Experimental and theoretical aspects of proton transfer in 4-methyl-2,6-diamidophenol at room temperature and 77 K

Abstract

The proton transfer processes of 4-methyl-2,6-diamidophenol (MDOH) have been investigated using nanosecond and picosecond transient emission spectroscopy, at room temperature and 77 K, in solution, both in presence and absence of triethylamine (TEA). At room temperature, the hydrogen-bonded closed conformer and anion (MDO −) have been identified in the ground state. The open conformer and MDO − are detected in the excited state. At 77 K, MDOH exhibits phosphorescence both in absence and presence of TEA. The energetics of the ground and excited state proton transfer in MDOH molecule has been studied by the configuration interaction method at the AM1 level of approximation. The ground singlet is predicted to have rather large activation barrier on the respective proton transfer paths. However, the barrier height is much lower on the excited singlet surface. The process is predicted to be endothermic in the ground state and exothermic in the excited singlet surface.