Donor-enhanced bridge effect on the electronic properties of triphenylamine based dyes: density functional theory investigations.

The geometries have been optimized by using density functional theory. The highest occupied molecular orbitals are delocalized on triphenylamine moiety while lowest unoccupied molecular orbital are localized on anchoring group. Intramolecular charge transfer has been observed from highest occupied molecular orbitals to lowest unoccupied molecular orbital. By replacing the vinyl hydrogens with methoxy as well as one benzene ring as bridge leads to a raised energy gap while extending the bridge decreases the energy gap compared to parent molecule. The HOMO energies bump up by extending the bridge. The LUMO energies of all the investigated dyes are above the conduction band of TiO(2) and HOMOs are below the redox couple except 3c. The distortion between anchoring group and triphenylamine can hamper the recombination reaction.