Chemically initiated electron exchange luminescence of silyloxyaryl-substituted spiroadamantyl dioxetanes: Kinetics and excited state yields

Article abstract of DOI:10.1111/j.1751-1097.1996.tb03070.x

The kinetics of the fluoride-induced decomposition of the thermally stable silyloxyaryl-substituted spiroadamantyl dioxetanes la,b and the excited state formation of this chemically initiated electron exchange luminescence (CIEEL) have been investigated. Two timing kinetic regimes flash and glow have been identified, which depend on the fluoride concentration, the first at high, the second at low [F^-] triggering, whose detailed kinetic analysis affords the rate constants for the deprotected dioxetanes 2a,b cleavage in acetonitrile and sulfoxide and chemiluminescence measurements the CIEEL and phenolate 4 (CIEEL emitter) excitation yields. Chloro-substitution in the spiroadamantyl dioxetane does not affect the deprotection step k₂ but leads toa ca five-fold faster cleavage of the deprotected dioxetane 2, while the chemiexcitation yield is the same for both dioxetanes. The energies of the first excited singlet and triplet states of the emitting phenolate 4 were estimated by AM1 configuration interaction calculations with explicit consideration of acetonitrile as solvent (self-consistent reaction field approach). The first excited singlet and triplet state of the CIEEL emitter phenolate 4 possess π,π* character, as suggested by the π-type molecular orbitals and the large singlet-triplet energy gap. The chemiexcitation of both singlet and triplet states of the excited phenolate 4 is feasible during the dioxetanes 1a,b cleavage, but the experimentally determined high singlet excitation yields suggest that preferentially the phenolate 4 singlet state is populated in the fluoride ion-triggered CIEEL process.