Ab Initio and Density Functional Study of the Electronic Transitions of Indoline and Indoline-2-Carboxylic Acid

In this study, a range of computational methods including time-dependent density functional theory, configuration interaction, and Zerner's spectroscopic intermediate neglect of differential overlap are used to classify spectroscopic properties of indoline and indoline-2-carboxylic acid. By examining transition densities, the 1 L a and 1 L b states of indoline and indoline-2-carboxylic acid are assigned. Aniline is used as a reference system. Excitation energies, oscillator strengths, dipole moments, and transition dipoles have been calculated and are found to be in close agreement with experiment. We find that the electronic transitions of indoline are similar to those for aniline. The lowest excited singlet state in indoline, as in aniline, is the 1 L b state with a low oscillator strength. The 1 L a state is higher in energy and possesses a larger oscillator strength as well as a larger dipole moment. For indoline-2-carboxylic acid, 1 L b - and 1 L a -like states can be identified, but an evaluation of their properties reveals mixed 1 L a and 1 L b character. Ground-state energies for conformations of indoline-2-carboxylic acid differing in the orientation of the carboxylic group indicate the presence of two ground-state conformations of similar energy.