α,α′-Diarylacenaphtho[1,2-c]phosphole P-oxides: Divergent synthesis and application to cathode buffer layers in organic photovoltaics

Article abstract of DOI:10.1002/asia.201200492

A divergent method for the synthesis of α,α'- diarylacenaphtho[1,2-c]phosphole P-oxides has been established; α,α'-dibromoacenaphtho[c]phosphole P-oxide, which was prepared through a Ti^II-mediated cyclization of 1,8-bis(trimethylsilylethynyl) naphthalene, underwent a Stille coupling with three different kinds of aryltributylstannanes to afford the α,α'-diarylacenaphtho[c] phosphole P-oxides in moderate to good yields. X-ray crystallographic analyses and UV/Vis absorption/fluorescence measurements have revealed that the degree of π-conjugation, the packing motif, the electron-accepting ability, and the thermal stability of the acenaphtho[c]phosphole π-systems are finely tunable with the α-aryl substituents. All the P=O and P=S derivatives exhibited high stability in their electrochemically reduced state. To use this class of arene-fused phosphole π-systems as n-type semiconducting materials, we evaluated device performances of the bulk heterojunction organic photovoltaics (OPV) that consist of poly(3-hexylthiophene), an indene-C₇₀ bisadduct, and a cathode buffer layer. The insertion of the diarylacenaphtho[c] phosphole P-oxides as the buffer layer was found to improve the power conversion efficiency of the polymer-based OPV devices. A convenient approach to α,α'-diarylacenaphtho[c]phosphole P-oxides through a Stille coupling of the α,α'-dibromo synthon has been developed. The effects of the α-aryl substituent on the structural, optical, and electrochemical properties have been revealed. The diarylacenaphtho[c]phosphole P-oxides were found to behave as promising cathode buffer materials in bulk heterojunction organic photovoltaics. Copyright

Full text of DOI:10.1002/asia.201200492

DOI: 10.1002/asia.201200492
a,a’-DiarylacenaphthoACTHNUTRGNE[UNG 1,2-c]phosphole P-Oxides: Divergent Synthesis and
Application to Cathode Buffer Layers in Organic Photovoltaics
Yoshihiro Matano,*[a] Arihiro Saito,[a] Yuto Suzuki,[a] Tooru Miyajima,[a] Seiji Akiyama,[b]
Saika Otsubo,[b] Emi Nakamoto,[b] Shinji Aramaki,[b] and Hiroshi Imahori[a, c]
Abstract: A divergent method for the
synthesis of a,a’-diarylacenaphtho[1,2-
c]phosphole P-oxides has been estab-
lished; a,a’-dibromoacenaphtho[c]-
phosphole P-oxide, which was prepared
through a TiII-mediated cyclization of
1,8-bis(trimethylsilylethynyl)naphtha-
lene, underwent a Stille coupling with
three different kinds of aryltributyl-
stannanes to afford the a,a’-diarylace-
naphtho[c]phosphole P-oxides in mod-
erate to good yields. X-ray crystallo-
graphic analyses and UV/Vis absorp-
tion/fluorescence measurements have
revealed that the degree of p-conjuga-
tion, the packing motif, the electron-ac-
cepting ability, and the thermal stability
of the acenaphtho[c]phosphole p-sys-
tems are finely tunable with the a-aryl
substituents. All the P=O and P=S de-
rivatives exhibited high stability in
their electrochemically reduced state.
To use this class of arene-fused phosp-
hole p-systems as n-type semiconduct-
ing materials, we evaluated device per-
formances of the bulk heterojunction
organic photovoltaics (OPV) that con-
sist of poly(3-hexylthiophene), an
indene-C70 bisadduct, and a cathode
buffer layer. The insertion of the diary-
lacenaphtho[c]phosphole P-oxides as
the buffer layer was found to improve
the power conversion efficiency of the
polymer-based OPV devices.
AHCTUNGTRENNUNG
Keywords: conjugation
coupling fused-ring systems
heterocycles · phospholes
·
cross-
·
·
Introduction
cient chemical and thermal stability is of particular
importance in terms of materials supply.
Bulk heterojunction organic photovoltaics (OPV) have been
extensively investigated in both industrial and academic
fields, as their advantages of flexibility, light weight, poten-
tially low-cost processability, and molecular-design versatili-
ty are beneficial to construct environmentally benign
energy-conversion devices.[1] To improve device performan-
ces such as power conversion efficiency (PCE) and durabili-
ty of OPV, there are awaiting issues that have to be over-
come or improved. Among them, the development of organ-
ic n-type semiconducting materials with high electron-ac-
cepting and electron-transporting properties as well as suffi-
Phosphole-containing p-conjugated materials have recent-
ly been receiving significant attention, as their characteristic
optical and electrochemical properties are potentially appli-
cable to organic devices.[2] In particular, arene-fused phosp-
hole derivatives bearing phosphorus(V) centers are known
to exhibit intriguing electron affinity owing to the resonance
and inductive effects of the PV functional groups.[3–8] In addi-
tion, several kinds of arene-fused phosphole P-oxides and
P-sulfides have exhibited high electron drift mobility up to
approximately 2ꢀ10À3 cm2 VÀ1 sÀ1 in the amorphous state (as
measured by a time-of-flight method).[3,8] Considering these
characteristic properties, the arene-fused phospholes are
promising candidates for n-type organic semiconducting ma-
terials that are applicable to OPV devices. Tsuji, Nakamura,
and co-workers reported OPV devices that incorporate ben-
zo[b]phosphole derivatives P1 and P2 as cathode buffer
layers,[9] which were found to keep constant PCE (h) after
annealing at high temperatures. This interesting device per-
formance was attributed to the morphological stability of P1
and P2, as represented by their high glass transition temper-
atures (Tg =148–1598C). To the best of our knowledge, the
literature contains only a few studies on the OPV devices
using n-type phosphole-based materials.[10]
[a] Prof. Dr. Y. Matano, A. Saito, Y. Suzuki, T. Miyajima,
Prof. Dr. H. Imahori
Department of Molecular Engineering, Graduate School of Engineer-
ing, Kyoto University
Nishikyo-ku, Kyoto 615-8510 (Japan)
Fax : (+81)75-383-2571
E-mail: matano@scl.kyoto-u.ac.jp
[b] S. Akiyama, Dr. S. Otsubo, E. Nakamoto, Dr. S. Aramaki
Mitsubishi Chemical Group, Science and Technology Research
Center, Inc. Aoba-ku
Yokohama, 227-8502 (Japan)
In 2009, we reported that naphthalene-fused phosphole P-
oxide 1a exhibited sufficient electrochemical stability and
moderate electron drift mobility of up to 8ꢀ
10À5 cm2 VÀ1 sÀ1.[8b] This result suggested that 1a and related
compounds would also be applicable to n-type semiconduc-
tors in organic devices. In this regard, the derivatization of
[c] Prof. Dr. H. Imahori
Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto
University
Nishikyo-ku, Kyoto 615-8510 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200492.
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
&
&
&
These are not the final page numbers! ÞÞ

FULL PAPER
acenaphtho[c]phosphole p-systems is an important subject
for their further development in materials chemistry. To
control the fundamental properties of this class of phosp-
hole-based p-systems, chemical modification of substituents
of the phosphole ring based on a cross-coupling method is
highly significant, as it could introduce various p-conjugated
groups from a common phosphole synthon. In our earlier
studies, we have demonstrated that Stille coupling of P3
connects various p-conjugated groups at the a,a’ positions
of the phosphole ring effectively.[11]
Scheme 1. Synthesis of a,a’-diarylacenaphtho[c]phospholes.
CH2Cl2/n-hexane; in the 31P NMR spectrum, a singlet peak
was observed at 42.5 ppm.
With the dibromide 5 in hand, we examined the Stille
coupling with three kinds of aryltributylstannanes 6b–d in
the presence of a catalytic amount of [PdACTHUNRTGNEUNG(PPh3)4]. As ex-
pected, the carbon–carbon bond formation proceeded
smoothly to afford a,a’-diarylacenaphtho[c]phosphole P-
oxides 1b, 1c, and 1d in 44%, 65%, and 74% yields, re-
spectively, based on 5. These results represent that the
cross-coupling protocol is effective for the derivatization of
acenaphtho[c]phosphole p-systems.[14] The P-oxide 1b was
further converted into P-sulfide 7b in 86% yield by treat-
ment with Lawessonꢂs reagent.
The structures of newly prepared diarylacenaphtho[c]-
phosphole P-oxides 1b–d and P-sulfide 7b were fully char-
acterized by standard spectroscopic techniques. In the
31P NMR spectra of 1a, 1b, 1c, and 1d in CDCl3, singlet
peaks appeared at 54.5, 54.7, 55.4, and 53.1 ppm, respective-
ly. In their corresponding IR spectra of KBr pellets, the P=
O stretching vibration modes were observed at n˜max 1195,
1194, 1192, and 1201 cmÀ1, respectively. These data indicate
that the electronic effects of the a-aryl groups on the polar-
izability and the multiplicity of the P=O function are not so
significant. The 31P NMR singlet peak of P-sulfide 7b was
downfield (dP =72.4 ppm) compared to that of P-oxide 1b.
The structures of 1b and 1c were further elucidated by X-
ray crystallography. Selected bond parameters are summar-
ized in Table 1 together with those of the previously report-
ed 1a. As shown in Figures 1 and 2, each phosphorus center
adopts a distorted tetrahedral geometry with C-P-O bond
angles of 111.60(6)–117.91(5)8 and 112.43(9)–117.03(9)8 for
We report herein a new, convenient method for the diver-
gent synthesis of a,a’-diarylacenaphthoACHTNUTRGNEUNG[1,2-c]phosphole
(hereafter denoted as diarylacenaphtho[c]phosphole) P-
oxides that is based on a Stille cross-coupling procedure.
The effects of the a-substituents on the structure, optical/
electrochemical properties, and thermal stability of the ace-
naphtho[c]phosphole p-systems were investigated. Further-
more, some derivatives were applied to cathode buffer
layers in bulk heterojunction OPV devices, and their sub-
stituent effects on the photovoltaic performances were eval-
uated.
Results and Discussion
Synthesis and Characterization
Scheme 1 illustrates the synthesis of new a,a’-diarylacenaph-
tho[c]phosphole derivatives. Treatment of 1,8-bis(trimethyl-
silylethynyl)naphthalene (2) with the Sato–Urabe low-valent
titanium reagent[12] generated a titanacycle intermediate
3.[13] Metathesis of 3 with dichloro
ACTHNUTRGNE(UNG phenyl)phosphine fol-
lowed by oxidation with m-chloroperbenzoic acid (m-
CPBA) afforded a,a’-bis(trimethylsilyl)acenaphtho[c]phosp-
hole P-oxide (4). The crude P-oxide 4 was used in the fol-
lowing reaction without purification. When crude P-oxide 4
À
À
1b and 1c, respectively. The P C and C C bond lengths as
À
À À
À À
was treated with N-bromosuccinimide (NBS), the two a-C
well as the P C C and C C C bond angles in the phosp-
hole rings of 1a–c are almost identical. The fused p-systems
in 1b and 1c are almost on the same plane, although the
phosphorus atom is slightly deviated by 0.08 (for 1b) and
Si bonds of 4 were cleaved to give a,a’-dibromophosphole
P-oxide 5 in approximately 80% yield. Compound 5 was pu-
rified by column chromatography and recrystallized from
&
&
&2
&
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

a,a’-DiarylacenaphthoACTHNUTRGNE[UNG 1,2-c]phosphole P-Oxides
Table 1. Selected bond lengths, bond angles, and dihedral angles of 1a,
1b, and 1c.
Compound
1a[a]
1b
1c
X
R
CH
H
CH
4-phenyl
N
6-(2-pyridyl)
Bond lengths [ꢃ]
a
a’
b
b’
c
d
d’
e
1.8174(16)
1.8183(17)
1.342(2)
1.347(2)
1.508(2)
1.472(2)
1.472(2)
1.473(2)
1.470(2)
1.4780(13)
1.8137(12)
1.8236(12)
1.3429(16)
1.3486(16)
1.5085(15)
1.4609(16)
1.4697(16)
1.4810(15)
1.4747(15)
1.4810(9)
1.807(2)
1.820(2)
1.347(3)
1.361(3)
1.513(3)
1.467(3)
1.470(3)
1.466(3)
1.466(3)
1.4861(15)
Figure 2. Crystal structure of 1c: top and side views (30% probability el-
lipsoids). Hydrogen atoms are omitted for clarity.
e’
P=O
benzene rings in 1a and 1b; this could be due to steric rea-
sons.
Bond angles [8]
ab
a’b’
bc
b’c
cd
107.51(12)
107.34(11)
115.48(14)
115.39(14)
107.00(14)
106.86(13)
107.11(8)
107.23(8)
116.09(10)
115.00(10)
107.57(10)
106.77(10)
108.16(15)
107.44(14)
115.17(17)
114.77(17)
107.38(16)
106.66(16)
Furthermore, there is a noticeable difference in the pack-
ing structures of 1b and 1c (Figure S1 in Supporting Infor-
mation). In 1b, the naphthalene units are stacked with
mainly slipping between the layers, and the biphenylene
units are located above the neighboring naphthalene unit in
an almost perpendicular orientation. As deduced from the
cd’
Sum of the bond angles [8]
SC-P-C
307.1
347.8
307.9
347.2
309.2
345.8
SC-P-O
À
relatively short C···C distance of 3.44 ꢃ, the C H···p interac-
Dihedral angles [8]
a
tion is likely to operate in the solid state of 1b. On the
other hand, the naphthalene units in 1c are stacked in an
antiparallel fashion (the p–p distance is ca. 3.4 ꢃ) with
mostly overlapping between the layers. It is evident that the
a-aryl groups have a significant impact on the packing
motifs of the acenaphtho[c]phosphole P-oxides in the solid
state.
46.7
40.9
70.9
50.3
26.5
14.8
a’
[a] Data from ref. [8b].
Optical and Electrochemical Properties
To reveal the substituent effects on the optical properties of
the acenaphtho[c]phosphole p-systems, UV/Vis absorption
and emission spectra of 1b–d and 7b were measured in
CH2Cl2, and the results are summarized in Table 2 and
Figure 3. All the P-oxides 1a–d are moderately fluorescent
(Ff =0.08–0.16), whereas the P-sulfide 7b is weakly fluores-
cent (Ff =0.02). The replacement of phenyl groups with the
Table 2. Optical data and redox potentials for 1a–d and 7b.[a]
[b]
[c]
[d]
[d]
Compound
labs (loge)
lem (FF)
Eox
Ered
Figure 1. Crystal structure of 1b: top and side views (30% probability el-
lipsoids). Hydrogen atoms are omitted for clarity.
1a[e]
1b
1c
1d
7b
439 (3.62)
457 (3.87)
466 (3.86)
549 (4.31)
448 (3.88)
552 (0.08)
576 (0.13)
541 (0.16)
583 (0.16)
553 (0.02)
+0.94
+0.86
+1.00
+0.94
+0.86
À1.82
À1.75
À1.61
À1.24[f]
À1.79
0.11 ꢃ (for 1c) from the cyclic 1,3-diene plane of the phosp-
hole ring. The aryl rings attached at the a carbons are twist-
ed against the phosphole five-membered ring with dihedral
angles of 40.9–46.7 for 1a, 50.3–70.9 for 1b, and 14.8–26.58
for 1c, thereby indicating that the pyridine rings in 1c are
more conjugated to the adjacent phosphole ring than the
[a] Measured in CH2Cl2. [b] The longest absorption maxima (in nm).
[c] Fluorescence maxima (in nm) excited at 440 nm. [d] Oxidation and re-
duction potentials (in V) versus Fc/Fc+ determined by DPV with
Bu4NPF6 (0.1m). [e] Data from ref. [8b]. [f] The second reduction poten-
tial is À1.59 V.
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3
&
&
&
These are not the final page numbers! ÞÞ

Yoshihiro Matano et al.
FULL PAPER
at an electric field of 2.5ꢀ104 VcmÀ1 (determined by a time-
of-flight method; Figure S2 in the Supporting Information).
Application to Cathode Buffer Layers in Organic
Photovoltaics
The phenyl, biphenyl, and bipyridyl derivatives 1a–c dis-
played relatively high thermal stability for device fabrica-
tion.[17] In the differential scanning calorimetry (DSC) meas-
urements of 1a–c, the molten samples after the first run
(heating) were rapidly cooled and subjected to the second
heating. The DSC traces displayed glass transitions at Tg =
868C for 1a, Tg =1368C for 1b, and Tg =1248C for 1c
(Table 3 and Figure S3 in the Supporting Information).
Figure 3. Absorption and fluorescence spectra of 1b, 1c, and 1d.
biphenyl, bipyridyl, or benzothiazolyl groups induced red-
shifts in the p–p* electron transitions (labs and lem in
Table 2). The spectral features of the benzothiazolyl deriva-
tive 1d differ significantly from those of the other deriva-
tives, probably owing to the effective p-conjugation between
the phosphole and thiazole rings. The relatively small Stokes
shift observed for 1d (1060 cmÀ1) could indicate that the
structure relaxation in the excited state of 1d is rather small
compared to the other derivatives.
Table 3. Photovoltaic characteristics of OPV devices.[a]
[b]
[c]
[d]
Device
Buffer layer (Tg
none (À)
)
VOC
JSC
FF[e]
h[f]
A
B
C
D
E
F
0.31
0.82
0.76
0.83
0.61
0.77
6.9
7.7
8.8
8.1
7.7
7.7
0.43
0.58
0.62
0.53
0.54
0.63
0.9
3.7
4.2
3.5
2.5
3.7
phosphole 1a (86)
phosphole 1b (136)
phosphole 1c (124)
phosphole 7b (NA)
BCP (62)
[a] Device configuration: ITO/PEDOT:PSS/P3HT:IC70BA/buffer layer/
Al. [b] Glass transition temperature (8C) determined by DSC. [c] Open
circuit voltage (V). [d] Short circuit current density (mAcmÀ2). [e] Fill
factor. [f] Power conversion efficiency (%). NA=Not available.
Redox potentials of 1b–d and 7b were determined by
means of cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) in CH2Cl2 in the presence of Bu4NPF6
(0.1m) as a supporting electrolyte. The first oxidation poten-
tial of the biphenyl derivative 1b (Eox = +0.86 V versus fer-
rocene/ferrocenium) is shifted to the negative direction,
whereas the first reduction potential of 1b (Ered =À1.75 V)
is shifted to the positive direction relative to the respective
potentials of the phenyl derivative 1a. The replacement of
the phenyl groups with bipyridyl groups (from 1a to 1c) and
benzothiazolyl groups (from 1a to 1d) also shifted the Ered
values in the positive direction, thus indicating that the re-
duction of 1b–d is easier than that of 1a. It should be noted
that the a-substituent effects on the reduction potentials
(DEred =0.07–0.58 V; 1b–d vs. 1a) are larger than those on
the oxidation potentials (DEox =0–0.08 V). This is reasona-
ble considering that the phosphole-based LUMO contrib-
utes significantly to the LUMO of the diarylacenaphtho[c]-
phosphole p-system.[8b] The LUMO levels of 1a–d and 7b,
as estimated from their reduction potentials[15] (2.98–
3.56 eV), are lower than those of P1 (2.71–2.72 eV),[3c] there-
by indicating that the electron affinity of 1a–d and 7b is
higher than that of P1. The electronic effects of the P=S
group on the redox potentials were found to be almost the
same as those of the P=O group (7b vs. 1b). Most impor-
tantly, the electrochemical reduction process occurred rever-
sibly for all the compounds examined; the repeated CV
scans for 1b and 1c (60 mVsÀ1 ꢀ50 times) did not show any
detectable degradation. These results imply that the present
diarylacenaphtho[c]phosphole derivatives are potential can-
didates for n-type semiconducting materials.[16] In fact,
a vacuum deposited film of the biphenyl derivative 1b
showed the modest electron mobility of 1ꢀ10À5 cm2 VÀ1 sÀ1
These data clearly show that the thermal stability of the ace-
naphtho[c]phosphole p-system can be tuned by changing the
a-aryl substituents. To utilize the acenaphtho[c]phosphole
derivatives as n-type semiconductors in organic electronics,
we finally evaluated photovoltaic performances of polymer-
based bulk heterojunction OPV devices incorporating 1a–
c or 7b as the cathode buffer layer. In the present study,
poly(3-hexylthiophene) (P3HT), indene-C70 bisadduct
(IC70BA),[18] and poly(3,4-ethylenedioxythiophene)-poly(-
styrenesulfonate) (PEDOT-PSS) were used as the photoac-
tive donor, acceptor, and anode buffer layer, respectively.
The LUMO level of IC70BA was reported to be 3.72 eV.[18a]
The fabrication of the present OPV devices is as follows:
a 1,2-dichlorobenzene solution containing P3HT and IC70BA
(a mixture of regioisomers, 1:0.95; 2.4 weight%) was spin-
coated onto a PEDOT:PSS-coated indium-tin oxide (ITO)
electrode to create an active layer with 200 nm thickness.
After pre-annealing for 10 min at 1508C under a nitrogen
atmosphere, a cathode buffer (6 nm) and aluminium metal
(80 nm) were vacuum deposited onto the surface. The
device was then post-annealed for 25 min at 808C. The pho-
tovoltaic characteristics of the resulting OPV devices
(4 mmꢀ4 mm) were determined under irradiation with
100 mWcmÀ2 incident light, using an AM 1.5G filter. The
photovoltaic characteristics of OPV devices are summarized
in Table 3, and the current–voltage curves of devices A–E
are depicted in Figure 4.
In our experiments, the OPV device without a cathode
buffer layer (device A) exhibited a PCE (h) of 0.9%. The
&
&
&4
&
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

a,a’-DiarylacenaphthoACTHNUTRGNE[UNG 1,2-c]phosphole P-Oxides
spectroscopy, CV/DPV, and thermal analyses) have revealed
that the aryl substituents on the phosphole ring have a signif-
icant impact on the optical and electrochemical properties
as well as thermal stability of the acenaphtho[c]phosphole
p-systems. In addition, we evaluated the photovoltaic per-
formances of the polymer-based (P3HT/IC70BA) bulk heter-
ojunction OPV devices that incorporate the acenaphtho[c]-
phosphole derivatives as the cathode buffer layer. The inser-
tion of the P-oxides was found to improve the power con-
version efficiencies up to 4.2%. We have assumed that the
intrinsically polarized PV =O functions not only enhance the
electron affinity of the adjacent p-systems but also have
good contact with the metal-electrode surface as the an-
chors. Although the device performances of the present
OPV are not as high as the reported OPV fabricated with
inorganic buffer materials, the packing motifs, electron affin-
ity, electron mobility, and thermal stability of the phosphole
derivatives are finely tunable by chemical functionalizations
at the phosphole-ring carbons and the phosphorus center. In
this regard, the present study corroborates that the arene-
fused phosphole derivatives will be further developed as n-
type semiconducting materials for use in organic electronics.
Figure 4. Current–voltage curves of devices A–E.
insertion of the phosphole 1a as the cathode buffer layer
(device B) dramatically improved the h value to 3.7% with
enhancement of all the parameters, open circuit voltage
(VOC), short circuit current (JSC), and fill factor (FF). When
the biphenyl derivative 1b was used in place of 1a, the VOC
value decreased from 0.82 V to 0.76 V.[19] On the contrary,
JSC and FF increased from 7.7 mAcmÀ2 and 0.58 to
8.8 mAcmÀ2 and 0.62, respectively. As a whole, the h value
increased from 3.7% (device B) to 4.2% (device C). While
the electron mobility of 1b is lower than that of 1a, the im-
provement in the device performance observed for 1b could
be attributable to the packing motifs and/or the reduced
contact resistance on the surfaces of the buffer layer.[20]
Device D fabricated with the bipyridyl derivative 1c showed
a slightly lower performance (h=3.5%) compared to device
B, owing to a slight decrease in FF (from 0.58 to 0.53). This
difference might also stem from the different packing motifs
of the acenaphtho[c]phosphole p-systems. The replacement
of 1b with 7b significantly decreased the h value from 4.2%
(device C) to 2.5% (device E) with a decrease in all three
parameters (see Table 3). This is in sharp contrast to the re-
sults reported by Tsuji et al. for the OPV devices fabricated
with P1 and P2, in which the h values were not significantly
affected by the P=E (E=O, S) functions.[3b] Although the
reason is not clearly understood, the efficiency of the pres-
ent polymer-based OPV devices is likely to rely on the
bonding nature of the anchoring P=E functions of the
phosphole buffer layer. The performance observed for
device C is appreciably higher than that observed for device
F fabricated with bathocuproine (BCP), which is widely
used as a standard n-type semiconductor. It is worth noting
that the Tg value of 1b (1368C) is considerably higher than
that of BCP (628C). In this context, the diarylacenaph-
tho[c]phosphole P-oxides are a new addition to cathode
buffer materials with high thermal stability.
Experimental Section
General
1H, 13C{1H}, and 31P{1H} NMR spectra were measured on a JEOL EX400
or AL300 spectrometer. Chemical shifts are reported in ppm as the rela-
tive values versus tetramethylsilane (1H, 13C) or H3PO4 (31P). High-reso-
lution mass spectra (HRMS) were obtained on a JEOL JMS-HS110 spec-
trometer. IR spectra were obtained on a JASCO FT/IR-470 Plus spec-
trometer. UV/Vis absorption and fluorescence spectra were obtained on
a PerkinElmer Lambda 900 UV/vis/NIR spectrometer and on a Horiba
FluoroMax-3 spectrometer, respectively. Fluorescence quantum yields
were determined by comparison with the reported value of Rꢄauꢂs 3,4-
C4-bridged 1-phenyl-2,5-bis(2-thienyl)phosphole (Ff =12.9%).[21] Electro-
chemical measurements were performed on a CH Instruments model
660 A electrochemical workstation using a glassy carbon working elec-
trode, a platinum wire counter electrode, and an Ag/Ag+ [0.01m AgNO3,
0.1m nBu4NPF6 (MeCN)] reference electrode. The potentials were cali-
brated with ferrocene/ferrocenium. Differential scanning calorimetry
(DSC) and thermogravimetric analysis (TGA) measurements were per-
formed on a SII EXSTAR DSC6200 calorimeter and a Shimadzu DTG-
60H calorimeter, respectively. The samples were heated at 108C minÀ1
.
Glass transition temperatures (Tg), crystalline temperatures (Tc), and
melting points (Tm) of 1a–c determined by DSC are listed in Figure S3 in
the Supporting Information. Diethyl ether was distilled from sodium ben-
zophenone ketyl before use. 1,8-Bis(trimethylsilylethynyl)naphthalene 2
was prepared according to the reported procedure starting from 1,8-diio-
donaphthalene.[22] Other chemicals and solvents were of reagent grade
quality and used without further purification unless otherwise noted.
Thin-layer chromatography was performed with Alt. 5554 DC-Alufolien
Kieselgel 60 F254 (Merck), and preparative column chromatography was
performed using UltraPure Silicagel (230–400 mesh; SiliCycle Inc) or
Silica Gel 60 (spherical, neutrality; Nacalai tesque). All the reactions
were performed under an argon atmosphere.
Conclusions
Synthesis of 5
The Stille coupling protocol has proven to be effective for
the divergent synthesis of a,a’-diarylacenaphtho[c]phosp-
hole P-oxides. The experimentally observed results (NMR
spectroscopy, X-ray crystallography, absorption/emission
To
a
mixture of 1,8-bis(trimethylsilylethynyl)naphthalene
2 (320 mg,
1.0 mmol), TiACHTUNGTRENNUNG
(OiPr)4 (0.29 mL, 1.0 mmol), and Et2O (7.5 mL), was added
an ethereal solution of iPrMgCl (2.0m, 1.0 mL, 2.0 mmol) at À708C, and
the resulting mixture was stirred for 2 h at À308C. The formation of 3
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
5
&
&
&
These are not the final page numbers! ÞÞ

Yoshihiro Matano et al.
FULL PAPER
was confirmed by acidolysis of the cyclic diene. Dichloro-
128.2, 128.4 (d, J
11.8 Hz), 129.8 (d, J
(P,C)=11.2 Hz), 131.6, 131.8, 132.2 (d, JACTHUNGTRENNUNG
N
ACHTUNGTRENNUNG(P,C)=
A
G
ACHTUNGTRENNUNG
tion of 3 at À308C, and the resulting suspension was stirred for 1 h at
08C and for an additional 68 h at room temperature. The reaction mix-
ture was concentrated under vacuum, and the residue was passed through
a short silica-gel column (CH2Cl2). To the eluent containing the crude
product was added m-chloroperbenzoic acid (mCPBA; 77% max,
132 mg). After stirring for 10 min at room temperature, the resulting mix-
ture was washed with a saturated NaHCO3 aqueous solution several
times. The organic layer was dried over Na2SO4 and the volatile materials
were evaporated under reduced pressure. The residue was subjected to
silica-gel column chromatography (CH2Cl2 then CH2Cl2/acetone=10:1).
A pale greenish yellow fraction was collected and evaporated to give an
J
G
d=54.7 ppm; IR (KBr): n˜max =1194 cmÀ1 (P=O); HRMS (EI): calcd for
C44H29OP: 604.1956; found: m/z=604.1957 [M+].
Compound 1c
1H NMR (CDCl3, 400 MHz): d=7.33 (ddt, 2H, J=1.0, 7.3, 7.3 Hz; bpy),
7.41–7.45 (m, 2H; PPh), 7.47–7.51 (m, 1H; PPh), 7.59 (pseudo t, 2H, J=
7.8 Hz; naphthalene), 7.75 (dt, 2H, J=2.0, 7.7 Hz; bpy), 7.87 (t, 2H, J=
7.8 Hz; bpy), 7.97 (d, 2H, J=7.8 Hz; naphthalene), 8.04 (d, 2H, J=
7.8 Hz; naphthalene), 8.03–8.08 (m, 2H; PPh), 8.25 (d, 2H, J=8.3 Hz;
bpy), 8.34 (d, 2H, J=7.8 Hz; bpy), 8.72 (pseudo d, 2H, J=4.4 Hz; bpy),
8.91 ppm (d, 2H, J=7.3 Hz; bpy); 13C NMR (CDCl3, 100 MHz): d=
oily residue, which contained
4 as a major product (confirmed by
1H NMR and MS). Crude product 4 was used for the following bromoly-
sis without further purification, as it was difficult to isolate in pure form.
N-Bromosuccinimide (NBS) (352 mg, 2.0 mmol) was added in one por-
tion to a solution of crude 4 (ca. 87 mg) in MeCN (8.0 mL), and the re-
sulting mixture was stirred at room temperature. After 2.5 h, water was
added, and the aqueous layer was separated and extracted with EtOAc.
The combined organic extracts were washed subsequently with a saturat-
ed Na2S2O3 aqueous solution and brine, dried over Na2SO4, and concen-
trated under reduced pressure to leave an oily residue, which was then
subjected to silica-gel column chromatography (CH2Cl2 then CH2Cl2/ace-
tone=40:1). The yellow fraction was collected, evaporated, and recrystal-
lized from n-hexane/CH2Cl2 to give 5 (72 mg, ca. 80% from 4) as
a yellow solid.
120.4, 121.6, 123.9, 124.1 (d, J
(P,C)=96.7 Hz), 128.9 (d, J(P,C)=12.3 Hz), 130.9 (d, J
131.0 (d, (P,C)=10.7 Hz), 131.5 (d, J=1.7 Hz), 131.9 (d,
3.3 Hz), 132.1 (d, J(P,C)=15.7 Hz), 136.7, 137.6, 145.0, 149.3, 150.4 (d, J-
(P,C)=26.4 Hz), 151.2, 151.3, 156.2 (d,
ACHTUNGTRENNUNG
J
N
U
ACHTUNGTRENNUNG
J
A
JACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
JACTHNGUTERNNUG
(P,C)=29.8 Hz); 31P NMR
(162 MHz, CDCl3): d=55.4 ppm; IR (KBr): n˜max =1192 cmÀ1 (P=O);
HRMS (EI): calcd. for C40H26N4OP: 609.1839; found: m/z=609.1826
[M+H+].
Compound 1d
1H NMR (CDCl3, 300 MHz): d=7.40–7.47 (m, 4H; PPh and benzothia-
zolyl), 7.53–7.60 (m, 3H; PPh and benzothiazolyl), 7.87 (dd, 2H, J=7.0,
8.1 Hz; naphthalene), 7.92 (d, 2H, J=8.1 Hz; benzothiazolyl), 8.04–8.10
(m, 2H; PPh), 8.11 (d, 2H, J=8.1 Hz; naphthalene), 8.24 (d, 2H, J=
8.1 Hz; benzothiazolyl), 9.64 ppm (d, 2H, J=7.0 Hz; naphthalene);
Compound 4
1H NMR (CDCl3, 400 MHz): d=0.29 (s, 18H; SiMe3), 7.36–7.40 (m, 2H;
PPh), 7.44–7.49 (m, 1H; PPh), 7.68 (dd, 2H, J=7.0, 8.4 Hz; naphtha-
lene), 7.77 (dd, 2H, J=7.8, 11.2 Hz; PPh), 7.86 (d, 2H, J=7.0 Hz; naph-
thalene), 7.91 ppm (d, 2H, J=8.4 Hz; naphthalene); HMRS (EI): calcd
for C26H29OSi2P: 444.1495; found: m/z=444.1493 [M+].
13C NMR (100 MHz, CDCl3): d=121.7, 122.6 (d,
123.4, 126.0, 126.8, 127.0, 127.9 (d, J(P,C)=97.4 Hz), 128.6, 129.1 (d, J-
(P,C)=12.4 Hz), 129.8, 130.9 (d, J(P,C)=14.3 Hz), 130.9 (d, J=1.9 Hz),
131.3 (d, J=11.2 Hz), 132.9 (d, J(P,C)=2.5 Hz), 136.0, 145.0, 151.5 (d, J-
(P,C)=23.6 Hz), 153.3 (d, (P,C)=1.2 Hz), 158.3 ppm (d, (P,C)=
JACTHUNGTERNNU(G P,C)=102.3 Hz),
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
J
A
JACHTUNGTRENNUNG
Compound 5
19.2 Hz); 31P NMR (162 MHz, CDCl3): d=53.1 ppm; IR (KBr): n˜max
1201 cmÀ1 (P=O); HRMS (EI): calcd. for C34H19N2OPS2: 566.0676,
found: m/z=566.0670 [M+].
M.p. 232–2338C; 1H NMR (CDCl3, 400 Hz): d=7.53 (ddd, 2H, J=3.4,
7.7, 7.7 Hz; PPh), 7.62–7.66 (m, 1H; PPh), 7.72 (dd, 2H, J=7.3, 8.3 Hz;
naphthalene), 7.87–7.92 (dd, 2H, J=7.0, 12.8 Hz; PPh), 7.98 (d, 2H, J=
8.3 Hz; naphthalene), 8.19 ppm (d, 2H, J=7.3 Hz; naphthalene);
Synthesis of 7b
13C{1H} NMR (CDCl3, 100 MHz): d=106.1 (d, J
124.8 (d, (P,C)=106.6 Hz), 128.3, 128.6, 129.2 (d,
130.9, 131.0, 131.5 (d, J(P,C)=10.7 Hz), 133.5 (d, J(P,C)=2.5 Hz), 144.2,
150.9 ppm (d, JACHTUNGTRENNUNG
(P,C)=27.1 Hz); 31P{1H} NMR (CDCl3, 162 MHz): d=
ACHTUNGTRENNUNG
To a solution of 1b (120 mg, 0.20 mmol) in toluene (30 mL) was added
Lawessonꢂs reagent (46.7 mg, 0.12 mmol) at room temperature, and the
resulting solution was stirred for 2.5 h at 1108C. The mixture was then
concentrated under reduced pressure, and the residue was subjected to
silica-gel column chromatography (toluene). The yellow fraction was col-
lected, evaporated, and recrystallized from n-hexane/CH2Cl2 to give 7b
(106 mg, 86%) as a yellow solid. 1H NMR (CDCl3, 400 MHz): d=7.36
(pseudo t, 2H, J=7.3 Hz; biphenyl), 7.45 (pseudo t, 4H, J=7.6 Hz; bi-
phenyl), 7.41–7.52 (m, 3H, PPh), 7.55 (dd, 2H, J=6.8, 8.3 Hz; naphtha-
lene), 7.62 (dd, 4H, J=1.5, 7.3 Hz; biphenyl), 7.63 (d, 4H, J=7.8 Hz; bi-
phenyl), 7.77 (d, 4H, J=7.8 Hz; biphenyl), 7.88 (d, 2H, J=8.3 Hz; naph-
thalene), 7.92 (d, 2H, J=6.8 Hz; naphthalene), 8.00–8.08 ppm (m, 2H;
PPh); 13C NMR (100 MHz, CDCl2CDCl2): d=121.1, 126.9, 127.2, 127.6,
(d, J=8.3 Hz), 128.2, 128.2 (d, J=71.1 Hz), 128.9, 128.9 (d, J=13.3 Hz),
129.0, 130.7 (d, J=78.6 Hz), 130.8 (d, J=11.6 Hz), 131.1, 131.2, 131.6 (d,
J=1.7 Hz), 131.8, 132.2 (d, J=2.4 Hz), 139.9, 141.1 (d, J=1.6 Hz), 144.4,
147.9 ppm (d, J=25.6 Hz); 31P NMR (162 MHz, CDCl3): d=72.4 ppm;
HRMS (EI): calcd. for C44H29PS: 620.1728, found: m/z=620.1729 [M+];
elemental analysis calcd. for C44H29PS: C, 85.14; H, 4.71; found: C, 85.01;
H, 4.76.
J
N
JACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
42.5 ppm; IR (KBr): n˜max =1213 cmÀ1 (P=O); HRMS (EI): calcd for
C20H11Br2OP: 455.8914; found: m/z=455.8911 [M+].
Synthesis of 1b–d
A mixture of 5 (72.1 mg, 0.16 mmol), 6c (308 mg, ca. 50 mol% purity),
[PdACHTUNGTRENNUNG(PPh3)4] (39.8 mg, 0.034 mmol), and toluene (8.0 mL) was stirred at
1108C. After 44.5 h, water was added, and insoluble substances were fil-
tered off through a Celite pad. The separated aqueous phase was extract-
ed with EtOAc, and the combined organic extracts were washed with
brine, dried over Na2SO4, and concentrated under reduced pressure to
afford an oily residue, which was then subjected to silica-gel column
chromatography (CH2Cl2 then CH2Cl2/acetone/MeOH=50:10:1). The
orange fraction was collected, evaporated, and recrystallized from
CH2Cl2/n-hexane to give 1c (42.3 mg, 44%) as an orange solid. Following
similar procedures, 1b and 1d were obtained by the Stille reactions of 5
with 6b and 6d, respectively.
Compound 1b
X-ray Crystallographic Analyses
1H NMR (CDCl3, 300 MHz): d=7.33–7.48 (m, 5H; PPh and biphenyl),
7.45 (t, 4H, J=7.0 Hz; biphenyl), 7.57 (dd, 2H, J=7.3, 8.1 Hz; naphtha-
lene), 7.63 (d, 4H, J=7.0 Hz; biphenyl), 7.65 (d, 4H, J=8.1 Hz; biphen-
yl), 7.84 (d, 4H, J=7.7 Hz; biphenyl), 7.89 (d, 2H, J=8.1 Hz; naphtha-
lene), 7.89–7.95 (m, 2H; PPh), 8.06 (d, 2H, J=7.3 Hz; naphthalene);
13C{1H} NMR (CDCl2CDCl2, 75 MHz): d=121.2, 126.9, 127.4, 127.7,
Single crystals of 1b and 1c were grown from CH2Cl2/n-hexane at room
temperature. X-ray crystallographic measurements were collected on
a Rigaku Saturn CCD area detector with graphite monochromated MoKa
radiation (0.71070 ꢃ) at À1308C. The data were corrected for Lorentz
and polarization effects. The structures were solved by using a direct
method[23] and refined by full-matrix least-squares techniques against F2
&
&
&6
&
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

a,a’-DiarylacenaphthoACTHNUTRGNE[UNG 1,2-c]phosphole P-Oxides
using SHELXL-97.[24] The non-hydrogen atoms were refined anisotropi-
cally, and hydrogen atoms were refined using the rigid model. All calcu-
lations were performed using CrystalStructure crystallographic software
package[25] except for the refinement.
2005; b) H. Spangaard, F. Krebs, Sol. Energy Mater. Sol. Cells 2004,
83, 125; c) S. Gꢅnes, H. Neugebauer, N. S. Sariciftci, Chem. Rev.
2007, 107, 1324; d) Organic Photovoltaics: Materials, Device Physics,
and Manufacturing Technologies (Eds.: C. Brabec, V. Dyakonov, U.
Scherf), Wiley-VCH, Weinheim, 2008; e) B. Kippelen, J.-L. Brꢄdas,
Energy Environ. Sci. 2009, 2, 251.
CCDC 881989 (1b) and 881988 (1c) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
[2] For recent reviews and accounts on the p-conjugated phosphole ma-
terials, see: a) M. Hissler, P. W. Dyer, R. Rꢄau, Coord. Chem. Rev.
2003, 244, 1; b) F. Mathey, Angew. Chem. 2003, 115, 1616; Angew.
Chem. Int. Ed. 2003, 42, 1578; c) T. Baumgartner, R. Rꢄau, Chem.
Rev. 2006, 106, 4681 (Correction: T. Baumgartner, R. Rꢄau, Chem.
Rev. 2007, 107, 303); d) P. W. Dyer, R. Rꢄau in Functional Organic
Materials (Eds.: T. J. J. Mꢅller, U. H. F. Bunz), Wiley-VCH, Wein-
heim, 2007, pp. 119–177; e) M. Hissler, C. Lescop, R. Rꢄau, C. R.
Chim. 2008, 11, 628–640; f) M. G. Hobbs, T. Baumgartner, Eur. J.
Inorg. Chem. 2007, 3611; g) Y. Matano, H. Imahori, Org. Biomol.
Chem. 2009, 7, 1258; h) Y. Ren, T. Baumgartner, Dalton Trans. 2012,
41, 7792.
Crystal data for 1b
3
¯
C44H29OP; MW=604.64, 0.50ꢀ0.15ꢀ0.08 mm , triclinic, space group P1,
a=10.8122(3), b=11.7692(2), c=14.2380(2) ꢃ, a=80.026(10), b=
68.396(8), g=66.412(7)8, V=1543.06(13) ꢃ3, Z=2, 1calcd =1.301 gcmÀ3
,
m=1.25 cmÀ1, 23972 collected reflections, 7028 independent reflections,
415 parameters, Rw =0.0948, R=0.0374 (I>2s(I)), GOF=1.042.
Crystal data for 1c
C40H25N4OP; MW=608.61, 0.20ꢀ0.10ꢀ0.06 mm3, triclinic, space group
[3] a) H. Tsuji, K. Sato, L. Ilies, Y. Itoh, Y. Sato, E. Nakamura, Org.
Lett. 2008, 10, 2263; b) H. Tsuji, K. Sato, Y. Sato, E. Nakamura,
Chem. Asian J. 2010, 5, 1294; c) H. Tsuji, K. Sato, Y. Sato, E. Naka-
mura, J. Mater. Chem. 2009, 19, 3364.
¯
P1, a=11.515(6), b=12.294(7), c=12.865(6) ꢃ, a=112.079(2), b=
97.303(5), g=111.748(5)8, V=1490.6(13) ꢃ3, Z=2, 1calcd =1.356 gcmÀ3
,
m=1.34 cmÀ1, 11587 collected reflections, 6486 independent reflections,
416 parameters, Rw =0.1174, R=0.0497 (I>2s(I)), GOF=1.050.
[4] A. Fukazawa, Y. Ichihashi, Y. Kosaka, S. Yamaguchi, Chem. Asian J.
2009, 4, 1729.
Time-of-flight measurement for 1b
[5] a) K. Geramita, J. McBee, T. D. Tilley, J. Org. Chem. 2009, 74, 820;
b) K. Geramita, Y. Tao, R. A. Segalman, T. D. Tilley, J. Org. Chem.
2010, 75, 1871.
[6] a) Y. Ren, Y. Dienes, S. Hettel, M. Parvez, B. Hoge, T. Baumgartner,
Organometallics 2009, 28, 734; b) S. Durben, T. Baumgartner,
Angew. Chem. 2011, 123, 8096; Angew. Chem. Int. Ed. 2011, 50,
7948; c) S. Durben, T. Baumgartner, Inorg. Chem. 2011, 50, 6823.
The well-dried sample was deposited onto the surface of indium-tin-
oxide (ITO) by sublimation in vacuo (0.7 nmsÀ1; >2.6ꢀ10À3 Pa; ULVAC
VPC-260F). The device was once exposed to the atmosphere, and the
aluminium electrode was made by vapor deposition (0.7 nmsÀ1; >2.6ꢀ
10À3 Pa; ULVAC VPC-410). The thickness of the organic layer was
1 mm, which was determined by a stylus surface profiler (dektak150).
Time-of-flight measurements on electron mobility were carried out at
room temperature on a measuring system comprised of a Tektronix
TDS2022 oscilloscope, a TEXIO PA120-0.6B power supply, and a Spec-
traPhysics VSL-337ND-S laser (lex =337 nm). Figure S2 in the Support-
ing Information depicts the field-dependency of the logarithmic electron
mobility of 1b.
˝
[7] P.-A. Bouit, A. Escande, R. Szucs, D. Szieberth, C. Lescop, L.
Nyulꢆszi, M. Hissler, R. Rꢄau, J. Am. Chem. Soc. 2012, 134, 6524.
[8] a) Y. Matano, T. Miyajima, T. Fukushima, H. Kaji, Y. Kimura, H.
Imahori, Chem. Eur. J. 2008, 14, 8102; b) A. Saito, T. Miyajima, M.
Nakashima, T. Fukushima, H. Kaji, Y. Matano, H. Imahori, Chem.
Eur. J. 2009, 15, 10000; c) Y. Matano, A. Saito, T. Fukushima, Y. To-
kudome, F. Suzuki, D. Sakamaki, H. Kaji, A. Ito, K. Tanaka, H. Im-
ahori, Angew. Chem. 2011, 123, 8166; Angew. Chem. Int. Ed. 2011,
50, 4615.
[9] In the OPV devices reported by Tsuji et al., tetrabenzoporphyrin
(BP) and bis(triorganosilymethyl)[60]fullerene (SIMEF) were used
as photoactive donor and acceptors, respectively. See ref. [3b].
[10] For patents, see: a) E. Nakamura, Y. Sato, H. Tsuji, K. Sato, JST,
JPA2010-182959, 2010; b) E. Nakamura, Y. Sato, H. Tsuji, K. Sato,
JST, JPA2010-129919, 2010; c) N. Yasukawa, Y. Ohkubo, T. Hattori,
Konica Minolta, JPA2011-49204, 2011; d) N. Yasukawa, Y. Ohkubo,
A. Wachi, Konica Minolta, JPA2012-89725, 2012.
[11] a) A. Saito, Y. Matano, H. Imahori, Org. Lett. 2010, 12, 2675; b) Y.
Matano, A. Saito, M. Fujita, H. Imahori, Heteroat. Chem. 2011, 22,
457; c) Y. Matano, Y. Kon, A. Saito, Y. Kimura, T. Murafuji, H. Ima-
hori, Chem. Lett. 2011, 40, 919.
[12] F. Sato, H. Urabe, S. Okamoto, Chem. Rev. 2000, 100, 2835.
[13] The acidolysis of 3 with an aqueous HCl solution produced a cis/
trans mixture of the protonated cyclic diene in good (>80%) NMR
yield.
Fabrication of OPV devices
The OPV devices were fabricated in an argon-purged glove box accord-
ing to the following procedure. On a clean glass substrate pre-coated
with an ITO layer with a sheet resistance of 8.4 WsqÀ1, PEDOT:PSS with
a
sheet resistance of 100000 WsqÀ1 (H.C.Starck, CLEVIOS
P VP
AI4083) was spin coated as a buffer layer (60 nm thickness). On the PE-
DOT:PSS layer, a 1,2-dichlorobenzene (Aldrich) solution containing re-
gioregular P3HT (Aldrich) and IC70BA (Frontier Carbon, a mixture of
diastereomers; 1:0.95; 2.4 weight%) was spin coated to make an active
layer with a thickness of 200 nm. After pre-annealing for 10 min at
1508C under a nitrogen atmosphere, the phosphole derivative 1 was de-
posited on the top of the active layer under vacuum (1.4ꢀ10À4 Pa) to fur-
nish the cathode buffer layer (6 nm). Subsequently, aluminum metal was
vacuum deposited, with 80 nm thickness, as an electrode. The device was
then post-annealed for 25 min at 808C. The photovoltaic characteristics
of the resulting OPV devices (4 mmꢀ4 mm) were determined by a solar
simulator under irradiation with 100 mWcmÀ2 incident light, using an
AM 1.5G filter. The J–V measurements of the devices were conducted
on a Keithley 2400 Source Measure Unit. Device F was fabricated with
BCP (TCI) as the cathode buffer layer without post-annealing.
[14] Compound 1a was prepared from 1,8-bis(phenylethynyl)naphtha-
lene by using a titanacycle method as described in ref. [8b].
[15] Electron affinity (EA) was estimated according to the following
equation: EA=4.80+Ered, in which Ered refers to the half-wave po-
tential (vs. Fc/Fc+) of the first reduction process observed by CV:
EA=2.98 eV for 1a, 3.05 eV for 1b, 3.19 eV for 1c, and 3.01 eV for
7b.
Acknowledgements
This work was supported by a Grant-in-Aid (No. 22350016) from MEXT,
Japan.
[16] The highest electron mobility of 1a was 8ꢀ10À5 cm2 VÀ1 sÀ1 at 1.0ꢀ
106 VcmÀ1. See ref. [8b].
[17] The 5% weight loss temperatures (Td5) of 1a, 1b, 1c, and 1d were
determined to be 355, 415, 410, and 3108C, respectively, by thermog-
ravimetric (TGA) analyses.
[1] For example, see: a) Organic Photovoltaics: Mechanism, Materials,
and Devices (Eds.: S.-S. Sun, N. S. Sariciftci), CRC, Boca Raton,
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
7
&
&
&
These are not the final page numbers! ÞÞ

Yoshihiro Matano et al.
FULL PAPER
[18] a) Y. He, G. Zhao, B. Peng, Y. Li, Adv. Funct. Mater. 2010, 20, 3383;
b) X. Fan, C. Cui, G. Fang, J. Wang, S. Li, F. Cheng, H. Long, Y. Li,
Adv. Funct. Mater. 2012, 22, 585. In ref. [18b], the h value of the two
types of devices ITO/PEDOT:PSS/P3HT:IC70BA/Ca/Al and ITO/
post-annealing (at 1208C) owing to its morphological instability. See
ref. [3b].
[21] C. Fave, T.-Y. Cho, M. Hissler, C.-W. Chen, T.-Y. Luh, C.-C. Wu, R.
Rꢄau, J. Am. Chem. Soc. 2003, 125, 9254.
MoO3/P3HT:IC70BA/Ca/Al were reported to be 6.20% (VOC
0.84 V, JSC =10.23 mAcmÀ2, FF=0.721) and 6.68% (VOC =0.85 V,
SC =10.61 mAcmÀ2, FF=0.741), respectively.
=
[22] H.-J. Knçlker, A. Braier, D. J. Brçcher, P. G. Jones, H. Piotrowski,
Tetrahedron Lett. 1999, 40, 8075.
[23] SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27, 435.
[24] SHELXL-97, G. M. Sheldrick, University of Gçttingen, Germany,
1997.
[25] CrystalStructure 3.8: Crystal Structure Analysis Package, Rigaku
and Rigaku Americas (2000–2007). 9009 New Trails Dr. The Wood-
lands TX 77381 USA.
J
[19] As the VOC values do not simply correlate with the reduction poten-
tials of 1a–c and 7b, the work function on the electrode surface may
also be affected by the steric factors (bulkiness, orientation, and pla-
narity) of the a substituents. This implies that the work function on
the metal surface may be tunable by changing the a substituents of
the phosphole ring.
[20] Tsuji, Nakamura, and co-workers reported that the performance of
the BCP-based OPV device (BP/SIMEF) dropped significantly after
Received: June 2, 2012
Published online: && &&, 0000
&
&
&8
&
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!

FULL PAPER
A convenient approach to a,a’-diaryla-
cenaphtho[c]phosphole P-oxides
through a Stille coupling of the a,a’-
dibromo synthon has been developed.
The effects of the a-aryl substituent on
the structural, optical, and electro-
chemical properties have been
Organic Photovoltaics
Yoshihiro Matano,* Arihiro Saito,
Yuto Suzuki, Tooru Miyajima,
Seiji Akiyama, Saika Otsubo,
Emi Nakamoto, Shinji Aramaki,
Hiroshi Imahori
&&&& — &&&&
revealed. The diarylacenaphtho[c]-
phosphole P-oxides were found to
behave as promising cathode buffer
materials in bulk heterojunction
organic photovoltaics.
a,a’-DiarylacenaphthoACTHNUGTRNEUNG[1,2-c]phosphole
P-Oxides: Divergent Synthesis and
Application to Cathode Buffer Layers
in Organic Photovoltaics
Chem. Asian J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
9
&
&
&
These are not the final page numbers! ÞÞ