Mesitylboron-substituted ladder-type pentaphenylenes: Charge-transfer, electronic communication, and sensing properties

Article abstract of DOI:10.1021/ja803627x

A series of dimesitylboron (B)- or ditolylamino (N)-substituted ladder-type pentaphenylenes (PP) has been designed and synthesized. The UV-vis absorption spectra of compounds BPPN, BPPB, and NPPN reveal an identical maximum wavelength at 432 nm, which indicates that the B and N centers have very similar contributions to the extended conjugation. A rather weak solvatochromism in the UV-vis absorption spectra is observed for compound BPPN, while a remarkable solvatochromic emission is achieved even though the distance between the B and the N centers is as huge as 22 A. The photoluminescence of BPPN shows a bathochromic shift of 108 nm when the solvent polarity is increased from cyclohexane (453 nm) to acetone (561 nm). Compound BPPN acts as a colorimetric and fluorescent chemosensor with high sensitivity (10^-5 M) and selectivity for F^- over other halogen ions. By inhibiting the charge transfer (CT) from the N center to the B center, the intense green CT emission of compound BPPN rapidly switches into the sky-blue emission of PP when F ^- is bound to the B center. Furthermore, a CT emission can be switched on and off when compound BPPB is used as F ^- sensory material. Such an intramolecular CT emission between the two B centers has so far never been reported. Corresponding studies by cyclic voltammetry and differential pulse voltammetry reveal a two-step reduction of the two bridged B centers in compound BPPB, which might suggest that the charge delocalizes through the whole molecule and that the terminal redox centers communicate through the pentaphenylene bridge.

Full text of DOI:10.1021/ja803627x

Published on Web 08/20/2008
Mesitylboron-Substituted Ladder-Type Pentaphenylenes:
Charge-Transfer, Electronic Communication, and Sensing
Properties
Gang Zhou, Martin Baumgarten, and Klaus Mu¨llen*
Max-Planck-Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
Received May 15, 2008; E-mail: muellen@mpip-mainz.mpg.de
Abstract: A series of dimesitylboron (B)- or ditolylamino (N)-substituted ladder-type pentaphenylenes (PP)
has been designed and synthesized. The UV-vis absorption spectra of compounds BPPN, BPPB, and
NPPN reveal an identical maximum wavelength at 432 nm, which indicates that the B and N centers have
very similar contributions to the extended conjugation. A rather weak solvatochromism in the UV-vis
absorption spectra is observed for compound BPPN, while a remarkable solvatochromic emission is achieved
even though the distance between the B and the N centers is as huge as 22 Å. The photoluminescence
of BPPN shows a bathochromic shift of 108 nm when the solvent polarity is increased from cyclohexane
(453 nm) to acetone (561 nm). Compound BPPN acts as a colorimetric and fluorescent chemosensor with
high sensitivity (10-5 M) and selectivity for F- over other halogen ions. By inhibiting the charge transfer
(CT) from the N center to the B center, the intense green CT emission of compound BPPN rapidly switches
into the sky-blue emission of PP when F- is bound to the B center. Furthermore, a CT emission can be
switched “on” and “off” when compound BPPB is used as F- sensory material. Such an intramolecular CT
emission between the two B centers has so far never been reported. Corresponding studies by cyclic
voltammetry and differential pulse voltammetry reveal a two-step reduction of the two bridged B centers in
compound BPPB, which might suggest that the charge delocalizes through the whole molecule and that
the terminal redox centers communicate through the pentaphenylene bridge.
materials,22 as well as emitters in organic light-emitting devices
(OLEDs).23-28 It has also been demonstrated that three-
Introduction
Boron-containing π-conjugated systems have attracted atten-
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properties.1-11 The conjugation of the vacant p-orbital on boron
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is responsible for some outstanding properties, such as charge
transfer from an electron donor to the boron center, unique
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the compound susceptible to n-doping. These have enabled
applications as nonlinear optical12-21 and charge-transport
coordinated boron compounds can be used as selective and
sensitive chemosensors29-34 for the detection of fluoride ions,
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A R T I C L E S
Zhou et al.
Chart 1
which are the smallest anions and play an important role in the
prevention of dental caries, osteoporosis, and fluorosis.35
Although fluoride sensors containing boron centers have been
exploited extensively, a surprisingly small amount of work has
focused on utilizing donor-acceptor charge-transfer (CT)
properties.28,36 All previously reported three-coordinated boron
sensors which produce intense CT fluorescence have very short
spacers bridging the boron and donor centers.37,38 Wang et
al.39,40 developed U-shaped and V-shaped sensor molecules with
donor and acceptor moieties; however, the geometric distances
between the amino and the boron centers were only ∼10 Å.
This was to ensure efficient charge transfer since the CT
interaction decreases remarkably with increasing spacer distance.
As we have recently reported, in bisarylamine-substituted
ladder-type pentaphenylene (NPPN) cation (Chart 1), the charge
delocalizes in the mixed-valence form NPPN+•, and both redox
centers can communicate through the pentaphenylene bridge.41
Herein, ladder-type pentaphenylene (PP), a planar and well-
conjugated spacer, was used to bridge the ditolylamino (N) and
dimesitylboron (B) centers or the two B centers, as shown in
Chart 1. Compared to other bridged boron-nitrogen or
boron-boron systems known so far, the new compounds show
several advantages: (i) Although the distance between the amino
and the boron centers is calculated to be as huge as 22 Å, intense
CT fluorescence was still observed. (ii) After binding to fluoride
ion, the fluorescence in most previously reported CT systems
containing boron centers changed from the CT emission to the
spacer emission. Since most of the reported spacers are short
and simple systems, the emissions are rather weak or occur in
the ultraviolet region and thus cannot be observed with the naked
eye. To facilitate the sensing process, therefore, blue fluorescent
ladder-type pentaphenylene with high fluorescence quantum
yield (QY)41 is selected as the spacer. Thus, the binding of F-
to the B center in compound BPPN can inhibit the CT transition
(green emission) and simultaneously activate the blue emission
of pentaphenylene, which can be easily detected even with the
naked eye. (iii) Redox systems based on conjugated triarylamine
units are well-established in studies of intervalence charge
transfer (IVCT) since they provide the simplest models for the
investigation of basic CT processes.42-47 However, bridged
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diboronic compounds have rarely been used for studying CT
phenomena.48,49 In this work, bis(dimesitylboron)-substituted
pentaphenylene (BPPB) (Scheme 1) was also designed and
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Mesitylboron-Substituted Ladder-Type Pentaphenylenes
A R T I C L E S
Scheme 1. Synthetic Route to Compounds BPPN, BPPB, and BPPH
synthesized. Its IVCT behavior due to the intramolecular
interaction between the two B centers was investigated by means
of fluorescence titration, cyclic voltammetry (CV), and dif-
ferential pulse voltammetry (DPV).
substituent. The addition of 2.2 equiv of n-butyllithium to the
solution of compound BrPPBr in tetrahydrofuran, followed by
the addition of 2.4 equiv of dimesitylboron fluoride, produced
compound BPPB in 80% yield. When compound BrPPBr was
treated with 1.1 equiv of n-butyllithium, followed by 1.2 equiv
of dimesitylboron fluoride, the asymmetrically substituted
intermediate compound BPPBr was obtained with a yield of
36%. Compound BPPN was then synthesized by Buchwald
coupling52 of BPPBr and ditolylamine with palladium acetate
as catalyst and purified by chromatography on silica gel in 74%
yield. For control experiments, model compound BPPH was
synthesized by lithiation of BPPBr with n-butyllithium and
quenching with water in 93% yield.
Results and Discussion
Synthesis and Structure Characterization. The synthesis of
the target compounds BPPN and BPPB begins with alkyl- and
aryl-substituted ladder-type dibromopentaphenylene (BrPPBr),
which has previously been developed in our laboratory.50,51 The
synthetic approach to the target compounds is depicted in
Scheme 1, in which the pentaphenylene (PP) derivatives are
named according to their different end groups, i.e., B for
dimesitylboron, N for ditolylamino groups, and H for no
The structures of the resulting compounds NPPB, BPPB, and
1
BPPH were proven by H NMR and 13C NMR spectroscopy
and elemental analysis. Additionally, the MALDI-TOF mass
spectra exhibited single intense signals corresponding to the
(50) Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.; Mu¨llen,
K. J. Am. Chem. Soc. 2004, 126, 6987.
(51) Zhou, G.; Pschirer, N.; Scho¨neboom, J.; Eickemeyer, F.; Baumgarten,
M.; Mu¨llen, K. Chem. Mater. 2008, 20, 1808–1815.
(52) Guram, A. S.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 7901.
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A R T I C L E S
Zhou et al.
Figure 3. PL spectra of compound BPPN in different solvents.
Figure 1. UV-vis absorption spectra of PP derivatives.
Figure 4. HOMO and LUMO diagrams of compounds BPPN and BPPB.
Figure 2. UV-vis absorption spectra of compound BPPN in different
solvents.
state.55 Upon excitation the electron transfer from the highest
occupied molecular orbital (HOMO), localized primarily on the
arylamino moiety, to the lowest unoccupied molecular orbital
(LUMO), localized on the dimesitylboron and pentaphenylene
moieties, the dipole is enhanced in the excited S1 state.
Therefore, a more polar solvent is able to stabilize such a
polarized excited state by the reorientation of the solvent
molecules to accommodate the increased dipole, lowering the
energy of the system and thereby leading to the bathochromic
shift in the PL spectra of compound BPPN.55 For comparison,
this remarkable CT emission could not be observed in compound
BPPB due to the absence of the amino center. However, BPPB
also demonstrates a slightly solvent-dependent PL. Molecular
orbital calculations (DFT, B3LYP, 6-31G*)56 revealed that the
HOMO of BPPB is dominated by the PP spacer, whereas the
LUMO includes the two boron centers and the PP spacer (Figure
4). Thus, the lowest electronic transition is consistent with the
charge transfer between the PP spacer and the two B centers.39
calculated masses of compounds BPPB, BPPB, and BPPH, as
illustrated in Figure S1 (Supporting Information).
Optical Properties. The UV-vis absorption spectra of a series
of dimesitylboron and ditolylamino end-capped pentaphenylenes
were measured in dichloromethane (DCM) solutions (ca. 10-5
M) (Figure 1). Stepwise incorporation of pentaphenylene with
dimesitylboron from HPPH to BPPH and from BPPH to BPPB
induces a bathochromic shift of 25 and 12 nm, respectively, in
the absorption spectra, which suggests that the electron-deficient
boron center contributes to extend the conjugation. As shown
in Figure 1, the absorption spectra of BPPN, BPPB, and NPPN
demonstrate identical maxima (λmax ) 432 nm), indicating that
the boron and amino groups have similar effects on the extent
of conjugation. The absorption onset of compound BPPN shows
a weak bathochromic shift compared to those for compounds
BPPB and NPPN, which could be ascribed to a contribution
from an overlapping CT band from the N to the B centers.36
Moreover, the absorption spectra of compound BPPN were
slightly solvent-dependent. As illustrated in Figure 2, with the
solvent polarity increasing from cyclohexane (428 nm) to
acetone (437 nm), a bathochromic shift of 9 nm could be
observed. In contrast to the weak solvatochromism in absorption
spectra, the differences in the corresponding photoluminescence
(PL) spectra are quite remarkable. Compound BPPN displayed
significant solvent-dependent PL (Figure 3), and a bathochromic
shift of 108 nm of the PL spectra for BPPN was observed when
the solvent polarity increased from cyclohexane (453 nm) to
acetone (561 nm). Such a bathochromic shift of more than 100
nm has already been reported53,54 and is characteristic for an
efficient charge transfer from the N center to the B center
through the extended bridge.39 Such a distinct solvatochromism
found in PL spectra is ascribed to the more polarized excited
Sensing Properties. The sensing properties of compound
BPPN with regard to different tetrabutylammonium anion salts
were characterized in 10 µM DCM solutions. Figure 5a shows
a photograph of BPPN in DCM solutions containing excess
-
amounts (ca. 1 mM) of various anions (F-, Cl-, Br-, I-, BF4
,
PF6-, and CN-). The solutions remained yellowish upon
addition of all the above anions, except for F- and CN-, where
the solution turned almost colorless (Figure S2). Upon addition
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Mesitylboron-Substituted Ladder-Type Pentaphenylenes
A R T I C L E S
Figure 7. PL spectra of compound BPPN upon addition of F-.
addition of excess amounts of anions (ca. 1 mM) are presented
in Figure 5b. The yellowish-green fluorescence of compound
BPPN in DCM solutions does not change upon the addition of
anions, except for F- and CN-. With the stepwise addition of
F-, the CT emission band at 532 nm is “turned off” and a new
blue emission band at 450 nm “turned on” (Figure 7), which is
characteristic of the PPN emission due to the inhibition of the
charge transfer from the N center to the B center (Figure 8).
Corresponding Stern-Volmer plots are shown in Figure S4.
Figure 5. (a) Photograph showing the interactions of anions with sensor
BPPN in DCM solutions. (b) Fluorescence of BPPN with anions in DCM
solutions. The cells are illuminated with a hand-held UV lamp. From left
to right: none, F-, Cl-, Br-, I-, BF4-, PF6-, CN-.
The detection limit for F- was measured to be around 10-5
M
under the experimental conditions, which suggests that com-
pound BPPN is a highly sensitive sensory material for F-.
Interestingly, the sensing behavior of bis(dimesitylboron)-
substituted pentaphenylene (BPPB) is much more complicated
than that of BPPN and provides detailed information on the
intramolecular interaction. The fluorescence titration could be
divided into two subprocesses, as shown in Figure 9. With the
stepwise addition of F-, the intensity of the emission band at
450 nm decreased, while another very broad shoulder appeared
at 520 nm with a clear isosbestic point at 505 nm. This can
only originate from the boron monoanion BPPB-F and is thus
assigned to the intramolecular charge transfer from the nega-
tively charged B center to the other neutral one (Figure 8).
Moreover, this long-wavelength emission band is solvent-
dependent. When the sensing behavior was investigated in
acetone solution, a similar broad CT emission shoulder also
appeared around 550 nm (Figure S5) with a bathochromically
shifted isosbestic point at 540 nm. However, when cyclohexane
was used as solvent, no long-wavelength CT emission band
could be observed (Figure S6). Although charge transfer from
anionic four-coordinate boronate species to cationic centers at
the other end of a conjugated spacer has been investigated,61,62
such an intramolecular CT emission band between two reducible
boron centers has never been reported. In most previously
described cases with multiple B centers, only fluorescence
quenching could be observed when sensing F-. Upon further
titration with F-, the green emission at 520 nm completely
disappeared, while an intense shoulder at 430 nm, with a clear
isosbestic point shifted from 505 to 487 nm, increased continu-
Figure 6. UV-vis absorption spectra of BPPN in DCM solutions upon
addition of F-.
of F- to the DCM solution of BPPN, a new absorption band at
424 nm appeared along with the disappearance of the main
absorption band at 432 nm (Figure 6). These absorption changes
indicate the appearance of the B-F complex and originate from
the occupation of the empty orbital and the interruption of the
extended conjugation including the B atom.57 This can be
identified by the titration of model compound BPPH with F-
(Figure S3). Similarly, upon adding F- to the DCM solution of
BPPH, the absorption band at 415 nm decreased while a new
band appeared at 409 nm due to the formation of a charged
boron center.
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In addition to serving as a colorimetric chemosensor,
compound BPPN could also be used as a fluorescent chemosen-
sor for F-.58-60 The corresponding images of BPPN illuminated
with a hand-held UV lamp in DCM solutions (ca. 10 µM) upon
(59) Sun, Y.; Ross, N.; Zhao, S. -B.; Huszarik, K.; Jia, W. -L.; Wang, R.
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11372.
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A R T I C L E S
Zhou et al.
Figure 8. Schematic representation of the different emission processes occurring in BPPN and BPPB upon coordination of F-.
Figure 9. PL spectra of compound BPPB in DCM solutions upon addition
of F-.
Figure 11. Differential pulse voltammograms of BPPN, BPPB, and BPPH,
measured in DCM (for oxidation) and THF (for reductions).
Figure S7, compound BPPB displays two reversible one-
electron cathodic redox steps, corresponding to the sequential
acceptance of electrons at B centers to form the stable radical
anion and dianion. Compared with the CV of monodimesityl-
boron BPPH, the first low-potential redox wave (E ) -1.94
V) fits well with that of BPPB, indicating that the first electron
is accepted at one of the B centers. However, unlike the one
reversible redox couple found for BPPH, BPPB shows two
reversible reduction processes in the low-potential region at E
) -1.88 and -1.99 V, respectively. This implies that the two
electrons are accepted successively from the two dimesitylboron
moieties and that a higher potential is needed to transform
BPPB-• into BPPB2-. The separation of 0.11 V suggests a low
electron coupling energy and a weak communication between
the two B centers through the long PP spacer.63,64 Correspond-
ingly, according to the peak integrals, the DPV of BPPB (Figure
11) also displays two one-electron reductions at -1.87 and
-1.98 V. The splitting of the reductions of two dimesitylboron
Figure 10. PL spectra of BPPH in DCM solutions upon addition of F-.
ously. This hypsochromic shift of the PL spectrum is obviously
due to the formation of dianion FB-PPB-F. When a similar
experiment was performed for model compound BPPH, as
shown in Figure 10, only a hypsochromic shift of 7 nm
(446f439 nm) was observed upon addition of F- into the DCM
solution of BPPH due to the absence of another B center, which
also excludes a CT interaction between the PP skeleton and
the B center.
Electrochemical Properties. To investigate the electronic
communication between the two B centers, the electrochemical
behavior of BPPB was studied by CV and DPV. As shown in
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12482 J. AM. CHEM. SOC. VOL. 130, NO. 37, 2008

Mesitylboron-Substituted Ladder-Type Pentaphenylenes
A R T I C L E S
Synthesis of 2,11-Dimesitylboron-6,6,15,15-tetra(p-octylphe-
nyl)-9,9,18,18-tetraoctyl(ladder-type pentaphenylene) (BPPB).
Under nitrogen atmosphere and at -78 °C, n-BuLi (1.35 mL, 1.6
M in hexane) was added dropwise to a dry tetrahydrofuran (40
mL) solution containing dibromopentaphenylene (1.79 g, 1 mmol).
After 30 min stirring, 0.6 g of dimesitylboron fluoride in 20 mL of
THF was added slowly to the reaction solution. The temperature
of the solution was raised back to room temperature, and after
another 12 h stirring, the reaction was quenched with brine. The
solution was extracted with ethyl acetate and subjected to flash
column chromatography (silica gel, DCM/hexane ) 1:10). A light
yellow solid was obtained in 80% yield (1.7 g). 1H NMR (300
MHz, CD2Cl2) δ (ppm): 7.74 (s, 2H), 7.62-7.49 (m, 6H),
7.36-7.29 (m, 4H), 7.14 (d, 8H, J ) 8.4 Hz), 7.03 (d, 8H, J ) 8.4
Hz), 6.74 (s, 8H), 2.47 (t, 8H, J ) 7.8 Hz), 2.22 (s, 12H), 2.00-1.72
(m, 32H), 1.51-1.41 (m, 8H), 1.21-1.17 (m, 40 H), 1.12-0.93
(m, 40H), 0.79-0.70 (m, 24H), 0.60-0.47 (b, 8H). 13C NMR (75
MHz, CD2Cl2) δ (ppm): 151.6, 151.3, 151.2, 150.6, 149.8, 149.7,
146.7, 144.8, 144.4, 144.2, 142.8, 142.7, 141.3, 140.7, 140.3, 140.0,
139.8, 139.7, 138.8, 137.7, 137.6, 134.7, 134.6, 131.3, 129.5, 128.9,
127.5, 127.4, 127.3, 123.2, 121.5, 119.3, 118.3, 117.4, 116.9, 116.7,
116.4, 115.5, 113.7, 63.5, 54.0, 39.7, 34.7, 31.1, 31.0, 30.7, 29.2,
29.1, 28.7, 28.6, 28.5, 28.4, 28.3, 23.1, 23.0, 22.3, 21.8, 20.1, 19.7,
13.1. Elemental analysis for C158H208B2. Calcd: (%) C, 89.14; H,
9.85. Found: (%) C, 88.61; H, 9.51. MALDI-TOF: m/z 2128.
Synthesis of 2-Bromo-6,6,15,15-tetra(p-octylphenyl)-9,9,18,18-
tetraoctyl-mesitylboron(ladder-type pentaphenylene) (BPPBr).
Under nitrogen atmosphere and at -78 °C, n-BuLi (0.65 mL, 1.6
M in hexane) was added dropwise to a dry tetrahydrofuran (40
mL) solution containing BrBBBr (1.79 g, 1 mmol). After 30 min
stirring, 0.3 g of dimesitylboron fluoride in 20 mL of THF was
added slowly to the reaction solution. The temperature of the
solution was brought back to room temperature, and after another
12 h of stirring, the reaction was quenched with brine. The solution
was extracted with ethyl acetate and subjected to flash column
chromatography (silica gel, DCM/hexane ) 1:15). A light yellow
units into two steps suggests charge delocalization through the
conjugated ladder-type pentaphenylene in its mixed-valence
radical monoanion BPPB-• and long-distance electron com-
munication between the two dimesitylboron branches. Compared
with the two oxidation couples at 1.1 and 1.5 V in the DPV
spectra of both BPPB and BPPH, compound BPPN displays
one more redox couple at 0.6 V, which is attributed to the
oxidation of the ditolylamino group.
Conclusions
In summary, boron-containing pentaphenylenes BPPN and
BPPB have been synthesized from BrPPBr. The charge-transfer
absorption band of compound BPPN exhibits slight solvato-
chromism, while the emission shows remarkable solvatochromic
effect even though the distance between the B and N centers is
as huge as 22 Å. With the solvent polarity increase from
cyclohexane to acetone, the PL spectrum of compound BPPN
in solutions shows a bathochromic shift of 108 nm. When F-
is bound to the B center of compound BPPN, the intense green
CT emission is “switched off”, while the strong blue emission
of the PP spacer is recovered, which can be easily observed
with the naked eye. Therefore, by suppressing this CT interac-
tion, compound BPPN acts as a highly selective and sensitive
colorimetric and fluorescent chemosensor for fluoride ions over
other halogen ions. Most importantly, we also report on the first
solvent-dependent intramolecular CT emission from one, nega-
tively charged B center to the other, neutral one in compound
BPPB when sensing fluoride ions. This intramolecular CT
emission in the long-wavelength region is “switched on” when
only one B center is charged by F- and “switched off” when
both are charged. Further CV and DPV investigations indicate
that the charges delocalize on the PP bridge and IVCT are
achieved in this reducible system. This unique study may offer
an effective way to improve the understanding of charge transfer
and charge-carrier transport in boron-containing conjugated
oligomers or polymers and facilitate their ongoing exploration
in optoelectronic applications. Our ongoing work is focused on
further in depth studies of OLED devices and two-photon
absorption measurements.
1
solid was obtained in 36% yield (710 mg). H NMR (300 MHz,
CD2Cl2) δ (ppm): 7.73 (s, 2H), 7.61-7.49 (m, 6H), 7.36-7.22 (m,
3H), 7.14 (d, 9H, J ) 8.1 Hz), 7.03 (d, 8H, J ) 8.1 Hz), 6.74 (s,
4H), 2.47 (t, 8H, 7.8 Hz), 2.22 (s, 6H), 1.90 (m, 20H), 1.50-1.40
(m, 8H), 1.21-1.17 (m, 40H), 1.09-0.95 (m, 40H), 0.79-0.67 (m,
24H), 0.55 (b, 8H). 13C NMR (75 MHz, CD2Cl2) δ (ppm): 152.5,
152.4, 152.3, 151.8, 151.7, 151.5, 151.1, 150.8, 145.6, 145.3, 143.9,
143.8, 142.4, 141.9, 141.5, 141.4, 141.2, 141.0, 140.7, 140.3, 139.8,
138.8, 135.8, 130.6, 128.7, 128.5, 128.4, 127.2, 127.0, 123.2, 119.9,
119.5, 118.1, 117.9, 117.8, 117.4, 115.0, 64.7, 55.2, 40.9, 40.8,
35.8, 32.2, 32.1, 31.9, 30.4, 30.3, 30.0, 29.9, 29.8, 29.6, 29.5, 24.2,
23.5, 23.0, 22.9, 21.3, 14.2. MALDI-TOF: m/z 1960.
Experimental Section
Measurement and Characterization. 1H and 13C NMR spectra
were recorded on a Bruker AMX 300 NMR instrument (300 and
75 MHz, respectively) with dichloromethane-d2 as solvent and
tetramethylsilane as internal standard. Chemical shifts are reported
in parts per million. FD mass spectra were performed with a VG-
Instruments ZAB 2-SE-FDP spectrometer. The elemental analyses
were carried out by the Microanalytical Laboratory of Johannes
Gutenberg University. The UV-vis-NIR absorption measurements
were performed on a Perkin-Elmer Lambda 15 spectrophotometer
and the PL measurements on a SPEX Fluorolog 2 type F212 steady-
state fluorometer. Cyclic voltammetry and differential pulse vol-
tammetry were performed on an EG&G Princeton Applied Research
potentiostat, model 273, in a solution of Bu4NPF6 (0.1 M) in dry
dichloromethane with a scan rate of 50 mV/s at room temperature
under argon. A platinum electrode was used as the working
electrode, an Ag wire as the reference electrode, and a platinum
wire as the counter electrode.
Material Synthesis. All chemicals and reagents were used as
received from commercial sources without further purification.
Solvents for chemical synthesis were purified or freshly distilled
prior to use according to standard procedures. All chemical reactions
were carried out under an inert atmosphere. Intermediate dibro-
mopentaphenylene BrPPBr was synthesized according to previous
work in our group.
Synthesis of 2-Mesitylboron-6,6,15,15-tetra(p-octylphenyl)-
9,9,18,18-tetraoctyl-p-tolyl(ladder-type pentaphenylene) (BPPN).
Under nitrogen atmosphere, a mixture of compound BPPBr (100
mg, 0.06 mmol), bis(p-tolyl)amine (50 mg, 0.25 mmol), Pd(OAc)2
(1 mg, 0.005 mmol), P(t-Bu)3 (2 mg, 0.01 mmol), and Cs2CO3 (44
mg, 0.14 mmol) in toluene (10 mL) was stirred and heated at 80
°C for 8 h. After the reaction solution cooled to room temperature,
brine was added. The solution was extracted with ethyl acetate and
subjected to flash column chromatography (silica gel, DCM/hexane
1
) 1:15). A yellow solid was obtained in 74% yield (80 mg). H
NMR (300 MHz, CD2Cl2) δ (ppm): 7.70 (d, 2H, J ) 6.9 Hz), 7.60
(d, 2H, J ) 6.0 Hz), 7.54-7.46 (m, 3H), 7.36-7.29 (m, 3H), 7.14
(d, 8H, J ) 7.2 Hz), 7.03 (d, 8H, J ) 8.1 Hz), 6.98-6.95 (m, 5H),
6.89 (d, 4H, J ) 8.4 Hz), 6.80-6.74 (m, 5H), 2.47 (t, 8H, J ) 7.5
Hz), 2.21 (s, 6 H), 2.15 (s, 6H), 1.90 (m, 20H), 1.49 (m, 8H),
1.20-1.16 (m, 40H), 1.11-0.92 (m, 40H), 0.76-0.69 (m, 24H),
0.52 (b, 8H). 13C NMR (75 MHz, CD2Cl2) δ (ppm): 152.6, 152.3,
151.8, 150.8, 145.6, 145.3, 143.8, 142.4, 141.9, 141.3, 141.1, 140.8,
140.7, 140.6, 140.5, 139.0, 138.9, 136.9, 136.8, 136.7, 135.9, 130.6,
128.7, 128.5, 128.3, 119.5, 118.1, 117.9, 115.0, 64.7, 55.2, 40.8,
35.8, 32.2, 31.9, 30.3, 29.8, 29.6, 29.5, 24.2, 23.5, 23.0, 22.9, 22.4,
9
J. AM. CHEM. SOC. VOL. 130, NO. 37, 2008 12483

A R T I C L E S
Zhou et al.
21.3, 14.2. Elemental analysis for C154H200BN. Calcd: (%) C, 89.09;
H, 9.71; N, 0.67. Found: (%) C, 88.82; H, 10.08; N, 0.39. MALDI-
TOF: m/z 2076.
151.4, 151.1, 150.8, 145.6, 145.3, 143.9, 143.8, 142.4, 141.9, 141.5,
141.4, 141.2, 141.1, 141.0, 140.7, 140.3, 139.7, 138.8, 135.8, 130.6,
128.7, 128.5, 128.4, 127.2, 126.9, 123.2, 119.9, 119.5, 118.1, 117.9,
117.8, 117.4, 115.0, 55.2, 40.9, 40.8, 35.8, 32.2, 32.1, 31.9, 30.4,
30.3, 29.8, 29.6, 29.5, 24.2, 23.5, 23.0, 22.9, 21.3, 14.2. Elemental
analysis for C140H187B. Calcd: (%) C, 89.40; H, 10.02. Found: (%)
C, 89.30; H, 9.99. MALDI-TOF: m/z 1880.
Synthesis of 2-Mesitylboron-6,6,15,15-tetra(p-octylphenyl)-
9,9,18,18-tetraoctyl(ladder-type pentaphenylene) (BPPH). Under
nitrogen atmosphere and at -78 °C, n-BuLi (0.1 mL, 1.6 M in
hexane) was added dropwise to a dry tetrahydrofuran (40 mL)
solution containing compound BPPBr (0.2 g, 0.1 mmol). After 30
min of stirring, the reaction was quenched with brine. The solution
was extracted with ethyl acetate and subjected to flash column
chromatography (silica gel, DCM/hexane ) 1:15). A light yellow
solid was obtained in 93% yield (90 mg). 1H NMR (300 MHz,
CD2Cl2) δ (ppm): 7.73(s, 2H), 7.61-7.49 (m, 6H), 7.36 (s, 1H),
7.32 (d, 1H, J ) 7.5 Hz), 7.26 (m, 1H), 7.14 (d, 10H, J ) 8.4 Hz),
7.03 (d, 8H, J ) 7.8 Hz), 6.74 (s, 4H), 2.47 (t, 8H, J ) 7.8 Hz),
2.21 (s, 6H), 1.90 (m, 20H), 1.50-1.39 (m, 8H), 1.21-1.17 (m,
Acknowledgment. This work was financially supported by the
German Science Foundation (SFB 625, Korean-German graduate
school IRTG). G.Z. gratefully acknowledges the Alexander von
Humboldt Stiftung for a research fellowship.
Supporting Information Available: Detailed UV-vis absorp-
tion and PL spectra upon titration. This material is available
free of charge via the Internet at http://pubs.acs.org.
40H), 1.12-0.95 (m, 40H), 0.79-0.67 (m, 24H), 0.57 (b, 8H). 13
C
NMR (75 MHz, CD2Cl2) δ (ppm): 152.5, 152.4, 152.3, 151.8, 151.6,
JA803627X
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12484 J. AM. CHEM. SOC. VOL. 130, NO. 37, 2008