Enhanced absorption and fluorescence efficiency of silylethynyl-functionalized oligothiophenes and thieno[3,2-b]thiopahene

Silylethynyl-substituted oligothiophenes and thieno[3,2-b]thiophene were synthesized by the Sonogashira coupling reaction. The absorption and fluorescence maxima of these compounds shifted to longer wavelength, and they exhibited higher absorption coefficients and quantum yields than the corresponding unsubstituted molecules and tert-butylethynyl derivatives. From the DFT calculation, the energy band gap between HOMO and LUMO decreases by the introduction of a silicon atom. Thus, silyl groups can play important role in enhancing the quantum efficiency and decreasing the band-gap of chromophores. Hence, Silylethynyl group can serve as a highly efficient auxiliary for use in optical devices.