Organometallics 2002, 21, 2343-2346
2343
The 3(ππ*) Emission of Cy3PAu(CtC)nAuPCy3 (n ) 3, 4). Effect of Chain Length upon Acetylenic 3(ππ*) Emission Wei Lu, Hai-Feng Xiang, Nianyong Zhu, and Chi-Ming Che* Department of Chemistry and the HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China Received December 27, 2001 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.
Chart 1
While rigid, π-conjugated sp carbon chains have been incorporated as building blocks into myriads of electronic optics (molecular wires, NLOs),1 spectroscopic investigations, especially regarding electronic transitions associated with (CtC)n2- chains, are sparse.1g,2-7 Fundamental studies on the spectroscopic properties of oligoynes will facilitate the design of advanced optoelectronic materials; for example, the triplet emission from (CtC)n2- chains could be of great interest for OLED applications8 and characterization of one-dimensional 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, Et Si, (η5∞ 3 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 the lowest-energy acetylenic 3(ππ*) excited states ac-
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 acetylenic 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 synthesized. 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 unprecedented dinuclear gold(I) complexes bridged by C62- and C82- rods. Although the cyclohexyl groups of the phosphine 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 explored. 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 unit. The two-coordinate Au atoms are bridged by a virtually linear C62- 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 welldocumented by Gladysz,4 Bruce,11 Lapinte,12 and Akita.13 The closest intramolecular nonbonded contacts
* To whom correspondence should be addressed. Fax: (852) 2857 1586. E-mail:
[email protected]. (1) Recent reviews: (a) Manna, J.; John, 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.; Johnson, 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.; Jaeger, 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. (6) Vila, F.; Borowski, P.; Jordan, 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
Figure 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).
Figure 2. UV absorption and normalized emission spectra for 3 and 4 in CH2Cl2 at 298 K.
in this structure are Au(1)-H(5) (1.80 Å) and Au(1)H(17) (1.92 Å). The solvated CH2Cl2 molecule is disordered over an inversion center ((1,0,1) for the reported asymmetric unit). Unlike the lower homologues,14 no close C-H‚‚‚π(CtC) distances ( 2σ(I)), wR2 ) 0.12 for GOF(F2) ) 0.95.
Acknowledgment. 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). Supporting Information Available: Tables giving crystallographic data for 3‚CH2Cl2. This material is available free of charge via the Internet at http://pubs.acs.org. OM011087F
