DFT studies of the photophysical properties of fluorescent and semiconductor polycyclic benzimidazole derivatives.

The photophysical and electrochemical properties of eleven polycyclic benzimidazole fused organic pigments (four based on phthalic anhydride, four based on naphthalic anhydride and three based naphthalene tetra carboxylic acid dianhydride) were investigated using density functional theory and time dependent density functional theory methods (B3LYP/6-31G(d) and M06/6-31G(d)). The predicted geometries are comparable using both functionals. The electrochemical properties are in good agreement with the experimental results. However, the experimental absorption-emission properties are closer to the values computed using the M06/6-31G(d) method. Both the methods perform equally well in explaining the intramolecular charge transfer characteristics. This work can help to understand the modern age functional materials at molecular level and to design new molecules.