Mechanistic Insights in Charge-Transfer-Induced Luminescence of 1,2-Dioxetanones with a Substituent of Low Oxidation Potential

Abstract

We have investigated the decomposition pathway of dioxetanones 1c with a phenoxide anion group by the B3LYP/6-31+G(d) method together with the second-order multireference Møller-Plesset perturbation (MRMP) theory and propose charge-transfer-induced luminescence (CTIL) with polarization-induced branching excitation processes. In the gas phase, the thermal decomposition of 1c occurs by an asynchronous two-stage pathway without a discrete intermediate; that is, the initial O-O bond breaking to generate a charge-transfer (CT) diradical species is immediately followed by the subsequent C-C bond breaking with simultaneous back CT, which is responsible for the surface crossing at the avoided crossing. The activation energy is dramatically reduced from 19.4 to 3.8 kcal mol(-)(1) by the deprotonation of phenol meta-1d to its anion meta-1c, showing an important role of the endothermic CT. The odd/even selection rule for the chemiluminescence efficiency can be explained by the orbital interaction for the back CT between the carbonyl pi orbital and either a HOMO or a LUMO of the generated light emitters. To examine the accessibility of the chemically initiated electron exchange luminescence (CIEEL) route, we considered the solvent effects on the free-energy change of meta-1c by using continuum solvent models. The bending vibration mode of the CO(2) fragment is specifically considered. Borderline features emerges from the solution-phase CT reaction of meta-1c, which depends on the solvent polarity: one is a nonadiabatic or adiabatic back CT process (polarization-induced concerted CTIL), and the other is a radical dissociation, i.e., complete one-electron-transfer process (CIEEL).

Which hybrid GGA DFT is suitable for Cu2O2 systems if the spin contamination error is removed?

“…As mentioned above, the NO analyses [34,35] are useful not only for elucidation of the pathway of magnetic interaction but also for the investigation of bond character [36][37][38][39]. The HONO and LUNO in the BS state are delocalized in the Cu 2 O 2 core as depicted in Fig.…”

“…T i = 0 for pure biradical and T i = 1 for the closed-shell pair [35,36]. In this way, magnetic interactions, the metal-metal bond nature, and degrees of electron correlation effect can be related to each other by NO analyses [37][38][39]. …”

The Chemistry of Bioluminescence: An Analysis of Chemical Functionalities

“…The metaphenolate compound shows a concerted mechanism while the para-phenolate shows a stepwise mechanism. [19] The comparative analysis on the decomposition of 1,2-dioxetane, dioxetanone, and thiazole-substituted dioxetanone reveals that the process for neutral thiazole-substituted dioxetanone compounds (H-TDO and OH-TDO) resemble the mechanisms of the two former species (1,2-dioxetane and dioxetanone). As seen for diaxetanone, the non-CT stepwise mechanism for the decomposition involves two discrete TSs and one excited-state intermediate.…”

“…Both are well explained in the theoretical study by Isobe et al performed on phenoxidesubstituted dioxetanone (Figure 3). [19] The authors compare the stepwise CIEEL to the concerted CTIL processes. In the CIEEL mechanism electron transfer (ET) from the electron-donating fragment to the dioxetane moiety forms a radical ion pair which is then annihilated by a back electron transfer (back ET) yielding an excited carbonyl compound ( Figure 9).…”

Photocatalytic oxygenation of olefins with oxygen

“…1,2-Dioxetanes have attracted considerable interest because of the key roles in chemiluminescence and bioluminescence [15,16], which have a broad range of biological, chemical, and medical applications [17,18]. The most common preparation of 1,2-dioxetanes is through the formal [2 + 2] cycloaddition of singlet oxygen ( 1 O 2 ) to electron-rich alkenes [19,20].…”