Dual phosphorescences of o-benzoylbenzoic acid and methyl-o-benzoylbenzoate in rigid glass matrixes at 77 K

Abstract

In solvents with an oxygen atom such as EPA (ether-isopentane-ethanol5:5:2 in volume ratio), ethanol, ethanolwater, and 2-methyltetrahydrofuran at 77 K, o-benzoylbenzoic acid (BBA) and methyl o-benzoylbenzoate (MBB) exhibit dual phosphorescences, and their decay curves can well be analyzed by biexponential functions with lifetimes almost equal to those of the triplet-triplet absorptions. Since phosphorescence excitation spectra in solvents stated above indicate the existence of two types of ground-state BBA (and MBB), we have proposed that the short-lived (Ta) and long-lived (Tb) triplet states are produced independently by excitation of the corresponding ground-state conformers. In solvents with no oxygen atom such as cyclohexane and 3-methylpentane, however, no dual phosphorescences can be seen. This may be due to the existence of a rapid interconversion between the T, and Tb states.