Multiband fluorescence spectral properties of QMOM

The spectral characteristics of the 1-methyl-2-(4-methoxyphenyl)-3-hydroxy-4(1H)-quinolone (QMOM) dye with dual fluorescence in acetonitrile were studied under selective excitation in a wide temperature range. This dye is a structural analog of 3-hydroxyflavone and exhibits excited-state proton transfer, which forms a fluorescent tautomeric form, while the solution is characterized by dual fluorescence. The thermal behavior of the relative band intensities revealed the kinetic character of the proton transfer. The third form showed itself as a maximum between the bands of the normal and tautomeric forms upon excitation in several regions of the absorption spectrum and became dominant in solution at 60–80°C. The characteristics of the third form were studied. Additional experiments showed that this was possibly the anionic form of the dye.