Attaching gold and platinum to the rim of pyrene: A synthetic and spectroscopic study

Article abstract of DOI:10.1021/om700716p

A series of pyrenyl complexes containing one or two AuPPh₃ or Pt(PEt₃)₂Br groups have been synthesized to probe the effects of metal on the absorption and emission properties of the organic molecule. The absorption spectra of the complexes showed perturbation of the metal centers on the pyrenyl ring, as manifested by a red shift of the π → π* transitions of pyrene and intensification of the forbidden ¹L_b band. The perturbation increased with the number of metal ions attached to the pyrenyl ring. The Pt ion was stronger than the Au ion in perturbing the electronic structure of the pyrenyl ring. All pyrenyl complexes displayed fluorescence and phosphorescence in degassed solutions. The heavy-atom effect of the metal ions enhanced the phosphorescence. The quantum yield of phosphorescence was sensitive to the positions of metalation.

Full text of DOI:10.1021/om700716p

6760
Organometallics 2007, 26, 6760–6768
Attaching Gold and Platinum to the Rim of Pyrene: A Synthetic
and Spectroscopic Study
Wendy Yuqing Heng, Jian Hu, and John H. K. Yip*
Department of Chemistry, National UniVersity of Singapore, 3 Science DriVe 3, Singapore 117543
ReceiVed July 18, 2007
A series of pyrenyl complexes containing one or two AuPPh3 or Pt(PEt3)2Br groups have been
synthesized to probe the effects of metal on the absorption and emission properties of the organic molecule.
The absorption spectra of the complexes showed perturbation of the metal centers on the pyrenyl ring,
as manifested by a red shift of the π f π* transitions of pyrene and intensification of the forbidden 1Lb
band. The perturbation increased with the number of metal ions attached to the pyrenyl ring. The Pt ion
was stronger than the Au ion in perturbing the electronic structure of the pyrenyl ring. All pyrenyl
complexes displayed fluorescence and phosphorescence in degassed solutions. The heavy-atom effect of
the metal ions enhanced the phosphorescence. The quantum yield of phosphorescence was sensitive to
the positions of metalation.
As part of our ongoing effort to develop the coordination
chemistry of AAH-based ligands,6 we explored the possibility
of using pyrene as a multidentate ligand in synthesizing poly-
metallic complexes. Pyrene has rich photophysical properties,4,7
and it has been invoked in building luminescent metal complexes
as part of the ligands.8 However, organometallic complexes of
pyrene are fewer by comparison. In most cases, the complexes
of pyrene are the so-called π-complexes in which the metal
center is attached to the ring via the π-bonding system.9 To the
best of our knowledge, only five σ-bonded organometallic
pyrene complexes have been reported, which contain Ru(II),8g
Introduction
Alternant aromatic hydrocarbons (AAH) are an important
class of chromophores, including molecules such as benzene,
naphthalene, anthracene, and pyrene.1 These organic molecules,
all displaying intense π f π* transitions in the UV and/or
visible region, occupy a central position in spectroscopy,
photophysics, photochemistry, and bonding theory.2 Although
the effects of substituents on the electronic structures of AAH
have been intensively investigated,2,3 most of the works have
focused on conventional substituents such as alkyls, amines,
and halides and corresponding studies on the effects of metals
have been rather limited. The electronic absorption and emission
spectroscopy of metalated AAH should provide insights into
the interactions between the metal and the extensive π-conju-
gated systems, the knowledge of which is crucial to developing
this class of molecules into new organometallic functional
materials. Because of strong exchange interaction, the singlet
and triplet states of AAH are widely separated and the
phosphorescence of highly conjugated AAH could occur in the
near-infrared region. However, the intersystem crossing from
the fluorescing singlet excited state to its corresponding
phosphorescing triplet state is slow because of the unfavorable
Franck–Condon factor due to the large singlet–triplet gap.2,4
The third-row transition metals are known to increase the rate
of intersystem crossing between the singlet and triplet excited
states of organic molecules in a phenomenon known as the
(3) (a) Reference 2a, pp 104–117. (b) Longuet-Higgins, H. C.; Coulson,
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3
heaVy atom effect, and this has the potential to enhance ππ*
phosphorescence of the compounds.2a–c,4,5 This property of
metalated AAH could be harnessed to create new near-infrared
emitting materials.
* To whom correspondence should be addressed. E-mail:
chmyiphk@nus.edu.sg.
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10.1021/om700716p CCC: $37.00
2007 American Chemical Society
Publication on Web 12/07/2007

Attaching Au and Pt to the Rim of Pyrene
Organometallics, Vol. 26, No. 27, 2007 6761
Scheme 1
Pd(II),10a Ir(III),10a Pt(II),10b and Au(I)10c ions. A fundamental
question we attempted to address is about the effects of a heavy
metal on the absorption and emission properties of pyrene when
it is attached to the ring via a σ-bond.11 Herein we present the
synthesis, characterization, and an investigation of the effect
of the number and position of substitution on the electronic
absorption spectrum and photophysical properties of a series
of gold(I) and platinum(II) σ-bonded complexes with pyrene
(Scheme 1). Che12 and Yam10c have separately demonstrated
the luminescence of arylgold(I) complexes. Our study showed
that the metal ions can strongly perturb the pyrenyl ring, and
interestingly the number and position of the metal ions play
important roles in modulating the electronic structure of the
organic moiety.
The initial advancement of arylgold(I) chemistry was largely
limited to simple aromatics such as phenyl and its polyfluoroaryl
derivatives,13 but it has been extended to more elaborated aromatics
such as vinylbenzene,14a biphenyl,14b and anthracene.14c The
complexes were usually prepared by metathesis between the gold
halides LAuX and standard aryl transferring reagents such as
Grignard reagents, organolithium, organothallium, and organo-
mercury compounds (L ) phosphines, isocyanides, arsine, car-
benes; X ) halides).13a–j A convenient entry route into arylplatinum
chemistry is through the oxidative addition of Pt(PEt3)4 to bro-
mopolyaromatic molecules.15 This method was used to prepare
the platinated pyrenes in this work.
Experimental Section
General Methods. The syntheses of all metal complexes were
carried out under N2 by using standard Schlenck techniques. All
solvents used in syntheses and spectroscopic measurements were
purified according to standard methods. n-butyllithium (1.6 mol
dm-3 in hexane) was obtained from Sigma-Aldrich and was titrated
before used. Au(PPh3)Cl,16 Pt(PEt3)4,17 1-bromopyrene18 and 1,3,6-
tribromopyrene19 were prepared according to literature procedures.
Physical Methods. 1H and 31P{1H} NMR spectra were recorded
on a Bruker ACF300 or AMX500 spectrometer, with 1H chemical
shifts (δ) given in ppm relative to residual nondeuterated CDCl3
(δ 7.26). 31P{1H} chemical shifts were reported relative to external
85% aqueous H3PO4 (δ 0.0). Positive electrospray ionization (ESI)
mass spectra were obtained with a Finnigan MAT 731 LCQ
spectrometer. Electronic absorption and emission spectra were
recorded by a Shimadzu UV-1601 spectrophotometer and a Perkin-
Elmer LS50B luminescence spectrometer, respectively. The excita-
tion wavelength used for all emission measurements was 320 nm.
All solutions used for luminescence measurements were degassed
with at least four freeze–pump–thaw cycles. Emission quantum
yields were calculated with anthracene as a standard. Elemental
analyses were carried out by the Elemental Analysis Laboratory,
Department of Chemistry, National University of Singapore.
Synthesis. 1,6- and 1,8-Dibromopyrene. These compounds
were prepared by double bromination of pyrene according to a
similar literature method for the preparation of 1-brompyrene.18
Pyrene (10.10 g, 0.050 mol) was dissolved in a mixture of Et2O
(200 mL) and CH3OH (200 mL). HBr solution (48%, 12.45 mL,
0.110 mol) was then added to the solution. To this mixture was
added dropwise H2O2 (30%, 10.30 mL, 0.100 mol) over 20 min.
The resulting pale yellow slurry was stirred for 12 h. The product
(9) Some example of metal-pyrene π-complexes: (a) Hasegawa, T.;
Sekine, M.; Schaefer, W. P.; Taube, H. Inorg. Chem. 1991, 30, 449. (b)
Reingold, J. A.; Virkaitis, K. L.; Carpenter, G. B.; Sun, S.; Sweigart, D. A.;
Czech, P. T.; Overly, K. R. J. Am. Chem. Soc. 2005, 127, 11146. (c)
Morrison, W. H., Jr.; Ho, E. Y.; Hendrickson, D. N. J. Am. Chem. Soc.
1974, 96, 3603. (d) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T.; Maekawa,
M.; Suenaga, Y.; Sugimoto, K. Inorg. Chem. 1997, 36, 4903.
(10) (a) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Organometallics
2006, 25, 1461. (b) Weisemann, C.; Schmidtberg, G.; Brune, H.-A. J.
Organomet. Chem. 1989, 365, 403. (c) Yam, V. W.-W.; Choi, S. W.-K.;
Cheung, K.-K. J. Chem. Soc., Dalton Trans. 1996, 3411.
1
was filtered and washed with hot EtOH (50 mL). The H NMR
spectrum showed that the major products (>95%) were 1,6- and
1,8-dibromopyrene in an approximate ratio of 1:1. The two isomers
were separated by fractional recrystallization from CHCl3. Yield:
16.60 g, 92%.
1-Au(PPh3)pyrene (1). To a stirred solution of 1-bromopyrene
(0.639 g, 2.27 mmol) in freshly distilled Et2O (30 mL) at 0 °C was
added a solution of n-butyllithium in hexane (1.42 mL, 2.27 mmol).
(11) During the preparation of this paper, Gray et al. reported the
syntheses and photophysics of two mononuclear gold(I)-pyrenyl complexes
with carbene and P(Cy)3ligands: Partyka, D. V.; Esswein, A. J.; Zeller,
M.; Hunter, A. D.; Gray, T. G. Organometallics 2007, 26, 3279.
(12) Hong, X.; Cheung, K.-K.; Guo, C.-X.; Che, C.-M. J. Chem. Soc.,
Dalton Trans. 1994, 1867.
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Lucassen, A. C. B.; Shimon, L. J. W.; van der Boom, M. E. Organometallics
2006, 25, 3308. (c) Strawser, D.; Karton, A.; Zenkina, O. V.; Iron, M. A.;
Shimon, L. J. W.; Martin, J. M. L.; van der Boom, M. E. J. Am. Chem.
Soc. 2005, 127, 9322. (d) Kim, D.; Paek, J. H.; Jun, M.-J.; Lee, J. Y.; Kang,
S. O.; Ko, J. Inorg. Chem. 2005, 44, 7886. (e) Lee, H. B.; Sharp, P. R.
Organometallics 2005, 24, 4875. (f) Kryschenko, Y. K.; Seidel, S. R.;
Muddiman, D. C.; Nepomuceno, A. I.; Stang, P. J. J. Am. Chem. Soc. 2003,
125, 9647. (g) Chantson, J. T.; Lotz, S.; Ichharam, V. New J. Chem. 2003,
27, 1735. (h) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang, P. J.
J. Am. Chem. Soc. 2003, 125, 5193. (i) Manna, J.; Kuehl, C. J.; Whiteford,
J. A.; Stang, P. J. Organometallics 1997, 16, 1897.
(13) (a) Usón, R.; Laguna, A. Coord. Chem. ReV. 1986, 70, 1. (b)
Schmidbaur, H. Gold Progress in Chemistry, Biochemistry and Technology;
Wiley: Chichester, U.K., 1999; p 648. (c) Calvin, G.; Coates, G. E.; Dixon,
P. E. Chem. Ind. 1959, 1628. (d) Coates, G. E.; Parkin, G. J. Chem. Soc.
1962, 3220. (e) Vaughan, L. G.; Sheppard, W. A. J. Am. Chem. Soc. 1969,
91, 6161. (f) Usón, R.; Laguna, A.; Buil, L. J. Organomet. Chem. 1975,
85, 403. (g) Usón, R.; Laguna, A.; Brun, P. J. Organomet. Chem. 1979,
182, 449. (h) Porter, K. A.; Schier, A.; Schmidbaur, H. Organometallics
2003, 22, 4922. (i) Laguna, A.; Laguna, M.; Gimeno, M. C.; Jones, P. G.
Organometallics 1992, 11, 2759. (j) Bardají, M.; Jones, P. G.; Laguna, A.;
Moracho, A.; Fischer, A. K. J. Organomet. Chem. 2002, 648, 1. (k) Sladek,
A.; Hofreiter, S.; Paul, M.; Schmidbaur, H. J. Organomet. Chem. 1995,
501, 47.
(16) Baenziger, N. C.; Bennett, W. E.; Soboroff, D. M. Acta Crystallogr.
1976, B32, 962.
(17) Yoshida, T.; Matsuda, T.; Otsuka, S. Inorg. Synth. 1990, 28, 122.
(18) Vyas, P. V.; Bhatt, A. K.; Ramachandraiah, G.; Bedekar, A. V.
Tetrahedron Lett. 2003, 44, 4085.
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Duchêne, A.; Thibonnet, J. J. Organomet. Chem. 2005, 690, 4835. (b) Porter,
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6762 Organometallics, Vol. 26, No. 27, 2007
Heng et al.
After 10 min, Au(PPh3)Cl (1.124 g, 2.27 mmol) was added to the
resulting orange-yellow suspension and the mixture was warmed
to room temperature. After this mixture was stirred for 2 h, 20 mL
of CH2Cl2 was added to the orange suspension and the mixture
was filtered. The filtrate was then concentrated, and hexane (100
mL) was added to precipitate the product as pale beige solids.
Recrystallization by layering of hexane onto a CH2Cl2 solution of
the solid afforded the product as orange-yellow crystals. Yield:
0.80 g, 53%. Anal. Calcd for C34H24AuP · 0.25CH2Cl2: C, 60.34;
MHz): δ 8.85 (d, 1H, 3JH10-H9 ) 9.0 Hz, H10), 8.18 (d, 1H, 3JH2-H3
3
3
) 7.9 Hz, JHPt ) 69 Hz, H2), 8.09 (m, 2H, JH6,8-H7 ) 7.6 Hz,
3
H
6,8), 7.98–7.88 (m, 4H, H4,5,7,9), 7.78 (d, 1H, JH3-H2 ) 7.9 Hz,
H3), 1.60–1.46 (m, 12H, PCH2CH3), 1.05–0.95 (m, 18H, PCH2CH3).
31P{1H} NMR (CDCl3, 121.5 MHz): δ 12.63 (s, JP-Pt ) 2700
1
Hz). ESI-MS (m/z): 631.1 [M - Br]+.
1,6-Bis[trans-Pt(PEt3)2Br]pyrene (6). The procedure used was
the same as that for 5, except that 1,6-dibromopyrene (0.490 g,
1.36 mmol) and 2 mol equiv of Pt(PEt3)4 (2.0 g, 3.0 mmol) were
used. Pale yellow crystals of the product were obtained from
diffusing Et2O into a CH2Cl2 solution of the crude product. Yield:
1.42 g, 85%. Anal. Calcd for C40H68Pt2P4Br2: C, 39.29; H, 5.61.
Found: C, 39.49; H, 5.76. 1H NMR (CDCl3, 300 MHz): δ 8.68 (d,
2H, 3JH5-H4 ) 9.0 Hz, H5,10), 8.06 (d, 2H, 3JH2-H3 ) 7.8 Hz, 3JH-Pt
) 65 Hz, H2,7), 7.85 (d, 2H, 3JH4-H5 ) 9.0 Hz, H4,9), 7.69 (d, 2H,
3JH3-H2 ) 7.8 Hz, H3,8), 1.60–1.46 (m, 24H, PCH2CH3), 1.05–0.95
(m, 36H, PCH2CH3). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 12.66
1
H, 3.62. Found: C, 60.05; H, 3.64. H NMR (CDCl3, 500 MHz):
3
3
δ 8.78 (d, 1H, JH10-H9 ) 8.8 Hz, H10), 8.33 (dd, 1H, JH2-H3
)
4
3
7.4 Hz, JHP ) 5.3 Hz, H2), 8.14 (d, 1H, JH3-H2 ) 7.4 Hz, H3),
8.08 (m, 2H, H6,8), 8.03 (d, 1H, JH4-H5 ) 8.9 Hz, H4/5), 8.01 (d,
1H, JH4-H5 ) 8.9 Hz, H4/5), 7.95 (d, 1H, JH9-H10 ) 8.8 Hz, H9),
7.94–7.91 (m, 1H, H7), 7.74–7.70 (m, 6H, Ph), 7.54–7.52 (m, 9H,
Ph). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 44.85 (s). ESI-MS (m/
z): 660.0 [M]+.
3
3
3
1
(s, JP-Pt ) 2720 Hz). ESI-MS (m/z): 1221.9 [M]+, 1142.1 [M -
1,6-Bis[Au(PPh3)]pyrene (2). The procedure used was similar
to that for 1, except that 1,6-dibromopyrene (0.471 g, 1.31 mmol)
and 2 mol equiv of n-butyllithium (1.64 mL, 2.62 mmol) and
Au(PPh3)Cl (1.296 g, 2.62 mmol) were used. Pale yellow crystals
of the product were obtained from diffusion of Et2O into a CH2Cl2
solution of the crude product. Yield: 1.19 g, 81%. Anal. Calcd for
C52H38Au2P2 · CH2Cl2: C, 52.89; H, 3.35. Found: C, 52.39; H, 3.65.
Br]+.
1,8-Bis[trans-Pt(PEt3)2Br]pyrene (7). This compound was
prepared from Pt(PEt3)4 (2.0 g, 3.0 mmol) and 1,8-dibromopyrene
(0.490 g, 1.36 mmol) by using the same procedure as for 6.
Recrystallization from vapor diffusion of Et2O into a CH2Cl2
solution of the crude product afforded the product as pale orange-
red crystals. Yield: 0.88 g, 53%. Anal. Calcd for C40H68Pt2P4Br2:
C, 39.29; H, 5.61. Found: C, 39.68; H, 5.73. 1H NMR (CDCl3,
3
1H NMR (CDCl3, 300 MHz): δ 8.69 (d, 2H, JH5-H4 ) 9.0 Hz,
H
5,10), 8.24 (dd, 2H, 3JH2-H3 ) 7.4 Hz, 4JH-P ) 5.3 Hz, H2,7), 8.05
3
(dd, 2H, 3JH3-H2 ) 7.4 Hz, 5JH-P ) 1 Hz, H3,8), 7.97 (d, 2H, 3JH4-H5
) 9.0 Hz, H4,9), 7.76–7.68 (m, 12H, Ph), 7.53–7.50 (m, 18H, Ph).
31P{1H} NMR (CDCl3, 121.5 MHz): δ 45.00 (s). ESI-MS (m/z):
1118.9 [M]+.
300 MHz): δ 8.77 (s, 2H, H5,10), 8.02 (d, 2H, JH2-H3 ) 7.7 Hz,
3
3JH-Pt ) 70 Hz, H2,7), 7.82 (s, 2H, H4,9), 7.69 (d, 2H, JH3-H2
)
7.7 Hz, H3,8), 1.60–1.46 (m, 24H, PCH2CH3), 1.05–0.95 (m, 36H,
PCH2CH3). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 12.30 (s, 1JP-Pt
) 2730 Hz). ESI-MS (m/z): 1221.9 [M]+.
1,8-Bis[Au(PPh3)]pyrene (3). The procedure used was same as
that for 2. except that 1,8-dibromopyrene (0.432 g, 1.20 mmol)
and 2 mol equiv of n-butyllithium (1.50 mL, 2.40 mmol) and
Au(PPh3)Cl (1.187 g, 2.40 mmol) were used in the reaction. Orange-
yellow crystals of the product were obtained from layering of
hexane onto a CH2Cl2 solution of the crude product. Yield: 0.80 g,
60%. Anal. Calcd for C52H38Au2P2 · CH2Cl2: C, 52.89; H, 3.35.
Found: C, 53.44; H, 3.41. 1H NMR (CDCl3, 300 MHz): δ 8.74 (s,
2H, H9.10), 8.24 (dd, 2H, 3JH2-H3 ) 7.4 Hz, 4JH-P ) 5.3 Hz, H2,7),
1,6-Bis[trans-Pt(PEt3)2Br]-3-bromopyrene(8)and1,8-Bis[trans-
Pt(PEt3)2Br]-3-bromopyrene (9). To a solution of Pt(PEt3)4 (2.0 g,
3.0 mmol) in toluene (60 mL) was added 1,3,8-tribromopyrene
(0.597 g, 1.36 mmol). The reaction mixture was stirred for 18 h,
the solvent was then removed, and the resultant white solid was
redissolved in a minimum volume of CH2Cl2. Hexane was slowly
added to precipitate out the less soluble 1,6-bis[trans-Pt(PEt3)2Br]-
3-bromopyrene as a beige solid, which was collected by suction
filtration. Removal of solvent from the filtrate gave a beige solid
containing 1,8-bis[trans-Pt(PEt3)2Br]-3-bromopyrene. Recrystalli-
zation from vapor diffusion of diethyl ether into a CH2Cl2 solution
of the former solid afforded complex 8 as yellow crystals. Repeated
recrystallizations from vapor diffusion of ether into a CH2Cl2
solution of the latter solid afforded complex 9 as pale orange-red
crystals. Yield: 1.58 g, 45% for each isomer. Data for 8 are as
follows. Anal. Calcd for C40H67Pt2P4Br3: C, 36.91; H, 5.19. Found:
3
5
8.05 (dd, 2H, JH3-H2 ) 7.4 Hz, JH-P ) 1 Hz, H3,6), 7.90 (s, 2H,
H
4,5), 7.76–7.68 (m, 12H, Ph), 7.52–7.50 (m, 18H, Ph). 31P{1H}
NMR (CDCl3, 121.5 MHz): δ 44.95 (s). ESI-MS (m/z): 1118.9
[M]+.
1,6-Bis[Au(PPh3)]-3-bromopyrene (4). The procedure used was
similar to that for 1, except that 1,3,6-tribromopyrene (0.440 g,
1.00 mmol) and 3 mol equiv of n-butyllithium (1.95 mL, 3.12
mmol) and Au(PPh3)Cl (1.50 g, 3.03 mmol) were used in the
reaction. Crystals of the product were obtained from Et2O/CH2Cl2.
Yield: 1.03 g, 86%. Anal. Calcd for C52H37Au2P2Br: C, 52.15; H,
1
C, 37.03; H, 5.36. H NMR (CDCl3, 300 MHz): δ 8.78 (d, 1H,
3
3JH5-H4) 9.3 Hz, H5), 8.68 (d, 1H, JH10-H9 ) 8.9 Hz, H10), 8.34
1
3
3
3.11. Found: C, 52.26; H, 3.38. H NMR (CDCl3, 500 MHz): δ
(s, 1H, JH-Pt ) 74 Hz, H2), 8.19 (d, 1H, JH4-H5 ) 9.3 Hz, H4),
3
3
3
3
8.79 (d, 1H, JH5-H4 ) 9.2 Hz, H5), 8.64 (d, 1H, JH10-H9 ) 9.0
Hz, H10), 8.50 (d, 1H, 4JH-P ) 5.7 Hz, H2), 8.33 (d, 1H, 3JH4-H5
9.2 Hz, H4), 8.27 (dd, 1H, 3JH7-H8) 7.5 Hz, 4JH-P ) 5.3 Hz, H7),
8.12 (d, 1H, JH7-H8 ) 7.7 Hz, JH-Pt ) 69 Hz, H7), 7.88 (d, 1H,
3JH9-H10 ) 8.9 Hz, H9), 7.72 (d, 1H, JH8-H7 ) 7.7 Hz, H8),
3
)
1.60–1.45 (m, 24H, PCH2CH3), 1.06–0.97 (m, 36H, PCH2CH3).
31P{1H} NMR (CDCl3, 121.5 MHz): δ 12.68 (s, 2P, 1JP-Pt ) 2710
Hz), 12.25 (s, 2P 1JP-Pt ) 2680 Hz). ESI-MS (m/z): 1301.8 [M]+,
1223.1 [M - Br]+. Data for 9 are as follows. Anal. Calcd for
3
5
8.08 (dd, 1H, JH8-H7) 7.5 Hz, JH-P ) 1 Hz, H8), 7.98 (d, 1H,
3JH9--H10) 9.0 Hz, H9), 7.74–7.69 (m, 12H, Ph), 7.53–7.50 (m,
18H, Ph). 31P{1H} NMR (CDCl3, 202.4 MHz): δ 44.94 (s), 44.44
(s). ESI-MS (m/z): 1198.9 [M]+.
1
C40H67Pt2P4Br3: C, 36.91; H, 5.19. Found: C, 37.13; H, 5.29. H
1-[trans-Pt(PEt3)2Br]pyrene (5). To a solution of Pt(PEt3)4 (2.0
g, 3.0 mmol) in toluene (60 mL) was added 1-bromopyrene (0.765
g, 2.72 mmol). The reaction mixture was stirred for 18 h at room
temperature, during which time an orange-yellow solution resulted.
The solvent was then removed and the resultant pale yellow solid
redissolved in a minimum volume of CH2Cl2. Cold hexane (150
mL) was added to precipitate out the product. Pale yellow crystals
were obtained from diffusing hexane into a CH2Cl2 solution of the
product. Yield: 1.57 g, 81%. Anal. Calcd for C28H39PtP2Br: C,
NMR (CDCl3, 300 MHz): δ 8.84–8.75 (m, 2H, H4,5), 8.31 (s, 1H,
3JH-Pt ) 75 Hz, H2), 8.19 (d, 1H, 3JH10-H9 ) 9.1 Hz, H10), 8.07 (d,
3
3
3
1H, JH7-H8 ) 7.9 Hz, JH-Pt ) 58 Hz, H7), 7.92 (d, 1H, JH9-H10
) 9.1 Hz, H9), 7.74 (d, 1H, 3JH8-H7 ) 7.9 Hz, H8), 1.60–1.45 (m,
24H, PCH2CH3), 1.05–0.93 (m, 36H, PCH2CH3). 31P{1H} NMR
(CDCl3, 121.5 MHz): δ 12.19 (s, 2P, 1JP-Pt ) 2720 Hz), 11.92 (s,
2P, 1JP-Pt ) 2680 Hz). ESI-MS (m/z): 1302.0 [M]+, 1222.0 [M -
Br]+.
X-ray Crystallography. Single crystals of the compounds were
mounted on a glass fiber and used for the diffraction experiments.
1
47.20; H, 5.52. Found: C, 47.71; H, 5.64. H NMR (CDCl3, 300

Attaching Au and Pt to the Rim of Pyrene
Organometallics, Vol. 26, No. 27, 2007 6763

6764 Organometallics, Vol. 26, No. 27, 2007
Heng et al.
Scheme 2
The X-ray intensity data were measured on a Bruker AXS SMART
CCD three-circle diffractometer using graphite-monochromated Mo
KR radiation (λ ) 0.710 73 Å) by a 2θ-ω scan. The software
used was SMART20a for collecting frames of data, indexing
reflection, and determination of lattice parameters, SAINT20a for
integration of intensity of reflections and scaling, SADABS20b for
empirical absorption correction, and SHELXTL20c for space group
determination, structure solution, and least-squares refinements on
|F|2. Positional and anisotropic atomic displacement parameters were
refined for all non-hydrogen atoms. The hydrogen atoms were
placed in their ideal positions. Restraints (DFIX20c for C-C bonds
and ISOR20c for thermal parameters) were applied during final
refinement cycles for the ethyl groups of 9. Some restraints on bond
lengths and thermal parameters were also applied to the ethyl groups
of 7. Crystallographic data and experimental details are given in
Table 1.
Results and Discussion
Synthesis of Aurated Pyrenes. The bromopyrenes were
lithiated by reacting bromopyrenes with a slight excess of
n-BuLi. Subsequent reactions of the lithiated pyrene with
Au(PPh3)Cl resulted in the formation of the monoaurated (1)
and diaurated (2-4) pyrene complexes in reasonable to good
yields of 53–86% (Scheme 1). Interestingly, reacting
Au(PPh3)Cl with lithiated 1,3,6-tribromopyrene only gave the
diaurated complex 4 as the only product. The auration only
occurred at the C1 and C6 positions; the Br at the C3 position
remained unreacted. This result suggested that lithiation of 1,3,6-
tribromopyrene is regioselective and is restricted to the C1 and
C6 positions. A possible explanation is that the two negative
charges are most widely separated when they reside on C1 and
C6 (cf. C1 and C3, and C3 and C6), and this contributes to the
stability of the lithiated intermediate. Further lithiation and
auration of 4 to produce a trinuclear complex were not
successful. Possibly, addition of an AuPPh3 group at C3 is
sterically hindered by the existing AuPPh3 group at C1.
Figure 1. ORTEP diagrams of 1 · 0.5CH2Cl2 (1a), 2 · CH2Cl2 (1b),
3 · CH2Cl2 (1c), and 4 · Et2O (1d). All H atoms and solvent
molecules are omitted for clarity. Thermal ellipsoids are shown at
the 50% probability level.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 1–4
1
2
3
4
Au1-C1
2.053(6)
2.2943(5)
2.042(3)
2.2820(9)
2.050(3)
2.3001(9)
2.033(11) 2.051(5)
The 31P{1H} NMR spectra of 1–3 all show a singlet at δ
∼45 ppm. This is indicative of the expected symmetry for 2
and 3 rendering the two AuPPh3 groups equivalent. For 4, two
singlets of equal intensity were observed at δ ∼44.94 and 44.44
ppm, respectively, and this is in agreement with the fact that
the two AuPPh3 groups at C1 and C6 are chemically inequiva-
Au1-P1
2.282(3)
2.065(12)
2.285(3)
2.2901(14)
Au2-C6/C8
Au2-P2
C1-Au1-P1
P2-Au2-C6/C8
177.11(16) 179.14(11) 173.4(3)
172.78(10) 175.1(3)
179.04(17)
1
lent. The H NMR spectra of 1-4 showed long-range P-H
our knowledge, no such long-range P-H coupling was reported
before in the literature for arylgold(I) phosphines.
couplings between the P atom and the H atoms ortho (4JH-P
)
4
5
or meta (5JH-P) to the Au atom with JP-H ) 5 Hz and JP-H
) 1 Hz (Scheme 2 and SF1). The P-H couplings were
confirmed by TOCSY experiments (SF2), which indicated that
these couplings were not long-range H-H couplings. Interest-
ingly, no 5JP-H coupling was observed between the P atom and
the H atom on a different six-membered ring. To the best of
Structures of Aurated Pyrenes. Parts a-d of Figures 1
display the crystal structures of 1 · 0.5 CH2Cl2, 2 · CH2Cl2,
3 · CH2Cl2, and 4 · Et2O, respectively, and selected bond lengths
and angles are given in Table 2. The Au ions in all the
complexes are two-coordinated with a linear geometry. All
complexes are monomeric with no discernible aurophilic

Attaching Au and Pt to the Rim of Pyrene
Organometallics, Vol. 26, No. 27, 2007 6765
interactions and π-π stacking of pyrenyl rings. The potential
aggregation of the molecules could be hindered by the bulky
PPh3 ligands. The Au-C bond lengths span from 2.033(11) to
2.065(12) Å and the Au-P bond lengths from 2.2820(9) to
2.3001(9) Å; the C-Au-P bond angles are close to linearity,
ranging from 172.78(10) to 179.04(17)°. These values are typical
for known arylgold(I) complexes.12,14–16 Complexes 3 and 5
show approximate C2h and C2V symmetry, respectively. The
structure of complex 4 shows a Br atom at C3 and two AuPPh3
groups at C1 and C6. The Br atom is disordered over two
positions (C3 and C3A, 50% occupancy at both positions),
which are related by an inversion center.
Synthesis of Platinated Pyrenes. Oxidative addition of
excess Pt(PEt3)4 to the bromopyrenes in toluene resulted in the
formation of the platinated pyrenyl complexes 5–9 in mostly
good yields (Scheme 1). The platination of 1-bromopyrene and
1,6-/1,8-dibromopyrene gave a single product, as expected.
However, the reaction of 1,3,6-tribromopyrene produced two
geometrical isomers, 1,6-bis[trans-Pt(PEt3)2Br]-3-bromopyrene
(8) and 1,8-bis[trans-Pt(PEt3)2Br]-3-bromopyrene (9), in ap-
proximately a 1:1 ratio. Only two out of the three Br atoms
could be replaced by Pt ions for 1,3,6-tribromopyrene, even with
excess Pt(PEt3)4. The Br at the C3 remained unreacted. This
could be due to the presence of the bulky Pt(PEt3)2Br group at
the position meta to the remaining C-Br bond, which hinders
the approach of another Pt(PEt3)4.
Complexes 5–7 display a singlet with Pt satellites in their
respective 31P{1H} NMR spectra. On the other hand, two
singlets with equal intensity at δ ∼12 ppm were observed in
1
the spectra of 8 and 9. The magnitude of JP-Pt (2680–2730
Hz) is consistent with the trans orientation of the two PEt3
groups in the complexes. Interestingly, no long-range P-H
coupling, as observed in the spectra of the gold complexes, was
found in the spectra of the Pt complexes. This suggests that the
P-H coupling is sensitive to the orientation of the P atoms with
respect to the pyrenyl ring in the Au and Pt complexes (see the
following section).
Structures of the Platinated Pyrenes. Parts a-d of Figures
2 show the crystal structures of 5-8, and Table 3 gives the
selected bond lengths and angles. The Pt ions in all complexes
show distorted-square-planar geometry, and the coordination
planes are nearly perpendicular to the pyrenyl rings with the
angles between the two planes ranging from 79.4 to 89.8°.
Complexes 6 and 7 show approximate C2h and C2V symmetry,
respectively. The Br(2) atom in 8 is disordered over two
positions which are related by an inversion center. The Pt-C
(2.027(5)–2.047(9) Å) and Pt-P (2.30019(2)-2.3065(2) Å)
bondlengthsarenormal.15 ThePt-Brbonds(2.5050(6)–2.5258(9)
Å) are longer than that in PtBr42- (2.446(6) Å),21 probably due
to the trans influence of the carbanion. Due to the motions of
its ethyl groups, complex 7 showed large thermal parameters,
and consequently the Pt-C bond length of the complex was
not determined accurately. Despite many attempts, we failed
to obtain good-quality crystals of 9. Nevertheless, the crystal
structure of the complex 9 (SF3) clearly showed the presence
of two Pt(PEt3)2Br groups at C1 and C8 and one Br atom at C3
Figure 2. ORTEP diagrams of 5 (2a), 6 (2b), 7 (2c), and 8 (2d).
All H atoms are omitted for clarity. Thermal ellipsoids of 5 are
shown at the 30% probability level, and those of 6–8 are shown at
the 50% level.
Table 3. Selected Bond Lengths (Å) and Angles (deg) of 5–8
5
6
7
8
Pt1-C1
Pt1-P1
2.027(5)
2.049(7)
2.001(11)
2.034(5)
2.3027(14)
2.3031(13)
2.3001(15) 2.3065(18) 2.295(3)
2.3015(12) 2.2994(19) 2.287(3)
2.5050(6)
Pt1-P2
Pt1-Br1
Pt2-C8
Pt2-P3
Pt2-P4
Pt2-Br2
P1-Pt1-P2
2.5258(9)
2.5007(18) 2.5117(6)
2.009(9)
2.283(4)
2.283(4)
2.5267(13)
177.13(5)
172.84(7)
176.33(13) 173.92(5)
(20) (a) SMART & SAINT Software Reference Manuals, Version
4.0;Siemens Energy & Automation, Inc., Analytical Instrumentation:
Madison, WI, 1996. (b) Sheldrick, G. M. SADABS: a Software for Empirical
Absorption Correction; University of Gottingen: Gottingen, Germany, 1996.
(c) SHELXTL Reference Manual, Version 5.03; Siemens Energy &
Automation, Inc., Analytical Instrumentation: Madison, WI, 1996.
(21) Kroening, R. F.; Rush, R. M.; Martin, D. S., Jr.; Clardy, J. C Inorg.
Chem. 1974, 13, 1366.
C1-Pt1-Br1 177.21(13) 176.15(18) 177.4(3)
P3-Pt2-P4
C8-Pt2-Br2
176.36(13)
176.7(2)
179.8(3)
and a perpendicular orientation of the groups with respect to
the plane of the pyrenyl ring.

6766 Organometallics, Vol. 26, No. 27, 2007
Heng et al.
Figure 3. UV–vis absorption spectra of the gold complexes 1–4
and pyrene in CH2Cl2 at 295 K. The asterisks indicate the 1Lb bands.
1
Figure 5. Plots of the red shifts of the La band of the Au and Pt
complexes from that of pyrene versus the number and position of
substitutions.
1
1Lb band (378–406 nm) that is lower in energy than the La
band is clearly observed in the spectra of 1, 5, 6, and 8, while
1
in the spectra of 2 and 4, the Lb band appears as a shoulder,
1
1
as it overlaps with the La band. The Lb band completely
merges with the 1La band in the spectra of 3, 7, and 9. Because
of the overlap, the I1/I2 ratios of the 1La band of 7 and 9 (∼1.5)
are higher than those of the other Pt complexes (∼0.8) (I1 and
I2 are the intensities of the first and second vibronic peaks of
1
the La band).
The absorption bands of the complexes are all red-shifted
from the corresponding absorptions of pyrene.4,22 Plots of the
∆La (∆La ) energy difference between the 1La bands of pyrene
and substituted pyrene) (Figure 5) reveal several interesting
features of the pyrenyl complexes. First, the effect of metal ions
on the red shift is additive, as the extent of shift increases as
the number of metal ions increases. Second, the perturbation
of AuPPh3 and Pt(PEt3)2Br groups on the pyrenyl ring is stronger
than that of the Br atom; e.g. the 1La band of 1,3,6-tribromopy-
rene is only red-shifted from that of pyrene by 2100 cm-1 in
comparison with the 3945 cm-1 shift displayed by 9. Third,
the influence of the Pt(PEt3)2Br group on the absorptions appears
to be slightly stronger than that of the AuPPh3 group; for
instance, the energy of 1La band of 5 is lower than that of 1 by
Figure 4. UV–vis absorption spectra of the gold complexes 5–9
and pyrene in CH2Cl2 at 295 K. The asterisks indicate the 1Lb bands
of 5, 6, and 8, respectively.
Table 4. Absorption and Emission Data of 1–9
1La
1Lb
1Ba
1Bb
λf
λp
complex (nm)a (nm) (nm) (nm) (nm)b (nm)c 103Φf 103Φp
1
2
3
4
5
6
7
8
9
360 378
378 385
240 282
240 289
240 292
∼250 294
247 286
249 292
250 295
250 296
252 298
e
605
e
∼1
3.90
398
395
416
397
412
406
419
417
619 9.90
613 61.00
630 0.67
608 0.87
625 0.50
626 2.72
634 0.42
635 1.17
1
530 cm-1. Fourth, the energy of the La band is sensitive to
382
384
d
d
0.72
2.60
1.17
2.88
0.80
2.31
0.62
the positions of metalation, as the 1La bands of the 1,6-metalated
3, 7, and 9 are lower than those of their corresponding 1,8-
metalated isomers 2, 6, and 8.
367 386
381 400
383
388 406
390
d
The 1Lb bands of the complexes (ꢀmax ) 2.2-33 × 103 M-1
cm-1) are far more intense than that of pyrene (ꢀmax ) 500
M-1 cm-1). The four absorption bands of pyrene arise from
the transitions from HOMO-1 and HOMO to LUMO and
LUMO+1. In the D2h symmetry of pyrene, the HOMO-1 f
LUMO, HOMO f LUMO, HOMO f LUMO+1, and HO-
MO-1 f LUMO+1 excitations lead to the four singlet excited
states 1B3u(1) 1B2u(1), 1B3u(2), and 1B2u(2), respectively.1b,2a–c,23
The two 1B3u states are degenerate and would mix strongly via
first-order configuration interactions, leading to a high-energy
d
a Positions of the lowest energy vibronic peak of the 1La band.
b Fluorescence maxima. c Phosphorescence maxima. d tThe 1Lb band
merges with the 1La band. e Cannot be determined accurately.
Absorption Spectroscopy. The UV–vis absorption spectra
of the complexes are dominated by intraligand π f π*
transitions of their pyrenyl rings (see Figures 3 and 4 for the
spectra of Au and Pt complexes, respectively, and Table 4 for
the spectral data).
+
1
-
1B3u state and a low-energy B3u state. The order of the
energies of the four singlet excited states is 1B3u- (1Lb) < 1B2u
All the spectra display a very intense band in the UV region
around 250 nm (extinction coefficient ꢀmax ) 5-8 × 104 M-1
cm-1), an intense band at 270–310 nm (ꢀmax ) 3.4–4.5 × 104
M-1 cm-1), and a vibronic band at 310–410 nm (ꢀmax ) 4.4–6.8
× 104 M-1 cm-1), which are assigned to the 1Ba, 1Bb, and 1La
bands (see below for the origins of the bands).2a–c,4 A sharp
(1La) << B3u (1Bb) < B2u (1Ba) (shown in parentheses are
1
+
1
(22) (a) Clar, E. Spectrochim. Acta 1950, 4, 116. (b) Yoshinaga, T.;
Hiratsuka, H.; Tanzaki, Y. Bull. Chem. Soc. Jpn. 1977, 50, 3096.
(23) Platt, J. R. J. Chem. Phys. 1949, 17, 484.

Attaching Au and Pt to the Rim of Pyrene
Organometallics, Vol. 26, No. 27, 2007 6767
Scheme 3
Figure 6. Emission spectra of 5–9 and pyrene in degassed CH2Cl2.
λex ) 320 nm.
the labels of the excited states in Platt’s nomenclature). The
1
1
1
transitions from the S0 ground state to the Lb, La, Bb, and
1Ba states lead to the 1Lb, 1La, 1Bb, and 1Ba bands, respectively.
1
symmetry of the pyrenyl ring. As a result, the degeneracy of
Because the S0 f Lb transition is pseudoparity forbidden,24
1
1
1
-
1
the two B3u states is removed and the Ag f B3u (S0f1Lb)
the Lb band of pyrene is very weak. Attaching the Au and Pt
transition is no longer forbidden.
groups to pyrene definitely relaxes the forbidden rule, as
evidenced by the intense 1Lb bands of the complexes. Notably,
the intensity of the 1Lb band increases more than 2-fold as the
number of Pt ions increases from 1 to 2 (ꢀmax ) 1.2 × 104 M-1
cm-1 for 5 and ∼3 × 104 M-1 cm-1 for 6 and 8). It corroborates
with the idea that the metal perturbation is additive.
1
It is interesting to find that the energy gap between the La
1
and Lb bands is sensitive to the position of metalation. The
peak-to-peak separation of the two bands in pyrene is 1400
cm-1. Similar separation is found in 1 (1300 cm-1). On the
other hand, the bands partially overlap in the 1,6-diaurated
complexes 2 and 4 and merge in the 1,8-diaurated complex 3.
The bands are separated by ∼1200 cm-1 in 5, 6, and 8. Similar
to the case for their gold analogues, these bands completely
overlap in the 1,8-diplatinated complexes 7 and 9. As discussed
The red shift of transitions and the intensification of the 1Lb
band are due to perturbation of the metal ion on the pyrenyl
ring. The AuPPh3, Pt(PEt3)2Br, and Br groups can affect the
ring via their inductive effects and through their orbital
interactions with the ligand.2 In a first-order approximation, the
change in the energy of a molecular orbital R (δER) due to
inductive effect is related to the change in Coulomb integral
(δR) by the equation δEk ) ∑icik2δRi, where cik is the linear-
combination-of-atomic-orbital (LCAO) coefficient of the 2pz
orbital of the substituted carbon atom i in molecular orbital k.3b
Semiempirical calculation on pyrene shows that the LCAO
coefficients for the 2pz orbitals of C1/3/6/8 in the HOMO (0.346)
and LUMO (0.348) are nearly the same (SF4 and ST1).
Accordingly, δEHOMO ≈ δELUMO. It is therefore unlikely that
the red shifts of the absorption bands, especially the 1La band,
are due to the inductive effect alone. Orbital interactions between
the metal ions and pyrene mainly involve the metal dπ orbitals
and the HOMO and LUMO of the ring. As the lowest energy
absorption is ligand-centered, it is reasonable to assume that
the metal dπ orbitals are lower in energy than the HOMO. Since
the dπ orbitals are closer in energy to the HOMO than to the
LUMO, the HOMO should be more destabilized than the
LUMO by the metal π donation.25 On the other hand, the 6pz
orbital of the metal ion is closer in energy to the LUMO than
to the HOMO, and accordingly interactions of these orbitals
would stabilize the LUMO more than the HOMO. Scheme 3
depicts a qualitative orbital interaction diagram for the metalated
pyrenes. The overall result is a smaller HOMO–LUMO gap and
red shift of the absorptions. The spectroscopic results showed
that the Pt(PEt3)2Br group is slightly stronger than the AuPPh3
group in term of perturbation on the pyrenyl ring. This could
be due to the fact the Pt(PEt3)2Br group with its strongly
electron-donating PEt3 is a better π donor than the AuPPh3
group.
1
in the next section, this variation of La–1Lb band gap could
have a significant effect on the emissions of the complexes.
Emission Spectroscopy. All the pyrenyl complexes are
luminescent in the solid state and solution. The emission
quantum yields are given in Table 4. The solid-state emission
spectra of 1–9 display intense fluorescence at 360–500 nm and
weak phosphorescence at 600–750 nm (SF5). The gold com-
plexes are unstable in solution and slowly decompose to pyrene
and colloidal gold. A CH2Cl2 solution of 1 showed an intense
375 nm emission of pyrene4 within 20 min after preparation.
Because pyrene is much more emissive than the gold complex
(fluorescence quantum yield Φf ) 0.4),4 the emission spectrum
of 1 was dominated by the fluorescence of pyrene. Nonetheless,
the extent of decomposition was small for freshly prepared
solution, as its UV–vis spectrum did not show any peaks
ascribable to pyrene (see Figure 3) and weak phosphorescence
at 600-750 nm arising from the Au complex was observed
(phosphorescence quantum yield Φp ≈ 0.001). Changing the
solvent to THF did not stop the decomposition.
Complexes 2-4 are more stable and display fluorescence and
phosphorescence in degassed CH2Cl2 solutions (SF6). The
phosphorescence of the 1,6-diaurated 2 (Φp ) 3.9 × 10-3) and
4 (Φp ) 2.6 × 10-3) is stronger than that of 1. Surprisingly,
the Φp value of the 1,8-diaurated 3 (7.2 × 10-4) is the lowest
among all the Au complexes.
The platinum complexes 5–9 are stable in solution, and
emission spectra of degassed CH2Cl2 solutions of the compounds
are shown in Figure 6.
Photoexcitation of degassed CH2Cl2 solutions of 5–9 at 350
nm caused fluorescence at 370–500 nm and vibronic phospho-
rescence at 600–750 nm. As with the electronic absorption
spectra, the more atoms substituted on pyrene, the more red-
shifted the fluorescence band became. It is noted that the Φp
value increases only in the series 5 < 6 < 8 involving the 1,6-
platinated complexes. Analogous to the Au counterparts, the
Φp values of 1,8-platinated 7 and 9 are lower than for the 1,6-
Another consequence of the metal–ligand interactions is that
the mixing of metal and ligand orbitals lowers the local D2h
(24) Pariser, R. J. Chem. Phys. 1956, 24, 250.
(25) Creutz, C.; Newton, M. D.; Sutin, N. J. Photochem. Photobiol. A
1994, 82, 47.

6768 Organometallics, Vol. 26, No. 27, 2007
Heng et al.
1
diplatinated complexes and even the monoplatinated complex
1. While pyrene is known to exhibit excimeric emission around
460 nm at high concentration,2a–c no such emission was
observed in the spectra of the complexes even at a concentration
of 10-4 M.
3Lb state. In other words, formation of the La state and its
subsequent decays compete with the intersystem crossing from
3
1Lb to Lb and thus reduce the Φp value.
Conclusion
The fluorescence of pyrene and substituted pyrenes mainly
arises from radiative decay of the lowest energy singlet excited
state 1Lb. Intersystem crossing from the 1Lb state to its
In this work, nine new gold and platinum complexes of pyrene
have been synthesized. Our study showed that it is not possible
to attach more than two AuPPh3 and Pt(PEt3)2Br units to the
rim of pyrene. The electronic spectroscopy of the complexes
demonstrated the perturbation of metal ions on the electronic
structures of the pyrenyl ring. The perturbation causes red shifts
of the π f π* absorptions and intensifies the otherwise
3
corresponding triplet Lb state, probably mediated by another
triplet state, gives rise to the phosphorescence.26 Because of
the unfavorable Franck–Condon factor and the spin-forbidden
nature of the intersystem crossing, phosphorescence of pyrene
has not been observed under normal circumstances. With their
strong spin–orbit coupling, the Au and Pt ions could facilitate
the intersystem crossing by mixing the spin parentages of the
states. Indeed, the metalated pyrenes display phosphorescence,
indicating the presence of an intramolecular heavy atom effect
in the complexes. The effect is particularly obvious for the Pt
complexes, in which an increase in the Φp value is accompanied
by a decrease in the Φf value.
1
1
forbidden S0 f Lb transition. The energy gap between the
1
1La and Lb states can be varied by changing the number and
position of the metal ion in the ring. The small 1La–1Lb energy
gap of the 1,8-dimetalated complexes is suggested to be the
cause of their relatively weak phosphorescence.
Acknowledgment. The authors thank National University
of Singapore for financial support and Ms. G. K. Tan and
Professor Kop Lip Lin for assistance with the X-ray crystal
structure determination.
Expectedly, the Φp value of the dimetalated complexes is
higher than that of the mononuclear complexes. However, all
1,8-dimetalated complexes show anomalously low Φp values.
1
This could be related to the complete overlap of the La and
Supporting Information Available: Figures and tables giving
1H NMR and TOCSY spectra of 4, the crystal structure of 9,
molecular orbitals and LCAO coefficents of pyrene, solid-state
emission spectra of 1–9, and solution emission spectra of the gold
complexes and CIF files giving crystal data for 1-9. This material
is available free of charge via the Internet at http://pubs.acs.org
1Lb bands of the complexes, which implies a close proximity
of the 1La and 1Lb states. A fast equilibrium between the states
1
would reduce the population of the Lb state and, hence, the
(26) (a) Barradas, I.; Ferreira, J. A.; Thomaz, M. F. J. Chem. Soc.,
Faraday Trans. 2 1973, 388. (b) Jones, P. F.; Siegel, S. Chem. Phys. Lett.
1968, 2, 486. (c) Shimizu, Y.; Azumi, T. J. Phys. Chem. 1982, 86, 22.
OM700716P