Multi-color photoluminescence induced by electron-density distribution of fluorinated bistolane derivatives

Article abstract of DOI:10.1016/j.jfluchem.2017.09.003

The aim of this study was to design and develop new fluorinated light-emitting materials with multi-color photoluminescence that are not limited by their states. For this purpose, fluorinated bistolanes with an amino substituent, such as carbazol-9-yl, di

Full text of DOI:10.1016/j.jfluchem.2017.09.003

Accepted Manuscript
Title: Multi-color photoluminescence induced by
electron-density distribution of fluorinated bistolane
derivatives
Authors: Shigeyuki Yamada, Masato Morita, Tsutomu Konno
PII:
S0022-1139(17)30375-5
DOI:
Reference:
http://dx.doi.org/10.1016/j.jfluchem.2017.09.003
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4-9-2017
4-9-2017
Please cite this article as: Shigeyuki Yamada, Masato Morita, Tsutomu
Konno, Multi-color photoluminescence induced by electron-density
distribution of fluorinated bistolane derivatives, Journal of Fluorine
Chemistryhttp://dx.doi.org/10.1016/j.jfluchem.2017.09.003
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Multi-color photoluminescence induced by electron-density distribution of
fluorinated bistolane derivatives
Shigeyuki Yamada,a,* Masato Moritaa and Tsutomu Konnoa
a Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology
Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
Tel: +81-75-724-7517; E-mail: syamada@kit.ac.jp
Graphical Abstract
Highlights




This study clarifies role of molecular design in altering photoluminescence color.
Fluorinated bistolanes with N-type electron-donating substituent were developed.
They exhibited photoluminescence both in dilute solution and the solid state.
They exhibited blue to green-color photoluminescence.

Abstract:
The aim of this study was to design and develop new fluorinated light-emitting materials with
multi-color photoluminescence that are not limited by their states. For this purpose, fluorinated
bistolanes with an amino substituent, such as carbazol-9-yl, diphenylamino, and dimethylamino
groups, as an electron-donating moiety were synthesized from readily available N,N-disubstituted
4-bromoaniline derivatives through five easy steps. The new fluorinated bistolane derivatives were
found to display photoluminescence in dilute solutions as well as in the solid state. The luminescent
color varied depending on the type of electron-donating group, and the emission color could be
controlled from blue to yellowish-green depending on the electron-density distribution induced by
electron-withdrawing pentafluorophenyl and electron-donating amino moieties. Moreover, the
bistolanes with a large molecular dipole were found to exhibit solvatochromic photoluminescence.
Therefore, multi-color luminescence from blue to yellow could be achieved in a single molecule
depending on solvent polarity.
Keyword: Fluorine; Bistolane; Luminescence; Solvatochromism; Electron-density distribution
tuning

1. Introduction
Organic light-emitting materials have widespread applications, such as in lighting devices,
displays for PC and TV monitors, and medical treatment using fluorescent diagnostics;
consequently, they have become one of the most essential materials for human life [1].
Many organic chemists have concentrated on developing innovative luminous molecules,
and successfully discovered a number of luminescent molecules.
Such luminescent molecules can be divided into three types depending on the state (Fig.
1). Most fluorescent molecules are generally available only in dilute solutions (Fig. 1A),
because their luminescence rapidly diminishes due to a quenching effect known as
aggregation-caused quenching (ACQ) in the concentrated solution or solid state [2], and
such fluorescent molecules can be applied in molecular-sensing or bio-imaging materials [3].
However, during the past couple of decades, materials that are emissive in the solid state
(Fig. 1B) have received considerable attention for practical applications, such as in organic
light-emitting displays (OLEDs) and electroluminescent (EL) displays [4]. Several
innovative studies that discovered by Tang et al. have contributed to the evolutionary
discovery of new solid-state luminescent materials and opened avenues for developing the
new class of luminous molecules [5,6]. They firstly developed luminous molecules
exhibiting intriguing phenomena in that they become non-emissive in dilute solutions but
their luminescent intensity is enhanced with the construction of molecular aggregates.
Methods of this type of enhancement include aggregation-induced emission enhancement
(AIEE) [5] and crystallization-induced emission enhancement (CIEE) [6]. With the rapid
expansion of the applicability of luminescent materials, developing efficient luminous
molecules not only in solutions but also in the solid state has drawn significant attention, and
it has been reported that several bistolane analogues with any substituents at the central
aromatic ring display such luminescent properties emitted both in solution and solid states
(Fig. 1C) [7,8].
Recently, our research interest has been directed toward the development of novel
light-emitting molecules showing such photoluminescence properties classified in Type-C
(Fig. 1C), and we also independently succeeded in the development of novel fluorophores,
viz. fluorine-containing dissymmetric bistolane (
photoluminescence ( em = 0.79 in solution; em = 0.66 in crystal) under UV irradiation [9].
The photoluminescence in dilute solution as well as in the solid state for is attributable to
1, Fig. 1C) that exhibits strong blue


1
the electron-density distribution based on the most electronegative fluorine substituents
[10,11]. However, such luminous molecules are still not satisfactory because of the

difficulty in achieving a distinct emission behavior [12]. Therefore, development of efficient
luminous molecules both in dilute solution and solid states has been recognized as one of the
most important issues in the field of luminescent materials.
On the basis of our preliminary investigation [9], in this study, we designed and
synthesized new bistolane-based fluorophores with multi-color luminescence that was achieved
by controlling the dipole moment caused by the combination of electron-withdrawing
pentafluorophenyl and electron-donating amino groups bound to both ends of the molecule.
Here was also disclosed the photophysical properties of the fluorophores in detail.
2. Results and discussion
2.1. Molecular design
The essential factors for designing the multi-color luminescent molecules that fulfilled our
purpose are as follows:
(i) Extended
-conjugated system with a linear molecular shape [8], which possesses
luminescent property in solution as well as in the solid state. The luminescence in the
latter has been reported to be achieved through aggregation-induced planarization [13].
(ii) Electron-density distribution by electron-rich and -deficient aromatic moieties
incorporated in a molecule, in which the molecular orbital and alignment can be
controlled through intramolecular charge transfer to alter photoluminescence color
[14].
Based on the molecular design and our preliminary understandings, a fluorine-containing
bistolane scaffold that possesses extended
-conjugation and constructs planar
conformations is suitable as the fundamental backbone. The favorable bias of
electron-density distribution caused by the selection of the combination of the
electron-donating or -withdrawing substituents can lead to the development of multi-color
photoluminescence molecules without depending on either dilute solution or solid state.
Accordingly, we selected three candidates 2a
an electron-withdrawing pentafluorophenyl group, e.g. bistolane with carbazol-9-yl 2a
diphenylamino (Ph2N) 2b, and dimethylamino (Me2N) substituent 2c
–c with an electron-donating amino group and
,
.
To evaluate the validity of our molecular design, we initially performed quantum chemical
calculations using the density functional theory (DFT) at the B3LYP/cc-pVDZ levels of theory
[15,16]. Fig. 2 shows the chemical structures of
1 and 2a–c and their molecular electrostatic

potential distributions obtained from theoretical calculation.
Fig. 2 shows that the pentafluorophenyl moiety appeared electron-deficient due to the effective
decrease in electron-density on the aromatic ring by the electron-withdrawing fluorine
substituents, whereas alkoxy- or amino-substituted aromatic ring were found to be
electron-rich due to the electron-donating properties. Accordingly, the candidates 2a–c showed
various electron-density distributions owing to the control of electronic structure by altering
the electron-donating substituent.
Additionally, in order to obtain information on the molecular orbitals in the excited state,
the time-dependent (TD)-DFT calculation was performed at B3LYP/aug-cc-pVDZ levels of
theory. Fig. 3 illustrates frontier-molecular orbital distributions for the highest occupied
molecular orbital (HOMO) and the lowest unoccupied MO (LUMO) as well as the HOMO–1
or HOMO–2 and LUMO+1 with a relatively large oscillator strength (f). The theoretical
parameters obtained by DFT or TD-DFT calculation are listed in Table 1.
Molecular orbitals at the HOMO level in all cases were found to be spread over the
electron-rich aromatic ring, whereas the orbital at the LUMO levels was locally distributed
at the electron-deficient aromatic moiety (Fig. 3); the HOMO→LUMO transition with a
large excited wavelength is likely to be assigned as intramolecular charge transfer (ICT). On
the other hand, HOMO–1→LUMO as well as HOMO→LUMO+1 transitions with a small
excited wavelength in the allowed electron-transitions seem to originate from
–*
transitions due to the delocalized molecular orbitals over the entire molecule in the HOMO–
1 as well as in LUMO+1. Similarly, HOMO–2→LUMO and HOMO→LUMO transitions in
the case of 2a can also be assigned as
multiple electron transitions in 2a
bistolane candidates 2a is potentially appropriate for multi-color luminescent molecules.

–

* and ICT transitions, respectively. Owing to the
–
c, it is believed that the design of new fluorinated
–
c

2.2. Synthesis and crystal structure
On the basis of the above theoretical investigations, the target fluorine-containing bistolanes
2a–c were prepared. The synthetic pathway for 2a–c is shown in Scheme 1.
The target molecule 2a–c can be synthesized from 4-bromoaniline derivative 3a–c as a
starting molecule through five steps. On treating N-(4-bromophenyl)carbazole (3a) with
(trimethylsilyl)acetylene (1.5 equiv.) in the presence of Cl2Pd(PPh3)2 (6 mol%), PPh3 (10
mol%), and CuI (10 mol%) in Et3N at 100 °C for 20 h, Pd(0)-catalyzed Sonogashira
cross-coupling reaction took place to provide the corresponding coupling product 4a in 83%
yield. The TMS group was easily deprotected by the treatment of 4a with K2CO3 in MeOH to
afford the corresponding terminal acetylene 5a in quantitative yield. Pd(0)-catalyzed
Sonogashira cross-coupling reaction of 5a with 4-(2-trimethylsilyl)ethynyl-1-bromobenzene
(1.5 equiv.) readily proceeded to produce the corresponding 6a in 55% yield. Subsequent
cleavage of the TMS group with the same protocol occurred, providing the corresponding 7a in
65% yield. Finally, Sonogashira cross-coupling reaction of 7a with bromopentafluorobenzene
was allowed to produce the target fluorinated bistolane 2a in 32% yield. With the same
synthetic protocol, other fluorinated bistolane derivatives 2b and 2c were successfully
synthesized and their molecular structures were fully identified through several spectroscopic
analyses, e.g. NMR, IR and HRMS, and the purity was verified through elemental analysis to
be sufficient for evaluating their optical behavior.
Among the novel fluorinated bistolanes 2a–c, carbazol-9-yl-substituted 2a and
Ph2N-substituted 2b successfully furnished single crystals after purification by column
chromatography (eluent: hexane/CH2Cl2 = 5/1), followed by recrystallization from
CH2Cl2/MeOH (1/1). X-Ray crystallographic analysis of 2a and 2b revealed aggregated crystal
structures. The obtained crystal structures are shown in Fig. 4.
2a and 2b were found to crystalize in triclinic P –1 space group and contain two
molecules in the crystal lattice. Although three aromatic rings in bistolane derivatives are
known to be in a rapid equilibrium between coplanar and twisted conformations via free
rotation of the alkyne-aryl single bond [13], the crystal structures of 2a and 2b were observed

to be coplanar among the three aromatic rings. Both 2a and 2b were found to construct
molecular aggregates with several / interactions between pentafluorophenyl and neighboring
benzene rings, indicated as red and blue arrows in Fig. 4b or 4e. In the case of 2a, the
interatomic ··· distances shown as red and blue arrows were 344 pm and 341 pm,
respectively, which are almost equal to the sum of van der Waals radius for two carbons (C:
170 pm) [17]. Additionally, 2a formed highly ordered structures with intermolecular
interactions: CH/ interaction between the core aromatic -face and the C–H bond (CH···:
318 pm) and hydrogen-bonding interaction between hydrogen and fluorine on the aromatic
moiety (H···F: 272 pm). Considering the van der Waals radius of C (170 pm), H (120 pm), F
(147 pm) atoms [17], the observed interatomic distances were quite close to the sum of van der
Waals radii for two atoms, which means that 2a in crystal forms molecular aggregate with
several weak intermolecular interactions. Similarly, as shown in Figs. 4e and 4f, 2b formed
ordered aggregated structures with multiple / and CH/ intermolecular interactions [18].
Resulting from the crystal structures, it can be concluded that electron-density distribution
induced by the electron-donating amino substituent and electronegative fluorine atoms is
attributable to the control of molecular alignment in the solid state.
2.3. Photophysical property in dilute solution
Our attention was directed towards investigating the photophysical properties of the designed
derivatives. Initially, we measured the absorption behavior of
2
in dilute CH2Cl2 solution (10–5
mol L–1 concentration). Fig. 5a shows the obtained absorption spectra, with the spectrum for
1
also shown for comparison.
Fluorinated bistolane
previously reported, possessed a single absorption band with an absorption maximum at 322
nm, along with a small shoulder at 350 nm [9]. In contrast, 2a with an amino substituent
1 with a methoxy substituent as an electron-donating unit, as
–c
displayed a distinct spectral shape possessing two or more absorption maxima. Wavelengths at
the observed absorption maxima as well as the molar extinction coefficient (/103) are listed in
Table 2.

As mentioned earlier, two allowed electron transitions with a relatively large oscillator
strength (f) obtained in all molecules were assigned as ICT for HOMO LUMO with a long
excited wavelength and –* transition for HOMO LUMO+1 (for and 2b ) or HOMO
LUMO (for 2a) with a short excited wavelength. Accordingly, the absorption band of
→
→
1
–c
–2
→
2 in
the long-wavelength region can be characterized as the ICT transition, and the other absorption
band in the short-wavelength region can be determined as –* transitions.
Subsequently, we evaluated the photoluminescence property of bistolanes 2a
solution (10–6 mol L–1 in CH2Cl2). Excitation light, with the wavelength of the absorption
maximum, was irradiated on the CH2Cl2 solution of and 2a , and the observed
–c in dilute
1
–c
photoluminescence spectra are shown in Fig. 5b. In addition, Fig. 5c shows the Commission
Internationale de l'Eclairage (CIE) chromaticity diagram and the photographs of
photoluminescence irradiated by UV (ex = 365 nm). The methoxy-substituted bistolane
1 in
dilute solution was reported to show deep blue photoluminescence with an emission maximum
at 405 nm [9]. Switching the electron-donating moiety from the methoxy to carbazol-9-yl
group, e.g. 2a, a slight shift of emission maxima to the long-wavelength region occurred,
resulting in an emission of light-blue photoluminescence. On the other hand, fluorinated
bistolane 2b with Ph2N-group or 2c with Me2N-group in CH2Cl2 displayed pale-blue
photoluminescence with an emission maximum at 495 nm for 2b and yellowish-green
photoluminescence with an emission maximum at 505 nm for 2c, which were found to
dramatically shift to the long-wavelength region by 90–100 nm, compared to 1. The dramatic
change of emission maximum wavelength is attributable to the energy gap between HOMO
and LUMO in the excited state. In Fig. 5b, the order of emission bands actually observed was:
1
<
2a << 2b
theoretical order of the luminescence band followed the order:
emission bands for 2a–c appeared in the longer-wavelength region than that for
<
2c. Resulting from the HOMO-LUMO energy gaps in the excited states, the
2a << 2c 2b. As expected,
. However,
1
<
<
1
the opposite order was observed between 2b and 2c in the actual observation. The opposite
order may result from the difference in electron-donating property between Ph2N and Me2N
groups. Comparing molecular dipole moment (ex) in the excited state, the ex for 2c (8.17)
was found to be larger than 2b (5.58). The change of dipole moment can be assumed to cause a
wavelength shift of the emission band to the longer-wavelength region. Consequently, the
photoluminescence color of the fluorinated bistolane derivatives can be switched depending on

the electron-density distribution, enabled by its significant influence on the energy gap between
HOMO and LUMO as well as the molecular dipole moment.
2.4. Solvatochromic photoluminescence property
Much attention has been paid to luminous molecules with a large molecular dipole since they
reveal intriguing photoluminescence behavior depending on the solvent polarity, called the
solvatochromic photoluminescence property [19,20]. Therefore, we investigated
photoluminescence behavior using 2b (ex: 5.58 Debye) as an example for dissolving in a
solution with various dielectric constants (). After preparing the dilute solution (10–6 mol L–1)
of 2b with various solvents, such as hexane ( = 1.88), CH2Cl2 ( = 8.93), acetone ( = 20.6),
and acetonitrile ( = 35.9), photoluminescence properties were observed by irradiation with
excitation light at 372 nm, and the spectra observed are shown in Fig. 6a. Fig. 6b shows the
CIE diagram obtained from the photoluminescence spectra and photographs of
photoluminescence in various solvents under UV irradiation (ex = 365 nm).
2b in CH2Cl2 exhibited pale-blue photoluminescence with a maximum emission
wavelength of 495 nm, whereas the 2b in hexane displayed deep-blue photoluminescence with
an emission band at 410 nm with a vibrational structure. In sharp contrast, by switching the
solvent from less-polar hexane to more-polar acetone or acetonitrile with a large dielectric
constant, the photoluminescence color dramatically changed from deep-blue to
yellowish-green in acetone or yellow in acetonitrile. Accordingly, it was clearly demonstrated
that the 2b with a large molecular dipole moment exhibited solvatochromic photoluminescence.
The phenomenon of solvatochromic photoluminescence of 2b can be explained as follows
[21]: irradiation of 2b in the ground state with excitation light promotes the formation of
excited species (2b*), which normally undergoes solvation in the dilute solution state. In the
less-polar solvent, the stabilization effect of 2b* by means of solvation is quite weak, and
therefore photoluminescence with high energy occurs, resulting in photoluminescence with an
emission band in the short-wavelength region. In the more-polar solvent, 2b* undergoes strong
stabilization by the solvation process through the solvent reorientation, and therefore, the
excitation state shifts to lower energy levels, leading to the emission of long-wavelength
photoluminescence.
2.5. Photophysical property in the solid state

Furthermore, we evaluated the photoluminescence behavior of the fluorinated bistolane
derivatives 2a–c in the solid state. The observed photoluminescence spectra and CIE color
diagram are shown in Fig. 7 and the photophysical data are also listed in Table 3.
As mentioned earlier, methoxy-substituted bistolane
1
displayed strong deep-blue
c were found to exhibit
photoluminescence (em = 0.66) [9]. Compounds 2a
–
photoluminescence even in the solid state; the maximum emission wavelengths were 457 nm
for 2a, 476 nm for 2b, and 488 nm for 2c (Fig. 7a, Table 3). As shown in Fig. 7b, the
photoluminescence color of 2a–c were found to switch by changing the substituent at the
electron-donating moiety: carbazol-9-yl-substituted 2a showed blue photoluminescence,
Ph2N-substituted 2b showed light-blue, and bistolane 2c with a Me2N-group exhibited
light-green. Our previous paper [9] revealed that the photoluminescence band of the crystal
state of the molecule with multiple intermolecular interactions dramatically shifted to the
longer-wavelength region compared the photoluminescence band obtained in dilute solution.
Comparing photoluminescence behavior of 2a–c in dilute solution and in the solid state, no
large difference could be observed in the photoluminescence wavelength. Photoluminescence
in the solid state may be similar to radiation in dilute solution, rather than the radiation from
the molecular aggregates, which may be significantly attributable to the molecular orbital of
the molecule.
The quantum yield (em) for
1 and 2a–c was em = 0.11–0.66 (Table 2), which is
relatively lower than that of the solution phase. Most luminous molecules are known to rapidly
quench in condensed phases (solid state) due to multiple non-radiative processes, such as
molecular vibration, rotation, and intermolecular energy transfer. Taking crystal structures for
2a and 2b shown in Figs. 4a and 4d into consideration, 2a and 2b in the crystal formed
coplanar conformation among three aromatic rings, which enhanced intermolecular /
stacking interaction between two aromatic rings. The / interaction may be attributable to the
significantly suppressed non-radiative deactivation due to restriction of molecular motion as
well as rotation in closely packed structures. Viewing the packing structures carefully, the
steric bulkiness of terminal electron-donating substituent, e.g. carbazol-9-yl group for 2a and
Ph2N-group for 2b, was observed to cause slight sliding along a short molecular axis, which
also retarded the non-radiative process by intermolecular energy transfer. These plural effects
may promote electron transition via the radiative process to induce photoluminescence in the

solid state. On the other hand, the em of 2c decreased to one-fourth of the em of 2a–b due to
the thermal deactivation caused by the molecular motion due to lack of steric bulk and the
high-energy stretching vibration of the sp3-hybridized C–H bonds in the NMe2 group.
2.6. Relationship between photophysical properties and molecular dipole
To investigate the influence of the primary molecular structure on photoluminescence, the
correlation between dipole moment in the excited state and photoluminescence maximum
wavelength was plotted (Fig. 8).
Plots for
were in alignment with the fitting line in the solid state and slight deviation in solution.
The results clearly indicate that no correlation exists between alkoxy-substituted and
amino-substituted bistolanes 2a , and a strong correlation was found among 2a with an
1 were found to be dramatically deviated from the fitting lines, whereas plots for
2a–c
1
–c
–c
electron-donating amino group; the photoluminescence color was switched in parallel
according to the strength of the electron-donating ability. Overall, the photoluminescence color
of fluorinated bistolane derivatives in dilute solution as well as in the solid state can be
controlled by the energy gap between HOMO and LUMO of the molecule and dipoles caused
by the electron-density distribution.
Conclusions
New fluorinated bistolanes possessing electron-donating amino substituent, such as carbazol-9-yl,
Ph2N-, and Me2N-group, were designed and synthesized through an easy five-step procedure
involving Sonogashira cross-coupling reaction as a key reaction step. After intensive evaluation of
their photophysical properties, the developed fluorinated bistolane derivatives were found to exhibit
photoluminescence in dilute solution as well as in the solid state. The three kinds of
photoluminescence colors—from blue to pale-green—were achieved by the optimal selection of the
amino group as the electron-donating substituent of bistolane. In addition, the new bistolane
derivatives exhibited a solvatochromic photoluminescence property in that photoluminescence color
changed depending on the solvent polarity. From theoretical studies using DFT and TD-DFT, the
dramatic color-switching of the photoluminescence can be attributed to the control of energy gap
between HOMO and LUMO of the molecule as well as dipoles based on the electron-density
distribution induced by strong electronegative fluorine atoms. This study successfully developed
novel and high-efficiency luminophores exhibiting blue to green-color photoluminescence. The role

of molecular design in altering photoluminescence color in solution and in the solid state has been
disclosed. The findings of this study provide guidelines for molecular design to discover new
multi-color luminous materials that are not limited by the state of materials.
4. Experimental
4.1. General
1H- and 13C-NMR spectra were measured with a Bruker AVANCE III 400 NMR
13
spectrometer (1H: 400 MHz and C: 100 MHz) in chloroform-d (CDCl3) solution and the
chemical shifts are reported in parts per million (ppm) using the residual proton in the NMR
solvent. 19F-NMR (376 MHz) spectra were measured with a Bruker AVANCE III 400 NMR
spectrometer in CDCl3 solution with CFCl3 (F = 0 ppm) as an internal standard. Infrared
spectra (IR) were determined with the KBr plate method using a JASCO FT/IR-4100 type A
spectrometer; all spectra are reported in wavenumber (cm–1). High resolution mass spectra
(HRMS) were determined using a JEOL JMS-700MS spectrometer with fast atom
bombardment (FAB) methods. Elemental analyses were conducted with a Yanaco CHN
CORDER MT-5 instrument. All reactions were carried out using dried glassware with a
magnetic stirrer bar. All chemicals were of reagent grade and purified in the usual manner
whenever necessary prior to use. Column chromatography was carried out on silica gel
(Wakogel® 60N, 38–100 m) and TLC analysis was performed on silica gel TLC plates
(Merck, Silica gel 60 F254).
4.2.
Typical procedure for the Pd(0)-catalyzed Sonogashira cross-coupling reaction of
N-4-bromophenyl cabazole (3a) with trimethylsilylacetylene
N-4-bromophenyl carbazole (3a, 1.6 g, 5.0 mmol), trimethylsilylacetylene (0.76 g, 7.5 mmol),
Cl2Pd(PPh3)2 (0.10 g, 0.15 mmol), PPh3 (0.13 g, 0.50 mmol), CuI (0.095 g, 0.50 mmol), and Et3N
(20 mL) were placed in a flask, and the mixture was stirred at 100 °C for 20 h. After stirring, the
precipitate formed during the reaction was separated by atmospheric filtration, and the filtrate was
poured into a saturated aqueous NH4Cl solution (20 mL). The crude product was extracted with
AcOEt (20 mL) three times and the combined organic layer was washed with brine (once). The
organic layer was collected and dried over anhydrous Na2SO4, which was separated by filtration.
The filtrate was evaporated in vacuo and subjected to silica-gel column chromatography (eluent:
hexane/CH2Cl2 = 5/1) to obtain the coupling product 4a in 83% yield (1.4 g, 4.3 mmol) as a white
solid.

4.2.1. 9-[4-{2-(Trimethylsilyl)ethynyl}phenyl]carbazole (4a)
The spectral data were fully in agreement with the reported data [22a]. Yield: 83% (white solid); 1H
NMR (CDCl3):  0.36 (s, 9H), 7.317.35 (m, 2H), 7.447.45 (m, 4H), 7.55 (d, J = 8.8 Hz, 2H),
7.74 (d, J = 8.8 Hz, 2H), 8.17 (d, J = 7.6 Hz, 2H) 13C NMR (CDCl3): –0.03, 95.4, 104.2, 109.7,
120.2, 120.3, 122.1, 123.5, 126.0, 126.7, 133.5, 137.7, 140.5.
4.2.2. 4-{2-(Trimethylsilyl)ethynyl}-N,N-diphenylaniline (4b)
The spectral data were fully in agreement with the reported data [22b]. Yield: 60% (yellow solid);
1H NMR (CDCl3):  0.26 (s, 9H), 6.97 (d, J = 8.8 Hz, 2H), 7.037.14 (m, 6H), 7.247.35 (m, 6H)
13C NMR (CDCl3): 0.06, 93.0, 105.4, 115.9, 122.1, 123.5, 124.9, 129.3, 132.9, 147.1, 148.0.
4.2.3. 4-{2-(Trimethylsilyl)ethynyl}-N,N-dimethylaniline (4c)
The spectral data were fully in agreement with the reported data [22c]. Yield: 88% (yellow solid);
13
1H NMR (CDCl3):  0.24 (s, 9H), 2.97 (s, 6H), 6.59 (d, J = 8.8 Hz, 2H), 7.34 (d, 8.8 Hz, 2H) C
NMR (CDCl3): 0.2, 40.1, 91.1, 106.5, 109.8, 111.5, 133.1, 150.1.
4.3. Typical procedure for the preparation of N-(4-ethynylphenyl)carbazole (5a)
9-[4-{2-(Trimethylsilyl)ethynyl}phenyl]carbazole (4a, 0.68 g, 2.7 mmol), potassium carbonate
(0.42 g, 3.0 mmol), and methanol (4.0 mL) were placed in a flask, and the suspension was stirred at
room temperature. After stirring for 3 h, the precipitate that was insoluble in the solvent was
separated by atmospheric filtration, and the filtrate was poured into saturated aqueous NH4Cl
solution (20 mL). The crude product was extracted with AcOEt (20 mL) three times and the
combined organic layer was washed with brine (once). The organic layer was collected and dried
over anhydrous Na2SO4, which was separated by filtration. The filtrate was evaporated in vacuo and
subjected to silica-gel column chromatography (eluent: hexane/CH2Cl2 = 5/1) to obtain the
deprotection product 5a in 99% yield (0.53 g, 2.0 mmol) as a white solid.
4.3.1. N-(4-ethynylphenyl)carbazole (5a)
The spectral data were fully in agreement with the reported data [22d]. Yield: 99% (white solid); 1H
NMR (CDCl3):  3.19 (s, 1H), 7.28–7.34 (m, 2H), 7.39–7.46 (m, 4H), 7.56 (d, J = 8.4 Hz, 2H), 7.73
13
(d, J = 8.4 Hz, 2H), 8.15 (dt, J = 7.6, 1.2 Hz, 2H); C NMR (CDCl3):  78.1, 82.9, 109.7, 120.2,
120.4, 121.0, 123.5, 126.0, 126.8, 133.6, 138.1, 140.4.
4.3.2. 4-Ethynyl-N,N-diphenylaniline (5b)
The spectral data were fully in agreement with the reported data [22e]. Yield: 86% (yellow oil); 1H

NMR (CDCl3):  s, 1H), 6.98 (d, J = 8.8 Hz, 2H), 7.07 (tt, J = 6.0, 1.2 Hz, 2H), 7.09–7.14 (m,
13
4H), 7.24–7.31 (m, 4H), 7.34 (d, J = 8.8 Hz, 2H); C NMR (CDCl3): 
3, 83.8, 114.7, 122.0,
123.5, 124.9, 129.3, 133.0, 147.0, 148.2.
4.3.3. 4-Ethynyl-N,N-dimethylaniline (5c)
The spectral data were fully in agreement with the reported data [22c]. Yield: 99% (brown solid);
1H NMR (CDCl3):  2.98 (s, 7H, N(CH3)2 and CCH), 6.62 (d, J = 8.8 Hz, 2H), 7.37 (d, J = 8.8 Hz,
2H); 13C NMR (CDCl3): 
1, 74.7, 84.8, 108.6, 111.6, 133.1, 150.3.
4.4. Typical procedure for the Pd(0)-catalyzed Sonogashira cross-coupling reaction of 5a with
4-{2-(trimethylsilyl)ethynyl}-1-bromobenzene
N-(4-ethynyl)phenyl)carbazole
(5a,
0.53
g,
2.0
mmol),
4-{2-(trimethylsilyl)ethynyl}-1-bromobenzene (0.76 g, 3.0 mmol), Cl2Pd(PPh3)2 (0.084 g, 0.12
mmol), PPh3 (0.052 g, 0.20 mmol), CuI (0.038 g, 0.20 mmol), and Et3N (20 mL) were placed in a
flask, and the mixture was stirred at 100 °C for 15 h. After stirring, the resulting precipitate was
separated by atmospheric filtration, and the filtrate was poured into saturated aqueous NH4Cl
solution (20 mL). The crude product was extracted with AcOEt (20 mL) three times and the
combined organic layer was washed with brine (once). The organic layer was collected and dried
over anhydrous Na2SO4, which was separated by filtration. The filtrate was evaporated in vacuo and
subjected to silica-gel column chromatography (eluent: hexane/CH2Cl2 = 5/1) to obtain the coupling
product 6a in 55% yield (0.48 g, 1.1 mmol) as a white solid.
4.4.1. N-[4-{4-(2-(Trimethylsilyl)ethynyl)phenyl}ethynyl]carbazole (6a)
The spectral data were fully in agreement with the reported data [21f]. Yield: 55% (white solid); 1H
NMR (CDCl3):  0.27 (s, 9H), 7.28–7.33 (m, 2H), 7.40–7.45 (m, 2H), 7.48 (d, J = 8.4 Hz, 1H), 7.51
(d, J = 8.8 Hz, 1H), 7.58 (d, J = 8.4 Hz, 2H), 7.75 (d, J = 8.4 Hz, 2H), 8.15 (d, J = 8.0 Hz, 2H); 13C
NMR (CDCl3):  –0.07, 89.9, 90.6, 96.5, 104.6, 109.7, 120.2, 120.4, 121.9, 123.1, 123.2, 123.6,
126.0, 126.8, 131.4, 131.9, 133.1, 137.8, 140.5.
4.4.2. 4-[4-{2-(Trimethylsilyl)ethynyl}phenyl]ethynyl-N,N-diphenylaniline (6b)
The spectral data were fully in agreement with the reported data [22f]. Yield: 49% (yellow solid);
1H NMR (CDCl3):  0.26 (s, 9H), 7.00 (d, J = 8.8 Hz, 2H), 7.07 (tt, J = 7.2, 1.2 Hz, 2H), 7.09–7.14
13
(m, 4H), 7.25–7.35 (m, 4H), 7.36 (d, J = 8.8 Hz, 2H), 7.43 (s, 4H); C NMR (CDCl3):  –0.07,
88.3, 91.7, 96.0, 104.8, 115.6, 122.0, 122.4, 123.6, 123.7, 125.0, 129.4, 131.2, 131.8, 132.5, 147.0,

148.0.
4.4.3. 4-[4-{2-(Trimethylsilyl)ethynyl}phenyl]ethynyl-N,N-dimethylaniline (6c)
The spectral data were fully in agreement with the reported data [22g]. Yield: 66% (yellow solid);
1H NMR (CDCl3):  0.25 (s, 9H), 3.00 (s, 6H), 6.66 (d, J = 9.2 Hz, 2H), 7.40 (d, J = 9.2 Hz, 2H),
7.41 (s, 4H); 13C NMR (CDCl3):  –0.06, 40.2, 87.2, 92.8, 95.7, 104.9, 109.6, 111.8, 121.9, 124.3,
131.0, 131.8, 132.8, 150.2.
4.5. Typical procedure for the preparation of N-[4-{4-(2-ethynyl)phenyl}ethnyl]phenylcarbazole
(7a)
N-[4-{4-(2-(Trimethylsilyl)ethynyl)phenyl}ethynyl]carbazole (6a, 0.48 g, 1.1 mmol), potassium
carbonate (0.23 g, 1.7 mmol), and methanol (4.0 mL) were placed in a flask, and the suspension
was stirred at room temperature for 3 h. The resulting precipitate was insoluble in the solvent. After
consuming the initial 4a, the precipitate was separated by atmospheric filtration, and the filtrate was
poured into saturated aqueous NH4Cl solution (20 mL). The crude product was extracted with
AcOEt (20 mL) three times and the combined organic layer was washed with brine (once). The
organic layer was collected and dried over anhydrous Na2SO4, which was separated by filtration.
The filtrate was evaporated in vacuo and subjected to silica-gel column chromatography (eluent:
hexane/CH2Cl2 = 5/1) to obtain the deprotection product 7a in 65% yield (0.26 g, 0.71 mmol) as a
white solid.
4.5.1. N-[4-{4-(2-ethynyl)phenyl}ethnyl]phenylcarbazole (7a)
1
Yield: 65% (white solid); M.p.: 170–171 °C; H NMR (CDCl3): 3.20 (s, 1H), 7.31 (ddd, J = 7.6,
6.4, 2.0 Hz, 2H), 7.40–7.47 (m, 4H), 7.50 (d, J = 8.4 Hz, 2H), 7.53 (d, J = 8.4 Hz, 2H), 7.59 (d, J =
13
8.8 Hz, 2H), 7.76 (d, J = 8.8 Hz, 2H), 8.15 (d, J = 8.0 Hz, 2H) C NMR (CDCl3): 79.0, 83.2,
89.7, 90.6, 109.7, 120.2, 120.4, 121.8, 122.1, 123.5, 123.6, 126.0, 126.8, 131.5, 132.1, 133.1, 137.8,
140.5; IR (KBr)  3285, 1450, 1334, 1225, 836 cm-1; HRMS (FAB) Calcd for (M+) C28H17N:
367.1361, found: 367.1367.
4.5.2. 4-[4-(2-Ethynylphenyl)ethnyl]phenyl-N,N-diphenylaniline (7b)
The spectral data were fully in agreement with the reported data [22h]. Yield: 85% (yellow solid);
1H NMR (CDCl3):  3.17 (s, 1H), 7.01 (d, J = 8.8 Hz, 2H), 7.07 (tt, J = 7.2, 1.2 Hz, 2H), 7.10–7.15
13
(m, 4H), 7.25–7.32 (m, 2H), 7.37 (d, J = 8.8 Hz, 2H), 7.46 (s, 4H); C NMR (CDCl3):  78.7,
83.4, 88.1, 91.8, 115.5, 121.4, 122.1, 123.6, 124.1, 125.0, 129.4, 131.3, 132.0, 132.5, 147.1, 148.1.

4.5.3. 4-[4-(2-Ethynylphenyl)ethnyl]phenyl-N,N-dimethylaniline (7c)
The spectral data were fully in agreement with the reported data [22g]. Yield: 66% (yellow solid);
1H NMR (CDCl3):  3.00 (s, 6H), 3.15 (s, 1H), 6.66 (d, J = 8.8 Hz, 2H), 7.40 (d, J = 8.8 Hz, 2H),
13
7.44 (s, 4H); C NMR (CDCl3): 
2, 78.4, 85.5, 87.0, 92.9, 109.5, 111.8, 120.8, 124.8, 131.0,
132.0, 132.8, 150.2.
4.6. Typical procedure for the synthesis of
4-[2-{4-(2-(2,3,4,5,6-pentafluorophenyl)ethynyl)phenyl}ethynyl]phenylcarbazole (2a)
Cl2Pd(PPh3)2 (0.029 g, 0.042 mmol), PPh3 (0.018 g, 0.070 mmol), CuI (13 mg, 0.070 mmol),
terminal acetylene 7a (0.26 g, 0.70 mmol), bromopentafluorobenzene (0.25 g, 1.0 mmol) and
triethylamine (20 mL) were placed in a 50 mL two-necked round-bottomed flask. The flask was
equipped with a stirrer bar, a reflux condenser, and an inlet tube for argon. The was mixture
subsequently stirred at 100 °C for 15 h. After stirring, the resultant product was cooled to room
temperature, followed by evaporation to remove the solvent. The crude product was extracted with
AcOEt (20 mL) and washed with saturated aqueous NH4Cl solution (20 mL) three times and brine
(once). The combined organic layers were dried over anhydrous Na2SO4, filtered, and concentrated
in vacuo. The filtrate was then subjected to silica-gel column chromatography (eluent:
hexane/CH2Cl2 = 5/1), followed by recrystallization from a mixed solvent (CH2Cl2/methanol = 1/1),
to obtain the corresponding bistolane 2a in 32% yield (0.12 g, 0.23 mmol) as a yellow solid.
4.6.1. 4-[2-{4-(2-(2,3,4,5,6-Pentafluorophenyl)ethynyl)phenyl}ethynyl]phenylcarbazole (2a)
1
Yield: 32% (yellow solid); M.p.: 221–222 °C; H NMR (CDCl3):  7.29–7.33 (m, 2H), 7.41–7.47
(m, 4H), 7.59–7.61 (m, 6H), 7.76–7.79 (m, 2H); 13C NMR (CDCl3):  75.0–75.1 (m, 1C), 89.8, 91.4,
100.2 (td, J = 18.5, 4.2 Hz), 101.1–101.2 (m), 109.9, 120.4, 120.5, 121.6, 121.8, 123.8, 124.6, 126.2,
19
127.0, 131.9, 132.0, 133.3, 136.4–139.3 (m), 138.1, 140.4–143.1 (m), 140.6, 145.8–148.6 (m); F
NMR (CDCl3):  –136.33 (dd, J = 20.7, 3.5 Hz, 2F), –152.71 (t, J = 20.7 Hz, 1F); –162.11 (td, J =
20.7, 6.7 Hz, 2F); IR (KBr):  3094, 2214, 1923, 1522, 1449, 1229, 989 cm–1; HRMS (FAB+) m/z
[M+] Calcd for C34H16F5N: 533.1203; found: 533.1248; Anal. Calcd for C34H16F5N: C, 76.55; H,
3.02; N, 2.63. found: C, 76.55; H, 3.25; N, 2.80.
4.6.2.
N-4-[2-{4-([2-(2,3,4,5,6-Pentafluorophenyl)ethynyl]phenyl]ethynyl]phenyl-N,N-diphenylamine (2b)
1
Yield: 61% (yellow solid); M.p.: 184–185 °C; H NMR (CDCl3):  6.99–7.03 (m, 2H), 7.06–7.14

(m, 6H), 7.26–7.31 (m, 4H), 7.36–7.39 (m, 2H), 7.50–7.55 (m, 4H); 13C NMR (CDCl3):  74.6 (d, J
= 3.7 Hz), 88.1, 92.6, 100.2 (td, J = 17.6, 4.3 Hz), 101.3 (d, J = 3.2 Hz), 115.3, 120.6, 122.0, 123.7,
125.1, 129.4, 131.4, 131.8, 132.6, 136.2–139.1 (m, 1C), 140.0–142.9 (m, 1C), 145.7–148.4 (m, 1C),
147.0, 148.3, one carbon in pentafluorophenyl was overlapped with other carbons; 19F NMR
(CDCl3):  –136.99 (dd, J = 20.7, 6.9 Hz, 2F), –153.54 (t, J = 20.7 Hz, 1F), –162.79 (td, J = 20.7,
6.9 Hz, 2F); IR (KBr):  3063, 3034, 2202, 1589, 1524, 1496, 1272, 988, 835 cm–1; HRMS (FAB+)
m/z [M+] Calcd for C34H18F5N: 535.1359; found: 535.1354; Anal. Calcd for C34H18F5N: C, 76.26; H,
3.39; N, 2.62. found: C, 76.47; H, 3.43; N, 2.61.
4.6.3. N,N-Dimethyl-4-[2-{4-(2-(2,3,4,5,6-pentafluorophen-yl)ethynyl)phenyl}ethynyl]aniline (2c)
Yield: 32% (yellow solid); M.p.: 210–212 °C; 1H NMR (CDCl3):  3.01 (s, 6H), 6.65–6.68 (m, 2H),
7.40–7.43 (m, 2H), 7.48–7.54 (m, 4H); 13C NMR (CDCl3):  40.3, 74.5 (d, J = 4.1 Hz), 87.2, 93.9,
100.5 (d, J = 4.6 Hz), 101.7 (d, J = 3.7 Hz), 109.6, 111.9, 120.3, 125.9, 131.4, 131.9, 133.0, 136.4–
19
139.3 (m), 140.2–143.0 (m), 145.8–148.6 (m), 150.5; F NMR (CDCl3):  –136.51 (dd, J = 21.4,
14.1 Hz, 2F), –153.19 (t, J = 21.4 Hz, 1F), –162.31 (td, J = 21.4, 6.7 Hz, 2F); IR (KBr):  3091,
3032, 2960, 2920, 2849, 2203, 1611, 1597, 1496, 1366, 1138, 983, 835 cm–1; HRMS (FAB+) m/z
[M+] Calcd for C24H14F5N: 411.1046; found: 411.1043; Anal. Calcd for C24H14F5N: C, 70.07; H,
3.43; N, 3.40. found: C, 69.68; H, 3.63; N, 3.30.
4.7. X-Ray crystallographic analysis
Yellow-colored crystals of fluorinated bistolanes with a carbazol-9-yl unit (2a) and a diphenylamino
group (2b) both with approximate dimensions of 0.15 × 0.10 × 0.10 mm were mounted on a glass
fiber. The omega scanning technique was used to collect the reflection data using a Bruker D8
goniometer with monochromatized Mo K radiation ( = 0.71075 Å). The initial structure of the
unit cell was determined by a direct method using APEX2. The structural model was refined by a
full-matrix least-squares method using SHELXL-2014/6 [23]. All calculations were performed
using the SHELXL program. The crystal data is summarized as follows:
Compound 2a: C34H16F5N, M = 533.48, triclinic, a = 9.5231(10), b = 10.6983(11), c = 14.0307(14)
Å,  = 95.981(3),  = 109.238(3),  = 103.197(3)°, V = 1288.7(2) Å3, T = 296 K, space group P –1,
Z = 2, 7524 reflections measured, 4330 uniques (Rint = 0.0973), which were used in all calculations.
The final R1 and wR2 were 0.0579 and 0.1842, respectively, (I > 2(I)).
Compound 2b: C34H18F5N, M = 535.49, triclinic, a = 5.9072(5), b = 11.4122(10), c = 20.3304(18)
Å,  = 78.195(3),  = 85.853(3),  = 82.326(2)°, V = 1328.1(2) Å3, T = 296 K, space group P –1, Z
= 2, 4554 reflections measured, 2836 uniques (Rint = 0.1009), which were used in all calculations.

The final R1 and wR2 were 0.0636 and 0.1821, respectively, (I > 2(I)).
Indexed data have been deposited in the Cambridge Crystallographic Data Centre (CCDC) database
(CCDC 1565483 for 2a and 1565484 for 2b). Copy of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk).
4.8. Computation
All computations were performed using the Gaussian 09 program package (Rev. C.01) [15] and
density functional theory (DFT) method. We used the standard basis set, cc-pVDZ levels of theory
for geometry optimizations.[16] Stationary points were characterized by frequency calculations to
confirm a correct number of imaginary frequencies. Minimum energy structures have no imaginary
frequency. The vertical excitation energies and oscillator strengths were estimated for the 6 lowest
S0→S1 transitions using TD-DFT with the same hybrid functional and basis set.
4.9. Photophysical properties
UV-vis absorption spectra were recorded using a JASCO V-630 absorption spectrometer.
Steady-state photoluminescence spectra were obtained using a JASCO FP-8500 fluorescence
spectrometer. Photoluminescence quantum yields were estimated using a calibrated integrating
sphere system (JASCO).
Acknowledgements
The present work was partially supported by the Hitachi-Metals•Materials Science Foundation. The
authors are sincerely grateful to Prof. Osamu Tsutsumi at Ritsumeikan University for his kind
assistance in X-ray crystallographic analyses. We also acknowledge Profs. Kensuke Naka and
Hiroaki Imoto at Kyoto Institute of Technology for their helpful support in photoluminescence
measurements.

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Fig. 1 Classification of fluorescent materials according to the state of molecules

Fig. 2 Electrostatic potential distribution of
1 and 2. Computations were performed for optimized
geometries at the DFT/B3LYP/cc-pVDZ levels of theory. The density isosurface value is 0.005, and
negatively and positively charged regions are indicated by red and blue, respectively. ex indicates
dipole moment in the excited state at the Franck-Condon geometry (B3LYP/aug-cc-pVDZ levels of
theory).
Fig. 3 Molecular orbitals (HOMO–1, HOMO, LUMO, and LUMO+1) for
1 and 2 computed at the

TD-DFT/B3LYP/aug-cc-pVDZ levels of theory, and the corresponding orbital energies in the ground
state.
Fig. 4 Crystal structures of 2a and 2b. (a), (d) Molecular structures in the crystal. (b) Packing structure
of 2a and (c) space-filling model viewing at the red-square region. (e) Packing structure of 2b and (c)
space-filling model viewing at the red-square region. Color legend: C: grey, H: light-grey, N: blue, and
F: light-green.

Fig. 5 (a) Absorption spectra of
spectra of ex = 330 nm), 2a
1
and 2a
–
c
in CH2Cl2 (10–5 mol L–1). (b) Corrected photoluminescence
ex = 372 nm) in CH2Cl2 (10–6 mol
and 2a , and
1
(

(
ex = 342 nm), 2b (372 nm) and 2c (
L–1 concentration). (c) Color diagram of the photoluminescence observed for
1
–c
photographs under UV irradiation (ex = 365 nm).
Fig. 6 (a) Photoluminescence behavior of 2b measured in various solvents (10–6 mol L–1 concentration,
ex = 372 nm). (b) Color diagram of photoluminescence observed for 2b depending on solvent polarity
(dielectric constant (
photographs under UV irradiation (

) for hexane: 1.88, CH2Cl2: 8.93, acetone: 20.6, and for acetonitrile: 35.9), and
ex = 365 nm).


Fig. 7 (a) Corrected photoluminescence spectra of
nm), and 2c ex = 371 nm) in the solid state. (b) Color diagram of the emission of
photographs of the compounds in the solid state under UV irradiation ( ex = 365 nm).
1
(
ex = 365 nm), 2a
(
ex = 371 nm), 2b
(
ex = 365
. Inset:
(
1
and 2a–c

Fig. 8 Relationship between molecular dipole moment in an excited state (
maximum wavelength ( max). Plots, and , indicate measurements in solution and in the solid
state, respectively, for (white), 2a (blue), 2b (green) and 2c (red). Blue line shows a linear fitting
function obtained by a least-squares regression among 2a in solution, and the red line also the linear
fitting estimated from 2a in the solid state.
ex) and photoluminescence

○
□
1
–
c
–
c