Efficient and tunable phosphorescence of new platinum(II) complexes based on the donor-π-acceptor Schiff bases

Article abstract of DOI:10.1016/j.jphotochem.2015.09.018

The condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-diaminomaleonitrile and benzene-1,2-diamine, respectively, afforded two donor-π-acceptor Schiff base ligands H₂L¹ and H₂L². For comparison, the

Full text of DOI:10.1016/j.jphotochem.2015.09.018

Accepted Manuscript
Title: Efficient and Tunable Phosphorescence of new
Platinum(II) Complexes Based on the Donor-␲-Acceptor
Schiff bases
Author: Jie Zhang Guoliang Dai Fengshou Wu Dan Li
Dongchun Gao Haiwei Jin Song Chen Xunjin Zhu Chenxiu
Huang Deman Han
PII:
S1010-6030(15)00371-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2015.09.018
JPC 10018
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
24-5-2015
18-9-2015
29-9-2015
Please cite this article as: Jie Zhang, Guoliang Dai, Fengshou Wu, Dan Li, Dongchun
Gao, Haiwei Jin, Song Chen, Xunjin Zhu, Chenxiu Huang, Deman Han, Efficient
and Tunable Phosphorescence of new Platinum(II) Complexes Based on the Donor-
rmpi-Acceptor Schiff bases, Journal of Photochemistry and Photobiology A: Chemistry
http://dx.doi.org/10.1016/j.jphotochem.2015.09.018
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

ARTICLE
Efficient and Tunable Phosphorescence of new Platinum(II) Complexes
Based on the Donor-π-Acceptor Schiff bases
Jie Zhanga,b* zhang_jie@tzc.edu.cn hdm@tzc.edu.cn, Guoliang Daic, Fengshou Wud wfs42@126.com, Dan Lie, Dongchun
Gaoa, Haiwei Jina, Song Chenf, Xunjin Zhuf xjzhu@hkbu.edu.hk, Chenxiu Huanga, Deman Hana
aSchool of Pharmaceutical and Chemical Engineering, Taizhou University, 318000 Taizhou, P. R. China.
bDepartment of Chemical and Biological Engineering, Zhejiang University, 310027 Hangzhou, P.R. China.
cSchool of Chemistry, Biology and Materials Engineering, Suzhou University of Science and Technology, 215009 Suzhou,
P. R. China.
dKey Laboratory for Green Chemical Process of the Ministry of Education, Wuhan Institute of Technology, Wuhan, P. R.
China.
eDepartment of Scientific Research, Taizhou University, 318000 Taizhou, P. R. China
fDepartment of Chemistry and Institute of Advanced Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong,
P.R. China.
*Corresponding author.

ARTICLE
Journal Name
Graphical abstract
The condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-diaminomaleonitrile and benzene-1,2-diamine, respectively,
afforded two donor-π-acceptor Schiff base ligands H2L1 and H2L2. And their corresponding platinum(II) complexes PtL1 PtL2
show yellow to red emissions with the highest quantum yield of 8.6% for PtL1
,
.

Journal Name
ARTICLE
Highlights
1) Donor‐π‐acceptor type platinum(II) Schiff base complexes were developed.
2) Their photophysical properties and electrochemical behaviors were investigated.
3) The HOMO and LUMO energy levels can be adjusted by the structure optimization.
4) The complexes emit in the range of yellow to red.
5) Their photophysical properties were investigated by density functional theory.

ARTICLE
Journal Name
Abstract
The condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-diaminomaleonitrile and benzene-1,2-diamine, respectively, afforded
two donor-π-acceptor Schiff base ligands H2L1 and H2L2. For comparison, the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with 4-
(trifluoromethyl)benzene-1,2-diamine produced the ligand H2L3. Subsequently, their corresponding platinum(II) complexes PtL1 PtL2 and PtL3
,
were prepared through the metallation of ligands with K2PtCl4. All the ligands and complexes were characterized by 1H NMR, infrared
spectroscopy and mass spectrometry. And their thermal stabilities, photophysical properties, and electrochemical behaviors were investigated
in detail. These complexes show yellow to red emissions with the highest quantum yield of 8.6% for PtL1. The decay times in microsecond
scale (1.97-2.35 μs) indicate their phosphorescence characteristics arising from the triplet state. The B3LYP density functional theory
calculations shows that the HOMO-LUMO gaps of PtL1, PtL2 and PtL3 are 2.53, 3.07 and 2.78 eV, respectively, which are well consistent with
their photophysical properties. With the advantages of preparative accessibility and high thermal stability, these new phosphorescent
platinum(II) complexes are attractive as emissive layer in organic light-emitting diodes.

Journal Name
ARTICLE
Transition metal complexes of N2O2 Schiff base derived from salicylaldehyde and diamines have attracted considerable interest as a promising
class of luminescent materials with the advantages of preparative accessibility and thermal stability.[1] Typically, the metal complexation leads to
the formation of geometrically constrained acentric, generally planar structural Schiff base complexes with an enhanced emission in comparison
with their related free ligands. Amongst them, zinc Schiff base complexes have been widely investigated.[2] Our group previously reported several
[3]
donor-π-acceptor zinc(II) and nickel(II) Schiff base complexes which possess two-photon induced fluorescence (TPIF).
Since these zinc
complexes can only emit in a singlet state with low quantum yield efficiency, some heavy metal Schiff base complexes such as Pt(II), Ir(III), Au(I)
et al. have been developed with enhanced intersystem crossing (ISC) due to the strong spin-orbit coupling, which overcomes the limitation of
25% efficiency of conventional fluorescent OLEDs with the nature of emission from pure singlet excitons [4]
In general, both singlet and
.
triplet excitons formed with the ratio of 1:3 under electrical excitation, therefore, contribute the light emission by the fast exciton energy transfer
in phosphorescent organic light-emitting diodes (PhOEDs) based on the heavy metal complexes, potentially resulting in a 100% quantum yields.
Currently, phosphorescent materials with triplet state emission have been widely and successfully applied in organic light-emitting diodes
(OLEDs) fabrication.[5]
Among those heavy metal complexes, phosphorescent platinum(II) complexes have been well studied by Thompson, Forrest, Che and
coworkers.[6] Compared with the most reported iridium complexes, platinum complexes have some different characteristics: (1) square planar
structure with four coordination; (2) rich photophysical properties suitable for OLEDs, sensor, organic photovoltaic (OPV) et al.; (3) existing
Pt…Pt and π-π interactions with adjustable emission wavelength and efficiency; (4) lower HOMO and higher LUMO level with better electron
injecting and transporting. Specifically, Che and his coworkers have devoted much effort in platinum(II) Schiff base complexes,[7] which show
strong triplet state emissions with high quantum efficiency. In these platinum(II) Schiff base complexes, it was found that the formation of
aggregate/excimer would reduce the emission efficiency and also affect the color purity at their high concentrations. This is mainly attributed to
the triplet-triplet annihilation, Pt…Pt and π-π interactions at the high concentration in solid state. In our previous work, a series of new
symmetric and asymmetric platinum(II) Schiff base complexes with bulky substituents such as tert-butyl and triphenylamino groups, have also
been developed, leading to a high efficiency in OLED devices due to effectively suppressing of the aggregation or excimer formation.[8]
In this contribution, three Schiff base ligands derived from the condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 2,3-
diaminomaleonitrile, and benzene-1,2-diamine, respectively, or 3,5-di-tert-butyl-2-hydroxybenzaldehyde with 4-(trifluoromethyl)- benzene-1,2-
diamine. Subsequently, their platinum(II) complexes were prepared and characterized. The strong electron withdrawing units involved in the
complexes such as dicyanovinyl and (trifluoromethyl)phenyl, and electron donating units such as 4-diethylaminophenyl and 3,5-di-tert-butyl-
phenyl can finely tune the emission wavelength from yellow to red and somewhat improve the emission efficiency.[9] With the advantages of
preparative accessibility and high thermal stability, these new phosphorescent platinum(II) complexes are attractive as emissive
materials in OLEDs.
Results and Discussion
Synthesis
The Schiff base ligands (H2L1–H2L3) were prepared via the condensation of the substituted 2-hydroxybenzaldehydes with diamines according to
the traditional method (Scheme 1).[10] Then the ligands were reacted with potassium tetrachloroplatinate(II) and KOH in DMF at 70℃ to give the
corresponding platinum(II) Schiff base complexes. These complexes PtL1, PtL2 and PtL3 show good solubility in common organic solvents. All
1
the new Schiff base ligands and platinum(II) complexes were characterized by H NMR, infrared spectroscopy (IR), mass spectrometry (MS),
UV-visible spectrum and elemental analysis.
Characterization of the ligands and complexes
The 1H NMR spectra of the Schiff base ligands H2L1, H2L2 and H2L3 in CDCl3 exhibit a board singlet peak at 12.49, 13.63 and 13.28 ppm for the
O–H protons, respectively. The chemical shift is typical for the resonance-assisted hydrogen bonded (RAHB) proton of O–H…N=C. Another
characteristic sharp singlet peaks appear at 8.57, 8.42 and 8.67 ppm for imino protons of the ligands H2L1, H2L2 and H2L3, respectively. The 1H
NMR spectra of their platinum(II) complexes PtL1, PtL2 and PtL3 in CDCl3 similarly exhibit a singlet peak at δ 8.31, 8.98 and 8.89 ppm for the
imino protons, respectively. All the new compounds were further characterized by IR and MS. The IR absorption peak for the ligands and
complexes between 1616–1636 cm-1 can be assigned as the C=N stretching vibrations. The MALDI-TOF-MS spectra of the three platinum(II)
complexes exhibit [M]+ or [M+H]+ peaks with values less than 5 ppm deviation from the theoretical ones.
UV-visible absorption of the ligand and complexes
The Schiff base ligands H2L1, H2L2 and H2L3 exhibit UV-visible absorption spectra between 200–600 nm (Figure 1), which can be assigned to
intra-ligand π-π* and n-π* transitions. Specifically, the ligand H2L1 shows a much red shifted absorption peak at 571 nm in comparison with
H2L2 and H2L3, which is consistent with the TD-DFT calculation data of the ligands, as shown in the Table S1 and Figure S3-S5
(
ESI).
Obviously, the structure of H2L1 is a donor-π-acceptor (D-π-A) type, leading to a very strong ligand-to-ligand charge transfer (LLCT)
character. In contrast, the structure of H2L2 and H2L3 are donor-
(D- ) and acceptor- (A- ) type, respectively, both characteristic of a
π
π
π
π

ARTICLE
Journal Name
relatively weak LLCT. As a result, the maximum absorption and emission peaks of D-
π
-A type compound locate at longer wavelengths
than its D-π and A-π counterparts. Based on the DFT calculation data, those absorption peaks of the ligands between 400–600nm are
mostly attributed to LLCT. On the other hand, three platinum(II) complexes show intense absorption bands in the range of 400–600 nm, which
can be assigned to π-π* transitions of LLCT mixed with metal-to-ligand charge-transfer (MLCT) (Figure 1).[7c] This assignment is also supported
by the DFT calculation data, as shown in Figure 4 and Table 3, in which the lowest absorption energy bands of the platinum complexes are
ranged in 500–600 nm, arising from MLCT and LLCT. Similarly, the maximum absorption peak of PtL1 is also red-shifted compared with PtL2
and PtL3, due to its donor-π-acceptor structural characteristics. In our previous study of the Schiff base complexes, it was found that the HOMO
mainly located on the phenolate fragments and metal ion while the LUMO located on the imino part.[3a] And the donor or acceptor groups at the
5-position of the phenolate fragments have little effect on the HOMO and LUMO energy levels. In contrast, the electron donating groups at 4-
position of the phenolate fragments and the electron withdrawing groups at the imino in PtL1 results in a donor-π-acceptor configuration with
efficient intramolecular charge transfer, which can effectively adjust the HOMO and LUMO energy levels.
Emission of the ligand and complexes
As shown in Figure 2，Figure S1 (ESI) and Table 1, the emission spectra of the platinum(II) Schiff base complexes exhibit yellow to red
emissions in the visible range of 531–776 nm. The platinum(II) complexes PtL1 modified by both electron-donating and electron-withdrawing
groups show a much red shifted emission in comparison with PtL2 and PtL3 only with either electron-donating group or electron-withdrawing
group. The quantum yields of the Schiff base complexes are moderate, from 0.87% to 8.6%, which are comparable with the reported values by
our group[8] and Che’s group[7]. The decay times in microsecond scale (1.97–2.35 μs) indicates the emission arise from the triplet state (Figure S2,
ESI). The triplet state emission can be attributed to intraligand charge transfer and metal-to-ligand charge-transfer (MLCT). [7c]
Electrochemical Properties and Thermal Stability
The cyclic voltammetry behaviour of platinum(II) Schiff base complexes have been examined. Cyclic voltammetry study can give fundamental
information on the number of oxidation/reduction processes and the redox potentials of the compounds. Furthermore, the HOMO-LUMO energy
gap can be estimated from its redox potentials. Cyclic voltammetry behaviors of the platinum(II) Schiff base complexes were recorded in
degassed acetonitrile with 0.1 M tetrabutylammonium hexafluorophosphate as supporting electrolyte at a scan rate of 50 mV s-1. A glassy carbon
electrode was used as working electrode, a platinum(II) wire was used as the auxiliary electrode with a Ag/Ag+ as the reference electrode. The
,
cyclic voltammogram of PtL1 PtL2 and PtL3 is shown in Figure 3, and the electrochemical data of the three complexes are listed in
Table 2. The irreversible anodic waves are attributed to the oxidation of Schiff base ligand.[7c] The onset of the first oxidation process
of PtL1 occurs at about 0.35 V, and PtL2 at 0.29V, while PtL3 shows a more anodic potential with the onset of the first oxidation at
about 0.71 V. Apparently, the electron releasing group of diethylamine at 4-position of the phenolate fragments accelerates the
[11]
oxidation of PtL1 and PtL2
.
The LUMO-HOMO energy gap can be calculated by UV-vis absorption spectra. The energy gaps of these
complexes are between 1.78–2.11 eV. Furthermore, the HOMO and LUMO energy levels of these complexes are estimated from the oxidation
and energy gap [calculated according to the following equations: HOMO = −(Eox + 4.71) eV and LUMO = (Egap−HOMO) eV] to be −5.42 to
−5.06 eV and −3.50 to −3.28 eV, respectively. [12] The complex PtL1 shows a comparable HOMO level as PtL2, but a much lower LUMO than
PtL2 due to the electron deficient cyano substituents at imino part. Similarly, PtL3 exhibits a lower LUMO than PtL2 due to the electron
withdrawing property of trifluoromethyl group at phenylene part.
The thermal stabilities of the complexes were investigated by thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) methods. As shown in Table 2, these complexes are thermally stable with decomposed temperatures as high as
352°C (Table 2).
Theoretical Calculation
The geometries of all the molecules were optimized by employing the B3LYP density functional theory method.[13] In the calculations, the 6-6-
311++G** basis set was used for the C, H, O, N and F atoms, and the effective core potentials (ECP) of Stuttgart basis set was used for the
platinum, the 6s and 5d in platinum atom were treated explicitly by a (8s7p6d) Gaussian basis set contracted to [6s5p3d].[14] The identification of
the real minimum is ensured by harmonic vibrational frequency analysis of each of the optimized geometries. All the three complexes were in
singlet ground states, and were calculated through direct minimization of the SCF energy. The major transitions based on the above
structures were obtained by the time-dependent density functional theory (TD-DFT) by the B3LYP method with the same basis set. All
calculations in this study were performed using the Gaussian 03 program.[15]
, , Figure S6-S8 and Table S3-S5 (ESI). It is
The optimized geometries of the complex PtL1 PtL2 and PtL3 are shown in Figure 4
clear that the platinum center and the Schiff bases are coplanar in all these three compounds. The Natural Atomic Orbital (NBO)
analysis[16] of the optimized geometries of the complexes indicate the platinum atom carries the positive charges, while both O and N
carry the negative charges. Therefore, the two O atoms and two N atoms form a negative charges cavity, which is conducive to the
coordination with metal platinum (Table S2).
The frontier orbital properties including the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO)
and nearby molecular orbitals can provide important information about the photophysical properties of a molecule. The stability of a complex is
also closely related to the energy level and gap of HOMO and LUMO. The calculated HOMO-LUMO gaps of PtL1, PtL2 and PtL3 were 2.53,
3.07 and 2.78 eV, respectively, which indicate they can be excited easily. All these data is consistent with the experiment results. The HOMOs

Journal Name
ARTICLE
mainly locate on the phenolate fragments and middle metal atom in the complexes. The HOMO (π orbital) was formed by p orbital of C, N and O
and d orbital of platinum, which contain a few proportion s orbital (Figure 5). The LUMOs mainly locate on the imino part, which is composed
by p-π* orbital of C, N and O. The electrons transfer from phenolate fragments and middle metal to imino part when they are excited from the
ground states to the excited states according to molecular orbital analysis. The Figure 5 shows the electron cloud distributions and composition
characteristics of the frontier molecular orbitals.
The electronic transitions of PtL1, PtL2 and PtL3 were calculated by Time-Dependent B3LYP methods, and their wavelength and transition
energies and oscillator strengths are listed in the Table 3. Take PtL2 as an example, HOMO is the π orbital composed of p orbital of C, N and d
orbital of middle metal (Figure 5, Table 3), and the S1 transition originates from the transition of HOMO→LUMO (π→π*, LLCT and MLCT).
The maximum UV-visible absorption wavelength of PtL2 was determined as 491 nm in experiment, which is consistent with the calculated value
of 506 nm. And the S1 transition of PtL1 (550 nm), originated from the HOMO-1→LUMO (π→π*, LLCT and MLCT) transition, is obviously
red shifted induced by the electron acceptor CN group. The p orbital of the N atoms of the CN groups was also involved in the LUMO orbital (π*
orbital), leading to the delocalization of the orbital.
Conclusions
In this work, a series of donor-π-acceptor platinum(II) Schiff base complexes have been developed. These compounds were fully
1
characterized by H NMR, IR, MS, UV-visible absorption, elemental analysis. And the three complexes emit yellow to red light with
the highest quantum yields of 8.6% for PtL1. The decay times are in microsecond scale (1.97-2.35μs) indicating the triplet state
characteristics of the emissions. The B3LYP density functional theory calculations show that the platinum center and the Schiff bases
,
ligands were coplanar and the HOMO-LUMO gaps of PtL1 PtL2 and PtL3 were calculated to be 2.53, 3.07 and 2.78 eV, respectively,
which are well consistent with their photophysical properties. Benefiting from tunable emissions with high phosphorescent quantum
yields, these platinum complexes are particularly interesting for OLEDs and OLEC applications.
Experimental Section
Materials and methods: The chemicals were purchased from Aladdin Reagent Company and used as received. Silica gel 60 (0.04–0.063 mm)
for column chromatography was purchased from Qingdao Haiyang Chemical Co., Ltd. NMR spectra were recorded on a Bruker Ultrashield 400
Plus NMR spectrometer. High-resolution matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra were recorded
with a Bruker Autoflex MALDI-TOF mass spectrometer. The C, H and N microanalyses were performed with a Carlo Erba 1106 elemental
analyzer. The IR spectra were recorded with a Shimadzu IRAffinity-1 FTIR spectrometer as KBr disc. Thermogravimetrical studies were
performed from 30 to 1000 °C at 10 °C/min under nitrogen on a TA Instruments SDTQ600 (TA instruments). Electronic absorption spectra in the
UV-visible region were recorded on a Shimadzu UV-2450 UV/Vis spectrophotometer, steady-state visible fluorescence and PL excitation spectra
on a FLS980 Photoluminescence Spectrometer (Edinburgh Instruments) and visible decay spectra on a pico-N2 laser system (PTI TimeMaster)
with λexc = 430 nm. Luminescence quantum yields (Φem) in degassed dichloromethane solution were determined with [Ru(bpy)3](PF6)2 (bpy =
2,2’-bipyridine) in acetonitrile as a standard reference solution (Φem = 0.062). It was calculated by Φs = Φr(Br/Bs)(ns/nr)2(Ds/Dr), where the
subscripts r and s denote reference standard and the sample solution, respectively, and n, D, and Φ are the refractive index of the solvents, the
integrated intensity, and the luminescence quantum yield, respectively. The quantity B is calculated by B = 1-10-AL, where A is the absorbance at
the excitation wavelength and L is the optical path length.
H2L1 To a stirred solution of 2,3-diaminomaleonitrile (63 mg and 0.58 mmol) in absolute ethanol (18 mL), 4-(diethylamino)-2-
hydroxybenzaldehyde (450 mg and 2.33 mmol) was added. The resulting mixture was refluxed 12 hours. After cooling to room temperature, the
1
green product filtered was washed with cold ethanol and petroleum ether to afford the target compound. Yield: 0.267 g (59%). H NMR (400
MHz, CDCl3): δ = 12.49(s, 2H, OH), 8.57（s, 2H, CH=N), 7.56(d, 2H, Ar-H), 6.43−6.46 (m, 2H, Ar-H), 6.16 (d, 2H, Ar-H), 3.32−3.47 (m, 8H,
CH2), 1.10−1.17 (m, 12H, CH3) ppm. IR (KBr): ῦ = 2925(-C−H), 2868, 2350, 1617 (-C=N-), 1577, 1519, 1463, 1416, 1360, 1327, 1259, 1173,
1128, 1077 and 785 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z = 458.2412 [M+H]+ (C26H30N6O2 H: calcd. 458.2425, Δm = 2.78
+
ppm). UV-Vis (CH2Cl2, 20°C): λmax = 377, 437 and 571 nm. Luminescence (CH2Cl2, 20°C): λmax = 612 nm. C26H30N6O2 (458.5554): calcd. C
68.10, H 6.59, N 18.33; found C 68.29 , H 6.64 , N. 18.11 .
H2L2 To a stirred solution of benzene-1,2-diamine (236 mg, 2.18 mmol) in absolute ethanol (20 mL), 4-(diethylamino)-2-hydroxybenzaldehyde
(888 mg, 4.59 mmol) was added. The resulting mixture was refluxed 12 hours. After cooling to room temperature, the brown product precipitated
1
was washed with cold ethanol and petroleum ether. Yield: 0.254 g (25%). H NMR (400 MHz, CDCl3): δ = 13.63（s, 2H, -OH), 8.42 (s, 2H,
CH=N), 7.12-7.26 (m, 6H, Ar-H), 6.19-6.23 (m, 4H, Ar-H), 3.37 (q, 8H, -CH2) and 1.19 (s, 12H, -CH3) ppm. IR (KBr): ῦ = 2969 (-C-H), 2892,
2358, 1635 (-C=N-), 1598, 1517, 1507, 1457, 1352, 1239, 1132, 1077, 977 and 784 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z =
459.2799 [M+H]+ (C28H34N4O2+H: calcd. 459.2754, Δm = 9.68 ppm). UV-Vis (CH2Cl2, 20 °C): λmax = 241, 359 and 400nm. Luminescence
(CH2Cl2, 20 °C): λmax = 515 nm. C28H34N4O2 (458.5952): calcd. C 73.33, H 7.47, N 12.22; found C 73.21 , H 7.39, N 12.34 .
H2L3 To a stirred solution of 4-(trifluoromethyl)benzene-1,2-diamine (152 mg, 0.86 mmol) in absolute ethanol (20 mL), 3,5-di-tert-butyl-2-
hydroxybenzaldehyde (606 mg, 2.59 mmol) was added. The resulting mixture was refluxed 12 hours. After cooling to room temperature, the
orange product precipitated was washed with cold ethanol and petroleum ether. Yield: 0.315 g (60%). 1H NMR (400 MHz, CDCl3): δ = 13.28 (s,
1H, OH), 13.26 (s, 1H, OH), 8.72 (s, 1H, CH=N), 8.69 (s, 1H, CH=N), 7.60 (t, 1H, Ar-H), 7.49−7.50 (m, 3H, Ar-H), 7.25−7.34 (m, 3H, Ar-H),

ARTICLE
Journal Name
1.35−1.59 (m, 36H, CH3) ppm. IR (KBr): ῦ = 2975 (-C−H), 2713, 2207, 1630 (-C=N-), 1564, 1508, 1482, 1436, 1341 (-C(CH3)3), 1231, 1204,
1186, 1135, 1078, 956, 827, 788 and 678 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z = 609.3610 [M+H]+ (C37H47F3N2O2+H:
calcd. 609.3662, Δm = 8.53 ppm). UV-Vis (CH2Cl2, 20 °C): λmax = 237, 285 and 334 nm. Luminescence (CH2Cl2, 20 °C): λmax = 611 nm.
C37H47F3N2O2 (608.7765): calcd. C 73.00, H 7.78, N 4.60; found C 73.25 , H 7.64 , N 4.46 .
PtL1 A solution of H2L1 (200 mg, 0.44 mmol), 2 equivalent of potassium hydroxide (49 mg, 0.88 mmol) were stirred about half an hour in 4ml
DMF under nitrogen at 70℃. Then, potassium tetrachloroplatinate (II) (181 mg, 0.44 mmol) in DMSO (3 mL) were added to the solution for 24 h
under nitrogen at 70℃. D. I. water was then added, the mixture was filtered extracted with CHCl3 and dry in the vacuum. The crude product was
purified by silica-gel column chromatography using a solvent mixture of hexane and CHCl3 as eluent to give an dark-green solid of PtL1. Yield:
113 mg (40%). 1H NMR (400 MHz, CDCl3): δ = 8.29 (s, 2H, CH=N), 7.71 (d, 2H, Ar-H), 6.56–6.59 (m, 2H, Ar-H), 6.30 (d, 2H, Ar-H), 3.35–
3.53 (m, 8H, -CH2) and 1.13–1.24 (m, 12H, CH3) ppm. IR (KBr): ῦ = 2958(-C–H), 2871, 2357, 1616 (-C=N-), 1579, 1466, 1436, 1361, 1330,
1271, 1200, 1172, 1116, 1077, 929, 825 and 774 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z = 651.1994 [M+H]+ (C26H28N6O2Pt:
calcd. 651.1918, Δm = 1.19 ppm). C26H28N6O2Pt (651.6235): calcd. C 47.92, H 4.33, N 12.90; found C 47.99, H 4.08, N 12.79.
PtL2 A solution of H2L2 (220 mg, 0.48 mmol), 2 equivalent of potassium hydroxide (54 mg, 0.96mmol) were stirred about half an hour in 4ml
DMF under nitrogen at 70℃. Then, potassium tetrachloroplatinate (II) (200 mg, 0.49 mmol) in DMSO (3 mL) were added to the solution for 24 h
under nitrogen at 70℃. D. I. water was then added, the mixture was filtered extracted with CHCl3 and dry in the vacuum. The crude product was
purified by silica-gel column chromatography using a solvent mixture of hexane and CHCl3 as eluent to give an red solid of PtL2. Yield: 147 mg
1
(47%). H NMR (400 MHz, d6-DMSO): δ = 8.98 (s, 2H，CH=N), 8.25 (s, 2H, Ar-H), 7.55 (d, 2H, Ar-H) , 7.25 (s, 2H, Ar-H), 6.37 (d, 2H, Ar-
H), 6.17(s, 2H, Ar-H), 3.42 (q, 8H, -CH2) and 1.17 (t, 12H, -CH3) ppm. IR (KBr): ῦ = 2969(-C–H), 2921, 2350, 1616 (-C=N-), 1597, 1560, 1490,
1351, 1250, 1198, 1141, 1078, 816 and 751 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z = 652.2280 [M+H]+ (C28H32N4O2Pt+H:
calcd. 652.2248, Δm = 4.88 ppm). C28H32N4O2Pt (651.6633): calcd. C 51.61, H 4.95, N 8.60; found C 51.02, H 4.99, N. 8.78.
PtL3 A solution of H2L3 (200 mg, 0.33 mmol), 2 equivalent of potassium hydroxide (37 mg, 0.66 mmol) were stirred about half an hour in 4ml
DMF under nitrogen at 70℃. Then, potassium tetrachloroplatinate (II) (137 mg, 0.33 mmol) in DMSO (3 mL) were added to the solution for 24 h
under nitrogen at 70℃. D. I. water was then added, the mixture was filtered extracted with CHCl3 and dry in the vacuum. The crude product was
purified by silica-gel column chromatography using a solvent mixture of hexane and CHCl3 as eluent to give black solid of PtL3. Yield: 105 mg
(40%). 1H NMR (400 MHz, CDCl3): δ = 8.97 (s, 1H, CH=N), 8.95 (s, 1H, CH=N), 8.28(s, 1H, Ar-H), 8.15 (d, 1H, Ar-H), 7.73 (s, 2H, Ar-H),
7.59 (d, 1H, Ar-H), 7.39 (d, 2H, Ar-H), 1.28−1.61 (m, 36H, CH3) ppm. IR (KBr): ῦ = 2974 (-C–H), 2920, 2214, 1616 (-C=N-), 1569, 1551, 1516,
1475, 1413, 1375 (-C(CH3)3), 1354, 1306, 1224, 1187, 1143, 107, 821 and 742 cm-1. HRMS (MALDI-TOF, positive mode, CH2Cl2): m/z =
802.3121 [M+H]+ (C37H45F3N2O2Pt+H: calcd. 802.3157, Δm = 4.49 ppm). C37H45F3N2O2Pt (801.8446): calcd. C 55.42, H 5.66, N 3.49; found C
55.81, H 5.88, N. 3.21.
Acknowledgements
This work was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LQ13B010001), National Natural
Science Foundation of China(No. 21501128, 21375092, 21203135), China Postdoctoral Science Foundation (No. 2014M560476) and
Key Disciplines of Applied Chemistry of Zhejiang Province, Taizhou University. We also thank the Project of Science and
Technology Innovation for College Students in Zhejiang Province(No.2014R428016), Natural Science Fund for Colleges and
Universities in Jiangsu Province (No. 14KJB150024) and Scientific Research Founding of Wuhan Institute of Technology (No.
K201542) for financial support. X. Zhu thanks the financial support from Hong Kong Baptist University (FRG2/14-15/034 and
FRG1/14-15/058).

Journal Name
References
ARTICLE
[1] (a) Y. Hai, J. J. Chen, P. Zhao, H. B. Lv, Y. Yu, P. Y. Xu, J. L. Zhang Chem. Commun., 2011, 47, 2435‐2437; (b) F. Gao,
L. Cui, W. Liu, L. Hu, Y. W. Zhong, Y. Z. Li, J. L. Zuo, Inorg. Chem., 2013, 52, 11164‐11172; (c) Z. Zhang, W. X. Peng, P. Y.
Su, X. Q. Lu, J. R. Song, D. Fan, W. K. Wong, R. A. Jones, C. Y. Su, Inorg. Chem., 2014, 53, 5950‐5960; (d) M. Nematirad,
W. J. Gee, S. K. Langley, N. F. Chilton, B. Moubaraki, K. S. Murray, S. R. Batten, Dalton Trans., 2012, 41, 13711‐13715.
[2] (a) S. S. Zhao, X. R. Liu, W. Y. Wong, X. Q. Lu, W. K. Wong, Inorg. Chim. Acta, 2014, 414, 160‐164; (b) M. Kuil, I. M.
Puijk, A. W. Kleij, D. M. Tooke, A. L. Spek, J. N. H. Reek, Chem. Asian J., 2009, 4, 50‐57; (c) A. W. Kleij, Eur. J. Inorg.
Chem., 2009, 193‐205.
[3] (a) J. Zhang, C. Zhong, X. J. Zhu, H. L. Tam, K. F. Li, K. W. Cheah, W. Y. Wong, W. K. Wong, R. A. Jones, Polyhedron,
2013, 49, 121‐128; (b) J. Zhang, M. Y. Teng, G. L. Dai, S. L. Zhao, J. L. Wang, P. Zhang, T. T. Song, Chinese J. Inorg.
Chem., 2014, 30, 499‐505.
[4] (a) B. H. Zhang, G. P. Tan, C. S. Lam, B. Yao, C. L. Ho, L. H. Liu, Z. Y. Xie, W. Y. Wong, J. Q. Ding, L. X. Wang, Adv.
Mater., 2012, 24, 1873‐1877; (b) M. C. Tang, D. P. K. Tsang, M. M. Y. Chan, K. M. C. Wong, V. W. W. Yam, Angew
Chem. Int. Edit., 2013, 52, 446‐449; (c) X. S. Xiao, W. L. Kwong, X. G. Guan, C. Yang, W. Lu, C. M. Che, Chem. Eur. J.,
2013, 19, 9457‐9462.
[5] (a) Y. H. Zheng, A. S. Batsanov, M. A. Fox, H. A. Al‐Attar, K. Abdullah, V. Jankus, M. R. Bryce, A. P. Monkman, Angew
Chem. Int. Edit., 2014, 53, 11616‐11619; (b) J. Jayabharathi, V. Thanikachalam, R. Sathishkumar, New J. Chem., 2015,
39, 235‐245; (c) Q. Wang, D. G. Ma, K. Leo, J. Q. Ding, L. X. Wang, Q. Q. Qiao, H. P. Jia, B. E. Gnade, Appl. Phys. Lett.,
2014, 104; (d) H. T. Cao, G. G. Shan, Y. M. Yin, H. Z. Sun, Y. Wu, W. F. Xie, Z. M. Su, Dyes Pigments, 2015, 112, 8‐16; (e)
C. O. Paul‐Roth, S. Drouet, A. Merhi, J. A. G. Williams, L. F. Gildea, C. Pearson, M. C. Petty, Tetrahedron, 2013, 69,
9625‐9632.
[6] (a) M. A. Baldo, M. E. Thompson, S. R. Forrest, Nature 2000, 403, 750‐753; (b) P. K. Chow, C. S. Ma, W. P. To, G. S.
M. Tong, S. L. Lai, S. C. F. Kui, W. M. Kwok, C. M. Che, Angew Chem. Int. Edit. 2013, 52, 11775‐11779.
[7] (a) F. Galbrecht, X. H. Yang, B. S. Nehls, D. Neher, T. Farrell, U. Scherf, Chem. Commun. 2005, 2378‐2380; (b) C. M.
Che, S. C. Chan, H. F. Xiang, M. C. W. Chan, Y. Liu, Y. Wang, Chem. Commun., 2004, 1484‐1485; (c) C. M. Che, C. C.
Kwok, S. W. Lai, A. F. Rausch, W. J. Finkenzeller, N. Y. Zhu, H. Yersin, Chem. Eur, J., 2010, 16, 233‐247; (d) G. S. M.
Tong, P. K. Chow, W. P. To, W. M. Kwok, C. M. Che, Chem. Eur. J., 2014, 20, 6433‐6443.
[8] J. Zhang, F. C. Zhao, X. J. Zhu, W. K. Wong, D. G. Ma, W. Y. Wong, J. Mater. Chem., 2012, 22, 16448‐16457.
[9] L. A. Duan, J. A. Qiao, Y. D. Sun, Y. Qiu, Adv. Mater., 2011, 23, 1137‐1144.
[10] W. K. Lo, W. K. Wong, W. Y. Wong, J. P. Guo, K. T. Yeung, Y. K. Cheng, X. P. Yang, R. A. Jones, Inorg. Chem., 2006,
45, 9315‐9325.
[11]Z. Asadi, M. Asadi, A. Zeinali, M. Ranjkeshshorkaei, K. Fejfarova, V. Eigner, M. Dusek, A. Dehnokhalaji, J. Chem. Sci.,
2014, 126, 1673–1683.
[12] Z. W. Liu, Z. Q. Bian, F. Hao, D. B. Nie, F. Ding, C. H. Huang, Org. Electron., 2009, 10, 247‐255.
[13] A. D. Becke, J. Chem. Phys., 1993, 98,1372‐1377.

ARTICLE
Journal Name
[14] M. Dolg, H. Stoll, H. Preuss, Theor. Chim. Acta., 1993, 85, 441‐450; (b) M. Dolg, H. Stoll, A. Savin, H. Preuss, Theor.
Chim. Acta., 1989, 75, 173‐194.
[15] M. J. Frisch, et al. Gaussian 03, Revision B04, Gaussian Inc., Pittsburgh PA, 2003.
[16] A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev., 1988, 88, 899‐ 926.

Journal Name
ARTICLE
Figure Captions
1.0
0.5
0.0
H2L2
PtL2
H2L3
PtL3
1.0
0.5
0.0
H2L1
PtL1
2
1
0
300 400 500 600
Wavelength (nm)
300 400 500 600 700
Wavelength (nm)
300
400
500
600
Wavelength (nm)
Figure 1. UV‐visible absorption spectra of the Schiff base ligands and their corresponding platinum(II) complexes in DCM (1.0 × 10‐5 M).

ARTICLE
Journal Name
PtL1
PtL2
PtL3
H2L1
H2L2
H2L3
1.0
0.5
0.0
1.0
0.5
0.0
500
600
700
800
400 500 600 700 800
Wavelength (nm)
Wavelength (nm)
Figure 2. Emission spectrum of Schiff base ligands (left) and complexes (right) in DCM (1.0 × 10‐5 M).

Journal Name
ARTICLE
PtL1
PtL2
PtL3
0.0
0.5
1.0
1.5
Voltage Vs Ag/Ag+ (V)
Figure 3. Cyclic voltammogram of the complexes.

ARTICLE
Journal Name
1.9794
2.0159
1.9794
2.0159
1.9752
2.0106
1.9752
2.0106
1.9718
2.0169
1.9723
2.0177
Figure 4. Optimized geometry of PtL1 PtL2 and PtL3; Bond lengths (Å) are written on the figure; dihedral angle were shown in Figure S6‐S8 (ESI)
, .

Journal Name
ARTICLE
PtL1
PtL2
PtL3
PtL1
PtL2
PtL3
LUMO+2
LUMO+1
LUMO
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO
HOMO-1
HOMO-2
Figure 5. The frontier molecular orbitals of PtL1 PtL2 and PtL3
, .

ARTICLE
Journal Name
Scheme 1. The synthetic routes for the Schiff‐base ligand H2L1 H2L2 and H2L3 and their platinum(II) complexes PtL1 PtL2 and PtL3
, , .

Journal Name
ARTICLE
Tables
Table 1. Summary of UV-visible absorption and luminescent data of complexes at room temperature in DCM (1.0×10-5 M).
Φ
b (%)
Luminescence
Compd
Absorption λmax (nm)a
τ (μs)
Kr (×103 s-1)c
Knr (×103 s-1)d
em
λ
max (nm)
H2L1
H2L2
H2L3
PtL1
PtL2
PtL3
378,437,571
241, 359, 400
237, 285, 334
607
511
-
-
-
8.6
4.4
-
-
-
-
-
-
-
-
-
412, 435
650,776
531, 601, 654
664
393, 453, 607
1.97
1.82
2.35
43.7
24.2
3.7
463.9
525.3
421.8
244, 336, 389, 407, 461, 491
376, 396, 458, 491, 575
0.87
aPhotophysical measurements were made with a concentration of 1 × 10-5 M in CH2Cl2 at room temperature. b Luminescence quantum yields (Φem) in degassed
dichloromethane solution were determined with [Ru(bpy)3](PF6)2 (bpy = 2,2’-bipyridine) in acetonitrile as a standard reference solution (Φem = 0.062) and 450 nm
as excitation wavelength. c Radiative rate constants Kr was calculated from the value of Φ τ. d Non-radiative rate constants Knr was calculated from the equation of
/
em
τ = (Kr+ Knr)-1.

ARTICLE
Journal Name
Table 2. Summary of cyclic voltammetry and TGA data.
c
Compound
PtL1
Eox
HOMOa
-5.06
LUMOb
-3.28
-2.89
Egap
Td (oC)
352
340
0.35
0.29
0.71
1.78
2.11
1.92
PtL2
-5.00
-5.42
PtL3
-3.50
350
aEstimated from the oxidation potentials HOMO = −(Eox + 4.71) eV . b Deduced from the HOMO and Egap. c Estimated from the UV-vis absorption spectra.

Journal Name
ARTICLE
Table 3. Theoretical results of major transition (percentage), transition energies (E), oscillator strengths (f) of PtL1,
PtL2 and PtL3.
Singlet excited state
Major transition
E(nm)
f
PtL1
S1
HOMO-1→LUMO(67%)
HOMO→LUMO(62%)
HOMO-2→LUMO(65%)
HOMO-4→LUMO(70%)
HOMO-3→LUMO(65%)
HOMO-5→LUMO(70%)
HOMO-1→LUMO+1(67%)
HOMO→LUMO+1(68%)
HOMO-6→LUMO(61%)
HOMO-7→LUMO(68%)
550.23
541.17
479.74
433.66
427.54
374.26
364.38
351.27
337.96
333.89
0.0254
0.6368
0.1676
0.0000
0.1603
0.0000
0.0001
0.1836
0.0124
0.1758
S2
S3
S4
S5
S6
S7
S8
S9
S10
PtL2
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
PtL3
S1
S2
S3
S4
S5
S6
S7
S8
S9
HOMO→LUMO(68%)
HOMO-1→LUMO(58%)
HOMO→LUMO+1(58%)
HOMO-2→LUMO(68%)
HOMO-1→LUMO+1(61%)
HOMO-4→LUMO(71%)
HOMO-3→LUMO(53%)
HOMO-4→LUMO+1(60%)
HOMO-2→LUMO+1(58%)
HOMO-3→LUMO+1(69%)
506.03
448.46
434.34
411.86
397.78
383.52
373.06
345.80
345.64
341.37
0.0447
0.4580
0.3710
0.0003
0.0652
0.0000
0.2410
0.0987
0.3034
0.0893
HOMO→LUMO(67%)
HOMO→LUMO+1(68%)
HOMO-1→LUMO(68%)
HOMO-3→LUMO(70%)
HOMO-1→LUMO+1(66%)
HOMO-2→LUMO(66%)
HOMO-5→LUMO(70%)
HOMO-4→LUMO (63%)
HOMO-3→LUMO+1(69%)
HOMO-2→LUMO+1(62%)
558.09
471.00
466.81
396.58
389.38
384.28
355.60
352.58
350.40
342.73
0.0676
0.0123
0.0261
0.0000
0.1528
0.5815
0.0000
0.0126
0.0002
0.1105
S10