Detection of Structural Changes upon One-Electron
Oxidation and Reduction of Stilbene Derivatives by Time-Resolved Resonance
Raman Spectroscopy during Pulse Radiolysis and Theoretical Calculations
- Publication date
- Publisher
Abstract
Stilbene
(St) derivatives have been investigated for many years
because of their interesting photochemical reactions such as cis–trans
isomerization in the excited states and charged states and their relation
to poly(<i>p</i>-phenylenevinylene)s. To clarify their charged
state properties, structural information is indispensable. In the
present study, radical cations and radical anions of St derivatives
were investigated by radiation chemical methods. Absorption spectra
of radical ion states were obtained by transient absorption measurements
during pulse radiolysis; theoretical calculations that included the
solvent effect afforded reasonable assignments. The variation in the
peak position was explained by using HOMO and LUMO energy levels.
Structural changes upon one-electron oxidation and reduction were
detected by time-resolved resonance Raman measurements during pulse
radiolysis. Significant downshifts were observed with the CC stretching
mode of the ethylenic groups, indicative of the decrease in the bonding
order. It was confirmed that the downshifts observed with reduction
were larger than those with oxidation. On the other hand, the downshift
caused by oxidation depends significantly on the electron-donating
or electron-withdrawing nature of the substituents