Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of Si[sbnd]Si bond polymers during aggregation in chiral fluidic media

Article abstract of DOI:10.1016/j.jphotochem.2016.01.027

Herein, we designed photoluminescent polymer aggregates surrounded by organic media containing (S)-/(R)-limonene and (1S)-/(1R)-α-pinene as an artificial model of an open-flow cell-wall free coacervate in a fluidic medium in the ground and photoexcited states. The aggregates were build-up of stiff circular dichroism (CD)-silent and circularly polarized luminescence (CPL)-silent bis(p-n-butylphenyl)polysilanes, nBuPS, and four other diarylpolysilanes. (S)- and (R)-limonene induced more efficiently to their chirality to nBuPS during aggregation, as proven by CD and CPL spectral analysis, compared to (1S)- and (1R)-α-pinene. The nBuPS aggregates generated in a mixture of limonene, methanol, and chloroform had a dissymmetry factor (g_abs) as high as +0.04 for (R)-limonene and ?0.03 for (S)-limonene at the first Cotton band and a weak dissymmetry factor (g_lum) of +0.004 for (R)-limonene and ?0.003 for (S)-limonene. The g_abs factor, however, greatly depended on the volume fraction and chirality of limonene in the tersolvents. These behaviors were ascribed to the tempo-spatial stability and instability of the aggregates suspension in the fluidic media, as revealed by time-course dynamic light scattering measurement.

Full text of DOI:10.1016/j.jphotochem.2016.01.027

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JPC 10126 No. of Pages 10
Journal of Photochemistry and Photobiology A: Chemistry xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Tempo-spatial chirogenesis. Limonene-induced mirror symmetry
breaking of SiꢀꢀSi bond polymers during aggregation in chiral fluidic
media
a
a
a,b
Michiya Fujikia, , Keisuke Yoshida , Nozomu Suzuki , Nor Azura Abdul Rahim
,
*
Jalilah Abd Jalila,b
a
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
School of Materials Engineering, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Herein, we designed photoluminescent polymer aggregates surrounded by organic media containing
(S)-/(R)-limonene and (1S)-/(1R)- -pinene as an artificial model of an open-flow cell-wall free coacervate
in a fluidic medium in the ground and photoexcited states. The aggregates were build-up of stiff circular
dichroism (CD)-silent and circularly polarized luminescence (CPL)-silent bis(p-n-butylphenyl)poly-
silanes, nBuPS, and four other diarylpolysilanes. (S)- and (R)-limonene induced more efficiently to their
chirality to nBuPS during aggregation, as proven by CD and CPL spectral analysis, compared to (1S)- and
Received 13 October 2015
Received in revised form 31 December 2015
Accepted 28 January 2016
Available online xxx
a
Dedicated to Prof. Yoshihisa Inoue, who
discovered entropy driven chirogenesis
and is a seeker for the origin of homo-
chirality on the Earth.
(1R)-a-pinene. The nBuPS aggregates generated in a mixture of limonene, methanol, and chloroform had
a dissymmetry factor (gabs) as high as +0.04 for (R)-limonene and ꢀ0.03 for (S)-limonene at the first
Cotton band and a weak dissymmetry factor (glum) of +0.004 for (R)-limonene and ꢀ0.003 for
(S)-limonene. The gabs factor, however, greatly depended on the volume fraction and chirality of limonene
in the tersolvents. These behaviors were ascribed to the tempo-spatial stability and instability of the
aggregates suspension in the fluidic media, as revealed by time-course dynamic light scattering
measurement.
Keywords:
Symmetry breaking
Homochirality
Far-from-equilibrium
Aggregates
ã 2016 Elsevier B.V. All rights reserved.
Circular dichroism
Circularly polarized luminescence
1. Introduction
using a quadrupole gravity measurement system discovered water
under the surface of Enkelados, one of 67 Saturnian moons [5]. The
In astronomy, astrochemistry, astrobiology, and astrophysics,
researchers seeking extra-terrestrial life have long assumed that
liquid water is inevitably needed for the evolution of life. In 2013,
Hubble space telescope (NASA) captured geysers of liquid water
from Europa covered with a crust of thick ice, one of the Jupiter
family [1]. The most spectacular events in 2014 might be
discoveries of several exoplanets located in habitable zones
[2–6]. Kepler (NASA) indicated that several habitable exoplanets,
named super-earths, exist [2]. Super-earth means that the planet’s
size is almost comparable to that of our Earth. Kepler found the first
super-earth with 1.2-Earth-radius, named Kepler-186f [3]. Tau Ceti
e, the nearest super-earth 11.9 light-years away from us, is
estimated to have an average surface temperature of ꢁ70 ꢂC [4].
Moreover, Cassini (a part of Cassini–Huygens missions of NASA)
Jet Propulsion Laboratory at NASA concludes that Titan, the largest
Saturnian moon, has extremely salty water involving inorganic
salts of sulfur, sodium, and potassium [6]. Rosetta (ESA) invoked
the detection of prebiotic constituents involving water, several
organic fragments, and SiO2 by a direct landing on comet
67P/Churyumov-Gerasimenko, the Jupiter family [7,8]. In 2015,
NASA confirmed that liquid water, though containing Ca(ClO4)2,
Mg(ClO4)2, and NaClO4 salts, is still flowing on the surface of Mars
by the detection of water-related 1.4
near-infrared region [9].
mm and 1.9 mm bands in the
If life existed in the past or is now existing on these exoplanets,
solar planets, moons, and comets, a big question with a great
curiosity is whether S-/R-point chirality (stereogenic centers)
and/or P-/M-helicity (stereogenic bonds) are identical to those on
our Earth [10,11]. Living organisms are always tempo-spatial and
metastable as a consequence of far-from-equilibrium open system
[12]. Life can survive only under open flows of energy and chemical
sources because life eats low-entropy food and solar energy [13].
* Corresponding author. Fax: +81 743726049.
E-mail address: fujikim@ms.naist.jp (M. Fujiki).
http://dx.doi.org/10.1016/j.jphotochem.2016.01.027
1010-6030/ã 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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The origin of homochirality on the Earth has been a mystery in
the modern scientific community over 150 years [10,14–24]
because life cannot exit without molecular asymmetry [14]. So
far, many scientists have proposed several plausible scenarios from
the primordial era to answer this big question. Scientists have long
argued about the possibility of exo-terrestorial life [10,15–22] as
well as the origin of life on Earth. Circularly polarized radiation
mass molecules exceeding 10,000 proposed by Staudinger were
not widely accepted [38]. Nowadays, high molecular mass
molecules are commonly known as polymers and macromolecules.
Most hypotheses assumed coacervate to be rigid hard particles
surrounded by water without any flows of energy and chemical
substances. If coacervates can adopt a more dynamic structure like
a swollen gel, this soft matter system should be adaptable to any
alterations of external biases, allowing flows of chiral chemical and
circularly polarized photon energy sources. This idea led us to
design a cell-wall free, semi-artificial coacervate model built up
from chain-like synthetic polymers surrounded by a mixture of
chiral and achiral organic solvents. This open system allows
investigation of tempo-spatial molecular chirality transcription of
the soft aggregates. Particularly, time-dependent alteration in the
size of optically active aggregates becomes measurable because
optically active aggregation becomes popular in recent years
[39–54].
Aiming at realizing the soft matter coacervate system enabling
open flows of chiral substances in the ground state and/or
circularly polarized radiation in the photoexcited state, the
following five bis(p-alkylphenyl)polysilanes, were chosen:
nBuPS,EtPS, iPrPS, iBuPS, and tBuPS (Fig. 1). These SiꢀꢀSi bond
polymers are non-charged chromophores and luminophores made
of multiple stereogenic bonds. Although the first synthesis of
nBuPS was reported by Miller and Sooriyakumaran three decades
ago, nBuPS is shown to adopt a notably stiff backbone with a
persistence length (q) of ꢁ10 nm, which is one third relative to the
q of double-strand DNA [55,56]. The long q value means that
ꢁ55 repeating nBuPS units behave as an ideal rod. The other four
EtPS, iPrPS, iBuPS, and tBuPS possibly adopt a similar stiff
backbone because they commonly have bulky diaryl groups
attached to the backbone. Non-polar (S)-/(R)-limonene and
sources, such as
g-ray, X-ray, and vacuum UV, may become a
trigger for the left-right selection of biomolecular substances
[15–22]. In 1969, mankind received an incredible gift of carbona-
ceous stone, known as the Murchison meteorite, from the
interstellar Universe [25]. The meteorite was contaminated with
terrestrial origin amino acids, of which L-enantiomers were in
excess over D-ones, revealed by a largely enriched 15N in 15N/14
N
ratio and marked depletions of 13C in 13C/12C ratio and D in D/H
ratio, relative to the biological origin amino acids on the Earth
[26,27]. A recent study demonstrated that a subtle imbalance in
L-/D-amino acids can catalyze the asymmetric generation of
carbohydrates with a high ee, which might be responsible for the
homochiral world [28]. Moreover, even nearly racemic substances
with 10ꢀ5% ee can be significantly amplified to nearly 100% ee, as
exemplified by the Soai-reaction [29].
The homochirality question, however, is a difficult one because
of a complete lack of any fossil record or trace amount of chiral
molecular evidence. However, marked depletion of 13C in
13C-/12C-isotopic ratio suggests evidence that methanogenic
microbial existed in the Archaean era at least 3.5–3.8 Gyrs ago
[30–32]. This conclusion was drawn from the fact that lighter 12C-
containing substances in living organisms are enriched during
their entire lifetime. Moreover, the recent snowball Earth
hypothesis with analysis of palaeomagnetism asserts that
Prokaryotes only inhabited Precambrian eras for more than
2 Gyrs [33,34], though critical argument has been still made to the
radical hypothesis [35].
In 1920s–1930s, a more radical idea was hypothesized by
Oparlin in Russia [36] and Haldane in UK [37]. They independently
claimed that the coacervate is a prototype of living cells during the
chemical evolution of life. The coacervate refers to spherical
aggregates surrounded by water – colloidal droplets – made of
stable organic matter, followed by spontaneous growing and
fermentation. This hypothesis relies on spontaneous association
during liquid–liquid phase separation resulting from non-covalent
electrostatic, hydrogen bonding, and van der Waals interactions.
(1S)-/(1R)-
limonene and
able solvents for several circular dichroism (CD)-silent and/or
circularly polarized light (CPL)-silent and -conjugated
a-pinene were chosen as chiral terpenes because
a-pinene are efficient stereogenic center transfer-
p
-
s
polymers [44,49–54]. CD-active and/or CPL-active aggregation of
these polymers occurs with the help of van der Waals force only
with these terpenes. Aggregation behavior is characterized
because Si
are chiroptical probes to detect chiralities in the ground- and
photoexcited states of the backbones [56–58]. Compared to
transitions associated with phonon side bands, very narrow
structure-less Si -Si * transition spectral bands facilitate to
s–Sis* transitions, characteristic of diarylpolysilanes,
p–p*
Coacervate size typically ranges from 1 to 100
m
m in diameter,
s
s
almost identical to that of living cells. However, the hypothesis was
mostly abandoned because coacervate did not evolve living life. At
the time, although colloids made of low-molecular mass organic
matter were commonly known among scientists, high-molecular
detect subtle imbalance between P- and M-motifs and helical
pitch, that are detectable by CD and CPL spectroscopies, and
dynamic light scattering (DLS) and fluorescence optical micro-
scopic (FOM) methods.
Fig. 1. Chemical structures of diarylpolysilanes, limonene, and
a-pinene used in this work.
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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3
2. Results and discussion
(3.139 eV) is a consequence of P- and M-157 helices that coexist in
the same backbone. Energy barrier height between P- and
M-helices is estimated to be as small as 5–6 kcal per Si repeating
unit [57,58]. This rotational barrier height is comparable to the
inversion barrier height of molecular ammonium. This uniqueness
makes nBuPS alter its preferential helix sense, P or M, susceptible
to external chiral chemical and photophysical biases. This means
that change in global conformation arises from cooperative helix-
to-helix transition, not due to rod-to-coil phase transition.
When nBuPS is dissolved in a mixture of limonene and CHCl3
(0.75/2.25 (v/v)), we can see ultra-weak CD signals at 395 nm, due
to subtle imbalance between P- and M-157 helices, as shown in
Fig. 3b. However, the degree of dissymmetry factor in the CD
spectra, gabs value, is defined as 2 ꢃ (AbsL ꢀ AbsR)/(AbsL + AbsR) =
2.1. Inherently CD-silent helical nBuPS
The five diarylpolysilanes are CD-silent and CPL-silent poly-
meric luminophores. Calculation of a 30-mer model as nBuPS
showed the existence of four local minima at 165ꢂ/195ꢂ dihedral
angle in the ground state, corresponding to P- and M-157 helices,
respectively, and 150ꢂ/210ꢂ dihedral angles corresponding to
P- and M-73 helices, respectively [57,58]. The four local minima
are due to the para-substitution of alkyl group at the phenyl group.
For comparison, from the calculation of the 30-mer model for
unsubstituted diphenylpolysilane, PS prefers global minima at
150ꢂ/210ꢂ angles, yielding P- and M-73 helices rather than 157
helices [57,58] (Fig. 2).
D
e/
e
, is only ꢁ1 ꢃ10ꢀ5 for (S)-limonene, but not detectable for
The 165ꢂ/195ꢂ dihedral sets are responsible for intense
(R)-limonene. The degree of nBuPS P–M imbalance induced by
limonene chirality in the good solvents is less than 5%, suggesting
that the |gabs| value of 73-helical dialkylpolysilanes is ꢁ2 ꢃ10ꢀ4. By
adding poor solvent (methanol) to the nBuPS solution, CD- and
CPL-active nBuPS is instantly formed during aggregation. This
terpene chirality induced aggregation process was already
established in our previous papers [44,49–54], however nBuPS
and related diarylpolysilanes were not studied.
excitonic CD-active and CD-silent Si
380–390 nm due to orbital overlap between Si
orbitals [57–60]. The latter dihedral set induces the Si
transition around 320 nm of dialkylpolysilanes due to the lack of
orbital overlap between Si and phenyl orbitals [59,60].
nBuPS has a high molecular mass (Mw = 85,000, ꢁ300 repeating
units), while the other four diarylpolysilanes had lower
s
–Si
s
* transitions around
and Phenyl
–Si
s
p
s*
s
s
p
a
molecular mass smaller than 4000–6000 (corresponding to
ꢁ20 repeating units). nBuPS and EtPS have non-branched alkyl
groups at the para-position of phenyl, while iPrPS, iBuPS, and
tBuPS carry para-branched alkyl groups. The substitutes and
molecular mass effects in the aggregation are discussed later.
2.3. UV–vis and CD characteristics of diarylpolysilane aggregates
Firstly, the UV–vis and CD spectra of nBuPS aggregates
produced in a mixture of CHCl3 and methanol (1.05/1.95 (v/v))
are displayed in Fig. 4a. Any detectable CD signals of nBuPS
aggregates are confirmed, though the SiꢀꢀSi exciton band at
391 nm (3.155 eV) slightly blue-shifted relative to the homoge-
neous solution. The absence of limonene chirality merely induced
CD-silent nBuPS aggregates.
The chiral solvent including limonene prompted to emerge
nBuPS exhibiting gigantic bisignate Cotton bands around 403 nm
during aggregation of nBuPS, as given in Fig. 4b. However,
baselines of UV–vis spectra are lifted upward due to Rayleigh
scattering of the aggregates, whilst induced CD signals are
insensitive to the aggregate scattering.
To evaluate the degree of limonene-chirality induced CD effect,
we corrected UV–vis signals with numerically subtracting UV–vis
signals by setting UV–vis signals to be zero at 500 nm. The UV–vis
signal at 500 nm does not come from the contribution of the
403-nm absorption tail. Raw data with dotted lines as baseline
correction are given in Appendix Fig. S1.
2.2. Chiroptical properties of nBuPS in homogeneous solutions
The UV–vis, CD, and PL (excited at 350 nm) spectra (wavelength,
nm in unit) of nBuPS in CHCl3 solution are given in Fig. 3a. For
comparison, the corresponding UV–vis and PL spectra (photon
energy, eV in unit) of nBuPS are given in Appendix Fig. S1a. The
Stokes’ shift of nBuPS is as small as 0.118 eV (ꢁ951 cmꢀ1). The full-
width-at-half maxima of UV–vis and PL spectra are 0.146 eV
(1180 cmꢀ1) and 0.125 eV (1010 cmꢀ1), respectively. These nar-
rower absorption and emission bands are characteristics of quasi-
one-dimensional (Q1D) exciton (photoexcited electron-hole pair)
confined in SiꢀꢀSi bond quantum wire. The exciton state in Q1D
polysilane wire stably exists with a high binding energy of ꢁ1 eV
[61]. The small Stokes’ shift indicates a very rigid SiꢀꢀSi bond
backbone and a minimal reorganization of the backbone in the
photoexcited state. These spectral characteristics have been
reported previously [58]. However, from the potential energy
surface in Fig. 2a, this intense, narrow exciton band at 395 nm
The evaluated gabs values at the first Cotton bands are ꢁ+0.04 at
408 nm for (R)-limonene and ꢁꢀ0.03 at 406 nm for (S)-limonene,
Fig. 2. Energy as a function of dihedral angle in model 30-mers of (a) nBuPS and (b) PS. Data taken from the original and unpublished data [58], followed by re-generation of
potential curves.
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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Fig. 3. (a) UV–vis, CD, and PL (excited at 350 nm) spectra of nBuPS in CHCl3 solution and (b) UV–vis and CD spectra of nBuPS in (R)- or (S)-limonene/CHCl3 = 0.75/2.25 (v/v).
Path length: 1.0 cm, [nBuPS]0 = 1.0 ꢃ10ꢀ4 Mꢀ1 cmꢀ1
.
respectively, whilst the gabs values at the second Cotton band are
ꢁꢀ0.1 at 391 nm for (R)-limonene and ꢁ+0.02 at 387 nm for
(S)-limonene, respectively. The gabs(R)-to-gabs(S) ratio at the first
Cotton band is ꢁ1.3 in the S0 state, while the gabs(R)-to-gabs(S) ratio
at the second Cotton band is ꢁ5.
CD-signals detect the S0-state chirality of substances in the
ground state, whilst CPL-signal reflects from the photoexcited S1-
state chirality with the lowest vibronic mode (Kasha’s rule).
Importantly, CPL and PL signals do not reflect from the scattering of
the aggregates. It should be noted that baselines of CPL and PL are
insensitive to the aggregate scattering. Thus, the glum value of CPL
signal can be defined as 2 ꢃ (IL ꢀ IR)/(IL + IR).
The other four diarylpolysilanes (EtPS, iPrPS, iBuPS, and tBuPS)
resulted in the corresponding CD-active aggregates in the presence
of (R)-limonene (or (S)-limonene). However, the absolute gabs
values at the first and second Cotton bands significantly reduced by
The normalized UV–vis and CD spectra of nBuPS aggregates
produced in limonene/chloroform/methanol = 0.75/0.30/1.95
(v/v/v) are shown in Fig. 5a. For comparison, the normalized PL
and CPL spectra of the aggregates are shown in Fig. 5b. The
dissymmetry factors, glum, at 410 nm in the photoexcited state are
+4.2 ꢃ10ꢀ3 ((R)-limonene) and ꢀ3.4 ꢃ10ꢀ3 ((S)-limonene), re-
spectively. The CPL-sign is identical to that of the CD-sign at the
first Cotton band. For example, (R)-limonene induces plus-sign CD
and plus-sign CPL, whilst (S)-limonene induces minus-sign CD and
minus plus-sign CPL.
two and three orders of the magnitude and on the order of 10ꢀ4
.
tBuPS does not show bisignate CD characteristics and has a single
sign weak-CD signals. This weakness arises from weakly entangled
aggregation due to lower molecular mass polymers (4000–6000),
whilst nBuPS has a high molecular mass able to form entangled
soft aggregates. Molecular mass may be a critical factor to induce a
highly dissymmetrical helical organization in the aggregates, as
proven by the enhanced CD signals.
The nature of bisignate couplet CD signals is greatly dependent
of the type of alkyl pendants at the para-aryl groups, as
summarized in Table 1. (R)-chirality of limonene induced the
positive couplet signals (positive-sign CD at the first Cotton and
negative-sign CD at the second band) for diarylpolysilanes with
non-branched n-butyl and ethyl groups, whilst the (R)-chirality
oppositely induced the negative couplet signals (negative-sign CD
at the first Cotton and positive-sign CD at the second band) for
diarylpolysilanes with branched alkyl groups, including isopropyl
and isobutyl. The choice of non-branched or branched alkyl moiety
is another critical factor determining the sign of CD signals in the
aggregates, although for unknown reasons.
The magnitudes in glum values markedly decreased by 1/10 for
(R)- and (S)-limonene, compared to the corresponding gabs values
at the first Cotton bands. The glum values decreased by 1/25 times
for (R)-limonene and by 1/6 times for (S)-limonene, compared to
the gabs values at the second Cotton bands. The glum(R)-to-glum(S) of
ꢁ1.2 in the S1 state is nearly identical to the gabs(R)-to-gabs(S) ratio
at the first Cotton band. The left-right symmetry of the aggregates
may be slightly broken in the ground and photoexcited states.
nBuPS aggregates in (R)-limonene/chloroform/methanol
(=0.75/0.30/1.95 (v/v/v)) are visualized by defocused optical
microscopic imaging. The bright field image under white light
illumination and the corresponding dark field fluorescence images
excited at 365 nm are displayed in Fig. 5c and d, respectively. Due
to the blurring effect, each aggregate clearly emits a purple–blue
color, though the actual size of the aggregates is smaller than
2.4. CD/UV–vis/CPL/PL spectral characteristics of nBuPS aggregates
Notably, an imbalance in the gabs values of nBuPS between
(R)- and (S)-limonene was observed (Fig. 4b) as a matter of fact. A
similar but weak limonene chirality tendency in gabs values can be
seen in EtPS, iBuPS, and tBuPS aggregates (Fig. 4c–f). In nBuPS
aggregates induced by limonene chirality, mirror symmetry
(mirror image relationship in CD spectra) in the ground state is
considerably broken, though (R)- and (S)-limonene purified in a
reduced pressure had an almost identical absolute specific optical
1.0 mm, as mentioned in a later section. Under non-blurring
condition, each nBuPS aggregates clearly emits as very small blue
color dots (Fig. S2). Possibly, each dot weakly emits the CPL signal
because of the CPL-active nBuPS aggregates.
2.5. The gabs value of nBuPS aggregates vs (R)- and (S)-limonene
fractions in tersolvents
rotation [a D
limonene chirality induced aggregation, we observed that invari-
ably the CD spectra of - and -conjugated polymers during
aggregating with (R)- and (S)-limonene are not an ideal mirror
image relationship for reason as yet unsolved [44,49–54]. Similar
]
with the opposite sign in neat limonene. In a series of
Recent knowledge and understanding of the conformational
structure indicated that (R)-limonene mainly exists as a mixture of
three stable rotational isomers with the quasi-equatorial orienta-
tion of the isopropenyl group on the cyclohexene ring [62,63].
Minor rotational isomers are three unstable isomers with the
quasi-axial orientation of the isopropenyl group on the cyclo-
hexene ring [62]. Although vibrational circular dichroism (VCD)
p
s
non-mirror image CD spectra of nBuPS induced by
a-pinene
chirality can be seen in this experiment (Appendix, Fig. S3a–d).
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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5
Fig. 4. CD and UV–vis spectra of diarylpolysilane aggregates induced by a mixture of limonene, chloroform, and methanol. (a) nBuPS (0.00/1.05/1.95 (v/v/v)), (b) nBuPS
(0.75/0.30/1.95 (v/v/v)), (c) EtPS (0.75/0.30/1.95 (v/v/v)), (c) iPrPS (0.40/0.30/2.30 (v/v/v)), (d) iBuPS (0.40/0.30/2.30 (v/v/v)), (e) iBuPS (0.40/0.30/2.30 (v/v/v)), and (f) tBuPS
(0.40/0.30/2.30 (v/v/v)). Path length: 1.0 cm, [diarylPS]0 = 1.0 ꢃ10ꢀ4 Mꢀ1 cmꢀ1
.
experiment followed by population analysis of neat (S)-limonene
was not reported by the same research groups [62,63], these
results prompted us to investigate the gabs value of nBuPS
aggregates in detail.
The gabs values at the first and second Cotton bands of nBuPS
aggregates as a function of volume fraction of (R)-limonene in a
mixture of (R)-limonene, chloroform, and methanol are given in
Fig. 6a. Similarly, the gabs values of nBuPS aggregates as a function
of volume fraction of (S)-limonene in a mixture of (S)-limonene,
chloroform, and methanol are given in Fig. 6b. Herein, chloroform
is fixed to 0.3 mL and a total volume is 3.0 mL. From Fig. 6a, it is
evident that the gabs value resonantly enhances at a specific volume
Table 1
Comparisons of Cotton CD sign, lmax, and lex values of diarylpolysilanes aggregates induced by limonene-containing tersolvent (data taken from Fig. 4).
lmax (nm)
lex (nm)
CD signs by (R)-limonene
1st Cotton band
2nd Cotton band
1st Cotton band
2nd Cotton band
nBuPS
EtPS
iPrPS
iBuPS
tBuPS
403(S and R)
377(S), 378(R)
380(S), 383(R)
380(S), 382(R)
363(S and R)
407–409
392–393
389
388
376
388–391
376
372
+
+
ꢀ
ꢀ
+
ꢀ
ꢀ
+
372
+
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polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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Fig. 5. (a) Normalized UV–vis and CD spectra and (b) PL and CPL spectra of nBuPS aggregates in 0.75/0.30/1.95 (v/v/v). Non-focused blurred optical microscopic images of
nBuPS aggregates produced in (R)-limonene/chloroform/methanol = 0.75/0.30/1.95 (v/v/v) under (c) bright field under white light illumination and (d) its dark field
fluorescence images upon 365 nm excitation (scale bar: 100 nm).
fraction of (R)-limonene (0.75 mL, 25% in volume), but weakly
magnifies at a 0.40–0.50 mL of (R)-limonene (13–17% in volume)
and at 0.90–1.0 mL of (R)-limonene (30–35% in volume). The gabs
value at the second Cotton band attains ꢁ0.1 (25% in volume),
equivalent to 5% of circular polarization. On the other hand, from
Fig. 6b, the gabs value resonantly magnified at three specific volume
fractions when ca. 0.50 mL (17% in volume), 0.75 mL (25% in
volume), and 0.88 mL (29% in volume) of (S)-limonene.
cyclohexenyl ring), ꢀ138.75ꢂ (conformer 2, methyl moiety of
isopropenyl is out-of-plane and up-geometry to the ring) and
ꢀ8.03ꢂ (conformer 3, methyl moiety of isopropenyl is out-of-plane
and down-geometry to the ring). The populations of conformers 1,
2, and 3 were estimated to 39:31:30, respectively. The calculated
[
a]D
values were +430ꢂ (conformers 1), ꢀ140ꢂ (conformers 2), and
ꢀ45ꢂ (conformers 3), respectively. Similarly, the calculated signs of
VCD signals at 1720 cmꢀ1 due to isopropenyl nC bond had very
¼
C
These specific two and/or three volume fractions of limonene as
a matter of fact may have a special meaning and be interpreted
with the three possible conformational isomers of limonene in the
mixed solution. The rotation of the isopropenyl group in limonene
is responsible for resonantly magnified gabs value of nBuPS
aggregates at the specific volume fractions.
intense (+)-sign (conformers 1), very intense (ꢀ)-sign (conformers
2), and intense (+)-sign (conformers 3), respectively. As a result,
optical rotation dispersion (ORD) and CD spectra of (R)-limonene
in solution greatly depends on the population of three conformers
in addition to nature of the solvent.
If the populations of three conformers are susceptibly
changeable by the polarity of a mixture of limonene, methanol,
and chloroform, certain conformers of (R)- and (S)-limonene may
be enriched within the aggregates at these specific volume
fractions. These results imply that a specific conformation among
six possible isomers of (R)- and (S)-limonene efficiently induces
According to a recent work [63], the magnitude and sign of [a D
]
and VCD signals depend on the dihedral angle (C9–C8–C4–H4) of
isopropenyl group on the quasi-equatorial cyclohexene ring [63].
The optimized dihedral angles of isopropenyl group were +129.52ꢂ
(conformer 1, methyl moiety of isopropenyl is in-plane to
Fig. 6. The gabs values at the first and second Cotton bands of nBuPS aggregates as a function of volume fraction of (S)- or (R)-limonene in a mixture of limonene, chloroform,
and methanol. (a) (R)-limonene and (b) (S)-limonene. Chloroform 0.3 mL and total volume 3.0 mL.
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polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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7
the nBuPS aggregates leading greatly magnified CD signals. For
example, one of three equatorial (R)-limonene conformers
selectively interacts with nBuPS, whilst all three equatorial
(S)-limonene conformers equally interact with nBuPS. It is noted
that the |gabs| value at the second Cotton band of (R)- and
(S)-limonene differs by 5 times, as mentioned above. (R)-limonene
more efficiently tends to induce CD-signal to nBuPS aggregates
than (S)-limonene, due to as yet unresolved reasons.
We verified the reproducibility of the anomaly, particularly,
around the resonantly enhanced volume fractions of (R)- and
(S)-limonene by employing multiple experiments in different days
and weeks. Typically, it took at least two days to obtain a series of
CD/UV-vis measurements for (R)-limonene ranging from 0.0 to
1.2 mL associated with 0.01–0.02 mL interval, followed by a series
of (S)-limonene chirality induced experiments. It thus needed
several days to yield several sets of (R)- and (S)-limonene induced
aggregation experiments. Similarly, we applied this protocol to
(1R)- and (1S)-pinene chirality induced aggregation experiments.
Similar to monocyclic limonene, bicyclic
couplet-like CD signals in nBuPS aggregates. Raw CD and UV–vis
spectra and their normalized nBuPS CD and UV–vis spectra
a
-pinene can induce
produced in a mixture of
a-pinene, chloroform, and methanol
(0.65/0.30/2.05 (v/v/v)) are given in Appendix, Fig. S3a and b.
Evidently, the gabs valuesatthe secondCotton bandattain ꢀ2 ꢃ10ꢀ2
for (1R)-pinene and +2 ꢃ10ꢀ2 for (1S)-pinene, although the
l value
at extremum wavelength (lext) in CD spectrum and lmax in UV–vis
spectrum are subtly different. The lext values are located at 402 nm
and 386 nm for (1R)-pinene, while they are 406 nm and 386 nm for
(1S)-pinene. The lmax values of (1R)- and (1S)-a-pinene are 399 nm
and 404 nm, respectively. These deviations in lext and lmax values
were reproducible by multiple experiments.
Similar to the case of limonene, the gabs values of
induced nBuPS aggregates depend somewhat on the volume
fraction of -pinene (Appendix, Fig. S3c and d). Although this
tendency is not obvious compared to the case of limonene, there
exist optimized volume fractions of -pinene to efficiently induce
the magnified CD-active nBuPS aggregates. Differences in
inducibility of molecular chirality between limonene and -pinene
a-pinene-
a
a
The refractive index at 656 nm (nc) and solution viscosity (
a function of volume fraction of (S)- and (R)-limonene in a mixed
solvent are plotted in Appendix, Fig. S1d. The values of and nc
h) as
a
h
to nBuPS may come from the adaptability of terpene; limonene
adopts a floppy monocyclic framework allowing three stable and
increased almost linearly with an increase of limonene fraction
regardless of (S)- and (R)-chirality. However, the nc value slightly
deviated to a lower value, as indicated by the red arrow, when
(R)-limonene was 0.85 mL (28% in volume). This subtle alteration
may be interpreted with the enhanced gabs value of nBuPS at
(R)-limonene around 0.75 mL.
A possible scenario for this anomaly may be ascribed to certain
impurities included in distilled limonene. Previously, we charac-
terized the enantiopurity of the distilled limonenes using chiral GC
three metastable conformations, though
a-pinene is in a rigid
bicyclic framework with one stable conformation.
At the moment, we cannot show up direct evidence that a
certain conformer among three conformers of (R)- and
(S)-limonene, depending on their solvent fractions, is specifically
interacted with the diarylpolysilane aggregates. A previous pape
showed the marked (R)- and (S)-limonene volume fraction
dependence including amplifications and multiple inversions in
gabs characteistics of three rodlike dialkylpolysilane aggregates
[50]. We assume that a floppy monocyclic terpene, limonene, is
one of the most adaptable chiral substances susciptible to the
natures of the surrounding solvents and rodlike polysilanes.
column (Supelco
[49]. The results were (R)-limonene >99.1% ee and [
(neat) and (S)-limonene >99.3% ee and [a 27 +103.19ꢂ (neat). At
b-DEX-120) as well as optical rotation at 589 nm
27
a
]
D +101.55ꢂ
]
D
the present stage, we do not think that the subtle differences in
27
enantiopurity and [a] D values between (R)- and (S)-limonene are
responsible for the this anomaly.
2.6. Alteration of aggregation size of nBuPS with aging time
Other reason arises from an inherent left-right asymmetry
between (R)- and (S)-limonene. Noting that (R)-limonene is a
naturally abundant terpene, while (S)-limonene is not. Similar
(R)–(S) asymmetry chirality inducibility can be invariably observed
in several polymer aggregations [39,44–47,49–54]. We infer briefly
that this limonene chirality anomaly may arise from universal
origin, as discussed in Section 2.8.
Tempo-spatial characteristics of aggregate size and its distri-
bution in the nBuPS aggregates were examined by DLS technique
at four different aging times (5, 15, 30, and 60 min) after evolution
(<1 min) of the aggregates (Fig. 7a and b). CD/UV–vis spectra
measurements of the fresh aggregate sample were completed
within 3 min. However, UV–vis measurements of prolonged
aggregate specimens were difficult due to a high turbidity.
Fig. 7. Alteration in aggregate sizes of nBuPS aggregates generated in various limonene, chloroform, and methanol fractions revealed by dynamic light scattering (DLS). (a)
(R)-limonene. Chloroform = 0.3 mL, total volume 3.0 mL. (b) (S)-limonene. Chloroform = 0.3 mL, total volume 3.0 mL.
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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Time-dependent alteration in the aggregate size was detectable
only by DLS technique. Because of the open-access condition
between interior and exterior of the aggregates surrounded by the
chiral and achiral constitutes, we can understand how the
aggregate propagates with aging time. All raw data are displayed
in Appendix, Figs. S4 and S5.
be seen. EtPS ((S)-limonene), EtPS ((R)-limonene), iPrPS
((R)-limonene), tBuPS ((R)-limonene), and tBuPS ((S)-limonene)
had mean aggregate size of ꢁ700–900 nm (5 min), while iPrPS
((S)-limonene), iBuPS ((S)- and (R)-limonene) had rather smaller
size of ꢁ150–200 nm. Moreover, iPrPS ((R)-limonene) and tBuPS
((R)- and (S)-limonene) at 30 min tend to further grow their
aggregate size, compared to those at 5 min.
As evident from Fig. 7a and b and Figs. S4 and S5, initial size (at
5 min aging) of the aggregates ranged from 250 and 550 nm for
(R)-limonene and from 200 and 500 nm for (S)-limonene. Larger
sizes were initially formed when 0.75 mL and 0.40 mL of
(R)-limonene were used. Similarly, larger sizes were initially
formed when 0.75 mL and 0.85 mL of (S)-limonene are employed.
In aggregates produced in 0.20, 0.60, and 1.20 mL of
(R)-limonene, the size increased with time, approaching a level-
off value at 400–700 nm. Aggregates in 0.40 mL and 0.85 mL of
(R)-limonene abruptly collapsed to two sizes (700 and 900 nm) at
15 min, then, approached a smaller level-off size of ꢁ400 nm and
ꢁ700 nm, respectively. Exceptionally, the aggregate size produced
in 0.75 mL of (R)-limonene existed stably at least for 60 min, and
was kept in its initial size of ꢁ450–500 nm. The 0.75 mL-(R)-
limonene induced the large gabs value among limonene containing
solvents tested in this work (Fig. 6a).
2.8. Comments on the subtle differences in the limonene chirality
induced aggregation
The origin of the limonene-chirality dependent stability of the
aggregate size is unresolved. However, subtle differences in L–D
(R–S or P–M) preferences of chiral bioresources including limonene,
amino acids, oligopeptides, and polymers under fluidic conditions
could be enriched into an interior of colloidal aggregates, followed
by the measurable values in their sizes [64–67].
A possibility of L–D preference at molecular level has been long
discussed by several researchers [64–73] in terms of hierarchical
scenarios due to inherent handedness ubiquitously existing in our
universe, for example, handed weak neutral currents and anti-
neutrinos [14,15,64–75]. Elemental particle physicists, astrophys-
icists, and molecular physicists assume that CP (charge-parity)
symmetry breaking, as proven by recent Bꢂ-meson decay experi-
ments at SLAC (USA) and KEK (Japan), should be responsible for
dominance of handed chiral matters over their anti-matters in our
universe [76–80].
Previously, Hegstrom et al. theoretically predicted the existence
of an ultratiny energy inequality (so-called PVED) between left-
and right-twisted ethylene on the order of 4 ꢃ10ꢀ20 Hartree
(ꢁ2 ꢃ10ꢀ17 kcal molꢀ1) due to parity violation at closed-shell
molecular level [68,69]. A possibility of whether the tiny inequality
is detectable has been long argued since 1960s [15,71]. If sterically
distorted isopropenyl group and/or cyclohexenyl ring were
regarded as models of the hypothetical twisted ethylene, the
subtle energy inequality could be enhanced as detectable level of
CD/CPL signals in liquid phase during the aggregation associated
with solvent quantity of isomeric limonene conformations.
Noticeable differences between (S)- and (R)-limonene in diary-
lpolysilane aggregates as chiroptical probes could infer the
consequence of the realistic models if handed, odd-parity weak
neutral current exists. It is thus awaited further comparative
studies between (S)- and (R)-limonene in liquid phases by means
of CD, ORD, VCD, Raman optical activity, NMR, and computational
calculations if the same and other research groups can verify our
radical speculations [62,63].
In aggregates produced in 0.20, 0.50, 0.60, and 1.20 mL of
(S)-limonene, the size monotonically increased with aging time,
approaching
a
level-off value of ꢁ550–900 nm. Aggregates
produced in 0.75 and 0.85 mL of (S)-limonene tended to fluctuate
between 350 and 650 nm. The 0.75 and 0.85 mL of (S)-limonene
afforded considerably enhanced gabs values to nBuPS aggregates
(Fig. 6b).
These DLS data were reproducible within deviation of ꢄ10–
20 nm in aggregate size based on three independent measure-
ments. It is thus assumed that tempo-spatial stability in the
aggregate sizes is interpreted to the gabs values of nBuPS during the
aggregation (Fig. 6a and b). The long-term stability of the
aggregates in 0.75 mL of (R)-limonene afforded the greatest gabs
value, while the fluctuating aggregates in the 0.75 and 0.85 mL of
(S)-limonene led to better gabs values. Other unstable aggregates
had weaker gabs values. When compared to the level-off value of
aggregate sizes at 60 min, (S)-limonene induced larger sizes in a
range of 550 and 900 nm, while (R)-limonene tended to afford
rather smaller sizes in a range of 400 and 700 nm.
2.7. Alteration in aggregation size of EtPS, iPrPS, iBuPS and tBuPS
with aging time
DLS measurements at two aging times (5 and 30 min) were
conducted for aggregates of EtPS, iPrPS, iBuPS and tBuPS
(Appendix, Fig. S6). In this case, a volume ratio between limonene,
CHCl3, and methanol was fixed to 0.40/0.30/2.30 (v/v/v) for iPrPS,
iBuPS and tBuPS aggregates, while 0.75/0.30/1.95 (v/v/v) for EtPS.
Although no significant differences in mean aggregate size
between (S)- and (R)-limonene for EtPS and iBuPS at aging times
(5 min and 30 min) were observed, noticeable differences between
(S)- and (R)-limonene (5 min and 30 min) for iPrPS and tBuPS can
3. Experimental
3.1. Materials
Five diarylpolysilanes, nBuPS, EtPS, iPrPS, iBuPS, and tBuPS,
were prepared by Wurtz coupling reaction with the corresponding
dichlorodiarylsilane with sodium in hot toluene in the presence of
Fig. 8. A general synthetic scheme of diarylpolysilanes.
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polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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9
diglyme as cocatalyst. Monomers and polymers used in this work
were prepared when M.F. worked for NTT-BRL and CREST-JST
during 1990–1999 as a part of the helical polysilane projects. A
general synthetic procedure of diarylpolysilanes is given in Fig. 8
and details are given in Appendix.
29Si (59.59 MHz) NMR spectra were taken in CDCl3 at 30 ꢂC or 40 ꢂC
with a Varian Unity 300 MHz NMR spectrometer using tetrame-
thylsilane as an internal standard.
3.3. Calculation
3.2. Characterization methods
Molecular mechanics calculations were carried out using
Molecular Simulation Inc. (MSI), the Discover 3 module, Ver.
4.00 on a Silicon Graphics Indigo II XZ computer. Standard
parameters (default) were SiꢀꢀSi bond length of 2.34 Å, an
SiꢀꢀSiꢀꢀSi bond angle of 111ꢂ, and the pcff force field (MSI) suited
for polymers. MSI built-in functions were used as the set-up
parameters, including simple-minimization under default con-
ditions with dihedral angle restraints, steepest descents for the
first derivative, iteration limit of 1000, movement limit of 0.2, and
derivative for 1.0 and simple dynamics with a constant volume and
temperature, initial temperature of 300 K, direct velocity scaling
with a time step of 1 fs, integration, and initial velocity of random
velocities from the Boltzmann distribution.
Spectroscopic grade methanol and chloroform were purchased
from Dojindo (Kumamoto, Japan). (R)- and (S)-limonene, (1R)- and
(1S)-a-pinene, that were purchased from Tokyo Chemical Industry
(TCI, Tokyo, Japan), were distilled in a reduced pressure and stored
in the dark. (R)-Limonene ([a 23
]
D = +97.5ꢂ (neat)), (S)-limonene
([a 23
and (1S)-
]
D = ꢀ98.3ꢂ (neat)), (1R)-
a-pinene ([a]
D = +38.6ꢂ (neat)),
23
a
-pinene ([a 23
]
D = ꢀ38.0ꢂ (neat)). The [a 23
]
value was
D
obtained with a JASCO P-1020 polarimeter.
The CD and UV–vis spectra of a homogeneous solution and
an aggregation suspension were simultaneously recorded on a
JASCO J-725 spectropolarimeter (Hachioji, Tokyo, Japan)
equipped with
a Peltier controlled housing and synthetic
quartz (SQ) cuvettes (GL science, Tokyo, Japan) under the
condition (light source: Osram water-cooled 450-W Xenon lamp
(Munich, Germany), path length: 1.0 cm, scanning rate: 200 nm
minꢀ1, bandwidth: 1 nm, response time: 2 s, a single accumula-
tion, data sampling: 0.5 nm interval) at 25 ꢂC. UV–vis spectra
were corrected by subtracting an increment in the background
signals due to particle scattering by adjusting to absorbance
zero at 500 nm in the original UV–vis data, while CD spectral
data were not susceptible to particle scattering and were used
without data processing. The CPL and PL spectra were recorded
on a JASCO CPL-200 spectrofluoropolarimeter (Osram 150-W
air-cooled Xenon lamp (Munich, Germany)), detected at an
angle of 0ꢂ with notch filter (1:106), a path length: 1.0 cm at
4. Conclusions
Aiming at realizing an artificial polymeric model of an open-
flow coacervate system in the ground and photoexcited states,
we designed soft-matter aggregates surrounded by non-polar
terpene and achiral solvents. The aggregates were made of
photoluminescent bis(p-n-butylphenyl) polysilanes (nBuPS)
which is a non-charged stiff CD-silent and CPL-silent polymer
with high molecular mass (Mw = 8.49 ꢃ104, Mn = 2.93 ꢃ104).
(S)- and (R)-limonene acted as efficient stereogenic center
transferable solvents during aggregation, though (1S)- and (1R)-
pinene were also efficient. The behavior of solvent chirality
induced aggregation was characterized by CD and CPL spectro-
ꢁ25 ꢂC,
a
scanning rate: 200 nm minꢀ1
,
a
bandwidth for
scopic data analysis. The nBuPS aggregates generated in a
excitation and monitor: 10 nm at 360 nm, a band width for
monitor: 10 nm, a response time: 2 s, no collimator lens, data
sampling: 0.5 nm interval. Here, incident light in the CPL
mixture of limonene 0.75 mL, methanol 1.95 mL, and chloroform
0.3 mL, had gabs values as high as +0.04 for (R)-limonene and
ꢀ0.03 for (S)-limonene at the first Cotton band (ꢁ407 nm) and
weak glum values of +0.004 for (R)-limonene and ꢀ0.003 for
(S)-limonene at ꢁ409 nm. The gabs factor, however, greatly
depended on the volume fraction and chirality of limonene in
the tersolvents. These behaviors were interpreted to the tempo-
spatial stability of aggregate size induced by limonene chirality
with the help of DLS measurement. Further comparative studies
between (S)- and (R)-limonene in liquid phases would be needed
to verify our results and speculations.
spectrometer used natural light that is
a simultaneous
irradiation of a mixture of left- and right-circularly polarized
light. With a reference of quinine sulfate (in conc. H2SO4) as a
standard, the quantum yield of nBuPS in tetrahydrofuran
was ꢁ 41%. PL spectra were recorded on a JASCO FP-6500 spectro-
fluorometer (a path length: 10 mm, a band width for excitation:
3 nm, a bandwidth for monitor: 3 nm, a response time: 2 s,
excitation: 380 nm, data sampling; 1.0 nm interval). The nc
(656 nm) values of solvents, that require parameters of DLS
measurements, were measured by an Atago DR-M2 thermo-
controlled refractometer at 656 nm (Tokyo, Japan). Weight-
average molecular mass (Mw) and number-average molecular
mass (Mn) were obtained with Shimadzu 10A gel-permeation
chromatography (GPC) (Kyoto, Japan) using an Agilent Technol-
Acknowledgements
M.F. learned a lot from Prof. Yoshihisa Inoue (Emeritus Prof.,
Osaka University) who found entropy driven chirogenesis and
demonstrated circularly polarized light origin photochirogenesis
along with Soai reaction. M.F. acknowledges financial supports
from a Grant-in-Aid for Scientific Research (26620155, FY2014–
2016), JST-CREST (FY1998–2003), and NTT (FY1990–1999). N.A.A.R.
acknowledges financial support from the NAIST Presidential
Special Fund. M.F. expresses a special thank his former colleagues
at NTT and core members of JST-CREST, who are Prof. Hideki
Sakurai (Emeritus Prof., Tohoku University), Prof. Nobuo Matsu-
moto (Shonan Institute of Technology), Prof. Kyozaburo Takeda
(Waseda University), Prof. Hiroyuki Teramae (Josai University),
Prof. Masaie Fujino (Gunma National College of Technology), Prof.
Julian R. Koe (International Christian University), Dr. Kazuaki
Furukawa, Dr. Seiji Toyoda, Dr. Hiroshi Nakashima, Hiromi Tamoto-
Takigawa, the late Prof. Akio Teramoto (Emeritus Prof., Osaka
University), Prof. Takahiro Sato (Osaka University), Prof. Ken Terao
(Osaka University), Prof. Junji Watanabe (Emeritus Prof., Tokyo
ogy Plgel mini-mix D (5
Denko Shodex KF806M (10
m
m, i.d. 4.6 mm, length 20 cm) or Showa
m, i.d. 8.0 mm, length 30 cm) with
m
special-grade tetrahydrofuran as an eluent with a calibration of
polystyrene standards. Aggregate size was analyzed by Otsuka
Electronics DLS-6000 (Hirakata, Osaka, Japan) detected at
633 nm (He–Ne laser) with an accumulation of 30 times using
solution viscosity data at 25 ꢂC obtained with
a Sekonic
viscometer VM-100 (Tokyo, Japan). Acquired data by these
methods were re-analyzed by KaleidaGraph (ver. 4.13, Synergy
software, Pennsylvania, USA).
FOM images as jpeg data were obtained with a Nikon (Tokyo,
Japan) Eclipse E400 with a filter block UV1A (365 nm for excitation,
dichroic mirror at 400 nm, a sharp edge, long pass filter at 400 nm)
under an Ushio high-pressure Hg lamp source (Kyoto, Japan) and a
tungsten halogen lamp as white light source. 13C (75.43 MHz) and
Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027

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Institute of Technology), Prof. Kento Okoshi (Chitose Institute of
Science and Technology), and Masao Motonaga (JST-CREST) for
their stimulating discussion. K.Y. thanks Prof. Hiroko Yamada
(NAIST), Dr. Ayako Nakao, and Takashi Matsuda for fruitful
discussion and Yoshiko Nishikawa for helping him DLS measure-
ment. Finally, we are thankful to Leigh McDowell (NAIST) for
English proofreading our manuscript.
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Please cite this article in press as: M. Fujiki, et al., Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of SiꢀꢀSi bond
polymers during aggregation in chiral fluidic media, J. Photochem. Photobiol. A: Chem. (2016), http://dx.doi.org/10.1016/j.jphoto-
chem.2016.01.027