Ab-initio calculations of nano-sized (∼1 nm) amorphous-TiO2 cluster and dye molecules (N3 and N719) have been carried out. Optimized structures of amorphous cluster and dye molecules have been obtained via molecular dynamics (MD) and density functional theory (DFT) calculations, respectively. The lowest excited state energies of the TiO2 cluster and the dye molecules have been obtained using time-dependent DFT. The calculations show that HOMO-LUMO gap and singlet-singlet excited state energies for amorphous cluster are very similar to that of a crystalline TiO2 cluster. Our calculations also show that the energy levels of the molecular dyes are well aligned with those of the amorphous cluster. © 2013 Elsevier B.V. All rights reserved.