Photochromic and redox properties of bisterpyridine ruthenium complexes based on dimethyldihydropyrene units as bridging ligands

Article abstract of DOI:10.1021/ic2003904

We report herein the synthesis and characterization of four new bisterpyridine dinuclear ruthenium complexes containing the dimethyldihydropyrene (DHP) photochrome as bridging ligand. A synthetic strategy has been developed based on a Suzuki coupling reaction to synthesize these novel terpyridine-DHPs. The reactivity of these different ligands and dinuclear ruthenium complexes with light was examined by ¹H NMR and monitoring the changes in their absorption spectra upon irradiation at controlled wavelengths. The free ligands and their corresponding ruthenium complexes all displayed photochromic properties with highly efficient conversion between the closed stable isomers (DHP) and their open forms (CPD). The properties of the compounds in their closed and open forms were investigated by cyclic voltammetry, spectroscopy, and luminescence measurements.

Full text of DOI:10.1021/ic2003904

ARTICLE
pubs.acs.org/IC
Photochromic and Redox Properties of Bisterpyridine Ruthenium
Complexes Based on Dimethyldihydropyrene Units as Bridging
Ligands
Neus Vilꢀa,* Guy Royal, Frꢁedꢁerique Loiseau, and Alain Deronzier
Dꢁepartement de Chimie Molꢁeculaire, UMR CNRS-5250, Institut de Chimie Molꢁeculaire de Grenoble,
Universitꢁe Joseph Fourier Grenoble I, FR CNRS-2607, BP 53, 38041 Grenoble Cedex 9, France
ABSTRACT: We report herein the synthesis and characterization of four
new bisterpyridine dinuclear ruthenium complexes containing the di-
methyldihydropyrene (DHP) photochrome as bridging ligand. A synthetic
strategy has been developed based on a Suzuki coupling reaction to
synthesize these novel terpyridineꢀDHPs. The reactivity of these different
ligands and dinuclear ruthenium complexes with light was examined by
1H NMR and monitoring the changes in their absorption spectra upon
irradiation at controlled wavelengths. The free ligands and their corre-
sponding ruthenium complexes all displayed photochromic properties
with highly efficient conversion between the closed stable isomers (DHP)
and their open forms (CPD). The properties of the compounds in their
closed and open forms were investigated by cyclic voltammetry, spectros-
copy, and luminescence measurements.
’ INTRODUCTION
out a systematic study of their trans/cis isomerization and the
concurrent change of the photophysical and electrochemical
properties.8 Terpyridine or bipyridine metal complexes asso-
ciated with a photochromic dithienylethene (DTE) unit were
also investigated by Abru~na and co-workers.9 It was shown that
their photochemical and electrochemical properties could be
finely tuned by changing the metal centers, the arrangement of
terpyridine and dithienylcyclopentene units, and the terminal
substituents. In particular, a dinuclear complex bridged by an
open DTE was found to be inert to ultraviolet photoirradiation
when OsII, RuII, or FeII was used, while the CoII system under-
went efficient photochemical cyclization.9a
Molecular switches, i.e., molecular systems that can be rever-
sibly converted between two or more different well-defined and
stable states by application of an external stimulus such as light,
electricity, or a chemical process, are the subject of intensive
research.1 In particular, optical switches appear very attractive for
construction of molecular devices and materials because their
control can be achieved using light at different wavelengths,
which is an easily controllable and clean energy that does
not need direct contact or connection.1,2 For example, some
fascinating studies have already demonstrated applications of
spiropyran,3 fulgides,4 or dithienylethene2a,3ꢀ5 derivatives in
electronic devices (e.g., memories, logic gates, molecular wires)
or for construction of mechanical work based on geometrical
structural changes of individual molecules induced by external
stimuli.
In this context, a very promising strategy for the elaboration of
multifunctional materials is to covalently combine organic
photochromic derivatives with metal complexes.6 Indeed, metal
complexes can have well-defined and tunable optical, redox, and
magnetical properties, and their association with optical switches
may result in multiresponsive molecular assemblies that can find
applications in many domains, such as in electronics (molecular
logic gates, switchable molecular wires...), energy conversion,
catalysis, or sensors. In particular, bipyridine and terpyridine
metal complexes have been widely employed because of their
high stability, well-defined geometries, and appealing redox,
photophysical, and photochemical properties.7 For instance,
Nishihara and co-workers constructed a number of polypyridylꢀ
transition metal complexes bearing azobenzene units and carried
Here, we report the synthesis and characterization of a series
of dinuclear rutheniumꢀbisterpyridine complexes containing
the dimethyldihydropyrene (DHP)10,11 photochrome moiety
as a bridge, and one mononuclear-DHP complex is also presented
(L1RuꢀL5Ru, Chart 1).
Our objective was to investigate the photochromic, redox, and
luminescence properties of the DHP unit when covalently
coupled to terpyridine metal complexes and to evaluate the
potentialities of these systems for further applications in switch-
able devices or materials. In addition, as fatigue resistance and
thermal stability are among the most important requirements
that a photochromic material should accomplish in order to be
suitable for use as a molecular switch in devices useful as memory
media, thermal reclosing rates and lifetimes of some of the
compounds synthesized have been determined.
Received: February 24, 2011
Published: August 19, 2011
r
2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
Chart 1. Mono- and Bis-Ruthenium Complexes L1RuꢀL5Ru
Chart 2. Optically Triggered Interconversion of the Di-
methyldihydropyrene (DHP)/Cyclophanediene (CPD)
System
by stronger donor pentamethylferrocene moieties that probably
quench the photoexcited state of the system preventing the ring
opening of the DHP. This result shows that the properties of the
DHP unit can be finely tuned and strongly depend on its
environment.
’ RESULTS AND DISCUSSION
Synthesis of the Ligands. The five new bisterpyridine
(L1ꢀL4) and monoterpyridine (L5) ligands (Chart 3) were all
prepared using the same methodologies involving bromination
of the DHP unit and Suzuki cross-coupling reactions. The
synthetic procedure for L1 is represented in Scheme 1.
The DHP photochrome, which was essentially exploited
by Mitchell and co-workers11,12 and belongs to the family of
diarylethene, is a large π-conjugated system that can be quanti-
tatively optically and reversibly converted to its less π-conjugated
cyclophanediene (CPD) isomers (Chart 2). Interestingly, it repre-
sents a rare example of negative-T-photochrome, i.e., the color-
less open form (CPD) usually reverts both photochemically and
thermally to the colored and more stable DHP closed isomer.
A great advantage of the DHP moiety is that it can be
chemically modified in many various ways and thus constitutes
a real molecular platform ideally suitable for construction
of multifunctional architectures. Nevertheless, compared to
other organic photochromic molecules such as the well-known
dithienylcyclopentene,5 DHP derivatives have been much less
intensively studied because of much longer synthetic pathways
involved to afford them and examples of DHP systems associated
to metal complexes are still rare.13 Recently, a reversible photo-
switching of the electronic communication between two ferro-
cenyl groups bridged by a DHP unit through π-conjugated
ethynyl connectors was demonstrated.13d In contrast, no photo-
isomerization occurred when the two ferrocene units were replaced
This synthesis starts from the 2,7-di-tert-butyldimethyldihy-
dropyrene (1, DHP), the tert-butyl groups being introduced for
synthetic and solubility reasons. 1 was prepared in seven steps
employing the tert-butyltoluene as starting material as previously
described by Tashiro14 and improved by Mitchell.12c Bromina-
tion of 1 in the presence of N-bromosuccinimide lead to the
different bromo-DHP precursors of the bisboronic-DHP deriva-
tives required for the Suzuki cross-coupling reaction.12c Several
synthetic strategies have been employed to afford L1 via Suzuki
cross-coupling reaction. Initial attempts to generate the corre-
sponding boronic ester from either the 40-(4-bromophenyl)-
2,20:60,200-terpyridine or the 40-chloro-2,20:60,200-terpyridine led
to low yields or repeatedly failed in the second case.15 Alterna-
tively, the known bis-bromide DHP (2)12c was first lithiated with
2 equiv of n-BuLi followed by addition of the tributyl borate to
give the bisboronic DHP ester (3), which could be used without
further purification in the next step. A Suzuki coupling16 between
the bisboronic DHP ester (3) and the 40-(4-bromophenyl)-
2,20:60,200-terpyridine afforded the desired ligand (L1) in good
yield (74%). Generation of the corresponding bisboronic DHP
acid (4) and subsequent Suzuki cross-coupling as described
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Inorganic Chemistry
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Chart 3. Bisterpyridine (L1ꢀL4) and Monoterpyridine (L5) Ligands Synthesized
Scheme 1. Overall Synthetic Pathways for Preparation of L1 via Suzuki Cross-Coupling Reaction and Preparation of L1Ru
above did not enhance the yield of the final product due to its low
solubility in most of the organic solvents tested. The same
synthetic route was employed to prepare L2. In the case of
ligands L3 and L4 the first step of Scheme 1 was analogous as for
ligands L1 and L2. However, in the second step 40-chloro-
2,20:60,200-terpyridine was employed instead of the 40-(4-
bromophenyl)-2,20:60,200-terpyridine, leading to notably lower
yields (32ꢀ40%). This fact is in good agreement with the well-
known lower reactivity of the aryl chlorides in palladium-
catalyzed reactions.17 Table 1 summarizes the yields of the
bridging ligands synthesized.
methyl protons are shielded by the strong diatropic ring current.
In addition, these peaks appear slightly deshielded from those of
the DHP (1) parent (δ = ꢀ4.04 ppm12c) and no longer identical
to each other for L2, L4, and L5 due to a loss of the symmetry.
Preparation of Mono- and Dinuclear Ruthenium Com-
plexes (L1RuꢀL5Ru). As depicted in Scheme 1 for L1Ru,
preparation of the ruthenium complexes L1RuꢀL5Ru was
carried out in the last step of the synthetic pathway through a
divergent manner. In this approach, ligands L1ꢀL5 previously
synthesized after Suzuki coupling as mentioned above were
directly complexed with either 1 or 2 mol equiv of (tpy)RuCl3
to give the mononuclear (L5Ru) or dinuclear (L1RuꢀL4Ru)
Full characterization for each compound is given in the
Experimental Section. Analysis of the 1H NMR spectra of ligands
L1ꢀL5 clearly corroborates that the closed forms were isolated.
1
Ru(II) complexes, respectively. The H NMR spectrum con-
firmed the metalation of the bisterpyridineꢀDHP ligands with
a significant deshielding of the internal methyl protons that
appeared at δ between ꢀ3.1 and ꢀ2.8 ppm (Table 1 and
Figure 1).
1
In each case, H NMR peaks were observed in the negative
region of the spectrum (Table 1 and Figure 1). These signals are
characteristic of dihydropyrenes units in which the internal
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Table 1. Summary of the Preparation Yields, 1H NMR, and Spectroscopic Data Obtained in the Synthesis of 1, Ligands (L1ꢀL5),
and Ruthenium Complexes (L1RuꢀL5Ru)
1H NMR data for the internal methyl
(DHP unit)b
λmax, nmd
(ε/105 L molꢀ1.cmꢀ1
)
3
synthetic yields
(%)
compounds
closed/open
closed/open
1
ꢀ4.04 (6H)e/1.25 (6H)
486 (0.7)e
L1
60a
40a
56a
32a
72a
41c
35c
47c
38c
56c
ꢀ3.68 (6H)/1.34 (6H)
479 (0.18)/252 (1.37)
481 (0.22)/250 (1.45)
477 (0.25)/265 (1.71)
482 (0.28)/252 (1.67)
478 (0.23)/255 (1.02)
487 (0.36)f/252 (1.83)
485 (0.42) f/252 (1.68)
486 (0.45) f/263 (1.54)
489 (0.44) f/255 (1.27)
490 (0.43)f/252 (1.21)
L2
ꢀ3.71 (3H), ꢀ3.73 (3H)/1.31 (3H), 1.35 (3H)
ꢀ3.55 (6H)/1.28 (6H)
ꢀ3.56 (3H), ꢀ3.58 (3H)/1.38 (3H), 1.42 (3H)
ꢀ3.75 (3H), ꢀ3.73 (3H)/1.26 (3H), 1.36 (3H)
ꢀ2.98 (6H)/1.23 (6H)
ꢀ2.93 (3H), ꢀ2.90 (3H)/1.30 (3H), 1.39 (3H)
ꢀ2.86 (6H)/1.42 (3H)
ꢀ2.89 (3H), ꢀ2.87 (3H)/1.46 (3H), 1.52 (3H)
ꢀ3.04(3H), ꢀ3.01 (3H)/1.41 (3H), 1.47 (3H)
L3
L4
L5
L1Ru
L2Ru
L3Ru
L4Ru
L5Ru
a Reported yields of the ligands are calculated considering the corresponding monobromo- and dibromo-DHP's derivatives as starting material.
b 1H NMR spectra were recorded in CD3CN. c Metalation yields. d Dimethyldihydropyrene core-based transition recorded in CH3CN. e From ref 12c.
f Overlapped with the MLCT absorption band.
Figure 1. Partial 1H NMR spectra in CD3CN of the L1ꢀL5 ligands (left) and corresponding ruthenium complexes (right) in their closed forms. Signals
correspond to the internal methyl protons of the DHP unit.
’ ELECTRONIC ABSORPTION SPECTROSCOPY AND
PHOTOCHROMIC BEHAVIORS
(cutoff filter λ g 490 nm) led to the ring opening of the DHP
unit as observed by the progressive changes of the bands in the
UV region and the disappearance of the long wavelength
absorption bands of the ligands in the visible part of the spectrum
as the light yellow cyclophanediene (CPD) isomer forms.
Subsequent irradiation of the solution containing the open forms
of the ligands at λ = 254 nm gave rise to regeneration of the
spectrum corresponding to the initial closed form, showing the
reversibility of the isomerization process.
This opening process could be also conventionally followed by
1H NMR in CD3CN, as represented in Figure 3 displaying the
evolution of the spectrum upon photoirradation with visible light.
Significant changes have been observed in the region corresponding
Absorption spectra of CH3CN solutions of ligands L1ꢀL5 all
exhibit a typical band (S0 f S1) of the DHP unit located in the
450ꢀ700 nm range (Table 1). Compared to the precursor 1, it
appeared that incorporation of the terpyridine functionalities did not
produce a significant shift in the absorbance band with lowest energy.
The photochromic behavior of freshly prepared solutions of
the systems was investigated by monitoring the changes of their
absorption spectra upon irradiation with a specific wavelength of
light in a 1 cm cell cooled at ∼0 °C (ice bath). Representative
spectra are displayed in Figure 2. Irradiation of the green-brown
solutions of ligands L1ꢀL5 in their closed forms with visible light
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ARTICLE
Figure 2. Evolution of the absorption spectra of solutions 10ꢀ5 M of (A) L1, (B) L2, (C) L1Ru, and (D) L2Ru in CH3CN recorded every 5 min during
irradiation of the sample at λ g 490 nm (opening process). The blue and red spectra correspond in all the cases to the closed and open isomers,
respectively. (Insets) Corresponding closing process during UV irradiation (λ = 254 nm).
Table 2. Kinetic Parameter Values Estimated from Experi-
mental Data Obtained at Different Temperatures for the
Thermal Isomerization Process
compound
T (K)
k (min-1)
τ1/2 (min)
Eact (kcal/mol)
L1
328
318
311
328
318
311
328
318
311
328
318
311
0.0273
0.0056
0.0012
0.0304
0.0058
0.0014
0.1154
0.0228
0.0057
0.0737
0.0149
0.0038
25.4
123.3
557.1
22.8
36.6
L3
36.8
35.7
35.2
118.7
504.5
6.1
Figure 3. 1H NMR of L1 in CD3CN before (bottom, closed form) and
after (top, open form) irradiation with visible light (cutoff filter λ g
490 nm).
L1Ru
L3Ru
30.4
121.6
9.4
to the internal methyl protons for L1 before and after irradiation.
With this ligand, conversion from the closed to the open form is
accompanied by a large shift from ꢀ3.7 to +1.3 ppm of the
internal methyl protons. The total disappearance of the peak at
ꢀ3.7 ppm could be reached, which indicates a quantitative
photoconversion between isomers. Similar quasi-quantitative
conversion yields were also observed for the four other ligands.
These results thus indicate that associating terpyridine or phe-
nylterpyridine to the DHP core does not result in inhibition of
the switching properties of the DHP unit.
46.5
181.8
of the free ligands because of the overlapping of the MLCT band
of the bisterpyridine ruthenium(II) moiety with the low-energy
band of the DHP unit (Figure 2C and 2D). When irradiated with
visible light, the deep red-purple solution of the complexes in
acetonitrile bleached to very pale violet in accordance with
formation of the cyclophanediene isomer. However, this opening
process appeared to be slightly less effective (estimated to >85%)
than in the case of ligands L1ꢀL5, probably because of some
In the case of the ruthenium complexes L1RuꢀL5Ru, the
same DHP to CPD conversion could be reached. However,
evolution of the UVꢀvis spectrum in the 450ꢀ700 nm range
during irradiation by visible light was less marked than in the case
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Table 3. Redox Potentialsa of L1ꢀL5 Ligands and L1RuꢀL5-
Ru Complexes Before (closed forms) and After Irradiation
(open forms) with Visible Light (λ g 490 nm)
closed
form
open
form
E1/2
Epa
E1/2
E1/2
compounds (DHP+/DHP) (DHP2+/DHP+) (RuIII/RuII) (|ipc|/ipa)
DHP (1)
L1
0.26
0.31
0.34
0.32
0.33
0.32
0.32
0.34
0.36
0.38
0.33
0.84
0.83
0.85
0.81
0.84
0.82
0.85
0.88
0.90
0.91
0.84
Epa = 1.13c
b
Epa = 1.14c
L2
Figure 4. Cyclic voltammograms on the anodic region of millimolar
solutions of (A) L1 and (B) L1Ru before (full line) and after (dotted
line) irradiation of the solutions at λ g 490 nm. All data were recorded in
L3
L4
b
CH3CN + TBABF4. Scan rate 100 mV. sꢀ1
.
L5
Epa = 1.12c
1.04 (0.69)
1.04 (0.61)
1.09 (0.61)
1.12 (0.69)
1.06 (0.62)
L1Ru
L2Ru
L3Ru
L4Ru
L5Ru
1.08
1.04
1.10
1.09
1.05
’ ELECTROCHEMICAL BEHAVIOR
In contrast to their photochromic properties, the electroche-
mical behavior of the DHP derivatives reported has been much
less extensively investigated.12c,13 In this study, both the DHP
(1) and the new L1ꢀL5 and L1RuꢀL5Ru compounds were
studied by cyclic voltammetry (CV) in CH3CN containing tetra-
n-butylammonium tetrafluoroborate (TBABF4, 0.1 M) as sup-
porting electrolyte. Table 3 summarizes the electrochemical
data obtained for all investigated systems in their closed and
open forms.
The anodic electrochemical CV curves of 1 and the tpyꢀDHP
ligands L1ꢀL5 recorded at a scan rate of 100 mV/s appeared to
be very similar. Typical voltammetric curves obtained with L1 are
given in Figure 4A. In their closed states, all systems displayed a
first reversible wave at E1/2 ≈ +0.3 V versus Ag/AgNO3 (10ꢀ2 M
in CH3CN) attributed to the monoelectronic oxidation of the
DHP unit (DHP+•/DHP couple)13d followed by an irreversible
peak at Epa ≈ +0.85 V accompanied during the reverse scan by a
new and ill-defined reduction wave at around ∼ꢀ0.2 V. This
signal was attributed to the second oxidation of the DHP core
(DHP2+/DHP+•),13d and its irreversibility results from a coupled
chemical reaction that follows electrogeneration of the unstable
dicationic DHP2+ unit.
Upon photoswitching of the solutions of 1 and L1ꢀL5 by
irradiation of the electrochemical cell at λ g 490 nm (cutoff
filter), the cyclic voltammogram of the corresponding open CPD
isomers all displayed very similar features with a single and an
irreversible oxidation wave at Epa ≈ +1.1 V associated to a weak
reduction wave observed during the reverse scan at ∼ꢀ0.2 V.
Irreversibility of the oxidation waves observed in both the open
and the closed isomers was ascribed to chemical reactions that
follow electron transfer, and detailed investigations using spec-
troelectrochemical techniques are currently under way in our
laboratory in order to determine the nature of the electrogener-
ated product(s). However, on the basis of the CV profiles, it is
clear that incorporation of the terpyridine units does not deeply
modify the electrochemical behavior of the switching DHP unit.
Only a modest positive shift of the first oxidation process can be
outlined in the presence of the tpy substituents (up to ∼80 mV
with L2).
a All potentials are given in volts referred to the Ag+/Ag (10ꢀ2
M
in CH3CN) reference electrode. E1/2 = (Ep + Ep )/2 at 0.1 V sꢀ1
b Not measured. c Fully irreversible system.
.
a
c
slight quenching of the excited state of the DHP unit by the low-
energy MLCT transition. In addition, as observed with the free
ligands, the initial closed forms of L1RuꢀL5Ru could be regen-
erated by irradiation at 254 nm. The L1RuꢀL5Ru complexes thus
display good photoconversion, and the DHP unit keeps its
photochromic properties in the presence of the metal centers.
’ THERMAL RECLOSING AND LIFETIMES OF THE CPD
ISOMERS
The thermal isomerization process from the open to the
closed forms was investigated in CH3CN for compounds L1,
L3, L1Ru, and L3Ru at 38, 45, and 55 °C. In all cases, thermal
closing was followed by UVꢀvis spectroscopy, taking advantage
of the characteristic absorption band of the closed isomers
located at 477ꢀ487 nm (Table 1). In addition, since L1Ru and
L3Ru displayed an important overlapping of such a characteristic
absorption band with the MLCT band, the results obtained in the
case of these compounds were confirmed by following the
thermal closing process by 1H NMR in CD3CN. Integration of
the internal methyl protons was conveniently used to estimate
the experimental rate constants in these cases. The rate constants
estimated are summarized in Table 2.
Comparing the half-life time values (τ1/2) reported in Table 2
for compounds L1 and L3 with the previously reported for 1 at
46 °C (113 min),12c we can conclude that substitution of the
DHP core with terpyridine derivatives does not result in sig-
nificant changes concerning the thermal closing isomerization
since the kinetic parameters estimated are of the same order of
magnitude. In contrast, complexation of the ligands with ruthe-
nium complexes resulted in a lower thermal stability of the
corresponding open isomers for compounds L1Ru and L3Ru
according to their τ1/2 values determined at 45 °C, 30.4 and
46.5 min respectively as summarized in Table 2. Thus, compared
to the τ1/2 reported for 1,12c the presence of the ruthenium
complexes increased the thermal closing rate by 3.7 and 2.4 times
for compounds L1Ru and L3Ru, respectively.
The electrochemical behavior of the ruthenium complexes
L1RuꢀL5Ru was then investigated (see data in Table 3). The
cyclic voltammogramm of the L1Ru complex in its closed state is
represented in Figure 4B and displays three well-separated
oxidation waves at E1/2 = 0.32 V, Epa = 0.85 V (irreversible
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Table 4. Photophysical Data of the Closed Form of Com-
pounds 1, L1ꢀL5, and L1Ru ꢀL5Ru at Room Temperature in
Acetonitrile Solutions
compounds
λem, nm
ϕ
τ, ns
1
648
652
652
653
660
649
649
649
648
648
649
3.0 ꢁ 10ꢀ3
2.4 ꢁ 10ꢀ3
2.5 ꢁ 10ꢀ3
2.7 ꢁ 10ꢀ3
3.1 ꢁ 10ꢀ3
2.8 ꢁ 10ꢀ3
5.1 ꢁ 10ꢀ4
6.6 ꢁ 10ꢀ4
5.8 ꢁ 10ꢀ4
5.2 ꢁ 10ꢀ4
9.8 ꢁ 10ꢀ4
5.4
5.0
4.9
5.0
4.8
5.4
5.6
5.1
5.4
5.8
5.6
L1
L2
L3
L4
L5
L1Ru
L2Ru
L3Ru
L4Ru
L5Ru
Figure 5. Emission spectra of L2Ru at room temperature in acetonitrile
solution before (closed form; gray line) and after (open form; black line)
irradiation at λ g 490 nm.
variously substituted DHPs have determined that their relatively
low quantum yields of fluorescence arise from the fact that the
singlet excited states mainly decay to the ground state of the
DHPs by nonradiative channels (>95%).18 The remaining excita-
tion energy is converted by (i) formation of the CPD forms (ring
opening occurs from the singlet excited state), (ii) intersystem
crossing to the triplet excited state of the CPD forms, and (iii)
fluorescence processes. After extensive irradiation of L1ꢀL5 by
visible light, the CPD open forms were obtained and loss of
conjugation of the annulene ring resulted in an important blue
shift of the absorption spectra as well as a loss of fluorescence on
passing from the closed to the open forms.
oxidation), and E1/2 = 1.08 V. By comparison with the CV curves
of the metal-free L1ꢀL5 ligands, these signals were attributed to
the first and second oxidation of the DHP moiety followed by the
reversible metal-centered oxidation of the two (tpy)2Ru units.
Upon conversion of L1Ru into its open CPD isomer by visible
light irradiation, the resulting CV curve was deeply modified with
a single and nonfully reversible oxidation wave (|ipc| < ipa) at
E1/2 = 1.04 V. This signal was attributed to the overlays of the
reversible oxidation of the two (tpy)2Ru groups with the irrever-
sible oxidation of the CPD (open) bridge, this last being logically
responsible for the partial reversibility of the curve (ipc < ipa).
It should be also outlined that the DHP (closed form) or CPD
(open form) bridges are oxidized at lower or at similar potentials,
respectively, than the Ru(II) centers, which logically prevent
efficient electronic communication between the two (tpy)2Ru
groups. For this reason, the equivalent ruthenium ions are
oxidized at close potentials, giving rise to a unique observable
CV wave.
The other investigated systems L2RuꢀL5Ru all displayed
very similar behaviors to the L1Ru complex with three oxida-
tion waves in their closed forms and a unique wave at
∼1.0ꢀ1.1 V in their open states (see Table 3). The number,
position, or nature of the (tpy)2Ru moiety appeared to have
only a small effect on the potentials observed for the different
redox couples with shifts e100 mV (see Table 3). Logically, a
smaller intensity of the peaks corresponding to the RuIII/II
couple was observed with the L5Ru system that incorporates
only one (tpy)2Ru unit instead of two in the four other
complexes.
Concerning the DHP-bearing ruthenium complexes, com-
pounds L1RuꢀL5Ru, in the closed forms they exhibited weak
luminescence with maxima at similar wavelengths as the tpyꢀ
DHP analogous ligands. The monoexponential lifetimes were all
about 5 ns, like in the case of the tpyꢀDHP photoswitches
(Table 4). Considering the narrow shapes of the emission spectra
as well as their energies and lifetimes, the emission could be
attributed to deactivation of the switching part of the systems.
This result is not surprising since the luminescence properties of
the (tpy)2Ru-like complexes are very weak and their emission
lifetimes and quantum yields are very low (τ = 0.25 ns; ϕ <
10ꢀ5);19 therefore, emission from the Ru complex part of the
molecules was not detected. The quantum yields were 5-fold
lower with respect to the free ligands; this decrease is likely due to
the increased number of vibrational modes in the molecules
compared to the L1ꢀL5 compounds. As expected during con-
tinuous irradiation of the solutions of L1RuꢀL5Ru in acetonitrile
at λ g 490 nm, the luminescence intensity decreased: the metal
complexes displayed the same behavior as the tpyꢀDHP com-
pounds, which corroborates that the emitting excited states
are centered on the photoswitches. However, as observed by
1H NMR, the conversion between DHP and CPD forms was
slightly less effective. As a consequence, a very weak residual
emission from the closed form was still detected after irradiation.
The ratio of the emission quantum yields of the closed forms
when compared to the open forms is ca. 1/60 in the case of the
metal complexes and 1/110 in the case of the free ligands. The
luminescence quantum yields of the open forms of all com-
’ PHOTOPHYSICAL PROPERTIES
The luminescence properties of all compounds at room
temperature have been studied in acetonitrile solutions before
and after irradiation with visible light, i.e., in their open and
closed forms. The results are gathered in Table 4, and an example
of data is represented in Figure 5. In the case of the ligands
L1ꢀL5, the closed forms exhibited emission maxima in the range
649ꢀ660 nm, with quantum yields around 3 ꢁ 10ꢀ3 and
lifetimes in the nanosecond time scale (see Table 4). The
emission spectra were very narrow with very small Stokes shifts,
indicating that the nature of the emitting state is singlet. Previous
photophysical studies and laser flash photolysis experiments on
pounds are about 10ꢀ5
.
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Table 5. Ring-Opening Isomerization of Compounds 1, L2,
L3, L2Ru, and L3Ru in Acetonitrile Solutionsa
measurements performed at three different temperatures is on
the same order of magnitude as that previously reported for other
DHP derivatives. Lifetimes close to 4ꢀ5 days at room tempera-
ture can be estimated from the experimental data and support the
potential of the compounds here reported for molecular electron-
ics applications. To our knowledge, this work represents the first
example of DHP covalently associated to polypyridyl metal
complexes, and these results show that these systems are very
promising candidates for further developments in molecular
electronics, as logic gates, molecular memories, or single-mole-
cule devices. In addition, the designed ligands have well-defined
linear (L1 and L3) or V-shaped (L2 and L4) geometries that are
particularly suitable for construction of supramolecular light-
responsive polynuclear 1D chains24 or rings.25
compounds
ϕ/10ꢀ3
1
1.3 ( 0.3
0.5 ( 0.1
L2
L3
0.20 ( 0.01
0.08 ( 0.01
0.08 ( 0.02
L2Ru
L3Ru
a Errors correspond to average deviations.
’ RING-OPENING ISOMERIZATION QUANTUM YIELDS
The ring-opening quantum yield of some of the representative
compounds (1, L2, L3, L2Ru, L3Ru) was determined by actino-
metry, i.e., by comparing the change in absorption upon irradia-
tion at 468 nm during specific time periods for the compounds
with unknown quantum yield to the change in absorption for a
standard with a photochemical process for which the quantum
yield is known when irradiated at the same wavelength. The
potassium ferrioxalate actinometer was used as a primary
standard;20,21 the results are presented in Table 5.
The ring-opening quantum yield of compound 1 was mea-
sured to compare with literature values and agreed with
them.18,22 The low value indicates that the transannular bond
cleavage is intrinsically a low-efficiency process. Two explana-
tions have been suggested: (i) the mechanism of isomerization is
an activated process with a weak probability and (ii) the
photocleavage could arise via biradical formation from the singlet
excited state.23 The presence of terpyridine or phenylterpyridine
substituents on 1 in (4,9) or (4,10) positions, molecules L3 and
L2, respectively, slightly lowers the quantum yield. Coordination
of ruthenium centers on the polypyridine ligands (L2Ru and
L3Ru) further decreases the ring-opening efficiency, which
appears to be more than 1 order of magnitude smaller than in
the case of compound 1.
’ EXPERIMENTAL SECTION
General Procedures. All air-sensitive reactions were performed
under a dry argon atmosphere using standard Schlenk techniques.
Solvents were dried over appropriate drying agents and distilled before
use. All other solvents and reagents were purchased and used as received.
1H and 13C NMR spectra were recorded at 298 K on a Bruker 400 MHz
NMR spectrometer in CD2Cl2 (unless specified for ligands L1ꢀL5)
using the solvent residual peak for calibration (5.15 ppm) and in
CH3CN (unless specified for L1RuꢀL5Ru) using the solvent residual
peak for calibration (1.92 ppm). Mass spectra were recorded on a CL-
ESI/ApCI-ITD (Agilent 1100 and Esquire 3000+Bruker Daltonics)
system using methane as a carrier gas for chemical ionization. Elemental
analyses were performed by the Service Central d’Analyses, CNRS,
Lyon, France.
Electrochemical Measurements. Electrochemical experiments
were conducted in a conventional three-electrode cell under an argon
atmosphere at 293 K using a CH Instrument (CHI660B). Measurements
were done with solutions of the compounds (∼0.5 mM) in CH3CN
containing tetra-n-butylammonium tetrafluoroborate (TBABF4, 0.1 M)
as supporting electrolyte. The reference electrode was Ag/AgNO3
(10 mM in CH3CN containing 0.1 M TBABF4). The potential of the
regular ferrocene/ferrocenium (Fc/Fc+) redox couple in acetonitrile is
0.07 V under our experimental conditions. The working electrode was
a carbon disk (3 mm in diameter) polished with 1 μm diamond paste
before each use.
Thermal-Closing Isomerization Process. The thermal-closing
process has been investigated by UVꢀvis at three different tem-
peratures.12c,13aꢀ13c In order to estimate kinetic parameters concerning
such isomerization process from the closed to the open forms, diluted
solutions of the L1, L3, L1Ru, and L3Ru have been prepared in CH3CN
and irradiated in an ice bath with λ g 490 nm to afford their
corresponding open isomers photochemically. Afterward, aliquots
of the initial solution have been taken and evolution of their UVꢀvis
spectra followed at three different temperatures. In particular, the
kinetic measurements have been carried out in all cases studied at 311,
318, and 328 K. The absorption maximum located around 480 nm and
characteristic of the DHP core has been selected to relate the
absorbance as a function of time with the concentration of the closed
isomer in solution. The concentration of the open isomer could be
determined assuming that no degradation of the samples occurs
during the time of the experiments and as a result the kinetic constant
of the thermal closing could be determined according to a first-order
chemical process. Due to the noticeable overlapping of the MLCT
band with the absorption band mentioned above characteristic of the
DHP isomer additional experiments where carried out to follow the
process by 1H NMR.
’ CONCLUSION
The synthesis of four dinuclear (L1RuꢀL4Ru) and one
mononuclear (L5Ru) bisterpyridine ruthenium complexes cova-
lently connected to the dimethyldihydropyrene photoswitch has
1
been successfully accomplished. It was shown by H NMR,
UVꢀvis spectroscopy, electrochemical, and luminescence mea-
surements that the presence of the ruthenium complexes does
not induce negative effects on the photochromic behavior of the
DHP unit, and all investigated complexes and ligands exhibited
reversible isomerization between closed and open isomers by
alternate irradiation with visible (λ g 490 nm) and UV (254 nm)
light. The electrochemical behavior of the Ru(II) complexes was
shown to be strongly dependent on the form of the systems with
three separated oxidation waves in the 0ꢀ1.2 V range in the
closed isomer and only one observable wave at ∼1.1 V in the
open one. In addition, the DHP derivatives exhibited lumines-
cence properties with light emission in the range 649ꢀ660 nm.
Upon opening of the photochromic unit by visible light, the loss
of conjugation of the annulene ring of the CPD moiety resulted
in an important blue shift of the absorption spectra as well as a
loss of fluorescence. In addition, kinetic parameters (rate con-
stants, half-life times, and activation energies) have been also
determined for the thermal ring-closing process taking place
from the most unstable isomer (CPD). The data estimated from
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Inorganic Chemistry
ARTICLE
Electronic Spectroscopic and Photophysical Experiments.
Electronic absorption spectra were recorded on a Cary 300 or a Cary 50
Scan UVꢀvis spectrophotometer using acetonitrile as solvent. Emission
spectra were recorded in CH3CN at room temperature on a Varian Cary
Eclipse fluorescence spectrophotometer. Samples were placed in 1 cm
path length quartz cuvettes. Luminescence lifetimes measurements were
performed after irradiation at λ = 400 nm obtained by the second
harmonic of a titanium:sapphire laser (picosecond Tsunami laser spectra
physics 3950-M1BB and 39868-03 pulse picker doubler) at a 800 kHz
repetition rate. Fluotime 200 from AMS technologies was used for the
decay acquisition. It consists of a GaAs microchannel plate photomul-
tiplier tube (Hamamatsu model R3809U-50) followed by a time-
correlated single-photon counting system from Picoquant (PicoHarp300).
The ultimate time resolution of the system is close to 30 ps. Lumines-
cence decays were analyzed with Fluofit software available from
Picoquant. Emission quantum yields ϕ were determined at room
temperature in acetonitrile solutions (λex = 430 nm) using the optically
dilute method.26 [Ru(bpy)3]2+ (bpy =2,20-bipyridine) in air-equilibrated
aqueous solution was used as quantum yield standard (ϕ = 0.028).27
Experimentaluncertaintiesare as follows: absorption maxima, 2 nm;molar
absorption, 20%; emission maxima, 5 nm; emission lifetimes, 10%;
emission quantum yields, 20%.
Photo-Opening Isomerization Quantum Yields Measure-
ment. Potassium ferrioxalate actinometer was used as a primary
standard. The change in absorption upon irradiation at 468 nm
(band-pass filter) during specific time periods for compounds 1, L2,
L3, L2Ru, and L3Ru was compared to the change in absorption for the
actinometer irradiated at the same wavelength. The monitoring wave-
lengths were 235, 476, and 643 nm for 1, 476 and 643 nm for L2 and L3,
and 378 and 643 nm for L2Ru and L3Ru. The compounds were
dissolved in acetonitrile; the concentration was such that the absorbance
at 468 nm was higher than 1.9. The solution of the actinometer was
0.15 M in a 0.05 M H2SO4 aqueous solution. After each irradiation, 8 μL
of the irradiated solution was placed into a 2 mL volumetric flask. A
100 μL amount of sodium acetate buffer solution (pH = 3.5) and 16 μL
of 0.01 M 1,10-phenanthroline aqueous solution were then added, and
the volume was completed with distilled water. The photoreduction of
the actinometer was followed at 510 nm. The absorption spectra for each
compound were recorded after each irradiation time without further
handling, and the total time was such that the isomerization of the
compound was less than 10%. The ring-opening quantum yields ϕx were
calculated according to eq 1
over silica gel using cyclohexane/CH2Cl2 (6:1) as eluant and subse-
quently recrystallized, giving 210 mg of the 4-Br-DHP.
1H NMR/ppm (400 MHz, CD2Cl2): ꢀ3.93 (s, 3H), ꢀ3.95 (s, 3H),
1.65 (s, 9H), 1.72 (s, 9H), 8.47 (br s, 3H), 8.56 (d, 1H), 8.62 (s, 2H),
8.80 (d, 1H).
Ligand L1. L1 was prepared by a Suzuki coupling reaction between
the 40-(4-bromophenyl)-2,20:60,200-terpyridine and the bisboronic ester,
3, following two different methods.
Method A. To a solution of 4,9-Br2-DHP (2, 100 mg, 0.199 mmol)
in dry diethyl ether (5 mL) at ꢀ78 °C was added dropwise n-butyllithium
(160 μL of a 2.5 M solution in hexane). The initial green solution
became dark reddish. After stirring for 1 h at this temperature, tributyl
borate (108 μL, 0.400 mmol) was added and the solution was further
stirred for 48 h at room temperature. This solution was then evaporated
to dryness to isolate the crude bis-boronic DHP ester (3).
A two-necked flask was charged with 75 mg of crude 4,9-
[B(OnBu)2]2DHP (3, ∼0.174 mmol), 40-(4-bromophenyl)-2,20:60,200-
terpyridine (93 mg, 0.348 mmol) and Pd(PPh3)4 (23 mg, 0.020 mmol)
under an argon atmosphere. To the flask was then added well-degassed
toluene (10 mL) and sodium carbonate (5 mL, 2 M). The mixture was
refluxed for 36 h. The solvent was removed, and the residue was washed
with water and then diethyl ether. The residue was extracted into
dichloromethane, and the solution was dried (MgSO4) and evaporated.
The residue was chromatographed on silica gel using hexane as eluent to
elute first the unreacted dibromide. Polarity of the eluent was gradually
increased up to hexane/ethyl acetate (50:50) to elute 80 mg of product
as a dark brown solid further purified by recrystallization from methanol.
Method B. In this procedure, the synthesis was carried out using the
bisboronic acid, 4,9-[B(OH)2]2DHP (4). Aqueous hydrochloric acid
10% (6.25 mL) was added directly to the solution described above
containing 3 and further stirring continued up to 3 additional hours.
After this period, the layers were separated and the aqueous phase was
extracted with diethyl ether. At this point, the procedure followed was
analogous to that described above when using the bis-boronic ester, 3
(method A).
Yield (method A): 60%. 1H NMR/ppm (400 MHz, CD3CN): ꢀ3.68
(s, 6H), 1.61 (s, 18H), 7.30ꢀ7.36 (m, 4H), 7.86 (d, 4H), 7.90ꢀ8.10 (m,
8H), 8.44 (br s, 2H), 8.48 (s, 2H), 8.58 (br s, 2H), 8.65 (d, 4H), 8.75 (d,
4H, overlapped), 8.98 (s, 4H). 13C NMR/ppm (100 MHz, CD3CN):
156.8 (4C), 155.1 (4C), 149.9 (4C), 145.9 (2C), 139.6 (4C), 138.5
(2C), 137.8, 137.2, 136.9, 131.3, 128.4 (8C), 127.9 (4C), 126.5, 124.2
(2C), 123.5 (2C), 122.7, 121.9, 121.5, 121.3, 121.1, 120.9, 120.5 (4C),
120.3, 117.8 (4C), 114.1, 36.9, 36.2, 32.5, 31.9, 29.7, 14.1 (4C). CI MS
m/z: 960.1 (M + H+). Anal. Calcd for C68H58N6: C, 85.14; H, 6.09; N,
8.76. Found: C, 84.86; H, 6.37; N, 8.77.
ϕsεsΔAxVxts
ϕx ¼
ð1Þ
εxΔAsVstx
Ligands L2ꢀL5. Preparation of ligands L2ꢀL5 has been performed
following the procedure described for L1, starting from the correspond-
ing brominated-DHP precursors, and in the case of L3 and L4, 40-chloro-
2,20:60,200-terpyridine was employed instead of 40-(4-bromophenyl)-
2,20:60,200-terpyridine.
where ϕs is the quantum yield of the standard, ε is the molar extinction
coefficient at the monitoring wavelength, ΔA is the change in absor-
bance at the monitoring wavelength, V is the volume of solution, and t is
the irradiation time. The subscripts s and x refer to the standard and the
compound of unknown quantum yield, respectively.
1
L2. Yield (method A): 40%. H NMR/ppm (400 MHz, CD3CN):
ꢀ3.73 (s, 3H), ꢀ3.71 (s, 3H), 1.66 (s, 9H), 1.68 (s, 9H), 7.32ꢀ7.40 (m,
4H), 7.66 (d, 4H), 7.94ꢀ8.01 (m, 8H), 8.40 (br s, 2H), 8.45 (s, 2H),
8.52 (br s, 2H), 8.67 (d, 4H), 8.70 (d, 4H, overlapped), 8,75 (s, 4H).
13C NMR/ppm (100 MHz, CD3CN): 157.7 (4C), 155.1 (4C), 149.9
(4C), 145.9 (2C), 139.6 (4C), 138.5 (2C), 137.8, 137.2, 136.9, 131.3,
128.4 (8C), 128.4 (4C), 126.5, 124.3 (4C), 122.7, 121.9, 121.5, 121.3,
121.1, 120.9, 120.5 (4C), 120.3, 117.8 (4C), 114.1, 36.9, 36.2, 32.1, 31.7,
29.3, 14.4 (4C). CI MS m/z: 960.3 (M + H+). Anal. Calcd for C68H58N6:C,
85.14; H, 6.09; N, 8.76. Found: C, 85.27; H, 6.29; N, 8.44.
Synthesis. 2,7-Di-tert-butyl-trans-10b,10c-dimethyl-10b,10c-dihy-
dropyrene (1), 4,9-dibromo-2,7-di-tert-butyl-trans-10b,10c-dimethyl-
10b-10c-dihydropyrene (4,9-Br2-DHP, 2), and 4,10-dibromo-2,7-di-
tert-butyl-trans-10b,10c-dimethyl-10b-10c-dihydropyrene (4,10-Br2-
DHP) were prepared following the procedure reported by Mitchell.12c
4-Bromo-2,7-di-tert-butyl-trans-10b,10c-dimethyl-10b-
10c-dihydropyrene (4-Br-DHP). To a solution containing the DHP
(150 mg, 0.44 mmol) in dry CH2Cl2 (80 mL) at ꢀ40 °C was slowly
added with stirring under argon atmosphere a solution containing NBS
(78 mg, 0.44 mmol) in dry DMF (15 mL). After addition, the reaction
mixture was stirred for an additional hour at room temperature.
Cyclohexane (100 mL) and water were subsequently added. The green
organic phase was separated and dried. The green product was purified
1
Ligand L3. Yield (method A): 56%. H NMR/ppm (400 MHz,
CD3CN): ꢀ3.55 (s, 6H), 1.70 (s, 18H), 7.32ꢀ7.40 (m, 4H), 7.86 (d,
4H), 8.51 (br s, 2H), 8.53 (s, 2H), 8.55 (s, 2H), 8.60 (d, 4H), 8.75 (d,
4H), 8.95 (s, 4H). 13C NMR/ppm (100 MHz, CD3CN): 157.5 (4C),
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155.7 (4C), 149.3 (4C), 145.5 (2C), 139.9 (4C), 138.3 (2C), 137.8,
137.5, 136.7, 131.1, 128.4 (8C), 128.7 (4C), 126.2, 124.1 (4C), 122.3,
121.5 (2C), 121.1 (2C), 120.7, 120.4 (4C), 120.3, 117.3 (4C), 114.6,
36.7, 36.5, 32.4, 31.7, 29.6, 14.1 (2C), 13.9 (2C). CI MS m/z: 808.1 (M
+ H+). Anal. Calcd for C56H50N6: C, 83.34; H, 6.24; N, 10.41. Found: C,
83.60; H, 6.29; N, 10.11.
[M ꢀ Ru ꢀ 2tpy ꢀ 4PF6]+. Anal. Calcd for C86H72F24N12P4Ru2: C,
50.25; H, 3.53; N, 8.18. Found: C, 50.49; H, 3.63; N, 8.02.
1
L4Ru. Yield: 38%. H NMR/ppm (400 MHz, CD3CN): ꢀ2.89 (s,
3H), ꢀ2.87 (s, 3H), 1.69 (s, 9H), 1.73 (s, 9H), 7.05 (t, 8H), 7.45 (m,
4H), 7.78 (m, 4H), 8.05 (m, 6H), 8.20 (d, 4H), 8.46 (br s, 2H), 8.58 (s,
6H), 8.69 (br s, 2H), 8.75 (d, 4H), 8.80 (d, 4H), 8.95 (s, 4H). MALDI-
MS: 2055.6 [M], 1910.61 [M ꢀ PF6]+, 1765.5 [M ꢀ 2PF6]2+, 1620.7
[M ꢀ 3PF6]3+, 1141.5 [M ꢀ Ru ꢀ tpy ꢀ 4PF6]+. Anal. Calcd for
C86H72F24N12P4Ru2: C, 53.31; H, 3.65; N, 7.61. Found: C, 53.59; H,
3.70; N, 7.28.
1
Ligand L4. Yield (method A): 32%. H NMR/ppm (400 MHz,
CD3CN): ꢀ3.58 (s, 3H), ꢀ3.56 (s, 3H), 1.67 (s, 9H), 1.70 (s, 9H),
7.32ꢀ7.40 (m, 4H), 8.03 (d, 4H), 8.45 (br s, 2H), 8.49 (s, 2H), 8.61 (br
s, 2H), 8.65 (d, 4H), 8.72 (d, 4H), 8.99 (s, 4H). 13C NMR/ppm (100
MHz, CD3CN): 156.9 (4C), 155.3 (4C), 149.5 (4C), 146.3 (2C), 138.9
(4C), 138.1 (2C), 137.3, 137.0, 136.5, 131.0, 129.7 (4C), 128.4, 124.1
(4C), 122.7, 121.9, 121.5, 121.3, 121.1, 120.9, 120.5 (4C), 120.3, 117.8
(4C), 114.1, 36.9, 36.1, 32.4, 31.6, 28.7, 14.3 (4C). CI MS m/z: 808.0 (M
+ H+). Anal. Calcd for C56H50N6: C, 83.34; H, 6.24; N, 10.41. Found: C,
83.56; H, 6.41; N, 10.03.
L5Ru. Yield: 56%. 1H NMR/ppm (400 MHz, CD3CN): ꢀ3.04
(s, 3H), ꢀ3.01 (s, 3H), 1.65 (s, 9H), 1.70 (s, 9H), 7.10 (t, 4H), 7.21
(d, 2H), 7.35 (m, 2H), 7.40 (d, 2H), 7.75 (m, 2H), 8.05 (m, 3H), 8.20
(m, 3H), 8.42 (br s, 2H), 8.53 (s, 3H), 8.67 (br s, 2H), 8.78 (br d, 3H),
8.82 (d, 2H), 9.00 (s, 2H). MALDI-MS: 1276.2 [M], 1131.2 [M ꢀ
PF6]+, 986.3 [M ꢀ 2PF6]2+, 884.7 [M ꢀ Ru ꢀ 2PF6 ꢀ 1H]+. Anal.
Calcd for C62H56F12N6P2Ru: C, 58.35; H, 4.42; N, 6.59. Found: C,
58.67; H, 4.75; N, 6.87.
1
Ligand L5. Yield (method A): 72%. H NMR/ppm (400 MHz,
CD3CN): ꢀ3.57 (s, 3H), ꢀ3.73 (s, 3H), 1.65 (s, 9H), 1.68 (s, 9H),
7.35ꢀ7.39 (m, 2H), 7.70 (d, 2H), 7.92ꢀ8.00 (m, 4H), 8.42 (br s, 3H),
8.51 (s, 1H), 8.58 (br s, 3H), 8.69 (d, 2H), 8.76 (d, 2H), 8.85 (s, 2H).
13C NMR/ppm (100 MHz, CD3CN): 157.3 (2C), 155.1 (2C), 150.1
(2C), 149.6, 146.5, 139.3 (2C), 138.5 (2C), 137.8, 137.2, 136.9, 131.3,
129.6 (4C), 128.4 (4C), 126.5, 124.3 (2C), 122.9, 122.3, 121.7, 121.3,
121.1, 120.9, 120.5 (2C), 120.3, 117.3 (2C), 115.3, 36.9, 36.2, 32.1, 31.7
(2C), 29.3, 14.5, 14.0. CI MS m/z: 652.8 (M + H+). Anal. Calcd for
C47H45N3: C, 86.60; H, 6.96; N, 6.45. Found: C, 86.92; H, 6.84; N, 6.24.
Preparation of L1Ru. L1 (35 mg, 0.043 mmol) and [(tpy)RuCl3]
(38 mg, 0.086 mmol) were dissolved in EtOH (40 mL). A few drops of
N-ethylmorpholine were added. The reaction mixture was heated under
reflux for 48 h, then filtered through Celite, and washed with EtOH. The
filtrate was concentrated under reduced pressure, and aqueous NH4PF6
was added to precipitate the product. The crude product was filtered,
washed with diethyl ether, and dissolved in CH3CN. It was purified by
column chromatography on silica gel (CH3CN:H2O:saturated KNO3
7:2:2). The third orange band (orange-red) was collected and concen-
trated under reduced pressure. Aqueous NH4PF6was added to precipi-
tate the product, which was collected and washed with diethyl ether and
dissolved in CH3CN. Removal of solvent gave [4,9-[Ru(tpy)2]2ꢀ
DHP](PF6)4 (L1Ru) as a dark red powder.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: (33) 04 76 51 42 67. E-mail: neus.vila@ujf-grenoble.fr.
’ ACKNOWLEDGMENT
The authors thank the Foundation Nanosciences (Grenoble-
RTRA POLYSUPRA Project) for their financial support and the
chemistry platform (Nanobio Campus) in Grenoble for lumi-
nescent lifetime measurement facilities. N.V. gratefully acknowl-
edges the Marie Curie program FP7-PEOPLE-IEF 2008.
’ REFERENCES
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Int. Ed. 2007, 46, 72.
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Yield: 41%. 1H NMR/ppm (400 MHz, CD3CN): ꢀ2.98 (s, 6H), 1.72
(s, 18H), 7.12 (t, 8H), 7.25 (d, 4H), 7.35 (d, 4H), 7.42 (d, 4H), 7.82 (m,
4H), 7.98 (m, 6H), 8.25 (d, 4H), 8.48 (br s, 6H), 8.51 (s, 2H), 8.67 (br s,
2H), 8.70 (d, 4H), 8,75 (d, 4H), 8.98 (s, 4H) . MALDI-MS: 2207.9 [M],
2063.0 [M ꢀ PF6]+, 1918.1 [M ꢀ 2PF6]2+, 1773.1 [M ꢀ 3PF6]3+,
1293.2 [M ꢀ Ru ꢀ tpy ꢀ 4PF6]+, 986.3 [M ꢀ Ru ꢀ tpy ꢀ Phtpy ꢀ
4PF6]+. Anal. Calcd for C98H80F24N12P4Ru2: C, 53.31; H, 3.65; N, 7.61.
Found: C, 53.72; H, 3.76; N, 7.22.
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Preparation of L2RuꢀL5Ru. These complexes were prepared
from a similar procedure as described above for L1Ru starting from the
corresponding L2ꢀL5 ligands. In the case of L5Ru, 1 mol equiv of
[(tpy)RuCl3] per ligand was used.
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Nishihara, H. Dalton Trans. 2008, 3260 and references therein. (c)
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1
L2Ru. Yield: 35%. H NMR/ppm (400 MHz, CD3CN): ꢀ2.93 (s,
3H), ꢀ2.90 (s, 3H), 1.69 (s, 9H), 1.73 (s, 9H), 7.05 (t, 8H), 7.21 (d,
4H), 7.38 (m, 4H), 7.42 (d, 4H), 7.78 (m, 4H), 8.01 (m, 6H), 8.23 (d,
4H), 8.42 (br s, 2H), 8.55 (s, 6H), 8.67 (br s, 2H), 8.75 (d, 4H), 8.84 (d,
4H), 9.02 (s, 4H). MALDI-MS: 2208.2 [M], 2062.8 [M ꢀ PF6]+, 1918.3
[M ꢀ 2PF6]2+, 1772.9 [M ꢀ 3PF6]3+, 1293.0 [M ꢀ Ru ꢀ tpy ꢀ 4PF6]+.
Anal. Calcd for C98H80F24N12P4Ru2: C, 53.31; H, 3.65; N, 7.61. Found:
C, 53.54; H, 3.55; N, 7.47.
1
L3Ru. Yield: 47%. H NMR/ppm (400 MHz, CD3CN): ꢀ2.86 (s,
6H), 1.70 (s, 18H), 7.12 (t, 8H), 7.42 (m, 4H), 7.71(m, 4H), 8.01
(m, 6H), 8.19 (d, 4H), 8.42 (br s, 2H), 8.58 (s, 6H), 8.65 (br s, 2H),
8.72 (d, 4H), 8.81 (d, 4H), 9.05 (s, 4H). MALDI-MS: 2055.8 [M],
1911.0 [Mꢀ PF6]+, 1765.8 [M ꢀ 2PF6]2+, 1621.1 [M ꢀ 3PF6]3+, 910.3
10590
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