7560
J. Am. Chem. SOC.1992,114, 7560-7561
Cubic Nonlinear Optical Properties of Group 4 Metallocene Halide and Acetylide Complexes Lori K. Myers,+ Charles Langhoff,t and Mark E. Thompson*$+ Department of Chemistry, Princeton University Princeton, New Jersey 08544 Central Research, I776 Building Dow Chemical Corporation, Midland, Michigan 48674 Received March 13, 1992
Third-order nonlinear optical (NLO) materials are of interest because they are potentially useful in a wide range of optical devices.' The study of molecular materials for third-order nonlinear optics has focused primarily on organic monomers and polymers.'"Y2 Most organic materials studied have delocalized x systems which are responsible for their large nonresonant third-order NLO susceptibilities. Recent reports of good NLO properties for group 10 metal acetylide oligomers suggest that organometallic complexes may be good candidates for NLO study.3 Electron delocalization in these organometallic complexes is achieved by strong metal to ligand charge transfer between the filled metal orbitals and vacant acetylide a* orbitals. A limited amount of data exists concerning the third-order NLO properties of other organometallic complexe~.~Herein, we report on a systematic study of the third-order nonlinear optical properties of group 4 metallocene complexes, Cp2MX2(M = Ti, Zr, Hf; X = F, Cl, Br, GCC6H5). Group 4 metallocene complexes are formally do, 16-electron complexes; therefore, electron delocalization cannot take place through a MLCT process, as in the group 10 complexes discussed above. Theoretical calculations show that the LUMO in these complexes is primarily a metal-centered orbital which lies in the MX2 plane, as shown in the Figure l.5J5b Strong ?r donation and ligand to metal charge transfer (LMCT) involving this vacant metal orbital are observed for amide and alkoxide ligands;6 spectroscopic evidence suggests LMCT processes may be important in acetylide complexes as well.7 This LMCT may lead to mixing between the x systems of the acetylide ligands to produce an extended network, leading to materials with good third-order NLO properties. Group 4 metallocene complexes were purchased or synthesized using literature procedures.' The third-order nonlinear optical + Princeton University.
* Dow Chemical Corporation.
(1) (a) Prasad, P. N.; Williams, D. J. Nonlinear Optical Effects in Molecules and Polymers; John Wiley and Sons, Inc.: New York, 1991. (b) Ulrich, D. R. Mol. Cryst. Liq. Cryst. 1990,189,3. (c) Abraham, E.; Seaton, C. T.; Smith, S. D. Sei. Am. 1983, 284, No. 2, 85. (d) Pepper, D. M. Sei. Am. 1986, 254, No. 1, 74. (2) For example, see: (a) Chemla, D. S.; Zyss, T. Nonlinear Optical Properties of Organic Molecules and Crystals; Academic Press, Inc.: Orlando, FL, 1987; Vol. 2. (b) Organic Materials for Non-Linear Optics; Hann, R. A., Bloor, D., Eds.; Royal Society of Chemistry: London, 1989. (c) Organic Materials for Nonlinear Optics; Hann, R. A., Bloor, D., Eds.; Royal Society of Chemistry: London, 1991. (3) (a) Frazier, C. C.; Guha, S.; Chen, W. P.; Cockerham, M. P.; Porter, P. L.; Chauchard, E. A.; Lee, C. H. Polymer 1987,28,553. (b) Frazier, C. C.; Chauchard, E. A.; Cockerham, M. P.; Porter, P. L. Mater. Res. Symp. Proc. 1988, 109, 323. (c) Guha, S.; Frazier, C. C.; Porter, P. L.; Kang, K.; Finberg, S. E. Opt. Lett. 1989,14,952. (d) Blau, W. J.; Byme, H. J.; Cardin, D. J.; Davey, A. P. J. Muter. Chem. 1991, I , 245. (4) (a) Ghosal, S.; Samoc, M.; Prasad, P. N.; Tufariello, J. J. J. Phys. Chem. 1990,94,2847. (b) Cheng, L.-T.; Tam, W.; Meredith, G. R.; Marder, S. R. Mol. Cryst. Liq. Cryst. 1990, 189, 137. (c) Calabrese, J. C.; Cheng, L.-T.; Green, J. C.; Marder, S. R.; Tam, W. J. Am. Chem. Soc. 1991,113, 7227. (d) Kafafi, Z. H.; Lindle, C. S.; Weisbecker, C. S.; Bartoli, F. J.; Shirk, J. S.; Yoon, T. H.; Kim, 0.-K. Chem. Phys. Lett. 1991,179,79. (e) Winter, C. S.; Oliver, S. N.; Rush, J. D.; Hill, C. A. S.; Underhill, A. E. J. Appl. Phys. 1992,71,512. (f) For a recent review, see: Nalwa, H. S. Appl. Organomet. Chem. 1991,5, 349. ( 5 ) Bruce, M. R. M.; Kenter, A.; Tyler, D. R. J. Am. Chem. Soc. 1984, 106,639. Lauher, J. W.; Hoffmann, R. J. Am. Chem. SOC.1976,98,1729. (6) (a) Vann Bynum, R.; Hunter, W. E.; Rogers, R. D.; Atwood, J. L. Znorg. Chem. 1980, 19, 2368. (b) Huffman, J. C.; Moloy, K. G.; Marsella, J. A.; Caulton, K. G. J. Am. Chem. Soc. 1980,102, 3009. (7) Sebald, A.; Fritz, P.; Wrackmeyer, B. Spectrochim. Acta 1985,41A, 1405.
0002-7863/92/ 1514-7560$03.00/0
Figure 1. Structure of Cp2MX2(side view) (a); proposed Cp2MX2compounds, M = Ti, Zr, Hf (top view) (b).
LUMO for
Table I. Third-Order NLO Coefficients Measured by Third Harmonic Generationu "pd (&!lax, nm) Cp',TiF, (324) Cp',TiCl, (394) Cp',TiBr, (428) Cp2ZrC12(338) Cp,Ti( -4), (4 10) Cp,Zr(C=C4)2 (390) CP,Hf(C=C4)2 (390)
d"d HC=C4
solvent
CHC13 CHC13 CHCl3 CHCl3 THF
THF THF THF
y (
esu)b
