Stepwise 1D growth of luminescent Au(I)-Ag(I) phosphine-alkynyl clusters: Synthesis, photophysical, and theoretical studies

Article abstract of DOI:10.1021/ic102204h

Reactions between the diphosphino-gold cationic complexes [Au ₂(PPh₂-C_2-(C₆H₄) _n-C₂-PPh₂)₂]²⁺ (n = 0,1,2,3) and polymeric acetylides (AuC₂Ph)_n and (AgC ₂Ph)_n lead to the formation of a new family ofheterometallic clusters with the general formula [Au_8+2nAg _6+2n(C₂Ph)_8+4n(PPh2C₂(C ₆H₄)_nC₂PPh₂) ₂]²⁺, n = 0 (1), 1 (2), 2 (3), 3 (4). Compounds 1-4 were characterized in detail by NMR and ESI-MS spectroscopy. Complex 1 (n = 0) crystallizes in two forms (orange (la) and yellow (1b)), one of which (1a) has been analyzed by X-ray crystallography. The luminescence behavior of 1-4 has been studied. Compounds 2 and 3 exhibited orange-red phosphorescence with quantitive quantum efficiency in both aerated and degassed CH₂Cl ₂, implying O₂-independent phosphorescence due to efficient protection of the emitting chromophore center by the organic ligands. Complex 3 exhibits reasonable two-photon absorption (TPA) property with a cross section of a s≈a 45 GM (800 nm), which is comparable to the value of commercially available TPA dyes such as coumarin 151. Computational studies have been performed to correlate the structural and photophysical features of the complexes studied. The metal-centered triplet emission within the heterometallic core is suggested to play a key role in the observed phosphorescence. The luminescence spectrum of 1 in CH₂Cl₂ shows dual phosphorescence maximized at 575 nm (the P₁ band) and 770 nm (the P₂ band). Both P₁ and P₂ bands possess identical excitation spectra, i.e., the same ground-state origin, and the same relaxation dynamics throughout the temperature range of 298-200 K. The dual emission of 1 arises from fast structural fluctuation upon excitation, perhaps forming two geometry isomers, which exhibit distinctly different P₁ and P₂ bands. The scrambling dynamics might require large-amplitude motion and, hence, is hampered in rigid media, as evidenced by the single emission for 1a (610 nm) and 1b (570 nm) observed in solid.

Full text of DOI:10.1021/ic102204h

ARTICLE
pubs.acs.org/IC
Stepwise 1D Growth of Luminescent Au(I)-Ag(I) Phosphine-Alkynyl
Clusters: Synthesis, Photophysical, and Theoretical Studies
Igor O. Koshevoy,*,† Chia-Li Lin,‡ Antti J. Karttunen,† Janne J€anis,† Matti Haukka,† Sergey P. Tunik,§
Pi-Tai Chou,*,‡ and Tapani A. Pakkanen*,†
†Department of Chemistry, University of Eastern Finland, Joensuu, 80101, Finland
‡National Taiwan University, Department of Chemistry, Taipei 106, Taiwan
§ Department of Chemistry, St.-Petersburg State University, Universitetskii pr. 26, 198504, St. Petersburg, Russia
S Supporting Information
b
ABSTRACT: Reactions between the diphosphino-gold cationic complexes [Au2(PPh2-C2-(C6H4)n-C2-PPh2)2]2þ (n = 0, 1, 2, 3)
and polymeric acetylides (AuC2Ph)n and (AgC2Ph)n lead to the formation of a new family of heterometallic clusters with the general
formula [Au8þ2nAg6þ2n(C2Ph)8þ4n(PPh2C2(C6H4)nC2PPh2)2]2þ, n = 0 (1), 1 (2), 2 (3), 3 (4). Compounds 1-4 were
characterized in detail by NMR and ESI-MS spectroscopy. Complex 1 (n = 0) crystallizes in two forms (orange (1a) and yellow
(1b)), one of which (1a) has been analyzed by X-ray crystallography. The luminescence behavior of 1-4 has been studied.
Compounds 2 and 3 exhibited orange-red phosphorescence with quantitive quantum efficiency in both aerated and degassed
CH2Cl2, implying O2-independent phosphorescence due to efficient protection of the emitting chromophore center by the organic
ligands. Complex 3 exhibits reasonable two-photon absorption (TPA) property with a cross section of σ ≈ 45 GM (800 nm), which
is comparable to the value of commercially available TPA dyes such as coumarin 151. Computational studies have been performed to
correlate the structural and photophysical features of the complexes studied. The metal-centered triplet emission within the
heterometallic core is suggested to play a key role in the observed phosphorescence. The luminescence spectrum of 1 in CH2Cl2
shows dual phosphorescence maximized at 575 nm (the P1 band) and 770 nm (the P2 band). Both P1 and P2 bands possess identical
excitation spectra, i.e., the same ground-state origin, and the same relaxation dynamics throughout the temperature range of 298-
200 K. The dual emission of 1 arises from fast structural fluctuation upon excitation, perhaps forming two geometry isomers, which
exhibit distinctly different P1 and P2 bands. The scrambling dynamics might require large-amplitude motion and, hence, is hampered
in rigid media, as evidenced by the single emission for 1a (610 nm) and 1b (570 nm) observed in solid.
’ INTRODUCTION
some of our reports.3,4 Thus, variation of the synthetic strategy
allowed for the selective preparation of two structurally different
AuI-AgI clusters (see Scheme 1), which also demonstrated
sharp contrast of their emissive properties.3,6
The heteronuclear complexes of group 11 metals attract
considerable attention, because of the rich variety of structural
patterns they adopt, theoretical interest to the metal-metal
interactions, and promising photophysical characteristics, which
have the potential for modern technological applications (e.g.,
OLED displays, luminescent sensors, and bioimaging labels).
These species often show a trend to form multiple heterome-
tallophilic bonds responsible for the unexpected structural
architectures and, consequently, rise or change of the photo-
emissive properties, which are strongly dependent on the dis-
tances between the interacting metals, the nature and number of
the constituting ligands, and the coordination geometry of the
metal centers.1 In our recent studies, we were mainly focused on
the heterometallic AuI, AgI, CuI alkynyl-phosphine complexes,
which demonstrate very strong room-temperature phosphores-
cence with a small to negligible oxygen quenching effect.2-4 The
dominating structural motif—an [AuxMy(C2R)2x] cluster inside
the triangular [Au3(PP)3]3þ “belt” (where PP = linear rigid
diphosphine)—was found for both AuI-CuI and AuI-AgI
bimetallic species.5-7 However, it has been already mentioned
that numerous AuI-AgI compounds were synthesized without
analogy with the AuI-CuI ones.8 This increasing structural
diversity of the gold-silver complexes was also confirmed by
Inspired by the attractive luminescent characteristics of I, we
intended to expand the family of the related compounds;
however, we unexpectedly were unable to obtain its congeners
by modifying the oligophenylene-based diphosphines or varying
the substituents of the phenylalkynyl ligands. Alternatively, our
interest switched to the family of dialkynyl-based P-ligands,
PPh2-C2-(C6H4)n-C2-PPh2 (n = 0-3), which, in comparison
to PPh2-(C6H4)n-PPh2 diphosphines, have (a) slightly different
spatial separation of the P atoms and (b) significantly different
electron-donating properties. These electronic and stereochem-
ical variations of the ligands, together with theoretical calcula-
tions on the stability of the expected heterometallic products,
suggest that the PPh2-C2-(C6H4)n-C2-PPh2 phosphines could be
the promising candidates in the synthesis of the clusters topolo-
gically similar to I.
Herein, we report on the reactions between the diphosphino-
gold cationic complexes [Au2(PPh2(C6H4)nPPh2)2]2þ (n = 0, 1,
Received: November 2, 2010
Published: February 08, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/ic102204h Inorg. Chem. 2011, 50, 2395–2403
|

Inorganic Chemistry
ARTICLE
Scheme 1. Formation of Two Types of AuI-AgI Aggregates
4,400-PPh2C2-(C6H4)3-C2PPh2 (P3P). The synthesis was carried
out under a nitrogen atmosphere. A solution of 4,400-diethynylterphenyl
(0.5 g, 1.80 mmol) in THF (60 cm3) was cooled to -78 ꢀC and a 1.6 M
solution of n-BuLi in hexanes (2.6 cm3, 4.16 mmol) was added dropwise
within 5 min under stirring. The resulting pale greenish suspension was
warmed up to -10 ꢀC within ca. 3 h, stirred for 0.5 h, then cooled to -
78 ꢀC again and treated dropwise with PPh2Cl (0.9 g, 4.08 mmol). The
reaction mixture changed to a yellow solution and was stirred below -
60 ꢀC for 1 h, then allowed slowly (ca. 2 h) to reach room temperature,
and stirred overnight. The solvents were evaporated, and the brownish
solid residue was washed with methanol (3 ꢀ 15 cm3) and vacuum-
dried. Crude P3P was dissolved in hot CHCl3 (ca. 30 cm3), treated with
activated charcoal, diluted with hexanes (7 cm3), passed through a silica
gel (150 mesh, 2.5 ꢀ 15 cm, eluent CHCl3/hexanes 4:1 v/v). Pale yellow
solution was evaporated, the solid obtained was washed with THF-
methanol mixture 1:2 v/v (2 ꢀ 9 cm3), diethyl ether (2 ꢀ 5 cm3) to give
pale yellowish ligand (0.71 g, 61%). Mp. 211-212 ꢀC. 31P{1H} NMR
1
(CDCl3; δ): -33.8 (s). H NMR (CDCl3; δ): 7.72-7.67 (m, 12H),
7.64(s, 8H), 7.41-7.35 (m, 12H). Anal. Calc. for C46H32P2: C, 85.43;
H, 4.99. Found: C, 84.94; H, 4.96.
[Au8Ag6(C2Ph)12(PPh2-C2-C2-PPh2)2](PF6)2 (1). (AuC2Ph)n
(69 mg, 0.232 mmol) and (AgC2Ph)n (48 mg, 0.230 mmol) were
suspended in CH2Cl2 (20 cm3), stirred for 10 min and
[Au2(P0P)2](PF6)2 (50 mg, 0.033 mmol) was added. The reaction
mixture was stirred overnight in the absence of light, resulting in a dirty
yellow solution and some insoluble residue. The solution was filtered
and evaporated, and crude 1 was repetitiously recrystallized via the gas-
phase diffusion of diethyl ether into its solution in CH2Cl2/acetone/
MeOH at þ5 ꢀC to give bright orange crystals (136 mg, 91%).
Crystallization of 1 via gas-phase diffusion of diethyl ether into its
acetone solution at þ5 ꢀC results in the formation of a yellow
microcrystalline form. Upon dissolution, the orange and yellow
forms show identical spectral characteristics. ES MS (m/z):
[Au8Ag6(C2Ph)12(PPh2C2C2PPh2)2]2þ 2136.4 (calcd 2136.4). 31P-
{1H} NMR (CD2Cl2; δ): 16.2 (s, 4P), -143.0 (sept, 2PF6). 1H
NMR (CD2Cl2; δ): diphosphine: PPh-1, 7.85, ortho-H, 8H, (dd,
J(HH) 7.1 J(PH) 14.7 Hz), 7.64, para-H, 4H, (t, J(HH) 7.6 Hz), 7.55
meta-H, 8H, (ddd, J(HH) 7.1, 7.6 J(PH) 3.0 Hz); PPh-2, 7.75, ortho-H,
8H, (dd, J(HH) 7.1 J(PH) 14.9 Hz), 7.31, para-H, 4H, (t, J(HH) 7.6
Hz), 7.15 meta-H, 8H, (dd, J(HH) 7.1, 7.6); [Au(C2Ph)2] rods:
(terminal) 7.67 ortho-H, 8H (d, J(HH) 7.1 Hz), 7.35, para-H, 4H, (t,
J(HH) 7.5 Hz), 7.20, meta-H, 8H, (dd, J(HH) 7.5, 7.1 Hz), (A) 7.14,
para-H, 4H, (t, J(HH) 7.8 Hz), 6.72, meta-H, 8H, (dd, J(HH) 7.8, 7.2
Hz), 6.23 ortho-H, 8H (d, J(HH) 7.2 Hz), (B) 7.11, para-H, 4H, (t,
J(HH) 7.8 Hz), 6.72, meta-H, 8H, (dd, J(HH) 7.1, 7.8 Hz), 7.04 ortho-
H, 8H (d, J(HH) 7.1 Hz). Anal. Calc. for Ag6Au8C152H100F12P6: C,
40.01; H, 2.21. Found: C, 39.49; H 2.40.
[Au10Ag8(C2Ph)16(PPh2-C2-C6H4-C2-PPh2)2](CF3SO3)2
(2). (AuC2Ph)n (101 mg, 0.339 mmol) and (AgC2Ph)n (71 mg, 0.340
mmol) were suspended in CH2Cl2 (20 cm3), stirred for 10 min, and then
[Au2(P1P)2](CF3SO3)2 (86 mg, 0.051 mmol) was added. The reaction
mixture was stirred for 1 h in the absence of light, resulting in a bright
yellow-orange solution and small amount of yellow residue. The
solution was filtered and evaporated, and crude 2 was washed
with acetone-hexane (3:2 v/v) mixture (3 ꢀ 5 cm3). Recrystalliza-
tion by gas-phase diffusion of diethyl ether into its CH2Cl2/THF
solution at -7 ꢀC gave mainly an orange crystalline material, together
with yellow-greenish crystals identified as [Au9Ag6(C2Ph)12
(PPh2C2C6H4C2PPh2)3](CF3SO3)3.7 The latter was removed by wash-
ing the solid with acetone/hexane 3:2 v/v mixture (4 ꢀ 5 cm3) and THF
(3 ꢀ 5 cm3). Orange powder (138 mg, 57%). Pure 2 is unstable in
solution at room temperature. ES MS (m/z): [Au10Ag8
(C2Ph)16(PPh2C2C6H4C2PPh21)2]2þ 2719.9 (calcd 2719.9). 31P{1H}
NMR (CD2Cl2; δ): 13.3 (s). H NMR (CD2Cl2; δ): diphosphine:
2, 3) and polymeric acetylides (AuC2Ph)n and (AgC2Ph)n,
leading to the formation of a new family of large heterometa-
llic clusters with the general formula [Au8þ2nAg6þ2n
(C2Ph)8þ4n(PPh2C2(C6H4)nC2PPh2)2]2þ, n = 0 (1), 1 (2), 2
(3), 3 (4). Details of the synthesis route, characterization, and
associated photophysical properties are elaborated as follows.
’ EXPERIMENTAL SECTION
General Comments. (AuC2Ph)n,9 (AgC2Ph)n,10 PPh2C2C2PPh2
(P0P),11 1,4-PPh2C2C6H4C2PPh2 (P1P),7 4,40-PPh2C2(C6H4)2C2-
PPh2 (P2P),7 and 4,400-diiodoterphenyl12 were synthesized according
to published procedures. Complexes [Au2(PP)2]2þ (where PP =
diphosphine) were prepared in a manner similar to the published
analogues.2,3 [Au2(P0P)2](PF6)2 has limited stability in solution; there-
fore, its preparation should be carried out as fast as possible. Tetra-
hydrofuran was distilled over Na-benzophenoneketyl under nitrogen
atmosphere prior to use. Other reagents and solvents were used as
1
1
received. The solution 1D H, 31P NMR and H-1H COSY spectra
were recorded on Bruker Avance 400 spectrometer. Mass spectra were
measured on a Bruker APEX-Qe ESI FT-ICR instrument, in the
positive-ion mode. Microanalyses were carried out in the analytical
laboratory of the University of Eastern Finland.
4,400-HC2-(C6H4)3-C2H. 4,400-Diiodoterphenyl (4.6 g, 9.54 mmol)
was suspended in THF (40 cm3), diluted with degassed NEt3 (30 cm3)
under a nitrogen atmosphere, and Pd(PPh3)2Cl2 (150 mg, 0.214 mmol),
CuI (50 mg, 0.262 mmol) and (trimethylsilyl)acetylene (2.5 g, 25.5
mmol) were added. The reaction mixture was stirred overnight at room
temperature, evaporated, washed with methanol (2 ꢀ 20 cm3) and
dried. Brownish solid was dissolved in CHCl3 (ca. 120 cm3), passed
through a silica gel (2.5 ꢀ 10 cm), evaporated and washed with diethyl
ether/methanol 1:1 v/v mixture (2 ꢀ 10 cm3) to give creamy crystalline
solid of 4,400-bis(trimethylsilylethynyl)terphenyl (3.85 g, 96%). Depro-
tection was carried out by suspending the intermediate in THF/
methanol 5:3 v/v mixture (80 cm3) and stirring with K2CO3 (2 g)
under a nitrogen atmosphere for 12 h. The reaction mixture was
evaporated and washed with H2O (20 cm3). Solid residue was extracted
with hot CHCl3 (4 ꢀ 70 cm3), passed through a layer of silica gel (150
mesh, 2.5 ꢀ 10 cm), evaporated and briefly washed with ethanol (15
cm3) to give pale-creamy crystalline product (2.46 g, total yield 93%). 1H
NMR (CDCl3; δ): 7.68 (s, 4H, -C6H4-), 7.60 (m, 8H, -C6H4-
C2H), 3.15 (s, 2H, -C2H). Anal. Calc. for C22H14: C, 94.93; H, 5.07.
Found: C, 94.62; H, 5.27.
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Inorganic Chemistry
ARTICLE
7.90,-t-C6H4-t-, 8H (s), PPh-1, 7.80, ortho-H, 8H, (dd, J(HH)
7.0 J(PH) 14.5 Hz), 7.51, para-H, 4H, (t, J(HH) 7.4 Hz), 7.44 meta-H,
8H, (ddd, J(HH) 7.0, 7.4 J(PH) 2.8 Hz); PPh-2, 7.70, ortho-H, 8H, (dd,
J(HH) 7.0 J(PH) 14.6 Hz), 7.14 meta-H, 8H, (dd, J(HH) 7.0, 7.5), 7.12,
para-H, 4H, (t, J(HH) ca. 7.5 Hz); [Au(C2Ph)2] rods: (terminal) 7.57
ortho-H, 8H (d, J(HH) ca. 7.5 Hz), 7.24, meta-H, 8H, (dd, J(HH) ca.
7.5, 8.0 Hz), 7.08, para-H, 4H, (t, J(HH) ca. 8 Hz); (A) 6.62, meta-H,
8H, (dd, J(HH) 7.0, 8.0 Hz), 7.06 ortho-H, 8H (d, J(HH) 7.0 Hz), 7.12,
para-H, 4H, (t, J(HH) 8.0 Hz); (B) 6.44, meta-H, 8H, (dd, J(HH) 7.0,
7.6 Hz), 6.79 ortho-H, 8H (d, J(HH) 7.0 Hz), 6.89, para-H, 4H, (t,
J(HH) 7.6 Hz); (C) 6.96, para-H, 4H, (t, J(HH) 7.6 Hz), 6.57, meta-H,
8H, (dd, J(HH) 7.1, 7.6 Hz), 5.97 ortho-H, 8H (d, J(HH) 7.1 Hz). Anal.
Calc. for Ag8Au10C198H128F6O6P4S2: C, 41.45; H, 2.25. Found: C,
41.56; H 2.52.
meta-H, 8H, (dd, J(HH) 7.5 7.6 Hz); (B) 6.90, para-H, 4H, (t, J(HH)
7.3 Hz), 6.53, meta-H, 8H, (dd, J(HH) 7.3, 7.4 Hz), 5.77 ortho-H, 8H
(d, J(HH) 7.4 Hz); (C) 6.66, para-H, 4H, (t, J(HH) 7.6 Hz), 6.55 ortho-
H, 8H (d, J(HH) ca. 7.6 Hz), 6.29, meta-H, 8H, (dd, J(HH) 7.6 Hz);
(D) 6.78, para-H, 4H, (t, J(HH) 7.6 Hz), 6.56 ortho-H, 8H (d, J(HH)
ca. 7.6 Hz), 6.43, meta-H, 8H, (dd, J(HH) 7.6 Hz); (E) 6.74, para-H,
4H, (t, J(HH) 7.6 Hz), 6.69 ortho-H, 8H (d, J(HH) ca. 7.6 Hz), 6.39,
meta-H, 8H, (dd, J(HH) 7.6 Hz). Anal. Calc. for Ag12Au14C286H184-
F6O6P4S2: C, 42.56; H, 2.30. Found: C, 42.43; H, 2.20.
Photophysical Measurements. Steady-state absorption and
emission measurements, both in solution and in the solid state, were
recorded on a Hitachi (U-3310) spectrophotometer and an Edinburgh
(FS920) fluorometer, respectively. Both the wavelength-dependent
excitation and emission response of the fluorometer have been cali-
brated. To determine the photoluminescence quantum yield in solution,
the samples were degassed by three freeze-pump-thaw cycles. 4--
(Dicyanomethylene)-2-methyl-6-(paradimethylaminostyryl)-4H-pyran
(DCM, λmax = 615 nm, Exciton) in methanol, with a quantum yield of
∼0.4, served as the standard for measuring the quantum yield. Solid-
state quantum yields were determined with a calibrated integrating
sphere system. The uncertainty of the quantum yield measurement was
in the range of <2% (an average of three replica). Lifetime studies were
performed with an Edinburgh FL 900 photon-counting system, using a
hydrogen-filled lamp as the excitation source. The emission decays were
fitted by the sum of exponential functions with a temporal resolution of
∼300 ps by the deconvolution of instrument response function.
The two-photon absorption cross section was measured using an
open-aperture Z-scan experiment.13 Briefly, in this study, a mode-locked
Ti:sapphire laser (Tsunami, Spectra Physics) was coupled to a regen-
erative amplifier that generated ∼180 fs, 1 mJ pulses (800 nm, 1 kHz,
Spitfire Pro, Spectra Physics). The pulse energy, after proper attenua-
tion, was reduced to 0.75-1.5 μJ and the repetition rate was further
reduced to 20 Hz to eliminate excited-state absorption. The laser beam
was focused through a 2.00 mm cell filled with the sample solution (1.3
ꢀ 10-3 M). When the sample cell was translated along the beam
direction (z-axis), the transmitted laser intensity was detected. The
TPA-induced decrease in transmittance, T(z), can be fitted with eqs 1
and 2, in which the TPA coefficient (β) is incorporated:14
[Au12Ag10(C2Ph)20(PPh2-C2-(C6H4)2-C2-PPh2)2](CF3SO3)2
(3). (AuC2Ph)n (100 mg, 0.336 mmol) and (AgC2Ph)n (70.5 mg, 0.337
mmol) were suspended in CH2Cl2 (20 cm3), stirred for 10 min, and then
[Au2(P2P)2](CF3SO3)2 (68 mg, 0.037 mmol) was added. The reaction
mixture was stirred for 1.5 h in the absence of light, resulting in an
almost-transparent bright yellow solution. The solution was filtered and
evaporated, and crude 3 was recrystallized via slow evaporation of its
CH2Cl2/acetone/heptane solution at þ5 ꢀC to give a yellow crystalline
material, which was dissolved in CH2Cl2 (4 cm3), diluted with acetone/
hexane 1:1 v/v mixture (4 cm3), filtered, and precipitated via the
addition of an excess of hexanes. The bright yellow powder was washed
with an acetone/hexane 3:1 v/v mixture (2 ꢀ 5 cm3) and diethyl ether
(2 ꢀ 5 cm3) and then dried (210 mg, 91%). ES MS (m/z):
[Au12Ag10(C2Ph)20(PPh2C2(C6H4)2C2PPh2)2]2þ 3303.0 (calcd
1
3302.9). 31P{1H} NMR (CD2Cl2; δ): 12.6 (s). H NMR (CD2Cl2;
δ): diphosphine: 7.96, -t-(C6H4)2-t-, 16H (AB system), PPh-1,
7.81 ortho-H, 8H, (dd, J(HH) 7.1 J(PH) 14.4 Hz), 7.49 para-H, 4H, (t,
J(HH) ca. 7.5 Hz), 7.43 meta-H, 8H, (ddd, J(HH) 7.1, ca. 7.5 J(PH) 2.3
Hz); PPh-2, 7.75 ortho-H, 8H, (dd, J(HH) 7.2 J(PH) 14.6 Hz), 7.28
para-H, 4H, (t, J(HH) ca. 7.5 Hz), 7.14 meta-H, 8H, (dd, J(HH) 7.2,
7.5); [Au(C2Ph)2] rods: (terminal) 7.50 ortho-H, 8H (d, J(HH) 7.1
Hz), 7.19, para-H, 4H, (t, J(HH) 7.5 Hz); 7.03, meta-H, 8H, (dd, J(HH)
7.5, 7.1 Hz), (A) 7.00, para-H, 4H, (t, J(HH) ca. 7.5 Hz), 7.00 ortho-H,
8H (d, J(HH) 7.4 Hz), 6.61, meta-H, 8H, (dd, J(HH) 7.5 7.4 Hz); (B)
6.94, para-H, 4H, (t, J(HH) 7.5 Hz), 6.57, meta-H, 8H, (dd, J(HH) 7.5,
7.5 Hz), 5.92 ortho-H, 8H (d, J(HH) 7.5 Hz); (C) 6.83, para-H, 4H, (t,
J(HH) 7.5 Hz), 6.67 ortho-H, 8H (d, J(HH) 7.3 Hz), 6.41, meta-H,
8H, (dd, J(HH) 7.5, 7.3 Hz); (D) 6.82-6.77, m, para-H and ortho-H,
12H, 6.39, meta-H, 8H, (dd, J(HH) ca. 7.8 Hz). Anal. Calc. for
Ag10Au12C242H156F6O6P4S2: C, 42.10; H, 2.28. Found: C, 42.00; H
2.53.
ð1Þ
¥
n
X
ð - qÞ
TðzÞ ¼
q ¼
3=2
n¼ 0 ðn þ 1Þ
βI0L
ð2Þ
1 þ ðz2=z0 Þ
2
where n is an integer number from 0 to ¥ and has been truncated at n =
1000, L is the sample length, I0 is the input intensity, z represents the
sample position with respect to the focal point, and z0 denotes the
diffraction length of the incident beam (Rayleigh range). After obtaining
β, the TPA cross section (σ2) can be deduced using the equation
[Au14Ag12(C2Ph)24(PPh2-C2-(C6H4)3-C2-PPh2)2](CF3SO3)2
(4). (AuC2Ph)n (150 mg, 0.503 mmol) and (AgC2Ph)n (105 mg, 0.502
mmol) were suspended in CH2Cl2 (25 cm3), stirred for 10 min and then
[Au2(P3P)2](CF3SO3)2 (108 mg, 0.054 mmol) was added. The reac-
tion mixture was stirred for 1.5 h in the absence of light, resulting in a
bright yellow solution and some yellow insoluble residue. The workup
procedure, which was identical to that of 3, gave 4 as a yellow powder
(195 mg, 56%). Pure 4 is very unstable in solution at room temperature.
ES MS (m/z): [Au14Ag12(C2Ph)24(PPh2C2(C6H4)3C2PPh2)2]2þ
3885.9 (calcd 3885.9). 31P{1H} NMR (CD2Cl2; δ): 12.4 (s). 1H
NMR (CD2Cl2; δ): diphosphine: 8.08, -t-(C6H4) -(C6H4 )-
(C6H4)-t-, s, 8H; 8.01,-t-(C6H4)-(C6H4) -(C6H4)-t-,
16H (AB system), PPh-1, 7.83 ortho-H, 8H, (dd, J(HH) 7.6 J(PH)
15.0 Hz), 7.52-7.39 m, meta þ para-H, 12H; PPh-2, 7.81 ortho-H, 8H,
(dd, J(HH) 7.6 J(PH) 15.0 Hz), 7.26 para-H, 4H, (t, J(HH) ca. 7.5 Hz),
7.15 meta-H, 8H, (dd, J(HH) 7.6, 7.5); [Au(C2Ph)2] rods: (terminal)
7.47 ortho-H, 8H (d, J(HH) 7.1 Hz), 7.19, para-H, 4H, (t, J(HH) 7.5
Hz); 7.06, meta-H, 8H, (dd, J(HH) 7.5, 7.1 Hz), (A) 7.08 ortho-H,
8H (d, J(HH) ca. 7.5 Hz), 6.94, para-H, 4H, (t, J(HH) 7.6 Hz), 6.52,
σ2NAd ꢀ 10-3
β ¼
ð3Þ
hυ
where NA is the Avogadro constant, d the sample concentration, and hν
the incident photon energy.
X-ray Structure Determinations. The crystal of 1 was im-
mersed in cryo-oil, mounted in a Nylon loop, and measured at a
temperature of 100 K. The X-ray diffraction (XRD) data was collected
on a Bruker AXS Smart ApexII diffractometer, using Mo KR radiation (λ
= 0.71073 Å). The APEX215 program package was used for cell
refinements and data reductions. The structure was solved by direct
methods using the SHELXS-9716 program with the WinGX17 graphical
user interface. A numerical absorption correction (SADABS)18 was
applied to the data. Structural refinement was carried out using
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Table 1. Crystal Data of 1
1
empirical formula
fw
C
154H110Ag6Au8F12O3P6
4645.19
100(2)
0.71073
orthorhombic
Pbcn
temp (K)
λ (Å)
cryst syst
space group
a (Å)
18.0224(4)
28.5223(6)
28.2868(7)
14540.6(6)
4
b (Å)
c (Å)
V (Å3)
Z
F
calc (Mg/m3)
μ(Mo KR) (mm-1
2.122
)
8.956
No. reflns.
127402
19909
Unique reflns.
GOOF (F2)
Rint
1.030
0.0783
R1a (I g 2σ)
0.0360
wR2b (I g 2σ)
0.0777
2
Figure 1. Photographs of the orange (1a, right) and yellow (1b, left)
crystalline forms of 1, upon exposure to ambient light (top) and UV
irradiation (bottom).
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ [w(Fo - Fc2)2]/ [w-
2 2
(Fo ) ]]1/2
.
SHELXL-97.16 The asymmetric unit of 1 contains a half a molecule.
The water of crystallization was partially lost; therefore, it was refined
with an occupancy of 0.5. The H2O and OH hydrogen atoms were
located from the difference Fourier map but constrained to ride on their
parent atom, with Uiso = 1.5Ueq (parent atom). Other hydrogen
atoms were positioned geometrically and were also constrained to
Scheme 2. Formation of Cluster 1 (CH2Cl2, 12 h, 298 K)
ride on their parent atoms, with C-H = 0.95-0.98 Å, and Uiso
=
1.2-1.5 Ueq (parent atom). The crystallographic details are summarized
in Table 1.
Computational Details. The geometries of complexes 1-4 were
optimized using the BP86 density functional method.19 The Ag and Au
atoms were described by a triple-valence-zeta quality basis set with
polarization functions (def2-TZVP),20 employing 28-electron and 60-
electron relativistic effective core potentials for Ag and Au,
respectively.21 A split-valence basis set with polarization functions on
non-hydrogen atoms was used for all the other atoms (def2-SV(P)).22
The multipole-accelerated resolution-of-the-identity technique was used
to accelerate the calculations.23 The lowest triplet states of the com-
plexes were studied using spin-unrestricted formalism. The reported
computational results were obtained using the observed D2 point group
symmetry to facilitate comparisons with the experiments. All electronic
structure calculations were carried out with the TURBOMOLE program
package (version 6.1).24
bright orange (1a) or yellow (1b) color (see Figure 1), depending
on the solvents used (see the Experimental Section), indicating
the existence of different types of crystal structures for 1.
This complex has been studied by 1H and 31P NMR spectro-
metry and ESI-MS. Its structure in the solid state (1a, orange
form) has been determined via XRD analysis (see Figure 2).
Unfortunately, the yellow crystalline material was not suitable for
X-ray study. The ESI-MS spectrum of 1 (Figure S1 in the
Supporting Information, ESI) displays the signal of the doubly
charged cation at m/z 2136.4, the isotopic pattern of which
completely fits the stoichiomety of the [Au8Ag6(C2Ph)12
(P0P)2]2þ molecular ion.
’ RESULTS AND DISCUSSION
Synthesis and Characterization. The synthetic methodol-
ogy employed for the synthesis of the novel AuI-AgI aggregates
is based on the depolymerization reaction of the equimolar
amounts of (AuC2Ph)n and (AgC2Ph)n with the appropriate
amount of cationic complex [Au2(PP)2]2þ that we have com-
municated recently.3 Thus, treatment of a slight excess of the
mixture of gold and silver acetylides with [Au2(P0P)2]2þ dimer
leads to clean formation of the stable heterometallic cluster
[Au8Ag6(C2Ph)12(P0P)2]2þ (1; see Scheme 2), which was
isolated after repetitious recrystallization as a crystalline solid of
Complex 1 consists of the heterometallic alkynyl cluster
[Au4Ag6(C2Ph)8]2þ placed between two neutral (PhC2Au)2
(μ-PPh2C2C2PPh2) molecules, which are held together by
Au-Au, π-CtC-Ag and Au-Ag bonds. This general struc-
tural arrangement of 1 is similar to that found for I (see
Scheme 1).3 The Au-Au bonds between the central framework
and external alkynyl-diphosphine fragments (3.0179(3) and
3.0316(3) Å) are typical for aurophilic interactions4,6,25 and
considerably shorter than those found in I (3.1247(4) and
3.1973(4) Å).3 These shorter and evidently more effective
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Figure 3. 1H-1H COSY spectrum of 1, CD2Cl2, 298 K. Signals of 1D
projection marked in red correspond to the phenyl protons of the
diphosphines, signals marked in green correspond to the dialkynyl
[Au(C2Ph)2]- rods, signals marked in black correspond to the P-
Au-C2Ph terminal fragments.
Figure 2. Molecular view of the dication 1a. Hydrogen atoms omitted
for clarity. Selected interatomic distances (Å): Au(1)-P(1),
2.2682(14); Au(1)-Au(2), 3.0179(3); Au(1)-Ag(1), 3.2090(5); Au-
(2)-Ag(2), 2.9818(5); Au(2)-Ag(1), 3.0279(5); Au(3)-Ag(3),
3.0146(5); Au(3)-Ag(2), 3.0279(5); Au(3)-Au(4), 3.0316(3); Au-
(4)-P(2), 2.2713(16).
measurements. The ESI-MS spectra (see Figures S3-S5 in the
Supporting Information) display the patterns of the doubly
charged molecular ions at m/z 2719.9 (2), 3303.0 (3), 3885.9
(4), which fit the stoichiometry previously given completely. The
solid-state structure of 3 has been determined by XRD study.
However, the weak diffraction and low quality of the crystals of 3
did not allow for high-quality refinement, but the crystallographic
data available, together with the spectral measurements, testify in
favor of the structural topology depicted in Scheme 3 (see ESI for
the structure determination details and molecular view of the
dication 3; Figure S6 in the Supporting Information).
contacts between the fragments probably determine higher
solution stability of 1, in comparison to I; the latter shows signs
of degradation within several hours.
The molecular forms of 1a and 1b existing in solution were
found to be identical. The solution NMR data corresponding to
both crystalline forms are consistent with the idealized D2
symmetry group found in the solid state for 1a. The 31P NMR
spectrum displays a singlet resonance at 16.2 ppm that points to
four equivalent P atoms of the diphosphine ligands. The 1D and
2D COSY (Figure 3) proton spectra show well-resolved “ortho-
meta-para” groups of the signals corresponding to two sets of
inequivalent phenyl rings of the P0P diphosphine ligand, which
are discriminated because of their different orientation, relative to
the central core of the complex (see Figure S2 in the Supporting
Information). The phenyl resonances of the diphosphine are
located in the low field part of the spectrum and display typical
31P-1H(ortho) coupling constants (ca. 15 Hz) similar to the
Au-Ag “rods-in belt” relatives.6,7 The signals of the phenyl
protons of alkynyl ligands are also segregated into a low-field-
shifted group of neutral “P-Au-C2Ph” terminal fragments and
two groups of high-field-shifted [Au(C2Ph)2]- rods (see Figure
S2 in the Supporting Information).
The use of the linearly extended ligands PPh2-C2-(C6H4)n-C2-
PPh2 (n = 1 (P1P), 2 (P2P), 3 (P3P)), employing synthetic
protocol similar to the preparation of 1 (Scheme 3), gave the
AuI-AgI assemblies of higher nuclearity, [Au10Ag8(C2Ph)16
(P1P)2]2þ (2), [Au12Ag10(C2Ph)20(P2P)2]2þ (3), [Au14Ag12
(C2Ph)24(P3P)2]2þ (4), which were isolated as crystalline
yellow solids in moderate to excellent yields. Complex 2, and
especially complex 4, appeared to be unstable in solution at room
temperature.
The proposed structural motif of 2-4 is similar to that
found for 1 and consists of two alkynyl-diphosphine AuI mole-
cules (PhC2Au)2(μ-PPh2-C2-(C6H4)n-C2-PPh2) (n = 1-3),
which accommodate the central clusters [Au4þ2nAg6þ2n
2þ
(C2Ph)8þ4n
]
(see also the computational section below).
The NMR spectroscopic characteristics of 2-4, as well as their
comparison with the data obtained for 1 and earlier for I,3
strongly support the structural arrangement of the molecules
corresponding to the D2 symmetry group. The singlet reso-
nances in the 31P NMR spectra are indicative of the equivalent P
atoms in accordance with the structural pattern suggested in
Scheme 3. The position of the phenyl rings of the “belt” dipho-
sphine ligands and those of the P-Au-C2Ph fragments in the
“rods-in-belt” structures of 1-4 are not subjected to substantial
changes upon growth of the diphosphine spacer length. Because
of this, the corresponding NMR signals of these fragments
disposed in the low-field part of the proton spectra are almost
identical; see Experimental Section, Figure 2, and Figures S7-S9
in the Supporting Information. In turn, the increase in the
number of -C6H4- moieties within the diphosphine spacers
gives additional signals of these fragments in the low-field
part of the proton spectra of 2-4. The growth in the diphosphine
length gives room for two more {Au(C2Ph)2} rods per
additional phenylene spacer, which results in the appearance of
The compositions and structures of the clusters 2-4 were
elucidated on the basis of ESI-MS and 1H and 31P NMR
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Scheme 3. Formation of Clusters 2-4, x = 8 (P1P), 10 (P2P), 12 (P3P) (CH2Cl2, 298 K)
quenching rate manifest the uniqueness of the titled supra-
molecules framework, in which the emission chromophores
(i.e., the central heterometallic alkynyl clusters) are very
well-protected by the bulky ancillary and bridging ligands (see
Figure 2).
To gain more insight into the spectroscopic features pre-
viously discussed, prior to the assignment of the absorption and
emission origin, we felt it necessary to execute computational
studies to explore the structure-electronic transition relation-
ship. Thus, density functional calculations were performed to
shed light on the photophysical behavior of Au(I)-Ag(I)
complexes 1-4. The geometries of the complexes were first
optimized at the BP86-DFT level of theory. Comparison of the
X-ray crystal structure of 1 with the theoretically optimized one
showed the Au-Au contacts between the external and central
parts to be elongated from 3.02 Å to 3.02-3.20 Å. The difference
is most likely due to the fact that the BP86 density functional
method is not completely capable of describing closed-shell
metal-metal interactions. Furthermore, the lack of the crystal
packing effects in the theoretical calculations is expected to result
in the deviations observed. However, the general structural motif
of clusters 1-4 was reproduced well by the theoretical methods,
and calibration calculations performed at the experimental
geometry showed that the electronic properties of the complexes
were not misrepresented because of the structural differences
(vide infra).
Figure 4. UV/vis absorption and normalized emission spectra of 1-4
in aerated CH2Cl2 at room temperature, λexcit = 450 nm. Note that
absorption and emission taken from batches 1a and 1b separately are
exactly overlapped.
an additional group of “ortho-meta-para” protons (20H) in
the high-field part of the proton spectrum, which can be easily
assigned in the corresponding 2D COSY spectrum (see Figures
S7-S9 in the Supporting Information). The number of the
signals in the proton spectra, as well as their multiplicity and
relative intensity, completely fit the structural hypothesis shown
in Scheme 3, which supports the validity of the synthetic strategy
developed in the present study.
Photophysical Characteristics. Figure 4 shows the UV/vis
absorption and emission spectra of complexes 1-4 in CH2Cl2 at
room temperature. Complexes 2, 3, and 4 exhibit highly intense,
single emission maximized at 592, 606, and 613 nm, respectively,
the quantum yield of 2 and 3 being nearly quantitative. As for
complex 1, despite different emission color in solid (vide infra),
luminescence for 1a and 1b in CH2Cl2 is identical, which consists
of weak, dual luminescene maximized at 575 (the P1 band) and
770 nm (the P2 band). These two bands also undergo the same
relaxation dynamics. The analysis of the photophysics of this
compound is given in the following sections. All pertinent
spectroscopy and dynamics data for 1-4 are listed in Table 2.
The order of radiative decay rate constant is deduced to be 104-
105 s-1, which suggests the triplet origin of the emissive excited
states, i.e., phosphorescence, for all complexes 1-4. Perhaps the
most striking feature of the luminescence of the heterometallic
clusters is the extremely high emission quantum yield.26 More-
over, the phosphorescence intensity is almost free from O2
quenching.3,4,27 The high quantum yield and negligible O2
The frontier molecular orbitals of the S0 and T1 electronic
states of the Au-Ag complex 1 are illustrated in Figure 5, and the
corresponding data for the larger complexes (2-4) are shown in
Figure S10 in the Supporting Information.
For complex 1, the frontier orbital characteristics calculated at
the theoretically optimized geometry were found to be very
similar to those calculated for the experimental structural data
(see Figure S11 in the Supporting Information). Only one
HOMO of the S0 state is illustrated here, but several lower
energy HOMOs were examined to confirm the nature of
HOMO. For all complexes, HOMO and LUMO of the S0
ground state are delocalized over the central fragment. The
relaxed geometry of the lowest-energy triplet state T1 is very
similar to the ground state structure for all complexes 1-4. The
highest singly occupied molecular orbital (HSOMO), occupied
by the excited electron, is closely related to LUMO of the S0 state,
and the lowest singly occupied molecular orbital (LSOMO) is
closely related to HOMO of the S0 state. The fact that both the
T1 LSOMO and HSOMO are composed of alkynyl and metal
orbitals of the central fragment suggests that spin-orbit coupling
due to the metal orbitals enables efficient radiative decay of the
excited triplet state.
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Table 2. Photophysical Properties of the Au-Ag Complexes in CH2Cl2
d
λab (nm) (10-4 ε (cm-1 M-1))
λem (nm)
Φa
Φb
Φc τobs (μs)a τobs (μs)b τobs (μs)c
kr (s-1
)
1a
1b
2
351sh (8.8), 447 (0.82)
(575, 770),a,b (610)c
(575, 770),a,b (570)c
592 (620)c
606 (582)c
613 (550)c
0.003
0.004
0.95
1
0.004
0.004
1
0.28
0.08
0.18
0.44
0.05
0.047
0.049
5.12
5.41
2.4
0.048
0.049
5.3
2.64
0.52
0.49
1.77
0.83
7.73 ꢀ 104
8.11 ꢀ 104
1.89 ꢀ 105
1.85 ꢀ 105
7.85 ꢀ 104
351sh (9.0), 447 (0.83)
319 (22.8), 329sh (17.9), 360sh (7.5), 449 (0.8)
319 (29.0), 450 (1.0)
3
1
5.42
2.4
4
323 (25.7), 450 (1.1)
0.19
0.19
a Measured in aerated CH2Cl2. b Measured in degassed CH2Cl2. c Measured in powder. d kr is deduced from data obtained in the degassed solution.
4-Dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) in methanol was used as a standard for the quantum yield (Φ) measure-
ments. The excitation wavelength is 450 nm for all measurements.
Figure 5. Frontier molecular orbital isodensity plots for complex 1 (isodensity value = 0.04 au). Hydrogen atoms and diphosphine-based phenyl rings
have been omitted for clarity.
Standing on the above theoretical basis, the higher-energy
absorptions below 300 nm for all of the titled compounds are
ascribed to the intraligand π f π* (CtC-Ar) transitions inside
the alkynyl groups. This assignment is consistent with the
previous reports on the relevant alkynyl analogues, for which
the dominant absorption band in the spectral region of 230-300
nm is ascribed to the characteristic band of the alkynyl-
phosphine fragments. The 300-400 nm absorption bands for
these complexes are mainly due to Ag-π-alkynyl fragment metal-
and cluster-centered transitions.2,7The lowest energy transition
extended to ∼500 nm, according to the frontier orbital analyses,
corresponds to the charge delocalization around metal-
alkyne moieties rather than to a pure metal-to-ligand
charge transfer (MLCT), because of the mixed feature for
both HOMO and LUMO. In solution, all the emission band
wavelengths are progressively red-shifted with the increase in
the size of the dialkynyl cluster nuclei from 575 nm (the P1 band)
for 1 to 592, 606, and 613 nm for 2, 3, and 4, respectively.
However, for the titled heterometallic clusters possessing a
massive, flexible framework, the corresponding structure
must be subjective to environmental perturbation, resulting in
changes of luminescence properties. Particularly, this effect may
become dramatic with transfer of the molecules from solution to
the rigid solid media, such as in crystal, in which the packing
forces should result in freezing of large-amplitude intramolecular
motion.
This hypothesis is supported by comparison of the data shown
in Figures 4 and 6. In sharp contrast to the bathochromic shift of
emission maximum in CH2Cl2 solution, 4 > 3 > 2, the hypso-
chromic shift of the emission in the order of 4 > 3 > 2 is observed
for the crystalline samples, indicating significant structural alter-
nation from solution to solid phase.
Particular attention was paid to the dual emission of the
complex 1 in solution. Note that this observation is independent
of whether the solution is prepared from solid crystal 1a or 1b.
Both emission bands are authentic because they possess identical
excitation spectra (see Figure S12 in the Supporting In-
formation), which are also overlapping with the absorption
spectrum. Accordingly, both 575 and 770 nm emissions originate
from the same ground state. Moreover, in solution, both P1 and
P2 bands have exactly identical relaxation dynamics to give a
decay time of ∼47 ns at 298 K (Table 3). The assignment of P1
and P2 bands to fluorescence and phosphorescence, respectively,
has been discarded, because of the much longer radiative decay
time (∼15 μs, vide supra) deduced. To gain further insight into
the dual emission, we also carried out the VT measurements in
the temperature range from 298 K to 200 K. The results shown in
Table 3 and Figure 7 clearly indicate that P1 and P2 bands, within
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Figure 7. Emission spectra of complex 1a in degassed CH2Cl2 at
298-203 K and 77 K.
Figure 6. Emission spectra of complexes 1-4 in solid state, λex
450 nm.
=
Table 3. Photophysical Properties of Complex 1a at Various
Temperatures (203-298 K and 77 K) in Degassed CH2Cl2
temperature (K) τ(P1) (ns)a (575 nm) τ(P2) (ns)b (770 nm) P1/P2
c
77
203
213
223
233
243
253
263
273
298
4150
102.3
101.5
97.2
93.1
83.2
80.3
75.8
68.7
60.7
46.3
10.5
10.9
10.0
96.6
92.3
85.5
78.3
75.3
67.3
60.2
47.7
8.15
7.86
7.09
7.23
7.61
8.17
a Emission monitored at 560 nm. b Emission monitored at 760 nm. c The
ratio of emission intensity for the P1 band versus the P2 band.
Figure 8. Proposed structural fluctuation between two isomers to
account for the observed dual phosphorescence in complex 1.
experimental error, reveal the same relaxation dynamics as well as
an almost-similar intensity ratio for the P1 versus P2 band
throughout the range of temperatures studied, implying the
proximity in energy between two emitting species with a rather
small barrier.
Further lowing temperature was not performed due to the
system limitation. Nevertheless, upon plunging the sample tube
into liquid N2, only one emission band maximized at ∼560 nm is
observed at 77 K (Figure 7). Also, the narrower full width at half-
maximum (fwhm) is noticed at 77 K, implying large reduction
broadening due to the system inhomogeneity.
current experimental and theoretical approaches are unable to
provide structural resolution. Although pending resolution, the
structural alternation, in part, may associate with the torsional
motion along the electronically excited alkynyl-diphosphine
moiety, which is thermally unfavorable in the ground state
(Figure 8). Since the structural fluctuation does not
involve bond breaking/formation, the interconversion between
these two conformers must be fast in the fluid phase, as evidenced
by the identical relaxation dynamics between the P1
and P2 bands. Such structural fluctuation may incorporate
large amplitude motions along the reaction coordinate and,
hence, is hampered in solid-state media, rationalizing a unique
emitting band observed in crystalline samples and the 77 K solid
matrix.
Summarizing the above experimental results, we herein tenta-
tively propose a rational mechanism based on the existence of
two structural conformers, TP and TP (Figure 8), in the triplet
1
2
manifold, which respectively render P1 and P2 emission. This
proposal has its stance in that different crystal packing, as shown
in Figure S13 in the Supporting Information, exhibits distinctly
different emission, namely single orange-red emission (610
nm) for 1a and yellow emission (570 nm) for 1b. Accordingly, it
is reasonable to expect that the fluctuation of this heterometallic
structure in solution, forming two conformers virtually, may be
subject to different intramolecular ligand-to-ligand, metal-to-
metal, or even ligand-to-metal interactions. Unfortunately,
As for one of the future perspective, because of the intense
(∼100% yield) and O2-quenching-free phosphorescence, com-
plex 3 was also examined for the two-photon absorption (TPA)
property. The aim is to explore its application toward nonlinear
and time-resolved phosphorescence imaging. Figure S14 in the
Supporting Information shows a typical Z-scan and a fitting curve
for compound 3 in CH2Cl2. As a result, the TPA cross section is
calculated to be σ ≈ 45 GM (800 nm) for 3. The magnitude of
this value is similar to that observed for commercially available
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TPA dyes such as coumarin 151 (σ ≈ 45 GM at 800 nm),28
making 3 promising as a two-photon absorption phosphores-
cence dye.
(b) Koshevoy, I. O.; Karttunen, A. J.; Tunik, S. P.; Haukka, M.;
Selivanov, S. I.; Melnikov, A. S.; Serdobintsev, P. Y.; Khodorkovskiy,
M. A.; Pakkanen, T. A. Inorg. Chem. 2008, 47, 9478–9488.
(6) Koshevoy, I. O.; Karttunen, A. J.; Tunik, S. P.; Haukka, M.;
Selivanov, S. I.; Melnikov, A. S.; Serdobintsev, P. Y.; Pakkanen, T. A.
Organometallics 2009, 28, 1369–1376.
’ CONCLUSION
In conclusion, a new family of heterometallic aggregates 1-4
has been designed and synthesized via self-organization of the
mixture of (AuC2Ph)n and (AgC2Ph)n polymers upon treatment
with cationic complexes [Au2(PPh2-C2-(C6H4)n-C2-PPh2)2]2þ
(n = 0, 1, 2, 3). Several intriguing and significant remarks can be
noted. In the solid, complex 1 exists as two crystalline forms (1a
and 1b) with different colors and different associated emissions.
In solution, this compound exhibits dual phosphorescence in the
yellow and near-infrared region. The results lead to a conclusion
that 1, upon excitation, undergoes fast structural fluctuation,
forming virtually two conformers in equilibrium, which accounts
for the dual emission. Complexes 2 and 3 demonstrate intense
phosphorescence with unity quantum efficiency. An equally
important point is that the phosphorescence, although having a
lifetime as long as 5-6 μs, does not display O2 quenching. The
result evidently manifests the uniqueness of their framework, in
which the emission chromophores—the central heterometallic
alkynyl clusters—are protected by the bulky ancillary and brid-
ging ligands from the dipole interaction with molecular oxygen.
(7) Koshevoy, I. O.; Ostrova, P. V.; Karttunen, A. J.; Melnikov, A. S.;
Khodorkovskiy, M. A.; Haukka, M.; J€anis, J.; Tunik, S. P.; Pakkanen,
T. A. Dalton Trans. 2010, 39, 9022–9031.
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’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallographic data in
b
CIF for 1, 1H-1H COSY spectra of 2-4, ESI-MS spectra of 1-
4, additional theoretical data, and optimized Cartesian coordi-
nates of the studied systems in atomic units. This material is
available free of charge via the Internet at http://pubs.acs.org.
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Corresponding Author
*E-mails: igor.koshevoy@uef.fi (I.O.K.), chop@ntu.edu.tw
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’ ACKNOWLEDGMENT
€
Financial support from the Academy of Finland (I.O.K.),
European Union/European Regional Development Fund (Grant
No. 70026/08 (A.J.K. and I.O.K.)), and Russian Foundation for
Basic Research (Grant No. 09-03-12309 ofi-m) and Federal
Agency on Science and Innovations (FC 02.518.11.7140) is
gratefully acknowledged.
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