The synthesis and one- and two-photon optical properties of dipolar, quadrupolar and octupolar donor-acceptor molecules containing dimesitylboryl groups

Article abstract of DOI:10.1002/chem.200801719

Two series of related donor-acceptor conjugated dipolar, pseudoquadrupolar (V-shaped) and octupolar molecular systems based on the p- dimesitylborylphenylethynylaniline core, namely, 4-(4- dimesitylborylphenylethynyl)-N,N-dimethylaniline, 4-[4-(4- dimesit

Full text of DOI:10.1002/chem.200801719

DOI: 10.1002/chem.200801719
The Synthesis and One- and Two-Photon Optical Properties of Dipolar,
Quadrupolar and Octupolar Donor–Acceptor Molecules Containing
Dimesitylboryl Groups
Jonathan C. Collings,[a] Suk-Yue Poon,[b] Cꢀline Le Droumaguet,[c] Marina Charlot,[c]
Claudine Katan,[c] Lars-Olof Pꢁlsson,[a] Andrew Beeby,[a] Jackie A. Mosely,[a]
Hanns Martin Kaiser,[a, d] Dieter Kaufmann,[d] Wai-Yeung Wong,*[b]
Mireille Blanchard-Desce,*[c] and Todd B. Marder*[a]
Abstract: Two series of related donor–
acceptor conjugated dipolar, pseudo-
quadrupolar (V-shaped) and octupolar
molecular systems based on the p-di-
mesitylborylphenylethynylaniline core,
mesitylborylethenyl)-N-n-butylcarba-
zole and tris(E-4-dimesitylborylethen-
ylphenyl)amine have been synthesised
by palladium-catalyzed cross-coupling
and hydroboration routes, respectively.
Their absorption and emission maxima,
fluorescence lifetimes and quantum
yields have been obtained and their
two-photon absorption (TPA) spectra
and TPA cross-sections have been ex-
amined. Of these systems, the octupo-
lar compound tris(E-4-dimesitylboryl-
ACHTUNGTRNEeNUNG thenylphenyl)amine has been shown
G
E
to exhibit the largest TPA cross-section
among the two series of approximately
1000 GM at 740 nm. Its TPA perfor-
mance is comparable to those of other
triphenylamine-based octupoles of sim-
ilar size. The combination of such large
TPA cross-sections and high emission
quantum yields, up to 0.94, make these
systems attractive for applications in-
volving two-photon excited fluores-
cence (TPEF).
namely,
ethynyl)-N,N-dimethylaniline, 4-[4-(4-
dimesitylborylphenylethynyl)phenyl-
ACHTUNGTRENNUNGethynyl]-N,N-dimethylaniline, 3,6-bis(4-
4-(4-dimesitylborylphenyl-
ACHTUNGTRENNUNG
dimesitylborylphenylethynyl)-N-n-bu-
tylcarbazole and tris[4-(4-dimesitylbor-
ylphenylethynyl)phenyl]amine, and on
À
Keywords: boron · C C coupling ·
the
motif, namely, E-4-dimesitylborylethen-
yl-N,N-di(4-tolyl)aniline, 3,6-bis(E-di-
E-p-dimesitylborylethenylaniline
hydroboration · luminescence · two-
photon absorption
ACHTUNGTRENNUNG
Introduction
as a p acceptor because of its vacant pz orbital, although the
fact that boron is more electropositive than carbon makes it
a s donor. However, three-coordinate boron tends to be sus-
ceptible to hydrolysis by moisture, including that present in
the air, unless protected by bulky groups with ortho substitu-
In recent years, there has been increasing interest in conju-
gated molecules containing three-coordinate boron for use
in functional materials.[1,2] Three-coordinate boron behaves
[a] Dr. J. C. Collings, Dr. L.-O. Pꢀlsson, Dr. A. Beeby, Dr. J. A. Mosely,
H. M. Kaiser, Prof. Dr. T. B. Marder
Department of Chemistry
[c] Dr. C. Le Droumaguet, Dr. M. Charlot, Dr. C. Katan,
Dr. M. Blanchard-Desce
Universitꢁ de Rennes 1, CNRS
Durham University, South Road
Durham, DH1 3LE (UK)
Chimie et Photonique Molꢁculaires (CPM)
Campus de Beaulieu Case 1003
Fax : (+44)191-384-4737
35042, Rennes Cedex (France)
E-mail: todd.marder@durham.ac.uk
Fax : (+33)22323-6617
E-mail: mireille.blanchard-desce@univ-rennes1.fr
[b] Dr. S.-Y. Poon, Prof. Dr. W.-Y. Wong
Department of Chemistry and
[d] H. M. Kaiser, Prof. Dr. D. Kaufmann
Centre for Advanced Luminescence Materials
Hong Kong Baptist University,Waterloo Road
Kowloon Tong, Hong Kong (P.R. China)
Fax : (+852)3411-7348
Institut fꢂr Organische Chemie der Technischen Universitꢃt Clausthal
Leibnizstr. 6, 38678, Clausthal-Zellerfeld (Germany)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801719.
E-mail: rwywong@hkbu.edu.hk
198
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Chem. Eur. J. 2009, 15, 198 – 208

FULL PAPER
ents, such as the 2,4,6-trimethylphenyl (mesityl=Mes) or
2,4,6-triisopropylphenyl (triptyl) groups. Experience has
shown that two mesityl groups are usually sufficient to
confer air stability under typical conditions. Compounds
containing only one mesityl group have been reported to
show decomposition products after approximately two
weeks in solutions exposed to air,[3] whereas compounds
with only one triptyl group are reported to be air stable.[4]
Conjugated molecular materials containing dimesitylboryl
electronic structures, and linear and nonlinear optical prop-
erties of conjugated molecules containing
BACHTUNGTRENNUNG(Mes)2
groups,[6,19] and have recently begun to explore their TPA
properties.[19] Herein, we present details of the synthesis and
optical properties, including TPA, of a series of dipolar,
pseudo-quadrupolar and octupolar molecules containing
both amino-based donor groups and dimesitylboryl-based
acceptor groups, based on the p-dimesitylborylphenyl-ethy-
nylaniline motif, namely, 4-(4-dimesitylborylphenylethynyl)-
N,N-dimethylaniline (1), 4-[4-(4-dimesitylborylphenylethy-
nyl)phenylethynyl]-N,N-dimethylaniline (2), 3,6-bis(4-dime-
sitylborylphenylethynyl)-N-n-butylcarbazole (3) and tris[4-
(4-dimesitylborylphenylethynyl)phenyl]amine (4), and the
E-p-dimesitylborylethenylaniline motif, namely, E-4-dimesi-
(BACHTUNGTRENNUNG(Mes)2) groups have been shown to exhibit sizable
second- and third-order nonlinear optical (NLO) coeffi-
cients.[5,6] Related compounds have been used as efficient
electron-transporting and/or emitting layers in organic light-
emitting diodes (OLEDs),[7,8] with one such compound
being found to produce desirable white-light emission,[9] or
tylborylethenyl-N,N-diACTHNUTRGNE(NUG 4-tolyl)aniline (5), 3,6-bis(E-dimesi-
as dopants in non-emissive host layers,[10] including
a
tylborylethenyl)-N-n-butylcarbazole (6) and tris(E-4-dimesi-
tylborylethenylphenyl)amine (7) to compare and contrast
their optical properties.
BACHTUNGTRENNUNG(Mes)2-substituted 2-phenylpyridyl iridium complex that
was found to be an efficient red phosphorescent emitter.[10b]
Numerous three-coordinate boron-containing compounds
have been shown to be effective colourimetric and lumines-
cent sensors for anions, especially fluoride ions.[11–15] Recent-
Results and Discussion
ly, a number of conjugated molecules with BACTHNUGTRENUNG(Mes)2 side
groups were shown to display very large Stokes shifts of up
to 195 nm, and high quantum yields both in solution and the
solid state, which has been attributed to the lack of close
Synthesis: As shown in Scheme 1, 4-(4-dimesitylborylphe-
AHCTUNGTREGnNNUN ylethynyl)-N,N-dimethylaniline (1) and 4-[4-(4-dimesityl-
borylphenylethynyl)phenylethynyl]-N,N-dimethylaniline (2)
were synthesised through the Sonogashira cross-coupling of
1-iodo-4-dimesitylborylbenzene[6f] with one equivalent of 4-
ethynyl-N,N-dimethylaniline and 4-(4-ethynylphenylethyn-
yl)-N,N-dimethylaniline, respectively, using 1 mol% each of
packing.[16] A copper complex with a B
ACTHNUTRGNE(UNG Mes)2-substituted
azaindole ligand also has a very large phosphorescence
quantum yield in the solid state.[13c] Three-coordinate boron-
containing molecules have recently been used to form
chiral, metal-containing coordination networks with second
harmonic generation (SHG) coefficients up to 35 times that
of quartz.[17]
[PdCl
temperature to give the products in 79 and 81% yields, re-
spectively. 3,6-Bis(4-dimesitylborylphenylethynyl)-N-n-butyl-
2ACHTUNGRTNE(NUNG PPh3)2] and CuI in triethylamine, under N2 at room
AHCTUNGTRENNUNG
Several molecules containing B
G
carbazole (3) was prepared by treatment of two equivalents
of 1-iodo-4-dimesitylborylbenzene with 3,6-diethynyl-N-n-
shown to exhibit large two-photon absorption (TPA) cross-
sections up to 1340 GM.[18,19] TPA is defined as the electron-
ic excitation of a molecule in-
duced by simultaneous absorp-
tion of two photons. It is the
focus of much attention due to
its potential applications in
laser scanning microscopy,[20]
3D optical data storage,[21] lo-
calised photodynamic thera-
py,[22] microfabrication and opti-
cal power limitation.[23] Both
experimental findings and theo-
retical studies have suggested
that quadrupolar[24] and octupo-
lar[25,26] molecules exhibit more
efficient TPA compared with
their dipolar analogues, which
has been attributed to intramo-
lecular charge transfer between
the ends and the centre of the
molecules.
butylcarbazole, using 2 mol% of [PdCl2ACHTUNTRGENUNG(PPh3)2] and CuI
For some time, we have been
investigating the molecular and Scheme 1. Synthesis of chromophores 1–4.
Chem. Eur. J. 2009, 15, 198 – 208
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199

W.-Y. Wong, M. Blanchard-Desce, T. B. Marder et al.
under identical conditions to give the product in 73% yield.
Note that in all of these reactions, in which the reagents
were exposed to strongly basic conditions, no degradation of
the dimesitylboryl groups was observed, which shows that
only four ortho-methyl groups adjacent to the boron atom
are required to ensure stability, in contrast to previous Sono-
gashira cross-coupling reactions involving three-coordinate
boron species in which six ortho-methyl groups on the
boron were employed.[27]
Similar conditions were initially tested for the coupling of
three equivalents of 1-iodo-4-dimesitylborylbenzene with
tris(4-ethynylphenyl)amine to give tris[4-(4-dimesitylboryl-
phenylethynyl)phenyl]amine (4; Scheme 1). However, signif-
icant amounts (approximately 10%) of a diyne side product
were detected by MALDI-TOF mass spectrometry, which
proved to be inseparable by column chromatography. The
diyne arises from oxidative alkyne homocoupling upon re-
duction of PdII to Pd0 during the catalyst initiation step.[28]
To obtain pure product, 3 mol% of the Pd0 complex, [Pd-
mately 1–3% too low, despite repeated column chromatog-
raphy and recrystallisation, whereas H and N values were
satisfactory for all compounds. This problem may be associ-
ated with the formation of ceramic boron carbides during
pyrolysis, although we do not understand how this is related
to the structure of the compound. Instead we were able to
obtain satisfactory accurate mass measurements by using EI
SECTOR for 2 and MALDI-TOF techniques for 3, 4, 6 and
7. The experimental m/z value for the lowest mass isotopo-
mer of 2 was found to be within 9 ppm of its calculated
mass, and the highest intensity peaks of the others were
each found to be within 8 ppm of the calculated masses for
their most abundant combinations of isotopomers.
Optical properties
Linear spectroscopy: The photophysical properties of the
series of chromophores, measured in toluene, are presented
in Table 1. All of the chromophores show an intense absorp-
tion band in the near UV-blue region and emission in the
violet-to-blue region.
ACHTUNGTRENNUNG(dba)2] was used with 6 mol% of PPh3, thus avoiding the Pd
reduction step. This reaction required heating to reflux for
one hour to reach completion, and the product was subse-
quently isolated in 61% yield.
Dipolar phenylene–ethynylene chromophores
Length effect: Interestingly, the UV/Vis absorption maxi-
mum lmax for the longer dipolar compound, 2, is blueshifted
The vinyl compounds E-4-dimesitylborylethenyl-N,N-diACTHNUTRGNEUNG(4-
tolyl)aniline (5), 3,6-bis(E-dimesitylborylethenyl)-N-n-butyl-
carbazole (6) and tris(E-4-dimesitylboryl-ethenylphenyl)-
ACHTUNGTRENNUNGamine (7) shown in Scheme 2, were prepared by hydrobora-
Table 1. Photophysical data for chromophores 1–7 in toluene.
[a]
[c]
[f]
labs [nm] e[b] [MÀ1 cmÀ1
]
lem [nm] f[d]
t[e] [ns] t0 [ns]
tion of the corresponding terminal alkyne precursors using
one, two and three equivalents of dimesitylborane, respec-
tively, in dry THF under N2 at room temperature to give the
products in 67, 83 and 71% isolated yields, respectively.
Some of these compounds, namely, the dimethylaniline-
based compounds 1 and 2, and the carbazole-containing
compounds 3 and 6 undergo discolouration over a period of
months if left exposed to the air, which is presumably
caused by oxidation of the amino groups. They can be re-
purified by filtration through a silica plug with an appropri-
ate solvent system. We were not able to obtain satisfactory
carbon analyses for any of the compounds apart from 1 and
5, because their experimental values were always approxi-
1
2
3
4
5
6
7
388
367
385
403
422
410
440
35000
47000
58000
84000
34500
47000
85000
462
466
417
448
489
431
480
0.91 1.78
0.89 1.30
2.0
1.5
1.5
1.4
4.2
5.8
2.7
0.85 1.26
0.94 1.27
0.47 1.99
0.04 0.23
0.73 2.00
[a] Experimental one-photon absorption maximum. [b] Experimental
molar extinction coefficient. [c] Experimental one-photon emission maxi-
mum. [d] Fluorescence quantum yield determined relative to fluorescein
in 0.1N NaOH. [e] Experimental fluorescence lifetime determined by
using picosecond domain time-correlated single photon counting. [f] Ra-
diative lifetime derived from fluorescence quantum yield and lifetime
values (t0=t/f).
by about 20 nm relative to its
tolan analogue 1. This effect
has been noted previously for
donor–acceptor
phenylene–ethynylene
substituted
oligo-
mers,[29] and is probably a result
of statistically poorer donor–ac-
ceptor interactions in the
ground state of the longer sys-
tems due to a number of possi-
ble rotameric conformations of
the three phenyl rings.[30] Be-
cause the barrier to ring rota-
tion in the ground state is
small, all twisted conformations
Scheme 2. Synthesis of chromophores 5–7.
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Luminescent Three-Coordinate Boron Complexes
FULL PAPER
are populated at room temperature, leading to a pro-
nounced blueshift of lmax, whereas the red edge of the ab-
sorption band corresponds to the all-coplanar arrangement
in which conjugation is maximised. We expect that the
lowest energy conformation of the S1 state is planar, and
that the rotation barrier is substantially larger in the excited
state, by analogy with closely related symmetric three-ring
arylene–ethynylene systems. This is consistent with the
slight redshift of the emission band of the longer dipolar
compound 2 relative to that of shorter compound 1 that
leads, at the same time, to a non-mirror relationship be-
tween absorption and emission spectra of chromophore 2
(see the Supporting Information).
significantly different from that of their dipolar analogues.
Thus, these V-shaped chromophores cannot be seen, even in
a first approximation, as the simple gathering of two dipolar
monomers. This could well be related to the ring structure
of the carbazole unit.
Connector effect—vinylene versus phenylene–ethynylene
spacer: Comparison of the absorption and emission data of
chromophores 1 and 5 (dipolar type), or 4 and 7 (octupolar
type) indicates that replacing a phenylene–ethynylene unit
by a vinylene unit induces bathochromic shifts of the ab-
sorption and emission maxima in both dipolar and octupolar
systems. This can be explained by the fact that insertion of a
double bond between the boron atom and the conjugated
core leads to a more planar structure allowed by the relief
of steric hindrance. However, such structural change also in-
duces a noticeable variation of the fluorescence quantum
yields. The fluorescence quantum yields for the phenyl-
Branching and core effect: The branching of dipolar units
such as 1 or 5 within three-branched octupolar structures
built from a triphenylamine-donating core (giving 4 and 7,
respectively) is examined first. The lmax value for the trigo-
nal octupolar phenylethynyl-based compound 4 is redshifted
by 15 nm relative to its dipolar analogue 1. A similar effect
is observed for the octupolar styryl compound 7, for which
lmax is redshifted by 18 nm relative to its dipolar analogue, 5.
This redshift is comparable to that of other three-branched
octupolar compounds based on the triphenylamine core.[25c,d]
Such behaviour, already observed for different octupolar de-
rivatives based on a triphenylamine core, reveals a notice-
AHCTUNGTREGeNNNU thynyl-based molecules 1–4 are all above 0.85, whereas
those of the vinyl-based molecules are somewhat lower, at
0.47 and 0.73 for 5 and 7, respectively, and only 0.04 for 6.
The fluorescence lifetimes of all chromophores except 6 are
in the 1–2 ns range. In contrast, chromophore 6 has a fluo-
rescence lifetime of 0.23 ns, which, in view of the low quan-
tum yield, can be attributed to a facile non-radiative decay
pathway for this compound. The long excited-state lifetimes
of the other chromophores provide a major advantage for
photoluminescence applications.
ACHTUNGTRENNUNG
able coupling (about 0.1 eV in a simple excitonic scheme)[25d]
between the dipolar branches in the ground state. In con-
trast, the emission bands are only slightly blueshifted for the
octupolar derivatives relative to their dipolar counterpart.
This must be related to a localisation of the excitation on a
dipolar branch prior to emission.[25c,d] We also observed that
the branching leads to an increase of the fluorescence quan-
tum yield. The marked increase observed for compound 7 is
comparable to that reported for other octupolar compounds
derived from a triphenylamine core.[25c,d] Such an effect is of
major importance for applications based on photolumines-
cence, for example, two-photon excited florescence (TPEF)
imaging.
Branching of the dipolar units (1 or 5) within two-
branched V-shaped structures (3 or 6) built from a carba-
zole-donating core leads to quite different behaviour. On
one hand, the lowest-energy absorption bands of 3 and 6 are
blueshifted, indicating that a simple excitonic picture does
not apply. Their absorption spectra have a much larger
bandwidth and reveal the presence of different bands, as can
be inferred from the non-mirror relationship between ab-
sorption and fluorescence spectra (see the Supporting Infor-
mation). First, for a V-shaped conformation, the doubly de-
generate first two excited states are one-photon allowed be-
cause of the angle formed between the two branches.[25d] In
addition, these charge-transfer absorption bands superim-
pose on the two carbazole bands located at 34100 and
29400 cmÀ1.[31] Such superimposition is more pronounced for
compound 3, owing to the blueshift with respect to the ab-
sorption band of compound 6. On the other hand, the emis-
sion bands show a marked blueshift suggesting that the
emitting excited state of the V-shaped compounds must be
The absorption and emission maxima of 1–7 were record-
ed in a range of solvents in addition to toluene, namely, cy-
clohexane, chloroform, ethyl acetate, THF and DCM. For
all of the compounds there is general trend of increasing
bathochromic shifts with increased solvent dielectric con-
stant, although the maxima in DCM for certain compounds
occur at shorter wavelength than those in less polar THF.
The largest solvatochromic shift occurs for 2, for which the
emission maximum shifts by 140 nm on going from cyclo-
hexane to THF. Large, positive solvatochromic shifts in
emission tend to be associated with large dipole moments in
the excited state. Such dramatic shifts are not observed for
any of their absorption maxima; these shifts tend to be
much smaller and are not correlated with solvent polarity,
indicating that the ground-state dipole moments are rela-
tively small.[6f] The clear positive emission solvatochromic
behaviour is observed for all compounds, indicating that
emission occurs from a strongly dipolar excited state in all
cases. This solvatochromic behaviour can be fitted by simple
Lippert–Mataga plots of the Stokes shifts between the ab-
sorption and emission maxima (in wavenumbers) versus the
solvent polarity parameter F (Figure S2 in the Supporting
Information). They show reasonable linear correlations with
R2 values above 0.9 for all of the compounds. Such plots
enable an estimate of the change in dipole moment between
the ground and excited states to be made, provided that the
values of the Onsager cavity radii are known. In view of the
somewhat arbitrary nature of the methods used to estimate
these radii, especially for rod-shaped molecules, we do not
feel that a quantitative treatment would be particularly
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201

W.-Y. Wong, M. Blanchard-Desce, T. B. Marder et al.
meaningful. Thus, we present Lippert plots to illustrate the
fact that there are significant excited-state dipole moments
for all of the compounds, including the trigonal ones, indi-
cating that the excitation localisation occurs on a dipolar
subunit in the excited state whatever the structure (including
trigonal and quadrupolar derivatives). This phenomenon has
already been observed and discussed for octupolar triphe-
nylamine derivatives,[25c] quadrupolar derivatives[32] and
other trigonal boron compounds.[31]
Two-photon absorption: Here, we aim to scrutinise the
structure–TPA-property relationships. TPA cross-sections,
s2, have been measured for compounds 1–4 (Scheme 1) and
5–7 (Scheme 2) in toluene in the femtosecond regime over
the range 700–900 nm. Both relative values within the two
series (Table 2) and comparison to literature chromophores
based on a triphenylamine core (Scheme 3 and Table 3) are
discussed. Given the experimental error on the determina-
tion of both position and amplitude of TPA maxima, values
reported in Tables 2 and 3 have been rounded up for the
main first two TPA bands when compared to the experimen-
tal data shown in Figures 1–3 and the original papers cited.
Dipolar derivatives
Length and connector effects: In Figure 1a, the TPA spec-
trum of dipolar chromophore 1 is compared to that of the
longer dipolar compound 2. The TPA response of 2 is
almost twice as large as that of 1 over the whole spectral
region investigated (Figure 1a and Table 2). This is consis-
tent with earlier findings,[33] as it shows that extension of the
p system by lengthening the phenylene–ethynylene con
ACHTUNGTRENNUNGor is indeed a good way to increase the TPA performance.
Surprisingly, whereas the one-photon absorption maximum
of 2 is significantly blueshifted with respect to that of 1
(Table 1), the first TPA bands of both chromophores appear
ACHTUNGTNERnNUNG ect-
Figure 1. Comparison of TPA spectra in toluene of dipolar compounds:
~
~
*
a) 1 ( ) and 2 ( ): length effect and b) 1 ( ) and 5 (+): connector effect.
at the same position. In fact,
the TPA maximum of 2 appears
in the vicinity of the red-edge
of the absorption previously as-
signed to the all-coplanar ar-
rangement. This is consistent
with the fact that conformations
with favoured conjugation yield
the largest TPA responses. It
also confirms that such con
ACHTUNGTRENNUNGnect-
AHCTUNGTRENGNoUN r lengthening allows high fluo-
rescence quantum yields to be
maintained (Table 1).[33]
Figure 1b compares TPA re-
sponses of compounds 1 and 5,
illustrating the connector effect.
Both TPA bands are located in
the vicinity of twice the one-
photon absorption maximum
(Table 2) as is expected for di-
polar chromophores. The TPA
amplitudes are comparable to
Scheme 3. Structures of reference compounds for comparison to literature chromophores: A,[25b] B,[25b,35] C,[26a]
D,[26a] E,[26b] F,[26a] G[36a] and H.[36b]
202
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Luminescent Three-Coordinate Boron Complexes
FULL PAPER
Table 2. Two-photon absorption cross-sections (s2) for the first two main
TPA bands of chromophores 1–7 in toluene.
2 labs[a] [nm]
l
[nm]
l
[nm] s2 [GM]
s2/N[c] [GM]
band1
TPA
band1
TPA
[b]
band1
TPA
band2
band1
TPA
band2
TPA
l
l
l
l
TPA
1
2
3
4
5
6
7
780
744
774
806
844
820
880
790
780
770
820
840
–
–
–
~200
~375
–
–
~200
~375
–
–
ꢀ700
~720
–
–
740
~350 ꢁ500 ~175 ꢁ250
~250 ~375
~200
<50 ~50
~75
~200
<25
~125
–
~25
~325
–
880
~200 ~1000 ~70
[a] labs corresponds to the experimental one-photon absorption maxi-
mum. [b] TPA cross-sections; 1 GM=10À50 cm4 s photonÀ1; TPEF mea-
ACHTUNGTRENNUNGsurements were performed by using a mode-locked Ti:sapphire laser de-
livering 150 fs pulses at 76 MHz, calibrated with fluorescein. [c] TPA
cross-sections normalised for the number of branches (N).
one another and very similar to that of the phenylene–vinyl-
ene-based analogue (188 GM; F=0.55, labs =403 nm),[18b] al-
though the latter values were measured in THF. This shows
that varying the connectors from phenylene–ethynylene (1)
to phenylene–vinylene[18b] to vinylene (5) leads to a signifi-
cant redshift and decrease of fluorescence quantum yields,
while maintaining comparable TPA performance.
Branching effect: The TPA spectra normalised for the
number of branches of compounds 1, 3, 4 and 5–7 are shown
in Figure 2a and b, respectively. All chromophores except
compound 6 show a first TPA band in the vicinity of twice
their one-photon absorption maximum (Table 2 and
Figure 2). For all branched chromophores, the correspond-
ing TPA amplitudes are significantly smaller than those ob-
served at the second TPA band that appears on the blue
side of the spectra. This is directly related to the selection
rules that apply to the first excited states in branched sys-
tems for symmetry reasons. The case of chromophores 3 and
6, which gather two dipolar units through a carbazole
moiety, is more complex than that of octupolar derivatives.
In fact, as already seen from the linear optical properties,
one-photon absorption spectra (see the Supporting Informa-
tion) extend over the whole spectral region explored for
TPA and consist of a superimposition of several transitions,
including local carbazole transitions.[31] For chromophores of
C3 symmetry, it is well known that the first excited state,
which is doubly degenerate, is mainly one-photon allowed,
while the third excited state is one-photon forbidden and
shows a much larger TPA activity.[25d,31] This is clearly visible
for compounds 4 and 7 from Figure 2 and Table 2.
On the red side of the spectra of both series, the dipolar
compounds 1 and 5 show by far the highest responses. This
is a clear indication that the branching strategy does not
lead to any cooperative enhancement in this spectral region,
contrary to what has been reported previously for branched
structures based on a triphenylamine core.[25c,d] On the blue
side of the spectra, the behaviour within the two series is
quite different. Compound 4 shows only little enhancement
when compared with three times its dipolar analogue 1,
whereas compound 7 shows a marked increase leading to a
Figure 2. Comparison of the branching effect on TPA spectra normalised
for the number of branches (N) in toluene: a) phenylethynyl-based chro-
mophores 1, 3, 4 and b) vinylene-based compounds 5, 6 and 7.
cooperative enhancement larger than a factor of ten with re-
spect to the dipolar branch 5.
Effect of the dimesitylboryl end groups—comparison with
other electron-withdrawing moieties: To investigate further
the structure–TPA relationships, octupolar compounds 4 and
7 are compared to other three-branched chromophores re-
ported in the literature (Table 3). Even though TPA cross-
sections are strongly wavelength dependent, we will mainly
concentrate on the amplitudes of TPA maxima at the two
first bands. TPA performance can be either compared from
the absolute TPA cross-section or based on some normalisa-
tion criterion that can be manifold and should be chosen de-
pending on the intended application. Data on corresponding
dipolar monomers are not available for most of the octu-
poles reported in the literature, so normalisation using the
number of branches is not possible. A first normalisation
procedure is based on the molecular weight, so as to obtain
a relevant figure of merit for applications such as optical
limiting.[25c,d] Alternatively, TPA cross-sections can be nor-
malised for the number of effective electrons according to
reference [34].
Chem. Eur. J. 2009, 15, 198 – 208
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www.chemeurj.org
203

W.-Y. Wong, M. Blanchard-Desce, T. B. Marder et al.
Figure 3 and Table 3 compare the TPA cross-sections of
compound 4 with those reported for two other octupolar
chromophores of similar size and which are also based on
The vinylene-based octupole 7, which shows the largest
TPA cross-sections of the two novel series, is compared in
Table 3 to six three-branched compounds (Scheme 3) all
based on a triphenylamine branching centre and among the
best TPA chromophores reported in the lit
AHCTUNGTRENNUNG
ACHTUNGTRENNUNGera-
ture.[25a,26a,b,36a,b] Compounds C, F and 7 are of similar size
and the relative ranking depends on the choice for the nor-
malisation criterion. Whereas normalisation for the number
of effective electrons shows similar effective cross-sections
at the TPA peak (band 2), normalisation for the molecular
weight leads to significantly poorer responses for the B-
AHCTUNGRTEG(NUNN Mes)2 derivatives. This difference is related to the fact that
over half of the molecular weight of compound 7 is attribut-
able to the mesityl groups, which are required for stability
and applications. Over the whole 700–950 nm range, chro-
mophore D, which bears a formyl end group, shows larger
absolute TPA cross-sections than compound 7 (Table 2) with
comparable fluorescence quantum yields.[25a] Whilst these
trends remain for the first TPA band in both normalisation
schemes, compound 7 shows a better normalised TPA cross-
section at the maximum of the second TPA band. Thus, de-
pending on the desired application (broadband versus single
wavelength), one chromophore surpasses the other. Finally,
three other reference octupoles (E,[26b] G[37] and H[36b]),
which are significantly larger than chromophore 7, show
comparatively higher absolute and normalised TPA cross-
sections at both band maxima (Table 2). These comparisons
suggest a route towards enhanced TPA responses, both TPA
amplitude and TPA broadening, through the synthesis of ex-
tended analogues of 7 with longer conjugated arms.
*
Figure 3. Comparison of TPA spectra of compound 4 ( ) with reference
[25b,35]
chromophores A[25b]
(
) and B
( ) in toluene: effect of the periph-
!
^
eral acceptor group.
phenylene–ethynylene spacers and triphenylamine cores
(Scheme 3). As a consequence of the redshift of the first ex-
cited states, the absolute TPA cross-section increases over
the whole spectral region investigated (Figure 3) when re-
placing the SO2Oct acceptor moieties (A)[25b] with B
ACTHNUTRGEN(UNG Mes)2
terminal groups (4). Further substitution by SO2CF3
(B)[25b,35] results in a comparable band position, while allow-
ing for greater TPA responses in the 700–850 nm range.
Both normalisation procedures (molecular weights and ef-
fective number of electrons) lead to the same ranking for
TPA performance (Table 3): SO2Oct<BACHTNUTRGNE(UGN Mes)2 <SO2CF3.
Thus, the TPA response of the chromophore 4 is intermedi-
ate between that of A and B, indicating that the dimesityl-
boryl is a weaker electron-withdrawing unit than the strong
trifluoromethylsulfonyl acceptor, but stronger than the oc-
tylsulfonyl acceptor.
Conclusion
We have designed and investigated two novel series of dime-
sitylboryl-based fluorophores. It is shown that dipolar, V-
shaped and octupolar compounds containing both amino
and dimesitylboryl groups can be synthesised by hydrobora-
tion and palladium-catalyzed cross-coupling, even in the
presence of strong bases, such as triethylamine, as solvents.
Investigation of their TPA properties revealed interesting
structure–TPA features. Comparison of the two novel dipo-
lar chromophores to their phenylene–vinylene analogue
showed that substitution of vinylene by phenylene–ethynyl-
Table 3. Comparison of TPA data for selected reported trigonal com-
pounds built from a triphenylamine core.
[b]
max[c]
r[a] Neff lband1 lband2 s2
[GM] s2max[c]/MW s2max/Neff
[GMgÀ1 mol] [GMeÀ1
lband1 lband2 lband1 lband2 lband1 lband2
[nm] [e] [nm] [nm]
]
AHCTUNGTREGeNNNU ne leads to comparable TPA responses and allows for sig-
4
1.7 28.4 820
~720 ~225 ~375 0.17 0.29
<740 ~150 >150 0.14
8
5
13
–
A[25b] 2.2 27.7 775
–
nificant blueshift (transparency in the visible range) and in-
crease of fluorescence quantum yields. Elongation by intro-
duction of an additional phenylene–ethynylene connector
leads to a twofold increase in the TPA amplitude over the
whole spectral region investigated without marked decrease
of the fluorescence quantum yield. This confirms previous
findings on quadrupolar chromophores based on phenylene–
ethynylene and phenylene–vinylene spacers.[33] The elongat-
ed dipolar compound presents a TPA maximum significantly
redshifted with respect to twice the one-photon maximum.
This may be related to a larger TPA oscillator strength for
the all-coplanar conformation that favors conjugation.
B[25b,35] 1.5 27.7 810
705
740
740
770
735
800
840
800
~400 ~700 0.42 0.74 14
~200 ~1000 0.19 0.94 10
~425 ~1350 0.45 1.42 15
~850 ~1250 0.51 0.75 22
~500 ~3700 0.22 1.64 10
~1200 ~2100 0.96 1.67 29
~1500 ~5000 1.00 3.31 32
25
50
50
33
76
50
105
26
7
1.5 20.2 880
C[26a] 1.5 27.7 820
D[26a] 1.7 38.1 850
E[26b] 2.9 48.5 860
F[26a]
1.5 41.6 880
G[36a,37] 2.3 47.4 975
H[36b] 2.4 52.0 950
900
1350 0.75 1.12 17
[a] Approximate molecular radius. [b] Effective number of p electrons in
the conjugated system defined according to reference [34]. [c] TPA cross-
sections (1 GM=10À50 cm4 s photonÀ1) as obtained from TPEF measure-
ments with fs pulses except for compound G (obtained with ns pulses)
and compound H (measured by fs Z-scan).
204
www.chemeurj.org
ꢄ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 198 – 208

Luminescent Three-Coordinate Boron Complexes
FULL PAPER
NMR spectra were obtained by using Varian Mercury 200 and 400 (1H:
200, 400 MHz) or Bruker Avance 400 (13C{1H}: 100 MHz) spectrometers.
All spectra were recorded in CDCl3. Chemical shifts are reported relative
to tetramethylsilane and are referenced to residual proton or carbon res-
onances in CDCl3. Mass spectra were recorded on Waters Micromass
LCT (ESI), Applied Biosystems Voyager DE STR (MALDI-TOF) spec-
trometers. Higher resolution MS were carried out by using an Autoflex
Tof/Tof (Bruker Daltonic GmBH) instrument fitted with a 337 nm N2
laser, with positive ions measured using a reflectron for improved accura-
cy and resolution, sample solutions (1 mgmLÀ1; compounds 3 and 6 in
DCM, compound 7 in THF) were mixed with matrix in a ratio of 1:9 di-
thranol (50 mgmLÀ1) in DCM. HRMS was performed on a Thermo–Fin-
nigan LTQ FT ICR MALDI-TOF spectrometer by using a 1 mg/5 mL
sample solution in THF/methanol (1:1 v/v) mixed with matrix in a ratio
of 1:9 DCTB (50 mgmLÀ1) in DCM. Accurate mass EI SECTOR MS
was performed by using a Finnigan MAT 95XP spectrometer at the
EPSRC National Mass Spectrometry Service Centre, Swansea. Elemental
analyses were performed on an Exeter CE 440 Analyzer by Ms. J. Dostal
at Durham University. Melting points were measured on a Gallenkamp
melting point apparatus and are uncorrected.
The branching strategy that has been shown to be very
successful for improved TPA properties[25c,d] has been inves-
tigated for V-shaped and octupolar dimesitylboryl deriva-
tives. Use of the carbazole connecting centre to build V-
shaped derivatives prevents qualitative analysis in terms of
simple models, such as the excitonic model. This may result
from sizable conjugation related to the central ring of the
carbazole unit. Furthermore, the carbazole connecting
centre is not effective in enhancing TPA responses. The
branching effect in the two octupolar compounds with dime-
sitylboryl end groups and triphenylamine branching centres
is quite different. Whereas the phenylene–ethynylene deriv-
ative does not present any cooperative enhancement with
respect to its monomeric analogue over the whole spectral
range investigated, the vinylene derivative does so in the
blue part of the spectrum. Interestingly, the former nicely
satisfies the level splitting predicted within the excitonic
scheme, whereas the latter does not because its TPA state is
significantly blueshifted by 40 nm. Such deviation was al-
ready observed for other three-branched systems, also based
on triphenylamine cores, which showed marked enhance-
ment on the blue side of the TPA spectra.[25c,d] Surprisingly,
the TPA broadening observed in the latter compounds is
not observed here.
Further comparison to related triphenylamine-based
three-branched systems shows that both novel octupolar di-
mesitylboryl derivatives lead to TPA peaks comparable to
those observed for compounds of similar size. It is also
shown that the respective ranking depends on the normali-
sation criterion chosen, and this must be selected by consid-
ering the desired application. Comparison to larger
branched chromophores reported in the literature suggests
that elongated analogues of such octupolar dimesitylboryl-
based fluorophores should provide improved TPA proper-
ties, thanks to TPA enhancement and broadening. Finally,
all novel chromophores except one display relatively long
excited-state lifetimes and high fluorescence quantum yields,
which are both significant advantages for photolumines-
cence applications.
4-(4-Dimesitylborylphenylethynyl)-N,N-dimethylaniline (1): 1-Iodo-4-di-
mesitylborylbenzene (0.45 g, 1.00 mmol), 4-ethynyl-N,N-dimethylaniline
(0.15 g, 1.00 mmol), [PdCl2ACHTUNRGTNEUNG(PPh3)2] (0.007 g, 0.01 mmol) and CuI (0.002 g,
0.01 mmol) were added to a 250 mL Schlenk flask, which was evacuated
and purged with nitrogen three times. Triethylamine (~100 mL) was
added by cannula under nitrogen. The reaction was stirred at room tem-
perature overnight. The solvent was removed in vacuo and the residue
was filtered through a 3 cm silica plug, eluting with a hexane/DCM (5:1
v/v) mixture. The filtrate was evaporated and the residue was recrystal-
lised from hexane to give a pale-yellow solid (0.37 g, 79%). M.p. 164–
1668C; 1H NMR (200 MHz): d=7.47 (s, 4H), 7.43 (m, 2H), 6.83 (s, 4H),
6.67 (m, 2H), 3.00 (s, 6H), 2.32 (s, 6H), 2.02 ppm (s, 12H); 13C NMR
(100 MHz): d=150.3, 141.7, 140.9, 138.7, 136.2, 132.9, 130.6, 128.2, 127.7,
111.8, 109.8, 93.2, 87.9, 40.2, 23.4, 21.2 ppm; MS (ESI): m/z: 469 [M+]; el-
emental analysis calcd (%) for C34H36BN: C 86.98, H 7.73, N 2.98; found:
C 86.81, H 7.77, N 3.26.
4-[4-(4-Dimesitylborylphenylethynyl)phenylethynyl]-N,N-dimethylaniline
(2): 1-Iodo-4-dimesitylborylbenzene (0.45 g, 1.00 mmol), 4-(4-ethynylphe-
nylethynyl)-N,N-dimethylaniline (0.24 g, 1.00 mmol), [PdCl2ACHTUNGTRENNUNG(PPh3)2]
(0.007 g, 0.01 mmol) and CuI (0.002 g, 0.01 mmol) were added to a
250 mL Schlenk flask which, was evacuated and purged with nitrogen
three times. Triethylamine (~100 mL) was added by cannula under nitro-
gen and the reaction was stirred at room temperature overnight. The sol-
vent was removed in vacuo and the residue was filtered through a 3 cm
silica plug, eluting with a hexane/DCM (4:1 v/v) mixture. The filtrate was
evaporated and the residue was recrystallised from hexane to give the
1
product as a bright-yellow solid (0.46 g, 81%). M.p. 198–2008C; H NMR
(200 MHz): d=7.50 (s, 4H), 7.48 (s, 4H), 7.43 (m, 2H), 6.83 (s, 4H), 6.67
(m, 2H), 3.00 (s, 6H), 2.32 (s, 6H), 2.02 ppm (s, 12H); 13C NMR
(100 MHz): d=150.3, 140.9, 138.9, 136.1, 132.8, 131.6, 131.2, 131.0, 128.4,
126.5, 124.4, 121.8, 111.8, 109.7, 93.0, 91.5, 91.2, 87.3, 40.2, 23.4, 21.2 ppm;
MS (EI) m/z calcd for C42H4010BN: 568.3285; found: 568.3280; elemental
analysis calcd (%) for C42H40BN: C 88.56, H 7.08, N 2.46; found: C 85.37,
H 7.02, N 2.43.
Experimental Section
Synthesis: All reactions were carried out under a nitrogen atmosphere
using standard Schlenk techniques or in an Innovative Technology
System 1 glove box. Triethylamine was dried and deoxygenated by heat-
ing at reflux over CaH2 under nitrogen, and THF was dried and deoxy-
genated by passage through columns of activated alumina and BASF-
R311 catalyst under argon pressure using an Innovative Technology SPS-
400 solvent purification system. Dimesitylborane was prepared by treat-
ing dimesitylboron fluoride with LiAlH4 in dry monoglyme.[38] 1-Iodo-4-
dimesitylborylbenzene was prepared according to the literature meth-
od.[6f] (Note: this compound was prepared from 1,4-diiodobenzene and
not 1-bromo-4-iodobenzene as shown incorrectly in Scheme 1 of refer-
3,6-Bis-(4-dimesitylborylphenylethynyl)-N-n-butylcarbazole (3): 1-Iodo-4-
dimesitylborylbenzene (0.90 g, 2.00 mmol), 3,6-diethynyl-N-n-butylcarba-
zole (0.27 g, 1.00 mmol), [PdCl2ACHTNUGTRNEUNG(PPh3)2] (0.014 g, 0.02 mmol) and CuI
(0.004 g, 0.02 mmol) were added to a 250 mL Schlenk flask, which was
evacuated and purged with nitrogen three times. Triethylamine
AHCTUNGERTG(NNUN ~ 50 mL) was added by cannula under nitrogen. The reaction was stirred
at room temperature overnight. The solvent was removed in vacuo and
the residue was filtered through a 3 cm silica plug, eluting with a hexane/
DCM (5:1 v/v) mixture. The filtrate was evaporated and the residue was
recrystallised from hexane to give the product as an off-white solid
(0.67 g, 73%). M.p. 270–2728C (dec.); 1H NMR (200 MHz): d=8.30 (s,
2H), 7.67 (m, 2H), 7.54 (m, 8H), 7.38 (m, 2H), 6.83 (s, 8H), 4.29 (t, 3J-
G
ACHTUNGTRENUN(NG 4-tolyl)-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
of 4-(4-ethynylphenylethynyl)-N,N-dimethylaniline will be reported in
ACHTUNGERTN(NUNG H,H)=7.2 Hz, 2H), 2.31 (s, 12H), 2.03 (s, 24H), 1.83 (m, 2H), 1.36 (m,
3
detail in a forthcoming paper on extended linear arylene ethynylenes.[43]
2H), 0.93 ppm (t, JACTHNGUTERNNUG
(H,H)=7.2 Hz, 3H); 13C NMR (100 MHz): d=145.3,
Chem. Eur. J. 2009, 15, 198 – 208
ꢄ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
205

W.-Y. Wong, M. Blanchard-Desce, T. B. Marder et al.
141.5, 140.8, 140.5, 138.7, 136.2, 130.9, 129.8, 128.2, 127.2, 124.3, 122.4,
113.6, 109.0, 93.0, 88.3, 43.1, 31.0, 23.4, 21.2, 20.5, 13.8 ppm; MS
(MALDI-TOF) m/z calcd for C68H67B2N: 919.548; found: 919.555; ele-
mental analysis calcd (%) for C68H67B2N: C 88.79, H 7.34, N 1.52; found:
C 87.00, H 7.49, N 1.47.
analysis calcd (%) for C78H84B3N: C 87.72, H 7.94, N 1.31; found: C
86.59, H 7.89, N 1.06.
Optical experiments
Tris-[4-(4-dimesitylborylphenylethynyl)phenyl]amine (4): 1-Iodo-4-dime-
sitylborylbenzene (1.35 g, 3.00 mmol), tris(4-ethynylphenyl)amine,
Optical absorption and emission spectroscopy: All photophysical proper-
ties were measured using freshly prepared solutions of the chromophores
in air-equilibrated toluene at room temperature (298 K). UV/Vis absorp-
tion spectra were recorded on a Jasco V-570 spectrophotometer. Steady-
state and time-resolved fluorescence measurements were performed on
dilute solutions (approximately 10À6 m; optical density <0.1) contained in
standard 1 cm quartz cuvettes using an Edinburgh Instruments (FLS920)
spectrometer in photon-counting mode. Emission spectra were obtained
for each compound under excitation at the wavelength of the absorption
maximum. Fluorescence quantum yields were measured according to lit-
erature procedures by using fluorescein in 0.1N NaOH as a standard
(quantum yield F=0.90).[44,45] The lifetime values were obtained from
the reconvolution fit analysis (Edinburgh F900 analysis software) of
decay profiles obtained by using the FLS920 instrument under excitation
with a nitrogen-filled nanosecond flashlamp. The quality of the fits was
evidenced by the reduced c2 value (c2 <1.1).
(0.32 g, 1.00 mmol), triphenylphosphine (0.015 g, 0.06 mmol), [PdACTHNUTRGEN(UNG dba)2]
(0.017 g, 0.03 mmol) and CuI (0.006 g, 0.03 mmol) were added to a
100 mL Schlenk flask, which was evacuated and purged with nitrogen
three times. Triethylamine (~100 mL) was added by cannula under nitro-
gen. The reaction was stirred at room temperature overnight, followed
by heating to reflux for 1 h. The solvent was removed in vacuo, and the
residue was filtered through a 3 cm silica plug, eluting with a petroleum
ether (40–608C)/DCM (5:1 v/v) mixture. The filtrate was evaporated
under reduced pressure and residual solvent was removed in vacuo, by
using a heat gun, to give the product as a pale-yellow solid (0.79 g, 61%).
1
M.p.>3008C; H NMR (200 MHz): d=7.44 (m, 18H), 7.07 (m, 6H), 6.83
(s, 12H), 2.30 (s, 18H), 2.01 ppm (s, 36H); 13C NMR (100 MHz): d=
146.8, 141.6, 140.9, 138.8, 136.2, 133.0, 131.0, 128.2, 126.7, 124.1, 117.9,
91.4, 89.8, 23.4, 21.2 ppm; HRMS (MALDI) m/z calcd for C96H9110B3N:
1287.7534; found: 1287.7555 [M+H]+.
E-4-Dimesitylborylethenyl-N,N-di
sitylborane (0.08 g, 0.30 mmol) in dry THF (20 mL) was added dropwise
to a solution of 4-ethynyl-N,N-di(4-tolyl)aniline (0.10 g, 0.30 mmol) in
ACHTUNGTRENUN(NG 4-tolyl)aniline (5): A solution of dime-
Two-photon absorption: Two-photon excited fluorescence spectroscopy
was performed by using a mode-locked Ti:sapphire laser generating a
76 MHz train of pulses with a duration of 150 fs and a time-averaged
power of several hundreds of mW (Coherent Mira 900 pumped by a 5 W
Verdi). Absolute values for the two-photon excitation action cross-sec-
tions s2F were obtained according to the method described by Xu and
Webb, using 10À4 m fluorescein in 0.01m NaOH(aq) as a reference,[46] ap-
plying corrections for the refractive index of the solvent.[47]
AHCTUNGTRENNUNG
dry THF (10 mL) and the reaction mixture was stirred for seven days at
room temperature under N2. The solvent was evaporated under reduced
pressure with diethyl ether added to assist in the removal of residual
THF. The residue was filtered through a 3 cm silica plug, eluting with a
hexane/DCM (5:1 v/v) mixture, and the filtrate was evaporated to give
the pure product as a bright-yellow solid (0.11 g, 67%). M.p. 234–2368C
(dec.); 1H NMR (400 MHz) d=7.39 (m, 2H), 7.21 (m, 1H), 7.10 (m,
5H), 7.02 (m, 4H), 6.94 (m, 2H), 6.83 (s, 4H), 2.31 (s, 6H), 2.29 (s, 6H),
2.19 ppm (s 12H); 13C NMR (100 MHz): d=152.9, 149.8, 144.6, 140.6,
138.1, 133.5, 130.3, 130.0, 129.2, 128.1, 125.4, 120.9, 23.3, 21.2, 20.9 ppm;
MS (MALDI): m/z: 547 [M+]; elemental analysis calcd (%) for
C40H42BN: C 87.74, H 7.73, N 2.56; found: C 87.23, H 7.77, N 2.58.
Acknowledgements
T.B.M. and A.B. thank One NorthEast for funding under the UIC Nano-
technology program. We thank the EPSRC National Mass Spectrometry
Service Centre at Swansea, UK, for mass spectrometry measurements.
W.-Y.W. thanks the Hong Kong Research Grants Council
(HKBU202106P) and Hong Kong Baptist University (FRG/05–06/II-71)
for financial support. M.B-D. acknowledges equipment grants from
CNRS and Rennes Mꢁtropole.
3,6-Bis-(E-dimesitylborylethenyl)-N-n-butylcarbazole (6): A solution of
dimesitylborane (0.53 g, 2.10 mmol) in dry THF (25 mL) was added drop-
wise to a solution of 3,6-diethynyl-N-n-butylcarbazole (0.27 g, 1.00 mmol)
in dry THF (15 mL) and the reaction mixture was stirred for three days
at room temperature under N2. The solvent was evaporated under re-
duced pressure with diethyl ether added to assist in the removal of resid-
ual THF. The residue was filtered through a 3 cm silica plug, eluting with
a hexane/DCM (9:1 v/v) mixture, and the filtrate was evaporated to give
the pure product as a yellow solid (0.64 g, 83%). M.p. 221–2238C (dec.);
1H NMR (400 MHz): d= 8.21 (s, 2H), 7.75 (m, 2H), 7.46–7.37 (m, 6H),
6.85 (s, 8H), 4.29 (m, 2H), 2.33 (s, 12H), 2.24 (s, 24H), 1.83 (m, 2H),
[1] a) C. D. Entwistle, T. B. Marder, Angew. Chem. 2002, 114, 3051;
Angew. Chem. Int. Ed. 2002, 41, 2927; b) C. D. Entwistle, T. B.
Marder, Chem. Mater. 2004, 16, 4574.
[2] S. Yamaguchi, A. Wakamiya, Pure Appl. Chem. 2006, 78, 1413.
[3] K. Parab, K. Venkatasubbaiah, F. Jꢃkle, J. Am. Chem. Soc. 2006,
128, 12879.
ACTHNUTRGNEUNG
1.36 (m, 2H), 0.94 ppm (t, 3J(H,H)=7.2 Hz, 3H); 13C NMR (100 MHz):
d= 154.3, 141.8, 140.5, 138.1, 134.9, 129.5, 128.1, 126.2, 124.6, 123.2,
121.2, 109.2, 43.0, 31.0, 23.3, 21.2, 20.4, 13.8 ppm; MS (MALDI-TOF)
m/z calcd for C56H63B2N: 771.516; found: 771.512; elemental analysis
calcd (%) for C56H63B2N: C 87.15, H 8.23, N 1.81; found: C 85.30, H 7.94,
N 1.76.
[4] S. Kim, K.-H. Song, S. O. Kang, J. Ko, Chem. Commun. 2004, 68.
[5] a) M. Lequan, R. M. Lequan, K. Chane-Ching, J. Mater. Chem.
1991, 1, 997; b) M. Lequan, R. M. Lequan, K. Chane-Ching, M. Bar-
zoukas, A. Fort, H. Lahouche, G. Bravic, D. Chasseau, J. Gaultier, J.
Mater. Chem. 1992, 2, 719; c) M. Lequan, R. M. Lequan, K. Chane-
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solution of tris(4-ethynylphenyl)amine (0.32 g, 1.00 mmol) in dry THF
(25 mL) and the reaction mixture was stirred for seven days at room tem-
perature under N2. The solvent was evaporated under reduced pressure,
with diethyl ether added to assist in the removal of residual THF. The
residue was filtered through a 3 cm silica plug, eluting with a hexane/
DCM (3:1 v/v) mixture, and the filtrate was evaporated to give the pure
product as a bright-yellow solid (0.76 g, 71%). M.p.> 2508C; 1H NMR
(200 MHz): d= 7.45 (m, 6H), 7.30 (m, 3H), 7.10 (m, 9H), 6.83 (s, 12H),
2.30 (s, 18H), 2.20 ppm (s, 36H); 13C NMR (100 MHz): d= 151.9, 148.0,
142.3, 140.6, 138.3, 133.0, 129.4, 128.2, 124.3, 23.6, 21.2 ppm; HRMS
(MALDI) m/z calcd for C78H84B3N: 1067.691; found: 1067.685; elemental
206
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Chem. Eur. J. 2009, 15, 198 – 208

Luminescent Three-Coordinate Boron Complexes
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