Inner Shell Excitation Spectroscopy of Biphenyl and Substituted Biphenyls: Probing Ring-Ring Delocalization

Jian Wang, Glyn Cooper, David Tulumello, and Adam P. Hitchcock*

Department of Chemistry, McMaster UniVersity, Hamilton, Ontario, Canada L8S 4M1

Received: August 19, 2005; In Final Form: October 1, 2005

Abstract:

Quantitative optical oscillator strength spectra for C 1s excitation and ionization of gas-phase biphenyl, decafluorobiphenyl, and 2,2'-bis(bromomethyl)-1,1'-biphenyl have been derived from electron energy loss spectroscopy recorded under electric dipole dominated conditions. The C 1s X-ray absorption spectrum of hexaphenylbenzene has been recorded in the solid state. The C 1s spectral features are interpreted with the aid of ab initio calculations for core excitation of benzene, biphenyl, hexafluorobenzene, and decafluorobiphenyl. A weak feature at 287.7 eV in biphenyl is identified as a C 1s -> p*deloc transition, characteristic of ring-ring delocalization. Its intensity and position are shown to be related to the average torsion angle and thus the extent of p-p-interaction between adjacent aromatic rings. The effects of perfluoro substitution on core excitation spectra are also characterized and discussed.

10.1021/jp054693n CCC:     © 2005 American Chemical Society