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Published on the web February 27, 2010
Two-photon Absorption Properties of Novel Conjugated Dyes Containing a Benzophenone Unit
Jian Liu, Fang Gao,* Long Yang, Chunfeng Wang, Hongru Li,* and Shengtao Zhang
College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, P. R. China
(Received December 24, 2009; CL-091140; E-mail: hrli@cqu.edu.cn)
A variety of new conjugated dyes bearing a benzophenone
unit were synthesized, and the linear absorption and emission
were determined. Two-photon absorption properties of the
derivatives have been measured by a Ti:sapphire femtosecond
laser tuning from 720 to 880 nm at intervals of 20 nm. One- and
two-photon optical properties of the derivatives were found to be
significantly dependent on their chemical structures.
C2, this branch was synthesized by Wittig-Horner reaction.
While for C3, this branch was built by thermal condensation.
Then, benzophenone was coupled as the other branch of the
derivatives by Wittig-Horner reaction. The final products were
purified by chromatography (silica gel) in the yield of
1
approximate 60%, and the structures were characterized by H,
13C NMR, IR, and elemental analysis.9
The linear optical properties of the derivatives C1, C2, and
C3 were investigated in benzene and ethyl acetate (EtOAc),
and the data are listed in Table 1. As shown in Figure 2, the
derivatives exhibit double absorption peaks in 275-500 nm. The
first absorption band is similar to the absorption of triphenyl-
amine, indicating that it may arise from the localized electronic
transition of triphenylamine core. The second absorption band
around 400 nm (for C1 and C2) and 430 nm (for C3) could be
assigned to ³-³* electron transition with large molar extinction
coefficients in the order of 105 dm3 mol¹1 cm¹1. As compared
with those of C1 and C2, the absorption maxima of C3 are red-
shifted, indicating that C3 has a larger internal charge transfer.
The derivatives C1 and C2 exhibit remarkably strong
fluorescence emission in benzene with the quantum yields as
high as 0.97 and 0.93, respectively. This is presumably due to
the increased structral stiffness by benzophenone unit. Although
one-photon emission of C1 and C2 is somewhat reduced in
EtOAc, they still exhibit remarkable emission with the quantum
yields as large as 0.52 and 0.29, respectively. The reduction
could be mainly ascribed to increases in the molecular geometry
twist and the extent of the internal charge transfer in EtOAc, and
thus nonradiative deactivation of the excited state is increased.9
As compared with the emission maxima of the derivatives in
benzene, they shift more to longer wavelength in EtOAc. The
emission displays more remarkable solvent effect than the
absorption, which could be due to the enhancement of internal
charge-transfer of (³, ³*) transition of the derivatives by benzo-
phenone unit, and the linear emission thus is more pronouncedly
sensitive solvent polarity in the excited state. While, one-photon
fluorescence intensity of C3 is lower than that of C1 and C2,
especially much lower in EtOAc. This could be ascribed to
larger internal conversion in the excited state of C3 due to the
nitro group and the fluorescence emission is thus prohibited.10
TPA emission and TPA cross sections of these derivatives
were determined with a Ti:sapphire femtosecond laser. TPA
cross sections were estimated by fluorescence based technique.9
The maximal TPA emission wavelength and TPA cross sections
(measured by 800 nm laser) of these derivatives are shown in
Table 1. It is interesting to observe that the maximal TPA
emission is almost identical to one-photon emission wavelength.
As compared with C1 and C2, C3 has not only red-shifted TPA
emission but a larger cross section (1443 GM in benzene,
1687 GM in EtOAc, 1 GM = 10¹50 cm4 s photon¹1). We notice
that two-photon cross section of C3 is much larger than that of
(p-nitrostyryl)triphenylamine,11 indicating that benzophenone
In recent decades, two-photon absorption (TPA) has been a
subject which attracts intensive attention in chemistry.1 One of
the central themes in organic and material chemistry is to
develop highly fluorescent and remarkable two-photon absorp-
tion dyes since they can be applied widely in optical and
biomedical fields, such as two-photon fluorescence sensors,2
two-photon fluorescence excitation microscopy,3 three-dimen-
sional optical data storage and microfabrication,4 optical limit-
ing materials,5 and two-photon photodynamic therapy.6 Thus,
many efforts have been devoted to develop new TPA dyes and
survey the relationship between molecular structure and optical
properties.7 Benzophenone is a well-known photoactive com-
pound and is used extensively in material and biomedical fields.8
We can imagine that if a two-photon chromophore is linked with
benzophenone via conjugated bond, the new dyes have great
application potentials in various fields. Furthermore, the intro-
duction of beznophenone branch could enhance two-photon
absorption due to the donor-accepor moiety. Novel conjugated
derivatives with benzophenone unit, namely, 4-(p-benzoylsty-
ryl)-4¤-styryltriphenylamine (C1), 4-(p-benzoylstyryl)-4¤-(3,4,5-
trimethoxystyryl)triphenylamine (C2), and 4-(p-benzoylstyryl)-
4¤-(p-nitrostyryl)triphenylamine (C3) (Figure 1) were developed
in this letter. As shown in Figure 1, the substituent group is in
one branch, and benzophenone locates at the other branch. Each
branch forms a ³-conjugated structure and the overall conjuga-
tion of the derivatives are efficiently extended.
The derivatives were synthesized by different synthetic
strategy to construct conjugated double bonds.9 The branch
without benzophenone was first introduced to triphenylamine-
core. For C1, this branch was constructed by Wittig reaction. For
O
O
O
N
N
N
H3CO
OCH3
OCH3
NO2
C1
C2
C3
Figure 1. Chemical structures of C1, C2, and C3.
Chem. Lett. 2010, 39, 324-325
© 2010 The Chemical Society of Japan
Liu, Jian
