title: On the Additivity of Molecular Fragment Dipole Moments of 5-Substituted Indole Derivatives.
abstract: The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations. Based on a natural-bond-orbital analysis, we discuss whether the vector additivity rule can be applied in a given electronic state. From a comparison of the experimental data with ab initio calculations, we deduced that the additivity model does not apply when the flow of electron density from the substituent is opposed to that inside the chromophore.
authors.affiliation: Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225, Düsseldorf, Germany.
authors.forename: Josefin
authors.initials: J
authors.lastname: Wilke
authors.affiliation: Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225, Düsseldorf, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Wilke
authors.affiliation: Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225, Düsseldorf, Germany.|University of Vienna, Faculty of Physics, VCQ, Boltzmanngasse 5, A-1090, Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Brand
authors.affiliation: Radboud University, Institute for Molecules and Materials, Felix laboratory, Toernooiveld 7c, 6525, ED, Nijmegen, The Netherlands.
authors.forename: W Leo
authors.initials: WL
authors.lastname: Meerts
authors.affiliation: Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225, Düsseldorf, Germany. mschmitt@uni-duesseldorf.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Schmitt
keywords: ab initio calculations; electric dipole moments; high-resolution spectroscopy; indole; substituent effects