Push–Pull (Iso)quinoline Chromophores: Synthesis, Photophysical Properties, and Use for White-Light Emission

Article abstract of DOI:10.1002/chem.202000817

The photophysical properties of a series of conjugated push–pull (iso)quinolines were studied. The compounds were synthesized by well-established and straightforward methodologies. The materials exhibited not only emission solvatochromism in a variety of

Full text of DOI:10.1002/chem.202000817

A Journal of
Accepted Article
Title: Push-pull (iso)quinoline chromophores: synthesis, photophysical
properties, and use for white light emission.
Authors: Zaina Ibrahim Mohamed Allaoui, Estelle le Gall, Arnaud
Fihey, Rodrigo Plaza-Pedroche, Claudine Katan, Françoise
Robin-le Guen, Julián Rodríguez-López, and Sylvain Achelle
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of the final Version of Record (VoR). This work is currently citable by
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202000817
Link to VoR: http://dx.doi.org/10.1002/chem.202000817
Supported by

Chemistry - A European Journal
10.1002/chem.202000817
Push-pull (iso)quinoline chromophores: synthesis, photophysical
properties, and use for white light emission.
[
a]
[b]
[a]
Zaina Ibrahim Mohamed Allaoui, Estelle le Gall, Arnaud Fihey,
[
c]
[a]
[a]
Rodrigo Plaza-Pedroche, Claudine Katan, Françoise Robin-le Guen,
[
c]
[a]
Julián Rodríguez-López,* and Sylvain Achelle*
[
a]
Université de Rennes, CNRS, Institut des Sciences Chimiques de Rennes - UMR 6226,
F 35000 Rennes, France; E-mail: sylvain.achelle@univ-rennes1.fr
[
b]
IUT de Lannion, Université de Rennes 1, Rue Édouard Branly, F 22300 Lannion, France.
[
c]
Área de Química Orgánica, Facultad de Ciencias y Tecnologías Químicas, Universidad de
Castilla-La Mancha, Avda. Camilo José Cela 10, 13071 Ciudad Real, Spain; E-mail:
julian.rodriguez@uclm.es
Graphical abstract
π
-bridge
π-bridge
D
D
D
(
iso)quinoline
H+
D
D = OMe, NPh2
H+
Abstract. The photophysical properties of a series of conjugated push-pull (iso)quinolines
have been studied. The compounds were synthesized by well-established and straightforward
methodologies. The materials exhibited not only emission solvatochromism in a variety of
non-polar solvents, but also tunable halochromism. Some of the compounds remained
moderately luminescent after protonation and these had a red emissive form, which was used
to obtain white light emission, both in solution and in thin film, by the controlled protonation
of the initially blue-green emitting materials. This methodology has potential applications in
white OLED fabrication with two forms of a single emitter in equilibrium.
Keywords: (iso)quinolines; fluorescence; white-light emission; push-pull chromophores.
1
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INTRODUCTION
Conjugated push-pull chromophores based on azaheterocyclic fragments have been
1
,2,3,4,5
intensively investigated in recent years.
Indeed, the photophysical properties of these
6
,7,8,9
8-10,11
materials can be easily tuned by environmental stimuli such as polarity,
pH,
or the
1
2
6,13
presence of metal cations. Six-membered nitrogen heterocycles such as pyridine,
3
1-5
quinoline or (benzo)diazines act as moderate-to-strong electron-withdrawing groups. When
protons or metal cations are added the photophysical properties are modified due to the
interaction with the electron lone pair of the nitrogen atoms of the heterocycle. Such
engagement of the electron lone pair leads to an increase in the electron-withdrawing
1
4
character and enhances the intramolecular charge transfer (ICT) into the chromophore. This
1
0,11
15,16,17
phenomenon has been used to obtain sensors
and a variety of optical switches.
The
protonation of azaheterocyclic push-pull chromophores generally leads to a bathochromic
8
,9,14
effect on the absorption spectrum.
However, the effect is less predictable for the emission.
Quenching is generally observed but in some cases a red shift accompanied by either an
8
increase or decrease in the intensity can be obtained.
1
8
There is currently great interest in obtaining white light emission. Pure white light
was defined in 1931 by the Commission Internationale de l'Eclairage (CIE) and it corresponds
to CIE chromaticity coordinates of (0.33, 0.33). White light can be obtained by a combination
of red, green and blue emitters in the appropriate proportions or by mixing any other two
1
8
complementary lights. Independent fluorophores are typically employed, but a new strategy
based on an equilibrium between two different forms of the same material has been proposed.
1
9,20,21
The two forms should emit complementary colors and can consist of monomer/excimer,
1
4,22,23,24
24,25
neutral/(de)protonated species,
or free/complexed ligand.
We recently described methoxy-substituted arylvinylpyrimidine derivatives that emit
2
6,27
blue light in their neutral form and red light upon protonation.
A mixture of the two forms
2
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10.1002/chem.202000817
in a precise proportion provided white light both in solution and in thin films. Analogously, a
mixture of purple-emitting carbazole-substituted pyrimidines and their yellow emitting
2
8
protonated forms also afforded white light emission. Unfortunately, it was found that the
low basicity of the pyrimidine ring (pK ≈ 1.1) precludes the fabrication of stable white light
a
emitting thin films, particularly when a volatile acid such as trifluoroacetic acid is used.
Pyridine derivatives have the advantage of stronger basicity (pK ≈ 5.2). Nevertheless, the
a
pyridine ring has a weaker electron-withdrawing character and stronger electron-donating
fragments are required as part of the π-conjugated push-pull structure (e.g., a diphenylamino
group). Although white luminescence could be obtained with this type of chromophore in
solution, the blue-shifted emission of both the neutral and protonated forms in solid state
2
9
precluded white emission.
The quinoline ring is a stronger electron-withdrawing group than the pyridine ring and
3
0
it has a slightly less basic character (pK ≈ 4.8–4.9). Several triphenylamine-substituted
a
3
1,32
quinolines have been reported to show red-shifted luminescence upon protonation.
Accordingly, we focused our efforts on investigating conjugated push-pull (iso)quinoline
derivatives. In this contribution, the synthesis of a series of such (iso)quinoline chromophores
is described and their photophysical properties are reported. The luminescence behavior upon
protonation with the aim of achieving white light emission both in solution and solid state is
also presented.
RESULTS AND DISCUSSION
Synthesis. 2- and 4-Arylvinylquinolines 1 and 2 were obtained by Knoevenagel
condensation of 2- and 4-methylquinoline, respectively, with the appropriate aldehyde.
Reactions were carried out according to a previously reported protocol using boiling aqueous
®
33
5
M NaOH as solvent and Aliquat 336 as a phase-transfer catalyst. Two equivalents of
3
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10.1002/chem.202000817
methylquinoline were employed in order to avoid the presence of unreacted aldehyde.
Compounds 1 and 2 were obtained in moderate to good yield (Scheme 1).
Scheme 1. Synthesis of 2- and 4-arylvinylquinolines 1 and 2.
These conditions were not efficient when 1-methylisoquinoline was used as the
t
starting material. In this case, a stronger base, i.e., potassium tert-butoxide (KBu O) in
refluxing THF, was required to form the 1-styrylisoquinolines 3 in low yield (Scheme 2). In
all cases, compounds 1–3 were selectively obtained with trans-configured vinylene bridges,
3
4
as commonly observed in the Knoevenagel condensation of methylazaheterocycles. It
should be noted that the synthesis of 3-arylvinylisoquinolines by this methodology proved
t
unsuccessful regardless of the base used (aqueous NaOH, KBu O, dimsyl potassium), and the
starting 3-methylisoquinoline was recovered.
Scheme 2. Synthesis of 1-styrylisoquinolines 3.
4
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The 2-arylquinoline 4 was prepared in moderate yield by Suzuki–Miyaura cross-
coupling reaction of 2-bromoquinoline with 4-(diphenylamino)phenylboronic acid under
classical conditions (Scheme 3).
Scheme 3. Synthesis of 2-[4-(diphenylamino)phenyl]quinoline (4).
The above compounds were perfectly stable in the solid state and could be stored
without special precautions. The compounds were highly soluble in common organic solvents,
e.g., dichloromethane, chloroform and THF. The structure and purity of each compound was
3
unequivocally established by NMR spectroscopy. The observed J(H,H) coupling constants of
~
16 Hz for the vinylic protons confirmed the trans configuration of the double bond. All
previously unreported materials were also characterized by high resolution mass spectrometry
HRMS).
UV-vis and fluorescence spectroscopy in solution. The UV-vis and
pholuminescence (PL) spectroscopic data for compounds 1–4, registered in CHCl at room
(
3
–
5
temperature, are presented in Table 1. Low concentration solutions (1.0–4.0 × 10 M) were
used to avoid aggregation and self-absorption effects. Trans to cis isomerization was not
observed under the analysis conditions.
As an example, the spectra of compounds 1b, 2b and 3b are provided in Figure 1. All
compounds exhibited structureless absorption and emission bands with rather large Stokes
–
1
shifts in the 4900–6300 cm range, which is associated with highly polarizable π-conjugated
3
5
systems due to intramolecular charge transfer (ICT). It is worth noting that 4-
arylvinylquinolines 2 presented higher Stokes shifts than their analogs 1 and 3. As expected,
5
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the presence of strong electron-donating diphenylamino groups resulted in significantly red-
shifted absorption and emission maxima as well as higher Stokes shifts in each series. With
the exception of compound 1c, the methoxy-substituted derivatives were poorly emissive (ΦF
≤
0.02). Diphenylamino substituted compounds 1–3b and 4 exhibited blue-green emission
with emission maxima increasing in the order: 4 << 1b < 3b < 2b. The 2-arylquinoline 4,
without a vinylene linker, showed an outstanding fluorescence quantum yield (0.98), which is
significantly higher than that of its 2-arylvinyl analog 1b. This phenomenon has been
4
,36
observed previously in other series of compounds. The quantum yield for 2-styrylquinoline
b (Φ = 0.61) was also substantially higher than those for the 4-styrylquinoline 2b and the 1-
1
F
styrylisoquinoline 3b (Φ = 0.29 in both cases).
F
Table 1. UV-vis and photoluminescence (PL) data for compounds 1–4 in CHCl solution.
3
a
–1
–1
–1
Stokes Shift (cm )
Compd
λabs (nm)
ε (mM cm )
λem (nm)
ΦF
1
a
346
399
354
347
397
354
360
402
374
16.4
37.9
24.9
17.7
21.0
16.2
17.1
25.4
24.7
417
502
430
429
519
450
441
512
462
0.02
0.61
0.15
< 0.01
0.29
0.02
< 0.01
0.29
0.98
4921
5142
4993
5508
6285
6026
5102
5344
1
b
1
c
2
a
2
b
2
c
3
a
3
b
4
5093
a
–5
All spectra were recorded at room temperature at c = 1.25–1.89 × 10 M.
Figure 1. Normalized absorption (dashed lines) and emission (solid lines) spectra of
compounds 1b (green), 2b (blue) and 3b (red) in CHCl solution.
3
6
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Solvatochromic behavior. Emission solvatochromism is one of the possible ways to
evaluate ICT. Push-pull chromophores generally exhibit limited absorption
a
solvatochromism and a large positive fluorosolvatochromism, i.e., a red shift is observed
when the solvent polarity is increased due to the stabilization of a highly polar excited
3
5,37,38
state.
Therefore, the emission properties of compounds 1–4 were studied in a variety of
aprotic solvents of increasing polarity. The results are summarized in Table 2. As
representative examples, the normalized spectra registered for 3b are shown in Figure 2 (see
Figure S1 in the Supporting Information for other compounds). The emission maxima,
expressed as wavenumber, were plotted versus the E (30) Dimroth–Reichardt polarity
T
3
9
parameters and in all cases a good linearity was observed (Figure 3 and Figure S2).
Regarding the diphenylamino series, the absolute value of the slope of the regression line is
somewhat higher for the 4-styrylquinoline 2b, which indicates a stronger ICT. Spectra
broadening could also be observed when the polarity was increased. Nevertheless, there is a
no clear correlation between the full width at half maximum (FWHM) expressed as difference
of wavenumber and E (30) (Table S1, Supporting Information).
T
Table 2. Emission solvatochromism of compounds 1–4 in various aprotic solvents.
Compd n-Heptane Toluene 1,4-Dioxane
THF CHCl
a
(37.4) (39.1)
CH Cl
2
Acetone MeCN
3
a
2
a
a
a
a
a
a
(
30.9)
390
448
399
411
451
418
425
460
410
(33.9)
400
466
410
424
480
434
434
479
430
(36.0)
402
471
412
425
487
430
438
480
437
(40.7)
419
513
434
437
538
454
451
521
474
(42.2)
421
517
437
445
550
459
449
528
480
(45.6)
433
544
448
454
569
465
453
549
499
1
a
409
495
427
433
519
447
444
511
458
417
502
430
429
529
450
441
512
1
b
1
c
2
a
2
b
2
c
3
a
3
b
4
462
a
–1
E (30) Dimroth–Reichardt polarity parameter in kcal mol .
T
7
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Figure 2. Normalized emission spectra of 3b in different aprotic solvents.
Figure 3. Emission maxima (ν ) for compounds 1–3b and 4 (diphenylamino series) as a
em
function of the E (30) Dimroth–Reichardt polarity parameters.
T
Protonation studies. The consequences of protonation on the photophysical
–
2
properties of the materials were studied in a 10 M solution of camphorsulfonic acid (CSA)
in chloroform. The results are given in Table 3 and the normalized absorption and emission
spectra of the neutral and protonated form of 1b are shown in Figure 4. In all cases a
significant red shift in the absorption and emission bands was observed. Whereas the
methoxystyryl derivatives 1–3a remained poorly emissive after protonation, the emission
8
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quantum yield of the methoxynaphthylvinyl derivatives 1c and 2c increased. The
diphenylaminostyryl derivatives 1–3b remained moderately emissive and afforded red-light,
although a noticeable decrease in the quantum yield was observed for all of these materials.
The fluorescence intensity of compound 4 decreased dramatically in the presence of CSA, as
3
1
reported previously for other acids.
–
2
Table 3. UV-vis and PL data of compounds 1–4 in acid solution (10 M CSA in CHCl ).
3
a
–1
–1
–1
Stokes Shift (cm )
Compd
λabs (nm) ε (mM cm ) λ (nm)
em
ΦF
1
a
412
509
428
412
509
427
413
512
467
25.0
52.3
18.3
21.9
17.3
14.8
17.5
23.8
31.9
502
660
541
505
672
545
513
674
650
0.04
0.18
0.31
< 0.01
0.22
0.08
4352
4495
4880
4470
4765
5071
4720
4694
1b
1
c
2a
2b
2
c
3a
< 0.01
0.20
3b
4
0.03
6029
a
–5
All spectra were recorded at room temperature at c = 1.25–1.89 × 10 M.
Figure 4. Normalized absorption (dashed lines) and emission (solid lines) of compound 1b in
–
2
CHCl with (red) or without (blue) CSA (10 M).
3
The changes observed for compound 1b in the UV-vis and emission spectra upon
addition of CSA are shown in Figure 5. The increase in the concentration of acid led to the
9
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progressive attenuation of the charge transfer absorption band and the appearance of a new
red-shifted band corresponding to the protonated species. An isosbestic point, which is
characteristic of an equilibrium between two species, was observed at ~440 nm (Figure 5,
left). A similar trend was observed for the fluorescence response: the addition of CSA also
caused a steady decrease of the emission band of the neutral form and the enhancement of a
new red-shifted band for the protonated form with an isoemissive point (Figure 5, right). Both
bands exhibited a similar intensity when 0.6–0.7 equivalents of CSA were added, at an
excitation wavelength of 440 nm. Similar behaviors were also found for compounds 1c, 2b
and 3b (see Figures S3–S5 in the Supporting Information). Fine tuning of the band ratio was
possible by changing the excitation wavelength (see Figure S6 in the Supporting Information).
2
6-29
In a similar way to pyrimidine and pyridine derivatives,
protonated forms of 1b, 1c, 2b and 3b in solution led to emission rather close to white light
Figure 6, see also Figures S7–S9 in the Supporting Information). The calculated CIE
the coexistence of neutral and
(
chromaticity coordinates are listed in Table 4.
Figure 5. Changes in the absorption (left) and emission (right, λ = 440 nm) spectra of a
exc
–
5
CHCl solution of 1b (c = 1.89 × 10 M) upon addition of CSA (0–1.5 equivalents).
3
1
0
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–
5
Figure 6. Changes in the color of a CHCl solution of 1b (c = 1.89 × 10 M) after the
3
–
2
addition of 0.9 equivalents (middle) and in 10 M CSA (right). Photographs were taken in the
dark upon irradiation with a hand-held UV lamp (λem = 366 nm).
–
5
Table 4. CIE coordinates in CHCl solution (c = 1.0–2.0 × 10 M).
3
Chromaticity coordinates (x,y)
Mixture of neutral
Compd Neutral form Protonated form
and protonated forms
a
1
b
(0.23, 0.50)
(0.15, 0.09)
(0.32, 0.57)
(0.07, 0.13)
(0.28, 0.55)
(0.15, 0.16)
(0.62, 0.35)
(0.36, 0.57)
(0.64, 0.34)
(0.39, 0.57)
(0.62, 0.36)
(0.61, 0.39)
(0.31, 0.47)
(0.26, 0.34)
(0.40, 0.51)
-
(0.36, 0.51)
-
b
a
1
c
2
b
2
c
a
3
b
4
a
b
0
.5 equivalents of CSA, λexc = 440 nm. 0.3 equivalents of CSA,
λexc = 385 nm.
Theoretical studies. Calculations based on Density Functional Theory (DFT) and its
time-dependent extension (TD-DFT) were performed on a selection of chromophores (1b, 2b,
3
b and 4) to gain a deeper understanding of the relation between molecular structure and
photophysical properties. As expected for this class of chromophore, all compounds exhibited
a lowest-energy transition (see Table 6) with non-negligible charge transfer character, which
is reasonably well described by the frontier molecular orbitals HOMO and LUMO (Figure
S27 and S28). Geometry optimizations of the neutral forms revealed that whereas 1b and 3b
are already planar in their ground state, 2b and 4 have a molecular backbone with a significant
twist angle in the ground state (27° and 19°, respectively) that vanishes in the excited state,
1
1
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thus undergoing significant structural reorganization in their excited state. The latter process
can be further captured through the variation of the bond length alternation (BLA), which is
summarized in Table 5 for the three compounds that have a vinyl bridge. For the neutral
forms, BLA are sizeable and consistent with the significant Stokes shift observed
experimentally (Table 1) and confirmed theoretically (Table 6). Clearly, 2b has the largest
Stokes shift as a result of largest structural reorganization between its ground and excited
states. With regards to the protonated forms, the BLA variation between the ground and
excited states of each compound (Table 5) is significantly smaller when compared to that of
their neutral counterparts. This in turn leads to markedly smaller Stokes shifts for the
protonated species. Interestingly, whereas the protonated form of 2b is almost planar in the
ground state, protonated 3b becomes twisted, probably due to the greater steric hindrance
produced by the proton and its counter anion, and the Stokes shift is comparable to that of 2b.
Among all computed excited state geometries, the protonated form of compound 4 is the only
one that retains a significant twist angle in the excited state (13° as compared to 25° in the
ground state). This is probably related to steric hindrance as a result of the missing vinyl
moiety between the phenyl and quinoline rings. The remaining twist may favor non-radiative
relaxation pathways and may be responsible for the very low radiative quantum yield
measured experimentally (Table 3).
Table 5. Computed Bond Length Alternation (BLA [Å] of the
C–C=C–C vinyl bridge for the neutral and protonated
compounds 1b–3b in CHCl (see computational details in the
3
Experimental Part).
a
BLA [Å]
Neutral form
Protonated form
Compd
GS
ES
GS
ES
1
2
3
b
b
b
0.1112
0.1108
0.1111
0.0050
–0.0009
0.0007
0.0669
0.0660
0.0707
0.0215
0.0248
0.0181
a
GS is the ground state and ES is the excited state.
1
2
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Table 6. Theoretical absorption and emission data for neutral and protonated compounds 1b–
b and 4 in CHCl with a linear response PCM model and state-specific (SS) values in
3
3
parenthesis.
a
f
a
f
–1
Stokes Shift (cm )
Compd
λabs (nm)
λem (nm)
1
2
3
b
b
b
371
SS: 384)
1.64
1.30
1.37
1.01
1.80
1.53
1.47
1.12
456
(SS: 454)
485
(SS: 481)
486
(SS: 474)
399
(SS: 424)
1.90
1.56
1.56
1.30
1.93
1.68
1.65
1.14
5024
(SS: 4015)
5977
(SS: 4336)
5197
(SS: 4029)
4264
(SS: 4039)
(
(
(
(
(
(
(
(
376
SS: 398)
388
SS: 398)
4
341
SS: 362)
476
+
+
+
+
1
2
3
4
b-H
b-H
b-H
b-H
543
2592
SS: 441)
(SS: 497)
573
(SS: 516)
(SS: 2555)
2350
(SS: 2172)
505
SS: 464)
486
568
2970
SS: 452)
(SS: 514)
499
(SS: 506)
(SS: 2669)
3489
(SS: 4450)
425
SS: 413)
a
f is the oscillator strength.
Photophysical properties in thin film. Simple thin films of polystyrene doped with 1
wt% of the diphenylamino-substituted derivatives 1–3b were prepared by spray deposition on
glass substrates. The films remained luminescent and exhibited blue emission, although the
emission maxima experienced a blue shift when compared to the CHCl solutions. The
3
addition of 0.06 equivalents of CSA to the solutions of 1b and 2b and 0.18 equivalents to the
solution of 3b used for the spray deposition resulted in a film that exhibited two emission
bands with CIE coordinates close to pure white (Figure 7, Table 5). Films of fully protonated
compounds led to emission maxima in the orange-red region. It is worth noting that the color
coordinates changed slightly when different areas of the films were irradiated, which can be
attributed to the inhomogeneities of the deposited layers. These significant changes in the
emission colors could be easily followed by the naked eye (Figure 7, see also Figures S10 and
S11 in the Supporting Information).
1
3
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1
1
1
b
1
00
b + 0.06 eq CSA
b + 1 eq CSA
▲
1b
8
6
4
2
0
0
0
0
0
●
■
1b + 0.06 eq CSA
1b + 1 eq CSA
4
00
500
600
700
wavelength (nm)
Figure 7. Fluorescence spectra (λexc = 366 nm), colors and CIE chromaticity diagram for
polystyrene thin films doped with 1b (1 wt%) in the absence and the presence of 0.06 and 1
equivalents of CSA (from left to right). Photographs were taken in the dark upon irradiation
with a hand-held UV lamp (λem = 366 nm).
Table 5. PL data and CIE coordinates of thin films of polystyrene doped with 1%wt 1–3b.
λ
em (nm)
Chromaticity coordinates (x,y)
Neutral Protonated
Neutral
form
Protonated
form
Mixture of neutral
Compd
form
form
and protonated forms
a
1b
2b
3b
475
632
(0.15, 0.26) (0.61, 0.35)
(0.16, 0.29) (0.58, 0.35)
(0.31, 0.32)
(0.33, 0.36)
(0.34, 0.33)
a
479
625
b
481
628
(0.15, 0.31) (0.56, 0.33)
a
b
0
.06 equivalents of CSA, λexc = 366 nm. 0.18 equivalents of CSA, λ = 366 nm.
exc
CONCLUSION
We have designed a series of conjugated push-pull (iso)quinolines that proved to be
effective materials for white light emission. Well-known methodologies based on the
Knoevenagel condensation and Suzuki–Miyaura reaction were used for the synthesis of these
compounds, in which either a methoxy or diphenylamino donor group was connected to the
(iso)quinoline acceptor fragment through different π-bridges. The study of the photophysical
properties revealed significant red shifts in the absorption and emission maxima on increasing
the electron-donating ability of the substituent, which is explained on the basis of an enhanced
ICT and confirmed by a stronger emission solvatochromism. The presence of diphenylamino
1
4
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Chemistry - A European Journal
10.1002/chem.202000817
groups also led to higher Stokes shifts and fluorescence quantum yields in each series. The
molecules could be easily protonated at the nitrogen atom of the (iso)quinoline fragment.
Protonation provided a substantial enhancement in the electron-withdrawing character and,
consequently, the appearance of a new red-shifted complementary emitting band. Albeit with
a noticeable decrease in the quantum yield, diphenylaminostyryl derivatives 1–3b remained
moderately emissive after the addition of acid. Thus, white light emission could be obtained
by controlled protonation both in solution and in solid state. This is a new example of the use
of a single emitting material with two forms of complementary emitting colors as a new
strategy to obtain white light.
EXPERIMENTAL PART
General information. All solvents were reagent grade for synthesis and spectroscopic grade
for photophysical measurements. The starting materials were purchased from Sigma-Aldrich
or TCI and were used without further purification. For air- and moisture-sensitive reactions,
all glassware was flame-dried and cooled under nitrogen. NMR spectra were recorded in
1
13
CDCl on Bruker Avance 300 ( H at 300 MHz and C at 75 MHz) and Bruker Avance Neo
3
1
5
00 ( H at 500 MHz) spectrometers. The chemical shifts δ are reported in ppm and are
1
referenced to the residual protons of the deuterated solvent or carbon nuclei ( H, δ = 7.27
13
1
ppm; C, δ = 77.0 ppm). The coupling constants J are given in Hz. In the H NMR spectra,
the following abbreviations are used to describe the peak patterns: s (singlet), d (doublet), dd
13
(
doublet of doublets), t (triplet), m (multiplet). In the C NMR spectra, the nature of the
carbons (C, CH, CH or CH ) was determined by performing a JMOD experiment. Acidic
2
3
impurities in CDCl were removed by treatment with solid K CO . Melting points (°C) were
3
2
3
measured on a Kofler hot-stage with a precision of 2 degrees (± 2 °C). High-resolution mass
analyses were performed at the ‘Centre Régional de Mesures Physiques de l’Ouest’ (CRMPO,
1
5
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Chemistry - A European Journal
10.1002/chem.202000817
Université de Rennes 1) using a Bruker MicroTOF-Q II apparatus. Analytical thin layer
chromatography (TLC) was performed on silica gel plates (Merck 60 F254) and compounds
were visualized by irradiation with UV light at 254 and 365 nm. Flash chromatography was
performed using silica Acros SI 60 (60–200 mesh ASTM). UV-visible and fluorescence
spectroscopy studies in solution were conducted on a Spex Fluoromax-3 Jobin-Yvon Horiba
spectrophotometer. Compounds were excited at their absorption maxima (band of lowest
energy) to record the emission spectra. All solutions were measured with optical densities
below 0.1. Fluorescence quantum yields (± 10%) were determined relative to 9,10-
bis(phenylethynyl)anthracene in cyclohexane (Φ = 1.00). Acidic impurities in solvents were
F
removed by treatment with Al O . Stokes shifts were calculated considering the lowest
2
3
energetic absorption band. Thin films were prepared by the direct nebulization of CHCl3
solutions of polystyrene doped with the appropriate compound (1 wt%, in the absence and the
presence of CSA) on various heated glass substrates through a fine spray nozzle obtained by
using an air compressor system. Fluorescence spectra of these films were recorded on a Jasco
FP-8300 spectrofluorometer at λexc = 366 nm.
General procedure for the synthesis of arylvinylquinoline derivatives. A stirred mixture
of the corresponding methylquinoline (2 mmol) and the appropriate aldehyde (1 mmol) in
®
aqueous sodium hydroxide (5 M, 10 mL) containing Aliquat 336 (22 mg, 0.05 mol) was
heated under reflux for 20 h. The mixture was cooled and the precipitate was filtered off and
washed with water. For compounds 1 and 2c, the precipitate was washed with acidified (HCl)
ethanol, solubilized in CH Cl and a few drops of NEt were added to neutralize the formed
2
2
3
quinolinium salt. The organic solution was washed with water, dried with MgSO , and the
4
solvent was evaporated under reduced pressure.
(E)-2-(4-Methoxystyryl)quinoline (1a). Cream solid, yield 74% (195 mg). Mp 124–126 °C
4
0
1
(
lit. : 125–127 °C). H NMR (300 MHz, CDCl ): δ 8.11 (d, J = 8.7 Hz, 1H), 8.06 (d, J = 8.4
3
1
6
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Chemistry - A European Journal
10.1002/chem.202000817
Hz, 1H), 7.77 (d, J = 8.1 Hz, 1H), 7.72–7.56 (m, 5H), 7.51–7.45 (m, 1H), 7.29 (d, J = 16.5
Hz, 1H), 6.94 (d, J = 8.7 Hz, 2H), 3.85 (s, 3H). The spectroscopic data were consistent with
3
9
those reported in the literature.
(E)-2-[4-(Diphenylamino)styryl]quinoline (1b). Orange solid, yield 37% (146 mg). Mp
32
1
1
50–152 °C (lit. : 150–151.4 °C). H NMR (300 MHz, CDCl ): δ 8.11 (d, J = 8.7 Hz, 1H),
3
8
.07 (d, J = 8.7 Hz, 1H), 7.76 (d, J = 8.1 Hz, 1H), 7.72–7.64 (m, 2H), 7.62 (d, J = 16.2 Hz,
1
H), 7.52–7.45 (m, 3H), 7.32–7.26 (m, 5H), 7.17–7.12 (m, 4H), 7.08–7.04 (m, 4H). The
3
2
spectroscopic data were consistent with those reported in the literature.
(E)-2-[2-(6-Methoxynaphthalen-2-yl)vinyl]quinoline (1c). Cream solid, yield 55% (171
1
mg). Mp 150 °C (dec.). H NMR (300 MHz, CDCl ): δ 8.11 (d, J = 8.7 Hz, 1H), 8.09 (d, J =
3
8
.7 Hz, 1H), 7.93–7.67 (m, 8H), 7.53–7.47 (m, 1H), 7.47 (d, J = 16.2 Hz, 1H), 7.18–7.15 (m,
1
3
2
H), 3.94 (s, 3H). C NMR and JMOD (75 MHz, CDCl ): δ 55.4 (CH ), 106.0 (CH), 119.2
3
3
(CH), 119.3 (CH), 124.3 (CH), 126.1 (CH), 127.3 (CH), 127.3 (C), 127.5 (CH), 127.9 (CH),
1
28.3 (CH), 129.0 (C), 129.2 (CH), 129.7 (CH), 129.8 (CH), 132.0 (C), 134.7 (CH), 134.8
(C), 136.3 (CH), 148.3 (C), 156.3 (C), 158.2 (C). HRMS (ESI/ASAP, TOF): m/z calcd for
+
C H NO [M + H] 312.1383, found 312.1387.
22
18
(E)-4-(4-Methoxystyryl)quinoline (2a). Purified by column chromatography (SiO2,
1
petroleum ether/EtOAc, 1/1). Pale yellow solid, yield 41% (144 mg). Mp 90–92 °C. H NMR
(
300 MHz, CDCl ): δ 8.87 (d, J = 4.8 Hz, 1H), 8.20 (d, J = 7.8 Hz, 1H), 8.13 (d, J = 7.8 Hz,
3
1
3
1
H), 7.72–7.53 (m, 6H), 7.27 (d, J = 16.2 Hz, 1H), 6.94 (d, J = 8.7 Hz, 2H), 3.84 (s, 3H). C
NMR and JMOD (75 MHz, CDCl ): δ 55.4 (CH ), 114.3 (CH), 116.7 (CH), 120.4 (CH),
3
3
1
23.5 (CH), 126.4 (CH), 128.5 (CH), 129.3 (CH), 129.4 (C), 130.0 (CH), 134.7 (CH), 143.3
(
C), 148.6 (C), 150.1 (CH), 160.3 (C). HRMS (ESI/ASAP, TOF): m/z calcd for C H NO [M
1
8
16
+
+
H] 262.1226, found 262.1231.
1
7
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Chemistry - A European Journal
10.1002/chem.202000817
(E)-4-[4-(Diphenylamino)styryl]quinoline (2b). Purified by column chromatography (SiO2,
1
petroleum ether/EtOAc, 1/1). Orange solid, yield 63% (229 mg). H NMR (300 MHz,
CDCl ): δ 8.87 (d, J = 4.8 Hz, 1H), 8.22 (d, J = 8.4 Hz, 1H), 8.13 (d, J = 8.4 Hz, 1H), 7.76–
3
7
.70 (m, 1H), 7.71 (d, J = 16.5 Hz, 1H), 7.61–7.55 (m, 2H), 7.50 (d, J = 8.7 Hz, 2H), 7.33–
13
7
.27 (m, 5H), 7.16–7.05 (m, 8H). C NMR and JMOD (75 MHz, CDCl ): δ 116.7 (CH, 120.6
3
(CH), 122.9 (CH), 123.5 (CH), 124.5 (CH), 124.9 (CH), 126.4 (CH), 126.4 (C), 128.1 (CH),
1
29.3 (CH), 129.4 (CH), 130.1 (CH), 130.3 (C), 134.6 (CH), 143.3 (C), 147.3 (C), 148.5 (C),
+
1
48.7 (C) 150.2 (CH). HRMS (ESI/ASAP, TOF): m/z calcd for C H N [M + H] 399.1856,
2
9
23
2
found 399.1855.
(E)-4-[2-(6-Methoxynaphthalen-2-yl)vinyl]quinoline (2c). Pale yellow solid, yield 73%
1
(
225 mg). Mp 110–112 °C. H NMR (300 MHz, CDCl ): δ 8.92 (d, J = 4.5 Hz, 1H), 8.28 (d, J
3
=
8.1 Hz, 1H), 8.14 (d, J = 8.4 Hz, 1H), 7.93–7.73 (m, 6H), 7.72–7.58 (m, 2H), 7.49 (d, J =
1
3
1
5.9 Hz, 1H), 7.20–7.17 (m, 2H), 3.95 (s, 3H). C NMR and JMOD (75 MHz, CDCl ): δ
3
5
5.4 (CH ), 106.0 (CH), 116.9 (CH), 119.4 (CH), 121.9 (CH), 123.5 (CH), 124.1 (CH), 126.4
3
(C), 126.5 (CH), 127.5 (CH), 127.8 (CH), 129.0 (C), 129.3 (CH), 129.8 (CH), 130.1 (CH),
1
31.9 (C), 134.8 (C), 135.3 (CH), 143.2 (C), 148.7 (C), 150.2 (CH), 158.3 (C). HRMS
+
(
ESI/ASAP, TOF): m/z calcd for C H NO [M + H] 312.1383, found 312.1385.
2
2
18
General procedure for the synthesis of arylvinylisoquinoline derivatives. 1-
Methylisoquinoline (143 mg, 1 mmol) and the corresponding aldehyde (1 mmol) were
t
dissolved in anhydrous THF (15 mL). KBu O (447 mg, 4 mmol) was slowly added at room
temperature and the solution was heated under reflux for 15 h. After cooling, water was
added, the THF was evaporated, and the mixture was extracted with CH Cl . The organic
2
2
layer was dried over MgSO and the solvent was removed under vacuum. The crude product
4
was purified by flash chromatography (SiO , petroleum ether/EtOAc, 7/3).
2
1
8
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Chemistry - A European Journal
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(E)-1-(4-Methoxystyryl)isoquinoline (3a). Pale yellow solid, yield 30% (75 mg). Mp 88–90
1
°
C. H NMR (300 MHz, CDCl ): δ 8.54 (d, J = 5.7 Hz, 1H), 8.37 (d, J = 8.4 Hz, 1H), 7.96 (d,
3
J = 15.6 Hz, 1H), 7.87 (d, J = 15.6 Hz, 1H), 7.82 (d, J = 8.7 Hz, 1H), 7.70–7.59 (m, 4H), 7.54
1
3
(
d, J = 5.7 Hz, 1H), 6.95 (d, J = 8.7 Hz, 2H), 3.85 (s, 3H). C NMR and JMOD (75 MHz,
CDCl ): δ 55.4 (CH ), 114.2 (CH), 119.6 (CH), 120.6 (CH), 124.5 (CH), 126.6 (C),
3
3
1
27.1(CH), 127.3 (CH), 128.8 (CH), 129.7 (C), 129.8 (CH), 135.4 (CH), 136.8 (C), 142.5
(
[
CH), 150.2 (CH), 154.9 (C), 160.1 (C). HRMS (ESI/ASAP, TOF): m/z calcd for C H NO
1
8
16
+
M + H] 262.1226, found 262.1229.
E)-1-[4-(Diphenylamino)styryl]isoquinoline (3b). Yellow solid, yield 21% (81 mg). H
NMR (500 MHz, CDCl ): δ 8.55 (d, J = 5.5 Hz, 1H), 8.37 (d, J = 8.0 Hz, 1H), 7.96 (d, J =
1
(
3
1
5.5 Hz, 1H), 7.89 (d, J = 15.5 Hz, 1H), 7.83 (d, J = 8.5 Hz, 1H), 7.70–7.67 (m, 1H), 7.64–
.61 (m, 1H), 7.58 (d, J = 9.0 Hz, 2H), 7.55 (d, J = 5.5 Hz, 1H), 7.31–7.28 (m, 4H), 7.16 (dd,
7
1
3
J = 8.5 Hz, J = 1.0 Hz, 4H), 7.10–7.06 (m, 4H). C NMR and JMOD (75 MHz, CDCl ): δ
3
1
19.6 (CH), 120.7 (CH), 122.9 (CH), 123.4 (CH), 124.5 (CH), 124.8 (CH), 126.7 (C), 127.1
(CH), 127.3 (CH), 128.4 (CH), 129.4 (CH), 129.8 (CH), 130.7 (C), 135.4 (CH), 136.7 (C),
1
42.5 (CH), 147.4 (C), 148.3 (C), 154.8 (C). HRMS (ESI/ASAP, TOF): m/z calcd for
+
C H N [M + H] 399.1856, found 399.1858.
29
23
2
2
-[4-(Diphenylamino)phenyl]quinoline (4). A stirred mixture of the corresponding 2-
bromoquinoline (208 mg, 1 mmol), 4-(diphenylamino)phenylboronic acid (433 mg, 1.5
mmol) and Pd(PPh ) (68 mg, 0.06 mmol) in degassed aqueous 2 M sodium carbonate (2
3
4
mmol, 1 mL)/ethanol (1 mL)/toluene (15 mL) was heated under reflux for 24 h under a
nitrogen atmosphere. The reaction mixture was cooled, filtered and EtOAc/water 1/1 (20 mL)
was added. The organic layer was separated and the aqueous layer was extracted with
additional EtOAc (2 × 10 mL). The combined organic extracts were dried over MgSO and
4
the solvent was evaporated under reduced pressure. The crude product was purified by flash
1
9
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Chemistry - A European Journal
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4
1
chromatography (SiO , CH Cl ). Yellow solid, yield 51% (191 mg). Mp 174–176 °C (lit. :
2
2
2
1
1
72–174 °C). H NMR (300 MHz, CDCl ): δ 8.17 (d, J = 8.7 Hz, 1H), 8.16 (d, J = 8.4 Hz,
3
1
H), 8.06 (d, J = 8.7 Hz, 2H), 7.83 (d, J = 8.4 Hz, 1H), 7.81 (d, J = 8.1 Hz, 1H), 7.72 (m, 1H),
7
.50 (m, 1H), 7.33–7.26 (m, 4H), 7.24–7.18 (m, 6H), 7.11–7.06 (m, 2H). The spectroscopic
4
1
data were consistent with those reported in the literature.
4
2
Computational details. All calculations were performed with the Gaussian 16 code.
Geometry optimizations for the different compounds were followed by frequency
4
3
calculations, to ensure the true nature of the energy minimum, at the PBE0 /6-311+G(d,p)
level. To obtain the absorption features Time-Dependent DFT calculations were performed at
4
4
this ground state equilibrium geometry in a vertical fashion using the CAM-B3LYP and the
6
-311+G(d,p) basis set, while the excited-state geometries were optimized with the same level
of theory to provide the emission properties. Bond Length Alternation (BLA) values were
computed for the ground state and excited state on the C–C=C–C vinyl bridge as a difference
between the mean value of the two simple bond distances and the double bond one.
In all of these steps the solvent effects were included trough the Polarizable Continuum
4
5
Model (PCM). For absorption and emission vertical transitions, both the non-equilibrium
4
6
47
Linear-Response (LR) PCM and the State-Specific (SS) PCM were used for the sake of
comparison. Note that for emission, only the final vertical transition, at the excited state
equilibrium geometry, was computed at the SS-PCM level, while the equilibrium LR-PCM
was used for the excited state relaxation process.
Acknowledgments. J. R.-L. thanks the Ministerio de Economía y Competitividad/Agencia
Estatal de Investigación/FEDER for financial support (project CTQ2017-84561-P). Funding
from the Junta de Comunidades de Castilla-La Mancha/FEDER is also gratefully
acknowledged by J. R.-L. and S. A. (project SBPLY/17/180501/000214).
2
0
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10.1002/chem.202000817
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