General and specific solvent effects in optical spectra of ortho-aminobenzoic acid

We describe studies about solvent effects on the absorption and emission properties of o-aminobenzoic acid (o-Abz), interpreting the results within the framework of general and specific solute-solvent interactions. Measurements were performed in several solvents and analysis of the absorption and emission wavelengths were made based on Lippert's model for general solvent effects and on the use of different parameters to describe the ability of the solvent to promote specific interactions with the solute. We observed low sensitivity of the Stokes shift upon changes in the medium polarity, and large deviation from the linearity predicted by Lippert's equation when the solvents were characterized as Bronsted acid in the Kamlet-Taft pi* scale. Quantum yield and fluorescence lifetimes were best interpreted based on the AN+DN scale used to describe the electron donor/acceptor properties of the solvent. The results indicated that non-radiative deexcitation processes are favoured in solvents which promote the formation of intramolecular hydrogen bond, while interactions with electron acceptor solvents lead to enhancement of fluorescence.