Synthesis and photophysical properties of dimethoxybis(3,3,3- trifluoropropen-1-yl)benzenes: Compact chromophores exhibiting violet fluorescence in the solid state

Article abstract of DOI:10.1002/asia.201100176

Dimethoxybis(3,3,3-trifluo-ropropen-1-yl)benzenes were prepared through palladium-catalyzed double cross-coupling reactions of diiododimethoxybenzenes with CF₃C=CZnCl, followed by reduction of CF₃C=C groups with LiAlH₄ or H₂ in the presence of the Lindlar catalyst. The edges of the absorption spectra of 1,2-(MeO)₂-4,5-(CF ₃CHC=CH)₂benzenes 1 and 1,3-(MeO)₂-4,6-(CF ₃CH=CH)₂benzenes 2 in cyclohexane ranged from 348 to 360 nm, whereas the absorption spectra of 1,4-(MeO)₂-2,5-[(E)-CF ₃CH=CH]₂ benzene ((E)-3) ended at 406 nm. These findings indicate that the effective conjugation length of (E)-3 was significantly larger than those of 1 and 2. Consistently, 1 and 2 in cyclohexane exhibited fluorescence with emission maxima in the UV region, whereas (E)-3 in cyclohexane emitted violet light with an emission maximum at 407 nm. All the fluorescence spectra of 1-3 in various solvents redshifted as the solvent polarity increased. The photoluminescence of 1-3 in the solid states was also observed with emission maxima in the violet region. It is important to note that the quantum yields of (E)-3 in a neat thin film and in a doped polymer film were 0.37 and 0.49, respectively. Density functional theory calculations suggested that the fluorine atoms contribute to a slight extension of both the HOMOs and the LUMOs, as well as narrowing of the HOMO-LUMO gaps when compared with the corresponding fluorine-free analogues. In the case of (E)-3, it is suggested that the HOMO-LUMO transition includes charge transfer from the ethereal oxygen atoms to the C(sp²)-CF₃ moieties. Copyright

Full text of DOI:10.1002/asia.201100176

FULL PAPERS
DOI: 10.1002/asia.201100176
Synthesis and Photophysical Properties of Dimethoxybis(3,3,3-
trifluoropropen-1-yl)benzenes: Compact Chromophores Exhibiting Violet
Fluorescence in the Solid State
Masaki Shimizu,* Youhei Takeda, Masahiro Higashi, and Tamejiro Hiyama[a]
Abstract: Dimethoxybis(3,3,3-trifluo-
ropropen-1-yl)benzenes were prepared
through palladium-catalyzed double
cross-coupling reactions of diiododime-
thoxybenzenes with CF3CꢀCZnCl, fol-
lowed by reduction of CF3CꢀC groups
with LiAlH4 or H2 in the presence of
the Lindlar catalyst. The edges of the
absorption spectra of 1,2-(MeO)2-4,5-
(CF3CHC=CH)2benzenes 1 and 1,3-
(MeO)2-4,6-(CF3CH=CH)2benzenes 2
in cyclohexane ranged from 348 to
360 nm, whereas the absorption spectra
of 1,4-(MeO)2-2,5-[(E)-CF3CH=CH]2
benzene ((E)-3) ended at 406 nm.
These findings indicate that the effec-
tive conjugation length of (E)-3 was
significantly larger than those of 1 and
2. Consistently, 1 and 2 in cyclohexane
exhibited fluorescence with emission
maxima in the UV region, whereas
(E)-3 in cyclohexane emitted violet
light with an emission maximum at
407 nm. All the fluorescence spectra of
1–3 in various solvents redshifted as
the solvent polarity increased. The
photoluminescence of 1–3 in the solid
states was also observed with emission
maxima in the violet region. It is im-
portant to note that the quantum yields
of (E)-3 in a neat thin film and in a
doped polymer film were 0.37 and 0.49,
respectively. Density functional theory
calculations suggested that the fluorine
atoms contribute to a slight extension
of both the HOMOs and the LUMOs,
as well as narrowing of the HOMO–
LUMO gaps when compared with the
corresponding fluorine-free analogues.
In the case of (E)-3, it is suggested that
the HOMO–LUMO transition includes
charge transfer from the ethereal
2
À
oxygen atoms to the C
ies.
U
Keywords: chromophores · fluores-
cence · fluorine · materials science ·
molecular electronics
Introduction
nated counterparts.[1] Originated from the highest electrone-
gativity of fluorine among all elements, fluorinated alkyl
and ethenyl groups and per- and semifluorinated aromatic
rings induce various attractive characteristics, such as excel-
lent thermal and oxidative stabilities, high electron affinity,
and weak intermolecular interactions, that are effective for
precise control of molecular assembly. Typical examples of
fluorine-containing electron-transporting semiconductor ma-
terials include perfluoropentacene,[2] perfluorinated oligo(p-
phenylene)s,[3] perfluoroalkylated oligothiophenes,[4] 4-per-
fluoroalkylphenyl-substituted oligoarylenes,[5] and perfluor-
oalkylene-bridge-containing oligothiophenes.[6] Fluorinated
oligo- and poly(phenylenevinylene)s are designed to en-
hance the electron mobility and tune the emission color of
their nonfluorinated counterparts.[7] A wide variety of liquid
crystalline compounds that possess fluorine atoms in a
mesogenic core, linking groups, and/or terminal chains, have
been designed and characterized; thus, systematic studies on
the influence of fluorine substituents on the properties of
these compounds have led to the development of superior
liquid crystals.[8] Therefore, exploration and characterization
Fluorinated p-conjugated molecules have attracted consider-
able attention in the field of functional organic materials be-
cause the presence of fluorine atoms in organic molecules
endows the molecules with unique chemical and physical
properties, which are distinct from those of their nonfluori-
[a] Prof. Dr. M. Shimizu, Dr. Y. Takeda, M. Higashi,
Prof. Dr. T. Hiyama+
Department of Material Chemistry
Graduate School of Engineering, Kyoto University
Kyoto University Katsura, Nishikyo-ku
Kyoto 615-8510 (Japan)
Fax : (+81)75-383-2445
E-mail: m.shimizu@hs2.ecs.kyoto-u.ac.jp
[+] Current address:
Research & Development Initiative
Chuo University
1-13-27 Kasuga, Bunkyo-ku
Tokyo 112-8551 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100176.
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Chem. Asian J. 2011, 6, 2536 – 2544

of novel fluorinated p-conjugated compounds that exhibit
unique properties owing to fluorine, are of particular inter-
est in view of the advancement of functional organic materi-
als.
photophysical properties, and theoretical calculations of di-
methoxybis(3,3,3-trifluoropropenyl)benzenes 1–3.
Considerable attention has been given to p-conjugated
compounds that emit visible light in the solid state because
they have the potential for use in optoelectronic devices,
such as organic light-emitting diodes (OLED),[9] organic
light-emitting field-effect transistors,[10] semiconductor
lasers,[11] and fluorescent sensors.[12] However, it is difficult
to develop organic chromophores exhibiting efficient solid-
state emission because the molecular aggregation of chro-
mophores in the solid state generally results in severe con-
centration quenching of luminescence. Accordingly, exam-
ples of organic solids that exhibit intense emission in the
visible region with high efficiency are extremely limited.[13]
The common structural feature of intensely emissive or-
ganic solids that have been developed to date is that they
contain multiple aromatic rings and/or polycyclic aromatic
hydrocarbon skeletons. The presence of multiple aromatic
rings in a molecule often causes a solubility problem, which
is one of the undesirable factors that hampers purification
and processing of organic materials. Hence, it is of great in-
terest to develop organic chromophores that exhibit high lu-
minescence efficiency in the solid state with a minimum
number of benzene rings as the aromatic component. To
Results and Discussion
Preparation of Dimethoxybis(3,3,3-
trifluoropropenyl)benzenes
Dimethoxybis(3,3,3-trifluoropropenyl)benzenes 1–3 were
prepared by reduction of the corresponding bis(3,3,3-tri-
fluoropropynyl)benzenes, which were prepared by a double
cross-coupling reaction of diiododimethoxybenzenes with in
situ generated 3,3,3-trifluoropropynylzinc chloride (5).[15]
Thus, treatment of 1,1-dichloro-3,3,3-trifluoro-2-tosyloxypro-
pene (4) with two equivalents of BuLi in tetrahydrofuran at
À788C followed by the addition of ZnCl2·TMEDA generat-
ed 5, which was coupled with 4,5-diiodo-1,2-dimethoxyben-
this end, we recently showed that 1,4-bis
G
zene (6) in the presence of [PdCl2ACTHNGUTERNNU(G dppf)] (dppf=1,1’-bis(di-
peridinobenzenes exhibit highly efficient solid-state fluores-
cence in the spectral region ranging from blue to red, which
can be tuned by selection of appropriate alkenyl groups.[14]
phenylphosphino)ferrocene; 10 mol%) and Ag2O (1 equiv)
to give bis(3,3,3-trifluoropropynyl)benzene 7 in 72% yield
(Scheme 1).[16] Stereoselective reduction of 7 with LiAlH4
gave (E)-1, whereas (Z)-1 was prepared in high yield by hy-
drogenation of 7 with the aid of the Lindlar catalyst.
The molecular design of diaminobisACTHUNTGRNEUNG(alkenyl)benzenes origi-
nated from our serendipitous finding that 1,2-dimethoxy-4,5-
bis[(E)-3,3,3-trifluoropropenyl]benzene ((E)-1), which was
obtained as an unexpected product in the attempted Berg-
man cyclization of 1,2-dimethoxy-4,5-bis(3,3,3-trifluoropro-
pynyl)benzene, was faintly violet-emissive on a TLC plate
upon irradiation with a UV lamp at 365 nm. This observa-
tion prompted us to examine the properties of benzene de-
rivatives characterized by the substitution of two dimethoxy
groups and two 3,3,3-trifluoropropenyl moieties as novel
and compact chromophores that emitted visible light in the
solid state. Reported herein are the preparation, structures,
Two-fold cross-coupling reaction of 1,3-diiodobenzene 8
with 5 was catalyzed by 10 mol% of [PdACHTNUTRGNE(UNG PPh3)4] to give 9 in
69% yield (Scheme 2).[17] Both (E)-2 and (Z)-2 were pre-
pared from 9 in a manner similar to that used to prepare 1.
When LiAlH4 reduction of 1,4-diethynylbenzene 11 pre-
pared from 1,4-diiodobenzene 10 with 5 was attempted, the
reaction resulted in the production of a complex mixture.
Abstract in Japanese:
Scheme 1. Synthesis of 1. THF=tetrahydrofuran.
Chem. Asian J. 2011, 6, 2536 – 2544
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M. Shimizu et al.
FULL PAPERS
Table 1. UV/Vis absorption data of 1–3.[a]
Solvent (e)[b]
Absorption maximum [nm]
(molar absorption coefficient [mÀ1 cmÀ1])
(E)-1
(Z)-1
(E)-2
(Z)-2
(E)-3
c-C6H12 (2.0)
Et2O (4.3)
304
301
324
312
360
G
G
G
N
ACHTUNGTRENNUNG
A
E
E
G
ACHTUNGTRENNUNG(9700)
CH2Cl2 (9.1)
CH3CN (37)
DMSO (47)
303
302
308
307
305
311
325
325
328
311
314
316
364
364
371
(11000)
(7900)
(6300)
G
(9000)
Scheme 2. Synthesis of 2.
(13400)
A
E
E
G
ACHTUNGTRENNUNG(8700)
Conversely, hydrogenation of 11 with the Lindlar catalyst
gave the expected (Z)-3 quantitatively, the Z configuration
of which was confirmed based on the coupling constant be-
tween the two olefinic hydrogen atoms (J=12.4 Hz) in the
crude products (Scheme 3). However, purification of the
crude products by column chromatography on silica gel
easily caused Z–E isomerization of (Z)-3 to give a 2:1 mix-
ture of (Z)-3 and (E)-3. Irradiation of the Z/E mixture by
using a UV lamp in the presence of a catalytic amount of
iodine induced complete isomerization of (Z)-3 to (E)-3;
therefore, (E)-3 was isolated as a sole product in good yield.
Figure 1. Absorption spectra of 1–3 in cyclohexane.
Scheme 3. Synthesis of (E)-3.
Photophysical Properties
The UV/visible absorption spectra of 1–3 were measured in
various solvents, and the results are summarized in Table 1.
The spectra of 1–3 in cyclohexane are shown in Figure 1.
The spectra of (E)-1 and (Z)-1 and those of (E)-2 and (Z)-2
were similar in shape, which indicated that the configuration
of the CF3CH=CH moieties had little effect on the electron-
ic structures of 1 and 2. The absorption edges of 1 and 2
ranged from 348 to 360 nm, whereas that of 3 was at
406 nm. In addition, the effective conjugation length of (E)-
3 was the longest among 1–3. In all compounds, a very small
bathochromic shift was observed with respect to solvent po-
larity.[18] The absorption spectra of (E)-3 in various solvents
are illustrated in Figure 2 as a representative example.
Figure 2. Absorption spectra of (E)-3 in various solvents.
the UV region, whereas (E)-3 yielded violet fluorescence
with an emission maximum at 407 nm (Figure 3). In all com-
pounds, the spectra redshifted as the solvent polarity in-
creased, as exemplified by those of (E)-3 in Figure 4. This
phenomenon suggests that the excited states consist of
charge-localized electronic structures. The fluorescence
quantum yields (Ff) of 1–3 in solution ranged from low to
moderate, with the highest value being for (E)-2. Investiga-
tion on the geometry of the trifluoropropenyl moiety in 1
and 2 revealed that E isomers ((E)-1 and (E)-2) exhibited
higher Ff values than Z isomers ((Z)-1 and (Z)-2).
The fluorescence properties of 1–3 in various solvents are
summarized in Table 2. In cyclohexane, 1 and 2 exhibited
violet luminescence with emission maxima (362–373 nm) in
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Dimethoxybis(3,3,3-trifluoropropen-1-yl)benzenes
Table 2. Fluorescence data of 1–3.[a]
Solvent[b]/film
Emission maximum [nm] (Ff)[c]
(Z)-1 (E)-2 (Z)-2
(E)-1
(E)-3
c-C6H12
Et2O
CH2Cl2
CH3CN
DMSO
362 (0.22) 373 (0.10) 366 (0.44) 364 (0.15) 407 (0.34)
370 (0.24) 370 (0.12) 370 (0.40) 370 (0.09) 420 (0.33)
379 (0.22) 378 (0.12) 374 (0.37) 370 (0.05) 425 (0.27)
389 (0.15) 389 (0.11) 379 (0.23) 379 (0.04) 431 (0.18)
392 (0.21) 400 (0.03) 383 (0.33) 379 (0.04) 438 (0.28)
neat thin film 406 (0.09) 409 (0.14) 400 (0.13) 392 (0.06) 434 (0.37)
PMMA film 379 (0.12) 384 (0.18) 409 (0.25) 413 (0.19) 428 (0.49)
[a] Excitation was effected by UV light at 265 nm. [b] Measured at 1ꢁ
10À5 m. [c] Absolute quantum yield determined by a calibrated integrating
sphere system. DMSO=dimethyl sulfoxide.
Figure 5. Fluorescence spectra of (Z)-1, (E)-2, and (E)-3 in neat thin
film.
Figure 3. Fluorescence spectra of 1–3 in cyclohexane.
Figure 6. Fluorescence spectra of 1–3 dispersed in PMMA film.
To gain insight into the efficient luminescence of (E)-3 in
the solid state, we analyzed its single crystal obtained by re-
crystallization from a solvent mixture of dichloromethane
and n-hexane by X-ray diffraction.[20] The molecules crystal-
lize in a triclinic lattice with a space group PÀ1. The asym-
metric unit is composed of two crystallographically inde-
pendent molecules, both of which adopt a nearly identical
conformation and have a center of symmetry at the centroid
of the benzene ring. As shown in Figure 7, the main frame-
À
À
work consisting of CF3CH=CH benzene CH=CHCF3 is
slightly twisted, with dihedral angles between the central
benzene plane and the CF3CH=CH moiety of 9 and 128, re-
spectively. A trifluoromethyl group adopts a bisected confor-
Figure 4. Fluorescence spectra of (E)-3 in various solvents.
Since we observed that 1–3 exhibited luminescence upon
UV irradiation on TLC, the fluorescence spectra of 1–3 in
neat thin films and dispersed in poly(methyl methacrylate)
(PMMA) films were measured. The neat thin films and
doped PMMA films were prepared on quartz plates by spin-
coating from dichloromethane solutions and chlorobenzene
solutions dissolving PMMA (15 wt%), respectively. The re-
sults are summarized in Table 2 and the spectra are shown
in Figures 5 and 6.[19] The emission maxima in the solid
states appeared in the violet to blue region and exhibited a
bathochromic shift when compared with those in solution.
Quantum yields of 1 and 2 in the solid states ranged from
0.06 to 0.25, whereas (E)-3 in both the neat thin film and
the doped PMMA film produced good quantum yields (Ff =
0.37 and 0.49, respectively).
À
mation with respect to an ethenyl plane, with a C F(1)
bond located in the benzene plane that bisects the bond
angle of F(2)-C-F(3).
Figure 7. Molecular structure of (E)-3 in a single crystal.
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M. Shimizu et al.
FULL PAPERS
The packing diagram of (E)-3 is shown in Figure 8. Each
molecule forms a layer structure (Figure 8a) in which ben-
zene rings in adjacent molecules are far apart from one an-
other. While the distance between the benzene ring of a
molecule in one layer and the ethenyl moiety of the closest
molecule in the next layer is 3.7–3.8 ꢂ, which may result in
intermolecular electronic interactions, the angle formed by
the long axes of the molecules is about 808 (Figure 8b). The-
oretical calculations have suggested that cross-stacking
should be advantageous to efficient solid-state lumines-
cence;[21] therefore, the high quantum yield of (E)-3 ob-
served in the neat thin film can likely be attributed to the
cross-stacked packing motif.
Figure 9. Conformers A–F of (E)-2 as initial geometries for structural op-
timization. Hydrogen atoms are omitted for clarity.
Figure 10. The optimized geometries G–I of (E)-2 with the dihedral
angles between the substituents and the benzene plane. Hydrogen atoms
are omitted for clarity.
À
ortho-positions. Each (E)-CF3CH=CH moiety of G and I
was located on the same plane of the central benzene ring,
À
whereas two (E)-CF3CH=CH moieties of H deviated from
a benzene plane by 10 and 138, respectively. The most stable
conformer was G; however, the energy differences among
the three local minima were very small (0.19 kcalmolÀ1 for
H and 0.097 kcalmolÀ1 for I with respect to G).
Structural optimization of (E)-3 was conducted by using
DFT at the B3LYP/6-31G(d) level with the structure ob-
tained by X-ray crystallographic analysis as an initial coordi-
nate. The optimized structure was almost identical to the ini-
tial structure (Figure 11). To gain insight into the effect of
fluorine on the electronic structures of (E)-2 and (E)-3, we
also optimized their nonfluorinated analogues (E)-2(H) and
(E)-3(H) by using the initial geometries defined by replac-
Figure 8. Crystal packing diagram of (E)-3: a) view from b axis, b) view
from a axis. Each molecule is colored gray and black according to the
symmetry equivalence in the crystal. Hydrogen atoms are omitted for
clarity.
Theoretical Calculations
Theoretical calculations of (E)-2 and (E)-3, which exhibited
higher fluorescence quantum yields among 1–3, were con-
ducted by using the Gaussian 03 package with DFT to eluci-
date the electronic structures.[22] First, the ground-state geo-
metries of (E)-2 were optimized at the B3LYP/6-31G(d)
level by using the six conformers (A–F) shown in Figure 9
as the initial structures. These structures gave rise to three
conformers G–I, as local minima (Figure 10).[23] The methyl
groups in all of the optimized structures were oriented to
À
the opposite side with respect to the adjacent CF3CH=CH
moieties and positioned on the benzene plane. The structur-
Figure 11. The optimized geometries of (E)-3, (E)-2(H), and (E)-3(H)
with the dihedral angles between the substituents and the benzene plane.
Hydrogen atoms are omitted for clarity.
al differences among G–I were due to the orientation of
À
(E)-CF3CH=CH moieties against methoxy groups at their
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Chem. Asian J. 2011, 6, 2536 – 2544

Dimethoxybis(3,3,3-trifluoropropen-1-yl)benzenes
ing CF3 in the initial geometries of (E)-2 and (E)-3 with
CH3. As shown in Figure 11, the calculated structures of G
and (E)-2(H) did not differ, whereas the dihedral angles be-
À
tween the CF3CH=CH moieties and the central benzene
ring in (E)-3(H) were found to be larger than those in (E)-3
(188 for (E)-3(H) and 88 for (E)-3). Thus, the presence of
fluorine atoms in benzene derivatives of type 3 causes the
conjugation between the two propenyl moieties and central
benzene to be more efficient than in the fluorine-free coun-
terpart.
HOMO and LUMO diagrams of (E)-2 and (E)-2(H) with
energy levels and gaps are shown in Figure 12. The HOMO
and LUMO of (E)-2 are slightly more extended over C-
Figure 13. Energy level and orbital diagrams of the HOMOs and
LUMOs of (E)-3 and (E)-3(H).
with bathochromic shift of the fluorescence spectra of (E)-3
that was observed in various solvents.
Conclusions
We prepared and characterized five dimethoxybis(3,3,3-tri-
fluoropropenyl)benzenes. All the benzene derivatives exhib-
ited fluorescence in the violet region with low to good quan-
tum yields in both the solution and the solid state. It should
be noted that 1,4-dimethoxy-2,5-bis[(E)-3,3,3-trifluoroprope-
nyl]benzene emits brilliant violet light in neat thin film and
in doped PMMA film with emission maxima at 434 (Ff =
0.37) and 428 nm (Ff =0.49), respectively. The fluorine
atoms of the benzene derivatives contribute to extension of
the frontier orbitals and a decrease in the energy gaps, al-
lowing visible light luminescence from the compact p-conju-
gated system. This study shed light on the trifluoropropenyl
moiety as a new entry of fluorinated p-modules that induce
unique properties in functional organic materials.
Figure 12. Energy level and orbital diagrams of the HOMOs and
LUMOs of (E)-2 and (E)-2(H).
2
À
G
of both the HOMO and LUMO of (E)-2 are lower than
those of (E)-2(H). Hence, the reduction in the energy levels
of HOMO is ascribed to the conjugation between s* orbi-
À
tals of C F bonds and the p orbitals of ethenyl moieties,
whereas the decrease in the LUMO energy results from
mixing of the s* orbitals and the p* orbitals. Since the
HOMO–LUMO gap of (E)-2 is smaller than that of (E)-
2(H), the s*–p* conjugation is more efficient than the s–p*
conjugation.
Experimental Section
The same fluorine effect leading to slight extension of the
frontier molecular orbitals and narrowing of the HOMO–
LUMO gap was confirmed for (E)-3 and (E)-3(H)
(Figure 13). It is important to note that the two ethereal
oxygen atoms participate in the HOMOs, but not in the
LUMOs. Thus, the HOMO–LUMO transition of (E)-3 in-
Typical Procedure for the Palladium-Catalyzed Cross-Coupling Reaction
of 3,3,3-Trifluoropropynylzinc Chloride with Diiodobenzene: Preparation
of 1,2-Dimethoxy-4,5-bis(3,3,3-trifluoropropynyl)benzene (7)
BuLi (1.4 mL, 2.2 mmol, 1.6m in n-hexane) was added to a THF (5.1 mL)
solution of 1,1-dichloro-3,3,3-trifluoro-2-tosyloxypropene (4, 0.34 g,
1.0 mmol) at À788C. The solution was stirred at À788C for 30 min before
the addition of ZnCl2·TMEDA (TMEDA=N,N,Nꢃ,Nꢃ-tetramethyl-1,2-
ethane, 0.28 g, 1.1 mmol) in one portion. The resulting solution was
stirred at À788C for 30 min and at room temperature for an additional
30 min. The mixture was added to a THF (3.0 mL) solution of 1,2-diiodo-
2
À
cludes charge transfer from the oxygen atoms to the C
G
CF3 moieties. The time-dependent DFT calculation indicat-
ed that the absorption band around 360 nm corresponds to
the HOMO–LUMO transition. These results are consistent
Chem. Asian J. 2011, 6, 2536 – 2544
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M. Shimizu et al.
FULL PAPERS
4,5-dimethoxybenzene (6, 0.10 g, 0.26 mmol), [PdCl
G
1,5-Dimethoxy-2,4-bis[(E)-3,3,3-trifluoropropenyl]benzene ((E)-2)
(21 mg, 26 mmol), and Ag2O (59 mg, 0.26 mmol), and the resulting mix-
ture was then heated at 808C for 15 h. Silica gel (1.0 g) and AcOEt
(30 mL) were added to the reaction mixture and the slurry was concen-
trated in vacuo. Column chromatography on silica gel with the silica gel
absorbed with the crude product (n-hexane/AcOEt 5:1) gave 7 (59 mg,
72%) as a colorless solid. M.p. 99.0–99.68C; Td (5 wt.%): 122.98C; Rf =
0.42 (n-hexane/AcOEt 4:1); 1H NMR (400 MHz, CDCl3): d=3.93 (s,
6H), 7.02 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=56.2, 79.0 (q,
J=52.9 Hz), 83.6 (q, J=6.9 Hz), 114.5, 114.7 (q, J=256.8 Hz), 115.5,
151.0 ppm; 19F NMR (282 MHz, CDCl3): d=À50.6 ppm; IR (KBr): n˜ =
2247, 1518, 1400, 1283, 1254, 1132, 999, 868, 718, 569 cmÀ1; MS (EI): m/z
(%): 322 (100) [M+], 300 (20); elemental analysis calcd (%) for
C14H8F6O2: C 52.19, H 2.50; found: C 52.00, H 2.75.
Purified by column chromatography on silica gel (n-hexane/AcOEt 9:1);
yield: 38%; a colorless solid; m.p. 108.8–109.98C; Td (5 wt.%): 130.88C;
Rf =0.36 (n-hexane/AcOEt 4:1); H NMR (400 MHz, CDCl3): d=3.94 (s,
6H), 6.26 (dq, J=15.6, 5.4 Hz, 2H), 7.30 (dq, J=15.6, 2.2 Hz, 2H),
7.46 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=55.7, 94.8, 114.9 (q,
J=33.5 Hz), 115.1, 123.9 (q, J=268.3 Hz), 129.1, 131.9 (q, J=7.2 Hz),
160.2 ppm; 19F NMR (282 MHz, CDCl3): d=À63.4 ppm (d, J=5.4 Hz);
IR (KBr): n˜ =2949, 1651, 1614, 1471, 1304, 1269, 1117, 1028, 827,
519 cmÀ1; MS (EI): m/z (%): 326 (100) [M+], 307 (10); elemental analysis
calcd (%) for C14H12F6O2: C 51.54, H 3.71; found: C 51.80, H 3.68.
1
1,5-Dimethoxy-2,4-bis[(Z)-3,3,3-trifluoropropenyl]benzene ((Z)-2)
Purified by GPC (CHCl3); yield: 60%; colorless solid; m.p. 89.7–91.28C;
Td (5 wt.%): 127.08C; Rf =0.34 (n-hexane/AcOEt 4:1); 1H NMR
(400 MHz, CDCl3): d=3.89 (s, 6H), 5.64–5.76 (m, 2H), 6.41 (s, 1H), 7.00
(d, J=12.8 Hz, 2H), 7.47 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=
55.7, 93.7, 115.0, 116.8 (q, J=34.8 Hz), 122.9 (q, J=269.9 Hz), 131.1–
131.3 (m), 133.9–134.0 (m), 159.1 ppm; 19F NMR (282 MHz, CDCl3): d=
À58.8 ppm (d, J=7.6 Hz); IR (KBr): n˜ =2982, 1612, 1497, 1319, 1209,
1115, 1026, 924, 822, 745, 559 cmÀ1; MS (EI): m/z (%): 326 (100) [M+],
307 (12); elemental analysis calcd (%) for C14H12F6O2: C 51.54, H 3.71;
found: C 51.66, H 3.75.
Typical Procedure for the trans-Reduction of Alkynes with LiAlH4:
Preparation of 1,2-Dimethoxy-4,5-bis[(E)-3,3,3-trifluoropropenyl]benzene
((E)-1)
LiAlH4 (8.7 mg, 0.23 mmol) was added to a solution of 7 (29 mg, 91
mmol) in THF (0.28 mL) at room temperature. The resulting solution was
stirred at room temperature for 1 h. The reaction mixture was quenched
with sat. aq. NH4Cl (10 mL) and extracted with AcOEt (10 mLꢁ3). The
combined organic layer was dried over anhydrous MgSO4 and concen-
trated in vacuo. The crude product was purified by column chromatogra-
phy on silica gel (n-hexane/AcOEt 8:1) to give (E)-1 (13 mg, 46%) as a
colorless solid. M.p. 124.2–125.28C; Td (5 wt.%): 119.48C; Rf =0.47 (n-
hexane/AcOEt 4:1); 1H NMR (400 MHz, CDCl3): d=3.95 (s, 6H), 6.05
(dq, J=16.0, 6.6 Hz, 2H), 6.94 (s, 2H), 7.39 ppm (dq, J=16.0, 2.1 Hz,
2H); 13C NMR (100 MHz, CDCl3): d=56.2, 109.0, 117.6 (q, J=33.6 Hz),
123.1 (q, J=267.9 Hz), 125.8, 133.7 (q, J=6.9 Hz), 150.3 ppm; 19F NMR
(282 MHz, CDCl3): d=À63.8 ppm (d, J=6.6 Hz); IR (KBr): n˜ =1601,
1516, 1319, 1283, 1097, 966, 665, 544 cmÀ1; MS (EI): m/z (%): 326 (45)
[M+], 307 (12), 257 (100); elemental analysis calcd (%) for C14H12F6O2:
C 51.54, H 3.71; found: C 51.63, H 4.00.
1,4-Dimethoxy-2,5-bis(3,3,3-trifluoropropynyl)benzene (11)
Isolated in 84% yield as
a colorless solid; m.p. 116.8–117.68C; Td
1
(5 wt.%): 129.68C; Rf =0.69 (n-hexane/AcOEt 4:1); H NMR (400 MHz,
CDCl3): d=3.87 (s, 6H), 7.02 ppm (s, 2H); 13C NMR (100 MHz, CDCl3):
d=56.5, 81.2 (q, J=52.9 Hz), 82.2 (q, J=6.1 Hz), 111.3, 114.7 (q, J=
257.1 Hz), 116.2, 154.9 ppm; 19F NMR (282 MHz, CDCl3): d=
À50.5 ppm. IR (KBr): n˜ =2259, 1506, 1402, 1288, 1134, 1030, 868,
667 cmÀ1; MS (EI): m/z (%): 322 (100) [M+], 307 (45); elemental analysis
calcd (%) for C14H8F6O2: C 52.19, H 2.50; found: C 51.90, H 2.56.
1,4-Dimethoxy-2,5-bis[(E)-3,3,3-trifluoropropenyl]benzene ((E)-3)
Typical Procedure for the cis-Reduction of Alkynes: Preparation of 1,2-
Dimethoxy-4,5-bis[(Z)-3,3,3-trifluoropropenyl]benzene ((Z)-1)
Pd/BaCO3 (5.0 mg, 5 wt.%) was added to pyridine (3.5 mL) in a Schlenk
tube at room temperature, and then the mixture was stirred for 10 min
before the addition of 11 (0.10 g, 0.31 mmol). After another 10 min of
stirring, the tube was filled with H2 gas and the whole mixture was stirred
at room temperature for 2 h. The resulting solution was filtered with a
pad of Celite and Florisi and the filtrate was concentrated in vacuo. The
crude product was purified by column chromatography on silica gel (n-
hexane/AcOEt 4:1), giving a mixture of (Z)-3 and (E)-3 (Z/E 2:1, 99 mg,
97%) as a colorless solid. I2 (2.0 mg, 7.9 mmol) was added to a CHCl3
(10 mL) solution of the mixture (29 mg, 89 mmol). The mixture was
stirred under irradiation of UV light (UVA-100HA Riko) at room tem-
perature for 8 h before quenching with sat. aq. Na2S2O3 (10 mL). The
aqueous layer was extracted with AcOEt (10 mLꢁ3). The combined or-
ganic layer was dried over anhydrous MgSO4 and concentrated in vacuo.
The residue was purified by column chromatography on silica gel (n-
hexane/AcOEt 6:1) to give only (E)-3 (22 mg, 77%) as a colorless solid.
M.p. 159.5–160.28C; Td (5 wt.%): 147.48C; Rf =0.63 (n-hexane/AcOEt
4:1); 1H NMR (400 MHz, CDCl3): d=3.88 (s, 6H), 6.36 (dq, J=16.4,
7.9 Hz, 2H), 6.94 (s, 2H), 7.39 (dq, J=16.4, 2.4 Hz, 2H), 7.47 ppm (s,
1H); 13C NMR (100 MHz, CDCl3): d=56.1, 111.0, 117.5 (q, J=33.5 Hz),
123.6 (q, J=268.4 Hz), 124.3, 132.3 (q, J=6.7 Hz), 151.9 ppm; 19F NMR
(282 MHz, CDCl3): d=À63.7 ppm (d, J=7.9 Hz); IR (KBr): n˜ =3017,
1661, 1499, 1414, 1310, 1281, 1215, 1111, 1040, 970, 905, 654 cmÀ1; MS
(EI): m/z (%): 326 (100) [M+], 311 (11), 242 (10); elemental analysis
calcd (%) for C14H12F6O2: C 51.54, H 3.71; found: C 50.99, H 3.99.
A drop of quinoline and Pd/BaSO4 (4.0 mg, 5 wt.%) were added to
methanol (2.5 mL) at room temperature and the mixture was stirred for
10 min before the addition of 7 (80 mg, 0.25 mmol). The reaction mixture
was stirred for another 10 min at room temperature and then filled with
H2 gas (1 atm.). The resulting solution was stirred at room temperature
for 1 h and filtered through a pad of Celite and Florisil. The filtrate was
concentrated in vacuo. The crude product was purified by GPC to give
(Z)-1 (75 mg, 93%) as a colorless solid. M.p. 57.4–58.18C; Td (5 wt.%):
109.78C; Rf =0.45 n-hexane/AcOEt 4:1); 1H NMR (400 MHz, CDCl3):
d=3.89 (s, 6H), 5.82 (dq, J=12.4, 12.7 Hz, 2H), 6.90 (s, 2H), 6.92 ppm
(d, J=12.4 Hz, 2H); 13C NMR (100 MHz, CDCl3): d=56.2, 113.4, 119.1
(q, J=33.9 Hz), 122.4 (q, J=270.0 Hz), 125.4, 137.2 (q, J=5.7 Hz),
148.7 ppm; 19F NMR (282 MHz, CDCl3): d=À58.2 ppm (d, J=12.7 Hz);
IR (KBr): n˜ =3011, 1717, 1508, 1279, 1134, 718, 419 cmÀ1; MS (EI): m/z
(%): 326 (78) [M+], 307 (19), 257 (100), 242 (14), 188 (12); elemental
analysis calcd (%) for C14H12F6O2: C 51.54, H 3.71; found: C 51.40,
H 3.80.
1,5-Dimethoxy-2,4-bis(3,3,3-trifluoropropynyl)benzene (9)
Purified by column chromatography on silica gel (n-hexane/AcOEt 4:1);
yield: 69%; colorless solid; m.p. 169.5–170.28C; Td (5 wt.%): 130.08C;
1
Rf =0.17 (n-hexane/AcOEt 4:1); H NMR (400 MHz, CDCl3): d=3.96 (s,
6H), 6.41 (s, 1H), 7.63 ppm (s, 1H); 13C NMR (100 MHz, CDCl3): d=
56.2, 79.0 (q, J=52.1 Hz), 82.1 (q, J=6.4 Hz), 94.6, 100.6, 114.8 (q, J=
255.9 Hz), 139.6, 164.4 ppm; 19F NMR (282 MHz, CDCl3): d=
À49.9 ppm; IR (KBr): n˜ =2247, 1609, 1506, 1290, 1175, 1111, 1020, 824,
552 cmÀ1; MS (EI): m/z (%): 322 (100) [M+], 303 (15), 253 (11); elemen-
tal analysis calcd (%) for C14H8F6O2: C 52.19, H 2.50; found: C 52.06,
H 2.60.
UV/Vis and Fluorescence Spectra of 1–3 in Solvents
Spectroscopic-grade solvents for measurements of UV/Vis absorption
and fluorescence spectra were purchased from Kanto Chemical Co. and
degassed by bubbling with argon before use. UV/Vis and fluorescence
spectra of 1–3 in solvents were measured with 1ꢁ10À5 m solution pre-
pared from degassed spectroscopic-grade cyclohexane. UV/Vis absorp-
tion spectra were measured with a Shimadzu UV-2550 spectrometer.
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Chem. Asian J. 2011, 6, 2536 – 2544

Dimethoxybis(3,3,3-trifluoropropen-1-yl)benzenes
Fluorescence spectra were measured by Hamamatsu Photonics C9920–02
Absolute PL Quantum Yield Measurement System and absolute quan-
tum yields were determined by using a calibrated integrating sphere
system. The absolute quantum yields were obtained by averaging values
of three to five measurements with different lots of samples.
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In a glass tube, (E)-2 (2.0 mg) was dissolved in CH2Cl2 (0.50 mL). The re-
sulting solution was dropped onto a quartz plate (10 mmꢁ10 mm) and
spin-coated with a MIKASA MS-A-100 spin coater at 100 rpm over a
period of 300 s. The deposited film was dried under reduced pressure at
room temperature for 2 h.
Typical Procedure for the Preparation of PMMA Films Doped with 1–3
In a glass tube, (E)-3 (5.0 mg) was dissolved in a PMMA chlorobenzene
solution (15 wt.%, 1.00 mL). The resulting solution was dropped onto a
quartz plate (10ꢁ10 mm) and spin-coated with a MIKASA MS-A-100
spin coater at 300 rpm for 20 s and then at 100 rpm over a period of
280 s. The film was dried under reduced pressure at room temperature
for 1.5 h.
Molecular Orbital Calculations
Molecular structures were optimized by DFT methods at the B3LYP/6-
31G(d) level by using the Gaussian 03 package. Cartesian coordinates for
the geometry optimization study are listed in the Supporting Information.
Energy levels of molecular orbitals were calculated at the B3LYP/6-
31G(d) level.
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Acknowledgements
This work was supported by Grants-in-Aid for Creative Scientific Re-
search, no. 16GS0209 and Scientific Research, no. 22350081, from the
Ministry of Education, Culture, Sports, Science and Technology, Japan.
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FULL PAPERS
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Received: February 22, 2011
Published online: June 30, 2011
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Chem. Asian J. 2011, 6, 2536 – 2544