Mini-Symposium, Paper M6

Density Functional calculations with Configuration Interaction for excited states of organic donor-acceptor systems

Andreas Parusel
Institute for Theoretical Chemistry and Radiation Chemistry
University of Vienna
Althanstr. 14, A-1090 Wien

Intramolecular electron transfer processes are discussed by means of the new Density Functional Theory based method with single configuration interaction for description of the excited states (DFT/SCI) [1]. This theory represents a reliable and fast method especially for large-scale systems [2].

The results on 4-(N,N-Dimethylamino)-benzonitrile (DMABN), a typical donor acceptor system with unusual emission properties, are presented. In polar solvents, a red-shifted fluorescence is observed originating from a highly polar charge transfer state which arises in addition to the emission from the primary excited (PE) state. The experimentally observed dual fluorescence is commonly explained by the so-called twisted intramolecular charge transfer (TICT) hypothesis [3]. The TICT state formed from the PE state is characterized by electron transfer from the donor to the acceptor group and by mutually perpendicular orientation of these subunits. Subsequently, the reliability of the DFT/SCI method has been tested for a series of DA-compounds.

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[2] A.B.J. Parusel, G. Köhler, S. Grimme, J. Phys. Chem. A, 1998, 102, 6297.
[3] Z.R. Grabowski, K. Rotkiewicz, A. Siemiarczuk, D.J. Cowley, W. Baumann, Nouv. J. Chim., 1979, 3, 443.