Synthesis and characterizations of star-shaped octupolar triazatruxenes-based two-photon absorption chromophores

Article abstract of DOI:10.1021/jo1017926

A series of star-shaped octupolar triazatruxenes (TATs, 1-6) with intramolecular "push-pull" structure were synthesized and their photophysical properties have been systematically investigated. These chromophores showed obvious solvatochromic effect, i.e.

Full text of DOI:10.1021/jo1017926

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Synthesis and Characterizations of Star-Shaped Octupolar
Triazatruxenes-Based Two-Photon Absorption Chromophores
Jinjun Shao, Zhenping Guan, Yongli Yan, Chongjun Jiao, Qing-Hua Xu,* and Chunyan Chi*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543
chmxqh@nus.edu.sg; chmcc@nus.edu.sg
Received September 15, 2010
A series of star-shaped octupolar triazatruxenes (TATs, 1-6) with intramolecular “push-pull”
structure were synthesized and their photophysical properties have been systematically investigated.
These chromophores showed obvious solvatochromic effect, i.e., significant bathochromic shift of
the emission spectra and larger Stokes shifts were observed in more polar solvents mainly due to
photoinduced intramolecular charge transfer (ICT). The two-photon absorption (2PA) cross-section
values were determined by two-photon excited fluorescence (2PEF) measurements in toluene and
THF. These chromophores exhibited large two-photon absorption cross-sections ranging from 280
to 1620 GM in the near-infrared (NIR) region. Compound 6 showed the largest 2PA action cross-
section (σ2Φ) of 564 GM and could be a potential two-photon fluorescent (2PF) probe. In addition,
compounds 1-6 all displayed good thermal stability and photostability.
Introduction
photodynamic therapy.6 These applications strongly depend
on the high 2PA cross-section of the specifically engineered
In recent years, two-photon absorption (2PA) has attracted
growing interest due to its potential applications in materials
science and biological imaging,1 including three-dimensional
optical data storage,2 lithographic microfabrication,3 optical
power limiting,4 two-photon fluorescence imaging,5 and
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Published on Web 01/06/2011
DOI: 10.1021/jo1017926
r
2011 American Chemical Society

Shao et al.
JOCArticle
organic molecules. This has led to a great number of
works on building π-conjugated dipolar,6 quadrupolar,7
and octupolar8 molecules with π-centers and functional
groups of electron-donating and/or electron-withdrawing
groups at the terminal sites.
building block has not been used to develop 2PA chromo-
phores. In this article, for the first time, we report the synthesis of
a series of TAT-based octupolar chromophores which show
large 2PA cross-section in the near-infrared (NIR) range.
Results and Discussion
Design of a star-shaped multipolar molecular structure is
one of the strategies7a,9 to obtain a large 2PA cross-section.
The coherent coupling between the branches will signifi-
cantly increase the 2PA cross-section. In addition, it was also
found that a planar, extended π-conjugated core usually
afforded better performance than the three-dimensionally
twisted, nonconjugated cores. Star-shaped octupolar triphenyl
amines and dendrimers based on planar truxene molecules10
have proved to be good 2PA chromophores. To further
exploit good 2PA active materials, we expect that the C3-
symmetry molecule, triazatruxene (TAT), could be another
good candidate (Figure 1). This idea is based on the follow-
ing considerations: (1) TAT can be considered as an extended
delocalized π-system in which three carbazole units share one
aromatic ring; (2) in comparison with its analogue truxene,
triazatruxene contains three nitrogen atoms which can serve
as good electron-donating groups like those in triphenyl
amines; and (3) selective chemical functionalizations around
the TAT core allow us to introduce electron-withdrawing groups
to form star-shaped octupolar chromophores such as 1-6
(Figure 1). So this design combines the advantages of the
electron-donating properties of aryl amines and the branched
feature of truxene. The additional thienylene vinylene units
in 4-6 can further improve the π-conjugation in each arm
and tune the 2PA properties. Although some research has
been done for the TAT-based materials,11 this interesting
Synthesis. The synthesis of the octupolar TAT molecules 1-6
is shown in Scheme 1. Three different electron-withdrawing
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FIGURE 1. Molecular structures of star-shaped octupolar triazatruxenes 1-6.
groups are introduced onto the TAT core at the periphery
sites to form a C3-symmetric structure and this results in
three dipoles at three directions with a net zero permanent
dipole moment. The synthesis started from alkylation of the
known hexabromotriazatruxene 711a with 1-bromododecane
in the presence of KOH to give compound 8 in a 90% yield.
Three dodecyl groups were introduced onto the TAT core to
increase the solubility and to facilitate the subsequent synth-
esis and purification.11h The reductive debromination of 8
was performed in refluxing THF in the presence of 10% Pd/C,
providing 9 in a 95% yield. The key step is the selective
introduction of three -CHO groups onto the para-positions
of the nitrogen atoms in 9. The Vilsmeier-Haack condition12
(POCl3/DMF) was first tested, but it failed to give the
trisformylated compound 10 even by increasing the reaction
temperature or prolonging the reaction time. Therefore a
more reactive condition, the CHCl2OCH3/SnCl4 system,13
was performed and compound 10 was obtained in a 55%
yield. Compound 1was then prepared as a red powder in an 83%
yield by a 3-fold condensation reaction between the -CHO
groups and excessive malononitrile (11) in the presence of
TiCl4 and pyridine in dichloromethane (DCM).14 The Horner-
Wadsworth-Emmons reaction15 between 10 and compounds
12,14c 13,16 and 1417 in dry THF afforded compounds 2, 3,
and 15 in 84%, 72%, and 85% yield, respectively.
Due to the high reactivity of the R-position of the periph-
ery thiophene molecule, the key intermediate compound 16
was easily obtained in a 93% yield by treating 15 with the
Vilsmeier-Haack condition (POCl3/DMF).12 Afterward,
the chromophore 4 was prepared through a 3-fold condensa-
tion reaction between 16 and malononitrile (11) with TiCl4/
pyridine in dichloroethane (DCE) instead of DCM because a
higher temperature was necessary to complete the conver-
sion. Chromophores 5 and 6 were synthesized via the Horner-
Wadsworth-Emmons reaction17 between 16 and com-
pounds 1214c and 1316 by using t-BuOK as the base in 82%
and 85% yield, respectively. It is worth noting that chromo-
phores 1, 2, and 3 were prepared via only four steps with an
overall yield of 39%, 40%, and 34%, respectively, and
chromophores 4, 5, and 6 were synthesized via six steps with
a good overall yield of 28%, 30%, and 32%, respectively. In
addition, all the double bonds formed under the Horner-
Wadsworth-Emmons reaction condition in the chromo-
phores 2, 3, 15, 16, 4, 5, and 6 were E-configured which
could be confirmed from the 1H-1H coupling constants of
the protons of the vinylene π-bridges (J = ∼16 Hz) in their
1H NMR spectra.18 1H NMR, 13C NMR spectroscopy, mass
spectrometry (MS), and elemental analysis were used to
identify the chemical structure and purity of all of these chro-
mophores (see the Experimental Section and the Supporting
Information (SI)).
One-Photon Spectral Properties. The one-photon UV-vis
absorption and fluorescence spectra of chromophores 1-6
were recorded in different solvents and the data are shown in
Figure 2, Figure S1 (in the SI), and Table 1. Compounds 1-3
in THF displayed broad intense absorptions with maxima at
428, 400, and 388 nm, and the emission peaks appeared at
575, 503, and 499 nm, respectively (Figure 2a), while chro-
mophores 4-6 showed absorption maxima at 512, 454, and
441 nm and emission maxima at 671, 570, and 554 nm,
respectively (Figure 2b). Interestingly, the absorption max-
ima of 5 and 6 are 54 and 53 nm red-shifted from those of 2
and 3, respectively, while that for 4 is 84 nm red-shifted from
1, which is probably because of attachment of very strong
electron-withdrawing dicyanomethylene groups.
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Xu, H.; Wang, Y. H.; Xie, W.; Hanif, M.; Xia, J.; Shen, F.; Yang, B.; Li, F.;
Ma, Y.; Yang, Y.; Shen, J. Adv. Funct. Mater. 2007, 17, 1551.
(13) Kedrowski, B. L.; Hoppe, R. W. J. Org. Chem. 2008, 73, 5177.
(14) (a) Kochurani, J.; Becker, J. Y.; Ellern, A.; Khodorkovsky, V.
Tetrahedron Lett. 1999, 40, 8625. (b) Sanguinet, L.; Williams, J. C.; Yang,
Z.; Twieg, R. J.; Mao, G.; Singer, K. D.; Wiggers, G.; Petschek, R. G. Chem.
Mater. 2006, 18, 4259. (c) Lartia, R.; Allain, C.; Bordeau, G.; Schmidt, F.;
Fiorini-Debuisschert, C.; Charra, F.; Teulade-Fichou, M. P. J. Org. Chem.
2008, 73, 1732.
(15) Guldi, D. M.; Swartz, A.; Luo, C.; Gomez, R.; Segura, J. L.; Martin,
N. J. Am. Chem. Soc. 2002, 124, 10875.
(16) Messmore, B. W.; Hulvat, J. F.; Sone, E. D.; Stupp, S. I. J. Am.
Chem. Soc. 2004, 126, 14452.
(17) (a) Jørgensen, M.; Krebs, F. C. J. Org. Chem. 2005, 70, 6004.
(b) Zheng, S.; Barlow, S.; Parker, T. C.; Marder, S. R. Tetrahedron Lett.
2003, 44, 7989. (c) Jen, A. K. Y.; Rao, V. P.; Wong, K. Y.; Drost, K. J.
J. Chem. Soc., Chem. Commun 1993, 90.
Although the solvent polarity has only little effect on the
absorption spectra (Figure 3a and in the SI Figure S1),
significant bathochromic shift of the emission band was
observed for each chromophore with increasing solvent polarity.
Taking compound 1 as an example, the fluorescence spectra
€
(18) Pretsch, E.; Buhlmann, P.; Affolter, C. Structure Determination of
Organic Compounds: Springer-Verlag: Berlin, Germany, 2000.
782 J. Org. Chem. Vol. 76, No. 3, 2011

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SCHEME 1. Synthetic Route of Chromophores 1, 2, 3, 4, 5, and 6
show pronounced bathochromic shift with the increasing
solvent polarity, i.e., from less polar toluene to highly polar
DCM, the emission maximum red-shifted from 528 to 591 nm
(Figure 3b). Such a positive solvatochromism was commonly
observed for many 2PA chromophores due to the photo-
induced intramolecular charge transfer (ICT)1b from the
center to the periphery. This could be explained by that the
symmetry of our octupolar molecules was broken in the excited
state by forming a relaxed, dipolar excited state localized
on one of the donor-acceptor pairs.8k It could also be
ascribed to the large steady state octupole moments in polar
solvents.
The observed large Stokes shifts (5970, 5119, 5733, 4628,
4482, and 4625 cm-1 for 1-6 in THF, respectively) indicate
that significant charge redistribution occurs upon excitation,
prior to emission, and that the emission originates from a
strongly dipolar emissive state.8k Potentially large 2PA cross-
sections can be obtained for these chromophores. All com-
pounds except 1 and 4 have moderate fluorescence quantum
yields (Φ, Table 1), which also depend on the solvent polarity.
The significant decrease in quantum yields for compounds 1 and
4 could be due to the strong intramolecular charge transfer.
This would promote the solute-solvent interactions, by
which the excited state of the chromophore would be readily
quenched and the quantum yield decreases.8i,19 The fluores-
cence lifetime was measured by using a time-correlated single
FIGURE 2. Normalized steady state absorption and fluorescence
spectra of chromophores (a) 1-3 and (b) 4-6 in THF.
photon counting (TCSPC) technique. The frequency-doubled
output of a mode-locked Ti:sapphire laser (Tsunami, Spectra-
Physics) at 400 nm was used for excitation of the sample. The
output pulses from Ti:sapphire centered at 800 nm had
a pulse duration of 50 fs with a repetition rate of 80 MHz.
(19) Ko, C.-W.; Tao, Y.-T.; Danel, A.; Krzeminska, L.; Tomasik, P.
Chem. Mater. 2001, 13, 2441.
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TABLE 1. Photophysical Data of Chromophores 1-6
compd
solvent
λ
abs (nm)a
ε (cm-1 M-1 b
)
λ
em (nm)c
Stokes shift (cm-1 d
)
Φe (%)
σ2 (GM)f
σ2Φ (GM)g
3
1
toluene
THF
toluene
THF
toluene
THF
toluene
THF
toluene
THF
toluene
THF
436
428
401
400
388
388
514
512
455
454
444
441
67200
65700
80700
86000
83200
89800
48700
59300
137500
142700
122900
133000
528
575
480
503
462
499
606
671
524
570
508
554
3996
5970
4104
5119
4128
5733
2950
4628
2894
4482
2837
4625
3
4
730 [820 nm]
840 [820 nm]
770 [800 nm]
1110 [800 nm]
1050 [800 nm]
1580 [800 nm]
540 [770 nm]
280 [770 nm]
1620 [740 nm]
1600 [740 nm]
1050 [740 nm]
1410 [740 nm]
22
34
2
3
4
5
6
19
22
15
16
8
146
244
158
253
43
2
6
21
22
34
40
340
352
357
564
aOne-photon absorption maximum, the experimental uncertainty is (1 nm. bMolar extinction coefficient at the absorption maximum. cOne-photon
emission maximum, the experimental uncertainty is (1 nm. dStokes shift = (1/λabs - 1/λem). eFluorescence quantum yields by using fluorescein
(pH ∼11, NaOH aqueous solution) as a standard; the experimental uncertainty is (5-10%. f2PA cross-section maximum in the measurable range; 1 GM =
10-50 cm4 s photon-1; the corresponding excitation wavelengths are shown in the square brackets; the experimental uncertainty on σ2 is of the order of
3 3
(()12-15% of the corresponding values for 2, 3, 5, and 6 and (()25% of the corresponding values for 1 due to its low quantum yield. g2P action cross-
section.
FIGURE 3. (a) Absorption spectra of chromophore 1 in different solvents with the same concentration of 1.0 ꢀ 10-5 M; (b) fluorescence
spectra of compound 1 in different solvents with the same concentration of 1.0 ꢀ 10-6 M under excitation at 440 nm.
The fluorescence intensity was collected by an optical fiber
that is directed to an avalanche photodiode (APD). The
signals were processed by a PicoHarp 300 module (PicoQuant)
with a temporal resolution of ∼150 ps. Monoexponential
decays were observed for all compounds (Figure 4) and the
fluorescence lifetimes in toluene were 1.78, 1.35, 2.24, 1.20,
1.44, and 1.29 ns for 1-6, respectively. We noted that the
fluorescence lifetimes do not correlate well with their fluor-
escence quantum yields for different chromophores in the
same solvent, although the fluorescence lifetimes of the same
chromophore in different solvents were found to correlate
FIGURE 4. Fluorescence decay curves of chromophores 1-6 in
toluene.
well with their quantum yields. The lack of correlation between
fluorescence lifetimes and quantum yields for different chro-
mophores might be due to different radiative decay rates of these
chromophores because of their different electronic structures.
Electrochemical Properties. The electrochemical proper-
ties of compounds 1-6 were investigated by cyclic voltam-
metry (CV) and differential pulse voltammetry (DPV) in
DCM. One or two quasi-reversible oxidation waves were
observed for each chromophore (Figure 5). Their HOMO,
LUMO energy levels and energy gaps are shown in Table 2.
The HOMO energy levels derived from the onset of oxidation
potential are -5.12, -5.15, -5.15, -5.11, -4.97, and -5.00 eV
for 1-6, respectively.20 Accordingly, the respective LUMO
energy levels are deducted as -2.61, -2.45, -2.36, -3.06,
-2.60, and -2.57 eV based on the equation LUMO =
HOMO þ Eg, where Eg is the optical energy gap.20 One
can see that compounds 1-3 have similar HOMO energy
levels probably because they have a common electron-rich
TAT core, but their LUMO energy levels are different due to
the attachment of different electron-withdrawing groups.
The stronger electron-withdrawing group such as dicyano-
methylene pulls down the LUMO energy level and as a
result, a smaller energy gap was observed for 1. For com-
pounds 4-6, the additional thienylene vinylene units further
increase the π-conjugation and lead to a lower lying HOMO
energy level and a convergence of the HOMO-LUMO
(20) (a) Chi, C.; Wegner, G. Macromol. Rapid Commun. 2005, 26, 1532.
(b) Chi, C.; Im, C.; Enkelmann, V.; Ziegler, A.; Lieser, G.; Wegner, G.
Chem.;Eur. J. 2005, 11, 6833.
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FIGURE 5. Cyclic voltammograms of chromophores 1-6 in DCM with 0.1 M Bu4NPF6 as the supporting electrolyte, AgCl/Ag as reference
electrode, Au as working electrode, Pt wire as counter electrode, and a scan rate at 50 mV/s. Inset: The differential pulse voltammograms of
chromophores 5 and 6 showing two distinguishable redox waves.
TABLE 2. Electrochemical Properties of the Chromophores 1-6
to extended effective π-conjugation length after incorporat-
ing a thienylene vinylene unit into the each branch. The
longer π-conjugated compound may have a larger number of
density of states which could provide more effective coupling
channels between the ground states and two-photon allowed
states, which in turn will enhance the 2PA cross-section.8j
Chromophores 1-3 showed their 2PA cross-section maxima
in the sequence 3>2>1, and chromopores 5 and 6 exhibited
comparable 2PA cross-section values with both larger than
that for 4.
It is clear to see the trend of 2P action cross-section
maximum values of the six chromophores as 3 > 2 > 1,
6>5>4 in toluene as well as in THF (Figure 7, and in the SI
Figure S3). The 2P action cross-section maxima of 2 and 3
are almost the same and much larger than that of 1, and this is
due to the relatively low quantum yield of 1. In the measurement
range from 740 to 860 nm, the 2P action cross-section of 6 is a
little bit larger than that of 5, and much larger than that of 4.
In addition, the 2P action cross-section of 2, 3, 5, and 6 are
larger in THF than those in toluene. It is worth noting that
compared with rhodamine B, one common commercial
fluorophore with a 2PA cross-section value of 200 GM and
2P action cross-section (σ2Φ) of 140 GM at 840 nm in
MeOH,22 both compounds 5 and 6 have much higher 2PA
cross-section and 2P action cross-section values. Thus, com-
pounds 5 and 6 could be potential efficient two-photon
fluorescent probes.
compd
Eoxonset a/V
HOMOb/eV
LUMOc/eV
Egd/ eV
1
2
3
4
5
6
0.32
0.35
0.35
0.31
0.17
0.20
-5.12
-5.15
-5.15
-5.11
-4.97
-5.00
-2.61
-2.45
-2.36
-3.06
-2.60
-2.57
2.51
2.70
2.79
2.05
2.37
2.43
aEoxonset is the onset potential of the first oxidation wave relative to
EFcþ/Fc. Fcþ/Fc was used as internal reference for these measurements,
E1/2 = 0.40 V for Fcþ/Fc vs AgCl/Ag. HOMO = -(4.8 þ Eoxonset).
b
cLUMO = HOMO þ Eg. dEg (optical energy gap) calculated from the
low-energy absorption edge.
energy gap in comparison to the corresponding chromo-
phores 1-3.
Two-Photon Absorption Characteristics of 1-6. 2PA spec-
tra of the chromophores 1-6 were recorded in toluene and
THF by two-photon excited fluorescence (2PEF) measure-
ments in the range of 740-860 nm (Figure 6 and in the SI
Figure S2). The 2PEF spectra of these samples were com-
pared with a reference solution of fluorescein at the corre-
sponding excitation wavelengths.21 All six chromophores
exhibited maximum 2PA cross-section (σ2) ranging from
280 GM to 1620 GM in the two solvents (Table 1). A quadratic
dependence of the 2PEF on the incident power was observed
(Figure S5, SI), indicating a two-photon absorption process.
A discernible trend of the two-photon absorption cross-
section (σ2) was observed for chromophores 1-3: the values
in toluene increase from 1 to 3 with the maxima 2PA cross-
section increasing from 730 GM to 1050 GM (Figure 6a). A
similar trend was observed in THF (Figures S2 and S4, SI).
Since 1-3 have a common TAT core with the same electron-
donating effect, such a difference must be due to the varied
electron-withdrawing groups and the different effective
π-conjugation length. Although the dicyanomethylene
group shows the strongest electron-withdrawing property,
2 and 3 have more extended conjugation length than 1, which
results in larger 2PA cross-sections than 1. Chromophores 2
and 3 have a similar conjugation length, while 3 has the -CN
groups at the terminal sites which may cause 3 to have larger
two-photon absorptivity than 2.7u,8j
There have been few theoretical studies to address the
solvent effect, and unfortunately the published results still lack
consensus.23 One recent experimental study by using vinyl-
benzene24a and vinylfluorene24b derivatives revealed that, unlike
one-photon transition, two-photon transition does not correlate
with the polarity of the solvent. However, Bazan et al.25 reported
(22) Xu, C.; Williams, R. M.; Zipfel, W.; Webb, W. W. Bioimaging 1996,
4, 198.
(23) (a) Luo, Y.; Norman, P.; Macak, P.; Agren, H. J. Phys. Chem. A
2000, 104, 4718. (b) Wang, C.-K.; Zhao, K.; Su, Y.; Ren, Y.; Zhao, X.; Luo,
Y. J. Chem. Phys. 2003, 119, 1208. (c) Ray, P. C.; Leszczynski, J. J. Phys.
Chem. A 2005, 109, 6689. (d) Terenziani, F.; Painelli, A.; Katan, C.; Charlot,
M.; Blanchard-Desce, M. J. Am. Chem. Soc. 2006, 128, 15742. (e) Paterson,
M. J.; Kongsted, J.; Christiansen, O.; Mikkelsen, K. V.; Nielsen, C. B. J. Chem.
Phys. 2006, 125, 184501. (f) Zhao, K.; Ferrighi, L.; Frediani, L.; Wang, C.-K.;
Luo, Y. J. Chem. Phys. 2007, 126, 204509. (g) Easwaramoorthi, S.; Shin, J. Y.;
Cho, S.; Kim, P.; Inokuma, Y.; Tsurumaki, E.; Osuka, A.; Kim, D. Chem.;
Eur. J. 2009, 15, 12005.
Compounds 4-6 in toluene show their maxima 2PA cross-
section (σ2) of 540 GM at 770 nm, 1620 GM at 740 nm, and
1050 GM at 740 nm, respectively, which are larger than those
of 1-3 (Figure S4, SI). This trend could be explained as due
(24) (a) Johnsen, M; Ogilby, P. R. J. Phys. Chem. A 2008, 112, 78319.
(b) Fitilis, I.; Fakis, M.; Polyzos, I.; Giannetas, V.; Persephonis, P.; Mik-
royannidis., J. J. Phys. Chem. A 2008, 112, 4742.
(21) (a) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481. (b) Tian,
N.; Xu, Q.-H. Adv. Mater. 2007, 19, 1988.
(25) Woo, H. Y.; Liu, B.; Kohler, B.; Korystov, D.; Mikhailovsky, A.;
Bazan, G. C. J. Am. Chem. Soc. 2005, 127, 14721.
J. Org. Chem. Vol. 76, No. 3, 2011 785

Shao et al.
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FIGURE 6. 2PA spectra of compounds 1-6 in toluene.
FIGURE 7. 2P action cross-section spectra (σ2Φ) of the compounds 1-6 in toluene.
that the 2PA cross-section value of distyrylbenzene chromo-
phores was solvent-dependent and nonmonotonic, and
the maxima 2PA cross-section values were observed in the
solvent with intermediate polarity. On the other hand, the
2PA cross-section values of octupolar molecules are expected
to show little solvent dependence on account of lack of perma-
nent dipole moment. However, theoretical and computational
studies indicate the influence of dipolar, quadrupolar, octupolar,
and higher-order interactions with the solvent.23c In our TAT-
based chromophores, no clear trend of the solvent dependence
was observed. In the nonpolar solvent such as toluene, the σ2Φ
values are slightly smaller than those in polar solvents such as
THF. The difference should be related to the conformation of
the chromophore molecules in excited states and solvation effect
in different solvents. The small difference may be due to the rigid
and planar core structure of these TAT-based chromophores.
Thermal Properties. The thermal stability is one of the key
requirements for some practical applications of organic
chromophores used in a solid matrix. The thermal stability
of the compounds is examined by thermogravimetric anal-
ysis (TGA) in N2 at a heating rate of 10 deg/min, and all the
compounds have high thermal stability, with decomposition
temperatures (Td, corresponding to a 5% weight loss) at 330,
347, 378, 352, 393, and 420 °C for compounds 1-6, respec-
tively (Figure 8). These results confirm that the triazatruxene-
containing chromophores are thermally stable.
photostability and 2PA cross-sections of chromophores 1-6
were compared with the commercially available Fluorescein via
photodecomposition experiments using the absorption method
(Figure 9 and in the SI Figure S6).26 A figure of merit (FM)26b,c
by which probes for 2PFM was defined as two-photon action
cross-section (Φσ2) normalized by their photodecomposition
quantum yields (η, see the SI), i.e., FM = Φσ2/η. The data are
shown in Table 3. The FM values of all chromophores are 1-3
orders of magnitude higher than that of fluorescein, providing
strong support for the fidelity of chromophore 5and 6relative to
commercial fluorescein probes for 2PFM biological imaging.
Conclusions
A new synthetic route was developed to prepare six new
star-shaped octupolar compounds based on triazatruxene.
The synthesis of the trisformylated precursor 10 was the key
for the synthesis of 1, 2, 3, and 15. Direct formylation
introduced three aldehyde groups onto 15, which was the key
intermediate to synthesize 4, 5, and 6. In general, all six
chromophores were readily obtained with a good overall yield
from the starting material 7. Solvent polarity has little effect on
the UV-vis absorption spectra, while significant bathochromic
shift of the emission spectra was observed together with a larger
Stokes shift in polar solvents due to intramolecular charge
transfer. Chromophores 1-6 show high two-photon absorptiv-
ity with the maxima 2PA cross-section ranging from 280 GM to
1620 GM. At the same time, 5 and 6 exhibit the large 2P action
cross-section (σ2Φ) andthefigureofmerit(FM), so they could be
the potential 2P fluorescent probes. In addition, all chromo-
phores show good thermal stability and photostability. We can
also expect that more modifications can be done on this TAT
core to further tune their 2PA properties by introducing multiple
branched or dendritic structures with more extended π-conjuga-
tion in the future. Construction of dendrimers based on TAT is
underway in our laboratories.
Photostability Test. The photostability of a chromophore
is of great importance regarding potential application for
two-photon fluorescent microscopy (2PFM) probes. Herein the
(26) (a) Corredor, C. C.; Belfield, K. D.; Bondar, M. V.; Przhonska,
O. V.; Yao, S. J. Photochem. Photobiol., A 2006, 184, 105. (b) Wang, X.;
Nguyen, D. M.; Yanez, C. O.; Rodriguez, L.; Ahn, H.-Y.; Bondar, M. V.;
Belfield, K. D. J. Am. Chem. Soc. 2010, 132, 12237. (c) Wang, X.; Yao, S.;
Ahn, H.-Y.; Zhang, Y.; Bondar, M. V.; Torres, J. A.; Belfield, K. D. Biomed.
Opt. Express 2010, 1, 453.
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FIGURE 8. TGA curves of compounds 1-6. TGA was obtained under N2 at a heating rate of 10 deg/min.
FIGURE 9. Absorption spectra of 4 in toluene (a) and fluorescein in 0.1 M NaOH (aq) (b) recorded after irradiation with a 457 nm diode laser
at 20 mW for different periods of time.
TABLE 3. Photophysical Data for 1-6 and Fluorescein
by using the capillary method and the data are not calibrated. Cyclic
voltammetry was performed on an electrochemical analyzer with a
three-electrode cell in a solution of 0.1 M tetrabutylammonium
hexafluorophosphate (Bu4NPF6) dissolved in dry DCM at a scan
rate of 50 mV s-1. A gold electrode with a diameter of 2 mm, a Pt
wire, and an Ag/AgCl electrode were used as the working electrode,
the counter electrode, and the reference electrode, respectively. The
potential was calibrated against the ferrocene/ferrocenium couple.
Thermogravimetric analysis (TGA) was carried out at a heating rate
of 10 deg/min under nitrogen flow.
The two-photon excited fluorescence (2PEF) method was
used to measure the 2PA cross-sections.21 The excitation source
was a femtosecond Ti:sapphire oscillator pumped by a 532 nm
diode laser. The output laser pulses have pulse duration of 50 fs,
a repetition rate of 80 MHz, and a center wavelength at 800 nm.
The power of the laser beam before the samples was adjusted to
100 mW by using neutral density filters for most measurements.
The samples were excited by directing a tightly collimated, high
intensity laser beam onto the sample. The emission from the
sample was collected at a 90° angle by a pair of lens and optical
fibers and directed to the spectrometer, which was a monochro-
mator coupled CCD system. To avoid internal filter effects, the
excitation volume was located near the cell wall on the collection
optics side. This configuration minimizes the fluorescence path
inside the sample cell and thus reduces self-absorption. A short
pass filter with cutoff wavelength at 700 nm was placed before
the spectrometer to minimize the intensity of pumping light
scattering. Samples were dissolved in toluene and THF at the
same concentration of 5 ꢀ 10-6 M and the two-photon induced
fluorescence intensity was measured at 740-860 nm by using
Fluorescein (5 ꢀ 10-6 M in water, pH 11) as the reference. The
intensities of the two-photon-induced fluorescence spectra of the
reference and sample under the same measurement conditions
106ηa
Φσ2
10-6FM
b
c
compd
1
2
3
4
5
6
0.04
1.22
9.0
0.28
0.07
0.87
7.16
22
146
158
43
340
357
33
550
120
18
154
4857
410
5
fluorescein
aPhotobleaching decomposition quantum yield; the experimental
uncertainty is (15%. b2P action cross-section maximum in the measur-
able range in GM. cFigure of merit in GM, FM = Φσ2/η.
Experimental Section
Materials. Anhydrous tetrahydrofuran (THF) and DCM
were obtained by distillation over sodium and CaH2, respec-
tively. Hexabromotriazatruxene (7),11a diethyl (benzothiazol-2-yl)-
methylphosphonate (12),14c diethyl (4-cyanophenyl)methylpho-
sphonate (13),16 and diethyl (thiophen-2-yl)methylphosphonate
(14)17 were prepared according to the literature procedure. All other
chemicals were purchased from commercial supplies and used
without further purification. Deuterated solvents for NMR spectro-
scopic analyses were used as received.
Characterizations. 1H NMR and 13C NMR spectra were
recorded in CDCl3 or CDCl2CDCl2. All chemical shifts are
quoted in ppm, relative to tetramethylsilane, using the residual
solvent peak as a reference standard. MS were recorded in either EI
mode or FAB mode and high resolution mass spectrometry were
recorded with a FAB ionization source. Matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) analysis was
performed by using dithranol as matrix. UV-vis absorption and
fluorescence spectra were recorded in HPLC pure solvents. Melting
points were checked on the Buchi Melting Point B-540 instrument
J. Org. Chem. Vol. 76, No. 3, 2011 787

Shao et al.
JOCArticle
were determined and compared. The 2PA cross-section of sample
δs, measured by using the two-photon-induced fluorescence
measurement technique, can be calculated by using the
equation
After 30 min at 0 °C the solution was warmed to room temperature
and stirred for another 36 h. The dark solution was poured into a
separatory funnel filled with 10 g of ice and shaken thoroughly. The
layers were separated, and the aqueous phase was diluted with water
(10 mL) and extracted with DCM (3 ꢀ 10 mL). The combined
organic layers were washed with water (2 ꢀ 50 mL) and saturated aq
NaHCO3 (2 ꢀ 50 mL), diluted with ether (75 mL), and washed with
brine (3ꢀ50 mL). The solution was dried over Na2SO4, and the
solvents were removed under reduced pressure to give the crude
product as a dark oil. Purification by flash chromatography (silica
gel, hexane/EtOAc = 8:1) gave a deep-red solid (0.83 g, 55%). 1H
NMR (500 MHz, CDCl3) δ (ppm) 10.13 (s, 3H), 8.66 (s, 3H), 7.97
(d, J = 8.8 Hz, 3H), 7.63 (d, J = 8.8 Hz, 3H), 4.80 (t, J = 8.2 Hz,
6H), 1.97 (quin, 6H), 1.31-1.14 (m, 54H), 0.86 (t, J = 7.0 Hz, 9H);
13C NMR (125 MHz, CDCl3) δ (ppm) 191.6, 144.4, 139.4, 129.5,
125.9, 124.07, 122.7, 110.7, 103.7, 47.2, 31.9, 30.1, 29.6, 29.5, 29.4,
29.32, 29.28, 26.5, 22.7, 14.1; EI-MS (m/z) calcd for C63H87N3O3
933.67, found 933.9 (Mþ). Elemental Anal. Calcd for C63H87N3O3:
C, 80.98; H, 9.38; N, 4.50. Found: C, 81.09; H, 9.26; N, 4.35.
5,10,15-Tridodecyl-3,8,13-tris((E)-2-(thiophen-2-yl)vinyl)-10,15-
dihydro-5H-diindolo[3,2-a:30,20-c]carbazole (15). Under N2 atmo-
sphere, t-BuOK (561 mg, 5.0 mmol, 5 equiv) was added in a small
portion to a solution of 14 (1.173 g, 5.0 mmol, 5 equiv) and 10
(0.934 g, 1.0 mmol) in dry THF (60 mL). After adding t-BuOK, the
reaction solution turned red. The mixture was stirred at 65 °C
overnight. After cooling to room temperature, the reaction solution
was diluted with DCM (60 mL) and washed with water (2 ꢀ 60 mL)
and brine (2 ꢀ 60 mL), then the organic layer was dried over
Na2SO4. After removal of solvents, the residue was purified by
column chromatography (silica gel, hexane/CHCl3 = 4:1 to 3:1) to
give the title compound 15 as a yellow solid (1.00 g, 85%). Mp
137-139 °C; 1H NMR (500 MHz, CDCl3) δ (ppm) 8.10 (s, 3H),
7.59 (d, J = 7.6 Hz, 3H), 7.48 (d, J = 8.2 Hz, 3H), 7.26 (d, J = 16.4
Hz, 3H), 7.20 (d, J = 5.0 Hz, 3H), 7.14 (d, J = 15.7 Hz, 3H), 7.10
(d, J = 3.2 Hz, 3H), 7.06-7.04 (m, 3H), 4.67 (t, J = 8.2 Hz, 6H),
2
FsΦrCrns
δs ¼
2 δr
FrΦsCsnr
where the subscripts s and r stand for the sample and
reference molecules, respectively. F is the integral area of
the two-photon fluorescence; Φ is the fluorescence quantum
yield; and C is the number density of the molecules in
solution. δr is the 2PA cross-section of the reference mole-
cule; n is the refractive indices of the solvents. The measure-
ments were conducted in a regime where the fluorescence
signal showed a quadratic dependence on the excitation
intensity, as expected for two-photon-induced emission.
The photostability of all the chromophores was determined
by the absorption method.26 For chromophores 1, 4, 5, and 6, a
solution in toluene was irradiated in 1 mm path length quartz
cuvettes with a 457 nm diode laser at 20 mW, and fluorescein
in 0.1 M NaOH(aq) was tested under the same condition; for
compounds 2 and 3, a solution in toluene was irradiated in 1 mm
path length quartz cuvettes with a 400 nm diode laser at 20 mW.
Synthesis. 2,3,7,8,12,13-Hexabromo-5,10,15-tridodecyl-10,15-
dihydro-5H-diindolo[3,2-a:30,20-c]carbazole (8). A mixture of hexa-
bromotriazatruxene 7 (2.45 g, 3.00 mmol) and KOH (1.68 g,
30.00 mmol) was heated to reflux in THF (30 mL) for 30 min. Then,
1-bromododecane (3.50 mL, 13.5 mmol) was added and the mixture
was refluxed for 13 h before it was cooled to room temperature. The
mixture was diluted with DCM (50 mL) and washed with 10%
aqueous HCl solution (2 ꢀ 50 mL) and with saturated aqueous
NaCl solution (2 ꢀ 50 mL) and dried over Na2SO4, then the solvent
was removed under vacuum. The residue was purified by silica gel
column chromatography with hexane as the eluent to give 8 as a
yellow solid (2.3 g, 90%). 1H NMR (500 MHz, CDCl3) δ (ppm)
7.95 (s, 3H), 7.49 (s, 3H), 3.97 (t, J = 7.5 Hz, 6H), 1.71 (br, 6H),
1.31-1.22 (m, 54H), 0.90 (t, J = 7.0 Hz, 9H); 13CNMR (125 MHz,
CDCl3) δ (ppm) 140.0, 138.6, 124.8, 122.7, 118.5, 115.2, 114.4,
101.2, 46.8, 32.0, 30.2, 29.69, 29.67, 29.60, 29.58, 29.4, 29.3, 26.5,
22.7, 14.1; FAB-MS (m/z) calcd for C60H81Br6N3 1323.15, found
1323.0 (Mþ), 1243.1 (Mþ-Br). Elemental Anal. Calcd for C60H81-
Br6N3: C, 54.44; H, 6.17; N, 3.17. Found: C, 54.54; H, 6.01;
N, 3.17.
1.99 (quin, 6H), 1.29-1.16 (m, 54H), 0.88 (t, J = 7.0 Hz, 9H); 13
C
NMR (125 MHz, CDCl3) δ (ppm) 143.70, 140.74, 139.1, 130.0,
128.9, 127.6, 125.1, 123.5, 123.4, 120.8, 120.5, 119.4, 110.6, 103.1,
47.1, 31.9, 30.2, 29.7, 29.6, 29.5, 29.4 26.9, 22.7, 14.1; HR-FAB-MS
(m/z) calcd for C78H99N3S3 (Mþ) 1173.7001, found 1173.6952
(error: -4.2 ppm); MALDI-TOF MS (m/z) calcd for C78H99N3S3
1173.700, found 1174.776 (M þ H)þ. Elemental Anal. Calcd for
C78H99N3S3: C, 79.74; H, 8.49; N, 3.58; S, 8.19. Found: C, 79.96; H,
8.27; N, 3.35; S, 8.36.
5,50,500-(1E,10E,100E)-2,20,200-(5,10,15-Tridodecyl-10,15-dihy-
dro-5H-diindolo[3,2-a:30,20-c]carbazole-3,8,13-triyl)tris(ethene-
2,1-diyl)trithiophene-2-carbaldehyde (16). To a three-necked flask
were added POCl3 (0.118 mL, 1.2 mmol) and dry DMF (0.116 mL,
1.5 mmol) dropwise to dry dichloroethane (DCE) (20 mL) at 0 °C
with stirring. The mixture was warmed to room temperature, stirred
for another 30 min, and cooled back to 0 °C. A cooled solution of
15 (117.5 mg, 0.1 mmol) in DMF (2 mL) was added dropwise over
5 min with stirring. The reaction mixture was heated to 85 °C for
10 h and poured into a stirred solution of brine and crushed ice
(30 mL). After 30 min, the whole was extracted with DCM (3 ꢀ
30 mL) and the combined organic extracts were washed with brine
(30 mL), dried over MgSO4, filtered, and concentrated in vacuo.
Purification by flash chromatography on silica gel (ethyl acet-
ate/hexane, 1:4) gave the title compound 16 as a red solid (117 mg,
93%). Mp >350 °C (the sample decomposes when the temperature
is higher than 350 °C, and the color of the solid changes from red to
black); 1H NMR (500 MHz, CDCl3) δ (ppm) 9.88 (s, 3H), 8.03 (s,
3H), 7.68 (d, J = 3.8 Hz, 3H), 7.62 (d, J = 8.8 Hz, 3H), 7.48 (d, J =
8.8 Hz, 3H), 7.30 (d, J = 15.8 Hz, 3H), 7.19 (d, J = 15.8 Hz, 3H),
7.12 (d, J = 3.8 Hz, 3H), 4.62 (br, 6H), 1.93 (br, 6H), 1.25-1.12 (m,
54H), 0.85 (t, J = 7.5 Hz, 9H); 13C NMR (125 MHz, CDCl3) δ
(ppm) 182.2, 153.3, 141.0, 138.6, 137.3, 134.4, 127.7, 125.7, 123.0,
121.5, 121.1, 118.1, 110.6, 102.8, 46.9, 31.9, 30.2, 29.72, 29.66, 29.61,
5,10,15-Tridodecyl-10,15-dihydro-5H-diindolo[3,2-a:30,20-c]car-
bazole (9). A mixture of 8 (0.662 g, 0.50 mmol), Et3N (0.55 mL,
4.00 mmol), HCOOH (0.16 mL, 4.00 mmol), and 10% Pd/C
(160 mg, 0.15 mmol) in THF (10 mL) was heated at 70 °Covernight.
The mixture was filtered through Celite, and the filtrate was diluted
with DCM (30 mL), washed with 10% aqueous HCl (3 ꢀ 30 mL),
and dried over Na2SO4, then the solvent was removed under
reduced pressure. The residue was purified by silica gel column
chromatography with pure hexane as eluent to give 9as a white solid
1
(0.404 g, 95%). Mp 63-65 °C; H NMR (500 MHz, CDCl3)
δ (ppm) 8.29 (d, J = 8.0 Hz, 3H), 7.64 (d, J = 8.0 Hz, 3H), 7.46
(t, J = 8.0 Hz, 3H), 7.35 (t, J = 8.0 Hz, 3H), 4.92 (t, J = 8.0 Hz,
6H), 2.00 (quin, 6H), 1.29-1.18 (m, 54H), 0.89 (t, J = 8.0 Hz, 9H);
13C NMR (125 MHz, CDCl3) δ (ppm) 141.0, 138.9, 123.5, 122.6,
121.5, 119.6, 110.5, 103.2, 47.0, 31.9, 29.8, 29.59, 29.58, 29.5, 29.4,
29.3, 29.2, 26.7, 22.7, 14.1; EI-MS (m/z) calcd for C60H87N3 849.69,
found 849.9 (Mþ). Elemental Anal. Calcd for C60H87N3: C, 84.75;
H, 10.31; N, 4.94. Found: C, 84.85; H, 10.20; N, 4.82.
5,10,15-Tridodecyl-10,15-dihydro-5H-diindolo[3,2-a:30,20-c]car-
bazole-3,8,13-tricarbaldehyde (10). Compound 9 (1.360 g,
1.60 mmol) was dissolved in dry DCM (10.0 mL) and cooled to 0 °C
under an N2 atmosphere. SnCl4 (0.57 mL, 5.20 mmol, 3.25 equiv)
was added dropwise with stirring, followed by slow addition of
dichloromethyl methyl ether (0.47 mL, 5.20 mmol, 3.25 equiv).
788 J. Org. Chem. Vol. 76, No. 3, 2011

Shao et al.
JOCArticle
29.5, 29.3, 26.9, 22.7, 14.1; MALDI-TOF MS (m/z) calcd for
1257.685, found 1258.737 (Mþ þ H). Elemental Anal. Calcd for
C81H99N3O3S3: C, 77.28; H, 7.93; N, 3.34; O, 3.81; S, 7.6. Found: C,
77.58; H, 7.84; N, 3.41; S, 7.81.
6H), 2.05 (quin, 6H), 1.26-1.12 (m, 54H), 0.86 (t, J = 7.0 Hz, 9H);
13C NMR (125 MHz, CDCl3) δ (ppm) 142.4, 141.3, 139.2, 133.7,
132.5, 128.5, 126.5, 124.3, 123.5, 121.5, 121.3, 119.1, 110.9, 110.0,
103.4, 47.2, 31.9, 30.1, 29.7, 29.64, 29.61, 29.58, 29.47, 29.3, 26.9,
22.7, 14.1; HR-FAB-MS (m/z) calcd for C87H102N6 (Mþ)
1230.8166, found 1230.8187 (error: 1.7 ppm); MALDI-TOF MS
(m/z) found 1232.139. Elemental Anal. Calcd for C87H102N6: C,
84.83; H, 8.35; N, 6.82. Found: C, 84.79; H, 8.27; N, 6.67.
2,20,200-(5,10,15-Tridodecyl-10,15-dihydro-5H-diindolo[3,2-
a:30,20-c]carbazole-3,8,13-triyl)tris(methan-1-yl-1-ylidene)trimalono-
nitrile (1). Compound 10 (187 mg, 0.20 mmol) and malononitrile
(11, 0.08 mL, 1.20 mmol, 6 equiv) were dissolved in DCM (10 mL)
under nitrogen atmosphere and then TiCl4 (0.14 mL, 1.20 mmol,
6 equiv) and pyridine (0.20 mL, 2.40 mmol, 12 equiv) were slowly
added at room temperature. The reaction mixture was heated to
reflux and the reaction was monitored by TLC. After 12 h the
reaction was cooled to room temperature and the mixture was
poured into water (80 mL) and extracted with DCM (3 ꢀ 80 mL).
The organic layer was dried over Na2SO4, and the solvent was
removed under vacuum. The crude concentrated extract was
dropped into a large amount of CH3OH to give the title compound
as a red precipitate (180 mg, 83%). Mp 179-180 °C; 1H NMR (500
MHz, CDCl3) δ (ppm) 8.93 (s, 3H), 7.95 (d, J = 8.8 Hz, 3H), 7.92
(s, 3H), 7.77 (d, J = 8.8 Hz, 3H), 5.07 (t, J = 8.0 Hz, 6H), 1.80
(quin, 6H), 1.26-1.01 (m, 54H), 0.85 (t, J = 7.5 Hz, 9H); 13CNMR
(125 MHz, CDCl3) δ (ppm) 160.2, 144.7, 139.9, 128.2, 124.7, 123.7,
123.6, 114.7, 114.1, 112.1, 104.3, 77.9, 47.4, 31.8, 29.52, 29.47, 29.37,
29.26, 29.0, 26.4, 22.6, 14.1; HR-FAB-MS (m/z) calcd for C72H87N9
(M þ H)þ 1078.7163, found 1078.7172 (error: 0.83 ppm); MALDI-
TOF MS (m/z) found 1078.571. Elemental Anal. Calcd for C72H87-
N9: C, 80.18; H, 8.13; N, 11.69. Found: C, 80.35; H, 8.11; N, 11.51.
2,20,200-(1E,10E,100E)-2,20,200-(5,10,15-Tridodecyl-10,15-dihy-
dro-5H-diindolo[3,2-a:30,20-c]carbazole-3,8,13-triyl)tris(ethene-
2,1-diyl)tribenzo[d]thiazole (2). Under N2 atmosphere, potassium
tert-butoxide (100 mg, 1.125 mmol, 9 equiv) was added in portion to
a solution of diethyl (benzo[d]thiazol-2-yl)methylphosphonate 12
(178 mg, 0.625 mmol, 5 equiv) and 10 (117 mg, 0.125 mmol) in dry
THF (20 mL). After adding potassium tert-butoxide, the reaction
solution turned red. The mixture was stirred at 65 °C overnight.
After cooling to room temperature, the reaction solution was diluted
with DCM (30 mL) and the organic layer was washed with water
(2 ꢀ 30 mL) and brine (2 ꢀ 30 mL) and dried over Na2SO4, then the
solution was concentrated under reduced pressure. The crude
concentrated extract was dropped into a large amount of CH3OH
to give the title compound as an orange powder (140 mg, 84%). Mp
190-191 °C; 1H NMR (500 MHz, CDCl3) δ (ppm) 8.25 (s, 3H),
8.01 (d, J = 8.0 Hz, 3H), 7.83 (d, J = 8.0 Hz, 3H), 7.74-7.67
(m, 6H), 7.57 (d, J = 8.0 Hz, 3H), 7.49 -7.46 (m, 6H), 7.36 (t, J =
7.5 Hz, 3H), 4.77 (br, 6H), 1.99 (br, 6H), 1.29-1.11 (m, 54H), 0.83
(t, J = 7.8 Hz, 9H); 13C NMR (125 MHz, CDCl3) δ (ppm) 167.6,
154.0, 141.55, 139.2, 138.9, 134.2, 127.4, 126.2, 125.0, 123.1, 122.7,
122.0, 121.8, 121.4, 119.7, 110.8, 103.1, 47.1, 31.9, 30.3, 29.86, 29.77,
29.74, 29.71, 29.66, 29.64, 29.4, 27.0, 14.1; HR-FAB-MS (m/z)
calcd for C87H102N6S3 (M þ H)þ 1327.7406, found 1327.7387
(error: -1.4 ppm); MALDI-TOF MS (m/z) found 1327.793. Ele-
mental Anal. Calcd for C87H102N6S3: C, 78.69; H, 7.74; N, 6.33; S,
7.24. Found: C, 78.86; H, 7.62; N, 6.18; S, 7.16.
2,20,200-(5,50,500-(1E,10E,100E)-2,20,200-(5,10,15-tridodecyl-10,15-
dihydro-5H-diindolo[3,2-a:30,20-c]carbazole-3,8,13-triyl)tris-
(ethene-2,1-diyl)tris(thiophene-5,2-diyl))tris(methan-1-yl-1-ylidene)-
trimalononitrile (4). Compound 16 (377 mg, 0.30 mmol) and
malononitrile (11, 119 mg, 1.80 mmol, 6 equiv) were dissolved in dry
dichloroethane (DCE) (20 mL) under nitrogen atomosphere
and then TiCl4 (0.2 mL, 1.80 mmol, 6 equiv) and pyridine (0.29 mL,
3.60 mmol, 12 equiv) were slowly added at room temperature. The
reaction mixture was heated at 85 °C and the reaction was mon-
itored by TLC. After 24 h the reaction was cooled to room tem-
perature and the mixture was poured into water (200 mL) and
extracted with DCM. The organic layer was dried over magnesium
sulfate and the solvent was removed under reduced pressure to give
the crude product as a red solid. Then 1.0 mL of CHCl3 was added
to dissolve the solid, followed by the addition of 15.0 mL of CH3OH.
The pure product was precipitated out as a purple-red solid (316 mg,
1
75%). Mp 219-220 °C; H NMR (500 MHz, CDCl3, 323 K)
δ (ppm) 8.12 (s, 3H), 7.72-7.66 (m, 6H), 7.62-7.55 (m, 6H), 7.39
(d, J =15.8Hz, 3H), 7.23(d, J=15.8 Hz, 3H), 7.16 (d, J =4.4 Hz,
3H), 4.75 (t, J = 7.5 Hz, 6H), 1.88 (br, 6H), 1.28-1.09 (m, 54H),
0.85 (t, J = 7.0 Hz, 9H); 13C NMR (125 MHz, CDCl3, 323 K)
δ (ppm) 155.8, 149.8, 141.9, 140.1, 139.1, 136.4, 133.2, 127.9, 126.2,
123.5, 122.2, 121.9, 117.8, 114.4, 113.8, 111.2, 103.7, 75.5, 47.2, 31.9,
29.8, 29.7, 29.59, 29.57, 29.5, 29.28, 29.26, 26.7, 22.6, 14.0; HR-
FAB-MS (m/z) calcd for C90H99N9S3 (M þ H)þ 1402.7264, found
1402.7224 (error: -2.9 ppm); MALDI-TOF MS (m/z) found
1402.762. Elemental Anal. Calcd for C90H99N9S3: C, 77.05; H,
7.11; N, 8.99; S, 6.86. Found: C, 77.16; H, 6.98; N, 8.76; S, 6.61.
2,20,200-(1E,10E,100E)-2,20,200-(5,50,500-(1E,10E,100E)-2,20,200-(5,
10,15-tridodecyl-10,15-dihydro-5H-diindolo[3,2-a:30,20-c]car-
bazole-3,8,13-triyl)tris(ethene-2,1-diyl)tris(thiophene-5,2-diyl))-
tris(ethene-2,1-diyl)tribenzo[d]thiazole (5). Under N2 atmosphere,
potassium tert-butoxide (253 mg, 2.25 mmol, 9 equiv) was added in
one portion to a solution of diethyl (benzo[d]thiazol-2-yl)methyl-
phosphonate 12 (357 mg, 1.25 mmol, 5 equiv) and 16 (315 mg,
0.25 mmol) in dry THF (30 mL). After adding potassium tert-
butoxide, the reaction solution turned red. The mixture was stirred
at 85 °C overnight. After cooling to room temperature, the reaction
solution was diluted with DCM, then washed with water and brine.
The organic layer was dried over Na2SO4 and the solution was con-
centrated under reduced pressure. The crude concentrated extract
was dropped into a large amount of CH3OH to give the title com-
pound as an red powder (338 mg, 82%). Mp 231-233 °C; 1HNMR
(500 MHz, Cl2CDCDCCl2, 313 K) δ (ppm) 8.17 (s, 3H), 7.99 (d,
J = 8.0 Hz, 3H), 7.85 (d, J = 8.0 Hz, 3H), 7.67-7.55 (m, 9H), 7.48
(t, J = 8.0 Hz, 3H), 7.37 (t, J = 8.0 Hz, 3H), 7.20-7.15 (m, 12H),
7.04 (d, J = 3.65 Hz), 4.76 (br, 6H), 2.09 (br, 6H), 1.37-1.18 (m,
54H), 0.82 (t, J = 7.1 Hz, 9H); 13C NMR (125 MHz, CCl2CDC-
DCCl2) δ (ppm) 165.8, 154.1, 145.5, 141.2, 139.1, 138.7, 134.5,
131.6, 129.8, 129.6, 128.8, 125.9, 125.7, 124.8, 123.6, 122.7, 121.3,
121.1, 120.5, 119.0, 110.6, 103.6, 47.2, 31.5, 29.7, 29.24, 29.21, 29.20,
4,40,400-(1E,10E,100E)-2,20,200-(5,10,15-Tridodecyl-10,15-dihy-
dro-5H-diindolo[3,2-a:30,20-c]carbazole-3,8,13-triyl)tris(ethene-
2,1-diyl)tribenzonitrile (3). Under N2 atmosphere, t-BuOK (200 mg,
2.25 mmol, 9 equiv) was added in a small portion to a solution of
diethyl (4-cyanophenyl)methylphosphonate 13 (200 mg, 1.25 mmol,
5 equiv) and 10 (234 mg, 0.25 mmol) in dry THF (30 mL). After
adding t-BuOK, the reaction solution turned red. The mixture was
stirred at 65 °C overnight. After cooling to room temperature, the
reaction solution was diluted with DCM (30 mL) and washed with
water (2 ꢀ 30 mL) and brine (2 ꢀ 30 mL), then the organic layer was
dried over Na2SO4 and concentrated to afford a crude solid. The
crude extract was dropped into CH3OH to give the title compound
as an yellow powder (220 mg, 72%). Mp 200-201 °C; 1H NMR
(500 MHz, CDCl3) δ (ppm) 8.30 (s, 3H), 7.73-7.61 (m, 18H), 7.44
(d, J = 16.4 Hz, 3H), 7.13 (d, J = 16.4 Hz, 3H), 4.89 (t, J = 7.5 Hz,
29.1, 28.9, 26.6, 22.2, 13.5; HR-FAB-MS (m/z) calcd for C105H114
-
N6S6 (Mþ) 1651.7463, found 1651.7460 (error: -0.2 ppm); MAL-
DI-TOF MS (m/z) found 1652.788. Elemental Anal. Calcd for
C105H114N6S6: C, 76.32; H, 6.95; N, 5.09; S, 11.64. Found: C, 76.22;
H, 6.72; N, 4.95; S, 11.56.
4,40,400-(1E,10E,100E)-2,20,200-(5,50,500-(1E,10E,100E)-2,20,200-(5,
10,15-tridodecyl-10,15-dihydro-5H-diindolo[3,2-a:30,20-c]car-
bazole-3,8,13-triyl)tris(ethene-2,1-diyl)tris(thiophene-5,2-diyl))-
tris(ethene-2,1-diyl)tribenzonitrile (6). Under N2 atmosphere,
J. Org. Chem. Vol. 76, No. 3, 2011 789

Shao et al.
JOCArticle
potassium tert-butoxide (240 mg, 2.0 mmol, 10 equiv) was added
in a small portion to a solution of diethyl (4-cyanophenyl)methyl-
phosphonate 13 (254 mg, 1.0 mmol, 5 equiv) and 16 (252 mg,
0.2 mmol) in dry THF (30 mL). After adding potassium tert-
butoxide, the reaction solution turned red. The mixture was stirred
at 85 °C overnight. After cooling to room temperature, the reaction
solution was diluted with DCM and washed with water and brine,
then the organic layer was dried over Na2SO4 and concentrated to
afford a crude solid. The crude extract was dropped into CH3OH to
give the title compound as an orange powder (264.2 mg, 85%). Mp
246-248 °C; 1H NMR (500 MHz, Cl2CDCDCCl2, 343 K) δ (ppm)
8.30 (s, 3H), 7.69-7.62 (m, 12H), 7.55 (d, J = 8.85 Hz, 6H),
7.32-7.25 (m, 9H), 7.11 (d, J = 3.75 Hz, 3H), 7.05 (d, J = 3.75 Hz,
3H), 6.91 (d, J = 15.75 Hz, 3H), 4.92 (t, J = 7.0 Hz, 6H), 2.13 (br,
6H), 1.42-1.21 (m, 54H), 0.87 (t, J = 7.0 Hz, 9H); 13C NMR
(125 MHz, CDCl3, 323 K) δ (ppm) 144.4, 141.6, 141.1, 139.9, 139.2,
132.4, 131.1, 128.9, 128.8, 126.5, 126.0, 125.7, 125.5, 123.7, 121.2,
120.7, 119.3, 118.8, 110.7, 110.5, 103.5, 47.3, 31.8, 30.1, 29.63, 29.58,
29.4, 29.31, 29.26, 29.20, 26.9, 22.6, 13.9; HR-FAB-MS (m/z)
calcd for C105H114N6S3 (M þ H)þ 1556.8379, found 1556.8376
(error: -0.2 ppm); MALDI-TOF MS (m/z) found 1556.890. Ele-
mental Anal. Calcd for C105H114N6S3: C, 81.04; H, 7.38; N, 5.40; S,
6.18. Found: C, 80.93; H, 7.21; N, 5.28; S, 6.34.
Acknowledgment. This work is financially supported by
the National University of Singapore under MOE AcRF
FRC grants R-143-000-444-112, R-143-000-412-112, and
R-143-000-403-112.
Supporting Information Available: Characterization data of
all of compounds and photophysical data of compounds 1-6.
This material is available free of charge via the Internet at http://
pubs.acs.org.
790 J. Org. Chem. Vol. 76, No. 3, 2011