PROTON-TRANSFER AND ANION FORMATION IN THE GROUND AND EXCITED-STATES OF 4-METHYL-2,6-DIFORMYL PHENOL IN HIGHLY POLAR APROTIC-SOLVENTS

From a detailed study of the fluorescence spectra, excitation spectra and time-resolved kinetics, two ground state conformers of 4-methyl-2, 6-diformyl phenol (MFOH) in two proton-accepting solvents (dimethylsul phoxide (DMSO) and N,N-dimethylformamide (DMF)) were identified: the 4 -methyl-2,6-diformyl phenolate (MFO(-)) anion and the hydrogen-bonded closed conformer. The yellow-green and blue emissions at 520 and 460 n m are assigned to MFO(-) and the hydrogen-bonded open conformer respec tively. At 77 K the fluorescence due to the open conformer is markedly suppressed, showing that this conformer is less stable than (MFO(-)) . At this low temperature the fluorescence spectrum is shown to be con taminated by phosphorescence. Fluorescence decay times were measured f or both species. Experimental evidence is in favour of an equilibrium between two conformers in both the ground and excited states. It is sh own that the short- to long-wavelength fluorescence intensity ratio is dependent on the excitation energy.