Synthesis and two-photon absorption properties of symmetrical chromophores derived from 2,3,5-trisubstituted quinoxaline units

Article abstract of DOI:10.1002/ejoc.201300345

A set of symmetrically substituted multibranched chromophores composed of three quinoxaline-based congeners has been synthesized and experimentally shown to possess strong and widely dispersed two-photon absorptivities in the visible to near-IR region und

Full text of DOI:10.1002/ejoc.201300345

FULL PAPER
DOI: 10.1002/ejoc.201300345
Synthesis and Two-Photon Absorption Properties of Symmetrical
Chromophores Derived from 2,3,5-Trisubstituted Quinoxaline Units
Tzu-Chau Lin,*[a] Wei Chien,[a] Che-Yu Liu,[a] Ming-Yu Tsai,[a] and Yu-Jheng Huang[a]
Keywords: Two-photon absorption / Chromophores / Fluorescence / Nonlinear optics / Quinoxaline
A set of symmetrically substituted multibranched chromo-
phores composed of three quinoxaline-based congeners has
been synthesized and experimentally shown to possess
strong and widely dispersed two-photon absorptivities in the
visible to near-IR region under the irradiation of femtosecond
and nanosecond laser pulses. The electronic properties of the
central π bridges incorporated into the final structures are
closely connected to the molecular two-photon activities of
these model compounds. Effective optical-power attenuation
and stabilization behaviors in the nanosecond time domain
of these dye molecules were also investigated. The structural
motif of these compounds provides a useful approach for the
molecular design of strong two-photon absorbing material
systems with the potential for quick-responsive and broad-
band optical-control related applications, particularly for
long-duration laser pulses in the near-IR region.
longer excited-state lifetimes are believed to benefit from
apparent nonlinear absorption because of two-photon-as-
sisted excited-state absorption (2PA-assisted ESA),[11] so
that the effective optical power attenuation will be en-
hanced. In our search for effective strategies to design
highly active 2PA chromophores, we have continuously ex-
plored the influence of the incorporation of heterocyclic
ring complexes and the electronic properties of the central
conjugation bridge on molecular 2PA in multibranched π
frameworks. Herein, we present the synthesis of a new series
of multipolar two-photon-active model chromophores 1–3
derived from functionalized quinoxaline moieties connected
by various π bridges as well as initial investigations of their
2PA properties in the femtosecond and nanosecond time
domains.
Introduction
Long after the first theoretical prediction of two-photon
absorption by Göppert-Mayer in 1931,[1] the advent of la-
sers in the 1960s helped scientists to experimentally verify
its existence through upconverted emission from substances
under the irradiation of laser light with wavelengths far
greater than the linear absorption bands of the substance.[2]
In the past two decades, the availability of stable and high-
peak-power lasers has further incited the momentum to ex-
plore two-photon-related technologies. Many potential
2PA-based applications in the emerging fields of photonics
and biophotonics have been proposed and explored, includ-
ing optical power limiting, frequency upconverted lasing,
3D data storage, 3D microfabrication, nondestructive bio-
imaging and tracking, and two-photon photodynamic ther-
apy.[3] For these applications, the demand for rationally de-
signed organic compounds that exhibit sufficiently large
2PA within the desired spectral region is consequently escal-
ating. The combination of several structural parameters,
such as the efficiency of intramolecular charge-transfer and/
or the effective size of the π-conjugation domain within a
molecule, is closely related to molecular 2PA.[4–10] In ad-
dition to strong 2PA, other photophysical properties may
also be required for the designed molecules for various
practical needs. For example, for use as optical power limit-
ers in the nanosecond regime, compounds that possess
Results and Discussion
I. Molecular Structures of Model Compounds
The chemical structures and the synthetic routes toward
the studied model compounds are illustrated in Figure 1
and Scheme 1, respectively.
This model-compound set contains three multibranched
congeners with various π linkers, namely, vinylene, fluorene,
and dialkoxybenzene, to connect 2,3-difunctionalized quin-
oxaline units and form fluorophores with a common ge-
neric “donor–quinoxaline–π–quinoxaline–donor” (D–Q–π–
Q–D) structure. Diphenylaminofluorene moieties are intro-
duced as the peripheral electron-donating units in this
model-compound system. The molecular design of these
chromophores originates from a simple attempt to con-
struct a set of symmetrically substituted π frameworks by
using various π bridges with different electronic properties
[a] Photonic Materials Research Laboratory, Department of
Chemistry, National Central University,
300 Jhong-Da Rd. Jhong-Li 32001, Taiwan
Fax: +886-3-4227664
E-mail: tclin@ncu.edu.tw
Homepage: http://140.115.43.2/index.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300345.
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Chromophores from 2,3,5-Trisubstituted Quinoxaline Units
Figure 1. Molecular structures of the studied model chromophores.
Scheme 1. Synthetic procedures toward target model chromophores.
to connect two identical functionalized quinoxaline moie- excitation of the resulting dye molecules may be different
ties. The extent of charge-transfer/redistribution upon light and this, in turn, is believed to correlate with molecular
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FULL PAPER
2PA. Furthermore, it would be interesting to analyze the
relationship between molecular 2PA and the arrangement
of structural units in a chromophore, so that either the ben-
eficial or deleterious effects caused by each structural unit
may be elucidated. On the other hand, we have attached
alkyl chains at the C-9 positions of all the fluorenyl units
to enhance the molecular solubility in common organic sol-
vents, which is another important issue to be considered in
the molecular design from both an experimental and practi-
cal viewpoint. The synthetic procedures toward these model
dye molecules mainly involve consecutive transformation of
functional groups on the fluorene moieties, quinoxaline ring
complex formation, and Heck coupling to prepare the key
intermediates and the targeted model compounds as shown
in Scheme 1. The details of the syntheses of these key inter-
mediates and the final model chromophores are described
in the Exp. Section. As shown in Figure 1, a previously re-
ported compound[10c] that represents the “D–Q” compo-
nents of the studied model compounds was selected as a
reference compound (R) for comparison.
Figure 2. Linear absorption and fluorescence spectra (inset) of 1–
3 in solution (1ϫ10–6 m in toluene).
II. Linear and Nonlinear Optical Property Measurements
Figure 2 illustrates the linear absorption and fluores-
cence spectra of the studied dye molecules in toluene solu-
tion. Each of the studied model chromophores shows three
distinct intense absorption peaks in the range 300–450 nm.
These model-chromophore solutions also exhibit strong
two-photon-excited blue to blue-green upconversion emis-
sion, which can be readily seen with the naked eye even
under irradiation with a low-intensity unfocused femto-
second laser beam at ca. 790 nm. Figure 3 (a) illustrates the
normalized 2PA-induced fluorescence spectra of 1–3. As an
excitation light source for this experiment, a wavelength-
tunable mode-locked Ti:sapphire laser (Chameleon Ultra
II, Coherent), which delivers ca. 140 fs pulses with a repeti-
tion rate of 80 MHz and a beam diameter of 2 mm was
utilized. The intensity level of the excitation beam was care-
fully controlled to avoid the saturation of absorption and
Figure 3. (a) Two-photon-excited fluorescence spectra of the
studied model chromophores. Inset: logarithmic plots of the power-
squared dependence of the 2PA-induced fluorescence intensity on
the input intensity of these compounds in toluene; (b) 2PA-induced
fluorescence decay curves.
photodegradation of the samples during the experiments. fitting of each decay curve to a single-exponential depen-
Also, the relative position of the excitation beam was ad- dence has revealed that these model chromophores possess
justed as close as possible to the wall of the quartz cell fluorescence lifetimes of 1.2–1.6 ns, and these data are col-
(10ϫ10 mm cuvette), so that only emission from the front lected in Table 1.
surface of the sample was recorded to minimize re-absorp-
To investigate and compare the dispersion of 2PA behav-
tion and the inner-filter effect. From each inset logarithmic iors of these dye molecules as a function of wavelength, the
curve in Figure 3 (a), one can see that the results (i.e., slope degenerate two-photon-excited fluorescence (2PEF) mea-
ca. 2) validate that a 2PA process is the major cause of the surement was conducted in the near-IR regime (680–
observed upconverted fluorescence emissions in all cases.
1000 nm) with fluorescein (ca. 80 μm in a pH 11 NaOH
The temporal behavior and lifetimes of the 2PA-induced solution) as the standard.[12–13] Figure 4 shows the mea-
fluorescence of the same sample solutions were also probed sured degenerate two-photon absorption spectra of 1–3 and
by the time-correlated single photon counting (TCSPC) R in toluene.
technique by using a highly sensitive photomultiplier
The reference compound R exhibits a relatively small but
equipped with an accumulating real-time processor as the detectable 2PA with a local maximum at ca. 800 nm (Fig-
max
detection system (PMA-182 and TimeHarp 200, Pico- ure 4, δ2
≈ 180 GM), whereas 1 exhibits a large 2PA
Quant). The same femtosecond laser system (vide supra) (Ն 500 GM) within the spectral range 720–860 nm, which
was employed for this experiment. The measured fluores- implies that the use of a vinylene group to connect two units
cence decay curves are depicted in Figure 3 (b). Theoretical of R offers a useful approach to expand the π domain and
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Chromophores from 2,3,5-Trisubstituted Quinoxaline Units
Table 1. Photophysical properties of 1–3 in solution.[a]
abs
em
[d]
max
[h]
λmax [nm][b]
λmax [nm][c]
ΦF
τ1PA–FL [ns][e]
δ2
[GM][f]
τ2PA–FL [ns][g]
Nπ
eff
1
308, 365, 434
310, 370, 432
310, 364, 454
312, 394
502
491
505
501
0.57
0.54
0.77
0.50
1.6
1.3
1.2
2.3
ca. 1250
ca. 1680
ca. 2300
ca. 180
1.6
1.3
1.2
2.3
72.03
85.70
83.74
36.06
2
3
R
[a] The concentrations were 1ϫ10–5 and 1ϫ10–4 m in toluene for 1PA-related and 2PA-related measurements, respectively. [b] One-photon
absorption maximum. [c] 1PA-induced fluorescence emission maximum. [d] Fluorescence quantum efficiency. [e] 1PA-induced fluorescence
lifetime. [f] Maximum 2PA cross-section value (with an experimental error of ca. Ϯ15%); 1 GM = 1ϫ10–50 cm4 sphoton–1 molecule–1. [g]
2PA-induced fluorescence lifetime. [h] Effective π-electron number.
cited-state absorption (2PA-induced ESA) because, from
the application standpoint, any medium that possesses a
large apparent nonlinear absorption over a wide spectral
range could be a very useful optical power attenuator for
long laser pulses.[14]
To study the effective power-limiting performance of
these model compounds, we utilized nanosecond laser
pulses. For example, we selected 3 as a representative com-
pound to demonstrate the power-limiting properties of
these fluorophores as it manifests very strong 2PA at
800 nm and is theoretically expected to show better optical
power control at this wavelength. In our experiment, the
nonlinear absorbing medium was a 1 cm path-length solu-
tion of the studied dye in toluene with a concentration of
0.02 m. A tunable nanosecond laser system [an integrated
Figure 4. Degenerate two-photon absorption spectra of 1–3
(1ϫ10–4 m) in toluene measured by the 2PEF method (experimen-
tal error ca. 15%).
Q-switched Nd:YAG laser and optical parameter oscillator
leads to greatly enhanced molecular 2PA. On the other
(OPO), model NT342/3 from Ekspla] was employed as an
hand, if one uses 1 as a reference, it is notable that all these
model chromophores not only exhibit a similar dispersion
excitation source to provide ca. 6 ns laser pulses with a con-
trolled average pulse energy in the range ca. 0.02–2 mJ and
pattern of their two-photon activities but also show ascend-
a repetition rate of 10 Hz. The laser beam was slightly fo-
ing overall magnitude of 2PA from 1 to 3 within the investi-
cused onto the center of the sample solution to provide a
nearly uniform laser beam radius within the whole cell path
gated spectral region (Figure 4). These features indicate that
the insertion of aromatic rings, such as fluorene and dialk-
length, and the transmitted laser beam from the sample cell
oxybenzene units, into the middle part of 1 (as is the case
was detected by an optical power (energy) meter. Figure 5
illustrates the measured power-attenuation performance at
800 nm based on this chromophore solution. Compound 3
for 2 and 3, respectively) further helps to promote the mo-
lecular 2PA without a dramatic shift of the 2PA band posi-
tion. Molecules with this property could be very useful for
displays fairly good power-restriction properties at 800 nm,
some particular applications, in which large multiphoton
and this initial finding suggests the potential of this model
absorptivities within a specific spectral region are desired.
fluorophore for broadband power-suppressing applications
Additionally, the insertion of an electron-rich dialkoxybenz-
in the nanosecond regime.
ene moiety offers a larger increment of molecular 2PA com-
In addition, the output/input curve shown in Figure 5
pared to the insertion of a fluorene unit, which implies that
represents a characteristic type of optical compression,
which is ideal for use in optical power (or intensity) stabili-
the electronic properties of the central π bridge play an im-
portant role in the promotion of molecular 2PA in this dye
system.
zation because a huge magnitude change of the input signal
will lead to only a small variation of the output level.[15]
This means that a larger input-power (or intensity) fluctua-
tion will lead to a much smaller output fluctuation when
III. Effective Optical-Power-Limiting Properties in the
the pulse passes through a nonlinear absorptive medium,
Nanosecond Regime
such as a solution of 3. The results of an optical-stabiliza-
The excited-state lifetimes of 1–3 are in the nanosecond tion study based on the solution of 3 are shown in Figure 5
range, which means that significant excited-state population (b) and (c). The curves in Figure 5 (b) and (c) are the in-
may be retained and, therefore, the occurrence of excited- stantaneous pulse energy changes of the input and output
state absorption within the tested sample is possible during laser pulses at 800 nm, respectively. For comparison, the
excitation by longer laser pulses. This, in turn, may lead average levels for both the input and output signals were
to strong apparent optical attenuation.[11] Such a feature is normalized to the same value. The input pulses possess a
particularly beneficial for optical-power-control applica- relatively large energy fluctuation as shown in Figure 5 (b),
tions in the nanosecond regime based on 2PA-induced ex- and after the pulse passes through the solution of 3, a re-
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Experimental Section
General: All commercially available reagents for the preparation of
the intermediates and targeted chromophores were obtained from
the Aldrich Chemical Co. and were used as received, unless stated
otherwise. Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl. 1H and 13C NMR spectra were recorded with
200 or 300 MHz spectrometers and are referenced to tetramethylsil-
ane (TMS) or residual CHCl3. A representative numbering scheme
for the assignment of the NMR signals of the C and H atoms
of the intermediates and model chromophores is provided in the
Supporting Information. HRMS was conducted by using a Waters
LCT ESI-TOF mass spectrometer. MALDI-TOF MS spectra were
obtained with a Voyager DE-PRO mass spectrometer (Applied
Biosystems, Houston, USA).
Synthesis: Compounds 4, 12, and 13 (Scheme 1) were obtained by
following established procedures.[9a,16] For the synthesis of other
key intermediates (5–8, 10, and 11) and the targeted model com-
pounds (1–3), a series of functionalization steps starting from 4
were conducted and are presented below.
9,9-Dihexyl-N,N-diphenyl-7-[2-(trimethylsilyl)ethynyl]-9H-fluoren-
2-amine (5): To a solution of 4 (8.4 g, 14.47 mmol) in THF
(130 mL) was added PdCl2(PPh3)2 (0.61 g, 0.87 mmol), CuI (0.28 g,
1.47 mmol), iPr2NH (8.8 g, 0.087 mol), and trimethylsilyl acetylene
(1.5 g, 15.27 mmol), and the resulting solution was stirred at 80 °C
under Ar for 18 h. The solution was cooled to room temp., and a
saturated NH4Cl solution (ca. 50 mL) was added. The mixture was
stirred at room temp. for 0.5 h. and then extracted with ethyl acet-
ate (3 ϫ 30 mL). The combined organic layers were dried with
MgSO4. After filtration and removal of the solvent, the crude prod-
uct was purified by column chromatography on silica gel with hex-
ane as the eluent to give the final purified product as pale yellow
Figure 5. (a) Measured optical-power-attenuation curve based on
a toluene solution of 3 under the excitation of nanosecond laser
pulses at ca. 800 nm, (b) measured instantaneous pulse-energy fluc-
tuation of the input laser pulses, and (c) measured instantaneous
pulse-energy fluctuation of the output laser pulses. The repetition
rate of the laser pulses was 10 Hz, and the average input pulse
energy level was ca. 1 mJ.
1
oil in a yield of 82.5% (13.83 g). H NMR (300 MHz, CDCl3): δ
= 7.65–7.60 (m, 2 H, H15, H12), 7.57–7.54 (d, J = 8.1 Hz, 2 H, H9,
H13), 7.38–7.33 (t, 4 H, H2), 7.26–7.24 (m, 5 H, H8, H3), 7.16–7.09
(m, 3 H, H6, H1), 2.06–1.90 (m, 4 H, Hf), 1.31–1.19 (m, 12 H, He,
Hd, Hc), 1.02–0.91 (m, 6 H, Ha), 0.78 (br., m, 4 H, Hb), 0.35 (s, 9
H, TMS CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 152.42 (C5),
150.41 (C16), 147.84 (C4), 147.60 (C7), 141.45 (C11), 135.38 (C10),
131.18 (C15), 129.15 (C2), 126.02 (C13), 123.90 (C3), 123.35 (C9),
122.63 (C1), 120.73 (C12), 120.39 (C8), 118.95 (C6), 118.83 (C14),
106.44 (sp C), 93.54 (sp C), 55.03 (Cg), 40.20 (Cf), 31.50 (Ce), 29.58
(Cd), 23.68 (Cc), 22.53 (Cb), 14.03 (Ca), 0.08 (TMS CH3) ppm.
HRMS (FAB): calcd. for C42H51NSi [M]+ 597.3791; found
597.3796.
duced fluctuation of pulse energy is observed for the output
signal as illustrated in Figure 5 (c).
Conclusions
We have synthesized a new multipolar chromophore set
composed of three analogues with various central π bridges
and functionalized quinoxaline moieties as the major build-
ing units. The initial experimental results indicate that these
model fluorophores manifest strong and widely dispersed
two-photon absorption in the near-IR region. Tentative
analysis of the correlation between the molecular structures
and the observed overall 2PA behaviors reveals that ex-
panding the size of the π domain through the insertion of
7-Ethynyl-9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine (6): A mix-
ture of 5 (12.85 g, 0.021 mol), diethyl ether (60 mL), and potassium
carbonate (5.94 g, 0.043 mol) in methanol (60 mL) was stirred at
room temperature for 4 h. A saturated NH4Cl solution (ca. 90 mL)
was then added, and the reaction mixture was stirred at room tem-
perature for 0.5 h. The solution was then extracted with ethyl acet-
different aromatic rings has a positive contribution to the ate (3 ϫ 30 mL). The combined organic layers were dried with
MgSO4. After filtration and removal of the solvent, the crude prod-
uct was purified by column chromatography on silica gel with hex-
ane as the eluent to give the final purified product as a pale yellow
promotion of 2PA in this compound system, and the inser-
tion of the electron-rich dialkoxybenzene unit provides a
larger increment of molecular 2PA. The model compound
3 exhibits both intense upconverted emission when excited
by a two-photon process and effective optical power-limit-
ing/stabilization properties for nanosecond laser pulses.
These observations may suggest that the functionalized
quinoxaline ring systems utilized in this work could be use-
ful structural units for the construction of highly active 2PA
chromophores for practical applications.
1
oil in a yield of ca. 100% (11.3 g). H NMR (300 MHz, CDCl3): δ
= 7.56–7.53 (d, J = 8.1 Hz, 2 H, H15, H12), 7.48–7.46 (m, 2 H, H9,
H13), 7.29–7.24 (t, J = 7.8 Hz, 4 H, H2), 7.18–7.15 (m, 5 H, H8,
H3), 7.08–7.00 (m, 3 H, H6, H1), 3.08 (s, 1 H, sp H), 1.93–1.89 (m,
4 H, Hf), 1.32–1.11 (m, 12 H, He, Hd, Hc), 0.86–0.81 (t, 6 H, Ha),
0.73–0.71 (m, 4 H, Hb) ppm. 13C NMR (75 MHz, CDCl3): δ =
152.41 (C5), 150.50 (C16), 147.82 (C4), 147.66 (C7), 141.64 (C11),
135.20 (C10), 131.17 (C15), 129.14 (C2), 126.24 (C13), 123.93 (C3),
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Chromophores from 2,3,5-Trisubstituted Quinoxaline Units
123.29 (C9), 122.64 (C1), 120.75 (C8, C12), 119.36 (C6), 118.89 (C14),
J = 9 Hz, 1 H, HC), 7.83–7.79 (d, J = 9 Hz, 1 H, HB), 7.58–7.50
84.77 (sp C), 76.86 (sp C), 55.00 (Cg), 40.11 (Cf), 31.44 (Ce), 29.53 (m, 8 H, H12, H15, H13, H9), 7.26–7.21 (m, 8 H, H2), 7.12–7.08 (m,
(Cd), 23.67 (Cc), 22.48 (Cb), 13.99 (Ca) ppm. HRMS (FAB): calcd. 10 H, H6, H3), 7.03–6.98 (m, 6 H, H1, H8), 1.74–1.72 (m, 8 H, Hf),
for C39H43N [M]+ 525.3396; found 525.3402.
1.10–1.02 (m, 24 H, He, Hd, Hc), 0.80–0.76 (t, J = 6.9 Hz, 12 H,
Ha), 0.64–0.62 (m, 8 H, Hb) ppm. 13C NMR (75 MHz, CDCl3): δ
= 154.78 (CG), 154.30 (CH), 152.63 (C5), 150.62 (C16), 147.89 (C4),
147.57 (C10), 141.95 (CE), 141.88 (CD), 141.66 (C7),139.82 (C11),
136.95 (CC), 136.85 (CF), 135.33 (CB), 133.04 (C15), 131.36 (C9),
130.39 (C12), 129.15 (C2), 124.33 (C13), 123.90 (C3), 123.34 (C14),
122.59 (C1), 120.89 (C6), 119.02 (C8), 118.89 (CA), 55.09 (Cg), 40.09
(Cf), 31.53 (Ce), 29.57 (Cd), 23.83 (Cc), 22.60 (Cb), 14.07 (Ca) ppm.
HRMS (FAB): calcd. for C82H87BrN4 [M]+ 1206.6114; found
1206.6104.
7-{2-[7-(Diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl]ethynyl}-9,9-di-
hexyl-N,N-diphenyl-9H-fluoren-2-amine (7): To a solution of 4
(11.48 g, 19.8 mmol) and 6 (10.42 g, 19.8 mmol) in THF (60 mL)
was added Pd(PPh3)4 (0.7 g, 0.61 mmol), CuI (0.38 g, 2.0 mmol),
and iPr2NH (3 g, 0.3 mol), and the resulting solution was stirred
at 80 °C under N2 for 18 h. The solution was cooled to room temp.,
and a saturated NH4Cl solution (ca. 50 mL) was added into the
reaction mixture, which was stirred at room temperature for 0.5 h.
The solution was then extracted with ethyl acetate (3ϫ30 mL). The
combined organic layers were dried with MgSO4. After filtration
and removal of the solvent, the crude product was purified by col-
umn chromatography on silica gel with hexane as the eluent and
recrystallized from methanol/hexane. The purified product was ob-
7-{3-[7-(Diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl]-6-vinylquinox-
alin-2-yl}-9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine (11): Com-
pound 10 (4 g, 3.3 mmol), Pd(OAc)2 (0.038 g, 0.169 mmol), and
PPh3 (0.174 g, 0.648 mmol) were dissolved in NEt3 (60 mL). Tribut-
yl(vinyl)stannane (1.58 g, 4.98 mmol) was then added, and the re-
sulting solution was stirred at 95 °C under N2 for 24 h. The solu-
tion was cooled to room temp., and saturated NH4Cl solution was
added into the reaction mixture, which was stirred at room temp.
for 1h. The solution was filtered, and the filtrate was then extracted
with ethyl acetate (3ϫ30 mL). The combined organic layers were
dried with MgSO4. After filtration and removal of the solvent, the
crude product was purified by column chromatography on silica gel
with ethyl acetate/hexane (1:20) to give the final purified product as
1
tained as a yellow powder in a yield of 52.5% (10.67 g). H NMR
(300 MHz, CDCl3): δ = 7.60–7.49 (m, 8 H, H15, H12, H9, H13),
7.27–7.22 (t, 8 H, H2), 7.13–7.11 (d, J = 7.8 Hz, 10 H, H6, H3),
7.03–6.99 (m, 6 H, H1, H8), 1.96–1.79 (m, 8 H, Hf), 1.16–1.06 (m,
24 H, He, Hd, Hc), 0.87–0.78 (t, 12 H, Ha), 0.66 (br., m, 8 H, Hb)
ppm. 13C NMR (75 MHz, CDCl3): δ = 152.46 (C5), 150.66 (C16),
147.90 (C4), 147.53 (C7), 141.13 (C11), 135.55 (C10), 130.63 (C15),
129.18 (C2), 125.72 (C13), 123.91 (C3), 123.44 (C9), 122.61 (C1),
120.75 (C8), 120.66 (C12), 119.06 (C6, C14), 90.52 (sp C), 55.10 (Cg),
40.30 (Cf), 31.56 (Ce), 29.64 (Cd), 23.76 (Cc), 22.58 (Cb), 14.04 (Ca)
ppm. HRMS (FAB): calcd. for C76H84N2 [M]+ 1024.6635; found
1024.6639.
1
a yellow powder in a yield of 91.6% (3.5 g). H NMR (300 MHz,
CDCl3): δ = 8.14–8.12 (d, J = 8.4 Hz, 1 H, HC), 8.12 (s, 1 H, HF),
7.91–7.87 (dd, J1 = 1.8 Hz, J2 = 1.5 Hz, 1 H, HB), 7.57–7.50 (m, 8
H, H12, H15, H13, H9), 7.26–7.21 (m, 8 H, H2), 7.12–7.07 (m, 10 H,
H6, H3), 7.03–6.98 (m, 6 H, H1, H8), 6.96–6.92 (d, J = 11.1 Hz, 1
H, vinyl H), 6.04–5.98 (d, J = 17.1 Hz, 1 H, vinyl H), 5.50–5.45 (d,
J = 11.1 Hz, 1 H, vinyl H), 1.75–1.70 (m, 8 H, Hf), 1.12–0.98 (m,
24 H, He, Hd, Hc), 0.80–0.76 (t, J = 6.9 Hz, 12 H, Ha), 0.64–0.61
(m, 8 H, Hb) ppm. 13C NMR (75 MHz, CDCl3): δ = 154.29 (CH),
153.61 (CG), 152.57 (C5), 150.50 (C16), 147.86 (C4), 147.40 (C11),
141.58 (CE), 141.29 (CD), 140.96 (C7), 138.75 (CC), 137.29 (C10),
136.13 (C15, CB), 135.44 (vinyl C), 129.11 (C12, C9), 127.29 (C2),
126.66 (CF), 124.32 (CA), 123.81 (C13), 123.34 (C3), 122.50 (C14),
120.82 (C1), 119.03 (C6), 118.90 (C8), 116.21 (vinyl C), 55.02 (Cg),
40.07 (Cf), 31.51 (Ce), 29.55 (Cd), 23.80 (Cc), 22.59 (Cb), 14.07 (Ca)
ppm. HRMS (FAB): calcd. for C84H91N4 [M + H]+ 1155.7165;
found 1155.7251.
1,2-Bis[7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl]ethane-1,2-di-
one (8): To a solution of 7 (10 g, 9.75 mmol) in CH2Cl2 (50 mL) was
added KMnO4 (6.16 g, 39 mmol), NaHCO3 (0.82 g, 9.76 mmol),
Aliquat 336 (0.06 g), and H2O (60 mL), and the resulting solution
was stirred at room temperature for 12 h. A saturated NaHSO3
solution (ca. 50 mL) and a 1 n HCl solution were added into the
reaction mixture. The solution was then extracted with dichloro-
methane (3ϫ30 mL). The combined organic layers were dried with
MgSO4. After filtration and removal of the solvent, the crude prod-
uct was purified by column chromatography on silica gel with
dichloromethane/hexane (1:8) to give the final purified product as
a saffron-yellow powder in a yield of 65 % (6.65 g). 1H NMR
(300 MHz, CDCl3): δ = 8.06 (s, 2 H, H15), 7.89–7.87 (d, J = 7.2 Hz,
2 H, H12), 7.65–7.62 (d, J = 8.4 Hz, 2 H, H13), 7.61–7.58 (d, J =
8.1 Hz, 2 H, H9), 7.25–7.23 (d, J = 5.1 Hz, 8 H, H2), 7.15–7.13 (d,
J = 5.4 Hz, 10 H, H6, H3), 7.07–7.01 (m, 6 H, H1, H8), 1.94–1.87
(m, 8 H, Hf), 1.27–1.06 (m, 24 H, He, Hd, Hc), 0.89–0.80 (m, 12 H,
Ha), 0.67 (br., m, 8 H, Hb) ppm. 13C NMR (75 MHz, CDCl3): δ =
195.00 (C=O), 153.71 (C5), 151.14 (C16), 148.94 (C11), 147.68 (C4),
147.43 (C7), 133.65 (C10), 130.84 (C15, C12), 129.16 (C2), 124.31
(C3), 123.07 (C1), 122.59 (C9), 121.73 (C13, C14), 118.76 (C6), 117.89
(C8), 55.15 (Cg), 39.79 (Cf), 31.32 (Ce), 29.37 (Cd), 23.62 (Cc), 22.38
(Cb), 13.89 (Ca) ppm. HRMS (FAB): calcd. for C76H84N2O2 [M]+
1056.6533; found 1056.6627.
Compound 1: A high-pressure tube was charged with Pd(OAc)2
(1.98 mg, 0.00882 mmol), P(o-tolyl)3 (16 mg, 0.053 mmol), 11
(0.51 g, 0.441 mmol), 10 (0.59 g, 0.488 mmol), NEt3 (5 mL), MeCN
(10 mL), and DMF (5 mL). The tube was sealed with a PTFE cap,
and the mixture was stirred at 110 °C under N2 for 24 h. The mix-
ture was cooled to room temp., and dichloromethane was added.
The resulting solution was stirred at room temp. for 10 min. and
then extracted with H2O (3ϫ30 mL). The organic layer was dried
with MgSO4. After filtration and removal of the solvent, the crude
product was purified by column chromatography on silica gel with
ethyl acetate/hexane (1:10). The purified product was obtained as
a yellow solid with yield of 72% (0.72 g) after recrystallization from
7-{6-Bromo-3-[7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl]-
quinoxalin-2-yl}-9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine (10): methanol. 1H NMR (300 MHz, CDCl3): δ = 8.31 (s, 2 H, HF),
A mixture of 8 (4.2 g, 3.97 mmol) and 9 (0.82 g, 4.42 mmol) in
8.22–8.19 (d, J = 8.7 Hz, 2 H, HC), 8.10–8.07 (d, J = 9 Hz, 2 H,
CH3COOH (65 mL) was heated to reflux under N2 for 6 h. The HB), 7.59–7.51 (m, 16 H, H12, H15, H13, H9), 7.24–7.22 (m, 16 H,
solution was cooled to room temp, and H2O (ca. 50 mL) was added
to the reaction mixture. The crude solid product was collected by
filtration and recrystallized from methanol. The purified product
was obtained as a green-brown powder in a yield of 96.6% (4.83 g).
1H NMR (300 MHz, CDCl3): δ = 8.37 (s, 1 H, HF), 8.05–8.02 (d,
H2), 7.12–7.08 (m, 20 H, H6, H3), 7.03–6.99 (m, 14 H, H1, H8,
vinylene H), 1.76–1.71 (m, 16 H, Hf), 1.13–1.03 (m, 48 H, He, Hd,
Hc), 0.81–0.77 (m, 24 H, Ha), 0.65–0.63 (m, 16 H, Hb) ppm. 13C
NMR (75 MHz, CDCl3): δ = 154.59 (CH), 153.77 (CG), 152.63
(C5), 150.59 (C16), 147.90 (C4), 147.46 (C11), 141.69 (CE), 141.48
Eur. J. Org. Chem. 2013, 4262–4269
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4267

T.-C. Lin, W. Chien, C.-Y. Liu, M.-Y. Tsai, Y.-J. Huang
FULL PAPER
(CD), 141.22 (C7), 138.24 (CC), 137.29 (C10), 137.24 (C15, CB), 127.64 (C9), 127.01 (C12), 126.76 (vinylene C), 126.60 (vinylene C),
135.47 (vinylene C), 130.09 (C12), 129.46 (C9), 129.14 (C2), 127.26
(CF), 124.38 (CA), 123.86 (C13), 123.37 (C3), 122.54 (C14), 120.86
125.91 (CFЈ), 125.66 (CCЈ), 124.40 (C13), 123.87 (C3), 123.41 (C14),
122.54 (C1), 120.84 (C6), 119.14 (C8), 118.94 (CA), 110.43 (CBЈ),
(C1), 119.08 (C6), 118.97 (C8), 55.07 (Cg), 40.10 (Cf), 31.54 (Ce), 109.54 (CEЈ), 71.98 (CfЈ), 56.38 (CiЈ), 55.09 (Cg), 40.12 (Cf), 39.75
29.59 (Cd), 23.85 (Cc), 22.62 (Cb), 14.09 (Ca) ppm. HRMS (FAB): (CeЈ), 31.56 (Ce), 31.02 (CdЈ), 29.61 (Cd), 29.30 (CcЈ), 24.30 (CgЈ),
calcd. for C166H176N8 [M]+ 2281.4019; found 2281.4089.
23.86 (Cc), 23.14 (CbЈ), 22.62 (Cb), 14.16 (Ca), 14.08 (CaЈ), 11.34
(ChЈ) ppm. HRMS (FAB): calcd. for C183H200N8O2 [M + H]+
2542.5872; found 2542.5930.
Compound 2: A high-pressure tube was charged with Pd(OAc)2
(1.71 mg, 0.0076 mmol), P(o-tolyl)3 (13.87 mg, 0.0456 mmol), 11
(0.92 g, 0.796 mmol), 12 (0.187 g, 0.38 mmol), NEt3 (5 mL), MeCN
(10 mL), and DMF (5 mL). The tube was sealed with a PTFE cap,
and the mixture was stirred at 110 °C under N2 for 24 h. The mix-
ture was cooled to room temperature, and dichloromethane was
added. The resulting solution was stirred at room temperature for
10 min. and then extracted with H2O (3ϫ 30 mL). The organic
layer was dried with MgSO4. After filtration and removal of the
solvent, the crude product was purified by column chromatography
on silica gel with ethyl acetate/hexane (1:10) and recrystallized from
methanol. The purified product was obtained as yellow solid in a
Supporting Information (see footnote on the first page of this arti-
cle): Representative numbering of carbon and hydrogen atoms on
various structural units, details of optical experiments, and NMR
spectra.
Acknowledgments
The authors thank the National Science Council (NSC), Taiwan
for financial support through grant number 101-2113-M-008-003-
MY2.
1
yield of 66% (0.66 g). H NMR (300 MHz, CDCl3): δ = 8.27 (s, 2
H, HF), 8.19–8.16 (d, J = 8.7 Hz, 2 H, HC), 8.07–8.03 (d, J =
8.7 Hz, 2 H, HB), 7.79–7.74 (d, J = 8.1 Hz, 2 H, vinylene H), 7.62–
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1.04 (m, 60 H, He, Hd, Hc, HeЈ, HdЈ, HcЈ), 0.81–0.77 (m, 30 H, Ha,
HaЈ), 0.65–0.63 (m, 20 H, Hb, HbЈ) ppm. 13C NMR (75 MHz,
CDCl3): δ = 154.40 (CH), 153.39 (CG), 152.62 (C5), 151.80 (CLЈ,
CAЈ), 150.58 (C16), 147.90 (C4), 147.43 (C11), 141.61 (CE), 141.42
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136.02 (CB), 135.51 (CC), 131.71 (C10), 129.14 (C2), 128.30 (CKЈ
,
CBЈ), 127.68 (C15), 127.13 (CIЈ, CDЈ), 126.50 (vinylene C), 126.28
(vinylene C), 126.02 (C9), 124.38 (C13), 123.86 (C3), 123.38 (C14),
122.54 (C1), 121.18 (CHЈ, CEЈ), 120.85 (C6), 120.18 (CJЈ, CCЈ), 119.09
(C8), 118.94 (CA), 55.07 (Cg, CgЈ), 40.12 (Cf, CfЈ), 31.55 (Ce, CeЈ),
29.74 (CdЈ), 29.59 (Cd), 23.85 (Cc, CcЈ), 22.62 (Cb, CbЈ), 14.09 (Ca),
14.00 (CaЈ) ppm. HRMS (FAB): calcd. for C193H211N8 [M + H]+
2640.6758; found 2640.6841.
Compound 3: A high-pressure tube was charged with Pd(OAc)2
(5.75 mg, 0.026 mmol), P(o-tolyl)3 (46.9 mg, 0.15 mmol), 11
(1.63 g, 1.41 mmol), 13 (0.304 g, 0.62 mmol), NEt3 (5 mL), MeCN
(10 mL), and DMF (5 mL). The tube was sealed with a PTFE cap,
and the reaction mixture was stirred at 110 °C under N2 for 24 h.
The mixture was cooled to room temp., and dichloromethane was
added. The resulting solution was stirred at room temperature for
10 min. and then extracted with H2O (3ϫ 30 mL). The organic
layer was dried with MgSO4. After filtration and removal of the
solvent, the crude product was purified by column chromatography
on silica gel with ethyl acetate/hexane (1:10) and recrystallized from
methanol. The purified product was obtained as a light orange so-
lid in a yield of 43% (0.7 g). 1H NMR (300 MHz, CDCl3): δ = 8.28
(s, 1 H, HF), 8.23 (s, 1 H, HF), 8.18–8.15 (d, J = 8.7 Hz, 2 H, HC),
8.08–8.02 (dd, J1 = 9 Hz, J2 = 9 Hz, 2 H, HB), 7.81–7.74 (dd, J1 =
16.2 Hz, J2 = 4.8 Hz, 2 H, vinylene H), 7.67–7.47 (m, 16 H, H12,
H15, H13, H9), 7.42–7.36 (d, J = 16.8 Hz, 2 H, vinylene H), 7.27–
7.22 (m, 18 H, H2, HBЈ, HEЈ), 7.13–7.08 (m, 20 H, H3, H6), 7.03–
6.99 (m, 12 H, H1, H8), 4.05–4.02 (d, J = 10.5 Hz, 2 H, HfЈ), 3.95
(s, 3 H, HiЈ), 1.96–1.86 (m, 1 H, HeЈ), 1.75–1.60 (m, 18 H, Hf, HgЈ),
1.51–1.42 (m, 6 H, HbЈ, HcЈ, HdЈ), 1.11–0.94 (m, 54 H, He, Hd, Hc,
HaЈ, HhЈ), 0.79–0.65 (t, J = 7.2 Hz, 24 H, Ha), 0.65 (br., 16 H, Hb)
ppm. 13C NMR (300 MHz, CDCl3): δ = 154.38 (CG), 153.37 (CH),
152.64 (C5), 151.68 (CDЈ), 150.57 (C16), 147.94 (C4), 147.45 (C10),
141.59 (CE), 141.00 (CD), 139.38 (C7), 137.39 (C11), 135.55 (CB),
129.15 (C2), 129.00 (CAЈ), 128.37 (CC), 128.25 (CF), 128.01 (C15),
4268
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 4262–4269

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Received: March 7, 2013
Published Online: June 3, 2013
Eur. J. Org. Chem. 2013, 4262–4269
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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