Charge-transfer emission involving three-coordinate organoboron: V-shape versus U-shape and impact of the spacer on dual emission and fluorescent sensing

Article abstract of DOI:10.1002/chem.200700364

New V-shaped bifunctional organosilicon compounds that contain an electron acceptor, B(Mes)₂, and an electron donor, N(1-naph)Ph, with the formulae Ph₂Si{p-C₆H₄B(Mes)₂}(p- C₆H₄N(1-naph)ph)} (1), Ph₂Si(p-C ₆H₄-(Mes)₂)(p-biphenyl-N(1-naph)ph) (2), and Si{p-C₆H₄B(Mes)₂)₂{p-C ₆H₄N(1-naph)ph))₂ (3) have been synthesized as model compounds for the investigation of through-space charge-transfer emission involving triarylboron and triarylamino centers. The photophysical properties of the new bifunctional organosilicon compounds are compared to two U-shaped compounds sBN and BN in which the boron acceptor and the amino donor groups are linked together by a rigid 1,10-naphthyl group. The results of our investigation establish that dual emission pathways, namely through-space donor-acceptor charge transfer and π-π* transitions coexist in the V-shaped molecules 1-3, while charge transfer emission is dominant in the U-shaped molecules. It is found that depending on the geometry of the linker and the B...N separation distance, the compound either displays dual emission bands simultaneously or single emission band. In addition, the dual emission pathways in these molecules can be selectively switched on or off by using fluoride ions. The sensitivity of response to fluoride ions by these molecules is also found to be highly dependent on the geometry of the linker and the B...N separation distance. The V-shaped molecules are found to be "turn-on" sensors to fluorides with a much higher sensitivity than the U-shaped molecules.

Full text of DOI:10.1002/chem.200700364

FULL PAPER
DOI: 10.1002/chem.200700364
Charge-Transfer Emission Involving Three-Coordinate Organoboron:
V-Shape versus U-Shape andImpact of the Spacer on Dual Emission
andFluorescent Sensing
[a]
Dong-Ren Bai, Xiang-Yang Liu, andSuning Wang*
Abstract: New V-shaped bifunctional
organosilicon compounds that contain
BN in which the boron acceptor and
the amino donor groups are linked to-
gether by a rigid 1,10-naphthyl group.
The results of our investigation estab-
lish that dual emission pathways,
namely through-space donor-acceptor
charge transfer and p–p* transitions
coexist in the V-shaped molecules 1–3,
while charge transfer emission is domi-
nant in the U-shaped molecules. It is
found that depending on the geometry
of the linker and the B···N separation
distance, the compound either displays
dual emission bands simultaneously or
single emission band. In addition, the
dual emission pathways in these mole-
cules can be selectively switched on or
off by using fluoride ions. The sensitivi-
ty of response to fluoride ions by these
molecules is also found to be highly de-
pendent on the geometry of the linker
and the B···N separation distance. The
V-shaped molecules are found to be
“turn-on” sensors to fluorides with a
much higher sensitivity than the U-
shaped molecules.
an electron acceptor, B
electron donor, N(1-naph)Ph, with the
formulae Ph2Si{p-C6H4B(Mes)2}{p-
C6H4N(1-naph)ph)} (1) , P2hSi{p-C6H4-
(Mes)2}{p-biphenyl-N(1-naph)ph} (2),
and Si{p-C6H4B(Mes)2}2A{p-C6H4N(1-
ACHTRE(UGN Mes)2, and an
ACHTREUNG
A
N
ACHTREUNG
A
ACHTREUNG
A
ACHTREUNG
A
G
C
ACHTREUNG
naph)ph)}2 (3)have been synthesized
as model compounds for the investiga-
tion of through-space charge-transfer
emission involving triarylboron and tri-
arylamino centers. The photophysical
properties of the new bifunctional or-
ganosilicon compounds are compared
to two U-shaped compounds sBN and
Keywords: boron · charge transfer ·
fluorescence · fluorides · sensors
Introduction
compounds usually display a highly efficient donor–acceptor
charge-transfer emission.[1–4] Two examples of system A de-
veloped by our groups are sBNPB and BNPB[2k,l] shown in
Scheme 1. In contrast to A is the U-shaped geometry C in
which the donor and the acceptor are pendent groups at-
A unique property of three-coordinate organoboron com-
pounds is their ability to accept electrons through the empty
pp orbital on the boron center. This property has been ex-
ploited extensively and successfully for applications of
three-coordinate organoboron compounds in nonlinear opti-
cal materials,[1] in organic light-emitting diodes (as electron
transport and emitters)[2] and in fluorescent sensing.[3–4]
The majority of three-coordinate boron compounds that
contain a donor group have the “linear” geometry A as
shown in Scheme 1, in which the donor and the acceptor are
connected together by a linear, and in most instances, conju-
gated spacer such as an aryl group. Such linear organoboron
tached to a 1,10-bisACHTRE(UNG aryl)naphthalene linker, an example of
which, the BN compound, was reported recently by us.[4] We
have observed that unlike the linear molecules that operate
primarily on charge-transfer emission, the BN compound
has two emission pathways, through-space charge transfer
and p–p* transition localized on the triarylamino portion
that can be reversibly and selectively switched on or off by
the addition of FÀ.[4] Encouraged by the unusual photophysi-
cal properties of the BN molecule and the various potential
applications of such switchable dual emission systems, we
have expanded our investigation to the V-shaped system B
in which the spacer is an organosilicon unit that provides a
greater rotational freedom to the donor and the acceptor
groups than the naphthyl linker in system C. Three new B-
type compounds (1–3)with different donor–acceptor separa-
tion distances and different numbers of chromophores have
been synthesized and investigated. Furthermore, we have
[a] D.-R. Bai, Dr. X.-Y. Liu, Prof. S. Wang
Department of Chemistry, Queenꢀs University
Kingston, Ontario, K7L 3N6 (Canada)
Fax : (+1)613-533-6669
E-mail: wangs@chem.queensu.ca
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5713

impact of donor–acceptor separation distance on charge-
transfer emission in the V-shaped organoboron compounds.
Third, although the B···N separation distance in 3 is about
the same as that of 1, the number of chromophores is dou-
bled in 3, thus allowing us to study the effect of the number
of chromophores on through-space charge-transfer emission.
The synthetic procedure for the intermediates 1a–3a and
the final products 1–3 are shown in Scheme 2. The (1-
naph)PhN-substituted intermediates 1a and 3a were synthe-
sized by using a copper-catalyzed Ullmann condensation re-
action[6] between an appropriate bromide and (1-nap)PhNH.
These coupling reactions were found to be heavily affected
by the reaction temperature. For example, when the reaction
was carried out at 2208C, 1a was only obtained in 20%
yield. At 2308C, the yield of 1a was doubled to 40%. Fur-
ther increasing the reaction temperature to 2408C increased
the yield by another 5% . However at this temperature, the
formation of the disubstituted product became evident, as
revealed by mass spectroscopy. The synthesis of the inter-
mediate 3a was more challenging due to the formation of
mono-, di-, tri-, and tetra-substituted products, which along
with unreacted starting materials in the reaction mixture
made the separation and purification of 3a difficult. The
similarity in polarity among the substituted products further
complicated the product isolation. As a result, 3a was only
obtained in 25% yield. The boron-substituted intermediate
2a was synthesized in 50% yield by lithiating di(p-bromo-
phenyl)diphenylsilane, followed by the addition of B
at À788C. Compound 1 was synthesized by lithiating the in-
termediate 1a, followed by the addition of B(Mes)2F, a pro-
ACHTREUNG(Mes)2F
AHCTREUNG
cedure similar to the synthesis of 2a. However, we have ob-
served that the halogen–metal exchange reaction at À788C
only afforded 10% of 1 with most 1a being recovered. Re-
moving the dry-ice bath to allow the reaction mixture to
reach ambient temperature slowly after nBuLi was added at
À788C resulted in a fivefold increase in yield to 50%. Com-
pound 2 was obtained by a Suzuki–Miyaura cross-coupling
reaction[7] between 2a and p-(1-naphthylphenylamino)phe-
nylboronic acid in the presence of Na2CO3 as a base and by
Scheme 1.
synthesized a new member of system C, compound sBN, a
smaller version of BN. These new compounds along with
BN allow us to conduct a comprehensive investigation on
the impact of the geometry of the linker and the donor–ac-
ceptor separation distance on charge-transfer emission in-
volving three-coordinate organoboron centers. The results
are presented herein.
using [PdACHTRE(UNG PPh3)4] as the catalyst in 35% yield. Compound 3
was prepared in 70% yield by using a substitution reaction
similar to that used for 1. The U-shaped sBN molecule, a
new member of system C, was synthesized according to
Scheme 3. Among the various methods we tried, the best
Results andDiscussion
way for the synthesis of sBN is by lithiating p-I-C6H4-N
naph)Ph first, followed by the formation of the ZnII complex
and its cross-coupling to 1-I-8-p-{(mesityl)2B}phenyl-
naphthalene (4a)in the presence of [Pd (PPh3)4] at ambient
ACHTREUNG(1-
Syntheses: Three new organosilicon compounds 1–3 func-
G
ACHTREUNG
tionalized by B
(Mes)2 (acceptor)and N
A
G
ACHTREUNG
groups were designed and synthesized based on the follow-
ing considerations. First, the Ph2Si spacer provides more ro-
tational freedom to the (Mes)2B-aryl leg and the (1-
naph)phN-aryl leg, compared to the 1,10-naphthyl spacer in
the BN compound,[4] thus allowing us to investigate the
impact of structural rigidity on charge-transfer emission in
three-coordinate organoboron. Second, molecular modeling
shows that the B···N separation distances in 1 and 2 are ꢀ10
and 14 Š, respectively, thus allowing us to examine the
temperature to produce sBN in ꢀ31% yield. Compounds
1–3 and sBN were fully characterized by NMR spectroscopy,
HRMS, or elemental analyses.
UV/Vis absorption spectra: The absorption spectra of com-
pounds 1–3 were examined in six representative solvents,
namely hexane, toluene, CH2Cl2, THF, DMF, and CH3CN.
The data recorded in hexane, CH2Cl2, and DMF (1.0”
10À5 m)for all three compounds along with BN, sBN, BNPB,
5714
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5713 – 5723

Sensors
FULL PAPER
except that the absorption co-
efficient of the latter is about
twice as large as the former;
this result is consistent with
the fact that the donor–accept-
or distance in these two mole-
cules are identical and there
are two sets of chromophores
in 3. The absorption spectrum
of 2 resembles those of 1 and 3
except that the lmax of the low-
energy band is red-shifted by
about 15 nm (lmax =325 nm),
attributable to the biphenyl
group in 2 that effectively de-
creases the p–p* transition
energy. Compared to the linear
system A (sBNPB and BNPB),
the lmax of the low-energy
band is blue shifted by 50–
60 nm from A to B; this result
accounts for the fact that
system A compounds are light
yellow, while system B com-
pounds are all colorless.
Electrochemical
properties:
The redox properties of com-
pounds 1–3 were examined by
using cyclic voltammetry and
compared to sBN and BN and
the linear molecule BNPB.
The data are summarized in
Table 2. All compounds dis-
Scheme 2. i)HN ACHTREUNG
phenyl-B(OH)2, [PdACHTREUNG
play
a reversible oxidation
peak at ꢀ1.0 V (versus Ag/
AgCl electrode), which is typi-
cal of oxidation of the (1-
naph)PhN group and similar
to the second oxidation poten-
tial of (1-naph)PhN-biphenyl-
NPhACHTRE(UNG 1-naph)(NPB; see Sup-
porting Information). Com-
pound 3 displays a shoulder
Scheme 3. i) nBuLi, ZnCl2, À788C; ii)[Pd (PPh3)4] at À308C.
A
and sBNPB are provided in Table 1 and shown in Figure 1.
For comparison purpose, the spectra of 1 in various solvents
are shown in Figure 2. The complete spectra for other com-
pounds are provided in the Supporting Information.
The spectra of compounds 1–3 resemble those of sBN and
BN. For 1 and 3, the low energy absorption band appears at
lmax= ꢀ310 nm (loge=4.8–5.1)covering the range of 260–
390 nm. This absorption band is attributed to the charge-
transfer transition between the N leg and the B leg and p–
p* transitions localized on the leg. This absorption band
does not change significantly with solvents as shown by
Figure 2, a behavior resembling that of sBN and BN. Com-
pounds 1 and 3 have nearly identical absorption spectra
oxidation peak in addition to the main oxidation peak, an
indication that some weak electronic communication be-
tween the two amino centers is present. For the V-shaped
silicon compounds 1–3, no well-defined reduction peaks
were observed. For the U-shaped compounds sBN and BN,
a quasi-reversible reduction peak at À1.8 to À1.9 V was ob-
served which is similar to that[2k] of the linear molecule
BNPB, attributable to the reduction of the three-coordinate
boron center (see Supporting Information). These data indi-
cate that the linear system A and the U-shaped system C
molecules provide more stability to the reduced boron
center than the V-shaped system B does. The strong interleg
p–p interaction in system C may play a role in the relatively
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5715

S. Wang et al.
Table 1. Absorption and luminescent properties of 1–3, sBN, BN,
sBNPB, and BNPB.[a]
Solvent
Absorp.
Loge
lex
lem
F
lmax [nm]
[nm]
[nm]
1
hexane
CH2Cl2
DMF
hexane
CH2Cl2
DMF
hexane
CH2Cl2
DMF
hexane
CH2Cl2
DMF
310
308
310
326
328
320
308
308
310
332
334
290,
330(sh)
330
334
334
4.85
4.86
4.94
4.92
4.77
4.75
5.11
5.11
5.14
4.67
4.48
4.78
318
320
308
330
334
337
321
319
313
345
339
359
392
507
435
398
436
444
391
508
434
454
507
528
462
454
507
528
459
415
459
476
418
486
513
0.35
0.27
0.07
0.64
0.36
0.15
0.31
0.27
0.03
0.17
0.19
0.15
2
3
sBN
ACHTREUNG
AHCTREUNG
BN
hexane
CH2Cl2
DMF
5.01
4.89
4.70
335
376
340
0.23
0.10
0.23
AHCTREUNG
AHCTREUNG
sBNPB
BNPB
hexane
CH2Cl2
DMF
hexane
CH2Cl2
DMF
376
374
376
374
378
382
4.31
4.45
4.47
4.68
4.79
4.72
374
374
374
378
378
378
1.00
0.62
0.45
1.00
0.82
0.48
[a] All spectra were recorded by using a solution of 1.0”10À5 m.
higher stability of sBN and BN toward reduction, while the
direct conjugation between the B center and the N center
appears to be the key for the relative stability of system A
molecules toward reduction. The redox potentials were con-
verted to HOMO and LUMO energy after being calibrated
using the FeCp2+/FeCp2 as the standard.[8] LUMO energy
levels for 1–3 were calculated by using the HOMO level and
the optical band gap. As shown by the data in Table 2, the
HOMO level changes little from system A to system C,
while some variation of the LUMO level is apparent.
Molecular orbital calculations: Previously we have shown
that for linear molecules in system A and the U-shaped mol-
ecules in system C, the HOMO level is dominated with con-
tributions from the amino group, while the LUMO level is
dominated by the empty p orbital of the boron center and
as a consequence the lowest electronic transition in these
molecules is B–N charge transfer. To determine if the silicon
compounds 1–3 have a HOMO–LUMO profile similar to
that of sBN and BN, we performed molecular orbital calcu-
lations for these molecules. Molecular modeling and geo-
metric optimization were carried out to obtain geometric
parameters for use in the calculation. The Gaussian suite of
programs[9] (Gaussian98)was employed. The calculations
were performed with the 6–311G** basis set for all com-
pounds. The orbital diagrams were generated by use of the
Molekel program.[10] All contour values are Æ0.025 au. The
results of our calculations show that the HOMO level for all
molecules consists of contributions from the N leg only,
while the LUMO level involves contributions from the B
leg only. For molecules 1–3, the silicon center does not con-
Figure 1. Absorption spectra in hexane (1.0”10À5 m)(top,) in CH 2Cl2
(1.0”10À5 m)(middle)and in DMF (1.0”10 À5 m)(bottom).
tribute to HOMO/LUMO at all. The second LUMO for all
three molecules is a p* orbital localized on the N leg. The
MO diagrams for the HOMO, LUMO, and the second
LUMO levels of 1 are shown in Figure 3 as a representative
5716
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5713 – 5723

Sensors
FULL PAPER
Solvent-dependent emission: The linear molecule BNPB is
known to display bright solvent-dependent luminescence
when irradiated with UV light.[2k,l] The smaller linear mole-
cule sBNPB shows similar solvent-dependent emission. The
Stokes shift of these two linear molecules was found to have
a linear relationship with the polarity of the solvents (see
Supporting Information), consistent with charge-transfer
emission and a highly polarized excited state.[1,11]
Compounds 1–3 also display solvent-dependent emission.
The emission spectra of 1 and 3 are essentially identical,
while the spectra of 2 are quite different as shown by
Figure 4 (the emission spectra of 3 are provided in Support-
ing Information). At the first glance, the spectral shift of
these compounds does not appear to have the same linear
Figure 2. Absorption spectra of 1 in various solvents.
Figure 3. MO diagrams of 1.
example. MO diagrams for other molecules can be found in
the Supporting Information. Based on the MO results, the
lowest electronic transition in these molecules can be as-
signed to charge transfer between the N leg and the B leg.
The optimized geometry from MO calculations produced
the B···N separation distance in 1–3, sBN and BN to be 10.1,
13.9, 10.2, 6.7, and 9.7 Š, respectively.
Figure 4. The normalized emission spectra of 1 (top)and 2 (bottom)in
various solvents (ꢀ1.0”10À5 m).
Table 2. Electrochemical and HOMO–LUMO data.[a]
Eox
[V]
Ered
[V]
HOMO
[eV]
LUMO
[eV]
LUMO from
optical gap [eV]
Optical energy
gap [eV]
Electrochem
energy gap [eV]
Solvent
(oxidation/reduction)
BNPB
1
2
3
sBN
BN
1.03
1.10
1.10
1.00
1.10
1.15
À1.88
N/A
N/A
À5.30
À5.40
À5.40
À5.30
À5.30
À5.35
À2.44
N/A
N/A
À2.44
À2.20
À2.20
À2.20
À2.29
À2.22
2.88
3.20
3.10
3.10
3.04
3.13
2.86
N/A
N/A
N/A
2.82
2.86
DCM/THF
DCM/DMF
DCM/DMF
DCM/DMF
DMF/DMF
DMF:THF/DMF:THF
N/A
N/A
À1.75
À2.48
À1.74
À2.49
[a] N/A=not applicable.
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5717

S. Wang et al.
relationship with solvent polarity as system A molecules do.
For example, the emission maximum of 1 and 3 in DMF and
CH3CN is at much shorter wavelengths than those in less
polar solvents such as THF and CH2Cl2. In addition, a
shoulder peak is evident in some of the emission spectra of
1 and 3. In CH2Cl2 and THF, this shoulder peak appears at a
shorter wavelength from the main peak, while in DMF and
CH3CN it appears at a much longer wavelength from the
main peak. The appearance of the emission spectra of 2 in
various solvents is distinctly different from those of 1 and 3.
In THF and CH2Cl2, the emission spectra of 2 have a
shoulder peak at ꢀ530 nm, while the main peak appears at
lmax = ꢀ432 nm as shown in Figure 4 (bottom). The other
notable difference between system A and B molecules is
that the former are highly efficient emitters with very high
emission quantum efficiencies (e.g., BNPB, F=0.82 in
CH2Cl2 and 0.48 in DMF)and the latter are much weaker
emitters (e.g. 1, F=0.27 in CH2Cl2 and 0.07 in DMF).
drastic emission intensity enhancement upon the addition of
fluoride ions in CH2Cl2 or THF. These previous findings in-
dicate that fluoride ions can be used to probe the structure
and the nature of luminescence for system B molecules.
The fluorescent titration diagrams for compounds 1 and 2
in THF by NBu4F are shown in Figure 6 (the titration dia-
The emission spectra of 1–3 are in sharp contrast to that
of sBN, which displays a single and well-defined emission
peak in various solvents that shifts to lower energy with in-
creasing solvent polarity, as the linear molecule BNPB does
(Figure 5). The BN compound, however, does display a
Figure 6. Top: The fluorescent titration diagram of 1 in THF by NBu4F
(1.87”10À6 m). Inset: photographs of the solution of 1 before (left)and
after the addition of FÀ with UV lamp excitation. Bottom: The fluores-
cent titration diagram of 2 in THF by NBu4F (1.67”10À6 m).
Figure 5. The normalized emission spectra of sBN in various solvents
(ꢀ1.0”10À5 m).
gram for 3 is provided in the Supporting Information). The
titration diagrams of 1 and 3 have similar appearance: the
addition of the fluoride ion causes the shift of the emission
band at lmax = ꢀ500 to ꢀ428 nm, and a visual change of
color from blue-green to blue as shown by the photographs
in Figure 6. More importantly the emission intensity experi-
enced a dramatic increase after the addition of FÀ. The dif-
ference between 1 and 3 is that 1 needs approximately one
equivalent of FÀ to reach saturation while 3 needs approxi-
mately two equivalents of FÀ to reach saturation as shown
by the Stern-Volmer plots in Figure 7, which is consistent
with the number of boron acceptor sites in these two mole-
cules. There are in fact two isosbestic points in the titration
diagram of 3 at 499 and 477 nm (see Supporting Informa-
tion), indicative of the formation of both [3·F]À and [3·F2]2À
species.[12] For compound 2 the addition of fluoride enhances
the emission intensity at 432 nm and decreases the intensity
of the shoulder peak at 510 nm and the saturation point is
reached after the addition of one equivalent of FÀ. The fact
broad emission band with a visible shoulder peak in some
solvents (see Supporting Information). Nonetheless, the
emission spectra of BN are consistently dominated by the
long wavelength peak. The clues that provide some insights
into the contrasting luminescent properties of 1–3, sBN, and
BN came from our investigation on luminescent change of
these molecules upon the addition of fluoride ions.
Luminescent response to fluoride ions: Yamaguchi, Gabbai,
Jäkle, and others have shown recently that three-coordinate
boron compounds can have highly selective response to
fluoride ions that can be monitored either by the absorption
spectral change or the emission spectral change if the com-
pound is luminescent.[3] In a preliminary communication[4]
we reported that the linear BNPB molecule experiences
fluo
ACHTREUNGrescent quenching, while the U-shaped molecule BN ex-
periences emission color change from green to blue and a
5718
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5713 – 5723

Sensors
FULL PAPER
Figure 7. The Stern–Volmer plots of 1–3 (intensity ratio of the emission
peak at the short wavelength, I2, versus the molar ratio of FÀ per com-
pound).
Figure 9. The Stern–Volmer plots of sBN and BN. The I2/I1 ratiometric
plot shows a similar trend and is provided in the Supporting Information.
that the saturation point was reached with approximately
stoichiometric amount of FÀ for all three compounds in the
V-shaped system B supports that these complexes have a
strong binding constant to fluoride ions. Due to the strong
binding, we have not been able to obtain reliable binding
constants for these molecules. The dramatic blue shift of
lmax and the enhancement of emission intensity displayed by
1 and 3 upon the addition of fluoride are similar to the be-
havior of sBN and BN (see Figure 8 and Supporting Infor-
tion experiments and fluorescent titration experiments (see
Supporting Information).
Based the fluorescent titration data, we conclude the fol-
lowing:
1)The main emission peak of 1 and 3 at ꢀ508 nm and the
shoulder emission peak of 2 at ꢀ510 nm in THF (or
CH2Cl2)originate from B–N charge-transfer transition.
The addition of fluoride ions blocks the through-space
charge-transfer transition, resulting in quenching of this
long wavelength emission peak. This is confirmed by the
linear relationship of the Stokes shift of the emission
band at the long wavelength with solvent polarity for 1
and 3 (See Supporting Information).
2)The shoulder emission peak of 1 and 3 at ꢀ430 nm and
the main emission peak of 2 at ꢀ430 nm in THF (or
CH2Cl2)originate from p–p* transitions localized on the
amino leg. Upon blocking of the charge-transfer emis-
sion by fluoride ions, the p–p* transitions become the
lowest electronic transitions and gain intensity, because
of their relatively high emission quantum efficiency. This
is supported by the fact that the known hole-transport
molecule NPB with a similar structure as the N legs in
1–3 emits at ꢀ430 nm with a much higher quantum effi-
ciency than those of 1–3 (see Supporting Information).
By the same rationale, the dominating emission peak at
the long wavelength of the BN molecule can be assigned
to charge-transfer emission, while the short wavelength
shoulder peak can be assigned to the p–p* transition.
3)Because the main emission peak of 1–3 in DMF and
CH3CN is at the same energy as the emission peak of
the FÀ adducts of 1–3 in THF, they may have the same
origin, that is, p–p* transition. Thus, DMF and CH3CN
solvent molecules must coordinate to the boron center in
the same manner as FÀ does. However, instead of com-
pletely quenching the charge-transfer emission band,
DMF or CH3CN only partially blocks the charge transfer
emission, as evidenced by the partially diminished inten-
Figure 8. The fluorescent titration diagram of sBN by NBu4F in CH2Cl2
(7.1”10À6 m).
mation). However, unlike the U-shaped sBN and BN, which
require ꢀ30 and ꢀ6 equivalents of FÀ, respectively, to reach
saturation as shown by Figure 9 (the binding constants of FÀ
for sBN and BN were estimated,[4,12] to be 1.4”104 mÀ1 and
4.0”104 mÀ1, respectively.), the response of compounds 1–3
towards FÀ is much more sensitive, making them better can-
didates as potential sensors for fluorides. Similar to sBN and
BN molecules, compounds 1–3 do not show any evident
change toward ClÀ or BrÀ, as confirmed by NMR competi-
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5719

S. Wang et al.
sity of the charge-transfer band, causing the abnormal
spectral shift. DMF molecules are also bound to the
boron center in sBN and BN as evidenced by the gradual
emission spectral shift in DMF with time to the shorter
wavelength (see Figure 10 and Supporting Information).
space charge transfer emission is to collisional/thermal
quenching by solvent molecules and hence the lower the
emission efficiency,[11,13] the emission spectral difference be-
tween 1 (or 3)and 2 can be attributed to the difference of
the B···N separation distance. The greater B···N separation
distance in 2 makes the charge-transfer emission much less
efficient relative to 1 and 3. As a consequence, the charge-
transfer band of 2 appears as a shoulder peak, instead of the
main peak as observed for 1 and 3. The much weaker re-
sponse of 2 toward fluoride as shown by Figure 7 is also at-
tributable to the weak charge-transfer emission band of 2
relative to that of 1 and 3.
The B···N separation distance in the U-shaped sBN and
BN is 6.7 and 9.7 Š, respectively. The fact that no dual emis-
sion bands were observed for sBN in solution can be attrib-
uted to its U-shape and the short B···N distance, which
greatly facilitates charge-transfer emission such that it be-
comes the sole emission peak observed. In contrast, due to
the much longer B···N separation distance, the charge-trans-
fer emission in BN is less effective, and as a result both
charge-transfer emission and p–p* emission are observed,
consistent with the observations for the V-shaped com-
pounds 1–3. The relatively weak binding of sBN to fluoride
ions, with respect to BN, can also be considered as a conse-
quence of the shorter B···N separation distance in sBN be-
cause it makes FÀ binding to the boron center more difficult
due to the increased steric congestion in sBN.
Figure 10. The emission spectra of BN in DMF before and after the addi-
tion of four equivalents of FÀ.
The slow DMF binding is likely caused by conformation-
al change upon DMF coordination because the DMF
binding is even slower in sBN due to increased conges-
tions. (The results of our mechanistic study on this phe-
nomenon will be published in due course.)Nonetheless,
DMF clearly cannot compete with fluoride for binding
to the boron center as shown by Figure 10 in which the
addition of FÀ to the solution of BN in DMF causes a
huge emission intensity increase (this phenomenon is
general for both U-shaped and V-shaped molecules).
The dual emission switching mechanism of 1–3 in the
presence of FÀ or donor solvent molecules such as DMF
is illustrated in Scheme 4.
Conclusion
Comparison of systems A, B, andC —impact of the spacer:
Based on the above results and discussions on system B and
C, we can conclude the following:
Origin of emission: For the linear system A, the emission is
dictated nearly entirely by B···N charge-transfer emission.
The emission efficiency of system A is in general very high
and attributable to the presence of the conjugated linear
linker. For the V-shaped system B, dual emission bands
from both B–N charge transfer and p–p* transition coexist
with a much lower total emission quantum efficiency than
system A, due to the much decreased efficiency of through-
space charge transfer, compared to the through-bond charge
transfer in system A. The appearance of the emission spec-
tra in system B is dependent on the B···N separation dis-
tance. With a shorter B···N distance, the emission is domi-
nated by the charge-transfer band, and with a longer B···N
distance the emission is dominated by the p–p* transition
band. The co-existence of dual emission bands in system B
is the consequence of the V-shaped Ar2Si linker that makes
the through-space charge-transfer emission possible, but in
the meantime, allows rotational freedom of the donor and
acceptor groups, thus diminishing the efficiency of through-
space charge-transfer emission and activating the p–p* tran-
sition. For the U-shaped system C, because of the face-to-
face geometry and the high rigidity of the donor and accept-
Scheme 4.
Impact of B···N separation distance on charge transfer emis-
sion: Figure 4 illustrates that the emission spectra of 1 and 3
in CH2Cl2 and THF have very different appearance from
that of 2. For 1 and 3, the dominating peak is the charge-
transfer band, while for 2 the dominating peak is the p–p*
transition band. The key difference between 1 (or 3)and 2
is the separation distance between the donor N atom and
the acceptor B atom. For 1 and 3 this distance is ꢀ10 Š,
while for 2 it is 14 Š. Because the further apart the donor
and the acceptor are, the more susceptible the through-
5720
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5713 – 5723

Sensors
FULL PAPER
or groups imposed by the 1,10-naphthyl linker, through-
space charge-transfer emission dominates, although some
contributions from the p–p* transition in the emission band
are evident for the BN molecule that has a long B···N sepa-
ration distance.
the separation distance between the donor and the acceptor
groups in three-coordinate organoboron compounds have a
profound impact on the emission pathway and the emission
efficiency. Among the three groups of compounds that bear
the same donor and acceptor groups, the V-shaped and the
U-shaped molecules are most promising as fluoride sensors
due to the “turn-on” response. However, the charge-transfer
emission in the V-shaped molecules is more sensitive to
donor solvent molecules or fluoride anions due to their rela-
tively open geometry than the sterically congested U-shaped
molecules. By manipulating the B···N separation distance
and the linkerꢀs geometry, it is possible to control the fluo-
rescent switching pathway by using fluoride ions, thus
achieving highly effective “turn-on” sensors for fluoride ions.
Fluoride sensing: For the linear system A the addition of FÀ
causes fluorescent quenching due to the blocking of the
boron acceptor site and the high quantum efficiency of the
charge-transfer emission. System A molecules, in general,
have a strong binding constant to FÀ and reaches saturation
with the addition of less than two equivalents of FÀ. For the
V-shaped system B the addition of fluoride ions quenches
the B–N charge-transfer emission band and enhances the p–
p* transition band due to the low quantum efficiency of the
through-space charge-transfer emission, resulting in both
color change and overall fluorescent intensity increase. Mol-
ecules in system B are therefore “turn-on” sensors for fluo-
ride. System B molecules show strong binding to fluoride
ions and reach saturation with the addition of approximately
stoichiometric amount of fluoride ions, a behavior similar to
system A. The response of the U-shaped system C mole-
cules toward fluoride resembles that of system B in that
they are all “turn-on” sensors with color change, due to the
low quantum efficiency of the charge-transfer emission.
However, unlike systems A and B, molecules in system C
display in general much weaker binding toward FÀ, and the
shorter the B···N separation distance, the weaker the bind-
ing, which is the consequence of strong steric interactions
between the donor and the acceptor legs imposed by the U-
shaped geometry.
Experimental Section
All starting materials were purchased from Aldrich Chemical Company
and were used without further purification. Solvents were freshly distilled
over appropriate drying reagents. All syntheses were carried out under a
dry nitrogen atmosphere by use of standard Schlenk techniques unless
otherwise stated. TLC was carried out on silica gel. Flash chromatogra-
1
phy was carried out on silica. H and 13C NMR spectra were recorded on
Bruker Avance 300, 400, or 500 MHz spectrometers. Excitation and emis-
sion spectra were recorded on a Photon Technologies International
QuantaMaster Model
2 spectrometer. Elemental analyses were per-
formed by Canadian Microanalytical Service, Delta, British Columbia
(Canada). Cyclic voltammetry was performed on a BAS CV-50W ana-
lyzer with a Pt working electrode, Pt auxiliary electrode, and Ag/AgCl
reference electrode. All experiments were performed at room tempera-
ture with 0.10m NBu4ACHTRE[UNG PF6] as the supporting electrolyte in either CH2Cl2
or CH3CN or DMF. High-resolution mass spectra were obtained using
electrospray mode with internal calibrants on an Applied Biosystems/
MDS-Sciex QSTAR XL spectrometer. Luminescent quantum yields were
determined relative to anthracene in CH2Cl2 at 298 K (Fr =0.36). The
quantum yields were calculated by previously reported procedures.[5]
Taking all factors into consideration, the V-shaped mole-
cules 1 and 3 are the best candidates as sensors for fluoride
ions because of their “turn-on” response and their high af-
finity toward fluoride.
Synthesis of intermediate (p-1-naphthylphenylaminophenyl)(p-Br-phe-
nyl)diphenylsilane (1a): Di(p-Br-phenyl)diphenylsilane (4.80 mmol,
2.40 g), 1-naphthylphenylamine (4.00 mmol, 0.880 g), cupric sulfate hy-
drate (0.20 mmol, 0.050 g), and potassium phosphate (3.16 mmol, 0.670 g)
were heated at 2408C for 48 h under nitrogen. After cooling to ambient
temperature, the reaction mixture was dissolved in CH2Cl2 (40 mL)and
washed by water (3”20 mL). The water layer was separated and extract-
ed with CH2Cl2 (3”30 mL). The combined organic layers were dried
over MgSO4, and the solvents were evaporated under reduced pressure.
The residue was subjected to column chromatography on silica gel
(CH2Cl2/hexane as eluent)to afford a colorless solid of 1a in 45% yield.
1H NMR (CDCl3, 258C): d=7.95 (d, J=8.0 Hz, 1H), 7.90 (d, J=8.0 Hz,
1H), 7.80 (d, J=7.2 Hz, 1H), 7.51 (m, 8H), 7.39 (m, 12H), 7.23 (m, 2H),
7.15 (m, 2H), 6.97 ppm (m, 3H); 13C NMR (CDCl3, 258C): d=149.79,
147.53, 142.95, 137.94, 137.21, 136.30, 135.32, 134.14, 133.83, 131.39,
131.03, 129.68, 129.22, 128.47, 127.93, 127.63, 126.93, 126.56, 126.39,
126.24, 124.60, 124.17, 124.05, 122.93, 122.63, 119.68 ppm; HRMS: m/z
(%): 670.0986 (100) [M+K]+ (calcd: 670.0968).
Impact of coordinating solvents: Coordinating solvent mole-
cules such as DMF bind to the boron center in systems B
and C, causing atypical spectral shift with solvent polarity.
Despite the coordination to the boron center by solvent
molecules such as DMF, the use of 1–3 as fluoride sensors is
not hindered in coordinating solvents, because—based on
this work and previous work by others—nothing except per-
haps CNÀ and OHÀ can compete with fluoride ions for bind-
ing to the sterically protected three-coordinate boron center
as in 1–3, sBN, and BN. The key advantage of our systems B
and C, with respect to other boron-based fluoride-sensing
systems, is that they are all “turned on” by fluoride with or
without the presence of coordinating solvent molecules. The
other advantage of the molecules reported here is that they
are all stable toward water and the fluorescence of the
boron compounds can be fully restored after the removal of
the fluoride ions by water.
Synthesis of intermediate (p-dimesitylboronylphenyl)(p-Br-phenyl)diphe-
nylsilane (2a): A solution of nBuLi in hexane (1.6m, 2.27 mL, 3.63 mmol)
was added at À788C to
a solution of di(p-Br-phenyl)diphenylsilane
(3.30 mmol, 1.650 g)in Et 2O (50 mL), and the mixture was allowed to
reach room temperature over a period of one hour, followed by another
hour stirring at room temperature. A solution of dimesitylboron fluoride
(0.990 g, 96%, 3.30 mmol)in Et 2O (40 mL)was added to the mixture.
The reaction mixture was stirred overnight before water (20 mL)was
added. The water layer was separated and extracted with CH2Cl2 (3”
30 mL). The combined organic layers were dried over MgSO4, and sol-
In summary, by investigating the photophysical properties
and the fluorescent response to solvent molecules and fluo-
ride ions of three distinct groups of organoboron com-
pounds, we have shown that the geometry of the linker and
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5721

S. Wang et al.
vents were evaporated under reduced pressure. The residue was subject-
ed to column chromatography on silica gel (CH2Cl2/hexane as eluent)to
afford pale yellow solid of 2a in 50% yield. H NMR (CDCl3, 258C): d=
Synthesis of di(p-1-naphthylphenylaminophenyl)di(p-dimesitylboronyl-
phenyl)silane (3):
A solution of nBuLi hexane (1.6m, 0.82 mL,
1
1.31 mmol)was added at À788C to a solution of 3a (0.565 g, 0.6 mmol)
in Et2O (45 mL), and the mixture was allowed to reach room tempera-
ture over a period of one hour, followed by another hour stirring at room
7.43 (m, 18H), 6.83 (s, 4H), 2.32 (s, 6H), 2.03 ppm (s, 12H); 13C NMR
(CDCl3, 258C): d=140.77, 138.77, 137.91 137.81, 136.41, 136.30, 135.75,
135.06, 133.43, 131.10, 129.85, 128.18, 128.05, 128.00, 127.87, 124.78. 23.43,
3.10 ppm; HRMS: m/z (%): 701.1834 (100) [M+K]+ (calcd: 701.1813).
temperature.
A solution of dimesitylboron fluoride (0.430 g, 96%,
1.44 mmol)in Et O (20 mL)was added to the mixture. The reaction mix-
2
ture was stirred overnight before water (20 mL)was added. The water
layer was separated and extracted with CH2Cl2 (3”30 mL). The com-
bined organic layers were dried over MgSO4, and the solvents were
evaporated under reduced pressure. The residue was subjected to column
chromatography on silica gel (CH2Cl2/hexane as eluent)to afford pale
Synthesis of intermediate di(p-1-naphthylphenylaminophenyl)di(p-Br-
phenyl)silane (3a): Tetra(p-Br-phenyl)silane (3.00 mmol, 1.960 g), 1-
naphthylphenylamine (7.50 mmol, 1.290 g), cupric sulfate hydrate
(0.33 mmol, 0.083 g)and K 3PO4 (4.72 mmol, 1.000 g)were heated at
2308C for 48 h under nitrogen. After cooling to ambient temperature, the
reaction mixture was dissolved in CH2Cl2 (40 mL)and washed with water
(3”20 mL). The water layer was separated and extracted with CH2Cl2
(3”30 mL). The combined organic layers were dried over MgSO4, and
the solvents were evaporated under reduced pressure. The residue was
subjected to column chromatography on silica gel (CH2Cl2/hexane as
eluent)to afford a white solid 3a in 25%. 1H NMR (CDCl3, 258C): d=
7.91 (t, J=8.7 Hz, 4H), 7.79 (d, J=8.4 Hz, 2H), 7.50 (m, 8H), 7.38 (m,
8H), 7.22 (m, 8H), 7.13 (m, 4H), 6.93 ppm (m, 6H); 13C NMR (CDCl3,
258C): d=149.81, 147.45, 142.88, 137.78, 137.06, 135.29, 133.70, 131.35,
131.02, 129.20, 128.45, 127.60, 126.93, 126.55, 126.37, 126.22, 124.62,
124.11, 123.85, 122.94, 122.66, 119.59 ppm; HRMS: m/z (%): 965.09147
(100)[ M+K]+ (calcd: 965.09590).
1
yellow solid of 3 in 70% yield. H NMR (CDCl3, 258C): d=7.95 (dd, J=
8.0, 1.0 Hz, 4H), 7.82 (d, J=8.0 Hz, 2H), 7.53 (d, J=8.0 Hz, 4H), 7.48 (t,
J=8.0 Hz, 8H), 7.38 (t, J=8.0 Hz, 4H), 7.33 (t, J=8.0 Hz, 4H), 7.23 (t,
J=8.0 Hz, 4H), 7.14 (t, J=8.0 Hz, 4H), 6.97 (m, 6H), 6.83 (s, 8H), 2.33
(s, 12H), 2.02 ppm (s, 24H); 13C NMR (CD2Cl2, 258C): d=149.73, 147.64,
142.98, 141.70, 140.70, 139.32, 138.76, 137.10, 135.75, 135.35, 134.85,
131.33, 129.13, 128.40, 128.08, 127.57, 126.80, 126.46, 126.39, 126.20,
124.90, 123.95, 122.76, 122.48, 119.73, 23.12, 20.90 ppm; HRMS: m/z
1305.624140 (100)[ M+K]+ (calcd: 1305.624800); elemental analysis
calcd (%)for C 92H84B2N2Si·1.3H2O: C 85.62, H 6.72, N 2.17; found: C
85.51, H 6.76, N 2.13.
Synthesis of intermediate 1-iodo-8-p-dimesitylboryphenylnaphthalene
(4a): A solution of nBuLi in hexane (3.2 mL, 1.6m, 5.12 mmol)was
added to a solution of p-bromophenyldimesitylborane, (2.0 g, 4.94 mmol)
in THF (50 mL)at À788C. The mixture was stirred for one hour followed
by the addition of anhydrous ZnCl2 (0.75 g, 5.50 mmol). The solution was
allowed to warm to room temperature. 1,8-Diiodonaphthalene (3.04 g,
Synthesis of (p-1-naphthylphenylaminophenyl)(p-dimesitylboronylphe-
nyl)diphenylsilane (1): A solution of nBuLi in hexane (1.6m, 1.15 mL,
1.84 mmol)was added at À788C to a solution of 1a (0.950 g, 1.5 mmol)
in Et2O (80 mL), and the mixture was allowed to reach room tempera-
ture over a period of one hour, followed by another hour stirring at room
8.00 mmol)and [Pd ACHTRE(UNG PPh3)4] (0.23 g, 5 mol%)were added sequentially.
temperature.
A solution of dimesitylboron fluoride (0.310 g, 96%,
The mixture was stirred overnight at room temperature. The solvent was
removed and the residue was purified by column chromatography in
silica gel. After removing unreacted 1,8-diiodonaphthalene and other im-
purities by using hexane as the eluent, 4a was isolated by using CH2Cl2/
hexane (1:9, v/v)as the eluent (1.34 g, 59% based on the boron starting
1.0 mmol)in Et 2O (20 mL)was added to the mixture. The reaction mix-
ture was stirred overnight before water (20 mL)was added. The water
layer was separated and extracted with CH2Cl2 (3”30 mL). The com-
bined organic layers were dried over MgSO4, and the solvents were
evaporated under reduced pressure. The residue was subjected to column
chromatography on silica gel (CH2Cl2/hexane as eluent)to afford pale
yellow solid of 1 in 50% yield. 1H NMR (CDCl3, 258C): d=7.96 (d, J=
8.4 Hz, 1H), 7.90 (d, J=8.1 Hz, 1H), 7.80 (d, J=8.1 Hz, 1H), 7.55 (m,
6H), 7.49 (m, 4H), 7.37 (m, 10H), 7.23 (m, 2H), 7.14 (m, 2H), 6.98 (m,
3H), 6.82 (s, 4H), 2.31 (s, 6H), 2.02 ppm (s, 12H); 13C NMR (CDCl3,
258C): d=149.66, 147.65, 146.90, 143.04, 141.82, 140.80, 139.06, 138.66,
137.27, 136.35, 135.85, 135.30, 134.97, 134.54, 131.39, 129.50, 129.17,
128.41, 128.14, 127.80, 127.59, 126.82, 126.53, 126.37, 126.20, 124.64,
124.20, 122.80, 122.45, 119.78, 23.44, 21.23 ppm; HRMS: m/z (%):
840.3577 (100)[ M+K]+ (calcd: 840.35991); elemental analysis calcd (%)
for C58H52BNSi: C 86.87, H 6.54, N 1.75; found: C 86.63, H 7.10, N 1.61.
1
material). H NMR (CD3Cl): d=8.20 (d, J=8.0 Hz, 1H; Ar), 7.92 (d, J=
8.0 Hz, 1H; Ar), 7.86 (t, J=5.0 Hz, 1H; Ar), 7.60 (d, J=8.0 Hz, 2H; Ar),
7.50(d, J=5.0 Hz, 2H; Ar), 7.35 (d, J=8.0 Hz, 2H; Ar), 7.11 (t, J=
8.0 Hz, 1H; Ar), 6.85 (s, 4H; Ar), 2.33 (s, 6H; Me), 2.10 ppm (s, 12H;
Me); 13C NMR (CD3Cl): d=144.37, 141.27,140.76, 138.93, 137.78, 131.29,
128.25 (8s, Ar), 23.42, 21.22 ppm (2s, Me); HRMS (TOF-EI+): m/z
calcd for C34H32BI [M]+: 578.1642; found: 578.1650.
Synthesis of 1-(p-1-naphthylphenylaminophenyl)-8-p-dimesitylboryphe-
nylnaphthalene (sBN): A solution of nBuLi in hexane (0.35 mL, 1.6m,
0.56 mmol)was added to a solution of iodo-4 ’-(1-naphthylphenylamino)-
benzene (0. 22 g, 0.52 mmol)in THF (20 mL)at À788C. The mixture was
stirred for one hour at À788C, followed by the addition of ZnCl2 (82 mg,
0.60 mmol). The cooling bath was removed after 40 min, and the reaction
mixture was continually stirred at room temperature for 20 min. A mix-
Synthesis of (p-1-naphthylphenylaminobiphenyl)(p-dimesitylboronylphe-
nyl)diphenylsilane (2): Degassed EtOH (15 mL), H2O (15 mL)and tolu-
ene (25 mL)was added to a mixture of p-1-naphthylphenylamino-phenyl
ture of 4a (0. 30 g, 0.52 mmol)and Pd CAHTRE(UNG PPh3)4 (30 mg, 0.026 mmol)was
boronic acid (0.680 g, 2.0 mmol), 2a (0.950 g, 1.43 mol), [PdACHTRE(UNG PPh3)4]
added to this solution at À308C . The solution was allowed to warm to
room temperature and was stirred overnight. The solvent was removed
and the residue was purified by column chromatography in silica to give
sBN as pale yellow microcrystalline solid using CH2Cl2/hexane (1:8, v/v)
as the eluent (50 mg, 31%). 1H NMR (CD2Cl2): d=7.81 (brd, J=8.0 Hz,
1H; Ar), 7.79 (brd, J=8.0 Hz, 2H; Ar), 7.67 (d, J=8.0 Hz, 2H; Ar),
7.44(ddd, J=8.0, 7.0, 2.0 Hz, 2H; Ar), 7.26–7.36 (m, 6H; Ar), 7.16 (ddd,
J=8.0, 7.0, 1.0 Hz, 1H; Ar), 7.10 (brd, J=7.0 Hz, 1H; Ar), 6.99 (brd,
J=8.0 Hz, 2H; Ar), 6.95 (brt, J=8.0 Hz, 2H; Ar), 6.72–6.82 (m, 9H;
Ar), 6.57 (brs, 2H; Ar), 2.23 (s, 6H; Me), 1.95 ppm (s, 12H; Me);
13C NMR (CD2Cl2): d=148.94, 148.72, 148.42, 146.92, 143.78, 141.98,
141.13, 140.93, 140.69, 138.80, 138.56, 137.46, 137.05, 136.00, 135.75,
131.54, 131.29,130.82, 130.45, 129.85, 129.60, 129.30, 128.79, 128.76,
128.56, 127.42, 126.62, 126.43, 125.78, 125.46, 124.61, 122.03, 121.89,
121.04 (s, Ar), 24.18 (brs, Me), 21.32 ppm (s, Me); HRMS: calcd for
C56H48BNK [M+K]+: 784.3517; found: 784.3525; elemental analysis calcd
(%)for C 56H48BN: C 90.19, H 6.49, N 1.88; found: C 89.54, H 7.00, N
1.86.
(0.085 g, 0.077 mmol), and Na2CO3 (2.50 g). The mixture was stirred and
heated at reflux for 3 days. The reaction mixture was dissolved in CH2Cl2
(40 mL)and washed with water (3”20 mL). The water layer was separat-
ed and extracted with CH2Cl2 (3”30 mL). The combined organic layers
were dried over MgSO4, and the solvents were evaporated under reduced
pressure. The residue was subjected to column chromatography on silica
gel (CH2Cl2/hexane as eluent)to afford a white solid of 2 in 35% yield.
1H NMR (CDCl3, 258C): d=7.96 (d, J=8.4 Hz, 1H), 7.91 (d, J=8.1 Hz,
1H), 7.80 (d, J=5.7 Hz, 1H), 7.58 (m, 10H), 7.46 (m, 4H), 7.38 (m,
10H), 7.24 (m, 2H), 7.09 (m, 4H), 6.99 (s, 1H), 6.82 (s, 4H), 2.30 (s, 6H),
2.02 ppm (s, 12H); 13C NMR (CDCl3, 258C): d=148.12, 148.07, 143.33,
141.78, 140.80, 138.70, 138.62, 136.84, 136.40, 135.86, 135.32, 135.03,
134.13, 133.58, 131.88, 131.28, 129.64, 128.43, 128.16, 127.90, 127.70,
127.35, 126.65, 126.50, 126.39, 126.20, 125.95, 124.24, 122.33, 122.09,
121.48, 23.44, 21.22 ppm; HRMS: m/z (%): 916.3878 (100) [M+K]+
(calcd: 916.39121); elemental analysis calcd (%) for C 64H56BNSi·0.7H2O:
C 86.33, H 6.45, N 1.57; found: C 86.17, H 6.76, N 1.62.
5722
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5713 – 5723

Sensors
FULL PAPER
Tamao, Angew. Chem. 2003, 115, 2082; Angew. Chem. Int. Ed. 2003,
42, 2036; g)S. Solꢂ, F. P. Gabbai, Chem. Commun. 2004, 1284; h)M.
Melaimi, F. P. Gabbai, J. Am. Chem. Soc. 2005, 127, 9680; i)A. Sun-
dararaman, M. Victor, R. Varughese, F. Jäkle, J. Am. Chem. Soc.
2005, 127, 13748; j)K. Parab, K. Venkatasubbaiah, F. Jäkle, J. Am.
Chem. Soc. 2006, 128, 12879; k)S. Aldridge, C. Bresner, I. A. Fallis,
S. J. Coles, M. B. Hursthouse, Chem. Commun. 2002, 740; l)Z. Q.
Liu, M. Shi, F. Y. Li, Q. Fang, Z. H. Chen, T. Yi, C. H. Huang, Org.
Lett. 2005, 7, 5481; m)C. Bresner, J. K. Day, N. D. Coombs, I. A.
Fallis, S. Aldridge, S. J. Coles, M. B. Hursthouse, Dalton Trans. 2006,
3660; n)C. Bresner, S. Aldridge, I. A. Fallis, C. Jones, L.-L. Ooi,
Angew. Chem. Int. Ed. 2005, 44, 3606; o)C. Dusemund, K. R. A. S.
Sandanayake, S. Shinkai, J. Chem. Soc. Chem. Commun. 1995, 333;
p)H. Yamamoto, A. Ori, K. Ueda, C. Dusemund, S. Shinkai, Chem.
Commun. 1996, 407; q)C. R. Cooper, N. Spencer, T. D. James,
Chem. Commun. 1998, 1365; r)S. Arimori, M. G. Davidson, T. M.
Fyles, T. G. Hibbert, T. D. James, G. I. Kociok-Koehn, Chem.
Commun. 2004, 1640.
Acknowledgements
We thank the Natural Sciences and Engineering Research Council of
Canada for financial support.
[1] a)Z. Yuan, N. J. Taylor, R. Ramachandran, T. B. Marder, Appl. Or-
ganomet. Chem. 1996, 10, 305; b)Z. Yuan, J. C. Collings, N. J.
Taylor, T. B. Marder, J. Solid State Chem. 2000, 154, 5; c)Z. Yuan,
N. J. Taylor, T. B. Marder, I. D. Williams, S. K. Kurtz, L. T. Cheng, in
Organic Materials for Nonlinear Optics, II (Eds.: R. A. Hann, D.
Bloor), The Royal Society of Chemistry, Cambridge, 1991, p. 190;
d)C. D. Entwistle, T. B. Marder, Angew. Chem. 2002, 114, 3051;
Angew. Chem. Int. Ed. 2002, 41, 2927; e)C. D. Entwistle, T. B.
Marder, Chem. Mater. 2004, 16, 4574; f)Z. Yuan, N. J. Taylor, T. B.
Marder, I. D. Williams, S. K. Kurtz, L. T. Cheng, J. Chem. Soc.
Chem. Commun. 1990, 1489; g)Z. Yuan, C. D. Entwistle, J. C. Col-
lings, D. Albesa-Jovꢂ, A. S. Batsanov, J. A. K. Howard, N. J. Taylor,
H. M. Kaiser, D. E. Kaufmann, S. Y. Poon, W. Y. Wong, C. Jardin, S.
Fathallah, A. Boucekkine, J. F. Halet, T. B. Marder, Chem. Eur. J.
2006, 12, 2758; h)R. Stahl, C. Lambert, C. Kaiser, R. Wortmann, R.
Jakober, Chem. Eur. J. 2006, 12, 2358; i)L. Porrꢃs, M. Charlot, C. D.
Entwistle, A. Beeby, T. B. Marder, M. Blanchard-Desce, Proc.
SPIE-Int. Soc. Opt. Eng. 2005, 5934, 92; j)M. Charlot, L. Porrꢃs,
C. D. Entwistle, A. Beeby, T. B. Marder, M. Blanchard-Desce, Phys.
Chem. Chem. Phys., 2005, 7, 600; k)Z. Yuan, N. J. Taylor, Y. Sun,
T. B. Marder I. D. Williams, L.-T. Cheng, J. Organomet. Chem. 1993,
449, 27.
[2] a)T. Noda, Y. Shirota, J. Am. Chem. Soc. 1998, 120, 9714; b)T.
Noda, H. Ogawa, Y. Shirota, Adv. Mater. 1999, 11, 283; c)Y. Shirota,
M. Kinoshita, T. Noda, K. Okumoto, T. Ohara, J. Am. Chem. Soc.
2000,122, 1102; d)T. Noda, Y. Shirota, J. Lumin. 2000, 87–89, 1168;
e)M. Kinoshita, H. Kita, Y. Shirota, Adv. Funct. Mater. 2002, 12,
780; f)H. Kinoshita, K. Okumoto, Y. Shirota, Chem. Mater. 2003,
15, 1080; g)M. Uchida, Y. Ono, H. Yokoi, T. Nakano, K. Furukawa,
J. Photopolym. Sci. Technol. 2001, 14, 305; h)Y. Shirota, J. Mater.
Chem. 2000, 10, 1, and references therein; i)W. L. Jia, D. R. Bai, T.
McCormick, Q. D. Liu, M. Motala, R. Y. Wang, C. Seward, Y. Tao,
S. Wang, Chem. Eur. J. 2004, 10, 994; j)M. Mazzeo, V. Vitale, F. D.
Sala, M. Anni, G. Barbarella, L. Favaretto, G. Sotgiu, R. Cingolani,
G. Gigli, Adv. Mater. 2005, 17, 34; k)W. L. Jia, X. D. Feng, D. R.
Bai, Z. H. Lu, S. Wang, G. Vamvounis, Chem. Mater. 2005, 17, 164;
l)W. L. Jia, M. J. Moran, Y. Y. Yuan, Z. H. Lu, S. Wang, J. Mater.
Chem. 2005, 15, 3326.
[4] X. Y. Liu, D. R. Bai, S. Wang, Angew. Chem. 2006, 118, 5601;
Angew. Chem. Int. Ed. 2006, 45, 5475.
[5] a)N. J. Demas, G. A. Crosby, J. Am. Chem. Soc. 1970, 92, 7262;
b)I. B. Berlman, Handbook of Fluorescence Spectra of Aromatic
Molecules, Academic Press, 1971.
[6] A. Klapars, J. C. Antilla, X. Huang, S. L. Buchwald, J. Am. Chem.
Soc. 2001, 123, 7727.
[7] a)N. Miyaura, Adv. Met.-Org. Chem. 1998, 6, 187, and references
therein; b)A. J. Suzuki, J. Organomet. Chem. 1999, 576, 147, and
references therein.
[8] J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bassler, M.
Porsch, J. Daub, J. Adv. Mater. 1995, 7, 551.
[9] Gaussian98 (RevisionA.6), M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski,
J. A. Montgomery, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J.
Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli,
C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q.
Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson, W.
Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle,
J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1998.
[10] D. E. Wong, T. H. Dunning, Jr., J. Chem. Phys. 1993, 98, 1358.
[11] P. Suppan, N. Ghoneim, Solvatochromism, The Royal Society of
Chemistry, Cambridge, 1997.
[12] K. A. Connors, Binding Constants, Wiley, New York, 1987.
[13] J. R. Lakowicz, Principle of Fluorescent Spectroscopy, 2nd ed.,
Kluwer Academic, New York, 1999.
[3] a)S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2000,
122, 6335; b)S. Yamaguchi, T. Shirasaka, K. Tamao, Org. Lett. 2000,
2, 4129; c)S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc.
2001, 123, 11372; d)S. Yamaguchi, T. Shirasaka, S. Akiyama, K.
Tamao, J. Am. Chem. Soc. 2002, 124, 8816; e)H. Shiratori, T. Ohno,
K. Nozaki, A. Osuka, Chem. Commun. 1999, 2181; f)Y. Kubo, M.
Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S. Yamaguchi, K.
Received: March 4, 2007
Published online: May 16, 2007
Chem. Eur. J. 2007, 13, 5713 – 5723
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5723