2,6-Bis[4-(p-dihexylaminostyryl)-styryl]anthracene derivatives with large two-photon cross sections

Article abstract of DOI:10.1021/ol047658s

(Chemical Equation Presented) Anthracene derivatives with a variety of donor-acceptor substituents have been synthesized and shown to exhibit large two-photon cross sections over a wide range of wavelengths.

Full text of DOI:10.1021/ol047658s

ORGANIC
LETTERS
2
005
Vol. 7, No. 2
23-326
2
,6-Bis[4-(p-dihexylaminostyryl)-
3
styryl]anthracene Derivatives with Large
Two-Photon Cross Sections
Seung Kyu Lee, Wen Jun Yang, Jin Joo Choi, Chang Ho Kim,
Seung-Joon Jeon,* and Bong Rae Cho*
Molecular Opto-Electronics Laboratory, Department of Chemistry and
Center for Electro- and Photo-ResponsiVe Molecules, Korea UniVersity,
1-Anamdong, Seoul 136-701, Korea
chobr@korea.ac.kr
Received November 13, 2004
ABSTRACT
Anthracene derivatives with a variety of donor−acceptor substituents have been synthesized and shown to exhibit large two-photon cross
sections over a wide range of wavelengths.
There is much interest in the development of organic
materials exhibiting large two-photon (TPA) cross sections
D) quadrupoles, multibranched compounds, dendrimers,
1
5-20
octupoles, and porphyrin.
The results of these studies
(
δ
TPA) for possible applications in a number of new areas,
reveal that δTPA increases with the donor/acceptor strength,
conjugation length, and planarity of the π-center. Among
the most extensively utilized π-centers are benzene, biphenyl,
fluorene, dithieniothiophene, and dihydrophenathrene. Very
recently, we reported that 2,6-bis(styryl)anthracene deriva-
tives show large two-photon cross sections, demonstrating
the utility of the anthracene as an efficient π-center for the
including the fluorescence imaging of biological samples,
optical limiting, photodynamic therapy, and three-dimen-
sional optical data storage and microfabrication.
extensively investigated structural motifs are donor-bridge-
acceptor (D-π-A) dipoles, donor-bridge-donor (D-π-
1-14
The most
(
(
(
(
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8f
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In this work, we have synthesized a series of 2,6-bis[4-
(p-dihexylaminostyryl)styryl]anthracene derivatives 1-5 with
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(
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1
0.1021/ol047658s CCC: $30.25
© 2005 American Chemical Society
Published on Web 12/22/2004

would significantly enhance the two-photon cross section.
Dihexylamino group has been employed as the terminal
donor to improve the solubility. We now report that 1-5
show large two-photon cross sections over a wide range of
wavelengths.
Scheme 1
Figure 1.
a variety of donor-acceptor substituents (Figure 1) and
measured the δTPA values by using the femtosecond (fs)
fluorescence method. We were interested in learning whether
the presence of additional donors and extended conjugation
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M. W.; Br e´ das, J.-L.; Marder, S. R.; Perry, J. W. J. Phys. Chem. A. 2002,
Synthesis of 1-5 is shown in Scheme 1. Sandmeyer
reaction of 2,6-diaminoanthraquinone followed by the reduc-
tive alkylation afforded A in 67% overall yield. Compound
2 was synthesized by Heck coupling between A and 4-(p-
dihexylaminostyryl)styrene (C). To prepare 1 and 3-5, B1
and B2 were reacted with appropriate benzaldehyde deriva-
tives. The structures of 1-5 were unambiguously character-
ized by H and C NMR and elemental analysis (see
Supporting Information).
The molar absorptivity spectra for 1-5 in toluene are
displayed in Figure 2. The peak positions of absorption and
1
06, 11470. (d) Zojer, E.; Beljonne, D.; Kogej, T.; Vogel, H.; Marder, S.
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P. N. Chem. Mater. 2000, 12, 284. (e) Adronov, A.; Fr e´ chet, J. M.; He, G.
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000, 12, 2838. (f) Maciel, G. S.; Kim, K.-S.; Chung, S.-J.; Swiatkiewicz,
J.; He, G. S.; Prasad, P. N. J. Pys. Chem. B. 2001, 105, 3155. (g) Chung,
S.-J.; Lin, T.-C.; Kim, K.-S.; He, G. S.; Swiatkiewicz, J.; Prasad, P. N.;
Baker, G. A.; Bright, F. V. Chem. Mater. 2001, 13, 4071. (h) Kannan, R.;
He, G. S.; Lin, T.-C.; Prasad, P. N.; Vaia, R. A.; Tan, L.-S. Chem. Mater.
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(
Commun. 1999, 2055. (b) Ventelon, L.; Charier, S.; Moreaux, L.; Mertz,
J.; Blanchard-Desce, M. Angew. Chem., Int. Ed. 2001, 40, 2098. (c) Mongin,
O.; Porres, L.; Moreaux, L.; Mertz, J.; Blanchard-Desce, M. Org. Lett. 2002,
4
, 719. (d) Mongin, O.; Brunel, J.; Porr e` s, L.; Blanchard-Desce, M.
Tetrahedron. Lett. 2003, 44, 8121. (e) Mongin, O.; Porr e` s, L.; Katan, C.;
Pons, T.; Mertz, J.; Blanchard-Desce, B. Tetrahedron. Lett. 2003, 44, 8121.
(
f) Porres, L.; Mongin, O.; Katan, C.; Charlot, M.; Pons, T.; Mertz, J.;
Blanchard-Desce, M. Org. Lett. 2004, 6, 47.
18) (a) Lee, W.-H.; Cho. M.; Jeon, S.-J.; Cho, B. R. J. Phys. Chem.
000, 104, 11033. (b) Cho, B. R.; Son, K. H.; Lee, S. H.; Song, Y.-S.; Lee,
Y.-K.; Jeon, S.-J.; Choi, J.-H.; Lee, H.; Cho, M. J. Am. Chem. Soc. 2001,
23, 10039. (c) Lee, W.-H.; Lee, H.; Kim, J.-A.; Choi, J.-H.; Cho, M.;
(
2
1
Jeon, S.-J.; Cho, B. R. J. Am. Chem. Soc. 2001, 123, 10658. (d) Cho, B.
R.; Piao, M. J.; Son, K. H.; Lee, S. H.; Yoon, S. J.; Jeon, S.-J.; Choi, J.-H.;
Lee, H.; Cho, M. Chem. Eur. J. 2002, 8, 3907. (e) Yoo, J.; Yang, S. K.;
Jeong, M.-Y.; Ahn, H. C.; Jeon, S.-J.; Cho, B. R. Org. Lett. 2003, 5, 645.
Figure 2. Molar absorptivity spectra of 1-5 in toluene.
(f) Yang, W. J.; Kim, D. Y.; Jeong, M.-Y.; Kim, H. M.; Jeon, S.-J.; Cho,
B. R. Chem. Commun. 2003, 2618. (g) Lee, H. J.; Sohn, J.; Hwang, J.;
Park, S. Y.; Choi, H.; Cha, M. Chem. Mater. 2004, 16, 456. (h) Yang, W.
J.; Kim, C. H.; Jeong, M.-Y.; Lee, S. K.; Piao, M. J.; Jeon, S.-J.; Cho, B.
R. Chem. Mater. 2004, 16, 2783. (i) Kim, H. M.; Jeong, M.-Y.; Ahn, H.
C.; Jeon, S.-J.; Cho, B. R. J. Org. Chem. 2004, 69, 5749.
emission spectra are summarized in Table 1. Interestingly,
(1)
λ
of 1 and 4 are blue shifted by approximately 30-50
max
(19) (a) Liu, Z. Q.; Fang, Q.; Wang, D.; Gang, X.; Yu, W. T.; Shao,
nm from those of the corresponding 2,6-bis(p-dihexylami-
Z.-S.; Jiang, M.-H. Chem. Commun. 2002, 2900. (b) Liu, Z. Q.; Fang, Q.;
Wang, D.; Cao, D. X.; Xue, G.; Yu, W. T.; Lei, H. Chem. Eur. J. 2003, 9,
nostyryl)anthracene derivatives (D and E), despite the
1
8f
extended conjugation (Table 1). This could be explained,
if the structures of 1-5 are significantly distorted to hinder
the effective conjugation. In addition, there are several peaks
5
074. (c) Liu, Z. Q.; Fang, Q.; Cao, D.-X.; Wang, D.; Xue, G.-B. Org.
Lett. 2004, 6, 2933.
20) (a) Iwase, Y.; Kamada, K.; Ohta, K.; Kondo, K. J. Mater. Chem.
003, 13, 1575. (b) Ogawa, K.; Ohashi, A.; Koboke, Y.; Ohta, K. J. Am.
Chem. Soc. 2003, 125, 13356.
(
2
(
1)
near λ
in the absorption spectra. This indicates an
max
324
Org. Lett., Vol. 7, No. 2, 2005

structure. The much larger Stokes shifts for 1 and 4 than for
D and E provide evidence supporting this explanation (Table
Table 1. One- and Two-Photon Properties of 1-5 in Toluene
1). Because the excited-state structure is expected to be more
(
1)
a
{fl} b
∆ ν˜ c
Φd
(2)
e
δmaxf
compd
λ
λ
λ
max
max
max
stretched than the ground-state structure, the difference
between the two structures, and hence the Stokes shift, should
be larger for more distorted compounds.
g,h
i
D
E
1
2
455
587
427
448
487
656
503
497
526
527
551
650
678
1444
1792
3540
2200
2000
2530
2770
3450
2640
0.78
0.11
0.64
0.75
800
990
800
770
800
770
800
980
980
1100
2290
1140
h,j
i
{
max
fl}
(1)
max
Overall, λ
shows a parallel increase with λ
(Table
1810
1900
2580
2490
5530
3650
4
76
465
78
1). This means that the energy gap between the ground and
lowest excited state monotonically decreases as the extent
of charge transfer of the electronic ground state increases.
All of the compounds show large Stokes shifts ranging from
3
0.66
4
4
5
a
531
575
0.13
0.064
-
1
2
000 for 2 to 3540 cm for 1. The Stokes shifts are
b
λmax of the one-photon absorption spectra in nm. λmax of the one-
photon fluorescence spectra in nm. Stokes shift in cm
quantum yield. λmax of the two-photon excitation spectra in nm. Peak
two-photon absorptivity in 10
pulses except otherwise noted. 2,6-Bis(p-dihexylamino)anthracene. Ref-
erence 18f. δmax measured by ns pulses. 9,10-Dicyano-2,6-bis(p-dihexy-
laminostyryl)anthracene.
c
-1
d
significantly smaller for compounds with OR groups, i.e.,
2,3 < 1 and 5 < 4, probably because the emitting states are
destabilized by these substituents. The fluorescence quantum
yields range from 0.75 for 2 to 0.064 for 5 and decrease as
the extent of charge transfer increases. The much smaller
quantum yields for 4 and 5 may be due to the much lower
energy of the emitting states, which may facilitate the
nonradiative pathways.
. Fluorescence
e
f
-
50
4
-1
cm s photon (GM) measured by fs
g
h
i
j
increased number of one-photon-allowed states near the
lowest energy Franck-Condon states. If the structure is
distorted, the intramolecular charge transfer (ICT) would be
significantly inhibited, which would in turn increase the
probability of the localized absorption.
The two-photon cross section δTPA was determined by the
two-photon-induced fluorescence measurement technique as
1
5b,18c
described previously.
due to the excited-state excitation, we have used femtosecond
fs) laser pulses. The pulse width and repetition rate of the
To avoid possible complications
The absorption spectra show a systematic bathochromic
(
(1)
shift in the order 1 < 2 < 3 < 4 < 5. The λ is shifted to
max
laser are 160 fs and 1 kHz, respectively (see Supporting
Information). As shown in Figure 4, the output intensity of
a longer wavelength as the 9,10-substituent is changed from
H to OPr to CN, i.e., 1 < 2 < 4, and as Y is changed to a
stronger donor, i.e., 1 < 3 and 4 < 5. This indicates that the
energy gap between the ground and Franck-Condon states
decreases as the conjugation is extended by the substituent
regardless of whether it is electron donating or withdrawing.
Furthermore, the charge-transfer bands for 4 and 5 are
virtually separated from the shorter wavelength bands. This
suggests a significant ICT from the donor to the acceptor.
The fluorescence spectra of 1-5 are displayed in Figure
3. As observed in the absorption spectra, the emission spectra
Figure 4. Dependence of output fluorescence intensity (Iout) of
compound 1 in toluene on the input laser power (Iin). The insert
2
shows the linear dependence of Iout on Iin (800 nm, 1 kHz, τ )
160 fs).
two-photon excited fluorescence is linearly dependent on the
square of the input laser intensity, indicating the occurrence
of nonlinear absorption.
The two-photon excitation spectra for 1-5 are displayed
Figure 3. Normalized fluorescence spectra of 1-5 in toluene.
(2)
in Figure 5. Table 1 shows that λ of 1-3 appear at 770-
max
8
00 nm. This turns out to be very important for practical
of 2 and 3 show shoulders, indicating the existence of more
than one emitting state. This is again due to the distorted
applications, because the most common source for the two-
photon excitation is the Ti/Sapphire laser, which emits an
Org. Lett., Vol. 7, No. 2, 2005
325

Figure 6. Normalized one-photon absorption (OPA) and two-
Figure 5. Two-photon excitation spectra of 1-5 in toluene.
photon excitation (TPE) spectra (left) and SPEF and TPEF spectra
(right) of 1. The two-photon spectrum is plotted against λ/2 (twice
the photon energy).
(2)
intense beam at around 800 nm. Moreover, λ
increases
max
dramatically to 990 nm when strongly electron-withdrawing
CN groups are attached at the 9,10-positions (Table 1). This
suggests an interesting possibility that the wavelength of the
maximum two-photon cross section could be tuned by using
an appropriate donor-acceptor substituent.
Moreover, the δmax value of 4 is more than twice as large as
that of E. The most interesting result from this study is that
1
-5 show large TPA cross sections over a wide range of
wavelengths, which will be useful for a variety of applica-
tions, including optical limiting. The results may be ascribed
to the molecular size. As the molecular size increases through
the extended π-conjugation, the density of states will
increase, providing more effective coupling channels between
the ground and two-photon-allowed states, which would in
turn increase the TPA cross section over a wide range of
wavelengths.
The δmax value gradually increases in the order, 1 < 2 <
3
< 4, reaching a maximum value of 5530 GM for 4.
(
1)
Because λ
increases in the same order, the substituents
max
seem to stabilize the excited state more than the ground state
to diminish the energy gap between the ground- and two-
photon-allowed states. This would predict a larger two-
photon cross section, because the smaller the energy gap,
1
8a-c
the higher the probability of the two-photon excitation.
In conclusion, we have synthesized a series of 2,6-bis[4-
(p-dihexylaminostyryl)styryl]anthracence derivatives with a
large δmax. The δmax values increase gradually in the order 1
< 2 < 3 < 4, reaching a maximum value of 5530 GM for
This result underlines the importance of ICT for obtaining a
TPA chromophore with a large δmax. The only exception to
this trend is 5, whose δmax is smaller than that of 4. At
present, the origin of this dichotomy is not clear.
2
2
4. Moreover, 1-3 show large TPA cross sections over a
wide range of wavelengths. These molecules may ultimately
find useful applications as two-photon materials.
Figure 6 shows that the two-photon-allowed state of 1 is
located at somewhat higher energy than the Franck-Condon
state, as predicted by the symmetry.21 A similar result is
observed for all compounds (Table 1). Nevertheless, there
is a significant overlap between the one- and two-photon
spectra in terms of the total absorption energy. Perhaps this
is why δmax values of 1-5 are so large, because the higher
the probability of the overlap between the one- and two-
photon-allowed states, the larger the two-photon cross
section. Moreover, the single-photon excitation fluorescence
Acknowledgment. This work was supported by KOSEF
(R02-2004-000-10006-0). S. K. Lee and J. J. Choi were
supported by BK21 program.
Supporting Information Available: Synthesis of 1-5
and measurements of two-photon cross section by the fs
fluorescence method. This material is available free of charge
via the Internet at http://pubs.acs.org.
(SPEF) and two-photon excitation fluorescence (TPEF)
spectra overlap with each other. This indicates that the
emission occurs from the same excited states, regardless of
the mode of excitation.
OL047658S
(22) Most efficient TPA chromophores showing the largest TPA cross
sections measured by fs fluorescence experiments are 2,7-bis{[7-(p-
dioctylaminostryl)-9,10-dihydrophenathren-2-yl]vinyl}-9,10-dihydrophen-
It is interesting to note that the δmax value of 1 is slightly
1
8f
larger than 1100 GM determined for D (Table 1).
(2)
max
17b
athrene (λ
) 740 nm, Φ ) 0.66, δmax ) 3760 GM) and the three-
(2)
branched fluorenylene-vinylene derivative (λ
) 740 nm, Φ ) 0.74,
max
δmax ) 3660 GM).1
7c
(21) MeClain, W. M. Acc. Chem. Res. 1974, 7, 129
326
Org. Lett., Vol. 7, No. 2, 2005