ON THE ORIGIN OF MATRIX-ELEMENTS FOR ELECTRONIC EXCITATION (ENERGY) TRANSFER

The origin of electronic energy transfer (EET) between two chromophore s (D and A) is explored further for several molecular situations that may be encountered in experiment - namely, nonoverlapping active-space orbitals of the D and A chromophores, forbidden electronic excitation s for both chromophores, and an allowed and a forbidden electronic exc itation for the D and A chromophores, respectively. The theory is illu strated via the results of calculations of the EET matrix elements for model systems with both four-eight active-space electrons and all of the electrons included explicitly. In each case, it is found that any overlap contribution to these matrix elements is associated much more with charge-transfer and penetration terms rather than it is with the Dexter exchange integral. The calculated magnitude of the latter integ ral is always smaller than that of the Coulomb integral. (C) 1996 Amer ican Institute of Physics.