Synthesis, characterization, and the photochromic, luminescence, metallogelation and liquid-crystalline properties of multifunctional platinum(II) bipyridine complexes

Article abstract of DOI:10.1002/chem.201003738

A series of multifunctional platinum(II) bipyridine complexes were designed, synthesized, and characterized by ¹H NMR, fast atom bombardment mass spectrometry (FAB-MS), and elemental analysis. Their electrochemical and photophysical properties

Full text of DOI:10.1002/chem.201003738

DOI: 10.1002/chem.201003738
Synthesis, Characterization, and the Photochromic, Luminescence,
Metallogelation and Liquid-Crystalline Properties of Multifunctional
Platinum(II) Bipyridine Complexes
Yongguang Li,[a] Anthony Yiu-Yan Tam,[b] Keith Man-Chung Wong,*[b] Wen Li,[a]
Lixin Wu,*[a] and Vivian Wing-Wah Yam*[a, b, c]
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Chem. Eur. J. 2011, 17, 8048 – 8059

FULL PAPER
Abstract: A series of multifunctional
platinum(II) bipyridine complexes
were designed, synthesized, and char-
organic solvents. In contrast to typical
thermotropic organogels and metallo-
gels, one of the complexes could form
metallogels in dodecane and is very
stable towards external stimuli. The
photochromic activation parameters
for the bleaching reaction of a repre-
sentative spironaphthoxazine-contain-
ing complex in a dodecane gel were de-
termined through kinetic studies at var-
ious temperatures. Lamellar liquid-
crystalline behavior was also observed
in one of the complexes, and the
liquid-crystalline properties were stud-
ied by thermogravimetry analysis
(TGA), polarized optical microscopy
(POM), differential scanning calorime-
try (DSC), variable-temperature X-ray
diffraction (XRD), and variable-tem-
perature infrared (IR) spectroscopy.
1
acterized by H NMR, fast atom bom-
bardment mass spectrometry (FAB-
MS), and elemental analysis. Their
electrochemical and photophysical
properties were investigated. The pho-
tochromic properties of the spironaph-
thoxazine-containing complexes were
also studied. Some of these complexes
were shown to be capable of forming
stable thermoreversible metallogels in
Keywords: liquid crystals · lumines-
cence · metallogels · photochrom-
ism · platinum · spironaphthoxazine
Introduction
and optical recording since the 1980s.[6m,n] Similar to spiro-
pyrans, the photochromic behavior of spirooxazines has
been attributed to the photochemical cleavage of the spiro
carbon–oxygen bond in SO forms that led to the planariza-
tion of the two originally orthogonal heterocycles to form
merocyanine (MC) structures, giving rise to an increase in
the extent of p-conjugation (Scheme 1). Much work has fo-
Square-planar platinum(II) polypyridine complexes repre-
sent a unique class of transition-metal complexes due to
their rich spectroscopic properties and propensity to form
aggregate species through Pt···Pt and p-p stacking interac-
tions in the solid and solution states.[1] Apart from the early
works on the spectroscopic properties of dichloroplati-
ACHTUNGTRENNUNG
num(II) polypyridine complexes[1a,2] and their dicyano ana-
logues,[1c,2b,3] the luminescent behavior of [Pt
ACTHNUTRGENNU(G phen)ACHTUNTGREN(NUNG C
ꢀ
CPh)2] (phen=1,10-phenanthroline, Ph=phenyl) has also
been reported.[4] Since then, this class of square-planar plati-
num(II) complexes has received much attention due to their
rich spectroscopic properties in both solid and solution
states.[5] While there are extensive studies on the electro-
chemical, photophysical, and photochemical properties of
this class of platinum(II) complexes, studies of their multi-
functional properties are rare.[2d,e] Only quite recently have
platinum(II) bipyridine complexes exhibiting photochro-
mic[2d] and liquid-crystalline properties been reported.[2e]
Amongst various families that exhibit photochromic be-
havior, spirooxazines (SO) represent an interesting class of
photochromic materials.[6] Owing to their high fatigue resist-
ance and excellent photostability, their photochromic behav-
ior has been extensively investigated for potential applica-
tion in the development of materials such as sunglass lenses
Scheme 1. Photoinduced ring-opening reaction of spironaphthoxazine.
cused on organic systems, in which high-energy UV excita-
tion is required for the intramolecular photosensitization of
the photochromic spirooxazine moiety. It was only quite re-
cently that examples of transition-metal complexes involving
photosensitization of the photochromic behavior through
excitation of lower-energy metal-to-ligand charge transfer
(MLCT) bands in the visible region were reported.[6e,h,i,p–s]
In the past two decades, there has been an increasing in-
terest in the study of new functional and stimuli-responsive
low-molecular weight organogelators, because of their
unique features and the increasing potential of the applica-
tions as soft matter in smart materials.[7–9] Early examples in-
clude the pioneering works of Weiss in anthracene- and an-
thraquinone-based gelators.[7a–c,f] It was found that the gela-
tors could form stable organogels at low concentrations (ca.
1% by weight) solely through weak van der Waals interac-
tions. Molecules exhibiting photochromic behavior have also
been employed in the design of functional organogelators,
including those of azobenzenes,[8a,10] diarylethenes,[11,12] spi-
ropyrans,[13] and 2H-chromenes.[14] Recently, we reported a
series of photochromic spironaphthoxazine-containing orga-
nogelators that is responsive to heat and acid.[15]
[a] Y. Li, Dr. W. Li, Prof. L. Wu, Prof. V. W.-W. Yam
State Key Laboratory of Supramolecular Structure and Materials
and College of Chemistry, Jilin University
Changchun 130012 (P.R. China)
[b] Dr. A. Y.-Y. Tam, Dr. K. M.-C. Wong, Prof. V. W.-W. Yam
Institute of Molecular Functional Materials and
Department of Chemistry, The University of Hong Kong
Pokfulam Road (Hong Kong)
E-mail: wwyam@hku.hk
[c] Prof. V. W.-W. Yam
Areas of Excellence Scheme
University Grants Committee (Hong Kong)
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V. Wing-Wah Yam, K. Man-Chung Wong et al.
Parallel to the growing interest in the development of or-
ganogels, there has also been an immense interest in the in-
vestigation of transition-metal complexes as supramolecular
gels,[16,17] for example, AuI,[17a] PtII,[17c,h,j,18] CuI,[17b] and ReI
complexes.[17i] Recently, alkynylplatinum(II) complexes with
a terdentate N^N^N ligand were demonstrated to be capa-
ble of forming stable metallogels and were shown to display
drastic color and emission changes during the gel-to-sol
phase transition.[18a–c] These remarkable spectroscopic
changes are believed to originate from the modulation of
metal-to-metal-to-ligand charge transfer (MMLCT) transi-
tion resulting from aggregation-deaggregation processes of
the square-planar platinum(II) complexes at different tem-
peratures.
Besides the development of organogels and metallogels,
liquid crystals have been investigated in supramolecular
chemistry due to their huge potentials for application in a
range of scientific and technological areas.[19] Phosphores-
cent metal complexes of AgI,[20] AuI,[21] PtII,[2e,22] and
PdII[2e,22b,23] have been shown to exhibit diversified liquid-
crystalline properties. Organometallic palladium(II) and
platinum(II) with 2-phenylpyridine (C^N) ligands represent
important classes of metallomesogens since rational modifi-
cation of the structures would give rise to different phases
of liquid crystals, including smectic phase, columnar meso-
phases, and nematic columnar mesophases.[22b,c]
Despite the development of photochromism, metallogela-
tion and metallomesogens, studies of platinum(II) bipyridine
complexes with multifunctional properties, such as photo-
chromic[2d] and liquid-crystalline properties,[2e] are rare and
often unexplored. Herein, we report the synthesis, electro-
chemistry, photophysical and photochemical properties of a
series of multifunctional luminescent platinum(II) bipyridine
complexes. Three of the complexes (2, 4, and 10) are found
to exhibit stable thermotropic metallogels in organic sol-
vents. The photochromic activation parameters for the
bleaching reaction of the spironaphthoxazine-containing
complex 10 in a dodecane gel were determined through ki-
netic studies at various temperatures. In addition, complex 2
was found to show liquid-crystalline behavior. Their proper-
ties were studied by thermogravimetric analysis (TGA), po-
larized optical microscopy (POM), differential scanning cal-
orimetry (DSC), variable-temperature X-ray diffraction
(XRD), and variable-temperature infrared (IR) spectrosco-
py.
alkyne ligands in the presence of a catalytic amount of cop-
per(I) iodide and diisopropylamine in dichloromethane. The
identities of all the newly synthesized platinum(II) bipyri-
dine complexes were confirmed by H NMR spectroscopy,
fast atom bombardment mass spectrometry (FAB-MS) and
satisfactory elemental analyses.
1
Electrochemistry: In general, the cyclic voltammograms of
the platinum(II) bipyridine complexes in dichloromethane
in the presence of nBu4NPF6 (0.1m) displayed one quasi-re-
versible reduction couple at about ꢁ1.29 to ꢁ1.39 V and an
irreversible anodic wave at approximately +0.80 to +1.30 V
versus SCE. The electrochemical data of all of the com-
plexes are summarized in Table 1. According to previous
electrochemical studies on platinum(II) bipyridine complex-
es,[5a,b] the quasi-reversible reduction couples originate from
the reduction of the bipyridine ligand. Apart from the
quasi-reversible reduction couples, additional irreversible re-
duction waves were also observed at ꢁ0.90 to ꢁ1.27 V
versus SCE in complexes 2–4, which contain ester groups. In
view of the observation of a similar irreversible reduction
Results and Discussion
Synthesis and characterization: Complexes 1 and 2 were
synthesized according to a modification of a previously re-
ported method for [Pt
using [Pt(dmso)2Cl2] as the starting material. Due to the
(bpy)Cl2][2] (bpy=2,2’-bipyridine)
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
lack of solubilizing groups in 1, it was found to be only
fairly soluble in chloroform and dichloromethane. Com-
plexes 3–10 were prepared by the reaction of the corre-
sponding dichloroplatinum(II) bipyridine precursors and
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Platinum(II) Bipyridine Complexes
FULL PAPER
Table 1. Photophysical and electrochemical data of platinum(II) bipyridine complexes.
Medium
(T [K])
Absorption
Emission
fem
Oxidation Reduction
[a]
lmax [nm] (emax [dm3 molꢁ1 cmꢁ1])
lem [nm]
(to [ms])
Epa [V]
E [V]
N
vs. SCE[b,c] vs. SCE[b]
[e]
[f]
1
2
3
4
5
6
7
8
9
CH2Cl2 (298) 281 (41910), 310 (17285), 324 (18410), 393 (5555)
solid (298)
572[d]
–
–
–
ꢁ1.35[g]
[i]
–
–
–
[i]
solid (77)
glass[j] (77)
[i]
[e]
[f]
CH2Cl2 (298) 283 (29910), 309 sh (7965), 322 (5425), 394 (2900)
solid (298)
550[d]
–
–
ꢁ1.22,[h] ꢁ1.30[g]
ꢁ1.29,[h] ꢁ1.38,[g]
ꢁ0.95,[h] ꢁ1.30[g]
ꢁ1.33[g]
[i]
–
–
–
[i]
solid (77)
glass[j] (77)
[i]
CH2Cl2 (298) 285 (56870), 402 (7850)
solid (298)
570 (0.72)
650
646
518
519 (0.61)
618
0.2
0.98[k]
solid (77)
glass[j] (77)
CH2Cl2 (298) 275 (31635), 309 sh (12330), 322 (8520), 371 (3460)
solid (298)
6.7ꢁ10ꢁ3 0.85[k]
4.0ꢁ10ꢁ3 1.04[k]
3.0ꢁ10ꢁ3 0.92[k]
2.3ꢁ10ꢁ3 1.13[k]
9.4ꢁ10ꢁ2
solid (77)
620
502
glass[j] (77)
CH2Cl2 (298) 286 (59140), 400 (9095)
solid (298)
582 (0.32)
[i]
-
-
-
[i]
solid (77)
glass[j] (77)
[i]
CH2Cl2 (298) 280 (44520), 346 sh (10175), 397 (5300), 442 sh (3,410)
solid (298)
619 (4ꢁ10ꢁ3
)
ꢁ1.29[g]
[i]
–
–
–
[i]
solid (77)
glass[j] (77)
[i]
CH2Cl2 (298) 291 (50165), 347 sh (8790), 391 (7540)
solid (298)
551 (0.78)
ꢁ1.30
[i]
–
–
–
[i]
solid (77)
glass[j] (77)
[i]
CH2Cl2 (298) 289 (70630), 348 sh (13025), 403 (8710)
solid (298)
612 (2.3ꢁ10ꢁ3
)
)
)
682
584
583
solid (77)
glass[j] (77)
CH2Cl2 (298) 289 (63965), 345 sh (13540), 403 (8805)
605 (1.5ꢁ10ꢁ3
9.4ꢁ10ꢁ2 1.03[k]
1.2ꢁ10ꢁ3 1.22[k]
ꢁ1.33
ꢁ1.39
solid (298)
solid (77)
glass[j] (77)
672
592
589
10 CH2Cl2 (298) 287 (36705), 310 sh (18900), 322 (18723), 347 sh (12125), 398 sh (6910) 609 (7.8ꢁ10ꢁ3
solid (298)
solid (77)
glass[j] (77)
660
656
[i]
–
[a] The luminescence quantum yield, measured at room temperature using [RuACHTNUTRGNEUNG(bpy)3]Cl2 as a standard. [b] In a dichloromethane solution with 0.1m
nBu4NPF6 (TBAH) as the supporting electrolyte at room temperature; scan rate 200 mVsꢁ1. [c] Epa refers to the anodic peak potential for the irreversi-
ble oxidation waves. [d] The emission was too weak to be measured. [e] The luminescence quantum yield was not obtained because the emission was too
weak to be measured with certainty. [f] An oxidation wave was not observed within the solvent window. [g] Quasi-reversible reduction wave; E1/2
=
(Epa +Epc)/2; Epa and Epc are the anodic peak and cathodic peak potentials. [h] Irreversible reduction wave. [i] Nonemissive. [j] In ethanol/methanol/di-
chloromethane=4:1:1. [k] Irreversible oxidation wave.
ꢀ
ꢀ
ꢀ
wave at ꢁ1.08 V versus SCE for the free bipyridine ligand
with an ester group in addition to the quasi-reversible bipyr-
idine reduction couple at ꢁ1.38 V versus SCE, the irreversi-
ble reduction wave is tentatively assigned to the reduction
of the ester group on the bipyridine or alkynyl ligands.[24]
Owing to the sensitivity of the potential of the oxidation
waves towards the electronic effect of the alkynyl ligands,
the irreversible oxidation is attributed to the oxidation of
PtII to PtIII, with substantial mixing of the alkynyl ligand
characters. This assignment was further supported by the ob-
servation that the ease of oxidation increases in the order of
7 (+1.13 V)<5 (+1.04 V)<6 (+0.92 V), which is in line
with the order of the electron-donating ability of the alkynyl
ligands, C CC6H4OMe-p (6)>C CPh (5)>C CC6H4CF3-p
(7).
Photophysical properties: The electronic absorption spectra
of complexes 1–10 in dichloromethane at 298 K showed in-
tense absorption bands at 275–348 nm and moderately in-
tense absorption bands at 371–442 nm. The photophysical
data of 1–10 are summarized in Table 1 and the electronic
absorption spectra of complexes 5–8 and 10 are shown in
Figure 1 (top). With reference to previous studies on plati-
num(II) bipyridine complexes[5] and related spironaphthoxa-
zine-containing transition-metal complexes,[6e,h,j] the high-
energy intense absorption bands are assigned to the intraACHTUNGTRENNUNGli-
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V. Wing-Wah Yam, K. Man-Chung Wong et al.
gands to complex 2 to yield complex 3, the emission was
found to be enhanced with the observation of a redshift in
energy. It is believed that the substitution of weak-field
chloro ligands by strong s-donating phenylalkynyl ligands
would lead to a larger d-d orbital splitting and thereby
raises the energy of the non-emissive ligand field excited
state. As a result, the 3MLCT/3LLCT emission was en-
hanced. It is interesting to note that the photoluminescence
quantum yield of 3 (fem =0.2) is much higher than that of 5
(fem =0.004). The substantial decrease in the photolumines-
cence quantum yield from 3 to 5 is attributed to an efficient
3
intramolecular energy transfer from the emissive MLCT ex-
cited state to the spironaphthoxazine moiety for the photo-
chromic process, rendering the photoluminescence from the
3MLCT excited state less efficient.[6h,r] However, one should
be aware that the assignments of electronic transitions be-
tween metal and/or ligand localized orbitals and singlet and
triplet states are only rough approximations because of the
possible extensive orbital mixing and spin-orbit coupling in
these complexes.
Figure 1. Top: UV/Vis absorption spectra of complexes 5–8 and 10 in a
solution of dichloromethane at room temperature. Bottom: Normalized
emission spectra of complexes 5–7 in degassed dichloromethane at 298 K.
Photochromic properties: On prolonged irradiation at l=
350 nm, complexes 1 and 5–10 in dichloromethane changed
color from yellow to blue. This was attributed to a photo-
chromic reaction, in which the relatively weak spiro carbon–
oxygen bond is photocleaved, resulting in the formation of
the MC complex (Scheme 1). Interestingly, prolonged exci-
tation into the absorption band of the admixture of singlet
MLCT and singlet LLCT (1MLCT/1LLCT) transition at l=
405 nm also leads to similar photochromic reactions. This
could possibly be ascribed to the fact that the
1MLCT/1LLCT excited state would undergo facile intersys-
A
naphthoxazine moieties and alkynyl ligands, whereas the
low-energy, moderately intense absorption bands are tenta-
tively assigned as an admixture of metal-to-ligand charge
transfer (MLCT) [dp(Pt)!p*
ACHTUNGTNER(NUNG bpy)] and ligand-to-ligand
ꢀ
charge transfer (LLCT) [p
(C C)!p*
ACHTUNGERTN(NUNG bpy)] transitions. The
MLCT/LLCT assignment was further supported by the ob-
servation that the low-energy absorption bands showed an
energy trend of 7 (391 nm)>5 (400 nm)>6 (442 nm), since
the electron-donating methoxy substituent on the arylalkyn-
ꢀ
3
tem crossing into the MLCT/3LLCT state, because of the
heavy-metal effect exerted by the platinum(II) center, caus-
ing an intramolecular photosensitization reaction of the spi-
ronaphthoxazine.[6e] On prolonged excitation at l=405 nm
in dichloromethane, a new absorption band at 600 nm ap-
peared. The lower absorption energy of the MC form rela-
tive to the SO form is ascribed to the planarization of the
molecule in the MC form, resulting in an increase in the
extent of p conjugation throughout the spironaphthoxazine
moiety.
yl ligand in complex 6 would raise the dp(Pt) and pACTHUNTGRNEUNG(C C)
orbitals in energy, which would result in a lowering of the
MLCT/LLCT energy.[15a,b,18b] Complexes 8 and 9 showed es-
sentially identical UV/Vis absorption patterns with similar
molar extinction coefficients, suggesting that the chain
length of the alkoxy groups on the arylalkynyl ligand has no
significant effect on the MLCT absorption.
Upon excitation at lꢂ400 nm, all of the complexes
except 1, 2, and 5–7 showed luminescence properties in solu-
tion, the solid state, and the glass state. In dichloromethane
at room temperature, all of the complexes showed a broad
emission band at about 519–619 nm. The emission spectra of
5–7 are shown in Figure 1 (bottom). The emission energies
of the complexes were found to be sensitive to the nature of
the substituents on the arylalkynyl ligand. Complex 6, which
contains an electron-donating methoxy substituent on the
arylalkynyl ligand, showed the lowest emission energy, while
complex 7 with most electron-poor trifluoromethyl substitu-
ent showed the highest emission energy. This trend is consis-
tent with an assignment of triplet 3MLCT excited state
Gelation properties: All of the complexes were tested for
gelation properties in various organic solvents. It was found
that 2 and 4 could form metallogels in decalin (a mixture of
trans and cis isomers) at 108C with their respective critical
gelation concentrations (c.g.c.) of 1.2ꢁ10ꢁ2 m and 3.1ꢁ
10ꢁ2 m, and complex 10 with cholesteryl moieties could form
stable gels in aliphatic solvents like heptane, octane, decane,
as well as dodecane at room temperature. It is interesting to
note that the metallogel of 10 in dodecane (2.4ꢁ10ꢁ3 m) was
found to be stable even at 1178C, which is close to the de-
composition temperature of complex 10. Also, the metallo-
gel of 10 in dodecane was not influenced even after ultra-
sonication for about 10 min. This may possibly be attributed
to strong interactions between the gelator molecules, result-
3
mixed with triplet LLCT character (3MLCT/3LLCT). It is
worth noting that upon introduction of phenylalkynyl li-
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Platinum(II) Bipyridine Complexes
FULL PAPER
ing in a tight entrapment of the solvent molecules inside the
gel network even at high temperatures. Since only complex
10 showed stable metallogelation behavior at room tempera-
ture, detailed characterization of the metallogel was only
carried out for 10 in dodecane, and the metallogel of 10 in
dodecane under visible light and under UV illumination are
shown in Figures 2a and b, respectively. Upon prolonged ir-
radiation at l=405 nm at 158C, the yellow gel turned blue
(Figure 2c).
While no significant spectral change was observed in the
variable-temperature electronic absorption study of the met-
allogel of 10 in dodecane, the corresponding emission study
at variable temperatures showed a slight blueshift in the
emission energy upon increasing the temperature (Figure 3,
top left). This could possibly be attributed to the influence
of the chromophoric interaction on going from the gel form
to the sol form at elevated temperatures.
Figure 3. Top left: Normalized emission spectra of the dodecane gel of 10
upon increasing the temperature from 108C to 708C. Top right: Time-de-
pendent UV/Vis absorption spectra of the dodecane gel of 10 (3.6ꢁ
10ꢁ3 moldmꢁ3) at 158C upon excitation at 405 nm. Bottom left: The ab-
sorption at 600 nm versus time. Bottom right: Normalized emission spec-
tra of the dodecane gel of 10 upon prolonged irradiation at 405 nm at 20
and 308C.
Upon prolonged excitation into the 1MLCT/1LLCT ab-
sorption band (l=405 nm) at 158C, the dodecane gel of
complex 10 changed from yellow to blue (Figure 2c) with
the growth of a new absorption band at about 600 nm
(Figure 3, top right). Similar to the results observed in di-
chloromethane, this was attributed to the photochromic re-
action of the spironaphthoxazine moiety, which was sensi-
3
tized by the MLCT/3LLCT excited state.[6e] The MC form
generated was found to be thermally unstable and under-
went rapid thermal bleaching to the SO form (vide infra), as
indicated by the disappearance of the 600 nm absorption
band after light irradiation even at 158C (Figure 3, bottom
left) In addition, the prolonged excitation would also influ-
ence the emission energy. In the dark, the metallogel of 10
in dodecane showed an emission band at 620 nm at 208C,
Figure 2. Photographs of the gel form of 10 (3.2ꢁ10ꢁ3 m) in dodecane a)
under visible light and b) under 365 nm irradiation. c) Optical image of
the dodecane gel of 10 at 158C showing the color change from yellow to
blue upon prolonged excitation (indicated by circle). d) SEM image of
the xerogel of 10 prepared from the dodecane gel of 10.
3
which is tentatively assigned as originating from the MLCT
3
The morphology of the dodecane gel of complex 10 was
studied by scanning electron microscopy (SEM), and the
SEM image of the xerogel is shown in Figure 2d. The xero-
gel showed a network of fibrous structures upon self-assem-
bly in the gel phase. The fibers underwent further cross-link-
ing to form three-dimensional fibrous networks to entrap
the solvent molecules.
of the SO form, with some mixing from the LLCT state.
1
Upon prolonged excitation into the MLCT/1LLCT absorp-
tion band, a new emission band at 664 nm was observed
with diminishment of the 620 nm emission band at 208C.
Upon increasing the temperature from 208C to 308C, the
664 nm emission disappeared with the revival of the emis-
sion at 620 nm (Figure 3, bottom right). At first glance, the
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V. Wing-Wah Yam, K. Man-Chung Wong et al.
664 nm band was thought to be due to the emission of the
MC form. Closer scrutiny indicated a rather unusual unsym-
metrical band shape, suggesting that such a redshift in the
emission energy upon irradiation may be a result of self-ab-
sorption effects arising from the growth of the MC absorp-
tion upon irradiation, because there is a significant overlap
between the absorption of the MC form and the
3MLCT/3LLCT emission. This was further supported by the
observation that a concentrated solution of 10 in dichloro-
methane showed similar redshifts in emission energy upon
irradiation, which became less obvious upon dilution. In ad-
3
dition, the revival of the MLCT/3LLCT emission at 620 nm
upon increasing the temperature to 308C could be attributed
to the thermal bleaching reaction of the photomerocyanine
form to afford the thermally stable SO form, in which self-
absorption effects became negligible.
The kinetics for the bleaching reaction of the photochro-
mic process of complex 10 in a dodecane gel after excitation
at 405 nm were studied by UV/Vis absorption spectroscopy
at various temperatures. The thermal backward reaction re-
sulted in the fading of the blue color and a decay of the
low-energy absorption band (Figure 3, top right). By moni-
toring the absorbance at 600 nm (Figure 3, bottom left), the
kinetics for the bleaching reactions were measured and the
activation parameters were determined using the Eyring and
Arrhenius equations. The Eyring and Arrhenius plots are
shown in Figure 4 and the activation parameters were deter-
Figure 5. Polarized optical micrograph (ꢁ200 magnification) observed for
complex 2 at 170 (top) and at 508C (bottom).
Figure 4. Eyring (left) and Arrhenius plots (right) for the thermal bleach-
ing reaction of the dodecane gel of 10.
mined. An activation energy (Ea) of 35.86 kJmolꢁ1, activa-
¼
tion enthalpy (DH ) of 32.85 kJmolꢁ1, and activation entro-
¼
py (DS ) of ꢁ158.60 Jmolꢁ1 Kꢁ1 were obtained for the
bleaching reaction of the metallogel of 10 in dodecane.
Liquid-crystalline behavior: Since only complex 2 showed
liquid-crystalline properties (Figure 5), it was subjected to
the thermogravimetric analysis (TGA), polarized optical mi-
croscopy (POM), differential scanning calorimetry (DSC),
variable-temperature X-ray diffraction (XRD) as well as
variable-temperature infrared (IR) spectroscopy. Based on
the TGA curve of complex 2 in the solid state (Figure 6, top
left), it was found to be thermally stable up to a temperature
close to 2008C. The POM study showed that complex 2 ex-
hibited two types of mesomorphic phases at 508C and
1708C upon cooling from the isotropic state, as shown in
Figure 6. TGA thermograms (top left) and DSC heating and cooling
curves (top right) of 2. Bottom left: Variable-temperature XRD patterns
of 2 in the temperature range from room temperature to 1708C. Inset
shows the magnified XRD patterns at high-angle regions. Bottom right:
IR spectra of 2 at 508C and 1708C.
8054
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Chem. Eur. J. 2011, 17, 8048 – 8059

Platinum(II) Bipyridine Complexes
FULL PAPER
Figure 5. The formation of these two phases was further
confirmed by DSC studies that revealed the presence of two
phase transitions in addition to the transformation into the
isotropic phase (Figure 6, top right). The data are summar-
ized in Table 2. The enthalpy change from the isotropic state
vigorous motion and the intercalations would become less
significant. As a result, the hydrophobic-hydrophobic and
the p-stacking interactions would become less significant.
Variable-temperature IR spectroscopy was also employed
to investigate the molecular packing of the liquid crystal
phase. The IR data for the second heating cycle are shown
in Figure 6 (bottom right). The stretching frequencies of the
CH2 antisymmetric and symmetric bands showed small
shifts from 2923 and 2852 cmꢁ1 at 508C to 2925 and
2854 cmꢁ1 at 1708C, respectively. It is known that the fre-
quencies of the CH2 antisymmetric and symmetric stretches
are sensitive to the conformation of the alkyl chains. Low
wavenumbers (2915–2920 and 2846–2850 cmꢁ1) are charac-
teristic of a highly trans conformation of the alkyl chains,
whereas their shifts to higher frequencies (2924–2928 and
2854–2856 cmꢁ1) are indicative of an increase in gauche con-
formers and an increase in the disorder of the alkyl chain
conformation. Therefore, it is believed that the long chain
has no significant influence on the packing of the molecules.
This result suggested that the actual molecular length is
smaller than that obtained by calculation (l=32 ꢂ).
Table 2. Optical and thermal data for 2.
Transition[a]
T [8C]
DH [kJmolꢁ1
]
C!SmC
19.3
111.9
168.6
165.6
89.2
34.26
4.85
1.32
ꢁ1.38
ꢁ1.40
ꢁ33.06
SmC!SmA
SmA!I
I!SmA
SmA!SmC
SmC!C
16.4
[a] C=crystal; SmA=smectic-A; SmC=smectic-C; I=isotropic liquid.
to the first mesomorphic phase during the cooling process
(DH=1.38 kJmolꢁ1) was relatively low, which suggested
that the first mesomorphic phase was poorly ordered and a
lamellar phase with two-dimensional positional order might
probably be formed.
In order to investigate the molecular packing structure of
the liquid crystal phase, variable-temperature XRD experi-
ments were performed. Upon cooling from the isotropic
state, a growth of elongated germs, so-called smectic bꢀton-
nets, was observed at 1708C. A commonly observed smectic-
C (SmC) appeared at lower temperatures, as revealed by
the broken texture (Figure 5, bottom), which resulted from
the cooling of the smectic-A (SmA) to give SmC.[25b,d] Ac-
cording to the XRD pattern (Figure 6, bottom left), the very
intense peak at the low-angle diffraction of 2q=2.48, corre-
sponding to the layer spacing,[25] and the diffuse halo at 2q
ꢃ208 are associated with the liquid-like two-dimensional or-
ganization of the mesogenic groups within the layer, sugges-
tive of the formation of the SmA phase. The XRD data at
1708C displayed one peak at 2.48 (2q, corresponding to a d
spacing of 37 ꢂ) in the higher angle region of the XRD pat-
tern, which lies between the length of a single molecule of 2
(l=32 ꢂ) and the length of two independent molecules
(2l=64 ꢂ). It is known that the director n in the SmA phase
and the optical axis are perpendicular to the smectic layer
plane. It can be suggested that a double layer is organized in
an intertwined fashion of the alkyl chains (2l/d=1.7). Two
broad peaks were also observed at the higher-angle region
of the XRD pattern (d spacing=4.5 and 3.5 ꢂ) at lower
temperatures, which could be attributed to the alkyl chain
halo and the p-stacking distance, respectively. Upon increas-
ing the temperature, the peak at low angle was shifted from
2.7 to 2.48 with diminishment of the intensity, and the broad
peaks in the high-angle region were found to gradually dis-
appear. These suggest that the order of the alkyl chains in-
creased and the hydrophobic–hydrophobic interactions be-
tween the long chains and the p-stacking interactions
became stronger at lower temperatures. This observation
could be readily rationalized by the fact that upon increas-
ing the temperature, the alkyl chains would undergo rapid
Conclusion
In summary, a series of multifunctional photochromic spiro-
naphthoxazine-containing platinum(II) bipyridine complexes
was designed, synthesized and characterized. Their electro-
chemical, photophysical, photochromic, gelation and liquid-
crystalline properties were investigated. Complexes 2, 4, and
10 were shown to be capable of forming stable thermorever-
sible metallogels in organic solvents. The activation parame-
ters for the bleaching reaction of the complex 10 in a dodec-
ane gel were determined by kinetic studies at various tem-
peratures. Complex 2 was shown to display lamellar liquid-
crystalline behavior, which was characterized by TGA,
DSC, variable-temperature XRD, and variable-temperature
IR studies.
Experimental Section
Materials and reagents: 4-(1,3,3-Trimethylspiroindolinenaphthoxazine-9’-
oxymethyl)-4’-methyl-2,2’-bipyridine,[6h,j] 3,4,5-tri(dodecyloxy)phenylace-
[2]
tylene, 3,4,5-tri(hexadecyloxy)-acetylene,[18c] and Pt
thesized as described previously.
ACHTUNGTERN(NGNU bpy)Cl2 were syn-
Syntheses
Synthesis of (4’-methyl-2,2’-bipyridin-4-yl)methyl-3,4,5-tris(hexadecyloxy)-
benzoate: 4-(Bromomethyl)-4’-methyl-2,2’-bipyridine (222 mg,
0.84 mmol) was added to a mixture of 3,4,5-tris(hexadecyloxy)benzoic
acid (600 mg, 0.72 mmol) and K2CO3 (165 mg, 1.2 mmol) in DMF
(70 mL), under a nitrogen atmosphere. The reaction mixture was heated
to reflux overnight. The reaction mixture was poured into deionized
water, and a white precipitate appeared. After filtration, the white pre-
cipitate was washed with water (100 mL) and then methanol (100 mL) to
1
yield the pure product. Yield: 302 mg, 41%. H NMR (500 MHz, CDCl3,
298 K, relative to Me4Si): d=0.88 (t, J=6.8 Hz, 9H; CH3), 1.26–1.30 (m,
72H; CH2), 1.45–1.46 (m, 6H; CH2), 1.72–1.81 (m, 6H; CH2), 2.45 (s,
3H; CH3 on bpy), 3.97–4.01 (m, 6H; OCH2), 5.43 (s, 2H; OCH2 on bpy),
7.15 (d, J=5.3 Hz, bipyridine proton at 5’-position), 7.32 (s, 2H; C6H2),
Chem. Eur. J. 2011, 17, 8048 – 8059
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8055

V. Wing-Wah Yam, K. Man-Chung Wong et al.
7.35 (d, J=5.0 Hz, bipyridine proton at 5-position), 8.25 (s, bipyridine
proton at 3’-position), 8.46 (s, bipyridine proton at 3-position), 8.53 (d,
J=5.3 Hz, bipyridine proton at 6’-position), 8.68 ppm (d, J=5.0 Hz, bi-
pyridine proton at 6-position).
9.52 ppm (d, J=5.2 Hz, bipyridine proton at 6-position); positive FAB-
MS: m/z: 1293 [M+H]+; elemental analysis calcd (%) for
C67H112Cl2N2O5Pt·CH2Cl2: C 59.40, H 8.36, N 2.04; found: C 59.53, H
8.44, N 2.24.
Synthesis of prop-2-ynyl-3,4,5-tris(hexadecyloxy)benzoate: Propargyl bro-
mide (476 mg, 4 mmol) was added to a mixture of 3,4,5-tris(hexadecylox-
y)benzoic acid (842 mg, 1 mmol) and K2CO3 (279 mg, 2 mmol) in DMF
(70 mL) under a nitrogen atmosphere. The reaction mixture was heated
to reflux overnight. The reaction mixture was poured into deionized
water and extracted with dichloromethane (3 times). The organic phase
was washed with deionized water (3 times) and dried over anhydrous
Na2SO4. Removal of the solvent under reduced pressure afforded the
crude product, which was purified by column chromatography on silica
gel using dichloromethane/hexane (2:1 v/v) as the eluent to give the de-
sired product. Yield: 430 mg, 49%. 1H NMR (500 MHz, CDCl3, 298 K,
relative to Me4Si): d=0.88 (t, J=6.8 Hz, 9H; CH3), 1.26–1.30 (m, 72H;
CH2), 1.45–1.46 (m, 6H; CH2), 1.72–1.81 (m, 6H; CH2), 2.51 (t, J=
Synthesis of 3: To a degassed solution of 2 (129 mg, 0.1 mmol) in di-
chloromethane (30 mL), diisopropylamine (5 mL), a catalytic amount of
CuI (2 mg) and phenylacetylene (30.6 mg, 0.3 mmol) were added. The re-
sulting solution was allowed to stir at room temperature for 24 h under a
nitrogen atmosphere. After removal of solvents, the residue was purified
by column chromatography on silica gel using dichloromethane/hexane
(5:1 v/v) as the eluent to give the desired product. Yield: 99 mg, 70%.
1H NMR (500 MHz, CD2Cl2, 298 K, relative to CD2Cl2): d=0.89 (t, J=
6.8 Hz, 9H; CH3), 1.23–1.41 (m, 72H; CH2), 1.44–1.53 (m, 6H; CH2),
1.70–1.86 (m, 6H; CH2), 2.91 (s, 3H; CH3), 4.02–4.05 (m, 6H; OCH2),
5.46 (s, 2H; COOCH2), 7.16–7.21 (m, 2H; C6H5), 7.26–7.31 (m, 4H;
C6H5), 7.33 (s, 2H; C6H2), 7.47–7.50 (m, 5H; bipyridine proton at 5’-posi-
tion, C6H5), 7.66 (d, J=5.5 Hz, 1H; bipyridine proton at 5-position), 7.93
(s, 1H; bipyridine proton at 3’-position), 8.10 (s, 1H; bipyridine proton at
3-position), 9.61 (d, J=5.5 Hz, 1H; bipyridine proton at 6’-position),
9.61 ppm (d, J=5.5 Hz, 1H; bipyridine proton at 6-position); positive
FAB-MS: m/z: 1425 [M+H]+; elemental analysis calcd (%) for
C83H122N2O5Pt: C 70.06, H 8.64, N 1.97; found: C 70.19, H 9.10, N 1.72.
ꢀ
2.4 Hz, 1H; C CH), 3.97–4.01 (m, 6H; OCH2), 4.82 (d, J=2.4 Hz, 2H;
ꢀ
OCH2C C), 7.23 ppm (s, 2H; C6H2).
Synthesis of prop-2-ynylcholesteryl formate: A solution of cholesteryl
chloroformate (449 mg, 1 mmol) in anhydrous dichloromethane (50 mL)
was added to a solution of propargyl alcohol (112 mg, 2 mmol) and trie-
thylamine (0.5 mL) in anhydrous dichloromethane (20 mL), under a ni-
trogen atmosphere, and the reaction mixture was stirred at room temper-
ature overnight. The reaction solution was washed with an aqueous
Na2CO3 solution (3 times) and dried over anhydrous Na2SO4. Removal
of the solvent under reduced pressure afforded the desired product.
Yield: 300 mg, 64%. 1H NMR (500 MHz, CDCl3, 298 K, relative to
Me4Si): d=0.67 (s, 3H; cholesteryl proton), 0.85–1.60 (m, 33H; cholester-
yl proton), 1.80–2.02 (m, 5H; cholesteryl proton), 2.37–2.40 (m, 2H; cho-
Synthesis of 4: The procedure was similar to that for complex 3, except
[Pt
oxy)
phenylacetylACHTUNGTRENNUNG
ACHTUNGTRENNUNG
N
N
2
CDCl3, 298 K, relative to Me4Si): d=0.88 (t, J=6.8 Hz, 18H; CH3), 1.19–
1.29 (m, 144H; CH2), 1.43–1.52 (m, 12H; CH2), 1.72–1.83 (m, 12H;
ꢀ
CH2), 4.01–4.04 (m, 12H; OCH2), 5.11 (s, 4H; OCH2C C), 7.38–7.40 (m,
6H; C6H2, bipyridine proton at 4-position) 8.12 (t, J=7.5 Hz, 2H; bipyri-
dine proton at 5-position), 8.25 (d, J=7.5 Hz, 2H; bipyridine proton at 3-
position), 8.78 ppm (d, J=6.3 Hz, 2H; bipyridine proton at 6-position);
positive FAB-MS: m/z: 2113 [M+H]+; elemental analysis calcd (%) for
ꢀ
lesteryl proton), 2.50 (t, J=2.4 Hz, 1H; C CH), 4.47–4.52 (m, 1H;
ꢀ
OCH), 4.70 (d, J=2.4 Hz, 2H; OCH2C C), 5.38 ppm (d, J=5.1 Hz, 1H;
HC=C).
C
126H214N2O10Pt·2.5CHCl3: C 64.10, H 9.07, N 1.16; found: C 64.02, H
Synthesis of 1: The complex was synthesized according to a modification
of a previously reported method for [PtACHTNUGTRENUNG(bpy)Cl2] except 4-(1,3,3-trime-
8.84, N 1.15.
thylspiroindolinenaphthoxazine-9’-oxymethyl)-4’-methyl-2,2’-bipyridine
was used instead of 2,2’-bipyridine. A mixture of 4-(1,3,3-trimethylspir-
oindolinenaphthoxazine-9’-oxymethyl)-4’-methyl-2,2’-bipyridine (671 mg,
Synthesis of 5: The procedure was similar to that for 3, except 1 (100 mg,
0.13 mmol) was used in place of 2. Yield: 60 mg, 54%. 1H NMR
(500 MHz, CDCl3, 298 K, relative to Me4Si): d=1.34 (s, 6H; CACHTUNGTRENNUNG(CH3)2),
1.3 mmol) and [Pt
(dmso)2Cl2] (513 mg, 1.2 mmol) in dichloromethane
2.51 (s, 3H; CH3 on bpy), 2.75 (s, 3H; NCH3), 5.39 (s, 2H; OCH2 on
bpy), 6.57 (d, J=7.5 Hz, 1H; indolinic proton at 7-position), 6.86–6.92
(m, 2H; indolinic proton at 5-position, naphthoxazinic proton at 5’-posi-
tion), 7.07–7.23 (m, 9H; indolinic proton at 4,6-position, naphthoxazinic
proton at 8’-position, C6H5), 7.30 (d, J=5.4 Hz, 1H; bipyridine proton at
5’-position), 7.50–7.52 (m, 4H; C6H5), 7.58–7.62 (m, 2H; naphthoxazinic
proton at 6’-position, bipyridine proton at 5-position), 7.70 (s+d, J=
9.1 Hz, 2H; naphthoxazinic proton at 2’,7’-position), 7.92–7.96 (m, 2H;
naphthoxazinc proton at 10’-position, bipyridine proton at 3’-position),
8.24 (s, 1H; bipyridine proton at 3-position), 9.50 (d, J=5.4 Hz, 1H; bi-
pyridine proton at 6’-position), 9.66 ppm (d, J=5.5 Hz, 1H; bipyridine
proton at 6-position); positive FAB-MS: m/z: 924 [M+H]+; elemental
analysis calcd (%) for C50H40N4O2Pt·0.5CHCl3: C 61.66, H 4.15, N 5.70;
found: C 61.68, H 4.47, N 5.79.
(40 mL) was allowed to stir overnight. After removal of the solvents, di-
ethyl ether (20 mL) was added. After filtration, the precipitate was
washed with diethyl ether (10 mL) to yield the pure product. Yield:
920 mg, 91%. 1H NMR (500 MHz, CDCl3, 298 K, relative to Me4Si): d=
1.35 (s, 6H; CACHTUNGTRENNUNG(CH3)2), 2.57 (s, 3H; CH3 on bpy), 2.76 (s, 3H; NCH3),
5.42 (s, 2H; OCH2 on bpy), 6.58 (d, J=7.7 Hz, 1H; indolinic proton at 7-
position), 6.89–6.93 (m, 2H; indolinic proton at 5-position, naphthoxazin-
ic proton at 5’-position), 7.09 (d, J=7.7 Hz, 1H; indolinic proton at 4-po-
sition), 7.18–7.24 (m, 2H; naphthoxazinic proton at 8’-position, indolinic
proton at 6-position), 7.35 (d, J=6.0 Hz, 1H; bipyridine proton at 5’-posi-
tion), 7.61–7.63 (m, 2H; naphthoxazinic proton at 6’-position, bipyridine
at 5-position), 7.73 (s+d, J=9.0 Hz, 2H; naphthoxazinic proton at 2’,7’-
position), 7.89 (s, 1H; bipyridine at 3’-position), 7.95 (d, J=2.6 Hz, 1H;
naphthoxazinic proton at 10’-position), 8.17 (s, 1H; bipyridine at 3-posi-
tion), 9.50 (d, J=6.0 Hz, 1H; bipyridine at 6’-position), 9.68 ppm (d, J=
6.1 Hz, 1H; bipyridine at 6-position); positive FAB-MS: m/z: 793 [M+
H]+; elemental analysis calcd (%) for C34H30Cl2N4O2Pt: C 51.52, H 3.82,
N 7.07; found: C 51.78, H 3.91, N 7.20.
Synthesis of 6: The procedure was similar to that for 3, except 1 (88.6 mg,
0.11 mmol) and 4-methoxyphenylacetylene (44 mg, 0.33 mmol) were used
in place of 2 and phenylacetylene, respectively. Yield: 55 mg, 50%.
1H NMR (500 MHz, CDCl3, 298 K, relative to Me4Si): d=1.34 (s, 6H; C-
AHCUTNERTGG(NNUN CH3)2), 2.43 (s, 3H; CH3 on bpy), 2.74 (s, 3H; NCH3), 3.70 (s, 6H;
Synthesis of 2: The complex was synthesized according to a modification
OCH3), 5.37 (s, 2H; OCH2 on bpy), 6.57 (d, J=7.8 Hz, 1H; indolinic
proton at 7-position), 6.71 (d, J=8.3 Hz, 4H; C6H4), 6.88–6.91 (m, 2H;
indolinic proton at 5-position, naphthoxazinic proton at 5’-position),
7.07–7.11 (m, 2H; indolinic proton at 4-position, naphthoxazinic proton
at 8’-position), 7.15 (d, J=5.6 Hz, 1H; bipyridine proton at 5’-position),
7.22 (dt, J=1.0, 7.7 Hz, 1H; indolinic proton at 6-position), 7.38–7.41 (m,
4H; C6H4), 7.48 (d, J=5.7 Hz, 1H; bipyridine proton at 5-position), 7.59
(d, J=8.8 Hz, 1H; naphthoxazinic proton at 6’-position), 7.66 (d, J=
8.9 Hz, 1H; naphthoxazinic proton at 7’-position), 7.67 (s, 1H; naphthox-
azinic proton at 2’-position), 7.87 (d, J=2.4 Hz, 1H; naphthoxazinic
proton at 10’-position), 8.00 (s, 1H; bipyridine proton at 3’-position), 8.23
of a previously reported method for [Pt
ACHTUNGTRENNUNG
2,2’-bipyridin-4-yl)methyl-3,4,5-tris(hexadecyloxy)benzoate
0.19 mmol) was used instead of 2,2’-bipyridine. Yield: 230 mg, 95%.
1H NMR (500 MHz, CDCl3, 298 K, relative to Me4Si): d=0.88 (t, J=
6.8 Hz, 9H; CH3), 1.26–1.30 (m, 72H; CH2), 1.46–1.55 (m, 6H; CH2),
1.77–1.85 (m, 6H; CH2), 2.54 (s, 3H; CH3 on bpy), 4.00–4.06 (m, 6H;
OCH2), 5.45 (s, 2H; OCH2 on bpy), 7.28 (d, J=5.3 Hz, bipyridine proton
at 5’-position), 7.30 (s, 2H; C6H2), 7.48 (d, J=5.2 Hz, bipyridine proton
at 5-position), 7.87 (s, bipyridine proton at 3’-position), 8.02 (s, bipyridine
proton at 3-position), 9.36 (d, J=5.3 Hz, bipyridine proton at 6’-position),
8056
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Chem. Eur. J. 2011, 17, 8048 – 8059

Platinum(II) Bipyridine Complexes
FULL PAPER
(s, 1H; bipyridine proton at 3-position), 9.28 (d, J=5.6 Hz, 1H; bipyri-
dine proton at 6’-position), 9.42 ppm (d, J=5.7 Hz, 1H; bipyridine
proton at 6-position); positive FAB-MS: m/z: 984 [M+H]+; elemental
analysis calcd (%) for C52H44N4O4Pt·1.5CHCl3: C 55.34, H 3.95, N 4.83;
found: C 55.12, H 4.34, N 4.64.
(%) for C146H232N4O8Pt·0.5CH2Cl2: C 73.04, H 9.75, N 2.32; found: C
72.90, H 9.43, N 2.25.
Synthesis of 10: The procedure was similar to that for 3, except 1
(158 mg, 0.20 mmol) and prop-2-ynylcholesteryl formate (281 mg,
0.60 mmol) were used in place of 2 and phenylacetylene, respectively.
Yield: 245 mg, 74%. 1H NMR (500 MHz, CDCl3, 298 K, relative to
Me4Si): d=0.66 (s, 3H; 3H; cholesteryl proton), 0.86–1.64 (m, 72H; cho-
lesteryl proton and -(CH3)2), 1.79–2.03 (m, 10H; cholesteryl proton),
2.35–2.37 (m, 4H; cholesteryl proton), 2.57 (s, 3H; CH3 on bpy), 2.74 (s,
3H; NCH3), 4.45–4.51 (m, 2H; OCH on cholesteryl proton), 5.11 (s, 4H;
Synthesis of 7: The procedure was similar to that for 3, except 1 (100 mg,
0.13 mmol) and 4-ethynyl-a,a,a-trifluorotoluene (66.3 mg, 0.39 mmol)
were used in place of 2 and phenylacetylene, respectively. Yield: 70 mg,
53%. 1H NMR (500 MHz, CDCl3, 298 K, relative to Me4Si): d=1.35 (s,
6H; CACHTUNGTRENNUNG(CH3)2), 2.55 (s, 3H; CH3 on bpy), 2.76 (s, 3H; NCH3), 5.42 (s,
ꢀ
OCH2C C), 5.35 (s, 2H; CH=C on cholesteryl), 5.50 (s, 2H; OCH2 on
2H; OCH2 on bpy), 6.58 (d, J=7.7 Hz, 1H; indolinic proton at 7-posi-
tion), 6.89–6.93 (m, 2H; indolinic proton at 5-position and naphthoxazin-
ic proton at 5’-position), 7.09 (d, J=7.2 Hz, 1H; indolinic proton at 4-po-
sition), 7.18 (dd, J=2.5, 8.9 Hz, 1H; naphthoxazinic proton at 8’-posi-
tion), 7.23 (t, J=7.7 Hz, 1H; indolinic proton at 6-position), 7.42 (d, J=
5.6 Hz, 1H; bipyridine proton at 5’-position), 7.48 (d, J=7.3 Hz, 4H;
C6H4), 7.58–7.60 (m, 4H; C6H4), 7.62 (d, J=8.8 Hz, 1H; naphthoxazinic
proton at 6’-position), 7.68 (d, J=5.7 Hz, 1H; bipyridine proton at 5-posi-
tion), 7.71 (s, 1H; naphthoxazinic proton at 2’-position), 7.73 (d, J=
8.9 Hz, 1H; naphthoxazinic proton at 7’-position), 7.95–7.96 (m, 2H;
naphthoxazinic proton at 10’-position and bipyridine proton at 3’-posi-
tion), 8.26 (s, 1H; bipyridine proton at 3-position), 9.54 (d, J=5.6 Hz,
1H; bipyridine proton at 6’-position), 9.70 ppm (d, J=5.7 Hz, 1H; bipyri-
dine proton at 6-position); positive FAB-MS: m/z: 1060 [M+H]+; ele-
mental analysis calcd (%) for C52H38F6N4O2Pt·0.5CH2Cl2: C 55.60, H
3.52, N 4.89; found: C 55.49, H 3.33, N 4.88.
bpy), 6.56 (d, J=7.8 Hz, 1H; indolinic proton at 7-position), 6.88–6.91
(m, 2H; indolinic proton at 5-position and naphthoxazinic proton at 5’-
position), 7.07 (d, J=6.6 Hz, 1H; indolinic proton at 4-position), 7.15
(dd, J=2.6, 8.9 Hz 1H; naphthoxazinic proton at 8’-position) 7.20–7.23
(m, 2H; indolinic proton at 6-position and bipyridine proton at 5’-posi-
tion), 7.51 (d, J=5.6 Hz, 1H; bipyridine proton at 5-position), 7.60 (d,
J=8.9 Hz, 1H; naphthoxazinic proton at 6’-position), 7.70 (s+d, J=
8.7 Hz, 2H; naphthoxazinic proton at 2’,7’-position), 7.79 (d, J=2.3 Hz,
1H; naphthoxazinic proton at 10’-position), 8.01 (s, 1H; bipyridine
proton at 3’-position), 8.25 (s, 1H; bipyridine proton at 3-position), 9.23
(d, J=5.6 Hz, 1H; bipyridine proton at 6’-position), 9.40 ppm (d, J=
5.6 Hz, 1H; bipyridine proton at 6-position); positive FAB-MS: m/z:
1657 [M+H]+; elemental analysis calcd (%) for C96H124N4O8Pt: C 69.58,
H 7.54, N 3.38; found: C 69.63, H 7.84, N 3.12.
Physical measurements and instrumentation: 1H NMR spectra were re-
corded on a Bruker DRX 500 (500 MHz) spectrometer at 298 K. Chemi-
cal shifts (d, ppm) were reported relative to tetramethylsilane (Me4Si).
Positive ion FAB mass spectra were recorded on a Finnigan MAT95
mass spectrometer. Elemental analyses of the complexes were performed
on a Flash EA 1112 elemental analyzer at Jilin University.
Synthesis of 8: The procedure was similar to that for 3, except 1 (110 mg,
0.14 mmol)
and
3,4,5-tri(dodecyloxy)phenylacetylene
(263 mg,
0.42 mmol) were used in place of 2 and phenylacetylene, respectively.
Yield: 232 mg, 82%. 1H NMR (500 MHz, CDCl3, 298 K, relative to
Me4Si): d=0.86–0.89 (m, 18H; CH3), 1.26–1.35 (m, 102H; CH2, C-
ACHTUNGTRENNUNG(CH3)2), 1.41–1.46 (m, 12H; CH2), 1.72–1.80 (m, 12H; CH2), 2.53 (s, 3H;
Cyclic voltammetric measurements were performed by using a CH In-
struments, Inc. model CHI 660C electrochemical analyzer. Electrochemi-
cal measurements were performed in a dichloromethane solution with
0.1m nBu4NPF6 (TBAH) as supporting electrolyte at room temperature.
The reference electrode was an Ag/AgNO3 (0.1 moldmꢁ3 in acetonitrile)
electrode and the working electrode was a glassy carbon electrode (CH
Instruments, Inc.) with a platinum wire as the counter electrode. The
working electrode surface was first polished with a 1 mm alumina slurry
(Linde) on a microcloth (Buehler Co.) and then with a 0.3 mm alumina
slurry. It was then rinsed with ultra-pure deionized water and sonicated
in a beaker containing ultra-pure water for five minutes. The polishing
and sonicating steps were repeated twice and then the working electrode
was finally rinsed under a stream of ultra-pure deionized water. The fer-
rocenium/ferrocene couple (FeCp2+/0) was used as the internal refer-
ence.[26] All solutions for electrochemical studies were deaerated with
pre-purified argon gas prior to measurements.
CH3 on bpy), 2.75 (s, 3H; NCH3), 3.91–3.96 (m, 12H; OCH2), 5.39 (s,
2H; OCH2 on bpy), 6.58 (d, J=7.8 Hz, 1H; indolinic proton at 7-posi-
tion), 6.76 (s, 4H; C6H2), 6.90–6.92 (m, 2H; indolinic proton at 5-posi-
tion, naphthoxazinic proton at 5’-position), 7.08 (d, J=7.2 Hz, 1H; indo-
linic proton at 4-position), 7.18 (dd, J=2.5, 8.8 Hz 1H; naphthoxazinic
proton at 8’-position) 7.22–7.24 (m, 1H; indolinic proton at 6-position),
7.38 (d, J=5.6 Hz, 1H; bipyridine proton at 5’-position), 7.61–7.65 (m,
2H; naphthoxazinic proton at 6’-position, bipyridine proton at 5-posi-
tion), 7.72 (s+d, J=9.0 Hz, 2H; naphthoxazinic proton at 2’,7 -position),
7.91–7.95 (m, 2H; naphthoxazinic proton at 10’-position, bipyridine
proton at 3’-position), 8.21 (s, 1H; bipyridine proton at 3-position), 9.66
(d, J=5.6 Hz, 1H; bipyridine proton at 6’-position), 9.83 ppm (d, J=
5.7 Hz, 1H; bipyridine proton at 6-position); positive FAB-MS: m/z:
2033
[M+H]+;
elemental
analysis
calcd
(%)
for
C
122H184N4O8Pt·0.5CH2Cl2: C 71.00, H 9.00, N 2.70; found: C 71.37, H
8.78, N 2.70.
Electronic absorption spectra were obtained using a Varian Cary 50 UV/
Vis spectrophotometer. Steady state excitation and emission spectra at
room temperature and at 77 K and emission lifetimes were recorded on a
Synthesis of 9: The procedure was similar to that for 3, except 1 (122 mg,
0.15 mmol) and 3,4,5-tri(hexadecyloxy)acetylene (369 mg, 0.45 mmol)
were used in place of 2 and phenylacetylene, respectively. Yield: 320 mg,
Horiba–Jobin–Yvon Fluorolog-3
fluorescence spectrofluorometer
1
88%. H NMR (500 MHz, CDCl3, 298 K, relative to Me4Si): d=0.80–0.91
equipped with a R928P PMT detector and a time-correlated single-
photon counting (TCSPC) system, respectively. For the lifetime measure-
ments, the excitation source was a 370 nm output of a nanoLED pulsed
laser diode. Luminescence decay signals were detected by a TBX-04 pho-
tomultiplier tube module and analyzed by using IBH lifetime analysis for
exponential fits. Solid-state photophysical studies were carried out with
solid samples contained in a quartz tubes inside a quartz-walled Dewar
flask. Measurements of the glass state in ethanol/methanol/dichlorome-
thane=4:1:1 or a solid-state sample at 77 K were similarly conducted
with liquid nitrogen filled in the optical Dewar flask. All of the solutions
for the photophysical studies were degassed on a high-vacuum line in a
two-compartment cell consisting of a 10 mL Pyrex bulb and a 1 cm path
length quartz cuvette that was sealed from the atmosphere by a Bibby
Rotaflo HP6 Teflon stopper. The solutions were rigorously degassed with
at least four successive freeze-pump-thaw cycles. Luminescence quantum
yields were measured by the optical dilute method reported by Demas
(m, 18H; CH3), 1.27–1.35 (m, 150H; CH2, CACTHNUGTRNEG(UN CH3)2), 1.41–1.50 (m, 12H;
CH2), 1.74–1.79 (m, 12H; CH2), 2.54 (s, 3H; CH3 on bpy) , 2.76 (s, 3H;
NCH3), 3.93–3.97 (m, 12H; OCH2), 5.43 (s, 2H; OCH2 on bpy), 6.58 (d,
J=7.8 Hz, 1H; indolinic proton at 7-position), 6.76 (s, 4H; C6H2), 6.91–
6.93 (m, 2H; indolinic proton at 5-position, naphthoxazinic proton at 5’-
position), 7.09 (d, J=7.2 Hz, 1H; indolinic proton at 4-position), 7.17
(dd, J=2.6 Hz, 8.9 Hz 1H; naphthoxazinic proton at 8’-position) 7.22–
7.25 (m, 1H; indolinic proton at 6-position), 7.35 (d, J=5.7 Hz, 1H; bi-
pyridine proton at 5’-position), 7.59–7.63 (m, 2H; naphthoxazinic proton
at 6’-position, bipyridine proton at 5-position), 7.72 (s+d, J=8.8 Hz, 2H;
naphthoxazinic proton at 2’,7’-position), 7.93–7.97 (m, 2H; naphthoxazin-
ic proton at 10’-position, bipyridine proton at 3’-position), 8.25 (s, 1H; bi-
pyridine proton at 3-position), 9.59 (d, J=5.7 Hz, 1H; bipyridine proton
at 6’-position), 9.83 ppm (d, J=5.7 Hz, 1H; bipyridine proton at 6-posi-
tion); positive FAB-MS: m/z: 2366 [M+H]+; elemental analysis calcd
Chem. Eur. J. 2011, 17, 8048 – 8059
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8057

V. Wing-Wah Yam, K. Man-Chung Wong et al.
and Crosby.[27] A degassed solution of [Ru
ACTHNUTRGEN(UNG bpy)3]Cl2 in acetonitrile (f=
Acknowledgements
0.062, excitation wavelength at 436 nm) was used as the reference.[28]
V.W.-W.Y. acknowledges support from The University of Hong Kong
under the Distinguished Research Achievement Award Scheme. We also
acknowledge support from the State Key Laboratory of Supramolecular
Structure and Materials, Jilin University and The University of Hong
Kong. This work has been supported by the University Grants Commit-
tee Areas of Excellence Scheme (AoE/P-03/08) and a General Research
Fund (GRF) grant from the Research Grants Council of Hong Kong
Special Administrative Region, China (HKU 7060/09P). A.Y.-Y.T. ac-
knowledges the receipt of a University Postdoctoral Fellowship from The
University of Hong Kong.
The kinetics for the bleaching reaction were determined by measurement
of the UV/Vis spectral changes at various temperatures with the use of a
Varian Cary 50 UV/Vis spectrophotometer, with the temperature con-
trolled by a single cell Peltier thermostat. Photoirradiation was carried
out using monochromatic light at 405 nm. The thermal bleaching reaction
of spironaphthoxazines is known to follow first-order kinetics at various
temperatures. The first-order rate constants were obtained by taking the
negative value of the slope of
a linear least-squares fit of ln-
A
U
A0, and A1 are the absorbance at the absorption wavelength maximum
of the open form at times t, 0, and infinity, respectively, and k is the rate
constant of the reaction. The kinetic parameters were obtained by a
linear least-squares fit of lnACTHNUGRTENUNG(k/T) against 1/T according to the linear ex-
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pression of the Eyring equation [Eq. (2)] and lnk against 1/T according
to the Arrhenius equation [Eq. (3)], in which DH° and DS° are the
changes in enthalpy of activation and entropy of activation, respectively,
Ea is the activation energy, T is the temperature, and kB, R, h, and A are
the Boltzmann constant, the universal gas constant, the Planck constant,
and the frequency factor, respectively.
ꢀ
ꢀ
ꢁ
ꢀ
AꢁA1
ln
ln
¼ ꢁkt
ð1Þ
A0ꢁA1
ꢁ
ꢁꢀ
ꢁ
ꢀ
ꢁ
k
T
DH°
R
1
T
kB
h
DS°
RÞ
ð2Þ
ð3Þ
¼ ꢁ
þ ln
þ
Ea
lnðkÞ ¼ ꢁ
þ ln A
RT
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4 cmꢁ1, from pressed KBr pellets. The heating rate was 5Kminꢁ1 over the
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method.
8058
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8048 – 8059

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Received: December 28, 2010
Revised: April 2, 2011
Published online: June 21, 2011
Chem. Eur. J. 2011, 17, 8048 – 8059
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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