Circular dichroism of donor-acceptor cyclophanes: (4R(p);12R(p))- and (4S(p);12R(p))-12,15-dimethoxy[2.2]paracyclophane-4,7-dicarboxylic acid derivatives.
The electronic circular dichroism (CD) spectra were recorded for three diastereomeric eclipsed-staggered pairs of charge-transfer cyclophanes with different substituents, i.e., (4R(p);12R(p))- and (4S(p);12R(p))-12,15-dimethoxy[2.2]paracyclophane-4,7-dicarboxylic acid derivatives (1a-c and 2a-c, where a, b, and c denote methyl ester, carboxylic acid, and carboxylate, respectively). The effects of altering the donor-acceptor interaction between the π systems on the chiroptical properties were experimentally investigated. The anisotropy (g) factors of eclipsed species 2 were not significantly affected by the sort of substituent, while staggered 1 behaved in a significantly different way in CD spectra depending on the charge, affording contrasting CD profiles for neutral a/b versus anionic c. This study provides not only the novel insights into the planar chirality of substituted [2.2]paracyclophanes but also a basis for the potential application of such dramatic CD spectral difference between the acid-base pair to the chiroptical pH-sensors.
Department of Applied Chemistry, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan.
Takahiro
T
Furo
Tadashi
T
Mori
Yoshihisa
Y
Inoue