Incorporating Methyl and Phenyl Substituted Stannylene Units into Oligosilanes. The Influence on Optical Absorption Properties

Molecules containing catenated heavy group 14 atoms are known to exhibit the interesting property of σ-bond electron delocalization. While this is well studied for oligo- and polysilanes the current paper addresses the UV-absorption properties of small tin containing oligosilanes in order to evaluate the effects of Sn–Si and Sn–Sn bonds as well as the results of substituent exchange from methyl to phenyl groups. The new stannasilanes were compared to previously investigated oligosilanes of equal chain lengths and substituent pattern. Replacing the central SiMe(2) group in a pentasilane by a SnMe(2) unit caused a bathochromic shift of the low-energy band (λ(max) = 260 nm) of 14 nm in the UV spectrum. If, instead of a SnMe(2,) a SnPh(2) unit is incorporated, the bathochromic shift of 33 nm is substantially larger. Keeping the SnMe(2) unit and replacing the two central silicon with tin atoms causes shift of the respective band (λ = 286 nm) some 26 nm to the red. A similar approach for hexasilanes where the model oligosilane [(Me(3)Si)(3)Si](2)(SiMe(2))(2) (λ(max) = 253 nm) was modified in a way that the central tetramethyldisilanylene unit was exchanged for a tetraphenyldistannanylene caused a 50 nm bathochromic shift to a low-energy band with λ(max) = 303 nm.