Bithiophenesilane Dendrimers: Synthesis and Thermal and Optical Properties

Abstract

For the first time the synthesis and thermal and optical properties of a number of first-generation bithiophenesilane dendrimers with alkyl end groups, namely, tris{5‘-[methylbis(5‘-hexyl-2,2‘-bithienyl-5-yl)silyl]-2,2‘-bithienyl-5-yl}methylsilane (1), tris{5‘-[methylbis(5-hexyl-2-thienyl)silyl]-2,2‘-bithienyl-5-yl}methylsilane (2), and tris{5‘-[methylbis(5-ethyl-2-thienyl)silyl]-2,2‘-bithienyl-5-yl}methylsilane (3), are described. The influence of the dendritic architecture on the thermal and optical properties was investigated and compared to those of the linear and branched bithiophenesilanes. The results obtained showed a significant increase of the fluorescence quantum yield Q with an increasing number of bithiophenesilane fragments being a constituent part of the dendritic molecule. It reaches 30% for dendrimer 1 with nine such fragments as compared to Q = 6% for 5,5‘-bis(trimethylsilyl)-2,2‘-bithiophene and Q = 1.8% for 5-hexyl-2,2‘-bithiophene. This effect was explained by the impact of the specific dendritic molecular structure on the fluorescence efficiency. It is noteworthy that the emission wavelength was maintained at the same violet-blue region (380−385 nm) for all the compounds under consideration. Tuning the terminal alkyl chains of the dendrimers allowed creating stable amorphous materials, in contrast to the dendrimer without alkyl chains, tris{5‘-[methylbis(2-thienyl)silyl]-2,2‘-bithienyl-5-yl}methylsilane (4), or model bithiophenesilanes, all of which tend to crystallize under different conditions. Bearing in mind the high thermal stability and excellent solubility of the bithiophenesilane dendrimers, these materials present a new promising class of violet-blue emitters for photonics, organic electronics, and other applications.