AM1 method was used to optimize the molecular structure of bispyrimidine, bisbarbituric acid and the entity formed from bispyrimidine and bisbarbituric acid in a 1:1 molecular ratio through multiple inter-molecular hydrogen bonds. Hydrogen bonding energy was obtained. On the basis of above geometry, the INDO-CI method was used to calculate and discuss the UV-vis spectra of the three molecules. The results are in good agreement with experimental ones. It is concluded that multiple hydrogen bonds lead to the formation of new supramolecular aggregates. The interaction principles of hydrogen bonds in the format procession of supramolecular aggregates are also discussed.

Key words: PYRIMIDINE P, HYDROGEN BONDS, ULTRAVIOLET SPECTROPHOTOMETRY, AB INITIO CALCULATION