Synthesis and properties of the diruthenium(II) complexes with diimine-linked polypyridine bridges

Article abstract of DOI:10.1166/jnn.2012.5888

The diruthenium complexes, [(bpy)₂Ru(II)-(bpy-DPDA)-Ru(II)(bpy) ₂][PF₆]₄ 3, (bpy: 2,2'-bipyridiyl; bpy-DPDA: Bis(2,2'-dipyridylketenylidene)-N,N-1,4-phenylenediamine}, and [(bpy) ₂Ru(II)-(Dbpy-DPDA)-R

Full text of DOI:10.1166/jnn.2012.5888

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Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 12, 4317–4320, 2012
Synthesis and Properties of the
Diruthenium(II) Complexes with
Diimine-linked Polypyridine Bridges
Dong Hwan Kim1, Hwa-Seon Kim1, Woong Kyu Jo1, Ho-Geun Ahn1, Chee Hun Kwak2,
Ji-Hoon Lee3, Dong Ho Kim4, Ruimao Hua5, and Min Chul Chung1ꢀ∗
1Department of Chemistry Engineering, Sunchon National University, Sunchon, Jeonnam 540-742, Korea
2Department of Chemistry, Sunchon National University, Sunchon, Jeonnam, 540-742, Korea
3Department of Polymer Engineering, Chungju National University, Chungju, Chungbuk 380-702, Korea
4Jeonnam TP, Suncheon, Jeonnam, 540-856, Korea
5Department of Chemistry, Tsinghua University, Beijing 100084, China
The diruthenium complexes, [(bpy)2Ru(II)-(bpy-DPDA)-Ru(II)(bpy)2][PF6]4 3, (bpy: 2,2ꢀ-bipyridiyl;
bpy-DPDA: Bis(2,2ꢀ-dipyridylketenylidene)-N,N-1,4-phenylenediamine}, and [(bpy)2Ru(II)-(Dbpy-
DPDA)-Ru(II)(bpy)2][PF6]4 4 {Dbpy-DPDA: Bis(2,2ꢀ-dipyridyl ketenylidene)-N,N-1,1ꢀ-(4,4ꢀ-dipheny-
lene)diamine}, were prepared by the reaction of (bpy)2Ru(II)Cl2 with diimine-linked polypyridine
bridges. These complexes were characterized by NMR, IR, UV/VIS, PL and cyclic voltammetry. In
the 13C-NMR spectra of 3 and 4, the carbon peaks of the Schiff Bases (>C N−) were shifted
to lower fields, and emissions were observed at 689 and 693 nm with quantum yields of 0.004
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and 0.006, respectively. The electrochemistry of complexes 3 and 4 showed four-reversible waves
IP: 61.228.209.16 On: Sat, 27 Feb 2016 03:16:57
(one oxidation wave and three reduction waves). The electrochemically measured band gaps for
Copyright: American Scientific Publishers
complexes 3 and 4 were 2.01 and 2.10 eV, respectively.
Keywords: Ruthenium, Schiff Base, Bipyridine, Pyridiyl, Cyclic Voltammogram, Emission.
1. INTRODUCTION
in recent years,10 the study of dinuclear complexes, bi-
site bridge ligands with Schiff bases, is less common.11
In this study, we explored the potential use of bi-site
bridge ligands with Schiff bases in dinuclear Ru(II)
complexes. We report the synthesis and characteristic
electronic and photophysical properties of the new diruthe-
nium complexes, [(bpy)2Ru(II)-(bpy-DPDA)-Ru(II)(bpy)2]
[PF6]4 (3),{bpy: 2,2ꢀ-bipyridiyl; bpy-DPDA: Bis(2,2ꢀ-dipy-
ridylketenylidene)-N,N-1,4-phenylenediamine}, [(bpy)2Ru
(II)-(Dbpy-DPDA)-Ru(II)(bpy)2][PF6]4(4), {Dbpy-DPDA:
Bis(2,2ꢀ-dipyridyl ketenylidene)-N,N-1,1ꢀ-(4,4ꢀ-dipheny-
lene)diamine}, in detail.
Recently, there have been a number of studies of binuclear
compounds using ꢀ-conjugated organic materials as a
bridge.1ꢁ2 This interest is fundamentally attributable to their
potential use as materials for molecular wires, and elec-
troluminescent materials.2–6 Welter et al. reported that the
compounds of these diruthenium complexes with a semi-
conducting polymer used for electroluminescent devices
can display two different colors (red/green), depending
on the applied voltage,7 Diruthenium(II) complexes based
on polypyridiyl ligands have attracted considerable atten-
tion due to their diverse properties. The bridging ligand,
mediating the two metal centers, plays a key role in the
determination of the properties of these systems. Planar
polyaromatic bridging ligands have been the focus of
some recent studies, due to their rigid nature.8ꢁ9 Although
a wide variety of bridging ligands have been introduced
2. EXPERIMENTAL DETAILS
2.1. General Considerations
For this experiment, THF (tetrahydrofuran), hexane,
pentane, and CH2Cl2 were purchased from Aldrich, dis-
tilled with CaH2 or Na/K alloy and then stored under
a nitrogen atmosphere. 1,4-phenylenediamine, methanol,
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 5
1533-4880/2012/12/4317/004
doi:10.1166/jnn.2012.5888
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Synthesis and Properties of the Diruthenium(II) Complexes with Diimine-linked Polypyridine Bridges
Kim et al.
2,2-dipyridyl ketone, formic acid, benzidine, cis-bis(2,2ꢀ-
bipyridine)dichlorideruthenium(II)hydrate, ethanol, and
[Cp2Fe][PF6] were purchased from Furuka and Aldrich
and used without purification. Bis(2,2ꢀ-dipyridylketeny-
lidene)-N,N-1,4-phenylenediamine (Dbpy-PDA) and
Bis(2,2ꢀ-dipyridyl ketenylidene)-N,N-1,1ꢀ-(4,4ꢀ-diphylene)
diamine (Dbpy-DPDA) were synthesized according to
the procedures described in the literature.11 All syntheses
were performed using a Schlenk tube under an argon
atmosphere. In addition, CD3CN, CDCl3 were used as the
solvents for NMR, after being dried using a molecular
sieve-4A and kept under an argon atmosphere. A SHI-
MADZU FTIR-8700 spectrophotometer was used for the
IR analysis. The 1H-NMR and 13C-NMR spectra were
determined by means of a Bruker AVANCE 400FT-NMR
spectrometer (1 H, 400 MHz). A JASCO V-570 was used
for the UV-Vis-Near-IR(NIR) analysis. The spectrofluo-
rometer used was a JASCO FP-6500. Cyclic voltammetry
(CV) was carried out in acetonitrile (0.1 M) with NBu4PF6
as an electrolyte using a Bioanalytical Systems lnc. E2.
A Pt disk was used as the working electrode, while Pt wire
and Ag/AgCl were used as the auxiliary and reference
electrodes, respectively. Potentials were internally refer-
enced to the Cp2Fe0/+ couple by adding Cp2Fe at the end
of the experiment.
2.4. Synthesis of the [(bpy)2 Ru(II)-(Dbpy-PDA)-
Ru(II)(bpy)2][PF6]4 Complex, 3
A solution of (bpy)2RuCl2 · xH2O (250 mg, 0.5 mmol)
and bis(2-2ꢀ-dipridiyl kentenylidene)-N,N-1,4-phenylene-
diamine (bpy-PDA, 105 mg, 0.238 mmol)) in 30 ml ꢁof
ethanol/water (2:1) and CHCl3 (2 ml) was heated at 80 C
for 2 hrs. The mixture was heated under argon until
the complete consumption of the starting materials was
observed. After the solution cooled to room temperature,
a solution of ammoniumhexafluorophosphate in water was
added, and upper liquid was removed. The precipitate was
washed with water (3×10 ml), and passed short alumina
using the acetonitrile. The fractions containing the pure
complex were evaporated to dryness and recrystallized
from acetonitrile/toluene. Complex 3 was finally obtained
with 55% yield.
1H-NMR(CD3CN), ꢃH, 8.42 (d, 8 Hz, 4 H), 8.34 (d,
8 Hz, 4 H), 8.22 (dd, 3.6 Hz, 0.7 Hz, 4 H), 8.13 (dq,
7.9 Hz, 1.0 Hz, 4 H), 8.09 (td, 8.4 Hz, 1.46 Hz, 4 H),
7.99 (td, 7.8 Hz, 1.4 Hz, 4 H), 7.93 (td, 8.05 Hz,
1.44 Hz, 4 H), 7.66 (dt, 5.77 Hz, 0.72 Hz, 4 H), 7.60
(dt, 5.6 Hz, 0.7 Hz, 4 H), 7.49∼7.54 (m, 4 H), 7.26∼7.31
(m, 8 H); 13C-NMR (CD3CN), ꢃC, 188.2 (>C N−),
159.1, 158.7, 157.3, 155.0, 154.6, 153.5, 140.3, 140.0,
130.7, 129.3, 129.2; FT-IR (KBr, cm−1ꢂ, 1970, 1682,
1692, 1604, 840; UV(ꢄ /nm), 222, 270, 304220(35,997),
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abs
2.2. Synthesis of the Bis(2,2 -dipyridyl ketenyli-
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246(35,870), 286(78,787), 428(13,596), 488(9,580).
dene)-N, N-1,4-Phenylenediamine (Dbpy-PDA), 1
Copyright: American Scientific Publishers
E.A, Found (Cal’d), C; 44.30 (44.21), H; 2.64 (2.84),
N: 10.43(10.62) for C68H52F24N14P4Ru2.
1H-NMR(CDCl3ꢂ, ꢃH, 8.53 (dq, 4.7 Hz, 0.87 Hz,
4 H), 8.06 (dt, 8.89 Hz, 1.05 Hz, 2 H), 7.72 (td,
7.86 Hz, 1.78 Hz, 2 H), 7.46 (td, 7.73 Hz, 1.75 Hz,
2 H), 7.0∼7.27 (m, 4 H), 6.94 (dt, 79 Hz, 1.05 Hz,
72 H), 6.50 (s, 4 H); 13C-NMR (CDCl3ꢂ, ꢃC, 166.4
(>C N−), 156.6, 154.9, 149.2, 149.1, 146.6, 136.5,
135.7, 124.7, 124.6, 123.4, 123.0, 121.3; FT-IR (KBr,
cm−1ꢂ, 1630, 1616, 1581,1565; Mass spectrum(m/e):
441; UV(ꢄabs/nm(ꢅmax/dm3 mol−1 cm−1ꢂ, 244(39,349),
268(34,841), 378(10,492), E.A, Found (Cal’d), C; 76.05
(76.35), H; 4.64 (4.58), N: 19.43(19.08) for C28H20N6.
2.5. Synthesis of the [(bpy)2 Ru(II)-(Dbpy-DPDA)-
Ru(II)(bpy)2][PF6]4 Complex, 4
Complex 2 was prepared using the same procedure as that
for complex 1 except that Bis(2,2ꢀ-dipyridyl ketenylidene)-
N,N-1,1ꢀ-(4,4ꢀ-diphylene)diamine (bpy-DPDA) was used
instead of Bis(2,2’-dipyridyl ketenylidene)-N,N-1,4-
phenylenediamine (bpy-PDA). Finally, complex 4 was
obtained. (yield: 62%).
1H-NMR(CD3CN), ꢃH, 8.49 (d, 8.1 Hz, 4 H), 8.41
(d, 8.1 Hz, 4 H), 8.29 (d5, 5.6 Hz, 0.61 Hz, 4 H),
8.20 (ddd, 7.94 Hz, 1.65 Hz, 0.58 Hz, 4 H), 8.16 (td,
8.05 Hz, 1.23 Hz, 4 H), 8.06 (td, 7.8 Hz, 1.4 Hz,
4 H), 8.0 (td, 8.05 Hz, 1.44 Hz, 4 H), 7.7 (dt,
5.73 Hz, 0.7 Hz, 4 H), 7.67 (dt, 5.6 Hz, 0.7 Hz, 4 H),
7.56∼7.60 (m, 4 H), 7.33∼7.60 (m, 8 H), 7.26 (d,
8.8 Hz, 2 H), 6.65 (d, 8.7 Hz, 2 H), 13C-NMR (CD3CN),
ꢃC, 186.3 (>C N−), 157.1, 156.7, 155.4, 153.0, 152.7,
151.6, 138.5, 138.2, 138.1, 128.8, 127.4, 127.2, 124.6,
124.2; FT-IR (KBr, cm−1ꢂ, 1973, 1669, 1659, 1604,
840; UV(ꢄabs/nm), 246(33,537), 288(79,207), 428(11,989),
496 (9,190); E.A, Found (Cal’d), C; 44.45(44.21), H;
2.74(2.93), N: 10.53 (10.20) for C74H56F24N14P4Ru2.
2.3. Synthesis of the Bis(2,2ꢀ-dipyridyl ketenyli-
dene)-N,N-1,1ꢀ-(4,4ꢀ-diphenylene)Diamine
(Dbpy-DPDA), 2
1H-NMR(CDCl3ꢂ, ꢃH, 8.5 (tq, 4.8 Hz, 0.87 Hz, 4 H), 8.13
(d, 7.9 Hz, 2 H), 7.77 (td, 7.82 Hz, 1.77 Hz, 2 H), 7.49
(td, 7.73 Hz, 1.74 Hz, 2 H), 7.11∼7.29 (m, 8 H), 7.0
(dt, 7.79 Hz, 1.05 Hz, 2 H), 6.74 (dt, 8.5 Hz, 2.33 Hz,
4 H); 13C-NMR (CDCl3ꢂ, ꢃC, 167.6 (>C N−), 157.9,
156.2, 150.6, 150.4, 137.8, 137.4, 137.2, 128.2, 125.9,
124.9, 124.6, 122.9; FT-IR (KBr, cm−1ꢂ, 1614, 1586,
1510, 1463; UV(ꢄabs/nm), 222(16,696), 270(27,703),
304(41,616), E.A, Found (Cal’d), C; 76.45(76.05), H;
4.64(4.68), N: 16.43(16.27) for C34H24N6.
4318
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Kim et al.
Synthesis and Properties of the Diruthenium(II) Complexes with Diimine-linked Polypyridine Bridges
Table I. Photophysical data for complexes in CH3CN solution at 295 K.
N
N
N
N
N
N
N
R
NH2+O
O+H2N
N
R
N
UV/Vis
(ꢄmax/nm) (nm)
PL
Eg
ꢇ
kr
ꢈknr
(s−1
N
Complexes
3
ꢉ
(eV) (ꢊs) (s−1
)
)
220,246
286, 340
428, 488
246,288
340, 428
496
689 0.004 2.01 8.6
465 1ꢋ15×
105
R
,
N
N
N
1
2
4+
4
693 0.006 2.10 10.2 882
9×
N
Ru lC
lC
105
N
N
N
N
N
N
N
N
N
Ru (bpy)+2ꢁ9
451,344
322,287
605 0.062 2.60 0.89 6ꢋ9×
10×
R
N
Ru
N
N
Ru
N
N
105
105
3, 4
octahedral d6 metal complexes.20 Both of the new com-
plexes are luminescent in degassed solution, displaying a
single, broad emission band. The luminescences of com-
plexes 3 and 4 (ꢄmax = 689 and 693 nm, respectively) are
substantially red-shifted with respect to that of the refer-
ence complex (Ru(bpy)+3 2, ꢄmax = 622 nm). As an absorp-
tion, this is attributed to the lowering of the bridge (N∧N)
ꢀ∗ orbital energy due to its increased conjugated as com-
pared to bpy. The relatively long luminescence life time,
ꢇ, of the complexes, which is in the range of 8.6∼10.2 ꢊs
in degassed solution at room temperature (Table I), is also
suggestive of their having a significantly ligand-centered
character in the excited state.
Scheme 1. Preparation of diruthenium complexes.
3. RESULTS AND DISCUSSION
Bis(2,2ꢀ-dipyridyl ketenylidene) diamine compounds (1, 2)
were prepared by gently melting 2 eq. of the diami-
nes (1:1,4-phenylene diamine, 2: 1,1ꢀ-(4,4ꢀ-diphenylene)
diamine) and 1 eq. of the ketene for 30 min (Scheme 1). In
the NMR spectrum, the carbon peaks of the Schiff Bases
(>C N−) were observed at 166.4∼167.6 ppm, which is
typical for Schiff Bases. The chemical shifts of the Schiff
Bases were in the range of 188.2∼186.3 ppm for com-
plexes 3 and 4, due to the ruthenium bond to the dipyridyl-
ketenylidene bridge ligand. In general, compounds 3 and
4 are dark-red in color in dilute solution. The absorption
The emission quantum yields, ꢌR, were measured at
ꢁ
20 C according to the following equation (for the buffer
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solutions, no refractive index correction was made).12
spectra of 3 and 4 in acetonitrile are shown in Figure 1.
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Table I lists the absorption maxima values and extinction
Copyright: American Scientific Publishers
coefficients of these complexes and a reference complex
(Ru(bpy)+3 2ꢂ. The electronic absorption spectra of com-
plexes 3 and 4 in acetonitrile at room temperature are
shown in Figure 1. The three peaks at 246, 428 and 488 nm
for complex 3 were assigned as the Ruꢆdꢀꢂ → bpy(ꢀ∗)
transitions. For complexes 3 and 4, the intense peaks at
286 and 288 nm, respectively, were assigned as the lig-
and centered (LC) bpy ꢀ → ꢀ∗ transitions, and the intense
peaks at 340 nm was attributed to metal centered (MC)Ru
d → d transitions such as the characteristic transition for
ꢌR = ꢌref ꢆIsAref /Iref Asꢂ
(1)
where I is the emission intensity calculated from the area
under the emission spectrum from 500 to 800 nm, A is
the absorbance, and the subscripts s and ref stand for
the samples and reference, respectively, An acetonitrile
solution of [Ru(bpy)3][PF6]2 was used as a standard with
ꢌref = 0ꢋ062.9ꢁ13 The luminescence quantum yields (ꢌRꢂ
of 3 and 4 were 0.004 and 0.006, respectively. Assuming
that the formation of the emissive state occurs with unity
efficiency, one may obtain an estimate of the unimolecular
Table II. Electrochemical properties for complexes in Acetonitrile at
298 K.
Oxidation (V)
Reduction (V)
E1/2, (ꢍaꢁp, mV)
E1/2, (ꢍaꢁp, mV)
[(bpy)2Ru(bpy-DPDA]
Ru(bpy)2]4+, 3
1.26(82) −0.75(74) −1.29(78) −1.39(82)
[(bpy)2Ru(Dbpy-DPDA] 1.40(82) −0.70(75) −1.30(75) −1.50(80)
Ru(bpy)2]4+
4
[(bpy)2Ru(bpy-Et-bpy]
Ru(bpy)2]4+ꢁ15
1.38(90) −0.92(1e) −1.16(1e) −1.35(2e)
[(bpy)2Ru(bpy-Bu-bpy] 1.35(90) −.090(1e) −1.12(1e) −1.33(2e)
Ru(bpy)2]4+ꢁ15
Fig. 1. UV/Vis absorption and emission spectra (ꢄexcitation: 428 nm) of
complex 3, and 4 in MeCN at 298 K.
[Ru(bpy)3]2+ꢁ9
1.27(65) −1.35(1e) −/154(1e) −1.79(e)
J. Nanosci. Nanotechnol. 12, 4317–4320, 2012
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Synthesis and Properties of the Diruthenium(II) Complexes with Diimine-linked Polypyridine Bridges
Kim et al.
The Ru(dꢀꢂ → bpy(ꢀ∗) transitions are observed at 246,
428 and 488 nm. The ligand centered (LC) bpy ꢀ → ꢀ∗
transitions (of complexes 3 and 4) are observed at 286
and 288 nm, respectively. The luminescences of complexes
3 and 4 (ꢄmax = 689, 693, respectively) are substantially
red-shifted with respect to that of the reference com-
plex (Ru(bpy)+3 2, ꢄmax = 622). The luminescence quantum
yields (ꢌRꢂ of 3 and 4 are 0.004 and 0.006, respectively.
From the radiative (kr ꢂ and nonradiative (ꢈknrꢂ, it can
be inferred that the lower emission quantum yield of the
complexes compared to that of the reference complexes
(Ru(bpy)+3 2, kr = 6ꢋ9 × 105, knr = 1ꢋ05 × 106ꢂ is due to
the reduced radiative rate constant and higher nonradia-
tive decay. The oxidation and reduction potentials for all
of the complexes were determined by cyclic voltammetry.
Oxidations of the ruthenium center were observed in the
region between +1ꢋ20 and 1.40 V for complexes 3 and 4,
whereas the reduction of the two coordinated ligands and
one bridge were observed in the negative potential region.
The oxidation peak was not split for the binuclear com-
plexes, indicating that the metal centers are not in strong
electronic communication with each other. The electro-
chemically measured band gaps were 2.01 and 2.10 eV for
complexes 3 and 4, respectively.
Fig. 2. Cyclic Voltammogram of complex 4 at 298 K (0.1 M MeCN
solution of (Bu4N)(PF6ꢂ, scan rate: 100 mV/s, Reference Fe/Fe+: 0.43 V).
radiative (kr ꢂ and nonradiative (ꢈknrꢂ decay rate constants
by the application of Eqs. (2) and (3).
ꢇ = 1/ꢆkr +ꢈknrꢂ
ꢌR = kr /ꢆkr +ꢈknrꢂ = kr ·ꢇ
(2)
(3)
The inspection of the parameters so obtained (Table I)
confirms that the lower emission quantum yield of the
complexes compared to that of the reference complexes
(Ru(bpy)+3 2, kr = 6ꢋ9×105, knr = 1ꢋ05×106ꢂ is due to the
Acknowledgments: This work was supported by GT-
FAM of the Sunchon National University through the
reduced radiative rate constant and the higher nonradiative
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Regional Innovation Center Program (RIC). Professor Hua
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decay.
Copyright: American Scientific Publishers
was supported by the Brain Pool Program of the Korea
Research Fund (061S-4-3-0027).
The oxidation and reduction potentials for all of the
complexes were determined by cyclic voltammetry. The
redox potentials for compounds 3 and 4 are listed in
Table II. The observed couples are all ‘reverse,’ where
the term reversibility used here implies that the separation
between the anodic and cathodic peak potentials was less
than 100 mV for a one-electron process and no degrada-
tion products were observed on the following scan. The
E1/2 values of ꢍE were calculated by subtraction of the
cathodic potentials from the anodic potentials for a specific
redox couple (Fig. 2).
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The general behavior of the complexes was very similar
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pounds (1 and 2). In the NMR spectrum, the carbon
peaks of the Schiff Bases (>C N−) were observed at
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chemical shifts of the Schiff Bases were in the range of
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Received: 7 May 2010. Accepted: 2 June 2011.
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