The 3(ππ*) Emission of Cy3PAu(C≡C)nAuPCy3 (n = 3, 4). Effect of chain length upon acetylenic 3(ππ*) emission

Article abstract of DOI:10.1021/om011087f

The synthesis of luminescent Cy₃PAu(C≡C)_nAuPCy₃ complexes (n = 3,4) was presented. the complexes featured the dinuclear gold(I) complexes bridged by C₆^2- and C₈^2- rods. The compo

Full text of DOI:10.1021/om011087f

Organometallics 2002, 21, 2343-2346
2343
3
Th e (ππ*) Em ission of Cy3P Au (CtC)n Au P Cy3 (n ) 3, 4).
3
Effect of Ch a in Len gth u p on Acetylen ic (ππ*) Em ission
Wei Lu, Hai-Feng Xiang, Nianyong Zhu, and Chi-Ming Che*
Department of Chemistry and the HKU-CAS J oint Laboratory on New Materials,
The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
Received December 27, 2001
Ch a r t 1
Summary: The Cy3PAu(CtC)nAuPCy3 (n ) 3 (3) , 4 (4))
complexes were prepared by the reaction of Me3Si-
(CtC)nSiMe3 (n ) 3, 4) with Cy3PAuCl in the presence
of NaOH. The molecular structure of 3‚CH2Cl2 was
determined by X-ray crystallography. Complexes 3 and
4 show vibronically structured acetylenic 3(ππ*) emission
with ν0-0 values of 19 920 and 17 420 cm-1, respectively;
hence, ν0-0 for Cy3PAu(CtC)∞AuPCy3 can be estimated
at ∼11 000 cm-1 from the plot of ν0-0 versus 1/ n.
While rigid, π-conjugated sp carbon chains have been
incorporated as building blocks into myriads of elec-
tronic optics (molecular wires, NLOs),1 spectroscopic
investigations, especially regarding electronic transi-
tions associated with (CtC)n2- chains, are sparse.1g,2-7
Fundamental studies on the spectroscopic properties of
oligoynes will facilitate the design of advanced opto-
quire sufficient allowedness via Au spin-orbit coupling
to appear prominently in both electronic absorption and
emission spectra. The λ0-0 lines for 1 and 2 are observed
at 331 and 413 nm, respectively. The following questions
naturally arise: what are the λ0-0 values of the acety-
lenic 3(ππ*) excited states of the higher homologues, and
is there a limit for the λ0-0 values? That is, how red can
the triplet emission of (CtC)n2- chains be manipulated?
The two higher homologues, Cy3PAu(CtC)3AuPCy3
(3) and Cy3PAu(CtC)4AuPCy3 (4), have been synthe-
sized. The reaction of Me3Si(CtC)3SiMe3 and Me3Si-
(CtC)4SiMe3 with Cy3PAuCl in MeOH in the presence
of NaOH gave the desired complexes as air-stable pale
yellow plates and needles, respectively, after flash
chromatography on alumina and recrystallization from
CH2Cl2/Et2O. These two complexes feature the unprec-
edented dinuclear gold(I) complexes bridged by C62- and
electronic materials; for example, the triplet emission
2-
from (CtC)n
chains could be of great interest for
OLED applications8 and characterization of one-dimen-
sional carbon allotrope, i.e., carbyne.9 On the basis of
the UV/vis spectra of monodispersed oligomers, Hirsch7
and Gladysz4a estimated the limit of the lowest energy
1(ππ*) absorption of R(CtC)∞R (R ) CN, tBu, Et3Si, (η5-
C5Me5)Re(NO)(PPh3)) to be λmax 550 nm, irrespective of
end groups. Our recent work10 on luminescent Cy3PAu-
(CtC)nAuPCy3 (n ) 1 (1), 2 (2)) (Chart 1) revealed that
3
the lowest-energy acetylenic (ππ*) excited states ac-
2-
C8 rods. Although the cyclohexyl groups of the phos-
phine ligands render improved solubility for these two
complexes, they are still difficult to dissolve in common
organic solvents, even CH2Cl2 and CHCl3. We have been
able to obtain dilute CH2Cl2 solutions of 3 and 4, so that
spectroscopic properties in fluid solutions can be ex-
plored.
Figure 1 shows the perspective view of 3‚CH2Cl2,
which has a dumbbell shape with the crystallographic
rotation center located at the center of the hexatriynediyl
* To whom correspondence should be addressed. Fax: (852) 2857
1586. E-mail: cmche@hku.hk.
(1) Recent reviews: (a) Manna, J .; J ohn, K. D.; Hopkins, M. D. Adv.
Organomet. Chem. 1995, 38, 79. (b) Bruce, M. I. Coord. Chem. Rev.
1997, 166, 91. (c) Swager, T. M. Acc. Chem. Res. 1998, 31, 201. (d)
Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 427. (e)
Schwab, P. F. H.; Levin, M. D.; Michl, J . Chem. Rev. 1999, 99, 1863.
(f) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350.
(g) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605.
(2) Lewis, J .; Khan, M. S.; Kakkar; A. K.; J ohnson, B. F. G.; Marder,
T. B.; Fyfe, H. B.; Wittmann, F.; Friend, R. H.; Dray, A. E. J .
Organomet. Chem. 1992, 425, 165.
(3) 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 and references therein.
(4) (a) Dembinski, R.; Bartik, T.; Bartik, B.; J aeger, M.; Gladysz, J .
A. J . Am. Chem. Soc. 2000, 122, 810 and references therein. (b) Mohr,
W.; Stahl, J .; Hampel, F.; Gladysz, J . A. Inorg. Chem. 2001, 40, 3263.
(5) Bruce, M. I.; Low, P. J .; Costuas, K.; Halet, J . F.; Best, S. P.;
Heath, G. A. J . Am. Chem. Soc. 2000, 122, 1949.
unit. The two-coordinate Au atoms are bridged by a
2-
virtually linear C6
chain with P(1)-Au(1)-C(1),
Au(1)-C(1)-C(2), C(1)-C(2)-C(3), and C(2)-C(3)-
C(3*) angles of 174.1(2), 172.6(8), 176.7(9), and
179.4(14)°, respectively. Comparable crystallographic
data for bridging acetylenic units have been well-
documented by Gladysz,4 Bruce,11 Lapinte,12 and
Akita.13 The closest intramolecular nonbonded contacts
(6) Vila, F.; Borowski, P.; J ordan, K. D. J . Phys. Chem. A 2000, 104,
9009.
(7) Schermann, G.; Gro¨sser, T.; Hampel, F.; Hirsch, A. Chem. Eur.
J . 1997, 3, 1105.
(8) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151.
(9) Baitinger, E. M. In Carbyne and Carbynoid Structures; Heimann,
R. B., Evsyukov, S. E., Kavan, L., Eds.; Kluwer Academic: Boston,
1999; Chapter 4, p 333.
(10) Che, C. M.; Chao, H. Y.; Miskowski, V. M.; Li, Y.; Cheung, K.
K. J . Am. Chem. Soc. 2001, 123, 4985.
(11) 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 and
references therein.
(12) Guillemot, M.; Toupet, L.; Lapinte, C. Organometallics 1998,
17, 1928 and references therein.
(13) Sakurai, A.; Akita, M.; Moro-oka, Y. Organometallics 1999, 18,
3241 and references therein.
10.1021/om011087f CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/03/2002

2344 Organometallics, Vol. 21, No. 11, 2002
Notes
F igu r e 1. ORTEP plot for 3‚CH2Cl2 (30% probability ellipsoids). Selected bond distances (Å) and angles (deg): Au(1)-
C(1) ) 2.011(8), Au(1)-P(1) ) 2.292(2), C(1)-C(2) ) 1.170(1), C(2)-C(3) ) 1.40(1), C(3)-C(3*) ) 1.18(1); P(1)-Au(1)-
C(1) ) 174.1(2), Au(1)-C(1)-C(2) ) 172.6(8), C(1)-C(2)-C(3) ) 176.7(9), C(2)-C(3)-C(3*) ) 179.4(14).
genated solvent has been observed for a Pt(II) tet-
radiynediyl complex.15
Both 3 and 4 are emissive in degassed fluid solutions,
rigid matrix, and solid state (Table 1). In CH2Cl2 at 298
K, sharp vibronically structured emissions are observed
for 3 and 4 with λ0-0 lines appearing at 498 and 575
nm, respectively (Figure 2). The large Stokes shifts from
the absorption spectra suggest triplet emissions, and
this has been confirmed by lifetime measurements of
the solid-state emission of 3. The single vibronic pro-
gression of ∼2120 cm-1 in the emission spectra of 3 and
4 is attributed to ν(CtC), which is only slightly larger
than the vibrational spacings found in the absorption
and excitation spectra and indicates minor structural
F igu r e 2. UV absorption and normalized emission spectra
for 3 and 4 in CH2Cl2 at 298 K.
2-
distortion of the (CtC)n
(n ) 3, 4) chains in the
3(ππ*) excited state. The unambiguously assigned 3(ππ*)
2-
emissions of the (CtC)n (n ) 3, 4) chains in fluid
solution at room temperature have no precedent in the
literature, though vibronically structured emissions
from Pt(II)-oligoyne conjugated polymer films have
been reported by Friend and co-workers.2 A highly
structured emission at a comparable energy level has
been observed, in our recent report,16 for the [(C∧N∧N)-
Pt(CtC)4SiMe3] (HC∧N∧N ) 6-phenyl-2,2′-bipyridine)
complex in CH2Cl2 solution at 298 K. Changes of solvent
and temperature have negligible effects on the emission
properties of complexes 3 and 4. There is perfect overlap
of the λ0-0 bands at 502 nm (for 3, Figure 3a) and 574
nm (for 4, Figure 3b) in the 77 K solid-state emission
in this structure are Au(1)-H(5) (1.80 Å) and Au(1)-
H(17) (1.92 Å). The solvated CH2Cl2 molecule is disor-
dered over an inversion center ((1,0,1) for the reported
asymmetric unit). Unlike the lower homologues,14 no
close C-H‚‚‚π(CtC) distances (<3.5 Å) were observed.
1
While the acetylenic (ππ*) transitions for 1-3 are
buried by red-shifted [5d(Au)] f [6p(Au), π*(phosphine)]
transitions,10 the highly vibronic absorption at 274-290
nm (with vibrational progression of 2010 cm-1) in the
absorption spectrum for 4 in CH2Cl2 (Figure 2) can be
unambiguously assigned to the dipole-allowed π f π*
2-
transition of the (CtC)4 bridge. This band is signifi-
3
and excitation spectra; hence, the (ππ*) excited states
cantly red-shifted when compared to the lowest-energy
dipole-allowed transition of the R(CtC)4R (R ) CN,
tBu, Et3Si) series (λmax < 240 nm);7 presumably this is
due to perturbation arising from Au-C interactions.
Due to their limited solubility, the forbidden acetylenic
3(ππ*) transitions for 3 and 4 have not been detected.
Furthermore, complex 4 is unstable in CH2Cl2 solution
upon prolonged standing. Within 1 h, the absorbances
at 290 and 274 nm decrease to half of their original
values, accompanied by enhancement of absorption
bands at 260 and 252 nm. Similar instability in halo-
2-
2-
for the bridging (CtC)3 and (CtC)4 chains can be
estimated to be 19 920 and 17 420 cm-1 above the
ground states, respectively. It is remarkable that the
3(ππ*) excited state of the (CtC)4 bridge can exhibit
2-
red emission, despite the fact that it has no discernible
absorption band in the visible region; the color of solid
3 and 4 are light yellow.
The unambiguous assignment of the 3(ππ*) excited
2-
states for monodispersed (CtC)n units will facilitate
spectroscopic characterization of the triplet emissions
of R(CtC)nR compounds. The emission data of 3 and 4
together with those of 1 and 2 afford an energy profile
(14) (a) Cross, R. J .; Davison, M. F. J . Chem. Soc., Dalton Trans.
1986, 411. (b) Bruce, M. I.; Grundy, K. R.; Liddell, M. J .; Snow, M. R.;
Tiekink, R. T. J . Organomet. Chem. 1988, 344, C49. (c) Mu¨ller, T. E.;
Mingos, D. M. P.; Williams, D. J . J . Chem. Soc., Chem. Commun. 1994,
1787. (d) Mu¨ller, T. E.; Choi, S. W. K.; Mingos, D. M. P.; Murphy, D.;
Williams, D. J .; Yam, V. W. W. J . Organomet. Chem. 1994, 484, 209.
(15) ALQaisi, S. M.; Galat, K. J .; Chai, M.; Ray, D. G., III; Rinaldi,
P. L.; Tessier, C. A.; Youngs, W. J . J . Am. Chem. Soc. 1998, 120, 12149.
(16) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Zhu, N. Y.; Lee, S.
T.; Che, C. M. Chem. Commun. 2002, 206.

Notes
Organometallics, Vol. 21, No. 11, 2002 2345
Ta ble 1. Em ission Da ta for 3 a n d 4
complex 3
toluene glassb
complex 4
toluene glassb
a
a
CH2Cl2
solida
solidb
CH2Cl2
solida
solidb
λ0-0 (nm)
498
557
632
726
0.57
494
554
629
725
0.62
505
564
641
740
2.03
25
502
561
639
739
1.02
31
575
655
763
571
650
754
575
655
760
574
653
758
λ0-1 (nm)
λ0-2 (nm)
λ0-3 (nm)
c
I
0-1/I0-0
0.42
0.41
0.37
0.45
τ (µs)d
φe
0.027
0.0004
a
b
d
At 298 K. At 77 K. c Defined by peak area. Some lifetime data are unavailable due to lack of absorption for these samples at the
laser output wavelengths of 355 and 266 nm. e Quinine sulfate in degassed 0.1 N sulfuric acid as reference (φr ) 0.546).
2
F igu r e 4. Lewis-Calvin plot (λ0-0 ) k′n) (O) and ν0-0
energies (cm-1) determined by steady-state emission spec-
tra versus 1/n (9) of Cy3PAu(CtC)nAuPCy3.
which is smaller than related values of ∼12 000-13 000
cm-1 for butadiyne6 and Pt(II)-oligoyne conjugated
polymers.3
Exp er im en ta l Section
All starting materials were used as received from com-
mercial sources. The compounds Me3Si(CtC)nSiMe3 (n ) 3,18
419) were prepared according to literature methods. Elemental
analyses were performed by the Institute of Chemistry at
Chinese Academy of Sciences, Beijing, People’s Republic of
China. Fast atom bombardment (FAB) mass spectra were
obtained on a Finnigan Mat 95 mass spectrometer. Nuclear
magnetic resonance spectra were recorded on Avance400
Bruker FT-NMR spectrometers. Infrared spectra were re-
corded on a Bio-Rad FT-IR spectrophotometer. UV-vis spectra
were recorded on a Perkin-Elmer Lambda 19 UV/vis spectro-
photometer. Emission spectra were obtained on a SPEX
Fluorolog-2 Model F11 fluorescence spectrophotometer. Emis-
sion lifetime measurements were performed with a Quanta
Ray DCR-3 pulsed Nd:YAG laser system (pulse output 355 nm,
8 ns). Errors for λ values ((1 nm) and τ ((10%) are estimated.
Gen er a l P r oced u r e for Syn th eses. To a mixture of Me3-
Si(CtC)nSiMe3 (n ) 3, 4, respectively; 0.1 mmol) and Cy3-
PAuCl (0.2 mmol) in MeOH (30 mL) was added NaOH pellets
(0.2 g). The suspension was stirred at room temperature for 1
h. The resulted brown solid was filtered and washed subse-
quently with water, methanol, and ether. The pure product
was obtained after column chromatography (Al2O3, CH2Cl2)
as a light yellow powder.
F igu r e 3. (a) Solid-state emission (λex ) 427 nm) and
excitation (λem ) 562 nm) spectra for 3 at 77 K. (b) Solid-
state emission (λex ) 360 nm) and excitation (λem ) 654
nm) spectra for 4 at 77 K.
for acetylenic 3(ππ*) excited states. According to the
empirical Lewis-Calvin equation,17 the plot of λ0-0
2
(nm2) versus number of repeated CtC units follows a
linear relationship with a slope of k ) 7.62 × 104 nm2
per triple bond (Figure 4). The average vibrational
spacing ∆λ of corresponding adjacent bands in each Cy3-
PAu(CtC)nAuPCy3 complex increases with longer chain
length. The plot of ∆λ versus n also shows linear
behavior (∆λ ) k′n) and provides a slope k′ of 20 nm
per triple bond. On the basis of the plot of ν0-0 energy
(cm-1) versus 1/n (Figure 4), the limiting λ0-0 value for
the triplet emission of Cy3PAu(CtC)∞AuPCy3 is esti-
mated to be 910 nm (11 000 cm-1). When the value 550
nm (18 180 cm-1) is taken from Hirsh7 as the 1(ππ*)
3: yield 0.085 g, 83%; FAB MS m/z 1027 (M+); IR (Nujol) ν
2109 (m, CtC) cm-1
;
13C{1H} NMR (CH2Cl2, 22 °C, TMS) δ
2
3
131.3 (d, J CP ) 131.4 Hz, AuC), 85.9 (d, J CP ) 25.0 Hz, Au-
CtC), 75.1 (s, AuCtCC), 32.3 (d, 1J CP ) 28.1 Hz, Cy), 30.0 (s,
2
Cy), 26.3 (d, J CP ) 11.8 Hz, Cy), 25.2 (s, Cy); 31P{1H} NMR
absorption of (CtC)∞2-, the singlet-triplet splitting of
(18) Rubin, Y.; Lin, S. S.; Knobler, C. B.; Anthony, J .; Boldi, A. M.;
Diederich, F. J . Am. Chem. Soc. 1991, 113, 6943.
(19) Weng, W.; Bartik, T.; Brady, M.; Bartik, B.; Ramsden, J . A.;
Arif, A. M.; Gladysz, J . A. J . Am. Chem. Soc. 1995, 117, 11922.
the (CtC)∞ chain is estimated to be ∼7000 cm-1
,
2-
(17) Lewis, G. N.; Calvin, M. Chem. Rev. 1939, 26, 237.

2346 Organometallics, Vol. 21, No. 11, 2002
Notes
(CH2Cl2, 22 °C, external H3PO4) δ 58.2. Anal. Calcd for
Dc ) 1.639 g cm-3, Mo KR radiation (λ ) 0.710 73 Å), µ(Mo
KR) ) 6.72 mm-1, F(000) ) 1096, T ) 301 K, 2θmax ) 51°, 3903
independent reflections, 226 variable parameters, R1 ) 0.049
(I > 2σ(I)), wR2 ) 0.12 for GOF(F2) ) 0.95.
C
6.24.
42H66P2Au2‚CH2Cl2: C, 46.45; H, 6.16. Found: C, 46.46; H,
4: yield 0.052 g, 50%; FAB MS m/z 1051 (M+); IR (Nujol) ν
2147 (m, CtC), 2066 (vw, CtC), 2007 (vw, CtC) cm-1
;
13C-
{1H} NMR (CH2Cl2, 22 °C, TMS) δ 136.0 (d, J CP ) 122.2 Hz,
2
Ack n ow led gm en t. We are grateful for financial
support from The University of Hong Kong and the
Research Grants Council of Hong Kong SAR, China
(Grant No. HKU 7298/99P).
3
AuC), 87.4 (d, J CP ) 24.9 Hz, AuCtC), 67.4 (s, AuCtCC),
1
62.8 (s, AuCtCCtC), 34.8 (d, J CP ) 28.0 Hz, Cy), 32.4 (s,
Cy), 28.7 (d, J CP ) 11.6 Hz, Cy), 27.6 (s, Cy); 31P{1H} NMR
2
(CH2Cl2, 22 °C, external H3PO4) δ 57.5. Anal. Calcd for
C
44H66P2Au2: C, 50.29; H, 6.33. Found: C, 50.00; H, 6.40.
X-r a y Cr ysta llogr a p h ic Deter m in a tion of 3‚CH2Cl2.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data for 3‚CH2Cl2. This material is available free
of charge via the Internet at http://pubs.acs.org.
Single crystals of 3‚CH2Cl2 were obtained by slow diffusion of
Et2O vapor into a CH2Cl2 solution. Crystal data: C43H68Cl2P2-
Au2, Mr ) 1111.75, monoclinic, P21/c (No. 14), a ) 12.420(3)
Å, b ) 17.719(4) Å, c ) 11.283(2) Å, V ) 2253.3(8) Å3, Z ) 2,
OM011087F