The first luminescent anionic bis(ethynylphenanthroline)gold(I)complex

Article abstract of DOI:10.1246/cl.2004.210

First anionic bis(ethynylphenanthroline)gold(I) complex and neutral diethynylphenanthroline-digold(I) complex have demonstrated an intense phosphorescence which is assignable to ³π-π*(C≡C) emission even at room temperature. It is appropriate to

Full text of DOI:10.1246/cl.2004.210

210
Chemistry Letters Vol.33, No.3 (2004)
The First Luminescent Anionic Bis(ethynylphenanthroline)gold(I) Complex
Youhei Yamamoto, Michito Shiotsuka,ꢀy Sigeru Okuno, and Satoru Onaka
Department of Environmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555
yDepartment of Socio Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555
(Received November 25, 2003; CL-031145)
First anionic bis(ethynylphenanthroline)gold(I) complex
and neutral diethynylphenanthroline–digold(I) complex have
demonstrated an intense phosphorescence which is assignable
to 3ꢀ–ꢀꢀ(CꢁC) emission even at room temperature. It is appro-
priate to highlight the role of gold(I) coordination which enables
the spin–orbit coupling and facilitates the observation of triplet
emissions.
= triphenylphosphine) with 3,8-bis(ethynyl)-1,10-phenanthro-
line (5) and 4, respectively (2/1 and 1/1 ratio respectively, with
an excess KOH or NaOMe). These complexes were character-
ised by ESIMS, H NMR, IR, UV–vis, emission spectroscopy,
and elemental analysis.
1
-
Au
N
N
N
N
Current research of luminescent gold(I) complexes1 has
gained great importance with respect to their potential applica-
tions to the burgeoning field of photonic devices and nano-mate-
rials, because particularly interesting properties as photoenergy
storage2 and nonlinear optical response3,4 have been discovered
from recent studies on gold(I) organometallics. Structural and
photophysical studies on neutral gold(I) ethynylarene complexes
have been extensively explored by Puddephatt et al.5 and Yam’s
groups6 in the past decade. These compounds are especially at-
tractive for usefulness as a photoactive nano-wire; these com-
pounds should be utilized as scaffolding to construct a rigid-
rod upon coordination with strictly linear bridging diethynylar-
ene ligands through the Au–C ꢁ-bonding. Most studies on
gold(I) ethynyl complexes have so far been made for gold(I)
ethynylarene complexes.5–7 In contrast to these compounds,
gold(I) ethynyldiimine complexes should have a high potential
ability of further coordination to other metal ions. However,
no precedent has been reported to the best of our knowledge.
The first synthetic report of anionic gold(I) arenediethynyl com-
plexes was recently made by Vicente et al.8 for the purpose of
finding some peculiar structural features. In addition to the struc-
tural idiosyncrasy, the luminescent property of anionic gold(I)
bis(ethynylarene) complexes is intriguing and significant studies
have been undertaken in connection with neutral alkynylgold(I)
complexes. Anionic gold(I) ethynyldiimine complex is further
advantageous for the construction of heterometallic system be-
cause of Coulomb’s law; the diimine ligand such as a bipyridine
and phenanthroline is generally coordinated to cationic metal
center. However, only one photophysical study on the anionic
gold(I) bis(ethynylbenzene) complex has so far been reported
to our knowlegde7 and their result has encouraged us to extend
the chemistry. Herein, we report the synthesis and photophysical
study of the luminescent anionic gold(I) bis(ethynyldiimine)
complex [(i-C3H7)2NH2][Phen–ꢁ–Au–ꢁ–Phen] (1) for the first
time and the neutral gold(I) diethynyl- and ethynyl-diimine com-
plexes (PPh3)Au–ꢁ–phen–ꢁ–Au(PPh3) (2) and phen–ꢁ–
Au(PPh3) (3) with ethynyl- or diethynyl-phenanthroline ligands
which coordinate to gold(I) ion through the Au–C ꢁ-bonding.
The anionic complex 1 was synthesised from Au(tht)Cl (tht
= tetrahydrothiophene) and 3-ethynyl-1,10-phenanthroline (4)
(1/2 ratio, with an excess diisopropylamine as a base), while
complex 2 and 3 were prepared by reacting Au(PPh3)Cl (PPh3
1
Ph3P Au
Au PPh3
N
N
2
3
Au PPh3
N
N
IR spectral data of these novel three complexes indicate that
the metal–carbon bond between Au(I) and ethynylphenanthro-
lines is of ꢁ-bonding. The characteristic ꢂ(CꢁC) bands are ob-
served at 2094 cmꢂ1(1), 2109 cmꢂ1(2), 2108 cmꢂ1(3), respec-
tively and the ꢂ(CC–H) bands at 3146 cmꢂ1(4), 3175 cmꢂ1(5)
are disappeared in these gold(I) complexes.9 The formation of
this type of Au–CꢁC bond is further supported by the 1H
NMR measurement; no assignable signal to ethynyl proton
was detected and all observed signals for 1–3 correspond to
the protons of the phenanthroline and/or the triphenylphosphine,
respectively. Furthermore, the negative ESIMS spectrum for 1
predominantly shows one signal set that is compatible with the
simulated pattern for mono anion [Phen–ꢁ–Au–ꢁ–Phen]ꢂ.
Figure 1 displays the absorption and emission spectra of
complex 1 in MeOH. The absorption bands at 345 nm are pri-
marily assigned to ꢀ–ꢀꢀ(CꢁC) absorption for 1. 2 and 3 show
similar absorption spectra in CH2Cl2 (Figure 2). Molar extinc-
tion coefficients for ꢀ–ꢀꢀ absorptions (337 and 357 nm) in 2
are twice as those (315 and 328 nm) of 3. As the absorption co-
efficient is proportional to the number of the Au(I)-ethynyl unit,
this finding lends further support to interpretation that the intense
absorptions are due to ꢀ–ꢀꢀ(CꢁC) transitions. The red shift of
the ꢀ–ꢀꢀ absorptions (337 and 349 nm in CH2Cl2) in 1 com-
pared with those (315 and 328 nm) in 3 should be attributed to
more electron delocalization between two ethynylphenanthoro-
line ligands via a gold(I) ion.
The emission spectrum of the complex 1 displays an intense
emission band in the visible region and a weak band in the UV
area, which are so called dual emission in deoxygenated metha-
nol at room temperature upon excitation at 328 nm (Figure 1).
The former intense luminescence is formally assignable to the
3ꢀ–ꢀꢀ phosphorescence, because the luminescence excitation
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.3 (2004)
211
Che et al.11 lends support to this interpretation of the emission
spectra for these complexes.
In summary, the gold(I) ethynyldiimine complexes have
been prepared for the first time and shown the obvious lumines-
cence assignable to 3ꢀ–ꢀꢀ(CꢁC) phosphorescence at room tem-
perature. It is appropriate to highlight the role of gold(I) coordi-
nation which enables the spin–orbit coupling and facilitates the
observation of triplet emissions. We are currently extending the
synthetic work of novel rhenium(I)–gold(I) complexes in which
these gold(I) complexes coordinate to the rhenium center in a
rhenium(I) diimine complex and an exploration for the mecha-
nism of photoinduced energy transfer process is continuing for
hetero organometallics.
This work was supported partly by Grant-in-Aid for Scien-
tific Research No. 15750048 from the ministry of Education,
Culture, Sports, Science and Technology, Japan.
Figure 1. Absorption (—) and Emission (- - - -) spectra of 1 in
MeOH purged N2 at room temperature. Emission spectrum
was detected upon excitation at 328 nm.
References and Notes
1
2
3
4
5
6
Recent reviews: a) R. J. Puddephatt, Cood. Chem. Rev., 216–
217, 313 (2001). b) V. W. W. Yam, K. K. W. Lo, and K. M.
C. Wong, J. Organomet. Chem., 578, 3 (1999). c) R. J.
Puddephatt, Chem. Commun., 1998, 1055.
a) J. C. Vickery, M. M. Olmstead, E. Y. Fung, and A. L.
Balch, Angew. Chem., Int. Ed. Engl., 36, 1179 (1997). b)
R. L. White-Morris, M. M. Olmstead, F. Jiang, D. S. Tinti,
and A. L. Balch, J. Am. Chem. Soc., 124, 2327 (2002).
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Arellano, P. G. Jones, M. G. Humphrey, M. P. Cifuentes,
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2968 (2000).
H. R. Naulty, M. P. Cifuentes, M. G. Humphrey, S.
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a) C. P. McArdle, S. Van, M. C. Jennings, and R. J.
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a) V. W. W. Yam, S. W. K. Choi, and K. K. Cheung,
Organometallics, 15, 1734 (1996). b) V. W. W. Yam and
S. W. K. Choi, J. Chem. Soc., Dalton Trans., 1996, 4227.
Figure 2. Absorption (left) and Emission (right) spectra of 2
(——) and 3 (- - - -) in CH2Cl2 purged N2 at room temperature.
Emission spectrum was detected upon excitation at 328 nm.
c) T. E. Muller, S. W. K. Choi, D. M. P. Mingos, D. Murphy,
¨
spectrum monitored at 488 nm of 1 between 250 and 450 nm is
approximately in accord with the absorption spectrum in this re-
gion. Under an aerobic condition, the emission spectrum of 1 ex-
hibits a quite weak phosphorescent band between 450 and
600 nm owing to 3O2 quenching. On the contrary, the weak flu-
orescent band10 between 350 and 450 nm is left intact. Entirely
similar spectral changes are observed for 2 and 3 under aerobic
and anaerobic conditions. Thus, these novel gold(I) complexes
exhibit an intense phosphorescence only under an anaerobic con-
dition at room temperature.
Another interesting finding is that these gold(I) complexes
show a vibronic structure of the emission spectra even at an am-
bient temperature. The emission spectrum of 2 (Figure 2) dis-
plays vibronic progressions and the vibrational spacing of the
main progression (ꢂ ¼ 1500 cmꢂ1) is in accord with aromatic
C–C stretching region (1300 to 1700 cmꢂ1). The latest photo-
physical study on gold(I) ethynylarene complexes reported by
D. J. Williams, and V. W. W. Yam, J. Organomet. Chem.,
484, 209 (1994).
7
a) D. Li, X. Hong, C. M. Che, W. C. Lo, and S. M. Peng, J.
Chem. Soc., Dalton Trans., 1993, 2929. b) C. M. Che, H. K.
Yip, W. C. Lo, and S. M. Peng, Polyhedron, 13, 887 (1994).
J. Vicente, M. T. Chicote, M. D. Abrisqueta, and M. M.
Alvarez-Falcn, J. Organomet. Chem., 663, 40 (2002).
The ꢂ(CꢁC) stretching mode in the case of Au–C ꢁ-bonding
for the gold(I) ethynylarene complexes characterized by X-
8
9
ray crystallography have been reported in the region between
2090 and 2125 cmꢂ1
.
3,4,6,7
10 Research on the fluorescence of several ethynylphenanthro-
lines have been reported. Example: E. Birckner, U.-W.
Grummt, A. H. Goller, T. Pautzsch, D. A. M. Egbe, M. Al-
¨
Higari, and E. Klemm, J. Phys. Chem. A, 105, 10307 (2001).
11 H. Y. Chao, W. Lu, Y. Li, M. C. W. Chan, C. M. Che, K. K.
Cheung, and N. Zhu, J. Am. Chem. Soc., 124, 14696 (2002).
Published on the web (Advance View) January 26, 2004; DOI 10.1246/cl.2004.210