title: Triplet Mediated C-N Dissociation versus Internal Conversion in Electronically Excited N-Methylpyrrole.
abstract: The photochemical and photophysical pathways operative in N-methylpyrrole, after excitation in the near part of its ultraviolet absorption spectrum, have been investigated by the combination of time-resolved total ion yield and photoelectron spectroscopies with high-level ab initio calculations. The results collected are remarkably different from the observations made for pyrrole and other aromatic systems, whose dynamics is dictated by the presence of πσ* excitations on X-H (X: N, O, S, ...) bonds. The presence of a barrier along the C-N dissociation coordinate that can not be tunneled triggers two alternative decay mechanisms for the S1 A″ πσ* state. While at low vibrational content the C-N dissociation occurs on the surface of a lower (3)ππ* state reached after efficient intersystem crossing, at higher excitation energies, the A″ πσ* directly internally converts to the ground state through a ring-twisted S1/S0 conical intersection. The findings explain previous observations on the molecule and may be relevant for more complex systems containing similar C-N bonds, such as the DNA nucleotides.
authors.affiliation: Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona , Campus de Montilivi, 17071 Girona, Spain.
authors.forename: Lluís
authors.initials: L
authors.lastname: Blancafort
authors.affiliation: Departamento de Química Física, Universidad del País Vasco (UPV/EHU) , Apart. 644, 48080 Bilbao, Spain.
authors.forename: Virginia
authors.initials: V
authors.lastname: Ovejas
authors.affiliation: Departamento de Química Física, Universidad del País Vasco (UPV/EHU) , Apart. 644, 48080 Bilbao, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: Montero
authors.affiliation: Departamento de Química Física, Universidad del País Vasco (UPV/EHU) , Apart. 644, 48080 Bilbao, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Fernández-Fernández
authors.affiliation: Departamento de Química Física, Universidad del País Vasco (UPV/EHU) , Apart. 644, 48080 Bilbao, Spain.
authors.forename: Asier
authors.initials: A
authors.lastname: Longarte