1214
Langmuir 1988, 4 , 1214-1216
(*CH3)z/DAcatalyst with ethylene produces the characteristic CPMAS spectral features of polyethylene1aJ8but undetectable (510%) changes in the relative intensities of Cp, Zr-*CH3, or Al-*CH3 resonances. This observation is in accord with a low percentage of active sites for ethylene polymerization, (i.e., a low percentage of Zr-*CH3 or AI-*CH3 functionalities undergoes insertion).Ia Efforts were also made to detect Zr(II1) speciesIg by ESR spectroscopy. Quantitative spin-counting measurementsz0 on 1/DA reveal that only ca. 1 X of the Zr sites exists as ESR-detectable Zr(II1) species after He treatment, (17) Hedden, D.; Marks, T. J., research in progress. (18) Van der Hart, D. L.; Perez, E. Macromolecules 1986, 19, 1902-1909. (19) (a) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-Zirconium and -Hafnium Compounds; Ellis Horwood: ChiChester, 1986; Chapter 13. (b) Bajgur, C. s.;Jones, s. B.; Peterson, J. L. Organometallics 1985, 4 , 1929-1936. (c) Schore, N. E.; Young, S. J.; Olmstead, M. M.; Hofmann, P. Organometallics 1983, 2, 1769-1780. (20) Wertz, J. E.; Bolton, J. R. Electron Spin Resonance; Chapman and Hall: New York, 1986; Appendix D.
and only ca. 3 X after Hztreatment. The present results demonstrate that highly active organozirconium catalysts can be generated on a Lewis acid surface that is also active for methyl group abstraction. Although an absolutely rigorous identification of the catalytically active sites as electrophilic, unsaturated cations (e.g., Cp,ZrR+; A among B and C) cannot be made, the data in combination with supported actinide’ and model solution studies6vz1offer increasingly persuasive support for this description.
Acknowledgment. This research was supported by the DOE under contract DE-FG02-86ER13511, D.H. thanks Dow Chemical Co. for a fellowship. We thank Dr. L. E. Schock for samples of several organozirconium compounds. Registry No. 1,12636-72-5;2,67108-80-9;3,81476-64-4;CHI, 74-82-8; C3Hs, 115-07-1;CzHs, 115-07-1;C3HB,74-98-6; CpzZr(CH,),, 115942-68-2;Al,03, 1344-28-1. (21) Lin, 2.; Marks, T. J. J. Am. Chem. SOC.1987, 109, 7979-7985.
Reversible Change in Alignment Mode of Nematic Liquid Crystals Regulated Photochemically by “Command Surfaces” Modified with an Azobenzene Monolayer Kunihiro Ichimura,” Yasuzo Suzuki, and Takahiro Seki Research I n s t i t u t e for Polymers and Textiles, 1-1-4 Higashi, Tsukuba, Ibaraki 305, J a p a n
Akira Hosokit Dainippon I n k and Chemicals, Inc., 35-58, 3-chome Sakashita, Itabashi-ku, Tokyo 174, J a p a n
Koso Aoki Toda Kogyo Corp., 4 - 1 -2 Funairi-Minami, N a k a - k u , Hiroshima 730, J a p a n Received February 26, 1988
Quartz plates were treated with an azobenzene compound having a triethoxysilyl group to modify the surface with the photosensitive unit and were employed for constructing a nematic liquid crystalline cell. The reversible change in the transmittance of the cell set between two crossed polarizers was induced by alternate exposure to UV and visible light, which resulted in the photoisomerization of the monolayered azobenzene.
Introduction The nature of substrate surface plays an essential role in liquid crystal (LC) alignment,’ and it has been illustrated that the modification of glass surface with monolayer lipid membrane causes homotropic alignment of LC molecules which are oriented parallel to the long axis of monolayered molecules substituted with long alkyl chains.z During the course of our investigation on photochromic LC systems, which possess potential value for optical information storage and display devices, we found that chiral nematic LCs composed of a nematic LC and an azobenzene +Present address: IC1 Japan Ltd., Japan Technical Center, 47 Wadai, Tsukuba, Ibaraki 300-42, Japan.
0743-7463/88/2404-1214$01.50/0
substituted with a chiral alkyl residue displayed a reversible change in the phase transition between the cholesteric and isotropic phase^.^ The photoinduced reversible phase change between nematic and isotropic phase has been reported recently in a system of a nematic LC containing an az~benzene.~ These phenomena involve the destruction of the mesophases by the drastic change in the molecular shape of the photoisomerized azobenzene units. These works inspired us to examine the possibility that the ho(1) Cognard, J. Mol. Cryst. Liq. Cryst., Suppl. Ser. 1982, 1, 1. (2) Hiltrop, K.; Stegemeyer, H. Ber. Bunsen-Ges. Phys. Chem. 1978, 82, 884.
(3) Ichimura, K.; Suzuki, Y.; Hosoki, A. in preparation. (4) Tazuke, S.; Kurihara, S.; Ikeda, T. Chem. Lett. 1987, 911.
0 1988 American Chemical Society
Langmuir, Vol. 4 , No. 5, 1988 1215
Letters
I 1
" 1
I
0
100
200
300
Time/sec
Figure 2. Reversible change of transmittance of He-Ne laser light through a liquid crystalline cell constructed with plate 2, which is set between two polarizers and exposed alternately to UV (365 nm) and visible (ca. 440 nm) light. I
I
1
300
400
500
I
Wavelength1 nm
with a mixture of C6AzOC5and ATS in a 1:9 molar ratio (plate 2, b) before and after 365-nm-light irradiation, respectively. 0 CH3-4CH&N=N
I b
+fCH&j!
CH~+CH&N=N+
