2-Arylbenzo[: B] arsoles: An experimental and computational study on the relationship between structural and photophysical properties

Article abstract of DOI:10.1039/d0dt02669g

Benzo[b]arsole derivatives, being arsenic analogues of indole, were synthesized by utilizing a safely prepared arsenic precursor. The structural and photophysical properties of the obtained 2-arylbenzo[b]arsoles were experimentally and computationally studied in comparison with those of 1,2,5-triarylarsoles and 9-phenylarsafluorene. It was found that the emission color and/or quantum yield were significantly affected by substituents on the luminescent center and metal-coordination to the arsenic atom. This is the first study on the structure-property relationship of benzo[b]arsole derivatives. This journal is

Full text of DOI:10.1039/d0dt02669g

View Article Online
View Journal
Dalton
Transactions
An international journal of inorganic chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. Ishijima, S.
Tanaka, H. Imoto and K. Naka, Dalton Trans., 2020, DOI: 10.1039/D0DT02669G.
Volume 46
Number 10
14 March 2017
Pages 3073-3412
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
An international journal of inorganic chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
rsc.li/dalton
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
ISSN 0306-0012
COMMUNICATION
Douglas W. Stephen et al.
shall the Royal Society of Chemistry be held responsible for any errors
N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl,
and tellurenyl cations (XH+, X = S, Se, Te)
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
rsc.li/dalton

Please do not adjust margins
Page 1 of 10
Dalton Transactions
View Article Online
DOI: 10.1039/D0DT02669G
ARTICLE
2-Arylbenzo[b]arsoles: an experimental and computational study
on relationship between structure and photophysical properties
Kosuke Ishijima,a Susumu Tanaka,a Hiroaki Imoto,*a,b and Kensuke Naka*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
Benzo[b]arsoles derivatives, being arsenic analogues of indole, were synthesized by utilizing a safely prepared arsenic
precursor. The structural and photophysical properties of the obtained 2-arylbenzo[b]arsoles were experimentally and
computationally studied with comparing to 1,2,5-triarylarsoles and 9-phenylarsafluorene. It was found that emission color
and/or quantum yield were significantly affected by substituents on the luminescent center and metal-coordination to the
arsenic atom. This is the first study on structure-property relationships of benzo[b]arsole derivatives.
DOI: 10.1039/x0xx00000x
was synthesized for systematic study on benzo[b]heteroles
containing various elements in 14, 15, and 16 groups,6 chemical
modification of benzo[b]heteroles to control their
Introduction
Considerable efforts have been devoted to heteroatom-fused
π-systems for advanced organic optoelectronic devices.
Benzo[b]heterole, benzene ring-fused five-membered
heterocycle, is an important structural motif to incorporate
heteroatoms into hydrocarbon-based π-conjugation.1 Its optical
and electronic properties are highly affected by the heteroatom
that bridges styrene skeleton because of the simple π-system.
Therefore, various elements as well as substituents have been
examined to develop highly functional benzo[b]heteroles. In
particular, a series of pnictogen-substituted benzo[b]heteroles,
being indole analogues, have received a lot of attention due to
the intrinsic nature of pnictogen atoms such as reactivity,
coordination ability, etc.2-5 Photophysical properties of
benzo[b]phospholes have been studied by altering the
substituents around the π-conjugated backbone.2,3
Substituents at the 2- and/or 3-positions affect the emission
behaviors. Quaternization, oxidation, and coordination to the
phosphorus atom can drastically change the materials
properties. Heavier pnictogens such as antimony and bismuth
photophysical properties remained to be examined to date.
Functional organoarsenic chemistry is a recently emerging
field.7 Conventionally, organoarsenic compounds are
synthesized from volatile and toxic precursors such as arsenic
chlorides or hydrides; 1-phenyl-BzA was, in fact, prepared from
dichlorophenylarsine.6a,b Serious concern to the danger of the
precursors had prevented chemists from experimental studies
on organoarsenic chemistry. To overcome this challenge, we
have developed practical synthetic methods by using
cyclooligoarsines, which can be prepared from non-volatile
inorganic precursors.8 Reactive species such as radicals,9
electrophiles,10 and nucleophiles11 are generated via cleavage
of the As–As bonds, and subsequently, reactions with adequate
reagents can produce As–C bonds to obtain target
organoarsenic compounds. Diiodophenylarsine (PhAsI2) is a key
intermediate for construction of arsenic-bridged π-systems,
e.g., arsole10,12 and arsepin13 derivatives. A solution of PhAsI2 is
prepared only by addition of iodine (I2) to
hexaphenylhexaarsine (Scheme 1).10 Notably, the solution can
be used for the next reaction without isolation process because
it contains negligible by-products. We have elucidated nature
and function of arsenic-based π-systems by fully utilizing the
practical synthetic protocol: photophysical properties,
aromaticity, reactivity, etc.
4,5
are introduced into benzo[b]heterole skeleton as well.
Gabbai et al reported that the σ* orbital based on the antimony
atom of benzo[b]stibole can coordinate anions such as fluoride
and chloride ions, leading to colorimetric response.4 Rivard et al
developed red-phosphorescent benzo[b]bismole polymers and
examined their self-assembly behavior.5
However,
benzo[b]arsole (BzA) has been rarely investigated in contrast to
benzo[b]heteroles of other pnictogens. Although 1-phenyl-BzA
Ph
[M]
[M]
Ph
As
Ph
Ph
As
Ph
Ph
As
As
As
As
I2
1/6
PhAsI2
As
Ph
a. Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology,
Gashokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
b. Materials Innovation Lab, Kyoto Institute of Technology, Goshokaido-cho,
Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
Scheme 1. Synthetic protocol for arsenic-bridged compounds
from hexaphenylhexaarisne.
Electronic Supplementary Information (ESI) available: X-ray data, NMR spectra, and
results of computational calculations. For ESI and crystallographic data in CIF see
DOI: 10.1039/c000000x/Supplementary crystallographic data: CCDC 2005446 (4b),
2005444 (5a), and 2005445 (7a). These data can be obtained free of charge from
Herein, various substituents were introduced to 2-aryl-1-
phenyl-BzA backbone to tune the photophysical properties. The
photophysical properties were drastically changed by altering
The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 10
ARTICLE
Journal Name
substituents and coordination to gold(I) chloride. Furthermore, showed both the characteristics of 8 and 9. TheVCiew5–ArCti7clebOonlninde
DOI: 10.1039/D0DT02669G
since the chemical structure of 2-aryl-1-phenyl-BzA is a length of 5a (1.402(6) Å) and the C3–C4 bond length of 8
combination
of
2,5-diaryl-1-phenylarsole
and
9- (1.407(6) Å) had benzene ring character due to the benzo
phenylarsafluorene (Figure 1), their structures and electronic groups. On the other hand, the C3–C13 bond length of 5a
properties were compared.
(1.348(6) Å) and the C1–C2 bond length of 9 (1.346(8) Å) had
double bond character. The C3–C6 and C7–C13 bond of 5a were
approximately C–C single bond (1.484(5) and 1.457(5) Å,
respectively). These results indicate that 5a adopts As-bridged
stilbene structure. Notably, the bond alternation in the arsole
ring of 5a implies non-aromatic character.
Ph
As
Ph
R2
Ph
As
As
Ar
Ar
R1
2,5-Diaryl-1-phenylarsole
2-Aryl-1-phenylarsole
9-Phenylarsafluorene
Fig. 1 Structural feature of 2-aryl-1-phenylbenzo[b]arsole,
target motif in the present study.
Results and discussion
Synthesis of 2-aryl-1-phenyl-BzA 4-7 are summarized in
Scheme 2. (Z)-β-Bromo-β-trimethylsilylstyrene derivatives were
prepared according to literature procedure.6b After dilithiation
of the starting materials, addition of diiodophenylarsine gave 2-
trimethylsilyl-BzA derivatives 1a and 1b, which have hydride
and methoxy groups, respectively, at the 6-position. Initially, we
examined bromination of 1, but arsine oxides were included as
by-products, which made purification difficult. Thus, BzA
bromides 3 were synthesized by pre-oxidation and then
reduction without isolation. Because isolation of 3a failed even
through this protocol, the product was used for the next
reaction after roughly purified. Pd-catalyzed Suzuki-Miyaura
coupling reaction produced 2-aryl-1-phenyl-BzA 4-7.
Fig. 2 Single crystal X-ray analysis and selected bond lengths (Å)
of 5a, 8,14 and 9.12a
The aromaticity of the arsole rings were estimated for 4a, 8,
and 1,2,5-triphenylarsole (10) by nucleus-independent
chemical shift (NICS) value and bond alternation (Figure 3).15
The geometries were fully optimized by density functional
theory (DFT) calculations based on B3LYP/6-31G+(d,p).16 The
NICS(1)zz values, which were obtained by GIAO-B3LYP/6-
311G+(d,p), were 1.6 (4a), 3.0 (8), and -2.3 (10). Considering
that the calculated NICS(1)zz value of benzene was -29.1, the
arsole rings of 4a, 8, and 10 were non-aromatic. We estimated
the Wiberg bond indices (WBIs) of the arsole centers in 4a, 8,
and 10 by conducting natural bond orbital (NBO) analysis using
DFT calculations at the B3LYP/6-31G(d) level of theory.17 For 4a,
the benzo-fused C=C bond had benzene character (WBI = 1.32)
in reference to the result of benzene (WBI = 1.44), while the
other C-C bonds (WBI = 1.72 and 1.12) and As–C bonds (WBI =
0.90) showed clear bond alternation. The C=C bonds of 8 had
benzene character (WBI = 1.35), and the C–C and As–C bonds
(WBI = 1.07 and 1.35, respectively) were single bonds. Bond
alternation was observed for 10 (WBI = 0.91 (As–C), 1.68 (C=C),
1.17 (C–C)). The NBO analysis indicates that the arsole rings of
4a, 8, and 10 were lack of conjugation.
TMS
As
TMS
H2O2
THF
TMS
PhAsI2
n-BuLi
Et2O
R1
Br
Li
R1
R1
Li
R1 = H:
R1 = OMe:
(40%)
1b
R1 = H or OMe
1a
(38%)
O
((CH3)2SiH)2O
NBS
As
TMS
O
R1
As
As
MeCN
Br
Br
R1
R1
R1 = H:
R1 = OMe:
(quant)
2b
2a
R1 = H:
(not isolated)
(quant)
not isolated
3a
R1 = OMe:
(31%)
3b
R1 = H, R2 = H:
(20%)
4a
R2 = OMe:
(18%)
5a
R2-ArB(OH)2
R2 = CF3:
(21%)
6a
R2 = NMe2:
(25%)
R2
7a
Pd(OAc)2
P(bp)Cy2
K2CO3
As
R1
R1 = OMe, R2 = H:
(61%)
4b
R2 = OMe:
R2 = CF3:
R2 = NMe2:
(46%)
5b
6b
(38%)
7b
(44%)
Scheme 2. Synthesis of 2-aryl-1-phenylbenzo[b]arsoles 4-7. The
isolated yields of 4a-7a were from 2a.
Single crystals of 4b, 5a, and 7a were successfully fabricated
for X-ray diffraction analysis. Herein, the data of 5a are
compared to those of 9-phenylarsafluorene (8)14 and 2,5-di(p-
anisyl)-1-phenylarsole (9)12a as shown in Figure 2. The As–C
bond lengths in the arsole ring of 5a (1.948(5) and 1.956(4) Å)
were similar to those of 8 (1.946(4) and 1.945(4) Å) and 9
(1.942(5) and 1.949(6) Å). The C=C bonds in the arsole ring of 5a
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 10
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
Ph
As
0.90
0.90
Ph
As
Ph
As
The HOMO and LUMO levels were raised or lowered by p-
methoxy (5) or p-trifluoromethyl (6) groups, respectively, but
0.91
Ph
1.68
0.90
1.35
View Article Online
DOI: 10.1039/D0DT02669G
Ph
1.72
Ph
the effects of these substituents were relatively weak. On the
other hand, the dimethylamino group of 7 gave narrower
HOMO-LUMO transition energies (E = 376.65 nm (7a) and
383.29 nm (7b)) than those of 5 (E = 334.81 nm (5a) and 362.59
nm (5b)). Frontier orbitals depicted in Figure 4b imply that the
lone pairs of the nitrogen atoms contribute to expansion of the
π-conjugated systems, resulting in the narrow HOMO-LUMO
gap of 7.
1.44
1.12
1.07
1.17
1.32
4a
1.6
8
3.0
10
-2.3
Benzene
-29.1
NICS(1)zz
Fig. 3 Wiberg bond indices and NICS(1)zz values of the arsole
rings of 4a, 8, and 10, and benzene.
Photophysical properties of 4-7 were examined as shown in
Table 1. Initially, the UV-vis absorption spectra were measured
in CH2Cl2 (c = 1.0 × 10-5 mol/L). Comparing 4a-7a and 4b-7b,
electron-donating methoxy group at the 6-positions caused red-
shifted absorption maxima (λabs). Introduction of p-methoxy
(5a: 340 m, 5b: 351 nm) and p-trifluoromethyl (6a: 331 nm, 6b:
350 nm) groups of the phenyl group had slight or negligible
effects on the λabs values compared with those of 4a (330 nm)
and 4b (346 nm). On the other hand, p-dimethylamino group
caused significant red-shifted absorption spectra (7a: 373nm,
7b: 375 nm). This behavior corresponds to the report on 2-aryl-
1-phenyl-benzo[b]phosphole oxides.18
DFT and time-dependent DFT (TD-DFT) calculations were
conducted to understand the relationship between chemical
structure and λabs (Figure 4). The energy levels of the highest
occupied molecular orbitals (HOMOs) and the lowest
unoccupied molecular orbitals (LUMOs), energies for the
HOMO-LUMO transitions (E), and oscillator strengths (f) were
calculated by Gaussian09 based on B3LYP-6-31G+(d,p).
Comparing the results of 4a-7a and 4b-7b, the methoxy group
at the 6-position raised both the HOMO and LUMO levels. In
reference to the frontier orbitals of 4a, the HOMO is located at
the stilbene moiety, while the LUMO is delocalized in whole of
the π-plane including the exocylic As–C bond via the σ*-π*
conjugation. Thus the HOMO was more highly affected than the
LUMO, resulting in the red-shifted absorption spectra of 4b-7b.
Table 1. Photophysical properties of 4-7 in CH2Cl2 solutions (1.0 × 10-4 mol/L).
Fig. 4 (a) HOMO (blue) and LUMO (red) levels (eV) of 4-7.
Energies (E) and oscillator strengths (f) due to HOMO-LUMO
transitions are shown. (b) HOMOs and LUMOs of 4a and 7a
(isovalue = 0.02).
[a]
[c]
[d]
λabs
ε[b]
λex
λem
τ[f]
[ns]
Φ[e]
[nm]
330
340
331
373
346
351
350
375
[L·mol-1·cm-1]
[nm]
348
356
351
401
360
370
371
402
[nm]
404
404
393
459
413
419
423
458
11500
19900
19500
23400
15100
19300
19900
23800
< 0.01
0.24
2.4
0.8
1.1
2.7
1.5
1.6
1.9
2.9
4a
5a
6a
7a
4b
5b
6b
7b
Our next interest then shifted to photoluminescence (PL)
properties. We measured PL spectra in solutions and solid
states, and herein those in solutions are discussed (for the data
of the solid samples, please see supporting information). The
order of emission maxima (λem) of 4-7 well corresponded to that
of their λabss. That is, the methoxy group at the 6-position and
p-dimethylamino group of the phenyl group gave red-shifted
emission, while the p-methoxy and p-trifluoromethyl groups of
the phenyl group had little effects. In terms of quantum yield
(Φ), electron-donation groups were effective; p-methoxy and p-
dimethylamino groups of the phenyl group and methoxy group
at the 6-position drastically enhanced the Φ values. The
radiative rate constants were not affected by the substituents
as sumamrized in Table S6. Thus we focused on the non-
< 0.01
0.90
0.41
0.40
0.63
0.82
[a] Longest absorption maxima. [b] Molar extinction coefficients at the
absorption maxima. [c] Excitation maxima monitored at the emission maxima.
[d] Emission maxima excited at the excitation maxima. [e] Absolute quantum
yield. [f] Emission lifetimes monitored at the emission maxima.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 10
ARTICLE
Journal Name
radiative deactivation processes. Because the Φ values of 4a
and 6a were still low in the solid states (Table S5), aggregation
induced emission was not observed in the present case. To
understand these phenomena, the excited states of 4-7 were
evaluated by TD-DFT calculations based on the fully optimized
geometries in their S1 states (B3LYP/6-31G(d) for C, H, N, O, F
and SDD for As). The energy levels against the ground (S0) states
of the singlet (Sn) and triplet (Tn) excited states were listed in
Figures 5 and S38. The excited states of 4a, 4b, 5a, and 7a are
discussed here (for other compounds, see supporting
information). Upon photo-excitation, the molecules in the S0
states are excited to the S1 states via the HOMO-LUMO
transitions according to the results shown in Figure 4a. In the
case of 4a, intersystem crossing (ISC) from the S1 state to the T2
one likely to occur because of the low-lying T2 state; the energy
level of the T2 state (2.38 eV) was lower than that of the S1 state
(2.57 eV). On the other hand, for 4b, 5a, and 7a, which possess
electron-donating groups, the energy levels of the S1 states
were significantly lower than those of T2 states, and were much
higher than those of the T1 states. Accordingly, it is rational that
there are few chances for 4b, 5a, and 7a to cause ISC from the
S1 state to the Tn states. When ISC from the S1 state to the Tn
ones occurs, the excitons would be deactivated through
phosphorescence emission and/or non-radiative pathways. The
luminescent lifetime (τ) measurement supported the idea that
the emissions of 4-7 are attributed to fluorescence because
their lifetimes were nanosecond-order (τ < 2.9 ns). In addition,
the PL spectra of 4-7 showed only fluorescence even at 77 K
though the emission efficiencies were enhanced. We thus
concluded that the excitons of 4a in the S1 state was dominantly
converted to those in the Tn states, and were deactivated
through non-radiative pathways rather than phosphorescence
emission. On the other hand, the excitons of 4b, 5a, and 7a in
the S1 state were deactivated through fluorescence emission
with circumventing ISC to the Tn states. This is why the Φ of 4a
was remarkably lower than those of 4b, 5a, and 7a.
View Article Online
DOI: 10.1039/D0DT02669G
Fig. 5 Energy levels of (a) 4a, (b) 4b, (c) 5a, and (b) 7a in the
singlet (blue line) and triplet (red line) excitation states against
the ground states. The full geometries were optimized at the S1
states.
Notably, the quantum yields (Φ) of 7 were quite high (7a:
0.90, 7b: 0.82). Though the reason for the high efficiency is still
unclear, this phenomenon is observed in other arsole
derivatives; introduction of p-dimethylaminophenyl group into
dithienoarsole enhanced emission efficiency as well.19 During
the investigation of PL properties, it was found that 7 showed
solvatochromism; the emission wavelength was varied in
dependence on solvent polarity (7a: 443-485 nm, 7b: 453-477
nm). Lippert-Mataga-plots were depicted with the values of
Stokes shift against solvent polarizability (Δf) (Figure 6). The
linear correlation for 7 indicate that the emissions should be
ascribed to intramolecular charge transfer (ICT). The ICT was
from the electron-rich dimethylamino moiety to the electron-
deficient arsole moiety including σ*-π* conjugation around the
arsenic atom.
Fig. 6 Lippert-Mataga-plots for (a) 7a and (b) 7b (Δf = [(-
1)/(2+1)]–[(n2–1)/(2n2+1)]; : permittivity, n: refractive index).
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 10
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
For further tuning of photophysical properties, gold(I) was quite large (S1: 2.51 eV, T1: 0.88 eV), ISC from the S1 state
View Article Online
DOI: 10.1039/D0DT02669G
chloride (AuCl) complex of 4a (4a-AuCl) was synthesized and its was hard to occur, resulting in the efficient fluorescence.
absorption and PL spectra were measured in CH2Cl2 (Scheme 3). Considering these absorption and luminescent behaviors, we
There was negligible difference between 4a and 4a-AuCl in λabs assumed that 4a has intermediate photophysical properties
and λem; λabs = 330 nm (4a) and 338 nm (4a-AuCl), and λem = 404 between 8 and 10.
nm (4a) and 398 nm (4a-AuCl). DFT calculations revealed that
the coordination lowered both the HOMO and LUMO levels
through lowering the electron density of the luminophore. On
the other hand, the Φ of 4a-AuCl (0.26) was remarkably
improved from that of 4a (< 0.01). The excited states of 4a and
4a-AuCl were estimated by TD-DFT calculations (Figure S38).
For 4a-AuCl, the T2 state (3.26 eV) had higher energy levels than
the S1 state (2.93 eV), in contrast to 4a, which had low-lying T2
state as described above. As a result, the excitons of 4a-AuCl
could avoid the ISC to the Tn states followed by non-radiative
deactivation. These results means that the complexation with
AuCl induced emission-enhancement without changing the
emission color.
Fig. 7 (a) UV-vis absorption (in 2-MeTHF, c = 1.0 × 10-5 mol/L)
and (b) PL spectra (in 2-MeTHF, c = 1.0 × 10-4 mol/L) of 4a, 8,
and 10 measured at room temperature (solid lines) and 77 K
(broken lines).
ClAu
AuCl
As
As
4a
Conclusions
CH2Cl2
r.t.
2 h
4a
4a-AuCl
We have newly synthesized a series of 2-aryl-BzA derivatives,
and their structures and photophysical properties were
systematically studied with experimental and computational
methods. X-ray crystallography revealed that 4b had a structure
combining half of 8 and half of 9. The substituents on the 6-
position and phenyl group affected emission color and quantum
yield, which were rationally explained by DFT and TD-DFT
calculations. The chance for ISC is probably dependent on the
number of low-lying Tn states close to the S1 states, and non-
radiative deactivation from the Tn states diminished the
quantum yields. It was found that electron-donation
substituents such as methoxy and dimethylamino groups were
effective for avoiding the ISC, resulting in the relatively high
quantum yields. In particular, 7a and 7b, having dimethylamino
groups, exhibited not only quite high quantum yields, but also
luminescent solvatochromism due to the ICT. Furthermore,
coordination to AuCl caused emission enhancement without
changing luminescent color. It has been demonstrated that the
properties of 2-aryl-BzA can be widely tuned by the
substituents. The new class of arsenic-containing conjugated
systems will expand heteroatom-fused organic materials
chemistry.
(78%)


abs = 330 nm
em = 404 nm


abs = 338 nm
em = 398 nm
4a-AuCl
 < 0.01
 = 0.26
Scheme 3. Complexation of 4a with AuCl. The photophysical
data are shown; absorption (c = 1.0 × 10-4 mol/L) and PL (c = 1.0
× 10-5 mol/L) spectra were measured in CH2Cl2. Photographs of
4a and 4a-AuCl were taken under irradiation at 365 nm.
Finally, the photophysical properties of 4a were compared
with those of 810 and 1012a in 2-methyltetrahydrofuran (2-
MeTHF). The λabs of 4a (330 nm) was longer than 8 (281 nm) and
shorter than 10 (374 nm) according to the order of conjugation
length (Figure 7a). This corresponds to the results of DFT
calculation, which revealed that their HOMOs were located at
the stilbene (4a), biphenylene (8), and diphenylbutadiene (10)
moieties, and that the LUMOs were delocalized in whole of the
π-planes. The PL spectra of 4a, 8, and 10 measured at room
temperature and 77 K (Figure 7b) showed completely different
behaviors. Fluorescence (λem = 353 nm) and phosphorescence
(λem = 488 nm) were dominant for 8 at room temperature and
77 K, respectively. On the other hand, only fluorescence was
observed for 4a and 10 even at 77 K (λem = 402 nm and 458 nm,
respectively). In addition, the Φ of 10 was much higher than 4a
whther at room temperature or 77 K; Φ (at room temperature)
= 0.05 (4a) and 0.60 (10) and Φ (at 77 K) = 0.46 (4a) and 0.87
(10). For understanding of these differences, the excitated
states were estimated by TD-DFT calculations (Figure S38). The
energy level of the T2 state (3.51 eV) of 8 was lower than that of
the S1 state (3.68 eV). This is beneficial for ISC, and the rigid
fused-ring structure of 8 could freeze molecular motions to
realize phosphorescence, whereas the excitons of 4a in the
triplet excited states were deactivated through non-radiative
pathways. Because the energy gap of 10 between the S1 and T1
Experimental
Materials
1,1,3,3-Tetramethyldisiloxane
and
(2-biphenyl)-
dicyclohexylphosphine (CyJohnPhos) were purchased from
Sigma-Aldrich (Hattiesburg, Mississippi, US). Hexane, methanol
(MeOH), ethyl acetate (EtOAc), hydrogen peroxide (H2O2, 30%
aqueous solution), tetrahydrofuran (THF), sodium thiosulfate
pentahydrate (Na2S2O3), chloroform (CHCl3), dichloromethane
(CH2Cl2), acetonitrile (MeCN), and toluene were purchased from
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 10
ARTICLE
Journal Name
Nacalai Tesque (Kyoto, Japan). n-Butyllithium (n-BuLi, 1.6 M in energies and the electron transition energies employed
View Article Online
hexane), diethyl ether (Et2O, super dehydrated grade), iodine B3LYP/6-31G+(d,p) set combinations byDuOsIi:n1g0.1t0h3e9/GDa0uDsTs0i2a6n6ꢀ91G6
(I2), distilled water, magnesium sulfate (MgSO4), sodium program package.16 The NICS values were calculated at the
chloride (NaCl), sodium hydrogen carbonate (NaHCO3), N- GIAO-B3LYP/6-311G+(d,p) level of theory. The WBIs were
bromosuccinimide (NBS), MeCN (super dehydrated grade), calculated at the B3LYP/6-31G(d) level of theory. The Sn and Tn
CHCl3 (super dehydrated grade), (4-methoxyphenyl)boronic states were estimated by TD-DFT calculations at the B3LYP/6-
acid, and potassium carbonate (K2CO3) were purchased from 31G(d) for C, H, N, O and SDD for As.
Wako Pure Chemical Industry (Osaka, Japan). Phenyl boronic
acid, (4-trifluoromethyl)phenylboronic acid, and palladium(II)
Synthesis
1-Phenyl-2-trimethylsilylbenzo[b]arsole (1a). An Et2O solution
(80 mL) of (Z)-β-bromo-β-trimethylsilylstyrene (2.03 g, 7.97
acetate (Pd(OAc)2) were purchased from Tokyo Chemical
Industry
Co.,
Ltd.
(Tokyo,
Japan).
(4-
mmol) was cooled to 0 °C under N2 atmosphere. To the solution
was slowly added a hexane solution of n-BuLi (1.6 M, 11.0 mL,
17.6 mmol) with a syringe. The reaction mixture was stirred at
ambient temperature for 2 h to obtain solution A. An Et2O
solution (48 mL) of I2 (2.41 g, 9.51 mmol) was separately
prepared, and hexaphenylcyclohexaarsine (1.45 g, 1.59 mmol)
was dissolved in the solution under N2 atmosphere to obtain
solution B. Solution A was cooled to 0 °C, and solution B was
slowly added with a syringe. After stirring at ambient
temperature for 20 h, the reaction was quenched by addition of
distilled water, and the organic layer was extracted by Et2O. The
combined organic layers were dried over MgSO4, and after
filtration, the volatiles were removed in vacuo. The crude
product was purified by column chromatography on silica gel
(eluent: hexane). The solvents were removed in vacuo, and the
residue was subjected to recrystallization (the crude product
was dissolved in hot methanol, and the solution was cooled to -
18 °C) to obtain 1a as white powder (1.04 g, 3.19 mmol, 40%).
1H-NMR (CDCl3, 400 MHz): δ 7.66 (s, H), 7.63 (d, J = 7.6 Hz, H),
7.56 (d, J = 8.0 Hz, H), 7.36 (td, J = 7.6, 1.2 Hz, H), 7.24-7.16 (m,
dimethylamino)phenylboronic acid was purchased from Acros
Organics (Geel, Belgium). Hexaphenylcyclohexaarsine8b and (Z)-
β-bromo-β-trimethylsilylstyrene derivatives6b were prepared
according to literature procedures.
Measurement
1H (400 MHz), 13C (100 MHz), and 19F (376 MHz) nuclear
magnetic resonance (NMR) spectra were recorded on a Bruker
AVANCE III 400 NMR spectrometer. High resolution mass
spectra (HRMS) were obtained on
a JEOL JMS-SX102A
spectrometer. UV/Vis spectra were recorded on a JASCO
spectrophotometer V-670 KNN. Emission and excitation spectra
were obtained on an FP-8500 (JASCO) spectrometer and the
absolute PL quantum yields (Φ) were determined by using a
JASCO ILFC-847S; the quantum yield of quinine sulfate as
reference was 0.52, which is in agreement with the literature
value.20 Emission lifetimes were measured by using
a
Quantaurus-Tau (Hamamatsu Photonics, Shizuoka, Japan)
instrument.
X-ray crystallographic data for single crystalline products
The single crystal was mounted on a nylon loop. Intensity data 6H), 0.07 (s, 9H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ 156.7,
were collected at room temperature on a Rigaku XtaLAB mini 150.3, 149.3, 148.4, 137.7, 133.2, 130.4, 128.7, 128.5, 128.2,
with graphite-monochromated MoKα radiation. The readout 126.5, 124.7, -0.3 ppm. HR-FAB-MS (m/z): calculated for
was performed in the 0.073ꢀmm pixel mode. The data were C17H20SiAs [M+H]+; 327.0550, observed; 327.0556.
collected at room temperature to a maximum 2θ value of 55.0°.
6-Methoxy-1-phenyl-2-trimethylsilylbenzo[b]arsole (1b). An
Et2O solution (36 mL) of (Z)-β-bromo-β-trimethylsilyl(4-
Data were processed by Crystal Clear.21 An empirical absorption
correction22 was applied. The data were corrected for Lorentz
methoxy)styrene (1.02 g, 3.57 mmol) was cooled to 0 °C under
and polarization effects. The structure was solved by direct
N2 atmosphere. To the solution was slowly added a hexane
solution of n-BuLi (1.6 M, 4.90 mL, 7.84 mmol) with a syringe.
methods23 and expanded by using Fourier techniques. The non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
The reaction mixture was stirred at ambient temperature for 2
were refined by using the riding model. The final cycle of the
h to obtain solution A. An Et2O solution (20 mL) of I2 (1.08 g, 4.27
full-matrix least-squares refinement on F2 was based on
mmol)
was
separately
prepared,
and
observed reflections and variable parameters. All calculations
were performed by using the CrystalStructure23 crystallographic
software package except for the refinement, which was
performed by using SHELXL2013.24 Crystal data and more
information on the X-ray data collection are summarized in
TablesꢀS1-S4.
hexaphenylcyclohexaarsine (0.644 g, 0.706 mmol) was
dissolved in the solution under N2 atmosphere to obtain
solution B. Solution A was cooled to 0 °C, and solution B was
slowly added with a syringe. After stirring at ambient
temperature for 20 h, the reaction was quenched by addition of
distilled water, and the organic layer was extracted by Et2O. The
combined organic layers were dried over MgSO4, and after
filtration, the volatiles were removed in vacuo. The crude
product was purified by column chromatography on silica gel
(eluent: hexane). The solvents were removed in vacuo, and the
residue was subjected to recrystallization (the crude product
was dissolved in hot methanol, and the solution was cooled to -
18 °C) to obtain 1a as white powder (0.481 g, 1.35 mmol, 38%).
1H-NMR (CDCl3, 400 MHz): δ 7.59 (s, H), 7.46 (d, J = 8.4 Hz, H),
Computational detail
DFT calculations were carried out to investigate the frontier
orbitals and the NICS values. In addition, the HOMO–LUMO
transition energies (ΔE), their oscillator strengths (f), and the
energy levels of the singlet (Sn) and triplet (Tn) excited states
were estimated by TD-DFT calculations using the structures
optimized in the S1 states. The calculations of the frontier orbital
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 10
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
7.26-7.18 (m, 6H), 6.88 (dd, J = 8.4, 2.4 Hz, H), 3.78 (s, 3H), 0.05 2-Bromo-6-methoxy-1-phenylbenzo[b]arsole (3b). VNieBwSA(rt0ic.l4e 7O1nlinge,
(s, 9H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ 158.7, 153.0, 2,64 mmol) was added to a solution of 2DbO(I0:.1801.1003g9,/D2.01D7T0m26m6o9Gl)
152.4, 148.0, 142.5, 138.0, 133.2, 128.7, 128.5, 125.3, 115.6, in MeCN (20 mL). The resulting mixture was stirred at 40 °C for
114.3, 55.4, -0.3 ppm. HR-FAB-MS (m/z): calculated for 7.5 h and distilled water was then added. The reaction solution
C18H21OSiAs [M]+; 356.0578, observed; 356.0590.
was extracted with CH2Cl2 and the combined organic layers
were washed with an aqueous saturated solution of Na2S2O3.
The organic layer was dried over MgSO4 and the solvents were
removed in vacuo to obtain the yellow oil (0.939 g). The solution
of the residue in CHCl3 (40 mL) was added to a CHCl3 solution
(10 mL) of 1,1,3,3-tetramethyldisiloxane (1.53 g, 11.4 mmol).
After stirring at ambient temperature for 18 h, the solvents
were removed in vacuo. The crude product was purified by
column chromatography on silica gel (eluent: hexane). The
solvents were removed in vacuo, and the residue was subjected
to recrystallization (CH2Cl2/hexane) to obtain 3b as a pale yellow
solid (0.248 g, 0.683 mmol, 31%). 1H-NMR (CDCl3, 400 MHz): δ
7.42 (s, H), 7.39-7.27 (m, 6H), 7.12 (sd, J = 2.4 Hz, H), 6.85 (dd, J
= 8.4, 2.4 Hz, H), 3.79 (s, 3H) ppm. 13C{1H}-NMR (CDCl3, 100
MHz): δ 158.7, 149.4, 141.9, 140.0, 136.9, 132.5, 129.3, 129.0,
128.5, 124.7, 116.4, 114.2, 55.5 ppm. HR-FAB-MS (m/z):
calculated for C15H12O79BrAs [M]+; 361.9287, observed;
361.9297.
1-Phenyl-2-trimethylsilylbenzo[b]arsole oxide (2a).
A THF
solution (3.0 mL) of 1a (0.300 g, 0.920 mmol) was cooled to 0
°C. To the solution was added a THF solution (2.0 mL) of H2O2
(30% aq, 0.132 g, 1.16 mmol). After stirring at ambient
temperature for 24 h, the reaction was quenched by addition of
saturated aqueous solution of Na2S2O3, and the organic layer
were extracted by CHCl3. The combined organic layers were
dried over MgSO4, and after filtration, the volatiles were
removed in vacuo to obtain 2a as white powder (0.306 g, 0.894
mmol, 97%). 1H-NMR (CDCl3, 400 MHz): δ 7.71 (d, J = 7.2 Hz, H),
7.67-7.64 (m, 3H), 7.55-7.50 (m, 2H), 7.46-7.39 (m, 4H), 0.16 (s,
9H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ 150.5, 141.9, 141.7,
134.7, 132.6, 132.6, 132.1, 130.3, 130.1, 129.7, 129.3, 126.1, -
1.0 ppm. HR-FAB-MS (m/z): calculated for C17H20OSiAs [M+H]+;
343.0499, observed; 343.0506.
6-Methoxy-1-phenyl-2-trimethylsilylbenzo[b]arsole oxide (2b).
A THF solution (3.0 mL) of 1a (0.310 g, 0.869 mmol) was cooled
to 0 °C. To the solution was added a THF solution (2.0 mL) of
H2O2 (30% aq, 0.140 g, 1.24 mmol). After stirring at ambient
temperature for 21 h, the reaction was quenched by addition of
aqueous saturated solution of Na2S2O3, and the organic layer
was extracted by CHCl3. The combined organic layers were dried
over MgSO4, and after filtration, the volatiles were removed in
vacuo to obtain 2b as white powder (0.321 g, 0.862 mmol, 99%).
1H-NMR (CDCl3, 400 MHz): δ 7.66 (dd, J =8.2, 1.2 Hz, 2H), 7.62
(sd, J = 0.4 Hz, H), 7.52 (t, J = 7.2 Hz, H), 7.45 (t, J = 7.2 Hz, 2H),
7.35 (d, J = 8.4 Hz, H), 7.27 (s, H), 7.01 (dd, J = 8.2, 2.4 Hz, H),
3.80 (s, 3H), 0.15 (s, 9H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ
General procedure for the synthesis of 4-7. A mixture of 3 (1 eq),
arylboronic acid (2.3 eq), (2-biphenyl)-dicyclohexylphosphine
[CyJohnPhos] (0.20 eq), Pd(OAc)2 (0.10 eq), K2CO3 (3.3 eq) in
(MeCN,/toluene/H2O = 2/2/1, v/v/v) was heated at 90 °C for 2
h. The mixture was diluted with water, and the aqueous layer
was separated and the organic layer was then extracted with
CH2Cl2. The combined organic layers were washed with brine,
and dried over MgSO4. After condensation, the residue was
subjected to column chromatography on silica gel. The solvents
were removed in vacuo, and the residue was subjected to
recrystallization to obtain 4-7.
161.7, 150.5, 138.5, 136.7, 134.5, 132.7, 132.1, 130.1, 129.3, 1,2-Diphenylbenzo[b]arsole (4a). Crude product of 3a (0.279 g)
126.8, 118.3, 115.1, 55.7, -0.9 ppm. HR-FAB-MS (m/z): was prepared from NBS (0.871 g, 4.89 mmol), 2a (0.802 g, 2.34
calculated for C18H22O2SiAs [M+H]+; 373.0605, observed; mmol) and 1,1,3,3,-tetramethyldisiloxane (1.63 g, 12.1 mmol)
373.0615.
according to the above-mentioned procedure. Phenylboronic
acid (0.240 g, 1.97 mmol) was used as an arylboronic acid. The
crude product was purified by column chromatography on silica
gel (eluent: hexane) and recrystallization (CH2Cl2/methanol) to
obtain 4a as a colorless crystal (0.1545 g, 0.468 mmol, 20%). 1H-
NMR (CDCl3, 400 MHz): δ 7.66 (s, H), 7.62 (d, J = 7.2 Hz, H), 7.59-
7.55 (m, 3H), 7.38-7.29 (m, 5H), 7.25-7.16 (m, 5H) ppm. 13C{1H}-
NMR (CDCl3, 100 MHz): δ 154.2, 148.7, 146.9, 137.8, 137.7,
134.8, 132.7, 130.4, 128.8, 128.7, 128.5, 127.7, 127.0, 126.4,
124.9 ppm. HR-FAB-MS (m/z): calculated for C20H15As [M]+;
330.0390, observed; 330.0398.
2-Bromo-1-phenylbenzo[b]arsole (3a). NBS (2.1 eq) was added
to a solution of 2a (1.0 eq) in MeCN. The resulting mixture was
stirred at 40 °C for 20 h, and distilled water was then added. The
reaction solution was extracted with CH2Cl2 and the combined
organic layers were washed with an aqueous saturated solution
of Na2S2O3. The organic layer was dried over MgSO4 and the
solvents were removed in vacuo to obtain the yellow oil. The
solution of the residue in CHCl3 was added to a CHCl3 solution
of 1,1,3,3-tetramethyldisiloxane (4-6 eq). After stirring at
ambient temperature overnight, the solvents were removed in
vacuo. The crude product was purified by column 1,2-Diphenyl-6-methoxy-benzo[b]arsole (4b). Phenylboronic
chromatography on silica gel (eluent: hexane). The solvents acid (0.165 g, 1.35 mmol) and 3b (0.200 g, 0.601 mmol) were
were removed in vacuo to obtain 3a (crude) as a yellow oil. 1H- used. The crude product was purified by column
NMR (CDCl3, 400 MHz): δ 7.55 (d, J =7.2 Hz, H), 7.49 (s, H), 7.44 chromatography on silica gel (eluent: hexane) and
(d, J = 7.6 Hz, H), 7.37-7.27 (m, 6H), 7.23 (td, J = 7.4, 1.6 Hz, H) recrystallization (CH2Cl2/methanol) to obtain 4a as a colorless
1
ppm. HR-FAB-MS (m/z): calculated for C14H1079BrAs [M]+; crystal (0.133 g, 0.369 mmol, 61%). H-NMR (CDCl3, 400 MHz):
331.9182, observed; 331.9181.
δ 7.61 (s, H), 7.55-7.53 (m, 2H), 7.46 (d, J = 8.4 Hz, H), 7.39-7.36
(m, 2H), 7.29 (t, J = 7.2 Hz, 2H), 7.23-7.18 (m, 5H), 6.89 (dd, J =
8.4, 2.4 Hz, H), 3.81 (s, 3H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz):
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 8 of 10
ARTICLE
Journal Name
δ 158.7, 151.0, 148.9, 141.6, 138.1, 137.9, 134.4, 132.7, 128.8, (the product was dissolved in hot methanol, andVitehweArsticoleluOtniloinne
DOI: 10.1039/D0DT02669G
128.7, 128.7, 127.3, 126.7, 125.6, 116.0, 114.3, 55.5 ppm. HR- was cooled to -18 °C) to obtain 6b as a yellow crystal (0.0326 g,
1
FAB-MS (m/z): calculated for C21H17OAs [M]+; 360.0495, 0.0761 mmol, 27%). H-NMR (CDCl3, 400 MHz): δ 7.68 (s, H),
observed; 360.0497.
7.62-7.60 (m, 2H), 7.53-7.50 (m, 3H), 7.36-7.33 (m, 2H), 7.25-
7.19 (m, 4H), 6.91 (dd, J = 8.4, 2.8, H), 3.82 (s, 3H) ppm. 13C{1H}-
NMR (CDCl3, 100 MHz): δ 159.1, 149.5, 149.2, 141.4, 141.1,
137.4, 136.6, 132.7, 129.0, 129.0, 126.7, 126.2, 125.7, 125.6,
122.9, 116.1, 114.6, 55.5 ppm. 19F-NMR (CDCl3, 376 MHz): δ -
63.5 ppm. HR-FAB-MS (m/z): calculated for C22H16OF3As [M]+;
428.0369, observed; 428.0366.
2-(4-Methoxy)phenyl-1-phenylbenzo[b]arsole
(5a).
Crude
product of 3a (0.3410 g) was prepared from NBS (0.868 g, 4.88
mmol), 2a (0.805 g, 2.35 mmol) and 1,1,3,3,-
tetramethyldisiloxane (1.63 g, 12.1 mmol) according to the
above-mentioned procedure. (4-Methoxy)phenylboronic acid
(0.368 g, 2.42 mmol) was used as an arylboronic acid. The crude
product was purified by column chromatography on silica gel 2-(4-Dimethylamino)phenyl-1-phenylbenzo[b]arsole (7a). Crude
(eluent: hexane/toluene = 3/1 v/v.) and recrystallization product of 3a (0.237 g) was prepared from NBS (0.656 g, 3.68
(CH2Cl2/methanol) to obtain 5a as a colorless crystal (0.1533 g, mmol), 2a (0.601 g, 1.76 mmol) and 1,1,3,3,-
0.426 mmol, 18%). 1H-NMR (CDCl3, 400 MHz): δ 7.60 (d, J = 7.2 tetramethyldisiloxane (1.41 g, 10.5 mmol) according to the
Hz, H), 7.54-7.51 (m, 4H), 7.37-7.7.32 (m, 3H), 7.24-7.15 (m, 4H), above-mentioned procedure. (4-Dimethylamino)phenylboronic
6.85 (d, J = 9.2 Hz, 2H), 3.80 (s, 3H) ppm. 13C{1H}-NMR (CDCl3, acid (0.272 g, 1.65 mmol) was used as an arylboronic acid. The
100 MHz): δ 159.5, 153.7, 149.0, 146.5, 138.1, 132.9, 132.7, crude product was purified by column chromatography on silica
130.5, 130.4, 128.8, 128.7, 128.5, 128.2, 126.0, 124.6, 114.2, gel (eluent: CHCl3/hexane/TEA
= 10/20/1 v/v/v.) and
55.3 ppm. HR-FAB-MS (m/z): calculated for C21H17OAs [M]+; recrystallization (CH2Cl2/hexane/TEA) to obtain 7a as a yellow
1
360.0495, observed; 360.0497.
crystal (0.186 g, 0.498 mmol, 25%). H-NMR (CDCl3, 400 MHz):
δ 7.58 (d, J = 7.6 Hz, H), 7.51-7.47 (m, 4H), 7.39-7.36 (m, 2H),
7.31 (td, J = 7.6, 1.2 Hz, H), 7.22-7.11 (m, 4H), 6.70 (s, 2H), 2.97
(s, 6H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ 154.1, 150.1,
149.4, 146.2, 138.5, 132.7, 130.8, 130.3, 128.7, 128.5, 128.4,
128.0, 126.0, 125.5, 124.1, 112.4, 40.4 ppm. HR-FAB-MS (m/z):
calculated for C22H20NAs [M]+; 373.0812, observed; 373.0809.
6-Methoxy-2-(4-methoxy)phenyl-1-phenylbenzo[b]arsole (5b).
(4-Methoxy)phenylboronic acid (0.0998 g, 0.657 mmol) and 3b
(0.0995 g, 0.275 mmol) were used. The crude product was
purified by column chromatography on silica gel (eluent:
hexane/ethyl acetate
= 10/1 v/v.) and recrystallization
(CH2Cl2/hexane) to obtain 5b as a yellow crystal (0.0489 g, 0.125
1
mmol, 46%). H-NMR (CDCl3, 400 MHz): δ 7.49-7.47 (m, 3H), 6-Methoxy-2-(4-dimethylamino)phenyl-1-phenylbenzo[b]arsole
7.43 (d, J = 8.4 Hz, H), 7.37 (dd, J = 7.4, 1.6 Hz, 2H), 7.23-7.17 (m, (7b). (4-Dimethylamino)phenylboronic acid (0.378 g, 2.29
4H), 6.87 (dd, J = 8.4, 2.4 Hz, H), 3.80-3.79 (m, 6H) ppm. 13C{1H}- mmol) and 3b (0.3037 g, 0.839 mmol) were used. The crude
NMR (CDCl3, 100 MHz): δ 159.1, 158.4, 150.6, 148.5, 141.9, product was purified by column chromatography on silica gel
138.2, 132.7, 132.5, 130.7, 128.8, 128.7, 127.8, 125.1, 116.0, (eluent: CHCl3/hexane/TEA
=
10/10/1 v/v/v.) and
114.2, 114.1, 55.5, 55.3 ppm. HR-FAB-MS (m/z): calculated for recrystallization (CH2Cl2/hexane/TEA) to obtain 7b as a yellow
C22H19O2As [M]+; 390.0601, observed; 390.0600.
crystal (0.147 g, 0.364 mmol, 44%). H-NMR (CDCl3, 400 MHz):
δ 7.46-7.44 (m, 3H), 7.41-7.38 (m, 3H), 7.20-7.16 (m, 4H), 6.85
(dd, J = 8.4, 2.4 Hz, H), 6.65 (d, J = 8.4 Hz, 2H), 3.79 (s, 3H), 2.95
(s, 6H) ppm. 13C{1H}-NMR (CDCl3, 100 MHz): δ 158.0, 151.1,
149.8, 148.1, 142.4, 138.7, 132.7, 130.5, 128.8, 128.5, 127.7,
126.4, 124.7, 116.0, 114.2, 112.5, 55.5, 40.5 ppm. HR-FAB-MS
(m/z): calculated for C23H22ONAs [M]+; 403.0917, observed;
403.0918.
1
2-(4-Trifluoromethyl)phenyl-1-phenylbenzo[b]arsole
(6a).
Crude product of 3a (0.408 g) was prepared from NBS (0.8713
g, 4.90 mmol), 2a (0.8018 g, 2.34 mmol) and 1,1,3,3,-
tetramethyldisiloxane (1.57 g, 11.7 mmol) according to the
above-mentioned
procedure.
(4-
Trifluoromethyl)phenylboronic acid (0.535 g, 2.82 mmol) was
used as an arylboronic acid. The crude product was purified by
column chromatography on silica gel (eluent: hexane) and Gold(I) chloride complex of 4a (4a-AuCl). A CH2Cl2 solution (4.0
recrystallization (CH2Cl2/methanol) to obtain 6a as a colorless mL) of 4a (39.9 mg, 0.121 mmol) and AuCl (34.4 mg, 0.148
crystal (0.196 g, 0.492 mmol, 21%).1H-NMR (CDCl3, 400 MHz): δ mmol) was stirred for 2 h under N2 atmosphere at room
7.72 (s, H), 7.66-7.54 (m, 6H), 7.39 (td, J = 7.6, 1.2 Hz, H), 7.33- temperature. Insoluble impurities were removed by filtration,
7.31 (m, 2H), 7.24-7.17 (m, 4H) ppm. 13C{1H}-NMR (CDCl3, 100 and the volatiles were removed from the filtrate in vacuo. The
MHz): δ 152.7, 148.2, 147.2, 141.2, 137.1, 136.9, 132.7, 130.6, residue was subjected to recrystallization (CH2Cl2/hexane) to
129.0, 129.0, 128.7, 127.0, 127.0, 125.7, 125.7, 125.4, 122.8 obtain 4a-AuCl as white powder (53.0 mg, 0.0943 mmol, 78%).
ppm. 19F-NMR (CDCl3, 376 MHz): δ -63.6 ppm. HR-FAB-MS 1H-NMR (CDCl3, 400 MHz): δ 7.74 (s, H), 7.65-7.52 (m, 7H), 7.46
(m/z): calculated for C21H14F3As [M]+; 398.0264, observed; (tt, J = 7.2, 1.2 Hz, H), 7.41-7.30 (m, 6H) ppm; 13C{1H}-NMR
398.0273.
(CDCl3, 100 MHz): δ 145.2, 143.1, 136.2, 135.8, 133.6, 132.7,
132.0, 131.9, 130.6, 130.0, 129.9, 129.4, 129.3, 129.0, 127.0,
126.2 ppm.
6-Methoxy-2-(4-trifluoromethyl)phenyl-1-phenylbenzo[b]arsole
(6b). (4-Trifluoromethyl)phenylboronic acid (0.125 g, 0.659
mmol) and 3b (0.1030 g, 0.284 mmol) were used. The crude
product was purified by column chromatography on silica gel
(eluent: hexane/ethyl acetate = 10/1 v/v.) and recrystallization
Conflicts of interest
There are no conflicts to declare.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 10
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
Yumura and K. Naka, Org. Lett., 2018, 20, 5952; (Vei)ewHA. rItmicloe tOon,liAne.
Urushizaki, I. Kawashima and K. Naka,DCOhIe:m10..1-0E3u9r/.DJ.0,D2T001286,6293G,
8058; (f) A. Urushizaki, T. Yumura, Y. Kitagawa, Y. Hasegawa, H.
Imoto and K. Naka, Eur. J. Org. Chem., 2020, 2020, 3965.
13. I. Kawashima, H. Imoto, M. Ishida, H. Furuta, S. Yamamoto, M.
Mitsuishi, S. Tanaka, T. Fujii and K. Naka, Angew. Chem. Int. Ed.,
2019, 58, 11686.
Acknowledgements
This work was supported by JSPS KAKENHI, grant Number
19H04577 (Coordination Asymmetry) and 20H02812 (Grant-
in-Aid for Scientific Research (B)) to HI.
14. S. Tanaka, H. Imoto, T. Yumura and K. Naka, Organometallics,
2017, 36, 1684.
15. (a) Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta and P.
von R. Schleyer, Chem. Rev., 2005, 105, 3842; (b) H. F.-B.-
Shaidaei, C. S. Wannere, C. Corminboeuf, R. Puchta and P. von
R. Schleyer, Org. Lett., 2006, 8, 863.
Notes and references
1.
B. Wu and N. Yoshikai, Org. Biomol. Chem., 2016, 14, 5402.
For reviews, see: (a) R. A. Aitken, Sci. Synth., 2001, 10, 789; (b)
T. Baumgartner and R. Réau, Chem. Rev., 2006, 106, 4681; c) Y.
Matano and H. Imahori, Org. Biomol. Chem., 2009, 7, 1258; (d)
Y. Ren and T. Baumgartner, Dalton Trans., 2012, 41, 7792; (e)
T. Baumgartner, Acc. Chem. Res., 2014, 47, 1613; (f) M. P. Duffy,
W. Delaunay, P.-A. Bouit and M. Hissler, Chem. Soc. Rev., 2016,
45, 5296.
For recent papers on benzo[b]phosphole, see: a) N. M.-W. Wu,
H.-L. Wong and V. W.-W. Yam, Chem. Sci., 2017, 8, 1309; (b) V.
V. Khrizanforova, K. V. Kholin, M. N. Khrizanforov, M. K. Kadirov
and Y. H. Budnikova, New J. Chem., 2018, 42, 930; c) A.
Wakatsuki, M. Yukimoto, M. Minoura, K. Fujii, Y. Kimura and Y.
Matano, Dalton Trans., 2018, 47, 7123; (d) D. Ma, J. Pan, L. Yin,
P. Xu, Y. Gao, Y. Yin and Y. Zhao, Org. Lett., 2018, 20, 3455; (e)
N. M.-W. Wu, M. Ng and V. W.-W. Yam, Angew. Chem. Int. Ed.,
2019, 58, 3027; (f) L. Liu, J. Dong, Y. Yan, S.-F. Yin, L.-B. Han and
Y. Zhou, Chem. Commun., 2019, 55, 233; (g) N. M.-W. Wu and
V. W.-W. Yam, ACS Appl. Mater. Interfaces, 2019, 11, 40290; (h)
J. Guo, C. Mao, B. Deng, L. Ye, Y. Yin, Y. Gao and S. Tu, J. Org.
Chem., 2020, 85, 6359.
(a) Y. Miquel, A. Igau, B. Donnadieu, J.-P. Majoral, L. Dupuis, N.
Pirio and P. Meunier, Chem. Commun., 1997, 279; (b) H. J.
Breunig, M. E. Ghesner and E. Lork, Chem. Commun., 2003,
274; (c) N. Pirio, S. Bredeau, L. Dupuis, P. Schütz, B. Donnadieu,
A. Igau, J.-P. Majoral, J.-C. Guillemin and P. Meunier,
Tetrahedron, 2004, 60, 1317; (d) S. Bredeau, E. Ortega, G.
Delmas, P. Richard, R. Fröhlich, B. Donnadieu, G. Kehr, N. Pirio,
G. Erker and P. Meunier, Organometallics, 2009, 28, 181; (e) A.
M. Christianson, E. Rivard and F. P. Gabbaï, Organometallics,
2017, 36, 2670; (f) A. M. Christianson and F. P. Gabbaï,
Organometallics, 2017, 36, 3013.
2.
16. Gaussian 16, Revision C.01, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M.
Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts,
B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L.
Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J.
Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G.
Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J.
Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene,
C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma,
O. Farkas, J. B. Foresman, and D. J. Fox, Gaussian, Inc.,
Wallingford CT, 2016.
17. A. E. Reed, L. A. Curtiss and F. Weinhold, Chem. Rev., 1988, 88,
899.
18. Y. Matano, Y. Motegi, S. Kawatsu and Y. Kimura, J. Org. Chem.,
2015, 80, 5944.
19. H. Imoto, I. Kawashima, C. Yamazawa, S. Tanaka and K. Naka, J.
Mater. Chem. C, 2017, 5, 6697.
20. Fluorescence Measurements, Application to Bioscience,
Measurement Method, Seriesꢀ3; Spectroscopical Society of
Japan, Academic Publication Center.
3.
4.
21. CrystalClear: Data Collection and Processing Software, Rigaku
Corporation (1998–2014). Tokyo 196-8666, Japan.
22. SIR2011: M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.
L. Cascarano, C. Giacovazzo, M. Mallamo, A. Mazzone, G.
Polidori and R. Spagna, J. Appl. Crystallogr., 2012, 45, 357.
23. CrystalStructure 4.1: Crystal Structure Analysis Package, Rigaku
Corporation (2000–2014). Tokyo 196-8666, Japan.
5.
6.
S. M. Parke, E. Hupf, G. K. Matharu, I. de Aguiar, L. Xu, H. Yu, M.
P. Boone, G. L. C. de Souza, R. McDonald, M. J. Ferguson, G. He,
A.Brown and E. Rivard, Angew. Chem. Int. Ed., 2018, 57, 14841.
(a) J. Kurita, M. Ishii, S. Yasuike and T. Tsuchiya, J. Chem. Soc.,
Chem. Commun., 1993, 1309; (b) J. Kurita, M. Ishii, S. Yasuike
and T. Tsuchiya, Chem. Phar. Bull., 1994, 42, 1437; (c) A.
Muranaka, S. Yasuike, C.-Y. Liu, J. Kurita, N. Kakusawa, T.
Tsuchiya, M. Okuda, N. Kobayashi, Y. Matsumoto, K. Yoshida, D.
Hashizume and M. Uchiyama, J. Phys. Chem. A, 2009, 113, 464.
For reviews, see: (a) H. Imoto, Polym. J., 2018, 50, 837; (b) H.
Imoto and K. Naka, Chem. Eur. J., 2019, 25, 1883.
(a) J. W. B. Reesor and G. F. Wright, J. Org. Chem., 1957, 22,
382; (b) P. S. Elmes, S. Middleton and B. O. West, Aust. J. Chem.,
1970, 23, 1559.
(a) K. Naka, T. Umeyama and Y. Chujo, J. Am. Chem. Soc., 2002,
124, 6600; (b) A. Nakahashi, K. Naka and Y. Chujo,
Organometallics, 2007, 26, 1827.
24. SHELXL2013: G. M. Sheldrick, Acta Crystallogr. Sect. A,
2008, 64, 112.
7.
8.
9.
10. T. Kato, S. Tanaka and K. Naka, Chem. Lett., 2015, 44, 1476.
11. S. Tanaka, H. Imoto, T. Kato and K. Naka, Dalton Trans., 2016,
45, 7937.
12. (a) M. Ishidoshiro, Y. Matsumura, H. Imoto, Y. Irie, T. Kato, S.
Watase, K. Matsukawa, S. Inagi, I. Tomita and K. Naka, Org.
Lett., 2015, 17, 4854; (b) T. Kato, H. Imoto, S. Tanaka, M.
Ishidoshiro and K. Naka, Dalton Trans., 2016, 45, 11338; (c) Y.
Matsumura, M. Ishidoshiro, Y. Irie, H. Imoto, K. Naka, K. Tanaka,
S. Inagi and I. Tomita, Angew. Chem. Int. Ed., 2016, 55, 15040;
(d) H. Imoto, T. Fujii, S. Tanaka, S. Yamamoto, M. Mitsuishi, T.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Dalton Transactions
Page 10 of 10
Graphical Abstract
Dalton Transactions
View Article Online
DOI: 10.1039/D0DT02669G
2-Arylbenzo[b]arsoles: an experimental and computational study on relationship between
structure and photophysical properties
Kosuke Ishijima, Susumu Tanaka, Hiroaki Imoto* and Kensuke Naka*
Benzo[b]arsole, being an arsenic analogue of indole, is an unexplored class of heteroatom-fused
conjugated molecules. In this work, 2-arylbenzo[b]arsoles have been widely studied by
experimental and computational means. Their emission color and/or emission efficiency were
widely tuned by introduction of substituents and metal-coordination. This is the first study on
structure-photophysical property relationship of benzo[b]arsoles.
1