Thermochemiluminescence of bicyclic dioxetanes bearing a 4-(benzazol-2-yl)-3-hydroxyphenyl moiety in solution and in the solid state

Uncatalyzed thermal decomposition of four bicyclic dioxetanes bearing a 4-(benzothiazol-2-yl)-3-hydroxyphenyl and their 4-(benzimidazol-2-yl) analogs effectively caused thermochemiluminescence (TCL) due to ESIPT (excited state intramolecular proton transfer) both in solution and in the solid state. The efficiency of TCL (Phi(TCL)) was similar to 15 times higher in the solid state than in solution. This high Phi(TCL) in the solid state was suggested to be the result of TCL experiencing hardly any aggregation-caused quenching because of a large Stokes shift based on ESIPT of an emitter and because TCL was reduced very little by temperature quenching, in contrast to the case in solution. The efficiency of singlet chemiexcitation (Phi(S)) appeared to increase, reach a peak, and then decrease with an increase in the reaction temperature. (c) 2023 Elsevier Ltd. All rights reserved.