Optimized trade-offs between triplet emission and transparency in Pt(II) acetylides through phenylsulfonyl units for achieving good optical power limiting performance

Article abstract of DOI:10.1039/c6tc01042c

Three Pt(ii) acetylides have been prepared by coupling trans-[PtCl₂(PBu₃)₂] to ethynyl aromatic ligands with electron-withdrawing phenylsulfonyl units in high yields (>85%). The investigation of their photophysical behavior has shown that the unique conjugation-breaking configuration of the -SO₂- linker in the phenylsulfonyl units can afford a very short cut-off wavelength (λ_cut-off) of <390 nm to the Pt(ii) acetylides, furnishing excellent transparency of these compounds. Critically, the triplet quantum yields (Φ_P) of the prepared Pt(ii) acetylides can be effectively enhanced from 0.52% to 15.92% through increasing the number of fluorine substituents on the phenylsulfonyl units in the organic ligands. Benefiting from their enhanced Φ_P, the phenylsulfonyl-based Pt(ii) acetylides can exhibit comparable or even better optical power limiting (OPL) performance against 532 nm lasers than the state-of-the-art OPL material C₆₀, indicating their great potential in the field of laser protection. All of these results have provided a new strategy to achieve consistency between high OPL ability and good transparency for OPL materials, representing a valuable attempt for coping with key problems in the field of nonlinear optics.

Full text of DOI:10.1039/c6tc01042c

Journal of
Materials Chemistry C
View Article Online
View Journal
PAPER
Optimized trade-offs between triplet emission
and transparency in Pt(II) acetylides through
phenylsulfonyl units for achieving good optical
power limiting performance†
Cite this:DOI: 10.1039/c6tc01042c
Miao An,ab Xiaogang Yan,a Zhuanzhuan Tian,a Jiang Zhao,a Boao Liu,a Feifan Dang,a
Xiaolong Yang,a Yong Wu,a Guijiang Zhou,*a Yixia Ren*ab and Loujun Gao*b
Three Pt(II) acetylides have been prepared by coupling trans-[PtCl2(PBu3)2] to ethynyl aromatic ligands with
electron-withdrawing phenylsulfonyl units in high yields (485%). The investigation of their photophysical
behavior has shown that the unique conjugation-breaking configuration of the –SO2– linker in the phenyl-
sulfonyl units can afford a very short cut-off wavelength (lcut-off) of o390 nm to the Pt(II) acetylides,
furnishing excellent transparency of these compounds. Critically, the triplet quantum yields (FP) of
the prepared Pt(II) acetylides can be effectively enhanced from 0.52% to 15.92% through increasing the
number of fluorine substituents on the phenylsulfonyl units in the organic ligands. Benefiting from their
enhanced FP, the phenylsulfonyl-based Pt(II) acetylides can exhibit comparable or even better optical power
limiting (OPL) performance against 532 nm lasers than the state-of-the-art OPL material C60, indicating
their great potential in the field of laser protection. All of these results have provided a new strategy to
achieve consistency between high OPL ability and good transparency for OPL materials, representing a
valuable attempt for coping with key problems in the field of nonlinear optics.
Received 11th March 2016,
Accepted 11th May 2016
DOI: 10.1039/c6tc01042c
www.rsc.org/MaterialsC
potential in the field of OPL.10 More importantly, Pt(II) acetylides
bearing organic phosphine ligands can exhibit outstanding trans-
Introduction
Accompanied by the wide application of lasers, the damage parency with very weak or even no absorption in the visible-light
of both human eyes and optical sensors caused by sudden region while maintaining greatly enhanced OPL ability even better
exposure to intense laser beams has pushed the development than C60, Cu(II)-phthalocyanine and Zn(II)-porphyrin at the same
of optical power limiting materials.1–3 Unfortunately, the most time.11–14 Furthermore, the transparency of these Pt(II) acetylides
effective traditional OPL materials, such as fullerenes (e.g., C60),4,5 can be optimized by tuning the configuration of the Pt(II) centers
phthalocyanines (Pc)6,7 and porphyrins8,9 cannot meet the require- as well as copolymerization with Hg(II) ions, indicating their great
ments of their applications in practical devices for the protection of advantages in achieving optimization between OPL activity and
human eyes due to the intense absorption bands in the visible-light transparency.11,12 The success of these Pt(II) acetylides lies in
region (ca. 400–700 nm) induced by their large p-conjugated their optimized consistency between transparency and triplet
structures.3 This also indicates the conflict between OPL activity emission quantum yield, which can improve the OPL ability
and transparency in traditional OPL materials, representing the key according to the reverse saturable absorption (RSA) mechanism.3
issue to be dealt with in the field of nonlinear optics. Recently, In addition, some phenylethynyl-type Pt(II) acetylides have also
it has been reported that transition metal acetylides can show been employed to make prototype OPL devices.15
nonlinear optical properties, which should demonstrate their
From the discussion aforementioned, a feasible strategy to
deal with the key issues in the field of OPL materials should be
fulfilling short absorption wavelengths as well as high triplet
quantum yields in Pt(II) acetylides. According to the reported
results, the electronic features of the organic acetylene ligands can
play a very crucial role in determining both the triplet quantum
yield and the transparency of transition metal acetylides.16–18
Hence, employing new acetylene ligands should represent a
feasible way to meet the purposes aforementioned. Owing to
their electron-withdrawing character, the phenylsulfonyl units
a MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed
Matter, State Key Laboratory for Mechanical Behavior of Materials, Institute of
Chemistry for New Energy Material, Department of Chemistry, School of Science,
Xi’an Jiaotong University, Xi’an 710049, P. R. China.
E-mail: zhougj@mail.xjtu.edu.cn; Fax: +86-29-8266-3914
b College of Chemistry and Chemical Engineering, Yan’an University,
Yan’an 716000, P. R. China. E-mail: renyixia1@163.com, glj@yau.edu.cn
† Electronic supplementary information (ESI) available: Synthetic details for the
organic ligands. See DOI: 10.1039/c6tc01042c
This journal is ©The Royal Society of Chemistry 2016
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
have been employed to develop high-performance materials in Optical power limiting measurements
organic lighting-emitting diodes (OLEDs).19,20 However, these
The optical power limiting properties of the Pt(II) acetylides were
phenylsulfonyl units have been rarely introduced into Pt(II)
acetylides for OPL purposes. On this basis, three Pt(II) acetylides
bearing organic acetylides with phenylsulfonyl groups have been
prepared to characterize their OPL properties. The phenylsulfonyl
groups can furnish the concerned Pt(II) acetylides with a good
OPL ability afforded by the enhanced triplet quantum yield and
also maintain excellent transparency with no absorption beyond
400 nm at the same time. Therefore, the concerned results will
present a new strategy for achieving optimized trade-offs between
high OPL activity and good transparency.
characterized by Z-scan measurements, which were performed at
532 nm for a Gaussian mode laser beam with a repetition rate of
20 Hz using a Q-switched Quantel Q-Smart 100 Nd:YAG laser.
The laser beam was split into two beams using a beam splitter.
One was used as the reference beam, which was received
by a power detector (D1), the other was focused with a lens
( f = 25 cm) for the sample measurement. After transmitting through
the sample, the light beam entered another power detector (D2).
The sample to be measured was moved automatically along a rail to
change the incident irradiance on it. The incident and transmitted
powers were detected simultaneously by the two power detectors
D1 and D2 individually. The OPL performance of each of our
samples was measured as a 92% transmitting solution at 532 nm
in CH2Cl2 filled in a 1 mm quartz cell.
Experimental
General information
The commercially available reagents were used directly as received
unless otherwise stated. All reactions were conducted under an
inert atmosphere. The solvents were purified by standard
methods under dry nitrogen prior to use. The reactions were
monitored by thin-layer chromatography (TLC) with Merck pre-
coated aluminum plates. Flash column chromatography
and preparative TLC were carried out using silica gel. All
Sonogashira reactions were carried out with Schlenk techniques
under a nitrogen atmosphere.
Computational details
Geometrical optimizations were conducted using the popular
B3LYP density functional theory (DFT). The basis set used for
the C, H, O, N, F, P and S atoms was 6-311G(d,p), whereas
effective core potentials with a LanL2DZ basis set were employed
for the Pt atoms.22,23 The energies of the excited states of
the complexes were computed by TD-DFT based on all of the
ground-state geometries. All calculations were carried out using
the Gaussian 09 program.24
Physical characterization
Synthesis
1H-, 13C-, 19F- and 31P-NMR spectra were measured in CDCl3
with a Bruker AXS 400 MHz NMR spectrometer with the 1H and
13C NMR chemical shifts quoted relative to SiMe4 and the
31P chemical shifts relative to an 85% H3PO4 external standard.
Fast atom bombardment (FAB) mass spectra were recorded on
a Finnigan MAT SSQ710 system. UV-vis spectra were recorded
with a Shimadzu UV-2250 spectrophotometer. The photolumi-
nescent (PL) properties of the Pt(II) acetylides were measured
The brominated phenylsulfonyl compounds S-0F-Br, S-1F-Br
and S-3F-Br were prepared using our previous method.20
The ethynyl aromatic ligands were prepared by the typical
Sonogashira coupling reaction.25–28 All of the synthetic proce-
dures are provided in the ESI.†
General synthetic procedure for the Pt(II) acetylides
with an Edinburgh Instruments FLS920 fluorescence spectro- Under N2 atmosphere, trans-[PtCl2(PBu3)2] (1.0 equiv.) was added
photometer. The lifetimes of the excited states were measured to the solution of the corresponding diethynyl aromatic ligand
by a single photon counting spectrometer from Edinburgh (2.1 equiv.) in EtN3. Then, a small amount of CuI was added. The
Instruments FLS920 with a 360 nm picosecond LED lamp reaction mixture was stirred for 10 h at room temperature. After
as the excitation source, while those at 77 K were obtained removing the solvent, the residue was purified by preparative
with the excitation from a xenon flash lamp. The PL spectra TLC. The title compounds were obtained in high yield.
and lifetimes at 77 K were obtained by dipping the degassed
Pt-S-0F: (yield: 88%). 1H NMR (400 MHz, CDCl3): d (ppm)
CH2Cl2 solution in a thin quartz tube into a liquid nitrogen 7.92 (d, J = 8.0 Hz, 4H), 7.76 (d, J = 8.0 Hz, 4H), 7.55–7.47 (m,
Dewar and recording the data after standing for 3 minutes. The 6H), 7.30–7.26 (m, 4H), 2.08–2.03 (m, 12H), 1.58–1.52 (m, 12H),
fluorescence quantum yields (FF) were determined in CH2Cl2 1.44–1.35 (m, 12H), 0.88 (t, J = 8.0 Hz, 18H); 13C NMR (100 MHz,
solutions at 298 K against quinine sulfate in 1.0 M H2SO4 CDCl3): d (ppm) 142.13, 136.75, 134.22, 132.88, 131.12, 129.18,
(FF ca. 0.55).21 Phosphorescence quantum yields (FP) were 127.50, 116.11, 115.97, 108.83, 26.31, 24.35, 23.90, 13.77; 19F NMR
measured at room temperature with deoxygenated samples. (376 MHz, CDCl3): d (ppm) À104.74 (s, 1F); 31P NMR (161.9 MHz,
Oxygen was removed using three successive freeze–pump– CDCl3): d (ppm) 3.44 (1JP–Pt = 2321 Hz). FAB-MS (m/z): 1081 [M]+.
thaw cycles. The FP values were determined by an integrating Elemental analysis calcd (%) for C52H72O4P2PtS2: C 57.71, H 6.71;
sphere from Edinburgh Instruments FLS920 with the excitation found: C 57.62, H 6.58.
wavelength at 340 nm. The laser-irradiation stability of the
Pt-S-1F: (yield: 90%). 1H NMR (400 MHz, CDCl3): d (ppm)
Pt(II) acetylides was characterized by comparing the 1H-NMR 7.95–7.92 (m, 4H), 7.74 (d, J = 8.0 Hz, 4H), 7.30 (d, J = 8.0 Hz,
spectra of the fresh samples and the corresponding samples 4H), 7.16 (t, J = 8.0 Hz, 4H), 2.07–2.03 (m, 12H), 1.57–1.52
after Z-scan measurement.
(m, 12H), 1.44–1.35 (m, 12H), 0.89 (t, J = 8.0 Hz, 18H); 13C NMR
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2016

View Article Online
Journal of Materials Chemistry C
Paper
(100 MHz, CDCl3): d (ppm) 141.86, 136.60, 131.17, 130.28, electron-withdrawing –F groups have been introduced to the
130.18, 127.39, 116.56, 116.34, 108.85, 26.28, 24.33, 23.88, phenylsulfonyl units. In order to obtain the target Pt(II) acetylides
13.76; 19F NMR (376 MHz, CDCl3): d (ppm) À104.74 (s, 1F); Pt-S-0F, Pt-S-1F and Pt-S-3F, the corresponding phenylsulfonyl-
31P NMR (161.9 MHz, CDCl3): d (ppm) 3.45 (1JP–Pt = 2321 Hz). based aromatic alkynes L-0F, L-1F and L-3F should be prepared.
FAB-MS (m/z): 1117 [M]+. Elemental analysis calcd (%) for The starting compounds S-0F-Br, S-1F-Br and S-3F-Br for prepar-
C
52H70F2O4P2PtS2: C 55.85, H 6.31; found: C 55.78, H 6.23.
ing the alkyne ligands L-0F, L-1F and L-3F were synthesized
Pt-S-3F: (yield: 86%). 1H NMR (400 MHz, CDCl3): d (ppm) 7.73 according to our previous methods20 and the synthetic details
(d, J = 8.0 Hz, 4H), 7.57 (t, J = 8.0 Hz, 4H), 7.32 (d, J = 8.0 Hz, 4H), have been provided in ESI.† Through highly efficient Sonogashira
2.07–2.03 (m, 12H), 1.58–1.52 (m, 12H), 1.43–1.37 (m, 12H), 0.89 cross-coupling, the brominated phenylsulfonyl compounds
(t, J = 8.0 Hz, 18H); 13C NMR (100 MHz, CDCl3): d (ppm) 152.43, S-0F-Br, S-1F-Br and S-3F-Br can be converted into S-0F-TMS,
149.90, 138.33, 135.06, 131.40, 127.69, 117.63, 112.71, 112.55, S-1F-TMS and S-3F-TMS, which can undergo the trimethylsilane
108.89, 26.30, 24.34, 23.92, 13.76; 19F NMR (376 MHz, CDCl3): cleaving reaction to form the aromatic alkyne ligands L-0F, L-1F
d (ppm) À129.25 (d, 4F), À151.28 (t, 2F); 31P NMR (161.9 MHz, and L-3F in high yields over 90% (Scheme 1). After obtaining all
CDCl3): d (ppm) 3.50 (1JP–Pt = 2315 Hz). FAB-MS (m/z): 1189 [M]+. of the key organic ligands, the designed Pt(II) acetylides can be
Elemental analysis calcd (%) for C52H66F6O4P2PtS2: C 52.47, easily prepared using the Sonogashira cross-coupling procedure
H 5.59; found: C 52.37, H 5.51.
between the ligands L-0F, L-1F and L-3F and trans-[PtCl2(PBu3)2]
in Et3N with CuI as catalyst (Scheme 1).
The Pt(II) acetylides bearing phenylsulfonyl units have been
fully characterized by 1H, 31P and 19F NMR spectra. In the
1H NMR spectra of these Pt(II) acetylides, the absence of a single
peak at ca. 3.2 ppm, assigned to the protons in the alkyne
Results and discussion
Synthesis and structural characterization
The synthetic pathways of the Pt(II) acetylides bearing phenyl- groups, indicates successful coupling between the alkyne groups
sulfonyl units are shown in Scheme 1. With the aim of in the organic ligands and trans-[PtCl2(PBu3)2]. The strong
tuning the electronic features of the Pt(II) acetylides, strong resonance peak with a P–Pt coupling effect at ca. 3.5 ppm in
Scheme 1 Synthesis of the Pt(II) acetylides bearing phenylsulfonyl units.
This journal is ©The Royal Society of Chemistry 2016
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
the 31P NMR spectra of these Pt(II) acetylides has clearly shown
the presence of the trans-Pt(PBu3)2 units. In the 19F NMR spectrum
of Pt-S-1F, the single resonance peak at ca. À104.74 ppm indicates
the only –F group on the pendant phenyl ring of the sulfonyl unit.
For Pt-S-3F, the two sets of resonance peaks at ca. À129.25 ppm
and À151.28 ppm in its 19F NMR spectrum are consistent with
its fluoro-substitution pattern.
Photophysical properties
The absorption properties of the phenylsulfonyl-based Pt(II)
acetylides have been characterized in CH2Cl2 at 298 K and the
data are summarized in Table 1. In their UV-vis absorption
spectra (Fig. 1), all the Pt(II) acetylides exhibit intense absorp-
tion bands, which can be assigned to the metal disturbed p–p*
transitions from the organic ligands.12,16,29 All of the absorp-
tion bands for these Pt(II) acetylides are located in the UV region
before 400 nm with absorption maxima at ca. 340 nm (Fig. 1 and
Fig. 1 UV-vis absorption spectra for the Pt(II) acetylides in CH2Cl2 at 298 K.
Table 1), indicating their excellent transparency in the visible in the quantum yield of T1 states (FP) (ca. 0.52% for Pt-S-0F,
light region (ca. 400–700 nm). In addition, the cut-off absorption 6.50% for Pt-S-1F and 15.92% for Pt-S-3F) (Table 1). Hence, it
wavelengths (lcut-off) for these Pt(II) acetylides show a slight seems that introducing fluorine substituents can effectively
bathochromic effect when increasing the number of fluorine increase the quantum yield of T1 states, which should benefit
substituents on the phenylsulfonyl units (ca. 380 nm for Pt-S-0F, the OPL performance of these Pt(II) acetylides.
382 nm for Pt-S-1F and 386 nm for Pt-S-3F).
In order to interpret the photophysical properties of
In the photoluminescent (PL) spectra of these Pt(II) acetylides these Pt(II) acetylides aforementioned, their frontier molecular
in CH2Cl2 solution at 289 K, all of the complexes exhibit two orbitals and transition characteristics, showing a tight relation-
emission bands centered at ca. 380 nm (Pt-S-0F and Pt-S-1F: ship with their photophysical properties, have been obtained
383 nm, Pt-S-3F: 384 nm) and 480 nm (Pt-S-0F: 476 nm, Pt-S-1F: by time-dependent density functional theory (TD-DFT) calcula-
478 nm, Pt-S-3F: 483 nm), respectively (Fig. 2a and Table 1). The tion. The theoretical calculation results clearly show that the
high-energy emission bands should come from the singlet states HOMO - LUMO (H - L) transition can represent the char-
(S1) of the metal disturbed organic ligand p–p* transitions due to acteristics of the S1 state of the Pt(II) acetylides, owing to its
their short lifetime in the order of nanoseconds (ns) (Table 1). large contribution to the transition of the S1 state (Table 2).
On the contrary, the much longer lifetimes in the order From the molecular orbital patterns corresponding to the
of microseconds (ms) together with the large Stokes shift of H - L transition (Fig. 3), the S1 states of these phenylsulfonyl-
ca. 130 nm should indicate the triplet state (T1) features of the based Pt(II) acetylides exhibit obvious ligand-centered p–p*
long-wavelength emission signals (Fig. 2a and Table 1). Further- character. Based on the theoretical results (Table 2), the for-
more, at a low temperature of 77 K, the long-wavelength emis- mation of the S1 states should correspond to the major absorp-
sion signals have been substantially enhanced, also indicating tion of these Pt(II) acetylides. Hence, the dominant absorption
their T1 features (Fig. 2b). What should be noted is that the bands of these Pt(II) acetylides show metal disturbed p–p*
intensity of the T1 emission signals of these Pt(II) acetylides features. Due to different contributions from the metal dp
enhances when increasing the number of fluorine substituents orbitals to their HOMOs and LUMOs (Table 2), the S1 states
on the phenylsulfonyl units (Fig. 2a). This trend is not only of these Pt(II) acetylides show some metal-to-ligand charge
supported by the decrease in the quantum yield of the S1 transfer (MLCT) features as well. From their noticeable con-
states (FF) from Pt-S-0F (ca. 0.11%) to Pt-S-1F (ca. 0.03%) then tribution to the LUMOs, the pendent phenyl ring in the
to Pt-S-3F (ca. 0.02%), but also indicated directly by the increase phenylsulfonyl units can host electrons in the MLCT process.
Table 1 Photophysical data for the Pt(II) acetylides
Absorption
labs (nm) 298 K
Emission
lem (nm) 298 K/77 K
Lifetime of excited statesd
S1 state (ns)/T1 state (ms)
lcut-off
(nm)
a
a
b
c
Compound
FF (%)
FP (%)
Pt-S-0F
Pt-S-1F
Pt-S-3F
267, 304sh, 340
262, 303sh, 341
262, 306sh, 346
383, 400sh, 476/468, 490
383, 402sh, 478/468, 490
384, 402sh, 483/469, 492
0.11
0.03
0.02
0.52
6.50
15.92
1.05 ns (383 nm)/48.3 ms (468 nm)
1.11 ns (383 nm)/43.2 ms (468 nm)
1.15 ns (384 nm)/28.7 ms (469 nm)
380
382
386
a
b
Measured in CH2Cl2 at a concentration of ca. 10À5 M, sh: shoulder. Measured using quinine sulfate in 1.0 M H2SO4 as the standard. According
c
to the UV-vis absorption of the compounds, the excitation wavelength was set at 313 nm while the FF of the standard is 55%. Measured using an
integrating sphere at 298 K, the excitation wavelength was set at 340 nm. The numbers in parentheses are the emission wavelengths of the S1 and
d
T1 states. The lifetime of the S1 state was measured at 298 K in degassed CH2Cl2 with the excitation at 360 nm and that of the T1 states was
measured at 77 K in the same solvent with the same excitation wavelength.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2016

View Article Online
Journal of Materials Chemistry C
Paper
the spin–orbit coupling (SOC) effect, which can facilitate the
formation of the T1 states through the intersystem crossing (ISC)
process. It has been shown that the SOC effect in the transition
metal acetylides can be enhanced effectively by mixing the d
orbitals of the heavy metal centers and the p orbitals of the
organic ligands. By this way, the transition processes in the
concerned systems will exhibit more obvious metal-involved
characters rather than just the ligand-centered p–p* features.
Hence, the effective mixing of the orbitals between both heavy
metal centers and organic ligands will enhance the SOC effect to
facilitate the formation of the T1 states. From the MO distribu-
tions of these Pt(II) acetylides (Fig. 3), it can be seen clearly that
the dp orbitals of the Pt(II) centers give noticeable contribution
(420%) to the HOMOs, while the LUMOs are mainly located on
the p orbitals of the organic ligands. Based on the calculation
results in Table 2, the H - L transitions can represent the
features of the transitions to the T1 states to a large extent. These
results indicate the effective mixing of the orbitals from the Pt(II)
centers and the corresponding organic ligands and hence there
is a strong SOC effect in these Pt(II) acetylides. As a result, all of
them can show T1 emission bands even at 298 K (Fig. 2a).
Besides the H - L transition, the HOMOÀ2 (HÀ2) -
LUMO+1 (L+1) transition also contributes to the character of
the T1 states associated with these Pt(II) acetylides (Table 2). The
p orbitals of the pendent phenyl ring in the phenylsulfonyl units
can substantially contribute to the LUMO+1 orbital of these Pt(II)
acetylides (Fig. 3). When increasing the number of fluorine
substituents on the pendant phenyl moieties, the contribution
from their p orbitals to the LUMO+1 increases (ca. 35.2% for
Pt-S-0F, 39.4% for Pt-S-1F and 45.3% for Pt-S-3F). Hence, increas-
ing the number of fluorine substituents can improve the degree
of orbital mixing between the Pt(II) centers and the organic
Fig. 2 Photoluminescence (PL) spectra for the Pt(II) acetylides in CH2Cl2
solution at both 298 K (a) and 77 K (b).
Clearly, increasing the number of fluorine substituents on the ligands. So, the SOC effect for these Pt(II) acetylides should fall
pendant phenyl moieties will enhance their electron-accepting in the order of Pt-S-3F 4 Pt-S-1F 4 Pt-S-0F. As a result, Pt-S-3F
ability, which will facilitate the H - L transitions and lower the can show the highest T1 emission intensity, while Pt-S-0F gives
energy level of the S1 states in these Pt(II) acetylides. As a result, the lowest T1 emission intensity (Fig. 2a).
the absorption maxima and lcut-off for these Pt(II) acetylides
Optical power limiting properties
should show a bathochromic effect from Pt-S-0F to Pt-S-3F,
which coincides well with the experimental results (Table 1).
Owing to their T1 states being induced by the heavy metal
According to the heavy atom effect, emission signals centers through the SOC effect, these Pt(II) acetylides can
from the decay of T1 states can typically be detected due to exhibit OPL behavior induced by the strong absorption ability
Table 2 Contribution of the metal dp orbitals to the HOMO and LUMO together with the TD-DFT calculation results
Oscillator
Contribution Contribution Largest coefficient
of dp orbitals of dp orbitals in the CI expansion
Percentage contribu- Largest coefficient Percentage contribu- strength ( f )
tion of the transition in the CI expansion tion of the transition of the S1 ’ S0
Compound to HOMOa
to LUMOa
9.0%
of the T1 stateb
to the T1 stateb
of the S1 stateb
to the S1 stateb
95.0%
transition
Pt-S-0F
Pt-S-1F
Pt-S-3F
a
20.5%
20.7%
21.0%
H - L (0.59511)
70.8%
H - L (0.68936)
358.61 nm
1.5324
HÀ2 - L+1 (0.24365) 11.9%
479.32 nm
9.0%
6.6%
H - L (0.59784)
71.5%
H - L (0.68998)
358.61 nm
95.2%
94.3%
1.5360
1.4718
HÀ2 - L+1 (0.24972) 12.5%
480.13 nm
H - L (0.58101)
HÀ2 - L+1 (0.23510) 11.1%
67.5%
H - L (0.68649)
362.00 nm
480.70 nm
b
The data were obtained by exporting DFT results with the software AOMix. H - L represents the HOMO to LUMO transition. CI stands for
configuration interaction.
This journal is ©The Royal Society of Chemistry 2016
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
Fig. 3 Critical molecular orbitals involved in the S1 and T1 transitions of the Pt(II) acetylides. (a) Pt-S-0F, (b) Pt-S-1F, (c) Pt-S-3F.
of the T1 states. From the PL spectra of the Pt(II) acetylides, the the transmittance (T) of the sample is a function of the
emission signals from the decay of the T1 states can even be Z-position (against focal point Z = 0) of the sample along the Z
observed at 298 K (Table 2). Hence, the phenylsulfonyl-based direction (Fig. 4), it can be seen clearly that the T of the Pt(II)
Pt(II) acetylides should show promising OPL ability. In addition, acetylide solution remains almost constant far from the focal
the OPL behavior of the Pt(II) acetylides bearing phenylsulfonyl point, showing linear optical properties (i.e. obeying Beer’s law).
units has been rarely investigated. So, it should be of great It means that the Pt(II) acetylide solution exhibits linear optical
importance to study the OPL performance of these Pt(II) behavior under weak incident irradiance. However, when the
acetylides in view of both evaluating their potential as new sample is moved towards the focus to increase incident irradi-
OPL materials and providing valuable structure–property infor- ance upon it, the T of the sample decreases and the OPL effect
mation for guiding the design of high-performance Pt(II) appears (Fig. 4) to show a nonlinear optical effect.
acetylides for OPL applications. Bearing this in mind, the
Based on the photophysical properties of these Pt(II) acetylides
OPL properties of these Pt(II) acetylides have been investigated. presented in the previous section, their OPL mechanism can be
From their UV-vis spectra, all three of the Pt(II) acetylides are explained as follows. According to the previous results and the
highly transparent at 532 nm, indicating their low ground-state obvious T1 emission bands (Fig. 2a and b), the OPL effect
absorption at this wavelength. This result makes them suitable associated with these Pt(II) acetylides can be assigned to reverse
for the characterization of their OPL properties against a saturable absorption (RSA) from the T1 states (Fig. 5a).12,16 The
532 nm laser beam. Hence, the OPL behaviors of these Pt(II) molecules of the Pt(II) acetylides in the ground state (S0) can be
acetylides have been characterized in CH2Cl2 with a linear excited initially to the first singlet state (S1) by laser irradiance.
transmittance To of ca. 92% (Fig. 4) through the Z-scan method Due to the strong SOC effect induced by the Pt(II) centers, the S1
under an open-aperture mode. From the Z-scan curves, where states can be swiftly converted into the T1 states through the ISC
process. Owing to the relatively long laser pulse duration in the
order of nanoseconds, the fast ISC process and the long-lived T1
state, the molecules in the T1 state can reach a certain population
easily and then absorb laser energy strongly to reach a higher
triplet state (Tn) in the laser pulse duration to induce the OPL
effect (Fig. 5a). Therefore, it is the strong absorption from the T1
states that furnishes these Pt(II) acetylides with OPL ability
(Fig. 5a). Owing to the very short lifetime (B1 ns) of the S1 state
(Table 1), the energy absorption from the S1 - Sn transition can
be neglected in the contribution to the nanosecond OPL response
in these Pt(II) acetylides. Clearly, if the proposed mechanism is
valid, the compound with a higher T1 quantum yield should
show better OPL performance. From the Z-scan curves, it is
obvious that the OPL ability of these Pt(II) acetylides falls in the
order of Pt-S-3F 4 Pt-S-1F 4 Pt-S-0F, which is in good agreement
with the order of their T1 quantum yields (Fig. 2a and Table 1).
This result should indicate that the proposed OPL mechanism
associated with these Pt(II) acetylides is reasonable.
Fig. 4 Open-aperture Z-scan results for the Pt(II) acetylides (To ca. 92%)
together with that for C60 (To ca. 86%).
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2016

View Article Online
Journal of Materials Chemistry C
Paper
state-of-the-art RSA OPL materials. Even at higher To of ca.
92%, Pt-S-0F can show nearly identical OPL ability to that of
C
60. More importantly, bearing organic ligands with stronger
electron withdrawing ability, both Pt-S-1F and Pt-S-3F can even
outperform C60 (Fig. 4). Besides the attractive OPL ability of
these Pt(II) acetylides, their exceptional transparency also
indicates their importance in the field of OPL. All of the Pt(II)
acetylide samples are off-white with nearly no absorption in
the visible light region (ca. 400–700 nm). However, traditional
C
60 displays a very dark color, indicating very poor transparency
in the visible light region (Fig. 5b). Furthermore, these Pt(II)
acetylides can show good laser-irradiation stability, since their
1H-NMR spectra can be maintained nearly unchanged before
and after Z-scan measurement (Fig. S1 in ESI†). All of these
results will definitely provide valuable clues for dealing with the
key issues associated with achieving trade-offs between high
OPL activity and good transparency.
Conclusions
Employing different phenylsulfonyl-based ligands bearing –F groups,
three Pt(II) acetylides have been successfully prepared. It has been
found that the fluorinated phenylsulfonyl ligands can effectively
enhance the quantum yield of the T1 states to benefit OPL perfor-
mance of these Pt(II) acetylides against a 532 nm laser. Hence, the
Pt(II) acetylides can show comparable or even better OPL perfor-
mance than the state-of-the-art OPL material C60, indicating their
potential in the field of OPL. Besides their encouraging OPL ability,
these Pt(II) acetylides can exhibit exceptional transparency with
nearly no absorption bands in the visible light region. Compared
with traditional analogs, the advantages associated with these
Pt(II) acetylides lie in the unique configuration and electron
withdrawing features of the phenylsulfonyl-based ligands to
fulfill excellent trade-offs between high OPL activity and good
transparency. The concerned results should represent a valuable
strategy to solve the key problems associated with RSA OPL
materials.
Fig. 5 (a) Optical power limiting mechanisms involved in the Pt(II)
acetylides. (b) Comparison of the color of the Pt(II) acetylides and C60
.
Based on the RSA mechanism for the nanosecond laser afore-
mentioned, developing materials with high triplet quantum yields as
well as short absorption wavelengths should represent a feasible
outlet to fulfill good trade-offs between high OPL activity and good
transparency. From the results aforementioned, employing organic
ligands with strong electron withdrawing fluorinated phenylsulfonyl
units can effectively promote the formation of T1 states (Fig. 2a and
Table 1) which can enhance the OPL ability of the concerned
compounds. Facilitating the formation of T1 states has also been
observed in the Pt(II) acetylides with electron withdrawing ligands
bearing oxadiazole and triarylborane units.16 However, the reported
Pt(II) acetylides show the absorption maxima located in much longer
wavelength regions (ca. 364 nm for the oxadiazole-based Pt(II)
acetylides and 381 nm for the triarylborane-based Pt(II) acetylides) Acknowledgements
due to the conjugation of the oxadiazole and triarylborane units.16
M. An and X. Yan contributed equally to this work. This research
However, the electron withdrawing ligands of these phenylsulfonyl-
based Pt(II) acetylides exhibit different features. The configuration of
the –SO2– linker can effectively break the conjugation between
the two phenyl rings in the phenylsulfonyl units. The theoretical
results have clearly proved this conclusion (Fig. 3). Hence, the short-
conjugated ligands bearing electron withdrawing –SO2– units and
–F groups will exhibit both much shorter absorption maxima (ca.
340 nm for Pt-S-0F, 341 nm for Pt-S-1F and 346 nm for Pt-S-3F) and
high T1 quantum yields (Table 1). So, in view of the reported Pt(II)
acetylides with electron withdrawing ligands, these Pt(II) acetylides
can show greater advantages in achieving excellent trade-offs
between high OPL activity and good transparency.
was financially supported by the Fundamental Research Funds for
the Central Universities (cxtd2015003), The Program for New
Century Excellent Talents in University, the Ministry of Education
of China (NECT-09-0651), the Key Creative Scientific Research Team
in Shaanxi Province (2013KCT-05), the China Postdoctoral Science
Foundation (Grant no. 20130201110034, 2014M562403), and the
National Natural Science Foundation of China (no. 20902072,
21572176). The financial support from the State Key Laboratory
for Mechanical Behavior of Materials is also acknowledged.
References
In order to evaluate the advantages of these Pt(II) acetylides
as OPL materials, their OPL performances and the transparency
features have been compared to that of C60, one of the
1 L. W. Tutt and T. F. Boggess, Prog. Quantum Electron., 1993,
17, 299.
This journal is ©The Royal Society of Chemistry 2016
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
2 C. W. Spangler, J. Mater. Chem., 1999, 9, 2013.
3 G. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2011, 40, 2541.
4 L. W. Tutt and A. Kost, Nature, 1992, 356, 225.
21 W. R. Dawson and M. W. Windsor, J. Phys. Chem., 1968,
72, 3251.
22 W. R. Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284.
23 P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299.
5 J. E. Riggs and Y. P. Sun, J. Phys. Chem. A, 1999, 103, 485.
6 Y. Li, T. M. Pritchett, J. Huang, M. Ke, P. Shao and W. Sun, 24 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
J. Phys. Chem. A, 2008, 112, 7200.
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven Jr.,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, 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. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, 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. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 09, revision
A.2, Gaussian, Inc., Wallingford, CT, 2009.
7 J. W. Perry, K. Mansour, S. R. Marder, K. J. Perry, D. Jr.
Alvarez and I. Choong, Opt. Lett., 1994, 19, 625.
8 K. McEwan, K. Lewis, G.-Y. Yang, L.-L. Chng, Y.-W. Lee,
W.-P. Lau and K.-S. Lai, Adv. Funct. Mater., 2003, 13, 863.
9 W. Su and T. M. Cooper, Chem. Mater., 1998, 10, 1212.
10 G. Zhou, W.-Y. Wong, D. Cui and C. Ye, Chem. Mater., 2005,
17, 5209.
11 G. Zhou, W.-Y. Wong, Z. Lin and C. Ye, Angew. Chem., Int.
Ed., 2006, 45, 6189.
12 G. Zhou, W.-Y. Wong, C. Ye and Z. Lin, Adv. Funct. Mater.,
2007, 17, 963.
¨
¨
13 R. Westlund, E. Malmstrom, C. Lopes, J. Ohgren, T. Rodgers,
Y. Saito, S. Kawata, E. Glimsdal and M. Lindgren, Adv. Funct.
Mater., 2008, 18, 1939.
14 R. Westlund, E. Glimsdal, M. Lindgren, R. Vestberg, C. Hawker,
¨
C. Lopesd and E. Malmstrom, J. Mater. Chem., 2008, 18, 166.
15 R. Zieba, C. Desroches, F. Chaput, M. Carlsson, B. Eliasson,
C. Lopes, M. Lindgren and S. Parola, Adv. Funct. Mater., 25 W.-Y. Wong, G. Zhou, Z. He, K.-Y. Cheung, A. M.-C. Ng,
ˇ ´
2009, 19, 235.
A. B. Djurisic and W.-K. Chan, Macromol. Chem. Phys., 2008,
16 G. Zhou, W.-Y. Wong, S.-Y. Poon, C. Ye and Z. Lin, Adv.
Funct. Mater., 2009, 19, 531.
209, 1319.
26 Z. Huang, B. Liu, Y. He, X. G. Yan, X. L. Yang, X. B. Xu,
G. J. Zhou, Y. X. Ren and Z. X. Wu, J. Organomet. Chem.,
2015, 794, 1.
27 Z. Huang, B. Liu, J. Zhao, Y. He, X. Yan, X. Xu, G. Zhou,
X. Yang and Z. Wu, RSC Adv., 2015, 5, 36507.
28 Z. Huang, B. Liu, J. Zhao, Y. He, X. Yan, X. Xu, G. Zhou,
X. Yang and Z. Wu, RSC Adv., 2015, 5, 12100.
17 C.-L. Ho and W.-Y. Wong, Coord. Chem. Rev., 2011, 255, 2469.
18 B. Liu, Z. Tian, F. Dang, J. Zhao, X. Yan, X. Xu, X. Yang,
G. Zhou and Y. Wu, J. Organomet. Chem., 2016, 804, 80.
19 X. Yang, G. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2015,
44, 8484.
20 J. Zhao, Y. Yu, X. Yang, X. Yan, H. Zhang, X. Xu, G. Zhou,
Z. Wu, Y. Ren and W.-Y. Wong, ACS Appl. Mater. Interfaces, 29 W.-Y. Wong and C.-L. Ho, Coord. Chem. Rev., 2006,
2015, 7, 24703.
250, 2627.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2016