Synthesis and photophysical properties of naphthyl-, phenanthryl-, and pyrenyl-appended bis(pyridyl)triazine ligands and their Zn(II) and Ru(II) complexes

Article abstract of DOI:10.1139/V08-134

A family made of four bis(pyridyl)triazine ligands with appended aryl rings, including three fused aromatic rings, have been synthesized, and their corresponding homoleptic Ru(II) and Zn(II) complexes have been prepared and characterized by several means.

Full text of DOI:10.1139/V08-134

2
54
Synthesis and photophysical properties of
naphthyl-, phenanthryl-, and pyrenyl-appended
bis(pyridyl)triazine ligands and their Zn(II) and
1
Ru(II) complexes
Francesco Nastasi, Frédérique Loiseau, Sebastiano Campagna,
Elaine A. Medlycott, Marie-Pierre Santoni, and Garry S. Hanan
Abstract: A family made of four bis(pyridyl)triazine ligands with appended aryl rings, including three fused aromatic
rings, have been synthesized, and their corresponding homoleptic Ru(II) and Zn(II) complexes have been prepared and
characterized by several means. The free ligands 2,4-di(2-pyridyl)-6-phenyl-1,3,5-triazine (L1); 2,4-di(2-pyridyl)-6-(1-
naphthyl)-1,3,5-triazine (L2); 2,4-di(2-pyridyl)-6-(9-phenanthryl)-1,3,5-triazine (L3); and 2,4-di(2-pyridyl)-6-(1-pyrenyl)-
1
,3,5-triazine (L4) were formed in triazine ring-forming reactions from the reactions of the cyano-functionalized aro-
matic rings with LiNMe followed by the addition of 2 equiv. of 2-cyanopyridine. The metal complexes examined in
2
2
+
2+
2+
2+
this study are the homoleptic Ru(II) complexes Ru(L1) (2a), Ru(L2) (2b), Ru(L3) (2c), and Ru(L4)2 (2d)
2
2
2
and Zn(II) complexes Zn(L1)22 (3a), Zn(L2)2 (3b), Zn(L3)2 (3c), and Zn(L4)2 (3d). Also, crystallographic data
for the free ligands and Zn(II) and Ru(II) complexes have been obtained in some cases. The redox behaviour and ab-
sorption spectra of all the species have been investigated, together with the luminescence properties of the free ligands
at room temperature in fluid solution and of the Ru(II) complexes both at room temperature in fluid solution and at
+
2+
2+
2+
7
7 K in rigid matrix. The redox data indicate that the free ligands are reduced twice at relatively mild potentials
(
< –2.30 V vs. SCE), with the first reduction almost independent of the nature of the substituted aryl group. The UV
absorption spectra of all the compounds are dominated by intense spin-allowed π–π* transitions mainly centered on the
bis(pyridyl)triazine moiety; however, in L2–L4, moderately intense intraligand charge-transfer (ILCT) bands are also
present. Such bands are red-shifted in the Zn(II) compounds, while they are obscured in the Ru(II) species by the more
intense spin-allowed metal-to-ligand charge-transfer (MLCT) bands. The free ligands exhibit interesting emission prop-
erties, ranging from fluorescence from π–π* states to excimeric (in L4) and ILCT (in L2 and L3) emission. In the
Ru(II) complexes, strong emission is found at 77 K from triplet MLCT states. For 2c and 2d, the emissive MLCT
states are mixed with low-lying triplet ligand-centered states.
Key words: triazine ligands, ruthenium complexes, zinc complexes, ILCT emission. 263
Résumé : On a effectué la synthèse d’une famille formée de quatre ligands bis(pyridyl)triazine portant des noyaux aro-
matiques, y compris trois noyaux aromatiques dont on a préparé et caractérisé les complexes homoleptiques correspon-
dants du Ru(II) et du Zn(II). Les ligands libres 2,4-di(2-pyridyl)-6-phényl-1,3,5-triazine (L1), 2,4-di(2-pyridyl)-6-(1-
naphtyl)-1,3,5-triazine (L2), 2,4-di(2-pyridyl)-6-(9-phénanthryl)-1,3,5-triazine (L3) et 2,4-di(2-pyridyl)-6-(1-pyrényl)-
1
,3,5-triazine (L4) ont été obtenus par des réactions conduisant à des triazines et impliquant l’action du LiNMe sur
2
des cyano portés par noyaux aromatiques fonctionnalisés, suivie par l’addition de deux équivalents de 2-cyanopyridine.
2
+
Les complexes métalliques examinés dans cette étude sont les complexes homoleptiques du Ru(II), Ru(L1) (2a),
2
2
+
2+
2+
2+
2+
2+
Ru(L2)2 (2b), Ru(L3)2 (2c) et Ru(L4)2 (2d) et du Zn(II), Zn(L1)2 (3a), Zn(L2)2 (3b), Zn(L3)2 (3c) et
Zn(L4)22 (3d). Dans certains cas, on a aussi obtenu des données cristallographiques pour les ligands libres et des
complexes du Zn(II) et du Ru(II). On a étudié le comportement redox et les spectres d’absorption de toutes les
+
Received 3 April 2008. Accepted 10 June 2008. Published on the NRC Research Press Web site at canjchem.nrc.ca on 11 October
008.
2
This paper is dedicated to Professor Richard Puddephatt for his great contributions in Organometallic Chemistry.
F. Nastasi and S. Campagna. Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina,
9
8166 Messina, Italy.
F. Loiseau. Département de Chimie Moléculaire, UMR CNRS 5250, ICMG– FR 2607, Université Joseph Fourier, BP-53, 38041
Grenoble CEDEX 9, France
2
E.A. Medlycott, M.-P. Santoni, and G.S. Hanan. Department of Chemistry, Université de Montréal, Montréal, QC H3T 1J4,
Canada.
1
This article is part of a Special Issue dedicated to Professor R. Puddephatt.
Corresponding author (e-mail: garry.hanan@umontreal.ca).
2
Can. J. Chem. 87: 254–263 (2009)
doi:10.1139/V08-134
© 2008 NRC Canada

Nastasi et al.
255
espèces, de même que les propriétés de luminescence des ligands libres, à la température ambiante et en solution fluide
ainsi que celles des complexes du Ru(II) tant à la température ambiante, en solution fluide, que celles à 77 K, dans
une matrice solide. Les données redox indiquent que les ligands libres sont réduits deux fois à des potentiels relative-
ment faibles (< –2,30 V vs SCE) et que la première réduction est pratiquement indépendante de la nature du substi-
tuant aryle. La région UV des spectres d’absorption de tous les composés est dominée par d’intenses transitions π–π*
permises par les spins et centrés principalement sur la portion bis(pyridyl)triazine; toutefois, dans les ligands L2–L4,
on observe aussi la présence de bandes de transfert de charge intraligand (TCIL) d’intensité moyenne. Ces bandes sont
déplacées vers le rouge dans les composés du Zn(II) alors que dans les espèces Ru(II) elles sont obscurcies par les
bandes de transfert de charge métal à ligand (TCML) permises par les spins et de grande intensité. Les ligands libres
possèdent des propriétés d’émission intéressantes allant de la fluorescence des états π–π* aux émissions excimères
(
dans L4) et aux bandes de transfert de charge intraligand (dans L2 et L3). Dans les complexes du Ru(II), à 77 K, on
observe une émission intense de transfert de charge métal à ligand à partir des états triplets. Pour les composés 2c et
d, les états d’émission TCML sont mixtes avec des états triplets de basse énergie centrés sur le ligand.
2
Mots-clés : ligands de triazine, complexes du ruthénium, complexes du zinc, émission de transfert de charge intraligand
(
TCIL).
[
Traduit par la Rédaction] Nastasi et al.
ganic group to act as an electron donor. Tpy is typically an
electron acceptor, and a variety of organic groups act as the
electron donor. Fused aromatic rings have previously been
employed as the organic, electron donating motif, as they of-
fer interesting properties in the excited state through excimer
and exciplex formation as well as offering a means of aggre-
gating cations in the solid state through π–π interactions (12,
14, 15, 17–19). Herein, we report the synthesis and charac-
terization of a family of triazine ligands with fused aromatic
rings appended. The absorption spectra and redox properties
of free ligands and of their Zn(II) and Ru(II) complexes are
also discussed, together with the luminescence properties of
free ligands and Ru(II) complexes.
Introduction
Complexes of polypyridine ligands have been the subject
of intense research because of their promising photophysical
properties and potential applications in areas of light-
harvesting devices, luminescent sensors, and photocatalysis.
In particular, complexes of d transition-metal ions show
promise in these fields because of their relatively long ex-
cited-state lifetimes and emission through low-lying MLCT
6
(
metal-to-ligand charge-transfer) states (1–5). Over the last
two decades, there has been considerable efforts to optimize
the photophysical properties of Ru(II) complexes based on
2
,2′:6′,2′′ -terpyridine (tpy) (2, 6). Indeed, the tridentate mo-
tif offers synthetic advantages over bidentate ligands based
on 2,2′-bipyridine (bpy), as the latter creates stereocentres in
metal complexes with octahedral geometry. Consequently, in
larger polynuclear systems, the separation of diastereomers
can be problematic despite synthetic advances in the purifi-
cation of isomers (7, 8). Unfortunately, Ru(II) tpy-type com-
plexes have poor photophysical properties, as the steric
strain imposed in N–N–N coordination in tridentate ligand
lowers the energy of non-emissive, metal-centred (MC)
states, which can be thermally accessed at room tempera-
ture. Synthetic strategies have been developed to overcome
the deactivation of MLCT excited states, primarily focusing
Results and discussion
Synthesis
The ligands were synthesized by using a slightly modified
version of a previously reported procedure (see Supplementary
data for full ligand structures) (20, 21). LiNMe was gener-
3
2
ated in situ through the slow addition of n-BuLi to HNMe2
in anhyd. diethylether. On addition of the cyano-precursors,
an amidinate intermediate formed, which was converted to
the appropriate triazine ligand by the addition of 2 equiv. of
2-cyanopyridine. The reaction proceeded slower than previ-
ously reported syntheses for non-symmetric triazine ligands
and with slightly lower yields. The presence of the adjacent
fused aromatic ring may lead to a stabilized amidinate inter-
mediate by intramolecular H-bonding with the C=N motif,
which interferes with the cyclization reaction (Scheme 1).
Complexes 2 were synthesized by addition of RuCl ·3H O
to 2 equiv. of the ligand, with 3 equiv. of AgNO in EtOH.
The complexes were purified by column chromatography
followed by anion exchange to afford complexes 2b–2d in
56%, 23%, and 11% yields, respectively. The Zn(II) com-
plexes were synthesized by the addition of Zn(ClO ) ·6H O
to a solution of the appropriate ligand in acetonitrile at re-
flux for 15 min. Precipitation of the product by the addition
3
3
on manipulating the energy of MLCT states relative to MC
states. Alternatively, ligand systems have been developed
with low energy emissive intraligand charge-transfer (ILCT)
states (9). The excited-state energy of the ILCT state in
Ru(II) complexes, or complexes of other transition-metal
ions, must be significantly lower in energy than the
MLCT/MC states to influence the excited-state lifetime (10–
–
3
2
3
1
4). Alternatively, d10 Zn(II) metal ions can be employed to
study the ILCT emission, as these polypyridine complexes
of such metal ions do not exhibit MLCT or MC states at low
energies, and their eventual emission can involve ILCT
states (13–16). An ILCT transition requires a coordinating
motif to acts as an electron acceptor and an appended or-
4
2
2
3
Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3836. For more in-
formation on obtaining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml.
©
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Can. J. Chem. Vol. 87, 2009
Scheme 1. Synthesis of ligands L1–L4 and the complexation of the ligands to form the Ru(II) complexes 2a–2d and Zn(II) complexes
a–3d.
3
1
of diethyl ether afforded the complexes 3a–3d in 68%, 55%,
4%, and 84% yields, respectively. The complexes were
characterized in solution by H NMR and in the solid state
by elemental analyses.
Fig. 1. H NMR spectra of L4 in CDCl (above), 2d (middle),
3
7
and 3d (below) in CD CN. H3,3′ ′, H4,4′ ′, H5,5′ ′, and H6,6′′ refer to
the pyridyl protons.
3
1
On complexation to the Ru(II) or Zn(II) metal ions, the
pyridyl and pyrenyl signals of ligands are both shifted to
lower field owing to the electron-withdrawing effect of the
metal ions (Fig. 1). The Zn(II) ion in complex 3d has a
greater electron-withdrawing effect on the pyridyl protons
closest to the metal centre (H5,5′′ and H6,6′′) when compared
with the Ru(II) complex 2d. Complex 3d has limited solubil-
ity and reaches saturation point in solution very rapidly as
compared with 2d presumably owing to aggregation caused
by the pyrenyl group.
Solid-state structures
Crystals suitable for analyses of L2 were obtained by
slow diffusion of hexane into a concentrated solution of L2
in chloroform. One molecule of water is found in the asym-
metric unit with H-bonding to N-pyridyl atoms with N–H
distances of 2.15 and 2.14 Å. Significant face-to-face π-
stacking interactions are observed in the extended lattice
with each triazine ring overlaying pyridyl rings above and
below the plane with centroid-to-centroid distances of 3.6–
3
.8 Å (Fig. 2).
Attempts to crystallize 2b and 3b as the PF and ClO
6
4
salts, respectively, were unsuccessful. Red crystals of 2b
were obtained by addition of excess NH BF in methanol to
4
4
a concentrated solution of 2b in acetonitrile followed by
slow diffusion of isopropyl ether. The complex crystallized
in the monoclinic space group P2(1)/n with two cations, four
anions, (three PF6– anions and one BF4– anion) and four
molecules of acetonitrile. The Zn(II) complexes could be
synthesized as the PF6– salts according to a literature proce-
both crystal structures, significant π-stacking interactions
were observed in the extended lattice between naphthyl
groups and coordinating pyridyl rings with centroid-centroid
distances of 3.66 and 3.71 Å for complex 2b and 3.89 and
3.96 Å in complex 3b (Fig. 3). The use of non-covalent in-
teractions to aggregate functional assemblies through crystal
engineering is appealing as conventional, covalent ap-
–
dure (22), and crystals of 3b were obtained as the PF6 salt
by slow diffusion of isopropyl ether into an acetonitrile solu-
tion of the complex. Complex 3b crystallized in the non-
centrosymmetric space group P2(1) with two cations, four
PF counter-ions and three acetonitrile solvent molecules. In
6
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Nastasi et al.
257
Fig. 2. ORTEP representation of solid-state structure L2 with H O solvent molecule (left) and pyridyl-triazine π-stacking interaction
2
(
right). Thermal ellipsoids are set at 30%.
Fig. 3. ORTEP representations of π-stacking interactions in the solid-state structures of 2b and 3b. Thermal ellipsoids are set at 30%.
Anions and solvent molecules of crystallization were omitted for clarity.
proaches require multistep syntheses (4, 17, 19, 22).
Naphthyl-pyridyl, π-stacking interactions were previously
observed in naphthyl-appended tpy-based Ru(II) and Fe(II)
complexes (19). We previously reported similar interactions
in the solid-state structure of complex 2c in which
phenanthryl groups π-stack with pyridyl groups (20). The
naphthyl groups twist away from the central triazine rings
by 16.6°–36.9° in complex 2b and 21.5°–29.1° in complex
the central triazine ring compared with the terminal pyridyl
rings as expected owing to the constrained bite angle im-
posed by tridentate ligands. The Ru–N bond distances, 1.97–
1.98 Å to the central triazine ring and 2.09–2.11 Å to the
terminal pyridyl rings, are in agreement to those previously
reported for related Ru(II) complexes of triazine-based lig-
ands (20, 21). The Zn–N bond distances are slightly longer
and similar to those reported for tpy-type ligands (22).
3
b for the four ligands of the two cations. Intramolecular
C–H–N(triazine) H-bonding interactions are still favouring
minimal twisting of the naphthyl group relative to the
triazine ring and thereby favouring significant mixing of
molecular orbitals.
Electrochemical properties
The redox data for the ligands and their complexes are
gathered in Table 1. The redox data of ligands L1, L2, and
L4 are reported in DMF owing to their poor solubility in
acetonitrile. In all of the ligands, an initial reversible
The M–N bond distances in both 2b and 3b are shorter to
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Can. J. Chem. Vol. 87, 2009
Table 1. Half-wave potentials for ligands L and complexes 2 and 3. Data are in acetonitrile at
00 mV s–1 vs. SCE, unless otherwise stated.
2
Compound
E1/2(oxidation)
E1/2(reduction)
L1a
–1.42(84)
–1.41(82)
–1.42(86)
–1.40(75)
–0.71(65)
–0.73(63)
–0.72(74)
–0.75(68)
–0.79(80)
–0.80(67)
–0.81(irr)
–0.76(68)
–2.25(irr)
–2.17(irr)
–2.15(irr)
–1.84(96)
–0.88(69)
–0.89(68)
–0.89(77)
–0.89(69)
–0.91(84)
–0.91(77)
–0.86(104)
–0.87(76)
a
L2
L3
L4
b
a
1.54 (irr)
1.51(81)
1.52(84)
1.52(85)
–2.17(irr)
–1.51(74)
–1.52(67)
–1.52(79)
–1.51(88)
–1.60(86)
–1.59(78)
–1.52(103)
–1.52(irr)
c
2
2
2
2
3
3
3
3
a
–1.75(78)
–1.75(80)
–1.75(90)
–1.74(irr)
–1.77(78)
–1.75(74)
–1.73(108)
b
b
c
d
a
b
1.46(irr)
1.66(irr)
b
c
d
1.45 (irr)
a
In DMF.
b
c
From ref. 20.
From ref. 21.
triazine-based reduction is observed at –1.40 to –1.42 V vs.
SCE. The negligible potential difference among all four lig-
ands indicates that the aryl substituent on the triazine has lit-
tle influence on this process. A second triazine-based
reduction is observed at –2.15 to –2.17 V in L2–L4. This
same reduction shifts to a more negative potential in L1
Table 2. Absorption data in acetonitrile.
λmax (nm) (ε, ((mol/L)–1 cm–1 × 10 ))
–3
L1a
243 (25.0); 276 (40.8)
L2
L3
L4
217 (55.8); 243 (27.9); 277 (21.9); 325 sh (9.6)
250 (56.8), 270(35.1), 325 sh (11.4)
240 (27.7); 285 (17.2); 370 (9.6); 400 (7.2)
242 (24.4); 284 (73.2); 481 (24.6)
211 (88.4); 274 (50.8); 487 (20.6)
250 (91.9); 271 (83.7); 345 (24.3); 490(30.3)
236 (79.9); 272 (76.5); 380 (20.0); 532(43.8)
249 (25.1); 293 (57.2)
(
–2.25 V), indicating the LUMO +1 molecular orbital in-
volves non-negligible mixing of the aromatic and triazine
motifs. An additional pyrenyl-based reduction is observed in
L4 at –1.84 V. No oxidative processes are observed in L1–
L3 within the solvent potential limits. However, the pyrene
motif is oxidized at +1.54 V in L4, which is more positive
than the tpy-pyrene ligand (+1.49 V) owing to the stabilizing
effect of the electron-deficient triazine ring (12). However,
overall a lower energy HOMO–LUMO gap is estimated by
electrochemistry: 2.94 V for L4 as compared to 3.15 V for
tpy-pyrene (12).
b
2
2
2
2
3
3
a
b
c
d
a
b
211 (121.8); 254 (49.1); 277 (47.7); 293 sh
(
38.2);388 (18.7)
3
3
c
d
253 (77.9); 276 sh, 390 (14.9)
238 (89.7); 257 (52.6); 268 (54.9); 281 (44.6);
2
97 (46.0); 394 (14.4): 460 (27.9)
The oxidative potentials for the Ru(II)/(III) couple in
complexes 2a–2c are in agreement with those previously re-
ported for Ru(II) complexes of triazine ligands (20, 21).
However, in complex 2d, the pyrene motif is oxidized prior
to the Ru(II) centre at +1.46 V, and the Ru(II)/(III) couple is
consequently at a more positive potential and irreversible. In
the Zn(II) complex 3d, the pyrene motif is oxidized at
a
From ref. 20.
From ref. 21.
b
does not exhibit a similar low energy absorption band, since
the phenyl group is a worse electron-donor group compared
with the other fused aromatic rings. On metal complexation,
such ILCT bands are expected to shift to lower energy, since
the bipyridyltriazine orbitals are stabilized by metal coordi-
nation. This is clearly evidenced in the Zn(II) complexes,
which exhibit ILCT absorption bands that extend to the
visible, in particular for complexes 3b–3d (see Fig. 4, bot-
tom). The ILCT transitions are red-shifted in comparison to
Zn(II) tpy complexes with fused aromatic rings (17), as a
consequence of the better acceptor properties of the
bis(pyridyl)triazine group compared with the terpy. In Ru(II)
complexes 2a–2d, the ILCT bands are largely obscured by
the spin-allowed metal-to-ligand charge-transfer (MLCT)
transitions, which are responsible for the relatively strong
absorption bands in the 450–560 nm region (Table 2, Fig. 4,
middle). However, the absorption in the 450–560 nm region
increases on passing from 2a (not shown in Fig. 4, middle)
and 2b to 2c, and even further on going to 2d, which exhib-
its a maximum at lower energy than the other complexes.
This cannot be attributed only to contribution of the ILCT
+
1.45 V. The electron-withdrawing effect of metal coordina-
tion results in significant positive shifts in the potentials for
the triazine-based reductions for both Ru(II) complexes 2a–
2
d and Zn(II) complexes 3a–3d. Each triazine ligand has
two reductions giving a total of four reductions for com-
plexes 2a–2d and 3a–3c.
Absorption spectra
The absorption spectral data for the ligands and their com-
plexes are gathered in Table 2. Figure 4 shows the absorp-
tion spectra of some representative compounds. At
wavelengths shorter than 350 nm, ligand-based spin-allowed
π–π* transitions dominate the spectra. However, less intense
bands are also present at longer wavelengths even for the
free ligands, particularly for L2–L4. These bands are as-
signed to aryl-to-bis(pyridyl)triazine charge-transfer transi-
tions (intraligand charge transfer, ILCT). Compound L1
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Nastasi et al.
259
Fig. 4. Top: absorption spectra of L2, L3, and L4. Middle: ab-
sorption spectra of 2b, 2c, and 2d. Bottom: absorption spectra of
Table 3. Luminescence properties of the free ligands.
λmax (nm)
τ (ns)
3
a and 3b. All the spectra are in acetonitrile.
L1
L2
L3
414
450
376 sh
1.7
2.6
20 (67%), 2.3(33%)
4
70
384, 406
71
2.0
L4
22 (85%), 1.7 (15%)
2.2
4
Note: In acetonitrile at 298 K. The percentage of the decay in
the biexponential analysis is reported in parentheses. The excita-
tion wavelength is 308 nm.
Fig. 5. Emission spectra of L2, L3, and L4 in acetonitrile.
ture. The luminescence data of the ligands are collected in
Table 3, and the emission spectra of L2, L3, and L4 are
shown in Fig. 5.
L1 is weakly emissive, with an unstructured emission
with a maximum at 414 nm in acetonitrile with an excited-
state lifetime of 1.7 ns. The emission is assigned to fluores-
cence from the π–π* singlet state, with only a partial phenyl-
to-bis(pyridyl)triazine charge-transfer character.
L2 exhibits a broad band with maximum at 450 nm and a
lifetime of 2.6 ns. The emission is too low-lying to be π–π*
fluorescence from the naphthalene subunit (23, 24), and also
too much red-shifted from that of L1 to be π–π* fluores-
cence mainly involving the bis(pyridyl)triazine. In fact,
naphthalene derivatives often exhibit a low-energy emission
of excimeric nature. However, naphthalene excimer emission
is normally in the range of 400–425 nm (23, 24). On the ba-
sis of such comments, we assign the emission of L2 to a
(
naphthalene-to-bis(pyridyl)triazine) intraligand charge-
bands in the visible, since the lowest energy bands in 3d, as-
signed to the ILCT transition, maximizes at 460 nm, with
negligible contribution at wavelengths longer than 500 nm.
Most likely, it is the intensity of the spin-allowed MLCT
bands, which increases in the series.
transfer (ILCT) excited state. Such a state should be very
sensitive to the presence of protons, since the acceptor sub-
unit is protonable; indeed, addition of triflic acid leads to
disappareance of the 450 nm emission band. As testified by
the change in the absorption spectrum of L2 upon triflic acid
addition (see Supplementary data, Fig. S1: the ILCT absorp-
tion band is significantly red shifted), protonation of the ac-
ceptor subunit leads to a stabilization of the ILCT level,
The absorption spectra of all the compounds are stable for
at least three days and do not exhibit any significant depend-
ence on the concentration, within the range investigated (8 ×
–
6
–5
3
1
0
– 5 × 10 mol/L).
which apparently becomes non emissive.
As far as L3 is concerned, an emission band is present
with maximum at 470 nm and 2.0 ns lifetime. However, on
the blue-edge of the emission band, another emission feature
appears, structured (see Fig. 5). When the emission decay is
Luminescence properties
The luminescence properties of the free ligands were stud-
ied in air-equilibrated acetonitrile solutions at room tempera-
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Can. J. Chem. Vol. 87, 2009
Fig. 7. Change of the emission spectrum of L4 upon
Fig. 6. Change of the emission spectrum of L3 upon protonation.
Concentration of L3 is 7.1 × 10 mol/L, and concentration of
–
6
–6
protonation. Concentration of L4 is 4.9 × 10 mol/L, and con-
+
–3
+
+
–3
+
H is 1.95 × 10 mol/L (molar ratio of L3:H is 1:3), (λ
=
centration of H is 1.95 × 10 mol/L (molar ratio of L4:H is
1:3), (λexc = 340 nm).
exc
3
03 nm, the isosbestic point).
perimental uncertainties) to the 480 nm emission lifetime
(
Table 3).
analyzed at 380 nm, a biexponential decay is found (see Ta-
ble 3), with a long-lived component (20 ns) following a
short-lived component (2.3 ns). The short-lived component
is assigned to the contribution of the emission with a maxi-
mum at 470 nm, and indeed its lifetime agrees with the
monoexponential decay recorded at 470 nm (Table 3),
whereas the longer-lived component is assigned to the struc-
tured emission taking place in the range of 350–400 nm.
This latter emission is attributed to fluorescence from the
phenanthryl-based π–π* singlet, and the dominant, lower-
energy emission is attributed to the ILCT excited state. To
support such an assignment, phenanthrene fluorescence in
polar solvents is reported to occur at 347 nm with a lifetime
of 60.7 ns (24, 25), values in good agreement with those ob-
tained for our substituted phenanthrene species. As for L2,
protonation stabilizes the ILCT level of L3, leading to red
shift of the low-energy absorption band and disappearence
of the ILCT emission (Figs. S2 and 6).3
L4 clearly exhibits a double emission: a structured band,
with a maximum at 380 nm, and a broad emission with max-
imum at about 470 nm (Table 3, Fig. 5). The higher energy
emission is assigned to the π–π* singlet state of the pyrenyl
subunit, which is reported to occur at about 375 nm in polar
solvents (24, 26), and the lowest-energy emission is assigned
to the excimer. Indeed, pyrene excimeric emission is re-
ported to occur at the same energy (23). Moreover, the even-
tual ILCT emission should occur at significantly lower
energy than 470 nm, as the ILCT level in L4 is stabilized
compared with the same level in L3 (see absorption spectra)
As for L2 and L3, addition of triflic acid leads to disap-
pearance of the lower-energy band, while the higher-energy
π–π* (monomeric) emission remains unaffected (Fig. 7; for
the changes on absorption spectrum upon acid addition, see
3
Supplementary data). Whereas the emission changes upon
acid addition of L4 are experimentally equivalent to those of
L3, their interpretation is slightly different, as the origin of
the 470 nm broad emission is different in the two com-
pounds. In principle, proton addition is not expected to have
a direct effect on excimer formation; in this case, it could
change the association constant for excimer formation, since
the pyrene “substituent” (i.e., the bis(pyridyl)triazine sub-
unit) is protonable, and the excimer would become posi-
tively charged. However, if this would happen, the monomer
emission would increase, and this is not found experimen-
tally; therefore, protonation seems to not affect monomer/
excimer ratio. This strongly suggests that the consequence of
the protonation is that the ILCT state, potentially a quencher
for both monomer and excimer emission, is displaced to
lower energy, thereby increasing the driving force for the
quenching process(es). This is supported by the effect of
protonation on the absorption spectrum of L4 (see Supple-
3
mentary data). It is suggested that quenching of the excimer
emission of L4 upon acid addition can be attributed to deac-
tivation of the excimer to the proton-stabilized ILCT state
(non emissive), which in the protonated species is signifi-
cantly lower-lying than the excimeric state, where it was al-
most isoenergetic in the non-protonated species, so that the
change in driving force is significant (it would pass from a
very small value to a significant value). Most likely, the
monomer emission is already partially quenched in L4 by
the ILCT state and increasing the driving force for this
quenching process as a consequence of protonation has only
negligible effects on monomer emission. However, this ex-
planation should be considered as tentative, since we cannot
perform quantitative calculations based on the effective driv-
ing force values, which are unknown.
(
27). A supporting experiment for the assignment of the low-
energy emission of L4 to an excimeric state is also the con-
centration dependence of the emission spectrum; indeed on
–
6
increasing concentration (e.g., from 5 × 10 mol/L to 2 ×
–
5
1
0
mol/L), the low-energy emission band significantly in-
creases with respect to the high-energy emission feature. As
for what found for L3, the analysis of the emission decay at
4
80 nm yields a monoexponential behaviour, while analysis
of the decay at 380 nm gives a biexponential behaviour, with
the shorter-lived component corresponding (within the ex-
Unfortunately, the study of the luminescence properties of
the Zn(II) complexes 3a–3d gave non reproducible results,
©
2008 NRC Canada

Nastasi et al.
261
Table 4. Luminescence of the Ru(II) com-
plexes.
Fig. 8. Luminescence properties of 2b, 2c, and 2d in
EtOH/MeOH 4:1 (v/v) at 77 K.
λmax (nm)a
τ (µs)
2
2
2
2
ab
b
c
672
665
665
690
1.4
1.5
24
d
25
Note: In EtOH/MeOH 4:1 (v/v) at 77 K.
The excitation wavelength is 408 nm.
a
Higher-energy feature.
From ref. 21.
b
most likely since the compounds were poorly stable at the
concentrations used for the luminescence experiments
–
6
(
lower than 8 × 10 mol/L), a somewhat not unexpected be-
haviour for Zn(II) polypyridine complexes (15). Lumines-
cence properties of the Zn(II) compounds 3a–3d are
therefore not investigated here.
cent level, even at 77 K and without affecting the energy of
the emitting level (31).
Ru(II) polypyridine complexes based on tridentate ligands
are very weakly emitting at room temperature (Table 4) be-
cause of the presence of a low-lying metal-centered (MC)
state, which deactivates the potentially luminescent MLCT
state (2, 3, 5, 28). This is evidently even more true for Ru(II)
complexes of bis(pyridyl)triazine ligands, as this ligand has
probably a weaker ligand field strength than tpy, like the ab-
sence of room-temperature emission of other homoleptic
Ru(II) complexes based on substituted bis(pyridyl)triazine
ligands seems to suggest (21). As a matter of fact, 2b, 2c,
and 2d are not luminescent at all at room temperature, and
Conclusion
Introducing fused aromatic rings to the triazine-based
tridentate ligands offers a means to significantly stabilize the
ILCT band compared with their analogous systems based on
tpy. As a consequence, room-temperature emission studies
of L2–L4 indicate that some of their emissive excited states
have significant charge-transfer character. In the case of L4,
an excimer emission is also found. On complexation, the
ILCT states are red-shifted in the Zn(II) complex, as clearly
evidenced by the absorption spectra. Unfortunately, lumines-
cence of the Zn(II) complexes cannot be investigated, since
the compounds are poorly stable at the low concentrations
needed for luminescence experiments. In Ru(II) complexes,
the potentially emissive MLCT excited states are quenched
at room temperature by the presence of low-lying metal-
centered states, whereas MLCT emission takes place at 77 K
in rigid matrix with (for 2c and 2d) some contribution from
closely lying LC (most likely, ILCT) triplet states.
2
a (21) is only weakly luminescent (λ = 710 nm, τ = 8 ns,
–5
Φ = 9 × 10 ). All of the four Ru(II) complexes are emissive
at 77 K from their lowest energy MLCT triplet (Table 4,
Fig. 8), demonstrating that the MC state is no longer popu-
lated in this condition. The emission is partially structured,
as expected for a MLCT emission at low temperature (29,
3
0), and the vibrational progression is typical of C=C and
C=N stretching. However, the 77 K emission properties of
a–2d show interesting differences, the larger one being the
2
longer lifetimes (one order of magnitude longer, see Table 4)
exhibited by 2c and 2d compared with 2a and 2b. The rea-
son for such longer lifetimes can have two origins:
Experimental section
(
i) delocalization of the MLCT state towards the larger
phenanthryl and pyrenyl moieties, which can be coplanar
with the triazine ring, so that the geometry of the excited
state becomes closer to the geometry of the ground state, de-
creasing Franck–Condon factor for radiationless decay;
General methods and equipment
NMR spectra were recorded in CD CN at RT on a Bruker
3
1
AV400 spectrometer at 400 MHz for H NMR and at
1
3
100 MHz for C NMR. Chemical shifts are reported in ppm
relative to residual solvent protons (1.93 ppm for
(
ii) mixing of the MLCT state with a closely-lying, longer-
3
3
lived ligand-centered ( LC) state. This LC state could be
the triplet of the ILCT state, which is expected to be lower
in energy for the phenanthryl- and pyrenyl-containing lig-
ands. In fact, hypothesis (i) would suggest that the first re-
duction potentials of 2c and 2d are less negative than those
of the other two ruthenium(II) complexes, but this is not the
case (see Table 1). Moreover, delocatization of the MLCT
state over the aryl moieties should red shift the emission
spectrum of 2c compared with 2a and 2b, and this is not ex-
perimentally found. For these reasons, hypothesis (ii) ap-
pears to be preferred. At this point, it should be recalled that
the presence of closely-lying states have already been re-
ported to be able to influence the dynamics of the lumines-
acetonitrile-d ) and the carbon resonance of the solvent. Ab-
3
sorption spectra were measured on a Cary 500i UV–vis NIR
spectrophotometer. Luminescence spectra were obtained
with a Horiba Jobin–Yvon Fluoromax P spectrofluorimeter
equipped with a Hamamatsu R3896 photomultiplier and
were corrected for photomultiplier response using a program
purchased with the fluorimeter. Emission lifetimes were
measured with an Edinburgh OB-900 single-photon counting
spectrometer equipped with a Hamamatsu PLP-2 laser diode
(pulse width at 408 nm, 59 ps) and with a PicoQuant PDL
800-D pulsed laser diode (pulse width at 308 nm, 50 ps).
The emission decay traces (emission lifetimes measured at
about the emission maximum wavelengths) were analyzed
©
2008 NRC Canada

2
62
Can. J. Chem. Vol. 87, 2009
by Marquadt algorithm. For each measurement, at least five
determinations were carried out.
Anal. calcd. C H N ·H O: C 72.8, H 4.5, N 18.5; found: C
72.6, H 4.6, N 18.5.
2
3
15
5
2
Electrochemical measurements were carried out in argon-
purged acetonitrile at RT with a BAS CV50W multipurpose
equipment interfaced to a PC. The working electrode was a
Pt electrode. The counter electrode was a Pt wire, and the
pseudo-reference electrode was a silver wire. The reference
was set using an internal 1 mmol/L ferrocene/ferrocinium
sample at 395 mV vs. SCE in acetonitrile and 432 mV in
DMF. The concentration of the compounds was about
L4
As per the general procedure using n-BuLi (1.6 mol/L in
hexanes, 5.1 mL, 8.1 mmol), HNMe (2 mol/L in THF,
4.1 mL, 8.1 mmol), 1-cyanopyrene (1.68 g, 7.42 mmol), and
2-cyanopyridine (1.44 mL, 15.0 mmol) in 150 mL anhyd.
2
1
ether. H NMR (CDCl , 400 MHz): 9.51 (d, J = 10 Hz, 1H)
3
H ; 9.12 (d, J = 8 Hz, 1H), H ; 9.06 (d, J = 4 Hz, 2H)
py
py
1
mmol/L. Tetrabutylammonium hexafluorophosphate was
used as supporting electrolyte, and its concentration was
.10 mol/L. Cyclic voltammograms were obtained at scan
H6,6′′ ; 8.94 (d, J = 8 Hz, 2H) H3,3′′ ; 8.39–8.07 (m, 7H) 7Hpy;
8.05 (td, J = 2 Hz, 8 Hz, 2H) H4,4′′ ; 7.61 (dd, J = 5 Hz, 6
Hz, 2H) H5,5′′
1
3
0
.
C NMR (100 MHz, CDCl ): 124.19,
3
rates of 50, 100, 200, and 500 mV/s. For irreversible oxida-
tion processes, the cathodic peak was used as E, and the an-
odic peak was used for irreversible reduction processes. The
criteria for reversibility were the separation of approximately
124.49, 124.65, 124.84, 125.56, 125.82, 125.89, 126.09,
127.07, 128.90, 129.07, 129.33, 129.73, 130.27, 130.30,
130.84, 133.63, 136.82, 150.22, 153.13, 171.15, 175.46,
176.75. Anal. calcd. C H N ·0.5H O: C 78.4, H 4.1, N
2
9
18
5
2
6
0 mV between cathodic and anodic peaks, the close to
15.8; found: C 78.7, H 3.3, N 15.5.
unity ratio of the intensities of the cathodic and anodic cur-
rents, and the constancy of the peak potential on changing
scan rate. The number of exchanged electrons was measured
with OSWV and by taking advantage of the presence of
ferrocene used as the internal reference.
Experimental uncertainties are as follows: absorption
maxima, ±2 nm; molar absorption coefficient, 10%; emis-
sion maxima, ±5 nm; excited-state lifetimes, 10%; and redox
potentials, ±10 mV.
Ruthenium triazine complexes 2b and 2d
RuCl ·3H O (0.032 g, 0.12 mmol) was added to a stirred
3
2
solution of the appropriate ligand (0.24 mmol) in EtOH
15 mL). The mixture was stirred at RT for 15 min and then
(
heated to reflux for 1 h. The reaction mixture was cooled
and satd. KPF (aq., 5 mL) was added. The solution was
6
diluted with a 100 mL of water and the red solid collected
and injected onto a silica column and eluted with
acetone/water/KNO (satd.) 9:0.9:0.1. The nitrate salt was
3
Synthesis
metathesized to the PF salt by the addition of NH PF and
6
4
6
Compounds L1, L3, 2a, 2c, and 3c were synthesized as
previously described (20, 21).
the solvent removed under reduced pressure. The product
was collected by dissolving the solid in acetonitrile and pre-
cipitated by addition to water and recrystallized from
acetonitrile/ether to afford 2b and 2d as red solids.
General procedure for L2 and L4
n-BuLi (1.6 mol/L in hexanes, 1.1 equiv.) was added
2
b
dropwise to a stirred solution of HNMe (2 mol/L in THF,
2
1
Red solid, 56%. H NMR (400 MHz, CD CN): 9.68 (d,
1
.1 equiv.) in anhyd. Et O under an inert atmosphere. The
3
2
J = 9 Hz, 2H) Hnap; 9.11 (d, J = 7 Hz, 4H) H3,3′′ ; 9.09 (m,
H) Hnap; 8.40 (d, J = 8 Hz, 2H) Hnap; 8.23 (d, J = 8 Hz, 2H)
Hnap; 8.17 (td, J = 8 Hz, 1 Hz, 4H) H4,4′′ ; 7.90–7.98 (m, 4H)
mixture was stirred for 20 min until a white suspension
formed and the cyano-arene (1 equiv.) was added to the mix-
ture. The mixture was stirred for 4 h further followed by ad-
dition of 2-cyanopyridine (2 equiv.). The reaction mixture
was stirred overnight and worked up by stirring for 30 min
2
Hnap; 7.88 (d, J = 6 Hz, 4H) H6,6′′ ; 7.81 (t, J = 8 Hz, 2H)
Hnap; 7.46 (td, J = 6, 2Hz, 4H) H5,5′′ . HR-MS: M2+ (–2PF ) =
6
4
3
62.0845. Anal. calcd. C H N RuP F ·4H O: C 46.6, H
.2, N 11.8; found: C 46.4, H 2.7, N 11.7.
in air followed by removal of Et O under reduced pressure.
46 30 10 2 12 2
2
The residue was recrystallized three times from water:ethanol
and the solid collected, washed with diethyl ether to yield
L2 as a white solid in 35% yield and L4 as a yellow solid in
2
d
1
2
6% yield.
Red solid, 11%. H NMR (400 MHz, CD3CN): 10.03 (d,
J = 10 Hz, 2H) Hpyrene; 9.52 (d, J = 8.3 Hz, 2H) Hpyrene; 9.18
(
(
(
(
d, J = 8 Hz, 4H) H3,3′′ ; 8.66 (d, J = 8 Hz, 2H) Hpyrene; 8.60
d, J = 9.3 Hz, 2H) Hpyrene; 8.38–8.53 (m, 8H) 4Hpyrene; 8.25
t, J = 7 Hz, 2H) Hpyrene; 8.19 (t, J = 8 Hz, 4H) H4,4′′ ;7.92
L2
As per the general procedure using n-BuLi (1.6 mol/L in
hexanes, 5.1 mL, 8.1 mmol), HNMe (2 mol/L in THF,
2
d, J = 5 Hz, 4H) H6,6′′ ; 7.47 (dd, J = 6 Hz, 6Hz, 4H) H5,5′′
.
4
.1 mL, 8.1 mmol), 9-cyanophenathrene (1.50 g, 7.39
Anal. calcd. C H N RuP F ·2H O: C 53.7, H 2.9, N
10.8; found: C 53.7, H 2.4, N 10.2.
5
8
38 10
2
12
2
mmol), and 2-cyanopyridine (1.44 mL, 15.0 mmol) in
1
1
1
8
50 mL anhyd. ether. H NMR (400 MHz, CDCl ): 9.07 (d,
3
H, J = 8.6 Hz) Hnap; 8.99 (dd, 2H, J = 4.3, 0.5 Hz) H6,6′′
;
.86 (d, 2H, J = 8.0 Hz) H3,3 ′′ ; 8.58 (d, 1H, J = 7.3 Hz)
Zinc triazine complexes 3a, 3b, and 3d
Hnap; 8.09 (d, 1H, J = 8.2 Hz) Hnap; 7.99 (m, 3H) H
,
C
Zn(ClO ) ·6H O (0.05 mmol, 0.018 g) was added to a
4,4 ′′
4 2 2
1
3
Hnap; 7.67 (2H, m) 2Hnap; 7.60 (3H, m) H5,5 ′′ , Hnap
.
stirred solution of the appropriate ligand (0.1 mmol) in
MeCN (15 mL). The mixture was refluxed for 15 min,
cooled, and the solvent removed under reduced pressure.
The solid was recrystallized from ethanol, followed by pre-
NMR (400 MHz, CDCl3): 124.59, 124.80, 125.31,
1
1
25.83,126.21, 127.20, 128.42, 130.83, 130.87, 132.35,
32.87, 133.76, 136.92, 150.03, 152.84, 170.95, 175.00.
©
2008 NRC Canada

Nastasi et al.
263
cipitation in acetonitrile/diethyl ether to yield complexes 3a–
6. (a) E.A. Medlycott and G.S. Hanan. Coord. Chem. Rev. 250,
1763 (2006); (b) E.A. Medlycott and G.S. Hanan. Chem. Soc.
Rev. 34, 133 (2005).
3
d.
3
a
7. T.J. Rutherford, D.A. Reitsma, and F.R. Keene. J. Chem. Soc.
Dalton Trans. 3659 (1994).
8. F.M. MacDonnell and S. Bodige. Inorg. Chem. 35, 5758 (1996).
1
White solid, 68%. H NMR (400 MHz, CD CN): 9.14 (d,
3
J = 8Hz, 2H) H2′′′,6′′′; 9.05 (d, J = 7 Hz, 2H) H3,3 ′′ ; 8.31 (t,
J = 8 Hz, 2H) H4,4 ′′ ; 8.24 (d, J = 4 Hz, 2H) H6,6 ′′ ; 7.93 (t,
J = 7 Hz, 1H) H ; 7.80 (t, J = 7 Hz, 2H) H3′′′,5′′′; 7.64 (dd,
J = 6 Hz, 7 Hz, 2H) H5,5 ′′ . Anal. calcd. C H Cl N O Zn:
9
. A.I. Baba, J.R. Shaw, J.A. Simon, R.P. Thummel, and R.H.
Schmehl. Coord. Chem. Rev. 171, 43 (1998).
0. A.C. Benniston, A. Harriman, D.J. Lawrie, and A. Mayeux.
Phys. Chem. Chem. Phys. 6, 51 (2004).
1. S. Baitalik, X.-Y. Wang, and R.H. Schmehl. J. Am. Chem.
Soc. 126, 16304 (2004).
12. W. Leslie, R.A. Poole, P.R. Murray, L.J. Yellowlees, A. Beeby,
and J.A.G. Williams. Polyhedron, 23, 2769 (2004).
3. J.F. Michalec, S.A. Bejune, and D.R. McMillin. Inorg. Chem.
4
′′′
1
1
38
26
2
10
8
C 51.5, H 3.0, N 15.8; found: C 51.7, H 3.2, N 16.1.
3
b
1
Yellow solid, 55%. H NMR (400 MHz, CD CN): 9.50 (d,
3
J = 9 Hz, 1H) Hnap; 9.09 (d, J = 8 Hz, 2H) H3,3 ′′ ; 9.05 (d,
J = 7 Hz, 1H) Hnap; 8.43 (d, J = 8 Hz, 1H) Hnap; 8.30–8.34
1
1
3
9, 2708 (2000).
(
(
m, 4H) H4,4 ′′ , H6′6 ′′ ; 8.20 (d, J = 8 Hz, 1H) Hnap; 7.90–7.93
m, 2H) 2Hnap; 7.78 (t, J = 7 Hz, 1H) Hnap; 7.69 (dd, J = 5
4. J.F. Michalec, S.A. Bejune, D.G. Cuttell, G.C. Summerton,
J.A. Gertenbach, J.S. Field, R.J. Haines, and D.R. McMillin.
Inorg. Chem. 40, 2193 (2001).
Hz, 6 Hz, 2H) H5,5 ′′ . Anal. calcd. C H C N O Zn·H O:
46
30 l2 10
8
2
C 55.0, H 3.2, N 13.9; found: C 55.1, H 3.6, N 14.1.
1
1
1
5. G. Albano, V. Balzani, E.C. Constable, M. Maestri, and D.R.
Smith. Inorg. Chim. Acta, 277, 225 (1998).
6. X.-Y. Wang, A. Del Guerzo, and R.H. Schmehl. Chem.
Commun. 2344 (2002).
7. H. Krass, E.A. Plummer, J.M. Haider, P.R. Barker, N.W. Al-
cock, Z. Pikramenou, M.J. Hannon, and D.G. Kurth. Angew.
Chem., Int. Ed. 40, 3862 (2001).
18. K.K. Patel, E.A. Plummer, M. Darwish, A. Rodger, and M.J.
Hannon. J. Inorg. Biochem. 91, 220 (2002).
9. H.-S. Chow, E.C. Constable, C.E. Housecroft, M. Neuburger,
3
d
1
Orange solid, 84%. H NMR (400 MHz, CD CN): 9.93
3
(
(
d, J = 9 Hz, 1H) Hpyrene; 9.49 (d, J = 9 Hz, 1H) Hpyrene; 9.19
d, J = 8 Hz, 2H) H3,3 ′′ ; 8.60–8.63 (m, 2H) 2Hpyrene; 8.47–
8
.54 (m, 3H) 3Hpyrene; 8.35–8.41 (m, 5H) Hpyrene, H4,4 ′′
,
H6 ; 7.72 (dd, J = 6 Hz, 6Hz, 2H) H5,5 ′′ . Anal. calcd.
C H Cl N O Zn·H O: C 60.4, H 3.2, N 12.2; found: C
6
,6 ′′
5
8
34
2
10
8
2
0.5, H 3.4, N 12.3.
1
and S. Schaffner. Dalton Trans. 2881 (2006).
Acknowledgements
20. E.A. Medlycott and G.S. Hanan. Inorg. Chem. Commun. 10,
29 (2007).
2
The authors (GSH, EM, MPS) would like to thank the
Natural Sciences and Engineering Research Council of Can-
ada (NSERC) and the Université de Montréal for financial
support. EAM thanks the ICCS for funding. SC thanks the
University of Messina and MIUR (PRIN project) for fund-
ing. FL thanks the CNRS for an “ATIP Jeunes Chercheurs”
funding. Johnson Matthey PLC is thanked for a loan of
2
1. (a) E.A. Medlycott, G.S. Hanan, F. Loiseau, and S. Campagna.
Chem. Eur. J. 13, 2837 (2007); (b) M.I.J. Polson, E.A.
Medlycott, G.S. Hanan, L. Mikelsons, N.J. Taylor, M.
Watanabe, Y. Tanaka, F. Loiseau, R. Passalacqua, and S. Cam-
pagna. Chem. Eur. J. 10, 3640 (2004); (c) M.I.J. Polson, N.J.
Taylor, and G.S. Hanan. Chem. Commun. 1356 (2002).
22. N.W. Alcock, P.R. Barker, J.M. Haider, M.J. Hannon, C.L.
Painting, Z. Pikramenou, E.A. Plummer, K. Rissanen, and P.
Saarenketo. Dalton–Trans. 1447 (2000).
RuCl . The authors would also like to thank F. Bélanger-
3
Gariépy for assistance with X-ray analyses.
2
3. M. Klissinger and J. Michl. Excited states and photochemistry
of organic molecules. VCH. New York. 1995.
4. Handbook of photochemistry. 3rd ed. Edited by M. Montalti,
A. Credi, L. Prodi, and M.T. Gandolfi. CRC. Boca Raton, FL.
2006.
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