1,8-naphthalimides as stereochemical probes for chiral amines:: A study of electronic transitions and exciton coupling

The absorption and magnetic circular dichroism (MCD) spectra of 1,8-naphthalimide are analyzed in terms of the number of contributing electronic transitions and their polarization. The experimental results are supported by semiempirical INDO/S calculations. It is demonstrated that the strongly allowed, pi --> pi* naphthalene transition of the 1,8-naphthalimide chromophore located at 231 nm is perfectly suited for absolute configuration assignments of amine derivatives on the basis of the bichromophoric exciton coupling. Both degenerate (bis-1,8-naphthalimide) and nondegenerate (1,8-naphthalimide-phthalimide, 1,8-naphthalimide-phenyl, or 1,8-naphthalimide-benzoate) couplings were studied. In the latter case, the sign of the exciton Cotton effect was opposite to the sign of the degenerate exciton Cotton effect for the same absolute configuration. An extension of the application of the exciton coupling to the 264 nm pi --> pi* transition of 1,9-anthraimide is also shown.