Fluorescence and phosphorescence of a series of silicon-containing six-membered-ring molecules

Article abstract of DOI:10.1016/j.jorganchem.2015.12.042

Various silicon-containing six-membered-ring molecules were synthesized by Pd-catalyzed coupling reaction of 1,2-bis(dimethylsilyl)arenes with 1,2-diiodoarenes in moderate yields. Their optical properties were investigated via UV-vis absorption, fluorescence and phosphorescence spectroscopies, which indicated that the σ?-π?conjugated system expanded owing to the silicon atoms. Some of the compounds exhibited enhanced luminescence, larger Stokes shift, and phosphorescence in comparison with 9,9,10,10-tetramethyl-9,10-dihydroanthracene. Density functional theory (DFT) studies were also performed to investigate the photophysical properties of the compounds.

Full text of DOI:10.1016/j.jorganchem.2015.12.042

Journal of Organometallic Chemistry 805 (2016) 27e33
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Fluorescence and phosphorescence of a series of silicon-containing
six-membered-ring molecules
a
a
a
a
Takayuki Nakashima , Masaki Shimada , Yu Kurihara , Mizuho Tsuchiya ,
a,
*
b
c
a, **
Yoshinori Yamanoi , Eiji Nishibori , Kunihisa Sugimoto , Hiroshi Nishihara
a
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Division of Physics, Faculty of Pure and Applied Sciences, Tsukuba Research Center for Interdisciplinary Materials Science (TIMS) & Center for Integrated
b
Research in Fundamental Science and Engineering (CiRfSE), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
c
Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2015
Received in revised form
Various silicon-containing six-membered-ring molecules were synthesized by Pd-catalyzed coupling
reaction of 1,2-bis(dimethylsilyl)arenes with 1,2-diiodoarenes in moderate yields. Their optical proper-
ties were investigated via UVevis absorption, fluorescence and phosphorescence spectroscopies, which
28 December 2015
indicated that the
pounds exhibited enhanced luminescence, larger Stokes shift, and phosphorescence in comparison with
,9,10,10-tetramethyl-9,10-dihydroanthracene. Density functional theory (DFT) studies were also per-
formed to investigate the photophysical properties of the compounds.
s*ep* conjugated system expanded owing to the silicon atoms. Some of the com-
Accepted 31 December 2015
Available online 5 January 2016
9
Keywords:
Silicon
©
2016 Elsevier B.V. All rights reserved.
Fluorescence
Phosphorescence
DFT
1
. Introduction
reaction between hydrosilanes with aryl iodides, we have shown
that this reaction provides a convenient route to various dibenzo-
siloles and dibenzogermoles [5]. In this work, we synthesized a
series of 9,9,10,10-tetramethyl-9,10-dihydro-9,10-disilaanthracene,
which are silicon-containing six-membered-ring compounds from
their corresponding 1,2-bis(dimethylsilyl)arenes and 1,2-
diiodoarenes, and investigated the fluorescence of the com-
pounds at room temperature and their phosphorescence at 77 K.
Much recent attention has focused on the unique properties of
certain aromatic compounds bridged with hetero-atoms [1]. Red-
or blue-shifts emerge in materials with
organosilicon compounds, as the energy gap between the HOMO
and LUMO is tuned. Silicon-containing conjugated molecules
are expected to be used in several kinds of materials such as
fluorescent-emitting or electron-transporting devices [2]. Adding
silicon directly to aromatic molecules induces hyperconjugation
sep conjugation, such as
sep
2. Result and discussion
between the
s orbital of the silicon and the aromatic p orbital.
UVevis absorption and fluorescence spectra are red-shifted and the
molecule's absorption coefficient and fluorescence intensity in-
Initially, we screened the optimal conditions of coupling reac-
tion between 1,2-bis(dimethylsilyl)benzene and 1,2-diiodobenzene
as the model reaction, included the modification of solvents, bases,
Pd catalysts, and temperature [6e8]. The reaction was monitored
by GC, and the results were summarized in Table 1. We found that
crease owing to the
dibenzosilole, a five-membered ring molecule that contains silicon
3]. However, structurally similar silicon-containing molecules with
sep conjugation. These effects are evident in
[
six-membered-rings have been less well investigated due to limi-
tations of their synthetic methodology [4]. During studies of the
1
,2-diiodobenzene was completely converted at the end of the re-
action and that Pd(P(t-Bu) (4-Me NC )) (catalyst) and N,N-dii-
sopropylethylamine (base) in 1,2-dichloroethane or propionitrile
solvent) at rt (temperature) for 1 d were the best conditions after
2
2
6 4 2
H
(
*
Corresponding author.
the careful optimization. Finally, the ratio of 1,2-bis(dimethylsilyl)
benzene and 1,2-diiodobenzene was tested, and larger amount of
1,2-bis(dimethylsilyl)benzene could improve the yield of the
** Corresponding author.
E-mail addresses: yamanoi@chem.s.u-tokyo.ac.jp (Y. Yamanoi), nisihara@chem.s.
u-tokyo.ac.jp (H. Nishihara).
http://dx.doi.org/10.1016/j.jorganchem.2015.12.042
0
022-328X/© 2016 Elsevier B.V. All rights reserved.

28
T. Nakashima et al. / Journal of Organometallic Chemistry 805 (2016) 27e33
Table 1
a
Screening of optimal reaction conditions for 9,9,10,10-tetramethyl-9,10-dihydro-9,10-disilaanthracene (1).
ꢁ
Yield (%)b
Entry
Catalyst
Pd(PPh
Temp ( C)
Solvent
Base
1,2-bis(dimethylsilyl)benzene/1,2-diiodobenzene
1
2
3
4
5
6
7
8
9
3
)
4
rt
rt
rt
rt
50
0
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
THF
THF
THF
THF
THF
THF
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
(i-Pr)
2
2
2
2
2
2
2
2
2
2
2
2
EtN
EtN
EtN
EtN
EtN
EtN
EtN
EtN
EtN
EtN
EtN
EtN
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
0
6
22
27
22
6
33
42
19
36
15
38
40
4
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
)
2
Ph)
2
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
6
H
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
CH
CH
3
CN
CH
3
2
CN
toluene
CH Cl
10
11
12
13
14
15
16
2
2
CHCl
CICH
3
2
2
CH Cl
CH
CH
CH
CH
3
CH
3
CH
3
CH
3
CH
2
2
2
2
CN
CN
CN
CN
Et
DABCO
c-C 11MeN
3
N
6
H
31
34
17
Pd(P(t-Bu)
2
2
(4-Me NC
6
H
))
4 2
rt
CH
3
CH
2
CN
1.2
0
18
19
20
21
22
23
24
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
Pd(P(t-Bu)
2
2
2
2
2
2
2
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
(4-Me
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
2
NC
6
H
6
H
6
H
6
H
6
H
6
H
6
H
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
))
4 2
rt
rt
rt
rt
rt
rt
rt
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
CN
CN
CN
CN
CN
CN
DBU
PO
CO
KOAc
KO(t-Bu)
1.2
1.2
1.2
1.2
1.2
1.5
1.5
0
21
16
10
0
K
3
4
CS
2
3
c
c
(i-Pr)
(i-Pr)
2
EtN
EtN
42
43
2 2
ClCH CH Cl
2
a
b
c
Reaction conditions: Pd catalyst (0.025 mmol), l,2-bis(dimethylsilyl)benzene (0.60 mmol), 1,2-diiodobenzene (0.50 mmol), base (3.0 mmol), solvent (1.0 mL), rt, 1 d.
GC yield with dodecane as an internal standard.
The amount of l,2-bis(dimethylsilyl)benzene was 0.75 mmol.
product (1) in up to 43%. In the improved synthetic protocol,
silicon-containing six-membered-ring molecules 1e8 shown in
Table 2 were synthesized by coupling 1,2-bis(dimethylsilyl)arenes
and 1,2-diiodoarenes under the optimized conditions. Compound
absorption maxima of 2 and 3, which contained methyl groups on
the aromatic ring, were slightly different from that of 1. However,
the extended p-conjugation of 4 caused its absorption maximum to
shift to a longer wavelength (286 nm) with stronger molecular
absorption coefficient relative to that of 1. Similar to 4, the ab-
sorption maxima of 5, 6, 7, and 8 were also shifted to longer
wavelengths, 277 nm, 292 nm, 297 nm, and 289 nm, respectively.
This indicates that conjugated systems were expanded by the
introduction of functional group through 1,2-bis(dimethylsilyl)
benzene moiety.
9
, the carbon analog of 1, was commercially available and used for
comparison. Although all the compounds were obtained here in
moderate yields in one-step reaction, it was difficult to prepare
unsymmetrical 9,10-dihydro-9,10-disilaanthracenes 2e7, including
double cyclized product 8, using previous methods. Importantly,
delicate functional groups toward organometallic reagents such as
the ester substituent of 6 were compatible with the reaction. The
main byproducts were reduced arene compounds and non-cyclized
products. Analytically pure compounds 1e8 were isolated by pu-
Next, the luminescence of these compounds in hexane solution
has been investigated. Compound 1 exhibited very weak fluores-
cence when excited at 266 nm (
analog) exhibited fluorescence at 286 nm (F
F
F
: < 0.01), while 9 (its carbon
: 0.08). Compound 1 in
rification with a GPC column (eluent: CHCl
of the crude product because the separation of cyclized and non-
cyclized products was difficult with SiO or Al column. These
3
) or by recrystallization
F
hexane showed a lower fluorescence quantum yield than did its
carbon analog. Similar to the UV absorption behavior, the fluores-
cence wavelength of 2 was close to that of 3, whereas the fluores-
cence maximum of 4 was shifted to a longer wave-length and
2
2 3
O
pure compounds were stable under air in the solid state and could
be stored without special precautions.
The optical properties of compounds 1e9 were investigated by
UVevis absorption, fluorescence, and phosphorescence spectros-
copies. The UVevis and fluorescence spectral data are listed in
Table 3. Compound 1, the simplest 9,9,10,10-tetramethyl-9,10-
dihydro-9,10-disilaanthracene congener, exhibited UV absorption
at 266 nm, 271 nm, and 277 nm (shoulder peak). The carbon analog,
higher quantum yield (
the aromatic ring dramatically reduced the fluorescence quantum
yield (5 and 6,
: ꢀ 0.01). Compound 7 showed red-shifted fluo-
rescence in high quantum yield due to its expanded -conjugation
em: 344 nm, : 0.09). The 9,9,10,10-tetramethyl-9,10-dihydro-
9,10-disilaanthracenes showed larger Stokes shifts than did
9,9,10,10-tetramethyl-9,10-dihydroanthracene (9), indicating that
their conformational changes from the ground state to the
F
F : 0.13). Electron-withdrawing groups on
F
F
p
(l
F
F
9
,9,10,10-tetramethyl-9,10-dihydroanthracene (9), exhibited ab-
sorption at similar wavelengths (256 nm, 263 nm, and 271 nm). The

T. Nakashima et al. / Journal of Organometallic Chemistry 805 (2016) 27e33
29
Table 2
Chemical structures of silicon-containing six-membered-ring molecules 1e8 synthesized by the coupling of 1,2-bis(dimethylsilyl)arenes (blue) and 1,2-diiodoarenes (red).a
a
2 2 6 4 2 2
Reaction conditions: Pd(P(t-Bu) (4-Me NC H )) (0.025 mmol), 1,2-bis(dimethylsilyl)arene (0.75 mmol), 1,2-diiodoarene (0.50 mmol), (i-Pr) EtN (3.0 mmol),
1
,2-dichloroethane (1.0 mL), rt., 1 d.
b
GC yield with dodecane as an internal standard.
c
1
H NMR yield by the comparison with methyl proton integrals at
d 0.56 vs 0.68 and 0.88.
Table 3
a
Optical properties of compounds 1e9 in hexane.
abs (nm)b
ε (dm mol cm
3
ꢂ1
ꢂ1
)
lex (nm)
l
em (nm)c
Stokes shift (cm
ꢂ1
)
F
d
t
F
(ns)e
Compound
l
F
1
2
3
4
5
6
7
8
9
266, 271, 277
265, 272
265, 272
286, 292
270, 277
286, 292
267, 275, 284, 297
289
486, 483, 273
502, 532
526, 575
3015, 2863
776, 674
1506, 1480
4327, 4770, 4272, 2279
336
489, 690, 598
266
272
272
286
270
286
275
289
263
-f
-f
-f
-g
g
314
303
317
312
341
344
354
286
4920
3760
3420
4990
5640
7290
6350
3060
<0.01
<0.01
0.13
<0.01
0.01
0.09
<0.01
0.07
-
-
g
1.0
g
-
0.3
36
g
-
-
h
256, 263, 271
a
All measurements were carried out at rt. Underlined values are wavelengths which have highest peak intensity.
Maximum absorption wavelength.
Maximum fluorescence wavelength excited at l .
ex
Absolute fluorescent quantum yield measured with an integrating sphere.
Fluorescence lifetime measured by photoexcitation at 280 nm.
Emission wavelength, Stokes shift, and quantum yield could not be determined accurately due to the weak fluorescence.
Fluorescence lifetime could not be determined accurately due to the weak fluorescence.
Fluorescence lifetime could not be determined accurately due to the small Stokes shift.
b
c
d
e
f
g
h
fluorescing state are larger than that of the carbon analog. Com-
pound 8 showed a fluorescence maximum red-shifted to 354 nm
compared with 1 under excitation at 289 nm.
heavier group-14 atoms is expected to increase the phosphores-
cence of the chromophore compared with the carbon chromophore
[9]. The phosphorescence spectra and photophysical data are
shown in the supplementary data and in Table 5, respectively.
These compounds, with the exception of 7, showed long-lived
phosphorescence with emission bands in the region of
400e460 nm in frozen 2-methyltetrahydrofuran at 77 K with
quantum efficiencies of 0.01e0.06. For comparison, compound 9,
which contained no atoms heavier than carbon, showed very weak
phosphorescence. The presence of electron deficient groups caused
a significant bathochromic shift (ca. 50 nm) of the emission
maximum. The decay lifetimes of these phosphorescence ranged
from 50 to 100 ms, close to previously reported triplet lifetimes of
Solid-state optical properties were also investigated (Table 4).
Fluorescence in the solid state was different from that in solution;
for example, the emission spectra were broadened. All compounds
showed small changes in the peak top of fluorescence wavelength.
Especially, quantum yield of 7 in the solid state were higher than
those in solution. The enhanced quantum yield may have been due
to the suppression of non-radiative relaxation channels by the rigid
structure in the solid state.
We also investigated the effects of structure on the phospho-
rescence of the 9,10-dihydro-9,10-disilaanthracenes. Introducing

30
T. Nakashima et al. / Journal of Organometallic Chemistry 805 (2016) 27e33
Table 4
molecules 6A and 6B in the crystal. The SieC distances in this
a
Optical properties of compounds 1e9 in the solid state.
molecule (1.859e1.886 Å) were in reasonable agreement with
published X-ray value for SieC distance (1.88 Å) [12]. Although the
crystal structure of 1 was reported as single form in crystal with
em (nm)b
F
F
c
Compound
l
ex (nm)
l
1
2
3
4
5
6
7
8
9
295
280
276
286
279
298
323
290
270
351, 359
305
0.06
<0.01
0.12
ꢁ
155 of the dihedral angle between the benzene ring planes, the
ꢁ
305
crystal structure of 6A has increased the dihedral angle (164.1 )
321, 348
304
0.09
while that of 6B has decreased made by the outer benzene rings
<0.01
<0.01
0.27
0.01
0.10
ꢁ
(
143.2 ) [13]. The ladder compound 8 also yielded crystals suitable
326
359
346
290
for X-ray analysis (Fig. 2). X-ray analysis revealed that this com-
pound crystallized in syn connectivity with four molecules in the
unit cell. Conspicuously, one 9,10-dihydro-9,10-disilaanthracence
a
group are less twisted from planarity (dihedral angle: 173.2 )
ꢁ
All measurements were carried out at rt.
Maximum fluorescence wavelength excited at
Absolute fluorescent quantum yield measured with an integrating sphere.
b
c
ꢁ
l
ex
.
compared to those on the opposite side (dihedral angle: 157.7 ). In
both cases, there was no
p-p stacking in crystal structure to sup-
press the intermolecular interaction. The variations in dihedral
angle may result from a balance between pseudoaxial and pseu-
doequatorial methyl substituents in crystal packing.
Table 5
Phosphorescence of 1e9.
a
Density functional theory (DFT) calculations were performed to
explore the effect of silicon atom binding. Molecular orbitals and
their energy levels calculated by DFT are summarized in Fig. S40.
We initially compared the result of compounds 1 and 9, whose
calculated structures of the bent and planar frameworks were in
good agreement with the X-ray analysis [14,15]. The calculations
indicated that the introduction of silicon atoms had little effect on
c
t
p
(ms)d
Compound
l
ex (nm)
l
em (nm)
F
P
1
2
3
4
5
6
7
8
9
266
272
272
286
270
286
275
284
263
405
406
406
419
406
455
0.05
0.03
0.02
0.03
0.03
0.06
55
53
101
56
57
44
b
b
b
-
-
-
the HOMO, but lowered the LUMO energy level owing to the
interaction between the silyl group and the -electron system. This
explains the HOMO-LUMO gap of the structurally modified
,9,10,10-tetramethyl-9,10-dihydroanthracene well, because an
extended -electron system usually has a lower HOMO-LUMO gap.
s*-p*
408, 421
0.01
47
p
b
b
b
-
-
-
a
Phosphorescence was measured at 77 K in degassed 2-methyltetrahydrofuran.
These values could not be determined accurately due to very weak
9
b
p
phosphorescence.
c
The HOMO orbital of each compound is mainly concentrated on
the electron-rich aromatic ring, whereas the LUMO orbital is
located over the whole molecule through the silicon atom with the
exception of 6. The orbital energies of both HOMO and LUMO in-
crease relative to those of 1 upon the introduction of an electron-
rich functional group. The HOMO-LUMO gap of 4 is slightly lower
than that of 2 and 3, which is attributed to the red-shift of 4. The
introduction of a fluorine atom (5) and ester groups (6) on the
benzene ring lowered the LUMO energy level. The 5,12-dihydro-
The phosphorescence quantum yields were determined relative to that of
benzophenone (
F
p
¼ 0.88 in EtOH at 77 K) as a reference. [10,11].
d
ex
Phosphorescence lifetime measured by photoexcitation at l .
organosilicon compounds [10].
The crystal structure of 6 and 8 were determined by X-ray
diffraction studies. Cell dimensions, data collection and refinement
parameters, and selected bond lengths and angles for 6A and 6B are
listed in Tables S1eS2, and those for 8 are in Tables S3eS4. As
described in Fig. 1, the structure shows six-membered ring with a
boat conformation and the unit cell of 6 contains two independent
5,12-disilanaphthacene
and
5,7,12,14-tetrahydro-5,7,12,14-
tetrasilapentacene linkages (7 and 8) were responsible for smaller
HOMO-LUMO gaps than those in compounds with 9,10-dihydro-
Fig. 1. (a) ORTEP drawing of alternating independent 6A and 6B units in the crystal structure of 6. Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms are
omitted for clarity. (b) Dihedral angle of 6A. (c) Dihedral angle of 6B.

T. Nakashima et al. / Journal of Organometallic Chemistry 805 (2016) 27e33
31
Fig. 2. (a) ORTEP drawing of crystal structure of 8. Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted for clarity. (b) Dihedral angle of 8.
2
2
9
,10-disilaanthracene linkages (1e6) due to the expanded
p
-
F
s
¼
F
r
ꢃ (I
s
/I
r
) ꢃ (A
r
/A
s
) ꢃ (n
s r
/n )
conjugation. Orbitals of 6 reveal that the electron density is
distributed over the ester moiety with little hyperconjugation. The
introduction of the ester groups significantly decreases the energy
level of the
orbital to interact with the
where I is the integrated area of the phosphorescence spectrum, A
is the absorbance at the same excitation wavelength, and n is the
refractive index of the solvent used. Subscripts s and r donate the
sample and reference, respectively [14,15]. Fluorescence and
phosphorescence lifetimes were measured by Hamamatsu C11367
apparatus.
p
* orbital of the aromatic ring. The inability of this
* orbitals of the SieC bonds leads to
s
electrons to be localized on the electron-withdrawing aromatic
group.
3
. Conclusion
4.2. Materials
We investigated the synthesis and optical properties of a series
All reagents were commercially available and used without any
purification. Solvents were distilled and dried by standard methods
for the synthesis. Dimethyl 4,5-diiodo-1,2-benzenedicarboxylate
[16], 1,2,4,5-tetrakis(dimethylsilyl)benzene [17], 1,2-diiodo-4,5-
dimethylbenzene [18] and 1,2-diiodo-4,5-dimethoxybenzene [18]
were prepared according to previously described procedures. 1,2-
Dimethyl-4,5-bis(dimethylsilyl)benzene and 1,2-dimethoxy-4,5-
bis(dimethylsilyl)benzene were synthesized by modified methods
based on the literature [19].
of
9,9,10,10-tetramethyl-9,10-dihydro-9,10-disilaanthracene.
*e * conjugated
Hyperconjugation led to the expansion of the
s
p
system especially in the excited state, causing these compounds to
display both fluorescent and phosphorescent emissions in the vi-
olet to blue region. The proposed method of forming molecules
with six-membered-rings containing silicon might be applicable to
the synthesis of other kinds of silicon-containing-ring molecules.
Moreover, this research can contribute to the development of blue
light-emitting devices using their phosphorescent properties.
4.3. X-ray crystallographic analysis
4
. Experimental section
Synchrotron radiation X-ray diffraction data of 6 were collected
4.1. General considerations
at 100 K. The diffractions were recorded on a CCD detector at
SPring-8 beam line BL02B1 (Hyogo, Japan). The total number of
ꢁ
All melting points were measured with a Yanaco Micro Melting
observed reflections was 66987 (2
q
< 20.135 ; d > 0.60 Å). The
Point apparatus and uncorrected. NMR spectra were measured
with a JEOL AL-400 spectrometer or a Bruker DRX-500 spectrom-
eter and referenced to an internal standard of tetramethylsilane
number of unique reflections was 9368. The structure was solved
by direct methods using SIR-2004 and was refined by the full-
matrix least-squares techniques against F implementing SHELXL-
2
1
13
(
0.00 ppm) for H NMR and CDCl
3
(77.0 ppm) for C NMR. GCeMS
2013.
spectra were recorded with a Shimadzu GC-MS-QP2010 spec-
trometer. Purification by preparative HPLC was carried out by using
Japan Analytical Industry LC-908 apparatus with GPC or ODS col-
umns. HRMS was performed on a double-focusing sector mass
spectrometer in FAB mode with a JEOL JMS 700P FAB MS. UVevis
absorption spectra were measured with a UV JASCO V-570 spec-
trometer. Fluorescence spectra were measured with a Hitachi F-
X-ray diffraction data of 8 were collected at 113 K with an
AFC10 diffractometer coupled with a Rigaku Saturn CCD system
equipped with
graphite-monochromated MoK
a
rotating-anode X-ray generator producing
radiation. Lorentz-polarization
a
and empirical absorption corrections were performed with the
program Crystal Clear 1.3.6. The structures were solved by the
direct method using SIR-92 program and refined by the full-
2
4
500 spectrometer. Fluorescent quantum yields were recorded
matrix least-squares techniques against
SHELXL-97.
F
implementing
with a Hamamatsu C9920-02 with an integrating sphere. Low-
temperature phosphorescence measurements were performed by
cooling a solution of the materials in 2-methyltetrahydrofuran to
CCDC numbers 1411405 and 1444280 contain the supplemen-
tary crystallographic data for compound 6 and 8, respectively.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
7
7 K. Phosphorescent quantum yields were determined by optically
dilute measurements with benzophenone in EtOH (quantum yield
of
¼ 0.88 at 77 K) as the reference:
F
p

32
T. Nakashima et al. / Journal of Organometallic Chemistry 805 (2016) 27e33
4
.4. Computational methods
7.43e7.41 (m, 2H), 7.36 (dd,1H, J ¼ 2.7, 9.3 Hz), 7.10 (ddd, 2H, J ¼ 2.5,
13
8
.2, 9.5 Hz), 0.47 (d, 12H, J ¼ 5.7 Hz). C NMR (125 MHz, CDCl
3
)
All calculations were performed at the B3LYP/6-31G* level to
d
163.2 (C , J ¼ 3.7 Hz), 144.3 (C ), 143.8 (C
q
, J ¼ 251.1 Hz), 148.0 (C
q
q
q
),
extract theoretical electronic properties and correlated with
experimental trends.
139.8 (C
q
, J ¼ 3.7 Hz), 135.6 (CH, J ¼ 6.4 Hz), 133.4 (CH, J ¼ 2.8 Hz),
128.4 (CH, J ¼ 10.1 Hz), 119.8 (CH, J ¼ 17.4 Hz), 115.6 (CH,
þ
J ¼ 19.3 Hz), 0.13 (CH
3
), ꢂ0.16 (CH
3
). EI-MS m/z 286 (M ). HRMS
Calcd for C15
þ
4
9
.5. Typical experimental procedure for the preparation of
,9,10,10-tetramethyl-9,10-dihydro-9,10-disilaanthracene by
(FAB) m/z: [MꢂCH
3
]
16 2 2
H F Si 271.0775; found
271.0774.
coupling of 1,2-bis(dimethylsilyl)arene and 1,2-diiodoarene
Dimethyl
9,9,10,10-tetramethyl-9,10-dihydro-9,10-
disilanthracene-2,3-dicarboxylate (6). GC yield: 25%. Isolated
1
,2-Diiodoarene, 1,2-bis(dimethylsilyl)arene (1.5 equiv), and
N,N-diisopropylethylamine (6.0 equiv) were added to a solution of
Pd(P(t-Bu) (4-Me NC )) (0.05 equiv) in 1,2-dichloroethane
0.5 M). The reaction progress was monitored by GC or TLC. After
yield of analytically pure compound: 7%. Colorless solid. Mp:
ꢁ
1
91.5e92.7 C. Eluent for TLC: hexane. H NMR (500 Hz, CDCl
3
) d 7.99
2
2
6 4 2
H
(s, 2H), 7.69 (dd, 2H, J ¼ 3.3, 5.5 Hz), 7.44 (dd, 2H, J ¼ 3.2, 5.7 Hz),
1
3
(
3.93 (s, 6H), 0.50 (s, 12H). C NMR (125 MHz, CDCl
149.2 (C ), 143.4 (C ), 133.5 (CH), 133.0 (CH), 130.9 (C
), ꢂ0.26 (CH
3
)
d
168.5 (C]O),
), 128.7 (CH),
). EI-MS m/z 284 (M ). HRMS (FAB) m/z:
Si 385.1293; found 385.1269.
the atarting material was consumed at room temperature (1 d), the
reaction mixture was quenched with water. The aqueous layer was
extracted with dichloromethane three times and dried over sodium
sulfate. The combined organic layer was analyzed by GC to estimate
the yield of product with dodecane as an internal standard. The
solvent was removed under reduced pressure and purified roughly
by flash column chromatography over silica gel. In the case of 7, the
yield was estimated by H NMR analysis at this stage. The methyl
proton integrals at
separately and used to determine the ratio of cyclized and non-
cyclized products. Analytical pure products were isolated by the
purification of crude products with GPC (eluent: CHCl
q
q
q
þ
52.7 (CH
3
3
þ
[MþH] Calcd for C20
H
25
O
4
2
5,5,12,12-Tetramethyl-5,12-dihydro-5,12-disilanaphthacene (7).
NMR yield: 39%. Isolated yield of analytically pure compound: 12%.
ꢁ
1
Colorless solid. Eluent for TLC: hexane. Mp: 131.5e132.5 C. H NMR
(500 MHz, CDCl
8.17 (s, 2H), 7.86 (dd, 2H, J ¼ 3.2, 6.1 Hz), 7.73
(dd, 2H, J ¼ 3.2, 5.4 Hz), 7.51 (dd, 2H, J ¼ 3.3, 6.2 Hz), 7.44 (dd, 2H,
3
) d
1
1
3
d
0.56 vs 0.68 and 0.88 ppm can be measured
J ¼ 3.2, 5.6 Hz), 0.56 (s, 2H). C NMR (125 MHz, CDCl
140.5 (C ), 133.7 (CH), 133.4 (CH), 132.9 (C ), 128.4 (CH), 127.8 (CH),
126.5 (CH), 0.2 (CH
Calcd for C20 318.1260; found 318.1239.
5,5,7,7,12,12,14,14-octamethyl-5,7,12,14-tetrahydro-5,7,12,14-
3 q
) d 144.7 (C ),
q
q
þ þ
). EI-MS m/z 318 (M ). HRMS (FAB) m/z: M
3
3
) and/or
H22Si
2
recrystallization from methanol.
9
,9,10,10-Tetramethyl-9,10-dihydro-9,10-disilaanthracene
(1)
tetrasilapentacene (8). GC yield: 15%. Isolated yield of analytically
[
4a-c]. GC yield: 43%. Isolated yield of analytically pure compound:
pure compound: 4%. Colorless solid. Eluent for TLC: hexane. Mp:
1
ꢁ
1
2
9%. Colorless solid. Eluent for TLC: hexane. H NMR (500 MHz,
CDCl
7.69 (dd, 4H, J ¼ 3.3, 5.5 Hz), 7.42 (dd, 4H, J ¼ 3.3, 5.5 Hz),
.48 (s, 12H). C NMR (125 MHz, CDCl
202.0e205.0 C. H NMR (500 MHz, CDCl
4H, J ¼ 3.4, 5.4 Hz), 7.42 (dd, 4H, J ¼ 3.2, 5.4 Hz), 0.51 (s, 24H).
NMR (125 MHz, CDCl 144.4 (C ), 144.0 (C ), 137.7 (CH), 133.3
). EI-MS m/z 458 (M ). HRMS (FAB) m/z:
458.1738; found 458.1743.
3
) d 7.96 (s, 2H), 7.69 (dd,
13
3
)
d
C
13
0
3
)
d
144.5 (C
q
), 133.4 (CH),
3
)
d
q
q
þ
þ
1
28.3 (CH), 0.0 (CH
,9,9,10,10-Pentamethyl-9,10-dihydro-9,10-disilaanthracene (2).
GC yield: 27%. Isolated yield of analytically pure compound: 12%.
3
). EI-MS m/z 268 (M ).
(CH), 128.3 (CH), 0.0 (CH
3
þ
2
M
Calcd for C26
H34Si
4
ꢁ
1
Colorless solid. Eluent for TLC: hexane. Mp: 69.0e70.0 C. H NMR
500 MHz, CDCl
7.68 (dd, 2H, J ¼ 3.2, 5.4 Hz), 7.59 (d, 1H,
J ¼ 7.4 Hz), 7.50 (s, 1H), 7.41 (dd, 2H, J ¼ 3.3, 5.5 Hz), 7.25 (d, 1H,
Acknowledgments
(
3
) d
The work was financially supported by CREST from JST, Tokyo
Kasei Chemical Promotion foundation, and Grant-in-Aids for Sci-
entific Research (C) (No. 15K05604), Scientific Research on Inno-
vative Areas “Molecular Architectonics: Orchestration of Single
Molecules for Novel Functions” (area 2509, Nos. 26110505 and
26110506) from the Ministry of Education, Culture, Sports, Science,
and Technology, Japan. The synchrotron radiation experiments
were performed at the SPring-8 with the approval of the Japan
Synchrotron Radiation Research Institute (JASRI) (Proposal No.
2015A1367).
13
J ¼ 7.4 Hz), 2.39 (s, 3H), 0.47 (s, 6H), 0.46 (s, 6H). C NMR (125 MHz,
CDCl 144.7 (C ), 144.6 (C ), 144.4 (C ), 140.7 (C ), 137.9 (C ), 134.1
CH), 133.5 (CH), 133.3 (CH), 129.3 (CH), 128.2 (CH), 21.6 (CH
3
)
d
q
q
q
q
q
(
(
3
), 0.13
þ
þ
CH
3
), 0.06 (CH
3
). EI-MS m/z 282 (M ). HRMS (FAB) m/z [MꢂCH
267.1025; found 267.1020.
,3,9,9,10,10-Hexamethyl-9,10-dihydro-9,10-disilaanthracene
3). GC yield: 23%. Isolated yield of analytically pure compound:
3
]
Calcd for C16H19Si
2
2
(
1
ꢁ
1
1%. Colorless solid. Eluent for TLC: hexane. Mp: 112.0e113.2 C. H
NMR (400 MHz, CDCl
7
(
1
3
)
d
7.67 (dd, 2H, J ¼ 3.3, 5.5 Hz), 7.44 (s, 2H),
13
.40 (dd, 2H, J ¼ 3.2, 5.4 Hz), 2.31 (s, 6H), 0.45 (s, 12H). C NMR
100 MHz, CDCl 144.8 (C ), 141.5 (C ), 136.9 (C ), 134.9 (CH),
33.3 (CH), 128.2 (CH), 19.8 (CH ). FAB-MS m/z 297
297.1495;
3
)
d
q
q
q
Appendix A. Supplementary data
3
), 0.2 (CH
3
þ
þ
(
[MþH] ). HRMS (FAB) m/z: [MþH] Calcd for C18
H25Si
2
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.12.042.
found 297.1479.
,3-Dimethoxy-9,9,10,10-tetramethyl-9,10-dihydro-9,10-
2
disilaanthracene (4). GC yield: 37%. Isolated yield of analytically
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