Dual luminescent dinuclear gold(I) complexes of terpyridyl-functionalized alkyne ligands and their efficient sensitization of EuIII and Yb III luminescence

Article abstract of DOI:10.1002/ejic.201000324

Reaction of (tpyC₆H₄C=CAu)_n {tpyC ₆H₄C=CH = 4'-(4-ethynylphenyl)-2,2':6',2 - terpyridine} with diphosphane ligands Ph₂P(CH₂) _xPPh₂ (x = 2 dppe, 3 dppp, 4 dppb, 5 dpppen, 6 dpph) in CH₂Cl₂ afforded the corresponding dual luminescent binuclear gold(I) complexes [(tpyC₆H₄C=CAu)_2- (μ-dppe)] (1), [(tpyC6H4C=CAu)2(|i-dppp)] (2), [(tpyC6H4C=CAu)2(|i-dppb)] (3), [(tpyC₆H₄C=CAu)₂(μ-dpppen)] (4), [(tpyC₆H₄C=CAu)₂(μ-dpph)] (5). Crystal structural analysis of complexes 1·2CH₂Cl₂ and 2·2CH₂Cl₂ show that the terpyridine moieties are free of coordination in these gold(I)-acetylide-phosphane complexes. Spectrophotometric titration between complex 1 and [Eu(tta)₃] (Htta = 2-thenoyltrifluoroacetone) or [Yb(hfac)₃(H₂O) ₂] (Hhfac = hexafluoroacetylacetone) gave a 2:1 ratio between Ln(β-diketonate)₃ (Ln = Eu, Yb) units and the complex 1 moiety, indicating the formation of Au₂Ln₂ complexes. Both the luminescence titrations and the luminescence quantum yields of Au ₂Ln₂ (Ln = Eu, Yb) solutions show that the energy transfer occurs efficiently from the binuclear gold(I) antennas 1-5 to Eu_III and Yb_III centers, and all complexes 1-5 are good energy donors for sensitization of visible and NIR luminescence of Eu_III and Yb _III ions.

Full text of DOI:10.1002/ejic.201000324

FULL PAPER
DOI: 10.1002/ejic.201000324
Dual Luminescent Dinuclear Gold(I) Complexes of Terpyridyl-Functionalized
Alkyne Ligands and Their Efficient Sensitization of EuIII and YbIII
Luminescence
Xiu-Ling Li,*[a] Ke-Juan Zhang,[a] Juan-Juan Li,[a] Xin-Xin Cheng,[a] and
Zhong-Ning Chen[b]
Keywords: Gold / Lanthanides / Dinuclear complexes / Sensitized luminescence / Alkynes
Reaction of (tpyC6H4CϵCAu)n {tpyC6H4CϵCH = 4Ј-(4-eth-
ynylphenyl)-2,2Ј:6Ј,2ЈЈ-terpyridine} with diphosphane li-
gands Ph2P(CH2)xPPh2 (x = 2 dppe, 3 dppp, 4 dppb, 5
dpppen, 6 dpph) in CH2Cl2 afforded the corresponding dual
luminescent binuclear gold(I) complexes [(tpyC6H4CϵCAu)2-
(µ-dppe)] (1), [(tpyC6H4CϵCAu)2(µ-dppp)] (2), [(tpyC6H4Cϵ
CAu)2(µ-dppb)] (3), [(tpyC6H4CϵCAu)2(µ-dpppen)] (4),
[(tpyC6H4CϵCAu)2(µ-dpph)] (5). Crystal structural analysis
of complexes 1·2CH2Cl2 and 2·2CH2Cl2 show that the terpyr-
idine moieties are free of coordination in these gold(I)-acet-
ylide-phosphane complexes. Spectrophotometric titration
between complex 1 and [Eu(tta)3] (Htta = 2-thenoyltrifluoro-
acetone) or [Yb(hfac)3(H2O)2] (Hhfac = hexafluoroacetyl-
acetone) gave a 2:1 ratio between Ln(β-diketonate)3 (Ln =
Eu, Yb) units and the complex 1 moiety, indicating the forma-
tion of Au2Ln2 complexes. Both the luminescence titrations
and the luminescence quantum yields of Au2Ln2 (Ln = Eu,
Yb) solutions show that the energy transfer occurs efficiently
from the binuclear gold(I) antennas 1–5 to EuIII and YbIII cen-
ters, and all complexes 1–5 are good energy donors for sensi-
tization of visible and NIR luminescence of EuIII and YbIII
ions.
coordinated water molecules in [Ln(β-diketonate)3(H2O)2]
compounds can be easily replaced by chelating chromo-
phores such as phenanthroline or polypyridine, which re-
sults in highly luminescent ternary complexes.[6–7,8a,9]
With respect to energy-transfer processes and minimi-
zation of nonradiative deactivation in the d-f assembly, it is
very advantageous to use polypyridine-functionalized alk-
ynyl ligands to assemble d-f arrays because they contain
both soft donors in the alkynyl positions and hard donors
in the polypyridine moieties.[6–7,8a] The polypyridine unit
can provide high coordination number and eliminate water
molecules from the first coordination sphere of LnIII cen-
ters effectively because of its good chelating ability. On the
other hand, the good linearity and conjugacy of polypyr-
idine-functionalized alkynyl ligands are favorable to the en-
ergy transfer from the antenna ligand to the LnIII lumines-
cence centers.[6–7,8a] A series of polypyridine-functionalized
alkynyl ligands were utilized for the construction of d-block
chromophores by incorporation with [Ln(β-diketonate)3-
(H2O)2] compounds achieving sensitized lanthanide lumi-
nescence in our previous work.[2a,6–7]
Introduction
Lanthanide(III) luminescence has attracted intensive re-
search efforts because of its distinct advantages such as high
color purity induced by narrow emission bands, long radia-
tive lifetimes of the excited states in the range of microsec-
onds to milliseconds, large Stokes’ shifts, and relatively im-
movable emission positions.[1–2] Because of these advan-
tages, lanthanide(III) complexes have been extensively ap-
plied to biomedical assays, optical communication, mag-
netic resonance imaging, lasers, and as components of the
emitter layers in multilayer organic light-emitting devices
(OLEDS), etc.[3–5] But direct excitation of the LnIII centers
always leads to inefficient luminescence because of the ex-
tremely weak absorption from Laporte-forbidden f-f transi-
tions of the LnIII ions.[1b] In order to improve the lumines-
cence yields of LnIII ions, one of the most feasible strategies
is to use strong absorbing organic or d-block metallorganic
antenna chromophores as ligands and sensitizers.[2a,6–8]
Ln(β-diketonate)3 moieties represent another efficient and
well-investigated type of LnIII co-ordinating unit. The two
Other important effects in achieving efficient energy
transfer from the antennas to LnIII (Ln = Eu, Yb) centers
include the energy match between the triplet state and the
5D0 energy level of the EuIII ions,[9b,10] and the overlap de-
gree between the emission bands of the antennas and the
[a] School of Chemistry and Chemical Engineering, Xuzhou
Normal University,
Xuzhou, Jiangsu 221116, China
E-mail: lxl@fjirsm.ac.cn
[b] State Key Laboratory of Structural Chemistry, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of
Sciences,
absorption spectra of YbIII [6]
So whether the triplet states
.
Fuzhou, Fujian 350002, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000324.
of the antennas can be determined easily, especially at room
temperature, becomes very important to avoid a blind at-
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FULL PAPER
tempt. The organometallic AuI phosphane acetylides have
exhibited easily observed phosphorescence emission proper-
ties due to the heavy atom effect of the AuI ions or auro-
philic interactions,[7d,11–14] so that their triplet states can be
easily concluded. In addition, their long phosphorescence
lifetimes favor energy transfer.[6,7,11d,12b,14b] It has been re-
ported that the AuI acetylide phosphane chromophores are
favorable antenna chromophores for sensitization of lantha-
nide luminescence when using 5-ethynyl-2,2Ј-bipyridine as
a bridging ligand in the Au4Ln4 or Au2Ln2 complexes, but
the reported quantum yields of EuIII complexes are rela-
tively low (0.010–0.012),[7d] and the triplet states of the an-
tennas in dichloromethane solutions could not be observed
at room temperature. In order to obtain an intensely phos-
phorescent system at room temperature, and understand
further how to better match the triplet states of gold(I) an-
tennas and the emitting levels of LnIII and figure out which
LnIII ions may be sensitized efficiently, the conjugated de-
gree of the alkyne system should be more extended because
most phosphorescent systems at room temperature have a
large conjugated degree apart from the heavy
atom.[6,7d,11,14b] On the basis of this consideration, the ter-
pyridyl-functionalized alkyne ligand 4Ј-(4-ethynylphenyl)-
Scheme 1. Synthetic routes to complexes 1–5.
Crystallographic Studies
2,2Ј:6Ј,2ЈЈ-terpyridine (tpyC6H4CϵCH) is
a judicious
choice, and a series of its intense room temperature phos-
phorescent PtII complexes have been synthesized and used
as efficient sensitized chromophores in our previous work.[6]
For this work a series of binuclear gold(I)-alkynyl-phos-
phane complexes were prepared by depolymerization of
polymeric (tpyC6H4CϵCAu)n with diphosphane ligands
Ph2P(CH2)xPPh2 (x = 2 dppe, 3 dppp, 4 dppb, 5 dpppen, 6
dpph) in CH2Cl2. The luminescence titrations and lumines-
cence quantum yields of Au2Ln2 (Ln = Eu, Yb) solutions
demonstrate that all complexes 1–5 are good energy donors
for sensitization of visible and NIR luminescence of EuIII
and YbIII ions.
The crystal structures of 1·2CH2Cl2 and 2·2CH2Cl2 were
determined by single-crystal X-ray diffraction. Selected
bond lengths and angles are presented in Table 1. The mo-
lecular structures of 1·2CH2Cl2 and 2·2CH2Cl2 are shown
in Figures 1 and 2, respectively. Complexes 1·2CH2Cl2 and
2·2CH2Cl2 crystallize in the triclinic system with space
¯
group P1 and monoclinic system with space group C2/c,
respectively. Complex 1·2CH2Cl2 adopts a trans conforma-
tion. Complex 2·2CH2Cl2 adopts a gauche conformation
with a P1–C71–C72–C71A torsion angle of 175(2)°. The
AuI centers in the two complexes adopt quasilinear coordi-
nation geometries as reported in many gold(I)-acetylide-
phosphane complexes,[11–14,17–19] and the C–Au–P angles
are in the range of 177.2(4)–178.5(2)°, deviating slightly
from 180°. The bond lengths of Au–P [2.271(2)–2.282(4) Å]
and Au–C [1.971(12)–2.027(6) Å] are in good agreement
with the lengths in analogous Au-acetylide sys-
tems.[11–14,17–20] The CϵC distances [1.162(10)–1.224(15) Å]
are comparable to those in the similar dinuclear gold(I)-
arylacetylide-phosphane complexes.[20] The intramolecular
Au···Au distances are 7.078 Å in 1·2CH2Cl2 and 5.294 Å in
2·2CH2Cl2, while the closest intermolecular Au···Au dis-
tances are 8.840 Å in 1·2CH2Cl2 and 6.556 Å in 2·2CH2Cl2.
Results and Discussion
Syntheses of Gold(I) Complexes and Characterization
The dinuclear gold(I)-phosphane-acetylide complexes
were prepared by general methods established previously[7d]
through the reaction of diphosphane ligands with the corre-
sponding gold(I) coordination polymer (tpyC6H4CϵCAu)n
(Scheme 1) and purified by chromatography on short silica-
gel columns using dichloromethane/methanol (100:2) as
eluent. Recrystallization was carried out through slow dif-
fusion of n-hexane into the corresponding concentrated
dichloromethane solutions, from which pale yellow crystals
of complexes 1·2CH2Cl2, and 2·2CH2Cl2 suitable for X-ray
diffraction were obtained. In the IR spectra, all the dinu-
clear gold(I)-phosphane-acetylide complexes 1–5 exhibit
νCϵC modes at about 2110 cm–1, which falls into the normal
range of terminally σ-coordinated alkynyl ligands.[6,7]
Lower frequency for the νCϵC bands is not observed, indi-
cating no π-coordination mode of the CϵC bond ex-
ists.[6,7,15–17]
Table 1. Selected bond lengths [Å] and angles [°] for 1·2CH2Cl2 and
2·2CH2Cl2.
1·2CH2Cl2
2·2CH2Cl2
Au–P1
Au–C23
C22–C23
C23–Au–P1
C22–C23–Au
C19–C22–C23
2.271(2)
2.027(6)
1.162(10)
178.5(2)
175.5(8)
178.7(8)
Au1–P1
Au1–C1
C1–C2
C1–Au1–P1
C2–C1–Au1
C3–C2–C1
2.282(4)
1.971(12)
1.224(15)
177.2(4)
173.8(11)
179.4(14)
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Dual Luminescent Dinuclear Gold(I) Complexes
Figure 1. ORTEP drawing of 1·2CH2Cl2 with atom labeling scheme showing 30% thermal ellipsoids. Phenyl rings of dppe, CH2Cl2
molecules, and hydrogen atoms are omitted for clarity (symmetry code for A: –x – 2, –y – 1, –z – 1).
Figure 2. ORTEP drawing of 2·2CH2Cl2 with atom labeling scheme showing 30% thermal ellipsoids. Phenyl rings of dppp, CH2Cl2
molecules, and hydrogen atoms are omitted for clarity (symmetry code for A: –x + 1, y, 0.5 – z).
These Au···Au distances are much longer than 3.6 Å,[11d] pendicular distance 3.486(3) Å, offset 1.222(3) Å]. Similar
indicating no intramolecular or intermolecular Au···Au in- weak interaction has been observed in the crystal structure
teraction in these complexes.
of [tpyC6H4CϵCAuPPh3].[14b] The 2-D layers further inter-
act with each other forming 3-D frameworks through C25–
H25A···Cl1 (–x – 2, –y, –z – 1) weak hydrogen bonds [dH···Cl
= 2.820 Å, dC25···Cl = 3.658 Å, ЄC25–H25A···Cl1 (–x – 2, –
y, – z – 1) = 151°] and Cl2···Cl2 (–x – 3, –y – 1, –z, 3.129 Å)
weak interactions (see Figure 4).[22] No obvious weak inter-
action was observed for 2·2CH2Cl2.
C–H···Au Interaction
Weak X–H···M hydrogen bonds have received much at-
tention in recent years, and they could be structurally sig-
nificant in constructing supramolecular architectures, espe-
cially when no other classical hydrogen bonds and M···M
interactions exist in a structure.[14b,19b–19d] As the metal cen-
ters act as Lewis bases, the electron-rich metals such as late
transition metals in low oxidation states are favored. The
X–H···M interactions with angles less than 130° have gen-
erally been excluded.[15,21] In the crystal structure of
1·2CH2Cl2, as shown in Figure 3, the molecules of 1 are
linked through C14–H14A···Au (–x – 3, –y – 1, –z) (dH···Au
= 3.067 Å, ЄC–H···Au = 154.7°) and C27–H27A···Au (x,
y + 1, z) (dH···Au = 3.163 Å, ЄC–H···Au = 159.5°) interac-
tions to produce 2-D layers, and the 2-D layers are rein-
forced through π···π stacking interactions occurring be-
tween two exactly parallel pyridine rings consisting of six
atoms (N2, C6–C10) and its symmetric ring at the –x – 3,
Figure 3. The 2-D layer of 1·2CH2Cl2 induced by C–H···Au and
π···π interactions. CH2Cl2 molecules and hydrogen atoms are omit-
–y – 2, –z position [intercentroid distance 3.694(4) Å, per- ted for clarity except H14A, H27A and their symmetrical atoms.
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some Au orbital character. The low-energy absorption
bands in complexes 1–5 display vibrational character with
the vibronic spacings around 1257 cm–1, corresponding to
vibrational stretching frequencies of the pyridyl in
CϵCC6H4tpy units.[6] In addition, complexes 1–5 exhibit
large molar absorption coefficients (ε = 7.972ϫ104 to
1.130ϫ105), which reveals their strong light-absorbing abil-
ity.[6,7d]
Figure 4. The 3-D framework of 1·2CH2Cl2. Phenyl rings of dppe
and most hydrogen atoms are omitted for clarity.
Luminescence
Photophysical Properties
The luminescence data, including emission wavelengths,
lifetimes, and quantum yields of 1–5, are presented in
Table 3. The emission spectra of 1–5 in the solid state and
in dichloromethane solution at 298 K are shown in Fig-
ures 6 and 7, respectively. All the dinuclear gold(I) com-
plexes 1–5 exhibit dual emission bands both in the solid
state and in dichloromethane solution at 298 K. Most low-
energy bands for complexes 1–5 in the solid state and in the
dichloromethane solution display vibronic character with
spacings in the range of 1225–1339 cm–1 which is typical of
the νC–C and νC–N aromatic vibrational modes in the alkynyl
Absorption Spectra
UV/Vis absorption data for 1–5 in dichloromethane solu-
tion at 298 K are summarized in Table 2. The correspond-
ing electronic absorption spectra are depicted in Figure 5.
Though the spacers between two P donors in the diphos-
phane ligands change, the absorption spectra of complexes
1–5 are similar throughout the series, and they all display
two distinct and intense absorption bands with one maxima
at ca. 232 nm, and the other at ca. 315 nm with a shoulder
absorption at ca. 303 nm. By comparison with the corre-
sponding absorptions of the complexes [Pt{Ph2P(CH2)n-
PPh2}(CϵCC6H4tpy)2] (n = 1, 2, and 3) in our previous
work and the analogous [tpyC6H4CϵCAuPPh3] and
[(tpyC6H4CϵCAu)2(µ-dppd)] {dppd = 1,10-bis(diphenyl-
phosphanyl)decane} complexes reported by the Vicente
group,[6,14b] the former higher energy bands arise primarily
from diphosphane-centered transitions, and the latter lower
energy bands are mainly due to intraligand (IL) πǞπ* tran-
sitions of the CϵCC6H4tpy units, mixed probably with
ត
ត
ligands.[6,14b] As no obvious π···π stacking and Au···Au in-
teractions are observed in the crystal structure of complex
2 and the emission bands of complexes 1–5 are similar, the
low energy emissions may arise from intraligand character.
Compared with the emission spectrum of tpyC6H4CϵCH,
together with consideration of the smaller Stokes’ shifts,[6]
the high-energy emissions of binuclear gold(I) complexes 1–
5 arise most probably from the 1(πǞπ*) excited state of the
alkynyl ligand. With reference to the larger Stokes’ shifts,[23]
the vibrational spacings of typical νC–C and νC–N aromatic
ត
ត
vibrational modes, and the emission properties of the re-
ported gold(I)-alkynyl-phosphane complexes, especially
those of [tpyC6H4CϵCAuPPh3] and [(tpyC6H4CϵCAu)2(µ-
dppd)],[7d,11,14b] the low-energy emission bands at ca. 490–
540 nm of complexes 1–5 are tentatively assigned to the
3(πǞπ*) excited state of the acetylide ligand, mixed proba-
bly with some Au orbital character. In order to obtain
deeper insight into the emissive properties, the radiation
lifetime of the intense low-energy emission band at ca.
502 nm of complex 4 in dichloromethane solution was de-
termined, and the long lifetime of 13.6 µs further proves the
triplet parentage of the low-energy band.[6] It is worth not-
ing that the lower energy emission band at ca. 502 nm of
complex 4 in dichloromethane solution is more obvious,
and it is red-shifted 7–11 nm relative to those of complexes
1, 2, 3, and 5, indicating that a stronger interaction between
AuI and the tpyC6H4CϵC unit may exist in complex 4, in-
ducing stronger spin-orbital coupling and the increasing
conjugated degree of the alkyne system. This can also be
observed from the comparison between complex 1 and 2. In
complex 1, the AuI–C distance is 2.027(6) Å, a little longer
(0.056 Å) than that of 1.971(12) Å in complex 2, which indi-
cates stronger interaction between AuI and the
tpyC6H4CϵC unit in complex 2, and the phosphorescence
emission of complex 2 in dichloromethane solution is more
Table 2. UV/Vis absorption data of 1–5 in dichloromethane solu-
tion at 298 K.
Compound
λ [nm] (ε [–1 cm–1])
1
2
3
4
5
232 (103500), 301 (90230), 315 (96660)
232 (99500), 303 (85910), 315 (90340)
232 (113000), 303 (93080), 316 (96310)
232 (94400), 303 (79720), 314 (82880)
232 (104500), 302 (89550), 314 (93580)
Figure 5. UV/Vis absorption spectra of 1–5 in dichloromethane
solutions at 298 K.
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Dual Luminescent Dinuclear Gold(I) Complexes
obvious than that of complex 1, and also a little red-shifted 2·2CH2Cl2. These gold(I)-alkynyl-phosphane complexes
relative to that of complex 1. In addition, the lower energy can therefore be used as building blocks to react, through
emission band at ca. 502 nm with a shoulder at 536 nm of the polypyridine chelation, with LnIII ions to form a
complex 4 is close to that of 503 nm with a shoulder at Au2Ln2 array as reported in our previous work.[6] We have
533 nm in [(tpyC6H4CϵCAu)2(µ-dppd)], which is assigned tried our best to synthesize the Au2Ln2 complexes, but no
3
to the intraligand (πǞπ*) excited state of the acetylide li- crystal suitable for single-crystal X-ray diffraction was ob-
gand.[14b]
tained. So in order to explore how the UV/Vis absorption
bands change when the dinuclear gold(I) complexes are co-
ordinated to LnIII ions, titrations were carried out by add-
ing Gd(hfac)3(H2O)2 to the dichloromethane solution of
complex 1. It must be mentioned that because significant
dissociation often occurs in very diluted solutions,[8f] the
original total concentrations of Au2 units were kept at ca.
1.0ϫ10–5 molL–1 and those of [Gd(hfac)3(H2O)2] at ca.
2.0ϫ10–5 molL–1. Figure 8 (a) shows that the absorbance
increases little by little, following the gradual addition of
the dichloromethane solution of Gd(hfac)3(H2O)2 to that
of 1, and a graph of absorbance at 360 nm gives a smooth
curve that fits well to a 2:1 binding ratio of Gd/Au2 (Fig-
ure 8, b), which is similar to those of [{Pt(PPh2(CH2)n-
PPh2)(CϵCC6H4tpy)2}{Ln(hfac)3}2] (n = 1, dppm; n = 2,
dppe; n = 3, dppp; Ln = Eu, Nd, Yb) complexes in the
previous work.[6]
Table 3. Luminescence data of 1–5.
[a]
Compound λem [nm]
λem [nm] (τem [µs])
(CH2Cl2)
Φem
(solid)
1
2
3
4
5
393 sh, 418
505 sh, 540
394, 416 sh
505, 540 sh
395, 420 sh
510, 544 sh
420
506, 540 sh
398, 420 sh
511, 541 sh
374
0.1089[a]
0.0745[a]
0.1419[a]
0.1331[a]
0.1340[a]
492 (w)
377, 400
495 (w), 530 sh
375
494, 529sh
375
502 (13.6), 536 sh
373
491, 525
[a] The quantum yields in degassed CH2Cl2 are determined relative
to that of [Ru(bpy)3](PF6)2 (Φ = 0.062) in degassed CH3CN.[24]
Figure 6. Emission spectra of 1–5 in the solid state at room tem-
perature.
Figure 8. a: Changes in the UV/Vis absorption spectra by titration
of 1 with Gd(hfac)3(H2O)2 in dichloromethane. b: Changes of ab-
sorbance at 360 nm vs. the ratio of Gd to Au2 moiety by titration
of 1 with Gd(hfac)3(H2O)2 in dichloromethane.
Luminescence Titration
For LnIII complexes, both the singlet and triplet states of
the ligand may transfer energy onto the LnIII ions, but be-
cause of the short-lived character of the singlet state, energy
transfer from it is often inefficient. So whether the energy
gaps between the lowest triplets of the “metal complexes
ligands” and LnIII emitting levels are suitable for achieving
sensitized luminescence of LnIII is of primary importance.
Though the triplet states of complexes 1–5 can not replace
the triplet states of their corresponding GdIII complexes,
the easily determined triplet states of complexes 1–5 and
their good luminescent properties at room temperature still
make possible in a first step the following evaluations: (1)
Figure 7. Emission spectra of 1–5 in fluid dichloromethane solution
at room temperature.
Spectrophotometric Titration
Absorption Spectra Titration
The structural determination indicates the terpyridine Whether complexes 1–5 can be used as sensitized chromo-
units are free of coordination in complexes 1·2CH2Cl2 and phores for LnIII luminescence; (2) which LnIII ions may be
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X.-L. Li, K.-J. Zhang, J.-J. Li, X.-X. Cheng, Z.-N. Chen
FULL PAPER
more efficiently sensitized. For example, all the triplet states Table 4. Luminescence data of 1-Ln2 to 5-Ln2 solutions at 298 K.
of complexes 1–5 in dichloromethane solution in the range
[a,b]
Solution
λem [nm] (τem [µs]) (CH2Cl2)
Φem
5
of 18904–20367 cm–1 are lower than the emitting D4 tran-
1-Eu2
2-Eu2
3-Eu2
618 (600.7)
618 (612.1)
618 (610.6)
618 (606.9)
398, 420 sh
511, 541 sh
618 (606.5)
980 (15.8)
980 (15.7)
980 (15.8)
980 (15.4)
980 (15.9)
0.0446[a]
0.0407[a]
0.0440[a]
0.0405[a]
sition of TbIII (20400 cm–1) and are therefore not expected
to sensitize TbIII emission, but they all exceed to a sufficient
5
extent the D0 level at 17241 cm–1 (580 nm) of the corre- 4-Eu2
sponding EuIII complexes (see Table 4), so it is possible to
4-Gd2
use complexes 1–5 as antenna chromophores to achieve the
5-Eu2
0.0400[a]
0.0079[b]
0.0079[b]
0.0079[b]
0.0077[b]
0.0080[b]
sensitized luminescence of EuIII centers. In order to obtain
more accurate data of the triplet states of the expected
Au2Ln2 complexes, the luminescence of the Au2Gd2 dichlo-
romethane solutions, which were prepared from complexes
1–5 and [Gd(hfac)3(H2O)2] according to the corresponding
1:2 ratio, were determined without O2. The lowest energy
emitting state of GdIII, at 32150 cm–1, is too high to be ex-
cited by the antenna AuI-alkynyl chromophores used in this
study. Consequently, the emission spectra of the GdIII com-
plexes show exclusively AuI-alkynyl-centered emission. The
corresponding data are summarized in Table 4. Only the
triplet states of 4-Gd2 can be observed at room temperature.
The emission spectrum of 4-Gd2 in dichloromethane solu-
tion is depicted in Figure 9. The energy gap between the
triplet state of 4-Gd2 at about 19342 cm–1 (517 nm) and the
5D0 energy level of EuIII is 2101 cm–1, which is suitable for
efficient energy transfer to EuIII ions and prevention of pos-
sible energy back transfer.[25] Since complexes 1–5 are ho-
mologous, they are expected to behave as good energy do-
nors to transfer energy to EuIII centers effectively. In order
to observe how the EuIII-centered emission intensity
changes when complexes 1–5 are coordinated to Eu(tta)3,
emission titrations were carried out in the aerated dichloro-
methane solutions. Upon excitation at 300–380 nm, the
EuIII-centered emission was enhanced greatly during the ti-
tration of [Eu(tta)3(H2O)2] by adding different amounts of
complex 1, following the different Au2/Eu ratios 0, 0.05,
0.10, 0.15, 0.20, 0.30, 0.40, and 0.50 (Figure 10). At a Au2/
Eu ratio higher than 0.50, the EuIII-centered emission inten-
sity decreased. The intensity of the EuIII-centered emission
at a Au2/Eu ratio of 0.50 was 2.74-times that of [Eu(tta)3-
(H2O)2]. This large enhancement confirms the energy trans-
fer from the [(tpyC6H4CϵCAu)2(µ-dppe)] unit to the EuIII
center effectively.
1-Yb2
2-Yb2
3-Yb2
4-Yb2
5-Yb2
[a] The quantum yields in degassed CH2Cl2 were determined rela-
tive to that of [Ru(bpy)3](PF6)2 (Φ = 0.062) in degassed CH3CN.[24]
[b] The quantum yields of YbIII complexes in dichloromethane
solution at 298 K were estimated by the equation Φ = τobs/τ0, in
which τobs is the observed emission lifetime and τ0 is the radiative
or “natural” lifetime of 2 ms. All the solutions containing Eu, Gd,
and Yb were prepared from complexes 1 and [Eu(tta)3(H2O)2],
[Gd(hfac)3(H2O)2], and [Yb(hfac)3(H2O)2] according to the corre-
sponding ratio 1:2.
Figure 9. The emission spectrum of 4-Gd2 in dichloromethane
solution at 298 K.
The maximum excitation wavelength of EuIII-centered
emission increased following the addition of [Eu(tta)3-
(H2O)2] to the dichloromethane solution of complex 1,
however it did not increase again when the Eu/Au2 ratio
was ca. 2.0 (Figure S1), confirming the 1:2 binding ratio
between complex 1 and Eu(tta)3. The EuIII-centered emis-
sion quantum yields of 1-Eu2 to 5-Eu2 in dichloromethane
solutions fall in the range 0.0400–0.0472, which is similar
to those (0.0373–0.0445) of mononuclear PtII-phosphane-
alkynyl-EuIII complexes of the same alkyne ligand
Figure 10. Changes in EuIII-centered emission intensity upon ti-
tration of Eu(tta)3(H2O)2 with complex 1 in dichloromethane upon
excitation with 300 nm.
tpyC6H4CϵCH,[6] further confirming that the efficient en- characteristic emission bands of EuIII ions at about 580,
ergy transfer occurred from the [(tpyC6H4CϵCAu)2(µ- 596, 618, 652, and 695 nm for 1-Eu2 to 5-Eu2 solutions (pre-
Ph2P(CH2)xPPh2)] (x = 2–6) series of units to the EuIII cen- pared from [Eu(tta)3(H2O)2] and complexes 1–5 according
ters. The luminescence data, including emission wave- to a 2:1 ratio) corresponding to the transitions D0Ǟ7F0,
5
lengths, lifetimes, and quantum yields of 1-Ln2 to 5-Ln2, 7F1, F2, F3, F4, respectively, with the dominant band at
7
7
7
are presented in Table 4. All the EuIII solutions exhibit 618 nm (Figure S2).
3454
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3449–3457

Dual Luminescent Dinuclear Gold(I) Complexes
spectroscopic grade. All other reagents were of analytical grade and
were used as received.
Upon titration of [Yb(hfac)3(H2O)2] with complex 1 in
dichloromethane solution, a dramatic enhancement of YbIII
emission was observed with the Au2/Yb ratios changing Preparation of Complexes: All reactions were carried out under dry
argon using Schlenk techniques at room temperature and a
vacuum-line system unless specified.
ynyl unit to YbIII centers. The intensity of YbIII-centered [(tpyC6H4CϵCAu)2(µ-dppe)] (1): Dppe (20.3 mg, 98%, 0.050
from 0, 0.10, 0.20, 0.30, 0.40 to 0.50 (Figure 11), which indi-
cates that efficient energy transfer occurs from the Au2-alk-
mmol) was added to a dichloromethane (15 mL) solution of
(tpyC6H4CϵCAu)n (52.9 mg, 0.10 mmol) with stirring at room
temperature for 30 min. The solution was concentrated and the
product was purified by chromatography on a short silica-gel col-
umn using dichloromethane/methanol (100:2) as eluent. Addition
of n-hexane to the concentrated solution gave the product as a pale
yellow powder (yield 45 mg, 62%). Pale yellow crystals were ob-
tained by layering n-hexane onto the concentrated dichloromethane
solution in the absence of light. C72H52Au2N6P2·CH2Cl2 (1542.06):
calcd. C 56.87, H 3.53, N 5.45; found C 56.57, H 3.59, N 5.36.
emission at ca. 980 nm with the Au2/Yb ratio at 0.50 was
3.37-times that of [Yb(hfac)3(H2O)2]. All the Au2Yb2 solu-
tions (prepared from [Yb(hfac)3(H2O)2] and complexes 1–5
according to a 2:1 ratio) exhibit the characteristic emission
2
bands of YbIII corresponding to the F5/2Ǟ2F7/2 transition
at ca. 980 nm. The intrinsic quantum yields of YbIII emis-
sion may be estimated by Φ = τobs/τ0, where τobs is the ob-
served emission lifetime and τ0 is the “natural lifetime”.[6]
The Au2Yb2 solutions show emission lifetimes from 14.6–
15.9 µs and intrinsic quantum yields from 0.0073–0.0080 ESI-MS: m/z (%) = 1457.4 [M + H]+, 1124.7 [M – tpyC6H4Cϵ
C]+. 1H NMR (CDCl3): δ = 8.75–8.72 (m, 8 H, tpyC6H4CϵC),
(see Table 4), which are comparable to those (0.0073–
3
0.0080) of PtII-phosphane-alkynyl-YbIII complexes of the
8.67 (d, JHH
= 8.0 Hz, 4 H, H3Ј), 7.90–7.85 (m, 8 H,
same alkyne ligand tpyC6H4CϵCH in our previous work.[6]
tpyC6H4CϵC), 7.72–7.66 (m, 12 H, tpyC6H4CϵC and PPh2), 7.53–
7.51 (m, 12 H, PPh2), 7.35 (m, 4 H, H5Ј), 2.70 (s, 4 H, CH2) ppm.
IR spectrum (KBr): ν = 2110 [m (CϵC)] cm–1.
˜
[(tpyC6H4CϵCAu)2(µ-dppp)] (2): This compound was prepared by
the same synthetic procedure as that of 1 except for using dppp
instead of dppe. Color: pale yellow, yield: 43 mg, 59%. Pale yellow
crystals were obtained by layering n-hexane onto the concentrated
dichloromethane solution in the absence of light. C73H54Au2N6P2
(1471.15): calcd. C 59.58, H 3.70, N 5.71; found C 59.63, H 3.77,
N 5.69. ESI-MS: m/z (%) = 1471.3 [M + H]+, 1138.2 [M –
C6H4CϵC]+. 1H NMR (CDCl3): δ = 8.74–8.72 (m, 8 H, H3 and
H6Ј), 8.67 (d, 3JHH = 8.0 Hz, 4 H, H3Ј), 7.87 (td, 3JHH = 8.0, 4JHH
= 2.0 Hz, 4 H, H4Ј), 7.84 (d, J = 7.2 Hz, 4 H, tpyC6H4CϵC), 7.77–
7.72 (m, 8 H, tpyC6H4CϵC and PPh2), 7.65–7.63 (m, 4 H, PPh2),
7.49–7.44 (m, 12 H, PPh2), 7.34 (m, 4 H, H5Ј), 2.87 (m, J = 4.5 Hz,
Figure 11. Changes of the YbIII-centered emission intensity upon
titration of Yb(hfac)3(H2O)2 with complex 1 in dichloromethane
upon excitation with 330 nm.
4 H, PCH ), 1.99 (m, 2 H, PCH CH ) ppm. IR spectrum (KBr): ν
˜
2
2
2
= 2110 [m (CϵC)] cm–1.
[(tpyC6H4CϵCAu)2(µ-dppb)] (3): This compound was prepared by
the same synthetic procedure as that of 1 except for using dppb
instead of dppe. Color: pale yellow, yield: 45 mg, 61%.
C74H56Au2N6P2 (1485.18): calcd. C 59.82, H 3.80, N 5.66; found
C 59.52, H 3.85, N 5.60. ESI-MS: m/z (%) = 1152.1 [M –
tpyC6H4CϵC]+. 1H NMR (CDCl3): δ = 8.74–8.72 (m, 8 H, H3 and
H6Ј), 8.67 (d, 3JHH = 8.0 Hz, 4 H, H3Ј), 7.87 (td, 3JHH = 7.6, 4JHH
= 2.0 Hz, 4 H, H4Ј), 7.84 (d, J = 8.0 Hz, 4 H, tpyC6H4CϵC), 7.71–
7.63 (m, 12 H, tpyC6H4CϵC and PPh2), 7.50–7.49 (m, 12 H, PPh2),
Conclusions
In conclusion, a series of dual luminescent binuclear
gold(I) complexes of terpyridyl-functionalized alkyne li-
gands have been synthesized. Spectrophotometric titration
and the quantum yields of LnIII demonstrate that they can
behave as good energy donors for sensitization of EuIII and
YbIII emission, and as efficient chromophores, they are
comparable to those of PtII complexes.[6]
3
4
7.35 (ddd, JHH = 8.0 and 4.8, JHH = 1.2 Hz, 4 H, H5Ј), 2.44 (m,
4 H, PCH ), 1.83 (m, 4 H, PCH CH ) ppm. IR spectrum (KBr): ν
˜
2
2
2
= 2110 [m (CϵC)] cm–1.
[(tpyC6H4CϵCAu)2(µ-dpppen)] (4): This compound was prepared
by the same synthetic procedure as that of 1 except for using
dpppen instead of dppe. Color: pale yellow, yield: 48 mg, 64%.
C75H58Au2N6P2 (1499.21): calcd. C 60.07, H 3.90, N 5.61; found
C 59.86, H 3.96, N 5.65. ESI-MS: m/z (%) = 1166.5 [M –
tpyC6H4CϵC]+. 1H NMR (CDCl3): δ = 8.73–8.72 (m, 8 H, H3 and
H6Ј), 8.66 (d, 3JHH = 8.0 Hz, 4 H, H3Ј), 7.87 (td, 3JHH = 7.6, 4JHH
= 2.0 Hz, 4 H, H4Ј), 7.85 (d, J = 8.0 Hz, 4 H, tpyC6H4CϵC), 7.74–
7.64 (m, 12 H, tpyC6H4CϵC and PPh2), 7.49–7.46 (m, 12 H, PPh2),
Experimental Section
Materials and Reagents: The reagents 1,2-bis(diphenylphosphanyl)-
ethane (dppe), 1,3-bis(diphenylphosphanyl)propane (dppp), 1,4-
bis(diphenylphosphanyl)butane (dppb), 1,5-bis(diphenylphos-
phanyl)pentane (dpppen), 1,6-bis(diphenylphosphanyl)hexane
(dpph), tetrahydrothiophene (tht), and H3[AuCl4] were commer-
cially available without further purification. 4Ј-[4-{2-(trimethyl-
silyl)-1-ethynyl}phenyl]-2,2Ј:6Ј,2ЈЈ-terpyridine (tpyC6H4CϵCTMS),
(tpyC6H4CϵCAu)n, [Eu(tta)3(H2O)2], and [Ln(hfac)3(H2O)2] (Ln =
Gd, Yb) were prepared by the published methods.[26,7d,27] All sol-
vents were purified and distilled using standard procedures before
use except those for spectroscopic measurements which were of
3
4
7.35 (ddd, JHH = 7.6 and 4.8, JHH = 1.2 Hz, 4 H, H5Ј), 2.41 (m,
J = 6.0 Hz, 4 H, PCH2), 1.69 [s, 6 H, PCH2(CH2)3] ppm. IR spec-
trum (KBr): ν = 2109 [m (CϵC)] cm–1.
˜
[(tpyC6H4CϵCAu)2(µ-dpph)] (5): This compound was prepared by
the same synthetic procedure as that of 1 except for using dpph
Eur. J. Inorg. Chem. 2010, 3449–3457
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3455

X.-L. Li, K.-J. Zhang, J.-J. Li, X.-X. Cheng, Z.-N. Chen
FULL PAPER
instead of dppe. Color: pale yellow, yield: 76 mg, 90%.
C76H60Au2N6P2 (1513.23): calcd. C 60.30, H 4.00, N 5.56; found
C 60.01, H 4.03, N 5.47. ESI-MS: m/z (%) = 1180.9 [M –
index of the solvents, the integrated intensity and the luminescence
quantum yield, respectively.[24,32] The quantity B in the equation
Φs = Φr(Br/Bs)(ns/nr)2(Ds/Dr) is calculated by B = 1–10–AL, where
tpyC6H4CϵC]+. 1H NMR (CDCl3): δ = 8.73–8.72 (m, 8 H, H3 and A is the absorbance at the excitation wavelength and L is the optical
H6Ј), 8.66 (d, 3JHH = 8.0 Hz, 4 H, H3Ј), 7.87 (td, 3JHH = 7.8, 4JHH path length. All the solutions used for determination of emission
= 2.0 Hz, 4 H, H4Ј), 7.83 (d, J = 8.4 Hz, 4 H, tpyC6H4CϵC),7.72–
lifetimes and quantum yields were prepared after rigorous removal
7.63 (m, 12 H, tpyC6H4CϵC and PPh2), 7.49–7.46 (m, 12 H, PPh2), of oxygen by three successive freeze–pump–thaw cycles under vac-
3
4
7.35 (ddd, JHH = 7.6 and 4.8, JHH = 1.2 Hz, 4 H, H5Ј), 2.43 (m, uum in a 10-cm3 round-bottomed flask equipped with a side arm
J = 7.5 Hz, 4 H, PCH2), 1.60 (s, 4 H, PCH2CH2) ppm. 1.48 (m, 4
1-cm fluorescence cuvette and sealed from the atmosphere by a
H, PCH CH CH ). IR spectrum (KBr): ν = 2111 [m (CϵC)] cm–1.
quick-release Teflon® stopper.[6b]
˜
2
2
2
Supporting Information (see also the footnote on the first page of
this article): Changes of the excitation spectra and the maximum
excitation wavelength with the emission at 618 nm upon titration
of complex 1 with [Eu(tta)3(H2O)2] in dichloromethane following
different Eu/Au2 ratios (Figure S1), and EuIII-centered emission
spectra of 1-Eu2 in dichloromethane solution (Figure S2).
Crystal Structure Determination: Crystals suitable for X-ray diffrac-
tion studies of 1·2CH2Cl2, and 2·2CH2Cl2 were obtained by layer-
ing n-hexane onto the corresponding dichloromethane solution in
the absence of light. Single crystals were sealed in capillaries with
mother liquors. 1·2CH2Cl2 and 2·2CH2Cl2 were measured with a
RIGAKU MERCURY CCD and RIGAKU SCXmini dif-
fractometer, respectively, using the ω-scan technique at room tem-
perature with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å). The CrystalClear software package[28–29] and Bruker
SAINT[30] were used for data reduction and empirical absorption
correction, respectively. The structures were solved by direct meth-
ods. The heavy atoms were located from the E-map, and the rest
of the non-hydrogen atoms were found in subsequent Fourier maps.
The non-hydrogen atoms were refined anisotropically, whereas the
hydrogen atoms were generated geometrically with isotropic ther-
mal parameters. The structures were refined on F2 by full-matrix
least-squares methods using the SHELXTL-97 program pack-
age.[31] The crystallographic data of 1·2CH2Cl2 and 2·2CH2Cl2 are
summarized in Table 1.
Acknowledgments
This work was supported financially by the National Natural Sci-
ence Foundation of China (NSFC) (20801047, 20931006, and
20772103), the Foundation of Xuzhou Normal University
(07XLA07, KY2007039, and XGG2007034) and the QingLan Pro-
ject of Jiangsu Province (08QLT001).
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Received: March 24, 2010
Published Online: June 16, 2010
Eur. J. Inorg. Chem. 2010, 3449–3457
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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