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2.3. Synthesis of metal complexes
2.3.1. Synthesis of 4-dimethylamino-
a-cyanocinnamic acid (L)
The tert-butylcyanoacetate 1.24 mL (8.8 mmol) was added to
the ethanolic (50 ml) solution of 4-dimethylaminobenzaldehyde
(1.19 g; 8 mmol) followed by catalytic amount (2 drops) of piperi-
dine. The orange yellow solid that appeared on stirring overnight at
room temperature, was collected by filtration, washed thoroughly
with ethanol and dried under vacuum. This solid was stirred for
2 h, with 6 mL of trifluoroacetic acid and then poured into 50 mL
of water. The orange yellow solid that separated, was collected
by filtration, washed with ethanol and finally dried under vacuum.
Yield: 90%. 1H NMR (400 MHz, DMSO, TMS, 25 °C): d 3.06 (s, 6H),
6.82 (d, 2H), 7.93 (d, 2H), 8.05 (s, 1H), 13.20 (bs, 1H). IR (KBr,
cmꢁ1): 2212, 1662.7. CHN found: C: 67.03, H: 6.03, N: 13.43.
C12H12N2O2 requires C: 66.59, H: 5.54, N: 12.43.
2.3.2. [Zn(bpy)(L)2] (1)
A methanolic solution (10 mL) containing 4-dimethylamino-a-
Figure 1. UV–visible absorption spectra of complexes (1–3). Inset shows molecular
structures of complexes 1–3.
cyanocinnamic acid (L), (0.27 g; 1.2 mmol), Zn(OAc)ꢀ2H2O (0.13 g;
0.63 mmol) and bypiridine (0.098 g; 0.63 mmol) were allowed to
stir for 24 h at room temperature. The bright yellow solid that sep-
arated upon stirring overnight was collected by filtration, washed
with methanol and dried under vacuum. Yield: 88%. 1H NMR
(400 MHz, DMSO, TMS, 25 °C): d 3.01 (s, 6H), 6.75 (d, 2H), 7.82
(d, 2H), 8.14 (d, 4H), 7.91 (s, 2H), 8.14 (bs, 2H), 8.88 (bs, 2H),
9.16 (bs, 2H). IR (KBr, cmꢁ1): 2200.1, 554.6, 1600.1. CHN found:
C: 63.54, H: 5.78, N: 13.55. C34H30N6O4Zn requires C: 62.62, H:
4.63, N: 12.88.
2. Experimental
2.1. Materials
All the chemicals used were of analytical grade. Solvents were
used as recieved. 4-Dimethylaminobenzaldehyde, tert-butylcya
noacetate, bypiridine were purchased from Sigma Aldrich and Zn
(OAc)ꢀ2H2O, Cd(OAC)2ꢀ2H2O and Hg(OAC)2ꢀ2H2O were procured
2.3.3. [Cd(bpy)(L)2] (2)
from Merck chemicals. 4-Dimethylamino-a-cyanocinnamic acid
Synthesis of this complex is also accomplished following a sim-
ilar procedure of complex 1 taking Cd(OAC)2ꢀ2H2O (0.168 g;
0.63 mmol) in place of Zn(OAc)ꢀ2H2O keeping other reactants un-
changed. The bright yellow solid that separated upon stirring over-
night was collected by filtration, washed with methanol and dried
under vacuum. Yield: 87%. 1H NMR (400 MHz, DMSO, TMS, 25 °C):
d 3.00 (s, 6H), 6.79 (d, 2H), 7.56 (d, 2H), 7.85 (d, 4H), 7.94 (s, 2H),
8.03 (bs, 2H), 8.46 (bs, 2H), 8.75 (bs, 2H). IR (KBr, cmꢁ1): 2207.3,
516.8, 1583.5. CHN found: C: 59.17, H: 4.51, N: 12.73.
was synthesized and characterized by reported procedure [13].
2.2. Instrumental
The 1H NMR spectra were recorded using Bruker AV 400 spec-
trometer operating at the frequency of 400 MHz. The spectra were
recorded in solution with DMSO as internal lock. Electronic spectra
were measured on a GBC UV–Vis double beam spectrophotometer
with 0.6 nm resolution in DMSO solution of the complexes in the
200–800 nm range. FT-IR spectra were recorded on a Thermo Nico-
let Avatar FT-IR spectrometer with 4 cmꢁ1 resolution as KBr pow-
der in the frequency range 400–4000 cmꢁ1. The C, H and N
contents were determined by Thermoflash EA1112 series elemen-
tal analyzer. The single beam Z-scan technique was used to mea-
sure the third-order nonlinear optical susceptibility of the metal
complexes. This technique allows simultaneous measurement of
nonlinear refraction (NLR) and nonlinear absorption (NLA). Exper-
iment was performed using a Q-switched frequency doubled Nd:
YAG laser (Spectra–Physics USA, Model-GCR170) with a temporal
pulse width of 7 ns (FWHM) at 532 nm and a repetition rate of
C
34H30N6O4Cd requires C: 58.41, H: 4.32, N: 12.02.
2.3.4. [Hg(bpy)(L)2] (3)
Synthesis of this complex is also accomplished following a sim-
ilar procedure of complex
1
taking Hg(OAC)2ꢀ2H2O (0.20 g;
0.63 mmol) in place of Zn(OAc)ꢀ2H2O keeping other reactants un-
changed. The bright yellow solid that separated upon stirring over-
night was collected by filtration, washed with methanol and dried
under vacuum. Yield: 84%. 1H NMR (400 MHz, DMSO, TMS, 25 °C):
d 3.02 (s, 6H), 6.81 (d, 2H), 7.45 (d, 2H), 7.86 (d, 4H), 8.01 (s, 2H),
8.04 (bs, 2H), 8.56 (bs, 2H), 8.77 (bs, 2H). IR (KBr, cmꢁ1): 2206.3,
515.1, 1571.2. CHN found: C: 52.06, H: 4.02, N: 10.87.
C
34H30N6O4Hg requires C: 51.87, H: 3.84, N: 10.67.
10 Hz. The input pulse energy used was 100 lJ, which corresponds
to an on-axis-peak irradiance of 2.39 GW/cm2. The transmittance
was measured using two Pyroelectric detector (RjP-735) connected
with Laser Probe Rj-7620 Energy meter. The output of the laser had
a nearly Gaussian intensity profile. A lens of focal length 26 cm was
used to focus the laser pulses into a 1 mm quartz cuvette contain-
ing the sample solution. The laser was run in the single shot mode
using a data acquisition programme, with an approximate interval
of 3–4 s between each pulse. This low repetition rate prevents
sample damage and cumulative thermal effects [17,18] in the
medium.
3. Results and discussion
3.1. Linear absorption spectra
The molecular structures of the complexes and their linear
absorption spectra are displayed in Figure 1. The linear absorption
spectra of the complexes were obtained at room temperature in
DMSO solvent. The spectra shows an absorption band for
complexes around 425 nm, which corresponds to intraligand elec-
tronic transition. The spectra also show negligible single photon