Multi-stimuli-responsive fluorescence of axially chiral 4-ene-β-Diketones

Article abstract of DOI:10.1016/j.dyepig.2020.108851

A unique series of simple, smart, and chiral binaphthalene-substituted 4-ene-β-diketones molecules has been designed and prepared. Their optical properties, charge contribution, and transition process highly depend on their chemical structures. These π-conjugated materials are highly emissive in both solution and solid (emission quantum yield up to 68%), owing to the inhibition of enol-keto tautomerization and the effect of steric hindrance from binaphthalene. Through ethylenic bond hydrolysis, they can be used for not only cation/anion sensing but also chiral amino acids recognition. Moreover, at low concentrations, they have little cytotoxicity to living cells and can stain cytoplasm. Therefore, they afford a new platform in the design of multi-stimuli-responsive, smart, and chiral materials.

Full text of DOI:10.1016/j.dyepig.2020.108851

Dyes and Pigments 184 (2021) 108851
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Multi-stimuli-responsive fluorescence of axially chiral 4-ene-β-Diketones
a
,
1
b
,
c,
1
a
a
a
a,*
Dehua Wu , Xinyi Fang
, Jintong Song , Lang Qu , Xiangge Zhou , Haifeng Xiang
,
b
,
**
c,***
Jun Wang
, Jin Liu
a
College of Chemistry, Sichuan University, Chengdu, 610041, China
b
c
State Key Laboratory of Oral Diseases, Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, 610064, China
Laboratory of Stem Cell Biology, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, 610064, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A unique series of simple, smart, and chiral binaphthalene-substituted 4-ene-β-diketones molecules has been
β-Diketones
Binaphthalene
designed and prepared. Their optical properties, charge contribution, and transition process highly depend on
their chemical structures. These -conjugated materials are highly emissive in both solution and solid (emission
π
Excited-state intramolecular proton transfer
quantum yield up to 68%), owing to the inhibition of enol-keto tautomerization and the effect of steric hindrance
from binaphthalene. Through ethylenic bond hydrolysis, they can be used for not only cation/anion sensing but
also chiral amino acids recognition. Moreover, at low concentrations, they have little cytotoxicity to living cells
and can stain cytoplasm. Therefore, they afford a new platform in the design of multi-stimuli-responsive, smart,
and chiral materials.
(
ESIPT)
Chiral recognition
1
. Introduction
Luminescent (fluorescent or phosphorescent)
a hydrogen-bonded six-membered ring via tautomerization between
keto and enol forms [19–21]. However, unlike that of = Nꢀ /ꢀ OH-based
π
-conjugated organic
ESIPT molecules [14,15], the tautomerization of β-diketones molecules
materials [1] have attracted great attention in recent decades owing to
their wide applications in organic light-emitting diodes (OLEDs) [2–4],
light-emitting electrochemical cells (LECs) [5,6], triplet–triplet annihi-
lation based upconversion [7,8], fluorescence probes [9–11],
bio-imaging [12,13], and so forth. In order to tune the emission band
from planar enol forms into twisted keto forms would destroy the mo-
lecular
π
-conjugated planarity and lead to the emission quenching
through the nonradioactive dissipation. Therefore, the simple phenyl--
β-diketones (Fig. 1(b)) is non-emissive and some chemical modifications
(Fig. 1(c)), such as electron-donating substituent (DA system) [22–25],
cyclization [26–31], alkene [26–34], and multiple intramolecular
hydrogen bonds [29,31], have been adopted to improve Φ. In addition,
β-diketones molecules are widely used as ligands to yield highly emis-
sive B(III) [35–38], Ln(III) [39], Ir(III) [40–42] and Pt(II) [43,44]
complexes.
(
λ
em) and quantum yield (Φ) of the organic materials, a number of
strategies, including extending -conjugation, substituent effect,
π
donor-acceptor (DA) system, F o¨ rster resonance energy transfer, intra-
molecular charge transfer (ICT), excimer [2–4,9–11], excited-state
intramolecular
proton
transfer
(ESIPT)
[14,15],
and
′
aggregation-induced emission (AIE) [16–18], are explored. Among
them, ESIPT, an intramolecular hydrogen bond between the proton
As a class of important axially chiral molecules, 1,1 -binaphthalene-
′
′
′
2,2 -diol (BINOL) and 1,1 -binaphthalene-2,2 -diamine (BINAM)
recently have become a hot field in optical materials for the applications
in chiral recognition [45–49] and circularly polarized luminescence
(CPL) [50–54]. However, it is still challenging to prepare highly emis-
sive binaphthalene-based materials, because the binaphthalene group
exhibits intramolecular motions through some small-angle rotations
around the chiral axis [53,55]. In the present work, combining the
–
–
donor (ꢀ OH and –NH
2
) and the proton acceptor (=Nꢀ and –C
O)
groups in close proximity to each other in a molecule, in particular offers
some advantages such as large Stokes shift with negligible
a
self-absorption and environment-sensitive dual (enol and keto)
emissions.
It’s well known that β-diketones molecules (Fig. 1(a)) usually exist in
*
Corresponding author.
*
*
* Corresponding author.
** Corresponding author.
E-mail addresses: xianghaifeng@scu.edu.cn (H. Xiang), wangjunv@scu.edu.cn (J. Wang), ljamelia@163.com (J. Liu).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.dyepig.2020.108851
Received 6 May 2020; Received in revised form 27 July 2020; Accepted 11 September 2020
Available online 28 September 2020
0
143-7208/© 2020 Elsevier Ltd. All rights reserved.

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
vapor diffusion of DCM/hexane. Based on the 1H nuclear magnetic
1
resonance ( H NMR) and x-ray single crystal analysis, 4-ene-β-diketones
molecules mainly exist as enol forms in both solution and solid (see the
later discussion).
2
.2. Photophysical properties
The photophysical properties, including UV/visible absorption and
fluorescence data (emission decay lifetime
τ and Φ), of all synthesized
compounds at room temperature are listed in Tables S1 and S2 (in
Supporting Information). The photophysical properties, except circular
dichroism (CD), of enantiomers are similar, which are consistent with
our previous reports [60–63]. The absorption spectra of all
ꢀ 5
ꢀ 3
4
-ene-β-diketones molecules in toluene (1.0 × 10 mol dm ) are given
in Fig. 3. The presence of weak electron-accepting ꢀ Cl and –F sub-
stituents [(S)1–F: λabs = 377 nm; (S)1–Cl: λabs = 386 nm], strong
electron-donating ꢀ OMe substituent [(S)1–OMe: λabs = 380 nm], and
π
-extended system [(S)-Naph, λabs = 387 nm) to the simplest (S)1–H
Fig. 1. (a) Enol-keto tautomerization for β-diketones. (b) Chemical structures
of non-emissive phenyl-β-diketones and (c) emissive β-diketones molecules.
(λabs = 380 nm) has little effect on absorption bands. However, strong
electron-donating ꢀ NEt
2
substituent [(S)1–NEt , λabs = 422 nm] and
2
double binaphthalenes [(S,S)2, λabs = 411 nm; (S,S)3, λabs = 445 nm]
lead to obviously red shifts in absorption spectra.
axially chiral and sterically bulky properties of BINOL, we have linked
β-diketones and BINOL by the alkene bridge to achieve chiral lumino-
phors 1–3 (8 pairs of enantiomers, Fig. 2) with large Stokes shifts (up to
Density functional theory (DFT) and time-dependent DFT (TD-DFT)
were performed by Gaussian 09 program package [B3LYP 6-31G(d,p)]
to investigate the UV/visible absorption spectra and charge transfer in
ꢀ
1
6
140 cm ) and high emission quantum yields (up to 68%). The pur-
excited states. In dilute toluene solution, (S)1–NEt
2
shows a dominating
poses of the presence of alkene linker are: 1) to easily synthesize; 2) to
achieve fully -conjugated molecular system; 3) to inhibit the tauto-
absorption peak (λabs = 422 nm), which is predicted well by the
π
merization from enol forms into keto forms; 4) to obtain reasonable
stability for multi-stimuli-responsive fluorescence through ethylenic
bond hydrolysis.
2
. Results and discussion
2
.1. Synthesis and characterization
All 4-ene-β-diketones molecules were prepared by the modified
′
′
methods [56,57] with 1,1 -binaphthalene-2,2 -diol-3-carbaldehyde [58]
and methyl-β-diketones [59] (Fig. 2). Most of them have a good solu-
bility in organic solvents, such as DMF, DMSO, dichloromethane (DCM),
toluene, ethyl acetate (EA) and EtOH, and a bad solubility in cyclo-
hexane and petroleum ether (PE). They don’t dissolve in H
2
O. Most of
them either in solution or in solid state are stable within several months
under air. We successfully obtained some good-quality single crystals of
(
S)1–H (yellow particles, CCDC 1963383), (R)1-F (yellow particles,
Fig. 3. Absorption spectra in toluene (1.0 × 10ꢀ mol dm ).
5
ꢀ 3
CCDC 1963384), and (S,S)2 (yellow particles, CCDC 1963385) by the
Fig. 2. Synthesis and chemical structures of chiral 4-ene-β-diketones molecules.
2

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
theoretical calculation (λabs = 430 nm) (Fig. 4) and can be contributed to
the highest occupied molecular orbital (HOMO) → the lowest unoccu-
pied molecular orbital (LUMO) (excited state 1, 436 nm, 100%, oscil-
lator strength fosc = 1.1415). The energy level diagram and frontier
HOMOꢀ 1 → LUMO (excited state 2, 398 nm, 95%, Fig. 4). The frontier
molecular orbitals of (S)1–H reveal that it has a totally different ICT
from the outside naphthalene ring to the other side benzene ring. In
addition, the outside naphthalene ring is orthogonal as well, and thus
the ICT of (S)1–H is blue shifted and less efficient (fosc = 0.8908)
molecular orbitals of (S)1–NEt
2
are depicted in Fig. 4 as well. The
electron-donating ꢀ NEt
2
is mostly contributed to the HOMO, whereas
compared with that of (S)1–NEt
2
.
the electron-accepting naphthalene ring (the inside naphthalene ring of
BINOL) is mostly contributed to the LUMO, clearly indicating the intense
The low-energy absorption band (λabs = 411 nm) of (S,S)2 is mainly
originated from
πꢀ π
* in HOMO → LUMO (excited state 1, 441 nm, 95%,
ICT from ꢀ NEt
DA charge transfer, the
22 nm. It is obvious that the outside naphthalene ring has no contri-
bution to the low-energy transition, because it is almost orthogonal to
the -conjugated molecular plane.
Compared with (S)1–NEt , however, (S)1–H without ꢀ NEt
blue-shifted absorption band (λabs = 380 nm), which can be assigned to
2
to the inside naphthalene ring [64,65]. Along with this
fosc = 1.2720, Fig. 4). Except the two outside naphthalene rings, the
π
ꢀ π
* transition of (S)1–NEt is red shifted at
2
central
π-functions of (S,S)2 is efficiently extended into the entire
4
molecule, and consequently (S,S)2 has red-shifted absorption compared
with (S)1–H. Since (S,S)2 is more symmetric than (S)1–NEt , little ICT
is observed for (S,S)2. This might be one of factors that (S,S)2 has blue-
shifted absorption compared with (S)1–NEt , even if (S,S)2 is more
conjugated than (S)1–NEt
For the series of (S)1, only (S)1–NEt
solvent of toluene (λem = 526 nm, Φ = 58%,
S2, and Fig. 5), because (S)1–NEt has an efficient DA system. This DA
system can be further identified by the obvious solvent effect on emis-
emits strong blue emission in non-polar solvent
2
π
2
2
has a
2
2
.
2
is highly emissive in non-polar
= 0.55 ns, Tables S1 and
τ
2
sion (Fig. 6). (S)1–NEt
2
of petroleum ether (PE, λem = 495 nm, Φ = 68%), but its emission be-
comes orange-yellow along with the emission quenching in the high
polar solvent of THF (λem = 564 nm, Φ = 5.5%). The emission spectrum
of (S,S)2 in toluene (λem = 500 nm, Φ = 17%) is blue-shifted compared
with that of (S)1–NEt
solvent effect than (S)1–NEt
and (S)1–NEt have different transition ways. When the protecting
groups of methoxymethyloxy (OMOM) are removed, the resultant (S,S)
exhibit red-shifted emission at 542 nm with a lower Φ of 5.4% in
toluene. In addition, (S)1–NEt and (S,S)2 are highly emissive in
and (S,S)2, respectively] and
2
. Moreover, (S,S)2 shows a relatively smaller
2
(Fig. S1), further identifying that (S,S)2
2
3
2
powder [Φ = 17 and 5.5% for (S)1–NEt
2
polymethyl methacrylate (PMMA) film [Φ = 48 and 33% for (S)1–NEt
and (S,S)2, respectively, Table S1, Fig. 5, and S2].
2
Fig. 4. Computational and experimental absorption spectra (in toluene), en-
ergy level diagram, and frontier molecular orbitals of (S)1–NEt , (S)1–H, and
S,S)2.
Fig. 5. Normalized emission spectra and photographs (under room and 360 nm
UV light) of 4-ene-β-diketones molecules in toluene (1.0 × 10ꢀ mol dm ),
5
ꢀ 3
2
(
powder, and PMMA film (1.0 wt%).
3

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
The absorption spectra of (S)1–NEt
2
and (S,S)2 have little changes
in different organic solvents (Figs. S4 and S5), revealing the absence of
solvent-induced enol-keto tautomerization. Based on DFT and TD-DFT
calculations (Fig. 8), the keto form of (S)1–NEt
2
is much more twisty
than enol form, and the former would has obviously blue-shifted ab-
sorption (λabs = 328 nm) compared with the later (λabs = 430 nm).
Indeed, the enthalpy (sum of electronic and thermal enthalpies) and free
energy (sum of electronic and thermal free energies) between the enol
and keto form of (S)1–NEt
2
is 5.81 and 4.37 kcal/mol, respectively. This
indicates that the enol-keto tautomerization is endothermic and enol
form is thermodynamically more stable than keto form. The absence of
solvent-induced enol-keto tautomerization can be further confirmed by
1
the H NMR analysis (Fig. 9 and S6). In CDCl
3
and DMSO‑d
6
solution of
1
1
2
(
S)1–NEt
2
, the H NMR peak area of reactive enol-H and ene-H is 0.34
3
and 0.50, respectively, corresponding to that of H (peak area = 1).
Furthermore, there is no 1H NMR signal of keto-H4 (δ = ~4.0) [72].
Therefore, (S)1–NEt
DMSO‑d solution.
At first, the solvent of toluene is used to examine photo-induced enol-
keto tautomerization of (S)1–NEt . As shown in Fig. S7, the low-energy
absorption of (S)1–NEt disappears under 360 nm UV irradiation, but it
2 3
mainly exists in the form of enol in both CDCl and
6
Fig. 6. Normalized emission spectra and photographs (under 360 nm UV light)
2
of (S)1–NEt
2
in different solvents (1.0 × 10ꢀ mol dm , excited at 425 nm).
5
ꢀ 3
2
would not be recovered in the darkness. This indicates that the change is
not reversible and UV irradiation would promote hydrolysis rather than
reversible enol-keto tautomerization. If the solvent is replaced by DMSO,
both (S)1–NEt2 and (S,S)2 show a good photostability (Fig. S7).
2
.3. Hydrolysis in THF solution
All the synthesized solid-state compounds are stable under air.
Except (S,S)3, they are stable in organic solvents. For example, the
absorption spectra of (S)1–NEt and (S,S)2 in THF exhibit negligible
2
2
.5. X-ray single crystal structures and mechanism of polar solvent-
changes (Fig. 7 and S3), but the low-energy absorption band of (S,S)3 in
THF decays along with time, resulting in color change from yellow into
colorless. Thin-layer chromatography (TLC) analysis reveals that (S,S)3
without protecting groups of OMOM would decompose through ethyl-
enic bond hydrolysis (see the later discussion) [66,67].
induced fluorescence
The molecule chemical structures and X-ray single-crystal arrange-
ments of organic luminescent materials act an important role in their
fluorescence properties. As expected, in solid, (S)1–H, (R)1-F, and (S,S)
2
exist in the enol form as well (Fig. 10). Two intramolecular = O⋅⋅⋅HOꢀ
2
.4. Inhibition of enol-keto tautomerization
hydrogen bonds are found in (S)1–H (1.735 Å) and (R)1-F (1.801 Å)
single crystal structures and the –OH groups are located in the side of
binaphthalene. For more symmetric (S,S)2, the enol hydrogen is sym-
metrically positioned between the two oxygen atoms (Fig. S8), and the
enol form is stabilized by resonance-assisted hydrogen bonding [73].
Except the outside naphthalene rings and protecting OMOM groups, all
the other atoms of (S)1–H, (R)1-F, and (S,S)2 are almost located in one
β-Diketones molecules are well known to have the tautomerization
between keto and enol forms [19–21]. In general, the
π
-conjugated enol
forms are more stable than the keto forms. The enol-keto tautomeriza-
tion would be influenced by many factors including solvent polarity
[
[
68], substitution groups [69,70], pH values, and UV light irradiation
22,71]. However, it should be noted that the enol-keto tautomerization
◦
plane. The dihedral angle between the two naphthyl rings is 97.2 ,
◦
◦
would generally quench emission through the n–
π
* triplet states of
94.2 , and 101.1 for (S)1–H, (R)1-F, and (S,S)2, respectively.
(S)1–H and (R)1-F molecules are cross-stacking, but (S,S)2 mole-
cules are arranged in a Z-type lamellar packing characteristic with a
distance of ~7.10 Å (Fig. S9). Owing to the effect of steric hindrance
from binaphthalene, there are no intermolecular hydrogen bonds and
π
-diketones [22].
Fig. 7. Absorption spectra of (S,S)3 (left) and absorbance at λabs of (S)1–NEt
2
,
Fig. 8. Computational absorption spectra and enthalpy and free energy levels
ꢀ 5
ꢀ 3
(
S,S)2 and (S,S)3 (right) in THF at different times (1.0 × 10 mol dm in THF
2
of the enol and keto form for (S)1–NEt and its optimized structure of
under room temperature, sunlight and lamplight).
keto form.
4

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
ꢀ
solution of (S)1–NEt
2
(λabs = 422 nm, λem = 564 nm, Φ = 5.5%), only I
dramatically brings down absorption and emission intensity. For (S,S)2,
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
however, I , Br , NO
2
, SCN , and S would obviously decrease the
ꢀ
absorption and emission intensity (Fig. 11). I was used to perform the
working curve (Fig. S18). The emission intensity (λem = 501 nm) of (S,S)
2
2
linearly reduces (correlation coefficient R = 0.978, n = 15) along
ꢀ
with 0.2–1.6 equivalents of I .
TLC analysis (Fig. S19) reveals that (S,S)2 would decompose to yield
the starting materials of BINOL-based formaldehyde and methyl-
β-diketones (Fig. 2) through ethylenic bond hydrolysis [66,67]. The
dynamics of the hydrolysis reaction is studied by time-dependent ab-
ꢀ
sorption and fluorescence (Fig. 11) spectra. The I -promoted hydrolysis
is very fast and needs about 20 min to reach equilibrium at room
temperature.
2
.7. Chirality and chiral recognition
The chirality properties of (R)/(S)1–NEt
2
and (R,R)/(S,S)2 are
investigated by CD spectra (Fig. 12). Even in dilute MeCN, the CD signals
1
Fig. 9. H NMR spectra of (S)1–NEt
2 3 6
in CDCl and DMSO‑d .
of (R)/(S)1–NEt
, the (S) enantiomers, show positive Cotton peak at ~340 nm and
negative Cotton peaks at ~270 and ~330 nm. (R)1-NEt and (R,R)2,
2
and (R,R)/(S,S)2 are still strong. (S)1–NEt
2
and (S,S)
2
2
the (R) enantiomers, exhibit exactly the mirrored CD spectra, indicating
that they are two pairs of enantiomers. Combining with previous work
[
45–49] these CD signals in shorter wavelength regions (<350 nm) are
mainly originated from chiral binaphthalene itself. It is strange that the
Cotton peaks in longer wavelength regions (>350 nm) are relatively
weak, even although they have strong absorption at 405–426 nm in
MeCN (Table S2) [78,79]. This might be caused by the fact that the
absorption at longer wavelength regions is mainly originated from the
central
π
-conjugations and the outside naphthalene rings (axial
chirality) have little contribution to the absorption at longer wavelength
regions (Fig. 4).
Fig. 10. X-ray single crystal structures of (S)1–H, (R)1-F, and (S,S)2.
πꢀ π interactions in X-ray single crystal structures of (S)1–H, (R)1-F, and
Chiral (S)1–NEt
2
and (S,S)2 might be used for the chiral recognition
of amino acids through intermolecular hydrogen bonds [45–49] or hy-
drolysis. When adding 19 pairs of chiral L-/D-amino acids and a achiral
amino acid of Gly to the (S)1–NEt2 THF solution, the intensity of ab-
sorption and emission peak shows little changes (Figs. S20 and S21),
(
S,S)2. Therefore, both (S)1–H and (R)1-F are highly emissive in both
solution and solid, combining the fact of inhibition of enol-keto
tautomerization.
revealing that (S)1–NEt can’t be hydrolyzed by amino acids and has no
2
ability to probe amino acids. On the other hand, the absorption and
2
.6. Ion probe properties
emission of (S,S)2 can be decreased obviously by many amino acids,
especially by D-Lys, L-Pro, L-Lys, D-Tyr, and D-Pro (Fig. 13).
Since β-diketones in the enol form is acting as an O^O bidentate
Interestedly, (S,S)2 has the ability of chiral recognition for L-/D-Tyr
(Fig. 14). The selective recognition of chiral molecular enantiomers is
related to the enantiomeric emission difference ratio, ef, according to ef
chelating agent can coordinate with many metal ions [35–44], (S)
1
–NEt (Figs. S10 and S11) and (S,S)2 (Fig. S12ꢀ S15) are used as metal
2
ion probes firstly. They have similar sensing performances. As example,
= (I
L
ꢀ I
0
)/(I
D
ꢀ I
0
), in which I
0
represents the emission intensity of re-
and I are the emission
the absorption band (λabs = 412 nm) of (S,S)2 in THF disappears soon
ceptor in the absence of a chiral substrate and I
L
D
2
+
(
30 min) upon adding Co excessively, but other metal ions, such as
intensities in the presence of L- and D-substrates, respectively. The ef of
L- and D-Tyr is up to 1.81 (Fig. S22) for (S,S)2. The Tyr-promoted hy-
drolysis of (S,S)2 is relatively slow and needs about 24 and 10 h to reach
+
3+
2+
2+
+
+
2+
2+
+
2+
2+
2+
Ag , Al , Ca , Cu , K , Li , Mg , Mn , Na , Ni , Pb , and Zn
would have much less effect. On the same time, the emission of (S,S)2
,
2
+
◦
(
λ
em = 501 nm, Φ = 18%) would efficiently be quenched by Co . The
equilibrium at room temperature and 50 C, respectively (Fig. S23).
fluorescence intensity decreases linearly upon the addition of 3–8
2
+
equivalents of Co
and then remains unchanged upon the further
2.8. Living cell imaging
2
+
addition of Co (Fig. S15), indicating that the sensing mechanism is
2
+
Co -promoted hydrolysis but not coordination reaction [74,75]. Of
course, we could not rule out the possibility that some other metal ions,
Fluorescent dyes are promising tools for turn-on, real-time, onsite
and non-invasive visualization of biological molecules and processes in
such as Cu2 and Ni , can coordinate with (S,S)2, because the addition
of these metal ions would result in emission quenching but little changes
in absorption spectra (Figs. S12 and S13).
+
2+
live cells and organisms. Since (R)/(S)1–NEt
2
have large Stokes shifts
(Table S2) and high resistance to photobleaching, anions and amino
acids, they are used for cell imaging. The metabolic viability of human
colon cancer cells (SW480) is determined through Cell Counting Kit-8
We recently reported that ESIPT salicylaldehyde-based Schiff bases
can be used as universal anion hosts/probes through intermolecular
(CCK-8) assay to evaluate the cytotoxicity of (R)/(S)1–NEt
with big
2
. (R)/(S)
hydrogen bonds[ [60–63], [76,77] and thus we tried to use (S)1–NEt
and (S,S)2 (Fig. 11 and S18–S20) as anion probes. As shown in Figs. S16
2
1–NEt
2
π
-conjugated system would have high cytotoxicity to
ꢀ 5
ꢀ 3
ꢀ 6
kill the cells if their concentrations are higher than 1.0 × 10 mol dm
ꢀ
ꢀ
ꢀ
and S17, upon excessively adding 100 equivalents of anions (Ac , Br ,
(Fig. S24). However, if their concentrations are lower than 1.0 × 10
2
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ 3
C
2
O
4
ꢀ
, Cl , CO
3
, H
2
PO
4
, HCO
3
, HPO
2ꢀ
4
, HSO
3
, IO
4
, NO
2
, NO
3
, OH ,
mol dm , (R)/(S)1–NEt
2
would have low cytotoxicity and promote cell
4
7
3ꢀ 2ꢀ
2ꢀ
ꢀ
2ꢀ
2ꢀ
ꢀ
P
2
O
, PO
4
, S , S
2
O
3
, SCN , SO
3
, SO
4
, S
2
O
8
, and I ) to the THF
growth (Fig. S25).
5

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
Fig. 11. Absorption and emission spectra of (S,S)2 (1.0 × 10ꢀ 5 mol dm in THF, excited at 400 nm) upon adding 100 equivalents of different anions (a and b) or
ꢀ 3
different equivalents of Iꢀ (c and d). Reaction dynamics of (e) absorption and (f) emission spectra after adding 1.5 equivalents of I ꢀ
.
nm, the strong green emission mainly from (R)/(S)1–NEt
The merge photos reveal that (R)/(S)1–NEt are located in cytoplasm
rather than cell nucleus. In addition, (R)/(S)1–NEt are one pair of
enantiomers, but they have the similar the staining locations in the cells.
2
are observed.
2
2
3
. Conclusions
In summary, we have prepared and reported a unique series of
alkene-linked BINOL-β-diketones molecules. The x-ray single crystal
structures and TD-DFT calculations reveal that small changes in chem-
ical structures would lead to big differences in charge distribution and
transition process. Since the presence of alkene linker and BINOL would
help to prevent from enol-keto tautomerization and intermolecular
πꢀ π
interactions, respectively, these -conjugated materials are highly
π
emissive in both solution and solid. Through alkene hydrolysis, they can
be used for not only cation/anion sensing but also chiral amino acids
recognizing. Moreover, at low concentrations, these fluorescent dyes
with little cytotoxicity to living cells can stain and light up cytoplasm.
Therefore, we believe that they potentially provide a new and simple
way to design multi-stimuli-responsive, smart, and chiral materials.
Further studies on CPL applications are currently underway in our
laboratory.
5
Fig. 12. CD spectra of (R)/(S)1–NEt
2
and (R,R)/(S,S)2 in MeCN (5.0 × 10ꢀ
ꢀ
3
mol dm ).
The SW480 cells have negligible background fluorescence without
staining the dye. If the cells are incubated with (R)/(S)1–NEt , however,
intense intracellular green emission is observed (Fig. 15). The cell im-
at a low concentration have
2
4
. Experimental section
aging also demonstrates that (R)/(S)1–NEt
2
little impact on the growth of living cells. Co-staining (R)/(S)1–NEt
2
4
.1. Materials and instrumentation
′
with a commercial cell nucleus dye of 4 6-diamidino-2-phenylindole
(
DAPI) are carried out further to reveal the location of the dye in the
All reagents were purchased from commercial suppliers and used
living cells. When excited by 400 nm, the co-stained cells give strong
blue emission mainly from DAPI. On the other hand, when excited 480
1
without further purification. H NMR (400 MHz) spectra were recorded
in DMSO‑d
6
.
Chemical shifts are reported in ppm using
6

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
Fig. 13. Absorption and emission spectra of (S,S)2 in THF (1.0 × 10ꢀ 5 mol dm , excited at 400 nm) upon adding different 100 equivalents of amino acids.
ꢀ 3
Fig. 14. Absorption and emission spectra of (S,S)2 in THF (1.0 × 10ꢀ 5 mol dm , excited at 400 nm) upon adding different equivalents of L-/D-Tyr.
ꢀ 3
tetramethylsilane as internal standard. UV/vis absorption spectra were
recorded using a U5100 (Hitachi) spectrophotometer with quartz cu-
vettes of 1 and 0.1 cm pathlength for solution and PMMA film, respec-
tively. Fluorescence spectra were obtained using F-7000 Fluorescence
spectrophotometer (Hitachi) at room temperature. The slit width was 5
nm and 2.5 nm for excitation and emission. The photon multiplier
voltage was 400 V. Emission decay lifetime was determined by Hama-
matsu FL920S instrument. CD spectra were recorded using a Chirascan
plus qCD (Applied Photophysics) at room temperature. HR-MS were
obtained with a Waters-Q-TOF-Premier (electrospray ionization mass
spectrometry, ESI).
dilute method with a standard of quinine sulfate (Φ = 0.55, quinine in
r
ꢀ 3
2
0.05 mol dm sulfuric acid) calculated by: Φ
s
r r s s r s
= Φ (B /B )(n /n ) (D /
D
r
), where the subscripts s and r refer to the sample and reference
standard solution respectively; n is the refractive index of the solvents; D
is the integrated intensity. The excitation intensity B is calculated by: B
–
AL
= 1–10 , where A is the absorbance at the excitation wavelength and L
is the optical path length (L = 1 cm in all cases). The refractive indices of
the solvents at room temperature are taken from standard source. The
quantum yield of a solid sample was measured by an integrating sphere.
4
.3. X-ray crystallographic analysis
4
.2. Measurement of fluorescence quantum yield (Φ)
The determination of the unit cell and data collection for four single
crystal samples were performed on a Xcalibur E X-ray single crystal
diffractometer equipped with graphite monochromator Mo K
(λ =
The quantum yield of a solution sample was measured by the optical
α
7

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
Fig. 15. Brightfield and fluorescence images of SW480 cells co-stained with DAPI and (a) (S)1–NEt
2
and (b) (R)1-NEt
2
excited at 380 and 460 nm for DAPI and (R)/
(
S)1–NEt
2
, respectively.
0
.71073 Å) radiation. The data collection was executed using CrysA-
4.7. Measurement of ion probes
Anion titration experiment was started with the dye (10 mL) of
lisPro program. Structures were solved by direct method and successive
Fourier difference syntheses (SHELXS-97), and were refined by full
matrix least-squares procedure on F2 with anisotropic thermal param-
eters for all nonhydrogen atoms (SHELXL-97).
ꢀ 5
ꢀ 3
known concentration (1.0 × 10 mol dm in THF). For the titration,
ꢀ
3
ꢀ ꢀ
various metal ions (1.0–0.10 mol dm NO
3
or Cl salts in water) and
ꢀ 3
anions (1.0–0.10 mol dm sodium or potassium salts in water) were
added by a microsyringe. All types of absorption and fluorescence
measurement were monitored at about 1 h after the addition of the ion
to the dye solution at room temperature.
4
.4. Computational details
Calculations were carried out using the Gaussian 09 software pack-
age [B3LYP 6-31G(d,p)] based on the X-ray single-crystal structure or its
modified structures. The ground state geometry was optimized using
DFT. The excited states were predicted using the ground state geometry
using TD-DFT, from where UV/Vis absorption (pcm method for solvent
effect; 100 excited states) were predicted.
4
.8. Measurement of amino acid probes
Amino acid titration experiment was started with the dye (10 mL) of
ꢀ 5
ꢀ 3
known concentration (1.0 × 10 mol dm in THF). For the titration,
ꢀ 2
ꢀ 1
ꢀ 3
various D- or L-amino acids (1.0 × 10 ꢀ 1.0 × 10 mol dm in water)
were added by a microsyringe. All types of absorption and fluorescence
measurement were monitored at about 24 h after the addition of the
amino acids to the dye solution at room temperature.
4
.5. Cell culture methods and imaging
The imaging of SW480 cells was finished by Fluorescence Vertical
Microscope-Zeiss AX10 imager A2/AX10 cam HRC. The human gastric
cancer cell lines (IM95 m), purchased from JCRB Cell Bank (NIBIO,
Osaka, Japan), was cultured in Modified PRMI Medium (Hyclone, Utah,
USA) supplemented with 10% fetal bovine serum (Gibco, California,
′
′
4
.8.1. Synthesis of (R)/(S)-3-formyl-2,2 -bis(methoxymethyloxy)-1,1 -
binaphthalene [58]
.3 M t-BuLi in pentane (45 mL, 58.5 mmol) was added dropwisely to
1
USA), 100 U/ml penicillin and 100
μ
g/ml streptomycin (Hyclone, Utah,
′
′
3
00 mL dry THF solution of (S)/(R)-2,2 -bis(methoxymethyloxy)-1,1 -
◦
USA) at 37 C in an atmosphere containing 5.0% CO . Cells were
2
◦
binaphthalene (10 g, 26.7 mmol) at ꢀ 78 C. After stirring for 1 h, DMF
routinely grown in 100-mm plastic tissue culture dishes (Corning, New
York, USA) and harvested using a 0.25% Trypsin-EDTA solution
(
(
2.8 mL, 36.4 mmol) was added dropwisely, after 1.5 h, additional DMF
1 mL, 12.9 mmol) was added to the reaction mixture. The mixture was
(
Corning, New York, USA) when they reached the logarithmic growth
allowed to warm to room temperature slowly, quenched with saturated
NH Cl after stirring for 9 h (total reaction time), and extracted with
EtOAc. The combined extracts were washed with water and brine, and
dried over Na SO . The solvent was removed under reduced pressure at
room temperature. Purification by column chromatography on silica gel
phase. Cells were maintained in these culture conditions for all experi-
ments. After removing the incubating media and rinse with PBS for three
times, the cells were incubated with the dye (the dye prepared by
4
2
4
ꢀ 6
diluting DMSO with PBS to the appropriate concentration of 1.0 × 10
ꢀ 3
mol dm ) in PBS for 2 h at room temperature. Then, the cells were
washed three times with PBS and incubated with aqueous alkali for 15
min. At last, the cells were imaged with confocal microscope.
(
PE/EtOAc = 20/1) gave the product in 56% yield (6 g) as a yellow solid.
2
0% (2 g) of the starting material was also recovered.
4
.8.2. General synthesis of 1-aryl-1,3-butadione [59]
4
.6. Cytotoxicity studies
To a suspension of NaH (1.60 g of dispersion in oil, 40 mmol) in
EtOAc (20 mL) was added a solution of 1-arylethanone (10 mmol) in
◦
To evaluate the toxicity of the fluorescent dyes, Cell Counting Kit-8
EtOAc (20 mL) slowly at 0 C, and then, the mixture was stirred at room
(
CCK-8 assay, Sigma, St. Louis, MO, USA) was used to assess the living
temperature for 12 h. The mixture was carefully treated with 10%
cells viability. The more toxic the fluorescent dyes are, the less viability
the cells have. Modified PRMI media with different concentrations of the
dye were added into each well, after the cells are seeded at a density of
aqueous NH
The aqueous phase was separated and extracted with EtOAc. The com-
bined organic extracts were dried over anhydrous Na SO and concen-
4
Cl (30 mL) and adjusted to pH 5 with hydrochloric acid.
2
4
2
000 per well in the 96-well plate. Thereafter, the CCK-8 assay was used
trated under reduced pressure. Purification by column chromatography
on silica gel (PE/EtOAc) gave the desired 1-Aryl-1,3-butadione (keto-
ꢀ enol mixture).
on 2 h and the OD value was measured by BioTek ELX800 (Bio-Tek,
Winooski, VT, USA) at the wavelength of 450 nm.
8

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
4
.8.3. General synthesis of (R)/(S)1 and (R,R)/(S,S)2 [56]
found 599.2044.
In a 100 mL round bottom flask, an acetylacetone derivative (5
(R)/(S)1-Naph (Yield: 60%): δ
H 6
(400 MHz, DMSO‑d ) 16.29 (1H, s),
mmol, 5 eq.) was dissolved in 15 mL of ethyl acetate. Boron oxide (174
mg, 2.5 mmol, 2.5 eq.) was added and the solution was stirred for 30
8.68 (2H, d, J = 61.8), 8.08 (8H, m), 7.67 (3H, m), 7.50 (1H, t, J = 7.4),
7.34 (4H, m), 7.03 (3H, dd, J = 16.0, 8.8), 5.19 (2H, dd, J = 30.5, 6.9),
◦
min at 60 C. Then, 20 mL of an ethyl acetate solution of the appropriate
4.61 (2H, dd, J = 49.0, 5.7), 3.12 (3H, s), 2.95 (3H, s). δ
C
(101 MHz,
′
′
(
R)/(S)-3-formyl-2,2 -bis(methoxymethyloxy)-1,1 -binaphthalene
(1
6
DMSO‑d ) 189.58, 179.18, 152.92, 152.08, 135.60, 135.53, 134.60,
mmol, 1 eq.) with the tributylborate (1.15 g, 5 mmol, 5 eq.) was added
and the solution was further stirred for 30 min at this temperature.
Finally, butylamine (73 mg, 1 mmol, 1 eq.) was added dropwise. The
133.66, 133.43, 132.80, 130.98, 130.51, 129.97, 129.52, 129.34,
129.26, 129.04, 128.55, 128.31, 128.19, 128.01, 127.55, 127.49,
127.27, 126.45, 126.41, 126.18, 125.62, 125.08, 124.45, 123.72,
◦
reaction was heated at reflux for 14 h. After cooling to 60 C, 30 mL of
119.16, 116.40, 99.50, 99.01, 94.38, 56.96, 55.95, 55.37. HRMS (ESI):
◦
+
0
.4 M HCl was added and the mixture was stirred for 30 min at 60 C.
Calculated for C39
(R)/(S)1–NEt
H
32
O
6
[[M+Na] ] 619.2097, found 619.2091.
After cooling, the aqueous phase was separated and extracted with
EtOAc. The combined organic extracts were dried over anhydrous
2
(Yield: 62%): δ H (400 MHz, DMSO‑d
6
) 16.60 (1H, s),
8.54 (1H, s), 8.05 (2H, dd, J = 9.6, 5.1), 7.98 (2H, m), 7.89 (2H, d, J =
9.0), 7.68 (1H, d, J = 9.2), 7.48 (1H, t, J = 7.5), 7.34 (3H, ddd, J = 15.7,
11.7, 7.3), 7.19 (1H, d, J = 16.0), 7.01 (2H, dd, J = 14.2, 8.5), 6.77 (2H,
d, J = 9.1), 6.67 (1H, s), 5.22 (1H, d, J = 6.9), 5.15 (1H, d, J = 7.0), 4.65
(1H, d, J = 5.6), 4.53 (1H, d, J = 5.6), 3.46 (4H, dd, J = 14.0, 7.0), 3.12
4
MgSO and concentrated under reduced pressure. Purification by col-
umn chromatography on silica gel (PE/EtOAc) gave the desired product.
4
.8.4. General synthesis of (R,R)/(S,S)3 [57]
To an ice-cooled solution of (R,R)/(S,S)2 (0.87 g, 1.0 mmol) in EtOH
(3H, s), 2.92 (3H, s), 1.14 (6H, t, J = 7.0). δ
C 6
(101 MHz, DMSO‑d )
(
20 mL) was added HCl (12 N, 15 mL), and the resulting mixture was
189.23, 175.35, 152.63, 151.66, 151.45, 134.05, 133.39, 132.89,
131.74, 130.77, 130.74, 130.25, 130.18, 129.29, 129.24, 129.21,
128.88, 128.29, 127.52, 127.43, 127.02, 126.00, 125.87, 125.77,
125.32, 124.81, 124.20, 123.58, 121.91, 118.93, 116.14, 110.82, 99.12,
◦
stirred at 0 C for 3 h, and then extracted with diethyl ether (3 × 50 mL).
The combined organic extracts were washed with brine, dried over
4
MgSO , and evaporated under reduced pressure. The residue was then
dried in vacuum to afford 0.65 g of (R,R)/(S,S)3 as an orange-yellow
97.60, 94.09, 56.67, 55.69, 44.15, 12.63. HRMS (ESI): Calculated for
+
solid. Yield: 95%
C
39
H
39NO
6
[[M+Na] ] 640.2675, found 640.2672.
(
R)/(S)1–H (Yield: 52%): δ
H
(400 MHz, DMSO‑d
6
) 16.26 (1H, s),
(R,R)/(S,S)2 (Yield: 75%): δ
H 6
(400 MHz, DMSO‑d ) 16.18 (1H, s),
8
.58 (1H, s), 8.19–8.03 (5H, m), 7.98 (1H, d, J = 8.0), 7.71–7.63 (2H,
8.65 (2H, s), 8.12 (6H, m), 7.99 (2H, d, J = 8.1), 7.68 (2H, d, J = 9.2),
7.50 (2H, t, J = 7.4), 7.35 (8H, ddd, J = 22.8, 14.8, 6.4), 7.02 (4H, dd, J
= 17.5, 8.5), 6.33 (1H, s), 5.19 (4H, dd, J = 27.4, 6.9), 4.60 (4H, dd, J =
m), 7.58 (2H, t, J = 7.5), 7.52–7.46 (1H, m), 7.41–7.23 (4H, m), 7.02
(
(
2H, dd, J = 16.7, 8.5), 6.89 (1H, s), 5.18 (2H, dd, J = 30.1, 6.9), 4.60
2H, dd, J = 48.7, 5.7), 3.11 (3H, s), 2.94 (3H, s). δ (101 MHz,
) 189.75, 179.31, 152.89, 152.03, 136.04, 135.59, 134.57,
C
47.2, 5.7), 3.12 (6H, s), 2.95 (6H, s). δ
C 6
(101 MHz, DMSO‑d ) 183.73,
DMSO‑d
6
152.89, 152.05, 136.36, 134.65, 133.61, 130.93, 130.52, 129.50,
129.30, 129.04, 128.56, 128.48, 128.11, 127.31, 126.30, 126.20,
125.59, 125.03, 124.48, 119.08, 116.40, 102.84, 99.46, 94.36, 65.39,
1
1
1
9
5
33.64, 133.62, 130.94, 130.51, 130.41, 129.50, 129.44, 129.26,
29.20, 128.55, 128.26, 128.25, 128.04, 127.85, 127.29, 126.36,
26.21, 125.60, 125.55, 125.04, 124.46, 119.10, 116.39, 99.47, 98.62,
56.99, 55.95. HRMS (ESI): Calculated for C55
891.3145, found 891.3112.
H
48
O
10 [[M+Na]+]
4.36, 56.96, 55.95. HRMS (ESI): Calculated for C35
69.1940, found 569.1929.
H
30
O
6
[[M+Na]+]
(R,R)/(S,S)3 (Yield: 95%): δ
9.47 (2H, s), 8.83 (2H, s), 8.52 (2H, s), 8.27 (2H, t, J = 10.3), 7.94 (8H,
m), 7.29 (11H, m), 6.93 (2H, d, J = 8.3), 6.83 (2H, m). δ (101 MHz,
DMSO‑d ) 180.77, 154.57, 152.20, 141.05, 135.68, 134.72, 130.51,
H 6
(400 MHz, DMSO‑d ) 16.79 (1H, s),
(
R)/(S)1–F (Yield: 60%): δ
H 6
(400 MHz, DMSO‑d ) 16.18 (1H, s),
8
7
.58 (1H, s), 8.16 (5H, m), 8.07 (1H, d, J = 8.1), 7.99 (1H, d, J = 8.1),
.70 (1H, d, J = 9.2), 7.49 (1H, t, J = 7.4), 7.41 (5H, m), 7.05 (2H, dd, J
C
6
=
15.7, 8.5), 6.89 (1H, s), 5.20 (2H, dd, J = 29.9, 6.9), 4.62 (2H, dd, J =
130.20, 129.44, 128.86, 128.63, 128.56, 128.13, 126.74, 124.89,
4
1
1
1
1
5
8.5, 5.7), 3.13 (3H, s), 2.95 (3H, s). δ
C
(101 MHz, DMSO‑d
6
) 188.88,
124.86, 124.34, 123.90, 122.92, 120.83, 119.30, 117.53, 113.36,
+
78.79, 166.78, 164.27, 152.90, 152.03, 135.59, 134.58, 133.63,
32.77, 130.94, 130.81, 130.72, 130.50, 129.51, 129.25, 129.20,
28.54, 128.26, 128.02, 127.26, 126.38, 126.18, 125.60, 125.37,
108.16. HRMS (ESI): Calculated for C47
H
32
O
6
[[M+Na] ] 715.2097,
found 715.2087.
25.05, 124.45, 119.12, 116.59, 116.38, 99.47, 98.47, 94.37, 56.93,
CRediT authorship contribution statement
+
5.93. HRMS (ESI): Calculated for C35
H29FO
6
[[M+Na] ] 587.1846,
found 587.1833.
R)/(S)1–Cl (Yield: 56%): δ
Dehua Wu: Investigation, Formal analysis, Writing - original draft.
Xinyi Fang: Cell imaging. Jintong Song: Conceptualization, Method-
ology. Lang Qu: computation. Xiangge Zhou: Methodology. Haifeng
Xiang: Resources, Supervision, Writing. Jun Wang: Resources, Super-
vision. Jin Liu: Resources, Supervision.
(
H
(400 MHz, DMSO‑d
6
) 16.13 (1H, s),
8
.56 (1H, s), 8.09 (5H, m), 7.97 (1H, d, J = 8.0), 7.66 (3H, m), 7.47 (1H,
dd, J = 11.1, 4.0), 7.31 (4H, m), 7.02 (2H, dd, J = 16.9, 8.5), 6.89 (1H,
s), 5.18 (2H, dd, J = 30.2, 6.9), 4.59 (2H, dd, J = 48.8, 5.7), 3.10 (3H, s),
2
1
1
1
6
.93 (3H, s). δ
C 6
(101 MHz, DMSO‑d ) 188.45, 179.47, 152.90, 152.04,
38.49, 135.91, 134.82, 134.61, 133.63, 130.93, 130.51, 129.60,
29.53, 129.51, 129.21, 128.73, 128.44, 128.05, 127.26, 126.29,
25.62, 125.50, 125.05, 124.45, 119.11, 116.39, 99.47, 98.60, 94.38,
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
0.22, 60.22, 56.94, 55.94, 55.37, 55.37. HRMS (ESI): Calculated for
+
C
35
H
29ClO
6
[[M+Na] ] 603.1550, found 603.1549.
(
R)/(S)1–OMe (Yield: 76%): δ
H 6
(400 MHz, DMSO‑d ) 16.39 (1H, s),
8
7
5
3
1
1
1
1
5
.58 (1H, s), 8.12 (5H, m), 7.99 (1H, d, J = 8.1), 7.71 (1H, d, J = 9.2),
.48 (1H, dd, J = 11.1, 4.0), 7.32 (4H, m), 7.08 (4H, m), 6.84 (1H, s),
.21 (2H, dd, J = 29.7, 6.9), 4.64 (2H, dd, J = 48.3, 5.7), 3.86 (3H, s),
Acknowledgements
This work was supported by the National Natural Science Foundation
of China (no. 21871192 and 81771114) and Sichuan Science and
Technology Program (no. 2018JY0559). We acknowledge the compre-
hensive training platform of the specialized laboratory of the College of
Chemistry, Sichuan University, for material analysis. We would like to
thank the Analytical & Testing Center of Sichuan University for CCD X-
ray single crystal diffractometer work and circular dichroism
.14 (3H, s), 2.96 (3H, s). δ
C 6
(101 MHz, DMSO‑d ) 189.73, 177.62,
63.81, 152.92, 152.02, 134.71, 134.50, 133.67, 131.41, 130.98,
30.48, 130.19, 129.52, 129.35, 129.21, 128.71, 128.53, 128.05,
27.89, 127.24, 126.36, 126.13, 125.60, 125.09, 124.44, 119.20,
16.40, 114.71, 114.62, 99.46, 98.20, 94.39, 56.92, 56.82, 55.98,
+
5.93. HRMS (ESI): Calculated for C36
H
32
O
7
[[M+Na] ] 599.2046,
9

D. Wu et al.
Dyes and Pigments 184 (2021) 108851
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