Organic triplet emissions of arylacetylide moieties harnessed through coordination to [Au(PCy3)]+. Effect of molecular structure upon photoluminescent properties

Article abstract of DOI:10.1021/ja0209417

A family of mono- and binuclear Cy₃P-supported gold(I) complexes containing various π-conjugated linear arylacetylide ligands, including the two homologous series (Cy₃P)Au(C≡CC₆H₄)_n-1 (C≡CPh) and (Cy₃P)Au(C≡CC₆H₄)_n C≡C≡Au(PCy₃) (n = 1-4), have been prepared. X-ray crystal analyses revealed no intermolecular aurophilic interactions in their crystal lattice. The lowest-energy singlet transitions are predominately intraligand in nature and exhibit both phenyl and acetylenic ¹(ππ*) character. Strong photoluminescence is detected in solid and solution states under ambient conditions, with lifetimes in the microsecond regime. For complexes with a single arylacetylide group, only phosphorescence from the arylacetylide ³(ππ*) state is observed. Vibrational spacings in the solid-state emission spectra can be attributed to a combination of phenyl ring deformation and symmetric phenyl ring and C≡C stretches. Additional delayed-fluorescence emission is recorded for complexes with multiple p-arylacetylide units, and this is attributed to a triplet-triplet annihilation process. The phosphorescence energy of these complexes are readily modified by altering the length of the conjugated arylacetylide system, while the intensity of phosphorescence relative to fluorescence decreases when the p-arylacetylide chain is elongated. Information regarding the nature and relative energies of arylacetylide singlet and triplet excited states has been derived from the two homologous series and extrapolated to polymeric arylacetylide species. The 3(ππ*) excited-state reduction potentials E° [Au⁺/Au*] (Au = 1a, 2, and 4) are estimated to be -1.80, -1.28, and -1.17 V versus SSCE, respectively.

Full text of DOI:10.1021/ja0209417

Published on Web 11/16/2002
Organic Triplet Emissions of Arylacetylide Moieties
Harnessed through Coordination to [Au(PCy3)]+. Effect of
Molecular Structure upon Photoluminescent Properties
Hsiu-Yi Chao, Wei Lu, Yanqin Li, Michael C. W. Chan, Chi-Ming Che,*
Kung-Kai Cheung, and Nianyong Zhu
Contribution from Department of Chemistry and HKU-CAS Joint Laboratory on
New Materials, The UniVersity of Hong Kong, Pokfulam Road, Hong Kong SAR, China
Received July 9, 2002
Abstract: A family of mono- and binuclear Cy3P-supported gold(I) complexes containing various
π-conjugated linear arylacetylide ligands, including the two homologous series (Cy3P)Au(CtCC6H4)n-1(CtCPh)
and (Cy3P)Au(CtCC6H4)nCtCAu(PCy3) (n ) 1-4), have been prepared. X-ray crystal analyses revealed
no intermolecular aurophilic interactions in their crystal lattice. The lowest-energy singlet transitions are
predominately intraligand in nature and exhibit both phenyl and acetylenic 1(ππ*) character. Strong
photoluminescence is detected in solid and solution states under ambient conditions, with lifetimes in the
microsecond regime. For complexes with a single arylacetylide group, only phosphorescence from the
arylacetylide 3(ππ*) state is observed. Vibrational spacings in the solid-state emission spectra can be
attributed to a combination of phenyl ring deformation and symmetric phenyl ring and CtC stretches.
Additional delayed-fluorescence emission is recorded for complexes with multiple p-arylacetylide units,
and this is attributed to a triplet-triplet annihilation process. The phosphorescence energy of these
complexes are readily modified by altering the length of the conjugated arylacetylide system, while the
intensity of phosphorescence relative to fluorescence decreases when the p-arylacetylide chain is elongated.
Information regarding the nature and relative energies of arylacetylide singlet and triplet excited states has
been derived from the two homologous series and extrapolated to polymeric arylacetylide species. The
3(ππ*) excited-state reduction potentials E° [Au+/Au*] (Au ) 1a, 2, and 4) are estimated to be -1.80,
-1.28, and -1.17 V versus SSCE, respectively.
and metal-containing acetylide complexes3 and polymers,4 have
been investigated for their nonlinear optical (NLO), liquid
Introduction
The search for new classes of organic and metal-organic
compounds with optoelectronic applications in materials science
has intensified in the past few years. Conjugated ethynylated
materials, such as arylacetylenes,1 poly(arylene-ethynylene)s,2
crystalline, electroluminescent, conducting, and electron/energy
transfer properties. From a photophysical viewpoint, arylacetyl-
enes do not display long-lived triplet emissions under ambient
conditions and phenylacetylene is virtually nonemissive at
wavelengths above 400 nm. Recent studies on fluorescence-
based poly(p-phenylene-ethynylene)s (PPEs) have elegantly
demonstrated that controlled manipulation of the polymer
conformation can yield intriguing photophysical changes,2 while
* To whom correspondence should be addressed. E-mail: cmche@hku.hk.
(1) (a) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350-
1377. (b) Stang, P. J.; Diederich, F. Modern Acetylene Chemistry; VCH:
Weinheim, Germany, 1995. (c) Carter, G. M.; Chen, Y. J.; Rubner, M. F.;
Sandman, D. J.; Thakur, M. K.; Tripathy, S. K. In Non-Linear Optical
Properties of Organic Molecules and Crystals; Chemla, D. S., Zyss, J.,
Eds.; Academic: Orlando, FL, 1987; Vol. 2, Chapter III-3, p 85.
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Swager, T. M. J. Am. Chem. Soc. 2002, 124, 7710-7718. (c) Cornil, J.;
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Kim, J.; Swager, T. M. J. Am. Chem. Soc. 2000, 122, 5885-5886. (i) Deans,
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9
14696
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10.1021/ja0209417 CCC: $22.00 © 2002 American Chemical Society

Organic Triplet Emissions of Arylacetylide Moieties
A R T I C L E S
applications in molecular electronics and sensory technology
have also been developed. Nevertheless, the triplet excited states
of arylacetylide groups and PPEs have not been fully elucidated.
A thorough understanding of their excited-state properties is
required before a rational design approach for π-conjugated
polymers can be realized. In this context, Hopkins has presented
a review on the bonding of metal-alkynyl complexes and
discussed the impact of the metal upon electronic transitions
involving the arylacetylide orbitals.3a
lying ligand-localized excited states and its bulkiness disfavors
metal-metal and π-π oligomerization processes. We now
present the synthesis and structural and spectroscopic properties
of a family of mono- and binuclear PCy3-supported gold(I)
arylacetylide complexes that are strongly luminescent. The
characteristics of the triplet excited states of organic arylacetyl-
ides will be described in detail. By probing the 3(ππ*) emissions
of the two homologous series Cy3PAu(-CtC-Ar)n and Cy3-
PAu(CtC-Ar)nCtCAuPCy3 (n ) 1-4), it is anticipated that
a structure-function (i.e. photoluminescence) relationship can
be established and valuable insight into the photophysical nature
of (sCtCsArs)n materials can be derived.
We envisaged that if the emission from the triplet excited
states of arylacetylides can be “switched on” under ambient
conditions, such compounds and their polymeric forms may be
exploited as emitting materials in organic light-emitting devices
(OLEDs) and luminescent sensors. One possible strategy to
achieve this is by ligation to heavy metal ions, which introduces
spin-orbit coupling. Friend and co-workers have previously
incorporated the Pt(PR3)2 moiety (R ) alkyl) into π-conjugated
polymers to give rigid-rod organometallic chains such as
[sPt(PnBu3)2sCtCsR′sCtCs]∞ (R′ ) alkyl or heteroaro-
matic ring(s)), and triplet ππ* emissions have been observed
at low temperatures.4a-f However, the low-energy d-d excited
state for Pt(II), which provides a facile means for nonradiative
decay, is a major obstacle for observing the triplet emission of
these polymers in solution. In this regard, Au(I) is a sagacious
choice because the d10 closed-shell configuration does not allow
low-lying d-d excited states. The photoluminescence of gold(I)
arylacetylide derivatives has been studied by several groups.5
Nevertheless, observations of 3(ππ*) emissions in these systems
are habitually complicated by intraligand excited states of
auxiliary phosphine ligands and by metal-centered excited states
arising from metal-ligand and/or metal-metal bonded exciplex
formation. The intraligand 3(ππ*) state is of particular interest
because its energy can be readily tuned through electronic
modification of the arylacetylide moiety.
Experimental Section
Materials. All starting materials were purchased from commercial
sources and used as received unless stated otherwise. The solvents used
for synthesis were of analytical grade. Details of solvent treatment for
photophysical studies have been described earlier.7 Trimethylamine and
diethylamine were freshly distilled over KOH pellets. HCtCCtCPh,8
1,4-diethynylbenzene,9 HCtC-1,4-C6H4-1,4-C6H4CtCH,9 4-ethynyl-
pyridine,10 HCtC-1,4-C6H4Ph,11 Me3Si(CtC-1,4-C6H4)3CtCSiMe3,11
Me3SiCtC-1,4-C6H4-CtCSiiPr3,12 and Au(PCy3)Cl13 were prepared
according to literature procedures. The synthesis of Me3SiCtC-1,4-
C6H4CtCPh was the same as that of (4-ethynylphenyl)(4′-pyridyl)-
acetylene except phenylacetylene was used instead of 4-ethynylpyri-
dine.14 H(CtC-1,4-C6H4)2CtCH was prepared by desilylation from
Me3Si(CtC-1,4-C6H4)2CtCSiiPr3 with tetrabutylammonium fluoride
in aqueous THF.12 Me3Si(CtC-1,4-C6H4)2CtCPh, Me3Si(CtC-1,4-
C6H4)3CtCPh, and Me3Si(CtC-1,4-C6H4)4CtCSiMe3 were synthe-
sized from the reaction of [(4-iodophenyl)ethynyl]trimethylsilane with
1-ethynyl-4-(phenylethynyl)benzene, H(CtC-1,4-C6H4)2CtCPh, and
H(CtC-1,4-C6H4)2CtCH, respectively.14
Synthesis. Full experimental and characterization data for complexes
1-12 are given in the Supporting Information. Synthetic details for
1a, 6, and 8 are provided here as examples. The procedure for 1a was
adopted for the synthesis of 1b-1d, 2-5, and 7 using the corresponding
acetylenes or trimethylsilylacetylenes in the presence of NaOMe or
KOH. The procedure for 6 was adopted for the synthesis of 12 using
Me3Si(CtC-1,4-C6H4)4CtCSiMe3 in the presence of KOH. The
procedure for 8 was adopted for the synthesis of 9-11 using the
corresponding diacetylenes or trimethylsilyldiacetylenes in the presence
of NaOMe or KOH.
Our recent reports on the binuclear Au(I) complexes Cy3-
PAu(CtC)nAuPCy3 (PCy3 ) tricyclohexylphosphine; n ) 1-4)
have established the nature of 3(ππ*) emissions originating from
the bridging (C2n)2- units.6 Tricyclohexylphosphine is a judi-
cious ancillary group for these studies because it has no low-
(4) (a) Wittmann, H. F.; Friend, R. H.; Khan, M. S.; Lewis, J. J. Chem. Phys.
1994, 101, 2693-2698. (b) Younus, M.; Ko¨hler, A.; Cron, S.; Chawdhury,
N.; Al-Mandhary, M. R. A.; Khan, M. S.; Lewis, J.; Long, N. J.; Friend,
R. H.; Raithby, P. R. Angew. Chem., Int. Ed. 1998, 37, 3036-3039. (c)
Chawdhury, N.; Ko¨hler, A.; Friend, R. H.; Wong, W. Y.; Lewis, J.; Younus,
M.; Raithby, P. R.; Corcoran, T. C.; Al-Mandhary, M. R. A.; Khan, M. S.
J. Chem. Phys. 1999, 110, 4963-4970. (d) Wilson, J. S.; Ko¨hler, A.; Friend,
R. H.; Al-Suti, M. K.; Al-Mandhary, M. R. A.; Khan, M. S.; Raithby, P.
R. J. Chem. Phys. 2000, 113, 7627-7634. (e) Wilson, J. S.; Chawdhury,
N.; Al-Mandhary, M. R. A.; Younus, M.; Khan, M. S.; Raithby, P. R.;
Ko¨hler, A.; Friend, R. H. J. Am. Chem. Soc. 2001, 123, 9412-9417. (f)
Ko¨hler, A.; Wilson, J. S.; Friend, R. H.; Al-Suti, M. K.; Khan, M. S.;
Gerhard, A.; Ba¨ssler, H. J. Chem. Phys. 2002, 116, 9457-9463. (g) Wilson,
J. S.; Dhoot, A. S.; Seeley, A. J. A. B.; Khan, M. S.; Ko¨hler, A.; Friend,
R. H. Nature 2001, 413, 828-831. (h) Nguyen, P.; Go´mez-Elipe, P.;
Manners, I. Chem. ReV. 1999, 99, 1515-1548.
Au(PCy3)(CtCPh) (1a). A solution of Au(PCy3)Cl (0.10 g, 0.20
mmol) in CH2Cl2/MeOH (1:1, 30 mL) was treated with phenylacetylene
(0.02 g, 0.20 mmol) and excess NaOMe (0.02 g, 0.37 mmol) in MeOH
(5 mL). The mixture was stirred at room temperature for 3 h. After
evaporation to dryness, the solid residue was extracted with CH2Cl2.
Diffusion of diethyl ether into the concentrated solution gave colorless
1
crystals. Yield 0.07 g (62%). H NMR (CDCl3) δ 7.51-7.48 (m, 2H,
phenyl), 7.25-7.15 (m, 3H, phenyl), 2.08-1.18 (m, 33H, Cy); 13C-
2
{1H} NMR (CDCl3) δ 136.1 (d, JCP ) 131 Hz, AusCtC), 132.1,
127.6, 126.3, 125.0, 103.4 (d, 3JCP ) 25 Hz, AusCtC), 33.2 (d, 1JCP
2
) 27 Hz, Cy), 30.7 (s, Cy), 27.1 (d, JCP ) 12 Hz, Cy), 25.9 (s, Cy);
(5) For selected examples, see: (a) Li, D.; Hong, X.; Che, C. M.; Lo, W. C.;
Peng, S. M. J. Chem. Soc., Dalton Trans. 1993, 2929-2932. (b) Shieh, S.
J.; Hong, X.; Peng, S. M.; Che, C. M. J. Chem. Soc., Dalton Trans. 1994,
3067-3068. (c) Xiao, H.; Cheung, K. K.; Che, C. M. J. Chem. Soc., Dalton
Trans. 1996, 3699-3703. (d) Yam, V. W. W.; Choi, S. W. K. J. Chem.
Soc., Dalton Trans. 1996, 4227-4232. (e) Yam, V. W. W.; Choi, S. W.
K.; Cheung, K. K. Organometallics 1996, 15, 1734-1739. (f) Tzeng, B.
C.; Lo, W. C.; Che, C. M.; Peng, S. M. Chem. Commun. 1996, 181-182.
(g) Irwin, M. J.; Vittal, J. J.; Puddephatt, R. J. Organometallics 1997, 16,
3541-3547. (h) Hunks, W. J.; MacDonald, M. A.; Jennings, M. C.;
Puddephatt, R. J. Organometallics 2000, 19, 5063-5070. (i) Lin, Y. Y.;
Lai, S. W.; Che, C. M.; Cheung, K. K.; Zhou, Z. Y. Organometallics 2002,
21, 2275-2282.
(7) Lai, S. W.; Chan, M. C. W.; Cheung, T. C.; Peng, S. M.; Che, C. M. Inorg.
Chem. 1999, 38, 4046-4055.
(8) Kende, A. S.; Smith, C. A. J. Org. Chem. 1988, 53, 2655-2657.
(9) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1980,
627-630.
(10) Ciana, L. D.; Haim, A. J. Heterocycl. Chem. 1984, 21, 607-608.
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P.; Marder, T. B.; Wittmann, F.; Friend, R. H. J. Mater. Chem. 1994, 4,
1227-1232.
(12) Lavastre, O.; Ollivier, L.; Dixneuf, P. H.; Sibandhit, S. Tetrahedron 1996,
52, 5495-5504.
(13) Al-sa’ady, A. K.; McAuliffe, C. A.; Parish, R. V.; Sandbank, J. A. Inorg.
Synth. 1985, 23, 191-194.
(6) (a) Che, C. M.; Chao, H. Y.; Miskowski, V. M.; Li, Y.; Cheung, K. K. J.
Am. Chem. Soc. 2001, 123, 4985-4991. (b) Lu, W.; Xiang, H. F.; Zhu,
N.; Che, C. M. Organometallics 2002, 21, 2343-2346.
(14) Wu, I. Y.; Lin, J. T.; Luo, J.; Sun, S. S.; Li, C. S.; Lin, K. J.; Tsai, C.;
Hsu, C. C.; Lin, J. L. Organometallics 1997, 16, 2038-2048.
9
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A R T I C L E S
Chao et al.
Chart 1. Mononuclear and Binuclear Gold(I) Arylacetylide
Complexes 1-12
Figure 1. Perspective view of one of the two independent molecules of 3
(50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg):
Au(1)sP(1) 2.291(2), Au(1)sC(1) 2.003(7), C(1)tC(2) 1.189(9), P(1)s
Au(1)sC(1) 176.0(2), Au(1)sC(1)tC(2) 175.7(8), C(1)tC(2)sC(3)
177.7(9).
31P{1H} NMR (CDCl3) δ 57.49 (s). IR (KBr): 2113 cm-1 (w, CtC).
MS-FAB (+ve): m/z 579 [M+]. Anal. Calcd for C26H38AuP: C, 53.96;
H, 6.62. Found: C, 53.90; H, 6.59.
Au(PCy3)[(CtC-1,4-C6H4)3CtCPh] (6). A solution of Au(PCy3)-
Cl (0.10 g, 0.20 mmol) in CH2Cl2/MeOH (1:1, 30 mL) was treated
with Me3Si(CtC-1,4-C6H4C)3CtCPh (0.1 g, 0.21 mmol) in THF (10
mL) and excess KOH (0.02 g, 0.36 mmol) in MeOH (10 mL). The
reaction mixture was sonicated to assist the formation of a homogeneous
solution. After filtration, the solution was evaporated to dryness. A
light yellow product was obtained after purification by column
Figure 2. Perspective view of 4 (50% thermal ellipsoids). Selected bond
lengths (Å) and angles (deg): Au(1)sP(1) 2.281(1), Au(1)sC(1) 2.007(5),
C(1)tC(2) 1.180(6), C(9)tC(10) 1.188(6), P(1)sAu(1)sC(1) 178.2(1),
Au(1)sC(1)tC(2) 176.4(4), C(1)tC(2)sC(3) 177.6(5), C(9)tC(10)s
C(11) 177.1(6).
1
chromatography (neutral alumina, CH2Cl2). Yield 0.14 g (82%). H
NMR (CD2Cl2) δ 7.57-7.37 (m, 17H, phenyl), 2.15-1.27 (m, 33H,
Cy); 13C{1H} NMR (CD2Cl2) δ 142.3 (d, 2JCP ) 132 Hz, AusCtC),
131.8, 131.5, 131.3, 128.6, 128.4, 126.3, 123.5, 123.3, 123.0, 122.9,
122.7, 120.5, 102.2 (d, 3JCP ) 24 Hz, AusCtC), 91.6 (s, CtC), 91.3
(s, CtC), 90.9 (s, CtC), 90.8 (s, CtC), 89.9 (s, CtC), 88.9 (s, Ct
show one to two weak ν(CtC) bands at 2067-2207 cm-1. The
Raman spectra of the binuclear derivatives 8 and 9 exhibit an
intense symmetric CtC stretch at 2111 and 2107 cm-1
,
1
2
respectively. The 13C{1H} NMR spectra of 1(a-d) display two
doublets at 137.9-135.3 (2JCP ≈ 131 Hz) and 103.7-102.4 (3JCP
≈ 25 Hz) ppm, which are assigned to the R- and â-acetylide
carbon atoms, respectively. These R-acetylide chemical shifts
are shifted downfield from that of Au(PCy3)(CtCtBu) (120.89
ppm),16 and this can be attributed to the greater electron-donating
ability of the tert-butyl group. The 31P{1H} NMR spectra of
1-12 reveal a singlet at 56.3-57.6 ppm, which is partially
shifted downfield from that of Au(PCy3)Cl (55.2 ppm).
C), 33.2 (d, JCP ) 28 Hz, Cy), 30.8 (s, Cy), 27.1 (d, JCP ) 12 Hz,
Cy), 26.0 (s, Cy); 31P{1H} NMR (CD2Cl2) δ 56.9 (s). IR (KBr): 2116
cm-1 (w, CtC). MS-FAB (+ve): m/z 880 [M+]. Anal. Calcd for
C50H50AuP‚(CH2Cl2)0.5(H2O)0.5: C, 65.20; H, 5.63. Found: C, 65.24;
H, 5.50.
{Au(PCy3)}2(µ-CtC-1,4-C6H4CtC) (8). A solution of Au(PCy3)-
Cl (0.15 g, 0.30 mmol) in CH2Cl2/MeOH (1:1, 40 mL) was treated
with 1,4-diethynylbenzene (0.02 g, 0.16 mmol) and an excess of
NaOMe (0.05 g, 0.93 mmol) in MeOH (10 mL). The mixture was stirred
at room temperature for 3 h. After evaporating to dryness, the solid
residue was extracted with CH2Cl2. Diffusion of diethyl ether into the
The molecular structures of complexes 1a-d, 2-5, 7, 8, and
9‚MeOH‚H2O have been determined by X-ray crystal analyses.
For 3, 4, and 9‚MeOH‚H2O, perspective drawings and selected
bond lengths and angles are depicted in Figures 1-3, and crystal
data are collected in Table 1 (see Supporting Information for
details of other complexes). The Au(I) coordination geometry
in all the structures are virtually linear with the P-Au-C angles
ranging from 175.4(2)° to 178.7(4)°. The Au-P bond distances
(2.281(1)-2.299(2) Å) are similar to those reported for gold(I)
arylacetylide derivatives with triphenylphosphine ligands
(2.263(3)-2.277(1) Å),15a,c,17 and Au(PCy3)Cl (2.242(4) Å).18
The Au-C (1.993(11)-2.03(1) Å) and C(1)tC(2) (1.180(6)-
1.223(10) Å) distances of these complexes also resemble those
1
concentrated solution gave colorless crystals. Yield 0.1 g (65%). H
NMR (CDCl3) δ 7.34 (s, 4H, phenyl), 2.08-1.18 (m, 66H, Cy); 13C-
2
{1H} NMR (CDCl3) δ 137.6 (d, JCP ) 131 Hz, AusCtC), 131.6,
123.0, 103.6 (d, 3JCP ) 24 Hz, AusCtC), 33.1 (d, 1JCP ) 27 Hz, Cy),
2
30.6 (s, Cy), 27.1 (d, JCP ) 8 Hz, Cy), 25.9 (s, Cy); 31P{1H} NMR
(CDCl3) δ 57.51 (s). IR (KBr): 2113 cm-1 (w, CtC). MS-FAB
(+ve): m/z 1079 [M+]. Anal. Calcd for C46H70Au2P2: C, 51.19; H,
6.54. Found: C, 50.81; H, 6.30.
Results
Synthesis and Characterization. The mononuclear (1-7)
and binuclear (8-12) gold(I) arylacetylide complexes were
prepared by reacting Au(PCy3)Cl with terminal acetylenes/
trimethylsilylacetylenes (1:1) and diacetylenes/trimethylsilyl-
diacetylenes (2:1), respectively, in the presence of NaOMe or
KOH.15 Their structures are shown in Chart 1. These complexes
are air-stable in the solid state and in solution. Aspects of their
characterization data are highlighted here. Their IR spectra (KBr)
(15) (a) Bruce, M. I.; Horn, E.; Matisons, J. G.; Snow, M. R. Aust. J. Chem.
1984, 37, 1163-1170. (b) Cross, R. J.; Davidson, M. F. J. Chem. Soc.,
Dalton Trans. 1986, 411-414. (c) Irwin, M. J.; Rendina, L. M.; Vittal, J.
J.; Puddephatt, R. J. Chem. Commun. 1996, 1281-1282.
(16) Vicente, J.; Chicote, M. T.; Abrisqueta, M. D.; Jones, P. G. Organometallics
1997, 16, 5628-5636.
9
14698 J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002

Organic Triplet Emissions of Arylacetylide Moieties
A R T I C L E S
Figure 3. Perspective view of 9 (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Au(1)sP(1) 2.291(2), Au(2)sP(2) 2.289(2), Au(1)s
C(1) 1.992(7), Au(2)sC(16) 2.017(7), C(1)tC(2) 1.223(10), C(15)tC(16) 1.177(10), P(1)sAu(1)sC(1) 176.9(2), P(2)sAu(2)sC(16) 175.7(2), Au(1)s
C(1)tC(2) 177.9(7), Au(2)sC(16)tC(15) 173.8(7), C(1)tC(2)sC(3) 179.0(8), C(16)tC(15)sC(12) 175.5(8).
Table 1. Crystallographic Data for 3, 4, and 9‚MeOH‚H2O
3
4
9‚MeOH‚H O
2
formula
Mw
AuC32H42P
654.62
AuC34H42P
678.65
yellow
0.25 × 0.15 × 0.07
orthorhombic
Pbca (no. 61)
18.663(3)
19.047(3)
16.774(3)
90
90
90
5962(1)
8
50.25
Au2C53H80O2P2
1205.09
pale yellow
0.30 × 0.15 × 0.10
triclinic
P1h (no. 2)
13.284(2)
14.460(2)
15.618(3)
97.15(2)
100.99(2)
115.93(2)
2574(1)
2
crystal color
crystal size [mm]
crystal system
space group
a [Å]
colorless
0.25 × 0.15 × 0.07
monoclinic
P21/n (no. 14)
13.273(1)
17.234(2)
25.080(2)
90
94.68(1)
90
5718(1)
8
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
µ [cm-1
]
52.37
1.521
58.12
1.555
Dc [g cm-3
]
1.512
2θmax [deg]
50
5271
613
0.028, 0.034
1.09
51
4300
325
0.030, 0.040
1.63
51
7325
531
0.047, 0.065
1.62
no. of reflns with I > 3σ(I)
no. of parameters
b
R,a Rw
GOF
2
a R ) Σ(|Fo| - |Fc|)/Σ|Fo|. b Rw ) [Σw(|Fo| - |Fc|)2/Σw|Fo| ]1/2
.
in analogous gold(I) arylacetylide complexes.5a-g,15a,c,17,19 The
C(2)-C(3) distance between the two acetylide groups in 2 is
1.383(7) Å, which is comparable to those observed in Ru(Ct
CCtCPh)(PPh3)2Cp (1.389(6) Å)20 and related Ms(CtC)2s
H (M ) Au,21a Fe,21b Ru21c) (1.374(8)-1.386(3) Å) complexes.
In complex 4, the two phenyl rings separated by an acetylide
unit are virtually coplanar with a dihedral angle of ∼4°. This
implies that the π orbitals within the [CtC-1,4-C6H4CtCPh]
fragment can undergo favorable overlap in the crystal lattice,
and hence, extended π delocalization is likely. In contrast, the
adjacent phenyl rings in complex 3 (dihedral angles ∼29 and
20°) and 9‚MeOH‚H2O (dihedral angle ∼30°) are skewed with
respect to each other because of steric repulsion between
proximal hydrogen atoms of the phenyl rings. No close
intermolecular gold‚‚‚gold contacts (<3.6 Å) are found in the
crystal lattices of the structurally characterized gold(I) complexes
in this work; as expected, the large cone angle (170°)22 of the
tricyclohexylphosphine ligand disfavors metal-metal and/or
ligand-ligand aggregation.
Electronic Absorption Spectroscopy. The electronic absorp-
tion data of complexes 1-12 are summarized in Table 2 (for
data of corresponding free arylacetylenes, see Supporting
Information). Figure 4 shows the absorption spectra of 1a, 2,
and 4-6 in dichloromethane solution. The absorption spectra
of 1a and phenylacetylene are similar in the 245-300 nm
spectral region, but the absorption peaks of the former occur at
slightly lower energies with higher extinction coefficients. For
1a, four absorption peak maxima are observed at 255, 267, 281,
and 290 nm. Similar absorption bands have been reported for
Au(L)(CtCPh) (L ) PPh3,5a PMe35d), {Au(CtCPh)}2(µ-Ls
L) (LsL ) 1,2-bis(diphenylphosphino)ethane (dppe)5a and bis-
(dimethylphosphino)methane (dmpm)5d), and Au(CtCPh)-
(CNC6H3Me2-2,6).5c We note that for (Cy3P)AuCtCAu(PCy3),6a
the [5d(Au)] f [6p(Au), π*(phosphine)] transitions occur at
(17) (a) Whittall, I. R.; Humphrey, M. G.; Houbrechts, S.; Persoons, A.;
Hockless, D. C. R. Organometallics 1996, 15, 5738-5745. (b) Naulty, R.
H.; Cifuentes, M. P.; Humphrey, M. G.; Houbrechts, S.; Boutton, C.;
Persoons, A.; Heath, G. A.; Hockless, D. C. R.; Luther-Davies, B.; Samoc,
M. J. Chem. Soc., Dalton Trans. 1997, 4167-4174.
(18) Muir, J. A.; Muir, M. M.; Pulgar, L. B.; Jones, P. G.; Sheldrick, G. M.
Acta Crystallogr. 1985, C41, 1174-1176.
(19) (a) Jia, G.; Puddephatt, R. J.; Scott, J. D.; Vittal, J. J. Organometallics
1993, 12, 3565-3574. (b) Irwin, M. J.; Jia, G.; Payne, N. C.; Puddephatt,
R. J. Organometallics 1996, 15, 51-57. (c) MacDonald, M. A.; Puddephatt,
R. J.; Yap, G. P. A. Organometallics 2000, 19, 2194-2199.
(20) (a) Bruce, M. I.; Hall, B. C.; Kelly, B. D.; Low, P. J.; Skelton, B. W.;
White, A. H. J. Chem. Soc., Dalton Trans. 1999, 3719-3728. (b) Low, P.
J.; Bruce, M. I. AdV. Organomet. Chem. 2001, 48, 71-288.
(21) (a) Bruce, M. I.; Hall, B. C.; Skelton, B. W.; Smith, M. E.; White, A. H.
J. Chem. Soc., Dalton Trans. 2002, 995-1001. (b) Akita, M.; Chung, M.
C.; Sakurai, A.; Sugimoto, S.; Terada, M.; Tanaka, M.; Moro-oka, Y.
Organometallics 1997, 16, 4882-4888. (c) Sun, Y.; Taylor, N. J.; Carty,
A. J. Organometallics 1992, 11, 4293-4300.
(22) Tolman, C. A. Chem. ReV. 1977, 77, 313-348.
9
J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002 14699

A R T I C L E S
Chao et al.
Table 2. Photophysical Data for 1-12
3
complex
medium (T, K)
λ
abs, nm(ꢀmax, dm mol-1 cm-1
)
λ
em, nm
φem (τ, µs)a
0.08 (18)
1a
CH2Cl2 (298)
255 (14 140), 267 (27 440), 281 (28 490),
290 (10 190) (sh)
419 (max), 439, 446, 458, 483 (sh)
MeOH/EtOH (77)
solid (298)
415 (max), 436, 446, 455, 469, 479, 491, 507
421 (max), 442, 451, 462, 474 (sh),
485, 497, 511 (sh)
0.22 (96)
0.03 (16)
1b
1c
CH2Cl2 (298)
254 (13 140) (sh), 265 (23 650),
278 (23 930), 287 (11 930) (sh)
418, 437, 444 (max), 456, 478 (sh)
solid (298)
CH2Cl2 (298)
420 (max), 439, 447, 459, 483, 496 (sh)
432 (max), 454 (sh), 461, 474, 497 (sh)
0.30 (145)
0.04 (16)
248 (7550) (sh), 260 (15 440), 272 (28 700),
284 (29 760), 291 (21 650) (sh)
solid (298)
427 (max), 448, 457, 469, 483 (sh), 493,
506 (sh), 523 (sh), 538 (sh)
424 (max), 445 (sh), 454, 463, 489 (sh)
0.20 (25)
0.04 (11)
0.26 (92)
0.03 (24)
1d
2
CH2Cl2 (298)
solid (298)
245 (6270) (sh), 258 (14 930), 269 (27 570),
281 (28 860), 290 (19 090) (sh)
422, 444, 452, 464, 476 (max), 503,
515, 529 (sh), 548 (sh), 562 (sh)
247 (68 360), 255 (56 910), 262 (10 600) (sh), 466 (max), 491, 499, 519, 545, 584
278 (19 510), 294 (33 340), 313 (30 470),
353 (230)
CH2Cl2 (298)
MeOH/EtOH (77)
solid (298)
CH2Cl2 (298)
459 (max), 482, 495, 511, 539, 557, 577
466 (max), 491, 502, 519, 548, 564, 584
0.008 (25)
0.005 (7),b
0.04 (33)c
0.01 (1.9),b
0.16 (209)c
3
4
264 (11 020) (sh), 277 (24 850) (sh),
294 (43 570), 304 (45 150)
330, 344 (max),b 495 (max),c 531, 573 (sh)
solid (298)
350, 367 (max),b 494 (max),c
528, 532 (sh), 568 (sh)
MeOH/EtOH (77)
CH2Cl2 (298)
321, 336 (max),b 484 (max),c 517
343 (max),b 356, 368 (sh), 512 (max),c
544, 556, 575 (sh)
248 (6510), 281 (16 100) (sh),
295 (33 770) (sh), 313 (59 540),
322 (47 110) (sh), 335 (55 180)
0.08 (47),b
0.02 (114)c
MeOH/EtOH (77)
solid (298)
336 (max),b 350, 354 (sh), 363, 378, 385 (sh), 395 (sh),
507 (max),c 530 (sh), 538, 552, 569, 589, 608
349, 364, 368, 376 (max),b 392, 399,
(1.5),b (3.0)c
409, 516 (max),c 548, 561, 579 (sh)
5
CH2Cl2 (298)
329 (74 270), 339 (83 680),
350 (75 310), 363 (64 850)
375, 390 (max),b 547 (max),c 584
0.66d (19),b (92)c
(0.3),b (0.4)c
MeOH/EtOH (77)
369 (max),b 387, 400, 419 (sh), 540 (max),c
577, 594 (sh), 615 (sh)
solid (298)
CH2Cl2 (298)
383, 406, 415 (max),b 432
390 (max),b 407
(4)b
6
7
275 (22 210), 354 (102 940),
374 (69 110) (sh)
0.69b, (0.29)b
MeOH/EtOH (77)
solid (298)
CH2Cl2 (298)
384 (max),b 406, 418 (sh), 436 (sh), 552 (max),c 592
400, 424, 436 (max), 456
408 (max), 430, 445, 467 (sh), 491 (sh)
(0.36),b (14.3)c
(0.30)b
0.02 (6)
254 (13 690), 267 (27 200),
281 (32 520), 311 (1030) (sh)
252 (11 620), 266 (24 060),
280 (28 950), 302 (510) (sh)
CH3CN (298)
408 (max), 433, 444, 465 (sh), 491 (sh)
0.02 (5)
solid (298)
CH2Cl2 (298)
410 (max), 429, 438, 448, 471, 481, 495, 521
488 (max), 517, 527, 547 (sh), 560 (sh), 580 (sh)
0.03 (16)
0.05 (81)
8
288 (32 000) (sh), 304 (80 900),
323 (130 600)
MeOH/EtOH (77)
solid (298)
482 (max), 492, 502, 511, 523, 535
493 (max), 513 (sh), 523, 535, 549,
570, 584, 614 (sh)
0.03 (66)
9
CH2Cl2 (298)
323 (72 700)
361 (max),b 376, 391 (sh), 536 (max),c 574, 605 (sh)
0.08 (25),b
0.02 (76)c
MeOH/EtOH (77)
363 (max),b 382, 403, 532 (max),c 558,
569, 581, 599, 614, 627, 642 (sh)
solid (298)
CH2Cl2 (298)
383 (max),b 403, 535 (max),c 573, 603 (sh)
366 (max),b 383, 394 (sh),
0.02 (1.6),b 0.02 (71)c
0.42d (49),b (192)c
10
315 (60 950), 325 (66 670), 335 (88 760),
345 (74 290), 360 (90 290)
413 (sh), 540 (max),c 575
MeOH/EtOH (77)
solid (298)
361 (max),b 377, 381 (sh), 393, 411, 430 (sh),
450 (sh), 535 (max),c 572, 584 (sh), 605 (sh)
372 (sh), 394 (sh), 404 (max),b 421, 440 (sh),
542 (max),c 576, 589 (sh), 609 (sh)
387 (max),b 407, 558 (max),c 599 (sh), 675
(0.3),b (0.2)c
(16),b (124)c
0.57d
11
12
CH2Cl2 (298)
295 (23 110) (sh), 312 (38 980) (sh),
339 (78 950) (sh), 353 (96 570),
376 (64 430) (sh)
butyronitrile (77)
383 (max),b 402, 408, 420, 429 (sh), 440, 449, 462,
554 (max),c 579, 591 (sh), 611 (sh), 634 (sh), 673
421 (sh), 466 (max)
(0.51),b (1.38)c
0.70b (0.29)b
solid (298)
CH2Cl2 (298)
290 (32 950), 358 (126 160),
375 (102 460) (sh)
397 (max), 417
MeOH/EtOH (77)
solid (298)
388, 419 (max),b 575 (max),c 620 (sh)
(0.36),b (57.6)c
(2.05),b (5.27)c
427 (sh), 443 (max),b 462 (sh), 586 (max)c
a Lifetime was measured at peak maximum. b Fluorescence. c Phosphorescence. d Total emission quantum yield.
9
14700 J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002

Organic Triplet Emissions of Arylacetylide Moieties
A R T I C L E S
Figure 4. Electronic absorption spectra of 1a, 2, and 4-6 in CH2Cl2 at 298 K.
270 and 283 nm (ꢀ ) 6840 and 3500 dm3 mol-1 cm-1
,
at 242-284 nm with vibrational spacings of ∼2000 cm-1 are
observed. These transitions are assigned to the spin-allowed
π f π* transition of the diacetylene unit. In the low-energy
region, 2 exhibits a weak absorption band at 353 nm (ꢀ ≈ 230
dm3 mol-1 cm-1); we tentatively assigned this to a spin-
forbidden π f π* transition. The intensity of this normally
undiscernible band has apparently been enhanced by the heavy-
atom effect of Au(I). Overall, a red shift of the ππ* excited-
state energy is observed from [PhC2-] to [PhC4-].
respectively). However, these extinction coefficients are sig-
nificantly lower than those observed for the band maxima at
267, 281, and 290 nm for 1a (ꢀ > 104 dm3 mol-1 cm-1). We
therefore assign the absorptions of 1a as predominantly [PhCtC-]
transitions that are red-shifted in energy through Au-C bonding
interactions.5g The spacings between the four maxima at 255-
290 nm are 1762, 1866, and 1105 cm-1, which correspond to
two kinds of vibrational stretching frequencies (i.e. acetylenic
and phenyl). Interestingly, the absorption spectra of 1b-d (see
Supporting Information) with electron-withdrawing and -donat-
ing aryl substituents are similar to that of 1a; hence, the
substituent on the phenyl ring imparts minimal effect on the
electronic transition energies. Complex 7 exhibits vibronically
structured absorptions with peak maxima at 254, 267, and 281
nm. The vibrational spacings (1917 and 1866 cm-1) appear in
the range expected for CtC stretching in the excited state, and
Complex 3 exhibits two absorption shoulders at 264 and 277
nm and two peak maxima at around 294 and 304 nm in dichloro-
methane. In contrast, free HCtC-1,4-C6H4Ph shows only a
broad band centered at 273 nm. Coordination of 4-ethynylbi-
phenyl to [Au(PCy3)]+ hence results in enhanced π f π*
transitions for the [CtC-1,4-C6H4Ph] moiety. Compared with
those of 1a, the absorption peak maxima of 3 are red-shifted
and more diffused. Complex 9 displays a broad band at 323
nm, and the corresponding free diacetylene also shows an
unresolved band at 290 nm. The electronic transition presumably
involves low-frequency torsional modes arising from the twisting
of the two phenyl rings in the ππ* excited state.23 The binuclear
complex 8 exhibits three absorption peak maxima at 288, 304,
and 323 nm (spacings 1828 and 1935 cm-1); they are slightly
red-shifted from the absorption of 1,4-diethynylbenzene at 249
(sh), 260, and 273 nm in dichloromethane and are assigned to
the 1(ππ*) transition localized on the acetylenic unit. The
absorption spectra for 10 and 11 show vibronic structures with
spacings of 865-1847 cm-1 that are very similar to the
corresponding arylacetylenes. These absorption bands are
likewise assigned as 1(ππ*) transitions involving acetylenic and
phenyl units. In the series (Cy3P)Au(CtC-1,4-C6H4)nCtCAu-
(PCy3) (n ) 1 (8), 2 (10), 3 (11), 4 (12)), the absorption bands
are red-shifted when n increases, and the red shift in absorption
energies compared to that of the free ligands decreases with
increasing n values (see Supporting Information).
1
these bands are assigned as predominantly (ππ*) acetylenic
transitions. An additional peak at 311 nm with a relatively small
extinction coefficient (ꢀ ≈ 1030 dm3 mol-1 cm-1) is tentatively
3
assigned to a (ππ*) acetylenic transition.
In the homologous series (Cy3P)Au(CtC-1,4-C6H4)n-1(Ct
CPh) (n ) 1 (1a), 2 (4), 3 (5), 4 (6)), the 0-0 absorption energy
is red-shifted from 1a to 6, as depicted in Figure 4. Their lowest
energy dipole-allowed transitions are similar, and, as discussed
for 1a above, are assigned to transitions that involve distortion
of the acetylenic and phenyl groups in the excited state. The
shifts to lower energies are due to greater conjugation across
the [(CtC-1,4-C6H4)n-1(CtCPh)] fragment with increasing n
values. In addition, the red shift of the absorption band relative
to the free arylacetylene decreases for greater n values.
The absorption spectrum of complex 2 in dichloromethane
(Figure 4) shows one shoulder (262 nm) and three intense bands
(278, 294, and 313 nm), for which the progressional spacings
are 2196, 1958, and 2065 cm-1, respectively. These spacings
can be ascribed to a single mode, namely ν(CtC). In the
absorption spectrum of HCtCCtCPh in hexane, absorptions
(23) Suppan, P. Chemistry and light; Royal Society of Chemistry: Cambridge,
U.K., 1994; p 76.
9
J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002 14701

A R T I C L E S
Chao et al.
Table 3. ν00 and ν1-ν3 Stretching Frequencies for Solid-State
Emissions at 298 K
complex
ν
00 (cm-1
)
ν1 (cm-1
)
ν2 (cm-1
)
ν3 (cm-1
)
1a
1b
1c
1d
2
23 752
23 809
23 419
23 696
21 459
1128
1030
1098
1174
1093
- -
1580
1438
1538
1573
1539
1324a
1446b
1513a
1608b
- -
2107
2023
2098
2145
2192
- -
3
28 571a
20 242b
29 761a
19 723b
27 100a
18 518b
26 042a
18 116b
24 390
- -
- -
4c
5c
6c
1190a
1136b
1261a
1187b
- -
2213a
2149b
2100a
2258b
2118a
- -
1683b
1411a
- -
1224b
1080
1163
1296a
1239b
1175a
1209b
1234a
1130b
- -
7
8
9
1559
1592
- -
2069
2069
- -
20 283
26 109a
18 691b
27 700a
18 691b
26 109a
18 050b
25 773a
17 391b
- -
2108b
2255a
2163b
2300a
2278b
1907a
- -
10c
11d
12c
1454a
1568b
1600a
1684b
- -
Figure 5. Solid-state emission spectrum of 1a at 298 K (λex ) 280 nm).
1262b
- -
a Fluorescence. b Phosphorescence. c In MeOH/EtOH 77 K glass. d In
butyronitrile 77 K glass.
allowed absorptions, plus the long emission lifetimes (in the
microsecond regime), are indicative of their triplet parentage,
3
and they are thus assigned to the (ππ*) excited states of the
arylacetylide ligands. It is appropriate to highlight the role of
the [Au(PCy3)]+ fragment, which introduces spin-orbit coupling
and facilitates the observation of arylacetylide triplet emissions
at room temperature. In our recent work on the binuclear gold(I)
complexes (Cy3P)Au(CtC)nAu(PCy3) (n ) 1-4), the acetylenic
2-
3(ππ*) emissions localized on the (CtC)n chain can be
“switched on” by ligation to [Au(PCy3)]+.6 In this study, the
incorporation of aryl ring(s) into the (CtC)n2- moiety increases
the vibrational modes that are observed in the emission spectra.
For complexes with longer arylacetylide chains (3-6 and
9-12), dual emissions (high-energy, 330-407 nm; low-energy,
495-558 nm) are recorded. Figure 7 shows the emission spectra
of 4, 5, 10, and 11 in dichloromethane at 298 K. To further
examine these emissions, the excitation spectra of 4 (Figure 8)25
and 11 (see Supporting Information) in 77 K glassy solutions
have been obtained. Well-resolved vibronic fine structures are
detected which match the corresponding room temperature
absorption spectra. For 4, the 298 nm shoulder and 318 nm
peak maximum, which are absent in the absorption spectrum,
appear in the 77 K excitation spectrum. Three kinds of
progressional spacings (∼1110, 1600, and 2100 cm-1) can
clearly be identified and attributed to the stretching frequencies
of the phenyl and acetylenic groups in the 1(ππ*) excited state.
The excitation spectra monitored at the high- and low-energy
emission bands have been found to be identical, suggesting that
both emissions originate from the same absorbing state. The
Figure 6. Solid-state emission spectrum of 2 at 298 K (λex ) 313 nm).
Steady-State Emission Spectroscopy. The excitation of
complexes 1-12 at λ > 280 nm in the solid state and in fluid
solutions at 298 K produces intense blue to yellow emissions;
the spectral data are listed in Table 2. For complexes with short
arylacetylide chains (1a-d, 2, 7, and 8), their spectra are
dominated by phosphorescence in the visible region. The solid-
state emission spectra of 1a and 2 at 298 K are given in Figures
5 and 6, respectively (see Supporting Information for 8). The
spectra display well-resolved vibronic structures, and three types
of vibrational spacings, ν1 (∼1100 cm-1), ν2 (∼1600 cm-1),
and ν3 (∼2100 cm-1), are identified. These spacings are
attributed to the ground-state phenyl ring deformation, sym-
metric phenyl ring stretch, and CtC stretching frequencies,
respectively, and clearly correlate with the peak frequencies
observed in the Raman spectra (for 1a, 1173, 1598, and
2117 cm-1; for 2, 1178, 1596, 2070, and 2192 cm-1). The ν00
(0′ f 0 emission energy), ν1, ν2, and ν3 deduced from the solid
state or 77 K glassy emission spectra are listed in Table 3.
Similar findings had previously been observed for the Au(PPh3)-
(CtCPh)5a and [Pt(PEt3)2(CtCPh)2]24 derivatives. The ob-
served large Stokes shifts of the emissions from the dipole-
(25) Complex 4 is sparingly soluble in MeOH/EtOH, and all solutions were
carefully filtered before excitation and emission measurements (the
absorbance at 313 nm is maintained at ∼0.1 to reduce the possibility of
aggregate formation). A solution of 4 in MeOH/EtOH/DMF (5:5:1), in
which the compound readily dissolves, was also prepared, and the 77 K
excitation and emission spectra of this glassy solution were basically
identical to those of the MeOH/EtOH glass. Furthermore, the emission
spectra of 4 in solid, fluid (CH2Cl2), and glassy states are very similar. It
is, therefore, highly unlikely that the dual emission originates from aggregate
species or a small amount of unmetalated impurity within an aggregate.
(24) Sacksteder, L.; Baralt, E.; DeGraff, B. A.; Lukehart, C. M.; Demas, J. N.
Inorg. Chem. 1991, 30, 2468-2476.
9
14702 J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002

Organic Triplet Emissions of Arylacetylide Moieties
A R T I C L E S
Table 4. Bimolecular Rate Constants for Oxidative Quenching of
1a by Pyridinium Acceptors in Acetonitrile (0.1 mol dm-3
nBu4NPF6) at 298 K
+
E°(A /A)b
kq
kq′c
quenchera
(vs SSCE) (dm mol-1 s-1) (dm mol-1 s-1
) lnkq′
3
3
N,N′-dimethyl-4,4′-pyridinium -0.45 9.97 × 109 1.99 × 1010 23.71
4-cyano-N-methylpyridinium
4-amido-N-ethylpyridinium
3-amido-N-benzylpyridinium
-0.67 7.45 × 109 1.19 × 1010 23.20
-0.93 5.17 × 109 6.97 × 109 22.66
-1.07 3.51 × 109 4.26 × 109 22.17
3-amido-N-methylpyridinium -1.14 3.12 × 109 3.70 × 109 22.03
N-ethylpyridinium
2,6-dimethyl-N-methyl-
pyridinium
2,4,6-trimethyl-N-methyl-
pyridinium
-1.37 8.55 × 108 8.93 × 108 20.61
-1.52 2.64 × 108 2.68 × 108 19.41
-1.67 3.86 × 107 3.86 × 107 17.47
a All quenchers are hexafluorophosphate salts. b Reference 28. c (1/kq′)
) (1/kq) - (1/kd), where kd is the diffusion-limited rate constant, taken to
be 2 × 1010 dm3 mol-1 s-1. Errors for kq and kq′ are estimated to be (5%.
examined by cyclic voltammetry in CH2Cl2. In general, one to
two irreversible oxidation waves are displayed at 0.8-1.0 V
versus Fc0/+. For example, 3 exhibits irreversible oxidation
waves at 0.81 and 0.96 V, and 8 shows an irreversible peak at
0.92 V versus Fc0/+
.
3
The (ππ*) states of these gold(I) arylacetylide complexes
are strong photoreductants.5a,c Because they do not display
reversible electrochemistry, their excited-state reduction poten-
tials cannot be precisely evaluated using spectroscopic and
electrochemical data. Oxidative quenching experiments of the
triplet emissions of 1a, 2, and 4 in acetonitrile by a series of
pyridinium acceptors (A+)28 have therefore been undertaken.
Table 4 lists the quenching data for 1a, and a nonlinear least-
squares fitting of ln kq′ versus E° (A+/A) using the Rehm-
Weller model (equation 1) has been performed (Figure 9) (for
2 and 4, see Supporting Information).
Figure 7. Emission spectra of 4, 5, 10, and 11 in CH2Cl2 at 298 K (λex
)
313, 339, 335, and 353 nm, respectively).
high-energy emission, however, exhibits lifetime in the micro-
second regime, and we tentatively assign it to “delayed
fluorescence”. In principle, delayed fluorescence can be pro-
duced by two types of pathways, namely thermally induced
delayed fluorescence (T1 f S1) and triplet-triplet annihilation
(T1 + T1 f S1 + S0, where S0, S1, and T1 are the ground state
and the lowest singlet and triplet excited states, respectively).26
On the basis of the shorter lifetimes of the high-energy emissions
(Table 2), we suggest that the delayed fluorescence detected in
this work is generated by triplet-triplet annihilation.27
Minimal solvatochromic effects on the absorption and emis-
sion spectra of these complexes have been detected. As a
prototypical example, the emission spectra of 2 in various
solvents at 298 K are shown in the Supporting Information.
The quantum yields (φem) and lifetimes (τ) decrease in the
order: CH2Cl2 (0.03; 24 µs) ≈ THF (0.03; 22 µs) > CH3CN
(0.01; 12 µs) ≈ MeOH (0.01; 12 µs). In addition, the complex
concentration imparts only a minor effect upon the emission
quantum yields and lifetimes. This is consistent with the self-
quenching rate constant ksq of 1.9 × 107 dm3 mol-1 s-1 for the
emission of 2 in dichloromethane (determined by the Stern-
Volmer equation: 1/τ ) 1/τ0 + ksq[M], where τ0 is the lifetime
at infinite dilution and [M] is the complex concentration).
Electrochemical and Photoredox Properties. The electro-
chemical properties of complexes 1-4 and 7-9 have been
(RT/F) ln kq′ ) (RT/F) ln(Kκν) - ∆G/2 -
[(∆G/2)2 + (λ/4)2]1/2 (1)
Here, K ) kd/k-d, which is approximately 1-2 dm3 mol-1 and
κ, ν, and λ are the transmission coefficient, nuclear frequency,
and reorganization energy for electron transfer, respectively; ∆G
is the standard free-energy change of the reaction given by eq
2. The work terms ωp and ωr associated with bringing the
reactants or products to mean separation are small and are
neglected in this case.
∆G ) E°[Au+/Au*] - E°(A+/A) + ωp - ωr
(2)
Thus, the excited-state reduction potentials E°[Au+/Au*] (Au
) 1a, 2, and 4) are estimated to be -1.80, -1.28, and -1.17
V versus SSCE (or -2.11, -1.59, and -1.48 V versus Fc0/+),
respectively. For 1a and 4, these values correspond to those
(less than -2.01 and -1.43 V versus Fc0/+, respectively)
estimated from the equation E°[Au+/Au*] ) E°[Au+/Au] -
E
0-0, where E0-0 is calculated from the spectroscopic data (2.94
(26) Turro, N. J. Modern Molecular Photochemistry; The Benjamin/Cummings
Publishing Company: Menlo Park, California, 1978; pp 146-148 and 343-
344.
(27) We have also examined the relationship between the fluorescence to
phosphorescence signal ratio and the energy of laser pulse at 266 nm
excitation. When the energy of laser pulse was increased from 0.57 × 10-3
to 7.18 × 10-3 joule/pulse, the ratio of fluorescence to phosphorescence
signal was observed to increase from 1.5 to 2.8. This is consistent with a
triplet-triplet annihilation mechanism for the delayed fluorescence. We
are grateful to the reviewers for suggesting this experiment.
and 2.43 eV, respectively) and E°[Au+/Au] is approximated
from Epa obtained in cyclic voltammetry measurements (less
than 0.93 and 1.00 V versus Fc0/+, respectively).29 The large
(28) Marshall, J. L.; Stobart, S. R.; Gray, H. B. J. Am. Chem. Soc. 1984, 106,
3027-3029.
(29) Because the electrochemical oxidation is irreversible, only the Epa of the
oxidation wave is determined.
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A R T I C L E S
Chao et al.
Figure 8. Excitation (λem ) 350 (‚‚‚) and 506 (- - -) nm) and emission (___) (λex ) 313 nm) spectra of 4 in MeOH/EtOH (4:1) at 77 K.
convenient; plus, no polynuclear gold(I) arylacetylide side
products were isolated. The arylacetylide bonding mode is
confirmed by IR/Raman spectroscopy and crystallographic
studies. The high ν(CtC) stretching frequency (2067-2188
cm-1) as well as the bond lengths of Au-CR (1.993(11)-2.03(1)
Å) and CRtCâ (1.180(6)-1.223(10) Å) demonstrate the σ-bond-
ing nature of the coordinated arylacetylide groups. While metal
complexes of arylacetylide ligands and their polymers are well-
documented, reports of well-defined molecular derivatives
bearing repeating arylacetylide or “oligo(phenylene-ethynylene)”
moieties such as complexes 6 and 12 are sparse in the
literature.30
The 3(ππ*) excited states of arylacetylides have been shown
to exhibit rich photochemical reactivities. The excited-state
reduction potentials of 1a, 2, and 4 (-1.80, -1.28, and -1.17
V versus SSCE respectively) span over a wide range, and the
trend for E° values follows the variation in triplet emission
energies. The excited-state potential of 1a is similar to E°[Au-
(CtCPh)(CNC6H3Me2-2,6)+/*] (-1.62 V versus SSCE).5c The
large negative values imply that these 3(ππ*) excited states are
strong photoreductants. It has been possible to tune the excited-
state reduction potential by modifying the arylacetylide chain
length, although a clear relationship linking these two parameters
has not been determined. Since arylacetylenes are a well-
established class of organic compounds with diverse structural
and electronic properties, the Cy3PAuCtCR complexes de-
scribed here represent a new family of metal-organic photore-
ductants with tunable triplet-state photophysical properties under
ambient conditions.
Figure 9. Plot of ln kq′ vs E°(A+/A) for the oxidative quenching of 1a by
pyridinium acceptors in acetonitrile: (+) experimental data and (s)
theoretical curve.
negative values of E°[Au+/Au*] indicate the strongly reductive
3
nature of the (ππ*) excited states of arylacetylides.
Discussion
General Remarks. Gold(I) arylacetylide compounds are
usually prepared according to two literature methods. The
reactions of [AusCtCR]n and [AusCtCsArsCtCsAu]n
with isocyanide or phosphine ligands were employed by
Puddephatt and co-workers to give mononuclear, binuclear, and
polymeric derivatives.19 Alternatively, the treatment of Au(PR3)-
Cl and Au2(PsP)Cl2 (PsP ) diphosphine ligands) with terminal
alkynes in the presence of a base can also afford acetylide
complexes.15 The method adopted in this work, using the stable
and easily prepared Au(PCy3)Cl as precursor, is direct and
Trends in Absorption Energies. The absorption spectra of
virtually all of the gold(I) arylacetylide complexes studied in
(30) For an example of extended arylacetylide complexes, see [Ru(CtC-1,4-
C6H4)2CtCC6H4NO2-4] species in: Hurst, S. K.; Cifuentes, M. P.; Morrall,
J. P. L.; Lucas, N. T.; Whittall, I. R.; Humphrey, M. G.; Asselberghs, I.;
Persoons, A.; Samoc, M.; Luther-Davies, B.; Willis, A. C. Organometallics
2001, 20, 4664-4675.
9
14704 J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002

Organic Triplet Emissions of Arylacetylide Moieties
A R T I C L E S
this work show vibronically structured absorption bands. Distinct
similarities between the absorption spectra of free arylacetylenes
and gold(I) arylacetylide derivatives indicate that the electronic
transitions in the latter are intraligand in nature and localized
on the coordinated arylacetylides. The red shifts in the absorption
spectra relative to the free acetylenes are attributed to the nature
of the Au(I)-C(arylacetylide) bonding interaction, which
decreases the energy difference between the arylacetylide π and
π* orbitals. The different magnitudes for the spacings between
the absorption peak maxima signify that the lowest dipole-
allowed electronic transitions of the gold(I) arylacetylide
complexes involve distortion of the phenyl and acetylenic groups
in the excited states.
When the length of the π-conjugated system in the homolo-
gous series (Cy3P)Au(CtC-1,4-C6H4)n-1(CtCPh) and (Cy3P)-
Au(CtC-1,4-C6H4)nCtCAu(PCy3) (n ) 1-4) is increased, the
corresponding absorption bands are red-shifted in agreement
with a reduction in the π f π* energy gap. The 0-0 absorption
energies for the two homologous series have been plotted against
1/n (n ) 1-4; see Supporting Information), and a linear
relationship was obtained. By extrapolation, a limiting value
for the absorption energy (i.e. for n ) ∞) is estimated to be in
the 399-411 nm range; this value approaches the absorption
energy of alkyl-substitued PPEs in solution (388 nm).31
Figure 10. Plot of ∆E(S0 - T1) against 1/n (9 ) mononuclear and O )
dinuclear series).
(p-phenylene) derivatives33 and around 1.9 eV for dialkoxy-
substituted PPEs4f (both at ∼77 K in 2-methyltetrahydrofuran
(Me-THF)).
A salient objective of this study is to gather in-depth
information regarding the energy levels of arylacetylide 1(ππ*)
3
and (ππ*) excited states. We have observed a good linear
Singlet and Triplet Excited States: S0-T1 Energy Gap
and Extrapolation to PPEs. Phosphorescence is observed in
the emission spectra of gold(I) arylacetylide complexes, while
delayed fluorescence becomes prominent for derivatives bearing
long arylacetylide chains (3-6 and 9-12). The detected vibronic
fine structure is in accordance with the assignment to arylacetyl-
1
relationship between the lowest arylacetylide (ππ*) excited-
state energy [∆E(S0 - S1)] and arylacetylide chain length (1/n;
see Supporting Information), and the limiting value for
∆E(S0 - S1) is estimated to be 2.74-2.82 eV. Hence, by
correlation of this value with ∆E(S0 - T1) (1.98-2.04 eV), the
∆E(S1 - T1) value for n ) ∞ is estimated to be ∼0.8 eV. This
corresponds directly with the S1 - T1 energy gap of 0.7 ( 0.1
eV reported by Friend and co-workers for a series of polymeric
platinum(II) arylacetylide complexes and dialkoxy-substituted
PPEs.4d,f Comparable S1 - T1 separations of 0.62-0.84 eV were
observed for related poly(p-phenylene) materials by Ba¨ssler and
co-workers,33 while Monkman reported separations of 0.6-1.0
eV for a variety of π-conjugated polymers.34 The S1 - T1 energy
gaps for the arylacetylide gold(I) complexes studied herein
(0.96-1.25 eV) are larger than the limiting value. This
phenomenon was observed for monomeric and oligomeric
platinum(II) arylacetylide analogues and has been attributed to
the confinement of the S1 state by Ko¨hler et al.4f There is a
linear relationship between the singlet- and triplet-state energies
(see Supporting Information). From the linear least-squares
fitting, the lowest triplet-state energy (T1) for 4-6 and 10-12
can be expressed by the equation: T1 ) 0.47S1 + 0.70. We
can estimate the triplet excited-state energy of PPE materials
by using the S1 - T1 energy gap (∼0.8 eV) derived in this
work.35 For example, by taking the fluorescent emission energy
of poly(2,5-dihexyl-1,4-phenylene-ethynylene) in fluid solution
(428 nm, 2.90 eV),31 the energy of the phosphorescence is
expected to be around 590 nm (2.10 eV).
3
ide (ππ*) states. We have been able to tune the energy of
phosphorescence by altering the functionality of the arylacetylide
ligand. The substituent on the phenyl ring in 1a-d exerts
minimal effect on the emission energy, suggesting large
3
acetylenic parentage in the (ππ*) excited state. The emission
energy of the gold(I) complexes in dichloromethane decreases
in the order: 1a (23 866 cm-1) > 2 (21 459 cm-1) > 8 (20 492
cm-1) > 3 (20 202 cm-1) > 4 (19 531 cm-1) > 9 (18 657 cm-1
)
> 10 (18 518 cm-1) > 5 (18 281 cm-1) > 6 (18 116 cm-1) >
11 (17 889 cm-1) > 12 (17 391 cm-1).32
To examine the relationship between the phosphorescent
emission energy and arylacetylide chain length, we have plotted
∆E(S0 - T1) (energy gap between S0 and T1) against 1/n [n is
the number of repeating arylacetylide units in mononuclear
(square) (Cy3P)Au(CtC-1,4-C6H4)n-1(CtCPh) (n ) 1 (1a), 2
(4), 3 (5), 4 (6)) and binuclear (circle) (Cy3P)Au(CtC-1,4-
C6H4)nCtCAu(PCy3) (n ) 1 (8), 2 (10), 3 (11), 4 (12))
complexes] to produce good linear fits (Figure 10). This allows
extrapolation of the line to reveal an estimated ∆E(S0 - T1)
value for infinite repeating units (i.e. [Cy3PAu]-capped PPE)
of ∼626 nm (1.98 eV) and ∼607 nm (2.04 eV) for the mono-
and dinuclear species, respectively. We consider these two
limiting ∆E(S0 - T1) values to be the same within experimental
uncertainties. This can be compared to the observed S0 - T1
separations (i.e. phosphorescence) of 1.90-2.08 eV for poly-
(33) Hertel, D.; Setayesh, S.; Nothofer, H. G.; Scherf, U.; Mu¨llen, K.; Ba¨ssler,
H. AdV. Mater. 2001, 13, 65-70.
(34) Monkman, A. P.; Burrows, H. D.; Hartwell, L. J.; Horsburgh, L. E.;
Hamblett, I.; Navaratnam, S. Phys. ReV. Lett. 2001, 86, 1358-1361.
(35) This estimate may be regarded as the approximate “intrinsic” value for the
polymer, since macromolecular effects such as interchain interactions have
not been considered; the estimated value may, therefore, be more appropriate
for an isolated polymer chain in dilute solutions or inert matrixes. See:
Cornil, J.; dos Santos, D. A.; Crispin, X.; Silbey, R.; Bre´das, J. L. J. Am.
Chem. Soc. 1998, 120, 1289-1299.
(31) Mangel, T.; Eberhardt, A.; Scherf, U.; Bunz, U. H. F.; Mu¨llen, K. Macromol.
Rapid Commun. 1995, 16, 571-580.
(32) Because complexes 6 and 12 do not display phosphorescence in dichlo-
romethane at 298 K, their phosphorescent emission energies are taken from
77 K alcoholic glasses.
9
J. AM. CHEM. SOC. VOL. 124, NO. 49, 2002 14705

A R T I C L E S
Chao et al.
When compared with the emission spectra of the free
arylacetylenes used in this work, which show fluorescence at
298-406 nm, phosphorescence has been “switched on” at
ambient temperature by substitution of the terminal proton for
a heavy gold atom, which induces intersystem crossing from
singlet to triplet states. We have found that as the arylacetylide
chain length increases, the intensity of the phosphorescence
relative to fluorescence decreases; the results are depicted in
Figure 7. This can be rationalized by the energy gap law, which
states that the nonradiative decay rate increases exponentially
upon decreasing the energy gap between two electronic states.4e,36
Hence, the lowering of the triplet-state energy results in a faster
nonradiative decay rate for the triplet state.
particular, two homologous series containing oligomeric aryl-
acetylide moieties. Subsequent extrapolations to infinite repeat-
ing arylacetylide units (i.e. (Cy3P)Au-capped PPE) have yielded
valuable information regarding the photoluminescent nature of
arylacetylide polymers (S0 - T1 and S1 - T1 energy separations
of around 2.0 and 0.8 eV, respectively, have been estimated)
and enabled comparisons with related π-conjugated polymeric
materials. The 3(ππ*) excited states of arylacetylides are
powerful photoreductants. Since this class of compounds exhibit
high quantum yields and tunable emission energies in the visible
region, they may display potential applications as photonic
materials.
Comparison between Aliphatic and Aryl Phosphine Aux-
iliaries. It is pertinent to compare the emissive properties of
the complexes described in this work with those of analogous
gold(I) arylacetylide derivatives bearing arylphosphine ligands.5
For the latter, which often display aurophilic interactions in their
crystal lattices, the solid-state emissions can originate from a
variety of different electronic excited states, such as 3[σ(Au-P)
f π*(phosphine)], 3[dσ* f pσ], or ligand-centered 3[π f π*].
Our strategy of employing the tricyclohexylphosphine ligand
suppresses the aggregation of gold(I) centers, so that other
possibilities are eliminated. Hence, the emissions of the gold(I)
complexes can be confidently assigned to the ππ* excited states
of arylacetylide moieties.
Acknowledgment. We are grateful for financial support from
the Research Grants Council of the Hong Kong SAR, China
[HKU 7077/01P], The University of Hong Kong, and The
Croucher Foundation (Hong Kong). We thank the reviewers
for helpful comments and suggestions.
Supporting Information Available: Details of instrumenta-
tion and photophysical measurements. Perspective views of
1a-d, 2, 5, 7, and 8 and CIF data for all crystal structures.
UV-Vis spectra of 1a-d in CH2Cl2 at 298 K. UV-vis spectra
of 8 and 10-12 in CH2Cl2 at 298 K. Emission spectrum of 8
in solid state at 298 K. Excitation and emission spectra of 11
in butyronitrile at 77 K. Normalized emission spectra of 2 in
CH3CN, CH2Cl2, MeOH, and THF at 298 K. Plots of ln kq′
versus E°(A+/A) for the oxidative quenching of 2 and 4 by
pyridinium acceptors in acetonitrile. Plot of 0-0 absorp-
tion energy against 1/n for 1a, 4 -6, 8, and 10-12. Plot of
∆E(S0 - S1) against 1/n. Plot of ∆E(S0 - S1) against
∆E(S0 - T1) for 4-6 and 10-12. Tables of selected bond
lengths and angles of 1a-d, 2-5, 7, 8, and 9‚MeOH‚H2O;
photophysical data for 1-12 (expanded) and free arylacetylenes;
bimolecular rate constants for the oxidative quenching of 2 and
4 by pyridinium acceptors. Characterization data for 1b-d, 2-5,
7, and 9-12. This material is available free of charge via the
Internet at http://pubs.acs.org.
Conclusion
Vibronically structured ππ* transitions are observed in the
absorption and emission spectra of the gold(I) arylacetylide
derivatives reported in this work. The organic triplet emissions
of arylacetylide groups have thus been “illuminated” at ambient
conditions by ligation to the [Au(PCy3)]+ fragment. The
tunability of the arylacetylide 3(ππ*) emission energy has been
illustrated, while delayed 1(ππ*) fluorescence for extended
arylacetylide units is proposed to occur via a triplet-triplet
annihilation mechanism. The singlet and triplet excited-state
energies have been probed in a systematic manner using, in
(36) (a) Siebrand, W. J. Chem. Phys. 1967, 47, 2411-2422. (b) Englman, R.;
Jortner, J. Mol. Phys. 1970, 18, 145-164.
JA0209417
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