A DFT study of electronic structures of thiophene-based organosilicon compounds

Three density functionals, B3LYP, BB95 and MPWB1K, were adopted to investigate the geometries and spectral properties of bis(3-cyano-thienyl)-dimethylsilane, bis(2-thienyl)dimethylsilane and bis(3-thienyl)dimethylsilane, respectively. The best agreement between theoretical and experimental geometries is in the MPWB1K results; the next is in the B3LYP ones, followed by the BB95 ones. MPWB1K functionals can well predict the characteristic frequencies of most vibrational modes, except for the silylmethyl C-H and the CN bond stretching vibration. BB95 functionals can give the best electronic absorption spectra, followed by MPWB1K and B3LYP one. The CN substitution as well as the connection way between the silylene and thienyl unit exerts the significant effects on the silylmethyl C-H in-plane rocking, thienyl C-H out-of-plane and bridging C-Si-C bond asymmetry stretching vibration. The most obvious difference of the electronic absorption spectra among 1, 2 and 3 is that 1 shows three strong peaks, while 2 as well as 3 shows only one.