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-naphtha limide are analyzed in terms of the number of contributing electronic trans itions and their polarization. The experimental results are supported by se miempirical INDO/S calculations. It is demonstrated that the strongly allow ed, pi --> pi* naphthalene transition of the 1,8-naphthalimide chromophore located at 231 nm is perfectly suited for absolute configuration assignment s of amine derivatives on the basis of the bichromophoric exciton coupling. Both degenerate (bis-1,8-naphthalimide) and nondegenerate (1,8-naphthalimi de-phthalimide, 1,8-naphthalimide-phenyl, or 1,8-naphthalimide-benzoate) co uplings were studied. In the latter case, the sign of the exciton Cotton ef fect was opposite to the sign of the degenerate exciton Cotton effect for t he same absolute configuration. An extension of the application of the exci ton coupling to the 264 nm pi --> pi* transition of 1,9-anthraimide is also shown.