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A quantitative model of mixed-valence excited-state spectroscopy is developed and applied to 2,3-diphenyl-2,3-diazabicyclo[2.2.2]octane. The lowest-energy excited state of this molecule arises from a transition from the ground state, where the charge is located on the hydrazine bridge, to an excited state where the charge is associated with one phenyl group or the other. Coupling splits the absorption band into two components with the lower-energy component being the most intense. The sign of the coupling, derived by using a neighboring orbital model, is positive. The transition dipole moments consist of parallel and antiparallel vector components, and selection rules for each are derived. Bandwidths are caused by progressions in totally symmetric modes determined from resonance Raman spectroscopic analysis. The absorption, emission, and Raman spectra are fit simultaneously with one parameter set.

Electron transfer (ET) in four symmetrically substituted naphthalene-bridged bis-hydrazine radical cations (1,4; 1,5; 2,6; and 2,7) is compared within the Marcus-Hush framework. The ET rate constants (kET) for three of the compounds were measured by ESR; the 2,7-substituted compound has an intramolecular ET that is too slow to measure by this method. The kET values are significantly dependent upon the substitution pattern of the hydrazine units on the naphthalene bridge but do not correlate with the distance between them. This is contrary to an assumption that is frequently made about intervalence compounds that the bridge serves only as a spacer that fixes the distance between the charge-bearing units. The internal vibrational and solvent portions (λv and λs) of the total reorganization energy (λ) have been separated using solvent effects on the intervalence band maximum, resulting in a λv that is the same, 9900 cm-1, for the differently substituted naphthalenes. This is in accord with the general assumption that λv is primarily dependent upon the charge bearing unit and not the bridge. However, the trends in λs cannot be explained by dielectric continuum theory. [ABSTRACT FROM AUTHOR]