PHYS 35 |
| The application of calculated density functional theory Kohn-Sham (DFT-KS) orbitals and orbital energies has recently gained increased popularity due to their ability to display and predict physico-chemical properties of large systems. Our interest in this area has been to identify a low-to-moderate level ab initio or density functional method that could predict the geometry and electronic structure of large size molecular and supramolecular donor-acceptor dyads with some certainty while utilizing reasonable computational time and commercially available computational software. The exchange-correlation hybrid functional, B3LYP, with a small 3-21G(*) basis provides a suitable ‘model' chemistry allowing comparison of the surprisingly localized KS orbitals with site of oxidation or reduction and comparison of the orbital energies with measured electrochemical and spectral properties. The highest occupied orbitals (HOMOs) track oxidation potentials (donor) while the lowest unoccupied orbitals (LUMOs) track reduction potentials (acceptor) of large systems such as covalently bonded or self assembled porphyrin-fullerene systems. Understanding the position of energy levels of these large donor-acceptor systems is important for studying the pathways of photo initiated electron or energy processes. The visualization of these levels provided by the DFT calculations correlates well with electrochemical measurement. Little noticed for systems with relatively isolated groups (e.g., fulleropyrrolidine functionalized to possess two groups like pyrene, naphthalene, ferrocene, etc), is the remarkable Benson-like group additivity of the total energies and the near constant orbital energies of the HOMO and lower orbitals, and the surprising orbital profile stability over a range of these triads. |
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Computational Electrochemistry for New Energy
8:20 AM-12:00 PM, Sunday, August 19, 2007 BCEC -- 160A, Oral
Division of Physical Chemistry |