Chemical triggering of dioxetanes derived from 9-adamantylideneacridanes: fluoride- and base-induced chemiluminescence (CIEEL) of siloxy- and acetoxy-substituted dioxetanes

Abstract

Photooxygenation of the methoxy-, siloxy- and acetoxy-substituted adamantylideneacridanes 3 afforded the corresponding dioxetanes 4. Thanks to the spiroadamantyl-substitution, these dioxetanes were sufficiently persistent to allow their isolation and full characterization. The activation parameters (E_a, log A, ωH^‡, ωS^‡) of the direct chemiluminescence for the methoxy-substituted derivatives 4a–c were determined by standard isothermal kinetic methods. The fluoride-ion- and base-induced decomposition of the siloxy- and acetoxy-substituted dioxetanes 4g,h,j,k was shown to involve intramolecular CIEEL emission. The CIEEL quantum yields (Φ^CIEEL) were independent of the nature of the protective group, but marked differences were observed between the 2- and the 3-substituted derivatives; the latter are about two orders of magnitude more efficient. The difference in the CIEEL quantum yields was attributed to the distinct fluorescence properties of the corresponding emitters 7 since fluorescence from the 2-substituted derivative 7(2) is too small to be measurable, while for the 3-substituted derivative 7(3) the fluorescence quantum yields (Φ^Fl) are as much as a few percent. AM1 calculations were conducted on the oxy-substituted acridone emitters 7 to explore the reasons. Presumably, the dominant charge-transfer excitation of the acridone chromophore is not appreciably perturbed by the oxy substituent for both regioisomeric emitters 7(2,3). Thus, the similar singlet excitation yields (Φ^S) for the regioisomeric oxy-substituted spiroacridane dioxetanes 6 generated on triggering reveal that they do not follow the odd/even rationale established for the related oxy-substituted benzoates and naphthoates.