Modifiziertes PPP-Verfahren zur Berechnung schwacher molekülkomplexe. Einfluss der struktur auf die UV-Spektren von TCNE-Komplexen phenylsubstituierter Äthylene

The CT-spectra of complexes of phenyl-substituted ethylenes, with TCNE as acceptor in various arrangements, are calculated. Conclusions about the structure of such weak complexes in solution may be drawn from a comparison with experimental electronic spectra. Within the framework of this static structural model the two observed CT-bands are explained by absorption from preferred arrangements; the acceptor is arranged about the double bond (first CT-band) or about one of the benzene rings (second CT-band). The calculations are performed by a modified PPP method. The good agreement with experimental results of both complexes and component molecules is mainly due to the unaltered intramolecular parameters in the complex and to the increased intermolecular electron-repulsion integrals (a factor of 1.5 was added to the Mataga—Nishimoto formula).