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S. Zeng et al. / Dyes and Pigments 94 (2012) 290e295
(CDCl3, 400 MHz) d: 24.3, 26.1, 112.8, 122.3, 127.6, 129.3, 133.3, 133.7,
137.7, 140.7, 173.3, 177.7; MS (MALDI-TOF) m/z: 690.3 (M þ H)þ;
Anal. Calcd for C48H43N5: C 83.57; H 6.28; N 10.15; found C 83.35; H
6.30; N 10.18.
Compound c: was synthesized by the following procedure. Under
refluxing temperature, a solution of 2,4,6-trimethyl-1,3,5-s-triazine
(0.13 g, 1.06 mmol) in 20 mL methanol were added dropwise into
a 100 mL flask containing methanol (10 mL), 4-(di-p-tolylamino)
benzaldehyde (0.97 g, 3.2 mmol) and KOH (0.168 g) in 2 h. The
reaction mixture was refluxed for a further 24 h and then solvent
was removed. The residue was purified by column chromatography
on silica gel using toluene/ethanol (10/1) as eluent. The light yellow
powder was obtained. Yield, 0.451 g, 43.7%; m.p.94e95 ꢂC; UVevis
Fig. 1. The setup of up-converted fluorescent measurement.
(THF) lmax: 424 nm; 1H NMR (CDCl3, 400 MHz)
d: 2.39 (s, 18H),
7.12e7.19 (m,18H), 7.47e7.51 (m, 12H), 7.55 (d, J¼15.80 Hz, 3H), 8.04
(d, J¼16.03 Hz, 3H), 8.60e8.61 (m, 6H); 13C NMR (CDCl3)
d: 175.8,
investigated the inletting velocity and concentration of hydrogen
chloride (HCl) gas. One can be concluded the HCl gas should be fast
inlet at the beginning of the reaction by analyzing the results of
many experiments. About 24 h later, the velocity should be reduced
to a half of the beginnings. When the ratio of HCl and acetonitrile
reaches about 1.2: 1, we can found the yield was also improved
significantly. For the synthesis of compound c, the concentration of
potassium hydroxide (KOH) was considered as a crucial factor to
obtain high yield of c. When the concentration is very low, the
reaction will not start or be very slow. If the concentration is
very high, a side product will be found in the system by itself
condensation of 4-(di-p-tolylamino)benzaldehyde. The optimiza-
tion concentration is 0.1 M by analyzing the results of many
experiments.
142.8, 142.4, 141.9, 129.7, 127.4, 126.3, 126.0, 123.5, 123.3, 123.0,
121.0, 120.3, 120.3, 115.1, 110.2, 110.0, 25.9; MS (MALDI-TOF) m/z:
973.5 (M þ H)þ; Anal. calcd for C69H60N6: C 85.15, H 6.21, N 8.63;
found C 84.93, H 6.23, N 8.66.
2.3. Z-scan and pump-probe measurements
The laser pulses were produced by a mode-locked Ti:Sapphire
laser (Quantronix, IMRA), which seeded a Ti:Sapphire regenerative
amplifier, and focused onto a 1-mm-thick quartz cuvette contain-
ing the solutions of the derivatives. The incident and transmitted
laser pulse energy were monitored by moving the cuvette along the
propagation direction of the laser pulses. The Z-scan experimental
system was calibrated using a piece of cadmium sulfide (CdS) bulk
crystal as a reference because it possesses large 2PA at the wave-
length of 780 nm and has been well investigated in our laboratory.
3.2. UVevis and fluorescent spectra
The 2PA coefficient of CdS was determined to be 6.4 ꢃ 0.6 cm GWꢁ1
,
The UVevis spectra of the derivatives were measured in THF
with concentration 2 ꢀ 10ꢁ5 M as shown in Fig. 2(a). Obviously, all
of them show only one absorptive band within a wavelength range
from 450 to 850 nm. They are highly transparent in the near
infrared range (w780 nm). As increasing numbers of branches, the
position of the maximal peak is bathochromically shifted from
318 nm (a), to 378 nm (b) and, to 392 nm (c) nm, respectively, and
their absorptive coefficients also increase significantly owing to the
which was in good agreement with theoretical values within the
experiment uncertainty [14].
Thestandarddegeneratepump-probeexperimentwascarriedout
using 450-fs laser pulses at 1 kHz repetition rate with lower average
power to minimize accumulative thermal effects. The laser pulses
were produced by the same laserused inthe Z-scansdescribedabove.
To eliminate any coherent effects, the polarizations of the pump and
the probe pulses were perpendicular to each other. The pump and
probe beams were focused onto the solutions of these samples with
increased
p-conjugated length. Their optical band gaps (Eg) are
calculated according to the onset of the absorption spectrum. The
value lies in ca. 3.46 ev for a, 2.95 for b, and 2.89 eV for c. The
nonlinear absorption is attributed to 3PA for a because the excita-
tion wavelength (lexc) used for the measurements fulfills the
a minimum beam waist of 30 ꢃ 5
mm. The probe pulse energy was
a small fraction (<a few percentage) of the pump pulse energy.
2.4. The up-converted fluorescent measurements
requirement (2labs <lexc < 3labs) for 3PA studies at 780 nm as
shown in Fig. 1. On the other hand, the corresponding b and c will
exhibit 2PA or 2PEA processes owing to their energy gaps at the
range of lexc to 2lexc. Their fluorescent spectra are shown in Fig. 2
(b) with the concentration of 2 ꢀ 10ꢁ5 M in THF. In Fig. 2(b), one
notices that three derivatives have similar fluorescence profiles,
and none of them have multiple peaks. All of the derivatives exhibit
strong one-photon fluorescence with the maximal peaks at 460 nm,
483 nm and 490 nm, respectively. One can be found in the figure a,
b and c show a gradual red-shift to about 490 nm, which are
The up-converted fluorescence was tested using an experi-
mental setup given in Fig. 1. The intensity of the laser pulse incident
on the sample is controlled by a half-wave plate/GlaneThompson
polarizer system. The excitation radiation (linearly polarized)
with a desired intensity is split into two beams: one beam (less than
1%) to a power meter (Newport 1835C) to monitor the incident
intensity, and the other beam is focused with a lens (focal length
150 mm) on the sample, which is placed in a glass tube with an ID
of 10 mm. The fluorescence light emitted from the sample collected
at 90ꢂ from the propagation direction of the excitation beam is
detected by a photomultiplier (PM) tube (Hamamatsu R1767).
attributed to the gradually increase of
derivatives.
p-conjugated length in the
3. Results and discussions
3.3. The nonlinear absorption properties of a, b and c
3.1. Synthesis
Fig. 3(aec) summarizes the nonlinear absorption (NLA) results
of a, b and c with the concentration of 0.001 M by the Z-scan
measurement technique. As in shown Fig. 3(aec), all Z-scans
display a symmetric valley with respect to the focus, typical of an
2,4,6-trimethyl-1,3,5-triazine was synthesized based on Jung0s
method [13]. In order to improve the yield of this reaction, we also