Abstract: The excited-state intramolecular proton transfer tautomerism reaction of 6-methyl-4-hydroxy pyri-midine monomers and dimmers was investigated by the ab initio method with the self-consistent reaction field(SCRF) with Tomas's polarized continuum mode(PCM) and CIS theories at HF level on the basis of 6-311+G* and 6-31G basis set. By studying the potential energy surface, it was found that the monomer's ground-state proton transfer process together with the excited-state proton transfer process is a molecular system of four energy level, but dimmers were not, which can be used to explain the fact that UV-visible absorption and fluorescence spectra of monomer and dimers all corresponded to quinoid. The UV-visible absorption and fluorescence spectra of 6-methyl-4- hydroxy pyrimidine monomers and dimers under a solvent effect condition were also investigated with hybrid time-dependent density functional theory(TD-DFT) at MPW1PW91 basis set.

Key words: 6-Methyl-4-hydroxy pyrimidine, Excited state, Proton transfer, Spectroscopy