Synthesis, characterization and density functional theory investigations of the electronic, photophysical and charge transfer properties of donor-bridge-acceptor triaminopyrazolo[1,5-a]pyrimidine dyes.

We have synthesized multifunctional dyes 3-(4-methyl-phenylazo)-6-(4-nitro-phenylazo)-2,5,7-triaminopyrazolo[1,5-a]pyrimidine (4a) and 3-(4-methyl-phenylazo)-6-(4-acetyl-phenylazo)-2,5,7-triaminopyrazolo[1,5-a]pyrimidine (4b), then characterized by IR, (1)H NMR and (13)C NMR techniques. The ground state geometries have been computed by using density functional theory at B3LYP/6-31G(*) level of theory. The absorption spectra have been calculated by using time dependent density functional theory with and without solvent. The highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are delocalized and localized on throughout the backbone, respectively. Solvent also play important role towards elevating the dipole moment. Significant red shift in absorption wavelengths have been observed in methanol compared to without solvent. We discussed the electron injection, electronic coupling constant and light harvesting efficiency.