9,10-Dichlorooctafluoroanthracene as a building block for n-type organic semiconductors

Article abstract of DOI:10.1021/jo070404a

(Chemical Equation Presented) 9,10-Dichlorooctafluoroanthracene (1) was synthesized from commercially available tetrafluorophthalic acid by an optimized solution-phase route. To establish 1 as a synthon for n-type organic semiconductors, the compound was reacted with phenylboronic acid under modified Suzuki-Miyaura coupling conditions to generate octafluoro-9,10- diphenylanthracene (7) in high yield. Cyclic voltammetry and X-ray crystallography indicate that 7 has a stabilized LUMO energy level and exhibits extended π stacking, which should lead to efficient electron transport in solid-state devices. 1,2,3,4,5,6,7,8-Octafluoroanthracene (2) was also synthesized as a potential n-type building block, but suitable C-C coupling conditions for this compound were not found, and 2 could not be converted into 9,10-dibromooctafluoroanthracene or octafluoro-9,10-diiodoanthracene.

Full text of DOI:10.1021/jo070404a

9,10-Dichlorooctafluoroanthracene as a Building Block for n-Type
Organic Semiconductors
John F. Tannaci, Masahiro Noji,† Jennifer McBee, and T. Don Tilley*
Department of Chemistry, UniVersity of California at Berkeley, Berkeley, California 94720
tdtilley@berkeley.edu
ReceiVed February 27, 2007
9,10-Dichlorooctafluoroanthracene (1) was synthesized from commercially available tetrafluorophthalic
acid by an optimized solution-phase route. To establish 1 as a synthon for n-type organic semiconductors,
the compound was reacted with phenylboronic acid under modified Suzuki-Miyaura coupling conditions
to generate octafluoro-9,10-diphenylanthracene (7) in high yield. Cyclic voltammetry and X-ray
crystallography indicate that 7 has a stabilized LUMO energy level and exhibits extended π stacking,
which should lead to efficient electron transport in solid-state devices. 1,2,3,4,5,6,7,8-Octafluoroanthracene
(2) was also synthesized as a potential n-type building block, but suitable C-C coupling conditions for
this compound were not found, and 2 could not be converted into 9,10-dibromooctafluoroanthracene or
octafluoro-9,10-diiodoanthracene.
Introduction
lowers LUMO energy levels, increases stability for devices
operating under ambient conditions,7 and can lead to donor-
acceptor interactions that direct extensive π stacking in the solid
state.9 Marks et al. have inserted perfluorophenyl groups into
oligothiophenes to obtain vapor-deposited OFETs with high
electron mobilities (up to 0.43 cm2 V-1 s-1, Ion/Ioff > 108).8
Extended perfluoroacenes are a potentially useful class of
efficient electron-transport materials. These compounds retain
many of the attractive physical properties of the parent
hydrocarbons due to the small size difference between fluorine
and hydrogen. For example, pentacene is one of the most
effective p-type organic semiconductors,10 and Suzuki et al. have
reported the related isostructural perfluoropentacene.11 Fluorine
substitution dramatically lowers the LUMO energy level to
-3.65 eV (relative to vacuum) and thereby enables fabrication
of n-type OFETs. The thin-film d-spacing of perfluoropentacene
remains similar to that of pentacene (15.8 and 15.4 Å,
respectively), which apparently results in good electrical contacts
when both materials are layered to form bipolar OFETs.
Organic semiconductors are an active area of research driven
by potential applications that include light-emitting diodes,1
photovoltaics,2 and field-effect transistors (OFETs).3 Many con-
jugated organic systems have inherently low electron affinities
and therefore behave as p-type semiconductors and as hole-
transport materials.4 Improved electron-transport (n-type) ma-
terials are generally needed to develop more efficient devices
and to enable other cost-effective applications such as comple-
mentary circuits.5
Electron-deficient heterocycles have been investigated as
n-type materials,6 and related π systems that feature fluorine
substituents have also been examined.7,8 Fluorine substitution
† Current address: Meiji Pharmaceutical University, 2-522-1, Noshio, Kiyose,
Tokyo 204-8588, Japan.
(1) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990, 347,
539.
(2) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
1995, 270, 1789.
(3) Sun, Y.; Liu, Y.; Zhu, D. J. Mater. Chem. 2005, 15, 53.
(4) Strukelj, M.; Papadimitrakopoulos, F.; Miller, T. M.; Rothberg, L.
J. Science 1995, 267, 1969.
(5) Crone, B.; Dodabalapur, A.; Lin, Y.-Y.; Filas, R. W.; Bao, Z.;
LaDuca, A.; Sarpeshkar, R.; Katz, H. E.; Li, W. Nature 2000, 403, 521.
(6) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem.
Mater. 2004, 16, 4556.
(8) Yoon, M.-H.; Facchetti, A.; Stern, C. E.; Marks, T. J. J. Am. Chem.
Soc. 2006, 128, 5792.
(9) Reichenba¨cher, K.; Su¨ss, H. I.; Hulliger, J. Chem. Soc. ReV. 2005,
34, 22.
(10) Klauk, H.; Halik, M.; Zschieschang, U.; Schmid, G.; Radlik, W. J.
Appl. Phys. 2002, 92, 5259.
(7) Katz, H. E.; Johnson, J.; Lovinger, A. J.; Li, W. J. Am. Chem. Soc.
2000, 122, 7787.
(11) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue,
Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc. 2004, 126, 8138.
10.1021/jo070404a CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/23/2007
J. Org. Chem. 2007, 72, 5567-5573
5567

Tannaci et al.
SCHEME 1. Synthesis of
SCHEME 2. Synthesis of
1,2,3,4,5,6,7,8-Octafluoroanthracene
9,10-Dichlorooctafluoroanthracenea
proceeded smoothly at 170 °C to generate 9,9,10,10-tetrachlo-
rooctafluoro-9,10-dihydroanthracene (5) in 83% yield.19 The
final aromatization was induced by heating 5 to 115 °C in the
presence of acetic acid.
a Key: (a) SOCl2, 90 °C, 14 h, 97%; (b) CsF, sulfolane/m-xylene (3:5),
160 °C, 30 min, 59%; (c) PCl5, phenylphosphonic dichloride, 170 °C, 24
h, 83%; (d) glacial AcOH, NMP, 115 °C, 24 h, 85%.
Synthesis of 1,2,3,4,5,6,7,8-Octafluoroanthracene (2). The
synthesis of 2 from 4 was accomplished in two steps as shown
in Scheme 2. Zinc dust in boiling acetic acid was used as the
reducing agent,20 and 1,2,3,4,5,6,7,8-octafluoro-9,10-dihydro-
anthracene (6) was collected after ether extraction. This crude
product was stirred under air with activated carbon21 in refluxing
toluene for 4 days to give 2 in 82% overall yield from 4. No
reaction occurred in the absence of activated carbon, and using
a pure oxygen atmosphere led to overoxidation. Also, standard
dehydrogenation reagents such as chloranil and DDQ were
ineffective at aromatizing 6 to 2.
Synthesis of Octafluoro-9,10-diphenylanthracene (7). Phen-
ylboronic acid was chosen as the initial coupling partner to
investigate 1 as a building block for n-type materials. Although
the aryl chloride is activated by electron-withdrawing groups,
standard Suzuki-Miyaura reaction conditions22 led to minimal
coupling. Improved reactivity was observed using bulky,
electron-rich tri-tert-butylphosphine as a ligand,23 but coupling
was slow and incomplete. The best results were obtained with
tris(dibenzylideneacetone)dipalladium(0) in the presence of
commercially available phosphine 8,24 which efficiently cata-
lyzed the coupling of 1 with phenylboronic acid (2.6 equiv)
(Scheme 3). The reaction was found to be quantitative by 19F
NMR spectroscopy, and workup followed by recrystallization
gave an 82% yield of 7.
Besides nucleophilic aromatic substitution12,13 few methods
exist for adding conjugated units to perfluoropentacene and
shorter, related homologues like perfluoroanthracene. Replacing
some of the fluorine atoms in perfluoroanthracene with func-
tional handles for C-C coupling should provide ideal building
blocks for novel n-type materials. To that end, this paper
describes the synthesis and preliminary C-C coupling chemistry
of 1,2,3,4,5,6,7,8-octafluoroanthracene derivatives 1 and 2. The
fluorinated compounds are fully characterized, and their elec-
tronic properties are probed by UV-vis/fluorescence spectros-
copy and cyclic voltammetry. The solid-state structures have
also been investigated.
Results and Discussion
Synthesis of 9,10-Dichlorooctafluoroanthracene (1). Com-
pound 1 was synthesized in four steps from tetrafluorophthalic
acid as shown in Scheme 1. The commercially available starting
material was reacted with thionyl chloride at 90 °C for 14 h to
give tetrafluorophthalic anhydride (3) in 97% yield.14,15 Sub-
sequent formation of 1,2,3,4,5,6,7,8-octafluoroanthraquinone
(4)16-18 was achieved by fluoride-promoted decarboxylation and
dimerization of 3. Chlorination of 4 with a combination of
phosphorus pentachloride and phenylphosphonic dichloride
Optimization of 1,2,3,4,5,6,7,8-Octafluoroanthraquinone
Synthesis. Compound 4 is typically produced in one step from
tetrachlorophthalic anhydride and excess potassium fluoride.16-18
At high temperatures (g300 °C) halide substitution occurs in
combination with the fluoride-promoted decarboxylation and
dimerization. Such harsh conditions are not ideal for lab-scale
synthesis, so modifications were made to enable a solution-
phase reaction at lower temperature. Halide substitution was
circumvented by using 3 instead of tetrachlorophthalic anhy-
(12) Geramita, K.; McBee, J.; Shen, Y.; Radu, N.; Tilley, T. D. Chem.
Mater. 2006, 18, 3261.
(13) Nitschke, J.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 10183.
(14) Gething, B.; Patrick, C. R.; Tatlow, J. C. J. Chem. Soc. 1960,
1574.
(15) Okumara, Y.; Ito, H.; Kaieda, O. Preparation of Fluorine-Containing
Phthalic Anhydride Derivatives. Jpn. Kokai Tokkyo Koho JP 06016656,
1994.
(19) Takebe, Y.; Murobuse, H.; Okazoe, T.; Kashiwagi, T.; Tamura, M.
Preparation of 9,9,10,10-Tetrachloro-9,10-dihydroanthracenes. Jpn. Kokai
Tokkyo Koho JP 11012203, 1999.
(20) Lu, L.; Chen, Q.; Zhu, X.; Chen, C. Synthesis 2003, 16, 2464.
(21) Nakamichi, N.; Kawabata, H.; Hayashi, M. J. Org. Chem. 2003,
68, 8272.
(16) Yakobson, G. G.; Odinokov, V. N.; Vorozhtsov, N. N., Jr.
Tetrahedron Lett. 1965, 49, 4473.
(17) Burdon, J.; Childs, A. C.; Parsons, I. W.; Tatlow, J. C. J. Chem.
Soc., Chem. Commun. 1982, 534.
(18) Kaieda, O.; Hirota, K.; Itoh, H.; Awashima, M.; Nakamura, T.
Fluorinated Quinones. Eur. Pat. Appl. EP 170190, 1986.
(22) Miyaura, N. In Metal-Catalyzed Cross-Coupling Reactions; de
Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004; Vol. 1, pp
41-123.
(23) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176.
(24) Billingsley, K. L.; Anderson, K. W.; Buchwald, S. L. Angew. Chem.,
Int. Ed. 2006, 45, 3484.
5568 J. Org. Chem., Vol. 72, No. 15, 2007

n-Type Organic Semiconductors
formed. Attempts to boost activity by using Rieke zinc29 (runs
3-6) were promising, but the reactions required freshly prepared
metal reagents and gave variable results. Zinc dust in 1-methyl-
2-pyrrolidinone/acetic acid (NMP/AcOH, 3:1) at 110 °C was
overly reducing, as it afforded 6 as the sole product in 92%
isolated yield (run 7). Fortunately, acetic acid in NMP at
elevated temperatures (run 8) was sufficient to cleanly aromatize
5 to 1.
SCHEME 3. Coupling Conditions for
9,10-Dichlorooctafluoroanthracene
Attempted Reactions of 1,2,3,4,5,6,7,8-Octafluoroan-
thracene. Recently, Fagnou et al. reported efficient coupling
between aryl halides and fluorinated aromatics using palladium
acetate, S-Phos,30 and potassium carbonate in isopropyl acetate.31
For example, mesityl bromide was reacted with pentafluoroben-
zene to give 2,3,4,5,6-pentafluoro-2′,4′,6′-trimethylbiphenyl in
98% yield. Unfortunately, these conditions were ineffective in
coupling bromobenzene with 2.
Halogenation of 2 was also attempted under a wide variety
of conditions, but neither 9,10-dibromooctafluoroanthracene nor
octafluoro-9,10-diiodoanthracene was observed. Direct haloge-
nation using several brominating or iodinating agents gave no
reaction, and deprotonation/halogenation routes using alkyl-
lithium reagents led to multiple side products. Piers et al.
encountered similar problems while trying to brominate fluori-
nated binaphthyl derivatives.32 These issues were overcome by
using LTMP as a base at low temperature in the presence of
tributyltin chloride (Bu3SnCl) as a quenching electrophile. The
resulting aryltin species was subsequently converted to the
desired compound. However, exposing 2 to LTMP/Bu3SnCl at
-78 °C returned the starting material, and allowing the reaction
to warm to higher temperatures gave an uncharacterized mixture
of products.
Electronic Properties. To investigate the electronic properties
of the octafluoroanthracene derivatives, compounds 1, 2, and 7
were characterized by UV-vis/fluorescence spectroscopy and
cyclic voltammetry. The parent hydrocarbons (anthracene,
9,10-dichloroanthracene, and 9,10-diphenylanthracene) were
studied under the same conditions to allow proper comparisons
between fluorinated and non-fluorinated analogues.
Solution-phase optical data is collected in Table 3, and
representative UV-vis/fluorescence spectra of 7 are shown in
Figure 1. All six compounds exhibit coupling in the absorbance
spectra due to CdC vibrational modes,33 but the fluorinated
materials have broader peaks that obscure some of the fine
vibronic structure. Fluorine substitution on the anthracene core
does not dramatically affect the optical HOMO-LUMO energy
gap leading to a small bathochromic shift in the onset of
absorbance (e0.14 eV). With regard to fluorescence, only
anthracene and 9,10-dichloroanthracene show sharp vibronic
coupling, with absorbance and emission spectra that display
distinct mirror symmetry. The fluorinated compounds exhibit
broad peaks in the fluorescence spectra as well as Stokes shifts
that are approximately 10 nm larger than those of the non-
fluorinated analogues.
TABLE 1. Optimization of 1,2,3,4,5,6,7,8-Octafluoroanthraquinone
Synthesisa
run
time (h)
solvent
yieldb (%)
1
2
3
4
2
3
4
0.5
DMF/m-xylene
NMP/m-xylene
DMSO/m-xylene
sulfolane/m-xylene
40
48
3
59
a CsF, 3, 160 °C. b Yield of 4 after sublimation and recrystallization.
dride, and cesium fluoride was used to improve fluoride
solubility and activity.
Preliminary attempts to synthesize 4 in m-xylene at 160 °C
gave dilactone 9 as the major product. Dilactone 9 has pre-
viously been postulated as an intermediate in this type of
reaction,16 and here full characterization, including structure
confirmation by X-ray crystallography,25 is reported. Decar-
boxylation of 9 was favored by increasing the polarity of the
solvent system (DMF/m-xylene, 3:5), giving 4 in 40% yield
after sublimation and recrystallization. Analysis of the sublima-
tion residue revealed substantial formation of lactone 10, which
may have been produced by trimerization of 3 followed by
rearrangement,26 although a more likely pathway is reaction of
4 with additional starting material.27
Substituting other polar solvents for DMF can significantly
affect the yield of 4, so optimization studies were performed as
shown in Table 1. Interestingly, DMSO (run 3) drastically
lowered the isolated yield of 4. Use of sulfolane/m-xylene as a
solvent system (run 4) led to a shortened reaction time and
maximum yield (59%) of the desired compound.
Optimization of 9,10-Dichlorooctafluoroanthracene Syn-
thesis. Aromatization of 5 to 1 (Table 2) based on reported
conditions28 (runs 1 and 2) was not selective, and mixtures in-
cluding unreacted starting material (5), the desired product (1),
9-chloro-1,2,3,4,5,6,7,8-octafluoroanthracene (11), and 2 were
(28) Takebe, Y.; Murofushi, H.; Okazoe, T.; Kashiwagi, K.; Tamura,
M. Preparation of 9,10-Dihaloanthracenes. Jpn. Kokai Tokkyo Koho JP
11012204, 1999.
(29) Wu, X.; Rieke, R. D. J. Org. Chem. 1995, 60, 6658.
(30) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J.
Am. Chem. Soc. 2005, 127, 4685.
(31) Lafrance, M.; Shore, D.; Fagnou, K. Org. Lett. 2006, 8, 5097.
(32) Morrison, D. J.; Riegel, S. D.; Piers, W. E.; Parvez, M.; Mcdonald,
R. Chem. Commun. 2006, 2875.
(33) Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic
Molecules; Academic Press Inc.: New York, 1965.
(25) See Supporting Information for crystallographic data.
(26) Yamato, T.; Sakaue, N. J. Chem. Res. Synop. 1997, 440.
(27) Carissimo-Rietsch, F.; Schmitz, C.; Aubry, J.-M. Tetrahedron Lett.
1991, 32, 3845.
J. Org. Chem, Vol. 72, No. 15, 2007 5569

Tannaci et al.
TABLE 2. Optimization of 9,10-Dichlorooctafluoroanthracene Formationa
reaction conditions
19F NMR molar ratiob
run
Zn source
solvent
temp (°C)
additive
DBEc
5
1
11
2
6
1
2
3
4
5
6
7
8
Zn
DMF
MeOH
THF
MeOH
NMP
DMF
NMP
NMP
25
25
25
25
25
25
110
115
89
14
6
11
20
Zn/ZnCl2
Rieke Zn
Rieke Zn
Rieke Zn
Rieke Zn
Zn
57
8
14
9
86 (74)
7
100 (91)
12
55
24
6
49
33
AcOH
AcOH
100 (92)
100 (85)
a From 5. b Isolated yields in parentheses. c 1,2-Dibromoethane.
TABLE 3. Optical Data for Anthracene Derivativesa,b
electrode), except for 9,10-diphenylanthracene and the chlori-
nated anthracene derivatives. An irreversible second oxidation
peak is seen for 9,10-diphenylanthracene at +1.45 V, which is
consistent with published values.35 As expected, extra reduction
peaks are observed for the chlorinated substrates because
chloride loss from the radical anion forms a neutral radical that
undergoes further reactions.36 Compared to the parent hydro-
carbons, HOMO energy levels are stabilized in the fluorinated
materials by 0.28-0.52 eV. More importantly, the fluorinated
anthracenes have substantially lowered LUMO energy levels,
with stabilizations ranging from 0.51 to 0.61 eV. Fluorine
substitution on the anthracene core stabilizes LUMO energy
levels more than HOMO energy levels, causing a small
contraction of the electrochemical HOMO-LUMO energy gap,
abs
em
op
λmax
λmax
Eg
compound
(nm)
(nm)
(eV)
anthracenec
357
380
373
359
394
377
402
431
408
412
458
441
3.24
2.99
3.05
3.17
2.85
3.00
9,10-dichloroanthracenec
9,10-diphenylanthracenec
2
1
7
op
a In THF. b Eg calculated from the onset of absorbance. c Consistent
with published values (see ref 33).
op
which corroborates the Eg data. Also listed in Table 4 are
effective n-type materials and their LUMO energy levels,7,11,37
to which the fluorinated anthracene derivatives, especially 1,
compare favorably. This electronic information indicates that
9,10-dichlorooctafluoroanthracene should be an ideal building
block for extended structures with n-type behavior.
Solid-State Structure. X-ray diffraction studies were per-
formed on crystals of 1 and 7 to determine the effect of fluorine
substitution on the solid-state structure. Yellow needles of 1
were grown by vacuum sublimation at 275 °C, and some
important packing features are shown in Figure 3. The parent
hydrocarbon, 9,10-dichloroanthracene, has two polymorphs, with
the â form (grown by sublimation) being the appropriate
comparison.39 This polymorph of the non-fluorinated analogue
shows slipped π stacking with an average distance between
planes of 3.5 Å and no C-C short contacts. A tilt angle of 43°
exists between the anthracene planes of neighboring π stacks,
and the chlorine atoms are coplanar with the rest of the molecule.
In contrast, 1 demonstrates π stacking with a shorter vertical
distance (3.27 Å between planes) but larger lateral slipping,
giving a C-C short contact of 3.39 Å. The edge-on C-F
interactions (at 3.00 and 3.03 Å) induce a much larger tilt angle
of 81° between the anthracene planes of adjacent π stacks in 1,
and the chlorine atoms bend 4° out of plane on opposite faces
of the ring system.
FIGURE 1. Normalized absorbance (dashed line) and emission (solid
line) spectra of 7 in THF.
To examine electronic interactions in the solid state, UV-
vis measurements were also conducted on thin films of 1 and
7.34 Films were drop cast from dichloromethane (1 mg/mL, glass
substrate) and were found to be of low quality by optical
microscopy. Repeated attempts to improve film quality through
spin casting, thermal annealing, or solvent-vapor annealing were
unsuccessful. Relative to solution-phase absorbance, both
compounds display thin-film bathochromic shifts of 10 nm as
well as low-energy shoulders. These features indicate increased
electronic delocalization even in low-quality films, presumably
through intermolecular π-π interactions.
More notably, fluorine substitution on the 9,10-diphenyl-
anthracene framework considerably improves π stacking. For
Cyclic voltammetry confirmed the Egop values and established
the extent to which fluorine substitution lowers the LUMO
energy levels of the parent hydrocarbons. Electrochemical
properties are listed in Table 4, and a representative cyclic
voltammogram of 7 is shown in Figure 2. Each compound
exhibits one oxidation peak and one reduction peak within the
potential window studied (-2.6 to +2 V, Ag/AgNO3 reference
(35) Perichon, J. In Encyclopedia of Electrochemistry of the Elements;
Bard, A., Lund, H., Eds.; Marcel Dekker: New York, 1978; Vol. XI, pp
71-161.
(36) Andrieux, C. P.; Blocman, C.; Dumas-Bouchiat, J.-M.; Saveant, J.
M. J. Am. Chem. Soc. 1979, 101, 3431.
(37) Xie, Q.; Pe´rez-Cordero, E.; Echegoyen, L. J. Am. Chem. Soc. 1992,
114, 3978.
(38) Matsumoto, T.; Sato, M.; Hirayama, S. Chem. Lett. 1972, 603.
(39) Burshtein, Z.; Hanson, A. W.; Ingold, C. F.; Williams, D. F. J. Phys.
Chem. Solids 1978, 39, 1125.
(34) See Supporting Information for thin-film UV-vis spectra of 1 and
7.
5570 J. Org. Chem., Vol. 72, No. 15, 2007

n-Type Organic Semiconductors
TABLE 4. Electrochemical Propertiesa
compound
Eoxb (V)
Eredb (V)
HOMOc (eV)
LUMOc (eV)
Egel (eV)
anthracened
+0.99
-2.40
-5.55
-5.75
-5.51
-6.07
-6.03
-5.93
-2.43
-2.85
-2.53
-3.03
-3.46
-3.04
-3.65
-3.91
-4.00
3.12
2.90
2.98
3.04
2.57
2.89
9,10-dichloroanthracened
+1.17
-1.97, -2.19e, -2.40e
-2.29
9,10-diphenylanthracened
2
+0.94, +1.45f
+1.53
+1.45
+1.39
-1.77
1
7
-1.49, -1.67e, -1.81e
-1.77
perfluoropentaceneg
h
C60
C8F15-NTCDIi
b
a Acetonitrile, (Bu)4NPF6 electrolyte, Ag/AgNO3 reference, 200 mV/s scan rate. Eox and Ered calculated from the potential at peak current (anodic and
cathodic sweeps, respectively). c HOMO and LUMO energy levels (relative to vacuum) calculated from the onset of oxidation and reduction, respectively.
d Consistent with published values (see refs 35 and 38). e Further reductions following decomposition of the radical anion. f Second oxidation. g LUMO
energy level estimated from ref 11. h LUMO energy level estimated from ref 37. i LUMO energy level estimated from ref 7.
FIGURE 4. View down the c-axis in crystals of 7, phenyl groups
removed for clarity and all values in angstroms.
FIGURE 2. Cyclic voltammogram of 7.
FIGURE 5. View down the a-axis in crystals of 7, hydrogen atoms
removed for clarity.
Conclusion
Compound 1 has been shown to be a viable building block
for potential n-type organic semiconductors. Other boronic
acids are currently being explored as coupling partners along
with aryltin reagents (Stille coupling41) and terminal alkynes
(Sonogashira coupling42). Expanding the coupling chemistry of
1 should lead to effective electron-transport materials through
FIGURE 3. Crystal packing in 1, all values in angstroms.
fine control of electronic properties and solid-state structure.
example, 9,10-diphenylanthracene packs in a herringbone pattern
Experimental Section43
(66° tilt angle) along the axis of the phenyl substituents.40 The
edge-on C-H interactions dominate the intermolecular forces
(no π stacking), and the phenyl groups are twisted 68° relative
to the anthracene plane. Conversely, 7 π stacks in a “bricklayer”
structure (C-C short contacts of 3.38 and 3.39 Å as shown in
Figure 4) with a slight tilt of 6° between alternating rows of
molecules. A view down the a-axis (Figure 5) clearly illustrates
the perpendicular nature of the phenyl substituents (89°) as well
as the 19° tilt between anthracene planes on neighboring π
stacks. Such extensive π stacking of perfluorinated aromatic
rings should lead to efficient electron transport in well-ordered
thin films.
Tetrafluorophthalic Anhydride (3). A 500 mL three-necked
flask equipped with a reflux condenser and an addition funnel was
charged with tetrafluorophthalic acid (129.01 g, 0.54 mol). Thionyl
chloride (168 mL, 2.30 mol) was added dropwise over 15 min at
60 °C. The subsequent white suspension was heated at 90 °C for
14 h to afford a light-brown solution. The excess thionyl chloride
was removed under vacuum (20 Torr) at 60 °C, and the resulting
(41) Mitchell, T. N. In Metal-Catalyzed Cross-Coupling Reactions; de
Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004; Vol. 1, pp
125-161.
(42) Marsden, J. A.; Haley, M. M. In Metal-Catalyzed Cross-Coupling
Reactions; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim,
2004; Vol. 1, pp 317-394.
(40) Adams, J. M.; Ramdas, S. Acta. Crystallogr., Sect. B 1979, 35, 679.
(43) See Supporting Information for general experimental details.
J. Org. Chem, Vol. 72, No. 15, 2007 5571

Tannaci et al.
ivory solid was dried under high vacuum. Sublimation (100 °C,
0.2 Torr) gave a colorless crystalline solid (115.36 g, 97%): mp
93-94 °C (lit.14 94-95.5 °C).
and brine (150 mL). Concentration of the organic layer afforded a
brown oil that was precipitated from methanol (200 mL). The crude
solid was then dissolved in chloroform and was passed through a
plug of silica gel (hexanes eluant) to give 6.12 g (85%) of bright
yellow powder: mp 172-173 °C (patent lit. 172 °C28). Single
crystals for X-ray diffraction were obtained by sublimation (275
°C) under static vacuum (0.02 Torr). 19F NMR: δ -137.09 (d, J
) 12 Hz, 4F), -152.35 (d, J ) 12 Hz, 4F). GC-MS (EI) m/z:
390 (M+). Anal. Calcd for C14Cl2F8: C, 43.00; H, 0.00. Found:
C, 43.02; H, <0.2.
Dilactone 9. A 500 mL flask equipped with a reflux condenser
was charged with 3 (10.00 g, 45.44 mmol) and m-xylene (50 mL).
The solution was heated to 160 °C, anhydrous cesium fluoride
(10.00 g, 65.83 mmol) was added, and the suspension was stirred
for 24 h. Another portion of cesium fluoride (10.00 g, 65.83 mmol)
was added, and the reaction was stirred for a further 24 h. The
organic products were extracted into hot toluene (150 mL) and were
washed with water (150 mL). Concentration of the toluene layer
afforded an ivory solid that was purified by sublimation (120 °C,
0.005 Torr). Recrystallization from ethanol gave 3.60 g (40%) of
colorless needles: mp 176-177 °C (lit.16 177-178 °C). Single
crystals for X-ray diffraction were obtained by slow evaporation
of a chloroform-d/dichloromethane solution. 19F NMR: δ -133.82
(m, 2 F), -139.28 (m, 2F), -141.39 (m, 2F), -144.37 (m, 2F).
GC-MS (EI) m/z: 396 (M+). Anal. Calcd for C15F8O4: C, 45.48;
H, 0.00. Found: C, 45.12; H, <0.2.
1,2,3,4,5,6,7,8-Octafluoroanthraquinone (4). A 500 mL flask
equipped with a reflux condenser was charged with 3 (5.00 g,
22.72 mmol) and m-xylene (50 mL). The solution was heated to
°160 C, and anhydrous cesium fluoride (5.00 g, 32.92 mmol) was
added. The resulting suspension was stirred for 30 min fol-
lowed by dropwise addition (over 5 min) of preheated (60 °C)
sulfolane (30 mL). When gas generation ceased (30 min) the red-
brown mixture was cooled to 120 °C and m-xylene was re-
moved under vacuum (20 Torr). Subsequent vacuum removal of
sulfolane (160 °C, 0.5 Torr) left a dark-brown residue that was
suspended in water/methanol (4:1, 50 mL) and was stirred at
ambient temperature for 1 h. A light-brown solid was collected by
filtration. The product was washed successively with water and
water/methanol (1:1) and was dried under vacuum at 50 °C. The
solid contained a 1:0.22 molar ratio of 4 and 10. Sublimation (220
°C, 0.005 Torr) over 14 h gave 2.52 g of a light-yellow solid that
contained 4 and a trace amount of 10, while the sublimation residue
mainly contained 10. The crude 4 was recrystallized from benzene
to afford 2.34 g (59%) of pale yellow needles: mp (DSC) 346-
347 °C (lit.16 342-343 °C). 19F NMR: δ -137.39 (m, 4F), -143.34
(m, 4F).
Lactone 10. The combined sublimation residues from several
optimization reactions were purified by column chromatography
(silica gel, cyclohexane/THF ) 20:1 to 5:1). Recrystallization from
toluene gave colorless fine needles: mp 294-296 °C. 19F NMR:
δ -135.96 (m, 1 F), -136.85 (m, 2F), -138.31 (m, 2F), -140.76
(m, 1F), -143.31 (m, 2F), -144.17 (m, 1F), -146.95 (m, 1F),
-148.60 (m, 2F). MS (EI) m/z: 528 (M+). Anal. Calcd for
C21F12O3: C, 47.75; H, 0.00. Found: C, 47.98; H, <0.2.
9,9,10,10-Tetrachlorooctafluoro-9,10-dihydroanthracene (5).
A 100 mL flask was charged with 4 (8.29 g, 23.54 mmol) and
phosphorus pentachloride (17.60 g, 84.52 mmol). Phenylphosphonic
dichloride (32 mL, 0.23 mol) was added, and the reaction was
initially heated to 130 °C for 2 h followed by stirring at 170 °C for
24 h. The resulting orange solution was diluted with toluene (200
mL) and was washed successively with water (2 × 200 mL), aq
NaHCO3 (saturated, 2 × 100 mL), and brine (100 mL). The organic
layer was then concentrated in vacuo to a yellow oil. Methanol
(200 mL) was added and the precipitate was collected by vacuum
filtration to give 9.00 g (83%) of white powder: mp 239-240 °C
(patent lit. 243 °C19). 19F NMR: δ -128.61 (m, 4F), -150.11 (m,
4F). MS (EI) m/z: 460 (M+). Anal. Calcd for C14Cl4F8: C, 36.40;
H, 0.00. Found: C, 36.27; H, <0.2.
9-Chloro-1,2,3,4,5,6,7,8-octafluoroanthracene (11). The com-
bined mixtures from several aromatization reactions were purified
by column chromatography (silica gel, hexanes). Recrystallization
from ethanol gave yellow needles that were contaminated with 4
1
mol % of 2. H NMR: δ 8.80 (s, 1 H). 19F NMR: δ -139.95
(m, 2F), -148.51 (m, 2F), -153.52 (m, 2F), -155.31 (m, 2F).
GC-MS (EI) m/z: 356 (M+). Anal. Calcd for C14HClF8 + 4 mol
% of C14H2F8: C, 47.34; H, 0.29. Found: C, 47.37; H, 0.10.
1,2,3,4,5,6,7,8-Octafluoro-9,10-dihydroanthracene (6). A 50
mL flask equipped with a reflux condenser was charged in air with
5 (0.54 g, 1.17 mmol), zinc dust (1.00 g, 15.29 mmol), NMP (9
mL), and glacial AcOH (3 mL). The suspension was stirred under
nitrogen at 110 °C for 16 h followed by cooling to ambient
temperature. The organic products were extracted with ether (25
mL) and were washed with water (2 × 25 mL), aq NaHCO3
(saturated, 2 × 25 mL), and brine (25 mL). Concentration of the
organic layer gave a tan solid that was rinsed with methanol (3 ×
10 mL) to afford 0.35 g (92%) of white powder: mp 145-147 °C.
1H NMR: δ 4.00 (s, 4H). 19F NMR: δ -144.64 (m, 4F), -159.65
(m, 4F). MS (EI) m/z: 324 (M+). Anal. Calcd for C14H4F8: C, 51.87;
H, 1.24. Found: C, 51.54; H, 1.15.
1,2,3,4,5,6,7,8-Octafluoroanthracene (2). A 250 mL flask
equipped with reflux condenser was charged in air with 4 (1.00 g,
2.84 mmol), zinc dust (4.00 g, 61.17 mmol), and glacial AcOH
(50 mL). The reaction mixture was stirred under nitrogen at 120
°C for 4 days followed by cooling to ambient temperature. The
organic products were extracted with ether (50 mL) and were
washed with water (2 × 50 mL), aq NaHCO3 (saturated, 2 × 50
mL), and brine (50 mL). Concentration of the organic layer left
crude 6, which was added to a 250 mL flask containing activated
carbon (1.00 g) and toluene (50 mL). The suspension was stirred
under reflux for 4 days in air and was then filtered to afford a faint
yellow solution. The removal of solvent in vacuo and subsequent
recrystallization from ethanol gave 0.75 g (82%) of colorless
needles: mp 175 °C. 1H NMR: δ 8.86 (s, 2H). 19F NMR: δ
-150.14 (d, J ) 15 Hz, 4F), -156.65 (d, J ) 15 Hz, 4F). GC-
MS (EI) m/z: 322 (M+). Anal. Calcd for C14H2F8: C, 52.20; H,
0.63. Found: C, 52.27; H, 0.45.
1,2,3,4,5,6,7,8-Octafluoro-9,10-diphenylanthracene (7). Phos-
phine 8 (0.03 g, 0.06 mmol), tris(dibenzylideneacetone)dipalladium-
(0) (0.01 g, 0.01 mmol), sodium carbonate (0.21 g, 2.00 mmol),
phenylboronic acid (0.24 g, 2.00 mmol), and 1 (0.30 g, 0.77 mmol)
were loaded into a 25 mL flask in a glovebox. A degassed mixture
of toluene (3 mL), THF (3 mL), and water (1 mL) was transferred
via cannula onto the solids, and the resulting solution was stirred
under reflux at 95 °C for 15 h. The organic products were extracted
with dichloromethane (25 mL) and were washed with aq NaHCO3
(saturated, 3 × 25 mL). The organic layer was passed through a
plug of silica gel (hexanes eluant) and was then concentrated to
afford a pale yellow solid. Slow cooling of a toluene solution gave
1
0.30 g (82%) of yellow crystals: mp (DSC) 328 °C. H NMR: δ
7.46-7.55 (m, 6H), 7.38-7.42 (m, 4H). 19F NMR: δ -134.94 (d,
J ) 13 Hz, 4F), -156.08 (d, J ) 13 Hz, 4F). GC-MS (EI) m/z:
474 (M+). Anal. Calcd for C26H10F8: C, 65.83; H, 2.12. Found:
C, 66.06; H, 2.10.
9,10-Dichlorooctafluoroanthracene (1). A 500 mL flask equipped
with a reflux condenser was charged in air with 5 (8.50 g, 18.40
mmol), NMP (150 mL), and glacial AcOH (50 mL). The solution
was stirred under nitrogen at 115 °C for 24 h, and the resulting
dark-brown mixture was cooled to ambient temperature. The organic
products were extracted with chloroform (150 mL) and were washed
with water (2 × 150 mL), aq NaHCO3 (saturated, 2 × 150 mL),
Acknowledgment. This work was supported by the National
Science Foundation research grant CHE0314709. The authors
5572 J. Org. Chem., Vol. 72, No. 15, 2007

n-Type Organic Semiconductors
UV-vis spectra of 1 and 7, cyclic voltammograms of 1 and 2, 1H
and 19F NMR spectra of 11, and crystallographic data (CIF) for 1,
7, and 9. This material is available free of charge via the Internet
at http://pubs.acs.org.
thank Professor David Milstein for helpful discussions on C-C
coupling chemistry and Dr. Barry Thompson for advice on
UV-vis/fluorescence spectroscopy and cyclic voltammetry.
Supporting Information Available: General experimental
details, UV-vis/fluorescence spectra of 1 and 2, thin-film
JO070404A
J. Org. Chem, Vol. 72, No. 15, 2007 5573