N^N Pt(II) Bisacetylide Complexes with Oxoverdazyl Radical Ligands: Preparation, Photophysical Properties, and Magnetic Exchange Interaction between the Two Radical Ligands

Article abstract of DOI:10.1021/acs.inorgchem.0c01575

To study the effect of a stable radical on the photophysical properties of a phosphorescent Pt(II) coordination framework and the intramolecular magnetic interaction between radical ligands in the N^N Pt(II) bisacetylide complexes, we prepared a series of

Full text of DOI:10.1021/acs.inorgchem.0c01575

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Article
N^N Pt(II) Bisacetylide Complexes with Oxoverdazyl Radical
Ligands: Preparation, Photophysical Properties, and Magnetic
Exchange Interaction between the Two Radical Ligands
Wenbo Yang, Andrei A. Sukhanov, Jong Hyeon Lim, Xiaoxin Li, Yinshan Meng, Jianzhang Zhao,*
Haoling Sun,* Jin Yong Lee,* Gagik G. Gurzadyan,* and Violeta K. Voronkova*
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ABSTRACT: To study the effect of a stable radical on the photophysical
properties of a phosphorescent Pt(II) coordination framework and the
intramolecular magnetic interaction between radical ligands in the N^N
Pt(II) bisacetylide complexes, we prepared a series of N^N Pt(II)
bis(acetylide) complexes with oxoverdazyl radical acetylide ligands. The
linker between the Pt(II) center and the spin carrier was systematically
varied, to probe the effect on the sign and magnitude of the spin exchange
interactions between the radical ligands and photophysical properties.
The complexes were studied with steady-state and femtosecond/
nanosecond transient absorption spectroscopy, continuous-wave electron
paramagnetic resonance (EPR) spectroscopy, and density functional
theory (DFT) computations. The transient absorption spectral studies
show that the doublet excited state of the radicals are short-lived (τD ≈ 2 ps) and nonfluorescent. Moreover, the intrinsic long-lived
triplet excited state (τT = 1.2 μs) of the Pt(II) coordination center was efficiently quenched by the radical (τT = 6.9 ps for one
representative radical Pt(II) complex). The intramolecular magnetic interaction between the radical ligands through the diamagnetic
Pt(II) atom was studied with temperature-dependent EPR spectroscopy; antiferromagnetic exchange interaction (−J S1S2, J = −5.4
0.1 cm−1) for the complex with the shortest radical−radical distance through bridge fragments was observed. DFT computations
give similar results for the sign and magnitude of the J values. For complexes with larger inter-radical distance, however, very weak
coupling between the radical ligands was observed (|J| < 0.7 cm−1). Our results are useful for the study of the effect of a radical on
the photophysical properties of the phosphorescent transition-metal complexes.
attached on meta-substituted phenyl moiety are usually
ferromagnetically coupled, while the para-counterpart is usually
antiferromagnetically coupled.6,7 The magnetic coupling
between radical ligands mediated by Cu(I), Cu(II), Mn(II),
and Au(I) coordination has been studied.4,8−13 Yet these
studies are not correlated with the photophysical changes of the
coordination centers with attachment of the radical
ligands.14−16 It should be mentioned that the photochemical
formation of ferromagnetic chains in two isomeric polymeric
Mn(II) complexes was studied. This brings out the importance
of the study of photophysical processes in the magnetic
materials.17
1. INTRODUCTION
Recently, stable organic diradicals and polyradicals have
attracted much attention, owing to the magnetic interaction
between these radicals and the observation of high-spin states,
as well as for their potential application as molecular magnetic
materials.1,2 Concerning this aspect, a transition-metal
coordination framework was rarely used as a scaffold to
construct stable organic radical-containing compounds for
study of the magnetic coupling between the radicals, as well as
the effect of radical on the photophysical properties of the
coordination framework.3,4 A combination of the two
manifolds, that is, transition-metal coordination framework
and stable radicals, will be, in particular, of interest, because the
rich photophysical properties of the transition-metal complexes
will be tuned by the spin exchange with the radical moiety.
Synergy of the optical property and the magnetic property may
lead to novel materials with interesting optomagnetic proper-
ties.5
Received: May 28, 2020
Organic diradicals are the typical model for the study of the
magnetic coupling between two spin carriers. Some empirical
roles have been established, for instance, the two diradicals
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Scheme 1. Structures of Oxoverdazyl Radical Ligands and Pt(II) Complexes Used in This Study
However, although some topological rules for the magnetic
interactions of the organic diradicals have been pro-
posed,1,2,6,18 the sign and the magnitude of the intramolecular
radical−radical electron-exchange interaction in metal com-
plexes is far from fully elucidated. Subtle variation of the radical
or the metal complex coordination structure may substantially
affect the electron-exchange interaction.10 For instance, the
direction of the deviation from the tetrahedral geometry, either
bringing the two oxoverdazyl radical moieties closer or moving
the two radicals further apart, will dictate the sign as well as the
magnitude of the electron exchange between the radical ligands,
with the former leading to a fairly strong ferromagnetic
interaction (J = 47(1) cm−1)8 and the latter leading to a
weak antiferromagnetic interaction (J = −2 cm−1).10
It should be pointed out that the geometric lability of the
Cu(I) coordination center upon photoexcitation is detrimental
to the establishment of a persistent electron-exchange
interaction between the radical ligands.8,19,20 In this aspect
another rigid coordination framework is desired for the study
of the effect of a radical ligand on the photophysical property,
as well as the magnetic coupling between the radicals within
the complex molecule. Previously ethynyl phenyl-nitronyl
nitroxide radical ligands were used for the preparation of
trans-Pt(II) bis(trialkylphosphine) bisacetylide complex.21
This kind of complex has a well-defined rigid coordination
geometry, which is different from the Cu(I) complexes.22,23
Magnetic coupling of the two radical ligands through the
diamagnetic Pt(II) atom was studied, and it was found that the
exchange interaction between the electron spins of the two
nitronyl nitroxide (NN) radical ligands is very weak (|J| < 1
cm−1) for the meta-substituted radical. For the para-substituted
radical complex, no exchange interaction between the two
radical ligands was observed, due to the larger distance
between the radical ligands; thus, the spin-exchange interaction
through the diamagnetic Pt(II) atom is weak.21 Furthermore,
the detailed photophysical property of the stable radical-
containing complexes was rarely reported.24−26
Our rationale is that, with the introduction of the radical
ligands, the photophysical properties of the coordination
center will be alternated. Although phenanthroline Pt(II)/
Pd(II) bispyridine complexes with an NN radical attached on
the pyridine moiety were reported, the geometry of the radical
ligands is cis, and thus the distance between the radicals is
small, and stronger exchange interaction may be expected.27
However, no intramolecular exchange interaction was observed
with electron paramagnetic resonance (EPR) spectroscopy,
and it was concluded that the 14 bonds pathway through the
diamagnetic center is too long for any significant exchange
interaction. The photophysical property of the complex was
not studied. A N^C^N Pt(II) acetylide complex with an NN
radical ligand was prepared.28 Because of the monoradical
feature of the molecular structure, no intramolecular magnetic
interaction between radicals was studied. The photophysical
property was not studied, although the N^C^N Pt(II)
acetylide complex is a typical phosphorescent chromophore
at room temperature.29,30 Recently a verdazyl radical-
containing Ru(II) complex was reported; there is only a
monoradical unit; thus, no intramolecular magnetic interaction
between the radical units was studied.26 The phosphorescence
of the Ru(II) coordination center was not quenched by the
radical ligand.
The N^N Pt(II) bisacetylide complexes have been
extensively investigated, owing to the feasible preparation,
the well-defined geometry and orientation of the two acetylide
ligands, the efficient intersystem crossing (ISC) and the long-
lived triplet excited state.31−34 These complexes have been
widely used as photocatalysts and photosensitizers and for
photoinduced charge separation and also for the study of the
fundamental photochemistry and photophysics.35−38 However,
to the best of our knowledge, no N^N Pt(II) bisacetylide
complexes have been prepared with the radical ligands. Thus,
neither the magnetic coupling between the radical ligands
through the diamagnetic Pt(II) atom nor the effect of the
coordinated radical ligands on the photophysical property of
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a
Scheme 2. Synthesis of Oxoverdazyl Radical Ligands and Pt(II) Complexes
a
(a) 1,10-Phenanthroline, CuI, finely ground K3PO4, iodobenzene, dried dimethylformamide, Ar, 90 °C, 20 h, yield: 37.2%. (b) MeOH, Ar, −30
°C, 1 h, yield: 63.4%. (c) K2CO3, MeOH, CH2Cl2, Ar, RT, 2 h, yield: 96.0%. (d) 4-Benzoquinone, toluene, Ar, 90 °C, 2 h, yield: 90.3%. Pyridinium
tosylate, MeOH, Ar, RT, 30 min, yield: (e) 66.4%, (g) 85.7%, (i) 68.9%. 4-Benzoquinone, toluene, Ar, 90 °C, 1 h, yield: (f) 71.3%, (h) 78.5%, (j)
75.0%. (k) CuI, CH2Cl2, i-Pr2NH, Ar, RT, 24 h, yield: 93.3%. CuI, CH2Cl2, i-Pr2NH, Ar, RT, 4 h, yield: (l) 72.5%, (m) 63.0%, (n) 74.0%. (o)
64.8%.
the Pt(II) coordination center was studied. The molecular
structural planarity of the Pt(II) complexes may assist in the
control of the molecular packing,27 which is also important for
the preparation of magnetic materials.
orientation of the magnetic orbitals of the two ligands,
determined by the Cu(I) coordination geometry, results in the
ferromagnetic interaction between the two coordinated ligands.
Thus, it will be interesting to investigate the exchange
interaction between the two coordinated acetylide radical
ligands in the N^N Pt(II) bisacetylide ligands, in which the
two radical ligands are in coplanar geometry and the magnetic
orbitals are not in orthogonal geometry.
However, the sign of the exchange interaction may be also
switched by using different spin carriers, such as an
oxoverdazyl radical, even with the same geometry of the
coordination center. For instance, replacing the imino
nitroxide radical (2J = +102(2) cm−1)9 with oxoverdazyl
radical in the Cu(I) complex switched the exchange interaction
between the two radicals to 2J = −4 cm−1; as such, the
interaction becomes antiferromagnetic.10 The stark difference of
the intramolecular electron-exchange interaction was attributed
to the different frontier molecular orbitals with the two
different radical ligands (imino nitroxide vs oxoverdazyl).10
However, the effect of the coordinated radical ligands on the
photophysical property of the coordination center, for
instance, the ISC and the triplet-state property, was not
studied.8,19,20
To probe the exchange interaction between the two radical
ligands in the N^N Pt(II) bistacetylide complexes, as well as
the photophysical property changes of the Pt(II) center in the
presence of a radical, for ISC and the triplet-state properties,
we prepared a series of N^N Pt(II) bisacetylide complexes
with radical ligands, in which the distance between the radical
moieties, as well as the linkers between the radical center and
the Pt(II) atoms, are systematically varied (Scheme 1). The
photophysical properties of the complexes were studied with
steady-state as well as femtosecond time-resolved optical
spectroscopies. We found that the photophysical properties of
the complexes were substantially changed upon attachment of
the radical ligands. Moreover, intramolecular magnetic
coupling between the radical ligands was studied with EPR
spectroscopy as well as with theoretical computations. These
studies are interesting, because the tuning of the optical
property of the Pt(II) coordination center and the magnetic
(exchange) interactions of the radical ligands were combined.
2. RESULTS AND DISCUSSION
To study the intramolecular electron-exchange interactions
of the radicals within a rigid coordination framework, we
prepared a series of N^N Pt(II) bisacetylide complexes, in
which the inter-radical distance through bridge fragments and
the substitution profile of the radicals are systematically varied
(Scheme 1). We selected the oxoverdazyl radical,39 a stable
radical moiety, as the spin carrier. The distance between the
2.1. Design and Synthesis of the Complexes.
Previously the electron-exchange interaction between the two
bidentate ligands containing an imino nitroxide radical moiety
mediated by a diamagnetic Cu(I) was proven to be
ferromagnetic with the exchange interaction of 2J = +102(2)
cm−1.9 The rationale for this result is that the orthogonal
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Figure 1. UV−Vis absorption spectra of the compounds. c = 1.0 × 10−5 M in toluene. 20 °C.
Figure 2. (a) Photoluminescence spectra of Pt-Ph under N2 and air atmosphere; (b) quenching of the phosphorescence of Pt-Ph by increasing the
VR-1 concentration under N2 atmosphere; (c) Stern−Volmer plot for the quenching of the phosphorescence of Pt-Ph by VR-1 under N2
atmosphere, monitored at 565 nm. λex = 420 nm, c[Pt-Ph] = 1.0 × 10−5 M in toluene. 20 °C.
radical and the Pt(II) center is small in Pt-0 but larger in Pt-1,
Pt-2, and Pt-3 (Scheme 1). The distance may exert a
significant effect on the electron-exchange interactions. More-
over, the substitution profile of the radicals in Pt-1, Pt-2, and
Pt-3 is unique in each case, which may affect the electron-
exchange sign and magnitude as well. All the complexes were
prepared feasibly with the routine synthesis methods (Scheme
2),40−45 and the yields are moderate to satisfactory.
2.2. UV−Vis Absorption and Luminescence Proper-
ties. The absorption spectra of the parent complex Pt-Ph,
Pt(II) complexes with radical ligands, and the native radicals
were compared (Figure 1). Pt-Ph gives a typical metal-to-
ligand charge transfer (MLCT) absorption band at 424 nm.
For all the Pt(II) complexes studied, this band is clearly
discernible. Upon coordination to the Pt(II) center, the VR-0
radical moiety in Pt-0 shows a marked red-shift to 604 nm as
compared to VR-0 itself, which is assigned to the radical π−π*
transition. This is due to the perturbation upon coordination
on the π-conjugation framework. This interaction may
efficiently mediate the electron-exchange interactions between
the two radical ligands.8 No absorption was observed at a
wavelength longer than 700 nm, indicating that the unpaired
electron is localized on the verdazyl radical; thus, no
intervalence absorption resulted.46 Previously, the N^N PtCl2
complexes (N^N is bidentate verdazyl-substituted pyridine
ligands) were prepared, and a metal-to-radical ligand
absorption band in the range of 550−700 nm was observed.47
For Pt-1, Pt-2, and Pt-3, an intervening phenyl moiety was
used as a linker to attach the radical moiety and the Pt(II)
atoms. There is not much difference between the absorption
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Figure 3. Cyclic voltammogram of the compounds. Ferrocene (Fc) was used as an internal reference. In deaerated CH2Cl2 solution containing 0.5
mM compound with 0.25 mM ferrocene, 0.10 M Bu4N[PF6] as supporting electrolyte, and Ag/AgNO3 as reference electrode; scan rates: 50 mV/s.
20 °C.
spectra of these complexes and the native radical ligands. This
result indicates that there is no perturbation upon coordination
on the radical moiety, which is different from Pt-0.
rate constant was calculated as 1.12 × 1010 M−1 s−1, and the
quenching efficiency was calculated as 89.5%, which indicates
that there is an efficient quenching process between VR-1 and
Pt-Ph. However, the phosphorescence of Pt-Ph has not been
totally quenched, even if VR-1 is 5 equiv compared with Pt-
Ph. Thus, the intermolecular quenching process is less efficient
than the intramolecular quenching process. The calculation
procedure is given in the Supporting Information.
2.3. Electrochemical Studies: Intramolecular Photo-
induced Electron Transfer. The cyclic voltammetry of the
native radicals and complexes was studied (Figure 3). For VR-
0, the reduction potential and the oxidation potential are both
more positive than the other radical ligands. This is due to the
influence of the phenyl part. All the oxidation waves and
reduction waves of the four radicals are reversible, and the
potentials are shown in Table 1.
For Pt-1, Pt-2, and Pt-3 in the cathodic scanning range, two
reversible reduction waves were observed (Figure 3f−h). They
are the sum of the reduction waves of Pt-Ph and the native
radical ligands (Supporting Information, Figure S38b−d). In
the anode region, a quasi-reversible wave was observed. For Pt-
0, there are two reversible reduction waves, which have the
half-wave potential E1/2 of −1.07 and −1.98 V. Comparing the
two waves with the reference complex Pt-Ph and the native
ligand VR-0, it gives a shift of ∼0.15 V (Supporting
Information, Figure S38a). In the anode region, a pseudor-
eversible wave with half-wave potential E1/2 of +0.62 V and an
irreversible wave at +0.42 V were observed. This is also
different from the other Pt(II) complexes. These results
indicate that there is an electronic interaction between the
radical parts and the Pt(II) center in Pt-0. However, in Pt-1,
Pt-2, and Pt-3, there is no such electronic interaction; this is
based on the fact that the reduction potentials of these Pt(II)
complexes are the same as that of the reference compounds.
It is known that the complex Pt-Ph gives phosphorescence
at room temperature (567 nm, ΦP = 42.4%).48 For the
complexes containing radical ligands, however, the phosphor-
escence was completely quenched. This strong quenching
effect may be due to the strong spin-exchange interaction
between the radical and the Pt(II) coordination framework of
the complexes and the formation of “trap states” to enhance
the internal conversion (EIC).18b
Previously the N^N PtCl2 and N^N PdCl2 complexes were
prepared (N^N is pyridine ligand attached with imino
nitroxide radical), and the intermolecular magnetic interaction
was studied. It was stated that the luminescence of the N^N
PtCl2 coordination center was quenched.49 However, the N^N
PtCl2 shows weak intrinsic phosphorescence at 77 K, which is
different from the N^N Pt(II) bis(acetylide) complexes used
in this study; the N^N Pt(II) bis(acetylide) coordination
center is strongly phosphorescent at room temper-
ature.40−42,44,50−53
To confirm that the quenching of the phosphorescence by
the radical is not due to an intermolecular interaction, we
studied the quenching of the phosphorescence of the parent
complex Pt-Ph by the radical compound VR-1 (Figure 2).
With the increasing concentration of VR-1, the intensity of the
phosphorescence band at 565 nm was reduced.
To study the kinetics of the intermolecular quenching
efficiency, the intensity of the phosphorescence band at 565
nm of Pt-Ph was monitored. The Stern−Volmer quenching
constant was calculated as KSV = 1.20 × 104 M−1 (Figure 2c).
The bimolecular quenching constant was calculated as 1.00 ×
1010 M−1 s−1 according to eq S2 in the Supporting
Information. The diffusion-controlled bimolecular quenching
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the photoinduced intermolecular electron transfer between Pt-
Ph and VR-1.
Table 1. Electrochemical Potentials of the Compounds (vs
a
Fc/Fc+)
2.4. Femtosecond Transient Absorption Spectrosco-
py. To study the decay kinetics of the excited states of the
radicals and the corresponding Pt(II) complexes, ultrafast
pump−probe experiments were performed for VR-0, VR-1, p-
VR, and m-VR at the appropriate pump wavelength of 550 nm
(Figure 4), and a white light continuum was used as a probe
beam. According to the steady-state absorption spectra (Figure
1), VR-0 should show a ground-state bleaching (GSB) band
around 550 nm, but it overlaps with the positive signal and
with strong scattered light from the excitation beam (Figure
4a). The positive signal across the probe window is attributed
to the excited-state absorption (ESA). We assign this ESA to
absorption from D1, which decays fast (1.5 ps). No
fluorescence was observed. The decay times of the ESA signal
at 430 nm are compiled in Table 3. The femtosecond transient
absorption spectra of VR-0, p-VR, and m-VR gave similar
results (Figure 4b−d). The doublet excited-state lifetimes of
these verdazyl radicals are ca. 2 ps. To the best of our
knowledge, the excited-state lifetimes of verdazyl radical were
not reported yet. All these stable radicals share a common
feature, that is, the doublet excited state (D1) is short-lived (<3
ps), and they are all nonfluorescent. An aromatic diimide
radical anion has been reported; the doublet excited-state
lifetime is 6 ps.54
Ultrafast pump−probe experiments were also performed for
Pt-Ph at the pump wavelength of 400 nm (Supporting
Information, Figure S39). The positive signal seen from 350 to
750 nm is due to ESA. The bleaching band at 380−450 nm
overlaps with the positive signal, where Pt-Ph gives steady-
state absorption bands. The absorption spectra did not change
in the probe window. By analyzing the decay curves we
determined the ISC process occurs faster than 20 fs (beyond
the resolution of our setup); otherwise, we should detect a
growth of the ESA band at 650 nm. The long-lived transient,
which does not decay in the pump−probe experiment, is due
to ESA from the triplet state, in agreement with the
nanosecond transient absorption spectra (Supporting Informa-
tion, Figure S40).
compound
oxidation, V
reduction, V
VR-0
VR-1
p-VR
m-VR
Pt-0
Pt-1
Pt-2
Pt-3
Pt-Ph
+0.59
+0.47
+0.49
+0.49
+0.42, +0.62
+0.47
+0.44
+0.45
+0.49
−0.91
−1.04
−1.01
−1.01
−1.07, −1.98
−1.04, −1.87
−1.04, −1.91
−1.04, −1.89
−1.87
a
Cyclic voltammetry in deaerated CH2Cl2 containing 0.10 M
Bu4NPF6 as supporting electrolyte; counter electrode is Pt electrode;
working electrode is glassy carbon electrode; Ag/AgNO3 couple as
the reference electrode. c[Ag+] = 0.1 M, 0.5 mM compound with 0.25
mM ferrocene in deaerated CH2Cl2. 25 °C.
This is in agreement with the magnetic property (discussed in
Sections 2.5 and 2.6), which indicates that Pt-0 is a stronger
antiferromagnetic system compared with the other complexes.
For all the complexes, the current for the first reduction is
almost double compared to the second reduction process
(Figure 3e−h). According to the Randles-Sevcik equation
(Supporting Information, eq S6), the magnitude of the current
is directly proportional to the concentration of the electro-
active species. In this work, one molecule contains two
verdazyl ligand moieties and one Pt-bpy moiety (bpy = 4,4′-di-
tert-butyl-2,2′-bipyridine), and thus the reaction concentration
of first reduction process (verdazyl ligand moiety) is double
that of the second reduction process (Pt-bpy moiety). The
redox potentials of the Pt(II) complexes and the native radical
ligands are summarized in Table 1.
The Gibbs free energy changes (ΔGCS) of the photoinduced
electron transfer shown in Table 2 were calculated with the
Table 2. Free Energy Changes of Charge Separation (ΔGCS)
and Charge-Separated States Energy Level (ECS) of the
Compounds in Different Solvents
a
ΔGCS, eV
ECS, eV
The ultrafast transient absorption spectra of Pt-0 in CH2Cl2
were recorded with 400 and 550 nm pumps, which selectively
excite the MLCT band (Figure 5a) and the radical moiety (D0
→ Dn transition, Figure 5b), respectively. With the pump at
400 nm (Figure 5a), the bleaching band at ca. 600 nm overlaps
with the ESA signal, which covers the visible range. In
consideration of the bleaching signals being overlapped with
the ESA signals in both Pt-Ph and Pt-0, the ESA signals are
similar in both cases. Thus, the ESA signal of Pt-0 is assigned
to triplet excited-state absorption. However, the triplet state of
Pt-0 has a dramatically short lifetime, τT = 6.9 ps (Figure 5c),
which is much shorter than the intrinsic T1 state lifetime
(3MLCT, 1.2 μs, Pt-Ph. Supporting Information, Figure S40).
Considering the electron spin-exchange interaction, the short
triplet-state lifetime of the coordination framework can be
explained by the spin-allowed decay of the radical moiety (D1
→ D0).18b,55 The ISC processes of both S1 → T1 and T1 → S0
can be enhanced by the radical unit.56 This significant
quenching of the excited state in the Pt(II) complex is
attributed to the direct link of the π-conjugated radical moiety
to the Pt(II) center, which is different from those of nitroxide
radical labeled chromophores, which may show long-lived
excited states.56−58 With the pump wavelength at 550 nm, the
TOL
DCM
ACN
TOL
DCM
ACN
b
b
b
b
Pt-0
Pt-1
Pt-2
Pt-3
−0.71
−0.24
−0.35
−0.26
−0.99
−0.86
−0.89
−0.86
−0.71
−1.07
−1.03
−1.03
−1.03
−0.90
+1.48
+1.96
+1.85
+1.93
+2.17
+1.20
+1.34
+1.31
+1.33
+1.48
+1.13
+1.17
+1.16
+1.17
+1.30
3Pt-Ph*→VR-1 −0.03
a
The emissive T1 state of Pt-Ph was used as the E00 value for the
b
calculation of the ΔGCS values. Direction of intramolecular electron
3
transfer is Pt* → radical. TOL stands for toluene, DCM stands for
dichloromethane, and ACN stands for acetonitrile.
Rehm−Weller equation (Supporting Information, eq S7). The
calculation procedure is given in the Supporting Information.
The free energy changes are negative values, even in a low-
polar solvent such as toluene. With the increase of solvent
polarity, the free energy changes become more negative. This
indicates in these complexes that it may have photoinduced
intramolecular electron transfer and that it should be more
significant in a highly polar solvent. Intermolecular photo-
induced electron transfer was also studied, and the ΔGCS
values were also shown in Table 2. The negative value indicates
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Figure 4. Femtosecond transient absorption spectra at different delay times of compounds. (a) VR-0, (b) VR-1, (c) p-VR, and (d) m-VR. Decay
curves of (e) VR-0, (f) VR-1, and (h) m-VR at 430 nm. Decay curve of (g) p-VR at 420 nm. λex = 550 nm, in toluene at 20 °C.
Table 3. Lifetimes of ESA of Different Compounds in
Ultrafast Pump−Probe Experiments
lifetime is longer than that of the native radical ligands (τD = 2
ps). The difference between the lifetimes can be due to the
coordination of the radical ligands to the Pt(II) center.
The ultrafast transient absorption spectra of Pt-2 and Pt-3 in
CH2Cl2 were recorded upon excitation with a 400 and 550 nm
pump (Supporting Information, Figures S41 and S42). The
photophysical processes are similar to those of Pt-1. The
kinetics in each case is given in the Supporting Information,
Table S1. The photophysical processes of the complexes and
the radical ligands are summarized in Scheme 3. Although the
spin−spin exchange interaction of the Pt complexes is
antiferromagnetic, the exchange is not strong (see below).
Thus, the singlet and triplet states due to the spin exchange of
the two radical ligands are energetically close to each other.
The states with almost equal energies are shown in the light
blue background (Scheme 3).
2.5. EPR Spectroscopy and the Magnetic Suscepti-
bility: Intramolecular Magnetic Interactions between
the Radical Ligands. The continuous-wave (CW) EPR
spectra of the radical ligands in fluid solution at room
temperature were first recorded (Figure 7). The radical ligands
show the typical hyperfine coupling (hfc) pattern, due to the
four 14N nuclei that are not equivalent in pairs. The spin-
Hamiltonian system is
compound
τ, ps (λex = 400 nm)
τ, ps (λex = 550 nm)
a
VR-0
VR-1
b
b
b
b
e
1.5
2.1
2.7
2.2
b
a
c
p-VR
a
m-VR
d
Pt-Ph
d
f
f
Pt-0
Pt-1
6.9
9.0
7.5
d
g
h
9.9 (86%)/1300 (14%)
a
b
c
Decay traces at 430 nm, in toluene. Not measured. Decay traces at
d
e
f
420 nm, in toluene. In CH2Cl2. Not observed. Decay traces at 500
nm. Decay traces at 460 nm. Decay traces at 440 nm.
g
h
radical moiety was excited (Figure 5b). By analyzing the decay
trace at 500 nm we obtained the excited-state lifetime: τ = 9.0
ps. This signal can be attributed to the D1 state of a radical
moiety in complex.
The ultrafast transient absorption spectra of Pt-1 in CH2Cl2
were also recorded upon two different excitation wavelengths
(Figure 6). With the pump wavelength at 400 nm (Figure 6a),
the MLCT band was selectively excited. The decay trace of the
ESA band of Pt-1 obtained at 460 nm contains two time
components (Figure 6c). The long component is 1300 ps
(14%), which is assigned to the quenched triplet state. The
short component is 9.9 ps (86%), which is assigned to the
lifetime of the D1 state of the radical. The absorption spectrum
at 21.4 ps delay time is the ESA from the T1 state, similar to
the ESA of Pt-0 (τT = 6.9 μs), considering the bleaching band
is overlapped with ESA band. With the pump wavelength at
550 nm (Figure 6b), the radical moiety is selectively excited.
The lifetime obtained by monitoring the decay at 440 nm is 7.5
ps, which is attributed to the D1 state of the radical. This
2
4
H = gμ S +
a SI +
a SI
N2 i
∑
∑
N1
i
B
(1)
i=1
i=3
1
2
where S = , and I = 1. The g factor and the hfc constants were
summarized in Table 4. These results are similar to those
observed for the oxoverdazyl radicals.59
The CW-EPR of the complexes in solution was also studied
(Figure 8). The EPR spectra of the complexes are shown
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Figure 5. (a, b) Femtosecond transient absorption spectra at different delay times; (c, d) decay curves at 500 nm of Pt-0. (a, c) λex = 400 nm (S0 →
1MLCT), (b, d) λex = 550 nm (D0 → D1). In CH2Cl2 at 20 °C.
Figure 6. (a, b) Femtosecond transient absorption spectra at different delay times; decay curves at (c) 460 and (d) 440 nm of Pt-1. (a, c) λex = 400
1
nm (S0 → MLCT). (b, d) λex = 550 nm (D0 → D1). In CH2Cl2. 20 °C.
the radical for the liquid solution is small. As will be shown
below for the frozen solution, both the shape of the spectrum
and the temperature dependence of the signal intensity
demonstrate the manifestation of exchange interactions
between radicals. The presence of the impurities of
monoverdazyl radical masks it in the spectra of the liquid
solution.
Scheme 3. Simplified Jablonski Diagram to Illustrate the
Photophysical Processes of the Native Radicals and the Pt
a
Complexes
We selected Pt-0 for a detailed study of the intramolecualr
electron spin-exchange interactions between the radicals
(Figure 9). The Pt-0 sample was dissolved in toluene and
liquid crystal 5CB with a concentration of 1 mM (Supporting
Information, Figure S43). In both cases there is the impurity of
monoverdazyl radical (monoVR). The shape of the EPR
spectra of Pt-0 in toluene is broad due to there being different
configurations of the molecule. Therefore, we used liquid
crystal 5CB as the matrix, which is oriented in a magnetic field.
The temperature dependence of the EPR integral intensity was
fitted by eq 2 (Figure 9b)
a
Key: S, D, T, and Q represent the singlet, doublet, triplet, and
quintet states, respectively. Pt-bpy represents Pt with the 4,4′-di-tert-
butyl-2,2′-bipyridine ligand moiety. R represents the oxoverdazyl
radical ligand moiety. The star (*) represents which moiety was
excited. 1Pt-bpy and 3Pt-bpy represent 1MLCT and 3MLCT,
respectively.
1
EPR intensity ≈
kT(3 + exp(−J/kT))
(2)
together with the spectra of the radicals, and they practically do
not differ from them apart from the width of the signals. An
exception is Pt-0, but the difference of the Pt-0 spectrum from
where J is the parameter of the isotropic exchange interaction,
and T is temperature. From a fitting of experiment data with an
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Figure 7. EPR spectra (black) and simulation (red) of (a) VR-0, (b) VR-1, (c) p-VR, and (d) m-VR. c = 1.0 × 10−4 M in 2-methyltetrahydrofuran.
20 °C.
netic coupling J = −29.73 0.03 cm−1.6 Recently a N^C^N
Table 4. Spin-Hamiltonian Parameters of Radicals in Fluid
Solution of Toluene
Pt(II) acetylide complex containing an NN radical acetylide
ligand was prepared,28 but the complex molecule contains only
a single radical; thus, the intramolecular magnetic interactions
between radical ligands is not applicable to the complex.
Previously N^N Pt(II)/Pd(II) bispyrdine complexes were
prepared with the nitronyl nitroxide radical attached on the
pyridine ligand. Despite the small intramolecular distance
between the radicals, no magnetic interaction between the
radicals was observed.27 Intramolecular magnetic coupling
between the two coordinated NN radicals in a trans-Pt(II)
bis(phosphine) bisacetylide complexes was studied, and it was
found that the exchange interaction through the diamagnetic
Pt(II) atom is weak (|J| < 1 cm−1).21 The intramolecular
parameters
VR-0
VR-1
p-VR
m-VR
g
0.0005
2.0037
17.78
13.53
2.0038
17.59
13.14
2.0037
17.55
13.15
2.0038
17.63
13.07
aN1 (MHz) 0.005
aN2 (MHz) 0.005
isolated two-spin model (H = −J S1S2), J = −5.4 0.1 cm−1
was obtained, that is, antiferromagnetic interaction. Previously
the intramolecular magnetic coupling of benzene-bridged
verdazyl diradicals were studied, and the results show that
the meta-diradical shows a ferromagnetic coupling of J = 19.3
1.7 cm−1, whereas the para-diradical shows antiferromag-
Figure 8. EPR spectra of (a) Pt-0, (b) Pt-1, and (c) Pt-2. c = 1.0 × 10−4 M in toluene. 20 °C.
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Figure 9. (a) Temperature dependence of the CW-EPR spectra of Pt-0. The impurity of the mono-VR-0 is not shown; (b) temperature
dependence of the EPR integral intensity. (inset) Temperature dependence of the product of the EPR integral intensity and of temperature. In
liquid crystal 5CB, c = 1.0 × 10−3 M.
Figure 10. (a) Temperature dependence of the χMT products for Pt-0, Pt-1, and Pt-3; the solid lines represent the fitting curves with the spin-
Hamiltonian H = −J S1S2. (b) Isothermal magnetization curves for Pt-1 at 3, 4, and 5 K.
magnetic interaction between the two NN radicals in a N^N
Pd(II) bis(nitronyl nitroxide) complex was reported to be
antiferromagnetic, J/kB = −36 K.46 A trans Ru(II) bisacetylide
complex [Ru(dppe)(−CC−R)2] (dppe = 1,2-bis-
(diphenylphosphino)ethane, R = p-phenyl oxoverdazyl radicals
or p-phenyl NN radicals) was prepared, and it was found that
the magnetic coupling between the two NN radicals through
the dimagnetic Ru(II) unit is antiferromagnetic (J = −2 cm−1
for the NN radical and J = −4 cm−1 for the verdazyl radical).60
To the best of our knowledge, for the first time the
photophysical property and the electron-spin exchange
interaction of the radical ligands in a N^N Pt(II) bisacetylide
complex were studied.
The variable-temperature magnetic susceptibility measure-
ment for Pt-0, Pt-1, andPt-3 were investigated in the
temperature range of 2−300 K under 1 kOe dc field (Figure
10). The experimental χMT values for the three complexes at
room temperature are 0.74, 0.75, and 0.74 cm3 mol−1 K,
respectively, which are consistent with the expected value of
0.75 cm3 mol−1 K for two S = 1/2 spins with g = 2. As shown
in Figure 10a, when cooled, the χMT values gradually go down
in a wide temperature range from 300 to 25 K for Pt-0 and
from 300 to 50 K for Pt-1 and Pt-3. Below 25 or 50 K, the χMT
values show a sharper decrease, reaching 0.52, 0.40, and 0.46
cm3 mol−1 K at 2 K for the three complexes, respectively. The
temperature dependence of χMT products was fitted with spin-
Hamiltonian H = −J S1S2 (Figure 10). The exchange coupling
constant J was obtained as −0.57 × 10−3 cm−1 (g = 1.97),
−0.28 × 10−3 cm−1 (g = 2.00), and −0.60 × 10−3 cm−1 (g =
1.99) for Pt-0, Pt-1, and Pt-3, respectively, indicating the
antiferromagnetic interaction in all three complexes. Variable-
temperature variable-field (VTVH) measurements were
performed on Pt-1 (Figure 10b). The isothermal curves
show negligible nonsuperposition, suggesting the absence of
zero-field splitting. The plots of 1/χM versus T can be well-
fitted by the Curie−Weiss law (Supporting Information, Figure
S44), yielding C = 0.67 °C, θ = −2.02 K for Pt-0, C = 0.77 °C,
θ = −5.02 K for Pt-1, C = 0.68 °C, θ = −4.16 K for Pt-3. It
should be mentioned that these data were obtained with
powder samples, which are different from that for the EPR
measurement (in frozen solutions) and density functional
theory (DFT) computations (see below, for individual
molecules, in vacuum); the intermolecular interaction may
also play a part and influence the fitting coupling constants.
2.6. DFT Computations: The Electron Exchange
Interactions between the Radical Ligands. To study the
intramolecular magnetic (spin) exchange interaction of the
diradicals, we performed unrestricted DFT calculations for
different spin states of the diradicals investigated. For the
oxoverdazyl radical ligands (Figure 11), the spin density
surfaces are similar to those of the previous report,6 and
significant spin leakage to the phenyl linker or the ethynyl
moiety was observed, which is important for the intramolecular
magnetic coupling either through Pt(II) or through space.
J
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tilted. The calculated highest occupied molecular orbital
(HOMO) energy levels (−3.72, −3.83, −3.78, and −3.78 eV
for Pt-0, Pt-1, Pt-2, and Pt-3, respectively) are consistent with
the order of oxidation potential (Pt-0 < Pt-2 ≈ Pt-3 < Pt-1).
The spin density surfaces of the singlet open shell, triplet,
and quintet states of Pt-0 and Pt-3 were also calculated (Figure
12). As expected, the spin density surfaces of the singlet and
triplet diradical open-shell states are localized on the ligands,
with no leakage to the N^N ligand moiety.
Pt-3 has both p-VR and m-VR radicals, which show similar
geometries and spin densities with Pt-1 and Pt-2 (Supporting
Information, Figure S45). Interestingly, in the case of the
triplet state of antiferromagnetic systems (Pt-0, Pt-1, Pt-2, and
Pt-3) we observed a spin density value at Pt(II). The spin
densities at Pt(II) are −9.7 × 10−3, −1.0 × 10−3, 1.4 × 10−3,
and 8.1 × 10−5 bohr−3 for the triplet states of Pt-0, Pt-1, Pt-2,
and Pt-3, respectively. The contribution of Pt(II) to the spin
density surface in Pt-0 is ∼10 times more than that of other
complexes. This result implies that the intramolecular magnetic
coupling interaction in Pt-0 would be stronger than those in
other complexes. Furthermore, the larger separation of the
radicals in Pt-1, Pt-2, and Pt-3 also makes the magnetic
coupling interaction in those systems much weaker than that in
Pt-0. The amount of separation can be analyzed by considering
the sum of linked bond lengths between radicals. For example,
the linked bonds between the radicals in Pt-0 are composed of
two C−N, two C−C, two CC, and two C−Pt. In this way,
the sum of the bond lengths in Pt-1, Pt-2, and Pt-3 is longer
(23.2, 20.5, and 21.8 Å for Pt-1, Pt-2, and Pt-3, respectively)
than that in Pt-0 (11.9 Å). This result is in good agreement
with the tendency of the calculated J values of the complexes (J
= −4.552, − 0.018, −0.097, and −0.680 cm−1 for Pt-0, Pt-1,
Pt-2, and Pt-3, respectively, although the J values depend not
only on bond lengths), in that Pt-0 is a strong antiferro-
magnetic system and the other complexes are a weakly coupled
system. The calculated J value of Pt-0 is close to the
experimental results, J = −5.4 0.1 cm−1.
Figure 11. Geometric structure and isosurfaces of the spin density of
(a) VR-0, (b) VR-1, (c) p-VR, and (d) m-VR. Calculated with the
Gaussian 09 program at the UB3LYP/6-31G(d) level.
The optimized geometries of Pt-0 and Pt-3 are shown in
Figure 12. The optimized geometries and spin density surfaces
of Pt-1 and Pt-2 are similar to those of Pt-3 depending on the
variance of the radicals (Supporting Information, Figure S45).
As shown in Figure 12, the optimized geometries of the N^N
Pt(II) bisacetylide complexes varied for different radicals. VR-0
and m-VR are coplanar with the Pt(II) coordination center,
while p-VR is tilted. The coplanar complexes show the
delocalization of π-electrons and account for the result of the
electrochemical potentials in Table 1. On the one hand, the Pt-
0 and Pt-2 have a coplanar geometry between radical ligands
and the Pt(II) moiety; on the other hand, both radical ligands
are tilted in Pt-1. In Pt-3, only one radical ligand (p-VR) is
Figure 12. Geometric structure and isosurfaces of the spin density of singlet open shell, lowest triplet, and quintet states (Q1) of (a) Pt-0 and (b)
Pt-3. Calculated with the Gaussian 09 program at the (U)B3LYP/6-31G(d) level for C, N, H, and O and at the (U)B3LYP/LanL2DZ level for Pt.
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Table 5. Dihedral Angles (deg) between the Pt(II) Coordination Center and Radical Ligands
electronic state
Pt-0
Pt-1
Pt-2
Pt-3
S0
11.35/11.34
11.37/11.37
33.25/−41.87
3.72/3.72
−79.09/−79.09
−79.09/−79.09
−31.27/−11.36
−5.45/−5.45
−15.12/−15.11
−15.12/−15.12
−10.18/−14.81
−13.10/−13.09
−14.58/−48.46
−15.29/−76.25
−16.73/−45.21
−13.71/−9.36
T0
T1
Q1
The quenched triplet state of the complexes by the presence
of the radical ligands can be understood by the coplanar
geometry in the quintet state (Figure 12). We inferred that the
planarity of complexes contributes the π-conjugation system
and induces strong electron-exchange interaction. To check
the effect of planarity on the magnitude of exchange coupling,
we calculated |J| values of complexes according to the rotation
along the C(sp)-C(sp2) bond, which connects the tetrazine (in
Pt-0) or phenyl (in Pt-1, Pt-2, and Pt-3) to the acetylide
ligand with dihedral angle of 0, 30, 60, 90, 120, 150, and 180°.
According to this calculation, the |J| value was found to
increase with the molecular tendency to adopt coplanar
geometry (Supporting Information, Figure S46). This is
beneficial for enhancing the ISC and may be responsible for
the fast decay of the triplet state of the Pt(II) coordination
center (no triplet state was observed for the complexes with
nanosecond transient absorption spectra).56,61 The dihedral
angles between the Pt(II) coordination center and the radical
ligands may also be related to the kinetics of the ISC. As seen
in Table 5, the arrangement of radical ligands showing more
planarity in lowest singlet (S0), lowest triplet (T0), and the
quintet (Q1) states of Pt-0 may cause the relatively faster ISC
in comparison with Pt-1, Pt-2, and Pt-3. The dihedral angles in
the T1 state of Pt-1, Pt-2, and Pt-3 are significantly reduced
compared with the T0 states. Thus, Pt-1, Pt-2, and Pt-3 may
also have a fast ISC through the T1.
exchange was successfully reproduced with DFT computations.
Our results show that, when radicals directly connect to a
Pt(II) center or with a phenyl linker, the radicals give a weak
antiferromagnetic interaction and also a short excited-state
lifetime in the N^N Pt(II) bisacetylide complexes. These
observations are useful for the further design of radical-
containing transition complexes with longer linkers for
optomagnetic applications.
4. EXPERIMENTAL SECTION
4.1. General Methods. Solvents were dried before used for
synthesis. Carbohydrazide and pyridinium tosylate were purchased
from Beijing Ouhe Technology Co., Ltd. 3-Trimethylsilylpropynal
was purchased from J&K Scientific Ltd. K2PtCl4 was purchased from
Aladdin Chemical Co., Ltd. 4-Ethynyl-benzaldehyde, 3-ethynyl-
benzaldehyde, and 2-ethynyl-benzaldehyde were synthesized accord-
ing to literature methods.62,63 Dichloro(4,4′-di-tert-butyl-2,2′-
bipyridine)platinum(II) (7) was synthesized according to a literature
method.64
All chemicals were analytically pure and used as received. NMR
spectra were recorded by a Bruker Avance II 400 spectrometer with
deuterated dimethyl sulfoxide (DMSO-d6) and CDCl3 as solvent and
tetramethylsilane (TMS) as standard at 0.00 ppm. High-resolution
mass spectrometry (HRMS) was accomplished with a time-of-flight
(TOF) mass spectrometer (Agilent), Q-TOF mass spectrometer
(Waters), a and matrix-assisted laser desorption/ionization (MALDI)
micro MALDI TOF mass spectrometer (Waters). Elemental analyses
(C, H, and N) were performed on a PerkinElmer model 240C
elemental analyzer. The Fourier transform infrared (FT-IR) spec-
troscopy was recorded on a Thermo Fisher Infrared Spectrometer
(6700) with a KBr disk. Absorption spectra were recorded on a
UV2550 UV−vis spectrophotometer (Shimadzu Ltd.). Luminescence
spectra were measured on an RF5301 PC spectrofluorometer
(Shimadzu Ltd.).
4.2. General Methods to Synthesize Pt-0, Pt-1, and Pt-2.
Complex 7 (80 mg, 0.15 mmol), verdazyl radical (132 mg, 0.375
mmol), and CuI (6 mg, 0.03 mmol) were dissolved in the mixture of
CH2Cl2 (15 mL) and i-Pr2NH (3 mL) under Ar. Then the mixture
was stirred for 4 h at RT. After the reaction was finished, water (20
mL) was added. The aqueous layer was extracted with CH2Cl2. The
combined organic layers were dried over anhydrous Na2SO4. The
solvent was removed under reduced pressure. The residue was
purified by column chromatography (silica gel, eluent: CH2Cl2/
MeOH = 100:1, v/v, for Pt-0; CH2Cl2 for Pt-1 and Pt-2). Pt-0 was
collected as a green solid (110 mg, 0.11 mmol), yield: 72.5%.
MALDI-TOF-HRMS ([C50H44N10O2P]−): calcd m/z 1011.3297,
found m/z 1011.3274. FT-IR (KBr, cm−1): 3434, 3066, 2961, 2925,
2119, 1696, 1618, 1487, 1417, 1316, 1217, 1175, 1121, 1029, 849. mp
> 250 °C. Elem. Anal. [C50H44N10O2Pt + 0.1 CH2Cl2 + C6H14],
calcd: C, 60.88; H, 5.30; N, 12.66; found: C, 60.89; H, 5.09; N,
12.34%. Pt-1 was obtained as a green solid (110 mg, 0.09 mmol),
yield: 63.0%. MALDI-TOF-HRMS ([C62H52N10O2Pt]−): calcd m/z
1163.3923, found m/z 1163.3898. FT-IR (KBr, cm−1): 3435, 3069,
2963, 2925, 2110, 1699, 1601, 1486, 1410, 1300, 1246, 1173, 1122,
1028, 845. mp > 250 °C. Elem. Anal. [C62H52N10O2Pt + 0.1 CH2Cl2
+ 0.9 C6H14], calcd: C, 64.84; H, 5.22; N, 11.20; found: C, 65.16; H,
4.85; N, 11.08%. Pt-2 was obtained as a green solid (129 mg, 0.11
mmol), yield: 74.0%. MALDI-TOF-HRMS ([C62H52N10O2Pt]−):
calcd m/z 1163.3923, found m/z 1163.3937. FT-IR (KBr, cm−1):
3438, 3064, 2961, 2926, 2106, 1700, 1617, 1485, 1416, 1298, 1250,
3. CONCLUSION
We prepared a series of N^N Pt(II) bis(acetylide) complexes
with oxoverdazyl radical acetylide ligands; the aim of this work
is to study the intramolecular electron spin−spin exchange
interaction between the radical ligands of the Pt(II) complexes
and the effect of the electron spin of the stable radical on the
photophysical properties of phosphorescent Pt(II) coordina-
tion framework. Steady-state and time-resolved transient
optical spectroscopies, EPR spectroscopy, as well as DFT
computations were used to characterize the complexes. We
found that the length of the linker between the Pt(II) center
and the spin carrier exerts a significant effect on the
photophysical property and the magnetic property of the
complexes. The intrinsic long-lived triplet excited state (τT =
1.2 μs) of the Pt(II) coordination center was efficiently
quenched by the presence of the radical (τT = 6.9 ps for Pt-0),
and the doublet excited state of the radicals was found to be
short-lived (τD ≈ 2 ps) and nonfluorescent. The intramolecular
electron-exchange interaction between the radical ligands
through the diamagnetic Pt(II) was studied with EPR. With
a shorter linker between the Pt(II) center and the oxoverdazyl
radical ligands, antiferromagnetic interaction between the two
radical ligands was observed (J = −5.4 0.1 cm−1); thus, the
ground state is a singlet state (S0 state), and a triplet state (T0
state) lies slightly above it. For the complexes with larger inter-
radical distance, however, very weak intramolecular spin
exchange between the radical ligands was observed (|J| < 0.7
cm−1). The sign and the magnitude of the electronic spin−spin
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1162, 1119, 1028, 848. mp 221.3−222.2 °C. Elem. Anal.
[C62H52N10O2Pt + 0.9 C6H14], calcd: C, 65.19; H, 5.24; N, 11.28;
found: C, 65.53; H, 4.82; N, 10.89%.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01575.
■
sı
4.3. Synthesis of Pt-3. Complex 7 (80 mg, 0.15 mmol), p-VR
(53 mg, 0.15 mmol), m-VR (53 mg, 0.15 mmol), and CuI (6 mg, 0.03
mmol) were dissolved in the mixture of CH2Cl2 (15 mL), and i-
Pr2NH (3 mL) was added under Ar atmosphere. Then the mixture
was stirred for 4 h at RT. After the reaction was finished, water (20
mL) was added. The aqueous layer was extracted with CH2Cl2. The
combined organic layers were dried over anhydrous Na2SO4. The
solvent was removed under reduced pressure. The residue was
purified by column chromatography (silica gel, eluent: CH2Cl2). Pt-3
was obtained as a brown solid (113 mg, 0.10 mmol), yield: 64.8%.
MALDI-TOF-HRMS ([C62H52N10O2Pt]−): calcd m/z 1163.3923,
found m/z 1163.3906. FT-IR (KBr, cm−1): 3435, 3066, 2964, 2927,
2109, 1699, 1618, 1485, 1409, 1299, 1248, 1172, 1121, 1030, 845. mp
195.9−197.2 °C. Elem. Anal. [C62H52N10O2Pt + 0.1 CH2Cl2 + 0.8
C6H14], calcd: C, 64.71; H, 5.15; N, 11.28; found: C, 64.73; H, 4.88;
N, 11.46%.
4.4. Cyclic Voltammetry. Cylic voltammetry was performed
under a 50 mV/s scan rate, in a CHI610D electrochemical
workstation. The measurements were performed at room temperature
with tetrabutylammonium haxafluorophosphate (Bu4N[PF6], 0.1 M)
as the supporting electrolyte, glassy carbon electrode as the working
electrode, and platinum electrode as the counter electrode. Dichloro-
methane was used as the solvent, and ferrocene (Fc) was added as the
internal reference. The solution was purged with N2 before
measurement, and the N2 gas flow was kept constant during the
measurement.
4.5. Femtosecond Transient Absorption Spectroscopy. The
transient absorption (TA) spectra were measured by optical
femtosecond pump−probe spectroscopy. The output of a mode-
locked Ti-sapphire amplified laser system (Spitfire Ace, Spectra-
Physics) with a wavelength of 800 nm, pulse width of 35 fs, repetition
rate of 1 kHz, and average power of 4 W was split into two beams
(10:1). The strong beam was converted into UV−vis−IR in the range
of 240−2400 nm by use of an Optical Parametric Amplifier (TOPAS,
Light Conversion) and used as a pump beam. The weaker beam after
passing a variable delay line (up to 6 ns) was focused in a 3 mm
thickness rotated CaF2 plate to produce a white light continuum
(WLC), which was used as a probe beam. A home-built pump−probe
setup was used for obtaining the transient absorption spectra and
kinetics.
The relative polarization direction between the pump and probe
beams was set to the magic angle (54.7°) to avoid the effect of the
molecular rotational diffusion on kinetics. The entire setup was
controlled by a personal computer (PC) with the help of LabView
software (National Instruments). All measurements were performed
at room temperature under aerated conditions. The experimental data
were fitted to a multiexponential decay function deconvoluted with
the instrument response function. The overall time resolution was
∼20−30 fs.
Experimental procedures, nanosecond and femtosecond
transient absorption experimental details, molecular
structure characterization, additional spectra (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
Jianzhang Zhao − State Key Laboratory of Fine Chemicals,
School of Chemical Engineering, Dalian University of
Technology, Dalian 116024, P. R. China; orcid.org/0000-
0002-5405-6398; Phone: +8641184986236;
Email: zhaojzh@dlut.edu.cn
Violeta K. Voronkova − Zavoisky Physical-Technical Institute,
FRC Kazan Scientific Center of RAS, Kazan 420029, Russia;
Email: vio@kfti.knc.ru
Jin Yong Lee − Department of Chemistry, Sungkyunkwan
University, Suwon 16419, South Korea; orcid.org/0000-
0003-0360-5059; Email: jinylee@skku.edu
Haoling Sun − Department of Chemistry and Beijing Key
Laboratory of Energy Conversion and Storage Materials, Beijing
Normal University, Beijing 100875, P. R. China; orcid.org/
0000-0002-2112-4331; Email: haolingsun@bnu.edu.cn
Gagik G. Gurzadyan − Institute of Artificial Photosynthesis,
State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian 116024, P. R. China; orcid.org/0000-
0003-0299-5120; Phone: +8641184986489;
Email: gurzadyan@dlut.edu.cn
Authors
Wenbo Yang − State Key Laboratory of Fine Chemicals, School
of Chemical Engineering, Dalian University of Technology,
Dalian 116024, P. R. China; orcid.org/0000-0003-2156-
0560
Andrei A. Sukhanov − Zavoisky Physical-Technical Institute,
FRC Kazan Scientific Center of RAS, Kazan 420029, Russia
Jong Hyeon Lim − Department of Chemistry, Sungkyunkwan
University, Suwon 16419, South Korea
Xiaoxin Li − Institute of Artificial Photosynthesis, State Key
Laboratory of Fine Chemicals, Dalian University of Technology,
Dalian 116024, P. R. China
Yinshan Meng − State Key Laboratory of Fine Chemicals,
School of Chemical Engineering, Dalian University of
Technology, Dalian 116024, P. R. China; orcid.org/0000-
0001-9963-4596
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c01575
4.6. Electron Paramagnetic Resonance Spectroscopy. The
CW-EPR spectra were recorded at room temperature using an Elexsys
E-580 spectrometer (Bruker) at the X-band, with a 100 kHz field
modulation. The temperature dependence of the EPR spectra in the
temperature range of 4−100 K was studied with a helium-flow
cryostat (Oxford Instruments).
4.7. Theoretical Computations. The DFT calculations were
performed using the Becke’s three parametrized Lee−Yang−Parr
(B3LYP) exchange correlation functional with the LanL2DZ effective
core potential for Pt and 6-31G* basis sets for the other atoms.
Singlet, triplet, and quintet spin states were considered for the
diradicals investigated. All the calculations were done by a suite of
Gaussian 09 programs.65
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
W.Y. thanks the National Natural Science Foundation of China
(NSFC) (21902020) for financial support. J.Z. thanks the
NSFC (21673031, 21761142005, and 21911530095) and the
State Key Laboratory of Fine Chemicals (ZYTS201901) for
financial support. J.Y.L. acknowledges the financial support by
the National Research Foundation grants funded by the
Korean government (2016R1A2B4012337). A.A.S. and V.K.V.
acknowledge the financial support from the government
M
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Article
Bis(hexafluoroacetylacetonato)manganese(II) with Diazodi(4-
pyridyl)methane in the Cis and Trans Configurations as Repeating
Units. J. Am. Chem. Soc. 1998, 120, 10080−10087.
assignment for FRC Kazan Scientific of RAS and Mega-grant
No. 14.W03.31.0028.
(18) (a) Cho, D.; Ko, K. C.; Lee, J. Y. Quantum Chemical
Approaches for Controlling and Evaluating Intramolecular Magnetic
Interactions in Organic Diradicals. Int. J. Quantum Chem. 2016, 116,
578−597. (b) Huang, Y.; Xu, Z.; Jin, S.; Li, C.; Warncke, K.;
Evangelista, F. A.; Lian, T.; Egap, E. Conjugated Oligomers with
Stable Radical Substituents: Synthesis, Single Crystal Structures,
Electronic Structure, and Excited State Dynamics. Chem. Mater. 2018,
30, 7840−7851.
(19) Garakyaraghi, S.; Crapps, P. D.; McCusker, C. E.; Castellano, F.
N. Cuprous Phenanthroline MLCT Chromophore Featuring
Synthetically Tailored Photophysics. Inorg. Chem. 2016, 55, 10628−
10636.
REFERENCES
■
(1) Abe, M. Diradicals. Chem. Rev. 2013, 113, 7011−7088.
(2) Gallagher, N. M.; Olankitwanit, A.; Rajca, A. High-Spin Organic
Molecules. J. Org. Chem. 2015, 80, 1291−1298.
(3) Brook, D. J. R.; Abeyta, V. Spin Distribution in Copper(I)
Phosphine Complexes of Verdazyl Radicals. J. Chem. Soc., Dalton
Trans. 2002, 4219−4223.
(4) Suzuki, S.; Wada, T.; Tanimoto, R.; Kozaki, M.; Shiomi, D.;
Sugisaki, K.; Sato, K.; Takui, T.; Miyake, Y.; Hosokoshi, Y.; Okada, K.
Cyclic Triradicals Composed of Iminonitroxide−Gold(I) with
Intramolecular Ferromagnetic Interactions. Angew. Chem., Int. Ed.
2016, 55, 10791−10794.
(5) Johnston, C. W.; McKinnon, S. D. J.; Patrick, B. O.; Hicks, R. G.
The First ″Kuhn Verdazyl″ Ligand and Comparative Studies of Its
PdCl2 Complex with Analogous 6-Oxoverdazyl Ligands. Dalton Trans.
2013, 42, 16829−16836.
(6) Gilroy, J. B.; McKinnon, S. D. J.; Kennepohl, P.; Zsombor, M. S.;
Ferguson, M. J.; Thompson, L. K.; Hicks, R. G. Probing Electronic
Communication in Stable Benzene-Bridged Verdazyl Diradicals. J.
Org. Chem. 2007, 72, 8062−8069.
(7) Okada, K.; Imakura, T.; Oda, M.; Murai, H.; Baumgarten, M.
10,10’-(m- and p-Phenylene)diphenothiazine Dications: Violation of a
Topology Rule in Heterocyclic High-Spin π-Systems. J. Am. Chem.
Soc. 1996, 118, 3047−3048.
(20) Lazorski, M. S.; Castellano, F. N. Advances in the Light
Conversion Properties of Cu(I)-Based Photosensitizers. Polyhedron
2014, 82, 57−70.
(21) Stroh, C.; Mayor, M.; von Hanisch, C.; Turek, P. Intra-
molecular Exchange Interaction in Twofold Spin-Labelled Platinum
Complexes. Chem. Commun. 2004, 2050−2051.
(22) Wong, W.-Y.; Ho, C.-L. Di-, Oligo- and Polymetallaynes:
Syntheses, Photophysics, Structures and Applications. Coord. Chem.
Rev. 2006, 250, 2627−2690.
(23) Zhou, G.-J.; Wong, W.-Y. Organometallic Acetylides of PtII, AuI
and HgII as New Generation Optical Power Limiting Materials. Chem.
Soc. Rev. 2011, 40, 2541−2566.
(8) Brook, D. J. R.; Yee, G. T.; Hundley, M.; Rogow, D.; Wong, J.;
Van-Tu, K. Geometric Control of Ground State Multiplicity in a
Copper(I) Bis(verdazyl) Complex. Inorg. Chem. 2010, 49, 8573−
8577.
(9) Oshio, H.; Watanabe, T.; Ohto, A.; Ito, T.; Nagashima, U. Fairly
Strong Ferromagnetic Interactions between Imino Nitroxide Ligands
through a Diamagnetic CuI Ion in [CuI(im-mepy)2](PF6). Angew.
Chem., Int. Ed. Engl. 1994, 33, 670−671.
(10) Barclay, T. M.; Hicks, R. G.; Lemaire, M. T.; Thompson, L. K.
Weak Magnetic Coupling of Coordinated Verdazyl Radicals through
Diamagnetic Metal Ions. Synthesis, Structure, and Magnetism of a
Homoleptic Copper(I) Complex. Inorg. Chem. 2001, 40, 6521−6524.
(11) Green, M. T.; McCormick, T. A. Controlling the Singlet−
Triplet Splitting in Bisverdazyl Diradicals: Steps toward Magnetic
Polymers. Inorg. Chem. 1999, 38, 3061−3065.
(12) Kitano, M.; Ishimaru, Y.; Inoue, K.; Koga, N.; Iwamura, H.
Exchange Interaction in Metal-Radical Systems: Chloro(meso-
t e t r a p h e n y l p o r p h y r i n a t o ) c h r o m i u m ( I I I ) ’ s a n d
(Hexafluoroacetylacetonato)manganese(II) Ligated with 3- and 4-
(N-Oxy-N-tert-butylamino)pyridines. Inorg. Chem. 1994, 33, 6012−
6019.
(13) Ishimaru, Y.; Kitano, M.; Kumada, H.; Koga, N.; Iwamura, H.
Regiospecificity in the Exchange Coupling of the Spins of Copper(II)
Ion Coordinated with the Ring Nitrogen Atoms and N-tert-
Butylaminoxyl Radical Attached as a Substituent on the Pyridine
and N-Phenylimidazole Rings. Inorg. Chem. 1998, 37, 2273−2280.
(14) Oshio, H.; Watanabe, T.; Ohto, A.; Ito, T.; Ikoma, T.; Tero-
Kubota, S. Ferromagnetic Interactions between Imino Nitroxides
through Diamagnetic Metal Ions: Crystal Structures, Magnetism, and
Electronic Properties of [MI(imino nitroxide)2](PF6) (M = CuI and
AgI). Inorg. Chem. 1997, 36, 3014−3021.
(15) Hicks, R. G.; Lemaire, M. T.; Thompson, L. K.; Barclay, T. M.
Strong Ferromagnetic and Antiferromagnetic Exchange Coupling
between Transition Metals and Coordinated Verdazyl Radicals. J. Am.
Chem. Soc. 2000, 122, 8077−8078.
(16) Barclay, T. M.; Hicks, R. G.; Lemaire, M. T.; Thompson, L. K.
Structure and Magnetic Properties of a Nickel(II) Complex of a
Tridentate Verdazyl Radical: Strong Ferromagnetic Metal-Radical
Exchange Coupling. Chem. Commun. 2000, 2141−2142.
(17) Karasawa, S.; Sano, Y.; Akita, T.; Koga, N.; Itoh, T.; Iwamura,
H.; Rabu, P.; Drillon, M. Photochemical Formation of Ferrimagnetic
Chains from a Pair of Polymeric Complexes Made of Octahedral
(24) Tsukahara, Y.; Kamatani, T.; Iino, A.; Suzuki, T.; Kaizaki, S.
Synthesis, Magnetic Properties, and Electronic Spectra of Bis(β-
diketonato)chromium(III) and Nickel(II) Complexes with a
Chelated Imino Nitroxide Radical: X-Ray Structures of [Cr-
(acaMe)2(IM2py)]PF6 and [Ni(acac)2(IM2py)]. Inorg. Chem. 2002,
41, 4363−4370.
(25) Brook, D. J. R.; Fornell, S.; Stevens, J. E.; Noll, B.; Koch, T. H.;
Eisfeld, W. Coordination Chemistry of Verdazyl Radicals: Group 12
Metal (Zn, Cd, Hg) Complexes of 1,4,5,6-Tetrahydro-2,4-dimethyl-6-
(2’-pyridyl)-1,2,4,5-tetrazin-3(2H)-one (pvdH3) and 1,5-Dimethyl-3-
(2’-pyridyl)-6-oxoverdazyl (pvd). Inorg. Chem. 2000, 39, 562−567.
(26) Ito, A.; Kobayashi, N.; Teki, Y. Low-Energy and Long-Lived
Emission from Polypyridyl Ruthenium(II) Complexes Having a
Stable-Radical Substituent. Inorg. Chem. 2017, 56, 3794−3808.
(27) Shemsi, A. M.; Ali, B. E.; Ziq, K. A.; Morsy, M.; Keene, T. D.;
Decurtins, S.; Fettouhi, M. Mixed-Ligand Platinum and Palladium
Complexes Based on Dinitrogen Chelating Ligands and a Pyridine
Bearing the Nitronylnitroxide Radical. Inorg. Chem. Commun. 2007,
10, 1355−1359.
(28) Zhang, X.; Suzuki, S.; Kozaki, M.; Okada, K. NCN Pincer−Pt
Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion.
J. Am. Chem. Soc. 2012, 134, 17866−17868.
(29) Tam, A. Y.-Y.; Tsang, D. P.-K.; Chan, M.-Y.; Zhu, N.; Yam, V.
W.-W. A Luminescent Cyclometalated Platinum(II) Complex and Its
Green Organic Light Emitting Device with High Device Performance.
Chem. Commun. 2011, 47, 3383−3385.
(30) Wu, W.; Zhao, J.; Guo, H.; Sun, J.; Ji, S.; Wang, Z. Long-Lived
Room-Temperature Near-IR Phosphorescence of BODIPY in a
Visible-Light-Harvesting N^C^N PtII−Acetylide Complex with a
Directly Metalated BODIPY Chromophore. Chem. - Eur. J. 2012, 18,
1961−1968.
(31) McClenaghan, N. D.; Leydet, Y.; Maubert, B.; Indelli, M. T.;
Campagna, S. Excited-State Equilibration: A Process Leading to
Long-Lived Metal-to-Ligand Charge Transfer Luminescence in
Supramolecular Systems. Coord. Chem. Rev. 2005, 249, 1336−1350.
(32) Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergamini, G.;
Balzani, V. Photochemistry and Photophysics of Coordination
Compounds: Ruthenium. Top. Curr. Chem. 2007, 280, 117−214.
(33) Chi, Y.; Chou, P.-T. Contemporary Progresses on Neutral,
Highly Emissive Os(II) and Ru(II) Complexes. Chem. Soc. Rev. 2007,
36, 1421−1431.
N
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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(34) Feng, Y.; Cheng, J.; Zhou, L.; Zhou, X.; Xiang, H. Ratiometric
Optical Oxygen Sensing: A Review in Respect of Material Design.
Analyst 2012, 137, 4885−4901.
(53) Sazanovich, I. V.; Alamiry, M. A. H.; Meijer, A. J. H. M.;
Towrie, M.; Davies, E. S.; Bennett, R. D.; Weinstein, J. A.
Photoinduced Charge Separation in a PtII Acetylide Donor−Acceptor
Triad Based on 2-(1-Pyrazole)-pyridine Modified with Naphthalene
Mono-Imide Electron Acceptor. Pure Appl. Chem. 2013, 85, 1331−
1348.
(54) Gosztola, D.; Niemczyk, M. P.; Svec, W.; Lukas, A. S.;
Wasielewski, M. R. Excited Doublet States of Electrochemically
Generated Aromatic Imide and Diimide Radical Anions. J. Phys.
Chem. A 2000, 104, 6545−6551.
(55) Dyar, S. M.; Margulies, E. A.; Horwitz, N. E.; Brown, K. E.;
Krzyaniak, M. D.; Wasielewski, M. R. Photogenerated Quartet State
Formation in a Compact Ring-Fused Perylene-Nitroxide. J. Phys.
Chem. B 2015, 119, 13560−13569.
(56) Kawai, A.; Shibuya, K. Electron Spin Dynamics in a Pair
Interaction between Radical and Electronically-Excited Molecule as
Studied by a Time-Resolved ESR Method. J. Photochem. Photobiol., C
2006, 7, 89−103.
(57) Ishii, K.; Hirose, Y.; Fujitsuka, H.; Ito, O.; Kobayashi, N. Time-
Resolved EPR, Fluorescence, and Transient Absorption Studies on
Phthalocyaninatosilicon Covalently Linked to One or Two TEMPO
Radicals. J. Am. Chem. Soc. 2001, 123, 702−708.
(58) Teki, Y.; Miyamoto, S.; Nakatsuji, M.; Miura, Y. π-Topology
and Spin Alignment Utilizing the Excited Molecular Field:
Observation of the Excited High-Spin Quartet (S = 3/2) and Quintet
(S = 2) States on Purely Organic π-Conjugated Spin Systems. J. Am.
Chem. Soc. 2001, 123, 294−305.
(59) Matuschek, D.; Eusterwiemann, S.; Stegemann, L.;
Doerenkamp, C.; Wibbeling, B.; Daniliuc, C. G.; Doltsinis, N. L.;
Strassert, C. A.; Eckert, H.; Studer, A. Profluorescent Verdazyl
Radicals - Synthesis and Characterization. Chem. Sci. 2015, 6, 4712−
4716.
(60) Lavastre, O.; Even, M.; Dixneuf, P. H.; Pacreau, A.; Vairon, J.-P.
Novel Ruthenium- or Iron-Containing Tetraynes as Precursors of
Mixed-Metal Oligomers. Organometallics 1996, 15, 1530−1531.
(61) Likhtenstein, G. I.; Ishii, K.; Nakatsuji, S. i. Dual Chromophore-
Nitroxides: Novel Molecular Probes, Photochemical and Photo-
physical Models and Magnetic Materials. Photochem. Photobiol. 2007,
83, 871−881.
(35) Stacey, O. J.; Pope, S. J. A. New Avenues in the Design and
Potential Application of Metal Complexes for Photodynamic
Therapy. RSC Adv. 2013, 3, 25550−25564.
̈
(36) Hari, D. P.; Konig, B. The Photocatalyzed Meerwein Arylation:
Classic Reaction of Aryl Diazonium Salts in a New Light. Angew.
Chem., Int. Ed. 2013, 52, 4734−4743.
(37) Fukuzumi, S.; Ohkubo, K. Selective Photocatalytic Reactions
with Organic Photocatalysts. Chem. Sci. 2013, 4, 561−574.
(38) Lee, S.-H.; Chan, C. T.-L.; Wong, K. M.-C.; Lam, W. H.; Kwok,
W.-M.; Yam, V. W.-W. Design and Synthesis of Bipyridine
Platinum(II) Bisalkynyl Fullerene Donor−Chromophore−Acceptor
Triads with Ultrafast Charge Separation. J. Am. Chem. Soc. 2014, 136,
10041−10052.
(39) Di Piazza, E.; Merhi, A.; Norel, L.; Choua, S.; Turek, P.; Rigaut,
S. Ruthenium Carbon-Rich Complexes as Redox Switchable Metal
Coupling Units. Inorg. Chem. 2015, 54, 6347−6355.
(40) Hissler, M.; Connick, W. B.; Geiger, D. K.; McGarrah, J. E.;
Lipa, D.; Lachicotte, R. J.; Eisenberg, R. Platinum Diimine
Bis(acetylide) Complexes: Synthesis, Characterization, and Lumines-
cence Properties. Inorg. Chem. 2000, 39, 447−457.
(41) Whittle, C. E.; Weinstein, J. A.; George, M. W.; Schanze, K. S.
Photophysics of Diimine Platinum(II) Bis-Acetylide Complexes.
Inorg. Chem. 2001, 40, 4053−4062.
(42) Wadas, T. J.; Lachicotte, R. J.; Eisenberg, R. Synthesis and
Characterization of Platinum Diimine Bis(acetylide) Complexes
Containing Easily Derivatizable Aryl Acetylide Ligands. Inorg. Chem.
2003, 42, 3772−3778.
(43) Pomestchenko, I. E.; Castellano, F. N. Solvent Switching
between Charge Transfer and Intraligand Excited States in a
Multichromophoric Platinum(II) Complex. J. Phys. Chem. A 2004,
108, 3485−3492.
(44) Castellano, F. N.; Pomestchenko, I. E.; Shikhova, E.; Hua, F.;
Muro, M. L.; Rajapakse, N. Photophysics in Bipyridyl and Terpyridyl
Platinum(II) Acetylides. Coord. Chem. Rev. 2006, 250, 1819−1828.
(45) Rachford, A. A.; Goeb, S.; Ziessel, R.; Castellano, F. N. Ligand
Localized Triplet Excited States in Platinum(II) Bipyridyl and
Terpyridyl Peryleneacetylides. Inorg. Chem. 2008, 47, 4348−4355.
(46) Suzuki, S.; Yokoi, H.; Kozaki, M.; Kanzaki, Y.; Shiomi, D.; Sato,
K.; Takui, T.; Okada, K. Synthesis and Properties of a Bis[(nitronyl
nitroxide)-2-ide radical anion]−Palladium Complex. Eur. J. Inorg.
Chem. 2014, 2014, 4740−4744.
(62) Wu, X.; Wu, W.; Cui, X.; Zhao, J.; Wu, M. Preparation of
Bodipy-Ferrocene Dyads and Modulation of the Singlet/Triplet
Excited State of Bodipy via Electron Transfer and Triplet Energy
Transfer. J. Mater. Chem. C 2016, 4, 2843−2853.
(63) Wu, Y.; Guo, H.; Zhang, X.; James, T. D.; Zhao, J. Chiral
Donor Photoinduced-Electron-Transfer (d-PET) Boronic Acid
Chemosensors for the Selective Recognition of Tartaric Acids,
Disaccharides, and Ginsenosides. Chem. - Eur. J. 2011, 17, 7632−
7644.
(47) McKinnon, S. D. J.; Gilroy, J. B.; McDonald, R.; Patrick, B. O.;
Hicks, R. G. Magnetostructural Studies of Palladium(II) and
Platinum(II) Complexes of Verdazyl Radicals. J. Mater. Chem. 2011,
21, 1523−1530.
(64) Egan, T. J.; Koch, K. R.; Swan, P. L.; Clarkson, C.; Van
Schalkwyk, D. A.; Smith, P. J. In Vitro Antimalarial Activity of a Series
of Cationic 2,2’-Bipyridyl- and 1,10-Phenanthrolineplatinum(II)
Benzoylthiourea Complexes. J. Med. Chem. 2004, 47, 2926−2934.
(65) Frisch, M. J.; Trucks, G. W.; Schlege, l. H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalman, i. G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, M. J.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09; Gaussian, Inc.: Wallingford, CT, 2009.
(48) Liu, Y.; Wu, W.; Zhao, J.; Zhang, X.; Guo, H. Accessing the
Long-Lived Near-IR-Emissive Triplet Excited State in Naphthalene-
diimide with Light-Harvesting Diimine Platinum(II) Bisacetylide
Complex and Its Application for Upconversion. Dalton Trans. 2011,
40, 9085−9089.
(49) Fettouhi, M.; El Ali, B.; Morsy, M.; Golhen, S.; Ouahab, L.; Le
Guennic, B.; Saillard, J.-Y.; Daro, N.; Sutter, J.-P.; Amouyal, E. Metal-
Dependent Ferro- Versus Antiferromagnetic Interactions in Molecular
Crystals of Square Planar {M(II) Imino-Nitroxide Radical}
Complexes (M = Pt, Pd). Inorg. Chem. 2003, 42, 1316−1321.
(50) Williams, J. A. G. Photochemistry and Photophysics of
Coordination Compounds: Platinum. Top. Curr. Chem. 2007, 281,
205−268.
(51) Hua, F.; Kinayyigit, S.; Cable, J. R.; Castellano, F. N. Green
Photoluminescence from Platinum(II) Complexes Bearing Silylace-
tylide Ligands. Inorg. Chem. 2005, 44, 471−473.
(52) Adams, C. J.; Fey, N.; Harrison, Z. A.; Sazanovich, I. V.;
Towrie, M.; Weinstein, J. A. Photophysical Properties of Platinum-
(II)−Acetylide Complexes: the Effect of a Strongly Electron-
Accepting Diimine Ligand on Excited-State Structure. Inorg. Chem.
2008, 47, 8242−8257.
O
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