Functionalized tetrafluorenylethylene-type chromophores: Synthesis, two-photon absorption and effective optical power-limiting properties in the visible-to-near IR region

Article abstract of DOI:10.1016/j.dyepig.2016.07.027

A series of novel multipolar fluorophores based on tetra-substituted olefinic scaffold using functionalized fluorenyl and indenofluorenyl units as the aryl substituents has been synthesized and investigated for their two-photon-related properties in the f

Full text of DOI:10.1016/j.dyepig.2016.07.027

Accepted Manuscript
Functionalized tetrafluorenylethylene-type chromophores: Synthesis, two-photon
absorption and effective optical power-limiting properties in the visible-to-near IR
region
Tzu-Chau Lin, Ying-Hsuan Lee, Bor-Rong Huang, Ming-Yu Tsai, Jhe-Yi Lin
PII:
S0143-7208(16)30335-7
10.1016/j.dyepig.2016.07.027
DYPI 5361
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 22 June 2016
Revised Date: 20 July 2016
Accepted Date: 21 July 2016
Please cite this article as: Lin T-C, Lee Y-H, Huang B-R, Tsai M-Y, Lin J-Y, Functionalized
tetrafluorenylethylene-type chromophores: Synthesis, two-photon absorption and effective optical
power-limiting properties in the visible-to-near IR region, Dyes and Pigments (2016), doi: 10.1016/
j.dyepig.2016.07.027.
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ACCEPTED MANUSCRIPT
[1] Medium-high up-converted emission
[2] Strong power-limiting response within visible
Nanosecond Vis-IR
Femtosecond IR
laser pulses
laser pulses
@550-1000 nm, ~5ns
@680-1080 nm, ~140fs

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Functionalized Tetrafluorenylethylene-type Chromophores:
Synthesis, Two-photon Absorption and Effective Optical
Power-Limiting Properties in the Visible-to-near IR Region
Tzu-Chau Lin,* Ying-Hsuan Lee, Bor-Rong Huang, Ming-Yu Tsai and Jhe-Yi Lin
Photonic Materials Research Laboratory, Department of Chemistry, National Central
University, Jhong-Li District, Taoyuan City 32001, Taiwan.
E-mail: tclin@ncu.edu.tw
Abstract
A series of novel multipolar fluorophores based on tetra-substituted olefinic scaffold using
functionalized fluorenyl and indenofluorenyl units as the aryl substituents has been
synthesized and investigated for their two-photon-related properties in the femtosecond
and nanosecond time domains. When probed by the femtosecond pulses, these
chromophores are found to possess appreciable intrinsic two-photon absorptivities with
their local maxima very close to the short-wavelength end of the dynamic tuning range of
a Ti: sapphire laser. While under the irradiation of nanosecond pulses, these dye molecules
exhibit promising nonlinear optical-power-attenuation properties across the visible-to-near
infrared region. Combining with their medium-high fluorescence quantum efficiencies,
such archetype represents a new class of structures that could be utilized as effective
broadband optical power-limiters and frequency up-converters especially with great
potentiality to work in the visible regime.
Keywords: Two-photon absorption, optical power-limiting, tetraarylethylene, Suzuki
reaction.

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1. Introduction
Just like the development path of many other science subjects, the theoretical prediction of
two-photon absorption (2PA) made by Maria Göppert-Mayer in 1931 is far ahead of its
experimental evidence[1] and the advent of lasers in 1960s has brought scientists
appropriate excitation light sources to experimentally study this nonlinear optical
phenomenon.[2, 3] The intrinsic quadratic dependence of 2PA on the incident light
intensity is one of the major characters that makes this third-order nonlinear optical
phenomenon applicable in many photonics and biophotonics applications such as optical
power-limiting, frequency up-converted lasing, 3-D data storage, 3-D microfabrication,
nondestructive bio-imaging and tracking, and two-photon photodynamic therapy.[4-11]
For the development of two-photon technologies, the exploration of new materials with
strong 2PA plays an equally important counterpart as the advancement of high peak-power
pulsed laser systems. Through rational molecular design, it is possible to construct organic
structures that exhibit several orders of intensified 2PA with other desired molecular
characteristics simultaneously integrated, which greatly compensates for the relatively
poor performance of commercialized dyes for the aforementioned applications. Up to now,
it has been realized that the combination of several structural parameters such as the
efficiency of intramolecular charge-transfer, effective size of π-conjugation domain, and
molecular dimensionality of a molecule is closely related to the molecular 2PA.[12-29]

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Therefore, the structural arrangement of the selected building units within a molecule is a
hinge for the molecular design toward highly active 2PA-chromophores.
So far, various two-photon absorbing organic conjugated structures with different
π-frameworks have been successfully demonstrated to show optical power-suppression
function against high peak-power laser pulses in the nanosecond to femtosecond time
domains[5, 8, 30-35] and most of the reported 2PA-based optical limiters are designed to
attenuate laser pulses within near-IR region. In contrast, relatively fewer efforts focus on
the molecular design toward nonlinear optical attenuation particularly in the visible range
due to the challenge of nonlinearity/transparency trade-off. Nevertheless, several organic
π-systems were explored and found to possess promising 2PA-based optical control of
nanosecond and femtosecond laser pulses in the visible regime.[36-38] In addition, it has
been experimentally shown that chromophores with branched π-frameworks could lead to
strong multi-photon absorption while retaining wide range of linear transparency[39, 40]
and this is a valuable general guideline to design effective broadband optical-limiters
based on 2PA. Following this motif of molecular design and our continuous efforts in
developing multi-branched and dendritic π-structures for multi-photon absorption,[25-29,
41] in this paper we present a series of newly synthesized model chromophores based on
functionalized tetrafluorenylethylene skeleton and the initial findings of their
two-photon-related as well as effective optical power-limiting properties across the visible

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and near-IR regions.
2
. Results and Discussions
.1 Model molecules and syntheses
2
The chemical structures and synthetic procedures for the targeted fluorophores (1-3) are
illustrated in Fig. 1 and Scheme 1, respectively. The backbones of these dye molecules are
conceptually based on the skeleton of tetraphenylethylene (TPE) but incorporate four
identical functionalized fluorene and indenofluorene moieties as the aryl arms extended
outward from the central ethylene unit. TPE-based molecules have been extensively
studied recently owing to their unique emission behaviors in various physical states as
well as their potential usage for fluorescent bio/chemosensors and electrochemical
switching devices.[42, 43] With the incorporation of beneficial structural units for the 2PA
promotion (i.e. functionalized fluorenyl and indenofluorenyl units) and retention of the
intrinsic non-coplanar nature of a TPE-type scaffold, we anticipate that these small
multi-branched dyes may serve as another test system for the optimization study of
nonlinearity/spectral transparency as well as exploration of their nonlinear absorption
behavior within visible to near-IR region. The syntheses of these chromophores are
relatively straightforward as outlined in Scheme 1, which mainly involve the preparation
of properly functionalized fluorenyl/indenofluorenyl boronic acids (7-9) as the major

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synthons to couple with the commercialized tetraiodoethene through Pd-catalyzed Suzuki
reaction protocol. Originally we did suspect that it would be difficult to attach four
comparatively bulky fluorenyl/indenofluorenyl units to a central ethylene core and either
low yield or incompletion of reaction due to such vicinal crowdedness may be
encountered but neither these situations was observed in our case and chromophores 1-3
were successfully obtained in acceptable average yield of ~40%. All the model
fluorophores are highly soluble in common organic solvents such as toluene, ethyl acetate,
dichloromethane (DCM), and tetrahydrofuran (THF). The detailed synthetic procedures
including the preparation of the key intermediates (7-9) and the final coupling reactions
toward these model structures are described in the Experimental section.
2.2 Optical properties characterization
2.2.1 Linear absorption and fluorescence properties
Fig. 2 presents the linear absorption and fluorescence spectra of compounds 1-3 in THF.
All these chromophores exhibit intense linear absorption in the UV-Vis region with the
5
−1 −1
lowest-energy peaks located at 325 nm for 1 (ε ~2.04×10 cm M ), 379 nm for 2 (ε
5
−1 −1
5
−1 −1
~
2.38×10 cm M ), and 402 nm for 3 (ε ~3.01×10 cm M ), respectively. It is noted
that the lowest-energy absorption bands are bathochromically shifted and the molar
absorption coefficients are increased monotonically when the molecular π-skeletons are
expanded from 1 to 3. Additionally, all these model compounds possess a wide window of

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linear transparency stretching over the visible and the near-IR spectral region, which
indicates that the originally expected structural crowdedness around the central ethylene
units should cause an interruption of the molecular π-conjugation to certain extent in these
dye molecules, rendering larger energy gaps between corresponding electronic
ground-states and excited-states. Therefore, the major absorption bands of these
chromophores are all located at the high-energy end of spectra. Such feature also implies
that these chromophores would manifest two-photon absorption within the visible region
and could be potential candidates for broadband optical-limiting and frequency
up-conversion applications particularly operated in the visible. These dye molecules also
emit strong visible fluorescence in their solution phase (in THF) under the irradiation of a
common UV-lamp with purple-blue color for 1 and cyan color for 2 and 3, which is in
agreement with the measured emission spectra (see the inset of Fig. 1). The combined
photophysical data of the studied model chromophores in solution phase are collected in
Table 1.
2.2.2 Two-photon-excited fluorescence (2PEF) properties
The studied model chromophores show observable two-photon-excited up-conversion
emission even under low power of excitation by an unfocused femtosecond laser beam at
an appropriate wavelength. Fig. 3(a) illustrates the 2PA-induced fluorescence spectra of
model chromophores 1-3. The sample solutions were freshly prepared at concentration of

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-4
1
×10 M in THF for this measurement. The excitation source utilized for this two-photon
induced fluorescence study is from a mode-locked Ti:Sapphire laser (Chameleon Ultra II,
Coherent) which delivers ~140 fs pulses with the repetition rate of 80 MHz and the beam
diameter of 2 mm. The intensity level of the excitation beam was carefully controlled to
avoid the saturation of absorption and photodegradation. Besides, the configuration of this
optical experiment was designed to ensure that only the emission from the front-surface of
the sample was recorded in order to minimize the re-absorption or inner-filter effect. It is
noted from Fig. 3(a) that for each model compound the shape and spectral position of the
measured 2PA-induced emission is virtually identical to its corresponding 1PA-induced
fluorescence band in Fig. 1, indicating that in our dye system the radiative relaxation
processes occurred within the studied samples are from the same final excited states
regardless of the excitation process.
The power-squared dependence of the 2PA-induced fluorescence intensity on the
excitation intensity of the studied fluorophores was also examined. Figs. 3(b)-(d) are
logarithmic plots of the measured data and the results (i.e. the fitting slope ≈ 2) validate
that 2PA is the major responsible process for the observed up-converted fluorescence
emissions in all cases.
2.2.3 Degenerate two-photon absorption spectra measurement
The 2PA spectra of the studied model chromophores was measured in the spectral range of

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680−1080 nm through degenerate two-photon-excited fluorescence (2PEF) technique
using the aforementioned femtosecond laser system as the excitation light source.[44, 45]
Fig. 4 shows the measured degenerate 2PA spectra of these three model compounds in
-4
THF (with the concentration of 1×10 M). As expected, the detected major 2PA bands of
all the studied compounds are close to the short-wavelength end of the investigated
spectral range. To be more specific, compound 1 exhibits a barely detectable 2PA band
with one local maxima located around 690 nm while compound 2 possesses a broader and
prominently enhanced 2PA band particularly around 710 nm in comparison to 1. This
feature implies that the incorporation of the electron-donating end-groups (i.e.
diphenylamino units) into this dye system has a salient and positive contribution on the
promotion of molecular 2PA. On the other hand, compound 3 manifests further elevated
overall molecular 2PA with two local maxima located around 690 nm and 750 nm, which
reveals that further extend the lengths of π-branches from fluorene units to indenofluorene
moieties will further increase the molecular 2PA in this model system.
Although the probing spectral range of their 2PA behavior is hampered by the dynamic
tuning range of our current Ti:sapphire laser system, it should be reasonable to anticipate
that the major 2PA bands of these model chromophores may locate within the visible
region (i.e. shorter than 680 nm) inferred from their hypsochromically positioned linear
absorption bands, which is a desirable feature for some specific applications utilizing

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two-photon technologies within the visible regime and further investigations on this aspect
are needed (vide infra).
3
. Photo-excitation efficiency spectra measurement using nanosecond laser
As mentioned in the preceding section, the studied fluorophores may exhibit appreciable
PA within the visible region and in order to gain further knowledge about the entire
2
dispersion of the up-converted emission behavior of these model compounds, we
tentatively utilize an integrated Q-switched Nd:YAG laser and OPO system (NT 342/3
from Ekspla) as the excitation light source to perform the photo-excitation experiment and
record the up-converted fluorescence intensity as a function of excitation wavelengths for
each model chromophore from 500 nm to 1000 nm. The pulse duration and the repetition
rate is ~5 ns and 10Hz, respectively in this experiment. In addition, the incident pulse
energy was controlled at 0.5 mJ for each probing wavelength to avoid any photo-damage
of the samples. The same optical configuration concern was also exercised to avoid
-3
re-absorption due to the relatively high concentration (2×10 M) of the sample solution
used in this measurement. The recorded fluorescence intensity was normalized by the
quantum yield of each model compound so that we can delineate and compare the
dispersion and the magnitude of relative excitation efficiency of these dye molecules
directly as illustrated in Fig. 5(a).

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It should be noted that using nanosecond laser pulses for the excitation of a sample with a
high concentration is generally thought to be extremely probable to distort the measured
fluorescence properties due to the combination of several effects including re-absorption,
nonlinear attenuation of the incident beam[46], and possible excited-state
absorption[47-48]. Nevertheless, we have determined the power-dependence of the
up-converted fluorescence intensity on the excitation intensity of each model
chromophore at some selected representative wavelengths in the visible region as shown
in Figs. 5(b)-(d) and the results (i.e. linear fitting slope ≈ 2) reveal that under our
experimental condition, the aforementioned effects may be negligible to some extent and
the measured up-converted emission is mainly caused by a two-photon-excitation process.
As we have originally conjectured, these chromophores possess higher 2PA-based
excitation efficiency in the visible compared to that in the near-IR region. Using
compound 1 as the parent structure, it is noted from the measured excitation efficiency
spectra that the attachment of electron-donating diphenylamino units to the structure of
compound 1 provides a salient leap in the increment of the excitation efficiency (as in the
case of compound 2) whereas further extension of the π-domain from compound 2 to
compound 3 offers a nearly two-fold of hyperchromic growth for the excitation efficiency
band and a broader spectral range coverage. This result implies that although both the
addition of electron-donating units and the extension of molecular π-framework are

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important structural alteration strategies to enhance the nonlinear excitation efficiency,
attaching electron-donor at appropriate site of the parent structure is found to be a
comparatively superior “booster” for the excitation efficiency promotion in this molecular
system.
4. Effective optical power-limiting properties
In this modern era, there is no doubt that lasers are ubiquitously used around us.
Laser-containing equipments such as CD/DVD players, barcode scanners, hand-held laser
pointers, laser ranging/alignment devices and laser line levels has become very common in
our daily life. On the other hand, the utilization of lasers for the medical purposes such as
cosmetic surgery, vision correction surgery as well as cancer diagnosis/treatment is
increasing[49] and all of these are due to the rapid advances of laser technology. While the
presence of lasers in “friendly” applications increases, the development of hostile usages
of lasers in weaponry for the military also keeps its pace and this has caused significant
threats to the eyesight of ground based military personnel, optical sensors, and aircraft
pilots.[50-53] Therefore, the need of effective countermeasure devices-“optical
power-limiters” to protect human eyes and optical sensors against laser-induced damage is
consequently escalating. Additionally, in the field of optical communication
power-limiting devices are also important for optical dynamic range compression and

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noise suppression in signal processing as well as nonlinear ultra-fast filtering/reshaping of
optical fiber signals. Ideally, an optical limiter is expected to show spectrally broad and
temporally agile response to the incident laser light. Various nonlinear optical mechanisms
have been employed to achieve optical-limiting and among them, two-photon absorption
(2PA) is theoretically considered as a potential process to approach the aforementioned
ideal characteristics for the optical control. The quadratic dependence of 2PA on the input
light intensity has made 2PA-materials applicable in optical-limiting applications because
such material is transparent to the incident light at low intensity but become opaque when
the input intensity levels up. Because of this optical control function stems from the
intrinsic physical property of the material, no external sensing and control mechanisms is
required to accomplish such optical suppression. Consequently, the response speed of a
2PA-based optical-limiter can be very fast and the structure of the device can be very
simple.
Since these model compounds are found to exhibit relatively strong photo-excitation
response based on 2PA within the visible range, they might as well manifest appreciable
nonlinear optical attenuation in the visible. In order to explore their effective spectral
range of nonlinear attenuation and/or power-suppression, we have utilized nanosecond
pulses as the probing tool to measure the nonlinear transmission spectra of these
choromophores in solution phase. In this experiment, the laser pulses were provided by the

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same nanosecond laser system used for the photo-excitation experiments and the pulse
energy was carefully controlled at ~1mJ to prevent any photo-bleaching or saturation
occurred during the experiment. The linear transmission spectrum of each studied sample
solution was also measured for the purpose of comparison. As illustrated in Figs. 6(a)-6(c),
compound 1 possesses a comparatively narrower attenuation band with a local minimum
nonlinear transmission of ~25% around 550 nm whereas both compounds 2 and 3
manifest broader response to the laser pulses across the spectral range of 580-850 nm and
exhibit very low nonlinear transmission (~20%) within a segment in the visible region.
These features may indicate that the studied model chromophores could be used as
potential optical-limiters working in the visible. It is noted that structural parameters such
as the presence of electron-donating units (i.e. diphenylamino groups) and the extension of
the π-framework (i.e. from 2 to 3) can effectively broaden the nonlinear attenuation range
of these dye molecules. From the viewpoint of applications, the obtained results suggest
that chromophores 2 and 3 may be feasible for the purpose of broadband optical-limiting
and compound 1 could act as a narrowband optical attenuator. The effective optical
power-limiting performance of the studied dye molecules are also tested at several
representative wavelengths where these compounds manifest distinguishable responses to
the laser pulses. One can see from Figs. 6(d)-6(f) that all these compounds display very
promising power restriction properties within the visible region as expected.

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5. Conclusions
In summary, a series of novel multi-branched chromophores based on the skeletal motif of
tetraarylethylene has been designed and synthesized via Pd-catalyzed Suzuki reaction
using tetraiodoethene and properly functionalized fluorenyl and indenfluorenyl boronic
acids as the primary synthons. Tentative structure-property analysis based on the initial
results from photo-excitation and nonlinear transmission experiments in the femtosecond
and nanosecond regime has indicated that the dispersion of nonlinear absorption activities
of these multi-polar fluorophores can be tuned by structural alteration such as attaching
electron-donating units at the peripheral positions and expanding the π-framework of the
molecule. It is also demonstrated that the studied model chromophores exhibit very
promising optical power suppression properties across a spectral segment of visible and
near-IR under the irradiation of nanosecond laser pulses and such structural motif may
suggest a new approach in molecular design to develop potential visible-to-near IR
broadband optical-limiters particularly working in the nanosecond time-domain.
6
. Experimental
.1 General
6
All commercially available reagents for the preparation of the intermediates and targeted
chromophores were purchased from Acros Organics or Alfa Aesar and were used as

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1
13
received, unless stated otherwise. H-NMR and C-NMR spectra were recorded on a 300
MHz spectrometer and referenced to TMS or the residual CHCl signal. MALDI-TOF MS
3
spectrum was obtained on a Voyager DE-PRO mass spectrometer (Applied Biosystem,
Houston, USA).
6.2 Photophysical methods
All the linear optical properties of the subject model compound were measured by
corresponding spectrometers and the detailed experimental conditions as well as the
optical set-ups for nonlinear optical property investigations are described in the
Supporting Information.
6.3 Synthesis
In Scheme 1, the compounds 4-6 are the major starting materials for the syntheses toward
studied model chromophores in this work. These aryl bromides were prepared through
established processes[54-56] and obtained in total yields of ~70% for 4, ~60% for 5, and
~55% for 6, respectively. Details of the synthetic procedures to prepare the corresponding
aryl boronic acids (7-9) and the targeted model compounds (1-3) are presented as the
following:
6.3.1
General procedure for the preparation of aryl boronic acids (7-9) in this work
To a solution of corresponding arylbromide (4-6; 1.0 equiv.) in dry THF (10mL) at -78 °C
was added n-butyllithium (in hexane, 1.6 M; 3.0 equiv.) under N atmosphere and stirred
2
at this temperature for 1hr. B(OMe) (3.0 equiv.) was then added slowly at -78 °C and the
3
resulting solution was stirred for another 1.5 hr without cooling bath before the addition of
6M HCl(aq) (10 mL). The acidified solution was continuously stirred at room temperature

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for overnight and then was extracted with ethyl acetate (20 mL×3). The combined organic
layer was collected and dried over MgSO4(S). After removing the solvent, the crude
product was purified through column chromatography on silica with properly combined
ethyl acetate and hexane as the eluent to give final purified product and was used for the
next step of synthesis directly.
6
9
2
.3.2
,9-Dihexyl-9H-fluoren-2-yl boronic acid (7)
,7-Dibromo-9,9-dihexyl-9H-fluorene (4, 3 g, 1.0 equiv.) , n-butyllithium (in hexane, 13.6
mL, 1.6 M; 3.0 equiv.), and B(OMe) (2.4 mL, 3.0 equiv) were used as the starting
3
materials for the preparation of this compound. Following the aforementioned standard
procedure (reaction time: 4 hours), the final product (colorless oil) was obtained in 72 % yield
after column chromatographic purification method on silica gel using ethyl acetate-hexane
(1:40) as the eluent.
6
7
7
.3.3
-(Diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl boronic acid (8)
-Bromo-9,9-dihexyl-N,N-diphenyl-9H-fluoren-2-amine (5,
5
g, 1.0 equiv.)
,
n-butyllithium (in hexane, 16.1 mL, 1.6 M; 3.0 equiv.), and B(OMe) (2.95 mL, 3.0 equiv)
3
were used as the starting materials for the preparation of this compound. Following the
aforementioned standard procedure (reaction time: 4 hours), the final product (colorless oil
)
was obtained in 75.5 % yield after column chromatographic purification method on silica gel
using ethyl acetate-hexane (1:20) as the eluent.
6.3.4
8-(Diphenylamino)-6,6,12,12-tetramethyl-6,12-dihydroindeno[1,2-b]fluoren-2-yl
boronic acid (9)
8
-Bromo-6,6,12,12-tetrahexyl-N,N-diphenyl-6,12-dihydroindeno[1,2-b]fluoren-2-amine (6,
.2 g, 1.0 equiv.) , n-butyllithium (in hexane, 4.92 mL, 1.6 M; 3.0 equiv.), and B(OMe)3
2
(
0.86 mL, 3.0 equiv) were used as the starting materials for the preparation of this compound.
Following the aforementioned standard procedure (reaction time: 4 hours), the final product
colorless oil) was obtained in 71.6 % yield after column chromatographic purification
method on silica gel using ethyl acetate-hexane (1:20) as the eluent.
(
6
.3.5
General synthetic procedure for Suzuki-coupling reaction (10-12) in this work
Aryl boronic acids (7-9; 4.6 equiv.), tetraiodoethene (1.0 equiv.), Pd(PPh (0.2 equiv.) in
dioxane: 2M Na CO (2:1) was added to a heavy-wall high pressure reaction tube
equipped with a magnetic stirrer and a rigid Teflon cap. The reaction mixture was heated
3)4
2
3
(aq)

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up to 110 °C under nitrogen atmosphere and kept at this temperature by means of an oil
bath or a heating mantle for 72 hours. After cooling to the room temperature, the reaction
mixture was then extracted with ethyl acetate (20 mL×3). The combined organic layer was
collected and dried over MgSO4(S). The crude product was purified by column
chromatography.
6.3.6
Compound 1
9
,9-Dihexyl-9H-fluoren-2-yl boronic acid (7, 1.7g, 4.6 equiv.) and tetraiodoethene (0.42g,
1
1.0 equiv.) were used as the starting materials for the preparation of this model compound.
H
Following the standard Suzuki-coupling procedure (reaction time: 72 hours), the final product
(
white powder) was obtained in 38 % yield after column chromatographic purification method
1
on silica gel using ethyl CH Cl -hexane (1:40) as the eluent. H-NMR (300MHz, CDCl ) δ:
2
2
3
7
1
1
1
.96~7.91 (m, 8H), 7.83~7.80 (m, 8H), 7.54-7.45 (m, 12H), 2.23-2.21 (d, J = 7.5Hz, 16H),
13
.25(s, 48H), 0.94 (t, J = 7.2Hz, 24H), 0.88 (m, 16H); C-NMR (75MHz, CDCl ) δ:
3
51.59, 151.12, 140.97, 140.71, 140.48, 128.90, 127.33, 127.15, 126.96, 126.23, 123.02,
21.55, 120.06, 119.89, 55.31, 40.58, 31.64, 29.88, 23.94, 22.74, 14.18; MALDI-TOF
+
(m/z): [M+H] calcd for C H , 1358.0408, found, 1358.0446.
102 133
6.3.7
Compound 2
-(Diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl boronic acid (8, 2g, 4.6 equiv.) and
7
tetraiodoethene (0.42g, 1.0 equiv.) were used as the starting materials for the preparation of
this model compound. Following the standard Suzuki-coupling procedure (reaction time: 72
hours), the final product (white powder) was obtained in 39.6 % yield after column
chromatographic purification method on silica gel using ethyl CH Cl -hexane (1:40) as the
2
2
1
eluent. H-NMR (300MHz, CDCl ) δ: 7.69-7.57 (m, 12H), 7.28-7.23 (m, 20H), 7.15-7.09
3
(
m, 20H), 7.05-6.98 (m, 12H), 1.98-1.86 (m, 16H), 1.82-0.77(m, 48H), 0.59 (t, J = 6.9Hz,
1
3
2
1
4H), 0.42 (m, 16H); C-NMR (75MHz, CDCl ) δ: 152.44, 152.42, 148.07, 147.09,
3
40.07, 139.80, 136.12, 129.32, 129.18, 126.00, 123.81, 123.66, 122.47, 121.16, 120.40,
1
19.54, 119.34, 55.20, 40.29, 31.53, 29.65, 23.83, 22.57, 14.07; MALDI-TOF (m/z):
+
[
M+H] calcd for C H N 2027.3347, found, 2027.3402.
150 169 4,
6.3.8
Compound 3
-(Diphenylamino)-6,6,12,12-tetramethyl-6,12-dihydroindeno[1,2-b]fluoren-2-yl boronic
8
acid (compound 9, 1g, 4.6 equiv.) and tetraiodoethene (0.14g, 1.0 equiv.) were used as the
starting materials for the preparation of this model compound. Following the standard
Suzuki-coupling procedure (reaction time: 72 hours), the final product (white powder) was

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obtained in 43.5 % yield after column chromatographic purification method on silica gel using
1
ethyl CH Cl -hexane (1:30) as the eluent. H-NMR (300MHz, CDCl ) δ: 7.82 (d, J = 7.8Hz,
2
2
3
8
1
1
1
H ), 7.68-7.55 (m, 20H), 7.28-7.22 (m, 16H), 7.15-6.98 (m, 32H), 2.10-1.93 (m, 32H),
13
.08(s, 96H), 0.78 (t, J = 6.6Hz, 24H), 0.73 (m, 16H); C-NMR (75MHz, CDCl ) δ:
3
52.62, 151.83, 150.46, 150.09, 148.09, 146.82, 140.73, 140.32, 140.11, 139.70, 136.97,
36.70, 129.16, 125.90, 123.90, 123.64, 122.35, 121.35, 120.08, 119.86, 119.49, 113.85,
1
13.45, 54.86, 54.79, 40.73, 40.57, 31.57, 29.74, 29.67, 23.80, 22.55, 14.05; MALDI-TOF
+
(m/z): [M+H] calcd for C H N 3053.7622, found, 3053.7710.
226 281 4,
Acknowledgements
We acknowledge the financial support from the Ministry of Science and Technology
MOST), Taiwan.
(

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Captions for Figures, Schemes, and Tables
Fig. 1 Chemical structures of the studied model chromophores.
Scheme 1. Synthetic procedures of the intermediates and the final chromophores.
Reagents and conditions: (a) Arylbromides (4-6; 1.0 equiv.), n-BuLi (3.0 equiv.),
B(OMe) (3.0 equiv.) in dry THF, -78˚C, 3h (yields: 72~75%); (b) Suzuki-coupling
3
process: arylborinic acides (7-9; 4.6 equiv.), tetraiodoethene (1.0 equiv.), Pd(PPh
equiv.) in mixed solvent system (dioxane: 2M Na CO ( = 2:1 (v/v)), 110˚C, 72h (yields:
8~41%).
3
)4 (0.2
2
3
aq)
3
Fig. 2 Linear absorption and fluorescence spectra (see the inset) of compounds 1-3 in
-6
solution phase (1×10 M in THF).
Fig. 3 (a) Normalized two-photon-excited emission spectra of fluorophores 1-3 in THF at
-
4
1
2
×10 M; (b)-(c) are the logarithmic plots of power-squared dependence of the
PA-induced fluorescence intensity on the input intensity of these compounds.
Fig. 4 Measured degenerate 2PA spectra of model chromophores 1-3 by 2PEF method in
-4
THF solution at 1×10 M (with experimental error ~15%).
Fig. 5 (a) Measured photo-excitation efficiency spectra of compounds 1-3 in THF solution
-3
at 2×10 M using nanosecond laser pulses as the probe; (b)-(d) power dependence of the
measured fluorescence intensity on the input intensity of compounds 1-3 probed by the
selected wavelengths in the visible. Inset photos, 2PA-based up-converted emission of 1-3
in THF solution excited by the corresponding visible light.
Fig. 6 (a)-(c) Linear and nonlinear transmission curves of compounds 1-3 in THF (0.02M;
light-path length = 1cm). The pulse energy was controlled at ~1 mJ for the nonlinear
transmission measurements; (d)-(f) power limiting performance of compounds 1-3 in THF
(0.02M; light-path length = 1cm) at several representative wavelengths.
Table 1. Photophysical properties of the studied model compounds 1-3 in solution phase.

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a
Table 1. Photophysical properties of the studied model compounds 1-3 in solution phase.
Abs c
1PA-FL
max
c
d
2PA
e
2P-Exc f
λmax
Compound λmax / nm logεmax
λ
/ nm
ΦF
δmax /GM
/ nm
1
2
3
325
379
402
5.31
5.38
5.48
363
425
441
0.86
0.83
0.74
~1.6 (at 690 nm)
~350 (at 710 nm)
~1200 (at 690 nm)
~540
~620, ~680
~640, ~680, 740
a
b
c
All photophysical data were obtain in THF solution. Linear absorption maxima. Spectral positions
d
of one-photon-absorption-induced fluorescence (1PA-FL) emission maxima. Fluorescence quantum
e
yield. Local 2PA maximal values measured by femtosecond pulses based on two-photon-excited
-50
4
f
fluorescence technique; 1GM = 1
× 10 cm s/photon-molecule. The spectral position of local
maxima of the photo-excitation efficiency spectra probed by nanosecond pulses.

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Scheme 1. Synthetic procedures of the intermediates and the final chromophores.
Reagents and conditions: (a) Arylbromides (4-6; 1.0 equiv.), n-BuLi (3.0 equiv.),
B(OMe) (3.0 equiv.) in dry THF, -78˚C, 3h (yields: 72~75%); (b) Suzuki-coupling
3
process: arylborinic acides (7-9; 4.6 equiv.), tetraiodoethene (1.0 equiv.), Pd(PPh
equiv.) in mixed solvent system (dioxane: 2M Na CO ( = 2:1 (v/v)), 110˚C, 72h (yields:
8~41%).
3
)4 (0.2
2
3
aq)
3

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C
6
H
13
C
6
H
13
13
C H
C H
6
6
13
13
C H
C H
6
6
13
13
C H
C H
6
13
6
1
N
N
C H
C H
6
6
13
13
13
C H
C H
6
6
13
13
C H
6
13
C H
6
13
C
6
H
13
C
6
H
N
N
2
N
N
C H
6 13
C H
6
13
C H
C H
6 13
6
13
C H
C H
6
6
13
13
13
C H
C H
6
13
6
13
C H
6
13
C
6
H
13
C H
C H
6
6
13
C H
C H
6 13
6
13
C H
C H
6 13
6
13
N
N
3
Fig. 1 Chemical structures of the studied model chromophores.

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3.0
2.5
2.0
1.5
1.0
0.5
0.0
1
2
3
6
6
6
5
5
5
5
1
1
1
8
6
4
2
.4x10
.2x10
.0x10
.0x10
.0x10
.0x10
.0x10
0
.0
400
450
500
550
600
650
Wavelength (nm)
300 400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
Fig. 2 Linear absorption and fluorescence spectra (see the inset) of compounds 1-3 in
-6
solution phase (1×10 M in THF).

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4
.6
(a)
(b)
4
.5
.4
4.3
.2
.1
.0
.9
3
2
1
0
Compound 1
4
λexc = 690 nm
4
4
4
Slope = 1.83
1.6 1.7 1.8
3
1
.5
.0 (c)
.8
.6
.4
.2
.0
6
Compound 2
5
λexc = 710 nm
5
5
5
Slope = 2.02
5
1
.5 1.6 1.7 1.8 1.9 2.0
5
.6
.4
.2
.0
.8
.6
Compound 3
(d)
5
λexc = 690 nm
5
5
4
Slope = 2.08
.5 1.6 1.7 1.8 1.9 2.0
4
1
350
400
450
500
550
600
Log(Input Intensity)/a.u.
Wavelength (nm)
Fig. 3 (a) Normalized two-photon-excited emission spectra of fluorophores 1-3 in THF at
-
4
1
2
×10 M; (b)-(d) are the logarithmic plots of power-squared dependence of the
PA-induced fluorescence intensity on the input intensity of these compounds.