TD-DFT study on some triphenylamine-based organic dyes as photosensitizers in DSSCs

Geometrical and molecular electronic structure calculations on a series of metal free organic dyes based on triphenylamine (TPA) moiety have been performed using the TD-DFT methods. The B3LYP/6-31G, B3LYP/6-31G(d,p), M06-HF/6-31G(d,p) and WB97XD/6-31G(d,p) levels of theory have been utilized to predict the relationships between chemical structure and theoretically calculated molecular electronic properties of the studied dyes which may help in optimizing the properties of TPA-based photosensitizers in DSSCs. The solvation process of these dyes has been taken into account by means of the polarizable continuum model. The light harvesting efficiency, the free energy change for the electron injection process to the surface of TiO2 nanocrystalline semiconductor and the open circuit potential are calculated using all of these methods in different media. Significant charge transfer character of the HOMO -> LUMO electronic transition which dominates the S-0 -> S-1 vertical excitation in these systems facilitates the electron transfer process to the surface of TiO2. The results of the present computations are reported and discussed.