2,4-Distyryl- and 2,4,6-Tristyrylpyrimidines: Synthesis and Photophysical Properties

Article abstract of DOI:10.1021/acs.joc.8b01653

The synthesis of a series of 20 new 2,4,6-tristyrylpyrimidines and three new 2,4-distyrylpyrimidines by means of combination of Knoevenagel condensation and Suzuki-Miyaura cross-coupling reaction is reported. This methodology enables us to obtain chromophores with identical or different substituent on each arm. The photophysical properties of the compounds are described. Optical properties and time-dependent density functional theory calculations indicate that photophysical properties of target compounds are mainly affected by the nature of the electron-donating group in C4/C6 positions, except when the C2 substituent is a significantly stronger electron-donating group. However, the C2 substituent has a strong influence on emission quantum yield: addition of a strong electron-donating group tends to decrease the fluorescence quantum yield, whereas a moderate electron-withdrawing group results in a significant increase of fluorescence quantum yield.

Full text of DOI:10.1021/acs.joc.8b01653

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Article
2,4-Distyryl- and 2,4,6-tristyrylpyrimidines:
Synthesis and photophysical properties.
Michaela Feckova, Pascal Le Poul, Francoise Robin-le Guen, Thierry
Roisnel, Oldrich Pytela, Milan Klikar, Filip Bures, and Sylvain Achelle
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01653 • Publication Date (Web): 04 Sep 2018
Downloaded from http://pubs.acs.org on September 4, 2018
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2,4-Distyryl- and 2,4,6-tristyrylpyrimidines: Synthesis and photophysical
properties.
†
, ‡
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Michaela Fecková, Pascal le Poul, Françoise Robinꢀle Guen, Thierry Roisnel, Oldřich
‡
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,‡
,†
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Pytela, Milan Klikar, Filip Bureš,* and Sylvain Achelle*
†
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) ꢀ UMR 6226, Fꢀ
‡
3
5000 Rennes, France. Institute of Organic Chemistry and Technology, Faculty of Chemical
Technology, University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic.
Corresponding authors: *Eꢀmails: sylvain.achelle@univꢀrennes1.fr; filip.bures@upce.cz
Synopsis TOC
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Abstract
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The synthesis of a series of twenty new 2,4,6ꢀtristyrylpyrimidines and three new 2,4ꢀ
distyrylpyrimidines by means of combination of Knoevenagel condensation and Suzukiꢀ
Miyaura cross coupling reaction is reported. This methodology enables to obtain
chromophores with identical or different substituent on each arm. The photophysical
properties of the compounds are described. Optical properties and TDꢀDFT calculations
indicate that photophysical properties of target compounds are mainly affected by the nature
of the electronꢀdonating group in C4/C6 positions, except when the C2 substituent is a
significantly stronger electronꢀdonating group. However, the C2 substituent has a strong
influence on emission quantum yield: addition of a strong electronꢀdonating group tends to
decrease the fluorescence quantum yield whereas a moderate electronꢀwithdrawing group
results in a significant increase of fluorescence quantum yield.
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Introduction
During the past two decades, there has been a great interest in the synthesis of
1
pyrimidine fluorophores. The pyrimidine is a sixꢀmembered heterocycle with two nitrogen
atoms (1,3ꢀdiazine) that exhibits a strong electronꢀwithdrawing character. When the
pyrimidine ring is combined with electronꢀdonating fragments via πꢀconjugated linkers,
1
intramolecular charge transfer (ICT) occurs leading, generally, to a strong emission.
Recently, pyrimidineꢀbased thermally activated fluorescent emitters (TADF) have been
developed and have been used for high external quantum efficiency organic lightꢀemitting
2
diodes (OLEDs). 4,6ꢀDistyrylpyrimidines have also been developed as twoꢀphoton excitation
3
4
emitters for biological microscopy and photoinitiator for multiphoton lithography.
Due to the electron lone pair of its two nitrogen atoms, the pyrimidine ring can catch protons,
coordinate metal cations, and link to various (bio)organic molecules leading to modification
5
of its emission properties. Various pyrimidine chromophores have been used as pH, metal
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cations, nitroaromatic , and protein fluorescent sensors. Mixtures of neutral and protonated
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forms of pyrimidine fluorophores have also been used as white light emitters. Recently, Kato
and coworkers have highlighted the influence of substituent in C2 position on the emission
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properties of pyrimidine derivatives.
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Yꢀshaped centripetal molecules have been subject to intensive research. In this context, the
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triazine core has been extensively used.
In these structures, peripheryꢀtoꢀcore
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multidimensional charge transfer lead to large secondꢀorder optical response and large two
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photon
absorption
cross
section.
Numerous
2,4,6ꢀtriarylꢀ
and
2,4,6ꢀ
triarylethnynylpyrimidine chromophores have been designed for their luminescence
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5,16
properties.
Styrylpyrimidines are generally obtained by Knoevenagel condensation of an aldehyde with
4
,5,8,9a,10, 17
methylpyrimidine under basic or acidic conditions.
This reaction can be easily
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carried out on the methyl group in positions C2, C4 and/or C6. Using this strategy, 2ꢀstyryl,
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c,9a,17
3,4,5a,8,10,17
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4ꢀstyryl
and 4,6ꢀdistrylpyrimidine
as well as 4,4',6,6'ꢀtetrastyrylpyrimidine
chromophores have been prepared so far; selected known 4,6ꢀdistyrylpyrimidines are
presented in Chart 1. To the best of our knowledge, only the unsubstituted 2,4,6ꢀ
20
tristyrylpyrimidine has been described to date.
5a,17a
Chart 1. Structures of selected known chromophores 4,6ꢀdistyrylpyrimidines.
In this contribution, we describe the design and synthesis of 2,4,6ꢀtristyrylpyrimidines and
,4ꢀdistyrylpyrimidines by combining SuzukiꢀMiyaura cross coupling reaction and
2
Knoevenagel condensation. This strategy enables the synthesis of compounds with different
substituents on each arm and, thus, allows modification of their electron donating or
withdrawing abilities. The molecular structure obtained by Xꢀray analysis of a selected
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chromophore is also described. The photophysical properties of target chromophores were
studied and thoroughly compared with the corresponding 4,6ꢀdistyrylpyrimidines. The DFT
and TDꢀDFT calculations were also performed on selected chromophores to rationalize their
photophysical properties.
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Results and discussion
Synthesis
Various strategies have been considered for the synthesis of 2,4,6ꢀtristyrylpyrimidines.
Threefold Knoevenagel condensation from 2,4,6ꢀtrimethylpyrimidine has been envisioned.
2
1
However, the pyrimidine starting material cannot be isolated easily in a good yield. The
synthesis of 2ꢀmethylꢀ4,6ꢀdistyrylpyrimidine was also considered by treating 4,6ꢀ
distyrylpyrimidine with methyllithium followed by in-situ rearomatization with DDQ
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2
according to known procedure but we failed in obtaining the desired product. We therefore
proposed third strategy, starting from commercially available 2ꢀchloroꢀ4,6ꢀ
a
dimethylpyrimidine and 2,4ꢀdichloroꢀ6ꢀmethylpyrimidine. A combination of Suzuki crossꢀ
coupling and Knoevenagel condensation has been developed leading to twentyꢀone
tristyrylpyrimidine chromophores (Schemes 1–2).
Chromophores 2 with identical substituents in C4 and C6 positions were obtained in two steps
from 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine. The first step consists of the in-situ conversion of
arylalkynes into styrylboronic acid by action of catecholborane followed by palladiumꢀ
2
3
catalyzed SuzukiꢀMiyaura cross coupling reaction. 2ꢀStyrylpyrimidine intermediates 1 were
obtained in moderate to good yields. 2,4,6ꢀTristyrylpyrimidines 2 were obtained by
condensation between the C4 and C6 methyl group and the corresponding aromatic aldehyde
5a,17a
in boiling aqueous 5 M NaOH using Aliquat 336 as catalyst.
Moderate to good yields
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were generally observed. The lower yields, observed in particular for unsubstituted styryl
derivatives, were due to more complicated purification process.
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Scheme 1: Synthesis of compounds 2.
To obtain 2,4,6ꢀtristyrylpyrimidines 5 with three different arms, a threeꢀstep synthetic route
employed 2,4ꢀdichloroꢀ6ꢀmethylpyrimidine as a starting material (Scheme 2). The first step
consisted in a C4 regioselective SuzukiꢀMiyaura cross coupling reaction with in situ formed
styrylboronic acid leading to intermediates 3. The observed regioselectivity of cross coupling
reaction in C4 over C2 position of the pyrimidine ring is in accordance with the
1
5b,16a, 24
literature.
The second step consisted in a second SuzukiꢀMiyaura cross coupling
reaction in C2 position leading to 2,4ꢀdistyrylpyrimidines intermediates 4 and finally a
Knoevenagel condensation of 4ꢀ( N,Nꢀdiphenylamino)benzaldehyde on the methyl group in
C6 position lead to chromophores 5.
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Scheme 2: Synthesis of compounds 5.
Starting from 2ꢀchloroꢀ4ꢀmethylpyrimidine, 2,4ꢀdistyrylpyrimidines were obtained in a
similar twoꢀstep synthetic pathway (Scheme 3).
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Scheme 3: Synthesis of compounds 7.
All new compounds are well soluble especially in chlorinated solvents (DCM, CHCl
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) and
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were characterized by H, C NMR and HRMS spectroscopic techniques. The selectivity of
the SuzukiꢀMiyaura cross coupling as well as condensation reactions was sufficiently high to
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a
generate all transꢀisomer within the limits of NMR detection as observed previously. The
stereochemistry of the double bounds was unequivocally established on the basis of coupling
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constant for the vinylic proton in the H NMR (J ≈ 16 Hz). No trans/cis isomerisation were
observed during photophysical experiments.
X-ray Analysis
Chromophore 2h provided crystals for Xꢀray analysis by slow evaporation of its
dichloromethane/ethyl acetate (1/1, v/v) solution. The measured crystal, a large fragment of a
large yellow and transparent prism, confirms the proposed molecular structure; in particular
the E configuration of the three vinylic linkers is confirmed (Figure 1). An orthorhombic
crystal system is observed with a Pna2 space group. The presence of a (modelled) disorder
1
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on one of the two C4/C6 arm, already observed for similar structures, can be shown. Solid
state supramolecular assembly of the chromophore revealed an orthorhombic crystal system
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with a Pna2 space group. The crystal structure shows that the angles between the planes of
three benzene rings and the pyrimidine central core lower than 20°, indicating that they are
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not completely planar, in accordance with other 4ꢀstyrylꢀ and 4,6ꢀdistyrylpyrimidines.
It
should be noted that the dihedral angle between the phenyl ring in C2 position and the
pyrimidine core is the lowest (∼7°). Bond length alternation (BLA) were calculated for the
vinylic linker on each arm and were revealed to be slightly lower for the C2 arm (0.1185 Ǻ),
than for C4/C6 arms (0.1205, 0.1600 and 0.1775 Ǻ) indicating that the C2 arm imparts
stronger ICT.
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Figure 1: ORTEP drawing of the chromophore 2h with thermal ellipsoid at 50%.
Thermal properties
2 3
Thermal behaviour of the final compounds 2, 5 and 7 as well as compounds A and A
was studied by differential scanning calorimetry (DSC). Figure 2 shows thermograms of
representative compounds 2i, 2m, A and A while Table 1 lists all measured melting points
2
3
m d
(T ) and temperatures of thermal decompositions (T ). All DCS curves are given in the SI.
The measured melting points range from 128 to 243 °C. The temperature of decomposition
was estimated within the range of 195ꢀ320 °C. Further discussion on the thermal properties is
provided in the SI.
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Figure 2: Representative DSC thermographs of compounds 2i, 2m, A and A obtained with a
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scanning rate of 3°C/min in the range 50ꢀ400°C
Table 1: DSC results for chromophores 2, 5, 7, A
2
and A
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.
T
m
T
d
T
m
T
d
T
m
T
d
T
m
T
d
Comp.
Comp.
Comp.
Comp.
(°C) (°C)
(°C) (°C)
200 295
(°C) (°C)
(°C) (°C)
137 290
185 305
243 265
2
2
a
b
193 300
128 290
/
/
183 305
/
/
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
2s
/
/
/
250
220
280
7a
7b
7c
7d
A2
/
/
/
/
/
/
250
240
310
195
310
290
2c
245
305
2d
2e
2f
210 265
/
250
/
/
/
300
240
210
191 260
205 320
250
270
5a
5b
A
3
2g
T
m
= melting point (the point of intersection of a baseline and a tangent of thermal effect =
onset). = thermal decomposition (pyrolysis in N atmosphere).
T
d
2
3 2
Common feature of tripodal (Dꢀπ) ꢀA or (Dꢀπ) ꢀAꢀ(πꢀA) chromophores 2a–s and 5a–b
is their resistance to crystallize and they often occur as solid glasses and amorphous solid.
This suggests a more sophisticated thermal behaviour of centripetal starꢀshaped systems.
Hence, their DSC curves are frequently similar and decorated by solidꢀsolid or glass
transitions. Based on the DSC analysis there are no evident general trends between type or
position of particular donor used and thermal behavior of tripodal chromophores. Structural
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modifications (donor variation) often influences the thermal properties of tripodal
chromophores only negligibly because the intrinsic nature of these molecules remains the
same.
In general, 2,4ꢀ and 4,6ꢀdisubstituted pyrimidines (7a–d, A
demonstrated a similar thermal behaviour. A presence of donor groups (NMe
quadrupolar molecules 7b and 7c increases the melting point up to 100 °C compared to
donor free” analogue 7a.
The of tripodal molecules 2i/2m and their quadrupolar analogous A
comparable (Figure 2) and dictated by the type of attached donors on the periphery.
Therefore, DMA 2i/A and TPA analogous 2m/A have demonstrated almost identical T
d
2
and A
3
) have
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
, OMe) in
“
T
d
2 3
/A are
2
3
values (250/260 and 310/320 °C, see Table 1).
Photophysical properties
The UV/Vis and photoluminescence (PL) spectroscopic data of compounds 2, 5 and 7
measured in CH Cl at room temperature are presented in Table 2. The analyses were carried
2
2
ꢀ5
out by using low concentrations of chromophores (0.5–1.5 × 10 M). To facilitate comparison
5a
of photophysical properties, 4,6ꢀdistyrylpyrimidines A were also included in Table 1. As an
example, the spectra of compounds 2b, 2c and 2d are provided in Figure 3.
1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3: Normalized absorption (solid lines) and emission spectra (dashed lines) of
compounds 2b (black), 2c (green) and 2d (green) in CH
2
Cl
2
solution.
For all the compounds, the less energetic absorption band (
λ
max = 312ꢀ429 nm) is attributed to
charge transfer. Except compounds 2a, 2h, 7a and 7b, that are however slightly emissive in
non polar heptane, all the compounds exhibit significant emission. In case of 2h, the absence
of emission is attributed to twisted intramolecular charge transfer excited state. For these
1
compounds, as generally observed for pyrimidine pushꢀpull chromophores, large Stokes
shifts were obtained, indicating large difference (vibrational, electronic, geometric) between
the FranckꢀCondon state and the excited state. For tristyrylpyrimidines 2 and 5, the position of
absorption and emission wavelength maxima depends mainly on C4/C6 substituents.
However, it should be noted that a significant redꢀshift in emission is observed when the C2
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substituent is a significantly stronger electronꢀdonating groups than C4/C6 substituents (2j
and 2k). Whereas the ICT generally occurs over the C4/C6 arm, in this case, the ICT is
probably prevailing on the C2 arm. The fluorescence quantum yield varies significantly when
the C2 substituent is modified. When tristrylpyrimidines 2bꢀ2d with unsubstituted styryl
group in C2 position are compared with 2,6ꢀdistyrylpyrimidines A1ꢀA3, it appears that the
addition of the styryl group in C2 position leads to a slight red shift of the emission maxima
and a significant increase of the fluorescence quantum yield. The presence of an electronꢀ
donating group (methoxy, dimethylamino or diphenylamino) on the C2 arm (compounds 2e-
2g, 2i, 2l, 2m) results in a slight blue shift of emission regarding the corresponding
unsubstituted styryl derivatives 2bꢀ2d. The opposite trend is observed for 2j and 2k probably
due to change in the ICT direction over the C2 arm. Whereas chromophores with
dimethylamino group on C4/C6 arms (compounds A2, 2c, 2f, 2l, 2o, 2r and 5a) are generally
highly luminescent, the incorporation of this fragment on C2 (chromophores 2hꢀ2j, 5b and
7c) leads to a dramatic decrease of fluorescence quantum yield. On the other hand, the
addition of a trifluoromethyl fragment, a moderately electronꢀwithdrawing group, on C2 arm
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
chromophores 2qꢀ2s) results in a significant increase of the fluorescence quantum yield up to
.00 for 2s. 2,4ꢀDistyrylpyrimidines 7 exhibits significantly blue shifted absorption and
emission with regards to their 4,6ꢀdistyryl and 2,4,6ꢀtristyrylpyrimidines analogues. All these
1
1
a,15aꢀb
trends are in accordance with the observation made on arylpyrimidine series.
Table 2: UV/Vis and PL data in CH Cl
UV/vis
2
2
.
λ
max, nm
PL
λmax, nm
439
Stokes shift
a
–1
–1
b
–1
Compd
(ε
, mM ·cm )
ΦF
cm
17a
A1
359 (36.0)
ꢀ
5076
4442
4901
5
5
a
a
A2
A3
429 (42.1)
427 (47.6)
530
540
0.40
0.55
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1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
a
312 (74.3)
–
–
–
2b
369 (35.9)
423 (48.1)
430 (55.0)
339 (64.0)
423 (45.6)
424 (68.9)
370 (94.0)
402 (97.3)
409 (112.9)
376 (61.7)
406 (42.4)
415 (86.2)
347 (61.6)
418 (52.5)
424 (69.7)
370 (26.8)
429 (49.1)
430 (60.4)
420 (40.4)
386 (58.1)
305 (41.3)
442
537
551
439
533
543
–
0.10
0.72
0.78
0.15
0.53
0.91
–
4476
5019
5107
6719
4879
5168
–
2
c
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2d
2
e
2f
2
g
2h
2i
536
577
558
533
544
443
536
544
441
545
554
549
548
–
0.22
0.03
0.10
0.59
0.56
0.11
0.52
0.75
0.21
0.72
1.00
0.68
0.02
–
6219
7118
7799
5869
5714
6245
5266
5202
4351
4961
5205
5595
7659
–
2
j
2k
2
l
2m
2n
2
o
2p
2q
2
2
r
s
5
a
5b
7
a
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7b
331 (53.9)
–
–
–
7c
395 (67.2)
402 (45.5)
493
527
0.04
0.72
5032
5900
7d
a
–5
–5
b
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
All spectra were recorded at room temperature at c = 0.5 × 10 M to 1.5 × 10 . Fluorescence
F
quantum yield (±10%) determined relative to 9,10ꢀbisphenylethynylanthracene in cyclohexane (Φ =
26
1
.00).
In order to gain further insights into the photophysical properties of these compounds, their
absorption and emission behavior was studied in a variety of aprotic solvents. While the
absorption maxima were not significantly shifted, an increase in solvent polarity, estimated by
27
DimrothꢀReichardt polarity parameter, led to bathochromic shifts of the emission maxima.
The results of emission solvatochromism are summarized in Table 3. As an example, the
spectra registered for compound 2g are shown in Figure 4 and the change in emission color
under UV irradiation for compound 2k, easily seen by the naked eye, can be seen in Figure 5.
This solvatochromic behavior, characteristic for fluorophore featuring intramolecular charge
transfer, can be explained by the stabilization of the highly polar emittting state by polar
28
solvents. For all the compounds, the emission maxima were plotted versus Dimrothꢀ
Reichardt polarity parameter (see Figures S106ꢀS112) and, in all cases, a good linearity was
observed. The emission solvatochromic behavior can be quantified by the slope of the
corresponding regression line. Once again, with the exception of compound 2k, the
substituents in C4/C6 arm are the most affected by the emission solvatochromism with
2 2
decreasing order: NMe > NPh > OMe. This is in accordance to the electronꢀdonating
strength of the substituents. The slopes for 2,4ꢀdistyrylpyrimidines 7c and 7d are significantly
lower than that of their 2,4,6ꢀtristyrylpyrimidine analogues 2i and 2m, indicating that both
arms in C4 and C6 position play a role on the emission solvatochromism and, therefore on
ICT into the chromophores.
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1
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1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 3: Emission solvatochromism of pyrimidine derivatives in various aprotic solvents.
Heptane
Toluene
THF
CH
2
Cl
a
2
Acetone
MeCN
DMSO
a
a
a
a
a
a
E
T
(30) = 30.9
E
T
(30) = 33.9
E
T
(30) = 37.4 ꢀE (30) = 40.7 ꢀE (30) = 42.2 ꢀE (30) = 45.6 ꢀE (30) = 45.1
Compd
T
T
T
T
λ
max, nm
λ
max, nm
λ
max, nm
432
526
520
432
522
515
521
512
511
521
514
433
520
519
436
533
526
542
436
484
502
λ
max, nm
442
537
551
439
533
543
536
547
558
533
544
443
536
544
441
545
554
549
441
493
527
λ
max, nm
450
563
563
440
559
555
558
552
572
561
555
445
565
558
452
565
567
571
452
523
531
λ
max, nm
470
587
591
453
581
583
577
574
627
584
589
463
586
586
463
587
600
594
463
513
546
λ
max, nm
471
601
596
461
598
584
601
577
622
596
586
471
597
585
475
592
599
589
475
527
547
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2b
2c
397, 420
453
408, 429
483
2d
464
482
2e
402, 421
450
410, 433
480
2f
2g
461
480
2i
450
479
2j
460
495
2k
439
466
2l
451
480
2
m
460
479
2n
401, 422
449
411, 433
480
2o
2
2
p
q
460
479
398
411
2r
456
486
2s
467
486
5a
5b
457
491
398
411
7c
433
455
7d
447
470
a
–1
Dimroth–Reichardt polarity parameter, kcal⋅mol
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2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
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3
3
3
4
4
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4
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4
4
4
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4
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5
5
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5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 4: Normalized emission spectra of 2g in different aprotic solvents.
Figure 5: Fluorescence color changes experienced by 2k in various solvents. Picture was
taken in the dark upon irradiation with a handꢀheld UV lamp (λem = 366 nm).
5,9
The ability of protonation of pyrimidine chromophores has been already demonstrated.
Generally, the protonation of aminoꢀsubstituted stryrylpyrimidines results in quenching of
emission; however, in the case of less electronꢀdonating substituents, such as methoxy groups,
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4
4
5
5
5
5
5
5
5
5
5
5
6
5
a,9a
the protonation lead to a redꢀshifted emission.
The changes in the emission spectra of 2q
upon addition of (1 )ꢀ(+)ꢀ10ꢀcamphorsulfonic acid are illustrated in Figure 6. The progressive
S
disappearance of the emission band of the neutral form at 441 nm is observed, whereas a new
redꢀshifted absorption band at 540 nm progressively appear corresponding to the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
9a
monoprotonated species. As shown on Figure 7, the neutral form of 2q emits dark blue light
under UVꢀirradiation whereas the protonated form emits green light. A mixture of the two
forms enables to obtain cyan light.
ꢀ5
2 2
Figure 6 Changes in the emission spectra of a CH Cl solution of 2q (c = 0.9642 ×10 M)
upon addition of (1
S
)ꢀ(+)ꢀ10ꢀcamphorsulfonic acid (0.1 – 50 eq.). λexc = 380 nm.
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3
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3
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3
3
4
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0
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0
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2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ5
Figure 7 Change in the color of a CH
2
Cl
2
solution of 2q (c = 0.9642 ×10 M) after the
addition of 0.8 equiv (middle) and 50 equiv of (1
S
)ꢀ(+)ꢀ10ꢀcamphorsulfonic acid (right).
Picture was taken in the dark upon irradiation with a handꢀheld UV lamp (λem = 366 nm).
DFT calculations
2
9
DFT calculations implemented in Gaussian 16 software package were employed to
investigate the fundamental properties of representative pyrimidines A3, 2g, 2j, 2k, and 2m
with a systematically varied structural arrangement. Their optimized geometries, the
HOMO/LUMO energies, and ground state dipole moments
ꢁ (Table 4) were obtained by DFT
B3LYP/6ꢀ311+g(2d,p) method. The calculated HOMO/LUMO levels were further visualized
in the energy level diagram as shown in Figure 8. Whereas the HOMOꢀLUMO gaps of all
molecules are almost identical (2.97ꢀ3.02 eV), the principal variations are seen at both
HOMO/LUMO levels. Hence, decoration of the central pyrimidine acceptor with two or three
donor arms affects the position of the HOMO and LUMO rather than the HOMOꢀLUMO
difference. This is in accordance to our latest observation and generalization on multipodal
30
chromophores. The frontier molecular orbitals are further visualized in Figure 9. In the
parent molecule A3, the HOMO is localized on both
N,Nꢀdiphenylamino donors but is also
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2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
mixed with the LUMO spread over the central pyrimidine and adjacent πꢀlinkers. This implies
lower charge separation. The situation is similar in 2g bearing weak additional
ꢀmethoxystyryl donor appended at C2 (the second ꢀdiphenylamino donor is occupied by
the HOMOꢀ1). However, by attaching strong electron releasing moieties, such as
dimethylamino or ꢀdiphenylamino groups, the HOMO has completely moved on the arms
4
N,N
N,Nꢀ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
N,N
appended at C2 regardless what type of donors are connected at C4/C6. Hence, for 2j, 2k, and
2m, the ICT dominates from the arm connected at pyrimidine C2.
Table 4: DFT calculated data of representative chromophores.
ꢁ
D
λ
max
E
HOMO
E
LUMO
ꢀE
eV
a
eV
eV
Compd
nm/eV
A
3
–5.26
–5.21
–5.09
–5.14
–5.14
–2.27
–2.19
–2.12
–2.13
–2.21
2.99
3.02
2.97
3.01
2.94
3.39
475/2.61
2g
2.00
1.41
3.89
1.60
468/2.65
458/2.71
403/3.08
464/2.67
2j
2k
2m
2
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Figure 8 Energy level diagram of the DFTꢀderived HOMO/LUMO energies.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
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9
0
Figure 9 Optimized geometries and HOMO (red) and LUMO (blue) localizations in
representative chromophores.
The electronic absorption spectra of representative chromophores were further calculated
using TDꢀSCF (nstates = 10) B3LYP/6ꢀ311+g(2d,p) method. The spectra are listed in Figure
S113 jointly with the experimental data; the calculated longestꢀwavelength absorption
maxima are given in Table 3. Their correlation with the experimental λmax values is very tight
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as shown in Figure S114. This implies that, despite the calculated values are generally redꢀ
shifted, the employed method is capable to described trends within the given series of
molecules. The spectra of representative chromophores feature a low energy lying CTꢀband
with the λmax appearing between 403ꢀ475 nm (376ꢀ428 nm experimentally). Compared to
tripodal molecules 2, the quadrupolar chromophore A3 showed the most bathochromically
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shifted CTꢀband (λmax = 428 nm). This may be explained by the Frenkel exciton model, which
predicts splitting of the singlet excited state into two and three bands for quadrupolar and
tripodal molecules, as compared to their linear analogue. Whereas for quadrupolar molecules
is the low energy band dominant, the low energy lying two states of a tripodal molecule are
degenerate while the third high energy state has zero oscillator strength. Hence, the absorption
spectra of both types of molecules are characterized by a single CTꢀband, eventually
accompanied by a shoulder for quadrupolar molecules and a blueꢀshift for tripodal ones.
According to the performed calculations, the CTꢀbands of quadrupolar A3 and tripodal 2g,
bearing weak methoxy electron donor, are almost exclusively generated by the
HOMO
donors, are dominated by the HOMO
transitions. Replacement of two amino donors at C4/C6 as in 2k led to a significantly redꢀ
shifted HOMO LUMO transition (~468 nm, see Figure S113) but with diminished oscillator
strength. Hence, the observed CTꢀband is generated by the HOMO LUMO+1 and HOMOꢀ
LUMO transitions.
Conclusions
→
LUMO transition. On the other hand, the CT bands of 2j and 2m, bearing all amino
→
LUMO, HOMOꢀ1 LUMO, and HOMO LUMO+1
→
→
→
→
1
→
In conclusion, we have successfully synthesized 2,4,6ꢀtristyrylpyrimidine and 2,4ꢀ
distyrylpyrimidine chromophores with identical or different substituent on each arm. In terms
of absorption and emission maxima, and calculated HOMOꢀLUMO gaps, 2,4,6ꢀ
tristyrylpyrimidines exhibits generally the similar properties as the corresponding 4,6ꢀ
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distyrylpyrimidines. Nevertheless, when the C2 substituent is a significantly stronger
electronꢀdonating substituents than C4/C6 ones, the ICT occurs mainly on this branch and
dictates the photophysical properties. In all cases, the C2 substituent play a key role on the
emission quantum yield. As one would expected, all these materials exhibit strong emission
solvatochromism and pH sensibility. Comparison of the twoꢀphoton absorption properties of
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
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0
2,4,6ꢀtristyrylpyrimidine with the corresponding 4,6ꢀdistyrylpyrimidines are currently under
investigation.
Experimental Section
General Conditions. In airꢀ and moistureꢀsensitive reactions, all glassware was flameꢀdried and
cooled under nitrogen. Thermal behavior of the target compounds was measured in open aluminous
2
crucibles under N inert atmosphere. DSC curves were determined with a scanning rate of 3 °C/min
within the range 25–400 °C. NMR spectra were acquired at room temperature. Chemical shifts are
1
13
given in parts per million relative to TMS ( H, 0.0 ppm) and CDCl
3
( C, 77.0 ppm). Acidic impurities
in CDCl were removed by treatment with anhydrous K CO . High resolution MALDI MS spectra
3
2
3
were measured on a MALDI mass spectrometer equipped with nitrogen UV laser (337 nm, 60 Hz) and
quadrupole analyser (positiveꢀion mode over a normal mass range (m/z 50ꢀ2000) with resolution
100 000 at m/z = 400). Transꢀ2ꢀ[3ꢀ(4ꢀtertꢀbutylphenyl)ꢀ2ꢀmethylꢀ2ꢀpropenylidene]malononitrile
(
DCTB) was used as a matrix. Mass spectra were averaged over the whole MS record for all measured
samples. UVꢀvis and fluorescence spectra were recorded using standard 1 cm quartz cells. Compounds
were excited at their absorption maxima (band of lowest energy) to record the emission spectra. The
F
Φ values were calculated using a wellꢀknown procedure with 9,10ꢀdiphenylethynylanthracene in
2
6
cyclohexane as standard. Stokes shifts were calculated by considering the lowest energetic
absorption band. All calculations were carried out in Gaussian 09W package at the DFT level of
theory. The initial geometry optimizations were carried out by the PM3 method implemented in
program ArgusLab and subsequently by the DFT B3LYP method using the 6ꢀ311G++(2d,f,p) basic
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set. The energies of the HOMO and LUMO (EHOMO and ELUMO), their differences (ꢀE) and ground
state dipole moments (ꢁ) were calculated by the DFT B3LYP/6ꢀ311++G(2d,f,p) method.
General procedure for Suzuki-Miyaura cross-coupling reaction. The corresponding
acetylene (1.57 equiv) was dissolved in THF (20 mL) and nitrogen was bubbled through the
solution for 10 min. Catecholborane (1.9 equiv of 1 M solution in THF) was added and the
reaction mixture was heated to reflux for 1.5 h. The second portion of catecholborane (0.7
equiv) was added and heating was continued for 2 h. The reaction mixture was cooled to room
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7
8
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4
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0
temperature and Pd(PPh ) (0.025 equiv) and corresponding pyrimidine (1 equiv) were added.
3 4
Solution was stirred for 20 min before 20% aqueous Na CO (5 mL) was added and the
2
3
mixture was stirred under nitrogen at reflux for 15 h. The reaction mixture was cooled and
then diluted with CH Cl (20 mL). The organic layer was washed with water (3x20 mL), then
with brine (20 mL), separated, dried over MgSO and the solvents were evaporated under
2
2
4
reduced pressure. The crude product was purified by column chromatography (SiO , indicated
2
solvents).
General procedure for Knoevenagel condensation. Aldehyde (1 equiv) and corresponding
4
ꢀmethylpyrimidine (1 equiv) or 4,6ꢀdimethylpyrimidine (0.5 equiv) were added in 5 M
aqueous NaOH (15 mL) containing Aliquat 336 (0.1 equiv). Solution was heated to reflux for
h and then cooled to room temperature. The precipitate was filtered off, washed with water,
and purified by recrystallization from CH Cl ꢀheptane and/or by column chromatography
SiO , indicated solvents).
3
2
2
/n
(
2
(E)-2-Styryl-4,6-dimethylpyrimidine (1a). Synthesized from phenylacetylene (161 mg, 1.57
mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine (143 mg, 1 mmol) following the general
procedure for SuzukiꢀMiyaura reaction. The crude product was purified by column
chromatography (SiO
2 f
, petroleum ether:EtOAc, 7:3). Yield: 78 mg (37 %); white solid. R :
3
1
1
0
.7 (SiO ; petroleum ether:EtOAc, 7:3). Mp: 47.5–49.4 °C (lit. 47ꢀ50°C). H NMR (300
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MHz, CDCl
3
):
.61–7.64 (m, 2H), 7.97 (d,
17.7, 127.7, 127.9, 128.8, 128.9, 136.4, 137.6, 164.3, 166.6 ppm. IR (ATR):
δ
= 2.50 (s, 6H), 6.86 (s, 1H), 7.21 (d,
J
= 15.9 Hz, 1H), 7.29–7.41 (m, 3H),
3
13
7
1
1
3
J = 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl ): δ = 24.1,
ν
= 3057, 1533,
ꢀ1
+
367, 978, 747, 692 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C14
H
15
N
2
[(M+H) ]
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
211.1230, found 211.1227.
(E)-2-(4-Methoxystyryl)-4,6-dimethylpyrimidine (1b). Synthesized from 4ꢀethynylanisole
415 mg, 3.14 mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine (286 mg, 2 mmol) following the
general procedure for SuzukiꢀMiyaura reaction. The crude product was purified by column
(
chromatography (SiO
2
, petroleum ether:EtOAc, 7:3). Yield: 257 mg (54 %); brownish solid.
1
Rf: 0.4 (SiO ; petroleum ether:EtOAc, 7:3). Mp: 87.9–90.2 °C. H NMR (300 MHz, CDCl ):
2
3
3
δ
7
5
1
= 2.48 (s, 6H), 3.82 (s, 3H), 6.82 (s, 1H), 6.89–6.92 (m, 2H), 7.07 (d,
J
= 15.9 Hz, 1H),
3
13
.54–7.57 (m, 2H), 7.92 (d,
J
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl ):
δ
= 24.1,
= 3004,
3
5.4, 114.3, 117.4, 125.6, 129.1, 129.2, 137.3, 160.4, 164.6, 166.6 ppm. IR (ATR):
ν
ꢀ1
574, 1511, 1242, 1178, 1028, 981, 839, 818, 770 cm . HRꢀMALDIꢀMS (DCTB): m/z
+
calculated for C15
H
16
N
2
O [M ] 240.1257, found 240.1256.
(E)-2-(4-Dimethylaminostyryl)-4,6-dimethylpyrimidine (1c). Synthesized from 4ꢀethynylꢀ
ꢀdimethylaniline (362 mg, 2.50 mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine (230 mg,
.61 mmol) following the general procedure for SuzukiꢀMiyaura reaction. The crude product
N,N
1
was purified by column chromatography (SiO , petroleum ether:EtOAc, 7:3). Yield: 244 mg
2
1
(59 %); yellow solid.
R
f
: 0.6 (SiO
2
; petroleum ether:EtOAc, 7:3). Mp: 112.8–115.2 °C. H
NMR (300 MHz, CDCl3):
δ = 2.47 (s, 6H), 3.00 (s, 6H), 6.69–6.72 (m, 2H), 6.78 (s, 1H), 7.01
3
3
13
(d,
J
= 15.9 Hz, 1H), 7.51–7.54 (m, 2H), 7.91 (d,
): = 24.2, 40.4, 112.2, 116.9, 123.2, 124.6, 129.1, 138.0, 151.0, 165.1, 166.4 ppm. IR
ATR):
J = 15.9 Hz, 1H) ppm. C NMR (75 MHz,
CDCl
3
δ
ꢀ1
(
ν
= 2919, 1580, 1443, 1356, 1165, 986, 820, 748 cm . HRꢀMALDIꢀMS (DCTB): m/z
+
calculated for C16
H
19
N
3
[M ] 253.1574, found 253.1562.
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(
E)-2-(4-Diphenylaminostyryl)-4,6-dimethylpyrimidine (1d). Synthesized from 4ꢀethynylꢀ
N
,N
ꢀdiphenylaniline (790 mg, 2.94 mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine (267 mg,
1
.87 mmol) following the general procedure for SuzukiꢀMiyaura reaction. The crude product
was purified by column chromatography (SiO
28 %); yellow solid. : 0.4 (SiO
NMR (300 MHz, CDCl ):
4H), 7.46–7.49 (m, 2H), 7.91 (d,
2
, petroleum ether:EtOAc, 8:2). Yield: 200 mg
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
(
R
f
2
; petroleum ether:EtOAc, 8:2). Mp: 132.7–135.7 °C. H
3
δ = 2.49 (s, 6H), 6.83 (s, 1H), 7.02–7.14 (m, 9H), 7.25–7.30 (m,
3
13
J
3
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl ): δ =
2
4.1, 117.3, 122.6, 123.5, 125.1, 125.6, 128.6, 129.4, 129.9, 137.3, 147.4, 148.6, 164.6, 166.5
ꢀ1
ppm. IR (ATR):
ν
= 3030, 1585, 1488, 1273, 749, 692 cm . HRꢀMALDIꢀMS (DCTB): m/z
+
calculated for C H N [M ] 377.1887, found 377.1888.
26
23
3
(
E)-2-[(6-Methoxynaphtalen-2-yl)ethenyl]-4,6-dimethylpyrimidine (1e). Synthesized from
2ꢀethynylꢀ6ꢀmethoxynaphtalene (286 mg, 1.57 mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine
143 mg, 1 mmol) following the general procedure for SuzukiꢀMiyaura reaction. The crude
product was purified by column chromatography (SiO , petroleum ether:EtOAc, 7:3). Yield:
(
2
2
30 mg (79 %); yellowish solid. Rf: 0.3 (SiO ; petroleum ether:EtOAc, 7:3). Mp: 133.5–134.9
2
1
°
C. H NMR (300 MHz, CDCl
3
):
δ
= 2.45 (s, 6H), 3.86 (s, 3H), 6.75 (s, 1H), 7.06–7.13 (m,
3
3
2H), 7.26 (d,
J
= 15.9 Hz, 1H), 7.66–7.77 (m, 3H), 7.88 (s, 1H), 8.09 (d,
):
28.4, 128.9, 129.9, 131.7, 134.9, 137.7, 158.2, 164.3, 166.4 ppm. IR (ATR):
J = 15.9 Hz, 1H)
1
3
ppm. C NMR (75 MHz, CDCl
3
δ
= 24.0, 55.3, 105.9, 117.4, 119.1, 124.4, 127.0, 127.3,
= 2931, 1582,
1
1
ν
ꢀ1
364, 1163, 1027, 860, 803, 665 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for
+
C
19
H
18
N
2
O [M ] 290.1414, found 290.1414.
(E)-2-(4-Trifluoromethylstyryl)-4,6-dimethylpyrimidine (1f). Synthesized from 4ꢀ
trifluoromethylphenylacetylene (426 mg, 2.50 mmol) and 2ꢀchloroꢀ4,6ꢀdimethylpyrimidine
(228 mg, 1.59 mmol) following the general procedure for SuzukiꢀMiyaura reaction. The crude
product was purified by column chromatography (SiO , petroleum ether:EtOAc, 7:3). Yield:
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22 mg (50 %); yellowish solid. Rf: 0.4 (SiO ; petroleum ether:EtOAc, 7:3). Mp: 94.9–96.5
2
1
3
°C. H NMR (300 MHz, CDCl
3
):
δ
= 2.50 (s, 6H), 6.89 (s, 1H), 7.26 (d,
J
= 15.9 Hz, 1H),
= 24.1,
CF = 32 Hz),
3
13
7
1
1
.60–7.71 (m, 4H), 7.97 (d,
J
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl ):
δ
3
1
3
2
18.2, 124.2 (q,
35.8, 139.9 (d,
J
CF = 270 Hz), 125.8 (q,
J
CF = 4 Hz), 127.7, 130.4, 130.5 (q,
J
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
J
CF = 1 Hz), 163.7, 166.8 ppm. IR (ATR):
ν
= 2929, 1583, 1319, 1103, 1064,
ꢀ1
+
831, 714 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C15
H
14
F
3
N
2
[(M+H) ] 279.1104,
found 279.1102.
(E,E,E)-2,4,6-Tristyrylpyrimidine (2a). Synthesized from 1a (300 mg, 1.43 mmol) and
benzaldehyde (303 mg, 2.85 mmol) following the general procedure for Knoevenagel
condensation. The crude product was purified by column chromatography (SiO , petroleum
2
ether:EtOAc, 9:1) and then by recrystallization from CH
2
Cl
; petroleum ether:EtOAc, 9:1). Mp: 193 °C (lit. 197ꢀ199°C).
3
H NMR (300 MHz, CDCl ): δ = 7.08–7.16 (m, 3H), 7.28–7.43 (m, 10H), 7.62–7.69 (m, 6H),
2
/nꢀheptane. Yield: 155 mg (28
20b
%); white solid.
f 2
R : 0.4 (SiO
1
3
3
13
7
1
.93 (d,
J
= 15.9 Hz, 2H), 8.11 (d,
J
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl
3
):
δ
=
13.7, 126.5, 127.7, 127.8, 128.3, 128.8, 128.9, 129.3, 136.0, 136.4, 136.7, 137.9, 162.9,
.
164.6 ppm All the atoms of carbon were not observed . IR (ATR):
ν = 3025, 1635, 1564,
ꢀ1
23 2
1514, 1368, 963, 739, 689 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C28H N
+
[
(M+H) ] 387.1856, found 387.1855.
(
E,E,E)-2-Styryl-4,6-bis(4-methoxystyryl)pyrimidine (2b). Synthesized from 1a (78 mg,
.37 mmol) and 4ꢀmethoxybenzaldehyde (102 mg, 0.74 mmol) following the general
procedure for Knoevenagel condensation. The crude product was purified by column
chromatography (SiO , petroleum ether:EtOAc, 8:2) and then by recrystallization from
0
2
CH Cl /
n
ꢀheptane. Yield: 40 mg (24 %); yellowish solid. Rf: 0.4 (SiO ; petroleum
2
2
2
1
ether:EtOAc, 8:2). Mp: 128 °C. H NMR (300 MHz, CDCl
3
):
δ
= 3.86 (s, 6H), 6.93–7.01 (m,
3
6H), 7.11 (s, 1H), 7.29–7.44 (m, 4H), 7.58–7.61 (m, 4H), 7.68–7.70 (m, 2H), 7.89 (d,
J
=
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3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
13
15.9 Hz, 2H), 8.11 (d,
J
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl
3
):
δ
= 55.5, 113.2,
1
1
14.5, 124.4, 127.8, 128.5, 128.9, 128.90, 128.91, 129.2, 136.2, 136.6, 137.6, 160.7, 163.1,
ꢀ1
64.5 ppm. IR (ATR):
ν
= 2837, 1604, 1560, 1501, 1251, 1171, 1152, 967, 749 cm . HRꢀ
+
MALDIꢀMS (DCTB): m/z calculated for C30
H
27
N
2
O
2
[(M+H) ] 447.2067, found 447.2064.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
E,E,E)-2-Styryl-4,6-bis(4-dimethylaminostyryl)pyrimidine (2c). Synthesized from 1a
(150 mg, 0.71 mmol) and 4ꢀ ꢀdimethylaminobenzaldehyde (213 mg, 1.43 mmol) following
the general procedure for Knoevenagel condensation. The crude product was purified by
column chromatography (SiO , petroleum ether:EtOAc, 8:2) and then by recrystallization
N,N
2
from CH
Cl
2 2
/n
f 2
ꢀheptane. Yield: 63 mg (17 %); black solid. R : 0.2 (SiO ; petroleum
1
ether:EtOAc, 8:2).
T
d
: 245 °C. H NMR (300 MHz, CDCl
3
):
δ
= 3.03 (s, 12 H), 6.71–6.74 (m,
3
4H), 6.91 (d,
J
= 15.9 Hz, 2H), 7.08 (s, 1H), 7.28–7.35 (m, 4H), 7.53–7.56 (m, 4H), 7.68–
3
3
13
7.70 (m, 2H), 7.86 (d,
CDCl ): = 40.4, 112.2, 112.4, 114.2, 114.7, 121.9, 124.3, 127.8, 128.7, 128.8, 129.2, 136.8,
37.2, 151.2, 163.4, 164.3 ppm. IR (ATR):
J = 15.9 Hz, 2H), 8.10 (d, J = 15.9 Hz, 1H) ppm. C NMR (75 MHz,
3
δ
1
8
ν
= 2892, 1602, 1555, 1503, 1363, 1162, 965,
ꢀ1
+
00, 746 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C32
H
32
N
4
[M ] 472.2622, found
472.2620.
(E,E,E)-2-Styryl-4,6-bis(4-diphenylaminostyryl)pyrimidine (2d). Synthesized from 1a
300 mg, 1.43 mmol) and 4ꢀ ꢀdiphenylaminobenzaldehyde (780 mg, 2.85 mmol) following
the general procedure for Knoevenagel condensation. The crude product was purified by
column chromatography (SiO , petroleum ether:EtOAc, 9:1) and then by recrystallization
(
N,N
2
from CH
2
Cl
2
/n
ꢀheptane. Yield: 220 mg (21 %); yellow solid.
f 2
R : 0.4 (SiO ; petroleum
1
3
ether:EtOAc, 9:1).
T
d
: 305 °C. H NMR (300 MHz, CDCl
3
):
δ
= 6.98 (d,
J
= 15.9 Hz, 2H),
3
7
1
1
.05–7.17 (m, 17H), 7.27–7.43 (m, 12H), 7.48–7.51 (m, 4H), 7.67–7.70 (m, 2H), 7.87 (d,
J
=
3
13
5.9 Hz, 2H), 8.10 (d,
3
J = 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl ): δ = 113.1, 122.5,
23.8, 124.4, 125.2, 127.8, 128.6, 128.77, 128.85, 128.88, 129.56, 129.59, 136.1, 136.6,
2
8
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Page 29 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
137.6, 147.3, 149.0, 163.1, 164.6 ppm. IR (ATR):
ν = 3033, 1559, 1490, 1274, 969, 748, 693
ꢀ1
+
cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C52
40 4
H N [M ] 720.3248, found 720.3252.
(E,E,E)-2,4,6-Tris(4-methoxystyryl)pyrimidine (2e). Synthesized from 1b (100 mg, 0.42
mmol) and 4ꢀmethoxybenzaldehyde (114 mg, 0.83 mmol) following the general procedure for
Knoevenagel condensation. The crude product was purified by recrystallization from
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CH Cl /
n
ꢀheptane. Yield: 156 mg (79 %); yellowish solid. Rf: 0.4 (SiO ; petroleum
2
2
2
1
ether:EtOAc, 8:2). Mp: 183 °C. H NMR (300 MHz, CDCl
3
):
δ
= 3.85 (s, 9H), 6.93–7.00 (m,
3
3
8
8
1
H), 7.08 (s, 1H), 7.18 (d,
J
= 15.9 Hz, 1H), 7.57–7.65 (m, 6H), 7.88 (d,
J
= 15.9 Hz, 2H),
3
13
.06 (d,
J
= 15.9 Hz, 1H) ppm. C NMR (75 MHz, CDCl
3
):
δ
= 55.46, 55.49, 112.8, 114.34,
14.4, 124.5, 126.3, 129.0, 129.2, 129.4, 136.1, 137.3, 160.4, 160.7, 163.1, 164.8 ppm All the
= 2933, 1602, 1559, 1506, 1245, 1169,
atoms of carbon were not observed.. IR (ATR):
ν
ꢀ1
1
28 2 3
028, 959, 868, 810, 767 cm . HRꢀMALDIꢀMS (DCTB): m/z calculated for C31H N O
+
[
M ] 476.2094, found 476.2094.
(
E,E,E)-2-(4-Methoxystyryl)-4,6-bis(4-dimethylaminostyryl)pyrimidine (2f). Synthesized
ꢀdimethylaminobenzaldehyde (125 mg, 0.83 mmol)
following the general procedure for Knoevenagel condensation. The crude product was
from 1b (100 mg, 0.42 mmol) and 4ꢀN,N
purified by recrystallization from CH
SiO ; petroleum ether:EtOAc, 8:2).
2
Cl
2
/
n
f
ꢀheptane. Yield: 154 mg (74 %); red solid. R : 0.3
1
(
2
T
d
: 250 °C. H NMR (300 MHz, CDCl
3
):
δ
J
= 3.03 (s,
= 15.9 Hz,
= 15.9 Hz,
3
1
1
1
2H), 3.85 (s, 3H), 6.71–6.74 (m, 4H), 6.88–6.95 (m, 4H), 7.07 (s, 1H), 7.17 (d,
3
3
H), 7.52–7.55 (m, 4H), 7.62–7.65 (m, 2H), 7.84 (d,
J
= 15.9 Hz, 2H), 8.05 (d,
J
13
H) ppm. C NMR (75 MHz, CDCl ):
δ = 40.4, 55.4, 112.1, 112.2, 114.3, 122.0, 124.3,
3
126.6, 129.1, 129.6, 136.6, 136.8, 151.1, 160.2, 163.3, 164.7 ppm All the atoms of carbon
ꢀ1
were not observed.. IR (ATR):
ν
= 2924, 1600, 1550, 1497, 1355, 1244, 1142, 971, 806 cm .
+
HRꢀMALDIꢀMS (DCTB): m/z calculated for C33
H
34
N
4
O [M ] 502.2727, found 502.2731.
2
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ACS Paragon Plus Environment