Health & Environmental Research Online (HERO)


Print Feedback Export to File
7617124 
Journal Article 
Raman Spectra of Persistent Radical Anions from Benzophenone, Fluorenone, 2,2'-Bipyridyl, 4,4'-Di-tert-butyl-2,2'-dipyridyl, and Anthracene: Excellent Agreement between DFT and Experiment for Highly Delocalized Radical Systems 
Juneau, A; Frenette, M; , 
2021 
Yes 
Journal of Physical Chemistry B
ISSN: 1520-6106
EISSN: 1520-5207 
AMER CHEMICAL SOC 
WASHINGTON 
1595-1603 
English 
33544614 
WOS:000621417600007 
We report detailed Raman spectra for the neutral and radical anion forms of benzophenone, fluorenone, 2,2'-bipyridyl, 4,4'-di-tert-butyl-2,2'-dipyridyl, and anthracene. Density functional theory (DFT) predictions for the Raman spectra of these molecules give additional insight into the assignment of each vibrational mode. While the use of DFT has been problematic in quantifying the thermochemistry of highly delocalized radicals, we find that DFT-predicted spectra using the popular B3LYP functional are in excellent agreement with the observed Raman spectra. In the case of the two bipyridyl compounds, the Raman spectra allowed us to conclude that the cis form of the radical anion complexed to a sodium cation was the preferred configuration. Benzophenone and fluorenone radical anions gave a significantly weakened C═O bond stretching vibrational frequency as expected from the population of an antibonding π* orbital. For benzophenone, the C═O vibration dropped from 1659 to 1403 cm-1 upon reduction. Similarly, fluorenone showed a C═O vibration observed at 1719 cm-1 for the neutral form that decreased to 1522 cm-1 for the radical anion. The structurally rigid anthracene showed relatively smaller Raman band shifts upon single-electron reduction as the π* orbital is more equally delocalized on the entire structure. In total, we correlated 65 DFT-predicted vibrational modes for the neutral molecules with an overall error of 7.1 cm-1 (root-mean-square errors (RMSEs)) and 67 DFT-predicted vibrational modes for radical anions with an overall error of 9.9 cm-1. These comparisons between theory and experiment are another example to demonstrate the power of DFT in predicting the identity and geometry of molecules using Raman spectroscopy.