Solvent effects on the ground and excited states proton transfer in 4-methyl- 2, 6-diformylphenol: Aprotic solvents

Abstract

The interaction of 4-methyl-2,6-diformylphenol (MFOH) with tributylamine and trioctylamine in different aprotic solvents has been studied quantitatively by means of electronic absorption and fluoresce spectroscopy with special attention to proton transfer at different temperatures. The acid-base interaction leads to different types of complexes, depending upon the dielectric constant of the solvents. In cyclohexane, dioxane or tetrahydrofuran hydrogen-bonded ion pair is formed, whereas a solvent-separated ion pair is formed in acetonitrile by the addition of amine in the ground state. The large, Stokes-shifted band in the fluorescence spectrum of this compound in the 530 nm region is attributed to the tautomer generated by intramolecular proton transfer in the excited state. In the presence of an amine the sharp band at 445 nm region in cyclohexane, dioxane and tetrahydrofuran has been assigned to the schiff base and the band at 520 nm in acetonitrile to the hydrogen-bonded ion pair. Some thermodynamic data have been evaluated and discussed.