Studies of the circular dichroism spectra of dissymmetric Schiff-bases by means of the exciton chirality method

The circular dichroism spectra of some dissymmetrical Schiff-bases derived from condensation of 2 mol salicylaldehyde with 1 mol of a chiral diamine a re analyzed in terms of a simple conformational model taking the angle betw een the aromatic chromophores as a variable. The rotatory strengths of the pi-->pi* transitions are calculated with AM1 molecular orbitals in combinat ion with the dipole-coupling approximation.. Calculated CD curves are found to be in reasonable agreement with the experimental CD spectra. Difference s in the CD spectra of the Schiff-bases are discussed in relation to variat ion of the theoretical CD curve of ethylenebis(salicylideneimine) as a func tion of conformation. (C) 2000 Elsevier Science Ltd. All rights reserved.