CoupledStates in Dinitrofluorene: Relationships betweenGround State and Excited State Mixed Valence.

The electronic absorption spectrumof 9,9-dimethyl-2,7-dinitrofluoreneradical anion in HMPA displays both a NIR intervalence charge transferand a visible excited state mixed valence transition. These transitionscontain a similar vibronic progression resulting from molecular orbitalsthat are common to both transitions. Vibrational frequency and intensitydata are acquired from the resonance Raman spectrum and used to calculatea best fit for the absorption spectrum. The normal coordinate distortionsare analyzed in terms of the electronic changes for both transitionsto explain their similarity. The Raman scattering intensity decreasesat lower excitation wavelength as a result of Raman de-enhancementcaused by interference between neighboring excited states. [ABSTRACT FROM AUTHOR]