Multiple Fused Anthracenes as Helical Polycyclic Aromatic Hydrocarbon Motif for Chiroptical Performance Enhancement

Article abstract of DOI:10.1002/asia.202000394

Polycyclic aromatic hydrocarbons consisting of three fused anthracene units were designed as new π-conjugated compounds having helical structures. These expanded helicenes were synthesized by Pt-catalyzed cycloisomerization of the corresponding ethynyl-su

Full text of DOI:10.1002/asia.202000394

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Multiply fused anthracenes as helical polycyclic aromatic
hydrocarbon motif for chiroptical performance enhancement
Authors: Kei Fujise, Eiji Tsurumaki, Gaku Fukuhara, Nobuyuki Hara,
Yoshitane Imai, and Shinji Toyota
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.202000394
Link to VoR: https://doi.org/10.1002/asia.202000394
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
Multiply fused anthracenes as helical polycyclic aromatic
hydrocarbon motif for chiroptical performance enhancement
Kei Fujise,[a] Eiji Tsurumaki,[a] Gaku Fukuhara,[a,b] Nobuyuki Hara,[c] Yoshitane Imai,[c] Shinji Toyota*[a]
[a]
K. Fujise, Dr. E. Tsurumaki, Prof. Dr. G. Fukuhara, Prof. Dr. S. Toyota
Department of Chemistry, School of Science
Tokyo Institute of Technology
2–12–1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)
E-mail: stoyota@chem.titech.ac.jp
[b]
[c]
Prof. Dr. G. Fukuhara
JST, PRESTO
4–1–8 Honcho, Kawaguchi, Saitama, 332-0012 (Japan)
N. Hara, Prof. Dr. Y. Imai
Department of Applied Chemistry, Faculty of Science and Engineering
Kindai University
3–4–1 Kowakae, Higashi-Osaka, Osaka 577-8502 (Japan)
Supporting information and the ORCID identification numbers for the authors of this article can be found via a link at the end of the document.
Polycyclic aromatic hydrocarbons consisting of three fused
anthracene units were designed as new π-conjugated compounds
having helical structures. These expanded helicenes were
synthesized by Pt-catalyzed cycloisomerization of the corresponding
ethynyl-substituted precursors. The nonplanar and helical structure
was confirmed by X-ray analysis and DFT calculations, and the barrier
to helical inversion was estimated to be 34 kJ mol–1. The enantiomers
of the diphenyl derivative were successfully resolved by chiral HPLC.
Enantiopure samples showed good chiroptical performance in the CD
(|De| 1380 L mol–1 cm–1) and CPL (|glum| 0.013) spectra, and these
values were considerably large for simple organic molecules. The
unique chiroptical properties are discussed on the basis of the
molecular structure and the electronic state with the aid of time-
dependent DFT calculations.
of the facile racemization (calculated barrier 54 kJ mol–1) via
helical inversion. In this study, we designed compound 4
consisting of three fused anthracene units as a new type of π-
conjugated expanded helicene, in which three benzene rings are
inserted into the structure of 1. The presence of three anthracene
substructures in 4 would give novel properties as chromophore
and fluorophores.[9,10] We herein report the synthesis, structures,
and photophysical properties of new expanded helicene 4. We
resolved the enantiomers of a phenyl-substituted derivative,
which showed excellent chiroptical performance in the CD and
CPL spectra compared with other helical hydrocarbons and
simple organic molecules. Because CPL-active compounds have
recently attracted attention as chiral organic devices,[11] we
discuss these novel properties of the anthracene system with the
aid of density functional theory (DFT) calculations.
Helicenes are the most fundamental motif for designing helical
chiral molecules from angularly fused benzene units.[1] A large
number of enantiopure helicenes and related compounds having
remarkable chiroptical properties, namely, optical rotation,
circular dichroism (CD), and circularly polarized luminescence
(CPL), were synthesized as nonplanar π-conjugated
compounds.[2] Their characteristic properties and functions owing
to the helical π systems have led to several applications in the
fields of material science, supramolecular chemistry, and so on.[3]
In order to construct novel structures, the fundamental helicene
structure ([6]helicene: 1) has been modified in several ways,
including the lengthening of the helical chain[4] and the
introduction of multiple helical sites.[5] Another way to enlarge the
helical structure is the insertion of a linearly fused benzene ring
into angularly fused units (Figure 1): such compounds are called
“expanded helicenes” according to the classification by Tilley et
al., who synthesized compound
2
by intramolecular
cycloaddition.[6,7] In 2018, Hirose and Matsuda et al. reported
expanded helicene 3 as a helical analog of kekulene, in which five
benzene rings are inserted.[8] However, the chiroptical properties
of these expanded helicenes were not well investigated because
Figure 1. Structures of [6]helicene (1) and its expanded analogs 2–4. Inserted
linearly fused benzene rings are highlighted in red.
1
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
The fused anthracene system was constructed by the
cycloisomerization reaction of 1-(2-ethynylphenyl)anthracene
derivatives because this reaction was occasionally utilized for the
synthesis of phenanthrene derivatives from 2-ethynyl-1,1’-
biphenyl derivatives via the 6-endo cyclization reaction.[12] The
reaction conditions were optimized for the PtCl2-catalyzed
cycloisomerization of 5 as the model reaction (Scheme 1 and
Table S1). When 5 was heated in toluene in the presence of
P(C6F5)3 ligand,[13] naphtho[1,2-a]anthracene (6) was obtained in
73% yield without the formation of a significant amount of other
cyclized products. Compound 7a was similarly reacted to give
doubly cyclized product 4a in 49% yield as a yellow solid. Phenyl-
substituted derivative 4b and 2,4,6-trimethylphenyl (mesityl)
substituted derivative 4c were similarly synthesized from the
corresponding precursors.[14] Compound 4a, dianthra[1,2-a:2’,1’-
j]anthracene, which consists of three fused anthracene units, is a
new aromatic ring parent. These products were characterized by
their NMR and mass spectra, and their structures were confirmed
by X-ray analysis as mentioned below.
this value was close to the theoretical maximum (50%) for
homonuclear coupling.[16] For 4b, restricted rotation of the phenyl
groups was observed by variable-temperature 1H NMR
measurements (Figure S3). The barrier determined by the
dynamic NMR method (DG‡298 = 53 kJ mol–1) was lower than that
of the enantiomerization mentioned later. This value of 4b is
comparable to the calculated rotational barrier of the phenyl group
in 1-phenylanthracene (DG‡298 = 55 kJ mol–1).[17]
The UV-vis and fluorescence spectra of 4a and 4b were
measured in CHCl3 (Figure S7 and Table 1). Compound 4a gave
an intense peak at 346 nm and a series of absorption bands
extending to 470 nm, which were bathochromically shifted by 50–
80 nm relative to those of anthracene and [6]helicene.[18] The
absorption at the longest wavelength (lmax 459 nm) was assigned
to the HOMO®LUMO transition according to the time-dependent
(TD)-DFT calculation mentioned later. In the fluorescence
spectrum, 4a showed an intense emission band at 467 nm (Ff
0.18, tf 9.6 ns). Its fluorescence quantum yield was much larger
than that of [6]helicene (Ff 0.03), which underwent intersystem
crossing rapidly at the excited state,[19] as revealed by the
increased fluorescence emission rate constant kf and the slightly
decreased nonradiative decay rate constant knr. The small Stokes
shift of 4a (370 cm–1) demonstrated that the structural change at
the excited state should be small. These bathochromic effects in
the absorption and emission spectra indicated that the π-
conjugation was effectively extended by the fused anthracene
units in 4a. Compound 4b having phenyl groups showed similar
absorption and emission spectra with bathochromic shifts by 4–6
nm relative to 4a.
PtCl2 (5 mol%)
P(C6F5)3 (5 mol%)
toluene
80 °C, 24 h
73%
5
6
PtCl2 (10 mol%)
Y
Y
X
X
Y
Y
P(C6F5)3 (10 mol%)
X
X
The X-ray structures of 4a are shown in Figure 2(a). The
molecule had a helical structure to avoid steric hindrance between
the terminal benzene rings. As a result, the interatomic distance
C(1)···C(19) (3.99 Å) was larger than the sum of their van der
Waals radii (3.40 Å). The torsion angles along the inner carbons
were ca. 10° for one [4]helicene moiety and ca. 20° for the other,
meaning that the two moieties had different torsional curves. The
angle between the mean planes of the terminal benzene rings (A
and I) was 30.2°, and this value was smaller than the
corresponding angle (59.5°) in [6]helicene[20] and larger than
those in 2 (6.3°)[6] and 3 (18.2°).[8] The interatomic distances
between the Ha and Hb atoms (1.88 and 1.78 Å) were much
smaller than the sum of the van der Waals radii (2.40 Å), being
consistent with the NMR data mentioned above. This helical
structure of 4a was nearly reproduced by DFT calculations at the
M06-2X/6-31G(d,p) level (Figure S25). The optimized structure
was ideally C2 symmetric and the dihedral angles along the inner
carbons in the [4]helicene region were 12.4° or 22.4°. The packing
HbHb
Ha
toluene
80 °C, 24 h
4b: 77%
4a: 49%
4c: 23%
a:
b:
c:
X = Y = H
X = Ph, Y = H
X = H, Y = 2,4,6-trimethylphenyl
7
4
Scheme 1. Synthesis of 6 and 4 by PtCl2-catalyzed cycloisomerization.
1
In the H NMR spectrum of 4a, the signal due to Ha in the
central anthracene unit was observed at 12.11 ppm as a singlet.
The unusual deshielding of the proton in the cove area was
attributed to the strong ring current effects of the surrounding
aromatic moieties as well as the steric compression effect.[15] In
fact, an intense nuclear Overhauser effect (41%) was observed
for the Ha signal upon irradiation of the Hb signal (Figure S1), and
Table 1. UV-vis and fluorescence spectral data of 4a, 4b, anthracene, and [6]helicene (1).[a]
UV-vis FL
max [nm] (e [L mol−1 cm−1])
Stokes shift
kf [ns–1
]
knr [ns–1
]
[cm–1
]
[d]
[e]
[b]
l
l
em [nm]
Ff
tf [ns] [c]
459 (2900), 346 (56300), 287 (105000)
465 (3000), 352 (56600), 298 (71900)
379 (9000)
4a
467
471
383
420
0.18
0.15
0.12
0.03
9.6
8.5
2.0
8.4
0.019
0.018
0.060
0.0036
0.086
0.10
0.44
0.12
370
270
280
580
rac-4b
anthracene
1 [f]
410 (250)
[a] Measured in CHCl3 at room temperature unless otherwise noted. [b] Absolute fluorescence quantum yield. [c] Fluorescence lifetime. [d] Fluorescence
emission rate constant: kf = Ff/tf. [e] Nonradiative decay rate constant: knr = (1−Ff)/tf. [f] Ref. 18. Measured in CH2Cl2.
2
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
diagram in Figure 2(b) showed that molecules of the same helicity
were stacked linearly via π···π interactions along the b axis, which
extended to the long axis of a needle-like single crystal. In the X-
ray structure of 4a, the bond alternation was significant for
benzene rings C, D, F, and G as parameterized by the HOMA
index (Table S3).[21] The C(6)–C(7), C(8)–C(9), C(11)–C(12), and
C(13)–C(14) bonds were shorter than the other bonds, and had
high double-bond character. The NICS(0) values were calculated
for each benzene ring in the optimized structure at the GIAO-
B3LYP/6-31G(d,p) level: A(I) −9.55, B(H) −11.52, C(G) −5.32,
D(F) −6.47, and E −11.57.[22] These experimental and theoretical
data indicated that the aromatic character was high for the linearly
fused benzene rings and low for the angularly fused benzene
rings, as illustrated in Clar’s structure in Figure 2(c).
singlet at room temperature and even at −90 °C in CD2Cl2 (Figure
S6). This observation meant that the enantiomerization occurred
much faster than the NMR time scale (barrier <35 kJ mol–1). The
DFT calculation revealed that the enantiomerization of global
minimum structure X proceeded in three steps via intermediate Y
and its enantiomer (Figure 3b). The calculated barrier to helical
inversion, namely the energy difference between X and TS2 (Cs
symmetric butterfly structure), was 25.2 kJ mol–1 at 298 K, and
this value is consistent with the above NMR observation. This
barrier was much lower than that of [6]helicene (151 kJ mol–1),[24]
and lower than those of expanded helicenes 2 and 3 (45–55 kJ
mol–1) in Figure 1.[6,8]
Figure 3. Enantiomerization via helical inversion of 4. (a) Site exchange of o-
Me groups in 2,4,6-trimethylphenyl groups in 4c. (b) Mechanism of helical
inversion of 4a calculated at M06-2X/6-31G(d,p) level.
The calculated barrier to enantiomerization of 4a was too
low to isolate enantiomers at room temperature. However, the
enantiomers of diphenyl derivative 4b were successfully resolved
by chiral HPLC with a Daicel CHIRALPAK-IC column (Figure S20).
The first and second eluted fractions showed negative and
positive Cotton effects, respectively, at 352 nm in the CD spectra.
Each enantiomer slowly racemized on heating at 90 °C in toluene,
Figure 2. X-ray structures of 4a. (a) Two views of ORTEP drawing with thermal
ellipsoids at 50% probability. Dihedral angles: C(20)–C(20a)–C(20b)–C(20c)
19.4°, C(20a)–C(20b)–C(20c)–C(21) 19.7°, C(21)–C(21a)–C(21b)–C(21c) 9.5°,
C(21a)–C(21b)–C(21c)–C(22) 11.1°. Interatomic distances: H(20)···H(21) 1.88
Å, H(21)···H(22) 1.78 Å, C(1)···C(19) 3.99 Å. Interplanar angle: plane(A)–
plane(I) 30.2°. (b) Packing diagram and a picture of the single crystal measured.
Red and blue models show P and M molecules, respectively. (c) Selected C–C
bond distances in Å. Blue and red values indicate long and short bonds,
respectively, relative to the normal aromatic bond.
and kinetic analysis gave barrier to enantiomerization DG‡
of
363
121 kJ mol–1. Because this barrier was much higher than the
estimated value of 4a, the phenyl groups effectively enhanced the
barrier to helical inversion by destabilization of the transition state.
The X-ray structures of 4b (Figures S15 and S16) showed that
the helical pitch [C(1)···C(19) 5.74 Å] was increased by the steric
effects of the phenyl groups.
Although the helical inversion in 4a resulted in
enantiomerization of the chiral compound, this compound lacked
a probe to observe this dynamic process by NMR spectroscopy.
Therefore, we measured the NMR spectra of the mesityl
derivative 4c, in which the two o-Me groups should be
nonequivalent in the fixed helical structure (Figure 3a).[23]
Because the rotation of the mesityl groups relative to the aromatic
framework was highly restricted,[23] the site exchange between the
MeA and MeB should occur by enantiomerization via the helical
inversion. The signal due to the o-Me groups was measured as a
In order to examine the chiroptical properties of 4b, we
measured the CD and CPL spectra of enantiopure samples in
CHCl3 at room temperature. As clearly shown in Figure 4, the
spectra of the enantiomers were mirror images of each other. In
the CD spectrum, the second fraction gave a large positive Cotton
effect at 352 nm (De +1380, gabs +0.024) and a large negative
Cotton effect at 297 nm (De −1020, gabs −0.014) in addition to a
weak one at 465 nm (De −44, gabs −0.015), in which gabs is
absorption dissymmetry factor defined by De/e. The magnitude of
the molar CD |De| rarely exceeded 1000 for small organic
3
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
molecules, and the value of 4b at 352 nm was larger than those
of a double-[6]helicene (801)[18] and a nanographene propeller
(1182)[25] as well as [6]helicene (284).[18] This characteristic
property is consistent with the general tendency that increased
twisting in aromatic moieties increase the Cotton effect.[26] We
calculated the CD spectrum of (P)-4b by the TDDFT method at
the B3LYP/6-31G(d,p) level (Figure S31). The shapes and signs
of the calculated bands agreed with the experimental spectrum of
the second eluted isomer. Therefore, we were able to determine
the absolute stereochemistry of 4b as (P)-[CD(+)352] or (M)-
[CD(−)352]. This assignment was also supported by the X-ray
analysis of the [CD(−)352] isomer, in which the Flack parameter
was nearly zero (0.028) on refinement of the M structure.[27]
emission,[2a] was +0.013 and –0.012 for (M)- and (P)-4b,
respectively. In general, non-aggregated small organic molecules
exhibit only small |glum| values of 10–5 to 10–3 order, if CPL-active,
and examples of the values in the 10–2 order are limited.[11,28] As
for carbohelicenes, typical reported values were 0.0009 for
[6]helicene,[18] 0.0025 for double-[6]helicene,[18] 0.032 for
bitriphenylene-type helicene.[29] Therefore, compound 4b
featured a very large |glum| value with retention of emissive
property.
To obtain further information about the optical and
chiroptical properties, we carried out TDDFT calculations of 4a at
the B3LYP/6-31G(d,p)//M06-2X/6-31G(d,p) level as the model of
4b (Figure 5).[30] The HOMO–LUMO gap of 4a (2.97 eV) was
smaller than that of [6]helicene (4.03 eV) as a result of the
extended π-conjugation in the former. The observed absorption
at 459 nm of 4a was attributed to the HOMO®LUMO excitation.
The calculated data of the electric ( ) and magnetic (m) transition
µ
dipole moments for important transitions in (P)-4a are compiled in
Table 3. The two transition dipole moments determined the CD
and CPL intensities according to the following equations: rotatory
strength R = |
4|m|cosq/|
|, where q is the angle between them.[31] The transition
||m|cosq and g = 4| ||m|cosq/(| »
µ µ µ
|2+|m|2)
µ
dipole moments for the symmetry-conserved S0→S1 transition in
the C2 symmetric structure of (P)-4a were antiparallel (q = 180°),
maximizing the magnitude of the angle term in R and g values.[2c]
In contrast, the two dipole moments were nonparallel (q = 68°) for
the transition at 353 nm (S0→S7), during which the orbital
symmetry was not conserved. Nevertheless, the ratio |m|/| | was
µ
so large that the g value (+0.0196) was still large. This value was
1.8 times larger than that of the corresponding transition of (P)-
[6]helicene 1 (S0→S3) (Table S8). The magnitude of the g value
was further enhanced to +0.0313 by the introduction of the two
phenyl substituents in (P)-4b (Table S7). This situation produced
the strong Cotton effect at 356 nm for enantiopure 4b. Table 3
also shows the transition dipole moments in the excited state
(S1→S0), which corresponds to the emission at 471 nm. For the
same reason as above, the dipole moments were antiparallel to
enhance the |glum| value (0.0043). This feature contrasted that of
[6]helicene, in which the two transition dipole moments were
nearly orthogonal, leading to very small |glum| (S1→S0) as well as
|gabs| value (S0→S1) values (Table S8). Thus, the intense CD and
CPL bands were reasonably explained by the magnitudes and
angles of the two transition dipole moments. This feature is
Figure 4. Chiroptical data of enantiopure 4b in CHCl3 at room temperature. (a)
CD and UV-vis spectra. (b) CPL and FL spectra. Blue line: first fraction, (M)-4b.
Red line: second fraction, (P)-4b.
The enantiomers of 4b were CPL-active; (M)- and (P)-4b
gave positive and negative bands, respectively, at 471 nm (Figure
4b). Luminescence dissymmetry factor glum, which is defined by
the relative difference between left- and right-circularly polarized
Table 2. Chiroptical properties of (P)-4b, (M)-4b, and (P)-[6]helicene (1).[a]
CD
FL
[b]
[c]
[d]
l [nm]
De [L mol−1 cm−1
]
e [L mol−1 cm−1
]
gabs
l
em [nm]
glum
465
352
297
465
352
297
410
325
−44
3000
−0.015
+0.024
−0.014
+0.015
−0.024
+0.014
−0.0012
+0.0092
(P)-4b
+1380
−1020
+43
56600
71800
3000
472
−0.012
(M)-4b
(P)-1 [e]
−1370
+1020
−0.3
56600
71800
250
469
420
+0.013
−0.0009
+284
27000
[a] Measured in CHCl3 at room temperature unless otherwise noted. [b] For (P)-4b and (M)-4b, molar absorption coefficients at peaks or troughs in the CD
spectra, read from the UV-vis spectrum of rac-4b. [c] Absorption dissymmetry factor, gabs = De /e. [d] Luminescence dissymmetry factor. [e] Ref 18. Measured
in CH2Cl2.
4
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
attributed to the anthracene based chromophores in the helical
system.
calculations indicated that the magnitudes and directions of the
electric and magnetic transition dipole moments in 4 were in good
balance to enhance the chiroptical performance, in contrast to
[6]helicene. These results demonstrate the critical role of the
structural expansion of helicenes in their chiroptical properties,
which would pave the way for designing novel advanced chiral
molecules and materials, in particular circularly polarized devices.
Further studies of synthesis of the further fused or expanded
anthracene compounds as well as the properties and functions of
these π-conjugated compounds are in progress.
Acknowledgements
This work was partly supported by JSPS KAKENHI Grant Number
JP20H02721 and Nagase Science and Technology Foundation.
The authors thank Professor Osamu Ishitani and Dr. Yusuke
Tamaki for the measurements of fluorescence spectra, Professor
Ken Ohmori and Professor Keisuke Suzuki for the use of a chiral
HPLC system, and Professor Kan Wakamatsu for the valuable
discussion on the theoretical calculations.
Figure 5. Frontier Kohn-Sham orbitals and orbital energy diagrams of 4a and
[6]helicene (1) calculated at the TD-B3LYP/6-31G(d,p)//M06-2X/6-31G(d,p)
level. Data of the transition of the lowest energy are shown. l: transition energy,
f: oscillator strength.
Conflict of interest
The authors declare no conflict of interest.
Table 3. Transition dipole moments for selected transitions of (P)-4a calculated
at the TD-B3LYP/6-31G(d,p)//M06-2X/6-31G(d,p) level.
Keywords: arenes • circular dichroism • circularly polarized
Transition
S0→S1
S0→S7
S1→S0
luminescence • density functional calculations • helical structures
l [nm] [a]
482
353
541
[1]
[2]
[3]
a) C.-F. Chen, Y. Shen, Helicene Chemistry: From Synthesis to
Applications, Springer, Berlin, 2017; b) Y. Shen, C.-F. Chen, Chem. Rev.
2012, 112, 1463–1535. (c) M. Gingras, Chem. Soc. Rev. 2013, 42, 968–
1006.
[b]
|
µ
|
111.78
0.1587
–1.000
–0.0057
423.79
5.4702
0.380
144.90
0.1559
–1.000
–0.0043
|m| [c]
a) Y. Nakai, T. Mori, Y. Inoue, J. Phys. Chem. A 2013, 117, 83–93; b) I.
Warnke, F. Furche, WIREs Comput. Mol Sci 2012, 2, 150–166; c) F.
Furche, R. Ahlrichs, C. Wachsmann, E. Weber, A. Sobanski, F. Vögtle,
S. Grimme, J. Am. Chem. Soc. 2000, 122, 1717–1724.
cosq [d]
g [e]
+0.0196
a) T. Verbiest, S. V. Elshocht, M. Kauranen, L. Hellemans, J. Snauwaert,
C. Nuckolls, T. J. Katz, A. Persoons, Science 1998, 282, 913−915; b) V.
Kiran, S. P. Mathew, S. R. Cohen, I. H. Delgado, J. Lacour, R. Naaman,
Adv. Mater. 2016, 28, 1957–1962; c) Y. Yang, R. C. da Costa, M. J.
Fuchter, A. J. Campbell, Nat. Photonics 2013, 7, 634–638; d) M. Gingras,
Chem. Soc. Rev. 2013, 42, 1051–1095.
Orientation
of
µ
and m
[4]
[5]
a) P. Sehnal, I. G. Stará, D. Šaman, M. Tichý, J. Míšek, J. Cvačka, L.
Rulíšek, J. Chocholoušová, J. Vacek, G. Goryl, M. Szymonski, I.
Císařová, I. Starý, Proc. Nat. Acad. Sci. USA 2009, 106, 13169–13174;
b) K. Mori, T. Murase, M. Fujita, Angew. Chem. Int. Ed. 2015, 54, 6847–
6851; Angew. Chem. 2015, 127, 6951–6955.
[a] Transition energy. [b] Magnitude of electric transition dipole moment in 10–20
esu cm units. [c] Magnitude of magnetic transition dipole moment in 10–20 erg
G–1 units. [d] q: angle between the electric and magnetic transition dipole
moments. [e] Dissymmetry factor, g = 4|
and glum for luminescence.
||m|cosq/(|
µ µ
|2+|m|2). gabs for absorption
a) C. Li, Y. Yang, Q. Miao, Chem. Asian J. 2018, 13, 884−894; b) K. Kato,
Y. Segawa, K. Itami, Synlett 2019, 30, 370−377; c) T. Hosokawa, Y.
Takahashi, T. Matsushima, S. Watanabe, S. Kikkawa, I. Azumaya, A.
Tsurusaki, K. Kamikawa, J. Am. Chem. Soc. 2017, 139, 18512–18521;
d) V. Berezhnaia, M. Roy, N. Vanthuyne, M. Villa, J.-V. Naubron, J.
Rodriguez, Y. Coquerel, M. Gingras, J. Am. Chem. Soc. 2017, 139,
18508–18511; e) Y. Wang, Z. Yin, Y. Zhu, J. Gu, Y. Li, J. Wang, Angew.
Chem. Int. Ed. 2019, 58, 587–591; Angew. Chem. 2019, 131, 597–601.
G. R. Kiel, S. C. Patel, P. W. Smith, D. S. Levine, T. D. Tilley, J. Am.
Chem. Soc. 2017, 139, 18456−18459.
In summary, expanded helicenes 4 consisting of three fused
anthracene units were synthesized by the Pt-catalyzed
cycloisomerization of alkynes. X-ray analysis and DFT
calculations revealed that substituent-free compound 4a had a
helical structure that underwent helical inversion rapidly at room
temperature. The enantiomers of diphenyl derivative 4b were
resolved by chiral HPLC and exhibited very intense Cotton effects
in the CD spectra and very large magnitudes of glum factors in the
CPL spectra for simple organic compounds. The TDDFT
[6]
[7]
Examples of other expanded helicenes. a) S. Han, A. D. Bond, R. L.
Disch, D. Holmes, J. M. Schulman, S. J. Teat, K. P. C. Vollhardt, G. D.
5
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
Whitener, Angew. Chem. Int. Ed. 2002, 41, 3223–3227; Angew. Chem.
2002, 114, 3357−3361; b) S. Han, D. R. Anderson, A. D. Bond, H. V. Chu,
R. L. Disch, D. Holmes, J. M. Schulman, S. J. Teat, K. P. C. Vollhardt, G.
D. Whitener, Angew. Chem. Int. Ed. 2002, 41, 3227–3230; Angew. Chem.
2002, 114, 3361–3364; c) N. J. Schuster, D. W. Paley, S. Jockusch, F.
Ng, M. L. Steigerwald, C. Nuckolls, Angew. Chem. Int. Ed. 2016, 55,
13519–13523; Angew. Chem. 2016, 128, 13717–13721; d) N. J.
Schuster, R. H. Sánchez, D. Bukharina, N. A. Kotov, N. Berova, F. Ng,
M. L. Steigerwald, C. Nuckolls, J. Am. Chem. Soc. 2018, 140, 6235–
6239; e) J. Nejedlý, M. Šámal, J. Rybáček, M. Tobrmanová, F. Szydlo,
C. Coudret, M. Neumeier, J. Vacek, J. V. Chocholoušová, M. Buděšínský,
D. Šaman, L. Bednárová, L. Sieger, I. G. Stará, I. Starý, Angew. Chem.
Int. Ed. 2017, 56, 5839–5843; Angew. Chem. 2017, 129, 5933–5937.
[17] D. Nori-shargh, S. Asadzadeh, F.-R. Ghanizadeh, F. Deyhimi, M. M.
Amini, S. Jameh-Bozorghi, THEOCHEM 2005, 717, 41–51.
[18] H. Tanaka, M. Ikenosako, Y. Kato, M. Fujiki, Y. Inoue, T. Mori, Commun.
Chem. 2018, 1, 38.
[19] a) O. E. Weigang, J. A. Turner, P. A. Trouard, J. Chem. Phys. 1966, 45,
1126−1134; b) M. Sapir, E. Vander Donckt, Chem. Phys. Lett. 1975, 36,
108−110.
[20] Y. Yoshida, Y. Nakamura, H. Kishida, H. Hayama, Y. Nakano, H.
Yamochi, G. Saito, CrystEngComm 2017, 19, 3626−3632.
[21] T. M. Krygowski, M. K. Cyrański, Chem. Rev. 2001, 101, 1385−1419.
[22] Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta, P. v. R. Schleyer,
Chem. Rev. 2005, 105, 3842−3888.
[23] S. Toyota, T. Oki, M. Inoue, K. Wakamatsu, T. Iwanaga, Chem. Lett.
2015, 44, 978–980.
[8]
[9]
Y. Nakakuki, T. Hirose, K. Matsuda, J. Am. Chem. Soc. 2018, 140,
15461−15469.
[24] a) R. H. Martin, M. J. Marchant, Tetrahedron 1974, 30, 347−349; b) R.
H. Janke, G. Haufe, E.-U. Würthwein, J. H. Borkent, J. Am. Chem. Soc.
1996, 118, 6031−6035; c) J. Barroso, J. L. Cabellos, S. Pan, F. Murillo,
X. Zarate, M. A. Fernandez-Herrera, G. Merino, Chem. Commun. 2018,
54, 188−191.
a) B. Valeur, M. N. Berberan-Santos, Molecular Fluorescence: Principles
and Applications, 2nd ed., Wiley-VCH, Weinheim, 2012, chap. 6; b) V.
Gray, D. Dzebo, A. Lundin, J. Alborzpour, M. Abrahamsson, B. Albinsson,
K. Moth-Poulsen, J. Mater. Chem. C 2015, 3, 11111–11121.
[10] a) M. Yoshizawa, J. K. Klosterman, Chem. Soc. Rev. 2014, 43, 1885–
1898; b) M. Nagaoka, E. Tsurumaki, M. Nishiuchi, T. Iwanaga, S. Toyota,
J. Org. Chem. 2018, 83, 5784−5790; c) S. Toyota, M. Yoshikawa, T.
Saibara, Y. Yokoyama, T. Komori, T. Iwanaga, ChemPlusChem 2019,
84, 643−654.
[25] Y. Zhu, X. Guo, Y. Li, J. Wang, J. Am. Chem. Soc. 2019, 141, 5511−5517.
[26] A. Bedi, O. Gidron, Acc. Chem. Res. 2019, 52, 2482–2490.
[27] S. Parsons, H. D. Flack, T. Wagner, Acta Cryst. 2013, B69, 249−259.
[28] Examples of other small organic molecules with high CPL activity. a) K.
Nakamura, S. Furumi, M. Takeuchi, T. Shibuya, K. Tanaka, J. Am. Chem.
Soc. 2014, 136, 5555–5558. (double azahelicene, |glum| = 0.028); b) S.
Sato, A. Yoshii, S. Takahashi, S. Furumi, M. Takeuchi, H. Isobe, Proc.
Nat. Acad. Sci. USA 2017, 114, 13097–13101 (chiral cylinder, 0.152); c)
C. Schaack, L. Arrico, E. Sidler, M. Górecki, L. Di Bari, F. Diederich,
Chem. Eur. J. 2019, 25, 8003–8007 (helicene, 0.025); d) J. Wang, G.
Zhuang, M. Chen, D. Lu, Z. Li, Q. Huang, H. Jia, S. Cui, X. Shao, S. Yang,
P. Du, Angew. Chem. Int. Ed. 2020, 59, 1619–1626; Angew. Chem. 2020,
132, 1636–1643 (anthracene macrocycle, ca. 0.1).
[11] a) E. M. Sánchez-Carnerero, A. R. Agarrabeitia, F. Moreno, B. L. Maroto,
G. Muller, M. J. Ortiz, S. de la Moya, Chem. Eur. J. 2015, 21, 13488–
13500; b) H. Tanaka, Y. Inoue, T. Mori, ChemPhotoChem 2018, 2,
386−402; c) N. Chen, B. Yan, Molecules 2018, 23, 3376; d) Y. Sang, J.
Han,
T.
Zhao,
P.
Duan,
M.
Liu,
Adv.
Mater.
doi.org/10.1002/adma.201900110.
[12] a) A. Fürstner, V. Mamane, J. Org. Chem. 2002, 67, 6264–6267; b) V.
Mamane, P. Hannen, A. Fürstner, Chem. Eur. J. 2004, 10, 4556–4575.
[13] J. Carreras, M. Patil, W. Thiel, M. Alcarazo, J. Am. Chem. Soc. 2012,
134, 16753–16758.
[29] Y. Sawada, S. Furumi, A. Takai, M. Takeuchi, K. Noguchi, K. Tanaka, J.
Am. Chem. Soc. 2012, 134, 4080−4083.
[14] The low yield of cycloisomerization of 7c to form 4c was mainly attributed
to the formation of an isomeric product.
[30] We also carried out the calculations of 4b (Tables S5 and S7), and
discussed the results in a similar manner to 4a.
[15] B. V. Cheney, J. Am. Chem. Soc. 1968, 90, 5386−5390.
[16] a) E. D. Becker, High Resolution NMR: Theory and Chemical
Applications, 3rd ed. Academic Press, San Diego, 2000, chap. 8.3; b) J.
Brison, C. de Bakker, N. Defay, F. Geerts-Evrard, M.-J. Marchant, R. H.
Martin, Bull. Soc. Chim. Belg. 1983, 92, 901−912.
[31] a) J. A. Schellman, Chem. Rev. 1975, 75, 323−331; b) F. S. Richardson,
J. P. Riehl, Chem. Rev. 1977, 77, 773−792.
6
This article is protected by copyright. All rights reserved.

10.1002/asia.202000394
Chemistry - An Asian Journal
COMMUNICATION
Entry for the Table of Contents
Chiral Aromatic Chemistry
K. Fujise, E. Tsurumaki, G. Fukuhara, N. Hara, Y. Imai, S. Toyota*
Multiply fused anthracenes as helical polycyclic aromatic hydrocarbon motif
for chiroptical performance enhancement
Helical expansion: A novel helical structure consisting of three fused anthracene units was constructed by cycloisomerization.
Enantiomers of the diphenyl derivative exhibited excellent chiroptical performance in the circular dichroism spectra and the circularly
polarized luminescence spectra as simple organic molecules.
7
This article is protected by copyright. All rights reserved.