Organometallics
NOTE
Figure 3. Partial KohnꢀSham orbital energy level diagram of model complex 20. Chloroform solvation is included with the polarizable continuum
model (PCM). Isodensity plots (contour level 0.03 au) of selected orbitals appear at right.
With gold substitution, this LUMOrHOMO promotion engages
in configuration interaction with at least one other state. For model
20, a transition to the gold-heavy LUMO+4 adds LMCT character.
We propose that this configuration interaction stabilizes the first
singlet excited state of 2 and lowers the first absorption energy.
These results add nuance to the effects of metalation on optical
spectra. We and others13ꢀ18,21,22,34 have shown that substitution
with gold(I) red-shifts the absorption spectra of aromatic mol-
ecules. These compounds gain triplet-state emission through the
heavy-atom effect. Gold also introduces empty 6s and 6p orbitals
that can accept electron density from aryl ligands. Configuration
interaction between the first excited singlet and states involving
these metal-based orbitals can contribute to red-shifted absorp-
tions, without making the carbonꢀgold bonds themselves chro-
mophoric. A similar red-shifting appears in the platinum(II)
σ-pyrenyls of Yip and co-workers,22 suggesting that the effect is
not specific to gold(I).
format. This material is available free of charge via the Internet at
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: tgray@case.edu.
’ ACKNOWLEDGMENT
The authors thank the National Science Foundation (grant
CHE-1057659 to T.G.G.) for support. T.G.G. is an Alfred P. Sloan
Foundation Fellow for 2009ꢀ2011. N.D. thanks the Republic of
Turkey for a graduate fellowship. The diffractometer at Case
Western Reserve was funded by NSF grant CHE-0541766.
’ REFERENCES
(1) Handbook of Oligo- and Polythiophenes; Fichou, D., Ed.; Wiley-
VCH: Weinheim, 1999.
(2) Gronowitz, S. Thiophene and Its Derivatives. In The Chemistry of
Heterocyclic Compounds; Weissberger, A., Taylor, E. C., Eds.; John Wiley
& Sons: New York, 1985ꢀ1992; Vol. 44, Parts 1ꢀ5.
(3) Gronowitz, S.; H€ornfeldt, A.-B. Thiophenes; Elsevier Academic
Press: San Diego, CA, 2004.
(4) Mishra, A.; Ma, C.-Q.; B€auerle, P. Chem. Rev. 2009, 109, 1141–1276.
(5) Geiger, F.; Stoldt, M.; Schweizer, H.; B€auerle, P.; Umbach, E.
Adv. Mater. 1993, 5, 922–925.
(6) Noma, N.; Tsuzuki, T.; Shirota, Y. Adv. Mater. 1995, 7, 647–648.
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Commun. 1989, 72, 381–384.
(8) Garnier, F.; Horowitz, G.; Peng, X.; Fichou, D. Adv. Mater. 1990,
2, 592–594.
(9) Fichou, D.; Nunzi, J.-M.; Charra, F.; Pfeffer, N. Adv. Mater. 1994,
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(10) Charra, F.; Lavie, M.-P.; Lorin, A.; Fichou, D. Synth. Met. 1994,
65, 13–17.
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’ EXPERIMENTAL SECTION
5,50-Bis[(triphenylphosphine)gold(I)]-2,20-bithiophene.
(Triphenylphosphine)gold(I) chloride was prepared using reported
methods.35 To a 50- mL round-bottom flask were added (PPh3)AuCl
(257 mg, 0.52 mmol), 2,20-bithiophene-5,50-diboronic acid bis(pinacol)
ester (110 mg, 0.26 mmol), and Cs2CO3 (345 mg, 1.06 mmol) under an
argon atmosphere. The reactants were suspended in 15 mL of dry,
degassed 2-propanol, and the resulting yellow mixture was stirred under
argon at 40 °C for 24 h. 2-Propanol was removed by rotary evaporation.
The remaining pale yellow residue was extracted into dry dichloro-
methane and filtered twice through Celite pads to yield a golden
solution. Dichloromethane was removed by rotary evaporation. Pentane
was used to triturate the resultant residue, and a yellow solid was
collected by filtration. Yield: 389 mg (69%). 31P{1H} NMR (CDCl3): δ
43.7 (s) ppm. Anal. Calcd for C44H34Au2P2S2: C, 48.81; H, 3.17. Found:
C, 48.90; H, 3.03.
’ ASSOCIATED CONTENT
(12) Arnason, J. T.; Chan, G. F. Q.; Wat, C. K.; Downum, K.;
Towers, G. H. N. Photochem. Photobiol. 1981, 33, 821–824.
(13) Partyka, D. V.; Zeller, M.; Hunter, A. D.; Gray, T. G. Angew.
Chem., Int. Ed. 2006, 45, 8188–8191.
S
Supporting Information. X-ray and computational details;
b
plot of the LUMO+4 of 20; crystallographic data for 2 in CIF
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dx.doi.org/10.1021/om2003267 |Organometallics 2011, 30, 5071–5074