Electronic spectra, and DFT calculations of some triazolo [1,5-a]pyrimidine derivatives

Ground state properties of 5,7-diphenyl-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine, compound 1, and its derivatives are investiga¬ted experimentally and theoretically in 1,4-Dioxane (Dioxane) and N,N- Dimethylformamide (DMF). The calculations show that all the studied compounds 1-7 are non-planar as indicated from the values of the dihedral angles, resulting in a significant impact on the electronic and structural properties. The ground state properties of compounds 1-7 at B3LYP/6-311G(df,pd) show that compound 2,which contains the nitro group, has the lowest ELUMO and Eg, indicating highest reactivity. Compound 7 is found to have the highest polarity. The observed UV spectra in Dioxane and DMF of compounds 1, 2, 4, 5 and 6 exhibit 2 bands in both solvents, compound 3 exhibits 4 bands in Dioxane and 3 bands in DMF, while compound 7 exhibits 3 bands in both solvents. The difference in the spectral features of the studied compounds can be attributed to the extent of the hyper conjugation of the triazolo[1,5-a]pyrimidine moiety and the nature of the substituent of the two phenyl groups. Band maxima (?max) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. The theoretical spectra computed at TD-B3LYP/6-311G(d,p) in gas phase, Dioxane and DMF nicely reproduce the observed spectra.