Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

Article abstract of DOI:10.1016/j.saa.2014.07.039

Four novel Zn(II) terpyridine complexes (ZnLCl₂, ZnLBr ₂, ZnLI₂, ZnL(SCN)₂) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorp

Full text of DOI:10.1016/j.saa.2014.07.039

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral and third-order nonlinear optical properties of
terpyridine Zn(II) complexes based on carbazole derivative with
polyether group
a
a
a
a
a
a
a
Ming Kong , Yanqiu Liu , Hui Wang , Junshan Luo , Dandan Li , Shengyi Zhang , Shengli Li ,
a,
⇑
a,b,
⇑
Jieying Wu , Yupeng Tian
a
Department of Chemistry, Key Laboratory of Functional Inorganic Material Chemistry of Anhui Province, Anhui University, Hefei 230039, PR China
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
2 2 2 2
Four novel Zn(II) terpyridine complexes (ZnLCl , ZnLBr , ZnLI , ZnL(SCN) ) based on carbazole derivative
ꢀ
ꢀ
ꢀ
ꢀ
Four Zn(II) terpyridine complexes
with different coordination anions
were designed and synthesized.
The linear and nonlinear
spectroscopic properties were carried
out.
The results revealed that two Zn(II)
complexes possessed larger TPA
cross-sections.
group were designed, synthesized and fully characterized. Their photophysical properties including
absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limit-
ing (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations
(TD-DFT). The results of NLO determination revealed that two Zn(II) complexes possessed larger two-
photon absorption cross-sections and ZnLCl complex showed superior optical power limiting property
2
which suggested a large polarizability, meeting the requirements for third-order NLO materials offering
promise for applications in optical limiting in the near infrared region.
2
The complex of ZnLCl showed
superior optical power limiting
property.
a r t i c l e i n f o
a b s t r a c t
Article history:
Four novel Zn(II) terpyridine complexes (ZnLCl , ZnLBr , ZnLI , ZnL(SCN) ) based on carbazole derivative
2
2
2
2
Received 27 March 2014
Received in revised form 8 July 2014
Accepted 18 July 2014
group were designed, synthesized and fully characterized. Their photophysical properties including
absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limit-
ing (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations
Available online 27 July 2014
(
(
TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence
OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated
Keywords:
Terpyridine
Carbazole derivative
in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture
Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080 nm. These results
⇑
Corresponding authors. Address: Department of Chemistry, Key Laboratory of
Functional Inorganic Material Chemistry of Anhui Province, Anhui University, Hefei
2
30039, PR China (Y.p. Tian).
E-mail addresses: jywu1957@163.com (J. Wu), yptian@ahu.edu.cn (Y.p. Tian).
http://dx.doi.org/10.1016/j.saa.2014.07.039
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

5
22
M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
Photophysical properties
TD-DFT calculation
Third-order nonlinear optical (NLO)
Optical power limiting
revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior
optical power limiting property.
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
To better identify the charge transition, time-dependent density
functional theory (TD-DFT) calculations were carried out in vacuo.
0
0
Among so many N-heteroatom ligands, analogous 2, 2 :6 ,
-terpyridine compounds as a electron acceptor (A) have been
Geometry optimizations were carried out with B3LYP functional
without any symmetry restraint, and the TD-DFT calculations were
performed on the optimized structure with B3LYP functional. All
calculations, including optimizations and TD-DFT, were performed
with the G03 software. Geometry optimization of the singlet
ground state and the TD-DFT calculation of the lowest 50 sin-
glet–singlet excitation energies were calculated with a basis set
composed of 6-31 G for C H N O atoms and the Lanl2dz basis set
for Cl, Br, I, Zn atoms. An analytical frequency confirmed evidence
that the calculated species represents a true minimum without
imaginary frequencies on the respective potential energy surface.
The lowest 40 spin-allowed singlet–singlet transitions, up to
energy of about 5 eV, were taken into account in the calculation
of the absorption spectra.
0
0
2
attracted considerable attention in diverse areas of current
research [1–7]. This kinds of terpyridine in constructing specific,
stable metal complexes and self-assembly with unique properties
have evolved from a fundamental scientific field into daily-life
applications such as biological medicine [8,9], nanotechnol-
ogy[10,11], catalysis [12–18], polymer science [19–21], optical
materials which have led to applications in solar cells, probe,
self-assembly, biopolymer, and for the localized release of bio-
active species [22–34]. Such these special optical materials exhib-
iting strong third-order nonlinear optical (NLO) absorptions have
attracted considerable interests because of their potential applica-
tions in optical switching, three-dimensional (3D) fluorescence
imaging, 3D optical data storage, 3D lithographic microfabrication
and optical power limiting [35–40].
NLO properties were measured by the Z-scan technique with a
femtosecond laser pulse and Ti: 95 sapphire system (680–
1080 nm, 80 MHz, 140 fs, Chameleon II) as the light source. The
beam was spatially filtered to remove higher-order modes and
tightly focused using a 5 cm focal length lens. The incident average
power of 400 mW was adjusted by a Glan prism. The thermal heat-
ing of the sample with high repetition rate laser pulse was removed
by the use of a mechanical chopper running at 10 Hz. A 1 mm cell of
Zinc (d10) possessed a great diversity of properties and can eas-
ily combine with terpyridine ligand [41–43]. As a result, four Zn(II)
terpyridine complexes with different coordination anions were
designed and synthesized to study how different kinds of anions
carry out an influence on their spectroscopic properties. Within
the ligand molecule, 9-(2-(2-methoxyethoxy) ethyl)-9H-carbazole
ꢁ
3
ꢁ1
group was introduced as a electron donor (D) and efficient
p
-elec-
the sample in DMF at 1.0 ꢂ 10 mol L was put in the light path,
tron bridge, polyether chain attached to the carbazole group was to
increase the solubility of these D–A type ligand (coordination
compounds). So this design strategy combined those advantages
to construct novel model terpyridine compounds. Herein, the syn-
thesis and their photophysical properties of them with different
coordination anions were systematically investigated experimen-
tally. In addition, time-dependent density functional theory (DFT)
calculations were also performed to offer a suggestion for the
relationships between the structures and properties.
and all measurements were carried out at room temperature.
Synthesis
Preparation of 9-(2-(2-methoxyethoxy) ethyl)-9H-carbazole-3 – carb-
aldehyde (m3)
m1 Tetrabutylammonium (1.37 g, 4.25 mmol) and 2-(2-(2-
2 2
methoxyethoxy)ethoxy) ethanol dissolved in 150 mL CH Cl were
added into 500 mL round-bottom flask and stirred at room temper-
ature for 1 h while 120 mL 30% NaOH was poured into it. 4-Meth-
ylbenzene-1-sulfonyl chloride (30.50 g, 160 mmol) dissolved in
Experimental section
2 2
150 mL CH Cl was added dropwise. After the reaction mixture
was stirred at room temperature for 24 h, the mixture was poured
into water and the liquid was collected. The oily liquid was dried
by anhydrous magnesium sulfate. Colorless oily liquid m1 was
got with yield 89.2%.
General methods
All chemicals were commercially available and used as
obtained. The solvents were purified by conventional methods
m2 NaH (4.80 g, 200 mmol) with DMF 25 mL were added
together into round-bottom flask, then 9H-carbazole (16.70 g,
100 mmol) dissolved in DMF was added dropwise using dropping
funnel isolating atmosphere. After 2 h m1(30.10 g, 110 mmol)
was added and stirred at 65 °C for 15 h. The mixture was poured
into plenty of water and its pH was adjusted to about 6 using
diluted hydrochloric acid. Ethyl acetate was used to extract the
mixture and dried by anhydrous magnesium sulfate. The residue
was chromatographed over silica gel. Yellow oily liquid m2 was
obtained with yield 82%.
1
13
before use. The H NMR and C NMR spectra recorded on at
5 °C using Bruker Avance 400 spectrometer were reported as
parts per million (ppm) from TMS. IR spectra were recorded on
2
ꢁ1
NEXUS 870 (Nicolet) spectrophotometer in the 400–4000 cm
region using a powder sample on a KBr plate. Elemental analyses
were performed with a Perkin Elmer 240C elemental analyzer.
Mass spectra were obtained on a Micromass MALDI-TOF-MS.
Absorption spectra were obtained on a UV-265 spectrophotom-
eter, Fluorescence measurements were performed using a Hitachi
F-7000 fluorescence spectrophotometer excited at the longest
absorption band. The concentration of sample solution was
m3 DMF (4.44 g, 60 mmol) was added in 250 mL round-bottom
flask and POCl (10.00 g, 65 mmol) was added dropwise using
3
ꢁ
5
1
.0 ꢂ 10 mol/L. For time-resolved fluorescence measurements,
dropping funnel slowly. After white solid was successfully gener-
ated, m2 (13.50 g, 50 mmol) dissolved in chloroform was added.
When the solid mixture was thawed out, it was stirred at 65 °C
for 18 h. The mixture was poured into large amounts of water
and its pH was adjusted to about 8.0 using NaOH aqueous solution.
Anhydrous magnesium sulfate was used for drying the mixture
the fluorescence signals were collimated and focused onto the
entrance slit of a monochromator with the output plane equipped
with a photomultiplier tube (HORIBA HuoroMax-4P). The decays
were analyzed by ‘least-squares’. The quality of the exponential fits
was evaluated by the goodness of fit (
2
v
).

M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
523
2 3 3
ZnLCl SOCD , 400 MHz) d (ppm) = 3.19 (s, 3H),
: 1H NMR (CD
after extracting the mixture by CH
2
Cl
2
. The residue was chromato-
graphed over silica gel using ethyl acetate–petroleum ether (vol-
3.56–3.58 (q, 2H), 3.90–3.93 (t, 2H), 4.64–4.66 (t, 2H), 7.32–7.36
(t, 1H), 7.54–7.56 (t, 1H), 7.62–7.64 (t, 1H), 7.72–7.76 (t, 1H),
8.05–8.09 (t, 1H), 8.31–8.35 (t, 1H), 8.68–8.78 (q, 4H), 8.91 (s,
ume ratio is 1:5). White solid m3 was obtained with yield 63%.
1
3 3
H NMR (CD COCD , 400 MHz) d (ppm) = 3.14 (s, 3H), 3.33–3.34
1
3
(
7
q, 2H), 3.49–3.50 (q, 2H), 3.91–3.94 (t, 2H), 4.64–4.66 (t, 2H),
.30–7.33 (t, 1H), 7.52–7.55 (t, 1H), 7.68–7.70 (d, 1H), 7.75–7.77
3 3
2H), 9.04 (s, 1H) (Fig. S3). C NMR (CD SOCD , 100 MHz) d
(ppm) = 156.47, 154.57, 152.30, 147.33, 140.78, 140.10, 137.01,
128.26, 127.88, 126.90, 125.70, 122.23, 121.27, 120.32, 120.88,
119.74, 118.76, 117.28, 110.35, 109.81, 71.34, 69.76, 68.85, 58.15,
(
(
d, 1H), 7.99–8.01 (d, 1H), 8.26–8.28 (d, 1H), 8.69 (s, 1H), 10.10
s, 1H).
ꢁ1
4
1
3.07. IR (KBr, cm ): 3441 (m), 3062 (vw), 2925 (w), 1594 (s),
2 4 2-
472 (s), 1118 (m), 791 (m), 748 (m). Anal. Cal. for C32 28Cl N O
H
0
0
00
0
Preparation of 3-([2,2 :6 ,2 -terpyridin]-4 -yl)-9-(2-(2-
Zn:C, 60.35; H, 4.43; N, 8.80; found: C, 60.31; H, 4.40; N, 8.74. m.p.
methoxyethoxy) ethyl)-9H-carbazole (L)
+
2
(
95 °C.MALDI-TOF-MS: cal.: 636.88, found: 598.48 ([M-Cl-3H] )
Fig. 1).
ZnLBr
.52–3.55 (q, 2H), 3.89–3.91 (t, 2H), 4.68–4.70 (t, 2H), 7.34–7.38
t, 1H), 7.55–7.58 (t, 1H), 7.74–7.77 (d, 1H), 7.87–7.88 (d, 3H),
m4 Pyridine (216 mL) and I
00 mL round-bottom flask. The mixture was heated to 65 °C stir-
ring until they were dissolved. 1-(Pyridin-2-yl) ethanone (21.60 g,
78 mmol) was added in above mixture and heated to 95 °C for 3 h.
2
(37.60 g, 150 mmol) was added in
5
1
2
3 3
: H NMR (CD SOCD , 400 MHz) d (ppm) = 3.16 (s, 3H),
3
(
8
1
And then, the reaction mixture was allowed to cool to room tem-
perature and the solid was collected on a fritted filter funnel. The
crude product was subsequently washed with CH Cl . The black
2 2
solid m4 was obtained with yield 64%.
m5 m3 (8.91 g, 30 mmol) Dissolved in ethyl alcohol (200 mL)
was added into 500 mL round-bottom flask. Subsequently 1-(pyri-
din-2-yl) ethanone (3.63 g, 30 mmol) and NaOH (2.80 g, 70 mmol)
were added into it under stirring. After 15 h, orange solid m5 was
collected with fritted filter funnel and washed with water.
L m5 (2.00 g, 5 mmol) and m4 (1.63 g, 5 mmol) were dissolved
1
3
.31–8.45 (m, 4H), 8.90–8.98 (q, 4H), 9.16 (s, 3H). C NMR (CD3-
100 MHz) (ppm) = 155.85, 155.17, 150.80, 149.90,
40.78, 140.47, 137.53, 128.49, 126.90, 124.62, 124.42, 123.25,
22.23, 120.95, 120.65, 119.36, 118.46, 117.86, 110.32, 109.87,
1.34, 70.57, 69.76, 68.85, 58.15, 43.07. IR (KBr, cm ): 3443 (m),
054 (vw), 2925 (w), 1593 (s), 1472 (s), 1101 (m), 790 (m), 747
SOCD
3
,
d
1
1
7
3
ꢁ1
(
2 4 2
m). Anal. Cal. for C32H28Br N O Zn:C, 52.96; H, 3.89; N, 7.72;
found: C, 52.91; H, 3.87; N, 7.69. m.p. 300 °C. MALDI-TOF-MS:
+
cal.: 725.78, found: 644.5 ([M-Br-H] ) (Fig. S5).
1
ZnL(SCN)
2
:
H NMR (CD
3
3
SOCD , 400 MHz) d (ppm) = 3.13 (s,
in 50 mL methyl alcohol. After stirring for 20 min, NH
4
Ac (2.31 g,
3
7
3
1
1
1
1
H), 3.49–3.51 (t, 2H), 3.86–3.88 (t, 2H), 4.66–4.68 (t, 2H), 7.33–
.35 (t, 1H), 7.53–7.55 (t, 1H), 7.72–7.74 (d, 1H), 7.88–7.90 (d,
H), 8.40–8.42 (q, 4H), 8.83 (s, 1H), 9.04–9.17 (m, 4H), 9.52 (s,
3
0 mmol) was added. The mixture was refluxed for 24 h. The crude
product was collected with fritted filter funnel and washed with
water. The mixture was drying with anhydrous magnesium sulfate
1
3
3 3
H). C NMR (CD SOCD , 100 MHz) d (ppm) = 156.37, 156.16,
and chromatographed over silica gel using CH
2 2 3
Cl ACH OH (vol-
50.50, 149.24, 141.11, 140.99, 137.19, 128.67, 127.38, 124.77,
24.56, 122.95, 122.96, 121.23, 120.76, 119.47, 118.89, 117.93,
10.57, 110.26, 71.32, 70.94, 69.72, 68.73, 58.31, 43.10. IR (KBr,
ume ratio is 10:1), giving brown solid L (0.77 g) with yield 31%.
1
H NMR (CD
q, 2H), 3.52–3.54 (q, 2H), 3.93–3.96 (t, 2H), 4.63–4.66 (t, 2H),
.26–7.30 (t, 1H), 7.47–7.53 (q, 3H), 7.66–7.68 (d, 1H), 7.81–7.83
d, 1H), 7.99–8.06 (q, 3H), 8.36–8.37 (d, 1H), 8.76–8.77 (d, 5H),
3 3
COCD , 400 MHz) d (ppm) = 3.18 (s, 3H), 3.36–3.39
(
7
(
8
ꢁ1
cm ): 3443 (m), 3062 (vw), 2920 (w), 2072 (vs), 1591 (s), 1472
s), 1101 (m), 789 (m), 747 (m) (Fig. S4). Anal. Cal. for C34
Zn:C, 59.86; H, 4.14; N, 12.32; found: C, 59.87; H, 4.107; N,
2.26. m.p. 321 °C. MALDI-TOF-MS: cal.: 682.14, found: 621.44
(
O
1
28 2 6-
H S N
13
2
.95 (s, 2H) (Fig. S1).
C
NMR (CDCl
3
,
100 MHz):
d
(
ppm) = 155.47, 155.23, 150.38, 149.24, 140.99, 140.80, 137.33,
+
(
[M-S-C-N-3H] ) (Fig. S7).
1
1
5
1
28.26, 126.09, 124.54, 124.35, 122.95, 122.27, 120.92, 120.78,
19.27, 118.79, 117.88, 110.39, 109.81, 71.23, 70.50, 69.78, 68.80,
ꢁ1
8.02, 43.06. IR (KBr, cm ): 3435 (m), 3049 (vw), 2908 (w),
Results and discussion
583 (s), 1466 (s), 1126 (m), 788 (m), 750 (m). m.p. 97 °C.
MALDI-TOF-MS: m/z, cal.: 500.2, found: 501.23 (Fig. S2).
Synthesis and characteristic discussion
Four new Zn(II) terpyridine complexes (ZnLCl
2
2 2
, ZnLBr , ZnLI ,
Preparation of Zn (II) complexes
2
ZnL(SCN) ) based on carbazole derivative group were synthesized
ZnLI
0.32 g, 1 mmol) dissolved in 4 mL methyl alcohol were added in
0 mL round-bottom flask then heated to refluxing. After the reac-
tion, the liquid was cooled to room temperature and the solid was
extracted by fritted filter funnel giving yellow solid ZnLI (0.68 g)
after washed several times with water and ethyl alcohol with yield
2 2 2 2
: L (0.5 g, 1 mmol) dissolved in 20 mL CH Cl and ZnI
by efficient synthetic routes and the processes were depicted in
Scheme 1 (seeing supporting information). Those target products
(
5
1
13
have been characterized by IR, H NMR, C NMR, elemental anal-
yses and MALDI-TOF-MS. From the infrared spectrum of ZnL(SCN)
2
,
2
ꢁ
1
a new peak at 2071.89 cm can be observed, which was contrib-
1
uted to the characteristic peak of SCN (Fig. S4). By contrasting
8
3
1
8
1
1
1
1
3 3
5%. H NMR (CD SOCD , 400 MHz) d (ppm) = 3.14 (s, 3H), 3.49–
1
the H NMR spectra of L with ZnLCl
2
or the other complexes, the
.53 (q, 2H), 3.89–3.92 (t, 2H), 4.72–4.74 (t, 2H), 7.37–7.40 (t,
H), 7.57–7.60 (t, 1H), 7.78–7.80 (d, 1H), 8.00–8.01 (d, 3H), 8.62–
chemical shifts of H located in the coordinated pyridine ring
shifted to low field because of the electron density of H decreasing
(Figs. S1 and S3). Comparing the MALDI-TOF-MS of four complexes,
.64 (d, 1H), 8.94 (s, 1H), 9.17–9.27 (m, 4H), 9.36 (s, 1H), 9.52 (s,
H). 1 C NMR (CD
3
3
SOCD
3
, 100 MHz) d (ppm) = 155.62, 155.55,
the ZnLBr
composed of polymeric fragment was found (Fig. S5). Only one
intense peak were found for the mass spectra of ZnLCl , ZnLI
ZnLSCN , and L (Fig. 1). All the characterizations indicated that
2
was different from others and another peak which was
50.50, 149.22, 141.08, 140.91, 137.30, 128.35, 126.29, 124.61,
24.55, 123.05, 122.43, 120.96, 120.65, 119.36, 118.16, 117.40,
10.92, 109.34, 71.34, 70.06, 69.46, 68.85, 58.15, 43.07. IR (KBr,
cm ): 3443 (m), 3049 (vw), 2925 (w), 1593 (s), 1472 (s), 1102
m), 790 (m), 748 (m). Anal. Cal. for C32 Zn:C, 46.88; H,
.44; N, 6.83; found: C, 46.78; H, 3.394; N, 6.81. m.p. 325 °C.
2
2
,
ꢁ1
2
the ligand and its metal complexes were successfully obtained.
(
3
28 2 4 2
H I N O
+
MALDI-TOF-MS: cal.: 819.78, found: 690.59 ([M-I-2H] ) (Fig. S6).
Linear absorption and TD-DFT studies
Other three complexes were prepared by a similar procedure
with that of ZnLI
Zn(SCN)
2
just with ZnI
2
replaced by ZnCl
2 2
, ZnBr , and
Table 1 summarized the photophysical data of all the com-
pounds in different solvents. Clearly, two intense absorption bands
2
.

5
24
M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
2
Fig. 1. MALDI-TOF-MS of ZnLCl .
4
of L in the range of 290–330 nm (
e
> 10 ) showed hardly any shifts
The influence of solvents on the fluorescence spectra was
observed. The fluorescence intensity of L was strongest than those
of the complexes. Clearly, the fluorescence (SPEF) spectra of L and
the four complexes displayed an remarkable red-shifting and
showed fluorescence quenching with increasing polarity of the
with increasing polarity of the solvents (Fig. 2). Three intense
absorption bands of the four Zn(II) terpyridine complexes were
observed, but showing weak solvatochromism, except ethyl alco-
hol solvent, indicating the complex molecules with fairly little dif-
ference in dipoles between ground and excited state (ZnLCl
2
as an
2
solvent, especially for ZnLI (Fig. S8). For example, in the spectrum
example in Fig. 3). However, the two bands of complexes in the
higher energy region are different from L. Compared with L, the
absorption of 310–320 nm experienced a bathochromic shift on
account of the formation of coordination bands which strengthens
the capability of electron delocalization resulting in the energy gap
decreasing between HOMO and LUMO. Also, a new emerging
absorption band was observed in the lowest energy band about
of L in ethyl alcohol solvent, excited at 320 nm, a novel band with
weak intensity was observed at 445 nm. The stocks shifting
ꢁ
1
reached a maximum of 8778 cm . One interpretation could be
given that the exited state energy was lower than ground state
with increasing polarity of the solvents because of a larger
enhanced dipole moment, and the energy gap between ground
state and excited state declines, which explains the sensitivity of
the emission spectra of these dipolar compounds to solvent
polarity [44]. Besides, the ethyl alcohol solvent could generate
intermolecular hydrogen bond with L resulting in an enhanced
non-radioactive transition [45,46]. As a response, the photolumi-
nescence (PL) quantum yields (U) of L were lowered at the lowest
3
70–395 nm showing weak solvatochromism. The maximum
absorption band in the highest energy region about 280–290 nm
causes an obvious blue shift contrasting with L (Fig. 4).
Table 2 exhibits the selected experimental and calculated opti-
cal data for the ligand and their Zn(II) complexes including ener-
gies and compositions of frontier orbital. The absorption spectra
of the investigated compounds showing similar features were sig-
nificantly confirmed by the means of theoretical calculation. Two
2 2
level of 0.10 and a similarly with that of ZnLCl and ZnLBr . Fur-
thermore, fluorescence lifetime of the complexes also prolonged
which suggested that the molecule polarity of excited state must
be larger than that of ground state enhancing dipole–dipole inter-
actions. Interestingly, the fluorescence spectra of four complexes
show weak bathochromic shift in the same solvent by the change
intense absorption bands of L in the range of 290–330 nm
4
(
e
> 10 ) which originating from HOMO(H)ꢁ2 ? LUMO(L)+1 and
*
H ? L+1 were assigned to
p
?
p
transitions of terpyridine and
*
ꢁ
ꢁ
p
?
p
from carbazole to terpyridine were observed. The three
of coordination anion from Cl to I ,while show obvious batho-
chromic shifts comparing with L (Fig. 4). However, the fluores-
absorption bands of four Zn(II) complexes were demonstrated to
*
*
p
(carbazole) ?
p
?
(terpyridine) ,
p
p
?
p
/ICT(terpyridine ? terpyri-
cence spectra intensity of ZnLI
2
was obvious quenched
*
dine) and ICT/
p
(carbazole ? terpyridine) from high energy
accompanying low fluorescence quantum yields comparing the
other three complexes (Fig. S8). This phenomenon was caused
by heavy atom effect of I which enhances spin–orbital coupling
and increases intersystem crossing rate from excited singlet state
to low energy regions which coming from identical transition
and performing approximate transition energy attributing. The
molecular orbital energy diagrams of the ligands and complexes
were expressed in Fig. S10. Overall, the absorption spectral fea-
tures were reasonably explained through the initial TD-DFT
calculations.
1 1
(S ) to excited triplet state (T ). Similarly, quenched effect of the
fluorescence spectra in benzene solvents was because of the low
solubility caused by the coordination band which enhanced the
molecule polarity and declined the soluble possibility in weak
2
polarity solvent. The fluorescence spectra of ZnL(SCN) show the
One-Photon Excited Fluorescence (OPEF)
most intensity contrasting other complexes. It was because of
the molecule unit containing highly delocalized conjugated sys-
tem formed by coordination anion of SCN (Fig. S9).
The one-photon fluorescence spectral data were listed in
Table 1 including fluorescence quantum yields and lifetimes.
ꢁ

M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
525
Table 1
2 2 2 2
Single-photon-related photophysical properties of L, ZnLCl , ZnLBr , ZnLI and ZnL(SCN) in several different solvents.
a
maxb)
c
d
Ue
f
ꢁ9
ꢁ1
ꢁ9
ꢁ1
Compounds
L
Solvents
k
max
(e
k
max
D
m
s
10
k
r
(s
)
10
knr (s
)
Benzene
295(3.96),323(1.73)
294(4.39),321(1.91)
293(4.24),320(1.88)
294(4.36),320(1.92)
292(4.37),321(1.90)
295(4.09),320(1.77)
388
410
401
445
425
430
5187
6762
6312
8778
7623
7994
0.30
0.27
0.24
0.10
0.22
0.30
2.56
2.76
2.55
–
–
4.57
11.7
9.8
9.4
27.3
26.4
29.8
Dichloromethane
Ethyl acetate
Ethyl alcohol
Acetonitrile
DMF
6.6
15.3
ZnLCl
2
Benzene
286(2.79),310(2.12),369(1.31)
282(4.16),314(2.95),377(2.11)
281(4.00),307(2.91),368(2.00)
282(4.29),316(2.58),390(1.88)
281(4.67),308(3.14),375(2.15)
286(4.92),317(2.72),382(0.83)
446
491
474
524
523
4679
6159
6077
6557
7546
0.23
0.12
0.20
0.06
0.09
2.65
4.80
3.82
3.00
3.73
8.68
2.50
5.24
2.00
2.41
29.1
18.3
20.9
31.3
24.4
Dichloromethane
Ethyl acetate
Ethyl alcohol
Acetonitrile
DMF
ZnLBr
2
Benzene
288(3.06),313(2.38),372(1.57)
283(4.14),314(2.98),382(2.23)
282(3.92),312(2.95),370(2.07)
283(4.35),316(2.62),390(1.98)
281(4.45),312(3.11),377(2.36)
286(4.72),317(2.65),382(0.90)
447
490
474
522
524
4510
5770
5930
6483
7441
0.10
0.23
0.19
0.04
0.06
2.52
3.46
3.04
2.99
3.74
3.97
6.65
0.63
1.34
1.60
35.7
22.2
26.6
32.1
251
Dichloromethane
Ethyl acetate
Ethyl alcohol
Acetonitrile
DMF
ZnLI
2
Benzene
286(4.41),315(3.25),374(2.21)
283(4.97),313(3.42),380(2.60)
281(4.89),308(3.49),373(2.57)
283(4.18),316(2.50),393(1.90)
281(4.82),312(3.11),382(2.37)
291(5.39),319(2.70),383(0.52)
440
490
476
521
527
4011
5908
5801
6251
7203
0.01
0.10
0.02
0.06
0.03
2.52
4.06
4.00
2.99
3.71
0.40
2.46
0.50
2.01
0.81
39.3
22.2
24.5
31.4
26.2
Dichloromethane
Ethyl acetate
Ethyl alcohol
Acetonitrile
DMF
ZnL(SCN)
2
Benzene
290(3.10),312(2.47),395(1.82)
282(5.59),317(3.67),387(2.71)
281(5.11),313(3.47),380(2.53)
282(3.87),314(2.33),388(1.67)
281(4.82),312(3.16),382(2.41)
287(5.34),321(2.97),380(1.11)
502
499
496
521
524
5396
5800
6154
6579
7094
0.01
0.10
0.02
0.06
0.03
1.94
4.92
4.97
3.00
3.71
0.52
2.03
0.40
2.00
0.81
51.0
18.3
19.7
31.3
26.2
Dichloromethane
Ethyl acetate
Ethyl alcohol
Acetonitrile
DMF
r
k Calculated fluorescence emission rate, knr calculated non-radiative transition rate.
a
Peak position of the longest absorption band.
Maximum molar absorbance in 10 mol L cm
b
c
d
e
f
4
ꢁ1
ꢁ1
.
Peak position of SPEF, exited at the maximum wavelength of absorption.
ꢁ1
Stokes shift in cm
.
Quantum yields determined by using quinine sulfate as standard.
The fitted fluorescence lifetime (ns).
Fig. 2. Absorption spectra and One-Photon Excited Fluorescence (OPEF) of L in different solvents.
The fluorescence quantum yields (
U
)
where the s and r indices designate the sample and reference sam-
ples, respectively, A is the absorbance at kexc is the average refrac-
,
g
The fluorescence quantum yields (
quinine sulfate as the reference according to the literature method
U
) were determined by using
tive index of the appropriate solution, and D is the integrated area
under the corrected emission spectrum.
[
47]. Quantum yields were corrected as follows:
Table 1 shows the quantum yields of L obtained in different sol-
vents. The ethanol solvent show the least, which could be
explained by the hydrogen bonds of ethanol molecules lowed some
energy from the excited state of the molecules. However, the
ꢀ
ꢁ
2
A
A
r
s
g
g
D
D
s
s
U
s
¼
U
r
2
r
r

5
26
M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
2
Fig. 3. Absorption spectra and One-Photon Excited Fluorescence (OPEF) of ZnLCl in different solvents.
explained that the strong spin–orbital coupling induced by mixing
*
of the ligand (p and p ) and metal d p orbital enhanced the nonra-
diative decay pathways.
Nonlinear optical properties
The NLO properties of ZnLCl
2
2
and ZnLBr were measured by the
Z-scan technique using a tunable femtosecond laser system.
However, the other two complexes showed no response to NLO
properties. Z-scan data for ZnLCl
2 2
and ZnLBr in DMF at
ꢁ3
ꢁ1
1
.0 ꢂ 10 mol L , were obtained under an open aperture and
closed aperture configuration (k = 700 nm).
As shown in Fig. 5, the open-aperture transmittance was
symmetric with respect to the focus (z = 0). The obvious minimum
transmittance unambiguously indicated
absorption which was attributed to TPA effect. The two-photon
absorption coefficient b and TPA cross-sections were determined
a biggish nonlinear
r
by the open-aperture Z-scan technique. The theoretical data were
fitted using the following equations [48,49]:
Fig. 4. Absorption spectra and One-Photon Excited Fluorescence (OPEF) of L, ZnLCl
ZnLBr , ZnLI , and ZnL(SCN) in CH Cl
2
,
2
2
2
2
2
.
X
1
m
½
ꢁq ðzÞꢃ
0
Tðz; s ¼ 1Þ ¼
for jq j < 1
ð1Þ
ð2Þ
3
=2
0
ðm þ 1Þ
m¼0
fluorescence quantum yields (
U
) show the decreasing tendency
0
bI L
eff
1 þ v2
q0ðZÞ ¼
from the ligand to the corresponding complexes. It could be
Table 2
Selected experimental and calculated optical data for the ligand and their Zinc(II) Complexes.
Compd.
L
OIa (Tc)b
D
E (eV)c
Cal. kmax (nm)d
Obs. kmax (nm)e
ff
Characterg
1
2
Hꢁ2 ? L+1(0.43)
H ? L+1(0.52)
4.25
3.68
292
337
295
323
0.2155
0.2662
p(tpy) ?
(cbz) ?
p
(tpy)*
(tpy)
*
p
p
ZnLCl
2
1
2
3
Hꢁ4 ? L+4(0.43)
Hꢁ8 ? L(0.51)
Hꢁ4 ? L(0.68)
Hꢁ4 ? L+4(0.50)
Hꢁ9 ? L(0.60)
Hꢁ4 ? L(0.50)
Hꢁ5 ? L+3(0.45)
Hꢁ9 ? L(0.64)
Hꢁ5 ? L(0.61)
Hꢁ4 ? L+3(0.57)
Hꢁ7 ? L(0.63)
Hꢁ4 ? L(0.69)
4.39
4.11
3.20
282
302
387
286
310
369
0.0377
0.1280
0.2768
p
p
ICT/
(cbz) ?
p
(tpy)*
*
?
p
/ICT(tpy ? tpy)
*
p
?
p
(cbz ? tpy)
(tpy)*
p /ICT(tpy ? tpy)
ZnLBr
2
1
2
3
4.37
4.09
3.18
283
303
389
288
313
372
0.0637
0.1748
0.1556
p(cbz) ? p
*
p
ICT/
?
*
p
?
p
(cbz ? tpy)
(tpy)*
p /ICT(tpy ? tpy)
ZnLI
2
4.36
4.09
3.15
284
303
394
286
315
374
0.0300
0.2322
0.1767
p(cbz) ? p
*
p
ICT/
?
*
3
p
?
p
(cbz ? tpy)
(tpy)*
p /ICT(tpy ? tpy)
ZnL(SCN)
2
1
2
3
4.25
4.09
3.01
292
303
411
290
312
395
0.0828
0.2152
0.2508
p(cbz) ? p
*
p
?
*
ICT/p ? p (cbz ? tpy)
a
b
c
d
e
f
Orbitals involved in the excitations.
Transition coefficients.
Excitation energies (eV).
Calculated peak position of the longest absorption band.
Observed peak position of the longest absorption band in benzene.
Oscillator Strengths.
g
tpy Instead of terpyridine; cbz instead of carbazole.

M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
527
c(3) = {(Rec ) + (Imc ) } , where e0 was the vacuum permittivity,
(3) 2
(3) 2 1/2
b was the nonlinear absorption coefficient of the solution, I
input intensity of laser beam at focus (z = 0) divided by
L)]/ was the effective length with the linear
absorption coefficient and L the sample length.
was the diffraction length of the beam with
0
was the
2
p
x
0
,
c was the light velocity in vacuum, n was the nonlinear refractive
index of DMF (n = 1.43), k = 700 nm. The third-order nonlinear
refractive index (v ) was determined by the close-aperture Z-scan
technique and the advantage of this method was that both the real
0
L
eff = [1 ꢁ exp(ꢁ
a
0
a
0
a
0
0
2
(3)
v
= z/z
0
, z
0
=
px
0
/k
x
0
the spot size at
(3)
focus, k was the wavelength of the beam and z was the sample posi-
tion. So the nonlinear TPA coefficient b (in units of cm/GW) can be
and imaginary parts of
v
can be determined simultaneously or
consecutively. Calculated data were summarized in Table 3. From
these data, it was obvious that both complexes possessed rather
low imaginary part, which means minimal nonlinear optical losses.
Also, the complexes with different coordination anions can influ-
ence their nonlinear optical properties.
deduced. Furthermore, the
relationship [50]:
r
could be determined by the following
3
r
¼ hc
b=N
A
d ꢂ 10ꢁ
ð3Þ
The optical limiting property was a nonlinear optical process
in which the transmittance of a material decreased as the input
light intensity increases. The transmittance of pure DMF solvent
in the same cell was also determined in order to eliminate the
influences studied by a standard open-aperture Z-scan technique
Here, h was the Planck constant,
laser, was molecular TPA cross-section, N
number, and d was the concentration (in units of mol L ). Based
on Eq. (3), the molecular TPA cross-section can be calculated.
By the equation of (2), the two-photon absorption coefficient b
of ZnLCl and ZnLBr were 0.2783 cm/W and 0.1211 cm/W. As
shown in Table 3, the two complexes exhibit two-photon absorp-
tions with a maximum corresponding to = 13,121 and 5710 GM
Goeppert–Mayer units) at 700 nm. By close-aperture Z-scan, an
effective third-order nonlinear optical refractive index g of the
compounds can be derived from the equations: p–v = 0.406
/k. In this experiment,
p–v = 0.1805 and 0.1203, s = 0.11. Through the above formula,
c
was the frequency of incident
r
A
was the Avogadro
ꢁ1
r
(k = 700 nm) at the focus. Fig. S10 showed the transmitted energy
2
2
changing with the increase of the incident beam intensity with a
ꢁ
1
1
mm cell of ZnLCl
2
in DMF at 1.0 ꢂ 10–3 mol L . At low energy,
r
the optical response obeyed Beer’s law. When the input light
energy reaches about 279 mW, the transmitted light energy
started to deviate from normal linear behavior and exhibited a
typical optical limiting effect. The damaging threshold was
(
D
T
0
.25
(
D
1 ꢁ s)
0 0 0 eff
|DU |, DU = xcI L , x = 2p
6
40 mW, compared to that of C60 which was considered as an
optical limiting materials [51]. These results certainly indicated
that the ZnLCl complex was valuable optical-limiting materials
T
ꢁ17
2
the refractive index
c
of the compound were 4.75 ꢂ 10
m /W. The effective third-order NLO susceptibil-
of the compound can be calculated according to the
m /W
ꢁ17
2
and 3.15 ꢂ 10
2
(
3)
that should have great potential to excel in the advancement of
practical devices.
ity
v
(3)
ꢁ4 ꢁ2
2
2
(3)
2
2
2
equations: R c esu = 10 e c n c/p, I c esu = 10 e c n kb/4p ,
e 0 0 m 0 0
ꢁ
3
ꢁ1
Fig. 5. Z-scan data for ZnLCl
2
and ZnLBr
2
in DMF at 1.0 ꢂ 10 mol L , obtained under an open aperture and closed aperture configuration (k = 700 nm). The blue dots are the
experimental data and the solid curve is the theoretical fitting. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of
this article.)

5
28
M. Kong et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 521–528
[10] R. Sakamoto, Y. Ohirabaru, R. Matsuoka, H. Maeda, S. Katagiri, H. Nishihara,
Table 3
Open and closed aperture Z-scan measurement data for the third-order nonlinearity
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2
and ZnLBr
2
.
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ZnLBr
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[
[
2
ꢁ17
ꢁ17
c
R
2
(m /W)
(3)) (esu)
PA coefficient b (cm/GW)
4.75 ꢂ 10
3.15 ꢂ 10
5
ꢁ15
ꢁ15
e
(
v
2.4561 ꢂ 10
0.2783
1.6246 ꢂ 10
0.1211
Two-photon cross section
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(GM)
13,121
5710
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(3)
ꢁ14
ꢁ14
ꢁ14
ꢁ14
I
v
m
(
v
) (esu)
(esu)
8.0211 ꢂ 10
3.4902 ꢂ 10
(
3)
8.0248 ꢂ 10
3.4940 ꢂ 10
[
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,
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ZnLBr , ZnLI , ZnL(SCN) ) based on carbazole derivative with
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2
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[
[
polyether group were designed, synthesized and fully character-
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was significantly tested. A detailed investigation in the present
study revealed that the different coordination anions can arouse
largely different optical properties, which was confirmed by both
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[
[
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requirements for third-order NLO materials offering promise for
applications in optical limiting in the near infrared region.
4
4
[
1
Acknowledgments
(
[
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This work was supported by Grants from the National Natural
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and 21275006), the Natural Science Foundation of Anhui Province
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Funded Projects Focus on returned overseas scholar.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.07.039.
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