On the energy landscapes of 3-indole acetic acid and 3-indole propionic acid. A study of side chain flexibilities in their S0 and S1 electronic states

The tandem of 3-indole acetic acid (IAA) and 3-indole propionic acid (IPA) is ideally suited for a detailed study of the intramolecular forces responsible for the conformational properties of species containing side chains. Toward this end, high resolution S1 ← S0 excitation spectra of the three origin bands in IAA and the two origin bands in IPA were recorded and analyzed. Each origin is assigned to a unique conformer. A discussion of the resulting energy landscape is given.