Synthesis and characterization of two-photon chromophores based on a tetrasubstituted tetraethynylethylene scaffold

Article abstract of DOI:10.1002/asia.201402094

A new series of model dye molecules composed of three multibranched analogues based on the tetrasubstituted tetraethynylethylene structural motif have been synthesized and experimentally shown to possess strong and widely dispersed two-photon absorption (2PA) in the near-IR region. It was found that the spectral position of the major 2PA band could be tuned by the electronic nature of the selected substitution units. The studied model fluorophores also exhibited fairly low photodegradation of their fluorescence intensity even under prolonged UV-light irradiation, which is beneficial for the development of fluorescence probes that are needed for long-term light exposure. Furthermore, representative chromophores were selected to demonstrate the power-control properties within the femtosecond and nanosecond time domains. Two is better than one: Multibranched chromophores based on the tetrasubstituted ethynylethylene skeleton with functionalized quinoxalinoids as aryl substituents are synthesized and shown to possess strong and widely dispersed two-photon absorption in the near-IR region. This molecular archetype is also demonstrated to possess optical power-limiting properties and optical power-stabilization properties toward laser pulses in various time domains.

Full text of DOI:10.1002/asia.201402094

FULL PAPER
DOI: 10.1002/asia.201402094
Synthesis and Characterization of Two-Photon Chromophores Based on a
Tetrasubstituted Tetraethynylethylene Scaffold
Tzu-Chau Lin,*[a] Yi-You Liu,[a] May-Hui Li,[a] Che-Yu Liu,[a] Sheng-Yang Tseng,[b]
Yu-Ting Wang,[b] Ya-Hsin Tseng,[b] Hui-Hsin Chu,[b] and Chih-Wei Luo[b]
Abstract: A new series of model dye
molecules composed of three multi-
branched analogues based on the tetra-
substituted tetraethynylethylene struc-
tural motif have been synthesized and
experimentally shown to possess strong
and widely dispersed two-photon ab-
sorption (2PA) in the near-IR region.
It was found that the spectral position
of the major 2PA band could be tuned
by the electronic nature of the selected
substitution units. The studied model
fluorophores also exhibited fairly low
photodegradation of their fluorescence
intensity even under prolonged UV-
light irradiation, which is beneficial for
the development of fluorescence
probes that are needed for long-term
light exposure. Furthermore, represen-
tative chromophores were selected to
demonstrate the power-control proper-
ties within the femtosecond and nano-
second time domains.
Keywords: absorption
·
chromo-
phores · heterocycles · nonlinear
optics · Sonogashira reaction
Introduction
a molecule are closely related to molecular 2PA.[2–10] This
also means that the arrangement of the selected building
units within a molecule plays a pivotal role in molecular
design towards highly active 2PA chromophores. Following
our continuous efforts in the search of effective structural
parameters for the enhancement of molecular 2PA in multi-
branched dye systems possessing heterocyclic ring com-
plexes, in this paper we present the synthesis of new multi-
polar two-photon-active model chromophores based on the
tetrasubstituted tetraethynylethylene (TEE) skeleton by
using functionalized quinoxaline, indenoquinoxaline, and
pyridopyrazine moieties as the substituents. We also report
initial investigations into their nonlinear optical properties
in both the femtosecond and nanosecond time domains.
The intrinsic quadratic dependence of two-photon absorp-
tion (2PA) on incident light intensity is one of the major
characters that makes this third-order nonlinear optical phe-
nomenon applicable in many photonics and biophotonics
applications such as optical power limiting, frequency up-
converted lasing, 3D optical data storage, 3D microfabrica-
tion, nondestructive bioimaging, and two-photon photody-
namic therapy.[1] For the development of two-photon tech-
nologies, the exploration of new materials with strong 2PA
plays an equally important role as the advancement of high
peak-power pulsed lasers. Through rational molecular
design, it is possible to synthesize organic chromophores
that exhibit several orders of intensified 2PA with other de-
sired molecular characteristics simultaneously integrated,
which helpfully compensates the relatively poor perfor-
mance of commercialized dyes for the aforementioned ap-
plications based on 2PA. So far, it has been realized that the
combination of several structural parameters such as intra-
molecular charge-transfer efficiency, effective size of the p-
conjugation domain, and the structural dimensionality of
Results
Model chromophores and synthesis
The chemical structures and the synthetic routes to the stud-
ied model compounds are illustrated in Figure 1 and
Scheme 1, respectively. The compound set contained three
multibranched analogues, the molecular structures of which
were constructed by attaching four identical functionalized-
quinoxalinoid lobes to a common central ethylene core
[a] Prof. T.-C. Lin, Y.-Y. Liu, M.-H. Li, C.-Y. Liu
Photonic Materials Research Laboratory
Department of Chemistry
ꢀ
through C C bonds. Alternatively, the central part of these
National Central University
300 Jong-da Rd. 32001 Jhong-Li (Taiwan)
Fax : (+886)3-4227664
model compounds can be viewed as a TEE moiety, which is
an attractive building unit for the construction of various p-
conjugated carbon-rich structures that exhibit c3 nonlineari-
ties and photochromic properties.[11] Therefore, we believed
that the 2PA-related properties of chromophores with an in-
corporated TEE skeleton deserved to be explored. In this
work we tentatively introduced the TEE unit as the connec-
tion center and constructed a multipolar model chromo-
E-mail: tclin@ncu.edu.tw
[b] S.-Y. Tseng, Y.-T. Wang, Y.-H. Tseng, H.-H. Chu, Prof. C.-W. Luo
Department of Electrophysics
National Chiao-Tung University
Hsinchu (Taiwan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201402094.
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Tzu-Chau Lin et al.
Figure 1. Molecular structures of the studied model chromophores.
phore system based on the tetrasubstituted TEE motif for
the investigation of the 2PA-related properties. We selected
quinoxalinoids as the major aryl substituents, as they were
recently found to be useful structural units for building
highly active 2PA dyes.[10c–e,12] The model compounds were
synthesized in acceptable yields by coupling terminal al-
kynes 10–12 with tetraiodoethylene under Sonogashira con-
ditions, as illustrated in Scheme 1. The aforementioned ter-
minal alkynes were obtained through consecutive function-
alization starting from 4–6, and the details of the syntheses
of the precursors and targeted model compounds are de-
scribed in the Experimental Section.
phores displayed intense one-photon absorption (1PA) in
the 300–470 nm range, and the lowest-energy absorption
bands were located at 441 (eꢁ1.63ꢁ105), 447 (eꢁ2.76ꢁ105),
and 470 nm (eꢁ1.17ꢁ105 cmÀ1 mÀ1) for 1, 2, and 3, respec-
tively. Solutions of these compounds also emitted intense
fluorescence under irradiation of a common UV lamp with
blue-greenish color for 1 and 2 and yellow-orange color for
3, which is in agreement with the measured emission spectra
(see Figure 2b).
Despite the symmetrical nature of their molecular struc-
tures, the fluorescence properties of all these model chromo-
phores possessed strong solvent effects, including band posi-
tions and lifetimes as shown in Figure 3 by using chromo-
phore 2 as a representative for this behavior. Similar behav-
ior has been observed for other multipolar chromophore
systems, and it is postulated that symmetry breaking owing
to electron-vibration coupling and dipolar solvation effects
are the major causes for this phenomenon.[13,14] The mea-
sured photophysical properties of these model chromo-
phores are collected in Table 1.
Linear and nonlinear optical properties
Linear absorption and fluorescence properties
Figure 2 illustrates the linear absorption and fluorescence
spectra of the studied dye molecules in the solution phase
by using toluene as the solvent. The studied model chromo-
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Figure 3. Fluorescence spectra of 2 in various solvents (concentration=
1ꢁ10À6 m for all cases). The measured fluorescence lifetime (t1PA-FL) of 2
in toluene, THF, and CH2Cl2 was 1.5, 4.2, and 5.4 ns, respectively.
The photostability of the studied dye compounds in the
solution phase (1ꢁ10À6 m in toluene) was tentatively evaluat-
ed by continuously monitoring the decay of their fluores-
cence intensity over the course of UV irradiation. We uti-
lized a set of UV lamps as the excitation light source to pro-
vide approximately 350 nm radiation with a total output of
64 W for this experiment. The detailed experimental ar-
rangement is described in the Supporting Information. As il-
lustrated in Figure 4, during the first 1 h of consecutive ex-
posure to UV light, all of the model compounds retain
ꢂ95% of their original emission intensity. Prolonged irradi-
ation further deteriorated the emissive properties of these
model chromophore solutions. Compound 3 showed a larger
fluorescence intensity drop (ꢁ22%), whereas this intensity
drop was kept within approximately 9% for 1 and 2 after
exposure to UV light for 3 h. Overall, model compounds
1 and 2 showed fairly good resistance to photodamage, and
their resistance was superior to that of compound 3 under
our experimental condition. We highly suspect that the
weak photoresistance of 3 may originate from the pyridine
unit in the ring complex, but clarification of this issue is cur-
rently beyond the scope of this work.
Scheme 1. Synthetic procedures for the target model chromophores.
Two-photon-excited fluorescence properties
The studied model chromophores exhibited strong two-
photon-excited fluorescence emission even under irradiation
of an unfocused femtosecond laser beam at approximately
800 nm at a low-intensity level. Figure 5 illustrates the 2PA-
induced fluorescence properties of the studied dye com-
pounds measured by the two-photon-excited fluorescence
(2PEF) technique. A wavelength-tunable mode-locked Ti:-
sapphire laser (Chameleon Ultra II, Coherent) that deliv-
ered approximately 140 fs pulses at a repetition rate of
80 MHz and a beam diameter of 2 mm was utilized as the
excitation light source for these experiments. The intensity
level of the excitation beam was carefully regulated to avoid
absorption and photodegradation saturation of the samples
during the course of the experiments. Furthermore, the rela-
tive position of the excitation beam was adjusted to be as
close as possible to the wall of the quartz cell (10ꢁ10 mm
cuvette) so that only the emission from the front surface of
Figure 2. Linear absorption spectra (a) and fluorescence spectra (b) of 1–
3 in the solution phase (1ꢁ10À6 m in toluene).
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Table 1. Photophysical properties of model chromophores 1–3 in toluene.[a]
Two-photon absorption spectra
measurement
abs
max
em
max
[e]
Chromophore
l
[nm][b]
log e[c]
l
[nm][d]
FF
t2PA-FL [ns][f]
dm2 ax [GM][g]
FFdm2 ax [GM][h]
ꢁ2950
1
302
365
441
306
361
447
5.28
5.31
5.21
5.34
5.39
5.44
521
496
0.69
0.66
2.4
ꢁ4280
(at 740 nm)
The dispersion of the 2PA be-
havior of these model molecules
as a function of wavelength was
probed in the near-IR regime
(680–1000 nm) by the 2PEF
method by using fluorescein (
ꢁ80 mm in pH 11 NaOH solu-
tion) as the standard.[15,16]
Figure 6 shows the measured
degenerate two-photon absorp-
tion spectra of these model
compounds in toluene. From
this figure one can see that all
of these model compounds ex-
2
1.5
(in toluene)
4.2
ꢁ8030
ꢁ5300
(at 750 nm)
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
3
300
368
470
5.22
5.26
5.07
576
0.66
ꢁ4000
ꢁ2640
(at 930 nm)
[a] Concentration was 1ꢁ10À6 and 1ꢁ10À4 m for 1PA-related and 2PA-related measurements, respectively.
[b] One-photon absorption maximum. [c] Molar absorption coefficient of the corresponding absorption band.
[d] 1PA-induced fluorescence emission maximum. [e] Fluorescence quantum efficiency. [f] 2PA-induced fluo-
rescence lifetime. [g] Maximum 2PA cross-section value (with experimental errorÆ15%); 1 GM=1ꢁ
10À50 cm4 s(photon-molecule)À1. [h] Two-photon action cross-section value.
Figure 5. a) Two-photon-excited fluorescence spectra of the studied
model chromophores; b–d) logarithmic plots of power-squared depend-
ence of the 2PA-induced fluorescence intensity on the input intensity of
these compounds in toluene.
hibited strong 2PA (ꢂ500 GM) within the major dynamic
tuning range of a Ti:sapphire oscillator (i.e., 680–950 nm),
which implies that the current structural combination based
on attaching four electron-donor-functionalized quinoxali-
noids to a central TEE core is a useful approach toward
strong 2PA dyes. To be more specific with regard to the 2PA
spectral distribution of the studied model chromophores,
compound 1 exhibited a broad 2PA band with two local
maxima located at approximately 740 (d2 ꢁ4280 GM) and
840 nm (d2 ꢁ3920 GM), whereas compound 2 possessed
a nearly identical 2PA dispersion pattern but with greatly
elevated cross-section values, particularly at approximately
750 nm (d2 ꢁ8030 GM), in comparison to 1, which indicates
that the replacement of the quinoxaline unit by an indeno-
Figure 4. Evaluation of the photostability: Fluorescence spectra of the
studied chromophores in the solution phase under consecutive irradiation
of UV light at 350 nm (insets: fluorescence intensity change over the
course of UV-light exposure).
the sample was recorded. Figure 5a illustrates the normal-
ized 2PA-induced fluorescence spectra of 1–3 in the solution
phase. The quadratic dependence of the fluorescence inten-
sity on the excitation light intensity of these model com-
pounds as shown in Figure 5b–d validates that 2PA is the
major process that causes the observed up-converted emis-
sion.
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structural units employed in these two compounds are
suitable for the development of robust fluorescence
probes that are needed for prolonged UV-light expo-
sure. We are also aware that the results from the current
photostability test may not fully represent the photore-
sistant character of these model compounds in other
spectral regions, especially within their two-photon-
active regime. Therefore, in addition to the presented
work, a more comprehensive evaluation on the photo-
stability of the studied chromophores under the expo-
sure of near-IR radiation is needed, and such an experi-
ment is one of the major subjects of our future work.
(3) Relative to the 2PA of compound 1, the noticeably hy-
perchromic 2PA of 2 in the shorter wavelength region
and the distinctly redshifted 2PA of 3 indicate that fluo-
rene can be an effective structural unit to enhance mo-
lecular 2PA with a roughly immobilized spectral position
of the 2PA band, whereas the pyridine scaffold can effi-
ciently redshift the 2PA and retain the same level of
2PA. These features are particularly useful for molecu-
lar design if either large 2PA at a specific spectral range
or a redshifted 2PA band with a fixed cross-section level
is required for different applications.
(4) Recent theoretical studies on certain organic structures
revealed that molecular 2PA is correlated to the square
of the effective p-electron number.[17] Although this ap-
proximation rule has not been verified yet to be totally
suitable for various classes of conjugated molecules with
different geometries, this scaling may serve as a refer-
ence for the tentative and qualitative analysis of our ex-
perimental results. From the viewpoint of molecular
structure, the major difference between these model
compounds is the heterocyclic part of each chromo-
phore, and if it is assumed that the p-electrons on each
model dye compound follow the same mode of contri-
bution to the nonlinear response, the one with a ring
complex that provides a larger number of p-electrons
can be expected to exhibit a higher maximum molecular
2PA. Therefore, compound 2 can be expected to show
the highest maximum molecular 2PA among the studied
model compounds, as its indenoquinoxaline units pro-
vide the largest number of p-electrons compared to the
p-electron numbers offered by the quinoxalines and pyr-
idopyrazines on compounds 1 and 3, respectively. In par-
allel, the maximum molecular 2PA cross-section values
of compounds 1 and 3 can be expected to be at the
same level, because the heterocyclic ring complex parts
of these two compounds possess the same numbers of
p-electrons.
Figure 6. Measured degenerate two-photon absorption spectra of model
chromophores 1–3 by the 2PEF method in toluene solution at 1ꢁ10À4
(experimental errorꢁ15%).
m
quinoxaline moiety in this dye system had a positive effect
on the promotion of molecular 2PA, especially at shorter
wavelengths. This feature could become very desirable if
large two-photon absorptivity within a specific spectral
region is needed for particular applications. Compound 3
also showed widely dispersed 2PA and a bathochromically
shifted local maximum at approximately 930 nm (d2
ꢁ4000 GM) compared to compound 1.
Discussion of the results
From the measured photophysical properties of the studied
model chromophores in the present work, the following fea-
tures can be seen:
1) On the basis of the measured linear absorption spectra
of the studied model chromophores by using compound
1 as a reference, compound 2 exhibited a distinct in-
crease in the linear absorption with nearly identical
spectral dispersion relative to compound 1, whereas
compound 3 showed relatively smaller linear absorption
and a redshifted lowest-energy band. These features in-
dicate that the involvement of a fluorene unit as part of
the heterocyclic ring complex in this molecular system
(as in the case of 2) is an effective approach to enhance
linear absorptivity without shifting the position of the
absorption band, whereas utilization of
a pyridine
moiety for the construction of a heterocyclic ring com-
plex (as in the case of 3) is useful for expanding the
spectral range of linear absorption by moving the
lowest-energy band bathochromically.
(2) Originally, we suspected that the TEE unit utilized as
a ramification center in this model chromophore system
could be photosensitive and consequently weaken the
photoresistance of these compounds because of the eth-
ynyl components in each structure; nevertheless, the ex-
perimental results revealed that this functional group is
fairly inert toward UV radiation at approximately
350 nm. Among these three model compounds, 1 and 2
exhibited good photostability, which implies that the
(5) Combining the medium-high fluorescence quantum
yields and the 2PA cross-section values, chromophores
1–3 exhibit comparable maximum two-photon action
cross-sections (FFdm2 ax, FF is fluorescence quantum yiel-
d),[1a–c,2a] and this property suggests that such a structural
motif could be useful to build an efficient frequency up-
converter for imaging-related applications such as two-
photon-excited fluorescence microscopy. Additionally,
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from the viewpoint of practical applications, it might be
interesting to explore the photophysical properties of
these model compounds in the solid state (e.g., in film
configuration) and such work is currently being ex-
plored.
Optical power-limiting and stabilization properties in
various time domains
Ideally, an optical limiter is expected to show spectrally
broad and temporally agile response to incident laser light.
Various nonlinear optical mechanisms have been employed
to achieve optical limiting, and among them, 2PA is theoret-
ically considered as a potential process to approach the
aforementioned ideal characteristics for optical control. The
quadratic dependence of 2PA on the input light intensity
has made 2PA materials applicable in optical-limiting appli-
cations, because such materials are transparent to the inci-
dent light at low intensity but become opaque if the input
intensity is increased. Given that this optical-control func-
tion stems from the intrinsic physical properties of the mate-
rial, no external sensing or control mechanism is required to
accomplish such optical suppression so that the response
speed of a 2PA-based optical limiter can be very fast and
the structure of the device can be very simple.
To demonstrate the 2PA-based power-limiting perfor-
mance of the studied fluorophores, we selected compound 2
as a representative and utilized femtosecond laser pulses
from a regenerative amplifier to probe its optical power-lim-
iting properties at approximately 800 nm. The sample solu-
tion for this study was prepared in toluene with a concentra-
tion of 0.02m, and the experimental setup for this measure-
ment is described in detail in the Supporting Information.
Figure 7 illustrates the measured data for the dependence of
the output power on the input power of the probing laser
beam. In this figure, the measured transmitted intensity data
are presented by solid hexagons, and the dark-gray solid line
is the theoretical curve, with the best fitting parameter of
b=2.25 cmGWÀ1. For comparison, the diagonal dotted line
shows the behavior of a medium without nonlinear absorp-
tion, and one can see that the measured input–output curve
starts to deviate from the linear transmission (diagonal
dotted line) at low pumping power and rapidly approaches
larger values of this deviation as the excitation power levels
up. Moreover, the 2PA cross-section value of this model
compound was calculated to be approximately 3100 GM
from the performed optical-power-limiting experiment,
which is very close to the result obtained from the 2PEF
method within experimental uncertainty. This validates that
2PA should be the major cause for the observed up-convert-
ed emission and optical-power restriction in this chromo-
phore system.
Figure 7. Measured output energy versus input energy of femtosecond
laser pulses at 800 nm based on a 1 cm path solution sample of 2 in tolu-
ene at 0.02m. The solid curve is the theoretical data with best-fit parame-
ter of b=2.25 cmGWÀ1
.
time of the studied material is on the same time regime with
the duration of the laser pulse.[18] Such behavior will lead to
larger apparent nonlinear attenuation of the incident light
and consequently to better optical-control performance.
From the viewpoint of fundamental research, it is important
to gain knowledge of the connection between molecular
structure and the 2PA-induced excited-state dynamics to es-
tablish a clear guideline for molecular design to precisely
fulfill various requests of different applications. So far, only
very limited experimental and theoretical attempts have
been conducted to study 2PA-assisted ESA on the basis of
organic dyes;[18,19] therefore, the dependence of excited-state
behavior on molecular structure is still lacking. Nevertheless,
from the standpoint of applications, any medium that pos-
sesses large apparent nonlinear absorption over a wide spec-
tral range could be very useful for effective optical-power
attenuators against long laser pulses.[20] These optical-power
attenuation properties can also be utilized to suppress the
power or energy fluctuation of laser pulses, which is very de-
sirable for many laser-based applications such as optical tel-
ecommunication, optical fabrication, and optical data proc-
essing. To tentatively test the effective optical-power-stabili-
zation properties against long laser pulses on the basis of
these model compounds, chromophores 2 and 3 were select-
ed for this experiment. Furthermore, given that the maxima
2PA of 2 and 3 are located at approximately 750 and 930 nm
(see Figure 6), these two wavelengths were utilized for this
test, because a higher 2PA-induced excited-state population
could be reached and, consequently, larger apparent nonlin-
ear absorption and better power-stabilization performance
was expected. As an excitation light source, a tunable nano-
second laser system (an integrated Q-switched Nd:YAG
laser and OPO: NT 342/3 from Ekspla) was employed to
generate 6 ns laser pulses with controlled average pulse
energy in the range from approximately 0.02 to 2 mJ with
a repetition rate of 10 Hz for this investigation. The experi-
mental results for the optical-stabilization study on the basis
It has been reported that two-photon-active materials
may also exhibit two-photon-assisted excited-state absorp-
tion (2PA-assisted ESA) under the irradiation of nanosec-
ond or longer laser pulses, especially if the excited-state life-
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Tzu-Chau Lin et al.
was a useful strategy to promote molecular 2PA, particularly
at short wavelengths, whereas the incorporation of a pyridine
moiety as a component of the heterocycles was beneficial in
shifting the 2PA band bathochromically without a huge de-
cline in the maximum 2PA. Moreover, model chromophore
2 was demonstrated to exhibit intrinsic 2PA-based optical-
power-limiting properties against femtosecond laser pulses.
In addition, both 2 and 3 were selected to test their optical-
power stabilization properties against long laser pulses at
wavelength positions for which these two model chromo-
phores exhibit maximum 2PA, and as expected, fairly good
power-stabilization performance of these two compounds
was observed. Combining the good photostability and strong
two-photon action cross-section (FFdm2 ax), these model chro-
mophores could be potential prototypes for the develop-
ment of 2PA-based fluorescence probes for long-term light
exposure.
Figure 8. a,c) Measured instantaneous pulse energy fluctuation of the
input laser pulses at 750 and ~930 nm; b,d) measured instantaneous
pulse energy fluctuation of the output laser pulses at corresponding
wavelengths after passing through solutions of 2 and 3. The repetition
rate of the laser pulse was 10 Hz, and the average input pulse energy
level was approximately 1 mJ.
Experimental Section
General
All commercially available reagents for the preparation of the intermedi-
ates and targeted chromophores were purchased from Acros Organics or
Alfa Aesar and were used as received, unless stated otherwise. 1H NMR
and 13C NMR spectra were recorded with a 300 MHz spectrometer and
referenced to tetramethylsilane or residual CHCl3. The representative
numbering of carbon and hydrogen atoms on each intermediate and
model chromophore for the assignment of the NMR signals was system-
atized and is illustrated in the Supporting Information. HRMS was con-
ducted by using a Waters LCT ESI-TOF mass spectrometer. MALDI-
TOF MS spectra were obtained with a Voyager DE-PRO mass spectrom-
eter (Applied Biosystem, Houston, USA).
of these two sample solutions are shown in Figure 8. The
curves in Figure 8a,c are the instantaneous pulse-energy
changes in the incident laser beam at the corresponding
wavelengths. The input pulses possess a relatively large
energy fluctuation, as shown in Figure 8a,c, and after pass-
ing through solutions of 2 and 3, reduced fluctuation of the
pulse energy was observed for the output signals for each
case, as illustrated in Figure 8b,d. For the purpose of com-
parison, the average levels of both the input and output sig-
nals were normalized to the same value, and from the mea-
sured data, compound 2 is a better optical-power stabilizer
than compound 3.
Photophysical methods
All of the linear optical properties of the subject model compound were
measured by the corresponding spectrometers. Detailed experimental
conditions as well as the optical setups for nonlinear optical properties
investigations are described in the Supporting Information.
Synthesis
It should be reiterated that the individual contributions
originating from intrinsic 2PA and possible ESA to the ob-
served optical-energy attenuation of the tested chromophore
systems is indistinguishable under the current experimental
conditions. Therefore, the results presented herein could be
assumed as a combined effect based on the aforementioned
nonlinear processes.
In Scheme 1, compounds 4–6 were the major starting materials for the
synthesis of each intermediate and model chromophore. These three
compounds were obtained by following established procedures.[10c] For
the synthesis of other key intermediates (i.e., compounds 7–9 and 10–12)
and targeted model compounds 1–3, a series of functionalization steps
starting from compounds 4–6 were conducted and are presented below.
7,7’-{6-[(Trimethylsilyl)ethynyl]quinoxaline-2,3-diyl}bis(9,9-dihexyl-N,N-
diphenyl-9H-fluoren-2-amine) (7): PdCl2ACHTNUTRGNE(UNG PPh3)2 (0.052 g, 0.074 mmol),
CuI (0.023 g, 0.12 mmol), trimethylsilyl acetylene (0.18 g, 1.86 mmol),
and iPr2NH (2.5 mL) were added to a mixture of 4 (1.5 g, 1.24 mmol) in
dry THF (10 mL). The resulting solution was stirred at 908C under an Ar
Conclusions
atmosphere for 21 h. After cooling to room temperature, H2O
(
ꢁ100 mL) was added to the reaction mixture. The above solution was
then extracted with CH2Cl2 (3ꢁ30 mL), and the organic layer was col-
lected and dried with MgSO4(s). After removing the solvent, the crude
product was purified by column chromatography on silica gel (THF/
hexane=1:10) to give the final purified product as a yellow powder
(1.4 g, 92.1%). 1H NMR (300 MHz, CDCl3): d=8.31 (s, 1H; H-F), 8.10–
8.07 (d, J=8.4 Hz, 1H; H-C), 7.78–7.76 (d, J=8.4 Hz, 1H; H-B), 7.75–
7.50 (m, 8H; H-9, H-12, H-13, H-15), 7.26–7.21 (m, 8H; H-2), 7.12–7.00
(m, 10H; H-3, H-6), 7.00–6.96 (m, 6H; H-1, H-8), 1.75–1.72 (m, 8H; H-
f), 1.12–0.94 (m, 24H; H-c, H-d, H-e), 0.94–0.74 (m, 12H; H-a), 0.64 (s,
8H; H-b), 0.31 ppm (s, 9H; methyl hydrogen atoms of the TMS group);
In conclusion, we synthesized a novel multipolar chromo-
phore set composed of three congeners on the basis of the
tetrasubstituted tetraethynylethylene structural motif by
using functionalized quinoxalinoids as the main aryl sub-
stituents. The initial experimental results showed that these
model fluorophores display widely dispersed and strong
two-photon absorption in the near-IR region. Tentative
structure–2PA properties analysis revealed that integration
of a fluorene unit as part of the heterocyclic ring complex
7
&
&
Chem. Asian J. 2014, 00, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ

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Tzu-Chau Lin et al.
13C NMR (75 MHz, CDCl3, tentative assignments based on calculated
values): d=154.62 (C-H), 154.22 (C-G), 152.61 (C-16), 150.59 (C-5),
150.51 (C-D), 147.87 (C-4), 147.50 (C-E), 141.80 (C-11), 140.80 (C-7),
140.70 (C-A), 137.05 (C-14), 135.39 (C-10), 132.67 (C-F), 132.54 (C-B),
129.13 (C-2), 128.98 (C-12, C-C-), 124.34 (C-15), 123.86 (C-3), 123.34 (C-
13), 122.55 (C-1), 120.86 (C-8), 118.91 (C-9), 118.82 (C-6), 104.39 (acety-
lene carbon), 97.12 (acetylene carbon), 55.05 (C-g), 40.09 (C-f), 31.53 (C-
e), 29.56 (C-d), 23.82 (C-c), 22.59 (C-b), 14.06 (C-a), À0.11 ppm (methyl
carbon atoms of the TMS group); HRMS (MALDI-TOF): m/z: calcd for
C87H96N4Si: 1224.7405 [M]+; found: 1224.7440.
d, C-d’), 23.84 (C-c), 23.77 (C-c’), 22.58 (C-b, C-b’), 14.06 (C-a, C-a’),
À0.25 ppm (methyl carbon atoms on TMS group). HRMS (MALDI-
TOF): m/z: calcd for C86H95N5Si: 1226.8258 [M]+; found: 1226.8293.
7,7’-(6-Ethynylquinoxaline-2,3-diyl)bis(9,9-dihexyl-N,N-diphenyl-9H-fluo-
ren-2-amine) (10): KOH (0.26 g, 4.57 mmol) was added to a mixture of 7
(1.4 g, 1.14 mmol) in THF/MeOH (5 mL/1 mL), and the resulting solu-
tion was stirred at RT under an Ar atmosphere for 15 h. Upon comple-
tion of the reaction, H2O (ꢁ100 mL) was added to the reaction mixture.
The above solution was then extracted with CH2Cl2 (3ꢁ30 mL), and the
organic layer was collected and dried with MgSO4(s). After removing the
solvent, the crude product was purified by column chromatography on
silica gel (THF/hexane=1:10) to give the final purified product as an
7,7’-{10,10-Dihexyl-8-[(trimethylsilyl)ethynyl]-10H-indeno
line-2,3-diyl}bis(9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine) (8): PdCl2
(PPh3)2 (0.074 g, 0.10 mmol), CuI (0.03 g, 0.18 mmol), trimethylsilyl acety-
ACHTUNGTREN[NGNU 1,2-g]quinoxa-
1
ACHTUNGTRENNUNG
orange powder (1.1 g, 83.4%). H NMR (300 MHz, CDCl3): d=8.35–8.34
lene (0.29 g, 2.96 mmol), and iPr2NH (3 mL) were added to a mixture of
5 (2.58 g, 1.76 mmol) in dry THF (10 mL). The resulting solution was
stirred at 908C under an Ar atmosphere for 17 h. After cooling to room
temperature, H2O (ꢁ100 mL) was added to the reaction mixture. The
above solution was then extracted with CH2Cl2 (3ꢁ30 mL), and the or-
ganic layer was collected and dried with MgSO4(s). After removing the
solvent, the crude product was purified by column chromatography on
silica gel (THF/hexane=1:10) to give the final purified product as an
orange powder (2.4 g, 92%). 1H NMR (300 MHz, CDCl3): d=8.41 (s,
1H; H-H), 8.07 (s, 1H; H-K), 7.86–7.82 (d, J=7.8 Hz, 1H; H-D), 7.62–
7.58 (m, 10H; H-9, H-12, H-13, H-15, H-B, H-E), 7.27–7.21 (m, 8H; H-
2), 7.12–7.07 (m, 10H; H-3, H-6), 7.04–6.98 (m, 6H; H-1, H-8), 2.19–2.01
(m, 4H; H-f’), 1.77–1.70 (m, 8H; H-f), 1.21–0.88 (m, 36H; H-c, H-c’, H-
d, H-d’, H-e, H-e’), 0.81–0.63 (m, 30H; H-a, H-a’, H-b, H-b’), 0.31 ppm
(s, 9H; methyl hydrogen atoms of the TMS group); 13C NMR (75 MHz,
CDCl3, tentative assignments based on calculated values): d=153.46 (C-
16), 153.03 (C-N), 152.58 (C-5), 151.24 (C-M), 150.57 (C-A), 150.48 (C-
L), 147.89 (C-4), 147.40 (C-F), 143.15 (C-J), 141.52 (C-I), 141.36 (C-G),
141.19 (C-11), 140.06 (C-7), 137.52 (C-14), 137.44 (C-14’), 135.54 (C-10),
131.55 (C-B), 129.12 (C-2, C-12, C-E), 126.52 (C-D), 124.37 (C-15),
123.83 (C-3), 123.38 (C-K), 123.20 (C-C), 122.51 (C-1), 122.29 (C-13),
120.83 (C-6), 119.09 (C-9), 118.96 (C-8), 118.71 (C-H), 105.82 (acetylene
carbon), 95.00 (acetylene carbon), 55.23 (C-g’), 55.04 (C-g), 41.37 (C-f’),
40.11 (C-f), 31.55 (C-e, C-e’), 29.71 (C-d’), 29.59 (C-d), 23.85 (C-c, C-c’),
22.61 (C-b, C-b’), 14.08 (C-a), 13.96 (C-a’), 0.01 ppm (methyl carbon
atoms of the TMS group). HRMS (MALDI-TOF): m/z: calcd for
C106H124N4Si: 1480.9596 [M]+; found: 1480.9642.
(d, J=1.2 Hz, 1H; H-F), 8.13–8.10 (d, J=8.7 Hz, 1H; H-C), 7.80–7.77 (d,
J=8.7, 1.2 Hz, 1H; H-B), 7.59–7.50 (m, 8H; H-9, H-12, H-13, H-15),
7.27–7.21 (m, 8H; H-2), 7.12–7.08 (m, 10H; H-3, H-6), 7.08–6.98 (m, 6H;
À
H-1, H-8), 3.27 (s, 1H; CꢀH), 1.74 (s, 8H; H-f), 1.13–0.94 (m, 24H; H-
c, H-d, H-e), 0.86–0.76 (m, 12H; H-a), 0.64 ppm (s, 8H; H-b); 13C NMR
(75 MHz, CDCl3, tentative assignments based on calculated values): d=
154.79 (C-G), 154.50 (C-H), 152.63 (C-16), 150.60 (C-5), 147.88 (C-4),
147.54 (C-D, C-E), 141.88 (C-11), 140.95 (C-7), 140.62 (C-A), 136.97 (C-
14), 135.35 (C-10), 133.07 (C-F), 132.48 (C-B), 129.15 (C-2), 129.00 (C-12,
C-C), 124.35 (C-15), 123.88 (C-3), 123.33 (C-13), 122.57 (C-1), 120.89 (C-
8), 119.01 (C-9, C-6), 83.07 (acetylene carbon), 79.55 (acetylene carbon),
55.07 (C-g), 40.09 (C-f), 31.53 (C-e), 29.57 (C-d), 23.83 (C-c), 22.60 (C-b),
14.08 ppm (C-a). HRMS (MALDI-TOF): m/z: calcd for C84H88N4:
1152.7009 [M]+; found: 1152.7042.
7,7’-(8-Ethynyl-10,10-dihexyl-10H-indenoACTHUNTGRENNG[U 2,1-g]quinoxaline-2,3-diyl)-
bis(9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine) (11): KOH (0.27 g,
4.85 mmol) was added to a mixture of 8 (2.4 g, 1.62 mmol) in THF/
MeOH (10 mL/2 mL), and the resulting solution was stirred at RT under
an Ar atmosphere for 5 h. Upon completion of the reaction, H2O (
ꢁ100 mL) was added to the reaction mixture. The above solution was
then extracted with CH2Cl2 (3ꢁ30 mL), and the organic layer was col-
lected and dried with MgSO4(s). After removing the solvent, the crude
product was purified by column chromatography on silica gel (THF/
hexane=1:10) to give the final purified product as an orange powder
1
(2.1 g, 92%). H NMR (300 MHz, CDCl3): d=8.44 (s, 1H; H-H), 8.10 (s,
1H; H-K), 7.89–7.86 (d, J=7.8 Hz, 1H; H-D), 7.63–7.52 (m, 10H; H-9,
H-12, H-13, H-15, H-B, H-E), 7.27–7.22 (m, 8H; H-2), 7.14–7.09 (m,
7,7’-{7-[(Trimethylsilyl)ethynyl]pyrido
ACHTUNGTRENNUNG
À
10H; H-3, H-6), 7.03–6.99 (m, 6H; H-1, H-8), 3.20 (s, 1H; CꢀH), 2.13–
hexyl-N,N-diphenyl-9H-fluoren-2-amine) (9): PdCl CTHUNGTRENNUNG
2.02 (m, 4H; H-f’), 1.84–1.74 (m, 8H; H-f), 1.11–1.04 (m, 36H; H-c, H-c’,
H-d, H-d’, H-e, H-e’), 0.86–0.66 ppm (m, 30H; H-a, H-a’, H-b, H-b’);
13C NMR (75 MHz, CDCl3, tentative assignments based on calculated
values): d=153.48 (C-16), 153.40 (C-16’), 153.11 (C-N), 152.58 (C-5),
151.34 (C-M), 150.58 (C-A), 150.50 (C-L), 147.89 (C-4), 147.41 (C-F),
143.00 (C-J), 141.54 (C-I), 141.39 (C-G), 141.16 (C-11), 140.35 (C-7),
137.49 (C-14), 137.41 (C-14’), 135.52 (C-10), 131.56 (C-B), 129.12 (C-2, C-
12), 128.92 (C-E), 126.79 (C-D), 124.36 (C-15), 123.83 (C-3), 123.37 (C-
K), 122.52 (C-1), 122.35 (C-13), 122.14 (C-C), 120.90 (C-6), 120.82 (C-6’),
119.08 (C-9), 118.96 (C-8), 118.90 (C-8’), 118.82 (C-H), 84.35 (acetylene
carbon), 77.92 (acetylene carbon), 55.23 (C-g’), 55.04 (C-g), 41.32 (C-f’),
40.11 (C-f), 31.54 (C-e, C-e’), 29.67 (C-d’), 29.58 (C-d), 23.84 (C-c, C-c’),
22.61 (C-b), 22.55 (C-b’), 14.07 (C-a), 13.94 ppm (C-a’). HRMS
0.09 mmol), CuI (0.03 g, 0.15 mmol), trimethylsilyl acetylene (0.22 g, 2.23
mmol), and iPr2NH (2.5 mL) were added to a mixture of 6 (1.80 g,
1.49 mmol) in dry THF (10 mL). The resulting solution was stirred at
908C under an Ar atmosphere for 24 h. After cooling to room tempera-
ture, H2O (ꢁ100 mL) was added to the reaction mixture. The above so-
lution was then extracted with CH2Cl2 (3ꢁ30 mL), and the organic layer
was collected and dried with MgSO4(s). After removing the solvent, the
crude product was purified by column chromatography on silica gel
(THF/hexane=1:10) to give the final purified product as an orange
powder (1.53 g, 83.9%). 1H NMR (300 MHz, CDCl3): d=9.16–9.12 (d,
J=2.1 Hz, 1H; H-B), 8.58–8.54 (d, J=2.1 Hz, 1H; H-E), 7.82–7.78 (d,
J=1.2 Hz, 1H; H-15), 7.71–7.14 (dd, J=8.1, 1.2 Hz, 1H; H-12), 7.63–7.58
(d, J=8.1 Hz, 1H; H-12’), 7.57–7.42 (m, 5H; H-13, H-13’, H-9, H-9’, H-
15’), 7.31–7.21 (m, 8H; H-3), 7.15–7.07 (m, 10H; H-2, H-6), 7.07–6.97 (m,
6H; H-1, H-8), 1.82–1.61 (m, 8H; H-f, H-f’), 1.14–0.92 (m, 24H; H-c, H-
c’, H-d, H-d’, H-e, H-e’), 0.81–0.75 (m, 12H; H-a, H-a’), 0.62 (s, 8H; H-b,
H-b’), 0.33 ppm (s, 9H; methyl hydrogen atoms of the TMS group);
13C NMR (75 MHz, CDCl3, tentative assignments based on calculated
values): d=156.91 (C-G), 155.93 (C-F), 155.72 (C-B), 152.75 (C-16),
152.62 (C-16’), 150.71 (C-5), 150.55 (C-5’), 148.75 (C-C), 147.83 (C-4, C-
4’), 147.71 (C-7, C-7’), 142.53 (C-11), 142.30 (C-11’), 139.97 (C-E), 136.49
(C-14), 136.08 (C-14’), 135.20 (C-10), 135.14 (C-10’), 134.95 (C-D), 129.72
(C-12), 129.14 (C-2, C-2’), 128.91 (C-12’), 124.45 (C-15), 124.31 (C-15’),
123.92 (C-3, C-3’), 123.29 (C-13, C-13’), 122.62 (C-1, C-1’), 121.18 (C-A),
120.99 (C-6), 120.93 (C-6’), 119.13 (C-9), 118.89 (C-8, C-8’), 118.56 (C-
13’), 100.99 (acetylene carbon), 100.81 (acetylene carbon), 55.23 (C-g),
55.05 (C-g’), 40.18 (C-f), 40.05 (C-f’), 31.57 (C-e), 31.52 (C-e’), 29.54 (C-
(MALDI-TOF): m/z: calcd for
1408.9240.
C
103H116N4: 1408.9200 [M]+; found:
7,7’-(7-EthynylpyridoACTHUNTGRENNG[U 2,3-b]pyrazine-2,3-diyl)bis(9,9-dihexyl-N,N-diphen-
yl-9H-fluoren-2-amine) (12): KOH (0.28 g, 4.99 mmol) was added to
a mixture of 9 (1.53 g, 1.24 mmol) in THF/MeOH/H2O (10 mL/5 mL/
1 mL), and the resulting solution was stirred at RT under an Ar atmos-
phere for 2 h. After cooling to room temperature, H2O (ꢁ100 mL) was
added to the reaction mixture. The above solution was then extracted
with CH2Cl2 (3ꢁ30 mL), and the organic layer was collected and dried
with MgSO4(s). After removing the solvent, the crude product was puri-
fied by column chromatography on silica gel (THF/hexane=1:10) to give
the final purified product as an orange powder (1.1 g, 76.3%). 1H NMR
(300 MHz, CDCl3): d=9.16–9.15 (d, J=2.1 Hz, 1H; H-B), 8.61–8.60 (d,
J=2.1 Hz, 1H; H-E), 7.81 (s, 1H; H-15), 7.71–7.68 (d, J=8.1 Hz, 1H; H-
&
&
8
Chem. Asian J. 2014, 00, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

www.chemasianj.org
Tzu-Chau Lin et al.
12), 7.64–7.58 (d, J=7.8 Hz, 1H; H-12’), 7.59–7.43 (m, 5H; H-13, H-13’,
H-9, H-9’, H-15’), 7.27–7.21 (m, 8H; H-2), 7.20–7.10 (m, 10H; H-3, H-6),
Compound 3: PdACTHNGUTERN(NUG PPh3)4 (0.013 g, 0.011 mmol), CuI (2.16 mg,
0.011 mmol), tetraiodoethene (0.12 g, 0.22 mmol), and NEt3 (2.5 mL)
were added to a mixture of 12 (1.1 g, 0.95 mmol) in THF (10 mL). The
resulting solution was stirred at 908C under an Ar atmosphere for 18 h.
After cooling to room temperature, H2O (ꢁ100 mL) was added to the
reaction mixture. The above solution was then extracted with CH2Cl2 (3ꢁ
À
7.08–6.98 (m, 6H; H-1, H-8), 3.42 (s, 1H; CꢀH), 1.81–1.68 (m, 8H; H-
f, H-f’), 1.26–1.02 (m, 24H; H-c, H-c’, H-d, H-d’, H-e, H-e’), 0.92–0.78
(m, 12H; H-a, H-a’), 0.77–0.75 ppm (m, 8H; H-b, H-b’); 13C NMR
(75 MHz, CDCl3, tentative assignments based on calculated values): d=
157.25 (C-G), 156.09 (C-F), 155.56 (C-B), 152.76 (C-16), 152.62 (C-16’),
150.75 (C-5), 150.56 (C-5’), 148.99 (C-C), 147.81 (C-4, C-4’), 142.62 (C-7,
C-7’), 142.38 (C-11, C-11’), 140.60 (C-E), 136.38 (C-14), 135.97 (C-14’),
135.13 (C-10, C-10’), 134.83 (C-D), 129.73 (C-12), 129.15 (C-2, C-2’),
128.90 (C-12’), 124.45 (C-15), 124.28 (C-15’), 123.93 (C-3, C-3’), 123.27
(C-13, C-13’), 122.64 (C-1, C-1’), 121.01 (C-6, C-6’), 120.09 (C-A), 119.19
(C-9), 118.86 (C-8, C-8’), 118.56 (C-9’), 82.57 (acetylene carbon), 79.97
(acetylene carbon), 55.24 (C-g), 55.06 (C-g’), 40.17 (C-f), 40.05 (C-f’),
31.57 (C-e), 31.51 (C-e’), 29.54 (C-d, C-d’), 23.85 (C-c, C-c’), 22.58 (C-b,
C-b’), 14.05 ppm (C-a, C-a’). HRMS (MALDI-TOF): m/z: calcd for
C83H87N5: 1153.6962 [M]+; found: 1153.6965.
30 mL), and the organic layer was collected and dried with MgSO4(s)
.
After removing the solvent, the crude product was purified by column
chromatography on silica gel (THF/hexane=1:10) to give the final puri-
fied product as
a
red powder (0.5 g, 47.6%). 1H NMR (300 MHz,
CDCl3): d=9.23–9.22 (d, J=2.1 Hz, 4H; H-B), 8.70–8.69 (d, J=2.1 Hz,
4H; H-E), 7.83 (s, 4H; H-15), 7.73–7.70 (dd, J=8.1, 1.2 Hz, 4H; H-12),
7.70–7.63 (d, J=8.1 Hz, 4H; H-12’), 7.60–7.57 (d, J=8.1 Hz, 8H; H-13,
H-13’), 7.52–7.48 (d, J=8.1 Hz, 4H; H-9), 7.48–7.44 (m, 8H; H-9’, H-15’),
7.27–7.22 (m, 32H; H-2), 7.13–7.08 (m, 40H; H-3, H-6), 7.03–6.99 (m,
24H; H-1, H-8), 1.84–1.69 (m, 32H; H-f, H-f’), 1.15–1.03 (m, 96H; H-c,
H-c’, H-d, H-d’, H-e, H-e’), 0.93–0.76 (m, 48H; H-a, H-a’), 0.63 ppm (s,
32H; H-b, H-b’); 13C NMR (75 MHz, CDCl3, tentative assignments based
on calculated values): d=157.48 (C-G), 156.33 (C-F), 155.40 (C-B),
152.73 (C-16), 152.57 (C-16’), 150.71 (C-5), 150.54 (C-5’), 149.17 (C-C),
147.74 (C-4, C-4’), 142.76 (C-7), 142.46 (C-11), 141.08 (C-E), 136.21 (C-
14), 135.79 (C-14’), 134.99 (C-10, C-A), 134.67 (C-D), 129.75 (C-12),
129.10 (C-2), 124.42 (C-15), 124.21 (C-15’), 123.90 (C-3), 123.20 (C-13),
122.61 (C-1), 121.01 (C-6), 119.27 (C-9), 119.18 (ethylene carbon atoms),
118.76 (C-8), 118.56 (C-9’), 79.95 (acetylene carbon atoms), 78.38 (acety-
lene carbon atoms), 55.19 (C-g), 55.01 (C-g’), 40.09 (C-f), 31.51 (C-e),
31.50 (C-e’), 29.48 (C-d), 23.79 (C-c), 22.53 (C-b), 14.01 ppm (C-a).
Compound 1: PdACHTUNGTRENNUNG(PPh3)4 (0.015 g, 0.011 mmol), CuI (3 mg, 0.011 mmol),
tetraiodoethene (0.12 g, 0.23 mmol), and NEt3 (3 mL) were added to
a mixture of 10 (1.1 g, 0.95 mmol) in THF (10 mL). The resulting solution
was stirred at 908C under an Ar atmosphere for 26 h. After cooling to
room temperature, H2O (ꢁ100 mL) was added to the reaction mixture.
The above solution was then extracted with CH2Cl2 (3ꢁ30 mL), and the
organic layer was collected and dried with MgSO4(s). After removing the
solvent, the crude product was purified by column chromatography on
silica gel (THF/hexane=1:10) to give the final purified product as
a yellow powder (0.6 g, 57.1%). 1H NMR (300 MHz, CDCl3): d=8.43–
8.42 (d, J=1.2 Hz, 4H; H-F), 8.16–8.13 (d, J=8.7 Hz, 4H; H-C), 7.86–
7.82 (d, J=8.7, 1.2 Hz, 4H; H-B), 7.60–7.50 (m, 32H; H-9, H-12, H-13,
H-15), 7.27–7.21 (m, 32H; H-2), 7.13–7.09 (m, 40H; H-3, H-6), 7.03–6.99
(m, 24H; H-1, H-8), 1.76–1.74 (m, 32H; H-f), 1.14–1.04 (m, 96H; H-c,
H-d, H-e), 0.82–0.76 (m, 48H; H-a), 0.65 ppm (s, 32H; H-b); 13C NMR
(75 MHz, CDCl3, tentative assignments based on calculated values): d=
155.00 (C-H), 154.67 (C-G), 152.64 (C-16), 150.64 (C-5), 150.58 (C-5’),
147.86 (C-4), 147.56 (C-E), 141.99 (C-11), 141.93 (C-D), 141.30 (C-7),
140.64 (C-A), 136.88 (C-14), 135.31 (C-10), 133.74 (C-F), 132.48 (C-B),
129.42 (C-C), 129.14 (C-2), 129.04 (C-12), 124.35 (C-15), 123.89 (C-3),
123.32 (C-13), 122.70 (ethylene carbon atoms), 122.58 (C-1), 120.90 (C-
8), 118.97 (C-9, C-6), 82.22 (acetylene carbon atoms), 76.16 (acetylene
carbon atoms), 55.07 (C-g), 40.08 (C-f), 31.53 (C-e), 29.56 (C-d), 23.83
(C-c), 22.60 (C-b), 14.07 ppm (C-a). HRMS (MALDI-TOF): m/z: calcd
for C338H348N6: 4635.6206 [M]+; found: 4635.6372.
Acknowledgements
We thank the National Science Council (NSC), Taiwan for financial sup-
port through grant number 101-2113M-008-003-MY2.
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Compound 2: PdACHTUNGTRENNUNG(PPh3)4 (0.02 g, 0.018 mmol), CuI (3.37 mg, 0.018 mmol),
tetraiodoethene (0.19 g, 0.35 mmol), and NEt3 (3.6 mL) were added to
a mixture of 11 (2.1 g, 1.48 mmol) in THF (12 mL). The resulting solution
was stirred at 908C under an Ar atmosphere for 12 h. After cooling to
room temperature, H2O (ꢁ100 mL) was added to the reaction mixture.
The above solution was then extracted with CH2Cl2 (3ꢁ30 mL), and the
organic layer was collected and dried with MgSO4(s). After removing the
solvent, the crude product was purified through column chromatography
on silica gel (THF/hexane=1:10) to give the final purified product as an
orange powder (1.1 g, 55%). 1H NMR (300 MHz, CDCl3): d=8.46 (s,
4H; H-H), 8.11 (s, 4H; H-K), 7.92–7.89 (d, J=7.8 Hz, 4H; H-D), 7.65–
7.52 (m, 40H; H-9, H-12, H-13, H-15, H-B, H-E), 7.27–7.22 (m, 32H; H-
2), 7.13–7.09 (m, 40H; H-3, H-6), 7.03–6.98 (m, 24H; H-1, H-8), 2.14–
2.11 (m, 16H; H-f’), 1.76–1.74 (m, 32H; H-f), 1.13–1.04 (m, 144H; H-c,
H-c’, H-d, H-d’, H-e, H-e’), 0.82–0.68 ppm (m, 120H; H-a, H-a’, H-b, H-
b’); 13C NMR (75 MHz, CDCl3, tentative assignments based on calculated
values): d=153.57 (C-16), 153.44 (C-16’), 153.23 (C-N), 152.60 (C-5),
151.49 (C-M), 150.60 (C-A), 150.53 (C-L), 147.91 (C-4), 147.43 (C-F),
142.84 (C-J), 141.59 (C-I), 141.54 (C-G), 141.49 (C-C), 141.18 (C-11),
140.86 (C-7), 137.47 (C-14), 137.39 (C-14’), 135.53 (C-10), 131.97 (C-B),
129.13 (C-2, C-12), 128.92 (C-E), 127.24 (C-D), 124.37 (C-15), 123.85 (C-
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(C-13), 120.83 (C-6), 119.10 (C-9, C-8, C-H), 83.21 (acetylene carbon
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(C-f’), 40.12 (C-f), 31.55 (C-e, C-e’), 29.69 (C-d’), 29.59 (C-d), 23.85 (C-c,
C-c’), 22.62 (C-b, C-b’), 14.08 (C-a), 13.96 ppm (C-a’). HRMS (MALDI-
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Received: February 20, 2014
Published online: && &&, 0000
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Chem. Asian J. 2014, 00, 0 – 0
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ÝÝ These are not the final page numbers!

FULL PAPER
Two is better than one: Multibranched
chromophores based on the tetrasub-
stituted ethynylethylene skeleton with
functionalized quinoxalinoids as aryl
substituents are synthesized and shown
to possess strong and widely dispersed
two-photon absorption in the near-IR
region. This molecular archetype is
also demonstrated to possess optical
power-limiting properties and optical
power-stabilization properties toward
laser pulses in various time domains.
Chromophores
Tzu-Chau Lin,* Yi-You Liu,
May-Hui Li, Che-Yu Liu,
Sheng-Yang Tseng, Yu-Ting Wang,
Ya-Hsin Tseng, Hui-Hsin Chu,
Chih-Wei Luo
&&&& — &&&&
Synthesis and Characterization of Two-
Photon Chromophores Based on
a Tetrasubstituted Tetraethynylethy-
lene Scaffold
11
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Chem. Asian J. 2014, 00, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ