SOLVENT-INDUCED CHANGES IN THE PHOTOPHYSICAL PROPERTIES OF N-ALKYLPHTHALIMIDES .2. TEMPERATURE AND ACIDITY EFFECTS

The fluorescence quantum yields of N-propylphthalimide were determined in methyl, ethyl, isopropyl and butyl alcohols, water and aqueous solutions of HClO4. An increase in the protic nature and polarity of the solvent resulted in higher fluorescence yields. Temperature effects were similar in water and ethanol. Solvent and temperature effects are interpreted in terms of electronic energy distribution, the increase in fluorescence quantum yield being ascribed to the mixing of the pi-pi* and n-pi* states. Prototropic equilibrium is shown to be present only in the ground state.