Synthesis, crystal structures and spectral properties of 6′-phenyl-2,2′-bipyridine derivatives and their CdLI2 complexes

Article abstract of DOI:10.1016/j.saa.2013.12.067

Two novel 6′-phenyl-2,2′-bipyridine ligands (L1, L2) and their CdL^1,2I₂ complexes (1, 2) were synthesized and characterized by elemental analysis, ¹H NMR, IR, MALDI-TOF spectroscopy, and single crystal X-ray diffraction analysis. The results reveal that the central cadmium(II) atom in the complexes was coordinated by two iodide ions and two nitrogen atoms from L1, L2, forming a distorted coordination geometry. The electronic absorption properties of them were investigated on the basis of theoretical calculations (TD-DFT).

Full text of DOI:10.1016/j.saa.2013.12.067

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal structures and spectral properties
of 60-phenyl-2,20-bipyridine derivatives and their CdLI2 complexes
Xuesong Zhao a,1, Yanxin Chen a,1, Junshan Luo a, Hui Wang a, Shengli Li a, Hongping Zhou a, Jieying Wu a,
,
⇑
Yupeng Tian a,b,
⇑
a Department of Chemistry, Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province, Anhui University, Hefei 230601, PR China
b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
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
Two novel 60-phenyl-2,20-bipyridine ligands (L1, L2) and their CdL1,2I2 complexes (1, 2) were designed,
synthesized. Spectral properties were studied based on both experimentally and theoretically.
ꢀ
Synthesis and characterization of two
novel 60-phenyl-2,20-bipyridine
ligands (L1, L2) and their CdL1,2I2
complexes are presented.
ꢀ
ꢀ
ꢀ
ꢀ
Single crystal study indicated that
Cd(II) ion is in a distorted tetrahedral
structure.
Linear absorption and single-photon
exited fluorescence properties have
been investigated.
The results showed that the complex
2 has the longest fluorescence
lifetime.
Linear absorption spectral features
are studied by TD-DFT methods.
a r t i c l e i n f o
a b s t r a c t
Two novel 60-phenyl-2,20-bipyridine ligands (L1, L2) and their CdL1,2I2 complexes (1, 2) were synthesized
and characterized by elemental analysis, 1H NMR, IR, MALDI-TOF spectroscopy, and single crystal X-ray
diffraction analysis. The results reveal that the central cadmium(II) atom in the complexes was
coordinated by two iodide ions and two nitrogen atoms from L1, L2, forming a distorted coordination
geometry. The electronic absorption properties of them were investigated on the basis of theoretical
calculations (TD-DFT).
Article history:
Received 30 October 2013
Received in revised form 9 December 2013
Accepted 11 December 2013
Available online 18 December 2013
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Bipyridine derivatives
Cadmium iodide complexes
Crystal structures
Spectral properties
Theoretical calculation
Introduction
Since the first 2,20:6,200-terpyridine and its complexes were
prepared in the 1930s [1–3], its derivatives and their complexes
have aroused widespread concern and great interest. The research
on terpyridine and its transition-metal complexes have became
intensive due to their attractive photophysical and electrochemical
⇑
Corresponding authors at: Department of Chemistry, Key Laboratory of
Functional Inorganic Materials Chemistry of Anhui Province, Anhui University,
Hefei 230601, PR China.
E-mail addresses: jywu1957@163.com (J. Wu), yptian@ahu.edu.cn (Y. Tian).
These authors contributed equally to this work.
1
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.12.067

X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
31
properties [4–7], which have been used in a wide range of applica-
tions including dye-sensitized solar cells, electrochromic and mag-
netic materials [8–16].
ground state and the TD-DFT calculation of the lowest 25 sin-
glet–singlet excitation energies were calculated with a basis set
composed of 6-31G for C H N O atoms and the Lanl2dz basis set
for the Cd and I atoms were download from the EMSL basis set li-
brary [37]. The lowest 25-spin allowed singlet–singlet transitions,
up to energy of about 5 eV, were taken into account for the calcu-
lation of the absorption spectra.
Recently, a large number of novel terpyridine derivatives on the
synthesis, properties and applications have been reported [17–22].
60-phenyl-2,20-bipyridine (NNC) compounds as a new class of poly-
pyridine ligands in the field of coordination chemistry, not only
have excellent optical properties, but also have special coordina-
tion ability with Pt, Ru, Pd and other transition metal ions to form
functionalized metal complexes [23–31]. Carbazole group as donor
was selected because of its good planarity, the photoelectric effect
and biocompatibility [32–34]. Furthermore, introduction of ali-
phatic group and ether oxygen chain on the N atom of carbazole
as a modifier was to improve the solubility of the ligand and their
metal complexes. On the basis of above considerations, two novel
ligands, 9-hexyl-3-(6-phenyl-[2,20-bipyridine]-4-yl)-9H-carbazole
(L1), 9-(2-(2-methoxyethoxy) ethyl)-3-(6-phenyl-[2, 20-bipyri-
dine]-4-yl)-9H-carbazole (L2) and their cadmium(II) complexes,
–CdL1I2 (1) and –CdL2I2 (2), were synthesized. Their structural
features, linear absorption spectra and the connections between
the structure and properties have been investigated combining
density functional theory.
Preparation of L1, L2 and Complexes 1, 2 (Scheme 1)
Synthesis of L1, L2
In 150 mL ethanol solution, 9-hexyl-9H-carbazole-3-carbalde-
hyde (M1) [32] (8.40 g, 0.030 mol) was added, stirring at room
temperature, then 4.00 g (0.033 mol) 2-acetylpyridine, 2% NaOH
solution were added in turn. After 12 h, filtered out solid, water
washed and dried, obtained light yellow solid M2 11.60 g. To a
mixture of methanol solution (150 mL) containing M2 (11.43 g,
0.030 mol) and acetophenone (3.60 g, 0.030 mol) was added
30.00 g NH4Ac after reflux 30 min, kept refluxing 24 h, then filtra-
tion, washed with methanol, column chromatography (silica, 10:1
petroleum ether: ethyl acetate), 4.66 g white solid were obtained,
yield: 37%. M.p. = 119 °C. 1H NMR(d6-DMSO, 400 MHz, ppm):
d = 0.79–0.83 (t, J = 6.8 Hz, 3H), 1.20–1.33 (q, 6H), 1.79–1.82 (t,
J = 6.6 Hz, 2H), 4.44–4.48 (t, J = 6.6 Hz, 2H), 7.25–7.29 (t,
J = 7.4 Hz, 1H), 7.49–7.53 (q, 3H), 7.58–7.62 (t, J = 7.2 Hz, 2H),
7.64–7.66 (d, J = 8.0 Hz, 1H), 7.77–7.79 (d, J = 8.4 Hz, 1H), 8.02–
8.06 (t, J = 7.6 Hz, 1H), 8.07–8.11 (d, J = 8.4 Hz, 1H), 8.37–8.44 (q,
4H), 8.65–8.67 (d, J = 8.0 Hz, 2H), 8.77–8.80 (q, 2H), 8.88 (s, 1H).
13C NMR(d6-DMSO, 150 MHz): 156.29, 155.55, 155.49, 150.33,
149.21, 140.64, 140.54, 138.78, 137.32, 129.20, 128.71, 128.08,
126.97, 126.11, 124.76, 124.27, 122.83, 122.25. 120.87, 119.23,
119.07, 117.81, 116.33, 109.83, 109.54, 42.33, 30.95, 28.48, 26.10,
21.98, 13.80. IR (KBr, cmꢁ1): 3436 (m), 3053 (vw), 2927 (w),
1582 (s), 1468 (s), 1154 (m), 791 (m), 731 (m). MALDI-TOF-MS:
482.26.
Experiments
Measurements and methods
All chemicals and solvents were dried and purified by standard
methods. IR spectra were recorded on NEXUS 870 (Nicolet) spec-
trophotometer in the 4000–400 cmꢁ1 region with samples pre-
pared as KBr pellets. 1H and 13C NMR spectra were obtained on a
Bruker Avance 400 MHz spectrometer (TMS as internal standard
in NMR). Elemental analyses were performed with a Perkin–Elmer
240B instrument. MALDI-TOF mass spectra were recorded using
Bruker Autoflex III Smartbeam.
A similar procedure was also adopted for L2. M.p. = 93 °C. 1H
NMR (d6-acetone, 400 MHz, ppm) d = 3.18 (s, 3H), 3.36–3.38 (q,
J = 4.8 Hz, 2H), 3.51–3.54 (q, J = 4.6 Hz, 2H), 3.93–3.96 (t, 2H),
4.63–4.66 (t, J = 5.4 Hz, 2H), 7.25–7.29 (t, J = 7.4 Hz, 1H), 7.45–
7.52 (q, 3H), 7.55–7.59 (t, J = 7.6 Hz, 2H), 7.65–7.67 (d, J = 8.0 Hz,
1H), 7.79–7.81 (d, J = 8.8 Hz, 1H), 7.97–8.01 (d, J = 7.6 Hz, 1H),
8.06–8.09 (d, J = 8.4 Hz, 1H), 8.31–8.33 (d, J = 8.0 Hz, 1H), 8.38–
8.41 (q, 3H), 8.74–8.77 (q, 2H), 8.81–8.82 (s, 1H), 8.87–8.88 (s,
1H). 13C NMR(d6-acetone, 150 MHz): 205.27, 156.77, 156.25,
156.11, 156.93, 149.15, 141.40, 141.30, 139.51, 136.86, 129.14,
128.95, 128.61, 127.01, 126.00, 124.72, 123.92, 123.51, 122.89,
120.96, 119.27, 118.91, 117.94, 116.80, 110.06, 109.65, 71.71,
70.40, 69.32, 57.90, 43.15. IR (KBr, cmꢁ1): 3439 (m), 3045 (vw),
2910 (w), 2873 (m), 1582 (s), 1469 (s), 1106 (m), 793 (m), 747
(m). MALDI-TOF-MS: 500.23.
UV–vis absorption spectra were recorded on UV-265 spectro-
photometer. Fluorescence measurements were performed using a
Hitachi F-7000 fluorescence spectrophotometer. For time-resolved
fluorescence measurements, the fluorescence signals were colli-
mated 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 (v2).
Crystal structure determination and refinement
The X-ray diffraction measurements were performed on a Bru-
ker SMART CCD area detector using graphite monochromated Mo
Ka
radiation (k = 0.71069 Å) at 298 (2) K. Intensity data were col-
lected in the variable -scan mode. The structures were solved
x
by direct methods and difference Fourier syntheses. The non-
hydrogen atoms were refined anisotropically and hydrogen atoms
were introduced geometrically. Calculations were performed with
SHELXTL-97 program package [35]. Details of the crystal parame-
ters, data collections and refinements were listed in Table 1, and
selected bond distances and angles were given in Table 2.
Synthesis of complexes 1, 2
A solution of L1 (0.48 g, 0.001 mol) in CH2Cl2 (20 mL) was
mixed with a cadmium iodide (0.32 g, 0.001 mmol) in methanol
(5 mL) and the reaction mixture was reflux for 4 h. The mixture
were cooled to room temperature and filtered. Light yellow solid
(0.68 g) was obtained. Yield: 85%. M.p. > 300 °C. Calcd for C34H31-
CdI2N3 (847.85) C 48.16; H, 3.69; N, 4.69; found: C, 49.20; H,
3.73; N, 4.67. 1H NMR(d6-DMSO, 400 MHz, ppm) d = 8.88 (s, 1H),
8.78–8.81 (t, J = 7.2 Hz, 3H), 8.66–8.68 (d, J = 8.0 Hz, 2H), 8.36–
8.42 (m, 4H), 8.03–8.08 (q, 2H), 7.72–7.74 (d, J = 8.8 Hz, 1H),
7.48–7.63 (q, 6H), 7.24–7.28 (t, J = 7.4 Hz, 1H), 4.39–4.42 (t,
J = 6.8 Hz, 2H), 1.75–1.79 (t, J = 7.0 Hz, 2H), 1.16–1.29 (q, 6H),
0.77–0.80 (t, J = 6.8 Hz, 3H). IR (KBr, cmꢁ1): 3441 (m), 3059 (vw),
2925 (w), 1591 (s), 1481 (s), 1123 (m), 791 (m), 753 (m).
Computational details
Optimizations were carried out with B3LYP [LANL2DZ] without
any symmetry restraints, and the TD-DFT {B3LYP [LANL2DZ]} cal-
culations were performed on the optimized structure. All calcula-
tions, including optimizations and TD-DFT, were performed with
the G03 software [36]. Geometry optimization of the singlet

32
X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
Table 1
Crystal data and structure refinement for complexes 1 and 2.
Compound
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Crystal size (mm)
a/Å
Cd L1I2(1)
C34H31CdI2N3
847.82
296(2)K
0.71073 Å
P21/n
Monoclinic
0.20 ꢂ 0.20 ꢂ 0.18
15.488(12)
10.062(8)
21.358(17)
90.000
Cd L2I2(2)
C66H58Cd2I4N6O4
1731.64
291(2)K
0.71073 Å
ꢀ
P1
Triclinic
0.26 ꢂ 0.25 ꢂ 0.24
10.044(5)
b/Å
c/Å
15.511(7)
21.046(10)
99.317
a
/(°)
b/(°)
101.178
90.139
c
/(°)
90.000
3265(4)
95.149
3222(3)
V/Å3
Z
4
4
Dc/Mg mꢁ3
1.725
2.586
1.785
2.627
l
/mmꢁ1
F(000)
1640
1672
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0467, wR2 = 0.1408
R1 = 0.0541, wR2 = 0.1471
1.050
R1 = 0.0559, wR2 = 0.1320
R1 = 0.0822, wR2 = 0.1431
1.035
Goodness-of-fit on F2
Table 2
Results and discussion
Synthesis and characterization
Selected bond distances (Å) and angles (°) for complexes 1, 2.
1
Cd(1)–N(2)
Cd(1)–N(1)
Cd(1)–I(1)
Cd(1)–I(2)
2.309(4)
2.325(5)
2.6960(19)
2.7128(17)
I(1)–Cd(1)–I(2)
N(1)–Cd(1)–I(2)
N(2)–Cd(1)–I(2)
N(1)–Cd(1)–I(1)
123.13(3)
102.29(11)
122.12(11)
110.95(11)
Synthetic routes of L1 and L2 were depicted in Scheme 1. The
60-phenyl-2,20-bipyridine derivatives were synthesized using the
related literature methods [38–40]. Interestingly, only by adjusting
the reaction sequence, the yield has been significantly improved, in
which 2-acetylpyridine was added first (step 1) to generate an
intermediate chalcone, and then acetophenone was added (step
2). They have been characterized by IR, 1H NMR, 13C NMR spectros-
copy. Although almost no difference is observed for the 1H NMR
spectra of L1 and 1, however, some multipeaks appeared for the
complex 1 (d = 8.4, 8.1, 7.4 ppm) as shown in supporting informa-
tion (Fig. S1), which indicates that the introduction of cadmium ion
has an obviously influence on the distribution of the electron cloud
within the molecule. In addition, 1H NMR spectra of L2 and 2
(Fig. S2) have similar properties to L1 and 1.
2
I(1)–Cd(2)
I(2)–Cd(2)
I(3)–Cd(1)
I(4)–Cd(1)
N(1)–Cd(1)
N(2)–Cd(1)
N(4)–Cd(2)
N(5)–Cd(2)
I(2)–Cd(2)–I(1)
2.7132(12)
2.6900(12)
2.7134(12)
2.6922(13)
2.319(6)
2.282(5)
2.306(6)
2.310(5)
121.55(3)
N(2)–Cd(1)–I(3)
N(1)–Cd(1)–I(3)
I(4)–Cd(1)–I(3)
N(4)–Cd(2)–N(5)
N(4)–Cd(2)–I(2)
N(5)–Cd(2)–I(2)
N(4)–Cd(2)–I(1)
N(5)–Cd(2)–I(1)
N(2)–Cd(1)–N(1)
121.78(13)
101.78(14)
122.80(3)
72.84(19)
114.11(13)
111.73(13)
100.24(13)
123.23(13)
72.72(19)
A similar procedure was also adopted for complex 2. Calcd for
C33H29CdI2N3O2 (865.82) C 45.78; H, 3.38; N, 4.85; found: C,
45.82; H, 3.40; N, 4.87. M.p. = 297 °C. 1H NMR(d6-DMSO,
400 MHz, ppm) d = 8.93 (s, 1H), 8.83–8.85 (t, J = 5.6 Hz, 2H),
8.71–8.73 (d, J = 8.0 Hz, 1H), 8.42–8.49 (m, 4H), 8.08–8.16 (m,
2H), 7.85–7.87 (d, J = 8.8 Hz, 2H), 7.72–7.74 (d, J = 8.4 Hz, 1H),
7.53–7.67 (q, 5H), 7.31–7.34 (t, J = 7.4 Hz, 1H), 4.66–4.69
(t, J = 5.2 Hz, 2H), 3.88–3.91 (t, J = 5.4 Hz, 2H), 3.52–3.55 (t,
J = 4.6 Hz, 2H), 3.18 (s, 3H). IR (KBr, cmꢁ1): 3437 (m), 3057 (vw),
2928 (w), 1591 (s), 1481 (s), 1116 (m), 790 (m), 754 (m).
Crystal structures
Crystallographic data, selected bond lengths and angles for
complexes 1 and 2 are summarized in Tables 1 and 2, respectively.
The molecular structures of 1 and 2 are shown in Figs. 1 and 2,
respectively. The packing diagrams of 1 and 2 are shown in Figs. 3
and 4, respectively.
Scheme 1. Synthetic route for ligand L1, L2 and complexes 1, 2.

X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
33
Fig. 1. Structure of complex 1; H atoms are omitted for clarity.
Fig. 2. Structure of complex 2; H atoms are omitted for clarity.
Fig. 3. The molecular packing diagram of complex 1.
Fig. 4. The molecular packing diagram of complex 2.
Crystal structure of complex 1
that the complex should show large difference in spectral proper-
ties when compared to the ligand. Besides, the hexyl chain is away
from the plane of the carbazole unit. Fig. 1 shows that in the crystal
structure, Cd(II) ion adopts a classic four-coordinate with distorted
tetrahedral geometry constituted by two iodine ions and two nitro-
gen atoms of the pyridine groups (L1). The Cd(1)–N(1) and Cd(1)–
N(2) bond lengths are 2.325(5), 2.309(4) Å, and Cd(1)–I(1)
(2.6960(19) Å) and Cd(1)–I(2) (2.7128(17) Å), which are all within
the normal range [41–44]. The main bond angles N(2)–Cd(1)–N(1)
and I(1)–Cd(1)–I(2) are 72.01° (15), 123.13° (3), respectively. As
This crystal belongs to monoclinic system with P21/n space
group. A side view of the whole molecule is slightly curved, due
to the coordination of the ligand with metal ions. Carbazole group
in the molecule has a good planarity. Dihedral angle of carbazole
and adjacent pyridine ring is 21.87°. The two pyridine rings are al-
most co-planar, whose dihedral angle is 13.42°, however, the dihe-
dral angle between the benzene unit and adjacent pyridine ring is
48.98°. The small dihedral angles indicate high electron delocaliza-
tion within the complex molecule containing two N atoms of L1
and the Cd ion(II), in which a favorable charge transfer upon elec-
tronic transition is expected. Thus, the structural features suggest
shown in Fig. 3, there are many C–Hꢃ ꢃ ꢃN, C–Hꢃ ꢃ ꢃ
p and p–p stacking
interactions in crystal structure. One-dimensional structure forms

34
X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
by
p
–
p
stacking interactions between the complex molecules, and
assigned to intramolecular charge transfer (ICT) transition, while
at shorter wavelength (calculated at 287 nm) mainly originates
further become a network crystal structure through C–Hꢃ ꢃ ꢃ
p
interactions.
from
p
?
p* transitions of HOMOꢁ1 to LUMO+2. The absorption
spectra of L2 shows similar features, with the lower energy spec-
tral region (calculated at 316 nm) originating from a HOMO-
Crystal structure of complex 2
p ?
p*
ꢀ
ꢁ7 ? LUMO being dominated by ICT transitions, while
Complex 2 crystallizes in triclinic system with P1 space group. A
unit cell of complex 2 contains two molecules. As shown in Fig. 2, a
side view of the whole molecule is slightly curved. Compared to
the hexyl chain in complex 1, an ether oxygen chain attached to
carbazole moiety displays a more flexible, the two ether oxygen
chains of molecules show different morphologicals (one is straight
chain, the other is curved). For the same reason, the complex is
twisted arrangement to meet the requirement of steric exclusion
in the crystal growth process, resulting in lower symmetry, so
forming the triclinic system. Molecular configuration of complex
2 is similar to 1, which Cd(II) ion also adopts tetrahedral geometry
coordinated by two iodine ions and two nitrogen atoms from the
pyridine groups (L2). The bond lengths (Cd–N, Cd–I) in the two
molecules of unit cell are not same [I(1)–Cd(2): 2.7132(12) Å,
I(2)–Cd(2): 2.6900(12) Å, I(3)–Cd(1): 2.7134(12) Å, I(4)–Cd(1):
2.6922(13) Å. N(1)–Cd(1): 2.319(6) Å, N(2)–Cd(1): 2.282(5) Å,
N(4)–Cd(2): 2.306(6) Å, N(5)–Cd(2): 2.310(5) Å]. The four Cd–N
lengths are different due to unequal repulsion which formed in
the progress of two-dimensional structure, as well as, one-dimen-
transition of carbazole unit is found at a higher energy (calculated
at 288 nm) originating from a HOMOꢁ1 ? LUMO+2.
The calculated frontier orbitals of complexes 1 and 2 are also
shown in Fig. 6. The lowest energy bands are calculated at
372 nm of 1 and 377 nm of 2. This band mainly originates from
transitions of HOMOꢁ3 ? LUMO+1 (1) and HOMOꢁ2 ? LUMO+1
(2), respectively, which can be assigned to a MLCT transition due
to the metal ion center characteristic HOMO and 60-phenyl-2,20-
bipyridine characteristic LUMO. The highest energy bands are
calculated at 302 nm of 1 and 2 transitions correspond to the
HOMOꢁ4 ? LUMO+3 (1) and HOMOꢁ4 ? LUMO+3 (2), respec-
tively, which can be assigned to
p ? p
* transition of carbazole moi-
ety. Therefore, it can be conclude that the results from the
experiments and theoretical calculations are well consistent.
Single-photon exited fluorescence (SPEF)
sional chain and two-dimensional structure are formed by
stacking, as shown in Fig. 4.
p–p
Single-photon-related photophysical data of L1, L2, 1, 2 in CH2-
Cl2 are collected in Table 4, including fluorescence quantum yields
and lifetimes. The SPEF spectra are measured at the same concen-
tration as that of the linear absorption spectra. The single-photon
excited fluorescence spectra of the four compounds (L1, L2, 1, 2)
have been measured in CH2Cl2 solution (Fig. 5b). As shown in
Fig. 5b, L1, L2 exhibit similar fluorescence feature because of their
structural comparability, so their CdI2 complexes 1, 2 are the same.
Compared strong fluorescence intensity of L1 and L2 at maximum
emission wavelength (420 nm), 1 and 2 have lower fluorescence
intensity and obvious red shift (490 nm), because the complexes
enhance the planarity of the molecule, electronic flow and transi-
tions easily, and more conducive to intramolecular charge transfer.
In addition, the quantum yields of ligands L1 and L2 are lower than
their corresponding complexes 1 and 2, due to their lower energy
of the emitting states, which may in turn facilitate the nonradiative
pathways [45]. Compared with L1 and L2, fluorescence lifetime of
complexes 1, 2 increased, due to internal rotation contributes to
the change in lifetime [46], which suggested that any restriction
of the rotation would marginalize the role of the nonradiative
pathway and lead to the subsequent increase fluorescence lifetime.
Therefore, the cadmium ions of the complexes rigidify the pyridine
and phenyl ring of ligands, benefiting to prolong their lifetime.
Linear absorption and TD-DFT studies
The linear absorption spectra of L1, L2, 1 and 2 (c = 1.0 ꢂ 10ꢁ5
mol/L) are shown in Fig. 5a. As can be seen, the linear absorption
spectra of L1 and L2 feature an intense absorption at 292 nm with
the corresponding molar extinction coefficient, which originates
from
(325 nm) is assigned to the intramolecular charge transfer (ICT)
transition. Complexes and emerge new band (about
p ?
p* transition of the carbazole moiety. Low-energy band
1
2
a
375 nm) but disappear one (at 325 nm) when compared to ligands
L1 and L2. The high-energy band (292 nm) is assigned to the
p
?
p* transition, while the low-energy band at about 375 nm is
assigned to the MLCT transitions between the Cd(II) d
p and the
ligand p* orbitals.
TD-DFT computational studies are performed to further eluci-
date the electronic structures of the ground state of L1, L2, 1 and
2. The schematic representation of the molecular orbitals of L1,
L2, 1 and 2 are exhibited in Fig. 6, the energies and compositions
of some frontier orbitals are listed in Table 3. The band originating
from HOMOꢁ5 ? LUMO for L1 calculated intense at 319 nm is
Fig. 5. (a) UV–vis spectra of L1, L2, 1 and 2 in CH2Cl2 solution (c = 1 ꢂ 10ꢁ5 mol Lꢁ1); (b) The single-photon exited fluorescence spectra of L1, L2, 1 and 2 in CH2Cl2 solution
(c = 1 ꢂ 10ꢁ5 mol Lꢁ1). Inset: Normalized intensity of L1, L2, 1 and 2.

X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
35
Fig. 6. Molecular orbital energy diagram for L1, L2, 1 and 2.
Table 3
Calculated linear absorption properties (nm), excitation energy (eV), oscillator strengths and major contribution for L1, L2, 1 and 2.
k(nm)b
Oscillator strengths
Nature of the transition
a
Compound
D
E1
L1
3.8780
4.3129
3.9133
4.2951
3.2319
3.8056
5.6732
3.0682
319
288
325
292
302
372
298
377
0.1036
0.4447
0.0684
0.7221
0.0242
0.0032
0.0242
0.0021
123(HOMOꢁ5) ? 129(LUMO)(0.53)
127(HOMOꢁ1) ? 131(LUMO+2)(0.35)
125(HOMOꢁ7) ? 133(LUMO)(0.27)
131(HOMOꢁ1) ? 135(LUMO+2)(0.35)
137(HOMOꢁ4) ? 145(LUMO+3)(0.43)
138(HOMOꢁ3) ? 143(LUMO+1)(0.69)
141(HOMOꢁ4) ? 149(LUMO+3)(0.49)
143(HOMOꢁ2) ? 147(LUMO+1)(0.69)
L2
1
2
a
The energy gap of the single-photon absorption band.
Peak position of the linear absorption band.
b
Correlations between the structures and absorption properties of
L1, L2 and complexes 1, 2 have been investigated by TD-density
functional theory (TD-DFT) calculations.
Table 4
Single-photon-related photophysical properties of L1, L2, 1 and 2 in CH2Cl2.
Compound
kabs(nm)a/
e
(ꢂ104)
kem(nm)b
Uc (%)
s
(ns)d
L1
L2
1
292(5.05) 318(2.31)
292(6.15) 320(2.85)
290(4.07) 375(1.25)
291(4.55) 374(1.45)
404
411
491
498
30.0
29.8
29.0
18.1
4.31
3.18
4.71
5.10
Acknowledgements
2
This work was supported by a grant for the National Natural
Science Foundation of China (21271004, 51372003, 21071001,
21271003), the Natural Science Foundation of Anhui Province
(1208085MB22, 1308085MB24), Ministry of Education Funded
Projects Focus on returned overseas scholar, Department of Educa-
tion of Anhui Province (KJ2012A025), Program for New Century
Excellent Talents in University (China), Doctoral Program Founda-
tion of Ministry of Education of China (20113401110004).
a
b
c
Peak position of the absorption band.
Peak position of SPEF, excited at the absorption maximum.
Quantum yields determined by using fluorescein as standard.
Fluorescence lifetime (ns).
d
Conclusions
In summary, two novel ligands L1, L2 and their CdI2 complexes
1, 2 were synthesized and studied. The crystal structures of the two
complexes exhibit similar properties due to their structural
comparability. UV–vis absorption and single-photon fluorescence
properties of the four compounds were also been investigated.
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.2013.12.067.

36
X. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 30–36
[28] K.J.H. Young, J. Oxgaard, D.H. Ess, S.K. Meier, T. Stewart, W.A. Goddard, R.A.
References
Periana, Chem. Commun. 22 (2009) 3270–3272.
[29] J.L. Chen, X.Z. Tan, X.X. Chen, J.Y. Wang, X.F. Cao, L.H. He, J.Y. Hua, H.R. Wen,
Inorg. Chem. Commun. 30 (2013) 120–123.
[30] R.W.Y. Sun, C.N. Lok, T.T.H. Fong, C.K.L. Li, Z.F. Yang, T. Zou, A.F.M. Siu, C.M. Che,
Chem. Sci. 4 (2013) 1979–1988.
[31] S.K. Meier, K.J.H. Young, D.H. Ess, W.J. Tenn, J. Oxgaard, W.A. Goddard, R.A.
Periana, Organometallics 28 (2009) 5293–5304.
[32] M. Grigoras, N.C. Antonoaia, Eur. Polym. J. 41 (2005) 1079–1089.
[33] E.M. Barea, C. Zafer, B. Gultekin, B. Aydin, S. Koyuncu, S. Icli, F.F. Santiago, J.
Bisquert, J. Phys. Chem. C 114 (2010) 19840–19848.
[34] Y. Tao, Q. Wang, C. Yang, C. Zhong, K. Zhang, J. Qin, D. Ma, Adv. Funct. Mater. 20
(2010) 304–311.
[35] G.M. Sheldrick, SHELXTL97, Program for Crystal Structure Solution; University
of Göttingen: Göttingen. Germany. 1997.
[36] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, Jr, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Tyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,
H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J. Ochterski, P.Y. Ayala,
K. Morokuma, G.A. Voth, P. Savador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.
Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.
Challacombe, P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople. Gaussian 03 (Revision B.04), Gaussion, Inc., Wallingford, CT, 2004.
[37] Q. Zhao, R.F. Li, S.K. Xing, X.M. Liu, T.L. Hu, X.H. Bu, Inorg. Chem. 50 (2011)
10041–10046.
[38] F. Neve, A. Crispini, S. Campagna, S. Serroni, Inorg. Chem. 38 (1999) 2250–
2258.
[39] F. Neve, A. Crispini, C. Di Pietro, S. Campagna, Organometallics 21 (2002)
3511–3518.
[40] S. Graber, K. Doyle, M. Neuburger, C.E. Housecroft, E.C. Constable, R.D. Costa, E.
Ortí, D. Repetto, H.J. Bolink, J. Am. Chem. Soc. 130 (2008) 14944–14945.
[41] H. Zhang, X. Wang, K. Zhang, B.K. Teo, Inorg. Chem. 37 (1998) 3490–3496.
[42] D.M. Epstein, S. Choudhary, M.R. Churchill, K.M. Keil, A.V. Eliseev, J.R. Morrow,
Inorg. Chem. 40 (2001) 1591–1596.
[1] G.T. Morgan, F.H. Burstall, J. Chem. Soc. (1932) 20–30.
[2] G.T. Morgan, F.H. Burstall, J. Chem. Soc. (1937) 1649–1655.
[3] G.T. Morgan, G.R. Davies, J. Chem. Soc. (1938) 1858–1861.
[4] E.A. Medlycott, G.S. Hanan, Chem. Soc. Rev. 34 (2005) 133–142.
[5] I. Eryazici, C.N. Moorefield, G.R. Newkome, Chem. Rev. 108 (2008) 1834–1895.
[6] R.D. Costa, E. Ortí, H.J. Bolink, F. Monti, G. Accorsi, N. Armaroli, Angew. Chem.
Int. Ed. 51 (2012) 8178–8211.
[7] Y.M. Zhang, S.H. Wu, C.J. Yao, H.J. Nie, Y.W. Zhong, Inorg. Chem. 51 (2012)
11387–11395.
[8] A. Reynal, E. Palomares, Eur. J. Inorg. Chem. 29 (2011) 4509–4526.
[9] Y. Numata, A. Islam, K. Sodeyama, Z.H. Chen, Y. Tateyama, L. Han, J. Mater.
Chem. A. 1 (2013) 11033–11042.
[10] N. Kaveevivitchai, L. Kohler, R. Zong, M.E. Ojaimi, N. Mehta, R.P. Thummel,
Inorg. Chem. 52 (2013) 10615–10622.
[11] L. Fillaud, G. Trippé-Allard, J.C. Lacroix, Org. Lett. 15 (2013) 1028–1031.
[12] X.S. Zhou, L. Liu, P. Fortgang, A.S. Lefevre, A. Serra-Muns, N. Raouafi, C.
Amatore, B.W. Mao, E. Maisonhaute, B. Schöllhorn, J. Am. Chem. Soc. 133
(2011) 7509–7516.
[13] M.K. Kashif, M. Nippe, N. Duffy, C.M. Forsyth, C.J. Chang, J.R. Long, L. Spiccia, U.
Bach, Angew. Chem. Int. Ed. 125 (2013) 5637–5641.
[14] M. Wałe˛sa-Chorab, A.R. Stefankiewicz, D. Ciesielski, Z. Hnatejko, M. Kubicki, J.
Kłak, M.J. Korabik, V. Patroniak, Polyhedron 30 (2011) 730–737.
[15] R. Gracia, D. Mecerreyes, Polym. Chem. 4 (2013) 2206–2214.
[16] E. Schott, X. Zarate, R. Arratia-Pérez, Dyes Pigments. 97 (2013) 455–461.
[17] A. Wild, A. Winter, F. Schlütter, U.S. Schubert, Chem. Soc. Rev. 40 (2011) 1459–
1511.
[18] L.M. Guard, J.L. Palma, W.P. Stratton, L.J. Allen, G.W. Brudvig, R.H. Crabtree, V.S.
Batista, N. Hazari, Dalt. Trans. 41 (2012) 8098–8110.
[19] J.H. Wang, Y.Q. Fang, L. Bourget-Merle, M.I.J. Polson, G.S. Hanan, A. Juris, F.
Loiseau, S. Campagna, Chem. Eur. J. 12 (2006) 8539–8548.
[20] C.N. Carlson, C.J. Kuehl, R.E. Da Re, J.M. Veauthier, E.J. Schelter, A.E. Milligan,
B.L. Scott, E.D. Bauer, J.D. Thompson, D.E. Morris, K.D. John, J. Am. Chem. Soc.
128 (2006) 7230–7241.
[21] S.G. Thangavelu, M.B. Andrews, S.J.A. Pope, C.L. Cahill, Inorg. Chem. 52 (2013)
2060–2069.
[22] J. Yang, R.X. Hu, M.B. Zhang, J. Solid State. Chem. 196 (2012) 398–403.
[23] M. Ichikawa, T. Yamamoto, H.G. Jeon, K. Kase, S. Hayashi, M. Nagaoka, N.
Yokoyama, J. Mater. Chem. 22 (2012) 6765–6773.
[24] S. Diring, P. Retailleau, R. Ziessel, Tetrahedron. Lett. 48 (2007) 8069–8073.
[25] J.L. Chen, X.X. Chen, X.Z. Tan, J.Y. Wang, X.F. Fu, L.H. He, Y. Li, G.Q. Zhong, H.R.
Wen, Inorg. Chem. Commun. 35 (2013) 96–99.
[26] K.J.H. Young, M. Yousufuddin, D.H. Ess, R.A. Periana, Organometallics 28 (2009)
3395–3406.
[43] H. Xu, L.F. Huang, L.M. Guo, Y.G. Zhang, X.M. Ren, Y. Song, J. Xie, J. Lumin. 128
(2008) 1665–1672.
[44] X.C. Liu, X.L. Guo, Y.Y. Niu, Q.Y. Wang, Q. Cui, H.W. Hou, X.R. Lv, S. Ng, J. Chem.
Crystallogr. 39 (2009) 147–150.
[45] W.J. Yang, D.Y. Kim, C.H. Kim, M.Y. Jeong, S.K. Lee, S.J. Jeon, B.R. Cho, Org. Lett. 6
(2004) 1389–1392.
[46] M.Y. Berezin, S. Achilefu, Chem. Rev. 110 (2010) 2641–2684.
[27] B. Boff, C. Gaiddon, M. Pfeffer, Inorg. Chem. 52 (2013) 2705–2715.