Characterization of persistent intermediates generated upon inclusion of 1,1-diarylethylenes within CaY zeolite: Spectroscopy and product studies

被引:10
作者
Lakshminarasimhan, P [1 ]
Thomas, KJ
Brancaleon, L
Wood, PD
Johnston, LJ
Ramamurthy, V
机构
[1] Tulane Univ, Dept Chem, New Orleans, LA 70118 USA
[2] Natl Res Council Canada, Steacie Inst Mol Sci, Ottawa, ON K1A 0R6, Canada
关键词
D O I
10.1021/jp990913j
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Inclusion of 1,1-diarylethylenes within activated CaY results in the formation of colored samples that are stable for prolonged periods. For example, diphenylethylene generates a green color within CaY. Two reactive intermediates have been shown to be responsible for this color. The species with the short wavelength (lambda(max) 410 nm) absorption has been established to be the diphenylmethyl cation. The identity of the species with the long wavelength ((lambda(max) 620 nm) absorption has been debated for three decades. We establish that the diarylethylene radical cation is not responsible for the long wavelength absorption. Laser flash photolysis studies show that a number of diarylethylene radical cations have a characteristic absorption in the 400 nm region in both solution and in NaY zeolite. The absence of this absorption for diarylethylene-CaY samples unequivocally eliminates the possibility that these radical cations are responsible for color formation. This is substantiated by the fact that a number of 2-methyl-substituted 1,1-diarylethylenes generate only the short wavelength cation absorption upon inclusion in CaY; radical cation formation would be expected to be equally facile for the methyl-substituted derivatives. Our results suggest that an allylic dimer cation is the most likely source of the long wavelength ((lambda(max) 620 nm) absorption within CaY.
引用
收藏
页码:9247 / 9254
页数:8
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