Abstract: The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of novel organic dye sensitizers JK16 and JK17 were studied by density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectra were investigated by time dependent DFT (TDDFT). Features of the electronic absorption spectra in the visible and near-UV regions were assigned based on a qualitative agreement between TDDFT calculations and experiments. The absorption bands are assigned to π→π* transitions. Calculated results suggest that the three excited states with the lowest excited energies in JK16 and JK17 are due to photoinduced electron transfer processes. The dimethylfluorenyl amino benzo [b] thiophene groups are the main chromophores that contribute toward the sensitization of photo-to-current conversion processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizers JK16 and JK17 is due to an electron injection process from excited dyes to the semiconductor’s conduction band. The role of vinylene in geometries, electronic structures, and spectral properties were analyzed in a comparative study of JK16 and JK17.

Key words: Dye sensitizer, Electronic structure, Density functional theory, Absorption spectrum