Highly packed and stretched polyterpyridinyl Ru2+ complexes and their photophysical and stability properties

Article abstract of DOI:10.1016/j.ica.2016.06.017

Two unique trinuclear terpyridine-ruthenium complexes having similar components placed at different angels were successfully synthesized and fully characterized for the purpose of determining the photophysical and electronic properties. The corresponding

Full text of DOI:10.1016/j.ica.2016.06.017

Inorganica Chimica Acta 450 (2016) 293–298
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Highly packed and stretched polyterpyridinyl Ru2+ complexes and their
photophysical and stability properties
Die Liu 1, Zhilong Jiang 1, Meng Wang, Xiaoyu Yang, Haisheng Liu, Tun Wu, Pingshan Wang
⇑
Department of Organic and Polymer Chemistry, College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, Hunan, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 May 2016
Received in revised form 4 June 2016
Accepted 6 June 2016
Available online 8 June 2016
Two unique trinuclear terpyridine-ruthenium complexes having similar components placed at different
angels were successfully synthesized and fully characterized for the purpose of determining the photo-
physical and electronic properties. The corresponding UV–vis absorptions and similar electrochemical
properties showed characteristic MLCT transitions in both complexes. However, complex C2 displayed
an intense emission at 77 K, as expected, where highly packed complex C1 is almost non-emissive.
This result may due to that a distinct configuration adopted by the complex impacts ligand field strength.
Ó 2016 Elsevier B.V. All rights reserved.
Keywords:
Polyterpyridine
Terpyridine-ruthenium complexes
Photophysical
Non-emissive
1. Introduction
complexes. In this paper, two trinuclear terpyridyl-ruthenium
complexes were synthesized and characterized by NMR spec-
Recently, ruthenium-polypyridyl complexes have attracted
considerable attention due to their photosensitive applications as
a result of their unique electrochemical and photophysical proper-
ties [1–3]. Among these complexes, the robust, bis-tridentate octa-
hedral ruthenium complexes are one of the most common and
provide an ideal building block for construction of multi-nuclear
complexes. For example, multinuclear Ru2+ coordination systems
can be adjusted by using different polyterpyridine derivatives upon
complexations [3,4]. It is known that tpy-Ru2+-tpy systems show
rather poor excited properties and are almost non-emissive com-
pared with that of [Ru(bpy)3]2+ at room temperature [5]. Much
work has been done to improve the luminescent properties of
ruthenium-polypyridyl complexes by incorporating different sub-
stituents to the polypyridine ligand [6], or by using heterocycles
or cyclometalating ligands which change the coordination sphere
[7–9]. An idealized terpyridine related metallo-organic octahedral
architecture should afford a longer excited-state lifetime, a more
conjugated ligand with higher delocalization. Such structure can
possess excellent photoelectric properties, since the higher energy
of the metal-centred (3MC) states increases the energy gap
between the metal-to-ligand charges transitons (3MLCT) and 3MC
states [8,9]. Therefore, the ligand environment is of great impor-
tance for the photophysical properties of ruthenium-polypyridyl
troscopy and electrospray ionization mass spectrometry (ESI-MS).
Further, their photophysical and stability properties were investi-
gated by UV–vis spectra, Emission spectra, cyclic voltammetry
(CV) and ESI-MS.
2. Results and discussion
Tristerpyridine Ligands L1 and L2 with similar structures and
both bearing three terpyridyl unities were synthesized using a
Suzuki coupling with two newly designed bromo-substituted
terpyridines (see ESI, Scheme S1), 6,600-dibromoterpyridine and
5,500-dibromoterpyridine. The structures of L1 and L2 were charac-
terized through 1H NMR (Figs. 1 and 2), 13C NMR and ESI-MS (see
ESI). The ruthenium complexes C1 and C2 were synthesized by
reacting L1 or L2 with (2,20:60,200-terpyridine)ruthenium trichloride
(tpyRuCl3) in ethylene glycol at 395 K for 24 h (Scheme 1).
1H-1H COSY, 1H-1H ROESY (see ESI), ESI-MS (Fig. 3) along with
the 13C NMR spectra (see ESI) were used for further characteriza-
tion of C1 and C2. The 1H NMR spectra for the ligands and com-
plexes have been assigned; the shifts of 1H NMR spectra are
shown in Fig. 1 for C1 and Fig. 2 for C2. Compared with the ligands,
the complexes show significant downfield shift in the 30,50-tpy pro-
tons and 3,300-tpy protons owing to the lower electron density after
coordination. Both 6,600-tpy protons show a dramatic upfield shift
because of the shielding effect from the metal centers. As usual,
the Ph-H in the 40-phenyl terpyridine tends to shift downfield after
coordination because of the reduced electron density [10]. To our
⇑
Corresponding author.
E-mail address: chemwps@csu.edu.cn (P. Wang).
1
These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.ica.2016.06.017
0020-1693/Ó 2016 Elsevier B.V. All rights reserved.

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D. Liu et al. / Inorganica Chimica Acta 450 (2016) 293–298
Fig. 1. 1H NMR spectra of (a) ligand L1 in CDCl3; (b) complex C1 in CD3CN.
Fig. 3. ESI-MS spectra of C1 and C2, the different charge states ions were derived
from losing different numbers of PFꢀ6 . C1 was measured at a normal condition; C2
was measured at the high source temperature and capillary voltage.
surprise, the Ph-Hc and Ph-Hd in C1 displayed the unexpected
upfield shifts due to the shielding effect produced by the
mid-(tpy-Ru-tpy) unity [11]. Ph-Hc in C1 which is closer to the
mid-(tpy-Ru-tpy) displayed a larger upfield shift (
compared to L1 (Ph-Hc in C2: d = 0.09 ppm compared to L2).
Likewise, a similar upfield shift happened for the Ph-Hd of C1
which was d = 0.47 ppm, while there is a downfield shielding
Dd = 1.99 ppm)
D
D
effect in C2 for Ph-Hd, which indicated a sufficient distance
between the Ph-Hd and mid-(tpy-Ru-tpy).
ESI-MS also validated the proposed structures for these com-
plexes. For complex C1 (Fig. 3), the peaks at m/z (Z = 4+) 593.37,
m/z (Z = 3+) 839.48 and m/z 1331.71 (Z = 2+) suitably correspond
to the structures of [Mꢀ4PFꢀ6 ]4+ (calcd m/z = 593.36), [Mꢀ3PFꢀ6 ]3+
(calcd m/z = 839.47), and [Mꢀ2PFꢀ6 ]2+ (calcd m/z = 1331.68),
respectively. The peaks in complex C2 (Fig. 3) at m/z (Z = 6+)
348.25, m/z (Z = 5+) 446.89, m/z (Z = 4+) 594.86, m/z (Z = 3+)
Fig. 2. 1H NMR spectra of (a) ligand L2 in CDCl3; (b) complex C2 in CD3CN.
Scheme 1. Synthetic routes to complexes C1 and C2.

D. Liu et al. / Inorganica Chimica Acta 450 (2016) 293–298
295
841.47, and m/z 1334.74 (Z = 2+) correctly assigned to the struc-
tures of [Mꢀ6PFꢀ6 ]6+ (calcd m/z = 348.24), [Mꢀ5PFꢀ6 ]5+ (calcd
m/z = 446.88), [Mꢀ4PF6ꢀ]4+ (calcd m/z = 594.84), [Mꢀ3PFꢀ6 ]3+ (calcd
m/z = 841.44), and [Mꢀ2PFꢀ6 ]2+ (calcd m/z = 1334.65), respectively.
Polypyridyl ruthenium complexes have essential applications as
photosensitizers due to the strong intraligand (IL) absorption in the
UV region and metal-to-ligand charge-transfer transitions (MLCT)
in the visible region. The optical properties associated with MLCT
absorptions are fundamentally involved with the structure of poly-
pyridyl ligands. In order to investigate the interrelationship of the
absorption of MLCT, the UV–vis spectra of complexes C1, C2 and
[tpy-Ru2+-tpy] (Scheme 1) were recorded (shown in Fig. 4). The
absorption of complexes C1 and C2 are identical at 485 nm (refer-
ence [tpy-Ru2+-tpy]: 475 nm). As we know, the MLCT absorption of
polypyridine ruthenium complexes is a result of the electronic
Fig. 4. UV–vis absorption spectra of [Ru(tpy)2]2+, C1 and C2 (5.0 ꢁ 10ꢀ5 M) in
CH3CN solution at 25 °C.
transition from the
of ligand [12,13]. The introduction of aromatic moieties at any
position of the terpyridine ligand enlarges the conjugated -sys-
D
-orbital of ruthenium atom to the p⁄-orbital
p
tem and lowers the energy of the p⁄-orbital, giving rise to the
red-shifted absorption and thus increasing the MLCT oscillator
strength. C1 and C2 show the intense absorption around 310 nm,
which can be attributed to characteristic ligand-centred (LC) tran-
sitions. At the same time, a slightly bathochromic-shift was
assigned to the ligand delocalization compared to the reference
[tpy-Ru2+-tpy] [14]. It also should be noted that, for the C1 and
C2, the absorption around 360 nm results from the mixed LC and
MLCT transitions [15].
The electrochemical activities of C1 and C2 were studied by cyc-
lic voltammetry (CV) (Fig. 5). The E1/2 value for the Ru2+/Ru3+ redox
couples was determined to be 1.34 V for C1 and 1.36 V for C2
which shows a small decrease in comparison to the E1/2 of the
[tpy-Ru2+-tpy] (1.39 V). The electrochemical datum is consistent
with the above analysis for the absorption spectroscopy. Compared
with tpy ligand, the ligands L1 and L2 have larger
systems [9,16], leading to smaller energy gaps between the Ru
-orbital and the ligand p⁄-orbital than the reference tpy ligand.
p-delocalized
Fig. 5. Cyclic voltammograms at a scan rate of 25 mV sꢀ1 in CH3CN/0.1 mol Lꢀ1
TBAP at a glassy carbon electrode (vs Ag/AgCl).
D
The tpy-Ru-tpy complex is relatively stable compared with other
transition metal complexes and shows excellent acid and alkali
resistance [10]. The two Ru-based complexes C1 and C2 show great
acidic resistance/stability, but they decomposed after heating
(80 °C) for 5 h under the alkaline conditions, which was evidenced
by changes of the UV–vis spectra (see ESI, Figs. S3 and S4). It is
speculated that multi-terpyridine Ru complexes which linked at
5,500 or 6,600 position are less stable than those at 40 position. Further
research of their thermostability had been performed by the ther-
mal gravity analysis (TGA) (shown in Figs. S5 and S6). Thermal
decomposition temperature for C1 was determined to be 403 °C,
which is lower than C2 (452 °C), indicating that C1 is easier to
decompose than C2.
Typically, tpy-containing Ru2+ complexes are very weak emit-
ters or virtually non-emissive at 25 °C in solution due to the short
luminescence lifetime [17]. Emission spectra of C1 and C2 were
measured at 77 K at 480 nm (Fig. 6). As expected, the reference
[tpy-Ru2+-tpy] and complex C2 present relatively intense lumines-
cence with the emission maximum at 602 nm and 646 nm, respec-
tively, but to our surprise, the complex C1 is almost non-emissive
at 77 K (Fig. 6). The emission of Tpy-Ru2+-Tpy is attributed to the
Ru ? tpy 3MLCT state [18] but it is often non-emissive at 25 °C
due to radiationless deactivation via short-lived metal-centred
(3MC) states which can thermally induce population from the
3MLCT state [2,13]. However, the radiationless deactivation can
be decreased at low temperature, so the complex C2 and
[tpy-Ru2+-tpy] show the intense emission at 77 K. On the contrary,
for the complex C1, there is a distorted octahedral geometry caused
by the extremely closed stacking of two pendant tpy-Ru-tpy
Fig. 6. Fluorescent emission spectra of complexes [Ru(tpy)2]2+, C1 (5.0 ꢁ 10ꢀ6 M)
and C2 (5.0 ꢁ 10ꢀ6 M) at 77 K in EtOH/MeOH (4/1, v/v).
moieties, so the overall tpy ligand-field strength is weak; therefore,
the process of a non-radiative decay from the 3MC state to the
ground state is thermally accessible and results in the weak emis-
sion of C1 [19].
Temperature-dependent 1H NMR spectra of C1 and C2 in CD3CN
were successfully recorded (Figs. 7 and S1). In terms of C2, when
temperatures rise to 335 K from 298 K, there is no obvious chemi-
cal shift except a slight upfield shift. However, for C1, a new shoul-
der peak from 30,50-tpy proton of mid-(tpy-Ru-Tpy) at 9.15 ppm

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D. Liu et al. / Inorganica Chimica Acta 450 (2016) 293–298
working electrode, Pt wire as the counter electrode, Ag/AgCl elec-
trode as the reference electrode. 0.1 M tetrabutylammonium hex-
afluorophosphate (TBAPF6) dissolved in CH3CN was employed as
the supporting electrolyte.
Thermal gravity analysis was performed on NSK TG/DTA7300
thermal analysis instrument under the heating rate of 10 °C/min
from 30 °C to 1000 °C.
All chemicals were purchased from commercial suppliers and
used without further purification unless otherwise specified.
4.2. Preparation of 6,600-dibrome-40-(4-decyloxyphenyl)-2,20:60,
200-terpyridine (2)
Fig. 7. Temperature-dependent 1H NMR spectrum of complex C1 in CD3CN.
To a round bottom flask, a mixture of 4-(decyloxy) benzalde-
hyde (1) (0.6 g, 2.08 mmol), 2-acetyl-6-bromopyridine (1.0 g,
5 mmol), absolute EtOH (40 mL), and powdered NaOH (0.6 g,
15 mmol) were added. After stirring at 30 °C for 8 h, the solution0s
color changed from yellow to red, after which 20 mL NHÅ3H2O
(25–28%) was added and the mixture was heated at 75 °C for
20 h to give a yellow solution. The mixture was cooled to 25 °C and
evaporated under reduced pressure, then extracted with CH2Cl2.
The organic phase was washed with water and dried over MgSO4.
After removal of the solvent, the residue was purified by recrystal-
lization with CH2Cl2 and CH3OH to give compound 2 (0.82 g, 63.2%)
as a white solid; m.p. 151–154 °C; 1H NMR (500 MHz, 298 K, CDCl3,
ppm): d = 8.65 (s, 2H), 8.58 (d, 2H), 7.83 (d, 2H), 7.71 (t, 2H), 7.53
(d, 2H), 7.05 (d, 2H), 4.04 (t, 2H), 1.83 (m, 2H), 1.49 (m, 2H), 1.29
(m, 14H), 0.89 (t, 3H); 13C NMR (500 MHz, 298 K, CDCl3, ppm):
160.34, 157.46, 154.32, 150.29, 141.63, 139.11, 130.12, 128.58,
128.10, 119.98, 119.18, 115.01, 68.32, 31.92, 29.60, 29.58, 29.43,
29.34, 29.27, 26.07, 22.70, 14.12; ESI/MS (m/z): 623.9 [2+H]+ (calcd
624.4). Anal. Calcd for C31H33Br2N3O: C, 59.72; H, 5.34; N, 6.74.
Found: C, 59.42; H, 5.48; N, 6.55.
appeared after the temperature rised to 335 K. Apparently, at
higher temperature, another undetermined configuration in C1
appeared or coexisted. Furthermore, when the ESI-Mass measuring
conditions were conducted in a higher temperature and capillary
voltage parameters, the spectra for C2 was no change (Fig. 3); on
the contrary of C1, the peaks (Fig. S2) at m/z (Z = 4+) 437.39 and
m/z (Z = 3+) 631.51 (calcd m/z = 437.38 and 631.49, respectively)
were validated as the fragments of one decomposed octahedral
tpy-Ru-tpy moiety, the decomposed position could be the middle
or side tpy-Ru2+-tpy group. Thus, we supposed that two pendent
and middle tpy-Ru2+-tpy moieties are particularly closed in C1
and stand the large strain and electrostatic repulsion, which may
leads to an unstable and twisted configuration.
3. Conclusions
In conclusion, a stretch and a packed trinuclear polyterpyridyl
ruthenium complexes containing three tpy-Ru-tpy moieties have
successfully been synthesized and characterized. The complex C2
displayed intense emission at 77 K, but owing to a unique twisted
configuration, complex C1 is almost non-emissive, even at 77 K. It
should be noted that the unique configuration resulted in the
reduction of the ligand field strength of the terpyridines. This dis-
covery provides useful results for molecular designs of polyter-
pyridyl ruthenium complexes to achieve the better photophysical
performance.
4.3. Preparation of 6,600-di(40-terpyridyl-p-phenyl)-40-(4-
decyloxyphenyl)-2,20:60,200-terpyridine (L1)
To a solution of 2 (312 mg, 0.5 mmol) and 40-(4-boronatophe-
nyl)[2,20:60,20’]terpyridine (424 mg, 1.2 mmol) in THF (30 mL),
aqueous NaOH (3.0 mL, 1 M) was added. The system was pumped
and backfilled with nitrogen; then Pd(PPh3)4 (70 mg) was added.
After refluxing for 48 h under nitrogen, the mixture was cooled
to 25 °C and evaporated under reduced pressure, and then
extracted with CH2Cl2. The organic phase was washed with water
and dried over MgSO4. After removal of the solvent, the residue
was purified by flash column chromatography (Al2O3), eluting with
4. Experimental section
4.1. Materials and methods
CHCl3 to give L1, as
a white solid: 275.4 mg (51%); m.p.
NMR spectra were recorded on a Bruker ADVANCE 400 or 500
NMR Spectrometer. 1H NMR chemical shifts are reported in ppm
downfield from tetramethylsilane (TMS) reference using the resid-
ual protonated solvent as an internal standard.
243–247 °C; 1H NMR (500 MHz, 298 K, CDCl3, ppm) d = 8.96 (s,
2H), 8.86 (s, 4H), 8.78 (d, 4H), 8.71 (m, 6H), 8.37 (d, 4H), 8.12 (d,
4H), 8.00 (t, 2H), 7.91 (m, 8H), 7.39 (t, 4H), 7.15 (d, 2H), 4.09 (t,
2H), 1.86 (m, 2H), 1.51 (m, 2H), 1.29 (m, 14H), 0.87 (t, 3H); 13C
NMR (500 MHz, 298 K, CDCl3, ppm): 159.92, 156.30, 156.22,
156.02, 155.86, 155.58, 149.69, 149.67, 149.17, 140.02, 138.85,
137.04, 136.88, 130.88, 128.47, 127.69, 127.51, 123.85, 121.41,
120.35, 119.94, 118.78, 118.67, 115.17, 69.09, 31.92, 29.63, 29.60,
29.45, 29.35, 29.32, 26.10, 22.69, 14.12; ESI/MS (m/z): 361.2
[L1+3H]3+ (calcd 362.1); 271.1 [L1+4H]4+ (calcd 274.0). Anal. Calcd
for C73H61N9O: C, 81.16; H, 5.69; N, 11.67. Found: C, 82.32; H, 5.92;
N, 11.67.
Mass spectra of complex C1 were determined on Waters Xevo
Q-Tof Mass Spectrometer under the following conditions: ESI cap-
illary voltage, 3050 V; cone voltage, 65 V; desolvation gas flow,
800 L/h; cone gas flow, 50 L/h; mass range (m/z), 100–2000. Mass
spectra of complexes C1 and C2 were determined on a Bruker
9.4T FT-ICR-MS Mass Spectrometer under the following
conditions: ESI capillary voltage, 2650 V for C1 and 2750 V for C2;
spray shield voltage, 1950 V for C1 and 2150 V for C2; dry gas flow,
5.0 L/min; neb gas flow, 3.0 L/min; mass range (m/z), 100–2000.
Absorption spectra were measured with Hitachi (model
U-3010) UV–vis spectrophotometer in a 1-cm quartz cell. Emission
spectra were measured with Hitachi (F-7000) fluorescence spec-
trophotometer in a 1-cm quartz cell.
4.4. Preparation of 5,500-dibrome-40-(4-(2-(2-(2-methoxyethoxy)
ethoxy)ethoxy)phenyl)-2,20:60,200-terpyridine (4)
To a round bottom flask, a mixture of 4-(2-(2-(2-methox-
yethoxy)ethoxy)ethoxy)benzaldehyde (3) (0.49 g, 1.82 mmol),
2-acetyl-5-bromopyridine (0.80 g, 4.0 mmol), absolute EtOH
Cyclic voltammetry (CV) was performed with a Zahner IM6
electrochemical workstation using glassy carbon discs as the

D. Liu et al. / Inorganica Chimica Acta 450 (2016) 293–298
297
(30 mL), and powdered NaOH (0.32 g, 8 mmol) were added. After
4.7. Preparation of C2
stirring at 30 °C for 8 h, the solution0s color changed from yellow
to red, after which 7.5 mL NHÅ3H2O (25–28%) was added and the
mixture was heated at 75 °C for 20 h to give a yellow solution.
the mixture was cooled to 25 °C and evaporated under reduced
pressure, then extracted with CH2Cl2. The organic phase was
washed with water and dried over MgSO4. After removal of the sol-
vent, the residue was purified by recrystallization with CH2Cl2 and
CH3OH to give compound 4 (0.47 g, 41.0%) as a white solid; m.p.
92–96 °C; 1H NMR (500 MHz, 298 K, CDCl3, ppm) d = 8.77 (s, 2H),
8.68 (s, 2H), 8.54 (d, 2H), 7.99 (d, 2H), 7.84 (d, 2H), 7.06 (d, 2H),
4.22 (t, 2H), 3.91 (t, 2H), 3.78 (t, 2H), 3.71 (t, 2H), 3.68 (t, 2H),
3.57 (t, 2H), 3.39 (s, 3H); 13C NMR (500 MHz, 298 K, CDCl3, ppm):
159.94, 155.00, 154.68, 150.16, 149.99, 139.45, 130.56, 128.46,
122.57, 121.24, 118.44, 115.11, 71.97, 70.91, 70.70, 70.61, 69.72,
67.58, 59.07; ESI/MS (m/z): 629.8 [4+H]+ (calcd 630.3). Anal. Calcd
for C28H27Br2N3O4ꢂ3CHCl3ꢂ4H2O: C, 35.14; H, 3.61; N, 3.97. Found:
C, 34.11; H, 3.58; N, 3.76.
The L2 (20.0 mg, 0.018 mmol) and (2,20:60,200-Terpyridine)
trichlororuthenium (26.5 mg, 0.06 mmol) was added to a 50 mL
flask, then 10 mL thylene glycol was added as solvent. The suspen-
sion was stirred at 120 °C for 24 h. After cooled to ambient temper-
ature, 20 mL CH3OH was added to the solution, followed by
precipitation with NH4PF6 to afford as a dark red solid, which
was washed with copious amounts of MeOH to give complex C2
(46 mg, 91%) as
a
dark red solid; m.p. >300 °C; 1H NMR
(500 MHz, 298 K, CD3CN, ppm) d = 9.15 (s, 2H), 9.00 (s, 4H), 8.90
(d, 2H), 8.88 (d, 2H), 8.79 (d, 4H), 8.67 (d, 4H), 8.63 (d, 2H), 8.54
(m, 5H), 8.45 (t, 2H), 8.42 (d, 2H), 8.33 (d, 2H), 8.26 (d, 4H), 8.03
(t, 2H), 7.96 (m, 8H), 7.74 (d, 4H), 7.65 (m, 4H), 7.41 (m, 10H),
7.31 (t, 2H), 7.20 (m, 8H), 4.37 (t, 2H), 3.95 (t, 2H), 3.75 (t, 2H),
3.68 (t, 2H), 3.65 (t, 2H), 3.56 (t, 2H), 3.37 (s, 3H); 13C NMR
(500 MHz, 298 K, CD3CN, ppm): 160.87, 158.13, 157.77, 157.06,
155.53, 155.28, 155.05, 154.86, 152.27, 152.19, 152.04, 150.09,
147.93, 146.62, 138.80, 137.85, 137.76, 137.49, 136.06, 135.98,
135.62, 135.59, 129.06, 129.01, 128.76, 128.22, 128.09, 127.32,
127.26, 127.18, 124.62, 124.59, 124.29, 124.24, 124.18, 123.76,
123.46, 121.23, 120.88, 120.86, 115.41, 115.38, 71.69, 70.52,
70.24, 70.11, 69.31, 68.01, 57.94.
4.5. Preparation of 5,500-di(40-terpyridyl-p-phenyl)-40-(4-(2-(2-(2-
methoxyethoxy)ethoxyphenyl)-2,20:60,200-terpyridine (L2)
To a solution of 4 (315 mg, 0.5 mmol) and 40-(4-boronatophe-
nyl)[2,20:60,20’]terpyridine (460 mg, 1.3 mmol) in THF (50 mL),
aqueous NaOH (3.0 mL, 1 M) was added. The system was pumped
and backfilled with nitrogen; then Pd(PPh3)4 (66 mg) was added.
After refluxing for two days under argon, the mixture was cooled
to 25 °C and evaporated under reduced pressure. The residue was
washed with 100 mL CH3OH. The precipitate was dried at 50 °C
in vacuo and purified by flash column chromatography (Al2O3),
eluting with CHCl3 to give L2, as a faint yellow solid: 330 mg
(61%); m.p. 135–138 °C; 1H NMR (500 MHz, 298 K, CDCl3, ppm)
d = 9.04 (s, 2H), 8.81 (s, 4H), 8.76 (m, 8H), 8.69 (d, 4H), 8.15 (d,
2H), 8.05 (d, 4H), 7.89 (m, 6H), 7.83 (d, 4H), 7.37 (t, 4H), 7.08 (d,
2H), 4.23 (t, 2H), 3.92 (t, 2H), 3.78 (t, 2H), 3.72 (t, 2H), 3.69 (t,
2H), 3.58 (t, 2H), 3.40 (s, 3H); 13C NMR (500 MHz, 298 K, CDCl3,
ppm): 159.80, 156.19, 156.06, 155.57, 155.46, 149.71, 149.43,
149.17, 147.51, 138.31, 138.25, 136.91, 135.72, 135.08, 130.91,
128.54, 128.08, 127.55, 123.90, 121.40, 121.37, 118.71, 118.35,
115.05 71.97, 70.91, 70.70, 70.61, 69.75, 67.56, 59.07; ESI/MS (m/z):
1086.5 [L2+H]+ (calcd 1086.4). Anal. Calcd for C70H65N9O4ꢂ5H2O:
C, 71.47; H, 5.57; N, 10.72. Found: C, 71.89; H, 5.87; N, 10.82.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (21274165), the Distinguished Professor
Research Fund from Central South University of China, the Funda-
mental Research Funds for the Central Universities from Central
South University (2013zzts014). The authors gratefully acknowl-
edge Prof. Dr. Carol D. Shreiner for her professional consultation.
The authors gratefully acknowledge the NMR measurements from
The Modern Analysis and Testing Center of CSU.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2016.06.017.
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