Synthesis and properties of bisphosphole-bridged ladder oligophenylenes

Article abstract of DOI:10.1002/asia.201200631

Ladder-type oligophenylenes (LOPP) with bridging heteroatoms are interesting systems as they offer novel electronic and photophysical properties on account of the rigid structural features, more efficient electron delocalization on the coplanar aromatic f

Full text of DOI:10.1002/asia.201200631

DOI: 10.1002/asia.201200631
Synthesis and Properties of Bisphosphole-Bridged Ladder Oligophenylenes
David Hanifi, Andrew Pun, and Yi Liu*[a]
Abstract: Ladder-type oligophenylenes
(LOPP) with bridging heteroatoms are
interesting systems as they offer novel
electronic and photophysical properties
on account of the rigid structural fea-
tures, more efficient electron delocali-
zation on the coplanar aromatic frame-
work, and strong intermolecular inter-
actions. LOPPs incorporating multiple
phosphorous centers combine the ex-
cellent electronic properties of phosp-
holes and rigidified conjugated frame-
work of LOPPs, thus positioning them-
selves as an attractive class of organic
semiconductors. To date, there still
lacks an effective synthetic methodolo-
gy towards LOPPs with multiple phos-
phorous bridges. Herein, we describe
the synthesis and properties of a new
class of bisphosphole-bridged ladder
oligo(p-phenylene)s and the related
phosphoxides. The synthesis of phosp-
holes was achieved by a four-fold free-
radical phosphanylation reaction of
a
tetrabromo p-terphenylene or bi-
phenyl-thiophene. Sequential trapping
of four highly reactive aryl radicals oc-
curred effectively to give the desired
phosphorous-containing ladder com-
pound. The oxides of the phospholes
are shown to be strong fluorophores
that can be used as potential n-type
building blocks for organic semicon-
ducting materials.
Keywords: free-radical phosphany-
lation · fluorescence · heteroacenes ·
organic semiconductors
holes
· phosp-
Introduction
Organic p-conjugated materials have attracted increasing at-
tention owing to their great potential as semiconducting ma-
terials for smaller, more efficient electronic devices.[1] Many
efforts have been directed towards modification of the mo-
lecular structures of the materials to obtain desired electron-
ic and optical properties. In particular, ladder-type p systems
with fully fused polycyclic conjugated skeletons offer[2]
novel electronic and photophysical properties because of
their rigid structural features, more efficient electron deloc-
alization on the coplanar aromatic framework, and strong
intermolecular p–p interactions. Incorporating heteroatoms
to replace the bridging carbon atoms into the p-conjugated
system has been an effective strategy in fine-tuning their
electronic structures. Ladder oligo(p-phenylene)s (LOPPs)
with bridging carbon atoms[3] or heteroatoms such as nitro-
gen,[4] sulfur,[5] and silicon[6] (Scheme 1) have been synthe-
sized and applied in electronic devices. Conjugated mole-
cules incorporating trivalent phosphorus centers,[7] the sim-
plest being phosphole,[8] have received considerable atten-
tion recently. Due to the orbital pyrimidalization on the tri-
coordinate phosphorus center, the phospholeꢀs lone pairs
Scheme 1. a) Classic phospholes, b) dibenzophosphole, and c) various bis-
bridged LOPPs.
have weakened interactions with the conjugated system.
This results in a low degree of electron delocalization rela-
tive to planar pyrrole analogs.[7a,d] The anellated ring systems
containing extended p systems, such as dithienophosphole,[9]
dibenzophosphole,[10] (Scheme 1b) or arene-fused phosp-
holes,[11] are considered nonclassical phospholes because the
aromatic character of the phosphole units is further reduced
due to strong retention of p electrons of the parent aromatic
units. On the other hand, the s*–p* interaction between the
endocyclic p system of the butadiene moiety and the s* or-
À
bital of the exocyclic P C bond results in a low-lying
LUMO energy level.[12] This hyperconjugation in phosp-
holes, including those with phosphorus (V) centers (the
oxides), makes them particularly attractive as n-type organic
semiconductors. Compounds that combine the excellent
electronic properties of phospholes and rigidified conjugated
framework of LOPPs, especially those with multiple phos-
phorous centers (2a and 3a in Scheme 1c), represent an at-
tractive class of p systems. However, an effective synthetic
methodology towards such compounds has been very limit-
ed despite the remarkable synthetic progress for phosphole-
bridged heteroaromatics.[13] Herein, we report the synthesis
of a bisphosphole-bridged LOPP and a related ladder bi-
phenyl-thiophene using a free-radical phosphanylation reac-
[a] D. Hanifi, A. Pun, Dr. Y. Liu
The Molecular Foundry
Lawrence Berkeley National Laboratory
One Cyclotron Road
Berkeley, California, 94720 (USA)
Fax : (+1)5104867413
E-mail: yliu@lbl.gov
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200631.
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tion protocol. Oxidation of such LOPPs into their corre-
sponding phosphoxides gives further opportunities for fine-
tuning the electronic and photophysical properties.
Results and Discussion
We first attempted the synthesis of the bisphosphole LOPP
2a using a standard lithiation and trapping method. Tetrali-
thiation of tetrabromide 4a[6g] followed by trapping with di-
chlorophenylphosphane only resulted in oligomeric side
products. We then turned to the recently developed radical
phosphanylation of reactive aryl radicals, which was a highly
efficient approach for the synthesis of arylphosphanes and
strained bis(phosphoryl)-bridged biphenyls.[14] This reaction
route, despite involving multiple radical phosphanylation of
a tetrabromide in one step, worked effectively to give the
desired product.
Scheme 3. Synthesis of bisphosphole 2b and the oxide 3b.
peaks at À9.6 and À23.6 ppm, and these peaks correspond
to the benzophosphole and thienophosphole moieties, re-
spectively. In the spectrum of oxide 3b, these peaks undergo
a characteristic downfield shift and now resonate at 32.9 and
22.5 ppm, respectively.
The photophysical properties of the ladder bisphospholes
and oxides were evaluated in CHCl3 by UV/Vis and fluores-
cence spectroscopy and the corresponding data are summar-
ized in Table 1, together with those of dibenzophosphole
oxide P2[10b] (R=Ph) and bissi-
The tetrabromide 4a was treated with readily prepared
(Me3Sn)2Ph at 1258C using 1,1’-azobis(cyclohexane-1-car-
bonitrile) (V-40) as the free-radical initiator (Scheme 2).
lole-bridged terphenyl 1d[6g]
(R=Ph) for comparison. The
absorption maxima at the lon-
gest wavelength for bisphosp-
holes 2a and 2b are at 330 nm
and
332 nm,
respectively
Scheme 2. Synthesis of bisphosphole 2a and the oxide 3a. V-40=1,1’-azobis(cyclohexane-1-carbonitrile).
Table 1. Photophysical properties of the bisphospholes, dibenzophole P2,
and bissilole 1d.[a]
From the cooled reaction mixture an isomerically pure bi-
sphosphole 2a in its trans geometry was isolated in 37%
yield as a white solid, which showed only one single reso-
nance in its 31P NMR spectrum (31P: d=À9.4 ppm). The
chemical shift is significantly upfield as compared to those
of the parent phospholes reported by Reau et al.[8a] (31P: d=
11–45 ppm), but very close to dibenzophosphole P2 (R=Ph,
31P: d=À12.8 ppm),[10a] consistent with its benzophosphole
characteristics rather than those characteristics of a classic
phosphole. Compound 2a is stable in the solid state while in
solution, it slowly isomerizes to give a mixture of trans/cis
isomers, as indicated by the appearance of a new peak at
À9.6 ppm (see Figure S1 in Supporting Information) in the
31P NMR spectrum, and it reaches a ratio of 3:2 (trans/cis)
in three weeks. Oxidation of trans-2a with H2O2 gave the
corresponding oxide trans-3a, which showed a single reso-
nance at 33.7 ppm in its 31P NMR spectrum.
The successful phosphanylation reaction on the p-terphen-
yl tetrabromide allows for the synthesis of new bisphosp-
hole-bridged LOPPs. As an initial test, we applied this reac-
tion protocol to the biphenyl-thiophene tetrabromide 4b,
which was synthesized from Suzuki coupling between iodide
5[6g] and boronic acid 6 (Scheme 3). After being subjected to
similar radical phosphanylation conditions, trans-2b was iso-
lated in pure form by simple filtration from the reaction
mixture, which was readily oxidized by H2O2 to give the
oxide trans-3b. The 31P NMR spectrum of 2b shows two
Compound
UV/Vis absorption
Fluorescence
labs [nm][b]
e [MÀ1 cmÀ1
]
lem [nm][c]
Ff[d]
trans-2a
trans-2b
trans-3a
trans-3b
P2[e]
330
332
383
381
332
328
9719
9400
2780
4819
794
409, 420
420
420
408, 423
366
395
0.21
0.05
0.81
0.11
0.04
0.56
1d[f]
40300
[a] In CHCl3. [b] Only the absorption maxima at longest wavelength are
listed. [c] Emission maxima upon excitation at 330 nm. [d] Absolute
quantum yields were measured by a calibrated integrating sphere system
with Æ3% error. [e] See ref. [10b]. [f] See ref. [6g].
(Figure 1), and are similar to the silole-bridged LOPP 1d. In
comparison, low-intensity absorption maxima at 383 and
381 nm are observed for the corresponding oxides 3a and
3b, respectively, which are attributed to intramolecular
charge transfer from the conjugated p systems to the phosp-
hole oxide groups. More pronounced peaks at around
330 nm are attributed to the p–p* HOMO–LUMO electron-
ic transitions. In addition, both 3a and 3b absorb at higher
wavelength than the monophosphole oxide P2 owing to ex-
tended p-electron delocalization in the ladder framework.
Compounds 2a, 2b, 3a, and 3b are blue fluorescent, with
the emission maxima all at around 420 nm (Figure 2). How-
ever, their quantum yields vary significantly. Both oxides
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Synthesis and Properties of Bisphosphole-Bridged Ladder Oligophenylenes
formation for 2a, 2b, and 3b. The frontier orbitals and ener-
gies were also computed by using DFT and are shown in
Figure 4. The p systems are well delocalized over the oligo-
Figure 1. UV/Vis spectra of trans-2a,b and trans-3a,b. Solvent: CHCl3.
Figure 4. Computed frontier orbitals and energy levels of trans-2a,b and
trans-3a,b.
phenylene skeleton. The highest occupied molecular orbitals
(HOMO) are antibonding combinations of the HOMOs of
constituent phenylene or thiophene units, with no (for 2a
and 2b) or little contribution (for 3a and 3b) from the sPÀPh
orbitals. On the other hand, the lowest unoccupied molecu-
lar orbitals (LUMO) are bonding combinations of the
LUMOs of the oligophenylenes, with contributions from the
sPÀPh* orbitals. The LUMO energy levels of the oxides 3a
and 3b are more than 0.6 eV lower than the corresponding
phospholes 2a and 2b, owing to the electron-withdrawing
effect of the oxygen atoms. The HOMO energies of both
oxides are also lower than the free phospholes, albeit to
a lesser extent (ca. 0.3 eV). Overall the oxidation of the
phosphorus centers into their pentavalent coordination ge-
ometry results in a decreased HOMO–LUMO gap, which
correlates well with the bathochromic shift observed in their
absorption spectra.
Figure 2. Normalized fluorescence spectra of trans-2a,b and trans-3a,b.
Solvent: CHCl3.
have higher quantum yields than the corresponding trivalent
phospholes, and 3a exhibits the strongest fluorescence with
a high quantum yield of 0.81.
Numerous efforts in growing crystals suitable for single
crystal X-ray analysis failed. The optimal molecular geome-
tries were then modeled by using density functional theory
(DFT) at B3LYP/6-31G** level. A highly coplanar conjugat-
ed framework was observed for 2a, 2b, 3a, and 3b, as
shown in Figure 3 for 3a and Figure S3 in the Supporting In-
The electrochemical properties of phosphole oxides 3a
and 3b were evaluated in CHCl3 using the standard three-
+
electrode setup[15] and the ferrocene/ferrocenium (Fc/Fc
)
redox couple as the internal standard. While the cyclic vol-
tammogram (CV) of 3a is irreversible, the CV of 3b shows
(Figure S3 in the Supporting Information) one quasi-reversi-
ble reduction peak at À1.40 V (vs Fc/Fc+). This reduction
potential is significantly more negative than the Ered value
of the monophosphole P2 (À1.93 V vs SCE or À2.41 vs Fc/
Fc+),[10b] thereby indicating that the incorporation of two
phosphole bridges in the LOPPs is effective in enhancing
the electron-accepting abilities. The low-lying LUMO
energy of À3.4 eV, derived from the following equation:
LUMO=À(Ered+4.8 eV),[17] affirms good n-type characteris-
tics of this type of LOPP.
Figure 3. Ball-and-stick representation of the optimized geometry of 3a
at B3LYP/6-31G** level. a) front view, and b) side view.
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(CDCl3, 298 K, 500 MHz): d=7.73 (dd, J=7.5 Hz, 1.0 Hz, 1H), 7.63 (s,
1H), 7.58 (s, 1H), 7.44 (dt, J=7.5 Hz, 1.0 Hz, 1H), 7.42 (d, J=3.0 Hz,
1H), 7.39 (d, J=3.0 Hz, 1H), 7.34–7.31 ppm (m, 2H); 13C NMR (CDCl3,
298 K, 125 MHz): d=143.3, 140.4, 139.7, 137.5, 135.3, 134.6, 132.8, 130.9,
129.9, 127.3, 125.5, 123.6, 123.3, 122.8, 122.0, 112.0 ppm. MS (HR-ESI):
[MÀBr]+ calcd for C16H8Br4S: 468.7897; found: 468.7899 (100%).
Conclusions
We have synthesized a new class of bisphosphole-bridged
ladder oligophenylenes from a four-fold free-radical phos-
phanylation reaction. The effective synthesis allows access
to other ladder heteroarene systems, as demonstrated in the
synthesis of a thiophene isologue of bisphosphole-bridged
LOPP. The electronic structures and photophysical proper-
ties of these bisphosphole LOPPs were characterized and
modeled by DFT calculations. The oxides of the phospholes
are shown to be strong fluorophores while having good elec-
tron-accepting characteristics, thereby rendering them as po-
tential n-type building blocks for organic semiconducting
materials. The synthetic protocol is to be extended to other
isologues of bisphosphole-bridged LOPPs. The implementa-
tion of such materials into organic electronic devices is cur-
rently underway.
Synthesis of trans-2a and trans-3a
A
mixture of tetrabromo-p-terphenyl (4a) (150 mg, 276 mmol), V-40
(33 mg, 138 mmol), and (Me3Sn)2PPh (450 mg, 1.02 mmol) in trifluoroto-
luene (15 mL) was heated under nitrogen at 1258C for 40 h. The mixture
was cooled to RT and the resulting precipitate was collected by filtration
and washed with trifluorotoluene. The precipitate was dried under high
vacuum to afford trans-2a (45 mg, 37% yield) as an off-white solid.
M.p. 319–3208C. 1H NMR (CDCl3, 298 K, 500 MHz): d=8.28 (d, J=
6.0 Hz, 2H), 7.97 (d, J=7.5 Hz, 2H), 7.71 (dd, J=7.5 Hz, 5.0 Hz, 2H),
7.48 (dt, J=7.5 Hz, 1.0 Hz, 2H), 7.39–7.27 ppm (m, 12H). 13C NMR
(CDCl3, 298 K, 125 MHz): d=143.8, 143.2, 142.9, 133.0 (d), 130.4 (d),
129.5, 128.8 (m), 127.7 (m), 123.2 (d), 121.5 ppm. 31P NMR (CDCl3,
298 K, 212 MHz): d=À9.43 ppm. HR-MS (MALDI-TOF): [M]+ calcd
for C30H20P2: 443.1040; found: 443.0432 (100%). When a CDCl3 solution
of 2a was left at RT in a degassed J-Young NMR tube for an extended
period of time, a new phosphorus signal slowly emerged, thereby indicat-
ing the trans/cis isomerization (trans-2a: À9.46 ppm; cis-2a: À9.60 ppm).
Experimental Section
2a (40 mg, 92 mmol) was dispersed in CH2Cl2 (8 mL), water (4 mL), and
H2O2 (50% in water, 0.4 mL), and the mixture was stirred at RT for 1 h.
The mixture was extracted with CH2Cl2 (3ꢂ20 mL), the organic phase
was washed successively with a saturated aqueous Na2S2O3 solution and
NaCl solution and dried over MgSO4. The solvents were evaporated
under reduced pressure to afford 3a (42 mg, 98%) as a white solid. The
filtrate from the phosphanylation reaction was evaporated to dryness to
give a yellow residue, to which CH2Cl2 (15 mL), water (9 mL), and H2O2
(50% in water, 0.9 mL) were added and the mixture was stirred at RT
for 1 h. The mixture was extracted with CH2Cl2 (3ꢂ20 mL), the organic
phase was washed successively with saturated aqueous Na2S2O3 solution
and NaCl solution and dried over MgSO4. The solvents were evaporated
under reduced pressure and the residue was subjected to column chroma-
tography (silica gel, CH2Cl2/Me2CO 10:1 to 1:1) and afforded 3a (15 mg,
12% yield) as a white solid. The combined yield for 3a over the two
steps (phosphanylation and oxidation) is 48%. 1H NMR (CDCl3, 298 K,
500 MHz): d=8.16 (dd, J=10.0 Hz, 2.5 Hz, 2H), 7.81 (dd, J=7.5 Hz,
2.5 Hz, 2H), 7.76–7.70 (m, 6H), 7.63 (t, J=7.5 Hz, 2H), 7.58 (t, J=
7.5 Hz, 2H), 7.50–7.43 ppm (m, 6H). 13C NMR (CDCl3, 298 K,
125 MHz): d=133.9, 133.5 (m), 132.7, 131.8 (m), 131.1 (d), 129.0 (d),
128.9 (m), 122.4, 121.8 ppm (d). 31P NMR (CDCl3, 298 K, 212 MHz): d=
33.70 ppm. MS (HR-ESI): [M+1]+ calcd for C30H20O2P2: 475.0939;
found: 475.0935 (100%).
General Methods
Thin-layer chromatography (TLC) was carried out using aluminum
sheets, precoated with silica gel 60F (Merck 5554). The plates were in-
spected by UV light. 1H NMR, 13C NMR, and 31P NMR spectra were re-
corded on a Bruker Avance500 II, using the deuterated solvent and tetra-
methylsilane (1H NMR and 13C NMR) or 85% phosphoric acid as inter-
nal standards (31P NMR). All chemical shifts are quoted in ppm, and all
coupling constants (J) are expressed in Hertz (Hz). High-resolution elec-
trospray mass spectra (HR-ESI-MS) were measured on a VG ProSpec
triple focusing mass spectrometer. Cyclic voltammetry was performed
using a 273 A potentiostat (Princeton Applied Research), wherein glassy
carbon, platinum, and Ag wire act as the working electrode, the counter
electrode and the pseudo-reference electrode, respectively. Samples were
prepared in a CHCl3 solution with tetrabutylammonium hexafluorophos-
phate (0.1m) as the electrolyte at a scan rate of 100 mVsÀ1, using ferro-
cene/ferronium (Fc/Fc+) redox couple as an internal standard. UV/Vis
spectra were recorded using a Cary 500 UV/Vis-NIR spectrometer. Fluo-
rescent spectra were recorded using Horiba NanoLog Spectrofluorome-
ter system. All chemicals were purchased from Sigma–Aldrich unless oth-
[14d]
erwise noted. Compounds 4a,[6g] 5,[6 g] and PhP
(SnMe3)2
were synthe-
sized according to literature procedures.
Computational Methods
Synthesis of trans-2b and trans-3b
All calculations were performed using Q-Chem 3.2.[17] The free software
Avogadro and Q-Chem User Interface (QUI) were used as the molecular
builder and the script editor, respectively. The geometry and energy level
of the HOMO and the LUMO of the molecules were carried out at the
DFT level[18,19] using B3LYP/6–31G** basis set. DFT/B3LYP/6–31G**
has been found to be an accurate formalism for calculating the structural
and electronic properties of many molecular systems.[20] No symmetry
constraints were imposed during the optimization process. The HOMO/
LUMO orbitals were plotted with an isovalue of 0.01.
A mixture of tetrabromide (4b) (300 mg, 0.544 mmol), V-40 (65 mg,
0.272 mmol), and (Me3Sn)2PPh (710 mg, 1.63 mmol) in trifluorotoluene
(15 mL) was heated under nitrogen at 1258C for 50 h. The mixture was
cooled to RT and the resulting precipitate was collected by filtration and
washed with trifluorotoluene. The precipitate was dried under high
vacuum to afford 2b (60 mg, 24% yield) as an off-white solid. M.p.>
4008C (dec.). 1H NMR (CDCl3, 298 K, 500 MHz): d=8.17 (d, J=6.0 Hz,
1H), 8.06 (d, J=5.0 Hz, 1H), 7.94 (d, J=7.5 Hz, 1H), 7.69 (dd, J=
7.5 Hz, 6.0 Hz, 1H), 7.55 (d, J=2.0 Hz, 1H), 7.45 (d, J=2.0 Hz, 1H),
7.44 (dt, J=7.5 Hz, 1.0 Hz, 1H), 7.42–7.31 ppm (m, 12H). The 13C NMR
spectrum was not acquired due to limited solubility. 31P NMR (CDCl3,
298 K, 212 MHz): d=À9.57, À23.56 ppm. MS (HR-ESI): [M+1]+ calcd
for C28H18P2S: 449.0204; found: 449.0204 (100%).
Synthesis of 4b
A mixture of 2,2’,5-tribromo-4-iodobiphenyl (5) (517 mg, 1.00 mmol),
boronic acid 6 (248 mg, 1.20 mmol), [PdACTHNUTRGNEUNG(PPh3)4] (58 mg, 50 mmol), and
K3PO4 (424 mg, 2.00 mmol) in N,N-dimethylformamide (DMF) (15 mL)
was stirred under N2 for 18 h at 1008C. After removal of the solvent by
evaporation, the residue was diluted with water and extracted with
CH2Cl2. The organic layers was combined and dried over anhydrous
MgSO4, filtered, and concentrated under reduced pressure. The mixture
was purified by column chromatography (silica gel, hexanes 100%) to
give 4b (380 mg, 69% yield) as a white solid. M.p. 208–2098C. 1H NMR
3a (40 mg, 89 mmol) was dispersed in CH2Cl2 (8 mL), water (4 mL), and
H2O2 (50% in water, 0.4 mL), and the mixture was stirred at RT for 1 h.
The mixture was extracted with CHCl3 (3ꢂ20 mL), the organic phase
was washed successively with saturated aqueous Na2S2O3 solution and
NaCl solution and dried over MgSO4. The solvents were evaporated
under reduced pressure to give 3b (44 mg, 92% yield) as a white solid.
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Synthesis and Properties of Bisphosphole-Bridged Ladder Oligophenylenes
The filtrate from the phosphanylation reaction was evaporated to dryness
to give a brown residue, to which CH2Cl2 (30 mL), water (10 mL), and
H2O2 (50% in water, 1 mL) were added and the mixture was stirred at
RT for 1 h. The mixture was extracted with CH2Cl2 (3ꢂ10 mL), the or-
ganic phase was washed successively with saturated aqueous Na2S2O3 so-
lution and NaCl solution and dried over MgSO4. The solvents were
evaporated under reduced pressure and the residue was subjected to
column chromatography (silica gel, CH2Cl2/Me2CO 10:1 to 1:1) to afford
3b (35 mg, 13% yield) as a white solid. The combined yield for 3b over
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1
the two steps (phosphanylation and oxidation) is 35%. H NMR (CDCl3,
298 K, 500 MHz): d=8.08 (dd, J=10.0 Hz, 2.5 Hz, 1H), 7.99 (dd, J=
10.0 Hz, 2.5 Hz, 1H), 7.82 (dd, J=5.0 Hz, 2.5 Hz, 1H), 7.78 (dd, J=
7.5 Hz, 2.5 Hz, 1H), 7.75–7.68 (m, 5H), 7.63–7.53 (m, 3H), 7.53 (t, J=
2.0 Hz, 1H), 7.49–7.42 ppm (m, 5H); 13C NMR (CDCl3, 298 K,
125 MHz): d=145.2, 145.0, 144.5, 143.7, 142.0 (dd)*, 140.8, 140.6, 139.3
(dd)*, 139.0, 138.2, 136.2, 125.3, 133.9 (d), 133.2, 132.7 (m)*, 132.5 (d)*,
132.3(d)*, 131.1 (dd)*, 130.7, 130.1 (m)*, 128.8 (m)*, 123.1 (t)*, 122.9
(t)*, 121.6 (d)*, 118.0 ppm (d)*. The star (*) symbols indicate multiplets
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due to C P coupling. 31P NMR (CDCl3, 298 K, 212 MHz): d=32.91,
À
20.52 ppm. MS (HR-ESI): [M+1]+ calcd for C28H18O2P2S: 481.0503;
found: 481.0504 (100%).
Acknowledgements
This work was performed at the Molecular Foundry, Lawrence Berkeley
National Laboratory, supported by the Office of Science, Office of Basic
Energy Sciences, Scientific User Facilities Division, of the U.S. Depart-
ment of Energy under Contract No. DE-AC02-05CH11231.
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Received: July 13, 2012
Published online: && &&, 0000
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Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

FULL PAPER
Oligophenylenes
David Hanifi, Andrew Pun,
Yi Liu*
&&&& — &&&&
Synthesis and Properties of Bisphosp-
hole-Bridged Ladder Oligophenylenes
A new class of bisphosphole-bridged
ladder oligo(p-phenylene)s have been
synthesized by a four-fold free-radical
phosphanylation reaction of a tetra-
bromo p-terphenylene or biphenyl-
thiophene. The oxides of the phosp-
holes are shown to be strong fluoro-
phores that could be used as potential
n-type building blocks for organic sem-
iconducting materials.
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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