Does Koopmans’ Paradigm for 1-Electron Oxidation Always Hold? Breakdown of IP/E_ox Relationship for p-Hydroquinone Ethers and the Role of Methoxy Group Rotation

Authors

Marat R. Talipov, Marquette UniversityFollow
Anitha Boddeda, Marquette UniversityFollow
Sergey V. Lindeman, Marquette UniversityFollow
Rajendra Rathore, Marquette University

Document Type

Article

Language

eng

Format of Original

6 p.

Publication Date

2016

Publisher

American Chemical Society

Source Publication

Journal of Physical Chemistry Letters

Source ISSN

1948-7185

Abstract

Koopmans’ paradigm states that electron loss occurs from HOMO, thus forming the basis for the observed linear relationships between HOMO/IP, HOMO/Eox, and IP/E_ox. In cases where a molecule undergoes dramatic structural reorganization upon 1-electron oxidation, the IP/E_oxrelationship does not hold, and the origin of which is not understood. For example, X-ray crystallography of the neutral and cation radicals of bicyclo[2.2.1]heptane-annulated p-hydroquinone ethers (^THE and ^MHE) showed that they undergo electron-transfer-induced conformational reorganization and show breakdown of the IP/E_ox relationship. DFT calculations revealed that Koopmans’ paradigm still holds true because the electron-transfer-induced subtle conformational reorganization, responsible for the breakdown of IP/E_ox relationship, is also responsible for the reordering of HOMO and HOMO-1. Perceived failure of Koopmans’ paradigm in cases of ^THE and ^MHE assumes that both vertical and adiabatic electron detachments involve the same HOMO; however, this study demonstrates that the vertical ionization and adiabatic oxidation occur from different molecular orbitals due to reordering of HOMO/HOMO-1. The underpinnings of this finding will spur widespread interest in designing next-generation molecules beyond HQEs, whose electronic structures can be modulated by electron-transfer-induced conformation reorganization.

Comments

Accepted version. Journal of Physical Chemistry Letters, Vol. 6, No. 17 (2016): 3373-3378. DOI. © 2015 American Chemical Society. Used with permission.

Recommended Citation

Talipov, Marat R.; Boddeda, Anitha; Lindeman, Sergey V.; and Rathore, Rajendra, "Does Koopmans’ Paradigm for 1-Electron Oxidation Always Hold? Breakdown of IP/E_ox Relationship for p-Hydroquinone Ethers and the Role of Methoxy Group Rotation" (2016). Chemistry Faculty Research and Publications. 560.
https://epublications.marquette.edu/chem_fac/560