Steady-State Spectroscopy of the 2-(N-methylacetimidoyl)-1-naphthol Molecule.
The steady-state spectroscopy of 2-(N-methylacetimidoyl)-1-naphthol (MAN) reveals composite absorption and emission spectra from 298 to 193 K in hexane. The ground electronic state (So) absorption can be assigned to the sum of three molecular structures: the OH normal tautomer, and two NH proton transfer tautomers. The NH-structures are the most stable ones in equilibrium with the OH tautomer for the S0 state. On photoexcitation of the OH tautomer the excited state intramolecular proton transfer is undergone, and the corresponding NH emission is monitored at 470 nm. On photoexcitation of the NH tautomers the previous emission is monitored in addition to another emission at 600 nm, which is ascribed to intramolecular hydrogen-bonded (IHB) nonplanar NH structures generated from the IHB planar NH tautomers. A Jabłoński diagram is introduced which gathers all the experimental evidence as well as the theoretical calculations executed at the DFT-B3LYP and TD-DFT levels. The MAN molecule is compared with other analogs such as 1-hydroxy-2-acetonaphthone (HAN), 2-(1'-hydroxy-2'-naphthyl)benzimidazole and methyl 1-hydroxy-2-naphthoate to validate the theoretical calculations. Photoexcitation of MAN generates two emission bands at longer wavelengths than that of the emission band of HAN. The MAN molecule exhibits a great photostability in hydrocarbon solution which depends on the photophysics of the NH tautomers (keto forms).
Department of Applied Physical Chemistry, Universidad Autónoma de Madrid, Madrid, Spain.
Juan Carlos
JC
Del Valle
Cristina
C
Díaz-Oliva