Base-assisted one-pot synthesis of N, N ′, N ″- triaryltriazatriangulenium dyes: Enhanced fluorescence efficiency by steric constraints

Article abstract of DOI:10.1021/jo3007732

In this paper we report the first synthesis of cationic N,N′,N″-triaryltriazatriangulenium dyes (Ar₃-TATA ⁺). Previously, only alkyl-substituted triazatriangulenium derivatives (R₃-TATA⁺) were known, a consequence of the low reactivity of anilines in the aromatic nucleophilic substitution reaction leading to the formation of the TATA⁺ core. The synthesis of Ar ₃-TATA⁺ was achieved by heating the tris(2,6- dimethoxyphenyl)methylium ion (DMP₃C⁺) in various anilines in the presence of NaH. In the solvent-free reaction all three aryl substituents could be introduced despite the low reactivity of the anilines. The symmetric Ar₃-TATA⁺ derivatives with Ar = phenyl (2), 4-methoxyphenyl (3), and 4-bromophenyl (4) were synthesized. Single crystal structures of 2 and 4 were obtained as BF₄^- salts, where torsional angles larger than 80° were observed between the TATA⁺ chromophore and the aryl substituents. The photophysical properties were studied in solution and in thin films. The results show that the Ar₃- TATA⁺ dyes have a surprising 3-fold increase in fluorescence quantum yields when compared to the parent alkyl-substituted R₃-TATA ⁺ salts. With a high quantum yield (>50%) and emission in the red (_fl = 560 nm) the Ar₃-TATA⁺ dyes represent a promising new addition to the family of superstable cationic triangulenium dyes. Additionally, the synthesized tribromo derivative 4 is shown to be a potential triagonal synthon for polymers and other macromolecules.

Full text of DOI:10.1021/jo3007732

Article
pubs.acs.org/joc
Base-Assisted One-Pot Synthesis of N,N′,N″-
Triaryltriazatriangulenium Dyes: Enhanced Fluorescence Efficiency
by Steric Constraints
Peter Hammershøj,† Thomas Just Sørensen,† Bao-Hang Han,‡ and Bo W. Laursen*,†
†Nano-Science Center & Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK2100 København Ø,
Denmark
‡National Center for Nanoscience and Technology, 11 Beiyitiao Zhongguancun, Beijing 100190, China
S
* Supporting Information
ABSTRACT: In this paper we report the first synthesis of cationic N,N′,N″-triaryltriazatriangulenium dyes (Ar3-TATA+).
Previously, only alkyl-substituted triazatriangulenium derivatives (R3-TATA+) were known, a consequence of the low reactivity of
anilines in the aromatic nucleophilic substitution reaction leading to the formation of the TATA+ core. The synthesis of Ar3-
TATA+ was achieved by heating the tris(2,6-dimethoxyphenyl)methylium ion (DMP3C+) in various anilines in the presence of
NaH. In the solvent-free reaction all three aryl substituents could be introduced despite the low reactivity of the anilines. The
symmetric Ar3-TATA+ derivatives with Ar = phenyl (2), 4-methoxyphenyl (3), and 4-bromophenyl (4) were synthesized. Single
−
crystal structures of 2 and 4 were obtained as BF4 salts, where torsional angles larger than 80° were observed between the
TATA+ chromophore and the aryl substituents. The photophysical properties were studied in solution and in thin films. The
results show that the Ar3-TATA+ dyes have a surprising 3-fold increase in fluorescence quantum yields when compared to the
parent alkyl-substituted R3-TATA+ salts. With a high quantum yield (>50%) and emission in the red (λfl = 560 nm) the Ar3-
TATA+ dyes represent a promising new addition to the family of superstable cationic triangulenium dyes. Additionally, the
synthesized tribromo derivative 4 is shown to be a potential triagonal synthon for polymers and other macromolecules.
and with high symmetry and (2) the unsubstituted azaoxa-
triangulenium dyes,28−33 which constitute a unique class of
fluorophores, with long fluorescence lifetime, emission in the
red, and a high quantum yield. On the synthetic pathway to the
triangulenium dyes, helical cationic dyes are found.34,35 Of
these especially dimethoxyquinacridinium (DMQA+) has been
investigated.35−40
INTRODUCTION
■
Triazatriangulenium (TATA+) belongs to the large group of
charged fluorescent dyes of which the most prominent are
fluorescein and rhodamine. The investigation of known
derivatives and the synthesis and characterization of new
derivatives of these fluorophores is an ongoing process.1−6 In
the past decades the focus has been more that of application:
The fluorescent dyes act as reporters of sensing events in
artificial or biological systems7−14 and as stains to image
biological systems.15−19 TATA+ has yet to be used in these
application, mainly because of a quantum yield of only 20%,
which makes TATA+ the least fluorescent of the triangulenium
dyes.20 The fluorescent triangulenium dyes fall in two groups:
(1) the donor-substituted amino-trioxatriangulenium dyes,21−26
which have photophysics similar to that of rhodamines and
fluoresceins,27 but with a manifold increase in cation stability
Recently, the cationic nature of TATA+ has been exploited to
form self-assembled ionic supramolecular assemblies, where the
combination of charge and other molecular properties has been
used to control the nanostructure of materials.41−44 A similar
approach to that of in ionic self-assembly (ISA), where distinct
properties of anions and cations combined with their mutual
Received: April 15, 2012
Published: May 22, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of Phenyl-TATA+ 2 (36%), 4-Methoxyphenyl-TATA+ 3 (24%), and 4-Bromophenyl-TATA+ 4 (22%)
Coulomb attraction are used to form unique materials.45,46 The
unique cation stability of the triangulenium salts allow them to
form materials where the cations are stacked on top of each
RESULTS AND DISCUSSION
Synthesis of Ar3-TATA+ Salts. Symmetric TATA+ cations
were synthesized in a one-pot procedure from the readily
■
other, resulting in segregation of cations and anion.47,48 In the
case of N,N′,N″-trialkyltriazatriangulenium (R3-TATA+), the
molecular conformation does, however, not allow for a
continuous, cofacial columnar stack of the planar cations and
only dimers are formed. For the bromide and tetrafluoroborate
salts this leads to a rare lamellar bilayer structure that self-
organizes with segregation of the alkyl side chains and the ions.
The result is that the TATA+ dimers are ordered in an infinite
2D lattice isolated between layers of alkyl chains.31,49 The high
symmetry and triangular nature of the triangulenium salts has
been exploited to form chiral and supramolecular struc-
tures.50−55 The cationic nature has been used to add functional
structures directly to the center carbon.56−59
In this paper we report on the synthesis and fluorescence
properties of a new series of TATA+ salts, where the three
substituents on nitrogen are aryl groups. The N,N′,N″-
triaryltriazatriangulenium (Ar3-TATA+) dyes have higher
quantum yields than the N,N′,N″-trialkyltriazatriangulenium
(R3-TATA+) dyes, and the dyes are relatively insensitive to
functionalization on the aryl arms. We show the possibility of
using Ar3-TATA+ as a trigonal building block in, e.g., porous
polymers,60−64 by demonstrating the possibility of metal-
catalyzed polymerization of the tribromo derivative. Metal-
catalyzed cross-couplings have previously been shown to be
compatible with the triangulenium skeleton.65,66 Through
crystal structures and thin film absorption spectra we show
that the bulk of the phenyl groups in Ar3-TATA+ inhibit the
formation of closely packed cofacial π−π dimers that otherwise
dominates the solid-state packing of other TATA+ salts.
available tris(2,6-dimethoxyphenyl)carbenium ion ((DMP)3C+
1) (Scheme 1), by three consecutive aromatic nucleophilic
substitution (SNAr) reactions with primary amines.29,30 In the
first step the amine attacks the carbenium ion 1 and replaces
two of the o-methoxy groups, forming a tetramethoxy-
acridinium ion (TMAcr+).67 For simple aliphatic amines the
first reaction is fast and proceeds readily at room temperature.
Introduction of the second and third nitrogen bridge requires
an increasing excess of the amine and elevated temperatures.
However, the low nucleophilicity of anilines have limited the
products to compounds with only one aryl group.30,50,65,66
Refluxing 1 in pure aniline yields Ph-ADOTA+, the product of
one amine SNAr substitution and two intramolecular ring-
closing oxa-bridge-forming reactions. To overcome this
limitation the reactivity of the anilines was enhanced by using
a strong base (NaH), essentially reacting 1 with the sodium
anilide.
In this way Ar3-TATA+ can be prepared directly from 1 using
a large excess of the appropriate aniline and sodium hydride.
The reaction mixture was gradually heated from room
temperature to 200 °C. As the temperature increases three
substitutions (a total of six MeO groups are substituted with
three anilines) were achieved. With each substitution a distinct
change in color and gas evolution was observed. Using this
procedure, the possible Ar3-TATA+ derivatives are limited as
anilines that can be applied in large quantities and have boiling
points above 180 °C are required. From the reaction with
aniline, triphenyl-TATA+ 2 was isolated in a yield of 36% (71%
per reaction) along with the double substitution product
diphenyl-DMQA+ in a yield of 15%. Scheme 1 includes the
expected intermediates/byproducts in the Ar3-TATA+ syn-
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Scheme 2. Suzuki Aryl−Aryl Coupling To Make Naphthalene-phenyl-TATA+ 5, 55%
thesis. If the temperature was set between 90 and 130 °C we
observed TMAcr+ and DMCA+ as the major products
(observed by MALDI-TOF mass spectrometry, not isolated).
At temperatures between 130 and 180 °C, DMQA+ and
DAOTA+ are the dominating products (observed by MALDI-
TOF mass spectrometry, not isolated). In this study, we did not
optimize the synthesis of the mono and double substituted
carbenium ions TMAcr+ and DMQA+. However, our
observations suggest that these compounds and their oxygen
ring-closed analogues can be obtained using the same
procedure reported here, but using lower temperatures. To
further functionalize the new Ar3-TATA+ system, functional
groups on the aryl side groups were introduced. From the
reaction of 1 with 4-methoxyaniline, tris(4-methoxyphenyl)-
TATA+ 3 was isolated in a yield of 24%. In the case of 4-
bromoaniline the reaction needed a longer period of time at
high temperature and gave tris(4-bromophenyl)-TATA+ 4 in a
yield of 22%. The observed order of reactivity and
intermediates in the NaH-assisted reaction with anilines clearly
indicates that the introduction of the aniline moieties indeed
takes place via the SNAr mechanism.
Figure 1. Absorption and emission spectra of triphenyl-TATA+
5
(black) and trioctyl-TATA+ (red) in acetonitrile solution. Both
absorption and emission spectra are normalized to the peak of the
main band.
Table 1. Photophysical Properties of Trioctyl-TATA·BF4 and
Triaryl-TATA·BF4 2−5 in Solution
λmax
(nm)
ε (M−1
λfl
ϕfl
compound
solvent
cm−1
)
(nm) (%)
To investigate post-modification of the functionalized Ar3-
TATA’s, 4 was modified by a triple Suzuki coupling reaction,
using naphthalene-1-boronic acid and (Ph3P)2PdCl2 in
refluxing toluene (Scheme 2). The 4-naphthyl-phenyl sub-
stituted tris(4-(naphthyl)-phenyl)-TATA+ 5 were obtained in a
yield of 55% (82% per reaction). This demonstrates that the
TATA+ ions are compatible with the Suzuki coupling
conditions as was previously shown for the ADOTA+ system.65
Spectroscopy. The photophysical properties of the aryl-
substituted triazatriangulenium dyes are at first glance very
similar to those of the trialkyl-TATA+ salts. The absorption and
emission spectra of triphenyl-TATA+ and trioctyl-TATA+ are
shown in Figure 1. A small red shift of 5 nm is observed in both
absorption and emission accompanied by a broadening of the
absorption and narrowing of the emission band. An increased
absorption in the region 200−300 nm, corresponding to the
absorption of the many isolated aniline and diaminophenylenes,
is not surprisingly observed for the Ar3-TATA+ compounds. All
spectra are included as Supporting Information. The photo-
physical properties are compiled in Table 1. It is evident that
substitutions on the aromatic N-substituents do not alter the
absorption or the emission spectrum of TATA+. Both Ar3-
TATA+ and R3-TATA+ show very little solvatochromism.49
The increase in observed absorption coefficient seen in Table 1
Oct-TATA+
acetonitrile
523
528
535
529
535
530
535
530
530
20,300
20,400
23,800
19,800
23,800
21,100
24,600
21,500
20,500
560
564
558
566
562
565
558
567
561
16
53
55
27
30
62
59
45
38
Ph-TATA+ 2
acetonitrile
dichloromethane
acetonitrile
4-BrPh-TATA+ 3
MeOPh-TATA+ 4
4-NpPh-TATA+ 5
dichloromethane
acetonitrile
dichloromethane
acetonitrile
dichloromethane
is due to a narrowing of the bands in dichloromethane
compared to acetonitrile. The integrated absorption is constant.
Only compound 5 behaves slightly different, with a higher
absorption coefficient in acetonitrile than in dichloromethane.
This is most likely due to solvation effects, as the TATA+
chromophore in this case is flanked by three large aromatic
plates.
The key feature of the Ar3-TATA+, when compared to R3-
TATA+, is the large increase in the fluorescence quantum yield.
The replacement of the simple alkyl chains in R3-TATA+ by
phenyl (2) or 4-methoxyphenyl (4) changes the fluorescence
quantum yield from 16% to 55−60% (Table 1), corresponding
to more than a 3-fold increase. Thus, this substitution of alkyl
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groups with aryl groups changes a mediocre fluorescent dye to
an excellent dye. This effect is surprising as the aryl groups
must have limited electronic overlap with the TATA+
chromophore and it is known that such non-coplanar π
systems most often favors non-radiative deactivation. The
observed reverse effect for the Ar3-TATA+ dyes we attribute to
the increased symmetry and structural constraints imposed on
the TATA chromophore by aryl relative to alkyl substituents.
As seen from the X-ray structures (discussed below) the aryl
groups are decoupled from the TATA chromophore due to
steric interactions between the two subsystems. The steric
interaction is also present in the alkyl derivatives.31 However,
for the alkyl derivatives the result is a symmetry lowering as the
alkyl chains can be located only on one side of the TATA
chromophore. This structural distortion will not be present in
the Ar3-TATA+ dyes because the aryl substituents are
symmetric with respect to the plane of the chromophore. We
speculate that this may be part of the reason for the enhanced
fluorescence efficiency of these dyes. Introduction of more
flexible groups, as in 5, or heavy atoms, as in 3, reduces the
quantum yield again.68,69 Most pronounced is the heavy atom
effect in 3.
the compound in a mixture of dichloromethane and toluene at
room temperature. Selected crystallographic data are shown in
Table 2.
Table 2. Selected Crystallographic Data for Triphenyl-
TATA·BF4 2 and Tris(4-Bromophenyl)-TATA·BF4 4
2·BF4
4·BF4
formula
CCDC
Mw
C37H24BF4N3
CCDC 865387
597.41
C37H21BBr3F4N3
CCDC 865823
834.10
crystal system
space group
a [Å]
monoclinic
P21/n
monoclinic
P21/c
14.75
14.52
b [Å]
10.62
10.94
c [Å]
18.40
19.67
α [deg]
β [deg]
γ [deg]
Z
90.00
90.00
99.04
101.56
90.00
90.00
4
4
V [Å3]
2847.7
3061.2
T [K]
F2
122
122
5.23
6.17
Solid State Structures. The molecular structure of
Rint
0.1059
0.1431
triphenyl-TATA+ (2) and tris(4-bromophenyl)-TATA+ (4)
Dcalcd [g/cm]
crystal size [mm]
1.393
1.810
−
was confirmed by single-crystal X-ray diffraction of their BF4
0.06 × 0.18 × 0.28
0.03 × 0.15 × 0.41
salts (Figure 2). Crystals suitable for single-crystal X-ray
diffraction were obtained by slow evaporation of a solution of
Ar3-TATA+ is an equilateral triangle with three flanking
phenyl rings; see Figure 2a and c. The aryl substituents are
oriented at an angle almost perpendicular to the TATA+ cores;
in the highly strained structure the phenyls adopt an average
angle of 80.5° with the plane of the TATA+ core. The large
torsion angle is a result of the intrinsic steric repulsion.31
The molecular packing of compound 2 and 4 in the obtained
crystals are characterized by a face-to-face arrangement of the
TATA+ cores in slipped dimers with moderate overlap as
shown in Figure 2b,c and 2e,f. This is in contrast to the
symmetric alkyl-substituted R3-TATA·BF4 salts that pack in
−
close cofacial dimers surrounded by the BF4 counterions in
the same plane.29,31,70 The packing of alkyl-TATA is possible
because the alkyl chains can all pack on the same side of the
TATA+ core and away from the dimer. In the Ar3-TATA·BF4
salts the aryl groups must occupy space on both sides of the
TATA+ core. The result is the slipped packing shown in Figure
2, where one of the aryl groups is located above the TATA+
core of the neighbor. The many competing forces in the crystal
packing result in an almost pyramidal aryl nitrogen and a
reduced overlap between the two TATA systems in the would-
be dimer. A further consequence of the steric demands of the
aryl groups is a larger TATA−TATA distance in this unit. For
all reported R3-TATA·BF4 salts close contact-dimers with a
stacking distance of 3.30 Å are found. In phenyl-TATA+ (2)
and 4-bromophenyl-TATA+ (4) the distance is significantly
increased to 3.58 and 3.79 Å.
The restricted dimer packing motif is also evident in the
absorption spectra of thin films of the Ar3-TATA·BF4 salts
(Figure 3). In thin films of R3-TATA·BF4 a large red shift of the
first absorption band (λmax(solution) = 525 nm vs λmax(thin
film) = 548 nm) is observed accompanied by a new band
around 425 nm. Both effects are assigned to the formation of
close cofacial TATA−TATA contact-dimers.31 For Ar3-
TATA·BF4 only a small red shift and a broadening are
observed. A very important observation is that no increased
Figure 2. X-ray structures of triphenyl-TATA+ (2, a−c) and tris(4-
bromophenyl)-TATA+ (4, d−f) with 50% of probability ellipsoids. All
hydrogen atoms are omitted for clarity (nitrogen, blue; bromine,
orange; fluorine, green; boron, pink).
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reaction the color changes from purple to red and then back to dark
purple. Furthermore, three violent gas evolutions were observed of
which the last at 180 °C was handled with concern (hence the 500 mL
flask). The reaction mixture was allowed to reach room temperature,
then quenched by slow addition of H2O (100 mL), and extracted with
CH2Cl2 (3 × 100 mL). The extracts were washed with brine (100 mL)
and evaporated to dryness in vacuo. The title compound was further
purified by dissolving in CH2Cl2 and precipitation by addition of Et2O.
The residue was subjected to dry column vacuum chromatography
(heptane/toluene/EtOH with 5% increment of EtOH in toluene).
Two compounds were isolated, one blue (DMQA+) and one red
(TATA+). Phenyl-DMQA+ was precipitated/crystallized in CH2Cl2/
toluene by slow evaporation of CH2Cl2 yielding blue crystals. Yield:
1
330 mg, 15%; mp >300 °C; H NMR (CDCl3, 500 MHz) δ 7.83 (m,
Figure 3. Absorption spectra of triphenyl-TATA+ 2 (black) and
trioctyl-TATA+ (red) in acetonitrile (dash) and as thin films spin-
casted from 5 mg/mL dichloromethane solution (full lines).
4H), 7.76 (t, 2H, J = 7.5 Hz), 7.69 (m, 3H), 7.45 (m, 4H), 6.93 (d,
2H, J = 8.0 Hz), 6.66 (d, 2H, J = 8.0 Hz), 6.60 (d, 2H, J = 8.0 Hz),
3.87 (s, 6H); 13C NMR (CDCl3, 101 MHz) δ 159.9, 144.9, 143.9,
139.7, 137.8, 137.5, 135.7, 132.4, 131.4, 130.9, 129.3, 128.0, 117.9,
113.1, 108.8, 106.7, 103.6, 56.0; MS (MALDI-TOF) m/z: calcd for
+
absorption is seen around 425 nm. This implies that the
changes in the spectrum relative to solution is due to the crystal
field and not formation of a new absorbing species, as is the
case for thin films of R3-TATA·BF4. The bulk of the aryl groups
prevents the formation of dimers, despite the fact that it is
energetically favorable from an electronic point of view. The
result is the contorted molecular structures observed in the
single crystal structures of compound 2 and 4.
C33H25N2O2 481.56, found 481.03. Anal. Calcd for C33H25BF4N2O2:
C, 69.74; H, 4.43; N, 4.93. Found: C, 70.01; H, 4.55; N, 5.02.
Phenyl-TATA+ 2 were precipitated/crystallized in CH2Cl2/toluene
by slow evaporation of CH2Cl2 yielding red crystals. Yield: 851 mg,
36%; mp >300 °C; 1H NMR (CDCl3, 500 MHz) δ 7.82 (t, 6H, J = 8.6
Hz), 7.72 (t, 3H, J = 7.6 Hz), 7.56 (t, 3H, J = 8.4 Hz), 7.45 (d, 6H, J =
8.3 Hz), 6.38 (d, 6H, J = 8.4 Hz); 13C NMR (CDCl3, 101 MHz)
δ142.34, 142.02, 137.85, 137.20, 132.30, 130.71, 128.55, 110.19,
+
107.30; MS (MALDI-TOF) m/z: calcd for C37H24N3 510.61, found
To summarize, we have reported the synthesis and
photophysical properties of the first N,N′,N″-triaryltriazatrian-
gulenium (Ar3-TATA+) salts. The introduction of aromatic side
groups on the TATA core results in a 3-fold increase in
fluorescence quantum yield, making the new Ar3-TATA+ salts
potent fluorophores. The bulk of the phenyl groups also
prevents formation of close contact-dimers in the solid state,
thus imposing monomer-like optical properties to spin-cast
films of Ar3-TATA+ salts. We further showed that Ar3-TATA+
can take part in metal-catalyzed cross-couplings, which will
make these compounds useful as a unique triangular platform
for fluorescent materials.
509.98. Anal. Calcd for C37H24BF4N3: C, 74.39; H, 4.04; N, 7.03.
Found: C, 74.46; H, 3.90; N, 6.81.
N,N′,N″-Tris(4-methoxyphenyl)-TATA Tetrafluoroborate (3).
The compound was prepared as in the case of compound 2, starting
from 4-methoxyaniline (5.0 g, 40.6 mmol), starting material 1 (2.0 g,
3.9 mmol), and NaH (60% w/w, 0.6 g, 15.0 mmol). The residue was
subjected to dry column vacuum chromatography (heptane/toluene/
EtOH with 5% increment of EtOH in toluene) and yielded a red
compound. Precipitation/crystallization in CH2Cl2/toluene by slow
evaporation of CH2Cl2 yielded red crystals. Yield: 540 mg, 24%; mp
>300 °C; 1H NMR (CDCl3, 500 MHz) δ 7.58 (t, 3H, J = 8.5 Hz), 7.34
(d, 6H, J = 9.0 Hz), 7.29 (d, 6H, J = 9.0 Hz), 6.43 (d, 6H, J = 8.5 Hz),
3.96 (s, 9H); 13C NMR (CDCl3, 101 MHz) δ 160.86, 142.26, 137.29,
129.99, 129.80, 117.38, 110.13, 107.35, 55.91; MS (MALDI-TOF) m/
+
EXPERIMENTAL SECTION
z: calcd for C40H30N3O3 600.7, found 600.3. Anal. Calcd for
■
C40H30BF4N3O3: C, 69.88; H, 4.40; N, 6.11. Found: C, 69.54; H, 4.32;
N, 5.97.
Unless otherwise stated, all starting materials were obtained from
commercial suppliers and used as received. Solvents were HPLC grade
and were used as received. Ground state absorption spectroscopy was
routinely recorded with a double beam spectrophotometer. Steady
state fluorescence was recorded with a standard L-configuration
fluorimeter with single grating monochromators. The absorbance at
the excitation wavelength was kept low, to avoid inner filter effect and
intermolecular interactions. 1H NMR and 13C NMR spectra were
N,N′,N″-Tris(4-bromophenyl)-TATA Tetrafluoroborate (4).
The compound was prepared as in the case of compound 2, starting
from 4-bromoaniline (10 g, 58.1 mmol), starting material 1 (2.0 g, 3.9
mmol), and NaH (60% w/w, 0.6 g, 15.0 mmol). The residue was
subjected to dry column vacuum chromatography (heptane/toluene/
EtOH with 5% increment of EtOH in toluene) and yielded a red
compound. Precipitation/crystallization in CH2Cl2/toluene by slow
evaporation of CH2Cl2 yielded red crystals. Yield: 640 mg, 22%; mp
1
recorded on a 500 MHz instrument (500 MHz for H NMR and 125
MHz for 13C NMR). Proton chemical shifts are reported in ppm
downfield from tetramethylsilane (TMS) and carbon chemical shifts in
ppm downfield of TMS, using the resonance of the solvent as internal
standard. Melting points were measured on a Gallenkamp apparatus
and are uncorrected. Matrix-assisted laser desorption ionization time-
of-flight (MALDI-TOF) mass spectra were recorded on a vertical
reflector instrument. Dry column vacuum chromatography was
performed on Kieselgel 60 (0.015−0.040 mm particle size). Thin
layer chromatography was carried out using aluminum sheets
precoated with silica gel 60F.
General Method. N,N′-Diphenyl-DMQA Tetrafluoroborate
and N,N′,N″-Triphenyl-TATA Tetrafluoroborate (2). A mixture of
aniline (20 mL) and starting material tris(2,6-dimethoxyphenyl)-
methylium tetrafluoroborate (1) (2.0 g, 3.9 mmol)29 was placed in a
500 mL round-bottom flask equipped with a large magnetic stir bar
and a reflux condenser. NaH (60% w/w, 0.6 g, 15.0 mmol) was added,
and the round-bottom flask was placed in an oil bath and heated from
room temperature to 200 °C over a period of 20 min. During the
1
>300 °C; H NMR (CDCl3, 500 MHz) δ 7.92 (d, 1H, J = 8.6 Hz),
7.56 (t, 1H, J = 8.5 Hz), 7.41 (d, 1H, J = 8.6 Hz), 6.38 (d, 1H, J = 8.5
Hz); 13C NMR (CDCl3, 101 MHz) δ 142.66, 141.84, 137.04, 136.83,
135.54, 130.75, 124.77, 110.55, 107.21; MS (MALDI-TOF) m/z:
+
calcd for C37H21Br3N3 747.3, found 748.0. Anal. Calcd for
C37H21BBr3F4N3: C, 53.28; H, 2.54; N, 5.04. Found: C, 53.40; H,
2.43; N, 4.89.
N,N′,N″-Tris(4-naphthalen-1-yl-phenylene)-TATA Tetrafluor-
oborate (5). To a flame-dried 100 mL three-necked round-bottom
flask equipped with a rubber septum and a reflux condenser were
added 4-bromophenyl-TATA 4 (100 mg, 0.12 mmol), naphthalene-1-
boronic acid (100 mg, 0.58 mmol), and toluene (150 mL). The
mixture was heated to 80 °C to dissolve 4-bromophenyl-TATA 4.
K2CO3 (3 g) and H2O (100 mL) was added, and the mixture was
degassed for 10 min via a syringe through the rubber septum.
(PPh3)2PdCl2 (50 mg, 0.07 mmol) was added, and the mixture was
heated to reflux for 12 h. The reaction mixture was allowed to reach
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room temperature and extracted with CH2Cl2 (3 × 100 mL). The
residue was subjected to dry column vacuum chromatography
(heptane/toluene/EtOH with 5% increment of EtOH in toluene).
Precipitation/crystallization in CH2Cl2/toluene by slow evaporation of
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1
CH2Cl2 yielded red crystals. Yield: 65 mg, 55%; mp >300 °C; H
NMR (CDCl3, 500 MHz) δ 8.09−8.04 (m, 1H), 8.03−7.96 (m, 4H),
7.78 (t, J = 8.4 Hz, 1H), 7.71−7.58 (m, 6H), 6.66 (d, J = 8.4 Hz, 2H);
13C NMR (CDCl3, 126 MHz) δ 143.30, 142.57, 142.19, 138.39,
137.20, 136.92, 133.93, 133.79, 131.24, 128.73, 128.63, 127.37, 126.66,
126.19, 125.47, 110.63, 107.44; MS (MALDI-TOF) m/z: calcd for
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+
C67H42N3 889.07, found 888.09. Anal. Calcd for C67H42BF4N3: C,
82.46; H, 4.34; N, 4.31. Found: C, 82.57; H, 4.49; N, 4.42.
Selected Crystallographic Data. Crystallographic data is
summarized in Table 2.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H (1D and COSY) and 13C NMR for all compounds, crystal
structures for compound 2 and 4 in CIF format, absorption
spectra for all compounds, solution fluorescence emission and
excitation spectra, and solid state emission spectra. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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3432.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: bwl@nano.ku.dk.
(30) Laursen, B. W.; Krebs, F. C. Chem.Eur. J. 2001, 7, 1773.
(31) Sørensen, T. J.; Hildebrandt, C. B.; Elm, J.; Andreasen, J. W.;
Madsen, A. O.; Westerlund, F.; Laursen, B. W. J. Mater. Chem. 2012,
22, 4797−4805.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(35) Herse, C.; Bas, D.; Krebs, F. C.; Burgi, T.; Weber, J.;
̈
The authors thank the Danish National Research Foundation
under the Danish-Chinese Centre for Self-Assembled Molec-
ular Electronic Nanosystems and the National Science
Foundation of China (grant 60911130231) for financial
support and the Danish Council for Independent Research
Technology and Production Sciences (grant 10-093546) for
financial support for T.J.S.
Wesolowski, T.; Laursen, B. W.; Lacour, J. Angew. Chem., Int. Ed. 2003,
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