Proton transfer reaction of 4-methyl-2,6-diamidophenol in some non-polar solvents at room temperature and 77 K

The fluorescence properties of 4-methyl-2,6-diamidophenol (MDOH) are examined in some non-polar solvents in relation to 4-methyl-2,6-diformyl phenol (MFOH) and quantum yield measurements are made at room temperature and 77 K. The excited state intramolecular proton transfer (ESIPT) is evidenced by a large Stokes-shifted emission (∼9000 cm−1) which is likely to originate from the enol tautomer. From nanosecond measurements and quantum yields of fluorescence, we have determined proton transfer rates. It is observed that the non-radiative channels are always dominant in the decay processes of the excited state of MDOH. At 77 K, MDOH exhibits, like MFOH, phosphorescence in all the non-polar solvents studied here and the conversion of fluorescence into phosphorescence in the case of MDOH is relatively slow compared to that of MFOH.