The molecular geometries of four 2,4-dimethyl-7-amino-1,8-naphthyridinederivatives were optimized with B3LYP/6-31G(d) method. The energies of theirfrontier molecular orbitals and the molecular structures were investigatedtheoretically. The theoretical electronic spectra were calculated with TD-DFT ingas phase, PCM-TD-B3LYP/6-31+G(d) and semiempirical ZINDO in CH2Cl2 solution. Theinfluences of solvent model and calculation methods on the electronic absorptionspectra were also probed. The calculated results show that delocalized π bondsexist in the four 1,8-naphthyridine derivatives, and their energy gaps (ΔE)between HOMO and LUMO are relatively small. The variation in their ΔE valuesgives a consistent trend with that of their electronic absorption with λmax.Theoretical spectra achieved prove that their absorptions are red-shifted whenthe delocalization of π electrons is enhanced or the capability to donateelectron by a substituted group is increased. The maximum absorption peaks of thefour derivatives originate from π(HOMO)→π*(LUMO) transition. The spectracalculated at the PCM-B3LYP/6-31+G(d) level have little difference fromexperimental results: the differences in wavelength are 2.6, 10.3, 5.3 and 6.9nm, whereas those in energies are 0.03, 0.09, 0.04 and 0.08 eV, respectively. Theobtained results suggest that electronic spectra calculated by TD-DFT on thebases of geometries optimized with B3LYP/6-31(d) are in agreement withexperimental ones, and can account for the different spectroscopic properties ofthe four 1,8-naphthyridine derivatives.spectra; TD-DFT