Aromatic fluorine-induced one-pot synthesis of ring-perfluorinated trimethine cyanine dye and its remarkable fluorescence properties

Article abstract of DOI:10.1021/acs.joc.9b00378

We have developed a novel aromatic fluorine-induced one-pot synthesis of ring-perfluorinated trimethine cyanine dye without the use of a pyridine by reacting hexafluorobenzoindolenine with 5 equiv of methyl trifluoromethanesulfonate in mixed solvents of dimethylformamide and toluene. The thus-obtained ring-perfluorinated trimethine cyanine dye shows much better fluorescence properties, including intensity, quantum yield, and lifetime, than the nonfluorinated dye, not only in CH₂Cl₂ solution and the poly(methyl methacrylate) film but also in the powder state. Furthermore, ring-perfluorinated trimethine cyanine dye 2a shows better photostability toward white light-emitting diode irradiation than nonfluorinated dye trimethine cyanine dye 2b.

Full text of DOI:10.1021/acs.joc.9b00378

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Article
Aromatic Fluorine-Induced One-pot Synthesis of Ring-Perfluorinated
Trimethine Cyanine Dye and Its Remarkable Fluorescence Properties
Kazumasa Funabiki, Yuki Saito, Takashi Kikuchi, Kazutaka Yagi, Yasuhiro Kubota, Toshiyasu
Inuzuka, Yohei Miwa, Michiyuki Yoshida, Osamu Sakurada, and Shoichi Kutsumizu
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00378 • Publication Date (Web): 19 Mar 2019
Downloaded from http://pubs.acs.org on March 19, 2019
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Aromatic Fluorine-Induced One-Pot Synthesis of
Ring-Perfluorinated Trimethine Cyanine Dye and Its
Remarkable Fluorescence Properties
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†
†
‡
†
†
Kazumasa Funabiki, * Yuki Saito, Takashi Kikuchi, Kazutaka Yagi, Yasuhiro Kubota,
⁋
†
†
†
Toshiyasu Inuzuka, Yohei Miwa, Michiyuki Yoshida, Osamu Sakurada, and Shoichi
†
Kutsumizu
†
Department of Chemistry and Biomolecular Science, Gifu University, 1-1, Yanagido, Gifu
501-1193, Japan.
‡ Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.
⁋
Division of Instrumental Analysis, Life Science Research Center, Gifu University, 1-1
Yanagido, Gifu 501-1193, Japan
funabiki@gifu-u.ac.jp
ORCID
Kazumasa Funabiki: 0000-0002-7880-6093
Yasuhiro Kubota: 0000-0002-9177-4364
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Toshiyasu Inuzuka: 0000-0001-6976-6993
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Yohei Miwa: 0000-0002-8048-2761
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Michiyuki Yoshida: 0000-0001-8990-218X
Shoichi Kutsumizu: 0000-0002-6837-7985
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Graphical abstract
We have developed a novel aromatic fluorine-induced one-pot synthesis of ring-
perfluorinated trimethine cyanine dye without the use of a pyridine by reacting
hexafluorobenzoindolenine with 5 equiv. of methyl trifluoromethanesulfonate in mixed
solvents of DMF and toluene. The thus-obtained ring-perfluorinated trimethine cyanine dye
shows much better fluorescence properties, including intensity, quantum yield, and lifetime,
than the non-fluorinated dye, not only in CH2Cl2 solution and PMMA film, but also in
powder.
Furthermore, ring-perfluorinated trimethine cyanine dye 2a shows better
photostability toward white LED irradiation than non-fluorinated dye trimethine cyanine dye
2b.
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1. Introduction
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Organic functional molecules and materials having a perfluorophenyl group have
attracted much attention because of their diverse biological and material applications
arising from the properties of ring-fluorines (Figure 1(a)).1 However, there have been only a
few reports on the synthesis of organic functional molecules carrying ring-perfluorinated
heterocycles despite the expectation that they would exhibit excellent properties due to not
only ring-fluorines, but also heteroatoms, such as nitrogen and sulfur (Figure 1(b)).2
Therefore, it would be important to develop new methods for the synthesis of organic
functional molecules carrying ring-perfluorinated heterocycles for a broad range of use in
material and biomedical applications.
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perfluorophenyl
(a) Recent examples of functinal molecules and meterials with
group
4
F
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F
F
F
F
8
9
F
F
F
F
F
R
S
F
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R
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R
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N
N
N
N
F
F
F
n
R
O
Au
NPs
F
Fe
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F
F
Me
O
O
R
S
R
=
R
S
O
F
O
R
S
9
R
S
SO3
R
S
R
S
SO3
light-emmiting material
nanoparticle (NP)
catalyst for rescuing damaged neuronal cells
ring-perfluorinated
(b) Functinal molecules and meterials with
heterocycles
F
F
F
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F
R
N
O
F
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S
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N
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F
N
S
N
N
S
F
O
N
N
-
F
F
F
EtSO4
O
R
F
F
photostable cyanine dye
elastic organic crystal emitter
F
F
electroluminescent material
Figure 1. Recent organic functional molecules and materials having a perfluorophenyl
group and ring-perfluorinated heterocycles
In this report, we describe not only a novel aromatic fluorine-induced one-pot synthesis of
trimethine cyanine dyes using ring-perfluorinated benzoindolenine, but also the excellent
fluorescence properties of the obtained ring-perfluorinated trimethine cyanine dye in
solution, PMMA film, and powder, compared with non-fluorinated dye. This synthetic
method offers a novel one-pot route to trimethine cyanine dyes that overcomes the
disadvantages of the reported method, such as the use of a pyridine as a solvent and the
necessity of two reaction steps, including alkylation.3
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Results and discussion
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The reaction of hexafluorobenzoindolenine 1a with methyl trifluoromethanesulfonate
(MeOTf) (5 equiv.) in DMF at 100 °C gave ring-perfluorinated trimethine cyanine dye 2a in
57% yield, together with 36% of monomethine cyanine dye 3a as a by-product (Table 1,
entry 3). Reduction of the amounts of DMF and MeOTf (1-3 equiv.) resulted in reduction of
the yields of dye 2a to 6-56% (entries 2,4, and 5). The use of a mixed solvent of DMF and
toluene (v/v = 1/1) gave dye 2a in 70% yield, together with 25% of 3a (entry 6).
Table 1. One-pot Synthesis of Ring-Perfluorinated Trimethine Cyanine Dye 2a.
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
MeOTf (5 equiv.)
+
+
N
Solvent, 100 C, 15 h
F
N
F
N
N
F
F
N
F
NMe2
F
Me
F
Me
Me
TfO
2a
Me
TfO
1a
4a
3a
(0.3 mmol)
Yield (%)a of
1a 2a 3a 4a
MeOTf
(equiv)
Entry
Solvent
none
DMF (0.12 ml)
DMF (0.9 ml)
DMF (0.9 ml)
DMF (0.9 ml)
5
5
5
3
1
5
1
2
3
4
5
6
0
0
0
0
81
0
0
0
74
10 22 65
57 36 tr
56 34 tr
6
tr
tr
0
DMF / PhMe (v/v = 1/1) (0.9 ml)
70 25
a Isolated yields.
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On the contrary, the reaction of non-fluorinated benzoindolenine 1b with MeOTf (5 equiv.)
in DMF at 100 °C also occurred under the optimized reaction conditions to give the
corresponding trimethine cyanine dye 2b in only 11% yield, together with a 79% of
monomethine cyanine dye 3b as a main product, as shown in Table 2 (entry 1). Even when
a mixed solvent of DMF and toluene (v/v = 1/1) was used, the yield of the trimethine
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cyanine dye 2b was not improved (entry 2). The use of dimethylacetamide (DMA) in place of
DMF gave no the corresponding trimethine cyanine dye.
Table 2. One-pot Synthesis of Fluorine-free Trimethine Cyanine Dye 2b
MeOTf (5 equiv.)
+
N
solvent, 100 C, 15 h
N
N
N
NMe2
1b
Me
Me
Me
TfO
TfO
3b
2b
Yield (%)a
Entry
Solvent
DMF
2b
3b
1
2
11
11
79
72
DMF/PhMe (v/v = 1/1)
a Isolated yields
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To
clarify
the
reaction
mechanism,
control
by
reactions
using
of
N-methyl
hexafluorobenzoindolenium
salt,
prepared
the
reaction
N-methyl
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hexafluorobenzoindolene with MeOTf, were carried out as shown in Scheme 1.
F
F
F
F
F
F
F
F
F
F
F
F
F
F
MeOTf
(4 equiv.)
DMF, 100 °C, 15 h
N
Me
F
(61%)
N
N
F
F
F
Me
Me
TfO
TfO
2a
(61%)
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
TfOH
(4 equiv.)
F
F
F
+
DMF, 100 °C, 15 h
N
Me
N
F
F
N
N
(5%)a
F
F
Me
F
F
Me
Me
TfO
2a
TfO
4a
(75%)
(5%)
Scheme 1. Control Reactions
N-Methyl hexafluorobenzoindolenium salt smoothly reacts with 4 equiv. of MeOTf in DMF
at 100 °C for 15 h to give the corresponding ring-fluorinated trimethine cyanine dye 2a in
61% yield. On the other hand, the reaction of N-methyl hexafluorobenzoindolenium salt
with 4 equiv. of trifluoromethanesulfonic acid in place of MeOTf produced only trimethine
cyanine dye 2a in 5% yield and enamine 4a in 75% yield. Based on not only the results in
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Scheme 1, but also the essentiality of DMF as previously shown in Table 1, the proposed
reaction mechanism is described in Scheme 2.
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As Lee et al. reported previously, MeOTf smoothly reacts with DMF to produce in situ the
methylated DMF cation, as shown in eq. 1 in Scheme 2, which is quite stable and could be
the true methylated reagent in this reaction.4
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OMe
OMe
OMe
TfO
O
MeOTf
(eq.1)
H
NMe2
H
NMe2
H
NMe2
H
NMe2
6
7
DMF
methylated DMF (MDMF) cation
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X
X
X
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X
X
X
X
X
X
X
X
MDMF
cation
MDMF
cation
X
TfOH
+
N
N
N
X
X
X
Me
Me
X
4a
4b
X
X
F
: X =
: X = H
TfO
1a
1b
F
: X =
: X = H
TfO
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
OMe
NMe2
N
N
N
X
X
NMe2
X
NMe2
- MeOH
Me
Me
Me
H
3a
3b
F
: X =
: X = H
TfO
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Me
NMe2
MDMF
cation
X
X
NMe2
X
X
4
Enamine
N
N
N
N
X
X
X
X
Me
Me
Me
Me
TfO
TfO
X
X
X
X
X
X
X
X
X
X
(eq.2)
N
N
X
X
Me
Me
TfO
2a
2b
F
: X =
: X = H
Scheme 2. Proposed Reaction Mechanism
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Benzoindolenines 1 react with methylated DMF cation to produce N-methyl indolenines,
followed by deprotonation leading to enamines 4. Enamines 4 react with methylated DMF
cation, and the elimination of MeOH produces monomethine cyanine dyes 3. The
generated monomethine cyanine dyes 3 react with other enamines 4, followed by
methylation of the dimethylamino group and Hoffman-type elimination to give the
corresponding cyanine dyes 2.
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Formation of the ring-perfluorinated enamine 4a from N-methyl hexafluorobenzoindolenium salt
would be much easier than non-fluorinated enamine 4b, since the acidity of the hydrogen at the
methyl group of the N-methyl hexafluorobenzoindolenium salt is higher than non-fluorinated
benzoindolenium salt due to the fluorine atoms on the aromatic ring. However, the nucleophilicity
of the ring-perfluorinated enamine 4a was lowered due to the electron-withdrawing property
of the fluorine atoms. Therefore, formation of the monomethine cyanine dye 3a was
suppressed and enamine 4a was left. The ring-perfluorinated monomethine cyanine dye 3a
showed high reactivity for the attack of nucleophiles, compared with non-fluorinated
monomethine cyanine dye 3b. Consequently, the ring-perfluorinated trimethine cyanine
dye 2a was obtained in higher yield than non-fluorinated 2b. On the other hand, the more
highly reactive non-fluorinated enamine 4b attacked the cation derived from DMF, and the
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monomethine cyanine dye 3b was produced. Because of the relatively fast rate of this
reaction, enamine 4b did not attack monomethine cyanine dye 3b and the yield of
trimethine cyanine dye 2b was low. The effect of toluene on the yield of 4a is not clear at
present.
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Both absorption and fluorescence spectra and photographs of the prepared ring-
perfluorinated or non-fluorinated trimethine cyanine dyes 2a,b in dichloromethane (CH2Cl2)
are shown in Figure 2. Tables 3 and 4 also summarize of UV-Vis absorption,
HOMO/LUMO, and fluorescence properties.
Figure 2. UV-Vis Absorption and Photographs under Irradiation by White LED (a),
Fluorescence Spectra and Pictures under UV (365 nm) Irradiation (b) of Dyes 2a,b in
CH2Cl2 Solution
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Table 3. UV-Vis Absorption and HOMO/LUMO Energies of Dyes 2a,b
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
max (nm)a, ()a
LUMO (eV)c
HOMO (eV)b
Dye
8
9
579 (156000), 542 (81000)
592 (119000), 554 (84000)
2a
2b
3.46
3.20
5.58
5.26
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a Measured in CH2Cl2 (5 x 10-6 M).
b Measured by CV in MeCN.
c Calculated by results of HOMO, the UV-Vis, and fluorescence.
Table 4. Fluorescence Properties of Dyes 2a,b
kf (109 s-1)e
Fmax (nm)a,b
fc
s (ns)d
knr (109 s-1)f
Dye
2a
2b
0.25
0.22
597, 640
612, 657
0.24
0.10
1.0
0.5
0.77
1.93
a Measured in CH2Cl2 (5 x 10-6 M) with low sensitivity.
b The excitation wavelengths (ex) were as follows:
2a
2b
6a
6b
(579 nm), (592 nm),
(548 nm), (550 nm).
c Measured using an integrating sphere method.
d Measured using a single-photon-counting method.
e Radiative rate constant (kf = f /s).
f Non-radiative rate constant (knr = (1 - f) / s).
As shown in Figure 2(a) and Table 3, the max values of the ring-perfluorinated dye 2a in
CH2Cl2 are 579 and 542 nm, which are at shorter wavelengths than those (592 and 554
nm) of the non-fluorinated dye 2b. The values of  for 2a were similar to those for 2b.
HOMO and LUMO of the trimethine cyanine dyes 2a,b are also summarized in Table 3.
HOMO can be determined by cyclic voltammetry (CV) measurements. Since no peak
corresponding to LUMO was observed by CV, LUMO was determined by caluclation with
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the HOMO level and the intersection of the absorption and emission spectra. As a result,
both HOMO and LUMO of the ring-perfluorinated dye 2a were shown to be a lower energy
level than those of the non-fluorinated dye 2b. Especially, since HOMO may be more
stable than LUMO due to the effect of fluorine atoms on the aromatic rings, the
HOMOLUMO gap of the dye 2a expands, and max and Fmax exhibit blue-shift compared
with non-fluorinated 2b.5
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As shown in Table 4 and Figure 2(b), the Fmax values of ring-perfluorinated dye 2a in
CH2Cl2 are 597 and 640 nm, which are at shorter wavelengths than those (612 and 657
nm) of non-fluorinated dye 2b. Dye 2a showed a stronger intensity of fluorescence than the
non-fluorinated dye 2b. Ring-perfluorinated dye 2a showed almost a two-fold higher
fluorescence quantum yield (f) and fluorescence lifetime (s) than non-fluorinated dye 2b,
as shown in Table 4. The radiative deactivation rate constants (kf) of dye 2a and dye 2b
are similar, while the nonradiative deactivation rate constant (knr) of ring-perfluorinated dye
2a is much smaller than that of non-fluorinated dye 2b. Thus, the introduction of fluorine
atoms into the benzoindolenine ring could increase the activation barrier of the nonradiative
deactivation step in the excited state6 and consequently could not only increase the
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intensity of the fluorescence but also enhance the quantum yield (f) of ring-perfluorinated
dye 2a.
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Figures 3,4 and Table 5 show fluorescence spectra, properties, and photographs under UV
(365 nm) irradiation of a PMMA film containing of 2a,b (7.35 x 104 M). The fluorescence
intensity and quantum yield (f : 0.70) of PMMA film containing 2a were much greater than
those (f : 0.24) of 2a in CH2Cl2 solution and also those (f : 0.47) of PMMA film containing
dye 2b.
Figure 3. Photographs of PMMA Films Containing 7.35 x 104 M of Dyes 2a,b (a), (b) of
Trimethine Cyanine Dyes 2a,b under Irradiation by White LED (8.5 W) (left) and under UV
Irradiation (365 nm) (right)
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Figure 4. Fluorescence Spectra and Photographs of PMMA Film Containing 7.35 x 104 M
of Dyes 2a,b under UV Irradiation (365 nm)
Table 5. Fluorescence Properties of PMMA Film Containing 7.35 x 104 M of Dyes 2a,b
kf (109 s-1)e
Fmax (nm)a,b
fc s (ns)d
knr (109 s-1)f
Dye
2a
2b
0.18
0.16
610, 635
653
0.70
0.47
4.0
3.0
0.08
0.18
a Measured in PMMA film (dye contents: 7.35 X 10-4 M, thickness:
0.2 mm) with very low sensitivity.
b The excitation wavelengths (ex) were as follows:
2a
2b
(577 nm),
(590 nm)
c Measured using an integrating sphere method.
d Measured using a single-photon-counting method.
e Radiative rate constant (kf = f /s).
f Non-radiative rate constant (knr = (1 - f) / s).
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Figures 5,6 and Table 6 show photographs of crystals and powder, and fluorescence
spectra, properties of dyes 2a,b under UV (365 nm) irradiation in the crystal and powder
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states. For the morphology of a crystalline state or an amorphous state, there is no big difference
between the dyes 2a,b, as shown in Figure 5.
Figure 5. Photographs of Crystals (a), (b) and Powder (c), (d) of Dyes 2a,b under Irradiation
by White LED (8.5 W) (left) and UV Irradiation (365 nm) (right)
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Figure 6. Fluorescence Spectra and Photographs under UV Irradiation (365 nm) of Dyes
2a,b in the Crystal and Powder States
Table 6. Fluorescence Properties of Crystal and Powder of Dyes 2a,b
kf (109 s-1)d knr (109 s-1)e
s (ns)c
fb
Dye
State
Fmax (nm)a
0.03
0.04
0.04
0.02
1.59
1.50
0.32
0.88
0.6
0.6
2.8
1.1
2a
2b
Crystal
695
0.02
0.03
0.12
0.02
Powder 683
Crystalf 724, 763
Powder 717, 781
a Measured with low sensitivity. The excitation wavelengths (ex) were as follows:
2a
: Crystal (421 nm), Powder (375 nm)
2b
: Crystal (435 nm), Powder (445 nm)
b Measured using an integrating sphere method.
c Measured using a single-photon-counting method.
d Radiative rate constant (kf = f /s).
e Non-radiative rate constant (knr = (1 - f) / s).
Crystal of
f
2b
contains H2O with an occupancy of 20%.
Fmax (crystal: 695 nm, powder: 683 nm for 2a; crystal: 724, 763 nm, powder: 717, 781 nm
for 2b) in crystal and powder states all show a bathochromic shift compared to those in
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CH2Cl2 solution due to F-F and - stacking.7 The intensity of fluorescence was
significantly decreased compared to that in CH2Cl2 solution. As shown in Figures 5 and 6,
crystals of ring-fluorinated dye 2a and non-fluorinated 2b, prepared by the vapor diffusion
method with acetone and hexane, both show red fluorescence. Contrary to the findings in
CH2Cl2 solution, the fluorescence intensity of non-fluorinated dye 2b is greater than that of
ring-fluorinated dye 2a, since a crystal of only dye 2b contains H2O with an occupancy of
20%,8 as revealed by single-crystal X-ray analysis (Figures 7 and 8). One possible reason
for the stronger intensity of the fluorescence of the crystals of the dye 2b could be the
inclusion of water in the crystals, with an occupancy of 20%, which means that a water
molecule exists in a small void of the crystal lattice with a probability of 20%. The inclusion
of solvent or water molecules in crystals often increases the fluorescence intensity of the
crystals.8 In fact, when crystals of non-fluorinated dye 2b were crushed into powder by
grinding, its fluorescence intensity decreased markedly, as shown in Figures 5 and 6.
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Another possible explanation is that, as shown in Figures 7 and 8, - stacking of the two
benzoindolenine planes of the non-fluorinated dye 2b are observed with a distance of 3.476
Å. On the other hand, in the case of ring-perfluorinated dye 2a, F-F stacking of the two
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benzoindolenine planes is observed with a distance of only 3.146 Å. Ring-perfluorinated
dye 2a also shows F-methine double-bond stacking with a distance of 4.381 Å.
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Figure 7. Packing of the Molecules in X-ray Diffraction Structures of Dyes 2a,b
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Figure 8. X-ray Diffraction Structures of Dyes 2a,b (Short Contacts)
In contrast to non-fluorinated dye 2b, interestingly, the powder of ring-perfluorinated dye
2a, prepared by grinding the crystal, has a stronger red fluorescence than the crystals, and
F
max was blue-shifted from 695 nm for crystals to 683 nm for powder, as shown in Figures 5
and 6(a), since intermolecular packing should be disturbed by mechanical stress compared
with that of the crystals of ring-perfluorinated dye 2a.9b
In order to confirm this hypothesis, powder X-ray diffraction (PXRD) analysis of the
crystals and powder of the dye 2a,b was carried out. Consequently, as shown in Figure 9,
the PXRD pattern of the both of the crystals of the dye 2a,b showed sharp and intense
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reflection peaks. On the other hand, these peaks of the crystals disappeared almost
completely by mechanical grinding and amorphous phase appeared.
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Figure 9. Powder X-ray diffraction of Dyes 2a,b
Furthermore, two significant differences were found between the crystals of ring-
perfluorinated and non-fluorinated dyes 2a,b. First, molecules of the non-fluorinated dye 2b
are all oriented in the same direction, whereas the direction of the molecules in the crystals
of ring-perfluorinated dye 2a is inverted for each column, as shown in Figure 7. Second,
ring-perfluorinated trimethine cyanine dye 2a is not planer, compared with non-fluorinated
2b, as shown in Figure 10. The twist and fold angles of the two perfluorinated
benzoindolenine planes of dye 2a are 14.96° and 6.46°, which are much bigger than those
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of the two nonfluorinated benzoindolenine planes of non-fluorinated dye 2b (twist angle:
1.48°, fold angle: 0°).
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Figure 10. X-ray Diffraction Structures of Dyes 2a,b (Twist Angles and Fold Angels)
Finally, the photostabilities of ring-perfluorinated dye 2a and non-fluorinated dye 2b in CH2Cl2
(concentration: 5 X 10-6 M) under white LED irradiation (8.5 W) in an incubator at 25 °C were
examined as shown in Figure 11.
Figure 11. Photostabilities of Dyes 2a,b in CH2Cl2 (concentration : 5 X 10-6 M) under White LED
Irradiation in an Incubator at 25 °C.
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Consequently, ring-perfluorinated dye 2a showed better photostability toward white LED
irradiation, and 78% of the dye still remained even after 10 days. This value for 2a is higher
than that for 2b (62%).
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Conclusion
In conclusion, we have developed a novel aromatic ring fluorine-induced one-pot synthesis
of ring-perfluorinated trimethine cyanine dye 2a. This synthetic method offers a novel one-
pot route to trimethine cyanine dyes that overcomes the disadvantages of the reported
method, such as the use of a pyridine as a solvent and the necessity of two reaction steps,
including alkylation. The thus-obtained ring-perfluorinated trimethine cyanine dye 2a shows
much better fluorescence properties, including intensity, quantum yield, and lifetime, than
non-fluorinated dye 2b, not only in CH2Cl2 solution and PMMA film, but also in a powder
state. Furthermore, ring-perfluorinated trimethine cyanine dye 2a showed better
photostability toward white LED irradiation than non-fluorinated dye trimethine cyanine dye
2b.
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Experimental section
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Measurement. 1H NMR spectra were measured at 392 or 400 MHz in deuterochloroform (CDCl3),
hexadeuteroacetone ((CD3)2CO) or hexadeuterodimethyl sulfoxide ((CD3)2SO) solutions with
residual solvents as internal standards using a JEOL ECS-400 or ECX-400P FT-NMR spectrometer.
13C NMR spectra were obtained at 99 or 101 MHz in CDCl3, (CD3)2CO or (CD3)2SO solution with
residual solvents as internal standards using a JEOL ECS-400 or ECX-400P FT-NMR spectrometer.
19F NMR spectra were recorded at 369 or 376 MHz in CDCl3, (CD3)2CO or (CD3)2SO solutions
using CFCl3 as an external standard using a JEOL ECS-400 or ECX-400P FT-NMR spectrometer.
The data are reported as (s = singlet, d = doublet, t = triplet, q = quartet, quint = quintet, m =
multiplet, br s = broad singlet, coupling constant(s), integration). Melting points were obtained on a
Yanagimoto MP-S3 micro melting point apparatus and are uncorrected. IR spectra were recorded on
a Shimadzu IR Affinity-1. Electrospray ionization mass spectroscopy (ESI-MS) analysis using
MeOH was performed with a JEOL JMS-T100LP (Accu TOF LC-plus). UV-vis absorption spectra
were taken on a Hitachi U-4100 and Perkin Elmer Lamda950. Fluorescence spectra were taken on a
Jasco FP-8600 spectrofluorometers. The absolute fluorescence quantum yields were obtained on
HAMAMATSU Quantaurus-QY C11347-01. Fluorescence life times were measured using
HAMAMATSU Quantaurus-Tau compact fluorescence life time spectrometer C11367-01. Cyclic
voltammetry was taken on an automatic polarization system HSV-110. The X-ray Crystal Structures
were collected on XtaLAB PRO MM007 with HyPix-6000HE and XtaLAB PRO FR-X with HyPix-
6000HE, respectively. Phase identifications were performed on both the single crystals and the
pulverized samples by Rigaku MiniFlex600 X-ray powder diffraction (XRD) using CuKαradiation.
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Materials. Pure products were isolated by column chromatography using Wakogel C-200
(100 mesh, FUJIFILM Wako Pure Chemical Co.). Analytical TLC was performed on
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Merck precoated (0.25 mm) silica gel 60 F254 plates. Octafluoronaphthalene was
purchased from Tokyo Chemical Industry Co., Ltd. DMF (super dehydrated) and toluene
(super dehydrated) were purchased from FUJIFILM Wako Pure Chemical Co. Poly(methyl
methacrylate) (average Mw ~120,000 by GPC) was purchased from Sigma-Aldrich. All
chemicals were of reagent grade and, if necessary, purified in the usual manner prior to use.
Single crystals of the 2a,b were prepared by vapor diffusion method with acetone and
hexane.
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Synthesis of (1,3,4,5,6,7,8-heptafluoronaphthalen-2-yl)hydrazine10
To an ethanol solution (10 ml) of octafluoronaphthalene (1.482 g, 5.45 mmol) was added
hydrazine monohydrate (0.760 g, 15.2 mmol) at room temperature. After being stirred at 50
°C for 1 day, the reaction mixture was quenched with pure water (200 ml) and extracted with
dichloromethane (100 ml X 3). The combined dichloromethane extracts were dried over
anhydrous Na2SO4, filtered, and concentrated under vacuum to give a solid. The solid was
suspended in hexane (150 ml), stirred rapidly for 1 h, and filtered to give the (1,3,4,5,6,7,8-
heptafluoronaphthalen-2-yl)hydrazine (0.994 g) in 69% yield. M.p.= 112.3-112.8 °C; IR (KBr)
3375 (NH) cm-1; 1H NMR (DMSO-d6)  4.57 (d, J = 5.9 Hz, 2H, -NHNH2), 7.34 (t, J = 5.9 Hz, 1H,
19
-NHNH2); F NMR (DMSO-d6)  143.0 (dm, J = 62.0 Hz, 1F), 146.7- 146.8 (m, 1F), 148.5
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(dm, J = 55.6 Hz, 1F), 149.6 (dm, J = 62.0 Hz, 1F), 151.1 (dm, J = 55.6 Hz, 1F), 157.5 (tm, J =
5
6
7
13
19.2 Hz, 1F), 161.7 (tm, J = 19.2 Hz, 1F); C NMR (DMSO-d6) δ 101.2-101.7 (m, 1C), 107.0-
8
9
107.7 (m, 1C), 130.3 (t, J = 11.3 Hz, 1C), 135.7 (dm, J = 238.4 Hz, 1C), 137.9 (dm, J = 238.4 Hz,
2C), 139.1 (dm, J = 238.4 Hz, 1C), 140.4 (dm, J = 238.4 Hz, 2C), 140.8 (dm, J = 238.4 Hz, 1C).
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Synthesis of 1-(3-methylbutan-2-ylidene)-2-(perfluoronaphthalen-2-yl)hydrazine11
To an ethanol solution (30 ml) of (1,3,4,5,6,7,8-heptafluoronaphthalen-2-yl)hydrazine (1.112
g, 3.91 mmol) was added 3-methyl-2-butanone (1.012 g, 11.75 mmol) at room temperature.
After being stirred at 80 °C for 3 h, the reaction mixture was concentrated to remove the
solvent. The residue was purified by silica gel chromatography (hexane/dichloromethane =
1/3) to give 1-(3-methylbutan-2-ylidene)-2-(perfluoronaphthalen-2-yl)hydrazine (1.0117 g) in
65% yield. Rf 0.71 (dichloromethane/hexane = 1/3); m.p. = 82.5-83.1 °C; IR (KBr) 1366 (C=N),
1
3618 (NH) cm-1; H NMR (CDCl3)  1.13 (s, 3H, -CH(CH3)(CH3)), 1.19 (s, 3H, -CH(CH3)(CH3)),
19
1.93 (s, 3H, -N=C(CH3)-), 2.57-2.72 (m, 1H, -CH(CH3)2), 6.83 (s, 1H, -NH-); F NMR (CDCl3) 
140.8 (dm, J = 64.9 Hz, 1F), 146.1- 146.1 (m, 1F), 147.0 (dm, J = 56.2 Hz, 1F), 147.5 (dm, J
= 64.9 Hz, 1F), 148.6 (dm, J = 56.2 Hz, 1F), 156.5 (tm, J = 19.5 Hz, 1F), 158.8 (tm, J = 19.5 Hz,
1F); 13C NMR (CDCl3)  12.3 (s, 1C), 19.9 (s, 2C), 37.0 (s, 1C), 104.8-105.2 (m, 1C), 107.8-108.5
(m, 1C), 125.0 (tm, J = 12.2 Hz, 1C), 137.7 (dm, J = 249.4 Hz, 2C), 139.0 (dm, J = 249.4 Hz, 1C),
140.5 (dm, J = 249.4 Hz, 1C), 141.3 (dm, J = 249.4 Hz, 1C), 141.7 (dm, J = 249.4 Hz, 2C), 158.9 (s,
1C).
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Synthesis of 4,5,6,7,8,9-hexafluoro-1,1,2-trimethyl-1H-benzo[e]indole (1a)10
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After a mixture of tetralin (5 ml) and 1-(3-methylbutan-2-ylidene)-2-(perfluoronaphthalen-2-
yl)hydrazine (0.394 g, 1.08 mmol) was stirred overnight at 200 °C, the reaction mixture was
purified by silica gel chromatography (hexane/dichloromethane = 1/4) to give 4,5,6,7,8,9-
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hexafluoro-1,1,2-trimethyl-1H-benzo[e]indole (1a) (0.116 g) in 34% yield.
Rf 0.23
1
(hexane/dichloromethane = 1/4); m.p. = 135.6-136.1 °C; IR (KBr) 1581 (C=N) cm-1; H NMR
(CDCl3)  1.51 (s, 3H, -CH(CH3)(CH3)), 1.52 (s, 3H, -CH(CH3)(CH3)), 2.40 (s, 3H, CH3); 19F NMR
(CDCl3)  140.1 (tm, J = 15.2 Hz, 1F), 143.9 (ddm, J = 68.2, 15.5 Hz, 1F), 144.8 (dtm, J = 68.2,
17.4 Hz, 1F), 149.0 (dm, J = 17.4 Hz, 1F), 156.6 (ttm, J = 17.4, 6.6 Hz, 1F), 157.6 (ttm, J = 17.4,
2.5 Hz, 1F); 13C NMR (CDCl3)  16.0 (s, 1C), 21.0 (s, 2C), 58.2 (s, 1C), 109.7-110.3 (m, 1C), 112.6-
113.0 (m, 1C), 134.8 (s, 1C), 137.9 (dm, J = 252.9 Hz, 1C), 139.2 (dm, J = 252.9 Hz, 1C), 141.7
(dm, J = 252.9 Hz, 2C), 142.2 (dm, J = 252.9 Hz, 1C), 143.8 (d, J = 11.3 Hz, 1C), 143.3 (dm, J =
252.9 Hz, 1C), 194.1 (s, 1C).
Synthesis of 4,5,6,7,8,9-hexafluoro-2-((1E,3E)-3-(4,5,6,7,8,9-hexafluoro-1,1,3-trimethyl-1,3-
dihydro-2H-benzo[e]indol-2-ylidene)prop-1-en-1-yl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium
trifluoromethanesulfonate (2a) (Table 1, entry 6)
To 4,5,6,7,8,9-hexafluoro-1,1,2-trimethyl-1H-benzo[e]indole (1a) (0.095 g, 0.298 mmol) in a
mixed solvent of DMF (0.45 ml) and toluene (0.45 ml) was added methyl
trifluoromethanesulfonate (0.252 g, 1.53 mmol). After being stirred at 100 °C for 15 h, the
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