Synthesis, properties, and structures of functionalized peri -xanthenoxanthene

Article abstract of DOI:10.1021/ol400790d

Three types of alkylated peri-xanthenoxanthene (PXX) have been synthesized employing efficient synthetic routes. These heteroaromatic compounds exhibited different electronic and crystal structures according to UV-vis spectra, electrochemical measurements, and X-ray structural analyses. Among them, 1,7-DOPXX has been demonstrated as an active material for organic field-effect transistors with promising mobility and a high on/off ratio simultaneously.

Full text of DOI:10.1021/ol400790d

ORGANIC
LETTERS
2013
Vol. 15, No. 10
2382–2385
Synthesis, Properties, and Structures of
Functionalized peri-Xanthenoxanthene
Na Lv,†,‡,§ Meilan Xie,† Weibing Gu,† Huanyang Ruan,† Song Qiu,*,†
Chunshan Zhou,† and Zheng Cui†
Printable Electronics Research Centre, Suzhou Institute of Nano-Tech and
Nano-Bionics, CAS, Suzhou, 215123, China, Technical Institute of Physical and
Chemistry, CAS, Beijing, 100190, China, and University of Chinese Academy of
Sciences, CAS, Beijing, 100049, China
sqiu2010@sinano.ac.cn
Received March 25, 2013
ABSTRACT
Three types of alkylated peri-xanthenoxanthene (PXX) have been synthesized employing efficient synthetic routes. These heteroaromatic
compounds exhibited different electronic and crystal structures according to UVꢀvis spectra, electrochemical measurements, and X-ray
structural analyses. Among them, 1,7-DOPXX has been demonstrated as an active material for organic field-effect transistors with promising
mobility and a high on/off ratio simultaneously.
The design and synthesis of polycyclic aromatic com-
pounds are of great interest owing to their potential
applications as organic semiconductors for electronic de-
vices, such as organic field-effect transistors (OFETs),1
light emitting diodes (LEDs),2 and photovoltaic cells.3 In
particular, heteroaromatic containing chalcogenophenes
(thiophene or selenophene) in fused aromatic ring systems
has been actively investigated because of their remarkable
electronic properties for OFETs.4 However, most of hetero-
aromatic compounds containing chalcogen are pentacyclic
instead of hexacyclic. From the synthetic chemistry view-
point, efficient synthetic strategies for conjugated hexa-
cyclic heteroaromatic compounds containing chalcogen
are limited.
peri-Xanthenoxanthene (PXX), which is a less reported
conjugated hexacyclic aromatic compound containing
chalcogen, has been employed as pigments5 and as the
species of charge transfer complexes.6 Recently, PXX and
its derivatives have been investigated by Merck and Sony
as organic semiconductors due to their excellent carrier
transport capacity and good environmental stability.7
To synthesize PXX, Tamotsu et al. used Cu(OAc)2 to
oxidize the alkaline solution of 1,10-bi-2-naphthol,8 and
† Printable Electronics Research Centre, Suzhou Institute of Nano-Tech
and Nano-Bionics, Chinese Academy of Sciences.
‡ Technical Institute of Physical and Chemistry, Chinese Academy of
Sciences.
§ University of Chinese Academy of Sciences.
(1) (a) Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Chem. Rev.
ꢀ
2012, 112, 2208–67. (b) Beaujuge, P. M.; Frechet, J. M. J. J. Am. Chem.
Soc. 2011, 133, 20009–20029. (c) Takimiya, K.; Shinamura, S.; Osaka, I.;
Miyazaki, E. Adv. Mater. 2011, 23, 4347–4370. (d) Dong, H.; Wang, C.;
Hu, W. Chem. Commun. (Camb) 2010, 46, 5211–22.
(2) (a) Tao, Y.; Yang, C.; Qin, J. Chem. Soc. Rev. 2011, 40, 2943–
2970. (b) Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kong, S.; Gong, Q.; Kido, J.
Adv. Mater. 2011, 23, 926–952.
(3) Liu, J.; Walker, B.; Tamayo, A.; Zhang, Y.; Nguyen, T.-Q. Adv.
Funct. Mater. 2013, 23, 47–56.
(4) (a) Yamamoto, T.; Nishimura, T.; Mori, T.; Miyazaki, E.; Osaka,
I.; Takimiya, K. Org. Lett. 2012, 14, 4914–4917. (b) Takimiya, K.;
Shinamura, S.; Osaka, I.; Miyazaki, E. Heterocycles 2011, 83, 1187–
1204. (c) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.;
(5) Prowse, W. G.; Arnot, K. I.; Recka, J. A.; Thomson, R. H.;
Maxwell, J. R. Tetrahedron 1991, 47, 1095–1108.
(6) Asari, T.; Kobayashi, N.; Naito, T.; Inabe, T. Bull. Chem. Soc.
Jpn. 2001, 74, 53–58.
€
Baumgarten, M.; Pisula, W.; Mullen, K. Adv. Mater. 2009, 21, 213–216.
(d) Nakano, M.; Mori, H.; Shinamura, S.; Takimiya, K. Chem. Mater.
2011, 24, 190–198.
(7) Kobayashi, N.; Sasaki, M.; Nomoto, K. Chem. Mater. 2009, 21,
552–556.
r
10.1021/ol400790d
Published on Web 05/09/2013
2013 American Chemical Society

Scheme 1. Synthetic Route to 2,8-Substituted PXX (M1) and 1,7-Substituted PXX (M2)
Philipp et al. used transition metal oxide (MnO2, CuO, etc.)
to oxidize 1,10-bi-2-naphthol at elevated temperatures.9
However, the isolated raw product had to undergo repeti-
tive sublimation to obtain pure PXX. The subsequent
functionalization was centered on the para-position of
oxygen atoms to give 3,9-substituted PXX, since it is the
most active site. However, due to the poor solubility of
PXX and Br-PXX, further modification is difficult and
may introduce impurity.
Here we report a simple and efficient method to synthe-
size substituted PXXs. To overcome the purification
difficulty, the precursor was functionalized before ring
closure. 1,10-Bi-2-naphthol (1) was prepared by a two-
phase oxidative coupling of 2-naphthol suspended in
aqueous Fe3þ solution.10 With direct bromation followed
by a hydroxy-protection reaction with sodium hydride and
chloromethyl methyl ether to obtain 6,60-dibromo-2,20-
bis(methoxymethoxy)-1,10-binaphthyl (3), we can realize
the functionalization at the 6,60-position through existing
coupling methods (i.e., Kumada, Suzuki, Stille coupling,
etc.). The importance of alkyl substituents has been
studied thoroughly, as it can improve solubility and impact
the packing of molecules through noncovalent-induced
ordering.11 The same principle was applied to alkyl-
substituted PXX, i.e. R = n-C8H17. The subsequent
deprotection with conc. HCl and microwave assisted
cyclization reaction in the presence of Cu(OAc)2 in O-di-
chlorobenzene at 220 °C yielded desirable 2,8-dioctyl-peri-
xanthenoxanthene (M1, 2,8-DOPXX).
Similarly, starting from 7-bromo-2-naphthol and using the
same synthetic procedure as mentioned above, we obtained
1,7-dioctyl-peri-xanthenoxanthene (M2, 1,7-DOPXX) in a
yield of 56.4% (Scheme 1).
When the hydroxy groups of 1,10-bi-2-naphthol were
protected first, selective bromation at the ortho-position
of the hydroxy group could be achieved via lithiation of
2,20-bis(methoxymethoxy)-1,10-binaphthyl (7) followed by
trapping with dibromotetrachloroethane, and then the
functionalization of (7) at the 3,30-position could be rea-
lized through many common coupling methods. However,
when it comes to alkylation, using bromoalkane with
the assistance of butyllithium to yield 3,30-dioctyl-2,20-
bis(methoxymethoxy)-1,10-binaphthyl (9) provedtobemore
simple and direct compared to Kumada coupling. The
subsequent deprotection and cyclization reaction yielded
5,11-dioctyl-peri-xanthenoxanthene (M3, 5,11-DOPXX)
(Scheme 2).
The intermediates and products were characterized by
1H NMR, 13C NMR, and mass spectrometry; the X-ray
crystal structures for three alkylated PXXs were also obtained.
To the best of our knowledge, crystal structures of substituted
PXXs at these positions have never been reported previously.
Figure 1 shows the UVꢀvis absorption spectra and
mirror-plane symmetrical emission spectra of the three
compounds. All of them show well-resolved vibrational
energy bands, which can be interpreted as a consequence
of a highly rigid, planar π-system in these PXX derivates.
Energy gaps estimated from absorption edges are 2.69,
2.68, and 2.72 eV for M1, M2, and M3, respectively.
Examination of Figure 1 reveals that the absorption
spectra of M3 are blue-shifted compared with M1 and
M2. We assume that the alkyl position may influence the
delocalization of electrons on the fused aromatic ring.12
(8) Asari, T.; Kobayashi, N.; Naito, T.; Inabe, T. Bulletin of the
Chemical Society of Japan 2001, 74, 53–58.
(9) Stoessel, P.; Buesing, A.; Heil, H. U.S. Patent No. US 2010/
0013381 A1.
(10) Ding, K.; Yang, W.; Zhang, L.; Yangjie, W.; Matsuura, T.
Tetrahedron 1996, 52, 1005–1010.
ꢀ
(11) Curiel, D.; Mas-Montora, M.; Uruvakili, A.; Orenes, R. A.;
(12) Wang, L.; Duan, G.; Ji, Y.; Zhang, H. J. Phys. Chem. C 2012,
116, 22679–22686.
Pallamreddy, H.; Molina, P. Org. Lett. 2010, 12, 3164–3167.
Org. Lett., Vol. 15, No. 10, 2013
2383

Scheme 2. Synthetic Route to 5,11-Substituted PXX (M3)
Single crystals of M1ꢀM3 were grown by slow diffusion
of ethanol into their tetrahydrofuran solution. Figure S2
shows the bond lengths of the three compounds from
X-ray analyses. The decreased bond equalization in M3,
i.e. the bond length of CdC bond adjacent to the C;O
˚
˚
bond, is equal to 1.379 A for M1 and 1.382 A for M2, while
˚
it is much shorter (1.361 A) in M3, revealing that the PXX
unit is less delocalized in M3 than in M1 and M2, which
may explain the blue shift of M3 in the UVꢀvis absorption
and fluorescence spectra.
The crystal packing of three compounds are compared
in Figure 2 (alkyl is omitted for clarity). M1 and M3 both
display a herringbone packing motif with the π-stacking
of the molecules extending along the b-axis. M1 adopts a
sandwiched herringbone structure in which the interplanar
Figure 1. (a) Normalized absorption and (b) emission spectra of
M1ꢀM3.
˚
packing distance is 3.40 A, and the shortest intermolecular
distance (CꢀH...C between two neighboring cores) is
Electrochemical characterization was carried out by cyclic
voltammetry in dichloromethane solution (Figure S1). All
compounds exhibit two reversible or quasi-reversible one-
electron oxidation peaks within the span of the electrolyte
window, which demonstrate the good electrical stability
of the PXX’s radical cation. The HOMO energy level
estimated from the oxidation onset are ca. ꢀ5.06, ꢀ4.92,
and ꢀ5.02 eV for M1, M2, and M3, respectively, matching
well with the work function of gold. The optical and
electrochemical characterization are summarized in Table 1.
Table 1. Optical, Electrochemical Characterization and OFET
Properties of M1ꢀM3
opt
Eg
(eV)a
EHOMO
(eV)b
ELUMO
(eV)c
μ
compd
(cm2/V s)d
Ion/Ioff
3
M1
M2
M3
2.69
2.68
2.72
ꢀ5.01
ꢀ4.92
ꢀ5.02
ꢀ2.32
ꢀ2.24
ꢀ2.30
0.04
0.5
2.6 ꢁ 107
3.9 ꢁ 106
1 ꢁ 105
Figure 2. Crystal structures of M1 (a), M2 (b), and M3 (c).
0.32
a Recorded in dichloromethane (10ꢀ5 M) at room temperature and
estimated from the absorption edge of the solution. b Electrochemically
determined vs Fc/Fcþ in CH2Cl2 (10ꢀ3 M) at room temperature,
˚
2.54 A. However, M3 packs in the conventional herring-
TBAPF6 (0.1 M), scan speed 0.1 V/s, SCE reference electrode, Pt
working electrode and calculated according to EHOMO = ꢀ(Eox
d Estimated from the saturation regime.
bone motif in which its dimers are packed in an end-to-face
manner with the interplanar packing distance similar to
˚
that of M1 (3.35 A), but the shortest intermolecular
1/2
þ
4.80). c Values calculated according to ELUMO = Eg
þ EHOMO
.
opt
˚
distance is longer (2.79 A). In contrast, M2 adopts a fairly
2384
Org. Lett., Vol. 15, No. 10, 2013

spin coating a 3 mg/mL solution of DOPXX in chloroben-
zene, and the subsequent chloroform vapor annealing13
would facilitate the formation of large area crystals.
The XRD patterns of thin films are shown in Figure S4.
The high crystallinity of M3 may contribute to the higher
mobility compared with M1; in fact, M1 tends to form
dendritic and discontinuous crystals other than large plate-
like crystals using the spin coating method. The prelimin-
ary results show the mobilities for M1, M2, and M3 to
be 0.04ꢀ0.5 cm2 V ꢀ1
s
ꢀ1 in the saturation regime with an
3
3
on/off ratio of 105ꢀ 107 (Figure 3, Figure S5). Further
experiments to optimize device fabrication, particularly
molecular arrangement in the thin-film state, are under-
way, and results will be reported in due course.
In summary, we have developed a simple and efficient
synthetic route for the preparation of peri-xanthenox-
anthene (PXX) derivatives with an alkyl in different
substituent positions. This synthetic approach offers the
opportunity to prepare a new class of functionalized
conjugated heteroaromatic compounds containing chalco-
gen, which show promising hole-transporting ability
and good stability. Furthermore, the different substitution
positions can influence the solid state packing mode of the
molecule to a large extent and has a strong influence on the
charge transporting property.
Figure 3. FET characteristics of M2: (a) transfer plots and (b)
output plots. (For M1 and M3, see Supporting Information.)
flat molecular structure without disturbance of the alkyl,
which leads to a one-dimensional slipped face-to-face
arrangement with a large slippage of molecules. The
˚
molecular stacking distance along the b-axis is only 2.83 A.
Meanwhile alkyl chains can interact with the aromatic
˚
system through CꢀH...π contact (2.34 A) and further
stabilize the packing, which is favorable for charge carrier
transport.
The thermal stability of the three compounds was eval-
uated by thermogravimetric analysis (TGA) (Figure S3).
The data reveal that they all have good thermal stability
with none of them showing significant mass loss up to
312, 296, and 285 °C for M1, M2, and M3 respectively
(corresponding to a 2% loss of weight).
Transistors with bottom contact and bottom gate geo-
metry were fabricated to investigate the charge transport
properties of the synthesized PXX derivatives. The gold
sourceꢀdrain electrodes were prepared by photolithogra-
phy and were treated with pentafluorothiophenol before
Acknowledgment. This work was supported by Natural
Science Foundation of China (91123034, 21104091),
the Knowledge Innovation Programme of the Chinese
Academy of Sciences (KJCX2-EW-M02).
Supporting Information Available. Synthetic details,
characterizations data, TGA, electrochemical studies,
OTFTs performance, and crystallographic information
files (CIF) for 2,8-DOPXX (M1), 1,7-DOPXX (M2), and
5,11-DOPXX (M3). This material is available free of
charge via the Internet at http://pubs.acs.org.
(13) Liu, C.; Li, Y.; Xu, Y.; Minari, T.; Li, S.; Takimiya, K.;
Tsukagoshi, K. Org. Electron. 2012, 13, 2975–2984.
The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 10, 2013
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