title: High-resolution electronic spectroscopy studies of meta-aminobenzoic acid in the gas phase reveal the origins of its solvatochromic behavior.
abstract: A theoretical and experimental investigation of meta-aminobenzoic acid (MABA) in the gas phase is presented, with the goal of understanding counterintuitive observations on the solvatochromism of this "push-pull" molecule. The adiabatic excitation energies, transition moments, and excited-state structures are examined using the complete active space self-consistent field approach (CASSCF and CASPT2), which shows the first excited electronic state of MABA to be of greater charge transfer character than was found in the para-isomer (PABA). The rotationally resolved electronic spectrum of MABA reveals the existence of two rotamers, owing to asymmetry in the carboxylic acid functional group. Stark measurements in a molecular beam show the change in permanent dipole moment upon excitation to be Δμ≈3.5 D for both rotamers, more than three times larger than that found in PABA. The excited state measurements reported here, along with supporting data from theory, clearly demonstrate how the meta-directing effects of asymmetric substitution in aniline derivatives can drive charge transfer pathways in the isolated molecule.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15217, USA.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Fleisher
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Morgan
authors.forename: David W
authors.initials: DW
authors.lastname: Pratt