Elucidating the chemiexcitation of dioxetanones by replacing the peroxide bond with S–S, N–N and C–C bonds

Abstract

Dioxetanone is one of the prototypical cyclic peroxide intermediates in several chemiluminescent and bioluminescent systems, in which thermolysis reactions allow for efficient singlet chemiexcitation. While the chemiexcitation mechanism of dioxetanone...

Tuning the Intramolecular Chemiexcitation of Neutral Dioxetanones by Interaction with Ionic Species

“…However, theoretical and experimental studies indicated the possible involvement of neutral dioxetanones in efficient chemiexcitation, instead of anionic species [26][27][28][29][30]. More specifically, theoretical calculations made by our team revealed seemingly more beneficial chemiexcitation profiles [26,29,30]. In turn, Hirano et al [27] performed an experimental and theoretical study of the chemiluminescence of Cypridina analogues and stated that the reaction mechanism of the chemiluminescence of neutral species should explain the highly efficient chemiexcitation of Cypridina bioluminescence.…”

“…From this resulted the Charge Transfer-Initiated Luminescence (CTIL) mechanism [24,25]. However, theoretical and experimental studies indicated the possible involvement of neutral dioxetanones in efficient chemiexcitation, instead of anionic species [26][27][28][29][30]. More specifically, theoretical calculations made by our team revealed seemingly more beneficial chemiexcitation profiles [26,29,30].…”

“…In fact, they stated that the CIEEL and CTIL mechanisms are not applicable for explaining the high singlet chemiexcitation yield in aequorin bioluminescence [28]. Furthermore, an analysis of different systems indicated that there was no clear relationship between CT/BCT and efficient singlet chemiexcitation, as some dioxetanones presented similar chemiexcitation profiles, despite their decomposition occurring with relevant differences in terms of CT/BCT [26,[29][30][31][32].…”

“…Nevertheless, CIEEL and CTIL mechanisms are still being widely used to rationalize the chemiexcitation of different peroxide-based systems [3,12,18,24,25,[33][34][35]. Indeed, CIEEL and/or CTIL could be operative in different CL/BL systems involving dioxetanones, because the S 0 activation energy (∆E act ) for the thermolysis reaction of ET/CT-based dioxetanones tends to be significantly lower than for non-ET/CT-based ones (~10 vs. over ~20 kcal/mol) [18,[24][25][26][27][28][29][30][31][32][33][34][35][36]. Furthermore, it should be noted that a lower ∆E act should be beneficial for CL/BL reactions, as it allows for higher light outputs [37].…”

“…Furthermore, it should be noted that a lower ∆E act should be beneficial for CL/BL reactions, as it allows for higher light outputs [37]. Given this, if external effects could tune the neutral dioxetanones to undergo an ET/CT-based S 0 thermolysis reaction, this could help to assess whether neutral dioxetanones could be responsible for efficient BL/CL, despite theoretical calculations describing them as having potentially too high ∆E act values [24][25][26][29][30][31][32].…”