Platinum(II) 1,10-phenanthroline complexes of acetylides containing redox-active groups

Article abstract of DOI:10.1039/b503794h

The new diimine ligand 3,8-di-n-pentyl-4,7-di(phenylethynyl)-1,10- phenanthroline (1) was used for the synthesis of a range of Pt^II complexes, viz. [Pt(1)Cl₂], [Pt(1)(C≡C-Ph)₂], [Pt(1)(C≡C-Fc)₂] and [Pt(1)(C≡C-p-C₆H ₄-C≡C-Fc)₂] (Fc = ferrocenyl). Crystal structure analyses were performed for [Pt(1)Cl₂] and [Pt(1)(C≡C-Ph) ₂] and revealed that the di(acetylide) π-tweezer of the latter binds a molecule of chloroform through C-H ... π hydrogen bonds. The redox and optical properties of 1 and its complexes were investigated by (spectro-)electrochemistry, UV-Vis and luminescence spectroscopy, and an energy level diagram was derived for [Pt(1)(C≡C-Fc)₂] and related compounds on the basis of the data collected. The ferrocenyl-substituted Pt ^II complexes are donor-sensitiser assemblies. Intramolecular quenching of the photoexcited Ptⁱⁱ diimine unit leads to very short luminescence lifetimes for [Pt(1)(C≡C-p-C₆H₄- C≡C-Fc)₂] (2 ns) and [Pt(1)(C≡C-Fc)₂] (0.3 ns), as opposed to [Pt(1)(C≡C-Ph)₂] (0.7 μs). Excimer formation has been observed for [Pt(1)(C≡C-Ph)₂] at room temperature in dichloromethane and at low temperatures in frozen glassy dichloromethane and 2-methyltetrahydrofuran solution, but not in the solid state. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503794h

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F U L L P A P E R
Platinum(II) 1,10-phenanthroline complexes of acetylides containing
redox-active groups†
Ulrich Siemeling,*a Kirstin Bausch,a Heinrich Fink,a Clemens Bruhn,a Marc Baldus,b
Brigitta Angerstein,b Regina Plessowc and Andreas Brockhinke*c
a Institute of Chemistry and Centre for Interdisciplinary Nanostructure Science and Technology
(CINSaT), University of Kassel, D-34109, Kassel, Germany. E-mail: siemeling@uni-kassel.de
b Department of NMR-based Structural Biology, Max Planck Institute for Biophysical
Chemistry, D-37077, Go¨ttingen, Germany
c Faculty of Chemistry, University of Bielefeld, D-33501, Bielefeld, Germany
Received 14th March 2005, Accepted 27th May 2005
First published as an Advance Article on the web 10th June 2005
The new diimine ligand 3,8-di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1) was used for the synthesis of a
range of PtII complexes, viz. [Pt(1)Cl2], [Pt(1)(C≡C–Ph)2], [Pt(1)(C≡C–Fc)2] and [Pt(1)(C≡C–p-C6H4–C≡C–Fc)2]
(Fc = ferrocenyl). Crystal structure analyses were performed for [Pt(1)Cl2] and [Pt(1)(C≡C–Ph)2] and revealed that
the di(acetylide) p-tweezer of the latter binds a molecule of chloroform through C–H · · · p hydrogen bonds. The redox
and optical properties of 1 and its complexes were investigated by (spectro-)electrochemistry, UV–Vis and
luminescence spectroscopy, and an energy level diagram was derived for [Pt(1)(C≡C–Fc)2] and related compounds on
the basis of the data collected. The ferrocenyl-substituted PtII complexes are donor–sensitiser assemblies.
Intramolecular quenching of the photoexcited PtII diimine unit leads to very short luminescence lifetimes for
[Pt(1)(C≡C–p-C6H4–C≡C–Fc)2] (2 ns) and [Pt(1)(C≡C–Fc)2] (0.3 ns), as opposed to [Pt(1)(C≡C–Ph)2] (0.7 ls).
Excimer formation has been observed for [Pt(1)(C≡C–Ph)2] at room temperature in dichloromethane and at low
temperatures in frozen glassy dichloromethane and 2-methyltetrahydrofuran solution, but not in the solid state.
such compounds, which contain ferrocenyl-substituted acetylide
ligands attached to a [Pt(phen)] core.
Introduction
There is great current interest in the photophysical properties
of diimine platinum(II) di(acetylide) complexes.1,2 Similar to
[Ru(2,2ꢀ-bipy)3]2+ and related species,3 such compounds may
Results and discussion
show bright emission with a long decay lifetime, usually
arising predominantly from 3MLCT, and potential fields of
application include electroluminescent devices,2h light energy
conversion1a,2c,f ,i and biosensors for DNA binding.2d In this
context, compounds containing functionalised acetylide ligands
have been attracting particular attention. Functional units
utilised so far include luminophores2a,e as well as ligating2b and
redox-active groups.1a,2c,f
Synthetic work
We decided to use the particularly rigid 1,10-phenanthroline
system as ligand platform. In order to extend the phenanthroline
p-system, phenylethynyl units were attached to the 4,7-positions.
In RuII terpyridine complexes, a similar modification has proved
beneficial in terms of excited state lifetimes,4 and Miller and
Karpishin have shown for the 1,10-phenanthroline system that
phenylethynyl units exhibit the most pronounced effect in the
4,7-positions.6 Additionally, n-pentyl groups in the 3,8-positions
were used for solubility reasons. The ligand of choice, 3,8-
di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1) was
synthesised following a route recently developed by Schmittel
and Ammon.7
In the related field of diimine RuII complexes, we have utilised
ferrocenyl-functionalised 2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridines for the construc-
tion of geometrically well-defined donor–sensitiser dyads and
triads.4 Although ferrocene derivatives are commonly known
as efficient luminescence quenchers and are themselves non-
luminescent, it has emerged that ferrocenyl groups may be
advantageously used as redox centres in multiresponsive, photo-
and electrochemically active assemblies.5 Quenching in such
assemblies turned out to be dependent on the redox-potential of
the ferrocenyl groups and on the nature of the spacer between
them and the photoexcited sensitiser. In the field of diimine PtII
complexes, related ferrocenyl-functionalised species, although
briefly mentioned in a recent review,1a have not been described
to date. We here report on the synthesis and properties of
Reaction of 1 with [PtCl2(NCPh)2] afforded the key com-
pound [Pt(1)Cl2], which was used as starting material for the
di(acetylide) complexes shown in Scheme 1, utilising a well-
established method originally developed by Sonogashira et al.8
† Electronic supplementary information (ESI) available: Solid-state
HETCOR NMR spectrum of [Pt(1)(C≡C–Ph)2] and [Pt(1)(C≡C–p-
C6H4–C≡C–Fc)2] (Fig. S1). ORTEP diagram of the molecular structure
of [Pt(1)Cl2]·2CHCl3 in the crystal (Fig. S2). Absorption spectra at room
temperature of [Pt(phen)(C≡C–Ph)2], [Pt(1)(C≡C–Ph)2], [Pt(1)(C≡C–
Ph–C≡C–Fc)2] and [Pt(1)(C≡C–Fc)2] in different solvents (Fig. S3).
Emission spectra upon shock-freezing of [Pt(1)(C≡C–Ph)2] in differ-
ent solvents and in microcrystalline form (Fig. S4). Concentration
dependence of normalised luminescence spectra of [Pt(1)(C≡C–Ph)2]
at 77 K in frozen glassy solution (Fig. S5). See http://www.rsc.org/
suppdata/dt/b5/b503794h/
Scheme 1
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4
2 3 6 5
©

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Owing to solubility problems, 13C NMR data could not be
obtained for most new compounds. Instead, solid-state cross
polarisation (CP)9 magic-angle spinning (MAS)10 13C-NMR
spectra using MAS rates around 25 kHz were exemplarily
recorded for [Pt(1)(C≡C–Ph)2] and [Pt(1)(C≡C–p-C6H4–C≡C–
Fc)2] (Fig. 1). The signals between ca. 20 and 40 ppm correspond
to the pentyl side chains, while those between ca. 120 and
150 ppm are due to the six-membered aromatic rings. The
ferrocenyl groups present in [Pt(1)(C≡C–p-C6H4–C≡C–Fc)2]
give rise to an intense signal at ca. 70 ppm. Resonances due
to the acetylenic carbon atoms present, which are expected
to be close to ca. 90 ppm, have not been observed. 1H–
13C HETCOR11 NMR spectra are nicely resolved for both
compounds, even differentiating between the two chemically
different phenanthroline CH units in each case (see ESI†).
Fig.
2
ORTEP diagram of the molecular structure of
[Pt(1)(C≡C–Ph)2]·CHCl3 in the crystal. Displacement ellipsoids
are drawn at the 30% probability level. H atoms are omitted for clarity,
except that of the hydrogen-bonded solvent molecule.
˚
lengths are 1.965(9) and 1.980(8) A. These structural parameters
are unexceptional and compare well with those of related
compounds, such as, for example, [Pt(phen)(C≡C–p-C6H4–
CH3)2],2i [Pt(5–Phphen)(C≡C–Ph)2] (5-Phphen = 5-phenyl-
1,10-phenanthroline),2h and [Pt(4,4ꢀ-tBu2bpy)(C≡C–Py)2] (Py =
4-pyridyl),12 where average Pt–C bond lengths of 1.948, 1.944
Fig. 1 Solid-state CP MAS 13C NMR spectrum of [Pt(1)(C≡C–Ph)2]
(top) and [Pt(1)(C≡C–p-C6H4–C≡C–Fc)2] (bottom).
˚
and 1.955 A, respectively, have been observed.
Crystal structures
Single-crystal X-ray diffraction studies were performed for
[Pt(1)Cl2] and [Pt(1)(C≡C–Ph)2]. The molecular structure of the
latter is shown in Fig. 2.
UV-Vis absorption spectroscopy
UV-Vis spectroscopic data for the new complexes in the three
solvents used in this study, viz. 2-methyltetrahydrofuran (2Me-
THF), dichloromethane (DCM) and acetonitrile (MeCN), are
collected in Table 1; the solvent column is arranged in the order
of increasing dipole moment. The absorption spectra of all
di(acetylide) complexes exhibit a broad band close to 400 nm,
which has been assigned to a charge transfer excitation from
a filled metal d orbital to a vacant p*diimine orbital (MLCT
band) in similar compounds.1,2 A slight blue-shift of this band
with an increase in the dipole moment of the solvent can be
noted. The intense higher energy bands (k < 330 nm) have
been shown to correspond to diimine- and acetylide-based
intraligand transitions (p–p*). For comparison, uncoordinated 1
is completely transparent above 380 nm. Its longest wavelength
absorption in DCM is located at kmax = 307 nm, exhibiting a
shoulder at k ≈ 335 nm.
Both compounds contain tetracoordinate Pt atoms in a
square-planar environment. The molecules are essentially flat
and contain extended p-systems. Not surprisingly, therefore,
crystal packing is dominated by p−p-stacking, leading to
˚
distances of ca. 3.5 A between neighbouring molecules. In
the case of the di(acetylide) complex a solvent molecule
(CHCl3) weakly interacts with the di(acetylide) unit through C–
H · · · p hydrogen bonds. Such interactions are well documented
for this class of compounds and have been rationalised as
the structural basis for vapoluminescent behaviour.12 H · · · C
˚
distances range from ca. 2.62 to 3.11 A (average value
ꢀ
˚
2.85 A), which is similar to the values observed for [Pt(4,4 -
tBu2bpy)(C≡C–p-C6H4–CH3)2]·CH2Cl2 (4,4ꢀ-tBu2bpy = 4,4ꢀ-di-
tert-butyl-2,2ꢀ-bipyridine).12 In contrast to [Pt(1)(C≡C–Ph)2],
Pt · · · Pt interactions may be present in [Pt(1)Cl2], as indicated
i
˚
by an intermolecular Pt–Pt distance of 3.6161(3) A (i: 1 −
Ferrocene shows a very weak absorption band at 440 nm
(e = 95 M−1 cm−1), which has previously been assigned to the
x, 1 − y, 1 − z). The Pt–Cl bond lengths are 2.294(1)
1
and 2.291(1) A, which is similar to the corresponding values
1A1g → E2g ligand-field transition (LF) in D5d symmetry.14 In
˚
found for related compounds such as, for example, [Pt(4,4ꢀ-
the case of the ferrocenyl-substituted compounds, the MLCT
band close to 400 nm therefore contains a shoulder on its
low-energy side, which is due to a ferrocenyl-based LF band.
Besides the band at k ≈ 420 nm, the spectrum of [Pt(1)(C≡C–
Fc)2] in 2Me-THF exhibits an additional broad low-intensity
absorption feature at k ≈ 570 nm (at k ≈ 540 nm in DCM).
Spectroelectrochemical investigations show that this band van-
ishes upon oxidation of the Fc groups (vide infra, Fig. 8).
We therefore ascribe this band to a ferrocenyl-based MLCT
Me2bpy)Cl2] (4,4ꢀ-Me2bpy = 4,4ꢀ-dimethyl-2,2ꢀ-bipyridine, av-
ꢀ
ꢀ
˚
erage Pt–Cl 2.345 A) and [Pt{3,3 -(MeOOC)2bpy}Cl2] (3,3 -
(MeOOC)2bpy = 3,3ꢀ-methoxycarbonyl-2,2ꢀ-bipyridine) average
13
˚
Pt–Cl 2.285 A). The Pt–N distances are 2.013(3) and 2.009(3)
˚
˚
A for [Pt(1)Cl2] and 2.064(6) and 2.067(7) A for [Pt(1)(C≡C–
Ph)2], the differences reflecting the larger trans influence of
the r-bonded acetylide ligand in comparison to chloride.2h
The acetylide units are essentially linear with triple bond
lengths ranging from 1.19(1) to 1.21(1) A. The Pt–C bond
transition, 1[(d(p)Fc6)] → [(d(p)Fc5)(p*phenPt)1], in accord with our
1
˚
2 3 6 6
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4

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Table 1 UV/Vis spectroscopic data at room temperature
Principal absorption bands (k > 280 nm)a
Lowest energy bands
Compound
Solvent
kmax/nm (10−3e/M−1 cm−1
)
kmax/nm (10−3e/M−1 cm−1
)
1
DCM
DCM
307 (45.9), 335sh
323 (48.8), 356 (35.6)
325 (38.1), 373sh
290 (68.4), 317 (53.2)
300 (44.3), 324 (56.3)
297 (37.7), 322 (48.5)
319 (47.5), 350sh
321 (47.8), 346sh
320 (49.2)
[Pt(1)Cl2]
MeCN
2Me-THF
DCM
MeCN
2Me-THF
DCM
MeCN
2Me-THF
DCM
[Pt(1)(C≡C–Ph)2]
428 (16.5), 484sh
422(18.4), 450sh
393 (20.9), 445sh
423 (13.5), 459sh, 573sh
383 (17.3), 439sh, 541sh
375 (18.1), 431sh, 520sh
435 (15.6), 496sh
[Pt(1)(C≡C–Fc)2]
[Pt(1)(C≡C-p-C6H4–C≡C–Fc)2]
326 (74.8), 336sh
325 (46.2), 333sh
408 (10.3), 475sh
b
b
MeCN
—
—
a Additional weaker bands and shoulders can be observed. b Solubility was too low to allow meaningful measurements.
results obtained for the related ferrocenyl-functionalised RuII
bis(terpyridine) complex [Ru(tpy)(4ꢀ-Fc–C≡C–tpy)]2+ (4ꢀ-Fc–
C≡C–tpy = 4ꢀ-ferrocenylethynyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine), which
showed essentially the same behaviour.4
Luminescence spectroscopy
With the exception of [Pt(1)(C≡C–Fc)2], all complexes proved
to be emissive at room temperature in fluid solution, in frozen
glassy solution at 77 K, and also in the solid state. For a detailed
determination of luminescence properties we have used the
novel excitation-emission spectroscopy approach by Brockhinke
et al.15 As a representative case, excitation-emission spectra
(EES) of [Pt(1)(C≡C–Ph)2] in three different solvents are shown
in Fig. 3. Here, the y axis corresponds to the excitation and the
x axis to the emission wavelength. Intensities are represented in
an alternating colour scheme. An EES file contains the complete
set of excitation and emission spectra of a given substance. Post-
processing allows luminescence spectra at different excitation
wavelengths (corresponding to horizontal profiles in the EES)
to be recovered, and excitation spectra at different emission
wavelengths with an arbitrary bypass to be determined (corre-
sponding to vertical profiles averaged over a given region). These
images are the basis for determining the quantum yields and
other spectroscopic information summarised in Table 2, which
also contains data for the reference compound [Pt(phen)(C≡C–
Ph)2].
Emission spectra in fluid solution at room temperature
As exemplarily shown in Fig. 3 for [Pt(1)(C≡C–Ph)2], the
shape of the emission spectra is independent of the exci-
tation wavelength for all compounds investigated, indicating
that luminescence always originates from the same levels. For
ferrocenyl-containing complexes, low overall quantum effi-
ciencies prevented measuring a complete EES. For the other
complexes, however, a detailed comparison between excitation
and absorption spectra has been possible. With the exception of
[Pt(1)(C≡C–Ph)2] in DCM, excellent agreement between both
has been observed. This shows that deactivation pathways are
independent of the initially excited level for these compounds.
This would be different if Fc states, which do not contribute
to luminescence, were excited directly.4 In comparison to the ab-
sorption spectrum, the excitation spectrum of [Pt(1)(C≡C–Ph)2]
in DCM shows a slightly more pronounced MLCT band. In this
case, excitation spectra in different solvents show a significant
shift of the MLCT band towards shorter wavelengths upon an
increase of the solvent polarity (Fig. 3). This shift can also be
observed in emission spectra at room temperature and is shown
in Fig. 4, along with the long-wavelength part of the absorption
spectra. For both 2Me-THF and MeCN, mirror symmetry
between MLCT bands in absorption and emission is observed.
Fig. 3 EES of [Pt(1)(C≡C–Ph)2] at room temperature in three different
solvents
Fig. 5 shows absorption and emission spectra of 1 in the free
form and in two different coordination environments. Even the
uncoordinated ligand emits luminescence. Upon binding to PtII,
both absorption (vide supra) and luminescence spectra change
significantly. UV-Vis spectra of the Pt complexes exhibit the
additional MLCT band at longer wavelengths. The emission
spectra clearly show that luminescence originates from the
energetically lower MLCT triplet state 3[(d(p)Pt)7(p*phenPt)1], and
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4
2 3 6 7

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Table 2 Excited-state properties at room temperature
Compound
Solvent
kmax/nm
Ua
sb/ns
600e
10−5krc/s−1
10−5knr d/s−1
[Pt(phen)(C≡C–Ph)2]
2Me-THF
DCM
MeCN
DCM
582
573
573
497
0.22
3.7
13
1700
15
1
0.02
[Pt(1)Cl2]
DCM
567, 610, 670sh
550, 590, 650sh
621, 688sh
598, 630sh
600, 625sh
1.8 × 10−4
6e
0.3
MeCN
2Me-THF
DCM
MeCN
DCM
12 × 10−4
[Pt(1)(C≡C–Ph)2]
0.015
670,e 680f
0.22
0.04
g
[Pt(1)(C≡C–Fc)2]
—
< 10−6
1.5 × 10−4
0.3f
2f
[Pt(1)(C≡C–p-C6H4–C≡C–Fc)2]
DCM
578, 614, 696sh
0.75
5000
a kexc = 410 nm. b kem = 580 nm. c Radiative decay rate kr = U/s. d Nonradiative decay rate knr = (1 − U)/s. e kexc = 375 nm. f kexc = 441 nm. g Insufficient
intensity.
Pt complexes always originates from the MLCT state, even if
ligand-centered states are initially populated by the absorption
step (kabs < 350 nm).
Observed quantum yields and lifetimes are relatively low (Ta-
ble 2) and are in the range expected for PtII diimine di(acetylides)
in the case of [Pt(1)(C≡C–Ph)2].1a This shows that radiationless
deactivation is the dominant process at room temperature.
Ferrocene units can efficiently quench photoexcited states by
two mechanisms, that is, reductively or by energy transfer.5 Not
surprisingly, therefore, the presence of ferrocenyl substituents in
the present system causes a dramatic decrease of U and s, which
is due to additional intramolecular quenching by these units. In
the case of [Pt(1)(C≡C–p-C6H4–C≡C–Fc)2] this leads to the very
high nonradiative decay rate of k = 5 × 108 s−1. The quenching
efficiency decreases with spacer length, leading to a particularly
short lifetime of s = 0.3 ns in the case of [Pt(1)(C≡C–Fc)2].
Luminescence was far too weak for this complex to determine
meaningful values of kmax and U and therefore prohibited the
Fig. 4 Normalised luminescence (black) and absorption (grey) spectra
of [Pt(1)(C≡C–Ph)2] in different solvents at room temperature. The
deconvoluted part of the excimer emission in DCM at c ≈ 40 lM is
shown in dark grey.
determination of decay rates for this species.
In comparison to the reference compound [Pt(phen)(C≡C–
Ph)2], it is evident that ligand 1 causes a shift of the emission
maximum tolower energy. This is consistent withamainly metal-
based HOMO and a p*diimine LUMO, since the energy of the
latter is lowered by extending the p-system with an electron-
withdrawing acetylenic substituent, the electronegativity of an
sp-hybridised C atom on the Pauling scale being 2.99.16
Comparison of the normalised emission spectra of
[Pt(1)(C≡C–Ph)2] in DCM at concentrations of 1 lM and
40 lM reveals a significant (albeit relatively small) difference at
higher emission wavelengths around kem ≈ 750 nm. The enlarged
difference spectrum is also shown as part of Fig. 4 and is most
likely due to excimer emission. Aromatic molecules are known
to be able to undergo excited-state dimerisation in solution.
Under suitable conditions, the formation of excited dimers
(excimers) can be monitored by the simultaneous appearance of
monomer and excimer luminescence.17 Emission of the excimer
is shifted towards longer wavelengths since the dimerisation
generates a state with lower energy. Spectroscopic properties
of the observed excimer emission (kmax = 757 nm, full-width
at half maximum intensity = 3850 cm−1 and DE = E0,0
−
mmax = 5800 cm−1) agree quite well with similar observations
for [Pt(phen)(C≡C–Ph)2] and other diimine platinum(II) com-
plexes at high concentrations.1a,2b,18 In our investigation room
temperature excimer emission was only visible for [Pt(1)(C≡C–
Ph)2] in DCM at concentrations higher than ca. 40 lM. No
excimer emission could be observed in 2Me-THF, even though
the solubility allowed measurements with similarly high con-
centrations. In MeCN, however, the solubility may very likely be
too low to observe excimer emission (maximum concentration
c ≤ 5 lM). In the case of the ferrocenyl-substituted complexes,
the low overall quantum yield prevented analysis of possible
contributions of excimers to the spectra.
Fig. 5 Normalised emission (full lines) and absorption (broken lines)
spectra of ligand 1 in free form and in two different coordinative
environments; obtained in DCM at room temperature.
not, as for the uncoordinated ligand, from a ligand-centred
state. The position of the emission maximum red-shifts from
kem ≈ 497 nm (uncoordinated 1) to kem ≈ 598 nm in the case of
([Pt(1)(C≡C–Ph)2]) and to kem ≈ 567 nm in the case of [Pt(1)Cl2],
which corresponds to an energy shift of 3400 and 2515 cm−1,
respectively (Table 2). Since the shape of all emission spectra is
independent of the excitation wavelength, luminescence of the
2 3 6 8
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4

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Table 3 Photophysical properties of [Pt(1)(C≡C–Ph)2] at 77 K
Solvent
2Me-THF
DCM
c/lM (T/K)
Principal emission bands kmax/nm
Excimer emission kexcimermax/nm
Vibronic spacinga Dm˜/cm−1
20
1
20
1
2
1
582, 634
751
1409
1403
1405
1431
1469
1437
1354
1321
578, 629, 690sh
604, 660, (≈720)b
593, 648, (≈705)b
605, 664, 724sh
602, 659, 723sh
605, 659, 726, (≈800)b
602, 654, 718, (≈790)b
(≈757)b
753
752
c
MeCN
solid
—
—
—
—
c
c
(77)
(293)
c
a Between first and second maximum; estimated error for Dm˜ is 50 cm−1
.
b Determined by a fitting procedure. c Not observed.
Using time-resolved measurements, Connick et al. could
unambiguously identify excimer emission in emission spectra
of 100 lM [Pt(phen)(C≡C–Ph)2] in DCM by comparing the
intensity decays at kem = 570 nm (only monomer emission) and
kem = 750 nm (emission due to both monomer and excimer).19
We could observe no significant difference in the time-resolved
spectra of [Pt(1)(C≡C–Ph)2] even at the upper concentration
limit in DCM (c ≈ 50 lM), which is due to the low contribution
of the excimer emission to the spectrum (3% at the positions of
the maxima, 6% contribution to the total emission), preventing
a quantitative comparison with literature results. The relatively
low concentrations achievable for the compounds investigated
in our study may also be an explanation for the fact that no self-
quenching could be observed. For other PtII diimine complexes,
both self-quenching and excimer formation have to be taken into
account at higher concentrations (c > 200 lM).1a
to a higher relative excimer contribution at lower concentra-
tions and a lower relative contribution at high concentrations.
Furthermore, it is interesting to note that the position of the
vibrational bands of the monomer emission in all three solvents
significantly red-shifts with increasing concentration.
Fig. 7(a) shows a comparison of the low-temperature spectra
at a concentration of 1 lM. In comparison to the room
temperature spectra (Fig. 4), we observe an inverse dependence
of the emission maxima on the solvent polarity (2Me-THF:
578 nm, DCM: 593 nm, MeCN: 605 nm).
Solid-state emission spectra
Additionally, spectra have been obtained for microcrystalline
samples of [Pt(1)(C≡C–Ph)2] and [Pt(phen)(C≡C–Ph)2]. For the
reference standard [Pt(phen)(C≡C–Ph)2], the emission spectrum
closely resembles that acquired in solution. Again, only a
broad, unstructured band can be observed. In contrast, the
spectrum of microcrystalline [Pt(1)(C≡C–Ph)2] resembles more
closely that acquired in the frozen solvents at 77 K. Fig. 7(b)
shows a comparison of the low-temperature spectra in frozen
solvents and of the microcrystalline solid at room temperature.
Vibrational bands are clearly visible, and even the width of
the bands is comparable. For a more detailed comparison,
77 K spectra have been obtained for the microcrystalline solid
as well (see Fig. 6(d) for temperature effects; see Fig. 7(a)
for a comparison of 77 K spectra of frozen solutions and
microcrystalline samples). The low-temperature emission is
slightly red-shifted by Dm˜ ≈ 750 cm−1 (Dk = 6 nm), the
maximum intensity increases by a factor of ca. 30 (the energy
per wavelength interval increases by a factor of ca. 10). It can
clearly be seen that the vibrational bands become narrower and
more prominent with decreasing temperature. This is due to
the more restricted movement of atoms and molecules in the
crystal. The solid-state spectrum closely resembles that obtained
in the frozen solvent, albeit with slightly narrower vibrational
bands. No excimer emission can be observed at 77 K in the solid
state. However, the similarity of luminescence spectra obtained
from microcrystalline [Pt(1)(C≡C–Ph)2] at room temperature
with those obtained at higher concentrations in 2Me-THF and
DCM at 77 K (Fig. 7(b)) raises the question whether solid
[Pt(1)(C≡C–Ph)2] possibly exhibits excimer emission at room
temperature. For a more detailed investigation, Figs. 6(b) and (d)
show normalised spectra of [Pt(1)(C≡C–Ph)2] in DCM and of
the microcrystalline solid as a function of temperature. Marked
differences can clearly be seen. In microcrystalline form, the
intensity of the long-wavelength bands decreases monotonically
upon cooling and a simultaneous narrowing can be observed.
For a quantitative analysis of this observation, a total of four
bands have been fitted to the observed spectra acquired at
each temperature. Excellent agreement has been found, and
intensity and width of the fitted curves vary monotonically
with the temperature. Such a fit is, however, not possible for
the 77 K spectra in DCM and 2Me-THF. Here, inclusion of an
additional fifth band with a large full-width at half maximum
Low-temperature emission spectra
Upon shock-freezing solutions of [Pt(1)(C≡C–Ph)2] from T =
293 to 77 K, an intense orange luminescence becomes apparent.
Emission intensity increases significantly upon cooling. The
emission band that is broad and unstructured at room tempera-
ture (Fig. 4) shifts and develops a pronounced fine structure with
four different vibrational bands (Fig. 6(a)–(c)). For [Pt(1)Cl2]
these bands can also be made out at room temperature to some
degree (Fig. 5). Spectral characteristics of the vibrational bands
have been compiled in Table 3. The energy distance between
adjacent bands (E ≈ 1400 cm−1) corresponds roughly to values
observed before for similar ligands.20
It is interesting to note the different behaviour of [Pt(1)(C≡C–
Ph)2] in the three solvents used. In 2Me-THF, the bands
shift continuously towards shorter wavelengths upon cooling
(Fig. 6(a)), and an additional excimer band becomes visible
at early times in the cooling process. This band displays a
hypsochromic shift with decreasing temperature as well (from
kem = 825 nm to kem = 755 nm at c ≈ 45 lM) and its intensity
depends strongly on the concentration (see ESI†). In contrast,
the emission maximum in DCM displays a hypsochromic shift
at intermediate temperatures, but a pronounced bathochromic
shift at low temperatures (Fig. 6(b)). Again, a distinct excimer
band becomes visible that displays a hypsochromic shift of 5 nm
upon cooling. In MeCN, only a slight red-shift of the bands
could be observed. In the concentration range that could be
accessed, no indication of excimer emission has been found
in this solvent. This is surprising, since excimer emission was
apparent in low-temperature spectra in DCM and 2Me-THF
even for concentrations as low as ca. 2 lM.
In contrast to the data obtained at room temperature,
pronounced spectral changes were observed at 77 K as a function
of the concentration (see ESI†). The most distinct changes have
been observed in 2Me-THF, where an intense excimer band
becomes visible. Here, the ratio between excimer and monomer
emission depends nearly linearly on the concentration. This
concentration dependence is less pronounced in DCM, leading
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4
2 3 6 9

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Fig. 7 Comparison of normalised 77 K spectra of [Pt(1)(C≡C–Ph)2] in
different solvents with the spectrum of the microcrystalline solid: (a) at
low concentrations; (b) at high concentrations and the microcrystalline
solid at room temperature.
and the high concentration necessary before significant excimer
emission could be observed. As a second possibility, aggregates
of two monomers in the correct orientation may directly form
in solution (preformed excimers). The actual excimer is formed
only after excitation of one of the monomers in this aggregate.
It is well documented that square-planar PtII complexes may
easily dimerise in solution by forming a Pt–Pt bond.21 This
solution behaviour is frequently reflected by the arrangement
of such molecules in the crystal, where Pt chains are formed
with ligands stacked in a way that allows formation of excimers.
However, this is not the case for the compounds investigated
here. Pt · · · Pt interactions can be ruled out altogether for
[Pt(1)(C≡C–Ph)2] (vide supra). While the diimine ligands have
the correct parallel orientation, the overlap area between the
p-systems is too low to allow formation of excimers. A similar
arrangement of molecules has been found for [Pt(phen)(C≡C–
Ph)2]1b and other platinum(II) diimine di(acetylide) complexes.1a
[Pt(phen)(C≡C–Ph)2] has already been the object of several
studies addressing excimer emission in solution. Since the
solubility of this complex is relatively high, measurements at
significantly higher concentrations than in the present study have
been possible, and both room-temperature excimer emission and
self-quenching has been observed.1a In accord with published
results, we could observe no excimer emission in the 77 K spectra
of [Pt(phen)(C≡C–Ph)2]. The commonly accepted explanation
for this behaviour is that room temperature excimer formation
is due to collisions of an excited molecule with a second one,
whereas no ground-state aggregates are formed under such
conditions. It seems reasonable to assume that [Pt(1)(C≡C–Ph)2]
behaves similarly. However, excimer emission in the frozen glassy
solvent cannot be explained by this model, since it would require
correct conformation and orientation of the ligands even before
Fig.
6 Normalised emission spectra upon shock-freezing of
[Pt(1)(C≡C–Ph)2] in different solvents and in microcrystalline form.
intensity (assigned to excimer emission) is necessary in order to
represent the measured spectra correctly. We therefore conclude
that exclusively monomer luminescence is observed in the
microcrystalline form of [Pt(1)(C≡C–Ph)2] at all temperatures.
Excimer formation
In solution, two different mechanisms might lead to the for-
mation of excimers.18 First, an excited molecule might collide
with another molecule during its luminescence lifetime. If the
aromatic diimine rings are parallel in this collision complex, an
excited dimer is formed. This seems possible, considering the rel-
atively high excited state lifetimes of the compounds investigated
2 3 7 0
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4

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the freezing starts. By analysing the temperature-dependent
emission in DCM and 2Me-THF, we propose that at low
temperatures ground-state aggregates are formed and remain
stable upon further lowering the temperature. Since we do not
observe excimer emission in the microcrystalline state, formation
of small crystals in solution due to decreased solubility at
low temperatures can be ruled out as an explanation. Another
indication for this hypothesis comes from the concentration-
dependent shifts observed in the frozen solution spectra at
77 K. These effects have been observed not only in 2-MeTHF
and DCM, but also in MeCN, where no excimer emission was
apparent. They must be due to different local environments of
the chromophores at different concentrations. This is compatible
with the formation of loose aggregates at low temperatures only,
since no spectral shift of the position of the emission maxima
as a function of the concentration has been observed at room
temperature.
We therefore conclude that excimer emission at low temper-
atures is due to the formation of aggregates which probably
exhibit a Pt · · · Pt interaction and/or pronounced stacking of
diimine ligands. The formation and nature of such aggregates
critically depends on the solvent. Even in MeCN, where no
excimer emission could be observed, the strong concentration
dependence of the 77 K spectra still suggests formation of aggre-
gates. It might be hypothesised that the maximum concentration
reachable in this solvent was too low to allow generation of
significant excimer emission. However, it seems more likely that
in MeCN either these aggregates have a different structure, or
enhanced noncovalent interactions with this particularly polar
and Lewis basic solvent leads to a perturbation of the highly
environment-sensitive [(diimine)PtII] luminophore.12
Fig. 8 UV-Vis spectroelectrochemical measurements of [Pt(1)(C≡
C–Fc)2] in DCM with 0.1 M n-Bu4NPF6. Oxidation of ferrocenyl
groups was reversible on the spectroelectrochemical time scale. Applied
potential: 0 to 0.2 V, 50 mV steps.
Electrochemistry and spectroelectrochemistry
The compounds shown in Scheme 1 were investigated by cyclic
voltammetry. Pertinent data are collected in Table 4.
All complexes were slightly more difficult to reduce than
uncoordinated 1. In accord with previous observations,2i
a
variation of the two co-ligands has only a small effect on the
E(0/−) value of the complexes. In each case, reversible one-
electron reduction was observed, corresponding essentially to
the addition of an electron to the LUMO of 1. The two formally
identical ferrocenyl groups of [Pt(1)(C≡C–p-C6H4–C≡C–Fc)2]
do not show any noticeable interaction, giving rise to a single
two-electron redox wave. In the case of [Pt(1)(C≡C–Fc)2], where
the ferrocenyl groups are held closer together owing to the
shorter spacer present, marginal wave splitting can be resolved,
which is indicative of a weak interaction between these units.
In the case of [Pt(1)(C≡C–Ph)2], two irreversible oxidations are
observed at Epa1 = 0.19 V and Epa2 = 0.96 V, reflecting most
likely an oxidation of the PtII centre.2c,h
The redox-functionalised complex [Pt(1)(C≡C–Fc)2] was also
investigated by UV-Vis spectroelectrochemistry, since it exhibits
a unique feature in the absorption spectrum, viz. a broad band
at ca. 540 nm in DCM (vide supra). The spectral changes
observed during oxidation and reduction are shown in Figs. 8
and 9, respectively. The weak band at ca. 540 nm vanishes upon
Fig. 9 UV-Vis spectroelectrochemical measurements of [Pt(1)(C≡
C–Fc)2] in DCM with 0.1
M
n-Bu4NPF6. Reduction was
quasi-reversible. Applied potential: −1.5 to −1.8 V, 50 mV steps.
oxidation of the ferrocenyl groups, indicating that this band
is due to the ferrocenyl-based charge transfer 1[(d(p)Fc)6] →
1[(d(p)Fc)5(p*phenPt)1]. While the intraligand band at kmax ≈ 320 nm
is almost unaffected by ferrocenyl oxidation, that at kmax
≈
380 nm due to the Pt-based MLCT 1[(d(p))8] → [(d(p))7(p*phen)1]
becomes more intense, since electron density transfer from the
ferrocenyl groups to the coordinated diimine cannot occur
any more. Reduction generates two new bands at ca. 500 and
730 nm, which are typical for intraligand transitions of a reduced
platinum-coordinated diimine ligand,2j,22 while the MLCT as
well as the intraligand band at 320 nm decrease.
1
Conclusion
Table 4 Electrochemical data for ligand 1 and its platinum complexes
On the basis of the data collected, we are able to propose
an energy level diagram for [Pt(1)(C≡C–Fc)2] (Fig. 10). The
maximum of the Pt-based MLCT at ca. 380 nm places the
excited state denoted 1[PtIII(phen−)(C≡CFcII)] at an energy
of almost 3.3 eV. The energy of the corresponding triplet
Compound
E(0/−)
E(Fc+/0
)
1
−1.50
−1.56
−1.62
−1.63
−1.61
[Pt(1)Cl2]
[Pt(1)(C≡C–Ph)2]
[Pt(1)(C≡C–Fc)2]
[Pt(1)(C≡C–p-C6H4–C≡C–Fc)2]
0.11a
0.15b
3
state [PtIII(phen−)(C≡CFcII)] can only be roughly estimated,
since this compound showed extremely weak luminescence.
In analogy to the more emissive complexes investigated, its
emission maximum is supposed to be between ca. 580 and
600 nm, corresponding to an energy of ca. 2.1 eV. The transition
a Average of two ill-resolved one-electron processes (DE ≤ 0.10 V).
b Unresolved two-electron process.
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4
2 3 7 1

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elsewhere.33 All other NMR spectra were obtained with a Varian
1
Unity INOVA 500 (500.13 MHz for H). Elemental analyses:
H. Kolbe (Mu¨lheim an der Ruhr) and microanalytical laboratory
of the University of Bielefeld.
Syntheses
3,8-Di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1)
was prepared starting from ethyl 3-oxo-2-n-pentylpropionate34
by slight modification of the procedure published by Schmit-
tel and Ammon for the synthesis of 3,8-di-n-hexyl-4,7-
di(phenylethynyl)-1,10-phenanthroline.7 Therefore, only spec-
troscopic and analytical data are given for 1 and the intermediate
products in its synthesis.
3,8-Di-n-pentyl-1,10-phenanthroline-4,7-dione. Mp > 320 ◦C.
1H NMR (DMSO-d6, 100 ◦C): d 0.94, 1.18, 1.85, 3.68 (4 m, br,
22H, C5H11). Calc. for C22H28N2O2: C, 74.97; H, 8.01; N, 7.95.
Found: C, 75.07; H, 8.21; N, 7.81%.
Fig. 10 Energy level diagram for [Pt(1)(C≡C–Fc)2] and related
compounds.
1
1[(d(p)Fc)6] → [(d(p)Fc)5(p*phenPt)1] at ca. 540 nm is equivalent to
an energy of 2.3 eV. The energy of the corresponding triplet state
3[(d(p)Fc)5(p*phenPt)1] may be estimated from the low-energy onset
of the underlying absorption band (ca. 650 nm), giving a value
of ca. 1.9 eV. The energies of the excited triplet states shown
in Fig. 10 most likely lie above the triplet energy of ferrocene,
which has been estimated to be between ca. 1.1 eV23 and 1.8 eV,24
and the ferrocenyl-centred triplet state of [Pt(1)(C≡C–Fc)2] is
expected to be located somewhere in this region as the lowest-
lying excited state.
4,7-Dibromo-3,8-di-n-pentyl-1,10-phenanthroline. Mp 135 ◦C.
1H NMR (CDCl3) d 0.89 (t, J = 7.3 Hz, 6H, Me), 1.38 (m, 8H,
CH2), 1.72 (m, 4H, CH2), 3.00 (t, J = 7.3 Hz, 4H, CH2–C4H9),
8.30 (s, 2H, H5,6), 8.88 (s, 2H, H2,9). 13C NMR (CDCl3) d 14.0
(Me), 22.4 (CH2), 29.5 (CH2), 31.5 (CH2), 34.4 (CH2–C4H9),
125.0 (C5,6), 127.7 (C3,8), 134.9 (C4a,6a), 138.2 (C4,7), 144.8
(C1a,10a), 151.4 (C2,9). Calc. for C22H26N2Br2: C, 55.25; H,
5.48; N, 5.86. Found: C, 54.89; H, 5.21; N, 5.94%.
1. Mp 162 ◦C. 1H NMR (CDCl3) d 0.94 (t, J = 7.3 Hz, 6H,
Me), 1.25 (m, 12H, CH2), 3.15 (t, J = 7.3 Hz, 4H, CH2–C4H9),
7.43 (m, 6H, Ph), 7.70 (m, 4H, Ph), 8.45 (s, 2H, H5,6), 9.05 (s,
2H, H2,9). Calc. for C38H36N2: C, 87.65; H, 6.96; N, 5.37. Found:
C, 87.46; H, 7.13; N, 5.04%.
Experimental
General
[PtCl2(PhCN)2],25 Fc–C≡CH26 and Fc–C≡C–p-C6H4–C≡CH27
were prepared according to published procedures. All other com-
pounds are commercially available. Synthetic work involving
air-sensitive compounds was performed under an atmosphere
of dry argon or nitrogen by using standard Schlenk techniques
or a conventional glovebox. Solvents and reagents were ap-
propriately dried and purified. Methods and instrumentation
used for electrochemistry28 and spectroelectrochemistry29 have
previously been described. Measurements were performed with
freshly prepared sample solutions, since slow degradation of
the platinum complexes occurred upon exposure to light.
Absorption spectra were measured with a UV–Vis double
path spectrometer (Kontron UVIKON 860), using the pure
solvent as reference. Steady-state emission spectra were recorded
using the novel excitation–emission spectroscopy approach
by Brockhinke et al.30 Quantum yield measurements were
performed with optically dilute (c ≤ 20 lM) solutions in
deaerated dichloromethane in order to minimise bimolecular
quenching effects. Quantum yields were determined using the
approach proposed by Demas and Crosby,31 as described
elsewhere.32 [Ru(bpy)3]2+ was used as reference standard. Solid-
state and low-temperature spectra were recorded in a front
surface configuration using a custom-built cuvette that can
be cooled to 77 K with liquid N2. Monochromatic light for
excitation was relayed to and fluorescence light was collected
from the sample cell by means of fibre optics. The front surface
configuration allowed an investigation even of solvents which
do not form a true crack-free transparent glass. Luminescence
lifetimes were determined by time-correlated single-photon
counting, using commercial equipment (PicoQuant FluoTime
200 spectrometer with TimeHarp 200 PCI board and FluoFit
3.1 software). NMR: Solid-state spectra were obtained on a
Bruker 14.1 T (600 MHz, proton resonance frequency) wide-
bore instrument using a 2.5 mm triple-resonance NMR MAS
probe. 13C detection periods involved high powder proton de-
coupling. Two-dimensional (1H,13C) heteronuclear correlation
(HETCOR) experiments were tailored to observe one-bond
(1H,13C) polarisation transfer. Further details can be found
[Pt(1)Cl2]. [PtCl2(PhCN)2] (1.56 g, 3.30 mmol) was added to
a solution of 1 (1.72 g, 3.30 mmol) in benzene (30 ml). The mix-
ture was heated to reflux for 24 h and was subsequently allowed
to cool to room temperature. The light orange microcrystalline
precipitate was filtered off, washed with benzene (2 × 5 ml) and
dried in vacuo. Yield 2.12 g (82%). 1H NMR (CDCl3) d 0.94 (t,
J = 7.3 Hz, 6H, Me), 1.29 (m, 8H, CH2), 1.80 (m, 4H, CH2), 3.10
(t, J = 7.3 Hz, 4H, CH2–C4H9), 7.49 (m, 6H, Ph), 7.70 (m, 4H,
Ph), 8.38 (s, 2H, H5,6), 9.65 (s, 2H, H2,9). 13C NMR (CDCl3) d
14.0 (Me), 22.4 (CH2), 30.1 (CH2), 31.8 (CH2), 33.2 (CH2–C4H9),
82.8 (C≡C), 107.8 (C≡C), 121.3 (Ph), 126.0 (Ph), 128.3 (Ph),
129.8 (C5,6), 130.6 (C3,8), 130.7 (C4a,6a), 132.2 (Ph), 142.4
(C4,7), 146.2 (C1a,10a), 149.5 (C2,9). Calc. for C38H36N2Cl2Pt:
C, 58.02; H, 4.61; N, 3.56. Found: C, 57.77; H, 4.76; N, 3.69%.
Di(acetylide) complexes [Pt(1)(C≡C–Ar)2]. The acetylene
component (5.50 mmol) was added to a stirred solution of
[Pt(1)Cl2] (1.97 g, 2.50 mmol), isopropylamine (1.5 ml) and
copper(I) iodide (50 mg, 0.26 mmol) in dichloromethane (30 ml).
After 12 h the precipitate was filtered off, washed with benzene
(2 × 5 ml) and dried in vacuo.
[Pt(1)(C≡C–Ph)2]. Orange microcrystalline solid. Yield
1.42 g (62%). 1H NMR (CDCl3) d 0.85 (t, J = 7.3 Hz, 6H, Me),
1.35 (m, 8H, CH2), 1.78 (m, 4H, CH2), 3.10 (t, J = 7.3 Hz, 4H,
CH2–C4H9), 7.15 (m, 6H, Ph), 7.42 (m, 4H, Ph), 7.45 (m, 2H,
Ph), 7.65 (m, 8H, Ph), 8.36 (s, 2H, H5,6), 9.35 (s, 2H, H2,9). Calc.
for C54H46N2Pt·0.5CH2Cl2: C, 68.15; H, 4.93; N, 2.92. Found: C,
68.02; H, 5.42; N, 3.23%.
[Pt(1)(C≡C–Fc)2]. Reddish brown microcrystalline solid.
1
Yield 1.42 g (40%). H NMR (CDCl3) d 0.90 (t, J = 7.3 Hz,
6H, Me), 1.45 (m, 8H, CH2), 1.89 (m, 4H, CH2), 3.20 (t, J =
7.3 Hz, 4H, CH2–C4H9), 4.15 (“t”, 4H, Fc), 4.27 (s, 10H, Fc),
4.58 (“t”, 4H, Fc), 7.45 (m, 6H, Ph), 7.70 (m, 4H, Ph), 8.43 (s, 2H,
H5,6), 9.84 (s, 2H, H2,9). Calc. for C62H54N2Fe2Pt·0.5CH2Cl2:
C, 63.81; H, 4.71; N, 2.38. Found: C, 63.87; H, 4.74; N, 2.25%.
2 3 7 2
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4

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[Pt(1)(C≡C-p-C6H4–C≡C–Fc)2]. Brownish red microcrys-
References
1
talline solid. Yield 1.33 g (40%). H NMR (CDCl3) d 0.90 (t,
1 For reviews, see: (a) M. Hissler, J. E. McGarrah, W. B. Connick, D. K.
Geiger, S. D. Cummings and R. Eisenberg, Coord. Chem. Rev., 2000,
208, 115–137; (b) C.-W. Chan, L.-K. Cheng and C.-M. Che, Coord.
Chem. Rev., 1994, 132, 87–97.
J = 7.3 Hz, 6H, Me), 1.45 (m, 8H, CH2), 1.88 (m, 4H, CH2),
3.17 (t, J = 7.3 Hz, 4H, CH2–C4H9), 4.21 (“t”, 4H, Fc), 4.29 (s,
10H, Fc), 4.49 (“t”, 4H, Fc), 7.38 (“d”, 4H, C6H4), 7.46 (m, 6H,
Ph), 7.50 (“d”, 4H, C6H4), 7.69 (m, 4H, Ph), 8.40 (s, 2H, H5,6),
9.84 (s, 2H, H2,9). Calc. for C78H62N2Fe2Pt: C, 70.23; H, 4.68;
N, 2.10. Found: C, 69.69; H, 4.83; N, 2.05%.
2 (a) I. E. Pomestchenko and F. N. Castellano, J. Phys. Chem. A, 2004,
108, 3485–3492; (b) Y. Kang, J. Lee, D. Song and S. Wang, Dalton
Trans., 2003, 3493–3499; (c) J. E. McGarrah and R. Eisenberg, Inorg.
Chem., 2003, 42, 4355–4365; (d) T. J. Wadas, R. J. Lachicotte and R.
Eisenberg, Inorg. Chem., 2003, 42, 3772–3778; (e) I. E. Pomestchenko,
C. R. Luman, M. Hissler, R. Ziessel and F. N. Castellano, Inorg.
Chem., 2003, 42, 1394–1397; (f) J. E. McGarrah, Y.-J. Kim, M.
Hissler and R. Eisenberg, Inorg. Chem., 2001, 40, 4510–4511; (g) C. E.
Whittle, J. A. Weinstein, M. W. George and K. S. Schanze, Inorg.
Chem., 2001, 40, 4053–4062; (h) S.-C. Chan, M. C. W. Chan, Y. Wang,
C.-M. Che, K.-K. Cheung and N. Zhu, Chem. Eur. J., 2001, 7, 4180–
4190; (i) M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah,
D. Lipa, R. J. Lachicotte and R. Eisenberg, Inorg. Chem., 2000, 39,
447–457; (j) C. J. Adams, S. L. James, X. Liu, P. R. Raithby and L. J.
Yellowlees, J. Chem. Soc., Dalton Trans., 2000, 63–67.
3 Selected reviews: (a) V. Balzani, A. Juris, M. Venturi, S. Campangna
and S. Serroni, Chem. Rev., 1996, 96, 759–833; (b) K. Kalyanasun-
daram, Photochemistry of Polypyridine and Porphyrin Complexes,
Academic Press, London, 1992; (c) V. Balzani, F. Barigeletti and L.
De Cola, Top. Curr. Chem., 1990, 158, 31–71; (d) A. Juris, V. Balzani,
F. Barigelletti, S. Campagna, P. Belser and A. von Zelewsky, Coord.
Chem. Rev., 1988, 84, 85–277.
4 U. Siemeling, J. Vor der Bru¨ggen, U. Vorfeld, B. Neumann, A.
Stammler, H.-G. Stammler, A. Brockhinke, R. Plessow, P. Zanello,
F. Laschi, F. Fabrizi de Biani, M. Fontani, S. Steenken, M. Stapper
and G. Gurzadyan, Chem. Eur. J., 2003, 9, 2819–2833.
5 Review: S. Fery-Forgues and B. Delavaux-Nicot, J. Photochem.
Photobiol. A: Chem., 2000, 132, 137–159.
6 M. T. Miller and T. B. Karpishin, Inorg. Chem., 1999, 38, 5246–5249.
7 M. Schmittel and H. Ammon, Eur. J. Org. Chem., 1998, 785–792.
8 K. Sonogashira, Y. Fujikura, T. Yatake, N. Toyoshima, S. Takahashi
and N. Hagihara, J. Organomet. Chem., 1978, 145, 101–108.
9 S. R. Hartmann and E. L. Hahn, Phys. Rev., 1962, 128, 2042–2053.
10 E. R. Andrew, A. Bradbury and R. G. Eades, Nature (London), 1958,
182, 1659.
X-Ray crystallography
For both compounds, a single crystal was mounted on a glass
fibre and all geometric and intensity data were taken from this
˚
sample. Data collection using Mo-Ka radiation (k = 0.71073 A)
was made at on a Stoe IPDS2 diffractometer equipped with a
two-circle goniometer and an area detector. The data sets were
corrected for Lorentz and polarisation effects. The structures
were solved by direct methods (SHELXS 97) and refined
using alternating cycles of least squares refinements against F2
(SHELXL 97).35 All non H atoms were found in difference
Fourier maps and were refined with anisotropic displacement
parameters, except those of the disordered alkyl chain in
[Pt(1)Cl2]·2CHCl3 which were refined with isotropic displace-
ment parameters. The disorder affects four carbon atoms and
was modelled by splitting them with nearly the same probability,
53(1) and 47(1)%, respectively. For both structures H atoms were
placed in constrained positions according to the riding model
with the 1.2-fold isotropic displacement parameters, except for
H34A–H34D of [Pt(1)Cl2]·2CHCl3 which were refined with fixed
displacement parameters. Graphical representations were made
using ORTEP-3 win.36 CCDC reference numbers 265808 and
265809 for [Pt(1)(C≡C–Ph)2]·CHCl3 and [Pt(1)Cl2]·2CHCl3,
respectively.
Crystallographic data for [Pt(1)Cl2]·2CHCl3. Orange prism,
dimensions 0.54 × 0.28 × 0.22 mm, T = 200(2) K, a =
11 P. Caravatti, L. Braunschweiler and R. R. Ernst, Chem. Phys. Lett.,
1983, 100, 305–310.
12 W. Lu, M. C. W. Chan, N. Zhu, C.-M. Che, Z. He and K.-Y. Wong,
Chem. Eur. J., 2003, 9, 6155–6166.
13 V. M. Miskowski, V. H. Houlding, C.-M. Che and Y. Wang, Inorg.
Chem., 1993, 32, 2518–2524.
14 (a) M. M. Rohmer, A. Veillard and M. H. Wood, Chem. Phys. Lett.,
1974, 29, 466–468; (b) Y. S. Sohn, D. N. Hendrickson and H. B.
Gray, J. Am. Chem. Soc., 1971, 93, 3603–3612; (c) D. R. Cott and
R. S. Becker, J. Chem. Phys., 1961, 35, 516–531.
˚
10.3536(8), b = 14.249(1), c = 14.957(1) A, a = 101.134(6),
◦
¯
b = 99.895(6), c = 95.782(6) , triclinic, space group P1 (no. 2),
3
−3
˚
V = 2112.2(3) A , Z = 2, F(000) = 1012, Dc = 1.612 g cm ,
l = 3.858 mm−1, Tmax/Tmin = 0.462/0.247. Within the h range
of 1.47 and 24.99◦ 23178 reflections were collected, 7356 unique
(Rint = 0.0599), of which 6621 were observed [I > 2r(I)]. At
final convergence, R1 = 0.0285, wR2 = 0.0709 [I > 2r(I)] and
R1 = 0.0328, wR2 = 0.0721 (all data), for 498 parameters and 6
restraints.
15 A. Brockhinke, R. Plessow, P. Dittrich and K. Kohse-Ho¨inghaus,
Appl. Phys. B, 2000, 71, 755–763.
16 J. Huheey, E. Keiter and R. Keiter, Anorganische Chemie, de Gruyter,
Crystallographic data for [Pt(1)(C≡C–Ph)2]·CHCl3. Orange
plate, dimensions 0.45 × 0.43 × 0.11 mm, T = 105(2) K, a =
Berlin, 2nd edn., 1995, p. 214.
17 See, for example: B. Valeur, Molecular Fluorescence, Wiley-VCH,
Weinheim, 2002, ch. 4.4.
◦
3
˚
9.6713(5), b = 25.395(1), c = 18.922(1) A, b = 94.043(5) ,
18 W. L. Fleeman and W. B. Connick, Comments Inorg. Chem., 2002,
˚
monoclinic, space group P21/n (no. 14), V = 4635.8(4) A ,
23, 205–230.
Z = 4, F(000) = 2080, Dc = 1.486 g cm−3, l = 3.239 mm−1,
19 W. B. Connick, D. Geiger and R. Eisenberg, Inorg. Chem., 1999, 38,
3264–3265.
T
max/Tmin = 0.736/0.550. Within the h range of 1.34 and 24.82◦
29016 reflections were collected, 7886 unique (Rint = 0.0908),
of which 5765 were observed [I > 2r(I)]. At final convergence,
R1 = 0.0570, wR2 = 0.1374 [I > 2r(I)] and R1 = 0.0786, wR2 =
0.1479 (all data), for 552 parameters.
20 V. M. Miskowski and V. H. Houlding, Inorg. Chem., 1991, 30, 4446–
4452.
21 See, for example: (a) V. W. W. Yam, K. M. C. Wong and N. Y. Zhu,
J. Am. Chem. Soc., 2002, 124, 6506–6507; (b) H. Kunkely and A.
Vogler, J. Am. Chem. Soc., 1990, 112, 5625–5627.
22 P. S. Braterman, J.-I. Song, F. M. Wimmer, S. Wimmer, W. Kaim, A.
Klein and R. D. Peacock, Inorg. Chem., 1992, 31, 5084–5088.
23 V. Balzani, F. Bolletta and L. Moggi, Spectrosc. Lett., 1978, 11, 525–
535.
CCDC reference numbers 265808 and 265809.
See http://www.rsc.org/suppdata/dt/b5/b503794h/ for cry-
stallographic data in CIF or other electronic format.
24 A. Maciejewski, A. Jaworska-Augustiniak, Z. Szeluga, J. Woytrzak
and J. Karolczak, Chem. Phys. Lett., 1988, 153, 227–232.
25 W. A. Herrmann and C. Zybill, in Synthetic Methods of Organometal-
lic and Inorganic Chemistry (Herrmann/Brauer), ed. W. A. Her-
rmann and A. Salzer, Thieme, Stuttgart, 1996, vol. 1, p. 159.
26 J. Polin, H. Schottenberger, B. Anderson and S. F. Martin, Org.
Synth., 1996, 73, 262–266.
27 R. P. Hsung, C. E. D. Chidsey and L. R. Sita, Organometallics, 1995,
14, 4808–4815.
28 M. Al-Anber, B. Walford, T. Stein and H. Lang, Inorg. Chim. Acta,
2004, 357, 1675–1681.
Acknowledgements
We are grateful to the Volkswagen Foundation for generous
support of this work. K. B. and U. S. thank Prof. Heinrich Lang
(Chemnitz) and Prof. Josef Salbeck (Kassel) for kindly providing
access to electrochemical equipment for cyclic voltammetry and
spectroelectrochemistry, respectively, and are also grateful to Ms
Irina Suske for help with spectroelectrochemical measurements.
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4
2 3 7 3

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29 J. Salbeck, Anal. Chem., 1993, 65, 2169–2173.
30 A. Brockhinke, R. Plessow, K. Kohse-Ho¨inghaus and C. Herrmann,
Phys. Chem. Chem. Phys., 2003, 5, 3498–3506.
31 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991–1024.
32 K. Lotte, R. Plessow and A. Brockhinke, Photochem. Photobiol. Sci.,
2004, 3, 348–359.
34 S. J. Davies, A. P. Ayscough, P. P. Beckett, R. A. Bragg, J. M. Clements,
S. Doel, C. Grew, S. B. Launchbury, G. M. Perkins, L. M. Pratt, H. K.
Smith, Z. M. Spavold, S. W. Thomas, R. S. Todd and M. Whittaker,
Bioorg. Med. Chem. Lett., 2003, 13, 2709–2713.
35 G. M. Sheldrick, SHELXS 97 and SHELXL 97, Programs for crystal
structure solution and refinement, University of Go¨ttingen, Germany,
1997.
33 S. Luca, H. Heise and M. Baldus, Acc. Chem. Res., 2003, 36, 858–
865.
36 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
2 3 7 4
D a l t o n T r a n s . , 2 0 0 5 , 2 3 6 5 – 2 3 7 4