Efficient light activation of a [Ru(bpy)(tpy)Cl]+ catalyst by a porphyrin photosensitizer at small driving force

Article abstract of DOI:10.1016/j.poly.2020.114775

Light activation of dyads containing porphyrins and a catalytic ruthenium complex having a high oxidation potential (~1 V vs SCE) is investigated by time-resolved spectroscopy. It is shown that activation of the ruthenium complex occurs through oxidative quenching of the chromophore in the presence of a reversible electron acceptor. Despite the lack of driving force for intramolecular electron transfer, an efficient intramolecular oxidation of the catalyst is observed, suggesting that porphyrins are attractive chromophores to activate oxidation catalysts throughout the visible spectrum.

Full text of DOI:10.1016/j.poly.2020.114775

Polyhedron 190 (2020) 114775
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Efficient light activation of a [Ru(bpy)(tpy)Cl]+ catalyst by a porphyrin
photosensitizer at small driving force
Georgios Charalambidis a, Asterios Charisiadis a, Sofia Margiola a, Athanassios Coutsolelos a,
,
⇑
Ally Aukauloo b,c, , Winfried Leibl c, Annamaria Quaranta c,
⇑
⇑
a Department of Chemistry, University of Crete, Laboratory of Bioinorganic Chemistry, Voutes Campus, 70013 Heraklion, Crete, Greece
b Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR-CNRS 8182, Université Paris-Sud XI, F-91405 Orsay, France
c Institut des Sciences du vivant Frédéric Joliot, SB2SM/Institut de Biologie Intégrative de la Cellule I2BC, UMR 9198, CEA, CNRS, Université Paris Sud, F-91191 Gif sur Yvette, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2020
Accepted 27 August 2020
Available online 08 September 2020
Light activation of dyads containing porphyrins and a catalytic ruthenium complex having a high oxida-
tion potential (~1 V vs SCE) is investigated by time-resolved spectroscopy. It is shown that activation of
the ruthenium complex occurs through oxidative quenching of the chromophore in the presence of a
reversible electron acceptor. Despite the lack of driving force for intramolecular electron transfer, an effi-
cient intramolecular oxidation of the catalyst is observed, suggesting that porphyrins are attractive chro-
mophores to activate oxidation catalysts throughout the visible spectrum.
Keywords:
Porphyrin
Photophysics
Catalysis
Ó 2020 Elsevier Ltd. All rights reserved.
Light activation
Ruthenium
Water oxidation
1. Introduction
excited state, or unproductive pathways. Understanding the ongo-
ing photophysical events is important in order to remediate the
Activation of a catalyst by light is a critical process in the
domain of artificial photosynthesis; besides the high performance
in terms of turn-over frequency (TOF), stability (turn-over number,
deleterious photophysical pathways and/or the limiting thermody-
namics steps on the way towards optimization.
In a previous study, we have investigated the activation by light
of the [Ru(tpy)(bpy)OH2]2+ complex also known as ‘‘Meyer cata-
lyst” [2,3] the first reported mononuclear ruthenium catalyst for
water oxidation, whose mechanism of action is not completely elu-
cidated [2,4–13]. We have shown that when the catalyst is linked
to a ruthenium polypyridine chromophore, the activation mecha-
nism proceeds either via energy transfer (antenna or photosensi-
tizer behavior) or via electron transfer (reaction center or
photoredox behavior) depending on the peripheral groups
attached to the chromophore [14]. When a porphyrin was used
as a photosensitizer to activate the catalyst precursor [Ru(tpy)
(bpy)Cl]+, a better collection of light and bidirectional energy trans-
fer between the chromophore and the catalyst resulted in a more
efficient activation of the [Ru(tpy)(bpy)Cl]+ unit [15]. In order to
render the catalyst more oxidizing and possibly increase its effi-
ciency, we have now modified the ruthenium moiety by introduc-
ing electron-withdrawing methoxycarbonyl groups on the
bipyridine ligand (Chart 1). In terms of catalytic performance, it
has been shown for an analogous catalyst, bearing COOH elec-
tron-withdrawing groups on the bipyridines, that such functional-
ization results in smaller TOF but higher TON compared to the
TON), selectivity and overpotential (g), the catalyst efficient
photo-activation is also required. Such process encompasses sev-
eral steps: light absorption, formation of charge-separated states,
as well as charge accumulation on the active site in the case of a
multi-electron process such as water oxidation, an energetically
and kinetically demanding 4-electrons, 4-protons reaction. An
attractive way to use light to drive the catalytic process consists
in integrating the chromophore and the catalyst in the same sys-
tem [1], grafted onto a semiconductor surface: Upon absorption
of light, the chromophore excited state injects electrons into the
semiconductor conduction band and activates the catalyst in an
oxidative reaction. In this configuration, the properties of the sen-
sitizer and the catalyst need to be matched for an efficient activa-
tion of the latter. To this end, several issues need to be considered,
such as energy losses occurring in exergonic reactions, competition
between different processes for the deactivation of the sensitizer
⇑
Corresponding authors.
E-mail addresses: acoutsol@uoc.gr (A. Coutsolelos), ally.aukauloo@u-psud.fr
(A. Aukauloo), annamaria.quaranta@cea.fr (A. Quaranta).
https://doi.org/10.1016/j.poly.2020.114775
0277-5387/Ó 2020 Elsevier Ltd. All rights reserved.

G. Charalambidis et al.
Polyhedron 190 (2020) 114775
and final compounds were fully characterized through MALDI-
TOF mass spectrometry, NMR (1H and 13C) spectroscopy (see SI)
and elemental analysis. The final dyads were also characterized
through Infrared (IR) spectroscopy (see SI).
2.2. Electrochemical characterization
The electrochemical properties of the dyads and reference com-
pounds, investigated by cyclic and square-wave voltammetry, are
reported in Table 1. In the reference compound RuCOOMe, as
expected, the presence of the carboxylates strongly impacts the
first reduction based on bipyridines, which presents a 280 mV ano-
dic shift as compared to the unmodified Rucat. The second reduc-
tion, based on the terpyridine, is less affected and it exhibits a
40 mV positive shift. On the anodic side, the oxidation, which is
ruthenium centred, occurs at 1.08 V (+140 mV shift), close to the
first oxidation process of the free-base tetra-phenyl-porphyrin
(H2P) at 1.14 V. As a consequence, in the H2P-RuCOOMe dyad the
first oxidation, occurring at 1.09 V, is a two-electron process (data
in SI). These data suggest that the Gibbs free energy (DG) for the
catalyst oxidation, driven by the oxidised porphyrin, is close to
zero. The process is endergonic in the case of the ZnP-RuCOOMe
dyad where, in the electrochemical experimental conditions, the
metal oxidation appears 190 mV more positive than the first oxida-
tion of the porphyrin.
2.3. Spectroscopic characterization
Chart 1. Investigated dyads: H2P-RuCOOMe, ZnP-RuCOOMe and reference dyad H2P-
Rucat.
Ground and excited state properties. The ground state absorp-
tion spectra of the reference RuCOOMe and the corresponding dyads
are given in Fig. 1. The RuCOOMe absorption spectrum is charac-
terised by a
MLCT d ? * centred at 533 nm. These bands are respectively ~ 50
and 20 nm red-shifted as compared to Rucat. Such shift has been
previously attributed to a low-lying * level on the bpy ligand
p ? p* transition at 373 nm, accompanied by the
parent molecule [5]. The smaller TOF, in the presence of electron-
withdrawing groups, has been attributed [16] to the diminished
accessibility of the water molecule to the RuV = O species which
constitutes the rate determining step in the water nucleophilic
attack mechanism proposed by Meyer [2]. The enhanced stability
p
p
incorporating electron withdrawing groups [19]. The H2P-RuCOOMe
absorption spectrum contains the characteristic porphyrin Soret
band at 415 nm, although significantly decreased compared to
H2P, and four Q bands at 515, 546, 588 and 645 nm, superposed
upon the bands originating from the Ru unit. It appears that the
individual features of the two moieties are slightly altered in the
dyads. Thus, the existence of an electronic communication
between the two moieties is anticipated. In the case of the ZnP-
RuCOOMe dyad the Soret band is shifted to 422 nm and the Q bands
occur at 554 and 595 nm.
has been attributed to the increased p-backbonding of the bipyri-
dine which is the most labile ligand and its dissociation is respon-
sible for the catalyst decomposition [16]. In the present study we
describe the photophysical properties of two new dyads containing
a porphyrin chromophore (free-base or zinc) linked through an
amide bridge to a modified version of the Meyer catalyst (Chart 1),
and the investigation of their photo-induced oxidation. A compar-
ison with the dyad bearing the unmodified Meyer catalyst (H2P-
Rucat) [15] is also established.
The steady-state emission spectrum of H2P-RuCOOMe, shown in
Fig. 2a, exhibits both porphyrin fluorescence (650 and 715 nm) and
RuCOOMe (780 nm) emission (SI, Fig S4). The fluorescence quantum
yield (UF) of the H2P-RuCOOMe dyad, when excited at 515 nm, is
1.1 ꢀ 10ꢁ3 (for calculation see SI) with the Ru band contributing
16% of the total emission. According to the molar extinction coef-
ficients of the two components, absorption of light at this excita-
tion wavelength is about equally shared between the porphyrin
(49%) and the Ru (51%) moieties. Thus, from the heterogeneity of
2. Results and discussion
2.1. Synthesis
The synthesis of the dyads presented in this paper is outlined in
Scheme 1. A two-step reaction was followed for the synthesis of
the terpyridine substituted porphyrin derivative H2P-tpy. The first
step included the conversion of the carboxy-terpyridine (tpy-
COOH) [17] to the corresponding acyl chloride after refluxing in
SOCl2. Subsequently, amino porphyrin (H2P–NH2) [18] was added
and the reaction was left under reflux in THF overnight, in the pres-
ence of Et3N, yielding H2P-tpy. The desired free base dyad H2P-
RuCOOMe was afforded by refluxing H2P-tpy and the corresponding
ruthenium complex Ru(bpy(-COOMe)2)(DMSO)2Cl2 in acetic acid.
Finally, the metalated dyad ZnP-RuCOOMe was prepared via metala-
tion of the free-base dyad with zinc acetate. The synthesis of the
reference compound RuCOOMe is shown in Scheme S1. Initially,
RuCl3 reacted with tpy-COOH and the desired compound was
obtained after the addition of bpy-(COOMe)2. All intermediates
singlet excited states arising from excitation at 515 nm, a
UF ~ 7.3-
ꢀ 10ꢁ2 should be expected for the dyad emission in the absence of
interactions between the two moieties. In contrast, the obtained
value is more than 60 times lower, indicating that the fluorescence
originating from the porphyrin is almost completely (98%)
quenched by the ruthenium unit. Upon excitation at 535 nm,
where porphyrin absorbs 27% of light, the UF is 5.5 ꢀ 10-4. These
results indicate the presence of a supplementary deactivation
channel for the singlet excited state of the porphyrin, that is either
energy or electron transfer to the ruthenium moiety. In order to
investigate the nature of the quenching, time-resolved measure-
ments were performed by exciting the sample with a laser pulse
2

G. Charalambidis et al.
Polyhedron 190 (2020) 114775
Scheme 1. Synthesis of compounds H2P-RuCOOMe and ZnP-RuCOOMe
.
Table 1
Electrochemical data.
Compound
E1/2 (P-/P2-
)
E1/2(tpy0/tpy-)
E1/2(P/P-)
E1/2(bpy0/bpy-)
E1/2 (P+/P)
E1/2(RuIII/RuII)
E1/2(P2+/P+)
RuCOOMe
Ru#cat
–
–
ꢁ1.38
ꢁ1.42
–
–
–
ꢁ0.97
ꢁ1.25
–
–
–
1.14
0.90
1.09
0.89
1.08
0.94
–
–
1.09
1.08
–
–
1.42
1.25
1.32
1.25
H2P#
ꢁ1.58
ꢁ1.08
ꢁ1.25
ꢁ1.07
ꢁ1.27
ZnP#
H2P-RuCOOMe
ZnP-RuCOOMe
–
–
–
ꢁ1.53
ꢁ1.33
ꢁ0.96
ꢁ1.33
ꢁ0.96
E1/2 = (Epa + Epc)/2 in Volts vs SCE, measured in benzonitrile, scan speed: 100 mV sꢁ1. # From ref [8].
hypothesis is further supported by the evaluation of the overlap
integral between the porphyrin emission and the RuCOOMe absorp-
tion (Fig. S5).
At longer times (greater than 50 ns) this depletion disappears
and the remaining absorption exhibits features that are character-
istic of the H2P triplet excited state which then decays within 15 ms
(Fig. S6). The final quantum yield of the triplet porphyrin within
the dyad, estimated using the comparative method [20] is 41%
(Fig. S6). Since the singlet excited state of the porphyrin is almost
completely quenched by the ruthenium moiety (steady-state mea-
surements) and is therefore unable to evolve directly into 3H2P*,
the formation of triplet porphyrin must be achieved by energy
transfer from the 3RuCOOMe* to the porphyrin unit. The presence
of triplet–triplet energy transfer had also been inferred for the
dyad H2P-Rucat [15] In both cases, the Dexter mechanism is oper-
ative since triplet–triplet energy transfer via a Förster mechanism,
which is spin-forbidden, is unlikely [21] Dexter mechanism is pos-
sible either when the two units are in close proximity [22] or if the
transfer is mediated by the bridge [23]. This is more likely to be the
case here since it has been shown that the amide linkage facilitates
the energy transfer via super-exchange mechanism [23,24]. To
summarise, these results can be rationalised as follows (Scheme 2):
excitation at 515 nm results in a heterogeneity of singlet excited
states with half of molecules forming the 1RuCOOMe* state and
the other half forming the 1H2P* state. Both singlet states evolve
almost quantitatively into 3RuCOOMe*, the former via inter-system
Fig. 1. UV–Vis absorption spectra of the dyads and the reference compound in
acetone/CH3CN (50:50) solutions.
at 515 nm. In differential transient absorption studies, at early
times (10 ns) a bleaching at 540 nm is observed. This is attributed
to the presence of the triplet excited state 3RuCOOMe* (Fig. 2b),
which can be formed via Förster energy transfer between the por-
phyrin singlet excited state (1H2P*) and the triplet 3RuCOOMe*. This
3

G. Charalambidis et al.
Polyhedron 190 (2020) 114775
Fig. 2. (a) Steady-state emission spectra obtained by excitation at 515 nm for optically diluted acetone/acetonitrile (50:50) solutions (absorption A515 = 0.1); (b) gated (10 ns)
transient absorption spectra (right) at different delays from laser pulse. Excitation at 515 nm with 8 mJ laser energy. A(515) = 0.32 in acetonitrile/acetone (50:50) solvent. The
spectra have been cut between 400 and 450 nm because of the high absorption of the Soret band in this region.
Scheme 2. Simplified energetics scheme of the H2P-RuCOOMe dyad describing the observed evolution of excited states upon excitation at 515 nm. Rate constants are given in
sꢁ1, quantum yields in brackets. For estimation of the different parameters, see SI.
3
crossing, and the latter by energy transfer. The resulting triplet
-
RuCOOMe* (ET = 1.83 eV, cf SI) then undergoes energy transfer to
form the triplet 3H2P*. The lifetime of the final 3H2P-RuCOOMe
*
state, formed with a quantum yield of ~ 0.41 is ~ 5 ms (kinetics in
Fig. S6). Thus about 40% of the photons absorbed by the dyad are
stored in a porphyrin triplet excited state having an energy
of ~ 1.5 eV [15].
2.4. Flash-quench experiments.
In order to investigate the possibility of activating the RuCOOMe
catalyst by the oxidised porphyrin, we performed flash-quench
experiments in the presence of methyl viologen (MV2+) as a rever-
sible electron acceptor. Upon excitation, the porphyrin triplet
excited state, formed according to the energy transfer mechanism
described above, is oxidatively quenched by methyl viologen creat-
ing a charge-separated state (H2P-RuCOOMe)ox
/MVꢂ+. This can be
inferred from the absorption changes in Fig. 3; between 100 and
500 ns, a peak is formed at 395 nm concomitantly with a band at
605 nm, both characteristic of the reduced MVꢂ+ species [25]. The
bimolecular rate constant for quenching of the excited state by
Fig. 3. Transient spectra obtained in the presence of 10 mM MV2+ upon excitation
at 515 nm with laser energy of 13 mJ. Absorption at 515 nm: 0.26. Solvent:
acetonitrile/acetone (50:50) vol.
4

G. Charalambidis et al.
Polyhedron 190 (2020) 114775
MV2+ is 2.2 ꢀ 108 Mꢁ1 sꢁ1. In the presence of 10 mM of MV2+, the
formation of the methyl viologen radical cation, was accompanied
by an absorption decrease at 540 nm corresponding to the oxida-
tion of Ru(II) to Ru(III).
ing the second activation step. In fact, upon formation of the chro-
mophore excited state, a reverse electron transfer between the
oxidised catalyst and the excited state may take place. However
this reaction should be less favourable if a deprotonation accompa-
nies the oxidation reaction. The H2P-Rucat dyad was investigated in
its ability to generate the doubly oxidised ruthenium species Ru
(IV), a species relevant for catalysis, but no charge accumulation
could be observed by pump-pump–probe experiments [29]. This
was rationalised as due to the competition between intramolecular
oxidation of Ru(III) to Ru(IV) by the porphyrin cation (for which
At MV2+ concentrations lower than 10 mM, the rate limiting
step for oxidation of the Ru catalyst appears to be the formation
of the charge-separated state (H2P-Ru )
COOMe ox/MVꢂ+ (Fig. S7),
while at higher concentrations (20 mM), the kinetics of intramolec-
ular Ru(III) oxidation can be isolated and the rate for intramolecu-
lar electron transfer determined to be 3.8 ꢀ 106 sꢁ1 (Fig. S8). In
terms of yield, 1.6
0.2 mM of the 3H2P* formed, results in
D
G ~ 0) and the reverse electron transfer from the porphyrin
excited state to the Ru(III) to give Ru(II) and H2Pꢂ+. For the reverse
electron transfer a high driving force ( G = -1.3 V) is present. A
1.3 0.2 mM of MVꢂ+ and 1.2 0.2 mM Ru(III), that is a yield for
intramolecular oxidation close to 100% (cf SI for details). Since, as
discussed above, the triplet porphyrin in the dyad is obtained with
a quantum yield of ~ 0.41, then a quantum yield of ~0.40 is
obtained for Ru(III). For comparison, in the case of dyad H2P-Rucat
under the same experimental conditions, excitation at 515 nm ini-
tially produces ~ 3.0 mM of 3H2P* (the porphyrin absorbs in this
case 70% of light) to finally give 2.6 mM of Ru(III), corresponding
to a yield for intramolecular oxidation of 87%.
D
more promising approach to minimize reverse electron transfer
is by kinetic out-competition. This could be achieved by anchoring
the porphyrin complex to n-type semiconductor particles like TiO2
which results in ultrafast deactivation of the excited state by elec-
tron injection in the semiconductor conduction band to form TiO2/
H2Pꢂ+ [30]. This can then enable the intramolecular oxidation of Ru
(III) to Ru(IV).
Spectroscopic and flash-quench studies were also performed on
the ZnP-RuCOOMe dyad. Upon excitation at 560 nm (A560 = 0.25),
deactivation of the porphyrin singlet excited state gives, as for its
free base analogue, the triplet excited state of the ruthenium moi-
ety 3RuCOOMe* and finally the formation of the triplet excited state
of 3ZnP*. This was supported by the observation of bleaching of the
Ru absorption at initial times in the differential transient absorp-
tion spectra, evolving toward a typical 3ZnP* triplet state which
has a lifetime of ~ 1.7 ms (Figs. S9 and S10). In the presence of
MV2+ mainly the formation of the ZnPꢂ+ radical cation was
observed (Fig. S11), confirming that Ru(III) oxidation by the ZnP
radical cation is an energetically uphill reaction.
4. Experimental
Materials. Compounds tpy-COOH [17], H2P–NH2 [18], were pre-
pared according to published procedures. Tetrahydrofuran was
freshly distilled from Na/benzophenone. All other chemicals and
solvents were purchased from commercial sources and used as
received.
NMR Spectra. NMR spectra were recorded on a Bruker AVANCE
III-500 MHz and Bruker DPX-300 MHz spectrometers using solu-
tions in deuterated solvents and the solvent peak was chosen as
the internal standard.
Mass Spectra. High-resolution mass spectra were obtained on a
Bruker UltrafleXtreme matrix assisted laser desorption ionization
time-of-flight (MALDI-TOF) spectrometer using trans-2-[3-(4-tert-
butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB) as
matrix.
3. Conclusions
In this paper we have collected photophysical data on a modi-
fied Meyer catalyst attached to a porphyrin chromophore which
exhibits an oxidation potential higher than 1 V vs SCE. The data
clearly point to the efficient light activation of the catalyst by the
oxidised porphyrin in the presence of a reversible electron acceptor
despite the fact that the potentials for H2Pꢂ+/H2P and Ru(III)/Ru(II),
estimated from the cyclic voltammetry experiments, are very
close. However, using the yield and the rate constants for
intramolecular oxidation, it is possible to infer the operating
from kIET/kBET = -RT*exp(- G) [26], where kIET and kBET are respec-
tively the forward and back electron transfer rate constants in the
equilibrium. This results in
exergonic process.
The collected results shows that porphyrins are attractive chro-
mophores to employ in the photoactivation of highly oxidising cat-
alysts. The dyad H2P-RuCOOMe shows an increased oxidation power
as compared to H2P-Rucat previously investigated. This is benefi-
cial for driving oxidation catalytic processes. However, in order
to advance in the catalytic cycle, successive oxidations of the
ruthenium moiety are necessary and they occur at higher poten-
tial. They are therefore thermodynamically more difficult to be
triggered by the oxidised porphyrin. It is nevertheless worth noting
that, upon exchange of the chloride ligand with a water molecule, a
step occurring spontaneously in aqueous solutions [5], the succes-
sive oxidations occur in a narrow albeit higher, potential window
because of proton-coupled electron transfer (PCET) processes
[27,28]. Indeed, PCET facilitates the advancing in the catalytic cycle
while preventing the building up of charged species, as well as sta-
bilising the oxidised state by decreasing the driving force for the
charge recombination. This is an important aspect when consider-
Elemental Analysis. Elemental analyses were carried out using
Carlo-Erba EA 1110 CHNS Eager 200 analyzer.
Electrochemistry. Cyclic and square wave voltammetry experi-
ments were carried out at room temperature using an AutoLab
PGSTAT20 potentiostat and appropriate routines available in the
operating software (GPES version 4.9). All measurements were car-
ried out in freshly distilled and deoxygenated benzonitrile with a
solute concentration of ca. 1.0 mM in the presence of tetrabuty-
lammonium tetrafluoroborate (0.1 M) as supporting electrolyte,
at a scan rate of 100 mV sꢁ1. A three-electrode cell setup was used
with a platinum working electrode, a saturated calomel (SCE) ref-
erence electrode, and a platinum wire as counter electrode. In all
measurements the ferrocene/ferrocenium couple was at 0.58 V
versus SCE under the above conditions.
Spectroscopy. Infrared (IR) spectra were obtained using an Agi-
lent Cary 630 spectrometer. Ground state absorption spectra were
measured either on a Shimadzu UV-1700 or an Analytic Jena Spe-
cord210 spectrophotometer. Steady-state emission spectra were
obtained using a JASCO FP-6500 fluorescence spectrophotometer
equipped with a red-sensitive WRE-343 photomultiplier tube
(wavelength range 200–850 nm). Fluorescence quantum yields
DG
D
DG ~ -25 meV, indicating a slightly
were calculated using 5,10,15,20-tetraphenylporphyrin
(Uf =
0.15) [31], as reference. All transient absorption experiments were
performed on an Edinburgh Instruments LP920 Flash Photolysis
Spectrometer system incorporating a Continuum Surelite OPO.
The OPO was pumped by a Q-switched Nd:YAG laser operating
at 355 nm. The LP920 system is equipped with a 450 W Xenon
arc lamp as the probe for the transient absorption measurements.
5

G. Charalambidis et al.
Polyhedron 190 (2020) 114775
In the time range 10 ns to 100 ms, the Xenon arc lamp was pulsed.
Detection in the LP920 system is performed either via a Czerny-
Turner blazed 500 nm monochromator (bandwidth: 1–5 nm) cou-
pled with a Hamamatsu R928 photomultiplier tube (kinetics
mode), or via a 500 nm blazed spectrograph (bandwidth: 5 nm)
coupled with a water-cooled ICCD nanosecond Andor DH720 cam-
era (spectral mode). Samples, having absorbances of ~ 0.3 at the
excitation wavelength, were purged with argon prior to each
experiment.
ClN10O5Ru: C 69.94, H 4.11, N 10.19. Found: C 69.78; H 4.20; N
10.28.
ZnP-RuCOOMe
:
A
solution of Zn(CH3COO)2ꢃ2H2O (85 mg,
0.39 mmol) in MeOH (3 mL) was added to a CH2Cl2 (20 mL) solu-
tion of H2P-RuCOOMe (27 mg, 0.02 mmol) and the mixture was stir-
red at room temperature overnight. After the volatiles had been
distilled off under vacuum, the residue was purified by silica col-
umn chromatography (CH2Cl2:MeOH (100:8)) to collect the desir-
able product (ZnP-RuCOOMe) as a purple solid (27 mg, 95%). 1H
NMR (500 MHz, (CD3)2SO): d 10.93 (s, 1H), 10.35 (d, J = 5.8 Hz,
1H), 9.43 (s, 1H), 9.39 (s, 2H), 9.14 (d, J = 1.3 Hz, 1H), 9.06 (d,
J = 8.3 Hz, 2H), 8.89 (d, J = 4.6 Hz, 2H), 8.81 (d, J = 4.6 Hz, 2H),
8.79 (s, 4H), 8.63 (d, J = 8.1 Hz, 2H), 8.52 (dd, J1 = 5.8 Hz,
J2 = 1.6 Hz, 1H), 8.47 (d, J = 8.1 Hz, 2H), 8.32 (d, J = 8.3 Hz, 2H),
8.31 (m, 8H), 8.11 (t, J = 7.7 Hz, 2H), 7.83 (m, 10H), 7.67 (d,
J = 6.1 Hz, 2H), 7.49 (m, 1H), 7.41 (t, J = 6.6 Hz, 2H), 4.12 (s, 3H),
3.87 (s, 3H). 13C NMR (125 MHz, (CD3)2SO): d 165.4, 164.7, 164.0,
159.3, 158.2, 157.3, 156.4, 153.2, 153.0, 152.3, 149.5, 149.3,
145.1, 142.8, 139.1, 138.6, 138.2, 137.7, 136.3, 136.2, 135.4,
134.2, 131.6, 128.8, 127.7, 127.5, 126.7, 125.9, 125.2, 124.5,
123.4, 122.8, 120.5, 120.4, 120.2, 118.6, 53.3, 53.1. IR: 1723 (v
(C@O) ester), 1660 (v(C@O) amide), 1258 (v(CAO) ester). HRMS
H2P-tpy: 4-([2,20:60’,20’-Terpyridin]-40-yl)benzoic acid (tpy-
COOH) (75 mg, 0.21 mmol) was dissolved in SOCl2 (2.8 mL) and
stirred at 80 °C for 2 h under argon atmosphere. After that, SOCl2
was removed under reduced pressure and the resulting acyl chlo-
ride terpyridine was dried under high vacuum at 50 °C for 1 h. The
resulting solid was dissolved in anhydrous THF (9 mL) and then
H2P–NH2 (44 mg, 0.07 mmol) and anhydrous triethylamine
(0.1 mL) were added. The reaction mixture was heated under argon
at 70 °C overnight. The solvent was removed under reduced pres-
sure, CHCl3 (80 mL) was added and the mixture was washed with
water (3 ꢀ 50 mL). The organic layer was dried with Na2SO4, fil-
tered and concentrated. The residue was purified by silica column
chromatography (CH2Cl2:MeOH (100:6)) to obtain the desired pro-
duct (H2P-tpy) as a purple solid (60 mg, 90%). 1H NMR (300 MHz,
(CDCl3): d 8.88 (m, 8H), 8.82 (s, 2H), 8.76 (d, J = 4.0 Hz, 2H), 8.69 (d,
J = 8.0 Hz, 2H), 8.34 (s, 1H), 8.22 (m, 8H), 8.17 (d, J = 8.4 Hz, 2H),
8.10 (d, J = 8.3 Hz, 2H), 8.05 (d, J = 8.4 Hz, 2H), 7.89 (dt,
J1 = 1.7 Hz, J2 = 7.7 Hz, 2H), 7.76 (m, 9H), 7.37 (ddd, J1 = 7.4 Hz,
J2 = 4.8 Hz, J3 = 1.0 Hz, 2H), –2.74 (s, 2H). 13C NMR (75 MHz,
(CDCl3): d 165.7, 156.4, 156.1, 149.3, 149.2, 142.3, 138.6, 137.8,
137.1, 135.4, 134.7, 131.2, 128.0, 127.9, 126.8, 124.2, 121.6,
120.3, 119.6, 119.1, 118.6. HRMS (MALDI-TOF) calcd for
(MALDI-TOF) calcd for
C
80H54N10O5RuZn [MꢁCl]+ 1400.2614,
found 1400.2602. Elemental Analysis: Calc. for C80H54ClN10O5-
RuZn: C 66.85, H 3.79, N 9.75. Found: C 66.97; H 3.68; N 9.84.
RuCOOMe: RuCl3ꢃ3H2O (120 mg, 0.58 mmol) and tpy-COOH
(180 mg, 0.58 mmol) were dissolved in EtOH and the reaction mix-
ture was heated for 5 h at reflux. Then, the brown intermediate [Ru
(tpy-COOH)Cl3] was isolated by filtration and then treated directly
with the bpy(COOMe)2 ligand (170 mg, 0.64 mmol) in H2O–EtOH
(1:1), heating at reflux overnight. After cooling, EtOH was evapo-
rated and the desired complex was precipitated, filtered and
washed with water. The solid was purified by flash chromatogra-
phy on silica gel using as eluent a mixture CH3CN/aqueous KNO3
solution at 10% of the saturating concentration. The pure product
was obtained after evaporation of CH3CN in the combined fractions
and addition of an excess of NH4PF6. The precipitate was filtered,
washed with water and acetone and dried under vacuum to give
RuCOOMe as red solid (320 mg, 74%). 1H NMR (500 MHz, (CD3)2-
SO + 10% (CD3)2CO): d 10.36 (d, J = 6.1 Hz, 1H), 9.41 (d,
J = 1.1 Hz, 1H), 9.30 (s, 2H), 9.12 (d, J = 1.4 Hz, 1H), 8.99 (d,
J = 8.1 Hz, 2H), 8.50 (dd, J1 = 5.9 Hz, J2 = 1.8 Hz, 1H), 8.47 (d,
J = 7.8 Hz, 2H), 8.25 (d, J = 7.8 Hz, 2H), 8.07 (dt, J1 = 1.4 Hz,
J2 = 7.8 Hz, 2H), 7.82 (d, J = 6.0 Hz, 1H), 7.67 (dd, J1 = 5.5 Hz,
J2 = 0.8 Hz, 2H), 7.47 (dd, J1 = 6.0 Hz, J2 = 1.8 Hz, 1H), 7.39 (ddd,
J1 = 7.3 Hz, J2 = 5.8 Hz, J1 = 1.2 Hz, 2H), 4.12 (s, 3H), 3.86 (s, 3H).
13C NMR (125 MHz, (CD3)2SO + 10% (CD3)2CO): d 166.9, 164.7,
163.9, 159.3, 158.2, 157.3, 156.5, 153.2, 153.0, 152.3, 145.1,
140.2, 137.6, 136.3, 135.4, 132.3, 130.1, 127.8, 127.6, 125.8,
125.1, 124.4, 123.3, 122.7, 120.5, 53.2, 53.0. HRMS (MALDI-TOF)
calcd for C36H26N5O6RuCl [MꢁH]+ 761.0615, found 761.0628. Ele-
mental Analysis: Calc. for C36H27ClN5O6Ru: C 56.73, H 3.57, N
9.19. Found: C 56.84; H 3.46; N 9.31.
C
66H44N8O [M]+ 964.3638, found 964.3645. Elemental Analysis:
Calc. for C66H44N8O: C 82.14, H 4.60, N 5.16. Found: C 82.22; H
4.73; N 5.21.
Ru(bpy(-COOMe)2)(DMSO)2Cl2: A solution of cis-[RuII(DMSO)4-
Cl2] (484 mg, 1 mmol) and dimethyl [2,20-bipyridine]-4,40-dicar-
boxylate (156 mg, 1 mmol) in mixed EtOH (9 mL) and DMSO
(1 mL) was refluxed for 1.5 h. After being allowed to cool to room
temperature, the resulting orange precipitate was filtered, washed
with cold EtOH, and dried in vacuum (320 mg, yield = 66%). The
obtained solid was a mixture of two isomers (cis- and trans-) and
used without any other purification. HRMS (MALDI-TOF) calcd
for C18H24N2O6RuS2Cl2 [M]+ 599.9496, found 599.9483. Elemental
Analysis: Calc. for C18H24Cl2N2O6RuS2: C 36.00, H 4.03, N 4.67.
Found: C 36.19; H 4.39; N 4.49.
H2P-RuCOOMe: The ruthenium complex Ru(bpy(-COOMe)2)
(DMSO)2Cl2 (55 mg, 0.11 mmol) was added to a solution of H2P-
tpy (65 mg, 0.07 mmol) an acetic acid (30 mL) and the mixture
was stirred under nitrogen at 100 °C overnight. After removing
the solvent, the residue was purified by silica column chromatog-
raphy (CH2Cl2:MeOH (100:7)) giving H2P-RuCOOMe as a purple solid
(73 mg, 76%). 1H NMR (500 MHz, (CD3)2SO): d 11.00 (s, 1H), 10.36
(d, J = 5.8 Hz, 1H), 9.44 (s, 1H), 9.40 (s, 2H), 9.14 (d, J = 1.4 Hz, 1H),
9.06 (d, J = 8.2 Hz, 2H), 8.95 (d, J = 3.9 Hz, 2H), 8.86 (m, 6H), 8.64 (d,
J = 8.3 Hz, 2H), 8.52 (dd, J1 = 5.8 Hz, J2 = 1.4 Hz, 1H), 8.47 (d,
J = 8.3 Hz, 2H), 8.37 (d, J = 8.4 Hz, 2H), 8.25 (m, 8H), 8.10 (t,
J = 8.0 Hz, 2H), 7.84 (m, 10H) 7.67 (d, J = 5.7 Hz, 2H), 7.49 (dd,
J1 = 6.1 Hz, J2 = 1.5 Hz, 1H), 7.41 (t, J = 6.3 Hz, 2H), 4.12 (s, 3H),
3.86 (s, 3H), –2.88 (s, 2H). 13C NMR (75 MHz, (CD3)2SO): d 165.4,
164.8, 164.0, 159.3, 158.2, 157.3, 156.4, 153.2, 153.0, 152.3,
145.1, 141.3, 139.2, 139.1, 137.7, 136.6, 136.2, 135.4, 134.8,
134.3, 131.7, 128.9, 128.6, 128.2, 127.7, 127.1, 126.7, 125.9,
125.2, 124.5, 123.4, 122.8, 120.5, 120.1, 120.0, 118.9, 53.3, 53.1.
IR: 1727 (v(C@O) ester), 1660 (v(C@O) amide), 1257 (v(CAO)
CRediT authorship contribution statement
Georgios Charalambidis: Writing - review & editing, Funding
acquisition, Supervision, Investigation, Methodology. Asterios
Charisiadis: Writing - review & editing, Investigation, Methodol-
ogy. Sofia Margiola: Investigation, Methodology. Athanassios
Coutsolelos: Supervision, Project administration, Resources. Ally
Aukauloo: Conceptualization, Supervision, Funding acquisition,
Project administration. Winfried Leibl: Validation, Visualization,
Resources, Writing - review & editing. Annamaria Quaranta: Writ-
ester). HRMS (MALDI-TOF) calcd for
1338.3479, found 1338.3488. Elemental Analysis: Calc. for C80H56
C
80H56N10O5Ru [MꢁCl]+
-
6

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Acknowledgements
This work was supported by the French Infrastructure for Inte-
grated Structural Biology (FRISBI), France ANR, France-10-INSB-05-
01. General Secretariat for Research and Technology (GSRT), Greece
and Hellenic Foundation for Research and Innovation (HFRI),
Greece (project code: 508) are gratefully acknowledged for the
financial support of this research. Also, the European Commission’s
Seventh Framework Program (FP7/2007-2013), Greece under grant
agreement no. 229927 (FP7-REGPOT-2008-1, Project BIO-SOLE-
NUTI) and the Special Research Account of the University of Crete,
Greece. In addition, this research has been co-financed by the Euro-
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Appendix A. Supplementary data
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7