Synthesis, structure, photo- and electroluminescent properties of bis{(4-methyl-N-[2-[(E)-2-pyridyliminomethyl]phenyl)]benzenesulfonamide}zinc(II)

Article abstract of DOI:10.1016/j.poly.2017.05.045

The synthesis, structure and spectroscopic properties of luminescent Zn(II) complex containing 4-methyl-N-[2-[(E)-pyridinylmethyl]phenyl]benzosulfimide ligand are described. The Zn(II) complex was characterized by single-crystal X-ray diffraction study. Time-dependent density functional theory calculations at the B3LYP/6-31G^? level were performed on Zn(II) complex to interpretation its experimental UV–Vis absorption spectrum. OLED device with Zn(II) complex as light-emitting layer has been fabricated. The electroluminescent spectrum of OLED showed a dominant yellow emission at 525?nm (Commission Internationale de l'eclairage (CIE) coordinates x?=?0.409 and y?=?0.506) and a weak shoulder at 650?nm without any other distinguishing emission from host or adjacent layers. The fabricated OLED generated luminance of more than 1000?cd/m² at 16?V, current density 600?mA/cm² and rather low turn-on voltage of ca. 4?V and power efficiency 1?lm/W.

Full text of DOI:10.1016/j.poly.2017.05.045

Polyhedron 133 (2017) 231–237
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Polyhedron
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Synthesis, structure, photo- and electroluminescent properties of bis{(4-
methyl-N-[2-[(E)-2-pyridyliminomethyl]phenyl)]benzenesulfonamide}
zinc(II)
d
Anatolii S. Burlov a, Eugenii I. Mal’tsev b, Valery G. Vlasenko c, , Dmitrii A. Garnovskii ,
⇑
Artem V. Dmitriev b, Dmitrii A. Lypenko b, Anatoly V. Vannikov b, Pavel V. Dorovatovskii e,
Vladimir A. Lazarensko e, Yan V. Zubavichus e, Victor N. Khrustalev f
a Institute of Physical and Organic Chemistry of Southern Federal University, Stachki Ave. 194/2, Rostov-on-Don 344090, Russian Federation
b A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of RAS, Leninskii Ave. 31/4, Moscow 119991, Russian Federation
c Institute of Physics of Southern Federal University, Stachki Ave. 194, Rostov-on-Don 344090, Russian Federation
d Southern Scientific Centre of Russian Academy of Sciences, Chekhova Ave. 41, Rostov-on-Don 344006, Russian Federation
e NRC Kurchatov Institute, 1 Acad. Kurchatov Sq., Moscow 123182, Russian Federation
f Department of Inorganic Chemistry, Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklay Str., 6, Moscow 117198, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, structure and spectroscopic properties of luminescent Zn(II) complex containing 4-
methyl-N-[2-[(E)-pyridinylmethyl]phenyl]benzosulfimide ligand are described. The Zn(II) complex was
characterized by single-crystal X-ray diffraction study. Time-dependent density functional theory calcu-
lations at the B3LYP/6-31G⁄ level were performed on Zn(II) complex to interpretation its experimental
UV–Vis absorption spectrum. OLED device with Zn(II) complex as light-emitting layer has been fabri-
cated. The electroluminescent spectrum of OLED showed a dominant yellow emission at 525 nm
(Commission Internationale de l’eclairage (CIE) coordinates x = 0.409 and y = 0.506) and a weak shoulder
at 650 nm without any other distinguishing emission from host or adjacent layers. The fabricated OLED
generated luminance of more than 1000 cd/m2 at 16 V, current density 600 mA/cm2 and rather low turn-
on voltage of ca. 4 V and power efficiency 1 lm/W.
Received 17 April 2017
Accepted 23 May 2017
Available online 1 June 2017
Keywords:
Azomethines
Zinc complex
Luminescence
TD-DFT
OLED
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
The PL and EL properties of chelate complexes of zinc contain-
ing an azomethine ligand derivatives of 2-hydroxybenzaldehyde
The use of Tang and Van Slyke [1] tris(8-hydroxyquinolinato)
aluminium Alq3 for the manufacture of the first OLED devices with
green photoluminescence (PL) and quantum yield of about 32%,
operating at low voltage (<20 V), gave impetus to the study of
metal chelate complexes, and in particular, zinc complexes as elec-
troluminescent layers. The interest in such Zn complexes is due to
their high photo – (PL) and electroluminescent (EL) characteristics
and electron-transport properties, thermal stability with high glass
transition temperature, variability of structures, the relative sim-
plicity of synthesis.
(or alkyl)amines have been studied by many authors [3–7]. The flu-
orescence band maximum of such complexes are observed in
kPL = 480–553 nm. On the basis of these compounds as emissive
layers has been made a number of electroluminescent devices.
For example, the OLED manufactured with the use of zinc com-
plexes, derivatives of salicylic aldehyde with various amines: bis
[N-(2-oxybenzoates)cyclohexylamino]zinc,
bis[N-(2-oxyben-
zoates)-4-tert-butylaniline]zinc and N,N0-bis[(oxybenzone)-1,2-
phenylendiamine]zinc, emitting in the blue, green and red spectral
regions of the spectrum, respectively [5].
Especially popular are electroluminescent materials that emit in
the range of 400–450 nm, blue emitters, as they are not only the
main component of red–green–blue full color OLED displays, but
the key components in the formation of the white light combina-
tion of blue and orange [2].
The maxima of the bands of EL OLED based on bis[N-(2-oxyben-
zoates)-4-tert-butylaniline]zinc kEL = 520 nm and N,N0-bis[(oxy-
benzone)-1,2-phenylendiamine]zinc kEL = 570 nm underwent
a
small bathochromic shift compared to the fluorescence of
these complexes kPL = 510 nm and kPL = 565 nm, however, for
bis[N-(2-oxybenzoates)cyclohexylamino]zinc, on the contrary,
undergoes the largest hypsochromic shift observed from the
kPL = 453 nm to kEL = 450 nm. OLED devices on the basis of these
⇑
Corresponding author.
E-mail address: v_vlasenko@rambler.ru (V.G. Vlasenko).
http://dx.doi.org/10.1016/j.poly.2017.05.045
0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.

232
A.S. Burlov et al. / Polyhedron 133 (2017) 231–237
zinc complexes showed a brightness of 120 cd/m2 (8.4 V), 360 cd/
m2 (12.7 V) and 360 cd/m2 (8.5 V) and the current efficiency was
1.4, 15, and 1.7 cd/A, respectively.
2. Experimental
2.1. Materials required and general methods
The electroluminescent device with an active luminescent layer
based on N,N0-bis[(2-hydroxibenziliden)-1,2-phenylendiamine]
zinc is made [8]. The device emits in the green spectral region,
has the brightness 480 cd/m2 at a voltage of 11.8 V and a current
density of 26 mA/cm2.
All starting materials and solvents were used as commercial
products. 2-aminopyridine, zinc acetate dihydrate (Alfa Aesar).
For the manufacture of electroluminescent devices there were
used commercial substances: Phthalocyaninecopper complex
(CuPc). ALDRICH. CAS 147-14-8; 4,40,400-Tris[2-naphthyl(phenyl)
amino]triphenylamine (2-TNATA) KINTEC. lot: KZ88BuOMEEO,
sales@kintec.hk; TPD –N,N0-Bis(3-methylphenyl)-N,N0-diphenyl-
benzidineSIGMA – ALDRICH. CAS 443263-5G; 2,9-Dimethyl-4,7-
diphenyl-1,10-phenanhroline (BCP) KINTEC. lot: KZ86BUOHRYO.
sales@kintec.hk; 4,7-Diphenyl-1,10-phenanthroline (Bphen) KIN-
TEC. lot: KZ88BuOMEEO. sales@kintec.hk; LiF, ALDRICH. CAS:
7789-24-4. 2-(N-Tosylamino)benzaldehyde has been synthesized
using the reported procedure [22].
Complex of zinc with ligands based on derivatives 8-amino-
quinoline used as emitter in the electroluminescent device
described in [9], which emits in the blue-green region of the spec-
trum and has a brightness of 140 cd/m2 at a voltage of 19 V and a
current density of 1.5 mA/cm2, showing an efficiency of 9 cd/A. A
manufactured OLED, where the electroluminescent substance
used, is one of oxyquinoline zinc complexes of 8-hydroxy-2-
methoxyquinoline or 8-hydroxy-2-methylinosine derivatives
[10]. This device emits in the green region of the spectrum with
the following parameters: brightness of 140 cd/m2 is achieved at
a voltage of 16 V and a current density of 24 mA/cm2, the current
efficiency was 4 cd/A. The complex of bis{3-methyl-1-phenyl-4
[(quinoline-3-imino)methyl]1-H-pyrazole-5-olato}zinc(II) used as
emissive layer in a multilayer electroluminescent device with the
structure ITO/CuPc/2TNTA/Spiro-TPD/zinc complex/BCP/BPhen/
LiF/Al and emitted in the yellow region of the spectrum (kEL = 600 -
nm) with brightness of 800 cd/m2 at a voltage of 10 V, which cor-
responds to a luminous efficiency of 0.5 Lm/W [11]. Also it was
manufactured an electroluminescent device based on the films of
bis(2-oxybenzene-4-tret-butylaniline)zinc (99%), and its mixture
with the Nile red (1%), emitting in the green and red spectral
regions, respectively. The green emission has a brightness of
480 cd/m2 at a voltage of 11 V and a current density of 2 mA/
cm2. The red emission has a luminance of 0.4 cd/m2 at a voltage
of 11 V and a current density of 30 mA/cm2 [12].
The replacing the 2-hydroxy group of the aldehyde fragment in
the complexes of zinc azomethine compounds onto the 2-N-tosy-
lamine group leads to the change of coordination environment of
the zinc ion with of ZnN2O2 on with ZnN4, that in most cases leads
to an increase in thermal stability of such complexes and undergoes
the largest hypsochromic shift of the bands in the spectra of PL.
Such complexes luminesce in the blue region kPL = 428–433 nm
with quantum efficiency of PL = 0.23–0.37 [13–21].
In search of new zinc complexes having fluorescence properties
and high thermal stability, we have obtained novel azomethine
compound 4-methyl-N-[2-[(E)–pyridinylmethyl]phenyl]benzosul-
fimide (I) and its complex with zinc (II).
C, H, N, elemental analyses were carried out on a Carlo Erba
TCM 480 apparatus using sulfanilamide as the standard. The metal
content was determined gravimetrically in the analytical labora-
tory of the Institute of Physical and Organic Chemistry (SFU, Ros-
tov-on-Don, Russia). Melting points were measured on a Kofler
bench.
Infrared spectra (4000–400 cmꢀ1) were recorded on a Varian
Excalibur-3100 FT-IR spectrophotometer in KBr pellets.
1H NMR spectra were measured on a «Varian University-300»
spectrometer at ambient temperature in CDCl3 with the signal of
residual 2H of the solvent as the internal reference.
Electron absorption spectra were obtained on a «Varian Cary
100» spectrophotometer, fluorescence spectra were obtained on a
«Varian Cary Eclipse» fluorescence spectrophotometer. Spectral
grade chloroform from Sigma–Aldrich was used for the preparation
of solutions. All UV–Vis and fluorescence spectra were recorded
using standard 1 cm quartz cell in CHCl3 solutions at room temper-
ature at c = 4.0ꢁ10ꢀ5 M.
The geometry of complex II in the ground state was fully opti-
mized at the DFT level using GAUSSIAN-03 computer program [23].
For calculations the hybrid three-parameter functional B3LYP
[24,25] and the standard split-valence polarization basis set 6-
31G(d) [26] were chosen. Simulations of UV–Vis absorption spectra
for these molecules were accomplished in the framework of Time
Dependent Density Functional Theory (TD-DFT) using optimized
atomic structure parameters with account of solvent effects by
the standard polarizable continuum model (PCM) with integral
equation formalism method [27].
3C
H
N
SO2
SO2
CH3
SO2
N
CH3
N
N
N
Zn
N
NH2
O
N
H
Zn(CH3COO)2
.
2H2O
N
NH2
N
SO2
N
I
II
CH3

A.S. Burlov et al. / Polyhedron 133 (2017) 231–237
233
2.2. Ligand synthesis
2.4. X-ray crystal structure determination
2.2.1. 4-methyl-N-[2-[(E)-2-pyridyliminomethyl]phenyl]
benzenesulfonamide (HL)
X-ray diffraction data were collected on the ‘Belok’ beamline
(k = 0.96990 Å) of the National Research Center ‘Kurchatov Insti-
tute’ (Moscow, Russian Federation) using a Rayonix SX165 CCD
detector. A total of 360 images were collected using an oscillation
range of 1.0° and u scan mode, and corrected for absorption using
the Scala program [28]. The data were indexed, integrated and
scaled using the utility iMOSFLM in CCP4 program [29]. For details,
see Table 1. The structure was determined by direct methods and
refined by full-matrix least squares technique on F2 with anisotro-
pic displacement parameters for non-hydrogen atoms. The hydro-
gen atoms were placed in calculated positions and refined within
riding model with fixed isotropic displacement parameters
[Uiso(H) = 1.5Ueq(C) for the CH3-groups and 1.2Ueq(C) for the other
groups]. All calculations were carried out using the SHELXTL
program [30].
A solution containing 0.55 g (2 mmol) of 2-(N-tosylamino)ben-
zaldehyde in 10 ml of toluene was added to the solution of 0.19 g
(2 mmol) of 2-aminopyridine in 10 ml of toluene. The mixture
was refluxed during 1 h with a Dean-Stark trap until water strip-
ping was completed. The precipitate formed was filtered off and
recrystallized from a chloroform-ethanol 1:2 mixture and dried
at 150 °C.
Yellow crystals, m.p. = 117–118 °C. Yield 78%. Anal. Calc. for
C
19H17N3O2S: C, 64.92; H, 4.84; N, 11.96. Found: C, 65.02; H,
4.74; N, 11.84%. IR spectrum in KBr, selected bands, cmꢀ1
:
3100–2870
m (NH), 1621 m (CH = N), 1342 mas (SO2), 1160 ms
(SO2). 1H NMR (CDCl3), d (ppm): 2.37 (3H, s, CH3), 7.09 – 7.84
(11H, m, CAr-H), 8.54 (1H, d, 3J = 4.8 Hz, CAr-H), 9.33 (1H, s,
CH = N), 13.13 (1H, s, NH).
Crystallographic data for IIꢁ2CHCl3 have been deposited with
the Cambridge Crystallographic Data Center, CCDC 1540143.
Copies of this information may be obtained free of charge from
the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax:
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk or www.
ccdc.cam.ac.uk).
2.3. Synthesis of complex
2.3.1. Bis{(4-methyl-N-[2-[(E)-2-pyridyliminomethyl]phenyl)]benzene
sulfonamide}zinc(II)
A
hot solution of 0.35 g (1 mmol) of 4-methyl-N-[2-[(E)-
2-pyridyliminomethyl]phenyl]benzenesulfonamide in 25 ml of
ethanol was added to solution of 0.11 g (0.5 mmol) zinc acetate
dihydrate in 5 ml of ethanol. The reaction mixture was refluxed
at 80 °C for 1 h. The precipitate of complex was filtered off and
crystallized from a chloroform-ethanol 1:2 mixture and dried at
150 °C.
3. Results and discussion
3.1. Spectroscopic properties
The structure of azomethine HL I has been determined from IR,
1H NMR and elemental analysis data. The infrared spectrum of the
free ligand HL showed a broad band at 2870–3100 cmꢀ1 which is
Yellow crystals, m.p.> 250 °C. Yield 84%. Anal. Calc. for
C
40H34N6O4S2Cl6Zn: C, 47.81; H, 3.41; N, 8.36, Zn, 6.51. Found: C,
47.78; H, 3.59; N, 8.31; Zn, 6.48%. IR spectrum in KBr, selected
bands, cmꢀ1: 1611 (CH = N), 1272 mas (SO2), 1139 ms (SO2).).1H
NMR (CDCl3), d (ppm): 2.29 (3H, s, CH3), 6.87–7.86 (11H, m,
Ar-H), 8.33 (1H, d, 3J = 4.8 Hz, CAr-H), 9.21 (1H, s, CH = N). UV–Vis
assigned to the m HN-tosyl fragment. The absorption band observed
at 1621 cmꢀ1 and intense absorption bands at 1342 cmꢀ1 and
m
1160 cmꢀ1 are attributed to the
SO2-group, respectively.
m HC@N and as-/s- vibrations of
C
The 1H NMR data (in CDCl3 solution) of the HL showed the res-
onance signals at 9.33 ppm and 13.13 ppm are attributed to HC@N
and NH protons, respectively.
spectrum in CHCl3 (nm): 308, 394. PL spectrum (nm): kPL = 498.
According to the elemental analysis data, the zinc complex II
possess the general formula ZnL2ꢁ2CHCl3 (IIꢁ2CHCl3). IR spectrum
of the complex IIꢁ2CHCl3 demonstrates disappearance of the band
Table 1
Crystallographic Data for IIꢁ2CHCl3.
m
NH, whereas the band m
HC@N is reduced by10 cmꢀ1 and
Compound
IIꢁ2CHCl3
C40H34N6O4S2Cl6Zn
1004.94
observed at 1611 cmꢀ1. The bands at 1272 cmꢀ1
1139 cmꢀ1 s, SO2) are reduced by 42 cmꢀ1 and 21 cmꢀ1 com-
(mas SO2) and
Empirical formula
fw
T (K)
(
m
pared with HL, respectively.
100(2)
Crystal size (mm)
0.20 ꢂ 0.20 ꢂ 0.02
monoclinic
C2/c
15.793(3)
16.783(3)
16.237(3)
92.08(3)
4300.9(14)
4
1.552
1H NMR spectrum of IIꢁ2CHCl3 displays the disappearance of
resonance signal at 13.13 ppm is attributed to NH protons of HL,
whereas the resonance signal from HC@N protons is slightly
shifted in upfield region compared to the free ligand, indicating
that the azomethine nitrogen atom is coordinated to the Zn(II)
ion after deprotonation [21,31].
Crystal system
Space group
a (Å)
b (Å)
c (Å)
b (°)
V (Å)3
Z
dc (g cmꢀ3
F(000)
)
3.2. Molecular and crystal structures of IIꢁ2CHCl3
2048
2.552
76.92
l
(mmꢀ1
)
Compound of IIꢁ2CHCl3 was characterized by single-crystal X-
ray diffraction study. Its structure is shown in Fig. 1 along with
the atomic numbering scheme and selected bond lengths and
angles. The full geometrical parameters for IIꢁ2chcl3 are available
as Supplementary material.
Zinc complex IIꢁ2CHCl3 possesses overall idealized C2 (2) sym-
metry and crystallizes in the monoclinic space group C2/c. The
intrinsic C2 symmetry is remained in the crystal – the molecule
occupies a special position on the twofold axis. The zinc atom is
a four-coordinated to the two monoanionic N,N-bidentate chelat-
ing ligands, which are bonded to the metal atom through sulfamide
2hmaximum (°)
Index range
ꢀ19 ꢃ h ꢃ 19
ꢀ21 ꢃ k ꢃ 21
ꢀ19 ꢃ l ꢃ 20
27108
4572 (Rint = 0.0851)
3281
4572/0/269
0.0760; 0.1057
0.1880; 0.2112
1.052
No. of reflections collected
No. of unique reflections
No. of reflections with (I > 2
Data/restraints/parameters
r
(I))
R1; wR2 (I > 2r(I))
R1; wR2 (all data)
Goodness-of-fit (GOF) on F2
Tminimum; Tmaximum
0.600; 0.930

234
A.S. Burlov et al. / Polyhedron 133 (2017) 231–237
Fig. 1. Molecular structure of IIꢁ2CHCl3. Displacement ellipsoids are shown at the
50% probability level. The labeling denotes symmetrically equivalent atom
A
relative to the twofold axis. Dashed lines indicate the intra- and intermolecular
C─Hꢁ ꢁ ꢁO hydrogen bonds. Selected bond lengths and angles (Å and): Zn1─N1
2.053(3), Zn1─N2 2.032(3), N1─C1 1.424(5), N2─C7 1.299(5), C1─C6 1.421(5),
C6─C7 1.437(5), N1─Zn1─N2 92.39(12), N1─Zn1─N2A 114.12(11),
N1─Zn1─N1A 124.54(15), N2─Zn1─N2A 122.12(15), Zn1─N1─C1 126.3(2),
Zn1─N2─C7 124.9(2), N1─C1─C6 120.6(3), N2─C7─C6 128.1(3), C1─C6─C7
127.7(4).
and imine nitrogen atoms. The coordination sphere around the
zinc atom can be described as distorted tetrahedral (the bond
angles range from 92.39(12) to 124.54(15)°), with a dihedral angle
between the planar six-membered chelating rings (rms deviation is
0.008 Å) of 81.56(7)°. The smallest N─Zn─N angles are the intra-
chelate, and the largest one is the Nsulfamide─Zn─Nsulfamide. The
weak intramolecular Zn1ꢁ ꢁ ꢁO2/Zn1ꢁ ꢁ ꢁO2A and Zn1ꢁ ꢁ ꢁN3/
Zn1ꢁ ꢁ ꢁN3A interactions at the distances of 2.812(2) and 2.906
(4) Å, respectively, might contribute to the distortion of the zinc
coordination polyhedron. Taking into account these interactions,
the coordination polyhedron of the Zn atom could be described
as a bicapped tetrahedron. The molecular geometry observed for
complex IIꢁ2CHCl3 is supported by the four intramolecular
C2─H2ꢁ ꢁ ꢁO1/C2A─H2Aꢁ ꢁ ꢁO1A [Cꢁ ꢁ ꢁO 3.012(5), Hꢁ ꢁ ꢁO 2.38 Å,
\C─HꢁꢁꢁO 124°] and C9─H9ꢁ ꢁ ꢁO2A/C9A─H9Aꢁ ꢁ ꢁO2 [Cꢁ ꢁ ꢁO 3.306
(4), Hꢁ ꢁ ꢁO 2.44 Å, \C─Hꢁ ꢁ ꢁO 152°] hydrogen bonds. The Zn─N
bond distances (2.032(3) and 2.053(3) Å) are slightly longer than
those found in the other related homoleptic zinc complexes with
N,N-bidentate ligands [32–36]. Apparently, this fact may be also
explained by the additional weak intramolecular Znꢁ ꢁ ꢁO and Znꢁ ꢁ ꢁN
interactions.
Fig. 2. Crystal structure of IIꢁ2CHCl3 demonstrating the zigzag-like chains propa-
gating toward [100]. Only hydrogen atoms participating in the formation of
hydrogen bonds are shown. Dashed lines indicate the intra- and intermolecular
C─Hꢁ ꢁ ꢁO hydrogen bonds and intermolecular secondary Clꢁ ꢁ ꢁCl interactions.
In the crystal, complex IIꢁ2CHCl3 forms the strong enough H-
bonded adduct with two solvate chloroform molecules by the
two intermolecular C20─H20ꢁ ꢁ ꢁO1/C20A─H20Aꢁ ꢁ ꢁO1A hydrogen
bonds [Cꢁ ꢁ ꢁO 3.130(5), Hꢁ ꢁ ꢁO 2.17 Å, \C─Hꢁ ꢁ ꢁO 159°] (Fig. 1). Fur-
ther the H-bonded adducts are linked by the intermolecular sec-
ondary Cl2ꢁ ꢁ ꢁCl2 [ꢀx, y, ½ ꢀ z] interactions (3.173(3) Å) into
zigzag-like chains propagating toward [100] (Fig. 2).
3.3. Electronic absorption spectra and photoluminescence
Electronic absorption spectra and photoluminescence of the
complex IIꢁ2CHCl3 were investigated. To interpret the experimen-
tal bands of the electronic absorption spectrum of complex
IIꢁ2CHCl3 there were carried out quantum-chemical calculations
in the approximation TD-DFT taking into account the solvent of
chloroform.
Fig. 3. Experimental electronic spectra (full blue line) registered at 298 K in CH2Cl2
and simulated electronic spectra (dashed black line) calculated by TD-DFT and
Photoluminescence spectrum (full green line) for complex IIꢁ2CHCl3. (Color online.)

A.S. Burlov et al. / Polyhedron 133 (2017) 231–237
235
The Fig. 3 shows the experimental electronic absorption spec-
trum of IIꢁ2CHCl3 in comparison with the results of TD-DFT calcu-
lations. In Fig. 3 also presents the photoluminescence spectrum of
compound IIꢁ2CHCl3. Upon excitation IIꢁ2CHCl3 the photolumines-
cence spectrum has a maximum at kPL = 498 nm and undergoes
bathochromic shift relative to HL (104 nm). The theoretical elec-
tronic excitation energy, wavelengths and oscillator strengths of
electronic transitions are listed in Table 2. This Table 2 also pre-
sents the interpretation of the specific ways the main electronic
transitions, indicating their contributions to the formation of
absorption bands.
The electronic absorption spectrum of IIꢁ2CHCl3 in chloroform
shows two main absorption bands at kabs = 308 nm and kabs = 394 -
nm. Comparison of experimental and calculated absorption spectra
of complex II shows their good agreement to within a few nm.
The transition metal complexes usually show three types of
electronic excitation bands: d–d transitions; transitions metal-to-
ligand charge transfer (MLCT) and ligand-to-metal charge transfer
(LMCT); transitions intraligand charge-transfer (ILCT) and
negligently transitions charge-transfer (LLCT). The absorption band
at 394 nm in the experimental UV–Vis spectrum of complex
IIꢁ2CHCl3 correspond to the three main theoretical electronic tran-
sitions (at 412.88, 402.80 and 396.33 nm) with high oscillator
strengths. All three crossings are determined by the transitions
between the frontier orbitals HOMO ? LUMO, HOMOꢀ1 ? LUMO,
HOMO ? LUMO + 1, respectively, with the maximum contribu-
tions from 87 to 96%. In Fig. 4 shows the isosurfaces of frontier
MO and the relevant electronic transitions for complex II. Analysis
of the MO shapes shows that for
p
(HOMO) and p⁄ (LUMO)the elec-
tron density localized in on azomethine aminopyridine ligand. As
can be seen from Fig. 3 for the long-wavelength transition is the
main type as LLCT charge transfer between different aminopy-
ridine ligands of the complex
p ?
p⁄, whereas the other two corre-
spond to the transition type ILCT charge-transfer within the same
aminopyridine ligand.
For the second intense absorption bands of the experimental
spectrum of complex IIꢁ2CHCl3 at kabs = 308 nm can be
assigned to two electronic transition HOMOꢀ3 ? LUMO and
Table 2
Calculated wavelengths k, the energy of vertical electronic transitions E between the relevant frontier MO, contributions from different electronic transitions and oscillator
strengths f for II obtained from TD-DFT calculations.
k, nm
E (eV)
Electronic transitions, (weight*, %)
f
Assignment
412.88
402.80
396.33
309.35
3.00
3.08
3.13
4.01
HOMO ? LUMO (96)
0.06
0.18
0.23
0.37
LLCT
ILCT
ILCT
ILCT
HOMOꢀ1 ? LUMO (90)
HOMO ? LUMO + 1 (87)
HOMOꢀ3 ? LUMO (71)
HOMOꢀ2 ? LUMO + 1 (8)
HOMOꢀ3 ? LUMO (6)
HOMOꢀ2 ? LUMO + 1 (73)
HOMOꢀ4 ? LUMO (89)
306.86
298.67
4.04
4.15
0.41
0.06
LLCT
LLCT
*
Only the main transitions are reported.
Fig. 4. Frontier molecular orbitals and associated electronic transitions for zinc complex II.

236
A.S. Burlov et al. / Polyhedron 133 (2017) 231–237
HOMOꢀ2 ? LUMO + 1 with very close energies and high oscillator
strength (around 0.4). These electronic transitions are also respon-
sible
p ?
p⁄ transfers charge aminopyridine azomethine ligands
and belong to two different types of ILCT and LLCT transitions,
respectively. Any d-d or MLCT transitions were not found in our
calculations, as the ion Zn(II) has a completely filled d-shell. This
result is confirmed by the absence of any absorption bands in the
wavelength region of the experimental electronic spectra of Zn
(II) set.
3.4. Electroluminescent properties of the complex IIꢁ2CHCl3
In order to study the electroluminescent properties of the com-
plex IIꢁ2CHCl3 as phosphor, a multilayered OLED structure was fab-
ricated. It consisted of a pre-cleaned ITO glass substrate coated
oxide (15 ohm/sq) as the anode, copper phtalocyanine (CuPc)
hole-injecting layer (5 nm), 4,40,400-Tris[2-naphthyl(phenyl)
amino]triphenylamine
(2-TNATA)
hole-transporting
layer
(35 nm), N,N0-Bis(3-methylphenyl)-N,N0-diphenylbenzidine (TPD)
electron-blocking layer (6.5 nm), light-emitting layer – complex
IIꢁ2CHCl3 (23 nm), 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline
(BCP) hole-blocking layer (5 nm), 4,7-diphenyl-1,10-phenantroline
(Bphen) electron-transporting layer (26 nm), LiF electron-injecting
layer (0.8 nm) and aluminum cathode (100 nm). In the manufac-
ture of the OLED only thermal vacuum deposition technique was
used. The complex IIꢁ2CHCl3 demonstrated high thermal stability.
The light-emitting area was 0.3 cm2. Electrical and light-emitting
properties were measured in an argon environment. Luminance
Commission Internationale de l’eclairage (CIE) color coordinates
(Fig. 5, insert), current–voltage and brightness-voltage curves of
electroluminescent device (Fig. 6) were measured using computer
controlled spectrophotometer Ava Spec 2048, Sours Meter Keithley
2601, Keithley 6485 and photometer TRA-04/3.
Fig. 6. Current density and luminance as a function of operating voltage for the
electroluminescent device.
the front direction. The fabricated OLED generated luminance of
more than 1000 cd/m2 at 16 V, currant density 600 mA/cm2and
rather low turn-on voltage of ca. 4 V and power efficiency 1 lm/W.
4. Conclusion
The azomethine compound 4-methyl-N-[2-[(E)-pyridinyl-
methyl]phenyl]benzosulfimide and its zinc complex were synthe-
sized and fully characterized by IR, 1H NMR, UV–Vis
spectroscopy, and elemental analysis. Bands in experimental UV–
Vis spectrum have been assigned based on computational results.
Photo- and electroluminescent properties of zinc complex have
been investigated. The performance of a new phosphorescent com-
plex as an emitter in OLED multilayered structure had been inves-
tigated. A device exhibiting stable yellow electrophosphorescence
has been fabricated. These preliminary results indicated that zinc
complex may be looked upon as a promising light-emitting mate-
rial for the development of yellow OLED light sources.
The EL spectrum showed a dominant yellow emission at
525 nm and a weak shoulder at 650 nm without any other distin-
guishing emission from host or adjacent layers, indicating effective
energy transfer from the host molecules to the dopant. CIE coordi-
nates of the emission band were x = 0.409 and y = 0.506. Device
efficiency was determined by measuring the light output only in
Acknowledgements
This work was supported financially by the Ministry of Educa-
tion and Science of the Russian Federation (Project
4.5388.2017/8.9).
The XRD analysis was supported by the Ministry of Education
and Science of the Russian Federation (the Agreement number
02.a03.21.0008).
Appendix A. Supplementary data
CCDC 1540143 contains the supplementary crystallographic
data for II. These data can be obtained free of charge via http://
dx.doi.org/10.1016/j.poly.2017.05.045, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2017.05.045.
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Fig. 5. Electroluminescence spectrum for the complex IIꢁ2CHCl3 and its CIE color
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