DFT and TD-DFT studies on osmacycle dyes with tunable photoelectronic properties for solar cells

B3LYP and CAM-B3LYP functionals have been used to determine structures, electronic and optical properties of osmium-bridged tricyclic aromatic compounds. Calculations show that the optical properties and charge separation features of these osmacycle derivatives can be well modified by incorporating different pi-bridge groups. In particular, the newly designed osmacycle dyes 5 and 6 by embedding thiophene and thienothiophene bridge units to osmium polycyclic aromatic system show very strong and broad adsorptions in the whole visible region and excellent charge separation in the first excited state of (1)(pi pi*) from the hightest occupied molecular orbital to the lowest unoccupied molecular orbital excitation. Furthermore, the predicted relatively high light harvesting efficiency and large driving force for electron injection suggest that they are quite promising for design of high-performance dye-sensitized solar cells.