Abstract
Four bicyclic dioxetanes bearing a phenolic substituent, 3‐tert‐butyldimethylsiloxy‐4‐chlorophenyl (3a), 5‐tert‐butyldimethylsiloxy‐4‐chloro‐2‐ethylphenyl (3b), 5‐tert‐butyldimethylsiloxy‐2‐ethylphenyl (3c), and 3‐tert‐butyldimethylsiloxy‐4‐ethylphenyl (3d), were synthesized. All dioxetanes 3a–3d gave intense blue light on treatment with tetrabutylammonium fluoride (TBAF) in DMSO or acetonitrile. Kinetic study on the fluoride‐induced CIEEL decay of these dioxetanes 3a–3d and the parent dioxetane 2b revealed that the para‐substitution with chlorine on the phenolic moiety of dioxetane increases free energy of activation (Δ__G__‡), while the para‐substitution with ethyl on the aryl decreases Δ__G__‡. On the other hand, substitution with an ethyl at the ortho‐position instead of the para‐position was found to increase Δ__G__‡ and to suppress the CIEEL decay. This fact is attributed to the steric factor of the ortho‐ethyl group which would prevent the aromatic ring from rotating freely around the axis joined to the peroxide ring, and supports the suggestion for a CIEEL‐active dioxetane bearing a phenolic moiety that an intramolecular electron transfer occurs preferentially from the phenolic donor to O–O of the dioxetane ring, when the aromatic ring lies in a certain conformation(s). Copyright © 2002 John Wiley & Sons, Ltd.