Abstract
π-Electron density of 2-phenylphthalimidine and its derivatives was calculated by the simp1e linear combination of atomic orbitals (LCAO) molecular orbital method and its relation to fluorescence was examined. In 2-phenylphthalimidines, contribution of ionic resonance structure increases in excited state than in ground state. For 2-phenylphthal-imidines to produce fluorescence, π-electron distribution must incline towards the phenyl group from phthalimidine nucleus in transition from the ground state to excited state. If this inclination is reverse or when such inclination is absent, the compound does not show any fluorescence. The calculated value of the wave length obtained from the energy difference between first excited state and ground state in π-system was in parallel with the observed values of the maximum wave length of fluorescence of 2-phenylphthalimidines was due to π*-π transition.
