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Aromatic Charge Resonance Interaction Probed by Infrared Spectroscopy
Author(s) -
Chatterjee Kuntal,
Matsumoto Yoshiteru,
Dopfer Otto
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201811432
Subject(s) - chemistry , solvation , dimer , infrared spectroscopy , resonance (particle physics) , spectroscopy , intermolecular force , molecule , infrared , photochemistry , pyrrole , atomic physics , organic chemistry , physics , quantum mechanics , optics
Charge resonance is a strong attractive intermolecular force in aromatic dimer radical ions. Despite its importance, this fundamental interaction has not been characterized at high resolution by spectroscopy of isolated dimers. We employ vibrational infrared spectroscopy of cold aromatic pyrrole dimer cations to precisely probe the charge distribution by measuring the frequency of the isolated N−H stretch mode (ν NH ). We observe a linear correlation between ν NH and the partial charge q on the pyrrole molecule in different environments. Subtle effects of symmetry reduction, such as substitution of functional groups (here pyrrole replaced by N ‐methylpyrrole) or asymmetric solvation (here by an inert N 2 ligand), shift the charge distribution toward the moiety with lower ionization energy. This general approach provides a precise experimental probe of the asymmetry of the charge distribution in such aromatic homo‐ and heterodimer cations.