Mesomorphism and luminescence properties of platinum(II) complexes with tris(alkoxy)phenyl-functionalized pyridyl pyrazolate chelates

Article abstract of DOI:10.1002/chem.201000994

A series of new mesomorphic platinum(II) complexes 1-4 bearing pyridyl pyrazolate chelates are reported herein. In this approach, pyridyl azolate ligands have been strategically functionalized with tris(alkoxy)phenyl groups with various alkyl chain length

Full text of DOI:10.1002/chem.201000994

DOI: 10.1002/chem.201000994
Mesomorphism and Luminescence Properties of Platinum(II) Complexes
with TrisACHTUNTRGNEU(GN alkoxy)phenyl-Functionalized Pyridyl Pyrazolate Chelates
Ching-Ting Liao,[a] Hsiu-Hui Chen,[a] Hsiu-Fu Hsu,*[a] Anurach Poloek,[b]
Hsiu-Hsuan Yeh,[b] Yun Chi,*[b] Kang-Wei Wang,[c] Chin-Hung Lai,[c] Gene-Hsiang Lee,[c]
Chun-Wei Shih,[c] and Pi-Tai Chou*[c]
Abstract: A series of new mesomor-
phic platinum(II) complexes 1–4 bear-
ing pyridyl pyrazolate chelates are re-
ported herein. In this approach, pyridyl
azolate ligands have been strategically
monomeric PtII complexes. In stark
contrast, the single-crystal X-ray struc-
ture determination of [PtACTHNUTRGNEN(UG C4pz)2] (1)
thin film at RT, the luminescence of 1–
4 is dominated by a red emission that
spans 630–660 nm, which originates
from the one-dimensional, chainlike
structure with Pt–Pt interaction in the
ground state. Taking complex 4 as a
representative, the emission intensity
and wavelength were significantly de-
creased and blueshifted, respectively,
on heating from RT to 2508C. Further
heating to liquefy the sample alters the
red emission back to the green phos-
phorescence of the monomer. The re-
sults highlight the pivotal role of tris-
shows the formation of a dimeric ag-
gregate with a notable Pt···Pt contact
of 3.258 ꢀ. Upon heating, all PtII com-
plexes 1–4 melted to form columnar su-
prastructures, for which similar intraco-
lumnar Pt···Pt distances of approx. 3.4–
3.5 ꢀ are observed within an excep-
tionally wide temperature range
(>2508C), according to the powder
XRD data. Upon casting into a neat
functionalized with trisACHTUNTRGNEUNG(alkoxy)phenyl
groups with various alkyl chain lengths.
As a result, they are ascribed to a class
of luminescent metallomesogens that
possess distinctive morphological prop-
erties, such as their intermolecular
packing arrangement and their associ-
ated photophysical behavior. In
CH2Cl2, independent of the applied
concentration in the range 10ꢀ6–10ꢀ3 m,
all PtII complexes exhibit bright phos-
phorescence centered at around
520 nm, which is characteristic for
AHCTUNGTRENN(GUN alkoxy)phenyl groups in the structural
Keywords: chelates · luminescence ·
metallomesogens · platinum · supra-
structures
versus luminescence behavior of these
PtII complexes.
Introduction
alized ligands and/or chelates around the central metal
cation, and which afford new materials with numerous tech-
nological applications.[1] In theory, the central metal atom
may dominate the fundamental properties of the metallo-
mesogens. For example, first-row transition-metal ions have
well-studied magnetic properties,[2] while lanthanide metal-
lomesogens are known to show narrow emission lines of
high color purity characteristic of the metal ions, and these
constitute the best studied class of luminescent metallomes-
ogens.[3] In addition, main group elements, such as gallium-
Metallomesogens are a unique class of liquid-crystalline ma-
terials that can be obtained by assembly of various function-
[a] C.-T. Liao, Dr. H.-H. Chen, Prof. H.-F. Hsu
Department of Chemistry, Tamkang University
151, Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137 (R.O.C.)
Fax : (+886)02-26209924
E-mail: hhsu@mail.tku.edu.tw
AHCTUNGTRENNUNG
[b] A. Poloek, H.-H. Yeh, Prof. Y. Chi
Department of Chemistry, National Tsing Hua University
101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan (R.O.C.)
Fax : (+35)711-082
AHCTUNGTRENNUNG
other hand, the coordination complexes of third-row d6 and
d8 transition metals allow easier access to RT phosphores-
cent mesogens[5] due to their enhanced spin–orbit coupling.
Thus, such complexes should provide complementary exam-
ples to the fluorescent metallomesogens already known.[6]
Moreover, d8 transition metals possess planar geometry,
E-mail: ychi@mx.nthu.edu.tw
[c] K.-W. Wang, Dr. C.-H. Lai, G.-H. Lee, C.-W. Shih, Prof. P.-T. Chou
Department of Chemistry, National Taiwan University
No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.)
Fax : (+886)02-23695208
E-mail: chop@ntu.edu.tw
546
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Chem. Eur. J. 2011, 17, 546 – 556

FULL PAPER
which readily gives rise to the formation of disklike mole-
cules, and these allow a favorable stacking arrangement for
mesomorphism.[7] Relevant mesomorphism and luminescent
properties of such systems have been investigated in PtII sys-
tems that contain both multifunctional cyclometalate and b-
diketonate coligands.[8]
One widely utilized strategy in the design of luminescent
metallomesogens is to incorporate functionalized bridging
pyrazoles, which are advantageous in these systems because
of their rigid p framework, their versatile and strong metal–
ligand bonding, as well as their capability to attain a particu-
lar geometry for achieving long-range order in the meso-
phases. In this context, a series of pyrazole-containing met-
allomesogens,[9] as well as the tris
ACTHNUTRGNE(NUG alkoxy)phenyl derivatives
of (pyrazolato)gold complexes have been synthesized; the
gold complexes exhibited remarkable hexagonal columnar
arrangement according to both single-crystal and powder X-
ray structural analysis of the mesophases.[10]
Scheme 1. i) NaH, ethyl picolinate, THF, reflux, 4 h; ii) N2H4, EtOH,
reflux, 2 h, yieldꢁ49%; iii) K2PtCl4, EtOH/H2O, 80 8C, 16 h, yieldꢁ52%.
fppz=5-(2-pyridyl)-3-trifluoromethylpyrazolyl.
Herein, we report on the utilization of pyridyl azolate as a
new class of ligands in the design of luminescent PtII metal-
lomesogens. In sharp contrast to the aforementioned bridg-
ing pyrazolates of gold complexes, which lack the pyridyl
counterpart, and thus are only capable of acting as mono-
dentate or, at most, bridging ligands, the pyridyl azolates
employed in the present studies are known to enhance
bonding interactions with metal ions in a similar way to sali-
cylaldimine, bipyridine, and diketonate chelates.[11] Thus, by
column chromatography and recrystallization. The general
synthetic procedures are akin to those reported for the
parent PtII pyridyl azolate complexes. Scheme 1 also depicts
the structure of the parent [Pt
gens synthesized in this work.
(fppz)2][14] and all PtII meso-
ACHTUNGTRENNUNG
13C NMR spectroscopy was used to determine the carbon
chain length of the alkoxyl substituents. Furthermore, all
1H NMR spectra of these complexes show a unique doublet
at d=10.78–10.67 ppm that can be attributed to the ortho-
hydrogen atom of the 2-pyridyl group. The notable down-
introducing a trisACHTUNGTRENNUNG(alkoxy)phenyl group onto these pyridyl
azolate chelates, it is possible to form square planar PtII
mesogens with tunable morphology. We report herein the
distinctive molecular and/or morphological arrangements of
these complexes in solution, and in the crystalline and
liquid-crystalline phases. We also report their associated
photophysical responses, which are of interest from both
fundamental and applied points of view.
field shifting is an indication of strong interACTHUNTGRNENUGliACHUTNTGERNNUGgand hydrogen
ꢀ
bonding (C H···N(azolate)), which stabilizes the trans, planar
arrangement of pyridyl azolates.[15] The nature of such hy-
ꢀ
drogen bonds is reminiscent of the N H···N bonding that
occurs in metal complexes associated with pyrazole (pzH)
and anionic pyrazolate (pz) ligands, which is expected to
show even greater hydrogen bonding strength, and hence
1
Results and Discussion
downfield-shifted H NMR signals.[14,16]
To further investigate the organizational preferences and
possible intermolecular stacking interactions that take place
between the PtII metal cores, the solid-state structure of the
n-butyl-substituted derivative 1 was established by single-
crystal X-ray diffraction. As shown in Figure 1, complex 1
Scheme 1 depicts the synthetic routes to the isolation of pyr-
idyl pyrazolate PtII complexes with dual 3,4,5-tris-
ACHTUNGTRENNUNG(alkoxy)phenyl substituents. The pyridyl azoles were derived
from 1-(3,4,5-trialkoxyphenyl)ethanone which, in turn, was
generated through a three-step manipulation that involved
alkylation of methyl 3,4,5-trihydroxybenzoate, hydrolysis of
the methyl ester in an excess of KOH, and treatment with a
methylation reagent, MeLi.[12,13] The corresponding pyridyl
pyrazole ligands were then obtained by Claisen condensa-
tion of 1-(3,4,5-trialkoxyphenyl)ethanone with ethyl picoli-
nate, followed by hydrazine hydrate induced cyclization in
ethanol under reflux (Scheme 1). Detailed procedures for
the preparation of all functionalized chelates are given in
the Experimental Section.
Figure 1. Diagram showing the selective atomic labeling of PtII complex 1
The mesogenic PtII complexes 1–4 were obtained by treat-
ment of the chelating pyrazoles with K2PtCl4 (0.5 equiv) at
808C in a 2:1 mixture of ethanol and water for 16 h. Isola-
tion and purification were typically achieved through both
ꢀ
and the inter-molecular stacking interaction; selected bond lengths: Pt
ꢀ
ꢀ
ꢀ
N1=2.026(3), Pt N2=1.955(3), Pt N4=2.028(3), Pt N5=1.994(3),
Pt···Pt=3.258 ꢀ; bond angles: N1-Pt-N2=79.18(13), N1-Pt-N4=
178.75(12), N2-Pt-N5=177.15(13), and N4-Pt-N5=79.08(13)8.
Chem. Eur. J. 2011, 17, 546 – 556
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547

H.-F. Hsu, Y. Chi, P.-Tai Chou et al.
ꢀ
adopts square-planar geometry, with the cis- and trans-N
ꢀ
Pt N bond angles showing only slight deviation from the
ideal values of 90 and 1808, respectively, which is typical for
PtII complexes with chelating pyridyl pyrazolates or azo-
lates.[14,17] The Pt N(az) distances are shorter than those of
ꢀ
ꢀ
Pt N(py), mainly due to the stronger Coulombic interaction
between the anionic pyrazolate fragment and the cationic
PtII metal center.[18] This complex exhibits an antiparallel
stacking arrangement along the z axis of each molecule to
give a dimerlike configuration. Furthermore, each PtII unit
of the dimer shows a 55.28 rotation along the unique Pt–Pt
vector, and exhibits a shortened intermolecular Pt···Pt dis-
tance of 3.258 ꢀ. The next shortest Pt···Pt distance is calcu-
lated to be 8.011 ꢀ within the unit cell. This elongated
Pt···Pt distance then rules out the formation of a one-dimen-
sional, infinite chainlike packing arrangement, which has
been reported for many PtII metal complexes.[19]
Polarizing optical microscopy (POM) and differential
scanning calorimetry (DSC) revealed that all alkoxy PtII de-
rivatives 1–4 show liquid-crystalline properties within very
wide temperature ranges; pertinent data are summarized in
Table 1. Upon heating of the crystalline samples to the crys-
Table 1. Phase behaviors of Pt(II) complexes 1–4.
Observed transition[a]
T [8C] (DH [kJmolꢀ1])[b]
Td [8C][c]
Figure 2. Optical micrographs obtained during the heating process;
a) Colr of 1 at 1608C, b) Colh of 1 at 2578C, and c) Colh of 4 at 1638C.
Samples were sandwiched between glass slides and viewed through
crossed polarizers. Textures recorded during the cooling process are not
shown due to potential ambiguity caused by thermal decomposition.
1
2
3
4
Cryst–Colr–Colh–Isop.d. 125.8 (40.40), 241.6 (1.47), 373.0[d] 403
Cryst–Colh–Isop.d.
Cryst–Colh–Isop.d.
Cryst–Colh–Isop.d.
98.4 (30.29), 342.3[d]
70.5 (23.14), 372.5[d]
67.6 (175.00), 320.3[d]
400
395
346
[a] Cryst=crystalline phase; Colh =hexagonal columnar mesophase;
Colr =rectangular columnar mesophase; Isop.d. =isotropic liquid with par-
tial decomposition. [b] The transition temperatures (T) and enthalpies
(DH) were determined by DSC at 108Cminꢀ1. [c] Td was measured rela-
tive to 5% weight loss. [b] Enthalpies were not determined due to partial
decomposition.
for 4, which possesses the longest dodecoxyl chains. The iso-
tropic points seem to be independent of chain length, and
are all >3208C. The high clearing points and low melting
points result in very wide mesophase temperature ranges of
over 2408C for all PtII analogues.
talline–mesophase transition temperatures, all four com-
plexes melt and exhibit birefringent textures until becoming
isotropically liquid, with minor decomposition at higher
temperatures. Thermal decomposition temperatures Td, rela-
tive to 5% weight loss, are >3408C in all cases. Upon cool-
ing, prior to clearing, a pseudofocal conic fan-shaped texture
typical for columnar mesophases is observed for all four PtII
complexes. The shortest butoxy
The mesophases exhibited by all PtII complexes were fur-
ther characterized by variable-temperature XRD studies,
and the results are summarized in Table 2. The diffracto-
grams of the hexagonal columnar phase of all complexes
showed peaks that can be indexed to not only the (10), (11),
and (20), but also the (21) reflections. In the wide-angle
analogue 1 melts at 1268C and
Table 2. X-ray diffraction data of PtII metal complexes.
reveals a pseudofocal conic fan-
shaped texture with incorporat-
ed striations (see Figure 2a).
Further heating to 2428C gives
a smoother pseudofocal conic
fan-shaped texture (see Fig-
ure 2b), which indicates the for-
mation of an additional meso-
phase. Upon lengthening the
alkoxy chains from C4 to C12,
the melting points decrease
from 1258C for 1 to about 708C
T
d spacing [ꢀ]
Miller index
Phase[a] Lattice
constants
[ꢀ]
[8C] observed
calculated
1
200 22.56 17.98 11.95 11.25 9.98 8.97 11.93 11.28 9.98 8.99
20 11 31 40 02 22
51 60 42 001
10 11 20 21 001
10 11 20 21 30 22
31 alkyl 001
Colr
a=45.12
b=19.60
a=23.29
a=25.37
8.19 7.51 7.38 3.42
300 20.17 11.65 10.09 7.65 3.42
200 21.96 12.66 10.96 8.26 7.32 6.34
6.11 4.50 3.41
250 24.04 13.88 12.03 9.12 8.04 6.98
6.71 4.76 3.44
8.20 7.52 7.40
11.65 10.09 7.62
12.68 10.98 8.30 7.32
6.34 6.09
13.88 12.02 9.09 8.01
6.94 6.67
Colh
Colh
2
3
4
10 11 20 21 30 22
31 alkyl 001
Colh
Colh
a=27.76
a=32.45
200 28.10 16.38 14.11 10.64 9.29 7.99 16.22 14.05 10.62 9.37 10 11 20 21 30 22
7.74 4.72 3.49 8.11 7.79 31 alkyl 001
548
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Mesomorphism and Luminescence Properties of Platinum(II) Complexes
FULL PAPER
regime, a broad peak centered at 4.5 ꢀ, typically ascribed to
interchain correlation, is observed for complexes 2 and 3.
This peak, though very broad, is barely identifiable for 4.
For complex 1, the peak is not detected. The very broad and
weak characteristics of the peak at around 4.5 ꢀ is most
likely due to the aforementioned antiparallel molecular
packing observed in the crystalline sample. A second nar-
rower peak centered at 3.4–3.5 ꢀ is also detected, for which
the distance is close to that of the intracolumnar stacking,
and is close to the p–p stacking distance and/or the Pt···Pt
distance perpendicular to the disc plane; the latter is mea-
sured to be 3.258 ꢀ in the single crystal of 1. As an example,
in the hexagonal columnar phase of 1, the sharp small-angle
peak at 20.17 ꢀ can be indexed to the (10) reflection; the
calculated lattice parameter of 23.29 ꢀ corresponds to the
intercolumnar distance, which is shorter than the molecular
length of 25.85 ꢀ, but longer than the rigid core length of
16.24 ꢀ. In addition to a hexagonal columnar mesophase, a
rectangular columnar mesophase is assigned based on the
XRD pattern at lower temperature (Figure 3). The intraco-
lumnar distance is calculated to be 3.42 ꢀ in both mesophas-
es of 1. It has been reported that shorter intracolumnar disk
to disk distances lead to higher charge-carrier mobilities
along this direction.[20] Because the observed intracolumnar
stacking distances of 3.4–3.5 ꢀ are at the shorter end of the
typical range (3.50–4.00 ꢀ) for semiconducting columnar
mesogens,[21] high charge-carrier mobility along columns can
be expected. Additional modulation at 6.8–7.0 ꢀ, double
distance of 3.4–3.5 ꢀ, could not be clearly resolved, which
may be hidden under other signals within this regime
(Figure 4). Thus, the proposed antiparallel dimeric molecu-
lar packing cannot be unambiguously proven at this stage.
Figure 5 depicts the absorption and emission spectra of 1–
4 in CH2Cl2 at 298 K, while pertinent photophysical data are
summarized in Table 3. As is the case for most PtII com-
plexes that possess cyclometalating chelates,[22] the absorp-
tion spectra of all complexes can be ascribed to several sep-
arate domains in terms of the magnitude of absorption coef-
ficients, together with molecular orbital analysis based on
time-dependent DFT (TDDFT) calculations (see the Exper-
imental Section and discussion below). The intense absorp-
tion bands of 1–4 in the higher-energy region (<300 nm),
with extinction coefficients of the order of about
104 mꢀ1 cmꢀ1, most probably originate from the ligand-cen-
tered 1p–p* azolate!pyridine transitions. This assignment
can be unambiguously supported by the similar transition
seen for the free anionic ligands.[23] The lower-energy ab-
Figure 3. Powder XRD patterns of 1: Colr phase at 2008C (top) and Colh
phase at 3008C (bottom).
Figure 4. Colh powder XRD patterns of 2 at 2008C (top), 3 at 2508C
(middle), and 4 at 2008C (bottom).
Chem. Eur. J. 2011, 17, 546 – 556
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549

H.-F. Hsu, Y. Chi, P.-Tai Chou et al.
p*ACHTNUTRGNEUNG(pyridyl)] mixed with a certain degree of pyrazolate (p)
to pyridine (p*) charge-transfer transition (see below).[17]
In degassed CH2Cl2 at RT, as shown in Figure 5a and
Table 3, all PtII complexes 1–4 show intense green lumines-
cence with peak wavelength located at about 520 nm, and
with emission quantum yield of 0.60 for 4 to near unity for
complexes 1–3. The emission is strongly quenched by O2,
which confirms its phosphorescence origin. Note that the
phosphorescence yields are higher than those reported for
other PtII complexes.[24] The high emission yields are plausi-
bly due to the higher degree of electron delocalization in
the excited state, which indicates that these complexes are
less coupled to other nonradiative deactivating modes. This
was recently confirmed by varying the lengths of alkoxyl
chains in the mesomorphic PtII complexes with both cyclo-
metalate and b-diketonate coligands.[8] Alternatively, these
types of square-planar complexes may exhibit an enhanced
Pt(dp)–Pt(dp) interaction, which may give rise to a possible
dimer or excimer formation in solution. Nevertheless, for all
complexes 1–4, independent of the applied concentration
(10ꢀ6–10ꢀ3 m), a unique phosphorescence band at about
520 nm was observed in CH2Cl2, which is a mirror image of
the lower-lying absorption profile. Thus, the emissions of 1–
4 in solution clearly originate from the monomer. Further
support for this spectral assignment was provided by our
computational results (see the Experimental Section for de-
tails). Table 4 lists the calculated energy levels and orbital
transition analyses of the representative complexes 1 and 4,
while Figure 6 depicts the corresponding frontier orbitals.
The results clearly indicate that the lowest lying S0!S1 tran-
sition for complexes 1 and 4 is largely contributed by the
HOMO!LUMO transition, in which the electron density is
Figure 5. a) UV/Vis absorption (dashed line) and emission spectra (solid
~
&
*
^
line) of complexes 1 ( ), 2 ( ), 3 ( ), and 4 ( ) in CH2Cl2. Note that the
normalized emission spectra were acquired in degassed CH2Cl2 and were
found to be superimposable. b) UV/Vis absorption and emission spectra
Table 4. Calculated energy levels and orbital transition analyses of PtII
complexes 1 and 4.
~
&
*
^
of complexes 1 ( ), 2 ( ), 3 ( ), and 4 ( ) in neat film at RT.
State
lcalcd [nm]
f
Assignment
1
4
T1
S1
T1
S1
546.0
500.0
544.8
498.9
0
HOMO!LUMO (+91%)
HOMO!LUMO (+95%)
HOMO!LUMO (+91%)
HOMO!LUMO (+94%)
0.0244
0
0.0244
sorption bands with relatively small extinction coefficients
around 380–500 nm (ca. 1000mꢀ1 cmꢀ1) can then be assigned
to the metal–ligand charge-transfer band (1MLCT) [dp(Pt)!
mainly located at PtII metal,
pyrazolate, and partially at the
phenyl ring for the HOMO,
while it is mainly distributed at
the pyridyl fragments for the
LUMO. Similar data (not
shown here) are obtained for
complexes 2 and 3. According-
ly, the lowest-lying excitation
should be ascribed to an MLCT
mixed with ligand (pyrazolate+
phenyl ring) to ligand (pyri-
dine) charge transfer in both
singlet and triplet manifolds.
Table 3. [a] Colh =hexagonal columnar mesophase; Colr =rectangular columnar mesophaseTable 3
Photophysical properties of PtII metal complexes recorded in CH2Cl2 at RT and neat film.
Abs. lmax[nm] (e, [Mꢀ1 cmꢀ1])
lem [nm]
tobs [ns)]
Fem
kr
1[a]
274 (12700), 302 (10600),
340 (5700), 428 (679), 450 (640)
522
5413
ꢂ1
1.8ꢂ105
1[b]
2[a]
638
524
145
5678
0.24
ꢂ1
1.7ꢂ106
274 (10300), 302 (8600),
340 (4600), 426 (530), 450 (520)
2[b]
3[a]
648
523
47
5793
0.10
ꢂ1
2.5ꢂ106
1.8ꢂ105
275 (10100), 302 (8500),
340 (4500), 428 (540), 450 (530)
3[b]
4[a]
656
523
47
5710
0.16
0.60
3.4ꢂ105
1.0ꢂ105
275 (13800), 301 (11500),
340 (6200), 427 (700), 449 (700)
4[b]
660
52
0.13
2.5ꢂ106
[a] in CH2Cl2. [b] neat film.
550
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Chem. Eur. J. 2011, 17, 546 – 556

Mesomorphism and Luminescence Properties of Platinum(II) Complexes
FULL PAPER
solid film may also exhibit a similar stacking arrangement
along the z axis of each molecule, giving a one-dimensional
chainlike configuration with a short intermolecular Pt···Pt
distance; for example, a distance of 3.258 ꢀ in 1, as shown
in the single-crystal structure (see Figure 1). Direct support
of this is provided by the luminescence of these complexes
in the solid thin film. As shown in Figure 5b, the lowest ab-
sorption band in CH2Cl2 solution (430–450 nm), is redshifted
to >500 nm for 1–4 after casting into a thin solid film. Upon
excitation, a unique, much longer emission band at 630–
660 nm is observed (specifically, 638 nm for 1, 648 nm for 2,
656 nm for 3, and 660 nm for 4; see Figure 5b and Table 3),
which is in sharp contrast to the monomer emission at
around 520 nm for the PtII complexes in CH2Cl2. The mirror
image between absorption and emission in the neat thin film
indicates that the emission could not be ascribed to an exci-
mer emission, but rather, possibly originates from a chain-
like configuration, in which each adjacent Pt should have
appreciable Pt–Pt interaction in the ground state. As a
result, the >500 nm absorption band observed in the thin
solid film may reasonably be assigned to the dz2(s*) (M2)!
s(p*) (py) metal/metal-to-ligand charge-transfer (MMLCT)
transition mixed, to a certain degree, with dz2(s*)!p(s)
metal-to-metal charge-transfer (MMCT) transitions. Like-
wise, the emission should originate from the corresponding
transitions in the triplet manifold.[26] Note that Kui et al.,[27]
after examining a series of diplatinum complexes with Pt–Pt
distances ranging from 2.998 to 3.432 ꢀ, have drawn the
conclusion of dimer formation. The Pt–Pt distance in 1
(3.26 ꢀ), ascertained by X-ray single-crystal analysis, fits
well in this range.
Figure 6. Selected frontier molecular orbitals for PtII complexes 1 and 4.
More importantly, the wavelengths of the T1–S0 transitions
are calculated to be 546 and 544 nm for 1 and 4, respectively
(see Table 4), which is close to the luminescence peak at
about 520 nm. This reaffirms the monomeric nature of the
PtII complexes in CH2Cl2.
The monomer emission of 1–4 in solution is in stark con-
trast to the formation of the dimer in the single crystal (see
above). It is well established that the planar arrangement of
PtII framework tends to favor intermolecular p–p stacking
interactions, which facilitate dimer or excimer formation.[25]
On the contrary, for an antiparallel arrangement, as shown
in the single crystal of 1, for example, the tris
(alkoxy)phenyl
Moreover, unlike the nearly identical peak wavelength
(ca. 520 nm) that is independent of the alkoxyl chain length
for the monomer phosphorescence, the emission peak wave-
length in the thin solid film is redshifted appreciably upon
increasing the alkoxyl chain length from 1 (638 nm) to 4
(660 nm). Evidenced by the absorption spectrum shown in
Figure 5b), the longest absorption band, and hence the
smallest emission gap for 4, are consistent with the decreas-
ing Pt–Pt distance along the metal chain or between each of
the diplatinum units with the increasing alkoxyl chain
length, and hence the enhancement of interaction (see
above). The quantum yield of excimer emission, which
ranges from 0.1 to 0.24 in the neat film (see Table 3), is
somewhat lower than that (0.6–1.0) of the monomer phos-
phorescence in solution. This is possibly due to quenching
associated with triple–triplet annihilation.
groups may occupy spatial positions away from each other,
conversely raising steric hindrance to destabilize dimeriza-
tion. This, together with the high solubility of 1–4 in CH2Cl2
upon introducing trisACTHNUGRTENUNG(alkoxy)phenyl groups, may account
for the prohibition of dimer/excimer formation in solution.
On the other hand, as revealed by the single crystal of 1 and
the structure drawing in Scheme 2, complexes 1–4 in the
To further explore the relationship between photophysical
properties and morphology, we carried out a temperature-
dependent luminescent study with complex 4 as a prototype.
In this approach, a confocal microscope with an incorporat-
ed adjustable heating plate was used to fine-tune the tem-
perature from 25 to 3208C (ꢃ0.58C). The spectral profile,
shown in Figure 7, reveals a temperature-dependent excimer
emission in view of both peak wavelength and intensity
from RT to about 3008C, despite the expected phase transi-
tion at around 708C. Upon heating from RT to 2508C, the
Scheme 2. The core structure of the antisymmetric chainlike architecture
of all PtII complexes after casting into a thin film; nitrogen atoms are
omitted for clarity.
Chem. Eur. J. 2011, 17, 546 – 556
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551

H.-F. Hsu, Y. Chi, P.-Tai Chou et al.
Figure 7. Temperature-dependent emission spectra of a neat thin film of
PtII complex 4.
emission-peak wavelength gradually blueshifted, and de-
creased in intensity. Interestingly, upon further heating to
liquefy the sample (>2508C), the emission peak wavelength
was then blueshifted to 520 nm, which is similar to that of
the monomer phosphorescence observed in CH2Cl2. The
continuous spectral changes upon heating indicate that the
luminescence properties are not directly related to phase
changes. Rather, the results can be rationalized by the ther-
mal perturbation that disrupts the antiparallel excimer
stacking, and hence causes the variation in Pt–Pt interac-
tions. The decrease of emission intensity on heating seems
to be mainly due to the increase in thermally activated radi-
ationless processes.
Figure 8. Temperature-dependent emission images of PtII complex 4 with
mercury lamp illumination. The compound was heated from RT to
2508C over 1 h and then recooled to RT. The last two photographs show
the restoration of excimeric emission on recooling, although the emission
intensity is not completely restored.
However, a certain amount of decomposition on heating
cannot be eliminated. This view is supported by the lumines-
cence imaging shown in Figure 8, which reveals the changes
of the luminescence as a function of temperature from 30 to
2508C. Note that the emission at 220–2508C is too weak to
show visualized intensity. However, their corresponding
spectral profiles were still clearly resolved in Figure 7. As
shown by the contrast of luminescence imaging the sample
did not fully recover, which indicates a certain degree of de-
composition during the heating–cooling process. Finally, the
drastic decrease in the 520 nm emission (300 to 3208C, not
shown here) in the melt may also be partly due to O2
quenching, as purging N2 increases the emission intensity
threefold. Thorough degassing, however, is not possible at
this stage based on the current experimental setup.
varying the alkyl chain length. All complexes 1–4 form col-
umnar suprastructures within exceptionally wide tempera-
ture ranges (>2508C). Their melting temperature ap-
proaches RT as the chain length increases, which should
allow facile processability in future device fabrication. In
CH2Cl2 only green phosphorescence (ꢂ520 nm) due to the
monomer is observed for 1–4, with high quantum yields of
0.6–1.0, whereas a large redshift is observed for the emission
at 630–660 nm in the thin solid film; this originates from the
chainlike arrangement with significant Pt–Pt interactions in
the ground state. Taking the thin film of 4 as representative,
the emission shows drastic temperature dependence in both
spectral profile and relative intensity. Because all four com-
plexes possess intracolumnar stacking distances of 3.4–3.5 ꢀ,
which are at the shorter end of the typical range (3.50–
4.00 ꢀ) for semiconducting columnar mesogens, high
charge-carrier mobility along columns can thus be expected.
As for future perspectives, the low emission quantum yield
of these PtII complexes (0.1–0.25) in their thin films may
hamper their application in organic light-emitting diodes
(OLEDs). On the other hand, OLED devices are normally
prepared by doping the host matrix materials with the metal
complexes. Therefore, our PtII complexes can be expected to
have decent emission efficiencies. Of particular interest is
Conclusion
A series of new mesomorphic platinum(II) complexes 1–4,
which bear pyridyl pyrazolate chelates functionalized by
trisACHTUNGTRENNUNG(alkoxy)phenyl groups with various alkyl chain lengths,
have been synthesized. Complexes 1–4 were found to be lu-
minescent metallomesogens, in which the distinctive liquid-
crystal properties, such as the stability of the mesogenic
phases and/or photophysical behavior can be fine-tuned by
552
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 546 – 556

Mesomorphism and Luminescence Properties of Platinum(II) Complexes
FULL PAPER
Synthesis of 3,4,5-tridodecoxybenzoic acid: Potassium hydroxide (1.63 g,
30 mmol) was added to a solution of methyl 3,4,5-tridodecoxybenzoate
(10 g, 15 mmol) in ethanol (95%, 200 mL). The mixture was heated at
reflux for 4 h and then cooled to RT. The solution was diluted with de-
ionized water (1 L) and acidified by addition of HCl (1n) to pH 1. The
precipitate was then filtered, washed with deionized water (50 mLꢂ2)
and diethyl ether (30 mL), and dried under vacuum; yield: 97%. Other
derivatives, such as 3,4,5-trioctoxybenzoic acid (98%), 3,4,5-trihexoxy-
benzoic acid (87%), and 3,4,5-tributoxybenzoic acid (93%) were synthe-
sized by using similar procedures.
Selected spectral data for methyl 3,4,5-tributoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.85 (s, 3H;
-OCH3), 1.80–1.66 (m, 6H; -CH2-), 1.52–1.45 (m, 6H; -CH2-), 0.93 ppm
(t, 9H; -CH3).
Selected spectral data for methyl 3,4,5-trihexoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.86 (s, 3H;
-OCH3), 1.80–1.72 (m, 6H; -CH2-), 1.47–1.31 (m, 18H; -(CH2)3-),
0.89 ppm (t, 9H; -CH3).
Selected spectral data for methyl 3,4,5-trioctoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.88 (s, 3H;
-OCH3), 1.84–1.71 (m, 6H; -CH2-), 1.47–1.27 (m, 30H; -(CH2)5-),
0.87 ppm (t, 9H; -CH3).
the generation of polarized emission for the corresponding
columnar mesogens, which is expected to offer superior ad-
vantages for their use in OLEDs as well as in back light
sources. Further research on this issue is currently in prog-
ress.
Experimental Section
General: All reactions were performed under nitrogen. Solvents were
distilled from appropriate drying agents prior to use. Commercially avail-
able reagents were used without further purification. Methyl 3,4,5-
trialkoxybenzoate, 3,4,5-trialkoxybenzoic acid and
1-(3,4,5-tris-
ACHTUNGTRENNUNG(alkoxy)phenyl)ethanone were synthesized according to previously re-
ported procedures.[12,13] All reactions were monitored by TLC with pre-
coated silica gel plates (Merck, 0.20 mm with fluorescent indicator
UV254). Compounds were visualized with UV irradiation at 254 or
365 nm. Flash column chromatography was carried out by using silica gel
obtained from Merck (230–400 mesh). Mass spectra were obtained on a
JEOL SX-102 instrument operating in electron impact (EI) or fast atom
1
bombardment (FAB) mode. H and 13C NMR spectra were recorded on a
Selected spectral data for methyl 3,4,5-tridodecoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.88 (s, 3H;
-OCH3), 1.81–1.77 (m, 6H; -CH2-), 1.45–1.24 (m, 54H; -(CH2)9-),
0.87 ppm (t, 9H; -CH3).
Bruker-400 or INOVA-500 instrument; chemical shifts are quoted with
respect to the internal standard, tetramethylsilane, for 1H and 13C NMR
data. Elemental analysis was carried out with a Heraeus CHN-O Rapid
Elementary Analyzer. DSC measurements were made on a Perkin–
Synthesis of 3,4,5-tridodecoxybenzoic acid: Potassium hydroxide (1.63 g,
30 mmol) was added to a solution of methyl 3,4,5-tridodecoxybenzoate
(10 g, 15 mmol) in ethanol (95%, 200 mL). The mixture was heated at
reflux for 4 h and then cooled to RT. The solution was diluted with de-
ionized water (1 L) and acidified by the addition of HCl (1n) to pH 1.
The precipitate was then filtered, washed with deionized water (50 mLꢂ
2) and diethyl ether (30 mL), and dried under vacuum; yield: 97%.
Other derivatives, such as 3,4,5-trioctoxybenzoic acid (98%), 3,4,5-trihex-
oxybenzoic acid (87%), and 3,4,5-tributoxybenzoic acid (93%) were syn-
thesized by using similar procedures.
Elmer Pyris1 DSC with heating and cooling rates of 5 and 108C minꢀ1
.
Thermogravimetric analysis (TGA) was measured on a Perkin–Elmer
Pyris 1 TGA with a heating rate of 108C minꢀ1. XRD data were collected
on the wiggler beam line BL17 A of the National Synchrotron Radiation
Research Center (NSRRC), Taiwan, by using a triangular bent SiACTHNUTRGNE(NUG 111)
monochromator and a wavelength of 1.3271 ꢀ. The sample in a 1 mm ca-
pillary was mounted on the Huber 5020 diffractometer. The BL17A
beamline is equipped with an air stream heater and the temperature con-
troller is programmable by personal computer with a proportional-inte-
gral-derivative feedback system.
Selected spectral data for 3,4,5-tributoxybenzoic acid: 1H NMR (CDCl3):
d=7.31 (s, 2H; ArH), 4.02 (m, 6H; -OCH2-), 1.81–1.68 (m, 6H; -CH2-),
1.49–1.45 (m, 6H; -CH2-), 0.88 ppm (m, 9H; -CH3).
Synthesis of methyl 3,4,5-tridodecoxybenzoate: Potassium carbonate
(45 g, 330 mmol) was added to a solution of methyl 3,4,5-trihydroxyben-
zoate (10 g, 54 mmol) in DMF (150 mL), which was then stirred at 608C
for 2 h. 1-bromododecane (41 mL, 170 mmol) was then slowly added and
the solution was heated at 608C for 8 h. The solution was filtered to
remove solids. Evaporation of the solvent gave a gummy solid, which was
then dissolved in ethyl acetate. The resulting solution was washed with
HCl (0.2 N; 30 mL) and deionized water (50 mLꢂ3), dried over anhy-
drous Na2SO4, filtered, and concentrated to dryness under vacuum. The
product was purified by column chromatography with an elution mixture
of ethyl acetate and hexane (1:5), followed by recrystallization from ace-
tone; yield: 82%. Methyl 3,4,5-trioctoxybenzoate (84%), methyl 3,4,5-tri-
hexoxybenzoate (87%) and methyl 3,4,5-tributoxybenzoate (87%) were
synthesized by using similar procedures.
Selected spectral data for methyl 3,4,5-tributoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.85 (s, 3H;
-OCH3), 1.80–1.66 (m, 6H; -CH2-), 1.52–1.45 (m, 6H; -CH2-), 0.93 ppm
(t, 9H; -CH3).
Selected spectral data for methyl 3,4,5-trihexoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.86 (s, 3H;
-OCH3), 1.80–1.72 (m, 6H; -CH2-), 1.47–1.31 (m, 18H; -(CH2)3-),
0.89 ppm (t, 9H; -CH3).
1
Selected spectral data for 3,4,5-trihexoxybenzoic acid: H NMR (CDCl3):
d=7.24 (s, 2H; ArH), 3.96 (m, 6H; -OCH2-), 1.79–1.71 (m, 6H; -CH2-),
1.44–1.29 (m, 18H; -(CH2)3-), 0.88 ppm (t, 9H; -CH3).
Selected spectral data for 3,4,5-trioctoxybenzoic acid: 1H NMR (CDCl3):
d=7.29 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 1.82–1.71 (m, 6H; -CH2-),
1.46–1.26 (m, 30H; -(CH2)5-), 0.86 ppm (t, 9H; -CH3).
Selected spectral data for 3,4,5-tridodecoxybenzoic acid: 1H NMR
(CDCl3): d=7.29 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 1.81–1.71 (m, 6H;
-CH2-), 1.45–1.24 (m, 54H; -(CH2)9-), 0.86 ppm (t, 9H; -CH3).
Synthesis of 1-(3,4,5-tridodecoxyphenyl)ethanone: Methyl lithium (2.2m
in diethyl ether, 10.3 mL, 22.7 mmol) was added dropwise to a solution
of 3,4,5-tridodecoxybenzoic acid (4 g, 5.93 mmol) in anhydrous THF
(50 mL) at 08C. The mixture was stirred at 08C for 1 h, warmed to RT,
and stirred for a further 3 h. The solvent was then removed and the resi-
due was dissolved in excess CH2Cl2. This solution was washed with HCl
(0.2 N, 30 mL) and deionized water (30 mLꢂ3), dried over anhydrous
Na2SO4, filtered, and dried under vacuum. The product was further puri-
fied by column chromatography with an elution mixture of ethyl acetate
and hexane (1:5), followed by recrystallization from acetone; yield: 76%.
The derivatives 1-(3,4,5-trioctoxyphenyl)ethanone (86%), 1-(3,4,5-trihex-
oxyphenyl)ethanone (82%) and 1-(3,4,5-tributoxyphenyl)ethanone
(84%) were synthesized by using similar procedures.
Selected spectral data for methyl 3,4,5-trioctoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.88 (s, 3H;
-OCH3), 1.84–1.71 (m, 6H; -CH2-), 1.47–1.27 (m, 30H; -(CH2)5-),
0.87 ppm (t, 9H; -CH3).
Selected spectral data for 1-(3,4,5-tributoxyphenyl)ethanone: 1H NMR
(CDCl3): d=7.15 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 2.53 (s, 3H;
-COCH3), 1.81–1.73 (m, 6H; -CH2-), 1.53–1.44 (m, 6H; -CH2-), 0.94 ppm
(m, 9H; -CH3).
Selected spectral data for methyl 3,4,5-tridodecoxybenzoate: 1H NMR
(CDCl3): d=7.24 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 3.88 (s, 3H;
-OCH3), 1.81–1.77 (m, 6H; -CH2-), 1.45–1.24 (m, 54H; -(CH2)9-),
0.87 ppm (t, 9H; -CH3).
Chem. Eur. J. 2011, 17, 546 – 556
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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553

H.-F. Hsu, Y. Chi, P.-Tai Chou et al.
Selected spectral data for 1-(3,4,5-trihexoxyphenyl)ethanone: 1H NMR
(CDCl3): d=7.15 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 2.53 (s, 3H;
-COCH3), 1.83–1.76 (m, 6H; -CH2-), 1.46–1.23 (m, 18H; -(CH2)3-),
0.87 ppm (t, 9H; -CH3).
Selected spectral data for 1-(3,4,5-trioctoxyphenyl)ethanone: 1H NMR
(CDCl3): d=7.15 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 2.54 (s, 3H;
-COCH3), 1.83–1.70 (m, 6H; -CH2-), 1.45–1.26 (m, 30H; -(CH2)5-),
0.86 ppm (t, 9H; -CH3).
Selected spectral data for 1-(3,4,5-tridodecoxyphenyl)ethanone: 1H NMR
(CDCl3): d=7.15 (s, 2H; ArH), 4.00 (m, 6H; -OCH2-), 2.54 (s, 3H;
-COCH3), 1.83–1.76 (m, 6H; -CH2-), 1.54–1.24 (m, 54H; -(CH2)9-),
0.86 ppm (t, 9H; -CH3).
-CH-), 4.06 (m, 12H; -OCH2-), 2.15–1.72 (m, 12H; -CH2-), 1.56–1.23 (m,
12H; -(CH2)), 0.98 ppm (m, 18H; -CH3). 13C NMR (100 MHz, CDCl3,
294 K): d=154.3, 153.1, 151.4, 150.4, 149.7, 138.2, 137.4, 130.4, 120.2,
117.7, 104.1, 99.7, 73.2, 68.9, 32.4, 31.6, 19.4, 19.3, 13.9 ppm; MS (FAB):
m/z: 1068 [M]+; elemental analysis calcd (%) for C52H68N6O6Pt: C 58.47;
H 6.42; N 7.87; found: C 58.78; H 6.56; N 7.59.
Spectral data for [PtACTHNUTRGNEUNG
(C6pz)2]: MS 1H NMR (400 MHz, CDCl3, 294 K):
d=10.75 (d, 2H; -CH-), 7.79 (t, 2H; -CH-), 7.11 (m, 6H; -CH-), 6.80 (s,
2H; -CH-), 4.04 (m, 12H; -OCH2-), 1.87–1.76 (m, 12H; -CH2-), 1.54–1.34
(m, 36H; -(CH2)3-), 0.91 ppm (m, 18H; -CH3). 13C NMR (100 MHz,
CDCl3, 294 K): d=154.3, 153.1, 151.4, 150.4, 149.7, 138.2, 137.4, 130.4,
120.2, 117.7, 104.1, 99.7, 73.6, 69.2, 31.8, 31.7, 30.4, 29.6, 25.9, 25.9, 22.7,
14.1, 14.1 ppm; (FAB): m/z: 1236 [M]+; elemental analysis calcd (%) for
C64H92N6O6Pt: C 62.16; H 7.50; N 6.80; found: C 62.02; H 7.46; N 6.92.
Synthesis
of
3-(3,4,5-tridodecoxyphenyl)-5-(2-pyridyl)
pyrazole
(C12pzH): A suspension of 1-(3,4,5-tridodecoxyphenyl)ethanone (1.8 g,
2.67 mmol) and NaH (0.13 g, 5.42 mmol) was stirred in anhydrous THF
for 1 h at RT. After addition of ethyl picolinate (0.37 g, 2.43 mmol) the
solution was heated at reflux for 4 h, and the unreacted NaH was
quenched with methanol (10 mL). The mixture was concentrated under
vacuum and the residue dissolved in ethyl acetate. This solution was then
washed with HCl (0.2n; 30 mL) and deionized water (50 mLꢂ3), dried
over anhydrous Na2SO4, filtered, and concentrated to afford the diketo-
nate solid.
Spectral data for [PtACTHNUTRGNEUNG
(C8pz)2]: 1H NMR (400 MHz, CDCl3, 294 K): d=
10.67 (d, 2H; -CH-), 7.71 (t, 2H; -CH-), 7.46 (d, 2H; -CH-), 7.06 (m,
6H; -CH-), 6.74 (s, 2H; -CH-), 4.05 (m, 12H; -OCH2-), 1.90–1.76 (m,
12H; -CH2-), 1.57–1.29 (m, 60H; -(CH2)5-), 0.88 ppm (m, 18H; -CH3);
13C NMR (100 MHz, CDCl3, 294 K): d=154.6, 153.2, 151.8, 150.6, 150.3,
138.6, 137.6, 130.3, 120.6, 117.9, 104.3, 100.0, 73.6, 69.3, 31.9, 31.9, 30.4,
29.6, 29.58, 29.42, 29.37, 26.3, 26.2, 22.7, 14.1 ppm; MS (FAB): m/z: 1404
[M+1]+; elemental analysis calcd (%) for C76H116N6O6Pt: C 64.98; H
8.32; N 5.98; found: C 65.08; H 8.47; N 6.23.
Without further purification, this diketonate solid was added to a solution
of hydrazine monohydrate (1.22 g, 24.4 mmol) in ethanol (30 mL) and
heated at reflux for 2 h. The solution was concentrated under vacuum
and the residue was dissolved in excess ethyl acetate. The organic solu-
tion was washed with water (50 mLꢂ3), dried over anhydrous Na2SO4,
filtered, and concentrated to dryness. The product C12pzH was purified
by column chromatography with an elution mixture of ethyl acetate and
hexane (1:5), followed by recrystallization from acetone at RT; yield:
63%. Other pyrazole ligands with distinctive alkyl chain lengths; namely,
C8pzH (49%), C6pzH (66%) and C4pzH (52%), were synthesized by
using similar procedures.
Spectral data for [PtACTHNUTRGNEUNG
(C12pz)2]: 1H NMR (400 MHz, CDCl3, 294 K): d=
10.78 (d, 2H; -CH-), 7.84 (t, 2H; -CH-), 7.60 (d, 2H; -CH-), 7.19 (t, 2H;
-CH-), 7.13 (s, 4H; -CH-), 6.84 (s, 2H; -CH-), 4.04 (m, 12H; -OCH2-),
1.87–1.74 (m, 12H; -CH2-), 1.54–1.16 (m, 108H; -(CH2)9-), 0.86 ppm (m,
18H; -CH3); 13C NMR (100 MHz, CDCl3, 294 K): d=154.4, 153.1, 151.5,
150.5, 149.9, 138.3, 137.5, 130.3, 120.4, 117.8, 104.2, 99.8, 73.6, 69.3, 31.9,
30.4, 29.8, 29.7, 29.6, 29.4, 26.3, 26.2, 22.7, 14.1 ppm; MS (FAB): m/z:
1741 [Mꢀ1]+; elemental analysis calcd (%) for C100H164N6O6Pt: C 68.97;
H 9.49; N 4.83; found: C 68.92; H 9.07; N 5.20.
Spectroscopic and dynamic measurements: Steady-state absorption and
emission spectra were recorded on Hitachi (U-3310) and Edinburgh
(FS920) spectrophotometers, respectively. Both the wavelength-depen-
dent excitation and the emission response were calibrated. A configura-
tion of front-face excitation was used to measure the emission of the
solid samples, in which the cell compartment was made by assembling
two edge-polished quartz plates with various Teflon spacers. Lifetime
studies were performed with an Edinburgh FL 900 photon-counting
system with a hydrogen-filled or nitrogen lamp as the excitation source.
Data were analyzed by using a nonlinear least-squares procedure in com-
bination with an iterative convolution method. The emission decays were
analyzed by the sum of the exponential functions, which allowed partial
removal of the instrument time broadening and consequently rendered a
temporal resolution of about 200 ps. To determine the photoluminescence
quantum yield in solution, samples were degassed by three freeze–pump–
thaw cycles with vigorous stirring. The solid thin film was prepared by
dissolving the corresponding samples in toluene, followed by a spin coat-
ing onto the glass substrate.
Selected spectral data for 3-(3,4,5-tributoxyphenyl)-5-(2-pyridyl) pyrazole
(C4pzH): 1H NMR (400 MHz, CDCl3, 294 K): d=8.62 (d, 1H; -CH-),
7.75 (m, 2H; -CH-), 7.24 (t, 1H; -CH-), 7.02 (s, 2H; -CH-), 6.98 (s, 1H;
-CH-), 4.01 (m, 6H; -OCH2-), 1.83–1.68 (m, 6H; -CH2-), 1.54–1.45 (m,
6H; -CH2-), 0.95 ppm (m, 9H; -CH3); MS (EI, 70 eV): m/z: 437 [M]+.
Selected spectral data for 3-(3,4,5-trihexoxyphenyl)-5-(2-pyridyl) pyrazole
(C6pzH): 1H NMR (400 MHz, CDCl3, 294 K): d=8.62 (d, 1H; -CH-),
7.73 (m, 2H; -CH-), 7.23 (t, 1H; -CH-), 7.01 (s, 2H; -CH-), 6.98 (s, 1H;
-CH-), 4.03 (m, 6H; -OCH2-), 1.81–1.72 (m, 6H; -CH2-), 1.46–1.21 (m,
18H; -(CH2)3-), 0.91 ppm (m, 9H; -CH3). MS (EI, 70 eV): m/z calcd: 521
[M]+; found: 521;
Selected spectral data for 3-(3,4,5-trioctoxyphenyl)-5-(2-pyridyl) pyrazole
(C8pzH): 1H NMR (400 MHz, CDCl3, 294 K): d=8.63 (d, 1H; -CH-),
7.71 (m, 2H; -CH-), 7.22 (t, 1H; -CH-), 7.00 (s, 2H; -CH-), 6.97 (s, 1H;
-CH-), 4.00 (m, 6H; -OCH2-), 1.80–1.70 (m, 6H; -(CH2)-), 1.46–1.26 (m,
30H; -(CH2)5-), 0.86 ppm (m, 9H; -CH3); MS (EI, 70 eV): m/z: 605 [M]+.
Selected spectral data for 3-(3,4,5-tridodecoxyphenyl)-5-(2-pyridyl) pyra-
zole (C12pzH): 1H NMR (400 MHz, CDCl3, 294 K): d=8.61 (d, 1H;
-CH-), 7.72 (m, 2H; -CH-), 7.24 (t, 1H; -CH-), 7.01 (s, 2H; -CH-), 6.96
(s, 1H; -CH-), 4.00 (m, 6H; -OCH2-), 1.84–1.72 (m, 6H; -CH2-), 1.46–
1.24 (m, 54H; -(CH2)9-), 0.86 ppm (t, 9H; -CH3); MS (EI, 70 eV): m/z:
774 [M]+.
Microphotoluminescence studies with variable-temperature measure-
ments were performed by combining the confocal microscope (a-SNOM,
Witec), a liquid-nitrogen cooled spectrometer (TriVista 555 in single
spectrograph mode, Princeton Instruments), and a variable-temperature
heating stage (THMS600, Linkam Scientific). A 406 nm diode laser
(GaN laser, Oxxius) was used as an excitation source for the spectral
analysis, while a mercury lamp (HBO 50, Carl Zeiss) with UV band-pass
filter (Hg01–365, Semrock) was inserted and used for photographs.
Synthesis of [PtACHTUNGTRENNUNG(C4pz)2]: A mixture of K2PtCl4 (137 mg, 0.33 mmol),
C4pzH (317 mg, 0.72 mmol), ethanol (18 mL), and water (6 mL) was
heated at 808C for 16 h. After cooling to RT, the solvent was allowed to
evaporate under vacuum, and the residue was purified by column chro-
matography with an elution mixture of ethyl acetate and hexane (1:5),
followed by recrystallization from ethyl acetate; yield: 54%. Single crys-
XRD studies: Single-crystal XRD data were collected with a Bruker
SMART Apex CCD diffractometer by using (MoKa
) radiation (l=
0.71073 ꢀ). The data collection was executed by using the SMART pro-
gram. Cell refinement and data reduction were performed with the
SAINT program. The structure was determined by using the SHELXTL/
PC program and refined with full-matrix least squares.
tals of [Pt
and methanol at RT. Other PtII metal complexes with formula [Pt-
(C6pz)2] (2, 56%), [Pt(C8pz)2] (3, 52%), and [Pt(C12pz)2] (4, 66%) were
synthesized under similar conditions.
Spectral data for [Pt
(C4pz)2]: 1H NMR (400 MHz, CDCl3, 294 K): d=
10.78 (d, 2H; -CH-), 7.83 (t, 2H; -CH-), 7.15 (m, 6H; -CH-), 6.82 (s, 2H;
ACHTUNGTRENNUNG(C4pz)2] (1) were obtained from a layered solution of CH2Cl2
A
R
ACHTUNGTRENNUNG
Selected crystal data for [PtACTHNUTRGNEUNG(C4pz)2]: C52H68N6O6Pt, M=1068.21, mono-
clinic; space group C 2/c; T=150(2) K; a=20.8487(7), b=22.8303(8), c=
ACHTUNGTRENNUNG
20.3255(7) ꢀ; b=93.8498, V=9652.8(6) ꢀ3; Z=8; 1calcd =1.470 mgmꢀ3; F-
AHCTUNGTERGUN(NN 000)=4384; lACHTUNGTRENNUNG ; crystal size=0.40ꢂ
(MoKa)=0.7107 ꢀ; m=2.962 mmꢀ1
554
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 546 – 556

Mesomorphism and Luminescence Properties of Platinum(II) Complexes
FULL PAPER
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Received: April 17, 2010
Published online: November 9, 2010
556
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