, 942, 927, 888, 822,
756 cmꢀ1. HRMS (ESIꢀTOF) calcd for C20H22BN4OF2S [M + H]+: 415.1575, found: 415.1576.
4-(3-(4-(Dimethylamino)phenyl)-1,1-difluoro-1H-1λ4,8λ4-thiazolo[3,2-
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c][1,3,5,2]oxadiazaborinin-7-yl)benzonitrile (5f) was obtained in 56% yield (43 mg) using
general procedure C from ligand 4f (67 mg, 0.19 mmol). Mp. 197.4–199.1 °C, yellow powder.
1H NMR (500 MHz, CDCl3): δ = 8.19 (2H, d, J = 9.0 Hz, ArꢀH), 7.82 (2H, d, J = 8.0 Hz, ArꢀH),
7.75 (2H, d, J = 8.0 Hz, ArꢀH), 6.87 (1H, s, thiazoleꢀH), 6.68 (2H, d, J = 9.0 Hz, ArꢀH), 3.10
(6H, s, 2 × CH3) ppm; 13C NMR (125 MHz, CDCl3): δ = 174.6, 166.6, 154.4, 143.8, 135.3, 132.6
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(2C), 132.2 (2C), 129.8 (2C), 118.3, 116.8, 113.4, 110.9 (2C), 110.6, 40.1 (2C) ppm; F NMR
(470 MHz, CDCl3): δ = –129.97 (d, J = 10.3 Hz), –130.02 ppm. IR (film): 3105, 2917, 2224,
1606, 1556, 1483, 1455, 1403, 1372, 1335, 1191, 1155, 1137, 1100, 1038, 948, 930, 882, 859,
832, 761, 736, 711 cmꢀ1. HRMS (ESIꢀTOF) calcd for C19H15BN4OF2SNa [M + Na]+: 419.0925,
found: 419.0916.
4-(1,1-Difluoro-7-(4-nitrophenyl)-1H-1λ4,8λ4-thiazolo[3,2-c][1,3,5,2]-oxadiazaborinin-3-yl)-
N,N-dimethylaniline (5g) was obtained in 68% yield (61 mg) using general procedure C from
1
ligand 4g (79 mg, 0.21 mmol). Mp. 201.3–203.6 °C, orange powder. H NMR (400 MHz,
CDCl3): δ = 8.31 (2H, d, J = 8.8 Hz, ArꢀH), 8.19 (2H, d, J = 9.2 Hz, ArꢀH), 7.89 (2H, d, J = 8.8
Hz, ArꢀH), 6.91 (1H, s, thiazoleꢀH), 6.68 (2H, d, J = 9.2 Hz, ArꢀH), 3.11 (6H, s, 2 × CH3) ppm;
13C NMR (150 MHz, CDCl3): δ = 174.7, 166.7, 154.4, 148.4, 143.4, 137.0, 132.6 (2C), 130.2
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(2C), 123.6 (2C), 116.8, 111.0 (2C), 110.9, 40.1 (2C) ppm; F NMR (375 MHz, CDCl3): δ = –
129.89 (d, J = 9.8 Hz), –129.96 (d, J = 9.8 Hz) ppm. IR (film): 3115, 2918, 1609, 1552, 1519,
1463, 1406, 1374, 1345, 1284, 1232, 1193, 1139, 1058, 946, 929, 890, 854, 823, 742 cmꢀ1.
HRMS (ESIꢀTOF) calcd for C18H16BN4O3F2S [M + H]+: 417.1004, found: 417.0996.
Keywords: boron complex • 1,3ꢀthiazole • thiazolo[3,2ꢀc][1,3,5,2]oxadiazaborinine •
aggregation induced emission (AIE) • fluorescence
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge via the Internet at http://pubs.acs.org at
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DOI:
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ORTEP diagrams for the Xꢀray structures 5a, 5c–5e; crystal data of complexes 5a, 5c–e; cyclic
voltammograms of 5a–g; photophysical properties of complexes 5a–g in different solvents;
fluorescence decays of dyes 5a–g; calculated properties of the 6 lowest singlet excited states for
complexes 5a–g determined through TDꢀDFT; optimized geometry for compounds 5a–g; NMR
spectra; IR spectra.
AUTHOR INFORMATION
Corresponding Author
*Eꢀmail: potopnyk@gmail.com
ORCID
Mykhaylo A. Potopnyk: 0000ꢀ0002ꢀ4543ꢀ2785
ACKNOWLEDGMENTS
This work was financially supported by the Research Council of Lithuania (project No TAP LUꢀ
2ꢀ2016).
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