INTERSYSTEM CROSSING IN MOLECULES OF AROMATIC-COMPOUNDS WITH THEIR HETEROATOM ON THE C-2 SYMMETRY AXIS - ACRIDINE

The electronic spectrum and matrix elements U-mp Of spin-orbit interac tions, mixing electronic states of different types (n pi and pi pi*) in an acridine (AC) molecule, are calculated in an INDO/S approximatio n. In planar molecules, the np(z) AO being on the C-2=C-z axis, the ra te constant values K-isc are found to differ by three orders of magnit ude depending upon the symmetry of the states Gamma(pi pi) = A(1) or B-2 (the elements U-mp are 10 and 0.3 cm(-1), respectively). The regul arity of U-mp variation, as the nuclear configuration of the molecule changes from planar to non-planar (in ''butterfly'' or ''arm-chair'' f orms), is established. Scheme I of electron energy levels and deactiva tion of the S-1(pi pi) state of the AC molecule is suggested instead of the Scheme K from previous studies. In Scheme I the main channel of deactivation results from the fast conversion S-1 squiggley arrow poi nting right T-3(K-isc = K-4 = 5 x 10(11)s(-1)) from the state (1)A(1)( pi pi) to B-3(1)(n pi*).