Bimanes VIII: Photophysical properties of syn- and anti-1,5-diazabicyclo[3.3.0] octadienediones (9,10-dioxabimanes)

Photophysical data for syn- and anti-1,5-diazabicyclo[3.3.0] octadienediones (9,10-dioxabimanes ((R₂, R₁)B)), a new class of small heterocyclic molecules, are reported. The syn and anti isomers differ greatly in the positions of the absorption maxima (λ_max(syn) ≫ λ_max(anti)), the solvent sensitivities of the absorption maxima (that of the syn isomer is greater than that of the anti isomer), the fluorescence quantum yields (φ_F(syn) ≫ φ_F (anti)), the phosphorescence quantum yields (φ_P(syn) ≪ φ_P(anti)), but they exhibit similar changes in some of these properties with respect to changes in substitution. The 4,6-bridged syn-bimanes absorb at shorter wavelengths than unbridged compounds do, but they fluoresce at similar wavelengths. The phosphorescence of the anti-(R₂, R₁)B appears at shorter wavelengths and has a somewhat shorter lifetime than that of the corresponding syn-(R₂, R₁)B.