Base-Induced Chemiluminescent Decomposition of Bicyclic Dioxetanes Bearing a (Benzothiazol-2-yl)-3-hydroxyphenyl Group: A Radiationless Pathway Leading to Marked Decline of Chemiluminescence Efficiency

Abstract

Charge-transfer-induced decomposition (CTID) of bicyclic dioxetanes <b>1b</b>–<b>d</b> bearing a 3-hydroxylphenyl moiety substituted with a benzothiazol-2-yl group at the 2-, 6-, or 5-position was investigated, and their chemiluminescence properties were compared to each other, based on those for a 4-benzothiazolyl analogue <b>1a</b>. Dioxetanes <b>1c</b> and <b>1d</b> underwent CTID to give the corresponding oxido anions of keto esters <b>8c</b> or <b>8d</b> in the singlet excited state with high efficiencies similarly to the case of <b>1a</b>. On the other hand, <b>1b</b> showed chemiluminescence with quite low efficiency, though it gave exclusively keto ester <b>2b</b>. The marked decline of chemiluminescence efficiency for <b>1b</b> was attributed to <b>1b</b> mainly being decomposed to <b>8b</b> through a radiationless pathway, in which intramolecular nucleophilic attack of nitrogen in the benzothiazolyl group to dioxetane O–O took place to give cyclic intermediate <i>cis</i>-<b>11</b>