Enhanced two-photon properties of tri-branched styryl derivatives based on 1,3,5-triazine

Article abstract of DOI:10.1246/cl.2004.470

Novel styryl derivatives with triphenylamine as donor and 1,3,5-triazine as acceptor were synthesized and their one- and two-photon properties were investigated. These molecules show large two-photon absorption (TPA) cross sections and strong two-photon f

Full text of DOI:10.1246/cl.2004.470

470
Chemistry Letters Vol.33, No.4 (2004)
Enhanced Two-photon Properties of Tri-branched Styryl Derivatives Based on 1,3,5-Triazine
Fanshun Meng, Bo Li,y Shixiong Qian,y Kongchang Chen, and He Tianꢀ
Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, P. R. China
yDepartment of Physics, Fudan University, Shanghai 200433, P. R. China
(Received January 14, 2004; CL-040050)
Novel styryl derivatives with triphenylamine as donor and
1,3,5-triazine as acceptor were synthesized and their one- and
two-photon properties were investigated. These molecules show
large two-photon absorption (TPA) cross sections and strong
two-photon fluorescence. TPA cross section is as large as
1:64 ꢁ 10ꢂ20 cm4/GW for the tri-branched molecule.
octupolar tri-branched structure containing three D-ꢁ-A sub-
units.
Equivalent 4-formyl-40-methoxytriphenylamine and o-
chloroaniline were refluxed in ethanol for 4 h to give 4-{[(2-
chlorophenyl)imino]methyl-N-(p-methoxyphenyl)-N-phenyl}-
benzenamine (1). The crude product was dried under high vac-
cum and used directly without further purification. The reactions
of 2,4,6-tris(p-methylphenyl)-1,3,5-triazine and 1 with the ratio
of 1:1, 1:2, and 1:3 were performed in the presence of t-BuOK at
100 ꢃC in DMF for 4 h to give styryl derivatives T01, T02, and
T03 in 51–67% yield, respectively. The final products were pu-
rified with chromatography (silica gel) and characterized with
1H NMR, 13C NMR and TOF–MS.20
Organic materials that can simultaneously absorb two pho-
tons have attracted considerable attention due to their increasing
applications in two-photon upconversion laser,1 two-photon la-
ser scanning fluorescence imaging,2 3D optical data storage,3 op-
tical limiting,4 and photodynamic therapy.5 These applications
request the materials with large two- photon absorption (TPA)
cross sections (ꢀ) and strong two- photon excited fluorescence.
The connection of donor and acceptor by ꢁ-conjugated bridge
to form D-ꢁ-D, A-ꢁ-A, or D-ꢁ-A structure is an effective
way to improve TPA cross sections.6–11 Recently, more research
has focused on octupolar,12 multi-branched,13–16 or dendrimer-
ic17–19 molecules, whose TPA cross sections can be significantly
improved by the increased chromophore density of the mole-
cules and the cooperative enhancement effect among the chro-
mophores.
In this letter, we describe the synthesis, one- and two-photon
properties of novel styryl derivatives (Figure 1). In these com-
pounds, triphenylamine serves as electron donor, 1,3,5-triazine
as electron acceptor and styryl as chromophore. T01 and T02
form D-ꢁ-A and D-ꢁ-A-ꢁ-D linear structure, while T03 forms
Figure 2. The absorption (1 ꢁ 10ꢂ5 M) and fluorescence (at the
same absorbance) spectra of T01, T02, and T03 in chloroform.
Table 1. The optical properties of T01, T02, and T03 in chloro-
form
H3C
CH CH
N
N
ab
fl
TPF
ꢂmax (nm) ꢂmax
/nm
ꢀa
ꢀb
ꢂmax
N
N
/10ꢂ20 cm4/GW
/nm
OCH3
T01
CH3
T01
T02
T03
293, 418
307, 425
312, 430
552 0.49
554 0.47
555 0.47
0.31
0.365
1.64
578
577
576
CH3
H3CO
OCH3
aFluorescence quantum yield determined using fluorescein in
0.1 N NaOH as the standard. TPA cross sections measured at
800 nm (140 fs).
N
N
N
b
N
CH CH
CH CH
N
T02
As shown in Figure 2 and Table 1, there are two strong ab-
sorption bands in the UV and visible regions. T01 shows the
maximum absorption wavelength at 418 nm, while the maxi-
mum absorption peaks for T02 and T03 are red-shifted to 425
and 430 nm, respectively. The absorption peak at longer wave-
length corresponds to ꢁ–ꢁꢀ excitation of the whole molecules,
whereas the shorter absorption peak attributes to localized exci-
tation. Both the maximum absorption wavelengths and the molar
extinction coefficients are increased with increasing chromo-
phore intensity, which means that the electrons are delocalized
over the whole molecules and interaction among the chromo-
N
CH CH
CH CH
N
N
N
N
H3CO
OCH3
OCH3
CH CH
N
T03
Figure 1. The chemical structures of T01, T02 and T03.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.4 (2004)
471
2
3
4
5
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cence under the irradiation of light at the maximum absorption
wavelengths. The fluorescence quantum yield was determined
to be about 0.47 using fluorescein in 0.1 N NaOH as the standard.
Although the absorption spectra are of great difference, these
compounds show similar fluorescence spectra with the peaks lo-
cated at about 554 nm. The Stokes’ shifts for T01, T02, and T03
are 134, 129 and 125 nm, respectively.
TPA cross sections of these compounds were determined by
femtosecond open aperture Z-scan technique according to previ-
ously described method.21 As shown in Table 1, the TPA cross
sections for T01, T02, and T03 are 0:31 ꢁ 10ꢂ20 cm4/GW,
0:365 ꢁ 10ꢂ20 cm4/GW and 1:64 ꢁ 10ꢂ20 cm4/GW, respective-
ly. These values are comparable to those of the most representa-
tive materials reported in the literatures measured with similar
molecular weight.9,11,13 The TPA cross section of T02 is only
slightly higher than that of T01 although its chromophore densi-
ty is much larger. But, the TPA cross section of T03 is nearly 5
times higher than those of T01 and T02. In compound T03,
1,3,5-triazine is connected with three styryl units and forms
tri-branched octupolar structure. The increased chromophore
density, delocalization interaction and the octupolar structure
are responsible for its much larger TPA cross sections than the
other two molecules.
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Under the excitation of 800 nm laser pulse (140 fs), com-
pounds T01, T02, and T03 emit strong frequency upconverted
fluorescence with the peaks located at 578, 577, and 576 nm, re-
spectively. The maximum wavelengths of two-photon fluores-
cence are red-shifted about 21 to 26 nm compared with those
of linear fluorescence emission. Since there is no absorption at
wavelength longer than 550 nm, the upconverted fluorescence
comes from two-photon process. As an example, the two-photon
fluorescence spectra of T03 under different laser intensity are
shown in Figure 3. The linear dependence of fluorescence inten-
sity on the square of the excitation intensity as shown in the inset
confirms that TPA is the main excitation mechanism of two-pho-
ton fluorescence.
`
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C. W. Spangler, J. Phys. Chem. B, 107, 7540 (2003).
20 T01: mp 174–176 ꢃC. 1H NMR (CDCl3, 500 MHz): ꢃ 2.48 (s, 6H),
3.82 (s, 3H), 6.87 (d, 2H, J ¼ 8:72 Hz), 7.02 (m, 3H), 7.10 (m, 4H),
7.26 (m, 4H), 7.37 (d, 4H, J ¼ 7:90 Hz), 7.41 (d, 2H, J ¼ 8:36 Hz),
7.66 (d, 2H, J ¼ 8:07 Hz), 8.66 (d, 4H, J ¼ 7:87 Hz), 8.73 (d, 2H,
J ¼ 8:02 Hz). 13C NMR (CDCl3, 100 MHz): ꢃ 22.39, 56.14,
115.51, 122.63, 123.21, 124.31, 126.53, 126.97, 128.19, 128.26,
129.59, 129.87, 129.95, 129.99, 130.80, 130.85, 134.41, 135.68,
140.98, 142.37, 143.52, 148.33, 148.79, 157.11, 171.66, 172.02.
TOF–MS (ESþ): 636.3 (M, 8%), 637.4 (M + 1, 100%), 638.3
3500
3000
576nm 1.66GW/cm2
2500
3000
2000
1500
2500
1000
500
(M
+
2, 30%). T02: mp 106–108 ꢃC. 1H NMR (CDCl3,
1.33GW/cm2
2000
1500
1000
500
0
0
500 MHz): ꢃ 2.48 (s, 3H), 3.82 (s, 6H), 6.87 (m, 4H), 7.02 (m,
7H), 7.10 (m, 9H), 7.25 (m, 6H), 7.37 (d, 2H, J ¼ 8:10 Hz), 7.41
(d, 4H, J ¼ 8:64 Hz), 7.66 (d, 4H, J ¼ 8:41 Hz), 8.66 (d, 2H,
J ¼ 7:15 Hz), 8.73 (d, 4H, J ¼ 8:33 Hz). 13C NMR (CDCl3,
100 MHz): ꢃ 21.745, 55.45, 114.79, 121.90, 122.50, 123.60,
125.80, 126.26, 127.50, 127.57, 128.89, 129.18, 129.25, 129.30,
130.06, 130.11, 133.64, 134.90, 140.25, 141.64, 142.84, 147.60,
148.05, 156.38, 170.87, 171.23. TOF–MS (ESþ): 921.5 (M,
37%), 922.5 (M + 1, 100%), 923.5 (M + 2, 30%). T03: mp
256–258 ꢃC. 1H NMR (CDCl3, 500 MHz): ꢃ 3.81 (s, 9H), 6.87
(d, 6H, J ¼ 8:81 Hz), 7.02 (m, 12H), 7.09 (m, 12H), 7.18 (d, 3H,
J ¼ 16:23 Hz), 7.24 (t, 6H), 7.39 (d, 6H, J ¼ 8:55 Hz), 7.62 (d,
6H, J ¼ 8:30 Hz), 8.68 (d, 6H, J ¼ 8:32 Hz). 13C NMR (CDCl3,
100 MHz): ꢃ 56.16, 115.49, 122.60, 123.20, 124.31, 126.51,
126.98, 128.21, 128.28, 129.88, 129.96, 130.80, 135.58, 140.95,
142.37, 148.29, 148.75, 157.06, 171.57. TOF–MS (ESþ): 1206.6
(M, 43%), 1207.6 (M + 1, 100%), 1208.7 (M + 2, 60%), 1209.7
(M + 3, 20%).
0.0 0.5 1.0 1.5 2.0 2.5 3.0
I2pump (GW2/cm4)
0.83GW/cm2
0.33GW/cm2
500
550
600
650
700
750
800
Wavelength /nm
Figure 3. The two-photon excited fluorescence spectra of T03
in chloroform.
We thank the National Science Foundation of China and
Shanghai Education Committee for the financial support.
References and Notes
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21 F. S. Meng, J. Mi, S. X. Qian, K. C. Chen, and H. Tian, Polymer,
44, 6851 (2003).
Published on the web (Advance View) March 23, 2004; DOI 10.1246/cl.2004.470