Concepts to Tailor Electron Delocalization: Applying QTAIM Analysis to Phenyl-Terpyridine Compounds
-
Presselt, Martin; Dietzek, Benjamin; Schmitt, Michael; Rau, Sven; Winter, Andreas; Jäger, Michael; Schubert, Ulrich S.; J\", ; urgen Popp,
- Abstract:
- To gain a deeper understanding of how structural modifications may influence photochemical properties of
4′-phenyl-2,2′:6′,2′′-terpyridines, the investigations presented here focus on electron delocalization in 4′-
phenyl-2,2′:6′,2′′-terpyridine derivatives and their Ru(II) and Zn(II) complexes. In those systems of neighboring
aromatic rings the considerable torsion between the rings is commonly regarded to be the limiting factor for
a well pronounced π-conjugation between the rings. A common approach to improve the π-conjugation is to
lower the steric hindrance, thus achieving a more planar geometry. Here, we present a fundamentally different
approach towards enhanced π-conjugation by manipulation of the electronic properties of the pyridine-phenyl
(py-ph) bond. This is accomplished by introducing various substituents at the phenylene moiety or coordinating
the terpyridine moiety to transition metal ions. The electron delocalization was quantified via the DFT-calculated
ellipticity in the bond-critical point (BCP) of the py-ph bond. This ellipticity can be modified due to substituents
in the para position of phenylene and via the transition metals coordinated to the terpyridine moiety. Changes
in electron density distribution induced by the substituents and the metal ions are further studied by means
of intermolecular electron density difference plots. It was shown that a NH2 group in the para position of the
phenyl ring as well as the coordination to Ru(II) or Zn(II) ions significantly enhances the π-character of the
py-ph bond. Surprisingly, an even higher π-character of the py-ph bond is achieved by introducing additional
NH2 groups in ortho position to the py-ph bond, despite the increased torsion between pyridine and phenylene.
The introduction of other substituents (-NO2, -Br, -CN, -vinyl, -ethynyl) studied within the presented
work enables an actuation of the electron delocalization between terpyridine and phenylene. In doing so, the
ellipticity is a concise quantity to characterize electron delocalization in the studied systems. Furthermore,
the ellipticity in the BCP of the py-ph bond is related to the corresponding geometrical properties (e.g.,
bond length and dihedral angle) and to the DFT-calculated HOMO and LUMO energies.
- Year:
- 2010
- Type of Publication:
- Article
- Journal:
- Journal of Physical Chemistry A
- Volume:
- 114
- Pages:
- 13163 - 13174