A triazine-based multi-branched platinum acetylide complex: Synthesis and photophysical properties

Article abstract of DOI:10.2174/1570178611310010007

A triazine-based multi-branched platinum(II) acetylide complex was synthesized and fully characterized. The photophysical properties, electrochemical properties and first order hyperpolarizability were studied.

Full text of DOI:10.2174/1570178611310010007

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22
Letters in Organic Chemistry, 2013, 10, 22-26
A Triazine-Based Multi-Branched Platinum Acetylide Complex: Synthesis
and Photophysical Properties
Jin Guo1, Zhaohui Huang2, Tingfeng Wang1, Liying Zhang2, Junfeng Shao1 and Fengqi Guo2,*
1State Key Laboratory of Laser Interaction With Matter, Changchun Institute of Optics, Fine Mechanics and Physics,
Chinese Academy of Sciences, Changchun 130033, P. R. China
2College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
Received September 04, 2012: Revised November 25, 2012: Accepted January 07, 2013
Abstract: A triazine-based multi-branched platinum(II) acetylide complex was synthesized and fully characterized. The
photophysical properties, electrochemical properties and first order hyperpolarizability were studied.
Keywords: Donor-acceptor structure, first order hyperpolarizability, multi-branched platinum (II) acetylide, photophysical
properties.
INTRODUCTION
In order to address these questions, a triazine-based
multi-branched platinum(II) acetylide complex containing
donor-acceptor structures (compound 1) was synthesized and
Organic molecules containing donor-acceptor structures
always show high second-order nonlinear optical effect [1],
and several groups also reported the two-photon absorption
effect of these kind of molecules as optical limiting materials
and up-conversion materials [2-3]. A significant conclusion
from the previous work could be made that chemicals with
donor-acceptor structures such as D-A, D-A-D, D-ꢀ-A, D-ꢀ-
D, and multi-branched structures generally exhibit excellent
two-photon absorption properties, and the two-photon ab-
sorption cross sections can be increased by extending the
molecular conjugated system or incorporating multi-dipole
structures into the molecules [4-7]. In addition, molecules
containing heavy metal ions and rigid structure always ex-
hibit large reverse saturable absorption due to the enhance-
ment of the intersystem crossing from the first singlet ex-
cited state to the first triplet excited state [8, 9]. These con-
clusions can provide helpful guidelines for designing materi-
als with large overall nonlinear optical properties.
1
characterized by HNMR, MS and elemental analysis in this
paper. The photophysical properties, electrochemical proper-
ties and the first order hyperpolarizability were preliminary
studied, and the detailed studies of the other properties, such
as time-resolved luminescence and nonlinear optical proper-
ties, will be done in the near future.
RESULTS AND DISCUSSION
The synthetic route to compound 1 was shown in Scheme
1. Compounds 2 to 5 were synthesized according to the lit-
eratures [12-15]. 3 was prepared using 2 and 4-propyl-
phenylacetylene, which was synthesized via Sonogashira
reaction from 1-iodo-4-propylbenzene, as starting materials.
6 was prepared by the condensation reaction of 4 and 5 un-
der basic conditions in methanol. 1 was synthesized by treat-
ing 3 with 6.
Platinum acetylides exhibit high linear transmission and
high nonlinear absorption over the visible to near infrared
spectral region [10-11]. Could molecules exhibit high sec-
ond-order nonlinear optical effect and the third-order nonlin-
ear optical properties (including two-photon absorption and
reverse saturable absorption) at the same time when the do-
nor-acceptor structure and the multi-branched structure are
introduced into a platinum acetylide complex? And how the
second-order nonlinear optical effect and the third-order non-
linear optical property affect each other corresponding to the
structure of the organic molecules? There are few papers
discussed the questions clearly according to our learning.
The strong absorption band of 1 at 420 nm (Fig. 1 up)
can be assigned to the interligand ꢀ-ꢀ* transition. The weak
absorption band at 362 nm can be assigned to ꢀ-ꢀ* transition
of the aryl rings. The weak absorption of 1 above 450 nm
provides a wide observation window for the application in
optical limiter. The maximum excited emission at 420 nm of
1 appears at 513 nm with a fluorescence quantum yield (ꢁ)
of 0.063 relative to quinine sulfate (in 0.5M H2SO4 solution)
[16]. The low fluorescence quantum yield indicated the pos-
sibility of the high quantum yield from S1 to T1. However,
the phosphorescence of 1 at room temperature was not ob-
served. Detailed research will be done soon. The excitation
spectrum of 1 reflects that the fluorescence band at 513 nm
is ascribed to the intraligand ꢀ*-ꢀ transition.
*Address correspondence to this author at the College of Chemistry
and Molecular Engineering, Zhengzhou University, Zhengzhou 450001,
P. R. China; Tel: 86-371-67739186; Fax: 86-371-67781205;
E-mail: fqguo@zzu.edu.cn
1 exhibited an oxidation potential at 1.05 V vs Ag/AgCl
attributed to a metal-centered Pt (IV/II) oxidation process
1875-6255/13 $58.00+.00
© 2013 Bentham Science Publishers

A Triazine-Based Multi-Branched Platinum Acetylide Complex
Letters in Organic Chemistry, 2013, Vol. 10, No. 1
C3H7
23
C3H7
C3H7
PBu3
Bu3P
PBu3
Pt Cl
PBu3
Pt
Bu3P
Pt
a
C3H7
Pt(PBu3)2Cl2
+
PBu3
3
2
N
N
N
c
CHO
N
N
N
b
+
N
N
Bu3P Pt PBu3
N
4
5
1
6
C3H7
Scheme 1. Condition and reagent. (a)CuI, TEA, rt; (b)KOH, CH3OH; (c) CuI, THF, rt.
The stereo structure of 1 was optimized using the density
functional theory (DFT) at 6-31g level for C, H, N, P atoms
and lans2dz level for Pt atom level, all the calculations were
performed with the Gaussian 03 software [19]. As shown in
(Fig. 1) (down), the six benzene rings and the triazine ring in
1 are co-planar along each long-axis of vinyl, benzyl, acety-
lenyl, Pt, acetylenyl, and benzyl groups. Each Pt (II) center is
square planar with the two phosphorus atoms trans- to each
other. These results show that 1 has great structural rigidity
and coplanarity, which are benefit for the transition from S1
to T1.
1.0
0.8
0.6
0.4
0.2
0.0
The first-order polarizability can be determined by the
solvatochromism method [20]. The simple expression of the
first-order polarizability is shown in Eq. 1: [21]
ꢀxxx(2ꢁ)=3/2 ꢂ2ꢃeg2 (ꢃe - ꢃg) ꢁeg2 / (ꢁeg2-ꢁ2)( ꢁeg2 - 4ꢁ2) (1)
250 300 350 400 450 500 550 600 650 700
Wavelength/nm
Where ꢁeg is the frequency of the transition from the ground
state to the first excited state, ꢂeg is the transition dipole mo-
ment between the ground state and the excited state, ꢂg is the
permanent dipole moment of the ground state, ꢂe is the per-
manent dipole moment of the excited state, and ꢁ is the laser
frequency. ꢁeg, found from the absorption band maximum of
1, is 4.50ꢀ1015 s-1. ꢂeg, gotten from the area under the absorp-
tion band, [22] is calculated to be 7.18ꢀ10-17 esuꢁcm. The
value of ꢂe - ꢂg could be derived from Eq. (2) to (4).
ꢄa -ꢄf = A + B (BK)
B=2 (ꢃe - ꢃg) 2/hca3
(BK)=[(ꢅ-1)/(2ꢅ+1)-(n2-1)/(2 n2+1)]/[1-(n2-1) /(2 n2+1)]2
[1-(ꢅ-1)/(2ꢅ+1)]
(2)
(3)
(4)
Where ꢃa -ꢃf is the Stokes shift in wave number [23]. A is the
radius of a spherical cavity in the solvent occupied by the
molecule and 10.02 Å was used in the calculation [24]. ꢀis
the dielectric constant of solvent, n is the refractive index of
solvent. BK is the Bilot-Kawski value of the solvent. The
parameters of 1 in five selected solvents are listed in Table 1.
The relationship between BK values and stoke shifts (Fig. 2)
is linear with a slope (B) of 2548.67 cm-1. ꢂe - ꢂg, derived
from Eq.3, is 5.06ꢀ10-18 esuꢁcm. The first-order polarizabil-
Fig. (1). Normalized emission spectrum (solid line) and absorption
spectrum of 1 (dash line) in chloroform at room temperature and
the optimized molecular structure of 1 by Gaussian 03.
and an irreversible reduction potential at -1.20 V vs Ag/AgCl
assigned to the reduction of the coordinated ligand [17]. The
electrochemical energy gap (Eg,ec = 2.25 eV) is much similar
to the value of Eg,opt (2.45 eV), which is calculated from the
absorption onset of 1 in chloroform [18].

24 Letters in Organic Chemistry, 2013, Vol. 10, No. 1
Guo et al.
Table 1. The Parameters of 1 Determined in Five Selected Solvents
Solvents
ꢁOD(cm-1)
ꢁex(cm-1)
ꢃꢁ(cm-1)
BK
Benzene
24272
21786
2486
Chloroform
23641
THF
24331
20408
3923
Methanol
24390
Acetonitrile
24272
19417
4855
19646
19646
3995
4744
0.0036
0.3710
0.5491
0.8547
0.8631
5000
4500
4000
3500
3000
2500
Acetonitrile
Methanol
Chloroform
THF
The linear correlation coefficient R=0.97
Benzene
0.0
0.2
0.4
0.6
0.8
1.0
The BK value
Fig. (2). The relationship between BK and ꢁ of 1 in different solvents.
ity |ꢁxxx| of 1 is calculated to be 7.81ꢀ10-29 cm5/esu by substi-
tuting the values of ꢄeg, ꢅeg , and ꢅe - ꢅg into Eq. 1.
and recrystallized from absolute ethyl alcohol to get the
white solid (1.20 g, 71%).
Such a compound may be a promising nonlinear material.
The syntheses and properties of more compounds are under
investigation.
1HNMR (400MHz, CDCl3) ꢀ: 2.00 (t, J = 8.0 Hz, 12H),
1.53~1.63 (m, 12H), 1.43~1.49 (m, 12H), 0.95 (t, J = 6.0 Hz,
18H).
Compound (3)
EXPERIMENTS
Pt(PPh3)2Cl2 (1.50 g, 2.2 mmol) and CuI (39.0 mg, 0.2
mmol) were dissolved in 15 mL triethylamine and 45 mL
THF, and then nitrogen was bubbled through the mixture for
20 min and 4-propyl-phenylacetylene (0.27 g, 1.8 mmol)
was added. Nitrogen was bubbled for another 20 min and
then the mixture was stirred for 3 days under nitrogen at-
mosphere. After the reaction was finished, the mixture was
filtrated to remove the undissolved solid and then the solvent
was removed under reduced pressure to obtain the crude
product. Purification of the crude product by flash chroma-
tography with petroleum ether/ dichloromethane (2:1) as the
eluant provided the product as yellow solid (1.20 g, 75.8%).
Materials and Methods
Silica Gel (GF254), 2-methylbut-3-yn-2-ol, K2PtCl4,
Pd(PPh3)2Cl2, PPh3, CuI, P(nBu)3, 4-propyl-phenylacetylene
and 4-bromobenzaldehyde are all commercial available
products and be used without more purification.
Pt(PBu3)2Cl2 (2) and 2,4,6-trimethyl-1,3,5-triazine (4) were
1
prepared according to literature methods [14, 24]. HNMR
spectra were recorded with a 400 MHz Varian spectrometer.
MALDI-TOF mass spectra were measured on AXIMA-CRF
system. Elemental analyses were carried on a Flash EA 1112
elemental analyzer (Thermo Electron SPA, Italy).
1H NMR (400 MHz, CDCl3) ꢀ 7.16 (d, J = 8.0 Hz, 2H),
7.02 (d, J = 8.0 Hz, 2H), 2.53 (t, J = 8.0 Hz, 2H), 2.10 – 1.92
(m, 12H), 1.69 – 1.51 (m, 14H), 1.51 – 1.37 (m, 12H), 0.93
(t, J = 6.0 Hz, 21H).
(Bu3P)2PtCl2 (2) [25]
K2PtCl4ꢀ1.04 gꢁ2.5 mmolꢂwas dissolved in 20 mL
distilled water, the resulted solution was purged with argon
for 20 min, and then P(n-Bu)3 (1.07g, 5.3 mmol) was in-
jected via a 2-mL injector. Argon was bubbled through the
solution for another 20 min, and the mixture was stirred at
room temperature for another 3 h under argon atmosphere.
After the reaction was finished, the solid was filtrated out
Compound (4) [14]
A mixture of 41 g (1.0 mol) acetonitrile, 46 g (1.0 mol)
absolute ethanol and 80 mL benzene were treated with hy-

A Triazine-Based Multi-Branched Platinum Acetylide Complex
Letters in Organic Chemistry, 2013, Vol. 10, No. 1
25
drogen chloride at 20-25 °C until 1.2-1.5 mol had been ab-
sorbed (about 2 h). Stirring was continued for 16~20 h. The
temperature was controlled below 40 °C to avoid the decom-
position of the product into acetamide and ethyl chloride (the
process was strongly exothermic). The crystallized product
was filtered and dried as quickly as possible under vacuum.
in 8 mL methanol was dropped into the flask within 4 h. The
reaction was refluxed for another 24 h after the addition, then
the solid was filtered out and washed by benzene/ethanol
(10/1, V/V). Purification by column chromatography (Silica,
CH2Cl2/Et2O 1:1) to provide 6 230 mg. yield: 50%.
1H NMR (400 MHz, CDCl3) ꢁ 8.26 (d, J = 16 Hz, 3H),
7.65 (d, J = 8.0, 6H), 7.56 (d, J = 8.0, 6H), 7.18 (d, J = 16
Hz, 3H), 3.21 (s, 3H).
52.0 g of ethyl acetimidate hydrochloride was added
quickly at 20-25 °C to the vigorously stirred mixture of 105
mL of methylene dichloride and 86 g of potassium carbonate
dissolved in 300 mL of water (slightly endothermic). The
organic phase was separated after mixed for 7~ 10 min and
the aqueous phase was extracted with 60 mL fresh methyl-
ene dichloride. The organic phases were combined and dried
with anhydrous potassium carbonate over night in a refrig-
erator. The dry solution was then concentrated by rapid dis-
tillation of the solvent. The residue contained about 80-85%
ethyl acetimidate hydrochloride. 3 mL (52.5 mmol) glacial
acetic acid was added to the residue gradually during 30 min.
The temperature of the resulting mixture was controlled be-
tween 25 to 30 °C during this addition process. Then the
mixture was stirred 17 h at RT. The solvent was removed,
and the residue was diluted with 30 mL of methylene chlo-
ride, the solid was removed by filtration. The solvent of the
filtrate was then removed. The residue was distilled and the
product was collected at 150 - 155 °C with yield 95%.
Compound (1) Compound (3) 1.10 g (1.44 mmol) and
CuI 29 mg (0.15 mmol) were dissolved in 10 mL triethy-
lamine and 30 mL THF, and then the mixture was bubbled
nitrogen for 20 min. Compound (6) 0.18 g (0.4 mmol) was
added. The mixture was bubbled nitrogen for another 20 min
and stirred for 3 days under nitrogen atmosphere. After the
reaction was finished, the undissolved solid was filtrated out
and the solvent was removed under reduced pressure to ob-
tain the crude product. Purification by flash chromatography
with petroleum ether/dichloromethane (2:1) as the eluant
provided the pure produce as yellow solid (0.51 g, 47.8%).
Yield: 45%.
1H NMR (400 MHz, CDCl3) ꢁ 8.25 (d, J = 16 Hz, 3H),
7.57 (d, J = 8.0 Hz, 6H), 7.33 (d, J = 8.0 Hz, 6H), 7.22 (d, J =
8.0 Hz, 6H), 7.12 (d, J = 16 Hz, 3H), 7.05 (d, J = 8.0 Hz 6H),
2.56 (t, J = 8.0 Hz , 6H), 2.16 (m, 36H), 1.65 (m, 36H), 1.42
(m, 42H), 0.95 (m, 63H). MS (TOF): m/z =2683.7[M+].
Anal. Calcd. For C138H213N3P6Pt3: C, 61.72; H, 8.00; N, 1.56.
Found: C, 62.25; H, 8.07; N, 1.54.
1H NMR (400 MHz, CDCl3) ꢂ 2.58 (s, 9H)
Compound (5)
To a mixture of PdCl2(PPh3)2 (175 mg, 0.3 mmol) and
CuI (190 mg, 1.0 mmol) in THF (30 mL), 4-
bromobenzaldehyde (1.85 g, 10 mmol), trimethylsilyl acety-
lene (1.12 mL, 12 mmol), and NEt3 (10 mL) were added.
The resulted mixture was stirred for 24 h at room tempera-
ture. The solvent was removed and 30 mL CH2Cl2 was
added. The mixture was washed with water (3 ꢀ 30 mL). The
organic phase was dried with MgSO4 and the solvent was
removed by rotary evaporation. Purification by column
chromatography (Silica gel, CH2Cl2/hexane 1:2) gave 4-(2-
(trimethylsilyl)ethynyl) -benzaldehyde derivative as white
solid (yield 85%).
CONFLICT OF INTEREST
The author(s) confirm that this article content has no con-
flicts of interest.
ACKNOWLEDGEMENTS
The authors thank the Opening Research Foundation
from the State Key Laboratory of Laser Interaction with Ma-
ter (China) [Grant No. SKILL1005] for the financial support.
SUPPLEMENTARY DATA
To a stirred solution of 4-(2-(trimethylsilyl)ethynyl) ben-
zaldehyde (5 mmol) in CH3OH (30 mL), K2CO3 (69 mg, 0.5
mmol) was added. The mixture was stirred for 24 h at room
temperature, and the solvent was removed. The residue was
diluted with 30 mL Et2O and washed with water (3 ꢀ 30
mL). The organic phase was dried over MgSO4 and the sol-
vent was removed by rotary evaporation. Purification by a
flash colum chromatography (Silica gel, Et2O) provide 5 as
white solid (546 mg, yield 84%).
The detailed experimental processes and character spec-
tra can be found in the supplementary data.
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