Origin of electronic absorption spectra of MLCT-excited and one-electron reduced 2,2′-bipyridine and 1,10-phenanthroline complexes

► Reduced and excited-state UV absorption spectra of diimine complexes are similar. ► Spectral similarities in the visible spectral region are largely coincidental. ► UV transitions of reduced and excited states have at least 50% IL character. ► Visible transitions are predominantly IL and LMCT for reduced and excited states, resp. ► Overlap of reduced- and excited-state spectra complicates electron transfer studies.