SOLVENT EFFECT ON THE SPECTROSCOPIC PROPERTIES OF INDOLE - SEMIEMPIRICAL QUANTUM-CHEMICAL STUDY

Using the semiempirical all-valence method (GRINDOL) together with the virtual charge method of Tapia et al. to represent solvent effect, the spectroscopic properties of the indole have been calculated. It is concluded that in the non-polar solvents fluorescence of indole originates from the ''L(b)'' state whereas in the polar solvents the ''L(a)'' emission occurs. It means however, that in some slightly more polar solvents, ''crossing'' of these close lying potential surfaces does occur. The large fluorescence red shift observed in polar solvents can be explained as a combination of the ''normal'' solvent effect and the specific interactions between the excited indole ring and solvent molecules via charge transfer mechanism.