Luminescence of ruthenium halide complexes containing a hemilabile phosphine pyrenyl ether ligand

Article abstract of DOI:10.1021/ic051795j

A series of Ru(II) complexes, tcc-RuX₂(POC4Pyr-P,O)₂ (X = Cl (3), Br (4), I (5)), containing the hemilabile phosphine pyrenyl ether ligand 4-{2-(diphenylphosphino)phenoxy}butylpyrene (POC4Pyr (1)) are reported. The synthesis and spectroscopic properties of both the ligand, POC4pyr (1), and ligand oxide, P(=O)OC4pyr (2), and the solid-state structure of 1 are reported. Complexes 3-5 react rapidly with CO to give complexes ttt-RuX ₂(CO)₂(POC4pyr-P)₂ (X = Cl (6), Br (7), I (8)). No pyrene excimer emission is detected from 3-5; however, different intensities of excimer emission are observed for 6-8. The intensity of excimer emission decreases through the series, with 6 showing the most intense response. The emission is solely due to intramolecular pyrene excimers at low concentrations (≤10^-4 M). Comparison of the UV-vis and steady-state fluorescence spectra shows overlap between the low energy d-d absorption of 7 and 8 with excimer emission (480 nm), suggesting nonradiative energy transfer may be occurring. Once excess CO is removed, complexes 6-8 isomerize to cis-dicarbonyl complexes cct-RuX₂(CO)₂-(POC4Pyr-P)₂ (X = Cl (9), Br (10), I (11)). The intensity of excimer emission from 9-11 increases with respect to the excimer emission observed for 6-8, with 9 showing a significant increase in excimer intensity.

Full text of DOI:10.1021/ic051795j

Inorg. Chem. 2006, 45, 4610−4618
Luminescence of Ruthenium Halide Complexes Containing a Hemilabile
Phosphine Pyrenyl Ether Ligand
Kristin M. Matkovich,† Lisa M. Thorne,† Michael O. Wolf,*,† Tamara C. S. Pace,‡ Cornelia Bohne,‡ and
Brian O. Patrick†
Department of Chemistry, UniVersity of British Columbia, VancouVer, British Columbia,
Canada, V6T 1Z1, and Department of Chemistry, UniVersity of Victoria, Victoria,
British Columbia, Canada, V8W 3V6
Received October 17, 2005
A series of Ru(II) complexes, tcc-RuX2(POC4Pyr-P,O)2 (X
pyrenyl ether ligand 4- 2-(diphenylphosphino)phenoxy butylpyrene (POC4Pyr (1)) are reported. The synthesis and
spectroscopic properties of both the ligand, POC4pyr (1), and ligand oxide, P( O)OC4pyr (2), and the solid-state
structure of 1 are reported. Complexes 3 5 react rapidly with CO to give complexes ttt-RuX2(CO)2(POC4pyr-P)2 (X
Cl (6), Br (7), I (8)). No pyrene excimer emission is detected from 3 5; however, different intensities of excimer
8. The intensity of excimer emission decreases through the series, with 6 showing
) Cl (3), Br (4), I (5)), containing the hemilabile phosphine
{
}
d
−
)
−
emission are observed for 6
−
the most intense response. The emission is solely due to intramolecular pyrene excimers at low concentrations
4
(
e
10- M). Comparison of the UV
−
vis and steady-state fluorescence spectra shows overlap between the low
d absorption of 7 and 8 with excimer emission (480 nm), suggesting nonradiative energy transfer may
be occurring. Once excess CO is removed, complexes 6 8 isomerize to cis-dicarbonyl complexes cct-RuX2(CO)2-
(POC4Pyr-P)2 (X Cl (9), Br (10), I (11)). The intensity of excimer emission from 9 11 increases with respect to
the excimer emission observed for 6 8, with 9 showing a significant increase in excimer intensity.
energy d
−
−
)
−
−
Introduction
the presence or absence of analyte, and the spacer joins the
receptor and reporter together.3 A major advantage of this
design approach is the ability to rationally adjust properties
of the sensor by changing the molecular structure of any of
the components.1
Molecule-based sensors, or chemosensors, are molecules
that are able to bind selectively and reversibly an analyte of
interest with a concomitant change in one or more measur-
able properties.1 Optical (absorption or luminescence),
electrochemical, magnetic, or mass spectrometric changes
may be measured.2 Special interest has been paid to the
development of chemosensors because of their widespread
applications in chemistry, biology, biochemistry, cell biology,
materials science, and clinical and medicinal sciences.1
In the modular design approach to chemosensors, a
receptor, reporter mechanism, and spacer are incorporated.3
The receptor is the site at which the analyte binds, the
reporter is where a measurable property change occurs in
Luminescence is an attractive reporter mechanism with
several advantages including high sensitivity (single molecule
detection is possible), quick response time, and direct real-
time detection with both spatial and temporal resolution.3
Furthermore, the properties of the fluorescent lumophores
may be tuned to achieve a specific response. To maximize
the response, fluorescence should be either ON-OFF or
OFF-ON. The quenching of aromatic hydrocarbon fluores-
cence by transition-metal ions is a well-known phenomenon.4
In previous work by others, transition-metal complexes were
designed and synthesized such that prior to exposure to the
analyte, the fluorescence of the fluorophore is quenched by
an open-shell transition metal via photoinduced electron
transfer (PET) and/or electronic energy transfer (EET) or
* To whom correspondence should be addressed. E-mail:
mwolf@chem.ubc.ca.
† University of British Columbia.
‡ University of Victoria.
(1) Prodi, L.; Bolletta, F.; Montalti, M.; Zaccheroni, N. Coord. Chem.
ReV. 2000, 205, 59-83.
(2) Haes, A. J.; Van Duyne, R. P. J. Am. Chem. Soc. 2002, 124, 10596-
10604.
(4) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A.
J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV. 1997,
97, 1515-1566.
(3) Valeur, B.; Leray, I. Coord. Chem. ReV. 2000, 205, 3-40.
4610 Inorganic Chemistry, Vol. 45, No. 12, 2006
10.1021/ic051795j CCC: $33.50
© 2006 American Chemical Society
Published on Web 05/18/2006

Luminescence of Ruthenium Halide Complexes
Scheme 1. Reactivity of tcc-RuX2(POC4Pyr-P,O)2 toward CO
Figure 1. ORTEP view of 1. The hydrogen atoms are omitted for clarity,
and thermal ellipsoids are drawn at 50% probability.
undergoes isomerization after excess CO is removed from
solution to form cct-RuCl2(CO)2(POC4Pyr-P)2 (9).
However, pyrene monomer fluorescence was observed
prior to exposure to CO for 3. One possible way of promoting
fluorescence quenching is by altering the energies of the
metal d-orbitals through substitution of the chloro ligands
for other halides. Herein we report the effect of changing
the halide ligand in tcc-RuX2(POC4pyr-P,O)2 (X ) Cl (3),
Br (4), I (5)) on the luminescence behavior with respect to
reaction with CO. The syntheses and characterization of the
new compounds, 4 and 5, their absorption and emission
spectra, and their reaction with CO are reported. Differences
in the degree of excimer emission between the complexes
are discussed. Furthermore, comparison to the phosphine
pyrenyl ether ligand POC4pyr (1) and the oxidized form of
the ligand P(dO)OC4pyr (2) provides insight into the type
of excimers formed as well as the behavior of the complexes
in solution.
the heavy atom effect.5-9 Addition of the analyte displaces
the fluorescent ligand, or fluorescent moiety of the ligand if
the ligand is hemilabile, from the metal center. As a result,
ligand fluorescence is revived.
Pyrene is a suitable fluorophore for application in chemosen-
sors because of its well-studied photophysical properties10-12
and demonstrated ON-OFF functionality via PET and/or
EET.6,13 Sensors based on PET have been developed in which
pyrene luminescence is quenched in the presence of open-
shell metal ions such as Fe3+,6 Cu2+, and Ni2+.3 Furthermore,
a Zn2+ sensor based on an alkyl pyrene group covalently
bonded to an aza-18-crown-6 at the nitrogen has been
synthesized in which the quenching of pyrene luminescence
was shown to depend on the length of the tether between
the receptor moiety of the sensor and the pyrene.13
Results and Discussion
In a preliminary communication, we demonstrated that tcc-
RuCl2(POC4Pyr-P,O)2 (POC4Pyr ) 4-{2-(diphenylphos-
phino)phenoxy}butylpyrene) (3) reacts with CO as shown
in Scheme 1.14 The metal center acts as the receptor via the
labile oxygen of the chelating phosphine pyrenyl ether ligand,
and luminescent reporting is provided by the pyrene moiety.
It was found that CO displaces both of the weakly coordi-
nated ether ligands to form the complex ttt-RuCl2(CO)2-
(POC4Pyr-P)2 (6). The reaction with CO is accompanied by
a color change of the solution and the appearance of excimer
emission. The initially formed trans-dicarbonyl complex
Synthesis and Characterization of 1 and 2. The synthesis
of the phosphine pyrenyl ether ligand 1 was previously
reported.14 Here, the solid-state structure and absorption and
emission properties are investigated. The oxide 2 was
synthesized by stirring 1 with H2O2 in a 1:1 mixture of DCM/
acetone. Both 1 and 2 (see Chart 1) were characterized by
1H and 31P{1H} NMR spectroscopies, elemental analysis,
mass spectrometry and by UV-vis and fluorescence spec-
troscopies. Crystals of 1 suitable for X-ray analysis were
grown from hot ethyl acetate solution. The solid-state
structure is shown in Figure 1. Intermolecular π-stacking is
observed in the unit cell between interpenetrating molecules
of 1 with a pyrene-pyrene interplanar distance of 3.71 Å.
The crystallographic data for 1 are presented in Table 1. The
C-X (X ) O, P) bond lengths and C-X-C (X ) O, P)
bond angles (Table 2) closely resemble those reported for
(o-methoxyphenyl)diphenylphosphine.15
(5) Bodenant, B.; Weil, T.; Businelli-Pourcel, M.; Fages, F.; Barbe, B.;
Pianet, I.; Laguerre, M. J. Org. Chem. 1999, 64, 7034-7039.
(6) Bodenant, B.; Fages, F.; Delville, M.-H. J. Am. Chem. Soc. 1998, 120,
7511-7519.
(7) Wolf, C.; Mei, X. J. Am. Chem. Soc. 2003, 125, 10651-10658.
(8) Cabell, L. A.; Best, M. D.; Lavigne, J. J.; Schneider, S. E.; Perreault,
D. M.; Monahan, M.-K.; Anslyn, E. V. J. Chem. Soc., Perkin Trans.
2 2001, 315-323.
The UV-vis absorption spectra of 1 and 2 are essentially
identical (Figure 2a,b). The structured absorptions in the UV
region arise predominantly from pyrene-based π-π* transi-
tions.10 Weaker absorptions from the rest of the molecule
are buried beneath the strong pyrenyl π-π* bands.14 The
(9) de Silva, A. P.; Fox, D. B.; Huxley, A. J. M.; McClenaghan, N. D.;
Roiron, J. Coord. Chem. ReV. 1999, 185, 297-306.
(10) Birks, J. B. Photophysics of Aromatic Molecules. Wiley-Interscience:
London, 1970.
(11) Winnik, F. M. Chem. ReV. 1993, 93, 587-614.
(12) Kalyanasundaram, K.; Thomas, J. K. J. Am. Chem. Soc. 1977, 99,
2039-2044.
(13) Ji, H.-F.; Dabestani, R.; Brown, G. M.; Hettich, R. L. Photochem.
Photobiol. 1999, 69, 513-516.
(15) Suomalainen, P.; Jaaskelainen, S.; Haukka, M.; Laitinen, R. H.;
Pursiainen, J.; Pakkanen, T. A. Eur. J. Inorg. Chem. 2000, 2607-
2613.
(14) Rogers, C. W.; Wolf, M. O. Angew. Chem., Int. Ed. 2002, 41, 1898-
1900.
Inorganic Chemistry, Vol. 45, No. 12, 2006 4611

Matkovich et al.
Chart 1
Table 1. Crystallographic Data for 1
ments were carried out, and the lifetimes for 1 and 2 in
dichloromethane are 90 ( 5 and 101 ( 2 ns, respectively.
Synthesis and Characterization of Complexes 3-5. The
dibromo complex 4 was synthesized using an analogous
procedure to that used to prepare 3,14 by reaction of
ruthenium(III) bromide with 1 in a 5:1 ethanol/toluene
mixture. The diiodo complex 5 was synthesized via a halogen
exchange reaction of 3 with NaI in acetone. Both complexes
were fully characterized by solution methods. No solvent
systems were found to yield crystals suitable for X-ray
crystallographic analysis. Previously, 3 was fully character-
ized and its spectral characteristics in solution were compared
to those of the complex tcc-RuCl2(POMe-P,O)2 (POMe )
2-methoxyphenyldiphenylphosphine).14 These assignments
were used to aid in the assignment of the structures of 4 and
5.
One singlet is observed in the 31P{1H} NMR spectra of
3-5 (Table 3). To confirm the relative stereochemistry of
the phosphines, a series of 13C{1H} NMR experiments were
previously carried out for 3.14 Complexes 4 and 5 are
presumed to have the same geometry with the two halide
ligands trans-disposed to one another and the two P,O-
coordinated phosphine ether ligands coordinated such that
the phosphines are cis-disposed to one another and are
chemically equivalent. The similarities in the 31P{1H} NMR
data for 3-5 support this assignment.
chemical formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C38H31PO
534.60
P21/c (No. 14)
24.212(3)
15.116(1)
7.6453(7)
90.0
98.276(5)
90.0
2769.0(5)
4
-100.0 ( 0.1
0.71073
1.282
1.30
0.051
Z
T (°C)
λ(Mo KR) (Å)
D
calcd (g cm-3
)
µ(Mo KR) (cm-1
)
R(Fo)a (I > 0.00σ(I))
2
Rw(Fo )b (I > 0.00σ(I))
0.103
0.134
0.129
2
R(Fo )a (all data)
2
Rw(Fo )b (all data)
2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) (∑(Fo - Fc )2/∑w(Fo )2)1/2
.
Table 2. Selected Interatomic Distances and Angles for 1
Bond Length (Å)
O(1)-C(21)
O(1)-C(20)
P(1)-C(26)
1.364(4)
1.450(4)
1.831(4)
P(1)-C(27)
P(1)-C(33)
1.825(4)
1.824(4)
Bond Angle (deg)
C(20)-O(1)-C(21) 116.9(3)
C(26)-P(1)-C(33) 102.45(17)
C(26)-P(1)-C(27)
100.64(18) C(27)-P(1)-C(33) 102.06(18)
Torsion Angle (deg)
P(1)-C(26)-C(21)-O(1)
-6.4(4)
The UV-vis absorption spectra of 4 and 5 are essentially
identical to that of 3 (Figure 3). Furthermore, the structured
absorptions in the UV region of the spectra for 3-5 closely
resemble those observed for 1 and 2. Each of the ruthenium
complexes also has a weak, metal-based visible absorption
band (d-d transition) that gives rise to the observed color
(Table 3). The PA ratios of complexes 3-5 (Table 3) are
less than those of 1 and 2 indicating that there is more
ground-state interaction between the pyrene moieties of
3-5.11 The molar absorptivities (ꢀmax) for the low-energy
pyrenyl absorption band vary with halide (3 < 4 < 5). This
is attributed to changes in the peak breadth, which has
previously been related to the degree of ground-state interac-
tion between the pyrene groups.11
The emission and excitation spectra for all three complexes
are shown in Figure 4. As with 1, excitation of each complex
in dilute solution (10-6 M) with UV light gives indigo-blue
emission, typical for the pyrene monomer.10 The emission
and excitation spectra resemble those of 1 and 2, and the
excitation spectra are identical to the absorption spectra.
None of the emission spectra for complexes 3-5 at any
concentration studied (e10-4 M) show excimer emission.
Pyrene monomer emission is not completely quenched in
PA values, defined as the ratio of the absorption intensity of
the La band (345 nm) to that of the adjacent minimum at
1
shorter wavelength (337 nm),11 for 1 and 2 are shown in
Table 3. Values of PA that are less than 3 indicate pyrene
preassociation in the ground state, where the degree of
preassociation increases the further the value deviates from
3. The PA values for 1 and 2 are slightly less than 3,
indicating a very small amount of preassociation of the
pyrene moieties in the ground state. No pyrene excimer
emission is observed for concentrations less than 10-4 M in
the steady-state emission spectra of 1 or 2 (panels c and d
of Figure 2), indicating that the small degree of preassociation
is not significant enough to influence excimer formation at
low concentrations. Excitation of both compounds in dilute
solution (10-6 M) with UV light leads to indigo-blue
emission, as is typically observed for the pyrene monomer.10
The emission and excitation spectra are near mirror images
of each other, and a small Stokes shift typical of fluorescent
aromatic molecules is observed.10 The excitation spectra
contain the same features as the absorption spectra. Quantum
yields for emission are 0.16 ((0.1) and 0.19 ((0.1) for 1
and 2, respectively. Single-photon counting (SPC) experi-
4612 Inorganic Chemistry, Vol. 45, No. 12, 2006

Luminescence of Ruthenium Halide Complexes
Figure 2. UV-vis absorption spectra for (a) 1 and (b) 2, [1] and [2] ≈ 10-5 M; excitation (- - -) and emission (s) spectra for (c) 1 and (d) 2, [1] and [2]
≈ 10-6 M; λex ) 345 nm; λem ) 398 nm.
Table 3. Summary of Characterization Data for 1-11
31P{1H} NMR
δ (ppm)a
υCO
b
c
e
compd
(cm-1
)
λ
max (ꢀmax
)
PA ratiod
λ
(d-d) (ꢀd-d
)
color
1
2
3
4
5
6
7
8
-14.2
27.0
63.7
64.7
66.0
27.1
26.0
22.5
13.9
10.2
5.1
345 (44 700)
345 (45 000)
345 (61 400)
345 (71 700)
345 (89 900)
345 (61 400)
345 (72 900)
345 (88 300)
345 (69 900)
345 (70 700)
345 (82 500)
2.8 ( 0.1
2.9 ( 0.1
2.5 ( 0.1
2.5 ( 0.2
2.4 ( 0.1
2.5 ( 0.1
2.3 ( 0.1
2.3 ( 0.1
2.5 ( 0.1
2.0 ( 0.1
2.2 ( 0.1
colorless
colorless
red
purple-red
gray-green
yellow
light orange
red-orange
white
517 (590)
542 (500)
577 (760)
440 (220)
455 (250)
502 (240)
none observed
none observed
shoulder at ∼500
2007
2001
2007
2059, 1998
2059, 2000
2055, 1989
9
10
11
yellow
light orange
a CDCl3. b CH2Cl2. c λmax (nm) and ꢀmax (M-1 cm-1) are, respectively, the maximum wavelength and the molar absorptivity of the lowest-energy vibronic
band of the La electronic transition of the pyrene chromophore (CH2Cl2, 25 °C). d Determined by averaging PA ratios from several samples. λ(d-d) (nm)
1
e
and ꢀd-d (M-1 cm-1) are respectively the wavelength and molar absorptivity of the metal-based d-d transition (CH2Cl2, 25 °C).
any of the complexes. This suggests that either the pyrene
moieties are not close enough to the metal center for emission
to be quenched, or that the changes in energies of the metal
d-orbitals with different halide ligands are not significant
enough to lead to quenching of pyrene monomer emission.
It has been reported that a tether length of four methylene
groups is too long to observe significant quenching of pyrene
emission via PET.13
When the steady-state emission spectra of 3-5 were
compared periodically over 48 h, the intensities of the
monomer emission increased with time. This suggests some
decomposition may be occurring in solution leading to the
formation of a more emissive species. The degree of
monomer emission increased more quickly for samples stored
in light versus those stored in the dark, suggesting a
photochemical process is involved. However, samples both
stored in the dark and stored in the light showed increases
in monomer emission over time suggesting thermal decom-
Figure 3. UV-vis absorption spectra of (a) 3, (b) 4, and (c) 5; [tcc-RuX2-
(POC4Pyr-P,O)2] ≈ 10-5 M.
position may also be occurring. No shifts in the emission
spectra were observed during this experiment. The formed
species was identified by 31P{1H} and 1H NMR spectroscopy
as 2, suggesting that oxidation of some dissociated ligand
occurs in solution. It is therefore impossible to exclude the
possibility that steady-state emission for 3-5 is partially due
Inorganic Chemistry, Vol. 45, No. 12, 2006 4613

Matkovich et al.
Figure 5. Visible d-d absorption bands of (a) 3 (s) and 6 (- - -), (b) 4
(s) and 7 (- - -), and (c) 5 (s) and 8 (- - -); [tcc-RuX2(POC4Pyr-P,O)2]
and [ttt-Ru(CO)2X2(POC4Pyr-P)2] ≈ 2 × 10-3 M.
Figure 4. Excitation (- - -) and emission (s) spectra of (a) 3, (b) 4, and
(c) 5; [tcc-RuX2(POC4Pyr-P,O)2] ≈ 10-6 M; λex ) 345 nm; λem ) 398
nm.
5). The molar absorptivities of the d-d bands for complexes
6-8 are similar to those for complexes 3-5 (Table 3).
At high concentrations of 3 (∼10-2 M), reaction with CO
under UV irradiation resulted in a change from the weak
indigo-blue emission of 3, characteristic of pyrene monomer
emission, to the strong blue-green excimer emission of 6.14
This observation is consistent with the formation of inter-
molecular excimers (Figure 6a).10 In dilute solution (∼10-6
M), a small amount of excimer emission was still observed.
Since intermolecular excimer formation is insignificant at
10-6 M, this must be due to intramolecular excimers (Figure
6b).10 It was proposed that an increase in conformational
freedom of the alkylpyrene moieties occurs after displace-
ment of the ether from the metal center influencing the ability
of the pyrene moieties to interact with one another.14
However, the displacement of the ether moieties from the
metal center does not significantly affect the PA values; that
is, it does not influence the ground-state interaction of the
pyrene moieties at ∼10-6 M.11 Thus, the formation of
intramolecular excimers appears to be a dynamic process as
a result of the increase in conformational freedom.
The intensity of excimer emission from 6-8 depends on
the nature of the halide ligand (Figure 7). The intensity of
excimer emission at 10-6 M is lower for 7 and 8 than for 6;
only a very small amount of intramolecular excimer is
observed for 7, and almost no intramolecular excimer is
observed for 8. One possible explanation of this is that the
d-d absorption for 7 and 8 is close enough in energy to the
pyrene excimer emission, centered at 480 nm, for energy
transfer to occur. Since EET is a nonradiative quenching
pathway, the extent of excimer emission observed would be
expected to be less for 7 and 8 compared to that of 6. An
alternative explanation is that because of the difference in
size between the small chloro ligands and the larger bromo
and iodo ligands, the alkylpyrene moiety cannot “fold over”
the complex as readily to form an intramolecular excimer
as shown in Figure 6b. The intensity of excimer emission is
limited by the ability of an excimer to form within the
lifetime of the excited state of the pyrene monomer4,11 and
by the stabilization of the excimer.11 Thus, if the lifetimes
of the excited states for 7 and 8 are sufficiently shorter than
that of 6 such that a conformation suitable for excimer
formation cannot be achieved or that the stabilization of the
to dissociated ligand (1) or ligand oxide (2). Thus, neither
reliable quantum yield values, nor SPC lifetimes for 3-5
could be obtained.
trans-Dicarbonyl Complexes 6-8. It has been shown that
complexes of the type RuX2(POL-P,O)2 (X ) halogen; POL
) hemilabile phosphine ether ligand) react with CO to form
RuX2(CO)2(POL-P)2 or RuX2(CO)(POL-P,O)(POL-P).16-20
Reaction of 3 with CO and accompanying changes in
photophysical properties have been described.14 Complexes
4 and 5 react similarly with CO (Scheme 1), and upon
exposure to CO an immediate color change is observed for
all three complexes in solution.
A summary of the characterization data for 6-8 is shown
in Table 3. Reaction of 3-5 with CO is accompanied by an
immediate shift in the 31P{1H} NMR resonance. For all three
complexes, the resonances shifted upfield relative to the
resonances prior to reaction with CO. Previously, a series
of 13C{1H} NMR experiments were conducted using 13C-
labeled CO to assign the relative stoichiometry of 6 as ttt.14
The stereochemistry of 7 and 8 are assigned in the same
way, supported by the similarities in the 31P {1H} NMR
chemical shifts and IR bands for the three complexes (Table
3).
The UV-vis absorption spectra of 6-8 are essentially
identical, with no significant change in the molar absorp-
tivities in the UV region. The absorption bands in the UV
region are identical in structure to those of 3-5. The PA
values changed very little relative to those determined for
the complexes 3-5 (Table 3), supporting a weak interaction
between the pyrene moieties of 6-8 in the ground state.11
This is somewhat surprising as the pyrene ligands are
disposed differently in 3-5 versus in 6-8. For each trans-
dicarbonyl complex, the weak metal-based transition is blue-
shifted relative to its position before exposure to CO (Figure
(16) Gill, D. F.; Mann, B. E.; Shaw, B. L. J. Chem. Soc., Dalton Trans.
1973, 311-317.
(17) Rauchfuss, T. B.; Patino, F. T.; Roundhill, D. M. Inorg. Chem. 1975,
14, 652-656.
(18) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658-2666.
(19) Krassowski, D. W.; Nelson, J. H.; Brower, K. R.; Hauenstein, D.;
Jacobson, R. A. Inorg. Chem. 1988, 27, 4294-4307.
(20) Lindner, E.; Gepraegs, M.; Gierling, K.; Fawzi, R.; Steimann, M. Inorg.
Chem. 1995, 34, 6106-6117.
4614 Inorganic Chemistry, Vol. 45, No. 12, 2006

Luminescence of Ruthenium Halide Complexes
Figure 6. Schematic structure of (a) an intermolecular excimer and (b) an intramolecular excimer for ttt-RuCl2(CO)2(POC4Pyr-P)2.
Figure 8. Excitation (- - -) and emission (s) spectra for (a) 9, (b) 10, and
(c) 11; [cct-Ru(CO)2X2(POC4Pyr-P)2] ≈ 10-6 M; λex ) 345 nm; λem
)
398 nm.
C-O stretching region are expected for cct-RuX2(CO)2-
(POC4Pyr-P)2; this was observed for all three complexes
(Table 3), supporting the assignment of these as cct.
The UV-vis spectra for the cct isomers also show typical
absorption from pyrene-based π-π* transitions in the UV
region.10 The metal-based d-d transition for 9 and 10 are
not observed; they are presumably shifted to higher energy
and are obscured by the strong pyrene absorption band.
Isomerization of other RuCl2(CO)2(phosphine)2 complexes
from the ttt to the cct isomer results in a color change from
yellow to white,19 consistent with the results observed for 9
and 10. Complex 11 does show an absorption band at ∼500
nm, which appears as a shoulder to the pyrene absorption
band, slightly blue-shifted from the absorption of the ttt
isomer 8. In addition, the PA values for each cct isomer are
essentially the same as those obtained for the corresponding
ttt isomer (Table 3), indicating a small degree of pyrene
preassociation in the ground state.11
Comparison of the fluorescence from the ttt isomers 6-8
with that from the cct isomers 9-11 is interesting. Previously
it was reported that strong excimer emission was observed
for 9, even in dilute solution.14 It was concluded that the
pyrene moieties in 9 must be able to more easily interact to
form an intramolecular excimer. At 10-6 M a small increase
in the excimer intensity of 10 is observed with respect to 7
(Figure 8b). Almost no excimer emission is observed for 11
(Figure 8c), similar to the result for complex 8. These results
support the conclusion that intramolecular energy transfer
Figure 7. Excitation (- - -) and emission (s) spectra for (a) 6, (b) 7, and
(c) 8; [ttt-Ru(CO)2X2(POC4Pyr-P)2] ≈ 10-6 M; λex ) 345 nm; λem ) 398
nm.
excimer cannot overcome the added steric repulsion resulting
from the interaction of the alkylpyrene moieties “folding
over” the larger bromo and iodo ligands, excimer emission
would be significantly reduced or eliminated completely.
cis-Dicarbonyl Complexes 9-11. Complexes of the type
ttt-RuX2(CO)2(PR3)2 are known to isomerize to the thermo-
dynamically more stable isomers cct-RuX2(CO)2(PR3)2.19,21
This isomerization typically occurs through a dissociative
mechanism.17 This mechanism is consistent with the obser-
vation that isomerization does not occur until excess CO is
removed from solutions of 6-8 by sparging the solutions
with N2 or by degassing via repeated freeze-pump-thaw
cycles (Scheme 1).
A summary of the characterization data for 9-11 is given
in Table 3. Like the ttt isomers, the cct isomers contain two
equivalent phosphines, as indicated by the singlet resonance
in the 31P{1H} NMR spectrum of each complex. The dichloro
complex 9 has previously been studied using 13C{1H} NMR
experiments with 13C-labeled CO to verify the stereochemical
assignment as cct.14 Complexes 10 and 11 are presumed to
have the same geometry. Complexes 9-11 were also
characterized by IR spectroscopy. Two absorptions in the
(21) Bader, A.; Lindner, E. Coord. Chem. ReV. 1991, 108, 27-110.
Inorganic Chemistry, Vol. 45, No. 12, 2006 4615

Matkovich et al.
Eclipse spectrofluorometer. Measurements were made in a 1-cm
quartz cell in air-saturated solutions. For the measurements, 5 nm
excitation and emission slit widths were used. Fluorescence spectra
for 1 and 2 and quantum yield measurements were obtained on a
Photon Technology International fluorimeter using a 1-cm quartz
cell. Excitation and emission slit bandwidths were all 4 nm. The
quantum yields were determined relative to anthracene. All solutions
for quantum yield measurements were sparged with nitrogen gas
for a minimum of 10 min. The relative quantum yields in solution
were calculated based on the expression22
may be responsible for the changes in excimer intensity. The
blue shift in the d-d band from the ttt isomers 6 and 7 to
the cct isomers 9 and 10 results in poorer overlap between
this band and the pyrene excimer, consistent with the increase
in excimer intensity for the cct isomers of these two
complexes. For both 8 and 11, the d-d band overlaps well
with the expected emission band energy from excimer, and
in these two complexes no excimer is observed. It is still
possible that the larger size of the bromo and iodo ligands
impedes the formation of intramolecular excimers, implying
that the formation of excimer in 9 is facilitated more easily
by the cis disposed chloro ligands rather than by the CO
ligands.
∞I (υ) dυ
S
0
1 - 10-A
η
∫
F
ΦF ) ΦSF
(
)( )
1 - 10-A ηS
∞IS(υ) dυ
∫
F
0
Conclusions
where ΦS is the quantum yield of the standard, integrals ∫ IF(υ)
∞
0
F
dυ and ∫0 ISF(υ) dυ are the areas under the spectrum of the
∞
The fluorescence of 3-5 is very similar because of
monomer emission from the pendant pyrenyl groups; after
exposure to CO and formation of the trans-dicarbonyl
product, excimer emission was observed. The dependence
of the excimer emission intensity is attributed to differences
in the extent of nonradiative energy transfer between the
excited-state pyrene moieties and metal-based states in 6-8.
Steric constraints may also play a role in favoring excimer
formation for 6 over 7 and 8. There are to our knowledge
no other examples in which tuning the electronics at a metal
via ancillary ligands results in changes in the intensity of
excimer emission from a second ligand. Here, binding with
CO triggers the formation of the excimer; however, binding
of other ligands in related complexes bearing such hemilabile
pyrenyl ligands should also be possible. Fluorescence-based
detection of nonfluorescent compounds is thus feasible.
Alteration of the ligating end of the hemilabile ligand would
allow increased control of binding selectivity and sensitivity.
Here, the selected alkyl tether is four carbons long. This
length was selected largely on the basis of synthetic
accessiblity; however, shorter lengths would clearly be of
interest as pyrene emission quenching may be enhanced in
these cases. Synthetic approaches to these ligands are being
explored.
compound and the standard (IF(υ)and IS(υ) are the intensity of
F
fluorescence of the compound and standard as a function of
wavenumber, respectively), A and AS are the absorptions of the
compound and standard, and η and ηS are the refractive indices of
the solvent used for the solutions of the compound and standard,
respectively.
Time-resolved fluorescence measurements were performed with
an Edinburgh Instruments OB 920 single-photon counting system
with a hydrogen flash lamp excitation source. The excitation and
emission wavelengths were set to 345 and 375 nm, respectively,
and the band-pass for the excitation and emission monochromators
was ca. 16 nm (2 mm slits). An iris was employed to ensure that
the frequency of the stop pulses was smaller than 2% of the start
pulse frequency. The number of counts in the channel of maximum
intensity was either 10 000 or 2000. A Lauda RM6 bath was used
to keep the sample at a constant temperature of 20 °C. The
instrument response function is very narrow for the measured time
scale (1 µs), and deconvolution of the instrument response function
from the decay was therefore not necessary. Data were fitted to
monoexponential decays using the Edinburgh software. The value
of ø2 (0.9-1.1) and visual inspection of the residuals and the
autocorrelation were used to determine the quality of the fit.23
Solutions were prepared in dichloromethane by preparing an
appropriate 1 mM stock solution and diluting to 1 µM. Solutions
were purged with N2 for at least 20 min prior to measurement.
Chemicals were used as received from the supplier (Aldrich,
Strem) unless otherwise specified. Deuterated solvents were used
as received from Cambridge Isotope Labs. Carbon monoxide was
obtained from Praxair and was used as received. Spectroscopic
grade CH2Cl2 used for UV-vis and fluorescence measurements
gave negligible background luminescence at the excitation wave-
lengths used for the fluorescence measurements. The synthesis and
characterization of POC4Pyr (1), tcc-RuCl2(POC4Pyr-P,O)2 (3), ttt-
RuCl2(CO)2(POC4Pyr-P)2 (6), and cct-RuCl2(CO)2(POC4Pyr-P)2
(9) are reported elsewhere.14
Experimental Section
General. All reactions were carried out under a nitrogen
atmosphere unless otherwise stated. NMR spectra were acquired
on either a Bruker AC-200, Bruker Avance 300, or Avance 400
instrument. Residual protonated solvent peaks were used as internal
1H references (vs TMS and δ 0). 31P{1H} NMR spectra were
referenced to 85% H3PO4 (δ 0). Elemental analyses and mass
spectra were both performed by the UBC Department of Chemistry
Microanalytical Services Laboratory. Electrospray (ES) mass spectra
were obtained on a Micromass LCT time-of-flight (TOF) mass
spectrometer equipped with an ES ion source. The samples were
analyzed in MeOH/CH2Cl2 (1:1) at 100 µM. IR spectroscopic
measurements were made using a BOMEM MB155S FTIR
spectrometer and using solution samples. All spectra were corrected
for solvent by subtracting the appropriate solvent spectrum. UV-
vis and fluorescence spectra were all carried out in HPLC grade
dichloromethane. UV-vis spectra were obtained using a Cary 5000
UV-vis-near-IR spectrophotometer. A 1-cm quartz cell was used.
Fluorescence spectra for 3-11 were collected using a Varian Cary
P(dO)OC4pyr (2). POC4pyr (0.096 g, 0.18 mmol) was dis-
solved in 20 mL of a 1:1 mixture of dichloromethane and acetone.
To the mixture, 30% H2O2 (0.05 mL) was added, and the solution
was stirred open to air at room temperature for 15 min. The solution
was washed with water (3 × 10 mL), and the organic layer was
(22) Kollar, J.; Hrdlovic, P.; Chmela, S.; Sarakha, M.; Guyot, G. J.
Photochem. Photobiol., A: Chem. 2005, 171, 27-38.
(23) Bohne, C.; Redmond, R. W.; Scaiano, J. C. Use of Photophysical
Techniques in the Study of Organized Assemblies. In Photochemistry
in Organized & Constrained Media; Ramamurthy, V., Ed.; VCH
Publishers: New York, 1991; pp 79-132.
4616 Inorganic Chemistry, Vol. 45, No. 12, 2006

Luminescence of Ruthenium Halide Complexes
dried over Na2SO4 and concentrated by rotary evaporation to yield
a clear, colorless oil. White analytically pure crystals were obtained
by drying the oil in vacuo. Yield: 99%. Anal. Calcd for C38H31-
PO2 (%): C, 82.89; H, 5.67. Found: C, 82.50; H, 6.02. ESI-MS:
m/z ) 551 (M + H)+. 31P{1H} NMR (121.4 MHz, 25 °C, CDCl3):
δ 27.0 (s). 1H NMR (200 MHz, 25 °C, CDCl3): δ 8.22-7.90 (m,
9H, pyrene), 7.80 (m, 2H, Ph), 7.70-7.55 (m, 6H, Ph), 7.50 (m,
2H, Ph), 7.15 (m, 2H, Ph), 6.80 (m, 2H, Ph), 4.85 (t, 2H, pyrene-
CH2(CH2)2CH2-O), 3.15 (m, 2H, pyrene-CH2(CH2)2CH2-O), 1.65
(t, 2H, pyrene-CH2CH2CH2CH2-O), 1.45 (t, 2H, pyrene-CH2CH2-
CH2CH2-O); assignments based on previous experiments done for
POC4pyr.14
minimum of 5 min after a color change had occurred. The initial
trans-dicarbonyl product was characterized immediately after
exposure to CO. Each solution was sparged with nitrogen in order
for the isomerization to occur.
ttt-RuBr2(CO)2(POC4Pyr-P)2 (7). Treatment of a red-purple
solution of 4 with CO yielded a yellow solution of 7. IR (CH2Cl2):
νCO ) 2001 cm-1
.
31P{1H} NMR (121.4 MHz, 25 °C, CDCl3): δ
1
26.0 (s). H NMR (200 MHz, 25 °C, CDCl3): δ 8.24-7.58 (m,
26H, pyrene), 7.36-7.12 (overlapping m, 14H), 6.91-6.78 (over-
lapping m, 6H), 3.94 (m, 4H, pyrene-CH2CH2CH2CH2-O), 3.18
(m, 4H, pyrene-CH2CH2CH2CH2-O), 1.67 (m, 4H, pyrene-CH2-
CH2CH2CH2-O), 1.40 (m, 4H, pyrene-CH2CH2CH2CH2-O).
tcc-RuBr2(POC4Pyr-P,O)2 (4). POC4Pyr (0.382 g, 0.710 mmol)
was heated in ethanol (60 mL) to reflux. Toluene (17 mL) was
then added to ensure that the ligand was completely dissolved.
Distilled water (15 mL) was added to RuBr3‚xH2O (0.122 g, 0.360
mmol), and the solution was sonicated for 10 min followed by
heating with a heat gun. This treatment was repeated two more
times. The ruthenium(III) bromide solution was diluted with an
equal volume of ethanol (15 mL) and was then added rapidly to
the ligand solution. The reaction was heated at reflux for 72 h.
Over the course of the reaction, the solution changed from opaque
black to red-purple in color. The reaction mixture was hot-filtered,
and the residue was washed with 200 mL of dichloromethane. The
filtrate was concentrated to ∼100 mL, by heating the solution to
reflux, and then diluted with 200 mL of hexanes. The solution was
again heated to reflux and, as the dichloromethane evaporated, a
purple-red powder precipitated. This was filtered from the hot
solution and washed with hexanes. The red-purple solid was dried
in vacuo. Yield: 39%. Anal. Calcd for C76H62Br2O2P2Ru (%): C,
68.63; H, 4.70. Found: C, 68.41; H, 5.00. ESI-MS: m/z ) 1249
(M - Br)+. 31P{1H} NMR (121.4 MHz, 25 °C, CDCl3): δ 64.7
ttt-RuI2(CO)2(POC4Pyr-P)2 (8). Treatment of a green solution
of 5 with CO yielded an orange solution of 8. IR (CH2Cl2): νCO
)
2007 cm-1
.
31P{1H} NMR (121.4 MHz, 25 °C, CDCl3): δ 22.5
1
(s). H NMR (200 MHz, 25 °C, CDCl3): δ 8.22-7.64 (m, 26H,
pyrene), 7.46-7.03 (overlapping m, 14H), 6.97-6.74 (overlapping
m, 6H), 3.87 (m, 4H, pyrene-CH2CH2CH2CH2-O), 3.10 (m, 4H,
pyrene-CH2CH2CH2CH2-O), 1.58 (m, 4H, pyrene-CH2CH2CH2-
CH2-O), 1.41 (m, 4H, pyrene-CH2CH2CH2CH2-O).
cct-RuBr2(CO)2(POC4Pyr-P)2 (10). Solutions of 4 treated with
CO in CH2Cl2 or CHCl3 and degassed with nitrogen after the color
change undergo conversion (36 h at room temperature) to the cis-
.
dicarbonyl product 10. IR (CH2Cl2): νCO ) 2059, 2000 cm-1 31P-
{1H} NMR (121.4 MHz, 25 °C, CDCl3): δ 10.2 (s). 1H NMR (200
MHz, 25 °C, CDCl3): δ 8.22-7.98 (overlapping m, 24H), 7.74-
7.58 (overlapping m, 4H), 7.32-7.20 (overlapping m, 14H), 7.12-
7.00 (overlapping m, 2H), 6.92-6.80 (overlapping m, 2H), 3.82
(m, 4H, pyrene-CH2CH2CH2CH2-O), 3.16 (m, 4H, pyrene-CH2-
CH2CH2CH2-O), 1.43 (m, 8H, pyrene-CH2CH2CH2CH2-O).
cct-RuI2(CO)2(POC4Pyr-P)2 (11). Solutions of 5 treated with
CO in CH2Cl2 or CHCl3 and degassed with nitrogen after the color
change undergo conversion (36 h at room temperature) to the cis-
.
dicarbonyl product 11. IR (CH2Cl2): νCO ) 2055, 1989 cm-1 31P-
1
(s). H NMR (200 MHz, 25 °C, CDCl3): δ 8.22-7.85 (m, 16H,
pyrene), 7.68 (d, 3JHH ) 8.0 Hz, 2H, pyrene), 7.38-7.05 (m, 26H,
Ph), 6.96 (m, 2H, Ph), 4.78 (m, 4H, pyrene-CH2(CH2)2CH2-O),
3.11 (m, 4H, pyrene-CH2(CH2)2CH2-O), 1.90 (m, 4H, pyrene-CH2-
CH2CH2CH2-O), 1.67 (m, 4H, pyrene-CH2CH2CH2CH2-O); as-
signments based on previous experiments done for tcc-RuCl2-
(POC4Pyr-P,O)2.14
{1H} NMR (121.4 MHz, 25 °C, CDCl3): δ 5.1 (s). 1H NMR (200
MHz, 25 °C, CDCl3): δ 8.22-7.97 (overlapping m, 24H), 7.76-
7.54 (overlapping m, 4H), 7.35-7.15 (overlapping m, 14H), 7.10-
6.98 (overlapping m, 2H), 6.92-6.83 (overlapping m, 2H), 3.81
(m, 4H, pyrene-CH2CH2CH2CH2-O), 3.18 (m, 4H, pyrene-CH2-
CH2CH2CH2-O), 1.50 (m, 8H, pyrene-CH2CH2CH2CH2-O).
tcc-RuI2(POC4Pyr-P,O)2 (5). Acetone (15 mL) was added to
tcc-RuCl2(POC4Pyr-P,O)2 (0.096 g, 0.080 mmol) and NaI (0.054
g, 0.36 mmol). The reaction was heated at reflux for 2 h. During
the reaction time, the solution changed from red to green and a
green precipitate formed. The reaction mixture was cooled, and
acetone was removed in vacuo to give a sticky green solid. The
solid was redissolved in dichloromethane and passed through a
Bu¨chner funnel to remove NaCl and unreacted NaI. The filtrate
was diluted with 100 mL of hexanes. The solution was heated to
reflux, and as the dichloromethane was evaporated a green powder
precipitated, which was filtered from the hot solution and washed
with hexanes. The gray-green solid was dried in vacuo. Yield:
94%. Anal. Calcd for C76H62I2O2P2Ru (%): C, 64.10; H, 4.39.
Found: C, 64.06; H, 4.79. ESI-MS: m/z ) 1297 (M - I)+. 31P-
X-ray Crystallographic Analyses. A colorless thin-plate crystal
of 1 was mounted on a glass fiber, and the data were collected at
-100.0 ( 0.1 °C. The structure was solved using direct methods24
and refined using SHELXTL.25 All measurements were made on a
Bruker X8 APEX diffractometer with graphite monochromated Mo
KR radiation.
The data for 1 were collected to a maximum 2θ value of 45.0°.
Data were collected in a series of φ and ω scans in 0.50° oscillations
with 60.0 s exposures. The crystal to detector distance was 38.02
mm. Data were collected and integrated using the Bruker SAINT26
software package and were corrected for absorption effects using
the multiscan technique (SADABS).27 The data were corrected for
Lorentz and polarization effects. All non-hydrogen atoms were
refined anisotropically. All hydrogen atoms were included in
calculated positions but not refined.
1
{1H} NMR (162 MHz, 25 °C, CDCl3): δ 66.6 (s). H NMR (400
MHz, 25 °C, CDCl3): δ 8.11-7.87 (m, 16H, pyrene), 7.69 (d, 2JHH
) 7.3 Hz, 2H, pyrene), 7.34-7.07 (m, 26H, Ph), 6.96 (m, 2H, Ph),
4.82 (m, 4H, pyrene-CH2(CH2)2CH2-O), 3.16 (m, 4H, pyrene-
CH2(CH2)2CH2-O), 2.04 (m, 4H, pyrene-CH2CH2CH2CH2-O),
1.71 (m, 4H, pyrene-CH2CH2CH2CH2-O); assignments based on
previous experiments done for tcc-RuCl2(POC4Pyr-P,O)2.14
Reactions with CO. Solutions of 3, 4, or 5 in either CH2Cl2 or
CHCl3 (ranging in concentration from 10-1 to 10-6 M depending
on the experiments being performed) were sparged with CO for a
(24) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1994, 26.
(25) SHELXTL, version 5.1; Bruker AXS Inc.: Madision, Wisconsin, 1997.
(26) SAINT, version 6.0.2; Bruker AXS Inc.: Madison, Wisconsin, 1999.
(27) SADABS: Bruker Nonius Area Detector Scaling and Absorption
Correction, version 2.05; Bruker AXS Inc.: Madison, Wisconsin,
2002.
Inorganic Chemistry, Vol. 45, No. 12, 2006 4617

Matkovich et al.
Supporting Information Available: X-ray crystallography data
in cif format for 1 and additional fluorescence spectra for 1-5.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. The authors thank the Natural Sci-
ences and Engineering Research Council of Canada (NSERC)
for funding this work. K.M.M. thanks the UBC Chemistry
Department for a graduate fellowship. L.M.T. thanks NSERC
and UBC for graduate fellowships. T.C.S.P thanks the
University of Victoria for a graduate fellowship.
IC051795J
4618 Inorganic Chemistry, Vol. 45, No. 12, 2006