Highly efficient multiphoton-absorbing quadrupolar oligomers for frequency upconversion

Article abstract of DOI:10.1002/chem.201002227

Two series of quadrupolar diphenylamino-endcapped oligofluorenes, PhN-OF(n)-NPh (n=2-5) and PhN-OF(n)-TAZ-OF(n)-NPh (n=1-4), which have an electron-withdrawing 1,2,4-triazole (TAZ) moiety as central core, with D-π-A-π-D structural motif (D=donor, A=accept

Full text of DOI:10.1002/chem.201002227

DOI: 10.1002/chem.201002227
Highly Efficient Multiphoton-Absorbing Quadrupolar Oligomers for
Frequency Upconversion
Xin Jiang Feng,[a] Po Lam Wu,[b] King Fai Li,[b] Man Shing Wong,*[a] and
Kok Wai Cheah*[b]
Abstract: Two series of quadrupolar di-
phenylamino-endcapped oligofluor-
luminescence. These D–p–D and D–p–
A–p–D quadrupolar oligofluorenes ex-
hibit superior three-photon absorption
properties compared to the respective
D–p–A counterparts with a highest
three-photon absorption cross-section
(s3) of up to 2.72ꢀ10ꢀ77 cm6 s2. Despite
the comparable linear and multiphoton
absorption properties of the two types
of quadrupolar oligomers PhN-OF(n)-
NPh and PhN-OF(n)-TAZ-OF(n)-
NPh, only the former exhibit remarka-
bly intense and highly efficient multi-
photon-excited frequency-upconverted
deep blue lasing, which gives rise to
record high lasing efficiency of 0.097%
and very narrow of full width at half-
maximum of the lasing spectra. Our
findings suggest that quadrupolar-type
molecules/oligomers are superior for
multiphoton excited frequency upcon-
verted lasing to their dipolar counter-
parts and also provide important guide-
lines to design highly efficient three-
photon absorption molecules for pho-
toluminescence and lasing applications.
enes, PhN-OF(n)-NPh (n=2–5) and
PhN-OF(n)-TAZ-OF(n)-NPh (n=1–
4), which have an electron-withdrawing
1,2,4-triazole (TAZ) moiety as central
core, with D–p–A–p–D structural
motif (D=donor, A=acceptor), have
been synthesized by palladium-cata-
lyzed Suzuki cross-coupling of 9,9-dibu-
tyl-7-(diphenylamino)-2-fluorenylbor-
onic acid and the corresponding (1,2,4-
triazole-based) aryl halide as key step.
On pumping with infrared femtosecond
lasers, these oligomers showed very
strong multiphoton-excited blue photo-
Keywords: laser chemistry · multi-
photon absorption · nonlinear op-
tics · oligofluorenes · photolumines-
cence
Introduction
photon-excited frequency-upconverted lasing,[5] which can
be easily achieved in liquids, films, or optical fibers without
stringent phase-matching requirements. The short lasing
wavelengths will offer new advantages and breakthroughs in
various laser-based applications. In addition, multiphoton-
excited lasing in dye-based systems provides the advantage
of tunable lasing wavelength, which is guaranteed by a rela-
tively broad spectral range of fluorescence emission of dye
materials.[6]
To exhibit MPA upconverted lasing, molecules are re-
quired to have high fluorescence quantum efficiency, a large
MPA cross section, a large Stokes shift, which could affect
the lasing threshold and the attainment of optical gain, as
well as high photochemical and thermal stability. Hence, it
is not guaranteed that the best MPA material can be used
for multiphoton pumped lasing. As a result, there are only a
few reported MPA molecules that can be used for multipho-
ton pumped lasing, and there are still no molecular-structur-
al guidelines that can assist to judge the MPA lasing capabil-
ity of a fluorophore. The common features of most reported
MPA-pumped lasing dyes are derived from donor–acceptor
p-conjugated chromophores such as stilbazolium salts.[7]
In the past decade, there was remarkable success in devel-
oping highly active two-photon-absorption chromophores;
however, there were far fewer studies on the structure–prop-
erty relationships for three-photon absorption.[8] We recently
demonstrated efficient multiphoton-excited frequency-up-
converted photoluminescence and lasing in a series of
Nonlinear optical materials that exhibit efficient multipho-
ton absorption (MPA) have drawn tremendous attention in
the past decades, as they show great potential in various
emerging technological applications, which include two-
photon excited fluorescence (TPEF) imaging and microsco-
py,[1] two-photon optical power limiting, three-dimensional
optical data storage,[2] two-photon photodynamic therapy,[3]
and two-photon microfabrication.[4] Another attractive ap-
plication of multiphoton absorption is fabricating low-cost
high-energy coherent light sources in the short-wavelength
region, such as deep blue and ultraviolet, by means of multi-
[a] X. J. Feng, Prof. M. S. Wong
Department of Chemistry and
Centre for Advanced Luminescence Materials
Hong Kong Baptist University
Kowloon Tong, Hong Kong SAR (P. R. China)
Fax : (+852)34117348
E-mail: mswong@hkbu.edu.hk
[b] P. L. Wu, Dr. K. F. Li, Prof. K. W. Cheah
Department of Physics and
Centre for Advanced Luminescence Materials
Hong Kong Baptist University
Kowloon Tong, Hong Kong SAR (P. R. China)
Fax : (+852)34115813
E-mail: kwcheah@hkbu.edu.hk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002227.
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FULL PAPER
donor–acceptor oligomers endcapped with diphenylamino
and 1,2,4-triazole groups, in which the multiphoton-excited
emission properties and upconversion lasing properties can
easily be modified/tuned by using various fluorene-based p-
conjugated cores.[9]
7-(diphenylamino)-2-fluorenylboronic acid (4) with Pd-
ACHUTNGREN(NUG OAc)2/2PACHUTGNTREN(NUNG o-tolyl)3 as catalyst afforded PhN-OF(1)-TAZ-
OF(1)-NPh in good yield. On the other hand, Suzuki cross-
coupling of dibromide 3 and 7-(trimethylsilyl)-2-fluorenyl-
boronic acid (5) afforded difluorene-substituted 1,2,4-tria-
zole derivative 6 in 74% yield. Iododesilylation of 6 was car-
ried out in the presence of silver trifluoroacetate at 808C af-
fording the corresponding diiodide 7 in excellent yield.
Double Suzuki cross-coupling of diiodide 7 and boronic acid
4 gave the desired PhN-OF(2)-TAZ-OF(2)-NPh in 81%
yield. The same reaction sequence was applied to further
extend the oligofluorenyl units: cross-coupling with 7-(tri-
methylsilyl)-2-fluorenylboronic acid, iododesilylation, and
cross-coupling with 9,9-dibutyl-7-(diphenylamino)-2-fluore-
nylboronic acid gave the higher homologues PhN-OF(3)-
TAZ-OF(3)-NPh and PhN-OF(4)-TAZ-OF(4)-NPh in good
yield (Scheme 1). The corresponding series of diphenylami-
no-endcapped oligofluorenes, PhN-OF(n)-NPh, was synthe-
sized according to the previously published procedures. The
new oligofluorenes were fully characterized by 1H and
13C NMR spectroscopy, MALDI-TOF MS, and elemental
analysis, which were found to be in good agreement with
their proposed structures. All oligofluorenes are highly solu-
ble in common organic sol-
To continue investigating the structural factors that can
enhance multiphoton-absorption responses, particularly
three-photon absorption, and exploring their potential for
applications, we report herein our systematic investigation
on multiphoton absorption properties of two series of quad-
rupolar-type oligofluorenes with D–p–D and D–p–A–p–D
structural motifs, which have been shown to exhibit superior
multiphoton-excited photoluminescence and blue lasing
properties compared to the respective D–p–A type dipolar
oligofluorenes. In contrast to two-photon absorption proper-
ties, incorporation of a 1,2,4-triazole electron-accepting cen-
tral core into the D–p–D type oligofluorenes does not en-
hance the three-photon absorption properties. Despite the
comparable linear and three-photon absorption properties
of the two quadrupolar series PhN-OF(n)-NPh and PhN-
OF(n)-TAZ-OF(n)-NPh, only PhN-OF(n)-NPh exhibit re-
markably strong MPA-excited frequency upconverted lasing
with record high blue lasing efficiency of 0.097%.
vents; PhN-OF(n)-TAZ-OF(n)-
NPh show high thermal stabili-
ties with decomposition temper-
atures greater than 4488C.
As shown by the absorption
spectra, these two series exhibit
similar absorption characteris-
tics, mainly composed of two
absorption bands: the n!p*
Results and Discussion
transition of triaryl amine moi-
eties and the p!p* transition of the oligomeric cores. Incor-
poration of a 1,2,4-triazole (TAZ) electron-withdrawing
group into the p-conjugated framework of PhN-OF(n)-NPh
as central core enhances the molar absorptivity but slightly
shifts (ca. 8 nm) the absorption spectra to shorter wave-
lengths. (Figure 1 and Table 1) On the other hand, both
series show almost identical blue photoluminescence spectra
Synthesis of the symmetrically diphenylamino disubstituted
oligofluorenes containing 1,2,4-triazole as central core,
namely, PhN-OF(n)-TAZ-OF(n)-NPh, is outlined in
Scheme 1. Double palladium-catalyzed Suzuki cross-cou-
pling of 9,9-dibutyl-7-(diphenylamino)-2-fluorenylboronic
acid[10] and 1,2,4,-triazole-based diaryl dibromides was used
as a key step to synthesize the
Table 1. Summary of linear optical, three photon absorption and thermal properties of PhN-OF(n)-NPh and
PhN-OF(n)-TAZ-OF(n)-NPh.
backbone of the oligofluorenes.
4-Bromobenzoyl chloride,
em [a, b]
max
[f]
[g]
lmax[a] [nm]
l
F[c]
3PA PL
peak[d]
[nm]
s3,max
[cm6 s2]
Tdecomp
[8C]
freshly prepared from 4-bromo-
benzoic acid (1) was treated
with anhydrous hydrazine in
the presence of triethylamine in
THF at room temperature to
afford disubstituted hydrazine 2
in 68% yield. Condensation of
2 with aniline in the presence
of POCl3 at 2008C afforded
(e [104 mꢀ1 cmꢀ1
]
[nm]
N
PhN-OF(2)-NPh
PhN-OF(3)-NPh
PhN-OF(4)-NPh
PhN-OF(5)-NPh
PhN-OF(1)-TAZ-OF(1)-NPh
PhN-OF(2)-TAZ-OF(2)-NPh
PhN-OF(3)-TAZ-OF(3)-NPh
PhN-OF(4)-TAZ-OF(4)-NPh
382 (8.04)
417
423
422
420
421
423
422
421
0.95
0.99
0.97
0.94
0.88
0.87
0.88
0.91
443
451
452
454
450
448
451
439[e]
1.50ꢀ10ꢀ77
1.20ꢀ10ꢀ77
2.35ꢀ10ꢀ77
2.21ꢀ10ꢀ77
1.01ꢀ10ꢀ77
2.28ꢀ10ꢀ77
2.61ꢀ10ꢀ77
2.72ꢀ10ꢀ77
385 (11.75)
385 (14.29)
385 (18.19)
377 (10.72)
378 (16.67)
377 (24.10)
376 (28.03)
485
451
451
448
1,2,4-triazole derivative
3 in
[a] Measured in toluene. [b] Excited at the absorption maximum. [c] With quinine sulfate monohydrate (F350
=
73% yield. Double palladium-
catalyzed Suzuki cross-coupling
0.58) as standard. [d] Measured in 0.02m toluene solution. [e] Measured in 0.002m toluene solution. [f] Deter-
mined by the relative method. [g] Determined by thermal gravimetric analysis with a heating rate of
of dibromide 3 and 9,9-dibutyl- 208Cminꢀ1 under N2.
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M. S. Wong, K. W. Cheah et al.
Scheme 1. Synthesis of PhN-OF(n)-TAZ-OF(n)-NPh (n=1–4).
peaking at about 422 nm upon excitation at the absorption
maximum (Figure 2) and very large fluorescence quantum
yields in toluene in the range of 87–91% for the PhN-
OF(n)-TAZ-OF(n)-NPh series and 94–99% for the PhN-
OF(n)-NPh series. In contrast to PhN-OF(n)-NPh, PhN-
OF(n)-TAZ-OF(n)-NPh show
a strong solvatochromic
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Quadrupolar Oligomers for Frequency Upconversion
FULL PAPER
Figure 2. Emission spectra of a) PhN-OF(n)-TAZ-OF(n)-NPh and
b) PhN-OF(n)-NPh in toluene
Figure 1. Absorption spectra of a) PhN-OF(n)-TAZ-OF(n)-NPh and
b) PhN-OF(n)-NPh in toluene.
sharp contrast to the typical trend often found in the two-
photon absorption properties. For both the series, the 3PA
cross sections initially increase with increasing chain length
and then show a tendency for saturation up to four fluorenyl
units. The cubic power dependence of 3PA fluorescence for
PhN-OF(n)-NPh (Figure 4) and PhN-OF(n)-TAZ-OF(n)-
NPh at 1.3 mm has a gradient in the range of 2.91–3.22, pro-
viding direct experimental evidence of a three-photon exci-
tation process. Figure 5 shows the three-photon-excitation
spectra of PhN-OF(n)-NPh and PhN-OF(n)-TAZ-OF(n)-
NPh measured by comparing the fluorescence intensity ex-
cited from 1100 to 1600 nm with that of the respective mole-
cule excited at 1.3 mm. As seen from the excitation spectra,
the maximum 3PA cross section occurs at about 1270 nm for
all oligomers and gives rise to the highest s3 of 2.72ꢀ
10ꢀ77 cm6 s2 for PhN-OF(4)-TAZ-OF(4)-NPh.
Upon pumping with femtosecond laser pulses at 800 nm,
all PhN-OF(n)-NPh exhibit intense two-photon upconverted
deep blue lasing peaking at 445–449 nm. The two-photon-
excited lasing spectra of all these homologous oligofluorenes
are almost identical, and the full width at half-maximum
(FWHM) of the lasing spectra are sharply narrowed relative
to the corresponding PL spectra (Figure 6). Figure 7 shows a
effect in the emission spectra in which the emission peak ex-
hibits a large redshift (67 nm) in polar solvents, suggesting a
dipolar or charge-transfer character in the excited state
(Figure 3).
The multiphoton absorption photoluminescence and
lasing properties were investigated by using a femtosecond
pulsed laser as an excitation source (Table 1). In spite of the
moderate two-photon absorption properties,[11] PhN-OF(n)-
NPh show strong three-photon excited photoluminescence
with a small redshift of the emission spectra due to a re-ab-
sorption effect. Remarkably, these oligomers exhibit large
three-photon absorption (3PA) cross sections in the range of
8.31ꢀ10ꢀ78 to 1.51ꢀ10ꢀ77 cm6 s2, as measured by the open-
aperture Z-scan technique at 1.3 mm, which are much larger
than those of dipolar diphenylamino- and 1,2,4-triazole-end-
capped oligofluorenes.[9] On the other hand, the incorpora-
tion of a TAZ moiety into the PhN-OF(n)-NPh system as a
central electron-withdrawing core, giving a D–p–A–p–D
structural motif, does not significantly affect/modify the 3PA
cross section of the resulting oligomers PhN-OF(n)-TAZ-
OF(n)-NPh, for which 3PA cross sections are in the range of
5.44ꢀ10ꢀ78 to 1.93ꢀ10ꢀ77 cm6 s2 at 1.3 mm. This finding is in
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M. S. Wong, K. W. Cheah et al.
with femtosecond laser pulses at 1.34 mm (Figure 8). The
three-photon-excited lasing spectra are nearly identical to
those of two-photon-excited lasing spectra with very narrow
FWHM and peak at around 447 nm indicating that the same
emissive state is involved. A plot of output versus input
power for PhN-OF(3)-NPh and PhN-OF(4)-NPh (Figure 9)
clearly indicates lasing threshold behavior. Compared to the
slopes in Figure 7, the slopes in Figure 9 appear to be gentle,
which is attributed to the intrinsically smaller 3PA cross sec-
tion, which results in weaker induced fluorescence and
hence smaller gain. The three-photon-excited lasing efficien-
cy also increases initially with increasing conjugation length,
up to 0.063% for PhN-OF(4)-NPh, and then decreases for
higher homologues. However, despite comparable linear
and nonlinear optical responses, PhN-OF(n)-TAZ-OF(n)-
NPh show no lasing behavior under the same experimental
conditions.
Conclusion
We have synthesized two series of quadrupolar diphenylami-
no-endcapped oligofluorenes, PhN-OF(n)-NPh (n=2–5)
and PhN-OF(n)-TAZ-OF(n)-NPh (n=1–4), which have an
electron-withdrawing 1,2,4-triazole moiety as central core,
with D–p–A–p–D structural motif, using palladium-cata-
lyzed Suzuki cross-coupling of 9,9-dibutyl-7-(diphenyla-
mino)-2-fluorenylboronic acid and the corresponding (1,2,4,-
triazole-based) aryl halide as key step. Despite exhibiting
saturation behavior of absorption and emission properties/
maxima, both series of oligofluorenes show an increase in
three-photon absorption cross-sections with increasing chain
length and reach a saturation limit at four fluorenyl units.
These D–p–D and D–p–A–p–D quadrupolar oligofluorenes
exhibit superior three-photon absorption properties com-
pared to the respective D–p–A counterparts, with a highest
three-photon absorption cross section (s3) of up to 2.72ꢀ
10ꢀ77 cm6 s2. In contrast to two-photon absorption properties,
incorporation of a 1,2,4-triazole electron-accepting central
core into the D–p–D type oligofluorenes does not enhance
the 3PA properties. Despite the comparable linear and mul-
tiphoton absorption properties of PhN-OF(n)-NPh and
PhN-OF(n)-TAZ-OF(n)-NPh quadrupolar oligomers, only
PhN-OF(n)-NPhs exhibit remarkably strong MPA excited
frequency upconverted lasing, which also achieves a record
blue lasing efficiency of 0.097%. Our findings suggest for
the first time that quadrupolar-type molecules/oligomers are
superior for multiphoton-excit-
Figure 3. Solvent effect of a) PhN-OF(1)-TAZ-OF(1)-NPh and b) PhN-
OF(2)-NPh.
plot of output versus input power for PhN-OF(n)-NPh (n=
2–5), which unambiguously shows evidence of lasing thresh-
old behavior. The decreasing lasing threshold with increas-
ing conjugation length of these oligofluorenes demonstrates
the merits of using higher homologues. Remarkably, the
lasing efficiency is also greatly enhanced with increasing
conjugation length, up to 0.097%, which is the highest value
for multiphoton-excited deep blue lasing reported so far
even though the excitation at the most easily accessible
800 nm is not optimized for the two-photon absorption pro-
cess in this series[11] (Table 2).
Consistently, all PhN-OF(n)-NPh exhibit prominent
three-photon upconverted deep blue lasing upon pumping
ed
frequency-upconverted
Table 2. Summary of two- and three-photon-excited lasing properties of PhN-OF(n)-NPh in toluene.
lasing compared to their dipolar
counterparts and also provide
important guidelines to design
highly efficient 3PA molecules
for photoluminescence and
lasing.
2PA lasing
peak
[nm]
FWHM
[nm]
Lasing
efficiency[a]
[%]
3PA lasing
peak
[nm]
FWHM
[nm]
Lasing
efficiency[b]
[%]
PhN-OF(2)-NPh
PhN-OF(3)-NPh
PhN-OF(4)-NPh
PhN-OF(5)-NPh
445
449
445
449
5.8
6.1
6.3
6.0
0.0245
0.0619
0.0856
0.0967
447
446
448
448
5.3
3.9
6.3
5.3
0.0295
0.0624
0.0627
0.0190
[a] Pumped at 800 nm. [b] Pumped at 1.34 mm.
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Quadrupolar Oligomers for Frequency Upconversion
FULL PAPER
Figure 4. Logarithmic plots of the power dependence of relative three-photon-induced fluorescence on pulse intensity with a femtosecond infrared laser
as an exciting source at 1.3 mm for PhN-OF(n)-TAZ-OF(n)-NPh (n=1–4). The solid line represents the best-fit straight line of all the data points.
chloroform was heated to reflux and stirred for 4 h. The solvent and
excess reagents were removed under vacuum. Dry toluene (20 mL) was
Experimental Section
added and then evaporated under vacuum. The light yellow oil was dis-
solved in dry THF and the solution added dropwise to a solution of hy-
Photoluminescence (PL) and cavityless upconversion lasing experiments
were performed on 2ꢀ10ꢀ2 m solutions of oligofluorenes in toluene in
drazine (0.16 mL, 3.4 mmol) and triethylamine (2.10 g, 20.8 mmol) in
quartz cuvettes. In the cavityless upconversion lasing experiment, the
THF cooled in an ice/water bath. The reaction mixture was allowed to
pump source was an Optical Parametric Amplifier (Topas, Coherent)
warm to room temperature and stirred overnight. Potassium carbonate
pumped by self-mode-locked Ti:sapphire laser with Spitfire Regenerative
solution was added to the reaction mixture. The resulting suspension was
Amplifier (Spectra Physics-Tsunami; 800 nm, pulse width 100 fs, repeti-
stirred for 2 h and then filtered. The collected solid was washed with
tion rate 1 kHz). The laser passed through a polarizer, focusing lens
(focal distance 100 mm), and IR filter (Hot Filter), used to block 800 nm
light. The incident laser was focused at the center of oligofluorene solu-
tion in the cuvette (1 cm in length). A second lens focused the transmit-
ted signal into the spectrometer (Ocean Optics, USB4000). The laser
powers at each wavelength were calibrated and monitored throughout
water and dried under vacuum, affording 1.36 g of 2 as a white solid in
68% yield. 1H NMR (400 MHz, [D6]DMSO): d=10.64 (s, 2H), 7.85 (d,
J=8.0 Hz, 4H), 7.75 ppm (d, J=8.0 Hz, 4H); 13C NMR (100 MHz,
[D6]DMSO): d=165.0, 131.7, 131.5, 129.6, 125.8 ppm; MS (FAB): m/z:
396.1 [M+].
the measurements. The beam size of the incident laser was about 1 mm.
The focal length of the lens was 100 mm. The minimum spot size of the
pump laser was 0.166 mm, and its Rayleigh length was calculated to be
2.48 cm. So the maximum peak power at spot area was less than
232 GWcmꢀ2. The same laser system was used for PL experiments. For
both PL and lasing excitation, the 800 nm laser line directly from the
Spitfire Regenerative Amplifier was used, and for lasing the threshold
pumping power was 6 mW. For three-photon upconversion excitation,
laser lines from an optical parametric amplifier pumped by the Spitfire
Regenerative Amplifier were used so that the laser wavelength could be
tuned for optimum excitation.
4-Phenyl-3,5-bis(4-bromophenyl)-1,2,4-triazole (3): POCl3 (4.3 mL,
46.3 mmol) was added slowly to a solution of aniline (12.94 g, 139 mmol)
in 120 mL of 1,2-dichlorobenzene with cooling in an ice/water bath. After
complete addition, the resulting mixture was allowed to warm to room
temperature and then 2 was added (9.22 g, 23.2 mmol). After refluxing
under nitrogen for 5 h, the reaction mixture was cooled to room tempera-
ture and washed with water. The organic layer was dried over anhydrous
Na2SO4 and purified by silica-gel column chromatography with 8:1 di-
chloromethane:ethyl acetate as eluent affording 7.69 g (73%) of a white
solid. 1H NMR (400 MHz, CDCl3): d=7.51–7.40 (m, 7H), 7.26 (d, J=
8.0 Hz, 4H), 7.13 ppm (d, J=8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d=154.0, 134.7, 131.7, 130.3, 130.1, 130.0, 127.6, 125.6, 124.0 ppm; MS
(FAB): m/z: 453.3 [M+].
N,N’-Bis(4-bromobenzyl)hydrazide (2): A solution of 4-bromobenzoic
acid (1, 1.37 g, 6.9 mmol) and thionyl chloride (2.49 mL, 34.3 mmol) in
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M. S. Wong, K. W. Cheah et al.
Figure 5. Three-photon excitation spectra of a) PhN-OF(n)-TAZ-OF(n)-
NPh and b) PhN-OF(n)-NPh measured in toluene from 1100 to 1600 nm.
Figure 6. Two-photon upconversion photoluminescence and lasing spectra
of PhN-OF(n)-NPh (n=4, 5) pumped at 800 nm.
4-N-Phenyl-3,5-bis{4-[9’,9’-di-n-butyl-7’-(diphenylamino)-2’-fluorenyl]-
phenyl}-1,2,4-triazole (PhN-OF(1)-TAZ-OF(1)-NPh):
(228 mg, 0.50 mmol), (979 mg, 2.00 mmol), Pd
0.04 mmol), P(o-tolyl)3 (27 mg, 0.09 mmol), 2m K2CO3 (3 mL), toluene
A
mixture of
3
4
ACHTUNGRTENUN(NG OAc)2 (10 mg,
ACHTUNGTRENNUNG
(25 mL), and methanol (10 mL) under nitrogen atmosphere was heated
at 758C overnight with magnetic stirring. After cooling to room tempera-
ture, the reaction mixture was poured into water and extracted with ethyl
acetate (35 mL), followed by dichloromethane (40 mL). The combined
organic layers were dried over anhydrous Na2SO4, evaporated to dryness,
and the residue was purified by silica-gel column chromatography with
20:1 dichloromethane:ethyl acetate as eluent affording 288 mg (74%) of
1
a light yellow solid. H NMR (400 MHz, CDCl3): d=7.64–7.48 (m, 19H),
7.21–7.28 (m, 10H), 7.12 (m, 10H), 7.03–6.98 (m, 6H), 1.92–1.83 (m,
8H), 1.09–1.01 (m, 8H), 0.60–0.70 ppm (m, 20H); 13C NMR (100 MHz,
CDCl3): d=154.6, 152.3, 151.3, 147.8, 147.3, 142.6, 140.8, 137.8, 135.5,
135.4, 130.1, 129.7, 129.1, 129.0, 127.9, 126.9, 125.9, 125.3, 123.8, 123.3,
122.5, 120.9, 120.4, 119.3, 119.1, 55.0, 40.0, 25.9, 22.9, 13.8 ppm; HRMS
(MALDI-TOF): m/z: 1183.6450 [M+]; elemental analysis (%) calcd for
C86H81N5: C 87.20, H 6.89, N 5.91; found: C 87.16, H 6.82, N 5.81.
Figure 7. Plot of output power versus input power of the two-photon
pumped lasing process for PhN-OF(n)-NP (n=2–5).
4-N-Phenyl-3,5-bis{4-[9’,9’-di-n-butyl-7’-trimethylsilyl-2’-fluorenyl]phen-
yl}-1,2,4-triazole (6): The synthetic procedure for PhN-OF(1)-TAZ-
OF(1)-NPh was followed using 3 (178 mg, 0.39 mmol), 9,9-di-n-butyl-7-
(trimethylsilyl)-2-fluorenylboronic acid (4, 456 mg, 1.17 mmol), Pd
(OAc)2
7.60 (d, J=8.4 Hz, 4H), 7.45–7.54 (m, 15H), 7.27 (dd, J=8.0 Hz, 1.2 Hz,
2H), 2.02–1.93 (m, 8H), 1.08–1.01 (m, 8H), 0.67–0.58 (m, 20H), 0.30 ppm
(s, 18H); 13C NMR (100 MHz, CDCl3): d=154.6, 151.6, 150.0, 142.6,
141.1, 140.9, 139.3, 138.7, 135.4, 131.8, 130.1, 129.7, 129.0, 127.9, 127.5,
126.9, 125.8, 125.4, 121.2, 120.0, 119.0, 54.9, 39.9, 25.9, 22.9, 13.7,
ꢀ0.9 ppm; MS (FAB): m/z: 993.7 [M+].
(8.6 mg, 0.04 mmol), P(o-tolyl)3 (24 mg, 0.08 mmol), 2m K2CO3 (3 mL),
ACHTUNGTRENNUNG
toluene (20 mL), and methanol (8 mL). The residue was purified by
silica-gel column chromatography with 20:1 dichloromethane:ethyl ace-
tate as eluent affording 389 mg (74%) of 6 as a white solid. 1H NMR
(400 MHz, CDCl3): d=7.73 (d, J=8.0 Hz, 2H), 7.67 (d, J=7.6 Hz, 2H),
2524
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 2518 – 2526

Quadrupolar Oligomers for Frequency Upconversion
FULL PAPER
Figure 9. Plot of output power versus input power of the three-photon
pumped lasing process for PhN-OF(3)-NPh (a) and PhN-OF(4)-NPh (b).
Figure 8. Three-photon upconversion photoluminescence and lasing spec-
tra of PhN-OF(n)-NPh (n=2, 3) pumped at 1.34 mm.
25H), 7.32–7.23 (m, 10H), 7.15–7.13 (m, 10H), 7.06–6.99 (m, 6H), 2.08–
1.89 (m, 16H), 1.16–1.06 (m, 16H), 0.77–0.68 ppm (m, 40H); 13C NMR
(100 MHz, CDCl3): d=154.6, 152.3, 151.7, 151.7, 151.4, 147.9, 147.1,
142.7, 140.7, 140.6, 140.2, 139.6, 139.4, 138.6, 135.8, 135.4, 130.1, 129.7,
129.1, 129.0, 128.0, 127.0, 126.0, 126.0, 125.4, 123.8, 123.4, 122.4, 121.2,
121.1, 120.3, 120.0, 119.3, 55.2, 55.0, 40.2, 39.9, 26.0, 26.0, 23.0, 23.0, 13.8,
13.8 ppm; HRMS (MALDI-TOF): m/z: 1737.0271 [M+]; elemental anal-
ysis (%) calcd for C128H129N5: C 88.49, H 7.48, N 4.03; found: C 88.35, H
7.33, N 3.91.
4-N-Phenyl-3,5-bis{4-[9’,9’-di-n-butyl-7’-iodo-2’-fluorenyl]phenyl}-1,2,4-
triazole (7): A mixture of 6 (1.88 g, 1.89 mmol), silver trifluoroacetate
(1.25 g, 5.67 mmol), and iodine (1.15 g, 4.53 mmol) in chloroform
(50 mL) was heated to reflux with stirring for 4 h. After cooling to RT,
the reaction mixture was filtered through Celite and the filtrate was
poured into sodium sulfite solution. The aqueous layer was extracted
with dichloromethane (3ꢀ40 mL). The combined organic layer was dried
over anhydrous Na2SO4 and evaporated to dryness. The crude product
was purified by chromatography on a short silica-gel column with 20:1 di-
chloromethane:ethyl acetate as eluent followed by recrystallization from
dichloromethane and MeOH to afford iodide 7 as a white solid in 97%
yield (2.01 g). 1H NMR (400 MHz, CDCl3): d=7.68 (d, J=8.0 Hz, 2H),
7.64 (d, J=7.6 Hz, 4H), 7.58 (d, J=8.4 Hz, 4H), 7.47–7.53 (m, 11H), 7.43
(d, J=8.0 Hz, 2H), 7.26 (d, J=6.8 Hz, 2H), 1.98–1.90 (m, 8H), 1.09–1.01
(m, 8H), 0.67–0.53 ppm (m, 20H); 13C NMR (100 MHz, CDCl3): d=
154.5, 153.2, 150.8, 142.4, 140.1, 139.9, 139.3, 135.8, 135.3, 131.9, 130.1,
129.7, 129.0, 127.9, 127.0, 126.1, 125.5, 121.5, 121.0, 92.7, 55.3, 40.0, 25.8,
22.9, 13.7 ppm; MS (FAB): m/z: 1101.27 [M+].
4-N-Phenyl-3,5-bis{4-[9’,9’,9’’,9’’-tetra-n-butyl-7’’-trimethylsilyl-2’,7’-bi-
fluorenyl]phenyl}-1,2,4-triazole (8): The synthetic procedure for PhN-
OF(1)-TAZ-OF(1)-NPh was followed using 7 (0.94 mg, 0.85 mmol), 9,9-
di-n-butyl-7-(trimethylsilyl)-2-fluorenyl
boronic
acid
(5;
0.99 g,
2.55 mmol), Pd(OAc)2 (21 mg, 0.09 mmol),
N
PACHTUNGRTNE(GUNN o-tolyl)3 (55 mg,
0.18 mmol), 2m K2CO3 (4 mL), toluene (50 mL), and methanol (15 mL).
The crude product was purified by silica-gel column chromatography
with 20:1 dichloromethane:ethyl acetate as eluent affording 1.31 g (81%)
1
of 8 as a white solid. H NMR (400 MHz, CDCl3): d=7.79–7.76 (m, 5H),
7.71 (d, J=7.6 Hz, 2H), 7.66–7.62 (m, 11H), 7.58–7.48 (m, 15H), 7.30 (m,
4H), 2.06–2.00 (m, 16H), 1.13–1.05 (m, 16H), 0.73–0.66 (m, 40H),
0.31 ppm (s, 18H); 13C NMR (100 MHz, CDCl3): d=154.6, 151.7, 151.7,
150.1, 142.6, 141.3, 140.7, 140.3, 139.7, 138.6, 131.8, 130.1, 129.1, 128.0,
127.5, 127.0, 126.0, 125.9, 125.5, 121.4, 121.2, 120.0, 120.0, 118.9, 55.2,
55.0, 40.2, 39.9, 26.0, 23.0, 23.0, 13.8, 13.7, ꢀ0.85 ppm; MS (FAB): m/z:
1545.8 [M+].
4-N-Phenyl-3,5-bis{4-[9’,9’,9’’,9’’-tetra-n-butyl-7’’-diphenylamino-2’,7’-bi-
fluorenyl]phenyl}-1,2,4-triazole (PhN-OF(2)-TAZ-OF(2)-NPh): The syn-
thetic procedure for PhN-OF(1)-TAZ-OF(1)-NPh was followed using 7
(500 mg, 0.45 mmol),
4
(888 mg, 1.81 mmol), PdACHTNGUTERNNU(G OAc)2 (10 mg,
0.05 mmol), P(o-tolyl)3 (31 mg, 0.10 mmol), 2m K2CO3 (3 mL), toluene
ACHTUNGTRENNUNG
(25 mL), and methanol (8 mL). The crude product was purified by silica-
gel column chromatography with 20:1 dichloromethane:ethyl acetate as
eluent affording 639 mg (81%) of PhN-OF(2)-TAZ-OF(2)-NPh as a
light yellow solid. 1H NMR (400 MHz, CDCl3): d=7.79 (d, J=8.0 Hz,
2H), 7.77 (d, J=8.0 Hz, 4H), 7.69 (d, J=8.0 Hz, 2H), 7.67–7.52 (m,
4-N-phenyl-3,5-bis{4-[9’,9’,9’’,9’’-tetra-n-butyl-7’’-iodo-2’,7’-bifluorenyl]-
phenyl}-1,2,4-triazole (9). The synthetic procedure for compound 7 was
followed using 8 (580 mg, 0.37 mmol), silver trifluoroacetate (231 mg,
0.91 mmol), iodine (252 mg, 1.14 mmol), and chloroform (20 mL). The
Chem. Eur. J. 2011, 17, 2518 – 2526
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2525

M. S. Wong, K. W. Cheah et al.
crude product was purified by chromatography on a short silica-gel
column with 20:1 dichloromethane:ethyl acetate as eluent followed by re-
crystallization from dichloromethane and MeOH to afford iodide 9 as a
brown solid in 90% yield (570 mg). 1H NMR (400 MHz, CDCl3): d=
7.79–7.72 (m, 6H), 7.67–7.45 (m, 29H), 7.29 (d, J=8.0 Hz, 2H), 2.05–1.93
(m, 16H), 1.12–1.07 (m, 16H), 0.70–0.63 ppm (m, 40H); 13C NMR
(100 MHz, CDCl3): d=153.3, 151.7, 151.7, 150.9, 142.6, 140.9, 140.6,
140.3, 139.9, 139.3, 138.7, 135.8, 135.4, 132.0, 130.1, 129.7, 129.1, 127.9,
127.0, 126.1, 126.1, 126.0, 125.9, 125.5, 121.4,121.3, 121.2, 120.1, 120.0,
92.4, 55.3, 55.2, 40.2, 40.0, 26.0, 25.9, 23.0, 23.0, 13.8, 13.7 ppm; MS
(FAB): m/z: 1653.9 [M+].
dichloromethane:ethyl acetate as eluent affording 560 mg (87%) of PhN-
OF(4)-TAZ-OF(4)-NPh as
a
light yellow solid. 1H NMR (400 MHz,
CDCl3): d=7.84–7.78 (m, 12H), 7.71–7.53 (m, 42H), 7.32–7.24 (m, 11H),
7.15–7.14 (m, 10H), 7.06–6.99 (m, 6H), 2.11–1.90 (m, 32H), 1.19–1.08 (m,
32H), 0.79–0.69 ppm (m, 80H); 13C NMR (100 MHz, CDCl3): d=154.7,
152.3, 151.8, 151.7, 151.4, 151.4, 150.9,147.9,147.1, 142.6, 140.7, 140.7,
140.6, 140.4, 140.3, 140.3, 140.3, 140.1, 140.0, 139.9, 139.8, 139.7, 139.5,
138.7, 135.9, 135.5, 130.1, 129.8, 129.1, 129.1, 128.0, 127.0, 126.1, 126.0,
125.5, 123.8, 123.4, 122.9, 122.5, 121.4, 121.3, 121.3, 121.2, 121.1, 120.3,
120.1, 129.9, 129.9, 129.7, 129.3, 129.3, 55.2, 55.2, 55.0, 40.2, 40.0, 26.1,
26.0, 23.0, 23.0, 13.9, 13.8 ppm; HRMS (MALDI-TOF): m/z 2842.7779
[M+]; elemental analysis (%) calcd for C212H225N5: C 89.56, H 7.98, N
2.46; found: C 89.67, H 7.93, N 2.44.
4-N-Phenyl-3,5-bis{4-[9’,9’,9’’,9’’,9’’’,9’’’-hexa-n-butyl-7’’’-diphenylamino-
2’,7’,2’’-terfluorenyl]phenyl}-1,2,4-triazole (PhN-OF(3)-TAZ-OF(3)-NPh):
The synthetic procedure for PhN-OF(1)-TAZ-OF(1)-NPh was followed
using 9 (520 mg, 0.31 mmol), 4 (615 mg, 1.26 mmol), Pd
ACHTUNGRTENN(UNG OAc)2 (7 mg,
0.03 mmol), P(o-tolyl)3 (18 mg, 0.06 mmol), 2m K2CO3 (3 mL), toluene
ACHTUNGTRENNUNG
(25 mL), and methanol (8 mL). The residue was purified by silica-gel
column chromatography with 20:1 dichloromethane:ethyl acetate as
eluent affording 554 mg (77%) of PhN-OF(3)-TAZ-OF(3)-NPh as a light
yellow solid. 1H NMR (400 MHz, CDCl3): d=7.82–7.77 (m, 8H), 7.70–
7.52 (m, 34H), 7.31–7.23 (m, 12H), 7.14 (d, J=7.2 Hz, 9H), 7.05–6.99 (m,
6H), 2.09–1.91 (m, 24H), 1.17–1.08 (m, 24H), 0.77–0.68 ppm (m, 60H);
13C NMR (100 MHz, CDCl3): d=154.6, 152.3, 151.8, 151.7, 151.4, 151.3,
150.9, 147.9, 147.1, 142.6, 140.7, 140.6, 140.4, 140.2, 140.1, 140.1, 139.8,
139.7, 139.5, 138.6, 135.9, 135.4, 130.1, 129.7, 129.1, 129.1, 128.0, 127.0,
126.7, 126.1, 126.0, 126.0,125.5, 123.8, 123.4, 122.9, 122.4, 121.3, 121.2,
121.2, 121.1, 120.3, 120.0, 119.9, 54.2, 54.2, 54.0, 39.2, 38.9, 28.6, 25.0, 25.0,
22.0, 22.0, 12.8, 12.8 ppm; HRMS (MALDI-TOF): m/z: 2289.4063 [M+];
elemental analysis (%) calcd for C170H177N5: C 89.15, H 7.79, N 3.06;
found: C 88.78, H 7.75, N 2.88.
Acknowledgements
This work is supported by GRF, Hong Kong Research Grant Council,
HKBU 202408.
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4-N-Phenyl-3,5-di-{4-[9’,9’,9’’,9’’,9’’’,9’’’-hexa-n-butyl-7’’’-trimethylsilyl-
2’,7’,2’’-terfluorenyl]phenyl}-1,2,4-triazole (10): The synthetic procedure
for PhN-OF(1)-TAZ-OF(1)-NPh was followed using
0.65 mmol), 9,9-di-n-butyl-7-(trimethylsilyl)-2-fluorenylboronic acid (5,
0.75 g, 1.94 mmol), Pd(OAc)2 (15 mg, 0.07 mmol), (o-tolyl)3 (40 mg,
8
(1.07 g,
A
PACHTUNGTRENNUNG
0.13 mmol), 2m K2CO3 (4 mL), toluene (50 mL), and methanol (12 mL).
The residue was purified by silica-gel column chromatography with 20:1
dichloromethane:ethyl acetate as eluent affording 1.06 g (78%) of 10 as
a white solid. 1H NMR (400 MHz, CDCl3): d=7.81–7.77 (m, 10H), 7.71–
7.62 (m, 21H), 7.59–7.48 (m, 16H), 7.31–7.28 (dd, J=8.0 Hz, 1.6 Hz,
2H), 2.11–2.00 (m, 24H), 1.16–1.06 (m, 24H), 0.77–0.67 (m, 60H),
0.31 ppm (s, 18H); 13C NMR (100 MHz, CDCl3): d=154.6, 151.7, 151.7,
151.6, 150.1, 142.6, 141.3, 140.6, 140.6, 140.4, 140.3, 140,2, 139.9, 139.7,
139.0, 138.6, 135.4, 131.8, 130.1, 129.7, 129.1, 127.9, 127.5, 127.0, 126.0,
125.9,125.5, 121.4,121.2, 120.1, 119.9, 118.9, 55.2, 55.2, 55.0, 40.2, 39.9,
26.0, 23.0, 23.0, 13.8, 13.7 ppm; MS (FAB): m/z: 2098.7 [M+].
4-N-Phenyl-3,5-bis{4-[9’,9’,9’’,9’’,9’’’,9’’’-hexa-n-butyl-7’’’-iodo-2’,7’,2’’-ter-
fluorenyl]phenyl}-1,2,4-triazole (11): The synthetic procedure for 8 was
followed using 10 (1.00 mg, 0.48 mmol), silver trifluoroacetate (0.32 mg,
1.43 mmol), iodine (0.29 mg, 1.14 mmol), and chloroform (40 mL). The
crude product was purified by chromatography on a short silica-gel
column with 20:1 dichloromethane:ethyl acetate as eluent followed by re-
crystallization from CH2Cl2 and MeOH affording iodide 11 as a brown
solid in 96% yield (1.01 g). 1H NMR (400 MHz, CDCl3): d=7.82–7.74
(m, 10H), 7.68–7.52 (m, 36H), 7.53 (d, J=7.6 Hz, 2H), 2.09–2.00 (m,
24H), 1.18–1.09 (m, 24H), 0.79–0.65 ppm (m, 60H); 13C NMR (100 MHz,
CDCl3): d=153.6, 152.3, 150.7, 150.7, 149.8, 141.6, 140.0, 139.6, 139.5,
139.3, 139.1, 139.1, 138.9, 138.7, 138.2, 137.7, 134.8, 134.4, 131.0, 129.1,
128.7, 128.1, 126.9,126.0, 125.1, 125.1, 125.0, 124.5, 120.4, 120.2, 120.2,
119.0, 119.0, 119.0, 91.4, 54.3, 54.2, 54.2, 39.2, 39.1, 39.0, 25.0, 25.0, 24.9,
22.0, 22.0, 12.8, 12.8 ppm; MS (FAB): m/z: 2206.7 [M+].
4-N-Phenyl-5-(4-tert-butylphenyl)-3-{4-[9’,9’,9’’,9’’,9’’’,9’’’,9’’’,9’’’’,9’’’’-octa-
n-butyl-7’’’’-diphenylamino-2’,7’,2’’,7’’,2’’’-quaterfluorenyl]phenyl}-1,2,4-tri-
azole (PhN-OF(4)-TAZ-OF(4)-NPh): The synthetic procedure for PhN-
OF(1)-TAZ-OF(1)-NPh was followed using 11 (500 mg, 0.23 mmol), 4
(333 mg, 0.68 mmol), PdACTHNUTRGNEN(UG OAc)2 (5 mg, 0.02 mmol), PAHCUTTGNREN(NUNG o-tolyl)3 (14 mg,
0.05 mmol), 2m K2CO3 (3 mL), toluene (30 mL), and methanol (8 mL).
Received: August 4, 2010
The residue was purified by silica-gel column chromatography with 20:1
Published online: January 24, 2011
2526
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 2518 – 2526