The Hammett correlation between distyrylbenzene substituents and chemiluminescence efficiency providing various ρ-values for peroxyoxalate chemiluminescence of several oxalates

Peroxyoxalate chemiluminescence (PO-CL) was investigated using eight oxalates with various phenol moieties and the distyrylbenzene (DSB) fluorophores with various substituents. The ρ-values in the Hammett correlation between the substituent constants (σp+) of the DSBs and the singlet chemiexcitation yields (ΦS) for the PO-CL reactions varied from −0.50 to −1.01 depending on the oxalate structure, and the reactive oxalates tended to afford the higher absolute ρ-values but with a few exceptions. Based on the CIEEL mechanism, these experimental observations suggest that the aryloxy groups still remain in the 1,2-dioxetanones (DOTs), which are the postulated high-energy intermediates, and control the electronic properties of DOTs as electron-acceptors. The LUMO energies of the DOTs calculated by the ab initio method with a B3LYP/6-31g(d) basis set reveal that the lower the DOT-LUMO energies, the higher the absolute ρ-values were provided for the corresponding oxalates, as predicted by the frontier molecular orbital (FMO) theory. Thus, the chemical species interacting with the DSBs would be not unitary and will be DOTs.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The Hammett correlation was applied to the distyrylbenzene (DSB) enhanced peroxyoxalate chemiluminescence of several aryl oxalates. ► The ρ-values of the Hammett correlation are related to the LUMO energies of the postulated 1,2-dioxetanones (DOTs). ► The frontier molecular orbital (FMO) theory predicts that the high-energy intermediates will be the DOTs rather than 1,2-dioxetanedione (DOD).