Oligothienyl catenated germanes and silanes: synthesis, structure, and properties

The synthesis of two new groups of oligothienyl catenated silanes and germanes, Me₅M₂Th_n (1a-b), Me₅M₂Th_nM₂Me5 (2a-c) (terminal), and Th_nM₂Me₄Th_n (За-d) (internal) (M = Si, Ge; n = 2,3; Th = 2- or 2,5-thienyl), is reported. The study of their structural parameters as well as of their spectral (NMR), electrochemical (CV) and optical (UV/vis absorbance, luminescence) properties has been performed in detail; in addition, the unexpected compound [Th₂Si2Me₄Th]2 (3a') is also studied. Theoretical investigations have been performed for model compounds in order to establish structure-property relationships. The molecular structures of 2a (Me₅Si2Th₂Si₂Me5), 2b (Me₅Ge2Th₂Ge₂Me5), 3a (Th₂Si₂Me₄Th2) and 3b (Th₂Ge2Me₄Th2) have been investigated by X-ray diffraction analysis. An effective conjugation with flattening of both Th planes in terminal 2a and 2b was observed. The main trends in the dependence of the optical and electrochemical properties on the structural parameters have been established. All of the compounds studied exhibit a strong emission within the 378-563 nm range, and the maximal quantum yield (up to 77%) is observed for the Si derivative 3a'. For the majority of the compounds, the quantum yields (20-30%) are significantly larger than for 2,2'-bi- and 2,2':5',5"-terthiophenes. Due to their good emission properties, these compounds could be used to develop new materials with specific spectral properties