Synthesis, characterization, luminescence, and non-linear optical properties of oxadiazole- and truxene-containing platinum(II) alkynyl complexes with donor-acceptor functionalities

Article abstract of DOI:10.1021/ic8017979

A series of luminescent platinum(ll) alkynyl complexes containing 2,5-diphenyl-1,3,4-oxadiazole (oxa-2,5) and 10,15- dihydro-5H-diindeno[1,2-a;1', 2'-c]fluorene (truxene) as the cores and different electron donors at the periphery has been synthesized and

Full text of DOI:10.1021/ic8017979

Inorg. Chem. 2009, 48, 2855-2864
Synthesis, Characterization, Luminescence, and Non-linear Optical
Properties of Oxadiazole- and Truxene-Containing Platinum(II) Alkynyl
Complexes with Donor-Acceptor Functionalities
Carmen Ka Man Chan,† Chi-Hang Tao,† Hoi-Lam Tam,‡ Nianyong Zhu,† Vivian Wing-Wah Yam,*,†
and Kok-Wai Cheah*,‡
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research and
Department of Chemistry, The UniVersity of Hong Kong, Pokfulam Road,
Hong Kong, P.R. China, and Centre for AdVanced Luminescence Materials, Hong Kong Baptist
UniVersity and Department of Physics, Hong Kong Baptist UniVersity, Hong Kong, P.R. China
Received September 19, 2008
A series of luminescent platinum(II) alkynyl complexes containing 2,5-diphenyl-1,3,4-oxadiazole (oxa-2,5) and 10,15-
dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene (truxene) as the cores and different electron donors at the periphery has
been synthesized and characterized. These complexes showed long-lived emissions in both solution and in the
solid state at room temperature and have been found to exhibit two-photon absorption (2PA) and two-photon
induced luminescence. Their 2PA cross-sections (σ2) have also been determined.
Introduction
todynamic therapy.14,15 To obtain materials with large two-
photon absorption (2PA) cross-sections, the design and
synthesis of chromophores or dendrimers with large differ-
ences in polarization upon excitation and extended π-con-
jugation within the molecule have received much attention.16
Large changes in polarization can be achieved through
various structural motifs, such as donor–π–acceptor, donor–
π–donor, acceptor–π–acceptor, donor-acceptor-donor or
acceptor-donor-acceptor, which have been found to display
remarkable improvements in 2PA capabilities.
There has been a growing interest in the development of
two-photon absorbing materials because of their various
applications, such as in optical data storage,1-3 frequency
upconverted lasing,4-7 three-dimensional microfabrication,8,9
fluorescence imaging,10-12 non-linear photonics,13 and pho-
* To whom correspondence should be addressed. E-mail: wwyam@
hku.hk (V.W.-W.Y.), kwcheah@hkbu.edu.hk (K.-W.C.). Fax: 852 2857
1586 (V.W.-W.Y.). Phone: 852 2859 2153 (V.W.-W.Y.), 852 3411 7033
(K.-W.C.).
†
The University of Hong Kong.
Hong Kong Baptist University.
Extended π-conjugated and star-shaped molecules have
shown interesting properties, such as conducting, optical,
non-linear optical and electroluminescent properties.17-23 In
particular, 2,5-diphenyl-1,3,4-oxadiazole (oxa-2,5) and 10,15-
‡
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10.1021/ic8017979 CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 7, 2009 2855
Published on Web 03/10/2009

Chan et al.
Scheme 1. Synthesis of Oxadiazole-Containing Dinuclear Platinum(II) Complexes
dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene (truxene) appear
to be promising building blocks for the construction of
functional materials because of their rigid structures, good
thermal and chemical stabilities, and relatively high lumi-
nescence quantum yields.17-25 In addition, the electron-
deficient nature of 2,5-diphenyl-1,3,4-oxadiazole (oxa-2,5)
has fostered its applications as electron-acceptors in the
development of 2PA chromophores.
Besides, symmetrical D–π–A–π–D or A–π–D–π–A mol-
ecules have been shown to exhibit relatively large 2PA cross-
sections. Works by various research groups have reported
that dendritic or branched molecules showed enhanced 2PA
because of an extended π-conjugation and an increased
intramolecular charge redistribution compared to singly
branched dipolar chromophores.18-20
Apart from the studies of organic compounds for 2PA,
there has been a growing interest in the study of metal
complexes for non-linear optical applications in recent
years.26-34 Some organotransition metal complexes, such as
ferrocenyl, nickel(II), ruthenium(II), manganese(I), and
gold(I), have been reported by various research groups to
show interesting non-linear optical properties.26-34 Recent
works have shown that metal alkynyls, through the stability
of the metal-carbon bond and the dπ-pπ overlap, might
serve as promising structural motifs for the construction of
optical limiting, second harmonic generating, two-photon
absorbing, and two-photon induced luminescence materi-
als.35-38 In particular, a series of thienylalkynyl complexes
of platinum(II) with dendronized end-groups has been found
to exhibit σ2 in the range of 5-10 GM and was also found
to show optical limiting properties.39,40
Although organic chromophores with oxa-2,517-19 and
truxene20-25 have been synthesized, the construction of
carbon-rich metal-containing complexes containing these
core ligands has been much less explored.41-43 With our
recent interests and efforts in the design and synthesis of
linear and branched luminescent metal alkynyl com-
plexes,44-50 a program was launched to explore the employ-
ment of the truxene and oxadiazole functionalities in the
construction of metal alkynyl complexes. The photophysical
and the 2PA properties have also been studied. Herein are
described the design, synthesis, characterization, and lumi-
nescence behavior of a series of branched platinum(II)
alkynyl complexes containing oxa-2,5 and truxene as the core
and various electron-donating groups, such as triphenylamine
and carbazole, as the peripheral units. The structure of
triethynylhexabutyltruxene has also been determined.
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2856 Inorganic Chemistry, Vol. 48, No. 7, 2009

Luminescent Platinum(II) Alkynyl Complexes
Scheme 2. Synthesis of Truxene-Containing Trinuclear Platinum(II) Complexes
Results and Discussion
previously by our group.45,49 These complexes were
prepared in refluxing toluene and piperidine in the
presence of a catalytic amount of CuI and an excess of
trans-[Pt(PEt3)2Cl2] to minimize the formation of undesir-
able oligomeric materials. The branched platinum(II) bis-
alkynyl complexes 2, 3, 5-8 were synthesized using a
copper(I)-catalyzed dehydrohalogenation approach with
the corresponding multinuclear complex precursors 1 and
4. Complexes 2, 3, 5-8 were obtained in reasonable yields
with different alkynyl ligands, which demonstrated that
precursor complexes 1 and 4 are versatile starting materials
for the syntheses of luminescent branched carbon-rich
metal-containing materials.
Synthesis and Characterization. The targeted branched
dinuclear and trinuclear platinum(II) complexes were
synthesized according to Scheme 1 and Scheme 2,
respectively. Chloroplatinum(II) complexes 1 and 4 were
obtained by modification of the preparation of the related
trinuclear platinum(II) complexes which were reported
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Inorganic Chemistry, Vol. 48, No. 7, 2009 2857

Chan et al.
Figure 2. Electronic absorption (left) and normalized emission spectra
(right) of complexes 3 (solid black line) and 6 (red dashed line) in benzene
at room temperature.
Table 2. Electronic Absorption and Photophysical Data for Complexes
1-8
λabs [nm]
medium
(T [K])
λem [nm]
(τo [µs]) Φlum
d
complex
(ε[dm3 mol-1 cm-1])a
Figure 1. Perspective view of triethynylhexabutyltruxene with atomic
numbering scheme. Only the ipso-carbons of the butyl chains were shown.
Hydrogen atoms (except the acetylenic hydrogens) have been omitted for
clarity. Thermal ellipsoids were shown at the 30% probability level.
c
e
1
362 (65790)
C6H6 (298)
solid (298)
solid (77)
c
527 (170)
glass (77)b 518 (380)
C6H6 (298) 528 (80)
solid (298) 532 (4.6)
Table 1. Selected Bond Lengths [Å] and Bond Angles [deg] for
Triethynylhexabutyltruxene with Estimated Standard Deviations in
Parentheses
2
3
4
5
6
7
8
370 (106100)
0.17
solid (77)
533 (80)
glass (77)b 520 (420)
Selected Bond Lengths [Å]
308 sh (53250), 370 (107990) C6H6(298) 528 (32)
solid (298) 529 (6.0)
0.20
C(1)-C(2)
C(26)-C(27)
1.179(5)
1.147(5)
C(18)-C(19)
1.174(5)
solid (77)
528 (280)
glass (77)b 520 (320)
Selected Bond Angles [deg]
c
e
316 (55100), 352 (148700)
C6H6 (298)
solid (298)
solid (77)
C(1)-C(2)-C(3)
C(26)-C(27)-C(28)
C(42)-C(17)-C(46)
178.2(7)
176.4(6)
113.0(4)
C(18)-C(19)-C(20)
C(50)-C(15)-C(54)
C(34)-C(16)-C(38)
178.5(6)
111.5(3)
111.3(3)
c
514 (166)
glass (77)b 506 (930)
354 (197200), 362 sh (183800) C6H6 (298) 514 (38)
solid (298) 522 (5.6)
0.10
0.13
0.10
0.08
All the complexes have been characterized by IR, positive
1
FAB-MS, H and 31P{1H} NMR spectroscopy and gave
solid (77)
522 (110)
glass (77)b 509 (700)
C6H6 (298) 515 (45)
solid (298) 519 (6.0)
satisfactory elemental analyses. The 31P NMR spectra of
complexes 1-8 all showed a singlet signal, which is
indicative of the highly symmetrical structure of the mol-
ecules, in the range of δ 14.8-15.1 ppm for the precursor
chloro complexes 1 and 4 and δ 11.0-11.7 ppm for the other
alkynyl complexes. Platinum satellites with JPt-P ∼ 2300 Hz
were observed in all the branched complexes which are
characteristic of a trans-P–Pt–P configuration.51
306 (91700), 366 (212900)
354 (178300), 364 (171800)
352 (261100), 362 (251200)
solid (77)
522 (52)
glass (77)b 508 (550)
C6H6 (298) 515 (22)
solid (298) 522 (4.8)
solid (77)
521 (120)
glass (77)b 510 (700)
C6H6 (298) 514 (56)
solid (298) 518 (5.5)
solid (77)
519 (75)
glass (77)b 508 (730)
Crystal Structure Determination. Figure 1 shows the
perspective drawing of triethynylhexabutyltruxene, and the
selected bond lengths and angles are given in Table 1. Only
the ipso carbons on the butyl chains are shown in the figure.
The CtC bond lengths of the three peripheral alkynes lie
in the range of 1.147-1.179 Å. The bond angles about the
sp hybridized carbons are close to the ideal value of 180°.
As shown in Figure 1, the truxene backbone is nearly
coplanar with six butyl chains lying out of the aromatic plane
which is expected for the sp3 hybridized carbons C15, C16,
and C17. As a result of the presence of these butyl chains
protruding from the planes of the truxene backbone, π
stacking does not exist, and the six butyl chains also served
to enhance the solubility of the molecule.
a Measured in C6H6 at 298 K. b Measured in EtOH-MeOH (4:1, v/v)
glass. c Non-emissive. d The luminescence quantum yield, measured at room
temperature using quinine sulfate in 1.0 N H2SO4 as the reference (excitation
wavelength ) 365 nm, Φlum ) 0.55). e Not determined.
m(II) complexes showed intense absorption bands at about
352-370 nm with extinction coefficients of the order of
104-105 dm3 mol-1 cm-1 (Figure 2). The photophysical data
of complexes 1-8 are summarized in Table 2. With reference
to previous spectroscopic studies on trans-[Pt(PEt3)2-
(CtCR)2],52-56 in which the absorption bands at about
300-360 nm were assigned as metal-to-alkynyl metal-to-
ligand charge transfer (MLCT) transitions, the low-energy
transitions in these branched complexes may also involve a
metal-to-alkynyl MLCT character. In view of the rich
vibronic structures and the very large extinction coefficients
observed for the chloroplatinum(II) precursors 1 and 4 that
are comparable to the corresponding oxadiazole and truxene
Electronic Absorption and Emission. The electronic
absorption spectra of these dinuclear and trinuclear platinu-
(51) Sebald, A.; Stader, C.; Wrackmeyer, B.; Bensch, W. J. Organomet.
Chem. 1986, 311, 233.
2858 Inorganic Chemistry, Vol. 48, No. 7, 2009

Luminescent Platinum(II) Alkynyl Complexes
alkynyl ligands, a substantial mixing of an intraligand
[πfπ*(CtC)2-oxa-2,5 or (CtC)3-truxene] character of the
central alkynyl core unit is likely. In addition, the electronic
absorption spectra of these complexes in acetone and benzene
are nearly identical. These absorption bands were found to
be relatively insensitive toward the polarity of the solvent,
which is in accordance with the largely intraligand πfπ*
character of these transitions. Therefore, the low-energy
absorptions in these branched complexes are described as
an admixture of IL [πfπ*(CtC)2-oxa-2,5 or (CtC)3-
truxene] and MLCT [dπ(Pt)fπ*(CtC)2-oxa-2,5 or (CtC)3-
truxene] transitions with predominantly IL character. For the
dinuclear complexes 2, 3 and the trinuclear complexes 5-8,
additional absorptions due to the IL (πfπ*) transitions of
the peripheral alkynyl ligands may also occur at similar
energies as related systems have been reported to display
absorption bands in similar regions.52-56 However, in view
of the relatively insensitive nature of the absorption energies
of the dinuclear complexes 2, 3 and trinuclear complexes
5-8 to the nature of the peripheral aryl-alkynyl ligands, the
low-energy absorptions in these branched complexes are
dominated by IL [πfπ*(CtC)2-oxa-2,5 or (CtC)3-truxene]
transitions, with mixing of MLCT [dπ(Pt)fπ*(CtC)2-oxa-
2,5 or (CtC)3-truxene or CtCR] and IL [πfπ*(CtCR)]
character.
Figure 3. Emission spectra of 2 (top) and 7 (bottom) in ethanol-methanol
(4:1, v/v) glass at 77 K. Excitation wavelength at 370 nm.
Upon excitation at λ g 365 nm, the branched complexes
2, 3, 5-8 display luminescence in deaerated benzene
solutions at room temperature (Figure 2) while all the
complexes exhibit luminescence at 77 K. All complexes
show large Stokes shift and lifetimes in the microsecond
range, which are indicative of their triplet parentage. In
contrast to the non-emissive behavior of precursor complexes
1 and 4 at room temperature, the bis-alkynyl complexes 2,
3, 5-8 show intense yellowish green vibronically structured
emission bands at room temperature, with emission maxima
at about 514-520 nm that are at nearly identical wavelengths
with similar vibronic structures as the emission bands of their
corresponding chloroplatinum(II) precursors 1 and 4 observed
Figure 4. Two-photon induced luminescence spectrum of complex 6 in
benzene at room temperature upon excitation with a mode-locked femto-
second Ti:Sapphire laser at 720 nm.
Table 3. Non-Linear Photophysical Data for Complexes 2, 3, 5-8
complex
λema/nm at λex ) 720 nm
σ2/GM
power dependence
2
3
5
6
7
8
530
530
518
518
517
514
17
41
21
32
27
11
2.18
2.07
2.52
2.11
2.11
2.15
3
at 77 K. This finding is supportive of a triplet IL [πfπ*-
(CtC)2-oxa-2,5 or (CtC)3-truxene] emission derived mainly
from the central core ligands. Emissions from the 3IL states
of the peripheral alkynyl ligands were not observed since
they were higher-lying in energy, indicative of a facile energy
transfer process. The energy absorbed by the peripheral
ligands would be transferred to the central oxadiazole or
truxene emitting core through directional energy transfer.
Similar findings have also been observed in other related
branched platinum(II) alkynyl complexes.45,49 The emission
spectra of complexes 2 and 3 in 77 K glass show rich
vibronic structures with vibrational progressional spacings
a Measured in C6H6 at 298 K.
of about 1060 and 1520 cm-1 (Figure 3), with the former
corresponding to the V(C-O) stretch and the latter to the
V(C)C) and V(C)N) vibrational modes. Additional vibronic
structures with progressional spacings of about 1220 and
2140 cm-1 from the highest energy emission band are
observed for complexes 5-8 at low temperature (Figure 3),
which are ascribed to the aromatic ring deformation and
V(CtC) vibrational modes, respectively. The emission
lifetimes in solid state at room temperature are considerably
shorter than that observed in dilute solutions, which may be
ascribed to originate from triplet-triplet annihilation or self-
quenching in the solid state.
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Two-Photon Induced Luminescence (TPIL). Complexes
2, 3, 5-8 are found to emit in the yellowish-green region in
benzene solutions upon excitation with a mode-locked
femtosecond Ti:Sapphire laser at 720 nm. The TPIL spectrum
of complex 6 in benzene at room temperature is shown in
Figure 4. Table 3 shows the emission maxima and σ2 at 720
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Phys. Chem. A 1997, 101, 9286.
Inorganic Chemistry, Vol. 48, No. 7, 2009 2859

Chan et al.
Table 4. Electrochemical Data for Triethynylhexabutyltruxene and
Complexes 1-8a
compound
b c
,
oxidation E1/2 [V versus SCE]
triethynylhexabutyltruxene
(+1.59)
1
2
3
4
5
6
7
8
(+1.40)
(+1.18)
+0.65, (+1.28)
(+1.06), (+1.28)
(+1.07), (+1.34), (+1.57), (+2.11)
+0.65, (+1.22), (+1.95)
(+1.15), (+1.45), (+1.81)
(+1.03), (+1.39), (+1.82)
a In dichloromethane (0.1 M nBu4NPF6); working electrode, glassy
carbon; scan rate ) 100 mV s-1 b Values in parentheses refer to the anodic
.
Figure 5. Power dependence of the up-converted luminescence intensity
(9) of complex 2 in benzene at room temperature. The black line shows
the theoretical curve for the quadratic function. The inset shows the
log(emission intensity) (2) vs log(laser power) and its linear regression
(red solid line).
c
peak potential (Epa) for the irreversible oxidation waves. E1/2 ) (Epa
+
Epc)/2; Epa and Epc are the peak anodic and peak cathodic potentials,
respectively.
that observed in organic 2PA chromophores.57 The incor-
poration of aromatic heterocycles into the truxene system in
complexes 5 and 8 did not give rise to higher σ2 values as
compared to complex 6 since the heterocycles are less
electron-rich than triphenylamine, as reflected by their more
positive oxidation potentials than that of triphenylamine in
the cyclic voltammetric study. These findings have demon-
strated that oxadiazole and truxene moieties could be building
blocks for the construction of two-photon induced lumines-
cent materials in addition to the commonly employed 1,4-
diethynylbenzene. More importantly, the peripheral chloro
ligands in complexes 1 and 4 would provide versatile handles
for the tuning of the σ2 values and the emission energies of
these classes of complexes by the incorporation of alkynyl
ligands with different electronic properties.
Electrochemical Properties. The electrochemical behav-
ior of the complexes has been studied in dichloromethane
(0.1 M nBu4NPF6). Table 4 summarizes the electrochemical
data. There is no observable reductive wave for all the
complexes upon scanning up to -2.0 V, which is similar to
that found in other structurally related platinum(II) alkynyl
complexes.48,58,59 The oxidative scans of complexes 1-3
show one to two redox waves at +0.65 to +1.40 V versus
saturated calomel electrode (SCE). Since there is no oxidative
nm determined using TPIL. No linear absorption in the
wavelength range of 500-820 nm was observed for these
platinum(II) complexes, indicating that the emission induced
by 720 nm excitation could not be attributed to a linear
process but rather to a non-linear process. The upconverted
emissions of these complexes are nearly identical to that
observed in their corresponding single-photon excited emission.
The dependence of the upconverted luminescence intensi-
ties on the incident laser power was measured and the power
dependence curve for complex 2 is shown in Figure 5. The
inset shows the plot of log(emission intensity) versus
log(laser power). A straight line plot with slope of about 2
was obtained. Since the 2PA has a quadratic dependence on
intensity, the TPIL is expected to show intensity dependence
on excitation. Theoretically, the log(fluorescence emission)
versus log(peak laser intensity) should give a straight line
with a gradient of 2.40 Therefore, the observed quadratic
dependence of the emission intensity on the incident laser
power further confirms the two-photon nature of the process.
The σ2 values of these branched complexes with excitation
wavelength at 720 nm have been determined using the TPIL
method and are found to be in the range of 11-40 GM,
which are comparable to the 5-10 GM observed in other
platinum(II) alkynyl complexes of bis((4-(phenylethynyl)phe-
nylethynyl)bis(tributylphosphine)),35,39,40 but smaller than
that recently reported by Schanze and co-workers on some
linear platinum alkynyl complexes,36 which show a more
extended π–conjugation in their donor–π or acceptor–π
structural motifs within the alkynyl ligands.36
The present study investigates the effects of the platinu-
m(II) alkynyl π-moiety as linker on TPA in a series of
platinum(II) complexes with electron-donating and electron-
accepting functionalities. Through a systematic comparison
study of these complexes, the σ2 values are found to be
slightly dependent on the electron-richness of the peripheral
substituents while the central oxadiazole or truxene moieties
have relatively small effects on the σ2 values. In general,
higher σ2 values could be observed for complexes with
relatively more electron-rich peripheral substituents. For
instance, the σ2 values of triphenylamine-containing com-
plexes 3 and 6 are relatively higher than that of the corre-
sponding tolyl analogues. This observation is in line with
wave
observed
for
2,5-bis-(4-ethynyl)phenyl-
1,3,4-oxadiazole and given the lack of peripheral alkynyl
moieties in complex 1, the irreversible waves at +1.18 to
+1.40 V for complexes 1-3 are ascribed to oxidation
processes that involve substantial metal-centered character.
The less positive potentials for complexes 2 and 3 than their
chloro precursor complex 1 are also in line with such an
assignment.
Two to four irreversible waves at +1.06 to +1.22, +1.28
to +1.45, +1.57 to +1.95 and +2.11 V versus SCE were
observed for complexes 4-8. It is found that the first
oxidation wave of triethynylhexabutyltruxene appears at
+1.59 V, which is more positive than the first oxidation wave
of complexes 4-8, and thus an assignment of a truxene
(57) Seo, J.-W.; Jang, S. Y.; Kim, D.; Kim, H.-J. Tetrahedron 2008, 64,
2733.
(58) Younus, M.; Ko¨hler, A.; Cron, S.; Chawdhury, N.; Al-Mandhary,
M. R. A.; Khan, M. S.; Lewis, J.; Long, N. J.; Friend, R. H.; Raithby,
P. R. Angew. Chem., Int. Ed. 1998, 37, 3036.
(59) Wong, W. Y.; Lu, G.-L.; Choi, K.-H.; Shi, J.-X. Macromolecules 2002,
35, 3506.
2860 Inorganic Chemistry, Vol. 48, No. 7, 2009

Luminescent Platinum(II) Alkynyl Complexes
1-Indanone (Aldrich, 99+%), 1-ethynyltoluene (GFS, 98%),
1-bromobutane (Lancaster, 98+%), n-butyllithium (Fluka, 1.6 M
solution in n-hexane), trimethylsilyl acetylene (GFS, 98%) and
fluorescein (Acros, 99% pure, laser grade) were purchased and used
as received. All solvents were purified and distilled using standard
procedures before use. All other reagents were of analytical grade
and were used as received.
ligand-centered oxidation is not favored. In view of a more
positive oxidation potential observed for a branched chlo-
ropalladium(II) complex relative to their chloroplatinum(II)
analogues,49 the involvement of a metal-centered character
in the highest occupied molecular orbital (HOMO) of these
d8 alkynyl complexes is likely. Thus, the irreversible
oxidative waves of these complexes at +1.06 to +1.22 V
versus SCE are likely to involve a certain degree of metal-
centered character. As with the oxadiazole complexes,
slightly less positive waves were observed for complexes
5-8 compared to their corresponding precursor complex 4.
This observation agrees with the slight red shift observed in
the lowest energy absorption bands in their respective
electronic absorption spectra relative to that of their chloro
precursors. Besides, reversible couples at about +0.65 V
were observed for the triphenylamine-containing complexes
3 and 6. In view of the close resemblance of these couples,
they are likely to be ascribed to triphenylamine-based
oxidation with some mixing of metal-centered character.
Similar oxidation potentials have been reported for triph-
enylamine-containing platinum(II) complexes.60
Syntheses. Tribromohexabutyltruxene. This was synthesized
according to modification of a literature procedure.22 To a solution
of hexabutyltruxene (1.11 g, 1.64 mmol) in dichloromethane (15
mL) was added dropwise bromine (0.42 mL, 8.21 mmol) in
dichloromethane (5 mL) over 5 min at room temperature in the
dark. The mixture was then stirred for 24 h at room temperature.
Excess bromine was removed by washing it with aqueous sodium
thiosulfate solution. The desired product was then extracted with
dichloromethane and washed successively with aqueous sodium
carbonate solution and deionized water. The organic fraction was
dried over anhydrous Na2SO4 and filtered. The crude product was
obtained after solvent removal. Subsequent recrystallization of the
crude product with ethanol afforded tribromohexabutyltruxene as
1
a bright yellow solid. Yield: 1.08 g, 72%. H NMR (400 MHz,
n
CDCl3, 298 K, relative to Me4Si): δ 0.40-0.59 (m, 30H; Bu),
0.80-0.99 (m, 12H; nBu), 1.99-2.09 (m, 6H; nBu), 2.81-2.91 (m,
n
6H; Bu), 7.52 (d, 3H, JHH ) 8.5 Hz; protons at C-3, C-8, C-13),
7.57 (s, 3H; protons at C-1, C-6, C-11), 8.19 (d, 3H, JHH ) 8.5
Hz; protons at C-4, C-9, C-14). Positive-ion FAB MS: m/z: 917
[M + 1]+.
Conclusion
A number of luminescent platinum(II) alkynyl complexes,
[{RCtCPt(PEt3)2CtC}2-oxa-2,5] (where R ) C6H4Me and
(C6H5)2NC6H4) and [{RCtC(PEt3)2PtCtC}3truxene] (where
R ) C6H4Me, C6H4OMe, carbazole-C6H4, 1-methylbenzimi-
dazole) were successfully synthesized and characterized. The
electronic absorption spectra of these complexes are dominated
by intraligand [πfπ*(CtC)2-oxa-2,5 or (CtC)3-truxene]
transitions, mixed with some [dπ(Pt)fπ*(CtC)2-oxa-2,5
or (CtC)3-truxene or CtCR] MLCT and IL
[πfπ*(CtCR)] character. These complexes were found to be
emissive at room temperature with rich vibronic structures. Their
lowest lying emissive states were assigned to be derived from
3IL states of the central oxadiazole and truxene moiety. These
complexes were also found to show 2PA, and their 2PA cross-
sections at excitation wavelength at 720 nm have been deter-
mined.
Triethynylhexabutyltruxene. This was synthesized according
to a modification of a literature procedure.66 A mixture of
tribromohexabutyltruxene (1.08 g, 1.18 mmol), Pd(PPh3)2Cl2 (0.12
g, 0.18 mmol), PPh3 (0.05 g, 0.18 mmol), and CuI (0.03 g, 0.18
mmol) were suspended in diethylamine (30 mL). Trimethylsilyl
acetylene (1.0 mL, 7.10 mmol) was added to the mixture, and the
mixture was heated to reflux under nitrogen overnight. The solvent
was then removed in vacuo. Diethyl ether was added to the organic
mixture, and the diethylammonium salt was filtered off. The filtrate
was evaporated under reduced pressure, and the residue was purified
by column chromatography on silica gel (70-230 mesh) using
hexane as the eluent to give tris(trimethylsilyl)ethynylhexa-
butyltruxene as a pale yellow solid after removal of the solvent.
The yellow solid (0.97 g, 1 mmol) was dissolved in dichlo-
romethane-methanol (1:1, v/v), and NaOH (1.6 g, 40 mmol)
dissolved in a minimum amount of deionized water was added.
The mixture was stirred under nitrogen for 2 h. The reaction was
quenched by deionized water, and the organic solvent was removed
under reduced pressure. It was then extracted with dichloromethane
and dried over anhydrous Na2SO4. Subsequent recrystallization from
dichloromethane-methanol afforded triethynylhexabutyltruxene as
Experimental Section
Materials and Reagents. trans-Dichlorobis(triethylphosphine)-
platinum(II) was obtained from Aldrich Chemical Co. 2,5-Bis-(4-
ethynyl)phenyl-1,3,4-oxadiazole ((CtC)2-oxa-2,5),61 10,15-dihydro-
5H-diindeno[1,2-a;1′,2′-c]fluorene (truxene),62 9-(4-ethynylphenyl)-
carbazole (carb),63 (4-ethynylphenyl)diphenylamine,64 and 2-ethynyl-
1-methylbenzimidazole (bzim)65 were synthesized according to literature
procedures. Tribromohexabutyltruxene was prepared according to slight
modification of a reported procedure.22
1
pale yellow crystalline solids. Yield: 0.72 g, 81%. H NMR (400
MHz, CDCl3, 298 K, relative to Me4Si): δ 0.37-0.53 (m, 30H;
nBu), 0.77-0.98 (m, 12H; nBu), 2.03-2.13 (m, 6H; nBu), 2.85-2.95
n
(m, 6H; Bu), 3.20 (s, 3H; CtCH), 7.55 (d, 3H, JHH ) 8.2 Hz;
protons at C-3, C-8, C-13), 7.59 (s, 3H; protons at C-1, C-6, C-11),
8.31 (d, 3H, JHH ) 8.2 Hz; protons at C-4, C-9, C-14). Positive-
ion FAB MS: m/z: 751 [M]+.
[{ClPt(PEt3)2CtC}2-oxa-2,5] (1). This was synthesized accord-
ing to a slight modification of a literature procedure with shorter
reaction time.49 trans-[Pt(PEt3)2Cl2] (1.00 g, 1.99 mmol) and 2,5-
bis-(4-ethynyl)phenyl-1,3,4-oxadiazole (0.13 g, 0.50 mmol) were
dissolved in a mixture of toluene (70 mL) and piperidine (5 mL).
The reaction mixture was heated to reflux for 30 min after which
(60) Jones, S. C.; Coropceanu, V.; Barlow, S.; Kinnibrugh, T.; Timofeeva,
T.; Bre´das, J.-L.; Marder, S. R. J. Am. Chem. Soc. 2004, 126, 11782.
(61) Dong, Y.-B.; Zhang, Q.; Wang, L.; Ma, J.-P.; Huang, R.-Q.; Shen,
D.-Z.; Chen, D.-Z. Inorg. Chem. 2005, 44, 6591.
(62) Dehmlow, E. V.; Kelle, T. Synth. Commun. 1997, 27, 2021.
(63) Sanda, F.; Kawaguchi, T.; Masuda, T. Macromolecules 2003, 36, 2224.
(64) MaIlroy, S. P.; Clo´, E.; Nikolajsen, L.; Frederiksen, P. K.; Nielsen,
C. B.; Mikkelsen, K. V.; Gothelf, K. V.; Ogilby, P. R. J. Org. Chem.
2005, 70, 1134.
(65) Satake, A.; Shoji, O.; Kobuke, Y. J. Organomet. Chem. 2007, 692,
635.
(66) Chen, Q.-Q.; Liu, F.; Ma, Z.; Peng, B.; Wei, W.; Huang, W. Synlett
2007, 20, 3145.
Inorganic Chemistry, Vol. 48, No. 7, 2009 2861

Chan et al.
CuI (5 mg, 0.03 mmol) was added, and the reaction mixture was
then refluxed under nitrogen for 2 days. The solvent was removed
under vacuum, and the yellowish oily residue was dissolved in
dichloromethane and washed successively with aqueous ammonium
chloride solution and deionized water. The organic fraction was
then dried over anhydrous Na2SO4 and filtered. The solvent was
evaporated under reduced pressure. Further purification was ac-
complished by column chromatography on basic aluminum oxide
(50-200 µm), in which the excess trans-[Pt(PEt3)2Cl2] was first
eluted with dichloromethane-hexane (1:1, v/v) followed by the
elution of 1 with dichloromethane. Subsequent recrystallization from
dichloromethane-hexane afforded 1 as a pale yellow microcrystal-
line solid. Yield: 0.46 g, 77%. 1H NMR (400 MHz, CDCl3, 298 K,
relative to Me4Si): δ 1.17-1.27 (virtual quintet (vq), 36H, J ) 8.0
Hz; -CH3), 2.03-2.13 (m, 24H; -CH2P), 7.36 (d, 4H, JHH ) 8.5
Hz; -C6H4-), 7.96 (d, 4H, JHH ) 8.5 Hz; -C6H4-). 31P{1H} NMR
(162 MHz, CDCl3, 298 K, relative to 85% H3PO4): δ 15.10 (s,
JPt-P ) 2374 Hz). IR (KBr disk, ν/cm-1): 2114 (m) ν(CtC).
Positive-ion FAB MS: m/z: 1203 [M + 1]+. Elemental analysis
calcd (%) for 1: C 41.97, H 5.70, N 2.33; found: C 41.76, H 5.74,
N 2.50.
Subsequent recrystallization of the crude product with dichlo-
romethane-n-hexane afforded 4 as a pale yellow microcrystalline
1
solid. Yield: 0.77 g, 72%. H NMR (400 MHz, CDCl3, 298 K,
relative to Me4Si): δ 0.43-0.58 (m, 30H; nBu), 0.86-0.91 (m, 12H;
nBu), 1.20-1.31 (vq, 54H, J ) 8.0 Hz; -CH3), 1.95-2.05 (m,
6H; nBu), 2.09-2.18 (m, 36 H; -CH2P), 2.82-2.92 (m, 6H; nBu),
7.30 (s, 6H; protons at C-1, C-3, C-6, C-8, C-11, C-13), 8.17 (d,
3H, JHH ) 8.7 Hz; protons at C-4, C-9, C-14). 31P{1H} NMR (162
MHz, CDCl3, 298 K, relative to 85% H3PO4): δ 14.84 (s, JPt-P
)
2392 Hz). IR (KBr disk, ν/cm-1): 2112 (m) ν(CtC). Positive-ion
FAB MS: m/z: 2149 [M]+. Elemental analysis calcd (%) for 4: C
51.99, H 7.18; found: C 51.88, H 7.21.
[{carb-C6H4CtC(PEt3)2PtCtC}3truxene] (5). The procedure
was similar to that for 2 except that complex 4 (0.22 g, 0.10 mmol)
and 9-(4-ethynylphenyl)carbazole (0.11 g, 0.40 mmol) were used
instead of complex 1 and 1-ethynyltoluene, respectively. Subsequent
recrystallization of the crude product with dichloromethane-n-
hexane afforded 5 as a yellowish-orange solid. Yield: 0.11 g, 40%.
1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si): δ 0.43-0.61
n
n
(m, 30H; Bu), 0.86-0.91 (m, 12H; Bu), 1.27-1.38 (vq, 54H, J
) 8.0 Hz; -CH3), 2.00-2.09 (m, 6H; nBu), 2.28-2.33 (m, 36 H;
-CH2P), 2.86-2.95 (m, 6H; Bu), 7.28 (d, 6H, JHH ) 7.7 Hz;
n
[{MeC6H4CtCPt(PEt3)2CtC}2-oxa-2,5] (2). This was synthe-
sized according to a slight modification of a literature procedure.49
Complex 1 (0.12 g, 0.10 mmol) and 1-ethynyltoluene (0.04 g, 0.30
mmol) were dissolved in a mixture of THF (20 mL) and triethy-
lamine (10 mL). CuI (5 mg) was added to this reaction mixture as
a catalyst. The yellow mixture was then stirred under nitrogen
overnight at room temperature, after which the solvent was removed
under reduced pressure. The yellow residue was then dissolved in
dichloromethane, washed successively with brine and deionized
water, and dried over anhydrous Na2SO4. The solution was then
filtered, and the solvent was removed under reduced pressure. The
yellow residue was chromatographed on basic alumina oxide
(50-200 µm) with dichloromethane as the eluent. Subsequent
recrystallization of the crude product with dichloromethane-
methanol afforded 2 as a yellow solid. Yield: 0.05 g, 35%. 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ 1.19-1.27 (vq,
36H, J ) 8.0 Hz; -CH3), 2.15-2.22 (m, 24 H; -CH2P), 2.30 (s,
6H; -C6H4Me), 7.03 (d, 4H, JHH ) 8.0 Hz; -C6H4-), 7.18 (d,
4H, JHH ) 8.0 Hz; -C6H4-), 7.38 (d, 4H, JHH ) 8.4 Hz; -C6H4-),
7.96 (d, 4H, JHH ) 8.4 Hz; -C6H4-). 31P{1H} NMR (162 MHz,
CDCl3, 298 K, relative to 85% H3PO4): δ 11.21 (s, JPt-P ) 2363
Hz). IR (KBr disk, ν/cm-1): 2099 (m) ν(CtC). Positive-ion FAB
MS: m/z: 1362 [M]+. Elemental analysis calcd (%) for 2: C 52.94,
H 6.07, N 2.06; found: C 52.97, H 6.10, N 2.29.
protons at 3,6-positions of carb), 7.30 (d, 3H, JHH ) 7.7 Hz; protons
at C-3, C-8, C-13), 7.37 (s, 3H; protons at C-1, C-6, C-11),
7.40-7.42 (m, 18H; protons at 2,7-positions of carb and -C6H4-),
7.50 (d, 6H, JHH ) 8.4 Hz; protons at 1,8-positions of carb), 8.14
(d, 6H, JHH ) 7.7 Hz; protons at 4,5-positions of carb), 8.20 (d,
3H, JHH ) 8.4 Hz; protons at C-4, C-9, C-14). 31P{1H} NMR (162
MHz, CDCl3, 298 K, relative to 85% H3PO4): δ 11.19 (s, JPt-P
)
2371). IR (KBr disk, ν/cm-1): 2099 (m) ν(CtC). Positive-ion FAB
MS: m/z: 2842 [M + 1]+. Elemental analysis calcd (%) for 5: C
64.68, H 6.70, N 1.48; found: C 64.87, H 6.89, N 1.58.
[{(C6H5)2NC6H4CtC(PEt3)2PtCtC}3truxene] (6). The proce-
dure was similar to that for 5 except that (4-ethynylphenyl)diphe-
nylamine (0.11 g, 0.40 mmol) was used instead of 9-(4-
ethynylphenyl)carbazole. Subsequent recrystallization of the crude
product with dichloromethane-n-hexane afforded 6 as a yellow solid.
1
Yield: 0.20 g, 72%. H NMR (400 MHz, CDCl3, 298 K, relative
to Me4Si): δ 0.44-0.57 (m, 30H, nBu), 0.83-0.96 (m, 12H, nBu),
1.24-1.31 (vq, 54H, J ) 8.0 Hz; -CH3), 1.97-2.04 (m, 6H; nBu),
n
2.24-2.27 (m, 36H; -CH2P), 2.83-2.91 (m, 6H; Bu), 6.94 (d,
6H, JHH ) 8.6 Hz; -C6H4-), 6.98 (t, 6H, JHH ) 7.4 Hz;
-C6H4NPh2), 7.08 (d, 12H, JHH ) 7.5 Hz; -C6H4NPh2), 7.17 (d,
6H, JHH ) 8.6 Hz; -C6H4-), 7.24 (t, 12H, JHH ) 7.4 Hz;
-C6H4NPh2), 7.28 (d, 3H, JHH ) 8.4 Hz; protons at C-3, C-8, C-13),
7.33 (s, 3H; protons at C-1, C-6, C-11), 8.16 (d, 3H, JHH ) 8.4
Hz; protons at C-4, C-9, C-14). 31P{1H} NMR (162 MHz, CDCl3,
298 K, relative to 85% H3PO4): δ 11.06 (s, JPt-P ) 2375 Hz). IR
(KBr disk, ν/cm-1): 2097 (m) ν(CtC). Positive-ion FAB MS: m/z:
2848 [M + 1]+. Elemental analysis calcd (%) for 6: C 64.54, H
6.90, N 1.48; found: C 64.25, H 6.96, N 1.53.
[{(C6H5)2NC6H4CtCPt(PEt3)2CtC}2-oxa-2,5] (3). The proce-
dure was similar to that for 2 except that (4-ethynylphenyl)dipheny-
lamine (0.08 g, 0.30 mmol) was used instead of 1-ethynyltoluene.
Subsequent recrystallization of the crude product with dichloromethane-
1
n-hexane afforded 3 as a pale yellow solid. Yield: 0.07 g, 52%. H
NMR (400 MHz, CDCl3, 298 K, relative to Me4Si): δ 1.20-1.28 (vq,
36H, J ) 8.0 Hz; -CH3), 2.15-2.23 (m, 24 H; -CH2P), 6.93 (d, 4H,
JHH ) 8.6 Hz; -C6H4NPh2); 6.98 (t, 4H, JHH ) 7.3 Hz; -C6H4NPh2);
7.07 (d, 8H, JHH ) 7.6 Hz; -C6H4NPh2); 7.16 (d, 4H, JHH ) 8.6 Hz;
-C6H4NPh2); 7.23 (t, 8H, JHH ) 7.3 Hz; -C6H4NPh2); 7.38 (d, 4H,
JHH ) 8.4 Hz; -C6H4-), 7.96 (d, 4H, JHH ) 8.4 Hz; -C6H4-).
31P{1H} NMR (162 MHz, CDCl3, 298 K, relative to 85% H3PO4): δ
11.24 (s, JPt-P ) 2365 Hz). IR (KBr disk, ν/cm-1): 2099 (m) ν(CtC).
Positive-ion FAB MS: m/z: 1668 [M]+. Elemental analysis calcd (%)
for 3: C 59.14, H 5.80, N 3.36; found: C 59.20, H 5.95, N 3.35.
[{Cl(PEt3)2PtCtC}3truxene] (4). The procedure was similar to
that for 1 except that triethynylhexabutyltruxene (0.38 g, 0.50 mmol)
was used instead of 2,5-bis-(4-ethynyl)phenyl-1,3,4-oxadiazole.
[{CH3C6H4CtC(PEt3)2PtCtC}3truxene] (7). The procedure
was similar to that for 5 except that 1-ethynyltoluene (0.05 g, 0.40
mmol) was used instead of 9-(4-ethynylphenyl)carbazole. Subse-
quent recrystallization of the crude product with dichloromethane-
methanol afforded 7 as a yellow solid. Yield: 0.18 g, 73%. 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ 0.44-0.56 (m,
n
n
30H; Bu), 0.87-0.94 (m, 12H; Bu), 1.25-1.31 (vq, 54H, J )
n
8.0 Hz; -CH3), 1.98-2.04 (m, 6H; Bu), 2.24-2.26 (m, 36H;
-CH2P), 2.27 (s, 9H; -C6H4Me), 2.83-2.93 (m, 6H; Bu), 7.03
n
(d, 6H, JHH ) 8.0 Hz; -C6H4-), 7.20 (d, 6H, JHH ) 8.0 Hz;
-C6H4-), 7.28 (d, 6H, JHH ) 8.4 Hz; protons at C-1, C-3, C-6,
C-8, C-11, C-13), 8.16 (d, 3H, JHH ) 8.4 Hz; protons at C-4,
2862 Inorganic Chemistry, Vol. 48, No. 7, 2009

Luminescent Platinum(II) Alkynyl Complexes
C-9, C-14). 31P{1H} NMR (162 MHz, CDCl3, 298 K, relative
to 85% H3PO4): δ 11.03 (s, JPt-P ) 2362 Hz). IR (KBr disk,
ν/cm-1): 2100 (m) ν(CtC). Positive-ion FAB MS: m/z: 2389
[M + 1]+. Elemental analysis calcd (%) for 7: C 60.36, H 7.35;
found: C 60.60, H 7.33.
according to eq 1. An unknown sample is compared to a reference
with known σ2 values. Fluorescein (1 × 10-4 M in 0.1 M NaOH
aqueous solution) was used as the reference in the present study.69
CrnrΦrSs
σ2(s)
)
σ2(r)
(1)
CsnsΦsSr
[{bzimCtC(PEt3)2PtCtC}3truxene] (8). The procedure was
similar to that for 2 except that 2-ethynyl-1-methylbenzimidazole
(0.06 g, 0.40 mmol) was used instead of 9-(4-ethynylphenyl)car-
bazole. Subsequent recrystallization of the crude product with
dichloromethane-methanol afforded 8 as a pale orange solid. Yield:
0.13 g, 53%. 1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si):
δ 0.45-0.60 (m, 30H; nBu), 0.83-0.95 (m, 12H; nBu), 1.24-1.32
(vq, 54H, J ) 8.0 Hz; -CH3), 1.99-2.06 (m, 6H; nBu), 2.24-2.28
(m, 36H; -CH2P), 2.85-2.92 (m, 6H; nBu), 3.83 (s, 9H; -CH3 at
bzim), 7.23 (s, 9H; protons at 4, 5 and 6-positions at bzim), 7.30
(d, 3H, JHH ) 8.1 Hz; protons at C-3, C-8, C-13), 7.35 (s, 3H;
protons at C-1, C-6, C-11), 7.70 (d, 3H, JHH ) 8.3 Hz; protons at
7-position of bzim), 8.19 (d, 3H, JHH ) 8.1 Hz; protons at C-4,
C-9, C-13). 31P{1H} NMR (162 MHz, CDCl3, 298 K, relative to
85% H3PO4): δ 11.71 (s, JPt-P ) 2353 Hz). IR (KBr disk, ν/cm-1):
2101 (m) ν(CtC). Positive-ion FAB MS: m/z: 2510 [M]+.
Elemental analysis calcd (%) for 8: C 59.03, H 7.07, N 3.33; found:
C 59.34, H 7.34, N 3.08.
Physical Measurements and Instrumentation. 1H NMR spectra
were recorded on Bruker DPX 300 (300 MHz) or Bruker DPX 400
(400 MHz) Fourier-transform NMR spectrometers with chemical shifts
reported relative to tetramethylsilane, Me4Si, while 31P{1H} spectra
were recorded either on a Bruker DPX 400 or a Bruker DPX 500
Fourier-transform NMR spectrometer with chemical shifts reported
relative to 85% H3PO4. Positive-ion FAB mass spectra were recorded
on Finnigan MAT95 mass spectrometer. IR spectra were obtained
using KBr disks on a Bio-Rad FTS-7 Fourier-Transform infrared
spectrophotometer (4000-400 cm-1). Elemental analyses were per-
formed on a Flash EA 1112 elemental analyzer at the Institute of
Chemistry, Chinese Academy of Sciences. The electronic absorption
spectra were obtained by using a Hewlett-Packard 8452 A diode array
spectrophotometer. Steady-state excitation and emission spectra at room
temperature and at 77 K were recorded on a Spex Fluorolog-2 Model
F111 fluorescence spectrofluorometer. Solid-state photophysical studies
were carried out with solid samples contained in a quartz tube inside
a quartz-walled Dewar flask. Measurements of the ethanol-methanol
(4:1, v/v) glass or solid-samples at 77 K were conducted by using
liquid nitrogen filled in the optical Dewar flask. All solutions for
photophysical studies were degassed with a high-vaccum line on a
two-compartment cell consisting of a 10 mL Pyrex bulb and a quartz
cuvette (1 cm path length) and sealed from the atmosphere by a Bibby
Rotaflo HP6 Telfon stopper. The solutions were rigorously degassed
with at least four successive freeze-pump-thaw cycles. Emission
lifetime measurements were performed by using a conventional laser
system. The excitation source was with a 355 nm output (third
harmonic) from a Spectra-Physics Quanta-Ray Q-switch GCR-150-
10 pulsed Nd:YAG laser. Luminescence decay signals were detected
by a Hamamatsu R928 photomultiplier tube, recorded on a Tektronix
Model TDS-620 A (500 MHz, 2 GS s-1) digital oscilloscope, and
analyzed by using a program for exponential fits.
where σ2 is the 2PA cross-section, C is the concentration, n is
refractive index, Φ is the luminescence quantum yield, and S is
the integrated luminescence signal. The subscripts r and s represent
the reference and the sample material, respectively. The σ2 and
luminescence quantum yield of fluorescein in 0.1 M NaOH solution
(pH ∼ 11) at 720 nm were assumed to be 19 GM (Gøppert-Mayer,
1 GM ) 1 × 10-50 cm4 sec photon-1 molecule-1) and 0.90,69
respectively. The time-averaged laser power at 720 nm was kept
constant for the sample and the reference. The laser pulses were
generated by a mode-locked Ti:Sapphire laser (Spectra-Physics,
Tsunami) operating at a repetition rate of 85 MHz. The pulses were
amplified up to 1 mJ per pulse by the Ti:Sapphire regenerative
amplifier (Spectra-Physics, Spitfire) with pulse duration of ∼120
fs and repetition rate of 1 kHz. The 720 nm laser output from the
OPA (Coherent, TOPAS-C light conversion) was used as the
excitation source. The laser output was passed through the sample
cell, and the luminescence intensity was monitored by the spec-
trometer system with monochromator (ACTON Research Corpora-
tion, SpectraPro 2300i) and photomultiplier tube (Hamamatsu,
R636-10). For the power dependence measurements, the laser beam
power was altered by using two polarizers, which was partially
reflected to a photodiode for the monitoring of the excitation power.
The experimental setup for the two-photon induced luminescence
studies is shown in Figure 6.
Figure 6. Schematic experimental setup for two-photon induced lumines-
cence (TPIL) measurement.
Cyclic voltammetric measurements were performed using a CH
Instruments, Inc., model CHI 750 A electrochemical analyzer.
Electrochemical measurements were performed in dichloromethane
solutions with 0.1 M nBu4NPF6 (TBAH) as the supporting
electrolyte at room temperature. The reference electrode was an
Ag/AgNO3 (0.1 M 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 1 µm alumina slurry (CH Instru-
ments, Inc.) and then with 0.3 µm alumina slurry (CH Instruments,
Inc.) on a microcloth (Buehler Co.). It was rinsed with ultrapure
deionized water and sonicated in a beaker containing ultrapure
(67) Xu, C.; Webb, W. W. Multiphoton Excitation of Molecular Fluoro-
phores and Nonlinear Laser Microscopy. In Topics in Fluorescence
Spectroscopy; Lakowicz, J. R., Ed.; Plenum Press: New York, 1997;
Vol. 5, Chapter 11, pp 471-537.
(68) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481.
(69) Albota, M. A.; Xu, C.; Webb, W. W. Appl. Opt. 1998, 37, 7352.
The 2PA cross-section (σ2) can be determined by two main
methods.67,68 Two-photon induced luminescence (TPIL) is one of
the methods to determine σ2 in which the luminescence intensity
generated by 2PA was measured and used to estimate the σ2 values
Inorganic Chemistry, Vol. 48, No. 7, 2009 2863

Chan et al.
deionized water for 5 min. The polishing and sonicating steps were
repeated twice and then the working electrode was rinsed under a
stream of ultrapure deionized water. The ferrocenium/ferrocene
couple (FeCp2+/0) was used as the internal reference. All solutions
for electrochemical studies were deaerated with prepurified argon
gas prior to measurements.
were generated by program SHELXL-97 program72 and were
calculated based on the riding mode with thermal parameters equal
to 1.2 times that of the associated C atoms and participated in the
calculation of final R-indices. Since the structure refinements are
against F2, R-indices based on F2 are larger than (more than double)
those based on F. For comparison with older refinements based on
F and an OMIT threshold, a conventional index R1 based on
observed F values larger than 4σ(Fo) is also given (corresponding
X-ray Crystal Structure Determination. Crystals of triethy-
nylhexabutyltruxene were obtained by recrystallization from dichlo-
romethane-methanol. Crystal data: [C57H66], M ) 751.10, orthor-
hombic, space group Pna21, a ) 16.570(3) Å, b ) 18.708(4) Å, c
to Intensity g 2σ(I)). wR2 ) {∑[w(Fo2 - Fc2)2]/∑w(Fo )2}1/2, R1 )
2
∑||Fo| - |Fc||/∑|Fo|. The goodness of fit (GoF) is always based on
) 15.787(3) Å, V ) 4893.8(17) Å3, Z ) 4, Dc ) 1.019 g cm-3
,
F2: GoF ) S ) {∑[w(Fo - Fc2)2]/(n - p)}1/2, where n is the
2
µ(Mo KR) ) 0.057 mm-1, F(000) ) 1632, T ) 301 K. A pale
yellow crystal of dimensions 0.6 mm × 0.4 mm × 0.25 mm in a
glass capillary was used for data collection at 28 °C on a MAR
diffractometer with a 300 mm image plate detector using graphite
monochromatized Mo KR radiation (λ ) 0.71073 Å). Data
collection was made with 1.5° oscillation step of ꢀ (120 images)
at 120 mm distance and 5 min exposure. The images were
interpreted and intensities integrated using program DENZO.70 The
structure was solved by direct methods by employing the SHELXS-
97 program71 on a PC. Most C atoms were located according to
the direct methods. The positions of the other non-hydrogen atoms
were found after successful refinement by full-matrix least-squares
using program SHELXL-9772 on a PC. There was one formula unit
in the asymmetric unit. Two n-butyl groups were disordered into
two sets of positions. Restraints were applied to the disordered C
atoms, assuming similar C-C and 1,3-C · · · C bond lengths or
distances, respectively. According to the SHELXL-97 program,72
number of reflections and p is the total number of parameters
refined. The weighting scheme is w ) 1/[σ2(Fo ) + (aP)2 + bP],
2
2
where P is [2Fc2 + max(Fo ,0)]/3. Convergence ((∆/σ)max ) 0.001,
av. 0.001) for 465 variable parameters by full-matrix least-squares
refinement on F2 reaches to R1 ) 0.0597 and wR2 ) 0.1396 with
a goodness-of-fit of 0.81; the parameters a and b for weighting
scheme are 0.0307 and 0.0. The final difference Fourier map shows
maximum rest peaks and holes of 0.165 and -0.145 e Å-3
,
respectively. Selected bond lengths and angles are summarized in
Table 1.
Acknowledgment. V.W.-W.Y. acknowledges support
from The University of Hong Kong under the Distinguished
Research Achievement Award Scheme. We also acknowl-
edge support from the University Development Fund and
the Faculty Development Fund of The University of Hong
Kong, and the URC Strategic Research Theme on Molecular
Materials. The work described in this paper has been
supported by a RGC Central Allocation Vote (CAV) Grant
(HKU 2/05C). C.K.M.C. acknowledges support from The
University of Hong Kong and the receipt of a University
Postgraduate Studentship. C.-H.T. acknowledges support
from The University of Hong Kong and the receipt of a
University Postdoctoral Fellowship.
73
all 8174 independent reflections (Rint equal to 0.0645, 3199
reflections larger than 4σ(Fo)) from a total of 32031 reflections
participated in the full-matrix least-squares refinement against F2.
These reflections were in the range -17 e h e 18, -22 e k e 22,
-19 e l e 18 with 2θmax equal to 51.30°. In the final stage of
least-squares refinement, disordered C atoms were refined isotro-
pically; other non-H atoms were refined anisotropically. H atoms
(70) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276:
Macromolecular Crystallography Part A; Carter, C. W., Jr.; Sweet,
R. M., Eds.; Academic Press: San Diego, 1997; pp 307-326.
(71) Sheldrick, G. M. SHELXS97, Programs for Crystal Structure Analysis,
Release 97-2; University of Go¨ttingen: Go¨ttingen, Germany.
Supporting Information Available: Tables of crystal data,
atomic coordinates, thermal parameters, and a full list of bond
distances and angles for triethynylhexabutyltruxene. This material
is available free of charge via the Internet at http://pubs.acs.org.
(72) Sheldrick, G. M. SHELXL97 Programs for Crystal Structure Analysis,
Release 97-2; University of Go¨ttingen: Go¨ttingen, Germany.
2
2
2
(73) Rint ) ∑|Fo - Fo (mean)|/∑[Fo ].
IC8017979
2864 Inorganic Chemistry, Vol. 48, No. 7, 2009