Design, synthesis and photoelectrochemical properties of hexagonal metallomacrocycles based on triphenylamine: [M6(4,4′-bis(2, 2′:6′,2″-terpyridinyl)triphenylamine)6(X) 12]; [M = Fe(II), PF6- and Zn(I

Article abstract of DOI:10.1039/b603691k

Synthesis of a novel bis(terpyridine) ligand, 4,4′-bis(2,2′: 6′,2″-terpyridinyl)triphenylamine, utilizing triphenylamine, as a specific angle controller, has led to the self-assembly of a unique hexagonal metallomacrocycle family, [Fe₆(2)₆

Full text of DOI:10.1039/b603691k

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Design, synthesis and photoelectrochemical properties of hexagonal
metallomacrocycles based on triphenylamine:
[M6(4,4ꢀ-bis(2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridinyl)triphenylamine)6(X)12]; [M = Fe(II),
−
−
PF6 and Zn(II), BF4 ]
Seok-Ho Hwang,a Charles N. Moorefield,b Pingshan Wang,a Frank R. Fronczek,c Brandy H. Courtneyc and
George R. Newkome*a
Received 13th March 2006, Accepted 18th May 2006
First published as an Advance Article on the web 30th May 2006
DOI: 10.1039/b603691k
Synthesis of a novel bis(terpyridine) ligand, 4,4ꢀ-bis(2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridinyl)triphenylamine, utilizing
triphenylamine, as a specific angle controller, has led to the self-assembly of a unique hexagonal
metallomacrocycle family, [Fe6(2)6(PF6)12] and [Zn6(2)6(BF4)12], utilizing
terpyridine–metal(II)–terpyridine connectivity. The crystal structure of the novel ligand shows that the
angle between the two terpyridinyl moieties is 119.69◦, which enabled the formation of the
hexagonal-shaped macrocycles. The crystal packing architectures of this starting ligand revealed
channels induced by solvent encapsulation. Following complexation of this ligand with transition
metals [Fe(II) or Zn(II)] in a one-pot reaction, the resultant structures were characterized by 1H and 13
C
NMR, UV/Vis and mass spectroscopies. The expected metal-to-ligand charge transfer (MLCT; kmax
582 nm) and emission (kem = 575 nm) characteristics were exhibited by both [Fe6(2)6(PF6)12] and
[Zn6(2)6(BF4)12]. The photoelectrochemical characteristics of these hexagonal metallomacrocycles
demonstrate that they can be used as sensitizers in dye-sensitized solar cells.
=
photoreceptor devices36 and organic light-emitting diodes.37,38
Here, we describe a new type of bis(terpyridine) ligand that can
form the desired hexagonal metallomacrocycle, possessing the
disubstituted triphenylamine unit, as an angle-control element
as well as potentially offering an opportunity to improve selected
photophysical properties. We expect that the incorporation of this
triphenylamine moiety into structurally rigid metallomacrocyclic
assemblies will start to expand the understanding of the optoelec-
tronic characteristics in specific supramolecular macroconstructs.
Introduction
The design and construction of supramolecular macrocyclic
architectures have been the subject of considerable attention by
many research groups over the past decade.1,2 Elegant work in
the area of self-assembly by Stang and coworkers,3–5 Lehn and
coworkers,6–8 Constable et al.,9–14 and many others15–19 has offered
a better understanding of (macro)molecular systems. This has
led to many successful strategies aimed at the construction of
metallomacrocyclic structures with motifs such as, triangles,20
squares,21–26 pentagons,27 and hexagons.28–30
The combination of various substitution patterns can result
in a plethora of predetermined internal bond angles within
molecular superstructures. So far, our strategy has been based
on m-bis(terpyridinyl)arenes possessing the specific 120◦ angle
with respect to the two ligating moieties for the construction of
hexagonal metallomacrocycles. This angle facilitates the assembly
of six programmed building blocks with six connecting transition
metals in the ubiquitous benzenoid shape, which is envisioned to
be the basis of a “modular building block set”31 capable of being
used to access “higher order” (fractal) architectures.
Results and discussion
Treatment of triphenylamine with excess of DMF and POCl3, the
well-known Vilsmeier reagent, gave the desired dialdehyde 1 in
52% yield (Scheme 1), which was supported by the appearance of
the characteristic absorption (13C NMR) at 191.72 ppm assigned
to the Ar–CHO and mass peak (ESI-MS) at m/z 323.8 [M +
Na]+. Reaction of dialdehyde 1 with 4.4 equiv. of 2-acetylpyridine
under basic conditions at 25 ◦C for 24 h, followed by addition
of excess NH4OAc in AcOH and then refluxing for 12 h gave the
angular building block 2 in 34% yield (Scheme 1). The successful
generation of 2 was evidenced by the appearance of the expected
new signals (1H NMR) at 8.73 (m, 6,6ꢀꢀ-tpyH, 3ꢀ,5ꢀ-tpyH), 8.67
(d, 3,3ꢀꢀ-tpyH) and 7.35 ppm (dd, 5,5ꢀꢀ-tpyH) attributed to the
terpyridinyl moieties and the presence of the definitive number
and position of the peaks in the 13C NMR; a mass peak (ESI-MS)
at m/z 816.3 [M + Ag]+ further confirmed the structure.
Owing to their relatively simple synthetic accessibility and
stability to oxidation, triarylamines have been widely used
as hole-transport components in optoelectronics32–35 in both
aDepartments of Polymer Science and Chemistry, The University of
Akron, Akron, OH, 44325-3909, USA. E-mail: newkome@uakron.edu;
Web: www.dendrimers.com
bMaurice Morton Institute of Polymer Science, The University of Akron,
Akron, OH, 44325-3909, USA
Vapor diffusion of hexane into a CHCl3 solution of 2 afforded a
single crystal for X-ray analysis (Fig. 1). The crystal structure data
revealed the terpyridines to be approximately coplanar and that
cDepartment of Chemistry, Louisiana State University, Baton Rouge, LA,
70803-1804, USA
3518 | Dalton Trans., 2006, 3518–3522
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
channels created by solvent encapsulation (Fig. 2(A)) while the side
view (Fig. 2(B)) of the crystal packing exhibits a layered stacking
˚
with an average separation of ca. 4.4 A. Inspection of the unit
cell reveals (see supporting information; CIF file) two antiparallel
terpyridine ligands.
The diamagnetic, hexameric Fe(II) complex 3, [Fe6(2)6(PF6)12],
was readily prepared by self-assembly of ligand 2 by treatment
with one equivalent of FeCl2·4H2O in MeOH for 12 h (Scheme 2).
The 1H NMR spectrum of 3 revealed a sharp singlet at 9.20 ppm
(3ꢀ,5ꢀ-tpyH), indicating the presence of a single homogenous
environment; this is in contrast to the broadened or multiple
signals realized for either linear or polymeric oligomers, as
demonstrated in related systems.29 The Fe(II) metallomacrocycle
was confirmed by the observed upfield shift for the doublet at
7.24 ppm (6,6ꢀꢀ-tpyHs; Dd = −1.49) and a downfield shift for
the singlet at 9.20 ppm (3ꢀ,5ꢀ-tpyHs; Dd = 0.47) when compared
to the absorptions for the uncomplexed starting material. The
hexagonal cyclic motif was further established (ESI-MS) by the
Scheme 1 Reagents and conditions: (a) POCl3, DMF, dichloroethane;
(b) (i) 4.4 equiv. 2-acetylpyridine, NaOH; (ii) NH4OAc, AcOH, reflux.
Fig. 1 ORTEP drawing of bis(terpyridine) ligand 2. The probability
chosen for the ellipsoids was 50%.
they possessed the desired angle (119.69◦) juxtaposition necessary
for hexamer formation. The pyridine rings of the terpyridinyl
moieties adopted the anti-conformation with N–C–C–N torsion
angles in the range 159.63(15)–176.25(17)◦, typical of all such
structures. The crystal packing architecture of ligand 2 revealed
Scheme 2 Reagents and conditions: (a) (i) FeCl2·4H2O, MeOH or
Zn(BF4)2·8H2O, MeCN, reflux; (ii) for 3, NH4PF6/MeOH.
Fig. 2 Crystal packing of ligand 2: (A) top view of packing morphology indicating solvent (CHCl3) encapsulation channel, (B) side view of the
asymmetric units packing.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 3518–3522 | 3519
©

View Article Online
Table 1 Photovoltaic performances of dye-sensitized solar cell device
(ITO:TiO2|hexamer:KI–I2 electrolyte|graphite) under 100 mW cm−2 light
source
definitive signals for multiple-charged entities ranging from a +8
to +11 charge state derived from the loss of PF5 and PF6−, either
separately or together.
The related yellow semicrystalline [Zn6(2)6(BF4)12] was gener-
ated (55%) by the treatment of a 1 : 1 mixture of ligand 2 with
Zn(BF4)2·8H2O inMeCN for 24 hat 80 ◦C. The absence (1H NMR)
of extraneous peaks excluded the presence of starting materials,
intermediates and linear oligomers. The diagnostic shifts of the
doublets at 7.87 ppm (6,6ꢀꢀ-tpyHs; Dd = −0.86) and the singlet at
8.99 ppm (3ꢀ,5ꢀ-tpyHs; Dd = 0.26) along with definitive ESI-MS
data (m/z 544.4 [M − 9BF4−]9+, 624.5 [M − 8BF4−]8+, 725.1 [M −
7BF4−]7+, 860.3 [M − 6BF4−]6+, 1049.6 [M − 5BF4−]5+, 1333.6
[M − 4BF4−]4+, 1807.8 [M − 3BF4−]3+), all support the structural
assignment.
The UV/Vis spectra of 3 and 4 were measured (MeCN) and
are shown in Fig. 3. The Fe(II) hexamer showed the lowest
energy ligand-centered p–p* transitions of the terpyridine moieties
at 423 nm. While the metal-to-ligand charge-transfer (MLCT)
transitions derived from the promotion of an electron from the
Fe(II) d-orbitals to unfilled ligand p* orbitals37 appeared at 582 nm.
Complex
Jsca/lA cm−2
Vocb/mV
ff c (%)
gd (%)
3
4
160
230
255
391
26.9
68.1
0.032
0.180
a Short-circuit photocurrent density. b Open-circuit photovoltage. c Fill
factor. d Photoconversion efficiency of the solar cell.
these devices allowed the calculation of the values shown in
Table 1. The fill factor (ff ), the short circuit photocurrent
(Jsc), as well as the open circuit photopotential (Voc) for the
Zn(II) metallomacrocycle, showed superior results over the Fe(II)
metallomacrocycle. Further, the total photoconversion efficiency
of the cell (g) using electromagnetic radiation spanning the visible
region of the spectrum exhibited better values than in the case of
the Zn(II) metallomacrocycle 4.
Conclusion
In the case of the Zn(II) hexamer 4, absorption bands at kmax
=
285, 319, 330, 433 nm originating from intraligand charge transfer
(1ILCT) were observed without MLCT peaks; the MLCT of the
Zn(II) terpyridine complex can be excluded.38 The Zn(II) hexamer
shows a strong yellow emission at 575 nm when excited with UV
light (400 nm). The fluorescence of the Zn(II) hexamer in MeCN
solution is shown in Fig. 3(B); whereas, the Fe(II) hexamer did not
show an emission peak.
A new ditopic triphenylamine-based bis(terpyridine) ligand pos-
sessingacritical119.69◦ anglerelativetoeachcoordinationsitehas
been crafted and demonstrated to form of a series of unique, self-
assembled, hexagonal metallomacrocycles. The structures of the
ligand and the corresponding metallomacrocycles were confirmed
by means of H and 13C NMR, UV-Vis spectroscopy and mass
spectrometry. Preliminary results of the photoelectrochemical per-
formances for these materials show their potential for application
in dye-sensitized solar cells.
1
Experimental
Chemicals were purchased and used without further purification.
Thin layer chromatography (TLC) was conducted on flexible
sheets precoated with Al2O3 (IB–F) or SiO2 (IB2–F) and visualized
by UV light. Column chromatography was conducted using basic
Al2O3, Brockman Activity I (60–325 mesh) or SiO2 (60–200 mesh)
from Fisher Scientific. The melting points were determined on
1
an Electrothermal 9100 heater. H and 13C NMR spectra were
recorded on a Varian Gemini 300 NMR spectrometer using
CDCl3, except where noted. Mass spectra were obtained on a
Bruker Esquire Electrospray Ion Trap Mass Spectrometer (ESI-
MS). UV/Vis absorption spectra were obtained on Hewlett-
Packard UV/Vis spectrophotometer. Photoluminescence spectra
were obtained using a Perkin-Elmer LS55 luminescence spectrom-
eter.
Fig. 3 UV/Vis absorption (solid line) and emission (dashed line) spectra
for metallomacrocycles 3 (A) and 4 (B).
4,4ꢀ-Diformyltriphenylamine (1)
Due to their light absorption properties, constructs 3 and 4
were also studied as sensitizer materials for solar cell devices.
Photovoltaic experiments using dye-covered nanocrystalline TiO2
electrodes (prepared by dipping the semiconductor substrate into
a 0.2 mM MeCN solution of each hexamer) properly fitted in
a solar cell device,27 were conducted using an AM 1.5 (100 mW
cm−2) incident light source and an electrolyte containing 0.3 M
KI + 0.015 M I2 dissolved in a 4 : 1 ratio of propylene
and ethylene carbonate. Discharge experiments conducted with
Phosphorus oxychloride (37.3 mL, 400 mmol) was added dropwise
to stirred DMF (62 mL) at 0 ◦C. The mixture was stirred at
0
◦C for 1 h and then stirred at 25 ◦C for another 1 h. After
the addition of triphenylamine (8.0 g, 32.6 mmol) dissolved in
◦
dichloroethane, the mixture was stirred at 80 C for 48 h. After
cooling, the solution was poured into cold water. The resulting
mixture was neutralized to pH 7 with aq. NaOH solution and
extracted with CH2Cl2. The extract was washed with sat. brine
solution and the solvent was evaporated in vacuo. The residue was
3520 | Dalton Trans., 2006, 3518–3522
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
purified by column chromatography (SiO2) eluting with a hexane–
was filtered through Celite, then Et2O (150 mL) was added to
precipitate the complex, ◦which was filtrated to afford 4 (>55%) as
a orange solid: mp >400 C (decomp.); 1H NMR (CD3CN): d 8.99
(s, 3ꢀ,5ꢀ-tpyH, 4H), 8.76 (d, J = 8.1 Hz, 3,3ꢀꢀ-tpyH, 4H), 8.25 (d,
J = 8.4 Hz, 3,5-ArH, 4H), 8.19 (dd, J = 8.1, 6.9 Hz, 4,4ꢀꢀ-tpyH,
4H), 7.87 (d, J = 4.5 Hz, 6,6ꢀꢀ-tpyH, 4H), 7.56 (dd, J = 8.4, 6.9 Hz,
3,5-ArꢀH, 2H), 7.49 (d, J = 8.4 Hz, 2,6-ArH, 4H), 7.45–7.39 (m,
4-ArꢀH, 5,5ꢀꢀ-tpyH, 5H); 13C NMR (CD3CN): d 156.36, 151.00,
150.89, 149.13, 149.07, 147.28, 142.31, 131.36, 130.89, 130.45,
128.55, 128.12, 124.65, 124.26, 121.59, 119.23; UV/vis (MeCN):
kmax/nm (e/dm3 mol−1 cm−1) 285 (5.97 × 105), 319 (3.72 × 105),
330 (3.62 × 105), 433 nm (4.29 × 105); ESI-MS: m/z 544.4 [M −
EtOAc (3 : 1, ◦v/v) mixture to afford 1 (52%) as a light-yellow
1
solid: mp 143 C; H NMR: d 9.90 (s, CHO, 2H), 7.78 (d, J =
8.4 Hz, 3,5-ArH, 3,5-ArꢀH, 4H), 7.41 (t, J = 7.5 Hz, 3,5-ArꢀꢀH,
2H), 7.27 (t, J = 7.2 Hz, 4-ArꢀꢀH, 1H), 7.21–7.17 (m, 2,6-ArH, 2,6-
ArꢀH, 3,5-ArꢀꢀH, 6H); 13C NMR: d 122.98, 124.75, 126.47, 127.28,
130.36, 131.52, 145.72, 152.23, 190.71; ESI-MS: m/z 323.8 [M +
Na]+ (calc. m/z 324.1).
4,4ꢀ-Bis(2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridinyl)triphenylamine (2)
The dialdehyde 1 (4.8 g, 15.9 mmol) was dissolved in EtOH
(100 mL) then 2-acetylpyridine (8.49 g, 70.1 mmol) was added,
followed after 2 min by NaOH powder (2.8 g, 70.0 mmol). After
the dark pink solution had been stirred at 25 ◦C for 24 h, the
solvent was evaporated in vacuo to yield a dark brown solid, as
the intermediate. Ammonium acetate (26 g, excess) and glacial
AcOH (100 mL) were added and the mixture was refluxed for
12 h. The dark brown solution was cooled and neutralized with
aqueous Na2CO3. The crude product was extracted with CH2Cl2
and column chromatographed (Al2O3) eluting with a hexane–
EtOAc (1 : 2, v/v) mixture to afford 2 (34%) as a yellow solid:
mp 290–291 ◦C (decomp.); 1H NMR: d 8.73 (m, 6,6ꢀꢀ-tpyH, 3ꢀ,5ꢀ-
tpyH, 8H), 8.67 (d, J = 7.8 Hz, 3,3ꢀꢀ-tpyH, 4H), 7.90–7.83 (m,
4,4ꢀꢀ-tpyH, 2,6-ArH, 6H), 7.35 (dd, J = 4.8, 7.2 Hz, 5,5ꢀꢀ-tpyH,
4H), 7.27–7.21 (m, 3,5-ArH, 2,5-ArꢀH, 3,5-ArꢀH, 7H), 7.14 (t, J =
4.8 Hz, 4-ArꢀH, 1H); 13C NMR: d 156.58, 156.12, 149.89, 149.53,
148.52, 147.27, 137.04, 132.86, 129.77, 128.52, 125.47, 124.16,
124.12, 123.97, 121.55, 118.60; ESI-MS: m/z 816.3 [M + Ag]+
(calc. m/z 816.2).
−
9+
−
8+
9BF4
]
(calc. m/z = 544.4), 624.5 [M − 8BF4
]
(calc. m/z
623.3), 725.1 [M − 7BF4
]
7+ (calc. m/z 724.8), 860.3 [M − 6BF4
]
−
−
6+
−
(calc. m/z 860.1), 1049.6 [M − 5BF4
]
5+ (calc. m/z 1049.4), 1333.6
−
4+
−
3+
[M − 4 BF4
m/z 1806.9).
]
(calc. m/z 1333.5), 1807.8 [M − 3BF4
]
(calc.
Crystal data for 2
¯
C48H33N7·CHCl3, M = 827.18, triclinic, space group P1, a =
˚
12.9078(10), b = 13.573(2), c = 13.602 (2) A, a = 90.432(6), b =
◦
3
˚
109.097(7), c = 115.196(6) , V = 2007.4(4) A , T = 110 K, Z =
2, l(Mo-Ka) = 0.275 mm−1, 13328 independent reflections, Rint
0.037, R1 = 0.057, wR2 = 0.154 (for all data).
CCDC reference number 601362.
=
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b603691k
Fabrication of the photovoltaic cell device
[Fe6(2)6(PF6)12] (3)
Nanocrystalline TiO2 electrodes were prepared by applying a
4 V potential difference39 between a steel sheet and an ITO
conducting glass substrate immersed in a 10 mL [0.5 g TiO2
(P25, Degussar AG, Germany, a mixture of ca. 30% rutile and
70% anatase, BET surface area 55 m2 g−1) in 5% 2-propanol in
water (v/v)] colloidal suspension for 40 s. Following previous
reports in the literature,40 the electrodes were then taken out of the
electrophoretic apparatus, sintered at 450 ◦C in air for 30 min and
characterized by general tools (AFM, XRD, Raman spectroscopy,
cyclic voltammetry and perfilometry). From the characterization
results, it was found that the electrode thus prepared consisted
of nanoparticulate TiO2 in the anatase phase, with roughness
factors of 540, an average thickness of ∼2 lm and a flat band
potential, EFB, of −0.2 V vs. NHE. This value agrees well with
previous reports,41,42 and is substantially more positive than that
reported for nanocrystalline electrodes prepared using the typical
spin coating protocol (−0.5 V vs. NHE). This effect, which has
been reported41 recently, is associated with an increase of Ti3+
dopant surface sites that result from hydrogen adsorption during
the electrophoretic deposition process. Hexamers, as the dye, were
coated onto the TiO2 layer by dipping the electrode for 12 h in
a MeCN solution (ca. 0.2 mmol L−1). The assembled devices
for photovoltaic measurements consisted of a dye-coated TiO2
electrode, Ti substrate covered with a film of colloidal graphite
as a counter electrode, the electrolyte containing a deoxygenated
0.3 M of KI + 0.015 M of I2 aqueous solution,43 and Teflon tape
that was used to maintain a 0.5 mm gap between the two electrodes.
A MeOH solution of one equivalent of FeCl2·4H2O (54 mg,
270 lmol) was added to a suspension of ligand 2 (190 mg,
270 lmol) in MeOH (40 mL). The mixture was stirred at
25 ◦C for 24 h. The resultant deep purple solution was filtered
through Celite, then a slight excess of methanolic ammonium
hexafluorophosphate was added to precipitate the complex, which
was purified by column chromatography (SiO2) eluting with a
H2O–CH3CN–sat. aq. KNO3 (1 : 7 : 1, ◦v/v/v) mixture to afford
1
3 (>50%) as a purple solid: mp >400 C (decomp.); H NMR
(CD3CN): d 9.20 (s, 3ꢀ,5ꢀ-tpyH, 4H), 8.64 (d, J = 7.8 Hz, 3,3ꢀꢀ-tpyH,
4H), 8.37 (d, J = 8.4 Hz, 3,5-ArH, 4H), 7.93 (dd, J = 7.2, 7.2 Hz,
4,4ꢀꢀ-tpyH, 4H), 7.58 (d, J = 6.9 Hz, 2,6-ArH, 2,6-ArꢀH, 4H), 7.45–
7.37 (m, 3,4,5-ArꢀH, 3H), 7.24 (d, J = 5.4 Hz, 6,6ꢀꢀ-tpyH, 4H), 7.11
(dd, J = 6.6, 6.0 Hz, 5,5ꢀꢀ-tpyH, 4H); 13C NMR (CD3CN): d 161.36,
159.26, 154.20, 150.68, 150.60, 147.60, 139.79, 131.61, 131.35,
130.19, 128.36, 127.95, 126.90, 124.91, 121.86, 119.19; UV/vis
(MeCN): kmax/nm (e/dm3 mol−1 cm−1) 224 (3.06 × 105), 283 (4.37 ×
105), 321 (3.43 × 105), 423 (1.77 × 105), 582 nm (2.88 × 105); ESI-
−
11+
MS: m/z 428.9 [M − 11PF6
]
(calc. m/z = 429.8), 494.2 [M −
6PF6 − 4PF5]10+ (calc. m/z 494.8), 558.1 [M − 9PF6
]
(calc.
−
− 9+
−
m/z 557.5), 657.2 [M − 3PF6 − 5PF5]8+ (calc. m/z 657.1).
[Zn6(2)6(BF4)12] (4)
Zn(BF4)2·8H2O (77 mg, 200 lmol) was added to a solution of 2
(143 mg, 200 lmol) in MeCN and the mixture was refluxed for
48 h. After the mixture had cooled to 25 ◦C, the resultant solution
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 3518–3522 | 3521
©

View Article Online
20 S.-H. Hwang, C. N. Moorefield, F. R. Fronczek, O. Lukoyanova,
L. Echegoyen and G. R. Newkome, Chem. Commun., 2005, 713–
715.
Acknowledgements
The authors gratefully acknowledge the National Science Foun-
dation (DMR-041780, INT-0405242), the Air Force Office of
Scientific Research (F49620-02-1-0428,02) and the Ohio Board
of Regents for financial support.
21 F. A. Cotton, C. Lin and C. A. Murillo, J. Am. Chem. Soc., 2001, 123,
2670–2671.
22 X. Liu, C. L. Stern and C. A. Mirkin, Organometallics, 2002, 21, 1017–
1019.
23 S.-S. Sun, J. A. Anspach and A. J. Lees, Inorg. Chem., 2002, 41, 1862–
1869.
24 F. A. Cotton, L.M. Daniels, C. Lin, C. A. Murillo and S.-Y. Yu, J. Chem.
Soc., Dalton Trans., 2001, 502–504.
25 H. Gang, G. Dong, D. Chun-Ying, M. Hong and M. Qing-jin,
New J. Chem., 2002, 26, 1371–1377.
References
1 U. S. Schubert, H. Hofmeier and G. R. Newkome, Modern Terpyridine
Chemistry, Wiley-VCH, Weinheim, 2006.
26 S. J. Lee and W. Lin, J. Am. Chem. Soc., 2002, 124, 4554–4555.
27 S.-H. Hwang, P. Wang, C. N. Moorefield, L. A. God´ınez, J. Manr´ıquez,
E. Bustos and G. R. Newkome, Chem. Commun., 2005, 4672–
4674.
28 G. R. Newkome, T. J. Cho, C. N. Moorefield, G. R. Baker, M. J.
Saunders, R. Cush and P. S. Russo, Angew. Chem., Int. Ed., 1999,
38, 3717–3721.
2 L. Cronin, Annu. Rep. Prog. Chem., Sect. A., 2004, 100, 323–383.
3 P. S. Mukherjee, N. Das, Y. K. Kryschenko, A. M. Arif and P. J. Stang,
J. Am. Chem. Soc., 2004, 126, 2464–2473.
4 M. Schweiger, S. R. Seidel, A. M. Arif and P. J. Stang, Inorg. Chem.,
2003, 41, 2556–2559.
5 Y. K. Kryschenko, S. R. Seidel, A. M. Arif and P. J. Stang, J. Am. Chem.
Soc., 2003, 125, 5193–5198.
29 G. R. Newkome, T. J. Cho, C. N. Moorefield, R. Cush, P. S. Russo,
L. A. God´ınez, M. J. Saunders and P. Mohapatra, Chem. Eur. J., 2002,
8, 2946–2954.
30 G. R. Newkome, T. J. Cho, C. N. Moorefield, P. P. Mohapatra and L. A.
God´ınez, Chem. Eur. J., 2004, 10, 1493–1500.
6 M. Ruben, U. Ziener, J.-M. Lehn, V. Ksenofontov, P. Gu¨tlich and
G. B. M. Vaughan, Chem. Eur. J., 2005, 11, 84–100.
7 M. Barboiu, G. Vaughan, R. Graff and J.-M. Lehn, J. Am. Chem. Soc.,
2003, 125, 10257–10265.
8 M. Ruben, J. Rojo, F. J. Romero-Salguero, L. H. Uppadine and J.-M.
Lehn, Angew. Chem., Int. Ed., 2004, 43, 3644–3662.
9 E. C. Constable, C. E. Housecroft, M. Neuburger, S. Schaffner and
C. B. Smith, Dalton Trans., 2005, 2259–2267.
10 H. S. Chow, E. C. Constable, C. E. Housecroft and M. Neuburger,
Dalton Trans., 2003, 4568–4569.
11 E. C. Constable, C. E. Housecroft and C. B. Smith, Inorg. Chem.
Commun., 2003, 6, 1011–1013.
31 J. K. Young, G. R. Baker, G. R. Newkome, K. F. Morris and C. S.
Johnson, Jr., Macromolecules, 1994, 27, 3464–3471.
32 S. Thayumanavan, S. Barlow and S. R. Marder, Chem. Mater., 1997,
9, 3231–3235.
33 B. E. Koene, D. E. Loy and M. E. Thompson, Chem. Mater., 1998, 10,
2235–2250.
34 K. Y. Law, Chem. Rev., 1993, 93, 449–486.
35 U. Mitschke and P. Ba¨uerle, J. Mater. Chem., 2000, 10, 1471–1507.
36 S. R. Forrest, Chem. Rev., 1997, 97, 1793–1896.
37 M. Beley, J.-P. Collin, J.-P. Sauvage, F. Heisel and A. Miech, J. Chem.
Soc., Dalton Trans., 1991, 3157–3159.
12 E. C. Constable, B. A. Hermann, C. E. Housecroft, M. Neuburger, S.
Schaffner and L. J. Scherer, New J. Chem., 2005, 29, 1475–1481.
13 C. B. Smith, E. C. Constable, C. E. Housecroft, E. Catherine and B. M.
Kariuki, Chem. Commun., 2002, 2068–2069.
38 X. Wang, A. D. Guerzo and R. H. Schmehl, Chem. Commun., 2002,
2344–2345.
14 E. C. Constable, E. Figgemeier, C. E. Housecroft, J. Olsson and Y. C.
Zimmermann, Dalton Trans., 2004, 1918–1927.
15 M. Oh, G. B. Carpenter and D. A. Sweigart, Acc. Chem. Res., 2004, 37,
1–11.
39 A. Wahl and J. Augustynski, J. Phys. Chem. B, 1998, 102, 7820–
7828.
40 G. P. Smestad and M. Gra¨tzel, J. Chem. Educ., 1998, 75, 752–756.
41 H. Pelouchova, P. Janda, J. Weber and L. Kavan, J. Electroanal. Chem.,
2004, 566, 73–83.
16 B. Gholarmkhass, H. Mametsuka, K. Koike, T. Tanabe, M. Furue and
O. Ishitani, Inorg. Chem., 2005, 44, 2326–2336.
17 E. Figgemeier, E. C. Constable, C. E. Housecroft and Y. C. Zimmer-
mann, Langmuir, 2004, 20, 9242–9248.
18 J. Rebek, Jr., Acc. Chem. Res., 1999, 32, 278–286.
19 A. E. Rowan and R. J. M. Nolte, Angew. Chem., Int. Ed., 1998, 37,
63–68.
42 J.-D. Kim, S.-I. Pyun and M. Seo, Electrochim. Acta, 2003, 48, 1123–
1130.
43 K. Hara, T. Horiguchi, T. Kinoshita, K. Sayama and H. Arakawa, Sol.
Energy Mater. Sol. Cells, 2001, 70, 151–161.
3522 | Dalton Trans., 2006, 3518–3522
This journal is
The Royal Society of Chemistry 2006
©