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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 (σ p + ) of the DSBs and the singlet chemiexcitation yields (Φ S ) 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.2

The Mulliken electron population analysis has been a standard feature of computer output from the quantum mechanical molecular calculation. An extension of the original analysis is proposed here. It produces a point-charge model of a molecule that retains the same electric dipole moment as calculated with the molecular wave function. The analysis offers visually more interesting information than the original Mulliken analysis. The extension can be made easily by extracting and printing out some additional numerical data usually once computed but discarded after being processed in molecular calculations.

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