Degenerate two-photon absorption and effective optical-power-limiting properties of multipolar chromophores derived from 2,3,8-trisubstituted indenoquinoxaline

Article abstract of DOI:10.1002/asia.201300223

Two analogous multipolar chromophores (1 and 2) that contained 2,3,8-trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two-photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi-branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical-power-limiting and stabilization behaviors in the nanosecond regime of dye molecule (2) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two-photon systems for quick-response and related broadband optical-suppressing applications, in particular for confronting laser pulses of a long duration. In pole position: Two multipolar chromophores that were derived from 2,3,8-functionalized indenoquinoxaline units manifest strong and wide dispersed two-photon absorption (2PA) in the NIR region under the irradiation of femtosecond laser pulses. Moreover, these model fluorophores could act as effective power-limiters/stabilizers against nanosecond laser pulses within the same spectroscopic regime. Copyright

Full text of DOI:10.1002/asia.201300223

FULL PAPER
FULL PAPER
In pole position: Two multipolar chro-
mophores that were derived from
2,3,8-functionalized indenoquinoxaline
units manifest strong and wide dis-
persed two-photon absorption (2PA)
in the NIR region under the irradia-
tion of femtosecond laser pulses.
Moreover, these model fluorophores
could act as effective power-limiters/
stabilizers against nanosecond laser
pulses within the same spectroscopic
regime.
Two-Photon Chromophore
Tzu-Chau Lin,* Fang-Ling Guo,
May-Hui Li, Che-Yu Liu
&&&& — &&&&
Degenerate Two-Photon Absorption
and Effective Optical-Power-Limiting
Properties of Multipolar Chromo-
phores Derived from 2,3,8-Trisubsti-
tuted Indenoquinoxaline
1
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Tzu-Chau Lin et al.
DOI: 10.1002/asia.201300223
Degenerate Two-Photon Absorption and Effective Optical-Power-Limiting
Properties of Multipolar Chromophores Derived from 2,3,8-Trisubstituted
Indenoquinoxaline
Tzu-Chau Lin,* Fang-Ling Guo, May-Hui Li, and Che-Yu Liu[a]
Abstract: Two analogous multipolar
chromophores (1 and 2) that contained
2,3,8-trisubstituted indenoquinoxaline
moieties have been synthesized and
characterized for their two-photon ab-
sorption properties, both in the femto-
second and nanosecond time regimes.
We demonstrated that their multi-
branched framework structures, which
incorporated appropriately functional-
ized indenoquinoxaline units, afforded
large molecular nonlinear absorptivi-
ties within the studied spectroscopic
range. Effective optical-power-limiting
and stabilization behaviors in the nano-
second regime of dye molecule (2)
were also investigated and the results
indicated that such a structural motif
could be a useful approach to the mo-
lecular design of highly active two-
photon systems for quick-response and
related broadband optical-suppressing
applications, in particular for confront-
ing laser pulses of a long duration.
Keywords: absorption
·
chromo-
phores · Heck reaction · indenoqui-
noxalines · nonlinear optics
Introduction
Therefore, the development of new organic compounds that
exhibit highly efficient 2PA within a specific spectroscopic
region is consequently in great demand. Based on the enor-
mous efforts that have been made in the investigation of
a wide range of molecular systems, it has been realized that
the combination of several structural parameters, such as in-
tramolecular charge-transfer efficiency and/or the effective
size of a p-conjugation domain within a molecule, are close-
ly related to the molecular 2PA.[4–11] In other words, the ar-
rangement of structural units plays a hinge role in the mo-
lecular design toward highly active 2PA chromophores.
Among the previously investigated p systems, multi-
branched structures seem to be a promising approach be-
cause they exhibit cooperative effects and lead to enhanced
molecular 2PA, whilst maintaining a broad spectroscopic
window of transparency.[5a–e,6,7c,8a–b,d,9c–d,f,10,11] Moreover,
branched skeletons also provide the opportunity for materi-
al chemists to combine disparate structural parameters into
one molecule so that the resulting compound could manifest
multi-functional character as desired for various practical
concerns.
As part of our ongoing search for useful structural param-
eters in molecular design for enhancing two-photon-absorp-
tion properties of conjugated systems, we are interested in
exploring the influence that may be caused by the electronic
properties of the incorporated heterocyclic structures and
the arrangement of the employed p units on the molecular
2PA when constructing multi-branched p structures. Herein,
we report the synthesis of a new set of two-photon-active
model chromophores (1 and 2) that were derived from
multi-functionalized indenoquinoxaline moieties, as well as
an initial investigation of their 2PA-related properties by
Degenerate two-photon absorption (2PA) processes can be
achieved within a linearly transparent—but nonlinearly ab-
sorbing—medium through the simultaneous absorption of
two photons at wavelengths far from the cutoff wavelength
of the medium’s linear absorption band. Although the
theory of such a nonlinear optical phenomenon was first
predicted by Gçppert-Mayer in 1931,[1] the lack of appropri-
ate light sources at that time held back scientists from exper-
imentally studying the details of this nonlinear process until
the advent of lasers in the 1960s.[2] Over the past two de-
cades, the availability of stable and high-peak-power lasers
has triggered further momentum in the exploration of two-
photon-related technologies. In conjunction with the intrin-
sic quadratic dependence of the incident light intensity in
the 2PA process, many potential applications in the emerg-
ing field of photonics and biophotonics have been proposed
and explored, including optical-power limiting/stabilization,
frequency up-converted lasing, 3D data storage, 3D micro-
fabrication, nondestructive bio-imaging, and two-photon-as-
sisted photodynamic therapy.[3] Nevertheless, the relatively
small two-photon-absorption cross-sections of commercially
available materials have limited their widespread utility.
[a] Prof. T.-C. Lin, F.-L. Guo, M.-H. Li, C.-Y. Liu
Photonic Materials Research Laboratory
Department of Chemistry
National Central University
300 Jhong-da Rd. 32001 Jhong-Li (Taiwan)
Fax : (+886)3-4227664
E-mail: tclin@ncu.edu.tw
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300223.
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using both femtosecond and nanosecond IR laser pulses as
probing tools.
materials that contain quinoxalinyl moieties.[13] Therefore,
the use of quinoxaline or quinoxalinoid units in the design
and synthesis of two-photon-active materials may be worthy
of further exploration. Our original molecular-design strat-
egies of these model chromophores were based on the idea
of tentatively placing an elongated version of quinoxaline,
that is, an indenoquinoxaline scaffold, between various elec-
tron-donating moieties with uneven electron-pushing
strengths, so that the polarizability of the resulting fluoro-
phores could be altered and tuned, owing to the manner of
structural arrangement, and, hence, the whole molecule may
possess larger multipolar character. Moreover, we attached
alkyl chains onto the C9 positions of all of the fluorenyl
units to enhance their molecular solubility in common or-
ganic solvents, which is another important issue to be con-
sidered in the molecular design, both in terms of experimen-
tation and application.
Results and Discussion
1. Molecular Structures and Syntheses
The chemical structures of the studied model compounds
are shown in Figure 1. Compound 1 was constructed by at-
taching two diphenylaminofluorene units onto the C2 and
C3 positions and one vinyltriphenylamine unit onto the C8
position of an indenoquinoxaline scaffold. The skeleton of
compound 2 constitutes an expanded version of compound
1 because it possesses two additional functionalized indeno-
quinoxaline arms to form a symmetrically substituted den-
dritic p framework. Although the electron-deficient qui-
noxaline ring complex has been utilized as an acceptor to
produce highly efficient bipolar luminescent materials,[12] so
far, there have only been a few reports on 2PA and/or c3
The syntheses of the target model compounds, which
mainly involve the preparation of the primary intermediates
(6 and 11) for the construction
of an indenoquinoxaline ring
complex (13), followed by one
or three Pd-catalyzed Heck
coupling reactions to furnish
the target chromophores (1 and
2), are shown in Scheme 1. For
the preparation of compound 6,
we employed a recently devel-
oped one-step Sonogashira re-
action procedure[14] to afford its
diarylacetylene precursor first
and then utilized KMnO4 as the
main oxidant for the prepara-
tion of the targeted deketone
(6). For the synthesis of dia-
mine 11, a series of functional-
group transformations starting
from compound
formed, as
3
was per-
outlined in
Scheme 1. The detailed synthe-
ses, including the preparation of
the major intermediates and
the final catalytic coupling reac-
tions toward the targeted model
fluorophores, are described in
the Experimental Section.
2. Optical Properties
2.1. One-Photon Absorption
(1PA) and Fluorescence Spectra
Measurements
Linear absorption and fluores-
cence spectra of the studied
compounds in toluene (concen-
tration: 1ꢁ10ꢀ6 m) are shown in
Figure 1. Molecular structures of the model chromophores.
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and lifetimes, as shown in
Figure 3. Similar properties
have been observed in other
multi-branched
symmetrical
chromophore systems and, in
those cases, the symmetry-
breaking phenomenon as in-
duced by electron-vibration
coupling and dipolar solvation
effects were proposed to ac-
count for this behavior.[15]
The power-squared depend-
ence of the 2PA-induced fluo-
rescence intensity on the excita-
tion intensity of these fluoro-
phores was also investigated at
a representative wavelength (lex
ꢁ800 nm). A wavelength-tuna-
ble mode-locked Ti:Sapphire
laser (Chameleon Ultra II, Co-
herent), which delivered 140 fs
pulses with a repetition rate of
80 MHz and a beam diameter
of 2 mm, was utilized as an ex-
citation light source for this ex-
periment. Figure 4b,c shows
the logarithmic plots of the ex-
perimental data and the results
(slope of linear fitꢁ2) confirm
that the 2PA process is respon-
sible for the observed up-con-
verted fluorescence emissions
in all cases. The temporal be-
havior and lifetimes of 1PA-
and 2PA-induced fluorescence
of the same sample solutions
were also probed based on the
time-correlated single-photon-
counting (TCSPC) technique by
Scheme 1. Synthesis of the key intermediates and final compounds (the
yield for each compound is given in parentheses). BINAP=2,2’-bis(diphe-
nylphosphino)-1,1’-binaphthyl, dba=dibenzylideneacetone, DMAc=dime-
thylacetamide.
Figure 2. The 1PA spectra were recorded on a Shimadzu
3501 PC spectrophotometer and the 1PA-induced fluores-
cence spectra were recorded on a Jobin–Yvon FluoroMax-4
spectrometer. All of these chromophores exhibited strong
linear absorption in the UV/Vis region with the lowest-
energy peaks located at about 450 nm. The molar absorption
coefficient (e) is about 6.9ꢁ104 cmꢀ1 mꢀ1 for compound
1 and about 2.42ꢁ105 cmꢀ1 mꢀ1 for compound 2. These dye
solutions also emit intense green/ACHTUNTRGNEUNGyellowish fluorescence
under the irradiation of a common UV lamp, in agreement
with the measured emission spectra (Figure 2, inset). Chro-
mophore 2 also exhibits strong solvent-polarity dependence
of their fluorescence properties, including band positions
Figure 2. Linear absorption and fluorescence spectra (inset) of com-
pounds 1 and 2 at a concentration of 1ꢁ10ꢀ6 m in toluene.
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Table 1. Photophysical properties of model chromophores 1 and 2 in toluene.[a]
using a highly sensitive photomultiplier that was
equipped with an accumulating real-time processor
as the detection system (PMA-182 and TimeHarp
200, PicoQuant). The same Ti:sapphire laser system
was employed for this experiment. The fluores-
cence-decay curves of solutions of the studied com-
pounds are shown in the Supporting Information,
Figure S3, over a 10 ns full scale for one- and two-
photon excitation (in the femtosecond regime).
Theoretical fitting of each decay curve to single-ex-
ponential dependence has revealed that, for each
solution of the chromophore, identical 1PA/2PA-in-
abs
max
[nm][b]
em
max
[nm][d]
[e]
[i]
l
loge[c]
l
FF
dm2 ax
[ns][f]
t2PAꢀFL
dm2 ax
[GM][h]
Nepff dm2 ax=Nepff
[ns][g]
1
2
446
449
4.84
5.38
486
491
0.70
0.78
1.3
1.1
1.3
1.1
3630
12200
50.2
85.7 142.4
72.3
[a] Concentrations of 1ꢁ10ꢀ6 m and 1ꢁ10ꢀ4 m for the 1PA- and 2PA-related measure-
ments, respectively. [b] One-photon absorption maximum. [c] Molar absorption coeffi-
cient. [d] 1PA-induced fluorescence emission maximum. [e] Fluorescence quantum ef-
ficiency. [f] 1PA-indueced fluorescence lifetime, approximate value. [g] 2PA-induced
fluorescence lifetime, approximate value. [h] Maximum 2PA cross-section (experimen-
tal error: about ꢃ15%); 1 GM=1ꢁ10ꢀ50 cm4 s/photon-molecule. [i] Effective p-elec-
tron number.[18]
duced fluorescence lifetimes were observed, which indicated
that this phenomenon was independent of the excitation
process. The experimental 1PA/2PA-induced fluorescence
lifetimes for solutions of each model compound are listed in
Table 1.
2.2. Degenerate Two-Photon-Absorption Spectroscopy
By using the aforementioned femtosecond laser system as
the probing tool, the distribution in 2PA activities of the
studied dye molecules was mapped out as a function of
wavelength within the spectral region of 680–1000 nm by
using the degenerate two-photon-excited fluorescence
(2PEF) technique; an 80 mm solution of fluorescein in
NaOH (pH 11) was used as the standard for these experi-
ments.[16,17] Figure 5 shows the experimental degenerate two-
photon-absorption spectra of these two model compounds
in toluene (concentration: 1ꢁ10ꢀ4 m) and the combined pho-
tophysical data are summarized in Table 1. Notably, all of
the studied compounds exhibit strong 2PA (d2 ꢂ500 GM)
within the spectroscopic range 700–870 nm. Moreover, both
of these model chromophores also possess a local 2PA maxi-
mum at around 800 nm, with 2PA cross-section values of
about 3630 GM for compound 1 and 12200 GM for com-
pound 2.
Figure 3. Fluorescence spectra of compound 2 in various solvents. For the
color version of the spectra, with photographs that show the distinct
color changes in compound 2 in different solvents, can be found in the
Supporting Information. t1PA-FL: fluorescence lifetime, t1PA-FL =1.11 and
2.18 ns in toluene and THF, respectively; concentration of compound 2=
1ꢁ10ꢀ6 m in all cases.
3. Discussion
There are several notable fea-
tures of the photophysical prop-
erties of the studied compounds
in this work: 1) Based on the
observed linear absorptions and
2PA behavior of these chromo-
phores and by using compound
1 as a reference material for
comparison, compound 2 exhib-
ited saliently promoted linear
absorption and 2PA, whilst re-
taining almost identical shapes
and spectroscopic positions to
those of compound 1. These re-
sults indicate that excitonic cou-
pling between branches of com-
pound 2 seems to be effectively
blocked so that only hyperchro-
Figure 4. a) Normalized two-photon-excited upconversion spectra of fluorophores 1 and 2 at a concentration
of 1ꢁ10ꢀ4 m in toluene. b,c) Logarithmic plots of the power-squared dependence of the 2PA-induced fluores-
cence intensity on the input intensity of these compounds in toluene.
mic enhancement on both one-
photon and two-photon absorp-
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nates from the same singlet state of each model chromo-
phore and is independent of the excitation process.[19]
4. Effective Optical-Power-Limiting Performance in the
Nanosecond Regime
An ideal optical limiter is expected to show an intensity-de-
pendent transmission feature so that it can act as a transpar-
ent medium when the incident intensity of light stays low
and, once the input intensity increases, the medium starts to
regulate the transmitted output intensity to be always below
a certain maximum value before any optical saturation or
damage occurs. This feature makes optical limiters not only
useful for the protection of human eyes and sensors against
hazardous light sources but it is also important for the com-
pression of the optical dynamic range and noise suppression
in signal processing, as well as the nonlinear ultrafast filter-
ing/reshaping of signals from optical fibers.
Figure 5. Experimental degenerate two-photon-absorption spectra of the
studied model chromophores by using the 2PEF method at a concentra-
tion of 1ꢁ10ꢀ4 m in toluene (experimental error: about ꢃ15%).
tivites can be observed. This feature could be useful for mo-
lecular design when large 2PA values within a specific spec-
troscopic range are required for various applications. In ad-
dition, the observed solvatofluorochromic behavior from
chromophore 2 (Figure 3) suggests that the relaxed excited
state of this model compound is highly dipolar and is sensi-
tive to the polarity of environment. 2) Chromophore 2 ex-
hibited a maximum 2PA cross-section that was slightly more
Recently, it has been pointed out that the intensity-depen-
dent 2PA-induced excited-state absorption (2PA-induced
ESA) plays an essential role in the observed large 2PA in
various organic systems under the irradiation of nanosecond
laser pulses.[20] From an application standpoint, any medium
that possesses a large apparent nonlinear absorption cover-
ing a wide spectroscopic range could be very useful for opti-
cal-power attenuators against long laser pulses.[21]
than three times that of compound
1
(i.e.,
We have utilized nanosecond laser pulses to demonstrate
the effective power-limiting performance of these model
compounds. In our experiment, the nonlinear absorbing
medium was a 1 cm path-length solution of the studied dye
in toluene at a concentration of 0.01m. A tunable nanosec-
ond laser system (integrated Q-switched Nd:YAG laser and
OPO:NT 342/3, Ekspla) was employed as an excitation laser
light source to provide laser pulses (about 6 ns) with con-
trolled average pulse energy within the range 0.02–2 mJ and
a repetition rate of 10 Hz. The laser beam was slightly fo-
cused onto the center of the sample solution to create an
almost-uniform laser-beam radius within the whole light
path length and the transmitted laser beam from the sample
solution was detected by using an optical power (energy)
meter with a large detection area (diameterꢁ25 mm).
Figure 6 shows the power-attenuation performance at
800 nm, based on these chromophore solutions. Compound
2 shows superior power-restriction properties at 800 nm
compared to compound 1, which suggests the potential of
using this model fluorophore as a candidate for broadband
power-control-related applications within the nanosecond
regime.
In addition, the output/input curve, as shown in Figure 6,
shows a characteristic type of optical compression, which is
ideal for use in optical-power (or optical-intensity) stabiliza-
tion because a huge magnitude change in the input signal
would only lead to a small variation in the output level,[22]
which means that a larger fluctuation in input power (or in-
tensity) would practically lead to a much-smaller fluctuation
in the output by passing through a nonlinear absorptive
medium, such as the solution of model chromophore 2. The
dm2 axð2Þ=dm2 axð1Þ ꢁ 3:36), which indicated that enlarging the
size of the molecule, which was accomplished by attaching
two more identical 2,3,8-trisubstituted indenoquinoxaline
branches onto the central triphenylamine core, only provid-
ed linearly promoted molecular 2PA. That is, we can assume
that the large overall 2PA for compound 2 is inherited from
compound 1 and, perhaps, the structure–property analysis
should be focused on the parameters that lead to the strong
2PA of compound 1. From the viewpoint of the molecular
structure of chromophore 1, the arrangement of the p units
in this compound may permit unsymmetrical charge trans-
fer/redistribution between the molecular termini and the
central heterocyclic ring complex under the excitation of
light because this p system utilizes an electron-deficient
fused pyrazine ring to combine various peripheral electron-
donating moieties with uneven electron-pushing strengths
within one molecule. Although at this stage, there is no
clear understanding of how this type of structural arrange-
ment is related to the molecular two-photon activities, our
preliminary results show that such structural combination
may help to promote the molecular 2PA. Moreover, the
maximum two-photon-absorption cross-sections of these two
model compounds are comparable to those of reported 2PA
chromophores that have similar effective p-electron num-
bers.[18] 3) Because the observed fluorescence emission spec-
tra (Figure 2 and Figure 4) and fluorescence lifetimes
(Table 1 and the Supporting Information, Figure S3) are
almost identical for one- and two-photon excitations for
each individual model compound, we may conclude that, in
these cases, the fluorescence emission predominantly origi-
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these processes relate to the molecular structures, in particu-
lar the effect of ESA in optimizing the materials on the mo-
lecular level for optical-control-related applications. Several
attempts have been made to map out the dispersion of 2PA-
assisted ESA by using pump-probe experiments[20a,23] and
such experiments are one of the major subjects of our future
work.
Conclusions
We have characterized the degenerate two-photon-absorp-
tion-related properties of a new set of model chromophores
with multi-branched molecular structures that were based
on tri-substituted indenoquinoxaline skeletons, both in the
femtosecond and nanosecond regimes, by using two-photon-
excited fluorescence and nonlinear transmission techniques
as the probing tools. We demonstrated that a chromophore
that was derived from a multi-substituted quinoxalinoid ring
complex with electron-donating units, which manifested
uneven electron-pushing strengths, possessed strong molecu-
lar 2PA within a specific spectroscopic region. Moreover, in-
creasing the branch number provided an efficient way of
promoting molecular 2PA without shifting the major 2PA
band. We also observed that model compound 2 exhibited
both intense upconverted emission when excited by a two-
photon process and effective optical-power limiting/stabliza-
tion against nanosecond laser pulses. These features make
this chromophore a potential candidate as an efficient fre-
quency upconverter and/or optical-power attenuator for var-
ious photonic applications.
Figure 6. Experimental optical-power-attenuation curve based on the
sample solution of compound 2 under the excitation of nanosecond laser
pulses at 800 nm.
Experimental Section
General
All commercially available reagents for the preparation of the intermedi-
ates and target chromophores were purchased from Aldrich Chemical
Co. or Alfa Aesar and were used as received, unless otherwise stated.
1H NMR and 13C NMR spectra were recorded on a 300 MHz spectrome-
ter and referenced to tetramethylsilane (TMS) or to residual CHCl3. The
representative atom-numbering of the carbon and hydrogen atoms on
each intermediate and model chromophore for the NMR assignment is
shown in the Supporting Information, Figure S1. High-resolution mass
spectroscopy (HRMS) was performed on a Waters LCT ESI-TOF mass
spectrometer. MALDI-TOF mass spectra were recorded on a Voyager
DE-PRO mass spectrometer (Applied Biosystem, Houston, USA).
Figure 7. a) Experimental instantaneous pulse-energy fluctuation of the
input laser pulses and b) experimental instantaneous pulse-energy fluctu-
ation of the output laser pulses. The repetition rate of the laser pulses
was 10 Hz and the average input pulse-energy level was about 0.8 mJ.
experimental results from an optical-stabilization study
based on the same sample solutions are shown in Figure 7.
The curves in Figure 7a,b show the instantaneous pulse-
energy changes in the input and output laser pulses at
800 nm. For the purpose of comparison, the average levels
of both the input and output signals were normalized to the
same value. Clearly, the input pulses possess a relatively
larger energy fluctuation (Figure 7a) and, after passing
through the solution of compound 2, a smaller fluctuation in
pulse energy is observed for the output signal (Figure 7b).
Notably, the individual contributions of 2PA and ESA to
the observed optical attenuation of the studied chromo-
phore system are indistinguishable under our current experi-
mental conditions. Nevertheless, it is very important for ma-
terial chemists in this research field to gain insight into how
Photophysical Methods
The linear optical properties of the model compound were measured on
their corresponding spectrometers and the detailed experimental condi-
tions, as well as the optical setups, for the investigation of nonlinear opti-
cal properties are described in the Supporting Information.
Synthesis
Compound 3 and 4 (Scheme 1) are the major starting materials for the
synthesis of the backbones in each intermediate and model chromophore.
These two compounds were obtained by following literature procedure-
s,[9a] from 2,7-dibromofluorene as the starting material through alkylation
at C9 position of the fluorene unit (to afford compound 3), followed by
Buchwald-type amination to afford compound 4 in about 80% and 50%
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yield, respectively. For the syntheses of other key intermediates (com-
pounds 6–12) and the target model compounds (1 and 2), a series of func-
tionalization steps from compounds 3 and 4 were performed, as present-
ed below.
ring of the phthalimide unit), 131.78 (CN), 130.82 (CB), 130.09 (CJ),
126.23 (CI), 125.13 (CD), 123.63 (benzene ring of the phthalimide unit),
121.27 (CK), 121.21 (CH), 120.07 (CC, CE), 55.62 (Cg’), 40.06 (Cf’), 31.40
(Ce’), 29.60 (Cd’), 23.73 (Cc’), 22.52 (Cb’), 13.94 ppm (Ca’).
Step 2: To
a solution of the product from the first step (4.63 g,
7-(2-(7-(Diphenylamino)-9,9-dihexyl-9H-fluoren-2yl)ethynyl-9,9-dihexyl-
8.31 mmol) in MeOH (65.3 mL) was slowly added hydrazine monohy-
drate (0.41 g, 8.31 mmol) and the mixture was stirred at 808C for 6 h.
After cooling to RT, the reaction solution was extracted with EtOAc (3ꢁ
50 mL) and the organic layer was collected and dried over MgSO4. After
filtration and removal of the solvent, the crude product was purified by
column chromatography on silica gel (EtOAc/hexanes, 1:25) to give the
final product as a brown oil (3.24 g, 91% yield). 1H NMR (300 MHz,
CDCl3): d=7.39–7.32 (m, 4H; HB HD, HE, HH), 6.55–6.51 (m, 2H; HI,
HK), 3.62 (s, 1H; NH), 1.87–1.84 (m, 4H; Hf’), 1.12–1.01 (m, 12H; Hc’, Hd’,
He’), 0.75–0.61 ppm (m, 10H; Ha’, Hb’); 13C NMR (75 MHz, CDCl3): d=
151.88 (CA), 151.81 (CL), 140.43 (CF), 130.69 (CG), 129.42 (CB), 125.51
(CD), 120.38 (CE), 119.35 (CH), 119.72 (CC), 113.73 (CK), 109.12 (CI),
54.80 (Cg’), 40.29 (Cf’), 31.24 (Ce’), 29.47 (Cd’), 23.42 (Cc’), 22.37 (Cb’),
13.80 ppm (Ca’); HRMS (FAB): m/z calcd for C25H34BrN: 428.4482
[M+H]+; found: 428.4361.
N,N-diphenyl-9H-fluoren-2-amine (5)
To a three-necked round-bottomed flask (250 mL) were added compound
4 (5.13 g, 8.84 mmol), acetylenedicarboxylic acid (0.50 g, 4.42 mmol), [Pd-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
2.26 mL), and DMSO (20.5 mL) and the reaction mixture was stirred at
1108C under a N2 atmosphere for 8 h. After cooling to RT, MeOH
(10 mL) and cold hexanes (10 mL) were added to the reaction mixture,
which was stirred at 08C for 20 min. After filtration, the crude product
was washed with MeOH and the final product was obtained as yellow
powder (3.31 g, 73% yield). 1H NMR (300 MHz, CDCl3): d=7.60–7.45
(m, 8H; H9, H12, H13, H15), 7.28–7.19 (m, 10H; H3, H8), 7.13–7.07 (m,
10H; H2, H6), 7.03–6.97 (m, 4H; H1), 1.95–1.83 (m, 8H; Hf), 1.16–1.06
(m, 24H; Hc, Hd, He), 0.82–0.77 (m, 12H; Ha), 0.66 ppm (m, 8H; Hb);
13C NMR (75 MHz, CDCl3): d=152.47 (C5), 150.67 (C16), 147.92 (C4),
147.54 (C7), 141.12 (C11), 135.56 (C10), 130.63 (C15), 129.17 (C2), 125.73
(C13), 123.91 (C3), 123.45 (C9), 122.61 (C1), 120.77 (C12), 120.65 (C6),
119.09 (C8), 119.02 (C14), 90.51 (sp C atoms), 55.10 (Cg), 40.29 (Cf), 31.55
(Ce), 29.64 (Cd), 23.76 (Cc), 22.56 (Cb), 14.01 ppm (Ca); HRMS (FAB): m/
z calcd for C76H84N2: 1024.6635 [M]+; found: 1024.6639.
N-(7-Bromo-9,9-dihexyl-9H-fluoren-2-yl)acetamide (8)
A mixture of compound 7 (3.24 g, 7.58 mmol), triethylamine (1.26 mL,
9.10 mol), and acetic anhydride (0.82 g, 9.10 mol) in CH2Cl2 (32.4 mL)
was stirred at 308C for 4 h. After cooling to RT, the solution was extract-
ed with EtOAc (3ꢁ50 mL) and the organic layer was dried over MgSO4.
After filtration and removal of the solvent, the compound was obtained
as a white solid (3.39 g, 95% yield). 1H NMR (300 MHz, CDCl3): d=
7.63–7.53 (m, 2H; NH, HE), 7.50–7.42 (m, 4H; HB, HD, HH, HK), 7.38–7.32
(m, 1H; HI), 2.21 (s, 3H; CH3 atoms of the acetyl group), 1.94–1.88 (m,
4H; Hf’), 1.14–1.03 (m, 12H; Hc’, Hd’, He’), 0.79–0.74 (m, 6H; Ha’), 0.61–
0.59 ppm (m, 4H; Hb’); 13C NMR (75 MHz, CDCl3): d=168.27 (C=O of
the acetyl group), 152.82 (CL), 151.46 (CA), 139.68 (CG), 137.63 (CF),
136.19 (CJ), 135.75 (CH), 129.86 (CB), 126.00 (CD), 120.56 (CE), 120.06
(CC), 118.52 (CK), 114.26 (CI), 55.48 (Cg’), 40.25 (Cf’), 31.43 (Ce’), 29.58
(Cd’), 24.66 (CH3 atom of the acetyl group), 23.64 (Cc’), 22.51 (Cb’),
13.92 ppm (Ca’); HRMS (FAB): m/z calcd for C27H36BrNO: 469.1980
[M]+; found: 469.1980.
1,2-bis(7-Diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl)ethane-1,2- dione
(6)
To a solution of compound 5 (3.31 g, 3.23 mmol) in CH2Cl2 (10.9 mL)
were added KMnO4 (2.04 g, 0.01 mol), NaHCO3 (0.27 g, 3.23 mmol), Ali-
quat 336 (0.13 g), and water (10.9 mL) and the resulting solution was
stirred at RT for 12 h. After the reaction was complete, a saturated aque-
ous solution of NaHCO3 (30 mL) and a 1m aqueous solution of HCl
(30 mL) was added to the mixture. The mixed solution was extracted
with CH2Cl2 (3ꢁ50 mL) and the organic layer was collected and dried
over MgSO4. After filtration and removal of the solvent, the crude prod-
uct was purified by column chromatography on silica gel (CH2Cl2/hex-
anes, 1:3) to give the final product as a red powder (2.43 g, 71% yield).
1H NMR (300 MHz, CDCl3): d=8.03 (s, 2H; H15), 7.88–7.84 (d, J=9 Hz,
2H; H13), 7.65–7.62 (d, J=9 Hz, 2H; H12), 7.60–7.58 (d, J=6 Hz; H9),
7.29–7.24 (m, 8H; H3), 7.14–7.10 (m, 10H; H2, H6), 7.07–7.01 (m, 6H; H1,
H8), 2.04–1.78 (m, 8H; Hf), 1.15–1.05 (m, 24H; Hc, Hd, He),0.82–0.77 (m,
12H; Ha), 0.64 ppm (m, 8H; Hb); 13C NMR (75 MHz, CDCl3): d=195.13
(C=O), 153.86 (C5), 151.29 (C16), 149.05 (C11), 147.77 (C7), 147.59 (C4),
133.82 (C14), 130.98 (C10), 130.84 (C15), 129.28 (C2), 124.44 (C3), 123.17
(C1), 122.74 (C12), 121.81 (C9, C13), 118.85 (C6), 118.09 (C8), 55.29 (Cg),
39.91 (Cf), 31.44 (Ce), 29.48 (Cd), 23.75 (Cc), 22.49 (Cb), 13.98 ppm (Ca);
HRMS (FAB): m/z calcd for C76H84N2O2: 1056.6533 [M]+; found:
1056.6627.
N-(7-Bromo-9,9-dihexyl-3-nitro-9H-fluoren-2-yl)acetamide (9)
A solution of compound 8 (3.39 g, 7.22 mmol) in acetic acid (50.8 mL)
and acetone (16.9 mL) was stirred for 5–10 min and then fuming HNO3
(2.43 mL; 0.06 mol) was added dropwise at 0–58C. After the reaction had
finished (by TLC), the reaction mixture was extracted with EtOAc (3ꢁ
50 mL) and the organic layer was dried over MgSO4. After filtration and
removal of the solvent, the crude product was purified by column chro-
matography on silica gel (EtOAc/hexanes, 1:10) to give the final product
1
as a yellow powder (2.98 g, 80% yield). H NMR (300 MHz, CDCl3): d=
10.59 (s, 1H; NH), 8.81 (s, 1H; HH), 8.47 (s, 1H; HK), 7.71–7.44 (m, 3H;
HB, HD, HE), 2.32 (s, 1H; CH3 atoms of the acetyl group), 2.02–1.97 (m,
4H; Hf’), 1.12–1.05 (m, 12H; Hc’, Hd’, He’), 0.78–0.73 (m, 6H; Ha’), 0.61–
0.59 ppm (m, 4H; Hb’); 13C NMR (75 MHz, CDCl3): d=168.92 (C=O of
the acetyl group), 159.27 (CL), 152.68 (CA), 137.45 (CF), 136.48 (CI),
135.71 (CG), 134.61 (CJ), 130.51 (CB), 126.32 (CD), 122.30 (CE), 121.29
(CC), 116.51 (CH), 116.10 (CK), 56.44 (Cg’), 40.05 (Cf’), 31.29 (Ce’), 29.37
(Cd’), 25.68 (CH3 of the acetyl group), 23.67 (Cc’), 22.40 (Cb’), 13.83 ppm
(Ca’); HRMS (FAB): m/z calcd for C27H35BrN2O3: 514.1831 [M]+; found:
514.1837.
7-Bromo-9,9-dihexyl-9H-fluoren-2-amine (7)
Step 1: To a three-necked round-bottom flask (250 mL) were added com-
pound 3 (7.42 g, 0.01 mol), potassium phthalimide (2.77 g, 0.01 mol), CuI
(2.87 g, 0.01 mol), and DMAc (148 mL) and the reaction solution was
stirred at 1658C for 48 h. After cooling to RT, the reaction mixture was
quenched with aqueous ammonia to scavenge the excess CuI. Then, the
solution was extracted with EtOAc (3ꢁ100 mL) and the organic layer
was collected and dried over MgSO4. After filtration and removal of the
solvent, the crude product was purified by column chromatography on
silica gel (EtOAc/hexanes, 1:10) to give the final product as a brown oil
(4.63 g, 55% yield). 1H NMR (300 MHz, CDCl3): d=8.00–7.97 (dd, 1J=
5.4 Hz, 2J=3.3 Hz, 2H; ArH of the phthalimide unit), 7.83–7.78 (m, 3H;
HI and ArH of the phthalimide unit), 7.62–7.59 (m, 1H; HE), 7.51–7.50
(m, 2H; HH, HK), 7.48–7.47 (m, 1H; HD), 7.44 (s, 1H; HB), 1.99–1.94 (m,
4H; Hf’), 1.30–1.09 (m, 12H; Hc’, Hd’, He’), 0.82–0.68 ppm (m, 10H; Ha’,
Hb’); 13C NMR (75 MHz, CDCl3): d=167.28 (C=O of the phthalimide
unit), 153.39 (CA), 151.05 (CL), 139.57 (CG), 139.23 (CF), 134.36 (benzene
7-Bromo-9,9-dihexyl-3-nitro-9H-fluoren-2-amine (10)
To a solution of compound 9 (2.98 g, 5.78 mmol) in MeOH (47.2 mL)
was slowly added H2SO4 (8.10 mL) and the solution was stirred at reflux
for 10 h. After cooling to RT, the solution was extracted with EtOAc (3ꢁ
30 mL) and the organic layer was dried over MgSO4. After filtration and
removal of the solvent, the crude product was purified by column chro-
matography on silica gel (EtOAc/hexanes, 1:10) to give the final product
as a red solid (2.73 g, 93% yield). 1H NMR (300 MHz, CDCl3): d=8.37
(s, 1H; HH), 7.64~7.36 (m, 3H; HC, HD, HE), 6.72 (s, 1H; HK), 6.26 (s,
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Tzu-Chau Lin et al.
2H; NH2), 1.96–1.79 (m, 4H; Hf’), 1.16–1.04 (m, 12H; Hc’, Hd’, He’), 0.79–
0.75(m, 6H; Ha’), 0.63–0.58 ppm (m, 4H; Hb’); 13C NMR (75 MHz,
CDCl3): d=159.52 (CL), 151.43 (CA), 144.97 (CJ), 138.31 (CF), 136.31
(CG), 130.44 (CI), 126.04 (CE, CD), 121.01 (CH), 120.72 (CC), 116.77 (CB),
112.33 (CK), 55.62 (Cg’), 40.76 (Cf’), 31.39 (Ce’), 29.52 (Cd’), 23.72 (Cc’),
22.49 (Cb’), 13.90 ppm (Ca’); HRMS (FAB): m/z calcd for C25H33BrN2O2:
472.1725 [M]+; found: 472.1722.
(75 MHz, CDCl3): d=153.81 (C5), 153.27 (C17), 152.60 (C18), 151.93 (C16),
150.56 (CA, CB), 147.93 (C4, CG’), 147.49 (C11), 147.37 (CF’), 143.79 (CG),
141.40 (CI, CJ), 141.23 (C7), 139.04 (CC), 138.53 (C8), 137.68 (CK), 137.61
(CH), 135.62 (C10), 131.40 (CD’), 129.27 (CI’), 129.12 (C2), 128.44 (CC’),
127.40 (CB’), 127.30 (CA’), 125.83 (C15), 124.55 (C14), 124.40 (CE’), 123.83
(C3, CH’), 123.45 (C13), 123.08 (CE), 122.50 (C1, CJ’), 122.18 (CB), 121.31
(CD), 120.79 (C6), 119.16 (C9), 118.92 (C8), 117.89 (C12), 55.05 (Cg’), 41.44
(Cf’), 40.11 (Cf), 31.54 (Ce, Ce’), 29.73 (Cd’), 29.59 (Cd), 23.85 (Cc, Cc’),
22.60 (Cb’, Cb), 14.06 (Ca’), 13.94 ppm (Ca); HRMS (FAB): m/z calcd for
7-Bromo-9,9-dihexyl-9H-fluoren-2,3-diamine (11)
C
121H131N5: 1564.0404 [M]+; found: 1654.0413.
To a mixture of compound 10 (2.00 g; 4.23 mmol) and stannous chloride
(9.55 g, 0.04 mol) was added EtOAc (41.5 mL) and the reaction solution
was stirred at 808C for 4 h. After the reaction had finished, the mixture
was quenched with an aqueous solution of NaHCO3. This solution was
extracted with EtOAc (3ꢁ50 mL) and the organic layer was dried over
MgSO4. After removal of the solvent, the crude product was purified by
column chromatography on silica gel (EtOAc/hexanes, 1:3) to give the
Compound 2
A solution of compound 12 (1.0 g, 0.68 mmol), tris(4-vinylphenyl)amine
(0.067 g, 0.21 mmol), PdACTHNUTRGENNUG(OAc)2 (2.78 mg, 0.012 mmol), and triACHTUNGTRENNUNG(o-totyl)-
phosphine (0.023 g, 0.074 mmol) in MeCN (8 mL) and NEt3 (4 mL) was
prepared in a heavy-walled tube (ACE Glass). The reaction mixture was
stirred at 1108C under a N2 atmosphere for 72 h. After cooling to RT, the
solution was extracted with CH2Cl2 (3ꢁ50 mL) and the organic layer was
dried over MgSO4. After filtration and removal of the solvent, the crude
product was purified by column chromatography on silica gel (THF/hex-
anes, 1:15) to give the final product as a yellow solid (1.00 g, 80% yield).
1H NMR (300 MHz, CDCl3): d=8.41 (s, 3H; HH), 8.09 (s, 3H; HK), 7.92–
final product as
a
yellow powder (1.33 g, 71% yield). 1H NMR
(300 MHz, CDCl3): d=7.37–7.36 (d, J=1.5 Hz, 1H; HB), 7.35–7.32 (dd,
1J=7.8 Hz, 1J=1.5 Hz, 1H; HD), 7.27–7.25 (d, J=7.8 Hz, 1H; HE), 6.92
(s, 1H; HK), 6.60 (s, 1H; HH), 3.44 (s, 4H; NH2), 1.85–1.80 (m, 4H; Hf’),
1.03–1.01 (m, 12H; Hc’, Hd’, He’), 0.77–0.72 (t, J=7.2 Hz, 6H; Ha’), 0.64–
0.62 ppm (m, 4H; Hb’); 13C NMR (75 MHz, CDCl3): d=152.59 (CA),
142.93 (CL), 140.62 (CF), 135.19 (CJ), 133.41 (CI), 132.02 (CE), 129.37
(CD), 125.50 (CB), 119.39 (CG), 118.82 (CC), 110.62 (CH), 108.08 (CK),
54.52 (Cg’), 40.32 (Cf’), 31.34 (Ce’), 29.55 (Cd’), 23.52 (Cc’), 22.44 (Cb’),
13.85 ppm (Ca’).
7.89 (d, J=7.8 Hz, 3H; HD), 7.59–7.52 (m, 36H; H9, H12, H13, H15, HA’
,
HB’, HB, HE), 7.27–7.18 (m, 36H; H2, HD’, HE’), 7.13–7.08 (m, 30H; H3,
H6), 7.03–6.99 (m, 8H; H1, H8), 2.15 (m, 4H; Hf’), 1.74 (m, 8H; Hf), 1.11–
1.05 (m, 36H; Hc, Hd, He, Hc’, Hd’, He’), 0.81–0.74 ppm (m, 30H; Ha, Hb,
Ha’, Hb’); 13C NMR (75 MHz, CDCl3): d=153.82 (C5), 153.33 (C17), 152.71
(C18), 152.63 (C16), 152.00 (C18’), 150.59 (C7’), 150.54 (C12’), 147.95 (C4),
147.40 (C11), 146.78 (CF’), 143.78 (CG), 141.45 (CI, CJ), 141.28 (C7), 139.22
(CC), 138.42 (C8), 137.67 (CH), 137.61 (CK), 135.64 (C10), 132.31 (CD’),
129.14 (C2), 128.31 (CC’), 127.59 (CA’, CB’), 125.94 (C15), 124.41 (C14, CE’),
123.85 (CD’), 123.43 (C13), 122.53 (C1), 122.24 (CB), 121.39 (CD), 120.83
(C6), 119.18 (C9), 118.95 (C8), 117.97 (C12), 55.08 (Cg’), 41.47 (Cf’), 40.03
(Cf), 31.56 (Ce, Ce’), 29.77 (Cd’), 29.61 (Cd), 23.87 (Cc, Cc’), 22.62 (Cb’, Cb),
14.08 (Ca’), 13.97 ppm (Ca); HRMS (MALDI-TOF): m/z calcd for
C327H363N13 (theoretical average): 4476.5986 [M+1H]+; found: 4476.6123.
7,7’-(8-Bromo-10,10-dihexyl-10H-indenoACTHNUTRGENUG[N 1,2g]quinoxaline-2,3-
diyl)bis(9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine) (12)
To a mixture of compound 11 (1.22 g; 2.76 mmol) and compound 6
(2.43 g, 2.30 mmol) was added acetic acid (30.5 mL) and THF (4.05 mL)
and the reaction solution was stirred at 1108C under a N2 atmosphere for
12 h. After cooling to RT, the solution was extracted with EtOAc (3ꢁ
150 mL) and the organic layer was dried over MgSO4. After filtration
and removal of the solvent, the crude product was purified by column
chromatography on silica gel (CH2Cl2/hexanes, 1:5) to give the final prod-
uct as a yellow solid (3.00 g, 89% yield). 1H NMR (300 MHz, CDCl3):
d=8.45 (s, 1H; HH), 8.11 (s, 1H; HK), 7.82–7.80 (d, 1H, J=8.1 Hz; HD),
7.58–7.55 (m, 10H; H9, H12, H13, H15, HB, HE), 7.30–7.25 (m, 8H; H2),
7.16–7.12 (m, 10H; H3, H6), 7.04 (m, 6H, H1, H8), 2.20–2.12 (m, 4H; Hf’),
1.78–1.68 (m, 8H; Hf), 1.29–0.89 (m, 36H; Hc, Hd, He, Hc’, Hd’, He’), 0.84–
0.69 ppm (m,30H; Ha, Hb, Ha’, Hb’); 13C NMR (75 MHz, CDCl3): d=
153.49 (C16), 153.07 (C17), 152.84 (C18), 152.58 (C5), 150.58 (CA), 150.50
(CG), 147.90 (C4), 147.40 (C7), 142.79 (CF), 141.28 (CJ), 141.18 (CI),
138.69 (C11), 137.47 (CK), 137.41 (CH), 135.52 (C10), 130.59 (C14), 129.11
(C2, C15), 126.70 (C12), 124.35 (C13), 123.83 (C3), 123.37 (C9), 122.51 (C1),
122.37 (CB), 120.81 (CD), 119.09 (C6), 118.93 (C8), 118.44 (CC), 55.47 (Cg’),
55.04 (Cg), 41.27 (Cf’), 40.09 (Cf), 31.52 (Ce, Ce’), 29.63 (Cd’), 29.57 (Cd),
23.83 (Cc, Cc’), 22.59 (Cb’), 22.53 (Cb), 14.05 (Ca’), 13.92 ppm (Ca); HRMS
(MALDI-TOF): m/z calcd for C101H115BrN4 (theoretical average):
1463.8305 [M+H]+; found: 1463.8384.
Acknowledgements
We acknowledge financial support from the National Science Council
(NSC), Taiwan, (101-2113M-008-003-MY2). F.L.G. also acknowledges the
great help from Ms. Ying-Hsuan Lee with the synthesis work.
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Compound 1
A solution of compound 12 (1.0 g, 0.68 mmol), (4-vinylphenyl)amine
(0.20 g, 0.75 mmol), PdACHTUNGTRENNUNG(OAc)2 (3.06 mg, 0.013 mmol), and triAHCTUNGTRENN(GUN o-totyl)-
phosphine (0.025 g, 0.082 mmol) in MeCN (8 mL) and NEt3 (4 mL) was
prepared in a heavy-walled tube (ACE Glass). The reaction mixture was
sealed and stirred at 1108C under a N2 atmosphere for 72 h. After cool-
ing to RT, the resulting solution was extracted with CH2Cl2 (3ꢁ50 mL)
and the organic layer was dried over MgSO4. After filtration and removal
of the solvent, the crude product was purified by column chromatography
on silica gel (EtOAc/hexanes, 1:40) to give the final product as a yellow
powder in (0.77 g, 83% yield). 1H NMR (300 MHz, CDCl3): d=8.41 (s,
1H; HH), 8.08 (s, 1H; HK), 7.90–7.87 (d, J=7.8 Hz, 1H; HD), 7.59–7.43
(m, 11H; H9, H12, H13, H15, HB, HE, HD), 7.26–7.21 (m, 13H; H2, HA’, HI’),
7.13–7.06 (m, 18H; H3, H6, HD’, HE’, HH’), 7.02–7.00 (m, 8H; H1, H8,
HJ’), 2.11 (m, 4H; Hf’), 1.75–1.66 (m, 8H; Hf), 1.11–1.05 (m, 36H; Hc,
Hd, He, Hc’, Hd’, He’), 0.81–0.69 ppm (m, 30H; Ha, Hb, Ha’, Hb’); 13C NMR
[5] For selected examples, see: a) O. Mongin, J. Brunel, L. Porrꢃs, M.
Blanchard-Desce, Tetrahedron Lett. 2003, 44, 2813–2816; b) O.
Mongin, L. Porres, C. Katan, T. Pons, J. Mertz, M. Blanchard-Desce,
9
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Tzu-Chau Lin et al.
Tetrahedron Lett. 2003, 44, 8121–8125; c) L. Porrꢃs, C. Katan, O.
Mongin, T. Pons, J. Mertz, M. Blanchard-Desce, J. Mol. Struct. 2004,
704, 17–24; d) L. Porrꢃs, O. Mongin, C. Katan, M. Charlot, T. Pons,
J. Mertz, M. Blanchard-Desce, Org. Lett. 2004, 6, 47–50; e) C.
Katan, F. Terenziani, O. Mongin, M. H. V. Werts, L. Porrꢃs, T. Pons,
J. Mertz, S. Tretiak, M. Blanchard-Desce, J. Phys. Chem. A 2005,
109, 3024–3037; f) F. Terenziani, C. L. Droumaguet, C. Katan, O.
Mongin, M. Blanchard-Desce, ChemPhysChem 2007, 8, 723–734;
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Received: February 20, 2013
Revised: March 27, 2013
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