Ground and Electronically Excited Singlet State Structures of the <i>syn</i> and <i>anti</i> Rotamers of 5-Hydroxyindole

Abstract

The electronic origin bands A and B of 5-hydroxyindole were measured using rotationally resolved electronic spectroscopy. From comparison of the experimental rotational constants to the results of ab initio calculated structures, we could make the assignment of band A being due to the syn conformer and of band B being due to the anti conformer. These conformers, which differ in the orientation of the hydroxy group with respect to the rest of the molecule, have considerably different S1 state life times. The most probable explanation for this surprising finding is a different conical intersection of the ππ* states of both conformers with the repulsive πσ* state.