Electronic structures of linear germane-silane copolymer radical anions [Me(SiMe2)n(GeMe2)nMe]-(n=3-7) in ground and low-lying excited states.: A theoretical study

The electronic structures for the ground and low-lying excited states of Linear germane-silane (Ge/Si) copolymer radical anions have been determined by means of the semi-empirical PM3-CI method. The permethylgermane-silane radical anion [Me(SiMe2)(n)(GeMe2)(n)Me](-) (n = 3-7) was chosen as a model compound of Ge/Si copolymer radical anion. In all Ge/Si copolymers, an unpaired electron is only localized on the Ge-site, although a Si atom binding to Ge atom has a slight spin density. The spin orbital is sigma* type composed of 4p orbitals in Ge atoms. The CI calculation predicted that the radical anions have an absorption band in IR region. The excitation energy for IR band is slightly blue-shifted as a function of number of chain atoms and the oscillator strength is largely increased. The band structure for the radical anions is discussed on the basis of theoretical results. (C) 1997 Elsevier Science S.A.